Plate tectonic, pioneers of plate tectonics, how do plates move, structure of Earth, layers of Earth, mechanical properties, composition, sismic waves. Plate boundaries: ocean ridge, trench.

1. PLATES TECTONIC
Earth, our changing planet

2. SEISMIC WAVES
BODY WAVES:
• P-waves: faster, compressional,
can travel through any type of material,
including fluids
• S-waves: slower, transverse, can travel
only through solids
SURFACE WAVES: Rayleigh
and Love waves
density temperaturemelting point

3. Geochemistry model
Compositional layers
The Earth is made up of 3
main layers:
Crust:
- Continental (10-70Km) less
dense and older. Granitic
- Oceanic (5-10 km) more
dense and younger. Basaltic.
Covers two-thirds of Earth's
solid surface
Mantle (2900 km):
- Silicate rocks. Peridotite
- Flows
- D" layer.
Core: Fe-Ni
- Outer core, liquid (2900- 5100 km)
- Inner core, solid (5100- 6370 km)
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4. Geochemistry model
Compositional layers
Schematic view of the interior of
Earth.
Layers:
1.Continental crust
2.Oceanic crust
3.Upper mantle
4.Lower mantle
5.Outer core
6.Inner core
Discontinuities
A: Mohorovičić discontinuity
B: Gutenberg discontinuity
C: Lehmann discontinuity.

5. Dynamic model
Mechanical layers
Lithosphere:
- Crust and the uppermost mantle.
It can be identified on the basis of its
mechanical properties.
- The lithosphere is subdivided into tectonic
plates.

6. Continental drift & Plates tectonics
- Alfred Wegener (1880-1930) was a German
meteorologist and geologist who proposed the theory
of continental drift as a unified theory.
- In his book, "Origin of Continents and
Oceans," he calculated that 200 million years
ago the continents were originally joined
together, forming a large supercontinent.
- He named this supercontinent Pangaea.

7. 1. Continents seemed
to fit together, not at
the continuously
changing shoreline,
but at the edge to
their continental
shelves.
CONTINENTAL DRIFT
EVIDENCES
GEOGRAPHICAL

8. 2. Fossil evidence, similar plant and animal fossils are
found around the shores of different continents,
suggesting that they were once joined.
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9. 3.Widespread
distribution of glacial
till deposits and
glacial striations in
the southern
hemisphere
300 my ago
CLIMATIC
Today

10. 4. Geological fits:
When the geology of
eastern South
America and
West Africa was
mapped it
revealed that
ancient rock
outcrops (cratons)
over 2,000 million
years old were
continuous from
one continent to
GEOLOGICAL

11. 5. Tectonic fit. Fragments of an old fold mountain
belt between 450 and 400 million years ago are
found on widely separated continents today.
Pieces of the Caledonian fold mountain belt are
found in Greenland, Canada, Ireland, England,
Scotland and Scandinavia.

12. 6.PaleomagnetismGEOPHYSICAL
Some rocks preserve a record of the Earth's
magnetic field. This
record provides
information on
the past the past
location of
tectonic plates.

13. TOWARD PLATE TECTONICS
The Seafloor
• Mid ocean ridge
New ocean floor is created on ridges
Mid-ocean ridge is an underwater mountain system:
- Having a valley known as a rift, running along its
spine, as wide as 10–20 km.
- It wraps around the globe for more than 65,000 km.
- The average depth to the crest of the ridge is 2,5 km
- Oceanic ridges are split up by transform faults and
fracture zones.

14. • Ocean trenches
Ocean trenches are the deepest parts of the ocean.
An ocean trench is a long, deep depression in the ocean floor near continental
shelves. Others are found near chains of volcanic islands, called volcanic arcs.

15. Harry Hess published ‘The History of Ocean
Basins' in 1962, in which he outlined a
theory that could explain how the continents
could actually drift. This theory later became
known as ‘Sea Floor Spreading'.
7. Seafloor spreading.
He suggest that oceans grew from their centres, with
molten material (basalt) up from the Earth’s mantle along
the mid ocean ridges. This created new seafloor which
then spread away from the ridge in both directions.

16. 7. Seafloor spreading.

17. Evidence of seafloor spreading
1. Frederick Vine and Drummond Matthews (1963) noticed there
was a symmetrical pattern of magnetic stripes on either
side of the mid ocean ridges.
This suggested that the ocean floor was created at the mid ocean
ridges, then was split in half by later activity and pushed sideways.
2. Basalts stripes were found to be the same age at similar
distances away from the ridge on each side.
A. Magnetic stripes

18. Lavas (igneous rocks)
are progressively
buried by sediments as
the seafloor spreads
away from the ridges.
So the thickness of
sediment on the
oceanic crust increases
with the age of the
crust. Oceanic crust
adjacent to the
continents can be
deeply buried by
several kilometres of
sediment.
B. Sediment thickness

19. 7.Earthquackes
The map above shows the distribution of
earthquakes with magnitudes greater than 5.0
that occurred between 1965 and 1995.

20. 7.Volcanoes
In the map below, each triangle represents the location of
a recently active (on a geologic time scale) volcanoes.

21. 7.Earthquackes and volcanoes

22. TECTONIC PLATES
The surface of the Earth (lithosphere) is broken up into large plates:
tectonic plates o lithospheric plate.
Earth surface is divided into 7 major and 8 minor plates

23. • Divergent
Plates move away from each other
Mid-Ocean ridges
TYPES OF
PLATE
BOUNDARY
• Convergent
Plates move towards each other
Trenches
• Transform
Plates slide past each other
Transform faults

24. • Spreading ridges
– Volcanic activity.
– Submarine earthquakes (related with transform faults)
DIVERGENT BOUNDARIES
– Where a divergent boundary forms:
• on a continent it is called a RIFT.
• under the ocean it is called an OCEAN RIDGE

25. • Iceland has a divergent plate
boundary running through its
middle
Iceland: An example of continental rifting

26. Rift valley: An example of continental rifting
East African Rift System

27. The Rift Valley and
Associated
Features
• Eventually a new plate
will form
• The sea will flood the
valley and connect to
the Red Sea

28. CONVERGENT BOUNDARIES
SUBDUCTIONThere are three styles of convergent
plate boundaries
– Oceanic-continent crust collision
– Ocean-ocean collision
– Continent-continent collision: forms
mountains
The Earth's unchanging size implies that the crust must be
destroyed at about the same rate as it is being created
Subduction:
- Trench
- Volcanic arc
- Volcanoes
- Mountain belt

29. SUBDUCTION:
1. The oceanic crust which is thinner and more dense than the
continental crust, sinks below the continental crust.
2. It dehydrates and releases water into the overlying
mantle wedge, inducing partial melting in the
overlying mantle wedge, new melt which rises up into
the overlying continental crust forming volcanoes.
Subduction is a way of recycling
the oceanic crust

30. Andes
(oceanic-
continent)

31. Ring of fire
(ocean-continental shelf)
Volcanic arc

32. Himalayas
(continent-continent)
Mountain belt, obdution and collision

33. TRANSFORM BOUNDARIES
The zone between two plates
sliding horizontally past one
another.
Most transform faults are found
on the ocean floor. However, a
few occur on land, for example
the San Andreas.
They commonly offset the active
spreading ridges, producing zig-
zag plate margins.
They are generally defined by
shallow earthquakes.

34. San Andreas
transform fault
6.7 Northridge earthquake 1994
7.8 earthquake 1906

35. WILSON´S
CYCLE

38. Magmas generated by
mantle rise up below t
erupt on Earth's surfac
systems, the longest m
the world. When the m
basalt, the planet's mo
the basis for oceanic c

40. Look next links about structure and
composition of Earth
• The Geological Society: Plate tectonics
• Smithsonian National Museum of Natural
History: The dynamic Earth.