1. Horizontal Movement of
Plate Tectonics
Horizontal Movement of
Earth’s Lithosphere
Additional Reading: USGS Plate Tectonics (Pdf) – class web site

2. Learning Objectives
Understand the processes that are continuously changing Earth’s surface as lithospheric plates move relative to one another.
Identify the role of oceanic ridges, transform faults and deep-sea trenches in defining the edges of lithospheric plates.
Explain the distribution of magnetic anomaly stripes, seismicity, and volcanism in terms of the concept of global plate tectonics.
Calculate spreading rates of ocean basins.

3. Plate Tectonics The Theory of Plate Tectonics Plate Boundaries
Spreading Centers
Subduction Zones
Transform Faults
Plate Movement

4. The Theory of Plate Tectonics
“Continental Drift” - theory* proposed by
Alfred Wagner, a German meteorologist (1915)
Explained by:
geologic fit
fossils
* Not accepted by scientific community
- no mechanism to explain plate movement

5. Plate Tectonics http://pubs.usgs.gov/gip/dynamic/dynamic.html

6. The Theory of Plate Tectonics (cont’d.)
Plate Tectonics - evidence for theory of continental drift by Hess, Heezen and Tharp (1960’s) found lithospheres plate boundaries that can be 3 types:
ridges (spreading centers)
trenches (subduction zones)
transform faults (plates sliding past one another)

7. The Theory of Plate Tectonics (cont’d.)
Lithospheric Plates
major plates:
Pacific – 105 x106 km2
Eurasian - 70 x106 km2
Antarctic - 60 x106 km2
Australian - 45 x106 km2
S. American - 45 x106 km2
African - 80 x106 km2
N. American - 60 x106 km2
minor plates:
Cocos - 5 x106 km2
Phillipine - 6 x106 km2
Caribbean - 5 x106 km2
Nazca - 15 x106 km2
Arabian - 8 x106 km2
Indian - 10 x106 km2
Scotia - 5 x106 km2
Juan de Fuca - 2 x106 km2

8. the Pacific Ring of Fire IS 40,000 km long chain of volcanoes caused by "convergent tectonic plates" coming together;

9. Convection cells cause frictional drag on lithosphere
Plate Boundaries
a) Spreading centers - ‘rift zones’ (cont’d.)
Convection cells form
Density differences – cool vs. hot
Convection cells cause frictional drag on lithosphere
Lithosphere stretches due to convective movement
Lithospheric crust weakens

10. Plate Boundaries (cont’d.)
a) Spreading centers - ‘rift zones’ (cont’d.)
Faulting – break in overlying lithosphere
Magma flows upward
New lithospheric crust formed

11. Creating new ocean crust

12. Plate Boundaries (cont’d.)
a) Spreading centers - ‘rift zones’ (cont’d.)
Plates split apart -‘divergent plate’ boundary
New crust formed - ‘constructive’ plate boundary
Evolution of a mid-ocean ridge system
Upwarping
Rift valley
Linear sea
Mid-ocean ridge system

13. Plate Boundaries (cont’d.)
b) Subduction zones
Lithospheric Plates collide - ‘convergent’ plate boundary
Crust destroyed - ‘destructive’ plate boundary
Forms trenches and mountains

14. Plate Boundaries (cont’d.)
b) Subduction zones (cont’d.)
3 types of subduction zones:
Ocean crust into continental crust – form trenches and
mountain ranges
Ex. a): Juan de Fuca plate into the N. American plate - forms Cascade Mtn. Range
Ex. b): Nazca plate into the S. American plate - forms Peru-Chile Trench and
the Andes Mtn. Range

15. Plate Boundaries (cont’d.)
b) Subduction zones (cont’d.)
Ocean crust into ocean crust – forms trenches and island arcs
Ex. A): Philippine plate into the Pacific plate – formed the Marianna Trench
and the Marianna Island Arc system
Ex. B): N. American plate into the Caribbean plate and then the N. American
plate into the S. American plate – formed the Isthmus of Panama

