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STRUCTURAL GEOLOGY
OCCURING ON THE EARTH
Dr. Danang Sri Hadmoko, S.Si., M.Sc.
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THE SOLID EARTH
The field of geology is concerned with the study of the
structure, history, and activity of the solid Earth, including its
interactions with the atmosphere, hydrosphere, cryosphere,and biosphere.
The structure of the body of the solid Earth contains four major
zones: the core(which is divided into inner and outer zones),
the (upper and lower) mantle, the asthenosphere, and thelithosphere.
The structure of the outer zones is not uniform and fixed over
the surface of the Earth, but shows much variability with
position and time.
The field ofplate tectonicsdeals with this spatial and temporal
variability.
Geological phenomena such as earthquakes, volcanoes, and
continental drift are accounted for by plate tectonics.
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The Structure of the Earth
1234
Internal structure of
earth1. Inner core
2. Outer core
3. Mantle
4. Crust
Rheological:
Lithosphere
Asthenosphere Mesosphere
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The Core
1. The inner part of the earth is the core.
2. This part of the earth is about 2,900 km below the earth's
surface.3. The core is a dense ball of the elements iron and nickel. It
is divided into two layers, the inner coreand the outer
core.
4. The inner core - the center of earth - is solid and about
1,250 km thick. The inner core pressures are so great that
it cannot melt, even though temperatures there reach
3700C.
5. The outer core is so hot that the metal is always molten,
but the outer core is about 2,200 km thick. Because the
earth rotates, the outer core spins around the inner core
and that causes the earth's magnetism.
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Inner core
Outer core
Mantle
Crust
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What Influence does the Core have? Because the core is so hot, it
radiates a natural heat to the upper layers.
Because of this a current of heat comes into being. Those are alsoknown as the convection currents.
The convection currents cause the movement of the tectonic
plates. This movement is called plate tectonics.
The outer core and the inner core together cause the earth's
magnetism. Because the earth rotates, the outer core spins, the
inner core doesn't spin because it's solid.
This gives a kind of dynamo effect and causes the earth'smagnetism. Magnetism has been used by sailors to find their way
on earth for thousands and thousands of years.
Magnetism also influences electro-particles outside the
atmosphere of the earth, up to more than 60,000 km into space
What Influence does the Core have?
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The Mantle
1. The layer above the core is the mantle.
2. It begins about 10 km below the oceanic crust and about 30
km below the continental crust (see The Crust).
3. The function of the mantle is to separate the inner mantle and
the outer mantle.
4. It is about 2,900 km thick and makes up nearly 80 percent ofthe Earth's total volume.
5. From this perspective, the outer mantle and the crust are
together. Here we make a difference in asthenosphere and
lithosphere.6. Asthenosphere: The tough liquid part of the outer mantle.
7. Lithosphere: The stiffer part of the outer mantle and the crust.
The lithosphere 'floats' on the asthenosphere, like ice on
water.
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What Influence does the Mantle Have?
Because the earth is very hot inside, a current of heat flows
from the core to the crust. This is called convection current and
it also takes place in the mantle.
This current cools down as it comes closer to the surface of the
earth. As a result, the rising of the current decreases and goes
into horizontal direction along the bottom of the crust. When the
current cools down more, the convection current descendsagain and goes to the inner earth. There the temperature
increases and the current rises again. This goes on and on.
When the current comes at a weaker part of the crust, for
example at a volcano, magma comes above the earth'ssurface. The convection current along the bottom of the crust
causes the moving of the tectonic plates. This is called plate
tectonics. The movement of these plates goes very slowly. The
bumping of two tectonic plates causes an earthquake.
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1. The crust covers the mantle and is the earth's hard outer shell,the surface on which we are living.
2. Compared to the other layers the crust is much thinner. It floats
upon the softer, denser mantle.
3. The crust is made up of solid material but this material is notthe same everywhere.
4. There is an Oceanic crustand a Continental crust.
5. The first one is about 6-11 km thick and mainly consists ofheavy rocks, like basalt.
6. The Continental crust is thicker than the Oceanic crust, 30 km
thick. It is mainly made up of light material like granite.
