Mineralogy and petrology of melt rocks from the Popigai impact structure, Siberia
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Bibliographic record
Abstract
Abstract— The late Eocene Popigai impact structure of Siberia comprises an approximately 0.5–1.5 km thick, ˜100 km diameter sequence of clast‐rich and clast‐poor andesitic to rhyolitic impact melt rocks and impact breccias, underlain by Archean to Proterozoic crystalline basement and Proterozoic to Phanerozoic sedimentary rocks. The fine‐grained to cryptocrystalline texture of the more melt‐rich rocks, despite their occurrence in bodies locally in excess of 800 m thick and 28 km long, suggests that the melt crystallized in response to (1) cooling by the clast load, and/or; (2) rapid nucleation on finely brecciated clasts, which have since been assimilated and/or; (3) crystallization enhanced by the relatively low water contents of the melts. Rapid crystallisation of the melt is indicated by the lack of zoning in minerals, the presence of glass, the lack of strain recovery features in clasts and the lack of evidence for fractionation in the major and trace elements, including the rare earth elements. Optical and analytical electron microscopy reveal that the previously reported division of the melt rocks into high‐ and low‐temperature variants based on hand sample appearance, or glass content, is not warranted. Clasts within the melt‐rich rocks exhibit a wide range of shock metamorphic features, though they are not distributed in the impact melts in a systematic manner. This indicates that the melt‐rich rocks were well mixed during their formation, thus juxtaposing unshocked with shocked material. Injection of mesostasis melt into partially melted checkerboard plagioclase and orthopyroxene clasts also occurred during this mixing stage.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| 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 it