Linking detrital minerals to their source: The use of U-Pb-Hf data to untangle Laurentian and Gondwanan (Ganderian) sources
Bibliographic record
Abstract
Abstract In the northern Appalachian orogen, the timing and extent of Gondwanan terranes accreting to Laurentia during the Ordovician to Silurian Periods remain unclear, especially in the Gaspé Peninsula (Québec, Canada), where basement rocks are covered by the thick sedimentary sequence of the Gaspé Belt. In such context, detrital mineral analysis from syntectonic sedimentary basins can help to constrain this timing. A compilation of zircon U-Pb and εHf data from Laurentian and Ganderian sources shows distinct differences, with Ganderian rocks having a Cryogenian to Late Ordovician primitive εHf signature, while Laurentian zircon grains display variable but mostly negative εHf values at these times. To better constrain the timing of Ganderia's accretion, we tracked sedimentary provenance shifts along the Laurentian margin using U-Pb + Hf isotope data from detrital zircon grains in Ordovician to Devonian sediments in the Gaspé Peninsula deposited on the Laurentian margin and in the Connecticut Valley–Gaspé trough. These were compared with zircon grains from Ganderian exposures in the Bathurst Supergroup, Miramichi terrane. The detrital zircon U-Pb ages mainly indicate Laurentian sources, with abundant Mesoproterozoic grains and varying proportions of Ordovician to Devonian ages, plus a few Ediacaran zircons in post-Taconic sediments. While Ediacaran zircons potentially constrain the timing of Ganderian accretion, εHf data significantly enhance source differentiation, revealing a distinct Middle Ordovician primitive εHf signature in Upper Ordovician sediments, which we interpret as Ganderian. This signature aligns with compiled U-Pb and εHf data from Ganderia and the newly analyzed rhyolitic Hayden Lake Formation of the Miramichi terrane, suggesting Ganderia contributed to the Gaspé Belt sediments during the Late Ordovician and was near the Laurentian margin. Our data underscore the importance of multiproxy analysis in provenance studies for identifying sediment sources, especially when source regions have similar ages.
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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".