Exhumation response to oceanic plateau accretion and oroclinal bending: Low-temperature thermochronology study of Wrangellia terrane on southern Vancouver Island, Canada
Bibliographic record
Abstract
Approximately 50 Myr ago, the triple junction of the Kula-Farallon-North America plates converged with the continental margin, causing ridge subduction and the formation, accretion and translation of two oceanic plateaus. We investigate the effects of this tectonic configuration on the exhumation of southern Wrangellia terrane on southern Vancouver Island since the Eocene. We report late Cretaceous to late Oligocene (85.4 to 23.3 Ma) apatite fission track ages (AFT) and, for the first time, Oligocene to early Miocene (36.6 to 14.0 Ma) apatite (U Th)/He ages (AHe) for 16 bedrock samples of Wrangellia. The thermal history modelling of these ages for 13 samples reveals variable cooling patterns between regions. Samples close to the major faults of a fold and thrust belt show accelerated cooling (4–5 °C/Myr) during the Eocene. In the central area, the modelled cooling rates have been slow and generally uniform throughout the Cenozoic (0.5–1.5 °C/Myr), whereas samples from the west coast yielded very slow cooling (<0.5 °C/Myr) from 70 to 30 Ma, followed by moderate cooling (1.5–3 °C/Myr) since. Combining ages, fission track length and thermal history models in this and previous studies, we interpret the moderate-accelerated exhumation of the fold and thrust belt in the Eocene to be a response to oroclinal bending following oceanic plateau accretion. The exhumation pattern of the western side of southern Wrangellia is linked to the ongoing Cascadian Subduction zone ca.30 Ma. This exhumation pattern also supports a hypothesis that all crust of southern Wrangellia was all overlain by sedimentary strata in Eocene before ∼50 Ma, and that an accretionary complex of the Pacific Rim terrane was partly the outboard equivalent of these strata. In the southern Wrangellia, no exhumation response to the Miocene oroclinal bending associated with formation of the Olympic mountains is observed. • New apatite fission track data and first apatite U-Th/He data for Vancouver Island. • The thermal history of southern Vancouver Island since Eocene is reconstructed. • Spatial change in the exhumation history of southern Vancouver Island is discussed. • Exhumation response to terrane accretion and subduction along boundary. • Eocene overlying sedimentary strata on southwest Wrangellia eroded during exhumation.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 teacher head, 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".