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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

This page is under construction!

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

antitaxial vein arrest lines blocky vein columnar joint conjugate joint set
cooling crack dessication crack dihedral angle en echelon exfoliation joint
free surface hackle hackle fringe joint joint nucleus
joint origin joint set joint spacing lineament lithospheric pressure
mode I crack mode II crack mode III crack nonsystematic joints opening mode crack
orthogonal joint set plume plume axis plumose structure shearing mode crack
sheeting joint shrinkage crack stress shadow systematic joints twist hackle
unroofing vein -- -- --

Some questions submitted by students related to this chapter

  1. The spacing of well-developed joints is about ___ (choose one: equal to, less than, greater than) the bed thickness.
  2. Why do joints form?
  3. How do you measure joint spacing?
  4. Why are joint surfaces in rock not perfectly smooth?
  5. What is the difference between syntaxial and antitaxial joints?
  6. How are plume marks (plumose structures) oriented relative to arrest lines?
  7. How does joint spacing in thin beds compare with joint spacing in thick beds.
  8. What is a group of systematic joints called?
  9. What are two types of vein fills?
  10. What are some of the primary minerals that commonly occur in veins (but not necessarily in the same veins)?
  11. What is the composition of syntaxial veins compared with the composition of the wall rock?
  12. If joint A terminates at its intersection with joint B, which joint is younger.

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