Electrical Conductivity of Omphacite as a Function of Water Content and Implications for High Conductivity Anomalies in the Dabie-Sulu UHPM Belts and Tibet

Baohua Zhang, Chengcheng Zhao, Jianhua Ge, Takashi Yoshino

Research output: Contribution to journalArticle

Abstract

Magnetotelluric surveys revealed high-conductivity layers in the lower crust beneath Tibet and in the shallow part of the upper mantle relevant to continental collision extending to the Dabie-Sulu ultrahigh-pressure metamorphic (UHPM) belts of eastern China, which have been interpreted by the presence of aqueous fluids/partial melts or hydrous phases. However, these explanations are not consistent with their petrological features and seismic properties. Hydrogen-bearing omphacite could be a probable candidate to explain such high-conductivity anomalies due to its high water-partitioning coefficient versus coexisting garnet in eclogite. In this study, we investigated electrical conductivities of Fe-free and Fe-bearing omphacite as a function of water content (0.005–0.122 wt.%) at 3 GPa and 500–1300 K. Our results show that water significantly enhances the electrical conductivity of omphacite, while iron facilitates conductivity by accelerating hydrogen diffusivity and lowering its activation enthalpy. Assuming a heat flow of 70 mW/m2, the high electrical anomalies observed beneath the Dabie-Sulu UHPM belts and the Tibetan Plateau can be reasonably explained by omphacite containing 0.07 wt.% water since water content higher than 0.07 wt.% in omphacite was frequently reported in naturally collected eclogite.

Original languageEnglish
JournalJournal of Geophysical Research: Solid Earth
DOIs
Publication statusAccepted/In press - Jan 1 2019

Fingerprint

Tibet
omphacite
Bearings (structural)
Water content
moisture content
electrical conductivity
eclogite
conductivity
water content
anomalies
anomaly
electrical resistivity
Water
Hydrogen
Magnetotellurics
water
Garnets
hydrogen
heat transmission
garnets

Keywords

  • Dabie-Sulu UHPM belts
  • electrical conductivity
  • high conductivity anomalies
  • omphacite
  • Tibet
  • water

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

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title = "Electrical Conductivity of Omphacite as a Function of Water Content and Implications for High Conductivity Anomalies in the Dabie-Sulu UHPM Belts and Tibet",
abstract = "Magnetotelluric surveys revealed high-conductivity layers in the lower crust beneath Tibet and in the shallow part of the upper mantle relevant to continental collision extending to the Dabie-Sulu ultrahigh-pressure metamorphic (UHPM) belts of eastern China, which have been interpreted by the presence of aqueous fluids/partial melts or hydrous phases. However, these explanations are not consistent with their petrological features and seismic properties. Hydrogen-bearing omphacite could be a probable candidate to explain such high-conductivity anomalies due to its high water-partitioning coefficient versus coexisting garnet in eclogite. In this study, we investigated electrical conductivities of Fe-free and Fe-bearing omphacite as a function of water content (0.005–0.122 wt.{\%}) at 3 GPa and 500–1300 K. Our results show that water significantly enhances the electrical conductivity of omphacite, while iron facilitates conductivity by accelerating hydrogen diffusivity and lowering its activation enthalpy. Assuming a heat flow of 70 mW/m2, the high electrical anomalies observed beneath the Dabie-Sulu UHPM belts and the Tibetan Plateau can be reasonably explained by omphacite containing 0.07 wt.{\%} water since water content higher than 0.07 wt.{\%} in omphacite was frequently reported in naturally collected eclogite.",
keywords = "Dabie-Sulu UHPM belts, electrical conductivity, high conductivity anomalies, omphacite, Tibet, water",
author = "Baohua Zhang and Chengcheng Zhao and Jianhua Ge and Takashi Yoshino",
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T1 - Electrical Conductivity of Omphacite as a Function of Water Content and Implications for High Conductivity Anomalies in the Dabie-Sulu UHPM Belts and Tibet

AU - Zhang, Baohua

AU - Zhao, Chengcheng

AU - Ge, Jianhua

AU - Yoshino, Takashi

PY - 2019/1/1

Y1 - 2019/1/1

N2 - Magnetotelluric surveys revealed high-conductivity layers in the lower crust beneath Tibet and in the shallow part of the upper mantle relevant to continental collision extending to the Dabie-Sulu ultrahigh-pressure metamorphic (UHPM) belts of eastern China, which have been interpreted by the presence of aqueous fluids/partial melts or hydrous phases. However, these explanations are not consistent with their petrological features and seismic properties. Hydrogen-bearing omphacite could be a probable candidate to explain such high-conductivity anomalies due to its high water-partitioning coefficient versus coexisting garnet in eclogite. In this study, we investigated electrical conductivities of Fe-free and Fe-bearing omphacite as a function of water content (0.005–0.122 wt.%) at 3 GPa and 500–1300 K. Our results show that water significantly enhances the electrical conductivity of omphacite, while iron facilitates conductivity by accelerating hydrogen diffusivity and lowering its activation enthalpy. Assuming a heat flow of 70 mW/m2, the high electrical anomalies observed beneath the Dabie-Sulu UHPM belts and the Tibetan Plateau can be reasonably explained by omphacite containing 0.07 wt.% water since water content higher than 0.07 wt.% in omphacite was frequently reported in naturally collected eclogite.

AB - Magnetotelluric surveys revealed high-conductivity layers in the lower crust beneath Tibet and in the shallow part of the upper mantle relevant to continental collision extending to the Dabie-Sulu ultrahigh-pressure metamorphic (UHPM) belts of eastern China, which have been interpreted by the presence of aqueous fluids/partial melts or hydrous phases. However, these explanations are not consistent with their petrological features and seismic properties. Hydrogen-bearing omphacite could be a probable candidate to explain such high-conductivity anomalies due to its high water-partitioning coefficient versus coexisting garnet in eclogite. In this study, we investigated electrical conductivities of Fe-free and Fe-bearing omphacite as a function of water content (0.005–0.122 wt.%) at 3 GPa and 500–1300 K. Our results show that water significantly enhances the electrical conductivity of omphacite, while iron facilitates conductivity by accelerating hydrogen diffusivity and lowering its activation enthalpy. Assuming a heat flow of 70 mW/m2, the high electrical anomalies observed beneath the Dabie-Sulu UHPM belts and the Tibetan Plateau can be reasonably explained by omphacite containing 0.07 wt.% water since water content higher than 0.07 wt.% in omphacite was frequently reported in naturally collected eclogite.

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