Download #20 - Plate Tectonics

#20 ­ Plate Tectonics
Plate Tectonics
20
Earth’s crust is broken into large pieces called _________________ .
tectonic plates
These plates move across the surface of the Earth because of __________________ in Earth’s convection currents
___________________ .
mantle
Continents have ___________ , ______________ collided
broken apart
and _________________________ at different times re­formed
in Earth’s past.
Pangea
_______________________________ is the super continent that formed _______________________ .
About 240 million years ago
Pangea
"whole earth"
__________________ means ____________________________ .
There are three main kinds of plate boundaries:
Convergent: two plates run into each other
_______________________________________
Divergent: two plates move away from each other
______________________________________
Transform: two plates slide past each other
______________________________________
page 5
Plate boundaries are mapped in the ESRT on _____ 1
#20 ­ Plate Tectonics
Divergent Boundaries
What happens here:
• Two pieces of crust move apart.
• Magma from the mantle seeps into cracks created by expansion
• New crust is created
Land forms associated with divergent boundaries:
a. mid­oceanic ridges
b. volcanoes
Evidence supporting the existence of divergent boundaries:
a. crust gets older as you move apart from ocean ridges
b. alignment of magnetic field in ocean crust
2
#20 ­ Plate Tectonics
Convergent Boundaries
What happens here:
Two pieces of crust collide into each other
Differences between oceanic and continental crust:
a. Oceanic: Thinner and more dense
b. Continental: Thicker and less dense
Land forms associated with Convergent Plate boundaries:
a. Mountain Ranges
b. Island Arcs
c. Ocean trenches
d. Fault zones & volcanoes
Original Horizontality: The idea that strata (layers of rock) were originally flat layers. As plate collisions happen, rock is bent, deformed and uplifted.
Deposition: rocks
formed in flat layers Deformation: rocks
lifted, bent, flipped over
Oceanic­Continental Collision
• A piece of oceanic crust collides with a piece of continental crust
• The oceanic crust is more dense, so it subducts. • The continental crust is less dense, so it overrides.
• Intense pressure causes rock to melt into magma below the collision
• Magma rises and creates a mountain range that may contain volcanoes. Rock is uplifted and deformed. Rock becomes metamorphic.
3
#20 ­ Plate Tectonics
Continental­Continental Collision
• Two pieces of continental crust collide with each other
• They have similar densities, so material from both plates is uplifted
• Intense pressure causes rock to melt into magma below the collision
• Magma rises and creates intrusions of igneous rock
Oceanic­Oceanic Collision
• Two pieces of oceanic crust collide with each other
• One subducts (dives down), the other overrides (goes over top)
• Intense pressure causes rock to melt into magma below the collision
• Magma rises and creates a chain of volcanoes called an island arc.
4
#20 ­ Plate Tectonics
Transform Boundaries
What happens here:
Two plates slide past each other
Things associated with transform boundaries:
a. Fault zones: a line of breaks in the Earth's crust, like the San Andreas Fault.
b. Earthquakes: as the plates move, they often jam against each other. Energy builds up until it is released all at once, causing an Earthquake
5