Abstract
Two continental terranes (Afif and Ar Rayn) of the eastern Arabian Shield are separated by the Al-Amar Suture Zone, the western boundary of which is marked by the Halaban Belt, the largest ophiolite sheet in the eastern shield. REE and other immobile trace element concentrations suggest the Halaban Ophiolite formed in an ensialic back-arc basin in a supra-subduction zone setting. Based on this, a new tectonic model for the eastern Arabian Shield was constructed. This model assumes the existence of a westerly-dipping subduction zone at about 700 Ma above which back-arc spreading resulted in the break up of the continental margin of the Afif Terrane and the formation of a short-lived marginal basin. Basin closure took place at around 680 Ma, but a westerly-dipping subduction zone continued to exist further east beneath the Ar Rayn Terrane for at least 60 Ma. In the period 620—600 Ma, collision with a continental mass (now concealed by Phanerozoic sedimentary rocks) gave rise to widespread granitic magmatism in the eastern shield, as well as crustal-scale strike-slip faulting.