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TRANSCRIPT
Mountain Building
FOLDS FAULTS
• Orogenesis: Processes that produces a
mountain belt.
• Deformation: all changes in the original
shape and/or size of a rock body.
Rock Deformation
Stress is the force
per unit area acting
on a solid.
Strain: The change
in shape or volume
of a body of rock as
a result of stress.
Factors effecting rock deformation
1. Temperature and Pressure
- Ductile deformation - produces a change in the
size and shape of an object without fracturing
the object.
- Brittle deformation - fracturing of an object
once its strength is exceeded.
2. Rock Type
• Mineral composition and texture of a rock also
greatly affect how it will deform.
3. Time
• Forces that are unable to deform rock when first
applied may cause rock to flow if the force is
maintained over a long period of time.
Rock Deformation Stresses The three types of stresses
Tensional
Compressional
Shear
Divergent boundaries
Convergent boundaries
Transform boundaries
FOLDS
1. Anticlines are
most commonly
formed by the
upfolding, or
arching, of rock
layers.
2. Synclines
are linear
downfolds in
sedimentary
strata.
FOLDS
3. Monoclines are large step-like folds in otherwise horizontal
sedimentary strata.
Four Types of Faults
1. Normal faults - hanging wall block
moves down relative to the footwall
block.
2. Reverse faults - hanging wall block
moves up relative to the footwall block.
3. Thrust faults - reverse faults with dips
less than 45o.
4. Strike-slip faults - movement is horizontal
and parallel to the trend, or strike, of the
fault surface.
NORMAL FAULT
Types of Faults and Stress
• Normal Fault: hanging wall moves down;
TENSION.
• Reverse Fault: hanging wall moves
up;COMPRESIONAL.
• Thrust Fault: Reverse faults that dip
greater then 45*; COMPRESIONAL.
• Strike Slip Fault: movement is horizontal
to strike of the fault; STRIKE—SLIP.
Joints
• Joints are
fractures along
which no
appreciable
movement has
occurred.
Types of Mountains
1- Folded Mountains - Mountains
that are formed primarily by folding
Mountains are classified by the dominant processes
that have formed them.
2- Fault-block mountains are
formed as large blocks of
crust are uplifted and tilted
along normal faults.
3 - Grabens are formed by
the downward displacement
of fault-bounded blocks. 4 - Horsts are elongated, uplifted
blocks of crust bounded by faults.
Types of Mountains
• Uplifted
mountains - circular or elongated
structures formed by
uplifting of the
underlying basement
rock.
Domes and Basins -
upwarping produces
a circular or elongated
structure
Mountain Formation Most mountain building occurs at convergent plate boundaries.
Colliding plates provide the compressional forces that fold,
fault, and metamorphose the thick layers of sediments
deposited at the edges of landmasses.
Ocean-Ocean Convergence
produces volcanic mountains.
Ocean-Continental Convergence
produce volcanic mountains and folded mountains.
Continental-Continental Convergence
collision between the continental
fragments will result and form folded mountains.
Divergent boundary
fault-block type mountains
Mountain Building by
Continental Accretion
Continental
Accretion -
process that
occurs when
crustal fragments
collide with and
stay connected to
a continental plate
Terranes - any
crustal
fragments that
have a geologic
history distinct
from that of the
adjoining
fragments.
Mountain Formation Not all mountains are formed by plate
boundaries. Some are formed by hot spots
or regional extension or stretching.
Isostatic Adjustment •Isostasy is the concept that Earth’s crust is floating in
gravitational balance upon the material of the mantle.