Week 1

Introduction. Read pages 2-37 in Chapter 1: Nature of Structural Geology.

• readings

• terms

• questions

• classnotes

You are expected to read all the sections listed below. Information from the sections in italics will be discussed in class. You are expected to read the other sections and you may be called on in class to answer questions based on that material.

• Deformation of the Earth's Crust p.2-4
• Architecture and Structures p.4-8
• Plate Tectonics and Structural Geology p.8-9
• The Fundamental Structures p.9-17
• Concept of Detailed Structural Analysis p.17-18
• Descriptive Analysis p.18-25
  The Scale of Things
  Structural Elements
• Kinematic Analysis p.25-29
  Penetrative Deformation
  Slip, Flow, and Distortion
• Dynamic Analysis p.29-32
  General Approach
  Physical Models
  Mathematical Models
• Two Examples of Detailed Structural Analysis p.32-35
  Detailed Structural Analysis of a Pizza
  Detailed Structural Analysis of the San Manuel Fault
• The Time Factor p.25-37

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You should become familiar with the following terms during this weeks lectures and readings:

You should be able to answer the questions below following this week:

1. What are the products of descriptive analysis?
2. What are the differences between descriptive, kinematic and dynamic analysis?
3. How would the descriptive and kinematic analyses of the bottom photograph in Figure 1.39 differ?
4. Can you list the periods and eras of the geologic time scale in order?

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Class notes for Week 1

Structural geology is concerned with deformation of the Earth's crust

What is deformation?

• events that result in changes in rock orientation and character
• physical and chemical processes that occur during change
• specific structural elements

Where is deformation occurring today?

• plate boundaries
• active orogenic belts
• (impact structures)

Where has deformation occurred in the past?

• identify ancient orogens
• relative ages of rocks vs. deformation

Why do we want to understand deformation?

• natural hazards
• economic resources
• basic science

The Fundamental Structures (p.9-17)

• contacts - boundaries between rock units
• primary structures - develop during formation of rock. 

In sedimentary rocks, may provide information on stratigraphic sequence:

- relative positions of older and younger rocks (facing)

- transport direction during deposition

examples: bedding, cross-beds, ripple marks, graded beds, sole marks, mud cracks

In igneous rocks, may be related to composition and/or viscosity of magma, or the environment in which rocks cooled

examples: flow structure (lava), (submarine) pillow lava, gas vesicles, columnar joints, schlieren

Secondary structures - develop as a result of deformation

joints

shear fractures

slickenlines

tensional fractures

faults

folds

cleavage

foliation

lineation

shear zones

Can you make a case that all contacts are secondary structures?

Detailed Structural Analysis

Note that secondary structures are defined by lines or planes for which an orientation can be measured. In analyzing structures we try to determine:

• their location, geometry, and orientation with reference to the earth's surface and a North-South-East-West coordinate system: descriptive analysis:
• the stages in the structure's evolution, involving movements that changed its location or orientation and changes in shape and size: kinematic analysis:
• the forces and stresses responsible for creating the structure: dynamic analysis.

Descriptive Analysis (p.18-25)

• requires that we can recognize and describe rock types (physical geology)
• describe their position today on and below the earth's surface (geologic mapping; surface and subsurface, geophysical techniques)
• describe their geometry and orientation (maps, cross sections, strike and dip, plunge and azimuth readings, stereographic projections)
• learn terms to describe structural elements: physical and geometric elements

Scale of observation important:

• penetrative vs. non-penetrative deformation
• minor structures as indicative of major structures

"... observations must match the scale of the problem we are trying to address" Jack Oliver quote

Kinematic Analysis (p.25-29)

Requires that we recognize potential movements and reorientation of rocks and/or the internal reconfiguration of the rock unit:

- translation

- rotation

- distortion

- dilation

Strain analysis = changes in shape and size (distortion and dilation)

But, keep in mind it must be defined by scale. Displacement on thrust faults in an orogen can change the shape and size of the orogenic belt but will include translations and rotations.

Dynamic Analysis (p.29-32)

Orientation and magnitude of stress responsible for deformation.

- Orientation: determined from measurement of structural elements

- Magnitude: difficult to define for ancient deformation; measurable in models and active deformation (sometimes)

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