16. DOCUMENTING TEXTURES AND MINERAL ABUNDANCES IN MINICORES FROM THE TAG ACTIVE HYDROTHERMAL MOUND USING X-RAY COMPUTED TOMOGRAPHY1

Margaret Kingston Tivey2

  ABSTRACT

X-ray computed tomography (CT) was used to image four 2.5-cm diameter minicores of material recovered from within the Trans-Atlantic Geotraverse (TAG) active hydrothermal mound. CT images allow examination of textural relationships among clasts, veins, and matrix of pyrite-silica, pyrite-silica-anhydrite, and pyrite-anhydrite breccias, estimation of mineral abundances, and extrapolation of observations made on two-dimensional thin sections to the scale of 2 to 3 cm in three dimensions. Information on mineral abundances, coupled with shipboard porosity measurements, was used to estimate the thermal conductivity of each minicore. Estimated values agree with measured values. Reasonable fits of estimated and measured thermal conductivities allow extrapolation of thermal conductivities of minicores to in situ conditions (~350C).

1Herzig, P.M., Humphris, S.E., Miller, D.J., and Zierenberg, R.A. (Eds.), 1998. Proc. ODP, Sci. Results, 158: College Station, TX (Ocean Drilling Program).
2
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, U.S.A. mktivey@whoi.edu