Description Usage Arguments Details Value References Examples
Plots UPb data on Wetherill and TeraWasserburg concordia diagrams, calculate concordia ages and compositions, evaluates the equivalence of multiple (^{206}Pb/^{238}U^{207}Pb/^{235}U or ^{207}Pb/^{206}Pb^{206}Pb/^{238}U) compositions, computes the weighted mean isotopic composition and the corresponding concordia age using the method of maximum likelihood, computes the MSWD of equivalence and concordance and their respective Chisquared pvalues. Performs linear regression and computes the upper and lower intercept ages (for Wetherill) or the lower intercept age and the ^{207}Pb/^{206}Pb intercept (for TeraWasserburg), taking into account error correlations and decay constant uncertainties.
1 2 3 4 5 6  concordia(x, tlim = NULL, alpha = 0.05, wetherill = TRUE,
show.numbers = FALSE, levels = NA, clabel = "",
ellipse.col = c("#00FF0080", "#FF000080"),
concordia.col = "darksalmon", exterr = FALSE, show.age = 0,
sigdig = 2, common.Pb = 0, ticks = NULL, anchor = list(FALSE,
NA), hide = NULL, omit = NULL, omit.col = NA, ...)

x 
an object of class 
tlim 
age limits of the concordia line 
alpha 
probability cutoff for the error ellipses and confidence intervals 
wetherill 
logical flag ( 
show.numbers 
logical flag ( 
levels 
a vector with 
clabel 
label for the colour legend (only used if

ellipse.col 
a vector of two background colours for the error
ellipses. If 
concordia.col 
colour of the concordia line 
exterr 
show decay constant uncertainty? 
show.age 
one of either:

sigdig 
number of significant digits for the concordia/discordia age 
common.Pb 
apply a common lead correction using one of three methods:

ticks 
an optional vector of age ticks to be added to the
concordia line to override 
anchor 
control parameters to fix the intercept age or common Pb composition of the discordia fit. This is a twoelement list.

hide 
vector with indices of aliquots that should be removed from the concordia diagram 
omit 
vector with indices of aliquots that should be plotted but omitted from concordia or discordia age calculation 
omit.col 
colour that should be used for the omitted aliquots. 
... 
optional arguments to the generic 
The concordia diagram is a graphical means of assessing the
internal consistency of UPb data. It sets out the measured
^{206}Pb/^{238}U and
^{207}Pb/^{235}Uratios against each other (‘Wetherill’
diagram) or, equivalently, the ^{207}Pb/^{206}Pb and
^{206}Pb/^{238}Uratios (‘TeraWasserburg’
diagram). The space of concordant isotopic compositions is marked
by a curve, the ‘concordia line’. Isotopic ratio measurements are
shown as 100(1alpha
)% confidence ellipses. Concordant
samples plot near to, or overlap with, the concordia line. They
represent the pinnacle of geochronological robustness. Samples that
plot away from the concordia line but are aligned along a linear
trend form an isochron (or ‘discordia’ line) that can be used
to infer the composition of the nonradiogenic
(‘common’) lead or to constrain the timing of prior lead loss.
if show.age=1
, returns a list with the following items:
a named vector with the (weighted mean) UPb composition
the covariance matrix of the (weighted mean) UPb composition
a vector with three items (equivalence
,
concordance
and combined
) containing the MSWD (Mean
of the Squared Weighted Deviates, a.k.a the reduced Chisquared
statistic) of isotopic equivalence, age concordance and combined
goodness of fit, respectively.
a vector with three items (equivalence
,
concordance
and combined
) containing the pvalue of
the Chisquare test for isotopic equivalence, age concordance and
combined goodness of fit, respectively.
a threeelement vector with the number of degrees of
freedom used for the mswd
calculation. These values are
useful when expanding the analytical uncertainties if
mswd>1
.
a 4element vector with:
t
: the concordia age (in Ma)
s[t]
: the estimated uncertainty of t
ci[t]
: the studentised 100(1α)\% confidence
interval of t
for the appropriate degrees of freedom
disp[t]
: the studentised 100(1α)\% confidence
interval for t
augmented by √{mswd} to account for
overdispersed datasets.
if show.age=2
, 3
or 4
, returns a list with the
following items:
the fitting model (=show.age1
).
a twoelement vector with the upper and lower intercept
ages (if wetherill=TRUE
) or the lower intercept age and
^{207}Pb/^{206}Pb intercept (if
wetherill=FALSE
).
the covariance matrix of the elements in x
.
a [2 x 2]
or [3 x 2]
matrix with the
following rows:
s
: the estimated standard deviation for x
ci
: the studentised 100(1α)\% confidence
interval of x
for the appropriate degrees of freedom
disp[t]
: the studentised 100(1α)\% confidence
interval for x
augmented by √{mswd} to account for
overdispersed datasets (only reported if show.age=2
).
the degrees of freedom of the concordia fit (concordance + equivalence)
pvalue of a Chisquare test for age homogeneity
(only reported if type=3
).
mean square of the weighted deviates – a
goodnessoffit measure. mswd > 1
indicates overdispersion
w.r.t the analytical uncertainties (not reported if
show.age=3
).
threeelement vector with the standard deviation of the
(assumedly) Normal overdispersion term and the lower and upper
halfwidths of its 100(1α)\% confidence interval (only
important if show.age=4
).
the number of aliquots in the dataset
Ludwig, K.R., 1998. On the treatment of concordant uraniumlead ages. Geochimica et Cosmochimica Acta, 62(4), pp.665676.
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