HR: 11:20h
AN: MR12A-05    [Abstracts]
TI: Optical properties of silica (SiO₂) at lower mantle conditions: Implications for conductivity of molten mantle
AU: * McWilliams, R S
EM: rmcw@eps.berkeley.edu
AF: Department of Earth and Planetary Science, 307 McCone Hall, University of California Berkeley, Berkeley, CA 94720 United States
AU: * McWilliams, R S
EM: rmcw@eps.berkeley.edu
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 United States
AU: Jeanloz, R
EM: jeanloz@berkeley.edu
AF: Department of Earth and Planetary Science, 307 McCone Hall, University of California Berkeley, Berkeley, CA 94720 United States
AU: Hicks, D G
EM: hicks13@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 United States
AU: Celliers, P M
EM: celliers1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 United States
AU: Eggert, J H
EM: eggert1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 United States
AU: Collins, G W
EM: collins7@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 United States
AB: Silica (SiO₂) is a major chemical constituent of the Earth, and its properties at high pressures and temperatures are important both for deep-earth geophysics and for studies of terrestrial impact events. A number of interesting phenomena, such as amorphization on static compression and the formation of microstructures on dynamic shock compression, were first experimentally observed in silica and subsequently seen in a wide variety of dielectric materials, including other planetary minerals. Here, we report experimental evidence for increased electrical conduction in molten SiO₂ at extreme pressures and temperatures. Using laser-driven shock waves, two initial forms of SiO₂, fused silica and alpha-quartz, were subjected to multi-Megabar pressures and temperatures of tens of thousands of Kelvin. Light at 532 nm reflected from the samples provides a measurement of the optical opacity or reflectivity of the shocked material. These measurements suggest that initially transparent silica, characterized by a wide gap between the electronic energy bands, exhibits a major increase in electrical conductivity: first, there is a discontinuous increase on melting, and then a continuous increase with temperature and pressure in the molten state, presumably in response to chemical dissociation of the SiO₂. It is likely that similar behavior will be identified in other dielectric materials, including the primary constituent of the Earths mantle, MgSiO₃ perovskite. These results may be crucial for understanding the properties of melts in the deep mantle, and add a new dimension to the physics of terrestrial impact events.
DE: 3914 Electrical properties
DE: 3924 High-pressure behavior
DE: 3944 Shock wave experiments
DE: 8136 Impact phenomena (5420, 6022)
DE: 8147 Planetary interiors (5430, 5724, 6024)
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005