Helium Diffusion in Natural Xenotime
Bibliographic record
Abstract
Abstract The typically high U and Th contents of xenotime ([Y,HREE]PO 4 ) make this accessory mineral a promising candidate for (U‐Th)/He thermochronometry if the 4 He diffusivity can be constrained well enough to estimate its closure temperature. We report new results for two 4 He step‐heating experiments on different‐sized fragments of a natural xenotime crystal from the Torghar district of Pakistan (FPX‐1). This material, which has a composition within the range of most natural xenotimes (72 mol % YPO 4 ), yields a laser ablation 238 U/ 206 Pb date of 28.82 ± 0.13 Ma and a (U‐Th)/He date of 15.32 ± 0.61 Ma (2 σ ). Results for our more detailed diffusion experiment display excellent linearity on an Arrhenius diagram and indicate kinetic parameters of E = 131.4 ± 1.1 kJ/mol and ln( D 0 / a 2 ) = 10.61 ± 0.20 ln( s −1 ). These results suggest that the bulk closure temperature for 4 He in the degassed crystal fragment is ∼75 °C for the nominal cooling rate of 10 °C/Ma. At equivalent cooling rates and for crystals with equivalent diffusion dimensions, the closure temperature for helium in xenotime is ∼20 °C lower than the closure temperature for helium in apatite. Because xenotime typically has high U and Th contents, it may serve as a high‐precision method for dating young, low‐temperature cooling histories of rocks in which it crystallized. Helium diffusion in xenotime is likely to be moderately anisotropic and moderately dependent on crystal chemistry, so closure temperature interpretations should be made cautiously.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.007 | 0.002 |
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; both teacher heads agree on what is shown here.
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".