High-temperature characteristics of a natural titanomagnetite

Abstract

Summary. Continuous recordings were made of thermal demagnetizations of Isr, ARM and TRM induced in artificial rock specimens. The artificial rock specimens contained well-defined grain-size fractions of a natural titanomagnetite, which under an optical microscope was homogeneous. Using a Transmission Electron Microscope it was shown that submicroscopic inclusions exist within the titanomagnetite. Screening of the remanence of these inclusions by the surrounding titanomagnetite is thought to be responsible for the occurrence of ‘peaks’ in the continuous thermal decay curves of Isr and ARM; higher ‘peaks’ observed in the case of TRM are thought to be caused by the combined effects of screening and an anti-parallel remanence in the titanomagnetite. Further submicroscopic exsolution processes, which occur in the titanomagnetite as a result of repeated heating, can be deduced from the development of new ‘peaks’, from changes in the temperature at which the ‘peak(s)’ occur, their shape and their relative height. The use of stepwise demagnetization techniques on the titanomagnetite yielded erroneous directional results due to the screening in the titanomagnetite; the biasing effects due to screening could be avoided by using continuous thermal demagnetization techniques.