Class 10 Rule of V’s and Three Point Problem - Lab

Objectives:  Recognize general dip directions from outcrop patterns using the Rule of V’s, and determine strike and dip of a formation from the outcrop pattern.

Procedure:

Part 1:

The “Rule of V’s” states that outcrop V’s point in the direction in which the formation lies underneath the stream (or valley).  Use a folded piece of paper to represent a stream valley, and elevate one end of the valley.  Use a magazine to represent a formation of rock.  Hold the magazine in a horizontal position to visualize the outcrop pattern, ie, where the magazine will intersect the piece of paper.  Hold the magazine vertical, and visualize the outcrop pattern.  Hold the magazine so it dips up the valley and then hold it so it dips down the valley.  Visualize the outcrop pattern in each situation.

Each of the topographic/geologic maps below shows a valley (as indicated by the contour lines) and the outcrop pattern of a formation (stippled).  Study the outcrop patterns of the formations and note how the contacts of the formation relate to the contour lines in each situation.

A:  The formation is horizontal, therefore the formation contacts, ie, the lines on the map where the top and bottom surfaces of the formation intersect the topography, are parallel to the contour lines.

B:  The formation is vertical, therefore the formation contacts transect the map as straight lines.

C:  The V points up the valley, therefore the formation dips beneath the valley in an up-valley direction. The formation dips steeply, much more steeply than the stream gradient, so the “V” pattern is shallow or blunt.

D:  The V points up the valley, therefore the formation dips beneath the valley in an up-valley direction. The formation dips gently, much more gently than the stream gradient, so the “V” pattern is exaggerated. 

E:  The V points down the valley at an angle which is steeper than the stream gradient.

Part 2:  Determine the strike and dip of the formation from the outcrop pattern which crosses over the valley.

1.  Locate the lower contact of the formation shown in orange on the topographic map below.  Draw dots where it intersects the 1500 foot contour line on each side of the valley on the right hand side of the map.  These points represent points of equal elevation within the plane of the formation.  Draw a line connecting the dots.  The line represents the strike orientation of the formation since it is a horizontal line within the plane formed by the lower contact of the formation.  Use a protractor to measure the bearing of the strike line.   

2. The dip is measured at right angles to the strike.  Measure the dip as follows:

i)  Draw a short line perpendicular to the strike line which has one endpoint on the strike line and one endpoint on the 1400 foot contour line.

ii)  Measure the length of this short perpendicular line.  Use the map scale to determine this map distance.  This is the horizontal distance or “run”.  The vertical change, or “rise”, along this line is equal to the difference in elevation between the strike line (1500 foot elevation) and the point where it intersects the 1400 foot contour line (1400 foot elevation).

iii)  The dip angle is found using the formula:

      Tangent dip angle = Change in altitude / Horizontal distance

                            = Rise  /  Run

Find the value for the rise divided by the run.  Determine the Cotangent of this value, which is the dip angle.

Download the “Faulting” video clip:

If your computer has Quick Time, download the "faulting" shockwave file and watch it.

Note the dip of the fault planes and the movement direction, or "slip", of the fault blocks on each side of the fault plane.

Browse the information and images contained in the following web sites:

Structural Geology Websites:

            http://www.rmmlf.org/SciTech/Lacy/fig8.JPG

            Examples of structural controls on vein deposits.