diseq {IsoplotR} | R Documentation |
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, m = 0, M = 20, x0 = 1, sd = 10),
ThU = list(x = 1, sx = 0, option = 0, m = 0, M = 20, x0 = 1, sd = 10),
RaU = list(x = 1, sx = 0, option = 0, m = 0, M = 20, x0 = 1, sd = 10),
PaU = list(x = 1, sx = 0, option = 0, m = 0, M = 20, x0 = 1, sd = 10),
buffer = 1e-05
)
Arguments
U48 |
a list containing seven items (x , sx ,
m , M , x0 , sd 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.
m , M specify the minimum and maximum search limits of
the initial 234 U/238 U activity ratio.
x0 and sd specify the mean and standard deviation of
the prior distribution for the the initial
234 U/238 U activity ratio.
|
ThU |
a list containing seven items (x , sx ,
m , M , x0 , sd 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.
m , M , x0 and sd are analogous to the
eponymous settings for ThU .
|
RaU |
a list containing seven items (x , sx ,
m , M , x0 , sd 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.
m , M , x0 and sd are analogous to the
eponymous settings for ThU .
|
PaU |
a list containing seven items (x , sx ,
m , M , x0 , sd 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.
m , M , x0 and sd are analogous to the
eponymous settings for ThU .
|
buffer |
small amount of padding to avoid singularities in the
prior distribution, which uses a logistic transformation:
y=ln(M+buffer−xx−m+buffer)
|
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:
Specify the assumed initial activity ratios and calculate how
much excess 206
Pb and 207
Pb these would have
produced.
Measure the current activity ratios to infer the initial
ratios. This approach only works for young samples.
The initial 230
Th/238
U activity ratio
can also be estimated by providing the Th/U-ratio of the magma.
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
See Also
mclean
, concordia
,
ludwig
Examples
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(0,700),ylim=c(0.05,0.5))
[Package
IsoplotR version 6.2
Index]