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granitoid
A granitoid or granitic rock is a variety of coarse grained plutonic rock similar to granite which mineralogically is composed predominantly of feldspar and quartz.〔Blatt, Harvey and Robert J. Tracy, ''Petrology,'' Freeman, 2nd Ed., 1996 ISBN 0-7167-2438-3〕 Examples of granitoid rocks include granite, quartz monzonite, quartz diorite, syenite, granodiorite 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.
While many granitoid rocks are located in areas that have experienced crustal thickening during orogenies, others known as ''anorogenic granitoids'' are unrelated to convergent boundaries or subduction zones.〔 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.〔
==References==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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