Geology of Ivory Coast
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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.[2] 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.[3]
Archean
Virtually all of Ivory Coast is underlain by very ancient rocks from the Archean and the Paleoproterozoic that form part of the West African Craton,[2] except for Cenozoic sediments and sedimentary rocks along the coast and in offshore basins. Weathering has rendered the upper layers of ancient Precambrian crystalline basement rock into sediments and soils.
Three billion year old Archean rocks are situated in the Kenema Domain and the Man Shield, centered around the city of Man, Ivory Coast. The rocks are granulite and migmatite gneiss, with some granitoids and banded iron formations in remnant supracrustal belts. Archean rocks were affected by two major orogeny mountain building events, the Leonian orogeny 3.5 to 2.9 billion years ago and the Liberian orogeny 2.9 to 2.5 billion years ago.[4]
Paleoproterozoic
Paleoproterozoic terranes are separated from Archean rocks by the Sassandra mylonitic zone. The Baoule-Mossi domain in eastern Ivory Coast continues into Ghana and includes northeast–southwest trending volcanic belts, with sedimentary basins in between. The 2.9 to 2.15 billion year old volcanic belts formed from a tholeiitic magma series that experienced low-grade metamorphism and was intruded by granitoids. The sedimentary basins have isoclinal folding and contain dacite volcaniclastic rocks, greywacke and argillite.
Central Ivory Coast has a more jumbled terrain. Volcanic belts, formed 2.1 billion years ago, lack clear spacing and do not run parallel and the intervening basins are filled with granitoids and gneisses. The quartz-pebble conglomerates, arkoses and sandstones of the Tarkwaian Group outcrop in a few isolated locations near Bondoukou in the northwest. The Eburnean orogeny, 2.1 billion years ago metamorphosed many of the Paleoproterozoic rocks, creating shear zones and intruding granitoid plutons which vary between tonalite and peraluminous granite.[5]
Mesozoic-Cenozoic (145 million years ago-present)
Coastal sedimentary basins formed as a result of the rifting apart of the supercontinent Pangaea, opening the Atlantic Ocean and now hold Ivory Coast's offshore oil and gas reserves. Clastic sediments formed throughout the Neogene and up to recent times.[4]
