LECTURE                              PLATE TECTONICS

In this lecture you will:

The Earth is not stable and unchanging. There is a lot of movement.  The major movement is called "plate tectonics". Earthquakes and volcanoes mostly occur at the boundaries of these plates as seen on right. 



1. Topology 

The plates of the continents "fit" together. 


2. MAGNETIC ORIENTATION at sites of newly formed crust

- the crust spreading alternates north and south 
-  mirror image on both sides of the ridge where new crust is being formed
- the age of the rocks are youngest close to the ridge and get older as they get farther away and are mirror image of each other on each side
- in the middle is a deep valley and at the bottom is oozing mantle
the melted rock (metal in it) has no magnetic orientation and as it cools it takes the orientation of the earths magnetic fields

Changing magnetic orientation on Earth 1 3

3. Continuation of geological features between Africa and south America.


4. Continuation  of fossil records

1. Sea floor spreading 

.. sea floor is thinner, more likely to occur where crust is thin rather than thick click on the link to see the ages connected with the ages.
- the AGES of the sea floor where it has spread gives a timeline

2. Crust spreading at rifts

Rift valley in Africa and Iceland where new material is oozing up out of the mantle and spreading. These are known as divergent boundaries
-- occur where two plates are moving away from each other
due to molten material wells up from the mantle and solidifies to form new crust along the edges of the separating plates.
-- usually happens on the sea floor, sea floor is thinner, more likely spreading occurs where crust is thin rather than thick

"The continent of Africa is thought to have been split by a series of rift valleys in various states of development. Those in East Africa are still in thick crust. Those in West Africa are associated with thick oil-bearing sediments. In the Red Sea area the rifting has gone so far as to form a narrow ocean. In the south-east Madagascar has been completely separated from Africa by rifting. "

3.  Plate interactions

http://www.ucmp.berkeley.edu/geology/tectonics.html has excellent animations of various eras... and includes a brief history of the eras and links to very interesting information
plate tectonics is the driving force of  continents drift.  Without plate tectonics continental drift was an hypothesis with no explanation of a driving force.
-- Pangea began to break up about 200 million years ago.
the boundary between the Triassic and Jurassic periods,
middle of the age of dinosaurs.
-- 65 million years ago,  end of the Cretaceous period and the age of dinosaurs,
 North America was still attached to Europe and Australia to Antarctica.
since then the continents have moved to their present positions, North and South America became attached, and India bumped into Asia.
During the next 50 million years or so the Atlantic Ocean will get larger and the
Pacific Ocean smaller.
-- Baja and southwestern California will move north and split from the continent along the line of the San Andreas fault.
-- Eastern Africa will split away from Africa along the Great Rift Valley.
  Australia and New Guinea will move north.  And India will move east.

3.  Plate interactions -convergent
1. Two thin (ocean) plates

1 side dives under the other and melts (subduction)
1 side rises to form an arc of mountain -- island mountains like the Aleutian Islands and Japan.

2. one thin (ocean) and one thick (continent)  plate meet

the ocean plate subducts
-- the continent plate rises to form coastal mountains like the Andes Mountains.

3. two thick plates meet

the Himalayan Mountains

4. plates slide past each other going in different directions


Discuss the theory of continental drift.  How is plate tectonics related to the drift theory?
How are continents and crustal plates different?
Why are some, but not entirely the same kind of dinosaur fossils
found in the major continents?
Why are there no mammals native to Australia?
Is the age of continental drift over? Explain why or why not.
Was Antarctica once in the tropics?
Why does the crust of Earth "ride" or float on top of the mantle?
Which part of the Earth's structure is responsible for its
magnetic properties?
Which part of the Earth's structure is essential for plate
tectonics to occur? Why do the plates move?
Is the crust the same depth everywhere
What supporting scientific evidence is there for plate tectonics?
Give two different lines of evidence.
What does the mid-Atlantic Ridge contribute to the theory of
plate tectonics?