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 Basalt lava flows sandstone shale coal glacial till Glossopteris fossils

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 magnetic anomaly

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 Eurasian Plate Arabian Plate Philippine Plate African Plate Antarctica Plate Juan de Fuca Plate Pacific Plate Cocos Plate Nazca Plate South American Plate Carribean Plate North American Plate Australian-Indian Plate

Structure of the plates Continental crust Oceanic crust Rigid upper mantle Asthenosphere Lithosphere

Types of Plate Motion A The ways that plates interact depends: relative motion nature of the plates (continental or oceanic plates A 3 types of boundary A divergent, convergent and transform plate boundary

Divergent Plate Boundary

Convergent Plate Boundary

Transform Plate Boundary

Produced by Hazel Lam Yeuk Wing Ricky Lau Chun Kit Gigi To Wai Chi