August 20-28,2004 Florence -Italy

Field Trip Guide Book - B16 GEOLOGICAL CONGRESS 32 Volume n°2-fromB16toB33 FROM RIFTINGTOINVERSION BOUNDARY RECONSTRUCTION SEDIMENTATION ANDPLATE THRUST-BELT: GEODYNAMICS, WESTERN PYRENEESFOLD-AND- Pre-Congress J. Muñoz,A.Teixell R. Bourrouilh,L.Moen-Maurel, Leaders: nd INTERNATIONAL B16 The scientific content of this guide is under the total responsibility of the Authors

Published by: APAT – Italian Agency for the Environmental Protection and Technical Services - Via Vitaliano Brancati, 48 - 00144 Roma - Italy

Series Editors: Luca Guerrieri, Irene Rischia and Leonello Serva (APAT, Roma)

English Desk-copy Editors: Paul Mazza (Università di Firenze), Jessica Ann Thonn (Università di Firenze), Nathalie Marléne Adams (Università di Firenze), Miriam Friedman (Università di Firenze), Kate Eadie (Freelance indipendent professional)

Field Trip Committee: Leonello Serva (APAT, Roma), Alessandro Michetti (Università dell’Insubria, Como), Giulio Pavia (Università di Torino), Raffaele Pignone (Servizio Geologico Regione Emilia-Romagna, Bologna) and Riccardo Polino (CNR, Torino)

Acknowledgments: The 32nd IGC Organizing Committee is grateful to Roberto Pompili and Elisa Brustia (APAT, Roma) for their collaboration in editing.

Graphic project: Full snc - Firenze

Layout and press: Lito Terrazzi srl - Firenze Volume n° 2 - from B16 to B33

32nd INTERNATIONAL GEOLOGICAL CONGRESS

WESTERN PYRENEES FOLD-AND- THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION

AUTHORS: R. Bourrouilh1, L. Moen-Maurel2, J. Muñoz3, A. Teixell4 1 Laboratoire CIBAMAR, Université Bordeaux 1, Talence Cedex - France 2 TOTAL, Pau Cedex - France 3 Departament de Geodinamica i Geofisica, Facultat de Geologia, Universitat de Barcelona - Spain 4 Departament de Geologia, Universitat Autònoma de Barcelona, Bellaterra - Spain

Florence - Italy August 20-28, 2004

Pre-Congress B16 Front Cover: 1. Thrusts and Folds structures of Les Eaux Chaudes in the Ossau Valley, France. DAY 2, Stop 2.5b. 2. Thrusts and Folds structures of the External Sierras, Spain. DAY 5, Stop 5.3. 3. Thrusts and Folds of Gavarnie at La Estiba, Spain. DAY 6, Stop 6.2. WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

Leaders: R. Bourrouilh, L. Moen-Maurel, J. Muñoz, A. Teixell

Introduction General geological This fi eld trip along a geotraverse through the north- setting (Plate 1, fi g.1 and 2). western and south-western Pyrenees area has three main purposes: Introduction 1. To analyse the present-day structures in the fold Situated between the European plate and the Iberian and thrust belt and to reconstruct their structural plate, the Pyrenean orogenic belt extends from the evolution in order to better understand the subsurface NW part of Spain or Galicia, to the Southern part of foreland structures (some of them being oil/gas traps the Alps and the Gulf of Genoa, in the Mediterranean. or prospects). It is thus a belt almost 2,000 km long, of which only 2. To describe the stratigraphic evolution of the the central part, or the Pyrenees, is a visible collisional Mesozoic and Tertiary formations (with respect to orogen, whereas both the Western part or the Bay of plate tectonics and to the Iberian plate drift) on several Biscay and the Eastern part or the Gulf of Lion and transects: along the Ossau Valley, the Aspe Valley, the Gulf of Genoa remain at subsea. Mendibelza and Orhy Massifs for the northern side, The Pyrenees resulted from an orogeny which and from the Orhy Massif to Jaca and Aïnsa for the developed over a previously thinned continental crust, southern side. but without an intervening oceanic crust between the 3. To give petroleum geoscientists the recent concepts two diverging plates. Underplating of the Iberian plate and keys for the Pyrenean foreland and foothills underneath the European plate led to the sinking of a hydrocarbon exploration. deep crustal root along a north-dipping plane while coeval delamination of the upper crust led to the The scenic landscapes of the Pyrenees mountain range propagation of a major fold-and-thrust belt to the provide an exceptional laboratory for examining the south as well as of a conjugate north-verging back- orogenic processes, from rifting to collision, both thrust system. Thus the range is characterized by a in the crustal lithosphere as well as in the foreland doubly-verging asymmetric thrust stack wedge: basins. - the southern fold-and-thrust belt (FTB) represents A comparison to more classical fold-and-thrust belts a south-verging imbricate fan affecting cover will be proposed along the way and in the wrap-up formations (Mesozoic and Cenozoic in age) conclusion of the fi eld trip. rooting into an antiformal stack of basement rocks (Precambrian to Paleozoic variscan folded series) in Field References: the axial zone. The piggy-back thrust sheets indicate a Topographic and Road maps : for example: crustal shortening which reaches over 100 km along, Michelin n°234 Aquitaine 1/ 200,000 i.e. 90% of the total orogen collision; Michelin n°573, Regional 1/400,000: - the northern fold-and-thrust belt is confi ned over Pais Vasco/Euskadi, Navarra, La Rioja. a narrower zone north of the axial zone or the High Michelin n°574, Regional:1/400,000: Chain, in a conjugate position to the underplating Aragon, Cataluña/Catalunya process (Moen-Maurel et al., 1999). Geological maps : The relatively minor inversion in the Northern FTB S.N.P.A. (Société Nationale des Pétroles d’ Aquitaine) protected the rifting series and structures from uplift (1972). Carte géologique des Pyrénées, scale and erosion, thus permitting the examination of the 1:250,000, P. Soler ed. 4 plates. initial processes of the orogenesis.

B.R.G.M. (1980). Carte Tectonique de la France, The genesis of the Pyrenean belt is the result of: B16 to B33 n° 2 - from Volume scale 1:1,000,000, B.R.G.M. Ed. - 1. the break-up of the 250 Ma old Wegener’s Pangea B.R.G.M.: 1/50,000 geological Maps: n° XIII-46, St and reactivation of its structural inherited fabrics, Jean Pied de Port; XIV-46, Tardets-Sorholus; XIV-47, - 2. the correlative propagation of the Atlantic Mid- Larrau ; XV-45, Pau; XV-46, Oloron Sainte Marie; Oceanic Ridge from Central Atlantic to the North, XV-47, Laruns (under press). with an Atlantic RRR triple junction along its Instituto Geologico y Minero de Espana, Geological Eastward opening branch entering Bay of Biscay, Maps at 1/ 250,000 and at 1/50,000: n°118 Zuriza, - 3. the Late Jurassic - Late Cretaceous diachronous n° 144 Anso, n°145 Sallent. Eastward opening of the Bay of Biscay which

3 - B16 Volume n° 2 - from B16 to B33 B16 - B16 rift never producedoceaniccrust:itcanthusbecalled junction pointaborted(R-->r),theNorth-Pyrenean Bay ofBiscay. In Turonian theEastward Atlantic R basins, suchastheN-Pyreneanbasinattipof Iberian plateandinthebirthofriftedinterplate resulted inthedriftandprogressive rotationofthe Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell the Pyrenees,fromEbroBasin(South)to Aquitaine Basin(North). Plate 1-1.StructuralMapofthePyreneeswithlocationcrosssection AB. 2.Transversal crosssection AB of Figure 1-Crustalscalebalancedcrosssection, ECORSseismicprofile, fromChoukrouneetal.,1989. as wellbytheclosureof Tethys, whichprovoked opening ofboththeSouth Atlantic andIndianOceans, south-east. This driftisduetotheCretaceousoceanic Stopping thefreedriftofIberianplatetoward the - 4.thenorthward pushbythelarge African plate “aulacogen”, WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

Figure 2 - Cross-section passing through the Lacq and Meillon gas fi elds (Moen-Maurel et al.1999). the migration of the African plate towards the NE and compensation responded to the collision and the then towards the N. This plate motion crushed the associated crustal thickening, creating a large open space between Europe and Africa and formed intraplate foreland over the Iberian plate, (the South- the Pyrenean-Alpine orogenic belt in a diachronous Pyrenean basin), and a retro-foreland basin on the compression which proceeded westwards along the Northern edge of the Iberian plate and over the northern margin of the Iberian plate. As a result of the collision between the Iberian and European plates, which began during the Turonian and continued: - 1. the rifted N-Pyrenean basin became a foredeep basin Volume n° 2 - from B16 to B33 n° 2 - from Volume - 2. a lithospheric

Plate 2 - 1. Transect Of The West-central Southern Pyrenees, from A. Teixell. 2. Cross-section of the Western Jaca basin and Ainsa basin across the Boltaña anticline, from J. Muñoz.

5 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell northern margin ofSpainshowing anincipient north- plates stillremainsopenintheBayofBiscay, the the west,spacebetweenEuropeanandIberian which leadstovarying deformationsalong strike. To incomplete orogenresultingfromplatedriftrotations The Pyreneescanbeconsideredanimmature, Structure ofthePyrenees subducted root. result oftheisostaticreboundcrustalPyrenean the glaciations.Itmostlyaffects theIberianplate,asa has occurredsincethePleistocene,following mainly -sedimentation, themainapparentmountainuplift Pyrenean orogeny, betweencompression-erosion Although anisostaticbalanceoccuredallalongthe the activation ofdetachmenthorizons. occur bothinmapview andwithdepthinfavour of deformation. A partitioningofthedeformationmust must befoundatdepth,decoupledfromthecover strike slipconvergence vector betweenthetwo plates convergence throughthemainorogenicphase. The (Dinares a vertical axisalongtheanalyzedcross-section planes andtheabsenceofsignifi cant rotationaround of thestructures,kinematiccriteriaalongthrust the tectonicevolution asdeducedbythemappattern was constantlyN-StoNNE-SSWthroughmostof Vergés andMuñoz,1990). Thrust transportdirection affecting syntectonicdeposits(Martínez development ofnew, minorout-ofsequencethrusts break-back reactivation oftheolderthrustsandby in thelaststageofevolution ofthethrust-belt,bya deformation inthesouthernPyreneeswas modifi been documented. The forward propagationofthe synchronous hindward internaldeformationhasalso migrated outwards inapiggy-backmanner, although Deformation ofthePyreneandouble-wedge fold-and-thrust piggy-backsheets. south (Ebrobasin)forelands,insuccessive shallow thrusted toward eitherthenorth(Aquitainebasin)and interplate (north)andtheintraplate(south)basins - 4. The post-Pangean sedimentaryinfi on eachsideofthedouble-wedge(Figs.1and2). Campanian timestwo forelandbasinsdeveloped, one stages ofthePyreneancollisionatLateSantonian- plate underneaththeEuropeanplate.Sinceinitial basement (Precambrian-Paleozoic) oftheIberian underthrusting orunderplatingofthePre-Pangean cross-section, resultingfromthecrustalductile - 3.thePyreneanorogenicbeltdisplaysafan-shaped European plate(the Aquitaine basin). et al.,1992). This impliesanearnormal et al.,1988, ll ofthe ed, into different structuralunits(fi and foothills.Itcanbesubdivided from north tosouth observable inthefield, inthePyreneanmountainbelt The crustalandcover structurationisclearly the basementaswellitscover. stacking ofsouth-verging foldsandthrustsinvolving basin. The platecollisionresultedinthepiggy-back sedimentary infi ll oftheSouth-Pyreneanintraplate affected thecover oftheHighChain,aswell shallow basalandinternalplasticdécollementsalso The south-verging thrustingalongsuccessive Triassic evaporites andtheUpperCretaceousfl by wrenching,orthrustalongthedetachmentsin the originaldipsenseofriftfaults, eithersheared either towards thesouthornorth,dependingon rifting stagewereaffected byinversion anduplifted, Thrust Front.Southofitsaxisthetiltedblocks axis, andremainednorthoftheNorth-Pyrenean rift structureswerelittleinverted northoftherift south-verging thrust(Plate1). The North-Pyrenean our geotraverse theNPFisconcealedunderneatha Pyrenean Fault) markstheplateboundary. Along one ofthefaults ofthesouthernriftmargin (North- associated strike-slip motionthatiswellvisiblealong (Fig.1 and2,Plate1).IntheCentralPyrenees building ofadeep-rootedfan-shaped mountainrange the deepfault network inthecrustalbasement,and fault network, thecollisionprovoked aninversion of ?) - Variscanpresent. UsinganinheritedPrecambrian( continental lithosphere,sincenooceanicfl sensu stricto,thecollisiondirectlyaffected the Iberian platesareinfullcontact,i.e.thePyrenees Between thesebelt-tipareas,wheretheEuropeanand Pyrenean belt. events (BourrouilhandGorsline,1979)overprints the consecutive totheBetico-Rifeancompressional to thesouth,NeogeneMediterraneanextension, inversion thrustsandfolds(Debelmas, 1974).More belt extends inthe Alps ofProvence, exhibiting minor verging subduction. To theeast,Pyreneanorogenic Pyrenean Frontal Thrust and was notgreatlyinvolved basin mainlydeveloped inthefootwall oftheNorth- are observed (BuyandRey, 1975). The Aquitaine marine platformsedimentsofLower Ypresian age latter arerepresentedbycontinentaldepositsasonly by anupto4kmthickPaleogene series.Mostofthe succession ofUpperCretaceousturbiditesoverlain of the Aquitaine basin,consistsofathick(few km) The northernforelandbasin,inthesouthernpart and 2)(Castéras,1974): g. 2andPlate1,fi or was oor ysch. g.1 WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

in the North-Pyrenean thrust system. The Axial Zone or High Chain (Plate 1, fi g. 2 and The southern part of the Aquitaine Basin is affected Plate 2, fi g. 1) is the highest part of the range, by folds with large curvature radii related to the and represents the present-day orographic axis. Pyrenean Tertiary tectonic phase. In this area the It is composed of Precambrian series, possibly Pyrenean compression is mainly Eocene in age. This folded (?) during the Late Proterozoïc, and of thick phase enhanced salt tectonics. Paleozoic series that were folded during the Variscan The Sub-Pyrenean Zone or northern folded foreland (Hercynian) orogeny and redeformed during the (which lies beneath and north of the North Pyrenean Upper Cretaceous to Tertiary Pyrenean tectonic Thrust Front (or NPTF) is characterized by north- phases. The High Chain basement is overlain by verging blind thrusts and asymmetric folds often discontinuous Permo-Triassic deposits and by a thick cored by a salt ridge or an inverted rift graben. Upper Cretaceous shelf carbonate series; this shelf The NPTF is composed of a series of en-echelon N- is overlain by the edge of an Upper Cretaceous to verging thrust faults running from the Bay of Biscay Tertiary synorogenic fl ysch basin, which developed up to the South-Western Alps. synchronously with the compression and with the The North Pyrenean Zone or NPZ, lies to the south of tectonic subsidence and deepening of the South and the NPTF and is characterized by north-verging thrusts North Pyrenean foredeep basins. and folds verging either north or south depending The basement rocks of the Axial Zone constitute an on the dip sense of the inverted normal faults. The antiformal stack. This antiformal stack only involves southern part of this zone has been deformed by upper crustal rocks, its fl oor thrust being located 15 schistose deformation and low-grade Pyrenean-age km below the top of the basement. In the Central metamorphism, at the contact with the NPF. Pyrenees it is constituted by three main structural Precambrian to Paleozoic basement outcrops in the units: Nogueres, Orri and Rialp thrust sheets NPZ, constituting the N-Pyrenean massifs. (Muñoz, 1992). The regional westward plunge of the The North Pyrenean Fault or NPF lies to the south of basement antiformal stack leaves only the Nogueres these units, and appears in various ways throughout – equivalent thrust sheet at outcrop level; it is then the belt. Its variable aspects take on the status of the called Gavarnie - Eaux Chaudes in the Western orogenic axis of the range (Iberian-European plate Pyrenees. The Nogueres-Gavarnie thrust sheet is the boundary), the change-over zone from northern uppermost of the antiformal stack and its southern tip to southern vergence (Central Pyrenees), the zone is the basement of the lower cover thrust sheets. In the of intense deformation (various schistosities), a central Pyrenees, the contact between the cover Upper metamorphic zone, and a lherzolite (mantle-derived Thrust sheets and the basement antiformal stack ultrabasic granulitic rock) injection zone (fi g. 2 and corresponds to a passive-roof backthrust (Morreres Plate 1, fi g. 2). backthrust). During the development and southward The fault evolved from an initial Albo-Cenomanian displacement of the basement antiformal stack the transtensional regime with the formation of pull- cover units have been wedged by delamination, and apart basins and the development of a thermal on the top of the basement, as described in other metamorphism (Debroas, 1990; Goldberg and orogenic belts (Price, 1986). A mirror image of this Maluski, 1988) to a later transpressional regime delamination of the cover by the basement thrust during the onset of convergence in Early Senonian sheets also exist in the North-Pyrenean foreland at the time (Puigdefàbregas and Souquet, 1986; Debroas, edge of the Paleozoic Basque Massifs, which make 1990). Lower crustal granulitic rocks as well as a cartographic salient and a splinter wedge into the ultrabasic upper mantle rocks (lherzolites) are northern foreland (Figure 1). observed embedded between the Lower Mesozoic The South Pyrenean Zone (Plate 2, fi g. 2) is metamorphic rocks along a narrow strip parallel to the characterized by South-verging thrusts and folds. B16 to B33 n° 2 - from Volume North Pyrenean Fault (Choukroune, 1976; Vielzeuf The stratigraphy is essentially represented by Permo- and Kornprobst, 1984). These rocks were carried to Triassic deposits, locally overlain by Jurassic, but upper crustal levels during the strike-slip faulting. mostly covered by Upper Cretaceous shelf carbonates Apart from this narrow strip parallel to the North passing to Eocene turbidites (in the western part) and Pyrenean fault neither post-Hercynian metamorphic Oligocene molasses conglomerates rocks nor lower crustal rocks are observed at the In the southern Pyrenees the cover Upper Thrust surface in the Pyrenees. Sheets (Muñoz et al., 1986) consist of Mesozoic and

7 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell ECORS-Pyrenees profi les (Choukrouneetel.,1989, from thedeepseismicrefl best constrainthePyreneancrustalstructureare anomalies, tomography, heatfl profi techniques (deeprefl ection andrefractionseismic has beeninvestigated bydifferent geophysical The crustalandlithosphericstructureofthePyrenees crustal structure Geophysical dataand late development stages(Coney, buried thesouth-Pyreneanthrustsystemduringits the enclosedbasinandprogressively backfi Eocene-Lower Miocenecontinentalclasticsfi paleogeographical closingoftheEbrobasin.Upper Priabonian evaporites. These evaporites representthe sediments oftheforelandbasinafterLower Thrust. Itismainlyfi foreland southoftheSouthernPyreneesFrontal The EbroBasinrepresentstheautochthonousexternal foreland basin. and thesedimentaryinfi ll oftheSouth-Pyrenean duplexes systemwhichaffects boththeHighChain and representstheFrontalthrustoframps from theeasttonorth-west(Plate1,Fig.2) The South-Pyrenean Thrust FrontorSPFTextends Sheets. tectonics isastructuralfeatureoftheUpper Thrust faults, mainlyLower Cretaceousinage.Inversion thrusts isstronglycontrolledbyprevious extensional N-S transportdirectioncanbededuced.Locationof confi probably relatedtotheoriginalMesozoicbasin Sheets show numerousobliqueandlateralstructures, Cretaceous) extensional faults. The Upper Thrust geometry imposedbyCretaceous(mainlyLower the Cretaceousstratigraphicunitscoupledwith progressive southwards thinningandpinchoutof 7km. This sedimentarywedgeistheresultof units andprogressively thickens northwards upto series isonlytensofmetersthickinthesouthernmost the easternPyrenees(Figs.1and2). The Mesozoic central PyreneesandthePedraforcathrustsheetsin Boixols, MontsecandSierrasMarginales) inthe Central-South Pyreneanthrustsheets(Cotiella, with theEbroforelandbasin(Fig.2). They arethe top ofautochthonousPaleogene rocksincontinuation evaporites. These thrustsheetswerelaterthrustedon detached fromthebasementover theUpper Triassic syntectonic Paleogene rockswhichwereinitially les, gravity, magnetotellurics,magnetic guration. Fromthesestructuresanapproximately lled bythelaststagecontinental ection profi ection ow). The datathat et al.,1996). les, mainlythe lled and lled lled Pyrenees (Pous and byamagnetotelluricprofi tomographic analyses(SouriauandGranet,1995) is compatiblewithothergeophysical datasuchas into themantle. This inferredcrustalsubduction was subductedtogetherwiththelithosphericmantle lower crust,below theuppercrustaldouble-wedge, (Fig. 4). Apparently, thecrustwas decoupledandthe the bestgeometryinwhichtointegrate allthesedata wedge involves onlyuppercrustalrocksprovides that anexplanation inwhichtheorogenicdouble- al., 1989,Mattauer, 1990,Muñoz,1992). We believe combined geologicalandgeophysicaldata(Roure of thePyreneeshave beengiven onthebasisof Several different interpretationsofthecrustalstructure et al.,1989,Muñoz,1992). construction ofcrustalbalancedcross-sections(Roure the Europeanoneandhasbeenbasisfor to show thesubductionofIberianplatebelow Roure 1989). These profi on theorderof80kmarereachedwestwards from shortening decreaseswestwards. Shorteningvalues as cross-sectionswestoftheECORSone,show that Srivastava, 1991). These paleomagneticdata,aswell motion ofIberiaafterpaleomagneticdata(Roestand plates asdeducedbyreconstructionofthepast the estimatedseparationofIberianandEuropean These shorteningcalculationsarecompatiblewith of theNorthPyreneanFault. the south-verging thrustsandantiformalstacks,south about 90%ofthecollisionshorteningisproducedby Pyrenean Fault (Moen-Maurel by thenorth-verging structuresnorthoftheNorth more than15kmofshorteningcanbeaccounted estimate ofabout125km(Vergés section intheeasternPyreneesyieldedashortening 1989). A shorteningcalculationforacrustalcross- over 100km(Deramond central Pyreneeshave estimatedshorteningvalues is restored.Othercross-sectionrestorationsofthe below thesolethrustofPyreneansystem up to160kmiftheinternaldeformationofcrust 147 km(Muñoz,1992).However, this value increases along theECORSprofi of acrustalcross-sectionthecentralPyrenees orogenic contraction(Fig.1). A geometricalsolution geological databut alsotoestimatetheamountof constructed notonlytointegrate geophysicaland Balanced andrestoredcross-sectionswere Balanced andrestored cross-sections et al.,1995). le gave atotalshorteningof les have beeninterpreted et al.,1985;Roure et al.,1995). Therefore le across thecentral et al.,1995).No et al., et WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

the ECORS cross-section (Grandjean, 1992, Teixell, Stratigraphic and 1996, 1998). geodynamic evolution The estimated duration of convergence in the central (Fig. 3) (See further on the contribution of A. Teixell Pyrenees is about 60 Ma, which gives a mean and of J. Muñoz for a more detailed study of the shortening rate of 2.5 mm/yr. A similar shortening Southern Pyrenean side). rate has also been deduced in the eastern Pyrenees According to Bourrouilh, Richert and Zolnaï, 1995, during a shorter period of convergence (Vergés et al., Richert et al., 1995, the stratigraphic and structural 1995). The latest deformation migrated westwards. It evolution of the Pyrenees can be summarized as Stopped during Middle Oligocene time in the eastern follows: Pyrenees and continued to the Middle Miocene in Precambrian to Paleozoic the westernmost Pyrenees (Vergés, 1993). In the The evolution of the Precambrian and Paleozoic central Pyrenees, along the ECORS cross-section, domain related to the geodynamics of the Pyrenees, deformation ended by Early Miocene times. Montagne Noire and Western Mediterranean has Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 3 - Geodynamic evolution of Bay of Biscay-Pyrenees and North-Pyrenean basins, from Bourrouilh et al., 1995, modifi ed.

9 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell from basetotop:postorogenic redconglomerates Germano-type i.e.athree-foldstratigraphy: The Triassic seriesareofatypical Triassic toEarlyLiassic(Fig.3) fl debris (Lucas1985)but alsobasaltic an andesiticvolcanism provides volcanic of continentalredbeds,inwhichlocally previously deformedseries.Itiscomposed The series. Variscan graniteslocallyintrudedthe and foldsmetamorphism.Upper orogeny was accompaniedbylarge thrusts (or Hercynian) orogenies. The Variscan affected byCaledonianand Variscan and Paleozoic basementwerethensuccessively section andtheredPermianmember. Precambrian a limyDevonian, asandy-shalycarboniferous (Gapillou, 1981),ablack-shalySilurianinterval, 1985), athickfi ne-grained silici-clasticOrdovician then locallystromatolithicCambrian(Bouquet main members:apost-orogenicconglomeraticand (Ursuya-Baigoura massif). The Paleozoic containssix (Agly massif)andradiochronologicallydated Generally, Precambrianseriesaremetamorphosed was acquiredduringtheLateProterozoïc(Cadomian). The structuralframework ofthePrecambrianbasement Bourrouilh andMirouse,(1984)others. by Winnock (1971), Autran andCogné(1980), Paleozoic hasbeenstudiedinthe Aquitaine area been synthetizedbyBourrouilhandal.(1980). The Lacq-Meilllon area(Total). Figure 4-Tectono-stratigraphic evolution ofthe ows, aswitnessesofoceanicexpansion. Permian liesunconformablyonthe et al., is againseparatedintotwo domains,alongthe In theLatePortlandiantoBerriasian,platform in average) areassociatedtothisregressive cycle. dolomitic facies oftheManoDolomite(200 m thick tectonic phaseleadstoageneralregression. The At theendofJurassic,Neo-Kimmerian synsedimentary salttectonicsalongbasementfaults. local condensedsedimentarydeposits,relatedto environment ofdeposition,affected onlyby to LateKimmeridgianperiodrepresentsastable Following thisphaseofdifferentiation, theMiddle limestones ofthelower CagnotteFormation. Ammonite marlsandLower Kimmeridgianshaly open marineenvironment tothewest : Oxfordian and BayseresFormations totheeastversus amore part withdolomitesandlimestonesoftheMeillon is subdivided intotwo majorprovinces: aninner platform (Canérot,1987). The localPangean platform paleogeographical differentiation onthe phase leadingtostructuraland associated toamoreactive extensional Early Kimmeridgiantimeperiodcanbe (Dogger-Malm). The Oxfordianthrough then mainlylimestoneplatformsequence upwards intoashallow-marine dolomitic, The Lower Liassicanhydritesgrade Jurassic present-day basincenter. taper off tozerotowards the Aquitaine several hundredsofmetres),whilethey southernmost riftedbasinedge(over distension, hasbeenemplacedalongthe thickest volcanic wedgeshowing crustal shales withevaporites andvolcanics. The and sandstones,marinecarbonatesred Figure 5-Cross-sectionoftheLacq-Meillon area (Total). WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

submeridian trend defi ned here above. At the Jurassic- The paleogeography changes completely, and Cretaceous boundary large areas became emergent as is entirely controlled by the important tectonic demonstrated by the presence of anhydrite, some movements taking place along the plate boundaries coal, red shale, clastics (sand), sand-rich carbonates (Peybernès and Souquet, 1984). As a result, the and intra-formational (desiccation) breccias. The fi rst subsiding zones shift to the south towards this very salt-movements (gentle swells and salt-cushions) mobile zone, while a massive transgression develops seem to have started as early as in the Portlandian over the entire area. The Late Albian sedimentation (Winnock and Pontalier 1970). Massive sand-bodies overlaps the earlier paleogeographies, demonstrating were deposited in the Parentis Basin during the the change of structural stress at this time. Locally salt Purbeckian-Wealdian period. The equivalent series tectonics enhanced erosion and subsidence, producing of the southern Aquitaine sub-basins are carbonates, the main hydrocarbon traps as they are known today. intraformational breccias and shales (Lacq). The Late Cretaceous sedimentation over the south-western part of the An important inversion occurred diachronously all basin indicates a deeper environment of deposition along the Europe-Iberia plate boundary. While the and a more continuous sedimentation during the Late western part remains extensive in a rift mode, the Jurassic – Early Cretaceous transition (Hauterivian eastern part of the domain progressively became in – Berriasian). Montagné’s thesis (1986) evidenced compression and in a foredeep mode. Correlatively, rifting during Late Jurassic, south of Bayonne. Later, two extensive carbonate platforms developed, ODP Leg 103 (1988) found turbidites in the off-shore covering to the north the major part of the Aquitaine Hauterivian sequences in the westernmost part of the Basin, and to the south the persistently high Iberian basin near Bilbao, indicating yet another opening plate, both carbonate and separated by the N-Pyrenean (rifting) attempt of the Bay of Biscay. fl ysch-furrow in between. Thus, the Late Cretaceous paleogeography shows three major domains from Early Cretaceous North to South: From Late Jurassic onward, a new paleogeography On the Aquitaine platform, to the north, the developed, provoking the formation of en-echelon syntectonic sedimentation of the foredeep evolves diamond-shaped grabens in relation with the laterally to a carbonate shelf (Dubois and Seguin, activation of inherited structural fabrics. 1980) of Cenomanian to Maastrichtian ages. Within these basins three major phases of This domain is located in a more distal and more subsidence associated to extensional phases can be stable environment within the Late Cretaceous distinguished: paleogeography. It is important to point out Barremian to Early Aptian. that, along the southern limit of the shelf (South The depocenters are associated to very thick black Aquitaine margin), the Cenomanian carbonates shale deposits, while the surrounding carbonate unconformably rest over the Upper Albian sediments. platforms show a very low rate of sedimentation. This unconformity fades out northwards into the One of the main salt diapiric event also occurs during platform. Salt-lineaments of varied orientations as this time along the border faults of the newly formed well as circular diapirs were also enhanced in this basins by migration of the Triassic evaporites from apparently stable platform and in the Parentis Basin. the subsiding depocenters towards the edges. They are located mostly along major faults and fault- Latest Aptian to Early Albian. intersections, such as the diapirs near the city of Dax, The shelf-basin confi guration is acquired during this and along the oil-bearing structures of the Arzacq period. The basins are yet characterized by a very high Basin, (Fig. 6). rate of subsidence and sedimentation of black shales. The N-Pyrenean basin progressively becomes Halokinesis is still going on, such as at the edges equivalent to a Cenomanian to Maastrichtian B16 to B33 n° 2 - from Volume of the Aptian-Albian pull-apart basins and rhomb- foredeep located immediately to the north of North- grabens, e.g. the huge Audignon anticline to the Pyrenean Fault (NPF), thus bordering the European- north of the Arzacq Basin. The shelf-basin transition Iberian plate boundary. The entire fast-subsiding, is marked by a system of limy patch reefs while the turbidite-fi lled, mobile belt becomes progressively platforms surrounding the shelves show a low rate of the North Pyrenean Zone, where the major part of sedimentation. the orogenic thin-skinned deformation of the North- Late Albian. Pyrenees will take place (Zolnai 1971). During the

11 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell However, asaresult oftheongoingnorth-westward unconformity. sediments and/orthebasement,withasharpangular Chaudes” or“calcairesdescañons”overlay the earlier Cretaceous carbonateseriesofthe“calcairesdesEaux massive, thick(about500m)IberianUpper Cretaceous carbonateplatformdeveloped. The To theSouth, infl salt-structures actedaspaleogeographicbarriersand Zolnai 1975). Within theNorthPyreneanfurrow the the mobiledomainsofforedeep(Stevaux and material (salt,shale)arealsoemplaced,mainlyinto and salttectonics.Olistostromescomposedof Triassic the Maastrichtian. Transpression provoked wrenching marls andendedwithathickmudstoneseriesduring furrow bynow becamefi The fl northwards, from Turonian toLower Maastrichtian. prominent, theaxisofforedeepmigrated As compressionbetweenthetwo platesbecame Maurel E-W asymmetricandnarrow troughorfurrow (Moen- a singleN-Pyreneanbasin,whichcorrespondstoan Cenomanian, theen-echelonriftbasinsmerged into uenced thedistribution oftheturbiditicsystems. Figure 6-Structuralframework andPetroleum Provinces oftheSouth Aquitaine andN-Pyreneanbasins(Total). yschsedimentationinthedeepNorthPyrenean et al.,1999). ontheIberianplate,anUpper ne-grained, dominatedby The easternandcentralpartsof theforelandbasins west again. diachronous andoblique,progressingfromeastto the controlofongoingcompression,whichis paleogeography anditsbasinevolution areunder of relatively reducedtectonicactivity, the Tertiary Srivastava, 1991). After aDano-Paleocene period convergence betweenEuropeand Africa (Roestand The Paleocene was atimewithrelatively low plate Tertiary cannibalisation oftheplatformedges. Trough sediments,asaresultoftheprogressive known betweentheplatformsandNorthPyrenean then aretro-forelandbasin.Notransitionalfacies are (Iberian plate)areseparatedbyafl p7latforms tothenorth(Aquitaine)andsouth In conclusion, study. the NorthPyreneanequivalent fl ysch basinisunder Pyrenees. Itsconnectionwithorindependencefrom High Chaininthepresent-daycentralandwestern Iberian carbonateplatformalongtheareaof Senonian fl ysch domainprogressedover theformer intraplate retro-forelandbasin,theSouthernUpper Pyrenean compressionandoftheformation thetwo UpperCretaceouscarbonate yc foredeep ysch WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

changed from marine to continental as topography large masses of coarse continental fanconglomerates developed and the amount of eroded material was (“poudingues”) deposited in successive sequences, in suffi cient to fi ll the basins. In the western Pyrenees the a suite of fans. crust would have recovered its initial thickness later The Ebro basin became closed and separated from than in the central and eastern Pyrenees as a result of the Atlantic because the tectonic relief growth during a greater extension of the Pyrenean crust during Early the inversion of the Lower Cretaceous basins in the Cretaceous times coupled with a younger and lesser western Pyrenees. Erosional debris of the Pyrenees amount of convergence. In this area Paleocene rocks and other surrounding chains of the Ebro basin are represented by deep-water carbonate and silici- (Iberian and Catalan Coastal Ranges) progressively clastic sediments deposited in continuity with the fi lled the basin and then backfi lled, to bury the fl anking Upper Cretaceous turbidites (Pujalte et al., 1989). thrust belts on its margins (Coney et al., 1996). This Two main events will arise : progressive backfi lling forced deformation to migrate 1. the N-Pyrenean foredeep basin will retreat from hindwards and as a consequence reactivation of east to west, and thus the related sedimentary facies previously developed thrust structures and break-back synchronously will do the same, recording the thrust sequences occurred (Vergés and Muñoz, 1990, orogenic evolution, horizontally and vertically. From Burbank et al., 1992b). The southern Pyrenees were east to west and from bottom to top, facies will pass almost completely buried by Early-Middle Miocene from syntectonic fl ysch facies to tidal deposits and times. then to syn- and post-orogenic fanglomerates. The greatest part of the Aquitaine Basin, to the north In detail: the Late Cretaceous-Paleocene time period of the orogenic foreland, nevertheless, remained is still marked by margin instability, with large shallow marine, until the general fi lling of the basin submarine collapses of carbonates mass-fl ows (see caused the sea to progressively retreat to the west. here below, Stop 1.2 at Le Tucq). The abrupt and subsequent Miocene-Pliocene re- In Late Paleocene-Eocene (Ypresian) rhythmic excavation of the southern Pyrenees and the Ebro sedimentation continued in the N-Pyrenean basin, basin to develop the present fl uvial system was some constituting a new thick fl ysch sequence. combination of the Miocene rifting of the western During the Early-Middle Eocene thrusting rate Mediterranean and the Messinian desiccation crisis. increased. Both foreland basins experienced a deepening which resulted into the widest extension Structural history of the Pyrenees of marine deposits in the Pyrenean foreland basins Inherited structures of Precambrian to Paleozoic (Puigdefàbregas et al., 1992, Burbank et al., 1992a). age affected the tectonic basement of the Pyrenean The thrust front in the southern side of the central orogeny, and had a fundamental infl uence on the Pyrenees strongly advanced because deformation of geometry of the Upper Jurassic to Upper Cretaceous the Mesozoic wedge on top of a weak detachment extensional (grabens and rift margins) and on the level (Triassic evaporites). Shallow marine deposits Upper Cretaceous to Tertiary compressive structures were deposited in the foreland as well as in the (frontal and lateral ramps). This combination of pre- piggy-back basins which demonstrate a subhorizontal rifting events produced three trends: mean topography over the southern frontal wedge. - N 20°E to 40°E: corresponding to the Garonne Strongly subsident troughs fi lled by turbiditic - Villefranche fault zone crossing through Toulouse sequences were developed south of the uplifted city. It is active in Late Variscan times as a left-lateral basement in the footwall of the upper thrust sheets. strike slip fault. Some relief existed hindwards as evidenced by the - N 90°E to N 120°E: its corresponds to the Celt- N-S river systems supplying basement clastics and Aquitaine hinge-line and to the North Pyrenean fault by the geometry and location of proximal alluvial zone which acts as a left-lateral strike-slip fault in B16 to B33 n° 2 - from Volume fans. A maximum topography of 1-2 km has been Late Variscan times. calculated based on paleotopographic reconstructions - N 160°E represented in the Axial Zone by kilometer- and fl exural modelling (Vergés et al., 1995, Millán et high folds and incipient cleavage of Variscan age. al., 1995). A succession of events affected the N-Pyrenean In Oligocene along the future Pyrenean foothills domain (fi g. 4 and 5), after the Variscan orogeny. i.e. the orogenic foreland, sedimentation became progressively more terrigenous from east to west, with The fi rst post-Variscan rifting attempt took place

13 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell place alongtheEuropean-Iberianplateboundaryin Biscay. Although themajortranscurrentmotiontakes Plate, whichresultedintheopeningofBay extension andanticlockwiserotation oftheIberian marked bytheparoxysmofgeneralnorth-south The EarlyCretaceous Transtension andpull-apartbasins sets offaults). (essentially theN20°E,50°E-70°Eand160°E controlled primarilybytheinheritedbasementfaults a result,theJurassicsedimentationappearstobe characterized bydiffuse W-NW/E-SE extension. As phase. In Aquitaine, theJurassicpaleogeography is between thetwo platesisrelatedtothatdeformation transtensional faults. A regional sinistralwrenching by N20°Eright-lateraland160°Eleft-lateral which createsE-Wstrikingnormalfaults connected Cretaceous “revolution” or phase oftheLateJurassic(Montagné,1986)-Early The BayofBiscayriftingcorrespondstotheextensive propagation totheNorthofMid-AtlanticRidge. the openingofCentral Atlantic Oceanandthe This periodischaracterizedbythebeginning of Jurassic- EarlytoMid-Cretaceous rifting well asgravity tectonics(Zolnaï,1975). km thick,allowed diapirism,foldingandthrusting,as detachment horizon,whichlocallycanbemorethan1 The thickKeuper evaporitic andshalypotential plate boundary, but alsotothenorth. and theLiassicanhydrites),nearIberian-European transition (approximatelybetweentheKeuper salts fl during theLate Triassic. Submarine(ophitic)volcanic edge, whichalternatedwithdeepcorridorsalready Grand Rieu)wereformedalongthesouthernbasin- Fault Zone).Highemerging blocks(e.g. Arbailles, the southernbasinedge,(nearNorthPyrenean event prevailed inboththeParentis Basin,andalong The Triassic -Jurassic (Gapillou 1981)nearStJeanPieddePort. SW-oriented) ElizondotroughinBasquecountry 1,000 m.Oneofthesegrabensisthetransverse (NE- clastics andvolcanic fl ows, withthicknessesupto the basinitself;they arefi grabens areknown inthePyreneesaswellunder deformed series.RoughlyN-SandE-Woriented, The Permianliesunconformablyonthepreviously the latestagesofpost-variscan peneplanation. as soonthe basin inthecentreofarea,while ows andintrusionstookplaceatthe Triassic-Jurassic Triassic was widelydepositedinafl EARLY PERMIAN geologicalevolution is lled withredcontinental third riftingepisode a secondrifting : , i.e.during at-lying Iberian platebecameincompressionalcontactwith Since atleastthebeginning ofLateCretaceous,the Compression comesfromtheEast... extension/collision Late Cretaceous – Tertiary diachronous known as“N-Pyreneanmetamorphism”. metamorphism allalongtheN-Pyreneanfault zone, the remobilizationoflherzolitesandapeculiarshear and Europeanplates(Plate1,fi and thedifferential driftmovements oftheIberian of Biscaysea-fl and theareasouthof Tarbes. Correlative totheBay emplaced withinthefl ysch furrow, betweenBilbao lava fl In themeantimetholeiticbasaltmasses(pillows and Cenomanian). turbidite (fl the basalwildfl yschs, thefi Souquet andDebroas1981)tothenorth. rst thicksandy-shaly Above which depositedintothedeepsea-arm(“aulacogen”, Pyrenees, offering sourceareasforcoarseclastics, country (BoirieandSouquet1982),orintheCentral to thesouthofMendibelzamassifinBasque the present-dayHighChainbecameemergent e.g. the Iberianmargin andlandmass.Large areasof faulted tiltedblocks(often-kmwidth),calved from opening oftheBayBiscayprogressedeastward, During LateJurassicandEarlyCretaceous,asthe North-Iberian marginandoceanisation: array. is lostbeyond thetransverse NE-SWPamplona- fault the different elementsoftheBasqueMassifs.Itstrace splits intoseveral E-Worientedbranches,separating easternmost PyreneestoBasquecountry, whereit over 500kminsuccessive segments, betweenthe Fault The W-E to WNW-ESE oriented and uplifts(withE-WNNW-SSE trendingedges. Richert andZolnaï,1995,R.Miranda Avilès, 2002) basins orpotentiallypull-apart(Bourrouilh, a setofNW-SE rapidlysubsiding,diamond-shaped (Canérot, 1989),allowing forthedevelopment of platform isdislocatedalongthesemainfault zones directions areusedasminorrelayfaults. The Jurassic 110°E inheritedfaults whiletheN40°Eand160°E sedimentation iscontrolledbytheactivation ofN by diffuse strike-slip movements. The highrateof Aquitaine Basin)totheEbroplatformisaffected entire region fromtheParentis basin(northofthe a Baja-Californiastyle(Miranda Avilès, 2002),the ows aswellsheeteddykes andsills)were was initiallyabraidedfault-system. Itstretches ysch) sequence was deposited (Albian- oor spreading,thestrike-slip tectonics gs. 1and2),provoked North Pyrenean WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

the NW moving African plate. Iberia progressively the sites for the major dislocations, and (b) major crushed the space between its northern margin and formations of the sedimentary column (e. g. Keuper the European plate. Compression was diffuse during salt, Lower Cretaceous marls, Albian to Tertiary Late Albian to Cenomanian; it became effective fl ysch and molasse series) were still extremely as early as in the mid Late Cretaceous (Turonian- incompetent during the period of compression. Large, Senonian) in the eastern part of the Pyrenees (Henry open synclines and anticlines were fi rst formed; the and Mattauer 1972, Souquet and Deramond 1989), synclines later became overthrusted, overturned and propagated progressively to the west during the and/or thinned, sheared by the overriding anticlines. Senonian. Compression provoked gigantic linear Specifi c structures or “ nappes ” were thus generated, gravity slope sequences or “Evolutionary-mass fl ow- which would seem uncommon in areas of greater megaturbidites” (Bourrouilh et al. 1983), which can crustal rigidity and with more competent sedimentary reach 90 km in length and a thickness of about 60 m. sequences (there are very few true fl at-and-ramp Similarly, in the southern Pyrenean Basin, but during thrusts and “duplexes” in the northern Pyrenees, the Eocene, compression is accompanied by the Moen-Maurel et al., 1999). emergence of a syntectonic cycle of gigantic mass- fl ow-megaturbidites extending over 140 km in map The North and South Pyrenean Thrust Fronts are view, and more than 200 m thick (Soler et al., 1970, actually tectonic envelopes, and not continuous, Johns et al., 1981). unique, sole faults. They are composed by segments The main north-south compressional event of which relay each other, sometimes with important the Pyrenees began nevertheless from MIDDLE offsets. On the Northern Pyrenean side, several EOCENE onward. The main ductile deformation structural arcs exist: the Basque Arc, along the north- occurred at the plate boundary, within the North western Pyrenees, the Lannemezan Arc in the central Pyrenean Fault Zone, which represents the most northern Pyrenees etc., but also on the southern strongly compressed, schistosed, crushed part of the side, such as the Graus-Tremp Arc in the southern belt (Choukroune, 1974), and along the northern Pyrenees; their tips all lay in lateral or oblique ramps edge of the Iberian block. Former normal faults and which were inherited from the rift basin edges. Two hingelines were inverted into overthrusts, the northern well-explored surface anticlines are centered in the limit of the highly compressed zone corresponding to northern arcs : the Ste. Suzanne structure to the west, the earlier boundary between the fl ysch furrow and and the “Petites Pyrénées” in the Central Zone. Thrust the northern carbonate plaform. This long-lived sheets do not exceed 12 km. tectonic edge has thus become the North Pyrenean Thrust Front. The Southern thrust sheets are therefore the most The main structural events created or re-activated in spectacular ones: this period from Late Cretaceous (Maastrichtian) to From Early Eocene to Oligocene, the Upper Thrust Oligocene are: Sheets (Muñoz et al. 1986) or the South Pyrenean N 110°E folds, cleavage, stylolites, reverse faults and Central Unit (Seguret, 1972), composed of Mesozoic thrust planes either to the north or to the south. to syntectonic Tertiary formations, were successively N 20°E to 40°E, left-lateral lateral ramps. transported along a sole of Keuper evaporites, argilites N 160°E, right-lateral lateral ramps. and marls (Bresson, 1903, Seguret, 1972, Muñoz et Normal faults are also present: in some areas they al. 1986). They are, from East to West, the Pedraforca, are striking N-S; some minor sub-E-W faults are also Boixols, Montsec, Cotiella Thrust sheets; the front of created in close relation to major thrusts trending E-W all outlines the South-Pyrenean Front Thrust, which and salt ridge keystone collapse. produced the Sierras Marginales (plate 1). During the orogeny, several compressional episodes In the High Chain, these cover thrust sheets root into B16 to B33 n° 2 - from Volume followed each other, the younger, more external the Upper Paleozoic basement, along with the deeper faults (sole-faults of allochthonous units or rafts) thrusts which are the Nogueras and the Gavarnie- deforming the earlier, more internal ones in a piggy- Mont Perdu Units. back fashion. The deformation and structural styles The total shortening of the Pyrenees is evaluated, appear controlled by the rheology of the material depending on the authors, between 100 to 160 km. involved: (a) the already fractured deep basement Pyrenean orogeny and inversion continued during complex was involved in the compression, setting the MIOCENE.

15 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell resulting inthediscoveries offi interest moved northward towards thebasinedges, during thesameperiod.In1970’s, exploration 7 Gm3 gas(110to250 BCF) werealsodiscovered Cassourat …) withaccumulationsrangingfrom 3 to smaller sizedfi elds (Ucha/Lacommande,Rousse, a surface anticline).Inthesame Arzacq basin,several discovery was madeusing2Dseismicdatashowing gas fi drilled ongravimetric anomalies)andtheMeillon Gm3 gas – 9.2TCF)(discovery1951 (260 wells were Lacq oilfield in1949,thedeepgiantLacqgasfi was thenconfi rmed bythediscoveries oftheupper on asurface anticline. The area’s positive potential (Comminges Basin). The discovery wellwas drilled Marcet GasFieldin1939(8 Gm3 ofgas–290BCF) in the1930’s andresultedinthediscovery oftheSt- South Aquitaine basins(forelandandfoothills)started since Romantimes,petroleumexploration ofthe province ofFrance. Although seepshave beenknown The Aquitaine arearepresentsthelargest oilandgas History Petroleum explorationframework southern vergence tonearvertical. former overthrust sheets,back-steepeningthoseof post-orogenic isostaticadjustment,alsodeformedthe by erosion. This upliftmovement, possiblyalate-or m MSL.),wherePaleozoic outcropswereexhumed day High“axial”mountainChain(+2,000to+3,500 former southern(Iberian)margin toformthepresent- an important episode ofthePyreneanorogeny seemstohave been The very latest, Neotectonic relaxation anduplift 160°E” (right-andleft-lateral). (mostly left-lateralduetoS-compression)and“N- the basementfaults produced“N-40°E”dip-slip 2002) aswellrotationalconstrainsinducedalong Partitioning ofthedeformation(seeMiranda Avilès, They representthemainpetroleum objectives; their Jurassic dolomitesandBarremian limestones Reservoirs province”) (fi along theedgesofforelandbasin(the“saltridges Meillon” domain),andanoiltrendtothenorth of thePyreneesFold and Thrust Belt (the“Lacq- along theleadingedgeandproximalforeland trends areclearlyidentifi ed: agastrendtothesouth Bonrepos-Montastruc, fi (Pecorade, Vic Bilh,Lagrave, CasteraLouand eld in1965(65 Gm3 gas–2.3 TCF) (this (Fig. 7). g. 6and7). relief development PLIOCENE toHOLOCENE g 6. w hydrocarbon Two 6). g. ve sizableoilfi , whichupliftedthe eld in elds most effi and anhydritesLower Aptian shales representthe Hauterivian to Valanginian shales,Barremianshales Barremian andJurassic plays Seals transcurrent fault system. away fromtheimmediatesettingof Tertiary Seron therefore reservoir capacitydecreasesignifi of theLagrave Fieldwheredolomitizationand Pyrenean faults. Itisdemonstratedbytheexample secondary dolomitizationinthevicinityofmain linked tothehighenergy facies distribution andtoa limestones (15to20%matrixporosity)areclosely platform. The goodreservoir characteristicsofthese (200 m to250 metres thick)oftheUpperCretaceous They correspondtotheLower Senonianlimestones The UpperCretaceous reservoirs fracturation. and permeabilityarealsoenhancedbyintense of theLacqgiantfi The Lower Barremian fracturing. again relatively poorbut enhancedbytheintense porosities rangingfrom 10 to15%.Permeabilityis the UpperBarremianlimestones,whichdisplay Within thissameareathereservoirs alsoinclude intervals characterizedbyahighenergy ofdeposition. again primarilyassociatedwithintensefracturingand better, they remainpoor(2to10%).Productionis Even thoughthepetrophysicalcharacteristicsare preserved asreservoirs withintheJurassicsequence. and Vic Bilhfi elds), onlytheManodolomitesare In theJurassic outershelf well productivity. vugs (duetosecondarydiagenesis),allowing forgood permeability isprimarilyduetojointfracturesand Meillon dolomite).For theseformations,effective porosity fortheManodolomitesand 4 to8%forthe characteristics areratherpoor(2to4%matrix structures. For thesetwo reservoirs thepetrophysical along theUcha,LacommandeandRoussetrendof gas-bearing ontheMeillongas-fi breccias. These reservoirs aretotallyorpartially Mano dolomites(150to200 m thick)andGarlin dolomites (200 m thickinaverage), thePortlandian represented bytheLower KimmeridgianMeillon On theJurassic easternshelf paleogeographic provinces describedearlier. domains canbedistinguishedinaccordancewiththe Earliest Cretaceouspaleogeographicsetting. Two occurrence iscloselylinked totheJurassicand (Fig. 7). cient sealsfortheoilandgasfi eld. Itslow porosities(2-11%) isalsooneofthereservoirs tothewest(Lacq,Pecorade eld trendaswell thereservoirs are elds inthe cantly WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

Figure 7 - Aquitaine basin : stratigraphic chart and Petroleum Systems (Total).

Arzacq basin. level of the Lower Cretaceous depocenters of the Upper Cretaceous plays Arzacq Basin and occurred during the Tertiary on Seals are composed of the Upper Senonian shaly both sides of the basin (fi g. 8). or marly intervals and by the Lower Tertiary slope The Kimmeridgian source rocks appear to have the shales. best potential. The organic matter is again primarily Source rocks (Fig. 7). of marine origin (type II-III). Important reserves of oil and gas have been discovered Trap types and hydrocarbon charge (Fig. 8). in the Aquitaine Basin, implying that sources with a The traps for the different fi elds are clearly related regional extension and good petroleum potential are to structures which are inherited from the Early present in order to expel signifi cant quantities of oil Cretaceous extension (platform to basin transition) and gas. Although some source potential has been and its associated salt tectonics along the limits recognized in the Tertiary, Albian and Liassic shales, of the basins (erosional pinch-out of the Jurassic these formations are low-quality source rocks. and Barremian reservoirs). These traps have been The main source rocks are clearly associated to the enhanced by the Pyrenean orogeny. Some of them are

Barremian and Kimmeridgian formations (Lons Fm) located in the Pyrenean fold and thrust belt (Saucede B16 to B33 n° 2 - from Volume as shown by the source-to-oil condensate and source- and Ledeuix); but most occur within the proximal to-gas correlations. (Lacq, Meillon, Ucha, Lacommande, Rousse fi elds) The Barremian organic matter is primarily of marine and distal forelands (Vic Bilh, Castera Lou, Lagrave). origin including woody material (type II-III). Across Exceptional productive traps can be even found in the basin the oil window is reached at – 3,000 metres episyenites (Moen-Maurel et al., 1996). on average, while the gas window is reached at – 4,000 metres (fi g. 8). It is noteworthy that expulsion of hydrocarbons started during the Late Albian at the

17 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell The anticlockwiserotationoftheIberianplatewith 2) Platemotionvector evolution : Moen-Maurel arc position(andpreservingitspetroleumsystems, basins oftheEuropeanplateinalittledeformedretro- mainly affected theIberianplate,leaving therift Pyrenean (LateCretaceoustoEocene)inversion differentiated passive margins. the BayofBiscaytoproduceanoceanicfloor andtwo times. However extension was never suffi basement fabrics thatwereacquiredinPaleozoic echelon, asaresultofthecontrolprevious oblique can beinvestigated inthesubsurface today, wereen- At theparoxysmof Albian rifting,many riftsthat to theEbrobasinandCantabriandomainSouth. wide) extending fromtheParentis basintothenorth the tethyandomainover abroadarea(400kmN-S of riftingfrom Triassic to Albian atthewesterntipof The continentalcrusthereunderwentdiffuse stages 1) Crustalcharacteristics characteristics shouldbepointedout: In comparisontoothersFTB,thefollowing striking Fold-and-Thrusts Belts Comparison withother et al.,1999). Figure 8- Aquitaine-Arzacq Basin:Evolution ofSourceRocks (Total). : cient eastof The existence of Triassic evaporites ledtohalotectonics 3) Salttectonics any majorobliquecollision. therefore thecover deformationcannotaccommodate thrust tipsstillexist attheoutcroporinsubsurface, phases from Turonian toMiocene.Nevertheless most to measuretheamountofstrike-slip intheshortening fl the Triassic evaporites andintheUpper Cretaceous During collisiontheuseofpotentialdetachmentsin al., 1999). more than5%horizontalstretching,Moen-Maurelet with minorhorizontaldisplacementsalongfaults (no diffuse extension whichproduceden-echelongrabens (supposedly reachingtensofkminstrike-slip), and strike-slip whichfocusedonspecifi led tothepartitioningofdeformationbetween European platesfromEarlyCretaceoustoCenomanian The obliqueextension betweentheIberianand the or strike-slip intheeast. the sametimeextension inthewestandcompression and senseofthedisplacementvectors, producingat to Cenomanianledvariations intrend,magnitude respect totheEuropeanplatefromEarlyCretaceous ysch ledtovarying structuralstylesmakingitdiffi c shear fault zones fault shear c cult WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

from Late Jurassic onward. Salt pillows and ridges were - the petroleum system trilogy series were protected re-activated as anticlines during compression while from uplift and erosion over the Parentis and North- evaporite-rich widespread units acted as detachments Pyrenean basins since they remain situated in the and thrust soles. The salt mobility triggered enhanced outer rim of the collision, in a little affected retroarc amplitude and curvature in fold axes, non-cylindricity position. After rifting subsidence, the additional burial and virgation, as well as a diachronous record of the which was achieved with the foredeep deposition led tectonic stress events. When salt is involved onset and to reaching the gas window and to the development of end ages of tectonic events may vary through time and large gas traps. space making it diffi cult to tie deformation to stress - salt tectonics eventually enhanced the amplitude of and/or plate tectonics. traps and their closure. Such providence makes the 4) Fold-and-Thrust belt structural style: Aquitaine oil and gas structures quite similar to North Thick-skinned thrusting affected the Iberian plate Sea oil and gas fi elds. margin along the underthrusting plane, resulting in antiformal stacks of basement (Paleozoic) producing To conclude, it should fi nally be emphasized that fi rst of the axial zone of the mountain range. The steep dips all, the structural history of the whole area is controlled of the basement ramps may have been facilitated by by a N110°E plate boundary crustal anomaly, running the oblique component of the collision initial vector from West Greenland to the Tethys and then to the and the existence of steep and weak shear zones from modern Mediterranean (R. Bourrouilh, 1970, 1973). the Early Cretaceous drift stage (such as the North- This lineament is evidenced by the N-Pyrenean Fault Pyrenean Faut system). and its peculiar metamorphism, the thinning of the Thin-skinned thrusting was possible when cover crust, the Biscay rifting, the injection of the mantle detachments could be activated over large distances: lherzolites. The plate boundary crustal anomaly seems for the southern FTB it resulted in transferring the to be Pre-Triassic, putting in contact an Iberian deeply uplift and the 100 km range shortening in piggy-back structured (with pre-existing crustal detachment faults) fashion over a few large thrust sheets towards the and thick continental lithosphere to the south, and a external sierras, and for the northern FTB it resulted in thin, less structured European one to the north. The producing a retroarc and in accommodating the axial Late Cretaceous to Tertiary tectonic shortening is overload with thrusts and nappes mostly affecting the asymmetric, being estimated, depending on the authors Upper Cretaceous to Eocene fl ysch basins. and the area, at 100 to 160 km over the Iberian plate, The shape and magnitude of the thrust sheets was and at 5 to 12 km over the European one. strongly infl uenced by the attitude and potential friction In its western part (Bay of Biscay), the Pyrenean of the detachment stratigraphic horizons: salt ridges in orogen is incomplete. To the east, it interferes with the the north favoured large amplitude (up to 5 km) upright Betico-Kabylo-Alpine orogen and is overprinted by the and overturned when they slid over fl ysch units. Rift extensive Neogene Mediterranean structures. grabens and fl ysch basins morphology infl uenced The result of the collision in the Pyrenees produces the location of both frontal and lateral ramps. This an asymmetric fan-shaped orogen, resulting from the stratigraphic control leads to structural styles that are crustal ductile underthrusting or underplating of the common along the alpine (tethyan) orogen, unlike Iberian Precambrian-Paleozoic basement underneath craton margin orogens where isopach formations the European plate. rather, led to fl at-and-ramp thrust propagation such as in the Appalachians and the Rocky Mountains. The Pyrenean orogenic complex of the Pyrenees 5) Petroleum evaluation is devoid of granitic intrusions and syn-orogenic The North-Pyrenean retro-arc basin was a prolifi c oil volcanism, there are no ophiolitic masses and the and gas province with giant fi elds (Perrodon, 1980) known metamorphism is restricted to the trace of B16 to B33 n° 2 - from Volume because: the North Pyrenean Fault Complex (Choukroune - the petroleum system trilogy (source rock, reservoir 1974). This indicates that the major orogenic event and seal) belonged to pre- and syn-rift series which are in the area was the variscan one (tectonics with major usually characterized by extensive and stable marine crustal shortening, penetrative metamorphism and sedimentation making hydrocarbon migration easy granitization). Parts of this structural crustal heritage (or and exploration more predictable even in areas of regional fabrics) were activated during the Mesozoic poorly imaged seismic prospecting (Moen-Maurel et extensions, re-utilized by the Late Cretaceous to al, 1995). Tertiary Pyrenean orogenic convergence.

19 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell Upper Cretaceous fl Le Tucq : theNorth-Pyrenean margin andthe Stop 2.1: from Pau toOloron SainteMarie [email protected] ** TOTAL, 64018Pau Cedex, France, e-mail : e-mail :[email protected] Avenue desFacultés, 33405 Talence Cedex, France, *Laboratoire CIBAMAR, Université deBordeaux1, By R.Bourrouilh*andL.Moen-Maurel**, I. A transectofthenorthern pyrenees Panorama ofthePyrenees :fi Stop 1.1: Briefi A. Teixell. By R.Bourrouilh,L.Moen-Maurel,J. Muñoz And Welcome tothefield tripandthePyrenees Pau Field Itinerary ng andintroductiontotheField Trip. Figure 1.1-GeologicalviewofthePyrenees,fromBoulevarddesPau. ysch : DAY 2 DAY 1 gure 1.1. Structural andsedimentologicallandscape: adjacent cartrack. and 2.1c,Guillampeausection)alongthesideof and themeasuredsection(fi gure 2.1b, Tucq section section islocatedinthecurve oftheroad(fi the road,justatlocality“Le Tucq”. The outcrop Access: the silici-clasticPaleocene sedimentation. closure ofthebasin,andwestward progradationof is now covered byroadwork) whichiscoeval withthe Cretaceous-Paleocene sedimentation(but theKTlimit The sectionstudiedinthisStoppertainstoUpper can reach7kminthickness. Biscay. The North-Pyreneanfl Ma totoday, forming,uptonow, themodernBayof and thefurrow rapidlyretreatedwestwards, from80 as recently80Maago,duringtheLateCretaceous However, theareaunderwentcompressionaltectonics up bysynriftanddriftcalcareousCretaceousFlysch. N-Pyrenean basinortrough,whichwas rapidlyfi basins merged inalongandnarrow furrow orthe black shales.DuringCenomanian(-96Ma),rifted created andfi lled bysyn-riftLower Cretaceous Bay ofBiscay. The N-Pyreneanriftedbasinswere as apassive riftedmargin duringtheopeningof Introduction fi gures 2.1a,b,c,2.1d theStopisonD934,rightsideof : theSouth Aquitaine margin developed yc sedimentation, ysch gure 1.1a) theD lled WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

Figure 2.1a - Flysch section at Guillampeau, top is on the right.

934 crosscuts the Upper Cretaceous fl ysch. The curve of the river, as well as that of the road are provoked by the top of the Upper Cretaceous fl ysch, containing large white mudstone mudfl ows, as well as reworked Triassic (fi rst diapiric) gravity slabs mass-fl ows, silici-clastic mass fl ows etc. In the landscape, the curve is marked by an old chalk oven, and prolonged by a smooth wooded cliff. Along the western side of the road two fi eld sections have been measured in the gently north-dipping Figure 2.1b - measured section at Le Tucq, from turbiditic and mass-fl ow sequences with internal R.Bourrouilh et al., 1993, unpub. data. slumps (Bourrouilh, Montagné and Doyle, 1993, unpublished data). and anoxic mud clasts, and by silici-clastic Bouma- The fi rst one, or the Tucq section is just on the curve type turbidites. Measured sedimentary fold axes are, of the road, in front of the Tucq restaurant, but is now successively, from bottom to top : N 60°, dip 35°E covered by road work (fi gure 2.1b): (unit 2, lower part), N 83°, dip 10° SE (small slump, The Upper-Cretaceous to Paleocene section is unit 3), N 175° (large slump, unit 3), N 90° to 110° 27 m thick and represents a mixed silici-clastic- (clast, base of unit 4), N 115°, dip 25°N, (base of unit carbonate sedimentation. Five sedimentary units 5), N 115°, dip 22° N-NE. can be distinguished. On the four basal units, the However, carbonate gravity sedimentation comes sedimentation is mainly constituted by successive back again and forms unit 5, considered the base of a silici-clastic mass-fl ow deposits, reworked mudstones large carbonate mud-fl ow. Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 2.1ca - measured section 1 at Guillampeau, from Figure 2.1cb - measured section 2 at Guillampeau, from R.Bourrouilh et al., 1993, unpub. data. R. Bourrouilh et al. 1993, unpub. data.

21 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell migration oftheinterplatecompression. basin-Bay ofBiscay, duetotheprogressive westward shelf andtotheprogressive closureoftheN-Pyrenean amount ofcarbonatesdepositedontheedge the Ypresian. This relative instabilityisduetoahigh vary asmuchbelow intheCampanianandabove in thicknesses acrosstheNorth-Pyreneandomaindonot Late CretaceoustotheEarlyPaleocene even though Pyrenean basinappeartobeinstableduringthelate Conclusions: 2.1cb) measured alongthesideofroad(fi The secondoneortheGuillampeausection 1993, unpub. data. Figure 2.1d-Schematic reconstructionoftheDano-Paleocene Aquitaine marginatLeTucq, fromR.Bourrouilhetal. fi gure 2.1d : themargins oftheN- Figure 2.2-Panoramic viewoftheMailh Arrouy andOssau Valley (Total). g. 2.1caand is G. Montagné,1986,Seyve, 1984. For furtherinformation: Stevaux andZolnaï,1975, Laruns, atSevignacq, ontherighttake thesmallroad Access: which isthelocallanguage: Aüssaü =highvalley). northward throughtheOssau Valley (inBéarnais, the HighRangeandPicduMidid’Ossau,fl frontal vallum oftheglacier, whichwentdown from The smallvillageofSevignacq isbuilt onthemorainic (fi and neotectonics:Sévignacq the Ossau Valley: uplifting,glaciers Stop 2.2: leaving themainroadD934fromPau to gure 2.2) owing WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

D 232, from Sevignacq to Bescat. The Stop is located relaxation at present. Rising of the mountain all after leaving Sevignacq and a few hundred metres around provoked in turn the Ossau river to change its down, after the cemetery, in the plain. course from north to west, cutting the moraine and the Structural landscape: the panorama shows, from left Urgonian limestone to the West. to right: the Mesozoic high mountain of Mont du Rey, The Ossau river now fl ows towards the west after the glacial U-shaped valley of Ossau, with the high cutting the frontal moraine and the cretaceous bedrock chain and the faulted caldera of Pic du Midi d’Ossau in a narrow deep neo-tectonic canyon, located in the in the background, and on the right, the Mesozoic western outskirts of Arudy village. Lazerque (1,368m) and Mailh Arrouy (1,251m) But an underground northward paleocirculation of the mountain range. Ossau waters still exists and fl ows to the north, under Interpretation: the Ossau glacier was one of the most the frontal moraine and producing a resurgent spring important Würmian Pyrenean glaciers, which fl owed in the karstifi ed limestone north of Rébénacq. There, south to north, from the High Chain to Sevignacq. At the river is called “Luy du Néez”. its front, it produced a large moraine, which surrounds us as a morainic vallum. Deglaciation began some Stop 2.3: 11,000 years ago and the glacier was about 1,000 m Arudy: opening of the rift as recorded by mud thick here. Melting of the ice provoked a reduction mound markers (fi g. 2.3a and 2.3b) of the ice weight on the crustal lithosphere, which Introduction: at the village of Arudy, several Aptian- began an upward isostatic buoyancy and slowly rose Albian mud-mounds are or were worked for marble. up. The mountain range is still being uplifted under Geological studies (Bouroullec et al., 1979), generally

Figure 2.3a - Stratigraphy and geodynamic evolution of the Arudy basin, from R. Bourrouilh, 2000. Volume n° 2 - from B16 to B33 n° 2 - from Volume

23 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell to thequarry, pastametalgate. left onagravel roadcrossingtheforestandleadingup West (Lurbe-St-Christaudirection). After 1km,turn own risk.Northof Arudy, follow D918towards the Visiting thequarry, even whenauthorized,isatyour at thePaloma quarryalongthe Arudy toLurberoad. Laplace foraccessauthorizationwellbeforevisiting excursion. Access tothequarryisrestricted. Ask Mr Dela quarry)andmudmound,willbevisitedinthis Access: development stageofthemud-moundcomplex. into theblackshalebasinof Arudy duringthelatest which representanuppermost Aptian mud-moundslid Here wewillonlyvisittheBoisduBagerquarry, their originalenvironment. they couldhave beengravitationally displacedfrom buildups couldbenotintheiroriginalpositionorthat changes but they didnotconsiderthatsomeofthese studied therelationshipofbuildups tosealevels basin. LenobleetCanérot(1993)and(1996), large blocksthathave slumpedintothe blackshale some reefsandmud-moundsof Arudy wereinfact sedimentological dataontheareaandtosuggestthat Digbehi (1987)was thefi dealt withstratigraphyandmicropaleontology. onlytheBoisduBagerquarry(orBorde Figure 2.3b-Sketch oftheBoisduBagerquarry, asvisiblein1997,fromR.Bourrouilh, 2000. rst topresentconsistent can tolerateacertainamountofturbidity inthewater. microsolenids candevelop inquitedeepwater and corals. According to L.Beauvais (pers.comm.1995), massive grey mudstonescontainingfl situated 2kmsouth-westof Arudy. Itconsistsof We willfocushereontheBoisduBagermud-mound, continent (Plate1,fig. 1and2). spreading oftheBayBiscayontoEuropean indicating theeastward progressionofseafl intruded bybasicvolcanism withfl basins. These pull-apartbasins wereprogressively These build-ups grew inacontext ofanoxicpull-apart Albian reefsandmud-mounds(Fig.2.3a2.3b). this platformwas marked bythegrowth of Aptian- the smallvillageof Arudy, southofthecityPau, Aptian-Albian carbonateplatformdeveloped: near and Ammonitic blackshalesweredeposited. Then an invaded theareasouthofPau duringtheBarremian lagoonal carbonates.FromtheBayofBiscay, thesea sandstones (GrèsdeLacq),thenbyLower Barremian Cretaceous disconformityisoverlain bycontinental transgressive sequence:anUpperJurassictoLower sequence (Fig.2.3a)shows atypicalextensional and southern edgeoftheN-Pyreneanrift,stratigraphic Structural landscape (R.Bourrouilh,2000):onthe at microsolenidae oods ofbasalts, oor WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

Those corals have umbrella-shaped morphologies, grew near the aphotic-subphotic zone transition, and indicating a low energy environment; they grow in certainly below storm wave base (no evidence of successive layers, indicating the stratifi cation and the wave action). Stratigraphy and original position of the upper part of the mound. mound is shown by the layering of microsolenids (So The base of the mound shows a locally deformed on Fig. 2.3b). contact with the underlying black shales (Fig. 2.3b). 2. Due both to growth and to the opening of the Along the basal contact, the lower part of the mound Arudy Basin, the mound slid and rotated 65° shows a slump breccia, with large mud-mound clockwise towards the NE (N 30°E). This rotation elongated clasts, some of them with microsolenidae, produced emergence of the SW fl ank of the mound; embedded in a black shale matrix. The mound also this emergence does not seem to refl ect a sea level exhibits two layers of black shale, locally contorted fall, as proposed by Canérot (1996). Emergence was and with load pockets. These layers of black shales accompanied by aerial and karstic erosion of the can be interpreted as recurrence of mud sedimentation, mound. The fl ank of the mound is eroded by karstic or they refl ect shale intrusions into the mound which cavities. Karstic erosion penetrated deep into the dead slid downwards with the mound itself. Observation mound, resulting in the formation of a large karstic of the orientation of the microsolenids show that cavity, which was then fi lled by a breccia (Fig. 2 .3b). these two black shales are obliquely oriented, and A large part of the breccia is autochtonous, but blocks clearly indicate that the mud-mound has tilted over of overlying shallow water units, some as long as 2 to an angle of about 90° from its normal position, metres, also fell down in the cavity. considering that the concave side of the umbrella- 3. These clasts are interpreted here as reworked shaped microsolenids faces upwards. The body of parts of coarse graded supratidal to intertidal storm the mound consist of massive grey microsolenidae deposits (Fig. 2.3b). The original deposits, where mudstones but it also shows a large karstic erosional they originate, are not observable in place, laterally cavity which refl ects emergence (Canérot, 1996). The or directly overlying the mound, but the presence of cave is fi lled with a karstic breccia, partly originating such clasts among the karstic breccia testify that near from the mound itself. (Fig. 2.3b). The breccia the emerged mound, supratidal to intertidal storm is partly dolomitized and locally impregnated by sediments were deposited. These fl at-lying clasts bitumen. indicate horizontal bedding during the karstifi cation In order to determine the diagenesis of the mound period, which is in agreement with the geometry of and the quality of the marmoreal limestone, a new the karstifi cation. We can suppose that the storm geophysical tool, the electrostatic quadripole was deposits have been eroded, broken and taken away as used (Benderitter et al, 1997). A precise resistivity clasts, which fell down in the karstic cavity. map of the diagenesis and of the fracturing was 4. Renewed tectonic activity led to an anticlockwise obtained, showing the mud-mound build-up, the 125° rotation of the mound towards the SW (N karstic cave and its brecciated karstic infi ll. 210°E). As a result, the mud-mound collapsed and This side of the mound is karstifi ed and the karstic slid down into the deep black shale basin, where it cavities are fi lled with black shales (Fig. 2.3b). This was buried, forming a large olistolith (the mound is area presents a white to light grey colour and it is covered up by, and embedded into the black shales). largely dolomitized. Study of the dolomitization The slumping resulted in the formation of a slump shows that this refl ects the contact of the mound with breccia (on the base of the mound, 4, Fig. 2.3b), and the phreatic lens (Bourrouilh-Le Jan, 1973, 1975), of the two intrusive black shale layers, parallel to the related to emergence. basal surface of the mound (4, Fig. 2.3b). These black Geodynamic interpretation: a provisional scenario shale layers are deformed and contorted. for this mound development is proposed hereafter 5. The dead mound was then buried in the black shales B16 to B33 n° 2 - from Volume based on geometry, stratifi cation, geopetal structures, and later in the basin evolution, oil migrated into the karst, fi lling of the karst, diagenesis (Fig. 2.3b) The karstic cave (5, Fig. 2.3b). following numbers refer to the numbers on Fig. 2.3b: 6. The thermal development which matured the oil 1. The Bois du Bager mud-mound began to develop also seems to have been responsible for exfoliation as soon as turbiditic black shale deposition input of the karstic cave wall, above the reworked decreased signifi cantly (microsolenids can tolerate “pebbles” (6, Fig. 2.3b). Fragments of exfoliated a certain amount of turbidity). The mound probably cave wall are observed lying perpendicularly to the

25 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell Cezy unconformity andstratigraphy ofthe Stop 2.4: (1991), Canérot(1996),Bourrouilh(2000) For furtherinformation: CanérotandLenoble mounds orintrabasinalhigh-porosityanomalies. HCs migrateandhow they canconcentrateintomud- mounds karsticcavities isagoodexample ofhow The hydrocarbonfi in theParentis Basin). shows inthe Arzacq Basin,MimizanNorthoilfi the playsof Aquitaine basin(Gaujacqdiapiricoil Clansayesian reefintervals alsorepresentoneof of subsurface analogs(Bonnefondfi the permeability(andthusproductivity) mud-mounds produceddissolutionswhichenhanced Hydrocarbons: black shalesandfracturationofthemound producing aN120°Esubvertical schistosityinthe 7. The Pyreneanorogeny foldedthewholearea, hydrothermal origin. between exfoliated wall fragmentsmayalsobeof basal clasts. White calciticcementsfi lling thepores Pal= Paleozoic, T=Triassic, C=Cenomanian,T=Turonian, Co=Coniacian,Sa=Santonian Figure 2.4a-Southverging ThrustsandFolds ofLesEauxChaudesandpanoramaCézy. the Aptian karststhataffect the lling oftheBoisduBagermud- ed. The eld). eld (fi observe theCezyUpperCretaceousunconformity North PyreneanFault, wewillStoponD934to so calledforitswarm thermalwaters relatedtothe Access: thrusts nearLesEauxChaudes. The roadwillcrossintheforestseveral south-verging with itscharacteristicU-shapedprofi the baseofglacierisclearlyobservable above, Devonian limestonesinadeepcanyon; meanwhile sub-glacier valley oftheOssauriver, whichcutsthe it ispossibletoobserve, ontherightside,deep road begins toturnleft,andbeforeenteringatunnel, scenic view shows theice-ageOssau Valley. When the metamorphosed Devonian limestones;totheright,a Bonnes and Aubisque pass,totheleftroadcuts plate. Passing thecrossroadwithD918toLesEaux Paleozoic basementofthehighchainandIberian at Laruns,wenow drive alongD934through the Introduction: 2.4a and2.4b). des cañons”or“calcaires desEauxChaudes”(fi Iberian UpperCretaceous limestonesor“calcaires gure 2.4a). crossing the village of “ Les Eaux-Chaudes ”, Les Eaux-Chaudes crossingthevillageof“ crossingtheNorthPyreneanFault le. g. g. WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16 Volume n° 2 - from B16 to B33 n° 2 - from Volume Figure 2.4b - Stratigraphy and geodynamic interpretation of the Iberian margin and of the “ Canyon Limestones ” or “Calcaires des Eaux Chaudes”, at locus typicus. A, B = location and structural sketch ; C= Iberian Margin evolution ; D= Cenomanian ; E= Turonian ; F= Coniacian. From R. Bourrouilh and M. Alhamawi, 1993.

Structural landscape (fi gure 2.4a): the High Chain is the panorama, we see the granites, abruptly eroded there composed by a huge Paleozoic series, intruded and overlain by the transgressive Cenomanian by the Variscan granites of Les Eaux-Chaudes, which shallow water limestones, followed by Turonian and metamorphosed the surrounding rocks. Observing Santonian (yellow) limestones. This autochthonous

27 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell and Alhamawi (1993). and Alhamawi For furtherinformation: Ternet (1965),Bourrouilh (Bourrouilh and Alhamawi, 1985). Campanian announcingcompressioninthe West fl sunk westwards. As aconsequence,deepcalcareous developed whiletheIberianplatedifferentially Pyrenean andNorth-Pyreneanforedeepbasins progressed duringtheLateCretaceous,South compression betweenIberianandEuropeanplates Alhamawi, 1985).However, asthetectonic features fromhurricanetrails(Bourrouilhand or “ limestone ofthecañons ” exibits sedimentation and, like intheBahamas,EauxChaudeslimestone environment quitesimilartothemodernBahamas occurred inashallow sea(fi gure 2.4b),inan Sedimentation oftheUpperCretaceouslimestone basin whichdeveloped north,alongaN110°axis. margin?) North-Pyrenean ofthedeep(-3,000m limestones, theIberiannorthernmargin was alsothe deposition oftheseUpperCretaceousshallow water resting above theEaux-Chaudesgranites.During erosional continentalsurface oftheIberianplateor Cenomanian toSantonian,sealingthepre-Cenomanian deposited directlyontheIberianplatebasement,from latitude. UpperCretaceousshallow water limestones located southofitsactualposition,inanintertropical transgression. Inthisperiod,theIberianplatewas the Cenomanian,seacameagaininageneral from herewestwards totheBayofBiscay. During deposited onthenorthernmargin oftheIberianplate, the Mendibelzaconglomerates.Suchfanglomerates fl by fl basement was eroded.Hugeerosionaccompanied such astheCezyMountain,emerged Iberian area uptotheCenomanian(-96Ma).Inlarge areas Biscay, theIberianplateremainedemerged inthis broke upinresponsetotheopeningofBay Interpretation: just above theparkingarea. Paleozoic basementformthepicdeGoupey (2,209m) fl again over theunderlyingthrust,forminganinverted series, stillrestingonevaporitic Triassic, isthrusted Cretaceous limestones. A secondUpperCretaceous base, followed upwards by a thickseriesofUpper composed byaslabofevaporitic Triassic atthe Upper Cretaceousseriesisoverlain byathrust, ysch facies appearhereduringtheLateSantonian- uvial anddeltaicconglomerates(1kmthick)called ank ofasouth-verging recumbentfold. The inverted uvial transportationledtodepositionofthick whentheJurassic Aquitaine platform of aPaleozoic crest. Artouste skiresort. A shortwalk willbringustothetop we willtake thetelepherique(cable-car)upto Access: fromthebankofFabrèges damreservoir cover south-verging thrusts. Pyrenean basin,andaseriesofsuccessive basement+ tectonic inversion ofthenorthernmargin oftheSouth compression migratedwestwards andprovoked the was overlain bydeepwater fl the shallow water limestonefacies deepenedand Senonian: thefutureHighChaindownwarped, An incipientcompressionbegan hereduringthe continued duringamajorpartoftheLateCretaceous. shallow marinelimestonesandthissedimentation basement theC then intrudedbygranites.Directlyonthiscontinental plate was foldedduringthe Variscan orogeny and Introduction: Les Eaux-Chaudes:figure 1.5andPlate1,fi Artouste: theSouth-verging Folds and Thrusts of Stop 2.5: 1993. Alhamawi, 1985,R.BourrouilhandM. Alhamawi, 1985, EauxChaudesmassif: Y. Ternet, 1965,M. For futherinformation: Ossaupeak:F. Bixel etal., overturned fold(Ternet, 1965, Alhamawi, 1985). south-verging thrustsheetofGourzy, whichisan north, thisthrustsheetisalsooverlain byanother verging thrustsheetofLes Arcizettes. Furthertothe unconformably andareoverlain bythelarge south- granites, theUpperCretaceouslimestonesrest of theHighChain(right),intrudedbyUpper Variscan see frontcover, fi gure 1:over thePaleozoic basement northward panoramaontheEauxChaudesmassif: crossing thecrest,wenow godownhill andhave a Stop 2-5b: glacier, now occupiedbytheFabrèges reservoir. glacial morphology, createdbytheQuaternaryOssau The highpartoftheOssau Valley clearlyshows a et al.,1985). the ChainproducedPicduMidid’Ossau(F. Bixel south; post-glacialerosionaswellrecentupliftingof the calderaandofringdyke werethrustedtothe then, duringthePyreneanorogeny, thenorthernhalfof the calderawas truncatedbyUpper Variscan faults and of anUpperCarboniferous-Permianvolcano. Later, surrounding alarge caldera(about7kmindiameter) the landscapeto West, isconstituted byaringdyke peak ofPicduMidid’Ossau(2,884m),springingout in thispanoramatothesouth(Fig.2.5a),highest Stop 2-5a: thePaleozoic basementoftheIberian enomanian transgressive seadeposited yc fce. Tectonic facies. ysch g.1 WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

Figure 2.5a - Southverging Thrusting of the Late Paleozoic Ring Dyke of the caldeira of the Pic du Midi d’Ossau.

