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Slide 1

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Plate Margins
We must now look at the 3
main types of plate margin:
· Constructive.
· Destructive.
· Conservative.
Each type of plate margin has
different rocks and types of
hazard…read more

Slide 2

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Destructive Plate Margins
May also be called convergent
plate margins.
What makes them converge?
There are 3 types of destructive
plate margins depending on
what types of plate are
· Oceanic v oceanic
· Oceanic v continental
· Continental v continental
Each will produce different
hazards and rocks.…read more

Slide 3

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Golden Rule 1
Why do plates/rocks melt:
1. Because the temperature has increased.
2. Because the pressure is decreased.
3. Because it is saturated in water.
If one or more of these situations exists then
the plate/rock will melt.…read more

Slide 4

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Golden Rule 2
What kind of magma is produced when a plate/rock melts?
Remember how we classify igneous rocks.
· Acid: > 66% quartz rich
· Intermediate: 52 ­ 66 %
· Basic: 44 ­ 52% quartz poor
· Ultrabasic: < 44%
Quartz is one of the first minerals to melt, so
When the initial magma melts the one it produces will be
richer in SiO2 and so will move towards the acid end of the
If you melt an ultrabasic rock it will produce a basic magma.
If you melt a basic rock the magma will be more intermediate.…read more

Slide 5

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Golden Rule 3
The more SiO2 in a magma the more explosive will be
the volcanic eruptions.
Because the magmas are more viscous/sticky.
Gasses come out of solution when a magma reaches
the surface (P drops) but they cannot escape easily.
They therefore expand putting pressure on the magma
Eventually the P is so great that the top/plug is blown
off or the side slips and a violent eruption occurs.…read more

Slide 6

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Oceanic v Oceanic collision
The features/landforms:
· Subduction zone: describes the
whole area where subduction is
taking place.
· Ocean Trench: is the deep valley
formed in the ocean floor as the
subducted plate bends.
· Benioff zone: zone of earthquakes
set off by the solid lithospheric
plate forcing it's way through the
· Island Arc: An arc of islands
running parallel to the
trench/subduction zone created
by volcanic activity fed by magma…read more

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