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DOI	10.1016/j.epsl.2020.116556
	Physical state of an early magma ocean constrained by the thermodynamics and viscosity of iron silicate liquid
	Sun Y.; Zhou H.; Liu X.; Yin K.; Lu X.
发表日期	2020
ISSN	0012821X
卷号	551
英文摘要	The initial cooling stage and crystallization of a magma ocean were significantly affected by the thermodynamics and viscosity of iron silicate liquid. Here, we use first-principles molecular dynamics based on density functional theory plus the Hubbard U method to study the structures, thermodynamics and viscosities of Fe2SiO4 liquid at 3000–6000 K under pressure conditions spanning the entire mantle. Our calculations show that the compressibility of Fe2SiO4 liquid is weakened at pressures above 50 GPa. The densification of Fe2SiO4 liquid under compression is mainly manifested by a decrease in the distance among Si–O polyhedra and an increase in the cation-anion coordination number. We find that the viscosity of the Fe2SiO4 liquid has a positive pressure dependence, and the effect of pressure on viscosity decreases with increasing temperature. The predicted behaviour of viscosity coefficients of the Fe2SiO4 liquid at different P-T conditions can be described well as: η(P,T) = exp[−7.89+0.0042P−0.0000632P2+(3800+61.6P+0.18P2)/(T−1000)]. Compared to Mg2SiO4 liquid, the viscosity of Fe2SiO4 liquid is lower under the pressure of the lower mantle along isotherms. We calculate the adiabat of the Fe2SiO4 liquid in a magma ocean, and the results show that the iron content has little effect on the adiabats of (Mg,Fe)2SiO4 liquid in the magma ocean. Combining our calculated thermodynamic properties and viscosities with those of previous studies, the physical properties of an early magma ocean were constrained. The upper bound of the potential temperature for magma ocean crystallization is 3250 K. We constructed the range of the viscosity profile of a magma ocean and found that the lower viscosity of iron-rich silicate liquid would maintain the viscosity of an early magma ocean in the range of several mPa s. As the magma ocean starts to crystallize, the lower bound of the viscosity at the surface and the core-mantle boundary are 0.0020 Pa s and 0.0068 Pa s, respectively. The weakening of the viscosity of the iron silicate liquids would have a significant impact on the evolution of the magma ocean. © 2020 Elsevier B.V.
关键词	fayalite first-principles magma ocean thermodynamics viscosity
英文关键词	Calculations; Compressibility of liquids; Density functional theory; Liquids; Magnesium compounds; Molecular dynamics; Negative ions; Oceanography; Silicates; Silicon; Thermodynamics; Viscosity; Core-mantle boundary; Effect of pressure; First principles molecular dynamics; Increasing temperatures; Lower viscosities; Potential temperature; Pressure conditions; Viscosity coefficient; Iron compounds; anion; cation; core-mantle boundary; crystallization; fayalite; iron; magma; P-T conditions; planetary evolution; silicate; thermodynamics; viscosity
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/202918
作者单位	State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu, 210023, China
推荐引用方式 GB/T 7714	Sun Y.,Zhou H.,Liu X.,et al. Physical state of an early magma ocean constrained by the thermodynamics and viscosity of iron silicate liquid[J],2020,551.
APA	Sun Y.,Zhou H.,Liu X.,Yin K.,&Lu X..(2020).Physical state of an early magma ocean constrained by the thermodynamics and viscosity of iron silicate liquid.Earth and Planetary Science Letters,551.
MLA	Sun Y.,et al."Physical state of an early magma ocean constrained by the thermodynamics and viscosity of iron silicate liquid".Earth and Planetary Science Letters 551(2020).