Download Folded Mountains

Section 3
Chapter 6
Key Concept
 Tectonic plate
motions deform
Earth’s crust.
Deformation causes
rock layers to bend
and break and
causes mountains to
form.
Deformation
 Rocks react differently
depending on the amount
of stress put on them.
 The process by which the
shape of a rock changes
in response to stress is
called deformation.
 Rock layers bend when
stress is placed on them.
 When enough stress is
placed on them they
break.
Folding
 The bending of rock layers in response to
stress in the earth’s crust is called folding.
 All folds have a hinge and 2 limbs. Limbs are
the sloping sides of a fold. A hinge is the bend
where the two limbs meet.
Anticlines and Synclines
 The two most common types of folds are
anticlines and synclines.
Anticline Folds
 In an anticline fold,
the oldest rock layers
are in the center of
the fold. The rock
limbs slope down
from the center to
form an arch.
Syncline Folds
 In a syncline fold, the
youngest rocks are in
the center of the fold.
The limbs slope up
from the center to
form a trough.
Coming up…
Shapes of Folds




Symmetrical
Asymmetrical
Overturned
Recumbent
Symmetrical Fold
 Symmetrical folds
are even and
balanced.
Asymmetrical Fold
 In an asymmetrical
fold, one limb may
dib more steeply
than the other limb
does.
Overturned Fold
 An overturned fold is
one in which one
limb is tilted beyond
90 degrees.
Recumbent Fold
 Rock layers which
are bent so much
that a fold appears to
be lying on its side
are called recumbent
folds.
Faulting
 When rock is placed
under so much stress
that it can no longer
stretch or bend, it may
break. The place that
rocks break and slide
past each other is
called a fault.
 The blocks of crust on
either side of a fault
are called fault blocks.
 When a fault is not vertical (straight up
and down) there are 2 kinds of fault
blocks—the hanging wall and the foot
wall.
Types of Faults
 Normal Faults
 Reverse Faults
 Strike-Slip Faults
Normal Faults
 Along a NORMAL FAULT,
the hanging wall moves
DOWN relative to the
footwall.
 Usually form where
tectonic plate motions
cause tension. Tension is
stress that pulls rocks
apart.
Reverse Faults
 In a REVERSE FAULT, the
hanging wall moves UP
relative to the footwall.
 Caused when tectonic
plate motion causes
compression.
 Compression is stress that
pushes rocks together.
 Common in subduction
zones.
Strike-Slip Faults
 The 2 fault blocks move
past each other
horizontally.
 Usually form where
tectonic plate motions
cause shear stress
parallel to Earth’s surface.
 Shear stress pushes
different parts of the rock
in different directions.
 Common in transform
boundaries.
Recognizing Faults
 Some faults are only a few
meters long, while other are
several hundred meters.
 Faults cause rock layers to
become offset.
 Also grooves, striations, or
polished surfaces called
slickenslides show where
rocks have moved.
 Fault offset is obvious along
faults that break surface for
many kilometers.
 Streams may change
direction at a fault.
 A scarp is a row of cliffs
formed by faulting.
Scarps
Plate Tectonics and
Mountain Building
 Edges of tectonic plates
grind against each other.
 Causes stress in Earth’s
crust because the plates
have a great deal of
mass.
 This process may
crumple and push up the
margins of the plates.
 Causes mountains to
form.
Types of Mountain
Formation
 Folded Mountains
 Fault-Block
Mountains
 Volcanic Mountains
Folded Mountains
 Occur when rock layers are squeezed
together and pushed upward
 Occur at convergent boundaries where
continents have collided.
Himalaya Mountains
are FOLDED MOUNTAINS
Fault-Block Mountains
 Occur when tension
in the crust causes
the crust to break
into a large number
of normal faults.
 Large blocks of crust
drop down relative to
other blocks.
Grand Teton Range, Wyoming
Volcanic Mountains
 Occur when molten rock erupts
onto Earth’s surface.
 Located at convergent
boundaries when hot mantle
rocks rise beneath the plate.
 Molten rock rises to the surface
and erupts.
 Form on land and the ocean
floor.
 Sometimes become islands.
 Most active volcanic mountains
have formed around the
tectonically active rim of the
Pacific Ocean.
Ring of Fire
Summary
 Deformation structures, such as
faults and folds, form as a result of
stress in the lithosphere. This stress
is caused by tectonic plate motion.
 Folding occurs when rock layers
bend because of stress.
 Faulting occurs when rock layers
break because of stress and then
move on either side of the break.
 Three major fault types are normal
faults, reverse faults, and strike-slip
faults.
 Mountain building is caused by the
movement of tectonic plates. Folded
mountains and volcanic mountains
form at convergent boundaries.
Fault-block mountains form at
divergent boundaries.