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Seven eclogite facies samples from lithologically different units which structurally underlie the Semail ophiolite were dated by the 40Ar/39Ar and Rb–Sr methods. Despite extensive efforts, phengite dated by the 40Ar/39Ar method yielded saddle, hump or irregularly shaped spectra with uninterpretable isochrons. The total gas ages for the phengite ranged from 136 to 85 Ma. Clinopyroxene–phengite, epidote–phengite and whole‐rock–phengite Rb–Sr isochrons for the same samples yielded ages of 78 ± 2 Ma. We therefore conclude that the eclogite facies rocks cooled through 500 °C at c. 78 ± 2 Ma, and that the 40Ar/39Ar dates can only constrain maximum ages due to the occurrence of excess Ar inhomogeneously distributed in different sites. Our new results lead us to conclude that high‐pressure metamorphism of the Oman margin took place in the Late Cretaceous, contemporaneous with ophiolite emplacement. Previously published structural and petrological data lead us to suggest that this metamorphism resulted from intracontinental subduction and crustal thickening along a NE‐dipping zone. Choking of this subduction zone followed by ductile thinning of a crustal mass wedged between deeply subducted continental material and overthrust shelf and slope units facilitated the exhumation of the eclogite facies rocks from depths of c. 50 km to 10–15 km within c. 10 Ma, and led to their juxtaposition against overlying lower grade rocks. Final exhumation of all high‐pressure rocks was driven primarily by erosion and assisted by normal faulting in the upper plate.

The metamorphic rocks associated with the Semail ophiolite in the Oman Mountains represent two different facies series. Amphibolites and greenshists at the base of the Semail ophiolite constitute a metamorphic sole formed in a high-temperature, lowpressure environment. Eclogites, blueschists, lawsonite schists and other metasediments occurring at different structural levels in the basement and shelf deposits of the continental margin formed at high pressures and low temperatures. The amphibolites of the metamorphic sole formed as a result of heat transfer from the hot overthrust ophiolitic slab to the underlying oceanic sediments and volcanics shortly following intraoceanic detachment at a collapsed spreading centre about 100–90 Ma. The underlying greenschists represent sediments and volcanics that were metamorphosed farther away from the spreading centre as the ophiolitic slab became cooler and moved closer to the continental margin. Eclogites, blueschists and crossite epidote schists formed in the Saih Hatat window as a result of A-type subduction (crustal thickening) of the basement and shelf units of the Oman continental margin in response to a change in plate motion between Africa and Eurasia and transpression or collision with a fragment of Gondwanaland about 131 Ma. A-type subduction along an east-dipping zone resulted in the burial of the eastern edge of the continental margin to a minimum depth of 30 km. High P/T metamorphic rocks formed by this process followed ‘clockwise’ P-T paths. The Late Cretaceous emplacement of the ophiolite onto the continental margin of Oman resulted in the imbrication of the continental shelf deposits, the development of low-grade, high- P/T metamorphic rocks in the ‘internal’ thrust piles due to tectonic overloading and the juxtaposition of the metamorphic rocks representing different facies series. Extensional deformation associated with culmination collapse in the Late Cretaceous and Tertiary led to the exhumation of the various high P/T metamorphic rocks and the distortion of the metamorphic zones.

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