Previous   |   Next

doi:10.2204/iodp.proc.324.105.2010

Paleomagnetism

Because no basalt was recovered, we only analyzed eight discrete samples from volcaniclastic sediments recovered from Hole U1348A. The samples likely carry a depositional remanent magnetization instead of a thermoremanent magnetization. Therefore, any directional result will be more complicated to interpret.

We used the 2G cryomagnetometer for the measurements because the natural remanent magnetization (NRM) of these samples was too weak to be measured on the Molspin Minispin magnetometer (a few tens of mA/m). Only alternating-field demagnetizations were carried out, using the DTech degausser. Three other discrete samples cut for physical property measurements were too weak even for measurement with the 2G cryomagnetometer; therefore, we could not use them for paleomagnetic measurements. NRM bulk magnetic susceptibilities were also measured. The NRM bulk magnetic susceptibilities are on the order of 10^–4 SI, which is 2 orders of magnitude smaller than the values of basalts recovered from Holes U1346A and U1347A.

The low magnetic susceptibilities (between 4 × 10^–4 and 8 × 10^–4 SI) indicate that magnetic minerals are not abundant in these samples. Compared to the basalt samples from Holes U1346A and U1347A, these samples have a higher median destructive field (between 10 and 25 mT), which suggests that the magnetization carriers are single-domain grains (Fig. F55). Principal component analysis (PCA) (Kirschvink, 1980) was used to isolate a stable component pointing toward the origin. In five cases, once the low-coercivity overprint is removed, PCA gives fairly good results, with maximum angular deviation values between 3° and 7° (Table T9). Inclinations are mostly shallow and positive, between 4° and 23°, although one sample gives a negative inclination (–9°).

Top of page   |   Previous   |   Next