A Late Cretaceous (ca. 90 Ma) kimberlite event in southern India: Implication for sub-continental lithospheric mantle evolution and diamond exploration |
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| Institution: | 1. Department of Geology, Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, India;2. Department of Geology, University of Johannesburg, Auckland Park 2006, South Africa;3. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;4. Mineral Resources, Technical University of Clausthal, 38678 Clausthal-Zellerfeld, Germany;1. Earth and Atmospheric Sciences Department, 1-26 Earth Sciences Building, University of Alberta, Edmonton, Alberta T6G 2E3, Canada;2. RJ Sweeney Consulting Ltd., 7 - 9 The Avenue, Eastbourne, East Sussex BN21 3YA, Great Britain, United Kingdom;1. Department of Geology and Geophysics, Indian Institute of Technology Kharagpur, India;2. Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia;1. Department of Earth and Climate Science, Indian Institute of Science Education and Research Pune, Dr. Homi Bhaba Road, Pune 411008, India;2. National Geophysical Research Institute, Council of Scientific and Industrial Research, Hyderabad 500007, India;1. Centre for Earth Sciences, Indian Institute of Science, Bangalore 560012, India;2. Department of Geology, The University of Leicester, Leicester LE1 7RH, UK;3. Département de Sciences Naturelles, Université de Toliara, Toliara, Madagascar;4. Department of Ocean Engineering, Indian Institute of Technology Madras, Chennai 600 036, India |
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| 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 ± 19 Ma (TK-1, microcrystic variant) and 1119 ± 12 Ma (TK-3). However, a perovskite population sampled from the macrocrystic variant of TK-1 gave a much younger Late Cretaceous age of ca. 90 Ma. This macrocrystic kimberlite phase intrudes the Mesoproterozoic microcrystic phase and has a distinct bulk-rock geochemistry. The Nd-isotope composition of the ~ 1100 Ma perovskites in the cluster show depleted εNd(T) values of 2.1 ± 0.6 to 6.7 ± 0.3 whereas the ~ 90 Ma perovskites have enriched εNd(T) values of ? 6.3 ± 1.3. The depleted-mantle (DM) model age of the Cretaceous perovskites is 1.2 Ga, whereas the DM model age of the Proterozoic perovskites is 1.2 to 1.5 Ga. 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. |
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