The nature of the subcontinental lithospheric mantle beneath the Arabian Shield: Mantle xenoliths from southern Syria

Rare earth element and Sr- and Nd-isotopic data are presented for clinopyroxenes and amphiboles from mantle harzburgite and lherzolite xenoliths from the Harrat As Shaam volcanic field in southern Syria. These rocks have sampled the subcontinental lithospheric mantle (SCLM) from beneath the Arabian Shield. Initial ε-Nd values for the mantle xenoliths from the Arabian SCLM plot within the field of crustal rocks from the region supporting the view that the felsic rocks of the Arabian Shield and the SCLM were derived from a common mantle source between about 750 and 950 Ma. Nd-isotope errorchrons for clinopyroxenes and for clinopyroxene-amphibole pairs indicate an event in the SCLM at around 750 Ma. This is identified as a melt infiltration event which resulted in the enrichment in light REE of the harzburgitic and lherzolitic clinopyroxenes and the lherzolitic amphiboles and coincides with the time of crust formation in the Arabian Shield (620-870 Ma). The present-day Nd-Sr isotopic composition of amphiboles in the lherzolite xenoliths overlaps the composition of one of the proposed source regions for alkali basalt lavas in this region. Hence it is proposed that the mantle equivalent in composition to the amphibole-lherzolites melted in the shallow SCLM, during Cenozoic lithospheric stretching. The Harrat As Shaam xenoliths provide a picture of SCLM refertilisation during the formation of juvenile crust.