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Neotethys Derived Obducted Ophiolite Nappes in the Eastern Alps

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Neotethys Derived Obducted Ophiolite Nappes in the Eastern Alps Hisashi SUZUKI 1) Ralf SCHUSTER 2) <[email protected]> Hans-Jürgen GAWLICK 1) <[email protected]> Richard LEIN 3) <[email protected]> Neotethys derived obducted ophiolite nappes in the Eastern Alps: Peter FAUPL 3) 1) University of Leoben, Departement of Applied Geosciences and Geophysics, Peter-Tunner-Str. 5, A-8700 Leoben, Austria 2) Geologische Bundesanstalt, Neulinggasse 38, A-1030 Wien, Austria 3) Institue for Geocsiences, Department for geodynamic and sedimentology, Geologische Bundesanstalt information from radiolarite pebbles of the Gosau Group Althanstraße 14, A-1090 Vienna, Austria Sponsored by the INTRODUCTION PETROGRAPHY Fig. 7: Sample RS8/01 and RS9/01. Three pebbles of blackish to greyish coloured radiolarite, pebbles size 1.5-2.0 cm in diameter: Since the dating of the Cretaceous eclogites of the Austroalpine unit in the In the outcrops badly sorted conglomerates with a reddish matrix are 1. Sarla anisica Kozur & Mostler 8. Scutispongus parvifoliatus Kozur & Mostler early 90ths of the last century (THÖNi & JAGOUTZ 1992), it was obvious visible. The content of exotic material reaches up to 30%, the components are 2. Triassocampe cf. eruca Sugiyama 9. Triassospongosphaera sp. that in the recent Eastern Alps at least two crustal scale subduction zones were well rounded and up to 30 cm in diameter. Along the road the pebble spectrum 3. Yeharaia cf. transita Kozur & Mostler 10. Pseudostylospaera cf. nazarovi (Kozur & Mostler) active. The most prominent of these subduction zones is Late Cretaceous to is variable. Even light greyish shallow water carbonates are dominating the 4. Pentactinocarpus sp. 11. Poulpos cf. phasmatodes De Wever 5. Capnuchosphaera ? sp. 12. Triassocampe cf. nova Yao Tertiary in age and can be traced throughout the Alpine orogene by the oceanic frequence of diverse carbonatic rocks, radiolarites, metaquartzite, phyllites, 6. Muelleritortis sp. 13. Triactoma cf. zlambachense (Kozur & Mostler) suture zone defined by the Penninic nappes (Fig. 1). On the other hand volcanic rocks and amphibolites is variable. During this study pebbles of 7. Pterospongus priscus Kozur & Mostler Jurassic and Cretaceous subduction processes, which are related to the closure radiolarites and limestones have been investigated. of the Neotethys ocean and indicated by the structural and metamorphic imprint of the Austroalpine unit, are not fully understood and still under Based on investigations on thin sections the following material could be discussion (GAWLICK et al. 1999, SCHWEIGL & NEUBAUER 1997, identified as components in the conglomerates (Fig. 3.): NEUBAUER et al. 2000, SCHMID et al. 2004). Triassic and Jurassic radiolarite (sample A4655) (Fig. 3A) Important reasons for the badly known plate tectonic arrangement during Tempestite from the Upper Werfen Formation (Lower Triassic) the closure of the Neotethys ocean are 1) the missing of a continuous oceanic (A4652) (Fig. 3B) suture zone and 2) the overprinting Late Cretaceous and Tertiary tectonic Middle Triassic reef limestones (A4653/3) (Fig. 3C) structures. In general remnants of the former Neotethys oceanic realm are Coated components of “Dachsteinkalk” (Nor) and “Plassenkalk” Fig. 8: Sample RS10/01 Pebble of black coloured radiolarite, size of pebble c. 2.5 cm in scarce in the Eastern Alps and most of the information comes from the tiny (Late Jurassic) (A4653) (Fig. 3D) diameter: Meliata klippen in the eastern part of the Northern Calcareous Alps and from Jurassic hemipelagic biomicrites (A4655) (Fig. 3E) 1. Gongylothorax aff. favosus Dumitrica 2.Tricolocapsa undulata (Heitzer) redeposited detritus, which is characteristic in the Late Jurassic and Late Liassic spiculite (Dürrnberg Formation?) (A4655) (Fig. 3F) 3. Williriedellum cf. dierschei (Suzuki & Gawlick) Cretaceous sediments of the Austroalpine unit (FAUPL & WAGREICH Altered basic subvolcanic and basic plutonic rocks (RS20/01) (Fig. 3G) 4. Williriedellum glomerulus (Chiari, Marcucci & Prela) 2000). This detritus is represented by serpentinites, basic metavolcanics, Altered basic volcanic rocks (RS07/01)(Fig. 3H) Triassic and Jurassic radiolarites and carbonatic rocks. DISCUSSION In this poster we present new data collected from the Cretaceous 1. Significance of the observed detritic material: sediments of the Lower Gosau Group from Pfennigbach (Austria/Lower Late-Anisian to Early-Ladin radiolarites can be expected on the distal Austria). In addition to other findings (see poster of SCHUSTER et al. at this shelf of the Austroalpine unit towards the Neotethys (Meliata-Hallstatt) conference) these data suggest similarities of the Jurassic to Early Cretaceous ocean. Their formation was promoted