JA Daily Science Report for Expedition 309, 10 August 2005


LOCATION: Site 1256


SCIENCE UPDATE: Coring of hard formations continued with penetration from 1118.5 to 1132.5 mbsf returning 14 m of core (Cores 141R to 143R; 42 % recovery), much of it lengthy continuous pieces that will be useful for core re-orientation and core-log integration. The uppermost pieces in Section 141R-1 include many complex cm-scale pyrite-rich halos developed along chilled margins and veins similar to the  spectacular altered dike contact recovered in Core 140R. Igneous Unit 48 starts ~60 cm into Section 141R-1 and is a microcrystalline to fine grained aphyric to sparsely ol-phyric basalt with the irregular

development of ophitic textures in some pieces. An angular xenolith of cryptocrystalline basalt is captured within this unit in Section 142R-2. The base of Unit 48 is marked by ~60 cm of brittly veined cryptocrystalline olivine-phyric basalt in Section 143R-1. Unit 49 is an aphyric microcrystalline basalt and a change in phenocryst abundance and a subtle grainsize decrease delineates the beginning of Unit 50, an olivine-phyric microcrystalline basalt (Section 143R-2).

Throughout these cores numerous blotchy to well defined light alteration patches are developed in groundmass and along some vein margins. These appear to result from the alteration of primary igneous minerals to albite, chlorite +/- pyrite.