Geochemistry of Neoproterozoic metavolcanic rocks from the Tahtai Logomiti area, Tigrai, Northern Ethiopia: Implication for petrogenesis and tectonic settings

Abstract

The Tahtai Logomiti area is characterized by metavolcanic and metavolcaniclastic interbedded with clastic and carbonate metasedimentary rocks of Neoproterozoic age. New geological, petrographic, major, and trace elements data were used to evaluate the metamorphism, petrogenesis, and paleo-tectonic setting of the area. The field and petrographic observation indicate that the area has undergone greenschist facies metamorphism. Based on mineralogy and geochemical attributes, these metavolcanic rocks are classified as basalt, basaltic-andesite, andesite, and dacite. The moderate degrees of light rare earth element (LREE) enrichment, flat heavy rare earth element (HREE) pattern, and low Nb/Y ratio, represent shallow mantle sources. In addition to that, the TiO₂/Yb vs. Nb/Yb diagram, high (La/Yb)N ratio (> 3.44), indicates shallow melting and depleted magma sources. However, the high ratios of (Th/Ta) > 3.8, (La/Ta) > 38, and low ratios of (Th/La) < 1, (Nb/La) < 1, and high Pb content would indicate crustal contamination of the magma. The discrimination diagram and trace element ratios (Nb/Y, La/Sc, La/Y, and La/Th) indicate that the metavolcanic rocks have a calc-alkaline affinity. In addition, the Zr-Nb-Y and Th-Hf-Ta plots show that the rocks formed under a volcanic-arc setting. The general petrological and geochemical characteristics of the Tahtai Logomiti metavolcanic rocks suggest that the area is associated with subduction-related arc accretion of the Arabian Nubian Shield.