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

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