10 Questions
What is the characteristic shape of the aggregates in pillow structure?
Ovoid
What is the term for the change in a rock's mineralogy, texture, and/or composition that occurs predominantly in the solid state?
Metamorphism
What is the effect of increasing temperature on sedimentary or volcanic rocks?
Increased grain size of minerals
What type of pressure is responsible for increasing pressure with depth in the Earth's interior?
Litho-static pressure
What is the result of a rock being heated to a temperature at which a particular mineral is no longer stable?
Reaction that consumes the unstable mineral and produces new minerals
What is the term for the fluid phase present in most metamorphic rocks at depth?
Metamorphic fluid
What is the primary cause of devolatilization reactions in metamorphic rocks?
Increase in temperature
What is the characteristic feature of the crust or rind of the ovoid masses in pillow structure?
Thick and vesicular
What is the primary agent responsible for the formation of pillow structure?
Rapid chilling of highly fluid lava
What is the result of the reaction that consumes unstable minerals and produces new minerals in metamorphic rocks?
Formation of a new mineral assemblage
Study Notes
Igneous Rocks
- Igneous rocks can form in two environments: intrusive (plutonic) and extrusive (volcanic)
- Intrusive rocks form below the surface of the earth, where temperatures are higher and cooling is slower, resulting in coarse-grained textures
- Extrusive rocks form on the surface of the earth, where temperatures are lower and cooling is faster, resulting in fine-grained textures
Types of Intrusions
- Dikes: small, shallow intrusions that show a discordant relationship to the surrounding rocks
- Sills: small, shallow intrusions that show a concordant relationship to the surrounding rocks
- Laccoliths: larger intrusions that result in uplift and folding of the surrounding rocks
- Plutons: bulbous bodies of magma that form deeper in the earth
- Batholiths: larger bodies formed by the coalescence of many plutons
Classification of Igneous Rocks
- Based on silica content: basic (45-52%), intermediate (52-66%), and acidic (more than 66%)
- Basic rocks: characterized by calcium-plagioclase, augite, and olivine
- Intermediate rocks: characterized by quartz, orthoclase, plagioclase, biotite, and hornblende
- Acidic rocks: characterized by quartz and feldspars
Classification Based on Depth of Formation
- Plutonic: formed at considerable depth, with slow cooling and coarse-grained textures
- Hypabyssal: formed at intermediate depth, with faster cooling and medium-grained textures
- Volcanic: formed at the surface, with rapid cooling and fine-grained textures
Common Structures of Igneous Rocks
- Pillow structure: formed by rapid chilling of highly fluid lava, characterized by ovoid masses with a thick vesicular crust and a coarser-grained interior
Metamorphism
- Refers to changes in a rock's mineralogy, texture, and/or composition that occur in the solid state
- Caused by metamorphic agents: temperature, pressure, fluid, and state of stress
Metamorphic Agents
- Temperature: promotes recrystallization, increases grain size, and can lead to devolatilization reactions
- Pressure: increases with depth, leading to litho-static pressure and confining pressure
- Fluid: plays a crucial role in metamorphic processes, often present as an intergranular fluid phase
Learn about the two environments of igneous rock formation: intrusive/plutonic and extrusive/volcanic. Discover how temperature and cooling rates affect the type of rocks formed.
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