Course: Geography of Ocean Transport Lecturer: K. Facey Plate Tectonics Course: Geography of Ocean Transport Lecturer: K. Facey

Plan Interesting Observations Continental Drift theory by A Wegener Sea Floor Spreading by H. Hess Transform Faults and Hot Spots by J. Tuzo Wilson Plate Tectonics Theory Types of crustal plates (major, minor, oceanic and continental) Types of Plate Margins Summary

Interesting Observations I After the major exploration of the 16th to 19th Centuries, the following observations were noted: (a) Parts of the earth appeared to be able to fit together. Eg East coast of S. America and West Coast of Africa

Interesting Observations II Some fossils (remains of plants or animals) that were from one or few areas were found in places now far apart. See below

Interesting Observations III Some coastlines have been found with the same rock and rock structure present. See below

Interesting Observations IV The following was also noted: Ancient climates : evidence was found the present climate in some areas are much different from past climates as seen in rock spaces. There has been changes in the direction of the N and S Pole as seen in older rocks

Continental Drift Theory Alfred Wegener proposed that the continents moving (drifting) over the mantle in 1910 According to Wegener, the earth used to look like this =>

Continental Drift Theory The Break up of the Continents involved several stages:

Continental Drift Theory Then the 2 super-continents split into:

Continental Drift Theory The movement of the continents continued over time Until they ended up at their present position or location

Sea Floor Spreading Harry Hess (1960’s) proposed the concept of Sea Floor Spreading. Plates moved apart following geo-thermal energy currents causing magma to escape unto the surface forming Mid- Oceanic Ridge

Sea Floor Spreading Sea floor was observed to occurring off the coast of South America in the Pacific Ocean in the 1960’s. This observation helped to cement the concept proposed by Hess and the role of geo-thermal energy currents in this process.

Transform Faults and Hot Spots J. Tuzo Wilson proposed that some crustal plates move pass each other following geo thermal currents instead converging or diverging. As the rub past each other then faults and major earthquakes would be produced. He also proposed that volcanoes do not occur only at Plate margins but also at areas where the crust is no very thick, i.e. Hot Spots.

Transform Faults and Hot Spots Plates are sliding past each other Look at where Hot spots are in relation to Plate Boundaries

Plate Tectonics Theory Definitions of terms: What is the meaning of the following terms? Crustal plate Crustal plate margins Geo thermal energy currents

Plate Tectonics Theory J. Tuzo. Wilson in the 1965 coined the term Plate Tectonics to describe the movement of crustal plates and the effect of their motion. This theory combines the work of Wegener, Hess, Wilson and others in a single theory. In 1967, Jason Morgan proposed that the Earth's surface consists of 12 rigid plates that move relative to each other.

Plate Tectonics Theory Two months later, Xavier Le Pichon published a synthesis showing the location and type of plate boundaries and their direction of movement. Since the mid-1960s, the plate tectonic model has been rigorously tested. Because the model has been successfully tested by numerous methods, it is now called the plate tectonic theory and is accepted by almost all geologists.

Types of Crustal Plates Crustal plates may be classified based on either: (a) their size ( major or minor) (b) their composition (continental or oceanic) Thus a crustal plate may be described using both criteria for classification. Eg major continental; minor continental; major oceanic and major continental. N.B. Crustal plates are named based mainly on the feature or landform that lies on top of them

Types of Crustal Plates Continental crustal plate see below Oceanic crustal plate see below

Types of Crustal Plates Some of the crustal plates found across the world

Caribbean Crustal Plates The Caribbean is a minor oceanic plate that shares boundaries or plate margins with several plates; these are: G = North American F= Caribbean E = Nazca D = Cocos

Types of Crustal Plate Margins Crustal plate margins are the areas where two or more crustal plates meet or interact. There are three main types of margins: (a) Destructive / Zone of Convergence (b) Constructive / Zone of Divergence (c) Conservative / Transform Fault Margin/ Neutral / Passive

Destructive Plate Margin Part 1 Destructive Plate Margin forms when two plates move towards each other forming either a Collision or a Subduction Zone. A Collision Zone (see below) is formed when two continental plates meet. They form Fold Mountains.

Destructive Plate Margin Part 2 Subduction zones are formed when mainly Oceanic and Continental crustal plates meet. This results in the formation of Deep Oceanic Trenches where Oceanic plate is drawn under the Continental Plate and volcanoes (in some cases Island Arcs)

Constructive Plate Margin This occurs when two plates , usually Oceanic are moving away from each other. This creates a gap to be created and eventually a Mid Oceanic Ridge to be formed. See diagram below:

Transform Fault Plate Margins This occurs when two plates are sliding past each other either as they go in opposite directions or the same direction at different speeds. This results in the formation of large cracks or faults on the earth’s surface and is associated with major earthquakes.

Summary of Crustal Plate Margins Complete this table to help you review what you have covered Name of Plate Margin Mov’t of plates Involves Associated Processes Resultant Landforms Destructive –Collision Zone Plates move towards each other Folding, slight Faulting. Earthquakes Fold Mts Destructive- Subduction Zone Mainly Continental and Oceanic plates Deep Oceanic Trench Volcanoes (Island Arcs) Constructive Plates move away from each other Mainly Oceanic plates Faulting, volcanic action, Earthquakes Transform Fault Either Oceanic or Continental plates Faulting and Major earthquakes Faults / Fissures

For further information Egger, Anne, (2014), ‘The Origins of Plate Tectonics’ Visionlearning Vol. EAS-1 (1), 2003. Available Online at: http://www.visionlearning.com/en/library/Earth-Science/6/The-Origins-of-Plate-Tectonic-Theory/65 Last Accessed: 15/10/2014 Oskin, Becky (2013), ‘What is Plate Tectonics ?’ Available Online at: http://www.livescience.com/37706-what-is-plate-tectonics.html