The post-Campanian tectonic evolution of the Central Oman Mountains: Tertiary extension of the Eastern Arabian Margin

Abstract

Abstract 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. Syn-sedimentary tectonic influences are summarized and integrated with the structural analysis to identify the style and timing of tectonism on the S margin of the Gulf of Oman from the Late Campanian/Maastrichtian to present. There is evidence to suggest that penecontemporaneous tectonics controlled rates of subsidence and facies development during this time. A major E-W trending palaeo-high running close to the present-day shoreline affected Palaeogene sedimentation. Unlike the northern Oman Mountains (Musandam Peninsula), there is no unequivocal evidence of mid-Tertiary (Zagros) compressional structures in the central Oman Mountains. Structural development of the cover sediments in the central mountain belt is believed to be controlled by underlying Late Cretaceous basement structures. In particular the Saih Hatat culmination was a positive structure throughout the Late Cretaceous and Early Tertiary, affecting both the stratigraphic and structural history of adjacent areas. The northern end of the Nakhl culmination seems to have had little effect on sedimentation but did influence deformation in the Tertiary.