Geochemistry, Mineralogy and Petrogenesis of El-Lajjoun Pleistocene Alkali Basalt of Central Jordan

The El-Lajjoun basalt (hereafter, LB) is a Wadi-fill flow that covers an area of about 10 km2 in Central Jordan. The tectonic evaluation carried out through lineament and fracture analyses indicates that the regional development is tectonically related to the opening of the Red Sea, and the development of the Dead Sea transform fault and other distinct regional tectonic features. The age of the LB (middle Pleistocene) can be correlated with the second stage of the opening of the Red Sea over the last 5 Ma. Petrographic data shows that rocks are plagioclase, olivine, pyroxene, and magnetite-phyric basalts. They correspond to alkali olivine basalts and basanites. The LB rocks are very similar in composition, and have comparable ranges of major and trace element concentrations. They are of undersatured silica type and belong to sodic to mildly alkaline magma series. The distinctive geochemical characteristics of LB indicated that LB was derived from a slightly fractionated magma as reflected by its high MgO (7-8 wt%) concentration, the Mg-number (0.60-0.63), the low silica content ( 43-46 wt%), and the relatively high Ni and Cr concentrations (193-271 ppm and 243-374 ppm, respectively). This basalt is resulted from a low degree of partial melting (10%) of a homogeneous garnet peridotite mantle source in the asthenosphere at a depth 100 km.