Plots Th-U data on a \(^{234}\)U/\(^{238}\)U-\(^{230}\)Th/\(^{238}\)U evolution diagram, a \(^{234}\)U/\(^{238}\)U-age diagram, or (if \(^{234}\)U/\(^{238}\)U is assumed to be in secular equilibrium), a \(^{230}\)Th/\(^{232}\)Th-\(^{238}\)U/\(^{232}\)Th diagram, calculates isochron ages.
evolution(x, xlim = NA, ylim = NA, alpha = 0.05, transform = FALSE,
detrital = FALSE, show.numbers = FALSE, levels = NA, clabel = "",
ellipse.col = c("#00FF0080", "#FF000080"), line.col = "darksalmon",
isochron = FALSE, model = 1, exterr = TRUE, sigdig = 2, ...)an object of class ThU
x-axis limits
y-axis limits
probability cutoff for the error ellipses and confidence intervals
if TRUE, plots \(^{234}\)U/\(^{238}\)U
vs. Th-U age.
apply a detrital Th correction by projecting the compositions along an isochron?
label the error ellipses with the grain numbers?
a vector with additional values to be displayed as different background colours within the error ellipses.
label of the colour legend.
a vector of two background colours for the error
ellipses. If levels=NA, then only the first colour will
be used. If levels is a vector of numbers, then
ellipse.col is used to construct a colour ramp.
colour of the age grid
fit a 3D isochron to the data?
if isochron=TRUE, choose one of three
regression models:
1: maximum likelihood regression, using either the modified
error weighted least squares algorithm of York et al. (2004) for
2-dimensional data, or the Maximum Likelihood formulation of Ludwig
and Titterington (1994) for 3-dimensional data. These algorithms
take into account the analytical uncertainties and error
correlations, under the assumption that the scatter between the
data points is solely caused by the analytical uncertainty. If this
assumption is correct, then the MSWD value should be approximately
equal to one. There are three strategies to deal with the case
where MSWD>1. The first of these is to assume that the analytical
uncertainties have been underestimated by a factor
\(\sqrt{MSWD}\).
2: ordinary least squares regression: a second way to deal
with over- or underdispersed datasets is to simply ignore the
analytical uncertainties.
3: maximum likelihood regression with overdispersion:
instead of attributing any overdispersion (MSWD > 1) to
underestimated analytical uncertainties (model 1), one can also
attribute it to the presence of geological uncertainty, which
manifests itself as an added (co)variance term.
propagate the decay constant uncertainty in the isochron age?
number of significant digits for the isochron age
optional arguments to the generic plot function
Similar to the concordia diagram (for U-Pb data) and
the helioplot diagram (for U-Th-He data), the
evolution diagram simultaneously displays the isotopic composition
and age of U-series data. For carbonate data (Th-U formats 1 and
2), the Th-U evolution diagram consists of a scatter plot that sets
out the \(^{234}\)U/\(^{238}\)U-activity ratios against the
\(^{230}\)Th/\(^{238}\)U-activity ratios as error ellipses, and
displays the initial \(^{234}\)U/\(^{238}\)U-activity ratios
and ages as a set of intersecting lines. Alternatively, the
\(^{234}\)U/\(^{238}\)U-ratios can also be set out against the
\(^{230}\)Th-\(^{234}\)U-\(^{238}\)U-ages. In both types of
evolution diagrams, IsoplotR provides the option to project
the raw measurements along the best fitting isochron line and
thereby remove the detrital \(^{230}\)Th-component. This
procedure allows a visual assessment of the degree of homogeneity
within a dataset, as is quantified by the MSWD.
Neither the U-series evolution diagram, nor the
\(^{234}\)U/\(^{238}\)U vs. age plot is applicable to igneous
datasets (Th-U formats 3 and 4), in which \(^{234}\)U and
\(^{238}\)U are in secular equilibrium. For such datasets,
IsoplotR produces an Osmond-style regression plot that is
decorated with a fanning set of isochron lines.
Ludwig, K.R. and Titterington, D.M., 1994. Calculation of \(^{230}\)Th/U isochrons, ages, and errors. Geochimica et Cosmochimica Acta, 58(22), pp.5031-5042.
Ludwig, K.R., 2003. Mathematical-statistical treatment of data and errors for \(^{230}\)Th/U geochronology. Reviews in Mineralogy and Geochemistry, 52(1), pp.631-656.
# NOT RUN {
data(examples)
evolution(examples$ThU)
dev.new()
evolution(examples$ThU,transform=TRUE,
isochron=TRUE,model=1)
# }
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