TO: Tom Davies
FM: Jay Miller
JA Daily Science Report for Expedition 304, 28 December 2004.
LOCATION: Site U1309 (prospectus site AMFW-01A)
Latitude: 30° 10.1195'N Longitude: 42° 07.1311'W
Water depth: 1645 mbsl
SCIENCE UPDATE: Cores U1309D-58R to -66R (300.4 to 343.6 mbsf, 60% recovery, 60% average recovery for hole). Serpentinized olivine-rich gabbro continues throughout most of this cored interval with common sharp, dipping contacts with coarse-grained olivine-bearing gabbro. Individual clinopyroxene oikocrysts in the coarse-grained gabbro can exceed 10 cm in long dimension. The gabbro is also characterized by subtle modal variations (manifested as changes in olivine abundance) and grain size changes. Thin (few cm to tens of cm) seams of oxide gabbro were also recovered. Below Core U1309D-60R we pass through an interval, at least 30 m thick (310 -340 mbsf) that is predominantly olivine-rich gabbro separated at sharp, moderately steeply dipping contacts with intervals (50 cm to 1 m thick) of varitextured coarse-grained gabbro. Some intervals in the olivine-rich gabbro approach wehrlitic and even dunitic compositions (very low plagioclase abundance). While the olivine-rich gabbro has a dark, mottled appearance imparted by the serpentinization of the abundant olivine, fresh kernels of olivine are common.