Late stage differential exhumation of crustal blocks in the central Eastern Alps: evidence from fission track and (U–Th)/He thermochronology

Abstract

Thermal history modelling based on zircon‐ and apatite fission track and apatite (U–Th)/He data constrain and refine the near‐surface exhumation of the south‐eastern Tauern Window (Penninic units) and neighbouring Austroalpine basement units in the Eastern Alps. Fast exhumation on both sides of the Penninic/Austroalpine boundary coincides with a period of lateral extrusion and tectonic denudation of the Penninic units in Miocene time (22–12 Ma). The jump to older ages occurs within the Austroalpine unit along the Polinik fault, which therefore defines the boundary between the tectonically denuded units and the hangingwall at that time. According to the different (U–Th)/He ages between the Penninic Hochalm‐ and Sonnblick Domes we demonstrate a differential cooling history of these two domes in the latest Miocene and early Pliocene.

Cretaceous to Miocene cooling of Austroalpine units southeast of the Tauern Window (Eastern Alps) constrained by multi-system thermochronometry

“…With the advance of low-temperature thermochronology since the late 80´s, a growing number of zircon and apatite fission track data (ZFT and AFT, respectively) helped to resolve processes in the deeper levels of the upper crust (e.g. Wagner et al, 1977;Grundmann and Morteani, 1985;Staufenberg, 1987;Hejl, 1997Hejl, , 1998Dunkl et al, 2003;Foeken et al, 2007;Wölfler et al, 2008Wölfler et al, , 2012. And finally, the (U-Th)/He methods available since the beginning of this century allowed scientists to track shallow crystal processes operating at temperatures <100C° in the shallowest levels of the upper crust (e.g.…”

“…4). ZFT and AFT ages range from 160 to 60 Ma (Dunkl et al, 2003;Wölfler et al, 2008), and from 30 to 19 Ma, respectively (Staufenberg, 1987;Wölfler et al, 2008) (Fig. 4).…”

“…And finally, the (U-Th)/He methods available since the beginning of this century allowed scientists to track shallow crystal processes operating at temperatures <100C° in the shallowest levels of the upper crust (e.g. Foeken et al, 2007;Glotzbach et al, 2008;Wölfler et al, 2008Wölfler et al, , 2012. One of the major challenges in geochronology is the proper reconstruction of thermal histories from measured data.…”

“…In this study we aim to unravel the yet constrained thermal history of the Polinik and Kreuzeck Blocks (Staufenberg, 1987;Wölfler et al, 2008) -two Austroalpine units to the southeast of the Tauern Window that are bound by steep fault zones. For this purpose we provide an original dataset comprising new Ar/Ar ages on micas and new ZFT-and AFT ages from bedrock samples.…”

“…3), an Upper Austroalpine nappe system, which experienced a metamorphic imprint under high-amphibolite to eclogite facies conditions during the Eo-Alpine metamorphism (Schuster et al 2001Schmid et al, 2004). Published geochronological data from the Polinik Block include Creta-_______________________ ___ ceous K/Ar-and Ar/Ar ages (~127 to ~67 Ma) on white mica and biotite (Oxburgh et al, 1966;Lambert, 1970;Hoke, 1990;Dekant, 2009), ZFT ages of ~45 to ~30 Ma, AFT ages of ~23 to ~7 Ma and apatite (U-Th)/He ages of ~17 to ~11 Ma (Dunkl et al, 2003;Staufenberg, 1987;Wölfler et al, 2008) (Fig. 4).…”