East Meets West: The Trace of the Mesoproterozoic Kibaran Event in the Mantle Lithosphere Beneath Eastern Tanzania

Abstract We present elemental geochemistry and multiple isotopic systematics (Re‐Os, Lu‐Hf, Sm‐Nd and Sr) for mantle peridotite xenoliths from Lashaine in northern Tanzania. We use the data to examine how the major Proterozoic tectono‐thermal events that affected the crust of the western Tanzanian craton are imprinted on the lithospheric mantle in the Mozambique belt adjacent to the eastern margin of the Tanzanian craton. Whole‐rock and mineral compositions together with 187 Os/ 188 Os ratios of Lashaine peridotites are consistent with Archean‐aged cratonic mantle assembled to create the root beneath the Tanzanian cratonic nucleus. Highly radiogenic 87 Sr/ 86 Sr ratios (0.70411−0.83604), unradiogenic Nd (ɛNd = −14 − +2) and variable Hf isotope ratios (ɛHf = +4 − +2,912) of minerals combined with the other geochemical features in Lashaine peridotites reflect extensive melt extraction followed by metasomatic enrichment of the lithospheric mantle by subduction‐related melts/fluids. Mineral Lu‐Hf isotopic compositions define a 1.4 Ga isochron and, together with the distinctive, robust Lu‐Hf model age (1.4 Ga) of one garnet with very high 176 Lu/ 177 Hf ratio (3.182), indicate that a major Mesoproterozoic subduction‐related metasomatic event reset Lu‐Hf isotope systematics of the Lashaine peridotites. This over‐printing of the mantle lithosphere indicates a clear link to the Mesoproterozoic Kibaran event along the western margin of the Tanzanian craton. We invoke a flat‐slab subduction model during the Kibaran event to introduce subduction‐related components in a pervasive Mesoproterozoic metasomatic event beneath Lashaine.