The detailed study of 455 basement samples from DSDP Leg 37 reveals magnetic properties, particularly inclinations and intensities, different from those commonly considered representative of Layer 2. Non-dipole inclinations are the most common. The deepest hole (582 m) has a vector average intensity of 24.3 × 10−4 emu cm−3 (24.3 × 10−1 A/m) and an inclination of only −14.5°. Induced magnetization never dominates and is usually much less than remanent magnetization, with Q ratio averaging 35 for basalts and 2.6 for plutonic rocks. Viscous magnetization acquisition constant, S, ranges widely from 0.001 to 1 × 10−4 emu cm−3 (0.001 to 1 × 10−1A/m), but is very rarely sufficient to cause VRM to dominate NRM.The major carrier of NRM is cation-deficient titanomagnetite produced by low-temperature oxidation of stoichiometric titantomagnetite. There is no trend of alteration with depth. All the magnetic properties are controlled by conditions within the individual basalt pillows or more massive units. A high degree of cation deficiency is associated with reduced NRM intensity, initial susceptibility, saturation magnetization, and VRM acquisition and increased MDF, Q ratio, and Curie point. Zones of low cation deficiency are presently found only in parts of massive units. With the exception of rare individual samples pillow sequences are highly oxidized throughout.A discussion is given of the kinds of ocean crust drilling and laboratory experiments required to solve the problems of the magnetic structure of Layer 2 as seen at the Leg 37 sites.

Close to 400 semioriented subsamples of oceanic basement rocks from DSDP Sites 332, 333, 334, and 335 have been tested for paleomagnetic properties. Eight nonbasaltic samples consist of a variety of plutonic rocks from a melange penetrated at Site 334. Basalt in situ remanence intensity, giving unit weight to each 9.5meter core length, is very close to 40 × 10~4 emu/cm 3 , or 40% of the value normally assumed in model studies. The ratio of remanent to induced magnetization is high, averaging 37. In terms of remanent intensity and induced magnetization, the basalts fit the requirements of the Vine-Matthews hypothesis. However, in terms of vertical polarity layering, and abundant very shallow, nondipole NRM inclinations at Sites 332 and 333, they do not fit the hypothesis. Equivalent magnetic source layer thickness varies from 570 to 820 meters for dipole NRM inclinations to in excess of 2.5 km for the observed shallow inclinations. Systematic alternating field NRM analysis results in significant inclination change in 44% of samples. Shallow original magnetization is confirmed for many samples from Sites 332 and 333. The explanation appears to lie between tectonic tilting or recording of an excursion of long duration of the geomagnetic field.Cleaned magnetic inclinations are tightly grouped when divided on the basis of lithologic units. However, in many cases, sequences of lithologic/magnetic units have indistinguishable (or nearly so) average cleaned inclinations (the magnetic superunits of this chapter), suggesting formation during single eruptions or short (~10 2 yr) eruptive episodes. It seems that a 2-km-thick section of oceanic layer 2 could be formed by about 20 major eruptions or eruptive episodes, together with some minor intrusives. The occurrence of many anomalous inclinations does not permit reliable absolute plate motion estimates to be obtained from the data.

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A detailed study has been made of the magnetic properties of four pillow lavas of differing ages from the Mid-Atlantic Ridge crest at 45°N. The pillows show radial variations in grain size and concentration of titanomagnetite due to the initial cooling history, and radial variation in their degree of titanomagnetite oxidation due to low temperature alteration by sea-water. The degree of titanomagnetite alteration not only increases from the interior to the exterior of the pillows, it also increases from the youngest to the oldest. Radial variation in NRM intensity results in average values for the pillows of as little as half the values for the freshest parts. The direction of the original NRM has been maintained throughout the alteration.

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