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Unit 5: Structural Geology

Unit Booklet

Name: ________________________

Geology 12: Structural Geology Page 1

Structural Geology References and Learning Outcomes

1. Physical Geology Text Chapter 9.

2. Lab Manual in Physical Geology Lab 10: Geologic Structures, Maps and Block Diagrams, pages 227-248.

Students are expected to:

1. Distinguish between dip-slip (normal, reverse, thrust), strike-slip (left lateral, right lateral) and transform faults from maps, cross-sections, or photographs.

2. Relate compression, tensional and shear forces to the various types of faults and folds.

3. Interpret the dip and strike of an outcrop to determine subsurface strcutures.

4. Diagram domes, basins, anticlines, synclines, over-turned folds, and unconformities, and identify these structures in maps, cross-sections, or photographs.

5. Show the inter-relationships among a geologic map, a cross section, a block diagram, and the subsurface structure and geologic history of an area (e.g. construct a geological map using appropriate data).


What is Structural Geology?

i) Faulted Folds in Eastern Iran ii) Plunging Folds in Morocco

The study of folding and faulting (deformation) of Earth’s crust and the structures that form through these processes.

-What are some common processes that produce folding and faulting?

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Some Important Terms and Ideas

Folding (Lab 234-235)

*BBC Men of Rock: Moving Mountains 14:48 to 16:48 http://www.youtube.com/watch?v=aWwoNdvDTAw

-What is folding and how is it produced?

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-There are several different types of fold structures:

a) Anticline

-An upward fold. In cross section it resembles the letter “A” and on a geologic map it looks like parallel lines.

-Oldest strata are found in the middle of the fold.

b) Syncline

-A downward fold. In cross section it resembles the letter “U” and on a geologic map it looks like parallel lines.

-Youngest strata are found in the middle of the fold.

*Note: In the above diagrams you can see that strata are bent around an axis (found at the middle of the curve). This is the Fold Axis (lies within the Axial Plane).


c) Plunging Anticlines

-The Fold Axis does not have to be horizontal, but can “plunge” at one end into the ground.

-On a map looks like a series of wavy lines or the letter “V”. The point of the “V” indicates the direction of the plunge.

-Oldest strata are found in the middle of the fold.

-Plunge: Angle between the fold axis and the horizontal

-Trend: Compass direction of the plunge (the direction it is inclined downwards).

d) Plunging Syncline

-On a map looks like a series of wavy lines or the letter “V”. The open end of the “V” indicates the direction of the plunge.

-Youngest strata is in the middle of the fold.


e) Overturned Folds

-The folds you have studied above all possessed two “limbs” on either side of the axial plane. If one limb is tilted so that it is below the other limb it is called “overturned”.

f) Recumbent Folds

-Occur when the axial plane are vertical instead of horizontal.

g) Monoclinic Folds

-A fold inclined in only one direction. It has two axial planes with two nearly horizontal limbs separated by an inclined limb.

Fold Summary:


g) Domes

-Resembles a circle on a geologic map.

-Oldest strata is in the centre.

h) Basins

-Resembles a circle on a geologic map.

-Youngest strata is in the centre.


Faulting (Lab 34)

Stress Applied Type of Fault and Diagram Plate Boundary

-Faulting can also result in mountain formation:

a) Horst: Mountain formed between two normal faults

b) Graben: Valley formed between two normal faults.


Strike and Dip

-For a great animated tutorial see: http://dandanowski.com/c/img/portfolio/brunton.swf

Strike: Compass direction of a horizontal line running across an inclined surface. (Right Hand Rule: Thumb points Strike Direction)

Dip Angle: Angle between the strike and inclined surface. This always points downhill and is at 90 degrees (perpendicular) to the strike.

Dip Direction: Compass bearing of the dip angle.

Azimuth: Measurement used to determine the strike direction. It is expressed as a three digit measurement between 000° and 360°. North is 000° or 360°, East is 90°, South is 180° and West is 270°.

See the following website for a tutorial on Azimuth: http://academic.brooklyn.cuny.edu/geology/leveson/core/wayne_web/distance%20and%20direction/protractor/protractor_roll.htm


http://dandanowski.com/c/img/portfolio/brunton.swf

Some Useful Terms and Ideas

Flatirons:

-Triangular shaped ridges found in series along mountain sides.

-They are resistant rocks, with the notches between them representing stream erosion.

-Their pointed tops are parallel to the strike and their slopes point in the direction of the dip.

Rule of V’s

-When a strata crosses a valley, the outcrop pattern will form a V. The tip of the V indicates the direction of the dip, no matter the gradient of the valley.

-When a strata crosses a ridge, the tip of the V will point in the opposite direction of the dip.

-A vertical bed will never V, it will just look like a straight line across the landscape.

*Identify the dip direction in the Flatirons image above.


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