A comparison of archaeointensity results from Chinese ceramics using microwave and conventional Thellier's and Shaw's methods

Palaeo- and archaeointensity determinations of the geomagnetic field are li mited by mineralogical alteration that may occur when samples are heated in the laboratory to produce a TRM (Thellier & Thellier 1959; Shaw 1974). By using microwave excitation of the magnetic grains we have been able to crea te a TRM without significantly heating the bulk samples, thereby avoiding t hermal alteration (Walton et al. 1993; Shaw et al. 1996). When applied to P eruvian ceramics in a manner analogous to the standard Thellier method, the microwave technique was found to reduce the scatter dramatically in the ar chaeointensity results (Shaw et al. 1996). In the present study we apply th is microwave technique to a collection of Chinese ceramics covering the tim e interval 270-7500 yr BP. These ceramics have already been investigated us ing adaptations of both Thellier's (Coe 1967) and Shaw's (Rolph & Shaw 1985 ) palaeointensity methods (Yang et al. 1993a). Although an acceptable agree ment was found between those two methods, the equivalent virtual axial dipo le moments (VADMs) were significantly lower than for the global model of Mc Elhinny & Senanayake (1982). The present study, using the microwave techniq ue with cooling-rate correction, has provided more consistent VADMs, and is much closer to the global model.