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Lead Evolution Geom for Stacey & Kramers (1975)

Source: R/ASTR_geom_stacey_karmers.R
geom_sk_lines.Rd

These Geoms draws and label isochron, geochron, and kappa lines used for isotope age model referencing in lead isotope biplots. The lines follows the model used by Stacey & Kramers (1975).

Usage

geom_sk_lines(
  mapping = NULL,
  data = NULL,
  system = c("76", "86"),
  Mu1 = 10,
  Kappa = 4,
  ...
)

geom_sk_labels(
  mapping = NULL,
  data = NULL,
  system = "76",
  Mu1 = 10,
  Kappa = 4,
  ...
)

Arguments

mapping

Set of aesthetic mappings created by aes(). If specified and inherit.aes = TRUE (the default), it is combined with the default mapping at the top level of the plot. You must supply mapping if there is no plot mapping.

data

The data to be displayed in this layer. There are three options:

If NULL, the default, the data is inherited from the plot data as specified in the call to ggplot().

A data.frame, or other object, will override the plot data. All objects will be fortified to produce a data frame. See fortify() for which variables will be created.

A function will be called with a single argument, the plot data. The return value must be a data.frame, and will be used as the layer data. A function can be created from a formula (e.g. ~ head(.x, 10)).

system

Character "76" or "86" defining the isotope plot axis (default "76").

Mu1

Second-stage 238U/204Pb ratio (default 10).

Kappa

Second-stage 232Th/238U ratio (default 4).

...

Additional parameters for the geoms (see Details) and other arguments passed on to ggplot2::layer(). These are often aesthetics used to set a fixed value, such as colour = "red" or alpha = 0.5.

Value

A ggplot2 layer object.

Details

The plotting system follows the convention of showing geochron and isochron lines for the 207Pb/204Pb vs. 206Pb/204Pb plot and the kappa lines for 208Pb/204Pb vs. 206Pb/204Pb plot.

The geoms accept the following additional parameters through ...:

  • Ti : Initial time of the second stage in years (default 3.7 Ga).

  • interval : Time interval for isochron labels in years (default 200 Ma).

  • show_geochron : Logical; should the Geochron be plotted? (default TRUE).

  • show_isochrons : Logical; should time isochrons be plotted? (default TRUE)

  • kappa_list : Numeric vector of Kappa values to plot in "86" system.

Note

Currently the plot will scale the xlim and ylim to their maximum bounds. To prevent this, use coord_cartesian(xlim, ylim) to force the axis range to the desired values.

Aesthetics

geom_sk_lines() and geom_sk_labels() accept the following aesthetic values:

  • alpha

  • colour (controls the polygon outline)

  • fill (controls the polygon fill)

  • linetype

  • linewidth (controls the outline thickness)

  • text.colour (controls colour of the text)

  • size.unit (controls size aesthetic in "mm", "pt", "cm", "in" or "pc")

    Learn more about setting these aesthetics in vignette("ggplot2-specs").

References

Stacey, J.S. and Kramers, J.D. (1975) Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters 26(2), pp. 207–221. https://dx.doi.org/10.1016/0012-821X(75)90088-6.

See also

Other Pb isotope functions: age_models

Examples

# example code

library(ggplot2)
set.seed(50)
df <- data.frame(
  pb64 = rnorm(10, 18,0.2),
  pb74 = rnorm(10, 15.7,0.1),
  pb84 = rnorm(10, 37.5,0.1)
)

# Creating the Pb 207/204~206/204 plot
ggplot(df, aes(x = pb64, y = pb74)) +
  geom_point() +
  geom_sk_lines(system = "76") +
  geom_sk_labels(system = "76") +
  coord_cartesian(
    xlim = range(df$pb64) * c(.99, 1.01),
    ylim = range(df$pb74) * c(.99, 1.01)
  ) +
  labs(
    x = expression({}^206*Pb / {}^204*Pb),
    y = expression({}^207*Pb / {}^204*Pb),
  )


# Creating the Pb 208/204~206/204 plot
ggplot(df, aes(x = pb64, y = pb84)) +
  geom_point() +
  geom_sk_lines(system = "86",
                show_isochrons = FALSE, show_geochron = FALSE,
                kappa_list = c(3.2, 3.4, 3.6, 3.8)) +
  geom_sk_labels(system = "86",
                 show_isochrons = FALSE, show_geochron = FALSE,
                 kappa_list = c(3.2, 3.4, 3.6, 3.8)) +
  coord_cartesian(
    xlim = range(df$pb64) * c(.99, 1.01),
    ylim = range(df$pb84) * c(.99, 1.01)
  ) +
  labs(
    x = expression({}^206*Pb / {}^204*Pb),
    y = expression({}^207*Pb / {}^204*Pb),
  )


# Creating the Pb 207/204~206/204 plot with a seperate Geocrone color

ggplot(df, aes(x = pb64, y = pb74)) +
  geom_point() +
  geom_sk_lines(system = "76", show_geochron = FALSE) +
  geom_sk_lines(system = "76", show_isochrons = FALSE,
                color = 'red', linetype = 'dashed') +
  geom_sk_labels(system = "76", show_geochron  = FALSE) +
  geom_sk_labels(system = "76", show_isochrons = FALSE, color = 'red') +
  coord_cartesian(
    xlim = range(df$pb64) * c(.99, 1.01),
    ylim = range(df$pb74) * c(.99, 1.01)
  ) +
  labs(
    x = expression({}^206*Pb / {}^204*Pb),
    y = expression({}^207*Pb / {}^204*Pb),
  )