HR: 09:15h
AN: B31E-06    [Abstracts]
TI: Laser Raman Spectroscopic Confirmation of Maskelynite in the Bedout Impact Breccia, Offshore, NW Australia.
AU: * Basu, A R
EM: abasu@earth.rochester.edu
AF: University of Rochester, Department of Earth and Environmental Sciences, 227 Hutchison Hall, Rochester, NY 14627 United States
AU: Chakrabarti, R
EM: ramananda@earth.rochester.edu
AF: University of Rochester, Department of Earth and Environmental Sciences, 227 Hutchison Hall, Rochester, NY 14627 United States
AU: Peterson, J
EM: jpsn@mail.rochester.edu
AF: University of Rochester, Department of Chemistry, Rochester, NY 14627 United States
AU: Poreda, R J
EM: poreda@earth.rochester.edu
AF: University of Rochester, Department of Earth and Environmental Sciences, 227 Hutchison Hall, Rochester, NY 14627 United States
AU: Becker, L
EM: lbecker@crustal.ucsb.edu
AF: University of California, Santa Barbara, Institute of Crustal Studies, Department of Geological Sciences, Santa Barbara, CA 93106 United States
AB: We report the results of a detailed laser Raman spectroscopic study of isotropic plagioclase laths ($\sim$An50) from the 9986 ft. core sample of the Bedout High, interpreted recently by us (Becker et al. Science, 304, p1469, 2004) as the possible remnant of an end-Permian impact crater, offshore of NW Australia. These plagioclase laths are associated with spherulitic glass fragments of nearly pure silica in composition, as well as pure albite and other heterogeneous glassy fragments in a highly brecciated volcanic-like host rock. We performed laser Raman analysis on the same grains shown in Fig 6 of our paper referred above and identified as maskelynite. We also performed a comparative analysis of other known shocked plagioclase grains from the Manicouagan Crater, Canada and from the Lonar Crater, India (to be reported in this meeting, Chakrabarti et al.) Raman scattering measurements were performed using the 514.5 nm line of an argon ion laser at an intensity of 40 kW/cm$^{2}$. An inverted microscope (Nikon TE3000) with 50x objective (NA 0.55) was used for confocal imaging. A holographic notch filter removed residual laser scatter and the Raman scattering was detected by a silicon CCD at -90$^{0}$ C (Princeton Instruments Spec10-400R). Raman spectra were collected from ~250 cm$^{-1}$ through 2000 cm$^{-1}$ in all these samples. An anisotropic plagioclase lath from the same 9986 polished thin section shows prominent peaks at 827 cm$^{-1}$, 1109 cm$^{-1}$ and 1180 cm$^{-1}$ with much smaller peaks at 433 cm$^{-1}$ and 634 cm$^{-1}$. The Raman spectra of the isotropic grains of Fig 6 from our earlier study are conspicuously featureless and show a progressive increase in the luminescent background with higher wave numbers. Our observations are consistent with the Raman spectra of experimentally shocked plagioclase (Heymann and Herz, 1990, Cont. Min. Petr. 17, 38-44, 1990) as well as those of plagioclases from the tektites of the Lonar Impact Crater. Therefore we strongly believe that we had correctly identified shock-induced maskelynite in the Bedout breccia.
DE: 3625 Descriptive mineralogy
DE: 3662 Meteorites
DE: 3934 Optical, infrared, and Raman spectroscopy
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting