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Upper mantle thermochemical heterogeneity from coupled geophysical–petrological inversion of terrestrial and satellite data

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If you have a question about this talk, please contact Yihe Xu.

The lateral and vertical thermochemical heterogeneity in the mantle is a long-standing question in geodynamics. The forces that control mantle flow and therefore Plate Tectonics arise from the density and viscosity lateral and vertical variations. A common approach to estimate the density field for geodynamical purposes is to simply convert seismic tomography anomalies, sometimes assuming constraints from mineral physics. Such a converted density field does not match in general with the observed gravity field, typically predicting anomalies, the amplitudes of which are too large. Knowledge on the lateral variations in lithospheric density is essential to understand the dynamic/residual isostatic components of the Earth’s topography linking deep and surface processes. The cooling of oceanic lithosphere, the bathymetry of mid oceanic ridges, the buoyancy and stability of continental cratons or the thermochemical structure of mantle plumes are all features central to Plate Tectonics that are dramatically related to mantle temperature and composition. We present a new global thermochemical model of the lithosphere and underlying upper mantle constrained by state-of-the-art seismic waveform inversion, satellite gravity (geoid and gravity anomalies and gradiometric measurements from ESA ’s GOCE mission), surface elevation and heat flow data: WINTERC -G. The model is based upon an integrated geophysical-petrological approach where mantle seismic velocities and density are computed within a thermodynamically self-consistent framework, allowing for a direct parameterization in terms of the temperature and composition variables. The complementary sensitivities of the data sets allow us to constrain the geometry of the lithosphere-asthenosphere boundary, to separate thermal and compositional anomalies in the mantle, and to distinguish dynamic vs isostatic surface-elevation contributions. At long spatial wavelengths, our model is generally consistent with previous seismic (or seismically derived) global models and earlier integrated studies incorporating surface-wave data at lower lateral resolution. At finer scales, the temperature, composition and density distributions in WINTERC -G offer a new state of the art image at a high resolution globally (225 km average inter-knot spacing).

This talk is part of the Bullard Laboratories Wednesday Seminars series.

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