Download Day 7 Presentation - Earthquakes and Plate Tectonics

Earthquakes and Plate Tectonics
Global Problems in Geology
Distribution of Continents
Mid-ocean Ridges
Trenches
Orogenic Belts
• Deformation
• Metamorphism
• Volcanism
• Earthquakes
Development of Continental
Drift
• Lots of people had noticed that the
coastlines of Africa and South America are
similar
• Frank Taylor (1910)
• Alfred Wegener (1912) Die Entstehung
Der Kontinente Und Ozeane
Jigsaw-Puzzle Fit of
JigsawContinents
• Continental Fit
Fit of
Continents
Across the
Atlantic
Atlantic 65 m.y. ago
Present Day Atlantic
Wegener’s
Theory
Theory of Plate Tectonics
Plate Tectonics
Plate Boundaries
Causes of Plate Tectonics
What is Plate Tectonics
• The Earth’s crust and upper
mantle are broken into
sections called plates
• Plates move around on top of
the mantle like rafts
The Lithosphere
The crust and the upper layer of the
mantle together make up a zone of rigid,
brittle rock called the Lithosphere.
The Asthenosphere
The asthenosphere is the
semi-rigid part of the
middle mantle that flows
like hot asphalt under a
heavy
weight.
Plate Tectonics
• The Earth’s crust is divided into 12 major
plates which are moved in various directions.
• This plate motion causes them to collide, pull
apart, or scrape against each other.
• Each type of interaction causes a
characteristic set of Earth structures or
“tectonic” features.
• The word, tectonic, refers to the deformation of
the crust as a consequence of plate
interaction.
The Lithospheric Plates
The crust of the Earth is broken into many pieces
called plates. The plates "float" on the soft, semirigid asthenosphere.
What is the Lithosphere
Lithosphere?
?
• The crust and part of the upper
mantle = lithosphere
–100 km thick
–Less dense than the material
below it so it “floats”
What are tectonic plates made of?
• Plates are
made of rigid
lithosphere.
The lithosphere is made
up of the crust and the
upper part of the mantle.
What lies beneath the tectonic plates?
• Below the
lithosphere
(which makes
up the tectonic
plates) is the
asthenosphere.
What is the Asthenoshere
Asthenoshere?
?
• The plastic layer below the
lithosphere = asthenosphere
• The plates of the lithosphere
float on the asthenosphere
2 Types of Plates
• Ocean plates - plates below
the oceans
• Continental plates - plates
below the continents
Plate Boundaries
Three types of plate boundary
• Divergent
• Convergent
• Transform
Divergent Boundaries
• Boundary between two plates
that are moving apart or rifting
• RIFTING causes SEAFLOOR
SPREADING
Divergent Boundaries
• Divergent boundaries are also present
– under continents during the early stages
– of continental breakup
Beneath a
continent,
magma
wells
up, and
the crust is
initially
elevated,
stretched
and thinned
Rift Valley
• The stretching produces fractures and rift
valleys.
During this
stage,
magma
typically
intrudes into the
fractures
and flows onto
the valley floor
Example: East
African Rift
Valley
Features of Divergent
Boundaries
• Mid-ocean ridges
• rift valleys
• fissure volcanoes
Divergent Boundaries
• Spreading ridges
– As plates move apart new material is erupted to
fill the gap
Convergent Boundaries
• Boundaries between two
plates that are colliding
• There are 3 types…
Continent--Continent Boundary
Continent
• Two approaching continents are initially
– separated by ocean floor that is being
subducted
– under one of them, which, thus, has a volcanic
arc
• When the 2 continents collide
Its
density
– the
continental lithosphere cannot subduct
is too low,
although
one
continent
may partly
slide under
the other
Type 1
• Ocean plate colliding with a
less dense continental plate
• Subduction Zone: where the
less dense plate slides under
the more dense plate
• VOLCANOES occur at
subduction zones
Andes Mountains,
South America
Type 2
• Ocean plate colliding with
another ocean plate
• The less dense plate slides
under the more dense plate
creating a subduction zone
called a TRENCH
Aleutian Islands, Alaska
Type 3
• A continental plate colliding
with another continental plate
• Have Collision Zones:
–a place where folded and thrust
faulted mountains form.
The 6,000-km-plus journey of the India
CARTOON SECTION SHOWING INDIA ASIA COLLISION
Collision Belts
Island Arc-Continent Collision Mountain Building
Continent-Continent Collision Mountain Building
Transform Fault Boundaries
• Boundary between two plates
that are sliding past each other
• EARTHQUAKES along faults
San Andreas Fault, CA
Causes of Plate
Tectonics
Convection Currents
• Hot magma in the Earth
moves toward the surface,
cools, then sinks again.
• Creates convection currents
beneath the plates that cause
the plates to move.
Plate Movement
• “Plates” of lithosphere are moved around by
the underlying hot mantle convection cells