Precambrian acid volcanism in Central India - Geochemistry and origin

The Early Proterozoic Bijli rhyolites (2180 +/- 25 Ma) constitute an import ant part of the Nandgaon group in the Central Indian craton, a tectonically active block sandwiched between the Dharwar craton in the south and the Bu ndelkhand craton in the north. The rhyolites are chemically heterogeneous. They have high SiO2 (74.4%), K2O (4.41%), Ba (834 ppm), and low MgO (0.22%) , CaO (1.0%), iron (2.8%) V, Cr and Ni (5, 6 and 1 ppm respectively). They contain moderate Sr (88 ppm), Rb (140 ppm),Th (27 ppm) and U (6 ppm). Total REE ranges from 223 ppm to 453 ppm with high LREE (Sigma LREE = 307) and a ll the rhyolites have low to high negative europium anomalies (Eu/Eu* 0.03 to 0.77). The overall chemical signatures support a crustal anatectic origi n for the rhyolites from a source of intermediate composition. Basalt pooli ng below the crust and associated rifting most likely initiated anatexis.