how are oceans formed? continents and ocean basins exist on lithospheric plates that move relative...
TRANSCRIPT
How are oceans formed?
Continents and ocean basins exist on lithospheric plates that move relative to eachOther. Between their margins, new land is always built or destroyed…
How are oceans formed?
New ocean basin is being made in areas such as the mid-Atlantic ridge…
These are referred to as divergent boundaries…New crust is generated; plates pull away from each other…
Rate of spreading of plates is about 2.5 cm / year.This would be enough for the Atlantic ocean to form over thelast 100-200 million years…
How are oceans formed?Iceland stands over the Mid-Atlantic ridge and has been an ideal place for studyof plate tectonics.
How are oceans formed?
Krafla volcano in eastern Iceland.
How are oceans formed?
The Atlantic ocean was formed by breakdown of Pangaea…
How are oceans formed?
Formation of the young Atlantic, cont….
Can you think of another area where this may be happening today?
How are oceans formed?
Plate Tectonics
As new land is made in diverging plate boundaries, old land is “destroyed” atconvergent plate boundaries, creating trenches, mountain ranges, etc.
Plate TectonicsSo what happens when two plates meet at convergent boundaries?
Ex: Nazca Plate pushes into South American Plate and is subducted.
South American Plate is lifted,creating the Andes mountains.
Plate Tectonics
Continental convergence zones also createtrenches that are thousands of miles long and 8-10 kilometers deep.
Many of the earth’s active volcanoes are also found around these oceanic-continental convergence zones.
Plate Tectonics
When oceanic plates meet, one platewill be subducted. Often, this processresults in formation of trenches:
e.g. Mariana Trench, where Pacificand Philippines plates meet, is almost11,000 meters deep!
These are also areas where one seesisland arcs such as the Marianas orthe Aleutian Islands…
Plate Tectonics
When continental crusts meet, there is onlyPartial subduction… Since the continentalRocks are relatively light, the crusts tendTo buckle and push upward…. Ex: theHimalayas
Plate Tectonics
Sometimes, plates slide by each other (rather than meeting head on), creatingtransform boundaries…
San Andreas Fault
Plate Tectonics
General Review…
Plate Tectonics – Hot Spots
A “hot spot” can develop over a fixed mantle plume. In these areas, magma risesto the surface, eventually creating volcanic islands… This phenomenon also creates island chains such as the Hawaiian Islands.
How are oceans formed?
How deep?