Primordial helium isotope signature from Plio–Quaternary alkaline basalts in Yemen

Abstract Isotopic compositions of He, Ne and Ar were measured on Plio–Quaternary alkaline basalts of Marib–Sirwah and Shuqra volcanic fields in Yemen, south-western Arabian Peninsula. Very high ³He/⁴He isotope ratios were found in olivine phenocrysts of some Quaternary alkaline basalts in both volcanic fields, located on the margin of the dispersed Afar mantle plume, compared with the Afar–Ethiopian province in the center of the mantle plume. This suggests that the Afar mantle plume source may consist of common component (C or focal zone (FOZO)) with variable primordial ³He/⁴He ratio rather than high μ mantle (HIMU) component. The three component mixing C as the Afar mantle plume, depleted mantle (DM) as upper mantle and lithospheric mantle with a hybrid enriched mantle I–II (EM I–EM II) characteristics may be adequate to explain He–Sr–Nd–Pb isotope variation for the Afar–Arabian Cenozoic volcanics. The occurrence of high ³He/⁴He ratios in the Marib–Sirwah volcanic field appears to show that the primitive basaltic magma, derived from the margin of the dispersed trous-like Afar mantle plume during 15–0 Ma, was not by contamination of lithospheric and upper mantle materials in comparison with that from the center of the Afar mantle plume as a result of relatively low thermal anomaly.