Neon Isotopes in Geothermal Gases From the Kenya Rift Reveal a Common Deep Mantle Source Beneath East Africa

Abstract

The seismic velocity structure beneath East Africa suggests interconnected corridors of hot mantle are upwelling beneath the continent. However, the geochemical evidence for deep mantle in Ethiopia-Kenya-Tanzania volcanism is sparse questioning the existence of superplume. The development of new geothermal fields in the region offers the opportunity to access high temperature magmatic-hydrothermal fluids. Well gases from the geothermal field in the Menengai caldera in the central Kenya Rift have C-He isotope systematics that are dominated by magmatic volatiles. High precision Ne isotope data confirm a primordial deep mantle that has experienced long-term convective isolation like that beneath Hawaii is present beneath the Kenyan rift. The Ne isotope composition of the gases is indistinguishable from volatiles in basalts from the Afar plume and Western Rift (and significantly more precise) providing the first geochemical evidence for a common deep mantle beneath the entirety of the East African Rift System.