Download Plate Tectonics - Paul J. Goodenough

Plate Tectonics Notes
Chapter 10
I. Continental Drift
A. Alfred Wegener (1912)
• German Meteorologist
• Continents moved slowly to their current locations.
• Pangaea- the single landmass of Earth that broke apart about
200mya. It means “All Land.”
B. Evidence
1. Puzzle-like Fit
• Coastlines of continents fit together like puzzle pieces.
• Examples: South America & Africa
2. Fossil Clues
• Certain fossils of ancient animals & plants are found on distant
landmasses.
a.) Freshwater/land-dwelling reptile Mesosaurus fossils have been
found on South America & Africa.
b.) Fossils of the ancient plant Glossopteris were found in Africa,
South America, Australia, India, & Antarctica.
3. Climate Clues
a.) Fossils of warm climate plants were found in present-day cold
climates. (Coal)
b.) Rocks deposited by glaciers from the ice ages have been found
in present-day warm climates.
4. Rock Clues
• Similar rock structures are found on different continents
separated by oceans.
a.) Appalachian mountains of the USA are similar to mountains
found in Greenland & western Europe.
b.) Rocks of South America match those in Africa
Main objection to Wegener’s hypothesis was its inability to provide a
mechanism for the movement of the continents.
II. Seafloor Spreading
A. Hypothesis
o Radio waves were used to map the ocean floor.
o Mid-ocean Ridges- underwater mountain ranges.
1. Less dense magma flows sideways dragging the seafloor along.
2. As the seafloor spread apart, magma flows up through cracks in at
the ridge forming new rock.
B. Evidence
1. Drilling: Ocean floor rock samples show that the age of the rock gets older
the further the rock is from the mid-ocean ridge.
2. Magnetism: Changes in the magnetic alignment of the Earth are found in
alternating bands in the seafloor rock.
III. Theory of Plate Tectonics
A. Theory
o Combined theory of Continental Drift & Seafloor Spreading.
o Earth’s crust & upper mantle (lithosphere) are broken into plates and
move around on a plastic-like layer of the mantle (asthenosphere.)
o Seven Major Plates: Pacific (largest), Atlantic, African, North American,
South American, Eurasian, Antarctic plates.
B. Plate Boundaries
1. Divergent Boundaries
– Two plates spread apart.
– Where seafloor spreading occurs.
– New crust is formed.
Example: Mid-Atlantic Ridge
2. Convergent Boundaries
– Two plates come together (collide)
– Oceanic plate will sink under a continental plate (subduction)
producing a deep trench.
Examples: Andes & Cascades
– Two oceanic plates will converge resulting in a volcanic island arc.
Examples: Mariana Islands
– Two continental plates will converge & crumple forming folded
mountains.
Examples: Himalayas, Appalachians, & Alps
3. Transform Fault Boundary
– Two plates slide past each other.
– Move at different rates.
– Also known as strike-slip faults.
Example: San Andreas Fault
C. Causes (Hypothesis)
• Convection Currents
– Hot magma rises in the mantle.
– Magma hits the crust & cools.
– Cooling magma sinks dragging the lithospheric plate with it
(centimeters.)
– Magma sinks into the mantle & reheats.
D. Features Formed by Tectonics
1. Faults
– Cracks in the tectonic plates caused by stress.
– Plate boundaries are also faults.
– Movement along faults cause earthquakes.
2. Volcanoes
• Magma produced by friction during subduction oozes up through the
crust, erupts, & forms volcanoes.
3. Mountains
• Convergent & Divergent boundaries form mountains.
• Process of mountain building is called orogenesis.
a.) Volcanic Mountains
b.) Folded Mountains
o Horizontal rock layers are squeezed from opposite sides,
causing them to buckle & fold.
Examples: Himalayans & Appalachians
c.) Fault-block Mountains
o Huge, tilted blocks of rock that are separated by faults.
Examples: Sierra Nevada
d.) Upwarped Mountains
o Blocks of Earth’s crust are pushed up by forces inside the
Earth. (Domes)
Examples: Rocky Mountains