The granite is meta-aluminous calc-alkaline with ilmenite, epidote, sphene, biotite, hornblende,plagioclase, microcline (megacrsyts) and quartz (Silica saturated) assemblages. The granite have mingled with basic magma to variable degree. Your suggestions will be valuable and helpful.
Hi, Mr. Nibin Tom,
There are plenty chemical diagrams to present and classify meta-aluminous granites. For instances,
Whalen, J.B., Currie, K.L., Chappell, B.W., 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contributions to Mineralogy and Petrology 95, 407–419.
Frost BR, Barnes CG, Collins WJ, Arculus RJ, Ellis DJ, Frost CD (2001) A
geochemical classification for granitic rocks. J Petrol 42(11):2033–2048.
Eby, G.N., 1992. Chemical subdivision of the A-type granitoids: petrogenetic and tectonic implications. Geology 20, 641–644.
Liu, W., Liu, X.J., Liu, L.J., 2013. Underplating generated A- and I-type granitoids of the East Junggar from the lower and the upper oceanic crust with mixing of mafic magma: Insights from integrated zircon U–Pb ages, petrography, geochemistry and Nd–Sr–Hf isotopes. Lithos, 179: 293–319.
In Fig. 13. Diagrams showing correlation of A/NKC [=Al2O3 / (Na2O + K2O + CaO)] vs. A/NK [=Al2O3 / (Na2O + K2O)] (molar) (a), evolution of A/NKC (b) and Na2O + K2O (c) with SiO2, and Sr–Ba variations (d).
The best proven diagrams for this purpose are the
ACF diagram
AKF diagram
AFM diagram
The relevant definitions are available on the web.
For distinguishing metaluminous from peraluminous granites, the A/CNK (i.e., Al2O3/(CaO+Na2O+K2O) versus A/NK (i.e., Al2O3/(Na2O+K2O) will help. However, you indicate that some mingling (or hybridization/mixing) has occurred with a mafic magma; therefore, the ASI (alumina saturation index = A/CNK) you calculate will not be a primary magmatic signature. It might be best to first define the representative composition of the unmingled components, which you can plot to illustrate their ASI, and then calculate the mixing/mingling proportions of the felsic versus mafic component.
Thanks all for your active participation and suggestions. Dear Guenter, the ACF (metabasites), AFM/ AKFM (pelites) are not useful for granite, I suppose. For Sphene-Epidote-Hornblende-Biotite-Plagioclase-Microcline-Quartz equilibrium assemblages in a meta-aluminous granite, is there any projection diagram?.Dear Emmanuel Sakoma, I want to see the equilibrium assemblages and reactions stable for a range of PT/XH2O, It is not meant for any chemical classification. I will be trying the mixing aspect at a later stage. Please do further additions of your valuable comments
From what you are explaining, you'd have to use approaches such as Shreinemakers:
ZEN, E-an (1966): Construction of pressure-temperature diagrams for multicomponent systems after the method of Schreinemakers : a geometric approach. Geological Survey Bulletin, 1225.
OR use some of the thermodynamics software for mineral equilibria in a peraluminous system (from calculation of mineral activities):
BALDWIN, J. & MOGK, D. Advanced Modeling Programs: Introduction to the THERMOCALC Mineral Equilibria Modeling Software. Http://serc.carleton.edu/research_education/equilibria/thermocalc.html
Or visit
http://www.thermocalc.com/start/
I do not have much experience in these; other paers by Calvin Miller (etc), locatable through "Googling" might be of help as well.
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