Hydrogen site-dependent physical properties of hydrous magnesium silicates: implications for water storage and transport in the mantle transition zone
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866908627989692416 |
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| author | Wang, Zifan He, Yu Mao, Ho-kwang Kim, Duck Young |
| author_facet | Wang, Zifan He, Yu Mao, Ho-kwang Kim, Duck Young |
| contents | The Earth's mantle transition zone (MTZ) is widely recognized as a major water reservoir, exerting significant influence on the planet's water budget and deep cycling processes. Here, we employ crystal structure prediction and first-principles calculations to identify a series of stable hydrous magnesium silicate phases under transition zone conditions. Our results reveal a pressure-induced hydrogen substitution mechanism in wadsleyite, where H+ preferentially migrates from Mg2+ sites to Si4+ sites near 410 km depth. This transformation leads to a substantial decrease in electrical conductivity, consistent with geophysical observations. We estimate the water content in the MTZ to be approximately 1.6 wt%, aligning with seismic and conductivity constraints. Furthermore, using machine learning-enhanced molecular dynamics, we discover double superionicity in hydrous wadsleyite and ringwoodite at temperatures exceeding 2000 K, wherein both H+ and Mg2+ exhibit high ionic mobility. This dual-ion superionic state has potentially profound implications for mass transport, electrical conductivity, and magnetic dynamo generation in rocky super-Earth exoplanets. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_02416 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Hydrogen site-dependent physical properties of hydrous magnesium silicates: implications for water storage and transport in the mantle transition zone Wang, Zifan He, Yu Mao, Ho-kwang Kim, Duck Young Geophysics The Earth's mantle transition zone (MTZ) is widely recognized as a major water reservoir, exerting significant influence on the planet's water budget and deep cycling processes. Here, we employ crystal structure prediction and first-principles calculations to identify a series of stable hydrous magnesium silicate phases under transition zone conditions. Our results reveal a pressure-induced hydrogen substitution mechanism in wadsleyite, where H+ preferentially migrates from Mg2+ sites to Si4+ sites near 410 km depth. This transformation leads to a substantial decrease in electrical conductivity, consistent with geophysical observations. We estimate the water content in the MTZ to be approximately 1.6 wt%, aligning with seismic and conductivity constraints. Furthermore, using machine learning-enhanced molecular dynamics, we discover double superionicity in hydrous wadsleyite and ringwoodite at temperatures exceeding 2000 K, wherein both H+ and Mg2+ exhibit high ionic mobility. This dual-ion superionic state has potentially profound implications for mass transport, electrical conductivity, and magnetic dynamo generation in rocky super-Earth exoplanets. |
| title | Hydrogen site-dependent physical properties of hydrous magnesium silicates: implications for water storage and transport in the mantle transition zone |
| topic | Geophysics |
| url | https://arxiv.org/abs/2511.02416 |