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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 January 1, 2027
Geophysical Impacts and Spectroscopic Identification of a Hydrous Iron Sulfate on Icy Worlds
Abstract Over geologic time‐scales, large volumes of exogenic sulfur ions from Io's plasma torus have been supplied to the surface of Europa and Ganymede, which, combined with recent interpretations of orbiter images, dynamical modeling, and surface‐subsurface exchange, suggests further sulfur transport into the interior of the icy worlds. These observations motivate mixed‐phase spectral modeling for interpreting orbiter spectroscopy data and determination of hydration states of candidate surface materials including hydrous sulfates. In this work, we present a combined experimental and theoretical study of the low temperature and high pressure vibrational spectral signature of the iron‐sulfate monohydrate endmember, szomolnokite (FeSO4·H2O). By employing synchrotron Fourier‐transform infrared spectroscopy (FTIR) in the diamond anvil cell up to 23 GPa and down to 20 K, we explore the extreme range of pressure‐temperature domains relevant to icy environments throughout our solar system and beyond. Combined with our density‐functional theory quantum‐mechanics molecular dynamics results, we demonstrate that experimentally observed infrared features in the O‐H stretching region commonly associated withnH2O (n > 1) hydration states can be attributed to a pure monohydrate without the need for pressure‐induced exsolved ice, other coexisting hydrous iron sulfates, or strong overtone and combination modes. We further discuss the possibility of lateral variations in density and shear properties on icy worlds associated with temperature variations and the high‐pressure phases of kieserite group monohydrated sulfates.
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- Award ID(s):
- 2303148
- PAR ID:
- 10687088
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Planets
- Volume:
- 131
- Issue:
- 1
- ISSN:
- 2169-9097
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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