6.) Sketch a schematic (approximate RS and q' as best you can, no calculations are required) strain ellipse, with S1 and S3 labeled, on Figure 2. (5 points) S1 is the red line; S3 is the green line; the blue lines are the lines of no finite longitudinal strain. This schematic strain ellipse is a graphical representation of the finite strain, along any orientation with respect to the shear direction, accomondated by the entire rock body. The location of the strain ellipse on the diagram is not significant. The orientation of the strain ellipse q' with respect to the shear direction is important. The center of the strain ellipse is not significant. However, the ratio of S1/S3 (RS)is important as it determines the shape of the ellipse and represents the relative magnitude of g.
7.) The fossil shell in this outcrop has maintained its original size and appears to be undeformed, even though the limestone containing has been deformed. How can this be so? Explain using the strain ellipse. (5 points)
This fossil lies parallel to the line of no finite
longitudinal strain that is at an angle to the shear direction as indicated
by the orientation of the strain ellipse for this outcrop.
8.) All the rock types present were subjected to one deformation event.
However, some units exhibit evidence of compression only, others extension
only, and still others of compression followed by extension. Explain how
this is possible with simple shear using the strain ellipse.
(5 points)
Simple shear is a non-coaxial deformation. Thus, the orientation of the principal stretch directions progressively rotate with respect to the shear direction with each new increment of strain (q' keeps decreasing). The original angle a that a line makes with the shear direction, and the value of the finite strain g will determine the value of S for features that parallel that line. Features, such as the basalt dike, with a values less than 90 will exhibit only extension. Features, such as the small quartz vein, with a values greater than 90 but less than 135 can exhibit contraction first (folding) followed by subsequent extension. Features, such as the large quartz vein, with a values greater than 135 but less than 180 are likely to exhibit only contraction.