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The Madagascar Plate or Madagascar block was once attached to the Gondwana supercontinent and later the Indo-Australian Plate. Rifting in the Somali Basin began at the end of the Carboniferous 300 million years ago, as a part of the Karoo rift system. The initiation of Gondwana Breakup, and transform faulting along the Davie fracture zone, occurred in the Toarcian (about 182 million years ago) following the eruption of the Bouvet (Karoo) mantle plume. At this time East Gondwana, comprising the Antarctic, Madagascar, Indian, and Australian plates, began to separate from the African plate. East Gondwana then began to separate about 115-120 million years ago when India began to move northward.〔Plummer, P. S., and E. R. Belle (1995), Mesozoic tectono–stratigraphic evolution of the Seychelles microcontinent, ''Sedimentary Geology'', 96, 73–91.〕 Between 84-95 million years ago rifting separated Seychelles and India from Madagascar. Since its formation the Madagascar block has moved roughly in conjunction with Africa, and thus there are questions as to whether the Madagascar Plate should be still considered a separate plate.〔 〕 ==Assembly of Gondwana== The Madagascar Plate was formerly located in the central part of the supercontinent Gondwana. It contains part of the East African Orogen, which formed in the Neoproterozoic to Cambrian assembly of the Gondwana. This heavily influenced the geology of central and northern Madagascar.〔Collins, Alan S., and Brian F. Windley. "The tectonic evolution of central and northern Madagascar and its place in the final assembly of Gondwana." The Journal of geology 110.3 (2002): 325-339.〕 The entire island can be divided into four tectonic and geologic units:〔Wit, Maarten J. de. "Madagascar: heads it's a continent, tails it's an island." Annual Review of Earth and Planetary Sciences 31.1 (2003): 213-248.〕 the Antongil block, the Antananarivo block, the Bekily Belt in the south, and the Bemarivo Belt in the far north. *The Antongil Block is characterized by a 3.2 Ga gneiss intruded by granite that has undergone greenschist facies metamorphism. *The Antananarivo Block contains 2.5 Ga gneiss layered with younger granitoids and gabbros. It has metamorphosed to granulite facies conditions. *The Bemarivo Belt contains two regions, metasedimentary gneisses in the southern part and granitic domes in the north. *The Bekily Belt is made up of mostly sedimentary protoliths and granulite and upper amphibolite grade gneisses. The blocks in the northern part of the island are made up of Archean cratonic material.〔 The Antongil block has been linked with the Dharwar Formation of India, however the Antananarivo block to the west has been too heavily altered to link easily to another continent.〔 The central part of the island contains metasediments from African and Indian continental shelves. This is the Itremo Group, which also contains intrusions of material from the Antongil block. The Itremo sheet was folded in the amalgamation of Madagascar ~700 Mya, and now contains upright folds, divergent reverse faults, and strike-slip faults.〔 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「Madagascar Plate」の詳細全文を読む スポンサード リンク
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