Mountain Building and Crustal Deformation

Economic Consequences of Geologic Structures

• Tracing Coal Seams, Aquifers, etc. • Ore Deposits are often localized along

faults and folds • Petroleum Traps

Isostasy

Thickness and Density

Isostatic Rebound in

Canada

Mountain Building (Orogeny)

Orogeny is the variety of processes that occur during mountain-building, including:

• Distinctive Patterns of Deposition • Deformation • Metamorphism • Intrusions • Volcanic Activity • Oceanic Trenches • Seismic Activity

A Subduction Zone

Metamorphism and Orogeny

Why Mountains are High

How Fast Can Folds Form?

Hutton’s Unconformity, Scotland

Large Fold, Turkey

Eroded Fold, Pennsylvania

Fold in Glacier, Antarctica

Anticlines and

Synclines

Folds, Pennsylvania

Which Way was Up?

Sedimentary Structures are governed by:• Gravity• Exposure to the SurfaceThey all have a “right way up”

Foliation

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

Foliation

In every case, the foliation is:

• In the direction of least resistance

• at right angles to the direction of greatest compression.

Axial Plane

Folds and Foliation

Folds and Foliation

• On a small scale (microscopic to centimeters), foliation forms

• On a large scale (centimeters to kilometers), rocks fold.

• Both foliation and the axial plane of the fold are at right angles to the direction of greatest compression.

Fold And Foliation

Growth of Minerals

The Importance of Minor Folds

Minor Folds and Foliation Are Clues to Much Larger

Structures

How Geologists Use These Clues

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

How Geologists Use These Clues

• We can mentally fill out the rest of the fold.

• Note that we still have no idea how big the fold is, only what kind it is.

Complex Folds, ScotlandComplex Folds, Scotland

Complex Folds, Scotland

Faults, Appalachians

Thrust Faults in Snow

Domes and Basins