HR: 1340h
AN: U23A-0862    [Abstracts]
TI: X-Ray Powder Diffraction as a Tool for the Identification of Impact Deformed Rocks
AU: * Huson, S
EM: sahuson@hotmail.com
AF: School of Earth and Environmental Sciences, Washington State University, Pullman, WA 99163, United States
AU: Pope, M
EM: mcpope@wsu.edu
AF: School of Earth and Environmental Sciences, Washington State University, Pullman, WA 99163, United States
AU: Foit, F
EM: foit@mail.wsu.edu
AF: School of Earth and Environmental Sciences, Washington State University, Pullman, WA 99163, United States
AU: Watkinson, A
EM: watkinso@mail.wsu.edu
AF: School of Earth and Environmental Sciences, Washington State University, Pullman, WA 99163, United States
AB: Previous X-ray powder diffraction (XRD) studies indicated shock deformed minerals have broader XRD peaks when compared to those of unshocked samples. Entire XRD patterns, single peak profiles and Rietveld refined parameters of carbonate samples from the Sierra Madera impact crater, west Texas and the Mission Canyon Formation of southwest Montana and western Wyoming were used to evaluate the use of X-ray powder diffraction as a tool for distinguishing impact deformed rocks from tectonically deformed rocks. Both sample locations contain rocks subjected to varying degrees of deformation. At Sierra Madera dolostone and limestone samples were collected from the crater rim (lower shock intensity) and the central uplift (higher shock intensity). Carbonate rocks of the Mission Canyon Formation were sampled along a transect across the tectonic front of the Sevier and Laramide orogenies. Peaks in the XRD patterns of shocked calcite in samples from Sierra Madera are generally broader than those of calcite samples from the Mission Canyon Formation whereas peak broadening of shocked dolomite in samples from the outer central uplift of Sierra Madera is similar to those of Mission Canyon Formation samples. Single peak profile patterns of calcite and dolomite samples from both locations are complex and their full width half maxima (FWHM) show no relationship to shock intensity, especially above ~80 ° 2θ. Rietveld refinement of peak shape parameters yields a more precise measure of the 2θ angular dependence of peak FWHM and, therefore, the degree of shock deformation. FWHM values obtained from Rietveld crystal structure refinements increase with shock intensity for all Sierra Madera samples. Additionally, FWHM values of some tectonically deformed Mission Canyon Formation calcites overlap with those of weakly shocked calcite from the crater rim of Sierra Madera. FWHM values of shocked dolomite from the central uplift of Sierra Madera are distinctly higher than tectonically deformed dolomite from the Mission Canyon Formation. This research suggests that while calcite subjected to significant shock intensities at the Sierra Madera impact crater can be differentiated from tectonically deformed calcite from the Mission Canyon Formation using Rietveld refined peak profiles, weakly shocked calcite from the crater rim may be indistinguishable from the tectonically deformed calcite. In contrast, Rietveld analysis readily distinguishes shocked Sierra Madera dolomite from tectonically deformed Mission Canyon Formation dolomite.
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
DE: 6022 Impact phenomena (5420, 8136)
SC: Union [U]
MN: 2007 Fall Meeting