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Mount Ngualla, often referred to simply as Ngualla, is a collapsed volcano located in the remote south west of Tanzania. It is approximately 200 km north of the Mbeya township. ==Formation== Ngualla is a Proterozoic carbonatite estimated to be about 1,000 million years old and is a plug-like intrusive carbonatite with a diameter of approximately 3 km, made up of various successive carbonatite phases.〔(University of Guelph, Rocks for Crops: Tanzania, page 382 )〕 Ngualla is intrusive into Precambrian gneisses, quartzites and rhyolite-dacite volcanics. It is a carbonatite-fenite complex of oval outline with a longer axis orientated approximately north-south.〔Lucien Cahen, N. J. Snelling, The geochronology and evolution of Africa, Issue 14, Clarendon Press, 1984〕 Over a north-south trending central ridge and an area of the north-western side of the complex carbonatite outcrops are found, surrounded by red soil. This is in turn surrounded by a ring of low-hills that are predominantly covered by fenites. The fenite zone is up to 1 km wide with a breccia zone adjacent to the carbonatite. The carbonatite is broadly of three types:〔James, T.C. 1954. A note on the Ngualla carbonatite, Chunya District. Unpublished Report, Geological Survey of Tanganyika〕 #An outer sovite that is banded and magnetite free. In this zone apatite, biotite, muscovite, quarts and chlorite are accessories. #An intermediate zone consisting of well banded sovite and contains euhedral megnetite and commonly dolomite. #A central zone comprising poorly banded sovite containing fluorite, biotite, amphibole, pargasite and rarely pyrochlore. Dolomitic and ankeritic veins are widespread throughout the complex as are calcite-quartz veins with minor galena, baryte and chalcopyrite. 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「Ngualla」の詳細全文を読む スポンサード リンク
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