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
We investigated high-grade gneiss from the Daltonganj region of the Chhotanagpur Granite Gneiss Complex (CGGC) in eastern India. EPMA monazite dating from the Daltonganj region revealed three age domains at ca. 1434, ca. 978, and ca. 850 Ma, which have been interpreted as the protolithic age and two metamorphic stages of high-grade gneisses, respectively. The Grt1 + Chl + Amp1 + Bt assemblages are thought to represent the first metamorphism as a pre-peak stage of high-grade gneiss, which could have occurred after ∼1434 Ma. The peak metamorphic stage is defined by relict porphyroblasts of orthopyroxene and garnet2 formed during ∼978 Ma in a burial process followed by an isothermal decompression or post-peak stage represented by a Crd + Grt3 + Amp3 assemblage at ∼850 Ma. The P-T conditions estimated for the pre-peak, peak, and post-peak stages using the NCKFMASH model system are 6.6-6.8 kbar/635-645°C, 8.65-9.42 kbar/772-788°C, and 5.71-6.18 kbar/745-762°C, respectively. The geochronology and metamorphic conditions define a clockwise P-T-t path for the high-grade gneiss, indicating that rocks experienced high-pressure conditions during burial metamorphism at subduction-related tectonic activity, followed by an isothermal decompression condition after the gneissic unit was exhumed. The geochemical composition of the high-grade gneiss reveals that the protolith is calc-alkaline basaltic magma formed in an island arc setting and that the restitic features of the gneisses developed after granitic melt segregation.
'%3e%3ccircle r='20' fill='%23008'/%3e%3ccircle r='17.5' fill='%23fff'/%3e%3ccircle r='3.5' fill='%23008'/%3e%3cg id='d'%3e%3cg id='c'%3e%3cg id='b'%3e%3cg id='a' fill='%23008'%3e%3ccircle r='.875' transform='rotate(7.5 -8.75 133.5)'/%3e%3cpath d='M0 17.5.6 7 0 2l-.6 5L0 17.5z'/%3e%3c/g%3e%3cuse xlink:href='%23a' transform='rotate(15)'/%3e%3c/g%3e%3cuse xlink:href='%23b' transform='rotate(30)'/%3e%3c/g%3e%3cuse xlink:href='%23c' transform='rotate(60)'/%3e%3c/g%3e%3cuse xlink:href='%23d' transform='rotate(120)'/%3e%3cuse xlink:href='%23d' transform='rotate(-120)'/%3e%3c/g%3e%3c/svg%3e)
'%3e%3ccircle r='120' fill='%230f47af'/%3e%3cg id='a'%3e%3cpath fill='%23fcdd09' d='m0-96-4.206 12.944 17.348 53.39h-23.13l-2.599 8h74.163l11.011-8H21.553z'/%3e%3cpath stroke='%23fcdd09' stroke-width='4' d='m25.863-35.597 30.564-42.069'/%3e%3c/g%3e%3cuse xlink:href='%23a' transform='rotate(72)'/%3e%3cuse xlink:href='%23a' transform='rotate(144)'/%3e%3cuse xlink:href='%23a' transform='rotate(216)'/%3e%3cuse xlink:href='%23a' transform='rotate(288)'/%3e%3c/g%3e%3c/svg%3e)
