Abstract
This paper presents new hafnium isotope data for the Bure volcanic rocks from the northwestern Ethiopian plateau to constrain the nature of mantle sources within the broad mantle upwelling. The 176Hf/177Hf values range from 0.282901 (εHf = 4.79) to 0.283206 (εHf = 15.71) for the Oligocene transitional tholeiite and 0.282915 (εHf = 5.45) to 0.283069 (εHf = 10.85) for the alkaline basalts; these ratios are distinct from MORB but typical to OIB sources. The εHf values correlate positively with εNd. The scattered variation between εHf and contamination indices (such as Nb/La and Ce/Pb) for the transitional tholeiites implies that most tholeiitic basalts are affected by crustal contamination processes. Components 1 (C1) and 2 (C2), which are proposed to be the end-member components for the Afar mantle plume, have a Hf isotopic signature of εHf = 15-17 and 5-9, respectively. The diversity of these compositions relies on the proportion of recycled materials in the deep source, its formation age, and proportion of sediments relative to oceanic crust in the recycled materials.
