TY - JOUR
T1 - Unstable graphite films on grain boundaries in crustal rocks
AU - Yoshino, Takashi
AU - Noritake, Fumiya
N1 - Funding Information:
The authors are indebted to E. Ito, D. Yamazaki, N. Tomioka, Y. Ogawa, K. Fuji-ta, M. Ichiki, E. Takahashi for benefit discussions and C. Oka for technical assistance. This paper benefited from reviews by J. Roberts and two anonymous reviewers. This work was supported by Grant-in-Aids for Scientific Research on Innovative Areas (Research in a Proposed Research Area), “Geofluids: Nature and Dynamics of Fluids in Subduction Zone” from the Japan Society for Promotion of Science.
PY - 2011/6/15
Y1 - 2011/6/15
N2 - The origin of high electrical conductive anomalies in the lower crust is a long-standing and controversial problem. Although it has been proposed that saturated saline water or partial melt increases electrical conductivity, graphite film has also been recognized as a potential cause of high conductivity since the discovery of fine graphite films on the grain boundaries of high-grade metamorphic rocks. To investigate the stability of graphite film on grain boundary of silicate minerals under lower crustal conditions, electrical conductivity of graphite film on synthetic grain boundaries of quartz bicrystals was measured by means of impedance spectroscopy at 1. GPa and up to 1200. K in a multianvil apparatus. At first heating, the electrical conductivity of the thin graphite film with thickness less than 100. nm was initially very high but decreased with time during annealing. Under high temperature conditions (> 1000. K), the conductivity of a thin carbon film rapidly decreases and approaches the quartz conductivity. This indicates that graphite film on a grain boundary between two quartz crystals is not stable at high temperatures. Optical microscopic observation of the run products suggested a disconnected feature of graphite on a quartz grain boundary. Disconnection of graphite film can be caused by higher interfacial energy between graphite and silicate minerals than that of the grain boundary energy. Therefore, a thin graphite film is not a likely candidate to account for high conductivity anomalies in the middle and lower continental crust.
AB - The origin of high electrical conductive anomalies in the lower crust is a long-standing and controversial problem. Although it has been proposed that saturated saline water or partial melt increases electrical conductivity, graphite film has also been recognized as a potential cause of high conductivity since the discovery of fine graphite films on the grain boundaries of high-grade metamorphic rocks. To investigate the stability of graphite film on grain boundary of silicate minerals under lower crustal conditions, electrical conductivity of graphite film on synthetic grain boundaries of quartz bicrystals was measured by means of impedance spectroscopy at 1. GPa and up to 1200. K in a multianvil apparatus. At first heating, the electrical conductivity of the thin graphite film with thickness less than 100. nm was initially very high but decreased with time during annealing. Under high temperature conditions (> 1000. K), the conductivity of a thin carbon film rapidly decreases and approaches the quartz conductivity. This indicates that graphite film on a grain boundary between two quartz crystals is not stable at high temperatures. Optical microscopic observation of the run products suggested a disconnected feature of graphite on a quartz grain boundary. Disconnection of graphite film can be caused by higher interfacial energy between graphite and silicate minerals than that of the grain boundary energy. Therefore, a thin graphite film is not a likely candidate to account for high conductivity anomalies in the middle and lower continental crust.
KW - Electrical conductivity
KW - Graphite
KW - Interfacial energy
KW - Lower crust
KW - Quartz
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U2 - 10.1016/j.epsl.2011.04.003
DO - 10.1016/j.epsl.2011.04.003
M3 - Article
AN - SCOPUS:79956333809
VL - 306
SP - 186
EP - 192
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
SN - 0012-821X
IS - 3-4
ER -