Along the Syrian rift, in continuity with the Dead sea fault, volcanic activity has been occurring since early Mesozoic times. The recent (Neogene-quaternary) volcanism is very basic (picrobasalts, basanites). Few volcanoes contain a number of ultrabasic xenoliths, notably Iherzolites, harzburgites and pyroxenites. Xenolith texture is protogranular or granular, with a variable (mostly limited) degree of local melting by the enclosing basalt.
Pure Co2- bearing fluid inclusions have been found in olivine and pyroxenes from xenoliths and in phenocrysts from enclosing basalts. Highest density fluids (up to 1.15 g/cm3), are observed in pyroxenites. They occur in primary, tubular inclusions adjacent to or even containing minute spinel grains, oriented along the exsolution lamellae of the clinopyroxene-host. P-T conditions of mineral equilibration in the xenoliths have been estimated from the pyroxene thermometer, and maximum density of fluid trapped in primary inclusions. They correspond to 900 < T ~ 1200 oC, 10 ~ P > 1.5 Kb respectively These P-T conditions do not show any significant variation between different regional occurrences, but well between various petrographical types, the maximum conditions being recorded in pyroxenites.
A Geodynamic modele is proposed. It suggests that some clinopyroxene at least has been formed by mantle metasomatism, caused by ephemeral carbonate magmas, in a mantle plume located under the Arab plate. There are no lateral displacement, but there is at the depth of the plume, from 100 Km in cretaceous to 50 Km in Neogene, which corresponds to an ascent of 50 Km approximately, in 200 millions years ago.
Damascus University, Syrian Arab Republic
Celebration date :
2 Tuesday September 2008
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