Effect of graphite on the electrical conductivity of the lithospheric mantle

Baohua Zhang, Takashi Yoshino

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

Graphite is considered as one of candidate to explain the high-conductivity anomalies revealed through magnetotelluric (MT) observations. To investigate the effect of interfacial energy on the interconnection of graphite in olivine matrix, we measured the electrical conductivity of polycrystalline San Carlos olivine mixed with 0.8 vol % graphite on the grain boundaries via impedance spectroscopy at 1 GPa and 300–1700 K in a cubic multianvil apparatus. The olivine-graphite dihedral angle of the recovered sample was also measured to determine interfacial energy between graphite and olivine. The bulk electrical conductivities and large activation enthalpy (∼1.32 eV) of the carbon-bearing sample were consistent with those of dry polycrystalline olivine. This behavior implies that graphite cannot be interconnected on olivine grain boundaries, which is also supported by the large dihedral angle (98°) of the olivine/graphite system. Impedance spectroscopy measurements were performed at 3 GPa and a temperature of up to 1700 K for carbon-coated olivine bicrystal samples to investigate the stability of graphite films on the grain boundaries of silicate minerals under upper-mantle conditions. The conductivities rapidly or slowly dropped as a function of time and graphite film thickness during annealing at the target temperature. This phenomenon exhibits that graphite film on the olivine grain boundary is readily destroyed under upper-mantle conditions as supported by microstructural observations on the recovered carbon-coated olivine bicrystal samples. Higher interfacial energy and larger dihedral angle (∼98°) between graphite and olivine would not allow the maintenance of graphite film on olivine grain boundaries. The activation enthalpy for the apparent disconnection rate of a graphite film on olivine grain boundaries is close to that of carbon diffusion in olivine grain boundaries, which suggests that the disconnection of the graphite film is likely to be controlled by carbon grain boundary diffusion. Therefore, graphite is an unlikely candidate to explain the high-conductivity anomalies revealed by MT surveys in the upper mantle.

Original languageEnglish
Pages (from-to)23-40
Number of pages18
JournalGeochemistry, Geophysics, Geosystems
Volume18
Issue number1
DOIs
Publication statusPublished - Jan 1 2017

Fingerprint

Graphite
graphite
olivine
electrical conductivity
Earth mantle
mantle
electrical resistivity
grain boundary
Grain boundaries
grain boundaries
Carbon
interfacial energy
Dihedral angle
Interfacial energy
Magnetotellurics
carbon
dihedral angle
upper mantle
Bicrystals
bicrystals

Keywords

  • electrical conductivity
  • graphite
  • lithospheric mantle
  • olivine

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Cite this

Effect of graphite on the electrical conductivity of the lithospheric mantle. / Zhang, Baohua; Yoshino, Takashi.

In: Geochemistry, Geophysics, Geosystems, Vol. 18, No. 1, 01.01.2017, p. 23-40.

Research output: Contribution to journalArticle

@article{8f559af580ad4f89a0d7c365a1d10aee,
title = "Effect of graphite on the electrical conductivity of the lithospheric mantle",
abstract = "Graphite is considered as one of candidate to explain the high-conductivity anomalies revealed through magnetotelluric (MT) observations. To investigate the effect of interfacial energy on the interconnection of graphite in olivine matrix, we measured the electrical conductivity of polycrystalline San Carlos olivine mixed with 0.8 vol {\%} graphite on the grain boundaries via impedance spectroscopy at 1 GPa and 300–1700 K in a cubic multianvil apparatus. The olivine-graphite dihedral angle of the recovered sample was also measured to determine interfacial energy between graphite and olivine. The bulk electrical conductivities and large activation enthalpy (∼1.32 eV) of the carbon-bearing sample were consistent with those of dry polycrystalline olivine. This behavior implies that graphite cannot be interconnected on olivine grain boundaries, which is also supported by the large dihedral angle (98°) of the olivine/graphite system. Impedance spectroscopy measurements were performed at 3 GPa and a temperature of up to 1700 K for carbon-coated olivine bicrystal samples to investigate the stability of graphite films on the grain boundaries of silicate minerals under upper-mantle conditions. The conductivities rapidly or slowly dropped as a function of time and graphite film thickness during annealing at the target temperature. This phenomenon exhibits that graphite film on the olivine grain boundary is readily destroyed under upper-mantle conditions as supported by microstructural observations on the recovered carbon-coated olivine bicrystal samples. Higher interfacial energy and larger dihedral angle (∼98°) between graphite and olivine would not allow the maintenance of graphite film on olivine grain boundaries. The activation enthalpy for the apparent disconnection rate of a graphite film on olivine grain boundaries is close to that of carbon diffusion in olivine grain boundaries, which suggests that the disconnection of the graphite film is likely to be controlled by carbon grain boundary diffusion. Therefore, graphite is an unlikely candidate to explain the high-conductivity anomalies revealed by MT surveys in the upper mantle.",
keywords = "electrical conductivity, graphite, lithospheric mantle, olivine",
author = "Baohua Zhang and Takashi Yoshino",
year = "2017",
month = "1",
day = "1",
doi = "10.1002/2016GC006530",
language = "English",
volume = "18",
pages = "23--40",
journal = "Geochemistry, Geophysics, Geosystems",
issn = "1525-2027",
publisher = "American Geophysical Union",
number = "1",