16. Plate Boundaries (cont’d.)
b) Subduction zones (cont’d.)
Continental crust into continental crust – form mountain ranges
Ex. A): Indian plate into the Eurasian plate – formed the Himalayas
Ex. B): Eurasian plate into the African plate - closing up of the
Mediterranean sea

17. Plate Boundaries (cont’d.)
c) Transform faults
Plates slide past one another
Lithospheric crust neither created nor destroyed - ‘conservative’ plate boundary
Ex. A) Pacific plate sliding past N. American plate – forms the San Andreas Fault

18. Type of boundary between plates:
Constructive margins  Midocean ridges
Destructive margins  Subduction zones
Conservative margins  Transform faults

19. Plate Movement How do we know these rates? (Rate=distance/time)
New crust is created at spreading centers at a rate of approximately
1-10cm per year
Old crust is destroyed at the same rate at subduction zones
How do we know these rates? (Rate=distance/time)

20. Creating new ocean crust

21. Driving Mechanisms for Plate Motions
SUMMARY
Constructive margins
Midocean ridges
Destructive margins Subduction zones
Driving Mechanisms for Plate Motions

22. Plate Movement (cont’d.)
Magnetic anomalies in ocean crust...look at spreading centers
paleomagnetism
every so often Earth’s magnetic field flips (every 300K-500K years)
magnetic signal recorded in crust at spreading center as it’s formed, forms bands of crust with either a weak or strong magnetic signal
determine rate of plate movement by distance of band from spreading center divided by age of rock in band (r=d/t)

23. More evidence of plate moving..

24. Plate Movement (cont’d.)
Hot spots
Islands of Hawaii
islands or sea mountains formed over hotspots
(fixed area where magma comes up)
lithosphere moves over hotspot and end up have volcanic mountain over hotspot as well as a series of mountains in ‘front’ of hotspot
determine rate of plate movement by distance of mountain from hotspot divided by age of rock in mountain (r=d/t)

25. Age of Ocean Crust

26. Creating new ocean crust
Oceanic crust moves away from MOR (Mid Oceanic Ridge) and cools and subsides

27. Driving Mechanisms for Plate Motions
Constructive margins
Midocean ridges
Destructive margins Subduction zones
Driving Mechanisms for Plate Motions

28. the Pacific Ring of Fire IS 40,000 km long chain of volcanoes caused by "convergent tectonic plates" coming together;

29. Type of boundary between plates:
Constructive margins  Mid ocean ridges
Destructive margins  Subduction zones
Conservative margins  Transform faults

30. Conservative margins
Transform faults

31. Conservative margins Transform faults
The San Andreas fault in southern California

33. Hot Spots?

34. Mantle plumes originate deep within the asthenosphere as molten rock which rises and melts through the lithospheric plate forming a large volcanic mass at a “hot spot”.
Mantle Plume

35. Coral Reefs

36. Air view

37. Spreading rates

39. Geological Periods

40. Geological Periods Precambrian 4.6 B - 570 Ma solidification
Cambrian Ma Gondwana, hard shell anim.
Ordovician Ma separation, coldest
Silurian Ma Laurentia collides with Baltica
Devonian Ma pre-Pangea, equatorial forests
Early Carboniferous 356 Ma
Late Carboniferous 306 Ma western Pangea is complete
Permian Ma deserts, reptiles, major ext.
Triassic Ma Life begins to rediversify,Pangea
Jurassic Ma Dinosaurs, Pangea starts to break
Late Jurassic 152 Ma Pangea rifts apart, Atlantic
Cretaceous 94 Ma New oceans, India
K/T extinction 66 Ma end of dinosaurs
Eocene Ma India collides with Asia
Miocene 14 Ma Modern look
Future World Ma N. Atlantic widens, Med. vanish
Future Ma new subduction
Future Ma new Pangea

41. Precambrian
break-up of the supercontinent, Rodinia, which formed 1100 million years ago.   The Late Precambrian was  an "Ice House" World, much like the present-day.
Source:
Cambrian Animals with hard-shells appeared in great numbers for the first time during the Cambrian.  The continents were flooded by shallow seas.  The supercontinent of Gondwana had just formed and was located near the South Pole.

