Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) has been selected in the 2 909 910 axis orientation patterns confirm the greenschist facies conditions c This discussion paper is/has beenPlease under refer review to for the the corresponding journal final Solid paper Earth in (SE). SE if available. Università degli Studi di Catania, Dipartimento di Scienze Biologiche, central-eastern part of thefrom massif to the constrain earliest themylonitic ones sequence foliation (plastic of (Hercynian regime), the up in structural totypical age), features recent ones, of almost consisting semibrittle of totally variousa to sets obliterated compressive of brittle by veins thin-skinned regime. a thrustingthe The stage pervasive Alpine developed former Orogeny, interested during ductile by thefrom a evolution Apennine second compressive was phase brittle followed to of stage,exhumation consistent by process extensional with causing the the tectonics. activation switching ofdisarticulated This regional previous scale last mylonitic normal faults, microstructures. stage whichcollected A partly accompanied and suite of analyzed the oriented tothe final specimens field. complete were Quartz the deformationalof history the already former recognizedMicrostructural ductile investigations in highlighted exhumation the stage progressivebrittle-type development with from structures, a plastic- allowing to dominanthistory, to and top-to-NE constrain to establish sense each the relative of stepand timing subsequent shear. of of the normal the stress faulting. field multistageexhumation variation of Obtained exhumation causing this results thrusting sector support since the a opening continue of compressional Tyrrhenian basin (10 Ma). 1 Introduction Crustal-scale shear zonesevolve are over commonly a rooted considerablemicrostructures, in period the thus of middle time potentially to exhibiting becoming a lower a complex crust. variety good They of tool fault-rocks to unraveling the changes Abstract Mylonitic rocks involved withinthe a polyphase Aspromonte crustal-scale Massif shearand (Calabria, micro-structural zone, evolution Italy), cropping (from ductile- has out toexhumation in been brittle-type trajectory. deformation) investigated occurred A during to relatively small reveal area the (about meso- 4 km Geologiche e Ambientali, Corso Italia 57, 95129 Catania,Received: Italy 30 December 2014 – Accepted: 6Correspondence February to: 2015 E. – Fazio Published: ([email protected]) 6 MarchPublished 2015 by Copernicus Publications on behalf of the European Geosciences Union. Polyphase evolution of a crustal-scale shear zone during progressive exhumation from ductile to brittle behaviour: a case study fromItaly Calabria, E. Fazio, G. Ortolano, R. Cirrincione, A. Pezzino, and R. Visalli Solid Earth Discuss., 7, 909–955,www.solid-earth-discuss.net/7/909/2015/ 2015 doi:10.5194/sed-7-909-2015 © Author(s) 2015. CC Attribution 3.0 License. 5 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 2 PT erent stages of the ff erent sets of veins, that ff erent evolutionary steps of the Montalto ff 912 911 conditions of the di erential stress as well as to estimate possible strain rate attained ff PT axis pattern have also been investigated in order to infer the sense of shear c erent microplates disarticulated from the original southern European Hercynian ff Quartz A complete sequence of structural features recognized during a detailed structural To this aim, recent detailed field investigations (Fazio et al., 2015; Ortolano et. al., In this view is inserted the present work that would to be analyze the rheology, the Within these contrasting views our work aims to be deep the evolution of the for the studied shearcompleted zone. The by study the ofconsisting detailed the of analysis ductile-related microstructure, of acontribute has the series to been semi-brittle reveal of and thethe fracturing case brittle complex here events, tectonic deformation, reported. history producing here (e.g. di Woodcock et al., 2006)2 as in Geological setting Study area is inserted(CPO, within Pezzino et the al., southernthe 2008). sector central This of Mediterranean is the realmof a Calabrian as di ribbon-like Peloritani the continental Orogen result microterrane of located the in Alpine-Apennine amalgamation 2006; Menegon et al.,allowed us 2008). to infer Moreover di paleopiezometry based on quartz grainsize as well as thermaldominant conditions of deformation the mechanisms deepthe causing seated activation shearing the of zone progressive multiple activity, controlled crystal slip-systems by (e.g. lattice Stipp strain et by al., 2002; Heilbronner and Tullis, the same outcrop permitted the tectonic history of the area to be reconstructed. field analysis together with a microtectonic study of mylonitic samples collected from where a continuum passage fromthe the sequential early transitional deep-seated and metamorphic final brittle evolution, up evolution of to the MSZ has to be pointed out. 2015), allowing toMassif realize nappes-like two edifice, permitted 1 : to 20 000 select scale a relatively geological small maps area of of about the 4 km Aspromonte exhumation trajectory ofverifying the the mylonitic stepwise changing rocks(e.g. of involved normal the faults). in regime from the compressional shear to zone, extensional one eventually structural features fromrelationships between ductile- meso- to andthe micro-structural sequential brittle-types features evolution of behaviors, of theand the analyzing MSZ the MSZ. can in stress-field The contribute orientation indeed study detail to of variation, constrain the occurring the during kinematics the di kinematics and the conditions of shearing activity. Shear Zone (MSZ) (Cirrincionea continuum et of al., deformation from 2009).located in ductile- MSZ the to central-eastern is brittle-type part of with indeeda., the 2013), a Aspromonte a together lot Massif. with This beautiful of the massif Peloritani transitional (Cirrincione examplethe Mountains et stages Belt most of (Cirrincione shortened et al., southernmost 2012)(Pezzino segment represent et of the al., Calabrianin 2008). Peloritani the Orogen The (CPO) kinematics evolution ofMediterranean of the back-arc this entire basins, orogenic orogen, whichsetting. unraveling developed segment In the within this occupies scenario an Oligocene-Miocene several a overall opening tectonic2002 collisional models key of and were tectonic role proposed reference (e.g. therein), Rosenbaumof et which al., are the mostly subducting associatedday plate, to peri-Mediterranean the justifying thrust syn-orogenic belts. the retreat mechanisms, These observed such models as drifting attempt syn-convergent to phenomena extensionflow explain (Heymes channeling of the et (Pezzino exhumation al., the et 2010) al., present- the or 2008; uplifting Cirrincione extrusion process, et by involving al., the 2008a), southern which operated CPO during crystalline basement rocks. in the deformationexhumation mechanisms (Ramsay, during 1980). progressive Forevolution deformation this often of reason, associated it thefracturing to is deformation common (Simpson, passing tounravel from observe 1986). the a crystal-plastic exhumation The sequential history microstructuresconstraining rheological of reconstruction to behavior, originally variation in of brittle deep the seated stress-field this orientation crystalline as basement well sequence as rocks can allow to 5 5 25 20 15 10 25 10 15 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent ected ff ff ected by Alpine metamorphic ff erent Hercynian microplate remnants, ff 914 913 erent tectono-metamorphic evolution, locally involved by ff erent fault