Transcript 5A_Plate Tectonics Lecturex

Plate Tectonics
Types of
Plate
Boundaries
Divergent
Convergent
Transform
 Plates move apart, resulting
in upwelling of material from
the Mantle to create new sea
floor.
Divergent
 Plates move together,
causing one of the slabs of
lithosphere to be consumed
into the Mantle as it decends
beneath the overriding plate.
Convergent
 Plates slide past each other,
without creating or destroying
lithosphere.
Transform Fault
W. W. Norton. Modified from Cox and Hardt, 1986.
Each plate is bounded by some combination
of types of boundaries.
Directions and Rates of Plate Motion
Upon entering the
hot
asthenosphere,
the plunging plate
(which is relatively
cold) begins to
warm and loses its
rigidity.
New lithosphere is continually being created at spreading
centers:
Since the total surface area of the Earth remains constant,
lithosphere must also be destroyed somewhere else.
Zones of Plate Convergence
When two plates collide, the leading edge
of one is bent downward, allowing it to
descend beneath the other plate.
Three types of convergent plate boundaries:
Oceanic - Continental
Oceanic - Oceanic
Continental - Continental
Oceanic-Continental Convergence
The less dense continental material (granitic) remains “floating”, while
the more dense oceanic slab (basaltic) sinks into the asthenosphere.
A region where an oceanic plate descends into the asthenosphere is
called a subduction zone.
As the oceanic plate slides beneath the overriding plate, the oceanic
plate bends, producing a deep-ocean trench.
Oceanic-Continental Convergence
As the oceanic plate subducts, partial melting
occurs at depth. Magma rises to the surface to
form continental volcanic arcs.
Oceanic-Continental Convergence
Most of this magma will be emplaced in the continental crust
and form intrusive igneous rocks.
The remaining magma will eventually migrate to the surface
as volcanic eruptions and will form extrusive igneous rocks.
Major Volcanoes of the World
Fig. 6.18
W. W. Norton
The Cascade Mountain
Range, in western US, is a
volcanic mountain range that
was formed as a result of
oceanic-continental
convergence.
Eruption of Mount St. Helens in 1980
The Cascade Mountain Range
is a result of the “Juan de
Fuca Plate” subducting under
the western US.
Earthquakes & Volcanoes
Deep earthquakes occur at subduction zones.
The deepest earthquakes occur at depths as great as 700 km
below the surface.
W. W. Norton
Largest Earthquakes Ever Recorded
4. Japan, 2011
Magnitude 9.0
3. Sumatra, 2004
Magnitude 9.1
5. Kamchatka, 1952
Magnitude 9.0
2. Alaska, 1964
Magnitude 9.2
1. Chile, 1960
Magnitude 9.5
The largest earthquake ever
recorded occurred along the
Nazca-South American plate
boundary.
Chile
May 22, 1960
Magnitude 9.5
Berkeley, CA Seismogram
Japan quake of 2011 is the 4th largest earthquake since 1900.
From: www.pbs.org/wgbh/nova/insidenova/2011/03/earthquake-geology.html
Three types of convergent plate boundaries:
Oceanic - Continental
Oceanic - Oceanic
Continental - Continental
Oceanic - Oceanic Convergence
When two oceanic plates converge, one descends beneath the other
initiating volcanic activity (similar to the oceanic - continental case),
but the volcanoes form on the ocean floor rather than on continents.
Dry land emerges from the ocean depths, forming a chain of
volcanic islands called a volcanic island arc.
Examples of island arcs are the island chains of the western
Pacific Ocean, such as Japan.
In the case of Japan, volcanic islands are being created by
the collision of the Pacific plate with the Eurasian plate. The
Pacific plate being subducted beneath the Eurasian plate.
From: www.pbs.org/wgbh/nova/insidenova/2011/03/earthquake-geology.html
The Deadliest Tsunami in History
Sumatra, 2004
Banda Aceh, Sumatra, Indonesia: 2004 Tsunami aerial photos
December 26, 2004
March 11, 2011
Sumatra, 9.1
Japan, 9.0
228,000 fatalities
21,000 fatalities
www.sms-tsunami-warning.com/pages/tsunami-sumatra-2004#.Up0-Z41RbP9
Three types of convergent plate boundaries:
Oceanic - Continental
Oceanic - Oceanic
Continental - Continental
Continental - Continental Convergence
When two plates carrying continental crust
collide, a continental collision occurs.
Continental - Continental Convergence
Continental collisions occur because of the relatively low
density, and thus the buoyant nature, of continental crust
(granitic).
W. W. Norton. Modified from Cox and Hardt, 1986.
India Colliding with Asia
A continental collision occurred when the onceseparated continent of India collided with Asia,
forming the Himalayan mountains.
The Himalayas
This process results in a new mountain range composed
of deformed and metamorphosed sedimentary rocks
and fragments of volcanic rocks.
 Plates move apart, resulting
in upwelling of material from
the Mantle to create new sea
floor.
Divergent
Convergent
 Plates move together,
causing one of the slabs of
lithosphere to be consumed
into the Mantle as it decends
beneath the overriding plate.
 Plates slide past each other,
without creating or destroying
lithosphere.
Transform Fault
Divergent Plate Boundaries