A New Find of Younger Dolerite Dykes with Continental Flood Basalt Affinity from, the Meso-Neoproterozoic Chhattisgarh Basin, Bastar Craton, Central India

摘要

Younger and fine-grained unmetamorphosed dolerite dykes intrude the Raipur Group sediments in the central part of the Meso-Neoproterozoic Chhattisgarh Basin in Central India. Petrologically these dykes consist of unaltered microphenocrysts of intermediate pigeonite (XMe=0.4Q), augite (XMs=0.595), calcic plagioclase (XCa=0.64), titanomagnetite and ilmenite. These rocks show high Fe,O3T (14.43 to 15.19%), TiO2 (2.75 to 2.87%) and P,O5 (0.27 to 0.29%) contents with an unusual Continental Flood Basalt (CFB) affinity. Significantly these dykes show lower K2O content (0.43%). The trace clement abundance such as Ba, Sr, Rb, Zr, Nb and trace element ratios Sm/Nd, Ba/Nb, Zr/Nb, Y/Nb, Th/Yb, Ta/Yb and K/Ba in these rocks chemically resemble the least contaminated Deccan Basalts. Chondrite/OIB normalized REE patterns of these rocks also show striking similarities with the Deccan tholeiitic basaltic flows. The available petrological, mincralogieal, major, trace and rare earth element data indicate that these within basin basaltic dykes of Raipur are intraplate basalts, which were derived from an enriched mantle source.