HR: 0800h
AN: MR41A-0912    [Abstracts]
TI: High-pressure vibrational study of dense hydrous magnesium silicate 10A Phase
AU: * Sanchez-Valle, C
EM: csanchez@ens-lyon.fr
AF: Department of Geology University of Illinois at Urbana-Champaign, 1301, W. Green Street NHB245, Urbana, IL 61801 United States
AU: Hellwig, H
EM: hhellwig@uiuc.edu
AF: Department of Geology University of Illinois at Urbana-Champaign, 1301, W. Green Street NHB245, Urbana, IL 61801 United States
AU: Li, J
EM: jackieli@uiuc.edu
AF: Department of Geology University of Illinois at Urbana-Champaign, 1301, W. Green Street NHB245, Urbana, IL 61801 United States
AU: Wang, J
EM: jwang11@uiuc.edu
AF: Department of Geology University of Illinois at Urbana-Champaign, 1301, W. Green Street NHB245, Urbana, IL 61801 United States
AU: Liu, Z
EM: zxliu@bnl.gov
AF: Geophysical Laboratory Carnegie Institution of Washington, 5241 Broad Branch Rd, Washington, DC 20015 United States
AU: Bass, J D
EM: jaybass@uiuc.edu
AF: Department of Geology University of Illinois at Urbana-Champaign, 1301, W. Green Street NHB245, Urbana, IL 61801 United States
AB: Dense hydrous magnesium silicates (DHMS) could be important hosts for H2O in the Earth's mantle and subduction zones, and their dehydration may be responsible for deep focus earthquakes. Among these phases, the so-called 10A phase (Mg3Si4O10(OH)2.nH2O) is characterized by a phlogopite-like structure which accommodates molecular water in the interlayer. However, the amount of interlayer water, its precise structural position and the response upon compression remain uncertain. To better understand the high pressure behavior of hydroxyl groups and interlayer water in 10A phase, we have conducted in situ synchrotron IR and Raman spectroscopic measurements up to 20 GPa at 25 C. Thanks to the brightness of the synchrotron IR radiation beam and the high spatial resolution available at the U2A beamline at NSLS, high-quality mid-IR spectra with high signal/noise ratio have been collected in the diamond-anvil cell. The 10A phase samples were synthesized at 6.5 GPa and 650 C in a Kawai-type multianvil press using talc and excess water as starting materials. At ambient conditions, the IR spectrum shows a strong band at 3675 cm-1 and two less intense and broader bands at 3258 and 3589 cm-1. With increasing pressure up to 5.5 GPa, the band at 3675 cm-1 displays a linear negative frequency shift. Near 6.2 GPa a new band emerges at 3680 cm-1 and its intensity progressively increases with pressure up to 15.5 GPa, indicating major changes in the hydrogen bonding. All pressure-induced changes in the IR spectra are fully reversible upon decompression and occur without any noticeable hysteresis. On the basis of combined high pressure IR and Raman results, we could reevaluate the assignment of the OH-vibrational bands of 10A phase and constrain the response to compression of silica tetrahedra, magnesia octahedra, hydroxyl units and molecular water.
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 3934 Optical, infrared, and Raman spectroscopy
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005