Transformations of magnetic mineralogy in rocks revealed by difference of hysteresis loops measured after stepwise heating: theory and case studies

Bernard Henry (1) , Diana Jordanova , Neli Jordanova , Maxime Le Goff (1)

1 CNRS - Centre National de la Recherche Scientifique

A new approach for tracking mineralogical alterations during laboratory stepwise heating experiments is proposed. It uses the hysteresis loop obtained as a difference between the loops measured after thermal treatment at two different consecutive temperatures. Depending on the nature of the mineralogical alterations (the formation of a new ferrimagnetic phase from a paramagnetic one, the thermal transformation of the originally present ferrimagnetic phases, grain size variation) and on their relative intensities, it is possible to distinguish between different cases. The examples shown reveal the significant alteration of magnetic carriers at low temperatures (up to 200°C) which usually is not identified by thermomagnetic analysis of magnetic susceptibility. The low temperature alteration of the remanence carriers has important consequences for the reliability and suitability criteria of palaeointensity determinations.

Mots clés: hysteresis loop; mineralogical alteration; thermal treatment

Domaines: Planète et Univers [physics]

Bernard Henry, Diana Jordanova, Neli Jordanova, Maxime Le Goff. Transformations of magnetic mineralogy in rocks revealed by difference of hysteresis loops measured after stepwise heating: theory and case studies. Geophysical Journal International, 2005, 162, pp.64-78. ⟨10.1111/j.1365-246X.2005.02644.x⟩. ⟨insu-03601116⟩