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 3 He/ 4 He 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 3 He/ 4 He ratio rather than high m 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 3 He/ 4 He 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.
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