Characterization of the magma source and melt generation mechanisms of the Cenozoic intra-plate magmatism at the Harrat al-Shamah, Syria

Abstract

Extensive Cenozoic intra-plate volcanism in West-Arabia reflects a geodynamic setting relating convergent, transform, and plume related divergent plate boundaries. I present a detailed analysis of mineral- and recrystallized melt inclusions from an extensive set of >1000 early crystallized olivine hosts derived from alkali basalts of the Harrat al-Shamah in Syria. Major and trace element geochemistry of olivine crystals and inclusions was determined by SEM, EMPA, and LA-ICPMS. Volume corrections for recrystallized melt inclusions were used in order to determine bulk major element compositions without re-homogenization. On the basis of a compositionally variable dataset, I discerned three distinct melt groups documenting a compositional progression. Covariance of major and trace elements in these primary melts indicates compositional control by polybaric melting and binary mixing of spinel- and garnet peridotite derived end-member melts. High Dy/Yb, Zr/Y, and low Zr/Nb ratios in incompatible element enriched magmas indicate a magma source of Red-Sea MORB-type mantle which was locally re-fertilized by OIB-type material. Olivine-melt thermometry indicates the majority of melt-generation to be located at the lithosphere-asthenosphere boundary, consistent with thermal erosion by hot mantle. I argue for West-Arabian intra-plate volcanism to be driven by migrating plume material which locally exploited tectonically generated zones of lithospheric weakness. My data shows no evidence for melting of metasomatic veins and/or a separate mantle plume underneath West-Arabia.