Provenance constraints from detrital zircon U–Pb ages in the NW Iberian Massif: implications for Palaeozoic plate configuration and Variscan evolution
Bibliographic record
Abstract
Detrital zircons from pre-orogenic Upper Ordovician to Devonian low-grade metasedimentary rocks have been dated by laser ablation–inductively coupled plasma mass spectrometry (LA–ICP-MS) to: (1) constrain the variations of zircon age populations within the autochthonous sequences of NW Iberia; (2) compare U–Pb detrital zircon ages with previous data; (3) test the hypothesis of the Armorica microplate as a peri-Gondwanan terrane separated from Gondwana. The similarity in the ages of detrital zircons found in the Palaeozoic samples studied here to those published for the Upper Proterozoic, Lower Cambrian and Lower Ordovician sediments of NW Iberia argues against the separation of Armorica, and points to a common source area for all of the Palaeozoic detrital formations of NW Iberia, the West African craton and the surrounding Pan-African belts. LA–ICP-MS U–Pb dating of zircons from a synorogenic flysch preserved in klippen in the core of a syncline establishes a maximum depositional age for this deposit as Early Namurian. This age is also a maximum age limit for thrusting and refolding in this part of the Iberian Massif. Correlation of the zircon age populations with published ages confirms the link between the emplacement of the allochthonous complexes of NW Iberia and synorogenic sedimentation.
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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 | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 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) | 0.001 | 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".