Petrogenesis and geochemical evolution of Chole basalts, Southeastern Ethiopian Plateau

Abstract

This study presents the trace element geochemistry of an 851-m thick basaltic succession from the central part of the southeastern Ethiopian plateau (Chole section) to assess the petrogenesis and temporal geochemical evolution of the Chole basalts. The composition of trace and major elements in the Chole section varied temporally, and three distinct magma types were identified; lower, middle, and upper basalts. The lower and middle basalts are highly enriched in incompatible trace elements with strong positive Nb and negative K anomalies in the primitive-mantle-normalized multi-elemental variation diagram. Both exhibit similar middle to heavy rare earth element fractionation patterns. However, the middle basalt shows distinctive negative U, Th, and positive Ba anomalies, with higher Ba/Th, Ba/Nb ratios, and more pronounced light-to-heavy rare earth element fractionation, suggesting varying degrees of mantle metasomatism and partial melting in the lithospheric mantle. The trace element signatures indicate that these basalts originated from the melting of garnet-bearing lithospheric mantle mixed with rising plume component. The upper basalt reveals two groups: the lower flows show moderate enrichment with a strong negative K anomaly, while the upper flows display highly enriched trace elements with crustal influence. Trace element signature in the uncontaminated upper basalt indicates partial melt contribution from the spinel-garnet transition zone of the depleted component, probably the melting of the sub-lithospheric mantle and hydrated lithospheric mantle or partial melting of the previously depleted part of the lithospheric mantle.

Graphical abstract