Tectonomagmatic evolution of the Bastar craton of Indian shield through plume-arc interaction: evidence from geochemistry of the mafic and felsic volcanic rocks of Sonakhan greenstone belt

Md. Erfan Ali Mondal, and Mahshar Raza

The Sonakhan Group of Bastar craton of the central Indian shield comprises volcano-sedimentary rocks. The lower part of this belt, referred to as Baghmara Formation, consists of two distinct units of volcanic associations: (1) the lower unit consisting entirely of mafic volcanic rocks of basaltic composition and (2) the upper unit comprising volcanic rocks of basalt-andesite-dacite-rhyolite (BADR) series. The geochemical characteristics of the lower unit basalts include tholeiitic nature with depletion in highly incompatible elements, Nb-maxima (Nb/Nb* = 0.93-1.48, relative to Th and La) and near flat rare earth element patterns. These metabasalts are distinguished as plume- related oceanic plateau basalt. The upper unit volcanic rocks are mafic, intermediate to felsic in composition with island arc geochemical signatures including enrichment in highly incompatible elements, large negative high field strength element anomalies, depletion of Nb (Nb/Nb* = 0.10-0.68) relative to Th and La and light rare earth element enrichment patterns. Field relationships in combination with geochemical characteristics of the Sonakhan Group reveal the co-existence of plume generated oceanic plateau basalts and island arc related volcanic rocks. It is proposed that the geodynamic evolution of Sonakhan greenstone belt initiated with the formation of a plume generated thickened, hot, buoyant oceanic plateau. This plateau served as a base for subduction of oceanic crust at its margin producing subduction-related mafic and felsic melts in an island arc setting. Our study reveals that Sonakhan greenstone belt of Bastar craton evolved by plume-arc interaction.