OS2-8
鉄に富むかんらん岩メルトの粘性率測定
Viscosity measurements of iron-rich peridotitic melts
河野義生 1, 小山千尋 2, 近藤望 3, 尾原幸治 4, 桑原秀治 5, 中田亮一 6, 渡邉勇基 7, 織田裕久 2,石川毅彦 2,Yoshio KONO1, Chihiro KOYAMA2, Nozomi KONDO3, Koji Ohara4, Hideharu KUWAHARA5, Ryoichi
NAKADA6, Yuki WATANABE7, Hirohisa ODA2, Takehiko ISHIKAWA2
関西学院大学，Kwansei Gakuin University.
宇宙航空研究開発機構，JAXA.
3 岡山大学，Okayama University.
4 島根大学，Shimane University.
5 愛媛大学，Ehime University.
6 高知大学，Kochi University.
7 株式会社エイ・イー・エス，Advanced Engineering Services Co., Ltd.
121. Introduction
Viscosity is the most fundamental transport property to understand nature and dynamics of magmas in theEarth. Efforts have been made to understand viscosities of SiO2-rich silicate melts such as basaltic and andesitic
compositions at high temperatures under atmospheric pressure condition1), which are important to discuss
dynamics of volcanoes in the current Earth. On the other hand, knowledge of the viscosity of SiO2-poor
peridotitic melt is fundamental to discuss nature and dynamics of the magma ocean in the early Earth.
However, the viscosity of peridotitic melt has not been well investigated, due to experimental difficulties suchas high melting temperature, high reactivity, and/or low viscosity.
Some studies have investigated viscosities of peridotitic melts using falling sphere viscometry under highpressure conditions2), 3). These studies provided important information on the viscosities of some peridotiticmelts. However, there are three issues in the current knowledge of the viscosities of peridotitic melts: (1)Temperature condition of the falling sphere viscosity measurement is limited just above the melting
temperature, because the probing sphere in the sample falls immediately after melting of the sample. Therefore,
it is not possible to determine temperature dependence of the viscosity, which is critical to model the viscosityof magmas in the Earth. (2) Since melting temperature is different in different sample compositions, whichmake it difficult to compare viscosities of different sample compositions. (3) It is difficult to conduct fallingsphere viscosity measurement in iron-rich silicate melt compositions, because of high reactivity of iron insilicate melt with the probing sphere made from metal.
In order to overcome these experimental difficulties, we utilize the electrostatic levitation furnace (ELF) at
the Internation Space Station (ISS). The ELF is capable of conducting high temperature melt experiment at>3000 K by laser heating, which enabled us to melt SiO2-poor peridotitic compositions and to investigate
temperature dependence of the viscosity at wide range of temperature conditions. In addition, the ELF
1 of 3

measures viscosity of molten sample under levitated environment, which avoids reaction of iron in silicate
melt sample with container material. In this study, we investigated viscosities of three iron-rich peridotitic
melts (Mg1.8Fe0.2SiO4, Mg0.7Fe1.2SiO4, Mg0.9Fe1.6SiO4.5) at high temperature conditions between 1980 K and 2569
K by using the ELF at the ISS.

2. Viscosity measurement
Viscosity measurements were conducted by using the drop oscillation method in the ELF at the ISS 4).
Sinusoidal voltages excite an oscillatory deformation on the melt sample. When the excitation voltage isstopped, the sample oscillation gradually weakens due to its viscosity. Fig. 1 shows an example of theoscillation obtained in the Mg1.8Fe0.2SiO4 melt sample at 2308 K. The obtained experimental oscillation data
was fit into the following equation:𝑡𝑦 = 𝐴𝑒 −𝜏 sin(2𝜋𝑓0 𝑡 + 𝜙) ,where A, , f0, and  is amplitude, decay time, resonant frequency, and phase, respectively. Then, the viscosity
 is calculated by:
𝜂=

𝜌𝑟 2
5𝜏,

where  and r is the density and radius of the sample.

Figure 1. An example of the experimentally obtained oscillation data of the Mg1.8Fe0.2SiO4 melt sample, and the fit result.

