Tectonics
Topic 1: Plate Tectonics
1.1 Plate Tectonics Theory
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Key Understandings for Tectonics
Topic 1: Plate Tectonics
Topic 2: Earthquakes and Volcanoes
Topic 3: Disaster Risk Management
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Topic 1: Plate tectonics
• KEY QUESTIONS:
• What is the plate tectonic theory?
• How does seafloor spreading support the
plate tectonic theory?
• How does magnetic striping support the
plate tectonic theory?
• What will happen to different tectonic
plates when they move at the different
plate boundaries?
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THINK: Why are some areas more prone to tectonic hazards?
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Topic 1.1: Plate Tectonics Theory
• KEY UNDERSTANDINGS:
• Earth’s internal structure consists of core, mantle and crust, including continental
and oceanic crusts
• explains how forces within Earth drives global plate movements
• Convection currents
• within the hot softened mantle below the crust
• being the driving force of overlying plates
• Slab-pull force
• gravity-controlled subduction of denser oceanic plate
• drags the rest of the plate along
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DO YOU KNOW?
• The plate tectonic theory
explains that:
– Earth has three-layered
structure
– The earth’s lithosphere is
broken into huge pieces
called ____________.
– Tectonic plates are
constantly
_____________.
– Plate movements result in
formation of
____________ (e.g.
mountain ranges, oceanic
trenches) and
phenomena (e.g.
earthquakes, tsunamis)
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LET US FIRST UNDERSTAND THE KEY TERMS:
Lithosphere and Asthenosphere
• Lithosphere- is made up of the crust and the
_____________________________________
• Asthenosphere- lies below the lithosphere;
– Semi-solid- why?
– Hot plastic layer
with ________________
– Explains how and why
plates move
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Lithosphere
Asthenosphere
Upper
mantle
Lower mantle
Core
Upper mantle? Asthenosphere? Lithosphere? Core?
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Earth’s Crust
• Earth’s ______________ layer
• Makes up less than 1% of the earth’s volume.
• Crust can range in thickness from a few km to more than 70 km.
• Divided into 2 types: ______________ & ___________ crusts
crust
upper mantle
lower mantle
outer core
oceanic
crust
continental
crust
inner core
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Earth’s Crust
• Earth’s outermost layer
• Divided into 2 types: oceanic & continental crusts
crust
upper mantle
lower mantle
outer core
oceanic
crust
continental
crust
inner core
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Earth’s Crust- SOME EXTRA INFORMATION
Continental crust
Oceanic crust
• thicker but less _________
• mainly made up of _______
• Make up the land masses
• thinner but ___________
• made up of ___________
• Make up of seafloor
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What is a tectonic plate? Recap
The Earth’s crust,
together with the rigid
uppermost part of the
upper mantle,
[lithosphere] is broken
into pieces known as
tectonic plates.
Earth’s major plates
Tectonic plates are thus part of the ________________ AND
THE PLATES MOVE in ___________ directions.
•Some plates consist mainly of continental crust; known as
continental plates.
•Others are made up of oceanic crust and are termed oceanic
plates.
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Most plates include portions of _______
continents & oceans
Continental Plates
= consist of MAINLY continental crust
(thicker & less dense)
Oceanic Plates
= consist of MAINLY oceanic crust
(thinner but denser)
Good to know!
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• There are 7 major crustal plates floating on the asthenosphere (upper
mantle).
– List the 7 major plates down:
• They vary in shape & size.
• Several smaller plates also exist:
• Among the 7 major plates, the PACIFIC plate is the largest.
• Most of the major plates include a continent and portions of its
surrounding ocean floor.
Eg. The South American plate includes the South American continent
and parts of the Atlantic Ocean.
• These plates move in different directions and at different speeds
ranging from 2 cm to 10 cm /yr.
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Distribution of Tectonic Plates
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SO WHY DO THE PLATES MOVE?
• There are two forces that are
responsible for plate movements:
–_____________ CURRENTS
–_____________ FORCE
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Convection currents
Tremendous heat in
the core heats up
the mantle causes
________ in the
mantle
(asthenosphere) to
move results in
______________
______________ in
the mantle.
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Definition of convection currents: Movements of heat within the
mantle which causes the mantle material to ________, _________
and _________ and _________ thereafter.
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plates moving
away from
each other
ocean
floor
plates
plates moving
towards each
other
plates moving
towards each
other
mantle
core
Tectonic plates float on _______________
(molten upper mantle), driven by heat energy/
convection currents
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How do convection currents lead to plate
movement?
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1.
2.
3.
4.
5.
6.
7.
How do convection currents lead to plate
movement?
The high temperatures in the mantle heat up the magma, causing it to
__________ up to the surface (just below the lithosphere).
As the magma rises towards the __________, it __________ beneath
the Earth’s surface and ____________.
This cooled magma then _________.
As the magma sinks, it is __________ up by the heat in the mantle and
___________ again.
CONVECTION Currents are created in the mantle by the ____________
rising and sinking of __________.
At places where the spreading magma cools and sinks, the plates are
_______________ together.
At places where the rising magma spreads out beneath the earth’s crust,
the plates are _______________apart.
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To sum up… convection currents
1. Mantle
heated up by
core (high
temperature)
2. Heated magma
expands and rises
3. Rising magma
spreads under the plates
and cools  causes
plates to be dragged
along & diverge.
4. Cooled magma
sinks. Plates pulled
along & collide
5. Sinking magma
heats up again &
whole process
repeats.
6. Sinking plate drives
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the downward moving
portion of convection
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currents (Slab-pull force)
How does SLAB-PULL FORCE contribute to plate movement?
https://www.youtube.com/wat
ch?v=9YPz9TQW4ZM
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SLAB-PULL FORCE
When two
plates
CONVERGE,
DENSER
oceanic crust
is PULLED
DOWN by
GRAVITY as it
SUBDUCTS
beneath the
less dense
crust.
Denser
oceanic crust
SINKS deeper
into the
mantle
UNDER ITS
OWN
WEIGHT,
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PULLING the
rest of the plate
with it,
contributing to
FURTHER
CONVERGENCE.
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Checkpoint:
Q1 Which one of the following is the innermost layer of the
Earth?
 Asthenosphere
 Core
 Crust
 Lithosphere
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Q2 What does the plate tectonic theory help us to understand?
You may select more than one option.
 It helps us understand the formation of volcanoes.
 It helps us understand why certain places often experience earthquakes.
 It helps us understand why Earth has a layered structure.
 It helps us understand why our world currently has seven continents.
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Q3 Study Figure below
which shows a map of the
plate boundaries. Which of
the following is an example
of plate boundary where
plates are moving apart from
each other?
Your Answer:
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Q4 “Convection currents result in the movement of tectonic
plates.” True or false?
 True
 False
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Q5 The following statements describe the process in which convection currents
cause tectonic movements. Arrange the statements in the correct order.
Your Answer:
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Q6 “We can observe slab-pull force at all plate boundaries.”
True or false?
 True
 False
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Q7 Slab-pull force describes how ________ pulls a sinking tectonic
plate down, causing it to sink under its own weight.
convection current
 gravitational force
 magnetic force
 heat
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Q8 “Slab-pull force contributes to plate divergence.”
True or false?
 True
 False
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