What does the term “igneous intrusion” refer to?

The term "igneous intrusion" specifically refers to magma that has cooled and solidified within pre-existing rock layers. When magma from beneath the Earth's surface reaches a cooler environment, such as surrounding rock strata, it begins to crystallize and form solid rock. This solidified mass is known as an intrusive igneous rock or pluton, and it often exhibits large crystal formations due to the slow cooling process that occurs underground. Common examples of intrusive igneous rocks include granite and diorite, which differ from extrusive rocks that have been erupted onto the surface and cooled much more rapidly.

The understanding of igneous intrusion is crucial in geology as it provides insights into the processes that shape the Earth's crust, the formation of various rock types, and the history of volcanic and tectonic activity in a region.