Geology of the Democratic Republic of the Congo

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Topographic map of the Democratic Republic of the Congo
Mount Stanley on the border with Uganda

The geology of the Democratic Republic of the Congo (DRC or Congo-Kinshasa, formerly Zaire and Belgian Congo) is extremely old, on the order of several billion years for many rocks. The country spans the

diamonds, coltan
and other valuable minerals.

Stratigraphy, tectonics & geologic History

Map of Western Gondwana with the Congo Craton

greenstone belts spanning into neighboring Central African Republic, Uganda and South Sudan
.

Angolan Shield

In Kasai, the metamorphic basement rocks of the Angolan Shield are bounded by a fault at 4 degrees south latitude, with underlying poorly exposed

alaskite gneiss, probably formed near granulite grade metamorphism and originating from charnockite, gabbro and norite
rocks in the Kasai-Lomami group. Geologists estimate that the Kanda Kanda gneisses are formed between 3.4 and 2.82 billion years ago.

The Kasai-Lomami group has two rock units. One is a mafic unit with gabbro, norite, amphibolite and anorthosite. Taken together, they are the remains of magma intrusions metamorphosed to granulite grade. The second unit contains dark gneiss and aluminium-rich granulite, which may have originated from sediments, along with metadolerite dikes. The metamorphism and deformation that affected both units likely happened 2.8 billion years ago.[1]

Foreland basin: West Congolian mobile belt

The West Congolian mobile belt became a foreland basin during the

Republic of Congo through Gabon. The massif has a north-south foliation and two generations of granitoids. Gray granodiorite shifts to quartz, diorite, biotite and amphibolite-rich types, cut by veins of pink, potassic migmatite. The Chaillu Massif granitoids are 2.7 billion years old and engulfed pre-existing schist and greenstone.[2]

Northeast Congo Craton

In northeastern DRC, Archean gneisses and granite-greenstones terranes are common. The

synform
structure in northern DRC. The different gneisses probably began to form 3.5 billion years ago from oceanic source material and were later intruded by tonalite around 3.41 billion years ago.

Granulite rocks in the same region as the West Nile Gneissic Complex pre-date the Watian orogeny 2.9 billion years ago and contain charnockitic dolerite dikes, with isoclinal folding of the rock. After the Watian orogeny, volcanic and sedimentary rocks in what is now northeast DRC metamorphosed into the Western Gray Gneissic Group with biotite, hornblende and microlite. The subsequent Aruan orogeny 2.68 billion years ago gave these rocks a northeast plunging fold.

The Ganguan Greenstone Belt is 3.2 billion years old and contains

tonalities.[3]

Neoproterozoic (1 Ga to 542 Ma)

The

pyroclastic flows in the Mwashya Group. The overlying Kundelungu Supergroup starts off with glacial sedimentary rocks from the Neoproterozoic Snowball Earth
event followed by a cap of carbonates.

The sediments in Katanga metamorphosed to greenschist and amphibolite grade during the Pan-African orogeny. Away from the mobile belts, the Congo Craton has large sedimentary rock formations leftover from the molasses areas associated with the different orogenies deep in the past, which include stromatolite and acritarch fossils. Some examples include the dolomitic shales, conglomerates, quartzites, siltstones and shales of the Mbuyi Mayi Supergroup in the southeast or the quartzites and carbonate assemblages of the Lindian Supergroup in the north, formed from stromatolites. [3]

Mesozoic and Cenozoic (251 Ma to present)

Downwarping of the crust of the Congo Craton in the

kimberlite pipe
eruptions at the time.

After a long period of relative tectonic quiet, volcanism started in the geologically recent past of the late

Kenyan Rift. The oldest basalt at the base of the Virunga Massif, east of the current rift is 14 million years old. Alkaline basalts erupted from 13 million to nine million years ago. In the late Pliocene, the fracture pattern changed to northeast-southwest, building up a chain of volcanic mountains formed from potassic, undersaturated lava. [4]

The Wembo-Nyama ring structure in Omeonga is a possible impact crater in DRC, the World Impact Crater list by Anna Mikheeva lists it as "potential".[5]

Hydrogeology

Zongo falls in DRC

The hydrogeology of DRC is poorly researched, although individual areas have been studied since the 1950s. Alluvial sand and gravel aquifers are common throughout the country. One unit in Oubangui and Cuvette Centrale is 120 metres (390 ft) thick, recharging rapidly from rainfall and river water. A large aquifer underlying the Batekes Plateau in southeast Kasai, in sandy loam and soft sandstone has poor recharge and transmissivity but sustains the baseflow of many different streams.

Other aquifers are situated in Cretaceous sandstones,

Oriental Province are in fractured Precambrian crystalline basement rock.[6]

Natural hazards

Nyiragongo lava lake in 2005

Eastern DRC has several active volcanoes. The eruption of

Mount Nyamulagira
on November 27, 2006 did not result in significant fatalities.

Mining in southern provinces like Katanga has seriously polluted some of DRC's aquifers.[7]

Natural resource geology

Diamond from the DRC
Photo by Rob Lavinsky

Historically, the

noble metals
and chlorine oxides. DRC has 3.1 million tons out of the 4.8 million tons of cobalt reserves in the copperbelt.

Political unrest and obsolete equipment caused a precipitous drop in gold production. In the early 1990s, many large mines closed.

Shaba Province has been curtailed by ethnic conflicts. Coltan, a mix of columbite and tantalite is common in eastern DRC, which yields tantalum when refined. With soaring demand for tantalum capacitors in cellphones, computers and other electronics, prices of the metal increased rapidly. Artisanal mining, often associated with rebels involved in the Kivu conflict
has arisen to meet international demand.

DRC also has large diamond deposits, mainly extracted through artisanal mining of alluvium near Mbuji-Mayi in

Kasai Province, although many of these reserves are becoming depleted. One third of the DRC's diamonds are smuggled out of the country every year. [8]

Limestone occurs in Kongo Central, Équateur and Haut-Katanga provinces.[9]

See also

References

Wikimedia Commons has media related to Geology of the Democratic Republic of the Congo.
  1. ^ Schluter, Thomas (2006). Geological Atlas of Africa (PDF). Springer. p. 78–80.
  2. ^ Schluter 2006, p. 78-80.
  3. ^ a b Schluter 2006, p. 79-80.
  4. ^ Schluter 2006, p. 80-81.
  5. ^ The Complete Catalog of the Earth's Impact structures by Anna Mikheeva
  6. ^ "Hydrogeology of Democratic Republic of Congo". British Geological Survey.
  7. ^ Schluter 2006, p. 82.
  8. ^ Schluter 2006, p. 81-82.
  9. ^ https://www.investindrc.cd/en/Mines Democratic Republic of the Congo National Investment Promotion Agency
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