Probing the composition of unexposed basement, South Portuguese Zone, southern Iberia: implications for the connections between the Appalachian and Variscan orogens
Bibliographic record
Abstract
Geochemistry and Sm–Nd and U–Pb (magmatic zircon) isotope data from a postcollisional batholith that crosscuts the allochthonous South Portuguese Zone (SPZ) of southern Iberia suggest that the basement is compositionally more juvenile than the exposed upper crust. The SPZ is an allochthonous terrane of the late Paleozoic Variscan orogen. The oldest exposed units in the SPZ are Late Devonian continental clastics, and as a result, the origins of the SPZ are unknown. Multifaceted inherited zircon cores from a granitoid batholith (Sierra Norte Batholith, SNB) reveal Neoproterozoic (ca. 561–647 Ma) and Mesoproterozoic ages (ca. 1075 – ca. 1116 Ma). Granitoid samples are characterized by εNd values ranging from +1.4 to –9.6 and model ages ca. 0.76–1.8 Ga. Conversely, the exposed Late Devonian clastics of the SPZ are characterized by more negative εNd values (–7.5 to –10.4). Taken together, U–Pb and Sm–Nd data indicate the lower crust that melted to yield the SNB was (i) Neoproterozoic (ca. 560–650 Ma) to Mesoproterozoic (ca. 1.0–1.2 Ga) in age, (ii) was not compositionally similar to the overlying Devono-Carboniferous continental detritus but was instead more juvenile, with model ages between ca. 0.9–1.2 Ga. This unusual relationship is similar to the relationship between the relatively juvenile basement and ancient upper crust documented in the exposed portion of the Meguma terrane in the northern Appalachians, which paleogeographic reconstructions show was immediately outboard of southern Iberia in the Late Devonian.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| 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".