Giant Plagioclase basalts from north-eastern part of Deccan Volcanic Province, India

The giant plagioclase basalts (GPBs) with plagioclase phenocrysts that reach up to 3 cm in length are found near Jabalpur in the north-eastern part of the Deccan Volcanic Province (DVP). The thickness of the basalt flow that contains the GPBs is ~20 m. This contribution presents mineral chemistry and whole rock geochemistry of the GPBs. This new occurrence of GPBs has implications for existence of local crustal magma chambers, feeders and vents in the north-eastern part of the DVP. The GPBs contain large (0.5-3 cm long) phenocrysts of plagioclase (An58-An64) in a fine grained matrix consisting of plagioclase, augite, Fe-Ti oxide minerals and glass. The plagioclase phenorysts display normal zoning and corroded borders and contain abundant, small post-crystallisation melt inclusions. Also included within large plagioclase grains are small rounded grains of plagioclase with different compositions (up to three generations). Some plagioclase crystals show resorption and reverse zoning. Single crystals show core to rim variations of up to 10% An. All these disequilibrium features in the GPBs reflect magma mixing, recharge and complex convection effects in a magma chamber.