Magnetic properties and heavy metals at DSDP Hole 83-504B

As in the upper part of the hole, reversely magnetized units predominate. Intensities of natural remanent magnetization vary widely, but the range of variation is an order of magnitude less than in the upper part of the hole.

This and the other properties measured indicate that the magnetic characteristics of basalts from Hole 504B have been strongly affected by hydrothermal alteration, particularly in the deeper, Leg 83 section. The alteration states of the magnetic samples were studies using Xray diffraction, electron microprobe, X-ray fluorescence, and ion coupled plasma. Our results suggest three alteration zones in Hole 504B: a low-temperature zone (274.5-890 m) and two high-temperature zones (890-1050 m and 1050- 1350 m), differing in the number of veins observed in the samples and presumably differing in the volumes of hydrothermal fluids which reacted with the basalts.