Nano-scale earthquake records preserved in plagioclase microfractures from the lower continental crust
Bibliographic record
Abstract
Abstract. Seismic faulting causes wall rock damage driven by both mechanical stress and thermal energy. In the lower crust, coseismic damage has important implications for wall rock permeability, the progress of subsequent fluid-driven metamorphic reactions, and rock rheology. Wall rock microstructures reveal high-stress conditions near the slip surface during lower crustal earthquakes, however, there is limited documentation on the thermal effect. Here, we present a transmission electron microscopy study of coseismic microfractures in plagioclase feldspar from lower crustal granulites from the Bergen Arcs, Western Norway. Focused ion beam foils are collected 1.25 mm and 1.8 cm from a 2 mm thick eclogite facies pseudotachylyte vein. Dislocation-free plagioclase aggregates fill the microfractures and record a history of recovery from a short-lived high stress-temperature (σ-T) state caused by seismic slip and frictional melting along the nearby fault surface. The plagioclase aggregates retain the crystallographic orientation of the host rock and shape preferred orientation relative to the fault slip surface. We propose that plagioclase partially amorphized along the microfractures at peak stress conditions followed by repolymerization to form dislocation-free grain aggregates within the timeframe of pseudotachylyte formation. The heat from the slip surface dissipated into the wall rock causing a short-lived temperature peak. Subsequent cooling led to exsolution of intermediate plagioclase compositions by spinodal decomposition within a few millimeters distance to the fault surface. Our findings provide microstructural evidence for the high σ-T conditions that are expected in the proximity of seismic faults, highlighting the importance of micro- and nanostructures for the understanding of earthquakes ruptures.
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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 | 0.000 |
| Scholarly communication | 0.000 | 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".