Rheological%20Structure%20of%20the%20Mantle%20of%20Super-Earths:%20Insights%20from%20Mineral%20Physics - PowerPoint PPT Presentation

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Rheological%20Structure%20of%20the%20Mantle%20of%20Super-Earths:%20Insights%20from%20Mineral%20Physics

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Rheological Structure of the Mantle of Super-Earths: Insights from Mineral Physics Shun-ichiro Karato Yale University Department of Geology and Geophysics – PowerPoint PPT presentation

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Title: Rheological%20Structure%20of%20the%20Mantle%20of%20Super-Earths:%20Insights%20from%20Mineral%20Physics


1
Rheological Structure of the Mantle of
Super-Earths Insights from Mineral Physics
  • Shun-ichiro Karato
  • Yale University
  • Department of Geology and Geophysics
  • New Haven, CT, USA

2
Dynamics of a super-Earth
  • mantle convection, thermal evolution
  • Does plate tectonic operate on super-Earths?
  • Does dynamo operate in super-Earths?
  • tidal heating
  • orbital evolution
  • How much have exo-planets migrated since their
    formation?
  • ? Rheological properties

3
Internal structure of a super-Earth
P to 1 TPa (1000 GPa) T to 5000 K
4
Viscosity of planetary materials depends strongly
on T and P. P-effect is potentially very large!
5
Viscosity-mass relationship
Viscosity of solids increases with P at low P.
Is this valid at higher P in super-Earths?
6
conventional models
new model
7
Internal structure of a super-Earth
(B1? B2 transition)
(dissociation of post-perovsktie
(?), Metallization (?))
MgO is the softest phase in a super-Earths
mantle.
8
MgO (V decreases with depth (pressure))
9
Viscosity changes also with crystal structure.
normalized temperature
MgO (B1 or B2) is the softest mineral in
the deep mantle.
normalize viscosity
B1
10
Materials with B1 structure are the softest among
various oxides. Materials with B2 structure are
even softer than those with B1 structure.
B2
B1
11
Viscosity changes when mechanisms of atomic
motion change.
Vvacancy gt0 Vinterstitial lt0
vacancy mechanism
interstitial mechanism
(from (Ito and Toriumi, 2007)) (from Karato
(1978))
12
B1
13
Conclusions
  • Viscosity of the deep mantle of a super-Earth
    might decrease with pressure.
  • the Rayleigh number increases with planetary
    mass
  • reduces plate thickness, increases convective
    stress with planetary mass making plate tectonics
    possible in large planets, which would otherwise
    be difficult.
  • high tidal energy dissipation

14
(No Transcript)
15
(low viscosity ? higher heating rate, faster
orbital evolution)
16
Could plate tectonics operate on a super-Earth?
How does resistance and driving force for plate
tectonics change with planetary
mass? resistance plate thickness ? Rayleigh
number driving force convective stress ?
Rayleigh number A large Rayleigh number ? high
stress, thin planet ? promote plate
tectonics How does the Rayleigh number change
with planetary mass?
(Valencia et al., 2007)
P-effect on viscosity is often ignored. Is it
justifiable?
17
P to 1 TPa (1000 GPa) T to 5000 K
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