CRUST : Continental and Oceanic Crust
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CRUST : Continental and Oceanic Crust
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CRUST : Continental and Oceanic Crust
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1. When you look at the globe, you see that the surface of the earthconsists of a lot of water (71%). The other 29% consists of land.
2. You can divide this land into six big pieces, called continents. The
different continents - arranged in decreasing order of size - are:
Eurasia (Europe and Asia together), Africa, North-America, South-
America, Antarctica and Australia. In the past the division of the
continents was different.
3. The earth's crust is the thickest below the continents, with an
average of about 30 to 40 km and with a maximum of 70 km and
older than the oceanic crust, some rocks are 3.8 billion years old.
4. The continental crust mainly consists of igneous rocks and is
divided into two layers. The upper part mainly consists of granite
rocks, while the lower part consists of basalt and diorite, granite is
lightly-colored, coarse-grain, magma.
Continental crustCRUST : Continental Crust
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a
b
c
d
e
f
g
h
Continental crust
CRUST : Continental Crust
C
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Continental crust
PLATE BOUNDARY
C ti t l t
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Continental crust
PLATE BOUNDARY
C ti t l t
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Convectioncurrent
Convectioncurrent
Oceanic plate Oceanic plate
What happens when oceanic plates move apart due toconvection currents in the Earths mantle?
Magma moves up tothe surface, coolsand forms newoceanic plate.
This is known asSEA-FLOORSPREADING.
Continental crust
DIVERGENT PLATE BOUNDARY
C t ti Pl t B d C ti t l t
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Constructive Plate Boundary Continental crust
DIVERGENT PLATE BOUNDARY
C ti t l t
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Spreading ridges
As plates move apart new material is erupted to fill the gap
Divergent BoundariesContinental crustDIVERGENT PLATE BOUNDARY
C ti t l t
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There are three styles of convergent plate
boundaries:
1. Continent-continent collision
2. Continent-oceanic crust collision
3. Ocean-ocean collision
Convergent BoundariesDivergent BoundariesContinental crustCONVERGENT PLATE BOUNDARY
C ti t l t
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Forms mountains, e.g. European Alps, Himalayas
Continent-Continent Collision
Divergent BoundariesContinental crustCONVERGENT PLATE BOUNDARY
Continental cr st
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Called SUBDUCTIONContinent-Oceanic Crust Collision
Divergent BoundariesContinental crustCONVERGENT PLATE BOUNDARY
Continental crust
OCEANIC CONTINENTAL
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What happens when an oceanic plate and a
continental plate collide?
The thinner, more dense oceanic plate is
driven down into the mantle.
Convection currentConvection current
Oceanic plate melted
This is known as
SUBDUCTION!
hicker, less dense continental plate
Thinner, more dense
oceanic plate
Divergent BoundariesContinental crustOCEANIC-CONTINENTALCONVERGENT PLATE BOUNDARY
dContinental crust
OCEANIC CONTINENTAL
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Divergent BoundariesContinental crustOCEANIC-CONTINENTALCONVERGENT PLATE BOUNDARY
i d iContinental crust
OCEANIC CONTINENTAL
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Oceanic lithosphere subductsunderneath the continentallithosphere
Oceanic lithosphere heats anddehydrates as it subsides
The melt rises formingvolcanism
E.g. The Andes
Subduction
Divergent BoundariesContinental crustOCEANIC-CONTINENTALCONVERGENT PLATE BOUNDARY
i d iContinental crust
OCEANIC CONTINENTAL
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Divergent BoundariesContinental crustOCEANIC-CONTINENTALCONVERGENT PLATE BOUNDARY
Volcanic activity, the production of molten rock (lava) and its
eruption to Earths surface (on land or in the oceans) is onemanifestation of tectonic activity.
Molten rock is produced as a result of the following two major types
of plate motion:
1. Separation (moving apart) of two crustal plates, which allowsmolten rock to rise to the surface between them.
2. Collision of two crustal plates, with one moving beneath the
other (subduction), resulting in the creation of molten rock from
surface materials on the subducted plate.
