The physical properties of primary crystalline rocks removed from depth and measured at atmospheric pressures are strongly related to both the original porosity and secondary porosity associated with stress unloading and the coring process. Alteration products, infilling of fractures and voids with secondary phases, and contributions from sediment, also influence the physical state of the recovered oceanic crust. Thus, physical properties measurements are indicators of lithologic type, texture, and degree of alteration and are used to assess the physical state of the oceanic crust with depth and to establish the correlation between downhole measurements and cored material.
MST measurements on whole-core sections from Hole 801C were obtained during Leg 185 and half-core sections within igneous basement were obtained during Leg 129. The MST includes instruments that measure magnetic susceptibility, gamma-ray attenuation evaluator (GRAPE) bulk density, and natural gamma radiation (NGR). We determined P-wave velocities from split cores in liners in the transverse x direction. Velocity measurements in the transverse (x and y) and longitudinal (z) directions on cut cubes allowed us to investigate possible velocity anisotropy. Index properties on cut samples including wet bulk density, grain density, porosity, and water content were calculated from measurements of wet mass, dry mass, and dry volume. We also measured thermal conductivity on split cores. MST measurements were the only physical properties data collected from Hole 801D (the single seafloor punch core) (see "Physical Properties" in the "Explanatory Notes" chapter.
Index properties were measured on 156 samples obtained adjacent to cut cubes that were used for velocity determinations. Additional samples were obtained in material that was too fragile to be cut into a cube. A salt correction assuming 3.5% interstitial fluid salinity was applied. The precision of these measurements (density, porosity, and velocity) is ~2% of the measurement for each property. Results are presented in Table T11 and displayed in Figure F63 and include comparable results obtained during Leg 129 for the igneous section (i.e., tables 6 and 7 in the "Site 801" chapter of Lancelot, Larson, et al., 1990). The average wet bulk density of all basement samples (including those from Leg 129) is 2.76 ± 0.17 g/cm3 and varies between 2.13 and 2.99 g/cm3, and porosity varies from 0.6% to 33.3% with a mean of 7.6% ± 5.6% and a median value of 6.1%. Density and porosity show the expected negative correlation (Fig. F64). These plots also indicate that samples classified as flows generally have higher density, higher velocity, and lower porosity than samples classified as pillows. The greatest variation in porosity and density is in Cores 185-801C-14R through 17R (~604-630 mbsf) and is associated with samples identified as interpillow material, hydrothermal deposits, and variably altered basalt. Neither density nor porosity appear to vary systematically with depth. The seven samples with porosity >20% are in the heavily altered flow units at 541 and 545 mbsf and in altered (pale green and dark green) pillow units at 621, 626, 627, 819, and 932 mbsf. These samples are also characterized by the six lowest average velocities (3237-4150 m/s), and the seven lowest densities (2.13-2.47 g/cm3). The lowest porosity measured (0.6%) is in silicified red-brown interpillow material from Core 185-801C-15R, but generally the lowest porosities are associated with the least-altered basalt. All samples classified as breccia have porosity above the median value.
Bulk density was measured by the GRAPE every 4 cm for 4 s on unsplit sections of core from Hole 801C drilled during Leg 185. The continuous GRAPE density measurements are compared to discrete samples of wet bulk density from Hole 801C in Figure F65. The large scatter in GRAPE density values results from the discontinuous core (empty space and/or rubble zones). The generally lower values (relative to discrete samples), where core is relatively continuous, are due to smaller core diameters than calibration cores. MST measurements, including GRAPE density values from Hole 801D, are shown in Figure F66. All reference to density in this report will be to the individual gravimetric samples.
We measured NGR every 10 cm for 20 s on unsplit sections of core from Hole 801C drilled during Leg 185 and on working-half cores from the basement section drilled during Leg 129. Peak values (15-20 cps) occurred only within the upper alkalic section above 510 mbsf. The majority of the tholeiitic section is characterized by low gamma-ray counts (<6 cps) punctuated by relatively high values (7-15 cps) in narrow zones, such as the highly altered basalt (celadonite and glauconite) at ~530 mbsf and within broader zones, also associated with obvious zones of alteration, between ~600 and 640 mbsf (Cores 185-801C-14R to 17R), and 805-850 mbsf (Cores 185-801C-36R to 40R) (see Fig. F65 and "Correspondence between MST-NGR Data and Features in the Core"). At the individual core scale, NGR often appears inversely correlated to magnetic susceptibility and appears to be qualitatively related to the amount of potassium-rich alteration products such as celadonite (i.e., high alteration associated with high NGR and low magnetic susceptibility). It is also possible that remobilization and fixation of uranium in zones of alteration contributes significantly to the total gamma-ray count in certain intervals. The NGR profile exhibits fluctuations and general trends that are similar to those of the downhole spectral gamma-ray logging data and will be particularly useful for core-log integration (see "Downhole Measurements").
