Crustal contamination and diversity of magma sources in the northwestern Ethiopian volcanic province

Abstract

Geochemical and isotopic data are presented for Bure volcanic rocks from the northwestern Ethiopian plateau to investigate the processes involved in the genesis of the erupted magma and the nature of mantle source compositions during plume-induced continental rifting. The Bure area is mainly composed of flood basalts (30-25 Ma), ranging from transitional tholeiite to alkaline basalts, with a probable Quaternary alkaline basalt single lava flow, scoria cones and trachyte plugs. The transitional tholeiites have variable incompatible elements and isotopic ratios (⁸⁷Sr/⁸⁶Sr = 0.70329-0.70429, ¹⁴³Nd/¹⁴⁴Nd = 0.51281-0.51304 and ²⁰⁶Pb/²⁰⁴Pb = 18.36-19.08). In contrast, the alkaline basalts display a homogeneous incompatible element and Sr-Nd isotopic ratios (⁸⁷Sr/⁸⁶Sr = 0.70311-0.70363 and ¹⁴³Nd/¹⁴⁴Nd = 0.51279-0.51288) with a wide range of Pb isotopes (²⁰⁶Pb/²⁰⁴Pb = 18.91-19.83). Isotope and trace element variations within the Bure lavas reflect the involvement of: 1) an intrinsic isotopically depleted plume component, 2) a plume component having radiogenic Pb isotope and 3) an enriched crustal component. The first and third components played a significant contribution in the initial stage of plume-induced continental flood basalt magmatism.