Quantifying the relationship between short‐wavelength dynamic topography and thermomechanical structure of the upper mantle using calibrated parameterization of anelasticity

Richards, F. D. and Hoggard, M. J. and White, N. J. and Ghelichkhan, S. (2020) Quantifying the relationship between short‐wavelength dynamic topography and thermomechanical structure of the upper mantle using calibrated parameterization of anelasticity. Journal of Geophysical Research-Solid Earth. ISSN 0148-0227 DOI https://doi.org/10.1029/2019JB019062 (In Press)

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Official URL: https://agupubs.onlinelibrary.wiley.com/doi/10.102...

Abstract

Oceanic residual depth varies on ≤5000 km wavelengths with amplitudes of ±1 km. A component of this short‐wavelength signal is dynamic topography caused by convective flow in the upper ~300 km of the mantle. It exerts a significant influence on landscape evolution and sea‐level change, but its contribution is often excluded in geodynamic models of whole‐mantle flow. Using seismic tomography to resolve buoyancy anomalies in the oceanic upper mantle is complicated by the dominant influence of lithospheric cooling on velocity structure. Here, we remove this cooling signal from global surface wave tomographic models, revealing a correlation between positive residual depth and slow residual velocity anomalies at depths <300 km. To investigate whether these anomalies are of sufficient amplitude to account for short‐wavelength residual depth variations, we calibrate an experimentally derived parameterization of anelastic deformation at seismic frequencies to convert shear wave velocity into temperature, density, and diffusion creep viscosity. Asthenospheric temperature anomalies reach +150°C in the vicinity of major magmatic hotspots and correlate with geochemical and geophysical proxies for potential temperature along mid‐ocean ridges. Locally, we find evidence for a 150 km‐thick, low‐viscosity asthenospheric channel. Incorporating our revised density structure into models of whole‐mantle flow yields reasonable agreement with residual depth observations and suggests that ±30 km deviations in local lithospheric thickness account for a quarter of total amplitudes. These predictions remain compatible with geoid constraints and substantially improve the fit between power spectra of observed and predicted dynamic topography. This improvement should enable more accurate reconstruction of the spatio‐temporal evolution of Cenozoic dynamic topography.

Item Type: Article
Uncontrolled Keywords: 2020AREP; IA76
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
08 - Green Open Access
Journal or Publication Title: Journal of Geophysical Research-Solid Earth
Identification Number: https://doi.org/10.1029/2019JB019062
Depositing User: Sarah Humbert
Date Deposited: 27 Jul 2020 23:53
Last Modified: 06 Jan 2021 01:00
URI: http://eprints.esc.cam.ac.uk/id/eprint/4821

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