gems, analytical, geology, Red Sea, Saudi Arabia, olivine basalts, Harrat Kishb

The Harrat Rahat lava field forms a major component of an extensive but poorly known continental alkali basalt province extending from Yemen in the south, through Saudi Arabia and Jordan, to Syria in the north. The continental intraplate volcanism which produced the Arabian lava fields (harrats) was contemporaneous with opening of the Red Sea, collision of the Arabian and Eurasian plates, and uplift of the Afro-Arabian dome. Harrat Rahat has evolved over the past 10 Ma. It contains two prominent lateritic disconformities which separate three stratigraphic units: the Shawahit (10–2.5 Ma), Hammah (2.5–1.7 Ma), and Madinah (1.7–Recent) basalts, comprising 68%, 19%, and 13% of the total harrat volume, respectively. Arabian harrat magmatism may have been initiated by partial melting of garnet peridotite in the asthenosphere at a depth >100 km. Accumulation of this partial melt at the crust–mantle boundary (37–44 km) may have resulted in Miocene uplift of the Afro-Arabian dome. Harrat Rahat volcanism began shortly after significant initial uplift with the voluminous extrusion of Shawahit olivine transitional basalt (OTB) lava. Chemical and petrographic data suggest that these OTB magmas ascended rapidly, with little crustal residence time. The data support a model of open-system fractionation for alkaline olivine basalt and hawaiite lavas of the younger Hammah and Madinah basalts.