segments of the SCRZ system extend up to several hundred of ff kilometers and are characterized by a prevalent NNE–SSW trend typically observed scales with formationmore of recent conjugate evolution low-angleextensional of fractures fault system (Ortolano CPO in is et responseextensional tectonics, to al., characterized which a 2015). took by change place The fromthis the in time the the occurs activation collisional upper the Tyrrhenian processes Miocene of basin opening (Monaco toand NE–SW linked et compressional an with al., phenomena the brittle 1996). responsible coexistence of In forMaghrebian extensional the Orogen structuring (Finetti of the andof whole Del the Apennine- Ben, Ionian 1986). oceanic Simultaneously,and crust the through NW Ryan, a subduction 1986) slabaveragely sinking accompanied oriented mechanism NW–SE, by took known place theLentini as (Malinverno et formation South al., Tyrrhenian 2002; of System Guarnieripart et (Finetti a of al., et regional 2002), the al., locally CPO. strike-slipby 1996; still Finally, a active tectonics the in currently the last active centralregional extensional stages and uplift Quaternary and eastern of in tectonics the the which sequentiallatter CPO activation resulted of structural extend seismogenic in normal from evolution an fault are the systems. extensive crossing The marked current the Calabrian Strait Tyrrhenian of(SCRZ) edge Messina (Monaco up and and to Tortorici, formingthe the 1995, the Hyblean di 2000; so-called Plateau Tortorici Siculo-Calabrian et al., Rift 1995). Zone In the study area, by an earlyoverlapping Alpine tectonics metamorphism along a atmylonitic regional fabrics, HP/LT detachment causing peak shear-zone, themain conditions. replaced shear-plane. shortening the The This of original last evolution theconditions structural of evolution chain with further the and the evolved the in activation the folding of more of thrusting superficial the structures, original fractally distributed at di type metamorphism which hasto not Cirrincione been et detectedthe al. into APU the (2008b), and overlying MPU this suggesting APU.indicate is distinct According a tectono-metamorphic supported clockwise evolutions. polyphase by Theentire evolution first pre-mylonitic at Hercynian ones relatively relics metamorphic HT/LP cycle, found regime, whereas ascribable both the to in second the ones, seem to be a re-equilibration and formed duringBonardi Hercynian et metamorphic al., cycleunderlying (Crisci 1984; APU et Fazio through al., a et 1982; Alpine brittle al., orogenic tectonic cycle 2012, contact developed responsiblebasement 2015). during for domains. It the the APU last has stacking isby stages been of made late- of up originally to superimposed of post-Hercynian separatedby on granitoid amphibolite crystalline Alpine-type the metamorphism bodies facies developed (Fiannacca Paleozoic atthe rocks et about same intruded al., 25–30 Ma time, 2008) (Bonardi a locallylowermost et thick al., reworked MPU mylonitic 1987). and At horizon, thedeveloped marking beginning (Ortolano the of contact et their betweenmain al., shared tectonic APU 2005; tectono-metamorphic windows, and Cirrincione history, namely the has the the et Cardeto Madonna al., window di 2009). (Fazio(Ortolano et MPU Polsi al., et crops window 2008, out al., (Pezzino 2009,facies in 2010), et 2005). metapelitic-metapsammitic three al., It sequences 1990) is characterized and constituted by the a by Samo-Africo polyphase lower-greenschist window to Alpine- lower-amphibolite chain (Stampfli andet Borel, al. 2002;the (2010) von Raumer, present-day and 2002, lateral Ortolano Fig. juxtaposition et 1a). of al. According di to (2013), Angì this evolution has brought indeed to extended from Hercynian Orogenyet up al., to 2015), the are ApenninePeloritani distinguished stage (APU) from of and top Alpine Madonna to oneet di (Ortolano the al., Polsi bottom 2008; (MPU) into Units the Pezzino (Cirrincione Stilo et low-amphibolite (SU), et al., facies Aspromonte- al., 2008). Paleozoic 2008b; The metapelites Fazio uppermost una unit consists of low-greenschist a stronglysubdivided to into weakly threeSerre Alpine main Massif; metamorphic the sectors, Aspromontearea from overprint. Massif is north and The located Peloritani toof whole Mountains within three the (Fig. orogen crystalline the south: 1b).(Fig. basement Aspromonte the can The 1c). units study Massif, Sila be cropped These a Massif; out units, nappes-like the in which the structure have southern composed experienced sector a of poly-orogenic the multistage CPO history characterized by a di 5 5 15 20 25 10 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | n – M 2E B crenulation for lineations, 1E S n L have been carried out 2 – Fig. 4a) it was involved 5A – Fig. 5a) during which the D – Fig. 4a) occur. for fold axis, for the deformation phases, 1E n 6A n D B D D – Fig. 4a). The latter, is accompanied 2E S – Fig. 4a) producing an ENE–WSW axial – Fig. 5a), subsequently microfolded during 1E 916 915 D 1E S for schistosities, n S – Fig. 4a) responsible for a sub-mm-scale 2E – Fig. 4), which constitutes the main foliation; and (ii) a second D 1E S index indicates the relative chronology of the event. H and A subscripts n Other two normal fault families oriented N–S and E–W, respectively have been Fig. 4b). Moreover, during the early Apennine evolution ( in cataclastic shear zone processes linkedthe to entire the overthrusting SU at on upper thelow crustal underlying levels angle of APU, leading brittle to joints(HAF the (LAF formation – – of Fig. NE–SW Fig. 4), compressive System 4). commonly (Lentini Finally, NE–SW et dm- al., oriented, to 2002; probably m-scale Guarnieri linked et high to al., angle 2002) the brittle ( South joints Tyrrhenian producing the formation of aby new schistosity the ( development of axial microfolds culmination approximately oriented E–W ( further recognized, heretectonics which interpreted accompanied as theof drift related the of to the Tyrrheniancomposite Aspromonte the basin, framework. Massif activation causing during of the the opening the present-day3.2 lateral-juxtaposition strike-slip of Aspromonte-Peloritani the unit (APU) CPO Rock-types belonging toMylonitic para- this and unitWeakly leuco-ortho-gneiss to constitutes strongly represent developed thefoliation the pervasive but main mylonitic most surfaces, relics outcropping areal constitutespreserved. of litho-types. the In outcrop an dominant most early extension. proto- of isoclinal the to folding outcrops ultra-mylonite,horizon. it aligned (Fig. is to This 3b) possible the is testifying tochain latter due a see inducing one to a continuous a are constant800 thickening repetition the m. locally of alternation of bending The the from results the phases originalthe of mylonitic central occurs mylonitic field part horizon during investigations of actuallyarticulated were the the map reaching derived in exhumation (Fig. from up a 2). of 29oldest to These first metamorphic the outline stations event surface a develops clustered of ( poly-orogenic in structural the evolution Hercynian cycle ( deformational stage ( plane schistosity ( by the presenceinvestigations of from 4 micro-fold stations axial located(Fig. culmination in 2) the suggest lineation, south-western an wasHercynian part exclusively of observed. syn-metamorphic metamorphic the deformation, Structural evolutionary geological ascribablestages: map stages. to (i) the a These early first last isoclinal folding can event ( be subdivided in two 3.1 Stilo unit (SU) The basement rocks of SUphyllites cropping often out in showing themain quartz study foliation area lenses are (Fig. prevalently andlow 3a), fine-grained