The Mid-Atlantic Ridge Near 45 °N. XIX. An Electron Microscope Investigation of the Magnetic Minerals in Basalt Samples

Abstract

Basalt samples from the vicinity of the Mid-Atlantic Ridge near 45 °N have been examined by electron microscopy, since many of the magnetic properties could be due to the fine structure of the titanomagnetites present. The observed remanence of axial material cannot be accounted for by multidomain or pseudo-single domain models. Furthermore, an explanation in terms of submicroscopic unmixing of titanomagnetite grains is shown to be untenable. However, electron microscopy did reveal the presence in all samples of a finely dispersed phase believed to be single-domain titanomagnetite grains. These will inevitably contribute to the remanence and may well be the dominant factor. The decay in remanence with distance from the ridge axis, which could similarly be associated with fine structure, is also discussed.