One line on the map: A review of the geological history of the Semail Thrust, Oman-UAE mountains

The Semail Thrust in the Oman-UAE mountains is mapped along the base of the Semail Ophiolite, a 10–15 km thick sequence of Cenomanian oceanic crust and upper mantle emplaced from NE to SW onto the previously passive, Mid-Permian to Cenomanian continental margin of Oman. The juxtaposition of the Semail ophiolite with a range of different rock types sourced from different depths suggest a complex tectonic history for this major fault and shear zone. Here we summarize previous work and present an overview of the tectonic history of the fault. The Semail Thrust is mapped along the base of the ophiolite as a single line on the geological map, yet it covers a variety of structural features spanning depths of 40–45 km to the surface, and a time scale from ∼96 Ma (or earlier) to Eocene time. The structural evolution of the Semail Thrust includes (a) the roof fault or ductile shear zone of an exhumed oceanic subduction zone (granulites, amphibolites and greenschists of the metamorphic sole), (b) a deep mantle ductile shear zone (Banded Ultramafic Unit), (c) a brittle fault above a foreland-directed fold-thrust belt, (d) an out-of-sequence brittle fault exhuming a higher ophiolite thrust sheet above deeper level lower crust granulites (e.g. Bani Hamid, UAE), (e) a late out-of-sequence thrust truncating underlying structural units (e.g. Hawasina Window), (f) a passive roof fault beneath exhuming HP rocks (e.g. ‘Semail Thrust’ below the Muscat peridotite, above the Ruwi mélange and high-pressure rocks of northern Saih Hatat), and (g) a reactivated normal fault bounding rising footwall culminations, notably of the Jebel Akhdar, Jebel Nakhl, and Saih Hatat anticlines. Different stages in the evolution of the Semail Thrust can be mapped out and interpreted from different regions along the Oman Mountains.