3D joint inversion modeling of the lithospheric density structure based on gravity, geoid and topography data — Application to the Alborz Mountains (Iran) and South Caspian Basin region

We present a 3D algorithm to obtain the density structure of the lithosphere from joint inversion of free air gravity, geoid and topography data based on a Bayesian approach with Gaussian probability density functions. The algorithm delivers the crustal and lithospheric thicknesses and the average crustal density. Stabilization of the inversion process may be obtained through parameter damping and smoothing as well as use of a priori information like crustal thicknesses from seismic profiles. The algorithm is applied to synthetic models in order to demonstrate its usefulness. A real data application is presented for the area of northern Iran (with the Alborz Mountains as main target) and the South Caspian Basin. The resulting model shows an important crustal root (up to 55km) under the Alborz Mountains and a thin crust (ca. 30km) under the southernmost South Caspian Basin thickening northward to the Apsheron–Balkan Sill to 45km. Central and NW Iran is underlain by a thin lithosphere (ca. 90–100km). The lithosphere thickens under the South Caspian Basin until the Apsheron–Balkan Sill where it reaches more than 240km. Under the stable Turan platform, we find a lithospheric thickness of 160–180km. ► 3D joint inversion of free-air gravity, geoid and topography data for lithospheric structure. ► Method allows integration of a priori knowledge from other Earth Sciences fields. ► Application to northern Iran and South-Caspian Basin. ► Evidence for crustal root under Alborz Mountains. ► Northward subduction of South-Caspian lithosphere under the Apsheron–Balkan Sill.