Ocean Drilling Program, United States

Paleomagnetic measurements were made on 52 samples from the igneous section of Ocean Drilling Program Hole 1213B for the purpose of determining paleoinclination and polarity and giving insight about volcanic emplacement. Samples were taken at approximately even intervals from the three basaltic sills that make up the section, and all samples were demagnetized using an alternating field or thermal methods in an effort to determine the characteristic magnetization direction. Half of the samples gave inconsistent results. Furthermore, natural remanent magnetization values were strong and median destructive field values were low, implying that the basalts are prone to acquiring an overprint from the drill string. In addition, hysteresis results show low coercivities and lie in the pseudosingle-domain field of a Day plot (M (sub r) /M (sub s) vs. B (sub cr) /B (sub c) ). All of these observations suggest that the samples are characterized by a low-coercivity magnetic mineral, such as titanomagnetite, that may not always preserve a stable characteristic remanence. Nevertheless, 26 samples produced consistent inclinations, giving shallow, negative values that are considered the likely characteristic direction. There is no statistical difference between mean inclinations for the three units, implying they erupted within a short time. Measurements from all reliable samples were averaged to give a paleoinclination of -9.3 degrees with 95% confidence limits from -41.8 degrees to 27.5 degrees , the large uncertainty resulting from the fact that paleosecular variation is not averaged. Although the large uncertainty makes a unique assignment of polarity difficult, the interpretation that is most consistent with other Pacific paleomagnetic data is that the magnetization has a reversed polarity acquired slightly north of the equator.