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Face of a mode I extension crack on the surface of a basalt flow along the Deschutes River, east-central Oregon.

Face of a mode I extension crack on the surface of a basalt flow along the Deschutes River, east-central Oregon. Photo by Vince Cronin.

Introductory Structural Geology, Joints and Veins

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Refer to Ben van der Pluijm and Steve Marshak, Processes in Structural Geology and Tectonics (psgt.earth.lsa.umich.edu), chapter 4, pages 89-107.

Terms you should work to understand and use properly

antiaxial antitaxial fringe antitaxial vein arrest line blocky vein
columnar jointing conjugate joints conjugate system cross joints dessication cracks
en echelon vein en echelon array en echelon exfoliation fibrous vein
Griffith cracks hackle zone ideal joint structure inhomogeneities inventory method
joint array joint origin joint set joint spacing joint system
joint trajectories joint lineament lithology membrane effect
orthagonal joints orthogonal system plastic yielding plumose structure pluton
Poisson effect poroelastic effect selection method sheeting joint sheeting
sigmoidal joints stress shadow syntaxial vein syntaxial systematic joints
tensile strength tensile twist hackle unroofing vein array
vein

Some submitted questions related to this chapter

  1. Give two possible limiters that could effect joint growth and describe how they do so.
  2. What is a group of veins called? Describe and give an example of a type of vein group.
  3. What information about stress can you infer from joint spacing?
  4. How do bedding planes and bed thickness influence jointing?
  5. In what environments do joints stop growing?
  6. How do fibrous and blocky veins differ in structure and mode of formation?
  7. As a joint grows, what happens to the joint propagation path?
  8. What factors determine the spacing between joints?
  9. Why do joints stop growing?
  10. Where does a plumose structure spread outward from?
  11. What is the spacing between joints determined by?
  12. A group of veins is referred to as what?
  13. What is the difference between a syntaxial and antiaxial vein?
  14. What determines the spacing between joints?
  15. Do rocks with smaller tensile strength develop more closely or more widely spaced joints?
  16. Unroofing causes change in the stress state for what three reasons?
  17. What causes exfoliation joints?
  18. What is one of the reasons why a joint would stop growing?
  19. Describe nonsystematic joint characteristics.
  20. Why does the dimple form at the origin?
  21. As the burial depth of rocks decreases, the rocks _ and _.
  22. Is it possible to find systematic AND nonsystematic joints in the same outcrop?
  23. Why do joint stress shadows exist?
  24. What does a change in extension direction form?
  25. The stiffness of a rock depends on what?
  26. Sheeting joints are commonly ________ to topographic surfaces?
  27. What are groups of veins called?
  28. What is the difference between joints and veins?
  29. What types of joints are there and how do they form?
  30. How do joints develop in a random seqence yet still have regular spacing?
  31. There is a zone on either side of a joint where there has been a decrease in tensile stress. What is the name of this zone?
  32. Name one of the four parameters that determine joint spacing?
  33. What happens when two joints that are not coplanar are growing towards each other, and enter each other's stress shadow?

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