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The geology of Central African Republic (CAR) is part of the broader geology of Africa. CAR occupies a swath of ancient rocks, dating back billions of years that record significant aspects of Earth history and yield minerals vital to the country's small economy.
Southern CAR is part of the Congo Craton, a stable landmass dating to the Archean that was once fused with the Sao Francisco Craton until the opening of the South Atlantic Ocean. Some of the oldest rocks in CAR belong to the 3.4 billion year old Bomu Complex which includes migmatite gneiss and metasedimentary schist spanning from the Democratic Republic of Congo. The Congo Craton once functioned as a small continent, until it was joined with Siberia during the formation of the supercontinent Columbia, between 2.1 and 1.8 billion years ago. A string of large igneous province (LIP) volcanic events took place in three pulses during the time that the craton was part of Columbia, until the supercontinent fragmented. The Congo Craton was subsequently joined to the supercontinent Rodinia between 1.3 billion and 750 million years ago after a period where it may have existed as a separate continent in the Southern Hemisphere. At the time, the continent was entirely barren with no land life and the region experienced large scale glaciation during the Cryogenian Period.
The northern part of the country is grouped with the Saharan Metacraton, which began to form between 3 billion and 2 billion years ago and accelerated with the Pan-African Orogeny and the creation of the Oubangides Belt in the Neoproterozoic. After the breakup of Rodinia, modern CAR was situated near the center of the subsequent supercontinent Pannotia, as part of the fully assembled basement rock of the current African continent. The region existed in the Southern Hemisphere as part of the supercontinents Gondwana and Pangaea.
Many aspects of Central African Republic's geologic history remain unknown. Along with the Brazilian state of Bahia, CAR is the only country known to host carbonados (black diamond aggregates), which some researchers have suggested may be connected to a Precambrian meteorite impact that could also have generated the Bangui magnetic anomaly.
Up to 60% of bedrock beneath the Central African Republic dates to the Precambrian. Much of the country is situated in the Archean Congo Craton. The North Equatorial Fold Belt, Pan-African granulites and greenstone belts are found in the north and center of the country. Cretaceous sandstones span the west and central areas of the republic. The Bakouma Formation includes extensive carbonates, glacial outwash and tillite deposits dated to the Neoproterozoic.
Stratigraphically, the lower units of Precambrian rock are granite, amphibolite, gneiss and gneissic-migmatite rock, likely dating to the Neoarchean. These sequences, divided into the Bandas Belt and Dekoa Belt, are often described as a greenstone belt. Granitoid batholiths and dolerite dikes dating to the Proterozoic frequently intrude into these layers. The upper sequence is Neoproterozoic age quartzite and schist and tends to be folded, but only weakly metamorphosed. In the west, the Mambere Formation and the Kombele Formation in the east each record glacial sediments, while erosion and river activity left behind the Cretaceous Mouaka-Ouadda and Carnot-Berberati sandstone formations, as well as the plateaus of the Eocene Bambio Sandstone. During the Quaternary extensive weathering of surface rocks took place, up to 40 meters deep.
Iron-rich plinthosols dominate most of the center of the country. Unconsolidated psamment deposits (also known as arenosols) occupy a section of the west and center of the country along with soils grouped under the FAO ferralsol classification of iron and aluminium-rich soils. Hydric, grayish-blue wetland gleysols are found in small locations in the north and along the border with the Congo.
The Proterozoic is a geological eon spanning the time interval from 2500 to 541 million years ago. It is the most recent part of the Precambrian "supereon." It is also the longest eon of the Earth's geologic time scale, and it is subdivided into three geologic eras : the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic.
The Congo Craton, covered by the Palaeozoic-to-recent Congo Basin, is an ancient Precambrian craton that with four others makes up the modern continent of Africa. These cratons were formed between about 3.6 and 2.0 billion years ago and have been tectonically stable since that time. All of these cratons are bounded by younger fold belts formed between 2.0 billion and 300 million years ago.
The Pan-African orogeny was a series of major Neoproterozoic orogenic events which related to the formation of the supercontinents Gondwana and Pannotia about 600 million years ago. This orogeny is also known as the Pan-Gondwanan or Saldanian Orogeny. The Pan-African orogeny and the Grenville orogeny are the largest known systems of orogenies on Earth. The sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.
The Kaapvaal Craton, along with the Pilbara Craton of Western Australia, are the only remaining areas of pristine 3.6–2.5 Ga crust on Earth. Similarities of rock records from both these cratons, especially of the overlying late Archean sequences, suggest that they were once part of the Vaalbara supercontinent.
