Major and trace element compositions of basaltic lavas from western margin of central main Ethiopian rift: enriched asthenosphere vs. mantle plume contribution

Daniel Meshesha; Takele Chekol; Sileshe Negussia

doi:10.1016/j.heliyon.2021.e08634

Major and trace element compositions of basaltic lavas from western margin of central main Ethiopian rift: enriched asthenosphere vs. mantle plume contribution

Heliyon. 2021 Dec 18;7(12):e08634. doi: 10.1016/j.heliyon.2021.e08634. eCollection 2021 Dec.

Authors

Daniel Meshesha^{1

2}, Takele Chekol^{1

2}, Sileshe Negussia²

Affiliations

¹ Mineral Exploration, Extraction and Processing Center of Excellence, Addis Ababa Science and Technology University, P.O. Box 16417, Addis Ababa, Ethiopia.
² Department of Geology, College of Applied Sciences, Addis Ababa Science and Technology University, P.O. Box 16417, Addis Ababa, Ethiopia.

Abstract

Major and trace element data are presented for basaltic lavas from western rift margin of central Main Ethiopian Rift located at Kella area to investigate the processes involved in the petrogenesis of the erupted magmas and the nature of mantle source compositions. Kella area is composed of Quaternary (<1.6 Ma), Miocene (10.6-8.3 Ma) and Oligocene basalts (30-29 Ma) ranging from alkaline to tholeiitic in composition. The geochemical variations of basaltic samples from Kella area exhibit two compositionally distinct basaltic groups. The Oligocene tholeiitic basalts display low MgO (5.29-6.11 wt.%), TiO₂ (2.15-2.47 wt.%), P₂O₅ (0.28-0.34 wt.%), and high ratio of CaO/Al₂O₃ (0.68-0.72) and La/Nb (0.89-1.10). Whereas Quaternary and Miocene alkaline basalts display high MgO (7.40-8.86 wt.%), TiO₂ (2.4-2.53 wt.%), P₂O₅ (0.44-0.52 wt.%) and low ratio of CaO/Al₂O₃ (0.62-0.66) and La/Nb (0.71-0.76). The contrasting incompatible element ratios (e.g., K/Nb, La/Nb, Rb/Zr and Zr/Nb) between tholeiite and alkaline basalts reflect differences in their mantle sources. Major and trace element variations, therefore, reflect the involvement of two geochemically distinct mantle sources in the petrogenesis of Kella basaltic lavas: i) the Oligocene tholeiite basaltic melts derived from enriched asthenosphere mantle source (E-MORB) and ii) the Miocene and Quaternary alkali basaltic melts show a close similarity with ocean island basalts (OIBs) geochemistry, and this end member ascribed to the arrival of Afar plume head. The geochemical modeling reveals that the Oligocene tholeiite basaltic melts produced by an equilibrium melting with 3-5 % degree of partial melting in spinel lherzolite mantle source, whereas the alkali basalts were produced with ∼2% degree of partial melting within spinel-garnet lherzolite transition zone mantle sources.

Keywords: Alkaline basalts; Crustal contamination; Main Ethiopian rift; Mantle source; Plume; Tholeiite basalts.