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Isua Greenstone Belt
The Isua Greenstone Belt is an Archean greenstone belt in southwestern Greenland. The belt is aged between 3.7 and 3.8 Ga, making it the home of the oldest rock in the world.〔 The belt contains variably metamorphosed mafic volcanic and sedimentary rocks. The occurrence of boninitic geochemical signatures offers evidence that plate tectonic processes may have been responsible for the creation of the belt.〔 However, this has recently been disputed by earth scientists who offer up a new theory for the formation of the Isua Greenstone Belt.〔 This new model is known as vertical plate tectonics and will be discussed further in the page.
==Overview==
The Isua Greenstone Belt, also known as the Isua supracrustal belt, is located in the Southwestern portion of Greenland, in the Isukasia terrane,〔 near the Nuuk region. The greenstone belt is made up of metamorphosed mafic volcanic and sedimentary rocks that are usually juxtaposed by mylonites or fault boundaries. By using Uranium-lead dating on zircon and titanite, the tectonic history was dated to be approximately 3700-3600 million years old. It has been studied by earth scientists because of the evidence the area holds for early earth plate tectonics, as well as the fact that the area houses one of the oldest, best-preserved ancient plate tectonic sequences on earth.〔 In addition, the area is large, exposed, and there are areas that have experienced relatively low deformation and alteration to the original rock sequences. The northern area of the Isua Greenstone Belt is mainly composed of amphibolite rocks, volcanic rocks, upper mantle peridotite, and layered gabbros; a suite which suggests crustal shortening.〔 Scientists have used different methods in order to determine how the Isua Greenstone Belt formed, some concluding that it formed at an ancient ocean-ocean convergent zone, where subduction caused partial melting and metasomatism of the mantle as well as the intrusion of tonalites partially melted the overlying supracrustal rocks and created the first continental crust. However, this area still remains under controversy in the scientific community, as scientists try to come to a consensus on how the Isua Greenstone Belt formed: whether due to a subduction zone or to some other process like vertical plate tectonics. Ultimately, a specific conclusion of how the Isua Greenstone Belt formed has not been reached, but some pieces of the puzzle have been proposed.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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