MAJOR AND TRACE ELEMENT GEOCHEMISTRY AND PB-ND ISOTOPES OF MAFIC DYKES, DHARWAR CRATON, INDIA

Much of the story of Earth’s Precambrian evolution can be unraveled through geochemical examination of Archean cratons and the intrusive bodies they host. The Dharwar Craton (Peninsular India) was formed through pulses of felsic plutonism and accompanying volcano-sedimentary deposition at 3.45-3.30 Ga, 3.23-3.15 Ga, 3.00-2.96 Ga, 2.70-2.60 Ga, and 2.56-2.52 Ga. The preserved crust is primarily of tonalite-trondhjemite-granodiorite (TTG) composition with interspersed greenstone belts. Both assemblages were intermittently intruded by swarms of mafic material at 2.37 Ga, 2.21 Ga, 2.18 Ga, 2.08 Ga, 1.89 Ga, 1.79 Ga, and 1.1-1.0 Ga in the Eastern Dharwar Craton (EDC). The N-S trending 2.53-2.52 Ga Closepet batholith that divides the craton into eastern and western blocks also marks the transition from felsic to mafic-dominated crustal generation in EDC. We examine this transition through major and trace element geochemistry and Pb and Nd isotope data from mafic-ultramafic dykes with ages of 2.37 Ga, 1.89 Ga, 1.79 Ga, and 1.1-1.0 Ga. The dykes range in composition from mafic to ultramafic, with MgO contents from 6-22%, and are variably altered, as indicated by sericitized plagioclase, chloritization of mafic minerals, and the presence of pyrrhotite. Chondrite-normalized REE patterns for the entire suite show remarkable similarities (given the timespan of emplacement) with LREE enrichment and flat HREE profiles, consistent with an arc-signature possibly derived from metasomatized Archean mantle lithosphere. However, primitive melt modelling for contemporaneous dykes within the Dharwar Craton have been interpreted to indicate a potential plume influence (Pandey and Chalapathi Rao, 2019).