ALBERT

Description: Permeability, electrical resistivity, and thermal conductivity measurements were performed on samples from the Bent Hill area of the Middle Valley on the northern Juan de Fuca Ridge. Thermal conductivity measurements were also made on samples from the Trans-Atlantic Geotraverse (TAG) hydrothermal area in the Mid-Atlantic Ridge for direct comparison with previous studies and the Middle Valley results. Electrical resistivity and permeability measurements were made as a function of confining pressure on 15 samples comprising different lithologic compositions found in the Bent Hill area. The effect of pressure on electrical resistivity values is relatively small and the observed frequency dependence is highly controlled by the sulfide content in these rocks. Permeabilities are in the 10**-16 to 10**-20 m**2 (0.1-100 µD) range. Although permeability does not recover in samples that undergo significant permanent deformation, the elastic permeability dependence on confining pressure is relatively small. Permeability correlates with porosity. Permeability anisotropy correlates with the presence of oriented sulfide veins with increased flow parallel to the veins. Thermal conductivity measurements made on 41 samples from Middle Valley and 9 samples from the TAG area show systematic variations due to changes in composition and a weak relationship with porosity for sedimentary samples from Middle Valley. A comparison between the divided-bar and the half-space needle-probe methods of measuring thermal conductivity shows good agreement for the Leg 169 measurements unlike previous results from Legs 139 and 158. The discrepancies observed in earlier studies seem to be related to the long times used in the older measurements for the optimal T vs. ln(t) data interval. The apparatus used during Leg 169 was smaller, sampled a smaller volume of core, and in high conductivity material was not influenced by boundary effects.

Description: Seismic velocities have been measured at confining pressures of 100 MPa and 600 MPa for sheeted dike samples recovered during Ocean Drilling Program Legs 137 and 140. The compressional- and shear-wave velocities show an increase with depth at Hole 504B, which is in sharp contrast to the atmospheric pressure velocity measurements performed as part of the shipboard analyses. Rocks exposed to different types of alteration and fracture patterns show distinct changes in their physical properties. The seismic reflectors observed on the vertical seismic profile (VSP) experiment performed during Leg 111 may have been caused by low velocity zones resulting from alteration. The amount of fracturing and hydrothermal alteration in several zones also may have contributed to the acoustic impedance contrast necessary to produce the E5 reflector. Poisson's ratios calculated from laboratory velocity measurements show several low values at depths ranging from 1600 mbsf to 2000 mbsf, which tends to follow similar trends obtained from previous oceanic refraction experiments. A comparison of physical properties between samples recovered from Hole 504B and ophiolite studies in the Bay of Islands and Oman shows a good correlation with the Bay of Islands but significant differences from the measurements performed in the Oman complex.