TO: Tom Davies
FM: Jay Miller
JA Daily Science Report for Expedition 305, 14 February 2005.
SCIENCE UPDATE: Cores 305-U1309D-238R to -245R (1143.9 to 1182.3 mbsf, 60% recovery) continue in fine- to medium-grained, olivine-rich troctolite. Plagioclase abundance in the troctolite ranges from <10% to 20%, and has a distinct interstitial character. The troctolite is intercalated with coarse-grained olivine gabbro, that becomes more abundant down section. Contacts between the troctolite and gabbro range from thin intervals with sharp contacts where gabbro veins crosscut the serpentine foliation in the troctolite, to thicker intervals of gabbro where the transition between troctolite and gabbro is gradational. The gradational contacts are marked by an increase in plagioclase abundance to more than 50% over a few cm of core. Locally the gabbro is pervasively altered, and it is moderately altered overall. Fractures and veins with cm or larger alteration halos are more abundant in the gabbroic intervals. Overall recovery for the day was ~70% olivine gabbro and 30% olivine-rich troctolite, with the last three cores recovering predominantly olivine gabbro.