Long-lived mantle plume for the emplacement of Paleoproterozoic Dharwar-Bastar Large Igneous Province: Geochemical and SrNd isotope constraints from mafic rocks of Dharwar craton, India

Abstract

A Paleoproterozoic large igneous province (LIP) has been identified between ∼1.89–1.85 Ga with evidence of precise U-Pb/Pb-Pb baddeleyite geochronology and spread over Dharwar, Bastar and Yilgarn cratons. Here, we present whole rock geochemistry and Sr, Nd isotopic results for the first time on precisely dated two disparate mafic dyke/sill swarms (∼1.89 Ga and ∼1.86 Ga) from the Dharwar craton to identify their mantle source signatures and emplacement mechanism. The majority of the samples from both swarms indicate basaltic composition and sub-alkaline tholeiitic nature. The ∼1.89 Ga and ∼1.86 Ga dykes exhibit enriched LREE and flat HREE patterns. Both swarms show LILE enrichment and negative Nb, Ta, and Ti anomalies, indicating that crustal components were involved in the generation of these dykes. Based on the batch melting model, the ∼1.89 Ga and ∼1.86 Ga swarms show varying degrees of partial melting (5–15% and 5–10%, respectively) and are emplaced from a shallower spinel lherzolitic source. The ∼1.89 Ga swarm is characterized by sub-chondritic Nd isotopic nature (_ƐNd_{(1.89 Ga)}=−8.9 to −3.1), while ∼1.86 Ga swarm decipher sub-chondritic to slight super chondritic Nd isotopic signatures (_ƐNd_{(1.86 Ga)}=−5.8 to +2.2). The correlation of Nd isotopic data with coeval mafic dykes from the Bastar and Yilgarn cratons indicates that the Dharwar and Bastar dykes originated from the partial melting of enriched subcontinental lithospheric mantle (SCLM), while Yilgarn dykes from the depleted SCLM during their emplacement at ∼1.89 Ga. Based on precise ages, dyke geometry, geochemical and Sr, Nd isotopic results of ∼1.89 to ∼1.85 Ga mafic events, the Indian dykes (Dharwar and Bastar cratons) and Western Australian dykes (Yilgarn craton) display different geochemical and isotopic characteristics, suggesting that these mafic events were emplaced in two separate pulses from a common plume source.