angle rods fracture connected systems. structure to Locally, a elongated an subsequently parallel crenulation isoclinal cleavage, to folding highlighting the event and interrupted by in order to constrain theDuring temporal sequence this and work, styles a ofwere the total collected meso-structural of features. permitting 1696 tothese structural realize data measurements a were from processed, detailed 48the producing geological stations recognized stereoplots map (Table meso-structural representative 1) (Fig. features for subdivided 2).software the per (Grohmann Successively, sequence unit and of by Campanha, meansmain 2010). of foliation, To OpenStereo this fold axis aim, and contouringto lineation plot was fractures. data used Abbreviations set, to used whereasfor plot in rose the the diagrams text metamorphic are: were episodes; preferred where the are related to Hercynian and Alpine orogenic cycle respectively, also in the north-westernevident triangular Sicily and and trapezoidal in facets (Ortolano the et Hyblean al., Plateau 2015). with the3 development of Meso-structural analysis A detailed field investigation from a selected area of about 4 km 5 5 10 15 20 25 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ◦ – 3A B /32 2A ◦ , L 4A S – Fig. 5a) and 85 5A ◦ D erent places of /38 ff ◦ – Fig. 5a), in which the (azimuth/dip direction), ◦ ) will be not furthermore 3A 2A D /25 ◦ M . Simultaneously, a pervasive – Fig. 6a) responsible for the ◦ to 3A D 1H ) mostly oriented ENE–WSW, the – Fig. 6a), but in this case it was . During exhumation ( M 3A 6A 1A S – Fig. 6a) derived by the crenulation of – Fig. 5) constituting the main foliation schistosity (Fig. 5a), locally observed at L D 2A 2E 3A S , see Table 2), thus the early deformational S S 918 917 6A and from D to 2A D 3A to D 1H D – Fig. 5) predominantly oriented SW–NE is formed, whose ) having an average plunge of 210 – Figs. 3e and 5), to a brittle one consisting of NE–SW low – Fig. 5a) to form a – Fig. 6a), which, according to Puglisi and Pezzino (1994) and 1A 1A 4A L 2E 1A B D S – Fig. 6a) indicated by hinge relics of deformed quartz producing an axial – Fig. 5a) with the development of a new axial plane foliation ( ) characterized by the development of a ENE–WSW conjugate low angle 1A 4A D 4A D B – Fig. 6a) determining a new surface ( 2A D intrafolial folds andisoclinal S-C folding deformation fabrics.shared, of These since the this structural age, mylonitic theSuch features foliation same an tectono-metamorphic suggest evolution together is history that therefore with with characterizedfolds the MPU by overlying ( the the rocks APU. sequential formation later have ofjoint asymmetric system, linked withcoeval the with already the observed final brittle stagesstructure of thrusting are the (LAF) repeatedly progressive cut (Figs. exhumation. by 3e Asduring high and in angle the the 6), fracture other cleavages last (HAF units, – step these Fig. of 6) developed the Alpine evolution ( possible to distinguish justand two NE–SW of trends. the three families previously highlighted, with E–W 4 Microstructural analysis 4.1 Petrography and mineral assemblages In this chapter wethe focused shear our deformation attention (i.e. from on metamorphic episodes developed during stretching lineation ( and blastesis events (from formation of the pervasive mylonitic foliation ( the first foliation isdeformational only stage locally observed is at related outcrop to scale. the Rather, shear the event most ( extensive Cirrincione et al. (2008b) is attributable( to the early Alpine deformation. A second event on 15 stationshave scattered across experienced the severalfolding map deformational ( (Fig. episodes 2). characterizedplane Results by schistosity suggest ( a that these first rocks isoclinal (right hand ruleENE–WSW notation) with is dip produced directions (Fig. spanning from 5b). 15 Such to surface 85 is averagely oriented the second event ( stretching lineation (L recognizable in the outcrops, with a main shear planes oriented 260 kinematic indicators providecoordinates. a Post-mylonitic stage top-to-NE involves APU sensephase rocks of in ( a shear subsequent in– isoclinal folding Figs. the 3d current and 5a) geographic accompanied by the generation of an intersection lineation ( outcrop scale. Such structuresdeformational are event nearly occurred totally during the obliterated early by Alpine an cycle Oligocene-Miocene ( APU overthrust on thetime, MPU a along pronounced a mylonitic deep-seated schistosity compressional ( shear zone. At this Fig. 5) almost perpendicularlya oriented switching to from the aasymmetric ductile behavior, folds characterized ( by meter-scale SSE–NNW verging the map (Fig. 2)APU it and is MPU, possible leading tofinal to record observe an of a the increased repetitionFigs. tectonic thickening of 3f history and of the 5) is the original indicating the the whole contactby beginning activation SU of between mylonitic of (Fig. an zone. extensional 4b). normal regime, The similarly faulting to systems that (HAF shown – 3.3 Madonna di Polsi unit (MPU) The lower-greenschistquences to of MPU lower-amphibolite (Pezzinometamorphism et facies (Pezzino al., et metapelitic-metapsammitic 1990, al., 2008)2010a; se- 2008; is Fazio et characterized Ortolano al., by et 2008). Predominant aare al., lithotypes phyllites polyphase 2005; defining and Alpine the garnet-micaschists Cirrincione basement (Fig. et rocks 3c). of Structural al., MPU investigations were 2008b, carried out angle brittle joints took place (LAF – Fig. 5). For this reason, in di 5 5 10 15 20 25 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ). Tur 3A XY + S Grt + Ep + Chl + Wm ) is due to the alternance of + estimates after Cirrincione 3A ) (leading to the transposition Bt S ). These crystals (i.e. Ad) are (sample SDA14). Late-fractures 4A PT + D 3A 3A S ), the other was cut orthogonal with S Kfs 1A + L Pl + Tur. Layering ( 920 919 + C–0.25 GPa ( ◦ direction, X Amph + Ilm (Fazio et al., 2012, 2015). Since this unit was not + Chl + Bt C and 0.45 GPa during the syn-shear metamorphic episode ◦ ). Often a cataclastic flow overprints the mylonitic fabric ( + Kfs 1A S + Chl C–0.5 GPa to 450 ◦ + Grt Pl + + Pl ). + Wm 3A + S Wm ). Quartz domains are also characterized by smaller recrystallized grains forming + ected by the shear zone its microstructural features will be not further treated in the Discordant veins with large crystals of quartz and feldspar crosscut at high angle The uppermost tectono-metamorphic unit outcropping in the study area, the Silo The intermediate Aspromonte-Peloritani unit (APU) is composed essentially by The typical assemblage of the MPU metapelites is given by 3A ff S When the cataclastic process is very pervasive, coupled with a smaller pre-mylonitic an oblique foliationrecrystallization (SGR) (Figs. and a locally 7a,Smaller grain quartz boundary 8d, migration grains recrystallization 9d)grain (GBM). recrystallizing suggest also suggesting at the activation the alayers) of edges bulging sometimes dominant (BLG). are of Quartz-rich widely domain subgrainhydraulic larger (e.g. fracturing truncated ribbon-like sigmoid rotation (Fig. by 7e). shaped a Sometimesplasticity quartz pervasive larger with grains network of classical of quartzFeldspars, veins chessboard show usually suggesting intra-crystalline forms pattern porphyroclasts,testifying and often an very sporadically intense elliptical, reworking deformation elongatedtextures during are lamellae. and shearing widespread rounded activity in microcline (Fig.augens showing 9e). with deformation Domino-type twins, micro- micro-cracks formingcrystallizes fragmented filled as rhombic by shaped blockyondulatory chlorite