Initiation and development of the Twelve Mile Bay shear zone: the low viscosity sole of a granulite nappe
Bibliographic record
Abstract
Structural, microstructural and petrological data have enabled determination of the mechanical and geochemical processes involved in dynamic weakening and fabric transposition along the margins of a granulite nappe [the Parry Sound domain (PSD)] during transport to mid-crustal levels of the Grenville Orogen. The data establish a genetic link between outcrop-scale structures in the southern PSD and the development of the underlying Twelve Mile Bay shear zone (TMBSZ). Following granulite facies metamorphism (∼11 kbar/∼850 °C) in the southern PSD, the emplacement of pegmatite dykes resulted in hydration reactions within adjacent wall rocks and the development of thin (<1 m) amphibolite facies (∼6.5 kbar/∼700 °C) shear zones. The shear zones exhibit bulk H2O and K2O enrichment and oxygen isotope values similar to the adjacent pegmatites, suggesting metasomatic alteration by pegmatite-derived fluids. Phase-equilibrium models indicate that the destabilization of the pre-existing pyroxene and garnet-bearing assemblages, as observed within discrete shear zones in the southern PSD and the TMBSZ, requires H2O-saturated conditions at these (amphibolite facies) P–T conditions. The spacing between discrete shear zones and the depth of hydration into the adjacent wall rock are of comparable length-scales (∼metres), suggesting that this type of reworking process can be an effective means of hydrating kilometre-scale areas of crust relatively rapidly. Furthermore, considering the well-established effects of hydrous fluids on the creep strength of anhydrous minerals, a fracture-initiated, localized hydration-and-shearing process may be an efficient mechanism for weakening strong, dry rocks (e.g. granulites) in the middle to lower orogenic 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".