Zircon U–Pb SHRIMP and monazite EPMA U–Th–total Pb geochronology of granulites of the western boundary, Eastern Ghats Belt, India: a new possibility for Neoproterozoic exhumation history
A. Chatterjee, K. Das, S. Bose, P. Ganguly, H. Hidaka, 2017. "Zircon U–Pb SHRIMP and monazite EPMA U–Th–total Pb geochronology of granulites of the western boundary, Eastern Ghats Belt, India: a new possibility for Neoproterozoic exhumation history", Crustal Evolution of India and Antarctica: The Supercontinent Connection, N. C. Pant, S. Dasgupta
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We present detailed and high-precision geochronological data on granulites occurring along the western boundary of the Eastern Ghats Belt, India. Age data on systematically sampled rocks coupled with geochemical observation have a potential to unravel the overprinted tectonothermal events operated during Precambrian time. Zircon U–Pb SHRIMP and monazite electron probe microanalysis (EPMA) U–Th–total Pb analyses, chemical zoning, microtextural investigation, and pressure–temperature calculations were carried out on samples of four different rock types. Inherited zircons from migmatitic quartzofeldspathic gneiss and mafic granulite yielded ages of approximately 2900–2350 Ma, representing an older crustal component. The age of granulite metamorphism recorded from charnockite and pelitic granulite ranges between approximately 950 and 930 Ma (from zircon and monazite). A possible decompression event from this area that occurred during Rodinia break-up is recorded from the Y-rich zones of monazite closely associated with porphyroblastic garnet in pelitic granulite and dates from approximately 800 to 750 Ma. Zircon grains of charnockite also yield a similar age. The youngest age of approximately 525–510 Ma documented from the monazite grains of migmatitic quartzofeldspathic gneiss and pelitic granulite, along with a spot age from zircon of migmatitic quartzofeldspathic gneiss, testifies to the final assembly of East Antarctica with cratonic India as a part of East Gondwana.
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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.