Granitoid

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Granite rock hand-sized sample

A granitoid is a generic term for a diverse category of

alkali feldspar.[1] Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz-poor monzonites to quartz-rich quartzolites.[2] As only two of the three defining mineral groups (quartz, plagioclase, and alkali feldspar) need to be present for the rock to be called a granitoid, foid-bearing rocks, which predominantly contain feldspars but no quartz, are also granitoids.[2] The terms granite and granitic rock are often used interchangeably for granitoids; however, granite
is just one particular type of granitoid.

Granitoids are diverse; no classification system for granitoids can give a complete and unique characterization of the origin, compositional evolution, and geodynamic environment for the genesis of a granitoid. Accordingly, multiple granitoid classification systems have been developed such as those based on: geochemistry, modal content,[jargon] emplacement depth, and tectonic regime.

Generalizations

Illustration of continental collision as a result of convergence

There are several generalizations that apply to the majority of granitoids. Typically, granitoids occur where

plutonic rocks outcrop.[3]  Granitoids can form in all tectonic environments.[3]

There are numerous exceptions to these generalizations.[4][3]  For example, granitoids can form in anorogenic environments, a granitoid source rock can be from the mantle (for example, at intraplate hotspots) and the melting mechanism can be radiogenic crustal heat.[4][5][6]

References

  1. ^ "USGS: Mineral Resources On-Line Spatial Data: Granitoid".
  2. ^
    S2CID 130569261
    .
  3. ^
    OCLC 890442947.{{cite book}}: CS1 maint: location missing publisher (link
    ).
  4. ^ a b Clarke, D. B. (1992) Granitoid Rocks, Chapman  & Hall, London.
  5. ^ Pitcher, W. S. 1982. Granite type and tectonic environment. In Hsu, K. J. (ed.) Mountain Building Processes, 19–40. London: Academic Press.
  6. ISSN 0072-1050
    .


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