Composizione dei Granati in esperimenti di anatessi di rocce crostali.

An experimental study on melting of pelitic rocks shows that garnet is an important residual phase coexisting with peraluminous granitic liquid. At 0.5 GPa garnet is present, but it is less abundant than cordierite. At 0.7 and 0.9 GPa garnet is the prevailing ferromagnesian phase and coexists with biotite and/or spinel, depending on temperature. Garnet compositions vary markedly with temperature and to a smaller extent with pressure. The almandine content decreases with increasing temperature, while pyrope content decreases. The grossular content changes little with temperature and pressure. The spessartine content is pressure-dependent, increasing with pressure decrease. As a consequence, spessartine rich-garnet is stable at 0.5 GPa, within the cordierite stability field. In coexisting garnets and cordierites, XMg of the two phases [XMg = Mg/(Mg+ Fe2+) molar) increases with increasing temperature and pressure, being XMgCordierite > XMgGarnet. Moreover, XMgGarnet is constantly higher than XMgLiquid, with the increasing temperature. This is in contrast with the observation of Ellis D.J. (1986), who finds XMgGarnet < XMgLiquid.