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

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

Apr 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011pepi..185...89g&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 185, Issue 3-4, p. 89-99.

Physics

1

Scientific paper

High-pressure and high-temperature phase transformations of Ca3Al2Si3O12 grossular garnet were examined at 19-26 GPa and 700-2000 K 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 22-26 GPa and 1000-1400 K. 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 20-24 GPa and temperatures above 1500 K 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 10.0 wt% 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 660 km depth discontinuity.

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