Download Plate Tectonics 10.2

Plate Tectonics
10.2
Objectives
Summarize the theory of plate tectonics.
Identify and describe the three types of plate
boundaries.
Identify the causes of plate movement.
Theory of Plate Tectonics
• By end of 1960s evidence supporting continental
drift and sea-floor spreading led to the
development of a theory called plate tectonics.
• Plate tectonics: Theory that Earth's outer shell is
divided into several plates that are in motion
(glide) over the mantle
• Helps explains why and how continents move and
is the study of the formation of features in Earth’s
crust
PLATE TECTONICS
the surface of the Earth is made of rigid plates

Size and position of plates can change over
time

PLATE BOUNDARIES Edges of plates, where
two plates “float” side-by-side, is where
geologic activity takes place

Plates movement is from convection currents
deep in the mantle
World Plates
The Crust
• This is where we live!
• The Earth’s crust is made of:
Continental Crust
- thick (10-70km)
- buoyant (less dense
than oceanic crust)
- mostly old
-Rich in silica
Oceanic Crust
-thin (~7 km)
- dense (sinks under
continental crust)
- young
-Rich in Fe & Mg
• 5 structural layers
–
–
–
–
–
Lithosphere
Asthenosphere
Mesosphere
Outer core
Inner core
• 3 Compositional Layers:
– Core
– Mantle
– Crust
Structure of the Earth
• Geophysical surveys: seismic, gravity, magnetices,
electrical,
– Acquisition: land, air, sea and satellite
– Geological surveys: fieldwork, boreholes, mines
How do we know what the Earth is
made of?
What are tectonic plates made of?
• Plates are made
of rigid
lithosphere.
– Consists of the
crust and upper
mantel
What lies beneath the tectonic plates?
• Below the
lithosphere (which
makes up the
tectonic plates) is
the asthenosphere.
– Lower part of mantel
– Mantel has molten
rock (magma)
How do we know where plate
boundaries are?
• Scientists identify plate boundaries by
studying data from earthquakes.
– When plates move, shifts occur along boundaries
– Sudden movements are called earthquakes
• Frequent earthquakes in given location are evidence of
a plate boundary
• The locations of volcanoes can also help
identify the locations of plate boundaries.
Earthquakes
There are thousands of small earthquakes every day
“Strong” earthquakes (~M7) occur once a month. >M8 occur about once/year.
Where are the deepest earthquakes?
For earthquakes of the past 2 weeks, go to http://www.iris.edu/seismon/
Earthquakes & Plate Boundaries
Notice that the earthquakes coincide with plate boundaries,
and the deepest quakes (blue) are in subduction zones.
Question: Where would you expect to see volcanoes?
Create your own maps at http://www.iris.edu/quakes/maps.htm
Modified from USGS Graphics
Volcanoes & Plate Boundaries
This map shows that locations of volcanoes (ones above sea
level) also tend to occur along the plate boundaries
Modified from USGS Graphics
Tectonic Plates
How fast are the plates moving?
Plates move 1-10 centimeters per year (≈ rate of fingernail growth).
Fingernail growth plotted: http://jclahr.com/science/earth_science/thumbnail/index.html
Modified from USGS Graphics