Marble enclaves in the melt sheet at the West Clearwater Lake Impact crater, northern Quebec
Bibliographic record
Abstract
The meteorite impact that formed the 32-km-diameter 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. At least seven marble enclaves have been mapped in the melt sheet; this report is based on observations made on samples from two of these enclaves. These blocks represent recrystallized remnants of a cover of Middle Ordovician limestone, now completely eroded in the area. While the impact melt was still above its solidus, the locally fossiliferous dolomite-bearing limestone recrystallized to granoblastic calcite + periclase marble. The silica content of the marble led to the formation of a sanidinite-facies assemblage of unusual nesosilicates such as spurrite, Ca5(SiO4)2(CO3), merwinite, Ca 3Mg(SiO4)2, and monticellite, CaMgSiO4. Aluminian srebrodolskite, Ca2(Fe3+,Al)2O 5, the Fe3+-dominant analogue of brownmillerite, Ca 2(Al,Fe3+)2O5, is found in material with a composition similar to "Portland cement clinker". At its type locality, srebrodolskite is attributed to the calcining of ankeritic carbonate. Phase equilibrium and stratigraphic data constrain peak conditions of metamorphism to at least, T ≈ 815º +/- 15ºC, P < 100 bar and X(CO2) > 0.1. Retrograde mineral assemblages indicate that X(CO2) < 0.1 was achieved shortly after peak metamorphism owing to influx of H2O. Portlandite, Ca(OH)2, is one of several species formed during late hydration of the assemblage upon cooling.
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 | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".