Petrogenesis and geotectonic setting of Berguda granitoids of Neoproterozoic Burji-Finchawa granite-gneiss complex, southern Ethiopia: implication for the cessation of subduction control magmatism in East African Orogeny.

Major and trace element data are presented for Berguda granitoids within the Neoproterozoic basement rocks of southern Ethiopia, East African Orogeny. Geochemical and petrological constrains indicate the presence of two distinct types of granitoid rocks: (1) Wolena Bokosa granitoid (WBG) and (2) Hida Korma granitoid (HKG). WBG is granite in composition with high SiO₂ content (73.38–79.38 wt.%) and wider Al₂O₃ values (10.68–14.81 wt.%). It has relatively high molecular values (ASI = 0.99–1.05) with low contents of CaO, MgO, Fe₂O₃, TiO₂, and P₂O₅. WBG is shoshonitic to high-k calc-alkaline, Al-rich metaluminous, and more felsic I-type granitoid, whereas HKG is quartz-monzonite in composition (SiO₂ = 65.31–68.26) with relatively low molecular values (ASI = 0.86–0.96) with high contents of CaO, MgO, Fe₂O₃, TiO₂, and P₂O₅. HKG is also shoshonitic to high-k calc-alkaline, metaluminous, and more mafic I-type granitoid. The observed positive anomalies in Rb, Th, K, Pb, and Zr and negative anomalies of Sr, P, Ti, Nb, and Ta in both groups reflect the involvements of crustal materials in their petrogenesis. In terms of geodynamic setting, WBG is classified as volcanic arc (VAG) and syn-collisional (syn-COLG) granite and inferred as syn-orogenic, whereas the HKG is classified as within-plate granite (WPG) with post-orogenic emplacement. Furthermore, this study infers that the transition from syn-orogenic calcic-alkalic WBG to alkalic HKG magmatism is marking the cessation of subduction control magmatism of the East African Orogeny (EAO) at about 529 ± 11 Ma. The continuation of the magmatism after the cessation of subduction control magmatism is shown by emplacement of more alkalic post-orogenic HKG with volcanic arc chemical affinities possibly the effect of previous subduction process. [ABSTRACT FROM AUTHOR]