HelioPlot, and the treatment of overdispersed (U-Th-Sm)/He data
Vermeesch, Pieter (2010) HelioPlot, and the treatment of overdispersed (U-Th-Sm)/He data. Chemical Geology 271 (3-4), pp. 108-111. ISSN 00092-541.
More often than not, (U–Th–Sm)/He ages are overdispersed with respect to the formal analytical uncertainty. The Mean Square of the Weighted Deviates (MSWD) is a useful tool for assessing the amount of overdispersion. If the MSWD is significantly greater than one, the ages can be parameterised by a (log)normal distribution with two sources of variance, which can be iteratively solved using the method of maximum likelihood. The overdispersion of replicate (U–Th–Sm)/He ages is caused by the overdispersion of the underlying U–Th–Sm–He compositions, the geometric mean of which gives rise to the so-called ‘central age’. These compositions can be normalised to unity and parameterised by a multivariate logistic normal distribution with two sources of variance, which can be iteratively solved by a multivariate generalisation of the aforementioned age-averaging algorithm. Exact and asymmetric confidence intervals for the central age are obtained using a deterministic Bayesian algorithm. HelioPlot is a Java application developed for the purpose of plotting U–Th–(Sm)–He data on ternary diagrams and logratio plots that implements all these calculations. The program can be downloaded from http://pvermees.andropov.org/helioplot.
|Keyword(s) / Subject(s):||(U–Th)/He, geochronology, statistics, software|
|School:||Birkbeck Schools and Departments > School of Science > Earth and Planetary Sciences|
|Date Deposited:||08 Feb 2011 09:39|
|Last Modified:||11 Oct 2016 12:01|
Additional statistics are available via IRStats2.