The long-lasting exhumation history of the tztal-Stubai Complex (Eastern European Alps): New constraints from zircon (U-Th)/He age-elevation profiles and thermo-kinematic modeling

The Eastern European Alps formed during two orogenic cycles, which took place in the Cretaceous and Cenozoic, respectively. In the tztal-Stubai Complex a thrust sheet of Variscan basement and Permo-Mesozoic cover rocks the record of the first (Eoalpine) orogeny is well preserved, because during the second (Alpine) orogeny the complex remained largely undeformed. We use new zircon (U-Th)/He (ZHe) ages and thermo-kinematic modeling to constrain the cooling and exhumation history of the central part of the tztal-Stubai Complex since the Late Cretaceous. The ZHe ages from two elevation profiles increase over a vertical distance of 1500 m from 563 to 693Ma (Stubaital) and from 502 to 714Ma (Kaunertal), respectively (Hlzer et al., accepted by Lithosphere). These ZHe ages and few published zircon and apatite fission track ages were used for inverse thermo-kinematic modeling. The modeling results show that the age data are well reproduced with a three-phase exhumation history. A first phase with relatively fast exhumation (~250 m/Myr) during the Late Cretaceous ended at ~70 Ma and is interpreted to reflect the erosion of the Eoalpine mountain belt. As Late Cretaceous normal faults occur at the margins of the tztal-Stubai Complex, normal faulting may have also contributed to the exhumation of the study area. Subsequently, a long period with slow exhumation (<10m/Myr) prevailed until ~16 Ma. This long-lasting phase of slow exhumation suggests a rather low topography with little relief in the tztal-Stubai Complex until the mid-Miocene, even though the Alpine orogeny had already begun in the Eocene with the subduction of the European continental margin. Accelerated exhumation since the mid-Miocene (~230 m/Myr) is interpreted to reflect the erosion of the mountain belt, due to the development of high topography in front of the Adriatic indenter and repeated glaciations during the Quaternary.