EGU25-21240, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-21240
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Re-defining early Alpine orogenesis in the ALCAPA domain (Late Jurassic to Early Cretaceous)
Oscar Fernandez1, Hugo Ortner2, Diethard Sanders2, and Bernhard Grasemann1
Oscar Fernandez et al.
  • 1Department of Geology, University of Vienna, Vienna, Austria
  • 2Department of Geology, University of Innsbruck, Innsbruck, Austria

It is commonly accepted that the Late Jurassic marks the onset of convergent tectonics in the ALCAPA (Alps-Carpathians-Pannonia) domain. However, the lack of generalized metamorphism, and the absence of structures and features that can be ascribed to this event make it challenging to understand its relevance and extent. Two areas have been historically documented in the ALCAPA where Late Jurassic tectonic features can be recognized: in the Inner Western Carpathians (Meliata and Borka localities) and in the central Eastern Alps (Lower Juvavic tectonic units). The interpretation of the structure and geodynamic significance of both of these areas has been strongly conditioned by assumptions on the paleogeographic position of the units involved. In these two areas, the Juvavic and Silica tectonic units (successions of Permo-Mesozoic strata derived from the Triassic passive margin of the ALCAPA, in the Eastern Alps and Western Carpathians respectively) have been traditionally interpreted to represent the most distal units of the Triassic passive margin of the ALCAPA. This in turn implies that these units are interpreted to be tectonically far travelled and emplaced in a complex succession of in- and out-of-sequence thrusts.

In this contribution we propose a revision to the conventional interpretation of the Juvavic units, based on the structural re-interpretation of key localities. We focus on the central Eastern Alps, where we describe the geometry, timing and interplay of different structures related to the earliest phase of contractional deformation. We further integrate the modern understanding of salt tectonics and carbonate sedimentology in this area to show that the pre-contractional paleogeographic arrangement of the Juvavic was likely more complex than previously assumed. In particular, we argue that pelagic Triassic facies have been misinterpreted as evidence for the distality of the Juvavic and Silica units, and that they deposited not only in distal passive margin settings but also in proximal settings of limited crustal thinning. This is consistent with the fact that structures previously assumed to be north-directed thrusts are in fact south-directed back-thrusts, and challenges the conventional interpretation of the Juvavic units. The revised structural interpretation in the central Eastern Alps indicates that Late Jurassic contraction was part of a regionally-coherent system of deformation (over 100s of kilometers).

Furthermore, Late Jurassic deformation is observed to form a temporal continuum with Early Cretaceous, that was eventually sealed by the Gosau Gp sediments. We therefore propose that the Late Jurassic to Early Cretaceous contractional deformation that we document in the Eastern Alps represents the best documented record of the onset of Alpine orogenesis.

How to cite: Fernandez, O., Ortner, H., Sanders, D., and Grasemann, B.: Re-defining early Alpine orogenesis in the ALCAPA domain (Late Jurassic to Early Cretaceous), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21240, https://doi.org/10.5194/egusphere-egu25-21240, 2025.

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