TO: Tom Davies
FM: Jay Miller
JA Daily Science Report for Expedition 305, 10 February 2005.
SCIENCE UPDATE: Cores 305-U1309D-207R to -210R (1015.2 to 1048.8 mbsf, 93% recovery) are a complex series of varitextured gabbro and olivine gabbro. Grain size ranges from fine (<2 mm average) to pegmatitic, mode varies from as much as 20% olivine to virtually none. Contacts between grain size changes are commonly sharp, but with variable attitude, while changes in mode are generally (but not exclusively) more gradational. For example, in Core U1309D-214R (~1030 mbsf) a medium-grained olivine gabbro has sharp upper and lower intrusive contacts within coarse-grained gabbro. The upper contact is planar and subhorizontal, while the lower contact is a sharp but crenulate, steeply dipping, sutured igneous boundary. In places variations in grain size occur in patches smaller than the diameter of the core, resulting in islands of coarser grained gabbro nestled within isotropic medium-grained gabbro. Alteration is low (less than 10% except in local intervals) and evidence of deformation is rare to nonexistent.