15th Emile Argand Conference on Alpine Geological Studies  

The most important geotectonic element within Polish/Slovakian/Ukrainian Western Carpathians basins has been the Czorsztyn Ridge (Swell), which originated during Early Bajocian time. Then, palaeogeographicaly during Middle Jurassic–Late Cretaceous span it has been the main object which separated two large Carpathians basins – the Magura Basin on NW side and the Pieniny Basin on SE side – and therefore the detail dating of its origin is crucial for recognition of its geodynamic significance. This first uplift is correlated with stratigraphical hiatus between sedimentation of dark/black shales of oxygen-poor environments (latest Pliensbachian–earliest Bajocian) and white/light grey crinoidal limestones of well oxygenated regimes (late Early Bajocian), which documented drastic change of sedimentation/palaeoenvironments which took place in meantime as effect of uplift. This stratigraphical gap was perfectly dated biostratigraphicaly by ammonites collected from the basal part of crinoidal limestones in several outcrops of the Polish part of the Pieniny Klippen Belt (PKB). The evidences of condensation event at the beginning of crinoidal limestones sedimentation are marked by: phosphatic concretions concentration, pyrite concretions, large clasts of green micritic limestones, fossils (ammonites, belemnites, brachiopods). On the other hand, high variable thickness of these limestones (from ca. 10 m up to 100 m) suggests origin of synsedimentary tectonic blocks and troughs during syn-rift episode. This Bajocian tectonic activity within Pieniny Klippen Basin corresponds very well with others Middle Jurassic Western Tethyan geodynamic reorganizations. Estimation of duration of aforementioned hiatus – based on a cyclostratigraphic analysis of the carbonate content from the Subalpine Basin in France, which indicates that the Early Bajocian only lasted c. 4.082 Ma – time necessary for origin/uplift of the Czorsztyn Ridge is about 2 Ma.

            Tectonic rejuvenation of Middle Jurassic structures took place during the earliest Cretaceous (Berriasian) times and have been connected with active volcanogenic events which occur now within several tectonostratigraphic units of the Ukrainian Carpathians, including PKB. In the Veliky Kamenets active quarry (PKB) a continuous section occurs with a Lower Jurassic (since Hettangian?) to the lowermost Cretaceous (Berriasian) sedimentary succession. The biostratigraphy of the Toarcian-Berriasian part of this section is very precisely based on ammonites, dinoflagellates and calpionellids. Basaltic rocks occur in the uppermost part and overlie creamy-white Calpionella-bearing limestones. They are directly covered by biodetritic limestones and synsedimentary breccias. The latter are the so-called Walentowa Breccia Member of the Łysa Limestone Formation, according to the Polish and Slovakian parts of the PKB, which are dated by calpionellids as middle and/or upper Berriasian and upper Berriasian, respectively. Importantly, in this breccia some clasts of basaltic rocks occur (sometimes developed as pillow lavas and/or peperites) which implies they are middle and/or upper Berriasian in age as well. New investigations are concentrating on radiometric dating of these basaltic rocks, which geochemically have previously been determined to be caused by intra-plate volcanism. Integrated litho-, bio-, chemo- and magnetostratigraphic studies carried out in this section can be here supplemented by absolute age determination of a submarine volcanic event. Additionally, this is a unique chance to calibrate the absolute age of the J/K boundary.

How to cite: Krobicki, M.: Origin of submarine swell (Czorsztyn Ridge of the Pieniny Klippen Belt, Polish/Ukrainian Carpathians) and it's geotectonic consequences by biostratigraphy/volcano-sedimentary record, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-19, https://doi.org/10.5194/egusphere-alpshop2022-19, 2022.

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AlpArray has challenged notions of lithospheric subduction along the Alps and its effects on the asthenosphere and orogenic lithosphere. Teleseismic V_p tomography reveals a slab of European lithosphere that is largely detached at and below 150 km in the Western and Central Alps. Only in the Central Alps is the slab still attached, possibly reaching down to the MTZ, where it may be connected to subducted remains of Alpine Tethys. Downgoing European lithosphere appears thicker and more heterogeneous than the Adriatic upper plate. Arcuate SKS directions beneath the Alps suggest that asthenosphere not only flowed passively around the sinking slab, but may have induced the anomalous northward dip of the detached slab segment beneath the Eastern Alps.

The structure of the orogenic lithosphere differs profoundly along strike of the Alps, as revealed by local earthquake tomography, ambient-noise studies, as well as S-to-P receiver-functions and gravity studies: In the Central Alps west of the Giudicarie Fault where the slab is still attached, the exhumed retro-wedge of the orogen overrides a wedge of Adriatic lower crust. East of this fault where the slab has detached, exhumation is focused in the orogenic core (Tauern Window) north of and above a bulge of thickened lower crust of presumed Adriatic origin. The Moho is not offset by the Giudicarie Fault and shallows eastward, from 50-60 km beneath the western Tauern Window to 20-30 km beneath the Pannonian Basin. This necessitates massive decoupling at and above the Moho to accommodate coeval Miocene N-S shortening, orogen-parallel thinning and eastward extrusion of Eastern Alpine orogenic lithosphere.

We propose a new model for Alpine orogenesis that invokes changing wedge stability and migrating subduction singularities above the delaminating and detaching Alpine slab in the east to explain east-west differences in Oligo-Miocene structure, magmatism, erosion and sedimentation in peripheral Alpine basins. A decrease in Adria-Europe convergence rate to <1 cm/yr after collision at ~35 Ma led to slab steepening and northward motion of the singularity, combined with increased shortening and taper of the Central Alpine wedge. There, rapid exhumation and denudation during this stage were initially focused in the retro-wedge just north of the Periadriatic Fault. In the Eastern Alps, slab pull during northward delamination drove subsidence and marine sedimentation in the eastern Molasse basin from 29-19 Ma, while the western Molasse basin filled with terrigeneous sediments. The dramatic switch at 23-21 Ma from northward advance and stagnation of the northern front in the Eastern Alps to southward advance of the southern front in the eastern Southern Alps, as well as rapid exhumation of Penninic units in the Tauern Window are attributed to slab detachment beneath the Eastern Alps combined with a northward and upward shift of the subduction singularity to the tip of the lower crust bulge. This is inferred to have reduced the wedge taper in the Eastern Alps. Rapid west-to-east filling of the eastern Molasse basin between 19-16 Ma is interpreted to reflect eastward propagation of the slab tear and the onset of Carpathian rollback subduction.

How to cite: Handy, M. R.: How AlpArray is guiding us to a new model of Alpine orogenesis, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-13, https://doi.org/10.5194/egusphere-alpshop2022-13, 2022.

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The India-Asia collision can have only a limited role as an actualistic model for the closure of Western Tethys and the subsequent Alpine orogenies because the impacting margins appear to have been sub-parallel and rather regular and the intervening ocean seems to have contained few volcanic edifices or continental fragments. A better guide to possible pre-collision processes is provided by the incipient Australia – Southeast Asia collision, which has already proved its worth as a key area for the study of small extensional zones within overall compressional environments. Insights into the possible roles of ridge-related features during oceanic closure are now being obtained from studies in the northern part of the Philippines Archipelago, which was largely formed by post-Middle Cretaceous volcanic activity associated with subduction of oceanic crust from both east and west. Double-sided subduction inevitably produces geomorphological complexity, but not all the anomalous features of the Philippines can be attributed to this cause. A sharp bend in topographic trends involving most of the southern part of the island of Luzon is here interpreted as a consequence of the impact on the east-facing subduction zone of the Anagolay volcanic massif formed by hot-spot volcanism associated with the spreading ridge in the West Philippine Basin. This bend can be considered a small-scale analogue of the syntaxes that define the limits of the India-Asia collision and demonstrates the way in which the presence of even a relatively small region of thickened crust can influence the morphology of an entire collision zone. Similar processes must have operated in other Alpino-type orogenic belts but may be hard to recognise because the generative units are no longer observable and their effects may be partly concealed by later tectonic over-printing.

How to cite: Milsom, J. and Barretto, J. A.: Anagolay: the shape of the Philippines and the Luzon Syntaxis, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-56, https://doi.org/10.5194/egusphere-alpshop2022-56, 2022.

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The Rute Plateau is a region located 25 km south of Ljubljana. Structurally, it belongs to the External Dinarides, which form an extensive fold and thrust belt. The study area is located in the eastern part of the Hrušica Nappe in a very complex tectonic area between two major NW-SE fault zones.
The peculiarity of the Rute Plateau consists in a varied succession of sedimentary and volcanoclastic rocks of Ladinian and Carnian age, while the whole area is divided into different tectonic blocks with local differences in stratigraphic evolution. The reason for these deformations and the variability of the paleotopography lies in the Middle Triassic extensional phase, which completely disintegrated the uniform Slovenian carbonate platform at the end of the Anisian age (for details see Rožič et al., this volume). Subsequently, the Ladinian strata of the External Dinarids reveals, that deep marine sediments in this area were deposited in small basins or tectonic depressions, while carbonate deposition continued on higher or relatively less subsided tectonic blocks (isolated platforms). During the Ladinian, tectonic movements were also accompanied by volcanic activity. 
Six sedimentological sections were logged in the studied area, and the Ladinian strata were divided into four different facies: F1 - deep marine (volcano)clastic rocks, F2 - hemipelagic limestone, F3 - resedimented limestones and F4 - shallow marine carbonates. Each of these Ladinian facies is characteristic of a particular sedimentary environment and is indicated from the most distal sedimentary environment (F1) to the most proximal carbonate platform environment (F4). Facies F1 consists of greenish to light ochre bentonitic clays, tuffitic sandstone, pelitic tuffs, and subordinate felsic extrusive rocks. Facies F2 consists of laminated black micritic limestone (mudstone to wackestone) with horizons of bioclastic packstone rich in filaments, limestone rich in organic residue and interbedded with dark chert laminas and marlstone. In facies F3 we find up to 30 cm thick beds of calcarenites, limestone breccias often with large olistoliths, graded and laminated calciturbidites - mostly packstone, grainstone and rudstone beds with rare chert laminas and nodules. Finally, facies F4 consists largely of massive, light grey calcimicrobial and dasycladacean limestone with horizons or lenses of white bioclasts and intraclasts derived from reefs. The last two facies are commonly dolomitized.
At the end of the early Carnian, the entire region was subjected to the regional emersion phase when deposition of clastic sediments began. It is characterized by facies F5 - red clastic sediments consisting mainly of sandstone with quartz grains and carbonate lithoclasts and conglomerate. Within all these facies, we were able to determine 28 different microfacies, which, based on their composition, further elucidate sedimentation in different paleoenvironments.

How to cite: Kocjančič, A., Rožič, B., Gale, L., Vodnik, P., Kolar-Jurkovšek, T., and Celarc, B.: Facies analysis of Ladinian and Carnian beds in the area of Rute Plateau (External Dinarides, Central Slovenia), 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-37, https://doi.org/10.5194/egusphere-alpshop2022-37, 2022.

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The largest Mesozoic paleogeographic perturbation of the present-day Alpine-Dinaric transition zone occurred in the Ladinian. The entire area was subjected to intense tectonic extension related to the rifting of the Neotethys Ocean. The most intense subsidence occurred in the central part of this segment of the continental margin, and the area remained deep-marine (called the Slovenian Basin) until the end of the Mesozoic. To the south, extension also resulted in differentiation, but the predominant paleoenvironments were either continental (often emerged areas) or shallow-marine. Locally, however, small-scale, short-lasting, deep-marine environment also developed. Herein we present the study of the Kobilji curek Basin in the Rute Plateau (central Slovenia, 25 km south of Ljubljana), where the the Ladinian platform to basin transition has recently been studied in detail. The study includes sedimentological analysis, biostratigraphy, mineralogical analysis, and detailed mapping. In the studied area, following Ladinian facies were outlined: F1 - deep marine (volcano)clastic rocks (bentonitic clays, tuffitic sandstone, tuffs), F2 - hemipelagic limestone (micritic and filament limestone), F3 - resedimented limestone (breccia and calcarenite), and F4 - shallow marine carbonates (bioclastic limestone and dolomite) (for details see Kocjančič et al, this volume). The base is Anisian dolomite and the top Carnian clastites. In contract, the highly variable Ladinian facies merge both laterally and vertically. Detailed geological mapping revealed that the area can be divided into four tectonic blocks with characteristic sequences, separated by roughly N-S and E-W trending paleofaults. In the NW tectonic block (B1), the most basinal succession is outcropping with two intervals of platform carbonates, while the sequence in the SE block (B4) is entirely characterized by platform carbonates. In the transition blocks (B2 and B3), platform carbonates predominate with minor basinal intervals. The entire Ladinian succession shows five major subsidence pulses followed by partial or twice also complete platform progradation. The first subsidence is documented exclusively in B2 and B3 (F1 and F2), followed by platform progradation (F4). During the second subsidence, the major paleofault between B1 and B2 is activated. This pulse is evident in B1 as a fairly thick basinal succession (F1) containing carbonate resediments (F3) in the upper part, indicating distant platform progradation. This pulse is also seen in B2 as thin deep marine limestone (F2 and F3), again followed by platform carbonates (F4). The third pulse is seen in B1 as coarse resediments (F3) followed by general platform progradation (F4), and in B2 as thin deep marine carbonates (F2 and F3) followed by platform carbonates (F4). This platform progradation seals the paleofault between B1 and B2. The fourth pulse is uniform in blocks B1 and B2 and consists of a continuous basinal interval (F1 and F2) followed by a final rapid platform progradation (F4). The fifth subsidence is uniform in B1, B2, and B3 and begins with hemipelagic limestone (F2) followed by (volcano)clastic rocks (F1) with some felsic extrusive rocks. In B4, this pulse either did not occur or the rocks were eroded during regional emersion in the early Carnian.

