Transcript Subduction Zones

Earth Structure
• Basic layers
• Layered surface
structure
• Spreading centers
• Subduction zones
• Hot Spots
• Transform faults
• Evidence
• Animations
Surface Layer Structure
All plate motions can
be described by
thinking about the
movement of plates on
a sphere.
Spreading Centers
Spreading centers form the longest mountain chain in the world, almost
60,000 km. They are areas of recently formed ocean crust, and have
reasonable levels of shallow seismicity.
Subduction Zones
Note that Earth is
density stratified, that
is, each deeper layer
is denser than the
layer above.
At the Peru-Chile Trench,
the oceanic lithosphere is
much denser than the
continental lithosphere, so it
sinks down into the mantle
Subduction zones are areas where
plates collide, usually resulting in
very deep earthquakes.
Ocean islands and basins can
both be created and
destroyed. Destruction
occurs when two pieces of
continental lithosphere or
island arc collide: they
accrete to each other and the
basin between is destroyed.
This process also brings old
seafloor (ophiolites) up onto
continent edges.
Hot Spots
Hot spots are areas of
mantle “plumes” where hot
material is rising to the
surface from deep within
the mantle. Plate
movements over a hot spot
form island chains, such as
the Hawaiian IslandEmperor Seamount Chain
in the Pacific Ocean.
Transform Faults
Transform faults form connections
between spreading centers and subduction
zones -- they are where plate boundaries
are moving in opposite, but parallel
directions.
Pacific NW has it all!
• 5 plates
• Subduction zones
• Spreading center (JdF Ridge)
• Transform faults
• Ophiolites (Olympics)
• Deep & shallow earthquakes
• Subduction volcanoes
• NEPTUNE - proposed regional
cabled observatory - see
http://www.neptune.washington.edu
Plate Tectonics: Topography
Plate Tectonics: Volcanoes
Plate Tectonics: Earthquakes
Plate Tectonics: Seafloor Age
Magnetic anomalies remain from
switch in magnetic polar
direction over time...left distinct
pattern on both seafloor and
some rocks on continents.
The Integrated Picture
The breakup of
Pangaea, a “Super
Continent” is
responsible for the
current plate
configuration.
Plate Motions through time