1. a geological theory that rocks, especially igneous rocks, formed from the cooling and solidification of molten material (magma) beneath or within the Earth's crust
Usage: historical geology term; contrasts with neptunism

Examples

• Plutonism was a major theory in 18th-century geology that explained the origin of granite and basalt.
• James Hutton championed plutonism as an alternative to the neptunist view of rock formation.
• The debate between plutonism and neptunism shaped early geological science.
• Modern geology has confirmed many predictions of plutonism about magmatic processes.
• Plutonism helped geologists understand how intrusive igneous rocks form deep underground.