This paper provides an overview of research on core from Oman Drilling Project Hole BT1B and the surrounding area, plus new data and calculations, constraining processes in the Tethyan subduction zone beneath the Samail ophiolite. The area is underlain by gently dipping, broadly folded layers of allochthonous Hawasina pelagic sediments, the metamorphic sole of the Samail ophiolite, and Banded Unit peridotites at the base of the Samail mantle section. Despite reactivation of some faults during uplift of the Jebel Akdar and Saih Hatat domes, the area preserves the tectonic “stratigraphy” of the Cretaceous subduction zone. Gently dipping listvenite bands, parallel to peridotite banding and to contacts between the peridotite and the metamorphic sole, replace peridotite at and near the basal thrust. Listvenites formed at less than 200°C and (poorly constrained) depths of 25 to 40 km by reaction with CO2-rich, aqueous fluids migrating from greater depths, derived from devolatilization of subducting sediments analogous to clastic sediments in the Hawasina Formation, at 400-500°. Such processes could form important reservoirs for subducted CO2. Listvenite formation was accompanied by ductile deformation of serpentinites and listvenites – perhaps facilitated by fluid-rock reaction – in a process that could lead to aseismic subduction in some regions. Addition of H2O and CO2 to the mantle wedge, forming serpentinites and listvenites, caused large increases in the solid mass and volume of the rocks. This may have been accommodated by fractures formed as a result of volume changes, perhaps mainly at a serpentinization front.

Studies of the high-pressure (HP) As Sifah eclogites in the NE part of the Saih Hatat window, Oman, have used different 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 association with the Samail Ophiolite. To determine the absolute timing of continental subduction, we coupled geochronological and geochemical analyses of major (garnet) and accessory phases (zircon, rutile) from the highest-grade metamorphic rocks in the Saih Hatat (As Sifah eclogites). 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, metamorphic assemblages, and rock textures consistently suggest a single metamorphic event, with garnet growth starting by ~81 Ma and ceasing by ~77 Ma, with slight but consistent offsets in the timing of metamorphic (re)crystallization between different lithologies. These new data confirm previous structural, metamorphic, and geochronological interpretations for continental HP metamorphism in a single NE-dipping subduction zone beneath the already obducted Samail Ophiolite; there is no robust evidence for a ~110 Ma event or a continental-ward dipping subduction zone. Combined with literature constraints, our data suggest that the As Sifah unit was subducted and exhumed relatively slowly (~5 mm/yr) compared to other continental high-pressure settings - likely associated with the dragging to mantle depths by a mafic root, followed by long residence in the lower to middle crust.