DI023-0012
Quantifying the water content in dense SiO2

Tuesday, 15 December 2020
Poster
Yanhao Lin, Carnegie Institution for Science Washington, Earth and Planets Laboratory, Washington, DC, United States, Qingyang Hu, Center for High Pressure Science and Technology Advanced Research, Shanghai, China, Jing Yang, Carnegie Institution of Washington, Earth and Planets Laboratory, Washington, DC, United States, Yue Meng, HPCAT, X-Ray Science Division, Argonne National Laboratory, Argonne, United States, Yukai Zhuang, Center for High Pressure Science and Technology Advanced Research, Beijing, China, Michael J Walter, Carnegie Institution for Science, Geophysical Laboratory, Washington, DC, United States and Ho-kwang Mao, Center for High Pressure Science & Technology Advanced Research, Shanghai, China
Abstract:
The distribution and transportation of water into Earth’s interior depends on the P-T stability of water-bearing phases. The transition zone in Earth’s mantle is generally accepted as an important potential water reservoir because its main constituents, wadsleyite and ringwoodite, can incorporate weight percent levels of H2O in their structures at mantle temperatures. The subduction of water in oceanic slabs is thought to be the primary mechanism for transporting water into the deep mantle. Recent studies indicate that stishovite, a nominally anhydrous mineral and a major phase in a subducted basaltic oceanic crust (~20%), has the potential to incorporate significant amounts of water but the storage capacity and incorporation mechanism of water in stishovite remain poorly constrained [1–4]. Here, we quantify the water contents in stishovite in-situ by monitoring unit cell volumes as a function of the predefined water contents of SiO2–xH2O mixtures at pressures of 44–72 GPa and temperatures of ~1380–1870 K. Our results demonstrate that the dense hydrous SiO2 phase can incorporate up to ~3.5 wt.% H2O in its crystal structure along a mantle geotherm, and that water solubility decreases at higher temperatures. Dehydration of serpentinized mantle lithosphere in cool/cold subducted plates in the transition zone may hydrate oceanic crust through incorporation of water in stishovite in the crustal portion of the slab. The large volume increase accompanying hydration can potentially provide a mechanism for deep-focus earthquakes, and hydrated stishovite has the potential to transport a significant quantity of water into the lower mantle.

Reference:

  1. Spektor, K. et al. (2011) Proc. Natl. Acad. Sci. USA 108(52), 20918–20922.
  2. Nisr, C. et al. (2017) Mineral. 102, 2180–2189.
  3. Lin, Y. et al. (2020) Natl Acad. Sci. USA 117, 184–189.
  4. Nisr, C. et al. (2020) Proc. Natl Acad. Sci. USA 117, 9747–9754.
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