Journal Article

Constraining mantle convection models with palaeomagnetic reversals record and numerical dynamos

G. Choblet, H. Amit and L. Husson

in Geophysical Journal International

Volume 207, issue 2, pages 1165-1184
ISSN: 0956-540X
Published online September 2016 | e-ISSN: 1365-246X | DOI:
Constraining mantle convection models with palaeomagnetic reversals record and numerical dynamos

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We present numerical models of mantle dynamics forced by plate velocities history in the last 450 Ma. The lower-mantle rheology and the thickness of a dense basal layer are systematically varied and several initial procedures are considered for each case. For some cases, the dependence on the mantle convection vigour is also examined. The resulting evolution of the CMB heat flux is analysed in terms of criteria to promote or inhibit reversals inferred from numerical dynamos. Most models present a rather dynamic lower mantle with the emergence of two thermochemical piles towards present-day. Only a small minority of models present two stationary piles over the last 450 Myr. At present-day, the composition field obtained in our models is found to correlate better with tomography than the temperature field. In addition, the temperature field immediately at the CMB (and thus the heat flux pattern) slightly differs from the average temperature field over the 100-km thick mantle layer above it. The evolution of the mean CMB heat flux or of the amplitude of heterogeneity seldom presents the expected correlation with the evolution of the palaeomagnetic reversal frequency suggesting these effects cannot explain the observations. In contrast, our analysis favours ‘inertial control’ on the geodynamo associated with polar cooling and in some cases break of Taylor columns in the outer core as sources of increased reversal frequency. Overall, the most likely candidates among our mantle dynamics models involve a viscosity increase in the mantle equal or smaller than 30: models with a discontinuous viscosity increase at the transition zone tend to agree better at present-day with observations of seismic tomography, but models with a gradual viscosity increase agree better with some of the criteria proposed to affect reversal frequency.

Keywords: Plate motions; Dynamo: theories and simulations; Reversals: process, time scale, magnetostratigraphy; Mantle processes; Dynamics of lithosphere and mantle

Journal Article.  15140 words.  Illustrated.

Subjects: Geophysics

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