FTIR Spectrum of Phenocryst Olivine as an Indicator of Silica Saturation in Magmas
Bibliographic record
Abstract
Fourier Transform infrared (FTIR) absorption spectra of hydroxyl were measured on olivine phenocrysts from hydrous basaltic melts that originated in island-arc tectonic settings. The basaltic melts encompass a wide range of silica activities from orthopyroxene-saturated hypersthene-normative to nepheline-normative compositions. The intensities and wavenumber placement of hydroxyl absorption bands correlate with the degree of silica saturation of the parent melt from which the olivine crystallized. Olivines from silica-undersaturated nepheline-normative melts absorb IR radiation in the wavenumber range 3430–3590 cm−1 (Group 1). In contrast, olivines from orthopyroxene-saturated boninitic melts exhibit hydroxyl absorption bands in the wavenumber range 3285–3380 cm−1 (Group 2). Olivines crystallized at intermediate silica activities exhibit a combination of the two groups of hydroxyl IR bands, where the proportion of Group 2 bands increases with increasing silica saturation of the parent melt. The positions of hydroxyl absorption peaks observed here for natural samples are consistent with previous measurements on experimentally annealed olivines. Thus protonation experiments can be employed to make spectroscopically dry olivine structures visible by IR, yielding information on the silica saturation of the parental magmas. Hydroxyl concentrations in the studied olivines were estimated to be 1–2 ppm, corresponding to an olivine–melt partition coefficient of ∼(1·0 ± 0·3) × 10−4.
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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 | 0.000 |
| 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 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".