HR: 0800h
AN: MR11A-0895    [Abstracts]
TI: The Relationship Between Thermal Diffusivity and Symmetry of Carbonates
AU: Schilling, F R
EM: fsch@gfz-potsdam.de
AF: GFZ Potsdam, D 230 Telegrafenberg, Potsdam, 14473 Germany
AB: Carbonates are among the most abundant rock forming minerals of the Earth's crust. Nevertheless, only little is understood about the thermal transport processes of carbonates. We'll present a comprehensive study on new thermal transport property data of carbonates, both, as a function of temperature (up to 600 $ \deg C$) and orientation. These data are a prerequisite to model the temperature distribution of the crust, in regions where carbonates are present. On the other hand, carbonates are an ideal group of minerals to study the influence of crystal symmetry, sound velocity, and atomic mass of cations on thermal transport properties, as isotyp carbonates exist with different -- light and heavy -- cations and various sound velocities (Maj, 1974). Furthermore, two carbonate polymorphs -- trigonal and orthorhombic -- are available to study the influence of symmetry on thermal transport properties. The higher symmetry of trigonal calcite like structures lead to a higher thermal diffusivity. It will be shown that increasing mass of cations decreases thermal diffusivity {--} from light Mg$^2$\textsuperscript{+} Magnesite [100] (6.22 mm$^2$/s at 25 $ \deg C$) to the heavy Pb$^2$\textsuperscript{+} Cerussite [100] (0.85 mm$^2$/s at 25 $ \deg C$). As expected from Debye's theory, thermal diffusivity decreases with increasing temperature. The anisotropy of thermal diffusivity reaches more than 80 % (Magnesite with 86 %) and decreases with increasing temperature. The results show that for carbonates mean free path length of phonons depends on sound velocity (H\"{o}fer & Schilling, 2002). Maj, S., 1974. A note on the relationship among phonon conductivity, density, and mean atomic weight for carbonate minerals. Acta Geophysica Polonica, 22 (3): 247- 250. H\"{o}fer, M. & Schilling, F. R., 2002. Heat transfer in quartz, orthoclase, and sanidine at elevated temperature. Phys. Chem. Min., 29: 571- 584.
DE: 5134 Thermal properties
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting