CEEES/SC 10111-20111

Planet Earth

  Structural Geology Laboratory

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Deformation of rocks presents itself on the surface in the form of different structures. It is critical that we understand how these extend into the subsurface.

A clear understanding of subsurface structures is vital for an understanding of groundwater resources, pollution migration, oil reserves, ore deposits, and the stability of road cuts, bridge footings, and building foundations.

Deformation is caused by stress – a force acting on a body  that tends to change its size or shape.

= force per unit area, so the magnitude of stress depends not only on the magnitude of the force, but also on the area to which it is applied.

Compressive Stress (compression) causes shortening.
Tensional Stress (tension) causes stretching.
Shear Stress cause one side of a body to slide past the other (transform plate boundaries).
Strain = physical deformation that occurs in response to stress.
Elastic Strain = temporary.
Plastic Strain = permanent.
Rupture = breaking of the rock beyond strain limit.

Deformation = rock breaks while undergoing elastic strain.
Ductile Deformation
= rock breaks while undergoing plastic strain.
Pressure, temperature and rate of deformation determines brittle versus ductile deformation.
Brittle deformation occurs commonly at the surface of the earth (lower temperature) – ductile deformation occurs at depth (higher temperatures).  Folds form at depth.

Stress/Strain conditions of common geologic structures.

Recognizing and Describing Deformed Rocks

Describing Surface Orientation

Geologic Maps

The "Rule of Vs"

Geologic Cross Sections

Block Diagrams