Intraplate deformation: Difference between revisions
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Many geophysical observations in [[Tibet]] show a weak crustal zone and suggest that the middle to lower [[Crust (geology)|crust]] may contain fluids and be partially melted.<ref name= "Ooze">{{cite journal | title=Topographic ooze: Building the eastern margin of Tibet by lower crustal flow | author=Clark and Royden | journal=Geology | year=2000 | month=August | volume=28 | issue=8 | pages=703–706|doi= 10.1130/0091-7613(2000)28<703:TOBTEM>2.0.CO;2|url=http://es.ucsc.edu/~rcoe/eart206/Clark_LowCrustFlowTibet_Geology00.pdf}}</ref> As the Himalayan-Tibet region began to rise, lateral [[extrusion]] of the crust in the Tibetan plateau gradually became the dominant mechanism for accommodating the collision and crustal shortening.<ref name= "Ooze"/> The lateral extrusion is sliding dominantly to the east and out of India's path. Eastern Tibet is traditionally interpreted as being part of a broad accommodation zone.<ref name="Kinematic">{{cite journal | title=Kinematic model of active deformation in central Asia | authors=Jean‐Philippe Tapponnier and Paul Avouc | year=1993|doi=10.1029/93GL00128|journal=Geophysical Research Letters|volume=20|issue=10|page=895}}</ref> Much of the eastern movement is due to major strike-slip faults.<ref name= "collision">{{cite journal | title=The collision between India and Asia | author=Molnar and Tapponier | journal=Scientific American | year=1977 | volume=236 | issue=4 | pages=30–41}}</ref> These strike-slip faults, along with the other faults in Tibet could still be interpreted as on a plate margin though. True intraplate deformation occurs farther north in areas such as [[Mongolia]] or the [[Tian Shan Mountains|Tian Shan mountains]]. These areas display true intraplate deformation because there is still much faulting and folding to accommodate some of the crustal shortening from the India/Eurasia collision hundreds of kilometers away from the plate margin. |
Many geophysical observations in [[Tibet]] show a weak crustal zone and suggest that the middle to lower [[Crust (geology)|crust]] may contain fluids and be partially melted.<ref name= "Ooze">{{cite journal | title=Topographic ooze: Building the eastern margin of Tibet by lower crustal flow | author=Clark and Royden | journal=Geology | year=2000 | month=August | volume=28 | issue=8 | pages=703–706|doi= 10.1130/0091-7613(2000)28<703:TOBTEM>2.0.CO;2|url=http://es.ucsc.edu/~rcoe/eart206/Clark_LowCrustFlowTibet_Geology00.pdf}}</ref> As the Himalayan-Tibet region began to rise, lateral [[extrusion]] of the crust in the Tibetan plateau gradually became the dominant mechanism for accommodating the collision and crustal shortening.<ref name= "Ooze"/> The lateral extrusion is sliding dominantly to the east and out of India's path. Eastern Tibet is traditionally interpreted as being part of a broad accommodation zone.<ref name="Kinematic">{{cite journal | title=Kinematic model of active deformation in central Asia | authors=Jean‐Philippe Tapponnier and Paul Avouc | year=1993|doi=10.1029/93GL00128|journal=Geophysical Research Letters|volume=20|issue=10|page=895}}</ref> Much of the eastern movement is due to major strike-slip faults.<ref name= "collision">{{cite journal | title=The collision between India and Asia | author=Molnar and Tapponier | journal=Scientific American | year=1977 | volume=236 | issue=4 | pages=30–41}}</ref> These strike-slip faults, along with the other faults in Tibet could still be interpreted as on a plate margin though. True intraplate deformation occurs farther north in areas such as [[Mongolia]] or the [[Tian Shan Mountains|Tian Shan mountains]]. These areas display true intraplate deformation because there is still much faulting and folding to accommodate some of the crustal shortening from the India/Eurasia collision hundreds of kilometers away from the plate margin. |
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=====North America===== |
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[[File:New Madrid Seismic Zone activity 1974-2011.svg|thumb|Figure 3: New Madrid Seismic Zone activity 1974-2011. Red dots represent earthquake locations.]] |
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One main contributor to intraplate deformation in North America is the [[New Madrid Seismic Zone]]. This location can be seen in Figure 3. This zone is made up of reactivated faults that formed when North America began to rift apart during the breakup of [[Rodinia]] in the [[Neoproterozoic]], around 750 million years ago.{{fact|date=December 2012}} The rifting failed but it left a zone of weakness in the crust.{{fact|date=December 2012}} This zone of weakness contains two major faults: A northwest to southeast trending thrust fault named the Reelfoot fault, and a northeast to southwest trending right-lateral strike-slip fault named the Cottonwood Grove Fault. Structural and [[Geomorphology|geomorphic]] analysis of the area shows an estimated slip rate for the Reelfoot fault to be 6.1±0.7 mm/year, and a slip rate of 1.8-2.2 mm/year on the Cottonwood Grove fault. |
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==See also== |
==See also== |
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Revision as of 08:00, 9 December 2012
Intraplate deformation is the folding, breaking, or flow of the Earth's crust within plates instead of at their margins. This process usually occurs in areas with especially weak crust and upper mantle, such as the Tibetan Plateau (Figure 1). Intraplate deformation brings another aspect to plate tectonic theory.
