The Trondhjemit is an igneous rock from the group of plutonic rocks. The name was introduced in 1916 by Victor Moritz Goldschmidt for an occurrence near the city of Trondheim and refers to a bright variety of tonalites.
The main constituents are quartz and oligoclase from the mixed batch of plagioclase. The content of dark particles is generally low; Biotite and hornblende and augite something are the most common. Characteristic is the content of euhedral titanite crystals, whose share can be up to 1% of the total rock. As more accessory ingredients apatite, allanite, magnetite and zircon can be included.
Formation and occurrence
The rock occurs worldwide, especially in the archaic cratons, mostly in metamorphic -independent form. Trondhjemite form together with tonalite and granodiorite in the melting of basaltic crust in subduction zones, forming the so-called TTG ( tonalite - granodiorite - Trondhjemit ) complexes, which often make up the oldest parts of the cratons.
Types of Trondhjemiten
- Tolga Tolga in Norway