Transcript Plate Tectonics_for_CMI_Class

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 geothermal 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
Destructive – Plates move
Collision
towards each
Zone
other
DestructiveSubduction
Zone
Plates move
towards each
other
Constructive
Plates move
Mainly
away from each Oceanic plates
other
Transform
Fault
Associated
Processes
Resultant
Landforms
Folding, slight
Faulting.
Earthquakes
Fold Mts
Mainly
Continental
and Oceanic
plates
Either Oceanic
or Continental
plates
Deep Oceanic
Trench
Volcanoes
(Island Arcs)
Faulting, volcanic
action,
Earthquakes
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/EarthScience/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-platetectonics.html
• Last Accessed: 15/10/2014