[S-IT17] Property and role of liquids inside terrestrial planets

[SIT17-04] Structure of hydrous sodium silicate melts at high pressures and high temperatures by in-situ neutron and X-ray diffraction experiments

*Tomonori Ohashi¹, Tatsuya Sakamaki¹, Ken-ichi Funakoshi², Takanori Hattori³, Akio Suzuki¹ (1.Department of Earth Science, Tohoku University, 2.CROSS, 3.Materials and Life Science Division, J-PARC Center, JAEA)

Keywords:water, deep mamga, synchrotron X-ray diffraction, neutron diffraction, high pressure and temperature

Behavior of high-pressure silicate melts, which is governed by their physico-chemical properties, is crucial to understand the deep magmatism of the Earth. Particularly, the H₂O content significantly affects the properties, such as density (e.g., Matsukage et al., 2005; Sakamaki et al., 2006), viscosity (e.g., Poe et al., 2006; Suzuki et al., 2011), and phase relation (e.g., Mysen, 2014). Since such physical properties can be largely determined by the atomic structure, there are considerable interests in revealing the structural changes of hydrous magmas with increasing pressure.
In this study, we determined high-P and -T structure of dry Na₆Si₈O₁₉ melt and hydrous melts with 5 wt% (N3S8-H5) and with 9 wt% H₂O (N3S8-H9) by in-situ X-ray diffraction (XRD). We also investigated the structure of the deuterated Na₆Si₈O₁₉ melt with 10 wt% D₂O (N3S8-D10) at high P-T by means of in-situ neutron diffraction (ND). The XRD experiments were carried out using a DIA-type cubic multi-anvil apparatus MAX80 installed at the AR-NE5C beamline of Photon Factory, KEK at Tsukuba, Japan. The experimental P-T conditions were 1.4–6.7 GPa and 900–1060 °C, respectively. The ND experiments were conducted by using a six-axis multi-anvil apparatus ATSUHIME installed at the BL11 PLANET beamline of MLF, J-PARC at Tokai, Japan. The P-T conditions were 1–5 GPa and just above the melting temperature.
The obtained neutron total structure factor, S^N(Q) for the N3S8-D10 melt exhibits significantly different oscillation compared to that of the dry N3S8 glass, especially in the low Q region below ~5 Å⁻¹. The neutron pair distribution functions, g^N(r) of the N3S8-D10 melt shows that the D-O peak is located at ~1 Å. The interatomic distances for Si-O, Na-O, O-O, Si/Na-Si/Na pairs are almost the same as those of dry glass and melt. These results imply that the water content gives a greater effect on the intermediate-range order structure than on the short-range order structure. Our preliminary results will be represented in the presentation.

References
Matsukage, K.N., Jing, Z., Karato, S., 2005. Density of hydrous silicate melt at the conditions of Earth’s deep upper mantle. Nature 438, 488–491. https://doi.org/10.1038/nature04241
Mysen, B., 2014. Water-melt interaction in hydrous magmatic systems at high temperature and pressure. Progress in Earth and Planetary Science 1, 4. https://doi.org/10.1186/2197-4284-1-4
Poe, B.T., Romano, C., Liebske, C., Rubie, D.C., Terasaki, H., Suzuki, A., Funakoshi, K., 2006. High-temperature viscosity measurements of hydrous albite liquid using in-situ falling-sphere viscometry at 2.5 GPa. Chem. Geol. 229, 2–9. https://doi.org/10.1016/j.chemgeo.2006.01.010
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