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, India, shows contrasting prograde assemblages of extremely aluminous orthopyroxene+cordierite+sapphirine and similarly aluminous orthopyroxene+Ti-rich spinel in closely associated domains. Textural and compositional characteristics indicate that both were derived from prograde dehydration-melting of biotite-plagioclase-quartz-bearing protoliths. The former assemblage was stabilized at relatively more magnesian bulk composition. Geothermobarometric data and petrogenetic grid considerations place 'peak' metamorphic conditions at c. 950 degrees C and 9 kbar. Subsequent to peak metamorphism, the rocks 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.