submarine plateau

oceanic plateau

or submarine plateau

Large submarine elevation rising sharply at least 660 ft (200 m) above the surrounding seafloor and having an extensive, relatively flat or gently tilted summit. Most plateaus are steplike interruptions of the continental slopes. Some, however, occur well beyond the continental margins. They stand alone, high above the surrounding seafloor, and are believed to be fragments of continents that were isolated during continental drift and seafloor spreading.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

Oceanic plateau

An oceanic plateau (also submarine plateau) is an undersea large igneous province, the equivalent of continental flood basalts such as the Deccan Traps in India and the Snake River Plain in the Pacific Northwest of the United States. An oceanic plateau, as its name suggests, rises above the level of the ambient seabed.

Geologists believe that oceanic plateaus may well represent a stage in the development of continental crust as they are generally less dense than oceanic crust while still being denser than normal continental crust.

Density differences in crustal material largely arise from different ratios of various elements, especially silicon. Continental crust has the highest amount of silicon (such rock is called felsic). Oceanic crust has a smaller amount of silicon (mafic rock). Oceanic plateaus have a ratio intermediate between continental and oceanic crust, although they are more mafic than felsic.

However, when a plate carrying oceanic crust subducts under a plate carrying an oceanic plateau, the volcanism which erupts on the plateau as the oceanic crust heats up on its descent into the mantle erupts material which is more felsic than the material which makes up the plateau. This represents a step toward creating crust which is increasingly continental in character, being less dense and more buoyant. If an oceanic plateau is subducted underneath another one, or under existing continental crust, the eruptions produced thereby produce material that is yet more felsic, and so on through geologic time.