Detrital zircon evidence for eclogite formation by basal subduction erosion—An example from the Yukon-Tanana composite arc, Canadian Cordillera
Bibliographic record
Abstract
The Yukon-Tanana terrane lies within the North American Cordilleran accretionary orogen and contains strongly deformed, coherent eclogite-bearing units that are candidates for wholesale subduction erosion of large blocks of crust. The Yukon-Tanana terrane is a composite continental arc built on a peri-Laurentian substrate that experienced subduction on both sides before it was accreted back onto Laurentia in the Mesozoic. Along the present-day eastern margin of the terrane, eclogites are found as layers and lenses in quartzofeldspathic schist derived from both igneous and sedimentary protoliths, all metamorphosed together during the Permian. In the St. Cyr area, coherent slices of eclogite-bearing crust up to 30 km long and 1–2 km thick have been mapped. Phengite with Si = 3.3–3.4 per formula unit from the host schists indicates that they also record eclogite-facies metamorphism. Detrital zircon was recovered from six host-rock samples collected at three high-pressure (HP) localities (St. Cyr, Ross River, and Last Peak), and from two eclogite-free units. Samples from the eclogite-free units and Last Peak have detrital zircon signatures with prominent Mesoproterozoic and Paleoproterozoic peaks typical of the Snowcap assemblage, the peri-Laurentian substrate of the Yukon-Tanana terrane. Detrital spectra from the St. Cyr and Ross River HP localities contain Precambrian, mostly Mesoproterozoic, zircon with significant Paleozoic peaks that match ages of igneous events in the Yukon-Tanana terrane. The coherent slices of crust containing eclogite, meta-tonalite, and arc-derived metasedimentary rocks are interpreted as pieces of Yukon-Tanana terrane that were eroded from the arc during subduction of oceanic lithosphere and reaccreted to the arc prior to Mesozoic emplacement of the Yukon-Tanana terrane onto North America.
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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) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.024 | 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".