Role of aqueous fluids during low pressure partial melting of pelites in the Adamello pluton contact aureole (Italy)

The contact aureole of the Adamello pluton (Italy) exhibits a rare combination of pelitic rocks anatexis around a shallow metaluminous pluton and formation of interconnected leucosomes, aplites and small lithium and cesium-enriched pegmatitic bodies. Contact metamorphic mineral assemblages are described in the non-graphitic pelites and psammites hosting the pluton in the central sector of the Adamello Massif. Three metamorphic zones are identified on the field: I – Muscovite-Biotite, II – Andalusite-Sillimanite-K feldspar, III – Melt zone. In the melt zone, the presence or absence of high temperature Crd defines two types of migmatites, a Crd-bearing metatexite characterized by orbicular textures and a Crd-absent stromatic metatexite. Peak P-T metamorphic conditions in the Adamello pluton thermal aureole were calculated at 690–700 °C and 3 kbar on the basis of phase equilibria and geothermobarometry. Phase equilibria modelling reveals that Crd-bearing migmatites, which produced around ...