Metamorphism

Definition

Metamorphism is the process through which existing rocks are altered in composition, texture, or internal structure due to changes in temperature, pressure, or the presence of chemically active fluids. This transformation occurs primarily in regions where tectonic forces lead to significant geological stress, particularly at convergent boundaries where one tectonic plate is forced under another, creating environments that promote metamorphic reactions.

5 Must Know Facts For Your Next Test

1. Metamorphism can occur over a wide range of temperatures and pressures, often exceeding 200°C and 1,000 bars.
2. At convergent boundaries, metamorphic rocks are typically formed under high pressure conditions as one tectonic plate is subducted beneath another.
3. Regional metamorphism is prevalent at continental-continental convergent boundaries, where large areas of rock are subjected to high pressures and temperatures over extensive time periods.
4. Metamorphic rocks can contain minerals that are stable only under specific conditions of pressure and temperature, such as garnet and kyanite.
5. The study of metamorphic rocks provides insight into the tectonic processes at play during the formation of mountain ranges and other geological features.

Review Questions

• How does metamorphism differ between the types of convergent boundaries, and what implications does this have for the resulting rock types?
  • Metamorphism varies significantly among the types of convergent boundaries. At oceanic-continental boundaries, subduction leads to high-pressure and low-temperature conditions, resulting in rocks like schist. In contrast, continental-continental collisions create regional metamorphism due to intense pressure and temperature over vast areas, producing gneiss. Understanding these differences helps geologists determine the tectonic environment in which these rocks formed.
• Analyze the role of fluids in the metamorphic process and how they influence mineral transformation at convergent boundaries.
  • Fluids play a crucial role in metamorphism by facilitating the movement of ions and promoting chemical reactions within rocks. At convergent boundaries, the presence of water released from subducted oceanic plates enhances metamorphic reactions, leading to the formation of new minerals. This fluid activity can also weaken rocks, allowing them to deform more easily under pressure, significantly influencing the texture and composition of the resulting metamorphic rocks.
• Evaluate the impact of tectonic activity on the formation of metamorphic rocks and how this can inform our understanding of Earth's geological history.
  • Tectonic activity directly influences the formation of metamorphic rocks by creating conditions of high pressure and temperature essential for metamorphism. By examining these rocks, scientists can reconstruct past tectonic events, such as mountain-building episodes during continental collisions. The presence and types of metamorphic rocks can indicate historical subduction zones or collisional settings, providing valuable insights into the dynamic processes that have shaped Earth's geological history.

Related terms

foliation: A characteristic texture of metamorphic rocks where mineral grains are aligned in parallel layers or bands due to directed pressure.

parent rock: The original rock from which a metamorphic rock forms, also known as the protolith.

thermal metamorphism: A type of metamorphism that occurs primarily due to increased temperature, often associated with igneous intrusions.