1. Visualizing structures An introduction to the geometry of geological structures in the field

2. Goals To familiarize you with the 3- dimensionality of geological structures in the field Provide you with simple rules to use in geologic mapping of structures

3. 3D spaces to deal with Topographic Depositional/intrusive Deformational They all intersect

7. Shaded Non-shaded

8. Any structures will intersect an irregular topography Try picturing how will a horizontal layer cut this relief

10. Horizontal plane - follows topo contours

11. Let us now put the real topography aside and step into the realm of “primary” geologic structures - layering of sedimentary units, intrusions, viewed in an idealized 3D framework

17. Complicating the issue a little bit… Unconformity, what is it?

20. Possible scenario: Deposition, erosion, deformation, new deposition

21. The way this would look in a canyon near Page, AZ

23. Igneous intrusions

25. Structures on block diagrams

29. Let us know try to drape structures onto topography and come up with some simple rules for the way they will plot on maps. To keep things simple for now, I will deal mainly with planes and not with lines. So what can a plane be? A bed, a fault, a dike, a sill an unconformity, anything that is planar.

30. The simplest scenario: a horizontal bed

31. Horizontal beds (a’la water line)

32. Some shallow tilt of a plane

36. Rule of v’s

37. An example

38. So then what is a geological map? An overlay of geologic structures (e.g. like the planes shown here on the 2D topographic map). Let’s take a look.

39. Tucson Mts.

42. Cross-sections

43. Remember The 3 spaces you deal with: topo, primary structures and deformational (secondary) structures); Rule of v’s, overall topography/structure intersections of any planes A structure looks very different depending from where you look at it!