SWEAT (hypothesis)
SWEAT is the hypothesis that the Southwestern United States was at one time connected to East Antarctica.
The hypothesis of a late Precambrian fit of western North America with the Australia-Antarctic shield region permits the extension of many features through Antarctica and into other parts of Gondwana. For example, the Grenville orogen may extend around the coast of East Antarctica into India and Australia, and the ophiolitic belt of the latter may extend into East Antarctica. The Wopmay orogen 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. Orogen boundaries provide useful piercing points for Precambrian continental reconstructions.
The model implies that Gondwana and Laurentia drifted away from each other on one margin and collided some 300 million years later on their opposite margins to form the Appalachians.
Evidence
A paper published by an international team of U.S. and Australian investigators led by John Goodge gives significant support to the theory. The team's findings were made in the Transantarctic Mountains and provide physical evidence that confirms the SWEAT hypothesis.The 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 approximately of ice. One rock, found atop Nimrod Glacier, was later determined to be a very specific form of granite which has a particular type of coarse-grained texture Chemical tests run on the rock revealed that it has a radiometric age and stable isotope ratios closely matching those of a distinctive belt of rapakivi granite in North America that stretches from California through New Mexico to Kansas, Illinois in the United States, and eventually New Brunswick and Newfoundland in Canada.
This belt of rock was a part of 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.