Formation

The Transantarctic Mountains are an unusual intraplate mountain belt situated wholly within the Antarctic Continent. It is most likely that they are related to thermal uplift along the edge of a rift system developed within the plate during the fragmentation of the Gondwana Supercontinent. The Range forms the Eastern 'shoulder' or flank of the rift and whereas the Western shoulder is less obvious due to its complex form as a series of separate 'blocks'. Topographically it is most pronounced in the Ellsworth Mountains (part of the "Ellsworth - Whitmore block").

Generally we can view the formation of mountain ranges by one of two processes. Either they arise from the subduction of one plate beneath another, such as in the Andes. Here earthquakes occurring beneath the ranges indicate the subduction of oceanic plate to the west of South America beneath the continent. Wet sediments dragged down promote the melting of crust and are recycled to erupt as volcanoes along the Peruvian, Chilean and Argentine mountain ranges. In the Himalayas we see the second process at work. Formed by the collision of the Indian sub-continent and the Eurasian plate, the two continents crumple as they collide, and in places parts of India are seen to dive beneath Eurasia. With the Transantarctic Mountain Range however there is little earthquake activity and little evidence which can explain the forces of formation occurring in the past and those working to uplift the range at present.

The Transantarctic Mountain Range forms the western margin of the Pre-Cambrian shield that is Eastern Antarctica. The mountain range reflects the tectonic activity and uplift that has occurred along the Pacific margin during the rifting and break up of Gondwana and also the activity occurring at the present. Current volcanic activity, continental setting and its linear nature indicate that the transantarctic rift is similar to the East African rift valley, the world's largest continental rift.

The current theories for uplift and in particular the unusually high uplift include the presence of a mantle plume or hotspot beneath the continent. This would be supported by the presence of an active rift system. The spread of some ten volcanoes (two currently active) along the range would suggest the plume to be very large indeed (if it does exist). Other research links the large uplift (4000m) of the eastern rift flank to that of lithospheric rigidity. Here large permanent uplifts have been found to develop along the flanks of passive rifts with the most likely mechanism being flexural bending of the lithosphere due to an isostatic load resulting from necking in the lithosphere (J. Chery et al 1992). The anomalously high uplift of the Transantarctic mountains is therefore explained by the high rigidty of the Precambrian craton of East Antarctica, and contrastingly the low uplift of the western (younger crust) flank.

Superimposed on this uplift may be an isostatic adjustment caused by loading from the thick inland ice sheet. This ice sheet has been spreading for some distance over and across part of the range and undoubtedly depresses the crust in the west and in the south of the region. There is a conspicuous regional tilt landward, which may be due to isostatic rather than tectonic causes.

The timing of the uplift of the Transantarctic Mountain Range is important as it relates to the separation of East and West Antarctica and ultimately to the break up of Gondwana. Apatite fission track age profiling has provided evidence of uplift and denudation of the Transantarctic Mountain Range. Initial research has shown the age of uplift to be post Jurassic, indirect evidence from Ross Sea sediments suggest the deformation took place mainly during Tertiary times, with initial movement beginning in the Late Cretaceous and the final stages of uplift occuring as recently as Plio-Pleistocene times (H.R. Katz ). Apatite fission track age profiling has provided further evidence of uplift and denudation of the Transantarctic Mountain Range. Two periods of uplift and denudation of the Scott Glacier in the early and late Cretaceous are indicated. Combining fission track evidence for uplift and data from other parts of the mountains in the early Cretaceous, with other evidence for uplift during the Plio Pleistocene, it can be suggested that at least four episodes of uplift of the Transantarctic Mountain Range took place in the early Cretaceous. Each of these older episodes coincide with major plate tectonic changes in the region (Stump, 1992)

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