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Wrench Tectonics:
Strike-slip Boundaries
Processes in Structural Geology & Tectonics
Ben van der Pluijm
© WW Norton+Authors, unless noted otherwise
4/2/2016 4:14 PM
We Discuss …
• Classes of Strike-slip Faults
• Transfer Faults
• Transcurrent Faults
• Strike-slip Systems
• Transpression and
Transtension
• Restraining and Releasing
Bends
• Strike-slip Duplexes
• Subsidiary Structures
• Continental Strike-slip Zones
• Transfer Faults
• Tectonic Extrusion
• Terrane Slicing
• Oceanic Strike-slip Zones
• Transform Faults
• Fracture Zones
Clipperton Fracture Zone (EPR)
San Andreas Fault (CA)
Alpine Fault (NZ)
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Today’s Plates and Strike-slip Boundaries
Divergent
Convergent
Strike-slip
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Wrench Faulting
Strike-slip faults
Faults on which displacement is (mostly) parallel to their surface
intersection. The term is purely geometric, and has no genetic,
tectonic or size connotation. Wrench faults are subdivided into two
kinematic classes: transcurrent faults and transfer faults
Transcurrent fault
Characteristics:
- it dies out along its length;
- the displacement across is less than length of the fault;
- the length of the fault increases with time and continued movement;
- displacement is greatest at center of fault trace and decreases toward its ends.
Transfer (or transform) fault
Characteristics:
- once formed, displacement across can be constant along length of the fault;
- displacement across can be much greater than length of the active fault;
- its length can be constant, increase, or decrease with time.
- it terminates at another fault (e.g., plate boundary)
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Wrench Faulting
Faults on which displacement is (mostly) parallel to fault strike, in present-day surface
coordinates. The term is purely geometric, and has no genetic, tectonic, or size
connotation. Strike-slip faults are subdivided into two kinematic classes: transcurrent
faults and transfer faults
Transcurrent fault
Characteristics:
- it dies out along its length;
- the displacement across is less than length of the fault;
- the length of the fault increases with time and continued movement;
- displacement is greatest at center of fault trace and decreases toward its ends.
Transfer (or transform) fault
Characteristics:
- once formed, displacement across can be constant along length of the fault;
- displacement across can be much greater than length of the active fault;
- its length can be constant, increase, or decrease with time.
- it terminates at another fault (e.g., plate boundary)
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Oceanic Transfer Faults or Oceanic Transforms
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Oceanic Transfer Faults
(=Oceanic Transforms)
TF
FZ
EPR’s Clipperton TF and FZ
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Oceanic Transforms and Fracture Zones
Transform Fault: Active displacement.
Fracture Zone: Fossil fault, no active
displacement.
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.
marine-geo.org
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Extensional Transfer Faults: Accommodation
Garlock Fault, southern California
extension
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Contractional Transfer Faults: Lateral Ramp (“Tear Faults”)
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Continental Transfer Faults: N&S Anatolian Faults (Turkey)
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Continental Transfer Faults: SAF
San Andreas Fault
(CA) is a continental
transform:
Displacement rate
unchanged while
length changes, but
total displacement
varies along growing
SAF.
Dx > Dy
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San Andreas Fault (38-0Ma)
T. Atwater (UCSB)
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Transfer faults: Length and Displacement
Transfer fault length with time:
a) same
b) decrease
c) Increase
Displacement rate always same (mm/yr), but total displacement can vary
along lengthening transforms (e.g., SAF case)
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Wrench Faulting
Faults on which displacement is (mostly) parallel to their surface intersection. The
term is purely geometric, and has no genetic, tectonic or size connotation. Wrench
faults are subdivided into two kinematic classes: transcurrent faults and transfer faults
Transcurrent fault
Characteristics:
- it dies out along its length;
- the displacement across is less than length of the fault;
- the length of the fault increases with time and continued movement;
- displacement is greatest at center of fault trace and decreases toward its ends.
Transfer (or transform) fault
Characteristics:
- once formed, displacement across can be constant along length of the fault;
- displacement across can be much greater than length of the active fault;
- its length can be constant, increase, or decrease with time.
- it terminates at another fault (e.g., plate boundary)
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Transcurrent Faults
Transcurrent faults lengthen (L) with increasing
displacement (D).
Rule of thumb:
Displacement = 0.03 . Length
(or, L = 30 . D)
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Transcurrent Fault Evolution
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Transcurrent Faults and Oblique Convergence: Terranes
Terrane accretion and terrane
slicing
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Wrench Systems: Subsidiary Faults and Structures
Riedel shears
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Wrench Systems: Fault Stepovers and Fault Terminations
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Wrench Systems: Fault Bends
Releasing bend
Restraining bend
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Wrench Systems: Transpression and Transtension
Contractional structures along SAF near
Palmdale, CA
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Wrench Systems: Flower Structures
Seismic-reflection profile across a strike-slip fault in Ardmore
Basin (Oklahoma), showing positive flower structure.
(a) Positive flower structure.
(b) Negative flower structure.
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Hybrid Wrench Systems: Transpression
Alpine Fault (New Zealand)
• Continental transpressional
transform
• Large (rapid) uplift and
exhumation of hangingwall
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Hybrid Wrench Systems: Lateral Escape
ATF
RRF
(a) Red River (RRF) and Altyn Tagh (ATF) continental transfer faults and the
Himalayan convergence zone.
(b) Progressive extrusion (or lateral escape) of tectonic blocks in SE Asia.
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