Magnetic properties of oceanic basalts — effects of pressure and consequences for the interpretation of anomalies

The stability of natural remanent magnetization of three samples of oceanic basalts (DSDP Leg 25) is tested by alternating fields, thermal and pressure demagnetization. The possibility of low-temperature oxidation is examined by means of thermomagnetic curves.The effects of uniaxial compressions on initial susceptibility and induced magnetization are studied for the three samples. These experiments, performed in a field comparable to the geomagnetic field have shown large variations of magnetization. The results of paleomagnetism, as well as the interpretation of anomalies when the effects of the pressure of water and of possible sediments far from the ridge itself are taken into account, are discussed. The results could partly account for the decrease of magnetic anomaly amplitudes with distance from the mid-ocean ridge.