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Questions and Answers
What defines the process of metamorphism in rocks?
What defines the process of metamorphism in rocks?
Which of the following types of metamorphism occurs in the presence of extreme heat and pressure over large areas?
Which of the following types of metamorphism occurs in the presence of extreme heat and pressure over large areas?
What characterizes prograde metamorphism?
What characterizes prograde metamorphism?
Which of the following is an example of a metamorphic rock formed from limestone?
Which of the following is an example of a metamorphic rock formed from limestone?
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Which statement about metamorphic textures is true?
Which statement about metamorphic textures is true?
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What characterizes metamorphic rocks derived from limestone?
What characterizes metamorphic rocks derived from limestone?
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How does temperature affect the metamorphic process?
How does temperature affect the metamorphic process?
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What is the relationship between pressure and depth in the Earth during metamorphism?
What is the relationship between pressure and depth in the Earth during metamorphism?
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What occurs in metamorphism when the parent material contains multiple minerals?
What occurs in metamorphism when the parent material contains multiple minerals?
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Which of the following minerals is commonly associated with metamorphic processes?
Which of the following minerals is commonly associated with metamorphic processes?
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Study Notes
Metamorphic Rocks
- Metamorphic rocks are rocks that have changed due to heat, pressure, or chemical reactions in fluids.
- Any type of rock (igneous, sedimentary, or metamorphic) can be transformed into a metamorphic rock.
- The changes occur without melting the rock.
- Increased pressure, temperature, and chemical reactions in fluids cause new mineral and texture formations.
- Metamorphic rocks are classified based on texture and composition into foliated and non-foliated types.
Metamorphism
- Metamorphism is the transformation of existing rock to a rock with a different mineral composition or texture.
- Metamorphism takes place at temperatures exceeding 150 to 200 °C (300 to 400 °F), often with elevated pressure or chemically active fluids.
- The rock remains mostly solid during transformation.
Types of Metamorphism
- Various forms of metamorphism exist, including regional, contact, hydrothermal, shock, and dynamic metamorphism.
- These differ in their characteristic temperatures, pressures, and the rate at which they occur, along with the involvement of reactive fluids.
- Prograde metamorphism occurs when pressure and temperature increase.
- Retrograde metamorphism occurs when pressure and temperature decrease.
Textural Changes
- As a rock undergoes metamorphism, some mineral grains grow larger while others shrink.
- The shapes of the grains can also change.
- Limestone is transformed into marble during metamorphism.
- Marble has large interlocking grains with no fossils.
Minerals in Metamorphic Rocks
- Key minerals found in metamorphic rocks include andalusite, garnet, sillimanite, kyanite, and staurolite.
- These are examples of minerals characteristic of metamorphic rocks.
Controlling Factors in Metamorphic Rocks
- Parent rock composition is a key factor.
- No new material is added during metamorphism.
- The resulting metamorphic rock has a composition similar to the original rock.
- If the parent material contains only one mineral, the metamorphic rock will have only that mineral.
- Minerals will often be recrystallized leading to alterations in the texture.
Texture Changes Examples
- Limestone has fragments of shells, while marble has interconnecting grains and no fossils.
Parent Material with Many Minerals
- If the parent material contains multiple minerals, the old minerals will combine to create new metamorphic minerals, like garnet or others.
Temperature during Metamorphism
- Heat originates from the Earth's interior.
- Minerals are stable within a temperature range.
- Temperatures exceeding this stable range can cause melting.
Pressure during Metamorphism
- Pressure in the Earth is equal in all directions throughout the depth of the Earth.
- Pressure increases by approximately 1 kilobar (kbar) per 3.3 kilometers of depth
- Increased pressure causes grains to pack together, decreasing the overall volume and producing more compact mineral grains.
Differential Stress during Metamorphism
- Tectonic forces create forces that are unequal in all directions—differential stress
- Compressive stress (pushing together) causes flattening that is perpendicular to stress.
- Shearing, (one surface sliding past another) causes flattening that is parallel to the stress direction
Fluids during Metamorphism
- Hot water (or water vapor) is the most significant fluid component involved in altering existing minerals.
- Heat causes unstable minerals to release water.
- Water reacts with surrounding rocks and transports dissolved minerals, altering the chemical composition over extensive periods of time.
Time during Metamorphism
- Metamorphism can take millions of years.
- Longer times allow minerals to grow larger, creating coarser-grained rocks.
Classification of Metamorphic Rocks
- Metamorphic rocks are categorized based on their texture.
- Foliated rocks display layered textures (e.g., slate, shale, gneiss).
- Non-foliated rocks have non-layered textures (e.g., marble, quartzite, hornfels).
Foliated Metamorphic Rocks Examples
- Examples include slate, shale, phyllite, schist, gneiss, and migmatite.
- Foliated rocks are formed through differential stress.
Non-Foliated Metamorphic Rocks Examples
- Examples include marble, quartzite, and hornfels.
Types of Contact Metamorphism
- Contact metamorphism occurs near magma bodies (intrusion) resulting in a zone of contact known as an aureole.
- Fine-grained rocks (e.g., hornfels) or coarse-grained rocks (e.g., marble) are typical outcomes.
Types of Regional Metamorphism
- Regional metamorphism occurs over extensive areas, especially in mountain ranges.
- Folded and deformed rocks yield foliated metamorphic types. Pressure and temperature conditions in these regions promote the creation of new and altered minerals.
Partial Melting in Metamorphism
- Migmatites are a product of partial melting during metamorphism.
- These high-grade metamorphic rocks exhibit both intrusive and metamorphic textures.
Shock Metamorphism
- Shock metamorphism is associated with impact events and high pressures.
- Rocks around impact craters exhibit "shocked" features.
Hydrothermal Metamorphism
- Hydrothermal metamorphism occurs when cold seawater interacts with hot basalt from intrusions.
- This creates alterations to the chemical and mineral composition of the basalt in altered zones.
Plate Tectonics and Metamorphism
- Regional metamorphism is associated with convergent plate boundaries.
- This process involves increasing pressure and temperature with depth
- These variations result in different metamorphic conditions that lead to different degrees or grades of metamorphism.
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Description
Explore the fascinating world of metamorphic rocks, including their formation, types, and the metamorphic processes that transform existing rocks into new forms. Learn about the influences of heat, pressure, and chemical reactions on rock composition and texture, as well as the distinctions between foliated and non-foliated rocks.
