Mantle dynamics and petrogenesis of Gomer basalts in the Northwestern Ethiopia: A geochemical perspective

This study investigates the petrological and geochemical characteristics of basalts from the Gomer area in the Northwestern Ethiopian Volcanic Province to explore their petrogenesis and mantle source characteristics. Traverse-based field mapping, petrographic investigation, and whole-rock geochemical analysis were conducted. The whole-rock geochemical analysis of basalts for major and trace elements was performed using inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry, respectively. The Gomer area comprises different textured basalts, including vesicular, amygdaloidal, scoriaceous, massive basalt, and interbedded agglomerates. These basalts are primarily composed of minerals such as olivine, clinopyroxene, plagioclase, and opaque phases in varying proportions. They exhibit highly porphyritic to glomeroporphyritic textures with abundant phenocrysts of clinopyroxene and plagioclase and subordinate olivine set in an intergranular textured groundmass of the same mineral assemblage. Based on the proportion of phenocryst mineral assemblage, the studied samples are grouped as plagioclase-pyroxene phyric basalt and plagioclase phyric basalt. Geochemically, the analyzed samples are tholeiitic in composition, with hypersthene- and quartz-normative mineralogy. The Gomer basalts exhibit trace element characteristics and ratios (e.g., Zr/Nb = 12.4–19.8, La/Nb = 1.13–1.5) similar to E-MORB. Low (La/Yb) N ratios (2.19–3.85) and relatively flat HREE patterns [(Tb/Yb) N = 1.29–1.7 and (Dy/Yb) N = 1.27–1.57] indicate a high degree of partial melting of an E-MORB-type mantle in the spinel stability field. Overall, the petrogenesis of the Gomer basalts is primarily governed by fractional crystallization involving olivine, clinopyroxene, plagioclase, and occasional spinel, with minimal crustal interaction. The geochemical characteristics and trace element ratios support derivation from an E-MORB-type mantle source. These findings provide new insights into mantle heterogeneity in continental rifting settings and allow comparisons with other large igneous provinces, such as the Deccan Traps and Icelandic basalts.