PETRO-TECTONIC EVOLUTION OF THE UAE-OMAN OPHIOLITE COMPLEX: NEW INSIGHTS FROM THE MÉLANGE GARNET METAGABBRO IN THE METAMORPHIC SOLE

The United Arab Emirates (UAE)-Oman ophiolite complex, also known as Semail ophiolite, consists of thrust sheets of Tethyan oceanic lithosphere that were emplaced onto the former passive continental margin of Arabia. It is located in the eastern part of the Arabian platform and is the largest and most widely studied ophiolite complex worldwide. The complex preserves the complete ocean plate stratigraphic section from mantle, lower crust, sheeted dikes, and pillow lavas of mid-ocean ridge basalt affinity, namely phase 1 magmatism, with intercalated pelagic sediments lying on top of the fault bounded metamorphic sole, providing a natural laboratory to study petro-tectonic evolution during the subduction to obduction events at a mantle wedge in a convergent boundary. The phase 1 crust is intruded by phase 2 magmatic rocks, consisting of high-level gabbro, dolerite, basalt, pyroxenite, wehrlite and tonalite with hydrous supra-subduction zone geochemical affinity.

We have focused on our study on the petrography, geochemistry, and LA-ICP-MS zircon U-Pb age dating and Hf isotope analyses of a mélange garnet metagabbro preserved within the metamorphic sole in the Masafi area and tonalite in the Dadnah area of the Khor Fakkan Block, the UAE part of the ophiolite belt for better understanding the petro-tectonic evolution at the mantle wedge from subduction to obduction processes. The results shows that (1) the is LREE enriched garnet metagabbro has positive εHf(t) values, ranging from 5.6 – 10.0 for the ages of ca. 89 – 96 Ma, and (2) the tonalite shows peraluminous-like geochemistry with εHf(t) values range from positive 5.1– 10.0 for the ages of ca. 87–92 Ma, overlapped with the garnet metagabbro. These imply that both the garnet metagabbro and tonalite studied in this study is originated from the mantle wedge below the overriding plate, and are affected by metasomatism of depleted mantle with fluids from the subducted slab, while the S-type tonalites indicate the involvement of subducted sediment during their interaction.