Formation of magnetic single-domain magnetite in ocean-ridge basalts with implications for sea-floor magnetism.

Shau, Y.-H., Peacor, D. R., and Essene, E. J.

Although magnetic data constitute the primary evidence for ocean floor spreading ,the processes by which magnetic phases in ocean-floor basalts are formed remain poorly constrained. Scanning transmissision electron microscopic observations show that magnetic single-domain magnetite in sheeted dike basalts of Deep Sea Drilling Project hole 504B formed by multiple processes: oxidation-exsolution of ilmenite in primary titanomagnetite, exsolution of ulvopinel lamellae, ulvopinel dissolution or replacement by sphene accompanied by recrystallization of magnetite through interaction with convecting fluids. The initial stable magnetization was thus modified by chemical remanent magnetization, and it appears to have a significant contribution to sea-floor magnetism.