Transcript Slide 1

Plate Tectonics
• Theory of plate tectonics describes the
forces within the Earth that create
continents, ocean basins, mountain
ranges, earthquake belts, volcanoes, etc.
• Lithosphere divided into 8 major plates
• Major interactions of the plate boundaries
results in most of the Earth’s seismic
activity
Folds
• Compressive forces cause rocks to
buckle and fold
• Anticline folds upward
• Syncline folds downward
Folding – formed the Appalachians
In central Pennsylvania, the segment known as the Valley and Ridge has
very distinctive topography: the ridges are curved, some shaped almost
like an arrowhead, and have generally uniform elevations (not pointed or
irregular like many western mountains).
Faults
• A fault is a large crack in the Earth's crust
where one part of the crust has moved
against another part.
• A fault can be described in terms of its dip
and strike. The strike is the direction of its
movement on surface of the earth. The
dip is a measure of how steeply the fault
plane slopes.
Dip-slip faults
• include both normal and reverse faults
• The “slip” occurs along the dip (fault plane)
direction. The slip is either a movement
upwards (reverse fault) or downwards
(normal fault).
Reverse Fault
• Caused by compression forces
• Hanging wall pushes up over footwall
Reverse faults
•
The Sierra Madre fault zone of
southern California is an example
of reverse-fault movement. There
the rocks of the San Gabriel
Mountains are being pushed up
and over the rocks of the San
Fernando and San Gabriel
valleys. Movement on the Sierra
Madre fault zone is part of the
process that created the San
Gabriel Mountains.
Thrust Fault
• Reverse fault with low angle
• Eastern flank of the Sierra Nevada, California
Normal Faults
• Sierra Nevada fault zones are examples of highangle normal faults where the hanging wall slips
down relative to the footwall
The Caldera. Long Valley Caldera a 15- by 30-km oval-shaped depression located 20 km south of
Mono Lake along the east side of the Sierra Nevada in east-central California.
Transform Faults
• Transform faults are also called strike-slip
faults. Here the “slip” or movement occurs
along the strike (lateral direction). The
fault plane is usually vertical, so there is
no true hanging wall or footwall
• The lateral or horizontal forces carry the
walls alongside each other
Horizontal (Transform) Fault
Photo of the San Andreas Fault near Gorman California, showing rocks of the Pacific Plate on
the left and the North American Plate on the right. Photograph copyright by David Lynch.
The San Andreas fault, with a length of more than 800 miles (1,200 kilometers), is the
longest fault in California, and one of the longest in North America.
On January 9, 1857 at 8:20 am, an earthquake with a estimated magnitude of 8.0
occurred just north of Carrizo Plain. This quake caused nearly 30 feet (9 m) of lateral
offset within Carrizo Plain, and ruptured the surface along the trace of the fault for about
220 miles (350 km). It was one of the greatest earthquakes ever recorded in the United
States.
Interesting facts about the San Andreas fault:
The waters of Tulare Lake were thrown upon its shores, stranding fish miles
from the original lake bed. The waters of the Mokelumne River rose well over
its banks, reportedly leaving the bed dry in places. The Los Angeles River was
reportedly flung out of its bed, too.
Since that event, this portion of the San Andreas fault has been locked in place seismically quiet for decades, however it is obvious a similar magnitude quake
today would cause billions of dollars of damage to Los Angeles, the southern
San Joaquin Valley, and Antelope Valley.
Retrieved from U.S. Department of the Interior – Bureau of Land
Management. 5-02-07
http://www.blm.gov/ca/st/en/fo/bakersfield/Programs/carrizo/geology.html
Plate Boundaries
• Where lithospheric formation and
destruction occur
• Plates move due to thermal convection
currents in plastic-like asthenosphere
• Three types: convergent, divergent,
transform fault
Divergent Boundary
• Tensional forces cause plates to move
apart
• Hot molten rock from asthenosphere is
less dense and rises, creating new
lithosphere
The Mid-Atlantic Ridge marks where two continents once were
one.
Continental divergence creates oceans. Also the location of sea floor
spreading.
