Accretionary history of the Rhenodanubian flysch zone in the Eastern Alps - evidence from apatite fission-track geochronology

The thermotectonic evolution of the East Alpine Rhenodanubian flysch zone ( RDFZ) and the collisional history along the orogenic front is reconstructed using apatite fission-track (FT) thermochronology. The apatite FT data pro vides evidence for a burial depth of at least 6 km for the samples, which w ere totally reset. Burial was not deeper than 11 km, since the zircon fissi on-track system was not reset. The RDFZ represents an accretionary wedge wi th a complex burial and cooling history due to successive and differential accretion and exhumation. The sedimentary sequences were deposited along a convergent margin, where accretion started before Maastrichtian and lasted until Miocene. Accretion propagated from a central area (Salzburg-Ybbsitz) both to the west and to the east. In the west, accretion lasted from Middle Eocene to Early Oligocene, reflecting underplating of the RDFZ by the Euro pean continental margin sediments. In the east, where three nappes (Greifen stein, Kahlenberg and Laab nappes) can be distinguished, the exhumation sta rted between Late Oligocene and Early Miocene. The Kahlenberg and Laab napp es show total resetting of the apatite FT ages, while in the Greifenstein n appe there is only partial resetting. According to a new paleogeographic re construction, the Kahlenberg and Laab nappes were placed on top of the Grei fenstein nappe by an out-of-sequence thrust.