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
Enakshi Das, Subrata Karmakar, Anindita Dey, Shreya Karmakar, Pulak Sengupta, 2017. "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", Crustal Evolution of India and Antarctica: The Supercontinent Connection, N. C. Pant, S. Dasgupta
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A 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
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The Proterozoic aeon involved at least three major continental readjustments. India and Antarctica appear in most models of supercontinent reconstructions, but their relative position has been the subject of debate. High-resolution petrological and geochronological data, especially from the Proterozoic mobile belts, provide the principal means of resolving this issue. The ice-covered nature of Antarctica allows only limited access to the rocks, and then only in coastal tracts, so detailed studies in more accessible Proterozoic terrains in India assume added significance.
This volume, a follow-up to the XII International Symposium on Antarctic Earth Science, Goa (a SCAR symposium), provides new data from selected locations in east Antarctica (Enderby Land and Dronning Maud Land) and from India, including the Eastern Ghats Mobile Belt (EGMB), Chota Nagpur Gneissic Complex, the Khasi Hills and the Aravalli–Delhi Mobile Belt. The presented geochronological data, constrained by petrological studies, are expected to provide new insights, especially into the EGMB–east Antarctica connection and the rate of continental readjustments in the post-Rodinia break-up.