Diverse signatures of deformation, pressure-temperature and anatexis in the Rayagada sector of the Eastern Ghats granulite terrane

The granulites and granitoids around Rayagada in the north central part of the Eastern Ghats belt display structural and petrological differences when compared to similar rocks from Chilka and Jenapore in the northern Eastern Ghats. The impress of F-1 deformation is almost erased while that of F-3 i s muted. The metapelites have a restricted chemical range and are non-migma titic. There are two varieties of leptynitic granitoids, one of which is in terlayered with yet another S-type granite containing cordierite. The maxim um recorded temperature from geothermometers is 780 degreesC, but the magni tude of pressure is comparatively low, the highest value being 6.3kbar. Ano ther distinctive feature of the pressure-temperature record is the absence of evidence of decompression in the lower realms of pressure and temperatur e. Metamorphic reactions that could be identified indicate cooling, a notew orthy reaction being the sillimanite to andalusite transformation. Integrat ion of data from pressure-temperature sensors suggest cooling at two pressu res, 6 and 5 kbar. The generation of two types of granitoids from metapelit es is interpreted to be due to intersection with solidus curves for pelitic and graywacke-like compositions, constrained by recent experiments, at 6 a nd 5 kbar. The first melting occurred on a prograde path while the second o ne was due to increase in temperature during exhumation at tectonic rates. Thus inspite of a broad similarity in the geodynamic scenario across the no rthern part of the Eastern Ghat belt, differences in exhumation rates and i n style of melting were responsible for producing different signatures in t he Rayagada granulite terrane.