Methods and Procedures for Evaluation of XRD and Micro-Raman Peak Broadening in Shock-Metamorphosed Carbonates from Carbonate-Target Bolide Impact Structures

Kean M. Bliss and Jared R. Morrow
San Diego State University

Extraterrestrial impact is an ongoing process that has fundamentally affected the geological and biological development of Earth. Since the late Precambrian, a significant percentage of Earth impacts involved carbonatebearing sedimentary target rocks; however, the details of how carbonate rocks and minerals respond to shock metamorphism remains under-studied.

Shock-metamorphic effects are not readily identified using petrographic techniques, resulting in the need for other diagnostic analyses to identify and constrain these effects. Peak broadening recognized in X-ray diffraction (XRD) and micro-Raman spectrometer (MRS) spectra is shown to be useful as a reliable, scalable indicator of shock metamorphism in both experimentally and naturally shocked carbonate materials. Analyses of carbonate samples from seven or eight confirmed carbonate-target impact structures that represent a range of expected shock pressures will be compared to carbonates from other natural high temperature-pressure geological settings (e.g., fault breccias, carbonatites, marbles) to determine whether peak broadening of XRD and MRS spectra in shocked carbonates is a phenomenon unique to impact structures.

Comparison of duplicate analyses of selected samples from confirmed carbonate-target impact rocks completed on both the XRD and MRS will test for similar peak broadening in carbonate peaks between the two methods. Comparable results will provide a new avenue for compiling evidence of shock metamorphism in materials that are suspected to be impact-related. If MRS analyses are shown to be as reliable as XRD methods, this technique can be completed more quickly and with less sample preparation and destruction, especially if thin sections of the sample already exist.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas