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Raymond Jeanloz - One of the best experts on this subject based on the ideXlab platform.
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Equation of state and strength of natural Majorite
Journal of Geophysical Research: Solid Earth, 2000Co-Authors: Abby Kavner, Raymond Jeanloz, Stanislav V. Sinogeikin, Jay D. BassAbstract:The bulk modulus of a natural sample of cubic Majorite, one of the primary components of the Earth's transition zone, has been determined by two independent methods: quasi-hydrostatic compression in the diamond anvil cell and Brillouin spectroscopy at room pressure. The two measurements agree well, and together yield a zero-pressure isothermal bulk modulus KOT = 162.7 (±3.3) GPa, and a pressure derivative KOT = 6.6 (±0.8). Additional compression experiments under nonhydrostatic conditions show that Majorite supports shear stresses of at least 2 to 3 GPa at pressures of 7–11 GPa, among the highest values yet documented in silicates or oxides at comparable pressures. These results imply a high strength for Majorite, suggesting that the transition zone could be strong to a degree that may influence deformation and heat transfer within the Earth.
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elasticity of natural Majorite and ringwoodite from the catherwood meteorite
Geophysical Research Letters, 1997Co-Authors: Stanislav V. Sinogeikin, Abby Kavner, Jay D. Bass, Raymond JeanlozAbstract:Sound velocities and elastic moduli of natural polycrystalline Majorite (Mg0.78Fe0.21Ca0.01)SiO3, and ringwoodite (Mg0.75Fe0.25)2SiO4 from the Catherwood meteorite were measured by Brillouin spectroscopy. These are the first acoustic measurements for such natural high-pressure phases with Fe contents comparable to that of the Earth's mantle. The adiabatic bulk modulus of Majorite is Ks=164(4) GPa, and the shear modulus is μ=87(2) GPa, which are typical values for garnet-structured silicates. Both the elastic moduli and the sound velocities of natural cubic Majorite are slightly lower than values for aluminosilicate garnets with comparable Fe contents. Moreover, the bulk and shear moduli of natural Majorite are indistinguishable from those of pure Mg Majorite, and the dependence of these moduli on Fe content is small. In contrast, ringwoodite (Ks=193(3), μ=113(2)) exhibits a pronounced change in the aggregate elastic moduli and sound velocities with increasing Fe content. The addition of 10% Fe to γ-phase changes the velocity by an amount comparable to the velocity change across the β→γ transition in Mg2SiO4. It is therefore necessary to account for the effect of Fe in constructing mineralogical models of the transition zone.
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electrical conductivity of a natural mg fe sio3 Majorite garnet
Geophysical Research Letters, 1995Co-Authors: Abby Kavner, Raymond JeanlozAbstract:The electrical conductivity of meteoritic Majorite, measured at 10 Hz under a nitrogen atmosphere at ambient pressure, is 3.8 (±1.8) × 10−7 S/m at room temperature and displays an Arrhenius behavior with an activation energy of 0.55 (±0.1) eV over the temperature range 290–370 K. Extrapolating these values to conditions of the Earth's mantle suggests that Majorite and spinel can account for the increase in electrical conductivity observed from the upper mantle to the transition zone, where these phases are stable.
Jay D. Bass - One of the best experts on this subject based on the ideXlab platform.
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elastic moduli of jadeite enstatite Majorite
Geophysical Research Letters, 2002Co-Authors: Hans J Reichmann, Stanislav V. Sinogeikin, Jay D. Bass, Tibor GasparikAbstract:[1] The adiabatic bulk (KS) and shear (G) moduli of a polycrystalline Majorite-garnet solid solution with composition (Na0.92Mg2.08)(Mg0.02Al1.06Si0.92)Si3O12 were measured at ambient conditions by Brillouin spectroscopy. KS and G were found to be 171.6 (3.5) GPa and 103.5 (2.0) GPa, respectively. Assuming a linear dependence of the elastic moduli on composition for the Mg2Si2O6 (enstatite-Majorite, En-Mj) – NaAlSi2O6 (jadeite-Majorite, Jd-Mj) join, the calculated KS and G of the fictive Jd-Mj end-member are 178 and 125 GPa, respectively. At ambient conditions, the shear velocity change associated with the pyroxene to Majorite transition increases dramatically with increasing Na content in the system. In contrast, there is virtually no shear velocity increase associated with the pyroxene to Majorite transition in MgSiO3. If this relationship holds at high pressures and temperatures, it suggests that for mineral assemblages containing an abundance of large radius cations such as Ca and Na, the pyroxene→garnet reaction will produce higher shear velocity gradients than assemblages that are relatively deficient in these elements. Such chemical effects could play a significant role in explaining high seismic velocity gradients in the transition zone.
