Geochemistry and Phase Equilibrium Modelling of Garnet-Biotite Gneiss from Mauranipur, Bundelkhand Craton, Northern India: Implication for Tectonic Setting and Metamorphism

Abstract

The Mauranipur region is situated along the central part of the Bundelkhand Craton (BuC) in the northern Indian shield, which consists of garnet- biotite gneisses with various deformational structures in the form of folding, faulting, augen and tail structures. These deformation structures are tectonic imprints that reveal the tectonic nature of the garnet-biotite gneisses. The groundmass of Grt-Bt gneisses is characterized by presence of garnet, biotite, plagioclase, K-feldspar, quartz, and ilmenite. The phase equilibrium modelling and geochemical attributes depict the tectonic activity and metamorphic evolution of the studied rocks. The P-T pseudosection has been calculated in the NCKFMASHT system, which revealed that the peak mineral assemblage stabilized in the P-T range of 6.35–6.75 kbar and 755–780ºC, and it further goes to retrograde metamorphism under P-T condition ranging from 4.80–5.28 kbar and 718–735ºC. These gneisses represent a calc-alkaline to high-K calc-alkaline series of protolithic origin. The negative anomaly of Nb and Ti for all samples indicates that a subduction tectonic setting has occurred in the BuC. The (La/Lu)N ratio and differences in the trace elements indicate heterogeneous sources and large variation in the degree of partial melting. The Y vs Nb and (Y+Nb) vs Rb tectonic discrimination diagrams indicate that the Grt-Bt gneisses have an affinity towards the volcanic arc granite and developed during subduction setting. The geochemical interpretation provides significant evidence that protoliths of Grt-Bt gneisses were further metamorphosed by the continent-continent collision. Keywords: Garnet-biotite gneiss, Pseudosection, P-T condition, Geochemistry, Bundelkhand