Lufilian arch

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The Lufilian Arch or Lufilian Belt is a fossilized, deformed sedimentary basin in central southern Africa , which contains low to high grade metamorphic sedimentary rocks (metasediments) of neoproterozoic age with small magmatic fractions. Deformation and metamorphosis took place in the course of Pan-African orogeny mainly through interaction between the Congo-São Francisco and Kalahari craton. The corresponding folding phase is also called Lufilian orogenesis .

Parts of the Lufilian arc are of particular economic importance, as significant deposits of copper , cobalt and other ores are mined there.

Geographical extension

The Lufilian-Bogen (in the following text abbreviated as LB) connects to the western zones of the Zambezi Belt and Irumide Belt of the Mozambique Belt and contacts the then still connected Congo-São Francisco (Congo-SF) craton in a north-west direction . In the southeast direction, the LB is bounded by the Kalahari craton and in the north by the Kibara belt. In the north-east direction, the LB connects to the Bangweulu block, while to the south it is delimited from the Zambezi belt by the Mwembeshi shear zone .

The LB is part of an orogen complex that stretches across southern Africa. This connects to the east of the Mozambique Belt and includes the Zambezi Belt, the LB and the Damara Belt. All are assigned to the broader Pan-African Orogenic Complex that arose during the formation of Gondwana .

This arch, which has a convex shape pointing to the north, is located roughly in the center of southern Africa and runs from north-west Zambia through the former Katanga province of the Democratic Republic of the Congo (DR Congo) to eastern Angola .

Geological evolution

Basement

The basement of the LB is formed by paleoproterozoic and mesoproterozoic rocks. The lower basement contains granite , gneiss, and mica schist formed during the Eburnean orogeny, 2,200 to 2,000 mya (million years old). In the upper basement, which is stored on the lower basement in Zambia and is only present in places in the LB, mainly mica slate, quartzite and quartz - muscovite mica slate occur.

During the Kibara orogeny, the African part of the Grenville orogeny , these rocks were deformed and metamorphically overprinted between 1,350 and 1,100 mya.

Rift and sedimentary basin formation, sediment deposits

The geological development of the LB began around 880 mya when the supercontinent Rodina began to disintegrate. It emerged intra-continental grave breaches (rifting) that the magmatism were accompanied. The basins formed by aulacogenic , relatively shallow rift breaks that do not lead to oceanic spreads were filled with sea water and absorbed 5 to 10 km thick layers of sediment, known as the Katanga Supergroup . The surrounding cratons , terrane and orogen served as a source of sediment .

The Katanga Supergroup is divided into three lithostratigraphic groups and several subgroups by default . The groups correspond to the respective rifts, while the sub-groups represent further basins that have arisen in the rifts.

The lowest is the Roan group, from 880 mya, which represents a continental rift valley with fluvial (river) and lacrustine (lake) sediments.

The Nguba group followed from 765 mya and was a proto-oceanic rift valley, similar to the Afar triangle / Red Sea .

From 650 mya the Kundelungu group deposited, which corresponded to an epi-continental lagoon . The uppermost subgroup (KU3) arose from around 542 mya and is regarded as the Lufilian foreland with continental clasts , from lacustine to fluvial river delta sediments, with red arcs , sandstones and fine-layer sediments (shales).

All except for the KU3 subgroup essentially contain marine, non- carbonate-containing clasts (siliclasts), carbonates, especially dolomite and dolomitic fine-layer sediments. The Roan and Nguba groups are separated by a glacial layer of diamictite / tillite ( large conglomerate layer ), which was deposited during the Sturtic Ice Age . The Nguba and Kundelungu groups are in turn separated by a glacial diamictite / tillite layer (small conglomerate layer), which comes from the Marino Ice Age .

Recently, the LB with its foreland and the adjacent Kibara Belt is seen in connection with the still little explored and poorly developed Rift Valley Basin, which branches off in a south-west direction from the western rift of the East African Rift Valley. This includes the Mwerusee , which lies in the LB foreland, and the Upemba ditch along the Kibara belt. These zones are seismically and geothermally active.

