Talk:Igneous intrusion

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Is this definition correct?

There is inconsistency between the use of this term. Here it any intrusive magmatic body, including sills, dikes and batholiths. The definition of a sill is consistent with this and begins "...a sill is a tabular pluton ..." However the section on batholiths states that a "batholith is formed when many plutons converge together to form a huge expanse of granitic rock. They are composed of multiple masses, or plutons, bodies of igneous rock of irregular dimensions (typically at least several kilometers) that can be distinguished from adjacent igneous rock by some combination of criteria including age, composition, texture, or mappable structures." So in this case a batholith is not a pluton and a pluton is a smaller unit. The term dike makes no mention of plutons, but is broad enough to include sedimentary as well as igneous intrusions.

The university of Penn. Geology website has these definitions of pluton and batholith "A pluton is a relatively small intrusive body (a few to tens of km across) that seems to represent one fossilized magma chamber. A batholith is much larger (up to hundreds of km long and 100 km across) and consists of many plutons that are similar in composition and appearance." Here a pluton is bigger than at least most dikes or sills but smaller than a batholith.

In other words there seems to be two uses for this term. One as a large mass of igneous intrusion, bigger than dikes and sills, but smaller than batholith, and a second that encompasses all of these. Someone with greater authority in this area needs to clean this up or if there is ambiguity in the definition make that clear. 96.252.103.113 (talk) 16:09, 14 November 2008 (UTC)

In my experience, although its not exactly my field, sills and dykes are not generally referred to as 'plutons' but form part of that group of intermediate depth to high-level intrusions that is sometimes called hypabyssal (although that article doesn't have much content). To define plutons to cover any type of intrusive body would mean that we didn't need the term 'intrusion'. The derivation of the word pluton suggests that it should only be used for igneous bodies that solidified at depth (although I'm not sure that I can define a upper limit). Regarding batholiths, they do form over long periods by the coalescence of repeated intrusive events, with the individual masses being referred to as plutons. I will try to find some good references to back all this up and alter the page accordingly. Mikenorton (talk) 18:41, 20 November 2008 (UTC)

Well it didn't take me long to find that there are two distinct (but overlapping) definitions out there and that this is fully reflected in our articles on intrusion and igneous rocks (and no doubt others).

• Definition 1 This uses pluton as a synonym for intrusion so igneous rocks are split into two

• subsurface - plutons/intrusions
• on the surface - extrusive rocks

• Definition 2 This confines plutons to deeper seated intrusions so in this case igneous rocks are split into three

• deep intrusion - plutons
• intermediate to shallow intrusions - hypabyssal intrusions
• on the surface - extrusive rocks

In general we don't know exactly how deep an intrusive rock crystallized so we actually use grain size as a proxy. Plutons = coarse-grained, hypabyssal = medium-grained and extrusive = fine-grained. Without other evidence that's going to be your best guess. Of course the grain size does not just depend on the depth of emplacement but also on the size of the intrusion. In searching for anything definitive about the usage of pluton etc., I came across these attempts to provide a uniform set of terms for use on geological maps[1][2] using something called a lithodemic hierarchy, something new to amaze my colleagues with. Anyway, these documents do support the three-fold subdivision into plutonic, hypabyssal and extrusive. On this basis I intend to modify the various articles accordingly when I get the time, and after allowing suitable time for those with other views to make their case. Mikenorton (talk) 22:23, 20 November 2008 (UTC)

Vulcanism as an alternative name

There's not much about the use the “Vulcanism” as an alternative name to Plutonism. (Maybe it needs a fact tag?) In any case, it was mistakenly mentioned as a third competitor with Neptunism. The article at Volcanism (the redirect target of Vulcanism) doesn't have anything about these two theories, so an "about" tag was added there to lead back here, and any links I could find to Vulcanism from pages in this set were removed if they were simply included as an alternative name to Plutonism. In the event, there was only one incidence and it was in this article. Best way to fix problems is before they happen :-) --Rfsmit (talk) 13:49, 3 May 2010 (UTC)

Are Plutons Igneous?

Plutons are distinct, variously shaped, coarsely crystalline bodies of rock created beneath the surface. Fluids were essential to their creation, most believe. Did they flow? Some granites show what geologists have interpreted as remnant bedding. This was, and perhaps is, a provocative subject. Both igneous & metamorphic plutons may exist.

