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Tonalite–trondhjemite–granodiorite (TTG) rocks are intrusive rocks with typical granitic composition (quartz and feldspar) but containing only a small portion of potassium feldspar. Tonalite , trondhjemite , and granodiorite often occur together in geological records , indicating similar petrogenetic processes. [ 1 ]
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. [6] Tonalites, together with granodiorites, are characteristic of calc-alkaline batholiths formed above subduction zones. [7]
Trondhjemite is a leucocratic (light-colored) intrusive igneous rock. It is a variety of tonalite in which the plagioclase is mostly in the form of oligoclase . [ 1 ] Trondhjemites that occur in the oceanic crust or in ophiolites are usually called plagiogranites .
The granitoid rocks were emplaced over a 500-million-year time span and can be divided into two suites: The tonalite-trondhjemite-granodiorite (TTG) suite (emplaced approximately 3.5–3.2 Ga), and the granite–monzogranite–syenite granite (GMS) suite (emplaced approximately 3.2–3.1 Ga). The GMS suite are found over large parts of the ...
The crustal evolution of the Limpopo Central Zone can be summarised into three main periods: 3.2–2.9 Ga, 2.6 Ga, and 2.0 Ga. The first two periods are characterised by magmatic activity leading to the formation of Archaean Tonalite-Trondhjemite-Granodiorite (TTG) such as the Sand River Gneisses and the Bulai Granite intrusion.
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According to the QAPF diagram, granodiorite has a greater than 20% quartz by volume, and between 65% and 90% of the feldspar is plagioclase. A greater amount of plagioclase would designate the rock as tonalite.
Rocks of the charnockite series may be named by adding orthopyroxene to the normal igneous nomenclature (e.g. orthopyroxene-granite), but specific names are in widespread use such as norite, mangerite, enderbite, jotunite, farsundite, opdalite and charnockite (in the strict sense); equivalents of gabbro, monzonite, tonalite, monzodiorite ...