Integration of white mica in situ 87Rb/87Sr with in situ and step-heat 40Ar/39Ar dates in orogenic settings
Bibliographic record
Abstract
White mica is common in continental rocks, and often (de)forms in response to structural and metamorphic processes in orogenic settings. It has been most typically dated via step heat or in situ 40 Ar/ 39 Ar methods. However, with in situ 87 Rb/ 87 Sr geochronology now possible via in line mass-chemical-mass filtering of Rb and Sr isotopes in tandem mass spectrometers, the contrasting accumulation of radiogenic Ar vs. Sr in white mica under deformation and metamorphism should allow for more nuanced and improved interpretations of the geological evolution of white mica. Here, we apply the in situ 87 Rb/ 87 Sr dating method to white mica previously dated with the in situ and step heat 40 Ar/ 39 Ar methods in three case studies with contrasting structural and metamorphic histories. The results of these comparative studies are used to propose a framework for interpreting paired white mica 40 Ar/ 39 Ar and 87 Rb/ 87 Sr datasets. In general, white mica 87 Rb/ 87 Sr ages are expected to be equivalent to 40 Ar/ 39 Ar ages under conditions of low temperature metamorphic, fluid-mediated, or dynamic (re-) crystallization. Under high temperature conditions of igneous or metamorphic white mica (re-)crystallization, 87 Rb/ 87 Sr ages are more likely to represent the (re-)crystallization event, with 40 Ar/ 39 Ar ages representing post-crystallization cooling. Deformation and/or dynamic (re-)crystallization of white mica can produce complex, spatially controlled age patterns for both chronometers, requiring more nuanced interpretations. These results and framework point to the value of combining both chronometers in orogenic studies to reduce uncertainties in interpretation and test assumptions in dating metamorphic and deformation processes in orogens. • In situ 87 Rb/ 87 Sr white mica dating provides distinct information from 40 Ar/ 39 Ar white mica dating. • Combining these data can be used to resolve orogenic processes such as metamorphism, deformation and metasomatism. • We present a framework for interpreting the geological significance of 87 Rb/ 87 Sr vs. 40 Ar/ 39 Ar age patterns in white mica.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.000 | 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 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".