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Title: Chemistry and P-V-T equation of state of FeO2Hx at the base of Earth’s lower mantle and their geophysical implications

Journal Article · · Science Bulletin
 [1];  [2];  [3];  [3];  [3];  [3];  [4];  [5];  [6];  [7];  [3];  [8];  [9];  [10]
  1. Center for High Pressure Science and Technology Advanced Research, Changchun (China); Changchun Univ. of Science and Technology (China)
  2. Center for High Pressure Science and Technology Advanced Research, Changchun (China); CAS Center for Excellence in Deep Earth Science, Guangzhou (China)
  3. Center for High Pressure Science and Technology Advanced Research, Changchun (China)
  4. Jilin Univ., Changchun (China)
  5. Univ. of Cambridge (United Kingdom); Tohoku Univ., Sendai (Japan)
  6. Cavendish Lab., Cambridge (United Kingdom)
  7. Center for High Pressure Science and Technology Advanced Research, Changchun (China); Chinese Academy of Sciences, Guiyang (China)
  8. Univ. of Chicago, IL (United States)
  9. Argonne National Lab. (ANL), Argonne, IL (United States)
  10. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
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The hydrogen-absorbing ability of a mantle mineral in its structure determines the capacity of the water reservoirs hosted by the mineral. Water reservoirs at the base of Earth’s mantle directly influence the fate of water brought down by slab subduction and the seismic heterogeneity such as ultralow-velocity zones (ULVZs) at the core-mantle boundary. Pyrite-FeO2Hx (0 ≤ x ≤ 1) presents a possibility of such reservoirs in the deep mantle. Ever since the discovery of this mineral phase, however, its chemistry at the lower mantle conditions has been debated. We conducted kinetics experiments of pyrite-FeO2Hx dehydrogenation at 110 GPa/2100 K, 110 GPa/2300 K, and 120 GPa/2300 K and P-V-T equation of state analysis using in situ synchrotron X-ray diffraction. We found that x approaches 0.80, 0.75, and 0.79, respectively, at the above conditions. The collective P-V-T data yield K0 = 241(13) GPa, K' = 4.2(4), dK/dT = –0.028(1) GPa/K, α0 = 4.32(13) × 10–5 K–1, and α1 = 0.31(10) × 10–8 K–2 for the composition of x = 0.75 ± 0.04. Our first-principles calculations indicate that FeO2H0.75 with a slightly distorted pyrite structure is stable at 100 GPa. These results indicate that this mineral is likely present in the deep mantle with rather a partially dehydrogenated composition than FeO2 or FeOOH. Furthermore, the results also clarify the difference between the ULVZs originated from pyrite-FeO2Hx and those from partial melting in terms of shear and compressional wave seismic velocity reduction ratio δlnVS/δlnVP.

Research Organization:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Organization:
National Key Research and Development Program of China; National Science Foundation (NSF); National Natural Science Foundation of China (NSFC); China Academy of Engineering Physics (CAEP); Royal Society United Kingdom; USDOE National Nuclear Security Administration (NNSA), Office of Defense Science (NA-113); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division
Grant/Contract Number:
AC02-06CH11357
OSTI ID:
1840008
Journal Information:
Science Bulletin, Vol. 66, Issue 19; ISSN 2095-9273
Publisher:
Elsevier; Science China PressCopyright Statement
Country of Publication:
United States
Language:
English

References (14)

Hydrogen-bearing iron peroxide and the origin of ultralow-velocity zones journal November 2017
Experimental evidence for the existence of iron-rich metal in the Earth's lower mantle journal March 2004
Tracking the origin of ultralow velocity zones at the base of Earth's mantle journal January 2021
Stability of ferrous-iron-rich bridgmanite under reducing midmantle conditions journal June 2017
A new probe of ULVZ S -wave velocity structure: Array stacking of ScS waveforms journal January 2006
Stability of Fe-bearing hydrous phases and element partitioning in the system MgO–Al2O3–Fe2O3–SiO2–H2O in Earth's lowermost mantle journal October 2019
Seismic Evidence for Partial Melt at the Base of Earth's Mantle journal September 1996
When water meets iron at Earth's core–mantle boundary journal September 2017
Large gem diamonds from metallic liquid in Earth’s deep mantle journal December 2016
Chemical Reactions Between Fe and H 2 O up to Megabar Pressures and Implications for Water Storage in the Earth's Mantle and Core journal February 2018
Dehydrogenation of goethite in Earth’s deep lower mantle journal January 2017
FeO2 and FeOOH under deep lower-mantle conditions and Earth’s oxygen–hydrogen cycles journal June 2016
The pyrite-type high-pressure form of FeOOH journal July 2017
Localized double-array stacking analysis of PcP: D″ and ULVZ structure beneath the Cocos plate, Mexico, central Pacific, and north Pacific journal March 2009

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Related Subjects

58 GEOSCIENCES
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY