Jurassic to Miocene Exhumation of the Purcell and Selkirk Mountains, Southeastern British Columbia
Bibliographic record
Abstract
This thesis investigates the Jurassic and younger exhumation history of the Purcell, Selkirk, and western Rocky Mountains of the southeastern Canadian Cordillera. It spans the time range during which the Cordilleran orogen developed, from regional compression to extension. Newly determined and compiled intrusion ages and emplacement depth estimates from the contact aureoles of Jurassic–Paleocene intrusions were used to elucidate the depth of the crust spatially and temporally in the orogen. The lower temperature exhumation history following magmatism was determined using the zircon (U-Th)/He, apatite fission track, and apatite (U-Th-Sm)/He thermochronological systems with nominal closure temperatures of 180 ± 20 °C, 110 ± 10 °C, and 75 ± 5 °C, respectively. Four phases of intrusive magmatism were identified from the new and compiled geochronology data: a Jurassic phase (~174–159 Ma); a mid-Cretaceous phase (~111–98 Ma); a late Cretaceous phase (78–76 Ma); and a Paleocene phase (66–60 Ma). Emplacement depth estimates, with a few exceptions, are 12–15 km for Jurassic intrusions and 8.5–11 km for mid-Cretaceous and younger intrusions. These results indicate that much of the region experienced 2–6 km of net exhumation between the Middle Jurassic and mid-Cretaceous, followed by very little exhumation between the mid-Cretaceous and the Paleocene. The intrusion ages and emplacement depths were then used as depth-time pins upon which the subsequent lower temperature exhumation history of the Purcell, Selkirk, and Western Rocky Mountains was built. The thermochronological data indicate three Cenozoic phases of exhumation in the region: a Paleocene–Eocene phase (66–40 Ma), which includes up to 6–8 km of exhumation within the Purcell Mountains, 6–10 km in the footwall of the Gallagher fault zone, and at least 12–15 km in the footwall of the Purcell Trench fault; a Middle Eocene to Oligocene phase (40–25 Ma), which includes 2–3 km of exhumation within the Purcell Mountains, 3-5 km in the footwall of the Gallagher fault zone, and 4–6 km in the footwall of the Purcell Trench fault; lastly, a Late Oligocene and younger phase (25–0 Ma) during which regional reactivation of normal faults occurred, including 1-2 km of differential exhumation across the Gallagher fault zone and the Purcell Trench fault. Together, these data provide evidence for previously unrecognized phases of exhumation and extension in the southeastern Canadian Cordillera during the latter stages of Cordilleran orogenesis.
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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 | 0.004 | 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) | 0.006 | 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".