Evaluation of physical properties at Site 1277 included nondestructive measurements of density, porosity, velocity, and thermal conductivity. Horizontal (x- and y-directions) and vertical compressional wave (P-wave) velocity (z-direction) were measured on cubes cut from half-core samples. Porosity and density were determined from cylinders shaped from the velocity-determination cubes. Thermal conductivity was measured on lithified half-core samples. Physical property data for Site 1276 can be extracted from the Janus database. Apart from an initial wash core (Core 210-1277A-1W), core recovery commenced at 103.90 mbsf and continued to 180.30 mbsf (Cores 2R through 9R). Because of the urgency to have cores split and made available to the structural and igneous petrology groups, the cores were not measured using the MST.
Bulk density, grain density, and porosity at Site 1277 were calculated from the wet mass, dry mass, and dry volume of discrete samples using the moisture and density (MAD) method C (Blum, 1997). These measurements were made on lithified sedimentary and igneous rocks in Cores 210-1277A-2R through 9R (103.90–180.3 mbsf). The majority of samples from Site 1277 are igneous and metamorphic rocks. MAD bulk density and grain density vary by 0.3–0.5 g/cm3 downhole (mean = 2.47 g/cm3 and 2.75 g/cm3, respectively) (Fig. F17). Relatively low bulk densities are associated with Cores 210-1277-4R, part of a mass-flow unit, and 9R, which consists of serpentinized peridotite mylonites and cataclasites. Although the majority of porosities are 10%–20%, values range from 2% to 25% (average = 15.9%), reflecting the variably fractured and brecciated nature of most of the recovered section (Fig. F17). There is no obvious downhole trend in porosity, and the maximum porosities are associated with the sediments and mass flows of Sections 210-1277A-4R-1 and 4R-2. The lowest porosities are associated with basalts and gabbros of Cores 210-1277A-3R and 5R and with the serpentinized peridotites in Core 7R. Porosities in the serpentinized peridotites range from 9% to 21%. The serpentinized peridotites show remarkably uniform bulk densities (~2.4 g/cm3) and grain densities (~2.66 g/cm3). Grain densities for the basalts and mass flows range between 2.76 and 3.00 g/cm3, and bulk densities range from 2.3 to 2.8 g/cm3.
Compressional wave velocities were measured with the P-wave sensor 3 (PWS3) contact probe system on ~8-cm3 cube samples of lithified sediments and igneous rocks. The cubes were used to measure velocities in the horizontal (x and y) and vertical (z) directions.
Measured velocities range from 3300 to 6300 m/s (Fig. F18). Velocity is lowest (~3270 m/s) in highly altered and veined breccia (Section 210-1277A-4R-2), and it is highest (6325 m/s) in a coarse-grained gabbro (Section 5R-3). Serpentinized peridotites show a range of velocity between ~3300 and 4700 m/s. There is no obvious downhole trend in velocity.
Velocity data in the x-, y-, and z-directions were used to define velocity anisotropy. Velocity anisotropy was calculated as follows:
where Vh is the mean horizontal (x and y) P-wave velocity and Vv is the vertical (z) velocity. The calculated anisotropy ranges from –9% (altered gabbros) to 6% (sediments) (average = –1.5%).
Thermal conductivity measurements were made on intact pieces of half-round core of at least 10 cm in length. Thermal conductivity in Hole 1277A ranges from 1.6 to 2.25 W/(m·K) (Fig. F19) with the majority of values ranging from 1.6 to 2.0 W/(m·K) (average = 1.86 W/[m·K]). There is a general increase in thermal conductivity between Core 210-1277A-2R (gabbro cataclasite and basalt) and Core 4R (sediments and mass flows). In contrast, the serpentinized peridotites show a relatively consistent thermal conductivity value of 1.75–2.0 W/(m·K) with depth.