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    Folds & Faults

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    content

    Introduction

    Definition of folds.

    Types of folds.

    Definition of faults.

    Types of faults.

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    Introduction

    Structural geology :

    is the study of three dimensional distribution of rock

    units with respect to their deformational histories

    The study of geologic structures has been of prime

    importance in economic geology

    Folded and faulted rock strata commonly forms traps or

    the accumulation and concentration of fluids such aspetroleum and natural gas

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    Folds The term fold is used in geology when one or a stack of

    originally flat and planar surfaces, such as sedimentary strata,are bent or curved as a result of plastic (i.e. permanent)

    deformation , Folds form under varied conditions of stress,

    hydrostatic pressure, pore pressure

    Types :-

    Anticline

    Syncline

    Tight Fold

    Overturned fold

    Recumbent Fold

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    Anticline

    In structural geology, ananticline is a fold that is convexup and has its oldest beds at itscore .

    Fold mountains are formed

    when the crust is pushed up astectonic plates collide. Whenformed, these mountains areusually enormous like the newlyformed Rocky Mountains inWestern Canada and the UnitedStates

    Anticlines and structural domesare favored locations for oil andnatural gas drilling

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    Syncline

    A syncline is similar to an anticline,in that it is formed by thecompression of a tectonic plate.However, a syncline occurs whenthe plate bends in a downwardmotion.

    The lowest part of the syncline isknown as the trough.

    on a geologic map, synclines are

    recognized by a sequence of rocklayers that grow progressivelyyounger, followed by the youngestlayer at the fold's center or hinge , Ifthe fold pattern is circular orelongate circular the structure is a

    basin.

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    Tight Fold

    A tight fold is a sharp peakedanticline or syncline.

    It is just a regular anticline orsyncline, but was compressed

    with a greater force causing theangle to be much smaller.

    Folds such as these occur to formsteep mountain slopes like those

    in Whistler, British Columbia.

    Angle between the folds limbsrang from 30 to 0

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    Overturned fold

    An over fold takes place when folding rock becomes bent orwarped.

    axial plane is inclined and both limbs in the same direction ,usually at different angle

    Sometimes the folds can become so disfigured that they mayeven overlap each other.

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    Recumbent Fold

    This type of fold is

    compressed so much that it

    is no longer vertical.

    There is a large extent of

    overlapping and it can take

    the form of an s.

    To the right is a diagram

    that shows the process of

    recumbent folding.

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    Faults Fault is planner fracture in rock in which the rock on one

    side of the fracture has moved with respect to the rock on the

    other side , Earth quakes are caused by energy release

    during rapid slippage along a fault

    Types :-

    Dip-slip fault

    - Normal Fault

    - Reverse Fault

    Strike-slip Fault

    Oblique-slip fault

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    Normal Fault

    In a normal fault, the blockabove the fault moves downrelative to the block below thefault. This fault motion is caused

    by tensional forces and results inextension. Other names: normal-

    slip fault, tensional fault orgravity fault.

    On the top right is the movementof a normal fault. A picture is

    also shown below. Notice thedisplacement of the differenttypes of rock on each side of thefault.

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    Reverse Fault Reverse faults are the opposite of

    normal faults. Rocks arecompressed such that one platemoves up while the other descends

    below it.

    When plates compress and crack,usually the more dense one isforced under the less dense one.This is similar to the action of thecontinental crust colliding with theoceanic crust. Here the moredense crust, being the oceanic

    crust is forced under thecontinental crust.

    To the right is an animation of areverse fault. Below that is a real

    picture of what a reverse fault

    looks like.

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    Strike-slip Fault

    A strike-slip fault , also known as a transform fault, occurs

    when two tectonic plates slide in a lateral motion past eachother.

    This type of fault causes the most severe earthquakes becausethey grind against each other. These earthquakes can either be

    shallow or deep and cause tremors over a short or long periodof time.

    Strike-slip faults can occur frequently, especially along thecoast of California.

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    Oblique Fault

    Oblique-slip faulting suggests both dip-slip faulting and strike-

    slip faulting. It is caused by a combination of shearing and

    tension of compressional forces.

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    Horst & Graben Fault

    A Horst is the opposite of arift valley. The land

    between the parallel faults isforced upward because thetwo faults are being pushed

    together. This process can take a long

    time to occur because theaverage plate movement isone inch per year

    There are examples of horstfaults on the left.

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    Summary

    Folding and faulting has a major influence on

    the way the earth looks. Mountains form and

    disappear over time, as well as large rift

    valleys and other features. This has an impact

    on where and how we live.

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    Thanks for your

    attention