Evolution of high-Mg-Al granulites from Sunkarametta, Eastern Ghats, India: evidence for a lower crustal heating-cooling trajectory

A suite of high-Mg-Al granulites from Sunkarametta, Eastern Ghats Belt, Ind ia, shows contrasting prograde assemblages of extremely aluminous orthopyro xene+cordierite+sapphirine and similarly aluminous orthopyroxene+Ti-rich sp inel in closely associated domains. Textural and compositional characterist ics indicate that both were derived from prograde dehydration-melting of bi otite-plagioclase-quartz-bearing protoliths. The former assemblage was stab ilized at relatively more magnesian bulk composition. Geothermobarometric d ata and petrogenetic grid considerations place 'peak' metamorphic condition s at c. 950 degrees C and 9 kbar. Subsequent to peak metamorphism, the rock s cooled to c. 700-750 degrees C, with slight lowering of pressure, and the retrograde reactions also involved melt-solid interaction. The inferred P- T trajectory is one of heating-cooling at lower crustal (25-30 km) depths.