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”