Petrochronology of Wadi Tayin Metamorphic Sole Metasediment, With Implications for the Thermal and Tectonic Evolution of the Samail Ophiolite (Oman/UAE)

Abstract

Ophiolite metamorphic soles preserve important records of ophiolite emplacement, but there have been few detailed investigations into their non-mafic portions. We present new thermobarometric and petrochronologic data from a metasediment and mafic restite in the upper Wadi Tayin sole exposure in the Samail (Oman-UAE) Ophiolite. Thermodynamic modeling suggests metasedimentary garnet nucleation at~4 kb,~550°C and final growth at 7.5 ± 1.2 kbar, 665 ± 32°C, occurring by 93.0 ± 0.5 Ma (Lu-Hf isochron). Zircon U-Pb dates of 106.9 ± 2.3 (detrital) and 98.7 ± 1.7 to 94.1 ± 1.6 Ma (metamorphic) bracket the initiation of metamorphism, and monazite U-Pb dates from~97-89 Ma suggest a lengthy period of growth or recrystallization. A mafic titanite U-Pb age of 92.2 ± 1.8 Ma records the earliest possible juxtaposition of high-and lower-grade sole rocks. These and other data suggest that (i) the Wadi Tayin sole preserves an inverted metamorphic, metasomatic, and age gradient,(ii) metasediment metamorphism occurred during, or soon after, crystallization of the overlying ophiolite (≤96.5 Ma); and (iii) sole metasediments define a thermal gradient continuous with hotter, higher-P amphibolites. Some of these data conflict with existing models for sole formation, and we propose several hypotheses to explain them. Cooling of the sole below Ar closure by~92 Ma suggests that strain rapidly partitioned away from the sole, leading to large-scale, thinskinned thrust emplacement of the ophiolite >100 km across the continental margin and the late, cool underthrusting of the continental margin.

The Origin of Felsic Intrusions Within the Mantle Section of the Samail Ophiolite: Geochemical Evidence for Three Distinct Mixing and Fractionation Trends

“…(2016) and Garber et al. (2020), respectively. The metasediment is composed of quartz + white‐mica + biotite + plagioclase + garnet + ilmenite + magnetite and occurs as a m‐scale layer within a section of amphibolite, see Garber et al.…”

“… b Major element data previously reported by Garber et al. (2020). …”

“…The metasediment is composed of quartz + white‐mica + biotite + plagioclase + garnet + ilmenite + magnetite and occurs as a m‐scale layer within a section of amphibolite, see Garber et al. (2020) for a detailed discussion of the petrogenesis and field relations.…”

Texture and Shape Analysis of Quartzite Mylonites of the Metamorphic Sole of the Samail Ophiolite (Oman): Evidence for Syn- and Post-Obduction Deformation

“…Simultaneously, a sequence of Permian to Upper Cretaceous distal deep marine sediments of the Haybi and Hawasina nappes was thrusted directly onto the autochthonous basement of the Arabian Plate [2,16]. The whole crustal section is characterized by an inverse metamorphic and age profile [4,6,8,15,17,18]. The separation of the ophiolite from its metamorphic sole is based on shear zones and the amphibolite geochemistry, which differs significantly from that of the basaltic rocks of the Samail ophiolite and is more similar to that of Triassic and Jurassic basalts of the Haybi and Hawasina units [2].…”

“…Linking them to different metamorphic conditions would mean an increase in temperature during the transition from SGR to GBM. The juxtaposition of the different parts of the sole and the ophiolite takes place after reaching the peak metamorphic conditions [3,18]. In general, the preserved quartz CPO and SPO in nature are a result of ductile deformation at temperatures equal to or below 700 • C [38].…”