Structure and density of basaltic melts at mantle conditions from first-principles simulations

Bajgain, S. K.; Ghosh, Debashri; Karki, Bijaya B.

doi:10.1038/ncomms9578

Cited by 87 publications

(125 citation statements)

References 37 publications

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“…Partial molar volume ( V m ) of water in the melt can be calculated using V m = ( V − V 0 )/ n , where V is the volume of hydrous melt, V 0 is the volume of anhydrous melt, and n is the number of water “molecules” in the supercell. The V m results at 4,000 K shown in Figure are comparable with the previous calculations on hydrous basaltic melt (Bajgain et al, ). The partial molar volume of water thus appears to be weakly sensitive to melt composition over a wide pressure regime.…”

Section: Resultssupporting

confidence: 90%

“…We take a eutectic‐like melt of 16 MgSiO 3 • 14 FeO• 20 H 2 O (E13–16) as an example to study the evolution of water speciation with pressure. The general trend is that hydrogen and oxygen become increasingly polymerized with pressure, consistent with previous computational studies (Figure S1; Bajgain et al, ; Karki & Stixrude, ). The H‐O coordination environment consists of different species, including uncoordinated, one‐fold, two‐fold and three‐fold coordination, whose proportions change with pressure (Figure a).…”

Section: Resultssupporting

confidence: 89%

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Fate of Hydrous Fe‐Rich Silicate Melt in Earth's Deep Mantle

Deng

Miyazaki

et al. 2019

Geophysical Research Letters

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Density of silicate melt dictates melt migration and establishes the gross structure of Earth's interior. However, due to technical challenges, the melt density of relevant compositions is poorly known at deep mantle conditions. Particularly, water may be dissolved in such melts in large amounts and can potentially affect their density at extreme pressure and temperature conditions. Here we perform first‐principles molecular dynamics simulations to evaluate the density of Fe‐rich, eutectic‐like silicate melt (E melt) with varying water content up to about 12 wt %. Our results show that water mixes nearly ideally with the nonvolatile component in silicate melt and can decrease the melt density significantly. They also suggest that hydrous melts can be gravitationally stable in the lowermost mantle given its likely high iron content, providing a mechanism to explain seismically slow and dense layers near the core‐mantle boundary.

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Section: Resultssupporting

confidence: 90%

Section: Resultssupporting

confidence: 89%

Fate of Hydrous Fe‐Rich Silicate Melt in Earth's Deep Mantle

Deng

Miyazaki

et al. 2019

Geophysical Research Letters

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“…Bajgain et al . [] presented density functional theory‐based results on the behavior of hydrous and anhydrous basaltic melts with pressure, noting steep gradients in the coordination increases of Ca‐O, Na‐O, and Si‐O from ambient pressure to about 40 GPa. This particular densification does not appear to affect the electron density near the nucleus of iron, as evidenced by the relatively flat trend of the IS up to about 20 GPa for both glasses.…”

Section: Discussionmentioning

confidence: 99%

Electronic environments of ferrous iron in rhyolitic and basaltic glasses at high pressure

et al. 2017

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The physical properties of silicate melts within Earth's mantle affect the chemical and thermal evolution of its interior. Chemistry and coordination environments affect such properties. We have measured the hyperfine parameters of iron‐bearing rhyolitic and basaltic glasses up to ~120 GPa and ~100 GPa, respectively, in a neon pressure medium using time domain synchrotron Mössbauer spectroscopy. The spectra for rhyolitic and basaltic glasses are well explained by three high‐spin Fe2+‐like sites with distinct quadrupole splittings. Absence of detectable ferric iron was confirmed with optical absorption spectroscopy. The sites with relatively high and intermediate quadrupole splittings are likely a result of fivefold and sixfold coordination environments of ferrous iron that transition to higher coordination with increasing pressure. The ferrous site with a relatively low quadrupole splitting and isomer shift at low pressures may be related to a fourfold or a second fivefold ferrous iron site, which transitions to higher coordination in basaltic glass, but likely remains in low coordination in rhyolitic glass. These results indicate that iron experiences changes in its coordination environment with increasing pressure without undergoing a high‐spin to low‐spin transition. We compare our results to the hyperfine parameters of silicate glasses of different compositions. With the assumption that coordination environments in silicate glasses may serve as a good indicator for those in a melt, this study suggests that ferrous iron in chemically complex silicate melts likely exists in a high‐spin state throughout most of Earth's mantle.

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“…The Pulay stress arising from the use of a finite cutoff of 400 eV at Γ point was added. Further details can be found elsewhere513.…”

Section: Methodsmentioning

confidence: 99%

“…Whether melt will ascend or descend in a partially molten mantle at a depth depends on density contrast between the melt and the surrounding solid mantle34567. Negatively buoyant (sinking) melts imply that a high degree of partial melting or a basal magma ocean may be present in the deepest parts of the mantle89.…”

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Solid-liquid density and spin crossovers in (Mg, Fe)O system at deep mantle conditions

Ghosh

Karki

2016

Sci Rep

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The low/ultralow-velocity zones in the Earth’s mantle can be explained by the presence of partial melting, critically depending on density contrast between the melt and surrounding solid mantle. Here, first-principles molecular dynamics simulations of (Mg, Fe) O ferropericlase in the solid and liquid states show that their densities increasingly approach each other as pressure increases. The isochemical density difference between them diminishes from 0.78 (±0.7) g/cm3 at zero pressure (3000 K) to 0.16 (±0.04) g/cm3 at 135 GPa (4000 K) for pure and alloyed compositions containing up to 25% iron. The simulations also predict a high-spin to low-spin transition of iron in the liquid ferropericlase gradually occurring over a pressure interval centered at 55 GPa (4000 K) accompanied by a density increase of 0.14 (±0.02) g/cm3. Temperature tends to widen the transition to higher pressure. The estimated iron partition coefficient between the solid and liquid ferropericlase varies from 0.3 to 0.6 over the pressure range of 23 to 135 GPa. Based on these results, an excess of as low as 5% iron dissolved in the liquid could cause the solid-liquid density crossover at conditions of the lowermost mantle.

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Structure and density of basaltic melts at mantle conditions from first-principles simulations

Cited by 87 publications

References 37 publications

Fate of Hydrous Fe‐Rich Silicate Melt in Earth's Deep Mantle

Fate of Hydrous Fe‐Rich Silicate Melt in Earth's Deep Mantle

Electronic environments of ferrous iron in rhyolitic and basaltic glasses at high pressure

Solid-liquid density and spin crossovers in (Mg, Fe)O system at deep mantle conditions

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