Tectonic Evolution of the Northern Oman Mountains, Part of the Strait of Hormuz Syntaxis: New Structural and Paleothermal Analyses and U-Pb Dating of Synkinematic Calcite

The Oman Mountains expose Permo-Mesozoic shelf rocks of Arabia overridden by continental slope/basinal sediments and Semail Ophiolites during Late Cretaceous. A major syntaxis is represented by the Musandam Peninsula and Dibba Zone. The overthrusting of allochthonous units onto the Musandam shelf carbonates initiated during the Cenomanian. Structural analyses in the Musandam Peninsula constrained top-to-the-west thrusting that took place 74–60 Ma ago (U-Pb datings of synkinematic calcites), about 15–30 Ma after the obduction of the Semail Ophiolite. The Dibba faults exhibit a first interval of thrusting (top-to-the-west) followed by dextral slip. We propose that SW vergent thrusts, initially parallel to those of the Central and Southern Oman Mountains, were subsequently rotated to their present-day NE-SW strike during the development of the syntaxis and then reactivated by dextral slip. Mixed layers illite-smectite (I-S) constrain the thermal evolution of the passive margin sequence and of the allochthonous deep-water sediments. In particular, the proximal Hawasina unit (Hamrat Duru) and Sumeini groups of the Dibba Zone are characterized by long-range ordered mixed layers I-S with an illite content of 90–95%, whereas Musandam carbonate units show mixed layers I-S with illite layers ranging from 80–90%, indicating deep diagenetic conditions. Such levels of thermal maturity were acquired during the Late Cretaceous emplacement of a 3.5-km-thick pile of allochthonous units, which were removed by erosion and denudation since the Campanian. U-Pb dating of synkinematic calcite vein highlights reactivation of thrusts at 13.2 Ma, likely due to the involvement of the Musandam area in the Arabia-Eurasia collision.