The presence of high-pressure (P) eclogites along the northeast margin of the Arabian continental plate beneath the Semail ophiolite demonstrates that subduction of thinned continental crust to pressures of 20 kbar (∼80 km depth) has occurred. Current debate centers on whether this high-P metamorphism occurred prior to, during, or following ophiolite emplacement, which is known to have started ca. 95–93 Ma. Five concordant U-Pb zircon ages from a garnet-clinopyroxene-phengite-crossite eclogite from As Sifah, northeast Oman, precisely constrain the age of high-P metamorphism at 79.1 ± 0.3 Ma. This age demonstrates that high-P metamorphism occurred during continental subduction 15 m.y. after formation of the ocean floor that subsequently became the Semail ophiolite.

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