|Ig. Home | Simp.Class. | Advanc.Class. | Alpha.List | Bowen's Reac.Srs. | ID Keys | Extrus/Intrus | Tect. | Self Tests|
Return to Classification; pdf version
Typical MineralsQUARTZ > 20%
PLAGIOCLASE is greater than
Orthoclase (may be absent all together)
Mafics - < 10%
DescriptionA felsic igneous rock from the bottom of Bowen's Reaction Series. Typically light colored (few mafic minerals) with sodium plagioclase the most obvious mineral, but quartz >20% is essential. It is not unusual for orthoclase to be present, but it is always less than plagioclase
This rock can be confused with a monzonite which appears superficially similar. The amount of quartz is the key: <20% and the rock is "quartz monzonite". Watch the mafics, however; if they exceed 5-10% then the rock is heading toward a diorite.
| Return to Classification; pdf version
Return to Previous Mineral
Tectonic AssociationPlagio-granite, is the result of fractional melting above a rapid subduction zone. It is commonly produced in volcanic arcs, and in cordilleran mountain building (subduction along the edge of a continent, such as with the Andes Mountains). Plagio-granite is a common component of the cores (cratons) of continents, especially the most ancient portions which were constructed from numerous small volcanic arcs with rapid subductions in the earth's earliest, hottest phases. Another common name for Plagio-granite is tonolite.
Tectonic Cross Section - pdf version
|Last Update: 9/29/00||