Geoscience Frontiers (Nov 2020)
Pb–Pb baddeleyite ages of mafic dyke swarms from the Dharwar Craton: Implications for Paleoproterozoic LIPs and diamond potential of mantle keel
Abstract
The Dharwar Craton in Peninsular India was intruded by a series of mafic dykes during the Paleoproterozoic and these mafic magmatic events have important implications on continental rifting and LIPs. Here we report ten precise Pb–Pb TE-TIMS age determinations on baddeleyite grains separated from seven mafic dykes and three sills, intruding into Archean basement rocks and Proterozoic sedimentary formations of the Eastern Dharwar Craton respectively. The crystallization age of the baddeleyite shows 2366.3 ± 1.1 Ma, and 2369.2 ± 0.8 Ma for the NE–SW trending dykes, 2368.1 ± 0.6 Ma, 2366.4 ± 0.8 Ma, 2207.2 ± 0.7 Ma and 1887.3 ± 1.0 Ma for the ENE–WNW to E–W striking dykes, 1880.6 ± 1.0 Ma, 1864.3 ± 0.6 Ma and 1863.6 ± 0.9 Ma for Cuddapah sills, and 1861.8 ± 1.4 Ma for the N–S trending dyke. Our results in conjunction with those from previous studies identify eight distinct stages of widespread Paleoproterozoic magmatism in the Dharwar craton. The mantle plume centres of the four radiating dyke swarms with ages of ~2367 Ma, ~2210 Ma, ~2082 Ma, and ~1886 Ma were traced to establish their proximity to the EDC kimberlite province. Though the ~2367 Ma and ~1886 Ma plume centres are inferred to be located to the west and east of the present day Dharwar craton respectively away from the kimberlite province, location of plume heads of the other two swarms with ages of ~2207 Ma and ~2082 Ma are in close proximity. In spite of the ubiquitous occurrence of dyke intrusions of all the seven generations in the kimberlite province, only few of these kimberlites are diamondiferous. Kimberlite occurrences elsewhere in the vicinity of older Large Igneous Provinces (LIPs) like the Mackenzie, Karoo, Parana-Etendeka and Yakutsk-Vilui are also non-diamondiferous. This has been attributed to the destruction of the lithospheric mantle keel (that hosts the diamonds) by the respective mantle plumes. The diamondiferous nature of the EDC kimberlites therefore suggests that plume activity does not always result in the destruction of the mantle keel.
