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doi:10.2204/iodp.proc.330.106.2012

Paleomagnetism

Hole U1375A

No paleomagnetic experiments were conducted on Core 330-U1375A-1R.

Hole U1375B

Archive-half core remanent magnetization data

The natural remanent magnetization (NRM) of the archive half of Core 330-U1375B-1R was measured at 2 cm intervals in the cryogenic magnetometer and progressively demagnetized in an alternating field (AF) at steps of 10, 15, 20, 25, 30, 40, 50, and 70 mT. After filtering out data near the piece ends, 10 measurements remained. Of these measurements, five were from Piece 2 and five were from Piece 5. Because there were so few data, the principal component analysis (PCA) directions were picked by hand. Of these, 50% had a maximum angular deviation of <5°. Fisher statistics were used to calculate the mean inclination (as opposed to inclination-only statistics) because all the reliable measurements were from a single piece (Piece 2) and the declinations suggest the constituent subpieces did not rotate relative to each other. The resulting inclination is 36.3° ± 1.6° (circular standard deviation), indicating reversed polarity in the Southern Hemisphere. However, no upper or lower boundaries to this microgabbro unit were recovered, and therefore the in situ confidence index (see “Igneous petrology and volcanology” in the “Methods” chapter [Expedition 330 Scientists, 2012a]) was determined to be not applicable (NA).

Discrete sample remanent magnetization data

Only one discrete sample was taken from the microgabbro (dolerite) of Core 330-U1375B-1R, at 43–45 cm. The NRM and bulk magnetic susceptibility of this sample are 1.41 A/m and 4.07 × 10^–2 SI, respectively, yielding a Königsberger ratio (Qn) of 0.95. The sample was subjected to stepwise AF demagnetization, but unfortunately a large spurious magnetization, probably of anhysteretic or isothermal origin, was unexpectedly imparted during demagnetization at low field levels (<10 mT). Despite further AF treatment at higher fields, an original remanent magnetization component could not be confidently isolated. Nevertheless, clustering of magnetization vectors about a northwest and downward direction (in geographic coordinates) was observed at treatments of 30 mT and above. This direction is broadly consistent with the AF demagnetization results from the archive-half cores.

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