Ternary diagrams
Although U, Th, and He are three variables, they can be constrained by a
constant sum in the (U-Th)/He age equation. Therefore, U-Th-He data only
represents two degrees of freedom worth of information, and can be visualised
on a two-dimensional surface. HelioPlot implements two methods to
achieve this, with ternary diagrams and logratio plots. Adding Sm as a
fourth variable increases the information content of these diagrams,
necessitating the use of colour as a visual aid. If the (U-Th)/He
option is selected in Options → Input, the the optional
[C] column is used. If (U-Th-Sm)/He is selected, then the
Sm content is used. Samples with missing [C] or Sm
are coloured white. The U, Th, and He end members of the ternary diagram can
be changed in the Options → Settings menu, affecting
the size and location of the error ellipses.
See Logratio plots,
Scale