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Geological Society, London, Special Publications; 1990; v. 49; p. 327-339;
DOI: 10.1144/GSL.SP.1992.049.01.20
© 1990 Geological Society of London

Evolution of the Oman Tethyan Continental Margin

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

J. Le Métour1, D. Rabu1, M. Tegyey2, F. Béchennec1, M. Beurrier2 & M. Villey2

1 Service Géologique National, B.R.G.M., 10 rue Henri Picherit, 44300 Nantes, France
2 Service Géologique National, B.R.G.M., B.P. 6009, 45060 Orléans Cedex, France

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 Permian-Cretaceous cover of the Arabian continental margin and from the oceanic floor of the Semail marginal basin that opened during the Albian-Cenomanian. Tectonic slicing and strike-slip faulting within the platform unit, on the northern margins of Jabal Akhdar and Saih Hatat, formed frontal and lateral ramps during the advance of the nappes onto the Arabian Platform.

During a third phase of deformation, probably during the Campanian-Maastrichtian, large-amplitude, long-wavelength, open, near-upright folding accompanied by poorly developed, subvertical, SSW-NNE fracture cleavage indicates moderate shortening during uplift perpendicular to the earlier structures.

The resulting Eo-Alpine foreland belt of the Oman Mountains was partly covered by marine carbonate deposits during the middle Maastrichtian to late Maastrichtian or early Palaeogene before being affected by Alpine tectonics during the Miocene.





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