Contrasting tectono-metamorphic evolutions during Pre-Alpine within the Southern Steep Belt (Central Alps)

In the Southern Steep Belt of the Italian Central Alps relicts of the pre-Alpine continental crust are exposed and preserve their structures and mineral associations. Between Valtellina (SO) and Val Camonica (BS) a polymetamorphic rock association occurs, belonging to the Upper Austroalpine units, which includes lithotypes from the Languard - Campo nappe (LCN) and the Tonale Series (TS). Rocks belonging to LCN and TS are low to medium grade muscovite-, biotite- and minor staurolite-bearing gneisses and micaschists with interlayered garnet- and biotite-bearing amphibolites, marbles, quartzites and pegmatites, sillimanite-bearing gneisses and micaschists. Post-Variscan (Permian) intrusives (granitoids, diorites and minor gabbros) occur. The tectono-metamorphic evolutions reconstructed for these rock associations, permit the distinction of two contrasting tectono-metamorphic units (UTM), pre-dating Permian intrusives. In this contribution we will discuss the geodynamic significance of these UTMs in the framework of the Variscan- Permian collision to extensional setting.