}

TY - JOUR

T1 - Effect of graphite on the electrical conductivity of the lithospheric mantle

AU - Zhang, Baohua

AU - Yoshino, Takashi

PY - 2017/1/1

Y1 - 2017/1/1

N2 - Graphite is considered as one of candidate to explain the high-conductivity anomalies revealed through magnetotelluric (MT) observations. To investigate the effect of interfacial energy on the interconnection of graphite in olivine matrix, we measured the electrical conductivity of polycrystalline San Carlos olivine mixed with 0.8 vol % graphite on the grain boundaries via impedance spectroscopy at 1 GPa and 300–1700 K in a cubic multianvil apparatus. The olivine-graphite dihedral angle of the recovered sample was also measured to determine interfacial energy between graphite and olivine. The bulk electrical conductivities and large activation enthalpy (∼1.32 eV) of the carbon-bearing sample were consistent with those of dry polycrystalline olivine. This behavior implies that graphite cannot be interconnected on olivine grain boundaries, which is also supported by the large dihedral angle (98°) of the olivine/graphite system. Impedance spectroscopy measurements were performed at 3 GPa and a temperature of up to 1700 K for carbon-coated olivine bicrystal samples to investigate the stability of graphite films on the grain boundaries of silicate minerals under upper-mantle conditions. The conductivities rapidly or slowly dropped as a function of time and graphite film thickness during annealing at the target temperature. This phenomenon exhibits that graphite film on the olivine grain boundary is readily destroyed under upper-mantle conditions as supported by microstructural observations on the recovered carbon-coated olivine bicrystal samples. Higher interfacial energy and larger dihedral angle (∼98°) between graphite and olivine would not allow the maintenance of graphite film on olivine grain boundaries. The activation enthalpy for the apparent disconnection rate of a graphite film on olivine grain boundaries is close to that of carbon diffusion in olivine grain boundaries, which suggests that the disconnection of the graphite film is likely to be controlled by carbon grain boundary diffusion. Therefore, graphite is an unlikely candidate to explain the high-conductivity anomalies revealed by MT surveys in the upper mantle.

AB - Graphite is considered as one of candidate to explain the high-conductivity anomalies revealed through magnetotelluric (MT) observations. To investigate the effect of interfacial energy on the interconnection of graphite in olivine matrix, we measured the electrical conductivity of polycrystalline San Carlos olivine mixed with 0.8 vol % graphite on the grain boundaries via impedance spectroscopy at 1 GPa and 300–1700 K in a cubic multianvil apparatus. The olivine-graphite dihedral angle of the recovered sample was also measured to determine interfacial energy between graphite and olivine. The bulk electrical conductivities and large activation enthalpy (∼1.32 eV) of the carbon-bearing sample were consistent with those of dry polycrystalline olivine. This behavior implies that graphite cannot be interconnected on olivine grain boundaries, which is also supported by the large dihedral angle (98°) of the olivine/graphite system. Impedance spectroscopy measurements were performed at 3 GPa and a temperature of up to 1700 K for carbon-coated olivine bicrystal samples to investigate the stability of graphite films on the grain boundaries of silicate minerals under upper-mantle conditions. The conductivities rapidly or slowly dropped as a function of time and graphite film thickness during annealing at the target temperature. This phenomenon exhibits that graphite film on the olivine grain boundary is readily destroyed under upper-mantle conditions as supported by microstructural observations on the recovered carbon-coated olivine bicrystal samples. Higher interfacial energy and larger dihedral angle (∼98°) between graphite and olivine would not allow the maintenance of graphite film on olivine grain boundaries. The activation enthalpy for the apparent disconnection rate of a graphite film on olivine grain boundaries is close to that of carbon diffusion in olivine grain boundaries, which suggests that the disconnection of the graphite film is likely to be controlled by carbon grain boundary diffusion. Therefore, graphite is an unlikely candidate to explain the high-conductivity anomalies revealed by MT surveys in the upper mantle.

KW - electrical conductivity

KW - graphite

KW - lithospheric mantle

KW - olivine

UR - http://www.scopus.com/inward/record.url?scp=85013321902&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85013321902&partnerID=8YFLogxK

U2 - 10.1002/2016GC006530

DO - 10.1002/2016GC006530

M3 - Article

VL - 18

SP - 23

EP - 40

JO - Geochemistry, Geophysics, Geosystems

JF - Geochemistry, Geophysics, Geosystems

SN - 1525-2027

IS - 1

ER -