IsoplotR (version 0.17)

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

Arguments

x

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

...

optional arguments

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

a list containing the following items:

mswd

the reduced Chi-square statistic of data concordance, i.e. \(mswd=SS/(2n-2)\), where \(SS\) is the sum of squares of the log[U/He]-log[Th/He] compositions and \(n\) is the number of samples. If x has class fissiontracks, then \(mswd=X^2/(n-1)\), where \(X^2\) is a Chi-square statistic of the EDM data or ICP ages.

p.value

the p-value of a Chi-square test with \(n-2\) degrees of freedom

age

a two-column vector with the central age and its standard error.

Additionally, if x has class UThHe:

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

OR, if x has class fissiontracks:

disp

the (over)dispersion of the ages (value between 0 and 1)

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)

# }