Igneous Petrology
Igneous petrology studies the origin, classification, and evolution of rocks crystallized from molten silicate magma.
Definition
The branch of petrology concerned with the formation, composition, classification, and crystallization of igneous rocks and the magmas from which they derive.
Scope
This area covers the generation of magma by partial melting, its ascent, differentiation, and crystallization; the classification of igneous rocks by mineralogy, chemistry, and texture; the contrast between volcanic and plutonic processes; and the experimental phase equilibria that constrain melting and crystallization paths. It links the chemistry of magmas to the tectonic settings in which they form.
Sub-topics
Core questions
- How and where does partial melting generate magma in the Earth?
- How are igneous rocks classified by composition and texture?
- What processes cause magmas to diversify as they cool?
- How do experimental phase diagrams predict crystallization sequences?
Key theories
- Bowen's reaction series
- As basaltic magma cools, minerals crystallize in a predictable order, a discontinuous series of ferromagnesian minerals alongside a continuous plagioclase series, driving the magma toward more silicic compositions through fractional crystallization.
- Partial melting and magma genesis
- Magmas form by incomplete melting of source rocks in the mantle and crust, with the degree of melting and source composition controlling magma chemistry and the variety of igneous rocks produced in different tectonic settings.
Clinical relevance
Igneous petrology underpins the interpretation of volcanic hazards, the formation of magmatic ore deposits, the reconstruction of plate-tectonic settings from rock chemistry, and the understanding of how continental crust is created and recycled.
History
Igneous petrology became quantitative with N. L. Bowen's experimental melting studies in the early twentieth century, which established fractional crystallization as the central mechanism of magma evolution. The IUGS classification led by Le Maitre standardized igneous nomenclature in the late twentieth century.
Key figures
- Norman L. Bowen
- Bruno Sander
- Roger W. Le Maitre
Related topics
Seminal works
- bowen1928
- winter2013
- lemaitre2002
Frequently asked questions
- What is the difference between magma and lava?
- Magma is molten rock below the surface; once it erupts at the surface it is called lava.
- Why are there so many kinds of igneous rocks?
- Variations in source composition, degree of melting, depth of crystallization, and processes such as fractional crystallization and magma mixing produce a wide spectrum of compositions and textures.