1. Plate Tectonics and Deformation
Landforms

3. Unifying Theory Plate Tectonics affects: Earthquakes Volcanoes
Oceanic circulation and global weather patterns
Natural resource distribution
Distribution of organisms

4. Early Hypothesis Alfred Wegener (1915)
Developed the hypothesis of continental drift
This suggested that all of the continents were once connected in a supercontinent called Pangaea
His ideas were rejected:
Due to the lack of mechanism
All of his evidence came from the southern continents

5. Classical Evidence
The continents fit, especially along the continental slope regions where erosion is minimal
Matching rock sequences and mountain ranges were found across continents
Africa and South America have similar mountain ranges
Rock type the same
Rock ages the same
Appalachian and European mountain ranges line up

6. Classical Evidence Glacial evidence Fossil evidence
Scouring patterns show landmasses were connected
Glaciers move outward from center of the ice mass
Fossil evidence
Glossopteris
Mesosaurus

7. Plate Tectonic Theory
The lithosphere is divided into plates, which move because of heat transfers deep in the Earth
This is a unifying theme in geology
There is overwhelming evidence to support it
It explains:
Mountain building
Earthquake activity
Volcanism
Distribution of life
Natural resource distribution

8. Supercontinent Cycles
Theory by J. Tuzo Wilson (sometimes called Wilson Cycles)
Supercontinents form, break up and reform throughout Earth’s history

9. Plate Boundaries Divergent Plate Boundary
Plates separate and move in opposite directions
Crust is extended and fractured
New ocean crust is formed
Large fractures, shallow-focus earthquakes and basaltic pillow lavas are features found in these areas

10. Plate Boundaries Old boundaries:
Look for faults, dikes, sills, specific sediment series in rift valleys
Pillow lavas
Aulacogens
This is where a rift valley was starting
The failed rift valley is called an aulacogen
Scientists supposed that the New Madrid fault zone is an aulacogen

11. Plate Boundaries Convergent Plate Boundary Ocean – Ocean
One plate is subducted, usually the older plate
You end up with a subduction complex:
Wedge of scraped-off sediments and lithosphere
Volcanic arc’s can also occur:
These are curved chains of volcanoes

12. Plate Boundaries Ocean – Continent Continent – Continent
Oceanic plate is subducted
Result in a continental volcanic arc that is andesitic
Continent – Continent
Continental plates collide and are welded together
This results usually in mountain building

13. Plate Boundaries Old Boundaries:
Look for igneous rocks, intensely deformed rock
Chaotic mixture of folded, faulted and metamorphosed rocks
Ophiolites
A series of rocks that contains slices of oceanic crust welded to the continental crust

14. Plate Boundaries Transform Plate Boundary
Plates move parallel, in opposite directions
Mostly occur on the seafloor
Results in earthquakes and fractures
Old boundaries
Evidence of old transform plate boundaries is sparse except for large displacements of rock systems.

15. Intraplate Features Hot spots: The mantle plumes are stationary
The plate moves over the plume and leaves behind a trail of progressively older volcanoes
This can be used to determine direction and rate of plate movements

16. Mechanisms of Plate Tectonics
The lithosphere is divided into plates, which move because of heat transfers
Continents and ocean floors move together
A convection current is hypothesized
Subduction occurs where cells descend
Spreading occurs where cells ascend

17. Deformation
Deformation is how a rock body responds to tectonic changes
Why is this important?
This becomes a record of past events
Helps us to find and recover resources
Helps us to plan structures like bridges and dams

18. Important Terminology
Stress
Application of force or pressure
Types:
Compressional
Tensional
Shear

19. Important Terminology
Strain
Deformation caused by stress
Can be:
Elastic  rocks return to original shape
Plastic  rock bend or fold
Brittle  rock fault
High temperature and pressure  plastic
Near Earth’s surface (low temp and pressure)  brittle

20. Important Terminology
The following are used to describe the orientation of rock.
REMEMBER: sediments accumulate in horizontal layers!!!
Strike
Direction of rock layer intersecting a horizontal plane
Dip
Angle of deviation from horizontal
Perpendicular to strike

21. Types of Deformation Folds Monocline Anticline Syncline
Simple bend or fold
Anticline
Limbs dip away from axis
Oldest rocks are at the core
Syncline
Limbs dip toward axis
Youngest rocks are at the core

22. Types of Deformation Inclined fold Overturned fold Recumbent fold
Asymmetrical limbs
Overturned fold
Limbs dip in same direction because one limb is rotated > 90˚
Recumbent fold
Axial planes are horizontal
Plunging fold
Axis is not horizontal (see usually as anticline or syncline)

23. Types of Deformation Domes and Basins
These are oval or circular equivalents of anticlines and synclines
Domes- oldest rocks are in the center (anticline)
Basin – youngest rocks are in the center (syncline)

24. Types of Deformation Joints Faults
Fractures along which NO movement has occurred
Faults
Fracture along which movement HAS occurred

25. Faults Hanging wall Foot wall
With a fault relative movement is described, one or both walls may have moved.

26. Faults Types: Dip-slip Faults  vertical movement in fault plane
Normal Fault
Hanging wall moves down, and foot wall moves up
Produced by tensional stress (divergent areas)
Reverse Fault
Hanging wall moves up, and foot wall moves down
Produced by compressional stress
Special kind of reverse  Thrust fault: reverse with dip less than 45˚

27. Faults Strike-slip Faults  horizontal movement
Left or right lateral movement is shown
Produced by shear stress (transform)
Oblique-slip Faults  both vertical and horizontal movement has occurred

28. Block Diagrams
A block diagram is a representation of a piece of the Earth.
We analyze block diagrams for relative time order (i.e. what happened first, second, third… last)

29. Block Diagrams
A few rules to remember to analyze basic block diagrams:
The oldest rocks are on the bottom
(Principle of Superposition)
Igneous intrusions or faults are younger than the rock it cuts through
(Principle of Cross Cutting Relationships)
Rock fragments in a layer are older than the rock itself
(Principle of Inclusions)

30. Practice 1 5 (youngest) Principle of Superposition
& Principle of Inclusions
& Principle of Cross
Cutting Relationships 3
Principle of Superposition
& Principle of Inclusions 4
Principle of
Cross Cutting
Relationships 2
Principle of Superposition
1 (oldest)
Principle of Superposition

31. Practice 2 6 5 4
7 (Reverse Fault) 3 2 1