Geodynamic and seismic constraints on the thermochemical structure and dynamics of convection in the deep mantle.
We revisit a recent study by Forte & Mitrovica in which global geophysical observables associated with mantle convection were inverted and the existence of a strong increase in viscosity near a depth of 2000 km was inferred. Employing mineral-physics data and theory we also showed that, although there are chemical anomalies in the lowermost mantle, they are unable to inhibit the dominant thermal buoyancy of the deep-mantle mega-plumes below Africa and the Pacific Ocean. New Monte Carlo simulations are employed to explore the impact of uncertainties in current mineral-physics constraints on inferences of deep-mantle thermochemical structure. To explore the impact of the high-viscosity peak at a depth of 2000 km on the evolution of lower-mantle structure, we carried out time-dependent convection simulations. The latter show that the stability and longevity of the dominant long-wavelength heterogeneity in the lowermost mantle are controlled by this viscosity peak.
Forte
Alessandro M
AM
Department of Earth Sciences, University of Western Ontario, London, Canada.
Mitrovica
Jerry X
JX
Espesset
Aude
A
D003198:Computer Simulation; D018481:Convection; D004190:Disasters; D018534:Earth, Planet; D004548:Elasticity; D019418:Evolution, Chemical; D019419:Evolution, Planetary; D019015:Geologic Sediments / Q000032:analysis; D005844:Geology / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008962:Models, Theoretical; D015203:Reproducibility of Results; D012212:Rheology / Q000379:methods; D012680:Sensitivity and Specificity; D013816:Thermodynamics; D014054:Tomography / Q000379:methods*; D014732:Vibration; D014783:Viscosity