Kamacite blocking temperatures and applications to lunar magnetism

The long-term stability of remanent magnetization is a requirement for paleomagnetic studies. Here we present calculations that predict the magnetic relaxation times of single domain crystals of the iron-nickel mineral kamacite as a function of their time-temperature history. Kamacite is one of the most abundant ferromagnetic minerals in the solar system and is the dominant remanence carrier on the Moon. We perform these calculations for a variety of grain sizes, times, and temperatures to derive a broad view of the remanence stability of kamacite over geologic timescales. Previously, such blocking temperature calculations were only available for the common Earth minerals magnetite, hematite, and pyrrhotite. Our results show that remanence in kamacite-bearing lunar samples is stable against typical thermal perturbations during the last several billion years of lunar history and residence on Earth. Our findings indicate that lunar paleomagnetism cannot be entirely an artifact due to sample storage in the Earth's magnetic field. Future paleomagnetic studies of iron-bearing samples can use our blocking temperature diagram to determine the effects of geologic heating events on magnetic remanence. (C) 2010 Published by Elsevier B.V.