Figure F245. Comparison of different demagnetization treatments from discrete samples within a single diabase interval. A, C, E. In all cases, the natural remanent magnetization (NRM) is dominated by a steep normal polarity magnetization component, presumably related to drilling. Low-temperature treatment prior to alternating-field (AF) demagnetization (LTD steps in C) removes a large proportion of the normal polarity component, confirming that this is carried by coarse multidomain magnetite. B, D. A reversed polarity component (representing only a small fraction of the NRM) is isolated by demagnetization at high alternating fields. E, F. In contrast, thermal demagnetization isolates only a single, normal polarity component indistinguishable from the low-stability direction defined by AF demagnetization and with a maximum unblocking temperature close to the Curie temperature of magnetite. Open circles = projections of the remanence onto the north-south vertical plane, solid circles = projections of the remanence onto the horizontal plane.
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