Geochemical Characterization of the Stratoid Series and Comparison to the Gulf Basalt Formation (Afar, Ethiopia)

Situated at the intersection between the Main Ethiopian Rift and the on-land portions of the Red Sea and Gulf of Aden Rifts, the Afar depression is a unique place to study on-land evolution and propagation of a rift system at the ocean-continent transition. Covering an area of ~55.000 km2 and up to ~1500 m thick the Stratoid series is the main formation outcropping in the Afar depression and is mainly dominated by flood basalt magmatism with minor felsic activity. The age of the Stratoids range from ~4 to ~1 Ma, preceding the ~1.1-0.6 Ma Gulf Basalts and the younger volcanism of the active magmatic segments (e.g., Erta ale, Manda-Hararo, Asal-Ghoubbet). Comparison between Stratoids and the recent magmatic formations (e.g. Gulf Basalts and axial segment volcanism) represent an excellent opportunity to investigate the rift evolution. Nevertheless, recent research mainly addresses the volcanism of the active magmatic segments while the Stratoids and the Gulf Basalts have not been the focus of systematic studies, so much so that many aspects regarding geochemistry, petrology and eruptive mechanisms remain unknown. In addition, the Gulf Basalts overlie the Stratoids within the main grabens and are distinct from the latter based on volume and morphological observations of the lava units but with no or very poor geochemical constraints on their distinction. Here we present preliminary major and trace elements analyses to evaluate the geochemical characteristic of the Stratoids and Gulf Basalts formations and to investigate the distinction between these two formations from a geochemical point of view. A first evaluation of the chemical variability of the Stratoids based on the distance from the Tendaho and Dobi graben will also be presented.