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Abstract The continental crust is produced by the solidification of aluminosilicate‐rich magmas which are sourced from deep below the surface. Migration of the magma depends on the density (ρ) contrast to source rocks and the melt viscosity (η). At the surface, these silica‐rich melts are typically sluggish due to highη > 1,000 Pa s. Yet at their source regions, the melt properties are complexly influenced by pressure (P), temperature (T), and water contents (). In this study, we examined the combinedP‐T‐ effects on the behavior of melts with an albite stoichiometry (NaAlSi3O8). We usedfirst‐principlesmolecular dynamics simulations to examine anhydrous (0 wt % H2O) and hydrous (5 wt % H2O) melts. To constrain thePandTeffects, we exploredP ≤ 25 GPa across several isotherms between 2500 and 4000 K. The melts show anomalousP‐ρrelationships at lowP ∼ 0 GPa and highT ≥ 2500 K, consistent with vaporization. At lithospheric conditions, meltρincreases with compression and is well described by a finite‐strain formalism. Water lowers the melt density (ρhydrous < ρanhydrous) but increases the compressibility, that is, 1/Khydrous>1/KanhydrousorKhydrous < Kanhydrous. We also find that the meltηdecreases with pressure and then increases with further compression. Water decreases the viscosity (ηhydrous < ηanhydrous) by depolymerizing the melt structure. The ionic self‐diffusivities are increased by the presence of water. The decreasedρandηby H2O increase the mobility of magma at crustal conditions, which could explain the rapid eruption and migration timescales for rhyolitic magmas as observed in the Chaitén volcano in Chile.
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This content will become publicly available on December 1, 2026
Viscosity of Dry and Hydrous Diopside Melts at High Pressures: Implications for Upper Mantle Magma Dynamics
Abstract Viscosity of silicate melts governs magma transport and influences mantle dynamics, yet effects of pressure and water on melt viscosity remain poorly understood. Here, we report in situ falling‐sphere viscosity measurements on diopside (Di) melts with 0–3 wt.% H2O along the liquidus up to 7 GPa and 2103 K using synchrotron X‐ray radiography. By incorporating our hydrous melt data into a previously validated model for the dry system, the effects of pressure, temperature, and H2O contents on Di melt viscosity can be satisfactorily captured by the function: whereT*is the homologous temperature,xH2Ois the molar % H2O,η0 = 8.90 (1.50) × 10−8 Pa s,b0 = 3.02 (0.10), andH*(P) = 15.72 (0.03)−0.35 (0.01)·P + 1.07 (0.07) × 10−2·P2−1.19 (0.14) × 10−4 P3, ×10−3 GPa−1. Adding 3 wt.% H2O systematically reduces viscosity by ∼0.7 log units. For both dry and hydrous melts, viscosity along the liquidus decreases monotonically with increasing pressure, suggesting that moderate hydration may not significantly alter the compressional behavior of Di melts. Combining the Di viscosity model with models for feldspar and olivine, we simulated the viscosity of analog basaltic magmas under mantle conditions. Increasing H2O content from 0 to 3wt.% raises mobility of basaltic magma increases by >1 order of magnitude. In hot plume settings, the mobility further increases by a factor of 30 relative to typical ambient mantle. Assuming a simple percolation model, the increased mobility corresponds to faster melt ascent in mantle plumes that could, in part, explain the voluminous magmatism of large igneous provinces.
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- Award ID(s):
- 2246803
- PAR ID:
- 10672636
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 130
- Issue:
- 12
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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