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

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

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.

• 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.

Layers of the Earth

• Three chemical

layers: the core, the mantle and

the crust.Core

Upper mantle

Crust

Lower mantle

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.

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.

• The outermost layers

of the earth:

lithosphere and

asthenosphere.

• The lithosphere is

the “plate” of the

plate tectonic theory

• 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.

Time for a short quiz!

1.What are the three major layers of the Earth?

2.What are the two outermost layers of the Earth?

Continental Drift

• Wegener showed the present-day continents were once part of a single supercontinent called Panagea in 1912

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

Continental Drift - Fossils

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

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

Continental Drift - Rock Sequences

Basaltlava flows

sandstoneshalecoal

glacialtill

Glossopterisfossils

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

These continents were adjacent to each other during glacial event

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

Problems with Wegener’s Model

• Lack of an adequate mechanism for moving the continents

Hess’s Sea-Floor Spreading

• Heat trapped in the earth caused convention

currents

• The current would rise and fall beneath continents

• 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

Testing the Model

• Lava erupted at

different times along

the rift at the crest of

the mid-ocean ridges

preserved different

magnetic anomalies

Clear Pictures to Show…..

Positive magnetic anomaly

Negative magneticanomaly

Time for you to think…..

• If new oceanic lithosphere is created at mid-ocean ridges, where does it go?

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

A picture to help you understand

Volcanic Eruption

• Natural Hazard

Feel the power of nature

by watching this short

movie yourself!!!

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

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”

Location of Plate Boundaries

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

Structure of the plates

Continental crustOceanic crust

Rigid upper mantle

Asthenosphere

Lithosphere

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

Divergent Plate Boundary

Convergent Plate Boundary

Transform Plate Boundary

Produced by

• Hazel Lam Yeuk Wing 98560141

• Ricky Lau Chun Kit 98718233

• Gigi To Wai Chi 98658333