'Hypabyssal' is a bit old-fashioned, I think. You might also mention that your list of plutons are classed by shape & size, and your list of rock are classed by mineral composition and relative amount. Geologist (talk) 23:04, 12 January 2012 (UTC)

External links modified (January 2018)

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Requested move 8 November 2020

The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review after discussing it on the closer's talk page. No further edits should be made to this discussion.

The result of the move request was: Moved (non-admin closure) (t · c) buidhe 21:44, 16 November 2020 (UTC)

---

Pluton → Igneous intrusion – The title of this article is problematic, and this is reflected in a lead that devotes most of its verbage to exploring the variety of definitions offered for the word "pluton". Defining the meaning of a word is a job for a dictionary, not an encyclopedia; an encyclopedia discusses subjects and the title of an article should precisely capture what the subject is. That is not possible with as ill-defined a term as "pluton". I therefore propose moving this article to "Igneous intrusion", which I think unambiguously captures what the subject of the article is. I note that Igneous intrusion is presently a redirect to Igneous rock which, while closely related, is really not the same subject. Focusing Igneous rock on petrology and "Igneous intrusion" on structure will, I think, improve both articles. Kent G. Budge (talk) 06:32, 8 November 2020 (UTC)

Support as per nomination. Kent, thanks for raising this issue. As plutons are only one type of igneous intrusion and as pluton is only a synonym for any non-tabular igneous intrusion except a batholith, I think description of plutons could be done in an article describing all types of igneous intrusion. I like your suggestion of two articles, "igneous rock" and "igneous intrusion", focusing on different aspects. One point about your suggested petrology versus structure focus split in the two articles: Igneous petrology includes the occurrence and structure, e.g. field relations, of igneous intrusions. This is not currently mentioned in Wikipedia's article about petrology. (By the way, structure and field relations of sedimentary and metamorphic rock units are also parts of sedimentary and metamorphic petrology, respectively). I suggest that this could be addressed by adding some text about structure and field relations, for all three main rock groups, into the "petrology" article. I suggest brief mention of igneous intrusions in the "igneous rock" article with a "main article" link to "igneous intrusion". If "pluton" is moved/renamed to "igneous intrusion", I suggest that mention of, and "main article" links to, other types of intrusion (i.e. tabular e.g. dykes and sills) should be included as soon as possible in the new "igneous intrusion" article. If the amount of information about plutons becomes large in the future, pluton could be resurrected as a standalone article. GeoWriter (talk) 16:45, 8 November 2020 (UTC)

Thanks, GeoWriter. I am interested in any ideas for better defining the scope of Igneous intrusion and Igneous rock and associated articles and redirects. Certainly igneous petrology is an aspect of structure, and vice versa, but I think the two subjects are distinct enough that a merge is not the right approach. But as it stands, this Pluton article is a bit of a mess, starting with a lead that makes it clear (to me) than "Pluton" is a bad choice of subject title.

One of the first things I did when I saw that dreadful lead paragraph was to start going through my sources -- and I quickly found that one defines pluton as any igneous intrusion whatsoever (Oxford Dictionary of Geology and Earth Sciences); another defines it as essentially a synonym for batholith (Levin The Earth Through Time); Philpotts and Ague avoid the word "pluton" entirely, using "igneous intrusion" consistently instead -- which gave me the idea for a better article title. And now you've suggested another definition, which is any non-tabular intrusion that is not a batholith. If I had been asked to define pluton before looking at this article and thinking about it, I would probably have leaned towards any nontabular intrusion. The term is clearly much too vague.

Of course, "Pluton" is still going to redirect here, so we'll have to mention it in boldface near the lead, but I think we can come up with a fair but pithy way of saying it's an imprecise term for some or all igneous intrusions. --Kent G. Budge (talk) 16:58, 8 November 2020 (UTC)

To clarify about plutons and batholiths. I was considering their relationship from the viewpoint that "a batholith is a large structure made of multiple plutons" and that multiple plutons are not the same as a single pluton. I may have been too restrictive.

