Midterm: Rock Deformation Flashcards
Tensional
Stretch and pull rock formations apart (common at divergent margins)
Compressive
Squeeze and shorten rock formations (common at convergent margins)
Shearing
Shear two parts of a rock formation in opposite directions (common at transform margins)
Brittle deformation
Rock fails as a rigid solid
Ductile deformation
Rock deforms plastically
What are the main features of brittle defamation
- Joints
- Faults
What are joints?
Fracture along which there’s been no appreciable movement. These can be due to tectonics or even local expansion/contraction of the rocks.
What are fractures?
Fracture along which there has been displacement, which can be described the the slip direction and offset. There are three types of faults:
What are the three kinds of faults?
- Dip-slip
- Strike-slip
- Oblique
What is dip-slip
Relative motion up-and-down. Two subtypes are normal faults (including horst-and-graben structures) due to tensional forces and reverse faults (including low-angle thrust faults) due to compressional forces.
What is strike-slip?
Relative motion side-to-side. Two subtypes are left-lateral and right-lateral, which describe the sense of shear due to tensional forces.
What is oblique?
Show both up-and-down and side-to-side motions
Landforms of the ductile regime
Predominate ductile landform is folding, which occur when planar beds are bent into sinuous structures. As ductile features, these must occur at depth and brought to the surface by mountain building and erosion.
What are common fold structures?
- Monoclines
- Anticlines and Synclines
- Structural Domes and Basins
Monoclines
Step-like folds in rock beds with a zone of deeper dip within otherwise horizontal (or gently dipping) beds
Anticlines and Synclines
Up-and-down folds that usually occur together and are caused by compressional stress. Axis of these folds can be parallel to the horizontal surface or at an angle, called plunging (see as block diagrams).
Structural Domes and Basins
Doubly-plunging anticlines and synclines, respectivelycircular or slightly elongated features where the Earth’s surface is arched upward, causing older rocks to be exposed at the center, while basins are the opposite, with the surface depressed, exposing younger rocks at the center.
