Earth 103-Structural Geology

structural geology

study of the geologic structures formed by deformation within the earth

Deformation: three ways

Translation, Rotation, Strain

second rank tensor

Stress-one vector is transformed into another

• Magnitude and direction changes based on the location on the object being acted on

• Brittle deformation:

• Fracturing and faulting

• Loss of cohesion, abrupt displacements

Ductile Deformation:

• No loss of cohesion

• Implies higher temperatures 

• Results in the development of tectonic fabrics (foliations and lineations)

Rock strength: definition and 6 things it depends on:

Definition: maximum differential stress that a rock can support before it fails

6 things:

• Pressure

• Temp

• Composition and grain size

• Differential pressure/Stress

• Water content

• Deformation rate 

Geometric description:

• Statement of what we can objectively see, akin to a still photograph 

• No interpretation of why and how; purely facts of what is observed

Kinematic description:

• interpretation about how a structure developed through time

• Describe how things form but not the cause

mechanical model

•  a simplified version of reality about why a structure formed the way it did 

Three principal types of plate margins and where they occur

• – Convergent margins (subduction and collision zones)

• – Divergent margins (mid-ocean ridges, continental rifts)

• – Transform margins (strike-slip boundaries)

Three types of continental margins:

• Atlantic-type

  • Passive

• Japan Sea-type

  • Extensional 

• Andean type

  • Convergent