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38 Cards in this Set
- Front
- Back
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Metamorphism |
Alteration of a rock due to a change in physical/ chemical environment |
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What is the name of a pre-existing "parent rock"? |
Protolith |
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What does metamorphism change? |
Mineralogy and texture (sometimes chemical composition) |
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What is the difference between low grade and high grade changes in metamorphic rocks? |
Low grade changes are slight changes (ex. Shale to slate) while high grade changes are substantial changes (ex. Basalt to eclogite) |
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How does high grade metamorphism occur? |
Strong compressional forces, high temperatures and pressures |
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During high grade metamorphism will the protolith rock melt? |
No, the rock may approach the temperature of melting but rocks will remain solid. |
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What grade of metamorphism will result in deformation or folding? |
High grade metamorphism |
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What are mineral polymorphs? |
Minerals with the same chemical composition but different structure in response to changing T and P conditions |
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What are the agents of metamorphism? |
Heat, pressure and chemically active fluids |
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What are the two main sources of heat for metamorphism? |
1) increasing temperature that occurs as we travel deeper into earth's interior 2) heat being released to the surrounding rocks when a magma body cools |
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What does heat provided to metamorphic rocks? |
It provides energy to drive chemical reactions and recrystallization |
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What is recrystallization? |
Re-arrangement of existing atoms into a new crystalline structure that is more stable in a new environment |
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Will minerals change with heat? |
They may or may not change |
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What is confining pressure? |
Pressure is Equal in all directions |
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What is differential pressure? |
Stress is greater in one direction , directed Pressure |
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What is the role of chemically active fluids in metamorphism? |
1) Hot fluids surround mineral grains and act as a catalyst for ion migration 2) speeds up recrystallization: ion migration within a crystal structure |
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What is foliated texture? |
A texture of metamorphic rocks that gives the rock a layer appearance |
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What happens to foliated metamorphic rocks? |
Minerals rotate or recrystallize with a preferred orientation, grains perpendicular to the direction of differential pressure |
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Is solid state flow associated with foliated or non-foliated rocks? |
Non-foliated |
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What is solid state flow? |
Slippage of crystal lattice positions by breaking existing chemical bonds and forming new ones (atoms shift positions) |
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Why are non-foliated rocks? |
Metamorphic rocks with interlocking crystals |
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What does the texture porphyroblastic look like? |
Some minerals (Garnet) forms a small number of very large crystals |
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What is a characteristic of slaty rock cleavage? |
Rock can easily split/ be cleaved |
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How is schistosity texture formed? |
At higher temperatures and pressures, large muscovite and biotite crystals grow. |
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What is gneissic texture? |
A texture of metamorphic rocks in which dark and light silicate minerals are separated, giving the rock a banded appearance |
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What are the 3 metamorphic environments? |
1) contact or thermal metamorphism 2) hydrothermal metamorphism 3) burial metamorphism 4) subduction zone metamorphism 5) regional metamorphism 6) fault zone metamorphism 7) impact metamorphism |
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What is contact or thermal metamorphism? |
Rock extruded by magma. Change in T by conduction of heat. (High-T; low P) |
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What is hydrothermal metamorphism? |
Hot fluids circulated through cracks in a rock, causing chemical alteration by enhancing recrystallization (low p, low-mid t) |
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What is burial metamorphism? |
Huge amounts of sediment or volcanic material accumulates in a basin- no deformation |
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What is subduction zone metamorphism? |
Rock and sediment carried to great depths ( oceanic plate is metamorphosed) |
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What is regional metamorphism? |
Large-scale metamorphism caused by increasing T & P (directional pressure) |
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What is fault zone metamorphism? |
Deformation within a fault zone at depth will produce a mylonite |
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What is a mylonite? |
Intense ductile flow |
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What is impact metamorphism? |
Hypervelocity impact of asteroid/ comet within the earths surface --> kinetic energy converted to heat and pressure |
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What are migmatites? |
High grade rocks (gneiss) heated sufficiently for melting to begin - low grade minerals melt -high grade minerals stay solid |
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What are examples of transitional rocks? |
Migmatites |
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What does Bowen reaction series show? |
That minerals crystallize at different temperatures |
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What are metamorphic facies? |
A group of associated minerals that are used to establish the pressures and temperature at which rocks undergo metamorphism |
