TY - JOUR
T1 - Electrical Conductivity in Texturally Equilibrated Fluid-Bearing Forsterite Aggregates at 800°C and 1 GPa
T2 - Implications for the High Electrical Conductivity Anomalies in Mantle Wedges
AU - Huang, Yongsheng
AU - Guo, Haihao
AU - Nakatani, Takayuki
AU - Uesugi, Kentaro
AU - Nakamura, Michihiko
AU - Keppler, Hans
N1 - Funding Information:
The authors are grateful to Catherine McCammon for her technical support in the piston cylinder experiments. The authors thank Tomohiro Ohuchi for providing the starting material. The authors would like to thank Wakana Fujita for providing directions for the CT imaging process. The authors are grateful to anonymous reviewers for thoughtful reviews and constructive comments. The authors thank Yves Bernabe for timely editorial handling of this manuscript. This work was supported by JSPS KAKENHI Grant Nos. JP16H06348 and JP16K13903 awarded to M. Nakamura, JSPS Japanese-German Graduate Externship, International Joint Graduate Program in Earth and Environmental Sciences, Tohoku University (GP-EES), and by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan under its Earthquake and Volcano Hazards Observation and Research Program, and by the Core Research Cluster of Disaster Science in Tohoku University (Designated National University). The synchrotron radiation experiments were performed at SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI; proposal nos. 2018A1471, 2018A1464, 2019B1785).
Funding Information:
The authors are grateful to Catherine McCammon for her technical support in the piston cylinder experiments. The authors thank Tomohiro Ohuchi for providing the starting material. The authors would like to thank Wakana Fujita for providing directions for the CT imaging process. The authors are grateful to anonymous reviewers for thoughtful reviews and constructive comments. The authors thank Yves Bernabe for timely editorial handling of this manuscript. This work was supported by JSPS KAKENHI Grant Nos. JP16H06348 and JP16K13903 awarded to M. Nakamura, JSPS Japanese‐German Graduate Externship, International Joint Graduate Program in Earth and Environmental Sciences, Tohoku University (GP‐EES), and by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan under its Earthquake and Volcano Hazards Observation and Research Program, and by the Core Research Cluster of Disaster Science in Tohoku University (Designated National University). The synchrotron radiation experiments were performed at SPring‐8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI; proposal nos. 2018A1471, 2018A1464, 2019B1785).
Publisher Copyright:
© 2021. The Authors.
PY - 2021/4
Y1 - 2021/4
N2 - Aqueous fluids are one of the principal agents of chemical transport in Earth´s interior. The precise determination of fluid fractions is essential to understand bulk physical properties, such as rheology and permeability, and the geophysical state of the mantle. Laboratory-based electrical conductivity measurements are an effective method for estimating the fluid distribution and fraction in a fluid-bearing rock. In this study, the electrical conductivity of texturally equilibrated fluid-bearing forsterite aggregates was measured for the first time with various fluid fractions at a constant salinity of 5.0 wt.% NaCl at 1 GPa and 800°C. We found that the electrical conductivity nonlinearly increases with increasing fluid fraction, and the data can be well reproduced by the modified Archie's law. The three-dimensional (3-D) microstructure of the interstitial pores visualized by the high-resolution synchrotron X-ray computed micro-tomography (CT) shows a change in fluid distribution from isolated pockets at a fluid fraction of 0.51 vol.% to interconnected networks at fluid fractions of 2.14 vol.% and above due to grain anisotropy and grain size differences, accounting for the nonlinear increase in electrical conductivity. The rapid increase in conductivity indicates that there is a threshold fluid fraction between 0.51 and 2.14 vol.% for forming interconnected fluid networks, which is consistent with the 3-D images. Our results provide direct evidence that the presence of >1.0 vol.% aqueous fluid with 5.0 wt.% NaCl is required to explain the high conductivity anomalies above 0.01 S/m detected in deep fore-arc mantle wedges.
AB - Aqueous fluids are one of the principal agents of chemical transport in Earth´s interior. The precise determination of fluid fractions is essential to understand bulk physical properties, such as rheology and permeability, and the geophysical state of the mantle. Laboratory-based electrical conductivity measurements are an effective method for estimating the fluid distribution and fraction in a fluid-bearing rock. In this study, the electrical conductivity of texturally equilibrated fluid-bearing forsterite aggregates was measured for the first time with various fluid fractions at a constant salinity of 5.0 wt.% NaCl at 1 GPa and 800°C. We found that the electrical conductivity nonlinearly increases with increasing fluid fraction, and the data can be well reproduced by the modified Archie's law. The three-dimensional (3-D) microstructure of the interstitial pores visualized by the high-resolution synchrotron X-ray computed micro-tomography (CT) shows a change in fluid distribution from isolated pockets at a fluid fraction of 0.51 vol.% to interconnected networks at fluid fractions of 2.14 vol.% and above due to grain anisotropy and grain size differences, accounting for the nonlinear increase in electrical conductivity. The rapid increase in conductivity indicates that there is a threshold fluid fraction between 0.51 and 2.14 vol.% for forming interconnected fluid networks, which is consistent with the 3-D images. Our results provide direct evidence that the presence of >1.0 vol.% aqueous fluid with 5.0 wt.% NaCl is required to explain the high conductivity anomalies above 0.01 S/m detected in deep fore-arc mantle wedges.
KW - Brine-bearing forsterite aggregates
KW - X-ray CT
KW - electrical conductivity
KW - mantle wedge
KW - subduction zones
KW - textural equilibrium
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U2 - 10.1029/2020JB021343
DO - 10.1029/2020JB021343
M3 - Article
AN - SCOPUS:85105019478
VL - 126
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
SN - 2169-9313
IS - 4
M1 - e2020JB021343
ER -