The basement in Hole 896A can be divided into three sections on the basis of its magnetic properties. The magnetic mineralogy was investigated by monitoring the effect of heating on susceptibility. These results suggest that titanomaghemites occur throughout the hole and that titanomagnetites occur mainly below 330 mbsf.
Some samples have evidence for minor amounts of hematite.
The main cause of variation in the susceptibility and the median destructive field can be related to grain size. The magnetic properties of the upper part of Hole 896A, above the massive flow Unit 24, correlate with the upper part of Hole 504B above Unit 2D, at depths of 3796 and 3773 m below sea level, respectively. We suggest that the upper section corresponds to a late volcanic pile extruded onto a ponded flow that masks the earlier basement topography. This flow has probably acted as a major barrier to hydrothermal circulation. These results have significant implications for the interpretation of magnetic field data from ridges.