HR: 08:45h
AN: V31H-04    [Abstracts]
TI: Water in anhydrous minerals of the upper mantle beneath continental margins
AU: * Peslier, A H
EM: anne.h.peslier@nasa.gov
AF: Jacobs Technology, ESCG Mail Code JE23, 2224 Bay Area Blvd, Houston, TX 77058, United States
AU: Luhr, J F
EM: luhr@volcano.si.edu
AF: Smithsonian Institution, Dept. of Mineral Sciences, National Museum of Natural History, Washington, DC 20013, United States
AB: Although nominally anhydrous, olivine and pyroxenes can accommodate small amounts of water, as protons inserted in mineral defects. These apparently trivial water contents actually have a disproportionate influence on many physical and chemical properties of peridotite, and therefore on that of the entire upper-mantle. Caution is required in interpreting measured water contents in olivines because they can loose a significant portion of their water during transport of the xenolith to the surface, in particular when the xenolith is brought up by alkali basalts, as is typical at continental margins. Pyroxenes, on the other hand, appear mostly immune to this H loss. Review of our and literature data on natural samples (FTIR and SIMS analyses) suggests that water content ranges are similar in the lithospheric mantle beneath continental margins and beneath cratons, namely 20-160 ppm water in bulk-rock peridotite. The main controls on hydrogen incorporation in mantle anhydrous minerals appear to be pressure, oxygen fugacity and mineral composition. Mantle wedge environments, represented by mantle xenoliths with un-ambiguous subduction-zone fluid or melt influence, will be a special focus of this study to assess if their water content is any different than that of mantle lithospheres with no subduction influence.
DE: 1025 Composition of the mantle
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1043 Fluid and melt inclusion geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting