Remanent crustal strain on Mars in non-poikilitic olivine of NWA 7721
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| Autores principales: | , , , , , , , |
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| Formato: | Preprint |
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2025
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| _version_ | 1866911259539013632 |
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| author | Li, Yaozhu Kalácska, Szilvia McCausland, Phil Flemming, Roberta L. Hetherington, Callum Zhao, Bo Yildirim, Can Detlefs, Carsten |
| author_facet | Li, Yaozhu Kalácska, Szilvia McCausland, Phil Flemming, Roberta L. Hetherington, Callum Zhao, Bo Yildirim, Can Detlefs, Carsten |
| contents | We present a multiscale microstructural analysis of olivine from the non-poikilitic lithology of the poikilitic shergottite NWA 7721, using dark-field X-ray microscopy (DFXM), electron backscatter diffraction (EBSD), and context in situ 2D micro-XRD. A single olivine crystal contains two distinct subgrain populations. Type 1 subgrains are fine (1-5 micrometers), randomly oriented, and nearly strain-free, whereas Type 2 subgrains are coarse (greater than 30 micrometers), aligned, and strongly strained. Layered DFXM data reveal slip-band features in Type 2 that are absent in Type 1. We interpret Type 1 as products of shock-induced recrystallization, whereas Type 2 preserves remnants of a highly deformed parent grain. This bimodal microstructure, not observed in other Martian meteorites including the paired NWA 1950 and ALH A77005, points to a heterogeneous response to impact influenced by pre-existing strain in the olivine grain. We propose that NWA 7721 olivine experienced substantial crustal or magmatic stress before impact. The subsequent shock wave imposed a rapid load-release cycle that mobilized dislocations and produced low-angle boundaries in Type 2, while driving recrystallization of Type 1. Grain-growth constraints limit the post-shock heating duration to approximately 2.3 s, consistent with rapid quenching. These results provide the first evidence that non-poikilitic olivine in NWA 7721 preserves dynamic crustal deformation on Mars in the Late Amazonian. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_08316 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Remanent crustal strain on Mars in non-poikilitic olivine of NWA 7721 Li, Yaozhu Kalácska, Szilvia McCausland, Phil Flemming, Roberta L. Hetherington, Callum Zhao, Bo Yildirim, Can Detlefs, Carsten Earth and Planetary Astrophysics Materials Science We present a multiscale microstructural analysis of olivine from the non-poikilitic lithology of the poikilitic shergottite NWA 7721, using dark-field X-ray microscopy (DFXM), electron backscatter diffraction (EBSD), and context in situ 2D micro-XRD. A single olivine crystal contains two distinct subgrain populations. Type 1 subgrains are fine (1-5 micrometers), randomly oriented, and nearly strain-free, whereas Type 2 subgrains are coarse (greater than 30 micrometers), aligned, and strongly strained. Layered DFXM data reveal slip-band features in Type 2 that are absent in Type 1. We interpret Type 1 as products of shock-induced recrystallization, whereas Type 2 preserves remnants of a highly deformed parent grain. This bimodal microstructure, not observed in other Martian meteorites including the paired NWA 1950 and ALH A77005, points to a heterogeneous response to impact influenced by pre-existing strain in the olivine grain. We propose that NWA 7721 olivine experienced substantial crustal or magmatic stress before impact. The subsequent shock wave imposed a rapid load-release cycle that mobilized dislocations and produced low-angle boundaries in Type 2, while driving recrystallization of Type 1. Grain-growth constraints limit the post-shock heating duration to approximately 2.3 s, consistent with rapid quenching. These results provide the first evidence that non-poikilitic olivine in NWA 7721 preserves dynamic crustal deformation on Mars in the Late Amazonian. |
| title | Remanent crustal strain on Mars in non-poikilitic olivine of NWA 7721 |
| topic | Earth and Planetary Astrophysics Materials Science |
| url | https://arxiv.org/abs/2511.08316 |