A new structural profile along the Muscat-Ibra transect, Oman: Implications for emplacement of the Samail Ophiolite

Abstract

The Oman Mountains preserve evidence for a long-lived, kinematically coherent, tectonic event linked to the emplacement of the Oman ophiolite. Three windows (Hawasina, Jabal Akhdar, and Saih Hatat) hold the keys to thepuzzle of the ophiolite obduction and the tectonic development of this part of the Arabian Peninsula. In the southeasternmost Saih Hatat window, where continental-shelf sequences have been subjected to blueschist- to eclogite-facies metamorphism, a major fold nappe and two major crustal-scale shear zones reveal the pre-emplacement geometry of the Arabian margin. They necessitate initial underthrusting toward the margin, rather than away from it as in most other published models. The stretching lineation is consistent in all of the units including the?Pre-Cambrian Hatat Schist in the core of a regional fold nappe, the major shear zones and schistosity of the fold nappes, the high-pressure rocks beneath the fold nappe, and the high-temperature sole (intraoceanic thrust) of the uppermost nappe (Samail ophiolite). This consistency suggests that the deformation and metamorphism displayed in the Saih Hatat window are part of this long-lived event. The tectonic environment for ophiolite obduction involved initial subduction and high-pressure metamorphism of a continental slab (microplate) toward the former Arabian margin followed by neutral buoyancy of the slab, causing intraoceanic thrusting, and then buoyant rise and internal deformation of the slab along the former subduction interface. Slab rise led to gravitational instability of the partially obducted ophiolite, thinning along normal faults, and eventual gravity-driven emplacement of the Samail nappe onto the Arabian margin.