HR: 0830h
AN: V31D-0966    [PDF]
TI: High-Pressure Studies of Hydrogen- and Carbon-Bearing Minerals
AU: * Shieh, S R
EM: sshieh@mail.ncku.edu.tw
AF: Department of Earth Sciences, National Cheng Kung University, No.1 University Rd., Tainan, 701 Taiwan
AU: Duffy, T S
EM: duffy@princeton.edu
AF: Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544 United States
AB: The study of volatile-bearing minerals (e.g., hydroxides, hydrous silicates, and carbonates) at high pressures and temperatures is of great importance to understand the dynamics of volatile transport and recycling in the Earth's deep interior. Results from x-ray diffraction can provide rich information such as the equation of state, crystal structure, and strain state. Results from spectroscopic studies can provide detailed local information as compared with x-ray diffraction. Therefore, these two powerful tools are mutually complementary for characterization of materials. Here we utilize x-ray, Raman, and infrared techniques to study H-bearing and C-bearing materials at high pressure. Calcite (CaCO$_{3}$) was compressed in a diamond cell and examined at room temperature be persist to the highest pressures. However, upon laser heating at 20-80 GPa calcite-III transformed to a previously unidentified new phase which could be temperature-quenched. Upon decompression of samples heated at 40 GPa or less, the high-pressure phase persisted until pressures close to 1 bar, at which point it transformed to a mixture of aragonite and calcite. Phase E and superhydrous phase B are two of the dense hydrous magnesium silicates (DHMS) and are regarded as potential H-host candidates in the Earth's mantle. The nonstoichiometric nature of phase E and lack of long-range order make it an interesting material to study. Phase E was compressed to about 42 GPa in a diamond anvil cell. Our quasi-hydrostatic data showed that the phase E did not encounter any structural change at pressure up to 42 GPa. Similar results were also observed from IR spectroscopic measurements. Superhydrous phase B, with is stoichiometric, was compressed to 58 GPa in a diamond anvil cell. Again, no phase transformation was observed to this pressure at room temperature. Cobalt hydroxide is isostructural with brucite, a prototype H-bearing material that has been extensively studied under compression. Here we report energy-dispersive x-ray diffraction data to 48 GPa to complement our previously reported Raman spectroscopy data (Shieh and Duffy, 2002). The new structural data are used to examine the equation of state, compressional anisotropy and have implications for H-sublattice amorphization and H$\dots$H repulsion in this fundamental material.
DE: 3620 Crystal chemistry
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting