Rb−Sr age of Gaik granite,Ladakh batholith,northwest Himalaya |
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Authors: | J R Trivedi K Gopalan Kewal Kisharma K R Gupta V M Choubey |
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Institution: | 1. Physical Research Laboratory, 380 009, Ahmedabad, India 2. Wadia Institute of Himalayan Geology, 248 001, Dehra Dun, India
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Abstract: | The Gaik Granite is a part of the Ladakh batholith outcropping between Gaik and Kiari in NW Himalaya. This is a pink porphyritic granite rich in biotite and poor in hornblende. Rb-Sr analyses have been made on six whole-rock samples of the Gaik Granite. Though the samples are poorly enriched in radiogenic Sr, they define a reliable isochron corresponding to an age of 235±13 (2σ) m.y. and initial87Sr/86Sr ratio of 0·7081±0·0004 (2σ). Biotite, plagioclase and potash feldspar fractions separated from two of the samples have yielded a much younger mineral isochron at 30±1·5 m.y. indicating a nearly complete redistribution of Sr isotopes between mineral phases at a time much later than the primary emplacement of the granite. The present results show that at least some components of the Ladakh batholith are of Permo-Triassic age. These rocks were isotopically re-equilibrated on a mineral scale during Upper Oligocene in response to the Himalayan orogeny. |
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