Ongoing formation of felsic lower crustal channel by relamination in Zagros collision zone revealed from regional tomography

Abstract

Complex interaction of rheologically contrasting layers within the lithosphere during the collision of continental plates leads to active faulting, which represents a serious hazard to the population and infrastructure. One of the collision scenarios presumes the existence of a middle-lower crustal channel composed of subducted silicic upper crustal rocks, which is thought to exist in the Tibetan-Himalayan system. Based on the results of seismic tomography, we argue that a similar mechanism of crustal channeling takes place beneath the Zagros mountain system in southwestern Iran. The 3D seismic velocity model reveals an inverted crustal architecture of the collision zone, in which the low-velocity felsic (granitic and sedimentary) upper crustal rocks of the Arabian plate form a seismically inactive lower crustal channel below the higher-velocity mafic (basaltic) middle-upper crustal layer of the Iranian crust. Based on existing numerical models, we suggest that the formation of the felsic channel is likely governed by separation (delamination) of the weak felsic upper crust of the subducting Arabian lithosphere and its ductile underplating under rheologically stronger upper-middle crust of the Iranian plate.

High‐Resolution Lithospheric Structure of the Zagros Collision Zone and Iranian Plateau

“…There are, however, differences between the two models. The low-velocity zone in the model of Talebi et al (2020) is deeper by about 10-20 km than the corresponding structure in our model. Its base reaches to Moho depth as estimated by our model and other models available in the literature.…”

“…This model proposes a doubling of the dense lower crust beneath the SSZ which compensates for the negative Bouguer anomaly and also shifts the anomaly southward over the High Zagros to match the observations. A recent regional P and S waves tomography study by Talebi et al (2020) revealed an elongated crustal low-velocity anomaly that slopes gently northeastward under the NW and central Zagros and SSZ. Talebi et al (2020) proposed that this layer and the higher-velocity layer beneath it represent the felsic and mafic parts of the Arabian crust, and as the Arabian margin underthrusts central Iran, its felsic layer forms a lower-crustal channel beneath the Iranian crust.…”

“…A recent regional P and S waves tomography study by Talebi et al (2020) revealed an elongated crustal low-velocity anomaly that slopes gently northeastward under the NW and central Zagros and SSZ. Talebi et al (2020) proposed that this layer and the higher-velocity layer beneath it represent the felsic and mafic parts of the Arabian crust, and as the Arabian margin underthrusts central Iran, its felsic layer forms a lower-crustal channel beneath the Iranian crust. This crustal architecture bears similarities to the internal structure of the crust in our model.…”

“…Talebi et al. (2020) proposed that this layer and the higher‐velocity layer beneath it represent the felsic and mafic parts of the Arabian crust, and as the Arabian margin underthrusts central Iran, its felsic layer forms a lower‐crustal channel beneath the Iranian crust. This crustal architecture bears similarities to the internal structure of the crust in our model.…”

Seismic Evidence for a Weakened Thick Crust at the Beaufort Sea Continental Margin

“…We use the Local Tomography Software (LOTOS) to estimate the three‐dimensional isotropic seismic velocity structure (Koulakov, 2009). LOTOS has been successfully applied to a variety of tectonic settings (e.g., collision zones: Talebi et al., 2020; Medved et al., 2021, subduction zones: Foix et al., 2019, ocean‐continent transition zone: El Khrepy et al., 2021 and paleo‐rift system in eastern Canada: Onwuemeka et al., 2021). Starting with a 1‐D (i.e., layered) velocity model, the software calculates the travel times based on a reference table of initial event locations, and uses a grid search method to relocate all events (Koulakov & Sobolev, 2006).…”