In situ X-ray observation of decomposition of hydrous aluminum silicate AlSiO3OH and aluminum oxide hydroxide d-AlOOH at high pressure and temperature

We clarified the stability limit of phase Egg, AlSiO3OH, a candidate for water reservoir in the siliceous sediment of slabs in the transition zone conditions by in situ X-ray observation using high energy X-ray from synchrotron radiation source of SPring-8. Phase Egg is stable at least up to 1625 degreesC at 17 GPa. We observed decomposition of phase Egg into delta-AlOOH and stishovite at pressures greater than 23 GPa at temperatures below 1200 degreesC. No water release occurs associated with the decomposition. At temperatures above 1200 degreesC at 23 GPa, we observed decomposition of phase Egg into corundum + stishovite + fluid. We also determined the phase boundary of the decomposition reaction of delta-AlOOH to corumdum + fluid based on the in situ X-ray diffraction at high pressure and temperature. (C) 2004 Elsevier Ltd. All rights reserved.