Fluid evolution in the Closepet granite: a magmatic source for CO₂ in Charnockite formation at Kabbaldurga?

Abstract

Fluid inclusion studies in the Closepet granite reveal the common occurrence of trapped fluids which show melting temperatures and laser excited Raman spectral-characteristics close to those for pure CO₂. The quartz-bound inclusions in this polyphase intrusive define two major genetic categories: an earlier CO₂-rich fluid with only minor traces of water and a late mixed carbonic-aqueous fluid. Compelling evidence for fluid immiscibility is preserved by coexisting inclusions with widely varying filling ratios and similar filling temperatures. Salinities upto 10 wt per cent NaCl are estimated from microthermometry, which ascribe relatively higher temperatures for fluid immiscihility in the CO₂-H₂O system. Our results indicate that this late Archaean granite body which truncates regional metamorphic isograds has probably been a major carrier of CO₂-rich volatiles, subsolidus exsolution and channelisation of which along structural locales caused incipient dehydration and the formation of Kabbaldurga-type arrested granulites in many adjacent localities. Our model seeks to associate advective transfer of both heat and volatiles required for dehydration with the Closepet magma.