Phase transformations of Ca3Al2Si3O12 grossular garnet to the depths of the Earth's mantle transition zone

Steeve Gréaux, Norimasa Nishiyama, Yoshio Kono, Laurent Gautron, Hiroaki Ohfuji, Takehiro Kunimoto, Nicolas Menguy, Tetsuo Irifune

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17 Citations (Scopus)

Abstract

High-pressure and high-temperature phase transformations of Ca3Al2Si3O12 grossular garnet were examined at 19-26GPa and 700-2000K using Kawai-type multi-anvil apparatus coupled with in situ X-ray diffraction (XRD). Recovered samples were analyzed by a combination of micro-focused X-ray diffraction (μ-XRD) and transmission electron microscopy (TEM). The results show that grossular garnet gradually transforms to an Al-rich CaSiO3 perovskite at 22-26GPa and 1000-1400K. The transition boundary can be expressed as P (GPa)=-0.0082×T (K)+33.05. When the garnet completely disappears, we observed orthorhombic CaSiO3 perovskite with a grossular composition. At 20-24GPa and temperatures above 1500K the CAS phase with the composition CaAl4Si2O11 appears to accommodate excess Al from the perovskite along with two distinct populations of Al-bearing CaSiO3 perovskites, with Al content of 3.7 and 10.0wt% Al2O3, respectively. The pressure and temperature of these transitions correspond to the lowermost part of the transition zone and therefore it suggests that Ca-rich aluminosilicates could provide alternative candidates to explain multiple seismic reflections near the 660km depth discontinuity.

Original languageEnglish
Pages (from-to)89-99
Number of pages11
JournalPhysics of the Earth and Planetary Interiors
Volume185
Issue number3-4
DOIs
Publication statusPublished - 2011 Apr
Externally publishedYes

Keywords

  • Al-bearing CaSiO perovskite
  • Experimental mineralogy
  • Grossular garnet
  • High-pressure
  • High-temperature
  • In situ X-ray diffraction
  • Phase relation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Geophysics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science

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