Transcript Document

The Story of Plate Tectonics
November 12, 2013
Last Week We Learned
• Continental Drift
• Why plate tectonics
move – convection
cells (like a lava lamp)
• Think back to density
Convection Cells in the Mantle
• Lithosphere: the solid outer
layer of the Earth that consists
of the crust and the rigid
(unable to bend) upper part of
the mantle
• Asthenosphere: the solid,
plastic layer of the mantle
beneath the lithosphere; made
of mantle rock that flows very
slowly and allows tectonic
plates to move on top of it
• Play movie at 3:57
Page 5 of ESRT
There are four types of plate boundaries:
1. Divergent boundaries -- where new crust is generated as
the plates pull away from each other.
2. Convergent boundaries -- where crust is destroyed as one
plate dives under another.
3. Transform boundaries -- where crust is neither produced
nor destroyed as the plates slide horizontally past each other.
4. Plate boundary zones -- broad belts in which boundaries
are not well defined and the effects of plate interaction are
unclear
Divergent Plate
Boundaries
• The Mid-Atlantic
Ridge, which
splits nearly the
entire Atlantic
Ocean north to
south, is probably
the best-known
and most-studied
example of a
divergent-plate
boundary.
Convergent Plate
Boundaries
3 Types of Convergent Boundaries
Ocean to Continent
Ocean to Ocean
Continent to Continent
• The
convergence of
the Nazca and
South
American
Plates has
deformed and
pushed up
limestone
strata to form
towering peaks
of the Andes
• The 6,000km-plus
journey of
the India
landmass
(Indian
Plate)
before its
collision
with Asia
(Eurasian
Plate)
about 40 to
50 million
years ago
Transform Boundaries
• The Blanco,
Mendocino,
Murray, and
Molokai
fracture
zones are
some of the
many
fracture
zones
(transform
faults) that
scar the
ocean floor
and offset
ridges
The San Andreas fault
zone, which is about
1,300 km long and in
places tens of
kilometers wide, slices
through two thirds of
the length of
California. Along it,
the Pacific Plate has
been grinding
horizontally past the
North American Plate
for 10 million years, at
an average rate of
about 5 cm/yr
Hotspots
Regions of earthquake and volcanic
activity which do not occur along
plate boundaries
• The vast majority of earthquakes and volcanic eruptions
occur near plate boundaries, but there are some
exceptions
• Map of part of the Pacific basin showing the volcanic trail
of the Hawaiian hotspot-- 6,000-km-long Hawaiian RidgeEmperor Seamounts chain