<sup>40</sup>Ar/<sup>39</sup>Ar Geochronology and Geochemical Reconnaissance of the Eocene Lowland Creek Volcanic Field, West‐Central Montana
Bibliographic record
Abstract
We report geochronological and geochemical data for the calc‐alkalic Lowland Creek volcanic field (LCVF) in west‐central Montana. 40Ar/39Ar age determinations show that the LCVF was active from 52.9 to 48.6 Ma, with tuff‐forming eruptions at $$52.9\pm 0.14$$ and $$51.8\pm 0.14$$ Ma. These dates span the age range of vigorous Eocene igneous activity in the Kamloops‐Absaroka‐Challis belt. The LCVF evolved upward from basal rhyolites ($$\mathrm{SiO}\,_{2}> 71\,\mathrm{wt}\,\% $$ ) to dacites and andesites ($$\mathrm{SiO}\,_{2}< 62\,\mathrm{wt}\,\% $$ ). Compositional change parallels a transition from early explosive volcanism to late effusive activity. Four geochemical components can be detected in the rocks. A component with $$^{206}\mathrm{Pb}\,/ {}^{204}\mathrm{Pb}\,< 16.5$$ and εNd near −15 is predominant in anhydrous, two‐pyroxene dacites; hydrous rhyolites, rhyodacites, and dacites with εNd below −10 are dominated by a second component; hydrous rocks with $$^{206}\mathrm{Pb}\,/ {}^{204}\mathrm{Pb}\,> 18.3$$ and $$\varepsilon _{\mathrm{Nd}\,}> -9$$ contain a third component; and an andesite with low Nd content and εNd near −9 probably contains a fourth component. The first three components probably derive from the lower and middle crust, whereas the fourth is probably from the lithospheric mantle.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.010 | 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".