Breakup of the Neoarchean supercontinent Kenorland: Evidence from zircon and baddeleyite U-Pb ages of LIP-related mafic dykes in the Coorg Block, southern India

The Coorg Block in southern Peninsular India is one of the oldest crustal blocks on Earth that preserves the evidence for continental crust formation during the Paleo-Mesoarchean through subduction-related arc magmatism, followed by granulite facies metamorphism in the Mesoarchean. In this study, we report for the first time, the ‘bar codes’ of a major Paleoproterozoic Large Igneous Province in the Coorg Block through the finding of mafic dyke swarms. The gabbroic dykes from the Coorg Block, dominantly composed of plagioclase-pyroxene assemblage, show a restricted range in SiO₂ values of 50.04–51.27 wt.%, and exhibit a sub-alkaline tholeiitic nature. These rocks show relatively flat LREE and constant HREE patterns and lack obvious Eu anomalies. Trace element modeling suggests that the dyke swarm was fed from a melt that originated at a shallow mantle level in the spinel stability field. Zircon grains are rare in the gabbro samples and those separated from two samples yielded ²⁰⁷Pb/²⁰⁶Pb weighted mean dates of 2214 ±12 Ma and 2221 ±7 Ma. The grains show magmatic features with depleted LREE and enriched HREE and positive Ce and negative Eu anomalies. Baddeleyite grains were dated from five gabbro samples which yielded ²⁰⁷Pb/²⁰⁶Pb weighted mean ages ranging between 2217 ±7 Ma and 2228 ±10 Ma. The combined data show a clear age peak at ca. 2.2 Ga. The mafic dykes in the Coorg Block show geochemical similarities with ca. 2.2 Ga mafic dyke swarms in different regions of the Dharwar and other cratons in Peninsular India and elsewhere on the globe. The data also support the inference that the global mafic magmatism at ca. 2.2 Ga was linked with intracontinental rifting of the Archean cratons through mantle upwelling or plume activity. We correlate the mafic dyke swarms in the Coorg Block with attempted rifting of the Neoarchean supercontinent Kenorland.