A drill-string packer was used during Leg 148 to conduct measurements of the bulk permeabilities of three depth intervals in the upper crustal section penetrated by Hole 896A. Located about 1 km southeast of Hole 504B, near a local heat-flow high, Hole 896A is cased through 179 m of sediment and the top 16 m of basement, and then penetrates to 469 mbsf, or 290 m into the upper oceanic crust. The packer was set in casing at 106 mbsf and in open hole at 233 and 385 mbsf, and standard slug and constant-rate injection tests were conducted to assess the transmissivities and bulk permeabilities of the respective intervals 195–469, 223–469, and 385–469 mbsf. The results indicate that the upper 38 m of open hole is quite permeable, on the order of 2 × 10^–13 m². The section below this zone, 223–469 mbsf, is less permeable, on the order of 1–2 × 10^–14 m², but certainly permeable enough to support passive off-axis hydrothermal circulation. The permeability structure in Hole 896A is quite consistent with values determined in the upper ~200 m of basement in Hole 504B, and supports the inference that the uppermost basement is permeable on a scale of kilometers around the sites. However, the measurements in Hole 896A show no sign of the sharp reduction in permeability previously reported below ~250 m into basement in Hole 504B.

Date of initial receipt: 12 August 1994
Date of acceptance: 17 February 1995

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