Wedge {GCDkit}R Documentation

Wedge diagrams (Ague 1994)

Description

Implementation of Wedge diagrams after Ague (1994) and Bucholz and Ague (2010) used for judging the mobility of elements or oxides in course of various geochemically open-system processes such as alteration or partial melting.

Usage

    Wedge(x = "Ti", y = NULL, protolith = NULL,
    outline = "chull", precision = 10, plotAltered = TRUE, 
    xmin = 0, ymin = 0, xmax = NULL, ymax = NULL, fun = NULL)

Arguments

x

a single geochemical species presumably immobile during the given rock transformation.

y

list of elements/oxides for plotting, separated by commas.

protolith

Boolean search pattern to specify the protolith samples in the data file.

outline

method for contouring the clusters of protolith and product compositions, see Details.

precision

precision of contours drawn, if 'outline'="contour", see Details.

plotAltered

logical; should be the altered analyses plotted or just contoured?

xmin, xmax

(optional) limits for shared x axes of the individual plots.

ymin

(optional) minimum for all of the y axes of the plots.

ymax

(optional) upper limits for each of the y axes of the plots.

fun

panel function to be applied to each of the individual plots.

Details

Wedge diagrams (Ague 1994) enable qualitative treatment of losses/gains of geochemical species (elements or oxides) during open-system geological processes, such as alteration, metamorphism or partial melting. As such they represent a viable alternative to the isocon plots (Grant 1986, 2005) or concentration ratio diagrams (Ague 1994). However, the Wedge diagrams have an advantage in that they take into account the overall variability of the whole dataset (both of the putative protolith and the altered product) and not just a selected whole-rock pair.

Wedge diagrams are simple binary plots of a potentially mobile element j versus a reference (immobile) element i. The compositionally heterogeneous protolith samples yield a cloud of points. The outer edges of this cloud define a wedge-shaped region that converges towards the origin.

As shown by Bucholz and Ague (2010), the altered samples that plot above and to the left of this wedge are thought to have gained the mobile species j, whereas those falling below and to the right suffered its loss. The samples that remain in the wedge but moved upwards are thought to record residual enrichment, and those shifted downwards to have underwent a residual dilution.

The samples defining the protolith variation can be selected based on combination of three searching mechanisms (by sample name/label, range or a Boolean condition) - see selectSamples for details.

Implemented are two methods for outlining the clusters of the protolith and altered compositions (as specified by the argument 'outline'), convex hull (chull) and contour (contour). For the latter, the shape of the contours drawn can be controlled using the parameter (precision). The higher it is, the smoother contours result. See contourGroups and chullGroups for further details. Wedge.png Optionally, the individual data points for the altered samples may be replaced by contours portraying their density, if plotAltered = FALSE.

Parameters xmin, xmax, ymin and ymax are passed to the function plotWithLimits used for the actual data plotting.

Optionally, panel function specified by fun with two arguments, xlab and ylab, is applied to each of the plots.

Value

Returns a matrix 'results' of slopes of tie-lines from individual protolith samples to the origin (with a component for each diagram, i.e. for each species evaluated). Lines of maximum and minimum slopes are those which are plotted as dashed lines, thus defining the wedge of the protolith variation (see Details).

Plugin

Isocon.r

Note

This function uses the plates concept. The individual plots can be selected and their properties/appearance changed as if they were stand alone Figaro-compatible plots. See Plate, Plate editing and figaro for details.

Author(s)

Vojtech Janousek, vojtech.janousek@geology.cz

References

Ague J J (1994) Mass transfer during Barrovian metamorphism of pelites, south-central Connecticut; I, Evidence for changes in composition and volume. Amer J Sci 294: 989-1057 doi: 10.2475/ajs.294.8.989

Bucholz C E, Ague J J (2010) Fluid flow and Al transport during quartz-kyanite vein formation, Unst, Shetland Islands, Scotland. J Metamorph Geol 28: 19-39 doi: 10.1016/0009-2541(67)90004-6

Grant J A (1986) The isocon diagram - a simple solution to Gresens equation for metasomatic alteration. Econ Geol 81: 1976-1982 doi: doi:10.2113/gsecongeo.81.8.1976

Grant J A (2005) Isocon analysis: a brief review of the method and applications. Phys Chem Earth (A) 30: 997-1004 doi: 10.1016/j.pce.2004.11.003

Gresens R L (1967) Composition-volume relationships of metasomatism. Chem Geol 2: 47-55 doi: 10.1016/0009-2541(67)90004-6

See Also

Ague, isocon, Plate, Plate editing, chull, contour contourGroups chullGroups, plotWithLimits

Examples

    data<-loadData("sazava.data",sep="\t")
    Wedge("Ti","SiO2,FeOt,MgO,CaO,Na2O,K2O",
        protolith="Intrusion=\"Sazava\"","chull")
    
    # Using the default precision of 10
    Wedge("Ti","Zr,Nb,Sr,Rb,Ba",protolith="Intrusion=\"Sazava\"","contour")
     
    Wedge("Ti","Zr,Nb,Sr,Rb,Ba",protolith="Intrusion=\"Sazava\"","contour",precision=100)
    
    

[Package GCDkit version 4.1 Index]