Student Name:                                                                                                                  Grade: _____      

                                    Physical Geology 101 Laboratory                  

       Structural Geology II – Drawing and Analyzing Geologic Block Diagrams

 

I. PRELAB SECTION  –   To be completed before labs starts:

 

A. Introduction & Purpose:  Structural geology is the study of how geologic rock units are initially arranged and later deformed.  Changing spatial relations between geologic units and the stress and strain that occur during deformation events are key aspects in understanding geologic structures.  The purpose of this lab is to both learn and apply the concepts of structural geology to reading and interpreting geologic structures, including tilted beds, folds, and faults.   The terms and concepts of geologic structures, the application of structural geology to mountain building events, and the techniques used to interpret geologic structures will be presented and discussed.   The three types of graphic representations of geologic structures: 1) geologic maps, 2) geologic cross sections, and 3) block diagrams will also be highlighted and discussed.

     The objective of this laboratory is to become successful at applying the principles of structural geology for both, interpreting surface and subsurface structural and geologic relations, stress and strain regimes, and solving structural problems, concerning geographic regions that expose a rock record of igneous, metamorphic, and sedimentary events, folding and faulting, and surface erosion.  

 

B.  Review of the Rules for Interpreting Geologic Structures

There is a set of 12 simple rules for observing and interpreting geologic structures found in Figure 10.11 in your lab manual.  Carefully study and make use of these rules for completing Part II.

The rules are listed below.

 

   1) The strike of a rock formation is parallel to its adjacent contacts.

   2) Tilted layers of rock dip perpendicular to the strike.

   3) Tilted layers of rock dip downward in the direction towards where the youngest rock layers are

            exposed at the surface.

    4) The older rocks are exposed in the center of eroded anticlines and domes.

    5) The younger rocks are exposed in the center of eroded synclines and basins.

    6) Plunging anticlines form "U" shaped outcrop belts that point in the same direction that the fold plunges.

    7) Plunging synclines form "U" shaped outcrop belts that point in the opposite direction that the fold plunges.

    8) The steeper the dip of the layer, the more narrow the width of its outcrop belt.

    9) The strike of a fault is parallel to its exposed fault line.

   10) In compressional faults, the hanging wall tends to move up relative to  the foot wall (pushed together).

   11) In tensional faults, the hanging wall tends to move down relative to the footwall (pulled apart).

 

II. IN-LAB SECTION: Drawing and Interpreting Geologic Structures in Block Diagrams

 

A. Introduction:  Three-dimensional geologic block diagrams are scaled-down, abstract, simple representations, or models of Earth's crustal rock structures, which include 1) formations, 2) unconformities, 3) faults, 4) folds, and 5) topography.  Block diagrams are a 3-dimensional composite of both, a geologic map (horizontal map-view) and geologic cross-sections (vertical side-views). The key to successfully completing the block diagrams lies in visualizing the 2-D representations as 3-D structure.

 

B. REVIEW OF STRIKE AND DIP OF TILTED PLANAR FEATURES

     1. Measure the strike and dip of the two planar objects the instructor has set up in the class:

 

              a)  Planar Object #X - Strike = _______ Dip = _____

  

              b) Planar Object #Z  - Strike = _______ Dip = _____

 

C. FAULT BLOCK EXERCISES

   1.  a) In map view (top of block), put strike and dip symbols on the beds and a fault dip symbol on fault.  b) Also put appropriate displacement arrows on the fault in the frontal cross-section. 

 

       What type of fault is shown below? ________________________.   

 

    2. a) Put appropriate fault displacement arrows, fault dip symbol, and strike and dip of beds symbols in both the map view and cross-section.   What type of fault is shown below if the

     slickensides are parallel to the dip?

                                                                       _____________________ 

 

 

 

3. a) Put appropriate fault displacement arrows, fault dip symbol, and strike and dip of beds symbols in both the map view and cross-section.  What kind of fault is shown below if slickensides are parallel to the dip? ________________ 

4. a) Draw the appropriate symbols for the fault in both the map view and cross-section. b) Draw   

    strike and dip symbols for the beds.  What type of fault is shown below if the slickensides are

    oriented horizontally? ______________

 

     Estimate the strike and dip of the fault: ________________ Estimate dip of beds.   _____

 

5.  What type of fault is shown below if the slickensides are oriented horizontally? __________

 

   Estimate the strike and dip of the fault: _____________   Estimate the dip of beds.   _____

 

D. FOLD BLOCK EXERCISES

  1. a) Complete the block (below).  b) Number the beds from oldest to youngest (1 being oldest).  c) Indicate the axial plane and fold axis with appropriate symbols in both the map view and cross section.  What is the name of this structure?  ________________

 

 

  1. a) Complete the block diagram (below).  b) Place strike and dip symbols on the map view (top of block) to indicate the structure. c)  Label the axial planes and fold axes with the appropriate

      symbols.  What is the name of this structure? ____________________________

 

 

  1. a) Complete the block (below).  Dip amount is arbitrary, but dip direction is not.  b) Number the beds from oldest to youngest (1 being oldest).  c) Indicate the axial plane and fold axis with appropriate symbols in the map view and cross-section of the block.  d) Place strike and dip symbols on top.  What is the name of this structure? ____________________________

 

4. a) Complete the block (below). b) Number the beds from oldest to youngest (1 being oldest).

    c) Indicate axial plane and fold axis with appropriate symbols in the map view and cross-section.

          What is the dip angle? _____.  What is the name of this structure? ___________

 

 

5. a) Complete the block (below).  b) Number the beds from oldest to youngest (1 being oldest).   

    c) Indicate the axial plane and fold axis with appropriate symbols in the map view and cross-

    section face of the block.  d) Draw strike and symbols on the map view.

     What is the fold plunge angle? _____.   What is the name of this structure? ___________

 

 

6. a) Complete the block (below).  b) Number the beds from oldest to youngest (1 being oldest). 

    c) Indicate the axial plane and fold axis with appropriate symbols in the map view and cross-

    section face of the block.  d) Draw strike and symbols on the map view. Note bed width for #2.

           What is the bed dip angle? _____.   What is the name of this structure? ______________

 

 

7.  a) Complete the block (below).  b) Number the beds from oldest to youngest (1 being oldest). 

     c) Indicate the axial plane and fold axis with appropriate symbols in the map view and cross-

    section face of the block.  d) Draw strike and symbols on the map view.

            What is the bed dip angle? _____.   What is the name of this structure? _____________

 

 

 

Part III – Structural Geology Laboratory Reflection

Directions:  Write a reflection (minimum 100 words in length) about your experience in doing the structural geology exercises lab today.  Include the following: 1) What was the purpose of the lab?; 2) What did you learned from this laboratory?; 3) What did you find interesting? 4) What were the problems and challenges you encountered; and 5) Your opinion on how this lab was designed and executed.