Talk:Pluton

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Is this definition correct?[edit]

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[edit]

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?[edit]

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)