Metamorphic
Processes I
Crustal Deformation

Changes in earth’s surface due to the folding, breaking,
or flow of rocks

Due to pressures that rocks experience within the earth

Pressures can be due to changes in temperature or
moisture, shifts in the Earth’s plates, sediment buildup
or even gravity
Types of Pressure / “Stress”
on the Crust

Compressional Stress


Tensional Stress


Forces that push inward or press upon
rocks/layers
Forces that pull in opposite directions
Shear

Two forces acting parallel to each other
but in opposite directions
Kinds of Crustal Deformation


Elastic

temporary

reversed when the source of stress is removed
Ductile


a permanent change to the shape or size of the
rock that persists even when the stress stops
Brittle

results in the breakage of the rock
Factors Affecting Rock
Strength
High
1. Temperature
•
•
2. Confining Pressure
•
(Equal stress on the material
coming from all directions)
Low
Molecules/bonds
can stretch/move
Materials will be
more ductile
•
Materials are more
brittle
Materials are less
likely to fracture or
break
•
Materials will be
more brittle and
tend to break sooner
3. Time
4. Rock Type
• Some minerals, like quartz, olivine, and feldspars are very brittle
• Others, like clay minerals, micas, and calcite are more ductile
• Dry rocks: more brittle
• Wet rocks: more ductile
Ductile Deformation Cause
FOLDS
Kinds of Folds: Monocline, Anticline, Syncline, Plunging
Monocline
Anticline
Syncline
Plunging
Slight bend
Upward fold
Downward fold
Occurs if the fold
axis is not
horizontal
The 2 sides of
The 2 sides of
the bend are still the fold dip
horizontal
away from the
center of the
fold
The 2 sides of
the fold dip
inward toward
the center of the
fold
Ductile Deformation Cause FOLDS
More Folds: Symmetrical, Assymetrical, Overturned, Recumbent
Symmetrical
Assymetrical
Overturned
Recumbent
The 2 sides of the
fold dip away from
the center at the
same angle
The 2 sides of the
fold dip away from
the center at
different angles
The layers on one
side of the fold have
been folded beyond
90⁰, making it go
nearly upside-down
More extreme than
an Overturned fold
where the central
axis of the fold is
almost horizontal
Ductile Deformation Form Structures
Ductile Structures: Domes, Basins, Hogbacks
Dome
Basin
Hogback
Looks like an
upside-down bowl
Looks like an
upright bowl
A long narrow ridge
Due to compression
and uplift
Due to compression
and down-warping
Formed when inclined
(monoclined) sedimentary
rockbeds are eroded, while the
harder rock layers on top resist
erosion.
Hogback
Brittle Deformation
When rock layers are placed under a high enough stress, they can
then fracture or break. Such fractures create either:

Joint


Fracture in rock that show no slippage or offset along the
fracture
Fault

Fracture shows slippage or
offset along the fracture
Brittle Deformation
Types of Faults

Dip Slip Fault

has an inclined fault plane

the displacement or offset is along the dip direction

Can either be:
 Normal

Fault
Tension acts in opposite directions. One
block is displaced up and the other down
 Reverse

Fault
Compression causes one block to be pushed
up and over the other block
 Thrust

Fault
A special type of Reverse Fault with a
dip below 45⁰, which can cause much
more displacement of a much larger
area
Strike Slip Fault
• has a vertical fault plane
• Shear stresses are exerted parallel to each other
Brittle Deformation
Structures Formed

Graben

produced when tensional stresses on
adjacent normal faults result in a block of
rock dropping down
• Half-Graben
• Bound by only one normal fault with a
curved fault plane which can cause the
down-dropped block to rotate
• Horst
• produced when compressional stresses on
adjacent reverse faults result in a block of rock
being pushed up
• Also called a Fault-Block Mountain
• Fault Scarp
• The exposed cliff-like face of the fault plane
Sources

http://www.tulane.edu/~sanelson/eens1110/deform.htm

http://scioly.org/wiki/index.php/GeoLogic_Mapping

http://web.gccaz.edu/~lnewman/gph111/topic_units/Fold_fault_eq/Fold_fault_eq2.ht
ml

http://www.physicalgeography.net/fundamentals/10l.html

http://www.geosci.ipfw.edu/PhysSys/Unit_4/structures_text.html

http://www.geocaching.com/geocache/GC239R3_cuesta-for-thehogback?guid=807b64fe-09d3-474a-99d0-e2bd224f0c08

http://classroom.synonym.com/deformation-earth-science-21924.html

http://www.gustrength.com/kinesiology:tension-compression-shear-torsion

https://www.uwgb.edu/dutchs/EarthSC202Slides/struslid.htm

http://itc.gsw.edu/faculty/bcarter/geomorph/struct/fault1.htm

www.engineeringtoolbox.com