Subduction accretion, thermal overprinting, and exhumation of high-pressure/low-temperature metasedimentary rocks of the south-central brooks range
Bibliographic record
Abstract
Lithological, petrological and structural observations and measurements of graphite thermometry, Si-in-phengite barometry, and 40Ar/39Ar phengite thermochronology were performed along two transects across the south-central Brooks Range of northern Alaska. The integrated data set reveals a history of accretion, protracted thermal overprinting of high-pressure/low-temperature (HP/LT) metamorphic assemblages, and subsequent exhumation. Tectonic domains characterized by upper greenschist facies metamorphic rocks display a dominant E-W axial planar cleavage/foliation fabric that overprints bedding and earlier metamorphic foliations. Raman maturation thermometry and Si-in-phengite barometry document a southward increase from greenschist facies conditions (ca. 360–400°C; 3–7 kbar) in the Doonerak window and Endicott Mountains allochthon to epidote-blueschist facies conditions (~515°C and 10–13 kbar) within the Schist Belt. Within the Central and Schist belts albite porphyroblasts overgrow the earlier deformation fabric and quartz microstructures exhibit evidence for diffusive recovery. This indicates thermal overprinting of deeper portions of the accretionary complex caused protracted (ca. 25 m.y.) greenschist facies overprinting of HP/LT assemblages within the Ar partial retention zone. The Schist Belt – Central Belt boundary is defined by a singular, penetrative foliation that displays a weak shear-band fabric. 40Ar/39Ar results along this boundary indicate that the fabric records deformation along the lower boundary of a nappe that began to move up the subduction channel as subduction ceased by ~135-130 Ma. Subsequent deformation along the Schist Belt – Phyllite Belt boundary reflects the exhumation of HP/LT rocks along a south-dipping normal-sense shear zone. Phengite 40Ar/39Ar age gradients coupled with the first arrival of coarse-grained Brooks Ranges detritus within the adjacent Yukon Koyukuk Basin indicate that tectonic denudation along this shear zone partly exhumed the Schist and Phyllite belts to mid-crustal depths by 110–105 Ma. Final exhumation of the HP/LT rocks was delayed until the Cenozoic which resulted in < 15 km of additional denudation.
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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".