42. Ordovician
During the Ordovician ancient oceans separated the barren continents of Laurentia, Baltica, Siberia and Gondwana.  The end of the Ordovician was one of the coldest times in Earth history.  Ice covered much of the southern region of Gondwana.
Silurian Laurentia collides with Baltica closing the northen branch of the Iapetus Ocean and forming the "Old Red Sandstone" continent.  Coral reefs expand and land plants begin to colonize the barren continents.

43. Devonian
By the Devonian the early Paleozoic oceans were closing, forming a "pre-Pangea".  Freshwater fish were able to migrate from the southern hemisphere continents to North America and Europe.  Forests grew for the first time in the equatorial regions of Artic Canada.
Early Carboniferous During the Early Carboniferous the Paleozoic oceans between Euramerica and Gondwana began to close, forming the Appalachian and Variscan mountains.   An ice cap grew at the South Pole as four-legged vertebrates evolved in the coal swamps near the Equator.

44. Late Carboniferous
By the Late Carboniferous the continents that make up modern North America and Europe had collided with the southern continents of Gondwana to form  the western half of Pangea.  Ice covered much of the southern hemisphere and vast coal swamps formed along the equator.
Permian Vast  deserts covered western Pangea during the Permian as reptiles spread across the face of the supercontinent.

45. Triassic
The supercontinent of Pangea, mostly assembled by the Triassic, allowed land animals to migrate from the South Pole to the North Pole; and warm-water faunas spread across Tethys. The first mammals and dinosaurs appeared;
Jurassic By the Early Jurassic, south-central Asia had assembled.  A wide Tethys ocean separated the northern continents from Gondwana. 
Subduction zone Rocky Mountains

46. Formation of the Rocky Mountains

47. Late Jurassic In the Late Jurassic the Central Atlantic Ocean was a narrow ocean separating Africa from eastern North America. 
Cretaceous
During the Cretaceous the South Atlantic Ocean opened.  India separated from Madagascar and raced northward on a collision course with Eurasia. Notice that North America was connected to Europe, and that Australia was still joined to Antarctica.

48. Dinosaur extinction The bull's eye marks the location of impact site of a 10 mile wide comet caused global climate changes that killed the dinosaurs and many other forms of life.  By the Late Cretaceous the oceans had widened, and India approached the southern margin of Asia.
Eocene
million  years ago India began to collide with Asia forming the Tibetan plateau and Himalayas (destroying the last of Tethys ocean).  Australia, which was attached to Antarctica, began to move rapidly northward.

49. Collision of continental crust – formation of Himalayas

50. Whereas oceanic ridges indicate tension, continental mountains indicate compression forces are squeezing the land together.
Sedimentary Rocks Squeezed by Compression

51. Miocene 20 million years ago, Antarctica was covered by ice and the northern continents were cooling rapidly.  The world has taken on a "modern" look, but notice that Florida and parts of Asia were flooded by the sea. Arabia moved away from Africa forming Gulf of Aden and Red Sea;
Last Ice Age
When the Earth is in its "Ice House" climate mode, there is ice at the poles.  The last expansion of the polar ice sheets took place about 18,000 years ago. 

52. Modern World
If we continue present-day plate motions the Atlantic will widen, Africa will collide with Europe closing the Mediterranean, Australia will collide with S.E. Asia, and California will slide northward up the coast to Alaska.

53. Future +100
Earth is ~ 4.6 bill years old – suggested cyclic of 500 mill year pattern of assembling and disassembling the land masses;
Future +250

54. The Wilson Cycle uses plate tectonic processes to show development and creation of ocean floor and ocean basins;

55. The Wilson Cycle