Plate tectonics generated by nonlinear rheology in mantle convection models & application to thermo-chemical evolution
From Published Papers
Viscosity (T) : how much?
Expect rigid lid: Earth unusual ?
Plates and mantle
Yield strength of
Strength profile of oceanic lithosphere
Surface Strain Rate and V
RaH=2e7; YS=50 MPa (2e4)
Characterizing plate tectonics
"Earth’s Tor/Pol ratio ~..."
Scaling of plate diagnostics with Yield Stress
Does low viscosity beneath the lithosphere help?
"Varying yield strength"
Greatly improves plate quality
So far…instantaneous rheology
Mantle shear zone in Greenland
X-section thru shear zone
Simplified 'Damage' evolution
Comparison of various rheologies
Forms lithospheric shear zones
…works with more realistic viscosity profile
Instantaneous flow with
strain rate weakening.
Simple 2-lyr model
Same with bigger box
Add SW to time-dep models
…but doesn’t have a large effect on diagnostics
Surface Strain rate
Pol- & Toroidal with depth
Continents aid 1-sided subduction, but add time-depn
Successes and failures
Things that 'help'
Mantle convection models and geochemistry
Integrating Geodynamic and Geochemical Models of Mantle Evolution and Plate Tectonics
TEST cartoon models: which ones “work” both geophysically and geochemically?
Geochemical evolution: Focus on 2 cases
Homogeneous start: after 1 and 2 Gyr
(after 3.6 Gyr)
Layered start: after 200 Myr and 2.5 Gyr
Layered start: present day (3.6 Gyr)
Noble gas outgassing: too much(?)
Ratios in melted material (last 150 Myr)
Pb ratios in melted material
Thermal evolution strongly affected by magmatism: simple example
Heat flow is almost constant
Temperature varies much less
Yielding generates “plate tectonics”