Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Tectonophysics

[S-IT19] Mineral-melt-fluid interaction and COHN volatile speciation in Earth and planetary

Sun. May 20, 2018 10:45 AM - 12:15 PM 201B (2F International Conference Hall, Makuhari Messe)

convener:Bjorn Mysen(Geophysical Laboratory, Carnegie Inst. Washington), Eiji Ohtani(Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University), Jun Tsuchiya(愛媛大学地球深部ダイナミクス研究センター), Chairperson:Ohtani Eiji(Tohoku University)

10:45 AM - 11:00 AM

[SIT19-07] Elasticity of superhydrous phase B at the mantle temperature and pressure: Implications for 800-km discontinuity and water flow into lower mantle

*Zhongqing Wu1, Dapping Yang1, Wenzhong Wang1 (1.School of Earth and Space Sciences, University of Science and Technology of China)

Keywords:elasticity at high pressure and temperature, hydrous phase, first-principle calculations

The water in Earth’s interior exerts a controlling influence on the dynamical and chemical evolution of the Earth. Many evidences from mineral physics, geophysics, and geochemistry suggest that the some of plate subductions transport water to the deep Earth. Superhydrous phase B (ShyB) is considered to be an important candidate for transporting water into the transition zone and lower mantle since it is stable up to ~ 31 GPa and 1400 ℃ and will decompose into bridgmanite, periclase and water at a depth of ~ 800 km [Komabayashi and Omori, 2006].

We investigated the elasticity of ShyB at high temperature and pressure using first principle calculations [Yang et al., 2017]. Our first-principles calculations indicate that the decomposition of ShyB will cause the Vp, Vs, and density increase by 7.5%, 15.0% and 12%, respectively. Thus the decomposition of a small amount of ShyB sufficiently generates 800-km the discontinuity and may be related to the seismic discontinuity at the depth of ~ 800 km in Western-Pacific Subduction Zones [Liu et al., 2016; Porritt and Yoshioka, 2016]. The water released from the decomposition of ShyB promotes the partial melt, which can further explain the low-velocity anomalies just above 800-km discontinuity. The result supports strongly the appearance of ShyB at the lower mantle and has many significant implications on deep water cycle.

Komabayashi, T., and S. Omori (2006), Internally consistent thermodynamic data set for dense hydrous magnesium silicates up to 35GPa, 1600°C: Implications for water circulation in the Earth's deep mantle, Physics of the Earth and Planetary Interiors, 156(1-2), 89-107.

Liu, Z., J. Park, and S. I. Karato (2016), Seismological detection of low-velocity anomalies surrounding the mantle transition zone in Japan subduction zone, Geophysical Research Letters, 43(6), 2480-2487.

Porritt, R. W., and S. Yoshioka (2016), Slab pileup in the mantle transition zone and the 30 May 2015 Chichi-jima earthquake, Geophysical Research Letters, 43(10), 4905-4912.

Yang, D., W. Wang, and Z. Wu (2017), Elasticity of superhydrous phase B at the mantle temperatures and pressures: Implications for 800 km discontinuity and water flow into the lower mantle, J. Geophys. Res. Solid Earth, 122, 5026–5037, doi:10.1002/2017JB014319.