Deformations, compressions

The LB was essentially subject to three main phases of deformation and compression of the rocks.

The first (D1) took place between 800 and 710 mya, with a peak around 790 to 750 mya. In this phase, which corresponds to the main deformation time in the Zambezi Belt, folds and thrust nappies developed with a north-eastward transport direction together with forward and backward opposing faults . Together they result in the characteristic thin-layer structure of the LB. This area corresponds to the Outer Region, which lies entirely in the DR Congo. The Kundelungu Plateau, which represents the foreland of the arch, connects to the north of the outer domain. The Kundelungu Plateau is located between the Kibara Belt and the Bangweulu Block.

The second deformation phase (D2) occurred between 690 and 540 mya when the cratons Congo-SF and Kalahari approached. It influenced the crusts of the first phase through several large, left-directed leaf shifts (strike-slip tectonic). These operations took place one after the other, and the east block of the LB rotated clockwise, creating the convex arc shape of the LB. During this phase the sedimentary cover was detached from the basement and pushed about 150 km further towards the Outer Region. This shift was facilitated by the release of fluids from evaporite-rich, watt-like deposits of the Roan group.

Structurally, this phase forms the central or cathedral region, which is located in the DR Congo and Zambia along the common western border. The cathedral region is characterized by a corridor of raised, tilted domes made of crystalline bedrock, which are characterized by metamorphic upper green schist and upper amphibolite facies. This region is home to significant copper ore deposits that make up the Katanga Copperbelt. In the Dom region intruded rows of plutons of gabbro . The Mwembeshi shear zone, which separates the LB from the Zambezi Belt, has also been activated.

The third (D3) phase followed after 540 mya as part of the annexation of East Gondwana to Africa. Tectonically it is used as interior region or fold belt (belt Synclinorial) denotes that completely extends into Zambia. On the southern edge of this region, in central Zambia up to the Mwembeshi shear zone, the Hook Granite Massif, a large batholith , intruded into the deposited sediments around 550 mya .

Post-orogenic events occurred up to the early Mesozoic Era , induced as long-range effects from the southern active continental margin of Gondwana.

Natural resources

The Lufilian Arc is of great economic importance due to the exploitation of the rich copper - and cobalt - ores in the Katanga Province of the DR Congo and the Copperbelt in Zambia.

Furthermore, u. a. Uranium, lead and tin deposits mined.

literature

  • Hubertus Porada, Volker Berhorst: Towards a new understanding of the Neoproterozoic-early palæozoic Lufilian and northern Zambezi belts in Zambia and the Democratic Republic of Congo . In: Journal of African Earth Sciences . tape 30 , no. 3 , April 2000, p. 727-771 , doi : 10.1016 / S0899-5362 (00) 00049-X .
  • C. Rainaud, S. Master, RA Armstrong, LJ Robb: Geochronology and nature of the Palaeoproterozoic basement in the Central African Copperbelt (Zambia and the Democratic Republic of Congo), with regional implications . In: Journal of African Earth Sciences . tape 42 , no. 1–5 , 2005, pp. 1-31 , doi : 10.1016 / j.jafrearsci.2005.08.006 .
  • S. Master, C. Rainaud, RA Armstrong, D. Phillips, LJ Robb: Provenance ages of the Neoproterozoic Katanga Supergroup (Central African Copperbelt), with implications for basin evolution . In: Journal of African Earth Sciences . tape 42 , no. 1–5 , 2005, pp. 41-60 , doi : 10.1016 / j.jafrearsci.2005.08.005 .

