A GIANT RADIATING DYKE SWARM IN THE DHARWAR CRATON, SOUTHERN INDIA: IMPLICATIONS FOR PALEOPROTEROZOIC CONTINENTAL RECONSTRUCTIONS

New high precision U-Pb ages on baddeleyite, together with new paleomagnetic data have been obtained from the NE-trending Karimnagar mafic dyke swarm, Dharwar craton, India. The results establish that the dykes are the same age as the 2367 Ma Bangalore swarm which was previously identified from high precision U-Pb dating across a more southerly expanse of the Dharwar craton. Our new data now define a single swarm (the Dharwar Giant Dyke Swarm, DGDS) occurring over an area of 140,000 km². A total of six U-Pb ages on these dykes are identical within error and suggest emplacement of this swarm within a geologically short time span of ~5 Myr or less. A systematic southward progression in the trend of dykes, from N48^oE to N128^oE, defines a fan angle of about 80^o with convergence to a focal point about 300 km west of the present-day Dharwar craton boundary, resulting in a spectacular radiating dyke swarm extending across the entire eastern Dharwar craton. The large areal extent, radiating dyke pattern and short duration imply a mantle plume origin for the DGDS. Dykes of this swarm are characterized primarily by plagioclase-pyroxene assemblages, and lack olivine. Despite their large aerial distribution, all dykes of the craton-wide DGDS are subalkaline tholeiites displaying general geochemical coherence. Although the Karimnagar dykes appear to be magnetically overprinted, some dykes carry the same remanence direction as that of the primary magnetization in the Bangalore dykes.