Petrogenesis of Amgaon Gneiss, northwestern part of Bastar Craton

Harshwardhan, . (2023) Petrogenesis of Amgaon Gneiss, northwestern part of Bastar Craton. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Harshwardhan (18MS052)) Thesis_18MS052.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

The Archean-Proterozoic boundary witnessed several important geological events, such as the production of voluminous different types of granitoids followed by the stabilisation of many cratons. However, the processes involved in crust formation in this transitional period are still much debated in the academic community. Therefore, to understand the crustal evolution mechanism at this transitional boundary, the rocks of this period are one of the key tools. The Amgaon Gneiss situated on the northwestern margin of Bastar Craton is one of the major rock units formed at this time. Even though being of such geological importance, only a few studies have been done on these rocks. From my study, I have witnessed that Amgaon Gneiss contains majorly two types of gneisses- i. granitoid gneisses and ii. mafic gneisses. This petro-mineralogical and geochemical study also revealed that granitoid gneisses are majorly potassic with some being sodic. Sodic Amgaon granitoids gneisses formed by the melting at deeper crustal depth as evident by depleted HREE pattern along with no Eu anamoly. In contrast, the potassic Amgaon granitoids gneiss formed by the melting at Shallower crustal depth as evident by enriched HREE pattern along with distinct negative Eu anamoly. Zilmili mafic gneisses are formed by melting chondritic mantle at shallow depth as evident by the flat REE pattern.

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