Detrital rutile chemistry and U/Pb geochronology for tracking loess provenance in Austria

Gábor Újvári1, Urs Klötzli2, Franz Kiraly2, Theodoros Ntaflos2
1 Geodetic and Geophysical Institute of the RCAES, HAS
2 Department of Lithospheric Research, University of Vienna

V 2.9 in Löss und terrestrische Archive (Fortsetzung)

18.09.2012, 15:10-15:30, H8



Previous studies on detrital rutiles in sandstones demonstrated that rutile trace element geochemistry (especially Cr and Nb contents) and Zr-in-rutile thermometry may yield diagnostic data on the lithology and metamorphic facies of possible source rocks. U-Pb geochronology of detrital rutiles is as yet rare in spite of its potential to date metamorphic events, thereby yielding useful information for provenance analysis. In this study we provide the first trace element and U-Pb data from detrital rutiles separated from loess in Austria and analyzed by EPMA and LA-MC-ICP-MS. Cr and Nb data clearly show that the majority (70-73%) of the rutiles are from metapelitic sources, ca. 9-14% from metamafic rocks, while the rest cannot be unambiguously attributed to any of these sources. Rutiles in loess sampled close to the Alps (Wels section) generally displayed lower metamorphic temperatures (580-650 °C) compared to those found in proximity to the Bohemian Massif (Krems, Stratzing profiles). The rutile U-Pb ages from loess at Krems cluster around 345-370 Ma. These ages, together with the calculated metamorphic temperatures of 700-850 °C, strongly favour a Bohemian Massif granulitic source for many of the detrital rutiles in loess of this region, whereas the lower temperatures found for the other samples clearly reflect Alpine amphibolite-grade metamorphic conditions.

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Letzte Änderung 07.08.2012