Stop 2.6: Valley in the North Pyrenean Zone. It is the domain the Benou Plateau : thrusts and folds in the Ossau of the Béarn Ranges dominated by E-W structures Valley: fi gure 2.6a and 2.6b. (Mailh Arrouy, Barescou syncline, Moulle de Jaout This Stop represents a panoramic view of the Ossau anticline …). Nevertheless, the Ossau Valley marks the occurrence of transverse structures (lateral ramp), Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 2.6a - The Benou Plateau : thrusts and folds in the Ossau Valley.

29 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell entire groupisthrusttothenorthwest over thefolded cover ofthePaleozoic sheetofGère-Bélesten. The of PladouSoum. The latterconstitutethedetached complex canbefoundinthefi ve imbricateslices towards the north. The extension ofthefoldedJaout the crestofIzeste Woods. The twistedseriesdips To theeast,Rey Mountainseriesoutcropagain on horses mixed withPaleozoic horses. fault). This fault zoneconsistsof Triassic ophite against thePortdeBéon Aptian units(PortdeCastet the south,inRey Mountain. This series isfaulted monocline series(Liasto Albian) dipping70°towards the PènedeBéonfaulted anticline)andthereverse Jaout Albian-Aptian foldedseries(Jaoutsyncline, Finally, Béon Triassic stripandintheLouviepass. west, whichissubvertical andoutcropsinthe Aste- The NorthPyreneanFault (NPF), especially, seeStop2.5b). of the“EauxChaudes”recumbentfolds(PicdeGer, Upper Cretaceouscover deformedinthecomplex The PyreneanHighChain, from southtonorth(Fig.2.6aand2.6b): the southernslopeofvalley shows thefollowing, plateau ontheBenoulateralmoraine. The view of middle Ossau Valley canbeobserved herefromthe Structural landscape: high-voltage electricpost. up tothevulturefeedinggrounds.Park aroundthe plateau above Bielle. Take thetrailthatheadsnorth, Access related toinheritedCretaceousnormalfaults. (Lenoble andCanérot,1992). Figure 2.6b-Structuralcross-sectionoftheN-PyreneanZoneinBiellearea,Ossau Valley, : headtowards theeasternendofBenou the NorthPyreneanZone, theglacialtopographyof withitsunconformable detailedbythe strikingeast- Casteras, 1974;Henry, 1987. For furtherinformation: LenobleandCanérot,1992; (transpression). subsequent development ofcompressionalstructures Mesozoic paleogeographicstructuresinthe that isplayedbyextension-related (transtension) ridge). This againdemonstratesthefundamentalrole running alongtheHauteSoulefi rst generationdiapir Albian Ossaufault andtheIbechfault (a W-E fault located exactly attheintersectionofthatN30° breccias) tothesouthofLassourdebasin,is generation ridge),marked bybrecciainfi demonstrated thatthePicdeLauriollediapir(second Ossau Horst.LenobleandCanérot(1992)have also Albian. That fault bordered thewesternedgeof during theLiassic,EarlyKimmeridgianand fault re-usedanancientN30°normalfault, active strike-slip component.Ithasbeenestablishedthatthe Mailh Arrouy). Itslateactivity hasa W-E right-lateral south-verging Benou thrustfront(andthatofthe Interpretation: thrust, strikes N30°E(LenobleandCanérot,1992). The fl exured thrustfault, calledtheOssautransverse WE, sub-vertical structuresofBergoueits Woods. Marie Blanquepass.Park nearthebridge which Barescou Valley totheOssau Valley throughthe Access: fi syncline (Jurassic reservoir andsource rocks) : Mailh Arrouy viewfrom Barescou Stop 2.7: gure 2.7aand2.7b. atEscot,take theroadthatleadsalong theOssauthrustclearlycuts ll (collapse ll WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16 Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 2.7a and b - Sequence Stratigraphy of the Middle Jurassic of the Mailh Arrouy (Total). crosses over the Barescou stream. evaporites and shales onto the Albian fl ysch of the Structural landscape: The topography of the Mail Barescou syncline (Fig. 2.7a and 2.7b). This series Arrouy reveals good outcrops of the Jurassic series shows, from base to top, the Lower and Middle that are thrusted southwards with a sole of Triassic Liassic limestones, the Upper Liassic marls, the

31 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell intercalated betweenthetubes. larger roundtipstothesouthwest. Smallerpillows are volcanic lava tubesdip20-30tothe southandendin in thesubsurface tothewest.Heresubmarine exposed afew kmtothewest,andthatareprevalent and teschenites(under-saturated syenites)thatare mesovolcanic magmaticrocksincludeepisyenites other partsoftheOgeuBasin. The epivolcanic to basaltic columnsandpyroclastic breccias,visiblein part ofasuitevolcanic textures alsodisplaying within the Albian blackmarls(Fig.2.8). They are Stratigraphy : to theleftoffarm gate. cliff besidethecorncrib. A pedestrianpathis located railroad crossing.Pillow-lava fl Arudy), parkattheCourrèges Farm justnorthofthe Access: fi Herrere :Pillow-lavas ofthe Albian riftstage: Stop 2.8: For furtherinformation: Henry, 1987. structure oftheMeillongasfi the southernedgeofblock)isalsosimilarto The geometryofthemonocline(andparticularly (Comminges basin–SaintMarcelfi in the Aquitaine basin,especiallyintheeasternsector The Liassicmarlsconstituteoneofthesourcerocks compared tothedolomiticlevels oftheMeillonfi constitute goodhydrocarbonreservoirs. They canbe thick andporous(especiallytheooliticshoals), Hydrocarbons: system tractinS6(pinnacleoftheMailh Arrouy). and S6).Notetherapiddevelopment ofthehighstand black dolomiteswerecutintotwo completeseries(S5 fl separating thelimestonecliffs comprisethemaximum series (transgressive systemtract). The grassyslopes lowstand systemtract) andthenafi upward series(highstandsystemtract,followed by Each sequencelimitbegins withacoarsening sequence limitsinthegrey scarpsofthelandscape. and S4,shown onFig. 16 aandb).Observe the were divided into3 third-order sequences(S2,S3 Sequence stratigraphy: base ofthe Triassic. of theLower Liassic limestones,andlaterallyatthe The thrustfault dips20°to30°northward, atthebase of recrystallizedooliticshoalsandlagoonalfacies. dolomites calledthe“Mailh Arrouy dolomites”made grey “fi lament limestones”ofthe Aalenian, lower gure 2.8 (Moen-Maurel ooding surfaces ofthesequences. The overlying southofHerrère(D920)betweenOloronand thepillow-lava fl theMailh Arrouy dolomitesare theBathonianlimestones et al.,1996). eld. ows arelocatedinthe ows areinterbedded eld). nn upward ning eld. down tothebasement,orlikely beneaththethrust that arelocatedover thePyreneanaxialzone(eroded controlled bydiamond-shapedfault patterns.Riftaxes limited tohalf-grabensen-echelonbasins,andbasins separation. IntheNorth-Pyreneandomainriftwas sign ofoceaniccrustdevelopment, norofmargin between IberiaandEurope.However thereisno magmatic expression ofthemid-Cretaceousrifting the outcrop. Volcanics andepisyenites representthe that favoured theupliftwas locatedtothenorthof tubes indicatesthatthenormal(extensional) fault Tectonic signifi fi the Aquitaine a kmthick,andthusprovide thebestsealover mostof as sourcerockandseal. The Albian marlscanbeover that wereaffected bymagmatism. These marlsacted sills. The sourcerockswerethe Albian black marls reservoir consistedofchilledmargins ofepisyenite which producedgas(Moen-Maurel frequency markers thatweredrilledatLedeuixand see at-1200m/SSasimilarantiformmadeoflow the Gave d’Oloron Thrust. Inthe3Dseismic, onecan axis oftheanticlineplungesgentlytowestbeneath metres tothenorthofpillow-lava outcrop. The Anticline whoseN110axisislocatedafew hundred of thetubeswas acquiredduringfoldingoftheBelair Structural settingandhydrocarbons: Figure 2.8-Pillow-lavas flows ofthe Albian riftstageat elds (Lacq,Meillon...). cance: Herrer (20cmlongpencilfor scale). thesouthward fl ow ofthe et al.,1996). The partofthedip WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

sheets, such as for the North-Pyrenean Fault) would Stop 3.2: be better candidates for the hundred-km long, left- Sarrance roadcut - Jurassic dolomites lateral strike-slip displacement that occurred between (reservoir formation). Iberia and Europe through the Mid-Cretaceous. Access: again driving south on the N 134 the Stop concerns the road-cut, three kilometres north of DAY 3 Sarrance. Park at the picnic grounds. Park on the side from Oloron Ste Marie to Saint Jean Pied de Port of the road-cut, please, put on the warning lights. Sequence stratigraphy: the road cuts across the Leaving Oloron by the southern road N 134 to Col du Jurassic rocks of the sub-vertical northern limb of Somport and the Spanish border, we enter the Aspe the Sarrance anticline (fi g. 3.1c). The road-cut reveals Valley, along which runs the Gave (river) d’Aspe. some sedimentary key points which have given rise Along the valley, there also exists a railway linking to a proposed sequence stratigraphy (Canérot et Oloron and the Spanish railway station of Canfranc. al., 1990) for the North Pyrenees dolomite series. This railway was cut a long time ago and discussions This study concerns the stratigraphic interval from between Spain and France are still taking place, to the Bathonian to the Upper Callovian in the Bearn restore it and the railway link. Entering the valley and Ranges. The set was divided into fi ve third-order the mountain, railway bridges, tunnels are visible on sequences, termed DSI to DSV (Lenoble, 1992). Only both sides of the N 134. part of sequences DS III to DS V can be observed here (Fig. 3.2). Stop 3.1: Sequence DS III (30 m): fi nely bedded dolomites Pont d’Escot - Ste Suzanne Formation (seal) : (outer shelf), grading into oolitic (offshore bars) and fi gure 3.1a, 3.1b, 3.1c fi nally reef deposits (colonial corals, fi g 3.2b). The Access: 15 km south of Oloron, on the N 134, we will series in this fi rst unit represents the highstand Stop in the parking lot, just after passing one of these system tract. The contact with sequence DS IV is not railway bridges, the Pont d’Escot. distinct. Stratigraphy, structural geology: from south to north, Sequence DS IV (40 m): bioclastic dolomites, thick the road cut reveals the Aptian sedimentary evolution and then fi nely bedded (offshore bars), characterizing of the Sarrance anticline’s sub-vertical northern the lowstand system tract. They are overlain by limb. The rapid transition from Bedoulian Ste- a striking ferruginous discontinuity, overlain by Suzanne marls, to Gargasian (Urgonian) limestones bioclastic horizon, interpreted as a transgressive (with Toucasia) is nevertheless progressive within surface. The oolitic bars (shoreface) and the overlying a highstand environment. Further up-section, the striped dolomites (inner lagoon) probably correspond Urgonian facies is prevalent within the lowstand to a highstand system tract. The maximum fl ooding of the next sequence (Fig. 3.1). The sequence limit surface has not been identifi ed. probably corresponds to a sedimentary hiatus, which Sequence DS V (15 m): thick dolomites (shoreface can be observed at the base of the thick beds with bars) overlain by striped dolomites (inner lagoon) abundant Rudistids. The schistosity is particularly correspond to lowstand and highstand system tract, well marked within the marly beds. Further south, and respectively. The transgressive interval and the upslope, the marls are interbedded with limestones, maximum fl ooding surface have not been clearly indicating that the marly series comprises two distinct observed. groups (Fig. 3.1b). This intermediate limestone and Because of intense fracturing, it was not possible dolostone is a regional seismic marker in the foothills to make a precise reconstitution of the described and foreland sub-surface. sequence. Stratigraphic determinations (Bathonian Volume n° 2 - from B16 to B33 n° 2 - from Volume Hydrocarbons: the Sainte Suzanne marl formation for DS III, Callovian for DS IV and DS V) are forms the upper or direct seal of many hydrocarbon based on the correlation scheme between the Béarn fi elds in Aquitaine (Vic-Bilh, Pecorade, Lacq), and dolomite series and the Basque series with abundant Meillon gas fi eld, located 30 km SE. Ammonites, which was not subjected to epigenetic For further information: Canérot, 1964; Castéras, processes. 1974. Hydrocarbons: the dolomite complex represented in the area was designated as the Mailh Arrouy formation, and considered as the equivalent of the

33 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell the Mailh Arrouy sequence). Kimmeridgian) thantheSarrancesequence(or probably muchyounger(UpperOxfordiantoLower research hasrevealed thattheMeillonformationis Meillon gas-bearingdolomiticformation.Further Figure 3.1a-Pont d’Escot:SainteSuzanne Aptian formation SequenceStratigraphy. Lenoble, 1992. For furtherinformation: Canérot Bedous :thesouthern margin of Stop 3.3: et al.,1990; WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

(Fig. 3.3). In the Bedous Valley, the Triassic includes Muschelkalk limestones, Keuper shales and ophites in the slivers of duplexes that were thrust to the south (visible along the halpin road). These rocks were thrust onto the fl ysch of the Upper Cretaceous cover in the High North- Range, around the village of Lées (Fig. 3.3). Further north, the crest of the Layens Mtn shows a thick Pyrenean sub-horizontal Jurassic and Lower Cretaceous series rift: fi gure belonging to the normal limb of a recumbent anticline 3.3. verging to the north. To the east of the viewpoint the Access: N 134 Bergon Mtn shows a hanging recumbent syncline to Accous village. with a top-to-the-north vergence. Entering Accous, Geodynamic interpretation: the Bedous area take the asphalt road marks the mid-point of the double vergence that to the east along a 3 km hairpin loop that leads to the viewpoint over Bedous Figure 3.2b - Colonial corals in Sequence DIII. and Stop there; a one mn walk to the hilltop to the west leads you to an excellent structural viewpoint. Structural landscape: the landscape shows the relation between the northern Pyrenean range, to the north, and the High Range, to the south, on the upstream side of the Aspe Valley

Figure 3.2a - Middle Jurassic Sequence Stratigraphy (Bathonian-Callovian), Northern side of Sarrance anticline, (Canérot and Lenoble, 1993). Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 3.3 - Structure of the High Range at Bedous, Aspe Valley, (Total). Fl= Upper Cretaceous Navarella fl ysch (Senonian), UK= Upper Cretaceous Canyon Limestones (Cenomanian- Lower Senonian), Tr= Triassic ophites.

35 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell Figure 3.4b-Thefolded Megaturbiditeinthelandscape. Figure 3.4a-MegaturbiditeatOsquich Pass. WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

characterizes the Pyrenean mountain range. Some to l’Hôpital St Blaise and Mauléon-Licharre and then authors traditionally set the North-Pyrenean Fault the D 918 to Col d’Osquich. at this location but this hundred-km long strike-slip The Stop is located on the road from Mauléon to fault is likely concealed beneath the south-verging Larceveau, D 918, about 1km after the Osquich pass, thrust sheets, and would occur further north in depth, at the fi rst curves in the road, just before the village of probably where some earthquakes still originate St Jean Ibarre. nowadays. The Megaturbidite concept was fi rst established To the South, subduction of Iberia beneath Europe by Soler and Puigdefàbregas, 1970; Rupke, 1976, was so large in magnitude that only south-verging for huge gravity deposits occurring among Eocene thrusts and nappes can be observed. To the north, deposits of the Southern Pyrenean basin. Later, depending on the original dip of the rift faults, Johnson and al (1981) studied the South-Pyrenean inversion produced either north-verging or south- basin and Labaume et al. (1983) studied these verging folds. The rift structures are located in a retro- deposits in detail. Megaturbidites were later identifi ed arc setting, which limited its inversion and its uplift among the Cretaceous North Pyrenean sediments and (and erosion), thus permitting the petroleum system were studied in detail by Bourrouilh, Coumes and to exist till today. Offroy (1984) and Offroy (1984) who interpreted the infi lling of the North-Pyrenean cretaceous fl ysch Stop 3.4: basin, demonstrating that: Osquich Pass: Upper Cretaceous Megaturbidites: - two large megaturbidites occurred in the basin. One fi gure 3.4a, 3.4b, 3.4c and 3.4d. of them extends over more than 90 km, and varies Access: from Stop 3.3, drive back to Accous and from 60m in thickness, near Pau, to 20m in its western now drive N 134 back to Oloron. At the entrance to part, near the Atlantic Ocean. Oloron, drive on D 936 to Navarrenx and Sauveterre - Megaturbidites originate as evolutionary mass-fl ow- de Béarn. 11 km from Oloron, take on the left the D 25 megaturbidites (fi gure 3.4d) Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 3.4c - Sedimentological interpretation of the Megaturbidite, from Offroy, 1984.

37 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell Introduction: We drive backtoMauléonbytheD918road. the Iberianmargin :(fi Ahusquy Pass: Structure ofthetiltedblocksand Stop 3.5: was internallystratifi intervals, whichdemonstratethattheturbiditicfl constituted bysuccessive but amalgamatedBouma’s (1983), Offroy (1984),thismegaturbidite is Interpretation: of theroad. of theroad,but alsointhelandscape,onleftside turbidite, 40mthick,whichoutcropsontherightside Structural landscape: in interval surfaces (fi kinetic energy. Vibratory ripplescanbealsoobserved and Offroy (1984),Offroy (1984),. Bourrouilh andOffroy, 1983,Bourrouilh,Coumes For furtherinformation: (fi affecting theflysch andparticularlytheMegaturbidite enough, wecanobserve large Pyreneankink-folds On theleftsideofroad,andiflightisoblique gure 3.4b). Figure 3.4d-TheEvolutionnary-Mass-Flow-Megaturbidite concept,R.Bourrouilhetal.,1984,Bourrouilh,1987. fromMauléontothesmallvillage studiedbyBourrouilhandOffroy ed, eachstratahaving aspecifi gure 3.4c). thepanoramashows amassive gure 3.5). Figure 3.5-Panorama from Ahusquy Pass. ow ow c The Arbailles anticlineisfollowed tothesouthbya frame ofthetiltedblockor“ Arbailles ”block. deposited. These competentlimestonesformthe marine partlyreefal limestonesoftheUrgonian were of “themarnesdeSteSuzanne”. Then, theshallow fi Hauterivian-Barremian shallow water limestonesand fan-like dipsoftheNeocomiancontinentalsands, tilted blockisdemonstratedbytheunconformable bauxitic remnants. The progressive rotationofthe the UpperJurassiclimestone,locallyshowing is clearlyregistered intheerosionalsurface affecting rift whichextended theBayofBiscay. This history southern margin oftheN-PyreneanLower Cretaceous dolomitic Jurassic. The tiltedblockwas partofthe typical Germantype Triassic, followed byacalcareo- Upper Carboniferous,unconformablyoverlain bya N110°E anticlineshows acompleteseries,fromthe deformed inaNEverging thrustedanticline. This margin (Arbaillesblock),whosenorthernedgeis deformed tiltedMesozoicblockoftheIberian to the Ahusquy pass,theroadwillcrossalittle- fl of Aussurucq, theroadcutsUpperCretaceous nally bythefi ysch oftheN-Pyreneantrough.From Aussurucq rst large transgressive marinedeposits WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

large syncline, formed by the Upper Aptian-Albian of us, at the Pic d’Orhy, at an elevation of 2,017m. black shales, in what was the downthrown part of the For further information: see the geological map at Arbailles block. 1/50 000 n° XIV-46, Tardets -Sorholus Access: on the way to Mauléon by road D 918, we will take the small road D 147 on the left to Mendy Stop 3.6: and to Aussurucq and then through the Forêt des Lutogagné: Structure of the Lower Cretaceous Arbailles massif, up to the Ahusquy pass. tilted blocks: fi gure 3.6. Structural landscape and Interpretation: Ahusquy Introduction: this is a general panorama along the pass is situated on the Upper Aptian-Albian black strike of the southern fl ank of the Arbailles, or the shales, which form the core of the Apanicé-Bois de Apanicé-Bois de Zouhoure syncline. Zouhoure syncline. Access: leaving the Ahusquy pass, we drive to the The southern fl ank of this syncline is verticalized. Iraty pass and we will progressively cross the Albian The underlying Urgonian limestones, which form the black shales of the syncline to reach the Triassic frame of the Arbailles anticline to the north, crops out outcrops and the panorama. here again, forming a continuous rocky ridge, reaching Structural landscape: we Stop near the Cayolar an elevation of 1,265 m at the Pic de Behorleguy. (mountain barn) of Arhansus. Looking to the north, The Jurassic and the evaporitic Triassic outcrop on we now examine the southern limb of the Arbailles the southern side of the syncline, in a narrow ridge syncline culminating locally in front of us at the separating it from the Mendibelza conglomerates; Lutogagné peak (1,097m). This southern fl ank is this N 110°E zone is generally interpreted as a major rotated vertically with the folding of the syncline, and Pyrenean Fault, extending to the West Souquet’s deeply fractured in this area. “Faille de Bigorre” (Souquet et Debroas, 1980). Interpretation: according to Canérot and Lenoble However, this hypothesis does not fi t with structural (1991), the Jurassic (Lower Lias to Bajocian) and drill-hole data and could be discussed during is covered by diapiric breccias (Etchebar the fi eld trip. Immediately south of this fault zone, collapse breccias) of Lower Cretaceous age, the thick black Albian-Vraconian conglomerates of and unconformably overlain by an uppermost the Mendibelza (this name means: black mountain Gargasian-Clansayesian limestone containing typical in Basque) range are directly discordant on the Foraminifera. (Peybernès and Garot, 1984). Therefore Paleozoics. In the background of the panorama, the most of the Jurassic and Barremian carbonates are Upper Cretaceous “calcaires des cañons” or “calcaires absent; a reconstruction with subcrop maps indicates des Eaux Chaudes” present a sheared unconformable the presence in the Barremian to Albian of a diapiric contact with the Paleozoics of the High Chain (see ridge which developed along the downfaulted side of Stop 2.4a and 2.4b, here above), which culminates at the Arhansus Fault. This ridge was then squashed by the Pic d’Anie (2,504 m high, to the left) and in front the subsequent compression between the upthrown Figure 3.6 - Lower Cretaceous tilted blocks. Volume n° 2 - from B16 to B33 n° 2 - from Volume

39 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Figure 3.7a-GeneralviewoftheMendibelzamassif. Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell result fromtheerosionofIberianplate. They Paleozoics, theMendibelza Albian conglomerates Introduction: fi Mendibelza massfl Stop 3.7: Canérot andLenoble,1991 For furtherinformation: Peybernès and Garot,1984, productive (Gaujacq). have beendrilled,andarelocallyHCbearing Tarbes basins,whereitcontainsreefstructureswhich sequence hasbeenobserved inthe Arzacq and platform (Aptian)tothe Albian marlbasin. This marks thevertical transitionfromtheUrgonian Hydrocarbons: downfaulted half-grabenofthe Arbailles Block. rift andthe Albian synclinewhichoccupiedthe block oftheIberianmargin oftheNorth-Pyrenean Figure 3.7b-SedimentologyofMendibelza conglomerates(Total). gure 3.7. directlyrestingunconformablyonthe theClansayesianseriesregionally ow conglomerates: Structural landscape: Access: growing divergent Iberianmargin. and slopefanglomerates, rapidlyslurrieddown onthe They areathickaccumulationoffl passage betweentheriftandearlyplatedriftstage. eastwards. Thus, thesefanglomerates markthe opening oftheBayBiscayrapidlyprogressed margin upliftoftheNorthIberianmargin, asthe conglomerates areinterpretedasresultingfrom grew upalongthe coast andthedeltabayous. The branches anddebris,ofthecoeval forestswhich also containlayerswithremnantsofleaves, broken water andreefal limestonesandblackshales. They subcontemporaneous Lower Cretaceousshallow Jurassic limestones(Digbehi,1987),aswell evaporites (bipyramidal quartz), Triassic ophites, Ordovician tothePermian,andalso, Triassic rework allthePaleozoic series,fromatleastthe ontheroadtoIratypass Interpretation: are observable, topontheleft. Digbehi, 1987;Miranda Avilès, 2002. Bourrouilh, CoumesandOffroy, 1984; For furtherinformation: Boirie,1981, fl isolated pebblesoutcroppingonthesea the formerdepositedsequences,leaving water current,whichtookoff apartof abruptly washed outbyahighenergy the topofmass-fl ow sequencesis fl mass-fl emplaced byimmature,i.e.proximal Lecumberry onroadD18,leaving the Access: Triassic ophitesandbipyramidal quartz. muscovite-rich greywackes, aswell limestones, carboniferousradiolaritesand quartz, Ordovician quartzites,Devonian reworking pebblesandgravels of including reefal limestones,and Cretaceous shallow water limestones, olistolithes ofPaleozoic blocks, Lower to observe large olistostromes,with Introduction: fi road, Mendibelza conglomeratesonIraty Stop 3.8: Saint Sauveur Chapelontheright, the oor. uvial (deltaic)overfl gure 3.8. ows, probablyresultingfrom down Iratypass,driving to several mass-fl thisStopallows us theseslurriedbedswere od. Frequently, oods. uvial tocanyon o sequences ow WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

Figure 3.8 - Olistostromes and olistolithes in Mendibelza conglomerates.

Stop begins about 1 km down from the Chapel Lecumberry, on the small slope of the road. crossroad, on the fi rst road curve (Fig. 3.8). Structural landscape and Interpretation: Structural landscape: the large olistostrome crops 1. The post-rifting, syn-drifting “ European ” plate out all along the right side of the road, over several is represented here by the western structure of the tens of metres, gently resting on channelized mass- Arbailles tilted-block, showing the southern limb of fl ow. Large pebbles and Paleozoic and Lower the Arbailles (Apanicé) syncline, culminating here at Cretaceous calcareous fossiliferous olistolithes are Behorleguy peak (1,265 m). clearly observable on the side of the road. The Urgonian ridge of the Behorleguy peak is The other side of the road shows the Mendibelza verticalized. The shallow water Urgonian carbonates massif and, far in the background the Atlantic coast rest unconformably on bauxitic deposits fi lling up and the Bay of Biscay. a previous karst and were mined. This diachronous Interpretation: the on-going growth of transtensional bauxite extends unevenly from here to Provence, over basins provoked inversion of the morphology of their 800 km away, testifying to complex and polyphased southern margin, revealed both by the infi lling of the emersions/submersions of the “Durancian isthmus”. basins by large amounts of fl uvial conglomerates The slope down the Behorleguy peak is formed by an (Mendibelza ones) and by large olistostromes, incomplete Jurassic series, the pre-Urgonian erosion reworking olistolithes of former deposits but also of reaching irregularly the Callovo-Oxfordian, the the subcontemporaneous reefal carbonates (Boirie, Dogger or even the Liassic. 1981, Souquet and Boirie, 1985, Digbehi, 1987). The Lecumberry valley strikes through the soft These transtensional basins are similar to the modern evaporitic to calcareous, and arenitic Triassic. Baja Californian divergent basins of the Gulf of The possible fault previously discussed at Lutogagné, California (Miranda Avilès, 2002). must run on the right side of the valley For further information: Boirie, 1981, Souquet et 2. the Iberian plate is constituted here by the Boirie, 1985, Digbehi, 1987, Miranda Avilès, 2002. large amount of Albian to Vraconian Mendibelza Volume n° 2 - from B16 to B33 n° 2 - from Volume conglomerates, unconformably resting on the Stop 3.9: Paleozoics. Far in the background, the Mendibelza tilted blocks and European-Iberian margin, 2 km conglomerates are locally covered by the Upper NW of Lecumberry : fi gure 3.9. Cretaceous “calcaires des Cañons”. Introduction : this Stop allows us to observe the For further information: see the geological map at Arbailles tilted block and the European-Iberian 1/50 000, n° XIII-46, St Jean Pied de Port. margin. Access: on road D 18, about 2 km NW from

41 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell Access: Lutetian progressively appears. Then, acarbonatefl ysch facies uptotheLower develop fromCenomaniantoLower Campanian. ” or“canyonThese “calcairesdescañons limestones” forming thehighpeaksofEauxChaudesMassif. these limestonesthefi the PyreneanHighChain. We alreadyobserved shallow water carbonatesformthemainframeof conglomerates, ahugeseriesofUpperCretaceous Introduction : Fold structures Pic d’Orhy South-verging Thrust and Stop 4.1a: Morning: us throughtheMendibelzaconglomerates. The roadtoLarrauandthePortdewilldrive from StJean Pied de Port toJaca fromLarrau,roadD26climbsuptothePort restingontheMendibelza DAY 4 rst day, intheOssau Valley, Figure 3.9-Tilted blocks andEuropean-Iberian margin. 1/50 000,n°XIV-47, Larrau. For furtherinformation: seethegeologicalmapat tectonic units. Here wecanseeoneofthehighestfold-and-thrust Eocene fl overturned syncline,formedbythePaleocene-Lower Cretaceous fl ysch, followed byansouth-verging a souththrustedanticline,involving theUpper verging foldsofthe Orhypeak,2,017mhigh,forming westwards wecanobserve theS-shapedsouth- Structural landscapeandinterpretation: elevation, nearthethrustsurface (fi de Larrau,1,575mhigh. We willStopat1,400m Structural landscapeandInterpretation: the Iberianplateinfrontofus. just below OrhyPeakandwiththeamplepanoramaof We arenow intheheartofPyreneanHighChain, m high. Access: Port deLarrau:StructuralPanorama Stop 4.1b: drive onD26uptothePortdeLarrau,1,573 ysch (fi g.4.1a2). g.4.1a1). theHigh looking WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

Figure 4.1a1 - Geological map of the Pic d’Orhy area, from BRGM Map, n° XIV-47, Larrau.

Chain now develops west and eastwards, the Upper This fl ysch joins the unconformable cover overlying Cretaceous to Lower Eocene “Calcaires des Cañons” the Paleozoic basement, in the High Range further to forming the mountain range. the south. To the south, the large south Pyrenean basin develops, Flattened and sheared (boudinage-affected) fi lled with Eocene fl ysch of the Hecho Group. Figure 4.1a2 - Aerial view of the Pic d’Orhy, courtesy of Stop 4.2a: Vivien De Feraudy (Total). Igountze Thrust and St-Engrace Thrust sheet. Access: take the D 26 back to Larrau and then along the Gave de Larrau to take road D113 on the right along the northern slope of the Ste-Engrace valley. Stop 500m east of the Kakoueta canyon road access.

Stratigraphy, structural geology: the Igountze unit B16 to B33 n° 2 - from Volume consists of the Devonian – Carboniferous basement and of its unconformable Albian cover comprising the Mendibelza conglomerates. This unit is southward thrusted, almost horizontally, over the Ste Engrace thrust sheet (fi g.4.2a1 and 4.2a2). The latter is also thrusted (fi g.4.2a3) over the so called canyon limestones (Cenomanian to Campanian) and the Navarella fl ysch (Campanian and Maastrichtian).

43 - B16 Volume n° 2 - from B16 to B33 B16 - B16 High Chain(Total). Figure 4.2a2-Structuralcross-sectionbetween theIgountze Massifandthe Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell in theMendibelzaconglomerates The diversity ofthemarinefacies from theHighRangebasement. fault separatedtheIgountzeblock fault. IntheEarlyCretaceousthis ancient north-dippingnormal Igountze Thrust reactivated an Structural interpretation: the mainthrustsheet. which isdisconnectedinfrontof Canyon limestonesandthefl Mendibelza conglomerates,the (Paleozoic covered bythe a klippewithcomplex structure south, Lakoura Peakismadeof limestone-fl duplex shearbelt,locatedatthe characterized byanorth-dipping beneath theIgountzethrustis Laterally theinternalshearingofSenonianseries sedimentary brecciasoccuratthebaseoffl ysch contact. To the ysch) the ysch. Figure 4.2a3-Larrau-LakhouraThrustsheet (Total). map n°XIV-47, Larrau. Saint-Engrâce area,fromBRGM Figure 4.2a1-Geologicalmapofthe to, but youngerthantheonein 1981). This organization issimilar drowning tothe south (Boirie, on atiltedblockwithincreasing these arecanyon-cone deposits towards thesouth),suggestthat deposition, gradualthickening sedimentary organization (onlap and siltstones)aswelltheir the Permian-Triassic sandstones that reworked thebasementand south, andthenpuddingstones Paleozoic fragmentsfromthe (enormous fanglomerates with For furtherinformation: Ribis, block collapsedintheSenonian, still high)oftheHighRange. The southernmost block(whichwas the basementbelongto conglomerates thatreworked collapsed duringthe Albian. The Pyrenean Iberianmargin that corresponds toaslabofthe The IgountzeBlocktherefore the Arbailles (seeformerStops). (Souquet South, duringtheLateCretaceous sedimentary basintowards the widening ofthePyrenean demonstrating theprogressive et al.,1985). WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

1965; Ducasse and Velasque 1988, Boirie 1981. duplexing contributed to the southward allochthonous transport of the Igountze-Ste-Engrace Thrust and the Stop 4.2b: Lakoura Thrust over a minimum of 7 km. The whole Intra-Senonian duplex underneath the Igountze sheared Navarella fl ysch acts as a detachment thrust and Lakhoura Thrusts. with a thick sole. Access: 500m east of the previous Stop. Park on the south side of the road. II. A transect of the Southern Stratigraphy and structural geology: the Navarella Pyrenees and Jaca basin turbiditic fl ysch (Campanian to Maastrichtian) is by Antonio Teixell mainly composed of alternating marly limestones Departament de Geologia, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain e-mail : [email protected]

Aim of the fi eld trip The aim of this itinerary is to examine thrust tectonics and interaction with sedimentary systems in the Southern Pyrenees. The Southern Pyrenees consist of south-vergent folds and Figure 4.2b - Larrau-Saint Engrâce-Lakhoura Thrust Sheet. thrusts and contain a very well- preserved record of synorogenic sedimentation. Synorogenic sediments are of uppermost Cretaceous to Lower Miocene age, and constitute the Jaca and Ebro basins (Plate 2, fi g.1). The fi eld itinerary will proceed from north to south from the Axial Zone -a large thrust culmination that forms the orographic axis of the Pyrenees- to the Jaca basin -a Paleogene foredeep now incorporated in the the orogen showing a typical turbidite to molasse succession-, and fi nally to the southern mountain front of the External Sierras –where the Pyrenees Figure 4.2b2 - Intra-formational antiformal duplex overthrust the present foreland of the Ebro basin. Navarella Flysch; St. Engrâce road Synthetic geological descriptions of the transect visited can be found in Teixell (1996, 1998). During the trip we will have the opportunity to study and marly sandstones. The beds are intensely sheared (fi g.4.2b). Intraformational duplexes result from features as 1) detailed kinematics and mechanics of the development of reversed parallel south-verging thrusting, 2) interactions between growing thrust ramps accompanying the motion of the Ste Engrace- faults and folds and proximal alluvial fans, and 3) Igountze Thrust sheet above, as well as that of the episodic evolution and progressive deformation of Larra Thrust further to the south.. At this Stop we can foreland basin deposits. observe an antiformal duplex, with a subhorizontal Afternoon: B16 to B33 n° 2 - from Volume fl oor shear plane and a roof shear plane folded along a Axial zone and Northern Jaca basin N 120 axis. The sub-NS hinges of gravity slumps are preserved in the internal layers of the duplex. Stop 4.3: This intense shear deformation occurred for at least 7 km southward, along a bedding plane slip zone at Pierre-Saint-Martin. The Larra thrust system. the top of the Canyon Limestones and underneath Access: follow the main road NA 1370 to the SW to the Igountze and Lakhoura Thrusts, to the south of cross the Spain/France border and park some 100 m the modern Kakoueta canyon. The intraformational after the signal, beside a road bend. Structural landscape: the Upper Cretaceous rocks

45 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell limestone memberandaupper, well-beddedand Cañons, attheboundarybetweenalower massive the LarrathrustislocatedwithinCalcairesdes thrust (Larrathrust)(Fig.4.3a).Inthestudyarea, vergent rampsthatrootinabedding-parallelfl system isathinduplex composedofnumeroussouth- of thisnorthernpartthe Axial Zone. The Larra system, characteristicoftheUpperCretaceousrocks In thisStopwecanobserve detailsoftheLarrathrust Alpine deformationinthisbasementmassif. area provides anuniqueopportunitytoconstrainthe Pyrenean Axial Zone(Plate2,fi g. 1),and thus the have beenerodedaway inmoreeasternpartsofthe visited region liesinthatpost-Hercynian rocks One specialinterestoftheCretaceousrocks Pyrenean thrustloading. can beattributed tofl exure attheinitialstagesof represent adrowning oftheSantonianplatformthat formations areofCampanian-Maastrichtianage,and visible inthelandscape(Ribis,1965). The latter marine shales,andasandstone/shaleturbiditicunit, the Paleozoic. Overlying thelimestonesareopen Cenomanian toSantonian)thatrestdirectlyon platform limestones(“CalcairesdesCañons”, that formthe Axial Zonecover consistofbasal oor SW (fi orientation ofminorstructuresrangefromN-StoNE- (contraction orshear)thatcanbededucedfromthe to bedding,isalsopresent. Transport directions prior tofolding. An incipientfoliation,oblique indicate anearlyepisodeoflayer-parallel shortening arrays have beentiltedtogetherwithbedding,they arrays ofcalciteveins. As theshorteningaxes ofthe rocks, therearecontractional,conjugateen-echelon foliation coherentwithrampshear. Within thewall is stronglydeformedanddisplaysaninternaloblique surfaces, whichencloseanintervening rockslicethat zone ischaracterizedbytwo mainsubparallelfracture is truncatedinaramp-over-ramp geometry. The fault this stratigraphicunitincontact(Fig.4.3a).Bedding bearing limestonememberandtheshalyupperpartof The thrustramp,bringsthemiddlepartofchert- inferences forthekinematicsofthrustsystem. with asetofassociatedminorstructuresthatprovide parking placeshow agoodoutcropofthrustramp, Back totheroad,cutslocatedjustnorthof imbrications onahillsideinthelandscape. for somemetrestogetapanoramicview ofthrust From theparkingareawecanwalk westwards limestones andtheZurizashales. Teixell chert-bearing limestonemember(Teixell, 1990; presented infi gure 4.4.Bedding-parallelveins are A detailedprofi densely packed stackofbedding-parallelcalciteveins. inspection shows thatitsfoliatedaspectisduetoa resembles amyloniticmarble.However, closer band ofstronglyfoliatedrockthat,atfi The Larrathrustappearsinoutcropasameter-thick antiform (Gavarnie thruststage). faulting duringthedevelopment ofthe Axial Zone angles totheN,duepost-thrusttiltingandnormal thrust dipsparalleltofootwall bedding,atgentle plane withoutrepetitionofstratigraphy. The Larra defi Structural landscape: border. outcrops bythesignalpostofSpain/France Access: Larra fl Pierre-Saint-Martin. Fault zonestructure ofthe Stop 4.4: Refugio deBelaguaislocatedsome 5kmtotheSW. Zone (Pierre-Saint-Martinarea)(afterTeixell, 1990).The a segmentoftheLarrathrustsysteminnorthern Axial Figure 4.3a-Detailedgeologicalmapandcross-sectionof nition ofadécollement:bedding-parallelslip g. 4.3b). oor thrust. walk down theroadbacktoroadside et al.,2000). The rampsabove cutthechert le ofthefault zoneatthislocalityis theLarrathrustfi rt sight, rst t the ts WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16 Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 4.3b - Outcrop sketch and plots of minor structures of the ramp locality at Pierre-Saint- Martin (stop 4.3) (after Teixell et al., 2000).

47 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell to beintheorderof5km.Displacementwas mostly of theLarrathrust,whichcanberegionally estimated scale, thesewerenotkey mechanismsinmovement recrystallization areconspicuousatthethinsection during shorttimespans.Even thoughtwinningand could accommodateappreciableincrementsofslip sills”) weresurfaces ofzeroshearstrengththat and fl uid, theopenextensional fractures(“water Being constitutedbyinterfaces betweensolid form ofbedding-parallelextensional fractures. weakening andlocalizedyield. Yield initiallytookthe change withinthelimestonecausedepisodicbrittle channeling. Fluidchannelingataslightlithologic the weakening was inducedbystressandfl for detachment. Teixell etal.(2000)proposedthat capacity ofthehostrockwerenotprimarycauses Hence rheologicalweaknessandwater-generating within amechanicallystronglimestoneunit. The Larrathrusthasthesingularityofbeinglocated and groupedinsets(Fig.4.4). mesostructures have beencorrelatedacrosstheprofi orientation andrelationshipstooneanother, the folds andminorfaults. Onthebasisofaspect, apart fromtheveins includevein breccias,stylolites, complex assemblageofdiverse mesostructuresthat, present, althoughlessabundant. Infact, thereisa observed. Cross-veins obliquetobeddingarealso twinning andrecrystallization.Nofi crystals withvariable internaldeformationby point ofview, veins arefi almost 100%vein material.Fromamicrostructural fault zonecenter, wheretherockappearsformedby footwall, andtheirfrequency increasestowards the abundant foratleast3minbothhangingwall and A veins ontheleft(afterTeixell etal.,2000). Orientations areontheright;percentageandfrequencyof and otherminorstructures,asindicatedinthelegend. ‘A’. Otherlettersrefer todifferent setsofveins, stylolites structures areshown. Thrust-parallelveins arelabelled Positions andobserved cross-cuttingrelationsofchief Larra floor thrustatPierre-Saint-Martin(stop4.3). Figure 4.4-Structuralprofile ofthefaultzone lled withblocky calcite br hv been have bers uid le (leading todécollementslip). 2) stressreorientationandbedding-parallelshear of 1)bedding-parallelstressandcrackdilation, thrust was achieved byacyclic repetitionofepisodes 2000). Hence,weinferthatmovement ontheLarra by differential elastic contraction(Teixell a shearstressonthefracture. This mayhave occurred have beensomesortofstressreorientationtoimpart displacement was paralleltobedding,theremust stress inathrustregime, but asmajorfl veins arecompatiblewithsubhorizontalmaximum A remainingproblemliesinthatbedding-parallel signature. accommodated bysliponthewater sills,leaving little numerous limestone-shalerepetitions, andshow system, formedearlier(Teixell, 1990). Thrusts cause the vicinityofRefugiobelongtoLarrathrust thrust faults deformingtheCretaceousformationsin landscape isabroadantiform.Minor, south-directed The large-scale structurethatcanbededucedinthe outcropping alongtheroadtoRefugio. Overlying thelimestonesarestrongly cleaved shales, close totheRefugiocontainshallow-water forams. in fi gure 4.5.UpperCretaceouslimestonesthatare Lakora klippe. A cross-sectionoftheareaisshown good overview ofthe Axial Zoneandtheoverlying Structural landscape: hut oftheRefugiodeBelagua(signal). Access: 4.5. fi of theCretaceous cover ofthe Axial Zone, Refugio deBelagua.Generalviewandstratigraphy Stop 4.5: Figure 4.5-Geologicalcross-sectionoftheBelagua- Indicated as«hut»isthepositionofRefugiode driving southonNA 1370uptothemountain Lakora area,locatedinthenorthern Axial Zone. fromtheRefugiothereisa Belagua (stop4.5). or thrust oor et al., gure WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

fault-related anticlines that bear an associated north- DAY 5 dipping slaty cleavage, especially in shaly rocks. from Jaca to Labuerda. Stop 4.6: Morning Roncal valley. The Eocene fl ysch of the Southern Pyrenees (Hecho group). Southern Jaca basin and Access: drive down the Roncal valley and stop along External Sierras the main road some 2 km south of the village of Roncal. Stop 5.1: The roadcuts at this stop provide a good outcrop of San Juan de la Peña. Oligocene conglomerates the Eocene turbidites of the Hecho group. Turbidites of the Jaca basin. consist of silici-clastic sandstone/shale decimetric- Access: drive from Jaca to the west along C134 scale cycles, in which the pelitic component is largely and then take the road to the left that drives to the dominant. They represent relatively distal, basin plain San Juan de la Peña monastery. On the way to the facies within the Hecho group, and they have been External Sierras, we stop at San Juan de la Peña for dated as Lutetian in age (Mutti, 1984; Labaume et an overview of the Campodarbe formation that forms al., 1985). the youngest infi ll of the Jaca basin (Puigdefàbregas, Structural landscape: the turbiditic beds describe a 1975). synclinal fold at the outcrop scale, to which an axial Structural landscape: the Campodarbe beds describe planar cleavage is associated. This fold illustrates the the Guarga synclinorium (the present-day axis of characteristic deformation style of the Hecho group, the Jaca basin), whose position in the general cross- which originally accumulated in a foredeep in front section can be observed in Plate 2, fi g. 1. Fluvial of the growing orogen, and was later deformed and sandstone channels and shales grade upwards to incorporated in the mountain chain (e.g. Plate 2, fi g. 1). layered and massive alluvial fan conglomerates, Above this outcrop, in the landscape, we can see a which constitute the San Juan de la Peña massif. carbonate megabreccia bed, also characteristic of the The age of these rocks is Upper Eocene to Lower Hecho group. Clasts within the megabreccia derive Oligocene. The conglomerates show growth strata from carbonate platforms that fl anked laterally the (progressive unconformities) within synclinal folds. turbiditic trough. The position of these platforms The San Juan de la Peña massif is best known by and the geodynamic signifi cance of the megabreccias its monastery of the X-XII centuries, picturesquely have been the subject of diverse interpretations. Some sheltered by the conglomeratic cliffs. authors have proposed a northern provenance of the resedimented material, from hypothetical platforms Stop 5.2: lying on top of the active thrust margin of the basin Embalse de la Peña. Stratigraphy of the (Séguret et al., 1984; Labaume et al., 1985), wheras External Sierras other authors have proposed a southern source area, Access: follow N240 to the south to stop in the from platforms existing in the distal (foreland) margin proximity of the reservoir Embalse de la Peña. of the basin (Barnolas and Teixell, 1994). Proceed along the roadcuts to the south of the The megabreccia bed that we observe is numbered reservoir and the bridge. 5 in the sequence of 8 main units like this in the Structural landscape: the External Sierras are the northern Jaca basin. It shows a large mushroom-like foothills that constitute the South Pyrenean thrust feature interpreted to be a giant water-escape structure front (Plate 2, fi g. 1). Emergent thrusts bring Mesozoic by Labaume et al. (1983). rocks to the surface, starting with Triassic shales and Volume n° 2 - from B16 to B33 n° 2 - from Volume evaporites (Keuper facies) that, when present, form the regional décollement level of the Pyrenean cover thrusts (Séguret, 1972). The stratigraphic succession of the External Sierras is sketched in Fig. 5.2. We can recognize the diverse units in the gorge of the río Gállego, which provides one of the best and most visited sections across the Sierras.

49 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell the area. They arebuilt byUpperOligocene-Lower stacks thatformawell-known touristic attractionof The Mallosisthelocalnameofagrouppicturesque Leonar. between thetwo prominentMallosuptotheCerro Mallos. Fromtheparkingplacewalk upalongthetrail and parkjustbelow theconglomeratepillarsof to Riglosontheleft(HU310).Crossvillage Access: interactions. Riglos. Thrust front andproximal alluvialfan Stop 5.3: basin, but muchreducedinthickness. Campodarbe bedsaresimilartothosewithintheJaca counterparts oftheHechoturbidites. The Arguís and formation (middleEocene)arethebasin-margin few hundredmofplatformlimestonetheGuara uppermost Cretaceoustolowest Tertiary age. The and lacustrinelimestones(Garumnianfacies) areof poorly constrainedextent, theoverlying redbeds Cretaceous age. Although theremaybehiatusesof Above theKeuper, wefi al., 1995). and Tertiary ofthe External Sierras(taken fromMillánet Figure 5.2-StratigraphiclogoftheMesozoic continuedown theN240andtake theroad nd rudist-bearingofUpper relationships withtheconglomerates. observed alongtheway up,alsoshow syntectonic 1995). Minorout-of-sequencethrusts,asthose to thelaterantiform(Teixell andGarcíaSansegundo, progressive unconformities(growth strata)associated the conglomeratesofMallos,thatinturnshow river. The leadingedgeofthethrustissealedby located beneathourfeet,justabove theGállego easterly plunge,soitdevelops afoldclosure The antiformthatarchesthethrusthasastrong appears unrootedandcompletelyoverturned. A andB),soitsleadingedge,isolatedbylatererosion, arch (seefrontcover, fig. 2,Platefi g.1, andfi anticline, athrustthatisitselffoldedinanantiformal thrust fault risingfromtheaxialplaneofatight They showed theexistence ofalarge south-vergent until thework byPuigdefàbregas andSoler(1973). puzzled geologistsfordecades,andwas notresolved overturned successions(seefrontcover, fi very complex, withrefoldedthrustsandlarge Gállego gorge. The structureoftheSierrasiscertainly view oftheentireExternalSierrasoverlooking the From thetopofitinerarywehave agoodpanoramic (Millán the area,providing evidence forthrustsequences thrust sheets. This kindofrelationshipiscommonin thrust faults, but areinturnoverridden byhigher-level pronounced paleorelief,sealingsomeoftheolder up theCerroLeonar, theconglomeratesonlapa sedimentation. As wewillclearlyseeby theitinerary The Mallosshow beautifulsignsofsyntectonic Fig. 5.3, A andB). segment ofthePyrenees(seefrontcover, fi the lastsynorogenicforelandbasindepositsofthis emergence oftheExternalSierras,andthey represent They accumulatedsynchronicallywiththemain (Puigdefàbregas, 1975;HirstandNichols,1986). south passrapidlytofl uvial sandstonesandshales formed withinsmallalluvialconesthattowards the from theMesozoicand Tertiary oftheSierras,and The conglomeratesarecomposedofclastsderived of ExternalSierras. Miocene conglomeratesattachedtothesouthernface Barcelona, Spain,e-mail:[email protected] Geologia, Universitat deBarcelona,Pedralbes,08028 Departament deGeodinamicaiGeofi By Josep Anton Muñoz, Basin III. The Ainsa Afternoon et al.,1995). sica, Facultat de g. 2).It g.2 and g.2 g. 5.3, WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

Introduction by a northwest-trending imbricate thrust system The Ainsa basin is located in the footwall of the and related folds. Two main thrusts in the footwall Cotiella-Montsec thrust sheet (Seguret, 1972) of the Cotiella thrust sheet, the Atiart and Los (Figs. 5.4b, 5.5a). This cover thrust sheet consists Molinos thrusts, detach the Ainsa turbiditic basin of Mesozoic and syntectonic Paleogene rocks that from underlying Paleocene and Lower Eocene have been detached from the Variscan basement on carbonate platform rocks. The Ainsa basin evolved Lower Triassic evaporites. During the Early Eocene to a piggy-back condition as thrusting propagating southward displacement of the Cotiella-Montsec, the forelandwards and the detachment Mediano anticline Tremp piggy-back basin developed on its hangingwall and the fault-propagation Boltaña fold developed. (Fig. 5.5a). The basin contains platformal and These folds developed during the fi lling of the Ainsa continental terrigenous facies that grade westward basin synchronously with their dextral rotation in the across an oblique lateral ramp of the Cotiella- footwall of the Cotiella thrust sheet. Montsec thrust sheet (in the region of the La Foradada The basin originated as a foredeep ahead of the fault, Fig. 5.5a) into the marine Ainsa turbidite basin innermost of these thrusts in the Early Eocene (Fig. (Nijman and Nio, 1975, Mutti et al., 1988). 5.5a) and evolved into a piggy-back setting as the The Ainsa basin is deformed by the Peña Montañesa thrust front propagated towards the foreland. The thrust system in the northeast, by the north-trending Mediano anticline in the south, and by the Boltaña Figure 5.3 - Cross-sections through the External Sierras anticline to the west (Fig. 5.4b). The structure of (after J. García Sansegundo, in Teixell & García the eastern part of the Ainsa basin is dominated Sansegundo, 1995). Volume n° 2 - from B16 to B33 n° 2 - from Volume

51 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell systems, packagesofturbiditesarefaulted and currents; however, inparticularpositionsofturbidite indicate depositionfromabroadvariety ofturbidity changes downslope. Mostofthefacies involved transitions andonesystempreserved signifi outcrops allow insightsonchanneltooverbank channels andassociatedoverbank elements. The length reachingupto20km,andmostlyformedby than 300m,few kilometreswide,withapreserved anatomy. The turbiditesystemsaregenerallythinner with outcropsallowing thereconstructionoftheir3D embedded. The lattercorrespondtoturbiditesystems mudstones wherecoarser-grained lithosomesare The Ainsa SlopeComplex consistsprimarilyof thick, morethan15kmwideandupto80long. dominated lobeelementsareseveral tensofmetres mudstone interbeddings. The individual sandstone- replaced downcurrent bybasinalsandstoneand termed “outer-fan” sandstonelobes,whichare complex intheJacabasinconsistsofclassically fl the southwestandevolved totheNWintoabasin- The slopecomplex hadafl uviodeltaic sourcein is upto4,000mthick,40kmlongand30wide. foredeep fi lled mostlywithaslopecomplex which oor complex (Figs.5.5aand5.5b). The basin-fl Figure 5.4b-Geologicalsketch mapoftheEasternpart the Ainsa BasinandoftheBoltaña Anticline. Figure 5.4a-Geologicalsketch mapoftheExternalSierras,Jaca Basin andthe Ainsa Basin. cant oor WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

deformed by slumping at diverse scales or transformed Within a single depositional cycle, an overall into debris fl ow deposits. The resedimentation process decreasing rate of tectonic deformation caused an interacted with turbidite deposition and introduced a overall decrease in slope gradient, in turn responsible degree of architectural complexity. for contrasts on facies, architectural style and external The interplay between tectonics and sedimentation geometry among stratigraphically consecutive in the Ainsa basin had different scales. Below is a turbidite systems (Fig. 5.5b). summary of these relationships, ordered from basin Pulses of increased deformation caused angular scale to the scale of individual turbidite channel unconfomities at the base of turbidite systems. These elements. evolved overall towards abandonment, trough cycles The propagation of the thrust front caused the Ainsa of channel-complex development and abandonment. basin fi ll to be segmented as four major depositional However, their internal architecture and external cycles which are delineated by widespread angular geometry varies between end-members: 1) vertically- unconformities and are stepped towards the foreland stacked and symmetrical in cross-section and 2) (Fig. 5.5b). These unconformities are submarine complexly juxtaposed and markedly asymmetrical. truncations, up to several hundreds of meters deep, The more complex patterns arose in zones left piggy- which laid parallel to the elongation of the basin and back between growing anticlines. The overall straight were carved by mass wasting. The potential for mass downslope platform of individual turbidite channels wasting was created by forelimb rotation along the was in some cases modifi ed by anticline-related active basin margin and by fl exural downwarping topographies. in the outer basin margin. These “cañons” acted as Objectives: to examine the tectono-sedimentation containers for further slope deposition. relationships of the Ainsa basin, growthg folds and the surrounding thrust systems.

Figure 5.5a - Palaeogeography of the South Pyrenean foreland basin at Early Lutetian. Turbiditic systems of the Ainsa basin had feeder fl uvial systems in the Tremp basin. Clast composition is dominated by limestone clasts derived from Paleocene and Mesozoic rocks, but it also includes granites, volcanic rocks and others, which correlates to the exposed rocks in the hinterland, as it is also indicated by alluvial fans fringing the Northeastern Tremp Basin. From Arbués et al. 1998. Volume n° 2 - from B16 to B33 n° 2 - from Volume

53 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell unconformity ;7:condensedsection8surfaceofsubmarinegravitational erosion.Codefor localnamesof turbidites ;2C:resedimentedcarbonates3delta;4alluvialplain5plain.Discontinuities Code for surfacesofsubamrinegravitationalerosion Mon :Montilobatfm.;CstCastissentCmCampanuéconglomerates(*)CpCapellaPrPerarrua fm.. Ainsa basin(afterPoblet etal.1988). Figure 5.6a-GeologicalmapoftheMedianoanticline, codes stratigraphic units Main depositionalfacies Figure 5.5b-Syntheticstratigraphyofthe Ainsa Basin. : FuFuendecampotectosedimentaryunit.From Arbués etal.1988. : Yb : Yerba marls(^);Gu&Gr:Guaralimestones(+)andGrustanmb(*)Cgl:Castilgaleufm :1 :carbonateshelf;2deltaandslope2Amudstones,2Bsilici-clastic : At : Atiart ;Ch-Lsz:Charo-LascorzFo :Formigales. Other surrounding structuresarevisible:theBoltaña From thisviewpoint the Ainsa basinandthe Structural landscape to thechurchattopofhill. follow theroadtovillageofGuaso. Take theroad Follow thisroadtoanintersection,turnrightand Guaso andtheGuaraparkaftercrossing Ara river. From Boltañadrive eastto Ainsa. Take theroadto Access : Ainsa basin. Tozal de Guaso.Panoramic viewofthe Stop 5.5: Eocene limestonesoftheBoltañaanticline. This Stopshows thesteep,west-dippinglimbof Boltaña anticline(Fig5.5a). a topographicbarrieratthepresentlocationof basin continuedbasinward intotheJacabasinwithout and 5.4c).Mostoftheturbiditesystems Ainsa basin andmostlyduringtheMiddletoLateEocene the lateststagesofturbiditefi boundary ofthe Ainsa basin,however itgrew during The Boltañaanticlineisconsideredthewestern intersection leadingtothevillageofJanovas. From Broto,drive eastto Ainsa. Stopinthe Access: Boltaña anticline Stop 5.4: lling ofthe Ainsa :6subaerial WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

Barbastro. Continue southwards past the now submerged village of Mediano. Turn left onto a small side road that leads to the village of Samitier and park the vehicles near the small square and fountain in the centre of the village. From the parking spot in the village take the farm track that leads off to the left and up the hill to the Ermita de San Emiterio and San Celedonio. Several good view Stops can be found along the way overlooking Mediano lake and the western limb of the Mediano anticline. Climb to the old church at the Ermita de San Emiterio and San Celedonio. From here there are excellent views of the Mediano anticline, the onlapping Ainsa turbidites, and the Buil syncline to the left. In the distance (if the weather is clear) the main ranges of the Pyrenean axial zone can be seen. Structural landscape The Mediano anticline is a north-plunging, north- trending detachment anticline developed above the Triassic evaporites (Fig. 5.6a). It is cored by massive to thick-bedded Eocene limestones (Fig. 5.6b). Eocene (Lutetian) turbidites onlap the anticline in a syn-folding growth sequence (Figs. 5.6a, 5.6b and 5.6c). The geometry, facies distribution (from alluvial to deep-water silici-clastics and carbonate rocks) plus the available magnetostratigraphy and biostratigraphy pose restrictions to the kinematic evolution of the anticline (Fig. 5.6c). Stop 5.7: Cotiella and Peña Montañesa thrust sheets. Access: drive back to Ainsa and Labuerda and continue north along the main road (N-138) until the village of Escalona. At this locality turn left to the Añisclo valley and immediately take the small road to the right to the village of Puertolas. Continue up the mountain and Stop just past the small village of Santa Maria before the village of Puertolas. Figure 5.6b - Mediano anticline evolution. Structural landscape From this viewpoint the large klippes at Peña anticline to the west, the Mediano anticline to the east Montañesa and the Cotiella thrust sheets can be and the Monte Perdido-Gavarnie, Peña Montañesa viewed. The fl at-lying fl oor thrusts of these thrust Volume n° 2 - from B16 to B33 n° 2 - from Volume and Cotiella thrust sheets to the north-northeast. sheets bring Mesozoic and Paleocene limestones This viewpoint is an excellent spot to discuss the on top of the Lower Eocene turbidites and marls of main geological features of the area, summarize the the Ainsa basin. The Atiart thrust (fl oor of the Peña structures observed these two days. Montañesa thrust sheet) merges hindwards with the Cotiella thrust. Stop 5.6: Ermita de San Emiterio and San Celedonio. Access: drive to Ainsa and take the C-138 towards

55 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell thrust sheetshows adistinctstratigraphy. Itinvolves Below theCotiella,MontePerdido-Gavarnie Eocene. southwards aminimumof20kmduringtheEarly Ainsa basin. The Cotiellathrustsheetwas displaced limestones intotheLower Eoceneturbiditesofthe up southwards inthefootwall fromthePaleocene lower thrustsheets. The Cotiellafl oor thrustclimbs extension anddipssouthwards inthenorthabove the dips subhorizontalyformostofitscartographic Perdido-Gavarnie andbasementthrustsheets).It emplacement ofthelower structural units (Monte thrust oftheCotiellasheetisfoldedby above the Triassic evaporites (Fig.6.1b). The fl succession (mostlyUpperCretaceous),detached units characterizedbyavery thickMesozoic (Muñoz 1972) ortheso-calledMesozoicUpper Thrust Sheets unit oftheSouthPyreneanCentralUnit(Seguret, part oftheMontsecthrustsheet,mostextended The Cotiellathrustsheet(Fig.6.1a)isthenortheastern Introduction By Josep Anton Muñoz Sheets Cotiella Thrust the Monte-Perdido-Gavarnie and Basement ofthe Axial Zoneand IV. The Alpine structure ofthe from Labuerda toPau. the Medianoanticline. Figure 5.6c-Synsedimentarygrowth andkinematicsof et al.,1986).Itconsistsofseveral structural DAY 6 oor of Triassic redbeds,unconformablyoverlying the cover oftheselowermost thrustsheetsonlyconsists rocks intrudedbyUpper-Hercynian granitoids.The consist ofmetamorphicLower andUpperPaleozoic with adifferent stratigraphyareexposed. They Below theGavarnie thrust, basement thrustsheets turbiditc successionofthe Ainsa basin. upwards intothelower partoftheLower Eocene (Seguret, 1972). The MontePerdidothrusts merge have been describedastheMontePerdidothrustsheet units show anincreasingdisplacementwestwards and Upper CretaceousandPaleocene formations. These shows apileofsmallthrustimbricatesrepeatingthe succession. Above thebasement,thisthrustsheet Devonian rockstothebottomofMesozoic southwards intothehangingwall fromtheSilurian- of theGavarnie thrustwhichclimsupsection and Medianoanticlinesarethesoutherncontinuation underneath). The thrustsrelatedwiththeBoltaña structurally incontinuationwiththe Ainsa basin(i.e The MontePerdido-Gavarnie thrustsheetis by theLower Eocenemarlsandturbidites. consists oflimestonesanddolomitesisoverlain the overlying Cotiellathrustsheet. The Paleocene the several kmthickUpperCretaceousseriesof hundred metersthick(800maprox.)incontrastwith Hercynian basement. They formasuccessionseveral and sandstonesrestunconformablyontopofthe and folds. The UpperCretaceouslimestones,marls shales andlimestonesaffected byHercynian thrusts and Carboniferousslightlytonon-metamorphosed Cotiella. The basementconsistsofSilurian,Devonian succession ismorereducedandmuchthinnerthanthe the Hercynian basementandtheMesozoic WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

Figure 6.1a - Geological sketch map of the Cotiella thrust sheet and location of stops. basement, Keuper above, and a thin bed (few tens of structural features of the Cotiella thrust sheet and its meters) of Upper Cretaceous limestones on top. The footwall (Fig.6.1a, 6.1b, 6.1c, 6.1d). On the other basement and the cover are both tightly folded and side of the valley the Cotiella thrust is visible at the affected by thrusts. bottom of the Upper Cretaceous limestone cliffs (1,200 meters high). It lies subhorizontaly above the Objectives: to examine the Alpine thrust structure of lowermost Eocene marls. Northwards of this locality the basement units of the Pyrenean Axial Zone as well the thrust as well as the Upper Cretaceous-Eocene as the structure of the main cover thrust sheets above beds in the footwall (Monte Perdido-Gavarnie thrust the basement. sheet) are tilted to the south 25-30º and truncated by a pair of E-W trending conjugate extensional faults Volume n° 2 - from B16 to B33 n° 2 - from Volume Stop 6.1: (Fig. 6.1c, 6.1d). Cotiella thrust and structure of its footwall. The Eocene marls are folded and affected by a Access: from Labuerda drive north to Bielsa (N-138) prominent N-S, NNW-SSE trending cleavage at a until the village of La Fortunada. Pass the village for high angle with the general E-W, ESE-WNW general 1 km before the road tunnel of Las Devotas. trend of the beds. This geometry is the result of a late Structural landscape tilting of the deformed marls and the Cotiella thrust The purpose of this Stop is to continue a general sheet by thrusting of underlying basement thrust cross section of the area as well as to observe some sheets.

57 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell Continue northtoBielsa(N-138)andturnleft Access thrust sheets.LaLarritectonicwindow. Cross-section oftheMontePerdido andGavarnie Stop 6.2: basin. Figure 6.1b-TheSyn-RaftingCotiellabasinreplacedinthetectono-stratigraphicevolution oftheSouth-Pyrenean This isoneofthemostspectaculargeological Structural landscape the river iscrossed. Walk for1hour. track immediatelybeforetheParador andparkonce Pineta-Parador NacionalMontePerdido. Take the locality for and akey the Pyrenees scenes of footwall. and ofits Thrust Sheet the Cotiella - Structureof Figure 6.1c WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

Figure 6.1d - Kinematics of the Cotiella Thrust sheet and the Mediano anticline. understanding the basement involvement into the in the footwall of the Gavarnie thrust outcrop. Alpine thrust structure and the structural relationships Climb the grassy slopes southwards of that valley between the cover and the basement thrust sheets. towards La Estiba in order to get a view of the The course will follow the Pineta glacier cirque across the lower part of the Upper Cretaceous succession of the Gavarnie thrust sheet. The trail climbs up into B16 to B33 n° 2 - from Volume the lateral glacier valley of La Larri where the Triassic red beds

Figure 6.2a - The Gavarnie Thrust at La Estiba.

59 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell Barnolas, A. and Teixell, A. (1994).Platformsedimentation Spain p.145-146. International Sedimentological congress García delCuraandJ.Soria(eds.), Abstracts ofthe of South-CentralPyrenees,Spain. surfaces inthesedimentaryinfill ofthe Ainsa basin(Eocene McClay, K..(1998).Signifi cance ofsubmarinetruncation Arbués P., MuñozJ.A.,PobletJ.;Puigdefàbregas C.and Université deBordeaux 1 d’Aspe, HauteChaîne,Pyrénées Atlantiques, supérieur delaMarge Ibérique: Vallée d’Ossau-Vallée sédimentaire etDiagenèsedescalcairesduCrétacé Alhamawi. M.(1992).Sédimentologie,Pétrtographie References Université deBordeaux1. Fieldtrip guidebookwas editedatLaboratoireCIBAMAR, to publishspecialin-housework andformaterialsupport. of Total (L.Moen-Maurel). We thank TOTAL forpermission , oftheUniversitat deBarcelona,Pedralbès(J.Muñoz),and Universitat Autonoma deBarcelona,Bellaterra(A. Teixell) of theUniversité deBordeaux1(R.Bourrouilh),ofthe Mountain belt.Ithasbenefi This work isacontribution totheknowledge ofthePyrenean Acknowledgements Florence End ofthefi eld tripandreturnoftheparticipantsto of theoutcroppinglower thrustsheets. Cretaceous, Triassic redbedsandgraniticbasement characterize thefoldandthruststructureofUpper between thevillagesofBielsaandParzan inorderto Several observations willbemadealongtheroadcuts Structural landscape leading totheFrenchborder. Drive backtoBielsaandreachmainroadN-138 Access the Gavarnie thrust.Bielsa-Parzán cross-section. Structure ofthegranitebasementinfootwall of Stop 6.3: (Fig. 6.2a,andFrontcover, fi differences betweenthehangingwall andthefootwall basement initshangingwall andthestratigraphic the foldedunconformityabove theHercynian with theGavarnie thrust.Noteitsantiformal attitude, bottom ofthevalley. This fault contactcorresponds and themetamorphicbasementoutcroppingat the UpperCretaceouslimestones-Triassic redbeds Upper Cretaceousrocksisvisible.Itrestsontopof basement oftheGavarnie thrustsheetbelow the northern ridge.Fromthisviewpoint, theDevonian DAY 7 , 320pages tedfromtheResearchprograms g.3). In: J.C.Cañaveras, M.A. , IAS, Alicante, Thèse 15th Pyrénées-Atlantiques, France. l’évaluation descarrièresdemarbres : exemple d’Arudy, F.G. (1997). Application duquadripôleélectrostatiqueà Benderitter Y., BourrouilhR.andBourrouilh-LeJan Geology, 12,1107-1110. foreland basin(Eocene,Jacabasin,southernPyrenees). and collapseinacarbonate-dominatedmargin ofaturbiditic Cretaceous examples ofSouthernFrance. extensional transformmargins: Devonian andLower Bourrouilh R.(2000).Mud-moundsondivergent and 81. Springer Verlag. Sierras deLevante deMajorque. Bourrouilh R.(1970).LeproblèmedeMinorqueetdes 25-43, 12fig. 1pl. l’Aquitaine méridionale. supérieur àfaciès urgonien dans les Pyrénéesoccidentaleset Organisations sédimentairesetpaléoécologiquesdel’Aptien Bouroullec J.,Delfaud J.andDeloffre R.(1979). Newsletter 7 corrélations Chaîne, PyrénéesCentrales,Sédimentologieetpremières Le Cambro-Ordovicien del’HospiceFrance, Haute Bouquet C.,BourrouilhR.,GuérangéB.et Vaché E.(1990). 405-435. des Pyrénées. Mendibelza : dépôtsdecônessous-marinsduriftalbien Boirie J.M.andSouquetP. (1982).LesPoudinguesde Université de Toulouse de Mendibelza(Pyrénées Atlantiques). Boirie J.M.(1981).Etudesédimentologiquedespoudingues BRGM ed,101p. d’années, itinérairesgéologiquesdansleparcnational. Mirouse R.andRogerP. (1985).Pyrénées : 500millions Bixel F., ClinM.,LucasCl.,Majeste-Menjoulas Pyrenees pays nord-pyrénéen. 1995b. Evolution géodynamiqueetpétrolièredel’avant- Biteau J.J.,LeMarrec A., Moen-MaurelL.andNoualG. 545-552. Pyrenean Basin. Megaturbidites inanInterplatebasin:example oftheNorth Bourrouilh R.(1987).Evolutionary Mass-Flow- cartes géol.1/50.000e. de Espana beticas enelMediterraneooccidental. (Baleares). La Terminacion NororientaldeLasCordilleras Tectonica delaIslaMenorcaydelNoresteMallorca Bourrouilh R.(1983).Estratigrafi a, Sedimentologiay géologiques. au 1/50.000etfondstopographiques,2planchesdecoupes planches dansletexte, 6horstexte :2cartesgéologiques Université deParis V bétiques enMéditerranéeoccidentale. (Baléares). Laterminaisonnord-orientaledesCordillères Tectonique del’îleMinorqueetduNEMajorque Bourrouilh R(1973).Stratigraphie,Sédimentologieet XC, fasc 4,p.363-380,13fi , Toulouse, Fieldtripguidebook. , t.99,1vol. 692p.,1vol. 95pl.ethors-textes, 2 , p.131-133,1fi in SassiandBourrouilh,Eds.,IGCPn°5, Bull. C.R.P. Elf-Aquitaine GeoMarine Letters Soc. Géol.France Spec.Meetingon , 115p. I, 2tomes,822p.,196fi g. et95 Géobios, Mémoire spécial g. g. C. R. Acad. Sci.Paris Ann. Soc.géol. Nord, , volume 7,n°2,p.69- Mem. Inst.Geol.Min. Thèse 3èmecycle, , vol . 6,n°2p. The Geological Thèse d’Etat. n°3, , 325, t. WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16

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Réunion Annuelle des Sciences de Pujalte, V., Robles, S., Zapata, M., Orue-Etxebarria, X. and B16 to B33 n° 2 - from Volume la Terre, abstracts. Garcia Portero, J. (1989). Sistemas sedimentarios, secuencias Montagné G. (1986). Les anomalies du fl ysch Nord- deposicionales y fenómenos tectono-estratigráfi cos del pyrénéen de Pau à Ascain (Pyrénées-Atlantiques). Thèse Maastrichtiense superior-Eoceno inferior de la cuenca Université de Pau, 328 p. Vasca (Guipúzcua y Vizcaya). XII Congreso Español de Muñoz, J.A. (1992). Evolution of a continental collision Sedimentología, Bilbao, Guia de Excursiones, 47-88. belt: ECORS-Pyrenees crustal balanced cross-section in: Ribis, R. (1965). Contribution à l’étude géologique du Thrust Tectonics (ed. by K.McClay). Editorial Chapman and Crétacé supérieur de la Haute-Chaîne dans la région de la Hall. 235-246. Pierre-Saint-Martin (Basses-Pyrénées). Thèse 3ème Cycle, Muñoz, J.A., Coney, P.; McClay, K. and Eevenchick, C. Université de Paris, 200 p.

63 - B16 Volume n° 2 - from B16 to B33 B16 - B16 Leaders: R.Bourrouilh,L.Moen-Maurel,J.Muñoz,A.Teixell de lageologiadel Alto Aragon Occidental. Soler M.andPuigdefàbregas C.(1970).Lineasgenerales Tome 1:129p,t.2:annexes :34pl,XVIIIp.Bibliographie. Pau. Thèse Crétacé/Tertiaire, duPaléocène etdel’YprésienauSud Seyve C.(1984).Etudemicropaléontologiquedupassage Taberner C.(1983).Evolución ambientalydiagenéticade (B9): 18117-18134. teleseismic data. of thelithospherebeneathPyreneesfromlocaland Souriau A. andGranetM.(1995). A tomographicstudy 53, fascicule 2,p.149-192,Université deGrenobleed.. (1977). LachaînealpinedesPyrénées Souquet P., Peybernès B.,Billotte M.andDebroasE.J. 9, 1,183-252. Cénomanien) danslesPyrénées. Peybernès B.(1985).LeGroupeduFlyschNoir(Albo- Dol J., Thieuloy J.P., BonnemaisonM.,Manivit H.and Souquet P., DebroasE.J.,PonsPh.,FixariG.,Roux J.C., Pyrénées (Espagne). d’avant-fosse. Exemple dusilloncrétacéversant Suddes chevauchements etséquencesdedépôtsdansunbassin Souquet P. andDeramondJ.,(1989).Séquence de International, Paris, des Pyrénées évolution desbassinsdesédimentation danslecycle alpin Souquet P. andDebroasE.J.(1981). Tectonogenèse et p. 5-20. Pyrenean Basin(NorthSpain). seismicity inthePyreneesfrommegaturbidites intheSouth- Seguret M.,LabaumeP. andMadariagaR.(1984).Eocene Géologie Structurale,n°21. Publication deUstela,Université deMontpellier, décollées delapartiecentraleduversant suddesPyrénées. Séguret M.(1972).Etudetectoniquedesnappes etséries 130. Southwestern Pyrenees, Rupke (1976).Larger scaleslumpinginafl evolution ofthePyrenees. balanced cross-sections,geometricconstraintstotracethe and DeramondJ.(1989).ECORSDeepSeismicdata Villien A., MatheronP., Bareyt M.,Seguret M.,CamaraP. Roure F., ChoukrouneP., Berastegui X.,MuñozJ.A., Geology, 19:613-616. North Atlantic fromtheLateCretaceoustopresent. plate boundariesbetweenEurasia,Iberiaand Africa inthe Roest, W.R. andSrivastava, S.P.(1991). Kinematicsofthe Fieldtrip pays Nord-Pyrénéen, (1995). Evolution géodynamiqueetpétrolièredel’avant- Richert, J.P., Moen-Maurel,L.,BiteauJ.J.,CanérotJ., Conference Field Trip Guidebook the vicinityofLacqandMeillongasfi (1995). The NorthernPyrenees Thrust BeltandForeland in Richert J.P., Moen-MaurelL.,CanérotJ.andBiteauJ.J., guidebook,62p. 3ème cycle, Université Pierre-et-Marie-Curie. in ColloqueC7,26èmeCongrèsGéologique Journal ofGeophysicalResearch Mémoire B.R.G.M C. R. Acad. Sc.Paris, Soc. Géol.France Annual Meeting, Jour geol. Soc.London Tectonics Mar. Geol., . 68p. Bull. CREPElf Aquitaine, , 8(1),41-50. . n°107p.213-233. in Géologie Alpine elds. 309,137-144. 55,117-131. Pirineos yc basin, ysch AAPG Nice , 132,121- , v. 96, série , 100 t. of thepyrenean Axial Zone. Teixell, A. (1990). Alpine thrustsatthewesterntermination 1-1400. de laCuenca Vic. los dépositosdel Terciario inferior(Paleoceno yEoceno) levels in thrustgeometry Pyrenean fold-and-thrustbelt:roleofforelandevaporitic Verges, J.,Muñoz,J.A.andMartinez, A. (1992).South Marine andPetroleum Geology pre-, syn-andpost-collisionalcrustal-scalecross-sections. S. (1995).EasternPyreneesandrelatedforelandbasins: Cires, J.,DenBezemer, T., Zoetemeijer, R.andCloetingh, Verges, J.,Millan,H.,Roca,E.,Muñoz,J.A.,Marzo,M., VI(2), 265-271. Soc. London Pyrenees: basementandcover thrustgeometries. Teixell, A. (1996). The Ansó transectofthesouthern 241-249. 238 Occidentales. de décrochementdansl’avant-pays norddesPyrénées Zolnai G.(1975).Surl’existence d’unréseaudefailles Paris. in Histoire structurale duGolfedeGascogne Zolnai G.(1971).LefrontnorddesPyrénéesOccidentales, 1.30, Technip, Paris. in Histoire structurale duGolfedeGascogne, d’Aquitaine (contribution àl’histoireduGolfedeGascogne), Winnock E.(1971).Géologiesuccinctedubassin 131, 3-19. Bulletin Technique Exploration-Production Elf Aquitaine, nord pyrénéenne :conséquencessurl’exploration pétrolière. Villien A. andMatheronP. (1989).Géodynamiquedelazone 155, 267p. Occidentales françaises. Viennot P. (1927).RecherchesstructuralesdanslesPyrénées Earth andPlanetaryScienceLetters, the emplacementofPyreneanlherzolitesandgranulites. Vielzeuf, D.andKornprobst, J.(1984).Crustalsplitingand (ed.). ChapmanandHall,London,255-264. the SouthernCentralPyrenees. Verges, J.,andMuñoz,J.A.(1990). Thrust sequencesin III, p.1301-1321. Jurassique duBassindeParis. application auxcorrélationschronostratigraphiquesdansle F. and Trifilieff V. (1987).Lastratigraphieséquentielleetson Vail P.R., ColinJ.P., JanDuCheneR.,Kuchly J.,Mediavilla Soc. Geol.España, sector centraldelaCuencaJaca(Pirineocentral). Teixell A. andGarcia-Sansegundo J.(1995).Estructuradel limestone. Stress andfl uid controlondecollementwithincompetent Teixell, A., Durney, D.W. and Arboleya, M.L.(2000). budget inthewestcentralPyrenees. Teixell, A. (1998).Crustalstructureandorogenicmaterial Journ. Struct.Geol., , 153,301-310. Rev. Géog. Phys.Géol. Dyn., 8,207-220. Tesis Doctoral, Univ. deBarcelona, Bull. Serv. CarteGéol.France in: Thrust tectonics in: Thrust Bull. Soc.géol. France. 22,349-371. . 12(8):893-915. Bull. Soc.Géol.France Bull. Soc.Géol.France, Tectonics, 67: 383-386. XVII,3,219- , McClay, K.R. p.IV1.1– 17,395-406. Jour. geol. , Technip, (8),6, Rev. , n° , 8, 8, Back Cover: Itinerary of the fi eld trip B16 FIELD TRIP MAP INTERNATIONAL GEOLOGICAL CONGRESS nd 32

Edited by APAT August 20-28,2004 Florence -Italy

Field Trip Guide Book - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg GEOLOGICAL CONGRESS 32 Volume n°2-fromB16toB33 AND CONTACT AUREOLE EMPLACEMENT MECHANISMS PETROLOGY, (EASTERN ALPS): DI RIES-RIESERFERNER INTRUSION OFVEDRETTE THE PERIADRIATIC Pre-Congress nd INTERNATIONAL B17 The scientific content of this guide is under the total responsibility of the Authors

Published by: APAT – Italian Agency for the Environmental Protection and Technical Services - Via Vitaliano Brancati, 48 - 00144 Roma - Italy

Series Editors: Luca Guerrieri, Irene Rischia and Leonello Serva (APAT, Roma)

English Desk-copy Editors: Paul Mazza (Università di Firenze), Jessica Ann Thonn (Università di Firenze), Nathalie Marléne Adams (Università di Firenze), Miriam Friedman (Università di Firenze), Kate Eadie (Freelance indipendent professional)

Field Trip Committee: Leonello Serva (APAT, Roma), Alessandro Michetti (Università dell’Insubria, Como), Giulio Pavia (Università di Torino), Raffaele Pignone (Servizio Geologico Regione Emilia-Romagna, Bologna) and Riccardo Polino (CNR, Torino)

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Layout and press: Lito Terrazzi srl - Firenze Volume n° 2 - from B16 to B33

32nd INTERNATIONAL GEOLOGICAL CONGRESS

THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS AND CONTACT AUREOLE

AUTHORS: B. Cesare1,2, A.M. Fioretti2, C. Rosenberg3

1Dipartimento di Mineralogia e Petrologia, Università di Padova - Italy 2C.N.R. Istituto di Geoscienze e Georisorse, Sezione di Padova - Italy 3Department of Geology, Freie Universität, Berlin - Germany

Florence - Italy August 20-28, 2004

Pre-Congress B17 Front Cover: The Collalto - Hochgall (3436 m a.s.l.) is the highest peak of the Vedrette di Ries massif. It is composed of fine-grained tonalite. THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

AND CONTACT AUREOLE B17

Leaders: B. Cesare, A.M. Fioretti, C. Rosenberg

Introduction this contact aureole. During the Oligocene the Alpine chain was the centre During the fi eld trip we will show the key outcrops of an extensive magmatism, mainly represented by of the pluton, discussing both the results and the new calc-alkaline, which resulted in a series of plutons ideas arising from detailed structural, petrologic and situated along and adjacent to the Periadriatic geochemical investigations performed over the past Lineament. These intrusives are hence referred to as twenty years. “Periadriatic plutons”. Geologic and topographic maps With an outcrop length of approximately 40 km, 1:25.000 topographic map, sheet n. 035 “Valle Aurina and a vertical exposure of 2500 m from base to roof, - Vedrette di Ries”, Ed. Tabacco. Vedrette di Ries (Rieserferner) represents one of the Cammelli F. (1994) Alpi pusteresi. Guida best exposed plutons worldwide (Figure 1). escursionistico-alpinistica. Available also in The intrusion of the pluton is characterised by three German, Ed. Athesia. major pulses of tonalitic to granodioritic composition, Carta Geologica d’Italia 1:100.000, sheet n. 4b with distinct petrographic and geochemical signatures. “Dobbiaco”. The ascent of these magmas was controlled by the Geologic Map of Italy 1:50.000, sheet n. 009 Defereggen-Anterselva-Valles (DAV) line, which “Anterselva” (in print). strikes along large parts of the southern margin of the Hammerschmidt K. 1981 Isotopengeologische pluton. The contact aureole of the intrusion developed Untersuchungen am Augengneis vom Typ in the metapelitic country rocks, and is characterised Campo Tures bei Rain in Taufers, Südtirol. by a complete zoneography from andalusite- Mem.Sci.Geol., 34, 273-300, with geologic map. staurolite to sillimanite-K-feldspar. The presence of Mager D. 1985 Geologische Karte des synmetamorphic andalusite-bearing veins, related to Rieserfernergruppe zwischen Magerstein und the dehydration of metapelites, is a unique feature of Windschar (Südtirol). ‘Der Schlern’, 6, Bozen. Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 1 - Geologic map of the Eastern Alto Adige (South Tyrol) from Dal Piaz (1934)

3 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg the Vedrette diRiespluton. The Dolomites, south Most oftheseunitsareoutcroppinginthearea Romandes» inSwitzerland. Penninic Unitsandthecover nappesofthe«Préalpes the two oceanicdomains,foundintheuppermost (4) theBriançonnais,amicrocontinentseparating the contactbetweenEuropeanand Adriatic units; by ophiolitesand«Buendnerschiefer»,locatedalong ocean andthePiedmont-Ligurianocean),represented (3) theremnantsoftwo oceanicdomains(the Valais Southalpine nappessouthofthePeriadriaticLine; the PeriadriaticLineandbyunmetamorphosed Austroalpine basementandcover nappes north of Adriatic (ApulianandInsubric)margin, foundinthe massifs, andthelowermost penninicnappes;(2)the represented bytheHelvetic cover nappes,theexternal Froitzheim etal.,1996):(1) The Europeanmargin, into thefollowing paleogeographicdomains (e.g. The Alpine chain(Figure2)maybesubdivided Regional geologicsetting Senarclens-Grancy W. (1972)GeologischeKarteder Schulz B.(1994)GeologischeKartedes Altkristallin Geol. B. A., Wien. westlichen Deferegger Alpen, Ostirol,1:25.000. 124; 1-28. östlich des Tauferer Tals. ErlangerGeol. Abh., Figure 2-MainStructuralandpaleogeographicaldomainsofthe Alps (fromDalPiazetal.,1975). European continentalmargin werealsosubducted,as (early Eocene),below the Adriatic plate.Parts ofthe Paleocene), followed bythatofthe Valais ocean of theJurassicPiedmont-Ligurianocean(early contrast, Tertiary eclogitesrefl Carpathians totheeastern Alps (Kozur, 1991).In Triassic oceanwhoseremnantsarefoundfromthe of theMeliata-Halstattocean(Neubauer, 1994),a eclogite metamorphismresultsfromtheclosure Alpine region (Froitzheimetal.,1996).Cretaceous events whichoccurredindifferent partsofthe ages ofeclogitizationcorrespondtodifferent tectonic Valais andPiedmont-Ligurianoceans. These two are partofthePenninicandophioliticunits the Austroalpine domains,whereasthelatterones occur inthe Alps. The formeronesarefoundin Eclogites ofCretaceousaswell Tertiary age margin. basement rocks(ZentralGneiss)fromtheEuropean window (Schieferhuelle),whilstitscoreexposes Ries. The oceanicunitsformtheborderof Tauern window (the Tauern window) northof Vedrette di European units,ascanbeseeninalarge tectonic Brianconnais?) arethrustedover theoceanicand of theintrusion. The latterunit(=thebasement?the the Austroalpine basementmakes thecountryrock of thepluton,belongtoSouthalpinedomain; ect thesubduction THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

AND CONTACT AUREOLE B17 shown by the occurrence of high-pressure and ultra- Alps and in the Po Plain affected the southern part of high pressure rocks in the Dora Maira massif of the the chain. western Alps (Chopin et al., 1991). During the Oligo-Miocene the eastern Alps and the The Periadriatic Magmatism and area of Vedrette di Ries were affected by intense N- Vedrette di Ries. S shortening, contemporaneous with orogen-parallel The Periadriatic magmatism took place along the extension, resulting in eastward extrusion. This entire Alpine chain during the Oligocene, (Exner, tectonic regime formed large pop-up structures (the 1976; Laubscher, 1985) i.e., long after the continental Tauern Window), delimited by syn-convergence, low collision between the African (Insubric) and European angle normal faults at its eastern (the Brenner Fault) plates, which occurred starting from the Eocene. and western margins (the Katschberg Fault). Lateral Based on their andesitic, calc-alkaline characters and extrusion, was accommodated by sets of conjugate geological setting these magmas were interpreted as dextral (e.g., the Periadriatic Line) and sinistral (e.g., products of a subduction process (Sassi et al., 1980, the SEMP Line) strike-slip faults. The widespread Bellieni et al., 1981, Kagami, 1991). Dal Piaz & occurrence of subhorizontal E-W striking stretching Venturelli (1983) and Laubscher (1985) questioned lineations and fold axes in the country rocks of this interpretation, and proposed that the magmatism, Vedrette di Ries records this phase of orogen-parallel postdating the main tectono-metamorphic event extension. related to the collision, developed during a short Ongoing shortening and thickening of the orogen extensional phase following the continental collision. caused a propagation of the deformation front According to these authors this extensional phase towards the more external zones of the chain in the triggered the ascent and emplacement of the middle- to late Miocene. Hence, the Jura Mountains Periadriatic plutons along a belt extending for ca. and thrusting in the Molasse basin were initiated to 700 km from the western Traversella body, in the the north of the Alps, whilst thrusting in the Southern Piemonte region, to the eastern Pohorje pluton in Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 3 - Simplifi ed tectonic map of the Alps, with enlargements of some segments of the PFS showing the spatial distribution of the Oligo-Miocene dikes and of the Periadriatic plutons. Only the major faults of Tertiary age are shown. Redrawn after Bigi et al. (1990). Faults: CL: Canavese Line; DAV: DAV Line; GL: Giudicarie Line; GTL: Gailtal Line; IL: Insubric Line; LT: Lavantal Line; PL: Pustertal Line. Plutons: A: Adamello; An: Andesites of the Canavese Line; B: Bergell; Bi: Biella; K: Karawanken; L: Lesachtal body; M: Miagliano pluton; P: Pohorje; R: Rieserferner; Re: Rensen; T: Traversella; TL: Tonalitic Lamellae. Full circles: dikes. Note that only part of the dikes are dated. Most of them are inferred to be Oligocene on the basis both of petrographic analogy with the dated ones and of crosscutting relationships with their country rocks. The size of the dikes is exaggerated by several orders of magnitude.

