Abstract

The northernmost extremity of the Oman Mountains, the Musandam Peninsula, is composed of an allochthonous sequence of Permian to middle Cretaceous shelf carbonates. These are separated from ophiolitic rocks to the south by a northeast-southwest-trending belt known as the Dibba zone. This structurally complex belt is composed of allochthonous slope- and basin-facies sediments, Haybi volcanic rocks, “Oman Exotic” limestones, sub-ophiolitic metamorphic rocks, and ultra-mafic slices.

Lithofacies correlation confirms that fragmentation and rifting of a vast east-facing carbonate platform occurred in Middle to Late Triassic time, resulting in the establishment of a shelf edge and small ocean basin. This margin was typified from northwest to southeast by ooid-skeletal lime sand shoals or small bioherms on the shelf edge, a bypass foreslope of well-laminated periplatform ooze, and basin-margin accumulations of carbonate turbidites or debris flows. The shelf edge now coincides with the northern boundary of the Dibba zone and appears to have remained stationary from Middle Triassic to Late Jurassic time. Periods of arrested carbonate sedimentation on the platform either because of exposure (Late Triassic and middle Cretaceous) or because of drowning (Late Jurassic) are represented in the basin by starved sedimentation and deposition of radiolarian cherts. A spectacular platform margin collapse occurred in the middle and Late Cretaceous, as represented by massive conglomerates, with clasts as young as Albian, above an unconformity that progressively removed all of the Lower Cretaceous.

The Tethyan basinal and ophiolitic rocks of the Dibba zone were emplaced from the east-southeast during the Turonian to lower Maastrichtian. After emplacement of these allochthonous units, compressional deformation in the mid-Tertiary resulted in large-scale, open, “whaleback” folds with wavelengths as much as 15 km, generally with north-south axes. In places, these folds, which affect the complete shelf and allochthonous sequences, are overturned toward the west, and thrusting has caused previously lower tectonic units of the Late Cretaceous stacking order to be thrust over previously higher tectonic units, thus reversing the Late Cretaceous tectonostratigraphy. The maximum amount of translation on the later thrusts is in excess of 5 km on the Hagab thrust, where the complete shelf carbonate sequence of the Musandam Mountains has been thrust west-northwest over the previously higher Hawasina and Haybi thrust sheets. The Tertiary folding and thrusting can be correlated in time and space with the Zagros fold belt of southwestern Iran.

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