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Questions and Answers
What is the primary factor that distinguishes metamorphic rocks from igneous rocks?
Which term describes the original rock from which a metamorphic rock forms?
At what temperature range does heat-driven metamorphism begin and continue to occur?
What type of pressure is specifically mentioned in relation to the affecting metamorphic rocks?
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How does temperature in the Earth's crust typically change with increasing depth?
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What is the primary effect of confining pressure on rocks?
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How does directed stress differ from confining pressure?
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What is the role of chemically reactive fluids in hydrothermal metamorphism?
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What characteristic defines foliated metamorphic rocks?
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Where does significant hydrothermal alteration occur?
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What is the primary factor that affects the final outcome of the metamorphic process?
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Which metamorphic facies is typically associated with low-grade metamorphism?
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In the Barrovian sequence, which mineral indicates the highest grade of metamorphism?
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What term describes the groups of minerals found in metamorphic rocks based on stable conditions of pressure and temperature?
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Which type of metamorphism occurs due to the intrusion of hot magma?
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During regional metamorphism, how does the degree of metamorphism typically change from the base to the top of a mountain range?
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What happens to clay minerals in shales during burial metamorphism?
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What characteristic distinguishes gneiss from other metamorphic rocks?
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What process typically occurs in the formation of non-foliated metamorphic rocks?
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Which of the following best describes the metamorphic grade?
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How does marble differ from quartzite in terms of testing?
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What defines phyllite in comparison to slate?
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Which index mineral signifies a high-grade metamorphic rock?
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In which scenario would you expect the presence of a hornfels?
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What visual characteristic is associated with schist?
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Study Notes
Metamorphic Rocks Overview
- Metamorphic rocks form from the transformation of existing rock types due to changes in temperature, pressure, and fluids, without melting.
- They provide geologists with insights into past tectonic processes and Earth's history.
Metamorphic Processes
- Metamorphic Source Rocks: Parent rocks (protoliths) undergo metamorphism, resulting in altered composition and texture without melting.
- Conditions of Metamorphism: Involves elevated temperature (200°C to 1,100°C), confining pressure, and chemically reactive fluids.
Temperature Effects
- Temperature influences mineral chemistry; increased energy causes atoms to vibrate and reconfigure while remaining solid.
- Metamorphic temperatures sit between sedimentary rock conditions and magma temperature.
Pressure Types
- Confining Pressure: Equal pressure from all sides due to overlying rocks; ranges from 3,000 to 50,000 bars deep within the crust and facilitates chemical reactions.
- Directed Stress: Unequal force operations leading to mechanical changes in mineral structure without altering chemical composition, such as crystals rotating or fracturing.
Role of Fluids
- Chemically reactive fluids, primarily water and CO2, significantly affect protoliths through hydrothermal processes, creating new minerals.
- Hydrothermal alteration often results in valuable mineral deposits near igneous intrusions.
Metamorphic Textures
- Foliated Textures: Minerals align in planes due to directed stress; examples include slate, phyllite, schist, and gneiss, characterized by distinct foliation styles.
- Non-foliated Textures: No preferred orientation, typically composed of single minerals like quartzite (from sandstone) or marble (from limestone).
Metamorphic Grade
- Refers to the intensity of metamorphism, classified from low to high grade, exemplified by the sequence: slate → phyllite → schist → gneiss.
- Index minerals like chlorite, muscovite, and garnet help identify the metamorphic changes and conditions.
Metamorphic Environments
- Burial Metamorphism: Occurs in sedimentary basins at depths over 2000 meters, influencing clay minerals to transform into illite.
- Contact Metamorphism: High temperature and low pressure due to magma intrusion lead to mineral changes like sandstone transitioning to quartzite and limestone to marble.
- Regional Metamorphism: Large-scale pressure and temperature changes in mountain ranges due to converging tectonic plates reflect the Barrovian Sequence of metamorphic rocks.
Notable Examples
- Granite intrusions, like the Little Cottonwood Stock in northern Utah, showcase hydrothermal deposits including argentite and chalcopyrite due to fluid interactions.
- The Barrovian Sequence illustrates the increasing metamorphic grade with minerals shifting from chlorite to sillimanite in mountain cores.### Subduction Zone Metamorphism
- Occurs when oceanic crust is subducted beneath continental crust, creating a high-pressure, low-temperature environment.
- Temperature increases slowly; pressure rises rapidly, leading to blueschist facies formation.
- Glaucophane, a blue index mineral, indicates blueschist facies.
- The California Coast Range contains blueschist, greenstone (metamorphosed basalt), and red chert from subduction zone metamorphism.
- Chlorite contributes to the green color of greenstone.
Fault Metamorphism
- Metamorphic rocks arising from faulting include rock flour, cataclastites, and mylonites.
- Rock flour consists of ground-up rock particles, akin to flour in texture.
- Cataclastites are chaotic mixtures of crushed rocks formed at lower depths.
- Mylonites form at greater depths through dynamic recrystallization; characterized by reduced grain size due to directed shear forces.
- Augen structures form when larger crystals (feldspar, quartz, garnet) deform into asymmetrical shapes within mylonitic materials.
Shock Metamorphism
- Results from impacts (meteor or bolide) creating high-pressure conditions rapidly.
- Produces features like planar deformation, tektites, shatter cones, and quartz polymorphs (coesite and stishovite).
- Shock laminae are glassy materials with distinct orientations found within silicate minerals.
- Shatter cones exhibit cone-shaped structures resulting from dynamic fractures; sizes can range from microscopic to several meters.
- Fine-grained rocks with shatter cones display unique horsetail patterns.
- Tektites are glassy materials ejected during impacts; lack water and phenocrysts, differing chemically from volcanic glass.
- Pseudotachylytes refer to geologic glasses formed by faulting or shear heating, resembling volcanic rock but created through different processes.
General Summary of Metamorphism
- Metamorphism transforms existing rocks (protoliths) into rocks with new minerals and textures through increased temperature and pressure with additional fluid interactions.
- Metamorphic rocks are primarily identified by their textures: foliated (layered) and non-foliated (lacking internal fabric).
- The grade of metamorphism indicates the intensity of the conditions a rock has undergone.
- Metamorphic facies represent a collection of minerals that reveal insights into a rock's metamorphic history.
- Tectonic environments driving metamorphism include continental collisions, subduction, faulting, and extraterrestrial impacts.
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Description
Explore the fascinating world of metamorphic rocks, which are one of the three rock categories in the rock cycle. This quiz covers how temperature, pressure, and fluids change rock materials, along with the processes involved in metamorphism. Discover the relationship between metamorphic rocks and plate tectonic motion.
