GEOLOGICA ULTRAIECTINA

Mededelingen van het Geologisch Instituut der Rijksuniversiteit te Utrecht

GRAVITY TECTONICS, GRAVITY FIELD, AND PALAEOMAGNETISM IN NE-ITALY. (With special reference to the Carnian Alps, north of the Val Fella-Val Canale area between Paularoand Tarvisio· Province of Udine-).

t I. 34 No. 1 Boer, J.C. den, 1957: Etude g~ologique et paleomagn~tique des Montagnes du Coiron, Ardeche, France

No. 2 Landewijk, J.E.J.M. van, 1957: Nomograms for geological pro- blems (with portfolio of plates)

No. 3 Palm, Q.A., 1958: Les roches cristalline des C~vennes m~dianes a hauteur de Largentiere, Ardeche, France

No. 4 Dietzel, G.F.L., 1960: Geology and permian palaeomagnetism of the Merano Region, province of Bolzano, N. Italy

No. 5 Hilten, D. van, 1960: Geology and permian palaeomagnetism of the Val-di-Non Area, W. Dolomites, N. Italy

No. 6 Kloosterman, 1960: Le VoIcanisme de la Region D'Agde (Herault France)

No. 7 Loon, W. E. van, 1960: Petrographische und geochemische Unter- suchungen im Gebiet zwischen RemUs (Unterengadin) und Nauders (Tirol)

Agterberg, F. P., 1961: Tectonics of the crystalline Bas'_ment of the Dolomites in North Italy

Kruseman, G.P., 1962: Etude pal~omagn~tique et s~dimentolo- gique du bassin permien de Lodeve, H~rault, France

Boer, J. de, 1963: Geology of the Vicentinian Alps (NE-Italy) (with special reference to their palaeomagnetic history)

Linden,W.J.M. van der, 1963: Sedimentary structures and facies interpretation of some molasse deposits Sense -Schwarzwasser area- Canton Bern, Switzerland

Engelen, G. B. 1963: Gravity tectonics of the N. Western Dolo- mites (NE Italy). IlGeologica Ultraiectjna" is een ongeregelde serie, hoofdzakelijk bestemd voor het opnemen van dissertaties afkomstig uit het Geolbgisch Instituut der Rijksuniver­ siteit te Utrecht. "Geologica Ultraiectina" is een voortzetting der "Geologisch-Geografische Mede­ delingen: Geologische Reeks", welke uitgave in 1947 gestopt is. "Geologica Ultraiectina" wordt toegezonden aan alle instellingen die ruilverkeer onderhouden met het Utrechtse instituut. Losse nummers zijn - voor zover de voorraad strekt - verkrijgbaar bij de administratie van het instituut, Gude Gracht 320, Utrecht.

"Geologica Ultraiectina" is an odd series with the main purpose of publishing D. Sc. theses from the "Geologisch Instituut" of the Utrecht State University. "Geologica Ultraiectina" I:;; a continuation of the "Geologisch-Geografische Mede­ delingen: Geologische Reeks", which came to an end in 1947. "Geologica Ultraiectina" is sent to all departments which exchange publications with the Utrecht institute. Separate copies - when available - may be obtained from the administrator of the Institute, Gude Gracht 320, Utrecht.

"Geologica Ultraiectina"est un serie irn3guliere de memoires qui vise essentielle­ ment 11 publier des theses de doctorat en Sciences presentees au "Geologisch Insti­ tuut" de L'Universite d'Etat d'Utrecht. "Geologica Ultraiectina" continue la serie des "Geologisch-Geografische Mede­ delingen: Geologische Reeks, achevee en 1947. Tout laboratoire faisant des echanges de publications avec l'institut d'Utrecht recevra "Geologica Ultraiectina" Les exemplaires disponibles sont deposes chez Uadministrateur de l'institut, Gude Gracht 320, Utrecht.

"Geologica Ultraiectina" erscheint in unregelmassigen Abstanden und enthalt hauptsachlich Doktorarbeiten des Geologischen Institutes der Uni versitat Utrecht. "Geologica Ultraiectina" ist die Forsetzung der "Geologische Geografische Mede­ delingen: Geologische Reeks" welche Ausgabe in 1947 eingestellt wurde. "Geologica Ultraiectina" wird allen Instituten zugesandt, welche mit dem Institut in Utrecht im Tauschverkehr stehen. Einzelnummern sind - soweit vorratig ­ bei der Institutsverwaltung , Utrecht, Gude Gracht 320, kauflich zu erhalten. This memoir contains a doctoral thesis defended before the Senate of the State University at Utrecht on· r'ebruary 3rd, 1964.

Ce memoire a fait l'objet d'une these de doctorat en Sciences a l'Universite d'Etat d'Utrecht Ie 3 Fenier 1964.

Diese Schrift ist eine Doktorarbeit, verteidigt VOl' dem Senat del' RcichsuniversiUit Utrecht am 3 Februar 1964. ORAVITY TECTONICS, GRAVITY FIELD, AND PALAEOMAGNETISM IN NE-ITALY. (With special reference to the Carnian Alps, north of the Val Fella-Val Canale area between Paularo and Tarvisio - Province of Udine -).

R. GUICHERIT

1964

DRUKKERI]: 1. van der Velde - Gibsonstraat 1-3 - Deventer PRO MOT 0 R : PRO F. DR. I R . R. W. VA N BE M MEL E N STE LLINGEN

I

De Tarvisslenk in de Karnische Alpen is; een gravttatleve reactie op de formatie van de Drauslenk ten Noorden ervan.

II

De "Calcari Lastroidi" behoren tot het Karn en niet tot het Infra- Ladien, zoals door Gortani wordt verondersteld. Gortani, 1936: Bologna Coop. Tip. Azzoguidi (prima parte)

III

De argumenten van di Colbertaldo voor een epigenetische ontstaanswljze van de lood-zink ertsen van Raibl zijn niet steekhoudend. di Colbertaldo, 1948: Rep. Int. GeoI. Congr. London XVIII Sess. 1963: Rep. Conf. Klagenfurt I Sess.

IV

De alkali distributie in hoog ingedrongen relatief zure vulkanische lichamen is onafhankelijk van het nevengesteente, maar wordt bepaald door interne migratie van alkali-ionen, volgens de temperatuur gradient. Orville, 1963: Am. Journ. of Sc.

V

Voor het palaeomagnetisch onderzoek geven gesteenten met een relatief hoog gehalte aan primaire haematiet de beste resultaten.

VI

Er schijnt geen verband te ZlJn tussen de "inclinatie fout" van het sedimentair remanent magnetisme en de "korrelgrootte" van sedimenten. Griffiths et al.1960:Proc. Roy. Soc. London.

VII

Uit dispersie van oppervlakte golven kan de structuur van de aardkorst niet "een­ duidig" bepaald worden.

VIII

De korstverkorting onder de Alpen kan niet ult gravimetrische profielen berekend worden.

IX Bij de genese van bauxieten spelen biochemische factoren een zeer grote roI. x

De absolute ouderdomsbepaling van diepzee sedimenten met de ionium-radium methode is niet betrouwbaar.

XI

De gemeenschappelijke veronderstelling, die de basis van het onderling dispuut tussen het "vitalistisch" en "materialistisch" denken in de biologie vormt, berust op een ernstig misverstand inzake de aard van de natuurwetenschap. Melsen, van, 1959: Symposium Evolutie

XII

A-seismische (laterale) oceanische ruggen kunnen belangrijke indicaties zijn hoe bepaalde continenten gedurende de geologische geschiedenis bewogen hebben. Wilson, 1963: Nature, No.4884, Vol. 198

XIII

De sexueel "gemiddelde" of "normale" mens is een ficUe.

XIV

Omdat het mytische Rijk van Atlantis in het oostelijke deel van de Middellandse Zee gelegen heeft en nlet in de Atlantische Oceaan, is de oude naam van deze wereldzee ("Westelijke Oceaan") te verkiezen boven de huidige naam. Galanopoulos, 1960: Publ. Ace. Athens , T. 35

R. Guicherit, 3 februari 1964 CONTENTS

Samenvatting 9 E. POST-TRIASSIC VOLCANISM 39 Summary 11 F. CONCLUDING REMARKS ON Riassunto 13 THE STRATIGRAPHY OF THE CARNIAN AND JU LIAN ALPS 40 Introduction 17

Chapter III: Tectonics Chapter I: Stratigraphy A. THE CONCEPT OF GRAVITY A. GENERAL . 19 TECTONICS. 42 B. UPPER CARBONIFEROUS 19 B. TECTONICS OF THE PER­ C. PERMIAN 21 MO-TRIASSIC SEDIMENTARY SERIES 46 D. TRIASSIC . 25 1. Scythian 25 1. The Tarvis fault 46 2. Anisian . 26 2. The Cocco fault. 48 3. Ladinian 29 3. The Tarvis graben . 50 4. Carnian. . 29 4. Compressive settling and 5. Norian and Rhaetian . 31 Diapirism of the Sedimen­ 6. Quaternary. 31 tary Rocks . 54 5. Dislocations of minor im­ portance . 56 Chapter IT: Volcanism 6. Structural evolution of NE Italy (with special refe­ A. GENERAL. 32 rence to the eastern Carnian kIps) . 56 B. PERMO-CARBONIFEROUS VOLCANISM 32 1. The amygdaloidal basalts 33 Chapter IV: Mining 2. Diabase Porphyrites . 33 3. Tuffs . 33 A. INTRODUCTION. 62 4. 111e Bolzano ignimbritic B. TECTONICS OF THE series 33 MINING REGION 62 C. TRIASSIC VOLCANISM 34 C. SOME REMARKS ON THE GENESIS OF THE PB-ZN 1. + 2. The Buchenstein and ORES OF RAIBL . 65 Wengen series. . 34 3. The Cassianer series . 35 4 .. The Ladino-Carnian in- and Chapter V: Geophysics extrusive rocks 35 D. ANALYSES OF THE PORPHYRY A. THE GRAVITY FIE LD OF NE ITALY . 70 SAMPLES 0 36 1. Introduction 70 7-12. Palaeomagnetic data 2. Reductions . 71 of the permo-carbonife­ 3. Interpretation of gravity rous and triassic rock- data 72 samples 91 4. Density of rocks 74 . 13. Interpretation of the 5. Discussion of the anomalies palaeomagnetic data 105 in northern Italy . 76

B. PALAEOMAGNETISM 1. Introduction 82 Chapter VI: 2. The remanent magnetization of rocks. 83 3. Magnetic cleaning. 85 APPENDIX I 115 4 .. Measuring and interpretation 86 APPENDIX II 117 of the results . 5. The earth's magnetic field 86 6. General results 89 BIBLIOGRAPHY 119 SAMENVATTING

In dit proefschrift is getracht een In het Permo-Trias, aan het be­ geologische, gravimetrische en palaeo­ gin van de alpiene geosynclinale daling, magnetische analyse te geven van ontstonden horst en slenk structuren, noord-oost ItaW~, waarbij de tekto­ die vooral in de Trias grote facies­ nische ontwikkeling van het oostelijke wisselingen in de sedimentatie, zowel deel van de Karnische Alpen, ten in horizontale zin, als in verticale noorden vanhet Pontebbana-Val Fella­ zin veroorzaakten. Val Canale dal, meer in rletail wordt behandeld. Vulkanisme: Vulkanisme heeft in de oostelijke Stratigrafie: Karnische Alpen en in de Julische De stratigrafische gegevens zlJn Alpen herhaaldelijk een belangrijke hoofdzakelijk ontleend aan publicaties rol gespeeldo In de oostelijke Kar­ van oostenrijkse en italiaanse geologen nische Alpen vindt men in het Onder uit de eerste decennia van :leze eeuw, Karboon (Kulm), in- en extrusies van die voortreffelijk stratigrafisch­ hoofdzakelijk basisch materiaaL Ge­ palaeontologisch werk verrichtten. durende het Anis en Ladin hebben Ret Pontebbana-Val Fella-ValCanale zowel in de Karnische Alpen als in dal ligt tussen de Karnische Alpen de Julische Alpen in-en extrusies in het Noorden en de Julische Alpen (deeIs submarien) van zuur materiaal in het Zuiden. Ret varistische en plaatsgevonden, terwijl explosies dikke alpiene gedeformeerde "basement" is en uitgestrekte tufpaketten leverden. in de Karnische Alpen ontsloten en bestaat uit palaeozoische gesteenten. Tektoniek: Rierop rust in de Karnische Alpen De "Tarvisslenk", waarvan de een stratigrafische kolom, die van het begrenzing aan de zuidzijde ten dele Perm tot het Karn (Boven Trias) met het Pontebbana-Val Fella-val loopt, terwijl in de Julische Alpen Canale lengtedal samenvalt, ontstond ook Jura en Krijt voorkomt. De per­ tijdens de tertiaire periode van de al­ mo-triadische serie bereikt een dikte piene gebergtevorming.De Tarvisslenk van 3-5 km. Ret Tertiair ontbreekt. wordt door twee normale afschuivings­ Ret oud Kwartair is vertegenwoordigd breuken begrensd: de Cocco-breuk door dikke morene en fluvio-glaciale in het Noorden en de Tarvisbreuk afzettingen, die tijdens en na de ijs­ in het Zuiden. De slenk splitst zich tijden ontstonden. In het jong-Kwartair in de bl:lurt van Pontebba in twee ontstonden enorme hoeveelheden hel­ nauwere slenken. lingpuin van de ladinische en norische Door afglijdingen zijn gesteente­ rifkalken en dolomieten, dat aan de massas van weerszijden der topo­ voet van de berghellingen plaatselijk grafische depressie, die door de grote puinkegels vormt. Tenslotte slenk gevormd werd, in de slenk ge­ kunnen nog rivier-terrassen en allu­ gleden. Ook zijn de begrenzende breu­ viale rivier afzettingen onderscheiden ken door secundaire (gravitatieve) worden. deformaties omgedrukt en in schijn­ bare opschuivingen getransformeerd, Venetiaans maximum). In het gebied zoals dit bekend is van de Gailbreuk nabij het Lago di Garda, splitst zich (van Bemmelen 1957, 1961), de Judi­ een NNW-SSE verlopende zone van carien breuk (Dietzel; 1960, van positieve anomalien (het Colli Euganei Riltenj 1960) en de Pusteria en Sugana maximum) van het Lombardo-Veneti­ breuk (Agterberg: 1961). aans maximum af. Ret Colli Euganei In de 3lenkzone heefthet diapirisme maximum loopt over de West Vicen­ een belangrijke doch locale rol ge­ tijnse Alpen, via de Monte Berici speeld. Dit verschijnsel heeft Engelen naar de Colli Euganei. Naar het (1963), op grotere schaal, ook voor Oosten toe, gaat dit maximum in een de NW Dolomieten beschreven. Door gebied met negatieve anomalien over het wegzakken van de midden tria­ (het Venetiaans minimum). Ret wordt dische riflichamen, werden de onder­ ervan gescheiden door de Vicenza liggende plastische boven karbonische­ breuk. en permo-triadische formaties wegge­ Ret Colli Euganei maximum kan perst naar de omliggende dalen, waar verklaard worden door de relatief ze nu als diapier-achtige structuren hoge ligging van het grondgebergte, aan de dag treden. De dalen zijn of gecombineerd met het effect van een tektonisch, of door rivier-insnijding groot plutonisch of sub-vulkanisch (veelal n'a de kwartaire ijstijden) ont­ lichaam met relatief grote dichtheid staan. De daling van de riffen, had in de diepte. Deze intrusie van basal­ hun desintegratie in een aantal blok­ tisch materiaal staat waarschijnlijk ken tot gevolg. Van deze blokken zijn in verband met de daling van de Po­ de bovenliggende, plastische "Raibler­ geosynclinale, waarbij basaltisch schichten" in de aangrenzende topo­ magma van onder het Po-gebied zij­ grafische depressies gegleden. waarts werd weggeperst. Ret tertiaire De Tarvisslenk is het gevolg van vulkanisme van de Vicentijnse Alpen rekbewegingen, die samenhangen met zou met deze magma migratie in de verzakking van de Karnische Alpen verband kunnen staan (de Boer 1963). in de Gailtrog ten noorden ervan (zie De anomalien van het Lombardo­ profiel D-D'). Deze slenk is dus een Venetiaans maximum enhet Venetiaans gravitatief tektogenetisch effect van minimum kunnen verklaard worden, de eerste orde op de vorming door trapbreuken in het grondgebergte van de grote Gailslenk. Vervol­ aan te nemen. Deze hangen samen gens zijn gravitatieve tektogenetische met de neogene opheffing van de reacties van de tweede orde zoals dia­ Alpen in het Noorden en de gelijk­ perisme en verglijdingen opgetreden, tijdige daling van de Adria in het die er naar streefden de "reliefener­ Zuiden. gie", die door de Tarvisslenk ont­ stond, weer te nivelleren. Palaeomagnetisme: De Palaeomagnetische richtingen, Gravimetrie: gemeten in georienteerde monsters De meeste gravimetrische ge­ van karbonische en permo-j;riadische gevens betreffende de Alpen werden gesteenten van noord-oost Italie blij­ door de Bruyn (1955) samengevat in ken grote verschillen te vertonen met een Bouguer- en een Isostatische richtingen gemeten in georienteerde anomalien kaart (schaal 1 : 5000 000). monsters van gesteenten van dezelf­ Onder de Centrale Alpen valt een de ouderdom, welke afkomstig zijn strook van negatieve anomalien (Cen­ van het "stabiele" meso-Europa. traaIAlpenminimum), met ten zuiden Een zo volledig mogelijk dis­ hiervan een strook van positieve iso­ cussie werd gegeven omtrent de mo­ statische anomalienop (het Lombardo- gelijke oorzaken hiervan (translaties en/of rotaties van continent massas, vroegere litteratuur genaamd) gedu­ seculaire variaties, anomalien van rende het Mesozoicum de rol van het magnetisch veld, etc.), Geconclu­ "transcurrent faults" ("geosuturen") deerd moet worden, dat noord-oost gespeeld kunnen hebben. De tertiaire ItaW~ sinds het Boven Karboon belang­ structurele, evolutie, zoals die in rijke translaties en locaal misschien het hoofdstuk betreffende de tektoniek ook rotaties heeft ondergaan van het onderzochte gebied beschreven Tenslotte moet erop gewezen. wor­ is, heeft een meer locaal, gravitatief den, dat de grote alpiene breuken, zo­ karakter en is gesuperponeerd op deze als de Peri-Adriatische storingszone oudere structureIe lijnen. ("Alpien-Dinarische grenszone" in

SUMMARY

In this thesis a geological, gravi­ sented by thick morene and fluvio­ metricaL and palaeomagnetical ana­ glacial deposits, left behind by the lyses of NE Italy is given, with special quaternary glaciers on their retreat. reference to the E Carnian Alps north Furthermore there are enormous of the Pontebbana-Fella-Canale Valley. masses of scree material, caused by by the weathering of the ladinian Stratigraphy: reef-bodies, which sometimes may Stratigraphic data are mainly de­ built up huge taluscones at the, moun­ rived from publications of Austrian tain feet. Finally mention should be and Italian geologists, who have done made of river-terraces and alluvial excellent stratigraphic and palaeonto­ deposits of the riyer valleys. logical work in the first decades of As a result of post variscan tec­ this century. tonic movements, during tile beginning The investigated region lies south of the alpine geosynclinal subsidence, of the great Gailfault and forms a horst and graben structures oriKinated, part of the Carnian- and Julian Alps. giving rise to great differences in In the Carnian Alps to the North, facies in the Tria.ssic, in horizontal the alpidic and variscan folded and as well as in vertical direction. faulted basement, consisting of palaeozoic rocks, is exposed. In the Volcanism: Carnian Alps the basement is over­ Volcanism has recurrently played lain by a stratigraphic column, of an important part during the history which the age of the strata ranges of the eastern Carnian Alps and Julian from the Upper Carboniferous to the Alps. In the lower carboniferous de­ Carnian (Upper Triassic), while in posits (Kulm) of the eastern Carnian the Julian AlpS also jurassic and cre­ Alps, in- and extrusions of mainly taceous deposits occur. The thickness basic igneous matter and tufflayers .of the permo-triassic sedimentary are met with. During the Anisil~m and series is about 3 to 5 km. The Tertiary Ladinian of the Carnian Alps and of is lacking. The Quaternary is repre­ the Julian Alps, in- and extrusions (partly submarine) of acid igneous The Tarvis graben was brought matter took place, while tuffexplo­ about by tension movements related sions gave rise to the· formation of to the settling of the Carnian Alps thick and extensive tuff layers. into the Gailtrough, to the north of it (see section D-D'). The Tarvis Tectonics: graben is also a gravitational tecto­ The 11 Tarvisgraben11 of which the genic effect of the first order resul­ southern borderline partly coincide ting from the formation of the major with the Pontebba-Fella-Canale Valley, Gail graben. Subsequently, gravita­ originated during the tertiary period tional reactions of the second order, ofthe alpidic orogenesis. The Tarvis­ such as diapirism and sliding move­ graben is bordered by two normal ments took place thus leveling the re­ faults; the Cocco-fault to the North, lief energy caused by the Ta,rvis and the Tarvis-fault to the South. graben. Near Pontebba the graben shows an abrupt bifurcation into two narrower Gravimetry: graben structures, one with an east­ Most of the gravimetric data of the western direction and the other with Alps were published by de Bruyn a more south-east/north-western (1955) as a Bouguer and Isostatic direction. anomaly map (scale 1 : 5 000 000). After the formation of the graben, Under the Central Alps a strip of rock units from both sides have slid negative anomalies can be observed into is topographic depression. The (minimum of the Central Alps); to normal faults bordering the Tarvis­ the south of this minimum a strip graben have locally also been trans­ of positive anomalies occurs (Lombar­ formed into (apparent) upthrusts do-Venetian maximum). The Colli through secondary gravitational re­ Euganei maximum is the south-eastern actions, as has been described for "leg" of this maximum, starting in the Gailfault (van Bemmelen; 1957, a region near Lago di Garda, and 1961), for the Judiacaria-fault (Dietzel; extending across the western part of 1960, van Hilten; 1960), and for the the Vicentinian Alps, via the Monte Pusteria and Sugana-fault (Agterberg; Berici to the Colli Euganei. To the 1961). East this maximum passes into a As has been exposed by Engelen region with negative anomalies (Vene­ (1963) for the NW Dolomites, also tian minimum). It is bordered from in the region under discussion dia­ this minimum by the Vicenzafaultzone. pirismhad played an important, though The Colli Euganei maximum can local part during its structural evo­ be explained by the relatively high lution. Owing to sU!Jsidence of the position, of the basement, together rigid and relatively heavy middle with the occurrence of plutonic masses triassic reef bodies, the underlying with relatively high specific density more plastic upper ~arboniferous and in the crust. The intrusion of this permo-triassic strata were squeezed basaltic material is probably related out to the encircling valleys, where to the subsidence of the Po-geosyncline, they now emerge like diapiric struc­ by which magmatic material of relati­ tures. Subsidence of the reefs also velyhigh specific density was squeezed caused their disintegration into va­ out towards the margins. The tertiary rious separate units. By gravitatio­ volcanism from the Vicentinian Alps nal gliding, the overlying plastic is probably related to this process "Raibliano" has slid like a mantle from of magma migration (de Boer, 1963). the reefs into the adjacent topo­ 'The anomalies of the eastern part graphic depressions. of the Lombardo-Venetian maximum and the Venetian mInImUm can be magnetic field etc. ) for this deviation explained by assuming the existance is given. It must be concluded that of stepfaults in the basement, due to NE Italy has Undergone considerable the neogene upheavel of the Alps to translations, and locally may be, the North, and simultaneous subsi­ also rotations since the Upper Car­ dence of the Adria to the South. boniferous with respect to its present day position. Palaeomagnetism: Finally it has to be pointed out Palaeomagnetic directions mea­ that the major alpine faults, such as sured from orientated upper carbo­ the Peri-Adriatic fault-zone ('!Alpine­ niferous and permo-triassic rock­ Dinaric boundary fault" in former samples from NE Italy show a con­ literature) may have acted as great siderable deviation from directions transcurrent faults C'geosutures") in from orientated rocksamples of the meso'Zoic time. However, the tertia­ same age of the tectonical "stable" ry structural evolution as described parts of the European continent. A in the chapter on tectonics, has a discussion of the possible causes more local, gravitational character (such as translations and/or rota­ and was superimposed on these older tions of continental blocks, secular structural lines. variations, anomalies of the earth's

RIASSUNTO

In questa tesi e fornita un'analisi nelle Alpi Carniche, da una serie geologica, gravimetrica, e paleomag­ stratigrafica, di eta compresa tra il netica dell'Italia nord-orientale, con Carbonifero superiore ed il Carnico particolare riferimento aIle Alpi Car­ (Trias superiore), mentre nelle Alpi niche orientali, a nord della Valle Oiulie si trovano anche depositi Pontebbana-Fella-Canale. giurassici e cretacei. La potenza della serie sidementaria permo-trias­ Stratigrafia: sica si aggira sui 3-5 km. Manca I dati stratigrafici sono derivati il Terziario.Il Quaternario e rappre­ soprattutto da pubblicazioni di geo­ santato da potenti depositi morenici logi italiani ed austriaci, che, nelle e fluvio-glaciali, formati dai giacciai prime decadi di questo secolo, hanno quaternari, e lasciati indietro dopo fatto eccellenti lavori stratigrafici e il loro ritiro. Esistono inoltre enormi paleontologici. masse di materiale detritico,derivante La regione investigata si trova a dalla degradazione delle scogliere sud della grande linea di Gail e ladiniche, che a volte costituiscono costituisce una parte delle Alpi enormi falde ai piedi delle montagne. Carniche e Giulie. Infine debbono essere ricordati i Nelle Alpi Carniche il basamento depositi alluvionali,anche terrazzati, alpino e varisico, ripiegato a fagliato, lungo Ie valli fluviali. affiora a Nord. Esso e ricoperto, A causa di movimenti tettonici post-varisici, durante l'inizio della (Agterberg, 1961). subsidenza del geosinclinale alpino, n diapirismo ha giocato una parte si formarono strutture a fosse e importante durante l'evoluzione struttu­ pilastri, cia che diede origi~e a grandi rale della regione. A causa della differenze di facies, sia in senso subsidenza delle rigide e relativa­ orizzontale, che verticale, nei depositi mente pesanti scogliere del Trias triassici. medio, i sottostanti strati dal Carboni­ fero superiore e del Permo-Trias, pili Vulcanismo: plastici, furono spremuti verso Ie n vulcanismo ha giocato a diverse valli circostanti, dove ora essi emer­ riprese un ruolo importante nella gono come strutture diapiriche. La storia delle Alpi Carniche orientali e subsidenza delle scogliere fu anche delle Alpi Giulie. la causa della lora frantumazione in Nei depositi del Carbonifero in­ varie, separate unita. Per scivola­ feriore (Culm) delle Alpi Carniche mento gravitativo il soprastante plastico orientali si incontrano intrusioni ed Raibliano si e spostato come una effusioni di materiale prevelentemente coltre, dalle scogliere verso Ie adia­ basico e depositi di tuffi. Durante centi depressioni topografiche. l'Anisico ed il Ladinico, sia nelle II graben di Tarvisio fu causato, Alpi Carniche, sia nelle Alpi Giulie, da movimenti di tensione, dovuti allo si ebbero intrusioni ed effusioni (in spostamento verso Nord (nella fossa parte sottomarine) di materiale acido, di Gail) della parte centrale delle mentre delle esplosioni originarono po­ Alpi Carniche orientali (v. Profilo tenti ed estesi depositi tufacei. D-D'). II graben di Tarvisio e dunque Tettonica: una reazione te~togenetica gravita­ II "Tarvis graben", il cui margine tiva, di primo ordine, alIa for­ meridionale coincide in parte con la mazione della fossa di Gail. Valle di Pontebbana-Fella-Canale, In sequito, si verificarono rea­ ebbe origine durante il periodo terzia­ zioni graVitative, di secondo ordine, rio dell'orogenesi alpina. II "Tarvis quali quelle prima menzionate, cosi graben" e limitato da due faglie nor­ riducendo "l'energia di rilievo" (,lre­ mali: la faglia do Cocco a Nord e la lief energy") derivante dell'esistenza faglia di Tarvisio a Sud. Vicino a del graben di Tarvisio. Pontebba il graben mostra un' impro­ vvisa biforcazione in due strutture Gravimetria: a fossa pili ristrette, una con dire­ I dati gravimetrici sulle Alpi zione E-W, l'altra con direzione furono per la maggior parte pubblicati maggiormente tendente alIa SE - NW. da de Bruyn (1955), sotto forma di Dopo la formazione del graben, carta delle anomalie di Bouguer ed Ie rocce scivolarono da entrambi i isostatiche (scala 1 : 5 000 000). margini entroquesta depressiohe topo­ Al di sotto delle Alpi Centrali si grafica. Le faglie normali delimitanti puo osservareuna fascia con anoma­ il graben di Tarvisio sono anche state lie negative (minimo delle Alpi Centra­ trasformate localmente in (apparenti) li) e, a sud di essa, una di ano­ faglie inverse, a causa di secondarie malie positive (massimo Lombardo­ reazioni gravitative cosi come e Veneto). n massimo dei Colli Euganei stato descritto per la linea di Gail rappresenta il prolungamento sud­ (van Bemmelen, 1957, 1961); per orientale del massimo Lombardo­ la linea delle Giudicarie (Dietzel, Veneto, iniziantesi in una zone presso 1960, van Hilten, 1960) e per la il Lago di Garda, e decorrente attra­ linea della Pusteria e della Sugana verso la parte occidentale delle Alpi Vicentine, lungo Monti Berici verso Carbonifero superiore e di Permo­ i Colli Euganei. Verso E, questo Trias dell'Italia di NE mostrano una massimo passa in una regione con deviazione considerevole rispetto anomalie negative (minimo Veneto); a quella di campioni orientati della esso e separato da tale minimo dalla stessa eta, provenienti delle aree zona di faglie di Vicenza. tettonicamente "stabili" del continente 11 massimo dei Colli Euganei pUG europeo. essere spiegato con la posizione del Una discussione delle possibili basamento relativamente alta, unita cause (translazioni e/o rotazioni delle all'esistenza nella crosta di masse zolle continentali variazioni; secolari; plutoniche a peso specifico relati­ anomalie del campo magnetico terres­ vamente alto. tre, ecc.) di questa deviazione viene L'intrusione di questa .materiale fomita. basaltico e probabilmente collegata Si deve concludere che 1'Italia di con la subsidenza del geosinclinale NE e andata soggetta a considerevoli padano, che comporto una spremitura traslazioni e, forse, localmente, anche verso i margini di materiale magma­ a rotazioni, a partire della sua po­ tico a peso specifico relativamente sizione nel Carbonifero superiore alto. n vulcanismo terziario delle per giungere a quella che essaha Alpi Vicentine e probabilmente con­ attualmente. nesso con questo processo di migra­ Finalmente deve essere sottolinea­ zione magmatica (de Boer 1963). to che Ie linee alpine maggore, come Le anomalie della parte orientale la linea peri-adriatica possono essersi del massimo Lombardo-Veneto e del comportate come parafore ("geosu­ minima Veneto possono essere spiegate ture") durante 11 Mesozoico. Tuttavia supponendo 1'esitenza di faglie a l'evoluzione strutturale terziaria, gradini nel basamento , dovute al descritta nel capitolo dedicato alIa sollevamentoneogenico delle Alpi cen­ tettonica, ha un carattere pili locale trali a Nord ed alIa simultanea sub­ gravitativo e si SVi 1 UPPO sopra queste sidenza dell'Adria a Sud. linee strutturali pili antiche.

