Geochemistry and volcanic features of Harrat El Fahda: A young volcanic field in northwest Arabia, Jordan

The wadi-fill basalt of Harrat El Fahda was derived from the youngest volcanic activity in northeast Jordan and forms one of the most recent harrats of the Arabia plate. It is characterized by the presence of abundant well-preserved pressure ridges and pahoehoe lava structures. It was developed due to intermittent eruption from an isolated volcanic center in a form of 3–5 successive basaltic pahoehoe flows. The associated pressure ridges are elliptical in shape, up to 50 m high and 200 m long. The orientation with regard to flow direction is sub-parallel along the margins and perpendicular along the center of the flow. These ridges were formed by inflation and heaving pressure from below. Petrographical data show that the basalt is hollocrystalline, fine-grained and golmeroporphyritic. Modally, three petro-types are recognized, olivine-plagioclase basalt (20%), olivine-pyroxene basalt (25%) and olivine basalt (55%). Geochemically, the three petro-types can be classified as alkaline to sub-alkaline and termed as alkali olivine basalt. They have similar compositional ranges of major and trace elements. The magmas may have been derived from low degrees (i.e. 5–9%) of partial melting, of an enriched garnet peridotite mantle source with limited fractionation and crustal contamination.