How to cite: Rožič, B., Kocjančič, A., Gale, L., Popit, T., Žvab Rožič, P., Vodnik, P., Zupančič, N., and Kolar-Jurkovšek, T.: Architecture and sedimentary evolution of the Ladinian Kobilji curek Basin of the External Dinarids (Rute Plateau, central Slovenia), 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-27, https://doi.org/10.5194/egusphere-alpshop2022-27, 2022.

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Ivanščica Mt. is an inselberg in the transitional area where S-verging Southern Alpine structures overprint NNW-verging Dinaric structures (van Gelder et al. 2015, and references therein). It is composed of Triassic to Cretaceous shallow to deep-marine sedimentary succession of the Adriatic continental passive margin (Šimunić et al. 1976), overthrust by ophiolitic mélange (Babić et al. 2002). Early Cretaceous siliciclastic flysch-type deposits continuously overlaying pelagic limestones clearly indicates distal position of these successions on the continental margin. However, so far complete Jurassic succession on Mt. Ivanščica was never found, causing different interpretations of its Mesozoic history. Babić (1974) assumed the existence of Jurassic pelagic succession on top of the Late Triassic shallow-water carbonates, describing up to few meters of Early to Middle Jurassic condensed pelagic limestone overlain by Late Jurassic radiolarian cherts and pelagic limestones. Contrary, Šimunić et al. (1976) assumed shallow-marine conditions throughout the Early Jurassic followed by emersion until latest Jurassic. Our study revealed for the first time complete shallow-water to pelagic Jurassic succession on Mt. Ivanščica.

Southern slopes of Ivanščica Mt. are mostly built of ophiolitic mélange, except for prominent hills built of the Late Triassic Dachstein limestone, which were so far interpreted as klippes (Šimunić et al. 1976), or olistoliths (Babić & Zupanič 1978). Our new data indicate continuous succession on top of Dachstein limestones composed of shallow-marine carbonates, represented by intraclastic-peloidal packstones to grainstones, gradually transitioning to wackestones with pelagic influence. The onset of pelagic sedimentation took place around the end of the Early Jurassic when thin bedded marls, shales, marly limestones with intercalated fine-grained calciturbidites were deposited. Higher in the succession Callovian to possibly early Tithonian radiolarian cherts are overlaid by calcarenites, late Tithonian to Early Cretaceous pelagic limestones and Early Cretaceous flysch-type deposits.

Discovery of the Jurassic pelagic sediments allows for a new interpretation of structural relations on the Ivanščica Mt. In our opinion occurrence of Dachstein limestone, previously interpreted as klippes or olistoliths represent an imbricate fan. Because the Southern Alps thrust front in this area was interpreted according to these mapped klippes and nappe contact, our findings may also have an impact on the redefining of the easternmost Southern Alps thrust front.

Babić, Lj. (1974). Jurassic−Cretaceous sequence of Mt. Ivanščica (North Croatia). Bull. Sci. Cons. Acad. Yugoslav. (A), 19/7−8, 180−181. Zagreb.

Babić, Lj. & Zupanič, J. (1978). Mlađi mezozoik Ivanščice. In Babić, Lj. & Jelaska, V. (ured.): Fieldtrip Guidebook 3. Skupa sedimentologa Jugoslavije, 11–23. Hrvatsko Geološko Društvo, Zagreb.

Babić, Lj., Hochuli P. A.. & Zupanič, J. (2002). The Jurassic ophiolitic mélange in the NE Dinarides: dating, internal structure and geotectonic implications. Eclogae Geologicae Helvetiae 95, 263–75.

Šimunić, A., Pikija, M., Šimunič, Al., Šikić, K. & Milanović, M. (1976): Stratigrafsko - tektonski odnosi centralnog i istočnog dijela Ivanščice. 8. Jugosl.geol.kongres, Bled, 1974., 2, 3003-313, Ljubljana.

van Gelder, I., Matenco, L., Willingshofer, E., Tomljenović, B., & Andriessen, P.,  Ducea, M., Beniest, A. & Gruić, A. (2015). The tectonic evolution of a critical segment of the Dinarides-Alps connection: Kinematic and geochronological inferences from the Medvednica Mountains, NE Croatia. Tectonics. 34. n/a-n/a. 10.1002/2015TC003937.

How to cite: Vukovski, M., Kukoč, D., Grgasovic, T., Fuček, L., and Slovenec, D.: Jurassic pelagic succession of NW Croatia – a key to better understanding tectonic setting of the Southern Alps – Dinarides transition zone, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-23, https://doi.org/10.5194/egusphere-alpshop2022-23, 2022.

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The pelagic succession from the Slovenian Basin (Petrovo Brdo section) covers the lower Tithonian to upper Berriasian interval (ca. 40 m). At 5 m of the section a sharp transition is observed between clay rich radiolarian cherts of Tolmin Fm and calpionellid limestones of Maiolica Fm.  Calpionellid associations are not numerous and poorly preserved, therefore only rough biostratigraphic dating is possible.  Crassicollaria (upper Tithonian) was documented between 8 and 13 m of the section, while the  beginning of the Calpionella alpina Subzone (present day J/K boundary) is situated at ca. 20 m.  Transition between Tolmin and Maiolica Fm  falls in the UAZ 12 radiolarian Zone (Gorican et al. 2012) which is close to the lower/upper  Tithonian boundary. Despite poor dating, the section supplied high-resolution magnetic susceptibility, as well as chemostratigraphic data (δ¹³C, main and trace elements), acquired with portable XRF device, gamma ray spectrometer and verified with ICP-MS laboratory measurements. Lithogenic elements (Al, K, Rb, Ti, Zr etc.) and MS show prominent decrease between Tolmin and Maiolica Fm, reaching minimum values in the upper Tithonian and lower Berriasian. Lithogenic input increases again  from ca 30 m of the section. As in numerous Tethyan sections (e.g. Western Carpathians, Northern Calcareous Alps, Western Balkan) the increase of marly sedimentation starts in the lower part of the Calpionellopsis Zone (magnetozone M16n), this level is tentatively interpreted as being close to the lower/upper Berriasian boundary. Relative variations of K and Ti content  (K/Ti, Ti/Al ratios) indicate enrichment of K  and depletion in Ti in the upper Tithonian/lower Berriasian interval  which accounts for decreased chemical weathering in the provenance areas. Additionally, the interval is enriched in redox sensitive trace metals (Cu, Zn, Cd) and decreased δ¹³C values, which accounts for bottom water stratification. The overall palaeoenvironmental trends might be interpreted in favor of aridification trend throughout the upper Tithonian and lower Berriasian and more humid episodes in the lower Tithonian and upper Berriasian. The trends seems to correlate throughout the Western Tethys domain and might be related with large-scale palaeoenvironmental perturbations.

How to cite: Grabowski, J., Iwańczuk, J., Rehakova, D., Rozic, B., Zvab-Rozic, P., Slapnik, L., and Gercar, D.: Climate changes on the Jurassic/Cretaceous bonduary on the geochemical indicators - new data from the Slovenian Basin, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-60, https://doi.org/10.5194/egusphere-alpshop2022-60, 2022.

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The Western Alpine Foreland Basin ("French Molasse Basin") is located along the western Alps and is composed of Oligo-Miocene formations resulting from the erosion of the alpine range. Although the Miocene molasse basin have been widely described since the last decades, Oligocene basins lack documentation in terms of palaeoenvironmental evolution and source to sink approach. Most of these basins formed under both the Alpine influence and the European Cenozoic Rift System influence and developed in lacustrine environment with local sedimentation next to active normal faults. Several fluvial formations with exotic materials have been briefly described and could correspond to a transport from the internal parts of the Alps, where collision started at the Eocene/Oligocene boundary. Here, we propose a new tectono-sedimentary study of these fluvial deposits based on extensive fieldwork (facies analysis, sequence stratigraphy, palynological analysis) and reinterpretation of available subsurface data (seismic profile, well data). The goal is to provide a new palaeoenvironmental reconstitution of the Oligocene molasse basin(s) with regional correlations and to determine the evolution of early alpine drainage network. We focus on the entire Western Alpine Foreland Basin from the Rhone Valley (Bas-Dauphiné, Valréas, Mormoiron) to the Digne Thrust where Oligocene molasse is called « Red Molasse » (Dévoluy, Faucon-du-Caire, St-Geniez, Esclangon, Barrême). First results show that Red Molasse is composed of massive meandering deposits, which evolve to braided river and alluvial fan in a regressive continental sequence following the flysch formation. Transition from marine distal turbidites is often missing except in Dévoluy syncline where tidal and shoreface deposits precede fluvial molasse. Exotic material from the internal alps is very common and indicates high landforms nearby. In the Rhone Valley, a massive fluvial system has been identified on seismic and well log data in the Bas-Dauphiné and we documented a 900 m field section with two meandering formations with exotic minerals in the Mormoiron basin. Paleocurrents and channels direction indicate a major divide located east of Diois-Baronnies range with Dévoluy fluvial systems flowing to the north and other Red Molasse sites located south of the divide converging to St-Geniez system. On a regional scale, it may be possible that early salt tectonic which has been widely described caused this particular drainage network. South of the divide, converging fluvial formations may have flowed in an Est-West valley between Diois-Baronnies range and Ventoux-Lure Montain where tectonic and Eocene landforms link to the Pyreneo-Provençal orogen have been documented. These deposits where probably connected with Mormoiron and Bas-Dauphiné fluvial formations and formed a major drainage system located in the Rhone Valley.

How to cite: Huet, B., Bellahsen, N., Loget, N., Lasseur, E., and Briais, J.: Palaeoenvironmental and drainage network reconstitution of the Oligocene Western Alpine Foreland Basin, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-48, https://doi.org/10.5194/egusphere-alpshop2022-48, 2022.

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Lake Turiec existed from Late Middle Miocene to Pliocene in the heart of the Western Carpathians in the intermontane Turiec Basin. Despite the long-lasting lacustrine deposition, which formed a muddy succession up to 900 m thick, specific history of this basin in Western Carpathians has been a puzzle due to the missing geochronological proxies. Authigenic ¹⁰Be/⁹Be dating method was applied to determine the existence duration and regression of the long-lived Lake Turiec. Altogether 35 samples were collected from 11 different localities of the basin representing different sedimentary environments such as lacustrine, fan delta, alluvial fan and braided river. Four different localities, Late Pleistocene alluvial fans Veľký Čepčín and Malý Čepčín, Holocene river floodplains Košťany and Kalamová were considered for determining the initial ratio. The initial ratio from the Veľký Čepčín alluvial fan was used for all other localities representing lacustrine, fan delta, alluvial fan and braided river to determine ages, because it is the only N₀ in agreement with the independent age proxies indicating that the lacustrine deposits cannot be older than 11.6 Ma. Another explanation of the suitability of the Veľký Čepčín initial ratio is its rapid deposition settings, preventing it from alteration by post-depositional processes and interaction with ground water, in contrary to the remaining intial ratio sites. Weighted mean depositional ages calculated using N₀ from Veľký Čepčín imply that the Lake Turiec existed from ~9.96 Ma for more than ~3.25 Myr and regression of the lake begun nearly ~6.71 Ma.

Determining the precise timing of the lake existence will have important implications for geodynamic phases of the Western Carpathians, since it mirrors rapid increase of accommodation followed by intense increase of sediment supply during regression. The presented application of authigenic ¹⁰Be/⁹Be yielded a first radiometric age of long-lived Lake Turiec as compared to roughly estimated age described in previous studies of the Turiec Basin. This novel method also appeared as a promising dating tool to determine the beginning of regression of the lake in an intermontane settings with complicated tectonic and sedimentary history.

