Numerical models of Farallon plate subduction: Creating and removing a flat slab
Bibliographic record
Abstract
Flat-slab subduction has affected parts of North America, South America, and Asia over the past 250 m.y. In these areas, reconstructions show that the subducting plate became subhorizontal below the continent for ~5 to >30 m.y., followed by foundering of the slab and resumption of steep-angle subduction. Using two-dimensional numerical models, we examine the factors that control the development and removal of a flat slab. Models are based on the Late Cretaceous to Oligocene Farallon flat slab below the southwestern United States. We find that the primary control on subduction geometry is the oceanic plate density structure. Subduction of a buoyant oceanic plateau creates a flat-slab segment that moves inboard at approximately the rate of continental trenchward motion (4–5 cm/yr). Steepening is initiated with eclogitization of the oceanic plateau crust. Once the plateau density exceeds that of the mantle, the slab undergoes rollback through progressive trenchward-directed detachment from the continent at a rate of 2–10 cm/yr. Rollback is enhanced by: (1) weakening of the overlying continental mantle lithosphere, inferred to result from slab-derived hydrous fluids, and (2) a slowdown in plate velocities; the rate and amount of oceanic eclogitization are second-order effects. Conversely, rollback is hindered by a strong oceanic plate and interactions between the slab and high-viscosity lower mantle. For the ~2000-km-long Farallon slab, the Conjugate Shatskey Rise plateau must have remained buoyant for 20–30 m.y. after subduction. This was followed by rapid rollback caused by both plateau eclogitization and continental weakening, leaving an area of thinned and hydrated continental lithosphere.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| 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".