Intrusion

Definition

Intrusion refers to the process where molten rock, or magma, moves into pre-existing rock formations, solidifying as it cools and creating igneous rock. This geological event can significantly alter the surrounding rocks, leading to the formation of various types of igneous rocks and impacting the rock cycle by introducing new materials and structures into the existing layers.

5 Must Know Facts For Your Next Test

1. Intrusions can vary in size from small dikes to massive batholiths, affecting local geology on different scales.
2. The process of intrusion can lead to metamorphism of surrounding rocks due to the heat from the molten magma.
3. Not all intrusions result in visible geological features; some may remain hidden beneath layers of other rocks.
4. The study of intrusions helps geologists understand the history of volcanic activity and tectonic movements in a region.
5. Common types of intrusive rocks include granite and diorite, which are characterized by their coarse-grained textures due to slow cooling.

Review Questions

• How does the process of intrusion influence the composition and structure of surrounding rocks?
  • Intrusion affects surrounding rocks by introducing heat and new materials as molten magma moves into existing rock formations. The intense heat can cause metamorphism in the neighboring rocks, altering their mineral composition and physical structure. Additionally, when the magma solidifies, it creates new igneous rocks, which contributes to the overall complexity and diversity of geological formations in that area.
• What are some common types of intrusive rocks formed through the process of intrusion, and how do their textures differ from extrusive rocks?
  • Common types of intrusive rocks include granite and diorite, both known for their coarse-grained textures resulting from slow cooling underground. In contrast, extrusive rocks like basalt or pumice cool quickly on the Earth's surface, resulting in finer grains or even glassy textures. The differences in texture between intrusive and extrusive rocks illustrate how cooling rates affect mineral crystal growth.
• Evaluate the role of intrusions in shaping the geological history of a region and how they contribute to our understanding of Earth's processes.
  • Intrusions play a critical role in shaping a region's geological history by revealing information about past volcanic activity and tectonic events. By studying intrusions, geologists can assess how magma has moved through the crust, understand the conditions under which specific rocks formed, and reconstruct past geological environments. This understanding helps scientists piece together Earth’s evolutionary story, including plate tectonics, volcanic activity, and sedimentation processes over millions of years.

Related terms

Igneous Rock:

A type of rock formed through the cooling and solidification of magma or lava.

Magma: Molten rock located beneath the Earth's surface that can lead to volcanic eruptions or form intrusive igneous rocks when it cools underground.

Pluton: A large body of intrusive igneous rock that has cooled and solidified beneath the Earth's surface.