Study on Al 2 O 3 content and phase stability of aluminous-CaSiO 3 perovskite at high pressure and temperature

Takafuji, Naoto; Yagi, T.; Miyajima, Nobuyoshi; Sumita, Tatsuya

doi:10.1007/s00269-002-0271-5

Cited by 18 publications

(15 citation statements)

References 9 publications

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“…Calculated volumes of Cor (light green line), CaPv (blue line), and an assemblage of CaPv and Cor (dense green line) are also shown. (b) The enthalpy differences of the CaPv + Cor mixture and the Pv structure with the grossular composition [ Takafuji et al , 2002] relative to grossular calculated based on the GGA.…”

Section: Resultsmentioning

confidence: 99%

“…Previous experimental studies on Ca 3 Al 2 Si 3 O 12 grossular garnet show that it dissociates into an assemblage of CaSiO 3 perovskite (Pv) and Al 2 O 3 corundum (Cor):

{Ca}_{3} {Al}_{2} {Si}_{3} O_{12} (grossular) \to {3CaSiO}_{3} (CaPv) + {Al}_{2} O_{3} (Cor),

at pressures of 23–25 GPa and temperatures of 1000–1600 K [ Takafuji et al , 2002]. Takafuji et al [2002] also reported that Pv with the grossular composition is formed when the annealing is not long enough at low temperatures (1000 K). Although Pv with the grossular composition is likely to be metastable because of the slow kinetics of grossular decomposition, the energetics of this particular Pv is still unclear.…”

Section: Introductionmentioning

confidence: 99%

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First principles investigations on the elasticity and phase stability of grossular garnet

Kawai¹,

Tsuchiya²

2012

J. Geophys. Res.

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[1] In order to understand the fate of subducted continental materials by means of mechanisms such as tectonic erosion and sediment subduction, it is important to understand the high-pressure stability and elastic properties of grossular garnet. We study these questions using the first principles computation method. Grossular garnet was found to dissociate into an assemblage of CaSiO 3 Ca-perovskite (Pv) and Al 2 O 3 corundum (Cor) at about 23.4 GPa, accompanied by remarkable jumps of compressional wave (8.0%), shear wave (11.6%), bulk sound (5.7%) velocities, and density (12.1%). Although Pv with the grossular garnet composition was suggested experimentally after the decomposition reaction, this phase was found to be less stable than an assemblage of CaPv and Cor at pressures higher than 20 GPa. This indicates that observed Pv with the grossular garnet composition is metastable but can be obtained because of the slow kinetics of the garnet decomposition reaction. Our results imply that the dissociation of grossular garnet (as well as that of jadeite) included in continental materials subducted into the deep mantle increases the complexity of the 660 km discontinuity and can explain seismically observed multiple reflections. We have also investigated the anisotropy of elastic velocities of grossular garnet, CaPv, and Cor and found that CaPv is the most anisotropic mineral. This implies that CaPv could produce seismic anisotropy in the uppermost lower mantle.

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Section: Resultsmentioning

confidence: 99%

“…Previous experimental studies on Ca 3 Al 2 Si 3 O 12 grossular garnet show that it dissociates into an assemblage of CaSiO 3 perovskite (Pv) and Al 2 O 3 corundum (Cor):

{Ca}_{3} {Al}_{2} {Si}_{3} O_{12} (grossular) \to {3CaSiO}_{3} (CaPv) + {Al}_{2} O_{3} (Cor),

Section: Introductionmentioning

confidence: 99%

First principles investigations on the elasticity and phase stability of grossular garnet

Kawai¹,

Tsuchiya²

2012

J. Geophys. Res.

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“…The compositional data of some CaPv which did not coexist with any other silicate phases are deliberately left out [ Fitz Gerald and Ringwood , 1991; Bläß et al , 2004; Kojitani et al , 2009]. CaPv without full compositional characterization is also excluded [ Irifune et al , 2000; Takafuji et al , 2002]. …”

