Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

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40K/40Ar Ages of a Suite of Lower Palaeozoic Post-Tectonic Granitoids, Southern India


Affiliations
1 Geological Survey of India, 40th Cross, Jayanagar, Bangalore 560041, India
2 Geochronology Division, Geological Survey of India, Calcutta 700 016, India
 

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Four 40K/40Ar mica ages of the granitoid suite around Kadavur range from 475 to 527 Ma with a mean around 500 Ma. Since (i) there is a close agreement in mica ages between variants of the granitoid suite and between size fractions and (ii) the dated minerals are from post-tectonic, undeformed and unmetamorphosed rocks, this mean age appears to closely approximate the age of intrusion of the granitoids. One hornblende separate from the older invaded hornblende leuco-gabbro of the Kadavur gabbro-anorthosite complex with a 40K/40Ar age of 492 Ma is most probably a thermally reset age.
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  • 40K/40Ar Ages of a Suite of Lower Palaeozoic Post-Tectonic Granitoids, Southern India

Abstract Views: 240  |  PDF Views: 152

Authors

M. N. Balasubrahmanyani
Geological Survey of India, 40th Cross, Jayanagar, Bangalore 560041, India
Amitabha Sarkar
Geochronology Division, Geological Survey of India, Calcutta 700 016, India

Abstract


Four 40K/40Ar mica ages of the granitoid suite around Kadavur range from 475 to 527 Ma with a mean around 500 Ma. Since (i) there is a close agreement in mica ages between variants of the granitoid suite and between size fractions and (ii) the dated minerals are from post-tectonic, undeformed and unmetamorphosed rocks, this mean age appears to closely approximate the age of intrusion of the granitoids. One hornblende separate from the older invaded hornblende leuco-gabbro of the Kadavur gabbro-anorthosite complex with a 40K/40Ar age of 492 Ma is most probably a thermally reset age.