STRAIN LOCALIZATION DUE TO RHEOLOGICAL HETEROGENEITY ACROSS A CRUSTAL-SCALE INTRACONTINENTAL SHEAR ZONE
Bibliographic record
Abstract
The relative importance of distributed versus localized strain remains a matter of intense debate regarding orogenic plateau development, particularly in Tibet where through-going crustal-scale faults are required to explain large magnitudes of displacement and strainpartitioning. We present results from an exhumed lower crustal shear zone that point to a rheological dichotomy during Paleoproterozoic transpressive strain in the western Canadian Shield. This dichotomy provides insight into the topography across eastern Tibet, i.e. the Longmen Shan region and Sichuan basin, which has been interpreted to be the result of strainlocalization induced by differences in crustal strength at depth. The Grease River shear zone (GRsz) is a 5-7 km-wide, >400 km-long shear zone that cuts the Athabasca granulite terrane, one of Earth’s largest exposures of continental lower crust (>20,000 km). The GRsz is dominated by penetrative NE-striking, steeply NW-dipping foliations with gently SW-plunging stretching lineations and dextral SW-over-NE kinematics. Neoarchean top-to-the-SE flow of weak lower crust (sub-horizontal fabric at ca. 2.60-2.55 Ga) in the Athabasca granulite terrane exposed SE of the GRsz was followed by >650 m.y. of nearisobaric cooling and strengthening of continental lithosphere. In contrast, melt-weakened flow and shallow SW-dipping fabric development in lower crust exposed NW of the GRsz occurred at ca. 1.93-1.90 Ga during culmination of the Taltson orogeny. Melt-weakened flow NW of the GRsz was coincident with ca. 1.92-1.90 Ga dextral transpressive strain along the GRsz. Southeast of the GRsz, deformation was restricted to discrete 10s of m-scale moderatelyto steeply-dipping shear zones in rocks that had previously dehydrated and isobarically-cooled in the Neoarchean. This pattern of pervasive ductile flow contrasted with localized strain illustrates the dramatic effects of rheological heterogeneity across a transcurrent shear zone. This is analogous to the inferred low viscosity flow of crust around the rigid basins that bound the Tibetan Plateau (i.e., the Sichuan and Tarim basins).
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".