Download Plate Tectonics

Plate Tectonics
6.E.2.2 Explain how crustal plates and ocean basins are formed, move
and interact using earthquakes, heat flow and volcanoes to
reflect forces within the earth.
Plate Tectonics Theory
• The lithosphere is divided into a number of large and small ___________ and the
plates are floating on the mantle.
• Lithosphere = the Earth’s _________ plus the upper portion of the mantle layer.
How Plates Move
• A Canadian scientist, J. Tuzo Wilson, claimed the lithosphere is broken into
separate sections called __________. These plates fit together along cracks in the
lithosphere.
• Scientists realized that the continental drift idea could be explained by sea floor
spreading. Wilson took what these scientists knew and combined it with his idea
about Earth’s plates into a single theory.
• A _______________ theory is a well-tested concept that explains a wide range of
observations.
• Sea floor spreading provides the driving mechanism for movement
• However, it is not the continents that are moving, but the “plates” of lithosphere
“floating” in effect on the asthenosphere
• The lithosphere is made up of about 20 plates which move relative to each other
in several ways
• The theory of ___________________________ states that pieces of Earth’s
lithosphere are in slow, constant motion, driven by convection currents in the
mantle. The theory of plate tectonics explains the formation, movement, and
subduction of Earth’s plates.
“Plates” of lithosphere are moved around by the underlying hot mantle convection cells
Convection & Convection Currents
• ________________ is heat transfer by the movement of currents within a fluid.
During convection, heated particles of fluid begin to flow. This flow transfers heat
from one part of the fluid to another.
• Heat from the core and the mantle itself causes convection _____________ in the
mantle.
• Many geologists think that plumes of mantle rock rise slowly from the bottom of
the mantle toward the top. The hot rock eventually cools and sinks back through
the mantle. Over and over, the cycle of rising and sinking takes place.
• There are also convection currents in the outer core. These convection currents
cause Earth’s magnetic field.
• As the Earth’s plates move, they collide, pull apart, or grind past each other,
producing spectacular changes in Earth’s surface. These changes include
volcanoes, mountain ranges, and deep-ocean trenches.
Types of Plate Boundaries
• __________________ boundaries (also called spreading centers) are the place
where two plates move apart.
• __________________ boundaries form where two plates move together.
• ________________________boundaries are margins where two plates grind past
each other without the production or destruction of the lithosphere.
Divergent Boundaries:
Oceanic Ridges and Seafloor Spreading
* _____________ ridges are continuous elevated zones on the floor of all major
ocean basins. The rifts at the crest of ridges represent divergent plate boundaries.
* ________ valleys are deep faulted structures found along the axes of divergent
plate boundaries. They can develop on the seafloor or on land.
* __________________ spreading produces new oceanic lithosphere.
Convergent Boundaries:
A ____________________ zone occurs when one oceanic plate is forced down into the
mantle beneath a second plate.
Oceanic-Continental
• Denser oceanic slab sinks into the asthenosphere.
• Pockets of magma develop and rise.
• Continental _________________ arcs form in part by volcanic activity caused
by the subduction of oceanic lithosphere beneath a continent.
• Examples include the Andes, Cascades, and the Sierra Nevadas.
Oceanic-Oceanic
• Two oceanic slabs converge and one descends beneath the other.
• This kind of boundary often forms volcanoes on the ocean floor.
• Volcanic _____________ arcs form as volcanoes emerge from the sea.
• Examples include the Aleutian, Mariana, and Tonga islands.
Continental-Continental
• When subducting plates contain continental material, two continents collide.
• This kind of boundary can produce new mountain ranges, such as the Himalayas.
Transform Boundaries:
• A ________________ boundary is a place where two plates slip past each other,
moving in opposite directions. Earthquakes often occur along transform
boundaries, but crust is neither created nor destroyed.
Make sure that you’ve read pages 150-172 from the textbook.