Weak and Slow, Strong and Fast: How Shear Zones Evolve in a Dry Continental Crust (Musgrave Ranges, Central Australia)
Bibliographic record
Abstract
Abstract The strike‐slip Davenport Shear Zone in Central Australia developed during the Petermann Orogeny (~550 Ma) in an intracontinental lower crustal setting under dry subeclogite facies conditions (~650 °C, 1.2 GPa). This approximately 5‐km‐wide mylonite zone encloses several large low‐strain domains, allowing a detailed study of the initiation of shear zones and their progressive development. Quartzo‐feldspathic gneisses and granitoids contain compositional layers, such as quartz‐rich pegmatites, mafic bands, and dykes, which should preferentially localize viscous deformation if favorably orientated. This is not observed, except for long, continuous, and fine‐grained dolerite dykes. Instead, many shear zones, typically a few millimeters to centimeters in width but extending for tens of meters, commonly exploited pseudotachylytes and are sometimes parallel to a network of little overprinted fractures. The recrystallized mineral assemblage in the sheared pseudotachylyte is similar to that in the host gneiss, without associated hydration due to fluid‐rock interaction. Lack of localization in quartz‐rich, coarser‐grained (typically >50 μm) rocks compared to mafic dykes, precursor fractures, and pseudotachylytes implies that localization in the dry lower crust preferentially occurs along elongate, planar fine‐grained layers. Transient high stress repeatedly initiated fractures, providing finer‐grained, weaker, planar precursors that localized subsequent ductile shear zones. This intimate interplay between brittle and ductile deformation suggests a local source for lower crustal earthquakes, rather than downward migration of earthquakes from the shallower, usually more seismogenic part of the crust.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| 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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".