Monday, September 10, 2012

The Rising of South America—Part V—Drainage Basins and the Submerged Falkland Plateau

As has been stated several times in these posts, the South American continent is made up of numerous intra-continental basins and is quite flat in most areas, not only in the Amazon Drainage Basin, an area nearly three million square miles, but in numerous other areas as well. Also, as has been shown in earlier posts, the Ancient Amazon Sea, along with the Amazon Arm (a flow-thru of sea water from the Atlantic between the Guiana and Brazil highlands or shields, was a natural channel to the sea as it is today to the Atlantic Ocean. While the Amazon is the largest drainage basin in the world, it is not the only one in South America.
1) Amazon Basin; 2) Parana Basin; 3) Orinoco Basin; 4) Xingu Basin; 5) Tocantins/ Araguaia Basin; 6) Rio de Plate Basin; 7) Magdalena Basin;8) Essequibo Basin; 9) Patagonia (several basins)
The Rio de la Plata drainage basin is 1.6 million square miles; the Parana River Basin is 997,000 square miles; the Orinoco Basin is 340,000 square miles, the Tocantins/Araguaia Basin is 314,000 square miles; the Rio de Plate Basin is 1.6 million square miles; the Xingu River Basin is 200,000 square miles; the Magdalena Basin is 105,405 square miles; and the Essequibo Basin is about 90,000 square miles—these seven basins, all independent of one another, total about 4,641,200 square miles, which would make that total area the second largest country in the world, second only to Russia.
Such an area, of course, of all these drainage basins (except Patagonia), all basically flat, all around sea level, could, with a slight change in either sea level or a low rising of the continental plate, bring the area either above or below sea level. While such an idea might be a great surprise to most people, the fact derived by numerous scientists from the sediments, rocks, fossils and other matter found in these areas shows that such has happened on more than one occasion in the past.
In addition, the Falkland plateau extends the South American continental shelf eastward occupying the north-central part of the plateau, which forms a 750-mile long continental promontory of South America. Should the Nazca plate, which is moving east along the west coastal area, continue to subduct under and lift the South American Plate, the entire Falkland plateau could rise up above sea level, creating a very different outline of southeastern South America (map green area below). It is also interesting that geologists claim the Falkland Plateau is mobile along with the southernmost South America.
(Yellow) Current western coast of South America; (Light Blue) Continental Shelf; (Dark Blue) Ocean; (Green) South America, including extended Shelf of East coast and the Falkland Plateau
Three connected basins surround the southern Falklands: 1) the Falkland Plateau Basin lies to the east; 2) the South Falkland Basin lies to the south; and 3) the Malvinas Basin lies to the west. The latter basin lies beneath 150 m to 250 m of water to the west of the Falkland Islands. The basin extends westwards to the Rio Chico High in Argentine waters, and then further westwards to the onshore area of Tierra del Fuego and southern Argentina, where it is termed the Austral or Magallanes Basin.
The origin of the southeast margin of the Falkland Islands as a volcanic rifted continental margin, and of the floor of the major part of the Falkland Plateau Basin as elevated oceanic crust is not far below the surface. In fact, the distance between the eastern coast and the Falkland Islands is only about 13,000 feet deep, the same distance below sea level, by the way, than where Darwin found ocean sea shells in the Andes at 13,000 feet above sea level, showing that high surface was once under water.
It should also be noted that the independent westward and clockwise rotation of the Falkland Islands block, suggests that southernmost South America was also a collection of microplates moving independently within a generally extensional environment—which is incompatible with assumptions of a rigid southernmost South America over this time, and a dominant role for a continuous dextral strike-slip Gastre Fault—an extension of the Lanalhue Fauilt located in south-central Chile on an imaginary line between Santiago and the Falkland Islands.
The Falkland Plateau, along the southern boundary of the South American Plate, butts into the Scotia Plate, where rocks were thrust upward during transpression of the plate as it slides around the South American Plate. Should the Scotia Plate press further north and ride onto the South American Plate, the Falkland Plateau could be lifted upward and surface much like the western South American Plate did as the Nazca Plate subducted beneath it along the Andean Fault line some time earlier.
The Scotia Plate is named after the sea which overlies it, and this region near the Scotia Sea in the southern Atlantic Ocean is a complex area of marginal basins bordered by the South America and Antarctic plates. The boundary motion between these two larger plates is predominately strike-slip, which results in a partitioning of one or both of the Scotia Sea boundaries. A movement northward, into the South American Plate is a likiely scenario as these plates continue to slip around and into one another—especially since the Sandwich Plate (to the east of the Scotia Plate) is moving rapidly eastward and that the westwared motiuon of the South American Plate has forced the Scotia Plate at its northern and southern ends respectively to squeeze around it as well as being subducted along its eastern boundary.
All of this merely points out that for those who think South America has always been the way it is now simply do not understand 1) Plate Tectonics and how they reshape the continents, especially in dynamic zones like those around South America, and 2) The fact that Earth has not always been in the appearance it now is.

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