Multiple-specimen absolute paleointensity determination: An optimal protocol including pTRM normalization, domain-state correction, and alteration test

A recent proposal of a multiple-specimen technique promises to be a viable alternative to the classical Thellier–Thellier method of absolute paleointensity determination. However, to exploit the full potential of the multiple-specimen approach, a thorough understanding of its theoretical foundation, and a detailed experimental verification of its implicit assumptions is required. Here, the validity of the multiple-specimen technique is studied on a collection of synthetic samples covering grain sizes ranging from single domain (SD) over intermediate pseudo-single domain (PSD), to multidomain (MD). The experimental data indicate that the multiple-specimen method in its present form systematically overestimates paleointensity for intermediate PSD to MD particle sizes. This finding is investigated theoretically by a statistical theory of weak-field thermoremanence, and quantified by a phenomenological thermoremanence model. Based on this theoretical framework, and on the new experimental evidence, an extended version of the multiple-specimen technique is designed, which is more reliable in the critical domain-state range. The new measurement scheme improves normalization, and quantifies the PSD and MD overestimate, which then can even be corrected for. Furthermore, the proposed measurement scheme includes a thermal repeat measurement to assess the effect of alteration upon the accuracy of the final paleointensity result. The new technique is verified experimentally for the synthetic samples investigated.