Post-collisional lithospheric delamination in eastern Iran, revealed by non-linear teleseismic tomography and residual topography

Abstract

The Eastern Iranian Mountain Ranges (EIR) emerged as a consequence of the Late Cretaceous collision between the Afghan and Lut blocks. However, the response of the uppermost mantle to this collision remains enigmatic. Additionally, although petrological evidence suggests that post-collisional delamination is possible, it has not been conclusively identified in prior regional seismic imagery. This observation leads us to further explore this possibility using a dense seismic network. To gain insight into the geodynamic implications for eastern Iran and address knowledge gaps, we extensively investigated the seismic structure of the uppermost mantle beneath the EIR using a dense seismic network of 34 temporary stations, complemented by data from nine additional local permanent stations. By meticulously analyzing 6589 relative arrival time residuals from teleseismic records with favorable signal-to-noise ratios, we applied a non-linear tomography method to map P-wave velocity perturbations in a relative sense. Our tomographic images unveiled distinct instances of rapid high-velocity anomalies beneath low-velocity regions in the shallow mantle, suggesting the potential occurrence of lithospheric dripping, followed by subsequent asthenospheric upwelling. This observation offers a plausible explanation for the observed post-collisional magmatism over the Lut Block. Furthermore, to maintain the approximately 1.5-km positive residual topography across the EIR, beyond the influence of crustal properties, additional support from the hot and buoyant asthenosphere becomes crucial, particularly in the absence of a substantial lithospheric mantle.