Chapter 7 - Metamorphism and Metamorphic Rocks Flashcards
What are the two types of metamorphism?
Contact and regional metamorphism.
What is foliation?
The alignment of minerals in metamorphic rocks under directed pressure, forming a layered texture.
What are index minerals?
Minerals that form at specific temperatures and pressures, indicating the metamorphic grade.
What is the difference between low-grade and high-grade metamorphism?
Low-grade occurs at lower temperatures and pressures (e.g., slate), while high-grade occurs at higher temperatures and pressures (e.g., gneiss).
What is metasomatism?
The process by which a rock’s chemical composition is altered by fluids during metamorphism.
How do heat and pressure individually and together contribute to the metamorphism of rocks?
Heat drives recrystallization of minerals, while pressure deforms rocks. Together, they cause minerals to align (foliation) and can lead to significant compositional changes in rocks.
Compare and contrast contact metamorphism with regional metamorphism in terms of the conditions and types of rocks formed.
Contact metamorphism occurs near igneous intrusions, producing non-foliated rocks (e.g., hornfels), while regional metamorphism is associated with tectonic forces, producing foliated rocks (e.g., schist, gneiss).
What are the three types of directed pressure in metamorphism?
Compressional, tensional, and shear pressures.
How do chemically active fluids contribute to metamorphism?
At high temperatures and pressures, minerals dehydrate, releasing ions that move to other sites, promoting recrystallization. This can change the rock’s composition, a process known as metasomatism.
What is metamorphic grade?
The intensity or degree of metamorphism that rocks have experienced, indicated by the appearance of specific index minerals and textures.
At what temperature does low-grade metamorphism typically occur, and which mineral is common in this stage?
Around 200°C, and chlorite is a common mineral at this stage.
What three factors influence the development of foliation in metamorphic rocks?
1) Rotation of platy minerals,
2) Changing the shape of grains into elongate forms,
3) Recrystallization to form new grains in the preferred orientation.
How does heat act as a metamorphic agent?
Heat drives the mobility and reactivity of chemically active fluids, promotes recrystallization, and different minerals become stable at varying temperatures.
How does confining pressure affect metamorphism?
Confining pressure applies forces equally in all directions, making rocks denser and harder, without altering their shape.
How does differential stress influence the texture of metamorphic rocks?
Differential stress reorients mineral grains, causing them to align perpendicular to the direction of stress, leading to the formation of foliated textures.
