He-Ne-Ar-N2-CO2 Isotope Characterization of the East Africa Rift System

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This project is to undertake a comprehensive study of the East African Rift System (EARS) concentrating on the analyses of the major (CO2) and trace volatile (He-Ne-Ar-N2) characteristics of geological samples from all three branches of current rifting and volcanism in eastern Africa. These are: the Main Ethiopian Rift, including the Afar Depression, and the Kenyan and Western rifts. The aim of the study is to utilize the isotopic and relative abundance systematics of the volatiles to define the nature of the underlying mantle (one or two deep-seated mantle plumes) and to understand its interaction with the overlying continental lithosphere throughout eastern Africa. The research plan involves analyzing geothermal fluids, mantle xenoliths, phyric lavas and tephras to gain an unprecedented overview of the volatile characteristics of this active region which incorporates continental rifting, dynamic uplift and formation of nascent oceanic crust. Through an integrated approach combining analyses of the light noble gases (He-Ne-Ar) and other volatiles (N2 and CO2), the team will determine if the postulated mantle plume supporting the Ethiopian Dome is the sole deep-seated anomaly beneath the EARS or whether a second plume is responsible for uplift of the Kenyan Dome. In this respect, they will test if the high 3He/4He provinces of the Main Ethiopian Rift and Afar Depression have unique volatile isotopic characteristics that can be defined and exploited to map the spatial extent of the deep-seated Ethiopian plume influence. Additionally, the hypothesis that provinces of the Kenyan and Western rifts, i.e., south of the Turkana Depression, also have unique volatile isotopic characteristics that can be defined will form the basis of testing the involvement of subcontinental mantle lithosphere (SCLM) and/or a second plume in the petrogenesis of magmas from the Kenyan Dome. All targeted volatiles - either alone (e.g., 3He/4He) or in combination with other volatiles (e.g., CO2/3He) possess characteristics that make them sensitive tracers of deep mantle provenance that allows distinction between magmatic sources that are derived from the lithosphere and which are shallow. Taken together, this study will provide the essential volatile database that addresses key questions that test the relationship between the continent-wide African superswell and magma source characteristics throughout different regions of the EARS.