Detrital zircon characterization of early Cambrian sandstones from East Avalonia and SE Ireland: implications for terrane affinities in the peri-Gondwanan Caledonides
Bibliographic record
Abstract
Abstract The Caledonides of Britain and Ireland include terranes attributed to both Laurentian and Gondwanan sources, separated along the Solway line. Gondwanan elements to the south have been variably assigned to the domains Ganderia and East Avalonia. The Midland Platform forms the core of East Avalonia but its provenance is poorly known. Laser ablation split-stream analysis yields information about detrital zircon provenance by providing simultaneous U–Pb and Lu–Hf data from the same ablated volume. A sample of Red Callavia Sandstone from uppermost Cambrian Stage 3 of the Midland Platform yields a U–Pb age spectrum dominated by Neoproterozoic and Palaeoproterozoic sources, resembling those in the Welsh Basin, the Meguma Terrane of Nova Scotia and NW Africa. Initial εHf values suggest that the Neoproterozoic zircon component was derived mainly from crustal sources < 2 Ga, and imply that the more evolved Palaeoproterozoic grains were transported into the basin from an older source terrane, probably the Eburnean Orogen of West Africa. A sample from Cambrian Stage 4 in the Bray Group of the Leinster–Lakesman Terrane shows, in contrast, a distribution of both U–Pb ages and εHf values closely similar to those of the Gander Terrane in Newfoundland and other terranes attributed to Ganderia, interpreted to be derived from the margin of Amazonia. East Avalonia is clearly distinct from Ganderia, but shows evidence for older crustal components not present in West Avalonia of Newfoundland. These three components of the Appalachian–Caledonide Orogen came from distinct sources on the margin of Cambrian Gondwana.
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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 | 0.000 | 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".