Paleomagnetismo; Le direzioni palaeomagnetiche misurate su campioni orientati di Outline of the Geological Mops of the investigated region in N.E. Italy

by R. Guicherit

o 10 20km IiE.~.--__I"--~ ..r--·_~3

I

I L Utrecllf /963 f. henzen

Fig. 1. INTRODUCTION

Geological research of this area the palaeozoic; Morgante (1934), who reaches back as far as 1868, when reported some petrographical data on Frans von Hauer mapped this region, the Rio Freddo porphyries; di Col­ by order of the "Geologische Reichs­ bertaldo (1948), with a paper on the anstalt" to make a geological map of mining region Cave del Predil; and the Austrian Monarchy. Assereto (1963). The next publication to appear was The geological data presented in from Guido Stache in 1873. In 1874 this thesis were collected during the this author issued a geological map summers of 1960, 1961, and 1962, (scale 1 : 2. 000. 000) and, finally, under the supervision of Prof. Dr. some other studies in 1878 and 1884. R. W. van Bemmelen of the University Very important geological work of Utrecht. was done by Frech, who published his The surveyed region lies WSW of famous monograph on the Carnian the boundary between Italy, Austria, Alps in 1894, and who, in 1887, had and Yugoslavia, as shown on fig. 1. already written an article on the Mapping was carried out on topographic Devonian of the Eastern Alps in the maps "Tavolette della Carta !taliana" review of the "Deutsche Geologische (scale 1 : 25.000), surveyed by the Gesellschaft". "Instltuto Geographico Militare" at From G. Geijer some papers ap­ Florence. Use was made of the sheets peared in 1895, 1899, and 1903, which Tarvisio, Camporosso, Cave del Predil, made the Permian of the Carnian Alps Fusine in Val Romana, Malborghetto, famous. Pontebba, and Paularo. For the com­ In 1911, Tillman wrote a paper on pletion of the geological map (sheet the tectonics of the palaeozoic base­ II and II a), use was made of the ment of the Carnian Alps, to be fol­ geological maps by di Colbertaldo lowed by Gortani's investigations in (1948), and by Kahler and Prey (1959). the region, discussed in some papers Since, until 1918, a part of this (1911, and 1936). area belonged to Austria, many geo­ We shall not give a complete sum­ graphic items carry german as well mary of all the publications concerned. as italian names; this may impede the It may be sufficient to mention the study ofthe literature. For this reason work of Heritsch (1915, 1934, 1936, in appendix II a list of italian names 1939, 1951); Desio (1925, 1926); with their german translation is given. Kahler (1934, 1937, 1938), who all In this thesis only the italian names did mainly stratigraphical work on are used.

,­ ~ I' ­ Limestones and STRATIGRAPHIC COLUMN Dolomitic Limestones

Main~

Dolomites

Flint bearing Dolomite Dolomitic Limestone ory L" n

Porphyries,

Tuffs and Lavas

Massive l/l

Dolomites

c l/l .2 ,g c 1200m. 3 j~ f~ Qj{j-g"

Limestores and dark Limestones Dark Limestones and tlulor Limestones Brecciated Limestones

Mall 160m. Conglomerates and Ii Breccias

t- Dolomitic Limestone Carbonatic Sandstones

400m. ~ ~ SChistp?e , i -'

Dolomites and dolomitic Limestones Eplomites and Cellular rmesfones C' tIDIes T .. ',", 0 :"T· T';-' j:"_. .~ Sandstones } Ma,200m If Limestone Br cias Trogkofel Limestone Lower Permian Fusulino bearing " dark Limestones and e::) Auernig Strata :'. Not to Scale "2 L.. ~ o~ ~ ~ -e.00 £- U...J fj~. c~ 2 0 ~~ ~~ CHAPTER I

STRATIGRAPHY

A. GENERAL

The investigated area forms a cause fossilizations are relatively part of the Carnian- and Julian Alps: scarce. It has an almost continuous strati­ In chronological succession a brief graphic column from the Ordovician description of the Carboniferous, the up to the base of the Upper Triassic Permian, and a part of the Triassic in the Carnian Alps, and from the will follow. No detailed treatment of Permian up to the Upper Cretaceous the different stratigraphic units has in the Julian Alps. The Tertiary is been attempted. The early palaeozoic not represented. The Upper Carboni­ and the post ladinic series have not ferous overlies unconformably the older closely been studied. Neither did we palaeozoic and the crystalline base­ pay special attention to the quaternary ment, which was previously subjected deposits. The latter are not recorded to the caledonian and variscan phase on our geological map, except where of mountain building. Because of the their occurrence is evident, or where older and the alpine tectonic move­ a geological interpretation of the sub­ ments, the thickness of some for­ surface is impossible, due to their mations are difficult to measure. presence. Moreover, it is often hard to distinguish A general outline of the strati­ between the various permo-triassic graphy is given in fig. 2. dolomitic limestones, especially be­

B. CARBONIFEROUS

This formation was not studied in (M. Cavallo 2239), and partly on the detail. As some samples of the Upper Silurian. It was only subjected to the Carboniferous of M. Auernig were alpidic orogenic phase, such in contrast taken for palaeomagnetical investiga­ with the early palaeozoic strata, which tions, we may confine ourselves, to were subjected to faulting and folding making some general remarks. during the caledonic, variscan and The Upper Carboniferous overlies alpidic orogeneses. unconformably the caledonic and varis­ The Hochwipfel Carboniferous can can-folded palaeozoic. It lies partly be correlated in age with the Carbo­ directly on the "Hochwipfel Carboni­ niferous of Notsch, north of the Gail ferous" of lower carboniferous age Valley, which forms the base of the (type locality Hochwipfel 2186), partly permo-triassic Dobratsch-unit (Her­ directly on grey devonian limestones itschandKiihn1951,Anderle 1950). It

- 19 ­ Table I.

Upper 'I Belkrophon strata Permian ("ZechsteinIt) Grodener Quartzsandstones and Conglomerates ("KupferschieferIt) Middle Saalic Tarvis Breccia ("Upper ~ Permian phase Trogkofel limestone Rotlie­ gendes") Upper Schwagerina limestone Ratten­ Boundery-land strata Lower dorf "Grenslandbanke" Permian strata Lower Schwagerina limestone

Upper non-carbonatic ro group "'-'ro 1-< "'-' "Ob. Kalkarme Gruppe" 00 - Upper carbonatic group 0 .-. Upper 0 Auernig­ "Ob. Kalkreiche Gruppe" Carbonife­ Sro strata 1-< Middle non-carbonatic Poi rous group

"0- .-. "Mitt. Kalkarme Gruppe" ~ N Lower a) Watschig 0Cl CIJ Z carbonatic strata group b) WaschbUhel "Untere strata Kalkreiche Gruppe

Variscan Sudetic ~ ~- _..,,-~ ,~~------l orogeny phase Early

Palaeozoic I Schematic outline of the stratigraphy of the Carboniferous and the Permian in the Carnian Alps. consists of slates, shales, sandstones 2. The Watschigstrata about 180 m rich in mica, and quartz conglomerates; thick and was subjected to intense folding A series consisting of sandstones, during the variscan orogenic phase. shales, limestones, and few conglo­ The Upper Carboniferous "Auernig­ merates. Locally intercalations of strata" (type locality M. Auernig anthracite layers occur. 1821 m), and lower permian strata 0. The middle group, poor in Iimestone (developed as terrestric, limnic, and about 170 m thick paralic deposits) overlie the Hochwip­ A series of sandstones and shales, fel Carboniferous transgressively, as rich in conglomerates. has already been stated at the begin­ 4. The upper group, rich in limestones ning of this century by Stache, Frech, about 90 m thick Schellwien, and Geijer. These upper Sandstones with many limestone carboniferous strata (with a thickness intercalations; conglomerates are of about 700 m) are nowhere exposed less frequent, than in number 3. in one complete section. Comprehen­ 5. The upper group, poor in limestone s ive comparative palaeontological about 11 0 m thick investigations, carried out by Kahler A series consisting of conglome­ (1934, 1937), Heritsch (1934), and rates and sandstones. Metz (1935), were necessary to re­ construct the stratigraphical situation, by linking up different sections. The Auernigstrata are rich in In table I a schematic outline of fossils, mainly fusulines, corals, the permo- carboniferous stratigraphy bryozoans, and pecten. There are is given. nine horizons of terrestrial plants, ofwhich the uppermost one corresponds 1. The Waschbiihelstrata about 130 m to the Westphalian E. thick The conglomerates consist of well­ A series consisting of limestones rounded quartz andlydite pebbles, with with argillaceous intercalations. diameters up to 5 cm.

C. PERMIAN

The Permian starts with the Ratten­ both sections are classic for the dorfstrata and ends with the Belle­ Lower Permian of the Carnian Alps. rophon horizon. The whole series is richer in limestones than the preceding Upper 1. The Lower Schwagerina limestone. Carboniferous; determinable plants are absent. Before describing the various formations, two sections are The oldest permian strata consist given, described by G. Geijer; one of dark limestones with some sand­ across the Reppwand and the Gartner­ stone intercalations. The limestones kofel (2195 fig. 3), and the other are rich in fossils and its maximum across the Trogkofel (2279 fig. 4); thickness is about 175 m.

- 21 ­ Rattendorf Strata ~ Bellerophon Dolomite ~.. Anisian Limestones

Trogkofel Limestone ~'" Werfenian Strata ~ Buchenstein Strata Grbdener Sandstones and Sholes [+ + + I Uggowitz Breccia k Schlern Dolomite

Fig. 3. Section across the Reppwand and t.he Gartnerkofel.

2. The borderland strata 2195 m). A series of light-grey to white, and pink-red to blood-red A series maximum of 80 m in limestones, containing locally at thickness, consisting of conglome­ their base pebbles of white quartz rates, shales and some limestone and lydite, which range from pea­ layers. This formation is the repe­ size to nut-size. In the grey parts tition of the facies of the Auernig­ of the limestone we frequently obser­ strata. ved quartz -veins and quartz -pockets. Its thickness varies considerably 3. The upper Schwagerina limestone. from one place to another. At the Trogkofel the formation is about 400 m A series of dark, thinly stratified thick; at Coccau, near the Pontebbana­ limestones, of maximum 60 m in road leading into Austria. ahout 150­ thickness. The occurrence of the Schwagerina limestones is restricted to certain areas of the main Carnian Mountain Range only; they have not been en­ N countered elswhere.

4. The Trogkofellimestone and Tarvis breccia. IOOOm Level Upper Carbaniferaus IBJJ Tragkatel Limestone

On top of the Rattendorf strata Quarfz Con~lomera1e ~ Umestone Breccias lies the Trogkofel limestone (type Rattendarf Strata locality Trogkofel or Creta di Aip rig. 4. Section across t.he TrogKofeL

- 22 ­ 180 m; at other places it was never disconformities in sedimentary series, deposited; for instance in the Paularo­ are merely the result of local epi­ Paluzza region. The lower permian rogenic movements and tilting of the series are rich in fossils. List of basement. So as time indicators, not fossils were given by Heritsch (1934, too much theoretical value should be 1936, 1939) and Kahler (1934, 1937, attached to these tectonic phases. 1938). The Tarvis Breccia points to tec­ tonical unrest and strong relief in The Tarvis breccia lower permian time. The breccia is about 15-20 m thick near Coccau Whereas the Lower Carboniferous and consists of fragments ofTrogkofel ends with the Sudetic phase of the limestone (components 5-10 cm), variscan orogenesis, the Saalic phase which are cemented by a red, sandy occurred at the end of the Trogkofel matrix, which locally contains fusulines. formation. It gave. rise to a breccia, formerly called the Uggowitz Breccia, 5. The Grodener Formation. with components of Trogkofel Lime­ (Italian: "Arenarie di Val Gardena") stone and occasionally also of the - underlyingSchwagerina limestone, see The Grodener formation lies lo­ Stache (1878), and Geijer (1899). The cally conformably on the Upper Car­ Uggowitz Breccia in a strict sense, boniferous and it is conformablyover­ howeve:c, (type locality near the village lain by the Bellerophon formation of Ugovizza), contains also components (Upper Permian). At M. Capin di of the lower triassic (scythian) lime­ Ponente NNW. of Tarvisio these stones, while in its matrix fossils of formations are exposed in one com­ anisian age were found. The strati­ plete section. In other places it over­ graphical position ofthese two breccias lies the Tarvis breccia (near Tarvisio is also totally different. Therefore, Centrale), and elswhere it lies di­ the name of the breccia on top of the rectly on the Trogkofel limestone Trogkofel-limestone was changed into (see section across the Reppwand Tarvis Breccia (type locality near fig. 3). Tarvisio Centrale). The strataconsist of fine-to-coarse The above mentioned two orogenic grained, wine-red sandstones, ce­ phases, which were distinguished by mented by an iron-bearing quartz Stille, are stated here only, because matrix, alternating with micaceous they are in such common use. The sandy shales, which form layers of dating of Stille's phases are,however, less than 5 em thickness. The sand­ inexact, so that it is dubious whether stone banks are 30-50 cm thick. certain unconformities belong to the Locally the strata contain nodules and same folding phase or not. In other lenses of dolomitic shales, about 5-11 words, it is uncertain, whether, the cm diameter, with yellowish and tectogenesis indicated by the Austrian greenish-colours. Frequently quartz­ geologists as the "Saalic-phase" in veins occur, occasionally containing the Carnian Alps, occurred at the same epidote and pyrite. time as the tectogenesis indicated by The transition from breccia to Stille as the "Saalic-phase". Further­ sandstone, and sandstone to shale is more, spectacular tectonic movements gradual. Near the top, at the road such as gliding tectonics and diapirism, from Paularo to Stua Ramaz, some may be the result of local stress dolomitic and gypsum-bearing layers fields and they have no direct rela­ ocour. which have also a considerable tions to worldwide orogenic phases. limestone content. This might be due Moreover, many unconformities and to a secondary (;alcification by circu­

- 23 ­ lating groundwater, which is rich in b. North of M. Capin di Ponente; calcium-bicarbonate, by lixiviation dark, thinbedded dolomites and of the overlying triassic series. In red, green, and locally black this locality the whole formation is lenses of shales. richer in shales; sandstones being onl"y a subordinate member. c. Near the road to Castel Valdaier In the sandstones and shales, in the Paularo region; grey shales cross-beddi ng and ripple-marks occur. with intercalations of gypsum. The absence of fossils is remarkable. The fossil-content of this formation, d. In the Slizza near Tarvisio; dolo­ found elswhere in the Alps, indi­ mitic limestone layers of about 20 cates a middle permian age. Its middle cm thickness, alternating with permian age is also confirmed by somewhat bituminous dolomitic nuclear geologic work of the labo­ beds of about 5 cm thickness. ratory at Pisa (G. Ferrara, H. Stauffer, and E. Tongiorgi 1960). According This basal member shows the first to Mittempergher (see van Bemmelen signs of the advancing sea, initiating 1961 pp. 218), the absolute age deter­ the alpine geosynclinal suite of sedi­ minations of the uranium mineraliza­ ments. tions in the Gardena formation in south The middle part of the Bellerophon Tirol, all give an age of approximately formation, about 60 m thick, consists 220. 106 y. Kulp (1~61) gives an ab­ of yellowish-grey, cellular dolomites solute age of 280-230. 106 y. by (Italian: "Dolomia Cariate"); near means of isotopic K/A determinations Paularo it consists of cellular lime­ from biotite and glauconite. Because st-ones, with abundant veins of gypsum. the uranium mineralization has a No fossils were found. The outcrops epigenetic ,post-sedimentary character, of the middle part of the Bellerophon the Gardena ~ormation itself is older formation are accompanied by sulphur than 220. 10 Y , which is the limit bearing mineral springs near Arta between Permian and Triassic accor­ (Tolmezzo), Paularo, and Bagni di ding to KlolJp'S geological timescale Lusnizza. (1959). The upper part of the Bellerophon formation of about 250 m thick, con­ sists of well-stratified, grey-coloured 6. The Bellerophon Formation. massive dolomites and dolomitic lime­ (Italian:" Formazioni a Bellerophon") stones, which alternate with marly, occasionally sandy shales. Many calcite This formation will be discussed veins are present. In this part the on the basis of a seetion, surveyed fossil Bellerophon rStachellaJ' by us in the Canale delle Volpe, '15outh has been found, after which this for­ of Camporosso. The lower part (8­ mation has been named. 12 m thick), forms the transition The Belleruphon formation was not between the Grodener series and the deposited elswhere in the Eastern proper Bellerophon formation. This Alps. In the Bergamasc Alps, the basal member has the following fa­ marine sedimentation started some­ cies: what later, during lower triassic a. In the Canale delle Volpe it is times. North of the great Gail fault, represented by silver-grey and at the northern side of the Carnian dark, gypsum bearing shales, Alps, this stage is absent according with intercalated lenses of red and to Geijer (1901) and Anderle (1950). green shales. Locally gypsum However, van Bemmelen (1957) re­ noduls occur. ports the occurrence of some gypsum

- 24 ­ bearing dolomitic banks, between the Alps to the North of them and also Grodener sandstones and Werfenian that the sedimentation of the Belle­ series. This indicates a gradual change rophon formation was not only re­ in facies between the Permian of the stricted to the south alpine facies, Carnian Alps and that of the GaUtaler as advanced by Anderle (1950).

D. TRIASSIC

Lower Triassic The general facies is that of se­ dimentation in shallow water, with a supply of mostly fine-grained terre,s­ 1. The Werfenian Formation (Scythian). trial detritus. Its thickness is about 400 m. The Werfenian Formation crops Three parts can generally be out at the base of the Julian Alps. It distinguished* . can be traced south of the Pontebbana road from Pontebba to the Fusine Lakes. A. The lower part consists of grey Lithologically it is a variable for­ and yellow, well stratified marly mation, generally consisting' of red, limestones, occasionally showing sandy, gay-coloured strata, with a internal' moulds of fossils on the considerable limestone content. Lu­ bedding planes. Many calcite veins machelle horizons, sandstones, and are observed. The passage into oolitic limestones are interbedded. the Bellerophon Stage is gradual; Detrital mica is a common constituent, -the limestone content gradually which causes a characteristic lustre increasing upwards. Its thickness on the bedding planes. Ripple marks amounts to about 30m. occur frequently in the sandstones, which are, for instance, well exposed B. The middle part is illustrated by at the mouth of the Rio Bombaso a section across the Canale delle near Pontebba. Volpe (see fig. 5). It is difficult to draw the limit between the Grodener and Werfenian a. An alternation of brown-grey Series at those places where, due sandstones, with pockets and to tectonical movements, the Belle­ veins of calcite, and yellowish­ rophon Formation is lacking, for in­ brown, red and green mica­ stance, SE of Monte Ruta, in the ceous sandstones, and silts. Rio Canale.

* The Austrian geologists distinguish only two parts. The lower part, called Seiser Schichten (It. Strati di Siusi), corresponds with our parts A and B. The upper part, called Campiller Schichten (It.. Strati di Campil), corresponds IDCLinly with our part C. The oOlitic limestone horizon, which occurs near Cocceu, corresponds probably to their "Gastropoden 01llith", It seperates the Seiser Schichten from the Campiller Schichten. In some places conglomeratic layers occur, which are called the conglomerate of Koken.

- 25 ­ b. Brown-red, compact sand­ h. Beds of compact sandstones stones, with grey and green (without limestone) about 5­ spots" Very much detrital mica 10 cm thick. occur. Banks are 8-10 em L Coarse grained sandstones, with thick~ The sandstones have a a limestone matrix, alternating. limestone matrix. with light grey limestones, c. Mica rich, shaly marIs, with which occur in layers of 60 cm calcite veins. thickness. d. An alternation of shaly marls and yellowish-brown, dolomitic Diener (1884) and Gortani (1925,1936) limBstones, Locally concretions describe some fossils from this part. of calcite, with diameters up to 10 em. C. The upper part consists of lime­ e. Bleu grey limestones, yellowish stones in beds of 6--10 cm thick, with on weathering. many thin calcite veins. The aggre­ f Platy limestones, with luma­ gate thickness ofthese dolomitic lime­ chelle horizons, and shaly, stones is about 140 m. marly limestones. g. Dark'-red, fine-grained sand­ 2. Anisian stones. with tmn Cft leitic veins.

" -, , , a. The Uggovitz Breccia (German: -r T ·.T. "Das Muschelkalk Konglomerat del' " -,- -r­ a Slid Alpen") .. --, -,- -, :.T····-.-· While the Middle and Upper Per­ .:.' ~ ~~+\ . ,.. mian and the Scythian are developed ," " ',' T ", " in the same facies over long distan­ ....,.~ b ,', ,. ,...... ,.. . ces, the Middle Triassic is charact­ I.... I--T T ....T I· 1 -I I-I I-I erized by many changes of facies. i- I-I 1~1 I- The Anisian starts with a conglome­ -I -I I-I I-I rate (Italian "Conglomerati e Brecce I- I-I I-I c 1/ 1/1 1/1 L a poHcromi"), called the Uggovitz i­ 1,...1 I-I Breccia (type locality near the village ....1 I-I 1-1 I-I of Ugovizza). It may be considered t: [7f 1/1 1/1 1/ as the aequivalent of the' "Richthoven o - I-T T I 1­ ~ d Conglomerate" of the Western and C'oI Central Dolomites. Already in the upper part of the e Werfenian Formation (Campiller -! 1 I - - - Schichten), thin lenses of conglo­ merates appear (M Capin di Ponente, - - - - - f and Rio Profondo). However, not - - - - until after this period was the thick 'T"'-""~ breccia of Ugovizza forming a well • l'l'""'I"~' g T' ,'-" ,. defined horiz on in the stratification '"T • T' ~. 'T' T" .,.0 "T"' '"':T~~"T."'T7';"'" _,:",~__"T' h deposited. ""T".-r·,·""T"·T· ... · The components of this breccia i ~..,..: -T :T:-- ~'T:'T : I are generally hardly rounded by trans­ port, though certain parts .aremore conglomeratic, with well-rounded Fig. 5 Stratigraphic-Lithologic Section of the middle part of the Werfenian. components. In these polichromaus

- 26 ­ and polimict breccias and conglome­ and Julian Alps. He was the first rates, the banks of which are 30-50 author who drew attention to the fact cm thick,· fragments of the under­ that these movements were accompanied lying Werfenian Formation were found by volcanic activity. Also Ogilvie in sizes as big as a man's head. Gordon (1929) explained the inter­ There are furthermore numerous fingering heteropy at Cortina d'Am­ pieces of Bellerophon dolomite and pezzo as horst and grabenlike struc­ red Grodener sandstones, and finally, tures ,originated by these movements; some rare components of dark fusu­ and Agterberg (1961) supposed, on lina limestone. the basis ofthe existing facies -heteropy The components are cemented by during the Ladinian, that horst- and a yellowish limestone matrix, in graben-structures existed even on a which fossils of anisian age are met larger scale than was proposed by with. Ogilvie-Gordon. This breccia is probably not the This development of the sedimen­ result ofa strongerosion which started tation suggests that the early stages at the end of the Scythian, exposing of subsidence of the alpine geosynclinal the preceding sediments down to the had more the character of a mozaic level of the Bellerophon Stage. North of blocks subsiding than a smooth ofUgovizzaeven fragments ofGrodener synclinal downwarp of the earth's sandstones and lower permian lime­ crust. stones were encountered. It is more likely that local escarpments were b. The Anisian Limestones and formed by faulting at that time. At Dolomites. the feet of these local escarpments (German: "Muschelkalk" or the breccias were deposited. Along "Mendel and SarI Dolomit" of the these faults igneous material ascen­ Central Dolomites). ded' which caused the anisian and ladinian volcanism, to be discussed The upper part dthe Anisian starts hereafter. with somewhat bracciated limestones, There are many indications for with components ranging from 0,5 to differential vertical movements after 2 cm in diameter and cellular dolo­ the Lower Permian. First, the Tarvis mites, which grade upwards into dark Breccia in the Middle Permian, then limestones, dolomitic limestones, and the Koken-conglomerate in the Upper dolomites. Scythian, and the Uggovitz Breccia In the M. Tersadia region, near and the Conglomerate of Richthofen Paularo, where the Uggovitz Breccia at the base of the Anisian; finally is lacking, the present 0 f springs similar coarsely clastic sediments indicates the facies change of the were formed between the Upper Ani­ strata, from impermiable Werfenian sian and Wengen Series in the Julian strata to the more karstlike hydrology Alps. of the Anisian. These tectonic movements may be The triassic volcanic activity started considered as the cause of the facies in this area during the deposition heteropy during the Middle Triassic, ofthe anisian limestones and dolomites, as was for the first time advocated as is clearly observable SE of Dierigo. by Von Mojsisovics (1879) for the The lower limestone beds are uncon­ Central Dolomites. Leuchs (1947) f()rmably overlain by tuffs, tuffaceous suggested that tectonic movements shales. and silts of greenish colour; caused also the heterotropic differ­ locally thick, acid effusive rocks are entation of sedimentation during the intercalated. The description of these Ladinian and Carnian in the Carnian volcanic rocks is given in chapter II.

- 27 ­ Table II CENTRAL OOLOMITES VICENTlNlAN ALPS CARNIAN A1J>S WESTERN JULIAN ALPS GAILTAL ALPS OBRATSCH...... -NW. KARA WA1'.1K.S

I Tar Strata -0 Raibler Strata Dolomites, Dark, thin, well stratified c Raibler Strata with Raibler Strata with a Vl Ra ibler Strata s.s. It: Raibliana ar Strati -0 a H Dolomitic limestones, marJy limestones 53: 'c 3 II Cordite Horizons 3 II Cordite Horizons" z di Raibl itumineous ::f ~ c: ~ Marls,and Benthonites It: Colcari Lastroidi ~.- ..2 Strata. It:Scisti (a, b, c). (stratified Limestones and z ~ ~ Vl « G: Raibler Schichten >..~ Ittialitici di Raibl olliite Series of the "" Fisc~sch u =a ~a t;: iefer von Ferlacher Horn) v ~ .3 Raibl. Amphiclinen chichten of W. Slovenia Vole;mic heies Carbonatic facies I Volcanic facies Carbonatic facies I Volcanic facies Carbonatic facies IVolcanic facies Carbonatic facies Carbonatic t facies Carbonatic facies

Upper ICass ian Strata Porphyries Porphyries It: Strati di San Cassiano and (Cordeval) c tuffs, and G: Cassianer 2" v ) Lacally Schichten :;; Melaphynes* Lavas (; E ::; c tuff inter- Wengen Strata ~ E ~ .- 0 ..c c v ­ 2 v " Z .~ Vl ~ ;;; cala­ Vl:.:: g ~ Wengen Wengen .­ -0 E ~ Middle It: Strati di E 0 E ~ -0 \" e c « c a :; 0 - 'e "E 2 a La Valle a ..c .>< (; 2 .~ 0 ::; - ~~~~ c (; 'e Vl" tions j ~ Strata a Strata a (Langabard) 0""00-0 g 'e OJ c Z 0 a a c (; c "0 .~ > c (; a - G: Wengen E § j ­ 0; 0; (; e0 a .>< Schichten o...!! ... ~ i -0 -0 " E a c: - -c 0 a. c a:l c :> " 0 ~ a v a ::; ... a E .. .S!. Vl .~ i!! " a a ...!!OV') --, « Q) :> a. '" 'e ..c i!! [; 0 .~ -fi ...0 .... Q ;;>. 2 0 >< (; 0 Vl=<-'-.J a:l" ~ 'e a ~ Buchenstein Strata ­ i;;" 0 Buchenste in 2 (; \~ - ~ ~ a lower N lit: Strati di 3: Livinallongo Strata (Fassan) - 'I Buchenstein G: Buchensteiner .­ Strata Schichten a.

Mendel and Sari Vl I Dolomites, Dolomites, Upper Sheil- \. Gutenstein Limestone Sturie Sansovinii Limestone It: Dolomia della Mendola Dolomitic Limestones, Dolomitic Limestones, Facies Series G: Obere MlJSchelkalk and Cellvlar Dolomites Z s.., and Cellular or Plattenkalk, (Partnach Facies of « I · ._". Tvlls partly Partnach V; Locally Agglamerates ~ G: Mendel und Sari c.."" and Dolomites Strata the Ferlacher Horn) "- Z (" Richthofen, ::::> Lavas and effusion of Lavas l « Conglomerate" , Dolomit dark Limestones, and TvIIs andstones, etc.).

