Phase transformations in diopside CaMgSi<sub>2</sub>O<sub>6</sub> at pressures Up to 25 GPa

Irifune, Tetsuo; Susaki, Junichi; Yagi, T.; Sawamoto, Hiroshi

doi:10.1029/gl016i002p00187

Cited by 56 publications

(17 citation statements)

References 7 publications

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“…This phase was fi rst reported by Liu (1987) as a high-pressure polymorph of diopside with the cubic perovskite structure. However, the result was not consistent with other studies in which diopside breaks down into a cubic CaSiO 3 perovskite phase and an orthorhombic MgSiO 3 perovskite phase at pressures above 21 GPa (e.g., Mao et al 1978;Tamai and Yagi 1989;Irifune et al 1989). Kim et al (1994) verifi ed that a (Ca, Mg)Si 2 O 6 -glass transforms to Ca 0.5 Mg 0.5 SiO 3 cubic CMperovskite at 13 GPa, whereas a diopside-crystal decomposes to CaSiO 3 cubic perovskite, Mg 2 SiO 4 spinel and stishovite at 17 GPa and 1000 °C using a laser-heated diamond anvil cell.…”

Section: Introductioncontrasting

confidence: 68%

Formation of metastable cubic-perovskite in high-pressure phase transformation of Ca(Mg, Fe, Al)Si2O6

Asahara

Ohtani

Kondo

et al. 2005

American Mineralogist

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We have carried out in-situ X-ray diffraction experiments on high-pressure transformations of a Ca-and Fe-rich pyroxene (Ca 1.03 Mg 0.61 Fe 0.23 Al 0.14 Si 2 O 6 ) to investigate the stability of Ca 0.5 (Mg, Fe, Al) 0.5 SiO 3 perovskite (CM-perovskite) in a multi component system at about 32 GPa and up to 1900 °C. We observed that cubic CM-perovskite was formed at about 1300 °C and decomposed into cubic Ca-perovskites and orthorhombic Mg-perovskites and stishovite at 1800 °C when using a glass starting material. In another experiment using a crystalline pyroxene starting material, two cubic perovskites; Ca-perovskite and CM-perovskite, and orthorhombic Mg-perovskite formed simultaneously during the initial stage of the transformation. However, the cubic CM-perovskite subsequently decomposed into Mg-and Ca-perovskites and stishovite at 1200 °C. These results indicate that the assembly of cubic Ca-perovskite, orthorhombic Mg-perovskite and stishovite is stable and cubic CM-perovskite is a metastable phase at around 32 GPa and temperatures over 1000 °C in this system. Chemical analyses of product phases showed that Mg, Fe, and Al were preferentially partitioned into Mg-perovskite and the compositions of Ca-perovskite were close to pure CaSiO 3 . The present study shows that CM-perovskite nucleates during the initial stage of Ca(Mg, Fe, Al)Si 2 O 6 pyroxene transformation. Therefore, cold subducting slabs and impacted meteorites are the possible places in which CM-perovskite could exist. The Ca-rich glassy phase in a shocked chondrite (Tomioka and Kimura 2003) might have formed by vitrifi cation of a metastable CM-perovskite-like phase.

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Section: Introductioncontrasting

confidence: 68%

Formation of metastable cubic-perovskite in high-pressure phase transformation of Ca(Mg, Fe, Al)Si2O6

Asahara

Ohtani

Kondo

et al. 2005

American Mineralogist

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“…Multianvil experiments show that above 250 kbar and 1773 K, spinel transforms to a CaFe20~ structure (Irifune et al 1991). Determining the underlying cause of the spectrum disappearance requires further experimentation.…”

Section: Change In Compressional Behaviormentioning

confidence: 98%

Vibrational spectroscopy of aluminate spinels at 1 atm and of MgAl2O4 to over 200 kbar

1991

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Abstract. Single-crystal Raman and infrared reflectivity data including high pressure results to over 200 kbar on a natural, probably fully ordered MgA1204 spinel reveal that many of the reported frequencies from spectra of synthetic spinels are affected by disorder at the cation sites. The spectra are interpreted in terms of factor group analysis and show that the high energy modes are due to the octahedral internal modes, in contrast to the behavior of silicate spinels, but in agreement with previous data based on isotopic and chemical cation substitutions and with new Raman data on gahnite (~ ZnAI204) and new IR reflectivity data on both gahnite and hercynite (~Feo.ssMgo.42A1204). Therefore, aluminate spinels are inappropriate as elastic or thermodynamic analogs for silicate spinels.Fluorescence sideband spectra yield complementary information on the vibrational modes and provide valuable information on the acoustic modes at high pressure. The transverse acoustic modes are nearly pressure independent, which is similar to the behavior of the shear modes previously measured by ultrasonic techniques. The pressure derivative of all acoustic modes become negative above 110 kbar, indicating a lattice instability, in agreement with previous predictions. This lattice instability lies at approximately the same pressure as the disproportionation of spinel to MgO and A1203 reported in high temperature, high pressure work.

