Mapping Seismic Tomography into Earth Structure: Implications for Dynamic Topography, Lithospheric Stability and Sea-Level Reconstructions

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• Fred Richards - Imperial College London
• Wednesday 05 February 2020, 16:00-17:00
• Marine/Wolfson Building lecture hall, Bullard Labs..

If you have a question about this talk, please contact Jenny Jenkins.

Advances in seismic tomography over the past four decades have dramatically improved our knowledge of Earth’s internal structure. Over the same period, observational constraints on mantle dynamics have steadily improved thanks to the growing accuracy and geographic coverage of gravity, heat flow and residual topography measurements.However, although mantle flow simulations that incorporate tomographically inferred buoyancy structure are able to fit the longest wavelength components of the gravityfield, the dynamic topography they predict tends to diverge significantly from observed patterns. Similarly, the inferred temperature structure of the mantle is often in poor agreement with constraints from mid-ocean ridge basalts and suites of mantle xenoliths. A significant source of discrepancy in these calculations can be linked to the simplistic methodology used to convert upper mantle seismic velocity variations into buoyancy anomalies. In this talk, I will show that much of the disagreement between modelsand observations of dynamic topography can be resolved by using experimentally de-rived anelasticity parameterisations to infer the temperature and density structure ofthe lithosphere and asthenosphere (e.g. Priestley and McKenzie, 2013; Yamauchi andTakei, 2016). This updated Earth structure is then used to investigate time-dependent changes in dynamic topography and lithospheric thickness. First, by simulating the history of mantle flow beneath Australia, I demonstrate that the associated spatio-temporal evolution of dynamic topography can explain the∼±250 m relative sea-level changes observed across the continent since the Mid-Pliocene Warm Period (MPWP;∼3 Ma). Removal of the dynamic topography signal from this dataset places import-ant constraint on eustatic sea-level and ice volume during the MPWP , the last time in Earth history that atmospheric CO2concentrations were similar to the present. Second,by comparing xenolith-derived palaeogeotherms with present-day temperature profiles inferred from seismic tomography models, I will present evidence for post-Cretaceous lithospheric thinning beneath Central Angola. However, this dynamism appears to be relatively rare. Similar comparisons in other regions and the distribution of ancient sediment-hosted mineral deposits along present-day cratonic edges, suggest that, in general, continental lithosphere is remarkably stable.

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

This talk is included in these lists:

• Bullard Laboratories Wednesday Seminars
• Department of Earth Sciences seminars
• Marine/Wolfson Building lecture hall, Bullard Labs.

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