New Proterozoic K-Ar ages for some kimberlites and lamproites from the Cuddapah Basin and Dharwar Craton, south India: evidence for non-contemporaneous emplacement

Abstract

We report new K-Ar age determinations carried out on mica separates from kimberlites and lamproites that occur within and adjacent to the intra-cratonic Cuddapah basin in southern India. This work includes the first ages obtained from the Ramannapeta lamproite (at the northeastern margin of the Cuddapah basin) and from one of the kimberlites in the Mahbubnagar district. The Ramannapeta lamproite and the Kotakonda kimberlite were both emplaced in the Proterozoic and have ages of 1384 ± 18 and 1363 ± 48 Ma, respectively. These dates are similar to the 1350 ± 52 Ma age obtained here for the Chelima lamproite (within the Cuddapah basin). The Muligiripalle kimberlite (Pipe 5 of the Anantapur district) on the other hand yielded a much lower age of 1153 ± 17 Ma. Our results demonstrate that the emplacement of the Indian kimberlites and lamproites during the Proterozoic did not take place within the span of 30 Ma around 1090 Ma as some workers have recently advocated, but occurred over a period of 300 Ma. The Chelima (within the Cuddapah basin) and Ramannapeta lamproites represent some of the oldest lamproites world-wide and, together with the Kotakonda kimberlite, they might constitute a hitherto unrecognised Proterozoic episode of potassic magmatism at ∼ 1350–1380 Ma.