Phases of enhanced exhumation during the Cretaceous and Cenozoic orogenies in the Eastern European Alps: new insights from thermochronological data and thermokinematic modeling

Wölfler, Andreas; Wolff, Reinhard; Hampel, Andrea; Hetzel, Ralf; Dunkl, István

Zusammenfassung

Austroalpine nappes in the Eastern European Alps have preserved the record of orogenies in the Cretaceous and Cenozoic but their cooling and exhumation history remains poorly constrained. Here we use low-temperature thermochronology and thermokinematic modeling to unravel the exhumation history of the Austroalpine nappes in the Gurktal Alps. Our data reveal marked differences between the exhumation of units located at different positions within the nappe stack and relative to the Adriatic indenter. Units located at a high structural level and farther away from the indenter cooled through the zircon fission track closure temperature in the Late Cretaceous and have resided at depths of ≤5-6 km since the Oligocene, as indicated by apatite fission track ages of 35-30 Ma. Thermokinematic modeling constrained that these units experienced enhanced exhumation (~0.60 km/Ma) between ~99 and ~83 Ma due to syn- to late-orogenic Late Cretaceous extension. After a phase of slow exhumation (~0.02 km/Ma), the exhumation rate increased to ~0.16 km/Ma at ~34 Ma due to the onset of the Europe-Adria collision. In contrast, zircon fission track ages from units at a lower structural level and near the indenter indicate cooling during the Eocene; apatite fission track ages cluster at ~15 Ma. These units were rapidly exhumed (~0.76 km/Ma) from ~44 Ma to ~39 Ma during an Eocene phase of shortening prior to the Europe-Adria collision. After slow exhumation (~0.13 km/Ma) between ~39 and ~18 Ma, the exhumation rate increased to ~0.27 km/Ma in the wake of Miocene escape tectonics in the Eastern Alps.