Tectonic and petrogenetic evolution of sub-horizontal granulite-grade fabric in lower continental crust: Constraints on lower crustal flow from the western Canadian Shield
Bibliographic record
Abstract
Ductile, weak flow of continental lower crust is inferred for a number of orogenic systems, including the Andes and the Himalayan-Tibetan system. Sub-horizontal, high-temperature fabrics in rare exposures of exhumed lower continental crust provide important directly observable constraints on the physical mechanisms of lower crustal flow. This study uses m- to tens-of-km-scale examples of sub-horizontal granulite grade fabric in a large exposure of exhumed lower continental crust to constrain the conditions and timing of lower crustal flow. High-resolution electron microprobe monazite geochronology and trace element analysis in oriented tectonites reveals a protracted record of Neoarchean (ca. 2.63-2.53 Ga) garnet growth and sub-horizontal fabric development in migmatitic felsic granulites during lower crustal flow and subsequent cooling. Penetrative, sub-horizontal gneissic fabrics were over-printed by discrete steeply-dipping shear zones and upright folds. In situ dating of shear zones constrains the timing of sub-horizontal shortening and dextral shear strain to ca. 1.92-1.8 Ga. The results demonstrate the dynamic and evolving strength of continental lower crust. In this particular case, flow of relatively weak lower crust during production of sub-horizontal fabrics in the Neoarchean was followed by a period of near-isobaric cooling and strengthening. Subsequent Paleoproterozoic deformation events produced steep fabrics, outcrop- to crustal-scale steeply-dipping shear zones, and local reactivation of early sub-horizontal fabrics—a record of strain partitioning and strain hardening in an isobarically-cooled anisotropic medium.
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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 | 0.000 | 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 | 0.000 |
| 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".