Drilling on the Ontong Java Plateau during Leg 192 provided an opportunity to examine the magnetic properties of oceanic basalts produced during eruption of the world's largest igneous province. We examined the magnetic fabric of basalt cores for evidence of anisotropy related to their style of emplacement and cooling history. Broadly similar AMS characteristics involving only minor anisotropy are observed for most samples from both pillowed and more massive flow units. Only a few samples display higher degrees of anisotropy, but many of these are associated with changes in ChRM inclination and are thought to reflect major boundaries between successive cooling units.
The axis of maximum magnetic susceptibility of individual samples is dominantly subhorizontal and is believed to provide a reliable estimate of local flow conditions. The azimuths of the maximum anisotropy axis for each site were used to identify any preferred azimuth that may reflect a sustained flow direction. Differences in the preferred azimuth at each of the four sites suggest that the flow directions may reflect local rather than regional conditions. Although Sites 1186 and 1187 exhibit the same strong directional bias along N155°, the other sites display different azimuths. Site 1185 has a predominantly east-west preferred azimuth that is interpreted to represent the dominant flow direction near the eastern edge of the plateau. Site 1183, which lies closest to the crest of the plateau, has only a weakly developed azimuthal bias along two orthogonal directions—one along N120°/300° and one along N30°/210°.
More detailed sampling and analysis are required to reliably identify individual flow units and to map changes in the flow regime across the plateau.