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elasticity of Majorite and a Majorite pyrope solid solution to high pressure implications for the transition zone
Geophysical Research Letters, 2002Co-Authors: Stanislav V. Sinogeikin, Jay D. BassAbstract:[1] High seismic velocity gradients in the transition zone have been attributed to large pressure derivatives of the elastic moduli of transition zone minerals, such as Majorite-garnet. Here we present Brillouin scattering measurements of the elasticity of polycrystalline Mg-Majorite (Mj100, Mg4Si4O12) and a Mj50Py50 Majorite - pyrope solid solution to pressures similar to those at the top of the transition zone (15.1(1) GPa and 12.8(1) GPa, respectively). The pressure derivatives of the adiabatic bulk (KS) and shear (μ) moduli of both Mj50Py50 and Mj100 are 4.2(3) and 1.4(2), respectively, and are equal to those of pyrope within the experimental uncertainties. We conclude that neither the adiabatic compression of Majorite-garnet nor any other likely transition zone phase is able to produce the high velocity gradients observed seismically. High velocity gradients are consistent with gradual transformations between minerals with very different elastic properties. The transformation of ∼25% or more of clinopyroxene into Majorite above 520 km, and the formation of Ca silicate perovskite below 520 km could produce the observed seismic gradients.
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Equation of state and strength of natural Majorite
Journal of Geophysical Research: Solid Earth, 2000Co-Authors: Abby Kavner, Raymond Jeanloz, Stanislav V. Sinogeikin, Jay D. BassAbstract:The bulk modulus of a natural sample of cubic Majorite, one of the primary components of the Earth's transition zone, has been determined by two independent methods: quasi-hydrostatic compression in the diamond anvil cell and Brillouin spectroscopy at room pressure. The two measurements agree well, and together yield a zero-pressure isothermal bulk modulus KOT = 162.7 (±3.3) GPa, and a pressure derivative KOT = 6.6 (±0.8). Additional compression experiments under nonhydrostatic conditions show that Majorite supports shear stresses of at least 2 to 3 GPa at pressures of 7–11 GPa, among the highest values yet documented in silicates or oxides at comparable pressures. These results imply a high strength for Majorite, suggesting that the transition zone could be strong to a degree that may influence deformation and heat transfer within the Earth.
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elasticity of natural Majorite and ringwoodite from the catherwood meteorite
Geophysical Research Letters, 1997Co-Authors: Stanislav V. Sinogeikin, Abby Kavner, Jay D. Bass, Raymond JeanlozAbstract:Sound velocities and elastic moduli of natural polycrystalline Majorite (Mg0.78Fe0.21Ca0.01)SiO3, and ringwoodite (Mg0.75Fe0.25)2SiO4 from the Catherwood meteorite were measured by Brillouin spectroscopy. These are the first acoustic measurements for such natural high-pressure phases with Fe contents comparable to that of the Earth's mantle. The adiabatic bulk modulus of Majorite is Ks=164(4) GPa, and the shear modulus is μ=87(2) GPa, which are typical values for garnet-structured silicates. Both the elastic moduli and the sound velocities of natural cubic Majorite are slightly lower than values for aluminosilicate garnets with comparable Fe contents. Moreover, the bulk and shear moduli of natural Majorite are indistinguishable from those of pure Mg Majorite, and the dependence of these moduli on Fe content is small. In contrast, ringwoodite (Ks=193(3), μ=113(2)) exhibits a pronounced change in the aggregate elastic moduli and sound velocities with increasing Fe content. The addition of 10% Fe to γ-phase changes the velocity by an amount comparable to the velocity change across the β→γ transition in Mg2SiO4. It is therefore necessary to account for the effect of Fe in constructing mineralogical models of the transition zone.
Donald J. Weidner - One of the best experts on this subject based on the ideXlab platform.
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relative strength of the pyrope Majorite solid solution and the flow law of Majorite containing garnets
Physics of the Earth and Planetary Interiors, 2010Co-Authors: Simon A. Hunt, Donald J. Weidner, David P. Dobson, John P. BrodholtAbstract:Even though the garnet phase is the second most abundant phase in the upper-mantle and transition-zone, no previous studies have directly measured the effect of Majorite content on the strength of garnet under mantle conditions. Here we report the results of constant strain-rate and stress-relaxation experiments on garnets in the pyrope-Majorite solid solution which constrain the strength of majoritic containing garnets relative to pyrope as a function of Majorite content and temperature. We find that at temperatures below 650 degrees C both pure pyrope and majoritic garnets have the same strength. Conversely, above 650 degrees C we find that majoritic garnets are initially stronger than pure pyrope but weaken with increasing temperature and Majorite content and with significant Majorite contents are weaker than pyrope above approximately 800 degrees C. We develop a flow law for the entire pyrope Majorite solid solution as a function of temperature and Majorite content. (C) 2010 Elsevier B.V. All rights reserved.
