Alkali basalts from the Arabian lithospheric mantle – The view from olivine phenocrysts

The origin of continental alkali basalts and basanites has long been debated between models that invoke convective mantle upwellings and those that emphasize metasomatized lithospheric mantle sources. Here, we investigate basanites and alkali basalts from the northwestern Harrat ash Shaam volcanic province in northern Israel (Northern Israel Basalts, NIB), integrating whole-rock geochemistry with olivine phenocryst compositions to constrain their mantle sources and place them in the broader context of Phanerozoic alkali magmatism across Gondwanaland. The bulk-rock and olivine data reveal systematic contrasts between domains enriched in amphibole-bearing pyroxenite veins and more peridotite-rich lithologies. Olivine phenocrysts crystallizing from magmas derived from vein-rich domains display elevated Zn/Fe and low Ni/Mg and Mn/Fe, together with depletions in Ca, Sc, V, and Cr. These signatures are consistent with partial melting of amphibole-bearing lithologies and deviate from MORB–OIB olivine trends. Carbonatitic metasomatism, while potentially contributing a diluted imprint (elevated Zr/Hf, low Ti/Eu), is not supported as a dominant factor, given the absence of diagnostic olivine Ca/Al enrichments, relatively low volatile contents, and lack of associated carbonatites in the region. We propose that the lithospheric mantle beneath the NIB is heterogeneous at kilometer scales, comprising variable proportions of amphibole-rich pyroxenite and peridotite. These metasomatized lithologies were generated during late Proterozoic subduction in the Arabian–Nubian Shield, as supported by radiogenic isotope systematics, and subsequently reactivated during Phanerozoic rifting and thinning of Gondwanaland fragments. The deviation of Harrat ash Shaam olivines from MORB–OIB trends, a feature shared with other continental alkali basalts, possibly underscoring the role of amphibole-bearing lithospheric sources in shaping continental basaltic magmatism.