Validity of the LTD-DHT Shaw and Thellier palaeointensity methods: a case study of the Kilauea 1970 lava

Abstract

The double heating technique of the Shaw method with low-temperature demagnetisation (LTD-DHT Shaw method) for determination of geomagnetic palaeointensity is applied to samples exhibiting high-temperature oxidation states from the Kilauea 1970 lava, Hawaii Island. Results are obtained for 11 of the 12 specimens prepared from five block samples, yielding an average palaeointensity of 38.2 ± 2.8 μT ( N = 11, ±1 σ). This value is consistent with the expected value determined from DGRF 1970 (35.8 μT), and does not appear to be significantly dependent on the high-temperature oxidation state. Coe's version of the Thellier method was also applied to nine specimens prepared from the same block samples, and successful results were obtained for seven specimens, giving an average palaeointensity of 43.2 ± 8.4 μT ( N = 7). Although this average is statistically consistent with the expected value, the results include erroneously high palaeointensities (52.1 and 55.4 μT) for specimens from one block sample of intermediate high-temperature oxidation state. The present results therefore reinforce the broader applicability of the LTD-DHT Shaw method for samples with high-temperature oxidation states compared with Coe's version of the Thellier method. It is also shown that the samples yielding overestimated Thellier palaeointensities tend to fall close to the mixing line between single-domain (and/or pseudo-single-domain) and multidomain components on the Day plot. This relationship may be useful as a pre-selection technique for application of the Thellier method.