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]