Microstructure Decoding the Deformation history of the highly shocked Martian Shergottite NWA 772
Bibliographic record
Abstract
Martian meteorites offer insights into Martian magmatic processes and impact history, critical for understanding terrestrial planet evolution. Among over 100 identified Martian meteorites (4.4 Ga-165 Ma; Nyquist et al., 2001; Moser et al., 2013), shergottites are the most common, resembling terrestrial basalts (McSween, 2015; Kizovski et al., 2019) but showing strong shock metamorphism. Key shock features include plagioclase-to-maskelynite transitions, olivine and pyroxene mosaicism, and planar fractures in olivine (Stöffler et al., 1986; Walton & Herd, 2006; Jones, 2014). However, deformation history interpretations using shock and post-shock features remain ambiguous due to limited quantitative constraints and direct observation at a mesoscale. This study analyzes olivine microstructures in poikilitic shergottite NWA 7721 using electron backscatter diffraction (EBSD) and dark-field X-ray microscopy (DFXM). We discovered a bimodal morphological subgrain distribution in the large olivine grain: (1) almost strain-free recrystallized crystallites (15 µm) with strong alignment and low-angle boundaries (< 15º). With DFXM, it further revealed two dislocation distributions in the 3D grain volume that 1) “dislocation network” formed by very-low-angle misorientation boundaries ( 0.3º). These textures suggest a complex deformation-recovery process for the emplacement of shergottite on Mars. The small crystallites formed via shock-induced heterogeneous nucleation at olivine grain edges and fractures (Walton & Herd, 2006), facilitated by eutectic melting followed by recrystallization during brief post-shock heating that is less than 0.2 hours of 1600-2000K (Takenouchi et al., 2017; Speciale et al., 2020). The irregular subgrain fragments are preserved olivine relics, isolated by very-low-angle boundary networks developed during compressive shock wave passage, migrating to form low-angle boundaries during rapid quenching. This records the final deformation episode before meteorite delivery to the Earth, shedding light on shock metamorphism and recovery processes in Martian rocks.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".