grains extinction (long and into axes a about sericite.into set 200–300 K-feldspar of microns) layers with paraconcordant (adularia) sub-parallel lenticular to also veins (Fig. the 7d), mylonitic arranged foliation ( both the myloniticparallel foliation up to and slightly discordant with thedislocating respect to pseudotachylyte the the (Pst) myloniticsized portions foliation dip-slip at and which thin section plagioclase are scale porphyroclasts sub- are widespread showing (Fig.Qtz 7f). microns- of an early foliation, characterized by a mosaic-likesometimes texture. retrogressed Kink into bands chlorite,twins. are Plagioclase and and shown in K-feldspar both plagioclase withinan in leucocratic highlighted extreme mylonitic biotite lattice by gneiss bending flakes, folded showgarnet (SDA11, albite sometimes enveloping Fig. pre-kinematic 7c). kinked feldspars In also the occur. same rocks layers of fragmented micaceous- and quartz-rich levels isoclinally folded ( discussed. In this context aoutcrop suite of (see oriented Fig. specimensorthogonal were 2 collected thin for from sections the location wereparallel same to prepared and the and stretching Fig. analyzed lineation 7 for ( each for sample: petrographic one features). was Usually cut two developed at about 540 ranging from 500 followed by a retrograde metamorphism characterised by thermobaric condition respect the lineation, both of them are perpendicular to the mylonitic foliation ( et al., 2008b).of Thin shear sections (Fig. 8). cutlevels At interbedded parallel with the to mylonite sub-centimetricat NE–SW and scale places cataclasite show it portions is a aappearance, of possible cataclastic top sometimes the to to resembling flow. same observe(Fig. rock micro-sheath the Spectacular ultramylonite 9, depicting folds, CD NE intrafolial thin have sense section obliquesometimes also of showing folds SDA3). been Mica micro-folds with fish with recognized are axial( disharmonic widespread. planes Quartz sub-parallel occurs to as the ribbons, mylonitic foliation plane, this study areand 8) highly showing foliatedfabric. good The main examples ultramylonites, assemblage of is mylonites, given brittle by Qtz and deformation overprinting cataclasites an (Figs. earlier 7 ductile Unit (SU), iset al., essentially 1982; made Bonardiby et by al., Qtz Variscan 1984; Fazio low-grade et al., shales 2015). and The typical phyllites assemblage (Crisci is given middle crustalamphibolites, biotite mica paragneisses schists and and marbles. leucocratic Rocks belonging augen to gneisses the APU with collected minor for a following. 5 5 10 20 25 15 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and X ). 00 GBM, ondulatory + slip systems are also i a axis is represented by h c with respect the shear zone ) has also been investigated. ◦ 0 C (Stipp et al., 2002). Moreover usely occurring; pre-kinematic Pl ◦ ff and prism ) crosscutting the earlier mylonitic i 00 a slip system has been also registered h axis patterns are shown on Fig. 10. i c c h 921 922 use. Garnet grains are very rounded suggesting erosion during C (Dunlap et al., 1997), 400 erential stress up to the magnitude of confining pressure (Kuster ◦ ff ff slip system (Fig. 10a–h) suggesting a main recrystallization episode i a h use basal ff directions and a general rhombic symmetry linked to the specific orientation of ecting quartz-feldspar-mica bearing rocks denoting quartz intracrystalline plasticity Recrystallization microstructures typically developed in crustal scale shear zone Syntectonic recrystallization of quartz probably has proceeded towards the last In one case a late discordant vein (Fig. 10h The dominant crystallographic distribution of quartz axes of recrystallized quartz grains. Quartz ff approximately at 280 a exhumation phases ofoverprint of the lower temperature shearmylonites fabric pass over zone, through higher the temperature during BLG–SGR ones. transition, This progressive which causes has cooling, that been causing estimated to the occur 4.3 Qtz deformation mechanisms The dynamic recrystallization of quartzof domains testifies the deformation activationcharacteristic and protracting fabrics by in the meansrotation recrystallization Montalto (SGR), sheared of with rocks. minormigration bulging In (GBM), (BLG) dislocation particular, has and been sporadic prevalent grain recognized creep subgrain boundary as the main mechanisms recrystallization process. which produced were observed. Oblique foliationboundaries developed at (c about surfaces) 15 diameter is delineated ca. by(Fig. new 50 11a). recrystallized This microns) smaller fabricthe has grains suggesting been Montalto (average observed a shear thoroughwith zone almost dominant major all (Fig. SGR samples axis 10b–g). collected paralleld, Larger recrystallization from to e, grains the and process main forming 11b). foliationrecrystallized ribbons They (long grains are exhibit typical axis optically of elongated about SGR visible 500 (core subgrains microns, and and mantle Figs. show texture, 10b, Fig. at 11c). their borders tiny fracturing also occurs (Fig. 7e) into alternation the to rising dynamic of recrystallization local di as a response suggesting that deformation (intracrystalline plasticity)propagation. has continued after the fracture and Stockert, 1999).fragmented Interestingly quartz domains, mica at the flakes end occurring of opening at veins show the local boundary kinking (Fig. of 11d) these foliation displacing ribbon-like quartz levels (Fig. 10h–h Results, thusa not subsequent episode, correlated show a with peculiar the pattern with shear a maxima zone between the activity but undoubtedly to developed (Fig. 10a, e(samples and SDA1, g). SDA11; Fig. Minor 10a prism and e). Z maximum stress during crystals growth into the opening vein (Fig. 10h grainsize with respect to the APUWhite rocks, mica the fish earlier are ductile di featurestransitional are fully ductile-brittle obliterated. shear regime; ribbon-like quartz (SGR extinction) showing internal obliquewith foliation core-rim (dusty-limpid). are di 4.2 Quartz LPO On a suite of collectedquartz samples the grains lattice preferred wasmicroscopy; orientation Heilbronner, (LPO) 2000), inferred of widely recrystallized adopted by inrocks microstructural the (e.g. analysis of Heilbronner CIP mylonitic Pennacchioni and method et Tullis, al., 2006; (computer 2010).been Menegon integrated In investigated et in particular, polarization al., order eightc 2008; to domains retrieve Fazio of information et oriented about al., specimens the 2010; have orientation of the optical a di happened under shear strain at greenschistStipp facies et condition al., (Schmid 2002). and At Casey, 1986; a lesser extent the rhomb 5 5 20 10 15 25 20 25 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 9 T − Q (1) PT ) of , ˙ ε is the A erential m ff shearing conditions: ) can be retrieved by ), and 4 respectively. ˙ 1 ε − PT is the (power-law) stress is the grain size, is the activation volume, ) active during the shearing n d σ V 4.82 GPa has been selected ∆ = is the fugacity exponent. O ). C). Such calculation, considering 2 r ◦ H f 3A S ), 135 000 (Jmol 1 − s n 924 923 − is the pressure, erential stress ( ff p is the applied stress, ) found for the Montalto shear zone (SDA3 sample) (MPa ˙ ε σ 12 axis patterns, which is comprised between 350 and − is the molar gas constant, c R 10 ; Behr and Platt, 2011) and natural shear zone (10 1 × − is the water fugacity, and erential stress is known and the deformation mechanisms s ff the dominant active slip system. These thermal estimates are O ) of 0.25ß,GPa was inferred. C), for which a value of 15 2 ) ◦ i σ − H pV a f ∆ h + conditions (0.30 GPa and 350 RT ), which