Frost_2008 {GCDkit} | R Documentation |
Classification of feldspathic igneous rocks proposed by Frost and Frost (2008).
Frost_2008(plot.txt = getOption("gcd.plot.text"), clssf = FALSE, GUI = FALSE)
plot.txt |
logical, annotate fields by their names? |
clssf |
logical, should the samples be classified? |
GUI |
logical, is the function called from a GUI? |
Classification scheme originally proposed by Frost et al. (2001) for (subalkaline) granitic rocks. It was modified and expanded for alkaline and/or mafic rocks by Frost and Frost (2008). It consists of four diagrams:
Fe number (FeOtot/(FeOtot+MgO)) vs. SiO2 (both parameters in wt. %). See Warning below.
SiO2 (in wt. %) vs. Modified alkali-lime index (MALI), defined as Na2O+K2O-CaO (in wt. %).
SiO2 (in wt. %) vs. Aluminium saturation index (ASI), defined as molecular Al2O3/(Na2O+K2O+CaO-1.67 P2O5).
In fact, this is the A/CNK parameter of Shand (1943), corrected for the Ca content in apatite. See also Warning below.
If some P2O5 concentrations are missing in the dataset, they are replaced by zero.
Feldspathoid silica-saturation index (FSSI) vs. Alkalinity index (AI), the former based on CIPW-normative minerals: (Q-(Lc+2*(Ne+Kp)))/100 and the latter defined as molecular Al2O3-(Na2O+K2O).
The following associations are distinguished:
ferroan, magnesian
alkalic, alkali-calcic, calc-alkalic, calcic
peralkaline, metaluminous, peraluminous
silica-undersaturated, silica-saturated
results |
The function returns table of calculated coefficients (Fe-number, MALI, ASI, FSSI). |
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.
Due to the specific design of this scheme (combination of multiple diagrams),
the classification option is not available via the pull-down menus.
Currently, the only way to apply Frost's classification in GCDkit on
individual samples is to call the function manually
from the Console: Frost_2008(clssf = TRUE)
.
Note that the Fe-number is calculated as weight proportion of FeOtot/(FeOtot+MgO). The approach used here should not be confused with the more common usage of the term "Fe-number" (as well as "Mg-number") for molecular proportions.
The equation for ASI in both original works of Frost et al. (2001) and Frost and Frost (2008) was stated erroneously as molecular proportions of elements, instead of oxides.
The equation for FSSI in Frost and Frost (2008) has apparently misplaced the outermost brackets, having been originally stated as: Q-[Lc+2(Ne+Kp)]/100.
Vojtěch Janoušek vojtech.janousek@geology.cz
& Vojtěch Erban, erban@sopky.cz
Frost BR, Frost CD (2008) A geochemical classification for feldspathic igneous rocks. J Petrol 49:1955-1969. doi: 10.1093/petrology/egn054
Frost BR, Barnes CG, Collins WJ, Arculus RJ, Ellis DJ, Frost CD (2001) A geochemical classification for granitic rocks. J Petrol 42: 2033-2048. doi: 10.1093/petrology/42.11.2033
Shand SJ (1943) Eruptive rocks, 2nd ed. John Wiley, New York, pp 1-444
Frost Shand CIPW classify Plate Plate editing plotPlate figaro
data(sazava) accessVar("sazava") # Plot the diagrams plotPlate("Frost_2008") # Classify the samples, suppress the graphical output Frost_2008(clssf = TRUE, GUI=TRUE)