Crustal deformation processes
The theory of plate tectonics states that the Earth's crust is made up of rigid plates that "float" on top of the mantle and move relative to one another. As the plates move, the crust deforms dominantly along the plate margins. Intraplate deformation differs from that respect by the observation that deformation can occur anywhere the crust is weak and not just at plate margins.
Deformation is the folding, breaking, or flow of rocks. There are many different types of crustal deformation depending on whether the rocks are brittle or ductile. The aspects that determine these properties are due to certain temperatures and pressures that rocks experience within the Earth. Therefore, temperature and pressure control deformation processes. Ductile rocks tend to bend, fold, stretch, or flow due to compressional or extensional forces. Brittle rocks, on the other hand, tend to break. The zone where the crust breaks is termed a fault. There are three main types of faults:[1] normal faults, reverse faults, and strike slip (transform) faults. All of these are ways the crust can deform is due to the different types of plate margins, which are:[2] divergent boundaries, convergent boundaries, and transform boundaries.
These three boundaries do not always form perfectly and this can lead to a mixed boundary. Mixed boundaries can be a combination of a transform with convergence or a transform with divergence.
Intraplate deformation examples
Asia
Central/East Asia is possibly the best example of large-scale intraplate deformation. The formation and uplift of the Tibetan plateau and the Himalayan mountain range started in the Cenozoic era around 50 million years ago when the Indian plate collided with the Eurasian plate.[3] The collision caused much shortening of the lithosphere, adding to increased crustal thickness and high stress in the Himalaya/Tibet region.[3]
Many geophysical observations in Tibet show a weak crustal zone and suggest that the middle to lower crust may contain fluids and be partially melted.[4] As the Himalayan-Tibet region began to rise, lateral extrusion of the crust in the Tibetan plateau gradually became the dominant mechanism for accommodating the collision and crustal shortening.[4] The lateral extrusion is sliding dominantly to the east and out of India's path. Eastern Tibet is traditionally interpreted as being part of a broad accommodation zone.[5] Much of the eastern movement is due to major strike-slip faults.[6] These strike-slip faults, along with the other faults in Tibet could still be interpreted as on a plate margin though. True intraplate deformation occurs farther north in areas such as Mongolia or the Tian Shan mountains. These areas display true intraplate deformation because there is still much faulting and folding to accommodate some of the crustal shortening from the India/Eurasia collision hundreds of kilometers away from the plate margin.
See also
References
- ^ Michael E. Ritter (21 June 2007). "Types of Faults". The Physical Environment: an Introduction to Physical Geography. University of Wisconsin Stevens Point. Retrieved October 15, 2012.
- ^ J. M. Watson (24 May 2012). "Understanding plate motions". U. S. Geological Survey Publications Warehouse. Retrieved October 13, 2012.
- ^ a b Molnar and Tapponnier (1975). "Cenozoic Tectonics of Asia: Effects of a Continental Collision" (PDF).
{{cite journal}}: Cite journal requires|journal=(help) - ^ a b Clark and Royden (2000). "Topographic ooze: Building the eastern margin of Tibet by lower crustal flow" (PDF). Geology. 28 (8): 703–706. doi:10.1130/0091-7613(2000)28<703:TOBTEM>2.0.CO;2.
{{cite journal}}: Unknown parameter|month=ignored (help) - ^ "Kinematic model of active deformation in central Asia". Geophysical Research Letters. 20 (10): 895. 1993. doi:10.1029/93GL00128.
{{cite journal}}: Unknown parameter|authors=ignored (help) - ^ Molnar and Tapponier (1977). "The collision between India and Asia". Scientific American. 236 (4): 30–41.