Detrital zircon U-Pb geochronology and Hf isotope geochemistry of Labrador \nand Curling group strata, Humber zone, Newfoundland Appalachians
Bibliographic record
Abstract
The Humber zone of the western Newfoundland Appalachians formed during the protracted (200 \nMyr) breakup of the supercontinent Rodinia and the opening of the Iapetus Ocean along NE \nLaurentia (ancestral North America). Deep-marine strata of the Humber Arm allochthon (Curling \nGroup) and shallow-marine strata of the parautochthonous Humber platform (Labrador Group) \nrecord changes in Ediacaran to Cambrian paleogeography and sediment dispersal in NE Laurentia \nduring and after breakup. While ion-microprobe-based detrital zircon U-Pb age results exist for \nsome these rock units, recent advancements in high-n, laser ablation microanalytical techniques \nallow for more robust assessment of their provenance and new constraints on the geology of the \nrift-drift transition, relationships between coeval syn- and post-rift shelf and slope strata, and types \nof continental rift mechanisms in western Newfoundland. New high-n detrital zircon U-Pb (~300 \nanalyses per sample) and Hf (~50 analyses per sample) isotope results from 11 rock samples from \nthe Curling and Labrador groups confirm an early Cambrian rift-drift transition, indicate Ediacaran \nto early Cambrian maximum depositional ages, and support low-angle detachment style rift models \nfor the NE Laurentian margin. Margin-normal transform fault systems that were active during \ncontinental extension divided sediment source areas between upper-plate and lower-plate margin \nsettings. Syn-rift, shallow-to-transitional marine (Bradore Formation) strata deposited along \nupper-plate margin segments mostly yield underlying Grenville basement-derived (950 – 1400 \nMa) detrital zircon grains, whereas coeval continental slope debris flow (Summerside and Blow \nMe Down Brook formations) strata deposited along lower-plate margins contain well-mixed, \npolycyclic Mesoproterozoic to Neoarchean detrital zircon grains sourced from the Canadian Shield \nand Grenville province and minor input from rift-related igneous rocks. The late early Cambrian \nonset of thermal subsidence resulted in similar sediment sources deposited across the shelf and \nslope regions of both upper- and lower-plate margins and point to the decreased role of marginnormal \nfault systems after lithospheric breakup. Post-rift, continental slope debris flow (Irishtown \nFormation) and tidal marine (Hawke Bay Formation) strata mostly yield well-mixed, Proterozoic \nand Archean detrital zircon populations from the Canadian Shield and Grenville province. Minor \nEdiacaran (558 – 620 Ma) detrital zircon grains in Labrador and Curling group strata have \nsuperchondritic Hf isotope signatures that overlap in age with rift-related magmatism in the \nwestern Newfoundland - Quebec Appalachians and likely indicate repeated partial melting of \nenriched continental lithosphere during polyphase extension.
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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 | 0.002 | 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) | 0.002 | 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".