3. Results and discussion
We succeeded to determined viscosities of Mg1.8Fe0.2SiO4 melt at 2197-2361 K, Mg0.7Fe1.2SiO4 melt at 20942569 K, and Mg0.9Fe1.6SiO4.5 at 1980-2283 K. The viscosity results at high temperature conditions are fit into an
Arrhenius relation. Our obtained viscosity results of the SiO2-poor and iron-rich peridotitic melts arecompared with those calculated based on the viscosity model of Giordano et al. (2008)1), which is determinedbased on the viscosity data of SiO2-rich silicate melt compositions. Extrapolation of the Giordano's model to2 of 3

SiO2-poor peridotitic melts yielded similar viscosity values at ~2200-2300K, while we found marked differencein the temperature dependence of the viscosities. Our results show markedly lower temperature dependencesof the viscosities of the Mg1.8Fe0.2SiO4, Mg0.7Fe1.2SiO4, and Mg0.9Fe1.6SiO4.5 melts than those calculated by theGiordano's model. On the other hand, temperature dependence of the viscosity of Mg2SiO4 melt calculated byfirst principles simulation5) is similar to our results, while our determined viscosity value of the Mg1.8Fe0.2SiO4
melt at 2300 K (32.2 mPa s) is 44 % higher than that of Mg 2SiO4 melt at the same temperature (18.1 mPa s)
calculated by Ghosh and Karki (2011)5).
In addition, our results show that viscosities of Mg0.7Fe1.2SiO4 melt are higher than those of Mg1.8Fe0.2SiO4
melt, which indicate increase of viscosity by increasing iron content. The result is in contrast to the Giordano's
model, in which iron decreases the viscosity. In addition, a previous experimental study6) has investigatedviscosities of Mg1.95Si1.05O4.05 melt at 2293-2461 K and Fe2SiO4 melt at 1439-1685 K. Although it is difficult todirectly compare these two results due to significantly different temperature conditions, the viscosity of theFe2SiO4 melt seems lower than that of Mg1.95Si1.05O4.05 melt, which is in contrast to our results. In addition, firstprinciples simulation studies show that viscosity of Fe2SiO4 melt7) is lower than that of Mg2SiO4 melt5). One
possible interpretation of the discrepancy is different effect of Fe2+ and Fe3+ on the viscosity of silicate melt.
Although valence state of iron in the silicate melt sample has not been reported in the previous study, wemeasured valence state of iron in our recovered samples by X-ray absorption near edge structure (XANES)
measurement at the BL27SU beamline in SPring-8. Our samples show the Fe3+/Fe ratio of 0.22-0.23. The Fe3+
may polymerize the melt structure8), and the polymerization by the Fe3+ may be the origin of the increase ofviscosity obtained in this study.

References
1)
2)
3)
4)
5)
6)
7)
8)

D. Giordano, J. K. Russell, J. K., and D. B. Dingwell: Viscosity of magmatic liquids: a model. Earth Planet. Sci. Lett., 271(2008), 123.
B. Cochain, C. Sanloup, C. Leroy, and Y. Kono: Viscosity of mafic magmas at high pressures. Geophys. Res. Lett., 44(2017), 818.
L. Xie, A. Yoneda, D. Yamazaki, G. Manthilake, et al.: Formation of bridgmanite-enriched layer at the top lowermantle during magma ocean solidification. Nat. Commun., 11 (2020), 548.
T. Ishikawa, C. Koyama, H. Oda, H. Saruwatari, P. F. Paradis: Status of the electrostatic levitation furnace in the ISS- Surface tension and viscosity measurements, Int. J. Microgravity Sci. Appl. 39 (2022), 390101.
G. B. Ghosh, and B. B. Karki: Diffusion and viscosity of Mg2SiO4 liquid at high pressure from first-principles
simulations. Geochim. Cosmochim. Acta, 75 (2011), 4591.
G. Urbain, Y. Bottinga, and P. Richet: Viscosity of liquid silica, silicates and alumino-silicates. Geochim. Cosmochim.
Acta, 46 (1982), 1061.
Y. Sun, H. Zhou, K. Yin, M. Zhao, S. Xu, and X. Lu: Transport properties of Fe2SiO4 melt at high pressure from classicalmolecular dynamics: Implications for the lifetime of the magma ocean. J. Geophys. Res.: Solid Earth, 123 (2018), 3667.
B. O. Mysen: Redox equilibria of iron and silicate melt structure: Implications for olivine/melt element
partitioning. Geochim. Cosmochim. Acta, 70 (2006), 3121.

© 2024 by the authors. Submitted for possible open access publication under theterms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/li censes/by/4.0/).

3 of 3