A geochronological framework for sedimentation and Mesoproterozoic tectono-magmatic activity in lower Belt–Purcell rocks exposed west of Kimberley, British Columbia
Bibliographic record
Abstract
The Matthew Creek Metamorphic Zone (MCMZ) exposes what is inferred to be the lowest structural level of the lower Aldridge Formation in the Canadian portion of the Belt–Purcell Supergroup. Zircon, monazite, and titanite were dated using the U–Pb system by LA–ICP–MS. The detrital zircon populations of quartzite layers in these rocks define a provenance dominated by sources of Laurentian affinity with a minor component of non-North American ages between 1600 and 1490 Ma. Special attention was paid to monazite in sillimanite-grade metapelitic schists that was analyzed using in situ LA–ICP–MS techniques guided by BSE imaging and compositional mapping. Textural and geochronological evidence indicate that coupled dissolution–reprecipitation affected detrital monazite at 1413 ± 10 Ma. This was followed by prograde monazite growth at 1365 ± 10 Ma, synchronous with crystallization of the nearby Hellroaring Creek peraluminous granite at 1365 ± 5 Ma. Late-stage pegmatite emplacement and ductile shearing along the contact of the MCMZ and overlying rocks occurred at 1335 ± 5 Ma, interpreted as a period of post-collisional extension, core complex formation, exhumation, and decompression melting. The entire package was subsequently affected by a pervasive ∼1050 Ma hydrothermal overprint that partially reset U–Pb dates in monazite, zircon, and titanite contained in all lithologies examined. The lowermost Belt–Purcell stratigraphy in southeast British Columbia preserves a detailed record of sedimentary provenance and a long history of episodic collision and extension that must be reconciled with plate reconstruction models for the break-up of the Nuna supercontinent and assembly of Rodinia.
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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 | 0.004 | 0.004 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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".