Volcanic activity near the west coasts of North and South Americais due to subduction of Pacific Ocean plates beneath the west
edges of the continents.
Some volcanic activity, such as in the Hawaiian Islands, is not
directly the result of plate motions.
Di B d iContinental crust
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When two oceanic plates collide, one runs over the
other which causes it to sink into the mantle forming asubduction zone.
The subducting plate is bent downward to form a very
deep depression in the ocean floor called a trench.
The worlds deepest parts of the ocean are found along
trenches.
E.g. The Mariana Trench is 11 km deep!
Ocean-Ocean Plate Collision
Divergent BoundariesContinental crustOCEAN OCEAN PLATE COLLISION
Di B d iContinental crust
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Divergent BoundariesContinental crustOCEAN OCEAN PLATE COLLISION
Di B d iContinental crust
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Plate A
Plate B
When two plates slide past each other, they dont do it
smoothly. The large friction forces involved mean thatstrain builds up and the plates move suddenly when the
strain gets too much.
This sudden movement of plates is called an earthquake and
it can be very destructive.
Divergent BoundariesContinental crustTRANSFORM PLATE BOUNDARY
Di t B d iContinental crust
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Where plates slide past each other ?
Above: View of the San Andreas
transform fault
Divergent BoundariesContinental crustTRANSFORM PLATE BOUNDARY
Di t B d iContinental crust
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Divergent BoundariesContinental crustPLATE BOUNDARY AROUND THE GLOBE
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Movement Rate of Plate Tectionic
Di t B d iContinental crust
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whats the connection?
Volcanoes and Plate Tectonics
Divergent BoundariesContinental crustPLATE BOUNDARY AROUND THE GLOBE
Di t B d iContinental crust
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Volcanism is
mostly focused at
plate margins
Pacific Ring of Fire
Divergent BoundariesContinental crustCONSEQUENCES OF PLATE BOUNDARY
Volcanoes are formed by:Di t B d iContinental crust
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- Subduction - Rifting - Hotspots
Volcanoes are formed by:Divergent BoundariesContinental crust VOLCANISM
Volcanoes are formed by:Di t B d iContinental crust
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Hot mantle plumes breaching the surface in
the middle of a tectonic plate
What are Hotspot Volcanoes?
Photo: Tom Pfeiffer / www.volcanodiscovery.com
The Hawaiian island chain are examples
of hotspot volcanoes.
Volcanoes are formed by:Divergent BoundariesContinental crust VOLCANISM
Volcanoes are formed by:Divergent BoundariesContinental crust
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The tectonic plate moves over a fixed hotspot forming a
chain of volcanoes
The volcanoes get younger from one end to the other
Volcanoes are formed by:Divergent BoundariesContinental crust VOLCANISM
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whats the connection?
Earthquakes and Plate Tectonics
Volcanoes are formed by:Divergent BoundariesContinental crust
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Volcanoes are formed by:Divergent BoundariesContinental crust EARTHQUAKE
As with volcanoes, earthquakes are notrandomlydistributed over the globe
At the boundaries between plates, friction causesthem to stick together. When built up energycauses them to break, earthquakes occur.
Where do earthq akes form?Volcanoes are formed by:Divergent BoundariesContinental crust
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Where do earthquakes form?
Figure showing the tectonic setting of earthquakes
Volcanoes are formed by:Divergent BoundariesContinental crust SUMMARY
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Plate Tectonics Summary
The Earth is made up of 3 main layers (core, mantle, crust)
On the surface of the Earth are tectonic plates that slowlymove around the globe
Plates are made of crust and upper mantle (lithosphere)
There are 2 types of plate
There are 3 types of plate boundaries
Volcanoes and Earthquakes are closely linked to themargins of the tectonic plates
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STRUCTURAL GEOLOGY
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
STRUCTURAL GEOLOGY
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Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesSTRUCTURAL GEOLOGY
1. Rocks below the earth's surface are hot andtend to flow, whereas rocks at the surface arerelatively cool and tend to be more brittle. Thus,rocks at the surface (or near-surface) fracture
while rocks deep inside the earth flow.
2. Deformation: when rocks are subjected tostresses (forces) greater than their own internal
strength. Caused by stress and resulting instrain.
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
STRUCTURAL GEOLOGY
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Stress -- force acting upon an object to createdeformationStrain -- resultant of the stress applied; endproduct
There are several types of stresses that can beapplied to a rock unit:1.Extensionor tension (pulling apart)
2.Compress ion(pushing together)3. Shear ing or twisting (one portion in onedirection, the other portion in another direction)
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesSTRUCTURAL GEOLOGY
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
STRUCTURAL GEOLOGY
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Deformation of Rocks
Folding and faulting are the most
common forms of deformation in thesedimentary, igneous and metamorphicrocks that compose theEarthscrust
Structural Geology is the study of thedeformation of rocks and its effects.
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesSTRUCTURAL GEOLOGY
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
STRUCTURAL GEOLOGY
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Dynamic forces within the Earth cause deformation.
Deformation is a general term that in geology applies to any
change in the shape or volume of rock layers, such as when
they are folded or fractured.
Deformation occurs in building large mountain ranges at
convergent boundaries thru:
Emplacement of plutons Volcanism
Metamorphism
Continental accretion
Deformation of Rocks
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesSTRUCTURAL GEOLOGY
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Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
R k D f ti H D it O ?
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Stress and Strain
How can you explain stress and strain by using anexample of an ice-covered pond?
When subjected to stress (force), ice on a pondmay bend (elastic deformation), or if the stress is
great enough, it will fracture, that is, the icestrained or deformed in response to stress.
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesRock Deformation - How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation Ho Does it Occ r?
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There can be two (2) resulting responses to stress:
1. Ducti le deformation -- usually occurring deeper and with highertemperatures; flow
2.Bri t t le deformation -- usually occurring shallower and with coolertemperatures
Ductile deformation producesfolds
:1. Ant ic l ine-- upwarping of rocks to produce an "A-like" structure
2. Syncl ine-- downwarping of rocks to produce "spoon-like" structure
3. Dome-- three-dimensional anticline resembling inverted cereal bowl
4. Basin-- three-dimensional syncline resembling upright cereal bowl
*When brittle deformation occurs and rocks fracture, they can simply crackproducing a fracture with no offset, called ajo int.
When brittle deformation occurs and rocks fracture, they can also crack
producing a fracture with offset, called afault.
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesRock Deformation - How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation How Does it Occur?
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Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesRock Deformation - How Does it Occur?
Types of Strain: Compression
In compression the rocks are squeezed towards oneanother along the same line.
Rock layers in compression are shortened the rocks byfolding or faulting.
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation How Does it Occur?
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Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesRock Deformation - How Does it Occur?
Action of oppositely directed forces actingtowards each other at the same time
Compression
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation How Does it Occur?
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Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesRock Deformation - How Does it Occur?
Types of Strain
Tension
In tension the forces along the same lineact in opposite directions.
Tension lengthens the rocks or pulls themapart.
Fig. 10.3b, p. 247
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation How Does it Occur?
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Tension
Action of coinciding and oppositely directedforces acting away from each other
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesRock Deformation - How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation How Does it Occur?
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Types of Strain
Shear
In shear the forces act parallel to oneanother, but in opposite directions
Deformation occurs along closely spacedplanes like the slip between cards in a deck.
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesRock Deformation - How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation How Does it Occur?
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ShearAction of coinciding and oppositely directedforces acting parallel to each other across asurface
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesRock Deformation - How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation How Does it Occur?
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Types of Strain
Rocks will deform elastically until they reach theelastic limit unless the force is applied quickly.
Elastic strain occurs if rocks return
to their original shape when thestress is released.
Plastic strain occurs when rocks foldor fracture when stress is applied
and do not recover their originalshape.
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesRock Deformation - How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation How Does it Occur?
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Types of Strain
What determines whether a rock will bend elastically,
plastically or fracture?
Type of stress applied
Pressure and temperature Rock type
Length of time
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesRock Deformation - How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation How Does it Occur?
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Types of Strain
Rocks will deform elastically until they reach theelastic limit unless the force is applied quickly.
Ductile rocks show a greatamount of plastic strain (they
bend) before they fracture.
Brittle rocks fracture after only
a small amount of plastic strain.
Fig. 10.4, p. 248
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesRock Deformation - How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation How Does it Occur?
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Behavior of Rocks to Stress and Strain
Elastic strain: strain in which a deformed bodyrecovers its original shape after the stress isreleased (ex: rubber band)
Elastic limit: the maximum amount of stress that canbe applied to a body before it deforms in apermanent way by bending or breaking
Ductile: capable of being molded and bent under
stress Brittle strain: cracking or rupturing of a body understress
Where do earthquakes form?o ca oes a e o ed by:Divergent BoundariesRock Deformation - How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation - How Does it Occur?
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Where do earthquakes form?yDivergent BoundariesRock Deformation - How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation - How Does it Occur?
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Strike and Dip on a Rooftop
Where do earthquakes form?yDivergent BoundariesRock Deformation - How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Strike and Dip-The Orientation of
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Strike and dip are measurements used to describe a
rock body's orientation with respect to the horizontal.
Strike is the intersection
of a horizontal plane with
an inclined plane.
Dip is the maximum angleof an inclined plane.
Where do earthquakes form?yDivergent BoundariesDeformed Rock Layers
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation - How Does it Occur?
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1 Fold
2 Fault
3 Joint
4 Fracture
Type of rock deformation
Where do earthquakes form?yDivergent BoundariesRock Deformation - How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation - How Does it Occur?
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Where do earthquakes form?yDivergent BoundariesRock Deformation How Does it Occur?
Deformation and Geologic Structures Folded Rock Layers
Folds are layers of rock that were once planar that are bent or
crumpled.
Folds form during compression and undergo plastic strain.
This occurs deep in the crust where the rocks behave ductilely. Produced by tectonic forces
Very common form of deformation that is viable in layered rock
Scale can be from centimeters to hundreds of kilometers
There are 3 kinds of folds: Monoclines
Anticlines
Synclines
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Rock Deformation - How Does it Occur?
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Fold Terminology
Axial plane: the plane of mirror symmetry dividing
the fold into two limbsAxis: the line formed by the intersection of the
axial plane and a bedding plane
Horizontal fold: fold where the axis is horizontalPlunging fold: fold where the axis is not horizontal
Where do earthquakes form?yDivergent BoundariesRock Deformation How Does it Occur?
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Folded Rocks
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Where do earthquakes form?yDivergent BoundariesFolded Rocks
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Folded Rocks
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Where do earthquakes form?ye ge t ou da esFolded Rocks
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Folded Rocks
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Where do earthquakes form?yg Folded Rocks
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Folded Rocks
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More Fold Terminology
Syncline: a sequence of folded rocks with
the youngest rocks on the inside of the fold
Anticline: a sequence of folded rocks withthe oldest rocks on the inside of the fold
Where do earthquakes form?yg Folded Rocks
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Folded Rocks
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Where do earthquakes form?yg Folded Rocks
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Folded Rocks
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Symmetrical folds: have beds dipping symmetrically on
each side of axial plane
Asymmetrical folds: have the bed on one side of folddipping more steeply than other
A fold with a plunging axis is called a plunging fold. If
you were to walk along the axis of a plunging fold, you
would be traveling uphill or downhill along the axis.
Overturned folds: one or both sides of fold dippingbeyond vertical
e e do ea t qua es o ?yg Folded Rocks
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Folded Rocks
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q yg Folded Rocks
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
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q yg Folded Rocks
Asymmetrical folds
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Deformation and Geologic Structures
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g
Fold axis is not horizontal
Axial plane may be
vertical or inclined
Folded Rock
Plunging folds
Plunging
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Anticline
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Folded Rocks
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Inclined and Overturned foldsIn these folds the axial plane is inclined.
Usually form under compression at convergentboundaries.
Overturned folds have both limbs dipping in the samedirection
Folded Rock Layers
qg
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
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qg
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
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Overturned folds
q
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Folded Rocks
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Folded Rock Layers
Recumbent foldsIn these folds the axial plane is horizontal or nearly
horizontal.
