The physical properties of the peridotites and gabbros cored in Holes 1271A and 1271B were characterized through a series of measurements on whole-core sections, split-core pieces, and discrete samples as described in "Physical Properties" in the "Explanatory Notes" chapter. We measured natural gamma ray (NGR) activity and magnetic susceptibility on the multisensor track (MST) system and thermal conductivity, compressional wave velocity, density, and porosity. The rock names reported in data tables correspond to the primary lithologies determined by the igneous core description group.
All cores recovered during Leg 209 were measured using NGR logger on the MST at intervals of 10 cm with a time period of 30 s. Results are output in counts per second. The cores from Holes 1271A and 1271B display natural radioactivity in the same range as the background radiation in the core laboratory on board the JOIDES Resolution. No significant peak was recorded in the NGR data in these cores.
Magnetic susceptibility values were acquired on the MST at 2.5-cm intervals for all recovered cores. Most cores from Site 1271 have high magnetic susceptibility (Fig. F65), which is related to the presence of magnetite in the serpentinized peridotites. The magnetic susceptibilities of the peridotites at Site 1271 are comparable to those at Site 1270 (see Fig. F105 in the "Site 1270" chapter) and the peridotites from Hess Deep (Gillis, Mével, Allan, et al., 1993) and the Kane Fracture Zone (MARK) area (Cannat, Karson, Miller, et al., 1995) (see Fig. F88 in the "Site 1268" chapter).
Thermal conductivity measurements were made at irregularly spaced intervals along cores from Holes 1271A and 1271D in six peridotite samples and one troctolite. The data are summarized in Table T6. The thermal conductivities of the peridotite samples range 2.5–3.2 W/(mˇK) (mean = 2.87 W/[mˇK]); the thermal conductivity of the troctolite ranges 2.88–2.93 W/(mˇK). These values are comparable to the thermal conductivities of peridotite from ODP sites at Hess Deep (Gillis, Mével, Allan, et al., 1993) and MARK (Cannat, Karson, Miller, et al., 1995) and to the values measured at Sites 1268 and 1270 (Fig. F66).
As described in "Thermal Conductivity" in "Physical Properties" in the "Explanatory Notes" chapter, measurements were taken in three directions on the cut face of the archive halves, whenever possible. The purpose of these measurements is to determine the degree of apparent anisotropy. The apparent thermal conductivity anisotropy of peridotites and the troctolite measured in cores from Site 1271 ranges 0.6%–5.5%. Apparent thermal conductivity anisotropies measured since the beginning of Leg 209 (including Sites 1268, 1270, and 1271) are compiled in Figure F67. Anisotropy ranges 0.2%–12.6% (mean = 4.63%) in gabbros, peridotites, and troctolites.
Bulk density, grain density, and porosity were measured on small sample chips (~3–6 cm3) from Holes 1271A and 1271D. P-wave velocity and wet bulk density were measured on cube samples, as described in "P-Wave Velocity" and "Porosity and Density" in "Physical Properties" in the "Explanatory Notes" chapter). These data are summarized in Table T7. With the exception of one troctolite, all of the samples are serpentinized peridotites.
The density and velocity data are compared with data from Legs 147 and 153, as well as Sites 1268 and 1270 (see "Porosity, Density, and Seismic Velocity" in "Physical Properties" in the "Site 1268" chapter and "Porosity, Density, and Seismic Velocity" in "Physical Properties" in the "Site 1270" chapter) in Figure F68. Velocity anisotropy in the serpentinized peridotite samples from Site 1271, which ranges from 2.4% to >8.1%, is comparable to the anisotropy in samples from Site 1268 and 1270. The lone troctolite sample is essentially isotropic. Velocities and densities in the peridotite and troctolite samples from Site 1271 are also comparable to the densities and velocities of the ultramafic samples from Sites 1268 and 1270 and are notably lower than the velocities and densities of samples from Legs 147 (Gillis, Mével, Allan, et al., 1993) and 153 (Cannat, Karson, Miller, et al., 1995) (Fig. F68). The velocity and density of the troctolite sample are comparable to the properties of gabbros from Leg 153.