The role of Upper Permian evaporites in the Mesozoic structural evolution of the northeastern part of the Transdanubian Range Unit

The Transdanubian Range Unit (TRU) forms a thick-skinned nappe within the Eastern Alpine–Western Carpathian orogenic wedge. It is composed of Variscan low-grade metamorphic formations overlain by a Permian to Cenozoic non-metamorphic succession. The northeastern part of the TRU displays several distinctive features: (1) the base of the Permian–Mesozoic succession includes Upper Permian evaporites, which are absent in the central and southwestern parts of the unit; (2) Upper Triassic platform carbonates, deposited along the Neotethyan passive margin, are disrupted by narrow, long-lived intra-platform basins in the northeast of the area; and (3) the Cretaceous fold-and-thrust structures in this region exhibit different orientations and geometries compared to those in the central and southwestern TRU.

Our work is based on field geology, borehole and geophysical data and archive studies. Based on this dataset, the pre-Cenozoic geological map of the study area and three geological cross-sections were constructed, providing new insights into the structural evolution of the region.

According to our model, the Upper Permian evaporites played a key role in the Mesozoic structural evolution of the study area. The narrow Late Triassic basins of the north-eastern TRU developed in the hanging walls of NW–SE-striking normal faults that detached within the Permian evaporites. The development of these faults is interpreted to be related to gravity-driven gliding along the passive margin of the Neotethys Ocean.

We suggest that a south-vergent thin-skinned fold-and-thrust belt developed in the northeastern part of the Transdanubian Range Unit above a relatively shallow detachment level within the Permian evaporites during the Cretaceous (Barremian–Cenomanian). We propose that the local, oblique, NW–SE-striking thrusts formed due to oblique inversion of Triassic normal faults.

The general E–W strike of thrusts and fault-related folds observed in the study area differs from the NE–SW strike typical for the central part of the Transdanubian Range Unit. We interpret this curvature of the compressional structures as a detachment-controlled salient. Based on this model, the thrust sheets underwent larger tectonic transport in the northeastern part of the TRU where Permian evaporites provided a basal detachment, compared to the central and southwestern parts of the unit where such ductile detachment was absent. This interpretation implies vertical axis rotation of the northeastern part of the TRU compared to its central part. The different rotation of the two parts of the unit is supported by Jurassic and Cretaceous paleomagnetic data compiled by Márton et al. (2025), while Late Triassic paleomagnetic data are inconsistent with it, highlighting the need for further investigation. Due to the Late Cretaceous growth of the Western Carpathian orogenic retro-wedge, the thin-skinned fold-and-thrust belt of the study area was re-folded by thick-skinned structures that also deformed the Variscan basement.