Apatite fission-track evidence for regional exhumation in the subtropical Eocene, block faulting, and localized fluid flow in east-central Alaska
Bibliographic record
Abstract
The origin and antiquity of the subdued topography of the Yukon–Tanana Upland (YTU), the physiographic province between the Denali and Tintina faults, are unresolved questions in the geologic history of interior Alaska and adjacent Yukon. We present apatite fission-track (AFT) results for 33 samples from the 2300 km 2 western Fortymile district in the YTU in Alaska and propose an exhumation model that is consistent with preservation of volcanic rocks in valleys that requires base level stability of several drainages since latest Cretaceous–Paleocene time. AFT thermochronology indicates widespread cooling below ∼110 °C at ∼56–47 Ma (early Eocene) and ∼44–36 Ma (middle Eocene). Samples with ∼33–27, ∼19, and ∼10 Ma AFT ages, obtained near a major northeast-trending fault zone, apparently reflect hydrothermal fluid flow. Uplift and erosion following ∼107 Ma magmatism exposed plutonic rocks to different extents in various crustal blocks by latest Cretaceous time. We interpret the Eocene AFT ages to suggest that higher elevations were eroded during the Paleogene subtropical climate of the subarctic, while base level remained essentially stable. Tertiary basins outboard of the YTU contain sediment that may account for the required >2 km of removed overburden that was not carried to the sea by the ancestral Yukon River system. We consider a climate driven explanation for the Eocene AFT ages to be most consistent with geologic constraints in concert with block faulting related to translation on the Denali and Tintina faults resulting from oblique subduction along the southern margin of Alaska.
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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 | 0.001 | 0.001 |
| 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) | 0.000 | 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".