apSaturation {GCDkit}R Documentation

Apatite saturation

Description

Calculates apatite saturation temperatures for observed whole-rock major-element compositions. Prints also phosphorus saturation levels for the given major- element compositions and assumed magma temperature.

Usage

apSaturation(Si = WR[, "SiO2"], ACNK = WR[, "A/CNK"],
P2O5 = WR[, "P2O5"], T = 0)

Arguments

Si

SiO2 contents in the melt (wt. %)

ACNK

vector with A/CNK (mol %) values

P2O5

vector with P2O5 concentrations

T

assumed magma temperature in C

Details

* Calculates phosphorus saturation levels following Harrison & Watson (1984):

ln(DP) = (8400 + 26400 (SiO2 - 0.5))/T - 3.1 - 12.4 (SiO2 - 0.5)

P2O5.HW = 42/DP

where 'T' = absolute temperature (K), 'DP' = distribution coefficient for phosphorus between
apatite and melt and 'SiO2' is the weight fraction of silica in the melt, SiO2 wt. %/100.

These formulae were shown to be valid only for metaluminous rocks, i.e. A/CNK < 1, and were modified for peraluminous rocks (A/CNK > 1) by Bea et al. (1992):

P2O5.Bea = P2O5.HW * exp(6429(A/CNK - 1)/(T-273.15))

and Pichavant et al. (1992):

P2O5.PV = P2O5.HW + (A/CNK - 1) exp(-5900/T - 3.22 SiO2 + 9.31)

Note that the phosphorus saturation concentrations are not returned by the function but printed only.

* Calculates saturation temperatures in C using the observed P2O5 concentrations (Harrison & Watson, 1984):

T.HW = (8400 + 26400 (SiO2 - 0.5))/(ln(42/P2O5) + 3.1 + 12.4(SiO2 - 0.5)) - 273.15

for peraluminous rocks (A/CNK > 1) the equation of Bea et al. (1992) needs to be solved for 'T' (in K) by iterations:

P2O5.Bea = 42/(exp(8400 + 26400 (SiO2 - 0.5))/T - 3.1 - 12.4 (SiO2 - 0.5)) * exp(6429(A/CNK - 1)/(T-273.15))

as is that of Pichavant et al. (1992):

P2O5.PV = 42/(exp(8400 + 26400 (SiO2 - 0.5))/T - 3.1 - 12.4 (SiO2 - 0.5)) + (A/CNK - 1) exp(-5900/T - 3.22 SiO2 + 9.31)

Value

Returns a matrix 'results' with the following columns:

A/CNK

A/CNK values

Tap.sat.C.H+W

saturation T of Harrison & Watson (1984) in C

Tap.sat.C.Bea

saturation T of Bea et al. (1992) in C, peraluminous rocks only

Tap.sat.C.Pich

saturation T of Pichavant et al. (1992) in C, peraluminous rocks only

Plugin

Saturation.r

Author(s)

Vojtech Janousek, vojtech.janousek@geology.cz

References

Bea F, Fershtater G B & Corretge L G (1992) The geochemistry of phosphorus in granite rocks and the effects of aluminium. Lithos 29: 43-56 doi: 10.1016/0024-4937(92)90033-U

Harrison T M & Watson E B (1984) The behavior of apatite during crustal anatexis: equilibrium and kinetic considerations. Geochim Cosmochim Acta 48: 1467-1477 doi: 10.1016/0016-7037(84)90403-4

Pichavant M, Montel J M & Richard L R (1992) Apatite solubility in peraluminous liquids: experimental data and extension of the Harrison-Watson model. Geochim Cosmochim Acta 56: 3855-3861 doi: 10.1016/0016-7037(92)90178-L


[Package GCDkit version 4.1 Index]