U-Pb Geochronology of Mid-Crustal Rocks Exhumed Along the Denali Fault in the Eastern Alaska Range
Bibliographic record
Abstract
For much of its length, the Denali fault juxtaposes the Wrangellia Composite terraneagainst the ancestral North American margin. However, the location of the main geologic\nboundary between the Wrangellia Composite terrane and the North American margin is obscured\nin the Alaska Range Suture Zone. In the Eastern Alaska Range, where persistent and rapid\nexhumation has been occurring since ~23 Ma, the origin and protolith of the rocks north of the\nDenali fault is unknown. We present new U-Pb detrital zircon geochronology from seven\nsamples collected in the eastern Alaska Range located within this region of focused exhumation.\nThe prevalence of suspected metamorphic grains, grains affected by lead loss, and newly\ncrystallized grains due to regional plutonism provided challenges when filtering our data. Grains\nfrom each data set with U/Th ratios > 10, Uranium content > 5,000 ppm, or U-Pb ages > 3%\nerror were removed. Additionally, neo-crystallized grains were identified and removed based on\nthe known distribution of U-Pb zircon ages of plutons in the immediate field area. The maximum\ndepositional age of our samples ranges from Late Devonian to Middle Triassic. These findings\ncontradict previous mapping and suggest that many assemblages in the eastern Alaska Range\nwill be mapped differently with future detailed mapping. It is possible rocks to the north of the\nDenali fault in the eastern Alaska Range have ties with the ancestral North American margin,\nwhich would be expected based on geographic location and would imply these rocks have\nremained in place. Alternatively, it is also possible that one of our samples has sediment sourced\nfrom the southern portion of the Alexander terrane, and two of our samples have sediment\nsourced from the Endicott Arm of the southeastern Yukon Tanana terrane. If these correlations\nare correct, this requires >1000 kilometers of transport, which requires slip on a separate\nstructure from the Denali fault.
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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 | 0.001 | 0.001 |
| 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) | 0.001 | 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".