New Occurrence of Intrabasinal Ignimbrites and Welded Tuffs from NE Part of the Meso- to Neoproterozoic Chhattisgarh Basin, Bastar Craton: Implications for Petrogenesis

A new occurrence of Within-Basin pyroclastic flow rocks (welded felsic tuffs and ignimbrites) is reported for the first time from Sukda area in the NE part of the Chhattisgarh basin. The flows are characterized by the presence of microporphyritic textures, feldspars, quartz, glass shards, volcanic rock fragments and magmatic garnet. High concentrations of Na₂O (-6.61 wt%), low K₂O (0.01 to 1.0 wt%) and high Sr contents (416 ppm) are found in these rocks. REE show a Well-Fractionated trend with high LREE enrichment, sloping HREE patterns and absence of Eu anomalies. Major, trace and REE geochemistry of the Chhattisgarh welded tuffs indicate that they are Na- Rhyolites. The characteristic high Sr/Y and La/Yb_N, ratios and low HREE contents suggest that the parental magmas of these rocks were produced by extensive partial melting of a mafic source in deeper crustal levels (lower crust) where garnet and or hornblende are residual phases.