Download Deforming the Earth`s Crust

Deforming the Earth’s Crust
Key Concept:
Tectonic plate motions deform Earth’s
Crust. Deformation causes rock layers to
bend and break and causes mountains to
form.
Deformation
• Stress is the amount of force per unit area
on any given material.
• When plates move, rocks layers on Earth
receive stress.
• Rocks react differently with stress,
sometimes they bend other times they
break.
Deformation continued
•Deformation is the process in which rocks change shape
in response to stress.
Folding
• Bending rock due to
stress is called folding
• Scientists assume
that all rock layers
started horizontally
Anticlines
• An anticline is a fold
which the oldest rock
layers are in the
center of the fold.
• Many times the rocks
fold in the center and
form an arch.
Syncline
• A syncline is a fold
which the youngest
rock layers are in the
center of the fold.
• Many times the rocks
fold in the center and
form a “U” Shape.
Shapes and Folds
• Folds do not always
have symmetrical
bends (look the same
on both sides).
• Sometimes
Asymmetrical bends
occur (look different)
• Folds may also be
turned on their side,
called a recumbent
fold.
Faulting
• When a rock has so
much stress that it
can no longer bend
or stretch it will
break.
• The surface along
the break is called a
fault.
• The broken crust at
the fault are called
fault blocks.
• Faults are
sometimes vertical.
Faulting cont.
• Sometimes a
fault block is not
vertical.
• The fault will
contain two
different fault
blocks. A foot
wall and a
hanging wall.
Normal Faults
• In a normal fault,
the two plates
move away from
each other.
• Tension is a force
that pulls apart.
• The hanging wall
slides on the
footwall.
• Example is a mid
ocean ridge.
Reverse Fault
• In a reverse fault the
hanging wall moves
up on the foot wall.
• Compression is the
stress that pushes the
plates together.
• Occurs in a
Subduction zone.
Strike-Slip Fault
• Along a Strike-Slip
fault, two faults move
horizontally past each
other.
• Occur at transform
boundaries.
Plate Tectonics and Mountain
Building
A) Continental-Continental Collision
B) Normal Fault
C) Strike-Slip Fault
D) Reverse Fault
• When giant plates moved
around, their edges grind
and cause stress.
• Over long periods of time,
this process may crumple
and push up the margin
of the plates.
• When this happens
mountain building may
occur.
• Three types of mountains
are: Folded, Fault-Block
and Volcanic.
Folded Mountains
• When rocks are
squeezed together and
pushed upward, folded
mountains form.
• This occurs at
convergent boundaries.
• The Appalachian
Mountains are an
example of folded
mountains.
Fault-Block
• When tension on the
earth’s crust causes it
to break into many
faults Fault-Block
mountains form.
• The layers of the
crust break and drop
in elevation compared
to surrounding layers.
• The Tetons are an
example.
Volcanic Mountains
• Occur when molten
rock erupt onto the
Earth’s surface.
• Most volcanic
mountains occur
around convergent
boundaries.
• Occur on land and in
the sea.
• Mt. Shasta is an
example.