Unstable graphite films on grain boundaries in crustal rocks

Takashi Yoshino, Fumiya Noritake

Research output: Contribution to journalArticle

47 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)186-192
Number of pages7
JournalEarth and Planetary Science Letters
Volume306
Issue number3-4
DOIs
Publication statusPublished - Jun 15 2011

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Keywords

  • Electrical conductivity
  • Graphite
  • Interfacial energy
  • Lower crust
  • Quartz

ASJC Scopus subject areas

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

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