Crustal Deformation

Take-Away Points 1.Structures in the earth have practical implications 2.Basic terms for earth structures 3.Small structures provide clues to much larger structures 4.The earth’s crust is floating on the denser mantle beneath 5.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?

Siesta Valley

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 is a sheetlike structure that forms when rocks are deformed. 3. Small structures provide clues to much larger structures

Foliation a.Flattening b.Grain Rotation c.Solution d.New Minerals e.Partial Melting f.Shearing 3. Small structures provide clues to much larger structures

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 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 Points 1.Structures in the earth have practical implications 2.Basic terms for earth structures 3.Small structures provide clues to much larger structures 4.The earth’s crust is floating on the denser mantle beneath 5.Gentle uplifts and downwarps affect the interiors of continents