Reconstructing the Phanerozoic Geodynamo
• Whole-Earth approach (mantle + core + time) to geodynamo history
• CMB heat flux from two models of the Phanerozoic mantle:1. Mantle convection with mobile plates and continents
(model HF1 by Zhang & Zhong, 2011)2. Present-day lower mantle seismic heterogeneity
• Core evolution determined by CMB heat flux, includinga) Inner core growthb) Chemical differentiation (Fe-Le)c) CMB heterogeneityd) Tidal breaking (via increase in length of day)
• Calculate dynamo time average magnetic fields and polarity reversals over 5 Myr long stages
• Tune dynamos to present-day (0-5 Ma) reversal rate
Box Model:Core Evolution
~ 700 Myr
T(r,t,)C(r,t)rICB(t)
3D Model:Numerical Dynamo
~ 5 Myr stages
T(x,t,)C(x,t)B(x,t)
ThermodynamicParameters
CMB Heat Flow Q(t)T(r,0), C(r,0), rICB(0)
Transport ParametersCMB Heat Flux q(x)W(t)
GPTSReversals
total ICB
HF1
CMB heat flow
Compositional
breakup assemblyPangea
Variable evolution Driver: mantle reconstruction HF1
(Zhang & Zhong, 2011)
Regular evolutionDriver: constant CMB heat flow
Phanerozoic Core Evolution(thanks to Renaud!)
Regular
Parametric Core Evolution
HF1
Regular
E/E(
0)
Ra/Ra(0)
Ma
Ma
Present-day (0-5 Ma) Reversal Records
Polarity Reversal Record Comparison
GPTS (5.4 Myr)