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elasticity of Majorite mgsio3 tetragonal garnet
Physics of the Earth and Planetary Interiors, 1997Co-Authors: Rosemary E G Pacalo, Donald J. WeidnerAbstract:Abstract The adiabatic elastic moduli of single-crystal MgSiO 3 in the tetragonal garnet structure have been measured at ambient conditions using Brillouin spectroscopy. The results (in GPa) are: C 11 = 286.4 ± 1.3; C 33 = 280.1 ± 1.8; C 44 = 85.0 ± 0.7; C 66 = 93.2 ± 1.1; C 12 = 83.0 ± 2.9; C 23 = 104.9 ± 2.4; C 16 = 1.4 ± 1.3. The isotropic properties of MgSiO 3 Majorite are K VRH = 159.8 ± 4.4 GPa and μ VRH = 89.7 ± 0.6 GPa. An empirical relationship describing garnet elasticity along the pyrope-Majorite join indicates that the bulk modulus increases by about 8% and the shear modulus by about 2% going from Majorite to pyrope. The tetragonal garnet structure is characterized by ordering on the octahedral site; axial elastic moduli differ as a result of differing axial arrangements of MgO 6 and SiO 6 units. The overall softening of the garnet structure with increasing Majorite content is attributed to the presence of weak magnesium octahedra and may also reflect the extensive cross-linking that is typical of garnets. Two factors contribute to the observed elasticity of Majorite: coupled substitution of aluminum by magnesium + silicon, and structural ordering on the octahedral site. In this case, the compositional effect is probably minor, but until we have elasticity measurements on completely disordered ‘cubic’ MgSiO 3 garnet, the relative importance of the two components cannot be easily distinguished.
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elastic properties of sodium rich Majorite garnet
Geophysical Research Letters, 1992Co-Authors: Rosemary E G Pacalo, Donald J. Weidner, Tibor GasparikAbstract:The adiabatic elastic moduli of a high-pressure sodium-rich Majorite garnet have been measured at ambient conditions using Brillouin spectroscopy. This garnet has the composition, Na1.87Mg1.18Si4.94O12, with sodium and magnesium in eight-fold coordination and silicon in octahedral and tetrahedral coordination. While the adiabatic bulk modulus, Ks = 173.5 GPa, falls within the range of common garnets, the shear modulus, μ = 114.7 GPa, is unusually large; sodium garnet is elastically similar to the low-pressure garnet grossular. The variation of elastic properties for garnets of differing composition within the cubic garnet structure can be expressed as a linear function of the ratio of average cation radii in the eight-fold versus the six-fold site. The cations in the AO8 polyhedra apparently brace the structure by controlling rotational freedom within corner-linked chains of alternating tetrahedra and octahedra.
Stanislav V. Sinogeikin - One of the best experts on this subject based on the ideXlab platform.
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elastic moduli of jadeite enstatite Majorite
Geophysical Research Letters, 2002Co-Authors: Hans J Reichmann, Stanislav V. Sinogeikin, Jay D. Bass, Tibor GasparikAbstract:[1] The adiabatic bulk (KS) and shear (G) moduli of a polycrystalline Majorite-garnet solid solution with composition (Na0.92Mg2.08)(Mg0.02Al1.06Si0.92)Si3O12 were measured at ambient conditions by Brillouin spectroscopy. KS and G were found to be 171.6 (3.5) GPa and 103.5 (2.0) GPa, respectively. Assuming a linear dependence of the elastic moduli on composition for the Mg2Si2O6 (enstatite-Majorite, En-Mj) – NaAlSi2O6 (jadeite-Majorite, Jd-Mj) join, the calculated KS and G of the fictive Jd-Mj end-member are 178 and 125 GPa, respectively. At ambient conditions, the shear velocity change associated with the pyroxene to Majorite transition increases dramatically with increasing Na content in the system. In contrast, there is virtually no shear velocity increase associated with the pyroxene to Majorite transition in MgSiO3. If this relationship holds at high pressures and temperatures, it suggests that for mineral assemblages containing an abundance of large radius cations such as Ca and Na, the pyroxene→garnet reaction will produce higher shear velocity gradients than assemblages that are relatively deficient in these elements. Such chemical effects could play a significant role in explaining high seismic velocity gradients in the transition zone.
