This paper documents the structural history of the central Oman Mountains after the obduction of the Semail ophiolite onto the eastern margin of the Arabian continent during the Late Cretaceous (Santonian/Campanian). The post-obduction history is recorded by a Late Campanian/Maastrichian-Tertiary sedimentary cover to the mountain belt. These sediments have been deformed within an extensional tectonic regime which is continuous northeastwards into the Gulf of Oman hinterland basin and southwestwards away from the SW foothills.Large-scale down-to-the-basin normal faults have been recognized on the Batinah Coastal Plain NE of the mountain belt. Localized block-faulting and roll-over folds are associated with major faults that separate the Late Campanian to Tertiary sediments from older basement rocks of the Oman Mountains and with Late Cretaceous thrusts reactivated as normal faults. To the SW of the mountains, large NW-SE striking folds are thought to be gravity structures developed above a decollement in Late Cretaceous shales.

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The structural history of pre-Permian basement rocks exposed in the domal uplifts of Jebel Akhdar, Jebel Nakhl and Saih Hatat, central and southeastern Oman mountains, is dominated by Late Palaeozoic and Late Cretaceous deformation and metamorphism. In Jebel Akhdar pre-Permian rocks have been deformed by large NE-SW trending thrusts and folds and intense cleavage during Late Palaeozoic compression. Later reactivation of these structures accompanied by a major flattening deformation caused by loading may be related to thrusting and folding in the overlying Permian to Cenomanian platform carbonates. These structures are ascribed partly to Late Cretaceous deformation. The complex internal structure of Saih Hatat is attributed to overprinting of possible Proterozoroic and Late Palaeozoic tectonic events by Late Cretaceous thrusting, folding and associated blueschist metamorphism. The identification of a major basement-cover duplex involving pre-Permian rocks and platform carbonates in Saih Hatat suggests that the pre-Permian basement and platform carbonates did not remain as autochthonous units during Late Cretaceous deformation. Instead, both basement and cover have been thrust southwards during emplacement of the Tethyan thrust sheets onto the Arabian continental margin. Sedimentological evidence from the Tertiary sequence reinforces the development of the Saih Hatat dome as a Late Cretaceous culmination above a deep seated thrust which may have been rejuvenated during the Tertiary. In Jebels Akhdar and Nakhl there is no evidence of a basement-cover duplex. Nevertheless, reactivation of pre-Permian structures and imbrication of cover rocks (Mesozoic platform carbonates) in Jebel Akhdar has important implications to the timing of its structural growth. An alternative model of under-thrusting of the N Arabian margin beneath a subduction trench is also proposed to explain the formation and subsequent elevation of the Oman blueschists.

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