Magnetic Properties of Basalts from DSDP Leg 49

Abstract

Rock magnetism is the study of the fundamental magnetic properties of the magnetic minerals present in rocks. In submarine basalts the dominant carriers of the magnetic signal are titanomaghemites, which are titanomagnetites that have been oxidized to varying degrees at low temperatures. They are single phase and retain the spinel structure of the original titanomagnetite. High-temperature oxidation is generally absent in submarine basalts. Our knowledge of the magnetic properties of titanomaghemites is very limited. The most exhaustive study is that by Readman and O'Reilly (1972), who examined some of the magnetic properties of synthetic samples; but although their samples spanned the whole composition range of the titanomaghemites, their study was limited by the necessity for keeping grain size small if one is to produce single-phase oxidation products. The mean grain size in their samples was about 0.1 μm. So until a method is found to produce large-grain synthetic titanomaghemites, we are confined to studies of the natural grains in submarine basalts.