SYNCING FAULT ROCK CLOCKS; DIRECT COMPARISON OF U-PB CARBONATE AND K-AR ILLITE FAULT DATING METHODS
Bibliographic record
Abstract
The timing of slip on brittle faults in Earth's upper crust is difficult to constrain, and direct radiometric dating of fault-generated materials is the most explicit approach.Here we make a direct comparison between K-Ar dating of fault gouge clay (authigenic illite) and U-Pb dating of carbonate slickenfibers and veins from the same fault.We have dated fault generated materials from the Big Creek fault, a northwest-striking, dextral strike-slip fault system in Yukon Territory, Canadian Cordillera.Both methods yielded dates at ca. 73 Ma and ca.60-57 Ma, representing at least two periods of fault slip that form part of a complex fault and fluid-flow history.The Cretaceous result lies within previous indirect estimates for major slip on the fault.The Paleocene-Eocene result coincides with the estimated timing of slip of the nearby Tintina and Denali faults, which are crustal-scale, northwest-striking dextral faults, indicating Big Creek fault reactivation during regional faulting.The coincidence of periods of carbonate-crystallizing fracturing and fluid flow with intervals of seismic, gouge-generating slip supports the fault valve model, where fault strength is mediated by fluid pressures, and fluid emplacement requires seismic pumping in otherwise impermeable aseismic fault zones.The reproducibility of slip periods for distinct fault-generated materials using different decay systems indicates that these methods provide complimentary results and can be reliably applied to date brittle fault slip, opening new opportunities for investigating fault conditions with associated mineralizing fluid events. DATING BRITTLE FAULTSBrittle faults record past seismic slip events and are major fluid conduits, channeling magma, ore-generating fluids, oil, gas, and water (Haines et al., 2016).In the fault valve model, fluids mediate fault strength, acting as a catalyst for seismic slip (Sibson, 1992).Determining periods of frictional slip and fault-related fluid flow is critical for testing fault strength models.Fault histories are also important for building regional tectonic frameworks, understanding ore genesis, forming basin evolution models, and studying seismically active faults that pose geohazards and engineering challenges (e.g., Zwingmann et al., 2010).Fault timing is typi-
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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 | 0.002 | 0.005 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 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".