Table II Simplified Scheme af the Facies Distribution dvring the Upper Anisian, Ladinian, and Carnian in some parts af the Eastern Alps. It:: Italian G:: German * The Term Melaphyre is hac used for a dark Porphyry as has been done by the Austrian and Italian Geologists. Later, this term has also been applied to carboniferous and permian basalts (Johanssen, 1931). To avoid confusion this term was dropped by us while describing the various volcanic units. The anisian limestones and dolomites. especially in the lower parts of the are about 100-150 m thick. Some series, where more limestone inter­ fossilizations, which are rather scarse, calations with darker colours occur; are given by Gortani (1936). mostly,however,they have a massive appearance. On fractures and near faults reddish 3. Ladinian colours are often observed. Some­ times dark streaks occur, probably One of the most spectacular rock­ indicating a sedimentary stratification. types in the region is the Schlern At the road to Osteria del Camoscio, dolomite of ladinian age. Principally west ofRefugio Gortani, these streaks all high mountains of the eastern are clearly observable. Locally also Carnian Alps and partly those of the breccias are intercalated. One of Julian Alps south of the Pontebbana these breccia levels can be seen near road are built up by this dolomite. point 975 of the road to M. Stabet The Schlern dolomite is a typical (1627) NW of Ugovizza. reef facies. The reef-building probably Di Colbertaldo (1948) is of opinion already started during the Lower that the formation of the dolomites Ladinian and continued during the is the result ofa metasomatic process, Middle and Upper Ladinian. It is con­ due to circulating magnesia bearing temporaneous or partly somewhat solutions. The dolomites are thus younger than the volcanic deposits thought to be secondary; primary lime­ of the Buchenstein and Wengen series. stone reefs, dolomitized by ascendentic An interfingering of the reef-facies solutions, which are closely related and the volcanic facies is very well­ to the formation of the mineral depo­ exposed west of Pontebba, near Stu­ sits of Raibl. The mineralization is dena Alta. restricted to the dolomites (It. "Dolo­ The volcanic facies of the Ladinian mia Metalifera"). The validity of the is characterized by the effusion of theory ofdi Colber~ 'lIdo on the genesis porphyries and lavas. It was during of the Raibl ores is questionable, this period that the triassic volcanism however, (see chapter IV). reached its maximum intensity. The thickness ofthe ladinian series The nomenclature of the volcanic north of the Pontebbana-road can series, as well as that of the dolo­ hardly be estimated, owing' to tecto­ mites, is very confusing; there is no nical movements. South of it their common use for various terms in the thickness is at least 1200 m. literature. Table II gives a scheme Fossils are scarce. Gortani (1936) of the facies distribution for various mentions some finds of fossils at parts of the Eastern Alps, during the Monte Capin di Ponente, Cima Muli, Upper Anisian, Ladinian, and Carnian. Monte Nero, and Monte Acomizza. However, this scheme is very much simplified, because it has often been observed that during these period the litho... facies limits do not coincide Upper Triassic with the claSSical time limits. The transition from the dolomitic 4. Carnian, ("Raibler Schichten"). anisian limestones to the thick ladinian dolomites is gradual; the dolomitiC In the permo-triassic sediments 'of character increases and the shaw the Eastern Alps one can distinguish intercalations between the dolomitic a megacycle of deposits starting and limestone beds disappear. The dolo­ ending with a supply of terrigenic, mites are sometimes clearly bedded, clastic products of erosian (see fig. 6)

- 29 ­ ------,-­Rhaetian

1--1--­ Norian

Not '0 Scale

----I Cornian r-­

Ladinian -~:~~~~f~~~~::~--- o I ~I ~-- _+--~C~C===~-----"--k,,--:::c ::~_ 200 _ --Ft------I_ =--~---1-~=====~===~*~~~-~-J- 400 f------__ .- 600

Werfenian 800m.

----': ------==-.j... ------t------­ ------I I'Belle,O~" -~-~-~::::::=---=-:.. -~.,,~--==--~--~----.-~.--.~.-.-.-~--- t~:.:.: ------=-- -­ r- -==:-:.. - -­ -- -===: ---~-j-----

T'oQkofel I F~Iamerato. umeS'lones Sand Clay Umestono, Dolomite and Breccia. -L .~ ~ ~______I _---'---__ t I Fig. 6. Lithological curve of the Permo-Triassic indicating a megacycle, wltich is only disturbed by the Bellerophon Dolomites and lower anisian Breccias. The latter, however. arc' due to post-variscan tectonic movements and ""renot considered by drawing the curve. The curve is also disturbed, when contributing a lower ladinian age to the "Calcari Lastroidi".

This supply of detrital material and shales (Italian: "Calcari Lastroidi") stopped entirely at the end of the occurring in the Carnian Alps, north Anisian (van Bemmelen 1957, 1961; of Tarvislo, north of Monte Mirnig, van Hilten 1960), and revived again NW of Val Bruna, and at Monte Cucco during the Carnian. We cannot agree NW of Malborghetto. with Gortani and Desi 0 (1927), di At Monte Cucco this series are Colbertaldo (1948), and Assereto clearly overlying conformably the (1963), who dated as Lower Ladinian upper ladinian dolomites. In Geijer's a series of dark, well bedded and section across the Reppwand and thinly stratified, marly limestones Gartnerkofel this formation is not in­

- 30 ­ dicated in the Lower Ladinian. When 5. The Norian and Rhaetian. dealing with the tectonics of this area we shall discuss the present position The Raibliano is followed in con­ of these strata at other places, which formable stratigraphic succession by caused the erreneous interpretation the Main Dolomite (Italian: "Dolomia oftheir stratigraphic position. Conform Principale";German: "Hauptdolomit"), to the scheme of facies development consisting of well stratified dolomites (fig. 6), these strata all belong to the and dolomitic limestones. During this Raibler deposits on top ofthe Ladinian. period the unstable sedimentation con­ Fossils were not found, with the ditions of the Middle Triassic finally exception of one mollusc, mentioned came to an end; the Norian is again by Goratni (1936). developed in the same facies over In the Julian Alps the Raibliano wide areas. overlies the "Metalliferous Dolomite" The Rhaetian is presented in the (type locality near the village of Raibl Julian and Venetian Alps by the facies - Italian: Cave del Predil -). of the Dachstein Limestones. These Three parts can be distinguished formations, both Norian and Rhatian, in these Rabliano strata: are absent in the eastern Carnian The base is made up of marly, Alps, where the mountain tops are bituminous limestones which are shaly composed of Schlern dolomite. at some places (Italian: Scisti ittio­ litici). 6. Quaternary. The middle part, the Raibler strata proper, consists of marls and marly The Quaternary appears as a cover limestones with Meralodus carinthiasis of morainic deposits left behind on the (German: Zwischen Dolomit, or retreat of the quaternary glacie rs. Megalodus Dolomit). Further, enormeous masses of scree The upper part, named "Tor strata", material, caused by the weathering of consists or marly limestones with the ladinian and norian dolomites, Co r bu l a ro s tho rn i (Corbula Lime­ cover the s lopes of the mountains dtone), dolomitic limestones with and the valleys. Finally, river terra­ Mef!alodus carinthiasis and chert- ces are found, and alluvial deposits bearing dolomites. cover the valley floors.

- 31 ­ CHAPTER II

VOLCANISM

A. GENERAL

Volcanism has recurrently played magma welled to the surface. The an important part in the history of eruptions were partly subaerial, part­ the South-Eastern Alps. The lower ly submarine. It was probably a shal­ Carboniferous ("Kulm,r), the Permo­ low sea from which some volcano­ Carboniferous (Upper Carboniferous islands emerged; numerous fossil and Lower Permian), the Anisian, plant remains found in the lower and the Ladinian, and the Tertiary were middle triassic volcanic series were the most significant periods of the described by D. Stur (1868) for the emplacement of igneous rocks. During Raibl and Rio Freddo region SE of the Middle and Upper Permian, the Tarvisio. Jurassic and the Cretaceous, hardly Dikes and stocks of porphyries any volcanic activity took place. occur together with lava-sheets and The intensity ofthe volcanism varied extensive, thick tuff-blankets. also from one place to anotherDu­ About 50 samples of these volcanic ring the subsidence of the Thetys series were taken for palaeomagnetic geosyncline, tension rifts and fissures investigations. The results of this were probably formed, through which study are discussed in chapter V.

B. PERMO-CARBONIFEROUS VOLCANISM

In the Palaeozoic of the Carnian The first detailed investigation Alps, volcanic activity was important was carried out by Milch, and the during the Silurian; no traces of volca­ results were published in 1894 in nic activity have been found during Frech's monograph on the Carnian the Devonian; in the Lower Carboni­ Alps. Next, also some petrographic ferous ("Kulm") again thick series data were given by Italians which, of volcanic material are present. The however, did not add essential new latterhave their maximum development facts. near Monte Paularo, Monte Dimon, North of Paularo, near the road Monte Pizzul, and in the River Chiarso along the River Chiarso, its strati­ region. This lower carboniferous vol­ graphic position is clearly between canic series consists of amygdaloidal the upper devonian reef-limestones and basalts, diabases, and tuffs, alterna­ the upper carboniferous "Auernig­ ting with dark, graywacke-like some­ strata". We have therefore dated this what metamorphic sedimentary rocks. formation as Lower Carboniferous,

- 32 ­ in accordance with the OpInIOn of 3. Tuffs Frech (1894) though Desio and Gor­ tani (1927) dated these rocks as Permo­ Near Monte Paularo and Cuesta Carboniferous. Robbia, north-west and north of Paularo respectively, multicoloured 1. The amygdaloidal basalts. tuffs, rich in feldspar crystals and some quartz, are exposed. These These are variegated spilitic rocks. tuffs have the appearance of por­ Black to grey, green to black, dark phyrites and they alternate with hori­ brown, and brown to red colours zons of volcanic agglomerates. In the prevail. Albite has been formed at whole series much secondary calcite the expense of calcic plagioclase as occurs, which in places has been a deuteric mineral. The plagioclase altered into calcite bands. is mostly altered into carbonatic and chloritic matter. Augite has been al­ 4. The Bolzano ignimbritic series tered into chlorite patches with sharply ("Bozener Quartzporphyr"). defined crystal outlines. The groundmass consists of chlorite, Although this volcanism is not ilmenite, or of chlorite, magnetite, known in the investigated region we and titanite. will give a brief discussion of the In the groundmass very good flow formation, because several samples structures have been preserved. The were taken for palaeomagnetic inves­ amygdales consist of calcite, some­ tigations in .NE Italy. times with an admixture of a chlorite­ During the Upper Carboniferous and like mineral, rarely of amorphous Lower Permian, the centres ofmaximal Si0 (opal) and chalcedony. 2 volcanic activity in the southern Lime­ stone Alps, were located in the Dolo­ 2. Diabase Porphyrites mites. Extensive and thick volcanic (Augite Porphyrites). series, the "Bozener Quartzporphyre" were formed. Its thickness, calculated These are light-green rocks which from seismic refraction investigations, have their maximum developmentin the often exceeds 1500 m (Benke, Giese, River Charso region. Prodehl, and di Visintini, 1961). With the naked eye large biotite From a central area ESE of Bol­ flakes can be distinguished, which zano, this deposit spread radially were mechanically deformed during over more than 100 km. In the Car­ later tectonic movements. Under the nian- and Julian Alps further to the microscope the rock appears to be East no traces of this volcanic action hydrothermally altered; much chlorite has yet been found. ThiS volcanism is observed, which is accompanied is, however, well known from several by uralitic hornblende. Often epidote places in the European continent (see and titanite grains can be distinguish­ van Hilten 1960, pp 15), and must be ed in the chlorite, which represent considered as the final act of the alteration products of augite. volcanic cycle of the variscan oroge­ The groundmass consists of chlorite, nesis (van Bemmelen, 1961). hornblende, fibres, feldspar, and In the. Bolzano and Trento areas quartz. Very much secondary calcite a division can be made in a lower, occur whiCh sometimes replaces more basic (trachy-andesitic) tuff metasomatically the quartz and feld­ series with intercalated melaphyr spar of the groundmass. flows, and an upper, more acid ex­

- 33 ­ trusive series. The upper part, the and van Bemmelen, 1961). This ig­ actual "quartz-porphyries", is a nimbritic series forms the base, deposit resulting from fissure erup­ having the shape of a 3500-4500 km2 tions of fluidized, two phase systems, plate, on· which the permo-triassic containing gas with tuffaceous particles strata of the Dolomites have been de­ (Maucher. 1960: Dietzel, 1960; posited. van Hilten, 1960; Mittempergher, 1961;

C. TRIASSIC VOLCANISM

In the region of the Carnian- and activity during the Ladinian, and they Julian Alps triassic volcanism started compare these rocks with the so­ during the Anisia:n and had its cul­ called "Pietra Verde" of the Southern mination during the Ladinian. This Alps. was the most significant volcanic In the Bleiberg mining district period during the geosynclinal subsi­ (Strehl, 1960) intercalations of ef­ dence in the area of the Southern fusive lavas in the Middle Triassic Alps, south of the Gail \ alley. were observed, and finally Schlager This volcanism was formerly be­ (1963), described volcanic series in lieved to be restricted to this southern the triassic "Partnach limestones" area, but later on also traces of of the Lienz Dolomites. volcanic intercalations have been The Ladinian volcanic series has found in the triassic carbonate series, been divided into three parts: north of the Gail. 1. The lower part or Buchenstein F. and G. Kahler (1953), who re­ Series (It: Strati di Livinallongo). studied the scythian section at the 2. The middle part or Wengen Series Loibl-pass south of Klagenfurt, dis­ (It: Strati di Wengen). covered a tuff-layer in the Campiller 3. The upper part or Cassian Series strata, while the Lower Anisian in (It: Strati di San Cassiano). this area contains pebbles of igneous As the ladinian volcanic serie's rocks. often have a similar lithological aspect Pilger and Schanenberg (1958) de­ this nomenclature has occasionally scribed middle triassic tuff horizons caused confuSion, for different names in the Dobratsch (eastern part of the have been used :lor the same deposits. Gailtal Alps). Holler (1960) found tuff-like inter­ calations in the Wetterstein (carbona­ 1+2. The Buchenstein and Wengen tic facies of the Ladinian) of the east­ Series. ern Gailtal Alps and the northern Karawanks. Meulekamp (to be pu­ Theseformations consist of coarse­ blished in van Bemmelen and Meule­ grained sandstones, tuffacious sand­ kamp, 1964), reports similar inter­ stones and plagioclase tuffs, with calations of greenish, dolomitized, pale-red to blue -green and dark-green shale-like marls and tuffs in the colours. The tuffacious material alter­ Ladinian of the Lienz-Dolomites. nates with silified limestones, s tra­ Both point to the relation with volcanic tified grey limestones locally with

- 34 ­ pyritic nodules, platy well-stratified In the whole region they are related limestones. bands of sandy, schistose to the same stratigraphical horizon. black material, and agglomerate hori­ Six varieties can be distinguished. zons. 1) The red to liver-coloured variety The principal components, of the' near Muda, Rio Freddo, and Val tuffs are plagioclase crystals, pro­ Bruna. bablywith a medium andesinic compo­ 2) The green-stained, rose-red variety sition, few qual~tz crystals, and some near Rio Porfido. remnants of igneous- and sedimen­ 3) The ash-coloured variety near the tary rocks. The feldspars are often road from Muda to Rio Freddo. kaolinizedand chloritized. The ground­ 4) The greenish-variety, with inclu-, mass has generally an vrientated sions of the red variety near Monte texture which consists of scoriae of Lussari. limonitic glass. 5) The vitreous variety near Rio Ciutte. These series have their maximum ::} The brecciated variety near the development in the north-western eastern "malga" of Monte Lussari. Julial'l Alps, and they seem to be absent in the eastern Carnian Alps, Morgante ~1934) has pointed out north of the Pontebbana road. that notwithstanding the variety in appearance their mineralogical com­ 3. The Cassianer Series position is more or less the same. 60-75% of the rock consists of a This series has not been deposited micro-crystalline to vitreous ground­ in this region. In the Central Dolo­ mass of quartz -feldspar, while the mites (see for instance Leonardi, rest consists of phenocrysts of ortho­ 1962) it consists of mainly tuffacious clase and plagioclase (An. 10-30%). material with a different lithological Phenocrysts of quartz are rare, aspect. accessory minerals are nearly ab­ sent. Some zircon and apatite have 4. The Ladino-Carnian In-ann Extru­ been observed. The feldspars are sive Rocks. often kaolinized. Karlsbad twins of orthoclase occur. Quartz -porphyries, quartz -free por­ The porphyries have caused contact phyries, and andesitic-porphyries are metamorphism in the Schlern-dolomite present in and the Wengen and Buchenstein 1) The Western Julian Alps (Raibl, Series. In both formations several Mt. Lussari, Val Bruna, etc.) veins and dikes of porphyritic magma 2) The Eastern Julian Alps (Jelovica) are met with. 3) The Eastern Carnian Alps (NW. Elsewhere lava-sheets lie as a blanket of Ugovizza, Val d'Aupa, etc.) on the dolomites, while contact meta­ 4) The Karawanks, and morphism in the sediments overlying 5) The Idria. the igneous rocks (Carnian Strata) has n~ver been observed. In the Western Julian Alps they Gortani (1936) dated these rocks have their main development; with a as infra-Ladinian. According to the thickness of about 250 m near Rio present author a ladino-carnian age Freddo (Raibl). seems more plausible.

- 35 ­ D. ANALYSES OF THE PORPHYRY SAMPLES

By means of the method of "Ront­ According to Morgante (1934) a genfluorescence" a number of quanti­ total of about 2,3% of the rock con­ tative chemical analyses of some sists of traces of Ti02 (average value porphyry samples was made. The ana­ 0,63%), MgO (average value 1,68%) lyses were made by Mr. van der and MnO (average value 0,02%). Weyden under the supervision of Miss Field observations' indicated that Dr. J. de Widt. the red porphyries occur near the First the samples were crushed to contact between the intrusive bodies nutsize.Next, the rock was mechani­ and the carbonatic country rock, cally ground and screened. Grinding while the colour becomes more green took place in agate bowIs with wolfram­ to the centre of the bodies. Samples carbide balls, and in slag-sapphire number 1 to 6 and number 11 to 8 bowIs, with balls of the same material. (M Lussari region) were taken from The screen size was 100 mesh*. locations at certain increasing dis­ The grain size of the samples after tances from the contact zone. Sample having been screenedwas about 115 J"I number 1 was located near the contact As the rock is very homogeneous, the while sample number 6 at about 150­ chance of selective analyses is negli­ 200 m from the contact. gible. It seemed that towards the contact Next 800 mg of samplepowder was the percentage ofSi02 decreased from melted together with 1200 mg borate, 78% (sample 4) to 68% (sample 1), in a platinum cup, at 900-10000 while near to the centre of the body the Celcius. silica percentage was about 72 %(sample The borate consists of a mixture of 5 and 6). LiB02 and Borax. The ratio of B203 The percentage of A1203 increased to LiOH to Borax being 10:6:13,3. from 11% to 18%, with an average By stirring and heating a homogeneous percentage of 15,5% near the centre. melt was made of these constituents. The K20 percentage increases regu­ After the powder had completely larly from 4, 1% near the centre of been dissolved in the borate, so that the body to 11 % near the contact, the melt was homogeneous it was while the percentage Na20 decreased poured out in the form of a "button" from 4, 4% near the centre to 1,2% on .a graphite plate, the temperature near the contact. of which was about 3000 C. The The increase of the potash conent "buttons" were then slowly cooled down of the Rio Freddo porphyries from to room temperature. The percentages 4% near the centre of the igneous of K20, Si02, A1203' CaO, and Fe203 bodies to 11 % near the contact may of these buttons was determined by be accounted for by assimilation of means of the "Rontgenfluorescence" the surrounding middle triassic lime­ (de Widt 1963). The percentag-e of stones and dolomites by an ascending Na20 was calculated by means of granodioritic magma, relatively poor Flame-photometer determinations. in quartz and rich in alkalis. The results listed below have The alkali content of the Rio Freddo been corrected for loss in ignition, magma crystallized mainly in the while the percentage of K20 is the feldspar phenocrysts and in the crypto­ average percentage calculated from crystalline groundmass. The sodium the "Rontgenfluorescence" and the content probably stayed longer in so­ Flame-photometer investigation. lution. The sodium is a "fugative " 100 mesh", 100 holes! inch:::. 40 holesj em

- 36 ­ Table III

Results of the analyses of the porphyry samples.

%Si0 No. Rock variety Locality 2 %A1203 %K2O %CaO %Fe203 %Na20 Total % 1 red to liver Rio Freddo 68, ° 18,0 11, ° 0,3 2,1 1,2 100,6 coloured por­ phyry.

2 Red to liver Rio Freddo 72, ° 15,0 8,3 0,1 2,0 2,8 100,2 coloured por­ phyry.

3 Red to liver Rio Freddo 75,0 13,0 7,7 0,1 0,4 3,0 99,2 coloured por­ phyry

4 Red to liver Rio Freddo 78, ° 11, ° 5,2 0,15 1,3 3,4 99,1 coloured por­ phyry

5 Green-co ­ Rio Porfido 70,8 14,2 5,1 1,3 2,4 3,3 97,1 loured por­ phyry

6 Green-co­ Rio Porfido 73, ° 16,9 4,1 0,8 1,6 4,4 100,8 loured por­ phyry

7 Red porphyry Val Bruna 72, ° 14,0 10,5 0,4 1,3 1,2 99,4 8 Red porphyry Mt. Lussari 69,8 19,3 9,8 0,3 1,8 2,0 103, °

9 Red porphyry Mt. Lussari 74, ° 13,0 10,0 0,3 1,8 1,1 100,2

10 Red porphyry Mt. Lussari 72, ° 12,0 10,6 0,05 2,0 1,1 97,8 11 Red porphyry Mt. Lussari 72, ° 14,0 11,9 0,3 1,7 1,0 100,9 12 Ash-coloured Muda 74,0 14,0 4,7 0,5 1,7 3,7 98,6 porphyry

13 Melaphyre Val d'Aupa 72,0 16,0 2,2 0,5 1,1 5,1 96,9

E x a c t n e s s ±,2~o +1% 1.°,2% ;!:.O,OS% =.0,1% =.0,1% constituent" because of its greater greater than for the potash. Theore­ affinity for the CaC03 of the country tically the following reactions between rock than the potash, while also the the Rio Freddo magma and the coun­ solubility of sodium for the deuteric try could have taken place. solutions (rich in bi-carbonate) is

Na feldspar + CaC0 ------Nepheline + Wollastonite + CO 3 2 Na feldspar + CaC0 Anorthite + Wollastonite + Na C0 (into solution) 3 2 3 Na feldspar + CaC0 Ca garnet + Wollastonite + (Na C0 + CO ) 3 2 3 2 Dolomite + 8i0 (+MgO) Diopsite + CO 2 2 Limestone + 8i0 (+A1 0 ) :Anorthite + CO 2 2 3 2

Because of the first three reactions cooling. the sodium content will escape from Orville (1958, 1963) studied a the igneous body to the surrounding ternary feldspar system that consisted rock (contact region), causing a rela­ of K-feldspar, Na-feldspar, and Ca­ tive accumulation of the potash content plagioclase, coexisting with an alkali­ in the residual magma near the contact chloride solution. He found that the (passive enrichment of the K). An more calcic the plagioclase coexisting increase of the potash content from with the alkali feldspars and the 4%to 9%, however, requires reactions alkali-chloridic solution, the higher of enormous mass'3S of igneous- and the proportion of potash in solution. country rock. From these experiments it also fol­ This would. give rise to the formation lowed that at lower temperatures a of different contact minerals, whif"lh solution of alkali chloride, coexisting are not observed by a microscopical with two alkali-feldspars is less rich investigation of the contact zone. Owing in K and more rich in Na, than at to the last two reactions the silica­ higher temperatures; provided, at least and alumina content of the magma will in the initial magma, the ratio of the decrease towards the contact. As kalium content to the (kalium + na­ appears from the analyses, there is trium) content, for certain tem­ a tendency for the silica to decrease perature- pressure circumstances, towards the contact region; however, does not exeeds a certain minimum. this tendency is not indicated by the This condition was fulfilled for the analyses for the alumina content. magma we are dealing with. It has been observed though that If magma cools down potash will the potash content of the majority crystallize as K-feldspar at for in­ of the igneous bodies increases to­ stance its margins, prOVided that wards the outer contact of the. body, there is enough exchange between the whereas for the sodium content the ions in the magma. Plagioclase rich contrary holds (Mehnert, 1960). This in calcllllll will later crystallize at strange distribution of alkalis in acid hotter places; so in the more central subvolcanic bodies seems to be in­ parts of the body the calcium feld­ dependant of the chemical composition spar content will increase. of the invaded country rock, so that The experiments also showed that the geochemistry of these elements two ternary feldspar systems (with is probably not governed by the reac­ different. proportions of anorthite in tions induced by assimilation of the the plagioclase feldspar which are country rock, but by internal reac­ in association with the same alkali­ tions of the intruded body during its bearing solution) can approach equi­

- 38 ­ librium only by exchange of K- and be compared with these experimental Na-ions. K-ions are driven from the circumstances. On this basis the dis­ more anorthite-rich plagioclase-alkali­ tribution of the alkalis in the Rio feldspar system to the less calcic Freddo porphyries can be explained plagioclase-alkali-feldspar system,and as internal migrations of ions in a Na-ions migrate in opposite direction. cooling silicate melt, independent of The centre and the marginal parts reactions induced by assimilation of of an intrusion of acid magma can country rocks.

E. POST TRIASSIC VOLCANISM

There are no definite proofs of panying the Insubric -fault. volcanic activity in the jurassic and The tonalites of Adamello at the cretaceous deposits of the Eastern junction of the Insubric and Judi­ Alps. caria fault. In the Lienz Dolomites (South The tonalites of Monte Croce and Austria) some dike-intrusions of Ivigna along the Judicaria fault mica-kersantites occur. These intru­ near Merano. sions were described by von Klebels­ The tonalites of Bressanone berg (1935), Mutschlechner (1952), (Brixen) and Riesenferner and Schlager (1962). The occurrence (Vedrette di Ries) accompanying SW of the "Kreithof", with its well­ the Pusteria fault. exposed contacts in the cretaceous The granites and tonalites of sediments is widely known. Their Eisenkappel and Susalite in the age is Cretaceous or Tertiary. Drauzone between the Northern In the Vicentinian Alps extensive and Southern Karakwanken Ranges extrusive masses of Tertiary basalts in South Carinthia. occur (J. de Boer 1963). At many In the Tauern Window, Karl (1959) other places in the Eastern Alps distinguished also tonalitic rocks, tonalitic intrusions of mid-tertiary which form the cores of the age are found. They are all related Pennine Nappes, exposed in that to the "Peri-Adriatic Line" (lnsubric­ great tectonic window. Judicaria-Pusteria-Gail/Drau line). These plutonic rocks are composed From West to East the following of plagioclase, quartz, amphibole, and massifs can be distinguished: biotite. The tonalites are relatively The syenites of Biella and Traver­ poor in potash. but they grade locally sella, and the granites, tonalites, into tonalites rich in kalifeldspar, and diorites of Bergello, accom- quartz -diorites, or even real granites.

- 39 ­ F. CONCLUDING .REMARKS ON THE STRATIGRAPHY OF THE CARNIAN AND JULIAN ALPS

The thickness of the permo-triassic hot and dry, (desert-like) with hardly sedimentary series of the Carnian and any vegetation. The intercalations of Julian Alps is about 3-5 km. The con­ gypsum, which occur near the top of ditions during sedimentation were the Gardena formation, suggest that unstable. there existed salt water lagoons. After the variscan orogenesis a Calcareous intercalations in the transgression occurred in the lower Gardena sandstones, with a marine Upper Carboniferous, Hereafter, du­ fauna described from an outcrop near ring the Upper Carboniferous and Redagno by Mutschlechner (1933), bear Lower Permian, periods of trans­ witness of a local marine facies of gression and regression succeeded this formation. one another. In the Upper Carboni­ Further subsidence and a reduction ferous sandy shales, sandstones, and of the supply of detrital matter from quartz-Iydite conglomerates were nearby land areas gave rise to the de­ deposited. These clastic rocks, alter­ position of the Bellerophon Formation. nated with limestone layers, form The base of this formation consists the base of the alpine series of sedi­ of dark, bituminous dolomites, with ments ir this area. They represent many lenses of gypsum, alternating a paralic facies. The Fusulina and with shales. This facies is charact­ Trogkofel limestones were deposited eristic for a lagoon deposit. The upper in deeper water (probably in some part consists of limestones which locally isolated depressions i.n a were deposited in open sea. shallow sea), free from admixtures of Whereas the Bellerophon Formation detrital matter. forms a relatively thick horizon in In the Bolzano area to the West, the Carnian- and Julian Alps, this in permian time, there existed a formation is almost entirely lacking centre of strong volcanic activity. in the Gailtal Alps, north of the On this permian quartz -porphyries Carnian Alps. series of Bolzano, which has the Only traces of it are found at the shape of a 4000 sq. Km. plate, with southern side of the Gailtal Alps (van a maximum thickness of at least Bemmelen 1957). The difference in 1,5 km, the permo-triassic sedimen­ facies north and south of the great tary series of the Dolomites were Pusteria-Gailfault is, however, not deposited. Further to the East, in greater than elsewhere in the South­ the Carnian- and Julian Alps, no ern Alps, as has been pointed out traces of this volcanic activity have by Cornelius (1949), Heritsch and been found. The volcanic activity of KUhn (1951) and van Bemmelen (1957, the Carnian Alps began already in the 1961). Lower Carboniferous and had its After the Bellerophon Formation maximal development near Paularo. the Lower Triassic (Scythian or In the Middle Permian enormous Werfenian) was deposited. The Middle masses of detrital matter were depo­ Werfenian has the facies of a shelf sited under land conditions (the deposit, with a fair supply of detrital Gardena Sandstones)~ so the supply of matter. It is an alternation of cal­ sediments was greater tpan the sub­ careous sandstones and sericitic shales, sidence, thus causing the temporary and some limestone layers. The retreat of the sea. The climate was Middle and Upper Triassic were de­

- 40 ­ posited in a completely marine en­ renewed invasion of detrital material, vironment. which had stopped entirely at the end While the Bellerophon Formation of the Anisian. and the Scythian are developed in In the Carnian and western Julian the same facies over wide areas, Alps the youngest deposits of the the Anisian and Ladinian are cha­ Thetys sea are of carnian and creta­ racterized by many sudden changes ceous age respectively. Elsewhere in in facies. This was partly due to the Southern Alps the sedimentary the formation of local escarpments, column extends upto the Tertiary. The on accdtmt of faulting in the sea thickness of the alpine sedimentary floor (Uggovitz Breccia), partly a column under discussion is estimated result of the existence 01 submarine at 3-5 km, but it may have had centres of volcanic activity. From a an initial thickness of more than shallow sea there emergeil some 5 km, the upper part of which has volcanic islands. The coral reefs been removed during the alpine which developed in this sea now form orogenesis, because of processes the rigid masses of Schlern dolomite, of tectonic and erosional denudation of which many mountain tops in this as described by van Bemmelen (1960, area are composed. 1961). In the Carnian time there was a

- 41 ­ LATEN WI] AFSPREKEN, DAT DIE HYPOTHESE WAAR IS, DIE DE MEESTE VERSCHIJNSELEN OP DE EENVOUDIGSTE MANIER VER­ KLAART .:.

