1. Figure G-54a shows a porphyroclast. What type is it?

2. The shear zone that contains this porphyroclast strikes 050° and dips 70° to the southeast. Mineral lineations plunge 70° toward 140° (down dip). The photographer who took this photograph was looking at a vertical cliff face, along the strike of the shear zone (i.e., toward 050°) so that northwest (NW) is on the left side of the photo and southeast (SE) is on the right. Describe in detail the type of movement on this shear zone. (Here is a generic example of a complete description: ‘‘normal-sense movement, northeast side down.’’)

Transcribed Image Text:

NW - SE Type of porphyroclast: Description of type of movement in the shear zone: Fig. G-54a Field photograph of a large porphyroclast in a vertical cliff face, for use in Problem 16.7. You are looking parallel to the strike of the shear zone (toward 050°). NW, northwest; SE, southeast. Scale bar is 5 cm.