Abstract:
The Dharwar Craton in southern peninsular India incorporates well developed Meso-Neoarchean greenstone terranes where komatiite-tholeiite and picrite-boninite-Nb-enriched basalt-high Mg-andesite- and adakite are well-preserved. These lithological associations and their geochemical and geochronological features offer important insights on mantle plume and subduction zone processes in the early Earth. The juxtaposition of these lithounits in most of the greenstone belts of western (WDC) and eastern (EDC) sectors of the Dharwar Craton attests to plume-arc accretion, generation of continental lithosphere and related mineral deposits. The iron and manganese deposits of the greenstone belts of WDC endorse the oxygenated protooceans and biogeochemical processes that are evidenced through the stromatolitic carbonates/cherts. The larger greenstone terranes of WDC and their gradual transition into smaller and fragmented belts appear to reflect a gradual change from plume-arc to arc-continent collision and the Archean higher geothermal gradient. The smaller plates and large number of subduction zones provided ideal setting for the generation of major metallic mineral deposits of Cu, Pb, Zn and Au. The shallow to deeper shelf environment became suitable loci for the deposition of iron and manganese formations. Secular cooling of the mantle was accompanied by a transition from stagnant lid tectonics to rapid development of plate tectonics from 3.5-2.0 Ga with a peak of mantle plumes, crustal growth, BIF deposition and gold mineralization in the greenstone terranes of the Dharwar Craton. The transition from mantle plume activity to subduction zone tectonics recorded in the greenstone belt lithologies of WDC and EDC provide insights into the thermal and tectonic transition in our planet during Archean.
