A record of Late Cretaceous to early Paleogene Insular terrane accretion within the northern Cordillera: Insights from monazite petrochronology across the Kluane Schist, southwest Yukon, Canada
Bibliographic record
Abstract
Abstract The Kluane Schist is a metamorphosed package of siliciclastic and lesser calcareous rocks that lies between the inboard pericratonic Intermontane terranes and outboard Insular terranes of the North American Cordillera within Yukon, Canada. The metamorphic sequence of the Kluane Schist preserves a record of the tectono-thermal evolution and timing of Insular terrane accretion. Here we document the timing of metamorphism and deformation across the Kluane Schist using in situ laser ablation–inductively coupled plasma–mass spectrometry U-Th-Pb monazite petrochronology. Monazite-bearing samples collected across an inverted metamorphic sequence preserved in the northern regions of the Kluane Schist yield dates ranging from ca. 70 Ma to 55 Ma. Complementary phase equilibria modeling and thin section analysis indicate monazite grew between ~450 °C and 3.0–3.5 kbar to ~700–715 °C and 4.0–4.5 kbar, coeval with the development of the Kluane Schist's inverted metamorphic sequence. Dating the four chemical zones preserved by monazite demonstrates its protracted growth during three distinct periods of garnet crystallization and breakdown, as well as coeval with melt generation. Our data illustrate that peak metamorphic conditions were reached at progressively younger ages with decreasing structural level within the Kluane Schist. Our results are consistent with Buchan-style metamorphism associated with the terminal accretion of the outboard Insular terranes and southwest-directed overriding of the inboard Yukon-Tanana terrane from ca. 70 Ma to 55 Ma. These findings are further congruous with a Late Cretaceous timing for the terminal accretion of the Insular terranes within southwest Yukon, facilitated by east-dipping subduction beneath a westward migrating North American continent.
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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) | 0.001 | 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".