HR: 0800h
AN: T41B-1208    [Abstracts]
TI: Effects of hydrogen impurities on the lattice thermal diffusivity of quartz and quartzites up to 1000\deg C
AU: * Branlund, J M
EM: joyb@levee.wustl.edu
AF: Washington University, Department of Earth and Planetary Sciences, 1 Brookings Drive, Saint Louis, MO 63130-4899 United States
AU: Hofmeister, A M
EM: hofmeist@wustl.edu
AF: Washington University, Department of Earth and Planetary Sciences, 1 Brookings Drive, Saint Louis, MO 63130-4899 United States
AB: The phonon contribution to thermal diffusivity (D$_lat$) in quartz single-crystals was measured using a laser flash apparatus between room temperature and 1000\deg C. Our measurements revealed differences in D$_lat$ between samples which most likely result from hydroxyl impurities. Variations in D$_lat$ between wet and dry samples persist above the $\alpha$ to $\beta$ transition. For all samples, D$_lat$ follows a 1/T trend. Unlike previous measurements, thermal diffusivity of $\beta$-quartz remains constant or decreases slightly with increasing temperature, showing that the technique removes radiative transfer effects. The difference between samples is of greatest interest. The two orientations of a quartz single-crystal containing 171 H/10$^6$ Si as OH defects have D$_lat$ vales at room temperature that are 22% and 41% lower than equivalent orientations for a dry sample. The effect of defects on D$_lat$ is amplified when the OH-dipole is parallel to the electromagnetic vector of the diffusing heat. Oriented milky quartz samples with 1260 to 2100 H/$^6$ Si have D$_lat$ 12-15% lower than dry quartz values, suggesting that fluid inclusions slow thermal diffusion to a smaller degree. Room temperature D$_lat$ of 5 different quartzite samples vary up to 24% from the highest quartzite value of 4.04 mm$^2$/s. For all samples, D$_lat$ is lower than that expected for randomly oriented, dry quartz. In quartzites, differences in D$_lat$ between samples decrease with temperature, such that little variation is seen for the $\beta$ phase. This behavior is expected if porosity, which ranges from 5% to 19%, hinders thermal transport in quartzite. Grain size does not appear to affect D$_lat$. If water plays an important role in heat transport, we should see it, since quartzite contains much more water than the single crystals. Because of the small number of samples examined, the dual speciation as silanol complexes on grain surfaces of some quartzites (up to 420 H/$^6$ Si) and as molecular water in all samples (ranging from 328 to 5103 H/$^6$ Si), combined with porosity variations, our understanding of water's effect in quarzites is impeded. Additional experiments are planned to probe the sensitivity of D$_lat$ to H impurities in these samples. Small amounts of water in quartz are known to affect physical properties such as electrical conductivity and strength. Studies of D$_lat$ presented here suggest that water, even in minute amounts, alters the thermal properties of quartz as well. Finding a similar effect in other anhydrous minerals would add to our understanding of mantle and lithosphere dynamics.
DE: 8130 Heat generation and transport
DE: 5134 Thermal properties
DE: 3934 Optical, infrared, and Raman spectroscopy
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting