Upper mantle structure under the Zagros collision zone; insights from 3D teleseismic P-wave tomography

International audienceWe map the lateral variations of P-wave velocity beneath the Zagros collision zone in Iran down to 800 km depth by regional travel time tomography. We invert 32,293 relative travel time residuals from five temporary seismic networks across the collision zone in NW and central Zagros and northern Iran, and a large number of permanent stations distributed over the Iranian Plateau. A salient feature of our model is a ~225 km thick lithosphere beneath the Zagros, almost twice as thick as in the rest of Iran. Slab detachment at a depth range of 250-300 km from the base of the subducted continental Arabia is clearly distinguishable in central Zagros. In NW Zagros detachment appears to be at an earlier stage. Beneath the central Iran Plateau, we observe shallow low-velocity regions down to 200 km depth, and smaller patches with significantly higher velocity in the 200-400 km depth range. This pattern could suggest a post-collisional foundering of the mantle lithosphere in the upper plate. The subducted slab seems to penetrate into the lower mantle in a segmented fashion, with no evidence for a stagnant slab above the 660 km interface