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February 2013

Combining CitcomS and MAG to Investigate Core Evolution

Olson et al.’s (2013) recent paper Controls on Geomagnetic Reversals and Core Evolution by Mantle Convection in the Phanerozoic uses two CIG codes, CitcomS and MAG, to model core-mantle thermal interaction and its effects on the geodynamo. The geodynamo is sensitive to conditions at the core-mantle boundary (CMB) and comparison to geomagnetic polarity reversals offers a test for competing histories of the lower mantle. Hence, 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. A dynamo model based on reconstruction of mantle convection with plate motions produces time variable CMB heat flux and an irregular evolution of the core. For this model, the figure shows CMB heat flux (left) with plate boundaries superimposed (black lines) and the corresponding time average dynamo radial magnetic field on the CMB (right). This model produces large fluctuations in reversal rate, including stable polarity at 275 and 475 Ma and frequent reversals at other times. As seen in the figure, this dynamo produces departures from geocentric axial dipole symmetry during the time of supercontinent Pangaea as well as a heterogeneous growth history of the inner core. http://dx.doi.org/10.1016/j.pepi.2012.10.003.

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