Ague {GCDkit} | R Documentation |
Implementation of Concentration ratio diagrams after Ague (1994) used for judging the mobility of elements or oxides in course of various geochemically open-system processes such as alteration or partial melting.
Ague(x = NULL, whichelems = "SiO2,TiO2,Al2O3,FeOt,MnO,MgO,CaO,Na2O,K2O,P2O5", immobile = NULL, bars = NULL, plot = TRUE)
x |
two sample names for analyses of the protolith and altered rock compositions, respectively. |
whichelems |
list of elements to be plotted. |
immobile |
list of (one or more) elements considered as immobile. |
bars |
optional name of the variable containing 1sigma errors |
for plotting error bars.
plot |
logical, should be the diagram plotted or just the results calculated? |
The Concentration ratio diagram shows concentration ratio of each geochemical species of interest (element or oxide) in the 'altered rock' to that in its presumed 'protolith'. These ratios are plotted on the y-axis, and the elements are arranged in any convenient order along x.
Following an open-system geological process, any of the perfectly immobile constituents i should ideally have exactly the same concentration ratio rinv defined as (Ague 2003):
rinv = c(A,i)/c(0,i)
where c(i) is the concentration of the species i, 0 refers to the 'protolith' and A to the 'altered rock'.
This ratio, however, would only exceptionally equate unity, when the mass of the whole system is conserved. Using the presumably immobile species i as the geochemical reference frame, the change in the rock mass can be defined as Ague (1994):
Delta_Mass = c(0,i)/c(A)-1
Thus rinv > 1 indicates overall rock mass loss due to removal of mobile constituents; this has the effect of increasing the concentrations of the immobile species ("residual enrichment"). Conversely, rinv < 1 shows an overall rock mass gain ("residual dilution").
The mass change of any mobile constituent j can be expressed as (Ague 1994):
Delta = 1/rinv*c(0,i)/c(A)-1
Mobile species j that have c(A,j)/c(0,j) ratios greater than rinv have been added to the system, and those with ratios lower than rinv have been lost.
In the GCDkit's implementation of the Concentration ratio diagrams, firstly the parental and altered rock samples can be chosen interactively from a binary plot MgO-SiO2, if not specified at the function call. Then the user is prompted for the elements/oxides to be plotted.
If not provided as a comma delimited list among the arguments, the presumably immobile elements are to be specified. To facilitate this choice, printed and plotted as barplots are ordered ratios of the elemental concentrations in the 'altered rock' to that in the 'protolith' (c(A,j)/c(0,j))).
Finally the concentration ratio diagram is plotted.
If the parameter bars
is given, error bars are also shown corresponding to
+/- 1 sigma.
Returns a matrix 'results
' with the following columns:
Altered/Protolith |
concentration ratios of the given geochemical species in the 'altered rock' to that in the 'protolith' - primary y axis of the plot |
Gain/loss in % |
relative gains (positive) or losses (negative) corrected for the rock mass change - secondary y axis of the plot |
Isocon.r
Vojtěch Janoušek, vojtech.janousek@geology.cz
Ague JJ (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
Ague JJ (2003) Fluid infiltration and transport of major, minor, and trace elements during regional metamorphism of carbonate rocks, Wepawaug Schist, Connecticut, USA. Amer J Sci 303: 753-816 doi: 10.2475/ajs.303.9.753
Grant JA (1986) The isocon diagram - a simple solution to Gresens equation for metasomatic alteration. Econ Geol 81: 1976-1982 doi: 10.2113/gsecongeo.81.8.1976
Grant JA (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 RL (1967) Composition-volume relationships of metasomatism. Chem Geol 2: 47-55 doi: 10.1016/0009-2541(67)90004-6
data(sazava) accessVar("sazava") # plot the diagrams Ague(c("Po-4","Po-1"), "SiO2,TiO2,Al2O3,FeOt,MgO,CaO,Rb,Sr,Ba,Zr,La,Nd,Eu,Gd,Yb,Y", "TiO2,SiO2,FeOt")