Effect of pressure on water solubility in aluminous magnesium silicate perovskite

Tuesday, 16 December 2014
Jiuhua Chen1,2, Martha G Pamato3, Toru Inoue4, Sho Kakizawa4, Bin Yang1, Chunli Ma1, Yangting Lin5, Tomoo Katsura3, Takaaki Kawazoe3 and Zhenxian Liu6, (1)Center for High Pressure Science and Technology, Changchun, China, (2)Florida International Univ., Miami, FL, United States, (3)Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, Germany, (4)Ehime University, Matsuyama, Japan, (5)Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, (6)Carnegie Inst Washington, Washington, DC, United States
We have conducted a sequence of high pressure experiments to study water solubility in aluminous magnesium silicate perovskite as a function of pressure at 1900oC. The experimental high pressures were generated using multi-anvil presses at Bayerisches Geoinstitut (BGI) for pressures up to 28 GPa and at Geodynamics Research Center (GRC) for pressures above 30GPa. The starting material for these experiments was a mixture of oxides (Mg(OH)2, Al2O3 and SiO2) with equivalent of about 5 mol % of Al2O3 and 15 wt % of H2O. The structure and composition of the perovskite phase after high P/T syntheses were examined using x-ray diffraction (XRD) and electron probe microanalysis (EPMA). Water concentration in the sample was measured using secondary ion mass spectroscopy (SIMS) and Fourier transform infrared spectroscopy (FTIR). The measurements yield that the aluminous magnesium silicate perovskite with about 2 wt% of Al2O3 may take as much as 0.13 wt % of H2O at the P/T condition of the top of the Earth’s lower mantle and this solubility increases significantly with pressure. At the bottom of Earth’s lower mantle, this perovskite may take nearly a couple of weight percent of water according to simple extrapolation of the experiment result, indicating that the capacity of water reservoir of the lower mantle can be as large as a few to ten oceans of water.