plate tectonics objectives learn the historical development of the plate tectonics theory learn the...
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Plate Tectonics
Objectives
• Learn the historical development of the Plate tectonics theory
• Learn the plate tectonics theory as their preliminary step of learning landforms
• Raise interests about the earth
• Increase the awareness of the ever-changing Earth
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Lesson Structure
1.The chemical and physical layers of the Earth
2.Historical development of the plate tectonic theory
3.The location and types of plate boundaries
4.Types of plate motion
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Introduction
• Plate tectonics is a relatively new theory.
• It has revolutionized the way geologists
think about the Earth.
• The surface if the Earth is broken into large
plates.
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• The edges if these plates, where they move
against each other, are sites of intense
geologic activity, such as earthquakes,
volcanoes, and mountain building.
• Plate tectonics is a combination of two
earlier ideas, continental drift and sea-floor
spreading.
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Layers of the Earth
• Three chemical
layers: the core, the mantle and
the crust.Core
Upper mantle
Crust
Lower mantle
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The core• divided into two layers: a solid inner core
and a liquid outer core.
The Mantle• middle part of the earth
• made of minerals rich in the elements iron, magnesium, silicon and oxygen.
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The Crust• rich in elements oxygen and silicon with
lesser amounts of aluminum, iron, magnesium, calcium, potassium and sodium.
• Two types of crust: oceanic crust and continental crust
• Oceanic crust is made up of relatively dense rock called basalt
• Continental crust is made of lower density rocks, such as andesite and granite.
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• The outermost layers
of the earth:
lithosphere and
asthenosphere.
• The lithosphere is
the “plate” of the
plate tectonic theory
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• The asthenosphere is part of the mantle that flows, a characteristic called plastic behaviour.
• The flow of the asthenosphere is part of mantle convection, which plays an important role in moving lithospheric plates.
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Time for a short quiz!
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1.What are the three major layers of the Earth?
2.What are the two outermost layers of the Earth?
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Continental Drift
• Wegener showed the present-day continents were once part of a single supercontinent called Panagea in 1912
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Evidence for Continental Drift
• Fit of the continents
• distribution of fossils
• similar sequence of rocks at numerous locations
• ancient climates
• apparent wandering of the Earth’s polar regions
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Continental Drift - Fossils
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Continental Drifts - Fossils• Fossils of the same species found on the
several different continent
• e.g.: Glossopteris - found on the continents of South America, Africa, India and Australia
• if the continents are reassembled into Pangaea Glossopteris can be accounted for over a smaller contiguous geographic area
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Continental Drift - Rock Sequences
• Rocks sequences in South America, Africa, India, Antarctica, Australia show similarities
– bottom - tillite (glacial deposit)
– middle - sandstone, shale and coal
– upper - basic lava flows
• glossopteris fossils are bottom and middle layers
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Continental Drift - Rock Sequences
Basaltlava flows
sandstoneshalecoal
glacialtill
Glossopterisfossils
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Continental Drift Glaciation
• Proposed by Wegener
• South America, Africa, India and Australia were covered by glaciers nowadays.
Problem:
The climate of these areas nowadays are warm which the evidence of glacial action cannot be found
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These continents were adjacent to each other during glacial event
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Evidence of Glaciation
• The distribution of specific rocktypes:
e.g glacial till and striations are shared among these polar, desert and tropical areas
• The distribution of climates zones:
the poles reminded fixed and that the continents changed their position relative to the poles
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Problems with Wegener’s Model
• Lack of an adequate mechanism for moving the continents
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Hess’s Sea-Floor Spreading
• Heat trapped in the earth caused convention
currents
• The current would rise and fall beneath continents
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• Ocean Floor moved laterally away from the ridge and plunged into the oceanic trench along the continental margin
• Trench: steep-walled valley on the sea floor adjacent to a continental margin
lithosphere
Oceanic lithosphere
asthenosphere
trench
Volcanic (island) arc
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Testing the Model
• Lava erupted at
different times along
the rift at the crest of
the mid-ocean ridges
preserved different
magnetic anomalies
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Clear Pictures to Show…..
Positive magnetic anomaly
Negative magneticanomaly
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Time for you to think…..
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• If new oceanic lithosphere is created at mid-ocean ridges, where does it go?
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Subduction
• Convention cell in the mantle help carry away from the ridge
• The lithosphere arrives at the continent and subducted into the asthenosphere
• Oceanic lithosphere is created at mid-ocean ridges and consumed at subduction at subduction zones
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A picture to help you understand
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Volcanic Eruption
• Natural Hazard
Feel the power of nature
by watching this short
movie yourself!!!
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Birth of Plate Tectonics
• Firstly introduced by Tuzo Wilson (1965)
• Jason Morgan proposed the Earth’s surface consists of 12 rigid plates
• followed by the actual orientation and the location of the plates
• widely accepted by geologists
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Plate tectonic theory - Why?
• According to the locations of frequent earthquakes and volcanic activity
• forming a belt that circle the Earth
• e.g. earthquake belt: mid-Atlantic belt, east Pacific ridges
• e.g.: volcanic activity belt: Pacific Ocean “Ring of Fire”
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Location of Plate Boundaries
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Location of Plates
EurasianPlate
Arabian Plate
Philippine Plate
AfricanPlate
Antarctica Plate
Juan de Fuca Plate
Pacific Plate
Cocos Plate
NazcaPlate
South American Plate
CarribeanPlate
North American Plate
Australian-Indian Plate
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Structure of the plates
Continental crustOceanic crust
Rigid upper mantle
Asthenosphere
Lithosphere
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Types of Plate Motion
The ways that plates interact depends:
• relative motion
• nature of the plates (continental or oceanic plates
3 types of boundary divergent, convergent and transform plate
boundary
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Divergent Plate Boundary
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Convergent Plate Boundary
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Transform Plate Boundary
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Produced by
• Hazel Lam Yeuk Wing 98560141
• Ricky Lau Chun Kit 98718233
• Gigi To Wai Chi 98658333