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| What occurs at plate boundaries that are
associated with seafloor spreading?
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| Question Date: 2008-09-25 | | Answer 1:
There are three types of boundaries that can
occur if you consider the relative movement of two
spherical caps on a sphere: 1. Converging
where one plate dives beneath the other. An
example is what happens off the coast of Japan
where the pacific plate dives underneath the Asian
plate
2. Diverging boundary: two plates move
away from each other. In this case, material from
below rushes up to fill the crack. This is how NEW
CRUST forms
3. Strike slip boundary. This is
where the two plates slide past each other --an
example is the san Andras fault. It represents the
boundary between the North American and pacific
plates. If we hold the pacific plate fixed, the NA
plate is moving NNW at about 3 inches per year. In
about 40 million years LA will be in the Aleutian
Islands and will dive underneath back into the
earth interior. | | Answer 2:
Oceanic crust is very dense compared with
continental crust, so it sinks beneath continental
crust. Ocean crust can be pulled in two opposite
directions because this sinking of oceanic crust
beneath continental crust. When this happens, the
two plates of oceanic crust being pulled in
opposite directions move apart, leaving a void at
the plate boundary. Magma fills the void where it
cools to create new oceanic crust. It is a
continual process. The new oceanic crust continues
to be pulled away from the plate boundary because
of the sinking of oceanic crust beneath
continental crust, and new magma continues to fill
the void created by spreading of the sea floor. | | Answer 3:
As ocean plates are pulled apart from
each-other, faulting occurs resulting in extremely
thin ocean crust. The extremely thin crust allows
the Earth's mantle to ooze in underneath. Partial
melting of the upper mantle occurs underneath the
divide due to the reduction in pressure by the
thinned crust. The magma that results from this
comes up through swarms of dikes that sometimes
but not always breaks the surface, filling in the
cracks created by the stressed crust, and forming
new crust at the boundary. | | Answer 4:
At plate boundaries associated with seafloor
spreading (divergent plant boundaries) the Earth's
crust is very thin and is pulled apart at a slow
rate. As the plates separate, magma that is
buoyant and just below the crust 'bubbles' up and
is instantly cooled by the ocean. This now cooled
crust is attached to the plate and as the plate
moves apart this happens over and over again.
Here is a link to a great website that shows
this in action: earth_science | | Answer 5:
Seafloor spreading accounts for roughly 80% of
the world's volcanism.At spreading centers, new
plates (continental crust) are created. Where
plates spread apart from each other, earth
material (called basalt) rises up to fill the
void. The basalt wells up as molten magma
extruding through effusive (non-explosive)
volcanic vents submersed on the sea floor.
Underwater, this molten materiel moves out, and
then cools to create the most common rock on the
earth, basalt. Basalt is a heavy (dense), black
rock formed of the minerals plagioclase-feldspar
and olivine, and it is derived directly from the
earth's mantle. Two-thirds of the earth is covered
by ocean, and oceanic plates are made up of
basaltic oceanic crust. When spreading
centers initiate on continental crust (above
land), these regions can be called continental
rift zones. Eventually the two continental plates
will move far apart and the ocean will flood the
basaltic crusts low-lying land.
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