Subduction and obduction: two stages in the Eo-Alpine tectonometamorphic evolution of the Oman Mountains

Abstract: The platform unit of the Oman Mountains is composed of shelf sedimentary and volcanic rocks, ranging in age from late Proterozoic to late Turonian-Coniacian, that were deformed mainly during the polyphase Eo-Alpine tectogenesis. In the late Turonian-Coniacian tangential shearing deformation with NE (oceanward) vergence occurred under HP/LT conditions of regional metamorphism. This tectonic phase was largely responsible for the structural and metamorphic zonation of the platform unit. A SW-NE gradient from external to internal zones has been recognized from the south flank of Jabal Akhdar, where fracture cleavage appears, to the eastern part of Saih Hatat, where schistose glaucophane ecologites are preserved. This tectonometamorphic event was related to partial subduction of the northeast corner of the Arabian platform beneath the neo-Tethyan oceanic lithosphere. A later phase of higher-level shearing deformation with SW (continentward) vergence, during the Campanian, accompanied the thrusting of the Hawasina Nappes and the obduction of the Semail Ophiolite. These tectonic units were transported SSW respectively from the Pcrmian-Cretaceous cover of the Arabian continental margin and from th