CHAPTER III

TECTONICS

A. THE CONCEPT OF GRAVITY TECTONICS

Differences in height caused by Haarmann (1930), van Bemmelen (1931), differential vertical movements and/or Schneegans (1938), Lugeon and Gagne­ erosion and sedimentation, gives rise bin (1941), Gignoux (1948), de Sitter, to the accumulation of potential energy Gogue!. and Migliorini (1950), Merla (relief-energy). Units with different (1951), and many other supported this relative elevation with respect to sea~ concept. levelhave a different potential energy. The restricted concept of gravity which causes gravitational stress tectonics in the form of gliding has fields. These stress fields are super­ been elaborated into a more general imposed on one another and the rocks theory of gravity tectonics by van are subjected to gradients of elastic Bemmelen (1952, 1955, 1958, 1960, strain of different intensity (steep­ 1963). Van Bemmelen points out that ness) in various directions. Tectonic stress fields caused by accumulation equilibrium is reached when these of potential energy extend also to stress fields and the resulting elas­ deeper levels of the crust. Not only tic strain on the rocks concerned. the sedimentary cover, but also the' have a minimum value, so that no deeper layers, such as the crystalline further deformations occur. basement and its hotter and more The reduction of the relief energy mobile, partly molten base are sub­ can be brought about by erosion and/ jected to these stress fields. He dis­ or sedimentation in a disperse state, tinguishes: or by non-disperse displacements of a. "epidermal" gravity tectonics masses from places with an excess (more or less plastic deformations of potential energy to places with a caused by gliding and diapirism of relative deficit (gravity flow; gravity relatively large and coherent masses tectonics). of the sedimentary cover). The idea that gravitational forces b. "meso-dermal"gravity tectonics cause tectonic deformations was intro­ (plastic deformations, and faulting duced into geology by Reyer (1892) tectonics of the crystalline basement, and Schardt (1898). Ransome (1915), due to gravitational stress fields).

42 c. "Bathy-dermal" gravity tecto­ $1 of the rocks (f = tg $1). From a nics (more or less plasticdeforma­ great number of experiments on rocks tions of the crystalline basement which and on. more or less consolidated has been mobilized by migmatization, sediments, it followed, that for most palingenesis, intusions, etc), and of the rocks 0 is about 300 (Krynine, d. "Sub-crustal" gravity tectonics· 1941; Handin and Hagar, 1957). So (hydrodynamic mass-Circuits in grea­ the minimal dip of the gliding plane 0 ter depths). by which gliding occurs is about 30 • We will only discuss the types of This, however, only holds when the gravity tectonics which are of im­ behaviour of the rocks is elastic. portance for the alpine tectonics of Although it has often been obser­ the area treated in this thesis. ved that rock-units have glided down­ slope, this phenomenon can never be 1. Gliding (epidermal slides, ecoule­ explained mechanically in a satisfac­ ment pax gravite, decollement, tory way when only elastic movements Gleittektonik). are considered. Overthrusts, with a low-angle thrustplane, and a large Let us startwith a simple problem tectonic overlap (such as the nappes <;>f mechanics. We consider a rock­ of the Alps), with horizontal compo­ unit on a gliding plane formed by an­ nents of displacement ranging from other rock-unit. 40 to 180 km, cannot be explained by thrusting, due to tangential forces. Mechanically it is impossible that z' rock-units of some kilometers thick­ ness could be displaced horizontally over many kilometers merely"by thrus­ ~ ting due to a force from the rear. The buckling resistance and cohesion is far from sufficient to transmit the pressure force from the root of the Fig. 7. nappe to the frontal parts, and to overcome the frictional resistance For an unity section perpendicular at the base. If the rocks had be­ to the base of the l:Hock (fig. 7.) the haved purely elastically, gravita­ normal component of pressure force tional gliding of rock-units (some tens of kilometers in length) along low-angle thrustplanes is (as has = gz (' cos Q been proved), mechanically also im­ S . 1 J possible. The opinion of Goguel, that This gives rise to a friction force the bigger the mass, the less the dip of the gliding plane, does not hold W = f S (f is the coefficient of for elastic mechanical movements. friction between the rock-units). Taking into account the factor geolo­ The tangential component gical time it appears, however, that tectonic deformations should rather -t= gZI ~ sin Q be considered as deformations of highly viscous fluids (Nettleton, 1943; Gliding occurs when the friction force Gignoux, 1948, 1950) to which the W equals the tangential component 1:, mechanics of rigid bodies cannot be so when . ~Ics= tg Q = f. applied. It is well known that the The coefficient of friction f is rela­ frictional forces occurring in the ted to the angle of internal friction process of gravitational gliding can

- 43 ­ ------~.- ... 2 ,"" . .,. .'. 0. I I # I. I' B ,.. . "

"l'

, ... ------...... , ...... , ,'" I , I I,,~ '2

+++.+ ++ + +++ 4§+if+ +~~~ + + + + o

,

Fig. 8. Transformation of the escarpments of normal faults by gravity tectonics. be reduced by more plastic layers into an overturned position (fig. such as clays, evaporites, shales, 8 A). etc, which act as lubricating hori­ b. By the formation of secondary ro­ zons. Also plastic deformation, fol­ tational slip faults, cutting the ding, and overthrusting at deeper primary normal fault. At the fron­ levels of the crust by increased tem­ tal parts of such faults. upthrus­ perature has the same effect. Accor­ ting movements occur (fig. 8 B). ding to Hubbert and Rubey (1959), the c. By sideward squeezing out of more frictional resistance to sliding of plastic formations under the weight rocks containing interstitial fluids, of overlying more competent strata, is also greatly reduced by the abnor­ because the plastic strata lost mally high pressures of these fluids their lateral support in the es­ in the formation, which serve as a carpment of the fault. gliding horizon. If the pressure of The more plastic formations can the pore fluids approaches geostatic accumulate to an abnormal thick­ values, the internal friction is re­ ness at the outcrop of such lateral duced to such a low value that gliding diapirs (fig. 8 C). of the strata is possible at very small d. By transformation of the originally inclinations. The angle of the slope normal faultplane due to the need not be greater than 10 to 30 if mushrooming effect of vertically the transported column of sediments rising diapirs of plastic masses is thick enough. As the compressi­ such as evaporites, shales, igneous bility of fluids is far less than that bodies, etc. (fig. 8 D). of the rock-particles, elastic (shock) e. After Wise, 1963 (fig. 8 E). waves, such as caused by earth­ quakes will, on their passage, also 3. Diapirism. temporarily reduce the internal fric­ tion. At that moment a pre-existing Diapirism sensu lato, comprises field of elastic strain, may produce all phenomena of forceful intrusion a small amount of plastic deformation of matter. It is the counterpart of in the rocks. In the course of time, gliding. During gliding the higher si­ series of earthquake shockwaves may tuated strata move farthest forward cause a jerky advance, accumulating and downward, whereas during the to great slides over small slopes. process of diapirism the deeper situ­ ated, more mobile strata, move sideward and upward, being squeezed 2. Transformation of normal faults out like toothpaste from a tube, by into apparent upthrusts and over­ a folding process or by load. Dia­ thrusts. pirism sensu lato, also comprises the ascent of matter with relatively The toppling over of the upper parts low density simply by its "Archime­ of normal faultplanes, so that the dian" upward pressure. outcrops resemble steep upthrusts, is The diapiric intrusion forms a a typical phenomenon of secondary core surrounded by abnormal con­ gravity tectonics in the investigated tacts with the pierced strata. Es­ region. pecially salt, gypsum, shales, and There are at least five ways by marls can easily be squeezed out; which the escarpments of normal faults but also diapirism of conglomerates, can be transformed by gravity tec­ sandstones, and stratified dolomites tonics: have been observed. a. More or less gradual bending of a In the investigated region the dia­ steeply dipping normal faultplane piric structures are mostly related

- 45 ­ to erosional and structural valleys. base of the Schlern masses towards The erosion and denudation (mainly the adjacent erosional and structural ':luring and after the quaternary gla­ valleys, where they emerged as dia­ ciations), created a strong relief, piric structures, sometimes causing with great differences of load on the a toppling over of the fault contatcs plastic strata. The tectonic subsi­ into the position of steep upthrusts, dence of the Tarvis-graben has been as has been discussed before. another factor in the creation of local The outward flow of matter from stress-fields due to relief energy. the base of the reef-bodies must be This subsidence of the Tanis-graben volumetrically compensated elswhere, forms a part of secondary tectonics for instance by further subsidence of on a larger scale, namely the collapse the reefbodies (assuming at least that of the flanks of the Gail trough, the compressibility of the matter is north of the Carnian Alps, as will zero). So a saucershaped form caused be discussed in paragraph 6 ofthis by further subsidence of the central chapter. For the surroundings of the parts of the reef relative to its mar­ Val Fella-Val Canale Valley, however, gins and disintegration into a number this subsidence represents primary of blocks might occur, which has been tectonics by differential vertical described for the NW Dolomites in movements which gave rise to secon­ the Province of Bolzano by Engelen dary gravity tectonics in that valley at (1963). The saucer shape of the cen­ a smaller scale. tral parts caused sliding of the plas­ Still another factor promoting the tic overlying strata from the tilted diapiric movements was the weight edges of the reefs towards its de­ of the heavy, competent bodies of pressed centre. The summit folding Schlern dolomite, overlying the more in the Italian Dolomites (German: plastic upper carboniferous and permo­ "Gipfelfaltung" Italian: "Dislocazioni triassic strata. Sinking of these rela­ di Vetta") described by Agterberg tively heavy, rigid masses into the (1961), Engelen (1963), and others plastic, deeper levels, caused a originated in this way. squeezing out of these strata from the

B. TECTONICS OF THE PERMO-TRIASSIC SEDIMENTARY SERIES

1. The Tarvis fault ("Fella fault"). Alps and the Venetian Alps to the South. It can be traced eastward along As the Tarvis fault is not exposed the Pontebbana road from Pontebba as a we 11 defined faultplane, but as to the frontier between Italy and Yugo­ a more than 500 m wide zone of tec­ slavia. From Pontebba to Malborghetto tonic disturbance, partly covered by it is marked by the valley of the vegetation and quaternary deposits, River Fella; for this reason this tec­ its tectonic character could only be tonic line is known as the Fella fault proved by indirect observations. in the italian literature. West of Pon­ The Tarvis fault forms the border­ tebba it can be traced to southwest of line between the eastern Carnian Alps Dierico. The distance between the to the North and the western Julian frontier between Italy and Yugoslavia

- 46 ­ and Dierico is about 40 km. of 850-1150 m could be established According to Frech (1894) it links by means of sections and measure­ on to the Sugana fault which borders ments of the strike and dip of the the Dolomite region at its southern strata on either side of the fault­ side. zone. The valley of the River Sava from In former syntheses of the struc­ Aszling to Lubljana which forms the ture of this part of the Alps, the eastern border of the Julian Alps, Tanis fault has generally been con­ is also a tectonic line of significance sidered as a northward overthrust and forms, according to Frech, the fold, (fig. 9) due to tangential com­ eastward extension of the Tarvis fault pression during the alpine orogene­ ("Sugana-Sava fault"). sis (Gortani, 1936: Selli, 1947; di The Sugana fault is a primarily Colbertaldo, 194t5). Field observa­ southward dipping normal fault which tions, however, do not confirm this in places has been overturned by se­ concept. condary tectonics, so that its out­ The following facts could be ob­ crop now forms an apparent up­ served: thrust. This fault is related to the a. Accompanying parallel faults with neogene uplift of the Cima d'Asta to drag phenomena in the Canale delle the North of it, and subsidence of Volpe are northward dipping nor­ the southern Limestone Alps to the mal faults (with relative subsi­ South. The Tarvis fault on the other dence of the northern block). hand, is an originally northward dip­ b. In the less competent strata at ping normal fault, parallel to the great the southern side of the Tanis Gail fault to the North of it. The tec­ fault, such as in the Werfenian tonic character of these faults (and shales west of Val Bruna, north­ this also holds for the Sava fault) is ward gliding movements parallel totally different, so that Frech's con­ to the bedding planes have oc­ cept seems inadequate. The Tarvis curred. fault has a more or less east-west c. The tectonic character of the Julian direction with a sub-vertical position Alps south of the Tarvis fault is of the faultplane. A vertical throw completely different from that of

N S /------­ / / ---- "" M Valfrassino /--~------"­ " I{ ! "7"~ I \ \ \'­ ~\. \ J'~,.,..,...... :::-< ,~

~=~~iiiiiiiiiiil"'~""iiiiiiiiiiiii~__~4 km.

6 Upper Triassic ~ Anisian Limestones IL\i11 Schlern Dolomite ~' .. Uggowitz Breccia 1+ ++1 Porphyries IN~'I Werfenian ~ "Buchenstein"

Fig. 9. Former interpretation of the Tarvis fault.

- 47 ­ the Carnian Alps north of this 2. The Cocco fault line. In the Carnian Alps the ("Hochwipfelbruch"). permo-triassic series have un-· dergone a considerable tectonic The Cocco fault forms the boun­ deformation, whereas the permo­ dary between the steeply dipping triassic series cropping out at the intensely folded palaeozoic strata along base of the Julian Alps are prac­ the crest of the Carnian Alps and the tically undisturbed. This is not less steeply south to SSW-warddipping in accordance with the concept that permo-triassic strata of the southern these stratahave been thrust north­ flank of the eastern Carnian Alps. ward against the Carnian Alps. This geat, southward dipping,. normal d. The' Uggowitz breccia near Monte fault has an east to west trend, which Priesnig (here called Priesnig­ apart from s·ome irregularities, is breccia) has been subjected to more or less parallel to the main drag during the formation of the trend of the Carnian Alps and the Tarvis fault. Tarvis fault. e. The occurrence of relatively young The Cocco fault is a fault zone sedimentary wedges of carnian age consisting of a system of sub-parallel against the fault. These wedges faults ("en echeIon"). Therefore the have a younger age than the rocks fault cannot be traced continuously. 011- either side. They originated The dip of the faultplanes amounts 0 0 by subsidence into tension rifts, to about 45 _60 • Their vertical throw which later on were subjected t9 has widely different values. Near compression due to secondary de­ Monte Acomizza the vertical throw formations of the sides of the rift. amounts to about 500 m. West of Similar wedges of eocene rocks Monte Cocco, for instance, the fault were described by Wiebols (1938) brings Schlern dolomite of middle and van Hilten(1960) along the Judi­ triassic age into contact with slates caria fault, while Agterberg (1961) of silurian age, which points to a described wedges of triassic rocks vertical throw of far more than one along the Pusteria fault. kilometer. According to these observations, These apparent differences of ver­ the Tarvis fault seems to be a north­ tical throw are due to the fact that ward dipping normal fault. Locally, wedges of permian and lower triassic however, the faultplane has been de­ sediments are pinehed between the formed by secondary (gravity) tec-. palaeozoic and the Schlern dolomite tonics so that the outcrop of the fault (see fig. 10). The f)resence of such obtained the character of an (apparent) wedges of subsided rocks along the upthrust. Near Pontebba, the more plastic r;ermo-triassic series are squeezed out from beneath the massive 'reef bodies ofSchlern dolomite which forms the high mountains south of the fault. This caused a piling up of the Werfe­ nian strata to masses of abnormal , POOIII. ttickness and toppling over of the fault plane into the position of a steep ~ .~....". Dol...... Belleroplloll . upthrust (fig. 8). Also north of Monte m AM..... Grell..... Florianca, secondary slip planes· were formed in the Werfenian series, trans­ FB ...... Ien p....oloic forming the normal fault plane into Pig. 10. Section of the M Acomizza region. an apparent upthrust (fig. 8). - 48 ­ R.Oaus Tamai N \;, '-.

R. Turriea "'.Zouf

600 m 0;:""....._2~'~O...... ~~00m.

N 2000m Fco ProdulinO M.Cullar ca 1762 F Plzzul ,...... I , I \ , I

;'" II 1500 I I I I I I 0 250 500m I 8-8' 2 I I "...--/ 11000

MOlvueric Basso 1813

1350

1100 S Clopeit diGlazat

o

C-C'

Fig. 11. Sections of the E Carnian Alps. Positions of the sections are indicated on the geological maps Sheet II and II A. For the legend see Fig. 14; Section H-H'. main fault points to tension during the structure of which the northern side formation ofthe fault; it is comparable has sunken deeper than the southern with the observation near Val Bruna side (to the North strata of ladinian where wedges of carnian strata occur age occur next to strata of silurian between Schlern dolomite and strata age, while to the South Werfenian of older age (see page 48). and Bellerophon strata occur next to South of Monte Capin di Ponente Schlern dolomite of ladinian age). the fault is hading with the dip of Tectonic graben structures are the strata (German: "Planparallele frequently met with in the Southern Normal Verwerfung"), giving the im­ Limestone Alps (Val Sugana graben pression that the contact between the structure for instance). They repre­ Lower Triassic (Werfenian) and the sent large tension rifts filled with Schlern dolomite (Ladinian) is normal, wedges of the overlying sedimentary and that the Anisian has never been strata. The faults bordering the Travis deposited in this region. graben are parallel or sub- parallel Concerning the origin of the Cocco to the strike of the sedimentary fault, Frech (1894) writes in his mo­ strata. nograph on the Carnian Alps: North of Pontebba, the Tarvis " ... durch die erneute Aufwolbung graben shows a bifurcation. The des alten palaeozoischen Ker­ southernmost graben is a very narrow nes del' Karnischen Haupt­ structure, bordered by the Tarvis kette sind zwei Abschiebungen fault to the South and the Caballo gebilded worden; die Gailabb­ fault to the North. The Caballo fault bruch im Norden und die Hoch­ is also a normal, steeply southward wipfelbruch im Sliden... 11 dipping fault, which brings devonian " ... The renewed arching up of the limestones at the northern side into old palaeozoic core of the contact with Schlern dolomite at the main Carnian Mountain Range, southern side. The northern graben caused two normal faults; the has a SE-NW direction: it runs Gail fault to the North and across the Gartnerkofel and Repp­ the Hochwipfel fault to be wand, reaching the valley of the River South... 11 Gail near Rattendorf in South Austria This is also Assereto's view (1961) (Kahler and Prey, 1963). At the north­ The present author is of the opmlOn ern side of this graben, triassic rocks that the Cocco fault and the Tarvis occur next to rocks of pre-silurian fault are both normal faults bordering age (which are at many places meta­ the "Tarvis graben" (see sub 3) at the morphic), while at the southern side northern and the southern side res­ triassic rocks occur next to rocks pectively. Their age is post-triassic. of upper carboniferous age. Like They may have been formed during the southern graben, the amount of the neogene uplift of the Tauern- Enga­ subsidence of the northern graben di­ din geanticline and the subsequent minishes westward, so that at the formation of the Gail trough as men­ northern side upper carboniferous tioned on page 46 and as will be dis­ strata occur side by side to pre­ cussedin paragraph 6 of this chapter. silurian strata, while at the southern side hardly any throw of the strata can be observed. 3. The Tarvis graben As Agterberg (1961) has pointed out, the bifurcation of tectonic graben The southern flank of the Carnian structures is a very strong argument Alps between the Cocco and the Tar­ that these structures present tension vis fault forms a tectonic graben phenomena.

- 50 ­ o .~ ...

- 52 ­ Falbo'll N 200rm. M.8rizzio 5 M. Bruce Pontebba ~ 561m.

\\­I

0-0'

?~""""Iiiiiiiiiiiiiil2~""'iiiiiiiii4km

M.Acuto 1783

Chiuso (did 1330

s

Vallon. d' RIo Blanco

TGoilitz NE

D QuaternarY,Alluvi

~ ~ Melaptly~es Rhaetian Porphyries I and Lovas ~ Scythian ~ Trookofel Limeston•• and 7CIrvi' 8reccio

Pre- Permian) inclulSl\le \b'lscanfolded ~ ~oci.~ ~ Norian Ladinian Vclconic Belleroohon s'age Corbonattc focllS tt.rl ~ ~~r~~~bOOlferousVolcanic faCM!&

Fig. 14. Sections of the E Carnian Alps. subsequently transformed into (appa­ forming the normal fault which bor­ rent) upthrusts by the formation of ders the graben at its southern flank, these secondary slip planes. This into an apparent upthrust. was already discussed in the para­ Farther to the East, near Cocco, graph concerning the Tanis fault, but an anticlinal structure is exposed it can also be observed north of Pau­ which has already been described laro along the road to Stua Ramaz. by Geyer in 1899. This structure, In the palaeozoic volcanic series near however, is more complicated than the gallery through which the road a normal symmetric fold, as des­ passes, secondary slip planes can be cribed by Geyer. The Cocca anti­ observed (section A-A') indicating a cline is an asymmetric fold with a relative displacement of parts of this steeply dipping northern flank and a unit towards the South, accompanied less steeply dipping southern flank. by upthrusting movements at the fron­ The dip of the axis of the anticline tal parts. is towards the SE, under the Schlern dolomite of Monte Leila. Towards the North, the anticline passes into a syn­ 4. Compressive settling and Diapi­ cline. In the core, Trogkofel lime­ rism of the Sedimentary Rocks. stones of lower permian age are ex­ posed, while its flanks consist of a. Compressive Settling Tarvis Breccia and Grodener sand­ stones. Because the Grodener sand­ Compressive settling is a kind of stones are much more plastic than gravitational tectogenesis. The struc­ the Tarvis Breccia and the massive tural deformations result from the Trogkofel limestones, considerable subsidence and concomittant compres­ movements have taken place along the sive deformation of a sedimentary contact between the formations. In the series towards the deeper parts of central parts of the anticline (in the a tectonic depression, - basin or Trogkofel limestones expol3ed at the graben, - (see van Bemmelen, 1954, road leading into Austria), a radiary fig. 21, Id). fault pattern can be observed, as the Because of compressive settling result of tension which prevailed during and the collapse of the flanks of the the formation of the anticline. Tarvis graben, the sedimentary strata which subsided into this topographic b. Diapirism of the sedimentary depressionhave been deformed. South­ series. ward decollement from the highly elevated Carnian Range, north of the On account of the subsidence of Tarvis graben, caused the intense massive triassic and noric reef­ folding of the gypsum-rich Bellerophon bodies into the Tarvis graben, the strata which are exposed east of underlying sedimentary' series were Paularo. The ridge of hills between squeezed out. Rio Costauda and Rio Turriae is form­ North of Malborghetto, along Rio ed by massive dolomites of the upper Malborghetto towards the North, the parts of the Bellerophon stage, ex­ follOWing formations can be observed posed here in the core of a syncline. successively: In the section (A-A') across this re­ a. Grey to dark grey upper carboni­ gion it is also indicated how by these ferous shales in contactwith Schlern southward decollements and compres­ dolomite. sive settling into the graben-depres­ b. permian breccias (Tarvis Breccia), sion the Werfenian strata were pushed c. upper carboniferous sandstones even over its southern flank, trans­ and shales.

- 54 ­ d. Werfenian strata intruded by car­ graph D, fig. 16). Here, the upper carbo­ boniferous shales, Grodener shales, niferous shales were also squeezed and Uggowitz Breccia: and finally out from beneath the reef-masses to­ again wards the surrounding valleys, where e. dark grey to black upper carboni­ they now emerge like diapiric struc­ ferous shales near the northern tures. contact with the Schlern dolomite. This is a good illustration of diapiric Directly south of the bifurcation movements of the deeper, plastic of the road north of Ugovizza (one strata during the compressive sett­ road leading to Osteria del Camoscio ling. As a result of the subsidence and the other leading to Monte Aco-' of the Stabet Horst (1627 m) which, mizza), intensively folded marls and as can be seen on the geological map shales occur. This formation can be of sheet II represents one big tec­ traced in an east to west direction to tonic unit, the underlying formations a region north of Coccau. According were squeezed out from underneath to Frech (1894) and Assereto (1961) and they are now exposed as diapi­ this formation represents an east­ ric structures at its margins. western elongated diapiric structure At the NE side of this horst, north (German: "Aufquetschung") of anisian of Ugovizza along the road from and lower ladinian limestones (Italian: Ugovizza to Osteria del Camoscio, "Calcari Lastroidi") in the middle anisian strata (mainly conglomerates) and upper ladinian Schlern dolomite. were squeezed out diapirically. The Along the Torrente Fella fault (to diapiric structure has a N to S dia­ be described in sub. 5 of this para­ meter of more than 1000 m. At the graph) one gets the impression that northern side of the structure the near the fault the formation is dipping contact with the country rock is not south, owing to drag by the fault; exposed. At its southern side, how­ but farther to the North it seems as ever, phenomena of mushrooming can if the formation dips under the Schlern be seen near the contact zone of the dolomite. However, its lithology is a conglomerates with the Schlern dolo­ strong argument against an infra-la­ mite of the horst. dinian age of the formation, as has At the southern side of the Stabet ~lready been remarked. From the Horst, west of Camporosso, the Auer­ lithological curve of fig. 6 it follows, nig strata were squeezed out diapi­ that after scythian times the supply rically. The structure consists of of detrital material stopped almost dark micaceous shales, alternating entirely. A renewed invasion of de­ with quartz-conglomerates; the com­ trital matter occurred during the Car­ ponents of which range from some nian. This rule has also been observed millimeters to about four centime­ in the Gailtal Alps (van Bemmelen; ters in diameter. In the quartz -conglo­ 1957, 1961), in the Lienz Dolomites merates, many lydite and sandstone (van Bemmelen; 1964), the Karawanks lenses occur. The bounderies of (Kahler;1955), in the Italian Dolomites this diapiric structure cannot be tra­ (van Hilten; 1960, Engelen: 1963). and ced with certainty, because of a thick in the Vicentinian Alps (de Boer, 1963). morainic cover which lies like a According to the present author it is blanket of overburden on the forma­ more probably that this exposure be­ tions of this region. longs to the Carnian formation, (plas­ In the Vallone delli Ucelli, east of tic RaibleI' strata); these strata reached Monte Bruca, and also south of Monte their present position by gliding tec­ Acuto in the Rio Bianco, upper carbo­ tonics in sub-recent times. This point niferous shales crop out (see photo­ of view is confirmed by the situation

- 55 ­ in the Monte Cucco region where a renee of extensive and thick, moraine formation of the same facies indeed deposits in the Monte Cavallar region. overlies subhorizontally the Schlern Along the road to Monte Coppa, dolomite. Moreover, north of Mal­ however, it can be seen that the borghetto; near Val Bruna (south of Schlern dolomite which is exposed near Monte Nebria); and in the Monte the road, has been totally crushed, Coppa region, the tectonic structures while rocks of lower to middle permian indicate that this formation has slid age (quartzitic sandstones), occur next down in a cascade of folds from the tp rocks of ladinian age (Schlern dolo­ slopes of the reef bodies. South of mite). This points to a throw of at Monte Nebria it can be seen that the least 400 m. less competent layers have glided farther southward over the more competent layers, while also dis­ 6. Structural evolution of NE Italy ruptions of the overturned flanks of (with special reference to the eas­ the folds indicate southward directed tern Carnian Alps). gliding tectonics. a. General Finally, it may be stated that Monte Tersadia (1960 m), SW of Pau­ The fieldwork of the author in the laro, and the whole east to west eastern Carnian Alps led to diagnostic running chain of Schlern dolomite south observations which are in full agree­ of the Tarvis fault, have more or ment with the prognoses derived from less influenced the underlying more the scheme of evolution exposed by plastic permo-triassic formations van Bemmelen (1960, 1961, 1963) as described on pp 45. for this part of the Alps. At least a part of the eastern Alps (including NE Italy) is likely 5. Dis locations of minor importance. to have undergone passive drift mo­ vements due to displacements of mass a. The Torrente Fella Fault in the underground in pre- oligocene times ("Tieforogene Phase" of the The Torrente Fella fault is ex­ east alpine orogenesis), as discussed posed in the valley of the River Fella, by us in Chapter V; B. During this NWof Camporosso, which has carved transport the alpine sedimentary se­ itself deeply into the zone of distur­ ries have not undergone major tecto­ bance. nic deformations. It is, however, The vertical throw of this normal very well possible that the Insubric­ southward dipping fault seems to be­ Judicaria- Pusteria-Gail/Drau line, come less to the SE. Because of up­ which acted as a normal fault in the doming of the diapiric structure N of southern flank of the east alpine ge­ Ugovizza, the southern block has been anticline (see sub "b" of this para­ tilted with respect to the northern graph) during the main tertiary phase block. of the east alpine orogenesis (Ger­ North of Camporosso the fault man: "Hochorogene Phase"), has cannot be traced with certainty on played the part of a transcurrent accotL.'1t of the alluvial cover. (shear) fault ("geosuture") or even a northward up- or overthrust during b. The Cavallar Fault earlier (mesozoic) times. The tertiary tectonics as discussed in this thesis The Cavallar fault cannot be traced had a more local, gravitational charac­ with certainty, as a result of the occur­ ter and was superimposed on such

- 56 ­ older alpine structures. Some of these the last stage of tectogenesis, namely older structures were reactivated du­ the gravitational southward spreading ring the young tertiary phases of al­ of the highly elevated central alpine pine mountain building. Their charac­ belt. tel' may have been totally different during these younger phases. c. The tertiary structural evolution of the eastern Carnian Alps. b. Discussion of the proper alpine tectonics of the post-Oligocene. The eastern Carnian Alps lie south of the Peri-Adriatic line in the eas­ During the Lower and Middle Ter­ ternmost part of North Italy. tiary, the Eastern Alps were domed The older and complicated variscan up (Tauern-Engadin axis), probably. tectonics in the eastern Carnian Alps by an asthenolite of anatectic sialic are not discussed in this thesis. The ;matter which was formed underneath Tarvis graben, which is the most this part of the alpine geosyncline spectacular tectonic phenomenon of (see section III in fig. 5; van the alpine tectonics in this area, is Bemmelen, 1960). This caused ten­ the main subject of our study. sion in the flanks of the geanticline, After the formation of the graben, giving rise to the formation of normal rock units form both sides have slid faults (possibly along zones of weak­ into the topographic depression which ness of earlier origine). In this way resultedfrom the structural subsidence. the great zone of dislocation of the Moreover, diapirism had played an im­ Eastern Alps originated as a huge rift portant part during the structural in the southernflank of the geanticline, evolution of the region. Owing to the namely the more than 600 km long subsidence of the rigid, relatively Insubrio-Judiacaria-Pusteria-Gai l/Drau dense and heavy middle triassic reef line (=Peri-Adriatic or Tonale line, or bodies, the underlying more plastic Alpine -Dinaric boundary zone), se­ upper carboniferous and permo-triassic parating the Central Alps (the com­ strata were squeezed out to the ad­ plex of intensively deformed "north jacent valleys where they emerged like verging" crystalline rocks, belonging diapiric structures. Finally, the over­ to the Pennides and the east alpine lying plastic strata of the "Raibliano" thrust sheets) from the Southern Alps slid from the reefs into the adjacent with less extreme deformations and topographic depressions. folds generally directed towards the The primary cause of the mecha­ South. Its vertical throw amounts to nism of tectonics is a tension field about 6 to 8 km. Along this zone of related to settling of the Carnian tension, magma of granitic composi­ Alps in the Gail trough to the North. tion rose toward the surface, causing Exactly north of the Tarvis graben, the intrusion of the peri-adriatic ig­ the normal slightly north dipping neous bodies (Bergell, Adamello, Gail fault is transforme d into a north­ Croce, IVigna, Bressanone, etc). ward upthrust, (between Weissbriach The concept that the Peri-Adriatic and Villach), as has been described line is a huge normal fault, accom­ by van Bemmelen (1961). The Tarvis panied by rifts and subsided wedges, graben is also a gravitative tectogene­ was proved by van Bemmelen (1957, tic effect on the formation of the ad­ 1961) for the eastern part, and by jacent Gail graben to the north of it. Dietzel (1960), van Hilten (1960), and The Gail graben or "Drauzug" itself, Agterberg (1961) for the western part. is an enormous wedge of alpidic se­ Its present character of a steep, diments, starting as a narrow strip reversed fault was brought about by to the West, becomes more broad to

- 57 ­ Taj;)le IV

Scheme of sequence and interrelation of sedimentation and deformations in the Eastern Alps during the Alpine Orogensis (wIfh specIal reference to the Eastern Carman Alps)

G eotectonic lateral (l) Differential vertical Movements Regional and Local lateral Movements Movements of the 13 Basement Complex 1= Primary Tectogenesis Secondary Tectogenesis (Drift) (Accumulation of gravitational Potential (Release of gravitational Potential Energy) Energy)

Subsidence of the Thetys geosyncline

~ (accumulation of sediments) 2 ~ ~ 0 .~ (l) In- and extrusions of submarine basic and ~ u o 0 til ultra -basic igneous rocks. ..o..;..J..j..J .... QI til 0. .... U :::u (Carboniferous "0p h iolites ") ...... QI OJ ~ Permo-triassic blockfaulting and calc-alkaline ~ .....o volcanism accompanied by the formation of the syn-sedimentary Pb.Zn. ores.