The study was supported by the Slovak Research and Development Agency under contract APVV-20-0120.

How to cite: Aherwar, K., Šujan, M., Vojtko, R., Braucher, R., Chyba, A., Hók, J., Rózsová, B., and Team, A.: Dating a long-lived lake in an intermontane basin: Late Miocene Lake Turiec in the Western Carpathians, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-46, https://doi.org/10.5194/egusphere-alpshop2022-46, 2022.

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The Permian-Triassic tectonic evolution of Western Adria has been variously interpreted either as the first rifting phase that led to the opening of the Alpine Tethys or as the result of continental-scale strike-slip movements. Additionally, a common view on the age of inception of the rifting of the Alpine Tethys, its duration and its relationship with the antecedent Variscan tectonic phases, is still lacking. The European Western Southern Alps expose the basement and cover rocks of Western Adria and therefore represent a key area for understanding and testing the post-Variscan to pre-rifting evolution of this plate. We focus, in particular, on a relatively poorly deformed sector of Northern Italy (Varese Area), where the outcropping Permo-Carboniferous sequence and the overlying Triassic to Early Jurassic units allow to investigate the crosscut relationships between structures that were active during pre-rift and syn-rift tectonic phases. By means of a 3D geological model of the Varese Area, built on a brand-new geological map, firstly we restored Alpine tectonics and then performed a progressive geological restoration of faults, aided by new preliminary thermochronological data. We unveiled a polyphasic strike-slip Permian tectonic phase that switch to an unexpectedly early inception of the rifting.

How to cite: Scaramuzzo, E., Livio, F. A., and Fellin, M. G.: From Permian to rift-inception: new insight from the Western Southern Alps (Varese Area), 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-50, https://doi.org/10.5194/egusphere-alpshop2022-50, 2022.

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The Canavese Zone (CZ) in the Western Alps represents the remnant of the distal passive margin of the Adria microplate, which was stretched and thinned up to mantle rocks exhumation during the Jurassic opening of the Alpine Tethys. Through detailed geological mapping, structural analysis, stratigraphic and petrographic observations, and documentation of relationships between tectonics and sedimentation, we redefine the multistage tectono-stratigraphic evolution of the CZ, which consists of a Variscan basement, post-Variscan magmatic bodies and a Late-Carboniferous to Cretaceous sedimentary succession (Festa et al., 2020, and references therein). The Variscan basement includes a Lower Unit, wherein micaschist and orthogneiss were metamorphosed under amphibolite-facies conditions and partly transformed into migmatitic gneiss during a post-Variscan high-temperature metamorphic event, and an Upper Unit, consisting of a metasedimentary succession metamorphosed under greenschist- to amphibolite-facies conditions during the Variscan orogeny. The two basement units were intruded by post-Variscan plutons and hypabyssal dykes of both mafic to acidic composition. The sedimentary succession, at its bottom, consists of continental fluvial deposits (Upper Carboniferous Basal Conglomerate Auct.) unconformably overlain by Permian volcanic and volcanoclastic rocks (Collio Formation), and it continues upward with Upper Permian to Lower Triassic conglomerates and sandstones (Verrucano Auct. and Servino Formation), which are followed by pre-rift Middle Triassic dolostone. The latter is overlain by Lower to Middle Jurassic syn-rift sediments (Muriaglio Formation) and by Middle Jurassic to Early Cretaceous post-rift sediments, consisting of Radiolarites, Maiolica micritic limestones and Palombini shale. We point out that (i) the whole CZ succession, since the Late Carboniferous, shows significant variations in both thickness and facies, documenting long-lived tectonic control on sedimentation, and (ii) Late Paleozoic – Triassic structural inheritances playing a significant role in the localization of both the Jurassic rifting of the Alpine Tethys and the subsequent convergent tectonics.

Festa, A., Balestro, G., Borghi, A., De Caroli, S. & Succo, A. (2020). The role of structural inheritance in continental break-up and exhumation of Alpine Tethyan mantle (Canavese Zone, Western Alps). Geosciences Frontiers, 11, 167–188.

How to cite: Balestro, G., Borghi, A., De Caroli, S., Barbero, E., and Festa, A.: Multistage tectono-stratigraphic evolution of the Canavese Zone (Western Alps), 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-14, https://doi.org/10.5194/egusphere-alpshop2022-14, 2022.

alpshop2022-14

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Component analyses of ancient Neo-Tethys mélanges along the Eastern Mediterranean mountain ranges allow both, a facies reconstruction of the Middle Triassic to Middle Jurassic outer passive margin of the Neo-Tethys and conclusions on the processes and timing of the Jurassic orogenesis. This Middle-Late Jurassic mountain building process in the Western Tethyan realm was triggered by west- to northwestward-directed ophiolite obduction onto the former passive continental margin (wider Adria) of the Neo-Tethys.

Ophiolite obduction onto the former passive continental margin started in the Bajocian and trench-like deep-water basins formed in sequence within the northwest-/westward propagating nappe fronts in the footwall of the obducting ophiolites, i.e. in lower plate position. Deposition in these basins was characterized by coarsening-upward cycles, i.e. forming sedimentary mélanges as synorogenic sediments, in cases tectonically overprinted. In the Middle Jurassic, the oceanic realm and the most distal parts of the former passive margin were incorporated into the nappe stacking. Bajocian-Callovian ophiolitic and Meliata mélanges were formed as most oceanward preserved relics of trench-like basins in front of the propagating ophiolitic nappe stack, often with incorporated components from the continental slope (Meliata facies zone). In the course of ongoing ophiolite obduction, thrusting progressed to the outer shelf region (Hallstatt Limestone facies zone). In Bathonian/Callovian to Early Oxfordian times the Hallstatt nappes with the Hallstatt mélanges were established, expressed by the formation of the up to 900 m thick basin fills comprising its material mainly from the outer shelf region. In Callovian to Middle Oxfordian times the nappe stack reached the former carbonate platform influenced outer shelf region and the reef rim. Newly formed basins received material from this shelf region, occasionally mixed with material from the approaching ophiolite nappes. Ongoing shortening led to the formation of the proximal Hallstatt nappes with concomitant mobilisation of Hallstatt Mélanges. Persistent tectonic convergence caused the partial detachment and northwest- to west-directed transport of the older basin groups and nappes originally formed in a more oceanward position onto the foreland.

Comparison of mélanges identical in age and component spectrum in different mountain belts (Eastern Alps/Western Carpathians/Dinarides/Albanides/Pelso) figured out one Neo-Tethys Ocean in the Western Tethyan realm, instead of multi-ocean and multi-continent scenarios. The evolution of several independent Triassic-Jurassic oceans is unlikely considering the fact that re-sedimentation into newly formed trench-like basins in front of a west- to northwestward propagating nappe stack including ophiolite obduction is nearly contemporaneous along the Neotethyan Belt. The Middle to Late Jurassic basin evolutions with their sedimentary cycles and component spectra are comparable everywhere.

How to cite: Gawlick, H.-J.: Middle-Late Jurassic ophiolite obduction and formation of sedimentary mélanges in the Western Tethys Realm, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-1, https://doi.org/10.5194/egusphere-alpshop2022-1, 2022.

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The Pannonian Basin is a continental extensional basin system with various depocentres within the Alpine–Carpathian–Dinaridic orogenic belt. Along the western basin margin, exhumation along the Rechnitz, Pohorje, Kozjak, and Baján detachments resulted in the cooling of variable units of the Alpine nappe stack. This process is constrained by thermochronological data between ~25–23 to ~15 Ma (Fodor et al., 2021). Rapid subsidence in supradetachment sub-basins indicates the onset of sedimentation in the late Early Miocene from ~19 or 17.2 Ma. In addition to extensional structures, strike-slip faults mostly accommodated differential extension; branches of the Mid-Hungarian Shear Zone (MHZ) could also play the role of transfer faults.

During this period, the hanging wall margin of the detachment system, i.e., the pre-Miocene rocks of the Transdanubian Range (TR) experienced surface exposure, karstification, and terrestrial sedimentation. After ~14.5 Ma faulting, subsidence, and basin formation shifted north-eastward and reached the TR where fault-controlled basin subsidence lasted until ~8 Ma.

3D thermo-mechanical forward models analyze this depocenter migration and predict the subsidence and heat flow evolution that fits observational data. These models consider fast lithospheric thinning, mantle melting, lower crustal viscous flow, and upper crustal brittle deformation. Models suggest ~150–200 km of shift in depocenters during ~12 Myr.

Simultaneously with depocenter migration, the southern part of the former rift system, near or within the MHZ, underwent ~N–S shortening; the early syn-rift basin fill was folded and their boundary faults were inverted. Deformation was dated to ~15–14 Ma („middle” Badenian) and continued locally to ~9.7 Ma while north of the MHZ the TR was still affected by modest extensional faulting. The particularity of this shortening is that it happened during the post-rift thermal cooling stage. The low-rate contraction and related uplift rarely exceeded this regional thermal subsidence.

MOL Ltd. largely supported the research. The research is supported by the scientific grant NKFI OTKA 134873 and the Slovenian Research Agency (No. P1-0195).

Fodor, L., Balázs, A., Csillag, G., Dunkl, I., Héja, G., Jelen, B., Kelemen, P., Kövér, Sz., Németh, A., Nyíri, D., Selmeczi, I., Trajanova, M., Vrabec, M., Vrabec, M. (2021): Crustal exhumation and depocenter migration from the Alpine orogenic margin towards the Pannonian extensional back-arc basin controlled by inheritence. Global and Planetary Change 201, 103475. 31p. https://doi.org/10.1016/j.gloplacha.2021.103475

How to cite: Fodor, L., Balázs, A., Csillag, G., Dunkl, I., Héja, G., Kelemen, P., Kövér, S., Németh, A., Nyerges, A., Nyíri, D., Oravecz, É., Selmeczi, I., Soós, B., Tőkés, L., Vrabec, M., and Zadravecz, C.: Migration of basin formation and contrasting deformation style in the south-western Pannonian Basin (central Europe), 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-61, https://doi.org/10.5194/egusphere-alpshop2022-61, 2022.

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Since the Late Cretaceous, after closure of the Neotethys ocean, tectonic processes in the central Balkan Peninsula were mainly controlled by the mutual interaction of the Adriatic and the Eurasian plates, and tectonic units in-between. Most of the tectonic structures that have been active during Cenozoic times were inherited from previous tectonic stages under different tectonic regimes. Tectonic activity within the Carpatho-Balkan orogen in eastern Serbia since Miocene is conditioned by the existence of the rigid Moesian promontory eastern of the research area, which limited thrusting of the Carpatho-Balkan units. Rather than that, further compression and complex rotations around the Moesian promontory have been accommodated by the formation of the large strike-slip fault systems (e.g. Cerna-Jiu fault, Timok fault), that accommodated up to 100 km of cumulative displacement. According to earthquake focal mechanisms, faults belonging to these fault systems are still active.

In this abstract, we present results about youngest and recently active faults in the area of the Carpatho-Balkanides in eastern Serbia, based on the studies of fault kinematics, seismicity and earthquake focal mechanisms, as well as tectonic geomorphological studies in karst caves.

Results show that the research area is primarily characterized by strike-slip tectonics, which most likely results from far-field stress generated by the Adria-push mechanism. However, such stress field showed to be highly heterogeneous, where local areas of transtension and transpression have also been important in controlling the recent fault kinematics in this part of the Carpatho-Balkanides.

How to cite: Mladenovic, A.: How active is recent tectonics in the central Balkans: Evidence from the Serbian Carpatho-Balkanides, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-62, https://doi.org/10.5194/egusphere-alpshop2022-62, 2022.

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Most of the Periadriatic Fault System have been active during Oligocene and Miocene times. Its western part seems to be inactive ever since, while the Lavanttal and Sava faults in the east show limited seismic activity. We conducted a systematic archaeoseismological survey along the Periadriatic-Sava fault system, assessing buildings and archaeological sites for earthquake damage. Eight sites, four Roman and four Medieval, display evidence for destructive earthquakes during the past 2000 years. These are San Candido (Medieval) and Lienz (Medieval) on the Pustertal fault, Teurnia (Roman) and Millstatt (Medieval) on the Mölltal fault, Arnoldstein (Medieval) and Magdalensberg (Roman) just north of the Karavanka fault, Roman Celeia (Celje) at the Savinja / Sava faults, and Roman Siscia (Sisak) nearby the Sava fault. Damaged upright walls of Medieval buildings and deformed floors of Roman settlements testify to local intensity up to IX. Ongoing studies of archaeological stratigraphy and construction history allow dating of one or more seismic events at each site, ranging from the 1^st century AD to the 17^th century. We would be cautious about pointing out epicentres at this moment. However, it is remarkable that sites, 70 km apart in average, along a a 380 km long segment of an ‘inactive’ fault zone carry evidence for so many high-intensity destructive events.

