1. Continental Tectonics and Mountain Chains
Chapter 9
Continental Tectonics and Mountain Chains

2. Guiding Questions
How does continental rifting begin and what environments of deposition does it produce?
How do rocks become folded?
How does a mountain chain form when a continental margin encounters a subduction zone?
Why does a foreland basin accumulate large volumes of sediment on the continent?
Why is continental crust not subducted?
What is the significance of ophiolites?
What is the zonation of a typical mountain chain?
How have the Andes formed?
How did the Pyrenees form?
What is an exotic terrane?
What broad features does rock deformation create in continents far from their margins?

4. Terranes
Geologically distinctive regions of Earth’s crust, each of which has behaved as a coherent crustal block

5. San Andreas Fault 5.5 cm/year
(~2 inches)
Moving L.A. (on the Pacific plate) closer to San Francisco (on the North American plate)

6. Rifting Triple junction Three-armed grabens at plate boundaries
Associated with doming
Hot spot
May have multiple types of plate boundaries

7. Rifting Formation of Atlantic Ocean Red Sea provides modern analogue
Three-armed rift forms
One may die out
Failed rift
Mississippi River
Amazon

8. Rifting
Rift valleys
Extension breaks continental crust into fault blocks
Blocks subside rapidly
Accumulate sediments, lakes
Rift Valley, East Africa

9. Rifting When rifting continues, continents separate along ridge axis
Margins cool, sink

10. Rifting Passive margin Active margin
Tectonically inactive areas of continental crust that accumulate sediment along shallow shelves
Eastern U.S.
Active margin
Zones of tectonic deformation and igneous activity
Western U.S.

11. Bending and Flowing of Rocks
Rocks can bend and flow under stress
Metamorphosis at high pressures and temperatures
Compressive forces
Folding

12. Bending and Flowing of Rocks
Syncline
Rocks folded concave up
Vertices at bottom
Anticline
Rocks folded concave down
Vertices at top

13. Bending and Flowing of Rocks
Dip
Angle that the bed forms with the horizontal plane
Strike
Compass direction that lies at right angles to the dip
Always horizontal
Regional strike
Overall trend of fold axes

14. Bending and Flowing of Rocks
Axial plane
Imaginary plane that cuts through fold and divides it symmetrically
Overturned fold
If either limb is rotated more than 90° from its original position

15. Bending and Flowing of Rocks
Axis of a fold
Line of intersection between axial plane and beds of folded rock
Plunging fold
Axis lies at an angle to the horizontal

16. Bending and Flowing of Rocks
Plunging fold
When eroded, produces a curved outcrop pattern

17. Mountain Building Orogenesis Process of mountain building Orogenies
Mountain building events

18. Mountain Building Continental Collision
Continental crust cannot be subducted
Suturing
Unification of two continents along a subduction zone
Ophiolite
Remnant of seafloor pinched up along suture

19. Mountain Building Magma rises into overlying continental slab
Volcanoes form, elevate crust
Mountain peaks
Plutons cool to form igneous core
Metamorphic Belt
Rocks on either side of core are deformed by core’s heat and other processes

20. Mountain Building Fold and Thrust belt Thrust sheets
On continental edge
Turned over away from core
Brittle deformation
Thrust sheets
Large slices of crust formed by thrust faulting
Slide along basal surface

21. Mountain Building Folds and faulting Increase folding
Develop overturned fold
Overturned fold can break

22. Mountain Building Cross-section of Rocky Mountains
Thrust faults slice through previously folded rocks

23. Deformation Processes
Deformation caused by
Pressure applied by subducted plate
Pushes mountain chain toward interior of continent
Folding near igneous arc and inland
Gravity spreading
Rock deforms under its own weight, spreads out
Deformation along folds and thrusts

24. Deformation Processes
Foreland basin
Downwarping of lithosphere beneath actively forming mountain chain beyond fold and thrust belt
Axis is parallel to mountain chain
Rapid formation
Deep, often flooded

25. Deformation Processes
Foreland basin sediments
Flysch
Shales, turbidites
Floods rapidly
Turbidites accumulate
Molasse
Nonmarine sediments
Mountain evolves
Fold and thrust moves inland
Chokes basin, folds flysch
Alluvial fans, floodplains, etc.
Clastic wedge

26. Andes Mountain Building
Igneous rocks added since Mesozoic
Continuing to build up
Bobs isostatically
Mountain chain is migrating inland

27. Andes Mountain Building
Magma shifting inland as subduction angle is reduced
Change in angle means change in plate movement

28. Andes Mountain Building
10 M years ago
Foreland basin connected to Atlantic along thin seaway
Infilling of foreland basin led to formation of Amazon River from seaway
Stranded marine animals that adapted to freshwater

29. The Pyrenees Formed when Iberia collided with Eurasia Exotic terrane
Cretaceous and Paleogene
Iberia originally part of Eurasia
Subduction began, reattached toward north
Ophiolites in northern Pyrenees mark suturing
Foreland basin received flysch then molasse
Exotic terrane

30. Continental Interiors
Structural basin
Circular or oval depression of stratified rock
Structural dome
Circular or oval uplift of stratified rock
Erosion leads to circular pattern

31. Continental Interiors
Black hills of South Dakota
Oblong dome

32. Continental Interiors
Domes and basins of North America

33. Continental Interiors
Michigan
Structural basin