Geochemistry of 2.21 Ga giant radiating dyke swarm from the Western Dharwar Craton, India: Implications for petrogenesis and tectonic evolution

Abstract

The Western Dharwar Craton (WDC) exhibits numerous exposures of NNW–SSE to NW–SE trending mafic dykes. Geochemistry of four 2.21 Ga NNW–NW trending dykes and 21 other similar trending dykes provides new insights into the geochemical behaviour, mantle source characteristics, and tectonic history of mafic magmatic event, which have also affected the Eastern Dharwar Craton (EDC). Based on modal mineralogy and texture, these dykes can be classified into dolerite, olivine dolerite, gabbro, and olivine gabbro. They show basaltic to basaltic‐andesitic composition and have sub‐alkaline tholeiitic nature. LaN/LuN ratio classifies the dykes into two groups: Group I, with values close to 2, shows relatively flat REE patterns while, Group II, with values 4–6, has inclined REE patterns. In general, both groups show LREE enrichment and most of the samples exhibit negative Nb–Ta and Ti anomalies, indicating crustal contamination. However, negative Zr–Hf anomaly and low Th/Nb values (0.14–0.73) noticed within the samples preclude significant crustal inputs. Petrogenetic modelling using batch melting equation suggests that the dykes fractionated from two distinct mantle melts and had slightly different sources, both within the spinel–garnet transition zone. The overall composition of these 2.21 Ga dykes is consistent with a mantle plume‐induced heterogeneous source that was previously modified by some ancient subduction event. Coeval dykes from EDC exhibit similar geochemical behaviour, mantle source characteristics, and tectonic history. These and other synchronous dykes from distant cratons, viz. Superior, Slave, Greenland, represent a 2.21 Ga large igneous province event, which is linked with the Sclavia/Superia supercraton.