I found Calcite in my granite sections so I am confused whether this is magmatic or Hydrothermal in origin .Is their any Major and Trace element differences in Magmatic and Hydrothermal Calcite? I consider texture well but need conformation on the basis of geochemical data.
Check out Kurt Kysers paper on using C isotopes in order to distinguish between calcite related to (hydrothermal) proximal propylitic alteration and regional greenschist metamorphic assemblages.
Hi Amjad,
The field observations are important: Hydrothermal calcites are mostly associated with veins, it can be a key factor.
If you have fluid inclusion and stable isotope facilities, you can easily detect the origin of your calcites.
Cheers,
Dear Amjad
We have two alternatives in relation to the origin of calcite as follows: the first option is that if the acidic magmatic fluid in the magma reservoir has come across an active and calcium carbonate-rich fluid, the calcite can be heterogeneously enriched by calcite mineral in certain margin zones of the magma chamber. The second alternative is the melting of the host rocks rich in CaO (e.g., carbonatic sedimentary rocks) or magma from a deeper source of high calcium origin. In this case, in the magma chamber, the enrichment of the calcium phenocrystalline and the calcium crystals can be a relatively homogeneous distribution. I think that this problem can be solved by performing both Sr-Nd isotope studies and CO2 fugacity experiments.
best
Özgür
Hi Amjad,
it is not possible to find magmatic calcite in granitic/rhyolitic magma.
Magmatic carbonates are found in strongly ultrabasic and mafic magmas (e.g., melilitites, nephelinites) and in mildly to strongly evolved intermediate compositions (e.g., trachytes-syenites) only. Never in granites.
Cheers,
michele
Dear Amjad: calcite in granitoid rocks is always of hydrotermal origin, either as inyected HT veins or as alteration of calcic-plagioclase (especially when plagioclase is andesine in diorites and similar rocks. I doubt your calcite comes from a asimilation of carbonate country rock, as carbonate would react readily with the silica in the magma to form Ca(Mg)-silicates, such as wollastonite, diopside, and the like. Precisely, one of thE nuisances when applying the R-Sr method of dating in granitoid rocks is the presence of secondary calcite, which means that the whole Sr-isotopic system has been seriously altered, making the method invalid. Regards, Sebastián.
Dear Jorge and Ajmad: one of the most productive magmatic-hydrothermal systems is the one resposible for the origin of the giant porphyry-Cu-Mo deposits, such as those in Chile, Perú, Arizona, Montana, British Columbia, the Urals and Shermanshah (Iran), and elsewhere. Therefore HT alteration can be contemporaneous with magmatism, as well as happenning after solidification of the magma body; in this latter case, it is usually produced by meteoric fluids infiltred in the upper crust heated by residual heat. I'm annexing a pair of papers downloaded from Geology Page which study meteoric water deep infiltration in an active orogen (the New Zealand Alps), which is going to be quite helpful.
Regards, Sebastián.
One profound question; is your outcrop of granite subaerial or subaquatic ?
Is it part of a stratigraphic sequence with roof rocks on top ?
H.G.Dill
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