Occurrence of granulite facies metamorphosed Archean cratonic rock in the Terrane Boundary Shear Zone: Implication for the Bastar craton unthrusting beneath the Eastern Ghats Belt

Fanthogs, Stanzin (2022) Occurrence of granulite facies metamorphosed Archean cratonic rock in the Terrane Boundary Shear Zone: Implication for the Bastar craton unthrusting beneath the Eastern Ghats Belt. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Stanzin Fanthogs (17MS190)) 17MS190_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (4MB)

Abstract

Eastern Ghats Belt is a Proterozoic mobile belt and Bastar craton is an Archean craton. Both sutured along the Terrane Boundary Shear Zone (TBSZ). Major rocks in TBSZ are charnockites, mafic granulite, leptynite, metapelites and Sapphirine bearing pelites. The garnet bearing charnockites are of Archean age. This thesis presents the detailed study of petrography and major element geochemistry of the granites of the Bastar craton and garnet bearing charnockite of Terrane boundary Shear Zone (TBSZ). Granite is classified into 2 types that is pegmatoidal granite and biotite hornblende granite both have similar minerology but differ in modal proportion of hydrous minerals like biotite and hornblende. The mineral assemblage of the granite is quartz + plagioclase +K-feldspar ± biotite ± amphibole and of garnet bearing charnockite is garnet + orthopyroxene + quartz + plagioclase + K-feldspar ± biotite ± amphibole. The garnet bearing charnockite have biotite inclusion in the garnet that suggest for biotite dehydration melting to form high grade minerals like garnet. For biotite dehydration melting the source rock should have biotite and the rocks near to TBSZ is only the biotite hornblende granite. In the Fe* plot and MALI plots the biotite hornblende garnet plots very near to garnet bearing charnockite and both are A type granites suggesting their compositional similarity. From recent papers it has shown that garnet bearing charnockite have undergone high pressure granulite facies metamorphism. To attain high pressure temperature condition the adjacent craton rocks that is biotite hornblende granite have to underthrust beneath the Eastern Ghats Belt. From the above discussion we conclude that the Bastar craton have been underthrusted beneath the Eastern Ghats Belt.

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