Simulation of Silicate Melts Under Pressure

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

doi:10.1016/b978-0-12-811301-1.00016-2

Cited by 20 publications

(41 citation statements)

References 90 publications

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“…En melt and, to a lesser extent, Di melt show a negative pressure dependence in some pressure ranges. Such an anomalous behavior was also reported in a basalt and another silicate melt 18 , based on both FPMD simulation 19 and experimental measurements 20,21 . The negative pressure dependence is due to either the Si-O bond weakening by the pressure-induced bending of the Si-O-Si angle 21,22 or possibly the increasing concentration of five-fold Si-O coordination species 23,24 .…”

Section: Resultssupporting

confidence: 70%

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Formation of bridgmanite-enriched layer at the top lower-mantle during magma ocean solidification

et al. 2020

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Thermochemical heterogeneities detected today in the Earth's mantle could arise from ongoing partial melting in different mantle regions. A major open question, however, is the level of chemical stratification inherited from an early magma-ocean (MO) solidification. Here we show that the MO crystallized homogeneously in the deep mantle, but with chemical fractionation at depths around 1000 km and in the upper mantle. Our arguments are based on accurate measurements of the viscosity of melts with forsterite, enstatite and diopside compositions up to~30 GPa and more than 3000 K at synchrotron X-ray facilities. Fractional solidification would induce the formation of a bridgmanite-enriched layer at~1000 km depth. This layer may have resisted to mantle mixing by convection and cause the reported viscosity peak and anomalous dynamic impedance. On the other hand, fractional solidification in the upper mantle would have favored the formation of the first crust.

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Section: Resultssupporting

confidence: 70%

“…Combining Eqs. (19)(20)(21), we can obtain dc numerically. The Reynolds number in MO is less than 20 when grain size in MO equals critical size ( Supplementary Fig.…”

Section: à á ð21þmentioning

confidence: 99%

Formation of bridgmanite-enriched layer at the top lower-mantle during magma ocean solidification

et al. 2020

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“…At core‐mantle boundary pressures, the proportion of sixfold silicon decreases with increasing temperature from 80% at 3,000 K to 70% at 4,000 K to 55% at 5,000 K. The proportions of silicon in fourfold, fivefold, and sixfold coordination in pyrolite melt are essentially identical to the proportions in CaMgSi 2 O 6 melt at all pressures (Figure S3). Compared to simulations on MORB melt (Bajgain et al, ; Karki et al, ), the proportions of fourfold and fivefold silicon are slightly larger in pyrolite melt and CaMgSi 2 O 6 melt (Sun et al, ) while the proportion of sixfold silicon is a bit lower because of the different degrees of polymerization or M: Si ratios (where M is Mg, Ca, Fe, and other network‐modifier cations), which cumulatively explains the larger average coordination of silicon in MORB melt. The average coordination of silicon at high pressure is likely dependent on the degree of polymerization of the melt.…”

Section: Discussionmentioning

confidence: 87%

“…At higher temperatures, the amount of threefold‐coordinated silicon increases, which has never been experimentally investigated, mostly due to the fact that experiments are limited in temperature. Although Karki et al () do not explicitly report threefold silicon in MORB melt, at 3,000 K and ambient pressure, it is reported that 91% of silicon is in fourfold coordination and 5% of silicon is in fivefold coordination with an average coordination of 4, indicating that 4% of silicon is in threefold coordination. At equivalent conditions, we predict that 5% of silicon is threefold, 93% is fourfold, and 1% is fivefold, in agreement with the results of Karki et al () despite the different melt chemistries.…”

Section: Discussionmentioning

confidence: 99%

“…Although Karki et al () do not explicitly report threefold silicon in MORB melt, at 3,000 K and ambient pressure, it is reported that 91% of silicon is in fourfold coordination and 5% of silicon is in fivefold coordination with an average coordination of 4, indicating that 4% of silicon is in threefold coordination. At equivalent conditions, we predict that 5% of silicon is threefold, 93% is fourfold, and 1% is fivefold, in agreement with the results of Karki et al () despite the different melt chemistries. The nontrivial amount of threefold‐coordinated silicon at >3,000 K suggests that it is more relevant than previously thought, particularly in the Early Earth's magma ocean where the surface temperatures were much above the liquidus, especially if an atmosphere was forming.…”

Section: Discussionmentioning

confidence: 99%

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Pressure‐Induced Coordination Changes in a Pyrolitic Silicate Melt From Ab Initio Molecular Dynamics Simulations

Solomatova

Caracas

2019

JGR Solid Earth

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With ab initio molecular dynamics simulations on a Na-, Ca-, Fe-, Mg-, and Al-bearing silicate melt of pyrolite composition, we examine the detailed changes in elemental coordination as a function of pressure and temperature. We consider the average coordination as well as the proportion and distribution of coordination environments at pressures and temperatures encompassing the conditions at which molten silicates may exist in present-day Earth and those of the Early Earth's magma ocean. At ambient pressure and 2,000 K, we find that the average coordination of cations with respect to oxygen is 4.0 for Si-O, 4.0 for Al-O, 3.7 for Fe-O, 4.6 for Mg-O, 5.9 for Na-O, and 6.2 for Ca-O. Although the coordination for iron with respect to oxygen may be underestimated, the coordination number for all other cations are consistent with experiments. By 15 GPa (2,000 K), the average coordination for Si-O remains at 4.0 but increases to 4.1 for Al-O, 4.2 for Fe-O, 4.9 for Mg-O, 8.0 for Na-O, and 6.8 for Ca-O. The coordination environment for Na-O remains approximately constant up to core-mantle boundary conditions (135 GPa and 4000 K) but increases to about 6 for Si-O, 6.5 for Al-O, 6.5 for Fe-O, 8 for Mg-O, and 9.5 for Ca-O. We discuss our results in the context of the metal-silicate partitioning behavior of siderophile elements and the viscosity changes of silicate melts at upper mantle conditions. Our results have implications for melt properties, such as viscosity, transport coefficients, thermal conductivities, and electrical conductivities, and will help interpret experimental results on silicate glasses. Key Points: • The proportion and distribution of cation-to-oxygen coordination environments in a pyrolite melt have been determined as a function of depth • We examine the distribution of lifetimes of cation-oxygen species at select pressure-temperature conditions • Our results are compared to previous ab initio calculations on mafic silicate melts and to experiments on various silicate phases Supporting Information:• Supporting Information S1• Data Set S1Correspondence to:

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Thermodynamics, structure, and transport properties of the MgO–Al2O3 liquid system

2019

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Simulation of Silicate Melts Under Pressure

Cited by 20 publications

References 90 publications

Formation of bridgmanite-enriched layer at the top lower-mantle during magma ocean solidification

Formation of bridgmanite-enriched layer at the top lower-mantle during magma ocean solidification

Pressure‐Induced Coordination Changes in a Pyrolitic Silicate Melt From Ab Initio Molecular Dynamics Simulations

Thermodynamics, structure, and transport properties of the MgO–Al2O3 liquid system

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