Magma genesis and mantle dynamics at the Harrat Ash Shamah volcanic field (southern Syria)

Abstract

A geochemical and petrological study of Miocene to recent alkali basalts, basanites, hawaiites, mugearites, trachytes, and phonolites erupted within the Harrat Ash Shamah volcanic field was performed to reconstruct the magmatic evolution of southern Syria. The major element composition of the investigated lavas is mainly controlled by fractional crystallization of olivine, clinopyroxene, ± Fe-Ti oxides and ± apatite; feldspar fractionation is restricted to the most evolved lavas. Na2O and SiO2 variations within uncontaminated, primitive lavas as well as variably fractionated heavy rare earth element ratios suggest a formation by variable degrees of partial melting of different garnet peridotite sources triggered, probably, by changes in mantle temperature. The isotopic range as well as the variable trace element enrichment observed in the lavas imply derivation from both a volatile- and incompatible element-enriched asthenosphere and from a plume component. In addition, some lavas have been affected by crustal contamination. This effect is most prominent in evolved lavas older than 3.5 Ma, which assimilated 30-40% of crustal material. In general, the periodicity of volcanism in conjunction with temporal changes in lava composition and melting regime suggest that the Syrian volcanism was triggered by a pulsing mantle plume located underneath northwestern Arabia. © The Author 2007. Published by Oxford University Press. All rights reserved.