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elasticity of Majorite and a Majorite pyrope solid solution to high pressure implications for the transition zone
Geophysical Research Letters, 2002Co-Authors: Stanislav V. Sinogeikin, Jay D. BassAbstract:[1] High seismic velocity gradients in the transition zone have been attributed to large pressure derivatives of the elastic moduli of transition zone minerals, such as Majorite-garnet. Here we present Brillouin scattering measurements of the elasticity of polycrystalline Mg-Majorite (Mj100, Mg4Si4O12) and a Mj50Py50 Majorite - pyrope solid solution to pressures similar to those at the top of the transition zone (15.1(1) GPa and 12.8(1) GPa, respectively). The pressure derivatives of the adiabatic bulk (KS) and shear (μ) moduli of both Mj50Py50 and Mj100 are 4.2(3) and 1.4(2), respectively, and are equal to those of pyrope within the experimental uncertainties. We conclude that neither the adiabatic compression of Majorite-garnet nor any other likely transition zone phase is able to produce the high velocity gradients observed seismically. High velocity gradients are consistent with gradual transformations between minerals with very different elastic properties. The transformation of ∼25% or more of clinopyroxene into Majorite above 520 km, and the formation of Ca silicate perovskite below 520 km could produce the observed seismic gradients.
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Equation of state and strength of natural Majorite
Journal of Geophysical Research: Solid Earth, 2000Co-Authors: Abby Kavner, Raymond Jeanloz, Stanislav V. Sinogeikin, Jay D. BassAbstract:The bulk modulus of a natural sample of cubic Majorite, one of the primary components of the Earth's transition zone, has been determined by two independent methods: quasi-hydrostatic compression in the diamond anvil cell and Brillouin spectroscopy at room pressure. The two measurements agree well, and together yield a zero-pressure isothermal bulk modulus KOT = 162.7 (±3.3) GPa, and a pressure derivative KOT = 6.6 (±0.8). Additional compression experiments under nonhydrostatic conditions show that Majorite supports shear stresses of at least 2 to 3 GPa at pressures of 7–11 GPa, among the highest values yet documented in silicates or oxides at comparable pressures. These results imply a high strength for Majorite, suggesting that the transition zone could be strong to a degree that may influence deformation and heat transfer within the Earth.
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elasticity of natural Majorite and ringwoodite from the catherwood meteorite
Geophysical Research Letters, 1997Co-Authors: Stanislav V. Sinogeikin, Abby Kavner, Jay D. Bass, Raymond JeanlozAbstract:Sound velocities and elastic moduli of natural polycrystalline Majorite (Mg0.78Fe0.21Ca0.01)SiO3, and ringwoodite (Mg0.75Fe0.25)2SiO4 from the Catherwood meteorite were measured by Brillouin spectroscopy. These are the first acoustic measurements for such natural high-pressure phases with Fe contents comparable to that of the Earth's mantle. The adiabatic bulk modulus of Majorite is Ks=164(4) GPa, and the shear modulus is μ=87(2) GPa, which are typical values for garnet-structured silicates. Both the elastic moduli and the sound velocities of natural cubic Majorite are slightly lower than values for aluminosilicate garnets with comparable Fe contents. Moreover, the bulk and shear moduli of natural Majorite are indistinguishable from those of pure Mg Majorite, and the dependence of these moduli on Fe content is small. In contrast, ringwoodite (Ks=193(3), μ=113(2)) exhibits a pronounced change in the aggregate elastic moduli and sound velocities with increasing Fe content. The addition of 10% Fe to γ-phase changes the velocity by an amount comparable to the velocity change across the β→γ transition in Mg2SiO4. It is therefore necessary to account for the effect of Fe in constructing mineralogical models of the transition zone.
Tibor Gasparik - One of the best experts on this subject based on the ideXlab platform.
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elastic moduli of jadeite enstatite Majorite
Geophysical Research Letters, 2002Co-Authors: Hans J Reichmann, Stanislav V. Sinogeikin, Jay D. Bass, Tibor GasparikAbstract:[1] The adiabatic bulk (KS) and shear (G) moduli of a polycrystalline Majorite-garnet solid solution with composition (Na0.92Mg2.08)(Mg0.02Al1.06Si0.92)Si3O12 were measured at ambient conditions by Brillouin spectroscopy. KS and G were found to be 171.6 (3.5) GPa and 103.5 (2.0) GPa, respectively. Assuming a linear dependence of the elastic moduli on composition for the Mg2Si2O6 (enstatite-Majorite, En-Mj) – NaAlSi2O6 (jadeite-Majorite, Jd-Mj) join, the calculated KS and G of the fictive Jd-Mj end-member are 178 and 125 GPa, respectively. At ambient conditions, the shear velocity change associated with the pyroxene to Majorite transition increases dramatically with increasing Na content in the system. In contrast, there is virtually no shear velocity increase associated with the pyroxene to Majorite transition in MgSiO3. If this relationship holds at high pressures and temperatures, it suggests that for mineral assemblages containing an abundance of large radius cations such as Ca and Na, the pyroxene→garnet reaction will produce higher shear velocity gradients than assemblages that are relatively deficient in these elements. Such chemical effects could play a significant role in explaining high seismic velocity gradients in the transition zone.
