HR: 0800h
AN: T41B-1181    [Abstracts]
TI: Hydrous Synthesis of Aluminum Bearing Silicate Perovskite: Implications for Hydrogen Storage in the Lower Mantle
AU: * Krawczynski, M J
EM: Mike_Kraw@brown.edu
AF: Department of Geological Sciences, Brown University, Box 1846, Providence, RI 02912 United States
AU: Fei, Y
EM: fei@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institute of Washington, 5251 Broad Branch Road, Washington, DC 20015 United States
AU: Hauri, E
EM: hauri@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institute of Washington, 5241 Broad Branch Road, Washington, DC 20015 United States
AB: It is suggested that the solubility of hydrogen in aluminous perovskite may be significantly enhanced because of oxygen vacancy formation associated with incorporation of Al$^{3+}$ in the structure. We have conducted perovskite synthesis experiments in the MgO-SiO$_{2}$-Al$_{2}$O$_{3}$-H$_{2}$O system in a multi-anvil press at 24 GPa and $1800\deg$ C to determine the correlation between the Al$_{2}$O$_{3}$ contents and water solubility in the perovskite structure. Starting materials were mixtures of Mg(OH)$_{2}$ and SiO$_{2}$ in a one to one mole ratio, with added Al$_{2}$O$_{3}$ contents ranging from 0-5 wt%. The mixture was loaded into a gold capsule and compressed to the stability field of silicate perovskite using an 8/3 multi-anvil cell assembly. Large perovskite crystals (up to 200 micron) were synthesized upon quenching. The product crystals were analyzed by Raman spectroscopy, and their chemical compositions were determined with electron microprobe. Hydrogen was analyzed using secondary ion mass spectrometry (SIMS) with a 6f Cameca ion probe. The experiments with low aluminum content in the starting materials produced pure large crystals of Al-bearing silicate perovskite (1.4 wt% Al$_{2}$O$_{3}$) coexisting with hydrous melt. SIMS analyses of these crystals showed the water content of 1268 ppm, indicating that the water solubility in silicate perovskites is strongly associated with the Al$_{2}$O$_{3}$ contents in the structure. The experimental results will be used to constrain the H$_{2}$O storage and to understand the role of Al$_{2}$O$_{3}$ in the Earth's mantle.
DE: 3630 Experimental mineralogy and petrology
DE: 3904 Defects
DE: 3924 High-pressure behavior
DE: 1025 Composition of the mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting