Earth

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Earths Deep Water Cycle
Suzan van der Lee Northwestern University
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Feng et al. (2007) Van der Lee and Wiens (EDWC)
mantle wedge seismically slow and wet, dry below?
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Rupke et al. (EDWC)
Mantle outgassing 90 efficient at least 10
stays in mantle, and likely more in slab
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Song and Helmberger (EDWC)
lvz on 410 (red o) right next to normal mantle
(white o)
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Karato et al. (EDWC)
melt on 410 from upwelling saturated wadselyite,
but
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Predicted melt layer thinner than observed lvz
lt 7 km
wd--gtol transition thickens with increasing H2O
at undersaturated conditions
Hirschmann et al. (EDWC)
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Calculations at D20 suggest that ol--gtwd
transition can be very thick at only 0.1 wt
water
gt25 km
(after Wood, 1995)
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Water would thus be an explanation for puzzling
receiver functions, but
VSL, Italy
PAB, Spain
KEG, Egypt
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lt15 km
Hirschmann et al. (EDWC)
With D5 and 0.1 wt H2O transition would be
less than 15 km thick
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V low and Q very low in mantle wedge --gt water
V low, but Q high below 200 km --gt warm
Conder and Wiens (2006) Roth et al. (1999) Van
der Lee and Wiens (EDWC)
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Separate effects of water from other effects
Shito et al. (EDWC)
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Water above 400 km, from upwelling TZ or from
slab Still some trade-off btw w and T
Shito et al. (EDWC)
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Use other seismic measurements to evaluate the
relative role of w and T, such as transition-zone
discontinuity properties
Smyth and Jacobsen (2006)
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Braunmiller et al. (EDWC)
TZ thickens but ol--gtwd does not deep SAm mantle
dry (or saturated)
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Suetsugu et al. (EDWC)
Vp and 660 gt1 wt water near slab
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410, 520, and Vs gt0.2 wt water
Courtier and Revenaugh (EDWC)
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VdLee Frederiksen (2005) Grand (2002)
low Vs lt 1 wt water low Vs above slab in top of
lower mantle
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Inoue et al. (EDWC)
Experiments show that Shy-B is stable in TZ and
cool slab
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Komabayashi (EDWC)
Calculations show that abc phases are stable
throughout upper mantle in cool slab breakdown
occurs in top of lower mantle.
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Hydrous TZ likely less dense than dry TZ,
and Water lowers the viscosity by 4-5 orders
of magnitude, at least above 300 km. Hydrous
mantle can well up and hydrate lithosphere.
Karato and Jung (2003) Karato (EDWC)
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Deformation model Temperature and
water-sensitive yield and thermal-mechanical
feedback
Mid Atlantic ridge
Ocean continent Boundary
Sediment loading
Seafloor age turned into temperatures 70 km
thick Lithosphere cross section shown
Regenauer-Lieb et al. (2001)
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Regenauer-Lieb et al. (2001)
wet rheology
dry rheology
time
0 km --
lithosphere
100 km --
lithosphere breaks only in wet conditions
subduction of dense lithosphere enabled.
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Connecting past and future episodes of subduction
200-300 m.y.
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Connecting past and future episodes of subduction
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Connecting past and future episodes of subduction
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Connecting past and future episodes of subduction
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Connecting past and future episodes of subduction
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Connecting past and future episodes of subduction
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Present
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Conclusions

• Deep water cycle may sustain plate tectonics over
  many Gy.
• Water in mantle is detectable in various ways
• seismic V from tomography or triplication
  branches
• Q/attenuation
• discontinuity depths and properties
• More work is needed
• mineral physics elasticity at p, T, and C
• seismology benchmarking, denser data (USArray!)