Coupled Mineral-Mechanical Changes During Plate Interface Cooling May Explain Catastrophic Subduction Initiation
Bibliographic record
Abstract
Subduction initiation often begins with slow, forced convergence, switches ‘on’ catastrophically as the slab collapses into the mantle, and then evolves to steady-state, self-sustained sinking that drives global plate movements. Numerical models suggest that the collapse phase implies sudden weakening of the plate interface. However, geological records of subduction infancy preserved as metamorphosed oceanic crust accreted beneath ophiolites (i.e., metamorphic soles) present a paradox. During the pre-collapse period that may last 2–15 million years, the nascent plate interface is hot, whereas during collapse, shear zone temperatures plummet, which typically strengthens rocks. So, how does cooling cause weakening? Here, we show microstructures of metamorphic sole rocks from Mont Albert (Québec, Canada) that demonstrate that upon cooling, metamorphic mineralogy became more heterogeneous, average grain size decreased, and deformation mechanisms shifted from dislocation-accommodated to fluid-assisted and grain size sensitive, which culminated in drastic rheological weakening. Quartz piezometry indicates that flow stress increased with cooling, but flow laws indicate that the colder rocks exhibited lower viscosity, and therefore could localize strain. Interface viscosity initially rose with cooling, but upon reaching a threshold where major metamorphic minerals changed, dropped from >10 18 to <10 17 Pa-s. Cooling-induced mineral-mechanical changes thus drove rheological weakening, and provide a general mechanism explaining slab collapse and the transition to self-sustaining subduction. This implies that strain localization is inherent to modern metamorphosed oceanic lithosphere, and does not require a ‘stress drop’. The next step to understanding subduction initiation is identifying causes of high temperatures and incipient cooling during the pre-collapse phase.
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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 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 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".