SIGNIFICANCE OF COOLING-RATE DIFFERENCE IN PALEOINTENSITY DETERMINATION

The effect of cooling-rate on the magnitude of thermoremanent magnetization (TRM) was experimentally tested. As the TRM intensity can be described as the Boltzmann statistics, a slowly cooled environment allows more chance to align individual magnetic particles parallel to the external magnetic field. Then it is natural to expect the slowly cooled rocks acquire stronger TRM than the rapidly cooled ones. Such a proposition has been experimentally validated to be true for the fine-grained magnetite- or titanomagnetite. For coarse-grained magnetite-bearing rocks, TRM is positively correlated with cooling-rate as the rapid cooling induced stronger magnetization due to the effect of self-demagnetization. In practice, the effect of cooling-rate on the remanence intensity appears to be insignificant for nominal grain ranges. Regardless of grain-size, it is also important to emphasize that a cooling-rate difference alone can cause a slight non-linear behavior in an Arai plot.