Download Plate Tectonics…What`s It All About?

Plate Tectonics…What’s It
All About?
Chapter 7: Plate Tectonics
Earth’s Structure
• The Earth is not just a ball
of solid rock…some parts
are liquid as well
• We can divide the Earth into
3 main layers: crust,
mantle, and core
• The crust can be
continental (thick and less
dense) or oceanic (thin and
more dense)
• The crust and the
uppermost part of the
mantle make up the
lithosphere
• The lithosphere is broken up
into pieces called plates,
which “glide” on the plasticlike asthenosphere
Structure Cont’d
• The asthenosphere
and the mesosphere
together make up the
mantle
• Below the mantle is the
core which has two
parts: inner and outer
• The outer core is liquid
iron and nickel
• The inner core is made
of the same stuff as the
outer core, but is
SOLID because of the
pressure applied by the
layers above it
Tectonic Plates
• The lithosphere is broken up into pieces called plates
• Many are named after continents or bodies of water
• 10 major plates: North American, South American,
African, Antarctic, Eurasian, Nazca, Pacific, IndoAustralian, Indian, Philippine
• Places where these plates meet are called boundaries
• Stress builds up along these boundaries as the plates move,
creating volcanoes and earthquakes
Why Do The Plates Move?
• The Theory of Plate Tectonics states that the Earth’s
lithosphere is divided into tectonic plates that move around
on top of the asthenosphere
• So what is the driving force behind plate movement?
Convection!
• What is convection? When hot, less dense mantle
material rises and cooler, more dense mantle material
sinks. It’s like a huge conveyor belt that carries the plates
with it!
When Plates Collide
•
•
•
A collision between plates creates a convergent
boundary
Compression pushes the plates together
Depending on the type of crust, there are three
possibilities:
1. Continental-continental: crust gets pushed upward to
form mountains (Himalaya Mountains)
2. Oceanic-oceanic: the more dense oceanic plate is pulled
down under the other oceanic plate, creating volcanic
islands (Aleutian Islands, Japan)
3. Continental-oceanic: also called subduction, the more
dense oceanic plate is pulled under the less dense
continental plate, creating trenches and volcanoes
along coastlines (Western coasts of North & South
America)
Divergent and Transform
• Where plates move away from one another due to
tension, a divergent boundary is created. An example
is the Mid-Atlantic Ridge.
• The most common feature at a divergent boundary is a
mid-ocean ridge or rift zone.
• Where plates move past each other horizontally, a
transform boundary is created.
• Shearing is the stress that makes the plates move past
one another, as seen at the San Andreas Fault in
California. Here, the Pacific plate is moving to the
northwest past the North American plate.
• The movement along transform boundaries is rarely
smooth. Instead, there are lots of jerks and jolts along
the way. Sometimes, the plates will get stuck for long
periods of time and then jerk past each other very
suddenly, creating violent earthquakes all along the San
Andreas Fault.