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Episodes 2021; 44(4): 443-466

Published online December 1, 2021

https://doi.org/10.18814/epiiugs/2020/020096

Copyright © International Union of Geological Sciences.

Characterization of multiple episodes of melt generation from lower crust during Archaean using amphibole composition

Kumar Batuk Joshi1, Nilanjana Sorcar1*, Naresh Chandra Pant2, V. Nandakumar1, Talat Ahmad2,3, J. K. Tomson1

1ESSO-National Centre for Earth Science Studies, Thiruvananthapuram, Kerala, India
2Department of Geology, University of Delhi, Delhi, India
3Vice Chancellors Office, University of Kashmir, Srinagar, India

Correspondence to:E-mail: nilageo83@gmail.com

Received: June 24, 2020; Revised: November 18, 2020; Accepted: November 18, 2020

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Spatial association of tonalite trondhjemite granodiorites (TTGs) and high-K granitoids (anatectic and hybrid granites) from the Bundelkhand Craton (BC), Central India, is well known. Geochronological data indicates multiple episodes of formation of these high silica rocks showing a spread of ~1 Ga during Paleo to Neoarchaean. In the present study, we try to understand the evolution of TTGs and high-K granitoids (hybrid granites) from the BC using amphibole composition. The amphibole in both TTGs and high-K granitoids (hybrid granites) from the BC are characterised as magmatic, zoned, and calcic in nature. We find that the amphibole composition of the studied rocks is dominated by magnesiohornblende along with less common occurrence of tschermakite, magnesiohastingsite and edenite. Overall variation in amphibole compositions in terms of exchange vectors show a well defined linear trend (except for a late stage low-grade metamorphic readjustment), which suggests melt control over crystallization and evolution of amphibole chemistry. Moreover, the geothermobarometric analysis points towards higher pressure formation of TTGs in comparison to that of high-K granitoids (hybrid granites), with nearly the same temperature conditions in both the cases. Combining all our findings, we propose the evolution of the two considered rock types through lower crustal melting under varying PH2O conditions at different depths of emplacement

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