A Low Temperature Investigation of the Natural Remanent Magnetization of Several Igneous Rocks

Summary The n.r.m. of samples of dolerite from the Great Whin Sill, and of basalts from Iceland and Argentina, have been examined during cooling and warming between the ambient and liquid nitrogen temperatures. At about - 150 "C magnetite undergoes a phase transition of the second kind. The thermo-remanent magnetization acquired when samples of these rocks, which contain magnetite, are cooled and reheated through this temperature has been studied. The name 'transition thermoremanent magnetization' (t.t.r.m.) is preferred for this kind of magnetization, rather than 'inverse' t.r.m. used by Japanese workers.