Transcript Document

Normal faults
Dominate extensional tectonic
environments
 Form locally in both convergent and
transcurrent tectonic settings
 Form locally in response to removal or
addition of material
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Starting point: rift to drift
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Note thinning of crust
and lithosphere
Asthenosphere
interacts with crust
Volcanism, normal
faults, high
geothermal gradient
Transform faults
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Transfer motion
between mid-ocean
ridge segments
Movement sense
dictated by variations
in rate of extension;
can change along
strike
Parallel movement
direction
Intracontinental extension
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‘Master faults’ are
normal faults
Strike roughly
perpendicular to
extension direction
(exception:
reactivation of older
faults)
Magnitude of extension in B&R
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Imagine state lines
were strain markers
Approximate
extension associated
with part of the B&R
is shown
Hamilton (1978)
Elements of an extensional
system in cross section
Note topography, producing sedimentary
depocenters
 Detachment faults allow rotation of blocks
bounded by high-angle normal faults
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Symmetry
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Two conceptual
models for extension
Both have ductile
thinning at depth
One has dominant
dip direction
(synthetic with
respect to
detachment)
Metamorphic core complexes
Metamorphic core complexes
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Exposed in belt
extending from
Canada into Mexico
Record greater
extension than highangle normal faults
Domino-style faulting
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Fault blocks rotate
with progressive
extension
Syntectonic
sediments record
tilting with
progressively
changing dip
Note this requires
detachment at depth
Drift structures
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Patterns recording
continental rifting
preserved on both
continental margins
Note that low-density
salt can also
participate in
extension
Continental extension in 3D
Transfer faults
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Form ‘hard’ links
between normal fault
segments with
different magnitudes
of displacement
Fault-related folds
terminate at transfer
faults
Gibbs (1990)
Folds related to dip-slip faults
‘Soft-linked’ normal faults
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Fault displacement
decreases toward tip
Overlapping (en
échelon) fault tips
produce relay ramp
Walsh and Watterson
(1991)
Relay ramps effect sed
transport
After Yielding and
Roberts (1992)
Duplexes may form in any
(curviplanar) fault system
Note the association between fault-plane
topography and duplexes
 Horses believed to form by ‘lopping off’
irregularities on fault surface
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