Modeling 3‐D density distribution in the mantle from inversion of geoid anomalies: Application to the Yellowstone Province

Abstract

AbstractWe developed a three‐dimensional scheme to invert geoid anomalies aiming to map density variations in the mantle. Using an ellipsoidal‐Earth approximation, the model space is represented by tesseroids. To assess the quality of the density models, the resolution and covariance matrices were computed. From a synthetic geoid anomaly caused by a plume tail with Gaussian noise added, the inversion code was able to recover a plausible solution about the density contrast and geometry when it is compared to the synthetic model. To test the inversion algorithm in a natural case study, geoid anomalies from the Yellowstone Province (YP) were inverted. From the Earth Gravitational Model 2008 expanded up to degree 2160, lower crust‐ and mantle‐related negative geoid anomalies with amplitude of approximately 70 m were obtained after removing long‐wavelength components (>5400 km) and crustal effects. We estimated three density models for the YP. The first model, the EDM‐1 (estimated density model), uses a starting model with density contrast equal to 0. The other two models, the EDM‐2 and EDM‐3, use an initial density derived from two S‐velocity models for the western United States, the Dynamic North America Models of S Waves by Obrebsky et al. (2011) and the Northwestern United States Teleseismic Tomography of S Waves (NWUS11‐S) by James et al. (2011). In these three models, a lower and an upper bound for the density solution was also imposed as a priori information. Regardless of the initial constraints, the inversion of the residual geoid indicates that the lower crust and the upper mantle of the YP have a predominantly negative density contrast (~ −50 kg/m3) relative to the surrounding mantle. This solution reveals that the density contrast extends at least to 660 km depth. Regional correlation analysis between the EDM‐1 and NWUS11‐S indicates an anticorrelation (coefficient of ~ −0.7) at 400 km depth. Our study suggests that the mantle density derived from the inversion of geoid could be integrated with seismic velocity models to image mantle anomalous features beyond the depth limit of investigation achieved combining gravity and seismic tomography. ©2013. American Geophysical Union. All Rights Reserved.