EESA06H3 Chapter Notes - Chapter 11: Thrust Fault, Convergent Boundary, Shear Stress

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25 Apr 2012
Chapter 3
Important Terms
- Structural geology: branch of geology concerned with the shapes, arrangement, and
interrelationships of bedrock units and the forces that cause them.
- Stress- a force unit per area
- Strain- the change in size, shape or both in response to stress.
- Compressive stress- something being pushed together or squeezed from opposite directions.
It’s common along convergent plate boundaries and typically results in rocks being deformed in
a shortening strain.
- Tensional stress- caused by forces pulling away from each other. Results in the stretching or
extension of material.
- Shear stress- produced when stresses act parallel to a plane. Results in shear strain parallel to
the direction of the stresses, occurs on active moving faults.
- Elastic- if something recovers from a stress or strain and returns to its original state then it is
elastic. Ex: an elastic band
- Elastic limit- rocks are elastic until they reach their elastic limit, at which point they will deform
permanently. Ex: breaking an elastic band.
- Ductile- a rock that bends under stress and does not return to its original state after the stress is
gone. Ex: pizza dough
- Brittle- rock that will fracture at stresses higher than its elastic limit. Rocks near the earth
surface in low temperature/pressure climates.
- Geologic map- uses standardized symbols and patterns to represent rock types and geologic
structures. Most often produced from a field map for a given area.
- Strike- compass direction of a line formed by the intersection of an inclined plane with a
horizontal plane.
- Angle of dip- no real definition, figure 11.7 shows an example..
- Direction of dip- compass direction in which the angle of dip is measured.
- Geologic cross section- represents a vertical slice through a portion of Earth.
- Folds- bends or wavelike features in layered rock.
- Anticline- upward arching fold
- Hinge line- basically the middle of a fold.
- Syncline- downward arching counterpart of an anticline
- Limb- shared by an anticline and a syncline.
- Axial plane- an imaginary plane that connects all the hinge lines of a fold.
- Plunging folds- folds where the hinge lines are not horizontal.
- Structural dome- when the beds dip away from a central point.
- Structural basin- when the beds are dipping towards the central point.
- Open folds- have limbs that dip gently. Usually, the more open the fold is, the less it has been
- Isoclinal fold- limbs are parallel to one another. Implies more stress/strain has occurred.
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