The Role of Tonalites and Mafic Dikes in the Generation of the Idaho Batholith

Formation of the Idaho batholith is thought to have been promoted by prolonged injection of high-temperature mantle magmas that caused partial melting of continental crustal rocks to form granitic magma. The mafic magmas are now represented at the surface by numerous synplutonic mafic dikes in the batholith and by early tonalite and quartz diorite plutons forming the western part of the batholith and scattered elsewhere around its margins. Variable degrees of mixing between the mafic magmas and the granites produced quartz diorite complexes, intermediate and composite dikes, and mafic-rich, inhomogeneous parts of the main-phase granites and granodiorites.