IsoplotR (version 0.11)

peakfit: Finite mixture modelling of geochronological datasets

Description

Implements the discrete mixture modelling algorithms of Galbraith and Green (1993) and applies them to fission track and other geochronological datasets.

Usage

peakfit(x, ...)
# S3 method for default
peakfit(x, k = "auto", sigdig = 2, log = TRUE, ...)
# S3 method for fissiontracks
peakfit(x, k = 1, exterr = TRUE, sigdig = 2,
  log = TRUE, ...)
# S3 method for UPb
peakfit(x, k = 1, type = 4, cutoff.76 = 1100,
  cutoff.disc = c(-15, 5), exterr = TRUE, sigdig = 2, log = TRUE, ...)
# S3 method for ArAr
peakfit(x, k = 1, exterr = TRUE, sigdig = 2, log = TRUE,
  i2i = FALSE, ...)
# S3 method for ReOs
peakfit(x, k = 1, exterr = TRUE, sigdig = 2, log = TRUE,
  i2i = TRUE, ...)
# S3 method for SmNd
peakfit(x, k = 1, exterr = TRUE, sigdig = 2, log = TRUE,
  i2i = TRUE, ...)
# S3 method for RbSr
peakfit(x, k = 1, exterr = TRUE, sigdig = 2, log = TRUE,
  i2i = TRUE, ...)
# S3 method for UThHe
peakfit(x, k = 1, sigdig = 2, log = TRUE, ...)

Arguments

x

either a [2 x n] matrix with measurements and their standard errors, or an object of class fissiontracks, UPb, ArAr, ReOs, SmNd, RbSr or UThHe

...

optional arguments (not used)

k

the number of discrete age components to be sought. Setting this parameter to 'auto' automatically selects the optimal number of components (up to a maximum of 5) using the Bayes Information Criterion (BIC).

sigdig

number of significant digits to be used for any legend in which the peak fitting results are to be displayed.

log

take the logs of the data before applying the mixture model?

exterr

propagate the external sources of uncertainty into the component age errors?

type

scalar indicating whether to plot the \(^{207}\)Pb/\(^{235}\)U age (type=1), the \(^{206}\)Pb/\(^{238}\)U age (type=2), the \(^{207}\)Pb/\(^{206}\)Pb age (type=3), the \(^{207}\)Pb/\(^{206}\)Pb-\(^{206}\)Pb/\(^{238}\)U age (type=4), or the (Wetherill) concordia age (type=5)

cutoff.76

the age (in Ma) below which the \(^{206}\)Pb/\(^{238}\)U and above which the \(^{207}\)Pb/\(^{206}\)Pb age is used. This parameter is only used if type=4.

cutoff.disc

two element vector with the maximum and minimum percentage discordance allowed between the \(^{207}\)Pb/\(^{235}\)U and \(^{206}\)Pb/\(^{238}\)U age (if \(^{206}\)Pb/\(^{238}\)U < cutoff.76) or between the \(^{206}\)Pb/\(^{238}\)U and \(^{207}\)Pb/\(^{206}\)Pb age (if \(^{206}\)Pb/\(^{238}\)U > cutoff.76). Set cutoff.disc=NA if you do not want to use this filter.

i2i

`isochron to intercept': calculates the initial (aka `inherited', `excess', or `common') \(^{40}\)Ar/\(^{36}\)Ar, \(^{87}\)Sr/\(^{86}\)Sr, \(^{143}\)Nd/\(^{144}\)Nd or \(^{187}\)Os/\(^{188}\)Os ratio from an isochron fit. Setting i2i to FALSE uses the default values stored in settings('iratio',...)

Value

a list with the following items:

peaks

a vector of peak locations

props

a vector of peak proportions

peaks.err

the standard errors of the peak locations

props.err

the standard errors of the peak proportions

legend

a vector of text expressions to be used in a figure legend

References

Galbraith, R.F. and Laslett, G.M., 1993. Statistical models for mixed fission track ages. Nuclear tracks and radiation measurements, 21(4), pp.459-470.

Examples

data(examples)
peakfit(examples$FT1,k=2)