- SWEAT (hypothesis)
SWEAT stands for southwestern
United Statesand East Antarctica, which theorizes that the southwestern United States was at one time connected to East Antarctica.A hypothesis for a late Precambrianfit of western North Americawith the Australia- Antarcticshield region permits the extension of many features through Antarcticaand into other parts of Gondwana, specifically, the Grenville orogenmay extend around the coast of East Antarctica into Indiaand Australia. The ophiolitic beltof the latter may extend into East Antarctica. The Wopmayorogen of northwest Canada may extend through eastern Australia into Antarctica and thence beneath the ice to connect with the Yavapai-Mazatzal orogens of the southwestern United States. Counterparts of the Precambrian-Paleozoic sedimentary rocks along the U.S. Cordilleran miogeocline may be present in the Transantarctic Mountains. Orogenic belt boundaries provide useful piercing points for Precambrian continental reconstructions. The model implies that Gondwanaand Laurentiadrifted away from each other on one margin and collided some 300 million years later on their opposite margins to form the Appalachians. [http://www.geosociety.org/news/pr/01-10.htm]
A paper published by an international team lead by
John Goodge, an NSF-funded researcher with the Department of Geological Sciencesat the University of Minnesota-Duluth, gives significant support to the theory. [cite web|url=http://www.dailygalaxy.com/my_weblog/2008/07/were-antarctica.html|title=Were Antarctica and North America Once Connected? A Single Boulder Says "Yes"|last=Hill|first=Josh Hill|date=July 18, 2008|publisher=The Daily Galaxy|language=English|accessdate=2008-07-29] cite web|url=http://www.nsf.gov/news/news_summ.jsp?cntn_id=111911|title=A Single Boulder May Prove that Antarctica and North America Were Once Connected|date=July 17, 2008|publisher= National Science Foundation|accessdate=2008-07-29]
Writing in the July 11 edition of the journal Science, this international team of U.S. and Australian investigators describe their findings, which were made in the
Transantarctic Mountains, and their significance to the problem of piecing together what an ancient supercontinent, called Rodinia, looked like. The U.S. investigators were funded by the National Science Foundation(NSF).Previous lines of scientific evidence led researchers to theorize that about 600-800 million years ago a portion of Rodiniabroke away from what is now the southwestern United States and eventually drifted southward to become eastern Antarctica and Australia.They argue that the team's find provides physical evidence that confirms the southwestern United States and East Antarctica (SWEAT) hypothesis.
John Goodge's team was searching in Antarctica's Transantarctic Mountains for rocks carried along by ice rivers that could provide clues to the composition of the underlying crust of Antarctica, which in most places is buried under 2 miles of ice. One rock, found atop the so-called
Nimrod Glacier, was later determined to be a very specific form of granitewhich has a particular type of coarse-grained texture. Chemical tests run on the rock revealed that it has a chemistry very similar to a unique belt of igneous rocksin North America that stretch from Californiathrough New Mexicoto Kansas, Illinoisand eventually New Brunswickand Newfoundlandin Canada.This belt of rock was a part of what is called Laurentia, thought by some geologists to be the core of Rodinia.This belt stops suddenly at its western margin, leading geologists to suspect that some piece of crust had rifted away from what is now the West Coast of the United States.cite web|url=http://news.yahoo.com/s/livescience/rockreunitesantarcticaandnorthamerica|title=Senior Writer|last=Thompson|first=Andrea|date=July 28, 2008|publisher=LiveScience.com|accessdate=2008-07-29] [cite web|url=http://www.sciencemag.org/cgi/content/abstract/321/5886/235|title=A Positive Test of East Antarctica–Laurentia Juxtaposition Within the Rodinia Supercontinent|publisher= Science (Journal)|accessdate=2008-07-29]
East Antarctica–Laurentia Juxtaposition
The positions of Laurentia and other landmasses in the Precambrian super continent of
Rodiniaare controversial. Although geological and isotopic data support an East Antarctic fit with western Laurentia, alternative reconstructions favor the juxtaposition of Australia, Siberia, or South China. New geologic, age, and isotopic data provide a positive test of the juxtaposition with East Antarctica: Neodymium isotopes of Neoproterozoic rift-margin strata are similar; hafnium isotopes of about 1.4 billion year old Antarctic-margin detrital zircons match those in Laurentian granites of similar age; and a glacial clast of A-type granite has a uraniun-lead zircon age of ~1440 million years, an epsilon-hafnium initial value of +7, and an epsilon-neodymium initial value of +4. These tracers indicate the presence of granites in East Antarctica having the same age, geochemical properties, and isotopic signatures as the distinctive granites in Laurentia.
* [http://www.livescience.com liveScience]
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