HR: 0800h
AN: T41B-1205    [Abstracts]
TI: Dependence of Water Solubility in Mantle Olivine on the Silica Activity
AU: Allen, K
EM: kaa23@case.edu
AF: Case Western Reserve University, Department of Geological Sciences, Cleveland, OH 44106 United States
AU: * Wang, L
EM: liping.wang@sunysb.edu
AF: State University Of New York, Mineral Physics Institute, Stony Brook, NY 11794 United States
AU: Chen, J
EM: jiuhua.chen@sunnysb.edu
AF: State University Of New York, Mineral Physics Institute, Stony Brook, NY 11794 United States
AU: Weidner, D J
EM: donald.weidner@sunysb.edu
AF: State University Of New York, Mineral Physics Institute and Dept. of Geosciences, Stony Brook, NY 11794 United States
AU: Liu, Z
EM: zxliu@bnl.gov
AF: Carnegie Institution of Washington, Geophysical Laboratory 5251 Broad Branch Road N.W, Washington D.C., 20015 United States
AB: Trace amount of hydrogen stored in nominally anhydrous minerals in the Earth's mantle plays an important role in the dynamics of solid state processes. It may change mineral physical properties such as strength, diffusion and creep rates, electrical conductivity, and transformation kinetics. There have been tremendous efforts to study the incorporation of hydrogen in mantle minerals. However, answers to problems such as incorporation mechanism and solubility of hydrogen in olivine, the most abundant mineral in the upper mantle, remain controversial and somewhat illusive. We present here the results from experimental studies of dependence of hydrogen solubility in olivine on the silica activities, which in turn help our understanding of the incorporation mechanism of hydrogen. Off-line high-pressure experiments were performed on SAM85 press equipped with a DIA module at beamline X17B2 of NSLS at 5-10 GPa and 800 - 1200C. Durations range from one to four hours. Standard cell assembly for DIA was used, each consisting pressure medium of amorphous boron mixed with epoxy, graphite heater, and BN sample capsule. San Carlos olivine was used as starting material. Three layers of sample separated by Pt foil were packed into the capsule, with a fine powder of olivine, a mixture of olivine and orthopyroxene, and a mixture of olivine and periclase in each layer. Several larger grains of olivine (few hundred microns) were embedded in each powder sample. Volatiles were provided by the decomposition of epoxy at high temperature. After experiments samples were cut and double-polished for FTIR analyses, which were conducted at beamline U2A of NSLS. Both powder and single crystal FTIR data revealed the following trend for water solubility in olivine in three samples: olivine + MgO $>>$ olivine $>$ olivine + opx. Water content in olivine in low silica environment (i.e., in sample olivine + MgO) is al least an order of magnitude higher than that equilibrated with high silica activity (i.e., in sample olivine + opx). However, no significant difference among IR patterns in terms of hydroxyl stretching bands for different samples was found, in contrary to findings in some earlier studies. Our results suggest the silica activity may be the dominant factor for water solubility in mantle olivine, and that hydrogen could prefer to enter Si vacancies in olivine.
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 3620 Crystal chemistry
DE: 3630 Experimental mineralogy and petrology
DE: 3934 Optical, infrared, and Raman spectroscopy
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting