Impactites of the Mistastin Lake impact structure: Insights into impact ejecta emplacement
Bibliographic record
Abstract
Abstract The Mistastin Lake impact structure is an intermediate‐size (~28 km apparent crater diameter), complex crater formed ~36 Myr. The original crater has been differentially eroded; however, a subdued terraced rim and distinct central uplift are still observed and impactites are well exposed in three dimensions. The inner portion of the structure is covered by Mistastin Lake and the surrounding area is locally covered by soil/glacial deposits and vegetation. The crystalline target rocks of the Mistastin Lake region are dominated by anorthosite, granodiorite, and quartz monzonite. Previous studies of the Mistastin Lake impactites have primarily focussed on the impact melt rocks. This study further evaluates the entire suite of impactite rocks in terms of their location within the crater structure and emplacement mechanisms. Locally, allochthonous impactite units including impact melt and various types of breccias are distributed around the lake in the terraced rim and are interpreted as proximal ejecta deposits. A multistage model for the origin and emplacement of impact melt rocks and the formation of impact ejecta is proposed for the Mistastin Lake impact structure based on a synthesis of the field and petrographic observations. This model involves the generation of a continuous ballistic ejecta blanket during the excavation stage, followed by the emplacement of melt‐rich, ground‐hugging flows during the terminal stages of crater excavation and the modification stage of crater formation. Impact melt‐bearing breccias—also termed “suevite” at other sites—are present in several distinct settings within the Mistastin Lake structure and likely have more than one formation mechanism.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".