Description Usage Arguments Details Value References See Also Examples
Computes the geometric mean composition of a continuous mixture of fission track or UThHe data and returns the corresponding age and fitting parameters.
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x 
an object of class 
... 
optional arguments 
alpha 
cutoff value for confidence intervals 
model 
choose one of the following statistical models:

mineral 
setting this parameter to either 
The central age assumes that the observed age distribution is the combination of two sources of scatter: analytical uncertainty and true geological dispersion.
For fission track data, the analytical uncertainty is assumed to obey Poisson counting statistics and the geological dispersion is assumed to follow a lognormal distribution.
For UThHe data, the UTh(Sm)He compositions and uncertainties are assumed to follow a logistic normal distribution.
For all other data types, both the analytical uncertainties and the true ages are assumed to follow lognormal distributions.
The difference between the central age and the weighted mean age is usually small unless the data are imprecise and/or strongly overdispersed.
If x
has class UThHe
, returns a list containing the
following items:
(if the input data table contains Sm) or uv (if it does not): the mean log[U/He], log[Th/He] (, and log[Sm/He]) composition.
the covariance matrix of uvw
or uv
.
the reduced Chisquare statistic of data concordance, i.e. mswd=SS/df, where SS is the sum of squares of the log[U/He]log[Th/He] compositions.
the fitting model.
the degrees of freedom (2n2) of the fit (only
reported if model=1
).
the pvalue of a Chisquare test with df
degrees of freedom (only reported if model=1
.)
age 
a three or fourelement vector with:

w 
the geological overdispersion term. If 
OR, otherwise:
a threeelement vector with:
t
: the central age.
s[t]
: the standard error of t
.
ci[t]
: the width of a 100(1α)\% confidence
interval for t
.
a threeelement vector with the overdispersion (standard deviation) of the excess scatter, and the upper and lower halfwidths of its 100(1α)\% confidence interval.
the reduced Chisquare statistic of data concordance, i.e. mswd=X^2/df, where X^2 is a Chisquare statistic of the EDM data or ages
the degrees of freedom (n2)
the pvalue of a Chisquare test with df
degrees of freedom
Galbraith, R.F. and Laslett, G.M., 1993. Statistical models for mixed fission track ages. Nuclear Tracks and Radiation Measurements, 21(4), pp.459470.
Vermeesch, P., 2008. Three new ways to calculate average (UTh)/He ages. Chemical Geology, 249(3), pp.339347.
weightedmean
, radialplot
,
helioplot
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