UPPER MATNLE STRUCTURES OF THE NW IRAN USING 3D TELESEISMIC TOMOGRAPHY

The Zagros mountain range is part of the Alpine-Himalayan Orogenic belt, and has formed as a result of the convergence between the Arabian and Eurasia plates. Most of the Iranian plateau is affected by complex Cenozoic geodynamic processes due to subduction and closure of the Neo-Tethys Ocean beneath the SW margin of Central Iran. This subduction followed by volcanism, slab detachment, possible mantle erosion in the overriding continent, and the final formation of the Zagros mountain belt and related tectonic provinces. The collision between Arabia and Iranian micro-continent started in the Early Miocene (~16-23 Ma) and final closure of the Neo-Tethys Ocean is suggested at ~12 Ma. The convergence of the Arabian plateau towards Central Iran (~25 mm/yr) is accommodated by transpressional faulting in the middle and southern part of the belt, and slip partitioning in the northern part throughout the simple fold thrust belt (SFTB) and the Main Zagros Thrust (MZT). In this study, we perform a 3D teleseismic tomography using relative teleseismic P wave travel times to estimate the relative velocity structures of the upper mantle and part of the lower mantle of the Iranian plateau to the depth of 800 km. We used 26000 P wave teleseismic relative travel times, recorded by Zagros01, Zagros03, Iran-China temporary networks and Iranian Seismological Center (ISC) and International Institute of Earthquake Engineering and Seismology (IIEES) permanent networks. Before inverting data we performed Moho depth, station elevation, and Earth radius variation corrections. For calculating the Moho depth variations, we performed a receiver function analysis on the three temporary networks and estimated the Moho depth corrections. We used the Aki et al. (1977) method for performing teleseismic tomography. In order to invert our data, we need to parameterize our study region. To do so we had divided our study region into 25×25×25 km blocks. For dealing with the singularity of Jacobean Matrix, estimation of the relative velocity in theunderdetermined part of the model, and smoothing of the output model, we add damping and smoothing constraints to the Jacobean Matrix, and finally, we invert the data using the LSQR method.

Keywords:

3D tomography , Geodynamic reconstruction , Upper mantle Structures , Slab break-off