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)