The Structure of The Earth Convection currents Tectonic Plates Plate Movements

Key Terms Lithosphere Athenosphere Collision Margin Conservative Margin Constructive Margin Crustal Plate Destructive Margin

The Structure of the Earth

Which am I? This part of the Earth is solid, extremely dense, extremely hot and relatively small. This part of the Earth is only about 100km thick and is both cool and solid. This part of the Earth is a very dense, very hot liquid. This part of the Earth is a thick layer of molten rock. Inner Core The Crust Outer Core The Mantle

What is ‘tectonics’? From Greek ‘tektonikus’ meaning building or construction Plate tectonics refers to the process of plate formation, movement, and destruction.

History of Plate Tectonics New theory for motion: Arthur Holmes (1930s) –thermal convective cells in the upper mantle (aesthenosphere) –theory is largely ignored

History of Plate Tectonics In the 1960s, Harry Hess and Robert Deitz (geophysicists) propose sea floor spreading along mid-oceanic ridges for plate motion.

Convection Currents

How Convectional Currents move Tectonic plates

What is a ‘Plate?’ Lithospheric plate: crust + upper mantle Aesthenosphere: plastic mantle

World Earthquakes

Plate Tectonics Theory Continental Drift + Sea Floor Spreading + new data  Theory of Plate Tectonics

Tectonic Plates In some locations plates move away from each other (a constructive margin). In some locations plates move towards each other (Destructive margin). In some places plates move past each other, either in opposite directions or in the same direction but at different speeds (a conservative margin).

Oceanic Constructive Plate Boundary Constructive Margin – The boundary between two crustal plates that are moving apart. Rising magma creates new crustal rock. New Crust is formed at this margin, with Iceland being a good example of this process.

Constructive Margin: Continental The East African rift valley East Africa is moving NE away from main African plate which is heading North. The valley extends for 4000Km (2 rifts) from Mozambique to the Red Sea. Rifts – Form when sections of crust between parallel fault lines subside. The area experiences volcanic activity suggesting that the crust has been weakened and thinned by tension. This results in rising magma escaping to the surface through volcanoes such as Mt Kilimanjaro.

Destructive Plate Boundary Destructive Margin – The boundary between two crustal plates that are moving towards each other. One of the plates subducts beneath the other and is destroyed. This forms volcanic mountain chains such as the Andes in South America

Collision margins Collision Margin – The boundary between two plates of continental crust that are moving towards each other. No subduction occurs, and so no new crust is created. Because they are of equal weight both are forced upwards creating mountain ranges such as the Himalayas in Asia.

Conservative Plate Boundary Conservative Margin That boundary between two plates that are sliding past each other, either in opposite directions or in the same direction but at different speeds. Crust is ‘conserved’; so no new crust is created and no existing crust is destroyed.