Monzonite

Monzonite is found in association with gabbro and granodiorite in the Khankandi pluton in the Alborz Mountains of Iran. The monzonite likely formed during the collision that closed the Tethys Ocean, from partial melting of upper mantle that had previously been altered by fluids released from a subducting ocean crust slab. Monzonite can also form in extensional crustal settings or by partial melting of lower crust of alkali basalt composition. Diorite, monzonite, and syenite are found together on the margins of the Paleoproterozoic North China craton. These likely formed during the assembly of Columbia and suggest the North China craton was in the interior of Columbia, between Laurentia and Siberia. The Bingham mine consists of porphyry copper deposits hosted in altered monzonite. Alteration has converted some of the monzonite to compositions resembling quartz monzonite or granite, by altering plagioclase to potassium feldspar and emplacing hydrothermal quartz. Fragments of monzonite have been found on the surface of the Moon. These likely formed as a mixture of immiscible granite liquid with cumulates composed of plagioclase and pyroxene, which supports the theory that lunar granites form through silicate liquid immiscibility. This is a process in which high-silica and low-silica components of a magma separate like oil and vinegar.

Monzonite was originally named after the Monzoni range in Val di Fassa (Trento Province, Italy) where it is abundant. As rock definitions have been systematized and codified, this association has lost any relevance to the rock's definition.