Trondhjemite
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Trondhjemites are leucotonalites, a variety of leucocratic tonalite in which the modal mineralogy mostly consists of plagioclase in the form of albite to andesine, >20% quartz, and <10% alkali feldspa
Tonalite-trondhjemite-granodiorite migmatite (left) and trondhjemitic gneiss (right) from northern China
Tonalite–trondhjemite–granodiorite rocks are intrusive rocks with typical granitic composition but containing only a small portion of potassium feldspar. Tonalite, trondhjemite, and granodiorite often
Trondhjemite
…are usually called plagiogranites. Trondhjemites are common in Archean terranes, occurring in conjunction with tonalite and granodiorite as the TTG (tonalite-trondhjemite-granodiorite) orthogneiss suite. Trondhjemite dikes also commonly form part of the sheeted dike complex of an ophiolite. The rock type was first described by Victor…
Archean TTG rock outcrop in Kongling Complex, South China Craton. The white TTG rock body is intruded by dark mafic dikes, as well as light color felsic dikes. The mafic minerals in the TTG rock body, possibly biotite, were weathered, which introduced a brownish coating on the TTG rock surface.
TTG rock sample (Tsawela gneiss) with foliation from the Kaapvaal Craton, South Africa. The white minerals are plagioclase; the light grey ones are quartz; the dark, greenish ones are biotite and hornblende, which developed foliation.