Paleomagnetic measurements were performed on discrete minicore samples and, where practical, on continuous pieces of the archive half-core. A standard 2.5-cm-diameter minicore sample was generally taken from each section of core for shipboard study. Minicore samples were chosen to be representative of the lithology and alteration mineralogy, and an effort was made to select samples near important structural features for possible reorientation using the remanent magnetization directions. The azimuths of core samples recovered by rotary drilling are not constrained. All magnetic data are therefore reported relative to the following core coordinates: +X (north) is into the face of the working half of the core, +Y (east) points toward the right side of the face of the working half, and +Z is down (e.g., Leg 153 Initial Reports "Explanatory Notes" chapter; Shipboard Scientific Party, 1995a).
The remanent magnetization of continuous core pieces was measured with the 2-G Enterprises (Model 760R) pass-through magnetometer equipped with superconducting quantum interference devices. An in-line alternating field (AF) demagnetizer capable of producing alternating fields up to 80 mT was used with the 2-G magnetometer. The Long Core v2.2 program developed by William Mills was employed. The maximum intensities that could be measured without significant flux jumps remaining depend on the velocity of measurements. Maximum intensities of 7 A/m, corresponding for example to ~20,000 flux counts for a half core measured on the Z sensor, could be measured at the slowest possible tray velocity of 1 cm/s. At 5 cm/s the maximum measurable intensity decreases to ~2 A/m. Archive-half cores were selected for remanence measurements depending on the susceptibility values measured with the multisensor track (MST) whole-core logger. Core pieces having susceptibilities (k) that are >0.05 (SI) were removed from the liner for remanence measurements. The natural remanent magnetization and the remanence remaining after demagnetization (typically at 5, 10, 15, and 20 mT) were measured at an interval of 2 cm.
Oriented discrete samples were obtained as standard 2.54-cm cylindrical samples. These also were measured with the 2-G magnetometer in the discrete sample mode of the Long Core v2.2 program. Because of the reduced volume (10 cm3) compared to half cores, maximum measurable intensities are on the order of 100 A/m. Samples were AF demagnetized up to 80 mT in steps of typically 3, 5, 10, 15, 20, 30, 40, 50, 60, and 80 mT with the integrated demagnetizer. A small number of samples were thermally demagnetized, using the Schönstedt Thermal Demagnetizer (Model TSD-1). The initial susceptibility was monitored between each temperature step as means of assessing mineralogical changes associated with heating.
The anisotropy of magnetic susceptibility was determined for most cylindrical samples, using the Kappabridge KLY-2 and the program ANI20, provided by the manufacturer Geofyzika Brno, Czech Republic. A 15-position measuring scheme is used to derive the susceptibility tensor and associated eigenvectors and eigenvalues.
In addition to standard paleomagnetic measurements, a limited number of discrete samples were given an anhysteretic remanent magnetization (ARM) with a Dtech D-2000 AF Demagnetizer employing peak AF fields of 200 mT and a direct field of 0.1 mT. The ARMs were also measured and AF demagnetized with the 2-G magnetometer.