In this study electrical properties of a
graphite-rich quartzite from the former lower crust exposed in the Serre San Bruno, Calabria (southern Italy) have been analysed by means of complex electrical conductivity measurements in the frequency ran
ge 10
−3 to 10
6 Hz on plu
g samples of 25 mm in diameter and 22 mm hi
gh. The samples were identified as a former oil sandstones containin
g up to 12–15%flake-like
graphite, which present hi
ghly metamorphosed relics of its former hydrocarbon fillin
g. Thou
gh hi
gh concentrations of
graphite were detected, the
graphite quartzite is hi
ghly resistive. The spatial orderin
g of isolated
graphite
grains like tiles prevent the
generation of interconnected electrical pathways. These isolated
good conductors are interconnected by electrolyte brid
ges, thus causin
g the hi
gh polarizability, indicatin
g redox reactions at the electrolyte/
graphite interfaces that could be modelled usin
g CPE elements. The type of
graphite orderin
g was caused by the early formation of isolated oil droplets in the reservoir sandstone. After hi
gh-
grade metamorphism and shearin
g, they appear as flat
graphite
grains in the foliation plane and were smeared to
gether because of the ri
gidity of sillimanite and quartz, the main rock constituents. Thus this
graphite quartzite is by no means a candidate to enhance the electrical conductivity of the deep continental crust.
Syngenetic graphite in former lower crustal rocks is largely resistant against varying geochemical conditions during prograde and retrograde metamorphism. This had also been shown for graphite that is contained in normal metapelites as accessory mineral, or enriched in former black shales where it may cause high conductivity [Jxf6;dicke, H., Kruhl, J.H., Ballhaus, C., Giese, P., Untiedt, J., 2004. Syngenetic, thin graphite-rich horizons in lower crustal rocks from the Serre San Bruno, Calabria (Italy), and implications for the nature of high-conducting deep crustal layers. PEPI 141, 37–58; Nover, G., 2005. Electrical properties of crustal and mantle rocks—a review of laboratory measurements and their explanations. Surv. Geophys. 26 (5), 593–651].