eArgon at Mac App Store analyse

This program has been written to facilitate the analysis and interpretation of argon geochronology data from step-heating experiments in vacuo in a furnace attached to a mass spectrometer. The program allows corrections for excess argon, using the analysis of York Plots to recognise trends. The program allows analysis of complex age spectra using the method of asymptotes and limits. Cumulated plots allow recognition of Frequently Measured Ages (FMAs). Gaussian plots present data using probability. Arrhenius Plots and Relative Radius Plots allow estimates for the diffusion parameters for individual samples. Data is input in XML format with data tags available for individual laboratories by request. The output document is in an XML format intended to become an industry standard, ensuring data interoperability between different programs and different laboratories.

All data is recorded in a single document using XML format, allowing recreation of the analysis, including isochrons, asymptotes and limits for individual spectra, and other parameters. Data for a single sample can be exported to the Wunderkind and MacArgon apps for inversion. Wunderkind uses 39Ar release data from ultra-high-vacuum (UHV) temperature-controlled step-heating diffusion experiments. MacArgon allows forward modelling of the effect of arbitrary pressure-temperature-time histories. Step colours are also saved in the eArgon document. A small screen format is also available for the Age Spectrum Window.

The weighted mean is used for isochrons on the age plot, using formula in Mahon 1996. If the MSWD is unacceptably high, a weighted average used instead reflecting the scatter of the individual steps [shown at the 2σ level] The Turner inverse 40Ar isotope correlation diagram uses the York 1969 regression as corrected by Mahon 1996 and Trappitsch 2018. The square root of the MSWD (Pearsons chi statistic) is used to assess the likelihood that the scatter in age is within the 95% probability limits defined using equations as set out by Wendt and Carl 1991 but here evaluating the approximations to the scatter distributions using the gamma function, and directly estimating the uncertainty in the chi-statistic.

Version §12 provides a document-based architecture that stores key aspects of the analysis of a set of argon age spectra, and other data associated with interpretation of associated argon isotope analyses. The weighted mean age is shown unless the scatter of the individual steps [shown at the 2σ level] nullifies the statistic . If the MSWD is too high to allow definition of a plateau segment the mean age is shown with the scatter of the mean ages of individual steps defining the uncertainty. Version §12.0.1 introduces the option to correct for the effect of argon recoil using isothermal duplicate steps or existing linear arrays as a control measure.

Version §12.2 modifies the portrayal of statistical information. Each age step displays the overall 2-sigma uncertainty, with the systematic uncertainties in age related to uncertainties in the J-factor and the decay constant discernible during mouse over events. Statistical analysis based on a section of steps is now bifurcated depending on age scatter. If the likelihood is less than 5% that the selected age steps defines a single age consistent with the measurement uncertainties, then the uncertainty is defined by the weighted scatter of the means, with the weighted MSWD where appropriate. Otherwise (for a MSWD implying 95% probability that the data is consistent with a single age) a regression is applied taking account of uncertainties in each step. Finally, the systematic age uncertainties due to J-factor uncertainty and decay constant uncertainty are reapplied, using a first-order Taylor expansion. By default, input without control parameters occurs as though only measurement uncertainty has been included. Use the toolbox options to remedy matters, if this is not correct.