New insights on the evolution of the Dharwar Craton from paleomagnetic and geochemical data

Abstract:

Proterozoic mafic dykes are unique recorders of the geological evolution of their host cratons. Elemental and isotopic geochemical data provide information on tectonomagmatic settings, crust-mantle interactions, and the general timing of formation, stabilization, and alteration of cratons. Paleomagnetic data combined with U-Pb geochronology provides information on cratonic movement through time. We consider these geochemical and paleomagnetic relations in the context of the Archean to Proterozoic history of the Dharwar Craton in southern India, where TTG and greenstone upper crust was intruded by mafic dykes at 2.37-2.36 Ga, 2.26-2.25 Ga, 2.22-2.18 Ga, 2.08 Ga, 1.89-1.88 Ga, 1.86 Ga, 1.84 Ga, 1.79 Ga, 1.19 Ga, and 1.14-1.08 Ga. Primitive mantle normalized trace element patterns for these dykes show consistent LREE enrichment and HFSE depletion, resulting from derivation from an enriched mantle source and/or crustal contamination during magma ascent and emplacement. Elemental geochemical data and Pb and Nd isotopic data suggest a common derivation from metasomatized Archean mantle lithosphere. The wide geographic distribution of many of the Dharwar Craton dyke swarms and coeval dykes in other Indian cratons indicate that the swarms were likely indicative of regional-scale episodes of extension rather than a result of post-orogenic relaxation. The Dharwar Craton’s robust paleomagnetic dataset allows determination of its paleoposition, tectonic setting, and correlation with other cratons in the Columbia and Rodinia supercontinents. Through a match with paleomagnetic data from the Aravalli – Bundelkhand Craton, the Dharwar Craton data suggest that modern Peninsular India coalesced by ~1.0 Ga, which is synchronous with estimates from metamorphic events.