I Metasedimenti della Zona Ivrea-Verbano nell'area di Premosello (Val d'Ossola).

In the Ossola Valley the exposed lower continental crust (i.e. the Ivrea Zone) is made of a metasedimentary sequence intruded by sills of mafic and ultramafic rocks. The metasediments studied here are located in the westernmost part of the Ivrea Zone, close to the Insubric line. They are metapelites, with minor meta-arenites and meta-greywackes, metamorphosed under granulite facies conditions. In the granulites five types of mineral assemblages can be distinguished. Whole-rock chemistry indicate that associations with very abundant grt+sil are strongly SiO2-depleted and enriched in relatively refractory elements (Mg, Fe, Al, Ti) and garnet-compatible elements (Y, Nb). These rocks are believed to be the residue left after the extraction of large amount of granitoid melts. Recent experimental results are used to constrain our residual mineral assemblages.