High-pressure phase relations and thermodynamic properties of CaAl4Si2O11 CAS phase

Akaogi, Masaki; Haraguchi, M.; Yaguchi, Miki; Kojitani, Hiroshi

doi:10.1016/j.pepi.2008.10.010

Cited by 18 publications

(20 citation statements)

References 33 publications

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“…The CAS phase is more stable at high pressure and high temperature than a mixture of grossular, stishovite, and corundum with a negative slope boundary. Therefore, the CAS phase has a wide stability field in the high‐pressure, high‐temperature regime [e.g., Akaogi et al , 2009]. However, since we consider materials subducted at low temperatures along the cold slab, we consider only grossular dissociation into CaPv and Cor in this study.…”

Section: Discussionmentioning

confidence: 99%

“…The present calculations show that these materials produce large velocity jumps in the transition zone associated with the grossular decomposition as well as with the jadeite decomposition [ Kawai and Tsuchiya , 2010]. While the postspinel transition of olivine with a negative Clapeyron slope of −2.9 MPa/K [ Yu et al , 2007] occurs in the surrounding mantle around depths of 660 km, decompositions of jadeite and grossular have Clapeyron slopes of +3.1 and ∼0 MPa/K, respectively [ Akaogi et al , 2009]. At a normal mantle temperature of 1800 K at the bottom of the mantle transition zone, the decompositions of grossular, jadeite, and spinel occur at almost the same pressures of 23.6 GPa.…”

Section: Discussionmentioning

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: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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

Kawai¹,

Tsuchiya²

2012

J. Geophys. Res.

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“…We use reported phase relations: jadeite ⇔ CF-type phase + stishovite (Kawai and Tsuchiya 2012a), grossular garnet ⇔ Cor + Ca-pv (Akaogi et al 2009;Kawai and Tsuchiya 2012b), stishovite ⇔ α-PbO 2 phase (Tsuchiya et al 2004), and K-hollandite I ⇔ II (Nishiyama et al 2005;Kawai and Tsuchiya 2012c). Since the high P-T dissociation boundary of grossular garnet and the phase transition boundary of K-hollandite have not been studied theoretically to date, we apply Clapeyron slopes determined experimentally (Akaogi et al 2009;Nishiyama et al 2005) to the static transition pressures obtained by theoretical studies Tsuchiya 2012b, 2013). They show that while the phase transition pressures of post-spinel, post-grossular, post-jadeite, and K-hollandite along a normal geotherm are 23.3, 23.6, 23.7, and 28.3 GPa, respectively, and those along a slab geotherm are 24.4, 23.6, 22.1, and 24.5 GPa, respectively ( Fig.…”

Section: Modeling Density and Seismic Velocity For Sediment And Averamentioning

confidence: 99%

Elasticity of Continental Crust Around the Mantle Transition Zone

Kawai

Tsuchiya

2015

The Earth's Heterogeneous Mantle

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The fate and amount of granitic materials subducted into the deep mantle are still under debate. The density, elastic property, and phase stability of granitic materials in the mantle pressures are key to clarifying them. Here, we modeled highpressure properties of the granitic assemblage by using ab initio mineral physics data of grossular garnet, K-hollandite, jadeite, stishovite, and calcium ferrite (CF)-type phase. We find that the ongoing subducting granitic assemblage, such as sediments and average upper crust rocks, is much denser than pyrolite in the pressure range from 9 GPa (~270 km), at which coesite undergoes a phase transition to stishovite, to around 27 GPa (~740 km). Above this pressure, granitic material becomes less dense than a pyrolite. This indicates that the granitic assemblage becomes gravitationally stable at the base of the mantle transition zone (MTZ). Results suggest a possibility that the granitic materials could accumulate around the 740 km depth if carried into the depth deeper than 270 km and segregated at some depth. Comparison of the velocities between granitic and pyrolitic materials shows that granitic materials can produce substantial velocity anomalies in the MTZ and the uppermost lower mantle (LM). Seismic observations such as anomalously fast velocities, especially for the shear wave, around the 660-km discontinuity, the complexity of 660-km discontinuity, and the scatterers in the uppermost LM could be associated with the subducted granitic materials.

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“…Later this phase was observed in the high-P experiments using the basaltic compositions as the starting materials, although its composition was slightly different to CaAl 4 Si 2 O 11 [6][7][8]. According to recent high-P experimental exploration [9][10][11], the CAS phase is stable from about 10 to about 30 GPa. On the other hand, the CAS also occurs as a natural mineral, and has been identified in shocked Martian meteorites [12].…”

mentioning

confidence: 98%

“…′ = 6.3(11) for the c-axis. The elastic anisotropy (K T-a :K T-c ) of the CAS phase, therefore, is about 2.19; in other words, the a-axis direction is much less compressible than the c-axis direction.…”

mentioning

confidence: 99%

Equation of state of CAS phase to pressure of the uppermost lower mantle at ambient temperature

Deng

et al. 2011

Sci. China Earth Sci.

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The CAS phase is a major constituent phase for the continental crust and basaltic compositions at the P-T conditions of the Earth's mantle, and potentially plays an important role in the geodynamic processes related to slab subduction. Its equation of state has been investigated here at ambient temperature up to about 25 GPa by using a diamond-anvil cell and synchrotron Xray radiation. Its P-V data, fitted to the third-order Birch-Murnaghan equation, yield an isothermal bulk modulus (K T ) of 185 (9) GPa and first pressure derivative ( T K ′ ) of 7.2 (12). If T K ′ is fixed at 4, the derived K T is 212 (4) GPa. Additionally, the CAS phase is strongly elastically anisotropic, with its a-axis direction much less compressible than c-axis direction: K T-a : K T-c = 2.19. anisotropic elasticity, CAS phase, equation of state, synchrotron X-ray radiation Citation: Liu X, He Q, Deng L W, et al. Equation of state of CAS phase to pressure of the uppermost lower mantle at ambient temperature.

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High-pressure phase relations and thermodynamic properties of CaAl4Si2O11 CAS phase

Cited by 18 publications

References 33 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

Elasticity of Continental Crust Around the Mantle Transition Zone

Equation of state of CAS phase to pressure of the uppermost lower mantle at ambient temperature

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