Petrography and U-Pb zircon geochronology of Caledonian age orthogneisses dredged from the Chukchi Borderland, Arctic Ocean
Bibliographic record
Abstract
The Caledonian orogenic belt developed in the Ordovician to Devonian affecting northern Europe, Greenland and Arctic Canada. Caledonian deformational trends continue into the Arctic region disappearing at the rifted margin of the Arctic Ocean. Syn-orogenic magmatism in the Barents region date deformation of Grenvillian basement during the Caledonian event to be between about 450-410 Ma (Johansson et al., 2005; Gee et al., 2006; Gee and Tebenkov, 2004). Over 500 kilos of metamorphic rock was dredged from outcrops in the central Chukchi Borderland in 2009 (HLY0905) that included amphibolites and orthogneisses metamorphosed to amphibolite facies continuing to deform under greenschist conditions. Zircons were separated from two orthogneiss samples from this dredge, and single grain zircon U-Pb ages were determined by SHRIMP analysis be 428 Ma ± 3.4 for both samples (N=60). One sample had several zircon grains with distinct igneous cores that ranged in age from about 850-1000 Ma. Grenville age plutons (1000-910 Ma) that were later involved in Caledonian deformation and intruded by 450-410 Ma aged plutons are found on western and eastern Svalbard (Johansson et al., 2005), eastern Greenland, and the Pearya Terrane of northern Ellesmere Island (Trettin,1986, 1992). The Franklinian basement of Arctic Alaska and Canada do not share these Grenvillian ages (Trentin et al, 1987). This suggests that the inherited zircon cores in the Chukchi Borderland orthogneisses were derived, at least in part, from an older Grenvillian basement like that of Pearya, Svalbard and parts of Greenland and later intruded by Caledonian aged granites.
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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 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 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 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".