gch l16 strike-slip-tectonics · 2014. 11. 30. · microsoft powerpoint -...
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Strike-Slip Tectonics
Earth Structure (2nd Edition), 2004
W.W. Norton & Co, New York
Slide show by Ben van der Pluijm
© WW Norton; unless noted otherwise
Lecture 16
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• A strike-slip fault, in the strict sense, is a fault on
which all displacement occurs in a direction
parallel to the strike of the fault (slip lineation on a
strike-slip fault are horizontal).
• Thus, strict strike-slip displacement does not
produce uplift or subsidence, but strike-slip
movement is usually accompanied by a
component of shortening or extension.
• Transpression occurs where there is a combination of strike-slip movement and
shortening, and can produce uplift along the fault.
• Transtension occurs where there is a combination of strike-slip movement and
extension, and can produce subsidence along the fault.
• Flower structure - An array of faults in a strike-slip fault zone that merges at depth into
a near-vertical fault plane, but near the structure ground surface diverges so as to have
shallower dips.
• A positive flower structure has a component of thrusting on faults
• A negative flower structure has a component of normal faulting.
Strike-slip Tectonics EPR’s Clipperton TF and FZ
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Distributed, complex structures in Strike-Slip Zones Fig. 19.12
Arrays of subsidiary structures associated with dextral shear.
Subsidiary strike-slip faults Riedel (R) and R’ shears en echelon folds, and en echelon thrusts
en echelon folds which formed and then were later offset by shear on a strike-slip fault
En echelon normal faults and veins.
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Distributed, complex structures in Strike-Slip Zones Fig. 19.15
• A map view of
dextral simple shear
in which a square
becomes a
parallelogram, and a
circle in the square
becomes an ellipse.
• A detail of the strain
ellipse showing that
folds and thrusts
form perpendicular
to the shortening
direction, while
normal faults and
veins form
perpendicular to the
extension direction
Strain models exemplifying subsidiary structures along a strike-slip fault.
• R and R′ shears form
at an acute angle to
the shortening
direction.
• Note that R and R′ are similar to
conjugate shear fractures formed
in rock cylinder subjected to an
axial stress.
“Riedel shears”
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Transform Faults Sec. 19.2
• J. Tuzo Wilson introduced the term “transform faults” to the geologic literature in the
early 1960s for plate boundaries that are not distinctly convergent or divergent
• Transform fault can be applied more
broadly to describe any strike-slip fault
that has the following characteristics:
• The active portion of a transform fault
terminates at discrete endpoints that
intersects other structures
• The length of a transform fault
can be constant or vary over time. Transform length increases as the two triple junctions (T1 and T2) defining the endpoints move apart.
Transform length decreases if the spreading rate at one endpoint is
less than the subduction rate at the other.
Transform length stays constant if spreading rates on ridge segments at both endpoints are the same.
SAP = South American Plate, NAP = North American Plate, AFP = African Plate, ANP = Antarctic Plate, NZP = Nasca Plate, PCP=Pacific Plate, SP = Scotia Plate, MAR = Mid-Atlantic Ridge.
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Oceanic and Continental Transform Faults Sec. 19.2
A continental transfer fault linking two rift segments can evolve into an oceanic transform offsetting mid-ocean ridges
Transform faults along the Mid-AtlanticRidge in the South Atlantic Ocean.
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Continental transform fault: San Andreas Fault (US) Fig. 19.1
North American and Pacific Plate Plate boundary
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San Andreas Fault (38-0Ma)
T. Atwater, UCSB
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Transform Faults Fig. 19.5
• The amount of displacement remains the same along the length of a transform if the length of the transform stays constant or decreases.
• If the transform length
changes with time, then the amount of slip varies along
the length.
Displacement at X is the same as the displacement at Y.
Displacement at X, in the middle of the fault,
is greater than displacement at point Y, near an endpoint.
(ex.) At time 1, the fault is fairly short.
At time 2, the length of the fault is longer.
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Continental transform fault: Alpine Fault (NZ) Fig. 19.2
The Alpine Fault in New Zealand links the Macquarie Trench (M) with the Tonga-KermadecTrench (TK)
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Transcurrent Faults Fig. 19.5
• Die out along their length, do not
terminate abruptly at another fault,
but either splays into an array of smaller faults (horsetails), or simply
disappears into a zone of plastic
strain.
• Depending on the direction of fault-tip
curvature and sense of displacement, movements will be accompanied
either by folding and uplift where
there is a thrust component, or by
tilting and subsidence where there is a normal component.
• Fault displacement measured in map view is
proportional to fault length.
• Displacement across a transcurrent fault is
greatest near the center of its trace and
decreases to zero at the endpoints of the fault
• The displacement on a transcurrent fault must
always be less than the length of the fault.
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Transcurrent Faults Fig. 19.9
• Initiate at a point and grow along their length
as displacement increases
Transcurrent Fault
Rule of thumb: Displacement = 0.03 or Length (L = 30 D)
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Distributed, complex structures in Strike-Slip Zones Fig. 19.11
Stepover along strike-slip faults.
