Metamorphism

Definition

Metamorphism is the process by which existing rocks undergo changes in mineralogy, texture, and chemical composition due to exposure to high temperature, pressure, and chemically active fluids. This transformative process occurs deep within the Earth's crust, allowing rocks to evolve into new types, such as metamorphic rocks, through various mechanisms including foliation and recrystallization.

5 Must Know Facts For Your Next Test

1. Metamorphism can occur under two main conditions: regional metamorphism, which happens over large areas under high pressure and temperature, and contact metamorphism, which occurs near igneous intrusions.
2. The intensity of metamorphism can vary widely, influencing the type of metamorphic rock that forms, from low-grade to high-grade metamorphic rocks.
3. Common examples of metamorphic rocks include schist, gneiss, and marble, each exhibiting distinct characteristics based on their parent rocks and metamorphic conditions.
4. Fluid presence during metamorphism can significantly affect the reactions and changes that occur, often leading to the development of new minerals.
5. Metamorphism plays a crucial role in the rock cycle by transforming sedimentary and igneous rocks into new forms, contributing to the dynamic processes of Earth's geology.

Review Questions

• How does the process of metamorphism contribute to the formation of different types of metamorphic rocks?
  • Metamorphism alters existing rocks through changes in temperature, pressure, and chemical environments. The original rock's composition influences the resulting metamorphic rock; for example, limestone transforms into marble under high pressure and temperature. The intensity and conditions of metamorphism determine whether low-grade or high-grade metamorphic rocks form, showcasing a variety of textures and mineral compositions.
• What are the primary differences between regional and contact metamorphism, and how do they impact rock formation?
  • Regional metamorphism affects large areas under uniform pressure and temperature conditions, typically related to tectonic forces. This process can lead to the development of foliated textures in rocks due to directional pressure. In contrast, contact metamorphism occurs when molten magma heats surrounding rocks over a smaller area, resulting in localized changes. Each type influences the final characteristics of the resulting metamorphic rocks differently.
• Evaluate how the presence of fluids during the metamorphic process influences mineral reactions and rock transformations.
  • The presence of fluids during metamorphism significantly enhances mineral reactions by facilitating chemical processes and transporting ions. This can lead to the growth of new minerals that may not have been present in the parent rock. Fluids also help break down existing minerals, promoting recrystallization and altering the rock’s overall texture and composition. This interplay is crucial in determining the final characteristics of the metamorphic rock.

Related terms

Foliation: A textural feature in metamorphic rocks where mineral grains are aligned in parallel layers or bands due to directional pressure.

Parent Rock: The original rock from which a metamorphic rock is formed, also known as the protolith.

Contact Metamorphism: A type of metamorphism that occurs when rocks are heated by nearby molten magma or lava, resulting in localized changes.