How to cite: Kazmer, M. and Gaidzik, K.: Seismic activity along the Periadriatic and Sava Faults in the past two millennia – an archaeoseismological assessment, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-35, https://doi.org/10.5194/egusphere-alpshop2022-35, 2022.

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The Western Alps current tectonics is characterized by seismically active radial extension in the core of the belt, combined with transcurrent to transpressive tectonics in its external zone and foreland associated with a moderate seismicity. We focus on the tectonic transfer from the W-Alps to their foreland, namely the French Rhône Valley, a region with high societal challenges, including demography, nuclear powerplants, and chemical industries. We combine seismotectonic and geodetic (GNSS) approaches to constrain the stress and strain fields of the area extended from the alpine External Crystalline Massifs to the eastern edge of the French Massif Central, which encompasses the Rhône Valley. Seismic strain rates for a set of subareas defined on tectonic arguments (seismotectonic zoning) have been evaluated. They are processed by combining the total seismic energy obtained with statistical integrations of Gutenberg-Richter distributions with representative focal-mechanisms obtained from stress inversions. Seismic strain rates are then compared to the geodetic strain field obtained from an updated GNSS solution focused on the study area. Seismic strain rates of subareas in the Rhone Valley and surroundings range between a few nanostrains/yr and 10E-2 nanostrains/yr. In terms of amplitude, geodesy seems to provide deformation rates one order of magnitude higher than seismicity. However, our seismic strain tensors are globally consistent with the geodetic ones, specifically in the front of the Alps (Belledonne region), where seismic and geodetic networks are denser. In a last step, we replace these strain and stress fields in a new 3D-structural model, which has been developed on purpose. It integrates the main crustal units and the main faults of the area, allowing to better constrain the relationship between the current deformation and stress patterns of the Rhône Valley under the Alpine influence, and the inherited fault system carving the entire domain.

How to cite: Sue, C., Walpersdorf, A., Bienveignant, D., Al Najjar, L., Hannouz, E., Lemoine, A., and Baize, S.: Tectonic Transfer from the Western Alpine Front to the French Rhône Valley in its 3D-Structural Context, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-20, https://doi.org/10.5194/egusphere-alpshop2022-20, 2022.

alpshop2022-20

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Neogene tectonics of the Alps is marked by the indentation of the Adriatic Plate into the Alpine Orogen and onset of escape tectonics in the Eastern Alps. This resulted in the formation of a system of strike-slip faults, mainly the Periadriatic Fault (PF), separating the Eastern and Southern Alps, and the sinistral Giudicarie Fault (GF), which offsets the PF. The GF is kinematically related to Neogene shortening in the Southern Alps but questions remain on its geometry at depth, in particular its relation to the crust/mantle boundary (Moho).

In this study, we compare geological cross-sections and pre-existing geophysical datasets (controlled-source seismology, local earthquake tomography) with a new high-resolution 3-D local earthquake tomographic model from the AlpArray and SWATH-D experiment along two N-S profiles west and east of the GF, as well as a NW-SE oriented section across the GF. These sections reveal differences in the style of indentation tectonics, specifically in the behavior of the Adriatic lower crust, between the Central and Eastern Alps. West of the GF, the lower crust of the Adriatic plate detached from its mantle lithosphere and wedged within the Alpine orogenic crust, whereas to the east of the GF, the Adriatic lower crust forms a bulge just to the south of the PF. The Adriatic upper crust responded by shortening and formation of a fold-and-thrust belt, while the Europe-derived orogenic crust underwent upright, post-nappe folding and exhumation in the Tauern Window. We discuss the possible causes for such along-strike variations in terms of changes in crustal rheology and structural inheritance within the Adriatic Plate, contrasting metamorphic histories within the Alpine orogenic crust west and east of the GF, and potential Neogene slab break-off beneath the Eastern Alps.

How to cite: Le Breton, E., Handy, M. R., McPhee, P., Jozi-Najafabadi, A., and Haberland, C.: Variation in style of Adriatic lower crust indentation west and east of the Giudicarie Fault, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-25, https://doi.org/10.5194/egusphere-alpshop2022-25, 2022.

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Since the 1980s’ the geodynamic evolution of the Alpine-Carpathian-Pannonian (ACP) region has been clearly dominated by two models: McKenzie (1978) and Royden (1984). The model of McKenzie was the first numerical model to explain the continental extension in terms of lithospheric stretching and following thermal subsidence. The model has envisaged that these two processes are recorded by the intervening sedimentary processes: the initial syn-rift phase characterized by extensional growth sequences and the subsequent thermal phase best described in terms of tectonic quiescence with no, or little deformation of the sedimentary cover. Its first application to the North-Sea has brought serious breakthrough in the understanding of its geodynamic evolution, and became a strong predictive tool for the oil and gas exploration community. Further on, the model has been tested on the Pannonian Basin by Sclater et al (1980). The results were ambiguous, and Bally and Snelson (1980) have highlighted that the syn-rift phase is not responding properly to the model. In spite of these early concerns, the McKenzie model has been widely accepted for the coming decades. Evidences from reflection seismic data coupled with well data, however were to confirm that the style and timing of extensional deformation is indeed out of the reach of model predictions. Shortly afterwards, Royden has proposed that the extension of the Pannonian Basin System area would be coupled with the compressional tectonics of the Carpathians. Royden et al.  has proposed that the motor behind the two concurrent processes would be the subduction roll-back which they thought to be represented by the Vrancea Seismic Zone (VSZ). This model was simple and elegant, to that extent that has been unanimously adopted by the whole geoscientific community without reserves for the coming four decades. While it is clear, that the VSZ is a well-documented geodynamic entity, it is problematic to pursue how far can be applied to the whole Intra-Carpathian Region (ICR). There is a growing evidence coming from a variety of regions from the ICR, such as the Transylvanian Basin, Apuseni Mountains, East-Carpathians and ultimately from the Pannonian Basin suggesting that the subduction roll-back model cannot be retained anymore as the sole and only viable solution to explain the Miocene-Pannonian geodynamics of the ACP region. Moreover, possible alternative interpretation(s) of the VSZ is calling for a full revision of the mechanisms of basin and orogenic evolution.

How to cite: Gyorfi, I., Petrescu, L., and Borlenu, F.: Alpine-Carpathian-Pannonian Geodynamics: McKenzie and Royden, how far?, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-26, https://doi.org/10.5194/egusphere-alpshop2022-26, 2022.

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In the evolution of the Alps, the Adriatic plate is traditionally considered as rigid indenter and research on collision and extrusion tectonics mainly focused on the areas north of it. However, the structure of the northernmost part of the Adriatic microplate in the eastern Southern Alps of Italy and Slovenia, referred to as Dolomites Indenter (DI), demonstrates significant internal deformation of a continental indenter that contains the structural memory of Jurassic extension leading to the formation of the Alpine Tethys. Here we argue that these pre-existing NNE-SSW trending normal faults are of paramount importance for understanding and explaining Paleogene to Neogene crustal deformation of the DI. In particular, we demonstrate through physical analogue modelling that lateral changes of thrust fault orientations are controlled by the inherited fault bound basin and platform configuration (e.g., in the Cadore area, where the Trento platform merges into the Belluno basin).

In our brittle and brittle-ductile analogue experiments, shortening is orthogonal or oblique to platform and basin configuration, which is represented by either (i) pre-scribed strength contrasts between platforms/basins or (ii) graben structures modelled by an initial extensional phase. This approach allows us to test various deformational wavelengths as well as timing and localisation of uplift of the DI’s upper to middle crust. Modelling results indicate that the localisation of deformation is controlled by lateral strength contrasts, as transitions from platforms to basins represent. Analyses of surface displacement vectors show that these areas are associated with changes in shortening directions, resulting in, curved faults. All models emphasise that the overall style of deformation is less dependent on the material of the basal décollement, but is ruled by the inherited platform and basin configuration, independent of orthogonal or oblique inversion.

To compare analogue modelling results with deformation in the DI, structural fieldwork accompanied by thermochronological sampling was carried out. Examined cross-cutting criteria covering the entire DI comprise evidence for four distinguishable deformation phases during Paleogene (Dinaric) shortening and subsequent Neogene (Alpine) continental indentation: Top SW, Top (S)SE, Top S and Top E(SE). However, shortening directions along several of the studied faults, e.g. the overall SSE-vergent Belluno thrust (Valsugana fault system), change locally from top SSW to top SSE along strike.

Based on our modelling results, we infer that the variability of shortening directions along these thrust faults may depend on inherited structures and do not necessarily reflect different deformation phases. As such the number of deformation phases in the Southern Alps may have been overestimated so far.

How to cite: Sieberer, A.-K., Willingshofer, E., Klotz, T., Ortner, H., and Pomella, H.: Internal deformation and tectonic evolution of the Dolomites Indenter, eastern Southern Alps: A combined field and analogue modelling study, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-45, https://doi.org/10.5194/egusphere-alpshop2022-45, 2022.

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The arc of the western Alps forms the western termination of the Alpine Chain. The E-W striking Austro-Italian-German and Swiss Alps turn into a N-S direction along the western margin of the Po plain, finally rotating back to an E-W strike along the Italian-French Mediterranean coast. The origin of this enigmatic shape was originally attributed to a variscan inheritance (Argand, 1916), but the vast majority of the present-day literature suggests that it results from the indentation of Adria during collision, as a result of a significant W-directed component of convergence. We briefly review previous interpretations and suggest a new kinematic model based on retrodeformation of syn-collisional shortening, on paleomagnetic results, on structural analysis of maps on the arc-scale, and on field-based structural investigations.

Retrodeformation of syn-collisional shortening around the arc of the Western Alps points to the existence of an arc of significant amplitude before the onset of collision. Paleomagnetic results from the External Zone (Dauphinois) suggest that most rotations around vertical axes only affect the Mesozoic cover above the Triassic, hence they do not provide an information on the kinematic of the entire crust. In the area of the Argentera Massif, where paleomagnetic data were derived from Permian beds, hence allowing to interpret rotations of the entire crustal block, it is shown that no significant rotations around vertical axes affected the area during Alpine orogeny. Structural analyses of maps indicate that the transition between the N-S and E-W striking parts of the arc in the External Zone is abrupt, taking place along the Var Valley. No progressive rotations of structures are observed there, instead N-S striking folds and thrusts appear to be interrupted by the E-W striking ones which continue all along the southern coast of France until the Pyrenees. In several localities, stratigraphic and structural evidences show that these E-W structures were initiated before the onset of Alpine collision, and amplified during Alpine collision.

Our field-based structural data and compiled ones point to the occurrence of a large-scale widely distributed system of sinistral shear zones, striking ENE-WSW, which affect the area north of the Argentera Massif including part of the Internal Zone. Such structure was often assumed to be the prime site accommodating the west-directed indentation of Adria. In spite of its significant extent, its newly mapped location within the Arc precludes such such a 1^st order kinematic role of this structure during collision.

To conclude, we suggest that the arc of the Internal Zone (Penninic Units) showing a progressive rotation of structures is not similarly observed in the External Zone, and we infer that this progressive, continuous curvature largely existed or formed during subduction. The arc of the western Alps as observed in the External Zone mainly reflects the existence of such a structure at the end of subduction and the transition between the Alps s.s. and the Pyrenean Chain, reactivated during Miocene time.

How to cite: Brunsmann, Q., Rosenberg, C., Bellahsen, N., and Molli, G.: The arc of the western Alps: a review and new kinematic model, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-55, https://doi.org/10.5194/egusphere-alpshop2022-55, 2022.

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The Sava suture zone of the internal Dinarides contains Maastrichtian trench-fill sediments, termed “Sava flysch” that record the closure of the northern branch of the Neotethys. Subsequent collision between Adria-derived thrust sheets and blocks of European affinity in Latest Cretaceous to Paleogene times culminated in the formation of the Dinarides fold-and-thrust belt. The suture zone hosts numerous Oligocene plutons of I-type granitic composition. Many of these intrusions are located in the center of metamorphic core complexes (MCCs) that were exhumed in early Miocene times. This phase of post-collisional extension was concomitant with the opening of the northerly adjacent Pannonian Basin and associated with granitic S-type magmatism. Both the processes responsible for extensional deformation and magmatic activity in the internal Dinarides are still a matter of debate.

