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The ‘conundrum of Samail’ revisited

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posted on 10.08.2022, 07:50 authored by Uwe RingUwe Ring

This figshare item accompanies a mansucript submitted to  Tectonics (manuscript# 2022TC007531) and reports the analytical procedure for isotopic dating using the Rb-Sr method. Here is the article title and abstract:

Some like it cold: The 'conudrum' of Samail revisited



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 rocks and a major shear zone of the uppermost nappes (Ruwi-Yiti Unit) of the Saih Hatat window in the Oman Mountains of NE Arabia. These ages allow to revisit the intraoceanic suprasubduction-zone evolution that formed the Samail Ophiolite and its metamorphic sole in the Samail subduction zone. Our new age data constrain waning high-pressure metamorphism of the Ruwi-Yiti Unit 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 high-pressure metamorphism (reflecting thermal gradients of ~8-10°C/km) overlap with published ages of ~105-102 Ma for initial Samail-subduction-zone prograde metamorphism (thermal gradients of ~20-25°C/km), subsequent partial melting of the metamorphic sole, and suprasubduction-zone crystallization of the Samail Ophiolite between ~100-93 Ma. Thermal considerations demand that two subduction zones existed at the mid-Cretaceous Arabian margin. High-pressure metamorphism overprinting the Ruwi-Yiti rocks occurred in a mature, thermally equilibrated 'Ruwi subduction zone' that initiated at or before ~110 Ma. This is earlier than the age of formation of the infant, thermally unequilibrated and, thus, immature, outboard intraoceanic Samail subduction zone at ~105 Ma. We further suggest that the Samail subduction zone was retired soon after the Samail Ophiolite formed, its metamorphic sole was exhumed by slab flattening and attached to the base of the ophiolite, and both were thrust together over the exhuming Ruwi-Yiti high-pressure rocks and onto the Arabian margin by ~91 Ma. 


Swedish Science Council (VR grant 2021-04075)


Affiliation (institution of first SU-affiliated author)

464 Institutionen för geologiska vetenskaper (IGV) | Department of Geological Sciences