LAMPROPHYRES OF CRETACEOUS DIATREMES ON THE SYRIAN RIFT

Abstract

Evidence of Mesozoic lamprophyre volcanism was established by us for the first time for Syria in the rift on the west margin of the Arabian platform. We studied the diatremes of Al Burgal, A'r R'band, Al Asued and Marqikh (sic) in the Quardahah district, as well as the eruption centers of Nabi-Matta and Rasafi (sic) southwest of Masiafa (sic). The lamprophyres are melanocratic, porphyritic and highly brecciated rocks. The Syrian lamprophyres are high in volatiles in general and in CO2 in particular (4 to 13 and 5 to 9 percent in rocks of diatremes and eruption centers, respectively). The other composition parameters also correspond to the chemistry of lamprophyre. On the whole, as compared with classic ultramafic lamprophyres of continental rifts the Syrian lamprophyres have various special features, of which their dominant sodium specialization is the most important. Such features of the Syrian lamprophyres (high mafic index, sodium specialization and others), as well as the dominance in them of crustal rather than mantle xenoliths, force us to assume for most of the examples of lamprophyre volcanism studied that special fluidized melts were generated at relatively shallow levels from the metasomatized upper mantle of a continental-margin rift.