Rise of the N-Adria tumor (partly submarine), Non-dispersed transport ~ ... and subsidence of the Pennine-Tauern ~ Foredeeps. a. f.ormation of the "Proto-Austride Nappes" (SiIvretta and Z ~ Otz crystalline) as a result of epidermal and dermal gra­ Q) ~ ..c: ("Austric ll and "Lamaric" Phase of the East vity tectonics. ",'" Alpine Orogenesis) tj ;:l-~ o.~ b. Injection of the "Proto-Pennides" in the Tauern foredeep '"1 o ..... OJ '" as a result of bathydermal gravity tectonics; intrusion of ..., U = QI H­ til OJ ~ ...., '" OJ magmatic material in the core of the Pennides (Venediger z OJ til I>ll ~ ....., ...... c: 0 tonaIites of the Tauern Window) ~ Uo...... oQlO c. Northward directed movements of the basement, the varis­ z '1""'1 s:: III can palaeozoic, and the alpine sedimentary epiderm of the tj t;::j ~ ~.S '"1 ..... o,ff Carnian Alps (Hl'ritsch, 1936), the Dobratsch Unit (Anderle, ~ ~ O~ 1950), the northern Karawanks (Kahler, 1955), the !sonzo .~.., >0 I Region (W. Julian Alps, Selli, 1947) and the Dolomites o '+; ..., "< QI (Engelen, 1963) o E::: z Dispersed transport t;::j ~ Erosion of the Adria tumor and flysch deposition >-< '"1 H­ (Upper Cretaceous up to Lower Tertiary) >0 >0 "< * l"'UU-Ul~pel'seu lransporl

a. Further northward d~collement of the frontal parts of the "Proto- Austrides" forming the Northern Limestone Alps"

b. Initiation of the southward d~collement of the epiderm on the southflank of the East Alpine geanticline forming the south ern Limestone Alps

c. Stepwise subsidence of great basement blocks towards the N. Adria, due to the formation of the great South Alpine longitudinal faults t Peri-Adriatic fault, accompanied by the periadriatic intrus ion of granitic magma and lampro­ phyric dyke swarms (Malc hites and Kersant ites of the Drauzonej Heritsch and Paulitschj 1958; Holzer, 1958); the Sugana Fault; the Bassano fault j the Venetian fault]

d. Formation of the "Drauzug" (a "Riftgraben") as the eastern extension of the Peri-Adriatic fault.

Dispersed transport

Erosion and deposition of Molasse sediments

Second Order accumulation of Second Order gravitational reactions in the Potential Energy "Drauzug" and the Eastern Carnian Alps

(Potential energy accumulation due to first a. Compressive settling Cf the sediments in the Drauzug; order grav itational reactions, such as anti­ collapse of its flanks. clines, synclines, fault escarpmertts, rift­ graben) b. Northward sagging of the crest of the Eastern Carnian Alps into the Drauzug, resulting in the formation of th, ~ Tarvis graben. ~ 1 ?

Third Order accumulation of Third Order gravitational reactions Potential Energy Potential energy accumulation due to J a. Sliding of rock-units into the Tarvis graben from both second order gravitational reactions, sides; transformation of its bordering normal faults into such as the formation of the Tarvis reversed faults [ graben; and due to selective erosion (fluvial and glacial), b. Compressive settling of the sediments in the Tarvis Graben >­... '"e c. Diapirism of the pre-ladinian strata due to subsidence Q) '-' of the middle triassic reef bodies into their plastic g'" base d. Down sliding of the "Raibliano" from the reefs

e. Redistribution of the Ph.Zn. ores by circulating meteoric water to economically valuable deposits. the East (Lienz Dolomites, Gailtal elevated Carnian block towards the Alps) and still farther to the East Gail graben (see fig. 14, section passes into the graben zone of Blei­ D-D'). The Tarvis graben originated berg-Villach-Klagenfurt (van Bemme­ during this northward sagging. len, 1957; 1961, and van Bemmelen We will conclude this chapter by and Meulenkamp, 1964). The Drauzug giving a scheme of the sequence and which must be considered as the the interrelation of the processes of eastern continuation of the Peri­ sedimentation and tectonic deforma­ Adriatic Line in South Austria (Carin­ tion in the eastern Carnian Alps. It thia), is bordered by the Drau fault has to be pointed out that the move­ to the North, and by the Gail fault ments and deformations indicated in to the South. It represents an enor­ this table may be (and partly certainly mous riftgraben in the southern flank are) superimposed on other movements of the east alpine geanticline, in which of geotectonic importance for which, a wedge of alpidic sediments has sunk however, the area of study provides about 5 to 8 km. This subsided wedge no direct evidence. had subsequently been compressed Of course not all problems of the owing to collapse of the flanks of the eastern Carnian Alps are explained graben (van Bemmelen 1957, 1961). by this scheme, but we will quote South of this Drauzug the Carnian Alps the words of W von Mojsisovics (a were pushed up, rising eastwards to geologist who, at the end of the nine­ considerable heights. The differential teenth century, studied the geology vertical movements of the subsiding ofNE Italy for years): .. ,. "Wir stehen Drau-zone and the rising Carnian Alps am Beginne des Erkennens und Be­ caused a stress field which, finally, greifens, ein weiter Weg liegt noch VOl' caused the northward sagging of the uns .... "

- 60 ­ A B

Fig. 15

Boundary between the Upper Werfenian ("Campiller Schichten") and Lowangle gliding plane in the Schlern dolomite with relative dis­ Lower Anisian (" Uggowitz Breccia") l'lacement of the upper block towards the left (= North)

Fig. 10

c D

-Folds of the "Raibliano" beds Diapirism of Upper Carboniferous shales. CHAPTER IV

MINING

A. INTRODUCTION

The lead-zinc mines of Cave del 160 ton ZnS, which is about 10% of Predil (Raibl) lie about 8 km south the daily production. of Tarvisio. They were already known The ore occurs as galena, sfalerite, at the beginning of the eleventh cen­ marcasite, and to a less extent as tury and they were worked form time pyrite, pyrrhotite, chalcopyrite, and to time during the Middle Ages. Toward cinnabar. the end of the nineteenth century their The deposits are restricted to production was rapidly increased by the Schlern dolomite of the Piccolo the Austrians, but their maximal Monte Re (bordered by the Rinnen­ development was reached after the graben-Barenklamm fault to the West annexation of this region by Italy, and the Aloisi fault to the East), in after the first world war. In 1923 the contact zone between this for­ the "Soc. An. Miniere Cave di Pre­ mation and the Raibler strata. dil" was founded by the Italian govern­ The deposit has been investigated ment in order to work these orebodies. by Posepny (1873), GobI (1903), Kraus The daily production amounts to (1913), and Tornquist (1931). At pre­ about 1800 to 2000 ton ore (personal sent the prospecting and scientific communication sept. 1960), with a research is carried out by di Colber-· total concentration of 40 ton PbS and taldo (1948, 1958).

B. TECTONICS OF THE MINING REGION

The mmmg region forms a part tangential pressure forces (due to of the Western Julian Alps. the relative displacement of Africa Before discussing its tectonics, we towards Europe), the tectonic trend will first make some general remarks lines are the result of compression on the tectonics of the western Julian in a more or less north-southern Alps. direction. In the Eastern Alps a general The E-W trendlines can also be east-westward direction of the folds observed in the Tarvisio region. and tectonic lines can be observed However, here the more important ("East-Alpine direction"). If one sup­ tectonic structures are tension pheno­ poses that the East-Alpine Mountain mena (see chapter III). These resul­ Range originated as the result of ted as the reactions to vertical uplifts.

- 62 ­ In the Julian Alps to the East, a Phase 4: The formation of N-S more or less northeast-southwestern trending faults after the tectonic trend can be observed torsional deformation of ~"Dinaric direction"). In the literature the alpine structural lines this deviating trend is thought to be and the formation of other the result of a tangential compression dinaric dislocations. in a southeast-northwest direction, due to dinaric influences. However, if interpretea according The western Julian Alps, of which to the concept of gravity tectonics, the Raibler Mining district forms a the deviating direction of the pressure part, lies in the region of interference gradients in the phase 3 and 4 could between both directions. not be a regional effect of the dinaric Selli (1947), in a monograph on orogenesis. but a more local feature, this region, distinguished 4 phases due to the great elevation of the in its structural evolution. Triglav dome (M. Tricorno 2863 m) Phase 1: The formation of folds in the western Julian Alps. during the Mesozoic, The sedimentary strata have with an east-west strike radially glided down from the highest (alpine direction). parts of the Triglav Massive. This Phase 2: The occurrence of im­ caused upthrusting movements to the portant northward up­ North, the North-West, the South­ thrusting movements, West, and to the South at the base due to compressional of this dome structure (see fig. 17). forces with an alpine south Di Colbertaldo (1948) distinguishes to north direction. three tectonic phases in the mining Phase 3: Torsional deformation of district of Raibl. the structures of phase Phase 1: During this tectonic phase, 1 and 2 due to pressure a set of. north-south forces directed more trending faults was for­ fromeasttowest (dinaric med ("dinaric direction") direction). with vertical displace­ ments ranging from 800 m (Aloisi fault) to 200 m (Abendschlag). These faults seem to be re­ stricted mainly to the ladinian reef-masses. Also the Struggle, Abend­ blatt, Morgenblatt, and Rinnengraben were form­ ed during this period. Phase 2: The occurrence of south­ ward - directed move­ ments (thrusting move­ ments with an alpine direction). A s lice of the reefmass, about 300 m wide, boun­ ded by the Aloisi and Fallbach faults, has moved Fig. 17. Tectonic sketchmap of the Western southward over a distance Julian Alps. of more than 50.0 m.

- 63 ­ Table V

The development of the Mineralization and its Relation to the Tectonic Phases according to di Colbertaldo (1948).

Phases of Mineralization and Tectonic Tectonic Phases -Repercussions on the deposited Minerals

Beginning Phase of mineralization st (crystalline sphalerite with galena and 1 Tectonic accessory pyrite) :­ Phase Some fracturing of the mineral deposits End at the beginning of the first phase.

1st Formation (yellow sphalerite, galena, pyrite, and accessory lInd Phase of marcasite) Interval of minerali­ nd Quiescence 2 Formation zation (red sphalerite, with little galena and marcasite)

nd Tearing of the minerals of the Aloisi, Fallbach, 2 Tectonic and Struggl, extreme South Phase

rd III Phase of barren dolomitization (mineral breccias, and large scale rd cataclastic phenomena at the Abendschlag, 3 Tectonic Barenklamm, Frauenstollen, etc., with Phase probable removal of a part of the mine­ rals from their original positions)

Next, subsidence of an­ movements which occur­ other slice of the reef­ red NW. of Piccolo mass, bounded by the Monte Re, two NE -SW faults of Fallbach, Cinque trending lines of dislo­ Punte, and Conzen oc­ cation originated, called curred. the Barenklamm fault Phase 3: The third tectonic phase and Muda fault. The must be considered as unit between them was the direct continuation of displaced about 150m in the second phase of de­ south-western direction, formation. Because of causing a left lateral

- 64 ­ offset of the north-south and Monte Strichezza near Val Bruna, faults. is a good example of such a "mega,. Table V shows the rela­ crack" tion between the tectonic Thereupon the reef may disinte­ phases and the phasesof grate into a number of seperate mineralization. blocks each having its own amount According to the present author of potential energy, which can per­ the Raibl faults are very recent lines form more or less independant move­ of disturbance. They are quite local ments. Di Colbertaldo's first tectonic phenomena which are neither the phase must beconsidered as the result result of the "dinaric" nor of the of such a disintegration of the reef "alpine," compression. masses of Raibl into several seperate In reef-bodies rising 1500-2000m sliver blocks, followed by their down­ above the surrounding valley floors, sinking to various levels. strong stress fields of a local extent During the er0sion, the cover of are present. The effect of these plastic carnian strata had slid already stress fields on local structures has southward from the reef masses recently been studied by Engelen (Cinque Punte, Monte Nero etc.) into (1963) in the NW Dolomites. The the valley which had been carved same principles can be applied to out by selective erosion. Then, the the situation encountered in the Raibl disintegration of the reefs, and the mining district. southward spreading of its slivers Because of the downsinking of toward the valley, perhaps after some such (reef) bodies into the under­ further erosion of the latter, caused lying more plastic formations, the a compression of the carnian slump latter were squeezed out towards mass between the Raibl reef blocks the valleys, in this case to the North, in the North and the Hauptdolomite where they emerge like diapiric struc­ Range in the South. tures. The outflow of matter from Thus the tectonic structure of underneath caused a downsin,l

C. SOME REMAKRS ON THE GENESIS OF THE LEAD-ZINC ORES OF RAIBL.

The genesis of the Pb-Zn ores of about the OrIgm of the ores; the Alps is a much discussed topic, a. an epigenetic mineralization and on which opinions differ greatly. It b. a syngenetic mineralization, with is beyond the scope of this thesis to various variants for both concepts. enter into details, so we will confine For an epigenetic mineralization ourselves only to some general re­ there is the possibility marks. a' . of a primary hydrothermal mine­ There are two main hypotheses ralization during the Te rtiary ,

- 65 ­ and the opinion that the belt of Pb-Zn ores a ". of regeneration of palaeozoic extends between the mesothermal ores during the Tertiary (pseudo­ copper and siderite deposits of the hydrothermal). graywacke zone and the katathermal The syngenetic mineralization may gold veins of the Central Alps. There be seems to be a gradual transition from b' . exogene sedimentary (the ore high temperature ores, to ores form­ content being supplied as an ero­ ed at lower temperatures. Further, sion product of the adjacent land the Pb ores seem sometimes to be area), or limited to other directions than the b". endogene sedimentary. (In the Zn ores, which has been interpreted latter case, the ore content being as the effect of different hydrothermal supplied during the sedimentation solutions which followed differ:ent tec­ by sub-marine exhalations, and tonic trendlines during their ascent. mineral springs of hydrothermal The authors advocating ~ hydro­ origin. thermal mineralization relate the triassic Pb-Zn ores (just as some In both cases subsequent tectonic other ores of the Alps) to one another. deformations may have caused later According to them the ores resulted deformations, migrations, concen­ from hydrothermal solutions emana­ trations, and recrystallizations of ting from a hypothetic magmatic mass the mineral content. underneath the Central Alps. Before discussing the genesis of They argue that (at least at Blei­ the Pb-Zn ores of Raibl, we will berg/Kreuth - south Austria - and first give a brief discussion of the Raibl) the ores occur preponderantly various hypotheses in general. as discordant veins and fissures. At places only 10% of the ore is concor­ dant, and these concordant ores must be considered as conformably exten­ 1. The hypothesis of a hydro­ sions ofthe discordant supply channels thermal mineralization. (feeders). The ores originated by metasomatic replacement of certain According to this hypothesis, the layers of a favourable facies and Pb-Zn ores of Raibl belong to the geochemistry, and by the filling of tertiary Alpine Mediterranean ore cavities in brecciated rocks, and of province. The ore deposits of this fissures and cracks in crUShed zones. province all belong to the same 01'0­ Moreover, this effect is s till in­ genetic-metallogenetic period. The tensified because some of the over­ deposits are characterized by the lying layers are impermeable for the occurrence of the same paragenesis ore solutions (in this case the shales with almost the same accessory mi­ of the Raibliano). nerals. Petrascheck (1960) disting­ Schneiderhbbn (1963) argues .that uished three ore districts: the mineralization during the Ter­ a. The eastern Mediterranean dis­ tiary, however, was not the result trict. of primary hydrothermal solutions, b. The Karpathian-Alpine district but resulted from a regeneration of (to which the Raibl ores belong), hercynian ore-deposits by pseudo­ and hydrothermal solutions His concept c. The western Mediterranean ore holds for all post-palaeozoic ores district. in the Alps, in other words, the real Holler (1953), Clar (1956), Pe­ source of the ores is not a magma trascheck (1960) and others are of of tertiary age, but they are derived

66 from palaeozoic rocks ahd ore bodies. genesis, which p.oints to resedi­ The latter may have been remobilized mentation, probably caused by during the geosynclinal stage of the descendentic solutions and not by Alps, when the palaeozoic formations a process of ascending hydro­ subsided to great depths and became thermal solutions. buried by younger sediments. In general f. The geochemistry of the Pb-Zn the same argOments pro and contra ores in the triassic strata in the holdfor a pseudo-hydrothermalgenesis Alps is different from that of othe.r as well as for a hydrothermai genesis. Pb-Zn ore deposits, of clearly pydrothermal origin, which points to a different genesis. 2.The hypothesis of a syn­ genetic (sedimentary) mi­ These arguments for a syn-sedi­ neralization of the ores. mel'ltary genesis are independent of the origin of the ore. Concerning the Supporters of this hypothesis are origin of the ore there are two possi­ Schneider (1953,1957,1963), ~aucher, bilities: (1957), van Bemmelen (1957, 1961), Hegemann (1958,1960)', Schulz (1959), 1. Exogenic; the ore has been supplied Seidl (1959), and others. by exogenic processes The main arguments for a sedi­ (by erosion of older ore mentary genesis of the Pb-Zn orelS occu:J;'rences and descen­ of the Alps are: ding solutions). 2. Endogenic; the ore has been sup­ a. The ores are strictly related to plied by endogenic pro­ some stratigraphic horizons in cesses viz. by ascending the Anisian, Ladinian, and Car­ hydrothermal solutions, nian. In other stratigraphic hori­ connected with the trias­ zons they were never observed, sic volcanism. in spite of the fact that the same rock type occurs, which would be Supporters of an exogenic sedimen­ favourable for the deposition of tary genesis are Schneider (1953, the ore bodies by ascending hydro­ 1957,1963), Taupitz (1954), ~aucher thermal solutions. (1957), and others, while supporters b. There exists no clear hydrother­ of the second possibility (th~ endo­ mal zoning of the ores in the Alps. genic sedimentary genesis) are van The Pb-Zn ores do not occur in Bemmelen (i957, 1961), Hegemann" a bilateral symmetric belt around (1958, 1960), and Schulz (1959). the ~rest of the Central Alps. The main arguments for an en­ Neither can a transition be ob­ dogenic sedimentary genesis are: served from ores formed at higher temperatures to low temperature a. The relation of the ore to the ores. traissic volcanism. c. No distinct supply channels (feeders) The ores always occur in strata of the ores have ever been ob­ deposited in periods during which served; all mineral veins fade volcanismwas active in that region, out downward. or shortly before it became ac­ d. The occurrence of conformably in­ tive. In the Northern Alps the tercalated ores, together with sedi­ triassic volcanic activity was less mentary phenomena andwithfossils. than in the Southern Alps; the e. The occurrence of a bizarre, mineralization is conformably less sometimes also pauperized para­ in the Northern Alps. The sub­

- 67 ­ marine exhalations and extrusions 3. The lead-zinc ores of of hydrothermal solutions, related RaibI. to this triassic volcanism, brought the metal compounds into the sea­ According to Krauss (1913) the water where they precipitated to­ ores of Raibl are related to the Rio gether with anions already present Freddo porphyries on the one side and in the sea-water (epigenetic supply the tectonics of the mining region on of the metal compounds). the other. Also Tornquist (1931) arrived It is a remarkable fact that the more or less at the same conclusions greater economically valuable after a comprehensive investigation mineralizations in the Wetterstein of the mineral deposits of the Eastern limestones of the Southern Alps Alps. The objections of di Colbertaldo occur in a narrow zone of over (1948) to this point of view are: 100 km length along the Drau 1. There is too long a time interval Zone (for instance Bleiberg in between the ladinian volcanism and Austria, Mezica in Slovenia). This the tectonic fault-lines (of pro­ indicates its relation with a major bably late tertiary age) to which fault zone during the Triassic. the mineralization is closely Lovering (1963) proposed the connected. term "diplogenetic" for a mineral 2. There is no proof of a direct deposit whose elements are in part genetic connection between the syngenetic and in part epigenetic. metalliZing solutions and the por­ The ores which originated in this phyries; and in addition, the large way will be mainly primary con­ amount of mineralization is out cordant, but it is clear that, at of proportion to the relatively least in deeper levels, there is a small amount of porphyries. Accor­ possibility of epigenetic ores, be­ ding to di Colbertaldo the minera­ cause the hydrothermal solutions lization is of amesothermal, which mineralized the younger apomagmatic, or even telemagma­ layers had to ascend through older tic type. Perimagmatic manifes­ formations. tations are either absent, or at b. The distribution of the Pb ores most, represented by traces of sometimes differs from that of the secondary minerals of doubtful Zn ores. This cannot be explained origin. Therefore, according to by assuming that the ore was de­ this a~thor, the source of minera­ posited in the basin together with lization must be connected with a the erosion products from the deeper-seated magmatic mass of continent. It also would require which the Rio Freddo porphyries enormous quantities of erosion might be an older manifestation. material for the formation of such According to di Colbertaldo this large amounts of ore. It seems, theory is in agreement with the however, that a great deal of the scheme of geotectonic evolution so-called tertiary tectonics ia the proposed by Dal Piaz (1931) for Alps is much older. The different the Alps. Dal Piaz supposes that directions for the Pb and Zn ores during the Tertiary a large, deep­ are related to this tectonics and seated batholith existed in the may be explained by it: namely by crust of the earth underneath the different hydrothermal solutions Alps, which caused all syntectonic connected with the triassic volca­ inirusions in the Peri-Adriatic nism, which followed different tec­ Alpine Arc (Adamello, Ivigna, tonic trendlines during their ascent. Bressanone, etc.) of oligocene­

- 68 ­ miocene age. Di Colbertaldo's contestable. First, the Raibl faults main arguments for an epigene- (as discussed before) are definitely tic mineralization are: not deep-going structures, but re­ a. The Raibl ores are restricted to stricted to the sedimentary epiderm a very complex system of deep- of permo-triassic or even only triassic going tectonic faults. Only the age. None of the really fundamental, faults which reach from the ladinian deep-going alpine faults (such as the Schlern dolomites into the over- Judicaria, Pusteria, Gail, Drau, lying Carnian strata ("RaibleI' Sugana, Tarvis, Cocco fault etc.) Schichten") are mineralized in a are mineralized. Moreover, all mine- very narrow zone around them. ral veins fade out downward. It is very well possible that some Van Bemmelen (1961) pointed out of these tectonic lines are re- that this is the reason why the "Blei­ activated fundamental zones of berg Mining Society" did not succeed weakness, which existed already in finding ore in their "mining pas- during pre-tertiary times. It is, sage" at Forolach (Gail Valley), to however, very hard to imagine the supposed fundamental fault under- that the great zones of dislocation neath the Mitterberger ore field. should be found just there, where Neither for the volcanic facies primary mineralized sediments of the Ladinian (Buchenstein and were available. Wengen series) nor for the Carnian b. The ores occur only near the con- (RaibleI' Schichten), has a syste­ tact between the Carnian strata matic chemical analysis on the prima­ (well stratified, marly rocks) and ry Pb and Zn content of the layers the ladinian Schlern dolomites, ever been published. Such studies are consisting of massive, dolomitic now made by the geologists of the limestones and dolomites. The Mezica lead-zinc mine in the eastern carnian strata probably acted as Karawanken Range (Slovenia, Yugo­ a sedimentary "trap". slavia). These studies will be published c. The RaibleI' strata are only mine- by I Strucl. . ralized near the faults and no- Field observations by the present where else. If the ore had been author indicate that much pyrite noduls transported from the sediment occur on the surface of the strata of to the fault-zones, traces of syn- some parts of the Buchenstein series. sedimentary ores should have to Taking into consideration the relation be found in the triassic rocks of the ores to the triassic volcanism which, however, according to di (this relation undoubtedly exists in the Colbertaldo (1963) seems not to Alps), one may draw the conclusion be the case. According to this that during the Ladinian a primary author, some horizons with concor- more or less diffuse, syngenetic mine­ dant ores near faults in the ralization mayhave taken place, caused Raibliano are secondary concor- by submarineexhalations and extrusions dant ores, and not primary con- ofhydrothermal solutions along an old cordant ores. fault zone (the Drauzone), or along d. The bizarre, sometimes pauperized old fault zones. The concentrations paragenesis, and other "typical of ore to economically valuable oc­ characteristics" of the Pb-Zn ores currences, however, happened much of the Alps, are also observed later, during the tertiary (alpine) in other ores which are "defini- orogenesis, by means of circulating tely" of epigenetic origin, accor- groundwater. The meteoric water ding to di Colbertaldo. dissolved the mineral compounds, and In the present author's opmIOn these were subsequently redeposited in all these arguments for an epigenetic fault zones near to the contact between (tertiary) origin are, however, highly _ 69 _ the Ladinian and Carnian. when speaking about the internal parts of the eartli,the languag.e of geophysicists undergoes a hlgh­ pressure transformat ion: "dubious" becomes "certain"­ "undoubtedly" means "perhaps"­ a "vague suggestion" becomes a "positive proof" ­ and with "pure iron", an "uncer­ tain mixure of all the elements" is meant ••• Birch.