by the minor carbonate production rates history of the eastern part of the Eastern Alps to the situation in the Dinarides. on the Austroalpine shelf at this time. In the Ladinian (Late-Danian) micrites They give additional indications for the presence of obducted ophiolite from the growing Wetterstein carbonate platforms were transported into the nappes and melange on the Late Jurassic-Early Cretaceous Austroalpine oceanic basin and radiolarites can only be expected in the distal oceanic areas margin as proposed by MANDL (2000). (GAWLICK et al. 2007). The same is true for Rhaetian times when the A B Dachsteinkalk carbonate platforms were growing. In the Middle Jurassic the carbonate platforms on the Austroalpine unit 17° 16° 15° 14° 10° 11° 12° 13° Tectonic map of the Alps Passau were drowned and radiolarites were deposited in the Neotethys ocean, but also S.M. Schmid, B. Fügenschuh, E. Kissling and R. Schuster , 2004 Donau Inn Graphics : S. Lauer Wien in large parts of the Austroalpine and Penninic realm. 5° 6° 48° 48° 7° München 8° 9° For this reason the Middle Triassic and Rhaetian radiolarites are of special n i e h R Basel interest, because they indicate fragments of the Neotethys realm in the source Zürich Besancon area of the investigated localities. Based on the CAI, the Triassic radiolarites 47° 47° Graz Bern experienced a thermal overprint which is lacking in the Jurassic radiolarites. Maribor Drava Genève 2. Relation to the other exotic material within the conglomerates 46° 46° Rhone According to GRUBER et al. (1992) the volcanic pebbles are alkalibasalts T C Zagreb D a g l i S a av m a e n t o Trieste ploting into the field of within-plate basalts in most of the discrimination Milano Venezia Verona Padova diagrams. Based on the association with serpentinites they argue for a Grenoble Torino 45° 45° Po 17° Po 16° 15° 13° 14° 100 km formation in a passive continental margin setting or within a thinned 11° 12° Penninic nappes: Upper Penninic nappes (Piedmont-Liguria ocean): South-Penninic ophiolites, Bündnerschiefer or Schist Lustrès, Southern Alps: Nappes Supèrieures des Prèalpes, Helminthoid flysch and Matrei mèlange continental crust. In such a setting tholeiitic and alkalibasaltic volcanic rocks Lower crust of the Southern Alps (Ivrea) Middle Penninic nappes (Brianconnais and Sub-Brianconnais terrane): Upper crustal basement of the Southern Alps Sedimentary cover of the Middle Penninic basement nappes Genova Post-Variscan volcanic and sedimentary cover of the Southern Alps Middle Penninic basement nappes are produced during initial rifting. With respect to the formation of the Adriatic micro-plate Detached Middle Penninic cover nappes ("Sub-Brianconnais" and "Brianconnais") 44° Permo-Carbonifereous sediments (Zone Houllière) Austroalpine Nappes: and their Mesozoic cover ("Brianconnais") e c n a r Northern Calcareous Alps and Grauwackenzone (Upper Austroalpine): Lower Penninic nappes (Valais ocean): u Neotethys (Meliata-Hallstatt) ocean the volcanic rocks might be Late Permian D Juvavic nappes (Mesozoic cover) Tertiary flysch sealing Lower Penninic accretionary prism (Cheval Noir Flysch) Tirolic nappes (Mesozoic cover of the uppermost nappe of (Noric nappe) North-Penninic ophiolites and Bündnerschiefer (including Rhenodanubian flysch) 5° 6° Nice 7° Bajuvaric nappes (Mesozoic cover of Silvretta nappe) to Middle Triassic in age. However, no geochronological age data exist. The 8° 9° 10° Sub-Penninic nappes (distal European margin): Greywackyzone Mesozoic cover of Sub-Penninic basement nappes (including cover of "Gotthard Massif") Upper Austroalpine basement nappes: Non-eclogitic Sub-Penninic basement nappes (including "Gotthard massif") 1 Mesozoic cover of the Austroalpine basement nappes occurrence of fine-grained alkaliamphibole in the ground mass of some of the Eclogitic Sub-Penninic basement nappes Drauzug-Gurktal nappe system (e.g. Tonale series, Steinach nappe, Basement of Drauzug, Gurktal nappe, Graz Paleozoic) Ötztal-Bundschuh nappe system Northern Alpine foreland and Helvetic nappes: 2 Dinarides: (Ötztal and Bundschuh nappes) Various units: Helvetic and Ultrahelvetic nappes (including Combeynot and Tavetsch “Massifs”) Koralpe-Wölz nappe system metabasalts argues that these rocks experienced a pressure-dominated Tiza unit Plio-Pleistocene (Po-plain, Pannonian basin) (Schneeberg, Millstatt, Wölz, Saualpe-Koralpe Complex) Helvetic flysch Internal Dinarides (including Dinaridic ophiolite zones) Tertiary cover in general (Molasse, Rhine Graben, Silvretta-Seckau nappe system (Campo-Sesvenna-Silvretta nappes, Schladming, Seckau Complex) Subalpine molasse intramontane basins) External Dinarides Oligo-Miocene post-tectonic cover (unconformable Deformed autochthonous and para-autochthonous pre-Teriary cover Lower Austroalpine nappes: of the northern Alpine foreland, including the
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