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Sarkari, Amitabha
- Geochronology and Geochemistry of Granite Plutons from East Khasi Hills, Meghalaya
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Authors
Subhasish Ghosh
1,
S. Chakraborty
2,
J. K. Bhalla
3,
D. K. Paul
1,
Amitabha Sarkari
1,
P.K. Bishui
1,
S. N. Gupta
1
Affiliations
1 Geochronology and Isotope Geology Division, Geological Survey of India, Calcutta-700 016, IN
2 Petrology Division, Geological Survey of India, North Eastern Region, Shillong, IN
3 Geochronology and Isotope Geology Division, Geological Survey of India, Calcutta - 700 016, IN
1 Geochronology and Isotope Geology Division, Geological Survey of India, Calcutta-700 016, IN
2 Petrology Division, Geological Survey of India, North Eastern Region, Shillong, IN
3 Geochronology and Isotope Geology Division, Geological Survey of India, Calcutta - 700 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 37, No 4 (1991), Pagination: 331-342Abstract
Discordant granite plutons at Kyrdem, Nongpoh and South Khasi intrude the basement gneisses and the overlying Shillong Group of metasediments in the Meghalaya Plateau. Porphyritic granitoids ranging in composition from quartz monzonite to granite represent the dominant component in all the three plutons. Common characteristics of these granitoids arc spatial association with hornblende dioritic rocks, dominantly potassic and metaluminous nature. A positive correlation of SiO2, Na2O + K2O, Rb, Rb/Sr and negative correlation of CaO, MgO, FcO(T), Sr, TiO2 with Differentiation Index in the Kyrdcm pluton point to fractional crystallisation processes. Rb-Sr whole rock isochron data of the plutons yield ages in the range 480-690 Ma wiLh initia1 87Sr/86Sr ratios ranging from 0.70948 -0.71482. Absence of post emplacement tcctonolhennal event is suggested by near concordant K-Ar biotite ages.A protracted thennal event during late Proterozoic-early Palaeozoic (500-700 Ma), possibly related to mantle upwelling, possibly triggered the generation of these granitoids.