The hysteresis properties of multidomain magnetite and titanomagnetite/titanomaghemite 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 (B-c) and the ratio of saturation remanence/saturation magnetization (M-rs/M-s) 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 presence of low-titanium magnetite in igneous rocks, notably MORB. (C) 2004 Elsevier B.V. All rights reserved.