Formation of multistage garnet grains by fragmentation and overgrowth constrained by microchemical and microstructural mapping
Bibliographic record
Abstract
Abstract Garnet is an exceptionally useful mineral for reconstructing the evolution of metamorphic rocks that have experienced multiple tectonic or thermal events. Understanding how garnet crystallizes and its mechanical behaviour is important for establishing a petrological and temporal record of metamorphism and deformation and for recognizing multiple geologic stages within the growth history of an individual crystal. Here, we integrate fine‐scale microstructural (electron backscatter diffraction [EBSD]) and microchemical (Laser Ablation Inductively Coupled Plasma Mass Spectrometry [LA‐ICP‐MS] mapping) data obtained on a polycyclic garnet‐bearing micaschist from the Alpine belt. Results suggest that fragmentation of pre‐Alpine garnet porphyroblasts occurred during the late pre‐Alpine exhumation and/or the onset of the Alpine burial, such that the older pre‐Alpine garnet fragments were transported/redistributed during Alpine deformation and acted as nucleation sites for Alpine garnet growth. These processes produced a bimodal garnet size distribution (millimetre‐ and micrometre‐sized grains). Thermodynamic modelling indicates that Alpine garnet grew during the final stage of burial (from 1.9 GPa 480°C to 2.0 GPa 520°C) and early exhumation (down to 1.6 GPa 540°C) forming continuous idioblastic rims on and sealing fractures in pre‐Alpine garnet grains. We propose that fragmentation–overgrowth processes in polycyclic rocks, coupled with ductile deformation, may produce a bimodal garnet size distribution in response to fragmentation and re‐distribution of pre‐existing grains; these clasts can act as new nucleation sites during a subsequent orogenic cycle.
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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 | 0.000 |
| 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) | 0.001 | 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 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".