JA Daily Science Report for Expedition 309, 19 August 2005


LOCATION: Site 1256


SCIENCE UPDATE: Cores 165R to 168R recovered 16.57 m of rock from 1227.8 to 1247.0 mbsf at the spectacular recovery rate for ocean floor basalt of 86%. From Section 165R-1 to 168R-5 four igneous units (60, 61, 62, and 63) were identified based on the occurrence of breccia and/or grain size changes. Units 60 and 61 are subdivided into two subunits based on cross-cutting intrusions (B subunits). Units 60A, 61A and 63 consist of aphyric cryptocrystalline to microcrystalline basalts and Unit 62 is sparsely (clinopyroxene-) plagioclcase-phyric microcrystallne basalt. Pieces 2-4, 6, 10 and 11 of Section 165R-3 have intricate and irregular dike (60B) contacts, and Pieces 14 and 16 of Section 166R-1 display multiple, cm-wide dike (61B) intrusions. The dike contacts are sharp to irregular chilled margins that are not brecciated. A xenolith of microcrystalline basalt (11 mm) is present in Piece 3 of Section 165R-1. Grey-green patches, where hydrothermal alteration to greenschist facies minerals is more intense, are commonly developed both in zones of more abundant mesostasis as well as along the margins of chlorite, quartz, pyrite ́ anhydrite veins.