metamorphism and metamorphic rocks a. metamorphic rocks: form at conditions between igneous and...
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Metamorphism and Metamorphic RocksA. Metamorphic rocks: Form at conditions
between igneous and sedimentary rocks
Definition
Protolith: parent rock, what the rock was before it was metamorphosed
Common Metamorphic Rocks
A. Foliated: mineral grains are aligned produced by directed pressure
1. Slate: first product of metamorphism of shale.
Temperature: 200-350C
Relatively low temperature and pressure
2. Phyllite: next product of shale
Temperature: 350-500C
Shiny rock with wavy layers
Low-intermediate temperature and pressure
Common Metamorphic Rocks
A. Foliated—mineral grains are aligned (produced by directed pressure)
3. Schist: next product of shale
Temperature: 500-650CShiny rock with individual mica
flakes now visible to the unaided eye
Intermediate-high temp and pressure
4. Gneiss: next product of shale, felsic igneous rocks
Temperature > 650CMinerals separate into light-
and dark-colored layersHigh temp and pressure
Metamorphism and Metamorphic Rocks
A. Foliated—mineral grains are aligned (produced by directed pressure)
5. Blueshcist: oceanic basalt formed in subduction zones
High pressure and low temperature
Metamorphism and Metamorphic Rocks
B. Nonfoliated Rocks: minerals aren’t aligned
Produced with high confining
Pressure (not directed pressure)
Contact metamorphism
Parent rock is monomineralic quartz or calcite (limestone); not elongate minerals
1. Marble: CaCO3
lack elongate mineralspure limestone
Metamorphism and Metamorphic Rocks
B. Nonfoliated Rocks: minerals aren’t aligned
Produced at high confining pressure (not directed pressure)
Contact metamorphism
Parent rock is monomineralic
Quartz or calcite (limestone); not elongate minerals
2. Quartzite SiO2 (quartz)
Lack elongate mineralsPure quartz sandstone (most
sandstones, coastal environments)
Metamorphism and Metamorphic Rocks
B. Nonfoliated Rocks: minerals aren’t aligned
Produced with high confining pressure (not directed pressure)
Contact metamorphism
Parent rock is monomineralic quartz or calcite (limestone); not elongate minerals
3. Hornfels: contact metamorphism
High temperature, low pressure
Metamorphism and Metamorphic Rocks
B. Nonfoliated Rocks: minerals aren’t aligned
3. Hornfels: contact metamorphism
High temperature, low pressure
Metamorphism and Metamorphic Rocks
B. Nonfoliated Rocks: minerals aren’t aligned
3. Hornfels: contact metamorphism
High temperature, low pressure
Metamorphism and Metamorphic Rocks
B. Nonfoliated Rocks: minerals aren’t aligned
Produced with high confining pressure (not directed pressure)
Contact metamorphism
Parent rock is monomineralic quartz or calcite (limestone); not elongate minerals
Metamorphism and Metamorphic Rocks
Metamorphism and Metamorphic Rocks
V. Metamorphism and Plate Tectonics
Plate Movements create much of the heat, pressure and hot fluids for metamorphism
Directed pressure @ convergent plate boundaries: Regional metamorphism most common
Tectonic history:Blueshists: Subduction zones
Hydrothermal metamorphosed basalts (not foliated: ocean basins
Metamorphism and Plate Tectonics
V. Metamorphism and Plate Tectonics
Plate Movements create much of the heat, pressure and hot fluids for metamorphism
Directed pressure - convergent plate boundaries, regional metamorphism most common
Tectonic history:Blueshists: subduction zones
Hydothermal metamorphosed basalts (not foliated): ocean basins
Metamorphism and Plate Tectonics
V. Metamorphism and Plate Tectonics
Plate Movements create much of the heat, pressure and hot fluids for metamorphism
Foliation direction of ancient tectonic compression
Metamorphic grade (slate, phyllite, schist, gneiss)
Burial depth & amount of heat
Metamorphism and Plate Tectonics
I. Types of Geological Dating
A. Relative Dating: compares two or more groups of rocks to determine which is older and which is younger.
Non-quantitative
B. Numerical Dating: Absolute time, how long ago in years that a rock was formed or an event occurred.
Quantitative measure.
Geochronology—the study of “Earth Time”