A New Lithospheric Density and Magnetic Susceptibility Model of Iran, Starting From High‐Resolution Seismic Tomography

We propose a new model for the crust and upper mantle in Iran by joint inversion of gravity and magnetic fields, constrained with a seismic tomography model. We then calculate shear modulus from the Vs velocities and densities. The crust and mantle tomography model is first converted to a density cube through empirical and petrological velocity-density relations. The starting susceptibility is assigned to a two-layer homogeneous model, above a heat flow-derived Curie depth. Considering the uncertainties in the density-velocity relations, and the starting layered susceptibility variation, we refine the model by a constrained inversion of the gravity and magnetic fields with a Bayesian approach, producing the final 3D density and susceptibility model. The area is tectonically active with high seismicity and active faulting which are regulated by the crustal density and rigidity variations. Higher rigidity matches lower seismicity and extended deserts and basins, suggesting the control of their development. The Neo-Tethys suture, extending similar to 1,500 km long, as well as the Paleo-Tethys suture match crustal scale density variations, defining characteristics of the lighter Arabian plate and denser Eurasian crust. The South Caspian Basin is enigmatic, due to focusing on the seismicity along all its borders, but with relatively low average rigidity, which is contrary to what is observed for Iran, where the reduced rigidity correlates with higher seismicity. The 3D density model will be useful for numerical geodynamic models and obtaining geologic inferences from the crustal-scale units. The inversion of potential fields may produce inconsistent results, since there are always multiple models that resolve the anomalies, and the use of other geophysical data sets is necessary. To resolve the problem, we extract information from a high-resolution seismic tomography. With seismic velocities and defining the different layers of the model, using data available in the literature, we realize an a-priori model, on which we perform a Bayesian joint gravity and magnetic inversion, to obtain a final 3D model of the Iranian lithosphere, with a detailed distribution of densities and susceptibilities. With density and velocity values, we also calculate the rigidity of the area. We then compare the models obtained, with geological and tectonic information of the area, observing how density and susceptibility distribution reproduce the position of the magmatic outcrops and the principal tectonic lineaments, indicating the position of the Neo-Tethyan and Paleo-Tethyan sutures. Also, the rigidity model is consistent with the seismicity distribution of the area. 3D Bayesian joint inversion builds a reliable model of the lithosphere in the Iranian collision belt, useful for rheological calculationsMost of the magmatic and tectonic features can be followed by density variations in the crust, partly extending to the lower crustJointly with the seismic Vs tomography, rigidity is obtained which explains the inhomogeneous distribution of seismicity in the area