Orocline formation at the core of Pangea: A structural study of the Cantabrian orocline, NW Iberian Massif
Bibliographic record
Abstract
The Variscan orogen provides the European record of the late Paleozoic continental collisions that culminated with formation of the supercontinent Pangea. An S-shaped pair of isoclinal coupled oroclines characterizes the Variscan orogen of the Iberian Massif. Though oroclines are common features of the world's orogenic belts, the mechanisms that drive oroclinal formation, and the manner in which these continental-scale vertical-axis folds of orogens are accommodated are poorly understood. The northerly Cantabrian and the southerly Central Iberian oroclines are structurally continuous and pericontemporaneous, suggesting that they formed in the same fashion. Exposures of the Ediacaran Narcea Slates within the so-called Narcea antiform trace a 150-km-long arcuate belt around the 180° Cantabrian orocline. In the western flank of the Narcea antiform, the Narcea Slates are characterized by a penetrative steep to vertical, rough to slaty cleavage (S1) and subparallel 2-km-wide reverse shear zones with a penetrative fabric (S2) that are postdated by asymmetric meso- to outcrop-scale vertical-axis folds (plunge >65°) with a dominant vergence toward the oroclinal hinge; i.e., fold geometry is dominantly dextral (Z-shaped) in the southern limb of the Cantabrian orocline and dominantly sinistral (S-shaped) in its northern limb. Axial planes are consistently steeply dipping, but they are typically oriented at a high angle to S1/S2 and are therefore variable in strike about the orocline hinge. Vertical-axis folds affecting the Narcea Slates are of the appropriate scale and geometry to be interpreted as parasitic structures developed in response to a component of flexural shear within the limbs of the forming Cantabrian orocline. A model of formation of the Iberian coupled oroclines by buckling accommodating significant orogen-parallel shortening along an initially linear Iberian Variscan belt is therefore supported, providing new insight into the complexities associated with the final stages of Pangean amalgamation.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".