The multisensor track (MST) was run for nondestructive measurements of wet bulk density, magnetic susceptibility, and natural gamma radiation on whole-round cores. Two whole-round samples were then taken for postcruise in situ permeability and physical properties measurements. After the samples were split and labeled, minicore samples were cut for moisture and density and P-wave velocity measurements.
Thermal conductivity measurements using the half-space method were made on the archive-half sections. A detailed description of the techniques used is given in the ODP Physical Properties Handbook (Blum, 1997) and is only summarized here.
The MST combines four sensors on an automated track to measure magnetic susceptibility, bulk density, P-wave velocity, and natural gamma ray emission on whole-core sections. P-wave velocity was not collected because of the incomplete coupling between the liner and the core.
Magnetic susceptibility was measured with a Bartington MS2 meter using an 80-mm internal diameter sensor loop (88-mm coil diameter) operating at a frequency of 565 Hz and an alternating field of 80 A/m (0.1 mT). The sensitivity range was set to the low sensitivity setting (1.0 Hz). The sampling interval was set to 2 cm. The quality of these results is degraded because samples were fragmented into 3- to 10-cm-sized pieces. Nevertheless, general trends are useful for the overview of the variability in basalt composition. The measured magnetic susceptibilities are relative and have not been corrected for differences between core and coil diameters.
Bulk density was estimated for whole-round core sections as they passed through the gamma ray attenuation (GRA) bulk densiometer with a sampling period and interval of 2 s and 10 cm, respectively. The gamma ray source was 137Cs. Since bulk densities are estimated by measuring the attenuation of gamma rays that pass through the core, a constant sample thickness is required. However, most samples were fragmented into 3- to 10-cm-sized pieces, which degraded the quality given the 10-cm sampling interval. Therefore, results can only be used for general trends.
Natural gamma radiation (NGR) analysis is a function of the random and discrete decay of radioactive atoms and is measured through scintillating detectors as outlined by Hoppie et al. (1994). During Leg 196, NGR emissions were measured for 20 s at 10-cm intervals. NGR calibration was performed at the beginning of the leg.
Bulk density, grain density, and porosity were calculated from measurements of wet and dry masses and dry volumes (Method C of Blum, 1997). Eleven ~10-cm3 samples were taken from split cores. Sample mass was determined using a Scientech electronic balance. The sample mass was counterbalanced by a known mass of 20 g so that only mass differences of usually <2 g were measured. The balance was also equipped with a computer-averaging system that corrected for ship accelerations. Dry mass was measured from samples that were oven-dried at 110° ± 5°C for 24 hr and cooled in a desiccator for 2 hr. Dry volumes were determined using a helium-displacement Quantachrome Penta-Pycnometer. Sample volume measurements were repeated up to five times until the last set of measurements had a standard deviation <0.01%. A purge time of 1 min was used before each run. A reference sphere of known volume was run with each group of four samples during all measurements. The standard was rotated systematically among cells to check for errors.
P-wave velocity was measured on basalt minicore samples using the PWL3 modified Hamilton Frame velocimeter (Boyce, 1976). The PWS3 contact probe system measures the traveltime of a 500-kHz signal through a sample, with the oriented sample (cube) placed directly between the transducers in the desired orientation (x-, y-, and z-direction; these directions are defined in Blum, 1997). The minicore samples had their sides cut with the parallel saw so that all three orientations could be measured. Sample thickness was measured directly by a digital caliper. The velocity data recorded in the Janus database are uncorrected for in situ temperature and pressure (such corrections can be made using the relationships in Wyllie et al., 1956).
Calibration of the system was performed according to Blum (1997). The separation between transducers was calibrated with four polycarbon standards with varying thickness (20-50 mm). The delay time was determined by a linear regression of traveltime vs. thickness (15.4-57.5 mm) of seawater. An external digital thermometer was used to record core temperature. The values were stored in the database but were not used in this report.
Anisotropy was calculated using the following equation:
where VPt is the transverse (z-oriented) P-wave velocity and VPl is the longitudinal velocity. VPl was determined as the average P-wave velocity in the x- and y-directions.
Thermal conductivity is the measure of a material's ability to transmit heat by molecular conduction and is required for heat flow determinations.
The TK04 system (Teka, Berlin) was used for thermal conductivity measurements. For basalt samples, a smooth surface was prepared on ~6-cm-long split-core specimens that had been placed in a seawater-filled bath until they were resaturated with seawater and thermally equilibrated. The half-space needle probe (#H19608) was secured onto the flat surface of the split core. The needle probe (1.9-mm diameter x 70-mm length) contains a heater wire and a calibrated thermistor.
At the beginning of each half-space measurement, temperatures in the samples were monitored automatically, without applying a heater current, until the background thermal drift was determined to be <0.04°C/min. The heater circuit was then closed and the temperature increase in the probe was recorded.
The reported thermal conductivity value for each sample is the average of four repeated measurements. Thermal conductivities were calculated from the rate of temperature rise while the heater current was flowing. Temperatures measured during the first 80 s of the heating cycle were fitted to an approximate solution of a constantly heated line source (Kristiansen, 1982; see Blum [1997] for details). Data are reported in W/(m·K) with a stated error of 5%-10%. The choices of measurement interval and assessment of thermal stability are automatic with the TK04 meter, which does not require shipboard calibration. Table T4 gives thermal conductivity measurements for two standard samples, Macor and red rubber. Other "legacy" standards (black rubber, 504B basalt, and fused silica) could not be found on the ship, which prevented construction of a calibration line for the half-space probes. However, measured values for Macor, which are close to basalt conductivities, match reported values very well. Thus we did not apply any further calibration afterwards. Also, corrections were not attempted for in situ temperature or pressure effects.