HR: 0800h
AN: T41B-1175 [Abstracts]
TI: Quantitative Polarized FTIR analysis of Trace OH in Populations of Disoriented Mineral
Grains
AU: Stein, L C
EM: leo@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd. M/C170-25, Pasadema, CA 91125
United States
AU: Mosenfelder, J L
EM: jed@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd. M/C170-25, Pasadema, CA 91125
United States
AU: * Asimow, P D
EM: asimow@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd. M/C170-25, Pasadema, CA 91125
United States
AU: Rossman, G R
EM: grr@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd. M/C170-25, Pasadema, CA 91125
United States
AB:
Use of Fourier-transform infrared (FTIR) spectroscopy as an accurate, quantitative method to measure concentrations of
hydrous species in minerals requires consideration of the anisotropic interactions of minerals with infrared light. This is
normally accomplished by determining the orientation of a crystal in advance and then sectioning it perpendicular to its
optic axes. Here we demonstrate a method that uses at least three randomly oriented grains, considered to be multiple samples
of a homogeneous population. We explain the theory whereby (1) the orientations of the polarization vectors of measurements
taken on these grains are determined by comparison to oriented standards of the same mineral, and (2) the principal-axis
spectra of the sample are synthesized from the randomly oriented spectra. By comparison to complementary
electron-backscattered diffraction (EBSD) data, we demonstrate that determination of orientations using the silicate overtone
bands in FTIR spectra is accurate and precise. We apply the technique to determine the OH concentrations in a population of
experimentally hydrated olivine grains.
DE: 3630 Experimental mineralogy and petrology
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 3994 Instruments and techniques
DE: 1025 Composition of the mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting