01 Interior Bumi Batas Lempeng

7/25/2019 01 Interior Bumi Batas Lempeng

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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.
http://mediatheek.thinkquest.nl/~ll125/en/crust.htmhttp://mediatheek.thinkquest.nl/~ll125/en/crust.htm


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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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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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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


i d iContinental crust

OCEANIC CONTINENTAL


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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



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Divergent BoundariesContinental crustOCEAN OCEAN PLATE COLLISION



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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



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Divergent BoundariesContinental crustPLATE BOUNDARY AROUND THE GLOBE


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Movement Rate of Plate Tectionic



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whats the connection?

Volcanoes and Plate Tectonics

Divergent BoundariesContinental crustPLATE BOUNDARY AROUND THE GLOBE



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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


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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



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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.


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)



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.



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



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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?


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.



Rock Deformation How Does it Occur?


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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.




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Action of oppositely directed forces actingtowards each other at the same time

Compression




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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




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Tension

Action of coinciding and oppositely directedforces acting away from each other





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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.





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ShearAction of coinciding and oppositely directedforces acting parallel to each other across asurface





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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.





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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





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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





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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?


Rock Deformation - How Does it Occur?


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Where do earthquakes form?yDivergent BoundariesRock Deformation - How Does it Occur?




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Strike and Dip on a Rooftop



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




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1 Fold

2 Fault

3 Joint

4 Fracture

Type of rock deformation





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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




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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?


Folded Rocks


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Where do earthquakes form?yDivergent BoundariesFolded Rocks


Folded Rocks


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Where do earthquakes form?ye ge t ou da esFolded Rocks


Folded Rocks


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Where do earthquakes form?yg Folded Rocks


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



Folded Rocks


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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


Folded Rocks


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q yg Folded Rocks


Folded Rocks


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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


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


Folded Rocks


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qg


Folded Rocks


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Overturned folds

q


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


Folded Rocks


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q


Folded Rocks


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q


Folded Rocks


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Folded Rocks


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Folded Rocks


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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


Folded Rocks


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ERODED DOME


Folded Rocks


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Folded Rocks


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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.



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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.



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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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01 Interior Bumi Batas Lempeng