5 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg tens ofsquarekilometersinthe central andnorthern 4). The roofoftheplutoncropsoutover several allowing ustoreconstructits3Dgeometry(Figure an exceptional exposure oftheintrusive body, Steenken etal.,2002)and2000mofreliefprovide Post-intrusive tiltingofthepluton(Borsietal.,1978; Geometry andemplacementofthepluton 1980; Bellienietal.,1982). as ageochemicallydistinctmagmaticbody(Bellieni, Vedrette diRiesplutoniccomplex, isnow recognized Cima di Vila pluton,onceconsideredpartofthe of theeasternPeriadriaticmagmatism. The smaller Vedrette diRiesconstitutesthemainplutonicbody emplacement alongtheactive Periadriaticlineaments. have anoverall E-Welongatedshape,refl –Altberg, Cimadi Vila –Zinsnock, Vedrette diRies) sector ofthechainmostplutons(Rensen,Monte Alto Southern Alps (DalPiazand Venturelli, 1983).Inthis occurrences arereportedinthenorthernpartof concentrated inthe Austroalpine domain.Onlyminor In theeastern Alps thePeriadriaticmagmatismis (Trommsdorff andNievergelt, 1983). Penninic crystalline,ophiolitesand Austroalpine crust intruding fi ve nappesofthe Alpine pile,including sedimentary cover, andbytheBregaglia-Iorio pluton the South Alpine basementanditsPermo-Mesozoic represented bythe Adamello batholith,whichintruded magmatism reachesitswidestextension andis Venturelli, 1983).InthecentralsectorPeriadriatic covers andhigh-Kandesiticdikes (DalPiazand Magmatism isrepresentedbysmallplutons,volcanic the overthrusted Austroalpine continentalcrust. Southern Alps andextend uptothelimitwith a NE-SWorientation,plutonsintrudemainlythe into threemainsectors.Inthewesternsector, with whole Periadriaticmagmatismcanbesubdivided and ultrapotassiclamprophiriccompositions. The well asdikes rangingfromandesitictoshoshonitic volcanic rocksofcalc-alkalineorogenicseries,as The Periadriaticmagmatismincludesplutonicand 1995). geochemical signature(Von Blankenburg andDavis, by thedistribution ofthemagmaticbodiesandtheir Periadriatic magmasbyslabbreak-off, assuggested interpretation isconsistentwiththegenerationof 1995; Steenken, 2000;Rosenberg, inpress). The latter in atranspressive tectonicsetting(Rosenberg etal., plutons showed that ascentandemplacementoccurred However, structuralinvestigations of someofthese Slovenia (Figure3). ectingtheir at highercrustallevels. feeder (Figure7),whichmayhave fedotherplutons representing theuppercontinuationof Vedrette level than themainbodyandisthereforeinferredas the plutoninmapview) representsa higher crustal continuation ofthesteepzone(theeasterntail DAV mylonites. As aresultoftilting,theeasternmost in thesouthernpartofpluton,adjacentto Therefore, ascentofthetonaliticmagmasoccurred zone actedasthefeederforintrusion(Figure7). steeply orientedpartoftheplutonsuggeststhatthis The spatialcoincidenceofthesestructureswiththe rocks. occur inotherpartsofthepluton,norenclosing hundreds ofmeters(Figure6).Suchstructuresdonot are foundfromtheoutcropscaletothatofseveral (Steenken etal.2000; Wagner etal.,inreview) patterns withsteeplyplungingmagmaticlineations Within partsofthissteepzone,concentricfoliation tectonic intrusion. solid-state mylonitesoftheDAV, suggestasyn- preserved magmaticfabrics, orientedparalleltothe country rocksandtotheDAV (Figure5).Locally dipping tothesouth,parallelfoliationof The southernmargin oftheintrusionissteeply inclined plane(Figure7; Wagner etal.,inreview). as resultingfromextensional fracturingalongagently instead ofstoping,thediscordantcontactsareinferred occur intheimmediatevicinityofcontact.Hence, 2000) andrarexenoliths, generally<50cmlong,only stoping. Stopedblocksarelacking(Steenken etal., in thecountryrocks,but thereisnofi Large partsoftheroofarediscordanttofoliation (Wagner etal.,inreview). of thetonaliteratherthanfromregional deformation associated domesresultfromforcefulemplacement from thepluton,suggestingthatthisfoldand to allregional structuresofthecountryrocksaway striking axialplaneofthesynformisperpendicular structures separatedbyasynform. The north-south show thattheroofof theplutonconsistsoftwo domal (Figure 6)andacontourmapofthecontact4) The foliationpatterninthemainbodyofintrusion dipping mainbodyofthepluton(Figure5) coarse-grained tonalitesissubhorizontalinthegently- 5). The contactbetweenthefi ne-grained andthe south-dipping, asitgetsclosertotheDAV (Figure km thick,relatively fl westernmost end. The mainbodyoftheplutonis~2 parts oftheintrusion,andbaseisexposed atits at-lying andbecomessteeply eld evidence for THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

AND CONTACT AUREOLE B17

Figure 4 - Contour map of the pluton contact. Modifi ed after Wagner et al., in review.

Figure 5 - N-S cross-section of the pluton. From Rosenberg, in press. Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 6 - Foliation trajectories in the Vedrette di Ries.

7 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg Figure 7- Ascent andemplacementmodelfor the Vedrette diRiespluton, from Wagner etal.,(2003). THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

AND CONTACT AUREOLE B17

Figure 8 - Distribution of Vedrette di Ries rocks on the QAP Figure 9 - TAS (Total Alkali Silica, Bellieni et al., 1995) classifi cation diagram (taken from Bellieni et al., 1976). classifi cation diagram for rocks from the Vedrette di Ries pluton. Igneous lithologies and fi eld relationships. Vedrette di Ries is a composite pluton, consisting mainly of granodiorite and tonalite, with minor amounts of granite and diorite (Figure 8 and Figure 9).

Three main suites of rocks can be distinguished both in the fi eld and from their geochemical characteristics (Bellieni et al. 1976, Bellieni et al., 1981, Steenken et al., 2000). Following their emplacement order we distinguish a fi rst, coarse-grained suite (Figure 10), characterized by the presence of “book biotite” in piles up to 0.5 cm thick, stubby amphibole, and up to centimetric magmatic garnet (Bellieni et al., 1979, Bassani et al., 1997). Figure 10 - Coarse-grained tonalite with up to centimetric garnet (Grt), stubby amphibole (Hbl), and frequent Mafi c Rocks of this suite are mainly located in the western Microgranular Enclaves (MME) part of the body and discontinuously decorate its northern and, to a lesser extent, southern borders Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 11 - Distribution of the various magmatic suites in the Vedrette di Ries Pluton (from Steenken et al. 2000).

9 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg generally presentinsmall“fl akes”, althoughsome amphibole, sometimesincoarsecrystals.Biotiteis abundance ofbiotiteandthepresence ofrare fi contact withthecoarse-grainedsuite,ismedium-to The secondsuite sharp contactsarealsoobserved (Figure 12). transitional withlocalevidence ofmixing, although The contactsamongdifferent lithologies aregenerally the suiteisevidenced bythepresenceofraregarnet. side ofthepluton.Graniteisrareanditsaffi (Western Geltal,areaNofRauchkofel, 2500masl). and tonaliteofthesecond,medium-tofi Figure 13-Initialstageofminglingbetween granodiorite dioritic bodiesarelocatedalongthesouth-eastern diorite togranodiorite,withdominanttonalite.Small (Figure 11). This suiterangesincompositionfrom the rightsideofReintal). granodiorite (2kmEofPonte Tobel, asmallquarryon enclaves aremoreaboundantintonalitethan observed inotherplaces. As arule,mafi granodiorite fromsuite2(left).Transitional contactswere garnet tonalitefromsuite1(right)andmedium-grained Figure 12-Sharpcontactbetween coarse-grained ne-grained andischaracterizedbytherelative , displayingasharptotransitional c microgranular ne-grained suite liation to and interlayering(Figs.14,15). transitional, withevidence ofmingling (Figs. 13,14) between tonaliticandgranodioriticrocksismainly to graniteanddonotany containgarnet. The contact Rocks ofthissuiterangeincompositionfromtonalite “book” crystalscanbeobserved inthecontactzones. layering (upperleft)between tonaliteandgranodiorite Figure 14-Mingling(lower partofthepicture)and Figure 15-Interlayeringofmedium-tofi from thesecondsuite(Western Geltal,areaNof granodiorite andtonalite. Rauchkofel, 2500masl). negrained THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

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Chemical characters of the Vedrette di Ries rocks and genetic hypothesis The intrusive rocks of Vedrette di Ries show a

calcalkaline character. They have invariably low TiO2

content (<0.8 wt%), high Al2O3 and low FeO/MgO ratio. From the geochemical point of view the three suites (Figure 17) can be distinguished based on their Ca, Sr, Rb (Figure 18) contents and trends (Bellieni et al., 1978).

Further investigations pointed out that, based on their REE contents, rocks of Vedrette di Ries can be Figure 16 - Sharp contacts between granodiorite subdivided into two main groups characterized by low and tonalite from the second suite. Dikes of evolved (<1.1) TbN/YbN and high TbN/YbN values (Figure 19). granodiorite magma cut and disrupt the (partially) crystallized tonalite (South of Riesernock, along the According to Bellieni et al. (1981) the rock series Hartdegenweg, 2320m asl). represents the product of a two-stage crystal/liquid Sharp contacts and dikes of granodiorite intruding fractionation starting from one and the same parent and dismembering the tonalite are also observed magma. During a fi rst stage, at high pressure, (Figure16). separation of hornblende + garnet lead to magmas with

high TbN/YbN, representing the ancestor of each suite. The third suite, located in the central-eastern part These magmas, during their rise at lower pressure, of the pluton and mostly surrounded by rocks of underwent a second stage of fractional crystallization the second suite, is medium- to fi ne-grained and with separation of hornblende + plagioclase, and then displays a rather homogeneous leuco-granodioritic evolved towards Sr-poor compositions. Processes of composition. Biotite, in accessory quantities, is contamination with crustal material and separation of the only mafi c mineral, and K-feldspar appears in accessory phases had an important role in determining centimetric individuals. Contacts with rocks of the the high 87Sr/86Sr values and the uneven distribution of previous suite are sharp (Steenken et al., 2000). some trace elements (Bellieni et al., 1981). Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 17 - Areal distribution of the three different suites of rocks in Vedrette di Ries as identifi ed by the Ca-Sr and Rb-Sr variation diagrams (taken from Bellieni, 1978).

11 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg initial evolution ofthesemagmas,asindicatedbytheirhigh country rocksactuallyplayedanimportantroleinthe in rocksfromthesecondsuite. Assimilation of “surmicaceous” xenoliths areparticularlyabundant areas ofthemagmaticbody. Smallmetamorphic close tothecountryrocks,but alsoin somecentral Metamorphic xenoliths are thereforegoodstrainmarkers (Figure21). interaction withthehostmagma(Figure20).MME magma whoseoriginalcompositionwas modifi (1989) argued thatMMErepresentblobsofmafi geochemical andisotopiccharacters,Bellienietal. the garnet-bearingsuite.Basedontheirpetrographic, hosts. GarnetisrestrictedtoMMEsampledwithin the mostmafic enclaves beingobserved inmostmafi host andtheircompositionrefl abundance decreaseswiththeincreasingSiO and occasionalinthethirdgranodioriticsuite. Their They areabundant inthefi Mafi Figure 18-Cumulative diagramofRbandSrvs (Taken fromBellieni,1978). third, central,homogeneousleuco-granodiorite. second, fine-to medium-grainedsuite.GD1representsthe garnet bearingsuite.SuiteT*-GD2-G2correspondstothe Suite T3-GD3-G3correspondstothefi curves for each suitetakes placeatdifferent Rb/Srvalues. defi taken asadifferentiation index.Thethreesuitesofrocks ne different trends.TheintersectionofRbandSr c microgranular enclaves (MME) 87 Sr/ 86 Sr isotopiccompositionandby its wide arelocallyabundant notonly rst, coarse-grainedsuite ects thatofthehost, rst, coarse-grained, arecommon. Rb/Sr 2 ofthe ed by ed c c to metric,have anoverall E-Worientation,andoften veins (Figure22). Acidic dikes rangefrom centimetric All suitesarecutbylateacidicandmafi variational range(Borsietal.,1979). (reported asB1,B2,B3).Stars:diorite;circles:tonalite; with highTb the threedistinctgeochemical trendsof Vedrette diRies Figure 19-Two maingroupsofrocks canbeidentifi low (<1.1)Tb in Vedrette diRiesbasedontheirTb rocks withhighTb (Differentiation Index)andCavsSrdiagrams, N triangles: granodiorites;squares:granite. /Yb N /Yb N (filled symbols).IntheSrversus D.I. N values(emptysymbols),androcks N /Yb N plotattheoriginofeach of N /Yb: rocks with c dikes and dikes c ed THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

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Figure 20 - Mafi c microgranular enclave surrounded by a centimetric reaction halo. Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 21 - Example of late fl attening on a mafi c microgranular enclave and an aplitic dike.

13 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg et al.,2000). Vedrette diRiesyieldsanageof26.3 determinations onalamprophyricdike within and Pennidicunits(Gattoetal.,1976).K-Arage the Austroalpine, but alsothe Southern Alpine “andesitic” l.s.dike activity thatinterestednotonly surrounding basement. They belongtoawidespread Mafi calcalkaline magma(Figs.24and25) magma isintrudedanddisruptedbyyounger unpublished degree thesis),wherepristine shoshonitic sometimes even withinthesamedike (Schiavon, calcalkaline andshoshoniticproductsarepresent, trachy-basalt tobasalticandesite(Figure21).Both to decametricandrangeincompositionfrom metamorphic countryrocks. They arecentimetric including apliteandpegmatite dikes, andthe magmatic cycle. They cutboththeplutonicrocks, Mafi host (Figure23). orientation, show sharpcontactswiththeintruded Lamprophyric dikes and evolution of Vedrette diRies. latest magmaticactivity linked totheemplacement may containspessartinegarnet. They representthe dikes aremorecommonthanpegmatitic onesand seldom intrudethemetamorphiccountryrock. Aplitic constitute swarms ofsubparallelindividuals thatonly (Fioretti etal.,unpublished). mafi Figure 22-TAS classification diagramfor acidicand c dikes within Vedrette diRiesPluton c dikes arecommonlyfoundalsointhe c dikes arenotpartofthe Vedrette diRies withadominantN-S ±3 Ma(Steenken an initialratioof0.709.Highervalues oftheinitial for Vedrette diRiesof30 Borsi etal.,(1979)reportedawholerockRb/Srage Geochronology 87 evidence indicatesthat Vedrette diRiesisyounger al., 1979,Cavazzini etal.,unpublisheddata).Field batches ofmagmasandfromsomegranite(Borsiet Figure 23-Mafic dike withmagmaticlineationalongthe Sr/ 86 Sr (uptoca.0.720)wereobtainedfromother Figure 24- Veining ofamafic dike bymoreevolved magma. Thehorizontallinesareglacial stripes. wall (S-SEofRifugioRoma). ±3 Maand 87 Sr/ 86 Sr with THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

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Figure 25 - Pristine magma disrupted by younger calcalkaline magma within the same dike. than the acidic porphyritic dikes outcropping in the Schulz, 1997); surrounding basement (Cescutti et al., 2003). These 3 - Eo-Alpine metamorphism under relatively high- dikes have been correlated (Cescutti et al., 2003) P/low-T conditions (7.5 ± 1.5 kbar and 450 ± 50 °C, with those outcropping at the Austroalpine-Penninic Stöckhert, 1984, 1987; Prochaska, 1981); limit north of Rensen (Figure 3), dated at 30.9±0.2 4 - “Main-Alpine” (“Tauern”) metamorphism under Ma by Müller et al. (2000). The late lamprophyric lower greenschist facies conditions (Sassi et al., dikes cross-cutting Vedrette di Ries are 26.3±3 Ma 1980); (Steenken et al., 2000). 5 - Oligocene contact metamorphism in the aureole of the Vedrette di Ries pluton (Bianchi, 1934; Prochaska, Metamorphism 1981; Schulz, 1989; Cesare, 1994a, 1999a): the last In the region between the Tauern Window and the metamorphic event recorded in the area. Periadriatic Lineament, the Austroalpine basement of Metamorphism was accompanied by intense the Eastern Aps forms an E-W trending belt, divided deformation during both the eo-Alpine (Stöckhert, into three blocks by two major tectonic lines: the 1987) and the late-Alpine events (Kleinschrodt, Defereggen-Anterselva-Valles (DAV) line and the 1987). Oligo-Miocene dextral and sinistral mylonites Kalkstein-Vallarga (KV) line (Borsi et al. 1978). are widespread throughout the area, pointing to an Unlike the other two blocks, which display an intense coaxial component of deformation in front essentially pre-Alpine tectono-metamorphic history, of the Dolomite indenter (e.g. Müller et al., 2001).

the block north of the DAV line was involved in Discrete mylonite zones of considerable thickness B16 to B33 n° 2 - from Volume the Alpine metamorphic cycle (Borsi et al., 1978): and lateral continuity occur far from (and north of) its polymetamorphic history can be summarized as the DAV line, in addition to numerous smaller and follows: discontinuous ones (Mancktelow et al., 2001). 1 - “Caledonian” metamorphism of undetermined However, parts of the block escaped the Alpine P-T conditions (Borsi et al., 1973; Hammerschmidt, structural reworking (not the metamorphic overprint) 1981) preserving pre-Alpine structures and metamorphic 2 - Variscan high grade metamorphism and anatexis at relict assemblages (Borsi et al., 1978). One of these P = 6±1 kbar and T = 650 °C (Stöckhert, 1985, 1987; areas is located south of the Vedrette di Ries tonalitic

15 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg population but alsoprotectedandactively maintained. development. The Park isnotonlyacceptedbythe considerate policy ofintegration andsustainable native populationfromusingit,but bypursuinga by imposingrestrictionsthateventually prevent the successfull example ofprotectingawideareanot and was founded13yearsago.Itconstitutesa The Park isthelargest oneinSouthern Tyrol in the“NaturparkRieserferner-Ahrn”. The areawearegoingtovisitiscompletelyenclosed Field tripitinerary 1994a, usingtheHoldaway’s (1971) Al metamorphism isestimatedat2.5-3.75kbar(Cesare, (1991) facies seriesscheme. The pressureofcontact which correspondtotype2biiofPattison & Tracy’s divided byCesare(1992)intofive mineralogiczones, is approximately1.5kilometreswideandhasbeen The contactaureoleofthe Vedrette diRiestonalite (Figure 26). antiform quasi-concordantwiththeplutonmargin represents thesouthernfl ank ofakilometer-sized W anddipssouth30°to60°;theoverall structure metamorphic layering,isoclinallyfolded,strikes E- and amphibolite. The well-developed Variscan layers ofpegmatite gneiss,marble,quartzite paragneisses aredominant,withminorinterbedded pluton; heremetapeliticschistsandmigmatitic showing theantiformal structureinthecountryrocks. Figure 26-North-southcross-sectionacrossthe Vedrette diRiespluton(fromDalPiaz,1934) metamorphic grade,closetotheplutoncontact. metamorphism andislocalizedinthezonesofhighest the earliermainfoliation,accompaniedcontact A weakdeformation,occurringasareactivation of point of,withmaximumtemperaturesof600-620°C. 2 SiO 5 triple tonalite quarriesandintroduction tothepetrologyand a) Riva di Tures valley (Reintal):avisittothe Hütte). (Ursprung) valley –RifugioRoma(Kasseler Taufers) -Riva di Tures (Reinin Taufers) -Sorgiva Brunico (Bruneck)-Campo Tures (Sandin not toleave any majortraceofyourpassage. take somesampleswithyou,wekindlyrequestyou considerate. Whereas youarecertainlyallowed to also gratefullyacknowledged (Figure27).Please, be population fortheirhomeland,andwhichGodis these placestestifi are proudlycultivated andtransmitted. The beautyof home forthepeopleliving here.Culturaltraditions The mountains,woods, water, andgrazingareasare Figure tonalite, Franziskusweg, NaturparkRieserferner-Ahrn. 27 -“MaytheLordbepraised”:carved block of es tothecareandlove ofthelocal DAY 1 THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

AND CONTACT AUREOLE B17 geochemistry of the composite pluton of Vedrette di Ries. b) Sorgiva-Ursprung valley: walk to the northern contact of the pluton. Outcrops of mylonites at the contact and intensely deformed tonalite. Discussion of the structural and chronological relationships between emplacement and ductile deformation, and of the role of the northern mylonite zone. c) A walk along the Hartdegenweg to the Rifugio Roma (2275 m a.s.l.): outcrops of various facies of the tonalite. Strain gradient in the tonalite, mingling and injection relationships between fi ne-grained and coarse-grained facies, aplitic, granitic and lamprophyric dikes cutting the main body. Figure 28 - Subhedral garnet with atoll inclusions (amphibole ± plagioclase ± biotite ± opaque minerals), Stop 1: surrounded by a thin reaction rim. Road between Campo Tures - Riva di Tures (Fig 29). (c. 1150m a.s.l.). Quarries of tonalite along the Rio The compositional range of rims is more scattered, di Riva Valley. Coarse-grained, Grt-bearing tonalite possibly due to different degrees of interaction with and granodiorite. Contact with the medium- to distinct magmas. fi ne-grained granodiorite without garnet. Granite The composition of included minerals shows some and aplitic dikes. Petrogenetic implications of the systematic differences compared to that of the same presence of garnet will be discussed. phases occurring in the rock. While plagioclase in Garnet is one of the main features of the coarse- the rock shows a marked zoning with bytownite core grained suite (Figure 10). In calc-alkaline magmas and up to oligoclase rim, plagioclase within garnet garnet is rare, but not unusual; experimental work by lacks the An-poor external rim, and its intermediate Green (1972) and Green & Ringwood (1972) have zones are very thin. Amphibole in garnet is Fe- demonstrated that it forms at pressure conditions > hornblende and is Al-richer than the Mg-hornblende 10 Kbar. However, the observations that magmatic of the rock. On the other hand, the composition of garnet-bearing rocks in Vedrette di Ries represent a biotite inside garnet and within the rock is almost the sort of belt around the pluton close to the contact with same. Petrographic and minero-chemical characters the metamorphic country rocks, and that all along fi t the hypothesis that minerals in inclusions formed the contacts magmatic rocks contain metamorphic by crystallization of portions of the magmatic xenoliths with abundant garnet, suggested that liquid trapped in garnet during its crystallization garnet in the Vedrette di Ries plutonic rocks might (Figure 30). The composition of minerals in the exclusively be linked to the assimilation of country reaction rim is rather homogeneous. Plagioclase is rocks. This problem was addressed by Bellieni et oligoclase, and amphibole composition straddles the al. (1979) and recently reconsidered by Bassani (unpublished degree thesis, 1996). Garnet in Vedrette di Ries tonalite and granodiorite is up to 2 cm wide and is generally idiomorphic. It is typically surrounded, and sometimes totally replaced, by a reaction rim made up of fi ne-grained plagioclase ± biotite ± quartz (± amphibole) (Figure 28). Volume n° 2 - from B16 to B33 n° 2 - from Volume Preserved individuals show concentric shells of Pl ± Qtz ± Bt ± Hbl inclusions, likely representing samples of the coexistent crystallizing magma. Garnet is zoned with a wide, rather homogeneous, nucleus of almandine composition (Alm 50-70%, Sps 2-10%) and a narrow more spessartine-rich rim (Alm 35- Figure 30 - Inclusion in garnet. The shape of the 40%, Sps 12-15%). The core composition of garnet inclusion, a negative garnet crystal, and the composition is independent from the rock, i.e. core composition of of the mineral phases suggest that included minerals garnet in diorite, tonalite and granodiorite is the same crystallized from a portion of trapped magmatic liquid.

17 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg substitution oftheoriginalgarnet. the reactionborderrangesfromathinrimtocomplete Figure 31-Reactionborderaroundgarnet.Thewidthof constant spessartinecontents. metamorphic rock (diamonds)andfromaplite(star).Magmaticcoresdefine anellipticalcoherent fi eld withrather Figure 29-Compositionofgarnetcorefromtonaliteandgranodiorite(fullsquarescircles),thecountry of themagmatowards shallower crustallevels (ca. is presumablylinked toarelatively rapiduprising marked plagioclasezoning(Bellienietal.,1976), The instabilityofthegarnet,accompainedbya (Figure 31). as suggestedbythepresenceofareactionborder instability conditionsonlyduringalaterstage, on relicsduringmagmaticcrystallization,andreached of approximately5%.Garneteitherformedorgrew with liquidusatP>10Kb, T<950°C andwater content et al.(1979)estimatedthatgarnetwas inequilibrium Taking intoconsiderationthegarnetcores,Bellieni fi elds ofFe-hornblendeandMg-Hornblende. THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

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2 Kb), where the magma eventually emplaced. An crystallization was proposed for these dikes (Cescutti identical conclusion was independently reached by et al., 2003). studying the crystallization of the cotectic minimum of the granitic rocks (Bellieni, 1977). Contact mineral Stop 4: assemblage of the country rocks (Bellieni, 1977; Path 8a to Rifugio Roma, 2320m a.s.l. The well- Cesare, 1992) further confi rms the fi nal emplacement exposed northern contact of the pluton. level of the Vedrette di Ries magma. Mylonitic paragneisses with transposed tonalitic dikes. The country rocks in this area are largely made Stop 2: of mylonitic paragneisses, containing numerous veins Path 8c, 1735m a.s.l.. Foliated, coarse-grained and apophyses of coarse-grained tonalite, transposed tonalite just before the bridge over Rio di Riva. and boudinaged within the foliation (Figure 32, see Foliations dip to the N-NW of 50-60°. also Steenken, 2002). In the paragneisses, biotite and fi brolitic sillimanite occur in the synkinematic Stop 3: assemblage. As sillimanite occurs in this area only as Path 8c from Riva di Tures (Loc. Säge) to a product of contact metamorphism, we can conclude Ursprungalm, along the river, 1850m a.s.l.. Strongly foliated country rocks at the northern intrusive contact. The mylonitic paragneisses contain both layer-parallel and discordant dikes and apophyses of coarse-grained tonalite. These relationships suggest that mylonitic deformation was active in this area during the initial stages of pluton emplacement, and that it stopped before the fi nal stages of emplacement.

Along path 8c to Ursprungalm several aspects and phenomena deserve consideration: 4) at 1900m a.s.l: paragneisses with transposed Figure 32 - Small tonalitic dike transposed in the foliation tonalite injections along mylonitic foliation; of country rock paragneisses. In the paragneiss, the 5) from 1900m to 2100m a.s.l: the path climbs up to foliation is outlined by synkinematic sillimanite (fi brolite). the north of a hill mostly made of amphibolites; 6) at 2290m a.s.l: the amphibolites and paragneisses are crosscut by a porphyritic dike (Cescutti et al., 2003). The dike is c. 3 m thick, and is strongly sheared within the dominant mylonitic foliation. This kind of dikes, of granitic composition, never crosscuts the Vedrette di Ries plutonic rocks, and is therefore older. Similar rocks, named “porphyritic tonalites” have been dated at 30.9±0.2 Ma by Müller et al. (2000). The mineral assemblage of this kind of dikes is plagioclase, quartz, K-feldspar, muscovite, and biotite. Garnet, allanite, apatite, opaque minerals and zircon are present in accessory quantities. Figure 33 - Boudinage of a dm-thick amphibolite layer B16 to B33 n° 2 - from Volume Based on petrographic evidence (garnet composition at the northern intrusive contact of the Vedrette di Ries and zoning, its presence inside the core of zoned tonalite, in the upper Val Sorgiva. plagioclase, overgrowth of new garnet around individuals not included in plagioclase, partial that the mylonitic foliation developed during contact resorption and subsequent crystallization of new metamorphism, i.e., that it was synchronous with plagioclase), and their chemical signature, a genesis pluton emplacement. by partial melting of deep crustal material and an Amphibolites, metacarbonates and calc-silicate rocks emplacement at shallow levels following a polybaric at the immediate contact. As also observed in the

19 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg characterized bythepresenceof marblesandcalc- Again, thecountryrocksatcontactare grained tonaliteatthenorthern contact. metre-sized zoneofmingling ofcoarse-andfi Path 8toRifugioRoma,c.2400ma.s.l. A ten- Stop 5: the pluton’s interior(Wagner etal.,inreview). enclaves of ~10:1rapidlydecreaseto3:1towards from themagmatictosolidstate. Aspect ratiosof found locally, suggesting acontinuousdeformation deformation. However, melt-bearingshearbandsare fabrics areentirelyoverprinted bygreenschistfacies subhorizontal stretchinglineations.Magmatic shearing alongasteep,E-Wstrikingzone,displaying the entireplutonanditischaracterisedbysinistral solid state. This arearecordsthelargest strainof of thetonalite,andhencetodeformationin paragneisses pointstoamorecompetentbehaviour Boudinage oftonalitewithintheenclosing layers (Figure33). beautiful examples ofboudinageintheamphibolite deformation canbeobserved alsointheserocks,with grain-size. As inthemetapeliticmylonites,astrong and clinopyroxene, andmaydevelop avery coarse calc-silicate rocks. The lattercontaingarnet,epidote grained, biotite-bearingamphibolites,marblesand contact ofthetonaliteareoftencomposedfi lower Val Sorgiva, countryrocksattheimmediate Figure 34-Remnantsofthepluton’s roof(darker colour)ontopoftheSpronedelle Vedrette Giganti. ne- ne- the Austroalpine basement; synintrusive deformation contact betweenthetonaliteandmetapelitesof at thefrontofMonteNevoso Glacier:intrusive intrusion of Vedrette diRies.Ice-polishedoutcrops Aplitic andlamprophyricdikes post-datingthemain Rifugio Romaandsurroundings. metamorphism (Cesare,1992,1994a). helping constraintheP-Tconditionsofcontact sillimanite” zone)hasbeenobserved inparagneisses, metamorphic assemblageMs-Kfs-Qtz-Sil(or“second only locationwherethedivariant KNASH contact delle Vedrette Giganti(Riesernock). That isthe of thepluton’s roof(Figure34)ontopofSprone eastern sectorofthemassif,withlarge remnants From theRifugio,apanoramicview towards the foliation isdiscordanttothewall ofthedikes. the alreadycrystallizedtonalite(seeFigure16). The Dikes ofevolved granodioritemagmacutanddisrupt and granodiorite. contacts betweenmedium-tofi Path 8toRifugioRoma,c.2320masl.Sharp Stop 6: some garnethere. silicate rocks. The coarse-grainedtonalitecontains DAY 2 ne-grained tonalite THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

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Stop 2: Ice-polished rocks at the base of the Tristenferner glacier, c. 1800 m south of Rifugio Roma, 2550 m a.s.l.. Here is one of the best exposures of the intrusive contact between underlying fi ne-grained tonalite and overlying metapelitic country rocks, thoroughly affected by contact metamorphism and synintrusive deformation. Rather than a sharp surface, the contact is an intrusion/interaction zone of some tens of metres in thickness, where several layer-parallel tonalite injections are observed. Overall, the contact is generally concordant with the country rocks’ Figure 35 - Replacement of andalusite by coarse-grained, foliation, and dips c. 30° to the north. This area can be prograde muscovite. Sillimanite (fi brolite) is the stable considered a part of the pluton’s roof. Al SiO polymorph, and occurs in the matrix 2 5 The country rocks are mostly migmatitic paragneisses around the nodular pseudomorph. (Hofmann et al., 1983) characterized by a Qtz-Pl-Ms- Bt-And-Sil-St-Spl-graphite assemblage. Although easily recognized in the hand specimen, staurolite and andalusite are metastable relicts of lower-grade contact metamorphism, and are transformed into

Figure 36 - The reaction of staurolite to hercynite accompanies the topotactic replacement of andalusite by sillimanite in the metapelites at Stop 2. Taken from Cesare (1994a). and contact metamorphism of the country rocks; oligocene Grt-Ms-Tur-Ber-bearing pegmatites. Figure 37 - Contact metamorphic prismatic sillimanite bent and wrapped by fi brolite-bearing foliation. Stop 1: Swarm of mafi c, lamprophyric dikes with a general N-S direction. Sharp, brittle contacts, intrusion of thin lamprophyre apophyses along fracture zones, and presence of angular granodioritic xenoliths within the dikes testify for their late emplacement. Chilled margin and magmatic foliation are well developed in B16 to B33 n° 2 - from Volume wider dikes (Figure 23). Subsequent intrusions along the same feeder are testifi ed by network of less mafi c veins (Figure 24) that eventually lead to the disruption of the already solidifi ed mafi c magma (Figure 25). Spherical to ameboid geodes of acicular amphibole in a medium grained matrix within the mafi c dikes suggest a crystallization at high P . H2O Figure 38 - Tourmaline and garnet in the pegmatites of likely Oligocene age.

21 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg hercynitic spinelas: formulated thedecompositionofstauroliteto In theabove microstructures,Cesare(1994a)has and hercynite (Figure36). muscovite (Figure35),topotacticprismaticsillimanite nodular pseudomorphsconsistingofcoarse-grained the rock layersstudiedandrespective samplenumbers.MineralzonesasinTable 1(inset). Figure 39-Simplified geologicalmap(afterMager, 1985)ofthesouthernaureole Vedrette diRies,withlocationof structural featuressuggestthatthese rockspost-date observe thepegmatites whichintrudethetonalites, this outcrop. Although inthislocationonecannot are somemeter-thick discordantdikes whichoccurin are likely toberelatedthe Vedrette diRiesintrusion inpegmatitic rocks. Among the few pegmatites which The Vedrette diRiesplutonistypicallypoor contact metamorphism. rocks developed, orwas reactivated, duringthe (Figure 37). Therefore, thefoliationofcountry to have been bentandwrappedbythefoliation sillimanite. Inaddition,prismaticsillimaniteappears foliation oftheparagneissesisoutlinedbyfi Like intheupper Val Sorgiva, thewell-developed metamorphism at2.5-3.75kbarand585-655°C. and hasconstrainedtheP-Tconditionsofcontact Fe-St = 3.85Her+5.1Sil2.55Qtz2H brolitic 2 O Anterselva. Afternoon: descenttoRiva di Tures andtripto undergoing adramaticretreat (Santilli etal.,2002). lakes. The glaciersofthe Vedrette diRiesmassif are terminal morains,ice-polishedrocksandsmallglacial little iceage(1450-1850),suchashugelateraland observation ofthegeomorphologicaleffects ofthe This areaisalsoparticularlyinterestingforthe abundant chloriteandepidote. low-temperature alteration,withdevelopment of also shows widespreadcataclasticdeformationand oriented, withelongatedmicrogranularenclaves. It The fi ne-grained underlyingtonaliteisstrongly green berylhasalsobeendiscovered here. muscovite, garnetandtourmaline(Figure38).Light quartz andfeldspars,thesepegmatites containbiotite, to thefoliationofhostparagneisses. Along with a setofparallelinjectionsathighanglecompared contact metamorphism.Infact, thepegmatites form THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

AND CONTACT AUREOLE B17

Figure 40 - Hand specimen of a graphitic schist Figure 41 - Metapelitic schist from upper Zone 3. from lower Zone 3, with abundant coarse-grained The light brown to orange nodules are polycrystalline andalusite porphyroblasts. aggregates of staurolite. See Figure 42 for a microscopic view of an aggregate from this rock.

DAY 3 affected by the Oligocene contact metamorphism. Rifugio Forcella Valfredda (Rieserfernerhütte) We will focus our attention on the effects of contact and surroundings. metamorphism on metapelitic lithologies. The southern contact aureole of Vedrete di Ries has been divided into fi ve mineralogical zones (Table Contact metamorphism and related phenomena in 1, Figure 39, Cesare 1992) which developed at c. 3 the southern aureole of Vedrette di Ries. Profi le kbar. In the metapelites, the most evident minerals of the outer, regionally metamorphosed (Variscan of contact metamorphic origin are the abundant and Alpine) metapelites up to the intrusive contact; and very coarse andalusite (up to 10 cm in length, observation of the well-developed St-And-Sil Figure 40), and the unusually fi ne-grained staurolite, zoneography; discussion of thermobarometric which often occurs in polycrystalline nodules constraints to depth of emplacement. The Andalusite- (Figure 41). bearing veins and their fl uid inclusions: a marker of fl uid-rock interactions during contact metamorphism. Another peculiarity of this area is that layers of a distinctive rock type crop out in at least four localities, Participants will walk along a S-N oriented profi le at variable distance from the intrusive contact (Figure covering the whole contact aureole up to the intrusive 39). These rocks allow for reconstruction of the contact with the fi ne-grained tonalite. We are not multi-stage pseudomorphic replacement of a primary dividing the day into stops, as there would be too garnet: here follows a summary of the microstructural many. However, we will refer to the maps provided study and of the main conclusions outlined by Cesare herewith. Here follow the detailed descriptions of (1999a, b), where further details and an updated the two main objects of this part of the fi eld trip: the reference list can be found. The layers have a thickness contact metamorphism and its zoneography and the of < 20 m, and consist of fi ne-grained mica-schists andalusite-bearing veins. with a marked millimetric compositional layering, with abundant quartz-rich ribbons, probably the result Contact Metamorphism at Vedrette di Ries of mylonitic deformation. The foliation wraps around

The area of Rifugio Forcella Valfredda is the ideal B16 to B33 n° 2 - from Volume lensoid domains in which garnet, kyanite, staurolite, place to observe the effects of contact metamorphism andalusite and muscovite are dominant in turns. The induced by the tonalite of Vedrette di Ries. The systematic distribution of Al SiO polymorphs in southern aureole is mainly composed of metapelites, 2 5 the aureole, and the resulting isograd pattern (Figure but orthogneisses, quartzites, amphibolites and 39), indicate that during the contact metamorphic marbles also occur. As previously stated, these rocks event only the layer closest to the contact (i.e. sample belong to the Austroalpine basement to the north VR466) reached temperatures suffi cient for the of the DAV line, and have undergone a complex crystallization of sillimanite. It follows that in all the and polyphase metamorphic evolution before being other layers any occurrence of sillimanite is attributed

23 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg VR491 analysis. SeeFigure39fortheirlocations. microstructural, bulk chemical,andmineral chemical of therocktypeateachlocation,andusedfor Four sampleshave beenchosenasrepresentative Sample description evolution ofthisarea. transformed duringthecomplex metamorphic primary rocktype(thesamefoldedlayer?),variably composition ateachlocality, mayrepresentthesame rocks, althoughshowing different mineralogical microstructural characteristicssuggestthatthese to earliermetamorphism.Bothfi eld appearanceand monomineralic aggregateofmuscovite wrappedbyfolia ofbiotiteandfibrolite. PL,wv=6.5mm. This suggestsreactivationofthemainfoliation duringcontactmetamorphism.PL,wv=6.5mm.h: VR466. Decussate the sericitematrix.Sericitearoundnodule(lower right)shows preferred orientationwithincipientshearbandcleavage. sericite aggregate(ser).Note(arrows) thecoarsergrain-sizeofstauroliteonperipheryaggregate,orisolatedin of moststaurolitecrystals(stars).Crossedpolars(CP),wv=6.5mm.g: VR480. Monomineralicnoduleofstauroliteina polarized light(PL),widthofview(wv)=6.5mm.f: VR496. Noduleofkyaniteandstaurolite.Kyanite occursatthecore biotite, ilmeniteandgarnet.Two kyanite-rich asymmetrictails(arrows) extendinthesubhorizontalmainfoliation. Plane- Figure 42-Close-upviewsofnodulesfromeach sample.e: VR491. Roundaggregateofmicrogranularkyanitewithminor as isolatedporphyroblasts,orassociated withkyanite typically <5mmindiametre.Garnetispresent,either schist, withabundant nodularaggregates ofkyanite, intrusive contact.Itisasilvery, muscovite-rich metamorphism. The samplefurthestfromthe : fromZone1(chlorite-biotite)ofcontact VR496 in theaggregates. biotite-rich matrixthatformslayers alternatingwith This massive rockisalmostblack,owing tothe location isvery close(approx50m)tothepluton. VR466 in thickness. staurolite. Quartzribbonsandrodsmayreachonecm mica-rich layersthatcontainbiotite,muscovite and Coarse porphyroblastsofandalusiteoccurinthe microgranular stauroliteupto1cmindiametre. rock, withorange-brown nodulescomposed of VR480 in themuscovite-rich layersofthe matrix. garnet. Andalusite crystals,upto3cminlength,occur brown sturolite.Stauroliteoftenformscoronasaround in garnetporphyroblastsandnodulesoffi Light gray, stronglylayeredbut massive schist,rich : fromZone4(sillimanite-garnet). The sample : fromtheinnerZone2. A dark-brown : fromtheouterZone2(andalusite-staurolite). ne-grained, THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

AND CONTACT AUREOLE B17 quartz ribbons and fi brolite-rich folia. Pink andalusite agreement with the presence, in sample VR491, of porphyroblasts are abundant, whereas the scarce untransformed garnet crystals adjacent to partially or muscovite is mainly concentrated within mm-sized completely pseudomorphed ones. nodules. The Kyanite Stage (VR491, VR496) - This is Figure 42 compares the general textural appearance represented by the nodules of microgranular kyanite of the four samples at the thin section scale. The which maintain their primary shape of garnet, but are most striking similarities are the presence of nodular not thought to have replaced it directly. The very fi ne aggregates of comparable size, wrapped around by grain-size of kyanite in the nodules is an anomalous the matrix, and the occurrence of quartz-rich ribbons. feature for metapelites; this peculiarity, and its In addition, all rock samples are graphitic, and contain possible cause, is discussed below. tourmaline crystals with similar, complex zoning. A As it is not clear whether sericite pre-dates kyanite progressive grain-size coarsening of matrix phases or is coeval with it, the possibility of a further (e.g. biotite and muscovite), aggregate phases (e.g. stage pre-dating the Kyanite stage, and represented staurolite), as well as nodular aggregates themselves, by sericite crystallization (the Sericite stage), has can be observed, even in hand specimens, in the to be considered. Sericite would form “shimmer transition from sample VR491 to sample VR 466. aggregates” upon replacing fi brolite, and leave relict This is consistent with the higher temperatures and needles within quartz and muscovite adjacent to the longer duration of contact metamorphism in the nodules. samples closer to the pluton. The Staurolite Stage (VR491, VR496, VR480) - This stage, initiated in sample VR491 and completed in A model for the evolution of a primary garnet site sample VR480, produces the nodules of microgranular The above microstructural information allow for staurolite. Microstructures indicate that staurolite reconstruction of the complex textural evolution of a crystallization is coeval with that of andalusite, or that primary garnet site, now represented by the nodules. it commenced slightly before, and continued during, Preservation of the subspherical shape of garnet was andalusite growth. As a consequence, the staurolite favoured by the very low strain experienced by these stage is related to the contact metamorphism. rocks after garnet crystallization, which resulted in The Muscovite Stage (VR466) - This is the fi nal the static growth of minerals in all the subsequent stage, in which decussate aggregates of muscovite metamorphic events. The textural sequence can be replace staurolite. Although this kind of pseudomorph divided into fi ve (or six) stages: is common during retrograde metamorphism, even in The Garnet Stage (VR491, VR496) - This is the earliest this area, in this sample it has been shown to represent microstructural stage, with garnet porphyroblasts of a prograde feature. Similar prograde pseudomorphs < 1 cm diameter wrapped by the micaceous layers. of muscovite after staurolite were fi rst described by Inclusions in garnet consist of quartz, biotite, ilmenite Guidotti (1968) in a regional metamorphic context. and muscovite, and provide no information regarding The inferred age of the stages can be summarized as the metamorphic history of the metapelite prior its follows: crystallization. The Fibrolite Stage (VR491, VR496) - Although there Stage Age Setting is no direct evidence for a stage where nodules were Grt Variscan Regional composed of fi brolite, several indications point to this Fib Variscan Regional occurrence. They include: i) the presence of fi brolite Ser Variscan? Eo-Alpine? Regional in close association with the nodules, formerly Ky Eo-Alpine Regional occupied by garnet; ii) the radiating arrangement St Oligocene Contact of needles, diverging from the nodule; iii) the Ms Oligocene Contact B16 to B33 n° 2 - from Volume presence of biotite with exsolution of ilmenite and iv) the proposed crystallization sequence, in which Andalusite-bearing veins at Vedrette di Ries fi brolite predates kyanite. These data are suggestive Schists outcropping in the southern aureole of of the high-T reaction of garnet to fi brolite + Ti-rich the Vedrette di Ries pluton contain several vein biotite. Thermodynamic modelling of this reaction generations distinguished by their mineralogical predicts a complex behaviour for garnet, which then composition. The following discussion considers may dissolve, grow or not react at all depending only those veins which are discordant compared to on the local confi guration of the matrix. This is in the pervasive regional foliation, indicating that they

25 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg 800 mfromtheintrusion;Site2, in thegarnet-fi (Figure 45).Site1isinthestaurolite-andalusitezone, Valfredda werechosenforfurther investigation Two siteswithabundant veins intheareaofForcella crystallization withinfl shape ofandalusitecrystals(Figure44)indicate The fine-grained pegmatitic structureand theeuhedral during orafterthevein formation. that majorductiledeformationdidnotaffect thearea south-dipping foliation,andarenotfolded,implying 5cm. From Cesare(1994b). zoning withFe-enriched darker areas.Baseofphoto: cluster atthestraightvein wall; theyexhibitconcentric from Site2,showing euhedralandalusite crystalswhich Figure 44-Polished surfaceofanandalusite-quartzvein (Figure 43). They are orientedatahighangletothe fractures, generallystraightandinparallelsets tonalite. The veins arethin,parallel-sided,fi bearing veins, whichoccurupto1kmfromthe deformation. Among thesearesomeandalusite- are youngerthan(orcontemporaneouswith) Alpine The vein isvery thinanddiscontinuous. Figure 43- Andalusite-quartz vein atSite1. uid-fi lled fi ssures. brolite lled At Site1 volumetric ratioisextremely low. single, thinveinlets. Therefore, thevein/host-rock vein occurrencesreportedinFigure45consistof and andalusitepresencewithinschists.Mostofthe the area,andrelationshipbetweenvein occurrence distribution ofthedifferent Al zone, isclosertothepluton.Figure45shows the host-rocks. the abundance ofgarnetintheimmediatelyadjacent which mayreachupto30%,isdirectlycorrelated and rareplagioclaseand/orwhitemica.Biotite, andalusite inequalamounts,withvariable biotite, no longerthan1metre. They containquartzand Andalusite veins arevery thin,usually< 1cm and subhorizontal stretchinglineation. foliation dippingsouthandawell-developed E-W chlorite). They preserve theolderpenetrative planar staurolite, biotite,ilmeniteandgraphite(±garnet ± schists containingquartz,plagioclase,andalusite, Figure 45-Occurrencesofandalusite-bearingveins and distribution ofthe Al , host-rocksarepelitichornfelsesand Vedrette diRiesaureole. After Cesare(1994b). 2 SiO 5 polymorphsinthesouthern 2 SiO 5 polymorphs in THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

AND CONTACT AUREOLE B17

At Site 2, the country-rocks are pelitic hornfelses, the central portion of the veins, alone or associated composed of quartz, plagioclase, biotite, muscovite, with andalusite. acicular and prismatic sillimanite, garnet, ilmenite The veins show a mineralogical zoning with and graphite, with abundant relicts of andalusite. andalusite and biotite abundant at the vein borders, Veins are larger and more abundant, and may in some whereas quartz is dominant at the centre. cases reach a few metres in length and up to fi ve cm All of the andalusite-bearing veins occur within those in thickness. parts of the aureole in which andalusite crystallized Veins are discordant, their direction being quite during contact metamorphism (cf. Figure 45), and are random, but always very steep. There are two end- always hosted by andalusite-bearing rocks. Where member types of andalusite-bearing pegmatitic veins veins occur in non-pelitic lithologies (e.g., pegmatitic at outcrop 2: biotite-absent, quartz-rich veins (the gneiss or quartzite), they do not contain andalusite or larger ones, Figure 44), and biotite-rich, quartz-poor biotite. In the few cases where veins crosscut different veins. In the fi rst type, euhedral andalusite crystals lithologes, there is a different mineral assemblage generally project from the vein walls into the quartz- in each part. The general relationships between rich inner zone as isolated prisms (up to 3 cm in the mineralogy of veins and that of host-rocks are length) or rosette aggregates. The second type occurs outlined in Figure 46. within garnet-bearing host-rocks; coarse-grained biotite is located at the vein walls, but also occurs in The orientation of veins can be consistently related Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 46 - Schematic diagram summarizing meso- and microstructural observations on the andalusite-bearing veins of the Vedrette di Ries aureole. Veins that formed in a layered rock (upper left) comprising metapelites and quartzite display a variable mineralogy, depending on the composition of the adjacent host-rock. A, B and C represent observed mineral composition and texture of veins in three end-member host-rock lithologies, respectively garnet-poor pelite, garnet-rich pelite, and quartzite. From Cesare (1994b).

27 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg high CO opening, migrationofmatter, andprecipitationof summarized. Itaccountsfortheprocessesoffracture (Cesare, 1994b;Cesareetal.,2001)ishere data, amechanismofsynmetamorphicveining Based onfi eld, microstructuralandfl quartz andandalusite. the degree ofstrainandtherelative abundance of are variously recordedineachsampleasafunctionof aluminum transport.Intheinclusions,densitychanges fl indicates thatincreasedsolubilityin‘aggressive’ minerals. The low salinityoftheaqueousfraction lithostatic fl P-T conditionsofveining, andwitharegime of H fl uid inequilibriumwithgraphite attheestimated these “primary”inclusionsareconsistentwithaC-O- H inclusions defi ned as Type A. These arewater-rich vein formationarethoseoccurringintheisolatedfl Their resultssuggestthatthefl and Hollister(1995). bearing veins (Figure47)have beenstudiedbyCesare The fl uid inclusionswithinquartzof Andalusite- principal stressintheschists. pluton, whichdefi nestheE-Wdirectionofminimum 1 areconcordantwiththemarked elongationofthe ã the underlyingtonalite,whichgives asubvertical to thestressfi from within Andalusite-bearing veins. Figure 47-Primaryfluid inclusionsinquartzcrystals uids (e.g.Kerrick, 1990)isnotrequiredforeffective 1 2 O-CO . Inparticular, theN-Svein directionsatoutcrop 2 2 /CH -CH uid pressureduring crystallization ofvein 4 4 eld generatedbytheemplacement of ratio. The compositionanddensityof -NaCl mixtures,withlow salinityand uids presentduring ud inclusion uid uid and thelackofinterconnected vein networks are thin, andalusite-bearingveins inthestudiedaureole, permanent fl ow. Frequentoccurrencesofisolated, will beattainedandinhibitpressuregradients mechanical stabilitybetweenfractureandhost-rock initial fl Vein Opening: Timing, Mechanisms,andFluid bearing veins. minerals duringtheformationof Andalusite- pressure inthevein mustbeequalto fi immediately drive fl uids intotheopencavities, become asourceforlocalpressuregradientswhich and aconsequentdropinporepressure.Fractures increase inthevolume available forthefl Opening offi ssures intherockgeneratesasudden mineral assemblage. in thehornfelsescapableofproducingvein can beproposedasoneplausibledehydrationreaction Grt +ChlMs= And +Bt+QtzH the reaction textural observation ofbiotitepseudomorpinggarnet, formation. Combiningtheabove datawiththe were undergoing dehydrationduringandalusite aureole, isclearevidence thathost-rockmetapelites proceeding upgradewithintheandalusitezoneof in modalchloriteandwhitemica,whichisrecorded release duringdevolatilization reactions.Decrease of vein openingwas hydrofracturing,causedbyfl minimal, itcanbeconcludedthatthemainmechanism Since thetypicalfeaturesofshearfracturingare rock (ç of minimumstress(ã occurs whenthefl uid pressure(P stress, andgeneratesfracturesperpendicularto requires elevated fl uid pressuresandlow deviatoric Hydraulic extension fracturing(hydrofracturing) at thetimeofvein formation. metamorphic reactionstakingplaceinthehost-rock was synmetamorphic:itwas synchronouswith coeval. Hence,mineralprecipitationinveins growth ofandalusite inveins andhost-rockswas schists wereundergoing furtherheating.Furthermore, of andalusite(T=500±50°C,Cesare,1992),and the P-Tconditionswerewithinstabilityfi before thecrystallizationofsillimanite. At thattime Veins formedduringthecontactmetamorphicevent, Behaviour to thestressfi is consistentwiththeorientationofveins compared In theexample studied,thehydrofracturingmodel lling them.However, tokeep avein open,fl 0 ud fl uid ), accordingtothefailure condition: ow toward thecavity, aconditionof eld inducedbytheunderlyingtonalite. P f 3 Gã ) andtensilestrengthofthe 3 + ç 0. f ), exceeds thesum ã 2 O (1) 3 : afterarapid uid phase, uid ã 3 uid uid eld . It THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

AND CONTACT AUREOLE B17 additional observations against large-scale fl uid and low-temperature deformation of the tonalite, and circulation. its relationships to the DAV mylonites. In this area Mass transfer and mineral deposition the southern contact of the pluton dips steeply to After the initial, transient fl ow, fl uid can be considered the south, concordantly to the mylonites of the DAV. as virtually stagnant, acting as a passive medium, No kinematic indicators have been found within the in thermal and mechanical equilibrium with the tonalite, but preserved magmatic foliations parallel to surrounding rocks. Moreover, chemical equilibrium the mylonitic foliation of the DAV call for syntectonic can also be assumed, given present theoretical models intrusion. This part of the pluton is inferred to be the and the equal parageneses and mineral chemistry in feeder of the main body located further to the north. vein and host-rock. It follows that crystallization of This conclusion is based on the occurrence of a steep vein minerals was simply controlled by heterogeneous magmatic foliation associated with steep lineations mineral reactions in the host-rock (e.g. reaction 1). (Steenken et al., 2000; Wagner et al., in review). The Nucleation of product phases (andalusite, biotite location of the feeders of the intrusive bodies along and quartz) is favoured on the strained minerals segments of the Periadriatic Lineament is a common at vein walls; once nuclei form, concentration and feature of the Periadriatic plutons. chemical potential gradients between reactants and Discussion of the emplacement mechanisms within products are established, and the transfer of chemical the framework of the Oligocene tectonics of the components, continuously provided by dissolving Eastern Alps. reactants, is activated. This implies synchronous growth of andalusite in vein and host-rock. Mass DAY 5 transfer from adjacent host-rock to the vein occurs Return to Florence - End of Field Trip. via intercrystalline diffusion, which can be very effective, and dominant during metamorphism. Since the fracture is fi lled with fl uid that allows for faster Acknowledgments diffusion, the growth of vein minerals is also faster Financial support was received from CARG-PAB, and grain-size coarser; this explains the pegmatitic the Province of Bolzano, from CNR-IGG, from the vein texture. University of Padova and from DFG (Project Ha Because intergranular diffusion is the mass- 2403/3-2). We wish to thank Gottfried Leitgeb (Rif. transfer process during synmetamorphic veining, Forcella Valfredda), Arnold Seeber (Rif. Roma) and diffusion halos around veins can be expected. The Maria Mair (Geltalalm) for their assistance during plagioclase-rich border zones that sometimes occur fi eld work. The critical reading of Giuliano Bellieni is at vein margins can be interpreted as diffusion halos. gratefully acknowledged. Conversely, such an explanation is not applicable to the biotite-rich zones, which are located within the veins, and cannot be interpreted as residual portions References of metasomatically-depleted country rocks. Bassani S., Fioretti A.M., Bellieni G. (1997). Il granato nelle masse intrusive di Rensen, DAY 4 Vedrette di Ries e Polland (Alpi Orientali). Anterselva (Antholz) valley - Passo Stalle Plinius n.18; 43-44. (Staller Sattel) - Brunico (Bruneck). Bellieni G. (1977). Caratteri geobarometrici delle intrusioni granitiche del plutone delle Vedrette Morning: descent to Anterselva. Outcrops of di Ries (Rieserferner)(Alto Adige Orientale) tonalite at Cima di Vila (Zinsnock): discussion of its alla luce dei sistemi sperimentali Q-Or-Ab-An- geochemical and petrologic features (Bellieni, 1980; H2O. Rend. Soc. It. Miner. Petr., 33, 631-645. B16 to B33 n° 2 - from Volume Bellieni et al. 1982) and of the genetic relationships Bellieni G. (1978) Caratteri geochimici del massiccio with the Vedrette di Ries Pluton. granodioritico-tonalitico delle Vedrette di Ries Afternoon: Drive to Passo Stalle (Staller Sattel) (Rieserferner)-Alto Adige Orientale. Rend. Soc. (2000 m asl): cross sections along the cataclasites It. Miner. Petr., 34, 527-548. and mylonites of the Defereggen-Anterselva-Valles Bellieni G. (1980) The Cima di Vila (Zinsnock) (DAV) line from the pass to the Vedrette di Ries Massif: Geochemical features and comparisons tonalite. Shear bands in greenschist facies rocks, with the Vedrette di Ries (Rieserferner) pluton indicating the sinistral kinematics of the DAV. High- (Eastern Alps-Italy). Neu. Jb. Mineral. Abh.,

29 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg Borsi S.,DelMoro A., SassiF.P., ZirpoliG.(1979). Borsi S.,DelMoro A., SassiF.P., ZirpoliG.(1973). Borsi S.,DelMoro A., SassiF.P., Zanferrari A., Bigi, G., A. Castellarin,M.Coli,G. V. Dal Piaz, Bianchi A. (1934).Studipetrografi Bellieni G.,Justin Visentin E.,ZanettinB.(1995). Bellieni G.,Cavazzini G.,Fioretti A.M., Peccerillo A., Bellieni G.,Peccerillo A., PoliG.(1982)REE Bellieni G.,Peccerillo A., PoliG.(1981). The Vedrette Bellieni G.,MolinG.M., Visonà D.(1979) The Bellieni G.,CominChiaramontiP., Visonà D.(1976). Rdsch., 68,41-60. massif anditsgeodynamicsignifi On theageof Vedrette diRies(Rieserferner) Geol. It.,12,549-571. radiometric andgeopetrologicdata. the southof Tauern Window (Eastern Alps): Metamorphic evolution ofthe Austridic rocksto 17pp. Window (Eastern Alps). austridic continentalmargin Southofthe Tauern radiometric dataonthealpinehistoryof Zirpoli G.(1978).New geopetrologicand (Italy). Structural modelofItaly, S.E.L.C.A.,Florence M. Sartori,P. Scandone,andG.B. Vai (1990) Univ. Padova, 10;243pp. orientale eregioni limitrofe.Mem.Ist.Geol.R. Petrol. problems andsuggestions.Soc.It.Mineral. Silica) forclassifi Use ofthechemical TAS diagram(Totali Alkali (Eastern Alps).Per. Mineral., 58,1-3,45-65. from the Vedrette diRiesplutoniccomplex geochemistry ofmicrogranularmafi Poli G.,ZantedeschiP. (1989).Petrologyand Mineral. Abh. signifi granodioritic complex anditspetrogenetic distribution intheCimadi Vila (Zinsnock) 145-156. on ItsGenesis.Contrib. Mineral. Petrol., 78, Petrological andGeochemicalDataBearing di Ries(Rieserferner)PlutonicComplex: Abh., 136,238-253. di Ries(Eastern Alps-Italy). Neu.Jb. Mineral. intrusive massifsofBressanoneand Vedrette petrogenetic signifi cance ofthegarnetsin Geol. It.,95,351-370. Vedrette diRies(AlpiOrientali).Boll.Soc. Contributo allaconoscenzadelplutonedelle 138, 244-258. cance (Eastern Alps, Italy). Plinius, 14,49-52. , 145,50-65. cation ofplutonicrocks: Mem. Sci.Geol. ci sull’Alto ci Adige cance. c enclaves c Mem. Soc. Neu. Jb. Geol. , 32, Chopin, C.,Henry, C.,andMichard, A. (1991) Dal PiazG.V., Von RaumerJ.,SassiF.P., ZanettinB., Dal Piaz,Gb., (1934).Studigeologicisull’Alto Adige Cescutti C.,Fioretti A.M., BellieniG.&CesareB. Cesare B.(1994b).Synmetamorphicveining: origin Cesare B.(1994a).Hercynite astheproductof Cesare B.,PolettiE.,BoironM-C.&Cathelineau Cesare B.andHollisterL.S.(1995). Andalusite- Cesare B.(1999).Multi-Stagepseudomorphic Cesare B.(1999).Multi-Stagepseudomorphic Cesare B.(1992).Metamorfi smo dicontattorocce Congress, Abstract Orientale). (Alto Adige austroalpino neidintornidi Vedrette diRies fi (2003). Studiopetrografi co egeochimicodei J. Mineral terrain, Dora-MairaMassif,western Alps. Eur. Geology andpetrologyofthecoesite-bearing Coy SquyresEd. The EarthSciencesSocietyof Italian Alps. Reprintedfrom“GeologyofItaly” Zanferrari A. (1975).Geologicaloutlineofthe 242 pp. di Geologia Regia Università diPadova orientale eregioni limitrofe.MemorieIstituto 121-136 based onfl inclusions. Journal ofMetamorphic Geology di Riescontactaureole,Eastern Alps, Italy. of andalusite-bearingveins inthe Vedrette 116, 239-246. Contributions toMineralogy andPetrology aureole of Vedrette diRies,eastern Alps, Italy. staurolite decompositioninthecontact Padova, 106pp. Orientali, Italia).Unp.PhD Thesis, Univ. pelitiche nell’aureoladi Vedrette diRies(Alpi Window: amodeloffl in theZentralgneisComplex oftheSW Tauern M. (2001). Alpine metamorphismandveining 13, 687-700. - Italy):fl bearing veins at Vedrette diRies(Eastern Alps Geology, 17,735–746 mineral assemblages.Journal ofMetamorphic polymetamorphism: 2.algebraicanalysisof replacement ofgarnetduring Geology, 17,723–73 their interpretation.Journal ofMetamorphic polymetamorphism: Microstructuresand replacement ofgarnetduring ln porfi loni uid phasecompositionbasedonfl ., 3,263-291. uid inclusions. uid rici acidiaffi Journal ofMetamorphicGeology pg.201 4 oranti nelbasamento udrc interactions uid-rock Tectonophysics GeoItalia 2003 , 12,643-653. , 336, , 10, uid , , THE PERIADRIATIC INTRUSION OF VEDRETTE DI RIES - RIESERFERNER (EASTERN ALPS): PETROLOGY, EMPLACEMENT MECHANISMS

AND CONTACT AUREOLE B17

the Libyan Arab Republic. Tripoli. Tauernfensters (Südtirol/Italien). Erlanger Dal Piaz G.V., Venturelli G., 1983. Brevi rifl essioni Geol. Abh., 114, 1-82. sul magmatismo post-ofi olitico nel quadro Kozur, H. (1991) The evolution of the Meliata- dell’evoluzione spazio-temporale delle Alpi. Halstatt ocean and its signifi cance for the early Memorie Società Geologica Italiana, 26, 5-19. evolution of the Eastern Alps and Western Exner C.H., (1976). Die Geologische Position der Carpathians. Paleogeogr. Paleoclimatol. Magmatite des periadriatischen Lineaments. Paleoecol. 87, 109-135. Verh. Geol., B 4:3-64. Laubscher H.P. (1985). The late Alpine (Periadriatic) Froitzheim, N., Schmid, S.M., and Fey, M. (1996) intrusions and the Insubric Line. Mem. Soc. Mesozoic paleogeography and the timing of Geol. It., 26, 21-30. eclogite-facies metamorphism in the Alps : A Mager D. (1985). Geologische Karte des working hypothesis. Eclogae geol. Helv., 89, Rieserfernergruppe zwischen Magerstein und 81-110. Windschar (Südtirol). Der Schlern, 6, Bozen Gatto G.O., Gregnanin A., Molin G.M., Piccirillo Mancktelow N.S., Stöckli D.F., Grollimund B., E.M., and Scolari A. (1976). Le manifestazioni Müller W., Fügenschuh B., Viola G., Seward D. Andesitiche polifasiche dell’Alto Adige and Villa I.M. (2001). The DAV and Periadriatic occidentale nel quadro geodinamico alpino. St. fault systems in the eastern Alps south of the Trentin. Sc. Nat., 53, 21-47. tauern Window. Int. J. Earth Sci., 90, 593-622. Guidotti C.V., (1968). Prograde muscovite Mann A. and Scheuvens D. (1998). Structural pseudomorphs after staurolite in the Rangeley- investigation of the northern contact of the Oquossoc areas, Maine. American Mineralogist, Rieserferner Plutonic Complex (Eastern Alps) 53, 1368-1376. - fi rst results. Terra Nostra, 98, 62. Green T.H. (1972). Crystallization of calc-alkaline Müller W., Mancktelow N.S. and Meier M. (2000). andesite under controlled high-pressure Rb-Sr microchrons of synkinematic mica in hydrous conditions. Contrib. Mineral. Petrol. mylonites: an example from the DAV fault of 34, 150-166. the Eastern Alps. Earth and Planetary Science Green T.H., and Ringwood A.E. (1972). Letters, 180, 385-397 Crystallization of garnet-bearing rhyodacite Müller W., Prosser G., Mancktelow N.S., Villa I.M., under high-pressure hydrous conditions. J. Kelley S.P., Viola G., and Oberli F. (2001). Geol. Soc. Aust. 19, 203-212. Geochronological constraints on the evolution Hammerschmidt K. (1981). Isotopengeologische of the Periadriatic fault system (Alps). Int. J. Untersuchungen am Augengneis vom Typ Earth Sci., 90, 623-653. Campo Tures bei Rain in Taufers, Südtirol. Neubauer, F. (1994) Kontinentkollision in den Mem. Sci. Geol., 34, 273-300. Ostalpen. Geowissenschaften 12, 136-140. Hofmann K.H., Kleinschrodt R., Lippert R., Mager Pattison, D.R.M. & Tracy, R.J., 1991: Phase equilibria D. und Stöchkert B. (1983). Geologische Karte and thermobarometry of metapelites. In: des Altkristallin südlich des Tauernfensters Kerrick, D.M. (ed.): Contact metamorphism. zwischen Pfunderer Tal und Tauferer Tal Reviews in Mineralogy, 26; 43-104 (Südtirol). Der Schlern, 57; 572-590. Prochaska W. (1981). Einige Gangesteine der Holdaway M.J. (1971). Stability of andalusite and Rieserfernerintrusion mit neuen radiometrischen the aluminum silicate phase diagram: American Altersdaten. Mitteilungen der Gesellschaft der Journal of Science, 271, 97–131 geologie und Berbaustudent, Wien, 27, 161- Kagami H., Ulmer P., Hansmann W., Dietrich V.,

171. B16 to B33 n° 2 - from Volume and Steiger R.H. (1991). Nd-Sr isotopic and Rosenberg, C.L., A. Berger, and S. M. Schmid (1995) geochemical characteristics of the Southern Observations from the fl oor of a granitoid Adamello (northern Italy) intrusives: pluton; inferences on the driving force of fi nal implication for crustal versus mantle origin. J. emplacement, Geology, 23, 443-446. Geophys. Res. 96, 14331-14346. Rosenberg, C. L., in press, Shear zones and magma Kerrick D.M. (1990). The Al SiO polymorphs. 2 5 ascent: A model based on a review of the Reviews in Mineralogy, 22. Tertiary magmatism in the Alps. Tectonics. Kleinschrodt R. (1987). Quarzkorngefügeanalyse im Altkristallin südlich des westlichen Sassi, F.P. & Zanettin, B. (1980) Schema degli eventi

31 - B17 Volume n° 2 - from B16 to B33 B17 - B17 Leaders: B.Cesare,A.M.Fioretti,C.Rosenberg Steenken A. (2002). The emplacementofthe Steenken A., Siegesmund, S.andHeinrichs, T. (2000). Schulz B.(1997).Pre-Alpinetectonometamorphic Schulz B.(1989).JungalpidischeGefügeentwicklung Santilli M.,OrombelliG.andPelfi ni M.(2002). Steenken A, Siegesmund S,Heinrichs T, Fugenschuh Alps, Tyrol) history ofthe Austroalpine basement(Eastern Line aswelltothekinematicandthermal Rieserferner PlutonanditsrelationtotheDAV- Austria). Rieserferner Pluton(Eastern Alps, Italy/ B (2002).Coolingandexhumation ofthe 120 pp. of Structural Geology magnetic fabrics andmicrostructures. Constraints fromfi The emplacementoftheRieserfernerPluton: Petrographische Mitteilungen Window. to thesouthofcentral Tauern evolution inthe Austroalpine basement Bundesanst. (Osttirol, Österreich).Jahrbuch. Geol. entlang derDefereggen-Antholz-Vals-Linie Quat. 25,61-76. Glaciological Committee. 1999 inferredbythedatasuppliedItalian Variations ofItalianglaciersbetween1980and Petrologia, 36;3-7. Rendiconti SocietàItalianadiMineralogia e metamorfi Int. J. EarthSci.,91,799-817. ci emagmaticinelle Alpi Orientali. , 132;775-789. Schweizerische Mineralogische Geotektonische Forschungen , 22,1855-1873 Geogr. Fis. Dinam. ed observations, eld , 77,281-297. Journal , 94, Wagner R.,C. Rosenberg L.,HandyM.R.,Möbus Wagner R.,C. L.Rosenberg, M.R.Handy, C.(2003). Stöckhert B.(1984).K-Ardeterminationson Trommsdorff V. andNievergelt P., (1983) The Stöckhert B.(1987).DasUttenheimerPegmatit-Feld Stöckhert B.(1985).Pre-Alpinehistoryofthe Von Blankenburg F. and Davis J.H.(1995). Pluton, Eastern Alps. Geol.Soc. Am. Bull. transpressive shearzone: The Rieserferner driven infl ation ofamid-crustalsillfedby C., and Albertz M.inreview, Buoyancy- Memorie diScienzeGeologiche (Padova), 54, 14, 120-131. Mineral. Abh valley, Southern Tyrol, Eastern Alps). Neu.Jb. the southofwestern Tauern Window (Ahrn Alpine deformationinthe Austridic basementto pegmatites, andtheminimumageofOld muscovites andphengitesfromdeformed relations. Bregaglia (Bergell) IorioIntrusive anditsfi 83-106. alpine Überprägung. (Ostalpines Altkristallin, Südtirol)Genese und Geol. Paläont. Mh., Caledonian versus Hercynian event. Tauern Window (Southern Tyrol, Italy). Austridic basementtothesouthofwestern magmatism andtectonicsinthe Alps. Slab breakoff: A modelforsyncollisional Mem. Soc.Geol.It.,26,55-68. ., 150,103-120. 618-642. Erlanger Geol.Abh Tectonics Neu. Jb. ., 114, eld Back Cover: Road map of the area NE of Brunico. Numbers in yellow dots indicate the localities of each field trip’s day as in the Guide. FIELD TRIP MAP INTERNATIONAL GEOLOGICAL CONGRESS nd 32

Edited by APAT August 20-28,2004 Florence -Italy

Field Trip Guide Book - B18 Associate Leaders:M.Boni,L.Meinert Leader: M.Benvenuti GEOLOGICAL CONGRESS 32 Volume n°2-fromB16toB33 (CENTRAL ITALY) AND ELBAISLAND SOUTHERNTUSCANY SKARN DEPOSITSIN Pre-Congress nd INTERNATIONAL B18 The scientific content of this guide is under the total responsibility of the Authors

Published by: APAT – Italian Agency for the Environmental Protection and Technical Services - Via Vitaliano Brancati, 48 - 00144 Roma - Italy

Series Editors: Luca Guerrieri, Irene Rischia and Leonello Serva (APAT, Roma)

English Desk-copy Editors: Paul Mazza (Università di Firenze), Jessica Ann Thonn (Università di Firenze), Nathalie Marléne Adams (Università di Firenze), Miriam Friedman (Università di Firenze), Kate Eadie (Freelance indipendent professional)

Field Trip Committee: Leonello Serva (APAT, Roma), Alessandro Michetti (Università dell’Insubria, Como), Giulio Pavia (Università di Torino), Raffaele Pignone (Servizio Geologico Regione Emilia-Romagna, Bologna) and Riccardo Polino (CNR, Torino)

Acknowledgments: The 32nd IGC Organizing Committee is grateful to Roberto Pompili and Elisa Brustia (APAT, Roma) for their collaboration in editing.

Graphic project: Full snc - Firenze

Layout and press: Lito Terrazzi srl - Firenze Volume n° 2 - from B16 to B33

32nd INTERNATIONAL GEOLOGICAL CONGRESS

SKARN DEPOSITS IN SOUTHERN TUSCANY AND ELBA ISLAND (CENTRAL ITALY)

AUTHORS: M. Benvenuti (Università di Firenze - Italy) M. Boni (Università “Federico II” di Napoli - Italy), L. Meinert (Washington State University - USA)

Florence - Italy August 20-28, 2004

Pre-Congress B18 Front Cover: Historic site of Rocca San Silvestro in the Campiglia Marittima mining district SKARN DEPOSITS IN SOUTHERN TUSCANY AND ELBA ISLAND CENTRAL ITALY B18

Leader: M. Benvenuti Associate Leader: M. Boni, L. Meinert

Introduction historical, mineralogical, and economic importance. The field trip will start with a general overview at Aim and Localities of the Field Trip the historic site of the Etruscan town of Populonia. IGC field trip B18 will investigate the classic skarn Following this, we will travel by ferry to the Island localities of Tuscany and the Island of Elba. Tuscany of Elba to examine the Fe-skarns at several localities. includes several different skarn types but the most The second day we will focus on the classically famous, and the ones that we will visit on this field zoned Zn-skarn system around Campiglia. The trip trip, are the Fe and Zn skarns at Isola d’Elba and will conclude with a visit to the archeometallurgically in the Campiglia Marittima district. These are of interesting beach slags at the Baratti Gulf. Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 1 - Itinerary of the field trip.

