Non-lithostatic eclogitization in exhuming continental crust
Bibliographic record
Abstract
During collisional orogeny, the lower continental plate is typically subjected to pressures no greater than 3 GPa (~100 km). Locally, however, ultrahigh-pressures (UHP) in excess of 5 GPa have been recorded, most commonly in included metamorphosed mafic-ultramafic rocks. Such pressures would suggest burial of continental crust to mantle depths; however, continental subduction to such depths is not observed in active orogens as it is hindered by the positive buoyancy of sialic crust relative to the mantle. An alternative explanation for extreme pressures recorded in continental crust is that they reflect non-lithostatic conditions, an idea that has been limited to modelling experiments and thus its applicability to natural systems is highly debated. Specifically, it was proposed that mechanical heterogeneities could explain extreme non-lithostatic pressures of c. 5.5 GPa obtained in enstatite eclogite veins cross-cutting a peridotite hosted in the archetypal subducted continental terrane, the Western Gneiss Complex (WGC) in Norway. Here, we use thermobarometry and Lu-Hf garnet geochronology to determine at what conditions and at what point in the burial cycle the enstatite eclogite assemblages actually equilibrated. The results show that the enstatite eclogites equilibrated at pressures of 4-5.5 GPa and at c. 393 Ma; these conditions are greater than those typical of ‘normal’ eclogites in the WGC and the age represents a time when the terrane had already exhumed to crustal depths (<2.5 GPa). Finite element modeling of mechanical pressure distribution can explain the seemingly spurious conditions recorded in these unusual rocks and demonstrates that these late extreme pressure excursions are feasible for the given rock system. Although the occurrence of non-lithostatic UHP conditions in deeply buried continental crust may, indeed, be unusual, it allows crucial simplification of models for continental subduction and validates the importance of integrating rock thermo-mechanics with geochronology and thermobarometry in interpreting observations from collision zones.
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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 | 0.000 | 0.001 |
| 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".