| The deepest drill penetration ever into the oceanic crust was achieved during Legs 37 and 45 of the Deep Sea Drilling Program. In the present study, the magnetic properties of a large collection of basalt samples from Legs 37 and 45 near the Mid-Atlantic-Ridge were measured.;For the basalt samples, hysteresis parameters, coercive force, H(,c), coercivity of remanence, H(,cr), saturation magnetization, J(,s), remanent saturation magnetization, J(,rs), and susceptibility were measured before and after heating. Curie temperatures, the stability of NRM to alternating fields and the importance of viscous magnetic components were also evaluated. It appears that most of the variation in magnetic properties can be attributed to changes in magnetic domain structure resulting from low-temperature oxidation of titanomagnetite to titanomaghemite.;The magnetic properties measured before and after heating were used to develop a set of criteria for choosing suitable samples for paleointensity estimates using the Thellier method. Only five samples from Leg 37 satisfied the criteria. These samples gave a paleointensity value of 0.53 (+OR-) .06 oe, close to the present-day value.;The rather complex behaviour of most samples upon heating is explained here by a two-stage unmixing process in which titanomaghemite first unmixes to a low-titanium, low-oxidation level titanomaghemite and a hemo-ilmenite at about 300(DEGREES)C. Secondly, the titanomaghemite unmixes further to nearly pure magnetite.;Knowledge of these magnetic properties is of interest for two reasons: First, such information is required to understand and interpret features of the marine magnetic anomalies which are fundamental to the Vine and Matthews (1963) hypothesis. Regions of weak or absent magnetic anomalies and regions of enhanced anomalies may be explained by variations in magnetic properties. The second reason is that the ocean floor could provide an easily-dated record of the history of the earth's magnetic field. Oceanic basalts have proved too complex for blind application of paleointensity measurements. Knowledge of their magnetic properties would allow suitable samples to be selected.;In addition, a number of explanations for the shallower-than-expected inclinations often observed in basalts from the Atlantic were considered. It is concluded that self-demagnetization of strongly magnetic lavas at the ridge axis and large tectonic rotations are the most likely explanations. |
