Dating Continental Subduction Beneath the Samail Ophiolite: Garnet, Zircon, and Rutile Petrochronology of the As Sifah Eclogites, NE Oman

Abstract

AbstractStudies of the high‐pressure (HP) As Sifah eclogites in the NE Saih Hatat Window, Oman, have used different combinations of radiometric dating results (Ar/Ar, Sm‐Nd vs. U‐Pb, Rb‐Sr) to interpret disparate tectonic models for the timing, geometry, and cause of continental subduction—including its relationship to the Samail Ophiolite. To determine the timing of continental subduction, we coupled petrochronological analyses of major (garnet) and accessory phases (zircon and rutile) from the highest grade metamorphic rocks (As Sifah eclogites) in the Saih Hatat. Early Permian (283.8 ± 0.7 Ma) tuffaceous zircon cores are consistent with earlier interpretations that the As Sifah rocks were sourced from a distal portion of the Arabian continental margin. Data from a range of bulk compositions and metamorphic assemblages consistently suggest a single metamorphic event with garnet growth from ∼81 to 77 Ma—though with slight, consistent offsets in the timing of metamorphic (re)crystallization between different lithologies. These new data confirm previous interpretations for continental HP metamorphism in a single NE‐dipping subduction zone beneath the obducted Samail Ophiolite; there is no robust evidence for an ∼110 Ma event or for SW‐dipping subduction beneath the Arabian plate. Combined with other constraints, our data suggest that the As Sifah unit was subducted at rates similar to other small continental HP bodies, followed by two stages of cooling and exhumation—likely associated with the dragging to mantle depths by a mafic root, an initial phase of rapid exhumation from mantle depths, and a lengthy residence (≤40 My) in the lower to middle crust.