T2

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.

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.

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.