Shear-wave velocity structure of upper mantle along the Zagros collision zone

Abstract

The lithosphere beneath the Zagros and central Iran has sustained long-lasting Neo-Tethyan subduction and subsequent collisional orogenesis, leading to the complicated crustal and lithospheric structure beneath the Iranian plateau. To better understand the geotectonic and geodynamic evolution of the Iranian plateau, we estimate the shear-wave velocity structure along profiles perpendicular to the Zagros using a self-parameterized Bayesian inversion of the Rayleigh wave group velocity dispersion curves in the period range of 5 to 120 s. Our velocity models, in line with a segmented slab model, show that different geodynamic processes have dominated along the Zagros. In the northern Zagros, the thick and high-velocity lithosphere beneath the Sanandaj-Sirjan Zone (SSZ) and Urumieh-Dokhtar Magmatic Arc (UDMA) is abruptly separated from the low-velocity lithosphere beneath central Iran, while the high-velocity anomaly underlies the UDMA and central Iran in the central and southern Zagros. We propose that the Arabian lithosphere near the suture has probably experienced a distributed thickening in the northern Zagros, and it underthrusts beneath central Iran in the central and southern Zagros. In the central and southern Zagros, a high-velocity anomaly elongates at a depth of 80–120 km between the low-velocity lithospheres of the UDMA and Lut block. This suggests that flat-slab subduction has not extended to the east of the Iranian plateau, therefore, the Eocene-Oligocene flare-up magmatism in the Lut block may be directly independent of the Neo-Tethys subduction. This study suggests that lateral tearing might be responsible for the slab detachment beneath the central and southern Zagros. The slab lithosphere may have started to tear from beneath the central UDMA and have propagated to the edges since ~10 Ma. Furthermore, the southeasternmost Zagros in the vicinity of the Makran zone, as a corner continental collision, has probably experienced slab tearing and break off during the Middle-Late Miocene.