Plate tectonics theory

This is a geographical theory which proposes the earth's outermost shell (that is the LITHOSPHERE, the crust and upper mantle) is broken into tectonic plates which FLOAT atop the semi molten ASTHENOSPHERE.
Where these plates meet are PLATE BOUNDARIES, there boundaries are responsible for tectonic activity, i.e. volcanoes and earthquakes, as the plates diverge and collide.

What are types of plate are there?
1. CONTINENTAL
-This crust material forms continents
-Sometimes called sial, due its composition of granitic rock
-Its is older in origin, around 1500 million years old
-It has a lower density than oceanic crust, 2.6 density, therefore more buoyant (You need to know facts and figures)
-35-70km thick, considerably thicker than oceanic crust

2. OCEANIC
-This type of crust forms ocean basins
-Sometimes called sima, due to its composition of basaltic rock
-Younger in age, 200 million years old
-Denser than continental crust, 3.0 density
-7-10km thick, a lot thinner

When describing plate characteristics one must go into the theory of polarity?
Oceanic crust can be created and destroyed. Therefore they have the ability to record changes in magnetic polarity.



You will also want to mention the 'relationship' between plates, that is, that they cannot overlap, thus on impact they are either subducted or compacted in fold mountains. There cannot be 'gaps' between plates, thus when divergence occurs magma outpours, creating new crust and shield volcanoes.

Plate Tectonics A2 Subject Content

Option 1: Plate Tectonics and Associated Hazards

Plate movement

Earth structure, plate tectonics theory: convection currents and sea-floor spreading. Evidence: continental drift and palaeomagnetism.
Destructive, constructive and conservative plate margins. Processes: seismicity and vulcanicity. Associated landforms: young fold mountains, rift valleys, ocean ridges, deep sea trenches and island arcs.
Hot spots associated with plumes of magma and their relationship to plate movement.

Vulcanicity

Variations in the type and frequency of volcanic activity in relation to types of plate margin and types of lava.
Forms of intrusive activity – dykes, sills, batholiths.
The above paragraph has been added. This addition will apply in the January 2012 and subsequent examinations.
Minor forms of extrusive activity – geysers, hot springs and boiling mud.
Major forms of extrusive activity – types of volcanoes.
Two case studies of recent (ideally within the last 30 years) volcanic events should be undertaken from contrasting areas of the world. In each case, the following should be examined:

• the nature of the volcanic hazard
• the impact of the event
• management of the hazard and responses to the event.

Seismicity

The causes and main characteristics of earthquakes: focus and epicentre; seismic waves and earthquake measurement.
Tsunamis – characteristics and causes.
Two case studies of recent (ideally within the last 30 years) seismic events should be undertaken from contrasting areas of the world. In each case, the following should be examined:

• the nature of the seismic hazard;  
• the impact of the event;
• management of the hazard and responses to the event.