Tonalite is a type of plutonic igneous rock containing quartz (20 – 60% of the felsic minerals) and abundant plagioclase. K-feldspar is rare or absent in a tonalite and, when present, it constitutes less than 10% of the feldspars. The composition of plagioclase typically ranges from oligoclase to andesine. Tonalites may contain several mafic minerals, like hornblende, biotite, and/or pyroxene, typically constituting 10 to 40% of the rock.
The name ‘tonalite’ derives from the Tonale Pass in the Adamello Group (Alto Adige, Italy). Trondhjemite and plagiogranite are two synonym terms that can be used for light-colored varieties (less than 10% of mafic minerals) of tonalite. The term ‘trondhjemite’ derives from the Norwegian town of Trondhjem, now Trondheim.
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Glikson, A. Y. (1979). Early Precambrian tonalite-trondhjemite sialic nuclei. Earth-Science Reviews, 15(1), 1-73.
Martin, H., Smithies, R. H., Rapp, R., Moyen, J. F., & Champion, D. (2005). An overview of adakite, tonalite–trondhjemite–granodiorite (TTG), and sanukitoid: relationships and some implications for crustal evolution. Lithos, 79(1-2), 1-24.
Smithies, R. H. (2000). The Archaean tonalite–trondhjemite–granodiorite (TTG) series is not an analogue of Cenozoic adakite. Earth and Planetary Science Letters, 182(1), 115-125.