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Léger et al. 1996
Léger, A., Mathez, E.A., Duba, A., Pineau, F. and Ginsberg, S. (1996). Carbonaceous material in metamorphosed carbonate rocks from the Waits River Formation, NE Vermont, and its effect on electrical conductivity. Journal of Geophysical Research 101: doi: 10.1029/96JB01757. issn: 0148-0227.

The relations among electrical conductivity and graphite content, metamorphic grade, and fluid:rock interaction are investigated for a suite of regionally metamorphosed graphitic carbonate rocks from the Waits River Formation, NE Vermont. Graphitization was complete by the lowest grade of metamorphism attained in the area (~450 ¿C and 450 MPa). In low-grade rocks, graphite occurs as inclusions within calcite and along grain boundaries, and in medium-grade rocks, it concentrates near porphyroblasts. In neither suite does graphite form interconnected networks. Average reduced carbon abundances are 4400 and 2800 ppm for the low- and medium-grade rocks, respectively. High-grade rocks are almost void of graphite, except for one specimen. The Δ13C values were determined for graphite and carbonates and Δ18O values were determined for the carbonates and silicate residues. There is no change in isotopic values between low- and medium-grade rocks. In contrast, high-grade rocks show marked decreases in Δ13C and Δ18O values of ~4% compared to low- and medium-grade rocks. Both isotopic analyses and graphite depletion in high-grade rocks were caused by influx of large quantities of magmatic water during peak metamorphism. Electrical conductivity was measured in the laboratory on representative specimens. Rocks with high carbon content (>7000 ppm) from both the low- and high-grade zones display almost an order of magnitude higher electrical conductivity than expected from their fluid content alone. Graphite does not form an interconnected network in these rocks, yet it combines with the saline fluids to significantly increase electrical conductivities. ¿ American Geophysical Union 1996

BACKGROUND DATA FILES

Abstract

Keywords
Physical Properties of Rocks, Magnetic and electrical properties, Mineralogy and Petrology, Metamorphic petrology, Geochemistry, Isotopic composition/chemistry
Journal
Journal of Geophysical Research
http://www.agu.org/journals/jb/
Publisher
American Geophysical Union
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