Dear all,
Garnet is a common mineral that appears in metamorphic rocks. It is also considered an accessory in igneous rocks and a detrital mineral in sedimentary rocks.
What are the key characteristics and approaches to differentiate between detrital, igneous, and metamorphic garnets in metasediments and igneous rocks?
MJ
Hello MJ, if I may:
For your information, I am not an expert in mineralogy or geochronology. However, here are some ideas I have and maybe they can be helpful to you. I suggest comparing and contrasting garnet and zircon in terms of the crystal structures to help you see whether it is feasible to apply the technique to distinguish origin of zircon to distinguish origin of garnet. It is highly that one cannot direct apply the technique to distinguish zircon to garnet. However, if there are enough similar physical characteristics between the two minerals, I think is possible to modify the techniques to then work with garnet.
Garnet in sedimentary rocks is always metamorphic or magmatic in origin, or has been derived from reworked sediments. Magmatic and metamorphic garnets are rarely monomineralic but s.s.s. such as "Grandite" (grossular+andratite = Ca/Al+Ca/Fe) or "Pyralspit" (pyrope+almandine+spessatine = Mg/Al+Fe/Al+Mn/Al). As you might conclude from the attached file you need to get an idea of the chemical composition and in some cases also of the valence state of Fe (see almandine and andratite)
I wish you much success with the table below which might help to come to grips with this issue.
HGD
There are innumerable case studies in the literature of detrital mineral provenance studies which address your question - I particularly recommend you take a look in the journal Sedimentary Geology.
Below I've highlighted some more generalized discussions and reviews, all of which contain useful surveys of the analytical techniques, diagnostic criteria, and data manipulation required to address detrital garnet origin and provenance discrimination.
Regards, Graham
Tolosana-Delgado, R., von Eynatten, H., Krippner, A., & Meinhold, G. (2018). A multivariate discrimination scheme of detrital garnet chemistry for use in sedimentary provenance analysis. Sedimentary Geology, 375, 14-26.
Schönig, J., von Eynatten, H., Tolosana-Delgado, R., & Meinhold, G. (2021). Garnet major-element composition as an indicator of host-rock type: a machine learning approach using the random forest classifier. Contributions to Mineralogy and Petrology, 176, 1-21.
Krippner, A., Meinhold, G., Morton, A. C., & von Eynatten, H. (2014). Evaluation of garnet discrimination diagrams using geochemical data of garnets derived from various host rocks. Sedimentary Geology, 306, 36-52.
Schönig, J., Meinhold, G., von Eynatten, H., & Lünsdorf, N. K. (2018). Provenance information recorded by mineral inclusions in detrital garnet. Sedimentary Geology, 376, 32-49.
Suggate, S. M., & Hall, R. (2014). Using detrital garnet compositions to determine provenance: a new compositional database and procedure. Geological Society, London, Special Publications, 386(1), 373-393.
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