BF: Bowen-Fenner index

In pvermees/GeoplotR: Toolbox for Geological Plots

Bowen-Fenner index

Description

Bowen-Fenner index for tholeiitic and calc-alkaline magma series

Usage

BF(A, F, M, T, twostage = TRUE)

Arguments

A	vector with (Na_2O+K_2O) concentrations (in wt%)
F	vector with (FeO + FeO_2O_3) concentrations (in wt%)
M	vector with MgO concentrations (in wt%)
T	vector with TiO_2 concentrations (in wt%)
twostage	logical. If TRUE, uses the two-stage magma evolution model. If TRUE, uses a simple one-stage model. Only used if T has been omitted.

Value

the Bowen-Fenner indices of the samples, where positive values indicate calc-alkaline and negative numbers tholeiitic compositions.

If F is provided, T is omitted, and twostage is FALSE: returns the BF_1 index of Vermeesch and Pease (2021).

If F is provided, T is omitted, and twostage is TRUE: returns the BF_2^F index.

If F is omitted and T is provided, returns the BF_2^T index.

If both F and T are provided, returns the BF_2 index, which is the mean of BF_2^F and BF_2^T.

References

Vermeesch, P. and Pease, V. 2021, A genetic classification of the tholeiitic and calc-alkaline magma series, Geochemical Perspective Letters.

Examples

data(cath,package='GeoplotR')

oldpar <- par(mfrow=c(2,2),mar=c(4,4.5,2,0))
on.exit(par(oldpar))

A <- cath[,'Na2O']+cath[,'K2O']
F <- cath[,'FeOT']
T <- cath[,'TiO2']
M <- cath[,'MgO']

CA <- (cath$affinity=='ca')
TH <- (cath$affinity=='th')

dCA <- list()
dTH <- list()

titles <- c('BF1','BF2F','BF2T','BF2')

dCA[[1]] <- density(BF(A=A[CA],F=F[CA],M=M[CA],twostage=FALSE))
dTH[[1]] <- density(BF(A=A[TH],F=F[TH],M=M[TH],twostage=FALSE))

dCA[[2]] <- density(BF(A=A[CA],F=F[CA],M=M[CA],twostage=TRUE))
dTH[[2]] <- density(BF(A=A[TH],F=F[TH],M=M[TH],twostage=TRUE))

dCA[[3]] <- density(BF(A=A[CA],M=M[CA],T=T[CA],twostage=TRUE))
dTH[[3]] <- density(BF(A=A[TH],M=M[TH],T=T[TH],twostage=TRUE))

dCA[[4]] <- density(BF(A=A[CA],F=F[CA],M=M[CA],T=T[CA],twostage=TRUE))
dTH[[4]] <- density(BF(A=A[TH],F=F[TH],M=M[TH],T=T[TH],twostage=TRUE))

for (i in 1:4){
    matplot(cbind(dCA[[i]]$x,dTH[[i]]$x),
            cbind(dCA[[i]]$y,dTH[[i]]$y),
            type='l',lty=1,col=c('red','black'),
            xlab='BF',ylab='')
    title(titles[i])
    legend('topleft',legend=c('Cascades','Iceland'),
           lty=1,col=c('red','black'))
}

pvermees/GeoplotR documentation built on Aug. 20, 2024, 4:45 a.m.