HR: 1340h
AN: MR13C-1399    [Abstracts]
TI: Grain Boundary Transport of Siderophile Elements in MgO at High Pressure
AU: * Watson, H C
EM: watson40@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550, United States
AU: Siebert, J
EM: siebert2@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550, United States
AU: Ryerson, F J
EM: ryerson1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550, United States
AU: Roberts, J J
EM: roberts17@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550, United States
AU: Hayden, L
EM: haydel@rpi.edu
AF: Rensselaer Polytechnic Institute Department of Earth and Environmental Sciences, 110 Eighth St., Troy, NY 12180,
AU: Watson, E B
EM: watsoe@rpi.edu
AF: Rensselaer Polytechnic Institute Department of Earth and Environmental Sciences, 110 Eighth St., Troy, NY 12180,
AB: The extent of interaction between the Earth's core and mantle remains an actively debated question. Siderophile element signatures in rocks that can be observed at the surface indicate that the mantle and core may have exchanged material over the history of the Earth. Here, a potential physical mechanism to facilitate this communication is considered. It has recently been shown that grain boundaries in lower mantle analog materials at 2.5 GPa act as reservoirs and fast transport pathways for incompatible elements, specifically siderophile elements [1]. In the present study, we conducted multi-anvil experiments held at 10 GPa and 1600^oC for 5 hours to examine the persistence of fast grain boundary transport at higher pressures. Thin layers of Os and Au powders were loaded in a standard 10/5 multi-anvil assembly and separated from a Pt foil by a cylindrical MgO plug approximately 1mm long. These two elements were expected to be among the slowest and fastest diffusers respectively. The final composition of the Pt foil was measured by electron microprobe. The presence of measurable siderophile element "blebs" in the Pt foil indicates substantial grain boundary diffusion. Our preliminary results suggest that siderophile element mobility and presence on grain boundaries may be affected slightly with increased pressure, but could remain a viable mechanism for transport on length scales applicable to communication within the deeper Earth over it's history. The effect of pressure and grain size on grain boundary diffusion, and potential reasons for a large variation between diffusivities of different siderophile elements will be discussed. [1] Hayden, L., and Watson, E.B., 2006. GCA Supp., v. 70, iss. 18, p. 238
DE: 3630 Experimental mineralogy and petrology
DE: 3900 MINERAL PHYSICS
DE: 3924 High-pressure behavior
DE: 5120 Plasticity, diffusion, and creep
DE: 5134 Thermal properties
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting