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. (C) 2010 Elsevier B.V. All rights reserved.