Deformation history and processes during accretion of seamounts in subduction zones: The example of the Durkan Complex (Makran, SE Iran)

The Durkan Complex is a tectonic element of the Makran Accretionary Prism (SE Iran) that includes fragments of Late Cretaceous seamounts. In this paper, the results of map- to micro-scale structural studies of the western Durkan Complex are presented with the aim to describe its structural and tectono-metamorphic evolution. The Durkan Complex consists of several tectonic units bordered by mainly NNW-striking thrusts. Three main deformation phases (D₁, D₂, and D₃) are distinguished and likely occurred from the Late Cretaceous to the Miocene-Pliocene. D₁ is characterized by sub-isoclinal to close and W-verging folds associated with an axial plane foliation and shear zone along the fold limbs. This phase records the accretion of fragments of the seamount within the Makran at blueschist facies metamorphic conditions (160-300 °C and 0.6-1.2 GPa). D₂ is characterized by open to close folds with sub-horizontal axial plane that likely developed during the exhumation of previously accreted seamount fragments. An upper Paleocene-Eocene siliciclastic succession unconformably sealed the D₁ and D₂ structures and is, in turn, deformed by W-verging thrust faults typical of D₃. The latter likely testifies for a Miocene-Pliocene tectonic reworking of the accreted seamount fragments with the activation of out of sequence thrusts. Our results shed light on the mechanism of accretion of seamount materials in the accretionary prisms, suggesting that seamount slope successions favour the localization and propagation of the basal décollement. This study further confirms that the physiography of the subducting plates plays a significant role in the tectonic evolution of the subduction complexes.