Key points from a few more definitions of "pluton": in Neuendorf et al.'s "Glossary of Geology", a pluton is deep-seated; in "Encyclopedia Britannica", a pluton is of uncertain dimensions. GeoWriter (talk) 17:41, 8 November 2020 (UTC)

Support Not being able to find an article on igneous intrusions when searching the term "igneous intrusion" is a really odd situation to be in, and this seems like a good way to fix that. --Licks-rocks (talk) 13:26, 9 November 2020 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Pluton - defintion

Kent G. Budge, thanks for making a start on the tasks covered in the recent move/merge discussion for pluton. I think there is a problem with your sentence describing a pluton, which currently states: "A pluton is an intrusion emplaced at a depth of 5 kilometres (3.1 mi) or more.[12] However, the term is often used more loosely,[13] sometimes as a synonym for all igneous intrusions,[14] for very large intrusions,[15] or for crystallized magma chambers." I think you are giving undue weight to the specific depth-based definition from a single source - you seem to be claiming/implying that this is the correct definition and there are some other less-authoritative definitions. I think the specific 5 km depth criterion could actually be a minority view even among geologists who define plutons by depth alone because many geologists describe plutons in the 1 to 5 km depth range. Instead of the current version of text in the article, which starts by favouring a random definition from one source then describes other often-used definitions, I suggest that perhaps we should start by emphasising that there is no consensus. Perhaps we could then say that definitions range from vague to specific, some focus on depth, some on shape etc. then list the often-used definitions. Alternatively, we could keep things as they are currently with the 5km depth version as the favoured definition but add reasons (with sources, of course) to explain why it is favoured over the other definitions. I know this is not an easy topic because of e.g. lack of consensus and fear of disappointing readers who could be frustrated by absence of a clear definition but I hope we can continue to work at it to find the best content and phrasing. GeoWriter (talk) 16:15, 17 November 2020 (UTC)

I feel some of that frustration myself. Aside from the need for a target for a redirect, the term "pluton" is used so widely in the literature that we need to find some way to come to grips with it. When I came across Blatt and Tracy's definition as a deep intrusion, it "felt right" and so I probably did put too much weight on it. Perhaps if we said "pluton" is a term often applied to deep intrusions, with Blatt and Tracy footnoted as an example, but left out a hard depth limit? My recollection is that they mention 5km more as a rule of thumb than as a hard definition. Feel free to take a crack at rewording it yourself.

I've taken one more crack at it myself first. Let me know what you think. I also googled up how it's used on the webs, and I can find multiple examples of every one of the definitions we've listed so far. For a term used so often, it's amazingly badly defined. (Hence the article move. :)

The other thing worrying me is that there is now a lot of duplication with Igneous rock. This is not unanticipated, but that article now needs some work to give it a tighter focus. --Kent G. Budge (talk) 16:26, 17 November 2020 (UTC)

I think your second attempt at the paragraph describing a pluton is better. Thanks for changing it. GeoWriter (talk) 19:42, 20 November 2020 (UTC)

Thanks.

I think the article is starting to shape up reasonably well. I think it needs a section on the room problem, which I'll try to add over the next couple of weeks if I can find the time and references -- you're welcome to take a crack at it first yourself if you like. I thought about a discussion of cooling of intrusions and things like cumulates, chilled margins, and such, but some of that probably belongs in Igneous rocks instead. I still think separate articles are justified but there's bound to be considerable overlap. --Kent G. Budge (talk) 20:14, 20 November 2020 (UTC)

I like your suggestion about including some details about cooling, chilled margins etc. Also, in case you haven't already come across it, the Methods of pluton emplacement article may also benefit from merging with this igneous intrusion article or revision without merging. GeoWriter (talk) 20:54, 24 November 2020 (UTC)

I hadn't come across that article. Sounds like something that really ought to be merged here. I'll look it over and see what I think. --Kent G. Budge (talk) 23:40, 24 November 2020 (UTC)

Expanded the Formation section to include discussion of cooling and cumulates, and put in a nod to the Methods of pluton emplacement article under the room problem. I can see keeping that article, but only if it's extensively rewritten -- it has fingerprints of an agenda on it in its current form, if you know what I mean. Correct me if I'm wrong -- it has been known to happen -- but my impression is that there is quite a lot of field evidence for stoping, but the article seems written to discount that process in favor of others. --Kent G. Budge (talk) 18:17, 26 November 2020 (UTC)