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Crustal Deformation . Take-Away Points. Structures in the earth have practical implications Basic terms for earth structures Small structures provide clues to much larger structures The earth’s crust is floating on the denser mantle beneath

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take away points
Take-Away Points
  • Structures in the earth have practical implications
  • Basic terms for earth structures
  • Small structures provide clues to much larger structures
  • The earth’s crust is floating on the denser mantle beneath
  • Gentle uplifts and downwarps affect the interiors of continents
economic consequences of geologic structures
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
The Big Picture

1. Structures in the earth have practical implications

anticlines and synclines
Anticlines and Synclines

2. Basic terms for earth structures

monoclines and homoclines
Monoclines and Homoclines

2. Basic terms for earth structures

axial plane
Axial Plane

2. Basic terms for earth structures

which way was up
Which Way was Up?

Sedimentary Structures are governed by:

  • Gravity
  • Exposure to the Surface

They all have a “right way up”

3. Small structures provide clues to much larger structures

foliation
Foliation

Foliation is a sheetlike structure that forms when rocks are deformed.

3. Small structures provide clues to much larger structures

foliation1
Foliation
  • Flattening
  • Grain Rotation
  • Solution
  • New Minerals
  • Partial Melting
  • Shearing

3. Small structures provide clues to much larger structures

foliation2
Foliation

In 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
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 foliation1
Folds and Foliation

3. Small structures provide clues to much larger structures

the importance of minor folds
The Importance of Minor Folds

3. Small structures provide clues to much larger structures

how geologists use these clues
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 clues1
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 clues2
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
What if we did it the other way?

3. Small structures provide clues to much larger structures

isostasy
Isostasy

4. The earth’s crust is floating on the denser mantle beneath

the airy model
The Airy Model

4. The earth’s crust is floating on the denser mantle beneath

the pratt model
The Pratt Model

4. The earth’s crust is floating on the denser mantle beneath

both ideas are correct at times
Both Ideas are Correct at Times

4. The earth’s crust is floating on the denser mantle beneath

how isostasy works
How Isostasy Works

4. The earth’s crust is floating on the denser mantle beneath

isostatic rebound in canada
Isostatic Rebound in Canada

4. The earth’s crust is floating on the denser mantle beneath

isostatic rebound in scandinavia
Isostatic Rebound in Scandinavia

4. The earth’s crust is floating on the denser mantle beneath

domes and basins
Domes and Basins

5. Gentle uplifts and downwarps affect the interiors of continents

domes and basins1
Domes and Basins

5. Gentle uplifts and downwarps affect the interiors of continents

domes and basins2
Domes and Basins

5. Gentle uplifts and downwarps affect the interiors of continents

take away points1
Take-Away Points
  • Structures in the earth have practical implications
  • Basic terms for earth structures
  • Small structures provide clues to much larger structures
  • The earth’s crust is floating on the denser mantle beneath
  • Gentle uplifts and downwarps affect the interiors of continents