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 Surface
They 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, Scotland
Complex Folds, Scotland
Faults, Appalachians
Thrust Faults in Snow
Domes and Basins