Hypothetical Orogeny: An Illustration of Tectonic Cycles and Mountain Building
1. initial rifting of large continental block
2. continent rifts into three blocks
3. plates (blocks) separate; new oceans formed
4. new rifts form and split off new small blocks
5. five separate plates; all passive margins
6. new oceans continue to widen
7. oceans continue to widen
8. two incipient subduction zones form
9. arcs build on two continental blocks adjacent to subduction zones
11. north oceans narrow while south ocean continues to expand
12. initial collision about to occur
13. ophiolite obduction marks final phase of north oceans
14. continent-continent collisions initiating
15. orogeny begins to north along oblique collision
16. orogeny spreads southward as continents sissor together
17. climax of orogeny as new subduction established at south margin of accreted continents
18. last remnants of southern ocean ridge subducted
19. new continental block rifts off southern continent; new ocean formed
20. old south ocean being subducted below north continent; back arc spreading developes to SW edge of north continent
21. new plate and subduction appear at NW margin of map; new rifting along southern continent
22. subduction on south margin of north continent closes ocean
23. oceans close in northern part of map; continue to spread in south
24. two collisions about to occur at margins of north continent
25. ophiolites obducted as old south ocean closes
26. initial collision at south margin of north continent
27. subduction begins to jump south of accreted block as orogeny developes
28. redeveloped southern subduction zone consumes new south ocean; ocean to NW closing
29. obduction of ophiolites in NW ocean as arc-continent collision begins; new south ocean closing
30. arc-continent orogeny underway
31. remnant ocean forms south of colliding arc between subduction zones; collision about to occur to south
32. oceanic plateaus and south continent about to collide with north megacontinent; ophiolites obducted
33. collision underway; note two remnant oceans
34. major continent-continent orogeny; note subduction zone has jumped to NW of accreted arc
35. subduction swings down around accreted continent; subduction zone to east reorganizing around accreted oceanic plateaus
36. several remnant oceans close resulting in more ophiolites
37. subduction expands to SE as major plate reorganization occurs; rifts forming to north
38. supercontinent bounded by several active and passive margins; rifts continue in several areas
39. rifts expand as supercontinent about to break up
40. break up underway as subduction zones continue to reorganize. LAST SLIDE
Email: ronald.blakey@nau.edu
Home Page: vishnu.glg.nau.edu/rcb/RCB.html
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