2019 Fiscal Year Annual Research Report
高圧実験と地震波観測による統合的アプローチを用いた沈み込み帯下の構造と進化の解明
| Project/Area Number |
19H02002
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| Research Institution | Ehime University |
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Principal Investigator |
GREAUX Steeve 愛媛大学, 地球深部ダイナミクス研究センター, 助教 (90543166)
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| Co-Investigator(Kenkyū-buntansha) |
肥後 祐司 公益財団法人高輝度光科学研究センター, 利用研究促進部門, 主幹研究員 (10423435)
河合 研志 東京大学, 大学院理学系研究科(理学部), 准教授 (20432007)
佐藤 友彦 東京工業大学, 地球生命研究所, 研究員 (80714831)
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| Project Period (FY) |
2019-04-01 – 2023-03-31
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| Keywords | mantle composition / high pressure / ultrasonic measurement / seismological model / triplication |
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| Outline of Annual Research Achievements |
P- and S-wave velocities (VP and VS) are the unique tool we have to explore the inaccessible deep Earth via comparisons with the observed seismic velocities.
In this FY we measured VP and VS of Mid-Ocean ridge Basalt (MORB) samples synthesized at mantle P and T conditions, using a combination of in situ ultrasonic interferometry, X-ray radiography and diffraction techniques, at high P and T in the multianvil press at the synchrotron SPring-8. The analyzed samples consisted of majorite, stishovite and clinopyroxene, or bridgmanite, Ca-perovskite, stishovite and Al-phases, according to the synthesis P.
Preliminary results indicated MORB VS/VP are lower than those of seismic models suggesting basaltic fragments could explain the low shear seismic velocities observed beneath subduction regions.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
In this FY, we completed a first set of data on the MORB composition, which will permit precise estimates of the seismic velocities of the subducted basaltic crust in the mantle. Analyses of the samples recovered from the synchrotron experiments however suggested that the sample at 27 GPa was not completely crystallized during the first cycle of ultrasonic measurements.
We were planning a second run at 27 GPa in the beamtime period 2020A to confirm the present results along with the new experiments on harzburgite compositions.
This plan is however delayed due to pandemic events leading to the lockdown of our laboratory (GRC, Ehime Univ.) and the synchrotron facility (SPring-8). Our beamtime have been officially reassigned to the period of 2020B by SPring-8, where we will resume this project.
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| Strategy for Future Research Activity |
In the next FY, we will carry out ultrasonic measurements on harzburgite, which constitute the main body of the subducted slab. The combined velocity data of MORB and harzburgite studies will provide improved knowledge on the structure of the subducted slabs in the deep mantle and the mechanisms of mass transportation in the Earth's deep interior.
We will fabricate harzburgite glasses, which are not commonly available because harzburgite composition contains iron and has a high melting T, and thus cannot be achieved by conventional method. We plan to use the laser levitation furnace currently build at Ehime Univ. with our contribution to the controlled atmosphere chamber.
Data will be compared to new local seismic models derived from the triplication methods developed by our team.
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| Remarks |
We held a small workshop: "Elucidating the Earth’s mantle beneath subduction zones using an integrated approach based on high-pressure experiments and seismic observations" in Matsuyama on Jan. 9th
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