Microwave archaeointensities from Peruvian ceramics

Abstract

Accurate determination of the strength of the ancient geomagnetic field is limited by mineralogical alteration that may occur when samples are heated to produce a thermoremanent magnetization (Thellier & Thellier 1959; Shaw 1974). By using direct microwave excitation of the magnetic grains we have been able to form a thermoremanent magnetization without significantly heating the bulk sample, thus avoiding thermal alteration (Walton et al. 1993). Incorporation of this new microwave heating technique with the conventional Thellier palaeointensity method has dramatically reduced the scatter of archaeointensity results from Peruvian ceramics and clearly defined how the field strength has varied in Peru over the past 2000 years. The new microwave technique will therefore enhance the feasibility of archaeointensity dating and provide accurate field strength data for geomagnetic modelling.