Controls on geomagnetic reversals and core evolution by mantle convection in the Phanerozoic

Numerical dynamos driven by non-uniform heat flux at the core-mantle boundary are used to investigate the connections between geomagnetic field structure, geomagnetic reversal frequency, core evolution, and mantle convection through Phanerozoic time. Polarity reversal sequences and time average magnetic field structures are calculated using dynamos driven by two representations of lower mantle history: a reconstruction of mantle convection with plate motions by Zhang and Zhong (2011) that produces time variable core-mantle boundary (CMB) heat flux and an irregular evolution of the core, and a second model based on hotspot locations with a time independent pattern of CMB heat flux derived from the present-day seismic shear wave heterogeneity of the lower mantle that produces a monotonic evolution of the core. For both mantle histories, present-day values of the dynamo control parameters are tuned to match Geomagnetic Polarity Time Scale reversal statistics for 0–5 Ma, and the time dependences of the dynamo control parameters are determined from the thermal evolution of the core, including time variability of CMB heat flow, inner core size, inner core chemical buoyancy flux, and rotation rate. The dynamo with time independent CMB heat flux shows minor fluctuations in reversal frequency with age, whereas the dynamo with time variable CMB heat flux shows reversal rate fluctuations including stable polarity at 275 and 475 Ma and frequent reversals at other times. This dynamo also produces departures from geocentric axial dipole symmetry during the time of supercontinent Pangaea and a heterogeneous growth history of the inner core.

► We model the thermal interaction between the core and mantle over Phanerozoic time.
► We calculate 5 Myr geomagnetic reversal sequences.
► We find that mantle convection produces a geomagnetic superchron cycle.