Greenschist Facies Metamorphic Zircon Overgrowths as a Constraint on Exhumation of the Brooks Range Metamorphic Core, Alaska
Bibliographic record
Abstract
Abstract Like many other mountain belts, the metamorphic core or hinterland of the Brooks Range fold and thrust belt in Arctic Alaska is characterized by multiply deformed and polymetamorphosed rocks whose histories have been challenging to decipher and thus difficult to relate to the supracrustal history of the orogen. The multiple greenschist and blueschist facies metamorphic events have been particularly difficult to resolve. This study provides petrologic context for recently identifiedlow‐temperaturemetamorphic zircon overgrowths at two localities across some 200 km of orogenic strike that offer a unique and precise constraint on the timing of events recorded in the Brooks Range hinterland. In consideration of microstructural context, graphite thermometry, metamorphic mineral inclusions, and zircon trace element and Lu‐Hf‐isotope data, metamorphic zircon growth at 114 ± 5 Ma in the southern Brooks Range is interpreted to coincide with greenschist facies metamorphism, most probably linked to decompression and/or increased temperatures within the orogenic core. Their age coincides with a proposed pulse of extension within a >600‐km shear zone along the southern flank of the Brooks Range and a regional flare‐up in magmatism and pronounced subsidence within hinterland depocenters (Yukon‐Koyukuk Basin). These regional events are consistent with subduction retreat/rollback in mid‐Cretaceous time. This study adds to a growing body of literature demonstrating the importance of searching for and characterizing metamorphic zircon growth in low‐ to medium‐grade metamorphic terranes to provide better constraints on otherwise cryptic tectonic events.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 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".