Coring operations were terminated when ROP slowed to a standstill and we decided to use our remaining time to address other cruise objectives. The combined results of two coring holes and one logging hole provided much information on this field characterized by extensive diffuse venting of low temperature fluids at the seafloor. The maximum borehole temperature measured was 314 C at 3560 mbsf. Drilling intersected relatively unaltered vesicular dacite-rhyodacite, the about 40 mbsf a rapid transition to intensely altered volcanic rocks. However, volcanic features such as vesicles, flow banding, and perlitic textures survive, together with sporadic volcaniclastic horizons.
Alteration varies with depth, and is complicated by overprinting relationships.
Clays are mostly illite, together with chlorite at depth. Both direct bacterial counting and ATP analysis established the presence of microbial mass within core samples down to about 50 mbsf. Anaerobic cultures were successful in the same samples up to 90 C. Magnetic susceptibility increases down section, and thermal conductivity is generally higher in the brecciated rocks as compared to massive altered volcanic rocks. Thermal demagnetization experiments indicate the dominant magnetic carrier in the upper part of the section is titanomagnetite with variable degrees of alteration. Deeper in the core magnetite and possibly maghemite may be the important sources of magnetization.