Contribution to the Mineral Chemistry of the Proterozoic Aravalli Mafic Meta-Volcanic Rocks from Rajasthan, NW India

Field, petrological and mineral chemistry for meta-volcanic rocks from the Aravalli sequence (Aravalli Craton, India) are presented. Field evidence such as volcanic flows and suspect pillow lava structures, dominant Fe-tholeiite lava flows intercalated with quartzites and argillaceous sediments, indicate rift tectonic environment. Primary mineralogy was obliterated during post-magmatic processes such as metamorphism corresponding to the greenschist to lower amphibolite facies conditions. The rock's mineral composition was overprinted by plagioclase-chlorite-amphibole-epidote assemblage. The relicts of clinopyroxene were observed. The P-T estimation indicates a temperature of 550-600 degrees C for the pressure ranging from 3.0 to 7.0 kbar for the majority of amphiboles and 8.0-10.7 kbar for the minority. Geochemically, these rocks are komatiitic (picritic) and high-Fe tholeiitic basalts with 45.06-59.2 wt.% SiO(2)and MgO content from 5 to 22.4 wt.% and Mg# of 17 to 71. They show large-ion lithophile elements (LILE) and light rare-earth elements (LREE) enrichment. Chondrite normalized rare-earth elements (REE) patterns for the Aravalli lava are moderately enriched with (La/Sm)(N)= 1.1-3.85, (La/Yb)(N)from 1.49 (komatiites) to 14.91 (komatiitic basalts). The trace element systematics with the negative Nb, P and Zr anomalies reflect their derivation from enriched sub-continental lithospheric sources, although minor crustal contamination cannot be ruled out. Aravalli rocks are considered to represent the transition from continental rift magmatism to shallow submarine eruption.