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dwzwy: Geology : 200607
STAG1032: PHYSICAL GEOLOGY (Geologi Fizik)
DYNAMIC EARTH (2 hours)
•Force, Stress and Strain. •Formation of folds, faults & Joints
Dr. Wan Zuhairi Wan YaacobProgram Geologi, UKM
dwzwy: Geology : 200607
Principal of original horizontality?
Horizontal layers of sediments accumulation
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Rock Deformation
• Deformation (de = out ; forma = form)– Changes in shape / size /volume of rock
• Stress (tegasan)– the result of force applied to a given area of rock
• Strain (terikan)– deformation caused by stress (i.e. intensity of stress
> rock’s internal strength)• Deformation ~ strain• 3 types of stress:
– (1) Compression (mampatan)– (2) Tension (regangan)– (3) Shear (ricihan)
dwzwy: Geology : 200607
StressF
• Stresses (tegasan); P = F/A– Depending on the direction of
forces– (1) Compression
• Forces directed toward one another
• Acts to compress objects– (2) Tensional
• Forces acting in opposite direction
• Acts to stretch objects– (3) Shear
• Forces act parallel but in opposite direction
dwzwy: Geology : 200607
Higher stressLow stress
The same force, applied to a rock over a broad surface area results in a low applied stress, whereas the same force, applied over a smaller area produces a much higher stress.
dwzwy: Geology : 200607
Types of Deformation (Strain)
• Three types of strain depending on the response of rocks to stress:-
• (1) Elastic deformation– Recoverable deformation– Directly proportional to applied load– When elastic limit is exceeded, permanent deformation
• (2) Plastic deformation– Non recoverable deformation– Ductile (folding & flowing)
• Rupture after plastic deformation
• (3) Brittle Deformation– Rupture before plastic deformation– Faults– Brittle failure of rock solids
dwzwy: Geology : 200607
dwzwy: Geology : 200607
Elastic-plastic deformation(Ductile rock)
Plastic fracture
Material A
dwzwy: Geology : 200607
Types of stress application and their resultant strain.
STRAINSTRESS
Shorteningcompression
lengtheningtensional
dL
σ
rotating
L
shear
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StrainType of strain depends on:--• (1) Kind of stress applied• (2) The amount of temperature & pressure
– Rocks near surface; low T & P ; brittle solid– Brittle (bryttian = to shatter)– At depth, high T & P ; rocks exhibit ductile behavior
• (3) The rock type– Rocks are considered either ductile / brittle depending on the amount of
plastic deformation– Influence by mineral composition and texture– Crystalline rocks (granit, basalt, quartzite)
• strong internal bonds• Fail by brittle fracture
– Sedimentary rocks (weakly cemented); metamorphic rocks (foliation)• Fail by ductile deformation / flow
• (4) Length of time the rock is subjected to stress– Small stress; longer time – plastic deformation– Large stress applied rapidly – fracture
dwzwy: Geology : 200607
An example of plastic deformation due to small stressbut was applied in a longer time span
dwzwy: Geology : 200607
DEFORMATION AND GEOLOGIC FRACTURES
• Folds (lipatan)
• Faults (sesar)
• Joints (kekar)
Type of rock?Type of stress ?
Type of rock?Type of stress ?
Type of rock?Type of stress ?
Ductile rocksCompression
Brittle rocksCompression/Tensional/shear
Brittle rocksCompression/Tensional
dwzwy: Geology : 200607
dwzwy: Geology : 200607
Primary vs. Secondary structures ??
(b)
Folds
(a) lamination
(c)
(d) Folds
faults
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FAULTS the terminology
• Fault– Fracture along which blocks on opposite
sides of the fracture move parallel with the fracture surface (fault plane)
• Fault scarp– A cliff formed as a result of vertical
movement (quickly modified by erosion)
• Fault breccia– Crushed and shattered rock (angular
blocks)
• Slickenside – Scratch or polish surface of a fault plane
• Hanging wall block– block of rock overlying the fault
• Foot wall block– Lies beneath the fault plane
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footwall
Fault drag
dwzwy: Geology : 200607
Some manifestations of faults
(PEPARIT)
(GOREKAN)
(muka upam)
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slickensides on the fault plane discovered at Jeram Besu, Benta Pahang
dwzwy: Geology : 200607 (KERUKAN)(BREKSIA)
A fault zone/plane with crushed and shattered angular blocks
Clay-like material that is produced by the movement of a fault.
dwzwy: Geology : 200607
Dip and strike?
• Fault planes are characterized by dip and strike similar to rock layers
• Strike:– Direction of a line formed
by intersection of a horizontal plane with an inclined plane
• Dip:– A measure of an inclined
plane’s inclination from horizontal
dwzwy: Geology : 200607
Strike and dip(jurus dan kemiringan)
dwzwy: Geology : 200607
Types of faults
• Movement parallel to the dip of the fault plane – Dip Slip Faults
• Movement in the direction of the fault plane’s strike – Strike Slip faults
• Combination of dip-slip and strike-slip movements is called oblique-slip fault.
