P–V–T equation of state of CaAl4Si2O11 CAS phase

Physics and Chemistry of Minerals (Impact Factor: 1.3). 38(8):581-590. DOI: 10.1007/s00269-011-0430-7

ABSTRACT The thermoelastic parameters of the CAS phase (CaAl4Si2O11) were examined by in situ high-pressure (up to 23.7GPa) and high-temperature (up to 2,100K) synchrotron X-ray diffraction,
using a Kawai-type multi-anvil press. P–V data at room temperature fitted to a third-order Birch–Murnaghan equation of state (BM EOS) yielded: V
0,300=324.2±0.2Å3 and K
0,300=164±6GPa for K′
0,300=6.2±0.8. With K′
0,300 fixed to 4.0, we obtained: V
0,300=324.0±0.1Å3 and K
0,300=180±1GPa. Fitting our P–V–T data with a modified high-temperature BM EOS, we obtained: V
0,300=324.2±0.1Å3, K
0,300=171±5GPa, K′
0,300=5.1±0.6 (∂K


=−0.023±0.006GPaK−1, and α0,T
=3.09±0.25×10−5K−1. Using the equation of state parameters of the CAS phase determined in the present study, we calculated a density profile
of a hypothetical continental crust that would contain ~10 vol% of CaAl4Si2O11. Because of the higher density compared with the coexisting minerals, the CAS phase is expected to be a plunging agent for
continental crust subducted in the transition zone. On the other hand, because of the lower density compared with lower mantle
minerals, the CAS phase is expected to remain buoyant in the lowermost part of the transition zone.

KeywordsCAS phase–CaAl4Si2O11
–Thermal expansion–Compressibility–High pressure–In situ X-ray diffraction

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