IsoplotR (version 0.18)

central: Calculate U-Th-He and fission track central ages and compositions

Description

Computes the geometric mean composition of a set of fission track or U-Th-He data and returns the corresponding age and fitting parameters.

Usage

central(x, ...)
# S3 method for default
central(x, alpha = 0.05, ...)
# S3 method for UThHe
central(x, alpha = 0.05, ...)
# S3 method for fissiontracks
central(x, mineral = NA, alpha = 0.05, ...)

Arguments

x

an object of class UThHe or fissiontracks, OR a 2-column matrix with (strictly positive) values and uncertainties

...

optional arguments

alpha

cutoff value for confidence intervals

mineral

setting this parameter to either apatite or zircon changes the default efficiency factor, initial fission track length and density to preset values (only affects results if x$format=2.)

Value

if x has class UThHe, a list containing the following items:

age

a four-element vector with:

t: the central age

s[t]: the standard error of s[t]

ci[t]: the \(100(1-\alpha/2)\%\) confidence interval for t for the appropriate number of degrees of freedom

disp[t]: the \(100(1-\alpha/2)\%\) confidence interval enhanced by a factor of \(\sqrt{MSWD}\).

mswd

the reduced Chi-square 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

df

the degrees of freedom (\(2n-2\))

p.value

the p-value of a Chi-square test with df degrees of freedom

uvw

(if the input data table contains Sm) or uv (if it doesn't): the geometric mean log[U/He], log[Th/He] (, log[Sm/He]) and log[Sm/He] composition

covmat

the covariance matrix of uvw or uv

tfact

the \(100(1-\alpha/2)\%\) percentile of the t- distribution for df degrees of freedom

OR, otherwise:

age

a three-element vector with:

t: the central age

s[t]: the standard error of s[t]

ci[t]: the \(100(1-\alpha/2)\%\) confidence interval for t for the appropriate number of degrees of freedom

disp

a two-element vector with the overdispersion (standard deviation) of the excess scatter, and the corresponding \(100(1-\alpha/2)\%\) confidence interval for the appropriate degrees of freedom.

mswd

the reduced Chi-square statistic of data concordance, i.e. \(mswd=X^2/df\), where \(X^2\) is a Chi-square statistic of the EDM data or ages

df

the degrees of freedom (\(n-2\))

p.value

the p-value of a Chi-square test with df degrees of freedom

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.

Vermeesch, P., 2008. Three new ways to calculate average (U-Th)/He ages. Chemical Geology, 249(3), pp.339-347.

Examples

# NOT RUN {
data(examples)
print(central(examples$UThHe)$age)

# }