Tectonic Evolution of the Eastern Southern Alps (Italy): A Reappraisal From New Structural Data and Geochronological Constraints

Abstract

The Eastern Southern Alps fold-and-thrust belt (ESA) is part of the seismically active S-verging retro-wedge of the European Alps. Its temporal tectonic evolution during continental shortening has so far been constrained by few and low-resolution indirect time constraints. Aiming at better elucidating the ESA spatiotemporal evolution, we gathered new structural and geochronological data from two regional thrust systems: the innermost south verging Valsugana Thrust (VT) and the more external Belluno Thrust System (BTS). Field work allowed us to constrain the geometry and kinematics of those thrusts and related folds and informed our sampling strategy to carry out fault gouge K-Ar and tectonic carbonate U-Pb dating from representative samples structurally associated with the VT and BTS. Our results suggest that the VT was active already in the Late Cretaceous (between ∼78 and 76 Ma) in response to far-field stresses, with repeated reactivation continuing to the Late Miocene (∼6 Ma). The BTS recorded two distinct deformation events during the Oligocene (∼30 Ma) and at the Oligocene-Miocene boundary (∼23 Ma). The VT was active for ∼72 Myr and partly acted during out-of-sequence thrusting. Based on regional correlations, we propose that the ESA share a similar spatiotemporal deformation history with the central Southern Alps farther to the west. We suggest a conceptual regional tectonic model wherein multiple, broadly coeval deformation events occurred in the entire Southern Alps during their long-lived orogenic deformation in response to generally continuous NW-SE shortening.