Integrative Approach for Inversion of Gravity, Seismic and Tomography Data: Application to Northern Eurasia

Abstract:

Mass anomalies in the Earth's mantle associated with thermal and compositional heterogeneities or with deflected boundaries between layers of different density produce stresses, which initiate mantle convection, plumes, subduction and deformations of the lithosphere. In particularly, the upper mantle plays a key role in controlling surface tectonics. Therefore, knowledge of density heterogeneity of the upper mantle is principal for understanding its dynamics and ongoing tectonic processes. This is particularly important for a complicated region such as Eurasia, where nearly all types of tectonic settings are present. There exist three main problems in construction of 3-D density models of the upper mantle. First, it is necessary to remove before hand the effect of the crust, which substantially masks the upper mantle gravity field. Second, the gravity effects of thermal and compositional density variations should be separated. And finally, the inverse gravity problem is usually underdetermined. In the present study we attempt to create a density model of the upper mantle based on improved interpretation methods and updated initial data sets. The impact of the crust to the observed gravity is estimated based on a new crustal model (Stolk et al., 2013). After removing this effect, we estimate the residual mantle anomalies of the gravity field. In the same way we estimate the residual topography, which is the second principal constraint used in the inversion. The impact of the mantle below 350 km is determined and removed based on recent mantle flow models. 3D density model of the lithosphere and upper mantle is constructed in an iterative inversion with tomography data. Contrary to most of previous studies, the thermal and compositional models are self-consistent. Many principal features of the compositional variations are not resolved by seismic tomography. The obtained density and thermal models can be used to model ongoing tectonic processes. Stolk W., Kaban M.K., Beekman F., Tesauro M., Mooney W.D., Cloetingh S. (2013). High resolution regional crustal models from irregularly distributed data: Application to Asia and adjacent areas. Tectonophysics, 602, 55–68.