Granitoid

A granitoid is a broad term referring to a diverse group of coarse-grained igneous rocks that are widely distributed across the globe, covering a significant portion of the Earth's exposed surface and constituting a large part of the continental crust. These rocks are primarily composed of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich to alkali-rich and from quartz-poor to quartz-rich . 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, feldspathoid-bearing rocks, which predominantly contain feldspars but no quartz, are also granitoids.

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Nomenclature and classification 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 composition, emplacement depth, and Tectonics.

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Generalizations There are several generalizations that apply to the majority of granitoids. Typically, granitoids occur where orogeny thickens continental crust either by subduction yielding a continental arc or by Tectonic Plate yielding continental collisions.

John D. Winter (2025). 9781292021539 ISBN 9781292021539

. Generally, the evolution to granitoid requires a thermal disturbance to ascent though continental crust.  Most granitoids are generated from crustal anatexis, the partial melting of the crust;  however the mantle may contribute both heat and material.  Granitoids can occur coeval with that have equivalent chemical composition (granite–rhyolite, syenite–trachyte, granodiorite–dacite etc.) however, these extrusive rocks are often Erosion so just the outcrop.  Granitoids can form in all tectonic environments.

There are numerous exceptions to these generalizations.Clarke, D. B. (1992) Granitoid Rocks, Chapman  & Hall, London.  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.Pitcher, W. S. 1982. Granite type and tectonic environment. In Hsu, K. J. (ed.) Mountain Building Processes, 19–40. London: Academic Press.

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