CHAPTER V

GEOPHYSICS

A. THE GRAVITY FIELD OF NE ITALY

1, Introduction a and b are constants related to the rotation and flattening of the earth. An adequate approximation of the The potential belonging to the earth's geoid is the Hayford-or "international gravity field is called "gravity poten­ ellipsoid of reference" accepted in the tial". In every point of space this Assembly of the International Union potential has a certain value ("U"). of Geodesy and Geophysics (UIGG) in Surfaces with constant U-value are Madrid (1924); it may be considered called "equipotential surfaces". The as a close approximation of the equi­ equipotential surface at mean sea­ librium form of a fluid earth. The level, which is supposed to coincide equator radius of this ellipsoid is with the surface of the sea and which 6 378 388 m. may be thought to be continued under The flattening is 1/297, o. the continents is called the "geoid". ge is 978, 049 gal. Because the distribution of mass within the earth is not regular the For ga' Cassinus deduced the follo­ geoid is a surface which cannot easily wing equation be described mathematically. If the 2 ge 978,049 (1 + 0, 0052884 sin Q earth was a homogeneous fluid, its = shape would be an ellipsoid of revo­ - 0,0000059 sin2 2Q). lution. From the Theorem of Stokes it This formula is called the International can be proved that the acceleration of Formula for Normal Gravity, accep­ gravity "g" at a certain place on the ted by the 1930 Assembly of the UIGG geoid with latitude Q satisfies the in Stockholm. The normal value of equation. 2 gravity is also the gravity exerted g = g (1 + a sin 2 Q- b sin 2Q). e e by a "normalized" earth which is g is the value of g at the equator defined by having the same mass as e the real earth and an equipotential sur­ of the earth. face coinciding with the international

- 70 ­ ellipsoid of 1924 which encloses all surface of reference, as if in free air. the masses, except those of the at­ mosphere. g = gobserved + gf From recent data, however, it gf= 0,3086 . H mgal (H is the ele­ must be concluded that this formula vation of the station above is not the best approximation for mean sea-level in meters). ge' This means that if in the future a new formula for ge will be accep­ g - ge is called the "free air anomaly". ted, all gravity anomalies should have to be recalculated. Note: In marine gravimetry, the same A better approximation of the geoid correction combined with twice is a "spheroid". The spheroid is the the attraction of an infinite slab equilibrium surface of a rotating fluid of water of a height equal to earth, which is thought to be built the distance between the appa­ up of layers with different specific 1'atus and sea-level is called density. The difference between the "free-air reduction". spheroid and the ellipsoid surface is small; that is why the geoid is mostly comparedwi th the more simple b. The Topographic Reduction. ellipsoid Because of irregular distribution By this reduction the effect of the of masses in the crustal or sub-crustal topography above and/or below sea­ parts of the earth, deviations between level is eliminated. The Bouguer the normal value of gravity and the Correction, in a strict sense, is the measured value exist at many places. first approximation for this correc­ These deviations are called "gravity tion. The effect of topography is anomalies". approximated by that of an infinite horizontal plate of which the height £', g = gobserved - ge equals the elevation of the station above mean sea-level. gB = - 0,04185f H mgal or 2. Reductions g = - 0,1118 . H mgal, if a spe­ cHic density of 2 ,67 for the material of the crust is accepted. In order to carry out a mutual If the curvature of the earth is comparision of the measured gravity taken into consideration (called factor values, reductions must be made for B) and the effect of irregulareties of the position of the measuring station the topography (the effect of masses with regard to the ellipsoidof reference or deficiency of mass between the and for visible and subsurface dis­ height of the station and the terrain, turbing masses. the so called "Terrain Correction"; The following reductions must be in German: "GeHinde-reduktion" applied. calledfactor C -),the Bouguel' Correc­ tion (s. 1.) becomes: gB = - 0, 1118 . H + B + C mgal. a. The Free Air Reduction. g after Free Air- and Bouguer By this correction the effect of Correction is different elevation of the measuring g' gobserved + gf + gB and stations is eliminated, supposing that there is no mass between station and g' - g 5.s called 'Bouguer anomaly". e

- 71 ­ c. The Isostatic Correction. d. The Geologic- and Geologic- Iso­ static Correction. Isostasy is the phenomenon that the masses between the earth's sur­ By applying this correction, the face and mean sea-level, and the effect of known geologic structures mass deficiency between sea-level and and their isostatic correction is sea-floor, are compensated by masses eliminated. Locally, rocks and bodies deeper in the earth with reverse sign. with a specific density different from The correction has a different magni­ that of the crust may occur, the effect tude according to the different ways by of which we may calculate. which the compensation occurs. The following systems are used: e. The Indirect or Bowie Reduction. The Pratt-Hayford system, based on the theory of Pratt. The purpose of this reduction is an The Airy-Heiskanen system, based on elimination of the effect of deforma­ the theory of Heiskanen. tion of the shape of the geoid on The Vening Meinesz system, based on gravity. In regions with an excess the theory of regional isostatic com­ of mass the geoid is curved outwards, pensation of Vening Meinesz. whereas in regions with a deficien­ Generally the Pratt system does cy of mass the geoid is curved in­ not hold, and will be left out of con­ wards: so in such regions the geoid sideration. Which of the remaining and ellipsoid surface (with regard systems should be applied is difficult to which ge has been calculated) are to decide. not identical, and this effect should According to Vening Meinesz and be eliminated. others, different parts of the earth's This correction, however, is not crust are compensated in a different so important for the problem we are way, so that for different parts of dealing with. the crust, different systems must be applied. Mountain chains such ast the Alps, 3. Interpretation of gravity continental shelfs and those parts of data. the earth's crust where the strength of the crust and/or of the underlying a. Reductions. substratum is not great enough to undergo deformations without "brea­ The usual routine is to apply dif­ kIng", are probably locally compen­ ferent isostatic reductions to the sated. Topographic phenomena caused measured gravity data for local com­ by erosion or sedimentation, volca­ pensation, as well as for different nism, or folding of the upper parts grades of regionality; in some cases of the earth's crust, are generally also geologic- and geologic-isostatic regionally compensated. corrections, till the anomalies be­ come a minimum value. Only then g after Free Air-, Topographic-, an attempt is made to interpret the and Isostatic Corrections is structure of the crust. Since many g'l gobserved + gf + gB + gI premisses have already been intro­ duced into the reduction of the pri­ g" - g is called the "isostatic e mary value of the measurement, it anomaly". is clear that the ultimate interpre­ tation need not be in accordance

- 72 ­ with the real situation in the under­ densities; only sufficient gravity data ground. In other words, it is not must be extant. known from which anomalies we must The interpretation of every gra­ start to give an interpretation of the vity picture is generally ambiguous, structure of the underground. because as stated before, a great According to Fermor (1914, 1938); number of mass distributions in the Holmes (1927); Mc. Donald (1954); underground may produce the same Kennedy (1959); Stishov (1963) and many picture. Only if certain conditions others, the "Moho-discontinuety" at are satisfied may something be said least under the continents is not a about the maximal depth at which the chemical discontinuity, but a phase anomalous mass is situated. Additio­ transition of the basaltic material of nal information, such as for instance the lower part of the crust to the geological data, are therefore needed material of the suhstratum. The crust to eliminate some of the possible of the earth need not to be in "floating interpretations of a gravity anomaly. equilibrium". The depth of transition As pointed out by van Bemmelen from the crust to the substratum is (1952), there are two ways to arrive dependent on temperature and pressure at a mass distribution in the under­ conditions in the crust, of which our ground, if the gravity field of a knowledge is poor. The application region is sufficiently known. of isostatic corrections, in the way The first method starts from it is done now, would be of little gravity data and gives in an induc­ significane in this case. tive way a mass distribution in the underground which is best in accor­ b. Calculations dance with the observed data, and which is moreover, geologically In the calculations, narrow and acceptable. elongated belts of anomalies may be The second method starts from considered as two-dimensional en­ geological data and arrives by a more tities. It can be proved that the effect or less purely geological reasoning of a structure, considered to be three­ at a picture of the mass distribution dimensional, is always less than the in the underground. Next, the gravity effect of the same structure considered field can be calculated that is caused to be two-dimensional. at the surface by such a mass dis­ An infinite number of mass dis­ tribution. This geological prediction tributions in the underground can or prognosis can than be compared produce a given gravimetric picture with the actually observed gravity at the surface. The gravity field of field (diagnosis). In this way some an anomalous mass, however, con­ indications about the probability of verges to a line or to a point to the the geological working hypothesis depth, if we consider two- or z;hree­ can be obtained. dimensional structures respectively. The first method, by which the This depth is the maximal depth at gravity field is the starting point which the mass can be present. For for the geological interpretation, is the calculations of this depth the very dubious because an infinite num­ magnitude of the anomaly and its ber of mass distributions can p:'oduce tangential components must be known. a gravity picture. The second method Bullard and Cooper (1948), gave a which starts from purely geological method to calculate the maximal depth data, is mostly preferable. of the anomalous mass which can produce a certain anomaly. This method is independent of the assumed

- 73 ­ 4. Density of Rocks. it may pass into high pressure phases with densities, that are considerably For the calculations a density higher than 2,67. Feldspars, feld­ of 2,67 has been used for the crys­ spathoids, common quartz, and many talline basement. The average density other silicates become unstable at of volcanic- and metamorphic rocks, some dozens of kilometers depth in with an acid and intermediate compo­ the earth, and pass into high-pressure sition has also nearly the same value. modifications Mc. Donald, (1954); For rocks with a basaltic composition Birch, Mc. Donald, Robertson (1957). a density of 3, °has been used. Owing to the I great number of The density of sediments gene­ variable factors, the diagnos tic value rally increases to the depth in a of most gravimetric analyses must linear way due to compaction. For seriously be questioned. Only if all many consolidated sediments values possible geological and geochemical of about D = 2,3 + 0,04 Z (Z = depth factores are thoroughly taken into in kilometers) are observed, and an consideration would some possible . average of D = 2,5 has been used for interpretations on the structure of the our calculations. crust make sense. Regional metamorphism causes a In calculations done for a two­ further increase of density (see Table layered crustal model (granite + basalt) VI). By ultra-metamorphism (migma­ a densHy of 2,67 has been used for tization, melting, and granitization), the granitic layer ("Sial") and a den­ however, the density of high grade sity of 3, ° for the basaltic layer metamorphic rocks is decreased. ("Salsima"). For the substratum Table VI ("Sima), a density of 3,27 has been applied. Relation between density of Rock and If we assume that the sial layer Metamorphic Facies. is T km thick and the salsima layer Mother Consolidatec Density T' km, it can be proved from disper­ Rock sion from Love- and Rayleigh waves Clay that the equation 2T + T' = 65,5 km Meta­ must be satisfied. Together with 2,2 morphic (K, AI, Mg, considerations on the isostatic equi­ Facies Fe) librium of the earth's crust (Heis­ kanen, 9th Assembly of the UraG Epi- at Brussels, 1951) and considerations 2,42­ Phyllite on the thermal behaviour of the earth Zone 2,58 lead to a thickness of 18 km for T j and an equal thickness for T'. Meso- I Mica-Schist 2,55­ From dispersion of Rayleigh waves 2,65 travelling across oceans, and seismic Zone I refraction investigations in the Atlan­ tic- and Pacific Ocean (papers presen­ Gneiss I Kata- I 2,67 ted at the Los Angelos meeting of Phacoidal the Seism. Soc. of Am. 1951), it Gneiss followed that the oceanic crust has Zone I a fairly uniform composition; it con­ Migmatite I I 2,58­ sists of a sedimentary layer of 0,7­ Granite 2,62 1,3 km, followed by a basaltic layer of about 5 km thickness, while the If matter of the sialic basement average thickness of the water layer complex is brought to great depths, amounts to about 4 kilometers.

- 74 ­ Fig. 18 5. Discussion of the gravity the graVimetric mInImUm of the Po­ anomalies in northern Italy. basin (with about -120 mgal as lowest value). Preliminary results of the dis­ Near the Colli Euganei, the maxi­ cussion of some of the anomalies mum seems to bifurcate, one branch were published by J. de Boer (1963) extending in the direction of Ferrara, with permission of the present author. and the other towards the Adriatic The possible relation between the re­ sea, south-west of Venice (see fig. 19). gional geology and the anomalies are Section B has a NNW -SSEtern direc­ also discussed in some detail. tion and runs across the centre of the Colli Euganei maximum. Calculations a. The gravity maximum over the have been made for two models; model Colli Euganei. I, two kilometers sediment (specific density 2,5) overlying the crystalline The gravity data from North Italy basement (specific density 2,7), and were placed at our disposal by the model II, two kilometers basalt (speci­ "Bataafsche Internationale Petroleum fic density 3,0) overlying the crys­ Maatschappij" (BIPM) at the Hague. talline basement, which is considered The maps, (- a bouguer- and an is0­ to be located at a depth of 1, 5 to 2 static anomaly map of Middle and km (see fig. 20). The problem was North Italy, Fig.18 and Fig. 19-) treated for these two extreme cases are mainly based on measurements and the calculations were done for of Cunietti (1952) and Morelli (1948, a pseudo-two-dimensional structure 1951, and 1954). They were published with no isostatic compensation, and on a scale of 1 : 5.000.000 by either only sediments, or only basalt J. W. de Bruyn (1955). overlying the crystalline basement. The Colli Euganei maximum is The effect of these suppositions is a southeastern offshoot of the great that the gravity values calculated Lombardo-Venetian maximum (Vecchia, in this way are maximal. The 1955). This region is characterized more complicated calculations for by a gravimetric excess which starts other models which are in better with relatively low values between agreement with the real situation Varese and Lugano, and gets more (namely a three-dimensional struc­ pronounced eastward. It can be traced ture with isostatic compensation, and up to southern Austria (South Carinthia). a sedimentary cover consisting of an The Colli Euganei maximum braches alternation of sediments and basalts), off from the main maximum between will always give values which are Garda and Recoaro. Its axis extends less extreme than those obtained from south-southeastward, by way of the calculations for model II. So even Monti Berici to the Colli Euganei. for the extreme case, in the centre After isostatic correction (T = 30, of the section positive anomalies of R = 0) the gravimetric data show 40 mgal remain between the calcu­ maxima which range from 60 mgal lated and observed curve (see fig. 21). in the Colli Euganei region, to 88 mgal Different positions of the basement, in the Monte Lessini region. The which are geological acceptable, cannot higher values at its north-western reduce the difference between the side may be related to the relati­ calculated and the observed curve; so vely high position of the basement extensive and large masses with a re­ in the Valli Recoaro region (de Boer, latively high specific density mus t 1963). To the ENE the maximum be assumed to be present at deeper is bordered by the Vicenza fault, and levels in the crust. The abundant to the WSW it gradually passes into tertiary basaltic volcanic features

- 76 ­ Fig. 19 a relatively high specific density was Posubio squeezed from under the Po-geo­ 2/06m syncline towards its marginal parts, giving rise to this gravimetric maxi­ mum at the surface. The eastward shift of the centres of volcanism du­

Casfrazzano ring the Tertiary may be related with the gradual bending down of the crust under the Po-basin (de Boer, 1963). The belt of positive anomalies o bordering the Po minimum at its southern side extends from Perugia,

N across Siena, by way of a region o somewhat north of Pisa to the south­ ern part of the Gulf of Genoa. .I'>o

(1) b. The Venetian minimum. o A field of negative isostatic anoma­ oCD lies extends NE of Venice; its mini­ Monl; Berie; mum is situated near the Village of o o Oderzo (-24 mgal). This field of ne­ ,.. gative values is bordered to the North 3 by the Schio-Bassano flexure zone which forms the boundary between the Southern Limestone Alps and the Venetian lowland. The effect of various Colli Eugonei geologically possible mass distribu­ tions has been calculated for a NNW­ SSE section running across Sacile to a region east of Belluno. Since the structure here may be assumed to be two-dimensional, calculations can easily be made by using nomograms. The observed anomalies are presented I in curve I of fig. 21 (section A). Sea level We will base our calculations on several assumptions. rig, 20. Two sect iOns aCrL)" till' .\k1nt i Bel' IL' i and the Colli Eugand. Upper Section: The crystaHine basement is . The sediments near the surface overlain by basalt. 1. we a specific density of 2, 5 which Lower Section: The crystalline basement is overlain hI' sediments. ii:> considerably less than that of the basement 2,67. There is no isostatic known in this region also indicate compensation. that probably a subvolcanic intrusion Calculations were made for three of basaltic (gabbrolc) composition is models. present in the underground. The gra­ Model a. The basement was thought vity maximum might be related with to be situated at a depth the subsidence of the Po-geosyncline, of 3 km in the centre and the former representing the compen­ of 1 km in the NNW and in sation of the latter. Material with the SSE.

- 78 ­ Model b. The basement was thought of the Bassano flexure, so that the to be situated at 4 km in southern part lies less deep than the the centre and of 1 km in northern part (fig. 22), The calcu­ the NNW and 2 km in the lated and observed curve show a still SSE. better conformity, if step-faults are Model c. The basement was thought assumed to be present in the base­ to be situated at 5 km in ment complex. the centre and of 1 km in the NNW and 3 km in the 2. The sediments near the surface SSE. have a density less than 2,67 (name­ the anomalies to be expected aTe ly 2,5). but now there is floating indicated in fig. 21. (isostatic) equilibrium. There is also at a certain depth a heavy mass J: ".... of compensation, of which the mass­ NNW SSE excess equals the mass -deficiency + 30 of the sediments. The negative effect 20 of the mass-deficiency of the sedi­

+ 10 __

10 .0 100 km density contrast of the sediments, greater thicknesses of the sediments are required to produce the same NNW SSE negative anomalies, .eo If we assume the structure to be pseudo-radial and two -dimensional, 70 and the depth of the compensation 60 maximal (namely at the base of a .0 I one- layered crust, with a density contrast of 0,6 between crust and 40 substratum) a thickness of 6 km se­ 30 diments is obtained, For all other 20 cases, thicknesses of more than 6 km m , ' are required to produce the gravity ."0 ,,! ' hcfion 8 picture. 0'---7.,------­ 10 50 100 '.0..,. 3. There is no isostatic equilibrium. Fig. 21 The sediments have. a density less than 2,67 (namely 2,5), but there Model a. corresponds with curve II exists a mass-deficiency at deeper Model b. corresponds wUh curve In levels (downwarp of the crust by com,.. Model c. corresponds with curve IV pressive forces). It is clear that curve II gives If we assume that during this pro­ the best approach to the gravimetric cess the thickness of the crust re­ pattern. The anomaly may also have mained constant, a sedimentary column been caused by a northward (antithe­ of 1300 m is required to give the ob­ tical) dip of about 10-120 of the whole served gravity values for a one-layered block of the basement complex south crust model, and only about 1200 m

- 79 ­ of sediments are needed in the case sity compensates the gravity of a two-layered model of the crust. maximum resulting from the re­ latively high position of the base­ 4. The anomalous masses are plutonic ment. bodies of granitic composition with a b. The second basement block under­ relatively low specific density (lower lies the belt of the Vicentinian Alps than 2,67), situated at some depth and the Venetian Limestone Alps, in the crust. As there are no geolo­ and is bordered by the Sugana fault gical data indicating the presence to the North and the Bassano of these plutonic bodies, we will leave flexure zone to the South. The this assumption out of consideration. basement complex is exposed in Drilling operations (Fabiani and the Schio region, where it reaches Facca, 1949) in this region esta­ elevations of about 600- 700 m blished that the thickness of the sedi­ above sea-level, while further mentary cover is indeed about 3000 m. eastwards it is overlain by at So the first assumption appears to least 1000 m of sediments. be the most probable one. 1000­ c. The third block underlies the 1500 m of sediments is also far too Venetian lowland plain, where little because this thickness is reached mainly quaternary deposits are already by the Miocene alone. So it found near the surface. appears most likely that the gravi­ This block is bordered by the metric pattern of the Southern Lime­ Bassano flexure zone to the North, stone Alps can be explained by while gravimetric and geologic assuming block-faulting in the crys­ data indicate that this block is talline basement complex. These faults bordered by an ENE-WSW direc­ occur in the hinge belt between the ted buried faultzone at its south­ Tauern-Engadin axis of uplift to the ern side, called Venetian fault by North and the simultaneous subsidence de Boer (1963). of the Adria block to the South, as The surface of this third block is supposed by van Bemmelen (1960). ranges from -3000 m at its north­ From North to South, three im­ ern side to about -1000 m at its portant ENE-WSW trending blocks can southern edge. The vertical throw be distinguished (fig. 22). of the bordering faults ranges from a. The northern, or Dolomite block; 5-9 km (for the Insubric fault bordered by the Insubric fault to near Merano) to 2 km (the Sugana the North and the Sugana fault and Bassano fault, see fig. 22). to the South. The Dolomites form a more or The upheave1 of the Tauern­ less saucer-shaped syncline with Engadin axis caused further to the the plate of quartz -porphyries of East (in south Austria) the formation Bolzano at the base. The base­ of an enormous riftgraben (the "Drau­ ment is exposed over large areas zug"). This tension structure in the at the northern and southern side southern flank of the east-alpine ge­ of the quartz -porphyries. It reaches anticline starts to the West as a elevations of more than 2000 m narrow strip of alpidic sediments, in the Cima d'Asta-Gosaldo area becomes broader to the East (Lienz at its southern side, and between Dolomites and Gailtal Alps), and still Brunico and Pennes at the north­ further to the East it passes into the ern side. grabenzone of Bleiberg-Vil1ach-Klagen­ The occurrence of plutonic bodies furt. The crystalline basement and (Cima d'Asta and others) which sedimentary cover has sunk down have a relatively low specific den­ over many kilometers.

- 80 ­ w z 0 w N Z I 0 N ~ ~ I ~ ~ ~ ~ c:t it it ~ ~ W j:!. it ii! (f) z c:t (f)E u c:t ir c:t~-.,. c:t 0 1= w ""(Xl z c:t ~ I- (f) w (f) 0 C\I g (f) Ci: Z ~ ~ c:t 0 W EU

• BASALTIC BODIES B TONALITE OF CHIUSO ~ "QUARTZ-PORPHYRIES"

~ GRANITIC INTRUSIONS ~ POST-CARBONIFEROUS IQQj CRYSTALLINE BASEMENT SEDIMENTS

Fig. 22. Sections across the Western Dolomites.

Hess (1957) has pointed out that clefts" down to great depths with a trench area could hardly depart subsiding wedges could originate. from floating equilibrium if it were Accordingtovan Bemmelen (1958), being pulled apart. So according to however, a decrease of pressure by this author, tension in the crust cannot tension may cause physico-chemical cause the subsidence of a graben. reactions in the deeper parts of the This criticism is based on the assump­ tectonosphere, by which high-pressure tion of a relatively low viscosity of modifications may pass into low­ the basement, so that no "tension- pressure modifications (polymorphic

- 81 ­ transitions). On the ground of thermo­ the result of restoration of the iso­ dynamical considerations these reac­ static equilibrium as, for instance, tions will be endothermic, with con­ can be supposed for the rise of the sequently a decrease of the temperature alpine geanticline with its negative and an increase of the flow limit and gravity anomalies. viscosity of the deeper parts of the The subsidence of the Po-geosyn­ crust and substratum. So pressure cline must be the result of other relief by tension will result in an forces, such as for instance tangen­ increased rigidity of the sUbstratum, tial pressure acting in the crysta1l1ne and hence in considerable delays in basement complex. the reestablishment of isostatic equi­ Hospers and Wijnen (1959) des­ librium. Gravity data over graben cribed something similar in the structures must show negative anoma­ Venozoelan Andes (Sierra de Merida). lies. The effect of the subsidence of The Sierra de Merida seems to be the Draugraben of 6-8 km is partly rising, notwithstanding the fact that compensated by its filling with highly it shows positive gravity anomalies. compressed sediments, As the sedi­ Consequently neither in this case can ments have a density far less than restoration of the isostatic equili­ 2,67, negative anomalies are still brium be held responsible for the dif­ to be expected. Isostatic anomalies, ferential vertical movements, and however, show positive values up to compressive forces, acting on the 25 mgal in this region. Intrusions crust of the earth, have to be accep­ of basic dikes (Hornblende-Augite­ ted. Malchites) in the eastern Carnian The motor of the subsidence of Alps and in the Gail Valley, of post the Po-basin and the rise of the Sierra variscan age (F and H Heritsch, de Merida has to be sought in dis­ 1932), point to intrusions of basaltic turbances of mass di.stribution outside matter of relatively high specific these areas. These belts merely form density at deeper levels of the crust a link in mass-circuits of greater in this region, probably causing the magnitude, as has been pointed out positive gravity values at the sur­ by van Bemmelen (1958, 1962, 1963). face. As has been discussed, the subsi­ The positive gravity anomaly of dence of the Po-geosyncline probably the Colli Euganei, however, must be caused the squeezing out of basaltic attributed to other causes than the material from underneath towards steplike subsidence of the basement the margins, giving rise to belts of complex between the Alps and the positive gravity anomalies at both Adriatic basin. its Sides (such as the Schio- Monti The Po-basin with its negative Berici - Colli Euganei belt at the north­ gravity anomalies seems to be still eastern side). subsiding. This subsidence cannot be

B. PALAEOMAGNETISM

1. Introduction Utrecht, Dietzel (1960) and van Hilten (1960) collected some orientated In connection with the program samples of the Bolzano quartz-por­ of palaeomagnetic studies, undertaken phyries of the Adige Valley between by the "Mineralogical-Geological Merano and Bolzano. Institute" of the State University of The magnetic properties were mea­ - 82 ­ sured at the Geophysical Department below the Curie-temperatu:re- of the of the Royal Netherlands Meteorologi­ ferromagnetic mineral constituents. cal Institute at the Bilt, Holland, under So .not all magnetism is acquired at the supervision of Professor Dr. a certain, fixed temperature, but in J. Veldkamp. a range of some tens of degrees, de­ A permian magnetic south pole pending on the mineralogy and the position of 1460 W and 45 0 N was found Curie-points of the ferromagnetic by Dietzel, and a permian south mineral components of the rock. pole position of 1180 W and 51, 40 N Experiments show that the direc­ by van Hilten. The latitude of these tion of this magnetism called the pole positions is in agreement with thermo-remanent magnetism (TRM) that of other permian rocks of the lies precisely in the direction of the European continent; their longitude ambient field. Thus, providing no deviates considerably. physical or chemical changes occurred The average European permian subsequently, igneous rocks which pole position is about 1690 E and 43 0 N. have cooled down from a temperature The divergence of the NE Italian above their Curie-point, preserved permian pole position from the West the local direction of the earth's European one might for instance be magnetic field at that time and at due to: that place. a. Secular variations of the earth's Sediments, especially the so magnetic field during permian called "red beds", obtain their re­ time. manent magnetism by the orienta­ b. Geotectonic processes such as a tion of small grains of magnetic mi­ counterclockwise rotation of the nerals according to the existing earth "Dolomite-block" around a ver­ magnetic field during their deposition. tical axis. These magnetic minerals are derived c. Anomalies of the earth's magnetic mainly from the weathering of older field during the Permian in some igneous rocks. This remanent magne­ parts of Europe; in particular tism is called sedimentary remanent those regions influenced by the magnetization (SRM) or (SM). Work Alpine orogenesis. done by Runcorn, Johnson, Murphy, d. Processes of continental drift, or and Torreson (1948) show that the of translations and!or rotations declination of magnetization of such of parts of continents. sediments agree closely with the In order to investigate which is horizontal direction of the earth's the most probable solution de Boer field;however, the inclination may be (1963) and the present author collec­ less than that of the earth's field, ted more than 200 orientated samples and can be attributed to two effects; of an age ranging from the Upper a. The tendency for any elongated Carboniferous to the Upper Triassic. or flattened magnetic grain to Before discussing the results, first align itself in more or less hori­ some general remarks on the pheno­ zontal position by sedimentation; mena of palaeomagnetism will be also merely from a rolling of made. spherical magnetic particles about a horizontal axis the inclination 2. The remanent magnetism error may result. of rocks. b. The effect of subsequent compac­ tion under the load of later sedi­ Igneous rocks, formed by cooling mentation, which rotates those of a silicate melt, acquire most of grains in a more horizontal po­ their magnetism as they cool down sition.

- 83 ­ Experiments by King (1955) further when they acquired their present show, that if the surface of deposi­ magnetization. In other words, one tion is not level, both declination and can never know whether these rocks inclination of sediments may not have acquired their remanent magne­ agree with that of the ambient field. tization during their entire history Experiments and palaeomagnetic in­ or, whether, the more important mag­ vestigations by Griffith et at. (1957), netizing processes occurred during however, showed no declination and the brief interval of time, at the time inclination errors for relatively re­ of their formation. Only in the latter cent sediments. It is also doubtful case will their remanent magnetization according to these authors whether be parallel to the geomagnetic field any correction should be made to the at the time of their formation. declination and inclination measured Still another difficulty is, that we from sediments. do not know exactly the effect of tec­ Changes in the ambient field after tonic stress fields or seismic shocks deposition may change the remanent on magnetization. Since Joule's expe­ magnetization of sediments. This riments (1842), the interaction be­ process is probably controlled by tween magneti?;ation and stress called the rate of consolidation of these "magnetostrictionII is well known by deposits. physicists. However, it is not yet Rocks, (igenous rocks as well as known to what extent the direction and sediments) occasionally are subjec­ intensity of magnetization of rocks ted to physical and chemical changes can be altered by magnetostriction, after their formation. This may lead and whether this is a reversible pro­ to a visceous and secondary chemi­ cess or not. cal (recrystallization) magnetization, Graham (1956, 1957) applied an which may disturb the direction of the uniaxial stress (up to 186 kg/cm2) original thermo-remanent magnetism to a variety of rocks, while there (TRM) or sedimentary magnetism (SM). was no applied field working on the This process is partly controlled by rocks. The direction as well as the the mineralogy of the ferro-magnetic intensity of magnetization changed, constituents and the texture of the and after releasing ,the stress most, rock. Since Neel (1949) could prove but not all, of the magnetizations that we have two kinds of remanent returned to their original direction magnetism in sediments, a stable and intensity. and an unstable form, according to Powell (1959) applied uniaxial stress the shape of the small magnetic up to 636 kg/cm2 to volcanic rocks, grains, "magnetic cleaning" is in­ in magnetic field of 0,6-2,4 Oersted, evitable. Magnetic cleaning is a pro­ directed along the stress axis. The cess by which we remove the secon­ response of the various samples be­ dary component of "induced" magne­ longing to one and the same formation tism in igneous rocks as well as in was different; but each appeared to sediments, to know the original direc­ have acqUired a component of magne­ tion of magnetization at the time the tization parallel to the applied stress rock was formed. field. Another difficulty in determining Experiments made by Hall and the sedimentary magnetism is that Neal (1960) show, that magnetostric­ the processes involved in the forma­ tion is usually not a reverSible pro­ tion of red-beds and the origin of the cess. The rotation of the T. R. M. ­ magnetic materials in them are not moment induced by pressure, together yet clear. Therefore, it is impossible with a reduction of the moment that to determine with certainty how and has been observed, is dependent upon

84 ­ the grain-size of the rocks, its mi­ magnetic data must be done with neralogical composition, and the angle caution. between the magnetizing field and the pressure axis. We may therefore 3. Magnetic cleaning conclude that these experiments do not solve this problem unequivocally As discussed in the previous either. paragraph and revealed by As and Nevertheless, it can be said that Zijderveld (1958), Dietzel (1960). in geological history magnetostriction van Hilten (1960) and others, the may locally have played a very im­ direction of magnetization of a spe­ portant part, because sediments as cimen of rock is often the result well as volcanic rocks have been of two components; one due to "in­ subjected to load of younger sedi­ duced" magnetism, and one due to ments on top of them. Also later on remanent or thermo-remanent mag­ during stages of deformation and netism (TRM) The "induced" magme­ mountain-building, extremely im­ tization is a secondary, more, or portant stress fields could have acted less isothermic component (IRM) , on rocks, whilst the then existing caused by induction by the magnetic earth magnetic field may have been field of the earth in times after the totally different from that at the time rock has already been formed. Only of origin of these rocks. (IRM) acquired in large fields asso­ ciated with lightning is a very strong Summerizing we may say: magnet~zation; therefore, rocks ex­ posed to lightning are not suitable a. The direction of magnetization mea­ for palaeomagnetic investigations to sured from "uncleaned" igneous calculate pole positions. rocks and sediments is often not By exposing the samples to an the primary one and therefore un­ alternating field of stepwise in­ reliable. Removal of a possible creasing strength (50-1000 Oersted)­ induced component ("cleaning") a proceas named "progressive de­ by alternating currents has to be magnetization"- it can be shown that attempted. in many instances these components are of different stability. The un­ b. The inclination of magnetization stable, or induced "soft-component", of cleaned sediments may be too with low coersive force, may be re­ low. Sediments deposited near the moved during the first stage of demag­ magnetic equator, of which the netization. Further demagnetization magnetization is the primary one, then only diminishes the magnetic in­ give correct pole-positions tensity of the stable component, whilst (Kruseman 1962) the direction of magnetization is hardly altered or not all. c. Rocks that have subsequently been By applying this treatment to a subjected to some kind of meta­ samples and plotting the results in a morphism, or that have been graph, It may be concluded at which altered by circulating solutions stage the unstable component is com­ are not suitable for the determi­ pletely removed (see for instance van nation of the earth's magnetic Hilten, 1960, fig. 43, PP. 76). The field at their origin. remaining component is the one we want to know; it represents the de­ d. In severely tectonized regions such clination and inclination of the earth's as the Alps and the Spanish Pyre­ magnetic field, active at the time and nees, the interpretation of palaeo­ the place of the formation of the rock.

