Carbonic fluid inclusions in ultrahigh-temperature granitoids from southern India

Abstract

The granite plutons of Vattamalai (VT), Gangaikondan (GK) and Pathanapuram (PT) intruding granulite facies rocks in southern India were emplaced during the Late Neoproterozoic tectonothermal event. Feldspar thermometry of mesoperthites from the granites yield temperatures of 800–1000 °C indicating high- to ultrahigh-temperature conditions, comparable to similar estimates derived from some of the host granulite facies rocks in the region. This study reports results from a detailed investigation of fluid inclusions in the three granite plutons. Carbonic inclusions characterize the major fluid species in all the cases and their unique abundance in some of these plutons indicates up to 1 wt.% CO2. In most of the cases, the inclusions show a near-pure CO2 composition as deduced from melting temperatures which cluster close to −56.6°C, and as confirmed by laser Raman spectroscopy. The VT granite preserves the highest density CO2 fluids among all the three plutons with a density up to 0.912 g cm−3 (molar volume of 48.25 cm3 mol−1). A combination of CO2 isochores, feldspar thermometry data and dehydration melting curves, and liquidus for water-undersaturated granitic systems clearly bring out a genetic link between these granites and granulitic lower crust. The ultimate origin of the CO2-rich fluids is linked to sub-lithospheric mantle sources through tectonic processes associated with the assembly of the Gondwana supercontinent. To cite this article: M. Santosh et al., C. R. Geoscience 337 (2005).