DATE2024.06.21 #Press Releases
General Circulation of Water Deep in the Earth's Mantle Revealed
Elucidating the causes of chemical heterogeneity in the mantle boundary region
Summary
A research group led by a graduate student Yutaro Tsutsumi, and Prof. Kei Hirose, at School of Science, the University of Tokyo used isotope microscopy at Hokkaido University to measure the water content in the SiO2 phase synthesized under very high pressure and temperature conditions corresponding to the Earth's core-mantle boundary (CMB) region.
Slabs subducted to the lower mantle carry water to the bottom of the mantle, using the SiO2 phase as the primary carrier of water. The slab is then almost completely dehydrated by the high temperatures just above the core, as previously thought. The water is thought to melt the rocks at the bottom of the mantle and chemically react with the metals in the core to form iron oxides, causing the seismic wave velocity anomalies observed in the CMB region.
In this study, we measured the water content in the SiO2 phase synthesized under ultrahigh-pressure and high-temperature conditions using isotope microscopy at Hokkaido University, and found that dehydration does not occur even in the CMB region, and that slab materials containing the SiO2 phase recycle toward the Earth's surface while retaining water. Seismic observations show a large velocity anomaly in the CMB region, which is believed to be due to chemical heterogeneity. The results of this study suggest that this chemical heterogeneity is not caused by water, but is most likely due to the magma ocean at the birth of the Earth.
Figure : Diamond anvil cell apparatus realizing a deep Earth environment (left) and samples synthesized under high pressure and high temperature (right)
Links：
Hokkaido University.（in Japanese）
Journals
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Journal name Nature Geoscience Title of paper