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Summary A series of laboratory experiments has been carried out using lava from Hawaii and Australia containing laboratory induced remanence to compare thermal and microwave palaeomagnetic techniques. Three samples of Hawaiian lava containing a known laboratory induced thermal remanence (TRM) were subjected to microwave palaeointensity experiments (using the Liverpool 8.2 GHz microwave system). Conventional modified Thellier palaeointensity experiments were carried out on the same three lava samples, this time containing a known microwave induced thermoremanent magnetisation (TMRM). Both palaeointensity techniques produced the correct intensity value, demonstrating the equivalence of TRM and TMRM. No indications of alteration during the experiment were evident during the microwave experiments, whereas alteration was pronounced after heating to 350°C in the Thellier experiments demonstrating that alteration during microwave palaeointensity analysis is reduced when compared to thermal techniques. In a second set of experiments, six samples (three Hawaiian and three Australian lava samples) were given a laboratory induced full TRM and a secondary perpendicular partial TRM (pTRM) (at lower temperatures). Sister samples were then demagnetised using thermal and microwave methods. Analysis of the orthogonal vector plots (OVPs) revealed little difference in separating the two components for five out of the six samples. For one sample, microwave demagnetisation did not clearly distinguish between the two components with the primary component not being resolved until 74 per cent of the moment had been demagnetised compared to just 4 per cent with thermal demagnetisation. For this one sample, it appears that the microwave unblocking spectra is not equivalent to the thermal unblocking spectra, probably due to a combination of microwave demagnetisation processes occurring. Comparison of the intensity of magnetisation plots during demagnetisation shows that the relationship between temperature and microwave power appears more logarithmic than linear. This study demonstrates the validity of the microwave palaeointensity technique and, as long as the primary component of magnetisation can be isolated from multicomponent remanence, then the microwave palaeointensity technique can be applied.

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