18 Questions
What is the primary driver of regional metamorphism?
Intense pressures from deep burial along continental-continental convergent zones
What is the primary driver of dynamic metamorphism?
High differential stress along fault zones
Which of the following is NOT a common location for contact metamorphism to occur?
Mid-ocean ridges
What is the term for the original rock from which a metamorphic rock is formed?
Protolith
What is the term for the process of minerals within a rock changing shape and structure due to the high pressures and temperatures of metamorphism?
Recrystallization
What is the term for the process of metamorphism that occurs when pressure and temperature are relieved?
Retrograde metamorphism
What is the term used to describe a group of characteristic minerals in a metamorphic rock?
Facies
How does the geothermal gradient of a rock depend on its formation environment?
Subduction zones have high pressure but low temperature, while volcanic regions have high temperature but low pressure.
What is the dehydration reaction of pyrophyllite (Al₂Si₄O₁₀(OH)₂) during metamorphism?
Al₂Si₄O₁₀(OH)₂ → Al₂SiO₅ + 3SiO₂ + H₂O
Which metamorphic environment is most closely associated with the pressure-temperature-time (P-T-t) path shown in the blue region of the phase diagram?
Pluton aureole
What is the purpose of identifying the minerals present in a metamorphic rock?
To identify the formation environment of the rock
What is the relationship between the stability fields of kyanite, andalusite, and sillimanite, as shown in the phase diagram?
Kyanite, andalusite, and sillimanite are polymorphs of Al₂SiO₅ and their stability fields are mutually exclusive.
What is the term used to describe metamorphic rocks that have undergone significant partial melting?
Migmatites
Which of the following features is NOT associated with foliated metamorphic rocks?
Presence of sedimentary structures like fossils
What is the term used to describe the pattern formed by alternating layers of minerals aligned perpendicular to the direction of stress in metamorphic rocks?
Foliation
In the progression of metamorphism for a typical shale protolith, what is the correct order of metamorphic facies?
Shale → slate → phyllite → schist → gneiss
Which of the following statements about metamorphic rocks is NOT true?
Rocks like quartzite and marble exhibit foliation due to the presence of micaceous minerals.
What is the primary reason for the recrystallization of minerals in metamorphic rocks?
To become more stable in their new environment
Study Notes
Formation of Metamorphic Rocks
- Metamorphic rocks form through regional, dynamic, and contact metamorphism
- Regional metamorphism occurs due to intense pressures from deep burial, typically along continental-continental convergent orogenic zones
- Dynamic metamorphism occurs due to high differential stress, typically along fault zones
- Contact metamorphism occurs due to high temperatures, typically next to a body of magma, along subduction zones, hotspots, and next to plutons
Characteristics of Metamorphic Rocks
- Metamorphic rocks can form from any other rock type
- The original rock is called the protolith
- Normal metamorphism is called prograde metamorphism, while reversal of the process is called retrograde metamorphism
- High pressures and temperatures cause minerals to change shape and structure through recrystallization
- Minerals can be identified to determine the conditions under which the rock formed
Features of Metamorphic Rocks
- Facies are groups of characteristic minerals that form under specific conditions
- Rocks follow a predictable geothermal gradient with increasing depth based on their formation gradient
- Foliation forms when minerals align perpendicular to the direction of stress, creating a layered structure
- Foliation can disappear due to recrystallization of micas
- Non-foliated rocks lack micaceous minerals and typical foliation patterns
- Compression of rocks removes pores and sedimentary structures like fossils
Metamorphic Facies
- Temperature and pressure increase during metamorphism, leading to a progression of metamorphic rocks
- Example progression: shale → slate → phyllite → schist → gneiss
- Certain conditions predictably create the same sets of characteristic minerals
Learn how to identify characteristic minerals in metamorphic rocks to determine the conditions under which they formed. Explore the geothermal gradient and understand how pressure and temperature vary in different geological settings. Get insights into the Metamorphic Facies Series.
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