Abstract
The Ar Ridayniyah ophiolitic mélange is one of a number of such complexes found within or at the peripheries of the Neoproterozoic Al-Amar Suture of the eastern Arabian Shield. This suture is sandwiched between the Ar Rayn island-arc terrane on the east and the much larger Afif continental block to the west, and is thought to represent the site of a 695—680 Ma back-arc basin that separated the two terranes. A thick and monotonous unit of metagraywacke (Abt Schist) underlies most of the suture along with scattered outcrops of metavolcanics and ophiolitic mélange. One of these bodies is the Ar Ridayniyah mélange, which occurs as a longitudinal belt of sheared ultramafic schists enclosing abundant blocks of oceanic serpentinites, as well as subordinate gabbros and basalts. The western boundary of this mélange is defined by the Ar Ridayniyah thrust fault. The 610—600 Ma ages obtained from the metagabbros of this complex are considered to record the reactivation of the Ar Ridayniyah Fault during continental collision, 60 Ma after ophiolite emplacement.