Tonalite
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 e 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.
Tonalite
Plutonic igneous rock
Felsic minerals:
• quarzo
• plagioclasio
• alkali feldspar
Mafic minerals:
• biotite
• orneblenda
• pyroxene
QAPF classification:
Q = 20 – 60%
Plagioclase/feldspars > 90%
Colored varieties:
• trondhjemite/plagiogranite (M < 10%)
• melatonalite (M > 40%)
Extrusive equivalent: dacite
Bibliografia
Drummond, M. S., Defant, M. J., & Kepezhinskas, P. K. (1996). Petrogenesis of slab-derived trondhjemite–tonalite–dacite/adakite magmas. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 87(1-2), 205-215.
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.
See also
Tonalite – Alexstrekeisen.it
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