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Plate tectonics and basin formation (view source)
Revision as of 16:57, 30 June 2015
, 16:57, 30 June 2015no edit summary
Plate tectonics regards the lithosphere broken into plate that are in motion. The plates move relative to another along plate boundaries, sliding upon the underlying asthenosphere (the layer below the lithosphere that is formed of molten rock). The theory of plate tectonics emerged since the 1960s, and until now this theory has successfully explained various geological events, such as earthquakes, tsunamis, and volcanic eruption, also explained how the formation of mountains, continents, and oceans.
Plate tectonics regards the lithosphere broken into plate that are in motion. The plates move relative to another along plate boundaries, sliding upon the underlying asthenosphere (the layer below the lithosphere that is formed of molten rock). The theory of plate tectonics emerged since the 1960s, and until now this theory has successfully explained various geological events, such as earthquakes, tsunamis, and volcanic eruption, also explained how the formation of mountains, continents, and oceans.
[[File:plate_tectonics_map_1_-_ivana.png|framed|Plate Tectonics Map <ref> http:http://earthobservatory.nasa.gov/Features/Tectonics/Images/schematic_map.gif </ref>]]
[[File:plate_tectonics_map_1_-_ivana.png|framed|center|Plate Tectonics Map <ref> http:http://earthobservatory.nasa.gov/Features/Tectonics/Images/schematic_map.gif </ref>]]
=List of Tectonic Plates <ref> https://en.wikipedia.org/wiki/List_of_tectonic_plates </ref>=
=List of Tectonic Plates <ref> https://en.wikipedia.org/wiki/List_of_tectonic_plates </ref>=
How basin can be created? On some cases with a small scale, fault movements can create relief of hundreds to thousands of meters laterally, resulting in small but often deep basins. But, the other main reason is because the continent rift. In plate tectonic theory, if one of plates rifting into pieces diverging apart then new basins being born, followed by motion reversal, convergence back together, plate collision, and mountain building.
How basin can be created? On some cases with a small scale, fault movements can create relief of hundreds to thousands of meters laterally, resulting in small but often deep basins. But, the other main reason is because the continent rift. In plate tectonic theory, if one of plates rifting into pieces diverging apart then new basins being born, followed by motion reversal, convergence back together, plate collision, and mountain building.
==The Wilson Cycle==
Wilson cycle is a cycle opening and closing an ocean basin. Wilson cycle begins with a hypothetical geologically (tectonically) quiet continent. The model is divided into nine stages, but the stages are arbitrary and do not exist naturally. Within the earth is an ongoing series of processes and it is more important to understand these processes, how they are related, and how one process leads to the next process.
[[File:Wilsncircl.jpg|framed|center|The Wilson Cycle <ref> http://csmres.jmu.edu/geollab/Fichter/PlateTect/Images/wilsncircl.gif </ref>]]
===Stage A===
The Wilson cycle begins in Stage A with a stable continental craton. A hot spot rises up under the craton, heating it, causing it to swell upward, stretch and thin like taffy, crack, and finally split into two pieces. This process not only splits a continent in two it also creates a new divergent plate boundary.
===Stage B===
The one continent has been separated into two continents, east and west, and a new ocean basin (the Ophiolite Suite) is generated between them. The ocean basin in this stage is comparable to the Red Sea today. As the ocean basin widens the stretched and thinned edges where the two continents used to be joined cool, become denser, and sink below sea level. Wedges of divergent continental margins sediments accumulate on both new continental edges.
===Stage C===
The ocean basin widens, sometimes to thousands of miles; this is comparable to the Atlantic ocean today. As long as the ocean basin is opening we are still in the opening phase of the Wilson cycle.
===Stage D===
The closing phase of the Wilson Cycle begins when a subduction zone (new convergent plate boundary) forms. The subduction zone may form anywhere in the ocean basin, and may face in any direction. In this model we take the simplest situation; a subduction zone developing under the edge of one continent. Once the subduction zone is active the ocean basin is doomed; it will all eventually subduct and disappear. These are remnant ocean basins.
===Stage E===
Most of the remnant ocean basin has subducted and the two continents are about to collide. Subduction under the edge of a continent has a lot of results. Deep in the subduction zone igneous magma is generated and rises to the surface to form volcanoes, that build into a cordilleran mountain range (e.g. the Cascade mountains of Washington, Oregon, and northern California.) Also, a lot of metamorphism occurs and folding and faulting.
===Stage F===
The two continents, separated in Stages A and B now collide. The remnant ocean basin is completely subducted. Technically the closing phase of the Wilson cycle is over. Because the subduction zone acts as a ramp the continent with the subduction zone (a hinterland) slides up over the edge of the continent without it (a foreland).
===Stage G===
Once the collision has occurred the only thing left for the mountain to do is erode down to sea level - a peneplain. The stage G drawing is a distortion, however. With the collision the continental thickness doubles, and since continental rock is light weight, both will rise as the mountain erodes, much like a boat rises when cargo is taken off of it. Thus, in reality, most of the hinterland continent will be eroded away, and the foreland continent will eventually get back to the earth's surface again.
