Behavior of oceanic crustal magnetization at high temperatures: Viscous magnetization and the marine magnetic anomaly source layer

Although the source layer for marine magnetic anomalies has been assumed to be the extrusive basalts of uppermost ocean crust, recent studies indicate that lower crustal rocks may also contribute. Because the temperature at w hich magnetization of crustal rocks achieves long-term stability is crucial to any soul ce layer contribution, we undertook high-temperature VRM (visc ous remanent magnetization) experiments on samples of basalt, dike and gabb roic sections. Samples were heated at temperature intervals up to T-c, whil e a magnetic field was applied for periods between 6 hours and 28 days. Res ults show that the dike and gabbro samples achieve maximum VRM acquisition near 250 degrees C, well below the T-c of 580 degrees C. The basalt sample shows a peak at 68 degrees C, also well below T-c. Results of this pilot st udy indicate that the critical isotherm for stable magnetization acquisitio n is defined by the VRM behavior of the specific crustal section.