Petrology, elasticity, and composition of the mantle transition zone

Ita, Joel; Stixrude, Lars

doi:10.1029/92jb00068

Cited by 411 publications

(252 citation statements)

References 158 publications

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“…We recognize that Ita and Stixrude [1992] found the behavior of pyrolite to agree very well with seismic observations throughout the upper mantle and transition zone. However, while density, Vp, and bulk sound velocity were compared with seismic observations, V•, was not discussed.…”

Section: Quantitative Estimation Of Thesupporting

confidence: 59%

Elastic wave velocities of forsterite and its β‐spinel form and chemical boundary hypothesis for the 410‐km discontinuity

Fujisawa¹

1998

J. Geophys. Res.

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Abstract. A method for measuring elastic wave velocities at pressures up to 15 GPa has been developed. Velocities of forsterite and/3-spinel were measured using a pistoncylinder apparatus with a pulse-echo-overlap method for pressures up to 4 GPa and using a split-sphere apparatus with a pulse-transmission technique for higher pressures. To validate the results, volume compression, incompressibility, and rigidity were estimated from measured travel times, and comparison was made between the present estimates and data from X ray, Brillouin, and acoustic measurements. The Vp and K values for/3-spinel are 3 and 8% higher than previous measurements at 10 GPa, i'espectively. Velocity jumps in Vp and Vs due to olivine to/3-spinel transition were about 1.34 and 0.80 km s -*, respectively, very different from seismological observations of velocity jumps at the 410-km discontinuity, which were concentrated around 0.45 km s -1 for the P wave and 0.22 km s -1 for the S wave. Velocity jumps in mantle peridotite were calculated using the experimental results, and comparison was made between these estimates and seismological observations at the 410-km discontinuity. The evidence does not support the phase-change hypothesis, and a chemical boundary was proposed as the origin of the 410-km discontinui.ty. An eclogitic mineral assemblage might be an alternative for the composition of the transition layer.

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Section: Quantitative Estimation Of Thesupporting

confidence: 59%

Elastic wave velocities of forsterite and its β‐spinel form and chemical boundary hypothesis for the 410‐km discontinuity

Fujisawa¹

1998

J. Geophys. Res.

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“…Shearer 1996;Flanagan and Shearer, 1998) at 520 km. The discontinuity at 520 km depth has been attributed to the wadsleyite to ringwoodite transformation by Shearer (1996) and to exsolution of Ca-perovskite from majorite garnet (Ita and Stixrude, 1992). The wadsleyite to ringwoodite transformation results in the lowering of anisotropy with depth (see Table 1) in the lower part of the transition zone, whereas the exsolution of Ca-perovskite from majorite garnet would result in an increase.…”

Section: Introductionmentioning

confidence: 99%

“…Weidner, 1985Weidner, , 1986Montagner and Anderson, 1989;Ita and Stixrude, 1992). The pyrolite and piclogite models of Ita and Stixrude (1992) are shown in Fig.…”

Section: Lower Mantlementioning

confidence: 99%

The Seismic anisotropy of the Earth's mantle: From single crystal to polycrystal

Mainprice¹,

Barruol²,

Ismaı̈l³

2000

Earth's Deep Interior: Mineral Physics and Tomography From the Atomic to the Global Scale

220

172

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The anisotropic single crystal seismic properties are reviewed in the light of recent experimental and theoretical determinations. Although considerable progress has been made on the determination of single crystal properties, data are still lacking, particularly for the temperature derivatives of transition zone and lower mantle phases. The common types of LPO of olivine, opx and cpx are presented together with their associated seismic properties. It is emphasized that simple seismic symmetry pattern of upper mantle rocks are a direct result of the interaction of olivine, opx and cpx. Using the standard structural frame (X lineation, Z pole to foliation) for typical LPOs of olivine, opx and cpx have the maximum Vp parallel to X, in the XZ plane and parallel to Y respectively. Destructive interference occurs between these minerals and hence P-wave anisotropy should be sensitive to the aggregate composition. For shear wave splitting (dVs) typical olivine and opx LPOs result in similar patterns with the maximum dVs in the YZ plane and the fast split shear wave (Vs1) polarized parallel to the foliation. A typical cpx LPO on the other hand produces destructive interference as the max dVs is close to X. By comparison with experiments and numerical simulations, it is estimated that upper mantle samples have an olivine LPO strength which recorded shear strain gamma of between 0.25 and 2.0. Pyrolite and piclogite models are compared with global transverse isotropic models. The slowly reducing P-wave anisotropy in the first 200 km can be explained by a model with constant composition and LPO strength. The sharp decrease in the observed anisotropy in the global models cannot be explained by the transformation of opx to cpx at 300 km, it is proposed that this decrease is due to a reduction in LPO strength from 200 to 350 km at the base of the lithosphere.

