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Questions and Answers
What is the characteristic feature of pillow structure in basic volcanic rocks?
What is the primary effect of increasing temperature on sedimentary or volcanic rocks?
What is the term for the pressure that increases with depth due to the weight of overlying rocks?
What is the primary outcome when a rock reaches a temperature at which a particular mineral is no longer stable?
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What is the term for the changes in a rock's mineralogy, texture, and/or composition that occur predominantly in the solid state?
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What is the characteristic feature of metamorphic fluids at depth?
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What is the outcome of devolatilization reactions in rocks?
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What is the primary factor that contributes to the formation of pillow structure?
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What is the term for the change of form in petrology?
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What is the characteristic feature of the interiors of pillow structures?
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Study Notes
Igneous Environments
- Two types of environments: intrusive (plutonic) and extrusive (volcanic)
- Intrusive environment: below the Earth's surface, characterized by high temperatures and slow cooling of magma, resulting in intrusive or plutonic igneous rocks
- Extrusive environment: on the surface of the Earth, characterized by lower temperatures and rapid cooling of magma, resulting in extrusive or volcanic igneous rocks
Types of Intrusions
- Tabular bodies: dikes and sills
- Dikes: small (< 20 m wide), shallow intrusions that show a discordant relationship to the rocks they intrude
- Sills: small (< 50 m thick), shallow intrusions that show a concordant relationship with the rocks they intrude
- Laccoliths: large intrusions that result in uplift and folding of the preexisting rocks above the intrusion
- Plutons: bulbous bodies that form deeper in the Earth
- Batholiths: large bodies formed by the coalescence of many plutons
Composition of Igneous Rocks
- Intermediate igneous rocks: 52-66% silica, quartz, orthoclase, plagioclase, biotite, hornblende, and augite
- Andesite: the most common intermediate volcanic rock
- Basic igneous rocks: 45-52% silica, calcium-plagioclase, augite, olivine, and hornblende
- Ultra-basic rocks: < 45% silica, calcium-plagioclase, olivine, and augite
Classification of Igneous Rocks
- Plutonic: formed by slow cooling at considerable depth, coarse-grained texture
- Hypabyssal: formed as small bodies of rock, medium-grained texture
- Volcanic: formed at the planetary surface, fine-grained texture
Structures of Igneous Rocks
- Pillow structure: formed by rapid chilling of highly fluid lava, consists of aggregates of ovoid masses
Metamorphism
- Defined as changes in a rock's mineralogy, texture, and/or composition that occur predominantly in the solid state
- Metamorphic agents: temperature, pressure, fluid, and state of stress
Effects of Metamorphic Agents
- Temperature: promotes recrystallization, increases grain size of minerals, and can lead to reaction and formation of new minerals
- Pressure: increases with depth, causes litho-static pressure, and can lead to changes in mineral composition and texture
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Description
Learn about the two main environments where igneous rocks are formed: intrusive and extrusive. Understand the characteristics of each environment and the types of rocks that form in them.