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comparative compressibilities of Majorite type garnets
Physics and Chemistry of Minerals, 1994Co-Authors: Robert M Hazen, Robert T Downs, Pamela G Conrad, L W Finger, Tibor GasparikAbstract:Relative compressibilities of five silicate garnets were determined by single-crystal x-ray diffraction on crystals grouped in the same high-pressure mount. The specimens include a natural pyrope [(Mg2.84Fe0.10Ca0,06) Al2Si3O12], and four synthetic specimens with octahedrally-coordinated silicon: Majorite [Mg3(MgSi)Si3O12], calcium-bearing Majorite [(Ca0.49Mg2.51)(MgSi)Si3012], sodium Majorite [(Na1.88Mgp0.12)(Mg0.06Si1.94)Si3O12], and an intermediate composition [(Na0.37Mg2.48)(Mg0.13Al1.07 Si080) Si3O12]. Small differences in the compressibilities of these crystals are revealed because they are subjected simultaneously to the same pressure. Bulk-moduli of the garnets range from 164.8 ± 2.3 GPa for calcium Majorite to 191.5 ± 2.5 GPa for sodium Majorite, assuming K′=4. Two factors, molar volume and octahedral cation valence, appear to control garnet compression.
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crystal chemistry of ca bearing Majorite
American Mineralogist, 1994Co-Authors: Robert M Hazen, Robert T Downs, Pamela G Conrad, L W Finger, Tibor GasparikAbstract:Single crystals of Ca-bearing Majorite, a garnet with composition (Cao.49Mg2sl)(MgSi)SiPI2' have been synthesized at 18.2 GPa and 2050 0c. This sample is the first silicate garnet to display ordering on both octahedral and dodecahedral sites- behavior that may increase the compositional flexibility of garnet, affect element partitioning at high pressure, and stabilize the garnet structure in the transition zone and upper portion of the lower mantle. The garnet is tetragonal [space group 14/a, Z = 8, a = 11.5816(9), C= 11.5288(13) A, V = 1546.39(29) A3] and, like MgSiO, Majorite, displays twinning by twofold rotation about [110].
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modulated microstructure in synthetic Majorite
American Mineralogist, 1993Co-Authors: Yanbin Wang, Tibor Gasparik, Robert C LiebermannAbstract:Transmission electron microscopy on Mg-end member Majorite crystals synthesized at 22 GPa and above 2350°C reveals a modulated microstructure, characterized by mutually intersecting linear contrasts parallel to the tetragonal {101} planes, with a typical wavelength of the modulation between 150 and 300 A. Streaking perpendicular to the {101} planes is observed in electron diffraction patterns. The modulated microstructure coarsens with decreasing synthesis and quench temperature and, by 2050°C, is completetly replaced by twin domains related by reflection operations across the tetragonal {101} planes. These results suggest that the structural modulation is due to a phase transformation in Majorite from cubic (space group Ia3d) to tetragonal (I4 1 /a) near 2350°C, probably through ordering of the Mg and Si atoms
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elastic properties of sodium rich Majorite garnet
Geophysical Research Letters, 1992Co-Authors: Rosemary E G Pacalo, Donald J. Weidner, Tibor GasparikAbstract:The adiabatic elastic moduli of a high-pressure sodium-rich Majorite garnet have been measured at ambient conditions using Brillouin spectroscopy. This garnet has the composition, Na1.87Mg1.18Si4.94O12, with sodium and magnesium in eight-fold coordination and silicon in octahedral and tetrahedral coordination. While the adiabatic bulk modulus, Ks = 173.5 GPa, falls within the range of common garnets, the shear modulus, μ = 114.7 GPa, is unusually large; sodium garnet is elastically similar to the low-pressure garnet grossular. The variation of elastic properties for garnets of differing composition within the cubic garnet structure can be expressed as a linear function of the ratio of average cation radii in the eight-fold versus the six-fold site. The cations in the AO8 polyhedra apparently brace the structure by controlling rotational freedom within corner-linked chains of alternating tetrahedra and octahedra.
