Abstract

In the laboratory the bulk density and the compressional wave velocity as a function of varying confining pressure (0.001 to 6.0 kb) was measured for 25 samples. Nineteen of these samples were fresh, unaltered basalts and, on the basis of their mineralogy, could be separated into olivine basalt (7), plagioclase basalt (9), and pyroxene basalt (3). The basalts had textures typical of extrusive and shallow intrusive volcanics. Of particular interest during the study was the effect of varying basalt mineralogy at confining pressures representative of the estimated lithostatic confining pressure of layer 2A. At 0.5 kb confining pressure, the average compressional wave velocity is olivine basalt (7) 5.62 km/sec (σ = 0.31), plagioclase basalt (5) 5.49 km/sec (σ = 0.19), pyroxene basalt 5.45 km/sec (σ = 0.32). There is no significant difference between the velocities of the three basalt groups, thus suggesting that at 0.5-kb confining pressure the control on velocity is principally textural. The other six samples (serpentinite (3), metagabbro (1), greenstone (1), and metabasalt breccia (1)) were recovered from the escarpments of fracture zone B. These rock types and their measured compressional wave velocities are typical of rocks recovered from transform faults.

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