Shock-produced high-pressure (La, Ce, Th)PO4 polymorph revealed by microstructural phase heritage of monazite
Bibliographic record
Abstract
The responses of uranium-bearing accessory minerals to shock metamorphism have received growing interest, because under extreme pressure and temperature conditions, these phases can form unique microstructures and/or polymorphs and their radiometric ages can be partially to wholly reset. This study presents new, high-resolution electron backscatter diffraction microstructural analyses of shock-deformed monazite, (La, Ce, Th)PO4, from the Haughton Dome, Nunavut, Canada, and the Nordlinger-Ries Crater, southern Germany. At each locality, shocked monazite grains contain distinctive lamellae comprising interlocking laths in four systematic crystallographic orientations. Modelling of orientation relationships among these lath-textured microstructures reveals that they were produced by reversion from lamellae of a previously undescribed high-pressure polymorph with a tetragonal symmetry. This is the first report of polymorphism found in natural (La, Ce, Th)PO4. The orientation relationships, lamellar forms, and ready reversion to monazite at low pressures are consistent with a deviatoric transformation. The former presence of this new (La, Ce, Th)PO4 polymorph is detected in moderately to highly shocked rocks, suggesting that it may be common at other impact craters.
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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".