The Hysteresis Properties of Multidomain Magnetite and Titanomagnetite/-maghemite in Mid Ocean Ridge Basalts

Hysteresis measurements have been carried out on a suite of ocean-floor basalts with ages ranging from Quaternary to Cretaceous. Approximately linear, yet separate, relationships between coercivity (Bc) and the ratio of saturation remanence /saturation magnetization (Mrs/ Ms) are observed for massive doleritic basalts with low-Ti magnetite and for pillow basalts with multi-domain titanomagnetites (with x = 0.6). Even when the MORB has undergone low-temperature oxidation resulting in titanomaghemite, the parameters are still distinguishable, although offset from the trend for unoxidized multidomain titanomagnetite. The parameters for these iron-oxides with different titanium content reveal contrasting trends that can be explained by the different saturation magnetizations of the mineral types. This plot provides a previously underutilized and non-destructive method to detect the occurrence of low-titanium magnetite in igneous rocks, notably MORB.