dwzwy: Geology : 200607
FAULTS (SESAR)
• DIP SLIP FAULTS– Normal faults– Reverse faults
• Dip>45 ; Reverse faults• Dip<45 ; Thrust faults
• STRIKE SLIP FAULTS– Right lateral strike slip fault– Left lateral strike slip fault– Transform fault; eg: San Andreas Fault
dwzwy: Geology : 200607
dwzwy: Geology : 200607
Normal Fault (Sesar normal)
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Reverse Fault (Sesar songsang)
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Thrust fault (Sesar sungkup)
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Lateral fault (Sesar mendatar)
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Some examples of faults
(1) DIP SLIP FAULTSNormal faultsReverse faults
Dip>45 ; Reverse faultsDip<45 ; Thrust faults
(2) STRIKE SLIP FAULTSRight lateral strike slip faultLeft lateral strike slip fault
dwzwy: Geology : 200607
dwzwy: Geology : 200607Bedding A
Bedding A
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1
2
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Normal fault
Normal fault
Reverse fault
dwzwy: Geology : 200607REVERSE fault
dwzwy: Geology : 200607
dwzwy: Geology : 200607Penjom Gold Mine, K.Lipis Pahang
dwzwy: Geology : 200607
dwzwy: Geology : 200607
Reverse fault
dwzwy: Geology : 200607
San Andreas Fault
• “California has its fault”• Transform fault ; i.e. motion between two
plates• Total length = 1300 kms• Types : Right lateral strike slip fault• Total displacement = 560 kms !!• 1906 earthquake (5m displacement)
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Conservative: San Andreas Fault
dwzwy: Geology : 200607
dwzwy: Geology : 200607
dwzwy: Geology : 200607
dwzwy: Geology : 200607
Right lateral offset of a gully by the San Andreas fault in southern California. The gully is offset about 21m
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offset
dwzwy: Geology : 200607
FOLDS(Lipatan)
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Folds
• Monocline• Anticline• Syncline• Overturned• Isocline• Recumbent
Assignment !!!: Due next week; Discuss Monocline and Isocline
Simple folds (upright/inclined)
Upright --- inclined --- overturned – isocline --- recumbent
dwzwy: Geology : 200607
Folds (Lipatan)
• Compression• Variable in size:--
– Minor – a few mm’ s– Major – up to 1-2km
• Syncline– arch downwards (palung)– Oldest rock layers in its core
• Anticline– arch upwards– Youngest rock layers in its core
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Size (Scale)
MINOR MAJOR
>20m ?
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1 mm
Micro structure / folds
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Fold (Terminology)
(the axis of the fold penetratesinto the ground)
Anatomy of folds
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Fold (Terminology)
(the greatest curvature exist)
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Fold (Terminology)
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Overturned folds (Terbalik)- axial planes inclined. – limbs on either side of the axial plane dip in the same direction
Recumbent folds (Rebah)- axial planes and limbs on either side of the plane are sub-horizontal
Types of folds
dwzwy: Geology : 200607
The tightness of folds:Gentle Fold (B > 120)open (limbs dip gently; B = 120 to 70o)close fold (B = 70-30o)tight (limbs dip steeply; B = <30o)isoclinal (limbs are parallel; B = 0o).
Satah paksi (axial plane)
Garis paksi (axial line)
B
B = angle between two limbs orinterlimb angle
dwzwy: Geology : 200607
Dip of axial plane:-0-12 ---- Recumbent fold (rebah)13-89 --- Inclined/overturned fold (terbalik)90 --- upright fold (tegak)
Limb - sayap
Upright (axial plane vertical, limbs symmetric), Overturned (axial plane moderately inclined, one limb overturned-terbalik), Recumbent (axial plane near horizontal, one limb inverted - songsang).
dwzwy: Geology : 200607
Types of folds
(axis is vertical)
(axis is inclined)
dwzwy: Geology : 200607
Types of folds
dwzwy: Geology : 200607
Some examples of folds
dwzwy: Geology : 200607Upright anticline and syncline
dwzwy: Geology : 200607
Anticline (Asymmetrical fold / inclined fold)
dwzwy: Geology : 200607
dwzwy: Geology : 200607Syncline
dwzwy: Geology : 200607Syncline
dwzwy: Geology : 200607
OVERTURNED fold
dwzwy: Geology : 200607
Overturned FOLD
dwzwy: Geology : 200607OVERTURNED fold
dwzwy: Geology : 200607
Recumbent fold
dwzwy: Geology : 200607Recumbent fold
dwzwy: Geology : 200607
RECUMBENT fold (lipatan REBAH)
dwzwy: Geology : 200607 Recumbent fold
dwzwy: Geology : 200607
Isoclinal fold
The limbs and axial plane are parallel and interlimb angle is zero
dwzwy: Geology : 200607
JOINTS (Kekar)
• Fractures along which no movement has occurred• Random or parallel groups (i.e. orientation)• 3 types of joints:-
– 1. Columnar Jointing – cooling of igneous rocks and create shrinkage fractures
– 2. Sheeting• Expansion of rock as erosion removes the
overlying material (i.e. pressure release)• Exfoliation
– 3. Tensional joints• Joints associated with folds
dwzwy: Geology : 200607
2 sets of JOINTS
dwzwy: Geology : 200607
Polygonal jointing in basaltic rock
Columnar Joints – cooling of igneous rocks and create shrinkage fractures
Basalt from Kuantan, PahangTensional stress due to the contractions of the magma
dwzwy: Geology : 200607
Sheeting (or exfoliation) @ pengelupasan kulit bawangExpansion of rock as erosion removes the overlying material
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Discontinuities / Ketakselanjaran
• planes of weaknesses within the rock mass
• Bedding / Perlapisan
• Faults / Sesar
• Folds / Perlipatan
• Joints / kekar
dwzwy: Geology : 200607
The END