Friday, May 28, 2010

A pluton, or plutonic rock, is an intrusive igneous rock body that crystallized from magma slowly cooling below the surface of the Earth. Plutonic rock is igneous rock formed beneath the surface of the earth by consolidation of magma. Yosemite National Park's Half Dome, in California, is a pluton that became exposed after it formed beneath the Earth.

Plutons include batholiths, dikes, sills, laccoliths, lopoliths, and other igneous bodies. In practice, pluton usually refers to a distinctive mass of igneous rock, typically kilometers in dimension, without a tabular shape like those of dikes and sills. Batholiths commonly are aggregations of plutons. The most common rock types in plutons are granite, granodiorite, tonalite, monzonite, and quartz diorite. The term granitoid is used for a general, light colored, coarse-grained igneous rock in which a proper, or more specific name, is not known. Use of granitoid should be restricted to the field wherever possible.

The term originated from Pluto, the ancient Roman god of the underworld. The use of the name and concept goes back to the beginnings of the science of geology in the late 1700s and the then hotly debated theories of Plutonism (or Vulcanism), and Neptunism regarding the origin of basalt.