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None of which answers any of the questions I asked you.Seismic Evidence for Water Deep in Earth’s Upper Mantle
A variety of evidence (11–14) has indicated that amounts
of 1500 parts per million (ppm) of water can
be present locally in the uppermost mantle.
This water is carried there by subducting
oceanic plates, which release most of the
subducted water at depths shallower than 150
km into the mantle wedge overlying the plate
(15). Reports of water being able to reside
below this depth are based on high-pressure
experiments (16) and seismic tomography
(17).
We interpret the broadening of the 410-km
- O. Sigmarsson, M. Condomines, J. Morris, R. Harmon,
Nature 346, 163 (1990).- P. Ulmer, Phys. Earth Planet. Inter. 127, 215 (2001).
- S. van der Lee, D. James, P. Silver, J. Geophys. Res.
106, 30821 (2001).- The Andean Continental Research Project Working
Group, Nature 397, 341 (1999).- A. Thompson, Nature 358, 295 (1992).
- D. J. Frost, Y. Fei, J. Geophys. Res. 103, 7463 (1998).
discontinuity deduced here as being caused by
water in the mantle minerals at this depth.
These minerals can contain a substantial
amount of water: as much as 1000 ppm by
weight of water in olivine and about 20,000
ppm by weight of water in wadsleyite (27). The
estimated water content in olivine for a transition
interval of 20 to 25 km is around 500 ppm
by weight (Fig. 3).
In addition to previous explanations
- D. Kohlstedt, H. Keppler, D. Rubie, Contrib. Mineral.
Petrol. 123, 345 (1996).
for this splitting (28), we speculate that
the split 520-km discontinuity could also be
explained by an increased water content in
the mantle transition zone.
28. A. Deuss, J. Woodhouse, Science 294, 354 (2001).
Never mind.
I understand it can be hard to just say ‘‘No’’ sometimes.
Sarah x