Metamorphism and Metamorphic Rocks Learning objectives: 1. Understand how metamorphism is related to plate tectonics. 2. Understand how the properties of metamorphic rocks relate to their histories.
Where we are Today: Deformed Rocks Next: Metamorphic Rocks One week: Midterm - covers through Deformed/Metamorphic Rocks
Today s Plan Sedimentary Rocks-wrap up Metamorphism - Definition - Importance - Agents of metamorphism - Types - Locations (e.g., Plate Tectonics) - Metamorphic Rocks: Minerals, Textures - Protoliths (parent rock)
Mud Cracks
Fossil Mud Cracks http://www.geology.wisc.edu/~struct/images/triparg.jpg
Sedimentary Environments
Sedimentary Environments Some Continental Environments: - Glacial - Alluvial fan - River channel (and flood plain) - Lake - Delta
Sedimentary Environments Some Continental Environments: - Glacial - Alluvial fan - River channel (and flood plain) - Lake - Delta Some Marine Environments: - Beach (and dunes) - Shallow marine shelf - Reef - Deep marine
Alluvial Fan
Changing sea level
Changing sea level Shallow, near-shore: beach (sandstone)
Changing sea level Shallow, near-shore: beach (sandstone) Deeper, off-shore: near-shelf (shale)
Changing sea level Shallow, near-shore: beach (sandstone) Deeper, off-shore: near-shelf (shale) Deep, far off-short: far-shelf (limestone)
Changing sea level Shallow, near-shore: beach (sandstone) Deeper, off-shore: near-shelf (shale) Deep, far off-short: far-shelf (limestone) [show transgression movie]
Test your understanding You are at a river and notice the sediment contains both: - well-sorted, round fine sand grains, and - some larger, more angular gravel. How could this happen?
Recap Weathering Erosion Transport Deposition Lithification Sedimentary Rock Sediment size, shape, sorting indicates transport Sedimentary structures indicate environment, up direction
What is it? Metamorphism
Metamorphism What is it? - One rock changing into another
Metamorphism What is it? - One rock changing into another - Due to heat, pressure, and stress
Why should I care about metamorphism?
Metamorphism of limestones when India collided with Eurasia may have released enough CO 2 to alter the global climate from ice age to tropical.
Fluids from hydrothermal systems created most of the ore deposits that we use in our technological society.
Most gems are formed by metamorphism!
Most gems are formed by metamorphism!
Most gems are formed by metamorphism!
Michelangelo would have had to use wood!
Michelangelo would have had to use wood!
Michelangelo would have had to use wood!
Michelangelo would have had to use wood!
Causes of metamorphism
Causes of metamorphism Temperature (T) - Changes minerals
Causes of metamorphism Temperature (T) - Changes minerals Pressure (P) - Changes minerals
Causes of metamorphism Temperature (T) - Changes minerals Pressure (P) - Changes minerals Stress (different from pressure) - Changes texture (shape & size of mineral grains)
Causes of metamorphism Temperature (T) - Changes minerals Pressure (P) - Changes minerals Stress (different from pressure) - Changes texture (shape & size of mineral grains) Fluid interaction - Changes minerals
Why do new minerals form?
Why do new minerals form? Original minerals formed at a certain T&P - Stable at that T&P, and nearby T&P
Why do new minerals form? Original minerals formed at a certain T&P - Stable at that T&P, and nearby T&P Changing T&P can make them unstable
Example: Graphite - Diamond
Bottom of continental crust Example: Graphite - Diamond
Types of metamorphism Contact Regional (others in your text) What are the main differences? - Extent of effects - Temperature, Pressure, Stress
Types of Metamorphism Consider the geothermal gradient (the deeper you go, the hotter it gets)
Regional Metamorphism Types
Contact Metamorphism
Contact Metamorphism
Contact Met.: Maine D.R.Jessey, CSU Pomona
Contact Met.: Utah D.R.Jessey, CSU Pomona
Types of metamorphism Contact Regional - Associated with mountain-building - Stress new textures foliation
Regional Metamorphism D.R.Jessey, CSU Pomona
Regional Metamorphism Associated with mountain-building D.R.Jessey, CSU Pomona
Regional Metamorphism Associated with mountain-building Occurs over large region (note scale) D.R.Jessey, CSU Pomona
Regional Metamorphism Associated with mountain-building Occurs over large region (note scale) Most of the Cascades! D.R.Jessey, CSU Pomona
Regional Metamorphism Associated with mountain-building Occurs over large region (note scale) Most of the Cascades! [Show North Cascades KMZ] D.R.Jessey, CSU Pomona
Where does this happen? Continental margins!
Metamorphic Textures Some are unfoliated: marble, quartzite - no platy minerals! - Original (sedimentary) texture is obliterated forms interlocking grains - What does that remind you of?
marble
Metamorphic Textures Why does the texture change, when platy minerals are present?
Metamorphic Textures Why does the texture change, when platy minerals are present? Compression deforms sedimentary texture
Metamorphic Textures Why does the texture change, when platy minerals are present? Compression deforms sedimentary texture New minerals grow in easy orientation - Only applies when minerals are long or flat! - [show foliation process movie]
Metamorphic Textures Compression and heat new crystals grow, oriented; form: slate - phyllite schist gneiss
Metamorphic Textures Compression and heat new crystals grow, oriented; form: slate - phyllite schist gneiss
Metamorphic Textures Compression and heat new crystals grow, oriented; form: slate - phyllite schist gneiss
slaty cleavage: platy minerals grow perpendicular to stress direction
gneiss: quartzrich and mica-rich layers form
Parent rocks (protolith)
Parent rocks (protolith) Limestone marble
Parent rocks (protolith) Limestone marble Quartz sandstone quartzite
Parent rocks (protolith) Limestone marble Quartz sandstone quartzite Shale slate schist gneiss - each stage represents higher temperature - and new minerals grow: 1. chlorite 2. biotite 3. garnet 4. staurolite 5. kyanite 6. sillimanite
Cooperative Quiz
Cooperative Quiz The metamorphism occurring adjacent to a pluton is A. precipitation B. contact C. regional D. dynamic
A-slate; B-marble; C-schist; D-gneiss
Protolith? A-limestone; B-shale; C-sandstone; D-granite
A-slate; B-marble; C-schist; D-gneiss
Protolith? A-limestone; B-shale; C-sandstone; D-granite
A-slate; B-marble; C-schist; D-gneiss
A-slate; B-marble; C-schist; D-gneiss
Protolith? A-limestone; B-shale; C-sandstone; D-granite
Recap Geothermal gradient describes how rock heats up as you dig down Contact metamorphism occurs around igneous plutons Regional metamorphism occurs with mountain building, requires high temperatures Regional metamorphism often creates a fabric in the rocks due to aligned platy minerals Different starting rocks (protoliths) produce different metamorphic rocks.