MESOZOIC MODIFICATION OF THE ARABIAN RIFT MARGIN: CONSEQUENCES FOR CENOZOIC EVOLUTION

Cenozoic collisional tectonics are responsible for the majority of deformation seen in the Zagros today. However, the late Mesozoic obduction of the Peri-Arabian ophiolite had profound effects on the crustal and lithospheric structure of the margin affecting both its Cenozoic collisional and subsidence history.

A new, lithosphere scale tectonic model for the late Mesozoic and Cenozoic evolution of the north-eastern margin of the Arabian craton is presented, integrating recent observations from Iran with tectonic models developed for the Oman margin. Late Mesozoic transient subduction of the Arabian craton in the Semail, intra-Tethyan subduction zone resulted in thermal erosion of the mantle lithosphere and metamorphism of the outboard portions of Arabia. Metamorphosed rocks of the distal Arabian craton were isostatically uplifted through the combined mechanisms of slab breakup and breakoff of the Tethyan oceanic slab. The Arabian mantle lithosphere was further attenuated by crustal extension during breakoff of the Tethyan slab and subsequent tectonic unroofing. Tectonic unroofing was accomplished by normal reactivation of the Semail thrust which juxtaposed young Semail oceanic crust with the Arabian craton. As such, the contact between continental crust and oceanic crust is marked by an abrupt fault juxtaposition of genetically unrelated rocks of dissimilar age. Thermal re-equilibration of the mantle lithosphere in the latest Mesozoic and Cenozoic resulted in a phase of renewed thermal subsidence of the proto-Zagros foreland basin, which continued until the latest Paleogene-Neogene continental collision. Subsidence associated with this thermal re-equilibration of the Arabian margin is recorded in tectonic subsidence curves from wells in the Oman foreland basin. Tectonic shortening of the Arabian margin by buoyancy driven thrusting of distal Arabian upper crust onto the craton during slab breakup, could influence plate tectonic estimates for the onset of continental collision by reducing the undeformed width of the passive margin. Isostatic rebound of the Arabian lower plate following slab break-off was rapid, lasting approximately 10 Ma and was immediately followed by renewed subsidence and onlap. Thermal subsidence appears to have overwhelmed isostatic uplift induced by slab breakoff.