Metamorphism Flashcards
What is metamorphism?
process of “changing form” in which a rock’s mineralogy, texture, and chemical composition are altered under elevated t and p without significant melting.
Why is the parent rock important in metamorphism?
Every metamorphic rock originates from a parent rock which undergoes physical and chemical changes during metamorphism.
What does metamorphic grade refer to?
degree of change a rock undergoes during metamorphism, low grade (low t and p) to high grade (high t and p).
What are the primary controls on metamorphism?
composition of the parent rock. four agents: T, P, (main drivers) Fluids, and Stress.
How do tectonic settings influence metamorphism?
Tectonic settings create specific metamorphic conditions: contact (high T, low P), regional (high T and P), and hydrothermal (hot, ion-rich fluids).
What is foliation and how does it develop?
planar alignment of platy or elongated minerals within a rock, created by directed stress during metamorphism. It leads to textures like slate, schist, and gneiss and is distinct from sedimentary bedding.
What role do index minerals play in metamorphic reactions?
They form at specific P and T conditions, marking metamorphic grade (e.g., kyanite, andalusite, sillimanite).
What are metamorphic facies?
assemblages of minerals that indicate the range of p and t conditions during metamorphism, allowing interpretation of the metamorphic environment and grade.
How do fluids affect metamorphism?
enhance ion migration and recrystallization, accelerating metamorphic reactions. they can lead to metasomatism, where the bulk chemical composition of the rock is altered.
Why is retrograde metamorphism uncommon?
It’s rare because lost volatiles aren’t replenished.
