HR: 1330h
AN: V12A-0570    [PDF]
TI: 3D X-Ray Imaging Study of Fe-Ti-Oxides of Experimental Partially Molten High-Temperature Pelite Cores
AU: * Wohlers, A
EM: Anke.Wohlers@img.unil.ch
AF: University of Lausanne, BFSH 2, Lausanne, VD 1015 Switzerland
AU: Baumgartner, L
EM: Lukas.Baumgartner@img.unil.ch
AF: University of Lausanne, BFSH 2, Lausanne, VD 1015 Switzerland
AB: We present 3D X-ray computer tomography of shape and distribution of oxide minerals in pelite cores which were partially molten at P = 2kbar, T = 700$\deg$ C, 750$\deg$ C and 800$\deg$ C for different run durations (76-508hrs). X-ray absorption images were obtained of the sample in steps of 0.68 and 0.90$\deg$ for a total rotation of 360$\deg$. X-ray tube conditions of 40 kV / 250 $\mu$A with a conical x-ray spot size of 5.5 $\mu$m was used. The image voxel size is 7 $\mu$m $^{3}$. Computed tomography images are recorded in 8-bit grayscale. Image analysis was accomplished with the Aphelion$^{TM}$ software. The results demonstrate prolific nucleation of oxides in all partial melting experiments. The original pelite sample contains a total of 2.3* 10$^{5}$ grains per 1 ccm of rock; 81.5 % of grains have a radius smaller than 20 $\mu$m. A sample melted at T = 800$\deg$ C for 76 hrs contains a total number of 6.5 * 10$^{5}$ oxide grains per ccm, where the majority of grains (89.7%) are smaller than 20 $\mu$m. This demonstrates nucleation of opaque crystals for this short run condition. An experimental run at T = 750$\deg$ C, and 170 hrs run duration, shows an intermediate number of crystals (total number of 4.1 * 10$^{5}$ crystals per ccm, with 85.7% smaller than 20 $\mu$m. It shows clear evidence of recrystallization; a maximum in a grain size histogram is observed for a radius of about 50 $\mu$m. The reaction leading to oxide nucleation and growth is muscovite + biotite (1) + quartz + andalusite + albite = melt + sillimanite + biotite (2) + k-feldspar + Fe-Ti-oxides at 700$\deg$ C; at 800$\deg$ C hercynite is also produced. These initial results demonstrate the usefulness of X-ray tomography in determining nucleation and recrystallization for experimental materials.
DE: 3600 MINERALOGY AND PETROLOGY (replaces
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
DE: 3660 Metamorphic petrology
DE: 3694 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting