Source of the Dalradian Supergroup constrained by U–Pb dating of detrital zircon and implications for the East Laurentian margin
Bibliographic record
Abstract
Detrital zircons in siliciclastic units of the Dalradian Supergroup yield U–Pb ages ranging from 3.2 to 0.5 Ga. Detrital zircons from the sub-Grampian Group basement and the Grampian Group are predominantly of Palaeoproterozoic and Mesoproterozoic ages with Archaean grains absent or rare. In contrast, the overlying Appin, Argyll and Southern Highland groups contain a significant contribution of Archaean detrital zircon grains, some of which locally preserve evidence for late Palaeoproterozoic overgrowths dated at c . 1.8 Ga. In addition, on concordia plots Archaean grains are slightly discordant with a lower intercept at c . 1.8 Ga suggesting they were affected by a tectonothermal event at this time. Late Palaeoproterozoic and Mesoproterozoic grains also show evidence for overprinting by a tectonothermal event around 1.0–0.9 Ga. These tectonothermal events occurred in the source region before accumulation of the siliciclastic detritus. The analysed samples contained no definitive evidence for having been affected by a late Neoproterozoic (Knoydartian) event or of containing detritus derived from a source showing evidence for this event. The overall age range of detritus, combined with sparse palaeocurrent data, is consistent with derivation from the Laurentian foreland, especially the Labrador–Greenland region. Archaean detritus overlaps with that of Archaean cratons, notably the Superior, whereas Palaeoproterozoic detritus corresponds to the timing of suturing of Archaean cratons by a series of orogenic belts (Ketilidian–Makkovik, New Quebec, Nagssugtoqidian, Torngat belts). Mesoproterozoic detritus is consistent with derivation from the Grenville Orogen. The presence of a series of detrital age peaks in the late Palaeoproterozoic and early Mesoproterozoic (1.8–1.5 Ga), the paucity of mid-Mesoproterozoic detritus (1.4–1.2 Ga), and evidence for a tectonothermal event between 1.0 and 0.9 Ga is typical of the geological history of the Labrador–Greenland region of Laurentia.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 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 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".