Along‐Strike Variation in the Magmatic Tempo of the Coast Mountains Batholith, British Columbia, and Implications for Processes Controlling Episodicity in Arcs
Bibliographic record
Abstract
Abstract The growth of the Coast Mountains batholith has been documented as episodic through time, and it has become a type example of a continental arc system that developed through non‐steady‐state magmatism. The magmatic record, however, is not well known along the length of the arc, hindering evaluation of the processes controlling the tempo and patterns of batholith growth. A new, robust geochronologic database (485 U‐Pb zircon and titanite ages, 120 of which are newly presented herein) covering nearly 1,000 km of arc length reveals significant along‐strike variation in the tempo of batholith emplacement, the timing of arc cessation, and the arc cooling history. Zircon ages range from ~180 to 40 Ma along the length of the arc and overlap with titanite ages, with the exception of parts of the central batholith where Eocene extension and exhumation of lower crustal rocks led to a more complex history. New analysis of zircon ages reveals significant along‐strike differences in the timing of high flux magmatic events. Small‐scale (<150 km) intra‐arc variations in magmatic tempo suggest that small‐scale processes, likely operating within the arc system, appear to have driven the episodic growth of the Coast Mountains batholith. In contrast, rates of Cretaceous‐Paleogene eastward arc migration are consistently ~2.5 km/Myr along the length of the arc. These rates are similar to those documented in North American arc systems, which suggests that arc migration has an external, plate‐scale driver and/or is an intrinsic, self‐modulating feature of most continental arcs.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".