Usually form under compression at convergent
boundaries.
q
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
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q
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
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q
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
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Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
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Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
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And Even More Fold Terminology
Dome: a sequence of folded rocks in whichall the beds dip away from a central point
Basin: a sequence of folded rocks in whichall the beds dip towards a central point
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Folded Rocks
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ERODED DOME
Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
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Where do earthquakes form?Volcanoes are formed by:Divergent BoundariesContinental crust
Folded Rocks
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Deformation and Geologic Structures
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Joints
Joints are fractures along which nomovement has taken place.
Joints occur in almost all surface rocks.
Form in response to compression, tension,
and shearing.
Brittle Strain Joints
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When shallow crust is strained
rocks tend to exhibit brittle strain
Brittle Strain Joints
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Faults are fractures along which the oppositesides have moved relative to one another and
parallel to the fracture surface.
Types of Faults
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yp
Dip-slip faults
Normal
Reverse
Strike-slip faults
Right-lateral
Left-lateral
Oblique-slip faults
Faults
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Hanging Wall: Term used by miners. Theycould hang their light on this side of the
fault because it was above them.
Footwall: Also from the miners, this sideof the wall upon which they could stand
below the hanging wall.
Faults
Normal Fault
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1. A fault in which the hanging wall has moved down
relative to the footwall is called anormal fault
The horizontal distance between points on opposite
sides of the fault, such as A and A greater after normalfaulting occurs.
3. Hence, a normal fault forms where tectonic tension
stretches the Earthscrust,pulling it apart.
Reverse Fault
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1. A reverse fault is structure that accommodates shortening.
2. In a reverse fault, the hanging wall has moved up relative to thefootwall.
3. The distance between points A and A is shortened by the
faulting.
Thrust Fault
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A thrust fault is a special type of reverse fault that is
nearly horizontal. In some thrust faults, the rocks of
the hanging wall have moved many kilometers over
the footwall.
Deformation and Geologic Structures
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Faults
Dip-slip Faults
All movement is in the direction of dip along dip-slip
faults.
Dip-slip faults are categorized as normal or reverse.
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Faults
Dip-slip Faults Normal faults form in response to tensional forces.
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Faults
Normal faults
Geo-inSight 1., 2., , p. 262
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Faults
Normal faults
Fig. 10.18a-b, p. 264
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Thrust faults are a type of reverse fault that dips atless than 45 degrees, oftenas low as 5 degrees!
Faults
Dip-slip faults
Reverse faults form in response to
compressional forces.
Deformation and Geologic Structures
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Faults
Reverse Faults
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Faults
Strike-slip faults
Faults in which all
movement is in the
direction of the strike of
the fault plane are known
as strike-slip faults.
Strike-slip faults are
classified as right-lateral
or left-lateral dependingon the apparent direction
of the offset between
blocks.
Fig. 10.16 d, p. 260
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Left-lateral
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Faults
Oblique-slip faults Oblique-slip faults have both strike-slip and
dip-slip components of movement.
Fig. 10.16e, p. 260
Deformation and the Origin of Mountains
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A mountain is an area of land that stands at least 300 meters
above the surrounding country and has a restricted summit area.
A mountain range is a group of linear peaks and ridges that
formed together.
A mountain system is a complex group of linear peaks and ridges
that is composed of several mountain ranges. Mountain systems
are the result of plate movements and interactions along plate
boundaries.
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DipStrike
THE PARTS OF A BRUNTON COMPASS
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1.Place the bottom EDGE of the compass flat
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ace t e botto G o t e co pass at
against the plane of interest.
2.Adjust the compass orientation, making
sure the bottom edge is always flat
3.against the plane, until the air bubble in
the "Bull's eye level" is centered.
4.Read either end of the compass needle to
obtain the value of strike.
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STRIKE
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STRIKE
AFTER you determine strike, rotate thecompass 90.
Place the SIDE of the compass flat against the
plane. Adjust the lever on the back of the compass
until the air bubble in the "Clinometer level" iscentered.
Read the dip directly from the scale in thecompass.
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