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“…Successful interpretation of these seismic models in terms of the variables above requires experimental and theoretical information on the elasticity of Earth materials under the elevated conditions that characterize the Earth's interior. One of the petrological models that has been tested extensively in the literature is that of pyrolite, which was proposed by Ringwood (3) based on the compositions of mantle peridotites and oceanic basalts (4)(5)(6)(7)(8).…”

mentioning

confidence: 99%

Indoor seismology by probing the Earth's interior by using sound velocity measurements at high pressures and temperatures

Li¹,

Liebermann

2007

Proc. Natl. Acad. Sci. U.S.A.

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The adiabatic bulk (KS) and shear (G) moduli of mantle materials at high pressure and temperature can be obtained directly by measuring compressional and shear wave velocities in the laboratory with experimental techniques based on physical acoustics. We present the application of the current state-of-the-art experimental techniques by using ultrasonic interferometry in conjunction with synchrotron x radiation to study the elasticity of olivine and pyroxenes and their high-pressure phases. By using these updated thermoelasticity data for these phases, velocity and density profiles for a pyrolite model are constructed and compared with radial seismic models. We conclude that pyrolite provides an adequate explanation of the major seismic discontinuities at 410-and 660-km depths, the gradient in the transition zone, as well as the velocities in the lower mantle, if the uncertainties in the modeling and the variations in different seismic models are considered. The characteristics of the seismic scaling factors in response to thermal anomalies suggest that anticorrelations between bulk sound and shear wave velocities, as well as the large positive density anomalies observed in the lower mantle, cannot be explained fully without invoking chemical variations.elasticity ͉ mantle composition ͉ mantle heterogeneity ͉ ultrasonic interferometry ͉ pyrolite S eismological investigations provide the primary source of information about the properties and processes of the Earth's interior, especially for depths greater than a few hundreds of kilometers (i.e., depths below which rock samples have not yet reached the Earth's surface). In addition to regional studies that provide detailed velocity structures of the upper mantle and the transition zone, global Earth models of velocity and density profiles versus depths have been generated by compiling thousands of seismic records and data of different types, e.g., the Preliminary Earth Reference Model (1) and AK135 (2). The variations of compressional wave (P wave) and shear wave (S wave) wave velocities and densities in these models presumably reflect radial and lateral variations of chemical composition, mineralogy, pressure, and temperature. Successful interpretation of these seismic models in terms of the variables above requires experimental and theoretical information on the elasticity of Earth materials under the elevated conditions that characterize the Earth's interior. One of the petrological models that has been tested extensively in the literature is that of pyrolite, which was proposed by Ringwood (3) based on the compositions of mantle peridotites and oceanic basalts (4-8).We use the pyrolite model to compare with seismic models of both global and regional nature.Over the past 40 years or so, the elastic properties of many mantle minerals as well as their high-pressure phases have been studied by using static and shock compression and various spectroscopic techniques. Such approaches provide important information about the variation of density (hence compressibility) ...

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Petrology, elasticity, and composition of the mantle transition zone

Cited by 411 publications

References 158 publications

Elastic wave velocities of forsterite and its β‐spinel form and chemical boundary hypothesis for the 410‐km discontinuity

Elastic wave velocities of forsterite and its β‐spinel form and chemical boundary hypothesis for the 410‐km discontinuity

The Seismic anisotropy of the Earth's mantle: From single crystal to polycrystal

Indoor seismology by probing the Earth's interior by using sound velocity measurements at high pressures and temperatures

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