OMAN BEFORE THE POST-MIOCENE OMAN MOUNTAINS: OPHIOLITE OBDUCTION RESULTING FROM PLATE BOUNDARY REORGANIZATION

Structural windows into the Oman Mountains constrain the Late Cretaceous destruction of the passive Arabian margin culminating with the emplacement of the Samail Ophiolite Complex over the telescoped Arabian continental shelf, continental slope and abyssal plain of the Hawasina Ocean. The Hawasina window provided the first evidence of the involvement of the stable platform with fold nappe development, e.g. Sumeini Group (parautothochtonous shelf carbonates) The Saih Hatat window 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 that is truncated by a Campanian shear zone that dips towards the craton. The shear zone separates Arabian platform rocks from a lower plate consisting of three subdomains which include the lawsonite-bearing Ruwi schist, the blueschist to greenschist of Hul’w window, and the As Sifah window containing glaucophane-bearing eclogite in a section of quartz-phengite schist, mafic schist with metatuff (early Permian), calcschist and marble. An Albian, east-trending lineation in the As Sifah subplate (that roughly parallels the spreading direction of the younger Samail ophiolite lower pillow lavas) marks this early Cretaceous peak of metamorphism and predates both the Cenomanian igneous age of the Samail Ophiolite and its allochthony (age of the metamorphic sole). The lower-plate exhumation lineation (Turonian) parallels the inferred emplacement direction of the Samail ophiolite and is roughly parallel to the spreading direction of feeder dykes of the Cenomanian upper pillow lavas of the Samail ophiolite (suprasubduction or intraoceanic overthrust phase). The proto-Oman Mountains record a major plate boundary reorganization event that occurred on the northeastern edge of the Arabian plate; the event predates both the early Tertiary initiation of northward subduction now represented by the Makran of Iran and the post-Miocene uplift of the Oman Mountains.