Description Usage Arguments Details Value References See Also Examples
Implements the discrete mixture modelling algorithms of Galbraith and Laslett (1993) and applies them to fission track and other geochronological datasets.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51  peakfit(x, ...)
## Default S3 method:
peakfit(x, k = "auto", sigdig = 2, log = TRUE,
alpha = 0.05, ...)
## S3 method for class 'fissiontracks'
peakfit(x, k = 1, exterr = TRUE, sigdig = 2,
log = TRUE, alpha = 0.05, ...)
## S3 method for class 'UPb'
peakfit(x, k = 1, type = 4, cutoff.76 = 1100,
cutoff.disc = c(15, 5), exterr = TRUE, sigdig = 2, log = TRUE,
alpha = 0.05, ...)
## S3 method for class 'PbPb'
peakfit(x, k = 1, exterr = TRUE, sigdig = 2,
log = TRUE, i2i = TRUE, alpha = 0.05, ...)
## S3 method for class 'ArAr'
peakfit(x, k = 1, exterr = TRUE, sigdig = 2,
log = TRUE, i2i = FALSE, alpha = 0.05, ...)
## S3 method for class 'KCa'
peakfit(x, k = 1, exterr = TRUE, sigdig = 2,
log = TRUE, i2i = FALSE, alpha = 0.05, ...)
## S3 method for class 'ReOs'
peakfit(x, k = 1, exterr = TRUE, sigdig = 2,
log = TRUE, i2i = TRUE, alpha = 0.05, ...)
## S3 method for class 'SmNd'
peakfit(x, k = 1, exterr = TRUE, sigdig = 2,
log = TRUE, i2i = TRUE, alpha = 0.05, ...)
## S3 method for class 'RbSr'
peakfit(x, k = 1, exterr = TRUE, sigdig = 2,
log = TRUE, i2i = TRUE, alpha = 0.05, ...)
## S3 method for class 'LuHf'
peakfit(x, k = 1, exterr = TRUE, sigdig = 2,
log = TRUE, i2i = TRUE, alpha = 0.05, ...)
## S3 method for class 'ThU'
peakfit(x, k = 1, exterr = FALSE, sigdig = 2,
log = TRUE, i2i = TRUE, alpha = 0.05, detritus = 0, Th02 = c(0,
0), Th02U48 = c(0, 0, 1e+06, 0, 0, 0, 0, 0, 0), ...)
## S3 method for class 'UThHe'
peakfit(x, k = 1, sigdig = 2, log = TRUE,
alpha = 0.05, ...)

x 
either an 
... 
optional arguments (not used) 
k 
the number of discrete age components to be
sought. Setting this parameter to 
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? 
alpha 
cutoff value for confidence intervals 
exterr 
propagate the external sources of uncertainty into the component age errors? 
type 
scalar valueindicating whether to plot the
^{207}Pb/^{235}U age ( 
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 
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 < 
i2i 
‘isochron to intercept’: calculates the initial (aka
‘inherited’, ‘excess’, or ‘common’)
^{40}Ar/^{36}Ar, ^{40}Ca/^{44}Ca,
^{207}Pb/^{204}Pb, ^{87}Sr/^{86}Sr,
^{143}Nd/^{144}Nd, ^{187}Os/^{188}Os or
^{176}Hf/^{177}Hf ratio from an isochron
fit. Setting 
detritus 
detrital ^{230}Th correction (only applicable
when

Th02 
2element vector with the assumed initial
^{230}Th/^{232}Thratio of the detritus and its
standard error. Only used if 
Th02U48 
9element vector with the measured composition of
the detritus, containing 
Consider a dataset of n dates \{t_1, t_2, ..., t_n\} with analytical uncertainties \{s[t_1], s[t_2], ..., s[t_n]\}. Define z_i = \log(t_i) and s[z_i] = s[t_i]/t_i. Suppose that these n values are derived from a mixture of k>2 populations with means \{μ_1,...,μ_k\}. Such a discrete mixture may be mathematically described by:
P(z_iμ,ω) = ∑_{j=1}^k π_j N(z_i  μ_j, s[z_j]^2 )
where π_j is the proportion of the population that belongs
to the j^{th} component, and
π_k=1∑_{j=1}^{k1}π_j. This equation can be solved by
the method of maximum likelihood (Galbraith and Laslett, 1993).
IsoplotR
implements the Bayes Information Criterion (BIC) as
a means of automatically choosing k. This option should be
used with caution, as the number of peaks steadily rises with
sample size (n). If one is mainly interested in the youngest
age component, then it is more productive to use an alternative
parameterisation, in which all grains are assumed to come from one
of two components, whereby the first component is a single discrete
age peak (\exp(m), say) and the second component is a
continuous distribution (as descibed by the central
age model), but truncated at this discrete value (Van der Touw et
al., 1997).
Returns a list with the following items:
a 3 x k
matrix with the following rows:
t
: the ages of the k
peaks
s[t]
: the estimated uncertainties of t
ci[t]
: the widths of approximate 100(1α)\%
confidence intervals for t
a 2 x k
matrix with the following rows:
p
: the proportions of the k
peaks
s[p]
: the estimated uncertainties (standard errors) of
p
the loglikelihood of the fit
a vector of text expressions to be used in a figure legend
Galbraith, R.F. and Laslett, G.M., 1993. Statistical models for mixed fission track ages. Nuclear Tracks and Radiation Measurements, 21(4), pp.459470.
van der Touw, J., Galbraith, R., and Laslett, G. A logistic truncated normal mixture model for overdispersed binomial data. Journal of Statistical Computation and Simulation, 59(4):349373, 1997.
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