Age of younger tonalitic magmatism and granulitic metamorphism in the South Indian transition zone (Krishnagiri area); comparison with older Peninsular gneisses from the Gorur-Hassan area

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Peucat, J.J. and Mahabaleswar, B. and Jayananda, M. (1993) Age of younger tonalitic magmatism and granulitic metamorphism in the South Indian transition zone (Krishnagiri area); comparison with older Peninsular gneisses from the Gorur-Hassan area. Journal of Metamorphic Geology, 11 (6). pp. 879-888. ISSN 0263-4929

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Official URL: https://doi.org/10.1111/j.1525-1314.1993.tb00197.x

Abstract

A major episode of continental crust formation, associated with granulite facies metamorphism, occurred at 2.55-2.51 Ga and was related to accretional processes of juvenile crust. Dating of tonalitic-trondhjemitic, granitic gneisses and charnockites from the Krishnagiri area of South India indicates that magmatic protoliths are 2550-2530+/-5Ma, as shown by both U-Pb and Pb-207/Pb-206 single zircon methods. Monazite ages indicate high temperatures of cooling corresponding to conditions close to granulite facies metamorphism at 2510+/-10 Ma. These data provide precise time constraints and Sr-Nd isotopes confirm the existence of late tonalitic-granodioritic juvenile gneisses at 2550 Ma. Pb single zircon ages from the older Peninsular gneisses (Gorur-Hassan area) are in agreement with some previous Sr ages and range between 3200+/-20 and 3328+/-10 Ma. These gneisses were derived from a 3.3-3.5-Ga mantle source as indicated from Nd isotopes. They did not participate significantly in the genesis of the 2.55-Ga juvenile magmas. All these data, together with previous work, suggest that the 2.51-Ga granulite facies metamorphism occurred near the contact of the ancient Peninsular gneisses and the 2.55-2.52-Ga 'juvenile' tonalitic-trondhjemitic terranes during synaccretional processes (subduction, mantle plume?). Rb-Sr biotite ages between 2060 and 2340 Ma indicate late cooling probably related to the dextral major east-west shearing which displaced the 2.5-Ga juvenile terranes toward the west.

Item Type: Article
Uncontrolled Keywords: juvenile tonalitic magmas; syn- to post-accretional granulites; 2550-2510 Ma; U-Pb, Sr, Nd isotopes.
Subjects: Faculty of Science > Earth Sciences > Geology
Divisions: Jnana Bharathi / Central College Campus > Department of Geology
Depositing User: Ms. Sathyavathi N
Date Deposited: 25 Oct 2016 09:37
Last Modified: 25 Oct 2016 09:37
URI: http://eprints-bangaloreuniversity.in/id/eprint/6998

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