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The Nias Basin (also known as the West Sumatra or Sibolga Basin) is a Forearc basin located off the western coast of Sumatra, Indonesia, in the Indian Ocean. The name is derived from the island that bounds its western edge, the island of Nias. The Nias Basin, the island of Nias (which is a subaerial part of the accretionary complex), and the offshore, submarine accretionary complex, together form a Forearc region on the Sunda Plate/Indo-Australian Plate collisional/subduction boundary. The Forearc region is the area between an oceanic trench and its associated volcanic arc. The oceanic trench associated with the Nias Basin is the Sunda Trench, and the associated volcanic arc is the Sunda Arc. The Nias Basin itself is structurally bounded to the west by the Mentawai Fault and bounded to the east by the Volcanic Arc island of Sumatra.〔Barber, A.J., M.J. Crow, and M.E.M. de Smet, 2005, Tectonic evolution, in A. J. Barber, M. J. Crow and J. S. Milsom, eds., Sumatra: Geology, Resources and Tectonic Evolution: Memoir, v. 31, Geological Society, London, p. 234-259.〕 It is a geologically independent basin from its neighbor basins; the Simeulue Basin to the north, and the Mentawai and Enggano Basin to the south.The Nias Basin spans ~250 kilometer length-wise, and ~100 kilometers width-wise.〔R. G. Matson, G. F. Moore. "Structural Influences on Seismic Stratigraphy of Nias Forearc Basin, West of Central Sumatra: ABSTRACT." AAPG Bulletin.〕 Overall, the Nias Basin can be divided into two sub-basins; the Singkel Basin to the north, and the Pini Basin to the south. These basins are distinguished by their independent development during the early formation of the primary basin, but later consolidated when subsidence of the area was more unified over the whole Nias Basin region.〔 ==Basin formation== The history of the Nias Basin begins with the initial subduction of the Indo-Australian plate underneath the Sunda Plate. Subduction of this plate, which was rich in water and volitiles, caused flux melting to occur in the mantle. This new magma eventually rose through the overriding plate, and formed the Sunda Arc. The sediment supply, and convergence rate in this case were adequate enough to allow for the Forearc to develop into an Accretionary Convergent Margin. This type of Forearc results in an accretionary complex forming along the Forearc-trench boundary, which resulted in uplift of that region. Uplift due to accretion formed a Forearc Ridge, which the island of Nias is part of. The resulting depression that formed between the Forearc Ridge and the primary volcanic ridge (Sunda Arc), allows for sediment deposition in that region. This depression in this case formed the Nias Basin. Presently, the Nias Basin lies under about 610 meters of water at its deepest point.〔〔 The Nias Basin can be divided into 2 sub-basins; the Pini Basin to the South, and the Singkel Basin to the North. These basins evolved independently from each other originally during a time of sea-level regression. These sub-basins themselves are bounded by normal faults, which were formed due to depression of the region during sediment subsidence, and extension events.〔Izart, A., B.mustafa Kemal, and J.a. Malod. "Seismic Stratigraphy and Subsidence Evolution of the Northwest Sumatra Fore-arc Basin." Marine Geology: 109-24.〕 The Nias Basin itself is relatively shallow compared to its surrounding basins. This could be due to more carbonate reef activity in this region creating thicker carbonate deposits in the Nias Basin, resulting in more sediment deposition, and shallower water depth.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nias Basin」の詳細全文を読む スポンサード リンク
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