3 - B18 Volume n° 2 - from B16 to B33 B18 - B18 Leader: M.Benvenuti become progressively youngereastward. stratigraphic unitsdepositedintheforedeepsystem, tion ofthethrustfront,Oligocene–Miocenetectono- gravity sliding.Duetotime–spaceoutward migra- very importantdetachmentplane for thrustingand Sea area. The baseofthethickevaporitic layerisa (Burano Fm.),gradingtodolomitesinthe Adriatic on about1000–1500m-thick Triassic evaporites composed ofcarbonaterocks.Bothsuccessionsrest lower successionofMesozoic–Cenozoicage,mainly formed bysiliciclasticforedeepsediments,anda 3000 m-thicksuccessionofOligocene–Mioceneage, and Umbria–Marcheunitsconsistofanupper2000– the Adria Platesincethemiddle Triassic. The Tuscan units, originallydepositedonthepassive margin of tectonically overlie the Tuscan andUmbria–Marche lites withtheirJurassictoEocenesedimentarycover, Apennines (modifiedfromBoninietal.,2001). Figure 2-Geologicalsketch-map of thenorthern yan ocean). The Ligurianunits,consistingofophio- the Ligurian–Piedmontesesectorof Alpine Teth- rides), originallydepositedinanoceanicrealm(i.e. 3, theuppermostareLigurianUnits(orLigu- (Finetti etal.,2001). As schematicallyshown in units, accompaniedbysecond-orderback-thrusts mainly composedofapileNE-verging tectonic chain (Fig. 2). The Northern Apennines chainis district: trip (i.e.,ElbaIslandandtheCampigliaMarittima The two areaswhichwillbevisitedduringourfield Geology andgeodynamics Regional setting Fig. 1)belongtotheNorthern Apennines Fig. range ofmafic tointermediaterockssuchaslam- acid peraluminousrhyolitesandgranites,awide They includecrustalanatectic Peccerillo etal.,1987). east (Civetta etal.,1978;Ferraraand Tonarini, 1985; Ma, showing atrendofdecreasingagesfromwestto sive bodieswereemplacedinthetimespanof8to0.2 land (mainlyinsouthern Tuscany). Volcanic tointru- ent crustallevels intheNorthern Apennines hinter- variety ofmagmaticbodieswereemplacedatdiffer- orogeny (fromLateMiocenetoPleistocene),alarge During thepost-collisionalphaseof Apenninic Neogene-Quaternary Magmatism Figure 4-Locationandageofmagmaticrocks ofthe Tuscany MagmaticProvince (Peccerillo etal.,2001) Figure 3-Schematic stratigraphiccolumnsofthe Tuscan andUmbria-Marche units (from Finetti etal.,2001) SKARN DEPOSITS IN SOUTHERN TUSCANY AND ELBA ISLAND CENTRAL ITALY B18

proites, high-potassium calcalkaline and shoshonitic rocks (Fig. 4). Rock compositions straddle the I and S fields of Chappel and White (1974), the most basic rocks being mainly I-type and the high-silica ones S- type (Peccerillo et al., 2001, and references therein). Most of the acid rocks appear to have undergone mixing and mingling with various types of mantle- derived calcalkaline to potassic melts (Poli, 1992). Mafic rocks, in fact, are commonly found as micro- granular enclaves and veins in most acid extrusive and intrusive bodies of the Tuscan Province. Several geochemical and petrological features, further sug- gest a heterogeneous mantle source for the mafic melts (Peccerillo, 1999). According to Peccerillo et al. (2001) the overall petrogenetic history for the Tuscan Province can be described in three main steps: 1) subduction-related metasomatism of upper mantle (both asthenospheric and lithospheric) by interac- tion with upper crustal material; 2) variable degrees of partial melting of heterogeneous mantle due to Figure 5 - The main mining districts of Tuscany asthenospheric uprise, and formation of various types (modified after Tanelli, 1983) of magmas; 3) injection of mafic magmas into the continental crust, uprise of isotherms, onset of crustal district) and lead-zinc(-copper) skarns (Temperino anatexis, and acid-mafic magma mingling. mine in the Campiglia M.ma district; Serrabottini near Massa Marittima). These deposits have been Ore Geology studied by Bartholomé, Evrard, 1970; Corsini et For about 30 centuries, Tuscany has been one of the al., 1980; Dimanche, 1971; Tanelli, 1977; Lattanzi, most important mining regions of Italy producing Tanelli, 1985; Del Tredici (1990), Torrini (1990) and a large variety of resources, including pyrite, iron, Dünkel (2002). According to Tanelli (1977) the Tus- base metals, geothermal steam and several industrial can skarn deposits formed by replacement of Triassic minerals and rocks (Lattanzi et al. 1994, and refer- ences therein). Today the mining industry in Tuscany is limited to industrial minerals (feldspars, halite), ornamental stones, and building materials. The Tus- can metallogenic province includes (Figs. 5 and 6): the Fe oxides deposits of Elba Island, the pyrite (± barite ± Fe oxides) deposits of southern Tuscany and Apuane Alps, the base-and precious-metals deposits of the “Colline Metallifere” district (southern Tusca- ny), the Hg deposits of the Monte Amiata area, the Sb deposits of the Capalbio-Monti Romani belt (cf. Cip- riani, Tanelli, 1983; Tanelli, 1983). The newest addi- tion to the metallogenic framework of Tuscany, is the discovery in the mid ‘80s of “Carlin-type” epithermal B16 to B33 n° 2 - from Volume gold mineralization. Most of the Au prospects, of lim- ited economic importance, are closely related to Sb deposits (Tanelli et al., 1991; Lattanzi, 1999). A number of different skarn deposits occur in the southwestern portion of the Tuscan metallogenic province (Fig. 7): they include calcic iron skarns (Capo Calamita, Ginevro, Sassi Neri and Ortano at Figure 6 - Distribution of main ore types Elba Island; Niccioleta in the Colline Metallifere of southern Tuscany

5 - B18 Volume n° 2 - from B16 to B33 B18 - B18 Leader: M.Benvenuti with attendantswarms ofapliticandpegmatitic dikes, presence ofanextensive Mio-Pliocenemagmatism, Tyrrhenian basin.Otherelementsofinterestarethe tion ofthe Apenninic chainaftertheopeningof the reconstructionoftectono-stratigraphicevolu- Northern Apennines, ElbaIslandisakey elementfor Due toitslocationmidway betweenCorsicaandthe The geologicframework Elba Island magmatic rocks(Lattanzietal.,1991). of lead(andothermetals?)fromNeogene-Quaternary tima andNiccioletadepositsmayreflectcontribution tion ofpyrite andgalenafromtheCampigliaMarit- On theotherhand,uniformleadisotopecomposi- sulfides/sulfates fromPermo-Triassic countryrocks). compatible withalocal,nonmagmaticsource(i.e., tion ofsulfurfromthe Temperino skarndepositis Corsini etal.(1980)maintainthatisotopiccomposi- for Tuscan skarndepositsarestillpoorly constrained. mation (cf. Dimanche,1971).Source(s)ofelements for instanceapliticdikes appeartopredateskarnfor- does notnecessarilyimplyageneticlink:atGinevro, of magmaticrocksincloseproximitytoskarnbodies various distances(Niccioleta,Ortano). The presence with magmaticrocks(e.g.,at Temperino mine),orat Tuscan Province. Skarnbodiesmaybeincontact crustal levels oftheNeogenemagmaticrocks processes triggeredbytheemplacementatshallow carbonate rocksofthe Tuscan Unitbymetasomatic (after Tanelli, 1977) Figure 7-LocationofTuscan skarndeposits the Porto Azzurro stockcauseddeactivation ofthe et al.,2003). At 6.2-5.0Ma,theemplacementof exploited atLaCrocettaandMarciana mines(Maineri (sericite replacingprimaryalbiteandK-feldspars) porphyritic aplitesandformationofthe“eurites” and resultingpervasive hydrothermal alterationof The ElbaCentralFault causedintensefluidcirculation top ofMonteCapannepluton. laccolith complex) fromtheiroriginalpositiononthe upper platerocks(includingComplex V withintruded controlled theeastward translationofabout10km detachment fault (ElbaCentralFault), which triggered themovement ofanimportantextensional that theemplacementofMonteCapannepluton rocks (>8.5-6.85Ma).Dinietal.(2002)suggest laccolith complex madeofsubvolcanic porphyritic associated withtheMonteCapannepluton),anda pegmatitic dikes (thelatteralmostexclusively found Azzurro (6.2-5.0Ma),several swarms ofapliticand pluton (6.9Ma),themonzograniticstockofPorto al., 2003,andreferencestherein):theMonteCapanne shallow crustallevels (cf.Dinietal.2002;Maineri the emplacementofseveral magmaticintrusionsat sional phase. This stagewas alsoaccompaniedby orogeny, and later affected byanimportantexten- tion duringthecompressionalstageof Apenninic were deformedandpiledupintotheirpresentposi- ited inquitedifferent palaeogeographicdomains, thrust surfaces. The various units, originallydepos- are separatedeachotherbyroughlyNSverging over- characterised byageneraltoptoeastvergence, and IneasternElbatheunitsofthistectonicpileare otti etal.,2001andreferencestherein). Flysch Unitand(9)Cretaceous(Bortol- Ophiolitic Unitwithseven subunits; (8)Paleogene (5) Tuscan NappeUnitand(6)Gràssera Unit;(7) Acquadolce Unit;(4)Monticiano-RoccastradaUnit, (1) Porto Azzurro Unit;(2)OrtanoUnitand(3) (from thegeometricallylowermost upwards): is madeupbythefollowing ninemajortectonicunits The tectonicframeofcentralandeasternElbaIsland sional events tookplace(Bortolottietal.,2001). Pliocene/? Quaternarysyn-andpost-magmaticexten- (Tuscany Domain)margins, intheLateMiocene- deformation oftheEuropean(Corsica)and Adriatic Eocene-Lower Miocenecollisionandpolyphase ocean (Ligurian-PiedmonteseBasin). After theUpper tiary withtheconsumptionofwestern Tethyan evolution begins intheLateCretaceous-Early Ter- tory startsinthePalaeozoic, but its Alpine tectonic ore deposits.ElbaIsland’s long-living geologichis- as welltheoccurrenceofworld-famous iron SKARN DEPOSITS IN SOUTHERN TUSCANY AND ELBA ISLAND CENTRAL ITALY B18

Elba Central Fault, although additional eastwards (data from Fabri, 1887; Pullè, 1921). To preserve this tectonic translations took place along another major long mining tradition a “Mining and Mineralogical low-angle fault, the Zuccale fault (Pertusati et al., Park” has been recently established in eastern Elba 1993). The emplacement of the Porto Azzurro pluton (cf. Tanelli and Benvenuti, 1999). caused also a strong thermometamorphic imprint As shown in Figure 8, the Fe deposits of Elba Island on the geometrically lowermost Units of the Elba are restricted to a relatively narrow belt extending NS structural edifice (namely, the Porto Azzurro, Ortano along the eastern coast of Elba Island, from Monte and Acquadolce Units). Crosscutting relationships Calendozio (Rio Albano mine) to the Calamita between the Zuccale fault and aplitic dikes indicate promontory. The ore bodies range from stratiform to that the detachment postdated, at least partially, the pod-like or vein-type, although the first appears to be emplacement of the magmatic dikes. The last tectonic dominant (Zuffardi, 1990). Stratiform Fe bodies are stage at Elba Island is mainly represented by N-S predominantly hosted by Palaeozoic-Triassic forma- trending high-angle extensional faults, affecting the tions belonging to the Tuscan domain. Many Fe ores entire N-Tyrrhenian basin. This last episode ended are associated with faults (Debenedetti, 1952; Gil- before about 3.5 Ma (Keller and Pialli, 1990). lieron, 1959): a first set of thrust faults, striking NS and dipping 30°-45° W, corresponding to the thrust Geology, mineralogy and textures surfaces among the various tectonic units, and two of Elba iron deposits sets of normal, high-angle faults, one striking NS and Iron ores from Elba Island have been mined without dipping 30°-60° E, the other one with strike NE-SW interruption for almost three millennia, since the and dips of 45°-70° to NW or SE. early Etruscan mine workings (early 1st Millennium As reviewed by Tanelli and Lattanzi (1986) there is BC: Corretti and Benvenuti, 2001) up to about twenty disagreement in the literature about whether all of years ago (1981, closure of the Ginevro mine). At the Fe deposits are genetically associated with late- least 60 million tons of Fe ore have been extracted Apenninic granitic stocks or whether in some cases from Elba deposits from ancient times to the present the intrusions simply metamorphosed and partly Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 8 - Location of main iron deposits of Elba Island. Legend: 1) Rio Albano; 2) Rio Marina; 3) Ortano; 4) Terranera; 5) Calamita; 6) Ginevro; 7) Sassi Neri.

7 - B18 Volume n° 2 - from B16 to B33 B18 - B18 Leader: M.Benvenuti goethite andtraceamountsof base metalsulfides. lenses andmassive bodiesofmagnetite±hematite, associated withbothtypesofskarn,andconsisted otti etal.,2001). The exploited oreswerespatially dolostones anddolomiticlimestones”ofBortol- and theoverlying carbonaticformation(“crystalline at thecontactbetweenMt.CalamitaFormation hedenbergite skarn(Torrini, 1990)developed mostly form garnet(andradite)-richskarnandlesserilvaite- by thePorto Azzurro Unit. At CapoCalamitastrati- Ginevro several skarn-bearingirondeposits(CapoCalamita, dent intheCalamitaPeninsula(see Azzurro pluton. This associationisparticularlyevi- associated withapliticdikes linked tothePorto Fe oresandskarnsofsoutheasternElbaIslandare age ofonehematitesample(Lippoltetal.,1995). development, basedupona7.3 tion appearstobecoeval andcogeneticwithskarn the nearbyPuntadelleCannelle. The ironmineraliza- are incloseproximitytoskarnbodiescroppingoutat ranera withintheMonticiano–RoccastradaUnit,and Lenses ofhematite+pyrite ±magnetiteoccurat Ter- Acquadolce Unitfromtheoverlying OrtanoUnit. phyllites alongacataclastichorizonseparatingthe skarn bodies,whichreplacemarblesandcalcareous magnetite), associatedwithpyroxene-epidote-ilvaite ferent oremineralogy(pyrite, pyrrhotite ±hematite, and Capod’Arco. The Ortanodepositshows adif- skarn bodiesoccuratOrtano,Porticciolo, Tignitoio Lotti (1886,pp.205-206).Moving southwards, other the Acquadolce calc-schists,asreportedindetailby 9). Skarnmineralsoccuralongschistosityplanesof extend alongthecoast(Torre diRioskarns, ± quartz,chlorite,magnetite,pyrite andpyrrhotite large skarnbodieswithhedenbergite-ilvaite-epidote 2001). ImmediatelysouthofRioMarinatown, very of theMonticiano-RoccastradaUnit(Bortolottietal., overlying JurassictoOligocenecarbonaticformation which arenow interpretedastectonicslicesofthe masses (the Vigneria limestonesofGillieron,1959), skarn bodiesreplacingwedge-shapedcarbonatic in the1950srevealed theexistence ofhematite-pyrite at depth.Drillingandlimitedunderground workings Even atRioMarinaskarnbodieswereencountered and/or apliticdikes becomesmoreanddistinct. sula, theassociationofironoreswithskarnbodies Moving fromRioMarinatowards theCalamitaPenin- Palaeozoic age(stage thermal sedimentaryenvironments of Triassic and/or least pre-concentrated,insedimentaryand/orhydro- remobilised theironoresthatwereformed,orat (Fig. 9a),SassiNeri,Stagnone)arehosted ii ofLattanzietal.,1994). ± 0.4Maradiometric Fig. 8),where Fig. Colline Metallifereand Alpi Apuane) isnotwell of ElbaIslandandother Tuscan districts(namely, As mentionedpreviously, thegenesisofirondeposits 1990). the garnetskarnandmagnetitelenses.(Torrini, exploited atCapoCalamitathe contactbetween ± malachite,azurite,chalcantite,etc.)werelocally of Fe-Cusulfides (pyrrhotite, pyrite, chalcopyrite normally forminalateparageneticstage.Masses abundant inthemagnetite-typedeposits, wherethey Marina –Rio Albano deposits,aresignificantly more Sulfides, whicharevery rareorabsentintheRio observed by Torrini (1990). early cassiterite+pyrite assemblage,whichwas not and Torrini (1990). The formerauthordescribesan posed fortheCalamitairondepositbyDünkel (2002) Figure 10 al., 1976). Bianco andCapoCalamitamines(cfr. Calanchiet exploited inthepast,especiallyatRio Albano, Capo tionary, sometimesstalactitic),whichwereactively types andmorphologies(earthy, massive, concre- mary Femineralsarelimoniticaggregates ofvariable primary pyrite. The final alterationproductsofpri- being derived fromoxidationandremobilisationof ±pyrite (±quartz)assemblageisparageneticallylate, Deschamps etal.(1983)suggestedthatthehematite ± pyrite, mostcomingfromtheRioMarinastopes. crystals ofhematite(variety “oligisto”=glazeiron) Elba isespeciallyfamous worldwide foritsbeautiful (1990) hasobserved thesametexture atSassiNeri. (1977), Torrini (190)andDünkel (2002).Del Tredici confirmed byCoccoandGaravelli (1954), Tanelli vite), asfirst suggestedby Vom Rath(1870)and as pseudomorphsafterprimaryhematite(mushketo- of theCalamitapeninsula. Typically, magnetiteoccurs sulfides) isenrichedintheskarn-associateddeposits deposits, whereasmagnetite(±pyrite±Cu,Pb,Zn,As,Bi a generalrule,hematiteisdominantinthenorthern relatively simple,beingmadeupofFeoxides. As Primary oremineralogyofElba’s irondepositsis detailed informationisthusavailable. a drillingproject,but was never exploited; no Finally, theStagnonedepositwas recognizedthrough minor amountsofhedenbergite, ilvaite andepidote. associated withgrossular-almandine garnetandonly Del Tredici, 1990). The skarnscontainferropargasite, a greatabundance ofapliticdikes (Dimanche,1971; tion totallyreplacedthecarbonaterocksandthereis deposits. At Ginevro, forinstance,skarnmineraliza- higher temperatureandmorereducedthantheother The Ginevro andSassiNeridepositsappeartobe shows thetwo parageneticsequencespro- SKARN DEPOSITS IN SOUTHERN TUSCANY AND ELBA ISLAND CENTRAL ITALY B18

Fig. 9 - Photographs of Elba Fe skarn features: a) Open Fe Ginevro mine along the Elba coast b) Interlayered brown garnet and green pyroxene at Rio Marina c) Coarse-grained radiating crystals of hedenbergitic pyroxene cut by black ilvaite veins at Capo Calamita d) Euhedral black ilvaite crystals intergrown with hedenbergitic pyroxene at Rio Marina e) Isoclinally folded metasedimentary host rocks at Rio Marina f) Distal pyroxene- magnetite veins cutting marble at Capo Calamita g) Beach slag deposit from early mining activities along the Baratti Gulf. Volume n° 2 - from B16 to B33 n° 2 - from Volume

9 - B18 Volume n° 2 - from B16 to B33 B18 - B18 Dünkel (2002);(B):Torrini (1990).Thevertical dashedlinesindicatedeformation episodes. Figure 10-Paragenetic sequencesoftheCapoCalamitaironskarndeposit.(A): Leader: M.Benvenuti (“Campiglia Ridge”)borderedby highangleN-Sand described asaN-Strendingwedge-shapedhorst Unit sequencecropoutinthisarea,whichcanbe lage (Fig. 11).Several formationsofthe Tuscan 2 kmnorthofCampigliaMarittima(Livorno) vil- The oredepositsof Valle del Temperino, arelocated Geologic framework Campiglia Marittima mation ofskarnbodies. related apliticdikes (6.2-5.0Ma),aswellthefor- the emplacementofPorto Azzurro intrusionand concentration couldhave preceded(atleastinpart) et al.(2001)suggestthattheprimarystageofiron deposits (Del Tredici, 1990; Torrini, 1990), Tanelli and theresultsobtainedforCalamitaPeninsula titative dataareavailable (cf.Lattanzietal.,1994), the regional framework, forwhichmuchmorequan- (Lippolt etal.,1995).However, taking intoaccount i.e., thesametimespanasPorto Azzurro stock and K/Arageofassociatedadularia,respectively), 0.4 and5.32±0.11Ma(U+ThvsHeageofhematite Terranera andRioMarinadepositfall between6.4± estimates ofthehematite+adulariaassemblagesfrom 1998) arestilllargely unpublished.Radiometricage 1990; SassiNeri:Del Tredici, 1990; Terranera: Seeck, research onspecific deposits(CapoCalamita: Torrini, deposits aremostlyincompleteandresultsofsome understood. Descriptive modelsfortheindividual long, 1,5kmwideand300mthick (Rodolico,1945; thermometamorphic aureole,approximately5km Massiccio” formation)ismarked byaN-Strending the hostrocks(mainlyrepresentedby“Calcare compositions (Lattanzietal.,2001). The contactwith rocks encounteredindrillholeshave granodioritic ai Marmistockplotinthesyenogranitefield; some Borsi etal.(1967).MostchemicaldatafortheBotro is the“GranitodiBotroaiMarmi”,datedat5.7Maby ic body, croppingoutintheCampigliaMaritimaarea mediate composition. The earliestemplacedmagmat- were emplaced,mostlywithanoverall acid tointer- Several kindsofbothplutonicandvolcanic bodies Marittima areaintheLateMiocene-Lower Pliocene. Magmatic activity stronglyaffected theCampiglia 1967; Costantinietal.,1993;Bossio1993). deposits (Giannini1955;GianniniandLazzarotto, sediments, consistingofalluvium,fluvialandbeach are thenunconformablyoverlain byQuaternary of UpperJurassictoEoceneage. The lattersequences consisting ofcalcareous,marlyandshalyturbidites allochthonous “Ligurian”and“Subligurians”Units, Unit formationsaretectonicallyoverthrust bythe gocene turbiditicsandstone(“Macigno”). The Tuscan sic massive limestone(“CalcareMassiccio”)toOli- which belongtothe Tuscan Unit,rangingfromLias- Campiglia Ridgeismadeupofseveral formations, margins, respectively (Acocellaetal., 2000). The NW-SE trendingfaults onthewesternandeastern SKARN DEPOSITS IN SOUTHERN TUSCANY AND ELBA ISLAND CENTRAL ITALY B18

Fig. 11 - Geological map of the Campiglia Marittima district (modified after Tanelli et al., 1993). Key to symbols: (1) Neoautochtonous (Quaternary); (2) Magmatic rocks: quartzmonzonites (~), quartzlatites (Ü), porphyries (L); (3) Ligurian and Subligurian Units; (4) Tuscan Unit (Middle Jurassic-Oligocene): Posidonomya Marls, Radiolarites, Polichromous Schists, Macigno Sandstone; (5) Tuscan Unit (Lower Jurassic): “Calcare Massiccio” (Massive Limestone) partially metamorphosed to marbles (shaded areas), Reddish Limestone with Ammonites, Cherty Limestones; (6) Tuscan Unit (Lower-Middle? Trias) stratified dolomitic limestomes metamorphosed to grey marbles; (7) ilvaite-hedenbergite skarns (Cu,Pb,Zn±Sn) ; (8) diopside skarns (Cu,Fe±Sn); (9) Fe gossans; (10) supergene (?) Fe oxyhydoxide deposits; (11) Fe oxyhydroxide±cassiterite (supergene/placer) deposits;

Costantini et al., 1993). The dominant calcite-tremo- ferentiate, with intermediate silica contents, high Mg- lite-diopside skarn assemblage suggests emplacement V (64-71), Ni and Cr, and relatively low Al2O3 and conditions characterized by temperatures F500°C and Na2O contents (Peccerillo et al., 1987). All the fertile pressures F1 kb (Barberi et al., 1967). skarn bodies exploited in the Campiglia Marittima Between 5 and 4 Ma, several swarms of porphyry district are closely related to the “Green Porphyry”. B16 to B33 n° 2 - from Volume dikes intruded the eastern part of the Campiglia The “Yellow Porphyry” and the quartz-monzonitic area (Peccerillo et al., 1987). According to Rodolico porphyry are acidic in composition (i.e., very similar (1931) and Barberi et al. (1967), three types of dikes to the the “Botro ai Marmi” intrusion), and display can be distinguished: quartz-monzonite, monzonitic a strong potassic alteration. The extensive degree of (also called “Green Porphyry”) and potassic alkaline alteration of the Campiglia porphyry dikes makes it porphyries (“Yellow Porphyry”). The “Green Por- difficult to establish whether the quartz-monzonite phyry” (“Porfido Verde”), also known as “augitic and “yellow” porphyries are both evolved products porphyry”, represents a diopside-bearing mafic dif- from the “Green Porphyry” or represent independ-

11 - B18 Volume n° 2 - from B16 to B33 B18 - B18 Leader: M.Benvenuti 4.4 Ma(Ar ing toPinarellietal.,1989)wereeruptedatabout Vincenzo rhyolites(actuallyquartz-latitesaccord- To thenorthofBotroaiMarmiintrusion,San with caution. (1967) fromthe Yellow Porphyry, shouldbeviewed reason, theageof4.3Ma,obtainedbyBorsietal. ent magmas(Peccerilloatal.,1987).For thesame The Valle del Temperino depositsoccurinanarea Green porphyrydikes. sion ofthealreadymentionednetwork of Yellow and more extensive, thoughnot outcropping,parentintru- the BotroaiMarmigranitestock,but insteadtothe the skarnoresofCampigliaareaarenotrelatedto Botro aiMarmiand/orrelatedintrusions.However, amorphism oftheLiassic“CalcareMassiccio”by enclosed inwhitemarbles,derived fromcontactmet- ( the Cu(Pb-Zn)orebodiesfrom Valle del Temperino with galena>sphalerite:e.g.,Cava delPiombo)and area of Valle deiLanzi(predominantPb-Zn,mostly can besubdivided betweenthoseoutcroppinginthe The skarn-sulfide depositsofCampigliaMarittima and rocksarealsominedinthedistrict. intrusion ( minor skarnoccursintheimmediateproximityof tial associationwith(4-5Ma?)porphyrydikes; only E andNEoftheBotroaiMarmistock,instrictspa- Cipriani and Tanelli, 1983). These depositslie1-2km inferred reserves ofabout700,000tons:datafrom at 4%Zn,2%Pb,0.8-1%Cu,and20-70g/t Ag, (with trict wereestimatedtobeintheorderof250,000tons Generale Mineraria”of1975,thereserves inthedis- can timesuptoafew decadesago.Inthe“Relazione al. 1980),whichhave beenexploited sincepre-Etrus- for Cu-Pb-Zn(±Fe,Ag,Sn)skarndeposits(Corsiniet The CampigliaMarittimaareahaslongbeenknown Ore geologyandmineralogy rhyolites. piglia dikes aswellextrusion oftheSan Vincenzo slip lineamentsandprobablycontrolledtheCam- Pliocene extensional tectonicsreactivated thestrike- the emplacementofBotroaiMarmiintrusion. western margin oftheCampigliaRidgefavoured formed duringright-lateralstrike-slip faulting onthe According to Acocella etal.(2000)areleasingbend Ferrara etal.,1989). possible calcalkalineaffinity (Pinarellietal.,1989; amounts ofsubcrustal,mafic-internediate meltof a crustal“anatectic”meltandminorbut significant 1994). They probablyresultedfrommixingbetween Fig. 11).Bothskarncomplexes arecompletely Fig. 11 40 /Ar 39 ). A numberofindustrialminerals radiometricage:Feldsteinetal., of about0.4Km crystals ofmagnetitewithquartz andtracesofpyrite, of a1mthick,massive aggregate ofcoarsesubhedral deepest levels oftheskarn-sulfide deposit;itconsists (Fig. 12). The magnetitezoneoccursonlyinthe Porphyry andthemetamorphosedLiassiclimestone ilvaite andhedenbergite occurbetweentheGreen mineralization, namelywithprevailing magnetite, According toCorsinietal.(1980),threezonesof and insmallgossans. als areonlypresentintheupperlevels ofthemines galenobismutinite (Tanelli, 1977). Supergene miner- (traces), arsenopyrite, bismuthinite,mackinawite and rhotite, sphalerite,galena,pyrite, magnetite,hematite Most commonoremineralsincludechalcopyrite, pyr- abundant inassociationwiththe Yellow Porphyry. Silvestro (Fig. 13d; Table 1 gite-johannsenite seriesoccursnearRoccaSan member johannseniteofthesolidsolutionhedenber- and ferroactinolite(Bartholomé&Evrard,1970).End epidote, andtracesofandradite,rhodonite,fluorite hedenbergite-johannsenite pyroxene, quartz,calcite, (Table 1;upto 9.5wt%MnO,afterRodolico1931), The skarncomplex consistsofmanganoanilvaite and K-feldsparassociation( veinlets bearingthecalcite-epidote-quartz,K-mica the orebodies,andiscrossedbysmallmineralized 12). The latterseemstobecompletelyembeddedin strictly associatedwiththe“GreenPorphyry” ( southeast elongatedmasses,whichappeartobe del Temperino consistsoftwo west-northwest-east- and Corsinietal.(1980),theskarncomplex of Valle to 50ma.s.l. According toCorsini& Tanelli (1974) if onasmallscale,fromthesurface at250mdown Figure 12-Schematic crosssectionofthe Valle del Temperino deposit (after Corsinietal.,1980) 2 wherethey have beenmined,even Fig. 13a). ). Epidoteisparticularly Fig. SKARN DEPOSITS IN SOUTHERN TUSCANY AND ELBA ISLAND CENTRAL ITALY B18

Fig. 13 - Photographs of Campiglia Marittima skarn features: a) The “green porphyry” dike (underground mine gallery, V. Temperino) b) Coarse- grained columnar hedenbergitic pyroxene (underground mine gallery, V. Temperino) c) Sphalerite-rich stope fill from historic mining when Zn was not an economic commodity (underground mine gallery, V. Temperino) d) Johannsenite from Grotta Johannsenite e) Contact between banded johannsenite skarn and marble from Grotta Johannsenite f) Metasomatic banding of Fe-Mn oxyhydroxides and carbonate from Campo alle Buche g) Distal johannsenitic pyroxene vein and dendritic Mn B16 to B33 n° 2 - from Volume oxide veinlets in marble near Rocca San Silvestro h) Distal hydrothermal breccia with near Rocca San Silvestro

13 - B18 Volume n° 2 - from B16 to B33 B18 - B18 Leader: M.Benvenuti ore assemblageconsistsofchalcopyrite, pyrite, iron- (27.6 wt%MnO)atthecontactwithmarbles. The the coreofskarnbody, toquitepurejohannsenite ed, frommanganoanhedenbergite (2.6wt%MnO)in the Mncontentofclinopyroxene hasbeenrecord- stone sideofthecomplex ( the skarnmineralsweregrowing toward thelime- and enclosedwithintheskarnbodies,showing that with longfibers ( radiating andconcentricaggregates ofclinopyroxene bergite zoneischaracterizedboth bywell-developed, moles% FeS(Corsiniand Tanelli, 1974). The heden- and hasanironcontentrangingfrom17.2to21.3 ite. Sphaleriteisquitelateinthesulfide paragenesis replaced bytheothersulfides, aswellbymagnet- seems tobeoneoftheearliestmineralphases,andis pseudomorphs afterlamellarhematite.Pyrrhotite sphalerite. Magnetiteoccursheregenerallyonlyas pyrrhotite, withminormagnetite,pyrite andFe-rich typical oreassemblageconsistsofchalcopyrite and directly atthecontactwithGreenPorphyry: pyrrhotite andchalcopyrite. The ilvaite zoneoccurs of the Valle delTemperino skarn-sulphide(afterCorsinietal.1980,Fig. 4) Figure 14-Summarydiagramofthespace-timerelationshipsasshown bythemainminerals Fig. 13b),andbymarblescorroded Fig. 13e ). An increasein hedenbergite andviceversa, indicatesthatthesetwo copyrite andpyrrhotite. The replacementofilvaite by The bandedrockscontainilvaite, hedenbergite, chal- cipitate, followed bysphaleriteandfinally bygalena. Cu-Pb-Zn sulfides, chalcopyrite beingthefirst topre- place. The thirdstagebroughttothedepositionof stage, crystallizationofilvaite andhedenbergite took a secondgenerationofpyrite (II).Duringthissecond generation (I)was formed,thenpyrrhotite, and then stage tookplace.Inthesecondstage,afirst pyrite quickly reducedagaintomagnetitebeforethesecond hematite toformatfirst intheouterzones,andtobe changes ofphysicochemicalparametersallowed tion ofironoxides,mainlymagnetite. Temporary stages ( stage process,whichcanbedivided intothreemain (Corsini etal.,1980)appearstohave beenamulti- The oremineraldepositionat Valle del Temperino and andradite. minerals arequartz,calcite,epidote,minorilvaite lamellar magnetiteandhematiteremnants.Gangue poor sphaleriteandfinally ofgalena,withonlyminor Fig. 14). The first corresponds to thedeposi- SKARN DEPOSITS IN SOUTHERN TUSCANY AND ELBA ISLAND CENTRAL ITALY B18

minerals overlap. noso”), both of them containing evaporites. As mentioned above, absolute age measurements A different type of mineralization, consisting of lay- and the geological reconstruction of the Campiglia ered iron minerals (mainly goethite, hematite, siderite area, indicate a Pliocene age for the formation of the ± marcasite, chlorite) and sparry calcite crystals, with Valle del Temperino skarn-sulfide complex. Regional apparently karstic features, occurs in the old min- stratigraphy indicates that the maximum thickness of ing locality of Campo alle Buche (Fig. 13f). This the sediments over the “Calcare Massiccio” during deposit has been exploited by both underground and the Pliocene was about 1500 to 2000 m (Bartholomé open pit mine workings in the XIX-XX centuries, & Evrard, 1970). Based on mineralogy and S-iso- although there are evidences of older (Etruscan?) tope data Corsini et al. (1980) estimated that sulfide mining activity. According to Bertolani (1958) skarn deposition at Valle del Temperino occurred during sulfide mineralization occurs at some depth below decreasing temperatures from about 400 °C to 250 the calcite-iron oxyhydroxides mineralization. The °C. They also sugget that sources of sulfur for these Campo alle Buche deposit has been regarded as deposits, may have been sulfate (Ä34S = 12÷14.6 ‰) a gossan-type ore by early authors (e.g. Ciampi, and/or sulfide (Ä34S = 5÷12 ‰) associated with the 1910); alternatively, it can be considered the product Paleozoic/Mesozoic basement formations (namely, of late-stage, low-temperature hydrothermal fluids the “Filladi di Boccheggiano” and/or “Calcare Caver- still related to the Pliocene magmatism which was responsible of the emplacement of the Cu-Pb-Zn(Ag,Sn) skarn bodies of the Campiglia Marittima district (cf. Tanelli, 1977; Tanelli et al., 1992).

A brief review of mining and metallurgy in Etruria Mineraria Mineral resources of Tuscany have long been exploited, at least since Chalcolithic times, and were very important in the development of Etruscan and Roman civilizations; in medieval times, numerous city- states derived important revenues from mining exploitation and metal production. The same applies, on a larger scale, after the unification of Tuscany under the Medici govern- ment in the 16th century. Even in more recent times some mineral resources, such as the Elba iron ore, were successfully exploited. However, despite their economic importance, the archaeology and history of the Tuscan mines has B16 to B33 n° 2 - from Volume not been well studied. Recently, a joint project carried out by the Dipartimento di Scienze della Terra of Firenze and the Dipartimento di Storia Medievale of Siena with

Table 1 Representative electron microprobe analyses of skarn minerals

15 - B18 Volume n° 2 - from B16 to B33 B18 - B18 Leader: M.Benvenuti century BC)andRoman(2 area duringthe1 cially, but notexclusively, iron)intheMediterranean A key roleintheproductionandtradeofmetals(espe- by ancientminers. minor occurrences,whichcouldhave beenexploited known mineralresources,frommajordepositsto These studiesprovide adetailedoverview ofall eralogical andhistorical-archaeologicalbackground. 1995), fromthedoubleperspective oftheirgeo-min- Colline Metallifere (Mascaro etal.,1991)withparticularattentiontothe review ofthemineralresourcesin Tuscany asawhole Regional Government), hasprovided anexhaustive the financial supportofRegione Toscana (Tuscany of Populonia-Baratti (modifiedafterBenvenuti etal.,2000) Figure 15-Sketch mapofthearchaeometallurgical site tant metalproductioncentreduringEtruscan(7 Etruscan town ofPopulonia.Populoniawas animpor- 40,000m area. The hugeheapsofslags(probablyinexcess of Cu-Pb-Zn-Fe-Ag-Sn oresoftheCampigliaMarittima deposits ofeasternElbaIslandandthepolymetallic its strategic location,midway betweenthelarge iron AD) times.Suchaprominentrolewas mainlydueto 3 ), discharged along theforeshoreofGulf st MillenniumBC,was playedbythe district(CuteroandMascaro, nd centuryBC–1 st century th -3 rd 3 some metallurgical scraps(Campo VI), datingtothe • distinguished, be relatedtodifferent metallurgical steps,have been • (Fig. 9g), the area,particularlyfromslagbeachdeposits coeval) coppermetallurgy canalsobedocumented in iron production,theexistence ofanearlier(andpartly gical depositsatBaratti-Populoniacanbeascribedto the mostlikely source areaforsmeltedcopperand, e.g. atMonte Valerio); thelatterdistrictappearstobe Marittima district(whereFe-Snoresarecommon, Elba and,toalesserextent, fromtheCampiglia analyses indicatethatironorescamemainlyfrom content ofsomeironslags: • per, i.e., byaddingunsmeltedcassiteritetorefined cop- data, bronzewas probablyobtainedbycementation, bronze production.Inagreementwitharchaeological rd two different typesofcopperslags,whichcould trace elementgeochemistry(e.g.,tinanomalous the mineralogicalandcompositionalfeaturesof centuryBCorearlier, provide evidence oflocal relationships, morphological, From theanalysisofstratigraphic be brieflysummarizedhere. 2003b, withreferences),andwill (Benvenuti etal.,2000,2003a, have beenpublishedelsewhere The mainresultssofar obtained the EtruscanandRomanperiods. provenance ofsmeltedoresin copper andtin),aswellonthe and non-ferrousmetals(mainly of metallurgical activities foriron establishing thetypesandextent been undertaken, withtheaimof ti beachdeposit: Casone, Campo VI andtheBarat- zone (PoggiodellaPorcareccia, the Populonia-Barattiindustrial four mainexcavation sitesin a detailedresearchprogramon Voss 1988).Inthelasttenyears, half amilliontonnesaccordingto sands tonnesofironbloom(upto iron productionofsomethou- of Baratticoulddocumentatotal • be concluded: cal materialsthefollowing can chemical featuresofmetallurgi- mineralogical, textural, and although mostarcheometallur- Fig. 16a ) andPb-isotope Fig. 15)has SKARN DEPOSITS IN SOUTHERN TUSCANY AND ELBA ISLAND CENTRAL ITALY B18

possibly, for tin. Trevisan (1950)’s Complex III rocks, preferentially at the contact between the Rio Marina Formation, or the Field Itinerary Verrucano, and the overlying calcareous levels (“Cal- Elba Island (August 18, 2004) care Cavernoso” Auctt.). According to some authors (cfr. Gillieron, 1959) at Rio Albano the setting of the Stop 1.1: orebodies is structurally controlled. Nevertheless, at The ilvaite-hedenbergite skarn bodies of least in the Valle Giove area, Deschamps et al. (1983) Torre di Rio discovered a pyrite-bearing horizon within Verru- The area is characterized by a NW-plunging sequence cano Fm. (“Schistes verts minéralisés”), which they of marbles and calc-schists (Fig. 9e) of variable size interpreted as a relic (syngenetic) of an iron protore. with minor grey/greenish quartzitic phyllites. They In the Rio Marina and Rio Albano deposits hematite belong to the Acquadolce Unit of Bortolotti et al. (“specularite”) is the main ore mineral which may (2001). Syn-metamorphic tight to isoclinal folds with show either a typical lamellar-micaceous habits or a pervasive axial plane schistosity are well exposed. flattened, rhombohedral crystals, often covered by Deino et al. (1992) obtained a 40Ar/39Ar radiomet- iridescent films of iron hydroxides. Pyrite is also ric age of 19-20 Ma for this schistosity. A 1-metre common, predominantly as pyritohedra, although thick, grey/whitish calc-schist level is well exposed octahedra or cubes have been observed as well. Exog- along the road. Moving southwards from the Appi- enous limonites, in massive or concretionary (some- ani Clock-Tower and along the coast, we can easily times stalactitic) forms may locally constitute the observe the gradational passage from calc-schists to main ore minerals, especially at Rio Albano and other the hedenbergite-ilvaite-epidote skarn bodies. Skarn mineral showings to the north. It should be noted that bodies consist of almost monomineralic masses of in the 1950’s-60’s underground mine workings partly garnet-epidote, hedenbergitic pyroxene and ilvaite exploited a hematite+pyrite orebody associated with (Fig. 9b), with associated quartz, chlorite and minor skarn silicates, known in the literature as “Rio Marina amounts of iron minerals (magnetite, pyrite and pyr- profondo” (= Rio Marina deep body”). rhotite), which justified limited exploitation activity in the past. Mesoscale textures clearly indicate that Stop 1.3: the replacement of minerals in the calc-schists by Along the Calamita mine road skarn minerals, occurred preferentially along the After leaving Capoliveri, we pass by the tectonic con- schistosity planes of the original rock, as pointed out tact between the Flysch Unit and the Porto Azzurro by Lotti (1886,pp. 205-206). Ilvaite is here exception- Unit, constituted by Mt. Calamita Fm. (Palaeozoic ally abundant (Fig. 9d): it occurs in beautiful, centi- grey to brown micaschists, phyllites and quartzites metric black, prismatic crystals, with typical vertical locally intruded by aplitic dikes) and the Barabarca striae and submetallic lustre. This is the type locality Fm. quartzites (Middle-Late Triassic). Just above the where ilvaite (so called after the Latin name of Elba sea-village of Pareti (down the cliff) we can observe Island: “Ilva”) was first discovered and described in along the road some lenticular dark green bodies 1802 (Franchini et al., 2002). of amphibolites (tremolite + andesinic plagioclase + chlorite ± sphene, apatite) which Puxeddu et al. Stop 1.2: (1984) referred to WPB metabasites. We finally reach The Rio Marina mining area the former Calamita Mine Headquarters (“Palazzo”), (seen from Torre di Rio) which is one of several open pit and underground Fe Looking from the Appiani clock-tower to the NW, mines along the coast (Fig. 9a). the landscape is dominated by the Rio Marina mines (from the left: Bacino, Zuccoletto, Valle Giove and Stop 1.4: B16 to B33 n° 2 - from Volume Vigneria mines) and by the Torre del Giove hill (351 The Calamita mine: northern stopes m), with the ruins of a castle of the XVIth century. In this area thermometamorphic carbonate rocks The Rio Marina ores are hosted in the Permo-Car- occur. They consist mainly of stratified dolostones boniferous (Rio Marina Fm.) and in the Triassic and dolomitic limestones, grey-whitish in colour, Verrucano Auctt.) metasiliciclastics of the Monti- with rare phyllitic intercalations (Late Triassic?). To ciano-Roccastrada Unit. The iron deposits of Rio the east, along the road, there are outcrops of whitish Marina (as well as Rio Albano, to the north) consist saccharoid marbles (Hettangian?), massive or poorly of stratiform, massive or vein-like bodies, hosted by stratified, with local grey dolomitic levels. These car-

17 - B18 Volume n° 2 - from B16 to B33 B18 - B18 Leader: M.Benvenuti “organic” mineralslike minguzzite(K have been reported. At Vallone Alto, moreover, rare of malachite,azurite,atacamite,paratacamite,etc. Cave) site,justbelow theU-shapedtrench,veinlets magnetite. At theso-called“GrottaRame”(=Copper were subsequentlyexploited almostexclusively for involved thelimoniticgossanofironores,which beginning ofthepastcentury production mainly main stopes(Vallone Bassoand Vallone Alto). At the easily visiblefromthemineroadseparatestwo 112 m.a.s.l.),excavated inthemetacarbonatesand (Punta dellaCalamita). A U-shapedtrench(altitude: of whichcanbeobserved justontheseaward cliffs hedenbergite-ilvaite skarnbodies,beautifulexamples focussed onseveral magnetitelensesassociatedwith visited duringthisfield trip)theexploitation activity In thesouthernstopesofCalamitaMine(nottobe (Torrini, 1990). between thegarnetskarnandmagnetitelenses chalcantite, etc.)werelocallyexploited atthecontact (pyrrhotite, pyrite, chalcopyrite ±malachite,azurrite, nite andpyrite. Moreover, massesofFe-Cusulfides amounts ofsphalerite,chalcocite,arsenopyrite, bor- tite). Additional phasesincludegoethiteandtrace massive bodiesofmagnetite(±kenomagnetite, hema- skarns describedabove, andconsistedoflenses exploited oreswereassociatedwithbothtypesof etta, Albaroccia, Macei,Polveraio, CotiNere. The is subdivided intoseveral mine-working areas:Civ- magnitude. The northernsectoroftheCalamitaMine iron reserves ofapproximatelythesameorder in theperiod1860-1920byopenpitmining,with least 2milliontonnesofironorehadbeenexploited Etruscan?-Roman times;accordingtoPullé(1921)at Mining activity atCalamitaprobablydatesbackto (Meinert 1992,1995,1997). zones (Fig. 9c,f the proximalsouthwesttopyroxene-ilvaite indistal Calamita Fm. The skarniszonedfromgarnet-richin tact betweenmetacarbonatesandtheunderlyingMt. (Torrini, 1990).Skarnbodiesmainlyoccuratthecon- most abundant, andanilvaite-hedenbergite skarn skarn: agarnet(andradite)-skarn,quantitatively the which ledtothedevelopment oftwo maintypesof latter have beenaffected byextensive metasomatism, the Mt.CalamitaFm.andcarbonaterocks. The the quartzitesofBarabarcaFm.occurbetween zoic cover oftheMt.CalamitaFm.:moretowest, bonate rocksmayrepresentpartoftheoriginalMeso- by Cocco,Garavelli (1954). H 2 O) andoxalite(FeC ), asistypicalofmostskarnsystems 2 O 4 · 2H 2 O) have beenreported 3 Fe(C 2 O 4 ) 3 ·3 Campiglia Marittimadistrict(August 19,2004) abundant concentrationsofepidotealsooccur. veins. (Fig. 13h tures like ahydrothermalbrecciaandsmallMn-oxide envelopes ( an outcropofthe“Yellow Porphyry”,with thinskarn road tothelimestonequarries,itispossibleobserve At thebaseofRoccaSanSilvestro, alonganinternal granite inthebackground. working inthelocalmines),withBotroaiMarmi from thegerman can enjoy thepanoramaof Valle deLanzi(Lanzi= in thisarea.FromthetopofRoccaSanSilvestro one and silver, derived fromtheearlymetallurgical works found alsosomeremnantsandslagswithcopper, lead als fromshallow skarnsandgossans.Herehave been medieval villagebuilt aroundtheminingofbasemet- We willstarttheascenttoRoccaSanSilvestro, anold nearby hydrothermal breccia vestro; “Yellow Dike” with skarn envelope and Valle deiLanzi. View from theRoccaSan Sil- Stop 2.1: whole area. books onthisthemeandthefauna andfloraofthe in asmall,but wellorganized shoparesoldseveral the miningdistrictsarealsoamongexhibits and taken fromtheCu-andZn-Pbmines.Oldmapsof contains somespectacularmineralogicalsamples ogy, mineralogyandmining historyofthisareaand Temperino. The Museumisdedicatedtothegeol- set upinoneoftheoldminebuildings at Valle del We willvisitthesmall,but very interestingMuseum, Mineral Museumof Valle del Temperino Stop 2.3: Massiccio” contactmetamorphism( bands, replacingthemarblesderived from“Calcare of Johannseniteoccurringaspinkishrosettesand very fine specimens(donothammertheoutcrop!!!) (Fig. 11).Herewecanobserve theoccurrenceof (walk) totheclassicallocalityofGrottaJohannsenite From theupperpartof Valle deiLanzi,wedrive Grotta Johannsenite (Gallerione) Stop 2.2: solution. members ofthehedenbergite-johannsenite solid assemblage andrepresentshereoneoftheend- Mn-pyroxene isatypicalcomponentoftheZn-skarn Fig. 13g),aswelldistalalterationfea- ) Around the“Yellow Porphyry”, Landsknechte , whowereattimes Fig. 13d,e ). This SKARN DEPOSITS IN SOUTHERN TUSCANY AND ELBA ISLAND CENTRAL ITALY B18

Stop 2.4: Underground Mine Valle del Temperino: Green Dike and Hedenbergite skarn This Stop will take us underground in one mine gal- lery of the copper mine of Valle del Temperino. The mine is not active anymore, having been converted into a popular tourist attraction, and it’s walls show the characteristic green patina of supergene copper minerals.. Nevertheless, there are still many interest- ing sites in the mine where geologists can observe the geological occurrence of the “Green Porphyry Dike” (Fig. 13a) thought to be genetically associ- ated with mineralization, the marble host rocks, and

Figure 17 - Location of the principal mine workings at Calamita Mine (after Calanchi et al., 1976). Legend: 1. Civetta; 2. Albaroccia; 3. Nuova Zona; 4. Macei Alto; 5. Polverio; 6. Coti Nere; 7. Le Piane; 8. Punta Rossa; 9. Macei Basso; 10. Vallone Alto; 11. Vallone Basso. hedenbergite skarns (Fig. 13b) with sphalerite and chalcopyrite. It is interesting to note that many of the old workings were backfilled with high grade Zn-ore, also occurring in the skarn, which was not economic in pre-industrial times (Fig. 13c). Stop 2.5: Mn-vein outcrops near mine exit along road to the “Gran Cava” pyroxene locality Out of the underground adit, we walk up a small mine road characterized by interesting exposures of distal Mn-oxide veins and internal sediment-filled frac- tures, as well by hydrothermal breccias that directly overlie the underground ores. Such distal alteration features are common in the periphery of most skarn districts in the world. The road will bring us to the

Figure 16 - Photomicrographs of archaeometallurgical “Gran Cava”, a small open pit also known as “Cava B16 to B33 n° 2 - from Volume samples from Populonia-Baratti: a) Backscattered Etrusca”, so called because it is thought to have been electron image of partially smelted mineral charge exploited already in Etruscan times. There we will showing micrometric globules of Fe-Sn phases (white), observe coarse-grained hedenbergite pyroxenes and sometimes surrounded by Fe-S phases. The groundmass a well-exposed skarn-marble contact. is composed of a glassy matrix and acicular crystals of hedenbergitic composition. Bar = 10 µm. b) Reflected light image of sulphidic droplets in (type-A) copper slags. Stop 2.6: Abbreviations: cc = chalcosite-djurleite; cv = covellite. Fe-Oxides at Campo alle Buche Width of field: about 500 µm. Our last outcrop is situated at the westernmost

19 - B18 Volume n° 2 - from B16 to B33 B18 - B18 Leader: M.Benvenuti the twentiethcentury. The mineralizedlithotypecon- was exploited forironoreuntiltheearlydecadesof of “CampoalleBuche”=literally“field withholes” with aNNE-SSWtrendingfault. The oldminingarea extremity oftheCampigliaarea,incloseproximity (modified afterCorsiniandTanelli, 1974) Temperino depositarea Figure 18-Schematic geologicmapofthe Valle del Figure 19-Proposedreconstruction ofEtruscanironfurnacesfromBaratti(afterBenvenuti etal.,2003b). venuti etal.,2000). Type-A types ofcopperslags:type-Aandtype-Bslags(Ben- beach slagdepositledtotherecognitionoftwo main on theirsurfaces. PreliminaryanalysesoftheBaratti spots (duetoexogenous alterationofcoppersulfides) copper slags,clearlyidentifiable bythegreenish bottom portionofthedepositmostlyconsists chalcocite/dijenite) (seeFig. 16b copper oxides(cuprite)andsulphides(covellite, droplets, mostlyfine aggregates ofmetalliccopper, magnetite, andminorglass,withabundant metallic ized byagroundmassofdominantolivine, pyroxene, (August 19,2004) The archaeometallurgical siteofPopulonia-Baratti that wereassociatedwithskarnformation. dizing environment, ofthesamehydrothermalfluids probably representsthedistalproduct,inamoreoxi- pi,. 1910). The CampoalleBuchemineralization as gossan-like depositsbyearlyauthors(e.g.Ciam- chlorite) withcalcitecrystals(Fig. 13f als (mainlygoethite,hematite,siderite±marcasite, sists hereofalternatingbandslaminatedFeminer- icagdoe neoinltrae( discharged over anerosionalterrace poorly cementedheapofEtruscanandRomanslags in ordertoobserve theremainsofslagdeposit,a gico diBaratti. We leave thebus andreachthebeach the roadtoPopulonia. We entertheParco Archeolo- district, wemove backtowards Piombino,and take At theendofourvisittoCampigliaMarittima The beachslagdepositatBaratti Stop 2.7: copper slagsarecharacter- ). Intype-Bcopper Fig. 9g).The ). Interpreted SKARN DEPOSITS IN SOUTHERN TUSCANY AND ELBA ISLAND CENTRAL ITALY B18

slags magnetite and cuprite are much less abundant, Bibliography metallic copper is consistently absent, and the metal- ABBATE E., BORTOLOTTI V., PRINCIPI G. (1980) lic globules (100-150µm in size) are mainly copper- – Apennine ophiolites: a peculiar oceanic crust. In: iron-sulphur phases (matte) showing fine exsolution Rocci, G. (ed), Tethyan Ophiolites, Western Area, textures. These features could indicate a multi-stage Ofioliti, Spec. Issue, vol.1, 5-96. copper smelting process, with type-B slags belong- BARBERI F., INNOCENTI F., MAZZUOLI R. ing to an earlier (matte production) stage than type-A (1967) – Contributo alla conoscenza chimico-petro- slags. grafica e magmatologica delle rocce intrusive, vulca- The largest portion of the slag deposit consists of iron niche e filoniane del Campigliese (Toscana). Mem. slags of different kinds (furnace slags, tapped slags, Soc. Geol. It., 6, 643-681. furnace conglomerates). The iron slags are mainly a BARTHOLOMÈ P., EVRARD P. (1970) – On the silicate groundmass of fayalitic olivine (with up to genesis of the zoned skarn complex at Temperino, 1.45% CaO) in an iron-rich interstitial glassy matrix Tuscany. In: Problems of hydrothermal ore deposi- (up to c25 wt.% FeO), which in itself is normally a tion; the origin, evolution, and control of ore-forming eutectic of anorthite and fayalite. Wüstite, magnetite, fluids. I.U.G.S., Series A(2), Stuttgart, 53-57. hercynite and partially smelted, relic phases like BENVENUTI M., CHIARANTINI L., NORFINI quartz, hematite and scheelite (?), occur in variable L., CASINI A., GUIDERI S., TANELLI G. (2003a) amounts, and are especially abundant in furnace - The “Etruscan tin”: a preliminary contribution slags. Fayalite crystals in tapped slags occur as from researches at Monte Valerio and Baratti- small laths associated with micrometric dendrites of Populonia (southern Tuscany, Italy). Colloqium on wüstite, while in furnace slags both minerals show a «Archéométallurgie: le problème de l’étain à l’origine significant increase in size. Unlike tapped and furnace de la métallurgie », XIV Congr. U.I.S.S.P., Liège, 2- slags, furnace conglomerates show abundant relics of 8 septembre 2001, Archeopress, BAR [in press]. hematite and quartz and a more silica-rich (and FeO- BENVENUTI M., MASCARO I., COSTAGLIOLA poor) glassy groundmass. Iron slags almost invariably P., TANELLI G., ROMUALDI A. (2000) – Iron, contain droplets of metallic iron. Some iron slags are copper and tin at Baratti (Populonia): smelting pro- enriched in tin and may contain micrometric globules cesses and metal provenances. Historical Metallurgy, of iron-tin alloys, approximating FeSn and FeSn2 in Historical Metallurgy Soc. Ed., London, England, 34 composition (Fig. 16a). (2), 67-76. Fragments of smelting furnaces are also commonly BENVENUTI M., MORELLI F., CORSINI F., present in the Baratti beach deposit. They are made MASOTTI A., LATTANZI P., TANELLI G. (1994) up of local Macigno sandstone and baked clay, possi- - New isotopic data on the pyrite (±Cu-Pb-Zn) deposit bly derived from the terrigenous Canetolo formation of Campiano (southern Tuscany). Mem. Soc. Geol. (see Fig. 18). The baked clays show characteristic It., 48, 691-697. colour zoning from red to black, corresponding to BENVENUTI M., PECCHIONI E., CHIARANTINI increasing reducing atmosphere and temperatures in L., CHIAVERINI J., MARIANI A., MASCARO the furnaces. The reconstruction of Etruscan (and/or I. (2003b) - An investigation on iron smelting fur- Roman?) iron furnaces proposed by Benvenuti et al. naces from the Etruscan site of Baratti-Populonia (2003b) is shown in Fig. 19. (Tuscany). Proceedings Volume of the 6th Int. Con- If time permits, we will visit some of the Etruscan gress on Ancient Ceramics (EMAC ’01), Fribourg tombs located in the nearby archeological site. (Svizzera), 3-6 Ottobre 2001 (in press). BOCCALETTI M., GUAZZONE G. (1974) – Rem- nant arcs and marginal basins in the Cainozoic devel- Volume n° 2 - from B16 to B33 n° 2 - from Volume opment of the Mediterranean. Nature, 252, 18-21. BONINI M., BOCCALETTI M., MORATTI G., SANI F. (2001) – Neogene crustal shortening and basin evolution in Tuscany (Northern Apennines). Ofioliti 26 (2a), 275-286. BORSI S., FERRARA G. & TONGIORGI E. (1967) – Determinazioni con il metodo K/Ar dell’ età delle rocce magmatiche della Toscana. Boll. Soc. Geol.

21 - B18 Volume n° 2 - from B16 to B33 B18 - B18 Leader: M.Benvenuti TAVARNELLI E.,ELTER F.M. (1993)–Geologia CANTELLI M.,MAZZANTIR.,SANDRELLIF., COSTANTINILAZZAROTTOMAC- A., A., 30: 337-345. Alps (northern Tuscany, Italy). Mem.Soc.Geol.It., - Barite-ironoxides-pyrite deposits from Apuane CORTECCI G.,LATTANZI P., TANELLI G.(1985) Marittima, Tuscany, Italy. Econ. Geol.,75,83-96. Zn) sulfide depositof Valle del Temperino, Campiglia G. (1980)-Sulfurisotopestudyoftheskarn-(Cu-Pb- CORSINI F., CORTECCI G.,LEONE TANELLI 30, 205-221. Toscana). Rend.Soc.ItalianaMineralogiaPetrologia, della Valle del Temperino (CampigliaMarittima, microsonda elettronicadelleblendedelgiacimento CORSINI F. & TANELLI G.(1974)– Analisi alla terranean Archaeology, vol. 14.,127-145. of NaturalHistoryinGeneva, 4-7June,1999,Medi- of Africa andtheMediterraneanBasin, The Museum First InternationalColloquiumon The Archaeology reference to beginning ofironmetallurgy in Tuscany; withspecial CORRETTI A., BENVENUTIM.(2001)- The 10: 269-350. ferro diCapoCalamita(Elba).Rend.Soc.Miner. It., alcuni problemigeochimicirelativi algiacimentodi COCCO G.,GARAVELLI C.(1954)-Studiodi Appennine. Nature,276:604-605. tic magmatismduetoanticlockwiserotationofthe (1978) -Eastward migrationsofthe Tuscan anatec- CIVETTA L.,ORSIG.,SCANDONEP., PECER. Firenze. Acc. Tosc. Sc.Lett.“LaColombaria”,48:241-283, rarie della Toscana: notestoricheedeconomiche CIPRIANI C., TANELLI G.(1983)-Lerisorsemine- 29 (1),156-164. sulle limonitidelCampigliese.Boll.Soc.Geol.It., CIAMPI A. (1910)– Alcune recentiosservazioni 102 pp. – Miniereemineralidell’Elbaorientale.Bologna, CALANCHI N.,DAL RIOG.,PRATI A. (1976) 17-98. del Neoautoctono Toscano. Mem.Soc.Geol.It.,49, (1993) –Rassegna delleconoscenzesullastratigrafia MAZZEI R.,SALVATORINI G.,SANDRELLIF. LAZZAROTTO A., LIOTTA D.,MAZZANTIR., L.M., COSTANTINIFORESI BOSSIO A., A., Ofioliti geology oftheCentralandEasternElbaIsland,Italy. PRINCIPI G.BABBINI A., CORTI S.(2001)- The BORTOLOTTI V., FAZZUOLI M.,PANDELI E., Italiana, 86,403-410. 26 (2a),97-150. Etruria Mineraria . Proceedingsofthe . G. (1992)-Datazioni DEINO A., KELLERJ.V.A., MINELLIG.,PIALLI Geol. It.,74:53-85. che nellezoneminerariedell’isolad’Elba.Boll.Serv. DEBENEDETTI A. (1952)-Osservazioni geologi- Firenze. ralogico: aspettinaturalisticiestorico-archeologici, lifere. Inventario delpatrimoniominerarioemine- CUTERO F., MASCARO I.(1995) -CollineMetal- Suppl. n.2,1-164. Quaderni MuseoStoriaNaturaleLivorno, Vol. 13, della provincia diLivorno aSuddelfiume Cecina. FERRARA G., TONARINI S.(1985)-Radiometric nol., 51,379-388. San Vincenzo rhyolites(Tuscany, Italy).Bull. Volca- S. (1989)–Petrologyandisotopegeochemistryof FERRARA G.,PETRINIR.,SERRI TONARINI 943-958. 58, Cosmochim. Acta, rhyolite, San Vincenzo, Tuscany (Italy).Geochim. microsampling constraintsonthehistoryofaS-type G.R., HALLC.M.(1994)–Isotopeandchemical FELDSTEIN S.N.,HALLIDAY A.N., DAVIES 162 pp. dell’Isola d’Elba.Mem.Descr. CartaGeol.It.,11, FABRI A. (1887)-Relazionesulleminierediferro Volume: 317-391. (1981) -Skarndeposits.In:Econ.Geol.75° Anniv. EINAUDI M.,MEINERT L.D.,NEWBBERRY R.J. S.276. 65, (TGA), A, tectonics. TübingerGeowissenschaftliche Arbeiten ore depositsandtheirinterrelationwithMessinian DÜNKEL, I.(2002)- The genesisofEastElbairon 139(3), 257-279. granitic complex ofElbaIsland,Italy. Geol.Mag., evolution ofthelateMiocenelaccolith-pluton-dike S., WESTERMAN D.S.(2002)- The magmatic DINI A., INNOCENTIF., ROCCHI S., TONARINI Dep., 6,356-379. et lesskarnsduGinevro (Iled’Elbe–Italie).Mineral. DIMANCHE F. (1971)-Lesmineraisdemagnetite Schweiz. Mineral.Petr. Mitt.,63:149-165. connaissance desgisementsde Toscane- I.Partie 1. (Rio Marina,Iled’ Elbe,Italie).Contribution àla - Legisementdepyrite-hématite de Valle Giove J, MARIGNAC C.,MAINEB.,SAUPÉ F. (1983) DESCHAMPS Y., DAGALLIER G.,MACAUDIER sis, Università diFirenze,200pp. skarn diSassiNeri(Isolad’Elba).Unpublished The- DEL TREDICI F. (1990)-Studiodelgiacimentoa 1A, Vol. Spec.1992/2:187-192. risultati preliminari.StudiGeol.Camerti,CROP 1- dell’Unità diOrtano-RioMarina(Isolad’ Elba): 40 Ar/ 39 Ar delmetamorfismo SKARN DEPOSITS IN SOUTHERN TUSCANY AND ELBA ISLAND CENTRAL ITALY B18

geochronology in Tuscany: results and problems. tion of mineral deposits in southern Tuscany, Italy. Rend. Soc. It. Mineral, Petrol., 40, 111-124. In: M. Pagel and J.L. Leroy (Eds), Source, Transport Franchini, M.B., Meinert, L. D., and Vallés, J.M., and deposition of metals. Proceedings of the 25 years 2002, First occurrence of ilvaite in a Au skarn SGA Anniversary Meeeting, Balkema, Rotterdam: deposit: Economic Geology, v. 97, p. 1119-1126. 317-320 GIANNINI E. (1955) – Geologia dei Monti di Cam- LIPPOLT, H.J., WERNICKE, R.S., BÄHR, R. (1995) piglia Marittima (Livorno). Boll. Soc. Geol. It., 84, - Paragenetic specularite and adularia, Elba Island, 1-77. Italy: Concordant, U+Th-He and K-Ar ages. Earth GIANNINI E., LAZZAROTTO A. (1967) – Studi Planet.Sci.Lett., 132: 43 – 51. geologici di una sezione tra i monti di Campiglia LOTTI B. (1886) - Descrizione geologica dell’isola Marittima e la parte centromeridionale dei Monti d’Elba. Mem. Descr. Carta Geol. d’ Italia, 2, 254 pp. del Chianti. Atti Soc. Tosc. Sc. Nat. Mem., Ser. A, MAINERI C., BENVENUTI M., COSTAGLIOLA 78-101. P., DINI A., LATTANZI P., RUGGIERI G., VILLA GILLIERON F. (1959) - Osservazioni sulla geologia I. (2003) - Alkali-metasomatic processes at La Cro- dei giacimenti di ferro dell’Elba orientale. L’Ind. cetta raw ceramic material mine (Elba Island, Italy): Miner., X (1), 1-10. interplay between magmatism, tectonics and minera- JUTEAU M., MICHARD A., ALBAREDE F. (1986) lization. Mineral. Deposita, Springer-Verlag, Berlin- - The Pb-Sr-Nd isotope geochemistry of some recent Heidelberg, 38, 67-86. circum-Mediterranean granites. Contrib. Mineral. MARINELLI G. (1975) - Magma evolution in Italy. Petrol., 92: 331-340. In: C.H. Squyres (Ed.), Geology of Italy. Earth Sci. KELLER J.V.A., PIALLI G. (1990) - Tectonics of Soc. Libyan Arab Republic, Tripoli, p. 165-219. the Island of Elba: a reappraisal. Boll. Soc. Geol. It., MASCARO I., GUIDERI S., BENVENUTI M. 109: 413-425. (1991) – Inventario del patrimonio minerario e mine- LATTANZI P. (1999) - Epithermal precious metal ralogico in Toscana. Aspetti naturalistici e storico- deposits of Italy: an overview. Mineralium Deposita, archeologici, Firenze, Ed. Regione Toscana, 2 vv. 34, 630-638. Meinert, L.D., 1992, Skarns and skarn deposits: LATTANZI P., BENVENUTI M., COSTAGLIOLA Geoscience Canada, v. 19, p. 145-162. P., MAINERI C., MASCARO I., TANELLI G., Meinert, L.D., 1995, Compositional variation of DINI A., RUGGIERI G. (2001) - Magmatic versus igneous rocks associated with skarn deposits - hydrothermal processes in the formation of raw cera- Chemical evidence for a genetic connection between mic material deposits in southern Tuscany. Proceed- petrogenesis and mineralization: in Thompson, ings 10th Int. Symposium on Water-Rock Interaction, J.F.H., ed., Magmas, fluids, and ore deposits, Min. Villasinius (Italy), 10-15 June 2001, 725-728. Assoc. Can. Short Course Series, v. 23, p. 401-418. LATTANZI P., BENVENUTI M., COSTAGLIOLA Meinert, L.D., 1997, Application of skarn deposit P., TANELLI G. (1994) - An overview on recent zonation models to mineral exploration: Exploration research on the metallogeny of Tuscany, with special and Mining Geology, v. 6, p. 185-208. reference to the Apuane Alps. Mem. Soc. Geol. It., 48 PECCERILLO A. (1999) - Multiple mantle metaso- (1992): 613-625, 6 figg., 2 tavv., Roma. matism in central-southern Italy: geochemical effects, LATTANZI P., BENVENUTI M., GALE N.H., timing and geodynamic interpretations. Geology, 27: HANSMANN W., KOEPPEL V., STOS-GALE Z. 315-318. (1997) - Pb-isotope data on ore deposits of Southern PECCERILLO A., CONTICELLI S., MANETTI P. Tuscany. Plinius, 18: 123-124. (1987) - Petrological characteristics and the genesis LATTANZI P., TANELLI G. (1985) - Le mineralizza- of the recent magmatism of Southern Tuscany and zioni a pirite, ossidi di Fe e Pb-Zn(Ag) della zona di Northern Latium. Period. Mineral., 56, 157-172. B16 to B33 n° 2 - from Volume Niccioleta (Grosseto). Rend. S.I.M.P., 40: 385-408. PECCERILLO A., POLI G., DONATI C. (2001) LATTANZI P.F., HANSMANN W., KOEPPEL V., - The Plio-Quaternary magmatism of southern Tus- COSTAGLIOLA P. (1992) - Source of metals in cany and northern Latium: compositional character- metamorphic ore-forming processes in the Apuane istics, genesis and geodynamic significance. Ofioliti, Alps (NW Tuscany, Italy): constraints by Pb-isotope 26 (2a), 229-238. data. Mineral. and Petrol., 45: 217-229. PERTUSATI P.C., RAGGI G., RICCI C.A., DURAN- LATTANZI, P., HANSMANN, W., KOEPPEL, V. TI S., PALMERI R. (1993) - Evoluzione post-colli- (1991) - Preliminary data on the Pb-isotope composi- sionale dell’Elba centro-orientale. Mem. Soc. Geol.

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Edited by APAT August 20-28,2004 Florence -Italy

Field Trip Guide Book - B19 Associate Leader:A.Landuzzi Leaders: M.Roveri GEOLOGICAL CONGRESS 32 Volume n°2-fromB16toB33 APENNINES FOREDEEPBASINS EVENTS INTHENORTHERN THE RECORDOFMESSINIAN Pre-Congress nd INTERNATIONAL B19 The scientific content of this guide is under the total responsibility of the Authors

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Field Trip Committee: Leonello Serva (APAT, Roma), Alessandro Michetti (Università dell’Insubria, Como), Giulio Pavia (Università di Torino), Raffaele Pignone (Servizio Geologico Regione Emilia-Romagna, Bologna) and Riccardo Polino (CNR, Torino)

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32nd INTERNATIONAL GEOLOGICAL CONGRESS

THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS

AUTHORS: M. Roveri1, A. Landuzzi 2, M.A. Bassetti 4, S. Lugli 3, V. Manzi 1, F. Ricci Lucchi 5, G.B. Vai 5

1Dipartimento di Scienze della Terra, Università degli Studi di Parma - Italy 2DISTART, Università degli Studi di Bologna - Italy 3Dipartimento di Scienze della Terra, Università di Modena e Reggio Emilia, Modena - Italy 4Departamento de Geologia y Paleontologia, Facultad de Ciencias, Salamanca - Spain 5Dipartimento di Scienze della Terra, Università degli Studi di Bologna -Italy

Florence - Italy August 20-28, 2004

Pre-Congress B19 Front Cover: Panoramic view of the Vena del Gesso (Gessoso-Solfi era Formation) along the west side of the Santerno valley at Borgo Tossignano THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

Leader: M. Roveri Associate Leader: A. Landuzzi

Introduction which extends from Bologna to Rimini. Why a fi eld trip on the Messinian salinity crisis in the Gypsum rocks formed during Messinian events Romagna Apennines? We believe there are many good constitute an almost continuous and prominent belt reasons indeed. We are going to introduce in these (the so called Vena del Gesso) along the Apennines brief notes only some of the most relevant arguments, foothills. This rocky belt is characterized by peculiar hoping the participants at the end of the fi eld trip will morphology and ecosystems, and has been attractive have completed their own list with many others. to man for various uses since antiquity, providing the Firstly, although not adequately recognized by the base for an important social, artistic, and economic scientifi c community, the Northern Apennines holds development. The large-size, twinned crystal variety of the most complete, and probably the best, record of gypsum, known as selenite, has been used as building the large amplitude paleoenvironmental changes that stone since Roman times, and maybe even before. affected the Mediterranean area during the Messinian A short walk downtown in Bologna may quickly age (i.e. the time interval lasting about 2 million years substantiate this; the basement of many Middle Age between 7.2 and 5.33 My), and usually referred to as buildings, included the famous towers, as well as the the “Messinian salinity crisis” (MSC). ancient walls (IV-VIII century AD) are made up of Moreover, in no places of the Mediterranean area has squared selenite blocks (Fig. 1), many of which were the fascinating history of the Messinian salinity crisis recycled from the Roman theatre. Selenite derived left so many indelible signs on both the physical and from quarries located in the foothills of Bologna, cultural landscape as in the Northern Apennines area, and more to the east, in the Santerno and Lamone valleys (western Romagna). Also from Messinian Figure 1 - Remnants of the IV-VIII century AD selenite gypsum-bearing successions, but dominated by the walls, preserved and recycled in the Ghisilardi Fava microcrystalline, thin-laminated variety of gypsum Palace at Bologna . known as balatino, derives the sulphur extensively exploited till the early 60s in many small quarries and mines in eastern Romagna, i.e. from the Rabbi to the Marecchia valleys. The great economic value of gypsum rocks stimulated early geological studies, at least since the beginning of the 18th century. As recently pointed out by Marabini and Vai (2003), Luigi Ferdinando Marsili, an outstanding scientist of the Istituto delle Scienze of Bologna, carried out, around 1717, what can well be considered the fi rst modern stratigraphic study at a regional scale. In an, unpublished manuscript, partially reproduced in Marabini and Vai (2003), he describes in great detail the vertical superposition of gypsum and shale beds in the sulphur mines of eastern Romagna, suggesting correlations and recognizing their close relationships with the selenite rocks occurring to the west, and pointing out the occurrence of a continuous gypsum belt from Bologna to Ancona. Volume n° 2 - from B16 to B33 n° 2 - from Volume Enclosed with Marsili’s manuscript, is what can be regarded to as the fi rst geologic map in the world (Fig. 2): an accurate representation of outcropping gypsum bodies connecting and accounting for a series of aligned sulphur mines in the Forlì and Cesena foothills. During the third and fourth day of this fi eld trip, we will run over Marsili’s outcrops again, which shows how geologic interest in this area has

3 - B01 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri more orlessdeeplycutbyasubaerialerosional margins arealways reducedandincomplete,being successions preserved onMediterraneancontinental In fact, contrarytothe Apennines, Messinian their geneticandstratigraphicrelationships. water settings,thusallowing thereconstructionof succession developed inbothshallow- anddeep- opportunity toobserve acomplete sedimentary the Messinianoutcropsofthisareastilloffer aunique Three centuriesafterthepioneeringwork ofMarsili, the main Apennine structuraltrend. settings areseparatedbyatectonicfeatureobliqueto limestones. Inthefi eld triparea,thesedepositional accumulated insomewhat deeperwaters –into diagenetic transformationofclasticgypsumdeposits– while extensive sulphurmineralizationisrelatedtothe gypsum fromdensebrinesinshallow-water settings, was formedthroughtheprimaryprecipitationof the Romagna Apennines. Roughlyspeaking,selenite geologic settingsdeveloped duringtheMessinianin by Marsili,mirrorstwo different stratigraphicand of seleniteandsulphurmines,asalreadyrecognized stood thetestoftime. The distinctspatialdistribution (from Marabiniand Vai, 2003). Figure 2-The1717geologicalmapbyL.F. Marsili science. interlacing ofgeology, culture,andhistoryof formed anddeveloped throughtime,inacontinuous character ofthisland,itspeopleandproducts, their own, wehopethey willappreciatethestrong who willusethisguidebooktomake thefi for thoroughdiscussion.For them,aswellforthose fi Concluding theseintroductorynotes,wehopethe controlling Messinianstratigraphicpatterns. usually overlooked topic,i.e.theroleoftectonicsin Messinian salinitycrisisand,inparticular, ona concerning thedifferent evolutionary stagesofthe will allow ustofocusonseveral stillopenquestions The completeandexpanded recordofthe Apennine be fullyunraveled. basins, whosetruenatureandstratigraphy stillwait to accumulations buried inthedeepestMediterranean that isstillmissing,recordedbythosehugesalt almost completelydriedup. The partofthestory model (Hsüetal.,1972),theMediterraneanbasin according tothepopular surface, developed inthetimespanduringwhich, chances ofunderstandingthesephenomena. The has certainlyimproved ourgeneralknowledge and calibrations andphysical-stratigraphicconcepts, the lastfew years,aftertheadoptionofastronomical great advance instratigraphicresolution, obtainedin during thecrisis,arestillpoorlyunderstood. The Messinian, andthepossiblyactive roleofbiota structure ofthewater columnthroughoutthe Mediterranean area,thephysicalandchemical The paleogeographyandpaleoclimatologyofthe Many importantquestionsremain unanswered. the MSCisalong-lived issueinthescientifi The comprehensionofthedifferent aspectsrelatedto often overlooked intheMessiniandebate. anomaly withinthegeneralpictureand,consequently, Apennine foredeephasalways beenconsideredan of adeep-water, nonmarinebasin.For thisreasonthe the otherMediterraneanbasins,andtopersistence that would have ledtoitsprematureisolationfrom the particularpaleoclimaticandstructuralcontext, has ever beenfound;whichisusuallyexplained by desiccation model.Noevidence forthedesiccation Apennine foredeepbasindoesnotsupportthedeep- sedimentary recordofMessinianevents ofthe In fact, ithaslongbeenrecognizedthatthe and modalities Messinian events, chronology, eldtripparticipantswillfi nditastimulatingchance “deep desiccatedbasin” eldtripby c debate. THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

Figure 3 - Chronology of Messinian events according to Krijgsman et al. (1999a-b).

Messinian stage is now well time-constrained; the Mare stage (~5.61-5.33 Ma), showing the widespread Messinian GSSP has been defi ned in the Oued Akrech development of non-marine deposits with Mollusk, section (Morocco), and an age of 7.251 Ma has been Ostracod, and Dinofl agellate assemblages of assigned to the Tortonian-Messinian boundary (Hilgen Paratethyan affi nity (Lago Mare biofacies; Ruggieri, et al., 2000); the top of the Messinian corresponds to 1967; Iaccarino & Bossio, 1999). The end of the MSC the Zanclean GSSP, defi ned in the Eraclea Minoa is represented by the sudden, catastrophic return to section (Sicily), with an age of 5.33 Ma (Van fully marine conditions at the base of the Pliocene Couvering et al., 2000). Although differing views still (Iaccarino et al., 1999). exist, in recent years, a growing consensus has been Based on astronomic-controlled cyclostratigraphic reached about the chronology of Messinian events, as considerations, the main Messinian events are proposed by Krijgsman et al. (1999a-b; Fig. 3). This considered to be synchronous throughout the has been made possible by the well-developed cyclical Mediterranean area, pointing to strong external arrangement of Messinian deposits. According to forcing, tectonic and/or climatic. The duration of the such a model, a classical three-fold subdivision of the various Messinian ‘phases’ can thus be estimated: 1.2 Messinian stage can be envisaged: 1) pre-evaporitic My for the pre-evaporitic, 0.35 My for the evaporitic, B16 to B33 n° 2 - from Volume (7.251-5.96 Ma), characterized by the common and 0.35 My for the post-evaporitic phase. This age- occurrence in deep-water settings of organic-rich, model fi ts quite well with the two-step MSC proposed laminated deposits, which record sea-bottom low- by Clauzon et al. (1996), which represents an updated oxygen conditions, related to a progressive reduction version of the Hsü et al. (1972) deep-desiccated of water circulation within the Mediterranean; 2) basin model. Such a model implies a diachronous Lower Evaporites (5.96-~5.61 Ma), the fi rst episode deposition of evaporites across marginal and basinal of shallow-water evaporites precipitation in marginal settings at the boundary between the evaporitic and basins; 3) Upper Evaporites, or post-evaporitic Lago post-evaporitic stages. In marginal settings, this

5 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri sub-basins, whilean Apennine-type succession succession canberecognizedinshallow, marginal Apennine foredeepsystem,atrueMediterranean-type can beclearlydefi ned. Inotherwords, allalongthe stratigraphic andgeneticrelationshipsbetweenthem evolution, bothmodalitiesactuallyoccurandthatthe due toitsgeodynamicsettingandpost-Messinian The true“anomaly”ofthe Apennine foredeepisthat, areas, the Apennine typetobasinaldeeps. settings: theMediterranean-typetomarginal, elevated - correspondtotherecordofdistinctmorphostructural end-member successionsbasically–andvery roughly offer adifferent pointofview tothediscussion. The and Apenninic modesoftheMSCevolution, wenow With respecttothesupposeddifferent Mediterranean record ofMessinianevents foredeepThe Apennine basin duringthewholeMSC. non-desiccated characterofthe Apennine foredeep and anApenninic-type successions: a simplicity, intotwo end-member be summarized,andtranslatedfor view, thedifferent modalitiescan et al.,2001). According tothis northwestern Mediterranean;Clauzon Apennine foredeep, Andalusia, geotectonic settingsinvolved (Sicily, distinct modalitiesacrossthedifferent proposed thattheMSCevolved with development, ithasbeenrecently events, whichsuggestsahomogenous unifying chronologyofMessinian Mare stage).Despitetheaccurateand waters ofParatethyan origin (Lago basins withfreshtooligohaline leading tothepartialrefill ofdesiccated pattern intheperi-Mediterraneanarea, responsible forchangingthedrainage Mediterranean. The dramaticsea-level dropwas also al., 1999a-b),relatedtothedeepdesiccationof the baseofpost-evaporitic stage(Krijgsmanet Neogene stillshows indeedagaplasting90kyr at The astronomicpolaritytimescale(APTS)forthe precipitation was shiftedtowards thedeepestparts. more than1000meters,andshallow-water evaporite the MSC,whenMediterraneansea-level dropped thought tohave beendeveloping duringtheacmeof surface, deeplycuttingthecontinentalmargins, and boundary isrepresentedbyasubaerialerosional Mediterranean-type , themaindifference beingthe Figures 4and5,assumesthedevelopment ofpre- been reconstructed.Suchamodelissummarizedin for the Apennine foredeepMessiniandepositshas et al.,2003),ageologicandstratigraphicmodel 2000; Roveri etal.,1998;Roveri etal.,2001;Roveri 1987; Rossietal.,2002;Bassetti1994;Bassetti, use ofaphysicalstratigraphicapproach(Gelatietal., integration ofsurface and subsurface, dataandthe ten yearsbyseveral researchgroups,throughthe of Messinianstratigraphy, carriedoutin thelast developed indeeperones.Basedonacarefulreview to thedismantlingandresedimentationofLower is strictlyrelatedtoaregional tectonicuplift,leading associated withanangulardiscordance,andhenceit Lower Evaporites throughouttheMediterranean,is perfect equivalent oftheerosionalsurface whichcuts foreland. The intra-Messinianunconformity, a migration oftheforedeepdepocenterstoward the emergence ofthe Apennine chain,andtheconcomitant a regional tectonicphase,determiningtheupliftand deposition iscoincidentwithaparoxysmalacmeof and deeperforedeepbasin. The endofevaporite front ledtotheprogressive fragmentationofalarger ensuing propagationofthe Apennine compressive formation datesbacktotheLate Tortonian, whenthe deposited onlyinshallow thrust-topbasinswhose Mediterranean basins.Primaryevaporites were with, andwiththesamemodalitiesas,other evaporitic andevaporitic stagesthat aresynchronous Apennine foredeep. Modified fromRoveri andManzi Figure 4-ChronologyofMessinianevents inthe (in press). THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

Evaporites in deep basins through large-scale mass- sedimentary succession can be easily correlated to that wasting and gravity fl ows in shelf and slope areas. By developed in wedge-top basins through very distinctive tracing down basin, the intra-Messinian unconformity physical elements. The distinction between the p-ev1 and is a problem solved, and its correlative conformity p-ev2 unit is substantiated by the clear upward transition is placed at the base of the resedimented evaporites from high-effi ciency to low-effi ciency turbidite systems. complex (Roveri et al., 1998, 2001). This unit Moreover, an ash layer of regional extent is an excellent accumulated in topographic lows during the subaerial key-bed in the p-ev1 unit. exposure of uplifted basin margins, thus allowing us The fi rst and second days of the fi eld-trip will be spent to bridge the last Messinian gap (Roveri & Manzi, in a marginal, Mediterranean-type context, the third and in press). Based on its physical characteristics, a fourth days, in a Apenninic-type one. This will give the high-resolution stratigraphic framework for the participants the chance to contrast and correlate the two post-evaporitic successions (discontinuities of stratigraphies and, consequently, to assess some basic different hierarchical rank, stacking pattern and cyclic Messinian features.

