Introduction Background
The evolution of the Zagros collision
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The evolution of the Zagros collisionA recent synthesis of GPS data and geologic constraints on plate circuits suggests that the convergence occurred at a rate of about 20 km/Myr since at least 22 Ma, following the separation of Arabia from Africa (Nubia) (Nilforoushan et al., 2003; Tatar et al., 2002; Vernant et al., 2004a; Vernant et al., 2004b). That agrees with stratigraphic and structural limitations in the Zagros region near the plate suture, which support a minimum age of 23–25 Ma for the Neo-Tethyan Ocean's final closure. This observation is in line with the 19.7 Ma synorogenic sandstones of the Razak Formation, which have been precisely dated by magneto stratigraphy (Vernant et al., 2004a), and the Lower Miocene sedimentation in the Zagros that replaced the Oligocene carbonates. Furthermore, recorded seismic lines from the Persian Gulf provide evidence for a flexural unconformity that dates to the Middle Miocene or possibly earlier (Soleimany and Sàbat, 2010). Together, these concurrent data show that the northern Zagros was experiencing uplift, erosion, and contraction and that the ultimate suture occurred in the early Miocene. Numerous pieces of evidence provide supportive information on a constructional episode in the Arabian margin before the Early Miocene. For instance, the Zagros carbonates sequence has an unconformity long-recognized middle Eocene-late Oligocene or Late Eocene-Lower Miocene (Berberian and Berberian, 1981). It extends the 15 Ma middle-late Eocene erosional or non-depositional hiatus to the northwest in the Lurestan area (Homke et al., 2010). The foreland basin's coarsening upward sedimentation began in the late Oligocene, close to the suture zone, according to a recent reevaluation of the stratigraphy of the coarse-grained facies (Fakhari et al., 2008). This finding shows that the large unconformity in the northern Zagros resulted in tectonic loading between the middle Eocene and the late Oligocene. According to (Khadivi et al., 2010) and (Mouthereau et al., 2007), this event occurred before the Zagros foreland basin reached the Miocene overfilled stage. As a result, it most likely marks the beginning of the current Zagros collision, which should be dated to the Late Eocene-Early Oligocene transition at about 35 Ma. A recent analysis of deformation chronology to the north of the suture zone confirms collisional shortening beginning in the Late Eocene-Oligocene. It is further corroborated by the discovery of detrital zircons in the late Oligocene conglomerates deposited in the northern Zagros with U/Pb ages of 45–50 Ma, sourced from the supervening Iranian microplate (Horton et al., 2008). Miocene sediments' apatite fission track ages point to a fast cooling in the NW Zagros belt at about 38 Ma (Homke et al., 2010). The rapid cooling and sedimentation occurred in the High Zagros between 19–15 Ma and 12–8 Ma utilizing helium dating on detrital zircon and apatite in the Dezful region of the northern Zagros (Gavillot et al., 2010). The youngest grain-age population of 22 Ma and AHe ages indicate that the Arabian edge exhumed between 20 and 10 Ma, and uplift and exhumation in the Zagros and Iranian plateaus were both by around 20 Ma. As a result, it was compared to the initial collision's 35 Ma. Although the precise sequential timing of collision events is still in question, there is no doubt that a marine gateway connecting the Mediterranean Sea and the Indo-Pacific Ocean existed at least until the early Miocene in Central Iran and until ca. 15 Ma on the Arabian margin in the Zagros, about 20 Ma after the initial collision. A continent-continent collision that started in the Tertiary gave rise to the Zagros fold and thrust belt (ZFTB), continued shortening of the mountain range, and formation of the Zagros foreland basin. The SW-NE oriented contraction resulted in the formation of NE dipping thrusts, NW-SE trending folds, and SW-verging folds in the Phanerozoic sedimentary cover. Above this basement is a separation zone for the Infra-Cambrian Hormuz evaporates. (Alavi, 1994). Download 0.84 Mb. Share with your friends:
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