End-member modelling as an aid to diagnose remagnetization: A brief review

Remagnetization of a palaeomagnetic signal is difficult to recognize independently of directional information. The situation becomes more complex when remagnetized rocks pass palaeomagnetic field tests, for example when the remagnetization of a rock sequence has occurred before folding. It is evident that palaeogeographic reconstructions are seriously flawed when actually remagnetized rocks are not identified as such. Here we discuss the merits and pitfalls of so-called end-member modelling of acquisition curves of the isothermal remanent magnetization (IRM) to recognize remagnetized strata. The technique requires no a priori information about the IRM acquisition curves. The algorithm unmixes a set of IRM acquisition curves into a number of invariant curves termed end members and calculates the mixing proportions of the end members for each sample. Since primary natural remanent magnetization (NRM) and remagnetized NRM are acquired by different processes, their signatures can be recognized from subtle differences in the magnetic properties. We illustrate the potential of the approach by three case studies, one from Spain and two from Turkey, in which the magnetic properties of remagnetized and non-remagnetized rocks are evaluated.