HR: 0800h
AN: MR11A-0917    [Abstracts]
TI: The formation of dislocations in single crystal Durango apatite
AU: * Eyssautier, C
EM: eyss0003@UMN.EDU
AF: University of Minnesota, 310 Pillsbury Dr SE, Minneapolis, MN 55455
AU: Fayon, A K
EM: fayon001@umn.edu
AF: University of Minnesota, 310 Pillsbury Dr SE, Minneapolis, MN 55455
AB: Low temperature thermochronometric tools such as apatite fission track (FT) analysis and apatite U-Th/He dating are commonly used to evaluate rates of surficial processes. The closure temperatures for these systems, as in other thermochronometric systems are a function of diffusion rates. However, little is known about the effects of microstructures on diffusion rates in thermochronometers, specifically apatite. Given that many thermochronometric studies involve rocks that have undergone the orogenic cycle, the minerals analyzed inevitably were deformed and generally contain deformation-produced defects. It is therefore critical to evaluate the effects of crystal defects on diffusion rates. The first step towards understanding these effects in apatite is characterization of crystal defect formation. The paucity of literature regarding conditions under which dislocations form necessitates a series of deformation experiments in apatite. New results from preliminary deformation experiments on single crystal Durango apatite are presented. Three experiments were conducted in a Paterson gas-medium press with a confining pressure of 300 MPa at a temperature of 1273 K and differential stresses from 125 MPa to 150 MPa. Single crystals were prepared using optically clear Durango apatite oriented such that the basal and prism planes were at approximately 45$\deg$ to the maximum principal stress, $\sigma$1, thereby maximizing shear stress acting on those crystallographic planes. Deformed surfaces parallel to $\sigma$1 were polished and etched in 5N HNO3 for 10 seconds to reveal any defects created. In all experiments, bands of high dislocation density are observed at 45$\deg$ to $\sigma$ 1, suggesting crystallographic control on band formation. The high-density bands are separated by virtually defect free zones. High dislocation density bands are cross cut by highly etched regions. Our preliminary interpretation of these regions is they represent zones of extremely high dislocation density. TEM analyses will aide in more accurate characterization of these zones and how they relate to defect free regions of the crystals. These results will serve as a foundation for diffusion experiments in the presence of these defects.
DE: 3902 Creep and deformation
DE: 3904 Defects
DE: 3999 General or miscellaneous
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting