IsoplotR (version 4.0)

diseq: Set up U-series disequilibrium correction for U-Pb geochronology

Description

The U-Pb method conventionally assumes initial secular equilibrium of all the intermediate daughters of the \({}^{238}\)U-\({}^{206}\)Pb and \({}^{235}\)U-\({}^{207}\)Pb decay chains. Violation of this assumption may produce inaccurate results. diseq sets up initial disequilibrium parameters that are subsequently passed on to the read.data function for incorporation in other functions.

Usage

diseq(
  U48 = list(x = 1, sx = 0, option = 0),
  ThU = list(x = 1, sx = 0, option = 0),
  RaU = list(x = 1, sx = 0, option = 0),
  PaU = list(x = 1, sx = 0, option = 0)
)

Arguments

U48

a list containing three items (x, sx and option) specifying the \({}^{234}\)U/\({}^{238}\)U disequilibrium.

If option=0, then x and sx are ignored and no disequilibrium correction is applied.

If option=1, then x contains the initial \({}^{234}\)U/\({}^{238}\)U ratio and sx its standard error.

If option=2, then x contains the measured \({}^{234}\)U/\({}^{238}\)U ratio and sx its standard error.

ThU

a list containing three items (x, sx and option) specifying the \({}^{230}\)Th/\({}^{238}\)U disequilibrium.

If option=0, then x and sx are ignored and no disequilibrium correction is applied.

If option=1, then x contains the initial \({}^{230}\)Th/\({}^{238}\)U ratio and sx its standard error.

If option=2, then x contains the measured \({}^{230}\)Th/\({}^{238}\)U ratio and sx its standard error.

If option=3, then x contains the measured Th/U ratio of the magma (assumed or determined from the whole rock or volcanic glass) and sx its standard error. This only applies for Th-bearing U-Pb data formats 7 and 8.

RaU

a list containing three items (x, sx and option) specifying the \({}^{226}\)Ra/\({}^{238}\)U disequilibrium.

If option=0, then x and sx are ignored and no disequilibrium correction is applied.

If option=1, then x contains the initial \({}^{226}\)Ra/\({}^{238}\)U ratio and sx its standard error.

PaU

a list containing three items (x, sx and option) specifying the \({}^{231}\)Pa/\({}^{235}\)U disequilibrium.

If option=0, then x and sx are ignored and no disequilibrium correction is applied.

If option=1, then x contains the initial \({}^{231}\)Pa/\({}^{235}\)U ratio and sx its standard error.

Value

a list with the following items:

U48, ThU, RaU, PaU

the same as the corresponding input arguments

equilibrium

a boolean flag indicating whether option=TRUE and/or x=1 for all activity ratios

Q

the eigenvectors of the disequilibrium matrix exponential

Qinv

the inverse of Q

L

a named vector of all the relevant decay constants

n0

the initial atomic abundances of all the parent and daughter isotopes (used by mclean)

Details

There are three ways to correct for the initial disequilibrium between the activity of \({}^{238}\)U, \({}^{234}\)U, \({}^{230}\)Th, and \({}^{226}\)Ra; or between \({}^{235}\)U and \({}^{231}\)Pa:

1. Specify the assumed initial activity ratios and calculate how much excess \({}^{206}\)Pb and \({}^{207}\)Pb these would have produced.

2. Measure the current activity ratios to infer the initial ratios. This approach only works for young samples.

3. The initial \({}^{230}\)Th/\({}^{238}\)U activity ratio can also be estimated by providing the Th/U-ratio of the magma.

See Also

mclean, concordia, ludwig

Examples

# NOT RUN {
d <- diseq(U48=list(x=0,option=1),ThU=list(x=2,option=1),
           RaU=list(x=2,option=1),PaU=list(x=2,option=1))
fn <- system.file("diseq.csv",package="IsoplotR")
UPb <- read.data(fn,method='U-Pb',format=2,d=d)
concordia(UPb,type=2,xlim=c(0,5000),ylim=c(0.047,0.057))
# }