From hot and strong to cold and weak: How ‘Refrigeration Weakening’ facilitates strain localization during subduction initiation
Notice bibliographique
Résumé
Temperature predictably controls mineral stability during metamorphism, and exerts first-order influence on rock viscosity during deformation, but the co-evolution of temperature-dependent metamorphic mineralogy and rock rheology is poorly understood. Thermally-controlled metamorphic-mechanical feedbacks must lead to strain localization during plate boundary formation. However, geologic observations from horizontally-forced, newly-destructive, intra-oceanic subduction plate boundaries consistently present a rheological paradox: hot rocks are strong and cold rocks are weak. Observations from geo-/thermochronology and metamorphic thermobarometry demonstrate that following a stage of initially slow, forced convergence along a hot plate interface when the slab tip resists downward translation, the lower plate suddenly collapses into the mantle. After this catastrophic collapse, subduction becomes self-sustaining (i.e., slab pull is established), stable, and cold. The physical mechanism triggering collapse is unknown, though geological studies show that collapse occurs contemporaneously with rapid cooling of the nascent plate contact and depression of slab-parallel isotherms, or “refrigeration”. These observations imply that hot rocks are strong (i.e., viscously sticky), and cold rocks are weak (i.e., viscously lubricating). It is puzzling why the resistance phase would be characterized by the highest temperature metamorphism, since high-temperature rocks are commonly viscously weak; furthermore, plate boundary “unzipping” and lithosphere-scale localization only occur during the rapid refrigeration phase, when rocks should, to a first order, be stiffer and less deformable. What mechanism(s) overcome stiffening, such that a temperature decrease leads to rock weakening, strain localization, and successful subduction initiation? Here, we compare microstructures from metamorphic rocks that formed along ancient hot, warm, and cold plate interfaces that correspond to different stages in the evolution of subduction zone formation from initiation to self-sustaining. We conclude that refrigeration drives changes in metamorphic mineral stability, distributions of strain-accommodating minerals, fluid content, and deformation mechanisms, which together dramatically weaken the developing plate boundary. We use flow laws and paleopiezometry to bracket ductile rock strength and demonstrate that cooling at the time of inferred slab collapse causes a minimum 3 order of magnitude viscosity reduction from ~1021 to 1018 Pa-s—the most drastic change in viscosity over a subduction zone’s lifetime. The viscosity reduction leads to a series of dynamic feedbacks, namely: interface decoupling and accelerated plate rates; increased and sustained interface cooling; and stabilization of a wetter, weaker interface. Our ‘refrigeration weakening’ hypothesis embodies a coupled metamorphic-mechanical process that is inherent to the evolution of common oceanic crust, and successfully explains observed changes in upper plate stress state, inferred slab velocity, and timing of proto-forearc seafloor spreading. If true, this mechanism motivates several new testable hypotheses regarding the dynamics of subduction zone development as a function of temperature changes in the modern Earth and throughout Earth’s history.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,001 | 0,001 |
| Communication savante | 0,002 | 0,002 |
| Science ouverte | 0,001 | 0,001 |
| Intégrité de la recherche | 0,001 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,007 | 0,002 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».