Ms. Izumi Mashino [Graduate School of Science, Tohoku University]

Title: Sound velocities of δ-AlOOH up to lowermost mantle pressures; Implications for the seismic anomalies in deep mantle

Time: 10:00 - 11:00 AM, Monday, February 27, 2017

Place: Conference room 410, HPSTAR (Shanghai)

Host: Dr. Ho-Kwang Mao

Abstract

It is widely recognized that the presence of water in the deep Earth’s interior, which may be transported to such depths by various hydrous minerals in subducting slabs, can significantly affect the physical and rheological properties of the mantle. Most hydrous minerals become thermodynamically unstable under the pressure-temperature conditions corresponding to the upper part of the upper mantle (e.g., Ohtani, 2006). However, recent experimental data indicate that the hydrous mineral δ-AlOOH can be stable throughout the lowermost mantle (Sano et al., 2008; Ohira et al., 2014; Ohtani et al., 2014). This phase is, therefore, a possible carrier and host of water in the deep mantle. To uncover the physical properties of δ-AlOOH under deep mantle pressure conditions, we have conducted high-pressure acoustic wave velocity measurements of δ-AlOOH by using Brillouin spectroscopy combined with high-pressure Raman spectroscopic measurements in a diamond anvil cell up to pressures of 134 GPa. There is a precipitous increase by ~14% in the acoustic velocities of δ-AlOOH from 6 to 15 GPa, which suggests that pressure-induced O-H bond symmetrization occurs in this pressure range. The best fit values for the high-pressure form of δ-AlOOH of K0 = 190 (2) (GPa), G0 = 160.0 (9) (GPa), (∂K/∂P)0 = K0′ = 3.7 (1), and (∂G/∂P)0 = G0′ = 1.32 (1) indicate that δ-AlOOH has a 20–30% higher VS value compared to those of the major constituent minerals in the mantle transition zone, such as wadsleyite, ringwoodite, and majorite. On the other hand, the VS of δ-AlOOH is ~7% lower than that of bridgmanite under lowermost mantle pressure conditions. By comparing our results with seismic observations, we can infer that δ-AlOOH is one of the potential causes of a positive VS anomaly observed at ~600 km depth beneath the Korean peninsula and a negative VS jump near 2800 km depth near the northern margin of the large low-shear-velocity province beneath the Pacific.

Biography of the Speaker:

Education:

Apr. 2014 – Mar. 2017: Ph.D. program, Department of EARTH SCIENCES, Tohoku University

Doctor research

Sound velocity and spin transition of Fe-bearing Bridgmanite to Mbar pressure with implications for the mineralogical model of the lower mantle

Apr. 2012 – Mar. 2014: M.S. program, Department of EARTH SCIENCES, Tohoku University

Master research

Physical Properties of Minerals in Subducting Slab: spin state of Fe3+-bearing perovskite and elastic properties of δ-AlOOH

Apr. 2008 – Mar. 2012: Department of EARTH SCIENCES, Tohoku University

Undergraduate research

Equation of state of Fe3+-bearing perovskite in Earth’s lower mantle and effects of spin transition of iron

Professional Experience:

Apr. 2015 - Mar. 2017: Japan Society for the Promotion of Science (JSPS) Research Fellowships for Young Scientists (Prof. Motohiko Murakami and Prof. Eiji Ohtani)

Oct. 2014 - Mar. 2015: Research assistant (Global Education and Research Center for Earth and Planetary Dynamics, Tohoku University)

Apr. 2014 - Mar. 2015: Research assistant (The Advanced Institute for Materials Research, Tohoku University)

Awards, Fellowships, and Honors:

Mar. 2016: Kuroda Chika Award (The Aoba Society for the Promotion of Science)

Apr. 2015 - Mar. 2017: Grant-in-Aid for JSPS Fellows

Project number: 515J020170

Title: Elastic properties of minerals in subducting slub at high pressure and temperature; Implications for global circulation of water