Intrusion

Definition

An intrusion is a geological process where molten rock, or magma, forces its way into pre-existing rock layers, solidifying as it cools. This process plays a vital role in the formation of igneous rocks and can alter the surrounding rock structures. Intrusions contribute significantly to the rock cycle by introducing new materials and influencing the geological landscape.

5 Must Know Facts For Your Next Test

1. Intrusions can vary in size from small dikes to massive batholiths, affecting large areas of the crust.
2. The cooling rate of magma during intrusion is slower compared to lava that erupts at the surface, leading to the formation of coarse-grained textures in the resulting igneous rock.
3. Intrusions can cause contact metamorphism in the surrounding rock, altering their mineral composition and structure due to heat and pressure.
4. Many valuable mineral deposits are associated with igneous intrusions, including gold, silver, and copper, which often concentrate in veins near the intrusive bodies.
5. The study of intrusions helps geologists understand the history of volcanic activity and tectonic processes in a region.

Review Questions

• How does an intrusion contribute to the rock cycle and affect surrounding rock layers?
  • An intrusion contributes to the rock cycle by introducing new igneous material into existing rock formations through the movement of magma. As magma rises and intrudes into cooler pre-existing rocks, it cools slowly underground, forming larger crystals and altering the texture and composition of surrounding materials through processes like contact metamorphism. This not only creates new igneous rocks but also influences the geological history and structure of an area.
• Discuss the differences between intrusive and extrusive rocks in terms of formation and characteristics.
  • Intrusive rocks form from magma that cools slowly beneath the Earth's surface, resulting in coarse-grained textures with larger crystals. In contrast, extrusive rocks are formed from lava that erupts onto the surface and cools quickly, leading to fine-grained textures with smaller crystals. The environment of formation also differs; intrusive rocks are typically found within the crust as plutons or batholiths, while extrusive rocks are present on the Earth's surface as lava flows or volcanic ash deposits.
• Evaluate the role of intrusions in mineral resource formation and their economic significance.
  • Intrusions play a critical role in forming economically significant mineral resources. As molten magma intrudes into surrounding rock layers, it can create conditions conducive to concentrating valuable minerals such as gold, silver, and copper. These minerals often form in veins associated with intrusions due to hydrothermal processes driven by heat from the cooling magma. Understanding these processes allows geologists to locate potential mining sites, making intrusions economically important for resource extraction.

Related terms

Magma: Magma is a molten rock material found beneath the Earth's surface, which can cool and solidify to form igneous rocks.

Igneous Rock: Igneous rock is formed from the solidification of magma or lava, which can occur either beneath the surface as intrusive rocks or on the surface as extrusive rocks.

Pluton: A pluton is a large body of intrusive igneous rock that has cooled and solidified beneath the Earth's surface, often visible today due to erosion of the overlying materials.