Can the magmatic conditions of the Martian nakhlites be discerned via investigation of clinopyroxene and olivine intra-crystalline misorientations?

1S. Griffin,1,2,3,4L. Daly,5S. Piazolo,2L. V. Forman,6B. E. Cohen,1M. R. Lee,7P. W. Trimby,8,9R. J. Baumgartner,2,10,11G. K. Benedix,1B. Hoefnagels
Journal of Geophysical Research (Planets) (in Press) Open Access Link to Article [https://doi.org/10.1029/2021JE007082]
1School of Geographical and Earth Sciences, University of Glasgow, UK
2School of Earth and Planetary Sciences, Space Science and Technology Centre, Curtin University, Australia
3Australian Centre for Microscopy and Microanalysis, The University of Sydney, Australia
4Department of Materials, University of Oxford, UK
5School of Earth and Environment, University of Leeds, UK
6Department of Materials, University of Oxford, UK. 5School of Geosciences, University of Edinburgh, UK
7Oxford Instruments Nano analysis, High Wycombe, UK
8School of Biological, Earth and Environmental Sciences, The University of New South Wales, Kensington, NSW, Australia
9CSIRO Mineral Resources, Australian Resources Research Centre, Kensington, WA, Australia
10Department of Earth and Planetary Sciences, Western Australia Museum, Australia
11Planetary Institute, USA
Published by arrangment with John Wiley & Sons

Deformation is a near ubiquitous process that is observed within nearly all naturally forming rocks. Electron backscatter diffraction (EBSD) is a technique that enables slip-systems (a form of plastic deformation) to be inferred from intra-crystalline misorientations at a comparable scale to representative CPO analysis (≥300 crystals for the nakhlites). Extensive laboratory and studies on naturally occurring samples have identified preferential mantle condition extrinsic parameters for specific slip-system signatures within olivine and clinopyroxene. Intra-crystalline misorientation patterns for olivine and augite (high Ca-clinopyroxene) for 16 different Martian nakhlite meteorites (21 sections) were analysed and assessed against these known parameters. Investigation of high and low deformation regions within the nakhlites revealed a shift in intra-crystalline misorientation patterns for 10 of the 21 sections. Interpreted as both shock (high deformations) and emplacement (low deformation) signatures. The observed variations in deformation patterns for the two main regimes of deformation indicate heterogeneous sampling of the nakhlite ejecta crater. Our findings indicate that shock deformation is prevalent throughout the nakhlites, and that great care needs to be taken when interpreting intra-crystalline misorientations of crystals within apparent lower deformation regions.

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