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Detrital chromian spinels in Rhenohercynian greywackes and sandstones (Givetian–Visean, Variscides, Germany) as indicators of ultramafic source rocks

Published online by Cambridge University Press:  01 July 1999

MARTIN GANSSLOSER
Affiliation:
Institut für Geowissenschaften der TU Braunschweig, Postfach 3329, D-38023 Braunschweig, Germany

Abstract

More than 75% of heavy mineral spectra of Rhenohercynian greywackes from the Harz Mountains (Famennian–Visean), the Werra greywacke (Frasnian–Famennian) and the Rhenish Slate Mountains (Frasnian–Visean) contain small amounts of detrital chromian spinels. Similar grains have also been proven in sandstones of the Givetian Stiege beds (East Harz nappe). These sandstones are derived from the area of the Mid German Crystalline Rise, which is commonly interpreted as the source area of the Rhenohercynian greywackes. Microprobe analyses have revealed mainly a picotite composition. Presumable source rocks were chiefly Alpine-type peridotites. Due to the onset of spinel sedimentation in Givetian times, these peridotites must be at least partly of pre-Givetian age, and are assumed to be linked to Cadomian subduction. Potential source rocks are not exposed in the present outcrops of the Mid German Crystalline Rise nor in the Rhenohercynian zone or the Northern Phyllite zone, which implies that the presumed mafic to ultramafic lithologies were completely eroded and/or downfaulted during later stages of the Variscan orogeny.

Type
Research Article
Copyright
© 1999 Cambridge University Press

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