Talk:Monzogranite

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The origin of the term "monzogranite," as well as that of monzonite, is derived from the name Monzoni Mountains. The "monzogranite outcrop", Le Mayet-de-Montagne, Allier, Auvergne, France is in the Monzoni Mountains.

Is the 'metagranite' mentioned in the monzogranite types a typo for monzogranite? The references given are not properly cited so I cannot check this up. — Preceding unsigned comment added by 86.135.70.222 (talk) 12:04, 27 November 2016 (UTC)[reply]

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Definition

The definition shown in this article seems to be derived from a single locality for that particular monzogranite. The only essential minerals in a monzogranite are quartz with alkali feldspar and plagioclase feldspar in roughly equal amounts (see the QAPF diagram that I just added to the article). They may be mica-bearing and that mica may be biotite, but it's not part of the definition. The same goes for them being the final fractionation products of a magma, that's definitely not the case generally. When I rewrote the aplite article it had been defined in much the same way from a single field example. Monzogranites are incredibly common, many granites fit into this compositional field. Mikenorton (talk) 14:10, 9 June 2024 (UTC)[reply]

Per your comment, I just lopped off the lede and replaced it with one sentence describing the region of the QAPF diagram. But clearly it needs more. — hike395 (talk) 16:14, 9 June 2024 (UTC)[reply]

The term is not used in many descriptions of granites, probably because it's so common, apparently large parts of the cornubian batholith are monzogranites but only some of the many sources for those rocks refer to them that way. One says that the Cornubian granites vary from monzogranites to syenogranites, which is basically just saying that they're granites in my understanding. I'm struggling to find something special to say about them that distinguishes them from granites as a whole. Mikenorton (talk) 21:18, 9 June 2024 (UTC)[reply]

Monzogranites are plagioclase rich granites. (Syenogranites are plagioclase poor granites, and alkali granites have even less plagioclase. Compositionally monzogranites are either Ca-rich or K-poor compared to syenogranites; I suspect the former is the usual state, but a K-poor granite could have a lot of albite/near-albite.

I think the revised lede is problematic. It implies that the rock is made up solely of QAP, while in practice biotite is commonly present, to which the Fe and Mg (and F and OH) in the melt is partitioned. Muscovite is often also present; is this to soak up any remaining F/OH, or is its presence driven by excess potassium? Lavateraguy (talk) 16:08, 11 June 2024 (UTC)[reply]

If they're really plagioclase rich, then they fall in the field of granodiorite, monzogranites are granites with a roughly even balance between the the two types of feldspar. Of course, you're right that QAPF isn't everything, it just happens to be how it's defined (the IUGS as recorded in Le Maitre et al. 2005^[1]). It's worth noting that the classification refers to the term as "optional". As to biotite, a lot of biotite granites and two-mica granites are monzogranites, they're just not part of the definition. I've tried to find a reliable source to confirm that 70% of all granites are monzogranites, which is something that gets said and is entirely plausible. I'm tempted to say that this article should just be redirected to the granite one as otherwise it's just a dictionary definition with a few examples. Mikenorton (talk) 16:42, 11 June 2024 (UTC)[reply]

The way I'd put it is that a plagioclase-rich rock (with free silica) is a granodiorite (or diorite); a plagioclase-rich granite is a monzogranite.

Fair enough I see your point, it just seems odd that a monzogranite that has say 36 % plagioclase and 64 % alkali feldspar should be called plagioclase-rich. Mikenorton (talk) 18:37, 14 June 2024 (UTC)[reply]

As for a merge there are similar syenogranite and leucogranite articles, but not alkali granite or melanogranite articles. There's also an aplite article, but microgranite is a redirect to granite. Covering the various forms of granite in the main article (with redirects) seems reasonable. Lavateraguy (talk) 18:23, 11 June 2024 (UTC)[reply]

I've suggested the redirects at Wikipedia talk:WikiProject Geology#Monzogranite not in great shape and I'll wait for any responses there before doing anything. As to the aplite article, I think that is specific enough that a standalone article is justified, although having recently rewritten it, I suppose that I would say that. Mikenorton (talk) 18:37, 14 June 2024 (UTC)[reply]

References

^ Le Maitre R.W.; Streckeisen A.; Zanettin B.; Le Bas M.J.; Bonin B.; Bateman P. (2005). Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks (PDF) (2 ed.). Cambridge University Press. p. 113. ISBN 9781139439398.

[LeMaitre2005-1] Le Maitre R.W.; Streckeisen A.; Zanettin B.; Le Bas M.J.; Bonin B.; Bateman P. (2005). Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks (PDF) (2 ed.). Cambridge University Press. p. 113. ISBN 9781139439398.

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