Crystal Size Distribution of Plagioclase and Amphibole from Soufriere Hills Volcano, Montserrat: Evidence for Dynamic Crystallization-Textural Coarsening Cycles
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Bibliographic record
Abstract
The crystal size distributions (CSDs) of plagioclase and amphibole were determined from andesites of the Soufri ere Hills volcano, Montserrat. Plagioclase occurs as separate crystals and as chadocrysts in large amphibole oikocrysts. The chadocrysts represent an earlier stage of textural development, preserved by growth of the oikocryst. Seventeen rock and eight chadocryst plagioclase CSDs are considered together as a series of samples of textural development. All are curved, concave up, and coincident, differing only in their maximum crystal size. Three amphibole CSDs have a similar shape and behaviour, but at a different position from the plagioclase CSDs. A dynamic model is proposed for the origin of textures in these rocks. Crystallization of plagioclase started following emplacement of andesite magma at a depth of at least 5 km. A steep, straight CSD developed by nucleation and growth. This process was interrupted by the injection of mafic magma into the chamber, or convective overturn of hotter magma. The magma temperature rose until it was buffered, initially by plagioclase solution and later by crystallization. During this period textural coarsening (Ostwald ripening) of plagioclase and amphibole occurred: small crystals dissolved simultaneously with the growth of large crystals. The CSD became less steep and extended to larger crystal sizes. Early stages of this process are preserved in coarsened amphibole oikocrysts. Repetitions of this cycle generated the observed family of CSDs. Textural coarsening followed the `Communicating Neighbours' model. Hence, each crystal has its own, unique growthsolution history, without appealing to mixing of magmas that crystallized in different environments.
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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 | 0.001 |
| 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 it