The West African Craton (WAC) is one of the five cratons of the Precambrian basement rock of Africa that make up the African Plate, the others being the Kalahari craton, Congo craton, Saharan Metacraton and Tanzania Craton. Cratons themselves are tectonically inactive, but can occur near active margins, with the WAC extending across 14 countries in Western African, coming together in the late Precambrian and early Palaeozoic eras to form the African continent. It consists of two Archean centers juxtaposed against multiple Paleoproterozoic domains made of greenstone belts, sedimentary basins, regional granitoid-tonalite-trondhjemite-granodiorite (TTG) plutons, and large shear zones. The craton is overlain by Neoproterozoic and younger sedimentary basins. The boundaries of the WAC are predominantly defined by a combination of geophysics and surface geology, with additional constraints by the geochemistry of the region. At one time, volcanic action around the rim of the craton may have contributed to a major global warming event.
The Aravalli Mountain Range is a northeast-southwest trending orogenic belt in the northwest part of India and is part of the Indian Shield that was formed from a series of cratonic collisions. The Aravalli Mountains consist of the Aravalli and Delhi fold belts, and are collectively known as the Aravalli-Delhi orogenic belt. The whole mountain range is about 700 km long. Unlike the much younger Himalayan section nearby, the Aravalli Mountains are much older that can be traced back to the Proterozoic Eon. The collision between the Bundelkhand craton and the Marwar craton is believed to be the primary mechanism for the development of the mountain range.
Huangling Complex represents a group of rock units appear in the middle of Yangtze Block in South China, distributed across Yixingshan, Zigui, Huangling and Yichang counties. The group of rock involves nonconformity that sedimentary rocks overlie the metamorphic basement. It is a 73-km long, asymmetrical dome-shaped anticline with axial plane orientating in north-south direction. It has a steeper west flank and a gentler east flank. Basically, there are three tectonic units from the anticline core to the rim, including Archean to Paleoproterozoic metamorphic basement, Neoproterozoic to Jurassic sedimentary rocks and Cretaceous fluvial deposit sedimentary cover. The northern part of the core is mainly tonalite-trondhjemite-gneiss (TTG) and Cretaceous sedimentary rock, it is called the Archean Kongling Complex. The middle of the core is mainly the Neoproterozoic granitoid. The southern part of the core is the Neoproterozoic potassium granite. Two basins are situated on the western and eastern flanks of the core respectively, including the Zigui basin and Dangyang basin. Both basins are synforms while Zigui basin has a larger extent of folding. Yuanan Graben and Jingmen Graben are found within Dangyang Basin area. Huangling Complex is an important area that helps unravel the tectonic history of South China Craton because it has well-exposed layers of rock units from Archean basement rock to Cretaceous sedimentary rock cover due to the erosion of the anticline.
The geology of the Republic of the Congo, also known as Congo-Brazzaville, to differentiate from the Democratic Republic of the Congo, formerly Zaire, includes extensive igneous and metamorphic basement rock, some up to two billion years old and sedimentary rocks formed within the past 250 million years. Much of the country's geology is hidden by sediments formed in the past 2.5 million years of the Quaternary.
The geology of Western Sahara includes rock units dating back to the Archean more than two billion years old, although deposits of phosphorus formed in the Mesozoic and Cenozoic have helped to prompt the current Moroccan occupation of most of the country.
The geology of Liberia is largely extremely ancient rock formed between 3.5 billion and 541 million years ago in the Archean and the Neoproterozoic, with some rocks from the past 145 million years near the coast. The country has rich iron resources as well as some diamonds, gold and other minerals in ancient sediment formations weathered to higher concentrations by tropical rainfall.
The geology of the Democratic Republic of the Congo is extremely old, on the order of several billion years for many rocks. The country spans the Congo Craton: a stable section of ancient continental crust, deformed and influenced by several different mountain building orogeny events, sedimentation, volcanism and the geologically recent effects of the East Africa Rift System in the east. The country's complicated tectonic past have yielded large deposits of gold, diamonds, coltan and other valuable minerals.
The geology of Cameroon is almost universally Precambrian metamorphic and igneous basement rock, formed in the Archean as part of the Congo Craton and the Central African Mobile Zone and covered in laterite, recent sediments and soils. Some parts of the country have sequences of sedimentary rocks from the Paleozoic, Mesozoic and Cenozoic as well as volcanic rock produced by the 1600 kilometer Cameroon Volcanic Line, which includes the still-active Mount Cameroon. The country is notable for gold, diamonds and some onshore and offshore oil and gas.
