User:Ladam26/Rough Draft:Tectonic Evolution of the Transantarctic Mountains
The Transantarctic Mountain range is one of the largest mountain systems in the world and yet little is know about it. This range is a major boundary stretching 3500km that divides East Antarctica and West Antarctica. The Transantarctic Mountains (TAM) define a lithospheric boundary because of the many tectonic cycles that occurred during orogeny.[1]
Tectonic Events: Exhumation and Uplift
[edit]Initiation of uplift of the Transantarctic Mountains explained by three regional events
- The separation of Antarctica and Australia during the Early Cretaceous
- During the Late Cretaceous the Antarctic plate was extended East and West due to low-angle faulting.
- The final event that started uplift was seafloor spreading that caused a rise in the East Antarctic lithosphere during the early Cenozoic.[1]
Cambrian to Ordovician
[edit]During this time period (445-540 Ma) the basement rock, that the current TAM resides on, is being deformed. This rock consists of mainly metamorphic rock with granitoid intrusions. This basement rock is then exhumed during the Ross Orogeny event. Further exhumation of the basement rock created the Kukri Erosion Surface (KES). The present day KES is buried under volcanic rock and shallow marine deposits. At this time (Cambrian-Ordovician) There is no known uplift of the TAM. Following these events there is very little tectonic activity in this region. There is also a 160 Ma section of onland geologic history of the TAM missing from the Jurassic to the late Cenozoic.[1]
Kukri and Dominion Erosion Surfaces
[edit]In places the KES has elevation of 4000 meters but along the major syncline associated with the TAM the elevation only reaches a max of 500 meters. The Dominion Erosion Surface (DEM) intersects the KES and has elevation up to 4000 meters but no lower than 1200 meters. It is located in the middle of the syncline where it cuts into lower basement rock such as the Beacon supergroup. These two erosional surfaces help geologists determine glacial erosion and possible uplift history of the TAM. .[2]
Cretaceous
[edit]The Cretaceous time period marks two of three main exhumation events regarding the TAM. The first exhumation occurred during the Early Cretaceous(140-100 Ma) and the second during the Late Cretaceous(85 Ma). At this point in the geologic record there is no evidence of surface uplift.[1]
Cenozoic
[edit]The initial uplift of the East Antarctic lithosphere is dated to the early Cenozoic, but the third exhumation event involving the TAM happened just a few million years before. Areas near Victoria Land show exhumation starting 55 Ma, but Areas along the southern end of the TAM exhibit exhumation beginning 45 Ma. The exhumation rate decreased enough in the early Cenozoic to allow surface uplift. The reason for the uplift is directly related to the seafloor spreading and propagation of the Adare Trough into the continental crust. The propagation advanced downward under the crust near the Western Ross Sea.[1] Due to this propagation and seafloor spreading many faults formed parallel to the syncline that is the TAM. The TAM started as basic tilted blocks such as grabens and horsts. Minor parallel faulting is seen along the entire range but major faulting occurred at the range front creating rapid uplift. A Terror Rift is associated with these low-angle faults. The TAM Terror Rift is similar to a subduction zone but in the case of Antarctica it is also an inclined lithospheric boundary.[3]During the early Cenozoic the TAM exhibits rapid uplift and orogeny. There is no other time that the TAM has this magnitude of mountain building events. The rate of uplift has slowly decreased since the middle Cenozoic.
Methods for Determining Tectonic History
[edit]There are a many different ways to determine tectonic history but only a select few can be applied to the TAM because of its thermal and geographic isolation. Seismic reflection is one proven method to visualize what is happening beneath the surface. It requires the use of teams on the ground setting off explosive charges beneath the surface and recording data from seismic waves that bounce back.[3] Another common method of reconstructing tectonics is the application of apatite fission-track thermochronology (AFTT). This requires vertical sampling across a region to create a profile that is age specific.[1] In places like Antarctica it is not always easy to reach some areas but with the use of satellites it has become a lot easier to determine tectonic features in these places. Certain satellites have the ability to interpret areas with the use of gravity fields and magnetic anomalies. When used correctly there is no need for surface exploration to make plate tectonic implications. [4]
References
[edit]- ^ a b c d e f Fitzgerald, Paul (2002). "Tectonics and landscape evolution of the Antarctic plate since the breakup of Gondwana, with an emphasis on the West Antarctic Rift System and the Transantarctic Mountains" (PDF). Royal Society of New Zealand Bulletin. 35: 453–469.
- ^ Webb, P-N.; Harwood, D.M.; McKelvey, B.C.; Mabin, M.C.G; Mercer, J.H. (1986). "Late Cenozoic tectonic and glacial history of the Transantarctic Mountains" (PDF). Antarctic Journal: 99–100.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ a b U.S. ten Brink, S. Bannister, B.C. Beaudoin and T.A. Stern (1993). "Geophysical Investigations of the Tectonic Boundary Between East and West Antarctica". Science. 261 (5117): 45–50.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: multiple names: authors list (link) - ^ McAdoo, David; Laxon, Seymour (1997). "Antarctic Tectonics: Constraints From an ERS-1 Satellite Marine Gravity Field". Science. 276 (5312): 556–560.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: multiple names: authors list (link)