Web links

Individual evidence

  1. ↑ Louis Kipata Mwabanwa: Brittle tectonics in the Lufilian foldand-thrust belt and its foreland. (PDF)
  2. ↑ Fernandez-Alonso et al: The Proterozoic history of the Proto-Congo Craton of Central Africa. (PDF)
  3. ↑ Armin Zeh, Axel Gerdes, Jackson M. Barton: Archean Accretion and Crustal Evolution of the Kalahari Craton — the Zircon Age and Hf Isotope Record of Granitic Rocks from Barberton / Swaziland to the Francistown Arc . In: Journal of Petrology . tape 50 , no. 5 , May 2009, p. 933-966 , doi : 10.1093 / petrology / egp027 ( PDF ).
  4. ↑ AB Kampunzu, J. Cailteux: Tectonic Evolution of the Lufilian Arc (Central Africa Copper Belt) During Neoproterozoic Pan African Orogenesis . In: Gondwana Research . tape 2 , no. 3 , July 1999, p. 401-421 , doi : 10.1016 / S1342-937X (05) 70279-3 ( PDF ).
  5. ↑ M. Fernandez-Alonso, H. Cutten, B. De Waele, L. Tack, A. Tahon, D. Baudet, SD Barritt: The Mesoproterozoic Karagwe-Ankole Belt (formerly the NE Kibara Belt): The result of prolonged extensional intracratonic basin development punctuated by two short-lived far-field compressional events . In: Precambrian Research . tape 216–219 , October 2012, pp. 63–86 , doi : 10.1016 / j.precamres.2012.06.007 ( PDF ).
  6. ↑ LS Andersen, R. Unrug: Geodynamic evolution of the Bangweulu Block, northern Zambia . In: Precambrian Research . tape 25 , no. 1-3 , 1984, pp. 187-212 , doi : 10.1016 / 0301-9268 (84) 90032-9 .
  7. ↑ Mwembeshi Shear Zone , English Wikipedia article.
  8. ↑ Emmanuel Egal, Denis Thiéblemont, Didier Lahondère, Catherine Guerrot, Cristian Adi Costea, Dan Iliescu, Claude Delor, Jean-Christian Goujou, Jean Michel Lafon, Monique Tegyey, Sory Diaby, Pascal Kolié: Late Eburnean granitization and tectonics along the western and northwestern margin of the Archean Kénéma-Man domain (Guinea, West African Craton) . In: Precambrian Research . tape 117 , no. 1–2 , 2002, pp. 57-84 , doi : 10.1016 / S0301-9268 (02) 00060-8 .
  9. ↑ Marek Wendorff: TECTONICS, SEDIMENTATION AND SEDIMENT SUPPLY SYSTEMS AT THE SOUTHERN MARGIN OF THE CONGO CRATON: THE KATANGA SUPERGROUP, NEOPROTEROZOIC-LOWER PALAEOZOIC OF CENTRAL AFRICA. Geology Department, Univ. of Botswana.
  10. ↑ Michael L. Zientek et al .: Sediment-Hosted Stratabound Copper Assessment of the Neoproterozoic Roan Group, Central African Copperbelt, Katanga Basin, Democratic Republic of the Congo and Zambia. In: USGS, Global Mineral Resource Assessment, Scientific Investigations Report 2010–5090 – T (PDF)
  11. ↑ a b MJ Batumike, AB Kampunzu, JH Cailteux: Petrology and geochemistry of the Neoproterozoic Nguba and Kundelungu Groups, Katangan Supergroup, southeast Congo: Implications for provenance, paleoweathering and geotectonic setting . In: Journal of African Earth Sciences . tape 44 , no. 1 , January 2006, p. 97-115 , doi : 10.1016 / j.jafrearsci.2005.11.007 .
  12. ↑ G. Mortelmans: Les antecedents Tectoniques you ditch de l'Upemba (Katanga) . In: Bulletin Volcanologique . tape 13 , no. 1 , December 1953, p. 93-98 , doi : 10.1007 / BF02596793 ( download ).
  13. ↑ Richard E. Hanson, Melissa S. Wardlaw, Terry J. Wilson, Giddy Mwale: U – Pb zircon ages from the Hook granite massif and Mwembeshi dislocation: constraints on Pan-African deformation, plutonism, and transcurrent shearing in Central Zambia . In: Precambrian Research . tape 63 , no. 3 , November 1993, pp. 189-209 , doi : 10.1016 / 0301-9268 (93) 90033-X .