Geochemistry and petrogenesis of granitoids of Lesser Himalayan crystallines,Western Arunachal Himalaya |
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Authors: | R K Bikramaditya Singh |
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Institution: | (1) National Research Centre on Yak, Dirang, West Kameng, Arunachal Pradesh, 790 101, India;(2) Department of Veterinary Microbiology, West Bengal University of Animal and Fishery Sciences, 37 K. B. Sarani, Kolkata, 700037, West Bengal, India;(3) College of Veterinary Science, Central Agricultural University, Aizwal, Mizoram, India;(4) Eastern Regional Station, Indian Veterinary Research Institute, 37 K. B. Sarani, Kolkata, 700037, West Bengal, India |
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Abstract: | Low to medium grade crystalline rocks locally known as Bomdila Group extensively covers the Lesser Himalayan region in Western
Arunachal Himalaya. This Group consists dominantly of mylonitic gneisses of granitic composition of Palaeoproterozoic age,
named as Bomdila mylonitic gneiss (BMG) and a small body of hornblende bearing granite of Mesoproterozoic age known as Salari
granite (SG). The BMG is affinity to peraluminous (A/CNK > 1.1) with high content of SiO2, K2O/Na2O ratio, normative corundum, high ratio of FeOt/MgO in biotite (3.21–5.11) that shows characteristics of S-type granite whereas SG has granodiorite composition with high
Na2O, low K2O, presence of hornblende, normative diopside, low A/CNK ratio (<1.1) and low FeOt/MgO ratio in biotite (1.58–1.60) indicates metaluminous I-type granite affinity. The SG has more fractionated nature of REE
(Ce/Yb)N = 9.06–18.53] and minor negative Eu anomalies EuN/Eu* = 0.69–0.94] as compared to BMG which has less fractionation of REE (Ce/Yb)N = 5.95–9.16] and strong negative Eu anomalies EuN/Eu* = 0.37–0.43]. Geochemical and petrological studies suggest that the SG and BMG are not genetically related; SG appears
to have derived from igneous source whereas the BMG have been derived from sedimentary source, however these granitoids might
have produced during the same thermal event. |
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