Our Study contributes spatio-temporal constraints to better understand the tectono-magmatic processes of this area. We present field-kinematic, geochronological, and thermobarometric data from two MCCs at the transition between the internal Dinarides and the Pannonian Basin. Both MCCs are characterized by plutonic rocks in the center, surrounded by up to amphibolite-grade mylonites of exhuming shear zones. Heterogeneous extensional reactivation of formerly contractional structures that gave rise to these core complexes as low-angle detachments in the early Miocene is indicated by a variation in deformation ages of 3 Ma, obtained by Ar-Ar in-situ dating of white mica from deformed rocks of the respective shear zones. While Motajica MCC was exhumed from within the Sava zone during E-W extension at approximately 20 Ma, Cer MCC was exhumed as part of the underlying Adriatic basement during N-S extension between 17-16 Ma. For the Cer MCC, a concordia age of 17.6±0.1 Ma (2σ) obtained by U-Pb LA-ICP-MS on zircons from an S-type granite in combination with an Ar-Ar inverse isochron age of 16.6±0.2 Ma (2σ) obtained on white mica from the same sample, indicate a cooling rate of approximately 400°C/Ma.

Our results contribute to the idea of rapid exhumation of mid-crustal material in the form of MCCs in response to the opening of the Pannonian Basin. This is further corroborated by results of Raman spectroscopy on carbonaceous material, as the temperature profile across the shear zone implies extremely condensed isotherms of 250°C/km. Additionally, U-Pb analyses show that zircons of the I-type intrusion contain inherited cores with age maxima at 270 Ma and 516 Ma and newly formed rims with an age maximum at 31.7 Ma, indicating the timing of intrusion. The S-type granite of Cer in parts reworks the I-type intrusion, as inherited cores include ages of 31-32 Ma, while the rims show an age of 17-18 Ma, suggesting a syn-extensional emplacement. Our data further shows that zircons of the I-type intrusion contain a significant amount of inherited cores with an age spectrum that resembles the detrital age spectrum from sediments of the Sava zone. This challenges the idea that these I-type melts were solely generated from igneous protoliths, and rather suggests a formation from melting of Paleozoic to Mesozoic successions constituting tectonically buried nappes of the internal Dinarides.

How to cite: Löwe, G., Prelević, D., Sperner, B., Schneider, S., Pfänder, J. A., Balling, P., Nabhan, S., von Quadt Wykradt-Hüchtenbruck, A., and Ustaszewski, K.: Exhumation of metamorphic core complexes of the internal Dinarides was triggered by the opening of the Pannonian Basin, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-34, https://doi.org/10.5194/egusphere-alpshop2022-34, 2022.

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The Dinarides fold and thrust belt resulted from the collision of the Adriatic Microplate with Eurasia and shows an overall SW-vergent and in-sequence structural architecture. In the Paleocene the ophiolite-bearing internal Dinarides were exclusively affected by crustal shortening. The outward SW propagation of the deformation front reached the eastern Adriatic passive continental margin mainly composed of Mesozoic carbonate platform rocks in Mid-Eocene times. This led to high crustal Mid Eocene to Oligocene shortening and the formation of the external Dinarides. Two balanced cross-sections across the external Dinarides show an along-strike contrasting deformation styles observed in two orogenic segments separated by  the 250 km long dextrally transpressive Split-Karlovac Fault:  the southern segment dominated by SW-vergent forethrusts, and the northern segment dominated by NE-vergent backthrusts, located to the SE and NW from the Split-Karlovac Fault, respectively. So far, it is not known why the regionally rather uniform Mesozoic Adriatic carbonate platform sequence had undergone such contrasting along-strike deformation.

To improve the understanding of the initiation of the NE-vergent backthrusts and to assess the amount of crustal shortening in the NW segment, a 2D kinematic forward model across the central Velebit Mt. was set up. The Velebit Mt. extends for about 130 km along the eastern Adriatic coast and form a SW-dipping monocline with topographic elevations reaching close to 1800 m. This fault-related monocline is formed in the hanging wall of a NE-vergent backthrust system. The 2D kinematic forward model approach applied to a pre-deformed lithostratigraphic template scaled to reported stratigraphic thicknesses enabled us to test various geometries and temporal successions of fault activity not only for the Mid Eocene – Oligocene contraction, but also for the Mesozoic passive margin extension. Through an iterative trial-and-error method, we were able to reproduce the present-day deformed reference section across the Velebit Mt. and the Lika Plateau in its northeastern hinterland.

Our best-fit balanced kinematic model suggests that the reactivation of Middle Triassic and Upper Jurassic basement-rooted half grabens played a key role in the initiation of the backthrusts. These half grabens were mainly reactivated by hanging wall shortcuts. This inversion of normal faults led to predetermination of the thin-skinned NE-vergent back thrusts, forming the upper part of a complex 68 km wide triangle structure. The structurally lower part comprised of a SW-vergent antiformal stack involving Paleozoic basement. We assessed a crustal shortening for the triangle structure of 47 km and a shortening of 98 km for the entire cross-section. Our results show that the differences in both the lithostratigraphic and Mesozoic half grabens along the eastern Adriatic passive margin played a crucial role in the Mid Eocene – Oligocene deformation of the external part of the Dinarides fold and thrust belt, which led to the contrasting along strike deformation styles to the NW and SE of the Split-Karlovac Fault.

How to cite: Balling, P., Tomljenović, B., and Ustaszewski, K.: The inversion of a passive continental margin portrayed by a 2D balanced kinematic forward model across the Velebit Mt.  in the northern external Dinarides fold and thrust belt, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-22, https://doi.org/10.5194/egusphere-alpshop2022-22, 2022.

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Fluid assisted Alpine fissure-vein and cleft formation starts at prograde, peak or retrograde metamorphic conditions of 450–550 °C and 0.3–0.6 GPa and below. Early-formed fissures become overprinted by subsequent deformation, locally leading to a reorientation. Deformation that follows fissure formation initiates a cycle of dissolution, dissolution/reprecipitation or new growth of fissure minerals enclosing fluid inclusions. Although fissures in upper greenschist and amphibolite facies rocks predominantly form under retrograde metamorphic conditions, this work confirms that the carbon dioxide fluid zone correlates with regions of highest grade Alpine metamorphism, suggesting carbon dioxide production by prograde devolatilization reactions and rock-buffering of the fissure-filling fluid. For this reason, fluid composition zones systematically change in metamorphosed and exhumed nappe stacks from diagenetic to amphibolite facies metamorphic rocks from saline fluids dominated by higher hydrocarbons, methane, water and carbon dioxide. Open fissures are in most cases oriented roughly perpendicular to the foliation and lineation of the host rock. The type of fluid constrains the habit of the very frequently crystallizing quartz crystals. Open fissures also form in association with more localized strike-slip faults and are oriented perpendicular to the faults. The combination of fissure orientation, fissure quartz fluid inclusion and fissure monazite-(Ce) (hereafter monazite) Th–Pb ages shows that fissure formation occurred episodically (1) during the Cretaceous (eo-Alpine) deformation cycle in association with exhumation of the Austroalpine Koralpe- Saualpe region (~ 90 Ma) and subsequent extensional movements in association with the formation of the Gosau basins (~ 90–70 Ma), (2) during rapid exhumation of high-pressure overprinted Briançonnais and Piemontais units (36–30 Ma), (3) during unroofing of the Tauern and Lepontine metamorphic domes, during emplacement and reverse faulting of the external Massifs (25–12 Ma; except Argentera) and due to local dextral strike-slip faulting in association with the opening of the Ligurian sea, and (4) during the development of a young, widespread network of ductile to brittle strike-slip faults (12–5 Ma).

How to cite: Gnos, E., Mullis, J., Ricchi, E., Bergemann, C., Janots, E., and Berger, A.: Episodes of open fissure formation in the Alps, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-2, https://doi.org/10.5194/egusphere-alpshop2022-2, 2022.

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The Ivrea-Verbano Zone (IVZ, Southern Alps) is a fossil exhumed passive margin section of the pre-Alpine middle to lower continental crust that escaped Alpine subduction. Following the Variscan orogeny, the IVZ was affected by Permian post-orogenic extension and Triassic-Jurassic polyphasic rifting stages. Rift-related deformation was accommodated by several km-scale shear zones active at different crustal levels (e.g., Beltrando et al., 2015). Due to the intrinsic importance of these tectonic structures, a detailed characterization of their compositional, metamorphic and structural patterns, as well as the timing of activity may provide key information for the models of shear development in relation to the evolution of the regional tectonics.

In this contribution, we investigate one of these major extensional structures - the Anzola shear zone - with the aim to assess the conditions that promoted the strain localisation. We also provide U-Pb dating on titanite as attempt to constrain the timing of the high-temperature crystal-plastic deformation occurred within the shear zone. Recent field and meso-structural investigations revealed that the Anzola shear zone overprinted basement rocks characterized by inherited lithological and structural heterogeneities (Corvò et al., 2022). Gabbroic rocks and migmatites define the hanging wall and footwall, respectively. According to the petrography and geochemistry (ultra-)mylonitic rocks developed at the expense of a multi-lithological sequence showing amphibolite to granulite facies metamorphic conditions and deformation features related to pre-shearing event. Estimated P-T conditions indicate that mylonitic deformation started at high temperature (~820°C) with presence of melt and continued as solid-state deformation down to amphibolite facies (~650°C). As regard the timing, we show preliminary petrochronological results from titanite of the mylonitic amphibolites that recorded recrystallization event under amphibolite facies at about 185 Ma, which is coeval to deformation occurred at different crustal levels in the IVZ (Simonetti et al. 2021).

On the base of our findings, we argue that the shear zone development was promoted by the rheological contrasts derived from the inherited compositional and structural patterns. Moreover, we emphasizes evidence of syn-deformational partial melting and small amounts of free fluids localized in certain layers that enhanced the viscosity contrasts within the multi-lithological complex. Melts/fluids played a key role in both weakening mechanisms controlling the strain localization, as well as the syn-tectonic growth-recrystallization processes of the titanite, resulting in a strong influence of the U-Pb petrochronology results. Finally, our results are discussed in the framework of the geodynamic evolution of IVZ.

How to cite: Corvò, S., Maino, M., Piazolo, S., Kylander-Clark, A., Seno, S., and Langone, A.: Multiscale heterogeneity control on the nucleation of a crustal shear zone: petro-structural investigation and U-Pb titanite dating from the Anzola shear zone (Ivrea-Verbano Zone, Southern Alps), 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-21, https://doi.org/10.5194/egusphere-alpshop2022-21, 2022.

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The Adriatic Indenter is subdivided into a western and an eastern domain termed Canavese-Insubric Indenter and Dolomites Indenter, respectively, and offset for ~75 km from late Oligocene onwards by the NNE‐SSW‐trending sinistral-transpressive Giudicarie fault system (GFS). The N(NW)-directed movement of the Dolomites Indenter (DI) modifies the early Cenozoic nappe structure of the Alpine orogen as the accommodated shortening changes substantially, depending on the oblique shape of the indenter and its counter-clockwise rotation. The Austroalpine basement units northwest of the GFS experienced open folding of the Cretaceous nappe stack and preserved Cretaceous metamorphic ages. In contrast, the previously deep-seated Neoalpine metamorphic Subpenninic and Penninic units of the Tauern Window in front of the DI’s tip are exhumed and the Austroalpine units adjacent to the DI are brought into a subvertical or even overturned position.

The combination of several thermochronological methods and structural field work allows for constraining time on this tectonic evolution: The Austroalpine units directly adjacent to the DI belong to the uppermost nappe system of the Eoalpine orogeny (Drauzug-Gurktal Nappe System) and experienced an anchizonal to lowermost greenschist-facies metamorphic overprint during the Alpine orogeny resulting in an only partial reset of Variscan Rb/Sr Biotite ages (Pomella et al., 2022). Fission track data from the western Tauern Window and the Austroalpine units adjacent to the north-western corner of the DI, indicate cooling below 180-200°C (Zircon Fission track data) in the Early Miocene and below the 100-120°C (Apatite Fission track data) in the Late Miocene (Klotz et al., 2019). (U‐Th)/He on Apatite data, derived from a horizontal section of the Brenner Base Tunnel and reaching from the DI into the Austroalpine nappe stack, indicate continuous differential uplifting of the northern block along the, in this area, approximately E‑W striking Periadriatic fault system until the Pliocene (Klotz et al., 2019).

