HR: 11:05h
AN: V22A-04 INVITED     [Abstracts]
TI: The Ins and Outs of Water in the Earth's Mantle
AU: * Hauri, E H
EM: hauri@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015 United States
AU: Gaetani, G A
EM: ggaetani@whoi.edu
AF: Department of Geology & Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Shaw, A M
EM: amshaw@dtm.ciw.edu
AF: Department of Geology & Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Kelley, K A
EM: kelley@dtm.ciw.edu
AF: Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882 United States
AU: Saal, A E
EM: Alberto_Saal@brown.edu
AF: Department of Geological Sciences, Brown University, Providence, RI 02912 United States
AB: Most of the hydrogen in the Earth's upper mantle is dissolved in nominally anhydrous minerals such as olivine, orthopyroxene, clinopyroxene and garnet as structural OH [e.g. 1 ]. Considering the significant influence of hydrogen on mantle properties such as solidus temperature, rheology, conductivity and seismic velocity, it is important to understand both the distribution of water among mantle phases and the mass transfer processes that influence water distribution in the Earth's mantle. Despite the important role of water in the mantle, experimental determinations of the equilibrium distribution of trace amounts of hydrogen among coexisting silicate phases remain extremely limited. Improved analytical techniques have recently paved the way for quantitative investigations of water partitioning and abundances in nominally anhydrous mantle minerals [e.g. 2]. Several studies of submarine glasses have revealed correlated increases in incompatible elements and water contents along segments of mid-ocean ridges approaching hotspots [e.g. 3,4]. A source-related increase in the water content of the mantle is typically postulated to explain such observations, but elevated hotspot H2O contents may also relate to pressure differences in partitioning of water, analogous to the case for rare-earth elements (e.g. the "garnet signature"). New experimental water partitioning data illuminate these differences. Hydrogen isotope ratios vary in submarine glasses from ocean ridges, back-arc basins and hotspots, and in hydrous phases from arcs and hotspots, suggesting significant hydrogen isotopic variability in the mantle, which may be related to the subduction of water. Water clearly enters the upper mantle at subduction zones, however the full water budget for any single subduction zone is highly uncertain [e.g. 5]. This uncertainty in the water budget at convergent margins indicates that we do not even know whether the present-day net flux of water is into or out of the Earth. This talk will highlight areas of both knowledge and ignorance on the origin and distribution of water in the Earth's mantle. [1] Bell, D.R. & Rossman, G.R., 1992, Science, 255: 1391-1397. [2] Koga, K. et. al, 2002, Geochem. Geophys. Geosys. 4, doi: 10.1029/2002GC000378. [3] Dixon, J. E. et. al, 2002, Nature 420, 385-389. [4] Asimow, P. D. et. al, 2003, Geochem. Geophys. Geosys. 5, doi:10.1029/2003GC000568. [5] Hilton D. R.. et. al, 2002, in Noble Gases in Cosmochemistry and Geochemistry, 47:319-370.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1012 Reactions and phase equilibria (3612, 8412)
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1037 Magma genesis and partial melting (3619)
DE: 1038 Mantle processes (3621)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005