![]() ![]() Reactivation of long-lived basement faults has significant influences on further deformation of collision zones. Reactivation versus reworking of the active continental margin during the Zagros collision: Mahallat-Muteh-Laybid complexes, Sanandaj-Sirjan zone, IranĪflaki, Mahtab Shabanian, Esmaeil Davoodi, Zeinab Mohajjel, Mohammad To balance plate circuits and documented shortening requires whole-sale subduction of ~500-800 km of continental Both a 25 and a 35 Ma collision estimate thus requires that a considerable portion of the Arabian plate subducted without recognized accretion of its upper crust. These estimates suggest that the orogen has shortened 200 to 300 km since the early Miocene. Shortening within Eurasia is estimated to be 53-75 km through the Kopet Dagh and Alborz Mountains, plus 38 km across Central Iran. Balanced cross-sections give 105-180 km of Zagros shortening (including estimates from the Zagros proper, 45-90 km, and the Zagros "crush" zone, 60-90 km). ![]() The Zagros fold-thrust belt consists of thrusted upper crust that was offscraped from subducted Arabian continental lithosphere. To assess the consequences of these collision ages for the amount of Arabian continental subduction, we compile all documented shortening within the orogen. Plate circuits indicate, from NW to SE along the collision zone 490-650 km of post-25 Ma Arabia-Eurasia convergence and 810-1070 km since 35 Ma. Africa-North America-Eurasia plate circuit rotations, combined with Red Sea rotations provides precise estimates of the relative positions between the northern Arabian margin and the southern Eurasia margin. However, upper plate deformation, exhumation and sedimentation are used to argue for an older, 35 Ma collision age. Both lower Miocene synorgenic strata with growth structures adjacent to the main Zagros fault and upper Oligocene to lower Miocene overlap strata over post-collisional thrusts are derived from Eurasia and require that collision was underway at least by ~25-24 Ma. Estimates on the age of collision for Arabia and Eurasia range from late Cretaceous to Pliocene, based on a wide variety of presumed geologic responses. When did continents collide, and how is convergence partitioned after collision are first order questions that seem to defy consensus along the Alpine-Himalyan orogen. Retrodeforming the Arabia-Eurasia collision zone : Age of collision and magnitude of continental subduction ![]()
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