Crustal Deformation

Economic Consequences of Geologic Structures

• Tracing Coal Seams, Aquifers, etc.

• Ore Deposits are often localized along faults and folds

• Petroleum Traps

Anticlines and

Synclines

Monoclines and

Homoclines

Axial Plane

How Fast Can Folds Form?

Which Way was Up?

Sedimentary Structures are governed by:

• Gravity

• Exposure to the Surface

They all have a “right way up”

FoliationFoliation is a

sheetlike structure that forms when rocks are deformed.

Foliationa. Flattening

b. Grain Rotation

c. Solution

d. New Minerals

e. Partial Melting

f. Shearing

Foliation

In every case, the foliation is:

• In the direction of least resistance

• at right angles to the direction of greatest compression.

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

Folds and Foliation

The Importance of Minor Folds

How Geologists Use These Clues

• Here's an outcrop that might be seen in the field.

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.

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.

What if we did it the other

way?

Isostasy

The Airy Model

The Pratt Model

Both Ideas are Correct at Times

How Isostasy Works

Isostatic Rebound in

Canada

Isostatic Rebound in Scandinavia

Domes and Basins

Domes and Basins

Domes and Basins