The “andesitic” magmatism in the south-western Tyrol and its geodynamic significance

The researches carried out on the recent dyke activity in the south-western Tyrol have revealed a widespread “andesitic” magmatism in the austroalpine realm. The magmatic activity developed at least in two distinct phases; but in this paper we are only concerned with the unmetamorphosed dykes which are younger than the alpine folding. The existence of a calc-alkaline magmatism mainly of the intermediate type, and the occurrence of garnet as the first mineral on the liquidus, imply a very deep origin of such a magmatism, which agrees with the geodynamic models, providing the subduction of oceanic crust recently hypothesized for the Alpine evolution. Regarding the age of dyke activity, very recent radiometric results (K/Ar) testify for the first time in the Alps an “andesitic” magmatism from Upper Cretaceous to Tertiary and suggest both continuous or separate subductive processes from the Upper Cretaceous onwards.