Earthquake focal solutions and satellite-based geodetic studies show, that indentation is ongoing today. The significant present-day seismotectonic activity concentrates in the Friuli area in the southeast, whereas there is currently no significant seismicity along the western and northern boundaries of the DI or in the northerly adjacent Austroalpine basement and the Tauern Window. Increased seismic activity can only be detected north of the Tauern Window, along, and north of the Inn Valley (Reiter et al., 2018). Based on field evidence and the thermochronological record, the recent seismic distribution indicates an important change in style and localisation of deformation compared to what is documented from the past.

Klotz, T., Pomella, H., Reiser, M., Fügenschuh, B., Zattin, M., 2019. Differential uplift on the boundary between the Eastern and the Southern European Alps: Thermochronologic constraints from the Brenner Base Tunnel. Terra Nova 31, 281-294.

Pomella, H., Costantini, D., Aichholzer, P., Reiser, M., Schuster, R., Tropper, P., 2022. Petrological and geochronological investigations on the individual nappes of the Meran-Mauls nappe stack (Austroalpine unit/South Tyrol, Italy). Austrian Journal of Earth Sciences 115, 15-40.

Reiter, F., Freudenthaler, C., Hausmann, H., Ortner, H., Lenhardt, W., Brandner, R., 2018. Active seismotectonic deformation in front of the Dolomites indenter, Eastern Alps. Tectonics 37, 4625-4654.

How to cite: Pomella, H., Klotz, T., Sieberer, A.-K., Reiser, M., Tropper, P., and Schuster, R.: The thermotectonic evolution in front of the Dolomites Indenter, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-39, https://doi.org/10.5194/egusphere-alpshop2022-39, 2022.

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The Badstub Formation is part of the Carboniferous of Nötsch sedimentary sequence, of the eastern Austroalpine domain. This formation outcrops in Carinthia (Austria), a few kilometres north of the Periadriatic line (Gailtal line), where a sequence of various conglomerates and breccias with interbedded sandstones, siltstones, and fossiliferous carbonatic schists is exposed. These rocks preserve pristine sedimentary features and even an outstanding fossil record, but multi-scale structural analysis revealed a tectonitic foliation localized in fine-grained rocks, different sets of mineralized faults and veins, and corona textures. Vein fillings and coronas are characterized by equilibrium mineral assemblages that include prehnite, pumpellyite, chlorite, phengite, winchite, and riebeckite. Chlorite-thermometry and thermodynamic modelling on mineralized veins and coronas revealed PT conditions of 260-310 °C and 0.25-0.50 GPa and testify that the Badstub Formation recorded a metamorphic imprint characterized by a low temperature/depth ratio (≈15 °C km^-1). The comparison between a 2D thermo-mechanical numerical model and the metamorphic conditions inferred with thermodynamic models suggest that the Badstub Formation underwent a thermal state consistent with that of the Alpine subduction. These results provide the first quantitative pressure constraints on Alpine subduction metamorphism on the Austroalpine Carboniferous covers nearby the Periadriatic line. Thus, within the Upper Austroalpine nappe system, pre-Alpine rocks were involved into the Alpine subduction at different structural levels and under metamorphic conditions, which therefore span from eclogitic to prehnite-pumpellyite facies.

How to cite: Zanoni, D., Filippi, M., Roda, M., Regorda, A., and Spalla, M. I.: Tectonic and metamorphic record in the Badstub Formation, Carboniferous of Nötsch, eastern Austroalpine, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-30, https://doi.org/10.5194/egusphere-alpshop2022-30, 2022.

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The internal structure of the Dora-Maira Massif is of key importance for understanding exhumation mechanisms of continental-derived HP-UHP rocks in the Western Alps. Numerous petrological-geochemical studies have been done on the world-famous UHP Brossasco-Isasca Unit in the southern Dora-Maira Massif, and recent syntheses have provided an updated view of its metamorphic (Groppo et al. 2019) and structural (Michard et al., 2022) history.

By contrast, the northern Dora-Maira Massif has been much less explored. We are presently undertaking a multidisciplinary project aimed at better constraining its geometry and history. We studied in detail an area comprised between the Germanasca and the Chisone rivers. The first results are as follows:

• The nappe stack comprises, from bottom to top, the Pinerolo (Carboniferous metasediments intruded by dioritic and granitic plutons), Chasteiran (UHP), Muret (polycyclic unit, made of a Variscan basement overprinted during Alpine HP metmorphism) and Serre (Permian rhyolitic to granitic rocks, and the associated epiclastic rocks; slices of Mesozoic cover) Units.
• The pre-Alpine history of the Muret Unit (6-7 kbar, 650 °C) dated at 324 Ma (U-Pb LA-ICP-MS on monazite inclusions in garnet) is well preserved in undeformed volumes (Nosenzo et al., 2022).
• A new, colder (garnet + Fe-rich chloritoid +coesite), UHP unit (the Chasteiran Unit) has been discovered (Manzotti et al., 2022 and this meeting). This Unit, located in the immediate hangingwall of the Pinerolo Unit, occupies the same structural position than the UHP Brossasco-Isasca Unit, but records temperatures 200°C lower.

Geological mapping, structural data, and petrological investigations provide new constraints on the geometry and kinematics of this part of the Dora-Maira Massif. The main foliation D₁ developed at different peak PT conditions in the different units. During their stacking, a new foliation D₂ developed associated with kilometer-scale, E-W trending folds. Final doming of the Dora-Maira nappe stack (D₃) is associated to the westward displacement of the Adria mantle indentor. Detailed geological maps and cross-sections will be provided for illustrating the main steps of the history.

Groppo, C., Ferrando, S., Gilio, M., Botta, S., Nosenzo, F., Balestro, G., Festa, A., & Rolfo, F. (2019). What’s in the sandwich? New P–T constraints for the (U)HP nappe stack of southern Dora-Maira Massif (Western Alps). European Journal of Mineralogy, 31, 665–683.

Michard, A., Schmid, S.M., Lahfid, A., Ballèvre M., Manzotti, P., Chopin, C., Iaccarino, S., Dana, D. (2022). The Maira-Sampeyre and Val Grana Allochthons (south Western Alps): a review and new data on the tectonometamorphic evolution of the Briançonnais distal margin. Swiss Journal of Geosciences, 115, in press.

Manzotti, P., Schiavi, F., Nosenzo, F., Pitra, P., Ballèvre, M. (2022). A journey towards the forbidden zone: a new, cold, UHP unit in the Dora-Maira Massif (Western Alps). Contributions to Mineralogy and Petrology, in press.

Nosenzo, F., Manzotti, P., Poujol, M., Ballèvre, M., & Langlade, J. (2022). A window into an older orogenic cycle: P-T conditions and timing of the pre-Alpine history of the Dora-Maira Massif (Western Alps). Journal of Metamorphic Geology, 40, 789-821.

How to cite: Nosenzo, F., Ballèvre, M., and Manzotti, P.: Nappe stacking and syn-nappe folding in the northern Dora-Maira Massif (Western Alps), 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-8, https://doi.org/10.5194/egusphere-alpshop2022-8, 2022.

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The Adula and Cima Lunga units show the best preserved record of the deformation and metamorphic history of the Central Alps. Alpine studies lasting more than a hundred years documented a complex tectono-metamorphic evolution, including the presence of relicts of ultra-high pressure and high temperature metamorphism. Throughout this long history of researches, a few key questions stand out, still challenging the geological community. Major questions regard how to reconcile the structural pattern with the metamorphic path, as well as the timing relationships.

The occurrence of ultrahigh-pressure and/or high-temperature rocks embedded within significantly lower grade metamorphic rocks rises a major challenge for developing a consistent geodynamic model for exhumation of such deep-seated rocks. Subduction zones are, in fact, efficient player driving material from the surface down into the Earth's mantle. However, the mechanisms to exhume part of this material (and particularly the denser oceanic rocks) back to the shallow crust are still highly debated. Scientists generally invoke either mechanical decoupling within a tectonic mélange or variable metamorphic re-equilibration during the retrograde path.  These interpretations are based on the common assumption that the mineral assemblages form under lithostatic pressure and near-equilibrium regional geothermal gradients. Hence, the resulting metamorphic histories based on the estimation of the pressure and temperature conditions represent the major tool for tectonic reconstruction as proxies of the burial and exhumation history of the rocks during subduction-exhumation phases.

Alternative explanations highlight the role of deformation in promoting the coexistence of multiple local equilibria, which cease to correlate with lithostatic conditions and thus burial depths. In this view, the non-hydrostatic stress and the local temperature deviations are accounted as important components potentially modifying the metamorphic system.

In this contribution, we show new structural, petrological and thermochronometric data from the Adula and Cima Lunga units. The wide dataset comprises new field mapping covering the entire nappes extension (several hundred square kilometres) and structural-petrochronological analyses at the meso- to micro-scale. Our results show the highly variable pressure-temperature-time-deformation paths experienced by the compositionally heterogeneous rocks of the Cima Lunga and Adula nappes. We present evidence of contrasting metamorphic records among the rocks of these nappes, providing arguments to discuss pros and cons of the tectonic models proposed to explain these contrasting metamorphic records.

How to cite: Maino, M., Schenker, F., Casini, L., Corvò, S., Perozzo, M., Langone, A., and Seno, S.: Challenges in the interpretation of the structural and metamorphic record in the Adula and Cima Lunga units (Central Alps), 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-9, https://doi.org/10.5194/egusphere-alpshop2022-9, 2022.

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Numerous outcrops of ultramafic rocks consisting mostly of peridotites occur in the area of Banovina, in Croatia. These rocks were formed as parts of the former Earth's mantle and belong to the Central Dinaride Ophiolite Belt (CDOB), which is direct proof of the existence and closure of the Neothetys ocean in the northern part of the Balkan area. Previous studies have considered these peridotites as fertile, subcontinental parts of the mantle with complex chemistry. This research presents a more detailed petrographic and chemical analysis, focused solely on peridotites as dominant ophiolitic member, with the intention to sort between different types of Banovina peridotites and offer the model for their petrogenesis.   

Detailed field work, mapping and petrographic analyses have revealed that Banovina peridotites occur as two texturally, lithologicaly and mineralogicaly different types, that crop out in two geographically different belts, the northern (N-belt) and the southern (S-belt). The N-belt contains mostly serpentinite breccias and serpentinized, depleted and mostly porphyroclastic spinel lherzolites that occur in the form of mélange, while S-belt comprises larger masses of peridotites which consist predominantly of fertile spinel lherzolites with equigranular to porphyroclastic textures. Bulk rock analyses have shown that spinel lherzolites from the S-belt have lower Cr# and Mg# and higher content of Al₂O₃, CaO, Na₂O, TiO₂ and REE than spinel lherzolites from N-belt, and same relations, excluding the REE, can be seen in the chemistry of clinopyroxenes and orthopyroxenes. Spinels from the N-belt spinel lherzolites have a significantly higher Cr# (12,7 – 50,7) then those from the S-belt spinel lherzolites (7,7 – 10,8). Two types of dunites, which were found only within S-belt peridotites, have very different petrographic and chemical characteristics. Pyroxene rich dunite is characterized by a coarse-grained protogranular to porphyroclastic texture, high modal pyroxenes (up to 10 vol. %) and spinels enriched in MgO, Al₂O₃ and NiO. The second type of dunite has small-grained equigranular texture, contains amphibole (up to 1 vol. %), pyroxene (< 1 vol. %) and spinels enriched in Cr₂O₃ and FeO_T. Geochemical analysis of all peridotites indicate that the S-belt peridotites represent a subcontinental mantle which have been formed through the initial rifting phase during which they ascended to the upper crust. Peridotites from the S-belt are classified as orogenic peridotites. The geochemical characteristics of N-belt peridotites indicate their origin from a suboceanic mantle formed within mid ocean ridge environment and are classified as ophiolitic peridotites. Dunites show different geochemical characteristics and may have been formed by different geological processes. The diverse lithology of ultramafics in the limited space of the S-belt indicates very heterogeneous nature of the subcontinental mantle. As a part of the CDOBs, peridotites from Banovina indicate that the CDOB record three different phases of ocean evolution, the early phase of the initial rift and opening of the ocean (S-belt peridotites), later phase of the already developed ocean (N-belt peridotites) and also the phase of ocean closure which is evident from the mélange occurrences.

How to cite: Bilić, Š., Garašić, V., and Woodland, A. B.: Two types of peridotites in the area of Banovina, Croatia and their petrogenesis, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-10, https://doi.org/10.5194/egusphere-alpshop2022-10, 2022.