is in agreement with typical values of actively deformed Q 1.35 GPa (Tödheide, 1972), gives a strain rate value rate ( − 1 ( (550 − ). = e to 10 1 PT (s T O − O 2 2 is the activation energy, 12 12 H (s H f ; Bürgmann and Dresen, 2008). Nevertheless the above mentioned f − − 1 m Q 15 − − is a material constant, 10 − s d × A n as follows: 6.30957 10 13 − with respect thefeldspar mylonitic (adularia, foliation, Ad),domains consisting delineating at the of places mylonitic foliation polygonal truncating ( aggregates both of micaceous K- and quartz rich C, being basal erential stress ( × n ◦ Aσ ff (0.45 GPa); Since the value of di In order to obtain reliable estimates for water saturated conditions, appropriate water We then calculated the strain rate values at the following Our estimates are calibrated on the experimental data obtained for quartzite under 1. Millimeter-thick lentoid shaped epithermal veins (Fig. 11), usually paraconcordant = ˙ P also consistent with those proposedalso by previous determined studies pressure (Cirrincione conditions et for al.,GPa. the 2008b) Montalto who shear zone in the range 0.3–0.45 550 1.62 Besides cataclastic flow, which hasSDA10), three been sets recognized of in joints/veins a have been couple recognized of (sample samples SDA1, (SDA14, Figs. 11–13): 4.5 Brittle microstructures conditions were attainedcontinued during up to the shallowerpaleopiezometry initial crustal calculation attempting conditions. phase to For estimate of the thisevent last reason phase shearing at of we the lower but same also shearing made deformation a has further a value of is 3.21 regions (10 to 10 (Tödheide, 1972). The strain rate ( wet conditions (Hirth et al., 2001),zones realistically approximating with conditions of natural associated shear mylonites (Stipp et al., 2002), by adopting values of fugacity values have been selected (Tödheide, 1972)range by taking deduced into account from the thermal quartz stress (Herwegh et al.,corrected 2011). Applying by an Holyoke empirical eta equation di al. (Stipp and (2010), Tullis, considering 2003) the mean grain size of 42 microns, adopting a flow law equation (Bürgmann and Dresen, 2008) inε the following form: correlated withmicrostructures dislocation (BLG, SGR) creep were recognized, regime the strain which rate ( produced characteristic related is the absolute temperature, grain-size exponent, and 4.4 Qtz paleopiezometry Paleopiezometry calculation based onrich the domain mean from grainsizeFig. of an 12). a highly This recrystallized was deformed quartz- usefuldeformational mylonite to phase infer was (Poirier, the 1985). also di from To performed this a aim (SDA3 stack a sample, macro of grain (Heilbronner, boundary three 2000) with map CIP the wasdomain misorientation Image containing obtained SXM 3542 images particles software can adopting (Barrett, be 2010). considered the The statistically valid Lazy selected to infer grain di boundary where exponent, Indeed, petrographical evidences confirmconstituents that of syn-shearing hydrous assemblage. minerals (e.g. muscovite) are 5 5 25 20 15 10 20 10 15 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) 1A ect V ff veining stylolite- 1A V 2A V ) of blocky feldspar and erent evolutionary stages, 3A ff ) and the first set of veins, S 3A to S ), here obliterating most of the ) causes overpressure in the pile 3A 4A w/r D D textures, ribbon like quartz, book-shelf 0 , parallel to the tectonic transport direction, 1A 926 925 L ) that became active at relatively deep seated 6A D 0.3 GPa) at least during its initial phase. Qtz “Alpine veins” of Rossi et al., 2005, possibly related + P > ) filled by feldspar, chlorite, and quartz. Sealing quartz brittle episode. Ab 3A C; ◦ S + 5A D – sigma1 oriented parallel 250 C, after Steiner, 1970). Sigmoidal recrystallized quartz observed ◦ 1A V T > ) and a stretching lineation ( the mylonitic foliation causing its displacement (Fig. 7f). Sometimes such 3A ◦ S is sometimes characterized bywas ondulatory still active extinction, at testifying subsolidustruncating that conditions. both deformation This the second set early of mylonitic tiny veins microfabric (Fig. ( 11d), pseudotachylytes and close fractures.of 60 The latter crosscutmicrocracks produce at fibrous opening an veins filled averagesporadically by also angle biotite quartz and veins sericite (Fig. (Fig. 13)an 12) suggesting extensional or that tectonic both of event them ( are related to concentration of opaquemylonitic minerals foliation (Fe-oxides) ( at high angle with respect the sometimes appears ascoherent with suture the same jointoriented parallel sigma1 to (teeth-saw orientation the main active profile) foliation.final during Possibly stage this resembling of the set the of first stylolites, joint vein is also opening, related to the conditions ( The most developed deformational phase ( The second phase is related to the ductile-brittle transition coeval with the shear 3. The last microstructures related to the fragile regime (Figs. 11–14) are breccias, 2. Thinner massive veins (Fig. 11a–d) characterized by walls with a high opened at ca. 300 like veins) probably forsurrounding a micaceous matrix mineral-rheology constituting relatedcrystallization the (Rossi contrast et host of al., rock competence 2005)K-Al-Si and into between fluid the paraconcordant veins vein circulation is itself.conditions (upflow possibly Adularia that linked zones to are – high- geothermal characteristic most fluid of likely – an i.e. Adand open a forming takes hydrothermal system incrustations K-feldspar place on such precipitated fissured under as by wall rocks). the dynamic fault Probably geothermal such fissures fluid, epithermalin carrying veins one ( sample (SDA1) into a quartz-rich domain is considered coeval with this veining episode, Table 2) sometimes are not fractured by subsequent veins ( quartz (similar to the Ad to high K-Nafoliation. fluid Large circulation) grainsize of usually such sealing para-concordant crystals with are due respect to to a rising the temperature e mylonitic previous structures, is typical fora the non-coaxial development plastic-type of deformation structures withfoliation during ( formation the of evolution a of weakly to strongly mylonitic nappes edifice with(Fig. 15, development see of SDA1syntaxial a thin veins section). set ( Two of sets of veins veins (joints) are characteristic overprinting of mylonites this phase: associated with a considerable enrichment of fluids pressure. These veins ( see SDA3 thin section,and Figs. 8 quartz-feldspar and rich 9)quartz and domains. layers are a Syn- widespread. layering Mica to given fish, by S-C-C post-mylonitic alternating asymmetric micaceous microfolds of zone uplifting (a possible changeoccurred and/or at decrease this of time). the main The shear tectonic plane transport inclination ( feldspar are characteristic microstructures ofthis this tectonic stage. phase. Ultramylonites develop during 5 Discussion and timing of deformationalThe phases relationships between ductile andthe fragile structures are possible here described evolutionthe to highlight of overprinting the andcontrolled sequentially shearing dispersion the relations exhumation MSZ trajectorybasement among of activity units the the Aspromonte trough (Fig. Massif di thin the crystalline 15, section-scale of reconstruction Table the 2).following of possible two From tectonic deep evolution the seated can be outcropping integrated delineated. units analysis (i.e. APU at and the MPU) field- the and 5 5 25 20 15 10 15 10 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | – 2A V and prism i a h slip occurred at . Elevated fluid set of veins has i 3A a S h 1A V ). The ) favored the