- 85 ­ 4. Mea s uri n g and i Q tel' p l' e­ and inclination and plotted in a steriu­ tation of the results. graphic projection. The inclination is considered positive when the direction The measurements took place by of magnetization points downwards and means of an astatic-magnetometer (As negative when the direction of magne­ and Zijderveld, 1958 and As, 1960). tization points upwards. In order to make the specimens suitable for measurements they were 5. The earth's magnetic built in cubes of paraffin with ribs of field. 10 cm in orientated position. The orientation in the cubes is such that The earth's magnetic field is a its ribs (a, b, and c) are pal'allel scalar potential which satisfies the to respectively me vertical, the N-S, Laplacian equation (\7 Z U== 0) in all and the E - W direction of the original source free regions of space, including position of the sample. From the the surface of the earth. The existing measurements, the direction of magne­ sources may be both internal and ex­ tization is expressed in a declination ternal to the surface of the earth.

The solution may be expressed in terms of the series

.x == east-longitude s == co-latitude l' == the radial distance em and Sm are numbers lymg between zero and one, representing the parts of the n n . harmonic term pm (cos e ) cos m in U. which at l' == a == radius of the earth, n sm m"t . are due to matter outside the earth (external origin).

If em == sm = 0 there are no external sources for the earth's magnetic field. n n If em == sm == 1 there are no internal sources for the earth's magnetic field. n n m D n'.' Emn are Gaussian coefficients which are usually sought in analysis. m P n (cos e) are the associated Legendre Polynomia. For the order m and the degree n, with m, n ~ 0 we have in the case m m == 0; P n (cos e) Pn, m (cos e) and when m) 0: pr;:(COS e) ~2 (n-m)!I(n+m)!~ ! Pn,m (cos e)

Pn, m (cos e) is also a multiple of the associated Legendre functions and defined by

Pn, m(cos e) = (Zn) ! /Zn I I' m ~ n-m (n-m)(n-m-1). n-m-Z + . n. (n-m) .sm e ~ cos e - Z (Zn-1) cos e (n-m)(n-m-1 )(n-m-Z)(n-m-3) n-m-4 ( Z . 4 . (2n-l) (2n-3) cos e .... ~ If the earth's magnetic field is developed in a series of spherical harmonics (Chapman and Bartels, 1940) it follows that the cause of the earth's magnetic field is situated for about 99q inside the earth and about 1% outside the earth; so U can approximately be written as

o =a /r3/Z C058/LJ".n" 05//r a :5ln. e 0',cos >... a illIrll 61n. e E" , Sin /'+\ . D0= 0,50 U 1.

a 3/1'2 cos e D~ denotes a dipole orientated along the earth's axis of rotation with strength M = a 3 D~ a 3/1'2 sine cos ~ D} denotes a dipole perpendicular to the preceding, in the direction A= 0 with strenght M = a 3 Df a3/r2Binesin ~Ei denotes a dipole perpendicular to the preceding, in the direction ~ = 900 with strenght M = a 3 E}

The terms of higher order indicate multipoles (quadripoles, octipoles, etc.) which fields are small compared with that of the dipole (about 1/10) - see table VII­ their corresponding contribution to the force component decreases outwards to­ wards the earth's surface rapidly when compared with that of the dipole, and may therefore be neglected on the earth's surface.

Table VII

Values of ID~' and IE~\ in i' according to various authors

1 0 1 2 . 1 DO D D D D E 1 1 ~ 2 2 2 2

Erman- 1829 32010 2840 6010 86 2570 40 40 Petersen Gauss 1835 32350 3110 6250 510 2920 20 120 Adams 1880 31680 2430 6030 490 2970 610 750 Fritsche 1885 31640 2410 5910 350 2860 680 750 Schmidt 1885 31680 2220 5950 500 2780 650 710 Dyson- 1922 30950 2260 5920 890 2990 1440 1240 Furner Vestine 1945 30750 2110 5810 1270 2960 1640 1660

The different values for D~ and Elf{ calculated by the various authors are partly due to different magnetic charts used for the calculations, and partly due to secular variations of the earth's magnetic field.

- 87 ­ 1 3 2 The resulting moment M == a ~ (D~)2 + (D~)2 + (E~)2 ~ and the angle between the dipole axis and the axis of rotation ~ = D~ / \ (D~)2 + (D~)2 + (Ei)2 ~ !

This mathemathical analyses of for any period in' the earth's history. the earth's magnetic field carried out The priciple of coincidence of the by the authors mentioned in table magnetic axis and the rotation axis can VII indicates, that the geomagnetic be checked by palaeoclimatological field is for about 90% that of a geo­ data, and it is also clearly demon­ centric dipole, nearly orientated strated by the "Dynamo Theory", along the earth's axis of rotation. The developed by Larmor (1919), Elsasser angle between the two axis is about (1939, 1950) and Bullard (1949), This 0 11 • The moment M is about 8, 1 . 1025 theory relates the origin of the earth's Gauss cm3. dipole field to processes governed So the mean earth's magnetic field by rotation of the earth; the magne­ approximates to a geocentric axial tic field is thought to be produced dipole, But if the magnetic field of and maintained by electrical currents, the earth is comparable to the field induced in the core by the motion which would be produced by a bar of fluid magnetic core material across magnet at the centre of, and aligned lines of electrical force. more or less along, the rotational Opic (1955) has argued that given axis of the earth, it would then follow the dynamo-theory for the origin of that the mean direction of the horizon­ the geomagnetic field, the rotation tal component "H" would always coin­ and the magnetic symmetry axis need cide with a geographical meridian, not coincide. He suggests that lateral and the inclination "I" would be a temperature differences in the mantle function of the latitude "6", the re­ may give rise to convective motions 1ation being tg 6 = ! tg 1. in the fluid core, not symmetrical If we ignore the possibility of about the rotation axis. Since a theo­ systematic differences between the retical analysis of his idea was never inclination of magnetism of rock and made, and reconstruction of the 1'0­ that of the earth's field at the time taLion axis from climatological evidence of the formation of the rock (which and the magnetic axis from palaeo­ sometimes does not hold for sedi­ magnetic measurements more or less ments), and provided that the re is confirm that these axis coincide, we no later induced component of magne­ should not attach great value to his tization in the sample. we can cal­ point of view. culate the magnetic latitude (e) from The concept that the earth's mag­ the relation for a dipole field tgI =2 tg 6. netic field was axially-dipolar, proba­ lithe samples are taken over a period bly also holds good for the non­ of time long enough so that the ave­ turbulent geological past: a period rage declination "D" at any place is of about the last 500. 106 to 1. 109 zero, the position of the geomagnetic years of the geological history, when pole can be determined. the earth had already reached an ad­ Supposing that also in pre-tertiary vanced state of consolidation and times, over a sufficient long period differentiation. (some 100-10 000 years), the axis The axial-dipolar character of the of rotation of the earth will coincide earth's magnetic fieldhas been demon­ with the magnetic axis, we can find strated by Hospers for late tertiary, the position of the axis of rotation quaternary, and historical times by

- 88 ­ means of palaeomagnetic observations that North America was translocated from lavas. It is also convincingly relative to Europe by 20-400 cannot proved by means of palaeomagnetism be based purely on palaeomagnetical for earlier times, since caluclations data and for this reason must in­ of the position of the poles, based on volve reference to other data such the dipole law for specimens from as geological, morphological, and different tectonically "stable" parts palaeoclimatological (Nairn, 1961). of one continent (which may differ even more than 4000 km in distance) 6. General results. lead to similar pole positions for the same epoch. From the measurements it appeared From physico-astronomical con­ that during geological time the virtual siderations it is difficult to assume pole position for each continent moved a shift of the earth's axis of rotation along a rather well-defined path. The with respect to the ecliptic. The pos­ paths meet at the present day position sibility that the earth's rotation axis of the earth's axis of rotation. There changed its orientation in space, de­ can therefore be no doubt that palaeo-' pends on the physical state of the magnetic measurements have very earth. Gold (1955), assuming a "Max­ strongly supported the view. th~lt there wellian earth" which lacks finite have been very large movements of land­ strenght, shows that the application masses during geological times, rela­ of a small external force, or the tive both to each other, as to the geo­ occurrence of changes in density lo­ graphical pole. It is highly improbable cally in the earth, can cause major that the deviations ofthe pole position of shifts of the earth's axis of rotation the same and the different continents for in space, given a sufficient time. various epochs might result from syste­ As a Maxwellian earth model is matic (measuring) errors, from secular not supported by the available geologi­ variations, or from the inadequacy of cal and geophysical data, the opinion the assumption that the geomagnetic of Gold (at least for a period since field always had a dipolar character. the Pre-Cambium) must be rejected. By studying palaeomagnetic data The position of a continent is fixed one comes to the following results: by Europe and North America seemed a. Its orientation of the contempora­ to have moved northwards since the ry pole derived from the declina­ Middle and Late Palaeozoic about tion of the remanent magnetization. 300 . 106 year ago, when their po­ b. Its distance from the contempo­ sition was near the equator. Europe rary pole which can be derived has meanwhile rotated clockwise by from the magnetic inclination, 500 relative to North America. predicting the geographical lati­ Africa moved from its position tude of the sampling side of the near the south pole during the Carbo­ continent. niferous to its present position. c. The longitudinal position of the Australia was situated 400. 106 year continent which can not be given ago near the equator, moved south­ by palaeomagnetic measurements. wards, and was approximately 200 So we only determine the latitudes from the pole about 200 . 106 year of a continent by means of palaeomag­ ago. Its subsequent movement was netism in the geological past. It is, to the North, to its present position however, impossible to determine its near the latitude of 250 South. longitude in this way. Therefore, con­ India was situated 150 . 106 year clusions concerning longitudinal con­ ago at about 500 South and it subse­ tinental shifts, such as the suggestion quently moved to the equator, where

- 89 ­ it was to be found 80 . 106 year ago, During the Triassic at least two after which it shifted again to its reversals have been found by Clegg present latitude of 200 North. et al.(1957) and Creer (1958). Of South America only few, rather The upper Middle Permian and Upper incomplete data are available, but Permian are "normal" (de Boer, it seems that this continent has under­ 1963; GUicherit, 1964). gone only relatively' small movements. The entire lower Permian, and The velocities of the movements lower Middle Permian are "reversed" are about 1-10 em/year. Some con­ Creer (1958), Clegg (1957), Nijen­ tinents moved faster than others. huis (1960), Kruseman (1962). India e. g. moved northwards by The upper carboniferous rocks 11-13 cm/year;Australia about 7-8 cm/ are normally magnetized, Belshe year. The velocities were also dif­ (1957), Guicherit (1964). ferent for different epochs, reaching Little is known of the pre-carbo­ a maximum during permo -triassic niferous times and of the post-triassic time. For comparision it can be Mesozoic. Irving found normal and stated that the movements along the reversed magnetized rocks during the San Andreas fault ascertained by pre-Cambrium. Rocks of cambrium triangulation are about 1-5 emIy. up to middle devonian age seem to The palaeomagnetic investigations be reversed; according to Lin'kova also showed that the earth's magnetic (1963) a part of the Upper Devonian field has repeatedly and suddenly (Frasnian and Famennian) is normally been reversed (the northpole becoming magnetized; jurassic rocks are nor­ southpole and vice versa). This occur­ mally magnetized, and rocks of the red at intervals of some tens of late cretaceous seem to be mainly thousands to some millions of years, reversed. and the reversals seem to be univer­ Through the work done by Hospere sal for various epochs of the earth's (1953) and by students of the history. Geological-Mineralogical Institute Table VIII

Direction of magnetization of the earth's magnetic field during the Cenozoic i.i.. Upper Pliocene N N

~ .....• Middle Pliocene R 00 N Upper Pl(\istocene N Pliocene N o~..... Lower 0 Middle Pleistocene N ~ '< Lower Pleistocene R l.;l Upper Miocene R ..... 1D N ~ Middle Miocene N ~ ...... , 00 N. p:l r-. Burdigal N o~ ,..... cj ..... (0 Lower Miocene 0 ~ t-j .­...... Aquitan R '< ::l r-. p:l Ci ~ N t-j Eo-< 0 Upper Oligocene I '< ~ >l>­ Middle Oligocene R 00 0 o~ Lower Oligocene 0 ~ -<:

~ >l>­ Upper Eocene 0 ~ ~• Middle Eocene N 000 o <';:: Lower Eocene 0 ~ -<: - 90 ­ (Utrecht), under the supervision of 7.Palaeomagnetism of the 10­ Professor Dr. M. G. Rutten, in Ice­ weI' carboniferous ("Kulm ") land; and work done by Roche (1951) volcanic series of th e in France and de Boer (1957), we have Torrente Chiarso River, quite a complete picture of the beha­ north of Paularo. viour of the earth's magnetic field during the Cenozoic (Table VIII). Fourteen orientated sample::> of this volcanic series were collected and N.Neel (1951) discussed four pos­ measured. The rock has been des­ sible mechanisms by which a material cribed in Chapter II. The tectonic could acquire a magnetism in the corrections range from 275/18-35 to opposite direction to the ambient 330/18-35. field. Two of these four mechanisms For the samples 41, 50, and 54 have been verified; one by Nagata the tectonic corrections were 290/70, in Tokyo and one by Gorter in Holland 70/50, and 30/35 respectively. (Phillips Lab. Eindhoven). Although The directions of magnetization some rocks have undoubtedly acquired of the samples obtained from the their reverse magnetism by one of measurements are presented in the these or similar mechanisms, it is diagrams of fig. 23 A, B. The ma­ very difficult to explain all reversely jority of the directions is situated magnetized rocks in such a way. Since in the lower hemisphere of the NE­ reversals of the earth's magnetic field ern quadrant of the steriographic seem to be universal for various epochs projection. in the earth's history, the earth's The directions of magnetization magnetic field must have been rever­ must be corrected for tectonic move­ sed a number of times in the geolo­ ments of the samples after their for­ gicalhistory. This is in strong support mation, and for a possible deviation of Bullard's "Dynamo Theory". Star­ of the direction of magnetization of ting from this theory one can demon­ the samples from the primary direc­ strate that minimal alterations in the tion of magnetization, caused by an flowing-systems in the core of the unstable component due to magne­ earth might cause a change in its tism induced in later times. direction of magnetization. It is often very difficult to deter­ It is not clear whether the rever­ mine the tectonic correction. The sals occurred by rapid rotation of tilt of sedimentary series can be the dipole axis by 1800 without a corrected by measuring the dip of change in its polarity, or whether the the bedding planes. Corrections for dipole broke down into multipolar rotations and/or translations, however, components and was once again re­ can not be applied. In the opposite constituted, but this time with the case, if during geological times the opposite polarity. From equal mag­ chang~s of the direction of magnetiza­ netization of the two classes of rocks tion, measured from rock samples of it could be deduced that the inten­ the more or less "tectonical stable" sity of the field was the same for regions of a continent are known, we both directions. may sometimes deduce something about a possible rotation and/or translation We shall discuss the results of de of less stable regionS of the same Boer (1963) together with our results continent by measuring the directions in the following paragraphs. of magnetization during the geological

- 91 ­ o· M N '.­ 0" 1 o· 0 0 0' J , '0 0' I • 0 •

o" o,.

/ /

B

c

,",PP(A ,.t.A80HIHAOUS CARBONIFEROUS

"ul ISle

E F

Fig. 23:' Stereographic projections of the Pa;laeomagnetic directions. For the Legend see fig. 29. history in those regions. Results of demagnetization experi­ For intrusive masses the tectonic ments on sample 44 and 45. * correction can hardly be established. Generally, no corrections are applied to these masses, although the bodies The influence of an alternating may have been tectonically disturbed magnetic field of (0-900) Oersted on by later tectonic movements. For these samples is shown by the graphs dikes we may apply the same tecto­ of fig. a;b. nic correction as for the sedimentary The graph of sample 44 shows strata they intruded, provided the in­ that the magnetization of this sample trusion was before the strata had been is not very stable. After being ex­ tectonically disturbed. The tectonic posed to alternating fields of more correction for dikes in metamorphic than 150 Oersted, its direotion lies series (such as the diorite dikes in close to that of the present axial the crystalline basement of the Dolo­ dipole field in the Paularo region. mites, measured by Nyenhuis pp 101). The graph of sample 45 shows an can be applied if the tectonics of the rectilinear course of the demagne­ basement is known after their intru­ tization process. As the curve does sion. A comprehensive study on the not pass through the origin of the "S"-planes and the "B"-axis of the coordinate system, it is not certain basement, as done by Agterberg (1961), that the magnetization of the sample may solve the problem. represents the primary magnetization. For effusive masses also no tec­ All other samples were exposed tonic correction can exactly be es­ to alternating fields. Sample 41, 43, tablished' because the contacts may 44, 45, 46, 48, 50, and 54 to a field be irregular. and the initial slope of 200 Oersted. of the topography is often unknown. Sample 1-6 to a field of 250 Oersted. Conformable intercalated thin lava The samples were measured again flows in sedimentary strata are more and the results were plotted in the favourable to the establishing of tec­ graphs of fig. 23, C;D. tonic corrections. Even after demagnetization and tec­ For some volcanic series, such as tonic correction the directions are the Bolzano ignimbrites, tectonic cor­ still widely scattered. Now four rections can sometimes be applied samples (1, 41, 48, and 50) have by means of direction of flow, com­ obtained a negative inclination. Since paction, and cooling planes. these four samples had a small ratio For the lower carboniferous samples between remanent magnetism/induced the directions of magnetization lie magnetism, not much value can be rather disperse even after tectonic attached to them. correction. Sample 1 seems to have Because of all uncertainties men­ a negative inclination. The remanent tioned above, no pole position was magnetization of the samples is gene­ calculated from the average direction rally very weak. For samples 46, of magnetization of the samples. How­ 48, 50, 54, and 1, the remanent ever, the important indication has been magnetism was even less than 15% obtained that the earth had a normal of the induced magnetism. Conse­ magnetic field during the Lower Car­ quently errors of measuring and other boniferous disturbing factors during the measure­ ment may be of the same order of * All demagnet ization curves are presented in magnitude as the effect of the remanent Appendix r of Chapter VI. magnetization of these samples.

- 93 ­ 8.Palaeomagnetism of the up­ rage direction of magnetization repre­ per carboniferous sand­ sentative for the Auernig strata. This stones ("Auernig strata"). mean direction has a declination of 0 0 24 and an inclination of 40,5 • The results of the primary mag­ The position of the upper car­ netic measurements, in terms of de­ boniferous pole can be deduced from clination and inclination of magneti­ this average direction of magneti­ zation in the rock specimen, are zation by using the following set of plotted in the steriographic projec­ formulas: tion of fig. 23 E. These directions all show a posi­ sin \!{l' -= cos 8 sin~t + sin 8 cos D tive inclination, i. e. the north-seeking cos ~t. pole of the magnetization vector points ctg (A -).j)-=(ctg 8 cos ~,l)/sin D ~ downwards. r The directions lie rather close to ctg D sin~ each other. The magnetization direc­ C~f- ~L)-=(sin ~~ tions after tectonic correction (300/15) sin 8 sin D)/ cos are given in fig. 23 F. ~ -= geographic latitude of the mag­ netic pole. Results of demagnetization experiments >-p-= geographic length of the mag­ on sample 1. netic pole. 8 magnetic co-latitude of the The influence of an alternating sample locality. field of 0-900 Oersted on this sample is given by the graph of fig. c. Ac­ 8 can be found from the formula cording to this figure, the points of tg I c-= 2 ctg 8, in which I is the in­ graph a/c and blc do not show a defi­ nite change of their position after clination of the mean direction of magnetization. application of an alternating field up to 900 Oersted. The magnetization D = declination of the mean direc­ of the sample does not diminish pro­ tion of magnetization. portionally to zero. This indicates: mean geographic latitude of the a. The original magnetization is very sampling area. strong, and there is no seconda­ mean geographic length of the ry component of induced magne­ sampling area. tism in the sample. b. There is a very strong stable By means of these formulas a po­ component of induced magnetism sition of the upper carboniferous mag­ in the sample, with a direction netic pole at 1450 E and 590 N was which deviates from the present found. The remanent magnetization of dipole field. the upper carboniferous rocks is nor­ mal. After this progressive demagne­ tization experiment, all samples were - 9.Palaeomagnetism of the exposed to an alternating field of Grodener Sandstones from 400 Oersted. After doing so, the Coccau. samples were measured again. The 21 samples of Grodener sandstones results of these measurements, be­ were collected so as to investigate fore and after tectonic correction, their magnetic properties. Eleven are given in fig. 24 A;B. samples were taken at Coccau and The vectorial addition of these ten samples from a region near Pau­ directions gives the resultant or ave­ laro. The samples from Paularo,

- 94 ­ N N

B

0, o.

•• 0, 0,

o' ...... I'E"AJII (IA_.E...._'O.oj (tIt_.u ...00110111:0,) ao.A,.t.

c o

o' o' 0' o'I ••' 0, o. 0, ...... o•

0' I'IIItMJAN (8lliiaE...... OS'O.Eo,)

~,.G A'~J.G.

E F

Fi~. 24. however, appeared to be unsuitable of the coordinate system. This is not for this investigation; after their de­ the case for graph b/c, which may be position their primary component of due to measuring errors. magnetization was nearly totally des­ The maximum of the produced troyed. They all had obtained a very alternating field was 1000 Oersted. strong and stable component of secon­ For technical reasons further demag­ dary magnetization, with a direction netization is not possible. Besides, ofthe present-dayfield. As an example in most cases the magnetic intensity sample 3 is given. The results obtained of the samples had decreased to hard­ by measuring the other samples from 1y measurable values when they had Paularo are therefore not published. been exposed to alternating fields of Three of the eleven samples from such high values. Coccauhadsuch a weak magnetization Sample no. 5 and no. 7 seemed that the results of the measurements to be very stable. Scattering of the obtained from measuring the samples points of the graph of sample no. 7 have also been left out of the graphs. are probably to be ascribed to mea­ The results of the measurements ob­ suring errors and other disturbing tainedfrom the nine remaining samples factors during progressive demagne­ have been plotted in the diagrams of tization of the sample. fig. 24 C;D. After tectonic correction Next all samples were exposed (130/60 and for sample 3 a correction to alternating fields of 750 Oersted. of 70/28), all samples seem to have Thereupon the samples were mea­ a positive inclination; their directions sured again and the results were of magnetization, however, are scatter­ plotted in the graph of fig. 24 E;F. ed over three quadrants of the stereo­ After demagnetization and tectonic graphic projection. Nevertheless, af­ correction all samples have a posi­ ter demagnetization and tectonic cor­ tive inclination, with a mean direc­ 0 rection, their directions of magneti­ tion of D = 35; I = 24 • The middle zation show a considerable concen­ permian pole position calculated from tration in one group (fig. 24 F). this direction, representative for the This again proves the importance Grodener sandstones is 1420 E; 450 N. of removing induced magnetism by demagnetization, especially of sedi­ 10.Palaeomagnetism of the La­ ments. All pole positions calculated dino-Carnian Porphyries. from rock samples which are not de­ magnetized are unreliable; and even Twenty-eight orientatedsamples of after demagnetization, pole positions upper triassic porphyries were collec­ calculated from sediments need not ted and measured palaeomagnetically. represent the real position of the pole The results of this investigation are during the epochs in which the sedi­ listed in table IX and plotted in the ments were deposited. diagrams of fig. 25. The samples nos. 2, 5, and 7 were subjected to progressive demag­ The influence of progressive demagne­ netization(fig.nos. d;e;f respectively). tization on the remanent magnetization The graph of sample 2 shows that of the samples no. 7 and no. 14. there was a very important component of induced magnetism in this sample. Sample no. 7 and no. 14 were This direction was destroyed only by subjected to stepwise demagnetization exposing this sample to an alternating by an alternating magnetic field up field stronger than 875 Oersted. The to 900 Oersted. The influence of the last part of the graph a/c runs more alternating field on the samples is or less straight through the origin shown by the graphs of fig. g and

- 96 ­ 0 23 .. 027 0 22 028 ,,0 ". 21• ..., g 019 2" 2" 0" 027 .. ~b", 0 OIS ~.£8 10 16 ~"O2801 -21 30 1 2 d olI 0'" 0 20 16

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UPPFR LA.DINIA.N UPPER LADINIAN

c o

PORPHYRIES PORPHYRIES

e~JC 32 •36 0 031

E F' Fig. 25. Table IX

Palaeomagnetism of the upper ladinian porphyries.

D I D I no. field no. 1oc. vol. orientation rock-type tectonic Results before demagnetization Results after demagnetization correction and tetonic correction and before tetonic correction

1 I Rio Freddo 54cc 50- 30 Red to liver 110-35 26°30' + 4° 27° + 5° coloured porphyry _ 4° 2 II Rio Freddo 184cc 32- 40 " " " " 28° 27° 30' _12° 3 III Rio Freddo 87cc 35- 40 23°30' + 5° 23° + 4° " " " " _ 6° _ 8° 4 N Rio Freddo 101cc 35- 40 " 11 " " 29° 29° 5 V Rio Freddo 105cc 40- 45 " " " " 27°30' - 26° 6 VI Rio Freddo 64cc 60- 45 " " " " 30° - 29°30' _14° 7 VII Rio Freddo 106cc 50- 45 " " " " 46°30' _12°30' 46°30' 8 00 Muda 114cc 20-297 Ash coloured 310-25 16030' +53° 7° _29° 9 porphyry 9 02 Muda 115cc 25-310 " " 297-20 35° + 9°30° 18° -30°30' 10 100-1 Rio Porfido 139cc 70-300 Greenish coloured 300-70 61°30' +12°30' 3° _23° porphyry 11 100-2 Rio Porfido 189cc 70-300 " " " " 87° +69°30' 8° +40° 12 100-5 M. Lussari 226cc 35-150 Red coloured 105-35 27° +75° 10° +53° porphyry 13 100-6 M.Lussari 161cc 36-105 A brecciated type " " 21°30' + 2° 21°30' + 2° porphyry 14 100-6A M. Lussari 199cc 36-105 " " " " 22° + 3°30' 25° + 3° 15 100-6B M.Lussari 78cc 36-105 " " " " 28° + 4°30' 28° + 4°30' 16 100-7 M. Lussari 100cc 34-100 Red coloured " " 16° +54° 77° +71° porphyry 17 100-8 M.Lussari 181cc 25­ 70 " " " " 31°30' _ 5°30' 32° - 5°0 18 100-8A M. Lussari 109cc 25- 70 " " " " 28° + 1° 28° +1,5 19 100-813 M. Lussari 101cc 25- 70 " " " " 34° _10° 34° _ 9° 20 100-9 M. Lussari 99cc 36-105 " " " " 84° +48°30' 79°30' +63° 21 100-10 M. Lussari 78cc 36-105 " " " " 337° _60° 19° _18° 22 100-11 M.Lussari 158cc 36-105 " " " " 28°30' _24° 27° -6'fJ 23 100-12 Valbruna 225cc 71- 97 " 11 97-32 7°30' + 2°30' 3°30' + 3° 24 100-12A Valbruna 144cc 71- 97 " " " " 22° _ 1°30' 23° - 11 25 100-12B Valbruna 97cc 45- 97 " " " 13° _32°30' 13°30' _20° 26 100-13 Valbruna 90cc 32- 97 " " " " 50 +52° 10° +4()D 27 100-14 Valbruna 105cc 41- 97 " " " " 4°30' ·712° 2° + 2° 100-15 28 Valbruna 127cc 32- 97 " " " " 33° I i 17030' I 29° I _15° fig. h respectively. 11.l=>alaeomagnetism of some The following can be said about permian samples from the magnetic behaviour of the samples the Italian Dolomites. during their stepwise demagnetization. The graph of sample no. 7 seems a. The violet Porphyries near Cavalese. to run straight towards the origin of the coordinate system, which means Six orientated samples of the that the direction of magnetization violet porphyries near Cavalese in does not change by demagnetization, the Fiemme Valley, southern Dolo­ and that only the intensity is de­ mites, were collected and measured creased. In sample no. 14 even the palaeomagnetically by van Lookeren intensity of the magnetization was Campagne (Utrecht, 1961). hardly affected by this treatment. This Directions before and after demag­ means also that the samples are very netization (500 Oersted) and tectonic stable. For the elimination of casual correction of about 100 are plotted errors of measuring and other possible in the graphs of fig. 25 E;F and influences, all the samples were mea­ fig. 26 A;B. Demagnetization curves sured once more, after being subjec­ are given in fig. i and j for sample ted to an alternating field of 250 Oer­ no. 32 and no. 33 respectively. sted. After demagnetization and tec­ The mean direction of magnetiza­ tonic correction all directions lie tion of the samples after demagnetiza­ close to one another, with the exep­ tion and tectonic correction (fig. 25, D) tion of sample no. 34. However, it is D = 28 I = + 430 . The ladino-car­ is very peculiar that of the five re­ nian pole-position calculated from this maining samples no. 32 and no. 33 .mean direction is N 570 E 1400 . have a positive inclInation. From the The topangle of the cone of confi­ demagnetization curves of sample dence can be calculated from Fischer's no. 32 and no. 33 it follows that both formula: samples were stable. If we assume that during reversals of the earth's 1 - cos j (l-p) = N~R ~ (1 /p)1/N-1_1 ~ magnetic field, the magnetic field changed its polarity by rapid rotation of the magnetic axis over 1800 with­ Topangle of the cone of confi­ J out a change of the polarity of the dence. axis, and if we further assume that The number of vectors. some of the samples were deposited The length of the resultant vec­ during a reversal of the _earth's mag­ tor, with l.. J.. l. netic field, the two directions may t~ c..o-~ ~ (~l~~~);.Li.'~, It (..Of> oL .. ) + .. )t represent some intermidiate position. As the latter assumption is highly and are the angles between yL improbable no satisfactory explanation a certain vector and the three can be given for these two directions. rectangular axis of the coordi­ The average direction of magneti­ nate system. zation D = 162; I = -23. p The probability of the mean being located within the cone b. The lower permian "Lagorai of confidence with top-angIe J. Quartz- Porphyries". Generally p = 0,05 (5%) is selected. These data are quoted from a pa­ laeomagnetic investigation by Find­ In this case the topangle of the hammer (internal report of the Geo­ cone of cinfidence becomes 4048'. logical Institute Utrecht, 1959).

- 99 ­ CAVALESE PORPHYRIES M N ."

