The document summarizes the theory of plate tectonics. It describes early evidence from continental drift and how modern evidence established the theory during the 20th century. This includes seismometer networks, mapping ocean floors, dating oceanic rocks, and paleomagnetism studies. The theory proposes that lithospheric plates are dynamic, with new plates generated at mid-ocean ridges and old plates subducting at trenches. There are three types of plate boundaries: divergent where plates spread apart, convergent where they collide, and transform where they slide past each other. This cyclical process can be modeled by the Wilson cycle of supercontinent breakup and reunification over geological time.

1. The Theory of Plate Tectonics

2. Scientific precedent: Continental Drift
Alfred Wegener:
1915. “The Origen of Continents and Oceans”

3. Paleolithic evidence

4. Geological evidence

5. Paleoclimatic evidence

7. Continental jigsaw puzzle

10. •What’s wrong with Continental
Drift?
•How long did we wait for a new
theory?
•How did it come?

11. During the second half of the 20th century:
• Seismometers network.
• Submerged relief of the oceans.
•Age of the rocks of the ocean floor.
•Paleomagnetism of the ocean floor.
•Distribution of earthquakes and volcanos.
Global Tectonics

12. Main concepts
• The lithosphere is divided into great
blocks.
• Lithosperic plates are dynamic.
• The ocean floor is continually generated
and destroyed.

13. Main tectonic plates

14. Types of plate boundaries
• Divergent or constructive boundaries.
• Convergent or destructive boundaries.
• Transform or passive boundaries.

16. Divergent boundaries
What do you see here? Come on, make the effort!
What geological phenomena are likely to occur here?
Would the study of the rock age help?

17. Divergent boundaries
•Molten material rises up and solidifies
on the surface, pushing the 2 plates in
opposite directions.
•New lithosphere is being formed
here, so:
• Do plates increase their size?
• Is the Earth’s surface increasing?

18. Divergent boundaries can be found on the sea floor or on land.
RIDGES
CONTINENTAL RIFTS

19. What is this?

20. Transform or passive boundaries
• Fractures where 2 plates slide horizontally
against each other.
• Is lithosphere being created here?
• What geological phenomena are expected?
• Do you know any of these transform faults by name?

21. Passive boundaries

27. Convergent or destructive boundaries
• Two plates moving towards each other interact.
what happens then?
• 3 types according to the composition of the
plates in the area of collision:
1. Continental and oceanic.
2. 2 oceanic plates.
3. 2 continental plates.

28. Types of
destructive
boundaries
Could you
define
subduction?
How do we
know this is
real?

29. Depth of hypocentres
The further you go from the trench, the deeper the hypocentres
are
plane of subduction or plane of Benioff.

30. Oceanic-Continental
• Oceanic plate
subducts under
continental.
• Quakes along a
sloping plane.
• Andean or
marginal
mountain ranges
with active
volcanoes.

31. Oceanic-Oceanic
• The oldest one
subducts. Why?
• Friction+high T melt
the rocks.
•Active volcanoes form
an island arc.

32. Continental-Continental
Continental lithosphere can’t subduct.
What now?
A mountain range is formed.
Earthquakes.
What about volcanism?

35. Types of boundaries. Summary.
Type of
boundary
Tye of
movement
Ocean floor
Landform
produced
DIVERGENT
Separation
Creates
oceanic
lithosphere
Ridges and
continental
rifts
Destroys
oceanic
lithosphere
Neither
creates nor
destroys
Trenches,
island arcs and
mountains
Transform
faults
CONVERGENT Collision
TRANSFORM
Lateral
displacement

36. The Wilson Cycle
John Tuzo Wilson (1909-1993):
• At least, two geological processes of rifting
and reuniting of supercontinents.
• This cycle brings together all the phenomena
studied so far.
• Can be organised in 3 stages:
1. Continental rifting.
2. Expanding ocean.
3. Continental collision.

37. Activity: Organise these images in a cycle.

40. Continental
fragmentation.
Plate dynamics and heat
under the continent can
fracture the continent.
First, it bulges and
breaks, then, it sinks down
and a CONTINENTAL RIFT
is formed.

42. Formation of an expanding ocean.
The Atlantic ocean is an example. Its size is increasing
steadily due to the production of new oceanic
lithosphere.
What’s going
on here?

43. Closing of the ocean
basin and continental
collision.
The oceanic lithosphere
near the edge of the
continent fractures and
stars to subduct.
Why?
 Increased density.
 Weight of sediments.

44. The evidence for the theory of plate tectonics
During the second half of the 20th century:
• Seismometers network.
•Distribution of earthquakes and volcanos.
• Submerged relief of the oceans.
•Age of the rocks of the ocean floor.
•Paleomagnetism of the ocean floor.
•Laser and GPS measurements.
Global Tectonics

45. Distribution of erthquakes and volcanoes

46. Mapping of the submerged relief

47. Study of the age of the rocks of the ocean floor

48. Study of the age of the rocks of the ocean floor

49. Paleomagnetism of the ocean floor

50. Laser and GPS measurements

51. Intra-plate phenomena

52. How do we explain the movement of
the plates?
1. Convection Currents.
2. Push exerted by new materials in the oceanic
ridges.
3. Pull due to the weight of sinking plates in
oceanic trenches.