The geology of Ivory Coast is almost entirely extremely ancient metamorphic and igneous crystalline basement rock between 2.1 and more than 3.5 billion years old, comprising part of the stable continental crust of the West African Craton. Near the surface, these ancient rocks have weathered into sediments and soils 20 to 45 meters thick on average, which holds much of Ivory Coast's groundwater. More recent sedimentary rocks are found along the coast. The country has extensive mineral resources such as gold, diamonds, nickel and bauxite as well as offshore oil and gas.
The geology of Mozambique is primarily extremely old Precambrian metamorphic and igneous crystalline basement rock, formed in the Archean and Proterozoic, in some cases more than two billion years ago. Mozambique contains greenstone belts and spans the Zimbabwe Craton, a section of ancient stable crust. The region was impacted by major tectonic events, such as the mountain building Irumide orogeny, Pan-African orogeny and the Snowball Earth glaciation. Large basins that formed in the last half-billion years have filled with extensive continental and marine sedimentary rocks, including rocks of the extensive Karoo Supergroup which exist across Southern Africa. In some cases these units are capped by volcanic rocks. As a result of its complex and ancient geology, Mozambique has deposits of iron, coal, gold, mineral sands, bauxite, copper and other natural resources.
The geology of Sierra Leone is primarily very ancient Precambrian Archean and Proterozoic crystalline igneous and metamorphic basement rock, in many cases more than 2.5 billion years old. Throughout Earth history, Sierra Leone was impacted by major tectonic and climatic events, such as the Leonean, Liberian and Pan-African orogeny mountain building events, the Neoproterozoic Snowball Earth and millions of years of weathering, which has produced thick layers of regolith across much of the country's surface.
The geology of Tanzania began to form in the Precambrian, in the Archean and Proterozoic eons, in some cases more than 2.5 billion years ago. Igneous and metamorphic crystalline basement rock forms the Archean Tanzania Craton, which is surrounded by the Proterozoic Ubendian belt, Mozambique Belt and Karagwe-Ankole Belt. The region experienced downwarping of the crust during the Paleozoic and Mesozoic, as the massive Karoo Supergroup deposited. Within the past 100 million years, Tanzania has experienced marine sedimentary rock deposition along the coast and rift formation inland, which has produced large rift lakes. Tanzania has extensive, but poorly explored and exploited natural resources, including coal, gold, diamonds, graphite and clays.
The geology of Uganda extends back to the Archean and Proterozoic eons of the Precambrian, and much of the country is underlain by gneiss, argillite and other metamorphic rocks that are sometimes over 2.5 billion years old. Sedimentary rocks and new igneous and metamorphic units formed throughout the Proterozoic and the region was partially affected by the Pan-African orogeny and Snowball Earth events. Through the Mesozoic and Cenozoic, ancient basement rock has weathered into water-bearing saprolite and the region has experienced periods of volcanism and rift valley formation. The East Africa Rift gives rise to thick, more geologically recent sediment sequences and the country's numerous lakes. Uganda has extensive natural resources, particularly gold.
The geology of Nigeria formed beginning in the Archean and Proterozoic eons of the Precambrian. The country forms the Nigerian Province and more than half of its surface is igneous and metamorphic crystalline basement rock from the Precambrian. Between 2.9 billion and 500 million years ago, Nigeria was affected by three major orogeny mountain-building events and related igneous intrusions. Following the Pan-African orogeny, in the Cambrian at the time that multi-cellular life proliferated, Nigeria began to experience regional sedimentation and witnessed new igneous intrusions. By the Cretaceous period of the late Mesozoic, massive sedimentation was underway in different basins, due to a large marine transgression. By the Eocene, in the Cenozoic, the region returned to terrestrial conditions.
The geology of Sweden is the regional study of rocks, minerals, tectonics, natural resources and groundwater in the country. The oldest rocks in Sweden date to more than 2.5 billion years ago in the Precambrian. Complex orogeny mountain building events and other tectonic occurrences built up extensive metamorphic crystalline basement rock that often contains valuable metal deposits throughout much of the country. Metamorphism continued into the Paleozoic after the Snowball Earth glaciation as the continent Baltica collided with an island arc and then the continent Laurentia. Sedimentary rocks are most common in southern Sweden with thick sequences from the last 250 million years underlying Malmö and older marine sedimentary rocks forming the surface of Gotland.
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