Elastic properties, chemical composition, and crystal structure of minerals

Shankland, T. J.

doi:10.1007/bf01449183

Cited by 66 publications

(6 citation statements)

References 57 publications

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“…Such behavior is preserved under large perturbations of assumptions for geotherms or the Hugoniot parameters. In accordance with velocity-density systematics [Shankland, 1977], the current data for iron are shown in Figure 6 as a function of density. Such a representation incorporates much (but not all) of the variation of velocity as a function of temperature and pressure through its volume dependence.…”

Section: Mcqueen Et Al [1970] Discussed the Effects Of Phase Transitsupporting

confidence: 76%

Phase transitions, Grüneisen parameter, and elasticity for shocked iron between 77 GPa and 400 GPa

Brown¹,

McQueen²

1986

J. Geophys. Res.

707

538

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Sound velocities determined in iron, shock compressed to pressures between 77 GPa and 400 GPa, indicate that two phase transitions exist on the Hugoniot. A discontinuity in sound velocities at 200 +_ 2 GPa may mark the transition of e iron to 7 iron. A second discontinuity at 243 _+ 2 GPa is believed to indicate the onset of melting. The calculated temperature at melting lies between 5000 K and 5700 K. When extrapolated from the Hugoniot melting point, the Lindemann criterion yields an estimate of 5800 +_ 500 K for the melting of pure iron at the inner core boundary pressure of 330 GPa. The product of density times the thermodynamic Grfineisen parameter in liquid iron, calculated from the present data, is 19.6 +_ 0.8 Mg m-3. A temperature profile ranging from 3800 K at the core-mantle boundary to 5000 K at the earth's center is calculated using the present data. Sound velocities for e iron provide a better match to seismic velocities for the earth's inner core than do those of 7 iron. A comparison between liquid iron velocities and the velocity profile through the outer core provides further evidence for alloying of iron with "lighter elements" in the core.

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Section: Mcqueen Et Al [1970] Discussed the Effects Of Phase Transitsupporting

confidence: 76%

Phase transitions, Grüneisen parameter, and elasticity for shocked iron between 77 GPa and 400 GPa

Brown¹,

McQueen²

1986

J. Geophys. Res.

707

538

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“…They show that for the entire lower mantle, from a depth of 700 km to the bottom of the mantle at 2900 km, the mean atomic weight is sensibly constant; it can be written as rh = 21.1 4-0.4, that is to say, the constancy is to within 2%. Furthermore, Shankland [1977] has studied the interpretation of this result within a wider framework of chemical and crystallographic properties of the type of compounds involved (oxides and silicates) and comes to the flat conclusion that 'on the basis of current velocity profiles of the earth, the mantle appears to be chemically homogeneous. '…”

Section: Critical Parameters: Homogeneity and Viscositymentioning

confidence: 99%

The depth of mantle convection

Elsasser¹,

Olson²,

Marsh³

1979

J. Geophys. Res.

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In this paper we elaborate on suggestions in the recent literature that the mantle convects uniformly through its entire depth. The main novel feature introduced here, which leads to a satisfactory account of earth temperatures, it the assumption of a thermal boundary layer at the mantle. Such a layer is produced by the contrast of thermal conductivities of core and mantle if, as is now generally believed, the effects of radiative heat transfer in the mantle are small. On assuming in agreement with much current geochemical thinking that the core is mainly a solution of FeS in Fe, it is possible to estimate crudely the temperature of the core‐mantle boundary as 4000±500°K. The temperature curve in the mantle can be approximated by adding two boundary layer temperature drops that can be calculated to the adiabat in between; this is also calculable, and the sum of these three agrees roughly with the numerical value just given. It has long been known that the Rayleigh number of the mantle is so large as to make convection likely. Lately, Golitsyn has introduced a scaling analysis that allows one to express the depth of the convective zone as a function of known parameters; this yields a depth in rough agreement with the depth of the entire mantle. Finally, we discuss the likelihood that mantle convection has been going on through the entire life of the earth, beginning with the early formation of the core; this has obvious geological implications.

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“…Despite the fact that the relative change in bulk sound velocity with density ()l,) at 670-km depth violates the velocitydensity systematics (i.e.,)l, • 1-2)[D. L. Anderson, 1967a; Shankland, 1972Shankland, , 1977, this cannot be used as evidence for a change in composition at that depth. The high-pressure silicate transformations exhibit a similar deviation from the systematics .…”

Section: Introductionmentioning

confidence: 99%

Phase transitions and mantle discontinuities

Jeanloz¹,

Thompson²

1983

Reviews of Geophysics

414

123

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Density and elasticity data are consistent with, but do not require, a uniform upper‐ and lower‐mantle composition. Such data cannot at present resolve the small changes in physical properties that would be required to keep distinct mantle reservoirs dynamically separated. Alternatively, the issue of chemical stratification in the mantle can be addressed by analyzing the details of the phase equilibria of the appropriate minerals. In order to do this we construct an internally consistent pressure calibration scale which is based in part on the coesite‐stishovite transition pressure Ptr(GPa) = 7.45(±0.3) + 2.1(±0.3) × 10−3T(°C) according to our reanalysis of the available data. We conclude that a discontinuous reaction occurs in the olivine component (α+γ = α+β) of the mantle at the conditions of the 400‐km seismological discontinuity; however, no discontinuous reactions corresponding to the 670‐km discontinuity have yet been identified. The only reaction observed in diamond cell experiments at approximately the pressures existing at 670‐km depth, the breakdown of γ‐spinel to form a silicate perovskite assemblage, appears not to satisfy the observed sharpness of this discontinuity. Thus it may be necessary to invoke either a univariant reaction that has not yet been observed experimentally or a chemical discontinuity at this depth. As the mantle is likely to be at temperatures higher than those of the experiments (estimated to be near 1000°C), additional univariant reactions involving the silicate ilmenite or garnet phases that are predicted to occur may be significant. One possible interpretation is that the mantle is of uniform composition and that such (hypothetical) reactions produce the 670‐km discontinuity. This would imply that the phase assemblages so far studied in high‐pressure‐temperature experiments are not those occurring in the mantle. Alternatively, the mantle could be chemically stratified.

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Elastic properties, chemical composition, and crystal structure of minerals

Cited by 66 publications

References 57 publications

Phase transitions, Grüneisen parameter, and elasticity for shocked iron between 77 GPa and 400 GPa

Phase transitions, Grüneisen parameter, and elasticity for shocked iron between 77 GPa and 400 GPa

The depth of mantle convection

Phase transitions and mantle discontinuities

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