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
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