IsoplotR (version 0.17)

concordia: Concordia diagram

Description

Plots U-Pb data on Wetherill and Tera-Wasserburg concordia diagrams, calculate concordia ages and compositions, evaluates the equivalence of multiple (\(^{206}\)Pb/\(^{238}\)U-\(^{207}\)Pb/\(^{235}\)U or \(^{207}\)Pb/\(^{206}\)Pb-\(^{206}\)Pb/\(^{238}\)U) compositions, computes the weighted mean isotopic composition and the corresponding concordia age using the method of maximum likelihood, computes the MSWD of equivalence and concordance and their respective Chi-squared p-values. Performs linear regression and computes the upper and lower intercept ages (for Wetherill) or the lower intercept age and the \(^{207}\)Pb/\(^{206}\)Pb intercept (for Tera-Wasserburg), taking into account error correlations and decay constant uncertainties.

Usage

concordia(x, tlim = NULL, alpha = 0.05, wetherill = TRUE,
  show.numbers = FALSE, levels = NA, ellipse.col = c("#00FF0080",
  "#FF000080"), concordia.col = "darksalmon", exterr = TRUE, show.age = 0,
  sigdig = 2, common.Pb = 0, ticks = NULL, ...)

Arguments

x

an object of class UPb

tlim

age limits of the concordia line

alpha

confidence cutoff for the error ellipses

wetherill

logical flag (FALSE for Tera-Wasserburg)

show.numbers

logical flag (TRUE to show grain numbers)

levels

a vector with additional values to be displayed as different background colours within the error ellipses.

ellipse.col

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.

concordia.col

colour of the concordia line

exterr

show decay constant uncertainty?

show.age

one of either:

0: just plot the data but don't calculate the age

1: calculate the concordia age

2: fit a discordia line

sigdig

number of significant digits for the concordia/discordia age

common.Pb

apply a common lead correction using one of three methods:

1: use the isochron intercept as the initial Pb-composition

2: use the Stacey-Kramer two-stage model to infer the initial Pb-composition

3: use the Pb-composition stored in settings('iratio','Pb206Pb204') and settings('iratio','Pb207Pb204')

ticks

an optional vector of age ticks to be added to the concordia line.

...

optional arguments to the generic plot function

References

Ludwig, K.R., 1998. On the treatment of concordant uranium-lead ages. Geochimica et Cosmochimica Acta, 62(4), pp.665-676.

Examples

# NOT RUN {
data(examples) 
concordia(examples$UPb)
# }