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

Abstract

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 provides evidence for a burial depth of at least 6 km for the samples, which were totally reset. Burial was not deeper than 11 km, since the zircon fission-track system was not reset. The RDFZ represents an accretionary wedge with 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 European continental margin sediments. In the east, where three nappes (Greifenstein, Kahlenberg and Laab nappes) can be distinguished, the exhumation started between Late Oligocene and Early Miocene. The Kahlenberg and Laab nappes show total resetting of the apatite FT ages, while in the Greifenstein nappe there is only partial resetting. According to a new paleogeographic reconstruction, the Kahlenberg and Laab nappes were placed on top of the Greifenstein nappe by an out-ofsequence thrust.

Albian microfossils in the calcarenite limestone from Dopplerhütte and Tulbingerkogel quarries (Northern Zone of the Rhenodanubian Flysch Zone, eastern Austria)

“…Picha et al (2006) pointed out, that the Wolfpassing Formation shows similarities to the Hluk Formation from the Bile Karpaty Unit (Magura Nappe) of Barremian -Albian age which is made up by black shales, marls and bioclastic limestones with cherts. The Bile Karpaty Unit is regarded as a prolongation of the Laab Nappe (Eliáš et al, 1990;Picha et al, 2006), however according to Oberhauser (1995), Trautwein et al (2001) and Mattern and Wang (2008) this unit may have been originally situated north of the Greifenstein Nappe.…”

Out-of-sequence thrusts and paleogeography of the Rhenodanubian Flysch Belt (Eastern Alps) revisited

“…A traditional view implies diverticulation of the Kahlenberg nappe to a degree that its northern part became isolated from the rest of the Fig. 3 Stratigraphy of the ERF, mainly drawn after Trautwein et al (2001b) on the basis of Prey (1980), Plöchinger and Prey (1974), Egger (1995), and Faupl (1996). Agsbach Member, Greifenstein Fm.…”

“…1 Study area (after Mattern 1997;Trautwein et al 2001b) with Rhenodanubian nappes. The Ü ntschen nappe represents a basin segment paleogeographically south of the Sigiswang nappe because outliers of flysch rocks north of the Ü ntschen nappe display basal structures similar to the hanging-wall ramp geometry of the Sigiswang nappe (Mattern 1999) Fig.…”

“…and Trautwein et al (2001b) independently concluded that the Western and Eastern Rhenodanubian Flysch (WRF/ERF, Fig. 1), respectively, contain out-of-sequence thrusts.…”

“…The thickness of individual thrust nappes measures 1-3 km. The flysch was overthrust mainly by Austroalpine nappes during the Eocene (Trautwein et al 2001b). The Helvetic thrust units and the Molasse foreland basin were overthrust by the flysch until the Early Miocene (Decker et al 1993).…”