Paleogeographic development of the east Laurentian margin: Constraints from U-Pb dating of detrital zircons in the Newfoundland Appalachians
Bibliographic record
Abstract
An upper Neoproterozoic to Ordovician Laurentian margin sedimentary sequence in the Newfoundland Appalachians records a cycle of ocean opening and closing. U-Pb dating by ion microprobe of 341 detritalzircon grains from six samples from this sequence yielded ages from 3592 +/- 5 Ma to 572 +/- 14 Ma. Three of the analyzed samples are from rift-related formations, two are from drift-related formations, and one is from a foreland-basin unit. The U-Pb data allow grouping of the zircons into four major age components: (1) Archean grains with a maximum age frequency between 2850 and 2600 Ma, (2) Paleoproterozoic grains ranging from 1950 to 1750 Ma, (3) Mesoproterozoic to early Neoproterozoic grains ranging in age between 1450 and 950 Ma, and (4) Neoproterozoic grains ranging between 760 and 570 Ma. The relative proportions of these four age components vary among samples. Mesoproterozoic detritus is present in all samples, whereas Neoproterozoic detritus is restricted to two of the three rift-related samples. Two samples - one from a rift-related formation and one from a drift-related formation, but both lying at the base of their stratigraphic column-lack Paleoproterozoic and Archean detrital zircons.Potential source regions for the detrital zircons occur within the Laurentian hinterland: zircons of Archean age correspond to the age of rock units formed during major magmatic and tectonothermal pulses in the Superior craton, zircons with Paleoproterozoic ages correspond to the ages of orogenic belts marginal to the craton (e.g., Ungava, New Quebec, and Torngat), Mesoproterozoic zircons correspond to the ages of lithologies from the Grenville orogen, and Neoproterozoic zircons are the age of rift-related igneous activity along the Laurentian margin that is now preserved within the Appalachian orogen. The youngest grains in the rift-related sedimentary rocks yield ages of 580-570 Ma and provide a maximum age for accumulation of the Newfoundland sedimentary sequence.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
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".