HR: 0830h
AN: V31D-0964    [PDF]
TI: Finite Element Modeling of Elastic Volume Changes in Fluid Inclusions: Comparison with Experiment
AU: * Burnley, P C
EM: burnley@gsu.edu
AF: Georgia State Univeristy, Department of Geology PO Box 4105, Atlanta, GA 30302-4105 United States
AU: Bruhn, D
EM: dbruhn@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg D329, Potsdam, 14473 Germany
AU: Schmidt, C
EM: hokie@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg D329, Potsdam, 14473 Germany
AB: Inclusions within mineral grains in rocks of all types are widely studied because they contain information about either the environment of formation of the mineral grain or conditions since. Understanding the mechanics of the inclusion-host system caused by differences in thermal expansion and compressibility is often essential for interpreting measurements made on the inclusion. We are studying the mechanics of inclusions by comparing elastic volume changes and deformation of synthetic pure water inclusions in quartz with finite element models of the individual inclusions. Synthetic fluid inclusions are ideal for such a study because the mechanical boundary conditions as well as the resulting deformation are either known or can be determined from the homogenization temperature and equation of state of the fluid. The experiments for this study were conducted using a hydrothermal diamond anvil cell with water as the pressure medium. The homogenization temperature of the inclusions was used to determine the inclusion volume at various confining pressures. The confining pressure was obtained from the homogenization or the ice I liquidus temperature of the pressure medium. After the experiment the homogenization temperature of the inclusion at 1 atm confining pressure was re-determined to confirm that the deformation of the inclusions was completely elastic. The inclusion shape for each model was determined from optical photomicrographs. The thickness of the synthetic fluid inclusions is consistently about 1 micron. We used a commercially available engineering package, MSC MARC/Mentat, to create and analyze two-dimensional and three-dimensional finite element models of the inclusions. The inclusions are assumed to have at least one mirror plane (parallel to the plane of the photograph) permitting a portion of the inclusion to be modeled. We assume a linear elastic response for the quartz host and have used both isotropic and anisotropic elastic moduli. Within the uncertainties associated with the inclusion's cross sectional shape and orientation within the quartz, the 3D models can reproduce the observed elastic volume changes for each loading condition. We also observe that sheet-like inclusions experience greater elastic volume changes than do elongate inclusion. For elongate inclusions, the length to thickness ratio has no measurable effect on the compressibility of the inclusion. This is consistent with systematics observed in our 2D axisymmetric models of prolate ellipsoids and cylinders terminated by cones. For these inclusions, the compressibility of the inclusion is highly dependent on its aspect ratio below about 5:1 and only slightly dependent on the aspect ration above 10:1. Ongoing work is focusing on improving the 3D characterization of the inclusions and on refining the estimates of stress in the quartz host.
DE: 3210 Modeling
DE: 3630 Experimental mineralogy and petrology
DE: 3902 Creep and deformation
DE: 3924 High-pressure behavior
DE: 5112 Microstructure
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting