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.
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a) Wegener’s Evidence (Continental Drift)
b) History of Plate Tectonics
c) Breakup and Appearence of Pangea
WHAT IS A PLATE?
Major continental and oceanic plates include:
Types of Earth’s Crust:
Plate tectonics (from the Late Latin tectonicus) is a scientific theory which describes the large scale motions of Earth's lithosphere.
THE DYNAMIC EARTH:
The earth is a dynamic planet, continuously changing both externally and internally. The earth’s surface is constantly being changed by endo-genetic processes resulting in volcanism and tectonism, and exogenetic processes such as erosion and deposition. These processes have been active throughout geological history. The processes that change the surface feature are normally very slow (erosion and deposition) except some catastrophic changes that occur instantaneously as in the case of volcanism or earthquakes. The interior of the earth is also in motion. Deeper inside the earth, the liquid core probably flows at a geologically rapid rate of a few tenths of mm/s. Several hypotheses attempted to explain the dynamism of the earth.
+ Horizontal movement hypothesis
+ Continental drift, displacement hypothesis
Development of the plate tectonic theory.
Plate tectonic theory arose out of the hypothesis of continental drift proposed by Alfred Wegener in 1912. He suggested that the present continents once formed a single land mass that drifted apart, thus releasing the continents from the Earth's core and likening them to "icebergs" of low density granite floating on a sea of denser basalt.
Seafloor Spreading
The first evidence that the lithospheric plates did move came with the discovery of variable magnetic field direction in rocks of differing ages.
Plate tectonics is the theory that Earth's outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core. The plates act like a hard and rigid shell compared to Earth's mantle. This strong outer layer is called the lithosphere.
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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.
14. Types of plate boundaries
• Divergent or constructive boundaries.
• Convergent or destructive boundaries.
• Transform or passive boundaries.
15.
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?
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?
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.
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.
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.
41.
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
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.
