FURTHER ZIRCON U-PB AGE DATA FOR THE DAGINKATTE FORMATION, DHARWAR SUPERGROUP, KARNATAKA CRATON

SHRIMP U-Pb analyses of zircons from a rhyolite sample collected from the Daginkatte Formation of the Chitradurga Group (Dharwar Supergroup) , close to the type locality, give an age of 2601 +/- 6 Ma (1 sigma; 2 3 of 24 analysed grains). This is within error of the 2614 +/- 8 Ma (2 sigma; 11 grains) recently reported by A.P. Nutman and his colleagues in 1996 from a sample of acid volcanic schist of the same formation, about 25 km along strike. Combining Nutman et al's (1996) published da ta with the new analyses reported here gives a pooled age of 2606 +/- 6 Ma (n=34, 1 sigma, chi(2)=1.31), within error of both of the separat ely determined ages. Having regard to the reported uniform lithology o f the Daginkatte Formation, the pooled age is probably that of a short magmatic event during which it was formed, and provides a firm constr aint relevant to this stratigraphic level of the Chitradurga Group; ho wever, it is now important to determine whether the rhyolitic rocks of the Daginkatte Formation are intrusive or extrusive.