On the virtues and pitfalls of combined <i>laser ablation</i> Rb-Sr biotite and U-Pb monazite-zircon geochronology: an example from the isotopically disturbed Cape Woolamai Granite, SE Australia
Bibliographic record
Abstract
Different mineral clocks in granite can provide age information reflecting various aspects of rock formation, including cooling or post-emplacement fluid-rock interaction. However, the dating tool chosen can yield inconclusive age information due to differences in closure temperatures and susceptibility to fluid alteration among chronometers. This has led to an inferred superiority of U-Pb in zircon over U-Pb in monazites or Rb-Sr in micas. Here, we investigate age systematics using Rb-Sr biotite grains, U-Pb in monazite and zircons in a Devonian granite from Australia. Single-grain laser ablation ICP-MS/MS biotite analyses are combined with zircon-monazite U-Pb ages and trace element systematics. Textural and trace element evidence combined with age systematics reveals a Rb-Sr closure age of ~360–330 Ma relative to a putative 364 Ma emplacement age, suggesting hydrothermal alteration of the granite. Trace element systematics and magnetic susceptibility in biotites reflect their partial chemical reset and fluid overprint in the granite. Similar systematics are, however, also observed for zircon and monazite. Our multiple chronometer dating approach, studied with modern laser-ablation methods, highlights the need for detailed investigation of isotope and trace element systematics in single grains and that individual ages should be used cautiously when dating altered granitoids.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".