Monzogranite

Monzogranite

Igneous rock

Monzogranite (Col des Croix, Haute-Saône, France)

Monzogranites are biotite granite rocks that are considered to be the final fractionation product of magma. Monzogranites are characteristically felsic (SiO₂ > 73%, and FeO + MgO + TiO₂ < 2.4), weakly peraluminous (Al₂O₃/ (CaO + Na₂O + K₂O) = 0.98–1.11), and contain ilmenite, sphene, apatite and zircon as accessory minerals. Although the compositional range of the monzogranites is small, it defines a differentiation trend that is essentially controlled by biotite and plagioclase fractionation. (Fagiono, 2002). Monzogranites can be divided into two groups (magnesio-potassic monzogranite and ferro-potassic monzogranite) and are further categorized into rock types based on their macroscopic characteristics, melt characteristics, specific features, available isotopic data, and the locality in which they are found.

MGr type I: Muscovite-biotite-metagranite. Small and equal grained, greyish-brown, yellow altered K-fsp (Saladillo, S. Chepes).

MGr type II: Muscovite-metagranite. Medium grained, porphyric, pink K-fsp, with "schollen", whitish-pink (with "Schollen").

MGr type III: Schollen-metagranite. Medium and equal grained, large and many "schollen", whitish-grey, only biotite (Tuaní, S. Chepes and S. Ulapes south).

MGr type IV: Biotite-metagranite. Medium to large, porphyric or equal grained pink K-fsp, reddish quartz (Chimenea, S. Chepes). MGr type V: Metagranite. Medium and equal grained reddish K-fsp whitish (El Abra, S. Ulapes).

MGr type V aplite: Metagranite, aplite dikes and layers. Pink small and equal grained, whitish K-fdsp, grey quartz, pink-white (S. Ulapes north).

Pilbara Granite–Greenstone Terrane c. 3.315 Ga monzogranites are typically highly fractionated, K rich, Al poor, and have trace element compositions consistent with remelting of an older tonalitic–trondhjemitic–granodioritic (TTG) crust.