JA Daily Science Report for Expedition 309, 03 August 2005
LOCATION: Site 1256
SCIENCE UPDATE: Cores 117R to 121R recovered 7.11 m of basalt from 1003.2 to 1027.3 mbsf (~30% recovery). Three igneous units (39-41) were distinguished on the basis of chilled contacts and phenocryst content. Cryptocrystalline to fine grained sheet flows continue to predominate although other intriguing features are present. The upper part (117R-1 90-130 cm) of Igneous Unit 40 has a complex texture with fine grained basalt intruded into and enveloping brecciated cryptocrystalline basalt. The fine grained basalt is irregularly quenched to glass in places and disrupted by an intense network of very fine saponite veins that strongly alter the surrounding groundmass imparting an incipient brecciation texture. A 3 mm-thick quenched intrusive margin is present in Core 120R that is tantalizingly reminiscent of a dike margin, but such is the capricious nature of hard rock basement drilling, the precise nature of this contact remains elusive. Saponite, silica and pyrite continue to be the major secondary minerals.