Petrogenesis of post-orogenic Lower Permian andesites in southern Europe: insights into the collapse of the Variscan range

In the post-Variscan Early Permian deposits of southwestern Europe, andesites belong to successions characterized by the constant occurrence of a basal rhyolite ignimbrite, followed by andesites, and by abundant dacite-rhyodacite products, interbedded with lacustrine sediments. The subalkaline andesite to K-andesite volcanism developed within intramontane basins following the collapse of the Variscan orogen. The compositional features, including trace element ratios and initial Sr (and Nd) of post-Variscan intermediate products allow excluding continental or island arc settings. The andesite composition of Lower Permian lavas was reproduced starting from two potential primary magmas: picrobasaltic and enriched MORB compositions. In particular, the picrobasalt was modified, by adding incremental amounts of a felsic granulite, from the lower continental crust. Mixing and fractional crystallization (MFC) were modelled by the MELTS software in a closed system under isobaric, isenthalpic conditions (P= 0.3 GPa). The computed residual liquid evolves to match closely the composition of Lower Permian andesite lavas after similar to 34% crystallization by adding similar to 27% of contaminant to the parental magma. (C) 2008 Lavoisier SAS. All rights reserved