normal faults dominate extensional tectonic environments form locally in both convergent and...
TRANSCRIPT
![Page 1: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/1.jpg)
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
![Page 2: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/2.jpg)
Starting point: rift to drift Note thinning of crust
and lithosphere Asthenosphere
interacts with crust Volcanism, normal
faults, high geothermal gradient
![Page 3: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/3.jpg)
Transform faults Transfer motion
between mid-ocean ridge segments
Movement sense dictated by variations in rate of extension; can change along strike
Parallel movement direction
![Page 4: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/4.jpg)
Intracontinental extension ‘Master faults’ are
normal faults Strike roughly
perpendicular to extension direction (exception: reactivation of older faults)
![Page 5: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/5.jpg)
Magnitude of extension in B&R Imagine state lines
were strain markers Approximate
extension associated with part of the B&R is shown
Hamilton (1978)
![Page 6: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/6.jpg)
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
![Page 7: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/7.jpg)
Symmetry Two conceptual
models for extension Both have ductile
thinning at depth One has dominant
dip direction (synthetic with respect to detachment)
![Page 8: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/8.jpg)
Metamorphic core complexes
![Page 9: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/9.jpg)
Metamorphic core complexes Exposed in belt
extending from Canada into Mexico
Record greater extension than high-angle normal faults
![Page 10: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/10.jpg)
Domino-style faulting Fault blocks rotate
with progressive extension
Syntectonic sediments record tilting with progressively changing dip
Note this requires detachment at depth
![Page 11: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/11.jpg)
Drift structures Patterns recording
continental rifting preserved on both continental margins
Note that low-density salt can also participate in extension
![Page 12: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/12.jpg)
Continental extension in 3D
![Page 13: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/13.jpg)
Transfer faults Form ‘hard’ links
between normal fault segments with different magnitudes of displacement
Fault-related folds terminate at transfer faults
Gibbs (1990)
![Page 14: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/14.jpg)
![Page 15: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/15.jpg)
Folds related to dip-slip faults
![Page 16: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/16.jpg)
‘Soft-linked’ normal faults Fault displacement
decreases toward tip Overlapping (en
échelon) fault tips produce relay ramp
Walsh and Watterson (1991)
![Page 17: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/17.jpg)
Relay ramps effect sed transport
After Yielding and Roberts (1992)
![Page 18: Normal faults Dominate extensional tectonic environments Form locally in both convergent and transcurrent tectonic settings Form locally in response to](https://reader035.vdocuments.mx/reader035/viewer/2022070402/56649f265503460f94c3e00d/html5/thumbnails/18.jpg)
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