Résumé
Among the 12 massifs constituting the Oman-United Arab Emirates (UAE) ophiolite belt, the Aswad massif has the simplest internal structure and is the best analogue for a fast-spreading oceanic ridge. Typically the Moho is horizontal along the western margin of the massif for more than 50 km. The vertical sheeted dike complex strikes north, at a right angle to the average trend of both the high temperature (high-T) plastic lineations in the mantle and the magmatic lineations in the crust. Below the ridge of origin, the high-T flow in the uppermost mantle was on average at a right angle to the ridge axis, diverging somewhat from a central north-trending axis centered on a mantle window. This axis could have been the axis of the paleoridge of origin, which was frozen in situ before the ophiolite obduction. The Moho Transition Zone (MTZ) between the mantle harzburgites and crustal gabbros is on average 50 m thick, but attains a thickness of 400 m in the central part of the massif. Thick MTZ is regarded as being issued from a mantle diapir, which is possibly located in the mantle window along the presumed ridge axis, within an area of steep mantle foliations and lineations, below a MTZ that is thick and rich in chromite deposits. The Aswad massif is separated to the south from the Fizh massif by a northwest-trending major shear domain. This could represent the transform domain between a propagating ridge segment (Aswad axis) and a doomed ridge segment (located to the west of Fizh).