Details

Autor(en) / Beteiligte

• Ring, Uwe
• Glodny, Johannes
• Scharf, Andreas
• Hansman, Reuben

Titel

Some Like It Cold: The “Conundrum of Samail” Revisited

Ist Teil von

• Tectonics (Washington, D.C.), 2023-01, Vol.42 (1), p.n/a

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2023

Link zum Volltext

Quelle

Wiley Online Library Journals Frontfile Complete

Beschreibungen/Notizen

• Most tectonic models consider that the “Samail subduction zone” was the only subduction zone at the mid‐Cretaceous convergent Arabian margin. We report four new Rb‐Sr multimineral isochron ages from high‐pressure (HP) rocks and a major shear zone of the uppermost Ruwi‐Yiti Unit of the Saih Hatat window in the Oman Mountains of NE Arabia. These ages demand a reassessment of the intraoceanic suprasubduction‐zone evolution that formed the Samail Ophiolite and its metamorphic sole in the Samail subduction zone. Our new ages constrain waning HP metamorphism of the Ruwi subunit at ∼99‐96 Ma and associated deformation in the Yenkit shear zone between ∼104 and 93 Ma. Our ages for late stages of deformation and HP metamorphism (thermal gradients of ∼8–10°C km−1) overlap with published ages of ∼105‐102 Ma for Samail‐subduction‐zone prograde‐to‐peak metamorphism (thermal gradients of ∼20–25°C km−1), subsequent decompressional partial melting of the metamorphic sole and suprasubduction‐zone crystallization of the Samail Ophiolite (thermal gradients of ∼30°C km−1) between ∼100 and 93 Ma. Thermal considerations demand that two subduction zones existed at the mid‐Cretaceous Arabian margin. High‐pressure metamorphism of the Ruwi‐Yiti rocks occurred in a mature, thermally equilibrated “Ruwi subduction zone” that formed at ∼110 Ma. Initiation of the infant, thermally unequilibrated and, thus, immature, outboard intraoceanic Samail subduction zone occurred at ∼105 Ma. The Samail Ophiolite and its metamorphic sole were then thrust over the exhuming Ruwi‐Yiti HP rocks and onto the Arabian margin after ∼92 Ma, while the bulk of the Saih Hatat HP rocks below the Ruwi‐Yiti Unit started to be underthrust in the Ruwi subduction zone. Plain Language Summary The Oman Mountains are famous because the oceanic lithosphere, with the boundary between the outer crust and the subcrustal mantle, is exposed at the Earth surface. This oceanic lithosphere formed above the Samail subduction zone, which is generally considered as the only subduction zone at the NE margin of Arabia in Oman during the late Cretaceous. We show, using Rb‐Sr geochronology, that there must have been two subduction zones. Key Points Rb‐Sr multimineral ages indicate that the uppermost tectonic unit of the Saih Hatat window underwent high‐pressure (HP) metamorphism before 99‐96 Ma The cold ≥99‐96 Ma HP rocks formed at the same time as the melting of the metamorphic sole in the Samail subduction zone Thermal consideration demand that the HP rocks and the metamorphic sole formed in two different subduction zones