GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 240-6
Presentation Time: 9:30 AM


JENKINS, Laura Elise1, FLEMMING, Roberta L.1, BURCHELL, Mark2, HARRISS, Kathryn2, PESLIER, Anne H.3, CHRISTOFFERSEN, Roy3, FRITZ, Jörg4 and MEYER, Cornelia5, (1)Earth Sciences, University of Western Ontario, 1151 Richmond St, Dept. of Earth Sciences, Biological & Geological Sciences Building, London, ON N6A5B7, Canada; Centre for Planetary Science and Exploration, Western University, 1151 Richmond St, London, ON N6A 3K7, Canada, (2)Center for Astrophysics and Planetary Science, University of Kent, Canterbury, CT2 7NZ, United Kingdom, (3)Jacobs, NASA Johnson Space Center, Houston, TX 77058, (4)Kosmogeologie, Saalbau Weltraum Projekt, Berlin, Germany, (5)Horizontereignis gUG, Berlin, Germany

Impact cratering, a ubiquitous geologic process, alters the mineralogy and texture of rocks via shock metamorphism. The peak shock pressure (PP) experienced by a rock can be quantitatively determined using in situ micro X-ray diffraction (µXRD) analysis of individual minerals. We expand two of these methods for clinopyroxene (CPX): 1) the lattice strain (ε) method, developed by Uchizono et al. (1999, Mineral J 21: 15) for experimentally shocked olivine to relate their lattice strain (ε), as measured with XRD, to the PPs they experienced, and 2) the strain-related mosaicity (SRM) method, developed by Izawa et al. (2011, MAPS 46: 638) for enstatite, correlates SRM-related streaking along Debye rings to meteorite shock stage. This work extends these methods to CPX, by measuring both SRM and ε in experimentally shocked CPX samples using µXRD to relate SRM and ε to their applied PPs.

Experimentally shocked CPX was obtained from three laboratories. Two calibration curves were created. The equation of the ε calibration curve is P=(ε-0.0815)/0.0031, where P is the shock pressure the CPX grain had experienced. Its standard error of the estimate (SEE) is ±12 GPa. The equation of the SRM calibration curve is P=(ε-0.03391)/0.1800, and its SEE is ±8 GPa. Both calibration curves were applied to the meteorites Nakhla and Zagami to compare their results to literature values. Using ε, Nakhla gave a PP of 8±12 GPa and Zagami gave PP of 35±12 GPa. Both PPs obtained from ε were within error of literature values (Jenkins et al. 2019, MAPS 54: 902; Fritz et al. 2005, MAPS 40: 1393), showing success. Using SRM, Nakhla gave a PP of 12±8 GPa and Zagami gave a PP of 43±8 GPa. Nakhla’s PP obtained with SRM was within error of literature values, however Zagami’s was not. This is likely due to the variability of SRM data. More SRM data is needed to improve the SRM calibration curve. These calibration curves will aid in evaluating shock metamorphism in CPX-bearing rocks, such as shergottites.