Petrogenesis and U[sbnd]Pb geochronology of charnockites flanking the Pranhita Godavari rift in peninsular India-link between the Bastar and Eastern Dharwar Cratons

Abstract

Charnockites constitute an integral component of granulite belts exposed on the northern and southern flanks of the Godavari rift, which marks the contact between the Bastar and Eastern Dharwar cratons in peninsular India. In this study, we attempt to constrain the petrogenesis of granulites from Gondpipri, Bhopalpatnam on the northern flank and Karimnagar on the southern flank of the Pranhita-Godavari valley using petrography, mineral and whole-rock geochemistry, fluid inclusion studies, and UPb zircon geochronology. The presence of relict magmatic textures and orthopyroxene chemistry is suggestive of an igneous protolith while CO2-rich fluid inclusions in quartz correspond to subsequent granulite-facies overprint. Geochemically, charnockites from both granulite belts are metaluminous, magnesian, and calc-alkaline, having similar Sr and Y concentrations, Rb/Sr, Sr/Y, LaN/SmN, GdN/YbN, and Eu/Eu* ratios, and positive BaPb and negative Nb-Ta-Ti anomalies. Zircons in charnockites from both granulite belts furnish magmatic crystallization ages of ~2.5 Ga (UPb isotope) and also record a metamorphic overprint at ca. 2473 Ma. The similarity in protolith composition and UPb ages of zircons in charnockites on the northern and southern flanks of the Godavari rift suggest that they constitute a cogenetic and coeval suite emplaced at ~2.5 Ga in an undivided and continuous Palaeo-Mesoarchean landmass that included the Bastar and Eastern Dharwar cratons, possibly as a part of the Ur-supercontinent. This undivided landmass subsequently got split along the Pranhita-Godavari rift zone into the Bastar and Dharwar cratons. The rift valley eventually developed into a sedimentary basin hosting the Proterozoic and Gondwana Group of sediments sequentially, apparently separating the two cratons on the map.