Petrogenesis and tectonic settings of Proterozoic mafic magmatism from the Northern Indian Shield and the Himalaya: possible role for interaction of mantle plume with the sub-continental lithospheric mantle (SCLM)

Northern Indian shield and the western Himalaya have an impressive record of mafic magmatism. The Aravalli Craton preserved 2.3 Ga komatiitic (picritic) and 2.1 Ga to 1.8 Ga tholeiities. Gwalior and Betul belts preserved 2.1 Ga and 1.5 Ga to 1.2 Ga tholeiites, respectively. Western Himalaya has preserved 2.1 Ga to 1.8 Ga tholeiites in Garhwal and Himachal regions. Studied rocks depict enriched REE, LILE and depleted HFSE. Whereas, komatiites/picrites represent higher degrees of partial melting (∼35-40%) at higher temperatures (∼1500° C), tholeiites represent lower degrees of partial melting (∼10%) at lower temperatures (∼1200° C). Our results indicate interaction of mantle plume with variably enriched SCLM sources, causing generation of these varied magmatic suites of rocks. Whereas, the higher temperature komatiitic/picritic melts from the Aravalli region appear to have been generated closer to the plume head, the lower temperature tholeiitic melts from the shield region and western Himalaya were generated towards the plume margins. Different terrains of the study have undergone plume tectonics causing development of the rift valleys, majority of these developed into aulacogens, except for the Aravalli basin, which developed into deeper marine facies.

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 °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.% SiO2 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.