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The Middle Triassic period represents a very dynamic time in a broader Tethyan region. Tectonic movements related to disintegration of Pangea and opening of the Neotethys gave rise to the formation of volcanic and volcaniclastic deposits. In the NW Croatia, these rocks outcrop in approximately 60 km long intra-Pannonian Mountain chain (Mts. Kalnik, Ivanščica, Strahinjščica, Kuna Gora, Desinić Gora and Ravna Gora), representing the junction between the Southern Alps and Internal Dinarides. Among these mountains, Mt. Ivanščica represents a complex structure built of shallow-marine to pelagic successions originating off the passive continental margin of Adria microplate. These deposits are found in a tectonic contact with ophiolitic mélange containing remnants of Neotethys. Middle Triassic volcanic and volcaniclastic rocks from this area include basic/intermediate to acidic effusive and pyroclastic lithologies and are interfingered with marine sediments.

The specific area of Vudelja quarry, situated in the central part of the northern Ivanščica slopes, is composed mainly of mafic lithologies and their volcaniclastic derivates. Volcanic and volcaniclastic rocks of basaltic composition were studied in detail to distinguish different facies and their spatial distribution. Facies characteristics enabled the interpretation of their genesis. Three different facies were recognized: 1) effusive coherent facies; 2) pyroclastic flow facies, and 3) resedimented autoclastic facies. Effusive coherent facies is composed of hyaline basalts, with incorporated clasts of the same lithotype. This facies was formed by effusion of basaltic magma. Basaltic clasts were likely incorporated by the primary effusive flow during magma ascent, or following effusion while flowing over the fragmented basaltic material. Quenching fragmentation of a basaltic effusion in the marine environment is another possible process explaining the formation of basalt clasts. Pyroclastic flow facies is composed of plagioclase crystalloclasts, basaltic lithoclasts and scoria fragments, with the flow texture indicated by clast arrangement and glassy matrix with flow features. This facies occurs only locally and its geographical extent is limited thus indicating a small volume of the flow, characteristic for basaltic pyroclastic flows of scoria and ash type. Resedimented autoclastic facies is dominant at the outcropping quarry front and is composed of several lithotypes with various grain sizes and types of matrix. Clast dimensions vary from block to ash size. Some samples exhibit common sedimentary features such as horizontal lamination. The facies was formed by the autofragmention processes of hot basaltic magma in contact with sea water, and subsequent resedimentation of newly formed volcaniclastic particles. Due to an intense tectonic disruption, spatial organization of determined facies is not clear, though the alienation from the primary source can generally be followed from south to north.

Studied locality presents a portion of Middle Triassic volcanic and volcano-sedimentary formations well known from the Southern Alps, Transdanubian Range and the Dinarides. Intense volcanic activity, related to the rifting between the future Adria microplate and southern edge of Laurasia, fed the material to a complicated pattern of sedimentary environments formed along the future Adria passive margin. Extensional tectonics created deep faults within the continental crust which might have served as conduits for submarine basaltic extrusions.

How to cite: Smirčić, D., Vukovski, M., Slovenec, D., Kukoč, D., Belak, M., Grgasović, T., Šegvić, B., and Badurina, L.: Differentiation and genesis of the Middle Triassic mafic volcaniclastic facies in NW Croatia, a case study from Vudelja quarry, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-43, https://doi.org/10.5194/egusphere-alpshop2022-43, 2022.

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Alpine landscapes form in mountain belts that likely experienced tectonic uplift during plate’s convergence, and efficient erosion dominated by glacial carving and circle retreat. In southern Patagonia N-S oriented late Miocene plutonic complexes are exposed in deep incised valleys with summits topographically above the glacial equilibrium line altitude. Two of the most emblematic ones are the Fitz Roy (Chaltén, latitude 49°S) and the Torres del Paine (latitude 51°S) plutonic complexes, ~2 km higher than the mostly flat bottom valley that is partially covered by the Southern Patagonian Icefield. This continental region is located above an asthenospheric window that opens and migrates from the latitude 54 °S towards the latitude 46 °S since ~16 Ma, and experienced dynamic uplift during episodes of spreading ridge collision with the continental margin. Here we present a new dataset of combined low-temperature thermochronometers from the Chaltén and Torres del Paine plutonic complexes, and their thermal history inversion numerical modeling, to identify the geodynamic processes forcing on the exhumation of the mountain belt. These complexes are separated by 200 km along the strike of the belt, and share a pulse of rapid exhumation at ca. 6 Ma, likely showing that glaciation was regionally starting at this moment. After a period of quiescence, in Torres del Paine the exhumation rate is accelerated from ~2 Ma to the present, interpreted as a signal of the Pleistocene climatic transition creating incise valleys. Only in the Fitz Roy a pulse of rapid exhumation is present at ca. 10 Ma, approximately coincident with the time range in which the ridge was subducting beneath the continent at that latitude. This allows us to separate the climatic from the tectonic/mantle forcing to the exhumation in southern Patagonia, and represents the first in-situ observation of the passage of the asthenospheric window in the low-temperature thermochronometric record of the region.

How to cite: Paiva Muller, V. A., Sue, C., Valla, P., Sternai, P., Simon-Labric, T., Gautheron, C., Martinod, J., Ghiglione, M., Baumgartner, L., Hérman, F., Reiners, P., Grujic, D., Shuster, D., Braun, J., Husson, L., and Bernet, M.: Exhumation response to climate and tectonic forcing in the southern Patagonian Andes (Torres del Paine and Fitz Roy plutonic complexes) , 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-4, https://doi.org/10.5194/egusphere-alpshop2022-4, 2022.

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The distribution of ultrahigh-pressure metamorphism (UHP) at the scale of a mountain belt is of prime importance for deciphering its past subduction history. In the Western Alps, coesite has been recognized in the southern Dora-Maira massif, in the lens-shaped Brossasco-Isasca Unit, but has not been found up to now in the other parts of the massif. We report the discovery of a new UHP unit in the northern Dora-Maira Massif (Western Alps), named Chasteiran Unit (Manzotti et al. 2022). It is only a few tens of metres thick and consists of garnet-chloritoid micaschists. Garnet inclusions (chloritoid, rutile) and its growth zoning allow to precisely model the P–T evolution. Coesite crystals, which are pristine or partially transformed to palisade quartz occur as inclusions in the garnet outer cores. According to thermodynamic modelling, garnet displays a continuous record of growth during the prograde increase in P and T (25–27 kbar 470–500 °C) (stage 1), up to the coesite stability field (27–28 kbar 520–530 °C) (stage 2), as well as sub-isothermal decompression of about 10 kbar (down to 15 kbar 500–515 °C) (stage 3). The main regional, composite, foliation, marked by chloritoid and rutile, began to develop during this stage, and was then overprinted by chlorite-ilmenite (stage 4). The Chasteiran Unit is discontinuously exposed in the immediate hangingwall of the Pinerolo Unit, and it is located far away from, and without physical links to the classic UHP Brossasco-Isasca Unit. Moreover, it records a different, much colder, P–T evolution, showing that different slices were detached from the downgoing subduction slab. The Chasteiran Unit is the fourth and the coldest Alpine UHP unit known so far in the entire Alpine belt. Its P–T conditions are comparable to the ones of the Tian Shan coesite-chloritoid-bearing rocks.

Manzotti, P., Schiavi, F., Nosenzo, F., Pitra, P., Ballèvre, M. (2022). A journey towards the forbidden zone: a new, cold, UHP unit in the Dora-Maira Massif (Western Alps). Contributions to Mineralogy and Petrology, in press.

How to cite: Manzotti, P., Schiavi, F., Nosenzo, F., Pitra, P., and Ballèvre, M.: A journey towards the forbidden zone: a new, cold, UHP unit in the Dora-Maira Massif (Western Alps), 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-6, https://doi.org/10.5194/egusphere-alpshop2022-6, 2022.

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Extensive rock recrystallization and element redistribution during retrogression often hampers our understanding of the early stages of metamorphism. Garnet is the mineral that best preserves information about its growth during the prograde history of the rock as compositional zoning. In most metamorphic rocks, garnet zoning varies between almandine, grossular, and pyrope end-members with minor spessartine content. This variability and the diffuse presence of mineral inclusions in garnet enables the coupling of thermodynamic tools (e.g., pseudosections) with classical element exchange and elastic geothermobarometry to gather information on their pressures and temperatures of equilibration. Such studies give their best results when applied to metapelites due to their relatively large mineral variability over the typical PT range of metamorphic rocks. However, monomineralic lithotypes, such as impure quartzite or marble, consist of minerals stable over a wide PT range and therefore lack mineralogic change. Furthermore, currently available solution models are not calibrated for use on unconventional bulk rock compositions and therefore do not guarantee reliable geothermobarometric results.

In this contribution, we use elastic geobarometry to track prograde garnet growth from low- to ultrahigh-pressure conditions in three Mn-rich garnets (up to 50% sps) from an impure marble from the Lago di Cignana Unit (Italy). The rock consists of mainly quartz and calcite with garnet porphyroblasts. The three garnets show a very large core-to-rim compositional zoning with Mn-rich cores, Fe-rich mantles, and rims with a slight increase in Mg. Mineral inclusions in garnet cores and mantles are mainly quartz, with minor titanite, calcite, and apatite. Coesite, aragonite, zircon, and rutile are instead present within garnet rims. The three investigated garnets vary in shape, zonation, inclusions type and size while having a comparable core-to-rim composition. In two garnets, quartz inclusions are tiny (20-30 μm) and spread evenly within the garnets. The third garnet has larger quartz inclusions (50-100 μm) in the core and smaller in the mantle, decreasing progressively in size from the inner to the outer mantle (50-10 μm). Elastic geobarometry on these quartz inclusions in garnet allowed the tracking of the pressures at which garnet cores and mantles formed. We can show that these garnets formed during multiple distinct growth stages along the prograde path from 1.2 GPa and 430°C to 1.8 GPa and 500°C and finally at UHP conditions, as testified by the coesite-bearing garnet rims. This difference in pressure and temperature of garnet growth might be due to local (cm-to-mm-sized) changes in chemical composition at the scale of the thin section and/or to reaction overstepping.

How to cite: Gilio, M., van Schrojenstein Lantman, H. W., Girani, A., Angel, R. J., Scambelluri, M., and Alvaro, M.: The prograde history of three Mn-rich garnets from the UHP Lago di Cignana Unit (Italy), 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-18, https://doi.org/10.5194/egusphere-alpshop2022-18, 2022.

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The first occurrence of ultra-high-pressure (UHP) metamorphism in the Western Alps was documented by Chopin in 1984 (Chopin, 1984) with the discovery of coesite in the southern Dora Maira massif. Since then, just one additional UHP terrain was discovered until the end of the 90’s. In recent times, new occurrences of coesite have been reported in different units of the Western Alpine belt, widening the distribution of UHP terrains, with important tectonic implications. Here, we report the first discovery of coesite in the meta-ophiolitic suite of the Monviso Massif, in the northern Lago Superiore Unit (LSU). Previous petrographic studies and thermodynamic modelling in the area suggested that these alpine units may have experienced UHP metamorphism, but no direct evidences (i.e., coesite occurrence) have been reported to date.  The presence of coesite is demonstrated by µ-Raman analyses. The Raman spectra show the typical peaks of coesite, slightly shifted towards higher wavenumbers. The main peak is located at 522 cm^–1, and the secondary peaks at 426, 270 and 178 cm^–1. Coesite inclusions consist of intact single crystals (10-60 µm) hosted by garnet, without evidence for re-equilibration features. Typical coesite-related features such as radial cracks in garnet host mineral and palisade texture are present in large polycrystalline quartz inclusions (>80 µm). Peak metamorphic conditions have been constrained through different techniques (detailed garnet inclusion analysis, elastic geobarometry and thermodynamic modelling).

The occurrence of UHP terrains along the Western Alps is becoming more common than expected. Our results, alongside with the novel evidence for UHP in the Western Alps, will lead to new tectonic models for the subduction and exhumation of UHP terrains, constraining the evolution of subduction-accretionary systems.

Chopin, C., 1984, Coesite and pure pyrope in high-grade blueschists of the western Alps: a first record and some consequences: Contributions to Mineralogy and Petrology, v. 86, p. 107–118, https://doi.org/10.1007/BF00381838.

How to cite: Ghignone, S., Scaramuzzo, E., Gilio, M., Bruno, M., Livio, F., and Alvaro, M.: First evidence of UHP in the Lago Superiore Unit (Monviso, Western Alps), 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-47, https://doi.org/10.5194/egusphere-alpshop2022-47, 2022.

