Basalt melts under pressure: Is there really a viscosity minimum?
Bibliographic record
Abstract
Basalts are the most numerous and voluminous magmas on Earth, the moon and many other terrestrial planets and moons. Melt viscosity plays a major role in modulating the rates and efficacy of many magmatic and volcanic processes (e.g., melt extraction, ascent rates, eruption styles). The pressure dependence of melt viscosity is particularly relevant to basalts because of the wide range of pressures they experience during ascent from their mantle sources to Earth's surface. Here, we review and critically analyse the published high pressure experimental data for the viscosity of basaltic melts. Our compilation of high-pressure measurements of basalt viscosity is relatively sparse comprising a total of 56 experiments. The experiments span a temperature range of 1275 to 2000 °C, pressures from 0.5 to 7 GPa, and anhydrous melt compositions ranging from MORB, to Hawaiian tholeiite, to alkali olivine basalt (AOB). We focussed our analysis on nineteen modern falling sphere experiments on MORB ( Sakamaki et al., 2013 ) and AOB ( Bonechi et al., 2022 ) melts that were imaged with real-time, x-ray radiography. Our analysis of these data suggests a monotonic positive pressure dependence for basaltic melt viscosity. On that basis, we present a predictive model for the Newtonian viscosity of AOB melts as a function of temperature (T), pressure (P): log η = − 4.55 + 7845.4 + 295.4 P GPa − 0.001 T K A similar model applied to the MORB dataset is consistent with a significantly lower (i.e. 13.3 vs. 295.4) positive pressure coefficient implying a less pressure-dependent viscosity. Our observations call into question the concept of a minimum in the pressure dependence of basaltic melt viscosity which has been argued to inhibit the ascent of basaltic magmas. • High-pressure experimental data ( N = 56) on basaltic melt viscosity are compiled. • Modern experiments ( N = 19) show basalt viscosity to have positive P-dependence. • Alkaline basalts have a stronger positive P-dependence than MORB. • Critical analysis of extant data suggests no P-driven minimum to basalt viscosity.
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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) | 0.003 | 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".