Figure 5 - The geologic-stratigraphic model for the Messinian deposits of the Apennine foredeep (Roveri et al., 2003). organization of depositional system, key horizons), Regional geologic setting has been reconstructed. A second, younger regional The Romagna Apennines, extending from the Sillaro unconformity splits the post-evaporitic Lago Mare valley to the west, to the Marecchia valley to the east deposits into two units; the lower one (p-ev1), only (Fig. 6), is part of the Northern Apennines, a ENE- occurring in structural depressions, is composed verging arc, characterized by compression along the of resedimented evaporites at the base, overlain by external front, and extension in the inner western part a siliciclastic coarsening and shallowing-upward (i.e. the Tyrrhenian area). succession; the upper unit (p-ev2), made up of coarser- The Apennine chain has been formed since the Late grained deposits, has a general transgressive trend, Eocene as a post-collisional fold and thrust belt, in and seals all the previously uplifted tectonic structures the more general context of convergence between the and generalized subsidence – and/or a base level rise African and Eurasian plates. The Romagna Apennine

– which preceded the Zanclean fl ooding. is characterized by an outcropping succession of B16 to B33 n° 2 - from Volume The relatively small fi eld trip area has the great advantage Lower Miocene to Pleistocene siliciclastic deposits, of being able to sumup all the elements of the larger-scale overlying buried Mesozoic to Cenozoic carbonates. stratigraphic model. This area corresponds to a series of This sedimentary succession represents the infi ll of wedge-top basins (Fig. 5) which are characterized by a foredeep basin system actively migrating to the different absolute paleobathymetry and subsidence northeast since the Oligocene (Ricci Lucchi, 1986), rates. The two main foredeep Messinian depocenters are and formed above the Adria plate in what is defi ned presently buried below the Po Plain, and crop out in the the Umbria-Marche domain, the lowest structural Southern Marche and Abruzzi (Laga Basin), and their unit of the Apennine orogenic wedge (for an updated

7 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri anticlines areburied byathicksuccessionofmarine et al.,1986,Castellarin,2001),whereseveral ramp belt liesinthesubsurface ofthePoPlain(Castellarin show thattheoutermostfrontof Apennine thrust propagation folds(Capozzietal.,1991).Seismicdata showing adeformationalstyledominatedbyfault from itscarbonatebasementalongabasalthrust,and 3000 mthick(RicciLucchi,1975,1981),detached Marnoso-arenacea Fm,aturbiditiccomplex morethan Apennine consistsoftheLanghiantoMessinian The uppermoststructuralunitoftheRomagna Boccaletti etal.,1990). Adria platesincetheOligocene(Kligfi Alpine compressionalphasesandthrustover the as anaccretionarywedgeduringtheLateCretaceous ophiolithic slabs(CastellarinandPini,1989),formed of JurassictoEocenedeep-marinesedimentsand by theLiguriannappe(Fig.6),achaoticcomplex To thewestofSillarovalley, thisunitiscovered 2001). review of Apennine geology, see Vai andMartini, Figure 6-Simplified structuralmapoftheNorthern Apennines. ed 1979; eld, comparison andcorrelationisthe mainaimofthe mentioned different Messinianstratigraphies,whose Such changesfi nally correspondtothetwo above- occur acrossstructuralhighsrelatedtotheForlì line. thickness changeswithintheMessiniansuccession Pliocene boundary(Fig.7),dramaticfacies and InaNW-SE cross-section, fl attened attheMiocene/ Roveri etal.,2002) at leastsincetheLate Tortonian (RicciLucchi,1986; primary roleinthegeologicalevolution ofthearea, trends intheeasternone. The Forlì line playeda by several thrust-relatedanticlineswith Apenninic arenacea Fm.,whilethesamesuccessionisdeformed Pleistocene deposits,restingabove theMarnoso- a gentleN-NEdippingmonoclineofMessinianto the surface; thefoothillsofwesternsectorshow this featurehave adifferent structuralarrangementat to the Apenninic trend. The two sectorsdefi Forlì line(FL,Fig.7),acomplex fault zoneoblique is splitintotwo sectors(westernandeastern)bythe Plio-Pleistocene deposits. The Romagna Apenninic ned by ned THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19 Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 7 - Simplifi ed geologic map (above) and cross-section (below) of the Romagna Apennines. The cross-section is fl attened at the Miocene/Pliocene boundary to better illustrate the great facies and thickness changes characterizing the Messinian succession across main structural elements (modifi ed from Roveri et al., 2003).

fi eld trip. consists of four formations (Vai, 1988; Fig. 8): The lithostratigraphy of the Langhian to Pliocene i) the Marnoso-arenacea Fm (MA, Langhian- sedimentary succession of the Romagna Apennines Messinian), made up of deep-water siliciclastic

9 - B19 Volume n° 2 - from B16 to B33 B19 - B19 evaporites duringthemainevaporative event. lithostratigraphy refers tomarginalsuccessions,i.e.thosecharacterized bydepositionofprimary, shallow-water Figure 8-Stratigraphicscheme ofthe Apennine foredeep Tortonian toearlyPliocenetimeinterval. Notethat Leader: M.Roveri turbiditic sandstoneandchaoticbodies;thisisinturn slope mudstones( laterally-continuous turbiditiclobesarereplacedby of thecompressionalfront. Towards thetop,thickand migrated towards theNE,following thepropagation elongated inaNW-SE direction,whosedepocenter up to3000metersthick,filling alarge foredeepbasin from thecentral Apennines, isahuge clasticwedge, turbidites, derived fromthe Alps and,subordinately, ghioli diletto)whichcontainminor The euxinicshalesspana1.5Mytime changes associatedwiththeensuingMSC. cyclical pattern,andrecordthepaleoceanographic Sicily andSpain,suchdepositsshow awelldeveloped Lower Messinian). Like the coeval Tripoli Fmin informally named organic anddiatomite-richlaminitesmudstones, boundary, andmadeupoffi overlain byaunitstraddlingthe Tortonian-Messinian euxinic shales (Upper Tortonian- nely-interbedded THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

interval, characterized by well-defi ned bio- and magnetostratigraphic events; their calibration with astronomical cyclicity allowed a detailed chronostratigraphy to be established (Krijgsman et al., 1999a,b; Vai, 1997). ii) the Gessoso-solfi fera Fm (GS, Messinian), is made up of both primary and clastic, resedimented evaporites, with interbedded organic-rich shales, deposited during the evaporitic and post-evaporitic stages of the MSC; iii) the Colombacci Fm (CO, Upper Messinian), consisting of mainly siliciclastic sediments derived from Apenninic sources, was deposited in both shallow and deep brackish or freshwater basins developed during the Lago Mare phase of the MSC. Based on a sharp vertical facies change, this unit has been subdivided by Roveri et al., (1998) into two informal units, the Tetto fm. (below), and the Cusercoli fm. (above). The Cusercoli fm is characterized in marginal basins by coarser-grained lithology and by the occurrence of thin lacustrine micritic limestone beds (colombacci limestones). iv) the Argille Azzurre Fm (AA, Lower Pliocene), is made up of relatively deep marine mudstones deposited in a series of more or less connected wedge top basins locally encasing fan-delta conglomerates, and shelf to perched-basin turbiditic sandstone bodies, and small, isolated carbonate platforms deposits (Spungone). From a physical-stratigraphic point of view, the Tortonian to early Pliocene succession has been subdivided into three large-scale synthems, separated by large-scale unconformities recording important phases of tectonic deformation of the Apennine

orogenic wedge. From base to top, they are the T2 (Tortonian-Messinian) synthem, the MP (Messinian- Pliocene), and LP (Lower Pliocene) synthems (Roveri et al., 1998; Roveri et al., 2001; Roveri et al., 2003). These large-scale units only slightly differ from those defi ned by Ricci Lucchi (1986) and can be further subdivided into lower rank U.B.S.U. delimited by minor unconformities and fl ooding surfaces (Roveri et al., 1998), still having a regional signifi cance. The more reliable key events for long-distance B16 to B33 n° 2 - from Volume correlations are the Tortonian/Messinian boundary (7.2 My), the Miocene/Pliocene boundary (5.33 My), and a widespread ash-layer within the post-evaporitic Lago Mare deposits, which holds a radiometric age of 5.5. My (Odin et al., 1997). Messinian deposits fall

in the T2 (pre- and evaporitic stage) and MP (post- Figure 9 - Stratigraghy of the western secctor.

11 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri T the SintriaandLamonevalleys. to importantdetailsfromoutstandingoutcropsalong day ofthefi eld trip. The seconddaywillbedevoted Santerno valley, whichwillbevisitedduringthefi is particularlywellexposed (Figs.9,10),alongthe The Tortonian toPliocenesuccessionofthissector important tectonicalignments,aspreviously reported. These physiographicboundariescorrespondtotwo to thewestupBidentevalley totheeast. The westernareaextends fromtheSillarovalley Western sector described separately. developing inthewesternandeasternsectorswillbe evaporitic stage)synthems.Hereafter, thesuccessions of the T In the T fl the basinaxis(i.e.inaNW-SE direction)inanearly deposition byunconfi ned currentsfl owing parallelto geometries andhighlateralcontinuity, suggesting stages, turbiditicdepositsarecharacterizedbytabular change withintheMarnoso-arenaceaFm.Inprevious In thewesternsector, thisiswellrepresented by narrowing (RicciLucchi,1981,1986). related toaregional phaseoftectonicupliftandbasin et al.,1999). This facies changehasusuallybeen strongly affected bytopographicconstriction (Mutti escape structures,suggestdepositionfromfl abundance ofbasalscours,cutandfi grained andshow alower lateralcontinuity;the at sea-bottom. 2 synthem(UpperTortonian-Messinian 2 2 synthemcorrespondstoanabruptfacies synthem,sandstonebodiesarecoarser- Figure 10-Panoramic viewofthestratigraphicsuccessioncroppingourinSanternovalley. ll, andwater- ) - The base ows ows rst The T layers. characterized bythedevelopment ofthincarbonate et al.,1999a; Vai, 1997). The topmostcycles are Vigliotti, 1988;Negri and Vigliotti, 1997;Krijgsman (Monte delCasino,Monte Tondo, Monticino,Fig.11; cyclostratigraphic reconstructionsinseveral sections have beenstudiedindetailforbio-,magneto-,and characterized byawell-developed lithologiccyclicity, of organic-rich mudstone unitiscappedbya40mthickhorizon derived fromminorturbiditicbodies.Inturn,the to 50mthick,characterizedbysandstoneolistoliths, section, themudstoneunitcontainsaslumpbody, up thinning-upward sequence.IntheSanternoriver turbiditic sandstonebodies,forminganoverall by amudstoneunit,withinterbedded,smaller-size upper part. The upperFontanelice systemisoverlain and atleasttwo distinctsandstonebodiesinthe indicating an Alpine source;RicciLucchi,1969), with basalconglomeratebars(pebblecomposition can beobserved. The sedimentaryfi and aspectacularNE-wards onlapofsandstonefi the basalerosionalsurface deepenstoward theSW, letto). Inasectionalmostnormaltothepaleocurrents, encased inUpper Tortonian mudstones( The larger andthicker upperchannelizedbodyis (Ricci Lucchi,1968,1969,1975,1981). depressions, andseparatedbyamudstonehorizon bodies confi ned withinlarge-scalethe Fontanelice erosional ”channels”,two turbiditicsandstone evaporites oftheGessoso-solfi 2 synthemistoppedbytheshallow-water euxinic shales . The euxinicshales, fr Formation, fera ll iscomposite, ghioli di ll THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

forming a continuous belt up to 150 m thick, from the can be observed; upper cycles are thinner, and Sillaro to the Lamone valleys. Gypsum deposits have autochthonous evaporite facies are much less well- a strong cyclical organization, as fi rst recognized by developed than the reworked clastic facies. Vai and Ricci Lucchi, (1977) which counted up to This suggests the superposition of an overall 16 small-scale, decametric-thick, shallowing-upward “regressive” trend on the smaller-scale, higher- cycles, recording the progressive evaporation of frequency cyclicity. This trend provides the guideline shallow lagoons. These cycles have been interpreted for a precise cycle-by-cycle correlation throughout more recently as controlled by periodic changes the Vena del Gesso basin, and further to the SE, in

Figure 11 - Panoramic view of the late Tortonian-Messinian succession in the Santerno valley (stop 1.4). Note the chaotic horizon below the euxinic shales and the deformed gypsum unit on top. of orbital parameters (Vai, 1997; Krijgsman et al., 1999b). The ideal complete cycle consists of the vertical superposition of 6 sedimentary facies (Fig. 12, 13, 14), fi ve of them made up of gypsum and carbonates; it starts with basal organic-rich shales (facies 1), deposited in shallow lagoons below the wave base; these shales are overlain by gypsifi ed limestone stromatolites (facies 2), massive autochthonous selenitic gypsum (facies 3), and well-stratifi ed autochthonous and reworked selenitic gypsum (facies 4). The size of selenite crystals usually decreases upwards; this change is usually thought to be related to the progressive evaporative draw-down, and Figure 12 - Facies 3 selenitic gypsum in a block of the increasing salt concentration of the lagoon. The upper Garisenda tower of Bologna. part of the modal cycles is characterized by nodular B16 to B33 n° 2 - from Volume gypsum, acicular gypsum, gypsarenites (facies 5), the Marecchia valley area (epi-Ligurian evaporites). and chaotic selenite breccia (facies 6). These deposits For correlation purposes, the complete succession of are interpreted as related to subaerial exposure and 16 evaporite cycles has been subdivided into 2 thin erosion at the end of an evaporative draw-down cycle, “basal” cycles (facies 1 and 2 only), 3 thick “major” with strong gypsum reworking by waves or torrential cycles (facies 5 missing), a very thick 6th cycle streams action (Vai and Ricci Lucchi, 1977). (complete sequence), and 10 thin “minor” cycles Progressive upward decrease in thickness and (complete sequences). The described longer-term different facies distribution within individual cycles

13 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri erosional surface (Vai, 1988),markingthe T An angularunconformityisassociatedwiththe MP synthem(Messinian-Pliocene) (MP). base oftheoverlying Messinian-Pliocenesynthem cutting thegypsumunitatitstop,andmarking trend culminateswithagreaterosionalunconformity Gesso evaporites(Vai andRicciLucchi, 1977) Figure 13-Theidealdepositionalcycleofthe Vena del Monticino section,nearBrisighella;Costaetal., which arerichinmammalfauna, werefoundinthe exposure (karsticdykes, filled bycontinentaldeposits surface preserves spectacularevidence ofsubaerial boundary, clearlyindicating itstectonicnature. This 2 /MP hypohaline faunal assemblage( mainly ofgraytovaricolored clays,containingan uppermost MessinianColombacciFmconsists separated bytheMiocene/Plioceneboundary. The Fm and Argille Azzurre Fm,arevery thin,and Deposits ofthissynthembelongingtotheColombacci deposits arecompletelymissing. where theevaporitic andpre-evaporitic Messinian southeastern endofthissector(Marzenovalley), with theMPunconformitydeepenstoward the 1986; DeGiulietal.,1988). The erosionassociated formation itself. The Miocene/Pliocene boundaryis locally named locally. Inplaces,awhitemicriticlayerisalsofound; pebbly sandstone,andcalcareousconglomerateoccur Limnocardium spp colombaccio .). Smalllensesofsandstoneand , itgives itsnametothe Melanopsis spp ., THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

Figure 14 - Vena del Gesso evaporites. A) Santerno river bed. Slumped stromatolitic limestone (F2) and limestone breccia (“calcare di base”) embedded in the topmost pre-evaporite mudstones; b) Rio Sgarba Quarry, Borgo Tossignano. B16 to B33 n° 2 - from Volume GS, cycle II: euxinic shales (F1), and calc-gypsum laminites enclosing meter-sized “palisade”-type crystals of stromatolite-bearing gypsum (F2); c) Montebello Quarry, Marecchia Valley. GS, cycle III: upright and well-packed “swallow-tail” selenite crystals (F3). The evaporite growth is interrupted by an intra-cycle dissolution surface; d) Monte TondoQuarry, cycle VI, reworked selenite (facies F4); e). “Swallow-tail” selenite crystal (F3): an opaque stromatolite- bearing core is surrounded by a transparent diagenetic overgrowth;f) Monte Tondo Quarry, cycle VII, reworked small selenite crystals with nodules and lenses of whitish selenite.

15 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri Roveri etal.,2003). to thewesternmostedge(Sillaro-Santernovalleys, rehydration, have beenobserved fromM.Penzola lithostatic loadingduringburial) andsubsequent (stop 1.8). Traces ofanhydritization(duetohigher for thevertical repetitionofthelower gypsumcycles (M. Penzola),shallow thrustfaults areresponsible river (seestop1.2Fig.27),whilefurthertothewest affect thegypsumunitonleftbankofSanterno extensional deformations.Rotationallistricfaults more discontinuous,shows bothcompressive and sector), thegypsumunit,whichisthinnerand characteristics. To thewest(Santerno-Sillaro From W toE,thedeformationshows different Colombacci Fm. Vai, 1985),andaresealedbyMPdepositsofthe the upperpartof deformations emanatefromadetachmentsurface in top oftheunderlying shallow thrustfaults, partiallyaffecting alsothe (Marabini and Vai, 1985),withrotatedblocksand by extensional andcompressionaldeformations The gypsumunitofthissectorischaracterized Deformation ofprimaryevaporites LP unconformity. related tothelocalstrongerosionassociatedwith deposits oftheMPsyntheminthisareaisessentially Lucchi, 1982). The shallowness oftheLower Pliocene derived fromtheLigurianunits(CremoniniandRicci chaotic deposits(pebblymudstonesanddebrisfl appearance withindeepmarineclaysofcoarse, recorded intheSillaro-Santernoareabysudden of the Apennine compressive front. This event is part oftheGilbertchron,andisrelatedtoadvance synthem. The LPunconformityoccursintheupper unconformity (LP)markingthetopofMP that alarge hiatusisassociatedwiththeregional out intheSanternoandMonticinosections,show whole area.Detailedbiostratigraphicstudiescarried et al.,1969)ofdeep-marinemudstonesdrapingthe according toColalongoetal.,1982,andCremonini a thinunit(only2mthickintheSanternosection, Lower Pliocenedeposits ofthissynthemconsist planktonic assemblagesofthebasalPliocene. such achangeiswitnessedbytherichanddiversifi marine torelatively deep-marinewaters isobserved; boundary, thetypicallyabrupttransitionfromnon- whose originisstillpoorlyunderstood. Through the marked byacharacteristicdark,organic-rich horizon, Figure 15-Stratigraphyoftheeasternsector. euxinic shales euxinic shales . Mostofthese (Marabiniand ow), ed THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

Figure 16 - Tortonian to late Messinian evolution of the Apennine foredeep basin (axial section) showing the longitudinal fragmentation due to the growth of the Forlì line - related structural high (Roveri et al., 2002)

To the east (Sintria valley), the deformation is more and pebbly sandstones, with frequent amalgamated severe. Here the gypsum unit forms a complex beds and basal scours. Such deposits form the Savio imbricate structure made of three or more SW verging turbidite system, a composite unit consisting of up to thrust sheets (Marabini and Vai, 1985; see Stop 2.2, fi ve sandstone bodies vertically arranged in a overall B16 to B33 n° 2 - from Volume Fig. 36). fi ning-upward sequence, with a maximum thickness of some 200 m, and cropping out discontinuously Eastern sector along the Savio valley. A direct genetic link with No obvious unconformities occur in this sector any the channelized systems of the western sector where in the considered stratigraphic interval. The (Fontanelice systems), has been recently suggested uppermost Marnoso-arenacea Fm. here consists (Fig. (Roveri et al., 2002; Roveri et al., 2003) on the basis 15) of a thick pile of tabular turbiditic sandstone of facies and regional geologic considerations. bodies, made up of thick-bedded, coarse to very coarse As in the western sector, these sandstone bodies are

17 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri synclines inFigs.7,15),possibly correspondingto in two large synclines(Giaggiolo-CellaandSapigno Upper MessinianandLower Pliocenedeposits occur Pliocene deep-marinedeposits. The bestoutcropsof deposits oftheColombacciFm,inturnfollowed by thickness (upto600meters)ofterrigenousnon-marine Clastic gypsumdepositsareoverlain byalarge cyclical pattern,canberecognized. Neither tracesofsubaerialexposure, noranobvious a moderateorganic content,decreasingupwards. al., 2001;Manzi,2001).Interbeddedmudstoneshave Ricci Lucchi,1972;1973;Roveri et by theobserved sedimentarystructures(Parea and waters, wellbelow thewave-base, assuggested These evaporites weredepositedinrelatively deep- contain large blocksofprimaryseleniticgypsum. gypsum turbidites,andhugeolistostromeswhich evaporites, madeupofwell-stratifi consists hereofathickcomplex ofresedimented shallow-water evaporites. The Gessoso-solfi western sectoristhetotalabsenceofprimary, The moststrikingdifference withrespecttothe unit, allowing reliablecorrelations. Tortonian/Messinian boundaryliesatthebaseofthis terrigenous content. As inthewesternsector, the a lessevident lithologiccyclicity, duetothehigher horizon; heresuchaunitisthicker (100m),andshow shales An organic-rich unitcorrespondingtothe some 300m. deposits (Lucenteetal.,2002);theirthicknessreaches bodies aremadeupofbothintra-andextra-basinal undisturbed muddyhorizon,400mthick. The chaotic and containingtwo chaoticbodiesseparatedbyan overlain byamudstoneunit,heremoredeveloped, geological mapofFig 24(fromRoveri etal.,2003). Figure 17-Linedrawingofaseismicprofile showing theburied culminationoftheRioloanticline.See location inthe ofthewesternareaoccursabove thechaotic e, thin-bedded ed, fera Fm. fera euxinic magneto-stratigraphic data,the T Using thisapproach,withtheintegration ofbio-and tectonic events. basin geometryanddrainagepatternsrelatedtomain would correspondtolarge-scale reorganization of sizes changesindeep-water deposits.Suchchanges characterized bybothcompositionaland/orgrain- the recognitionofabruptvertical facies changes, reliable stratigraphicframework canbebasedon basinal character. Insuchadepositionalcontext, a Summarizing, theMessiniansuccessionhasanoverall horizon. boundary, characterizedbythetypicalblackshale Argille Azzurre Fm.)aswelltheMiocene/Pliocene sector (epibathyalmudstonesbelongingtothe here thesamefacies characteristicsasthewestern orogenic wedge. The basalPliocenedepositshave local Messiniandepocentersdeveloped above the ev The MPsynthemcanbesubdivided intotwo units(p- primary evaporites. would representthedeep-water counterpartofthe “Mediterranean-type” successions. This horizon rich, barrenhorizon,never observed inmarginal, 2001) pointedouttheoccurrenceofahighlyorganic- Preliminary bio-magneto-stratigraphicdata(Manzi, evaporites occurswithinthelocaleuxinicshales. the MPsynthem,andatimeequivalent ofprimary view, theGessoso-solfi evaporitic complex ofthisarea. According tothis correlative conformityatthebaseofresedimented (2001), suggestedthatitcouldbetracked intoa western sector, Roveri etal.(1998,2001)andManzi As fortheMPunconformity, clearlydeveloped inthe be tracedatthebaseofSavio turbiditesystem. 1 andp-ev 2 , seeRoveri etal.,2001;Fig.4),separated fera Fm.would belong to 2 unconformitycan THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

by a minor unconformity which marks important paleogeographic and structural changes.

The lower unit (p-ev1) only occurs in structural depressions, and bridges the fi nal Messinian gap (Krijgsman,

1999a,b). The p-ev1 unit consists of a basal complex of resedimented evaporites, overlain by a thick, monotonous succession of fi nely laminated mudstones and siltstones, and containing minor turbiditic sandstone bodies and showing an overall coarsening-and shallowing- upward trend, related to the progressive and rapid basin infi ll (Tetto fm.); an ash layer, dated at ca. 5.5 My (Odin et al., 1997), represents an exceptional lithostratigraphic marker throughout the whole Apennine foredeep basin, allowing us to recognize the p-ev1 unit across different sub-basins (Bassetti et al., 1994). Sedimentary facies and vertical trends, together with geometric characteristics (the cross-section triangular shape, and stratal convergence towards structural highs, reconstructed through surface and subsurface data), indicate the syntectonic nature of this unit.

The upper unit (p-ev2), is tabular and thickens in structural depressions, but also overlies and seals all the previously uplifted and subaerially exposed areas. This unit consists of a cyclic alternation of coarse and fi ne- grained tabular lithosomes, arranged in a overall fi ning-upward trend. The basic cyclicity records the periodical, climatically controlled activation of fl uvio-deltaic systems dominated by catastrophic fl oods (Roveri et al., 1998). 3 to 4 sedimentary cycles are normally observed in the upper unit; B16 to B33 n° 2 - from Volume a similar, but less evident, cyclicity is observed in the upper part of the p-ev1 unit. The overall fi ning-upward trend

Figure 18 - Evolution of the Riolo anticline during the Upper Tortonian- Lower Pliocene time interval (from Roveri et al., 2003).

19 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri phase affected the Apennine thrust belt,leadingtothe systems. DuringtheMessinian,animportantuplift distribution andvertical evolution ofdepositional of tectonically-derived topographyontheareal of the Apennine thrustbelt,isthestrongcontrol fi The mostimportantfeaturethatclearlyarisesfrom the Apennine foredeep basinduringtheMessinian. allow ustoreconstructthesedimentaryevolution of eastern sectorsoftheRomagna Apennines (Fig.7) The comparisonandcorrelationofthewestern of the Apennine foredeep Messinian events andthetectonicevolution at thetopofcoarserdivision.B)thick layerwithtwo climbingrippledivisionsshowing oppositepaleocurrents. related tooriginalgrain-size. A) Noteloadstructuresatthebaseofthickest layerandlongwavelength climbingripples Figure 19-Gradedgypsarenitelayers(Fanantello section,stop.3.3).Each layeriscomposedbyalight-darkcouplet characteristic dark,organic-rich horizon. marked, aselsewhere inthe Apennine foredeep,bya uppermost oneliesjustbelow theM/Pboundary, here horizons ( with muddyunitscontainingthreelimestone Coarse-grained bodiesareregularly interbedded of thefi eld trip),werelocatedalongtheForlì line. outcropping intheGiaggiolo-Cellasyncline–day4 feeding theeasternRomagnabasins(extensively show thattheentry pointsoffl facies changes(Manzi,1997;Roveri etal.,1998) size ofthefluvio-deltaic sediments.Paleocurrents and progressive upward decreaseofthicknessandgrain- of thisunitagainsttheForlì structuralhigh,andthe Geological cross-sectionsclearlyshow theonlap possibly relatedtotheprogressive basinenlargement. suggests abacksteppingoffl eld dataofthis,aswelltheothersectors colombacci ). As inthewesternsector, the ui-eti systems, uvio-deltaic uvio-deltaic systems uvio-deltaic Figs. 7and16).Seismicdataallowed Roveri etal. anticline relatedtotheForlì line(Rioloanticlinein developed above, andwas delimitedby, anuplifting type Messiniansuccessionofthewesternsector ,and themainMessinianevents. The Mediterranean- recognized betweenthetectonichistoryofarea is theclosetimeandgeneticrelationshipthatcanbe of thesedimentationrate. The mostimpressive fact in sedimentcomposition,andthedramaticincrease drainage system,aswitnessedbytheabruptchange to thedevelopment ofanembryonic Apenninic to theemergence ofthe Apennine backbone,and Po Plain. This phaseoftectonicdeformationled in amoreexternal position,now buried underthe wedge, andtothedevelopment ofanew depocenter foredeep basin,toitsaccretiontheorogenic closure andfragmentationoftheMarnoso-arenacea The larger volume fl of turbiditicfl arenacea basinwithconsequentlateralconfi leading totheprogressive narrowing oftheMarnoso- topographic reliefelongatedparalleltothebasinaxis, of theRioloanticline,was thecreationofasmall evolution ofthearea. The first evidence ofthegrowth 18), was responsiblefortheobserved sedimentary of thisstructure,startingfromtheLate Tortonian (Fig. eastern lateralramp(Fig.17). The continuousuplift plunging tothewest,ofwhichFLrepresents to reconstructasingleENEverging arcuate structure (2003) totracethisstructureinthesubsurface, and ows runningfromtheNWtoSE. ows, acceleratedbythis lateral nement THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19 Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 20 - Genetic and stratigraphic relationships between resedimented and primary evaporites (from Manzi, 2001).

21 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri evident cyclicity, especiallyinthelower part having astrongersyntectoniccharacter, show aless- further down-basin tofeedtheSavio turbiditesystem. “channels”); theirsedimentloadwas probablycarried cut large-scale erosionalfeatures (theFontanelice constriction, increasedtheirerosionalpower, and pattern especiallyintheupperunit(p-ev Post-evaporitic depositsshow awell-developed cyclic succession withastronomicallyforced insolationcyclicity. Figure 21-CorrelationofMessinian Apennine foredeep 2 ).; p-ev 1 deposits, tectonically-active slopewas characterizedbystrong and amuddyslopedeveloped inbothsectors. This off fromcoarse-grainedturbiditicsedimentinput, east. The formerforedeepbasin was graduallycut west, andasubsidingbasintothenorth two different subbasins:anupliftingbasintothe the frontalandlateralramp,splitforedeepinto smaller volume fl ows. The anticlinegrowth, along considered aslobesformedinaconfi ned basinby The thicksandstonebedsof“channel”fi lls canbe THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

area from turbidity currents. During the Messinian, the role of the Riolo anticline is clearly defi ned. Primary, shallow-water evaporites were deposited only in the western sector within a large, semiclosed wedge-top basin. The longer-term shallowing-upward trend, superposed on the small-scale gypsum cycles, suggests a gradual upward reduction in the amount of accommodation space created. The evaporites are cut by an erosion surface – the intra-Messinian unconformity – of inferred subaerial origin, that can be traced to the SE on the outcropping culmination of the structural high associated with the Forlì line lateral ramp, and to the NE above, the buried anticline crest, which has been revealed by seismic and well data. The unconformity is associated with an angular discordance, and was formed during a paroxysmal phase of tectonic activity. The time elapsed during erosion in marginal uplifting areas, is recorded in topographic depressions by a volume of sediment which corresponds to the lower post-evaporitic unit that occurs in the eastern sector. As a consequence, in the Apennine foredeep basin, a large-scale tectonic pulse stopped primary evaporite deposition, and caused the transition from a hypersaline to hyposaline basin. Deep-water settings never experienced desiccation, and evaporitic sediments were emplaced by gravity fl ows, forming a thick unit with tabular Figure 23 - Isotopic composition of colombacci limestones showing the clear evolution toward the quasi-marine values fi eld, suggesting higher water concentration or true incipient connection with ocean waters (from Bassetti et al., submitted).

Figure 22 - Ideal evolution of uppermost Lago Mare cyclicity in the Apennine foredeep basins. Modifi ed from Roveri et al. (1998). instability, leading to huge sediment failures. The deeper and more subsiding character of the eastern sector is demonstrated by the higher thickness of the Tortonian to Lower Messinian succession, and by the higher terrigenous content of the local euxinic shales. Independent evidence for the uplift of the western sector during the Late Tortonian and Early Messinian Volume n° 2 - from B16 to B33 n° 2 - from Volume comes from sediment rates and paleobathymetric reconstruction (Kouvenhowen et al., 1999; Van der Meulen et al., 1999); their combination suggests a sediment rate decrease, and a concurrent shallowing upward trend. The decrease of sedimentation rate is essentially due to the suppression of the terrigenous component, related to the progressive cut-off of this uplifting

23 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri 1 -TheonsetoftheMSC Messinian record. larger scaleimplicationsof the Apennine foredeep should stimulateandfocusthediscussionaround and interpretationspresentedinthisfi eld trip,and topics arebriefl In thissection,someofthe“hottest”Messinian Hot Messiniantopics Miocene/Pliocene boundary. Riccòsection(western Emilia Apennines; fromRoveri andManzi,inpress). Figure 24-Thecharacteristic black layerunderlying thesharptransitiontoopenanddeepmarineconditionsat belong totheuppermostp-ev intra-Messinian unconformityinthewesternsector, Messinian,; theLagoMaredeposits,restingabove the phase, theFLstructuralhighwas sealedinthelatest After theemergence, following theevaporitic margins. geometry andonlapterminationsagainstbasin thick Plio-Pleistocenecover. culmination oftheRioloanticlineburied bya1500m to thepresent-daystructuralsetting,withnorthern generalized NE-ward tiltingofthewesternsectorled area (RicciLucchi,1986).Duringthisphase,a of the Apennine thrustfronttowards thePoplain unconformity), markingasignifi important tectonicevent occurredat4.2My(LP throughout the Apennine orogenicwedge. A new fi phase lastedthewholeEarlyPliocene,duringwhich following theintra-Messinian tectonicpulse. This generalized subsidenceandbasinenlargement, fl basal Pliocenefl ooding occurredover analmost the occurrenceofcolombaccilimestones. The ne-grained, deep-water sedimentsaccumulated at topographydeveloped inaphaseofslow and y introduced. They derive fromdata 2 unit,asindicatedby cn propagation cant original substratum. A possiblevertical displacement superposed tosedimentsdeeperthanthoseabove its translation alongthispaleoslope,gypsumisactually thin-skinned deformation. According totheextent of shales, thusaccountingfortheobserved SWverging unit onadetachmentsurface withintheeuxinic triggered large-scale gravity failures ofthegypsum during theintra-Messiniantectonicphasecouldhave southern, innerfl ank oftheanticline.Renewed uplift angle W-SW dippingpaleoslope,correspondingtothe arguments fortheMessinian development ofalow- to theuplifthistoryofRioloanticline,alsoprovide evolution ofthewesternsectorasessentiallyrelated the reconstructionofsedimentaryandtectonic by Manzi(2001)andRoveri etal.(2003).Indeed, of suchdeformationshasbeenrecentlycontested The commonly-envisaged purelytectonicorigin that arecharacterizedbyabundant shearplanes. out withintheupperpartofeuxinicshales, severe post-depositionaldeformations,fl other hand,theLower Evaporites areaffected by a shallow-water origin(i.e.thephoticzone).On base oftheevaporitic unit,donotnecessarilyimply Moreover, thestromatoliticlimestones,marking to low oxygenconcentrationsatthesea-bottom. in theupperpartofpre-evaporitic deposits,due However, noreliablepaleodepthindicatorsoccur foredeep marginal successions,isapparentlyabrupt. to seleniticgypsum,observed inthe Apennine et al.,2001). The transitionfromeuxinicshales not well-constrained(100maccordingtoClauzon associated withasea-level fall whoseamplitudeis The onsetoftheevaporitic stageiscommonly attening THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19 Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 25 - Geological map of the western sector 25 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri the UpperEvaporites orLagoMare stages ofthe The transitionbetweentheLower Evaporites, and the intra-Messinianunconformity 3 -Thetectonicvs.eustaticoriginof intra-Messinian tectonicpulse. uplift; thelatterwas possiblyheraldingthestrong competition betweensea-level riseandtectonic reduction intherateofspacecreation,suggesting small-scale cycles. This indicatesagradualupward term shallowing-upward trendissuperposedupon of the Apennine foredeepindicatethatalonger- facies changesobserved intheevaporitic cycles composition (Flecker andEllam,1999). The vertical Ocean, asalsosupportedbytheevaporite isotopic imply alarger water exchange withthe Atlantic The latterhypothesis(Clauzonetal.,2001),would implies ageneralizedsubsidenceorsea-level rise. Mediterranean geodynamicsettings,andnecessarily Evaporites isacommonfeatureacrossallthe The aggradationalstackingpatternoftheLower development. valley), suggestingexternal forcingfactors onfacies (i.e. inthesamecycle) inotherareas(Marecchia have beenobserved atthesamestratigraphiclevel understood yet.Suchanomalousfacies sequences 4) occur, andtheirsignifi cance hasnotbeenfully inverse facies trendsorsymmetricalrhythms(4-3- (facies sequence3-4-5)isconcerned;insomecases, of facies, withdecreasingsizeofselenitecrystals especially concerningtheregular superposition ideal cycle ofprimaryevaporites canbeobserved, Actually, many differences fromtheabove described of Lower Evaporites 2 -Cyclicityandstacking patterns overestimated. from euxinicshalestoprimaryevaporites couldbe As aconsequence,the“abrupt”vertical transition of 150-200mhasbeencalculated(Manzi,2001). eastward fromTossignano. Figure 26-Stop1.3.ThespectacularLower Evaporitesoutcrop(RioSgarbasect.),looking sandstones” croppingoutintheLagabasin(the 1960s-early 1970stoindicatesome“gypsiferous The termclasticevaporites was fi rst usedinthelate and signifi 4 -Resedimentedevaporites:origin climate have notbeeninvestigated yet. consequences ofsuchpaleogeographicchangeson it markstheemersionof Apennine chain. The deformational phasesincetheEarlyMiocene,as unconformity isassociatedwiththemostimportant the Mediterranean.In Apennine foredeep,this the marineconnectionsbetween Atlantic and km) ofthe African-Iberian margin requiredtoclose of the Alboràn volcanic belt,andthelarge uplift(1 to explain theabruptchangesinmagmacomposition mantle processes,occurringbetween6.3and4.8My, et al.,(2003)envisaged complex deep-crustalor collisional margin (Meulenkampetal.,2000).Duggen reorganization allalongthe African-Eurasian This suggestsanimportantphaseofstructural associated withanangularunconformity. Mediterranean), thiserosionalsurface isclearly Basin, Sicily, theEasternMediterranean, Western foredeep, the Tyrrhenian basins,the Tertiary Piedmont in different geodynamicsettings(the Apennine rejected. However, inmany basinswhichdeveloped regional deformationalphasehasbeencommonly of theintra-Messinianunconformitytoasupra- The attribution ofthetectonically-enhancednature 1978; Ryan&Cita,1978). front oftheNile,Rhone;Clauzon,1973,1982;Ryan, canyons infrontofthelargest rivers (forexample, in a hugefl uvial rejuvenation withtheincisionofdeep exposure ofMediterraneancontinentalmargins andto basins. Suchacatastrophicevent ledtothesubaerial implying desiccationofthedeepestMediterranean evaporative sea-level fall inexcess of1,000meters, of thiserosionalsurface iscommonlyrelatedtoan cance amplitude. The origin amplitude. The hiatus ofvariable associated witha unconformity), intra-Messinian surface (the of alarge erosional by thedevelopment Mediterranean area basins ofthe in allmarginal MSC, ismarked THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

Figure 27 - Stratigraphic columns of the Vena del Gesso in the western side of the Santerno Valley (after Landuzzi, 1985): A= euxinic shales and stromatolitic limestones; B= euxinic shales, calc-gypsum laminites and gypsifi ed B16 to B33 n° 2 - from Volume stromatolites (facies 1-2); C= massive autochthonous selenite (facies 3); D= interbedded autochthonous and reworked selenite (facies 4); E= entirely reworked selenite (facies 4?); F= clastic, acicular and nodular gypsum (facies 5); G= chaotic gypsum in a clayey matrix (facies 6); H = post-evaporite deposits (see details in Figure28). southern depocenter of the Messinian Apennine deep-water primary evaporitic facies. The occurrence foredeep). These deposits were often associated with within the “balatino gypsum” of sedimentary the “balatino gypsum”, a well-laminated alternation of structures, interpretable as megaripples (Fanantello gypsum and bituminous shales, usually interpreted as a River, Schreiber, 1973; see stop 3.3; Fig. 19), was

27 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri trigger mechanismsfortheinitiation offl gypsum detritusproduction,andthedefi provides someconstraintsfor the modalitiesof strictly linked withthegeodynamicmodel,which turbidites. This sedimentologicalinterpretationis which impliesaclosesimilaritywithsiliciclastic and ageneticmodelforresedimentedevaporates, (submitted), have proposedanew facies classifi petrographic andgeochemicalstudy, Manzietal. recent times.Basedonanintegrated sedimentological, occurrence, they have beenvirtuallyignoreduntil Manzi etal.,submitted).Despitetheircommon Ricci Lucchi,1973;Manzi,2001;Roveri etal.,2001; below thewave base(Parea andRicciLucchi,1972; through gravity processesintorelatively deepwaters, of primary, actually clasticdepositsderived fromthedismantling Most oftheevaporites ofthe Apennine foredeepare level withintheeuxinicshales.Transport was totheS-SW. faulting, glidingandthrustingonashallow detachment offset offaultedblocks suggestsgravity-driven normal mark aspectacularangularunconformity. Therotational are sealedbypost-evaporiteMessiniandeposits,which very smallreverse faultsoffset theevaporitecycles,and side oftheSanterno Valley (M. Astorri). Normalfaultsand Figure 28- Air photoofthe Vena delGessointhewestern rocks, theirstudyisavery diffi diagenetic effects typically undergone byevaporitic gravity fl of depositsshouldbedealtwithasthesiliciclastic turbidity currents. As amatteroffact, thisclass deposits, rangingfromolistostromestolow-density facies ispartofawidespectrummass-fl deposited fromturbiditycurrents. The “balatino” of the Apennines hasclearlytobere-interpretedas structures), almostallthe“balatino”gypsumfacies gradation, cross-lamination,andtractions-plus-fallout structures (loadcasts,fl due totherecognitionofvery indicative sedimentary Actually, not adequatelytaken intoconsideration. ow depositsare.However, duetothestrong in situevaporites, andresedimented uid-escape structures,bed cult task. ow. nto of nition cation, ow ow sediments ofthep-ev as witnessedbythecompositionofterrigenous drainage onlyformedattheendofthisupliftphase, A landareawitharelatively well-developed fl which ledtothefi very beginning oftheintra-Messiniantectonicphase Resedimented evaporites wereaccumulatedatthe the paleogeographicsettingofMessinian. fl a genesisfromsubmarinecollapses.Fluvial in theresedimentedevaporite unitcouldsuggest The generalpoor-to-absent terrigenouscomponent general picture. topography provides furthercomplicationstothe Marche basin.Ofcourse,localtectonically-induced the Forlì LinetotheeasternRomagnaandnorthern facies distribution alongaNW-SE transectfrom currents. This isclearlyevident whenconsidering down currentinto high andlow-density turbidity gravitational instability, andweretransformed assumed tohave beentriggered bytectonic-induced collapses andglides;theseglidesare in shallow thrust-top basinsthroughlarge submarine of theremoval ofprimaryevaporites whichformed distribution isingoodagreementwiththehypothesis facies associationshave beenrecognized. Their areal On thebasisofthisapproach,several facies and diagenetically-transformed deposits. to indirectlydefi ne thisimportantparameterin size andsedimentarystructuresisproposedinorder a siliciclastic-derived relationshipbetweengrain size ofclasticevaporites; inManzietal.(submitted), One basicproblemisthedefi nition oforiginalgrain- containing large blocksoflithifi ed primaryselenite. dominated byslumpingandolistostromes,often part madeupofdisorganized, very coarseclastites, well-stratifi very oftenoccurs,withalower partmadeupof in theresedimentedevaporite unit;aclearbipartition suggested bythevertical facies sequences observed oods canbethusdiscarded,alsoconsidering e, fi ed, ne-grained deposits,andanupper rst emersionofthe Apennine chain. 1 andp-ev 2 units. This isalso uvial THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19 Volume n° 2 - from B16 to B33 n° 2 - from Volume Figure 29 - Stratigraphic columns of the Colombacci fm (upper Messinian p-ev2 unit) in the western side of the Santerno Valley (after Landuzzi, 1985): C-G = GS facies 5- Valley side of the Santerno 29 - Stratigraphic columns of the Colombacci fm (upper Messinian p-ev2 unit) in western Figure ne-grained limestone lenses; H4 = silty clays with fi ne-grained clastic limestone; H3 = “varve”-like 27); H1 = limestone breccia with gypsum moulds; H2 fi 6 (see Figure clays; H6 = variegate green and red H7 poorly sorted calcareous bodies; H8 conglomerates in small channel laminated silty clays; H5 = variegate green and yellow Azzurre Pliocene marine clays (Argille clays; P = Lower pebbly mudstones; H10 = dark organic-rich bodies; H9 = fossil-rich sandstones in small channel = festoon-bedded Fm).

29 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri timing ofsulfurformationareunknown, anddetailed was formedbysulfate reduction.Characteristics and These characteristicsindicatethatelementalsulfur sulfuric acidandmethane. calcite, celestite,barite,bitumen,andemissionsof and massive textures. Native sulfurisassociated with and breccia-veins textures, andlesscommonribbon 12 %. The sulfurmineralizationshows mostlynodular sulfur meanreachupto40%,but isgenerally around a few metersthick,but generallylessthan1m. The limestone layersappeartoreplacesulfate layersupto particularly organic-rich shaleinterbeds.Sulfur- higher stratigraphiclevels, insulfate layershaving (Perticara), themineralizationisalsopresentin organic-rich shales(euxinicshales).Insomeareas at thecontactofsulfate layerswiththebasal the baseofevaporite formation,andparticularly of discontinuous,thinlenses,mostlyrestrictedto (Scicli, 1972). The sulfurmineralizationconsists were minedfromRomantimesuntilthe1960s Marche Apennine containssulfurdepositsthat The Gessoso-solfi fera Fm. oftheRomagnaand of sulphurmineralization 5 -Gypsumdiagenetictransformation andorigin Mediterranean deepdesiccation. would putintodiscussionthetrueextent ofthe associated withtheintra-Messinianunconformity, of othersubaqueously-depositedclasticevaporites, environmental changes.Ofcourse,therecognition comprehension oftheMessinianpaleogeographyand would representafundamentalstepforbetter of theMediterraneanarea. Their correctrecognition could beacommonfeatureinotherMessinianbasins Tortonian slope mudstones.Resedimentedevaporites from theeuxinicshalesandunderlyingUpper up withthemuddydepositsofp-ev1 unitderiving resedimented evaporitic complex, whichcouldfollow a sortof“inverted stratigraphy”isrecorded bythe olistostromes anddebrisfl ows. As aconsequence, grained primaryevaporites lower cycles couldproduce of theearly-cemented,thicker-bedded, andcoarser- unlithifi erosion ofthethinner-bedded, mainlyreworked, and resedimented evaporites couldderive fromthe 20). According tothisview, basalfi units formedabove oraroundstructuralhighs(Fig. exhumation anddenudationofprimaryevaporitic rather recordstheprogressive upliftandconsequent tectonic deformation;however, webelieve thatit “progradation” ofthesystemrelatedtoongoing This vertical organization couldwellrefl ed uppermostcycles. The subsequenterosion ect asortof ne-grained hiatus was bridgedbythelower partofthep-ev subsiding basins,therecordiscontinuous,and sector oftheRomagna Apennines); indeeper, only occursabove upliftedareas(e.g.thewestern As statedabove, inthe Apennine foredeep,thisgap base-level. of Paratethyan waters byalowered Mediterranean most commonly-acceptedexplanation isthecapture a dramaticpaleogeographicchangeareobscure;the Mare stage. The causes,modality, andtimingofsuch hypersaline tohyposalinewaters leadingtotheLago important Messinianevents: thatis,theswitchfrom gap doesnotallow afullunderstandingofthemost deeper basins(Krijgsmanetal.,1999b;Fig.3). This Ma isusuallyassociatedwiththedesiccationof common stratigraphicgapbetween5.50and~5.60 In MessinianMediterraneansuccessions,the of theLagoMareevent 6 -Theclosureofthe‘Messiniangap’,andonset by groundwater duringtherehydrationofanhydrite. oxidation ofsulfuricacidbydissolved oxygencarried Most sulfurdepositionpossiblyoccurredthroughthe buried atarelatively shallow depth(~500-1000m). can beexcluded becausetheevaporite formation was thermochemical sulfate reductionoriginforthesulfur from theassociatedorganic-rich shalesandmarls. A reduction, triggeredbyhydrocarbons,migrated most sulfuroriginatedthroughbacterialsulfate synsedimentary formationwas negligible, andthat the Vena delGessoBasin. This suggeststhatearly and notintheunaffected autochthonousseleniteof were transformedintoanhydrite atburial diagenesis, evaporites oftheRomagna-Marchearea,which concentrations arepresentonlyintheclasticsulfate aspects isthateconomicallyimportantsulfur at theirinitialstage.Oneofthemostsignifi textural, petrographic,andgeochemicalstudiesare deposition oftheresedimented evaporite complex. already establishedimmediatelyafterorduringthe means thatthetypicalLagoMarehydrologywas above theresedimentedevaporite complex. This pollen anddynofl agellate assemblagesimmediately the recognitionoftypicalLagoMareostracod,and a continuouscore(Campeawell,stop4.1)have led to Preliminary observations andanalysiscarried outon carried outbyamultidisciplinaryresearchgroup. reason, adetailedstudyofthisinterval isbeing successions have recordedsuchevents, andforthis sediments (Figs.5,21). This meansthatthe Apennine and byathickpileofterrigenous,fi unit, whichismadeupofresedimentedevaporites, ne-grained cant 1 THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

Cores have also pointed out the occurrence of well- origin of small-scale sedimentary cycles, as occurred defi ned organic-rich horizons, which are being studied during the pre-evaporitic and evaporitic stages. By to assess their paleoenvironmental meaning, and their this way, the p-ev2 unit would span a very short time potential as regional lithostratigraphic markers. interval of 60-80 Ky, and a tentative correlation of its small-scale sedimentary cycles with the insolation 7 - High-frequency Milankovitch-type curve is shown in Fig. 21. According to Roveri et climatic cyclicity in the Lago Mare deposits al. (1998), the basic lithological cyclicity given by Like pre-evaporitic deposits and lower Evaporites, the the vertical repetition of sharp-based coarse-to-fi ne- Lago Mare successions show a fairly well-developed grained couplets, observed in both shallow, marginal cyclic organization that can be used to establish a basins developed above the orogenic wedge, as well high-resolution stratigraphy, otherwise impossible to as in the foredeep depocenters, would refl ect the obtain in a non-marine unit encompassing a very short periodic activation of catastrophic fl ood-dominated time span. According to Krijgsman et al. (1999a-b), fl uvial systems carrying coarse sediments into the the Lago Mare stage lasted more or less 270 Ky, 90 of Lago Mare during dry intervals, or at the transition them recorded by deep Mediterranean evaporites and between dry and wet periods (Fig. 22). During these by the basal p-ev1 unit of the Apennine foredeep (Fig. phases (Fig. 5), small forestepping deltaic systems 21). The bipartite character is an easily-recognizable, formed in shallow basins with low gradient shelves; but usually overlooked, feature of the Lago Mare in basins with reduced or steep shelves, fl uvial fl oods successions, not only in the Apennine foredeep, but could develop hyperpycnal fl ows which were able to also in many other basins (see for example the Upper carry their sediment load down-basin, forming small Evaporites and Arenazzolo Fm. of Sicily). Only the turbidite systems of “low-effi ciency” (sensu Mutti upper part of the lower unit, locally characterized et al., 1999). Water carried with sediments to the by the deposition of shallow-water, sabkha-like basin contributed to a rapid rise in the base-level and evaporites (Sicily), is there a well-developed cyclical caused, together with a concomitant climate change lithological pattern. towards wetter conditions, the de-activation of In the Apennine foredeep basins, up to fi ve cycles, fl ood-dominated deltaic systems, and their landward defi ned on the basis of the regular alternation of migration. During wet phases, the base level reached coarse and fi ne-grained lithosomes, can be recognized its maximum, but sediment input was drastically above the ash layer, and can provide an independent, lowered for both the reduction of the catchment area, even if not particularly accurate, time calibration. and the possibly lower erosion rate which was due to

The upper p-ev2 unit, which is widely recognized the increased vegetation cover. In this phase only fi ne- on a Mediterranean scale, is characterized by a grained, thinly-laminated mudstones accumulated in well-developed, high-frequency cyclical pattern the basin. In some places, the rhythmic alternations superimposed upon an overall transgressive trend. of light and dark mudstone horizons give a typical These two characteristics represent good criteria for banded aspect to the deposit, probably representing a high-resolution long-range correlations; 3 to 4 main distal lacustrine facies. Thin-bedded, fi nely-laminated cycles have been traced from shallow to deep-water limestone horizons (“colombacci”) are usually found successions of the Apennine foredeep (Roveri et al., in the upper half of the cycles associated with mudstone 1998; Ricci Lucchi et al., 2002), 4 cycles have been deposits. According to Bassetti et al. (submitted - see recognized in the uppermost Messinian deposits topic 8), they derive from the inorganic precipitation at Cyprus (Rouchy et al., 2001), 3-4 cycles in the of micrite-size crystals in a relatively deep-water uppermost Messinian Nile Delta deposits (Abu-Madi environment which was possibly anoxic and related Fm., Dalla et al., 1997), 4 cycles in the fl uvio-deltaic to permanent water mass stratifi cation events during deposits of the Tertiary Piedmont Basin (Ghibaudo periods of lake level maxima, and associated peaks of B16 to B33 n° 2 - from Volume et al., 1985); 3 to 4 cycles are reported from a thick reduced terrigenous input. However, the concomitant terrigenous Lago Mare succession unconformably occurrence, in the same part of the cycles, of dark, overlying the Lower Evaporites in the Corvillo basin organic-rich clay horizons, rich in specialized (Sicily; Keogh and Butler, 1999). As a consequence, Mollusk assemblages (Congerie) and interpreted as a total of 8/9 cycles can be recognized in the 180 palustrine deposits, suggests a far more complicated ky interval between the ash-layer and the Miocene/ stratigraphic architecture and more complicated Pliocene boundary. evolutionary trends, as tentatively illustrated in This is consistent with a precessionally-driven climatic the model of Fig. 22. Palustrine horizons, found

31 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri the basinalmudstonesofp-ev are atypicallithofacies closelyassociatedwith As previously reported,thecolombaccilimestones 8 -Originofthecolombaccilimestones Cyprus (Rouchyetal.,2001). succession, whichhave beenrecentlydescribedin the LagoMarecycles fromthetopmostMessinian meaning; however, they appeartobeanalogouswith better theirorganization andpaleoenvironmental deposits isbeingcarriedoutinordertounderstand clastic sedimentsources.Detailedstudiesofthese condensed sectionmarkingthemaximumretreatof colombacci exposure surfaces duringinitialbase-level rises;the palustrine horizonscoulddevelop above thesubaerial removed any trace. According tothemodelofFig.22, produced bycatastrophicfl paleosoil development; moreover, the erosion each cycle, mightnothave beensuffi encompassed bysubaerialexposure phaseswithin However, thepossiblyvery shorttimespans syncline). traces (Botteghino sectionintheGiaggiolo-Cella overlies anirregular surface withweakpedogenetic marking theMiocene/Plioceneboundary, locally (Roveri etal.,unpublisheddata),wherethedarklayer An exception isrepresentedbytheuppermostcycle paleosoils, have beenclearlyrecognizedsofar. prograding coastaldeposits,norclearevidence of the uppermostpartofcycles. However, neither words, aregressive hemicycle couldbepreserved in produced duringbaselevel fall indryphases.Inother unit, thelattertoppedbyasubaerialerosionalsurface into alower transgressive, andanupperregressive fi According totheirpositionwithineachcycle, the compatible withasimpledeepeningupward cycle. at different levels withinmudstoneunits,arenot or atleastahighdegree ofwater dilution. The negative As ageneralrule,isotopiccompositionsshow structure ofthebasinsandtheirdegree ofconnection. provides goodelementstoderive thehydrological Mediterranean basins;theirgeochemicalcomposition is quitecommonintheLagoMaredepositsof lake-water stratifi possibly driven byclimatically-inducedevents of the periodicsupersaturationofepilimnion, Bassetti etal.(submitted),theirprecipitationrequired the surface waters oftheLagoMare. According to abiotic, andformedasinorganic precipitatesfrom ne-grained lithosomecouldactuallybesubdivided 18 O values, indicatingfreshwater conditions, limestoneswould representasortof cation. This carbonatelithofacies uil fl uvial oods would have 2 unit. They are cet for cient the aggradationalstackingpatternofp-ev ocean. The latterwould beingoodagreementwith basins or, onthecontrary, atrueconnectionwiththe strong concentrationduetoevaporation inrestricted “normal marine”range. This couldeitherindicatea horizon haslessnegative values, almostfalling inthe strongly negative isotopicvalues; theuppermost show thatthetwo lower horizonshave homogenous, trends. The results(Fig.23;Bassettietal.,submitted), verify possiblearealgradientsandstratigraphic in eachcycle indifferent sub-basins,andhenceto compositions ofcolombaccilimestonesoccurring foredeep madeitpossibletocompareisotopic high-resolution stratigraphicmodelofthe Apennine emerged withtheintra-Messinianuplift.Signifi submersion ofthe Apennine backbone,previously subsidence, thatprobablyledtothealmostcomplete in aphaseoftectonicquiescenceandgeneralized the Apennine foredeep,wheresuchatransitionoccurs transgressive sequence. This isparticularlyclearin Messinian LagoMaredeposits,aspartofalonger-term reported. MPl1sedimentsarealways associatedwith older thantheuppermostMessinian,hasnever been direct superpositionofMPl1depositsabove rocks 1999). A peculiarlyinterestingfeatureisthatthe event ataMediterraneanscale(Iaccarinoetal., return tofullymarineconditions,isasynchronous The Mio/Plioceneboundary, markingthesudden 10-TheMio/Plioceneboundary investigated. small-size, dwarfed specimensneedtobethoroughly observed foraminiferaassociationsmadeupof Lago Maresuccessions.However, thecommonly incursions have beenfoundinthe Apennine foredeep notes werewritten,noclearindicationsofmarine was presentintheMediterranean. As far asthese during thefi nal partofthisstage,alarge water body (Keogh andButler, 1999),suggestthepossibilitythat composition ofthetypicalfaunal associations Spezzaferri etal.,1998;Snel2001).Isotopic (Blanc-Valleron etal.,1998;Pierre especially onthebasisofnannoplanctonassemblages been reportedfromdifferent Mediterraneanbasins, marine incursionsintheLagoMaredepositshave composition oflimestonehorizons,occasional Besides theabove considerationsbasedontheisotopic Lago Marestage? 9 -Marineincursionsduringthe the Zancleanfl suggesting aoverall “transgressive” trendheralding ooding. cantly, 2 unit, THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

in successions deposited around topographic highs, valley, the core of the Coniale anticline is where the and characterized by the permanent activation of fan- oldest stratigraphic level of the Marnoso-arenacea Fm delta systems, the Miocene/Pliocene transition appears is exposed. Further upstream, between S. Pellegrino to be very gradual and such a boundary becomes and Firenzuola, the sand-rich Firenzuola system very diffi cult to recognize (Roveri and Gennari, turbidites crop out in the southern fl ank of the Coniale unpublished data). Elsewhere, a black, organic-rich anticline. layer always underlies the lowest deep-marine MPl1 sediments (Fig. 24). Its nature and signifi cance are DAY 1 not clear, and its systematic study is currently being carried out. As previously reported (topic 7), in some Stop 1.1: cases, this organic-rich horizon seems to be associated The reception center of the Vena del Gesso Natural with a slightly erosional surface and weak paleosoil Park, Tossignano. Depending on time availability and traces. weather conditions, this optional stop will be devoted According to the above-mentioned possible to visiting a small museum exhibiting materials occurrence at the end of the Messinian of a large about nature, geology, mining activities, history, and Mediterranean non-marine water body, and a higher country life in the unusual environment of the Vena degree of connection between the different sub-basins, del Gesso. the Miocene/Pliocene transition would be rather explained by a sudden hydrologic change associated Stop 1.2: with a bathymetric change of lower amplitude than Rocca di Tossignano. The ruins of the medieval castle usually thought. This would point to the Zanclean on the hilltop are a wonderful place for a panoramic fl ooding being less catastrophic in character. view over the Santerno valley and the Apennine foothills monocline (see cover photo and Fig. 26). Field trip itinerary From SW to NE, the geologist can visually explore up-section the following stratigraphic units, whose Introduction to Days 1 and 2 details will be dealt with in the next stops: These two days will be spent in an area between the - Marnoso-arenacea Fm, Fontanelice member: coarse Sillaro and the Lamone valleys (Fig 25). The Santerno sandstone and conglomerate bodies, composed of Valley, that will be visited during day 1, surely offers multiple or individual “channel” fi lls. one of the most continuous and spectacular Neogene sections of the Northern Apennines, and is particularly - Marnoso-arenacea Fm., “ghioli di letto” unit: fi ne- famous for the outcrops of the Miocene Marnoso- grained, thin-bedded turbidites and marls in an overall arenacea Fm, described in great detail in classical thinning- and fi ning-upward trend. papers by Franco Ricci Lucchi and his co-workers - Marnoso-arenacea Fm, “euxinic shales” unit: marls in the late 1960s and 1970s. The local stratigraphic embedding cyclic intercalations of bituminous clays. succession that can be observed spans in age from The Tortonian-Messinian boundary is situated about Lower Serravallian to Pliocene. The Marnoso- 60 m below the unit top. arenacea Formation is overlain by the Messinian - Gessoso-solfi fera Fm: it is composed of up to 16 evaporites which, in turn, are unconformably overlain evaporite cycles, subdivided into 2 “basal” ones (not by uppermost Messinian continental deposits and visible), 3 “major” ones (grey selenite), a very thick marine Pliocene-Pleistocene strata. The geology 6th one (grey selenite and white clastic gypsum), and of the Santerno valley is relatively simple at the up to 10 “minor” ones (mostly white clastic gypsum). All 16 cycles crop out only in the eastern side of the

surface, where strata form a regular homoclinal, B16 to B33 n° 2 - from Volume gently dipping to the northeast, i.e. down the valley. Santerno valley (Rio Sgarba quarry, stop 1.4). In the Moving upstream from Imola, we drop down into western valley side (Fig. 27), a maximum of 15 cycles progressively older stratigraphic levels. A packet is found in the old Paradisa quarry, while 7 cycles crop of vertical to slightly overturned strata interrupts out at Mt. Penzola, and only 4 ones crop out at Orzara. this regular bedding attitude at Coniale; these beds Near the Santerno river bed, this W-ward reduction represent the northern limb of the ramp anticline of the evaporite succession is clearly explained by associated with the Mt. Castellaccio thrust, a tectonic a Upper Messinian angular unconformity (Fig. 27), feature elongate in a NW-SE direction, that can be while further to the W, a non-depositional hiatus is traced as far as the Savio valley. In the Santerno also possible. This alternative explanation would be

33 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri embedded inthe8 distinguished andcorrelated. Two slumphorizons quarry. Basal,major, andminorcycles canbeeasily Riva SanBiagiocliff (Fig.26),totheRioSgarba Park. This panoramic view covers theGSfrom Tossignano, Resistance(II World War) Memorial Stop 1.3: Upper Messiniandeposits(p-ev - Colombaccifm:ahard-to-seehorizonofcontinental the Sillarovalley (Fig.26). individual evaporite cycles fromtheSeniovalley to in agreementwiththeoverall W-ward thinningofthe Topics: 2. the othersideofSanternovalley. gravity-failure structures,like thosedocumentedon Perhaps thosenormalfaults canbeassociatedwith structure symmetricaltothebeddingplanes(Fig.30). Messinian normalfaults belongingtoa Terme high(Fig.25).Evaporites areoffset byUpper important constrainttotheevolution oftheRiolo of thoseslumpsisstillunknown, but mightbean be usedasadditionalmarker beds. The provenance morphology (cover photo;Fig.28). all Plioceneunitsisclearlyrefl epi-Ligurian fan-deltas. The well-stratifi ed settingof thick bodiesofresedimentedconglomerates,fedby Santerno Valley, claysembedolistostromesand Pliocene age.Closetothewesterndivide ofthe - Argille Azzurre Fm:marinesiltyclaysofLower better representedwithinstructuraldepressions. and sandstonepockets (facies H7-H8inFig.29)are evaporite unit(Fig.28).For instance,conglomerates fm arecontrolledbystructuralhighsandlows ofthe the pre-evaporite shales. Thickness andfacies ofthis unconformably cover theGessoso-solfi fera Fmand th and10 th ectedinthelandscape evaporite cycles can 2 sequence),which Graben Messinian deposits(p-ev2). the evaporitecycles,andaresealedbypost-evaporite (FCN, FMA)andtransverse (FCL)normalfaultsoffset side oftheSanterno Valley (M. Astorri). Longitudinal Figure 30- Air photoofthe Vena delGessointheeastern from the6 of themodalcycle canbeassessedindetail,starting (1973) was elaborated. The peculiarfacies architecture investigated whenthemodelof Vai andRicciLucchi bank oftheSanternoriver. Bothsitesweredeeply valley, andtotheoldquarryatParadisa, ontheleft deviations totheabandoned quarryintheRioSgarba Road Tossignano - Borgo Tossignano –Codrignano; Stop 1.4: The uppermost“channel”bodyoftheFontanelice deformation featuresoftheMAclasticwedge. views illustratetheclosurefacies andtheearliest Road Fontanelice –Gesso. Other panoramic Stop 1.6: Topics: 2. Riolo Terme high(Fig.25). be relatedtotheLate Tortonian nucleationofthe 31). The inferredslumpingdirectiontotheS-SWcan within thefi framing ofa50-60mthickintraformationalslump bed towards thewesternsideofvalley allows the Campola. A panoramicview fromtheSanternoriver Road Borgo Tossignano -Fontanelice, Molino Stop 1.5: Topics: 2,7. the “hotMessiniantopics”chapter. controlling evaporite depositionaresummarizedin the 6 erosion surface whichmarkstheonsetoffacies 5in is representedbythesharpandstronglyirregular Gesso, Sassofeltrio). Another basin-scaleproblem basin oftheMarecchia-Concaarea(Montebello, and fromittothesemi-allochthonousevaporite the para-autochthonous Vena delGessobasin, modal cycles. Indeed,they canbetracedthroughout same impressive correlationpotentialastheentire possibly relatedtobrinedilutionepisodes,have the intervals arecommon. These intra-cycle features, dissolution surfaces (Fig.14c),andreworked selenite 3 complex andanomalouscrystalsizevariation inthe an interestingsubjectfordebate.For instance,the scale discrepancieswiththebasicmodelrepresent example ofacompletefacies sequence.Smaller rd , 4 th th and5 cycle. Someofthepossiblelarge-scale factors ne-grained closurefacies oftheMA(Fig. th th cycle, whichisthefi cycle (Fig.27),wherereverse gradation, rst andthickest THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

member (Figs. 9, 10), the already described slump and the overall thinning- and fi ning-upward trend, are coherent indications of foredeep fragmentation and basin narrowing. Topics: 1, 2. Stop 1.7: Pieve di Gesso and Sassatello valley. A panoramic view on the so-called “Sillaro line” portraits the synsedimentary overthrust of the Liguride nappe in Messinian times (Fig. 32). Olistostromes coming from the Liguride and epi-Ligurian units have been Figure 31 - Closure facies of the Marnoso-arenacea Fm continuously forerunning the nappe advancement. in the western side of the Santerno Valley: two sandstone olistoliths mark a slump horizon in a fi ning-upward Many of them were tectonically incorporated in succession of thin-bedded turbidites. Local slumping the nappe itself, while others were embedded in the transport was possibly to the S-SW. autochthon succession. An example of the second type is the Upper Messinian Sassatello olistostrome, are the Lower Pliocene clays and conglomerates, the enclosed in the para-autochthonous p-ev unit. Its 2 angular unconformities in the post-evaporite p-ev2 composition is characterized by Lower-Middle sequence, and the Late Messinian tectonics. The most Miocene marls and typical Messinian carbonates, such attractive features of this itinerary are the M. Penzola as pre-evaporite and evaporite-derived limestones. A thrust (Fig. 33), and a short but complete section of closer inspection of the olistostrome and the local the Colombacci fm (Fig. 34, Fig. 29), featuring a Gessoso-solfi fera Fm, gives us the opportunity to very good outcrop of the Miocene/Pliocene boundary. discuss the diagenetic transformations of primary Discussion is expected on the role of gravity vs. evaporites. tectonics in the cortical deformation style of the Topics: 1, 2, 5. evaporite unit. Stop 1.8: Topics: 1, 2. The “Mt. Penzola walk” We walk along the Santerno DAY 2 – Sellustra watershed from Mt. la Pieve to Mt. Penzola and Debolezza, then we go down to Casetta Stop 2.1: Gessi, and reach the nearest bridge on the Santerno Visit to the reception center of the Vena del Gesso River. (Fig. 28) The main subjects that are dealt with Natural Park, Riolo Terme. This is another optional

Figure 32 - The Liguride nappe thrusting over the western Romagna para-autochthon: Messinian pre-evaporite (MA), evaporite(GS) and post-evaporite units are truncated atop by the overthrust surface, a gentle ramp dipping to the W. Olistostromes fed by Liguride and epi-Ligurian units occur both above and below the tectonic contact. Near Sassatello, a peculiar Messinian olistostrome is embedded in the p-ev2 unit of the para-autochthon. Volume n° 2 - from B16 to B33 n° 2 - from Volume

35 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri unit. Another importantcharacteristicofthispeculiar back-thrusts arestrictlyconfi ned totheevaporite in theMA,nor Argille Azzurre Fm.Indeed, the neighborhood,nosimilarstructureisfound,neither and theupperpartofpre-evaporite succession.In Upper Messinianthrust-sheets,whichinvolve theGS is awell-developed imbricatestackofSW-verging Valley (Fig.35),themostprominenttectonicfeature panoramic view over thewesternsideofSintria Zattaglia -Brisighellaroad,nearLa Torretta. Ina Stop 2.3: Topics: 1,2. levels). clays (disoxiclevels), andcommonmarlyclays(oxic shales (anoxiclevels), non-laminatedorganic-rich dark-light alternationofthin-laminatedbituminous The typicalpre-evaporite Messinianisadm-scale, boundary, andextends upwards totheGSbase. section, whichstraddlesthe Tortonian-Messinian participants willbedriven tothesiteofMt. Tondo on thecyclicity ofthepre-evaporite unit.Ifpossible, Vena delGessobasin.Discussionwillmainlyfocus astronomic datingofthemainMessinianevents inthe resolution cyclostratigraphy, magneticcalibrationand are thetwo mostimportantsamplingsitesforhigh- western divide oftheSeniovalley. Actually, they Casino arerespectively situatedontheeasternand Messinian outcrops.Monte Tondo andMontedel Rivola: theMt. Tondo quarry, andtheadjoining Road Riolo Terme -Casola Valsenio, stopatBorgo Stop 2.2: socio-economic importanceof Vena delGesso. stop aboutthegeological,ecological,historicaland tectonic thrusting. complex accommodationofglidingblocks, orfrom“real” gravity structures.Thisanomalymightresulteitherfrom contrary totheS-SWtransportofall Vena delGesso cycle over the5thone.TheN-NEvergency ofthethrustis Valley: athin-skinned thrustcarriesthe2ndevaporite Figure 33-MontePenzola, western sideoftheSanterno Topics: 1,2. introduction ofthisGuide. and gliding.Othervalid reasonsarereviewed inthe likely tohave beenformedbygravitational failure cropping outintheSintriaandLamonevalleys are a merelystructuralpointofview, theback-thrusts in thelower partsoftheslope.Summarizing,from other. This way, astackofuprootedrockslicesforms the faulted blockskeep gliding,andthrustover each rotational normalfaults, whileinitslower parts, the evaporite unitisextended anddismemberedby driven slopefailure. Intheupperpartsofslope, get simplerifweconsideraprogressive gravity- if interpretedasapurelytectonicfeature. Things big problemsforany cross-sectionreconstruction, out intheriver bed. This anomalous setting creates has “roots”inthevalley-fl oor, asnogypsumcrops imbricate stackisthatnotoneofthethrust-sheets karstic Neptuniandikes sealedbypost-evaporite 36). Subaerialerosionofgypsumisdocumentedby Gessoso-solfi by animpressive angularunconformitybetweenthe evaporite unitinLateMessiniantimesaretestifi gypsum quarry Brisighella: theMonticinoSanctuaryandadjoining Stop 2.5: Topics: 1,2,3. sub-vertical gypsumstrata. superimposed onUpperMessinianthrust-faults and opportunity toseerecentkarsticmorphologies A shortoff-road walk gives theparticipants Carne’ NaturalPark and/or Tanaccia cave entrance. Stop 2.4: Figure 34-NorthernslopeofMontePenzola: anabout 5 mthick Colombaccifm(seeFigure 29)separatesthe GS (6thcycle,facies5)fromthelower Plioceneclays. The typicaldarklayermarkingtheMiocene/Pliocene fera FmandtheColombacci(Fig. boundary isslightlyoffset bynormalfaults. . Deformation andemersionofthe ed THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

Figure 35 Monte Mauro and the western side of the Sintria Valley, from the S: the SW-verging thin-skinned thrusts that involve the evaporite unit can be explained by gravity-driven block-gliding, on a shallow detachment level within the euxinic shale unit (MA). As in the Santerno Valley example (Figure 28), the initial effect of gliding was the development of SW-dipping normal faults dismembering the evaporite unit. During the subsequent gliding progression, the same faults were rotated and partly reactivated as thrusts (dashed lines).

Messinian deposits (p-ev2). From 1985 to 1988, Introduction to Day 3 and 4 a very rich fauna of continental vertebrates was In the Santerno section we examined a reduced, found in those paleo-karsts (Marabini & Vai, 1988). Mediterranean-type Messinian succession, developed Panoramic and close views point out the present-day above a structural high (Fig. 4). An abrupt facies and state of the quarry, which is being converted into an thickness change within the successions across the open-air geological museum. Forlì line ,that separates the marginal Vena del Gesso Topics: 1, 2, 3, 10. basin to the west, from the eastern Romagna basins, is the best evidence of the strong structural control on Stop 2.6: Messinian deposition (Fig.7). Brisighella: participants will be offered a leisurely In the Savio valley area, we will examine Messinian walk from the medieval castle to the Clock Tower, deposits cropping out in the Sapigno and Giaggiolo- along faulted, vertical-bedded and karstifi ed gypsum Cella synclines (see geological map of Fig. 38), two ridges. wedge-top basins bounded to the west by the Forlì Topics: 2. Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 36 - Monticino Quarry, Brisighella: the mining front represents the best possible exposure of the angular unconformity between the depositional sequences T2 and p-ev2. Some fractures sealed by the unconformity have been highlighted for their virtual relationship to the famous Vertebrate-bearing upper Messinian sedimentary dykes. Figure 38 – Stop 3.1. Suggested along basin correlation of upper Tortonian deposits between the Santerno and Savio valleys (datum plane: ~ the Tortonian/Messinian boundary; From Roveri et al., 2002).

37 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri Figure 37-Geologicalmapoftheeastern sector THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

Figure 38 - Stop 3.1. Suggested along basin correlation of upper Tortonian deposits between the Santerno and Savio valleys (datum plane: ~ the Tortonian/Messinian boundary; From Roveri et al., 2002). thrust, and fi lled up with more than 600 m of mainly the ongoing tectonic uplift and erosion of the Apennine post-evaporitic deposits. Shallow-water primary chain following the intra-Messinian phase. Facies evaporites are lacking and are replaced by resedimented characteristics, paleoenvironmental meaning, and cyclic evaporites (turbiditic gypsarenites, olistostromes, stacking pattern of uppermost Messinian deposits will be olistoliths, and breccias made up of selenitic and also dealt with during these two days. alabastrine gypsum). Sedimentary features (graded beds with erosional bases, traction plus fallout structures, sole DAY 3 marks, load casts, climbing ripples, coarse-grained beds deposited by hyperconcentrated fl ows, debris fl ow, small Stop 3.1: to large-scale intraformational slumpings), show that Savio valley, panoramic views along the National these gypsum facies were deposited by gravity fl ows road to Mercato Saraceno. The Upper Tortonian- in a subaqueous setting. Siliciclastic deposits form the Lower Messinian succession of the Savio valley: bulk of basin fi ll during the post-evaporitic stage. A very correlation with the Santerno valley (Fig. 38). high sedimentation rate of more than 2mm/yr refl ects Topics: 1, 4. Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 39 - Stop 3.2. Panoramic view looking west from Maiano of the Messinian succession of the Sapigno syncline. Note the clear bipartite character of the resedimented evaporite complex overlying the local euxinic shales, also well detectable from slope morphology: the tabular gypsarenitic bodies of the lower part are overlain through an irregular surface by a huge chaotic gypsum complex.

