COUPLING LOW-TEMPERATURE THERMOCHRONOMETRY AND SEQUENTIAL RESTORATION OF BALANCED CROSS-SECTIONS: NEW CONSTRAINTS ON THE TECTONIC EVOLUTION OF THE WESTERN CARPATHIANS (POLAND, SLOVAKIA AND UKRAINE)

The tectonic evolution of the Western Carpathian belt has been studied for a long time but remains a matter of debate. This thrust and fold belt formed after the collision between the European Platform and the Alcapa and Tisza-Dacia microplates from the Late Jurassic up to the Neogene. According to the most common interpretation, subduction of the oceanic lithosphere started 30 My ago and came to a stop when the Carpathian accretionary wedge collided with the European Platform. The subsequent asthenospheric upwelling drove the opening of the Pannonian Basin in the retro-wedge position. We tested this scenario using FetKin, a finite element solver that takes as input a series of balanced cross-sections. It solves the heat flow equations in 2D together with the predicted thermochronometric ages, which can be compared to the measured data. This software provides a level of detail that allows for the investigation of samples in very complex structural setting. Moreover, the spatial distribution of burial depths, cooling ages and the rate of exhumation were correlated with the heat flow, topographic relief, crustal and lithospheric thickness. The non-homogeneous burial and exhumation history suggests that different exhumation processes controlled the latest stages of the Carpathian evolution. In particular, the data unravel that in the western area exhumation was mainly produced by erosion during the thrusting stage. In the central sector, exhumation was mainly due to post-thrusting tectonic denudation. The easternmost area was likely affected by a post-thrusting exhumation associated with the uplift of the accretionary wedge. The data show no progressive younging of cooling ages toward the SE, that are instead predicted by models involving the lateral propagation of a slab tear. Furthermore, the integration of the above-mentioned thermal indicators with the geophysical parameters and structural data suggests that there is no evidence for subduction. The opening of the Pannonian basin, being coeval with the latest stages of shortening in the Outer Carpathians, could be triggered by the gravitational instability of the lithospheric mantle recorded under this region.