Petrological evolution of a suite of spinel granulites from Vizianagram, Eastern Ghats Belt, India, and genesis of sapphirine-bearing assemblages

Abstract

A suite of spinel-cordierite granulites from Viziangram, Eastern Ghats Belt, India preserve mineral assemblages and reaction textures indicative of peak metamorphic conditions of >1000 °C, >8<10 kbar, followed successively by near isobaric cooling (down to 750-800 °C), near isothermal decompression (to 4-5 kbar), and late hydration. P-T conditions of each stage are evaluated through a combination of petrogenetic grid approach and thermobarometry. Sapphirine is developed in sillimanite-bearing acid pegmatite veins that intruded the spinel-cordierite granulite close to peak metamorphic conditions, and also in the host rock in immediate contact with the pegmatite. Both sillimanite and sapphirine in the pegmatite are considered to be magmatic phases. Field observations and textural characteristics suggest that Al-metasomatism of the spinel-cordierite granulite due to the intrusion of pegmatite was responsible for sapphirine formation in the spinel granulite.