Compositional changes during fractionation of felsic granites from western Tasmania, Australia

Geochemical and Sr isotopic signatures of Late Devonian to Early Carboniferous granites of western Tasmania indicate they were derived from four main source rocks, two metaluminous (I-type Housetop and Meredith Suites) and two peraluminous (S-type Pieman and Interview Suites). All granites are felsic with SiO₂ greater than 70%, and show fractionation trends indicating fractionation near the ternary minimum in the Ab-Q-Kf system. The behaviour of trace elements during the fractionation is dependent on the alumina saturation index and oxygen fugacity of the magmas. In the oxidised metaluminous Housetop Suite Rb, Th and Y, and possibly Nb and U are incompatible. The weakly metaluminous Meredith Suite has only Rb, Y and U incompatible. Rb, Nb, Sn and U are incompatible in the weakly peraluminous Pieman Suite, and in the strongly peraluminous Interview Suite P₂O₅, Rb, Nb, Sn, and U are incompatible.