Mid-Atlantic Ridge
Rifts and Rift Valleys
Convergent Boundaries
• Plates moving towards each other due to
compressional forces
• One plate drops below other plate, or
folding/faulting occur
• Regions of great mountain building
• Three subgroups: oceanic-oceanic,
oceanic-continental, continentalcontinental
Oceanic-oceanic convergent zones are mostly hidden under the sea. Only
arcs of volcanic islands mark them, made of dark and heavy basaltic lavas.
The western Pacific Ocean is full of these—from north to south they include
the Aleutian, Kuril, Japanese, Ryukyu, Izu-Bonin, Philippine, Mariana,
Solomon and Tonga-Kermadec island arcs. In the Atlantic are the Caribbean
and South Sandwich island arcs. In the Indian Ocean is the tangle of arcs that
makes up the Indonesian archipelago.
Characterized by earthquake and volcanic activity.
Aleutian Islands
Marianis Trench
Oceanic-continental convergent zones are the classic case. The oceanic plate
undergoes subduction and the volcanic arcs arise on land …. The west coast of
the Americas is the major example, with volcanic zones in Alaska, the Pacific
Northwest states, and a continuous stretch from Central America to Tierra del
Fuego ("land of fire"). Italy, Greece, Kamchatka and New Guinea also fit this
type.
Characterized by earthquake and volcanic activity.
• In Northern California, the collision of the
Pacific and Juan de Fuca plates have
given rise to the Cascade mountains and
Mount Saint Helens eruption in 1980
• the subduction of the Pacific plate under
the Eurasian plate has created the
Japanese islands and volcanoes
Cascade Mountains
• The "Ring of Fire" is an arc stretching from
New Zealand, along the eastern edge of
Asia, north across the Aleutian Islands of
Alaska, and south along the coast of North
and South America. The Ring of Fire is
composed over 75% of the world's active
and dormant volcanoes.
• Ring of Fire is located at the borders of the
Pacific Plate and other major tectonic
plates.
• As the Pacific Plate collides with another
tectonic plate, a great amount of energy is
produced. This energy is transformed into
heat, and can heat the rock into magma.
This rises to the surface through
volcanoes. When it reaches the surface
the magma is called lava.
• In addition to creating heat, the Pacific
Plate is actually sliding down below the
other tectonic plate, creating what is called
a subduction zone
• About 10 percent of the world’s active
volcanoes are located in the United States
Andes Mountains
• The subduction of the Nazca Plate below
the South American Plate has led to the
creation of the Andes mountain range
• There are also many active volcanoes in
this area
Andes Mountains
(Western side of South America)
Continent-continent convergent zones are tectonic sumo wrestling
matches in which neither plate is subducted, because continental rock is
too light to be carried very far into the dense mantle (about 150 km down at
most). Instead the continental crust crumples into thick knots—tectonic
mountain ranges—exposing deep-seated granites and gneisses with
relatively little volcanism. The continental crust may also be cracked in
pieces and shoved aside. Both of these responses are seen to perfection in
the great foldbelt that stretches from Turkey to China. There the African,
Arabian and Indian plates are moving northward into the Eurasian plate,
respectively raising the Anatolian, Makran (Iranian) and Himalayan/Tibetan
highlands.
Continental-Continental Collision
• No drastic difference in density so no
subduction occurs
• Preceded by an oceanic-continental
collision
• Compression causes plates to buckle and
fold
• Earthquakes are characteristic, but
volcanoes are NOT
Himalayas
(due to India pushing up against Asia)
Himalayas
SOURCES
•
http://geography.about.com/gi/dynamic/offsite.htm?zi=1/XJ&sdn=geography&cdn=education&tm=9&gps=115_28_
1020_568&f=00&su=p897.1.336.ip_&tt=2&bt=0&bts=1&zu=http%3A//vulcan.wr.usgs.gov/Glossary/PlateTectonics/
Maps/map_plate_tectonics_world.html
•
•
•
http://geography.about.com/cs/earthquakes/a/ringoffire.htm
http://geology.about.com/library/bl/maps/blplatetypesehem.htm
http://geology.about.com/library/bl/blnutshell_convergence.htm