39 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri Apennine thrustbelt. relationship withthestructuralevolution ofthe their timeandspacedistribution suggest astrong represent aclassictopicfor Apennine geology; fl Messinian deep-water chemiohermrelatedtocold “Lucina limestone”,anUpper Tortonian-Lower Montepetra. CloseinspectionoftheMontepetra Stop 4.1: the basalpost-evaporitic succession; thetransition and thephysical-stratigraphiccharacteristicsof Panoramic andclose-upviews ongeneralfacies Giaggiolo-Cella syncline. Road Piavola - PiandiSpino.Northernlimbofthe Stop 3.7: Topics: 7.8,9,10. Pliocene transition(Fig.24). evaporitic (LagoMare)deposits,andtheMiocene/ core data(Montepetrawell)oftheuppermostpost- Road Perticara-Montepetra.Panoramic views and Stop 3.6: Topic: 5. Perticara: visittothelocalMineMuseum. Stop 3.5: Topics: 4,6. Mare successionoftheSapignosyncline. gypsum olistostrome,andofthepost-evaporitic Lago Road Sapigno-Perticara.Panoramic view ofthe Stop 3.4: Topics: 4. characteristics ofthebalatino spectacular chanceforacloseview ofthefacies complex cropsoutalongtheriver bed,offering a basal, stratifi section (1hwalk alongthe‘Fanantello gorge’). The Road Sarsina-S.AgataFeltria:theRioFanantello Stop 3.3: Topics: 3,4. geometry andstackingpattern. complex oftheFanantello section(Fig.39).Body Panoramic view oftheresedimentedevaporites Road Sarsina-S.AgataFeltria,deviation toMaiano. Stop 3.2: uid seepageonthesea-fl oor. The Lucina limestones ed partoftheresedimentedevaporite (optional) DAY 4 gypsumfacies. the p-ev synsedimentary Messiniantectonics.Facies detailsof to hyposalineconditions-the5.5Maashlayer Topics: 7 decrease offl record theabandonmentofsystemduetoasudden by catastrophicfl oods. Fine-graineddepositsontop lacustrine basinofasmalldeltaicsystemdominated character, andrecordstheprogradationinashallow sigmoidal bars. The facies sequencehasaregressive by low-angle-inclined conglomeratesforming bedded, rippledsandstones;lobesarelocallyoverlain hummocky, cross-stratifi ed sandstones,and tothin- chips (depositionallobe),passingdown-current to sandstones, withscourederosionalbasesandclay of amalgamatedmassive sandstonesandpebbly (Fig. 40). They consist oftabular bodiesmadeup deposits formingthebaseofsmall-scalecycles Topics: 4. still easilyrecognizable. original textures, but generalfacies characteristicsare recrystallization makes itdiffi with possibleevidence offl ow rebound.Gypsum head, andanupper, fi ne-grained laminateddivision, clasts, erodedandincorporatedwithinthefl a lower coarserdivision withlarge-size mudstone siliciclastic turbiditicbeds,thisgypsumlayerhas by large-volume, high-densitygravity fl exceptionally thickgypsumlayer(>12m)deposited the Giaggiolo-Cellasyncline.Closeview ofan Road toPieve diRivoschio. Southernlimbof Stop 4.2: the p-ev Corbara. Flood-dominated,fl uvio-deltaic systemsof Road Pieve diRivoschio - Voltre (closeview) - Stop 4.4: Topics: 7. limestones laterally-persistent limestonehorizons( separated bylacustrineclays,characterizedthin, backstepping, fl unit (Cusercolifm). This unitismadeupofthree trends, andstratigraphicarchitectureofthep-ev general depositionalcharacteristics,sedimentary Giaggiolo-Cella synclinefromitssouthernfl of thepost-evaporitic successioncroppingoutinthe Road Pieve diRivoschio – Voltre. Panoramic views Stop 4.3: Topics: 6. 1 2 depositsinthecoresofCampeawell. unit.Close-upview ofthecoarse-grained ). ow volume. ui-eti cas-rie bodies coarse-grained uvio-deltaic cult toassessthe ows.with As colombacci ank; ow ow 2 THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

Figure 40 - Facies and thickness distribution of the lowermost corse-grained body of the Cusercoli fm (Corbara hzn)

Stop 4.5: acknowledge: L. Capece, R. Gennari, A. Laffranchi, Road Voltre - Pian di Spino. Anatomy of the upper F. Rizzini, and M. Castellari. Lago Mare cycles from outcrop and core data The authors are also indebted to G. Papani, S. (Cà Blindana well). The sedimentological and Iaccarino, R. Flecker, C. Schreiber, W. Schlager, palaeoenvironmental meaning of fi ne grained deposits and E. Mutti, for their encouragement and helpful discussions about the different Messinian problems. of the p-ev2 unit. Facies characteristics and the origin of the “colombacci” limestones and of intervening black, organic-rich mudstones. References cited Topics: 7, 8, 9. Bassetti M.A., Ricci Lucchi F., Roveri M., 1994. Physical stratigraphy of the Messinian post-evaporitic Stop 4.6: deposits in Central-southern Marche area (Appennines, Road Voltre - Cusercoli. Panoramic view, showing Central Italy). Mem. Soc. Geol. It. 48, 275-288. the clear stacking pattern of the uppermost Messinian Bassetti M.A., 2000. Stratigraphy, sedimentology and deposits. Climatic vs. tectonic control of high- paleogeography of upper Messinian (“Post-evaporitic”) frequency cyclicity; the uppermost Messinian deposits in Marche area (Apennines, central Italy). ‘transgression’ and the Pliocene marine fl ooding. Mem. Sci. Geol. 52/2, 319-349 Topics: 7 Blanc-Valleron M.M., Rouchy J.M., Pierre C., Badaut- Trauth D., Schuler, 1998. Evidence of Messinian Stop 4.7: (optional) nonmarine deposition at Site 968 (Cyprus lower slope), Road Cusercoli-Meldola, Bidente valley. Close- Proceedings of the Ocean Drilling Program: Scientifi c B16 to B33 n° 2 - from Volume up view of the Miocene/Pliocene boundary in the Results, Volume 160, Pages 437-446 Buttafuoco section. Boccaletti M., Calamita F., Deiana G., Gelati R., Massari Topics: 10. F., Moratti G. and Ricci Lucchi F. 1990 Migrating foredeep-thrust belt system in northern Apenines and Acknowledgments southern Alps. Palaeogeography, Palaeoclimatology, The compilation of these notes wouldn’t have Palaeoecology 77, 3-14, Elsevier Science Publisher, been possible without the helpful work throughout Amsterdam. the years of several students, that we gratefully

41 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri Geologia delmargine appenninicopadano:Guide Cremonini G.,andRicciLucchiF., 1982.Guidaalla Giornale diGeologia,v. 35,p.85-96. sezioni plio-pleistocenichedell’Appenninoromagnolo: Osservazioni geologicheesedimentologichesualcune Cremonini G.,ElmiC.,andMonesi A., 1969. d’Italia, v. 12,p.221-235. dike setting(Brisighella,Northern Apennines): Legrotte Vertebrate fauna Preserved inaPaleokarst-neptunian Masini F., Torre D.and Vai G.B,1986.LatestMessinian Costa G.P., ColalongoM.L.,DeGiuliC.,MarabiniS., 166. Italiana: Bologna,Societàgeologicaitaliana,p.161- Guide GeologicheRegionali dellaSocietàGeologica Guida allaGeologiadelmargine appenninicopadano. romagnolo), inCremoniniG.,andRicciLucchiF., eds): E., 1982.IlPlio-PleistocenedelSanterno(Appennino Colalongo M.L.,RicciLucchiF., GuarnieriP, Mancini Workshop, Sabadell2001, Abstract Book,17-18. framework ofatwo phasesmodel.2ndEEDEN modalities oftheMessiniansalinitycrisisin Clauzon G.,RubinoJ.L.,CaseroP., 2001.Regional crisis: controversy resolved? Geology24,363-366. 1996. Alternate interpretationoftheMessiniansalinity Clauzon G.,SucJ.P., GautierF., Berger A., LoutreM.F., France 24,597-610. Cita etRyan,1973):BulletinSocietéGeologiquede preuve decisive du“desiccateddeep-basin model”(Hsü, Clauzon G.,1982.Lecanyon messinienduRhone:une Washington XIII,1251-1256. K. J.Etal.InitialreportoftheDeepSeeDrillingProject. Pliocene cuttingoftheRhonevalley InRyan W. B., Hsü Clauzon G.,1973. The eustatichypothesisandthepre- Geologica Italiana,39,127-142. padano (Appenninobolognese).MemoriedellaSocietà in postodelle Argille Scagliosealmargine appenninico A.M. andRabbiE.,1989.L’arco delSillaro: la messa Castellarin A., PiniG.A.withthecontribute ofBorsetti Publishers, Dordrecht-Boston-London,177-196. adjacent Mediterraneanbasins.Kluwer Academic I.P., Eds, Anatomy ofanorogen:the Apennines and frontal Appennines relations.In: Vai G.B.andMartini Castellarin A., 2001.Alps-AppenninesandPoPlain- Giornale diGeologia,471/2,47-75. - Analisi strutturaledelFronte Appenninico Padano. contribute ofRabbiE.,PiniG.A.andCrestanaG.(1986) Castellarin A., Eva C.,GigliaG, Vai G.B,with a speciale (1991/1),pp.36-278. neogenica romagnola.StudiGeologiciCamertivolume deformativi edevoluzione Tettonica dellasuccessione Capozzi R.,Landuzzi A., Negri A., Vai G.B.,1991.Stili Iaccarino S.,CastradoriD.,CitaM. B.,DiStefano E., 15-46. Pliocene. Vol. dedicatoaS. Venzo, Univ. StudidiParma, Val Secchia:stratigrafi a erapporticonilsubstrato dell’Appennino Settentrionaledalla Val d’Ardaalla Iaccarino S.,Papani G.,1980.IlMessiniano 540. Ocean DrillingProgram,Scientifi Comas M.C.andKlaus A. (Eds.),Proceedingsofthe Mediterranean (sites974,975and978)In:ZahnR., of uppermostMessiniansequencesinthewestern Iaccarino S.,M.,Bossio A., 1999.Paleoenvironment desiccation oftheMediterranean.Nature,242,240-244. Hsü K.J.,Ryan W.B.F., CitaM.B.,1972.LateMiocene 182, 237-251. (Atlantic Morocco).EarthandPlanetaryScienceLetters, astrochronology oftheMessinianGSSPatOued Akrech R., Negri A., Villa G.,2000.Integrated stratigraphyand Hlgen F. J.,BissoliL.,IaccarinoS.,Krijgsman W., Meijer Italiana, v. 104,p.349-397. Scrivia eLemme):Bollettinodella SocietàGeologica Bacino Terziario Ligure-Piemontese(Valli Borbera, dei depositimiocenicidelmargine sud-orientaledel fi Ghibaudo G.,ClariP., andPerelloM.,1985.Litostratigra 323. Italy (preliminaryresults).Mem.Soc.Geol.It.39,319- Apenninic margin ofthePadan forelandbasin,northern the Messinianunconformity-boundedsequencesin Gelati R.,RoglediS.,RossiM.,1987.Signifi of theGeologicalSociety, London,156,847-854. Messinian salinitycrisis,EasternMediterranean.Journal of marginal basinsusingSrisotops:anexample of and tectonicsignalsinthesedimentarysuccession Flecker R.,Ellam,R.M.,1999.Distinguishingclimatic salinity crisis.Nature,422,602-606. Phipps Morgan J.,2003.DeeprootsoftheMessinian Duggen S.,HoernleK.,BoogardP.v.d., Rupke L., Faenza, March28-31,1988,Guidebook,p.65-69. Continental Faunas attheMio-PlioceneBoundary, valley, Romagnaapennines,International Workshop: C., and Vai, G.B.eds.,Fossil Vertebrates intheLamone Mammal Fauna oftheMonticinoquarry, inDeGiuli, De GiuliC.,MasiniF. and Torre D.,1988, The 1997, 1819-1824. Delta Basin,Egypt). The LeadingEdge,December from thelateMessinian Abu MadiFormation (Nile exploration inacomplex incisedvalley fi Dalla S.,HarbyH.,SerazziM.,1997.Hydrocarbon pp. Geologiche Regionali, SocietàGeologicaItaliana,248 a,sedimentologia edevoluzione Tettonico-sedimentaria c eut 11 529- 161, Results c ll: An example cance of cance THE RECORD OF MESSINIAN EVENTS IN THE NORTHERN APENNINES FOREDEEP BASINS B19

Gaboardi S., McKenzie J.A., Spezzaferri S., Sprovieri Mediterranean. Nature 400, 613-614. R., 1999. The Miocene/Pliocene boundary and the Meulenkamp J.E., Sissingh W. et al., 2000. Late signifi cance of the earliest Pliocene fl ooding in the Tortonian. In: S. Crasquin (Ed.), Atlas PeriTethys, Mediterranean. Mem. Soc. Geol. It. 54, 109-131. PalaeCogeographical maps – Explanatory notes. CCGM/ Keogh S. M. and Butler R.W.H., 1999. The Mediterranean CGMW, Paris, 195-201. water body in the late Messinian: interpreting the record Mutti, E., Tinterri, R., Remacha, E., Mavilla, N., Angella, from marginal basins on Sicily. Journal of the Geological S. and Fava, L., 1999. An introduction to the analysis of Society, London, 156, 837-846. ancient turbidite basins from an outcrop perspective: Kligfi eld R., 1979. The Northern Apennines as a AAPG Continuing Education Course Note Series, #39, collisional orogen: American Journal of Science, v. 279, Negri. A and Vigliotti L. 1997. Calcareous Nannofossil p. 676-691. biostratigraphy and paleomagnetism of the Monte Tondo Kouwenhoven T.J., Seidenkrants M.S. and Van der and Monte del Casino sections (Romagna Apennines, Zwaan G.J., 1999. Deep-water changes: the near- Italy) In (A. Montanari G.S. Odin and R. Coccioni, synchronous disappearance of a group of benthic Eds): Miocene Stratigraphy - An Integrated Approach, foraminifera from the Late Miocene Mediterranean: Elsevier 478-491 Palaeogeography, Palaeoclimatology, Palaeoecology, v. Odin G.S., Montanari A., and Coccioni R., 1997. 152, p. 259-281. Chronostratigraphy of Miocene stages: a proposal for Krijgsman W., Hilgen F. J., Marabini S., Vai G. B., the defi nition of precise boundaries, in (Montanari A., 1999a. New paleomagnetic and cyclostratigraphic age Odin G. S., and. Coccioni R, eds): Miocene Stratigraphy constraints on the Messinian of the Northern Apennines - An Integrated Approach, Elsevier, p. 597-629. (Vena del Gesso Basin, Italy) Mem. Soc. Geol. It. 54, Parea G.C., Ricci Lucchi F., 1972. Resedimented 25-33 evaporites in the periadriatic trough (upper Miocene, Krijgsman W., Hilgen F.J., Raffi I., Sierro F.J., Wilson Italy) Israel Journal of Earth-Sciences 21, 125-141. D.S., 1999b. Chronology, causes and progression of the Ricci Lucchi F., Bassetti M.A., Manzi V., Roveri M., Messinian salinity crisis. Nature 400, 652-655. 2002. Il Messiniano trent’anni dopo: eventi connessi Lucente C.C., Manzi V., Ricci Lucchi F. and Roveri M., alla crisi di salinità nell’avanfossa appenninica.Studi. 2002. Did the Ligurian Sheet cover the whole thrust belt Geologici Camerti 1, 127-142. in Tuscany and Romagna Appennines? Some evidence Ricci Lucchi F., 1973. Resedimented evaporites: from gravity emplaced deposits: Memorie della Società indicaCtors of slope instability and deep-basins Geologica Italiana, 1, 393-398. conditions in PeriCadriatic Messinian (Apennines Manzi V., 1997. Analisi di facies dei depositi messiniani foredeep, Italy). Koninklijke Nederlandse Akademie Van post-evaporitici tra il Fiume Bidente ed il Fiume Wetenshappen. Messinian Events in the Mediterranean. Savio: tra Corbara e Pieve di Rivoschio (Appennino Geodynamics Scientifi c ReCport n° 7 on the colloquium romagnolo): unpublished Thesis, University of Bologna, held in Utrecht, March 2-4, 1973,142-149. 124 pp. Ricci Lucchi F., 1968. Chanellized deposits in the Manzi V., 2001. Stratigrafi a fi sica, analisi middle Miocene fl ysch of Romagna (Italy). Giornale di sedimentologica microscopica e caratterizzazione Geologia, 36, 203-282. magnetostratigrafi ca dei depositi connessi all’evento Ricci Lucchi F., 1969. Recherches stratonomiques et evaporitico del Messiniano (Formazione Gessoso- sédimentologique sur le Flysch Miocéne de la Romagne solfi fera l.s.). Ph.D. thesis Earth Science Department, (Formation Marnoso-arenacea). Proceedings of the Bologna University, Italy. 4th session, Committee on Mediterranean Neogene Marabini S., Vai G.B., 1985. Analisi di facies e Stratigraphy, Giornale di Geologia, 36, 163-198. macroTettonica della Vena del Gesso in Romagna. Ricci Lucchi F., 1975. Depositional cycles in two B16 to B33 n° 2 - from Volume Bollettino della Società Geologica Italiana, v. 104, p. turbidite formations of northern Apennines. Journal of 21-42. Sedimentary Petrology, 45, 1-43. Marabini S. and Vai. G.B., 2003. Marsili’s and Ricci Lucchi F., 1981. The Miocene Marnoso-arenacea Aldrovandi’s early studies on the gypsum geology of the turbidites, Romagna and Umbria Apennines. In: Ricci Apennines. In Vai and Cavazza eds., Fourth Centuries of Lucchi F., Ed., Excursion Guidebook, 2nd European the word Geology: Ulisse Aldrovandi 1603 in Bologna. Regional Meeting of International Association of Minerva Edizioni. Sedimentologists, 231-303. McKenzie J. A., 1999. From desert to deluge in the Ricci Lucchi F., 1986. The Oligocene to Recent foreland

43 - B19 Volume n° 2 - from B16 to B33 B19 - B19 Leader: M.Roveri indicators ofaseveral-kiloCmeters-deep Mediterranean distribution oftheMessininan erosionalsurface - Ryan W.B.F., CitaM.B.,1978. The natureand Editors Adams C.G.and Ager D.V., 283-290,Palermo. pubblication no.7, Aspects ofthe Tethyan biogeography. of theMediterraneanSea.Systematicsassociation Ruggieri G.,1967. The Mioceneandlaterevolution Palaeoclimatology, Palaeoecology. In press. looking foranew paradygm?Palaeogeography, Roveri M.,Manzi V.. The Messiniansalinity crisis: Society of America Bulletin115,387-405. for theonsetofMessiniansalinitycrisis.Geological Gesso basin(Northern Apennines, Italy):Implications Sedimentary andtectonicevolution ofthe Vena del Roveri M.,Manzi V., RicciLucchiF., RoglediS.,2003. University andENI– AGIP Division Conference andExibition.ExcursionGuidebook.Parma equivalents: problemswithclassicmodels.64thEAGE Marnoso-arenacea Formation andtheirbasin-margin Lucchi F., Roveri M.Eds.Revisiting turbiditesofthe of theMarnoso-arenaceaFormation. In:MuttiE.,Ricci Mutti E.2002.Stratigraphy, facies andbasinfi Roveri M.,RicciLucchiF., LucenteC.C.,Manzi V., Apennines, Italy).GiorCnalediGeologia60,119-142. post-evaporitic stageineastern-Romagna(northern Ricci LucchiF., 1998.StratigraphyoftheMessinian Roveri M.,Manzi V., BassettiM.A.,MeriniM., 214. foredeep perCspective. Sedimentary Geology140,201- MediCterranean Messiniansalinitycrisis:an Apennine Roveri M.,BassettiM.A.,RicciLucchiF., 2001. The Lago-Mare. Sed.Geol.,145,93-117. (southern CyprusbaCsins):significance oftheMessinian Pliocene boundaryintheeasternMediterranean I., 2001.Paleoenvironmental changesattheMessinian- Pierre C.,Riviere M.,Combourieu-NeboutN.,Panayides Rouchy J.M.,Orszag-SperberF., Blanc-Valleron M.M., sectors. Boll.Soc.Geol.It.,1,437-477. area andcomparisonwiththeLombardianRomana Apennines: theEmiliafoldsinReggio-Modena of theMessinianpigybackbasinoNorthern S., Papani G.,2002. Tectono-stratigraphic architecture Rossi M.RoglediS.BarbaciniG.,CasadeiD.,Iaccarino Spain: ReplySedimentaryGeology133,175-184. the “SalinityCrisis”erosionsurface on-landinsoutheast Mediterranean desiccation:topography signifi Riding R.,BragaJ.C.,MartinM.,2000.LateMiocene Sediment. 8,105-139. basins ofthenorthern Apenines. Spec.Publs.Int. Ass. ll hystory cne of cance of Plioceneseries.Episodes,23(3),179-187 J., andRioD.,2000. The baseoftheZancleanStageand Van Couvering J. A., CastratoriD.,CitaM.B.,HilgenF. 1988, Guidebook,p.61-62. at theMio-PlioceneBoundary, Faenza, March28-31, apennines, International Workshop: ContinentalFaunas eds., Fossil Vertebrates intheLamonevalley, Romagna section 1987(Faenza, Italy),inDeGiuli,C.,and Vai, G.B. Vigliotti L.,1988.Magnetostratigraphy oftheMonticino and PlanetaryScienceLetters154,230-219. reCfl 1999. Lateralshiftsof Apenninic foredeepdepocentres Van derMeulenM.J.,MeulenkampJ.E., Wortel M.J.R., Academic Publishers,632p. the Apennines and adjacent Mediterranean,Kluwer Vai G.B.andMartiniI.P., 2001. Anatomy ofanorogen: Northern Apennines.: Sedimentology, v. 24,p.211-244. evaporite basin:acasehistoryfromtheMessinianof autochthonous andclasticgypsuminacannibalistic Vai G.B.andRicciLucchiF., 1977. Algal crusts, 463-476. Elsevier,p. Integrated Approach:Amsterdam, and Coccioni,R.,eds.,:MioceneStratigraphy - An Messinian stageduration:inMontanari, A., Odin,G.S., Vai G.B.,1997.Cyclostratigraphicestimateofthe Faenza, March28-31,1988,Guidebook,p.7-37. Continental Faunas attheMio-PlioceneBoundary, valley, Romagnaapennines,International Workshop: and Vai, G.B.eds.,Fossil Vertebrates intheLamone Apennine geology. The Lamonevalley inDeGiuli,C., Vai G.B.,1988. A fi eld tripguidetotheRomagna EEDEN Workshop, Sabadell2001, Abstract Book, 69. the Atlantic/Mediterranean andtheParatethys. 2nd Miocene-Early Pliocenemarineconnectionsbetween Snel E.,MarunteanuM.,MeulenkampJ.E.,2001.Late pp. 728. della regione EmiliaRomagna. Artioli Editore,Modena, Scicli A., 1972.L’attività estrattiva elerisorseminerarie 2-4, 1973.101-110 Report n°7onthecolloquiumheldinUtrecht,March Events intheMediterranean.GeodynamicsScientifi Nederlandse AkademieVanWetenshappen. Messinian of themessinianchemicalsedimentsKoninklijke Schreiber C.B.,1973.Survey ofthephysicalfeatures Geology 27,349-363. southeastern margin oftheMediterraneanSea.Marine Ryan W.B.F., 1978.Messinianbadlandsonthe in theMiocene.MarineGeology27,193-230. ecting detachmentofsubducedlithosphere.Earth c Back Cover: fi eld trip itinerary FIELD TRIP MAP INTERNATIONAL GEOLOGICAL CONGRESS nd 32

Edited by APAT August 20-28,2004 Florence -Italy

Field Trip Guide Book - B21 PRESSURE ROCKSOFSAXONY ULTRAHIGH ANDHIGH GEOLOGICAL CONGRESS 32 Volume n°2-fromB16toB33 Associate Leader:H.-J.Bautsch Leader: H.-J.Massonne Pre-Congress nd INTERNATIONAL B21 The scientific content of this guide is under the total responsibility of the Authors

Published by: APAT – Italian Agency for the Environmental Protection and Technical Services - Via Vitaliano Brancati, 48 - 00144 Roma - Italy

Series Editors: Luca Guerrieri, Irene Rischia and Leonello Serva (APAT, Roma)

English Desk-copy Editors: Paul Mazza (Università di Firenze), Jessica Ann Thonn (Università di Firenze), Nathalie Marléne Adams (Università di Firenze), Miriam Friedman (Università di Firenze), Kate Eadie (Freelance indipendent professional)

Field Trip Committee: Leonello Serva (APAT, Roma), Alessandro Michetti (Università dell’Insubria, Como), Giulio Pavia (Università di Torino), Raffaele Pignone (Servizio Geologico Regione Emilia-Romagna, Bologna) and Riccardo Polino (CNR, Torino)

Acknowledgments: The 32nd IGC Organizing Committee is grateful to Roberto Pompili and Elisa Brustia (APAT, Roma) for their collaboration in editing.

Graphic project: Full snc - Firenze

Layout and press: Lito Terrazzi srl - Firenze Volume n° 2 - from B16 to B33

32nd INTERNATIONAL GEOLOGICAL CONGRESS

ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY

AUTHORS: H.-J. Massonne (Universität Stuttgart - Germany) H.-J. Bautsch (Humboldt Universität - Germany)

Florence - Italy August 20-28, 2004

Pre-Congress B21 Front Cover: Microdiamonds in garnets from quartzofeldspathic rock (saidenbachite), outcropping at the Saidenbach reservoir, Saxonian Erzgebirge, seen under refl ected light. Striations around the diamonds allow to detect them easily. Image width is 3mm. ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

Leader: H.-J. Massonne Associate Leader: H.-J. Bautsch

Introduction from the Erzgebirge. In addition, lamellae of garnet Ultrahigh pressure (UHP) metamorphic rocks and clinopyroxene in clinopyroxenite from the were fi rst detected in the western Alps through the nearby Granulitgebirge are interpreted as exsolution indicator mineral coesite (Chopin, 1984). Soon after of former majoritic garnet (Massonne and Bautsch, this detection it turned out that UHP rocks are more 2002). widespread than expected after the fi rst fi nd. Coesite The aim of our fi eld trip is to present key occurrences was also recognised in rocks of the Norwegian of rocks formed at UHP and near-UHP conditions. Caledonides, the Dabie Shan in China and orogenic These rocks are representative for high-pressure regions elsewhere (Chopin, 2003). Evidence for UHP (HP) and UHP metamorphism in the Variscan metamorphism, proven by both indicator minerals and orogen or at least in the Bohemian Massif. To mineral equilibria, has been reported only recently gain detailed information on the regional geology from the Variscan orogen in Europe. Typically, this we recommend having a look at the series of orogen resulted from continent-continent collision “Geologische Meßtischblätter”. These maps with in Phanerozoic times as the previously mentioned a 1: 25000 scale are distributed by “Sächsisches orogens with UHP rocks. Landesamt für Umwelt und Geologie” at Dresden. In In portions of the Bohemian Massif, which is situated addition, explanatory text is available for each map. on the northwestern edge of the Variscan orogenic The following sheets cover the areas visited during chain (Fig. 1), occurrences of eclogites and garnet our fi eld trip: GK25 4943 Gehringswalde, GK25 peridotites were recognised more than a century 4944 Waldheim, GK25 5042 Burgstädt, GK25 5043 ago and subsequent detailed mapping has revealed Mittweida, GK25 5044 Frankenberg, GK25 5144 several hundred mostly small bodies spread over Flöha, GK25 5245 Lengefeld, GK25 5345 Zöblitz, a very large area. Hints at UHP metamorphism and GK25 5543 Kurort Oberwiesenthal. Relevant came from specifi c mineral compositions (Al in overview maps with scale 1 : 200000 are GKÜ200 orthopyroxene) and considerations of mineral M33-VII Chemnitz, GKÜ200 M33-VIII Dresden, equilibria, for instance, related to the Al-celadonite GKÜ200 M33-XIII Plauen, and GKÜ200 M33-XIV component in phengite. More recently, the Annaberg-Buchholz. indicator minerals coesite (Massonne, 2001) and microdiamond (Massonne, 1999) were detected in Regional geology eclogites and quartzofeldspathic rocks, respectively, It has become a common view that the Variscan orogen resulted from colliding continental plates. These were Gondwana and Laurentia-Baltica (or Laurussia). The latter were formed from originally separate plates during the Caledonian orogeny at the end of Early Palaeozoic times and, thus, shortly before the onset of Variscan events. It is assumed that after the end of the Caledonian orogeny (420-410 Ma) a single oceanic basin (Rheic ocean: e.g., Robardet et al., 1990; Tornquist Sea: Oliver et al., 1993) or two (e.g., Rheic ocean + Massif Central - Galician ocean, Matte, 1986; Rheic ocean + subsequently Palaeotethys, Stampfl i et al., 2002) and more basins separated Gondwana and B16 to B33 n° 2 - from Volume Laurentia-Baltica. The extension of the ocean(s) and the time of fi nal closure is still a matter of debate (e.g., narrow: McKerrow et al., 2000; wide: Tait et Figure 1 - Location of exposed basement areas of the Upper Palaeozoic Variscan orogen in Europe (Fig. 1 of al., 2000), which also includes the involvement of O’Brien, 2000). These are subdivided in those belonging microplates, such as Armorica (see Tait et al., 1994: to the Saxothuringian Zone, Moldanubian Zone and other Armorican Terrane Assemblage), Avalonia (Murphy zones. Not shown are fragments of Variscan basement et al., 1999) or the Hun terrane (Stampfl i, 1996), involved in the Cretaceous-Tertiary Alpine orogen. between Gondwana and Laurentia-Baltica. The many

3 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne Bohemian Massif. (1998) redrawnbyO‘Brien(2000)for thenorthern Figure 2-Thesubduction-collisionmodelbyMatte account theexistence ofHPandUHProcks,isthat such recentreconstructions,whichalsotake into also consideraclosurealreadyabout400Ma. Among geoscientists toreconstructthe Variscan orogeny Ma agoatthelatest.However, attempts bysome The basinoftheRheicoceandisappeared340 Matte, 1986;Franke, 2000). taken intoconsiderationbyseveral geoscientists(e.g., from eachotheroreven towards eachother, werealso subduction zoneswithoppositedirections,away of the Variscan orogen,two simultaneouslyactive the bilateralsymmetryofstructuralelements by others(e.g.,Matte,1998).However, becauseof and Stein,2000)but theoppositedirectionisfavoured to have beendirectedsouthorsoutheast(e.g.,Franke crust atafi nal stage,isassumedbymany scientists accepted. The subduction,alsoinvolving continental implying thesubductionofoceaniccrust,isgenerally motion ofGondwana towards Laurentia-Baltica, 2002). Inspiteoftheabove uncertainties,therelative of Gondwana (Tait etal.,2000;Hartzand Torsvik, microplates wereprobablyoncecontiguousto,orpart magmas intrudedthe Variscan crust Contemporaneously, large volumes ofgranitoid and UpperCarboniferoussedimentsweredeposited. In these,uptoseveral km-thicksequencesof Viséan only smallbasinsremainedorwerenewly formed. Gondwana andLaurussia(calledhere:Rheicocean) (Fig. 3). After closureoftheoceanicbasinbetween during thecourseofseveral tensofmillionsyears (+ Tibetan Plateau)typeorogenbyunderplating continental plateundertheothertoreachaHimalaya these authorsproposedunderthrustingofone and O’Brien(2003)Massonne(inpress).However, model forthe Variscan orogenpresentedbyMassonne of years(Fig.2). This alsoconcernsthegeodynamic thickened crustlastingforseveral tensofmillions narrow mountainchain characterisedbystrongly by theslabbreak-off modelresultinginarelatively by Matte(1998)proposingaprocessassuggested Erzgebirge. minerals (seeabove) have only been foundinthe units characterisedbyHProcksbut sofar indicator only afew Mayounger. UHProcks mayoccurinall and theGföhlunit.Coolingagesareonaverage hory inCzech),the Mountains), theErzgebirge (OreMountains,Krušné for HProcksoftheGranulitgebirge (Granulite Clearly youngerages(345-340Ma)weredetermined Mountains) andthe Tepla-Barrandian unit(Fig.4). from theMünchberg Massif,theGórySowie (Owl with upto20Mayoungercoolingages,werereported rocks arebimodal. Ages between400and380Ma, out by Willner etal.(2000),theagedatarelatedtoHP restricted tospecifi and garnetperidotites,are,infact, abundant but are HP rocksintheBohemianMassif,suchaseclogites like aspect. Variscan area,areresponsibleforthepresentcollage- 1996), whicharewidespreadintheentirenorthern well asmajorfault andshearzones(e.g.,Krohe, Nappe tectonics(e.g.,Schulmannetal.,1991)as contemporaneous (e.g.,Franke andEngel,1986). Both sedimentaryandmetamorphicagescanbe that arepredominantlyonlyanchimetamorphic. units, regions withPalaeozoic sedimentsexist Lugian =Sudetes(Fig.4).Betweenthebasement and intheeastnortheast:Moravo-Silesian and Saxothuringian, Moldanubian, Tepla-Barrandian in ageandmetamorphicevolution. These aretermed collage ofseveral smallerbasementareasdiffering of the Variscan orogenatitseasternmargin. Itisa The BohemianMassifexposes themetamorphiccore c areas(darkinFig.4). As pointed Ŋnieŧnik (Snowy Mountains) . ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

Figure 3 - Collision of Gondwana and Laurussia presented by the position of these continental plates relative to each other in the Lower Devonian (left hand side), Lower Carboniferous and Upper Carboniferous (right hand side) according to Massonne (in press). The positions of the plates refer to palaeomagnetic data (see Tait et al., 2000). For orientation the current shapes of the continental plates, except portions overprinted by the Alpine orogeny (see Northern Africa), and other typical geographic shapes (Hudson Bay, Newfoundland, Great Britain, Black Sea) are shown. The estimated shapes of the continental plates at the corresponding times are displayed by dotted lines (northern margin of Africa refers to pre-Alpine times). Thick dashed lines mark orogenic zones (= thickened continental crust). Arrows point Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 4 - Simplifi ed geological map of the Bohemian Massif according to Willner et al. (2000). In addition to major units, specifi c areas are named (italics and 1 = Münchberg Massif, 2 = Zone of Erbendorf-Vohenstrauß, 3 = Gföhl Unit). Grey dots point to locations with HP rocks geochronologically dated.

5 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne Sa. =Sayda, W. = Waldheim. = Freiberg, O.W. =Oberwiesenthal, Rei.=Reitzenhain, Czech Republic,CHEM=Chemnitz,DREDresden,Fr. E.Z.R.F. =Erzgebirgssüdrand fault,D=Germany, CR= Abbreviations: FZ=Frankenberger Zwischengebirge, - granitoidbodiesintheSGG,black -serpentinitebodies. - phyllitessurroundingtheSGG,horizontallyhatched Eibenstock, Bergen,andSchneeberg, swungdashes of largereclogitebodies,crosses-granitebodies - orthogneissesoftheEZ,trianglesoccurrences (EZ) accordingtoBlümel(1995). Vertically hatched of theGranulitgebirge (SGG)andtheErzgebirge Figure 5-Simplified geologicalmapfor theregion O’Brien, 2003). Erzgebirge iscloseto340Ma(e.g.Massonne& the HPmetamorphisminbothGranulitgebirge and in general,itcanbepointedoutthattheageof This alsoreferstotheGranulitgebirge. However, specifi the P-Tconditionsoftheseunitswillbegiven in not containany HProcks.Detailedinformationon lenses, whereastheRedandGrey GneissUnitdoes - EclogiteUnit(GEU),containabundant eclogite Mica-schist -EclogiteUnit(MEU)andGneiss unit, thePhylliteUnit. Two ofthesethreeunits, metamorphic rockssurroundedbyalow-grade three majorunitsforthemediumtohigh-grade the proposalby Willner etal.(2000)whosuggested subdivide themetamorphicrocks.Here,weprefer of metamorphicdegree. Various suggestionsexist to rocks intheErzgebirge aremorevariable interms bodies oryoungergranitoids(Fig.5),whereasthe either felsicandbasicgranuliteswithsomeultrabasic The outcroppingrocksintheGranulitgebirge are anchimetamorphic tolow-grade metamorphicrocks. (Fig. 5). They aresurroundedand,thus,covered by ellipsoidal shapeextending in WSW-ENE direction and Erzgebirge areanticlinalstructureswith The crystallinecomplexes ofbothGranulitgebirge c text portionsrelatedtocorrespondingrocks. Stop 1.1: parking areanearby. road curvingtotheright,weturnleftandstopat the old“Fischerschänke” inn.Insteadoffollowing the an underpass. After about1.5kmnorth,weseeahead reaching theinnertown andcrossthehighway with metres towards Frankenberg, weturnrightbefore at exit 72Frankenberg. After headingafew hundred Heading forChemnitzonthishighway, weleave it Dresden towards thenearest access toHighway A4. The routeoftheexcursion startsinthecityof position ofthevarious stops. overview mapatthebackofguidebookshows the according tothenumberoffi eld tripdays. The The fi eld itineraryissubdivided into4portions Field itinerary fi fi granulites theslateshave turnedtomicaschistsand intercalations, increasedramatically. Closetothe of thepsammopeliticrocks,containingsomebasic next 1.5km,itisobvious thatthemetamorphicdegree see slatesoutcroppingontherighthandside.For the building areaoftheformer“Schlossmühle”wecan road below “Sachsenburg” castle. After crossingthe look atthecliffs ofmassive greenschistsonthemain the Zschopauriver (Fig.6).Beforestarting,wehave a area alongahikingtrailclosetotheeasternbanksof demonstrate this,wewalk northwestfromtheparking the borderregions ofthecrystallinemassifs.Inorderto The target ofthisstopistoshow atypicalexample for rst appearanceofgranulitesismarked bycliffs along nally tomigmatitic rockscontainingcordierite. The at thesouth-easternmarginofGranulitgebirge. The Figure 6-Simplified geologicalmapoftheborderzone section shown islocatedintheZschopau valley. DAY 1 ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

the hiking trail. These rocks are massive to platy and relatively fi ne-grained due to a mylonitic foliation. Felsic granulites are the dominant rock type there. They contain quartz, plagioclase, K-feldspar, minor garnet and kyanite. Biotite and amphibole seem to be retrograde phases of a medium temperature overprint. The intercalations and larger massive bodies of mafi c

Figure 8 - Chemical zonation of garnet in basic granulite E301-3b. The grey code displays higher element con centrations by lighter tones. Scale bar represents 100 µm. are orthopyroxene, rutile and quartz, which, however, can also be lacking. Amphibole, ilmenite and biotite are at least to some extent retrograde phases as in the felsic granulites. Orthoamphibole and chlorite can also occur as retrograde minerals. Most minerals in the granulites are slightly zoned, thus, allowing estimations on the P-T evolution. For instance, garnet typically shows fairly homo geneously composed cores. Rims can be Figure 7 - Photomicrograph of basic granulite E301-3b. signifi cantly poorer in Ca and Mg as well as richer Plagioclase, amphibole, and ilmenite have formed at the in Fe (see Fig. 8 and Table 1). This chemical change expense of garnet (Gt), clinopyroxene (Cpx), and rutile. follows the grain boundaries and is, thus, very likely The latter phase is present as inclusion in garnet. Image width is 2 mm. due to a diffusional process at high temperatures. Clinopyroxene compositions tend to show decreasing granulites are mainly formed from clinopyroxene, jadeite contents towards the rim. For the granulites plagioclase, and garnet (Fig. 7). Minor constituents minimum P-T conditions were estimated to be 10 kbar and 800°C. It is not unlikely that the original Gt core Gt rim Cpx core Cpx rim Plag Ilmenite Amph Amph Biotite 1321/12 1306/25 1306/15 1321/29 1319/5 1306/21 1320/19 1321/4 1320/3

SiO2 38.76 37.78 50.43 51.60 60.05 44.19 40.53 35.63 TiO2 0.16 0.08 0.43 0.25 51.93 1.96 2.70 3.32 Al2O3 21.38 20.92 3.35 2.12 26.21 0.07 9.97 14.51 14.19 Cr2O3 0.00 0.06 0.03 0.08 0.01 0.07 0.01 0.00 FeO 24.44 27.46 12.01 11.73 0.39 46.15 16.36 13.66 20.22 MnO 0.46 0.80 0.19 0.12 0.61 0.15 0.09 0.04 MgO 6.40 5.34 11.13 12.53 0.02 10.85 10.52 11.34 CaO 8.98 6.42 20.97 20.76 7.91 0.04 11.19 11.22 0.04 Na2O 0.66 0.35 6.76 1.24 1.58 0.10 K2O 0.29 0.92 2.20 8.89 Total 100.57 98.86 99.34 99.53 101.61 98.83 96.90 *97.13 *95.40

Si 5.947 5.980 1.917 1.950 2.637 6.570 6.067 5.535 AlIV 0.083 0.050 1.356 0.002 1.430 1.933 2.465 Ti 0.018 0.010 0.012 0.007 0.997 0.220 0.304 0.388 AlVI 3.866 3.902 0.067 0.044 0.002 0.316 0.627 0.132 Volume n° 2 - from B16 to B33 n° 2 - from Volume Cr 0.000 0.008 0.001 0.002 0.000 0.008 0.001 0.000 Fe3+ 0.134 0.090 0.040 0.015 0.014 0.570 0.208 Fe2+ 3.002 3.545 0.342 0.356 0.985 1.463 1.502 2.626 Mn 0.059 0.107 0.006 0.004 0.013 0.020 0.012 0.006 Mg 1.463 1.259 0.630 0.706 0.001 2.404 2.347 2.625 Ca 1.476 1.089 0.853 0.841 0.372 0.001 1.783 1.800 0.006 Na 0.049 0.025 0.575 0.357 0.458 0.029 K+Ba 0.016 0.174 0.426 1.861

Table 1 - EMP analyses (in wt.%) of minerals from basic granulite E301-3b taken at the southeastern margin of the Granulitgebirge (Zschopau valley). *= total contains 0.11 wt.% (Amph) and 1.63 wt.% (Biotite) of BaO.

7 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne about 150mupwards totheentranceofanabandoned about 400m. We stopattheroadtothenwalk for turn righttomove alongthebanksofabrook for Greifendorf. Closetothecentreofthisvillage,we and drive foranadditional4kmuntilreaching Döbeln. After about11kmwecrossHighway A4 following routeB169headingforHainichenand Again justbeforereachingthetown, weturnleft “Fischerschänke”, wemove backtoFrankenberg. After returningtotheparkingareanearinn crustal levels. of lower crust,theGranulitgebirge, insuchshallow cause forthefi nal emplacementofalarge fragment suggested byReinhardtandKleemann(1994)asa the mantlerocksanextensional environment was 10 km(~3kbar). According tostrainindicatorsin granulites. This event occurredat depths ofonly was drasticallyheatedclosetothecontact mantle asthehangingwall oftheGranulitgebirge 700°C (seeFig.9).Onthecontrary, thephyllite a strongpressurereleaseattemperaturesstillabove The retrogradealterationhappenedmainlyduring metamorphic conditionsweresignifi according toReinhardtandKleemann(1994). (HPG) andtheschist mantle(SM)oftheGranulitgebirge Figure 9-P-Tpathsfor thehighpressuregranulites cnl higher. cantly quarry atRubinberg hill(Fig.10). conserved lherzolitesonecanreconstructthefabric 1.2 tothenortheastbyabout3km.Frompartially lherzolite bodythatextends fromthequarryofstop relics ofthemineralassemblage(Fig.11)aformer Rubinberg onecaneasilyfi nd serpentiniteswith including pyroxenite bodiesintheserocks. At the of theGranulitgebirge, formergarnetlherzolites, The target ofthisstopistoshow typicalserpentinites Stop 1.2: garnet withdecomposedinclusionminerals.The Figure 10-Simplified geologicalmapoftheRubinberg is inserpentinisedlherzoliteGR99-1B. A largerrelicof Figure 11-Photomicrographofamarginallyaltered relics ofolivineandorthopyroxene arealsopresent. clinopyroxene (Cpx)isdiscerniblenearby. Smaller area, south-easternGranulitgebirge. Image widthis3.5mm. ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

Gt Gt Cpx Cpx Opx Ol core rim rim 4-1B 1-1B 16-1B 29-1B 26-1B 18-1B

SiO2 42.24 42.41 53.62 52.61 56.60 40.54 TiO2 0.31 0.36 0.48 0.60 0.09 0.02 Al2O3 23.09 22.38 4.46 6.39 2.99 0.00 V2O3 0.03 0.04 0.06 0.08 0.01 0.00 Cr2O3 0.68 1.39 1.22 0.86 0.29 0.01 FeO 8.61 9.32 2.86 2.76 6.88 9.94 MnO 0.37 0.34 0.05 0.10 0.14 0.13 MgO 20.98 20.91 15.52 14.77 33.93 49.18 NiO 0.09 0.01 0.08 0.42 CaO 4.72 4.58 20.32 21.03 0.33 0.03 Na2O 0.05 0.05 2.05 1.92 0.00 K2O 0.01 0.00 0.00 Total 101.11 101.82 100.73 101.13 101.33 100.27 Figure 12 - Photomicrograph of an equigranular portion Si 5.889 5.909 1.929 1.886 1.932 0.992 of sample GR99-1A rich in garnet (Gt) and clinopyroxene AlIV 0.071 0.114 0.069 0.000 (Cpx). Plagioclase (Plag) and some amphibole occur Ti 0.033 0.038 0.013 0.016 0.002 0.000 AlVI 3.795 3.676 0.118 0.157 0.052 along grain boundaries of garnet and pyroxene. Cr 0.075 0.153 0.035 0.024 0.008 0.000 Cpx contains numerous tiny inclusions of SiO2 and V 0.003 0.005 0.002 0.002 0.000 0.000 alkali feldspar all perfectly oriented. Fe3+ 0.127 0.167 0.016 Image width is 1.5 mm. Mg 4.360 4.344 0.832 0.789 1.726 1.793 Mn 0.044 0.040 0.002 0.003 0.004 0.003 comes from garnet-rich pyroxenite outcropping Fe2+ 0.877 0.920 0.086 0.083 0.196 0.188 at the south-western wall of the quarry. This rock Ni 0.003 0.000 0.002 0.008 Ca 0.705 0.684 0.783 0.808 0.012 0.001 contains mainly mm-sized, equigranular garnet and Na 0.014 0.013 0.143 0.134 0.000 clinopyroxene. However, rare cm-sized garnet can K 0.001 0.000 be detected as well. The large garnets are interpreted, similar to garnet in the lherzolite, as Table 2 - EMP analyses (in wt.%) of minerals from pre-recrystallisation mineral. Some plagioclase and serpentinised garnet lherzolite GR99-1B taken from the rare amphibole have formed along grain boundaries Rubinberg quarry, Granulitgebirge. mainly of clinopyroxene (Fig. 12). Small garnets before serpentinisation. Garnets of several mm-size seem to be also associated with plagioclase and are in an equigranular matrix of signifi cantly smaller amphibole. A process of partial melting is suggested clinopyroxene, orthopyroxene, and olivine. Together also because of the irregular shape of garnet and the with the information on the chemical composition estimated temperature of about 1100°C for the rim of the minerals (see Table 2) it is suggested that the compositions of garnet and clinopyroxene (Table 3). relatively large, nearly homogeneous garnets belong The corresponding pressure amounts to 22 kbar. Core to a pre-recrystallisation stage. Only the garnet rim compositions yielded somewhat higher temperatures adjusted chemically to the other silicates that were at pressures of 26 kbar. At this stage the rock was an affected by deformation to recrystallise. In terms of eclogite as the jadeite content in clinopyroxene was relative pressure conditions, the chemical compositions above 20 mol% (Table 3). In the clinopyroxene cores are interpreted as follows. Garnet contains more Cr numerous, tiny and transparent rods could be detected at the rim than in the extended core because of the (Fig. 12). Compositional investigations suggest SiO2 breakdown of spinel as a result of pressure increase. and alkalifeldspar as exsolution of clinopyroxene. This Afterwards the matrix recrystallised. On the basis of phenomenon was assigned to UHP metamorphism, for Volume n° 2 - from B16 to B33 n° 2 - from Volume geothermobarometry with garnet-clinopyroxene pairs instance, by Dobrzhinetskaya et al. (2002). Pressures as reported by Massonne and Bautsch (2002), P-T as high as 30 kbar result at least from EMP analyses conditions close to 19 kbar and 1000°C can be derived of clinopyroxene using a strongly defocused electron for this stage. These data are compatible with the Al beam to obtain integral analyses of clinopyroxene and content in orthopyroxene associated with olivine and exsolution minerals (Table 3). garnet. Subsequent pressure release is documented by Returning to B169 at Greifendorf we move to the increasing Al in clinopyroxene from core to rim. right but leaving the federal road almost immediately Additional information on the P-T evolution afterwards to go to Reichenbach and further on to Waldheim. In the centre of the town of Waldheim we

9 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne meshes areorientedwithanaxial symmetrysimilar orthochrysotile formingamesh-like fabric. The The serpentiniteconsistsofabout60% ultrabasic rocks. Veins andlarger bodiesofgranitoidscrosscutthe or boudinsparalleltothelayeringofserpentinite. 13). Pyroxenites occuraslayers,10to50cmthick, as thick100moutcroppingover alarger area(Fig. surrounding felsicgranulites. The ultrabasicbodyis This layeringisconcordanttothefoliationof layered duetoapenetrative deformationevent. of stop1.2,theserpentinitebodyhereissignifi other trash.Incontrasttothemassive serpentinite now toslowly fi ll upwithconstructiondebrisand “Terrazzo”. However, thequarryseemstobeused and toproduceanartifi cial constructionstonecalled Granulitgebirge was orstillisquarriedformacadam Here anotherlarge serpentinitebodyofthe Stop 1.3: on theright-handside. of thisvillage,analmostabandonedquarryislocated then turnswestheadingforReinsdorf. At theentrance to thesouthforsomehundredmetres. The mainroad cross Zschopauriver toturnleftfollowing theriver -1A taken fromtheRubinbergquarry, Granulitgebirge. host +exsolution)fromgarnetpyroxenite (eclogite)GR99 Table 3-EMPanalyses (inwt.%)ofminerals(integr. = i5835841891891862.697 1.806 1.859 1.819 5.834 101.73 100.58 5.843 100.12 100.61 99.78 Al 101.07 Si 101.45 Total n .904 .600 .400 0.31 5.93 7.26 0.00 36.87 19.47 0.00 0.04 0.21 17.25 11.63 0.06 6.78 18.27 10.20 8.20 0.06 6.13 10.22 11.56 11.69 0.43 5.94 10.05 Na 0.29 17.97 CaO 16.59 MgO MnO FeO Al K SiO a0030090260220100.731 0.282 0.140 0.767 0.242 0.667 0.246 0.717 0.009 1.285 0.013 1.811 K Na Ca V TiO n0060030020020010000.006 0.255 0.000 0.000 0.001 0.637 0.002 0.549 0.002 0.558 0.053 2.547 0.036 2.191 Fe Mn Mg i0010050020060090010.993 0.001 0.029 0.016 0.022 0.015 0.021 Al Ti Cr r0030030010010020000.000 0.004 0.000 0.003 0.002 0.004 0.001 0.003 0.001 0.006 0.003 0.003 Fe V Cr 2 2 VI IV 2 2 O O 2+ 3+ 2 O O 2 2 .500 .634 .78.51 1.97 3.46 3.46 0.03 0.05 O 3 3 3 21 31 31 N1 91 61 31-1A 56-1A 59-1A 8N-1A 43-1A 53-1A 42-1A .4 .0 .8 .8 0.209 0.185 0.182 2.106 1.948 0.091 0.081 0.00 24.76 9.84 60.88 11.27 49.15 11.24 51.49 22.65 49.63 22.69 39.90 39.95 .1 .0 .0 .3 0.232 0.339 0.304 3.902 3.911 .200 .300 .600 0.01 0.00 0.06 56.16 0.13 0.03 0.03 0.10 0.03 1.03 0.14 0.03 0.60 0.03 0.02 0.79 0.05 0.13 0.19 oesali tintegr. inGt small core tGt Gt CxCxCxPa Ilm Plag Cpx Cpx Cpx .0 .0 .0 0.015 0.001 0.001 0.000 .8 .4 .9 1.293 0.194 0.141 0.181 .000 .20.26 0.02 0.02 0.00 .0 0.013 0.008 cantly 0.712 0.021 0.000 1.11 the garnet(gt)lamellae,which aretopotaxially and Bautsch(1984)hadconfi crossed nicols(Fig.14A).X-raystudiesbyReiche same interferencecolourinathinsectionunder eye, andidenticallyorientedsince they displaythe regularly spaced,ascanbeseen withthenaked clinopyroxene (cpx)lamellae,whicharefairly Portions oftype1pyroxenite consistof parallel types 2and3seemtohave disappeared. collected alongtheeasternwall ofthequarrywhereas orthopyroxene andgarnet. Type 1pyroxenite canbe of megacrysts consistingnow ofthicklamellae 3. orthopyroxene-rich pyroxenite withsomerelics the grainboundariesofcoarse-grainedclinopyroxene; 2. clinopyroxenite withgreenspinelandgarnetalong 1. Those consistingofgarnetandclinopyroxene only; The pyroxenites canbesubdivided intothreegroups. was foundaswell. body. However, very raregarnetupto1cminsize with thenaked eye inmany portionsoftheserpentinite pseudomorphs aftergarnet canbeeasilydetected was abundant but itisstronglyaltered.Nevertheless, result offl as carbonatesappearclosetothegranitoidsa lizardite occurs.Moreover, specifi c mineralssuch granulites. Inadditiontoorthochrysotile,2030% to theorientationofquartzc-axes inthenearby the villageofReinsdorf, southeasternGranulitgebirge. Figure 13-Simplified geologicalmapofanarea east of uid-rock interaction.Originally, garnet rmed thisalsofor ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

Figure 15 - Orientation of recrystallised orthopyroxene in type 3 pyroxenite (a-axes on the left, c-axes on the right hand side). by various kinds of symplectites (Fig. 14F) often consisting of orthopyroxene and spinel but also of clinopyroxene, amphibole, potassic white mica and feldspars. The latter minerals are rather constituents of late alteration. Coarse-grained clinopyroxene is much rarer altered compared to garnet. Electron microprobe analyses (Table 4) and element concentration maps (Figs. 16 and 17) show that garnet, Figure 14 - Photomicrographs under crossed nicols clinopyroxene, and spinel in the clinopyroxenites (A-C) and under plain polarised light (D) as well as are slightly non-homogeneously composed, thus, back scattered electron images (E,F) of pyroxenite allowing to estimate various P-T conditions on the types 1 (GR00-1: A-C) and 2 (PR 9457: D-F). Scale basis of the equilibria: (1) almandine (in gt) + 3 bars represent 1 mm (A-D) and 100 µm (E,F). The grey diopside (in cpx) = pyrope (in gt) + 3 hedenbergite symplectites around spinel (Spi) in D have replaced garnet (in cpx) and (2) 2 grossular (in gt) + pyrope (in gt) = 3 (Gt) at various stages as can be seen in F. CaAl2SiO6 (in cpx) + 3 diopside (in cpx). For a sample intergrown with clinopyroxene ((100)cpx//(110)gt of type 1 pyroxenite Massonne and Bautsch (2002) and [001]cpx//[100]gt as well as (100)cpx//(100)gt computed P-T data of about 25 kbar and 1000°C for and [001]cpx//[110]gt; Jekosch and Bautsch, 1991). an early stage due to formation of exsolution lamellae. As the lamellae can run parallel over cm, they were Afterwards the mantle fragment was inserted into the interpreted as former megacrysts (> 10 cm) with lower portion of a thickened continental crust during exsolution texture similar to those in pyroxenite type the Variscan orogeny causing deformation and, thus, 3 (Reiche and Bautsch, 1985). The recrystallised signifi cant recrystallisation of the pyroxenite. This fabric of equigranular garnet and clinopyroxene (Fig. event was estimated to have happened close to 11 14B) close to the lamellae in pyroxenite type 1 is the result of deformation as we can see all kinds of transition from lamellar to equigranular fabric such as curved lamellae starting to recrystallise (Fig. 14C). Lamellar exsolution can also be observed in the mm- sized clinopyroxenes of type 2 pyroxenites. Here, formation of small garnet and more rarely spinel lamellae in clinopyroxene is obvious (Fig. 14E). But also the appearance of coarse grained garnet (and B16 to B33 n° 2 - from Volume spinel?) along the grain boundaries of clinopyroxene is interpreted as reaction fabric (Fig. 14D). The orientation of clinopyroxene grains in pyroxenite Figure 16 - Concentration maps of Al (left) and Ca (right types 1 and 2 is more or less isotropic whereas the hand side). A,B: Area (as in Fig. 14A) with lamellar microfabric of clinopyroxene and garnet (light in A and recrystallised orthopyroxene grains in pyroxenite C). C,D: Strongly recrystallised area (as in Fig. 14B) type 3, which frequently exhibit subgrain boundaries, close by. Lighter tones of the grey code refer to higher are strongly oriented (Fig. 15). Finally, it is worthy concentrations of the corresponding elements. of note that garnet can be replaced signifi cantly Scale bars represent 200 µm.

11 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne the righthandside.Scalebarsrepresent 400µm. (increasing elementconcentrationstowards thetop)ison section ofsamplePR9457.Thescalefor thegreytones Figure 17-Concentrationmapsof Al andCaofa the compositionofmono-tobimineraliclayersas common rockssuchasgabbros. They ratherrefl pyroxenites (Table 5)arenotsimilar tothoseof The bulk rockcompositionsoftype1and2 general (seeFig.9). estimated forthegranulitesofGranulitgebirge in late stageexhumation iscompatiblewiththeP-Tpath resembles thatderived fromtype1pyroxenite. The metamorphic stage. The subsequentexhumation path km attemperaturesabove 1000°Cduringanearly signifi and Bautsch,2003). This path(Fig.18)shows a be derived fromatype2pyroxenite (Massonne kbar and900°C. A moredetailedP-Tpathcould at thevillageofReinsdorf, Granulitgebirge. Table 4-EMPanalyses (inwt.%)ofmineralsfrompyroxenite types1(GR00-3)and2(PR9457)intheserpentinitebody compositions; Gt3,Gt4,Cpx3,Cpx4=compositionsoflamellaeandblebsincoarse-grainedCpx. Gt1, Cpx1,Spin1=coreofcoarse-grainedgarnet,clinopyroxene,andspinel,respectively;Gt2,Cpx2,Spin2correspondingrim i .0 .0 .5 .5 .0 .0 .1 0.045 0.019 0.000 0.008 0.255 0.250 22.49 0.000 22.90 2.95 6.17 2.85 15.72 7.76 0.054 9.95 16.95 0.046 18.95 9.36 0.004 0.484 18.00 0.000 0.418 14.65 22.92 19.73 11.69 0.235 22.00 20.92 0.000 0.155 22.65 3.21 14.96 22.65 0.081 3.85 13.13 0.118 9.56 16.91 2.75 0.044 15.17 5.40 2.21 0.028 13.69 10.68 13.68 0.607 16.73 7.29 12.97 0.585 16.19 Na 8.62 0.336 18.97 CaO 0.368 8.65 NiO MgO MnO FeO V Cr Al TiO i574571581588189 .17170 .53000 .03584586198 1.843 1.9185 5.866 5.834 100.47 0.0003 100.18 0.0000 101.19 1.8583 100.78 1.7308 1.9167 100.91 1.8591 100.99 100.62 5.818 100.02 5.821 100.28 99.99 5.731 5.754 102.07 100.78 101.22 Al 101.80 Si Total i000 .00005 .02001 .00000 0.0013 0.0006 0.0000 0.0010 0.0052 0.0050 0.0000 0.0500 0.0420 0.0000 0.0002 0.8675 0.8865 0.8435 0.926 0.9125 1.168 3.956 0.0001 0.0016 3.770 0.0000 0.0014 0.0000 0.0574 0.7406 0.8881 0.0057 0.0498 0.0513 0.7748 0.8592 0.0046 0.0448 0.8773 0.0068 0.8063 0.006 0.0437 0.0050 0.0049 0.8791 0.0102 0.7134 0.0717 0.0033 0.0326 0.9110 0.0328 1.457 0.0036 0.0025 0.8190 0.0020 0.0011 0.0036 0.0018 0.822 0.0346 0.0039 0.0013 2.902 0.0442 1.598 0.0025 0.0024 0.0009 3.544 0.0020 1.076 0.0045 0.0731 0.0018 3.370 0.0065 0.0704 0.0025 Na 0.0032 3.892 0.0397 0.0052 Ca 0.0060 0.0429 0.0011 Ni 0.0531 0.0039 Mg 0.0234 0.0024 Mn 0.0199 Fe 0.0200 Fe V Cr SiO i004 .01002 .06004 .03004 .02000 .05002 .02001 0.0018 0.0010 0.0022 0.0026 0.0005 0.0004 0.0032 0.0044 0.0023 0.0049 0.0046 0.0021 0.0071 0.0043 Al Ti 2 VI IV 2 2 O 2+ 3+ 2 O O 2 2 .1 .0 .0 .1 .2 .2 .3 0.732 0.634 0.624 1.020 0.013 0.008 0.007 0.012 O 3 3 3 cantburial oftherocktodepthsatleast100 .8 .8 .4 .6 .69003 .14007 .13020 .1 .6 .3 0.031 0.035 1.062 1.010 0.1335 0.0610 0.2500 3.858 0.2173 3.866 0.0970 0.1174 1.9031 0.0831 1.9276 0.0669 0.1562 1.564 0.2645 0.063 0.0898 1.541 0.1649 0.000 0.989 0.018 0.987 3.878 0.009 3.997 3.959 3.969 .2 .3 .1 .5 .8 .1 .2 .5 .9 .0 .9 .60190.199 6.84 0.212 0.159 0.171 3.34 0.06 0.068 0.295 23.38 0.035 0.091 51.19 0.295 23.33 0.02 53.11 0.100 1.74 41.89 0.025 64.14 0.091 41.49 2.25 65.83 0.028 0.159 6.99 0.013 0.085 0.022 0.224 0.000 0.068 12.42 0.113 0.118 0.063 4.06 0.183 51.39 0.162 0.087 47.48 7.16 0.085 0.053 53.02 0.472 0.180 0.010 23.13 51.31 0.208 0.035 0.043 23.87 0.180 0.022 40.91 0.020 24.05 0.184 40.97 0.068 24.46 41.04 0.042 41.79 t t t t p1Cx p3Cx pn pn t t p1Cpx2 Cpx1 Gt2 Gt1 Spin2 Spin1 Cpx4 Cpx3 Cpx2 Cpx1 Gt4 Gt3 Gt2 Gt1 R9457 PR .49003 .620.1417 0.2692 0.0833 0.1409 ect inferred fromgeochemical studies(seetext).Thedashed- Granulitgebirge. Thebroken lineofthepathatUHPwas in theserpentinitebodynearvillageofReinsdorf, Figure 18-P-Tpath(solid)derived for pyroxenites .25008 .9 .0 .5 0.058 0.051 0.102 0.092 0.0585 0.0255 dotted curve representsthemantlegeotherm. .0 .0 .9 0.717 0.597 0.000 0.001 R00-3 GR .850.157 0.0815 ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

Sample PR9457 GR00-3L GR00 Alteration in % 80 40 0

SiO2 in wt.% 46.6 48.0 48.6 TiO2 0.10 0.05 0.05 Al2O3 14.3 10.7 10.8 FeO 4.72 5.77 5.67 CaO 16.8 16.7 17.6 MgO 14.6 16.2 16.3 MnO 0.15 0.19 0.19 K2O 0.38 0.20 0.00 Na2O 0.28 0.48 0.50 P2O5 0.00 0.00 H2Otot 0.59 0.45 CO2 0.26 Sum 98.7 99.3 100.0

Li in ppm 84.5 31.8 22.5 Sc 91.5 112 112 V (XRF) 426 741 802 Cr (XRF) 1661 1247 1190 Ni 232 307 312 Cu 7.51 2.41 2.89 Zn 4.71 10.2 9.2 Ga 7.29 7.67 7.60 Rb 19.3 11.0 1.0 Figure 19 - REE pattern of clinopyroxenites occurring Sr 20.7 22.9 23.4 in the serpentinite body near the village of Reinsdorf, Y 11.0 8.92 9.3 Zr (XRF) 4 150 119 Granulitgebirge. The data were obtained by ICP-MS Nb 1.10 0.70 0.61 analyses and subsequently normalised to chondrite. Sn 1.87 Ba 45.8 < 20 could be that the syenite was an ordinary felsic rock Hf/Zr b.d.l. 0.035 chemically altered by fl uid-rock interactions with Ta 1.44 0.70 0.55 the serpentinite. This interpretation should hold true Pb 0.04 Th b.d.l. 1.28 1.33 for the pyknotropites (see Fig. 13) which are former U b.d.l. 0.89 0.90 granitoids transformed to alkalifeldspar-rich rocks.

Table 5 - XRF analyses of type 1 (GR00-3L) and type 2 We return to Waldheim but stop soon after reaching (PR 9457) pyroxenites from the serpentinite body at the the edge of town. We are now at the western banks of village of Reinsdorf, Granulitgebirge. The concentrations of most trace elements were determined by ICP-MS. the Zschopau river. From here we walk southwards on GR00 shows values extrapolated to 0 % alteration using a tourist trail along the river. several analyses of similar rocks with various degrees of alteration. b.d.l.= below detection limit. Stop 1.4: (optional) Along the walk (see Fig. 20) cliffs appear on the right can be also inferred from the original megacryst side of the tourist trail. Similarly, as seen during the nature at least of type 1 pyroxenites. On the basis walk of stop 1.1, we can discern felsic granulites as of the REE patterns of the pyroxenites ((Yb/Nd) N well as basic intercalations. It was about here where > 10, Fig. 19), Massonne and Bautsch (2002, 2003) Rötzler and Romer (2001) discovered coarser grained concluded that the pyroxenite layers originally metabasites and in them garnet with enclosed relics of consisted of majoritic garnets. For type 1 pyroxenite, omphacite. These authors used the original eclogitic such a garnet would have once contained about nature of the rock to estimate early metamorphic P- 50 mol% of (Mg,Ca) Si O component. If this is 4 4 12 T data. These were close to 1000°C and 22 kbar as true, the rock must have resided in the transition B16 to B33 n° 2 - from Volume also determined by Massonne and Bautsch (2002) for zone of the Earth’s mantle (depths > 400 km). The clinopyroxenites from the nearby village of Reinsdorf uplift of the rock (for possible P-T path see Fig. 18) (see Fig. 18). Romer and Rötzler (2001) used the U- could have been facilitated by melts within a mantle Pb system to determine the metamorphic event to 342 plume. In the search for hints at such melts, boudins Ma. A very fast exhumation of the rock was deduced of quartz-free syenite, which are spatially related to from almost identical U-Pb ages obtained from the pyroxenites, were investigated (Massonne et al., zircon, titanite, and apatite concentrates. 2002). However, the trace element pattern of the syenite showed no relation to ultrabasic rocks. It

13 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne close tothevillageofDiethensdorf, Granulitgebirge. Figure 21-Lithologicalrelationsseenatthewalls ofthelargequarryinChemnitzvalley south ofthetown of Waldheim. to outcropsatthewestern banksofZschopau river Figure 20-Simplified geologicalmaprelated 22). Moreoften,however, aggregates ofsillimanite kyanite arediscernibleunderthemicroscope(Fig. plagioclase, K-feldspar, andsomegarnet.Relicsof The felsicgranulitesconsistmainlyofquartz, of theexcellent exposure inthequarry(Fig.21). country rockscanbewellinvestigated herebecause extension ofthesebodiesandtheirrelationtothe ultrabasic andbasicbodiesinthefelsicmatrix. The felsic granulitesoftheGranulitgebirge but also The target ofthisstopistoshow againthetypical Stop 2.1: Steinwerke”, ontheoppositesideofriver. hand sideandalarge quarry, runby“Westsächsische metres thereareabundant parkinglotsontheleft valley tothenorthwest. After aboutafew hundred crossing totherightfollowing theChemnitzriver after crossingtheChemnitzriver weturnattheroad by arelatively smallroadmostlygoingdownhill. Just Diethensdorf, weturntotherightpassingthisvillage Chemnitz. After about12km,closetotheentrance this town wechangetofederalroadB107headingfor We turntothesouthwestheadingforRochlitz.Close to Harthawherewehave accesstofederalroadB175. The routeoftheexcursion continuesfrom Waldheim DAY 2 ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

Gt Gt Plag Kf Alkfs Bt Sill large small small with small core lamel. 2-8b 15-8b 13-8b 23-8c 25-8c 21-8c 19-8c

SiO2 37.98 38.27 65.35 66.02 66.73 37.42 36.95 TiO2 0.11 0.09 0.04 0.03 0.06 3.52 0.01 Al2O3 21.83 21.80 23.54 19.46 20.87 15.86 62.71 Cr2O3 0.01 0.03 0.00 0.01 0.01 0.05 0.00 FeO 29.16 30.76 0.09 0.03 0.01 13.58 0.56 MnO 0.50 0.61 0.00 0.00 0.03 0.01 0.01 MgO 6.71 8.16 0.00 0.01 0.00 14.59 0.02 CaO 4.23 1.02 3.90 0.05 1.10 0.00 0.01 Na2O 0.00 0.00 8.39 1.01 4.77 0.19 0.01 K2O 0.77 15.04 8.27 9.61 0.01 BaO 0.01 0.13 0.07 0.16 0.01 Total 100.53 100.77 102.09 101.79 101.92 94.98 100.32

Si 5.836 5.868 2.821 2.980 2.939 2.787 0.995 AlIV 1.198 1.035 1.083 1.213 Ti 0.013 0.010 0.001 0.001 0.002 0.197 0.000 AlVI 3.954 3.940 0.179 1.990 Cr 0.002 0.004 0.000 0.000 0.000 0.003 0.000 Fe3+ 0.045 0.057 0.003 0.001 0.001 0.013 Mg 1.536 1.865 0.000 0.001 0.000 1.620 0.001 Fe2+ 3.703 3.889 0.846 Mn 0.065 0.079 0.000 0.000 0.001 0.000 0.000 Ca 0.696 0.168 0.181 0.003 0.052 0.000 0.000 Na 0.000 0.000 0.702 0.088 0.407 0.027 0.001 K 0.042 0.866 0.465 0.913 Ba 0.000 0.002 0.001 0.005

Table 6 - EMP analyses (in wt.%) of minerals from the felsic granulite GR02-8c taken in the quarry at Diethensdorf, Granulitgebirge. occur which have replaced kyanite. Biotite is probably a retrograde product only. Small portions of the rock contain mm-sized garnets being signifi cantly larger than the ordinary garnets (Fig. 22). These Table 7 - XRF analyses of garnet-rich pyroxenites portions seem to have been unaffected by the usual from the Granulitgebirge.GR02-3c is from stop 1.2 penetrative deformation that has led to fi ne-grained (Rubinberg). GR02-7b was sampled close to stop 1.4 strongly foliated granulites. The composition of where railroad tracks are cut into the crystalline rocks a the extended cores of the large garnets differs few hundred metres south of Waldheim station. GR02-8b signifi cantly from that of their rims, which is nearly is from the large quarry close to Diethensdorf (stop 2.1). identical to the compositions of the small garnets (Table 6). Assuming 850°C and an anorthite activity of 0.2 in plagioclase (plag), the equilibrium: (3) grossular (in gt) + 2 kyanite + quartz = 3 anorthite (in plag) yields pressures as high as 17 kbar for the core composition of large garnets whereas pressures

below 10 kbar result using the compositions of the B16 to B33 n° 2 - from Volume Figure 22 - Photomicrographs taken from felsic granulite small garnets. sample GR02-8c (quarry close to Diethensdorf) under The bulk compositions of garnet-rich pyroxenites plain polarised light. Relics of kyanite (Ky) can be seen associated with serpentinites were determined. on the left hand side. Image width is 1.3 mm. On the Examples are given in Table 7. Whereas those from right hand side, a large garnet (Gt) is discernible whereas the Rubinberg quarry and from a body southwest of garnets of common size in this rock are enriched Waldheim (see Fig. 20) are, for instance, relatively in a layer below the big garnet. An aggregate rich in Ti, Al and light REE, the one in Table 7 from of sillimanite (Sill) is a pseudomorph after kyanite. Image width is 2.5 mm. stop 2.1 is more similar to the garnet clinopyroxenites

15 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne Saxonian Erzgebirge. basement aroundthetown of Augustusburg, relations ofthePermian rhyolitestothecrystalline Figure 23-Geologicalmapshowing thesimplifi the massive appearanceofthereddishrhyolite canbe to thecastle. At thewalls oftheabandonedquarry somewhat hiddenbut closetothepaved roadleading about 200mtothenorth(Fig.23). The oldquarryis of thecastlehillbywalking fromtheparkingarea a smallabandonedquarryatthesoutheasternbase Permian rhyoliticlava fl 16th century, issettledontopofaremnant Saxonian electorsinonly4yearsattheendof The famous castleof Augustusburg, erectedbythe Stop 2.2:(optional) right-hand sidethereisaparkingareaforvisitors. we keep goingstraightonfor150mmore.Onthe town, following theroadsigntoLeubsdorf,otherwise to stop2.3wehave toturnleftatatraffi heading for Augustusburg. Ifwewant togodirectly Zschopau river inthevillageofPlaue. We continue 2 kmafterpassingthistown weturnleftcrossing on itswesternsideB80directedtoFlöha. About Frankenberg. This time we arepassingFrankenberg several kmweleave thehighway againatexit 72 at thenortherncitylimitsheadingforDresden. After alternative usingHighway A4. We have accessto A4 instead ofpassingthecityChemnitzwetake the Then, wecontinueheadingforChemnitzbut We returntoB107passingDiethensdorfagain. presence ofsulphidesinthegarnetpyroxenite. concentrations ofNiandCuarehererelatedtothe from thequarryatReinsdorf.Relative high ow. We recommend visiting ow.Werecommend clightinthe ed phenocrysts (Fig.24). A fl seen. The rockcontainsnumerousquartzandfeldspar is asmallabandonedquarryhiddenintheforest. our roadleadsto,becauseontheright-handsidethere to stop2.3. We parkca.50minfrontofanotherroad Borstendorf.The roadontheleftleadsusafter1.7km side closetoanotherroadwhichturnstheright small roadbetweenhousesappearsontheleft-hand right intotheroadtoReifl andthendriving 1.6km. A Eppendorf. Nearthecentreofthisvillageweturn Leubsdorf whichwepasstofollow theroadto We returntothetraffi easily recognised. P-T conditionsoftheeclogite stagecouldbe within thebasicrocks. is apeliticprotolithsoriginallypresentasthinstrata interpretation ofeclogiticlayersrichinwhitemica H mica mightbealsoareactionproductofinfi eclogite stage. The rareenrichmentofpotassicwhite as afew cm. This reactionstilltookplaceduringthe form amphibole(Fig.26)whichcouldbeaslarge Occasionally, omphacite +H symplectites ofamphiboleandplagioclaseaswell. this mineralcanbecompletelyalteredtofi the quarrycancontainfreshomphacite.However, vicinity ofstop2.3. These blocksandtherocksin along thebordersbetweenfi elds andwood inthe but abundant bigblocksofeclogitecanbefound ground, furtherexposure ofeclogitedoesnotexist of thelarge eclogitebodiesassumedtobebelow assembly ofseveral eclogitelenses(Fig.25).Inspite eclogite belongingprobablytoabiglensoran At thisquarrywehave agoodexposure ofmassive Stop 2.3: Figure 24-PhotomicrographofaPermian rhyolitefrom 2 O whenitcontainedpotassium. Another Augustusburg containingphenocrystsofquartz and feldspars. Imagewidthis8.5mm. c lightheadingthentowards uidal texture canalsobe 2 O have reactedto ne-grained ltrating ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

Gt Omph Phe core rim core rim core rim 1109/09 1109/91 1109/80 1109/12 1109/33 1109/72

SiO2 38.32 38.04 54.87 54.39 50.45 48.25 TiO2 0.12 0.10 0.08 0.23 1.55 1.12 Al2O3 21.66 21.63 10.19 10.80 26.98 30.60 Cr2O3 0.01 0.04 0.00 0.03 0.02 0.01 FeO 21.07 20.96 4.63 4.25 1.28 1.29 MnO 0.38 0.43 0.00 0.07 0.00 0.00 MgO 5.65 6.13 8.81 9.03 4.01 2.71 CaO 13.12 11.85 15.21 15.76 0.00 0.00 BaO 0.18 0.11 Na2O 5.40 5.33 0.47 0.83 K2O 9.57 9.00 Total 100.33 99.19 99.36 99.88 94.51 93.93

Si 5.811 5.830 1.976 1.949 6.705 6.437 AlIV 0.024 0.051 1.295 1.563 Ti 0.013 0.012 0.002 0.006 0.155 0.113 AlVI 3.871 3.907 0.409 0.405 2.932 3.247 Figure 25 - Simplifi ed geological map of an area in the Cr 0.001 0.005 0.000 0.001 0.002 0.001 GEU of the Saxonian Erzgebirge, southeast of Eppendorf, Fe3+ 0.128 0.088 0.000 0.003 with large eclogite bodies (grey) embedded in gneiss. Fe2+ 2.544 2.598 0.139 0.125 0.142 0.144 Mn 0.049 0.056 0.000 0.002 0.000 0.000 determined from phengite-bearing eclogite which Mg 1.277 1.400 0.473 0.483 0.795 0.539 contained quartz, common as a minor constituent of Ca+Ba 2.131 1.946 0.587 0.605 0.010 0.006 Na 0.389 0.371 0.120 0.216 the eclogites, and kyanite as a rare accessory phase K 1.623 1.531 in the eclogites. Mineral equilibria of geobarometric importance are here those using components in Table 8 - EMP analyses (in wt.%) of minerals from phengite (phe) as, for instance: (4) pyrope (in gt) + eclogite E174c taken from the large eclogite body SE 2 grossular (in gt) + 3 Al-Mg-celadonite (in phe) = of Eppendorf (stop 2.3), Saxonian Erzgebirge. 6 diopside (in cpx) + 3 muscovite (in phe) and (5) 2 kyanite + grossular (in gt) + 3 Al-Mg-celadonite (in + 2 kyanite = pyrope (in gt) + grossular (in gt) + 2 phe) = 3 diopside (in cpx) + 3 muscovite (in phe) quartz/coesite could be also used for metamorphic + 2 quartz/coesite. In addition, the equilibrium: (6) pressure estimation. As the minerals are moderately muscovite + 2 rutile = 2 quartz + Ti-muscovite (= chemically zoned (Table 8) a small portion of the P-T path for the eclogite could be deciphered. Due KAl3SiTi2O10(OH)2) can be applied because rutile is omnipresent in the eclogites. In the absence of to the signifi cant decrease of Si in phengite this path phengite, the equilibrium: (7) 3 diopside (in cpx) is related to exhumation at maximum temperatures around 800°C (Massonne, 1994). The path starts at UHP conditions of somewhat more than 30 kbar ending close to 20 kbar and 700°C. UHP conditions are required for the occurrence of K-cymrite (KAlSi3O8·H2O). According to Massonne et al. Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 27 - Photomicrograph (right hand side) of inclusions (Rt = rutile, Phe = phengite) in omphacite of Figure 26 - Photomicrograph of an amphibole eclogite E174c (stop 2.3) under crossed polarisers. porphyro blast in eclogite sample Erz02-2 under crossed The inclusion (length about 140 µm) seen in the left polarisers. The sample is from the quarry 2.5 km SE of corner at the bottom is also displayed as back-scattered the village of Eppendorf, Saxonian Erzgebirge. electron image on the left hand side demonstrating Image width is 4.5 mm. the intergrowth of quartz and K-feldspar.

17 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne 6=E103c (1.2kmEofstop2.3). the hamletofHutha),4=KD59(as3),5=E174c(stop2.3), village ofMittelsaida),2=Erz98-4(as1),3=KD39(NE the GEUofSaxonianErzgebirge. 1=Erz98-3(atthe Table 9-XRFandICP-MSanalysesofeclogitesfrom = 5-36,(Sr) = 48-52wt.%,see Table 9)arecharacterisedby(Nb) Massonne andCzambor(2003). These eclogites(SiO locality andeclogitebodiesnearbywerereportedby Results ofgeochemicalanalyseseclogitesfromthis aggregate. host mineralaroundtheenclosedK-feldspar-quartz for thoseaftercoesitealsobecauseofcracksinthe 27). These pseudomorphscanbeeasilymistaken replaced byK-feldsparintergrown withquartz(Fig. mainly ofomphacitebut alsoingarnet.Now itis (2000), thismineralwas enclosedinmineralcores Großwaltersdorf. After passingthisvillagewe We take theroadonleftheadingfor to P-MORBsisdiscernible. MORBs. However, inadditiontoN-MORBsatrend & Czambor(2003)referredthesedatatooriginal 0.5-1.5, and(Sm/Yb) TiO FeO P n .802 .701 .00.17 5.31 0.20 6.33 0.18 11.79 7.11 0.17 12.30 7.79 9.40 0.20 5.78 9.67 0.18 5.52 11.89 11.52 K MnO MgO CaO .203 .503 .40.09 0.13 0.14 1.45 0.16 0.34 0.26 1.59 274 0.51 0.35 0.34 2.37 0.58 42 0.35 1.87 0.76 4.35 1.90 0.88 0.040 0.22 1.27 1.01 61 86 2.10 85 0.032 31.8 2.80 0.81 1.45 0.74 19.4 0.034 3.33 71 39.7 9.73 131 111 4.55 0.028 1.17 8.4 24.5 12.7 0.054 164 31 1.68 148 16.8 89 94 21.0 0.043 24.2 4.12 U 1.69 109 18.3 139 56 3.0 69 Th 116 34.5 59.0 3.88 - 187 Pb 125 61.4 60.1 1.7 95 Ta 200 26 150 116 336 Hf/Zr 92.1 36.4 18.4 4.2 298 Ba (XRF) 88 16 353 76.7 43.9 Sn 18.7 261 Nb 120 60.7 236 55.0 31.0 57 Zr (XRF) 252 49.7 50.6 112 22.4 Y 225 80 Sr 240 48.4 36.9 99.20 365 Rb 307 99.02 Ga 48.3 24.2 326 Zn (XRF) 99.26 31.2 Cu (XRF) 99.49 Ni 59.3 100.87 Cr (XRF) 98.23 V (XRF) Sc Li inppm Sum CO H Al SiO Na 2 2 2 2 O O O 2 O 2 2 2 O 5 tot tot i t%4.64.35.85.54.050.29 49.50 51.25 51.58 49.93 49.76 3 inwt.% N =5-17, Ta/Yb =0.07-0.25,(La/Sm) 57 56 64 61 48 16.70 14.80 16.14 16.47 15.60 15.78 01 17 .61.51.010.26 11.30 10.05 9.46 11.76 10.11 .823 .226 .22.48 2.32 2.62 2.52 2.39 2.78 .601 .501 - - - - 0.13 0.15 0.12 0.31 0.05 0.13 0.23 0.12 0.10 0.21 0.16 0.84 0.29 0.16 1.67 1.92 1.54 1.32 2.06 1.88 .900 .303 .30.40 0.23 0.38 0.13 0.09 0.09 123456 N <1.8(seeFig.28).Massonne N = N 2 we stopnearthelittlebridgecrossing theSaidenbach of Forchheim headingforLippersdorf. After 1.8km the southweturnrightatentrancetovillage Annaberg-Buchholz. After about23kmonB101to The routeoftheexcursion continuesfromFreiberg to and many more. instance, relatedtopreciousstonesandmeteorites, ore depositsofeasternGermany, specialities,for collection, aregional collectionofmineralsand exhibitions show asystematicmineralandrock Weisbach, Kolbeck, andvon Philipsborn. The famous namessuchas Werner, Mohs,Breithaupt, Especially themineralogicalcollectionislinked to important geoscientifi c collectionsintheworld. belong tothe10oldestofcurrentlymorethan500 century. The Freiberg collections,foundedin1765, town centreclosetothedomeerectedin13th Academy atFreiberg. The museumislocatedinthe petrological, andoremineralcollectionoftheMining At thisstopwewant tovisitthemineralogical, Stop 2.4: Freiberg. B101. We turnlefttodrive ca.19kmtothecentreof continue toMittelsaidawherewereachfederalroad localities seeTable 9. Thedatawere obtainedbyICP-MS Figure 28-REEpatternsofeclogitesinthenorthernto central portionoftheGEU,SaxonianErzgebirge. For analyses andsubsequentlynormalisedtochondrite. DY 3 DAY ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

brook. From here we have good access to the it is only rarely preserved as inclusion in omphacite Saidenbach reservoir by walking on forest roads. As and garnet (Fig. 30) where it is then only partially we want to visit fi rst coesite-bearing eclogites at the transformed to quartz. Ba-rich potassic white micas northern shore of the reservoir (see Fig. 29), we take with clearly decreasing Ba contents from core to rim the trail on the north-western side of the brook. We were found in eclogite containing also cymrite but walk for somewhat less than 2 km to reach the start only as rare inclusion mineral (Table 10). Cl-rich of our tour along the shore of the reservoir provided apatite was reported by Massonne and Burchard that the water level is at least a few metres below (2000). This mineral, which is, untypical for apatite, maximum. However, this is usually so from July to signifi cantly decomposed in the fresh eclogite, September. contained relative high amounts of Sr (> 4 wt.% SrO). Kyanite can be a rare constituent in eclogite blocks Stop 3.1A: from this locality. Moreover, eclogites were found At this site we can easily fi nd numerous blocks of formed from conspicuous amounts of carbonate. eclogite along a 300 m section of the strand. Most Calcite, probably former aragonite, and dolomite can of these blocks still contain fresh omphacite. The coexist in a single rock. variety of eclogite here is surprising. Massive and The bulk rock compositions of eclogites from stop foliated types exist as well as fi ne and coarser grained 3.1A (Table 11) differ from those of MORBs. Instead varieties. The eclogitic mineral assemblages are also of these rocks, magmatic protoliths related to oceanic variable. Rutile and quartz seem to be omnipresent. islands, active continental margins or intraplate In a few cases, coesite could be detected in eclogite magmatism are conceivable. The REE patterns shown blocks from this locality (Massonne, 2001). However, in Fig. 31 are compatible with such protoliths. Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 29 - Simplifi ed geological map of the area around the Saidenbach reservoir. The map in the inlet shows the distribution of the GEU and MEU in the Saxonian Erzgebirge.

