A theoretical treatment of paleointensity determination experiments on rocks containing pseudo-single or multi domain magnetic particles

A phenomenological theory of thermoremanent magnetization (TRM) is applied to model the possible results of paleointensity determination experiments using the Thellier method. It is shown that intrinsic curvature of the Arai plot for samples containing pseudo-single or multi domain particles can be attributed exclusively to the presence of remanences which are unblocked below their blocking temperature. Thus the thermal demagnetization tail of partial TRM (pTRM) is not a direct measure for a sample’s tendency to yield a curved Arai plot. Here it is proposed to use the advancing decay of a pTRM(T1, T2) which during heating occurs already below the lower temperature T1<T2 as a more reliable pre-selection criterion. In addition, the effect of an average magnetostatic interaction on the Thellier experiment turns out to be negligible. An extended Thellier method which compares the thermal demagnetization of natural remanent magnetization with that of an artificial TRM according to the applied TRM theory should result in a perfectly linear modified Arai plot even for pseudo-single or multi domain samples if no alteration or viscous effects occur.