tonalite

{{Short description|Igneous rock}}

File:Tonalite.png from Tjörn, Sweden]]

File:Qapf tonalite.png with tonalite field highlighted]]

Tonalite is an igneous, plutonic (intrusive) rock, of felsic composition, with phaneritic (coarse-grained) texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with alkali feldspar making up less than 10% of the total feldspar content. Quartz (SiO₂) is present as more than 20% of the total quartz-alkali feldspar-plagioclase-feldspathoid (QAPF) content of the rock.{{Cite journal|last1=Le Bas|first1=M. J.|last2=Streckeisen|first2=A. L.|title=The IUGS systematics of igneous rocks|journal=Journal of the Geological Society|volume=148|issue=5|pages=825–833|doi=10.1144/gsjgs.148.5.0825|bibcode=1991JGSoc.148..825L|year=1991|citeseerx=10.1.1.692.4446|s2cid=28548230}}{{Cite journal|date=1999|title=Rock Classification Scheme - Vol 1 - Igneous|url=http://nora.nerc.ac.uk/id/eprint/3223/1/RR99006.pdf|journal=British Geological Survey: Rock Classification Scheme|volume=1|pages=1–52}} Amphiboles and biotite are common in lesser quantities, while accessory minerals include apatite, magnetite and zircon.https://geologyscience.com/rocks/igneous-rocks/intrusive-igneous-rocks/tonalite/ Tonalite Page in Geology Science{{cite book |last1=Allaby |first1=Michael |title=A dictionary of geology and earth sciences |date=2013 |publisher=Oxford University Press |location=Oxford |isbn=9780199653065 |edition=Fourth |chapter=tonalite}}

In older references tonalite is sometimes used as a synonym for quartz diorite. However the current IUGS classification defines tonalite as having greater than 20% quartz, while quartz diorite varies its quartz content from 5 to 20%.

The name is derived from the type locality of tonalites, adjacent to the Tonale Line, a major structural lineament and mountain pass, Tonale Pass, in the Italian and Austrian Alps. The name was first applied by Gerhard vom Rath in 1864.{{cite book |editor1-last=Jackson |editor1-first=Julia A. |title=Glossary of geology. |date=1997 |publisher=American Geological Institute |location=Alexandria, Virginia |isbn=0922152349 |edition=Fourth |chapter=tonalite}} The term adamellite was originally applied by A. Cathrein in 1890 to orthoclase-bearing tonalite (likely a granodiorite) at Monte Adamello, Italy, in 1890, but later came to refer to quartz monzonite, and is now a deprecated term.{{cite journal |last1=Streckeisen |first1=A. |title=To each plutonic rock its proper name |journal=Earth-Science Reviews |date=1 March 1976 |volume=12 |issue=1 |pages=1–33 |doi=10.1016/0012-8252(76)90052-0}}

Trondhjemite is an orthoclase-deficient variety of sodium-rich tonalite with minor biotite as the only mafic mineral, named after Norway's third largest city, Trondheim.{{sfn|Jackson|1997|loc="trondhjemhite"}}

Tonalites, together with granodiorites, are characteristic of calc-alkaline batholiths formed above subduction zones.{{cite journal |last1=Castro |first1=Antonio |title=Tonalite–granodiorite suites as cotectic systems: A review of experimental studies with applications to granitoid petrogenesis |journal=Earth-Science Reviews |date=September 2013 |volume=124 |pages=68–95 |doi=10.1016/j.earscirev.2013.05.006}}

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