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The Significance of Densely Sampled Observations of Mantle Dynamic Topography

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Dynamic topography is generated from mantle convection and can be isolated from isostatic topography using observational constraints. Quantifying observable dynamic topography yields valuable information on mantle convective processes. This study presents a revised and augmented dataset of 10,874 residual depth measurements from oceanic crust, which originate from 7,601 seismic experiments. The isostatic component of topography is identified and removed by correcting for sedimentary loading and crustal thickness variation. Methodological improvements are implemented for both sedimentary and crustal corrections. Residual depth measurements typically deviate by $\pm$1~km from the predicted plate cooling trend. Positive and negative anomalies correlate with independent geological and geophysical observations of uplift and subsidence. This oceanic dataset is combined with a continental dataset to generate globally continuous spherical harmonic representations out to degree 40. The resultant power spectrum demonstrates that most power occurs at degree 2 (i.e., wavelengths of $\sim10^4$~km), while considerable power exists out to and including degree 40 (i.e., wavelengths of $\sim10^3 km).Thepowerspectrumofobservabledynamictopographyisrobustusingdifferentinversemethods.Ananalyticalpowerspectrumisgeneratedthatisconsistentwiththeobservedpowerspectrum.Collatingaglobaldatabaseofresidualdepthmeasurementshasyieldedanumberofusefulancillarydatasets.Forexample,interpretingthesedimentbasementinterfacealong7,601seismicprofilesprovidesabenchmarkforglobalmapsofsedimentarythicknessvariation.Inaddition,asynthesisofcrustalthicknessmeasurementsfrom278modernwideangleexperimentsyieldsarevisedmeanoceaniccrustalthicknessof6.38\pm$1.12~km. Residual depth measurements also yield information on the plate cooling trend. Hence, a suite of new plate cooling models are developed by jointly inverting depth-to-basement observations (n = 10,874) and heat flow observations (n = 3,753). A numerical model, in which pressure and temperature vary with depth, yields a temperature, Tp, of 1326C, a lithospheric thickness, zp, of 111~km, and a ridge depth, zr, of 2.92~km. These recovered parameters are in close agreement with independent constraints of mantle potential temperature, lithospheric thickness and ridge depth. This study also demonstrates that improving the parameterization of an analytical model recovers values that are similar to a more complex numerical model. Passive margins provide an excellent natural laboratory for studying the influence of dynamic topography. Despite tectonic quiescence, topography along passive margins is highly variable. Elevated passive margins are often associated with temperature anomalies in the asthenosphere, inferred from slow shear-wave velocity anomalies, elevated residual depth measurements, Neogene-Quaternary volcanism, elevated marine stratigraphy, thin lithosphere and positive long wavelength gravity anomalies. These observations suggest that mantle dynamics play a fundamental role in the formation of elevated passive margins. Uplift caused by an asthenospheric density anomaly is modeled at several locations. Results suggest that low density anomalies create sufficient uplift to account for elevated topography. The presence of slow shear-wave velocity anomalies and Neogene-Quaternary volcanism suggests escarpment uplift may be youthful.





White, Nicholas


Dynamic topography, Residual depth measurements, Lithospheric cooling, Escarpment


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Gates Cambridge Trust