Analyzing absolute paleointensity determinations: Acceptance criteria and the software ThellierTool4.0

Abstract

The ThellierTool4.0 is an intuitive and easy‐to‐use software which provides the possibility to analyze a wide range of different modifications of the Thellier absolute paleointensity experiment (available at http://earthref.org/tools/). Besides the Arai plot for paleointensity determination, orthogonal projections of the direction, decay of NRM during thermal demagnetization, and additional plots regarding alteration and multidomain checks enable the user to visualize the quality of individual determinations. Experimental checks for magnetomineralogical changes, either in‐field or zero‐field pTRM* checks, are evaluated regarding their differences to the corresponding pTRM* acquisition in two most commonly used ways. Furthermore, a measure for the cumulative alteration differences beginning at room temperature is calculated, and the possibility to correct for magnetomineralogical changes is provided. Two different experimental methods to check for multidomain bias are supported and analyzed by the software. Intensity differences recorded by pTRM*‐tail checks are calculated. Accounting for the directional difference between applied laboratory field and magnetization of the sample, the effective pTRM*‐tail is determined, and thus failures of Thellier's law of independence are monitored. Failures of the law of additivity, experimentally observed by additivity checks, are also evaluated by the software. The vectorial character of individual measurements is fully considered for all calculations. Uniform selection criteria for acceptance and rejection of determinations can be applied, and a set of such criteria with emphasis on minimal bias due to alteration, multidomain remanence, and analysis/experimental inaccuracies is suggested.

The intensity of the geomagnetic field in the late-Archaean: new measurements and an analysis of the updated IAGA palaeointensity database

“…This is because, in palaeointensity experiments where samples do not behave in a strictly single-domain manner with respect to pTRM acquistion, pTRM checks can fail despite the absence of any alteration (Biggin and Thomas, 2003b). To ensure this was not the case here, we analysed the results of the pTRM tail checks and used the strict criteria outlined for 'Class A' results by Leonhardt et al (2004) to exclude any samples which may be subject to MD behaviour. Leonhardt et al estimate the magnitude of the imparted pTRM tail using a parameter called t * which takes the intensity and direction of the applied field relative to the NRM into account.…”

Weaker axially dipolar time-averaged paleomagnetic field based on multidomain-corrected paleointensities from Galapagos lavas

“…3). The standard Thellier-series experimental data can thus also be used to estimate paleointensities by traditional methods (27), which allows us to evaluate the effectiveness of the MD correction. The MD correction technique does require that samples have not experienced significant thermophysicochemical alteration upon completion of the original Thellier-series heating steps, which can be supported independently by hysteresis and thermomagnetic measurements on subsample chips for the Galapagos lavas (SI Appendix).…”

Paleomagnetic directional groups and paleointensity from the flood basalt in the Tarim large igneous province: implications for eruption frequency

“…(5) The pTRM check should be within 7% of the corresponding pTRM (δ(CK) ≤ 0.07). These are similar to the default "Class B" criteria of ThellierTool (Leonhardt et al 2004). As discussed below, the paleointensity experiments were rather unsuccessful, and no "Class A" data (Leonhardt et al 2004) were obtained.…”

“…The laboratory magnetizing field intensity was set to range from 20 to 40 μT. The results were analyzed using the ThellierTool software version 2.0 (Leonhardt et al 2004). (5) The pTRM check should be within 7% of the corresponding pTRM (δ(CK) ≤ 0.07).…”