Crustal Deformation
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Transcript of Crustal Deformation
Crustal Deformation
Take-Away Points1. Structures in the earth have practical
implications2. Basic terms for earth structures3. Small structures provide clues to much
larger structures4. The earth’s crust is floating on the denser
mantle beneath5. Gentle uplifts and downwarps affect the
interiors of continents
Economic Consequences of Geologic Structures
• Tracing Coal Seams, Aquifers, etc. • Ore Deposits are often localized along
faults and folds • Petroleum Traps
1. Structures in the earth have practical implications
The Big Picture
1. Structures in the earth have practical implications
Anticlines and
Synclines
2. Basic terms for earth structures
Monoclines and
Homoclines
2. Basic terms for earth structures
Axial Plane
2. Basic terms for earth structures
How Fast Can Folds Form?
Which Way was Up?
Sedimentary Structures are governed by:• Gravity• Exposure to the SurfaceThey all have a “right way up”
3. Small structures provide clues to much larger structures
FoliationFoliation is a
sheetlike structure that forms when rocks are deformed.
3. Small structures provide clues to much larger structures
Foliationa. Flatteningb. Grain
Rotationc. Solutiond. New
Mineralse. Partial
Meltingf. Shearing
3. Small structures provide clues to much larger structures
FoliationIn every case, the
foliation is:• In the direction of
least resistance• at right angles to
the direction of greatest compression.
3. Small structures provide clues to much larger structures
Folds and Foliation• On a small scale (microscopic to
centimeters), foliation forms by a variety of mechanisms, but always at right angles to the direction of greatest compression
• On a large scale (centimeters to kilometers), rocks fold. The axial plane of the fold is also at right angles to the direction of greatest compression
3. Small structures provide clues to much larger structures
Folds and Foliation
3. Small structures provide clues to much larger structures
The Importance of Minor Folds
3. Small structures provide clues to much larger structures
How Geologists Use These Clues • Here's an outcrop that might be seen in
the field.
3. Small structures provide clues to much larger structures
How Geologists Use These Clues • Picture the axial
plane of the fold as parallel to the foliation.
• The other side of the fold is roughly a mirror image of the side we can see.
3. Small structures provide clues to much larger structures
How Geologists Use These Clues • We can mentally
fill out the sketch to get an idea of the shape of the fold.
• Note that we still have no idea how big the fold is, only what kind it is.
3. Small structures provide clues to much larger structures
What if we did it the other
way?
3. Small structures provide clues to much larger structures
Isostasy
4. The earth’s crust is floating on the denser mantle beneath
The Airy Model
4. The earth’s crust is floating on the denser mantle beneath
The Pratt Model
4. The earth’s crust is floating on the denser mantle beneath
Both Ideas are Correct at Times
4. The earth’s crust is floating on the denser mantle beneath
How Isostasy Works
4. The earth’s crust is floating on the denser mantle beneath
Isostatic Rebound in
Canada
4. The earth’s crust is floating on the denser mantle beneath
Isostatic Rebound in Scandinavia
4. The earth’s crust is floating on the denser mantle beneath
Domes and Basins
5. Gentle uplifts and downwarps affect the interiors of continents
Domes and Basins
5. Gentle uplifts and downwarps affect the interiors of continents
Domes and Basins
5. Gentle uplifts and downwarps affect the interiors of continents
Take-Away Points1. Structures in the earth have practical
implications2. Basic terms for earth structures3. Small structures provide clues to much
larger structures4. The earth’s crust is floating on the denser
mantle beneath5. Gentle uplifts and downwarps affect the
interiors of continents