Section: Chemistry Of Capvmentioning

confidence: 99%

“…Since the MA experiments in the CAS system [ Gréaux et al , 2011b] were either done with a glass starting material of the Gr composition at very low T (OS1777 at 1127°C for 4 h), or done with the Gr starting material (S2152 at 1427°C for a few minutes; OS1714 at 1727°C for 10 h), and since the diamond‐anvil cell (DAC) experiment was done with an anorthite starting material which is rich in Al 2 O 3 [ Gautron and Madon , 1994], we tend not to believe that all these experiments reached their full chemical equilibrium, and that the removal of Al 2 O 3 from the Gr or An composition was fully achieved in all cases. Indeed, the MA experiments carried out by Takafuji et al [2002] with a Gr starting material demonstrated that the Al pfu of their stable CaPv was only ∼0.12–0.16 whereas that of their metastable CaPv reached ∼0.4–0.5. Therefore, it appears that the substitution mechanism, equation (8), is probably an artifact, which deserves more experimental work.…”

Section: Chemistry Of Capvmentioning

confidence: 99%

High‐Pbehavior of anorthite composition and some phase relations of the CaO‐Al₂O₃‐SiO₂ system to the lower mantle of the Earth, and their geophysical implications

et al. 2012

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[1] Multianvil experiments with long experimental durations have been made with the anorthite composition CaAl 2 Si 2 O 8 at pressure-temperature (P-T) conditions of 14-25 GPa and 1400-2400 C. At subsolidus conditions, these experiments demonstrated three phase assemblages, grossular (Gr) + kyanite (Ky) + stishovite (St) at $14 GPa, Gr + calcium-alumino-silicate phase (CAS) + St at $18 GPa, and CAS + CaSiO 3 -perovskite (CaPv) + St at above $20 GPa, which are related by the reactions Gr + Ky = CAS + St and Gr + St = CAS + CaPv. Following the method of Schreinemakers, we combined our data with the literature data to deduce a P-T phase diagram for a portion of the CaO-Al 2 O 3 -SiO 2 system at subsolidus conditions, which subsequently helped to solve some long-lasting discrepancies in the high-P behavior of the compositions of anorthite and grossular. The crystal chemistry of the CAS and CaPv solid solutions was examined, and new substitution mechanisms were firmly established. Along the solidus, the melting reaction at $14 GPa is peritectic while that at $22 GPa is eutectic. For both pressures, St is the first phase to melt out and the melt is generally andesitic. For the An composition, its density starts to be significantly higher than the density of pyrolite at $2.5 GPa, a much lower pressure than that for the Or, Ab or Qtz composition ($7.5-10 GPa), so that the An-enriched continental crust material should readily plunge into the upper mantle.Citation: Liu, X., H. Ohfuji, N. Nishiyama, Q. He, T. Sanehira, and T. Irifune (2012), High-P behavior of anorthite composition and some phase relations of the CaO-Al 2 O 3 -SiO 2 system to the lower mantle of the Earth, and their geophysical implications,

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“…The choice of minerals and phases shown in Table 1 Takafuji et al [2002]). In the absence of a complete set of parameters (i.e.…”

Section: Basic Conceptsmentioning

confidence: 99%

Synthetic tomographic images of slabs from mineral physics

Ricard

Mattern

Matas

2005

Earth's Deep Mantle: Structure, Composition, and Evolution

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Study on Al 2 O 3 content and phase stability of aluminous-CaSiO 3 perovskite at high pressure and temperature

Cited by 18 publications

References 9 publications

First principles investigations on the elasticity and phase stability of grossular garnet

First principles investigations on the elasticity and phase stability of grossular garnet

High‐Pbehavior of anorthite composition and some phase relations of the CaO‐Al₂O₃‐SiO₂ system to the lower mantle of the Earth, and their geophysical implications

Synthetic tomographic images of slabs from mineral physics

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Study on Al 2 O 3 content and phase stability of aluminous-CaSiO 3 perovskite at high pressure and temperature

Cited by 18 publications

References 9 publications

First principles investigations on the elasticity and phase stability of grossular garnet

First principles investigations on the elasticity and phase stability of grossular garnet

High‐Pbehavior of anorthite composition and some phase relations of the CaO‐Al2O3‐SiO2 system to the lower mantle of the Earth, and their geophysical implications

Synthetic tomographic images of slabs from mineral physics

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High‐Pbehavior of anorthite composition and some phase relations of the CaO‐Al₂O₃‐SiO₂ system to the lower mantle of the Earth, and their geophysical implications