Journal
GEOLOGICAL JOURNAL
Volume 55, Issue 4, Pages 2851-2880Publisher
WILEY
DOI: 10.1002/gj.3552
Keywords
Chotanagpur Granite Gneiss Complex; East Indian shield; pelitic granulite; phase equilibria modelling; supercontinental cycle; Th-U-total Pb monazite dating; U-Pb zircon dating
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Funding
- Fund for Centre of Advanced Studies (Phase VI)
- Fund for Improvement of Science and Technology (FIST-Phase II)
- Fund for Promotion of University Research and Scientific Excellence
- Council of Scientific and Industrial Research (CSIR)
- University Grants Commission (UGC)
- Rashtriya Uchchattar Shiksha Abhiyan (RUSA 2.0)
- Shyama Prasad Mukherjee (SPM) Research fellowship
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The north-eastern part of the Chotanagpur Granite Gneiss Complex (CGGC) in the East Indian shield contains enclaves of migmatitic pelitic granulites (PG) within felsic orthogneiss (FOG). Field observations, petrology and geochronology (LA-MC-ICP-MS U-Pb dating of zircon and EPMA Th-U-total-Pb dating of monazite) of the PG suggest two distinct metamorphic events. The earliest event M1, which is characterized by high-temperature (>850 degrees C) granulite facies metamorphism, occurred in the timespan of similar to 1680-1580 Ma. Extensive dehydration melting of biotite + sillimanite + quartz-rich protoliths led to stabilization of the restitic assemblage (garnet + alkali-feldspar + quartz + sillimanite + ferrian-ilmenite) together with large volumes of felsic melts (leucosomes). Collisional tectonics followed by delamination and asthenospheric upwelling could have triggered the M1 event. Subsequently, at similar to 1470-1400 Ma, the igneous protolith of the host FOG intruded and hydrated the PG. Thereafter, a second metamorphic event, M2, accompanied by compressional structures, affected both the rock types. A clockwise P-T path that culminated at >= 10 kbar similar to 760-850 degrees C and is followed by a steeply decompressive retrograde path characterizes this event. The P-T path and the inferred geothermal gradient (<27 degrees C/km) are compatible with a continent-continent collisional setting. Geochronological findings suggest a protracted orogeny for the M2 event with its major pulse during similar to 970-950 Ma. When combined with the published information, this study supports the view that a large (if not the entire) portion of the Indian shield and the granulite terranes of east Antarctica share similar tectonothermal events that led to the formation of two supercontinents, Columbia and Rodinia.
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