Mantle control of the geodynamo: Consequences of top‐down regulation

Abstract

The mantle global circulation, including deep subduction and lower mantle superplumes, exerts first‐order controls on the evolution of the core, the history of the geodynamo, and the structure of the geomagnetic field. Mantle global circulation models that include realistic plate motions, deep subduction, and compositional heterogeneity similar to the observed large low seismic velocity provinces in the lower mantle predict that the present‐day global average heat flux at the core‐mantle boundary (CMB) exceeds 85 mW m−2. This is sufficient to drive the present‐day geodynamo by thermochemical convection and implies a very young inner core, with inner core nucleation between 400 and 1100 Ma. The mantle global circulation also generates spatially heterogeneous heat flux at the CMB, with peak‐to‐peak lateral variations exceeding 100 mW m−2. Such extreme lateral variability in CMB heat flux, in conjunction with the high thermal conductivity of the core, implies that the liquid outer core is thermally unstable beneath the high seismic velocity regions in the lower mantle but thermally stable beneath the large low seismic velocity provinces. Numerical dynamo simulations show how this pattern of heterogeneous boundary heat flux affects flow in the outer core, producing localized circulation patterns beneath the CMB tied to the mantle heterogeneity and long‐lived deviations from axial symmetry in the geomagnetic field.

Record of massive upwellings from the Pacific large low shear velocity province

“…1b), which can be related to fluctuations of mantle-core heat fluxes5657, further supports the hypothesis of deep mantle origin for LIPs. Thus, if LIP-producing plumes were rooted in a boundary layer at the base of the mantle (LLSVP) it is possible that instabilities of the buoyant perovskite-bearing peridotite equivalent progressively entrained recycled components41058 making them less buoyant with time and thus explaining the potential cyclicity observed during the Cretaceous.…”

On the Scales of Dynamic Topography in Whole‐Mantle Convection Models

“…Ra is the Rayleigh number as defined in equation (2); H, the internal heat production rate; CBL means chemical basal layer; Y oc is the surface oceanic lithosphere yield stress; P, the plateness; M, the mobility; Q 0 , the surface heat flow; h RMS , the surface total RMS topography; Q 0 ∕Q CMB , the ratio of CMB to surface heat flow; T LAB , the sublithospheric temperature; and 0 , the reference viscosity. f After removal of continental crust heat production, according to Olson (2016). = Poorly-constrained parameters for Earth.…”

“…We varied Ra between 10 5 and 5×10 7 . Most estimates of Earth's core heat flow range between 7 and 17 TW (Olson, 2016), which would represent >17% of Earth's total heat flow, excluding crustal radioactive heat production. Most estimates of Earth's core heat flow range between 7 and 17 TW (Olson, 2016), which would represent >17% of Earth's total heat flow, excluding crustal radioactive heat production.…”

Heat Flow in Earth's Core From Invariant Electrical Resistivity of Fe‐Si on the Melting Boundary to 9 GPa: Do Light Elements Matter?

“…Thus, the stability and a type of convection (thermal versus compositional) depend closely on κ (and related ρ ), as well as viscosity of liquid Fe alloy (Davies et al, ). Additionally, the energy budget of the core and the rate at which that energy is extracted across the CMB imposes constraints on the nature of the geomagnetic field (Olson, ; Olson et al, ). The magnetic field is generated through the conversion of kinetic energy of the convecting molten alloy into electrical and magnetic energy (e.g., Davies, ; Gubbins et al, ; Labrosse, ).…”