In situ mica Rb–Sr geochronology and microstructural analysis to evaluate the timing and sense of shear zone movement: Shannon and d'Abbadie Faults, Yukon, Canada
Bibliographic record
Abstract
This study examines the microstructural and geochronological record in specimens collected along transects away from the Shannon fault and d'Abbadie fault, in the northern Canadian Cordillera. Microstructural analysis for both shear zones indicate dextral shear and an increase in paleostress and inferred strain magnitude toward each fault. In situ mica Rb–Sr geochronology from across a strain gradient developed by a single phase of deformation within the Shannon pluton, adjacent to the Shannon fault, dominantly records syn-emplacement deformation and/or rapid cooling at ca. 100 Ma with sparse analyses ranging to as young as ca. 63 Ma. U–Pb geochronology in apatite from the same specimens returns three ca. 100 Ma dates and two ca. 85 Ma dates. In contrast, lithologically heterogenous specimens that have experienced multiple deformational events, collected in proximity to the d'Abbadie fault, exhibit more variation in Rb–Sr dates, ranging from presumed regional cooling at ca. 195 Ma, a possible thermo-tectonic event at ca. 150 Ma, syn-pluton emplacement deformation and/or rapid cooling at ca. 100 Ma, and local partial resetting of Rb–Sr in mica most likely by brittle fault movement at ca. 80 Ma. U–Pb in apatite geochronology in the same specimens also records the ca. 100 Ma event. The results of this study demonstrate that lithological differences and multi-phase deformational histories create complexity in patterns of in situ Rb–Sr geochronology, and require interpretation within thermal and structural contexts, to quantify the timing of deformation in ductile high-strain shear zones.
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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 | 0.002 | 0.003 |
| Science and technology studies | 0.002 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".