We measured magnetic susceptibility every 4 cm for 4 s on unsplit sections of core from Hole 801C drilled during Leg 185 and on working-half cores from the basement section drilled during Leg 129 (Fig. F65). At the individual core scale, magnetic susceptibility varies inversely with gamma-ray counts and is low within intervals of relatively high alteration, hydrothermal deposits and interpillow material and uniformly high within thick massive flow units. Comparison of three independent susceptibility measurements, the MST, AMST, and discrete samples are discussed in "Paleomagnetism" in the "Explanatory Notes" chapter.
We determined compressional wave velocities in three mutually perpendicular directions (x, y, and z) on discrete samples (cubes) and in the x direction on split-core sections in a liner (Tables T11, T12; Fig. F63). Velocities from the split core correspond well with those from individual cubes. The average velocity value from each sample cube (i.e., [Vx + Vy + Vz]/3) ranges from 3237 to 6591 m/s with an average 5153 ± 640 m/s through the entire igneous section drilled during Legs 129 and 185. The greatest variation in velocity occurs in Cores 185-801C-14R to 17R (~604-630 mbsf) and is associated with samples identified as interpillow material, hydrothermal deposits, and variably altered basalt. Velocity values on discrete samples correlate well with those of in situ downhole velocity measurements (see "Downhole Measurements"). Velocity anisotropy is negligible (<5%) for the majority of samples; however, four values of over 15% anisotropy correspond to interpillow sediment and a pillow with a vertical carbonate vein. There is no clear relationship between depth and velocity, although, velocity, density, and porosity are well correlated throughout the section (Fig. F64). A set of samples exhibiting velocities >6000 m/s fall outside the linear trend between velocity vs. density and velocity vs. porosity (Fig. F64). These samples are all within massive tholeiites in Cores 129-801C-5R to 12R (~542-581 mbsf) and correspond to the greatest resistivity values observed at Site 801 (see "Downhole Measurements"). Similar zones of relatively high velocities (and resistivities) occur within thick flow units in Cores 185-801C-27R to 28R, 30R to 31R, and 37R to 38R. An extended zone of relatively low velocities (<5100 m/s) is found within Cores 185-801C-43R through 46R.
Thermal conductivity measurements were taken once per core on split-core sections on samples that were at least 20 cm long, massive, and relatively unaltered (i.e., no interpillow, hydrothermal, or breccia was sampled). Thermal conductivity is listed in Table T13 and plotted with depth in Figure F67. Thermal conductivity of igneous basement cored during Legs 129 and 185 ranges from 1.49 to 4.98 W/(m·K) and averages 1.85 ± 0.53 W/(m·K). Although thermal conductivity varies little downhole, there is a clear offset at ~585 mbsf, from values above 2 W/(m·K) to values below 1.8 W/(m·K).
Physical properties of oceanic basement at the hand-sample scale are strongly influenced by the extent of alteration as well as lithologic type and texture. We developed preliminary relationships between physical properties and the visible indications of basalt alteration and with various important components of oceanic crust (interpillow material, sediment, and hydrothermal deposits). These relationships were used to establish the correlation between cored material and physical/chemical measurements obtained with downhole tools and are, therefore, an important component in the fundamental objective of reconstructing a complete crustal stratigraphy through core-log integration. For example, the observation that hydrothermal deposits are of lower porosity and of higher density and velocity relative to highly altered basalt (and are thus relatively high resistivity units), allowed the correlation of continuous, high-resolution resistivity images using the Formation MicroScanner tool (FMS) within the hydrothermal interval in Core 185-801C-16R (see "Downhole Measurements" below). The clear relationship between the NGR signature and patent alteration features also formed the basis for a K budget for the core (see "Using Natural Gamma Ray to Calculate Potassium Budgets".