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Plate Tectonics and Mountain Building
Transcript of Plate Tectonics and Mountain Building
is divided into pieces called
Plate tectonics is the theory that describes the
large-scale movement of Earth's lithosphere.
What causes tectonic plates to move???
About 250 million year ago, the continents were joined in a single large landmass called
Alfred Wegener proposed a hypothesis of
, saying that the continents once formed a single landmass, broke up, and drifted.
Evidence of continental drift: mountain ranges, rock formations, fossils, ancient climatic conditions
Underwater mountain ranges that form along cracks in the oceanic crust
The process by which new oceanic lithosphere
forms when magma rises to Earth's surface at mid-ocean ridges and solidifies as older, existing sea floor moves away from the ridge
If the sea floor has been spreading for millions of years, why is Earth not getting larger?
Scientists discovered the answer when they found huge trenches, like deep
, in the sea floor.
At these sites, dense oceanic crust is sinking into the asthenosphere.
Older crust is being
at the same rate new crust is
The major tectonic plates include the Pacific, North
American, Nazca, South American, African, Australian
Eurasian, Indian, and Antarctic plates.
plate has only oceanic crust.
Types of Plate Boundaries
1. Convergent boundaries
2. Divergent boundaries
3. Transform boundaries
-form when 2 plates
When 2 plates of continental
plates collide, they buckle and
thicken. This causes
When a plate of oceanic lithosphere
collides with a plate of continental
lithosphere, the oceanic lithosphere
subducts, because it is denser.
zone- Boundaries where
one plate sinks beneath another plate
When 2 plates of oceanic lithosphere
collide, the older, denser plate subducts
under the other plate.
-where 2 plates move
from each other
-most are located on the
-The separation of plates allows
the asthenosphere to rise toward
the surface and partially melt. This melting creates magma, which erupts as lava. The lava cools and
hardens to form new rock on the
-a boundary at which 2 plates
move past each other horizontally
-this friction causes
How can tectonic plate motion cause deformation?
The movement of tectonic plates places
Stress is the amount of
per unit area that is placed
on an object.
is the process by which rock changes shape
When rocks bend,
When rocks break,
2 Types of Folds
1. Synclines- the youngest layers
are found at the core of a fold, usually look like
rock layers are arched upward, like a bowl
2. Anticlines- the youngest layers are found
on the outside of the fold
What are the 3 kinds of faults?
1. Strike-slip fault
2. Normal fault
3. Reverse fault
Strike Slip Fault
-In a strike slip fault, fault blocks move
past each other
-Form when rock is under shear stress
is stress that pushes rock
in parallel but opposite directions.
-Ex. San Andreas fault in California
-In a normal fault, the hanging wall moves down relative to the
-Form when rock is under tension
is stress that stretches or pulls rock apart
-In reverse faults, the hanging wall moves
relative to the footwall.
-Form when rocks undergo compression
is stress that squeezes or pushes
-The crack that forms when large blocks of rock
break and move past each other is called a
-The blocks of rock on either side of the fault are called
-The location where 2 fault blocks meet are called the
-The block above the fault plane is called the
-The block below the fault plane is the
What are the 3 kinds of mountains?
1. Folded mountains
2. Volcanic mountains
3. Fault-block mountains
-Form when rock layers are squeezed together
and pushed upward
-Usually form at
-Ex. Appalachian Mountains
-Form when melted rock erupts onto
-Can form on
or on the ocean floor
-Most of Earth's active volcanoes are concentrated
around the edge of the Pacific Ocean- this area
is known as the
Ring of Fire
-Form when tension makes the lithosphere
break into many
. Some pieces
drop down; the pieces left standing form
-Ex. Sierra Nevada Mountains