RB-SR AGES ON THE GRANITE AND PEGMATITIC MINERALS FROM BASTAR-KORAPUTPEGMATITE BELT, MADHYA-PRADESH AND ORISSA, INDIA

Rb-Sr isotopic date on 12 samples of the Paliam and Darba granites of the Bastar Craton in Central India have defined an isochron age of 230 8 +/- 48 Ma. with initial Sr-isotopic ratio of 0.7354 +/- 0.0097. Mine ral ages on perthite, biotite and muscovite from tin- and rare metal-m inearlised as well as non-minearlised pegmatites of the Bastar-Koraput Pegmatite belt within this craton have indicated two important dates of about 2050 and 1620 Ma. These dates are interpreted as (a) emplacem ent of the granite around 2300 Ma., (b) derivation of the pegmatites f rom this parent granite around 2050 Ma and (c) resetting of Rb-Sr syst em at about 1620 Ma .. concomitant with the metamorphic/uplift event i n the nearby Eastern Ghats. The very high initial Sr-87/Sr-86 of 0.735 for granite indicates that they are crustal derived, possibly from a metasedimentary source.