Transcript Theory of Plate Tectonics IV

Plate Tectonics
 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
Oceanic - Continental
Oceanic - Oceanic
Continental - Continental
When the leading edge of a plate capped with continental
crust converges with oceanic crust:
The less dense continental material (granitic) remains
“floating”, while the more dense oceanic slab (basaltic)
sinks into the asthenosphere.
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.
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.
Prior to a continental collision, the
landmasses are separated by oceanic crust,
formed during an earlier episode of seafloor spreading.
As the continental blocks converge, the
intervening sea floor is subducted beneath
one of the plates.
The decending oceanic slab generates either
a volcanic arc (on one of the continents) or
an island arc (at some distance into the
ocean).
Erosion of newly formed volcanic rocks adds
sediment to the continental margins.
As the continents
collide, the
sediments are
squeezed, folded,
and deformed.
This process results in a new mountain range
composed of deformed and metamorphosed
sedimentary rocks and fragments of volcanic rocks.
Plate Tectonics
Earthquakes
Location, year and number of fatalities (in parenthesis)
for earthquakes in India in the past 200 years. (From
Bilham and Gaur, 2000).
Magnitude 7.7
Gujarat, India
January 26, 2001
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
W. W. Norton. Modified from Cox and Hardt, 1986.
The Appalachian
Mountains (along the
eastern seaboard of
North America) were
formed by a continental
collision in which Africa
and Europe collided with
North America about
250-350 million years
ago.
From “Written in Stone” by
Chet Raymo and Maureen Raymo
Many of the geological
structures found in and
around the Boston area
were formed during the
continental collision in
which Africa and Europe
collided with North
America about 250-350
million years ago.
From “Written in Stone” by
Chet Raymo and Maureen Raymo
From “Written in Stone” by Chet Raymo and Maureen Raymo
From “Written in Stone” by Chet Raymo and Maureen Raymo
 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
1906 San Francisco
Earthquake
1906 San Francisco
Earthquake
This picture, taken near
Bolinas in Marin County by
G.K. Gilbert, shows a fence
that was offset about 8.5
feet along the trace of the
fault (from Steinbrugge
Collection of the UC Berkeley
Earthquake Engineering
Research Center ).
“Elastic
Rebound”
Theory of
Earthquakes
Earthquake Probabilities ???
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
October 17, 1989 Loma Prieta
(“World Series”) California
Earthquake.
Collapse of the Cypress Street
elevated section of I-880
(near downtown Oakland).
Izmit, Turkey
August 17, 1999
Magnitude 7.4
Plate Tectonics
Northridge, CA 1994
Plate Tectonics
Earthquakes
W. W. Norton. Modified from Cox and Hardt, 1986.
1975-2002
Magnitude  3