Tectonic Structures

Tectonics is the study of crustal deformation and structural behavior.
Plate Tectonics is the deformation and structural behavior of crustal plates.

Stress

Stress is any force which acts to deform rocks.
Compression - a stress that acts to press or squeeze rocks together.
Tension - a stress that acts to stretch a rock, or pull a rock apart.
Shear - a stress which acts tangential to a plane through a body, causing two contiguous parts to slide past each other.

Structural Behavior

As a general rule:
1) Rocks tend to have a relatively high compressive strength
2) Rocks tend to have a relatively low tensile and shear strength

Strain

Strain is the change in shape or volume of a body as a result of stress; deformation.

Ductile Deformation

During ductile deformation rocks bend or flow.

Folds

Anticlines

Folds which arch up
• Anticline Example #1
• Anticline Example #2
• Anticline Block Diagram
Click here to view an animated Anticline development.

Synclines

Folds which sink down
• Syncline Example #1
• Syncline Example #2
• Syncline Example #3
• Syncline Block Diagram
Click here to view an animated Syncline development.

Monoclines

Folds in which rock layers on both sides of the fold are horizontal but at different levels.
• Monocline Example #1
• Monocline Example #2
• Monocline Example #3
• Monocline Example #4
• Monocline Example #5
• Monocline Block Diagram
Click here to view an animated Monocline development.

Domes

Folds which are equivalant to anticlines, but are comprised of layers which are shaped like an inverted bowl.
• Dome Example #1
• Dome Example #2

Basins

Folds which are equivalant to synclines, but are comprised of layers which are shaped like a bowl.
• Basin Example #1

Folded Terrains

Landforms found in areas of anticlinal and synclinal structures
Ridge and Valley terrain
Anticlinal mountains
Anticlinal valleys
Synclinal mountains
Synclinal valleys
Water gaps - breaks in the ridges due to water erosion
Wind gaps - breaks in the ridges but no water is flowing through the gap

Dome Landforms

Central core - uplifted or folded area in central portion of the dome
Hogback ridges - folded, resistant strata around perimeter of dome
Annular drainage pattern

Brittle Deformation

During brittle deformation rocks break or fracture.
Two main styles of fracture: Joints and Faults.

Joints

Joints are fracture surfaces along which there has been no displacement.
Joints can form from compressional, tensional and shear stress, and can range in size from microscopic to kilometers in length.
Joint sets and jointing has a major influence on landform development.
Erosion is able to occur at a faster rate along joints.
• Joint Example #1
• Joint Example #2

Faults

Faults are fractures along which there has been displacement of the material on either side of the fault.
Faults are classified based on:
1) the sense of movement (the direction in which the blocks on either side of the fault move) - this is controlled by the type of stress that is applied.
2) the orientation of the fault surface (the angle of the plane of fracture)

Fault Terminology

Fault Plane - the plane along which the rock or crustal material has fractured.
Hanging Wall Block - the rock material which lies above the fault plane.
Footwall Block - the rock material which lies below the fault plane.

Strike-Slip Faults

Fault plane is generally vertical.
Stress:
1) Left-Lateral Strike-Slip - displacement is such that the material on the other side of the fault appears to be displaced to the left.
• Left-Lateral Strike-Slip Fault Block Diagram
2) Right-Lateral Strike-Slip - displacement is such that the material on the other side of the fault appears to be displaced to the right.
• Right-Lateral Strike-Slip Fault Example
• Right-Lateral Strike-Slip Fault Block Diagram

Normal Faults

Fault plane is oriented between 30 and 90 degrees (measured from horizontal)
Stress:
The hanging wall moving down relative to the footwall.
• Normal Fault Block Diagram
• Normal Fault Example 1
• Normal Fault Example 2
• Normal Fault Example 3
• Normal Fault Example 4
• Normal Fault Example 5
• Normal Fault Example 6
• Normal Fault Example 7
• Normal Fault Example 8

Detachment Faults

Fault plane is at less than 30 degrees
Stress:
Hanging wall moves down relative to the footwall
• Detachment Fault Block Diagram
• Detachment Fault Example 1

Reverse Faults

Fault plane is oriented between 30 and 90 degrees (measured from horizontal)
Stress:
The hanging wall moving up relative to the footwall.
• Reverse Fault Block Diagram
• Reverse Fault Example 1
• Reverse Fault Example 2
• Reverse Fault Example 3
• Reverse Fault Example 4

Thrust Faults

Fault plane is at less than 30 degrees
Stress:
The hanging wall moving up relative to the footwall.
• Thrust Fault Block Diagram
• Thrust Fault Example 1
• Thrust Fault Example 2 - Thrust Fault Example 2 Diagram
• Thrust Fault Example 3

Horsts and Grabens

Horsts are up thrown blocks bounded on either side by non-parallel normal faults.
Grabens are downthrown blocks bounded on either side by non-parallel normal faults.
• Horst and Graben Block Diagram

Click here to view an animated Horst-Graben development.

Half-Graben

Half-grabens develop when parallel faults on either side of a block develop, but the block becomes tilted instead of dropping down as in a graben.
• Half-Graben Block Diagram

Click here to view an animated Half-Graben development.

Faulted Terrain

Fault scarps
Erosion is able to occur at a faster rate along joints and faults.
Why?
Many stream valleys follow fault zones

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