The role of gravitational instabilities, density structure and extension rate in the evolution of continental margins
Bibliographic record
Abstract
Abstract Formation of rifted continental margins is associated with localized thinning and breakup of the continental lithosphere, driven or accompanied by the ascent of the lithosphere–asthenosphere boundary. Thinning creates sharp density and viscosity contrasts and steep boundaries between cold deformed lithosphere and hot upwelling asthenosphere, thus providing conditions for the development of positive (asthenosphere) and negative (mantle lithosphere) Rayleigh–Taylor (RT) instabilities. The evolution of many continental margins (e.g. Newfoundland margin and Iberian margin) is characterized by slow spreading rates. This allows the RT instabilities to grow at the timescale of rifting. The impact of positive RT instabilities (asthenospheric upwelling) is well studied. The negative RT instabilities, associated with mantle down-welling, remain an overlooked factor. However, these instabilities should also affect the rift evolution, in particular, they may cause mantle thinning or thickening below the rift flanks. Our numerical experiments suggest that the ratio of the RT-growth rate to the extension rate controls the overall rift geometry and evolution. Even if the effect of negative RT instabilities is more important for slow extension rates of 2×5 mm year −1 (Deborah number, De <1), it is still significant for 2–3 times higher extension rates of 2×15 mm year −1 ( De <10). The numerical experiments for extension rates of 2×15 mm year −1 and mantle–asthenosphere density contrasts of 10–20 kg m −3 demonstrate a number of structural similarities with continental margins characterized by low De (e.g. Flemish Cap and Galicia margin). In particular, rift asymmetry results from interplay between the RT instabilities and differential stretching at De <1. Formation of interior basins occurs at De ≈1–3. The best correspondence with the observed geometry of rifted margins is obtained for chemical density contrast of 20 kg m −3 and extension rate of 2×15 mm year −1 , which is twice that of the averaged values inferred from the observations. This suggests that margins may initially (prebreakup stage) extend at higher rates than the average extension rates characterizing rift evolution. The influence of RT instabilities is strongly controlled by extension rate, density, rheology and thermal structure of the lithosphere; this implies that we need better constraints on these parameters from the observations.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| 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".