SWEAT (which stands for

Southwestern United States The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural region of the United States that generally includes Arizona, New Mexico, and adjacent portions of California, Colorado, N ...

and East

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

) is the hypothesis that the Southwestern United States was at one time connected to East Antarctica. The hypothesis of a late

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of th ...

fit of western

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

with the

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and othe ...

shield A shield is a piece of personal armour held in the hand, which may or may not be strapped to the wrist or forearm. Shields are used to intercept specific attacks, whether from close-ranged weaponry or projectiles such as arrows, by means of ...

region permits the extension of many features through

and into other parts of

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...

. For example, the Grenville orogen may extend around the coast of East Antarctica into

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...

and

, 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 The Yavapai are a Native American tribe in Arizona. Historically, the Yavapai – literally “people of the sun” (from ''Enyaava'' “sun” + ''Paay'' “people”) – were divided into four geographical bands who identified as separate, i ...

- Mazatzal orogens of the southwestern United States. Counterparts of the Precambrian-Paleozoic sedimentary rocks along the U.S. Cordilleran

miogeocline A miogeocline is an area of sedimentation which occurs along the passive margin of a continent. The deposits occur as typically shallow water clastic sediments which thicken seaward to form a clastic wedge parallel to a tectonically quiescent coa ...

may be present in the

Transantarctic Mountains The Transantarctic Mountains (abbreviated TAM) comprise a mountain range of uplifted (primarily sedimentary) rock in Antarctica which extend, with some interruptions, across the continent from Cape Adare in northern Victoria Land to Coats Land. ...

. Orogenic belt boundaries provide useful

piercing point In geology, a piercing point is defined as a feature (usually a geologic feature, preferably a linear feature) that is cut by a fault, then moved apart. Reconfiguring the piercing point back in its original position is the primary way geologists ...

s for Precambrian continental reconstructions. The model implies that

and

Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, althoug ...

drifted away from each other on one margin and collided some 300 million years later on their opposite margins to form the

Appalachians The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...

Evidence

A paper published by an international team of U.S. and Australian investigators led by John Goodge, an NSF-funded researcher with the Department of Geological Sciences at the University of Minnesota-Duluth, gives significant support to the theory. The team's findings were made in the

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 2 miles of ice. One rock, found atop

Nimrod Glacier The Nimrod Glacier is a major glacier about 135 km (85 mi) long, flowing from the polar plateau in a northerly direction through the Transantarctic Mountains between the Geologists and Miller Ranges, then northeasterly between the ...

, was later determined to be a very specific form of

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...

which has a particular type of coarse-grained texture (called '' rapakivi'' 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 California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

through

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

Kansas Kansas () is a U.S. state, state in the Midwestern United States, Midwestern United States. Its Capital city, capital is Topeka, Kansas, Topeka, and its largest city is Wichita, Kansas, Wichita. Kansas is a landlocked state bordered by Nebras ...

Illinois Illinois ( ) is a state in the Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolitan areas include, Peoria and Rock ...

in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

, and eventually

New Brunswick New Brunswick (french: Nouveau-Brunswick, , locally ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. It is the only province with both English and ...

and

Newfoundland Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...

. This belt of rock was a part of

, thought by some geologists to be the core of

Rodinia Rodinia (from the Russian родина, ''rodina'', meaning "motherland, birthplace") was a Mesoproterozoic and Neoproterozoic supercontinent that assembled 1.26–0.90 billion years ago and broke up 750–633 million years ago. were prob ...

. 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.

East Antarctica–Laurentia juxtaposition

The positions of Laurentia and other landmasses in the Precambrian super continent of

are 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 uranium-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.

External links

liveScience

References

{{Continents of the world Precambrian Geology of North America Geology of the United States Southwestern United States Geology of Antarctica

Evidence

East Antarctica–Laurentia juxtaposition

See also

External links

References