Mount Erebus(photo NASA)

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The role of mantle plumes in the Earth's heat
budget
Guust Nolet
With thanks to Raffaella Montelli Shun
Karato . and NSF
Chapman Conference, August 2005
Mount Erebus(photo NASA)
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44 TW (observed)
8 TW
space
23 TW
upper mantle
44-1331 TW
lower mantle
D
core
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Fluxing 31 TW through the 670 discontinuity
8-15 TW
16-23 TW
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Plume flux from surface observations
rw rm
Davies, 1998
Buoyancy flux B measured from swell elevation e B
Dr e width vplate a Cp
Qc Observed B indicates low plume flux (3TW)
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DVP/VP () at 1000 km depth
PRI-P05
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DVP/VP () at 1000 km depth
PRI-P05
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DVS/VS () at 1000 km depth
PRI-S05
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DVS/VS () at 1000 km depth
PRI-S05
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(No Transcript)
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Cape Verde to Azores
PRI-P05 PRI-S05
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PRI-P05 PRI-S05
Easter Island
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PRI-P05 PRI-S05
Hawaii
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PRI-P05 PRI-S05
Kerguelen
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PRI-P05 PRI-S05
Tahiti
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• Tahiti comparisons (D T)
• PRI-P05
• Zhao et al., 2004
• PRI-S05
• Ritsema et al., 1999

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PRI-P05 PRI-S05
Richard Allen
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CMB origin
Upper Mantle only
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Bottom line Plumes are obese (or we would not
see them), with DTmax 100-300K, Ergo they
contain a lot of calories, Either they carry an
awful lot of heat to the surface, or they go
terribly slow.
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Can we quantify that qualitative notion?
The plume contains H ? cP??T d3x Joules
But we do not know how fast it rises to the
surface!
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Excursion, back to textbook physics
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Tahiti, 1600 km, D T gt 150K
output of resolution test
actual tomogram DT (gt150K)
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Tahiti, 1600 km
Tahiti rise velocity underestimated by factor of
4
Vz from actual tomogram
Vz from resolution test image
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For wider plume (D Tgt 110K) vz underestimated by
factor 3
Tahiti, 1600 km
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observed
reduction in tomography
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But what parameters to use at depth?
6 1022Pa s
Forte Mitrovica , 2001 Lithgow-Bertelloni
Richards, 1995
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Tahiti estimated heat flux as function of depth
well resolved values, corrected for bias
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700 km
Tahiti
1500 km
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• Inferred heat flux Q is too high. Possible
  solutions
• The buoyancy flux at surface underestimates Q at
  depth

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flux loss factor wB
Escape into asthenosphere
heat diffusion, entrainment
B wB Cp Qc/a
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• Inferred heat flux Q is too high. Possible
  solutions
• The buoyancy flux at surface underestimates Q at
  depth
• The reference viscosity 6 1022 Pas (at 800 km)
  is too low

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• Inferred heat flux Q is too high. Possible
  solutions
• The buoyancy flux at surface underestimates Q at
  depth
• The reference viscosity 6 1022 Pas (at 800 km)
  is too low
• Iron enrichment makes the plume heavier
• H2O increases dV/dT, therefore lowers DT

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• Conclusions
• High viscosity in lower mantle makes convection
• there 'sluggish' at best
• Large viscosity contrast points to two strongly
• divided convective regimes in the Earth
• Large flux loss may also imply plume resistance
• at 670 and/or escape into asthenosphere

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• Speculations
• Exchange of material between sluggish lower
• mantle and less viscous upper mantle is limited
• (most likely periodic).
• Plumes may carry all of the upward flow of heat
• (gt16TW) through the 670 km discontinuity.
• The next breakthrough (flood basalt?) may be
• at Cape Verde/Canary Islands, Chatham or
  Tahiti.

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Equal mass flux hypothesis Over time, slabs
transport as much mass into the lower mantle as
plumes return to the upper mantle. There is no
other mass flux through the 670 discontinuity