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| Titel |
The Standard Hydrous Olivine (SHO) conductivity model: A new tool for probing water in the upper mantle |
| VerfasserIn |
Emmanuel Gardés, Fabrice Gaillard, Pascal Tarits |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250099047
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| Publikation (Nr.) |
 EGU/EGU2014-14790.pdf |
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| Zusammenfassung |
| It has long been assumed that the incorporation of water in olivine has dramatic effects on the
physical properties of the mantle, affecting large scale geodynamic processesand triggering
most electrical conductivity anomalies in the mantle. But the conductivity models for hydrous
olivine based on experimental measurements predict contrasting effects of water (e.g.
Wang et al. 2006; Yoshino et al. 2009), precluding any unequivocal interpretation of
electrical conductivities in the mantle. Our thesis is that the uncertainties and biases
in the water contents of the olivines used for experiments were inappropriately
appreciated, resulting in apparent incompatibilities when analysing the different datasets
and in significant biases in the models outside of their range of calibration. Here,
we analyse all published experimental work and provide a new model, SHO, that
settles these major inconstancies. SHO is calibrated on the largest database of raw
conductivity measurements on oriented single crystals and polycrystals of hydrous
olivine, with water concentrations and temperatures spreading over 0-2220 wt. ppm
and 200-1440°C. Our model provides both oriented conductivities, allowing for
calculating conductivity anisotropy, and isotropic conductivity, relevant for olivine
aggregates without preferential orientation. SHO isotropic conductivity (S/m) is given
by
2.93 - 157000 -1.54 - 87000-1820C1-H32O
Ïă = 10 e RT + 10 CH2Oe RT ,
where CH2O is the water concentration in olivine (wt. ppm), T the temperature (K) and R =
8.314 J/K/mol. In the normally hot mantle, our model predicts a moderate effect of water on
the conductivity of olivine. High conductivities (~ 0.1 S/m) are obtained at great depths and
elevated water concentrations only (> 350 km and > 400 wt. ppm). The strongest
effects are therefore expected in the coldest regions of the mantle, like cratonic
lithospheres or subduction zones, where higher incorporation of water in olivine is
allowed.
Wang, D., Mookherjee, M., Xu, Y., Karato, S. The effect of water on the electrical
conductivity of olivine. Nature 443, 977–980 (2006)
Yoshino, T., Matsuzaki, T., Shatskiy, A., Katsura, T. The effect of water on the electrical
conductivity of olivine aggregates and its implications for the electrical structure of the upper
mantle. Earth Planet. Sc. Lett. 288, 291–300 (2009) |
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