skip to main content
DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Stability of Fe-bearing hydrous phases and element partitioning in the system MgO–Al2O3–Fe2O3–SiO2–H2O in Earth’s lowermost mantle

Abstract

We performed high pressure–temperature (P-T) experiments on a model composition of hydrous subducted slabs in the MgO–Al2O3–Fe2O3–SiO2–H2O system using laser-heated diamond anvil cells. The phase assemblages were characterized combining in-situ synchrotron X-ray diffraction and ex-situ transmission electron microscope techniques. The hydrous δ-phase AlOOH–FeOOH–MgSiO2(OH)2–SiO2 coexists with bridgmanite (Bdg), post-perovskite (pPv), or both in a broad P-T range of 104–126 GPa and 1750–2500 K. The hydrous pyrite-type FeOOHx phase was observed in-situ over a P-T range of 112–123 GPa and 1750–2300 K, coexisting with the pPv phase. Chemical analysis on recovered samples showed that considerable amount of Fe2O2(OH)2 (8–13 mol%) and SiO2 (9–13 mol%) in the δ-phase does not reduce its thermal stability compared to the Al-endmember, indicating that the Fe-bearing δ-phase can transport water to the lowermost mantle along the mantle geotherm. In this hydrous system, we observed that Al depletion in both the Bdg and pPv phases can significantly reduce the width of the Bdg to pPv transition in contrast to a wide two-phase coexistence region in a dry Al-rich system. Meanwhile, the Fe enrichment in the pPv phase relative to the coexisting Bdg phase lowers the transition pressure to the depth of the D" discontinuity. Accordingly, the depth andmore » thickness of the Bdg to pPv transition in subducted basaltic crustal materials can explain the seismically detected D" discontinuity. Partial melting could be triggered by dehydration of the Fe-bearing hydrous phases due to a steep temperature gradient at the core mantle boundary (CMB), and therefore the ultralow-velocity zones (ULVZs) might be the regions where partial melting occurs at the lowermost mantle.« less

Authors:
ORCiD logo [1];  [1]; ORCiD logo [2];  [3];  [4];  [4]
  1. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai (China)
  2. Tohoku Univ., Sendai (Japan). Dept. of Earth Science
  3. Argonne National Lab. (ANL), Argonne, IL (United States). HPCAT, X-Ray Science Div.
  4. Univ. of Chicago, IL (United States). Center for Advanced Radiation Sources (CARS)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE; National Natural Science Foundation of China (NNSFC); Japan Society for the Promotion of Science (JSPS)
OSTI Identifier:
1562108
Alternate Identifier(s):
OSTI ID: 1546112
Grant/Contract Number:  
AC02-06CH11357; FG02-94ER14466
Resource Type:
Accepted Manuscript
Journal Name:
Earth and Planetary Science Letters
Additional Journal Information:
Journal Volume: 524; Journal Issue: C; Journal ID: ISSN 0012-821X
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; bridgmanite; deep lower mantle; hydrous phase; multigrain analysis; post-perovskite; synchrotron X-ray diffraction

Citation Formats

Yuan, Hongsheng, Zhang, Li, Ohtani, Eiji, Meng, Yue, Greenberg, Eran, and Prakapenka, Vitali B. Stability of Fe-bearing hydrous phases and element partitioning in the system MgO–Al2O3–Fe2O3–SiO2–H2O in Earth’s lowermost mantle. United States: N. p., 2019. Web. doi:10.1016/j.epsl.2019.115714.
Yuan, Hongsheng, Zhang, Li, Ohtani, Eiji, Meng, Yue, Greenberg, Eran, & Prakapenka, Vitali B. Stability of Fe-bearing hydrous phases and element partitioning in the system MgO–Al2O3–Fe2O3–SiO2–H2O in Earth’s lowermost mantle. United States. doi:10.1016/j.epsl.2019.115714.
Yuan, Hongsheng, Zhang, Li, Ohtani, Eiji, Meng, Yue, Greenberg, Eran, and Prakapenka, Vitali B. Fri . "Stability of Fe-bearing hydrous phases and element partitioning in the system MgO–Al2O3–Fe2O3–SiO2–H2O in Earth’s lowermost mantle". United States. doi:10.1016/j.epsl.2019.115714. https://www.osti.gov/servlets/purl/1562108.
@article{osti_1562108,
title = {Stability of Fe-bearing hydrous phases and element partitioning in the system MgO–Al2O3–Fe2O3–SiO2–H2O in Earth’s lowermost mantle},
author = {Yuan, Hongsheng and Zhang, Li and Ohtani, Eiji and Meng, Yue and Greenberg, Eran and Prakapenka, Vitali B.},
abstractNote = {We performed high pressure–temperature (P-T) experiments on a model composition of hydrous subducted slabs in the MgO–Al2O3–Fe2O3–SiO2–H2O system using laser-heated diamond anvil cells. The phase assemblages were characterized combining in-situ synchrotron X-ray diffraction and ex-situ transmission electron microscope techniques. The hydrous δ-phase AlOOH–FeOOH–MgSiO2(OH)2–SiO2 coexists with bridgmanite (Bdg), post-perovskite (pPv), or both in a broad P-T range of 104–126 GPa and 1750–2500 K. The hydrous pyrite-type FeOOHx phase was observed in-situ over a P-T range of 112–123 GPa and 1750–2300 K, coexisting with the pPv phase. Chemical analysis on recovered samples showed that considerable amount of Fe2O2(OH)2 (8–13 mol%) and SiO2 (9–13 mol%) in the δ-phase does not reduce its thermal stability compared to the Al-endmember, indicating that the Fe-bearing δ-phase can transport water to the lowermost mantle along the mantle geotherm. In this hydrous system, we observed that Al depletion in both the Bdg and pPv phases can significantly reduce the width of the Bdg to pPv transition in contrast to a wide two-phase coexistence region in a dry Al-rich system. Meanwhile, the Fe enrichment in the pPv phase relative to the coexisting Bdg phase lowers the transition pressure to the depth of the D" discontinuity. Accordingly, the depth and thickness of the Bdg to pPv transition in subducted basaltic crustal materials can explain the seismically detected D" discontinuity. Partial melting could be triggered by dehydration of the Fe-bearing hydrous phases due to a steep temperature gradient at the core mantle boundary (CMB), and therefore the ultralow-velocity zones (ULVZs) might be the regions where partial melting occurs at the lowermost mantle.},
doi = {10.1016/j.epsl.2019.115714},
journal = {Earth and Planetary Science Letters},
number = C,
volume = 524,
place = {United States},
year = {2019},
month = {8}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Citation Metrics:
Cited by: 2 works
Citation information provided by
Web of Science

Save / Share: