1976 Articles

Viscous Remanent Magnetization in Basalt Samples

Lowrie, William; Kent, Dennis V.

Remanent magnetization measurements were made on four specimens of fresh, fine-to coarse-grained basalt from Site 321 and seven specimens of fresh medium-grained diabase at Hole 319A. The natural remanent magnetizations of these rocks were very unstable, characterized by median destructive fields of less than 100 oe in every sample and large directional changes during partial demagnetization. The samples were able to acquire large viscous remanences (VRM) in the laboratory in a 1.0-oe field. Moreover, the intensity of VRM acquired in the presence of the NRM was twice that acquired under similar conditions but after AF demagnetization. Whether acquired from the demagnetized or NRM state, the VRM acquired in 500 hr amounted to a very large fraction of the NRM intensity, particularly at Hole 319A. These results suggest that the large vertical component of magnetization observed in samples from this site may be in part a VRM acquired while drilling the hole in the presence of the drill pipe ambient field.