Reconstructing detailed P-T-t paths of kyanite-bearing, migmatitic metapelites through combined petrochronology and garnet diffusion modelling
Bibliographic record
Abstract
This contribution presents new results of multi-component garnet diffusion modelling (with the software CZGM 1 ) for wellstudied kyanite-bearing migmatitic metapelites from the northern Monashee Complex in the southeastern Canadian Cordillera.In the immediate footwall of the Monashee décollement, a controversial tectonic boundary, garnet with diameters >2.5 mm preserve prograde zoning defined by bell-shape X sps (Mn endmember in garnet), saddle-shape X prp (Mg end-member) and inverse saddle -shape X grs (Ca end-member).In contrast, zonation for all garnet end-members in grain examined from the immediate hanging wall of the shear zone is flat irrespective of grain size.Plausible Pressure-Temperature-time (P-T-t) paths are well-documented in three published petrochrological studies based on phase equilibria modelling and U(-Th)-Pb geochronology on zircon and monazite.This timing information demonstrates that only the garnet diffusion-parameters derived from Chu&Ague (2015 2 ) are able to model the preservation of the observed X sps profiles in the footwall.The diffusion modelling results indicate a maximal T of <800 o C and implies that the shortest T-t path (<10 Myrs at T >700 o C), plausible within the uncertainties of the petrochronological data, is required to preserve the observed X sps , X prp profiles.Diffusion modelling of hanging wall garnet, in contrast, indicates that a thermal history including peak T = 900 o C, 40 Myrs at T >700 o C and 28 Myrs at T>800 o C are required to completely flatten X grs zoning.The differential results demonstrate that the Monashee décollement juxtaposes rocks with completely different T-t histories, and, therefore, constitutes a major tectonic discontinuity.Results presented herein further demonstrate that diffusion modelling and petrochronolgy provide the complementary information required to derive a complete P-T-t path of migmatitic metapelites.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".