Significance of assimilation and fractional crystallization (AFC) process in the generation of basaltic lava flows from Chhotaudepur area, Deccan Large Igneous Province, NW India

摘要

Basaltic and basaltic andesitic flows have been identified from the Chhotaudepur area in the Deccan Large Igneous Province. The $m{SiO_{2}}$ content of these flows varies from 46.7 to 53.7 wt%. None of the samples have primary magma signatures as they exhibit low Mg# (0.42a??0.68), Ni (4.8a??33.4 ppm) andCr (33.08a??143.06 ppm). Highly variable concentrations of the LILE [Rb (2a??74 ppm), Ba (52a??351 ppm), Cs (0.1a??1 ppm) and Sr (273a??745 ppm)] and relatively enriched LREE are also noticed. The coherent chondrite normalized REE diagram and primitive mantle normalized multi-element diagram suggests a consanguinity among the flows. Low $m{(Nb/Th)_{PM}}$ (0.30a??1.09), high $m{(Th/Yb)_{PM}}$ (3.09a??16.58) ratios and marked variations in Rb concentration (2.4a??74.11 ppm) with variable La/Yb (5.5a??23.7) ratios suggests that magmas in the Chhotaudepur region were assimilated by the crustal components. The elevated Th/Ta and La/Yb relation further indicate concurrent assimilation and fractional crystallization process was involved in the genesis of the flows. Assimilation and fractional crystallization modelling of the flows was carried out with 20% olivine, 25% clinopyroxene, 45% plagioclase and 10% titano-magnetite as fractionating minerals and upper continental crust as the assimilant. The results reveal that all the flows were modified by AFC process.