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The state of mantle minerals

Ahrens, Thomas J. (1972) The state of mantle minerals. Tectonophysics, 13 (1-4). pp. 189-219. ISSN 0040-1951. http://resolver.caltech.edu/CaltechAUTHORS:20141222-100758080

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Abstract

The static pressure-volume, high-pressure X-ray, shock, and ultrasonic equation of state data are used to describe the seismic properties in terms of the mineralogy of the upper mantle, the spinel-zone, and the post-spinel or lower mantle. For the upper mantle, elastic properties have been measured for olivines, pyroxenes, and garnets. The effect of pressure, temperature and the Fe/Mg ratio on elasticity is less well known for pyroxene and garnet than for olivine. In the spinel zone, ~ 400- ~ 650 km depth, the major minerals include β- and γ-(Mg,Fe)_2SiO_4 and a complex garnet, largely composed of aluminum-silicate garnet and pyroxene components. The zero-pressure bulk moduli of these phases lie in the range 1.8–2.1 Mbar. Although the high-pressure X-ray measurements of the bulk moduli of the Fe-rich γ- or spinel phase (ringwoodite) are reported, the shear properties of the silicate spinels are unmeasured, as are all the properties of the distorted spinel, β-phase. The bulk modulus of the complex-garnet phase is known approximately from shock-wave data for pyroxene, but since standard specific volumes are unknown, reduction of these data to adiabats is uncertain. The major minerals of the lower, or post-spinel, mantle are thought to be (Mg,Fe)_2SiO_4 in the close-packed Sr_2PbO_4-structure, and the pyroxene and garnet component, initially in the close-packed ilmenite structure, and at greater depths probably transforming to the perovskite structure. Only shock-wave data and results inferred from the elasticity of the close-packed oxides are available in this regime. Except for garnet, the zero-pressure densities of the shock-induced high-pressure phases are not known; this difficulty, and the lack of data or a theory for the Grüneisen parameter make reduction of these data difficult.


Item Type:Article
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http://dx.doi.org/10.1016/0040-1951(72)90020-0 DOIArticle
http://www.sciencedirect.com/science/article/pii/0040195172900200PublisherArticle
Additional Information:© 1971 Elsevier Publishing Company. Received September 17, 1971. This work was supported by the National Science Foundation under GA 12703. Discussions of this work with D.L. Anderson and A. Albee and a review of the manuscript by R.V. Gibbons are appreciated.
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Funding AgencyGrant Number
NSFGA 12703
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Caltech Division of Geological and Planetary Sciences2052
Record Number:CaltechAUTHORS:20141222-100758080
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20141222-100758080
Official Citation:Thomas J Ahrens, The state of mantle minerals, Tectonophysics, Volume 13, Issues 1–4, April 1972, Pages 189-219, ISSN 0040-1951, http://dx.doi.org/10.1016/0040-1951(72)90020-0. (http://www.sciencedirect.com/science/article/pii/0040195172900200)
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ID Code:53079
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:22 Dec 2014 18:29
Last Modified:22 Dec 2014 18:29

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