Necking of the Lithosphere: A Reappraisal of Basic Concepts With Thermo‐Mechanical Numerical Modeling
Bibliographic record
Abstract
Abstract We investigate lithosphere necking using two‐dimensional thermo‐mechanical numerical simulations without strain softening or weakening mechanisms. The models have an initial small sinusoidal perturbation of the Moho depth, whose wavelength corresponds to the model width. Applied boundary conditions (constant extension velocity or bulk extension rate) and initial model width significantly impact the necking dynamics. For constant bulk extension rates, wider models generate more intense necking with locally higher strain rates, whereas for constant velocity extension, models evolution is similar independent on their initial width. However, the width of the final necking zones ranges consistently between 45 and 105 km, independent on the type of applied boundary conditions and the initial Moho wavelength. The modeled widths are similar to along dip necking zones widths of natural rifted margins that formed during a single, unidirectional, and relatively continuous extensional event (e.g., Iberia‐Newfoundland margins, Porcupine Basin, Gulf of Aden). When the crust is mechanically decoupled from the mantle by a weak ductile lower crust, models exhibit three characteristic stages: (1) distributed thinning and extension associated with progressive subsidence; (2) upper mantle necking compensated by flow of the weak lower crust, which hampers both crustal thinning and subsidence at the rift center; and (3) crustal necking associated with fast subsidence after the mantle has necked. Decoupled models display regions of relatively thick crust on one or both sides of the rift center, comparable to the Galicia, Rockall, Hatton, and Porcupine Banks along the North Atlantic rifted margins.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.002 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".