Mesoproterozoic kimberlites in south India: a possible link to ~1.1 Ga global magmatism

Abstract

Precambrian kimberlites are relatively rare in the geological record and yet those that do exist tend to form in relatively narrow windows of geologic time. We report new age information for three Proterozoic kimberlites from two distinct clusters in the Eastern Dharwar craton, India: a U-Pb perovskite age of 1124 + 5/-3 Ma for Wajrakarur Pipe-2, a Rb-Sr phlogopite age of 1102 ± 23 Ma for Wajrakarur Pipe-6 and a Rb-Sr phlogopite-whole rock composite isochron age of 1093 ± 4 Ma based on two samples from the recently discovered SK-1 kimberlite pipe at Siddanpalli. These new age results are identical to a number of previously reported kimberlite emplacement ages (1085-1099 Ma) from several clusters in the Eastern Dharwar craton, India and contribute to a growing database that documents extensive kimberlite magmatism encompassing an area of more than 30,000 km² within this province alone. Coeval ˜1.1 Ga kimberlite/lamproite/carbonatite magmatism in central India (Majhgawan) about 1000 km north of the Eastern Dharwar craton kimberlite clusters, and in North America, Greenland, Scandinavia, Southern Africa, Liberia, and Australia confirms a significant period of global ultrapotassic and alkaline magmatism at this time. The timing of this Mesoproterozoic kimberlite magmatism coincides with the development of several Large Igneous Provinces and attendant intracontinental rifting; such as those formed in the intervals 1109-1086 Ma in Laurentia (Midcontinent Rift), 1112-1102 Ma in the Kalahari craton (Umkondo), and 1079-1070 Ma in west central Australia (Warakurna). The association of wide spread contemporaneous ultrapotassic, alkaline and mafic magmatism at ˜1100 Ma may be linked to a global period of enhanced short-lived mantle plume activity and/or a major change and re-organization of the mantle convection regime at this time.