A Late Cretaceous (ca. 90 Ma) kimberlite event in southern India: Implication for sub-continental lithospheric mantle evolution and diamond exploration

Abstract

We report groundmass perovskite U–Pb (SIMS) ages, perovskite Nd isotopic (LA-ICPMS) composition and bulk-rock geochemical data of the Timmasamudram diamondiferous kimberlite cluster, Wajrakarur kimberlite field, in the Eastern Dharwar craton of southern India. The kimberlite pipes gave similar Mesoproterozoic ages of 1086±19Ma (TK-1, microcrystic variant) and 1119±12Ma (TK-3). However, a perovskite population sampled from the macrocrystic variant of TK-1 gave a much younger Late Cretaceous age of ca. 90Ma. This macrocrystic kimberlite phase intrudes the Mesoproterozoic microcrystic phase and has a distinct bulk-rock geochemistry. The Nd-isotope composition of the ~1100Ma perovskites in the cluster show depleted εNd(T) values of 2.1±0.6 to 6.7±0.3 whereas the ~90Ma perovskites have enriched εNd(T) values of −6.3±1.3. The depleted-mantle (DM) model age of the Cretaceous perovskites is 1.2Ga, whereas the DM model age of the Proterozoic perovskites is 1.2 to 1.5Ga. Bulk-rock incompatible trace element ratios (La/Sm, Gd/Lu, La/Nb and Th/Nb) of all Timmasamudram kimberlites show strong affinity with those from the Cretaceous Group II kimberlites from the Bastar craton (India) and Kaapvaal craton (southern Africa). As the Late Cretaceous age of the younger perovskites from the TK-1 kimberlite is indistinguishable from that of the Marion hotspot-linked extrusive and intrusive igneous rocks from Madagascar and India, we infer that all may be part of a single Madagascar Large Igneous Province. Our finding constitutes the first report of Cretaceous kimberlite activity from southern India and has significant implications for its sub-continental lithospheric mantle evolution and diamond exploration programs.