Reaction textures, pressure–temperature paths and chemical dates of monazite from a new suite of sapphirine–spinel granulites from parts of the Eastern Ghats Province, India: insights into the final amalgamation of India and East Antarctica during the formation of Rodinia

Abstract

AbstractA suite of Mg–Al granulites from two new localities in the Eastern Ghats Province are investigated to put constraints on: (a) the thermal and baric evolution of these rocks; (b) the timing of high-grade metamorphisms (chemical dating of monazite); (c) the tectonic setting where the high-grade metamorphisms occurred; and (d) a possible link between India and East Antarctica during the formation of the Rodinia supercontinent. Supporting the proposition of polymetamorphism over single metamorphism, our study documents at least two distinct phases of high-grade metamorphism that occurred in two contrasting tectonic settings. Reconstructed pristine spinel composition from oxide aggregates, the Al content of coronitic orthopyroxene over sapphirine and spinel, and the constraints of the FeO–MgO–Al2O3–SiO2 (FMAS) topology in the FMAS system document temperatures in excess of 1070°C at 8–9 kbar pressure (>1100°C GPa−1). This study shows that such an extreme metamorphic condition was reached along a counter-clockwise P–T trajectory presumably in an extensional setting at approximately 1.2 Ga. The eventual collision of India and East Antarctica reworked the near-isobarically cooled assemblages of the first event, and triggered exhumation of the former lower crust to the upper-crustal depth along a steeply decompressive trajectory during the formation of the Rodinia supercontinent (c. 0.95–0.90 Ga).Supplementary material: Representative electron microprobe analyses of monazite in wt%, calculated apparent ages and ±2σ error are available at https://doi.org/10.6084/m9.figshare.c.3771044