Plate Tectonics
Not a form of Dubstep
I. Plate Tectonics –
Relatively new theory
(1929) explaining
movements of earth’s
lithosphere. Helps
explain the following.
Alfred Wegenercirca 1931
A. Locations of
volcanoes, faults,
earthquakes and
mountains.
B. Origin of most
landforms and
ocean floor
features.
C. How continents and
ocean floor formed
and why they are
different.
D. Continuing changes
of Earth’s surface.
E. Distribution of past
and present life on
earth.
II. Evidence
supporting
continental drift.
A. Accurate maps
began to suggest
the continents “fit”
together like a
puzzle.
- Rock sequences
match along
Corresponding
coastlines.
B. Measuring the Age of
the ocean floor
Confirmed that the
seafloor was spreading.
-Newer near Oceanic
ridges and becoming
older as one moves
away (from ridges).
-Heat flow also
DECREASES as one
moves away from the
oceanic ridges
C. Fossils Provide
evidence as
well.
1. Tell us
relative age of
seafloor.
2. Show similar
organisms on
once joined
coasts.
3. Provide hints
about past
climates.
D. Continental drift
was confirmed
by the location
of magnetic
poles through
geologic time.
1. Magnetite – Contained in nearly all igneous rock.
Is naturally magnetic.
-So, while still magma (liquid), magnetite aligns
with polar magnetism.
2. Studying
alignment of
Magnetite around
globe indicated
poles have
“wandered”
through time.
a. However, the wandering curve observed on
Eurasia and America were slightly different.
-There can be only one pole at a time
-So the crust had to have moved (continental
drift)
E. Seafloor magnetic pattern
1. Magnetic fields are symmetrical and parallel
to the oceanic ridges.
2. Every new “stripe” of seafloor created at
the Oceanic ridge, has a unique magnetism.
So we get banding.
III. Revisit Continental and Ocean crust.
A. Isostasy – explains why continent floats and
ocean floor sinks.
- While much more complicated it is
basically the principal of bouyancy.
B. Continental Crust –
1. Thick
2. Sedimentary rock…Granite (mostly)
3. Less dense.
4. Floats like a marshmallow.
C. Oceanic crust.
1. Thin
2. Dense
3. Made of igneous rock (basalt from volcanic
ridge)
4. Sinks like brick.
D. Remember the
Lithosphere?
- Physical, outermost
division of the earth
layers.
-**Contains mostly
Crust, but also a little bit
of Mantle (from the
chemical divisions).
IV. Processes
A. Convection
cells – The
Engines for
movement of
Earth’s plates.
1. Caused by
heating and
cooling Mantle.
2. Fueled by
Radioactivity in
the mantle.
3. Hot mantle rises
at ridges (eg.
Mid-Atlantic
ridge..a plate
boundary.), cools
as it moves away
from ridge and
sinks at Trenches
(a different kind
of boundary like
Mariana trench).
B. Hotspots. – caused by
huge plumes of hot
magma within the
mantle.
1. The crust moves over
these and eruptions
through time leave trails
a. Hawaiian islands are
an example.
b. Yellowstone
national park is
another.
2. Some found under continental masses.
3. Most often associated with Oceanic Ridges.
V. Plate Boundaries.
A. Three types of movement at plate
boundaries (Divergent, Convergent,
Transform)
1. Divergent plate boundaries
a. An example is the crest of the midocean ridge.
b. this is where new crust is being formed and
the plates are moving apart.
c. A rift valley is formed at continental
divergent boundaries. The Red Sea is an
example.
2. Convergent Plate boundaries
a. Deep sea trenches and mountain ranges are
examples of features found at convergent
boundaries (eg. Himalayan mts. Or Mariana
Trench) Rocky Mountain Link (Nat. Geo)
Age of the seafloor and plate convergence directions in the epicentral area of the 2004 Sumatra–
Andaman earthquake.
Kanamori H Phil. Trans. R. Soc. A 2006;364:1927-1945
©2006 by The Royal Society
b. At Oceanic-oceanic convergent plate
boundaries Volcanic Island Arcs often form.
c. At Oceanic-Continental convergent
boundaries, Andesitic volcanoes often form.
THE END
No…Wait……ask me about Moment
Magnitude.
And The Red Sea