Geochemical and Nd, Pb, and Sr isotope data from deccan alkaline complexes- Inferences for mantle sources and plume-lithosphere interaction

Previous chemical and isotopic: studies based on alkaline rocks and carbona tites associated with large, continental flood basaltic provinces indicate their important role in monitoring plume-lithosphere interaction. We report new major and trace element data, and Nd; Pb, and Sr isotope ratios for va rious alkaline silica-undersaturated rocks and carbonatites from several De ccan alkaline complexes in an attempt to evaluate the relative contribution s of Reunion plume and Indian sub-continental mantles in their source regio ns. Major and trace element abundances for the most primitive silicate samp les are consistent with an origin via small-degree partial melting of metas omatized mantle. Initial Sr-87/Sr-86, Nd-143/Nd-144 and Pb isotope ratios f or the most primitive alkaline silicate samples and associated carbonatites exhibit a large variation, and ale attributed to mixing of three distinct mantle components-Reunion plume, continental lithosphere and asthenosphere (Indian MORB-like). For the silicate rocks, isotope ratios correlate with m ajor and trace element composition and support derivation from distinct man tle sources. The data obtained here nle consistent with previous models inv oking Reunion plume-continental lithosphere interaction to explain the orig in of Deccan alkaline complexes, which suggest a more prominent role of Reu nion mantle during the early stages of Deccan volcanism involving small-deg ree melting of Plume-modified lithosphere. With time, the isotope systemati cs of both alkaline and tholeiitic magmatism record a larger lithospheric i mprint.