Asymmetric magma chamber beneath the Red Sea system controlled Cenozoic alkaline magmatism on the western margin of the Arabian Shield

The western margin of the Arabian Shield along the Red Sea between Jordan and Yemen is littered with numerous mostly middle Miocene to Quaternary harrats (basalt fields). Harrat Uwayrid (HU) is one of them and comprises a NW–SE oriented elongated field that extends for about ~230 km in NW Saudi Arabia. Magmatic activities include older alkaline lava flows of transitional basalt, alkali basalt, hawaiite, and basanite and younger scoria basanite that erupted through the central segment of the older lavas. Based on chondrite-normalized Sm/Yb vs. La/Yb and Tb/Yb vs. La/Sm, the older transitional lavas were generated from spinel lherzolite whereas the younger lavas were generated from garnet lherzolite. Primitive mantle-normalized patterns are similar to OIB. ⁴⁰Ar/³⁹Ar plateau dating yield eruption ages of 10.15 ± 0.09 to 9.87 ± 0.04 Ma (n = 3) for the older alkaline basalts and 0.96 ± 0.03 to 0.16 ± 0.03 Ma (n = 5) for the younger basanites. ¹⁴³Nd/¹⁴⁴Nd ratios for both the older lavas and younger scoria are 0.51285–0.51292 whereby É›Nd (4.0–5.4) is positive; ratios of ⁸⁷Sr/⁸⁶Sr are low (0.7032–0.7039). ²⁰⁶Pb/²⁰⁴Pb (18.5305–19.3701) and ¹⁴³Nd/¹⁴⁴Nd vs. ⁸⁷Sr/⁸⁶Sr overlap FOZO-type mantle; we interpret the FOZO signature to indicate metasomatism of the asthenosphere from slabs subducted during construction of the 900–550 Ma Arabian–Nubian shield. HU record possible plume-related, potential temperatures of 1400–1490 °C and pressures of 2.0–4.4 GPa (~70–140 km depth) within the range of the Afar Plume. Some HU scoria and lava also fall within the isotopic range of the Red Sea trough, Yemini flood basalt, and Afar Plume basalt. After Arabia–Eurasia collision in the Miocene, subsequent eastern movement of the Arabian Shield caused asymmetric drag of upwelling asthenosphere and possibly the Afar Plume, and magma chambers to beneath the western limb of the Arabian shield.