GEOLOGIC CONSTRAINTS ON THE ORIGIN AND OBDUCTION OF THE OMAN OPHIOLITE: 40 YEARS AFTER GLENNIE ET AL

The formation and obduction of the Samail Ophiolite despite the wealth of data are still controversial. The timing of the metamorphic sole and the igneous age of the ophiolite requires the allochthony of the ophiolite to occur consanguinously with formation at a spreading center (Cenomanian). The destruction of the passive Arabian margin culminated with the emplacement (Campanian) of the Samail Ophiolite Complex over the telescoped (<300 km shortening) Arabian continental shelf and continental slope and abyssal plain of the Hawasina Ocean (Permo-Triassic to Late Cretaceous). The relative structural sequence and the geochronologic data from Saih Hatat window (SE block) requires that the earliest deformation and peak high P-low T metamorphism of the continental shelf rocks of the Saih Hatat Lower Plate (Albian) predates the ophiolite's allochthony and suggests that the tectonic transport direction changed by almost 90 degrees similar in magnitude and bearing to the change in spreading direction between the upper and lower pillow lavas of the ophiolite. The Saih Hatat window also exposes a large (100 km scale) recumbent nappe that is pinned to the undeformed, stable Arabian platform. Strain in the nappe increases into a rolling hinge zone that becomes the highly-strained, generally overturned, carpholite-bearing lower limb (also high P-low T) that is truncated by a Campanian shear zone that dips towards the craton, i.e. the boundary with the Lower Plate. The Lower Plate exhumation lineation (Turonian) parallels the inferred emplacement direction of the Samail ophiolite and roughly parallels the spreading direction of feeder dykes for the Cenomanian upper pillow lavas of the Samail ophiolite (suprasubduction or intraoceanic overthrust phase). The changes in lineations in the high pressure metamorphic rocks and in spreading direction appear to record the change in plate motions seen in reconstructions of Afro-Arabia’s motion relative to Eurasia. The current NNE transport direction of the Arabian plate must date to the Albian. Ophiolite obduction onto Arabia and Alpine-style deformation of the formerly passive margin occurred with at least two thrust systems without a suture zone setting the stage for the future collision with Eurasia while Arabia was an ocean away (>1400 km) from the current collisional boundary.