RB-SR AGE OF THE METALUMINOUS GRANITOIDS OF SOUTH KHASI BATHOLITH, MEGHALAYA - IMPLICATIONS ON ITS GENESIS AND PAN-AFRICAN ACTIVITY IN NORTHEASTERN INDIA

Metaluminous granitoids of the South Khasi batholith (SKB) in the West Khasi Hills district of Meghalaya define a Rb-Sr whole-rock isochron age of 757 +/- 60 Ma, with (Sr-87/Sr-86)(i) Of 0.71069 +/-0.00092. SKB and other granitoids of Meghalaya like Mylliem, Nongpoh and Kyrdem ha ve many common features such as the presence of basic enclaves of horn blende gneiss and amphibolite, late- to post-tectonic nature, predomin ance of biotite amongst mafic silicates, overall metaluminous nature a nd high (Sr-87/Sr-86)(i) of more than 0.709. All these indicate much s imilarity in the genesis of their melts due to partial melting of lowe r crustal rocks. The Rb-Sr isochron ages of SKB and other granitoids i n Meghalaya Feint to a major tectonomagmatic activity during ca. 760-4 80 Ma, which is almost coeval with ca. 800-500 Ma Mid-Upper Pan-Africa n activity. The data, thus imply the possible imprint of the widesprea d Pan-African activity in northeastern India, besides southern India.