Precise 40Ar/39Ar age determinations of the Kotakonda Kimerlite and Chelima Lamproite, India; implication to the timing of mafic dyke swarm emplacement in the eastern Dharwar Craton

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Authors:Chalapathi Rao, N. V.; Miller, J. A.; Gibson, S. A.; Pyle, D. M.; Madhavan, V.
Author Affiliations:Primary:
University of Cambridge, Department of Earth Sciences, Cambridge, United Kingdom
Other:
Bullard Laboratories, United Kingdom
Kakatiya University, India
Volume Title:Journal of the Geological Society of India
Source:Journal of the Geological Society of India, 53(4), p.425-432. Publisher: Geological Society of India, Bangalore, India. ISSN: 0016-7622
Publication Date:1999
Note:In English. 33 refs.; illus., incl. 2 tables
Summary: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±4.6 Ma 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.
Sections:Age determination
Subjects:Absolute age; Ar/Ar; Dates; Dike swarms; Emplacement; Igneous rocks; Kimberlite; Lamproite; Lamprophyres; Mafic composition; Mesoproterozoic; Plutonic rocks; Precambrian; Proterozoic; Ultramafic composition; Upper Precambrian; Andhra Pradesh India; Asia; Dharwar Craton; India; Indian Peninsula; Chelima Lamproite; Kotakonda Kimberlite
Coordinates:N152700 N164500 E0784200 E0773002
Abstract Numbers:99M/3440
Record ID:2000067786
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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