Bibliographic record
Abstract
The meteorite impact that formed the 32-km-wide Upper Pennsylvanian (285 ± 23 Ma) West Clearwater structure, situated about 125 km east of the Hudson Bay arc, northern Quebec, formed a sheet of impact melt now exposed on a central ring of islands. Crater-fill deposits exposed on the ring of islands can be divided into three major successive units, which are, in ascending order: 1) a red, friable impact-melt-bearing fragmental breccia 0 to 20 m thick cut by small (cm to dm) dykes of impact melt; 2) a red, massive, clast-rich impact-generated melt about 18 meters thick containing up to 25% clasts > 1 mm in size, and 3) a massive poorly jointed clast-poor impact-generated melt containing <15% clasts greater than 1 mm in size, at least 85 m thick, with a matrix that shows an ophitic to subophitic texture. The average composition of the West Clearwater Lake impact melt, which has a bulk composition similar to that of a trachyandesitic volcanic rock, can be modeled by mixing the average chemical compositions of three types of lithologies present in the vicinity of the impact structure: 1) granitic rocks, 2) granodioritic, enderbitic and tonalitic rocks, and 3) mafic and ultramafic rocks, according to the following proportions: 1) 31%, 2) 62% and 3) 6%. The order of crystallization of the melt was plagioclase + Fe-Ti oxides + clinopyroxene + sanidine + apatite + quartz. The initial clast content in the clast-poor melt, before the onset of crystallization, must have been much higher. This conclusion is supported by the widespread occurrence in the clast-poor impact melt rock of plagioclase grains with an irregular, partially resorbed relict core. In thin section, plagioclase xenocrysts now form ~5% to ~15% of the clast-poor impact melt rock, depending on the thin section. The preferential preservation of plagioclase as a clast implies that the melt quickly equilibrated to temperatures below the liquidus and within the range of plagioclase crystallization. Two-feldspar thermometry calculations suggest that the last plagioclase and the first alkali feldspar crystallized at temperatures of about 781 to 816°C (±44°C). Quartz, the last phase to crystallize in the clast-poor impact melt rock, formed at temperatures of 700 to 730°C, with an activity of Ti in quartz between 0.5 and 0.6. This study is the first to employ Ti-in-quartz geothermometry to estimate the temperature of solidification of a melt sheet created by a meteoritic impact. Because the melt crystallized anhydrous minerals, it is possible that the melt was highly undersaturated at the liquidus but had achieved H2O saturation at the solidus.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| Science and technology studies | 0.002 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.010 | 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".