<ref> http://csmres.jmu.edu/geollab/vageol/vahist/wilsonsimp.html </ref>
==Basin Formation Method <ref> https://en.wikipedia.org/wiki/Sedimentary_basin </ref> ==
Basins form primarily in convergent, divergent and transform settings. Convergent boundaries create foreland basins through tectonic compression of oceanic and continental crust during lithospheric flexure. Tectonic extension at divergent boundaries where continental rifting is occurring can create a nascent ocean basin leading to either an ocean or the failure of the rift zone. In tectonic strike-slip settings, accommodation spaces occur as transpresional, transtensional or transrotational basins according to the motion of the plates along the fault zone and the local topography pull-apart basins.
===Lithospheric Stretching===
If the lithosphere is caused to stretch horizontally, by mechanisms such as ridge-push or trench-pull, the effect is believed to be two fold. The lower, hotter part of the lithosphere will flow slowly away from the main area being stretched, whilst the upper, cooler and more brittle crust will tend to fault and fracture. The combined effect of these two mechanisms is for the Earth's surface in the area of extension to subside, creating a geographical depression which is then often unfilled with water and/or sediments.
An example of a basin caused by lithospheric stretching is the North Sea - also an important location for significant hydrocarbon reserves. Another such feature is the Basin and Range province which covers most of the USA state of Nevada, forming a series of horst and graben structures.
Another expression of lithospheric stretching results in the formation of ocean basins with central ridges; The Red Sea is in fact an incipient ocean, in a plate tectonic context. The mouth of the Red Sea is also a tectonic triple junction where the Indian Ocean Ridge, Red Sea Rift and East African Rift meet. This is the only place on the planet where such a triple junction in oceanic crust is exposed sub-aerially. The reason for this is twofold, due to a high thermal buoyancy of the junction, and a local crumpled zone of seafloor crust acting as a dam against the Red Sea.
===Lithospheric Compression or Shortening and Flexure===
If a load is placed on the lithosphere, it will tend to flex in the manner of an elastic plate. The magnitude of the lithospheric flexure is a function of the imposed load and the flexural rigidity of the lithosphere, and the wavelength of flexure is a function of flexural rigidity alone. Flexural rigidity is in itself, a function of the lithospheric mineral composition, thermal regime, and effective elastic thickness. The nature of the load is varied. For instance, the Hawaiian Islands chain of volcanic edifices has sufficient mass to cause deflection in the lithosphere.
The obduction of one tectonic plate onto another also causes a load and often results in the creation of a foreland basin, such as the Po basin next to the Alps in Italy, the Molasse Basin next to the Alps in Germany, or the Ebro basin next to the Pyrenees in Spain.
===Strike-slip deformation===
Deformation of the lithosphere in the plane of the earth occurs as a result of near horizontal maximum and minimum principal stresses. The resulting zones of subsidence are known as strike-slip or pull apart basins. Basins formed through strike-slip action occur where a vertical fault plane curves. When the curve in the fault plane moves apart, a region of transtension results, creating a basin. Another term for a transtensional basin is a rhombochasm. A classic rhombochasm is illustrated by the Dead Sea rift, where northward movement of the Arabian Plate relative to the Anatolian Plate has caused a rhombochasm.
The opposite effect is that of transpression, where converging movement of a curved fault plane causes collision of the opposing sides of the fault. An example is the San Bernardino Mountains north of Los Angeles, which result from convergence along a curve in the San Andreas fault system. The Northridge earthquake was caused by vertical movement along local thrust and reverse faults bunching up against the bend in the otherwise strike-slip fault environment. In Nigeria, the dominant type of basement rock intersected by wells drilled for hydrocarbons, limestone, or water is granite. The three sedimentary basins in Nigeria are underlain by continental crust except in the Niger delta, where the basement rock is interpreted to be oceanic crust. Most of the wells that penetrated the basement are in the Eastern Dahomey embayment of western Nigeria. A maximum thickness of about 12,000 m of sedimentary rocks is attained in the offshore western Niger delta, but maximum thicknesses of sedimentary rocks are about 2,000 m in the Chad basin and only 500 m in the Sokoto embayment.
=Reference=
=Reference=
<references />
<references />
* Carlson, Plummer, Hammersley. ''PHYSICAL GEOLOGY: Earth Revealed''. 9th edition. New York: The McGraw-Hill Companies, Inc, 2011. ISBN 978-0-07-122184-9
* Christian Vérard, Cyril Hochard, Peter O. Baumgartner, Gérard M. Stampfli. 2015. ''Geodynamic evolution of the Earth over
the Phanerozoic: Plate tectonic activity and palaeoclimatic indicators''. Journal of Palaeogeography, 4(2): 167-188.
* http://csmres.jmu.edu/geollab/vageol/vahist/plates.html
* http://file.upi.edu/Direktori/FPIPS/JUR._PEND._GEOGRAFI/195901011989011-YAKUB_MALIK/HANDOUT_TEKTONIK_LEMPENG.pdf
* http://www.springer.com/cda/content/document/cda_downloaddocument/9783540788362-c1.pdf?SGWID=0-0-45-615210-p173825306
* http://www.le.ac.uk/gl/art/gl209/lecture3/lecture3.html
* http://ocw.mit.edu/courses/earth-atmospheric-and-planetary-sciences/12-110-sedimentary-geology-spring-2007/lecture-notes/ch11.pdf
* http://csmres.jmu.edu/geollab/Fichter/Wilson/Wilson.html