Laccolith

Definition

A laccolith is a type of intrusive igneous rock formation that occurs when magma intrudes between layers of sedimentary rock and causes the overlying strata to bulge upward, forming a dome-shaped structure. These features are significant as they illustrate the processes by which magma can manipulate and interact with existing rock layers, contributing to our understanding of intrusive igneous features and plutons.

5 Must Know Facts For Your Next Test

1. Laccoliths typically form when magma is less dense than the surrounding rock, allowing it to rise and spread out between layers.
2. The shape of a laccolith resembles a mushroom, with a flat bottom and a dome-like top, creating unique topographical features on the Earth's surface.
3. Famous examples of laccoliths include the Henry Mountains in Utah, which were formed during the late Mesozoic Era.
4. Laccoliths can sometimes cause metamorphism in the surrounding sedimentary rocks due to the heat from the intruding magma.
5. Studying laccoliths helps geologists understand the dynamics of magma movement and its effects on geological structures.

Review Questions

• How do laccoliths differ from other intrusive igneous formations such as sills and dikes?
  • Laccoliths differ from sills and dikes primarily in their shape and formation process. While laccoliths are dome-shaped and form by causing overlying rock to bulge upwards, sills are horizontal sheets that intrude parallel to existing rock layers, and dikes are vertical structures that cut across layers. This distinction is important because it highlights different mechanisms of magma intrusion and how they affect the geology of an area.
• What role do laccoliths play in understanding the processes of magma intrusion within sedimentary layers?
  • Laccoliths are crucial for understanding magma intrusion processes because they provide direct evidence of how magma can create pressure within sedimentary rock layers. By studying laccolith formations, geologists can learn about the characteristics of the magma that caused the intrusion, including its viscosity and temperature. This knowledge aids in reconstructing past geological events and understanding how similar features may form in different environments.
• Evaluate the impact that laccoliths have on landscape formation and geological studies, particularly regarding tectonic processes.
  • Laccoliths significantly impact landscape formation by creating distinctive topographical features that can influence erosion patterns and hydrology. Their formation often reflects underlying tectonic processes, such as plate movements and volcanic activity. Evaluating these features allows scientists to gather insights into past tectonic settings and volcanic behavior, further enhancing our understanding of geological history and the forces shaping Earth's surface.

Related terms

Pluton: A pluton is a body of intrusive igneous rock that crystallizes from magma cooling below the surface of the Earth.

Sill:

A sill is a tabular sheet of igneous rock that intrudes parallel to the layering of the surrounding rock.

Dike:

A dike is a vertical or steeply inclined sheet of igneous rock that cuts across pre-existing layers of rock.