F-M-W diagram {GCDkit}R Documentation

Ohta + Arai (2007) FMW weathering index

Description

Assigns data for the F-M-W diagram by Ohta & Arai (2007) into Figaro template (list 'sheet') and appropriate values into 'x.data' and 'y.data'.

This function is meant to be used with plotDiagram.

Usage

    OhtaArai(fixTi=F)

Arguments

fixTi

logical, if TRUE, the TiO2 value of samples where this is not determined (or 0) will be replaced by FeOt/7.

Details

This (ternary) diagram has been proposed by Ohta & Arai (2007) to identify chemically weathered igneous rocks. It turns out to be also very useful to separate para- from orthogneisses (Moyen et al. 2017).

The values of the apices are complex combination of oxides defining three end-members: M (mafic igneous rocks), F (felsic igneous rocks) and W (chemical weathering):

M = exp(-0.395×ln(SiO2)+0.206×ln(TiO2)-0.316×ln(Al2O3)+ 0.160×ln(Fe2O3t)+0.246×ln(MgO)+0.368×ln(CaO)+ 0.073×ln(Na2O)-0.342×ln(K2O)+2.266 )

F = exp(0.191×ln(SiO2)-0.397×ln(TiO2)+0.020×ln(Al2O3)-0.375× ln(Fe2O3t)-0.243×ln(MgO)+0.079×ln(CaO)+0.392× ln(Na2O)+0.333×ln(K2O)-0.892)

W = exp(0.203×ln(SiO2)+0.191×ln(TiO2)+0.296×ln(Al2O3)+0.215× ln(Fe2O3t)-0.002×ln(MgO)-0.448×ln(CaO)-0.464× ln(Na2O)+0.008×ln(K2O)-1.374)

ohtaarai.png

Value

A list containing the Figaro template. In addition the following global variables are modified:

sheet

list with Figaro Style Sheet data

x.data

x coordinates in ternary projection

y.data

y coordinates in ternary projection

Author(s)

Jean-François Moyen, jfmoyen@gmail.com

References

Ohta T, Arai H (2007) Statistical empirical index of chemical weathering in igneous rocks: a new tool for evaluating the degree of weathering. Chem Geol 240: 280-297 doi: 10.1016/j.chemgeo.2007.02.017

Moyen JF, Laurent O, Chelle-Michou C, Couzinie S, Vanderhaeghe O, Zeh A, Villaros A, Gardien V (2017) Collision vs. subduction-related magmatism: two contrasting ways of granite formation and implications for crustal growth. Lithos 277: 154-177. doi: 10.1016/j.lithos.2016.09.018

See Also

figaro plotDiagram

Examples

    data(sazava)
    accessVar("sazava")
    
    # Plot the diagram
    plotDiagram("OhtaArai",FALSE)

[Package GCDkit version 6.1 Index]