-Stage 2-

Structural Geology

        Typically topographic maps would come first, then geologic maps and then structural geology but since I feel it is useful to know the structures before dealing with them in map form I am doing them before the maps.

Before we start a quick lesson on strike and dip:

• Rock Unit - Any group of rocks with similar properties that formed about the same time

• Strike - The direction the rock unit forms on the earth's surface

• Dip - The direction the rock is tilted in the earth

• The angle of the dip is the written next to the strike and dip

• The strike and dip symbols are always perpendicular to each other

Now onto the main portion of Structural Geology. There are 2 main divisions:

Folds and Faults

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Folds

Geologic Rock Units

• The list on the left is a representative of a geologic map legend

• Rocks on maps are listed in age order

• The rocks on the top of the list are the youngest

• The one's on the bottom are the oldest

• This resembles real-life where rocks are deposited

   then the "younger rocks" are deposited later on top of them

• The rock units will be used in the proceeding pictures

Anticline

• A fold in the rocks resulting in a "A" shape (A for Anticline)

• The top side of the box on the left represents the Earth's surface

• The front of the box shows the type of fold

• The dotted line represents the "fold axis"

• The resulting fold has the oldest rocks in the center

• Then rocks repeat on both side of the center symmetrically

• The width of the units on the surface are equal on both sides of the center unit

Syncline

• A fold in the rocks resulting in a "U" shape

• The top side of the box on the left represents the Earth's surface

• The front of the box shows the type of fold

• The dotted line represents the "fold axis"

• The resulting fold has the youngest rocks in the center

• Then rocks repeat on both side of the center symmetrically

• The width of the units on the surface are equal on both sides of the center unit

Plunging

Plunging Syncline                                                    Plunging Anticline                               

• The direction of plunge is visible along the side of the blocks

• This changes the symmetrical pattern seen along the surface

• The new pattern is giant curves on the earths surface

• The "arrow" pattern points in the direction of plunge in an anticline

• The "arrow" points in the opposite direction in a syncline

Nonsymmetrical Folds

• Nonsymmetrical folds cause the same rock units to be different widths on either side of the center unit

• Synclines and Anticlines will both have the unequal unit widths

• The thinner side of the unit widths overly the steeper portion of the fold

    Non-Symmetrical Anticline

Identifying Folds

• When identifying folds there are 3 types of descriptions that must be used for a complete description

• Anticline or Syncline

• Symmetrical or Nonsymmetrical

• Plunging or Non-plunging (typically you don't say non-plunging, you would just leave off that term)

ex - Plunging Symmetrical Anticline

Nonsymmetrical Syncline

Faults

There are 3 main types of faults

Normal Faults

• Main parts of a fault first:

  • Hanging Wall (H) - The block that rests on top of the fault

  • Foot Wall (F) - The block the lies below the fault

  • These are the always the same no matter the direction of the movement

• Normal Fault - When the hanging wall moves down and the foot wall moves up

• Extension - The large arrows on the side show the movement of the blocks

• This is when the blocks move away from each other

Reverse Faults

• Reverse Fault - Pretty much the opposite of a normal fault

• The hanging wall moves up while the foot wall moves down

• Compression - The blocks are pushed together

• Thrust Fault - When a reverse fault is extremely shallow it is called a thrust fault

Strike-Slip Faults

There are 2 types of strike-slip faults depending on the direction of movement

• Strike-Slip Fault - This is when two blocks slide past one another

• The San Andreas Fault is a strike-slip fault

Right Lateral

• Right Lateral - Say you were standing on the X, a right lateral is when the opposite block moves rightwards compared to where you were standing

Left Lateral

• Left Lateral - Again it is the opposite of a right lateral

• When you are standing on the X, the opposite block moves to the left

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