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The Adula nappe in the Swiss-Italian Central Alps is a continental basement nappe from the former European margin that was subducted to depths indicating (ultra)-high-pressure conditions. Many studies were performed to understand the pressure-temperature-time evolution of the Adula nappe. However, the pressure data derived from classical thermobarometry from eclogite and garnet peridotite lenses cannot be correlated with the tectonic record without several difficulties. The pressure gradient is very high, the structural record for the often suggested extrusion model is missing and the directly surrounding nappes show consistently lower pressures. Furthermore, it was discovered that at least parts of the Adula nappe underwent eclogite-facies metamorphism during the Variscan and the Alpine orogenic cycles. These two cycles were distinguished by age dating and the chemical zonation patterns of garnet, although in some cases it can be ambiguous. Otherwise, the Variscan and Alpine parageneses are hardly, if at all, possible to tell apart. Therefore, existing pressure and temperature data that were obtained using classical geobarometers rely on mineral equilibria, which may not have yielded true Alpine metamorphic conditions.

For this study, around fifty felsic and metabasic samples were collected from different lithologies on a N-S transect through the Adula nappe parallel to the direction of subduction. Raman spectroscopy on quartz inclusions (RSQI) in garnet was used as a geobarometer to measure minimum peak pressures. The advantages of this method are its independence of a chemical equilibrium and the ability to yield reliable pressure constraints even if the high-pressure mineral assemblage has been retrogressed. The Variscan and Alpine garnet domains were carefully identified using the Electron Microprobe (EMP) and the Scanning Electron Microscopy (SEM). Temperatures were determined by means of Zr-in-rutile thermometry by measuring the Zr content with EMP.

As a result, the obtained temperatures exhibit a gradient increasing from the north at ca. 500-550 ^oC to the south at around 700 ^oC. The minimum peak pressures in the northern and central Adula nappe range between 2.09 GPa and 2.17 GPa for metasediments and 1.41 GPa and 2.02 GPa for metabasites. 1.53 GPa were determined for an orthogneiss from the central part of the nappe. Lower pressures between 1.14 GPa and 1.31 GPa in the southern Adula nappe were potentially caused by viscous relaxation of the quartz inclusions during the high-temperature Lepontine metamorphism. Our new pressure data imply a very weak pressure gradient. Therefore, it is in contrast to the results of previous works, in which barometers based on a chemical equilibrium were applied. Additionally, no systematic difference in minimum peak pressures is observable for the different lithologies.

How to cite: Brunsmann, O., Germer, M., Pohl, A., Kohn, V., Könemann, V., Zhong, X., Pleuger, J., and John, T.: Barometric studies on different rock types from the Adula Nappe (Central Alps) by Raman spectroscopy of quartz inclusions in garnet, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-33, https://doi.org/10.5194/egusphere-alpshop2022-33, 2022.

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We have studied eclogite, garnet clinopyroxenite, and garnet-bearing micaschist and gneiss from the southeastern flank of the Pohorje Mountains (Mts.) in order to better understand the pressure-temperature (P-T)-time evolution of these rocks. Geochronology was performed by in-situ analyses of monazite in different textural positions with an electron microprobe and a laser-ablation inductively coupled plasma mass-spectrometer. P-T trajectories were obtained by thermodynamic modelling considering strongly the chemical zoning of garnet and mica and the mineral inclusions in these phases. In addition, we calculated the influence on intracrystalline cation diffusion on garnet zoning also to gain time constraints.

Two high-pressure (HP) events were proved for metamorphic rocks of the Pohorje Mts. These events occurred at temperatures between 570-650 °C for micaschist and 670-740 °C for eclogite + garnet clinopyroxenite in Late Cretaceous and Eocene times. In addition, we found that a micaschist sample taken close to the Pohorje pluton was partially overprinted in the Miocene (18.9±0.2 Ma) by this intrusion at depths of 30-32 km. Thus, the subsequent uplift of the Pohorje pluton and its surrounding occurred at a mean rate of 1.6-1.7 mm/a. The studied metamorphic rocks were also significantly exhumed probably soon after the Eo-Alpine event that had led to peak pressures up to about 2.3 GPa. This exhumation was accompanied by cooling. Another burial process followed during which Eo-Alpine rocks were significantly overprinted at peak pressures up to 2.4 GPa in the Eocene. For example, two generations of potassic white mica (phengite) formed in micaschist. The Eo-Alpine one was relatively coarse grained, whereas the Eocene generation replaced this coarse-grained phengite by newly grown small flakes. No indications for ultrahigh-pressure metamorphism were found.

We interpret our findings, including previous results on rocks of our study area in the Pohorje Mts., in a geodynamic context as follows: A first collision of continental (micro)plates occurred in the Late Cretaceous after a branch of the Neotethys Ocean was closed. The subduction of the corresponding oceanic plate including sediments on top led to eclogite (+ HP garnet clinopyroxenite) and HP micaschist which were exhumed during the continent-continent collision in an exhumation channel. About 45 Ma after this Eo-Alpine collisional event, another part of the Neotethys Ocean was closed followed by a second collision of continental (micro)plates. This process led to clearly overthickened crust and deep burial of rocks residing in the Eo-Alpine exhumation channel. Exhumation of the studied metamorphic rock units, probably mainly caused by surface erosion, followed this Eocene collisional event. A particular event in the Miocene is characterized by intrusions of large volumes of acidic magma. These intrusions formed the Pohorje pluton, which produced discernable contact metamorphism, for instance in micaschist, close to its margin.

How to cite: Massonne, H.-J. and Li, B.: Pressure-temperature-time evolution of Austroalpine metamorphic rocks from the southeastern Pohorje Mountains, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-7, https://doi.org/10.5194/egusphere-alpshop2022-7, 2022.

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Skarnoid calc-silicate xenoliths composed of anorthite, clinopyroxene and Mg-Al spinel were discovered in an alkali basalt quarry located in the Belinsky vrch lava flow, near Fiľakovo (Southern Slovakia). Randomly oriented tschermakite pseudomorphs are replaced by olivine, spinel, and plagioclase. The relict amphibole within the pseudomorphs is characterized by high ^VIAl (1.95 to 2.1 apfu), and very low occupancy of the A-site (<0.1 apfu), which are a diagnostic feature of high-pressure metamorphic rocks. Pyroxene compositions plot along continuous mixing line extending from nearly pure diopside-augite towards a Ca(Fe³⁺Al)AlSiO₆ endmember with an equal proportion of ^VIAl³⁺ and Fe³⁺. Forsterite (Fo_72–83) and Fe³⁺-rich ilmenite crystallized from the melt, leaving behind the residual calcic carbonate with minor MgO (1–3 wt%). Euhedral aragonite and apatite embedded in the fine-grained calcite or aragonite groundmass indicate slow crystallization of residual carbonatite around the calcite-aragonite stability boundary. Olivine-ilmenite thermometry (Andersen & Lindsley, 1981) yielded temperatures between 770 and 860 °C. Pressures of 1.8–2.1 GPa were estimated by intersection of the olivine-ilmenite thermometer with the calcite-aragonite stability boundary calculated for a CO₂ saturated environment using Perple_X (Connolly, 1990). Tschermakite touching interstitial plagioclase was suitable for the application of the barometer of (Molina et al., 2021), which yielded 781±13 °C and 2.05±0.03 GPa consistent with the olivine-ilmenite-calcite-aragonite thermobarometry. The estimated PT conditions fall well inside the garnet stability field, although no garnet has been observed in the mineral assemblage. However, the presence of esseneite and kushiroite with melilite inclusions suggest high CO₂ partial pressure, low SiO₂ activity and strongly oxidizing conditions, in which the high Al, Fe pyroxenes are formed at the expense of the garnet (Ohashi & Hariya, 1975). The protolith is still ambiguous, and two options have been considered. The relict tschermakite in spinel-plagioclase-forsterite pseudomorphs suggests a metamorphosed calc-silicate marble originating from a sedimentary protolith. High Cr contents in spinel and pyroxene, abundant Cu-sulfides, and high CaO contents, 0.3–1.0 wt% CaO, in forsterite, suggest a magmatic protolith, similar to layered gabbro-anorthosite complexes modified by interaction with calcic carbonatite melt.

References:

Andersen, D., & Lindsley, D. (1981). A valid Margules formulation for an asymmetric ternary solution: revision of the olivine-ilmenite thermometer, with applications. Geochimica et Cosmochimica Acta, 45(6), 847–853.

Connolly, J. (1990). Multivariable phase diagrams; an algorithm based on generalized thermodynamics. American Journal of Science, 290(6), 666–718.

Molina, J., Cambeses, A., Moreno, J., Morales, I., Montero, P., & Bea, F. (2021). A reassessment of the amphibole-plagioclase NaSi-CaAl exchange thermometer with applications to igneous and high-grade metamorphic rocks. American Mineralogist, 106(5), 782–800.

Ohashi, H., & Hariya, Y. (1975). Phase relation of CaFeAlSiO6 pyroxene at high pressures and temperatures. The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists, 70(3), 93–95.

How to cite: Reato, L., Huraiová, M., Konečný, P., and Hurai, V.: Formation of esseneite and kushiroite in calc-silicate skarnoid xenoliths from Southern Slovakia, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-11, https://doi.org/10.5194/egusphere-alpshop2022-11, 2022.

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The Alps, as part of the Alpine-Mediterranean Mountain chain, are one of the classical localities for orogenic studies, where the Mesozoic-Cenozoic tectonic evolution is well known. Many classical models have been proposed to explain the tectonic evolution from Mesozoic rifting and breakup to Late Mesozoic-Cenozoic subduction, plate collision and exhumation. However, the pre-Mesozoic tectonic evolution of the pre-Alpine basement remains poorly known because of the lack of sufficient age data due to complex polyphase deformation and multiple metamorphic overprints. New data from mainly amphibolite-facies pre-Alpine basement of the Austroalpine mega-unit indicates that this basement is composed of a heterogeneous series of continental units, island arcs, ophiolites, subduction mélanges, accretionary wedges, and seamounts affected by different metamorphic grades. This study (Chang et al., 2021) presents new results of LA-ICP-MS U-Pb zircon dating and MC-ICP-MS Lu-Hf isotopic tracing of zircons from three key areas of Austroalpine basement, including the: i) Wechsel Gneiss and Waldbach Complexes, and Wechsel Phyllite Unit, (ii) Saualpe-Koralpe-Pohorje, and (iii) Schladming areas. We determine the Wechsel Gneiss Complex to be a continental magmatic arc formed during 500–560 Ma in the proximity to a continental block with a ‘memory’ of Late Archean to Early Proterozoic continental crust. The Wechsel Gneiss Complex has Hf model ages of 2.1 to 2.2 Ga and 2.5 to 2.8 Ga that indicate a close relationship to northern Gondwana, with depleted mantle Hf model ages as old as 3.5 Ga. The Wechsel Phyllite Unit structurally overlying the Wechsel Gneiss Complex has partly different sources, including juvenile crust formed at ca. 530 Ma. In contrast, the Waldbach Complex constantly added new crustal material during 490–470 Ma period and bears considerably more positive εHf(t) values than the underlying Wechsel Gneiss Complex and gives relatively young, depleted mantle model ages of 700 to 500 Ma. The Waldbach Complex is, therefore, interpreted to be part of a magmatic arc that formed during closure of the Prototethys and was metamorphosed during Variscan orogenic events at ca. 350–330 Ma. The Schladming-Seckau and Wechsel Complexes represent a Cambro-Ordovician magmatic arc system formed by Prototethys subduction processes with the associated Late Neoproterozoic to Early Ordovician ophiolitic Speik complex having formed in its back-arc basin or as Prototethyan lithosphere. The Plankogel Complex and structurally overlying micaschist and amphibolite units represent accreted ocean, ocean island, and continent-derived materials, interpreted to be an accretionary complex formed during the Permo-Triassic closure of the Paleotethys. Many granites with Permian ages (e.g., porphyric granite called Grobgneiss and other granite gneisses and associated pegmatites) were likely formed in an extensional environment that culminated in the opening of the Middle-Late Triassic Meliata oceanic rift. These granites formed by partial remelting of crust with mainly Middle Proterozoic Hf model ages. Taken all these data together, we find that the Austroalpine basement is heterogeneously composed and includes complexes of different ages, different tectonic evolutionary histories and different remolten sources representing different locations before final accretion. The composite of pre-Alpine complexes in the Austroalpine mega-unit likely assembled not earlier than Late Permian or Early Triassic.

How to cite: Chang, R., Neubauer, F., Genser, J., Liu, Y., Yuan, S., Guan, Q., and Huang, Q.: Hf isotopic constraints for Austroalpine basement evolution of Eastern Alps: review and new data, 15th Emile Argand Conference on Alpine Geological Studies, Ljubljana, Slovenia, 12–14 Sep 2022, alpshop2022-29, https://doi.org/10.5194/egusphere-alpshop2022-29, 2022.

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