HR: 11:20h
AN: DI42A-05 [Abstracts]
TI: Hydrogen solubility in garnet at high pressures
AU: * Mookherjee, M
EM: mainak.mookherjee@yale.edu
AF: Yale University, Department of Geology and Geophysics, Kline Geology Laboratory, New
Haven, CT 06511, United States
AU: Karato, S -
EM: shun-ichiro.karato@yale.edu
AF: Yale University, Department of Geology and Geophysics, Kline Geology Laboratory, New
Haven, CT 06511, United States
AB:
Garnet is the most important secondary mineral whose fraction ranges from ~ 20% in the shallow upper
mantle for the pyrolite model to ~ 80% in the transition zone for the piclogite model. Therefore
understanding the solubility and dissolution mechanisms of hydrogen in garnet is important for water budget as
well as for understanding plastic properties of the mantle. However, there is little consensus on the solubility and
dissolution mechanisms of hydrogen in garnet. For example, under deep upper mantle conditions (P>7 GPa),
Withers et al. (1998) concluded virtually no hydrogen solubility in pyrope whereas Lu and Keppler (1997) showed
small hydrogen solubility (~ 200 ppm wt of H2O).
In order to address possible causes of such discrepancy, we have initiated a systematic study on hydrogen
solubility under a broad range of pressure and controlled chemical environment. In contrast with the previous
study, preliminary results indicate that natural garnet crystal surrounded by powder of olivine, orthopyroxene and
clinopyroxene, could host around 1000 ppm wt of H2O at 9 GPa and 1100 °C conditions. Possible
interpretation is that the enrichment of hydrogen is due to the increased Mg/Si ratio (activity of MgO) due to the
coexistence of garnet with olivine. If hydrogarnet substitution (O4H4) is the dominant mechanism of
hydrogen dissolution, then the increase in the activity of MgO will increase the hydrogen solubility. Further
experiments are performed (i) to investigate the hydrogen solubility under deep upper mantle conditions (P=6-9
GPa T=1373-1573 K) where the previous results have a major discrepancy, and (ii) to investigate the kinetics and
the influence of oxide buffer on hydrogen solubility.
DE: 3600 MINERALOGY AND PETROLOGY
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3900 MINERAL PHYSICS
DE: 3904 Defects
DE: 3924 High-pressure behavior
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting