Duluth Complex <scp>FC1</scp> Apatite and Zircon: Reference Materials for (<scp>U‐Th</scp>)/He Dating?
Bibliographic record
Abstract
The accuracy and validation of geo‐ and thermochronological dating hinges on the availability of well‐characterised age reference materials. The Mesoproterozoic gabbroic anorthosite FC1 from the Duluth Complex, Minnesota is a reference material for zircon U‐Pb and a suggested reference material for apatite fission‐track dating. We evaluate FC1 as (U‐Th)/He reference material, and determine its apatite U‐Pb, and zircon and apatite (U‐Th)/He age. Our dating results constrain the thermal history of FC1, showing that fast cooling occurred between ~ 1099 and 1040 Ma from ≥ 600 °C to ~ 200 °C. The zircon (U‐Th)/He data from air‐abraded grains give a robust isochron age of 1037 ± 25 Ma (2 s ) without overdispersion. The within‐grain homogeneity of U and Th, the availability of FC1 zircon, and the absence of radiation‐damage effects on the (U‐Th)/He age support its use as reference material. Unabraded zircon grains give lower and more dispersed ages, highlighting the usefulness of air abrasion to control for α‐ejection in (U‐Th)/He dating. Our apatite (U‐Th‐Sm)/He single‐grain ages vary between 180 and 300 Ma. Their wide dispersion argues against the use of FC1 apatite as (U‐Th‐Sm)/He reference material and makes the interpretation of their low‐temperature thermal history complicated.
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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 | 0.005 | 0.008 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 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".