At a releasing stepover,
extension and subsidence occur.
At a restraining
stepover,
compression and thrusting
occur.
• A stepoveroccurs where fault slip is relayed from one fault to another
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Transcurrent fault evolution Fig. 19.14
• A clay cake rests on two wooden blocks that were pressed together.
• The clay represents the weak uppermost crust, and the wood blocks represent the stronger lower crust.
• The vertical boundary between the two blocks represents the strike-slip fault.
Laboratory model of strike-slip fault
development. As deformation begins, Riedel shears develop
A mature transcurrent fault system showing a through-going fault, in which Riedel shears have been linked by P fractures.
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Transcurrent fault evolution Fig. 19.14
An example of a clay-cake experiment for left-lateral shearA side-scan radar image from the Darien Basin in eastern Panama showing an array of en echelon anticlines. The field of view is about 50 km.
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Block Rotation in Strike-Slip Zones Fig. 19.16
Mechanisms of block rotation in a right-lateral strike-slip zone.
• The grid lines rotate and
fault-bounded blocks may
rotate intact as slip on
bounding faults increases
(bookshelf model).
• Alternatively, smaller, less
organized fault blocks may
form with varying directions
and amount of rotations.
• Paleomagnetic declination
data give rotaitons for each
block (solid arrows) realtive
to a reference direction
(dashed line).
• Map view of a grid
being subjected to
dextral simple
shear.
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Continental Strike-Slip Faults: Anatolia (Turkey) Fig. 19.25
Lateral escape in response to the northward movement of the Arabian Plate is squeezing Turkey out to the west.
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Continental strike-slip faults: Red River and Altyn Tagh faults (E Asia)
Sketch map showing India colliding with southern Asia.
• Strike-slip faults have developed in several settings here.
• The Chaman Fault (CF) is a transform boundary that
delimits the northwestern edge of the Indian subcontinent.
• Strike-slip faults also form due to oblique collision, oblique
convergence, and lateral escape.
• Small rifts have developed just north of the Himalayas.
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Transtension, Transpression, and Fault Bends
• Transpression occurs where
there is a combination of strike-
slip movement and shortening, and can produce uplift along the
fault.
• Transtension occurs where
there is a combination of strike-
slip movement and extension, and can produce subsidence
along the fault.
• Restraining
bend at which
thrust faults form transverse
uplifts.
• Releasing bend
at which normal
faults form a pull-apart basin
Simple wood block model illustrating the concept of transpression and transtension.
When blocks shear and pull apart sand sags.
When blocks shear and squeeze together sand is pushed up
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Transtension, Transpression, and Fault Bends
San Andreas Fault north of Los Angeles (LA)
Restraining
bend
Releasing
bend
Transverse mountain rangeIs where a fold-thrust belt forms at a restraiing bend causing uplift
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Transpressions and Transtension
Structures along SAF near Palmdale, CA
Pressure ridge in a road cut across the San Andreas Fault near Palmdale, Ca.
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Flower Structure - An array of faults in a
strike-slip fault zone that merges at depth into a near-
vertical fault plane, but near the structure ground surface diverges so as to have shallower dips.
Seismic-reflection profile across strike-slip fault in Ardmore Basin, Oklahoma, showing positive flower structure
A positive flower structure has a
component of thrusting on faults
A negative flower structure has a
component of normal faulting.
Strike-Slip Duplex Fig. 19.21
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Map-view sketch of
strike-slip duplexes
formed along a dextral
strike-slip fault.
• A strike-slip duplex consists of an array of several faults that parallels
a bend in a strike-slip fault
Walnut Brook, Flemington Fault
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Strike-slip faulting at oblique convergent margin Fig. 19.24
• Map-view sketches showing
progressive stages during
oblique docking of an exotic
terrane.
• Note how the terrane is sliced
by faults subsequent to
docking, and slivers slip along
the length of the orogen.
Relative movement of the subducting plate.
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Strike-Slip Faulting in Fold-Thrust Belts
• Map of the Pine Mountain thrust
system in the southern
Appalachians (eastern USA),
showing lateral ramps (Jacksboro
Fault and Russell Fork Fault).
• Block diagram
indicating the
concept of a
lateral ramp or
tear fault.
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Strike-Slip Faulting in Rifts and Accomodation Zones
Garlock Fault, southern California
Map and block model of the Garlock Fault, southern California (USA), accommodating the offset from the extended Basin and Range Province to the north and the Mojave Desert to the south.
Each segment in a rift is linked to its neighbor by an accommodation zone.
In places where an accommodation zone consists of a strike-slip fault, it can also be called a transfer fault
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Oceanic Transform Faults and Fracture Zones
• Transform Fault: Active displacement.
• Fracture Zone: Fossil fault, no active displacement.
marine-geo.org
Clipperton fracture zone (FZ) and transform zone (TZ) of the East Pacific Rise (EPR).
Note intersection highs at ridge tips, and trough and ridges along the transform zone.