GEMOC ARC National Key Centre

Lian-Kun Sha¹, Bruce W. Chappell²

1 Department of Geology, ANU

2 GEMOC ANU

The contribution of feldspars to the whole-rock phosphorus budget of I- and S-type granites from the Lachlan Fold Belt (LFB) has been quantitatively estimated based on the analysis of P contents of plagioclase, K-feldspar and the host granites. The contribution increases exponentially with decreasing CaO and increasing SiO2 contents of granites. In the most mafic I-type granites, the maximum contribution is relatively small, ranging upwards from around 1% to 5%, and increases to higher values in the more felsic rocks. In the S-type granites, feldspars contribute a significant amount, ~ 10% to 50%, to the whole-rock P budget of the most mafic rocks, with the remainder mainly hosted in apatite. In felsic I- and S-type granites containing < 1% to 2% CaO, all of which are peraluminous, feldspars become the dominant P reservoir and can contain over 94% of the whole-rock P abundances.