Lithospheric mantle beneath Arabia: A Pan-African protolith modified by the Afar and older plumes, rather than a source for continental flood volcanism?

Abstract

The geochemistry of Oligocene-Miocene flood volcanic rocks associated with breakup of the Africa-Arabian continent reveals possible source contributions from the shallow mantle lithosphere, the nature and origin of which can be delimited by the study of mantle xenoliths entrained by posterosional Pliocene-Quaternary volcanoes located on the uplifted margin. Trace element and isotopic studies of these xenoliths show that the Arabian lithospheric mantle contains several components including one formed during, or shortly after, accretion of the Arabian Pan-African shield ca. 700 Ma. Since that time influx of small volume melts has modified the lower lithosphere and, most recently, the Afar plume may have acted as a source for small volume metasomatizing melts. No evidence exists in the geochemistry of the spinel Iherzolite xenoliths for Pan-African accretion of arc terranes (suprasubduction) or the presence of an Archean keel (>2500 Ma). The pre-Oligocene enriched component of the Arabian lithospheric mantle is too minor to have played a role in generating significant volumes of enriched melt that could have produced such characteristics in some Oligocene flood basalts with similar enriched isotopic characteristics. It seems that mantle plumes and asthenospheric-derived melts have repeatedly overprinted the lithospheric mantle in this region, rather than having been contaminated by melts derived from lithospheric mantle sources.