Granitoid

A granitoid or granitic rock is a variety of coarse grained plutonic rock — granite or similar — which mineralogically is composed predominantly of feldspar, quartz and mica.[1] Examples of granitoid rocks include granite, quartz monzonite, quartz diorite, syenite, granodiorite, tonalite and trondhjemite. Many are created by continental volcanic arc subduction or the collision of sialic masses. Volcanic rocks are common with granitoids and typically have the same origins. However, they are normally worn away after years of erosion.

Grus sand and granitoid (upper left)

Many granitoid rocks are located in areas that have experienced crustal thickening during orogenies but others, known as anorogenic granitoids, are unrelated to convergent boundaries or subduction zones.[1] These anorogenic granitoids may represent the deep sources for rift volcanism exposed where erosion has removed the volcanic rocks and other evidence of rifting. These A-type granitoids may have been produced by hotspots or mantle plumes.[1]

References
  1. Blatt, Harvey and Robert J. Tracy, Petrology, Freeman, 2nd Ed., 1996 ISBN 0-7167-2438-3


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