Forearc strike-slip displacement as an alternative to subduction erosion, with examples from Mexico and California (sinistral Nacimiento fault)
Bibliographic record
Abstract
Slip on the Nacimiento fault of the central Coast Ranges of California has been variably interpreted as dextral, sinistral, or reverse. The currently prevailing interpretation is that the Nacimiento fault represents subduction erosion, by which the central to eastern part of the Cretaceous California batholith was thrust over the western part of the batholith and forearc basin, resulting in juxtaposition of the Salinian batholithic block against the Franciscan Complex, concurrently with Laramide flat-slab subduction (75–55 Ma) and underplating of the Pelona-Orocopia-Rand schist. No modern convergent plate margin includes such overthrusting. The closest modern analog to the likely configuration of the Salinian continental margin near the end of the Laramide deformation is southern Mexico, where arc plutons are exposed near the trench. Although commonly considered an example of subduction erosion, this margin is “missing” parts of the plutonic arc and forearc because they have been displaced to the southeast by sinistral slip. By analogy, the Nacimiento forearc was modified as a trench-trench-transform triple junction migrated southeastward along the continental margin during flat-slab subduction. This model makes testable predictions involving northwest-to-southeast younging of deep-marine deposits on batholithic crust underlain by contemporaneous schist. Correct restoration of later Cenozoic primarily dextral slip and Maastrichtian – Early Eocene primarily sinistral slip must result in realignment of north–south-trending belts of the Sierra Nevada – Salinia – Peninsular Ranges batholith, Great Valley forearc, and Franciscan Complex. These modern and ancient examples suggest that several “erosional” subduction zones are more plausibly explained by strike-slip truncation of forearcs.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| 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".