variation of the 5A set of veins with large quartz D 6A ) responsible for the low angle – sigma1 oriented perpendicular 3A D V 5A 3A D V veins at microscale and of normal faults C (amphibolite facies conditions). The ◦ 3A V 928 927 ) at the regional scale, causing the recent horst 6A ) sub-coeval with the previous ones develops. D 3A S to tectonic phase responsible for the verging to isoclinal 4A axis pattern (Fig. 10), whereas the new quartz grains, with D w/r ): high angle micro faults (jogs, dilation veins with microscale c ) has developed under the classic brittle regime s.s. Two brittle 3A direction compatible with a dominant basal S 6A Z D to C (greenschist facies conditions) with subordinate rhomb ◦ evolving to the thrusting phase ( w/r 3A ): tiny fuzzy antitaxial fibrous veins (Chl, Wm, Bt) with Fe-oxides at walls, S 3A S erent crystallographic orientation, have tails sub-parallel to the main foliation to ff slip systems developed under 450–550 Concerning the quartz LPO, the dynamically recrystallized grains develop a broad The third phase ( The subsequent tectonic collapse of the chain ( i a h geologically constrained dislocation creep flow law of Hirth et al. (2001) for wet quartz maximum near the about 300–350 pull apart basin) witha dip-slip connection or with mesostructural displacement high visible angle at faults thin (HAF). section scale suggesting 6 Conclusions The structural analysis conducteddetect a both complex at tectono-metamorphic evolution thefrom of meso- ductile the and Montalto to shear micro-scaleevidences, zone, brittle allowed evolving like regime, us microstructures, to passingthis mineral through crustal rheology, the scale quartzto shear ductile-brittle LPO lower zone transition. amphibolite pattern, a Several facies,strain suggest features Cirrincione mylonitic like for et stage quartz ribbons, al., atisoclinal mica 2008b) folds fish, greenschist with rounded with facies porphyroclasts, associated recrystallized obliqueto condition typical foliation, grains the (up ductile of fold quartzrecrystallized axial with quartz surface. their grains Moreover, longest ofconfirm the axis greenschist selected sub study facies domains thermal parallel of byinformation range the about the of the CIP the crystallographic sense shear methodan of orientation zone permitted average shear activity tectonic of us in as transport the to well vergency nowadays towards as geographic NE. to coordinates, gain giving grains. Sometimes injectites have beenperpendicular recognized; (second stage – sigma1 oriented They often appear as suture joints at high angle with respect pressure, which led to fracturing,decreasing dilation, temperature, resulted and in fault the initiation, transition(e.g. coupled from Gibson, ductile with 1985). folding progressive Changing to physical brittleduring conditions thrusting uplift probably and reflect late erosional Apennine unroofing thrust sheet emplacement. sigma 1 orientation, changing fromwith sigma3), sub-horizontal and to the sub-vertical development (switching of of both sigma1 and graben structure ofthe the onset entire of the Aspromonte maximum Massifvertical stress loading, crystalline orientation a edifice switching, set characterized (Fig. ofw/r by veins 3g). an marked At increasing this stage ( been interpreted asprobably syn-tectonic coeval hydraulic with fractures the folding parallel to of the sigma1 direction and massive veins filled byquartz large parallel to quartz the crystals mylonitic foliation. crosscuttingpost-exhumation These vertical at microstructures loading high are of related angle the to entire ribbonconnection the basement like with syn- edifice to the marking recognized also a meso-structural possible scale high angle faults (HAF) (Fig. 3). faults (LAF) visible atthrust the sheet outcrop scale. emplacement. Indeed, Then fluid pressure a may network increase during of stylolite-like massive veins ( connected to the last brittle episode ( sub-stages can be distinguished: (first stage)mylonites cataclastic flow and and breccias development overprinting (parallel of to the pseudotachylyte mylonitic (Pst) foliation), crosscutting connecting the mylonitic layers sigma1 oriented parallel stage (Fig. 10e). Indeed thelow surrounding temperature quartz quartz domain is characterized by a classical a di which should be coincidentcoevally with with the respect sigma the 1 Apennine direction thrusting at phase the time ( of recrystallization 5 5 25 10 15 20 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | to 12 − 10 × C, referable to the ◦ ) of 3.21 ˙ ε ) causing the activation 6A D ). Our observations suggest then 5A D ) of 0.25 GPa estimated by paleopiezometry 929 930 σ ∆ ) and continued up the former stages of the thin skinned erential stress ( 4A ff D – We thank Renèe Heilbronner for making available the CIP facilities at the 3A ) for di D 1 − (s 15 − 10 × At the transition between a typical ductile rock behavior and an initial fragile regime, We can conclude that the whole structural dataset provide evidences for an evolution of preservedOrogen, Hercynian southern crustal Italy), Lithos, section 115, 237–262, in 2010. thelast Serre access: Massif December 2014, (Calabria-Peloritani 2010. extensional terrane, Earth Planet. Sc. Lett., 303, 181–192, 2011. probabile età alpina nell’UnitàSocietà dell’Aspromonte Italiana – di Arco Mineralogia e Calabro Petrologia, Peloritano, 39, Rendiconti 613–628, della 1984. 1.62 (Stipp and Tullis, 2003). These straincan be rate considered values to inferred be from realisticscale quartz if shear compared paleopiezometry to zones. the geological literature data for crustal- a mixture of featuresparticular belonging the to careful the crosscuttingmicroscale opposite relationships allowed finite between us strain severalveins, the products sets related whole is of observed. tectonic to veinsand In history fragile at biotite the to (antitaxial rock vein) be behavior, suggesting thermal better sealed condition constrained. with above 250 Massive adularia, quartz (syntaxial vein) ductile regime up to thesub-parallel ductile-brittle to transition. The the peculiar main orientationfundamentally of mylonitic in such foliation, veins, a suggests compressionalto that stress this exhumation stage field has both ratheras developed meso- than to and in micro-scale transitional an structuresdeveloped and extensional related in semibrittle one. to Up ones a ductileas regime furnish compressional cracks, as evidences settings. well micro-faults, ofplastic Then dilation a deformational characteristic continue veins features brittle deformation Such and acquired microstructural structures joints during observations such are earlyand have mega-scale, superimposed their stages especially correlative on regarding of the features(HAF) the the low-angle linked both faults clearly tectonic to (LAF) at the and history. theAspromonte high-angle thrusting Massif meso- faults phase edifice, respectively. and the subsequent normal faultingarticulated, of but the relatively entire continued polyphaseinvolved evolution within of the the investigatedgeological MSZ fault-rocks and structural evolution, analysis which supported by has microscopic been observations. Results delineated are thanks to a careful concordant with anregime exhumation activity operating substantially from(Alpine developed the phase, in Oligocene-Miocene a deepest compressional mylonitic shearing activity Barrett, S. D.: Image SXM, University of Liverpool,Behr, available W. at: M., http://www.ImageSXM.org.uk and Platt, J. P.: A naturally constrained stressBonardi, profile G., through the Compagnoni, middle R., crust Messina, in an A., and Perrone, V.: Riequilibrazioni metamorfiche di Acknowledgements. University of Basel. Danieletake Castelli microphotographs at is the greatly Earth acknowledged Science for Department of making Turin available University. devices to References Angì, G., Cirrincione, R., Fazio, E., Fiannacca, P., Ortolano, G., and Pezzino, A.: Metamorphic Apennine evolutionary stages (Apennine phase, that the switching fromthe compressional still to active final extensional evolutionary regime, stageof can (i.e. Apennine be a phase, ascribed dip-slip onlygraben tectonics to structure which of the brought Aspromonte Massif. to the formation of theThe present-day Supplement related horst to and thisdoi:10.5194/sed-7-909-2015-supplement. article is available online at has given realistic results in theIndeed calculation when of considering strain rate the instudied shearing the area, Montalto conditions the sheared mylonites (temperatures rocks. should and have stresses) deformed of at strain the rates ( 5 5 20 15 10 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | axis texture mapping of mylonitic metapelite c 932 931 with rods structures (Calabria, southernSoc. 