|
The Lufilian Arc (or Lufilian Belt) is part of a system of orogenic belts in southern Africa formed during the Pan-African orogeny, a stage in the formation of the Gondwana supercontinent. It extends across eastern Angola, the Katanga Province of the southern Democratic Republic of the Congo and the northwest of Zambia. The arc is about long. It has global economic importance owing to its rich deposits of copper and cobalt. ==Evolution== The Katanga Supergroup of Neoproterozoic sediments rests on a basement formed in the Paleozoic or Mesoproterozoic eras. The lower basement is made of granites, gneisses and schists formed during the Eburnean age, about 2100–2000 Ma. The upper basement extends under part of the arc in Zambia and is mostly made of schists, quartzites and quartz-muscovite schists. The Kibaran orogeny deformed and metamorphosed the upper basement between 1350 Ma and 1100 Ma. The Katanga supergroup sediments are from to thick. Rifting between the Congo and Kalahari cratons around 880 Ma opened two basins, first the Roan rift and then the Nguba rift, both of which gathered sediments. Extension was replaced by compression as the Kalahari and Congo cratons moved back towards each other at the start of the Pan-African orogeny. Nappes advancing from the south deposited olistostrome detritus into the Fungurume foreland basin to the north of the arc. Nappe overthrusting and deformation of the foreland followed before the olistostrome sediments had lithified. The crust was shortened by up to between 590 and 512 Ma in the Pan-African orogeny. Compression deformed the Katanga supergroup sedimentary rocks into a fold and thrust belt, the Lufilian Arc. Tectonic inversion raised up deposits from the deepest levels. The orogeny lifted and folded Roan strata holding copper and cobalt deposits, which later became exposed through erosion. In several areas they are now accessible through open pit mines, as in the Kambove mines in Katanga. The Mwembeshi Shear Zone forms the southern boundary of the Lufilian Arc, separating it from the Zambezi belt. The shear zone also dates to the Pan-African orogeny. It allowed a change in the structural vergence, or direction of folding, between the Zambezi Belt and the Lufilian Arc. The Hook granite massif, in the inner arc just north of the Mwembeshi Shear Zone, is a large composite batholith (emplacement of igneous rock) that has intruded into the arc's Kundelungu strata of sediments during or after tectonic activity. Uranium-lead dating of samples of syntectonic granite in the massif gives ages of 559±18 and 566±5 Ma, with 533±3 Ma for post-tectonic granite, showing that the intrusion developed around the same time as the shear zone, presumably from the same causes. 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「Lufilian Arc」の詳細全文を読む スポンサード リンク
|