19 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne and 0,65mm(atthebottom). by quartz(Qz).Imagewidthsare1.3 mm(atthetop) The sampleisfromstop3.1A.Coesite(Cs)surrounded of eclogitesampleE99-24underplainpolarisedlight. dolomite, Ky=kyanite, Phe=phengite, Rt=rutile)ingarnet Figure 30-Photomicrographsofinclusions(Dol= formulae were calculatedasgiven inTable 12andasfollows: cymrite-16valencies,carbonates2cationswithoutC. Saxonian Erzgebirge. Mostanalyseswere taken fromMassonneandBurchard (2000)andMassonne(2001).Structural Table 10-EMPanalyses(inwt.%)ofmineralsincoesite-bearingeclogiticrocks fromtheSaidenbach reservoir, We Erzgebirge). Thedatawere obtainedbyICP-MSanalyses Figure 31-REEpatternsofeclogitesfromthenorthern shore oftheSaidenbach reservoir (GEU,Saxonian and subsequentlynormalisedtochondrite. ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

We continue to walk to the east for a few hundred metres and stop where the (former) Saidenbach brook changes direction. Stop 3.1C: At this corner, boulders of an eclogitic rock are concentrated. It seems to be that we can see here a real exposure of the rock. In contrast to the eclogites of stop 3.1A, this rock is homogeneous and non-foliated. Similar to the diamondiferous rock of stop 3.1B, mm- sized garnets are homogeneously distributed in the rock although the concentration of garnet is higher and the matrix is different compared to the rock of stop 3.1B. The matrix originally consisted mainly of phengite, quartz, and abundant omphacite. However the omphacite is entirely replaced by relatively coarse-grained symplectites of plagioclase and diopside-rich clinopyroxene or amphibole. Phengite is rarely completely but at least marginally substituted by biotite and plagioclase but also, probably during a late retrograde stage, by a fi ne-grained micaceous material. Microdiamonds could not be detected as inclusion mineral but omphacite rarely survived as inclusion in garnet (for more details see stop 3.1F). We walk north to cross Saidenbach brook. Afterwards, we continue on the eastern strand heading south for several hundred metres and then to the west for several hundred metres more. Table 11 - XRF and ICP-MS analyses of eclogites from the northern shore of the Saidenbach reservoir, Stop 3.1D: GEU of the Saxonian Erzgebirge. Again we meet with blocks of diamondiferous rocks seen before at stop 3.1B. Such blocks can be move along the strand to the northeast. After crossing the issue of a little brook into the reservoir we walk for a few hundred metres to the southeast. Stop 3.1B: At this site we can recognise boulders differing from those of migmatitic gneisses (“Flammengneise”) which appeared along the strand after we left the area with blocks of eclogites. These boulders consist of a non-foliated quartzofeldspathic rock with a homogeneous distribution of abundant mm-sized garnets. Muscovite forms a considerable portion B16 to B33 n° 2 - from Volume of the matrix. Microdiamonds can be detected as inclusion in garnet and other phases (for details see stop 3.1D). Boulders of this rock, proposed Figure 32 - Photomicrograph of microdiamonds enclosed to be named after the type locality saidenbachite in garnet (Gt) from quartzofeldspathic rock E97-3 seen (Massonne, 2003), occur very locally, so that this under refl ected light. Striations around the diamonds occurrence is interpreted as a lensoid body in the allow to detect them easily. Image width is 3 mm. underground surrounded by migmatitic gneisses (see map of Fig. 29).

21 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne Scale barsrepresent250µm. element concentrationstowards thetop)isinmiddle. in sampleE97-2.Thescalefor thegreytones(increasing Figure 33-ConcentrationmapsofCaandMggarnet low Caconcentrations(Fig.33).contentsofthe of garnet. This intermediatezoneischaracterizedby Fig. 32)areenclosedinaspecific compositionalzone (see Table 12)confi rm thatthemicrodiamonds(see Detailed analyticalstudiesofthemineralcompositions diamondiferous quartzofeldspathicrockissub surface. westward. Thus, itis concludedthatalarger bodyof found forthenext 500metrescontinuingtowalk eightfold coordinatedcations,kyanite-cationsum=3,mica42valencieswithoutinterlayercations. calculated (asinpreviousandsubsequentTables) asfollows: clinopyroxene (here:jadeite)-4cations,garnet10six-and The analyseswere taken fromMassonne(1999)aswell asMassonneandNasdala(2003).Structuralformulae were Table 12-EMPanalyses(inwt.%)ofmineralsindiamondiferous quartzofeldspathic rocks fromtheSaxonianErzgebirge. 34), canoccurinanintermediatezoneaswell.Inthe general, areliconlyasitisalteredtowhitemica(Fig. Micro-diamond inclusionsinkyanite, whichis,in garnet coreandthethinirregular rimarehigher. 2003). Inthecoreofcrystalabundant smallgarnets Figure 34-Photomicrographofalargekyanitefrom sample E97-3seenundercrossednicols(Massonne, are enclosed. Arrows pointtomicrodiamonds. Image widthis4mm. ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

Figure 35 - SEM image of a polyphase diamond-bearing inclusion in garnet from quartzofeldspathic rock of the Saidenbach reservoir, central Saxonian Erzgebirge (Stöckhert et al., 2001). Arrows point to rational mica garnet interfaces. qz = quartz, par = paragonite, phl = phlogopite, ap = apatite. kyanite core numerous small garnets are occasionally enclosed. Another interesting feature is the association of diverse minerals with diamond within a single inclusion in garnet (Fig. 35). Such minerals are quartz, feldspars, various micas, and occasionally apatite and rutile. Stöckhert et al. (2001) interpreted the polyphase inclusions as trapped siliceous fl uid. In zircon, also containing microdiamonds (Nasdala and Massonne, 2000) in an intermediate growth zone, rare Figure 37 - P-T path derived for diamondiferous inclusions of garnet and jadeite were observed (Fig. quartzofeldspathic rock from the Saidenbach reservoir, 36). In addition, inclusions of phengite, quartz, and central Saxonian Erzgebirge. HP TiO2 is TiO2 with rutile occur in garnet cores. From these inclusion |-PbO2 structure. The lower pressure limit of this phase minerals, P-T conditions close to 18 kbar and 600°C was redetermined by Massonne et al. (2003). were derived by geothermobarometry (Massonne and of a thickened continental crust. Subsequently, the Nasdala, 2003). This result is almost identical to that protolith was deeply subducted into the mantle to be by Willner et al. (1997) for gneisses in the vicinity of heated to about 1200°C (Massonne, 2003). This caused the saidenbachites. It was interpreted by Massonne considerable anatexis. The melts originated this way, and Nasdala (2003) as evidence for the location still containing, for instance, garnet (cores), ascended of the protolith of the saidenbachites at the base from at least 200 km depth. Evidence for such depths is the appearance of a nanocrystal of HP TiO2, which was found by Hwang et al. (2000) in a saidenbachite. During ascent, garnet and kyanite but also rutile, zircon, and diamond crystallised from the magma. Finally, the magma was emplaced in deep portions of thickened continental crust at P-T conditions of 15 to 18 kbar (55-60 km) and circa 750°C as determined by Volume n° 2 - from B16 to B33 n° 2 - from Volume phengite geothermobaro metry (Massonne, 1999). At this stage considerable quantities of muscovite were formed by a peritectic reaction from the remaining melt (Massonne, 2003). During the subsequent retrogression some biotite formed at the expense of Figure 36 - Cathodoluminescence image of zircon from muscovite. It is worthy of note that microstructural sample St6100. This mineral contains a jadeite inclusion features were observed pointing to the formation of (black) in the dark core zone. Microdiamond (black) coesite, jadeitic pyroxene, and K-cymrite (Massonne, appears in the lighter zone. Scale bar is 50 µm.

23 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne rare „magmatic“portionsinzirconcoresyielded ± 3.6Ma,andmonazite-332.53.8Ma.Onlyvery (very lightbut lackinginzirconsofFig.36)-329.9 zone (lightinFig.36)-336.0±2.4Ma,outer (dark inFig.36)-336.1±2.2Ma,diamond-bearing late stageminerals. The subsequentagedatafor the matrixofsaidenbachitesand,thus,seemtobe monazites weredated,whichappearexclusively in Th-Pb-systems (Massonneetal.,2001).Inaddition, dated onzirconswithaSHRIMPapplyingtheU- The various metamorphic-magmaticstageswere of thesaidenbachiticmagma. 2003; MassonneandNasdala,2003)duringtheascent * taken closetodiamondiferous rocks SWofForchheim. SW ofthevillageForchheim, 5,6=ordinarygneisses body atZöblitz,4=gneissunusuallyrich inNasampled aspect similarto1,2taken northeastoftheserpentinite Saidenbach reservoir, 3=rock withoutdiamondsbut with Erzgebirge. 1,2=diamondiferous rocks fromthe quartzofeldspathic rocks fromtheGEUofSaxonian Table 13-XRFand ICP-MSanalysesof and =XRF dataasanexception. 238 U with2 ã errorwereobtained:zirconcore 206 Pb The recentinvestigation ofthe not more. pressures ashigh20kbar(Willner etal.,1997)but isolated bodiesinrocksthathadexperienced, infact, to bethatsaidenbachitesandotherUHProcksform segment extending over many kilometres.Itseems saidenbachites arepreserved portionsofanUHP and Massonne(2001)disproved theideathat have avery signifi cant Euanomaly. Thus, Düffels REE patterns(Fig.38)becauseallcountrygneisses and Y of Table 13). This difference alsoconcernsthe surrounding countryrocks(see,forinstance,Cr, Ni, 3.2). Saidenbachitesshow cleardifferences fromthe reservoir andtheserpentinitebodyatZöblitz(stop rocks fromtheGEUoccurringbetweenSaidenbach geochemical signaturesofvarious quartzofeldspathic Düffels andMassonne (2001)investigated the into thebaseofastillthickened continentalcrust. to maximumdepthandalsoafterinsertingtheserocks after transportoftheprotolithssaidenbachites of zirconandmonaziteformationhappenedsomeMa Ma oreven less. The growth oftheoutermostlayer process affecting thediamondiferousrockstookafew the GEU. Thus, thesubsequentburial andexhumation obtained byKrönerand Willner (1998)forgneissesof zircon coresarecompatiblewiththosearound340Ma ages ashigh396Ma. The dataof336Maforthe microdiamonds insaidenbachiteyielded chondrite. InsampleE99-32(N)monaziteislacking, thus, by ICP-MSanalysesandsubsequentlynormalisedto Figure 38-REEpatternsofsaidenbachites fromthe GEU, SaxonianErzgebirge. Thedatawere obtained explaining theexceptionalpatternof thelightREE. 13 C signatureof Ä 13 C(PDB) ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

values close to -30 ‰ (Massonne and Tu, 2003). This result is interpreted as an indication of an organic source of the carbon. Because bulk rock analyses of saidenbachites are very similar to those of clastic sediments (Table 13), organic material could have been already part of a sedimentary protolith. After sedimentation in Devonian times, according to the age of rare zircon cores with magmatic zonation features (Massonne et al., 2001), these rocks were deeply buried. Stop 3.1E: Already at the western end of the saidenbachite lens of stop 3.1D (see map of Fig. 29) but more obvious somewhat further to the southwest, blocks Figure 39 - Photomicrograph of a garnet (Gt) with of quartzofeldspathic rocks appear containing cm- inclusions of phengite (Phe) and omphacite (Cpx) from eclogite sample E42-1d seen under crossed polarisers. sized plagioclase crystals. The feldspar blastesis Outside garnet, muscovite (Ms) occurs. Concentration is interpreted as the result of an interaction of the map of Mg with scale for the grey tones (increasing country rocks at deep crustal levels with an alkali- element concentrations towards the top) is on the right rich fl uid phase. The source of this phase could be hand side. Scale bar represents 100 µm. the saidenbachites where it formed after the main crystallisation of the saidenbachitic magma. altered to symplectites but omphacite relics as well as phengite were found to be enclosed in garnet (Fig. 39). Stop 3.1F: Continuing along the strand for a few hundred metres Phengite geothermobarometry yielded P-T data above further to the south we meet with outcropping eclogitic 30 kbar and 1000°C for the early metamorphic stage rocks that are virtually identical to that of stop 3.1C. of the eclogite. In fact, no microdiamonds were found Again the omphacite of the rock matrix was completely in the rock but UHP conditions or even a magmatic evolution similar to the saidenbachite cannot be excluded for this basic rock type. Volume n° 2 - from B16 to B33 n° 2 - from Volume

Table 14 - EMP analyses (in wt.%) of inclusion minerals Figure 40 - REE patterns of eclogites from the eastern in garnet from eclogite E42-1d as well as phengite from portion of the Saidenbach reservoir, GEU of the Saxonian pegmatoid E42-1e (2 analyses on the right hand side). Erzgebirge. The data were obtained by ICP-MS analyses Both samples were taken from stop 3.1F. and subsequently normalised to chondrite.

25 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne kbar forthephengitecoreand 15 kbarfortherim Phengite geobarometryyieldedpressuresbetween18 The compositionofthephengiteisgiven in Table 14. in theeclogite,asquartzandfeldspars,byblastesis. contains cm-sizedphengiteswhichhave alsoformed schlieren intheeclogitebodyratherthanavein. It An interestingrockatthissiteisapegmatoid forming contents arerelatively high(see Table 15). protoliths (marls)arelikely, althoughSc, V, Cr, andNi environments cannotbeexcluded but sedimentary to magmaticrocks,forinstance,fromoceanicisland reservoir (Fig.40).Protolithsoftheseeclogitesrelated investigated samplesfromtheeasternportionof typical featureistheclearnegative Eu-anomalyinall parameters are:(Nb) Similar totheeclogitesfromnorthernshore,critical The rocksarebasaltictoandesiticincomposition. 15) werestudiedbyMassonneandCzambor(2003). the easternportionofSaidenbachreservoir (Table The geochemicalcharacteristicsoftheeclogitesfrom Saxonian Erzgebirge. the easternshoreofSaidenbach reservoir, GEUofthe Table 15-XRFand ICP-MSanalysesofeclogitesfrom (La/Sm) N =1.2-2,and(Sm/Yb) N * =XRF dataasanexception. >20,(Sr) N >10, Ta/Yb >0.14, N >1.4. A further southeast toanotherexposure ofeclogiticrocks(Fig.41). From theeclogiteoutcropwewalk about400mto the composition at700-750°C. Stop 3.1G: been broughttothisplace. We practicallycrossthe castle ofForchheim, provided thatavehicle has about 1.5kmthetouristparkingareaatlittle Lippersdorf orfurthertotheeastreachafter starting pointattheroadbetweenEppendorfand From hereononecouldwalk eitherbacktothe biotite ingarnet-richlayers(Fig.42). kyanite, but phengiteitselfcanbestronglyalteredby relics ofkyanite. Infact, phengiteshave replaced into garnet-richquartzofeldspathicrockscontaining bands inlessbasicrocksoccasionallyeven grading At thissitehowever, theeclogitesoccur insteadas Figure 41-Exposureofstop3.1Gatlow water level ofthe width is650µm.B)Phengiticmuscovite (Ms)marginally sample E42/1bundercrossedpolarisers. A) Kyanite (Ky) replaced bybiotite.Gt=garnet.Imagewidthis850µm. relic marginallyreplacedbypotassicwhitemica.Image Figure 42-Photomicrographsofobjectsinmetapelitic Saidenbach reservoir. ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

federal road B101, heading uphill for Wernsdorf and then downhill to the Flöha valley. We cross the valley to move to Sorgau and then further to Zöblitz. Shortly after passing the town limit we must turn left to reach the entrance to the big serpentinite quarry after about 500 m. Here are parking lots on the right-hand side. The quarry is on the left-hand side (Fig. 43).

Figure 43 - Simplifi ed geological map of the serpentinite body at the town of Zöblitz, GEU of the Saxonian Erzgebirge. Volume n° 2 - from B16 to B33 n° 2 - from Volume

Table 16 - EMP analyses (in wt.%) of minerals from serpentinised garnet lherzolite, Erz03-6d, and garnet-rich clinopyroxenite (eclogite), 18270, of the serpentinite body at the town of Zöblitz, Saxonian Erzgebirge.

27 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne Scale barsrepresent500µm. increasing elementconcentrationstowards thetop. in sample18270.Thescalefor thegreytonesshows marginally recrystallisedtogarnet+clinopyroxene, Figure 45-ConcentrationmapsofCaandMgingarnet, polarisers (right).Imagewidthis4mm. polarised light(lefthandside)andseenundercrossed clinopyroxenite (eclogite)sample18270underplain Figure 44-Photomicrographofgarnetsin according toequilibrium(7):pyrope (ingt)=3 results usingthe Al-content inorthopyroxene (opx) and Bautsch(2002). Virtually identicalpressure 1000°C applyingthemethodreportedbyMassonne (Table 16)at P-Tconditionsofabout26kbarand of thematrixminerals(cores)andgarnet rim It started,accordingtothechemicalcomposition because ofdeformationduringtheexhumation event. fabric isinterpretedastheresultofrecrystallisation cores arechemicallyhomogeneous. The observed amphibole. Inaddition,thelarge extended garnet olivine, clinopyroxene, orthopyroxene, andminor 1.2), thematrixconsistsofmm-sizedequigranular crystals. As intheultrabasicrockatRubinberg (stop found. Insuchrocksgarnetcanformuptocm-sized portions oftheoriginalgarnetlherzolitecanbe pseudomorphs aftergarnet.Occasionally, preserved In addition,aggregates ofchloriteoccurwhichare antigorite arepresentasminorserpentinephases. consists mainlyoflizarditebut clinochrysotileand active quarryistoproducemacadam. The serpentinite and palaces.Nowadays, themainpurposeofstill a rockforfacing, forinstance,theinteriorofchurches In pastcenturiesserpentinitewas quarriedatZöblitzas Stop 3.2: MgSiO that uptocm-sizedgarnetshave beenmarginally accessory phase.Somepyroxenites even show clinopyroxene andgarnet.Rutileisacommon occur. These, whenfresh,mayconsistmainlyof Within the peridotitebody, layersofpyroxenite garnet peridotiteatZöblitz. at temperaturessomewhat below 1000°Cforthe Evans (1997)estimatedhigherpressureupto33kbar Table 17-XRFand ICP-MSanalysesofultrabasic 3 (inopx)+ Al rocks fromtheserpentinitebodyatZöblitz, GEU oftheSaxonianErzgebirge. 2 O 3 (inopx).Schmädicke and ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

transformed to smaller garnet crystals and equigranular clinopyroxene (Fig. 44). The remaining palaeocrysts are chemically zoned as shown in Fig. 45. Again, P-T conditions were determined on the basis of mineral analyses given in Table 16. For the rim composition, 16.6 kbar and 865°C were obtained. Core compositions gave much higher pressure of almost 39 kbar at 1100°C. Another possible indicator for such high or even higher pressure are abundant tiny, perfectly oriented ilmenite rods in some olivine cores of the preserved garnet lherzolite. Although no quantifi cation in regard to the Earth’s depth is possible yet, a similar exsolution feature, e.g. reported by Green et al. (1997) from the peridotite massif of Figure 47 - Photomicrographs of porphyroblasts of Alpe Arami, was taken as a hint at UHP conditions. amphibole (Amph), clinozoisite (Czs), and phengite (Phe) Summarizing the petrological information on the in eclogite 18333 (stop 4.1) under crossed polarisers. ultrabasic body at Zöblitz, it can be concluded that Image width is 900 µm each. the exhumation history is virtually the same as for the ultrabasic rocks from the nearby Granulitgebirge. Here it is possible to talk to the owner of the eclogite Geochemical analyses of garnet pyroxenites from quarry. This quarry, however, can be reached by Zöblitz (Table 17) show that these rocks can vary taking the next dirt road to the left. This road ends at signifi cantly in composition. The garnet lherzolite the eclogite quarry after about 1.3 km (Fig. 46). (Table 17) is somewhat depleted in light REE. Stop 4.1 From the serpentinite quarry we go to the centre of the town of Zöblitz to meet with federal road B171 heading At this stop we can visit what is left of a lens of to Marienberg and then on to Wolkenstein. After passing homogeneous eclogite about 500 m long. In spite of the this town we reach federal road B101. From here it is as destruction of a formerly romantic site in the wood, as the far as 9 km to the town of Annaberg-Buchholz. Stümpelfelsen cliffs were considered, the relationships to the gneissic country rocks are well exposed now. DAY 4 In fact, the eclogites at the Stümpelfelsen can be distinguished by lighter and darker varieties, but they The excursion continues from Annaberg-Buchholz are all massive and not as foliated as other eclogites via federal road B95 to the south reaching in the vicinity. Another common aspect is produced Hammerunterwiesenthal after 17 km. In the centre of by mm long, non-oriented amphibole crystals in a this village we turn right heading uphill to Neudorf. relatively fi ne-grained matrix consisting mainly of Close to the Hammerunterwiesenthal exit a dirt road fresh omphacite and garnet (Fig. 47). A few larger on the left leads to “Steinbruchbetriebe Richter”. single white mica fl akes are also discernible with the naked eye in the common eclogite. In addition, several mm-sized amphiboles and oriented white mica fl akes can be strongly enriched on mm thick planes often between eclogite and quartz segregations crosscutting the eclogite body. Also crosscutting are cracks, occasionally running parallel with dm spacings, along which late retrograde minerals, such as chlorite Volume n° 2 - from B16 to B33 n° 2 - from Volume and actinolite, have formed. These caused a darker colouring in the mm range around the cracks. In the light coloured variety the eclogitic mineral assemblage is characterised by garnet, omphacite, phengite, talc, amphibole, clinozoisite, quartz, rutile, and accessory phases. At a late stage (III) Figure 46 - Simplifi ed geological map of an area in the of metamorphism porphyroblasts of amphibole, MEU of the Saxonian Erzgebirge close to the village clinozoisite, and phengite formed. Paragonite of Hammerunterwiesenthal. joined the assemblage even during a later stage

29 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne village ofHammerunterwiesenthal. 18333 fromtheStümpelfelsen cliff closetothe grains ofthematrixandasporphyroblastsineclogite Figure 48-Compositionalvariationofphengiteassmall eclogite startsatabout480°Cand25kbar(stage talc strongly. The constrainedP-Tpathforthe methods wereappliedconsideringphengiteand On thebasisofthis,various geothermobarometric exemplary shown byFigs.48to50and Table 18. (IIIb). The chemicalzonationofthemineralsare MEU oftheSaxonianErzgebirge. Thedatawere taken fromMassonneandKopp (submitted). Table 18-EMPanalyses (inwt.%)ofmineralsfromeclogite18333sampledattheStümpelfelsen cliff (stop4.1), At thepeakP-Tconditionsof720°Cand27kbar increase (stageII)atslightlyincreasingpressures. Ib inFig.51)followed byasignifi for thegreytonesshows increasingelementcon centrations Outside theporphyroblastisomphacite(Omph).Thescale 47. Several grainsenclosedinamphibolearegarnet(Gt). sample 18333withanamphiboleandclinozoisite(Czs) porphyroblast alsoshown onthe lefthandsideofFig. Figure 49-ConcentrationmapofCafor asectionof towards thetop.Scalebarrepresents250µm. cant temperature cant ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

Figure 50 - Concentration map of Mg for a matrix section of eclogite sample 18333 from the Stümpelfelsen cliff close to the village of Hammerunterwiesenthal. Gt = garnet, Omph = omphacite, Phe = phengite, Tc = talc. The scale for the grey tones shows increasing element concentrations towards the top. Scale bar represents 100 µm.

Figure 51 - P-T paths derived for low-temperature eclogites from the MEU of the Saxonian Erzgebirge. Bold: eclogite from stop 4.1. Roman numbers refer to metamorphic stages. Medium line: eclogite taken a few kilometres north of the town of Marienberg (Massonne, 1992). Dashed: eclogites of the MEU, in general, according to Schmädicke et al. (1992). Volume n° 2 - from B16 to B33 n° 2 - from Volume

Table 19 - XRF and ICP-MS analyses of eclogites from the MEU of the Saxonian Erzgebirge. 1 (E96-15b) and Figure 52 - REE patterns of eclogites from the western 2 (E96-15d) = stop 4.1, 3 (E22a) and 4 (E22c) = stop 4.3 Erzgebirge´s crystalline massif. However, samples Analyses 5 and 6 represent small volumes of rocks, either Erz02-8 and E7c were taken a few kilometres north and with pegmatoid or granitoid character, directly in contact east, respectively, of the town of Marienberg. The data to eclogites. 5 (Erz03-4) = stop 4.3, 6 (E42-1e) = stop 3.1F. were obtained by ICP-MS analyses and subsequently *=XRF data as an exception. normalised to chondrite.

31 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne similar tothoseofthenearbyeclogites. Itisalsoobvious portion ofthequarry. Suchmarblesformelongatedbodies marble withsomesiliceouslayers(Fig.53)inthenorthern of theErzgebirge. Another reasontovisitthisquarryisa number ofsuchstockspenetratingthecrystallinemassif in theEger-graben tothesouth,but therearequitea the Tertiary. Infact, thistypeofvolcanism concentrated many alkali-dominatedsubvolcanics whicheruptedin In thisquarrywecanseeagoodexample foroneofthe Stop 4.2:(optional) quarry ontheleft-handside(seeFig.46). 1 kmattheentrancetoalarger, apparentlyabandoned On theway backtothemainroad,westopafterabout rocks hastobecalledintoquestion. major event responsiblefortheexhumation ofthese rocks fromthewesternandcentralErzgebirge, asingle time difference betweenmetamorphismof(U)HP western Erzgebirge. Ifthereisreallyaconsiderable ages asold355Mafortheeclogitesfrom Erzgebirge. Schmädicke etal.(1995)alsodetermined metamorphosed atthesametimeasthoseofcentral temperature eclogitesofthewesternErzgebirge were orogen. Unfortunately, itisnotclearyet,ifthelow- pressure rocksfromtherootzoneofacollisional this byamodelinvolving rapidexhumation ofhigh- eclogites. Willner etal.(2000,2002)triedtoexplain T datadiffer signifi cantly fromthosederived forthe 560°C forthesubsequenttemperaturepeak. These P- 525°C forthepressureclimaxaswell8kbarand authors estimatedP-Tconditionsof12kbarand chloritoid, was studiedbyRötzleretal.(1998). These diameter. The latterrocktype,whichcanalsocontain schists occasionallywithlarge garnetsseveral mmin gneisses, probablyformergreywackes, andmica are outcroppingaswell. These arequartz-rich In thequarryofstop4.1typicalcountryrocks instance, bytheREEpatternsoftheserocks(Fig.52). could beassignedtoformerMORBsdemonstrated,for the Stümpelfelsencliff (Table 19). These eclogites (2003). Among theanalysedsampleswerethosefrom MEU was investigated byMassonneandCzambor The geochemicalcharacteristicsofeclogitesfromthe zonation onthemicrometerscale. of theeclogiteincludingpreservation ofchemical unusual lateP-Thistorymightexplain thefreshness 520°C and18kbaratreducedwater activities. This Stage IIIbischaracterisedbyP-Tconditionsaround signifi buoyancy forcesupliftingtheeclogite.Subsequently, fl porphyroblasts began togrow byinvading hydrous uids. Possiblytheresultingdensityreductioncaused cant coolingoccurredatstillhighpressures. extend forafew hundredmetresinanorthwestdirection. Already aftersometensofmetrescliffs occurwhich west byabout600m. Then weturnrightintotheforest. is closedtothepublic,wehave towalk furthertothe to parkourvehicle(s) ontheleft-handside. As theroad house “Siebensäure”. After 1.8km,wepassthisbuilding railroad track,weturnleftheadingfortheforester´s the villageofNeudorfafter4km.Justcrossing After goingbacktothemainroadweturnleftreach pressure conditions. with carbonatesinparticulardoesnotallow toquantify assemblage amphibole,clinopyroxene, andphlogopite metamorphism ofthemarblewere. The commonmineral exist. ItisalsonotclearwhattheP-Tconditionsof over awidearea,but arealcontactbetweenbothdoesnot that bothrocktypesmarblesandeclogitesareassociated Figure 54-Simplified geologicalmapofanareainthe marble fromstop4.2seenundercrossedpolarisers. Figure 53-Photomicrographofasiliceouslayerin MEU oftheSaxonianErzgebirge afew kilometres The silicatesareamphiboleandphlogopite. west ofthevillageNeudorf. Image widthis4mm ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

Figure 55 - Photomicrograph of a large garnet, seen under crossed polarisers, in a foliated matrix of sample E22h from stop 4.3. The matrix consists mainly of amphibole and clinozoisite. Image width is 4 mm. At the end, another paved forest road appears. Stop 4.3: Figure 56 - Photomicrograph of a preserved portion The cliffs in the forest consist of eclogites which form of palaeocrysts in eclogite E22h seen under crossed either a larger strongly elongated lens or, as shown polarisers. The superposed inlet is a concentration map on the map of Fig. 54, a number of smaller lenses. showing rising Fe contents by increasingly In fact, the eclogite of stop 4.3 is geochemically lighter grey tones. Image width is 2.7 mm. identical to that of stop 4.1 (see Table 19), but here it is, as typical for the western Erzgebirge, clearly foliated. Occasionally, we can fi nd in the cliffs of stop 4.3 a preserved fabric in the cm range, formed before deformation. In these preserved portions, mm-sized garnet and omphacite occur (Figs. 55 and 56). These minerals are strongly chemically zoned. From the core compositions of these minerals and a relatively coarse-grained phengite (see Table 20) about 24 kbar and 500°C were calculated for an early metamorphic stage. Rim compositions yielded 26 kbar and 650°C. The resulting P-T path resembles that obtained for eclogites from stop 4.1. Formation of amphibole and clinozoisite, from which the fi ne- grained foliated matrix mainly consists of, as well as deformation happened at the P-T climax and/or during the beginning of exhumation. An interesting feature in the outcrop are granite-like segregations at the contact between eclogite and country rock. The composition of this granitoid is characterised by high Na2O (> 10 wt.%, see Table Volume n° 2 - from B16 to B33 n° 2 - from Volume 19) and, thus, high plagioclase contents. The same is true for similar segregations in the serpentinite body at Zöblitz and to some extent for the pegmatoid schlieren in eclogite of stop 3.1F (Table 19). However, no genesis model can be currently presented. After going back to Neudorf, we take the road to the left and turn after a few hundred metres slightly Table 20 - EMP analyses (in wt.%) of minerals in to the left heading for Crottendorf and the village eclogite E22h taken from stop 4.3. of Scheibenberg which we reach after 8 km. We

33 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne Planetary ScienceLetters212,1-14. tracing continentalcrustintothemantle.Earthand Chopin, C.(2003).Ultrahighpressuremeta morphism: and Petrology86,107-118. and someconsequences.Contributions toMineralogy grade blueschistsofthe Western Alps: afi Chopin, C.(1984).Coesiteandpurepyrope inhigh Springer Verlag, Berlin,295-308. (Dallmeyer, R.D.,Franke, W. and Weber, K.,Eds.), “Pre-Permian geologyofcentralandeasternEurope” metamorphic nappes2.Metamorphicevolution. In Blümel, P. (1995). V. SaxothuringianBasinC.Exotic References and preparationofsomefi microprobe work, calculationsofstructuralformulae, Theye and Andreas Brandeliksupportedourelectron (project No.Ma1160/2andMa1160/19). Thomas was foundedbyDeutscheForschungsgemeinschaft contributed toasignifi cant portionofthisguide, Research intheSaxonianErzgebirge, which Acknowledgements reached afterabout70km. for highway A4 headingforDresden. This cityis At thenorthwesternedgeofthiscityisjunction there isaccesstohighway A72 headingforChemnitz. the centreoftown. About 2kmnorthofStollberg After reachingStollberg weturnnorthbeforeentering although relatively far away. times aswell. The columnsarestilldiscernible the Erzgebirge’s crystallinemassifduring Tertiary great vertical columnsofnephelinitewhichintruded Scheibenberg. This naturalmonumentconsistsof the so-called“Orgelpfeifen” (Fig.57)whenleaving further toStollberg. Donotforget tohave alookat and, atitsexit, turnleftheadingforZwönitz and turn rightintofederalroadB101,passthevillage, Figure 57-ColumnsofnepheliniteatScheibenberg hill. gures. rst record rst F. (2000).Nanometer-size Hwang, S.-L.,Shen,P., Chu,H.-T. and Yui, T.- Iapetus Ocean.Geology30,255-258. down: A new platetectonicmodelforRodiniaandthe Hartz, E.H.and Torsvik, T.H. (2002).Balticaupside 279, 1-21. from theMantle Transition Zone? Tectonophysics Jin, Z.-M.(1997). Alpe Arami: a peridotitemassif Green, H.W. II,Dobrzhinetskaya,L.,Riggs,E.M.and Special Publication179,337-354. and Tanner, D.,Eds.),GeologicalSocietyofLondon, Variscan Belt”(Franke, W., Haak, V., Oncken, O. Processes: Quantifi constraints andgeodynamicconcepts.In“Orogenic grade rocksintheSaxo-ThuringianBelt:geological Franke, W. andStein,E.(2000).Exhumationofhigh- Soc. geol.France1986II,25-33. sedimentation inthe Variscan beltofEurope.Bulletin Franke, W. andEngel, W. (1986):Synorogenic Special Publication179,35-61. and Tanner, D.,Eds.),GeologicalSocietyofLondon, Variscan Belt”(Franke, W., Haak, V., Oncken, O. Processes: Quantifi boundaries andplatetectonicevolution. In“Orogenic the Variscides: tectonostratigraphicunits,terrane Franke, W. (2000). The mid-Europeansegment of Nostra, 5/2001,24-26. adjacent rocksfromtheErzgebirge, Germany. Terra signatures ofdiamondiferousgneissesandtheir Düffels, K.andMassonne, H.-J.(2001).Geochemical Geology 20,481-492. Evidence ofdeepsubduction.Journalmetamorphic omphacite fromeclogiteat Alpe Arami, Switzerland: H.-J. andGreen,H.W. II(2002).Silicaprecipitatesin Dobrzhinetskaya, L.F., Schweinehage,R.,Massonne, 2, 1523-1526. International Symposium,Park City, Utah,U.S.A., Y.K. andMaest, A., Eds.),Proceedingsofthe7th rocks. In“Water-rock interaction WRI-7” (Kharaka, determination ofwater activities relevant toeclogitic Massonne, H.-J.(1992). Thermochemical 1388. weak continentallithosphere. Tectonics 15,1364- Europe: Postaccretionaryintraplatedeformationof Krohe, A. (1996). Variscan tectonicsofcentral Petrology 132,1-20. Saxony, Germany. Contributions toMineralogyand quartz-feldspar rocksinthecentralErzgebirge, and peakof Variscan HP-HTmetamorphismof Kröner, A. and Willner, A.P. (1998). Time offormation Kristallographie, Supplement,4,134. Entmischungen inPyroxenen. Zeitschriftfür Jekosch, U.andBautsch,H.-J.(1991).Orientierte metamorphism. Science288,321-324. garnet: athermobarometerforultrahigh-pressure cation andModellinginthe cation andModellinginthe |-PbO 2 -type TiO 2 in ULTRAHIGH AND HIGH PRESSURE ROCKS OF SAXONY B21

Massonne, H.-J. (1994). P-T evolution of eclogite Volume, 216. lenses in the crystalline complex of the Erzgebirge, Massonne, H.-J. and Bautsch, H.-J. (2003). P-T Middle Europe: An example for high-pressure evolution of a spinel-garnet-bearing clinopyroxenite to ultrahigh-pressure metabasites incorporated from the Granulitgebirge. Berichte der deutschen into continental crust. First Workshop on UHP mineralogischen Gesellschaft, Beihefte zum European metamorphism and tectonics, Stanford University, Journal of Mineralogy 15, No. 1, 127. Abstract Volume, A29-A32. Massonne, H.-J., Burchard, M., Frost, D. and Theye,

Massonne, H.-J. (1999). A new occurrence of T. (2003). Thermodynamic properties of TiO2 with microdiamonds in quartzofeldspathic rocks of |-PbO2 structure based on HP experiments. Berichte the Saxonian Erzgebirge, Germany, and their der deutschen mineralogischen Gesellschaft, Beihefte metamorphic evolution. Proceedings of the 7th zum European Journal of Mineralogy 15, No. 1, 128. International Kimberlite Conference, Cape Town Massonne, H.-J. and Czambor, A. (2003). Protoliths 1998, P.H. Nixon Volume, 533-539. of eclogites from the Variscan Erzgebirge. Norges Massonne, H.-J. (2001). First fi nd of coesite in geologiske undersøkelse Report 2003.055, Eclogite the ultrahigh-pressure metamorphic region of the Field Symposium, Abstracts, 93-94. Central Erzgebirge, Germany. European Journal of Massonne, H.-J. and Nasdala, L. (2003). Mineralogy 13, 565-570. Characterization of an early metamorphic stage Massonne, H.-J. (2003). A comparison of the through inclusions in zircon of a diamondiferous evolution of diamondiferous quartz-rich rocks from quartzofeldspathic rock from the Erzgebirge, the Saxonian Erzgebirge and the Kokchetav Massif: Germany. American Mineralogist 88, 883-889. are so-called diamondiferous gneisses magmatic Massonne, H.-J. and O’Brien, P.J. (2003). The rocks? Earth and Planetary Science Letters 216, 347- Bohemian Massif and the NW Himalaya. In 364. “Ultrahigh Pressure Metamorphism” (Carswell, Massonne, H.-J. (in press). Paläozoische Hochdruck- D.A. and Compagnoni, R., Eds.), EMU Notes in und Ultrahochdruck-Metamorphite in Mitteleuropa Mineralogy 5, 145-187. und ihre Beziehungen zur variszischen Orogenese. Massonne, H.-J. and Tu, W. (2003). Ä13C-Signature Zeitschrift für geologische Wissenschaften. of microdiamonds from the Saxonian Erzgebirge, Massonne, H.-J. and Burchard, M. (2000). Exotic Germany. Norges geologiske undersøkelse Report minerals in eclogites from the Central Erzgebirge – 2003.055, Eclogite Field Symposium, Abstracts, evidence for fl uid-rock interaction at UH metamorphic 91-92. pressures: Berichte der deutschen mineralogischen Massonne, H.-J. and Kopp, J. (submitted). A low- Gesellschaft, Beihefte zum European Journal of variance mineral assemblage with talc and phengite Mineralogy 12, No. 1, 122. in an eclogite from the Saxonian Erzgebirge, Middle Massonne, H.-J., Dobrzhinetskaya, L. and Green, Europe, and its P-T evolution. Journal of Petrology. H.W. II, (2000). Quartz - K-feldspar intergrowths Matte, P. (1986): Tectonics and plate tectonics model enclosed in eclogitic garnet and omphacite. Are they for the Variscan belt of Europe. Tectonophysics 126, pseudomorphs after coesite? Extended Abstract, 31st 329-374. International Geological Congress, Rio de Janeiro, Matte, P. (1998). Continental subduction and Brazil: 4 pp. (on CD, search for Massone). exhumation of HP rocks in Paleozoic orogenic belts: Massonne, H.-J., Nasdala, L. and Kennedy, A. (2001). Uralides and Variscides. Geologiska Föreningens U-Th-Pb dating of zircons and monazites from Stockholm Förhandlingar 120, 209-222. diamondiferous gneisses of the Saxonian Erzgebirge McKerrow, W.S., Mac Niocaill, C., Ahlberg, P.E., – implications for their UHP/HP evolution. 6th Clayton, G., Cleal, C.J. and Eagar, R.M.C. (2000). International Eclogite Conference, Niihama, Japan, The Late Palaeozoic relations between Gondwana and Abstract Volume, 88. Laurussia. In „Orogenic Processes: Quantifi cation and

Massonne, H.-J. and Bautsch, H.-J. (2002). An Modelling in the Variscan Belt“ (Franke, W., Haak, V., B16 to B33 n° 2 - from Volume unusual garnet pyroxenite from the Granulitgebirge, Oncken, O. and Tanner, D., Eds.), Geological Society Germany: origin in the transition zone (>400 km of London, Special Publication 179, 9-20. Earth’s depths) or in a shallower upper mantle region? Murphy, J.B., Keppie, J.D., Dostal, J. and Nance, R.D. International Geology Reviews 44, 779-796. (1999). Neoproterozoic - early Paleozoic evolution Massonne, H.-J., Bautsch, H.-J., Kopp, J. and Theye, of Avalonia. In “Laurentia-Gondwana connections T. (2002). Enigmatic origin of syenite boudins in before Pangea” (Ramos, V.A. and Keppie, J.D., Eds.), a serpentinite from the Variscan Granulitgebirge, Geological Society of America, Special Papers 336, Germany. 18th General Meeting of the International 253-266. Mineralogical Association, Edinburgh 2002, Abstract Nasdala, L. and Massonne, H.-J. (2000).

35 - B21 Volume n° 2 - from B16 to B33 B21 - B21 Leader: H.-J.Massonne under contrastingP-T-conditions. Contributions to Erzgebirge, Germany: highpressuremetamorphism (1992). Eclogite-facies rocksinthesaxonian Schmädicke, E.,Okrusch,M.andSchmidt, W. Journal ofMineralogy10,261-280. Western Erzgebirge (Saxony, Germany). European evolution injuxtaposedhigh-pressureunitsofthe geodynamic implicationsofcontrastingmetamorphic and Willner, A.P. (1998).Characterizationand Rötzler, K.,Schumacher, R.,Maresch, W.V. of Petrology42,1995-2013. Granulite Massif,Germany. Part I:Petrology. Journal of ultrahigh-temperaturegranulitesfromtheSaxon Rötzler, J.andRomer, R.L.(2001).P-T-t evolution Journal ofPetrology42,2015-2032. Granulite Massif,Germany. Part II:Geochronology. of ultrahigh-temperaturegranulitesfromtheSaxon Romer, R.L.andRötzler, J.(2001).P-T-t evolution London Memoirs12,411-419. W.S. paleogeography andbiogeography”(McKerrow, during EarlyPalaeozoic times.In“Paleozoic Palaeogeographic evolution ofsouthwesternEurope Robardet, M.,Paris, F. andRacheboeuf,P.R. (1990). 238, 71-94. Saxonian GranuliteMassif,Germany. Tectonophysics pressure, high-temperaturemetamorphisminthe unroofi Reinhardt, J.andKleemann,U.(1994).Extensional 12, 29-33. ortho pyroxene. PhysicsandChemistryofMinerals microscopical studyofgarnetexsolution in Reiche, M.andBautsch,H.-J.(1985).Electron Gesteinen. Freiberger Forschungshefte C393,19-33. mischungsstrukturen inPyroxenen auseklogitischen Reiche, M.andBautsch,H.-J.(1984).Ent- of theGeologicalSocietyLondon150,355-369. suture zonebetweenBalticaandGondwana. Journal Pb agesfromSWPoland:evidence foraCaledonian Oliver, G.J.H.,Corfu,F. andKrogh, T.E. (1993).U- Publication 179,369-386. D., Eds.),GeologicalSocietyofLondon,Special (Franke, W., Haak, V., Oncken, O.and Tanner, Quantifi at different temperatures. In“OrogenicProcesses: different depthsand high-pressuremetamorphism problem: high-temperaturemetamorphismat O’Brien, P.J. (2000). The fundamental Variscan European JournalofMineralogy12,495-498. Germany: insitumicro-Ramancharacterisation. Microdiamonds fromtheSaxonianErzgebirge, and Scotese,C.R.,Eds.),GeologicalSocietyof ng ofgranuliticlower crustandrelatedlow- cation andModellinginthe Variscan Belt” dome (Saxony, Germany): Constraintsontherapid Interrelated P-T-t-d pathsinthe Variscan Erzgebirge Willner, A.P., Krohe, A. andMaresch W.V. (2000). 38, 307-336. Erzgebirge (Saxony, Germany). JournalofPetrology pressure, granulite-facies history fromtheCentral feldspathic metamorphicrockswitharelichigh- Pressure-temperature andfl uid evolution ofquartzo- Willner, A.P., Rötzler, K.andMaresch, W.V. (1997). Society ofLondon,SpecialPublication179,21-34. V., Oncken, O.and Tanner, D.,Eds.),Geological Modelling inthe Variscan Belt”(Franke, W., Haak, terranes. In“OrogenicProcesses:Quantifi palaeogeography ofGondwana andEuropean H. (2000).Palaeomagnetism andPalaeozoic Tait, J.,Schätz,M.,Bachtadse, V. andSoffel, Research 99,2897-2907. data fromCentralBohemia.JournalofGeophysical paleogeography of Armorica: new paleomagnetic Tait, J.,Bachtadse, V. andSoffel, H.C.(1994).Silurian 29, 391-394. included ingarnet,Erzgebirge, Germany. Geology precipitated fromsupercriticalCOHsilicatefl H.-J. (2001):Microdiamonddaughtercrystals Stöckhert, B.,Duyster, J., Trepmann, C.&Massonne, 364, 263-280. Eds.), GeologicalSocietyof America, SpecialPapers J.R., Hatcher, R.D.Jr., Arenas, R.andDíazGarcía,F., the LatePaleozoic Basement”(MartínezCatalán, “Variscan-Appalachian Dynamics: The Buildingof From Gondwana tothe Variscan collision.In (2002). Paleozoic evolution ofpre-Variscan terranes: Stampfl Eclogae Geol.Helvetiae 89,12-42. palaeotethyan remnantinthe Stampfl Geologische Rundschau80,73-92. of theBohemianMassif:akinematicinterpretation. (1991). Evolution ofnappesintheeasternmargin Lardeaux, J.M.,Urban,M.andLobkowicz, M. Schulmann, K.,Ledru,P., Autran, A., Melka, R., 127, 57-74. Massif. Contributions toMineralogyandPetrology their relationtoothersettingsintheBohemian bearing ultramafi c rocksfromtheErzgebirge, and Schmädicke, E.andEvans, B.W. (1997).Garnet- Journal ofMetamorphicGeology13,537-552. facies rocksfromtheErzgebirge, BohemianMassif. (1995). Variscan Sm-Ndand Ar-Ar agesofeclogite Schmädicke, E.,Cosca,M.A.andOkrusch,M. Mineralogy andPetrology110,226-241. i, G.M.,von Raumer, J.andBorel,G.D. i, G.(1996). The intra-Alpineterrain: a Alpine Variscides. cation and cation uids Back Cover: fi eld trip itinerary FIELD TRIP MAP INTERNATIONAL GEOLOGICAL CONGRESS nd 32

Edited by APAT August 20-28,2004 Florence -Italy

Field Trip Guide Book - B22 GEOLOGICAL CONGRESS 32 Volume n°2-fromB16toB33 Associate Leaders:J.M.Lardeaux,P. Matte Leader: M.Faure BÉZIERS TOLYON A CROSSSECTIONFROM FRENCH MASSIFCENTRAL PALEOZOIC OROGENIESINTHE Pre-Congress nd INTERNATIONAL B22 The scientific content of this guide is under the total responsibility of the Authors

Published by: APAT – Italian Agency for the Environmental Protection and Technical Services - Via Vitaliano Brancati, 48 - 00144 Roma - Italy

Series Editors: Luca Guerrieri, Irene Rischia and Leonello Serva (APAT, Roma)

English Desk-copy Editors: Paul Mazza (Università di Firenze), Jessica Ann Thonn (Università di Firenze), Nathalie Marléne Adams (Università di Firenze), Miriam Friedman (Università di Firenze), Kate Eadie (Freelance indipendent professional)

Field Trip Committee: Leonello Serva (APAT, Roma), Alessandro Michetti (Università dell’Insubria, Como), Giulio Pavia (Università di Torino), Raffaele Pignone (Servizio Geologico Regione Emilia-Romagna, Bologna) and Riccardo Polino (CNR, Torino)

Acknowledgments: The 32nd IGC Organizing Committee is grateful to Roberto Pompili and Elisa Brustia (APAT, Roma) for their collaboration in editing.

Graphic project: Full snc - Firenze

Layout and press: Lito Terrazzi srl - Firenze Volume n° 2 - from B16 to B33

32nd INTERNATIONAL GEOLOGICAL CONGRESS

PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON

AUTHORS: M. Faure (University of Orléans - France) P. Ledru (BRGM, Orléans - France) J.M. Lardeaux (University of Nice - France) P. Matte (CNRS, University of Montpellier - France)

Florence - Italy August 20-28, 2004

Pre-Congress B22 Front Cover: View of gneiss-migmatite of the Montagne Noire axial zone (visited during D2) looking to the north. The village of Olargues is located in the micaschist envelope of the dome. The picture is taken from the northernmost part of the recumbent folds of the Montagne Noire southern side (visited during D1). PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

Leader: M. Faure Associate Leaders: J.M. Lardeaux, P. Ledru, P. Matte 1. Introduction The formation of the continental substratum of The French Massif Central is one of the largest Medio-Europa occurred in Paleozoic times. The pieces of the Variscan Belt. The whole Massif Central names of “Hercynian” or “Variscan” are used to deal provides a reference cross section throughout the north with the geodynamic processes that took place from Gondwana margin deformed and metamorphozed Cambrian to Carboniferous. It is now widely accepted during the Paleozoic. During the last two decades, that this Paleozoic Belt that crops out from Iberia to and recently through the GéoFrance 3D program, Bohemia (Fig. 1) results from a complex interplay of developments made in the areas of geochronology, rifting, convergence and collision between three large structural geology, metamorphic and magmatic continents, namely Laurentia, Baltica and Gondwana petrology, allow us to draw a comprehensive and several microcontinental stripes such as Avalonia structural map of the Massif Central and to discuss or Armorica (Matte, 2001). Continental drifting and a possible scenario accounting for the Paleozoic welding resulted in the opening and closure of several tectono-thermal evolution. oceans such as Iapetus, Rheic and Medio-European. This fi eld trip presents representative lithological, There is however a wide range of opinions concerning structural, magmatic, metamorphic and the location and width of these oceanic domains and geochronological data of the French Massif the number, kinematics and timing of collisional Central from unmetamorphozed kilometer-scale processes (e. g. Autran and Cogné, 1980; Franke, recumbent folds to UHP metamorphic rocks. Most 1989, 2000; Ledru et al., 1989; Matte, 1991; 2001; of the controversial aspects of collisional orogens Faure et al., 1997). such as continental subduction and exhumation

Figure 1 - Location of the French Massif Central in the frame of the Paleozoic belt of Medio-Europa (Matte, 1991). Volume n° 2 - from B16 to B33 n° 2 - from Volume

3 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure Tarare. St-Symphorien-sur-Coise; n°697 Yssingeaux; n°745St-Etienne;n°721 n°839 Langogne;n°840Burzet;n°792 n°862 Mende;n°863LeBleymard; n°1014 St-Chinian;n°988Bédarieux; Geologic mapsBRGM1/50000: Etienne-Le Puy;n°51Lyon-Grenoble. Mende; n°59Privas-Alès; n°50St- n°65 Béziers-Montpellier;n°58Rodez- Topographic mapsIGN1/100000: Field References addressed. setting ofplutonemplacementwillbe tectonics, crustalmeltingandtectonic syn- topost-orogenicextensional kinematics, inverted metamorphism, of ultrametamorphicrocks,nappe Neoproterozoic toOrdovician ageis stratigraphic agesarelacking,a beds andvolcanic rocks. Although micaschists”) withsomequartzite series (alsocalled“Cévennes of athickmetapelite-metagrauwacke overthrusts theprevious unitconsists ii) The Para-autochthonous Unitthat area (Arthaud,1970). well observed intheMontagneNoire within kilometer-scale recumbentfolds Carboniferous. The seriesisdeformed spanning fromEarlyCambrianto more orlesscontinuoussedimentation margin/platform seriesrecordinga Thrust Beltinvolves asetofcontinental i) The SouthernPalaeozoic Fold and tectonic unitsaredistinguished. also fromsouthtonorth,sixmain 1994 Fig.3).Fromtoptobottomand is astackofnappes(Ledruetal.,1989, structure oftheFrenchMassifCentral It isnow widelyacceptedthatthe French MassifCentral. 2.1. A structural mapofthe geological setting 2. Regional Lèvezou klippe (Matte,1991). an alternative sectionthroughthe and throughMassifCentral(C).C’ is Massif Armoricain to Ardenne (B) Figure 2-Cross-sectionsfromthe PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

metamorphism is reached locally near Lyon, coesite-eclogite facies rocks crop-out (Lardeaux et al., 2001). The protoliths of the UGU also include metasediments and granitoids. The upper part of the UGU consists of migmatites formed by the partial melting of pelitic and quartzo-feldspathic rocks within which amphibolite block are preserved as restites. Radiometric dates show that the magmatism occurred in Early Ordovician times (ca. 480 Ma) and the high-pressure metamorphism in Late Silurian (ca. 420-410 Ma, Pin and Lancelot, 1982; Ducrot et al., 1983). Due to the occurrence of rare metagabbros and serpentinized ultramafi cs, the UGU is considered by some authors as a remnant of an oceanic domain, the Medio- European Ocean, that opened in Early Paleozoic times during the rifting that led to the separation of Armorica from North Gondwana (e. g. Dubuisson et al., 1989; Matte, 1991). However, it is worth noting that the Upper Gneiss Unit is not a true ophiolitic sequence since oceanic sedimentary rocks Figure 3 - Structural map of the Massif Central such as radiolarites or siliceous (adapted from Ledru et al., 1989). shales are lacking and ultramafi cs or serpentinites are rare. A likely interpretation would be to consider generally accepted. that the UGU is a transitional crust between true iii) The Lower Gneiss Unit (LGU) is lithologically continental and oceanic ones. quite similar to the Para-autochthonous Unit. Early v) The Thiviers-Payzac Unit that crops out in the Cambrian and Early Ordovician alkaline granitoids, south Limousin, is the highest tectonic unit of the now transformed in augen orthogneiss, are also allochthonous stack in the French Massif Central. It is widespread. Both the Para-autochthonous Unit and formed by Cambrian metagraywackes, rhyolites and Lower Gneiss Unit are interpreted as Proterozoic- quartzites intruded by Ordovician granite. Conversely Early Paleozoic remnants of the northern Gondwana to the underlying UGU, the Thiviers-Payzac Unit Volume n° 2 - from B16 to B33 n° 2 - from Volume margin that experienced crustal thinning and rifting in never experienced the high-pressure metamorphism. Ordovician times. As revealed by seismic refl ection line (Bitri et al., iv) The Upper Gneiss Unit (UGU) is made up of a 1999), these relatively low grade rocks tectonically bi-modal association called “leptynite-amphibolite” overly the UGU. sequence which is a peculiar assemblage of mafi c vi) In the NE Massif Central, near Lyon, the and felsic rocks. This unit experienced a higher Brevenne Unit consists of mafi c magmatic rocks metamorphic pressure under eclogite and HP (pyroclastites, pillow basalts, diabases, gabbros), granulite facies (ca. 20Kb). Ultra high-pressure serpentinized ultramafi cs, acidic volcanic rocks,

5 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure acidic rocksaredatedof366 and siliceoussediments(radiolarites,siltites). The Structural informationrelatedtothehigh-pressure 2.2. The tectono-metamorphicevolution. Carboniferous ageislikely (seebelow). unconformity ofLeGoujet(eastLyon) anEarly the Early Visean calcareoussandstoneofthefamous but sincethemetamorphicrocksareconcealedbelow 1999). The preciseageofthethrustingisunknown dextral strike-slip (Feybesse etal.,1988;Leloix to theNWover theUGUfollowed byaNE-SW 1998). The Brevenne Unitrecordsanearlythrusting Ohnenstetter, 1986;Pin,1990;PinandPaquette, back-arc basinopenedwithintheUGU(Siderand oceanic sequenceformedwithinanora extension intheBeaujolaisareaisaMiddleDevonian geochemistry show thattheBrevenne Unitandits on zircon,PinandPaquette, 1998).Petrologyand Figure 4-Structuralandgeochronologic features relatedtotheLateSilurian-MiddleDevonian D1event. ± 5Ma(U/Pbmethod rocks (e.g. Villedé d’Ardin,Génis,Somme,Belfort Devonian stratigraphicageoftheunmetamorphozed rocks. The radiometricdatescomplywiththe of theexhumation ofthehigh-pressuremetamorphic upper partoftheUGU,itoccurredduringoratend the D1event isfoundinthemigmatitesthatform al., 1994;RoigandFaure, 2000;Figs.4,5).Since Costa, 1992;BoutinandMontigny, 1993;Duthouet Ma (e.g.Floc’h,1983;QuenardelandRolin,1984; metamorphism andanatexis datedaround385-380 an intermediatepressure/intermediatetemperature a top-to-the-SWshearingdeveloped coevally with characterized byaNE-SWtrendinglineationwith The earliestdeformationfoundintheUGU,D1,is main synmetamorphicductileevents arerecognized. draw ageneralview ofthisevent. Moreover, three known onlyasrelics.Itisthereforequitediffi evolution ispoorlydocumentedsincetheserocksare metamorphism andtheprogrademetamorphic cult to cult PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

Figure 5 - P-T paths of the Silurian-Devonian and Carboniferous events for the different units. areas, Fig. 4). Although a direct unconformity is never this Early Carboniferous deformation is coeval with observed, fi eld relationships suggest that D1 is older the closure of the Rheic Ocean and collision between than Middle Devonian. Gondwana and Laurussia. The second event, D2, is characterized by a NW- The third event, D3, is restricted to the southern part SE trending lineation coeval with a barrovian type of the Massif Central. In the Para-autochthonous metamorphism (Figs. 5, 6). 40Ar/39Ar dates on biotite, Unit of Cévennes-Albigeois, upper greenschist to muscovite and amphibole range around 360-350 Ma. amphibolite facies rocks are deformed by top-to-the- Most of the shear criteria developed along the NW-SE south ductile shearing along a submeridian lineation lineation indicate a top-to-the-NW shearing. In the (Fig. 7). Available 40Ar/39Ar dates on the metamorphic Rouergue area, the Naucelle thrust is related to this minerals yield Visean ages around 340 Ma (Monié event (Duguet and Faure, in press). The last increment et al., 2000; Faure et al., 2001). This thrusting of the ductile deformation in the metamorphic series propagates southward in the Fold and Thrust Belt is associated with the emplacement of peraluminous where kilometer-scale recumbent folds develop from cordierite bearing granitoids such as the Guéret Visean to Namurian. Although in the South Massif pluton that is the largest massif of this type. These Central south-directed compressional regime lasts granitoids exhibit magmatic to sub-solidus fabrics from Visean to Namurian (345 to 325Ma), conversely, that comply with the synkinematic character of these in the northern part of the massif, the Late Visean (ca. plutons (e. g. Roig et al., 1998). A similar tectonic- 340 Ma) is a turning point in the tectonic evolution. metamorphic-magmatic pattern is also recognized in From Morvan to Limousin, the Late Visean time the south part of the Massif Armoricain. The closure corresponds to the onset of syn-orogenic extension Volume n° 2 - from B16 to B33 n° 2 - from Volume of the Brevenne oceanic basins is chronologically caracterized by a huge crustal melting. Structural and kinematically in agreement with the D2 event studies indicate that the syn-orogenic extension is (Leloix et al., 1999). The geodynamic signifi cance controled by a NW-SE maximum stretching direction of the NW-SE lineation parallel to the belt is not (Fig. 7). The NW-SE spreading of the inner part of clearly understood yet. Several hypotheses have the Massif Central is also partly accommodated by been proposed (e. g. Burg et al., 1987; Bouchez and ductile wrench faults well developed in Limousin Jover, 1986; Mattauer et al., 1988) but none of them (e. g. La Courtine or S. Limousin faults, Fig. 7) and appears fully convincing. As discussed in section 2.4, in the Massif Armoricain. In the scale of the whole

7 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure metamorphozed andincludedinthe stackofnappes. or Ordovician magmaticrocksareductilelydeformed, amphibolite complex intheUGU,andCambrian responsible fortheformationofleptynite- detail here. The EarlyOrdovician bimodal magmatism, 2.3.1. The pre-orogenicmagmatismisnotpresentedin et al.,1984). migmatites andgranitoidsarerecognized(e.g.Duthou derived fromcrustalmelting.Several generationsof also characterizedbyavoluminous magmatismmainly Like allthe Variscan massifs,theMassifCentralis 2.3. A magmatic outline. they willbeconsideredinthenext section. belt. Sincethey arecloselyassociatedtomagmatism, younger ones)tookplaceduringthecollapseof The lastductiledeformationevents (ca.320Maand thrusts in Ardenne andSEEngland. responsible forthedevelopment ofnorth-directed belt, theLate Visean toNamurian compressionisalso 2002). The migmatitesandcordieritegranitesofthe Chemical U/Th/Pbmethodonmonazite(BeMezème, anatexis isdatedbetween333and324Mabythe or pre-Velay migmatites(Faure etal.,2001). The ortho- andparagneisscalled“ the MasméjeanUnit ” Para-autochthonous Unitisunderlainbymigmatitic orogenic collapse.InthenorthernCévennes, the a NW-SE stretchingrelatedtotheearlystageof structural controlofdyke intrusion complieswith magma isalsolikely (Pinand Duthou,1990). The Moreover, amantlecontribution asthesource of melting was triggeredbyheat imputfromthemantle. microgranites. Geochemistryindicatesthatcrustal series”, rhyolitictodaciticdykes andhypovolcanic pyroclastic deposits,called“Tufs anthacifères consists inaerialproductswithlava fl north andwestpartofthemassifCentral(Fig.7).It 2.3.4. The Visean magmatismiswelldeveloped inthe same strainfield thantheD2deformation(Fig.6). emplacement was controlledbythe fabric suggeststhatthoseplutons aluminous plutons. Their magmatic by theGuéret-typegranitesper- collisional magmatismisrepresented 2.3.3. TheTournaisianlate- be discussedinsection2.4. arc. Itsgeodynamicsignifi cancewill the deeppartofsameDevonian Lameyre, 1971),areinterpretedas time intheLimousin(Didierand alcaline rockswellknown foralong magmatic arc.Moreover, mafi interpreted astheaerialpartofa Meilleraie series. These rocksare basaltic pillow lavas formthe Armoricain, Eifelian-Givetian 1989). InthesouthpartofMassif (Fig. 8;Pinetal.,1982;Delfour, series) belongtoamagmaticarc Morvan area(calledtheSomme clastic rocksthatcropoutinthe calc-alkaline volcanic andvolcani- 2.3.2. The MiddletoLateDevonian Paris Basin). event (AMBP:Magnetic Anomaly of Late Devonian-Early Carboniferous D2 geochronologic features relatedtothe Figure 6-Structural,magmaticand ows, ignimbrites, c calk- PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

Figure 7 - Structural and geochronologic features related to the Visean-Namurian D3 tectonics and Late Visean magmatism (AMBP: Magnetic Anomaly of Paris Basin).

Montagne Noire Axial Zone (cf D2 fi eld itinerary in section 3) yield similar ages. In the present state of knowledge, this Late Visean event is still poorly studied. It is likely that other pre-Velay migmatites are not yet recognized also within the Velay dome.

2.3.5. The Namurian-Westphalian plutonism corresponds to the main period of magma production in the French Massif Central. It is well acknowledged (Didier and Lameyre, 1971) that this magmatism is represented by two types of granitoids, namely porphyritic monzogranites, such as the Margeride or Pont-de- Montvert-Borne plutons, and biotite-muscovite leucogranites such as the Brame or Millevache

Figure 8 - Map showing B16 to B33 n° 2 - from Volume the distribution of the Devonian plutons and volcanic rocks related to the magmatic arc and ophiolites (Brè venne, Ligne Klippes) interpreted as back arc basins (adapted from Faure et al., 1997).

9 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure and correlatively driftingandrewelding of Armorica opening andclosureoftheMedio-EuropeanOcean cycle, (CambriantoEarlyDevonian), isrelatedtothe 1997). According tothismodel,anEarlyPaleozoic out apolycyclic evolution (Pin, 1990;Faure etal., 1991, Lardeauxetal.,2001). The secondonepoints from SiluriantoEarlyCarboniferous(e.g.Matte, convergence betweenGondwana andLaurussia fi proposed. The for theevolution oftheFrenchMassifCentralare geodynamic evolution model.Presently, two scenari The above-presented dataallow ustodiscussa 2.4. A possiblegeodynamic scenario. Carboniferous St-Etiennebasin. north ofthePilatfault formthesubstratumofLate and micaschistsbelongingtotheLGUthatcropout ductile normalfault (Malavieille etal.,1990).Gneiss bounded tothenorthbyadetachmentfault, thePilat formations inthecoalbasins. The Velay domeis rarely alkalinebasaltsinterlayerswithterrigeneous dome, andalsobyacidictuf,ashlayersmore by cordieritegraniteandmigmatitesofthe Velay 2.3.6. The Stephanianmagmatismisrepresented (Faure, 1995). orogenic extensional tectonicsoftheMassifCentral pattern isinterpretedastheconsequenceofsyn- the Argentat ductilenormalfault. This structural slickenline. A similarkinematicsisalsofoundalong normal fault thatalsoexhibits aNW-SE trendinghot pluton isboundedtothewestbyNantiatductile rocks (Fig.9).InthenorthLimousin,Brame ans andalusitecontactmineralsintheplutonhost lineation. The sametrendisalsoobserved inbiotite NW-SE trendingmineral,stretchingandmagnetic that thesebodiesarecharacterizedbyaconspicuous studies oftheNamuri-Westphalian plutonsshow types emplacedcoevally. Petro-structuraland AMS geochronology show thatthesetwo magmatic from different magmas, but fi eld relationships and the northandwestparts. The two typeswerederived of themassifandlatertypeismoreabundant in is bestrepresentedinthecentralandsouthernparts out throughouttheMassifCentral,formertype massifs (Fig.9). Although bothgranitetypescrop Figure 9-Distribution ofthemaingraniticplutons tectonics. Duringthisevent, thepre-Visean GuÈret coeval withthestretching lineationandkinematics related totheNamurian-Westphalian extensional rst oneemphasizesacontinuous pluton behaves asarigidbody. the leptynite-amphibolitecomplexes. As amatterof continental riftingiscoeval withtheemplacementof Duthou, 1990).IntheUGU,crustalthinningdueto to crustalcontamination(Duthouetal.,1984;Pinand calc-alkaline” geochemistryofthesegranitoidsisdue continental rifting.Itisworth notingthat“pseudo- alkaline Ordovician granitoidsalsocomplywith pelite series(PinandMarini,1993).InLGU,the lava), diabasedykes, gabbrointrudethegrauwacke- Unit, alkalinemafic volcanics (sometimeswithpillow inferred frommagmatism.InthePara-autochthonous al., 1994).EvidenceofanOrdovician riftingisalso as theresultoferosionontiltedblocks(Robardetet Late Ordovician andSiluriandepositsisinterpreted in Devonian byacarbonateplatform. The lackof corresponds toaterrigeneousenvironment, followed study ofMontagneNoire,theCambrian-Ordovician which extends fromSouth America toChina.Fromthe belongs tothenorthernpassive margin ofGondwana From CambriantoEarlySilurian,theMassifCentral 2.4.1. The breakingofthenorthGondwana margin. model, thefollowing stagesareacknowledged. of Gondwana andLaurussia. Whatever thepreferred which theclosureofRheicOceanandcollision Middle Devonian toCarboniferousaccountsfor to Gondwana. A secondorogeniccycle rangingfrom PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

Ocean started in Silurian. All authors accept a northward subduction of the Gondwana margin, however, structural constraints (i. e. kinematics coeval with the development of high-pressure assemblages) or geodynamic evidence (i. e. relics of a magmatic arc) are lacking. By Middle Devonian time, the Armorica microcontinent is rewelded to Gondwana. In NE Massif Central, (North of Lyon), undeformed and unmetamorphozed Givetian sedimentary rocks unconformably cover the migmatites and high pressure rocks (Delfour, 1989; Godard, 1990). Subduction of oceanic and continental rocks is followed by their exhumation in Early to Middle Devonian, around 390-385 Ma. The lack of large volumes of Devonian clastic rocks suggests that exhumation was tectonically assisted. Exhumation results in the extensive retrogression of the high-pressure rocks of the UGU and migmatisation of the pelitic parts.

2.4.3. Mid-Devonian magmatic arc-back arc system. Frasnian-Fammenian calc-alkaline volcanism in the NE Massif Central and Vosges argue for subduction. In addition, the 380-370 Ma calc- alkaline diorite, tonalite, granodiorite plutons that crop out in NW Massif Central are interpreted as the deep part of this magmatic arc. However, in their present position, these plutons are rootless and tectonically included into the Hercynian nappes. Southward subduction of the Rheic Ocean is viewed as the cause of the calc-alcaline magmatism. At the same time, distension also Figure 10 - Devonian geodynamic reconstruction (map occurred in the upper plate, giving rise to limited and section) showing the closure of the Rheic Ocean oceanic zones such as the Brévenne in the Massif by southward subduction below Gondwana and related Central or other areas in the Massif Armoricain and microcontinents (from Faure et al., 1997). Vosges. Therefore, an arc-back arc pattern appears as the most likely geodynamic setting for Devonian fact, the Cambrian-Ordovician period is characterized times (Fig. 10). However a discussion of the Léon by the formation of continental stripes, such as the and microcontinents is beyond the scope of this Armorica microcontinent drifted from the north presentation. Gondwana margin. The question of the maximum width of the intervening Medio-European Ocean has 2.4.4. The closure of the Rheic Ocean and the B16 to B33 n° 2 - from Volume not been not settled yet (see discussion in Robardet, Tournaisian collision. 2003). A rough estimate suggests that this oceanic Since the Late Fammenian, a complete closure area was of limited extension (i. e. between 500 and of the Rheic Ocean led to a collision between the 1000 km). North European continent made by the assembly of Laurentia, Baltica and Avalonia during the Caledonian 2.4.2. The closure of the Medio-European Ocean. orogeny and Gondwana, including Armorica On the basis of available dates on the high-pressure microcontinent rewelded to it. Intracontinental metamorphism, the closure of the Medio-European shortening follows the Lizard ophiolite obduction

11 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure In theCentralandsouthernMassif Central,thethermal of kilometer-scale recumbentfoldsand thrusts. still undercompressionasshown bythe development such asMontagneNoireand Ardenne respectively, are and northernexternal zonesoftheHercynian Belt, inner partofthebelt(Fig.7).However, thesouthern for anincipientstageofsyn-orogeniccollapseinthe by aNW-SE maximumstretchingdirectionandargue Visean plutonsanddykes emplacement iscontrolled related plutonism. The structuralanalysisoftheLate for the“tufsanthracifères”acidicvolcanism and Massif Centralexperienced crustalmeltingresponsible As soonasLate Visean (ca335Ma),thenorthern syn-convergence extension. 2.4.5. Late Visean-Namurian Fold and Thrust Belt. in thePara-autochthonous Unitto330-325Mainthe progressively youngingsouthward: ca.345-340Ma shearing andrecumbentfoldingdevelops witha In thesouthernpartofMassifCentral,southward widespread inwesternandnorthernMassifCentral. metamorphism, anddatedaround360Maisalso coeval withmiddletemperature/pressure in themafi under uppergreenschist-lower amphibolitefacies area ischaracterizedbytop-to-the-NWshearing Massif Central,theclosureofBrévenne oceanic the SouthofEnglandto Ardennes. Inthenorthern of Paris Basin).North-directedthrustsdevelop from (which probablyextends alongtheMagnetic Anomaly lithosphere scalecross (modified fromFaure magmatism andheat regimes (extensional and compressional), Belt inLate Visean. section throughthe Mantle lithosphere contrasted tectonic French Hercynian flow inthecentral delamination may account for the part ofthebelt Interpretative et al.,2002). c rocks. Top-to-the-NW ductile shearing Figure 11- rnormalfaultswith a bounded bypurenormalfaults or structural typesofbasinsarerecognized:1)half-graben setting ofintra-mountainStephaniancoalbasins. Two belt. Extensionalregime iswellrecordedbythetectonic Massif Centralcorrespondstothecollapseofwhole The laststageoftheHercynian orogeny intheFrench 2.4.6. Stephanianpost-orogenicNNE-SSWextension mesothermal golddeposits. corresponds alsotothemainmetallogeneticepochfor maximum stretchingdirection. This tectonicstage synkinematic plutonsexhibit thesameNW-SE and MassifCentralthewrenchorextension controlled it isworth notingthatbothintheMassif Armorican dextral wrenching(e.g.Berthéetal.,1978).However, There, they aresyn-kinematicplutonscoeval with Massif Armoricain, leucograniticarealsowidespread. granodiorites intheMassifCentral(Fig.9).In by emplacementfabrics ofleucogranitesand Ma), orogenparallelextension iswellrecorded From Namurianto Westphalian (ca325-310 account forthemagmatism(Fig.11). delamination, islikely toplayasignificant roleto lithospheric mantlefromcrust,i.e. tectonic regime) isnotsettledyet.Decouplingof tectonic setting(namelyextensional orcompressional event. However, inthepresentstateofknowledge, the of thelateCarboniferous Velay massifbelongto this crop outintheMontagneNoire Axial Zoneandsouth granite formation. The ca330Mamigmatitesthat overprint isreponsibleformigmatiteandcordierite PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

Figure 12 - Massif Central map showing the Carboniferous extensional structures: coal basins, Velay granite- migmatite dome. Volume n° 2 - from B16 to B33 n° 2 - from Volume

13 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure and Vielzeuf,1983). temperature granulitizationofthelower crust(Pin Heat imputfromthemantleisresponsibleforhigh migmatitic-granitic Velay dome(Ledruetal.,2002). most spectacularstructureisthe100kmdiameter than duringsyn-convergence extension. The to LateCarboniferousextension arelessdeveloped Magmatism andmid-crustaldeformationassociated that accommodatedifferent amountsofextension. and Argentat fault areinterpretedastransferfaults trending wrenchfaults suchastheSillonHouiller the Massif Armoricain. Several N-StoNNE-SSW rare inwesternMassifCentralandalmostlacking are widespreadineasternMassifCentralbut are east. NE-SWextension andcorrelatively coalbasins The amountofextension increasesfromwestto NE-SW stretching,NW-SE andvertical shortening. pattern ofStephanianextension ischaracterizedby In thescaleofMassifCentral,deformation graben isnotsettledyet(MattauerandMatte,1998). control, eitherasaleft-lateralpullapartorhalf- of theStephanianstage.Nevertheless thestructural famous sinceitcorrespondstothepara-stratotype basins, theSt-Etiennecoalbasinisoneofmost wrench faults (Fig.12). Among theseintra-mountain strike-slip componentor2)pull-apartcontrolledby (1970). and Arthaud Figure 13-StructuralmapoftheMontagneNoiremodifiedfromGèze(1949) column ofthePaleozoic seriesfound intheMontagne Noire southernsiderecumbentfolds Figure 14-Schematic stratigraphic (adapted from Arthaud, 1970). stratigraphy (Lower Cambrian, worldwide famous forPaleozoic during D2. The SouthernSideis the Axial Zonewillbepresented the previous two. The geologyof This lastareaislessstudiedthan and aNorthernSide(Fig.13). Southern Side,an Axial Zone from SouthtoNorth,intoa Noire areaisclassicallydivided Arthaud (1970),theMontagne Following Gèze(1949)and A. Geologicsetting de Ladarez Cessenon D136toSt-Nazaire Montpellier--> Béziers--> Noire Southern Side Montagne Recumbent folding inthe 3. Fielditinerary DAY 1 PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

Figure 15 - Sketch of the main units observed in the eastern part of the Montagne Noire.

Five tectonic units are recognized in the southern side of the Montagne Noire, namely from top to bottom (Fig. 15): i) The Pardailhan Nappe (or recumbent fold) ii) The Mont Peyroux Nappe iii) The Monts de Faugères Unit iv) The Cabrières Unit v) The Para- autochthonous domain The Pardailhan Nappe consists of Lower Ordovician, Devonian, Carboniferous) and the folded and overturned Cambrian to Devonian rocks. development of kilometer-scale recumbent folds (or The Mont Peyroux Nappe includes Ordovician to nappes). The stratigraphic column is schematically Visean rocks. The Monts de Faugères Unit consists summarized in Fig. 14. of several overturned folds of Devonian to Visean rocks. The Cabrières Unit is an olistostrome, with large-scale olistoliths of Carboniferous and Devonian limestones, Silurian volcanites and Ordovician turbidites are resedimented within a wild-fl ysch matrix corresponding to the foreland basin of the belt (Engel et al., 1980). The Pardailhan Nappe exhibits a conspicuous axial planar cleavage, whereas in the Mont

Peyroux Nappe, the B16 to B33 n° 2 - from Volume transition between ductile deformation with axial planar cleavage folds and synsedimentary structures can be observed. On the basis

Figure 16 - D1 route map.

