Origin of post-collisional A-type granites in the Mahakoshal Supracrustal Belt, Central Indian Tectonic Zone, India: Zircon U-Pb ages and geochemical evidences

Abstract

There are several A-type granitic plutons in the central and western parts of the Mahakoshal Supracrustal Belt (MSB), India. We report new whole-rock elemental and Nd isotope data along with zircon U-Pb ages on these granites. The ID-TIMS zircon U-Pb ages of these granites are 1645 ± 25 Ma, 1695 ± 9 Ma, and 1796 ± 17 Ma. These granites are metaluminous to weakly peraluminous, alkali-calcic to calc-alkalic and ferroan in composition. They are characterized by enrichment in REEs (except Eu) and HFSEs (Zr, Y), and depletion in LILEs (Ba, Sr). They have high Ga/Al (2.6–5.4) ratios and elevated magmatic temperatures (≥900 °C). Elemental ratios such as Y/Nb, Nb/Ta, Th/Nb, La/Nb and Ce/Pb coupled with negative Nb, Sr, Eu, and Ti anomalies suggest their derivation from crustal sources. They have very low εNd(t) values (−11.4 to −5.6) and older Nd model ages (TDM: 2481–3225 Ma) confirming their crustal derivation. We propose that partial melting of the Archean tonalitic-granodioritic crust of basement Bundelkhand Craton in low-pressure high-temperature conditions generated the parental magma of these granites. Their A2-type affinity (Y/Nb < 1.2) further suggests their emplacement in an extensional environment related to post-collisional tectonic setting.