1. “I CAN” Statements Theory of Plate Tectonics
2010_011ES092Seafloor Spreading
12/4/2018
“I CAN” Statements Theory of Plate Tectonics
Explain each type of plates interactions, and give example of the end result(s) i.e. geological features [L2]

3. A scientific revolution begins
2010_011ES092Seafloor Spreading
12/4/2018
A scientific revolution begins
PALEOMAGNETISM (evidence of past magnetism preserved in the rocks)
was the most convincing evidence set forth to support the concepts of continental drift [polar wandering] and seafloor spreading [magnetic reversals].

4. Basalt is rich in iron-bearing materials, like magnetite.
As the basalt lava cools, the Fe-bearing minerals become oriented parallel to the Earth’s magnetic field.

5. 2010_011ES092Seafloor Spreading
12/4/2018
As the lava hardens, the magnetic orientation is preserved and provides a record of the current Earth’s magnetic field.
Curie Point: temperature above which it is impossible for the atoms to magnetize. For magnetite it is 580C

6. Theory of Plate Tectonics
From the hypotheses of Continental Drift and
Seafloor Spreading was formulated the
Theory of Plate Tectonics
TECTONICS is the study of the features of the Earth’s crust [tektonikos = construction]

7. Theory of Plate Tectonics
 The Earth’s crust and rigid upper mantle
[LITHOSPHERE] are broken into huge slabs
or plates.
 Those plates are riding/floating onto the
asthenosphere [like wood blocks on water], at different rates and different directions.

8. Directions and rates of plate motions
Subduction
Spreading

9. The oceans and the continents are carried as passengers onto the moving plates.

10. The constant movement of those plates is responsible for the changes to the Earth’s surface by the way of:

11. EARTHQUAKES

12. ERUPTIONS
VOLCANIC

13. MOUNTAIN RANGES

14. 8 major plates: North American South American Eurasian African
Pacific [largest]
Indian/ Australian
Antarctica
Nazca
The minor ones:
Juan de Fuca, Cocos, Caribbean, Scotia, Arabian, Philippine

16. BOUNDARIES Tectonic plates interact at places called BOUNDARIES.
The continents / oceans do not necessarily resemble the outline of the plate boundaries.
There are three types of boundaries
Divergent
Convergent
Transform

17. Divergent Boundaries
Two plates moving AWAY from each other and forming a gap or RIFT.
Mostly associated with OCEANIC crust [seafloor spreading = Mid-Atlantic Ridge]
as molten rock [MAGMA] from the asthenosphere rises the plates move apart, and fills the space between the plates.
as it cools, it hardens onto the edges of the plates and creates new crust.

18. DIVERGENT PLATES

19. Divergent Boundaries Some involve the CONTINENTAL crust
when it begins to separate, the stretched crust forms a long, narrow, depression called a RIFT VALLEY
it is currently happening between the African and Arabian plates  Red Sea is therefore widening

21. The African and Arabian plates continue to rift apart, with the result that the Red Sea is ever widening
RIFT VALLEYS

22. Mediterranean Sea
Rhine Valley in Northern Europe is another example.

23. Divergent Boundaries Some involve the CONTINENTAL crust
the crust can also stretch to the point of forming FISSURE VOLCANOES

25. Convergent Boundaries
Two plates moving TOWARDS each other.
Direct COLLISION of one plate with another one.
There are three POSSIBILITIES:
CONTINENTAL – OCEANIC
OCEANIC – OCEANIC
CONTINENTAL – CONTINENTAL

26. CONTINENTAL - OCEANIC
As the plates are colliding, the denser plate will be forced downwards
Since oceanic crust is denser than the continental crust [3.0 vs. 2.7g/cm3], the ocean plate is pushed under continental plate. [crust destruction] The area is called a SUBDUCTION ZONE, and forms a deep-ocean trench
As the plate sinks into the asthenosphere, it melts and becomes magma. The magma rises through the continental plate [WHY?] and forms a volcanic chain

27. OCEANIC
 
CONTINENTAL

28. Cascades range was originally a volcanic arc that later uplifted…
Cascades range was originally a volcanic arc that later uplifted…. [partial explanation]

29. Mount St. Helens, Washington
Cascades range

30. Volcanic mountains of the Andes, (Nazca and South American Plates)

31. TRENCH

33. Mariana trench and the Mariana Islands in the west Pacific ocean
OCEANIC – OCEANIC
The more dense of the 2 will go under and form a subduction zone / OCEAN TRENCH
The new mantle material produced from the melting of the subducted plate will eventually resurface to produce chain of volcanic islands on the ocean floor called ISLAND ARCS
As magma accumulates over time, the volcanoes may rise above sea level to form volcanic islands:
Mariana trench and the Mariana Islands in the west Pacific ocean

34. OCEANIC-
OCEANIC CONVERGENCE
“DESTRUCTIVE”

37. CONVERGENT PLATES

38. CONTINENTAL - CONTINENTAL
As the 2 continental plates are colliding, neither plate is subducted i.e. neither plate goes beneath the other  WHY?
because the Continental crust is too buoyant to sink into the asthenosphere [2.7 vs. 3.3 to 5.5g/cm3]
The colliding edges buckle [crumple] and are pushed upward [uplift] to form mountain ranges. Indian/Australian plate collide with the Eurasian plate to form the HIMALAYAS.
Alps and Appalachians are other examples

39. CONTINENTAL CONVERGENCE–
CONTINENTAL CONVERGENCE

40. The collision of India and Asia produced the Himalayas (before)

41. The collision of India and Asia produced the Himalayas (after)

42. Mountain Building