Trace element geochemistry of parts of the Closepet granite, Mysore State, India

Abstract

Trace elements in twenty samples of the Closepet granite (grey and pink varieties) and the related rocks have been determined by neutron activation analysis (Th, Rb, and Cs), fluorometry (U), flame-photometry (K), and emission spectroscopy (Pb, Sr). The trace element contents of the grey and pink varieties are generally similar. An analysis of the magnitudes of the trace element and other ratios (K/Rb, 235; Th/U, 6.4; U/K (Ø 10⁶), 0.7; K/Cs (Ø10^-4), 3.6; Th/K (Ø10⁴), 5.3; Fe₂O₃/(FeO +Fe₂O3), 0.27) as well as ⁸⁷Sr/⁸⁶Sr initial ratio (0.705; Crawford, 1969) of the Closepet granite indicate two possible modes of genesis : Either the granite magma was not highly differentiated and the vapour phase was relatively insignificant; the crystallization of the magma took place under essentially non-oxidizing conditions; the pink variety, which followed the grey variety, crystallized under essentially the same conditions as the grey variety. Or the Closepet granite had a two-stage history--palingenesis (starting from the Peninsular gneiss) and metasomatism involving the enrichment in K, Rb, Pb, and Th and depletion of Sr and Cs, among others.