Experiments and models on H2O retrograde solubility in volcanic systems
Bibliographic record
Abstract
We present a suite of 36 high-temperature (900-1100 °C) experiments performed on 10 × 10 mm unjacketed cores of rhyolitic obsidian from Hrafntinnuhryggur, Krafla, Iceland, under atmospheric pressure. The obsidian is bubble- and crystal-free with an H2O content of 0.11(4) wt%. The obsidian cores were heated above the glass transition temperature (Tg), held for 0.25-24 h, then quenched. During each experiment the volume of the samples increased as H2O vapor-filled bubbles nucleated and expanded. Uniquely, the bubbles did not nucleate on the surface of the core, nor escape, conserving mass during all experiments. Within each isothermal experimental suite, the cores increased in volume with time until they reached a maximum, after which continued heating caused no change in volume (measured by He-pycnometry). We interpret these T-t conditions as representing thermochemical equilibrium between the melt and exsolved vapor. These experiments are modeled to recover the 1-atm, temperature-dependent solubility of water in the rhyolite melt. Our results define the magnitude of retrograde solubility (-7.1 × 10-3 wt% H2O per 100 °C) and provide estimates of the enthalpy and entropy of the H2O exsolution reaction [ΔH° = 17.8 kJ/mol, ΔS° = 107 J/(K·mol)]. We conclude by modeling the implications of retrograde solubility for the glass transition temperatures (Tg) of cooling volcanic systems at pressures relevant to volcanic conduits and the Earth's surface. All volcanic systems cool; the effects of retrograde solubility are to allow melts to rehydrate by H2O dissolution as they cool isobarically, thereby depressing Tg and expanding the melt window. Ultimately, the melt is quenched at higher H2O contents and lower temperatures where the isobaric retrograde solubility curve "catches" the evolving Tg.
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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) | 0.000 | 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".