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 which magnetization of crustal rocks achieves long-term stability is crucial to any source layer contribution, we undertook high-temperature VRM (viscous remanent magnetization) experiments on samples of basalt, dike and gabbroic sections. Samples were heated at temperature intervals up to Tc, while a magnetic field was applied for periods between 6 hours and 28 days. Results show that the dike and gabbro samples achieve maximum VRM acquisition near 250°C, well below the Tc of 580°C. The basalt sample shows a peak at 68°C, also well below Tc. Results of this pilot study indicate that the critical isotherm for stable magnetization acquisition is defined by the VRM behavior of the specific crustal section.
Bowles, Julie A. and Johnson, H. Paul, "Behavior of oceanic crustal magnetization at high temperatures: Viscous magnetization and the marine magnetic anomaly source layer" (1999). Geosciences Faculty Articles. Paper 8.