Ab initio study of the elastic behavior of MgSiO<sub>3</sub> ilmenite at high pressure

Silva, Cesar R. S. da; Karki, Bijaya B.; Stixrude, Lars; Wentzcovitch, Renata M.

doi:10.1029/1999gl900149

Cited by 30 publications

(12 citation statements)

References 21 publications

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“…This may be due to subductive flow or to the difference in temperature between a cold slab and the surrounding mantle. This difference allows for the possibility that anisotropic metastable olivine, with a preexisting anisotropic fabric [ Sandvol and Ni , 1997], and/or ilmenite (MgSiO 3 ) [ Da Silva et al , 1999], and/or hydrous minerals and free fluids might be present down to mantle transition zone depths. In this last case, the shear wave speed may be slow enough to provide a large contrast against coexisting minerals, which is needed to develop a fine‐scale, laminated structure [ Brudzinski and Chen , 2001].…”

Section: Discussion and Comparison With Other Studiesmentioning

confidence: 99%

SKS splitting measurements in the Apenninic‐Tyrrhenian domain (Italy) and their relation with lithospheric subduction and mantle convection

2003

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[1] We present a compilation of singular shear wave splitting measurements in the Italian region. We used the method of Silver and Chan [1991] to determine the splitting parameters of fast direction and delay time from broadband SKS waveforms. The stations analyzed were mainly deployed in temporary experiments; a few are permanent MedNet broadband stations. The splitting parameters reveal the presence of strong seismic anisotropy in the mantle beneath Italy. The fast polarization directions define two anisotropic domains: a Tyrrhenian domain with E-W prevalent fast directions and an Apennines-Adriatic domain with NW-SE to NNW-SSE prevalent fast directions. The stations along the boundary between these two main domains show fast polarization directions that vary for earthquakes coming from different back azimuths. This variability is a sign of a complex upper mantle structure (also shown by seismic tomography) but allows us to constrain the depth of the anisotropic layer in the 100-250 km range, at least in the boundary zone between the two domains. Data at station VSL (Sardinia) suggest the presence of depth-dependent anisotropic structure, where the shallower signature is consistent with the Tyrrhenian domain results and the deeper one is possibly related to the presence of a subhorizontal slab laying on the 670-km discontinuity. We argue that the complex pattern of fast directions is strictly related to the upper mantle structure and is caused by asthenospheric flows induced by slab rollback and contemporary deformation of the overriding Tyrrhenian plate.

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Section: Discussion and Comparison With Other Studiesmentioning

confidence: 99%

SKS splitting measurements in the Apenninic‐Tyrrhenian domain (Italy) and their relation with lithospheric subduction and mantle convection

2003

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“…At the 660 km seismic discontinuity (ca 23 GPa) the Vp and Vs anisotropy would be 6.5% and 12.5% respectively. The MgSiO 3 ilmenite of trigonal symmetry is very anisotropic at ambient conditions (Weidner and Ito, 1985;Da Silva et al, 1999) with Vp anisotropy of 21.1% and Vs of 36.4%.…”

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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“…A considerable amount of experimental studies of its physical properties including vibrational spectrum, can be found in the literature [ Ross and McMillan , 1984; McMillan and Ross , 1987; Madon and Price , 1989; Hofmeister and Ito , 1992; Liu et al , 1994; Reynard and Rubie , 1996; Chopelas , 1999]. While the structural and elastic properties of MgSiO 3 ilmenite at high pressures have recently been investigated with first‐principles approaches [ D'Arco et al , 1994; da Silva et al , 1999; Karki et al , 2000a], its vibrational properties are yet to be explored theoretically. Such studies are important because experimental measurements are so far limited to only a subset of zone center modes and over a limited pressure range [ Reynard and Rubie , 1996; Chopelas , 1999].…”

Section: Introductionmentioning

confidence: 99%

First‐principles lattice dynamics and thermoelasticity of MgSiO₃ ilmenite at high pressure

Karki

Wentzcovitch

2002

J. Geophys. Res.

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[1] Phonon dispersions of MgSiO 3 ilmenite, a major mantle mineral, are calculated at high pressures by using first-principles density functional perturbation theory. Our results for the zone center modes and their initial pressure dependencies agree very well with the experimental Raman data. However, comparison with infrared data shows some discrepancy. The calculated eigenvectors indicate that low-frequency modes are primarily associated with the stretching of weak Mg-O bonds, whereas high-frequency modes are dominated by the stretching of stiff Si-O bonds. All the mode frequencies are shown to increase monotonically with increasing pressure and no soft modes exist over the pressure regime studied (À11 to 33 GPa). Several thermodynamic properties including the thermal equation of state, thermal expansivity, entropy, and heat capacity that can be useful to better understand the contribution of the silicate ilmenite phase to the composition and dynamics of the Earth's mantle are successfully presented at geophysically relevant pressure-temperature conditions.

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Ab initio study of the elastic behavior of MgSiO₃ ilmenite at high pressure

Cited by 30 publications

References 21 publications

SKS splitting measurements in the Apenninic‐Tyrrhenian domain (Italy) and their relation with lithospheric subduction and mantle convection

SKS splitting measurements in the Apenninic‐Tyrrhenian domain (Italy) and their relation with lithospheric subduction and mantle convection

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

First‐principles lattice dynamics and thermoelasticity of MgSiO₃ ilmenite at high pressure

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Ab initio study of the elastic behavior of MgSiO3 ilmenite at high pressure

Cited by 30 publications

References 21 publications

SKS splitting measurements in the Apenninic‐Tyrrhenian domain (Italy) and their relation with lithospheric subduction and mantle convection

SKS splitting measurements in the Apenninic‐Tyrrhenian domain (Italy) and their relation with lithospheric subduction and mantle convection

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

First‐principles lattice dynamics and thermoelasticity of MgSiO3 ilmenite at high pressure

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Ab initio study of the elastic behavior of MgSiO₃ ilmenite at high pressure

First‐principles lattice dynamics and thermoelasticity of MgSiO₃ ilmenite at high pressure