EESA06H3 Chapter Notes -Hypocenter, Stratovolcano, Clastic Rock

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Published on 18 Apr 2013
School
UTSC
Department
Environmental Science
Course
EESA06H3
Professor
Chapter 3
Earthquakes usually on mid ocean rides and continental edges.
Divergent boundary:
-two plates move apart and magma fills the space between the plates. Usually
causes earthquakes.
-mid ocean ridges are divergent plate boundaries where new oceanic lithosphere
forms.
-a narrow rift forms along the mid ocean ridge because of crust that slip down as
spreading occurs. This movement causes small to moderate size earthquakes.
-As the plates move apart, solid mantle in the asthenosphere rises toward the
surface, which becomes magma and the magma eventually becomes part of
oceanic lithosphere
-stretching of the crust may split continents apart and cause lakes(red sea) to form,
and with continual seafloor spreading, the lake becomes wider and eventually
becomes an ocean, just like Atlantic ocean
Convergent boundary: two plates move toward one another. One plate slides
under the other. Usually causes volcanoes. Called subduction. Many major
earthquakes occur in subduction zones.
-can include two oceanic plates, oceanic/continental or 2 continental
Ocean-ocean convergent
-when plate subducts, temperature rises and magma erupts and forms island
arcs which are volcanos.
Ocean-continental convergent
-oceanic plate subducts underneath continental.
-volcanos form on the continental and uplifts the region producing high
mountain range.
Continental-continental convergent
-since both continents are thick and have same density, they cannot be easily
subducted. They stack up to each other and form enormous mountains.
Transform boundary: two plates move past each other. Usually causes
earthquakes.
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-transform faults combine with spreading centers to form zigzag pattern on
seafloor.
Magnetite:
-at MOR, lava erupts to the surface and cools down, as rocks cool, the magnetic
field is recorded by the iron rick mineral magnetite. Magnetic stripes tell us the
polarity. Study has shown that earths magnetic poles has switched many times.
-young crust near the ridge. Sediment should thicken outward from the ridge. Ships
drill holes in seafloor to determine the geologic history.
-hot spots form a series of volcanic islands, If the plate is moving beyond the
hotspot. The older the volcano, the smaller they get because they subside.
Chapter 5
Texture of Igneous Rocks
Texture refers to sizes, shapes and arrangements
underground= intrusive/ plutonic ; cools slowly; forms coarse crystals
at surface= extrinsic/volcanic; cools quickly to form fine crystals
classified by composition and texture.
Light colour minerals are felsic rocks and dark rocks are mafic or
ultramafic
Felsic are abundant in quartz and feldspar while mafic is rich in
magnesium and iron
Temperature and pressure inside Earth
Radioactive decay of elements
Temperature increases as we move deeper in the Earth
Relates to plate tectonics
Conduction: Heat transfer by direct contact
Radiant Heat transfer: heat radiates through the air.
Convection: Flow of liquid
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How do rocks melt
Rise in temperature causes rocks to melt
Rise in pressure causes rocks to become solid
Adding water can lower the temperature at which the rock will melt
How do Igneous Rocks Form
First, the process of melting occurs 40-150km beneath the surface in
deep crust or mantle. Magma rises up because it is less dense than
rocks and may accumulate to form a magma chamber inside the crust,
some magma may solidify at the chamber and never reach the surface.
Some magma may crystalize in the magma chambers and get carried
to the surface. When magma reaches the surface we call it lava and
rocks that form on the surface are called extrusive rock.
Any igneous rock that solidify below surface is called intrusive rock.
Complete melting is rare; most rocks melt by partial melting
Felsic minerals melt at lower temp. than mafic, therefore partial
melting produces magma more felsic than the source. Felsic is also less
dense so it floats upward and mafic sink to bottom.
Since mafic magma is hotter, it can melt felsic walls and mix together
called assimilation
How does magma move?
When rocks melt, the volume of the melt is greater than original; so it
is less dense and will rise upward if overlying rocks let it through.
There are 4 constraints on how magma ascends: Magma Pressure,
density, gas pressure and stress. Pressure pushes the magma into
any available direction. Pressure decreases as magma rises.
Mafic magma may be denser than crustal rock so it stops to form a
magma chamber.
If magma has low content of dissolved gas, it will not assist in magma
upward.
Tectonic stress may trap the magma or help the magma.
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Document Summary

Earthquakes usually on mid ocean rides and continental edges. Two plates move apart and magma fills the space between the plates. Mid ocean ridges are divergent plate boundaries where new oceanic lithosphere forms. A narrow rift forms along the mid ocean ridge because of crust that slip down as spreading occurs. This movement causes small to moderate size earthquakes. As the plates move apart, solid mantle in the asthenosphere rises toward the surface, which becomes magma and the magma eventually becomes part of oceanic lithosphere. Stretching of the crust may split continents apart and cause lakes(red sea) to form, and with continual seafloor spreading, the lake becomes wider and eventually becomes an ocean, just like atlantic ocean. Convergent boundary: two plates move toward one another. Can include two oceanic plates, oceanic/continental or 2 continental. When plate subducts, temperature rises and magma erupts and forms island arcs which are volcanos.

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