Emplacement history of mafic-ultramafic volcanic rocks in the northern Pontiac subprovince, Quebec, Canada
Bibliographic record
Abstract
Detailed geological mapping of volcanic, sedimentary and intrusive rocks in the northern Pontiac subprovince of the Superior Province has identified multiple volcanic-sedimentary contacts at the margins of a 30 km long volcanic package of high-Fe tholeiites and Munro- to Barbertontype komatiitic flows and sills. Breccias displaying blocky, globular and tendril-like juvenile clasts in a massive sedimentary matrix were observed along the contacts of mafic-ultramafic intrusions with their host sedimentary rocks. These textures are consistent with peperite, a rock formed by the mixing and mingling of magma with wet, unconsolidated sediments. Geochemical data for one of the peperites indicates that the igneous component has a similar trace element composition to spinifex-bearing komatiite flows and the sedimentary component has a similar composition to the Pontiac Group wackes. Additionally, conformable unstrained contacts were observed between effusive volcanic rocks and turbiditic wackes. These relationships indicate a previously unrecognized ca. 2682 Ma mafic and ultramafic volcanic event synchronous with the deposition of the Pontiac subprovince sedimentary rocks. This suggests that the mafic-ultramafic volcanic package is synsedimentary and autochthonous, which is not consistent with previous interpretations of these rocks as structural thrust panels. We propose that the mafic-ultramafic volcanic package was emplaced during a previously unrecognized plume-related extensional event that facilitated the upward flow of mantle-derived magmas along major, mantle-penetrating structures during Pontiac sedimentation. Shortly after, tectonic compression folded and imbricated the Pontiac rocks and accreted them to the southern margin of the Abitibi subprovince.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".