2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 14
Presentation Time: 11:35 AM


LABOTKA, Theodore C., Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996-1410, FAYEK, Mostafa, Earth and Planetary Sciences, Univ of Tennessee, 306 Geology Bldg, Knoxville, TN 37996 and COLE, David R., Chemical Sciences Division, Oak Ridge National Lab, 1 Bethel Valley Rd, Oak Ridge, TN 37831-6110, tlabotka@utk.edu

The self diffusion of O atoms in the carbonate minerals dolomite and magnesite was measured at a pressure of approximately 0.1 MPa and in the temperature range of 500–625 °C. Single crystals of the minerals were pre-annealed in a CO2 atmosphere for 24 h. The crystals were encapsulated in platinum, the capsules were evacuated, and CO2 was transferred to the capsule before welding. The CO2 had the isotopic composition of ∼98% 13C and 90% 18O. The samples were heated in a muffle furnace for periods ranging from 61 to 74 d. After experimentation, the 18O/(18O + 16O) ratio was measured on a cleavage surface by secondary ionization mass spectrometry depth profiling. The exchanged profile in dolomite is 75 to 200 nm thick, indicating diffusivities of 1.05×10−17 cm2/s at 600 °C to 9.33×10−19 cm2/s at 500 °C . Profiles in magnesite are much shallower, 25–40 nm at 500 and 600 °C, respectively. The data are noisy and give values of D of 2.8–3.1×10−19 for both temperatures. The diffusivities of O in dolomite are similar to those in calcite, measured previously, but are about an order of magnitude greater than that in magnesite.