Granulite facies

Definition

Granulite facies is a high-grade metamorphic condition characterized by elevated temperatures and pressures, leading to the formation of granulite, a rock type that often contains granular textures and a limited amount of water. This metamorphic facies typically forms at depths greater than 15 kilometers and is associated with tectonic processes such as continental collision and crustal thickening, making it essential for understanding the evolution of the Earth's crust.

5 Must Know Facts For Your Next Test

1. Granulite facies typically indicates metamorphic conditions with temperatures ranging from 600 to 800 degrees Celsius and pressures between 6 to 10 kilobars.
2. Common mineral assemblages found in granulite facies include plagioclase, quartz, garnet, and pyroxene, which reflect the high-grade conditions during formation.
3. The presence of dry conditions in granulite facies is significant, as it suggests that water was not involved in the metamorphic reactions, differentiating it from other facies.
4. Granulite facies are often associated with ancient continental crust, providing clues to the geological history and tectonic processes that shaped the Earth's surface.
5. The transition from amphibolite facies to granulite facies represents a major shift in metamorphic conditions, often occurring during continental collision events.

Review Questions

• How do temperature and pressure conditions differentiate granulite facies from other metamorphic facies?
  • Granulite facies is distinguished by its high temperature and pressure conditions, generally ranging from 600 to 800 degrees Celsius and between 6 to 10 kilobars. This is significantly higher than those found in lower-grade metamorphic facies like amphibolite or greenschist. The extreme conditions lead to unique mineral assemblages and textures that reflect intense metamorphism, highlighting the geological environments where these rocks form.
• Discuss the significance of mineral assemblages within granulite facies and how they reflect the conditions under which these rocks formed.
  • The mineral assemblages found in granulite facies, including plagioclase, quartz, garnet, and pyroxene, are indicative of the specific high-grade metamorphic conditions experienced during their formation. These minerals form under dry conditions without significant water involvement, showcasing how temperature and pressure influenced their stability. Understanding these assemblages helps geologists reconstruct the tectonic history of regions that have undergone high-grade metamorphism.
• Evaluate the role of granulite facies in interpreting the tectonic history of ancient continental crust.
  • Granulite facies play a crucial role in interpreting the tectonic history of ancient continental crust as they provide evidence for past high-grade metamorphic processes associated with continental collisions and crustal thickening. By analyzing the distribution and mineralogy of granulite-facies rocks, geologists can infer patterns of plate tectonics and ancient subduction zones. This understanding is vital for reconstructing the geological evolution of continents over time, revealing insights into how they have interacted through various tectonic events.

Related terms

metamorphism: The process by which rocks are altered in mineralogy, texture, and chemical composition due to changes in temperature and pressure.

gneiss:

A high-grade metamorphic rock often found in the granulite facies, characterized by its foliated structure and banded appearance.

decompression melting: The process where rising mantle rocks undergo melting due to a decrease in pressure as they ascend, often occurring in tectonically active regions.