Relationship between 2.37 Ga Boninitic Dyke Swarms of Indian Shield: Evidence from the Central Bastar Craton and NE Dharwar Craton
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2018
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The Indian Shield is cross-cut by a number of distinct Paleoproterozoic mafic dyke swarms. The density of mafic dyke swarms in the Dharwar and Bastar Cratons is amongst the highest on Earth. Globally, Proterozoic boninitic (high SiO2 and MgO, low TiO2) dyke swarms are rare compared to tholeiitic dyke swarms and yet they are common within the Southern Indian Shield. In this study, the geochronology and geochemical results were used to constrain the petrogenesis and relationship of the boninitic dyke in the central Bastar Craton and the NW Dharwar Craton. A single U-Pb baddeleyite age from a boninitic dyke near Bhanupratappur of the Central Bastar Craton yielded a weighted-mean 207Pb/206Pb age of 2365.6 ± 0.9 Ma and is within error of boninitic dykes (2368.5 ± 2.6 Ma; U-Pb, baddeleyite) near Karimnagar and further south near Bangalore (2365.4 ± 1.0 Ma to 2368.6 ± 1.3 Ma; U-Pb, baddeleyite) of the Dharwar Craton. Dykes in both Karimnagar and Bhanupratappur region have boninitic characteristic (SiO2 = 52.9 to 56.1 wt%, MgO = 5.9 to 19.0 wt%, and TiO2 = 0.31 wt% to 0.78 wt%). The Nd isotopes (εNd(t) = –6.4 to +4.5) of the Bhanupratappur dykes are more variable than Karimnagar dykes (εNd(t) = –0.7 to +0.6) but overlap. The variability Nd isotopes may be related to crustal contamination either during fractional crystallization or during emplacement. Rhyolite-MELTS modeling using the least contaminated sample (B/29) indicates that fractional crystallization may partly influence the geochemical variability of the boninitic dykes in these areas. The trace element modeling shows the primary melt may be derived from a pyroxenite mantle source near the spinel-garnet transition zone. The chemical and temporal similarities of the Bhanupratappur dykes with the dykes of the Dharwar Craton (Karimnagar, Dharwar) indicate they are all members of the same giant radiating dyke swarm. It is possible that the dyke swarm was related to a mantle plume which assisted in break-up of an unknown supercontinent. Furthermore, the results indicate that the Bastar and Dharwar Cratons were adjacent but likely had a different configuration before 2.37 Ga.
The Indian Shield is cross-cut by a number of distinct Paleoproterozoic mafic dyke swarms. The density of mafic dyke swarms in the Dharwar and Bastar Cratons is amongst the highest on Earth. Globally, Proterozoic boninitic (high SiO2 and MgO, low TiO2) dyke swarms are rare compared to tholeiitic dyke swarms and yet they are common within the Southern Indian Shield. In this study, the geochronology and geochemical results were used to constrain the petrogenesis and relationship of the boninitic dyke in the central Bastar Craton and the NW Dharwar Craton. A single U-Pb baddeleyite age from a boninitic dyke near Bhanupratappur of the Central Bastar Craton yielded a weighted-mean 207Pb/206Pb age of 2365.6 ± 0.9 Ma and is within error of boninitic dykes (2368.5 ± 2.6 Ma; U-Pb, baddeleyite) near Karimnagar and further south near Bangalore (2365.4 ± 1.0 Ma to 2368.6 ± 1.3 Ma; U-Pb, baddeleyite) of the Dharwar Craton. Dykes in both Karimnagar and Bhanupratappur region have boninitic characteristic (SiO2 = 52.9 to 56.1 wt%, MgO = 5.9 to 19.0 wt%, and TiO2 = 0.31 wt% to 0.78 wt%). The Nd isotopes (εNd(t) = –6.4 to +4.5) of the Bhanupratappur dykes are more variable than Karimnagar dykes (εNd(t) = –0.7 to +0.6) but overlap. The variability Nd isotopes may be related to crustal contamination either during fractional crystallization or during emplacement. Rhyolite-MELTS modeling using the least contaminated sample (B/29) indicates that fractional crystallization may partly influence the geochemical variability of the boninitic dykes in these areas. The trace element modeling shows the primary melt may be derived from a pyroxenite mantle source near the spinel-garnet transition zone. The chemical and temporal similarities of the Bhanupratappur dykes with the dykes of the Dharwar Craton (Karimnagar, Dharwar) indicate they are all members of the same giant radiating dyke swarm. It is possible that the dyke swarm was related to a mantle plume which assisted in break-up of an unknown supercontinent. Furthermore, the results indicate that the Bastar and Dharwar Cratons were adjacent but likely had a different configuration before 2.37 Ga.
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Indian Shield, Boninitic Dyke Swarm, Geochronology, Crustal Contamination, Paleoproterozoic, Indian Shield, Boninitic Dyke Swarm, Geochronology, Crustal Contamination, Paleoproterozoic