15 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure The landscapeshows Eocene limestone Visean flyschwith limestoneblocks. Stop D1.1: 17). Para-autochthonous domainunderneath (Figs.16, structural aspectsoftheMontPeyroux nappeand The stopswillshow mostofthelithological and B. Stopdescription Zone dome(cf.D2). deformation linked withtheformationof Axial develop afterrecumbentfoldingduringanupright to North,however mostoftheobserved structures deformation andmetamorphismincreasefromSouth to MiddleCarboniferous(Visean). Along thisroute, ranges fromEarlyOrdovician (Tremadoc-Arenig) river (Fig.16). There, thestratigraphic succession through aSouthtoNorthcrosssectionalongtheOrb deformation oftheMontPeyroux recumbentfold The aimofthisfi rst dayistopresentthepolyphase Visean-Namurian times(around330-325Ma). of stratigraphy, thosenappeswereemplacedin Figure 17-SyntheticcrosssectionoftheMontagneNoirewithlocationD1andD2stops. and nearly200mtothenorthofthisstop. Visean turbiditeisseenontheothersideofvalley limestone blocks.Devonian limestoneoverlying the exposes disruptedbedswithsandstonelensesand (20E 60). The northernpartthatisfoldedandsheared fl rocks. The S.partofthesectionexposes Visean unconformably overlying atlow anglePaleozoic extinction intheEarthhistory(Kapperetal.,1993). Crisis” responsibleforoneofthemostsevere mass series correspondstothe“Famenian Biological Section fortheFrasnian/Famennian boundary. This section hasbeenchosenastheGlobalStratotype “Griotte marble”(griotteisatypeofcherry). This Devonian (365 Ma)Goniatitelimestonecalled de Janeiro). The vertical beds(N30. 90)areLate in Washington, ortheMaisondelaFranceinRio exported allover theworld (e. g.the White House This oldquarrywas minedforrednodularlimestone -Frasnian/Famennian boundary. Coumiac quarry(protected area) Stop D1.2: ysch withcontinuoussandstonebedsdippingeast PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

Stop D1.3: phases. Recumbent isoclinal folds (F1) are deformed Early Ordovician turbidite. NE of Lugné. by upright open folds (F2) with axes plunging 50° In the landscape, looking to the SE, the vertical cliffs NW. F1 are related to the Mont Peyroux recumbent are Early Devonian limestones continuous with those fold and F2 belong to the kilometer-scale upright seen in the previous stop (D1-2) in the Coumiac folding responsible for the Roquebrun synform, quarry. Vieussan synform, and Axial Zone antiform (Fig. Sandstone-mudstone alternations lie subhorizontally, 17). however graded bedding and load cast show that the sequence is upside down. Folds are apparently Stop D1.7: overturned to the north but correspond in reality to Ordovician-Devonian contact. North the inverted limb of the Mont Peyroux recumbent of Roquebrun. fold. This Early Ordovician turbidite is interpreted This stop shows the inverted stratigraphic contact as deposited along the northern passive margin of between Ordovician detritals and Devonian carbonates Gondwana. in the northern limb of the Roquebrun synform. From south to north: Ordovician turbidite with top-to-the-S Stop D1.4: base (with load casts) dipping southward is underlain Early Ordovician turbidite. by Devonian calcareous sandstone, followed by A few hundred meters from the previous stop. limestone and dolomite. At the northern end of the The subvertical to north dipping upside down of outcrop, undeformed crinoid stems can be observed the beds exhibits numerous load casts, ripple marks in the Devonian carbonates. and bioturbation evidence (worm burrows). Locally Lingula shells can be abundant. Sandstones contain Stop D1.8: abundant fl oatted muscovite and heavy minerals. Visean fl ysch. Chapelle St-Poncian, S. of Ceps. In this outcrop, like the previous one, cleavage is Looking to the NW, the white rocks above the village lacking. of Ceps are inverted Devonian limestone, and to the W and SW, the vineyards are located in the Ordovician Stop D1.5: turbidite. The highest white cliff in the background Panorama on Roquebrun synform and the Orb (La Tour du Pin summit) is the northern extension of River. Col de la Vernède. Devonian formations. Below the cliff and up to Ceps, Below the road, the vineyards and Orb river are the lowest parts of the mountains are made of Visean located in the Ordovician turbidites which form the fl ysch, belonging to several tectonic units. core of the Roquebrun synform. Looking northward, The outcrop exposes Visean mudstone-sandstone with above the Roquebrun village, the white cliffs are limestone intercalations dipping south-westwards Devonian limestones. In the background, the hills (S0-1: 130 SW 50). Contrasting with the Visean with bushes are Visean fl ysch and in the distance, the rocks observed at the fi rst stop (point D1-1), here the last hills are made of Devonian limestone belonging Visean pelites are slightly metamorphosed (sericite) to the Monts de Faugères Unit. To the West (left), and exhibit a N70E trending crenulation lineation. the highest mountain is the Pic de Naudech made Chevron folds and south-directed brittle shear zones of inverted Cambrian rocks overlying inverted with quartz veins deform S0-1. Along the road, Ordovician turbidites belonging to the Pardailhan Devonian rocks are not observed, a late fault separates Nappe. Lastly, the farthest mountain to the NW is the the Visean and Devonian rocks. Mt Caroux composed of orthogneiss belonging to the Axial Zone. Stop D1.9: Volume n° 2 - from B16 to B33 n° 2 - from Volume Along the other side of the road, the Ordovician Monts de Faugères Unit. Large curve of Orb River turbidite is complexly folded. Superimposed folds are below Chapelle St-Geminian. observed in the next stop. Tournaisian (?)-Visean limestone and sericite metapelite present a westward (170W40) dipping Stop D1.6: foliation and a well marked mineral, stretching and Superimposed folds in Ordovician turbidite. 200 m crenulation lineation trending N 70E. Pressure- down to Roquebrun. solution is the dominant deformation mechanism. The Ordovician turbidite experienced two folding S0-1 is also cut at high angle by west dipping tension

17 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure Devonian limestones. limb ofthe Vieussan antiform,wellmarked inthe the rightprovides aclearpanorama ofthenorthern Turning leftonD177,toBerlou,thelarge curve to Optional. Landscapeonthe Vieussan antiform. Stop D1.11’: top-to-the-NE senseofshear. direction. InXZsection,pressureshadows indicate to thefoldaxisandthusathighangletransport is worth notingthatstretchinglineationtrendsclose folds belongingtothesamelarge-scale structure.It Plate 1,B)andlimestoneareinvolved inisoclinal normal limb. To thesouth,radiolarianchert(Color overturning. The horizontalpartoftheoutcropis Bedding-cleavage relationshipsshow asouthward folded LateDevonian limestone(partlydolomitized). This famous outcrop(ColorPlate1, A) exposes a de Graïs. Recumbent fold inDevonian limestone.Moulin Stop D1.11: marked bynumerousquartzveins (nostop). autochthonous seriesandtheMontPeyroux nappeis Back tothemainroad,contactbetweenPara- Pin andleLaufolds)overturned totheSouth. autochthonous seriesisfoldedbytwo anticlines(Le and intersectiondevelops. Regionally, thispara- due toelongatednodulesandgoniatites,crenulation the anticlinegeometry. A N70Ecompositelineation cleavage refractioninsandstonebedscomplywith Pin “anticline.Bedding-cleavage relationshipswith respectively. This S-SEverging foldiscalled“Le limestone to Visean fl ysch frombottomtotop, the successionbecomesnormalfromDevonian Faugères) and Visean fl ysch. Northofthisoutcrop, (lydiennes) andnodularlimestones(calcairesde cleavage; Tournaisian radiolarianblackcherts (S0: 60NW60)withaninverted limbsubhorizontal nodular limestone(griottemarble)withgoniatites down sequenceconsists oftheUpperDevonian red the Orbsection.FromNorthtoSouth,upside of LePin,thisoutcropexposes thedeepestpartof the underlyingPara-autochthonous Domain.North Turning righttotheroadofLePin,wecanobserve anticlines. Para-autochthonous Domain.LePinandLau Stop D1.10: gashes fi lled byfi brous calcite. event occurringinthehinterland. tourmaline supportapre-Devonian metamorphic volcanic quartzgrains,mica,garnet, zircon,rutile, northern sourceoftheterrigeneoussediments.Detrital that sedimentologyofeo-Devonian rocksindicatesa in theinternalzoneofBelt.Itisworth noting metamorphic event thattookplacemoretothenorth as asedimentaryconsequenceofremotetectonic- the MontagneNoiresouthernsidecanbeinterpreted the lackofLateOrdovician-Silurian rocksinmostof between Ordovician andDevonian formations,and the Ordovician sandstone. The angularunconformity Isoclinal foldswithcurved hingescanbeobserved in the leftandEarlyDevonian sandstonetotheright. stratigraphic contactbetweenOrdovician turbiditeto recumbent fold(Fig.18). The outropexposes inverted along thebasalthrustcontactofPardailhan masses correspondingtoDevonian limestoneboudins Looking West, thehillslopeshows several white Ordovician/Devonian contact.N.of Vieussan. D1.12: Back to Vieussan bythesameroad. shearing, thelimestoneisweaklyorundeformed. the tightcurve northofEscagnès.Inspiteintense of thePardailhan recumbentfoldcanbeobserved in limestone boudinsmarkingthebasalthrustcontact the MontPeyroux recumbentfoldandtheDevonian contact betweenOrdovician turbiditebelongingto deformed bothbyisoclinalanduprightfolds. The turbidite oftheMontPeyroux recumbentfold Southward, theroadgoesthroughOrdovician fold “Queuedecochon (pig’s tail)” Basal thrustcontactofthePardailhan recumbent Stop D1.11»: foliation axialplanartoF2. few biotitegrainscanbeobserved inthevertical S2 trending folds(F2)andN50Eisoclinal(F1). A pelite andsandstonedeformedbyuprightN80E At theoutcropscale,Ordovician rocksareblack Vieussan antiform. is Ordovician turbiditeatthewestern periclineofthe built onDevonian marbles(D1-14),thefrontview d’Heric visitedonD2. The villageof Tarassac is Axial ZonegneissandtheentranceofGorges Looking tothenorth,landscapepresents Peyroux recumbent fold. Nof Vieussan. Ordovician turbiditeinthenorthpartofMont Stop D1.13: . PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

Stop D1.14: 17). The foliation of micaschists and gneiss defines a para-autochthonous Devonian marble. Tarassac, NE-SW long axis elliptical dome whose western part parking of VVP. is disturbed by the Eocene Mazamet thrust. Some Muscovite bearing Devonian marble with pink calcite authors argued that the Axial Zone metamorphic crystals corresponding to deformed crinoid stems rocks correspond to the Precambrian basement of the exhibit a southward dip (70S60) and well marked Paleozoic series observed in the recumbent folds. In subhorizontal mineral and stretching lineation. This the present state of knowledge, there is no argument marble is separated from the overlying Ordovician to support the existence of a Neo-Proterozoic (i. e. turbidite by a major thrust contact corresponding Cadomian) orogen in the Massif Central. Therefore, to the basal thrust surface of the Mont Peyroux the reality of a Precambrian basement in the Montagne recumbent fold. The Devonian marble and the Noire Axial Zone is not supported by the data. The underlying metapelites attributed to Ordovician augen orthogneiss seen in the gorges d’Heric, are (not seen here) are a normal sequence belonging porphyritic granites intruding a Neo-Proterozoic to to the Para-autochthounous Unit. 40Ar/39Ar date on Paleozoic metasedimentary series of micaschists muscovite gives 297 ± 3 Ma which is interpreted as and gneiss and transformed into augen gneiss during the age of a Late Carboniferous gravity sliding event Hercynian tectonics. Recent U/Pb dating supports an related to the formation of the Axial Zone (Maluski Early Paleozoic age for the magmatism. The presence et al., 1991). of penninic style recumbent folds overturned to the north has also been assumed (Demange, 1975). End of the 1st day. Overnight stay in Olargues Although possible, this interpretation cannot be demonstrated, mainly due to poor outcrop conditions.

Figure 18 - Panoramic view of the contact between the Pardaillhan (top) and Mont-Peyroux nappe (bottom) marked by Devonian limestone boudins called “ pig’s tail ”.

DAY 2 The Axial Zone gneiss experienced a HT/LP type Migmatite dome of the Montagne metamorphism up to partial melting giving rise to Noire Axial Zone migmatites and anatectic cordierite granites (e. g. Laouzas granite). U/Pb dating on single grain zircon A. Geological setting and monazite give a ca 330 age. Isograds of this HT/ B16 to B33 n° 2 - from Volume The Montagne Noire Axial Zone remains one of the LP metamorphism define the same domal geometry most controversial area in the geology of Massif as the foliation. Within the micaschist enveloppe, Central (cf extensive references in Soula et al., 2001). kyanite relics are locally found (K in Fig. 13). P-T The Late Visean-Early Namurian recumbent folds paths for the gneiss core and metamorphic envelope examined during D1 are overprinted by metamorphic have been proposed (e. g. Soula et al;, 2001; Fig. 19). and structural features related to a granite-migmatite It is worth noting that some amphibolites included in gneiss dome developed in the Axial Zone (Figs. 13, the gneiss are retrogressed eclogites (E in Fig. 13) with estimated pressure and temperature around 9 ± 2

19 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure kbar and750 (from Soulaetal.,2001). and newHTmetamorphicmineralscrystallize of themigmatiticcore,earlyisogradsaredeformed the MontagneNoire Axial Zone.Duringupward doming Figure 20-Interpretationofthepresent-daygeometry southern andnorthernsidesoverprints therecumbent NE-SW trendingstretchinglineationwhichinthe The Axial Zone ischaracterizedbyaconspicuous folding ofthePaleozoic sedimentary sequence. to compressionaltectonicscoeval withrecumbent of theductiledeformationgneissisrelated is thatthehigh-pressuremetamorphismandapart is available fortheeclogites,apossibleinterpretation at ca25-30kmdepth. Although noradiometricdate units situatedundertherecumbentfoldwereburied These high-pressurerockssuggestthatthetectonic ± 50°Crespectively (Demange,1985). from Soulaetal.,2001andDemange,1985). Axial Zonemicaschist andmigmatiticgneiss(modified Figure 19-P-Tpathsinferred for theMontagneNoire the development ofaNE-SW crenulation,strengthens lineation keeps thesameN60-70Etrend.Furthernorth, After thesecondbridge,foliationfl dykes arefl southwards whereasnearthetopofmountain, entrance ofthegorges d’Héric,mostofthedykes dip pegmatitic dykes obliquelycutthefoliation. At the are themostcommonrock-types. Tourmaline-garnet The Hericaugenorthogneissandparagneisssepta SE partofthe Axial Zone,called“CarouxMassif”. The morningisdedicatedtotheobservation ofthe gorges d’Hérictrack,1.5km,aneasywalk. Cross sectionoftheCaroux Massifalongthe Stop D2.1: B. Stopdescription on zirconandmonaziteat327 that crosscutsthemigmatitefoliationisdatedbyU/Pb the Axial Zone.Indeed,the Vialais granite(Fig.21) hypothesis cannotaccountforthebulk structureof Graissessac coalbasin);theextensional gneissdome (Stephanian) tectonics(e.g.syntectonicinfi role toaccountfortheLateCarboniferous Although extensional tectonicsplaysanimportant in Soulaetal.(2001). 92). A recentdiscussionofthisproblemcanbefound core complex” (Van denDriesscheetBrun,1991- 1960, Faure etCotterau,1988);iv) “metamorphic diapir andregional NE-SWshortening(Schuilling, et al.,1998;iii)interferencebetweenmigmatitic NE-SW antiformalstack(Mattaueretal.1996,Matte (Nicolas etal.,1977;EchtlerMalavieille, 1990);ii) proposed, namely:i)NE-SWductilewrenchzone doming remainsdisputed.Several interpretationsare the tectonicsignificance oftheMontagneNoire to theupliftofmigmatiticcore(Fig.20).However, combination ofthetectonicandthermalstructuresdue The presentshapeoftheisogradsresultsfroma morning. famous sectionof“gorges d’Héric”visitedinD2 shear criteriaareambiguous,asseenalongthe However, alongthesubvertical domelonglimbs, is down dip,i.e.top-to-the-NE andSWrespectively. northeastern andsouthwesternterminations,shearing provides contrastedshearcriteria. Around thedome folds (cf.stopD1-14). The kinematicanalysis 1998). at lying. (Fig. 21) ± 5Ma(Matteetal., attens but the ll ofthe PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

Figure 21 - D2 route map the gneissic linear fabric. In the paragneiss, meter folds in augen gneiss and meter to millimeter-scale scale isoclinal folds are refolded by NE-SW trending crenulation. upright folds. Pegmatites dykes are also deformed by upright ptygmatitic folds and veins parallel to the fold axes are Stop D2.2: boudinated. Along the stream, amphibolite boulders Augen gneiss and sheare pegmatite veins at the (containing garnet locally) including retrogressed eastern part of the Caroux dome. Le Vernet . eclogites, boulders of migmatites and migmatized From gorges d’Héric Æ east to Le Poujol Æ north augen gneiss, sometimes containing sillimanite (left) to Combes. nodules are widespread. Outcrop of migmatite will Fine grain augen gneiss (Sx 40SE 30) with a N70E not be visited along this route. trending stretching lineation at the eastern termination In spite of a clear stretching and mineral lineation, of the Caroux antiform. Sigmoidal K-feldspath the sigma-type porphyroclast systems exhibit both indicates a down-dip, top-to-the East sense of shear.

dextral and sinistral asymmetry at the outcrop Pegmatite dykes cross cutting the foliation are also B16 to B33 n° 2 - from Volume scale. The ambiguous sense of shear might be due sheared to the East. Along the road next curves, to superimposed deformation (namely doming many asymmetric pegmatite boudins can be observed overprinted upon low angle shearing) or to strain within weathered gneiss (no stop). partitioning with a signifi cant component of pure shear (Color Plate 1, C) during doming. Stop D2.3: The bulk structure of the Heric section is a gneiss Biotite-Garnet-staurolite micaschists. Crossing of antiform overturned to the north (Figs. 13, 17). the road to Forêt des Ecrivains Combattants. The antiform hinge zone is parallel to upright The gneiss-micaschist series experienced a high-

21 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure on topofthemountains. quality, EarlyCambriancarbonatescanbeobserved Northern Side.Inspiteofgloballypoorexposure North ofGinestet,begins theMontagneNoire et al.,1991). muscovite andbiotiteindicate297 unconformably cover thePaleozoic (Cambrian- can beobserved too.Stephanianbedsdipping110S10 Cambrian limestoneblockthatisprobablyanolistolith and limestone. Along theroad,adecameter-scale cm tomsizeblocksofEarlyCambriansandstone The LateCarboniferousconglomeratecontains exposed. landscape, theEarlyCambrianlimestonecliffs are the StephanianGraissessaccoalbasin.Innorthern At thepassofCroixdeMounis,roadentersinto Stephanian conglomerate.Falaise d’Orques. Stop D2.5: to theEspinousenormalfault. and bearsaN60Etrendingslickenline corresponding shearing, theNW-SE trendingfoliationdips50NE The migmatiticorthogneissexperiences aductile S. ofGinestet. Sheared augengneissandmigmatite. Stop D2.4’: Optional there. and parkingdiffi culties, theexcursion willnotstop Vialais granite,however duetopoorexposure quality the pass,roadcrossesnorthernborderof preserved. Migmatisationisdatedat330Ma. After orthogneiss but MFKandgneissicfabric arestill Partial meltingdevelops attheexpense oftheHeric Migmatitic orthogneiss.Coldel’Ourtigas. Stop D2.4: antiform andtheEspinousedome. folded HT/LPmicaschistsbetweentheCaroux Rosis synformwhichconsistsofcrenulatedand After theColdeMadale,roadrunswithin Plate 1,D). shear bandsindicateatop-to-theEastshearing(Color pressure shadows, helicitic garnetandstaurolite, to-the-E shearcriteriadevelops. Inthinsection,quartz stretching lineationtrendingN70Ealongwhichtop- (160E15) bearsacompositecrenulation,mineraland tight isograds. The eastward dippingfoliation characterized bybiotite,garnet,andalousite,staurolite temperature andlow-pressure metamorphism 40 Ar/ ± 3Ma(Maluski 39 Ar dateson basin. Espinouse domefromtheStephanianGraissessac ductile dextral-normal Espinousefault separatesthe Espinouse gneissdomedippingnorth-eastward. The the landscapetoeastshows thefoliationof At thecrossingwithD22EroadtoCastanet-le-Haut, the depositionofStephanianrocks. Graissessac basin(Castanetfault) isreactivated after Thus strictlyspeaking,thesouthernborderfault ofthe Ordovician) sedimentaryrocksoftheNorthernSide. Axial Zonemicaschists.Nostop. forms anextensional allochthonemplaceduponthe de St-Gervais Unit)belongstotheNorthernSide,and Cambrian (grèsdeMarcory). This Unit(calledMonts sandstone andpelitecorrespondingtotheEarly unmetamorphosed andundeformedgreenish East of Verenoux, theroadgoesthrough overturned totheSEcanbeobserved atthisoutcrop. the Axial Zone.Centimeter- tometer-scale folds outermost partofthemetamorphicrockssurrounding greenish sandstone-peliteseriescorrespondtothe Weakly deformed andweaklymetamorphosed Castanet-le-Bas. Weakly metamorphosed schists. West of Stop D2.7: the Espinousefault. Quartzveins arewelldeveloped. Paleozoic rocksoftheNorthernSide)isshearedby The Graissessacbasinsubstratum(i.e.early N. ofNougayrols. Sheared rocks alongtheEspinousefault. Stop D2.6: Permian (Autunian) conglomerate. Stop D2.9: there. but unfortunatelythecontactcannot be observed conglomerates, sandstonesandpelitesdipping0E20, rocks areunconformablycovered byEarly Permian the Southcanbeobserved. These LateCarboniferous mine (notvisited)synsedimentaryfoldsoverturned to mesures. IntheancientopenpitofGraissessac Decollement surfaces maydevelop alongcoal dipping 120NE30withcoalintercalations. Graissessac coalbasin. They arefl The LateCarboniferousrocksbelongtothe mesures. EastofLaMouline. Stephanian massive sandstoneandcoal Stop D2.8: uitl deposits uviatile PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

West of La Tour-sur-Orb. Leaving Millau to the North, the road crosses Continental conglomerates with quartz, sandstone the Jurassic limestone plateau called Causse de pebbles. Sauveterre. Near Séverac-le-Château, Toarcian black shales were mined for oil. The Jurassic sedimentary Stop D2.10: series observed along the road, is deformed by Permian extensional tectonics. decameter to kilometer-scale wave-length upright Mas d’Alary quarry. folds and reverse faults. These structures are related In the ancient open pit formerly mined for uranium, to the Eocene compression due to the Pyrenean continental red beds are cut by north dipping normal orogeny. faults. Alike other early Permian basins in S. France (e. g. St-Affrique, Rodez), the Lodève basin is a half- A. Geological setting graben bounded to its southern margin by normal The Marvejols area (Fig. 22) is a famous place in the faults. geology of the French Massif Central since it is one of the fi rst places where Variscan syn-metamorphic End of the 2nd day. Drive to Millau (ca 60 km), nappe thrusting has been documented on the basis overnight. of geochronology, metamorphism and tectonics (Pin, 1979). The metamorphic inversion with HP rocks of DAY 3 the Upper Gneiss Unit upon the Lower Gneiss Unit The stacking of Upper and Lower Gneiss Units was used as an argument for tectonic superposition and post-nappe crustal melting (Fig. 23). The contact between the two units is a MillauÆ Highway to La Canourgue Exit n° 39 high temperature mylonitic zone (Faure et al., 1979). Moreover, radiometric dates document the tectonic

Figure 22 - D3 route map Volume n° 2 - from B16 to B33 n° 2 - from Volume

23 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure lineation whichiswidespreadthroughouttheMassif signifi 342 from theLotSeriesmicaschistyields351 by various magmatic bodies: succession ofmetapeliteandmetagrauwacke intruded locally theLotSeries,consistsofamonotonous evolution ofthearea. The Lower GneissUnit,called (Fig. 24). in thefootwall oftheUpperGneissUnitoverthrust example oftheinverted metamorphismdeveloped metapelites. The Marvejols areaisoftentaken asan andalousite andmuscovite arewidespread inthe pressure metamorphism.Biotite,garnet,staurolite, coeval withanintermediatetemperature-intermediate and stretchinglineation. This ductiledeformationis foliation andaconspicuousNW-SE trendingmineral Lower GneissUnitischaracterizedbyasubhorizontal As seeninthefirst stopsofD3 day, theLotSeriesof 1. Quartz-diorite orthogneissisdatedat540 4. Other smallgneissmassesarerecognizedinthe 4. Anacidicaugenorthogneisswithmyloniticzones 3. 2. Pink K-feldsparorthogneissofalkaline Figure 23-GeneralcrosssectionfromMarvejols tothe metasediments (Pin,1981). as hypovolcanic granitesorvolcaniclastic Lower GneissUnit,someofthemareconsidered data). Ma isobtainedonmonazite(A.Jolyunpublished A preliminarychemicalU/Th/Pbageof370 developed intheLower GneissUnit(cfbelow). particularly withtheNW-SE stretchinglineation does notcomplywithmicrostructuraldataand the UpperGneissUnit.However, thisconclusion synkinematic plutoncoeval withthethrustingof radiometric agethisorthogneissisinterpretedasa 8 Ma(Pin,1981).Duetoitstectonicsetting,and populations gives alower interceptageof346 Lower GneissUnitcontact. An U/Pbageonzircon crops outimmediatelybelow theUpperGneiss- an EarlyCambrianageisgenerallyaccepted. orthogneiss intheMontagneNoirenorthernside, zircons. BycomparisonwiththeMendic composition isnotwelldatedduetoinherited 352 linear structure.40Ar/39Ardatingonbiotitegives exhibits awellmarked post-solidus planarand populations (PinandLancelot,1978). This rock Ma byU/Pbisotopicdilutionmethodonzircon Truyère areashowing thetectonicsuperpositionof ± 4Marespectively (Costa,1989). The tectonic cance oftheNW-SE trending stretching ± 1Ma(Costa,1989). Upper GneissUnitupontheLower GneissUnit 40 Ar/ 39 Ar datesonbiotiteandmuscovite and theshapeofMargeridepluton ± 4Maand ± 12 ± 12 ± PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

Figure 24 - Metamorphic map of the Lower Gneiss Unit around the west part of the Margeride pluton (Marvejols, Truyère, Châtaigneraie) showing the inverted metamorphism (adapted from Burg et al., 1984).

Central is not clearly settled yet. metagabbro at 484 ± 7 Ma. An orthogneiss intrusive The mylonitic zone at the base of the Upper in the paragneiss gives 478 ± 6 Ma. These dates Gneiss Unit is characterized by a N-S trending are interpreted as the evidence for an Ordovician mineral and stretching lineation. In spite of intense magmatism related to the rifting of Armorica from recrystallization and post-kinematic annealing, Gondwana. Moreover, the 415 ± 6 Ma age of zircon top-to-the-south shearing can be observed. 40Ar/ populations from a high-pressure trondhjemite is 39Ar dating of synfolial biotite gives 358 ± 4 Ma considered as the age of melting coeval with eclogite interpreted as the age of thrusting. Moreover, a late facies metamorphism. Pressure and temperature muscovite developed upon the early foliation is dated constraints on this rock are 16 ± 4 kb and 800 ± 50°C at 340 ± 4 Ma (Costa, 1989). respectively. In the Marvejols area, the Upper Gneiss Unit consists Upper and Lower Gneiss Units stacking was followed of a lower part called “leptynite-amphibolite” by huge crustal melting produced under distinct P-T sequence and an upper part with migmatitic gneiss conditions (Fig. 25). The second part of the D3 and the and micaschist. The leptynite-amphibolite sequence whole D4 days are devoted to the observation of some B16 to B33 n° 2 - from Volume contains metamorphosed mafi c rocks of magmatic or manifestations of the Middle to Late Carboniferous sedimentary origin such as metagabbro, metabasalt, crustal melting. From older to younger, three stages amphibolite rare serpentinites and acidic rocks (i. e. are distinguished. leptynites) Meter to centimeter scale acidic-mafi c alternations are probably of volcani-clastic origin. 1. Pre-Velay Cévennes migmatites, dated between Several U/Pb ages on zircon populations are available 333 to 324 Ma by chemical U/Th/Pb method on (Pin and Lancelot, 1982). Namely, an amphibolite monazite (Be Mezème, 2002). boudin is dated at 487 ± 6 Ma, and a coronitic 2. Namurian-Westphalian plutonism dated around

25 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure 3. Velay migmatitesandcordieritegranitedated Velay area (simplified fromMonteletal.,1992). Figure 25-P-Tpathsofpre-Velay and Velay events constructedfrommetamorphicrocks sampledinthesouthpartof 40 Lancelot, 1978)fortheemplacementofthispluton. populations gives a540 to theLower GneissUnit.U/Pbdatingonzircon originally intrudesmicaschists(stopD3-2)belonging A fi ne-grained biotite-hornblendequartzdiorite Ajustons, S.ofMarvejols. Cambrian quartz-diorite.N88,EastofPont des Stop D3.1: B. Stopdescription NW-SE deformation. This wellfoliatedandlineatedrockexperienced a corresponding tothetectonicevent (Costa,1989). Ar/ during D4. around 300Ma. This large massifwillbeexamined are coeval. relationships show that thesetwo magmatictypes massifs derived fromdifferent magmas,fi (Signaux andRoclesplutons). Although distinct Montvert-Borne plutons)andalsobyleucogranite porphyritic monzogranite(Margeride orPont-de- 320-315 Ma. This magmatismischaracterizedby 39 Ar datesonbiotiteprovide a352 ± 12Maage(Pinand ± 1Maage eld Ma (Joly, unpublisheddata). An U/Th/Pbchemicalageonmonazitegives 370 gives alower interceptageof346 SE senseofshear. U/Pbdateonzirconpopulations asymmetric K-feldsparaugenindicateatop-to-the- the foliationandparalleltoNW-SE lineation, with myloniticfabric. Insectionsperpendicularto The Lower Gneiss Unit includesaugenorthogneiss Pessil. Augen orthogneisswithintheLotseries.Pont de Stop D3.3: 39 shear (ColorPlate1,E).Biotiteandmuscovite stretching lineation,indicatingatoptoNWsenseof foliation bearsaconspicuousNW-SE mineraland porphyric graniteandmetadiorite. The fl ± staurolitemicaschistsoriginallyintrudedby The Lotseriesarecomposedofbiotite-garnet Lower GneissUnitoftheLotseries. Stop D3.2: The UpperGneissUnitoutcropsNorthof Gneiss Unit.LeCroisier. Coronitic metagabbro belongingtotheUpper Stop D3.4: unconformably overly themetamorphicrocks. 1989). Inthebackground,EarlyJurassiclimestones Ar agesarerespectively 351and342 ± 8Ma(Pin,1981). ± 4Ma(Costa, a lying at 40 ± 12 Ar/ PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

Marvejols city. Metabasites, locally with mylonitic amphibolite complex which becomes migmatized fabric, underwent the Eovariscan high-pressure northward. The migmatite is not dated here. By metamorphism (Color Plate 1, F). However, due to comparison with other places in the Massif Central, a the heterogeneity of deformation, magmatic textures ca 380 Ma age can be inferred. are still preserved. This rock is dated by U/Pb method on zircon populations (upper intercept) at 484 ± 7 Ma Stop D3.7: (Pin and Lancelot, 1982). Middle Carboniferous Margeride pluton. Truc de Fortunio. Stop D3.5: Drive to St-Amans Æ Estables Leptynite-amphibolite complex The Margeride massif is one of the largest granitic (Upper Gneiss Unit). Along the main road (N9). plutons in the French Massif Central (3200 km2). It This outcrop exposes a typical section of the consists mainly of a porphyritic monzogranite with “leptynite-amphibolite complex” made of alternations large (up to 10cm) K-feldspar megacrysts. On the of mafi c and acidic rocks considered as a volcani- basis of biotite content, three facies, namely dark, clastic formation. The foliation exhibits meter to intermediate and light facies, are distinguished

Figure 26 - Example of ponctual dating on monazite decameter-size amphibolite boudins (Color Plate 2, single grain by U/Th/Pb chemical method A). Zircon populations from an amphibolite give a U/ (Be Mezème et al., 2003). Pb age of 487 ± 6 Ma age (upper intercept) interpreted

as the rock formation age (Pin and Lancelot, 1982). B16 to B33 n° 2 - from Volume The lower intercept at 340 ± 4 Ma is close to the (Couturier, 1977). Nevertheless, more than 80% thermal event (ca. 345-330 Ma) that overprints the of the massif is made of the intermediate facies. tangential tectonics. Moreover, muscovite-K-feldspar leucogranite intrude the monzogranite. Most of the leucogranites Stop D3.6: are meter-scale dykes, but east of the massif the Early Variscan migmatisation. Grandrieu leucogranite represents a kilometer-sized Gorges du Val d’Enfer. pluton. The monzogranite yields a Rb-Sr whole rock The road runs from South to North in the leptynite- age of 323 ± 12 Ma (Couturier, 1977) and an isotopic

27 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure

Figure 27 - A: Map of the planar and linear structures in the Margeride pluton inferred from AMS study (from J-Y. Talbot, unpublished). B: Stereograms represent the magnetic lineation (K1) and the pole of foliation (K3). PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

dilution U/Pb monazite age of 314 ± 3Ma (Pin, 1979); the Grandrieu leucrogranite is dated at 305 ± 4 Ma (U/Pb method, Lafont and Respaut, 1988). The Margeride pluton is a subhorizontal of 4 to 8 km thick (Fig. 23). Petrostructural and AMS studies (J-Y. Talbot, work in progress, Fig. 27) show a complex pattern of the foliation trajectories. Although the foliation trajectories do not show a consistent shape, at the scale of the whole pluton, the foliation presents a fl at lying attitude. The lineation pattern exhibits a well-defi ned NW-SE trend. It is worth noting that such a trend is widespread throughout the whole Massif Central and corresponds to the maximum stretching direction of the Namurian-Westphalian syn- orogenic extension (Faure, 1985). Stop D3.8: Augen orthogneiss below the Para-autochthonous Unit. Drive to Châteauneuf-de-Randon Æ Montbel Æ NE of Belvezet SE of the Margeride pluton, the Cévennes area exposes the para- autochthonous Unit of the Massif Central. Below the unconformity of the Mesozoic sedimentary rocks, an augen orthogneiss and its host rocks crop out in a tectonic window below the Para-autochthonous Unit (Cévennes micaschists). The augen orthogneiss exhibits a subhorizontal foliation and NE-SW trending stretching lineation. The age of the granitic magmatism is not determined here but assumed to be Early Cambrian (ca 550 Ma) by comparison with other orthogneiss B16 to B33 n° 2 - from Volume in the Massif Central. The chemical U/Th/Pb age of 560 ± 18 Ma in the core of monazites grains from migmatitic orthogneiss supports this interpretation (cf. Stop D3-9)

29 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure Vanderhaeghe etal.,1999). The Velay migmatite- (Brown andDallmeyer, 1996;Gardienetal.,1997; the roleofpartialmeltingduringorogenicevolution migmatitic complexes isofgreatinteresttostudy exposes numerousgraniticintrusionsandlarge and Teyssier, 2001). Thus, the Variscan beltwhich its behaviour duringorogeniccollapse(Vanderhaeghe rheology ofthethickened crust andlargely control collision tectonicsimpliesamajorchangeinthe development ofapartiallymoltenmiddlecrustduring (Clemens, 1990;Brown, 1994).Moreover, the inaccessible locationoftheirproductionsites still discussedinparticularbecauseofthedeep, by crustalmeltingduringorogeny isaprocess The generationoflarge granite-migmatitecomplexes during orogenic evolution melt generationandgraniteemplacement The Velay dome(French MassifCentral): End ofthe3 again alongthe Allier river. to Langogne,themigmatiticorthogneisscropsout (Schistes desCévennes). FromLaBastidePuylaurent, the roadislocatedinPara-autochthonous Unit of Permianage.SouthLaBastide-Puylaurent, The roadfollows thebrittleleft-lateral Villefort fault In Prévenchères, turntothenorth(left)Langogne. (Be Mezèmeetal.,2003;fi chemical U/Th/Pbmethodonmonaziteat316 the metamorphicrocks.Muscovite dyke isdatedby Pink granitedykes andleucogranitedykes intrude Boudinaged dykes ofleucogranites. interpreted astheageofmigmatization. Mezème, 2002,Cocherieetal.,inpress). The latteris ± 6Maforthegrainscoreandrimrespectively (Be U/Th/Pb datesonmonazitegive 560 orthogneiss fabric remainswellpreserved. A chemical melting giving risetodiatexites. Locallythe To theeast,orthogneissexperiences apartial Migmatitic orthogneiss.BarragedePuylaurent. Stop D3.10: correspond totheorthogneisshostrock. cordierite) paragneissandquartz-micaschist A few kilometers eastward, biotite,garnet( Stop D3.9: rd day. Overnight inLangogne DAY 4 g. 26). ± 18Maand324 ± 5Ma ± • • • Variscan belt,byshowing: dome inconnectionwiththetectonicevolution ofthe generation andgraniteemplacementofthe Velay The aimofthefourthdayistoillustratemelt on theevolution ofthe Variscan orogeniccrust. generation ofalarge volume ofpartiallymoltenrocks anatexis andtheconsequencesofpresence thermal conditionsrequiredforwidespreadcrustal 28, 29,30)offers auniqueopportunitytoexamine the granite domelocatedintheSEMassifCentral(Fig. A. Geologicalsetting • • • • models work inthisareaprovided thefollowing resultsand (Didier, 1973;DuprazandDidier, 1988).Previous (25%) andgranites(5%)ofvarious natureandsize and prismaticcordieritebyenclaves ofgneisses (about 70%)characterizedbyabundance ofnodular diameter, iscomposedofperaluminousgranites The Velay dome(Fig.28,29),about100kmin the Velaydome. Etienne Stephanianbasinonthenorthernfl extensional tectonicsandformationoftheSt the relationbetweengraniteemplacement, the cordierite-bearinggranitesandmigmatites; southern margin; pre-tectonic graniteandmetasedimentsonthe incipient stagesofmeltingintheLateNeoproterozoic underplating ofmafic magmas(Fig.31). evolution overprinted byathermal peakduetothe Velay domehasfollowed aclockwiseP-T-time and Barbey etal.(1999),indicatethatthe Williamson etal.(1992),Montel(1992) (Malavielle etal.,1990) developed duringthecollapseof Variscan belt zone ofthePilat,onemajornormalfaults expansion ofthegranitesbelow thedetachment pattern ofthe Velay domerecordssouthward lateral Lagarde etal.(1994)suggestedthatthedeformation during late-orogenicextension. instabilities withinapartiallymoltenmiddlecrust migmatites andgranitesrefl the amplifi cation ofthe Velay domecoredby Burg and Vanderhaeghe (1993)proposedthat dehydration conditions. with biotitestablefollowed bymeltingunderbiotite of anatexis, fi Montel etal.(1992)describetwo successive stages Geochemical andpetrologicaldatapublishedby rst underwater-saturated conditions et gravitational ects ank of ank PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22 Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 28 - Simplifi ed geologic map of the eastern margin of the Massif Central, Day 4 and Day 5 localities

31 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure • al., 1994a,b): the collisionhistoryof Variscan belt(Ledruet dome ishostedbygneissicunitsstacked during 1. The hostrocks. The Velay granite-migmatite 28, 30): illustrated duringthisfourthday, aredefi Four mainstructuralzones,thatwill bepartially The formationofthe Velay dome,coeval with • • • phenomena. dome resultsfromtheconjunctionofseveral that theformationof Velay migmatite-granite petrologic andgeochronologicaldataindicate According toLedruetal.,2001,structural, indicated asspecificgeochronological markers. Day 4and5localities. Ages ofsomegranitesare main tectonicunitsandtheirstructuralrelationships, eastern marginoftheMassifCentralshowing the Figure 29-Simplifiedcrosssectionthroughthe presently inanuppergeometricposition, thisunit of EarlyPaleozoic oceanicormarginal basinsis Partial meltingofthethickened cruststartedat Partial meltingtookplacewithinadominantly the UpperGneissUnit,thatcontainsremnants collapse. molten crustallayerinresponsetogravitational potentially correspondstofl ow ofapartially the activation ofcrustal-scaledetachements, the migmatitesandgranitesof Velay dome. large volume ofthethickened crustandgenerate provided theextra heatsourcerequiredtomelta upwelling coeval withorogeniccollapsehave mantle-derived magmasandalsoasthenospheric However, itisproposedthatheatadvection from the evolution ofthe Variscan orogeniccrust. likely causedariseintemperatureduring heat productionfollowing crustalthickening the migmatite-granitedome. decompression associatedwithexhumation of prograde metamorphicpathandendedduring and indicatethatmeltingstartedattheendof solidus todestabilizationofhydrousminerals evolved fromthewater-saturated granitic fertile peliticcompositions.Meltingreactions metasedimentary crustallayerdominatedby hence lastedabout40My. generation oftherocksforming Velay dome Ma. Crustalanatexis responsibleforthe during collapseoftheorogeniccrustat~300 of the Variscan beltwas stillactive, andended about 340Ma,whilethrustinginthehinterland Thermal relaxationandincreasedradioactive ned (Fig. ned PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22 Volume n° 2 - from B16 to B33 n° 2 - from Volume

Figure 30 - Extension of Meso and Neovariscan metamorphism and foliation trends within the host rocks of the Velay migmatite-granite dome

33 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure the southernhostrocks ofthe Velay granite(oblique-ruled boxes, after Monteletal.,1992) ruled boxes, afterGardienetal.,1997,andMontel1992),(3)inthemigmatitic partof migmatitic orthogneissandgraniteinthesouthernpartofdome(oblique- andhorizontal- stage isindicatedbyarrows (1)inthePilatmicaschist (afterGardienetal.,1990),(2)inthe biotite; As =aluminiumsilicate;Lliquid.ThetransitionfromtheM3toM4metamorphic Grt =garnet;Msmuscovite; Qtz= quartz;Kfs=potassiumfeldspar; Pl=plagioclase;Bt Mineral abbreviations: Ky =kyanite;Silsillimanite; And =andalusite;Cdcordierite; Figure 31-Pressure-temperatureevolution fromthegneissesto Velay granite • Devonian, priorto350Maintheinternalzone the UpperGneissUnitwhichoccurredduring metamorphism attributed tothethrustingof margin underwentageneralmedium-pressure sedimentary parautochthonoussequence. This R’Kha Chahametal.,1990),and(b)amainly granite datedat528±9 Ma (Rb-Srwholerock, Fix”) originatingfromperaluminousporphyric and argilites, andaugenorthogneiss(the“Arc de composed ofmetasedimentsderived frompelites is representedby(a)aLower GneissUnit The northGondwana continentalmargin al., 2001). while subductionwas stillactive (Lardeauxet 420-400 Matolessthan30kmat360-380 show theserockswere exhumed from90kmat (450-400 Ma).Structuralandradiometricdata Eovariscan stageoflithosphericsubduction are preserved withinbasiclayersmarkingan tuffs andgrauwackes. Numerouseclogiticrelics granites, microgranites,acidandbasicvolcanics, at itsbaseoverlain bygneissesderived from contains dismemberedbasic-ultrabasiccomplexes • identifi the gneissichosts,following meltingreactionsare the roofof Velay dome.Inthemigmatitesandin 2. The gneiss-migmatitezone,attheperipheryand quartz-feldspathic rocks,withbiotiteremaining conditions exceeding thoseforwater-saturated The fi rst meltingstagedeveloped underP-T ( to Ar diffusion hasbeendatedat335-340Ma Burg, 1993; Arnaud, 1997). The closureofmicas thickening estimatedatabout15km(Arnaudand synchronous withsouthward thrustinganda muscovite-chlorite-garnet paragenesesbeing are thereestimatedat500 °C, 5 kbar, withthe conditions duringthemetamorphicevolution the parautochthonousdomain.MaximumP-T the Cévennes micaschistsareinterpretedas so-called “vaugnerite”. Inthesouth(Fig.2), Ma, includingmagnesio-potassicplutons,the of the Velay domeemplacedbetween335-315 is intrudedbysyntectonicgranitesprecursor (Mesovariscan period). The Lower GneissUnit 40 ed (Fig.31): Ar/ 39 Ar, Caronetal.,1991). peraluminous contain 1997). They Malek, zircon, Aït U-Pb respectively on (207Pb-206Pb and ± 3and314±Ma are alsodatedat313 mantellic affi monzodiorite, with High-K magnesian (Mougeot etal.,1997). age of314±5Ma indicates aminimum U-Pb monazitedate Malek etal.,1995). A this meltingevent (Aït prograde characterof of muscovite andthe the initialpresence enclaves confi corundum paragneiss 1992). The presenceof stage ofMonteletal., the graniticcore(M3 envelope, 5 kbar in the metamorphic within 4kbar 700 °C, stable: around nity rms PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

xenoliths that record a fi rst stage of isothermal (Vitel, 1985). Cordierite may be prismatic, decompression at 700-800 °C, 8-10 kb, consistent cockade-type or mimetic overprinting previous with a source located more than 30 km deep, biotite - sillimanite assemblages. Most of the followed by a stage at 5-6 kb (Montel, 1985). In heterogeneous granites indicate mixing between view of the water-saturated conditions, it is unlikely melts of lower-crustal origin and melts from the that large quantities of granite (i.e. < 10-20%) were para- and ortho-derived host rock (Williamson et produced and extracted at this stage (Patiño Douce al., 1992). and Johnston, 1990). - a homogeneous leucocratic biotite-cordierite • The second stage of melting is characterized by granite with mainly cockade-type cordierite. Its high-temperature metamorphism in the cordierite emplacement has been dated at 301 ± 5 Ma using stability fi eld, with biotite destabilized: 760-850 °C, the U-Pb method on monazite (Mougeot et al., 4.4-6.0 kbar (stage M4 of Montel et al., 1992). 1997). Leucosomes were dated at 298 ± 8 Ma based on - a homogeneous granite with biotite and prismatic Rb-Sr whole rock isochron (Caen-Vachette et al., cordierite as a primary ferromagnesian phase, 1982), and Rb-Sr whole rock-biotite isochrons with few enclaves. The heterogeneous and yield ages between 305 and 276 Ma (Williamson homogeneous granites with prismatic cordierite, et al., 1992). An age of 301 ± 5 Ma was obtained with a high Sr content, have a mixed isotopic for the homogeneous parts of the granite using the signature between the host rocks and a lower- U-Pb monazite method (Mougeot et al., 1997). crustal origin. The deep source is considered to Therefore, this second melting stage is considered be the melting of the lower mafi c/felsic plutonic to be generally synchronous with emplacement of crust (Williamson et al., 1992). the main cordierite-bearing granites. The volume of - a leucocratic granite with cockade-type cordierite, cordierite-bearing granites generated makes a case without enclaves. The cordierite-quartz aggregates for massive partial melting at this stage, associated posdate primary biotite bearing assemblages and to destabilization of hydrous minerals. probably prismatic cordierite. • The late magmatic activity that includes: 3. The migmatite-granite domain. The various - homogeneous granite with K-feldspar granites that appear in the Velay dome defi ne a suite, porphyrocrysts and common prismatic cordierite, with 3 main granite types distinguished according basic and micaceous inclusions (the Quatre Vios to age, structure, homogeneity, mineralogy and massif) (Fig. 10d). These granites are defi ned as geochemistry: late-migmatitic and are considered to originate • A heterogeneous banded biotite granite, found from the melting of aluminous sediments at mainly on the western margin of the dome and 4.5-5.5 kbar and 750-850 C, under water- locally on the southern and eastern margin. It undersaturated conditions and have a signifi cant corresponds to the fi rst generated granite of the mafi c component (Montel et al., 1986; Montel Velay suite. Foliation trajectories are in continuity and Abdelghaffar, 1993). Ages at 274 ± 7 Ma with porphyric granites in the external rim of the (Rb/Sr whole rock, Caen Vachette et al., 1984) dome suggesting continuity between these precursor are considered to be partially reset during granites and the development of the heterogeneous Permian or Mesozoic hydrothermal event. banded biotite granite. - Stephanian leucogranites, microgranite and • A main biotite-cordierite granite, in which several aplite-pegmatite dykes, Permian rhyolites. sub-types may be distinguished, in particular Microgranite dykes have been dated at 306 ± according to the cordierite habitus (Barbey et al., 12 and 291 ± 9 Ma and a Permian hydrothermal 1999). event at 252 ± 11 and 257 ± 8 Ma (microprobe B16 to B33 n° 2 - from Volume - a heterogeneous banded granite with abundant dating of monazite, Montel et al., 2002). enclaves. Most of these enclaves represent incorporated and partly assimilated pieces of 4. The Stephanian intracontinental basin of St- the Lower Gneiss unit and precursor plutons Etienne. This basin is formed along the hanging wall originating from the host rocks, although some of the Mont Pilat extensional shear zone (Malavieille enclaves with refractory composition or granulite et al, 1990). The Mont Pilat unit, attributed to the lower facies metamorphism have a lower crustal origin gneissic unit at the scale of the French Massif Central

35 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure the inheritedstructure.Structural orientationsthen second meltingstagetendtobediscordantwith with cockade-typecordieriteproducedduringthis Critical MeltPercentage(Arzi,1978).Leucosomes of meltbeyond 30-50%,thevalue oftheRheological breakdown ofbiotiteisresponsiblefortheproduction although K-feldsparaggregates arepreserved. The that areinequilibriumwiththegraniteeutecticpoint, plagioclase aggregates arereplacedbyassemblages accompanied bythegrowth ofsillimanite. Quartz- existing foliation. The breakdown ofmuscovite isthen fi detail inthiszonebyDallainetal.(1999). Anatexis annealing tomeltingprocesshasbeenstudiedin textural evolution inthetransitionfromsubsolidus The progressive development oftheanatexis and orthogneiss. “vaugnerite”) areintrusive andboudinatedwithinthe melanosome. Magnesio-potassicdykes (theso-called the quartzofeldspathicaggregates andbiotite-rich marked bytheelongationandcrystallizationof type ofthegraniteprotolithwhilefoliationis phenocrists ofK-feldsparattesttheporphyric bearing graniticpatches(ColorPlate2,B).Large inherited foliationandlocallydiscordantcordierite- the segregation ofcordierite-freemeltsalongthemain granite-migmatite dome. The meltingismarked by constitutes analmostcontinuousrimaroundthe Velay Ma (Rb-Srwholerock,R’KhaChahametal.,1990), 9 from peraluminousporphyricgranitedatedat528± An augenorthogneiss(the“Arc deFix”),originating within theorthogneissofLower GneissicUnit. Stop D4.1shows theincipientstageofmelting N102, Roadcut. Meyras, Roadfrom LePuy-en-Velay to Aubenas, Stop D4.1: B. Stopdescription (3- 5Kbarand700-780°C,Gardienetal.,1997). pressure -hightemperaturemetamorphicconditions was coeval withtheprogressive development oflow Ma (39Ar/40Ar, Malavieille etal.,1990). This event with atop-northextension datedbetween322and290 criteria, observed atdifferent scales,arecompatible whole rock,Caen-Vachette etal.,1984).Shear plane andhave beendatedat322±9Ma(Rb/Sr outcrop moreorlessparalleltothismainfoliation stretching lineation.Numerousleucograniticpods north-dipping foliationplanebearinganorth-south orthogneisses andamphibolites. This unithasagently consists ofaluminousmicaschists,metapelites, rst develops withtheresorptionofquartzalong (Fig. 28,29) randomly oriented. increases, withfoldsbecomingabundant and become morevaried astheleucosomeproportion attributed toS3(Barraudetal.,2003). saddle reefandaxialplanesofthefoldingthatis melts: cordierite-freeleucosomesaccumulatein that playanactive roleinthesegregation ofanatectic Plate 2,C). The outcropischaracterizedbyopenfolds (named regionally S2)andpolyphasedfolding(Color tectonic evolution thatresultedinacompositefoliation microstructure developed duringthepre-migmatitic Numerous resistersfromrefractorylayerspreserve 2003). (Macaudière etal.,1992)andfolding(Barraud of earlymeltingiscontrolledbyfoliationanisotropy refractory quatz-richandcalciclayers) The location intrusive insediments(pelitesandargillites, including metagranite observed atthestop4.1.isoriginally within paragneissoftheLower GneissicUnit. The Stop D4.1shows the incipientstageofmelting Aubenas, N102,River banksofthe Ardèche river. Pont deBayzan,Roadfrom LePuy-en-Velay to Stop D4.2: the earlyphaseofmeltingto endofthemagmatic presence ofameltphase.Cordieriteisformedfrom cordierite isformedattheexpense ofbiotite,inthe (Color Plate2,D).Detailedobservation indicatesthat petrographic typeofthe Velay migmatite-granitedome cockade-type cordierite,thatrepresentsoneofthe Stop D4.4shows anhololeucocraticgranite,with D578, Road-cut. Volane river, Roadfrom Aubenas toMezilhac, Stop D4.4: granite andmigmatitesyieldaU-Pbageat289 the NorthandPradesbasininSouth. Apatites in found intheconglomeratesofStephanianbasin Stephanian asbouldersofgranitesandgneissesare Velay granite-migmatitedomeoccurredduringthe migmatitic paragneiss. The exhumation ofthe sandstone over alteredgraniteandbiotite-sillimanite Stop D4.3shows theunconformityofMesozoic Ucel, Roadfrom Aubenas toMezilhac,Road-cut. Stop D4.3: this unconformity. fresh roadcutprovides aspectacularillustrationof the Trias sandstoneandconglomerate. A recentand regional unconformityischaracterizedatthebaseof of the Vealy region (Mougeotetal.,1997).Finally, a that isinterpretedasacoolingageduringtheuplift ± 5Ma PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

evolution of the Velay granite. However some garnets Stop D4.7: are present in cordierite nodules, indicating that, in Moulin de Sezigneux, Road from St Chamond to that area, melting started in the garnet stability fi eld. Le Bessat, D2, Road cut. The cordierite-andalusite-bearing micaschist of the Stop D4.5: Pilat Unit, seen at stop D4.7, displays extensional Volane river, Road from Aubenas to Mezilhac, tectonics and HT-LP metamorphism within the Pilat D578, Road-cut. series (Lower Gneissic Unit). This outcrop offers a Stop D4.5 shows a late-migmatitic homogeneous good example of a low-pressure metamorphic unit, granite and relations with migmatitic gneisses and with micaschists and paragneisses intruded by syn- heterogeneous cordierite-bearing granite. In the upper tectonic pegmatite dykes and pods. The main foliation part of the outcrop, a late-migmatitic granite, the plane is gently dipping to the North and shear criteria Quatre-Vios granite, is intruding the heterogeneous are well marked mainly around the pegmatitic pods banded granite: it is a coarse grained peraluminous indicating top to the North extensional tectonics. In granite with prismatic cordierite and frequently the metamorphic rocks, the common mineralogy oriented feldspar phenocrysts. It contains abundant is: quartz + feldspars + biotite + andalusite and /or mafi c microgranular enclaves and surmicaceous cordierite ± muscovite. enclaves including biotite, garnet, cordierite, sillimanite, hercynite, ilmenite and rare plagioclase. D4.8: Moulin de Sezigneux, Road from St Chamond This unusual mineralogy (absence of quartz and to Le Bessat, D2, River banks. potash feldspar) and the corresponding chemical Structure and metamorphism of the orthogneiss composition indicate that these enclaves are restites. of the Lower Gneissic Unit are illustrated at stop P-T conditions calculated from this mineralogy D4.8. Ultramylonite and pseudotachylite textures yielded water-undersaturated conditions estimated at are developed within the orthogneiss and S-C-C’ 4.5-5.5 kbar and 750-850 C. The mafi c microgranular structures indicate top to the North shear criteria (biotite+plagioclase) enclaves correspond to frozen compatible with extensional tectonics. Shear bands blobs of mafi c magma. Locally, another type of late- are underlined by syntectonic recrystallized biotites migmatitic fi ne-grained granite, with typical acicular dated around 320-300 Ma (40Ar/39Ar). In the highly biotite and devoid of enclaves, crosscuts the Quatre- sheared parts of the outcrop ultramylonite bands and Vios granite. pseudotachylites are observable. The main foliation In the lower part of the outcrop, another dyke of plane bears a north-south oriented stretching lineation. late-migmatitic granite is intrusive within migmatitic The metamorphic mineralogy is characterized by the orthogneiss in which the second stage of melting is association of quartz + feldspars + biotite + muscovite. well marked by the biotite breakdown that produces Rare small-sized cordierites can also be observed. Fe-rich garnet and cordierite. This zone is itself enclosed within the heterogeneous banded granite that End of the 4th day. Overnight stay in St Etienne contains a lot of enclaves of migmatitic paragneiss. DAY 5 Stop D4.6: High to ultra-high pressure metamorphism and Mont Gerbier-de-Jonc, Road from Mezilhac to Le arc magmatism: records of subduction processes Puy-en-Velay, D378, Sight as seen from the road. in the French Massif Central The Velay volcanism is made up of an eastern chain of Mio-Pliocene basaltic to phonolitic volcanoes and The main goal of Day 5 is to present the geological a western Plio-Quaternary basaltic plateau (Mergoil and petrological records of subduction processes Volume n° 2 - from B16 to B33 n° 2 - from Volume et al., 1993). The road to Le Puy-en-Velay shows in the eastern Massif Central that preceeded the nice sightseeing of this phonolitic chain that extends development of the Velay migmatite-granite dome over more than 55 km with more than 180 points of illustrated during Day 4. These records are: remnants extrusion, emplaced between 14 and 6 Ma. of high to ultra-high pressure metamorphism in both The Mont Gerbier-de-Jonc is known as the spring crustal and mantle-derived lithologies in the Mont du of the Loire river. It is a phonolitic protrusion that Lyonnais unit, a partially preserved back-arc derived displays a rough prismatic jointing. ophiolitic sequence, the Brévenne unit.

37 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure

Figure 32 - Geological maps of the eastern margin of the Massif Central through time showing the progressive edification of the belt. The geodynamic cartoons show the possible position of the Monts du Lyonnais eclogites during the four critical periods illustrated (a to d). PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

A. Geological setting lavas that, fi nally, are overlain by siltstones with 1. Eclogites and garnet peridotite from The Monts pyroclastic intercalations (Milési et Lescuyer, 1989; du Lyonnais unit (Fig. 32a) Feybesse et al., 1996). A prograde greenschist to The Monts du Lyonnais unit belongs to the upper lower amphibolite facies metamorphism is recorded gneissic unit (Lardeaux, 1989; Ledru et al., 1994a). (Peterlongo, 1960; Fonteilles, 1968; Piboule et al., It comprises metasediments, orthogneisses (with 1982; Feybesse et al., 1988). The Brévenne ophiolite protoliths of Ordovician age), leptynites (i.e. meta underwent a polyphase deformation. An early event, rhyolites), amphibolites and minor marbles. This unit well developed in the northern part of the unit, is also contains lenticular relics of either crustal (mafi c characterized by a NW-SE stretching lineation with and acid granulites, eclogites, Lasnier, 1968; Coffrant top to the NW shearing (Leloix et al., 1999). During and Piboule,1971; Dufour,1985; Dufour et al.,1985; the second event, the ophiolitic unit is overthrusting Lardeaux et al.,1989) or mantle origin (garnet and / the Monts du Lyonnais along a dextral transpressional or spinel bearing peridotites, Gardien et al., 1988, zone in which syntectonic granites emplaced between 1990). Eclogites outcrop, in close association with 340 and 350 Ma (Fig. 32c, Gay et al, 1981; Feybesse garnet-bearing peridotites, in the southernmost part et al., 1988; Costa et al., 1993). Subsequently, of the Monts du Lyonnais unit. Eclogites and related monzonitic granites of Namurian- Westphalian age garnet amphibolites also occur in a similar structural and a contact metamorphism aureole postdate this situation farther north (in the Morvan unit, Godard, tectonics (Delfour, 1989). 1990) and also southeast of the Monts du Lyonnais unit (in the Maclas-Tournon area, Gardien and 3. The development of the Velay migmatite granite Lardeaux, 1991). In the Monts du Lyonnais unit, three dome and the collapse of the orogen (Fig. 32b) ductile strain patterns were distinguished (Lardeaux The tectonic evolution of the eastern Massif Central and Dufour, 1987; Feybesse et al., 1996) and related is achieved during Westphalian and Stephanian. to high pressure and medium pressure metamorphic The formation of the Velay dome, coeval with the conditions: activation of crustal-scale detachements, potentially • The relictual high-pressure structures corresponds to fl ow of a partially molten crustal layer • A main deformation imprint, contemporaneous with in response to gravitational collapse. amphibolite facies conditions, corresponds to a NW -SE crustal shortening with a fi nite NNE-SSW B. Stop description (Fig. 28, 29) stretching direction (Fig. 32b) Stop D5.1: • A deformation event developed under a transpressional regime dated between 335 and 350 The Bois des Feuilles, Road from St Symphorien- Ma (Rb/Sr whole rock, Gay et al., 1981; 40Ar/39Ar, sur-Coise to Rive de Gier, D2. Costa et al., 1993) which is correlated to the main This outcrop consists of garnet bearing peridotites deformation within the Brévenne ophiolite in and eclogites occuring as boudins within garnet relation with its overthrusting. (Fig. 32c) sillimanite paragneisses. The coesite-bearing With respect to this transpressive strain pattern, in eclogite occurs in the southern part of the Monts the southern part of the Monts du Lyonnais unit, du Lyonnais unit, near St Joseph in the Bozançon the eclogites outcrop exclusively in the strongly valley (1/50.000 geological map “ St Symphorien folded domains where they behave as rigid bodies Sur Coise “, Feybesse et al., 1996) in association with in a deformed ductile matrix. We never found any “common” eclogites and serpentinites. In the whole eclogitic body within the shear zones. area, eclogites are preserved in low-strain lenses 2. The uppermost part of the magmatic arc: the (meter scale boudins) wrapped by amphibolites or Volume n° 2 - from B16 to B33 n° 2 - from Volume Brévenne ophiolite (Fig. 32b) amphibolite facies paragneisses. For practical reasons The Devonian Brévenne ophiolitic unit consists of an (diffi cult access), we shall observe only garnet- association of metabasalts and metarhyolites together peridotites and “common eclogites”. with intrusive intruded by trondhjemitic bodies Well-preserved peridotites occur as metric to (Peterlongo, 1970; Piboule et al., 1982,1983). The decametric scale bodies within the paragneisses. In ophiolitic unit was initially emplaced in a submarine the less retrogressed samples, garnets in equilibrium environment (Pin et al., 1982; Delfour et al., 1989). with olivine, clinopyroxenes and orthopyroxenes can These intercalations are cut and overlain by intrusive be observed. Frequently, garnets contain inclusions gabbros and dolerites and by submarine basaltic of spinels and pyroxenes, while in some samples

39 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure Piboule, 1971;Coffrant, 1974;Blanc,1981;Piboule As pointedoutbyvarious authors(Coffrant and • • • can bedistinguished: Petrographically, threetypes ofeclogitefacies rocks bearing amphiboliteswithrelicsofeclogiticminerals. of thecases,mafic boudinsarecomposedofgarnet conditions, andin80% amphibolite facies under granuliteand strongly retrogressed Lyonnais unitare the Montsdu the eclogitesfrom As ageneralrule, temperature decrease. by bothpressureand decrease followed isothermal pressure fi evolution characterized document aretrograde transformations These mineralogical chlorite andserpentine. talc, amphibole, are transformedinto olivine andpyroxenes the porphyroclastsof orthopyroxene while replaced byspineland garnets arepartly In many samples, (Gardien etal.,1990). temperature increase to amoderate increase associated a strongpressure T pathinvolving metamorphic P- during aprograde lherzolite facies from spineltogarnet indicate anevolution These microstructures by coronasofgarnet. spinels arereplaced rst byastrong facies conditions. textures) onlypartlyre-equilibrated undereclogite coarse-grained meta-gabbros(withcoronitic eclogites fi fi ne-grained light-colored,oftenkyanite-bearing ne-grained dark-coloredkyanite-free eclogites and titaniumrich(Fe0+Fe and Briand,1985),dark-colouredeclogitesareiron contents (Al while light-colouredeclogiteshave higheraluminium > 2%), Al-poor metabasalts(Al that theseeclogitescanberegarded asthe variably (Blanc, 1981;PibouleandBriand,1985)have shown (TiO magnesium values but lower titaniumcontents Figure 33-P-TpathoftheMontsduLyonnais coesite- 2 <1,3%).Detailedgeochemicalinvestigations bearing eclogite(seedetailedlegendofthereactions 2 O 3 near17-20%),andhigheraverage 2 O in Lardeauxetal.,2001). 3 near13%and TiO 2 O 3 near13-15%), 2 PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

fractionated members of a volcanic tholeiitic suite. • Clinopyroxene + orthopyroxene + plagioclase ± amphibole + ilmenite, In the less retrogressed samples, the following mineral • Garnet + clinopyroxene + othopyroxene + assemblages, representing the relicts of eclogite facies plagioclase ± amphibole + ilmenite. metamorphism, are recognized in the dark (1-2) and In acid granulites (Dufour, 1982; Lardeaux et al., light (3-4) eclogites from the Monts du Lyonnais (Fig. 1989), the common mineralogy consists of quartz 33): + plagioclase + K-feldspar + garnet + sillimanite ± • Garnet - omphacite - quartz - zoisite - rutile - apatite spinel ± biotite. Kornerupine - bearing granulites have - sulfi des, been also locally recognized in this outcrop (Lardeaux • Garnet - omphacite - quartz - zoisite - colourless et al., 1989). amphibole - rutile - sulfi des, In this northern part of the Mont du Lyonnais unit, • Garnet - omphacite - quartz (or coesite) - zoisite the metamorphic imprint is typical for Intermediate - kyanite - colorless amphibole - rutile, Pressure granulite facies and there is no trace of • Garnet - omphacite - quartz - zoisite - kyanite - eclogitic high-pressure facies metamorphism. phengite - rutile. Coesite and quartz pseudomorphs after coesite Stop D5.3: were exclusively detected as inclusions in two The Yzeron quarry, Road from Ste-Foy- garnet grains within one sample of kyanite-bearing l’Argentière to Craponne, D489. eclogite (Color Plate 2, E, F). SiO2 polymorphs were Stop D5.3 shows the migmatitic orthogneisses distinguished optically, i.e. coesite was fi rst positively from the northern Monts du Lyonnais. These identifi ed relative to quartz by its higher refractive rocks are metamorphosed and strongly foliated index, and then confi rmed by Raman spectroscopy, under amphibolite facies conditions. Their typical by observation of the characteristics Raman lines mineralogy is an association of quartz + plagioclase 177, 271, 521 cm-1. Only two coesite grains are + K-feldspar + biotite ± sillimanite. Muscovite preserved as relics and, generally, coesite is otherwise and chlorite are developed during retrogression. completely transformed into polycrystalline radial In the Yzeron quarry, superposed fold systems quartz (palisade texture) or into polygonal quartz have been described in relation with progressive surrounded by radiating cracks. The extremely rare deformation under amphibolite and greenschist preservation of coesite in the Monts du Lyonnais facies metamorphic conditions. The main foliation eclogites is clearly the result of the high temperature observed in the orthogneisses is folded and / or conditions (near 750°C, see details in Dufour et reworked in the ductile strike-slip shear zones related al., 1985 and Mercier et al., 1991) reached during to the development of a regional scale transpressive decompression as well as the consequence of fl uid regime. infl ux (hydration) during retrogression. Indeed, the The northern Monts du Lyonnais area, with kinetics of the coesite ---> quartz transformation are intermediate–pressure granulite and amphibolite strongly temperature and fl uid dependent (Gillet et facies metamorphic rocks can be interpreted as al., 1984; Van der Molen and Van Roermund, 1986; remnants of the upper overriding continental crust on Hacker and Peacock, 1995; Liou and Zhang, 1996) which the magmatic arc and the Brévenne back-arc and consequently in the studied area, coesite has been were emplaced. In this model, the southern part of the almost entirely transformed into quartz. Monts du Lyonnais unit corresponds to a subduction complex (remnant of subduction channel) located on Stop D5.2: the top of the lower plate (i.e. Pilat – Velay units). St-André-la-Côte, Road from St-André-en-Haut to Mornant. Stop D5.4: B16 to B33 n° 2 - from Volume Migmatites and granulitic rocks outcrop in the Brévenne valley, road cut: bimodal magmatic northern part of the Monts du Lyonnais. Near St- sequence. André-la-Côte village, mafi c and acid granulite Stop D5.4 shows different lithologies, like facies rocks are well exposed. In mafi c granulites the metabasalts, metarhyolites, metapyroclastites and following metamorphic assemblages are described metasediments, typical for the Brévenne ophiolitic (Dufour, 1985; Dufour et al., 1985): unit. All the lithologies are metamorphosed under • Garnet + plagioclase + orthopyroxene + ilmenite, greenschist facies conditions. In mafi c lithologies, the • Garnet + plagioclase + amphibole + ilmenite, common mineralogy corresponds to an association of

41 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure et l’anticlinoriumdel’Iglesiente(Sardaigne). Thèse : lesnappesde la MontagneNoire(France) hercyniens microtectonique comparéededeuxdomaines Arthaud, F. (1970).Etudetectoniqueet Paris 317,1441-1447. détermination deleurcinématique. chevauchements varisques danslesCévennes et des mylonitesschisteuses:cartographie Arnaud, F. andBurg, J.P. (1993).Microstructures 286, 351pp. Polytechnique deLorraine,DocumentsduBRGM, schisteuses. Thèse 3èmecycle, InstitutNational déformation dansleszonesdecisaillement français). Microstructuresetmécanismesde varisque :lesCévennes centrales(MassifCentral barométrique d’unsystèmedechevauchements Arnaud, F. (1997). Analyse structuraleetthermo- Acad. Sci.Paris 321,959-966. implications pourlemétamorphismeardéchois. : une vaugnérite del’Ardèche(Massifcentralfrançais) Bertrand, J.M.(1995).Desxénolites àcorindondans Ait Malek,H.,Gasquet,D.,Marignac,C.and l’INPL, Univ. Nancy, 297pp. de l’anti-Atlasoccidental(Maroc). Thèse doctoratde exemples duSE Velay (Massifcentralfrançais)et géochronologie U/Pbd’associationsacide-basiques: Ait Malek,H.(1997).Pétrologie,Géochimieet 184. of partiallymeltedrocks. Arzi, A.A. (1978).Criticalphenomenaintherheology References cited preparing thisguidebook. provided agreathelpduringthefi of thisguidebook.MrsS.MatratandD.Quiniou O. Monodisthanked forhisreview ofthefi Acknowledgements End ofthe5 upper plateofasubductionsystem. Devonian, inaback-arcbasindeveloped uponthe origin oftheBrévenne ophioliticsequence,during Recent geochemicalinvestigations supportthe Monts duLyonnais unitataround350– 340Ma. regional transpressive regime whichaffects alsothe vertical axialplanes. These foldsarerelatedtothe involved intoaregional scalefoldsystemwithsub- The different lithologies arealsodeformedand ± quartz. plagioclase +actinolitechloritesphene th dayinLyon (airportandrailway station) Tectonophysics C. R. Acad. Sci. nal stagesfor 44,173- rst draft rst ± calcite C. R. sédimentaires post-hercyniens, 26 Géologie del’EuropeduPrécambrienauxbassins hercynienne. (J.CognéJ.andM.Slansky M.Eds.), et saplacedansledéveloppement delachaîne de l’orogenèsevarisque dansl’OuestdelaFrance Autran, A. andCogné,J.(1980).La zone interne p. 1305-1320. Appalachians andtheUrals. Africa: resultofrightlateralshearzonebetween strike slipfaulting insouthernEuropeandnorthern Arthaud F. andMatteP. (1977) -LatePaleozoic d’Etat, Univ. Montpellier, France,175pp. Boutin, R.andMontigny, R.(1993).Datation nord-ouest. : unchevauchement detypehimalayenvers l’ouest- Bouchez, J.L.,andJover, O.(1986). LeMassifCentral cycle, Univ. Lyon 1,152p. migmatites. P. (2003). Analog modelsofmelt-fl ow infolding Barraud, J.,Gardien, V., Allemand, P. andGrandjean, Petrology 40,1425-1441. Velay granitecomplex (Massif Central,France emplacement ofcrustalgraniticmagmas:the growth texture andtheconditionsofgenesis J., Gasquet,D.andJabbori,J.(1999).Cordierite Barbey, P., Marignac,C.,Montel,J.M.,Macaudière, XCIX, 90-111. Int., Coll.C6,Paris 1980.Ann.Soc.géol. Nord minéralogique etgéochimique. Thèse Doctorat3 des montsduLyonnais. Etudepétrographique, Blanc, D.(1981).Lesrochesbasiquesetultrabasiques 777. central français).C.R. Acad. Sci.Paris 329,771- sismique réfl exion verticale (GéoFrance3D:Massif et despièges associésdanslachaînevarisque : paléochamps hydrothermaux As-Sb d’échellecrustale P., Milési,J.P. andRoigJ.Y. (1999)-Imageriedes Bitri, A., Truffert, C.,Bellot,J.P., Bouchot, V., Ledru, zone. of granite:theexemple oftheSoutharmoricanshear Orthogneiss myloniteandnoncoaxialdeformation Berthé, D.,Choukroune,PandJegouzo, P. (1978). français. tectono-metamorphic event inwesternMassifCentral J.L. (1977)-Radiometricevidence foran Acadian Bernard-Griffi 40 pp. Massif Centralfrançais.Masterthesis,Univ. Orléans, de migmatitesetgranitoïdestardi-hercyniens du de datationàlamicrosondeélectroniquemonazite Be Mezème,E.(2002). Application delaméthode J. Struc.Geol. Contrib. C. R. Acad. Sci.Paris 302,675-680. J. Struct.Geol ths, J.,CantagrelJ.M.andDuthou Mineral. Petrol 1,31-42. . inpress. Geol. Soc. Am. Bull . 61,199-212. ème Cong.Géol. , Lille . 88, ). J. ème PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

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45 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure thickened crust. An Variscan tectonicevolution bythinningofanearlier Maluski, H.,Costa,S.andEchlerH.(1991).Late Geodinamica Acta mais unanticlinalpost-nappeàcœuranatectique. n’est pasun“ metamorphic corecomplex ”extensif La zoneaxialehercynienne delaMontagneNoire Matte, P., Lancelot,J-R.andMattauer, M.(1998). 1128. Armorica microplate : areview. (480-290 Ma)andthetectonicdefi nition ofthe Matte, P. (2001). The Variscan collageandorogeny 329-374. Turland M.(1993).Le Velay. Sonvolcanisme etles Mergoil, J.,Boivin, P., Blès,J.L.,Cantagrel,J.M.and 010 DEX(fi contrat MAIM-0030-F(D).Rapp.BRGM89DAM their enrichedzonesinFranceandPortugal.CEE markers ofhigh-grademassive sulphidedepositsof Central, France).Project:identifi Brévenne volcano-sedimentary belt(easternMassif Zn-Cu-Ba massive sulphidedepositandtheDevonian Milési, J.P. andLescuyerJ.L.(1989). The Chessy 10, 131-140. Noire, southernMassifcentral,France. paths ofthefrenchMassifCentraleclogites. On thetectonicsignifi cance oftheretromorphicP-T Mercier, L.,Lardeaux,J.M.andDavy, P. (1991). 287-304. for thevariscan beltofEurope. Matte, P. (1991). Tectonics and platetectonicsmodel dextre. bassin pull-apartenrelationavec undécrochement extension tardi-hercynienne généralisée:c’estun stéphanien deSt-Etiennenerésultepasd’une Mattauer, M.andMatte,P. (1998).Lebassin 315. Montagne Noire. étirement subhorizontaldansleversant Suddela Plissements hercyniens synschisteuxpost-nappeet Mattauer, M.,LaurentP. andMatteP. (1996). 306, 671-676. hercynienne duMassiffrançais. une nouvelle analogie entrel’Himalayaetlachaîne Failles normalesductilesetgrandschevauchements : Mattauer, M.,Brunel,M.andMatte,P. (1988). Carboniferous basin. Pilat extensional shearzoneandStEtienneupper Variscan crustintheFrenchMassifCentral:Mont and Gardien, V. (1990).Collapseofthethickened Malavieille, J.,Guihot,P., Costa,S.,Lardeaux,J.M., Geodinamica Acta nal report) C. R. Acad. Sci.Paris. 322,309- 11,13-22. 40 Tectonophysics Ar/ 39 11,23-31. Ar studyoftheMontagne C. R. Acad. Sci.Paris cation ofdiagnostic Terra Nova Tectonophysics 177,139-149. Lithos Tectonics 13,122- 126, 26, Faure, M.andRoig,J.-Y. (2000). Monié, P., Respaut,J.-P., Brichaud,S.,Bouchot, V., Géologie delaFrance formations associées,noticedelacarteà1/100000. and aluminousgranulites. implications fortheoriginofperaluminousgranitoids equilibria andmeltproductivity inthepelitic system: Patiño Douce, A.E. andJohnston, A.D. (1990).Phase continental shearzones. J-P. (1977).Geologicalaspectsofdeformationin Nicolas, A., Bouchez,J-L.Blaise,J.andPoirier, Eur. J. Mineral of the Velay anatecticdome(FrenchMassifCentral). C. (1997).U-Pbchronologyonaccessoryminerals Mougeot, R.,Respaut,J.P., Ledru,P. andMarignac, (French MassifCentral).J. Metam.Geol. the Hercynian low-P, high-T Velay anantecticdome M. (1992). Thermobarometry andgranitegenesis : Montel, J.M.,Marignac,C.,Barbey, P. andPichavant, France 1,15-20. Velay (MassifCentralFrançais).Géologie dela C. andCeret,K.(2002). Age desmicrogranitesdu Montel, J.M.,Bouloton,J., Veschambre, M.,Pellier, et géochimiques. Central): principalescaractéristiquespétrographiques granites tardi-migmatitiquesdu Velay (Massif Montel, J.M.and Abdelghaffar, R.(1993).Les Sci. Paris 302,647-652. genèse desgranitestardi-migmatitiques. du Velay (MassifCentralfrançais)etconditionsde (1986). Thermobarométrie dudomaineanatectique Montel, J.M., Weber, C., Barbey, P. andPichavant, M. 301, 615-620. profonde tardihercynienne. français). Indicationssurl’évolution delacroute les doléritesduPeyron, en Velay (MassifCentral Montel, J.M.,1985.Xénolithesperalumineuxdans Minières, Orléans. BRGM 297,BureaudeRecherchesGéologiqueset in Europe”,(V. Bouchot,Ed.),pp.77-79.Document Massif Central,France).In:“Orogenicgolddeposits the Cévennes andChâtaigneraiedistricts(Southern geochronology appliedto Au-W-Sb metallogenesisin Central Français). métamorphique delaBrévenne (Rhône,Massif variolitique etmatricebasiquedanslasérie Peterlongo, J.M.(1970).Pillows-lavas àbordure Fac. Sci.Univ. Clermont-Ferrand4,(1),187 monts duLyonnais (MassifCentralfrançais).Ann. Peterlongo, J.M.(1960).Lesterrainscristallinsdes 107, 202-218. . 9,141-156. Géologie delaFrance C.R. Acad. Sci.Paris 2,190-194 3,3-96. Tectonophysics Contrib. C. R. Acad. Sci.Paris 40 Ar/ Mineral. Petrol 39 42,55-73. 1,15-28. Ar andU-Pb 10,1-15. C. R. Acad. . PALEOZOIC OROGENIES IN THE FRENCH MASSIF CENTRAL A CROSS SECTION FROM BÈZIERS TO LYON B22

Piboule, M., Briand, B. and Beurrier, M. (1982). bimodal suite in the Hercynian Belt: Nd isotope and Géochimie de quelques granites albitiques dévoniens trace element evidence for a subduction-related rift de l’Est du Massif Central (France). Neues Jb. Miner. origin of the Late Devonian Brévenne metavolcanics, Abh., 143, 279-308. Massif Central (France). Contrib Mineral Petrol 129, Piboule, M., Beurrier, M., Briand, B. and Lacroix, P. 222-238. (1983). Les trondhjemites de Chindo et de St-Veran Quénardel, J.M. and Rolin, P. (1984). Paleozoic et le magmatisme kératophyrique associé. Pétrologie evolution of the Plateau d’Aigurande (N-W. Massif et cadre géostructural de ce magmatisme Dévono- Central, France). In “Variscan tectonics of the North Dinantien. Géologie de la France I, 2, (1-2), 55-72 Atlantic region” (D. Hutton and D. Sanderson, Eds.), Piboule, M. and Briand, B. (1985). Geochemistry of pp. 63-77, Geol. Soc. London Spec. pub, 14. eclogites and associated rocks of the southeastern area R’Kha Chaham, K., Couturié, J.P., Duthou, J.L., of the French Massif Central: origin of the protoliths. Fernandez, A. and Vitel, G. (1990). L’orthogneiss Chem. Geol. 50, 189-199 oeillé de l’Arc de Fix : un nouveau témoin d’âge Pin, C. (1979). Géochronologie U-Pb et cambrien d’un magmatisme hyper alumineux dans le microtectonique des séries métamorphiques anté- Massif Central français. C. R. Acad. Sci. Paris 311, stéphaniennes de l’Aubrac et de la région de 845-850. Marvejols (Massif Central). Thèse 3° cycle, Univ. Robardet, M., Verniers, J., Feist R. and Paris, F. Montpellier, France, 220pp. (1994). Le Paléozoïque anté-varisque de France, Pin, C. (1981). Old inherited zircons in two contexte paléogéographique et géodynamique. Géol. synkinematic variscan granitoids: the “granite du de la France 3, 3-31. Pinet” and the “orthogneiss de Marvejols” (southern Robardet, M. (2003). The Armorica ‘microplate’: French Massif Central). N. Jb. Miner. Abh. 142, 27- fact or fi ction? Critical review of the concept 48. and contradictory palaeobiogeographical data. Pin, C. (1990). Variscan oceans: ages, origins and Palaeogeography, Palaeoclimatology, Palaeoecology geodynamic implications inferred from geochemical 195, 125-148. and radiometric data. Tectonophysics 177, 215-227. Roig, J-Y. and Faure M. (2000). La tectonique Pin, C. and Lancelot, J. (1978). Un exemple de cisaillante polyphasée du Sud-Limousin (Massif magmatisme cambrien dans le Massif Central : les Central français) et son interprétation dans un modèle métadiorites quartzites intrusives dans la série du Lot. d’évolution polycyclique de la chaîne hercynienne. Bull. Soc. Géol. France 7, 203-208. Bull. Soc. Géol. Fr. 171, 295-307. Pin, C. and Lancelot, J. (1982). U-Pb dating of an Roig, J-Y., Faure, M. and Truffert, C. (1998). Folding early paleozoïc bimodal magmatism in the French and granite emplacement inferred from structural, Massif Central and of its further metamorphic strain, TEM, and gravimetric analyses: the case study evolution. Contrib. Mineral Petrol, 79, 1-12. of the Tulle antiform, SW French Massif Central. J. Pin, C., Dupuy, C. and Peterlongo, JM. (1982). Struct. Geol. 20, 1169-1189. Répartition des terres rares dans les roches volcaniques Sider, J-M. and Ohnenstetter, M. (1986). Field and basiques dévono-dinantiennes du nord-est du Massif petrological evidence forfor the development for central. Bull. Soc. Géol. Fr. 7, 669-676. an ensialic marginal basin related to the Hercynian Pin, C. and Vielzeuf, D. (1983). Granulites and orogeny in the Massif Central, France. Geol. related rocks in Variscan median Europe: a dualistic Rundschau 75, 421-443. interpretation. Tectonophysics 93, 47-74. Soula, J.C., Debat, P., Brusset, S., Bessière, G., Pin, C. and Duthou, J.L. (1990). Sources of Hercynian Christophoul, F. and Déramond, J. (2001). Thrust granitoids from the French Massif Central: inferences related, diapiric and extensional doming in a frontal from Nd isotopes and consequences for crustal orogenic wedge: example of the Montagne Noire, B16 to B33 n° 2 - from Volume evolution. Chemical Geology 83, 281-296. southern French Hercynian Belt. J. Struct. Geol. 23, Pin, C. and Marini, F. (1993). Early Ordovician 1677-1699. continental break-up in Variscan Europe: Nd-SR Van den Driessche J. and Brun, J-P. (1991-92). isotope and trace element evidence for bimodal Tectonic evolution of the Montagne Noire (French igneous associations of the southern Massif Central, Massif Central): a model of extensional gneiss dome. France. Lithos 29, 177-196. Geodinamica Acta 5, 85-99. Pin, C and Paquette, JL (1998). A mantle-derived Vanderhaeghe, O., Burg, J.P. and Teyssier, C. (1999).

47 - B22 Volume n° 2 - from B16 to B33 B22 - B22 Leader: M.Faure The pressurepathofsoildinclusionsinminerals:the Van derMolen,I.and Van Roermund,H.L.M.(1986) 451-472. melting andfl ow oforogens. Vanderhaeghe, O.and Teyssier, C.(2001).Partial London and S.D. Willett (Eds.)181-204, fl “Exhumation processses:normalfaulting, ductile Canadian CordilleraandFrench Variscides. Exhumation ofmigmatitesintwo collapsedorogens: ow anderosion”U.Ring,M.T. Brandon,G.S.Lister , SpecialPublications,154, Tectonophysics Geological Society, 342, In: Royal Soc.Edinburgh Velay granitecomplex, MassifCentral,France. underplating andgranitegenesis:anexample fromthe (1992). The relationshipbetweencrustalmagmatic Williamson, B.J.,Downes, H.and Thirlwall, M.F. R. Acad. Sci.Paris 300,407-412. amphibolite danslesenclaves basiquesdu Velay Vitel, G.(1985).Latransitionfaciès granulitefaciès 19, 317-324 retention ofcoesiteinclusionsduringuplift. , Earth Sciences 83,235-245. Trans. Lithos . C. Back Cover: fi eld trip itinerary FIELD TRIP MAP INTERNATIONAL GEOLOGICAL CONGRESS nd 32

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