Carboniferous high-pressure metamorphism of Ordovician protoliths in the Argentera Massif (Italy), Southern European Variscan belt

The age of high-pressure metamorphism is crucial to identify a suitable tectonic model for the vast Variscan orogeny. Banded HP granulites from the Gesso-Stura Terrain in the Argentera Massif, Italy, have been recently described (Ferrando at al, 2008) relicts of high-pressure metamorphism in the western part of the Variscan orogen. Bulk rock chemistry of representative lithologies reveals intermediate silica contents and calc-alkaline affinity of the various cumulate layers. Enrichment in incompatible elements denotes a significant crustal component in line with intrusion during Ordovician rifting Magmatic zircon cores from a PI-rich layer yield scattered ages indicating a minimum protolith age of 486 +/- 7 Ma Carboniferous zircons (340.7 +/- 4.2 and 336.3 +/- 4.1 Ma) are found in a Pl-rich and a Pl-poor layer, respectively. Their zoning, chemical composition (low Th/U, flat HREE pattern and Thin-zircon temperature) and deformation indicate that they formed during the high-pressure event before decompression and mylonitisation The proposed age for high-pressure metamorphism in the Argentera Massif proves that subduction preceded anatexis by less than 20 Ma. The new data allow a first-order comparison with the Bohemian Massif. which is located at the eastern termination of the Variscan orogen Similarities in evolution at either end of the orogen support a Himalayan-type tectonic model for the entire European Variscides (C) 2010 Elsevier B.V All rights reserved