HR: 11:35h
AN: DI42A-06    [Abstracts]
TI: Solubility of Hydrogen in Olivine as a Function of Pressure and Oxygen Fugacity
AU: * O'Leary, J A
EM: oleary@dtm.ciw.edu
AF: Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, United States
AU: Hauri, E H
EM: hauri@dtm.ciw.edu
AF: Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, United States
AU: Gaetani, G A
EM: ggaetani@whoi.edu
AF: Woods Hole Oceanographic Institution, McLean 200A, MS#8, Woods Hole, MA 02543, United States
AB: The incorporation of hydrogen into olivine is influenced by many of thermodynamic variables (pressure, temperature, oxygen fugacity, etc.) [1, 2, 3]. Given the strong influence that water has on the melting and mechanical behavior of mantle peridotite, it is necessary to determine the solubility of hydrogen in olivine over the range of chemical environments found in the upper mantle. We present results from new high temperature water-saturated hydration experiments to determine the effect of pressure and oxygen fugacity on hydrogen solubility in San Carlos olivine at upper mantle conditions. Our results indicate that at 1 to 2 GPa varying the fugacity of oxygen between the Fe-FeO and Ni-NiO buffers produces significantly smaller change in the concentration of hydrogen in the olivine than has been found at in previous experiments carried out at 300 MPa. Experiments were carried out in a piston-cylinder device at 1 to 2 GPa and 1200 °C using natural San Carlos olivine as a starting material. The fugacity of oxygen was controlled at Fe-FeO, FeO-Fe₃O₄ and Ni-NiO using solid buffers. Water content in experimental products was measured by secondary ionization mass spectrometry. Variable duration experiments indicate that hydrogen is homogeneously distributed in the olivine at 12 hrs. Our experimental results indicate that pressure strongly effects water content, in agreement with previous studies. For example, as pressure increases from 1 to 2 GPa, the water content of olivine increases from 32 ± 3 to 78 ± 7 ppm at the Ni-NiO buffer, and from 29 ± 3 to 69 ± 3 ppm at the FeO- Fe₃O₄ buffer. At each pressure the water content is only weakly affected by changing oxygen fugacity conditions, a result that disagrees with a recent report of a 5 times increase in water content between Fe-FeO and Ni-NiO at 2 GPa [3]. Differences between studies may result from variable degrees of defect equilibration or from differences in measurement techniques. However, when compared with the relationship between olivine water content and {\f}O₂ determined by [2], data from both this study and [3] suggest that the effect of oxygen fugacity on total water content is significantly weaker at upper mantle pressures than at 300 MPa. [1] Kohlstedt, Keppler, and Rubie (1996) Contrib Mineral Petrol 123:345-357. [2] Bai and Kohlstedt (1993) Phys Chem Minerals 19:460-471. [3] Grant et al. (2007) EPSL, doi:10.1016/j.epsl.2007.06.024
DE: 1037 Magma genesis and partial melting (3619)
DE: 1042 Mineral and crystal chemistry (3620)
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting