TO: Tom Davies
FM: Jay Miller
JA Daily Science Report for Expedition 305, 21 January 2005.
SCIENCE UPDATE: Cores 305-U1309D-108R to -115R (535.0 to 573.4 mbsf, 84% recovery) are relatively fresh (<15% altered) medium- to coarse-grained gabbro with patchy intervals of olivine-bearing gabbro and thin (few centimeter) seams of oxide- and sulfide-bearing gabbro. Below are intervals of pegmatitic gabbro in medium-to coarse-grained gabbro. Gabbro grades into medium-grained, olivine-rich gabbro, and eventually into an ~2 m thick interval of serpentinized wehrlite. Plagioclase abundance then gradually increases down section and olivine abundance decreases, coincident with an increase in grain size to coarse-grained gabbro. Below this interval, grain size decreases and olivine abundance increases, and we recovered another 50-cm-thick interval of serpentinized wehrlite. The upper and lower contacts in this interval are indistinct or not recovered, however, through most of the interval there is an anastomosing, subvertical contact with medium-grained olivine gabbro. Below the olivine-rich interval, the core returns to medium-coarse grained olivine gabbro with thin intervals of very coarse-grained to pegmatitic gabbro. Evidence of deformation is mostly restricted to thin intervals of cataclasis with no robust evidence of significant strain (also reflected in high recovery). Alteration overall is slight to moderate, but more intense near veins and fractures.