HR: 0800h
AN: V31D-0659    [Abstracts]
TI: In-situ Visible Microspectroscopy of Color Change Processes of Olivine by High Temperature Oxidation
AU: * Yamanoi, Y
EM: yuta@ess.sci.osaka-u.ac.jp
AF: Earth and Space Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043 Japan
AU: Nakashima, S
EM: satoru@ess.sci.osaka-u.ac.jp
AF: Earth and Space Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043 Japan
AU: Tani, A
EM: atani@ess.sci.osaka-u.ac.jp
AF: Earth and Space Science, Osaka University, Machikaneyama-cho 1-1, Toyonaka, Osaka, 560-0043 Japan
AB: Olivine has been found to be one of the origins of red coloring of volcanic eruptive materials such as Takatsukayama scoria, North-east Izu, Japan (Yamanoi et al., 2004). Color change processes of olivine thin sections in high temperature oxidation have been investigated by means of newly developed in-situ high temperature visible microspectroscopy (Yamanoi and Nakashima, in press). Olivine thin sections put on a synthetic alumina plate are heated on a heating stage at 600 - 800 _E#8249;C under an visible microspectroscope. Changes in visible absorption spectra are monitored every 60 seconds for 5 hours. The obtained high temperature visible spectra showed an gradual increase with time in absorbance in the shorter wavelength region (400 - 600 nm). The changes of 430 nm absorbance (ligand field transition of Fe3+) increased with time more at higher temperatures. This increasing of 430 nm absorbance was considered to be due to production of Fe3±bearing olivine (similar to ferriolivine / laihunaite; Khihina et al., 1995; 1998). These oxidation processes were supported by Raman spectroscopy and electron micro probe analyses of olivine thin sections. Assuming diffusional transport in plane sheets, apparent diffusion coefficients were determined at temperatures of 600 - 800 _E#8249;C. The activation energy for this diffusion in olivine is 208 (17) kJ/mol. This activation energy value is similar to those for the metal vacancy diffusion in olivine (e.g. Kohlstedt and Mackwell, 1998). Therefore, the visible spectral change kinetics of olivine at 600 - 800 _E#8249;C studied here can be considered to be controlled by metal vacancy diffusion with oxidation of Fe2+ to Fe3+ from the olivine surface.
DE: 3900 MINERAL PHYSICS
DE: 8400 VOLCANOLOGY
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005