The Oman Mountains as a Part of the Alpine-Himalyan Orogen

The Oman Mountains, part of the Alpine-Himalayan orogen, are some 700 km long near the leading edge of the Arabian plate east of the Oman line (Strait of Hormuz) and dying out against the Owen Basin of the Indian Ocean to the east. The Samail Ophiolite is slice of Cretaceous Tethys oceanic lithosphere (“north” trending ridge system, east-west spreading) obducted (SSW) onto the Arabian platform and now represents the structurally highest allochthonous unit in the mountain range. In contrast to the Zagros suture west of the Oman line, remnants of Cretaceous oceanic crust underlie the Gulf of Oman to the north and are now being subducted underneath the Makran (Iran). The ophiolite overlies a succession of Hawasina Group nappes that represent oceanic sedimentary rocks that transition from abyssal depths to continental slope units; the succession interpreted as a telescoped passive margin subducted (footwall) beneath the hanging wall of the obducted Samail Ophiolite. The geology of the Saih Hatat dome south of Muscat complicates this simple interpretation with the discovery of a Campanian age northward-facing fold nappe developed in the formerly autochthonous Arabian platform. The upper limb of the nappe is pinned to the undeformed Arabian margin whereas the overturned, lower-limb high strain zone truncates against a crustal discontinuity underlain by a high P/low T, composite lower plate consisting of lawsonite schist (Ruwi schist) to eclogite facies rocks (As Sifah window, Aptian age peak metamorphism). Strain analysis of the upper plate nappe suggests a rolling hinge zone involving the Arabian platform rocks driven by underthrusting of the exhumed lower plate on a discontinuity that dips towards the Arabian margin. These Cretaceous structures and post-obduction shallow Tertiary marine sediments are folded in the Neogene into the current configuration of the Oman Mountains, a precursor to Oman's future closing against the Makran.