Geochemistry of ~2.08 Ga radiating mafic dyke swarm from the Dharwar Craton, India, and their implications on initiation of the Cuddapah Basin.

A spectacular chain of radiating mafic dykes with precise Pb–Pb and U–Pb baddeleyite ages (~2087–2080 Ma) are reported from the Dharwar Craton, southern India. These radiating dykes are spatially disposed over an extent of 70,000 km2 and flank the northern and western flanks of the Cuddapah Basin in the Eastern Dharwar Craton. Here, we present the geochemical results of four precisely dated dykes and 15 similar trending dykes (N134ºW–N28ºE), which gives first insight into the geochemical behaviour, mantle source characteristics, and geodynamic history of the mafic magmatic event at ~2.08 Ga. Field observations, mineralogy and textures classify them as fine to coarse-grained dolerites, exhibiting insignificant post-magmatic alterations. Basaltic komatiite to high-Fe tholeiitic character, variation in Mg-number (Mg#) (50–75) and crystallisation trends suggest their primary to evolved nature. Enriched light rare earth element (LREE) patterns, negative Nb–Ti anomalies and moderate Th/Nb values (0.5–0.7) in few samples suggest crustal input in the genesis. Petrogenetic modelling using batch melting equation and elemental proxies (La/Yb, Dy/Yb) indicate derivation of these dykes from a heterogeneous spinel to spinel-garnet lherzolitic source. The study postulates that a mantle plume activity at ~2.08 Ga, led to mantle upwelling, causing domal uplift beneath the Cuddapah Basin and emplacement of the Cuddapah dyke swarm (~2.08 Ga). This magmatism was followed by crustal extension and thinning, supervened by thermal relaxation and subsidence, that ultimately led to the formation of the Cuddapah Basin. Several geophysical surveys also concur a high-density material peculiar to a mafic volcanic province present beneath the southwest Cuddapah Basin. The Cuddapah dyke swarm is coeval with Fort Frances dykes, Cauchon Lake dykes and Lac Esprit dykes of the Superior Craton, but their paleolatitudes and geochemical behaviour do not represent an obvious match for the two cratons. The study highlights the significant role of ~2.08 Ga mafic dyke swarm in the evolution of the Cuddapah Basin. [ABSTRACT FROM AUTHOR]