Transcript The Theory of Plate Tectonics

The Theory
of Plate Tectonics
Plate Tectonics

The inner structure of the
Earth has different layers:
is made of two layers
•Core (Inner and outer)
•Mantle
•Crust (Oceanic and
Continental)
The Earth’s interior
1000 C
4000 C
7000 C
The Lithosphere (crust and
outer mantle) floats on the
Asthenosphere (fluid
layer).
 The Lithosphere is broken
up into tectonic plates.

The Plates
* Hover over for names
The plates move in relation
to each other and form
three different types of
plate boundaries:
•Convergent
•Divergent
•Transform
How does it work?
Plates move due to convection
currents in the Astenosphere.
The inner fluids become hotter
than the outer ones. Hot fluids
are less dense than cold ones,
so they ascend while the colder
ones descend. This makes what
we call convection currents.
mantle convection
Heat transfer from the core to the
mantle produces slow convection
of the mantle material
(in the order of centimetres per year)
Mantle convection produces lateral
forces at the boundary between the
mantle and the crust
Lateral forces at the crustmantle boundary push the
crust around – in different
directions – and this leads to
the motion of the plates.
The plates are moving at rates
of cm/year
Kinds of Plate
Boundaries
Convergent
Occurs when plates
collide. There are
three types.
Divergent
Occur when two plates
are moving apart and
new crust is created
by magma pushing up
from the Earth’s
mantle.
Divergent

Divergent boundaries create
the mid-ocean ridges, where
the ocean floor is created.
This process is called Seafloor spreading. As a
consequence, the older rocks
of the ocean floor are always
closer to the continents.
Hydrothermal vents

In mid-ocean ridges, there
are fractures that allow the
sea water to seep down and
get heated by the mantle.
The hot water then forces its
way back up through the
crust and emerges in
hydrothermal vents, or deepsea hot springs.
Hydrothermal vents

The hot water coming from
the mantle has sulfide
minerals dissolved, that will
precipitate when the water
emerges from the vent and
cools. These minerals form
deposits, like the chimneylike black smokers.
Transform
Occur where plates grind past each
other. As a consequence,
earthquakes occur frequently in
these areas.
Transform boundary
Hot Spots

Hot spots are places where a
plume of hot magma rises
from the mantle and forces its
way through the Lithosphere
to form volcanoes. As the
plate moves, new volcanoes
are created. One example are
the Hawaiian Islands.