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“…In the past 4 decades, a wealth of knowledge has been accumulated on garnet through intensive experimental studies, including crystal structure compression mechanisms [ Hazen et al , 1994; Zhang et al , 1998; Morishima et al , 1999], cation order‐disorder transitions at elevated temperatures [ Angel et al , 1989; Phillips et al , 1992; Wang et al , 1993; Heinemann et al , 1997] and the transition with Al substitution [ Nakatsuka et al , 1999], thermodynamic properties [ Anderson et al , 1991; Kavner et al , 2000], elasticity [ Gerald Pacalo and Weidner , 1997; Gwanmesia et al , 2000; Sinogeikin and Bass , 2002], vibrational spectroscopy [ Chopelas , 1999; Rauch et al , 1996; Hofmeister et al , 2004], and phase transformations [e.g., Ringwood , 1967; Akaogi and Akimoto , 1979; Irifune et al , 1989; Gasparik , 1990; O'Neill and Jeanloz , 1994; Akaogi et al , 1987; Yusa et al , 1993; Akaogi and Ito , 1999; Hirose et al , 2001a]. But many problems still remain unsolved.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic properties of MgSiO₃majorite and phase transitions near 660 km depth in MgSiO₃and Mg₂SiO₄: A first principles study

Yu¹,

Wentzcovitch²,

Vinograd³

et al. 2011

J. Geophys. Res.

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[1] Thermodynamic properties of MgSiO 3 tetragonal majorite have been calculated at high pressures and temperatures within the quasi-harmonic approximation based on density functional theory using the local density approximation (LDA) and the generalized gradient approximation (GGA). The LDA results compare exceptionally well with measured thermodynamic properties. A classical Monte Carlo simulation based on results from a cluster expansion method demonstrates that disorder between magnesium and silicon in the octahedral sites in MgSiO 3 majorite does not occur below 3600 K at transition zone pressures. The ensuing calculations on phase boundaries of MgSiO 3 between majorite, perovskite, and ilmenite show that a much better agreement with experiment can be obtained by using GGA rather than LDA, for LDA underestimates the transition pressures by as much as 11 GPa. The Clapeyron slopes predicted by GGA and LDA are close to each other: 0.9-1.7 MPa/K for majorite-perovskite transition, 6.9-7.9 MPa/K for majorite-ilmenite transition, and −7-−3 MPa/K for ilmenite-perovskite transition. The triple point predicted by GGA is located at 21.8 ± 1 GPa and 1840 ± 200 K which is ∼400 K lower in temperature than most experimental estimates. This result suggests that ilmenite is restricted to lower temperatures and that the majorite to ilmenite transition may occur in cold subducting slabs in the transition zone. Our calculation also reveals that wadsleyite decomposes to an assemblage of majorite plus periclase above 2280 K with a large negative Clapeyron slope (−22-−12 MPa/K) and that ringwoodite decomposes to ilmenite plus periclase below 1400 K (1.2 MPa/K). These two decomposition transitions may influence hot plumes and cold slabs near 660 km depth, respectively. Further calculations show that discontinuities in density, bulk modulus, and bulk sound velocity associated with the majorite to perovskite transition in MgSiO 3 are much larger than those from the postspinel transition in Mg 2 SiO 4 at conditions close to 660 km depth. This suggests that the large density discontinuity at 660 km depth as proposed by PREM (9.3%) might be accounted by a piclogite compositional model or marginally accounted by a pyrolite compositional model with, for example, 50 vol % ringwoodite, 45 vol % majorite, and 5 vol % other phases (such as calcium perovskite) at the bottom of the transition zone, provided that the density contrast between majorite and perovskite will not be greatly altered by the presence of other elements such as Fe, Al, Ca, and H. On the other hand, the smaller density discontinuity at 660 km depth as derived from impedance studies (4-6%) disfavors sharp contributions to seismic discontinuities from the majorite to perovskite transition.

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Phase transformations in diopside CaMgSi₂O₆ at pressures Up to 25 GPa

Cited by 56 publications

References 7 publications

Formation of metastable cubic-perovskite in high-pressure phase transformation of Ca(Mg, Fe, Al)Si2O6

Formation of metastable cubic-perovskite in high-pressure phase transformation of Ca(Mg, Fe, Al)Si2O6

Vibrational spectroscopy of aluminate spinels at 1 atm and of MgAl2O4 to over 200 kbar

Thermodynamic properties of MgSiO₃majorite and phase transitions near 660 km depth in MgSiO₃and Mg₂SiO₄: A first principles study

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Phase transformations in diopside CaMgSi2O6 at pressures Up to 25 GPa

Cited by 56 publications

References 7 publications

Formation of metastable cubic-perovskite in high-pressure phase transformation of Ca(Mg, Fe, Al)Si2O6

Formation of metastable cubic-perovskite in high-pressure phase transformation of Ca(Mg, Fe, Al)Si2O6

Vibrational spectroscopy of aluminate spinels at 1 atm and of MgAl2O4 to over 200 kbar

Thermodynamic properties of MgSiO3majorite and phase transitions near 660 km depth in MgSiO3and Mg2SiO4: A first principles study

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Phase transformations in diopside CaMgSi₂O₆ at pressures Up to 25 GPa

Thermodynamic properties of MgSiO₃majorite and phase transitions near 660 km depth in MgSiO₃and Mg₂SiO₄: A first principles study