Evolution of Austro-Alpine and Upper Penninic Basement in the Northwestern Alps from Variscan Convergence to Post-Variscan Extension

摘要: The oldest protoliths of the Austro-Alpine nappe system from Western Alps consist intimate association metapelites, tholeiitic metabasites and marbles which closely recalls lithology metamorphic evolution lower crustal section South-Alpine Ivrea-Verbano kinzigitic complex. This may tentatively be interpreted as an Early Palaeozoic accretionary wedge, later deformed, thermally reworked consolidated during collisional Variscan orogeny; it was further characterized by Permian igneous underplating, low-P/high-T re-equilibration production anatectic melts. Similar high-T paragneisses are also in Penninic Monte Rosa Gran Paradiso nappes, although lesser amounts mafic rocks especially recorded here; likewise basement displays a late cordierite-rich