Zircon U-Pb age and petrogenetic constraints on granitic magmatism from the southwestern Chhotanagpur Granite Gneiss Complex: Implications for Proterozoic crustal growth in the Central India

Abstract

The Chhotanagpur Granite Gneiss Complex (CGGC) is an integral part of the Central Indian Tectonic Zone (CITZ), which records the Proterozoic tectono-thermal evolution of the Indian Shield. In this study, we carried out detailed petrography, bulk rock geochemistry, Nd isotopic studies and U-Pb zircon geochronology for granitoids from the southwestern CGGC. Four episodes of granitic magmatism from this area are documented, which are (i) c. 1660 Ma granite gneiss, (ii) c. 1565 Ma foliated granite, (iii) c. 1462 Ma porphyritic granite, and (iv) c. 1140 Ma equigranular granite. The c. 1660 Ma granite gneisses are migmatitic, I-type, and their Nd isotopic compositions are mildly sub-chondritic (εNd_(t) = –0.90 to –2.55). The geochemical characteristics suggest them sourced from mafic to intermediate sources with inputs from pre-existing crustal rocks. The c. 1565 Ma foliated granites are peraluminous, S-type, and have evolved Nd isotopic composition (εNd_(t) = –2.40 to –4.69) with Mesoarchean model ages, which suggests their derivation from a metasedimentary source. The c. 1462 Ma porphyritic granite and c. 1140 Ma equigranular granites have geochemical attributes similar to the A₂-type granites. The strongly evolved Nd isotopic signatures (εNd_(t) = –4.39 to –5.38 and –6.81 to –8.38) for porphyritic granite and equigranular granite, respectively, suggest inputs from both enriched mantle and pre-existing crustal sources. Based on these findings, the Proterozoic evolution of the CGGC can be broadly divided into four stages, with stages 1 and 2 corresponding to c. 1660–1565 Ma arc magmatism, where the granite gneisses were emplaced, followed by the emplacement of foliated granites in the waning stage. Stage 3 corresponds to the emplacement of c. 1462 Ma A-type granites associated with the extensional environment. Stage 4 is associated with post-collisional setting where the c. 1140 Ma equigranular granites were formed. The presence of recrystallized zircon domains with c. 900–1000 Ma in all granitoid variants supports widespread Grenvillian high-grade metamorphism in the CITZ. These results suggest that granitoids from the southwestern CGGC exhibit a transitional tectonic regime with an initial arc followed by extensional tectonics, culminating in a post-collisional environment, possibly linked with the breakup of Columbia and the amalgamation of Rodinia supercontinents.