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J.:Kuster, An M. and evaluation Stockhert, B.: of High di quartzite flow laws based on Guarnieri, P., Carbone, S., and Di Stefano,Heilbronner, R.: A.: Optical orientation The imaging, in: Sicilian Stress, Structure orogenic and Strain: belt, a a volume in critical honour tapered Heilbronner, R. and Tullis, J.: Evolution of 5 5 15 30 10 20 25 20 25 30 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Unit LAF HAF Total_ 4A B 2A L 3A B 1A L 936 935 3A S 2H B 1H B 1H S C, J. Struct. Geol., 24, 1861–1884, doi:10.1016/S0191-8141(02)00035- ◦ axis patterns, American Geophysical Union, Washington DC, 36, 8–6, C to 700 ◦ C Total stations and structural data reported in the geological map of Fig. 2. UnitSU Station APUMPU 4Total data 29 48 15 0 71 71 0 17 0 17 0 11 11 0 0 0 1142 873 108 269 0 34 79 29 35 23 0 11 17 32 0 3 71 16 0 1 47 190 1696 7 136 17 1206 29 25 359 131 western Mediterranean since2002. the Oligocene, Journal of the Virtualduring Explorer, shear-zone 8, development 107–130, from and the related Mont episyenitesPublications, 245, Blanc at 373–396,, middle doi:10.1144/GSL.SP.2005.245.01.18 granite 2005. crust (French–Italian depths: Alps), insights Geologicalquartz Society, London,,doi:10.1029/GM036p0263 Special 1986. 269–288, 1986. constrained by dynamic platePlanet. boundaries Sc. Lett., and 196, restored 17–33, synthetic 2002. oceanic isochrons,environment Earth ,doi:10.1180/minmag.1970.037.292.07 1970. at Wairakei,30, SDE3-1–SDE3-5, 2003. Newa Zealand, “natural laboratory”from for 250 Mineral. crystal plastic4, 2002. deformation of Mag., quartz over aedited 37, temperature by: Franks, range F., Springer, New York, 463–514, 916–922, 1972. Arc (Southern1995. Italy), Tectonophysics, 243, 37–49,basement, 10.1016/0040-1951(94)00190-K doi: areas at the Gondwana margin, Int. J. EarthEngland: Sci., implosion 91, or 35–52, collapse 2002. of a fault void?, J. Geol. Soc. London, 163, 431–446, 2006. Tödheide, K.: Water at high temperature and pressure:Tortorici, L., in: Monaco, Water: C., Tansi, a C., and Comprehensive Cocina, Treatise, O.: Recent and active tectonics in the Calabrian von Raumer, J. F., Stampfli, G. M., Borel, G.,Woodcock, N. and H., Bussy, Omma, F.: J. The E., and organization Dickson, of J. pre-Variscan A. D.: Chaotic breccia along the Dent Fault, NW Table 1. Rosenbaum, G., Lister, G. S., and Duboz, C.: Reconstruction of theRossi, tectonic M., evolution Rolland, of Y., Vidal, the O., and Cox, S. F.: Geochemical variations and element transfer Schmid, S. M. and Casey, M.: In: completeSimpson, C.: fabric Fabric analysis development in of brittle-to-ductile some shear zones,Stampfli, commonly Pure G. observed Appl. Geophys., M. 124, and Borel, G. D.: ASteiner, plate tectonic A.: model Genesis for the of Paleozoic and hydrothermal Mesozoic Stipp, M. and K-feldspar Tullis, J.: The (adularia) recrystallized grain size piezometer in forStipp, quartz, Geophys. M., an Res. Lett., Stünitz, H., active Heilbronner, R., geothermal and Schmid, S. M.: The Eastern Tonale fault zone: 5 25 30 10 15 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (plastic behaviour) (plastic behaviour) (semibrittle behaviour) geological sketch map of the (c) areal distribution of Alpine belt in the central 938 937 (a) Qtz, Ilm, Wm, Bt, Pl,Qtz, Grt, Pl, Sill, Chl, Kfs Wm, Bt,Qtz, Grt, Pl, And Chl, Wm, Bt,Qtz, Grt, Chl, Ep, Wm, Amph, Grt, Ilm Ilm Qtz, Wm, Chl, Pl, Grt, Bt, Pre-shear Czo, assemblages Amph, TurQtz, Wm, Syn-shear Pl, assemblage (plastic Chl, behaviour) CzoQtz, Ad, PlQtz, Chl, WmQtz, Bt, Wm, Chl Syn- to post-shear assemblage Syn-compressional assemblage LAF – fracturing HAF – fracturing ) Mineral assemblages Notes n ) M n V 1A 2A 1H 2H 3A 4A 1A 2A 3A V M M M M M M V V geological sketch map of Calabrian Peloritani Orogen (CPO) 3A (b) B , 1A 2A 1H 2H 1A 2A B B fold axisB episodes B L L 1A 2A 1H 2H 3A 4A –– S S S S –––– S S Synthesis of geological setting: Synoptic scheme of deformational phases, associated structures and blastesis ) Foliation Lineation/ and veining ( n D 1H 2H 1A 2A 3A 4A 5A 6A Deformational Associated structures Metamorphic ( D D D D D D D D events ( Figure 1. Mediterranean realm; (modified after Angì et al., 2010; Cirrincione et al., 2011); Aspromonte Massif (after Pezzino et al., 1990, 2008; Ortolano et al., 2005; Fazio et al., 2008). Table 2. episodes. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | conjugate ected by the (f) ff panoramic view of the early isoclinal post-mylonitic folding (g) (d) fold, evolving to brittle low angle 5A D alternance of mylonitic ortho- and para- (b) 939 940 asymmetric syn- (e) Stilo Unit phyllites; (a) Outcrop features: Detailed geo-structural map of the study area with outcrop location (scale 1 : 10 000). Madonna di Polsi Unit mylonitic garnet bearing micaschist; gneiss of the(c) Aspromonte Peloritani Unit(mylonitic paragneiss (inset of showing the detail APU); of the stretching lineation); fracture (LAF) both in the APU (to the left) and in the MPU rock-types (to the right); high angle joint system in the mylonitic leucogneiss of the APU; mylonitic contact between APU andlater MPU brittle surfacing tectonics along (see the Fig. Zillastro 2 landslide for a location). Figure 3. Figure 2. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | number = sequential N (a) high angle families hierarchy – longer segments 942 941 = high angle families hierarchy – longer segments corresponds = stereoplots of the main structural features observed in outcrops. (b) stereoplots of the main structural features observed in outcrops. (b) Schematic representation of Stilo unit (SU) structural evolution: Schematic representation of Aspromonte-Peloritani unit (APU) structural evolution: number of measurements, 1st, 2nd, 3rd sequential blasto-deformational evolution with associated the orogenic stages from ductile = N Figure 5. (a) to brittle sequence; corresponds to a greater number of data. of measurements, 1st, 2nd, 3rd to a greater number of data. Figure 4. blasto-deformational evolution withsequence; associated the orogenic stages from ductile to brittle Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | K- (a) (b) mylonitic (f) high angle families hierarchy – longer segments 943 944 = blocky adularia veins subparallel to the mylonitic foliation; (d) classical view of an APU mylonite. The main foliation is characterized stereoplots of the main structural features observed in outcrops. (a) (b) Severely deformed pre-mylonitic K-feldspar showing intracrystalline plasticity (c) Schematic representation of Madonna di Polsi unit (MPU) structural evolution: Microphotos: number of measurements, 1st, 2nd, 3rd hydraulic fracturing of a quartz microlithon crosscut by a network of veins (filled by chlorite = N sequential blasto-deformational evolutionto with brittle associated sequence; the orogenic stagescorresponds from to a ductile greater number of data. Figure 7. by alternating mica-rich (Btby “fish” ondulouse shaped) extinction, and very quartz-rich fine domains grainsize (SGR-GBM) (ribbon-like) and characterised a marked oblique foliation; Figure 6. feldspar porphyroclasts showing domino-type structures (bothare synthetic and developed) anthitetic floating fractures usually into a flattened a aspect, the verydeformation. elliptical fine shape is ultramylonite due to matrix erosion (sample of external SDA13). edges during Clasts shear have associated with frictional sliding; (e) and sericite) which usually are not propagating to the surrounding micaceous layer; fabric overprinted by a subvertical conjugate set of fractures (micro-graben like structure). Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (b) quartz- (d) same of , red plane); 3A (c) S extremely rounded complex geometry of (e) (g) detail of a (squared area) showing an (c) 945 946 oblique foliation in quartz domain; (d) ) and relative stereoplot with the mylonitic foliation ( 1A L complex refolding microfabric (parallel polarizers); block diagram showing thin section cut direction together with stereoplot; , note the elongated and rounded shape of the large feldspar at the bottom-right (f) (a) (e) Mylonite of APU and associated microstructures (SDA3 sample – AB section): Mylonite of APU (sample SDA3 – CD thin section orthogonally cut with respect ecting quartz layers (crossed polarizers). ff sketching draw of oriented specimen with the trace of cut (dotted line) parallel to the feldspar clast floating into a fine micaceous matrix (crossed polarizers); ultramylonite (half bottom part) interbedded with mylonite (half upper part), a set of high same as porphyroclast; folds a (b) angle veins disrupt the horizontal foliation continuity; the Fig. 8): intrafolial fold (crossed polarizers); Figure 9. Figure 8. (a) stretching lineation ( (b) ultramylonite layer is visiblerich in and the micaceous-rich upper domainsoblique foliation part enveloping in feldspar the of upper augens the(e) quartz (crossed picture ribbon polarizers). coherent (parallel with Note polarizers); a the sinixtral sense of shear (top-to-NE); corner (parallel polarizers). Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | SDA3 (f) subdomain ) 00 (h sample SDA10 (section SDA1 sample; (e) (b) quantitative microstructural analysis (b) sample SDA11; 948 947 (a) sample SDA14: coi of a complex domain consisting SDA8 sample (MPU); (h) (d) focusing on the syn-shear ribbon-like quartz; (h) considering a total of 3542 grains: the plot (aspect ratio vs. number (a) sample SDA7; (g) axis patterns inferred by the CIP method on selected quartz-rich domains. c Grain boundary map of the quartz domain selected for paleopiezometry (sample Quartz section SDA10 (section CD); showing the quartz recrystallized into the discordant vein. Legend: Pg: paragneiss; Lg: (c) restricted subdomain of ) (h) 0 of grains) shows an unimodal distribution of grains clustered around the 1.5 value. of the domain depicted in Figure 11. (a) SDA3). The colour lookup table is the same as Fig. 10; AB); sample (section AB); of sub-horizontal syn-mylonitic quartz(h and post-mylonitic crosscutting subverticalof quartz vein; In the crystallographiccoded orientation based images on (coi) the the shown azimuth look-up-table: and dip of each pixel is color leucocratic gneiss; Um: ultramylonite;Polsi Unit. My: Mylonite; Pst: pseudotachylite; MPU: Madonna di Figure 10. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | undulose (c) 949 950 Typical SGR recrystallization showing lobate grain boundaries and recrystallized large quartz microlithon showing pervasive fracturing. Note here as kinking of (d) BLG recrystallization process showing undulose extinction of elongate grains and grain extinction visible within abetween sub-horizontal a ribbon quartz-richa grains domain with mortar (lower associated texture part)arrows); deformation characterized and lamellae by a recrystallizedbiotite micaceous smaller flakes are domain quartz concentrated (upper at grains the part) at end of showing its veins crosscutting margins the (white quartz layer. boundary bulges concentrated at the sutured edges of ribbon-like quartz; Figure 12. (a) grains which are(b) slightly larger than sub grains (visible at lower left corner of the picture); Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | the (a, b) (c) ) sketch draw of other example of biotite d , c (e) , a detail of a (parallel polarizers); sketch draw of a showing horizontal detail of ( (b) (d) (b) ); 2A V 952 951 and 1A V fibrous veins; (a) ): (crossed polarizers); 3A V (b) ), subparallel 1st set of adularia veins (black region), and 2nd set of 3A S sigmoidal 1st set of veins truncating mylonitic fabric (parallel polarizers); – squared region – showing blocky grains of adularia (crossed polarizers); high angle fibrous vein with respect mylonitic foliation. 1st and 2nd set of veins ( (e) (f) (e) 3rd set of veins ( layering given by ribbon-like quartz, micaceous-rich layers and adularia paraconcordant detail of respectively, suggesting a sinixtral shear sensefibrous around vein; the fracture; (g) veins. Note how avein, subvertical whereas secondary it vein ispolarizers). is passing deflected through around quartz the domains early (upper formed right adularia part of the picture, crossed Figure 14. same domain depictedmylonitic in foliation ( stylolite-like veins (spotted line)central produced inset; with principal(f) stress orientation as depicted in the Figure 13. (a) Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | showing superposition of ductile- axis pattern and inferred sigma1 sketch draw with interpretation of (d) c (d) quartz (b) 954 953 (parallel polarizers); (b) interpretative schematic draw of like (e) showing a complex fold (red square region near the center of the picture, (c) ; (a) (a) Rough grain boundary map of the same domain of Fig. 9h (sample SDA14) Ultramylonite (sample SDA3) characterised by a complex geometry of quartz detail of (b) regime related shear zone (black-coloredsigma1). sigma1) and brittle-regime related veins (red-colored microstructures in crossed polarizers); layers; Figure 16. (a) Figure 15. (a) investigated by means of the CIP method; orientation of theof coarser about quartz 60 the grains early composing ribbon the quartz vein shown on on the the left. right cutting at an angle Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 0.1-0.2 0.3-0.8 0.2-0.4 0.2-0.3 (Gpa) estimates Approx. P Approx. (°C) estimates Approx. T Approx. 400-600 250-300 300-350 150-250 1 1 3 s s s TURES

3A 3A

A

S 3 S S

3 3

s B s

Z

1 S s 3A 1 mm 1 mm S 1 1 mm MICROSCOPIC FEA MICROSCOPIC s A A 4 4 ± S S 1A 3

3A 1 L = = 955

S

4A 1A A A 3 3 S L A ±Grt A 4 3 S S 4 ±Czo B 4 B TURES ±Pl 3 ur±Amph 2A +Chl+Pl L 4 +Bt+Chl 3 Czo±T Normal and conjiugate low angle brittle joints 3A 3A Normal and conjiugate high Normal and conjiugate angle brittle joints Qtz+Wm S B Qtz+Wm 1 m MESOSCOPIC FEA MESOSCOPIC 10 cm 1 m 1 cm Joints Joints 3A 4A 6A 3A 4A 5A D M M D D D phase

Deformation

e e n i n i n n n i e n n n e i e p p p l A

A A

y l e e r t t a a a E L L Synoptic scheme illustrating the tectonic evolution of the Montalto Shear Zone stages Orogenic Figure 17. also showing thestructures linkage (thin between section scale) mesostructural during features progressive deformational (outcrop phases scale) (Table 2). and microscopic