Geochemistry of Metavolcanic Rocks from Northern Ethiopia: Insights for Neoproterozoic Tectonic Setting of Arabian–Nubian Shield

Major and trace element data were presented for the Mai Kenetal–Werii metavolcanic rocks within the Arabian–Nubian Shield to examine the petrogenesis and the tectonic setting of the area. Based on field observations and geochemical data, the metavolcanic rocks were classified into basalts, andesites, and dacite-rhyolites. The rocks are dominantly subalkaline (tholeiite to calc-alkaline) in composition. The low contents of Ni (0.1–78 ppm), Co (2–53 ppm), Cr (10–351 ppm), TiO2 (0.18–1.59 wt %), MgO (0.62–9.16 wt %) and relatively with high contents of Al2O3 (10.39–18.51 wt %) indicate that the rocks were formed from more evolved magmas. The chondrite-normalized REE patterns also showed moderate fractionation, with (La/Yb)N values ranging from 2.28 to 9.22, slightly negative to positive Eu anomalies (Eu/Eu*, 0.50–1.16), and relatively flat heavy REEs ((Gd/Yb)N = 0.12–1.79). The rocks display slight enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) relative to high field strength elements (HFSEs), representing rocks that were derived from more evolved magmas in a mature island arc setting. Whereas, the low ratios of Nb/La (0.17–1.66) and Nb/Yb (0.61–2.23), combined with low total REE content (ΣREE = 49.58–151.3 ppm), low Nb content (0.6–6.5 ppm), and high Zr/Nb ratios (20.7–96.67) indicate depleted mantle source. In addition, trace element ratios (Y/Nb = 4.11–15.44, Nb/Y = 0.06–0.24, La/Sc = 0.1–2.67, La/Y = 0.32–1.51 and La/Nb = 2.68–6.23) and discrimination diagrams (Zr/4–2Nb–Y, Th–Hf/3–Ta, and Th–Zr/117–Nb/16), indicate that the metavolcanic rocks have a calc-alkaline affinity that was formed in an island arc tectonic setting from subduction-related magmas within Arabian-Nubian Shield.