Download Tectonics and Stratigraphy

Tectonics and Stratigraphy
7 Major Plates
• African Plate, covering Africa - Continental plate
• Antarctic Plate, covering Antarctica - Continental plate
• Australian Plate, covering Australia (fused with Indian
Plate between 50 and 55 million years ago) - Continental
plate
• Eurasian Plate covering Asia and Europe - Continental
plate
• North American Plate covering North America and northeast Siberia - Continental plate
• South American Plate covering South America Continental plate
• Pacific Plate, covering the Pacific Ocean - Oceanic plate
What Drives Tectonics?
Convection
• Definition : The cycle of movement in the
asthenosphere that causes the plates of the lithosphere
to move. Heated material in the asthenosphere becomes
less dense and rises toward the solid lithosphere,
through which it cannot rise further. It therefore begins to
move horizontally, dragging the lithosphere along with it
and pushing forward the cooler, denser material in its
path. The cooler material eventually sinks down lower
into the mantle, becoming heated there and rising up
again, continuing the cycle. See also plate tectonics.
What Kind of Boundaries are
Between Plates
• Main Motions
• Convergent Boundaries
• Divergent boundaries
Convergent Boundaries
• 3 Types
- Ocean to Ocean
- Continental to Continental
- Ocean to Continental
Ocean to Ocean
•
One plate is subducted, initiating
andesitic ocean floor volcanism on the
other. It eventually forms an island arc
volcanic island chain with a deep ocean
trench by its side. It is described by a
progression from shallow to deep focus
earthquakes from the trench toward the
island arc. Also a back-arc basin may form
if subduction rate is faster than forward
motion of overriding plate
Ocean to Continental
•
Oceanic plate is dense and more heavey which causes
it to subduct under the Lighter continental plate. It
produces a deep ocean trench at the edge of the
continent. About half the oceanic sediment descends
with the subducting plate; the other half is piled up
against the continent. The Subducting plate and
sediments partially melt, producing andesitic or granitic
magma. This produces volcanic mountain chains on
continents called volcanic arcs and batholiths. Part of the
oceanic plate can be broken off and thrust up onto the
continent during subduction (obduction). Obduction can
expose very deep rocks at the surface. It is
characterized by shallow to intermediate focus
earthquakes with rare deep focus earthquakes
Continental to Continental
• Continental crust cannot subduct, so
continental rocks are piled up, folded, and
fractured into very high complex mountain
systems. It is characterized by shallowfocus earthquakes, rare intermediatefocus earthquakes and practically no
volcanism
Divergent Boundaries
• Divergent bounders where the plates move
away from one another, creating a environment
that seems to stretch, characterized by shallowfocus earthquakes and volcanism. A release of
pressure may causes partial melting of mantle
and produces basaltic magma. This magma
rises to surface and forms new oceanic crust.
When it occurs with oceanic crust (oceanic
ridges) and in continental crust (rift valleys).
Rift Valleys
Mid-Atlantic Ridge
• The Mid-Atlantic Ridge forms part of the global
mid-oceanic ridge system and, like all midoceanic ridges, is thought to result from a
divergent boundary that separates tectonic
plates: the North American Plate from the
Eurasian Plate in the North Atlantic, and the
South American Plate from the African Plate in
the South Atlantic. These plates are still moving
apart, so the Atlantic is growing at the ridge, at a
rate of about 5–10 centimeters per year in EastWest direction.
Stratigraphy and Structure of the
Boundaries
Divergent Boundaries
• Continental to continental: Rift valleys are produced by
tensional tectonic forces which occur at divergent plate
boundaries. Rift valleys typically appear as a
downdropped Graben between a pair of faults, or vertical
Earth movements. Rift valleys are often associated with
and flanked by Volcanoes. The margins of rifts are
commonly uplifted, so that the downfaulting of the rift
floor is associated with the uplift of both margins. Also
inn continental rift valleys the true cross-sectional form is
typically asymmetric, with the rift floors tilted toward the
most elevated flank. Most of the subsidence is controlled
by one border fault system, and most of the internal
faults parallel the dip of the border faults
Con’t
• Ocean to Ocean: Where 2 plates are moving
away from each other, deep rifts are opened
through the crust that allows magma from the
upper mantle to rise to the surface and cool.
Newly differentiated mantle material which
include structures and sediments from and of
basaltic flows, pillows, and breccias; basalt is a
dark, fine-grain, high density igneous rock. All
this up and down involves distorting the crust
several things can happen like fractures, joints,
slips, faults, and folds
• The rocks of the oceanic crust are not older than
200 million years. The material of which the
oceanic crust consists is for the greater part
tholeiitic basalt (this is basalt without olivine).
Basalt has a dark, fine and gritty volcanic
structure.
• The basalts the are from magma or lava when
it reaches are made of the elements silicon,
oxygen, aluminum, iron, magnesium, calcium,
sodium, potassium, phosphorus, and titanium.
Have layers of basaltic rock which are from the
oceanic crust
An Image of basalts called Rowena Gap in Washington/Oregon
Convergent Boundaries
• Also deal with oceanic and Continental
crust
Continental Crust
• The continental crust is the layer of
granitic, sedimentary, and metamorphic
rocks which form the continents and the
areas of shallow seabed close to their
shores, known as continental shelves.
Granitic- A crystalline igneous rock that consists largely of alkali
feldspar (typically perthitic microcline or orthclase, quartz, and
plagioclase (commonly calcic albite or oligoclase). finer-grained rocks
of this composition include rhyolite and aplite, and coarser-grained
ones are granite pegmatite (Hart 1998).
Over View
Subduction
• Have oceanic sinking under the
continental
• Making basalt on the bottom with granite
compositions on top
• Main featured are mountains with volcanic
activity
• Magma rising from the mantle
Colliding plates
• Massive pilling up
• Granite formations
• Mountains
• Examples is the Himalayas
Cited Work and References
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Websites
U.S. Geological Survey Special Publication:
wc.pima.edu/.../setting/geology_platetec.htm
http://wc.pima.edu/~bfiero/tucsonecology/setting/images/
plates_ooc01.gif
gpc.edu/~pgore/Earth&Space/GPS/platetect.html:
Pamela J.W. Gore
Georgia Perimeter College
http://www.cotf.edu/ete/modules/msese/earthsysflr/plates
3.html
http://www.cotf.edu/ete/modules/msese/elevator.html
http://mediatheek.thinkquest.nl/~ll125/en/crust.htm
Con’t
• Kious, W.J., and Tilling, R.I., 1996, THIS DYNAMIC
EARTH--THE STORY OF PLATE TECTONICS: U.S.
Geological Survey Special Publication, 77 p
• Courtillot, Vincent and Vink, G.E., 1983, HOW
CONTINENTS BREAK UP: Scientific American, v. 249,
no. 1, pp. 42-49
• Bird, J.M., ed., 1980, PLATE TECTONICS (revised ed.):
Washington, D.C., American Geophysical Union, 986 p.