Precise 40Ar/ 39Ar Age Determinations of the Kotakonda Kimberlite and Chelima Lamproite, India: Implication to the Timing of Mafic Dyke Swarm Emplacement in the Eastern Dharwar Craton

⁴⁰Ar/ ³⁹Ar age spectra of groundmass phlogopite separates from the Kotakonda kimberlite (Eastern Dharwar craton) and the Chelima lamproite (Cuddapah basin) are dominated by major plateaus at 1401.4±4.6Ma and 1417.8±8.2 Ma respectively. These ages are consistent (within their error limits) with the conventional K-Ar dates on phlogopite separates from the same samples earlier reported by us. This study supports our contention that the emplacement of Kotakonda kimberlite and Chelima lamproite was contemporaneous and these pipes are older than the Anantapur kimberlites (-1090 Ma) of the Eastern Dharwar craton. The agreement of ages obtained by employing more than one technique is a testimony of confidence in our results and, therefore, firmly establishes an episode of Proterozoic mafic potassic magmatic activity in the Eastern Dharwar craton and adjacent Cuddapah basin at ca. 1400 Ma. The concordance of plateaus and correlation of isochron plots for both these bodies suggests that at least these parts of the Eastern Dharwar craton and Cuddapah basin have not been subjected to any subsequent tectono-thermal activity. Our results contrast with the recent suggestion that a ∼ 1000 Ma thermal event in and around the Cuddapah basin led to argon loss and was responsible for the variable K-Ar ages of dyke swarms in the Eastern Dharwar craton.