Australia: The Land Where Time Began

A biography of the Australian continent 

Antarctica - Palaeozoic Orogenic Events

The East Antarctic interior has remained mostly tectonically stable since the Precambrian. Intermittent deformation and intrusive activity occurred on the margin of the East Antarctic Shield between the Ross Sea and the Weddell Sea from the Late Proterozoic [Neoproterozoic] to the early Mesozoic. In West Antarctica there were several orogenic events.

Ross orogeny

The ancestral Transarctic Mountains, that were formed by the earlier Beardmore Orogeny, were reduced by erosion and during the Early Cambrian the region was covered by an advancing broad epicratonic sea. According to the author1 this relatively wide sea possibly extended over much of west Antarctica (Elliot, 1975a). Included among volcaniclastic sequences that were preserved within the Transantarctic Mountains are shallow marine clastics, platform carbonates, and deep water turbidites (Borg, DePaolo & Smith, 1990; Stump, 1992, 1995). About 500 Ma in the Early Palaeozoic (Kleinschmidt et al., 1992; Stump, 1995) the Ross Orogeny influenced the region of the Transantarctic Mountains, forming the roots of the present TAM. Metamorphism and Plutonism accompanied the Ross Orogeny on a continent-wide scale (Tingey, 1991).

Ross Orogeny

During the early phases of the Ross Orogeny bimodal magmatism and extension occurred along the Transantarctic Mountains that were precursors to the increased intensity of tectonism that occurred at a later time. Sedimentary rocks on the margin underwent deformation, metamorphism, and the intrusion of granitic batholiths during the Late Ross orogeny (Craddock, 1972; Adams, Gabites & Grindley, 1982; Borg, 1983; Grindley & Oliver, 1983; Borg, DePaolo & Smith, 1990; Stump, 1995). A subduction zone that was westward-dipping along the palaeo-Pacific border of the East Antarctic Craton during the Ross orogeny (Borg, 1983) is indicated by the S-type granitoid and I-type granitoid distribution around Antarctica, as well as their similarity, geochemically, to granitoids of major circum-Pacific batholiths. Thrusts directed towards the craton are aligned perpendicular to the trend of the Transantarctic Mountains (Kleinschmidt et al., 1992). I has been argued (Tessenshon, 1994) that evidence of a major compressive plate boundary near the Transantarctic Mountains during the Ross Orogeny may not be consistent with the SWEAT hypothesis.

According to the author1 there are striking similarities between the deformed sequences of the Ross OrogenicBelt and sequences that are deformed in the Adelaide Fold Belt in southeastern Australia (Ravich, 1982a). Prior to the disassembly of Gondwana southeastern Australia was continuous with Victoria Land, Antarctica, which suggests there was a continuous Ross-Adelaide geosyncline extending for more than 8,000 km through the Transantarctic Mountains and southeastern Australia.

In Marie Byrd Land and the Thurston Island region, West Antarctica, sequences that have been radiometrically dated have ages indicative of their being influenced by the Ross Orogeny are found outcropping at widely scattered locations. In these areas metasedimentary and metavolcanic rocks are found that have a similar lithology and deformation style to the deformed sequences found in the Transantarctic Mountains (Craddock, 1972; Wade & Wilbanks, 1972). As a result of limited exposure, complexities of structure and stratigraphy, and limited radiometric age data, the age relationships and extent of influence by the of the Ross Orogeny on the deformed rocks of West Antarctica are not well understood. .

An additional link between the Ross Orogeny and West Antarctica has been provided by the finding of basement rocks of marble gneiss in the DSDP Site 270 in the eastern Ross Sea (Ford & Barrett, 1975). These rocks are similar to Koettlitz Marble from the Palaeozoic exposed in the Transantarctic Mountains of Victoria Land, that was deformed during the Ross Orogeny. It has been pointed out (Goldstrand, Fitzgerald, Redfield, Sump & Hobbs, 1994) there are similarities in rocks from the Early Palaeozoic of the Ellsworth Mountains, parts of the Pensacola Mountains, and eastern South Africa that suggest these regions were located inland of the deformation zone affecting the proto-Pacific margin of Gondwana during the Ross Orogeny.

The Lützow-Holm Bay area is the only place where evidence has been found of orogenic activity in the interior regions of East Antarctica in the Early Palaeozoic. It was in that area that high-grade metamorphism that was associated with folding of the Lützow-Holm Complex and the Yamoto-Belgica Complex of East Antarctica occurred in the Cambrian (553 ± 6 Ma and 521 ± 9 Ma) (Shiraishi et al., 1994).

 

Sources & Further reading

  1. Anderson, John B., 1999, Antarctic Marine Geology, Cambridge University Press
 
Author: M. H. Monroe
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Last updated 31/07/2013
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading