Southern peninsular India preserves records of Late Neoarchean−Early Paleoproterozoic continental building and cratonization. A transect from the Paleoarchean Dharwar Craton to the Neoarchean arc magmatic complex in the Nilgiri Block across the intervening Moyar Suture Zone reveals an arc-accretionary complex composed of banded iron formation (BIF), amphibolite, metatuff, garnet-kyanite schist, metagabbro, pyroxenite and charnockite. Here we investigate the petrology, geochronology and petrogenesis of the pyroxenite and garnet-clinopyroxenite. The pyroxenite is mainly composed of orthopyroxene and clinopyroxene with local domains/pockets enriched in a clinopyroxene-garnet assemblage. Thermobarometric calculations and phase equilibria modeling suggest that the orthopyroxene- and clinopyroxene-rich domains formed at 900–1000 °C, 1−1.2 GPa whereas the garnet- and clinopyroxene-rich domains record higher pressure of about 1.8−2 GPa at similar temperature conditions (900−1000 °C). Zircon U–Pb SHRIMP dating show weighted mean 207Pb–206Pb age of 2532 ± 22 Ma, with metamorphic overgrowth at 2520 ± 27 Ma and 2478 ± 27 Ma. We propose a tectonic model involving decoupling and break-off of the oceanic plate along the southern flanks of the Dharwar Craton, which initiated oceanic plate subduction. Slab melting eventually built the Nilgiri volcanic arc on top of the over-riding plate along the flanks of the Dharwar Craton. Our study supports an active plate tectonic regime at the end of the Archean Era, aiding in the growth of paleo-continents and their assembly into stable cratons.
Bibliographical noteFunding Information:
We thank Editor-in-Chief Prof. Marco Scambelluri and two anonymous referees for constructive comments which improved our manuscript. This research was supported by the 2017R1A6A1A07015374 (Multidisciplinary study for assessment of large earthquake potentials in the Korean Peninsula) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT , Korea to V. O. S, and 2015R1D1A1A09058914 to S. Kwon. V.O.S. also thank the Ministry of Earth Sciences, Government of India, project MoES/P.O. (Geosci)/26/2014 for providing funds for fieldwork, laboratory consumables, and geochemical analysis. This manuscript is also supported by Ministry of Earth Sciences , Government of India project MoES/P.O. (Geosci)/26/2014 to K. Sajeev.
© 2018 Elsevier B.V.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology