2022 Fiscal Year Annual Research Report
Mapping Water in the Deep Mantle
| Project/Area Number |
20K04126
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
ハウザー クリスティーン 東京工業大学, 地球生命研究所, 特任助教 (20723737)
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| Co-Investigator(Kenkyū-buntansha) |
土屋 旬 愛媛大学, 地球深部ダイナミクス研究センター, 准教授 (00527608)
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| Project Period (FY) |
2020-04-01 – 2023-03-31
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| Keywords | Earth composition / mantle transition zone / hydrous minerals / global seismology / molecular dynamics / mineral physics / plate tectonics |
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| Outline of Annual Research Achievements |
The mantle transition zone is the layer separating the Earth’s upper and lower mantle. The unique mantle transition zone minerals have the largest water storage capacity in the mantle such that mapping water in this region is critical to understanding the Earth’s total water budget. PI Houser measures and interprets seismic reflections, and Co-I Tsuchiya develops ab initio molecular dynamics to examine the stability of dense hydrous magnesium silicates in Earth’s deep mantle. We find hydrogen leaking into mantle during subduction would be stored in the rare hydrous mineral phases, leaving the overall mantle generally dry. We observe water as small local patches rather than a layer saturated to the maximum capacity. Additional work shows that nitrogen in today’s mantle most likely originated from early subducted sediments rather than a magma ocean. Our results support the ingassing through subduction rather than outgassing from a magma ocean of volatile elements from Earth’s mantle.
PI Houser constructs 3D maps of slow and fast velocity regions in the lower mantle by measuring variations in seismic wave travel times. The relative magnitudes compressional (P) and shear (S) waves reveal the temperature and composition of rocks circulating in the deepest Earth. By isolating the slow and fast regions we made the first detection of the iron spin crossover and the unique identification of ferropericlase as well as broad regions where P and S wave velocities are uncorrelated. We find the chemical signature of plate tectonics extends across the entire Earth’s mantle.
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