Postobductional Kinematic Evolution and Geomorphology of a Major Regional Structure—The Semail Gap Fault Zone (Oman Mountains)

The Semail Gap/Semail Gap Fault Zone is one of the most prominent tectonic features in the Oman Mountains and is located between the Jabal Akhdar Dome in the west and the Saih Hatat Dome to the east. The two domes were uplifted during the Late Eocene to Early Miocene. Uplift led to monoclinal bending with a “fold axis” parallel to the Semail Gap. Subsequently, dextral transtensional faulting along the Semail Gap Fault Zone ensued. This fault zone follows a major preexisting fault, which explains the distribution differences of Neoproterozoic and Phanerozoic sedimentary formations (partly omissions) across this structure. The vertical and horizontal displacements along the Semail Gap amount to up to ~5.5 and ≤2 km, respectively. Vertical displacement may be a combination of monoclinal bending and later faulting along the Semail Gap Fault Zone. Its latest activity mainly preceded the Quaternary because there is only minor faulting of Quaternary deposits. Despite ongoing uplift of the Oman Mountains, which may amount to ≤50 m during the Quaternary based on incision of wadi/alluvial terraces, only insignificant seismicity is observed and attributed to minor movements along this fault zone. The transtensional deformation is a result of uplift and orogenic/gravitational collapse of the Jabal Akhdar/Saih Hatat domes. The neighboring two hanging wall blocks of each dome moved downward, ESE/SE and SSW/SW, which explains dextral transtension along the Semail Gap Fault Zone. The Semail Gap Fault Zone has a sinistral transtensional counterpart at the southwestern margin of the Nakhl Subdome/Saih Hatat Dome.