Lecture 4 Notes

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3 Jul 2011
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EESA01 CLASS 4
Embryonic Ocean, a new ocean: Red Sea
Rifting through young oceans and closing because the floor of the oceans become sub ducted
The floor of the ocean crust, as you move away from the mid oceanic ridge, the
thickness of the oceanic crust increases because it is cooling away from the ridge
Thick heavy rock on the mantle below will result in it sinking back into the mantle
New ocean forming pushes the lands apart
The history of the continent is dictated by the history of oceans
If we look at the Atlantic there is a spine that runs up the middle of the Atlantic which is
called the mid ocean ridge. They are under water volcanoes and they are active all the time.
To accommodate the new volcano material, it pushes the North American and European
plates apart.
_____________________________________________________________________________________
1. INTRODUCTION TO MIDOCEAN RIDGES: MODERN AND
ANCIENT FOSSIL MORs (CALLED OPHIOLITES)
When ocean close, the floors get pushed up on landophiolites
By looking at the rocks and structures, we can see the processes of ocean life
They are important economically, because they are mineral rich; oceanic crust
ancient pieces of ocean
2. WHY ARE MORs FRACTURED? THE ROLE OF TRANSFORM
FAULTS
The mid ocean ridge is not strictly continuous, there are cracks called fractures
These fractures enable ocean floor spreading on the curved surface of the earth
Dikes or dykes are orange strikes on rocks (picture with his motorcycle)
They are the result from hot magma intruding into older rocks along fractures
As this happens, the rocks are being extended and pushed apart. This is the basic
behind plate tectonic/movement
The continuous feeding or magma and dikes
Sheeted dikes: so many closely spaced dikes
When the magma reaches the ocean floor it cools very rapidly and we find the
pillowed lava where the basalt magma was cooled
Below the magma chamber we can see Gabbro chemically equivalent to basalt but
it has larger crystals because it cools slowly
Sheared peridotites equals to mantle. It is made of olivine, green colour. When
it is polished it is known as peridot
The top section is a vertical section like a snapshot
The bottom diagram shows what happens when we spreads the ridge; symmetrical
distribution of magma on both sides
What is feeding the MOR: ploons
Distillation basalt and gabbro are distilled from huge mantle ploons
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