A

o LAGORAI PORPHYRIES

B·~T.C

• • ." • • • • •• • V.' • • • •• ... • 0 •

0 • C

o • lAGORAI PORPHYRIES LAGORAI PORPHYRIES "~TC

• • •

• • o E Fig. 26. F Fourty-two kilometers SE. of Bol­ c. The permian basic dikes near zano and 50 km NE. of Trento, 38 Chiusa. orientated samples of lower permian ignimbrites were collected. The These data are qouted from the Lagorai ignimbrites are the southern investigation by Nijenhuis (internal part of the Bolzano quartz-porphyry report of the Geological Institute, shield, forming the Lagorai range Utrecht, 1960). (north of Cima d'Asta), a plate of Three kilometers north of Chiusa. about 300-500 m thickness, dipping near the Val Funes (Villnoss Valley), 20-300 to the NW. eight orientated samples of permian The results of the primary mag­ basic dikes, intrusive in the quartz­ netic measurements are plotted in phyllite series, were ta;'en. The rock the steriographic projection of fig. is a diabase-porphyry consisting of 26 C;D. The directions lie rather basic plagioclase and uralitized augite; close together, with declinations accessory ilmenite, magnetite, and 0 0 ranging from 101 to 194 and incIi­ pyrite. nations ranging from -30 tot _650 . The results of the primary magne­ Demagnetization experiments on tic measurements are plotted in fig. several samples, with alternating cur­ 27 A. The directions lie strongly rents up to 1000 Oersted showed'" dispersed, all but no. 5 have a po­ that the component of secondary mag­ sitive inclination. " netization of the samples was com­ pletely destroyed by an alternating Results of demagnetization experi­ current of 250 Oersted, and that at mentsonthesamples no.1 and no.2.. 1000 Oersted still measurable rema­ nent magnetization was present. This The influence of progressive de­ means that the primary component magnetization on these samples _is of magnetization of the samples was shown in the graphs of fig. k and fig. very stable. Thereupon the samples 1. According to these figures, the were exposed to alternating fields graphs of progressive demagnetization varying from 400 up to 1000 Oersted. can be di vided into two parts, one The results of these measurements from 0 to 50 Oersted, and the other before and after tectonic correction part from 50 to 500 Oersted. The are plotted in the diagrams of fig. latter part runs more or less straight 26 E;F. to the origin of the coordinate sys­ Six samples seem to have acquired tem. This means again, that after a positive inclination; most of the exposing the samples to a field of samples, however, have a negative 50 Oersted, the direction of magne­ inclination. The vectorial addition tization does not change anymore of the directions gives the average by increased demagnetization, and only direction of magnetization being: its intensity diminshes by it. The D = 1370 30 ;I=-8030' ,with a unstable component, induced at later cone of confidence according to times, has apparently been removed Fischer's formula of ~ = 5043' . after exposing the samples to an al­ The position of the lower permian ternating field of 50 Oersted. pole calculated from this average , Next all samples were again expo­ direction of magnetization is 1140 o sed to alternating fields. W; 34 N. Sample no.6 to a: field of 100 Oersted, Sample no.3 to a field of 180 Oersted, * These data are not quoted in this Sample no. 1, 2, 5, 7, and 8 to a thesis . field of 500 Oersted, and Sample no.4 to a field of 600 Oersted.

- 101 ­ BASIC DIKES MEAR CHIUSA BASIC DIKES MEAR CHIUSA B0A-Te. A.On;IC.

02

01 06

0 6 ,. 03 2 •• 7 z.5 A 4~~8 B 07 8: O.

OG

02

°G

PERMIAN PERMIAN GRODENER SANDSTONES GRODENER SANDSTONES B·°;BTC B%IC

c D

02 03 02

OG OG OA BOx OF OE

PERMIAN PERMIAN GRODENER SANDSTONES GRODENER SANDSTONES A%IC A OJ. IC.

E Fig. 27. F After doing so the samples were e. The ladinian melaphyres from the again measured and the results are Col Ponsin Region near Fonta­ given in fig. 27 B. All directions nazzo (NW. Dolomites, province except that of no. 3, now have a of Bolzano, Italy). negative inclination. The average direction of magne­ tization has a declination of 1730 and Four orientated samples collected an inclination of -80 30: by van Lookeren Campagne (1961) were measured palaeomagnetically by the present author (Fig. 28). d. The Grodener sandstones of Fig. 28 D gave the average direction Piccolino and San Martino. of magnetization of: declination 26 0 and inclination +29 0 .

Of the Grodener sandstones of the Italian Dolomites three samples were taken near Ortisei along the road to 12.Palaeomagnetism of the Ponte Gardena and twelve samples extrusives in the Ladi­ from a region near San Martino. nian of the DObrlltsch The results of the first series (eastern Gail Alps, of measurements without correction Carinthia, Austria). for dip and before demagnetization are shown in fig. 27 C. Fig. 27 D gives the same results with correction for dip. The step by step demagne­ Eight orientated samples of upper tization curves of sample no. F, and anisian or lower ladinian lavas from no. H, are given by the graphs of the Dobratsch Unit (District of Blei­ fig. m and fig. n respectively. berg in the eastern end of the Gail From the curves it follows that Alps, Carinthia, Austria) werecol­ sample no. H was stable, and that lected with the cooperation of Prof. from about 250 Oersted the magne­ Dr. F. Kahler (Klagenfurt), Dr. tic vector of sample no. F, has W. Fritsch and Mr. E. Strehl and stopped rotating (the unstable com­ measured by van Lookeren Campagne ponent(s) being removed), and only (1961). continue to decrease. We assume The demagnetization curves of that after 250 Oersted the remaing sample no. 5, no. 6, and no. 8 magnetism of high coercive force show, that their magnetization becomes is the original upper middle permian stable after exposing the samples magnetization, and that the compo­ to alternating fields with values of nent of younger induced magnetism more than 200 Oersted (fig. p, q of lower coercive force is removed. and r). After tectonic corrections 0 0 After this the samples were mea­ (ranging from 10 to 25 ) the ave­ sured again after having been exposed rage direction of magnetization of the to alternating fields of 350 Oersted. samples becomes: declination 180 and The outcome of the measurements inclination + 500 30: This direction after magnetic cleaning and combined lies rather close to the present field, with correction for dip are illustrated so that it may represent a stable field, in fig. 2 7 E; F . induced in young neozoic time. There­ The average direction of magneti­ fore no conclusions can be based on zation has a declination of 3330 and this direction. an inclination of +26 0 .

- 103 ­ 07 05 06 08 M N

LADINIAN (DOLOMITES) LADINiAN I DOLOMITES) BD/aTC a Of,. TC

A B

70.

08

a

LADINIAN ([)OLOMITES) LAI:»IIAN (DOl.OMlTES) AO '°!aTC hTC

c o

LAONIAN (8LEIBERGI LADINIAN (8LEIBERG) B 0 lATe 8.°/8T C

E F .. Fig. 28 . O. 03 7 01"0.0 o~' 00

lADlMAN IBl£l8ERGl lAOlNIAN (BLEIBERGI A%Te AD'" T.e

A B Fig. 29. Stereographic projections of the Palaeomagnetic directions

BD/BTC Before Demagnetization,Before 'Pecton ic Correction BD/ATC Before Demagnetization/After Tectonic Correction AD/BTC After Demagnetization,Before Tectonic Correction AD/ATC After Demagnetization,After Tectonic Correction

o Positive inclination (lower hemisphere of the Stereographic projection) Negative inclination (upper hemisphere of the Stereographic projection) x;;r; • Average Directions

1 13 . Interpretation 0.£ the have been quoted. palaeomagnetic data. From table X it follows that the carboniferous poles from areas of the geotectonically more "s table 11 Before discussing the palaeomagne­ parts of the European continent have tic history of NE Italy, a summary an average position of N 37,50 ; will be given in Table X of the ave,­ E 146,5°. The upper carboniferous rage values obtainedfrom the measure­ pole measured by the present author ments. in the eastern Carnian Alps is loca­ 0 0 In the first column the average ted at N 59 ; E 145 • The two poles age of the samples is given, in the diffel' about 20° in latitude, while second column the number of samples their longitudes are about the same. on which the average direction of The different positions of the NE magnetization is based. In column 3 Italian upper carboniferous pole and the rock material is indic..ated (I for the carboniferous pole of the "s table 11 igneous rocks and S for sediments), parts of Europe might be due to the and in column 4 the region from which follOWing causes: the samples were taken. The average a. The character of the earth's mag­ intensity of magnetization (in c.g. s. netic field was different in the units/cm3) is given in .column 5. The geological past; in other words, a,veiage direction of magnetization the earth's magnetic field had not of the samples and the pole position a dipole character. (calculated from this 'average direc­ As discussed in the introduction tion) are given in column 6 and 7 to this chapter, this argument respectively. In column 8 the authors seems hardly applicable, since are mentioned from whom the data pole positions calculated from the

105 ­ Table X

1 2 3 4 5 6 7 8

Present Inclination of 1 he magnetic field in NE Italy at N.460 +64,5

MMl Middle Miocene 7 I Vic ent inian Alps 0,2.10-3 351 +64 De Boer 1963 ;:, r<1 0 ..... ;>.. ... L.Li 0,1. 10-3 _ M02 til Middle Oligocene 16 I Vicentinian Alps 184 .~ -61,5 De Boer 1963 2,6.10-3 '"'... In OJ C! f-< L/) "

-18q 6 Ladino-Carni an 28 I S. of Tarvis 0,8_10-5 LICS y 28 +43 N57 E140 Guicherit 1964 ° N.460 30' E.130 30' 1,2.10-4 ­

L6 Ladinian 8 I Dobratsch N.46°.36' E.130 39' 18 +50,5 LookerenCampagne 1961

L7 () Ladinian 4 I Fontanazzo (It. Dolomites) '- N.460 15' E.l10 42' 2,6.10-4 26 +29? Guicherit 1964 '" 5 L8 '" Ladinian 7 I Vicentinian Alps 50.10- 330 +49 De Boer 1963 til

.~ ... 3,7.10-5 A9 Anisian 9 I Vicentinian Alps - 331 +49 De Boer 1963 f-< ;:, 47,2.10-5 N 2-...... 11,5.10-5_ US10 Upper Scythian 11 I L.Li Vicentinian Alps 5 331 +40 De Boer 1963 76,0.10­

en 0,5.10_5 _ LS11 Lower Scythian 15 I..,.S "anastones) IU ::> N. 'lbv'lU' t..IIu:'j' U,~.IU - ;););) +~o \JuICnerll: l:1U,,*

UMP Upper Middle Permian Coccau 0.3.10-5 _ 14 (Gr~dener Sandstones) 9 S N.46030' £.13°40' 0.8.10-5 35 +24 N45 E142 Guicherit 1964

LMP Lower Middle Permian Average "Europe" N43 E169,5 Cox and Doell 1960 15 Kalashnikov e t al. 1961

MP16 Middle Permian 5 S Vicentinian Alps 0,2.10-5 150 -22 De Boer 1963 N.45045' E.ll020'

P/C17 Permo-Carboniferous 8 I Chiusa 173 -8,5 Nijenhuis 1960 N.46039' E.ll°31'

P/C18 Permo-Carboniferous 38 I Lagorai Range 137,5 -8, 5 N34 W114 Findhammer 1959 N.46015' E.ll028'

P/C19 Permo-Carboniferous 51 I Merano Region 5.10-7 - 164 -10,5 N45 W146 Dietzel 1960 N.46040' E.llo15' 5.10-4

270 6 P/C20 10 Y Permo-Carboniferous 6 I Cavalese Region 1. 2-10-4 162 -23 Lookeren Campagne 1961 N.46019' E.ll0 28'

P/C21 Permo -C arboniferous 7 I Vicentinian Alps 1,2.10-5 148 -29 N51 Wl18 De Boer 1963 N.45045, E.ll°20'

P/C22 Permo -C arboniferous 39 I Val-di-Non Area 1, 1.1O-~_ 150 -31 N51,5 Wl18,6 van Hilten 1960 N.46025' E.ll09' 9,4.10­

PP UC? Pre-Permian (Upper 7 I Vic entinian Alps 1,8.10-5 143 _34 de Boer 1963 23 Carboniferous?) N.45045' E.ll020' 45,9.10-5­

UC24 Upper Carboniferous Average "Europe" N37,5 E146,5 Cox and Doell 1960 Kalashnikov eta 1. 1961

UC25 Upper C arboniferous 9 S Pramollo Region 0,9.10-5 24 +40,5 N59 E145 Guicherit 1964 N.46030' E.13020' dipole law for tectonical "stable" stones of the eastern Carnian- Alps regions of the same continent, which must be excluded. may lie more than 4000 km apart, As discussed in the introduction give the same pole position for the to this chapter it is not exactly same epoch. known to what extent magnetostric­ b. The tectonic correction for the tion may effect the direction of samples was incorrect and/or magnetization of rocks, and whether incomplete. Since the NE Italian this process is reversible or not. upper carboniferous pole position For different parts of the SE Alps, has been calculatedfrom sediments, which were subjected to pressure the dip of the strata could accura­ and tension forces of different tely be established. Only rotations intensity, the same anomalous and or translations of the upper values for different ages has been carboniferous sedimentary series found. could not be established by the lo­ Further, it has never been ob­ cal field data. served that magnetostriction evi­ c. Variations of the geomagnetic field dently affected the direction of mag­ ("Secular variations"). Secular netization of rocks, so we must con­ variations are slow variations of clude that the effect of this pro­ the intensity and direction of the cess on the measured samples magnetic field, It seems that pe­ is negligible. riods during which secular varia­ e. The occurrence of. I'l.utonic bodies. tions occur are relatively short under the SE Alps whlch caused local (102-104 y). The stretch of time, anomaliesln the geomagnetic field. during which the deposition of the Plutonic bodies will only cause upper carboniferous strata occur­ anomalies in the geomagnetic field red which were sampled, is after the cooling down of their much longer than a period of se­ ferromagnetic mineral constituents cular variations. So, if the theo­ below the Curie-point. If such 1'y concerning the earth's magnetic plutonic masses were present field also holds for the geologi­ during the Upper Carboniferous, cal past, and if the processes re­ causing anomalies of the geomag­ lated to the earth's magnetic field, netic field, they would also have such as secular variations, were caused .anomalies in the subse­ more or less the same in the geo­ quent times up to the present logical past, it is highly improbable day. Such a permanent trend of that secular variations could be the geomagnetic field in NE Italy the cause of the deviation of the has not been observed, however. the upper carboniferous pole posi­ f. The directions of magnetization tion of NE Italy from the average of the samples do not represent carboniferous pole position of the primary vector of magnetiza­ Europe outside the mobile Thetys tion acq~ired in upper carboni­ zone. ferous time. d. Metamorphism and/or magne- As all samples were demagnetized, tostriction of the magnetic materials. thus removing the vectors of mag­ The rocks of the investigated re­ netizrltion obtained in later (possi­ gion have not been subjected to bly subrecent) time, major errors metamorphism since their depo­ regarding the stability of magne­ sition, so metamorphism as a tization seem to have been avoided. factor that may have caused a g. Italy might have belonged to the magnetization not representative African continent during the Upper for the upper carboniferous sand- Carboniferous;so the upper carbo­

- 108 ­ niferous pole position of NE Italy 13 cm/y. This makes it highly im­ should be compared with the ave­ probable that a divergence of more rage upper carboniferous pole po­ than 200 in latitude between the upper sition of Africa, rather than with carboniferous pole position of the that of the European continent. This, eastern Carnian Alps and the average however, seems not to be the upper carboniferous pole position of case either, because there is a the geotectonically more "stable" parts considerable deviation between the of the European continent, can be upper carboniferous and also the explained by an inadequate time cor­ triassic pole positions of Africa relation between the poles. on the one side, (Cox and Doell, i. The tectonic unit of the SE Alps 1960), and those of NE Italy on (so also NE Italy) has been sub­ the other. (No permian data of jected to large (geotectonic) lateral Africa are available). displacements (drift movements). h. Inadequate correlation between the This seems the most probable poles. solution for the explanation of the The average palaeomagnetic pole deviation of the palaeomagnetic position for a continent can be cal­ directions found in the samples culated for a certain period by from the upper carboniferous (and rneahs of a great number of mea:­ the permo-triassic) of the SE Alps surements, based on samples and in the samples from strata of collected in the "stable" part of the the same age in the more stable continental shield. parts of Europe.

According to Kulp (1961), the Car­ Assuming that we are dealing with boniferous started about 350.106 Y a geocentric axial dipole field, the ago and lasted about 80. 106y. The magnetic equator and isoclines of Permian started about 270. 106y ago equal magnetic inclinationfor a certain and lasted about 50. 1 06y , while the magnetic pole position can be con­ Triassic started about 225. 106y ago structed (van Hilten, 1962). So the and lasted about 40. 106y . magnetic situation for each epoch of The lower carboniferous poles of which the palaeomagnetic pole position Europe lie so strongly scattered, that is known, can be presented by means no average pole position can be based of constructing the palaeomagnetic on them. According to Kramov (1961) isoclines on the concerning shields. and Irving (1963) the earthIS magne­ From these maps it can now easily tic field changed its polarity from be seen, which parts of the continents normal to reversed during the Upper do not fit in the general picture; in Carboniferous. This happened within other words which parts of the conti­ the Westphalian or between the West­ nents show a discrepancy between phalian and Stephanian. For continen­ the palaeomagnetic inclination (acquired tal Europe the average carboniferous from measurements on rock samples pole position is mainly based on upper from these parts of the continent), carboniferous data from normal mag­ and the calculated inclination, computed netized rocks, so over a time interval from the average pole position repre­ of about 10 to 15 million years. The sentative for the "stable" parts of upper carboniferous samples from the continent for one and the same the eastern Carnian Alps were taken period. Consequently displacements from strata which have a span of of these parts of the continent relative about 3 to 5 million years. The velo­ to the "stable" parts can be established. cities of displacement of continental This procedure is discussed below. masses are estimated to be 2 to From an isocline map, based on

- 109 ­ 20 WOE 20 40 60 80 100

UPPER CARBONIFEROUS PALEOMAGNETIC ISOCLINES PERMIAN PALEOMAGNETIC ISOCLINES OF EUROPE I-t .-'f--+--­ OF EUROPE I , I I 1 1 I 1 20 W E 20 00 .20 W o E 20 40 60 80 100

20 WOE 20 40 60 80 100 20 W 0 E 20 40 60 80 100 /~ '\.:/V 8 .1 I I 1 r pi ! I.-' I 1/ ~ I I rV\' ~ I 1;J - IF /1 ~ wvrr~~ * !~ ,~ t'-... 80 i I , Yi l I ( i : -­ 6 Ii, V ( .I , I J....- I I ~ V [j'{ J:9 I-r-. 70 I < f.l. nQI ( D( , if 160 i L­ "~" 1----­ ."" -I o­ ld h)\ U 50 I J...--t/ ~lr-:

\\ ,'v 30 U1:t: 20 2~ 10

I p [.;it--r- I ':'\ o , i / N 0 ,\ I f"J

TRIASSIC PALEOMAGNETIC ISOCLINES I i K-iI RECENT PALEOMAGNET IC ISOCLINES OF EUROPE I OF EUROPE i-rr-' , I I I I 1 r I I r i I. I I, I 1 20 WOE 20 40 SO 80 100 20 W 0 E 20 40 60 80 00

Fig. 30. Magnetic isocline maps with the relative position of NE Italy - (.) - during the Upper Carboniferous, the Permian, and the Triassic. the average carboniferous pole position time (fig. 30). From measurements of the parts of Europe that are situated on permian rocks of NE Italy (de outside the mobile Thetys zone (fig. Boer, 1963; and present author) and 30), it follows that NE Italy should also Russian data (Kalashnikov, 1961), have been situated on the 5 to 100 iso­ it followed, that the earth's magne­ cline. From our measurements, how­ tic field changed its polarity from ever, it follows that during the reversed to normal during the Middle Carboniferous NE Italy was situated, Permian. The average permian pole with respect to Europe, somewhere position for the "stable" part of the on the 400 isocline. During carboni­ European continent, on which the ferous times this 400 isocline ex­ isocline map is based, has been cal­ tended across the Baltic Shield (fig. culated from "reversed" samples 30). It cannot be calculated from pa­ and is, therefore, the average permian laeomagnetic data where, at this iso­ pole position representative for the cline, NE Italy was situated. As it Lower- and Lower Middle Permian. is geologically impossible that two The magnetic inclination of the per­ crustal parts occupy the same posi­ mian samples from NE Italy, how­ tion at the same time, NE Italy must ever, (igneous rocks as we11 as se­ 0 have been situated outside the Euro­ diments)rangefrom-8° 30"to -22 • * pean Shield at the intersection of this In view of an average inclina­ isocline with the mobile Thetys zone. tion of -150 of NE Italy during lower­ The latter has approximately an east and middle permian times, NE Italy to west direction and will have been must have been situated at the inter­ situated with respect to Europe, more section of the -150 isocline and the or less in the belt adjacent to Meso­ mobile Thetys zone; that is some­ Europe, where it is found now. Ac­ where east of what is now Iran. cording to this line of reasoning du­ ring the Upper Carboniferous NE 133. From palaeomagnetic isocline Italy was situated near Kashmir (in maps of Europe during triassic Times, the western Himalya). based on the average "European" Because of the incompleteness triassic pole position, it follows of the areal distribution of the samples that NE Italy should have been situ­ (measurements are only available ated on the 250 to 300 isocline at from the Vicentinian Alps, the Italian Dolomites, the eastern Carnian Alps, * The inclinat ion of _300 found for the "lower and the western Julian Alps), the size permian" samples from the Val-di-Non region by van Hlll~n (1960) and from the Vicentinian and the bounderies of the tectonic Alps by de Boer (1963) are probably still upper unit displaced, cannot be established. carboniferous inclinations. As mentioned before, the earth's magnetic field already cllanged its 2 polarity from normal to reversed during the upper 13 . Now the inclination of the palaeo­ carboniferous, and moreover it has never de­ magnetic vector of the NE Italian finitely been proved that the entire Bolzano permian rocksamples will be com­ porphyry series is of lower permian age. Accor­ ding to Vacek and Hammer (1911), Heritsch pared with the inclination, calculated (1939), Leonardi (1955), Gianotti (1958), Tedesco from the average "European" per­ (1958), Accordi (1959), and recent work of the mian pole position at the location nuclear geological Laboratory staff of Pisa, at least a part of the eruptions which led to the of the sampling sides of the rocks. formation of the 1800 m thick Bolzano quartz­ From palaeomagnetic isocline maps porphyry plate took place during upper carboni­ of Europe during permian times, ferous times. The conclusion that tbe Posina igneous mass (Vicentinian Alps) is of IO\\Cf per­ based on the average "European" per­ mian age (de Boer, 1963), is based on a com­ mian pole position, it follows, that parision with the data of van Hilten (1960) for NE Italy should have been situated the "lower permian" quartz porphyries of the Val-di-Non region. near the magnetic equator at that

- 111 ­ that time (fig. 30). The magnetic in­ a. A WNW-ward movement, which clination of the triassic samples from mainly took place during upper NE Italy measured by de Boer (1963) palaeozoic- and mesozoic times. range from 400 to 490 , while our It had reached already its present measurements of the Rio Freddo days position before the flysch­ porphyries of ladino-carnian age, or "Gosau phase" of the alpidic gave inclinations with an average of orogenesis (younger Cretaceous). 0 43 • Thus the triassic inclination of This means a displacement of about the magnetic vector in NE Italy is 4800 km in about 180 . 106y, at about 150 too high. This means that a rate of 3 cm/y. It is also pos­ NE Italy must have been situated at sible that some time after the that time somewhere in the east of Gosau-phase of the alpidic oro­ what is now Turkey. genesis, a renewed NW movement Not enough jurassic and cretaceous of NE Italy took place, which en­ data are available for a reconstruction ded during early tertiary times. of the former position of NE Italy b. A WNW-ward movement of NE in those times. However, measure­ Italy along a more or less straight ments on middle eocene- and oligocene path, which took place more or rocksamples led de Boer (1963) to less continuously during upper the conclusion that NE Italy should palaeozoic, mesozoic, and early have been situated about 800 km south­ tertiary times. At the beginning ward of its present day position du­ of the Oligocene its present posi­ ring the Lower Tertiary. on a palaeo­ tion had been reached. This means j socline which extended across a displacement at a rate of about southern Italy to Greece. NE Italy 2 to 3 cm/y. would have reached its present day C. The WNW-ward movement of NE position in middle oligocene time. Italy along a more or less straight De Boer's assumption is based on path, took place in two stages (de a difference in inclination of about Boer, 1963); 50. However, this difference in in­ c! First, a westward movement over clination is less than the possible about 4800 km from the Upper measuring errors, so that the palaeo­ Carboniferous to the Middle Eocene, magnetic data do not defenitely prove or to the Middle Cretaceous. this point of view. c'~ANW-wardmovementover 800 km As a matter of fact, for post­ (from a region somewhere in South triassic times, the difference between Italy to its present days position) measured and calculated inclination or more during the Middle and will become gradually smaller, be­ Upper Eocene, and the Lower coming even less, than the possible Oligocene, or during post-middle measuring errors. Therefore, it will Cretaceous and pre-Oligocene be impossible to establish a displace­ times. ment of NE Italy after triassic times, by means of palaeomagnetic data Geological data (Pavoni, 1961;Rod, only, from Europe and the adjacent 1962; Brunn, 1963; Glangeaud, 1957, parts of the Thetys. 1963) indicate the occurrence of la;ge For the translation of NE Italy right lateral shear faults (which ac­ from a region originally situated some­ companied the mesozoic WNW drift where in the area now occupied by of NE Italy) in the Thetys zone (see the western Hymalaya to its present fig. 31). From geologic data it also position in southern Europe, the followed that most of these great folloWing possibilities for the course faults were zones of weakness, which and the time of the translation might existed already during upper palaeo­ be given: zoic times and along which movement - 112 ­ o· GEOTECTONIC SKETCHMAP OF THE MEGASHEARFAULTS IN THE TETHYS ZONE. UTILIZING SOME DATA BY

GLAHGEAUD (1951,19821, AlVOHI (1981), ROD (1982).

RUSSIAN SHIELD , o AFRICAN SHIELD ARA8/AN SHIELD 60

Fig. 31. again took place during the alpidic Western Dolomites, and the Vicentinian orogenesis. Alps also show a considerable deviation DurIng early tertiary times NW from the average declination of mag­ movements seem to have occurred netization of the stratigraphically com­ along the Vardar zone in Yugoslavia parable samples taken from the tec­ (Brunn, 1963), and along a great tonically "stable" parts of Europe. shear fault running east of Sardinia However, neither the ladinian samples and Corsica (Zacher, 1963). As a from Fontanazzo, near Col Ponsin result of these movements NE Italy (Italian Dolomites), nor the upper might have undergone a NW drift palaeozoic and triassic samples from during early tertiary times. the eastern Carnian Alps, and the Large scale drift movements could western Julian Alps, show this devia­ also be indicated palaeomagnetical­ tion (see Table X). ly for the Indian continent, the Ara­ De Boer has tried to estimate the bian shield and the African shield. rotation of the parts of NE Italy (in It is not yet possible, however, to particular the Italian Dolomites and integrate these and other drift move­ the Vicentinian Alps), which show ments into a composite path of trans­ an average magnetic declination de­ lation of NE Italy. viating from the average declination of the samples from the European continent outside the mobile Thetys 4 13 . The declination of the samples. zone. De Boer (1963) supposes that NE Italy (the Dolomites and the Vi­ centinian Alps) have rotated (in re­ Up to now only the inclination of 1ation to the European shield) over the samples has been considered. The about 600 anti-clockwise around a average declination of magnetization sub-vertical axis. This rotation would of the permian, and lower and middle have taken place during the late triassic rocks, of the Central and Triassic.

- 113 ­ As so many assumptions must be the remarkable fact can be stated made to make a comparision and as that some anomalies of the palaeo­ we are still without sufficient data magnetic declination exist in the (the data from Table X, also show Italian Dolomites and the Vicentinian a considerable mutual deviation), it Alps, whereas such anomalies do not is questionable whether a valid con­ occur in the western Julian Alps and clusion about such a rotation can be the eastern Carnian Alps where also reached in the present s tate of our no geological indications exist for palaeomagnetic knowledge. However, such rotations (present author).

- 114 ­ APPENDIX I Demagnetization curves of some samples. Values of the alternating fields ranged from 0-1000 Oersted. alb = a component plotted against the b component. scale unit = Xi.10-4 cgs units/cm3 (Xi has various values)

N .. -t----o~r---.-----~--.C..

100

.A ·c ~ •• 5 '"

a b c

N • A N • A .. ~ :00

10

0 ~ ~ ~

5

t.C 5 ••I

.e 10 d ., +C e •• f

N N +A .A 100 'lE ~ ---+c 50 1% gO 80 ~/ ------% ~ 50

.c /~ 900 80 160 +c 'Yo 80 ,eo

gO ,B .e .B g h i N +A IC IA 1IO

50

k 50 1 ." IA

N -B -I

1/

_c -A '-~:-----=------cr----....."....c

n o -C -A ill ..

p q

-·-----~'o'------=-----:r------''"-lt-- I N .. 'A,_-",,~_-_-_----'1f--_- --~o'o~-- I o

r ....,----.jL;j2~~-----,------~-- APPENDIX IT List of Italian-Austrian topographic names.

This list is added for the benefit of the reader, who studies austrian literature on this area.

Bistrizza Feistritzeralm Camporosso Saifnitz Cave del Predil Raibl Cima Alpel Eibelkopf Cima Bella Schonwipfel Cima del Cacciatore Steinener Jager Cima di Mezzo Mitterwipfel Cima Muli Mulei Berg Cinque Punte Fiinfspitzen Coccau Goggau Colina Kolm Wiesen Creta di Aip Trogkofel Fusine Weiszenfels Jof Fuart Wischberg Jof di Miezegnot Mitternachtskofel Lago di Predil Raiblsee Madonna della Neve Maria Schnee Monte Acomizza Achomitzerberg Monte Bruca Brtickenkopf Monte Cavallo Roszkofel Monte Cerchio Zirkelberg Monte Cocco Kokberg Monte Coppa Kopa Monte Coron Kronalpe Monte Malvueric Malurchberg Monte Nero Schwarzerberg Monte due Pizzi Zweispitz Monte Prisenca Priesnigberg Monte Pucher Bucherspitze

- 117 ­ Monte Re Koningsberg Pascolle Hinterschlosz pSo di Gais Gaisriicken p So di Pramollo Naszfeldpass Plezzut Flitsch Pontebba Pontafel PraU di Bartolo Bartolo Wiesen

Rio d rArgento Silbergraben Rio Bianco Weiszenbach Rio dei Carri Wagenbach Rio della Chuisa Klausbach Rio dei DetriU Schuttbach Rio Freddo Kaltwasser Rutte Greuth San Leopoldo Laglesie Leopoldskirchen San Valfrassino Eschal Tarvisio Tarvis Tor. Pleccia Pletschagraben Tor. Pontebbana Trattengraben Ugovizza Uggowitz Val Bruna Wolfsbachtal Val Romana Romertal Vetta Secca Diirerwipfel

- 118 ­ BIBLIOGRAPHY

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