Transcript Plate Tectonics

Chapter 10.2
Plate Tectonics
Putting It All Together ...
Plate Tectonics
Plate Tectonics –the theory that combines
elements of continental drift and seafloor
spreading into a more far-reaching explanation
that not only explains that continents and ocean
basins move, but explains how they move.
http://www.youtube.com/watch?v=6CsTTm
vX6mc
http://www.youtube.com/watch?v=6CsTTmvX6mc
The Lithosphere and the Asthenosphere
 Lithosphere – the Earth’s crust (both oceanic and
continental) combined with the rigid, upper mantle that
forms the outer shell of the Earth.
 Asthenosphere – the “plastic” (i.e. It flows.), lowerupper mantle directly underneath the lithosphere. The
asthenosphere is plastic because of the pressure on it
from the lithosphere above.
The less dense, lithospheric plates, including the oceanic
and continental crust, “float” on the more dense, “plastic”
asthenosphere directly below.
Earth’s Crust …
Its Not All Created
Equally!!!
 Oceanic Crust – the Earth’s crust under the oceans that
makes up the ocean basins (ranges from 5 to 10 km thick).
 Continental Crust – the Earth’s crust that makes up the
continental landmasses (ranges from 15 to 80 km thick).
Ocean crust is made of a more dense material than continental
crust.
Plate Tectonics
 According to Plate Tectonics, the Earth’s crust is
broken up into a series of at least 15 constantly moving
plates that interact at their boundaries in order to form
and constantly reshape the Earth’s surface.
How do we know that plates are there?
Two Major Surface Features That Show Border Tectonic Plates are:
1. Mountain Ranges
2. Deep Trenches
When there is movement along a plate boundary, an earthquake may
occur (http://earthquake.usgs.gov/eqcenter/index.php).
A well-known feature that may help identify a plate boundary is a
volcano (ex. the volcanoes of the Pacific Ring of Fire).
Plate Tectonic Action …
Types of Lithospheric Plate Boundaries
 Divergent Boundaries - two plates are moving away from each other.
 Convergent Boundaries - two plates coming together and colliding.
 Transform Fault Boundaries - two plates sliding past one another
and grinding.
http://www.thetech.org/exhibits_events/online/quakes/plates/divergent.html
Divergent Boundaries
At these divergent boundaries, magma upwells between the two plates
as they diverge. Most of these plates are ocean ridges (ex. a MidOcean Ridge).
Click below to learn more about divergent boundaries.
file://localhost/Volumes/Faculty_Groups/Science/Earth Science/MU Earthquake Wkshp/EarthScope
CD/3_Animations & Movies/Plate Interaction_Converge Diverge Transform/Plates
Diverge_Extension/DivergentPlateMargin.mov
Convergent Boundaries … Type 1
The first type of convergent boundary is a subduction zone.
At a subduction zone, a denser, ocean plate is forced beneath a less
dense, continental plate. As the ocean plate moves down towards the
mantle, it melts, causing an upwelling of magma. This upwelling of
magma produces volcanic mountains (ex. the Andes Mountains in South
America).
file://localhost/
Volumes/Facult
y_Groups/Scie
nce/Earth
Science/MU
Earthquake
Wkshp/EarthSc
ope
CD/3_Animatio
ns &
Movies/Plate
Interaction_Co
nverge Diverge
Transform/Plat
es
Converge_Co
mpression/Sub
duction&Volcan
oes_Narrated.
mov
file://localhost/Vol
umes/Faculty_Gr
oups/Science/Eart
h Science/MU
Earthquake
Wkshp/EarthScop
e
CD/3_Animations
& Movies/Plate
Interaction_Conve
rge Diverge
Transform/Plates
Converge_Compr
ession/Subductio
n&VolcanoesUCSB.mov
Click below to learn more about convergent boundaries.
Convergent Boundaries … Type 2
The second type of convergent plate boundary occurs when two
continental plates converge. Since the two plates have similar
densities, rather than one going under the other, the crumple, fold,
and uplift forming a mountain range (ex. the Himalayas in Asia).
file://localhost/Volumes/Faculty_Groups/Science/Earth Science/MU
Earthquake Wkshp/EarthScope CD/3_Animations & Movies/Plate
Interaction_Converge Diverge Transform/Plates
Converge_Compression/SubductionW:ContCollision_UCSB.mov
Convergent Boundaries … Type 3
The third type of convergent plate boundary occurs when two
oceanic plates converge. One plate is subducted under the other,
forming a deep trench. The subducted plate melts and an island
chain, called an island arc, forms (ex. the Japan in Asia).
Transform Fault Boundaries
At these transform fault boundaries, rough spots may cause sudden
spurts in tectonic activity (i.e. earthquakes) followed by relatively no
activity (ex. the San Andreas Fault in San Francisco, CA).
How Plates Move … Convection Cells
Currently, scientists believe that plates move because of
convection currents that occur deep within the Earth.
Like a pot of boiling water bubbling on a stove,
magma warms, becomes less dense, and upwells, and is in
turn replaced by cooler, more dense, sinking material.
This movement, called a convection cell, appears to be
greatest at plate boundaries and may explain the
movements of plates at those locations.
Cold fluid
Warm fluid
How Plates Move … Ridge Push/Slab Pull
Ridge push - as the cooling lithosphere sinks
at a ridge, the warmer asthenosphere below
pushes on the under side of the plate as it
flows out and away from the ridge.
Slab Pull - as the leading edge of a subducting
lithospheric plate is pulled downward, it pulls the
rest of the plate down with it.
Ridge push
Slab Pull
The End
All images came from Google and are for educational purposes only!!!