Petrologie et structure des ensembles metamorphiques au SE de Poli (nord Cameroun) : roles respectifs du socle Proterozoieque inferieur et de l'accretion crustale pan-africane

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Titanium minerals in Cameroon

The mineral rutile (TiO2) is a major ore of titanium, which is used in products such as white pigment and titanium metal. The global consumption of titanium minerals in 2011 was c. 6.7 million tonnes of which 0.7 million tonnes were rutile and 6 million tonnes ilmenite (TiFeO3). Rutile is almost pure TiO2 and therefore more valuable than ilmenite (c. 1500 $/t and 300$/t, respectively). Compared with ilmenite, rutile can be processed with lower consumption of chemicals and yields less waste products. Rutile was mined in Cameroon between 1935 and 1955 when a total of 15 000 tonnes of rutile were extracted from alluvial deposits. The French Bureau de Recherches Géologiques et Minières conducted a drilling programme in Cameroon in the 1980s which identified c. 2.6 million tonnes of rutile in discontinuous occurrences with concentrations of c. 1%. Most of the occurrences are located in small- to medium-sized riverbeds with a thickness of 1.5–4.5 m. The main alluvial rutile area is located around the town of Akonolinga, 80 km east of Yaoundé, the capital of Cameroon (Fig. 1). The rutile in the alluvial deposits was derived from the bedrock by weathering, and at some sites major, residual rutile deposits are reported from Quaternary lateritic deposits. The Geological Survey of Denmark and Greenland conducted a project together with the Institut de Recherches Géologiques et Minières in Cameroon to gain a better understanding of how rutile formed in the bedrock before it was weathered out and try to tie the rutile in the alluvial deposits to its source rocks. This is done by studying the compositional variation of the rutile in the alluvial deposits and comparing it with possible bedrock sources. The compositional variation of ilmenite and monazite ((La,Ce)PO4)) and the age distribution of zircon (ZrSiO4) in alluvial sand and bedrock were also investigated. The chemical compositions of minerals in the sediments are used to infer the bedrock source of the minerals. This has particular application in many areas of Cameroon, such as the southern part of the country which is characterised by low relief and dense rain forest with bedrock outcrops that are sparse and difficult to find. Cameroon is a country in west central Africa (Fig. 1) and is called ‘Africa in miniature’ because of its cultural, geological and landscape diversity. The landscape includes beaches, deserts, mountains, rain forests and savanna. The highest point is the active volcano Mount Cameroon (4095 m), and the country is home for over 200 different linguistic groups with French and English as the official languages. Compared with other African countries, Cameroon is politically and socially stable. The country covers an area of 475 442 km2 with a population of c. 20 million of which 70% are Christians and 20% Muslims

Mineralogical constraint for metamorphic conditions in a shear zone affecting the Archean Ngoulemakong tonalite, Congo craton (Southern Cameroon) and retentivity of U–Pb SHRIMP zircon dates

International audienceMineralogical constraint for metamorphic conditions in a shear zone affecting the Archean Ngoulemakong tonalite, Congo craton (Southern Cameroon) and retentivity of U–Pb SHRIMP zircon date

Reply to comment by Ngako and Njonfang on “The Adamawa-Yade domain, a piece of Archaean crust in the Neoproterozoic Central African Orogenic belt (Bafia area, Cameroon)”, by Jacqueline Tchakounté et al., Precambrian Research 299 (2017) 210–229

International audienc

Shrimp U–Pb zircon age evidence for Paleoproterozoic sedimentation and 2.05Ga syntectonic plutonism in the Nyong Group, South-Western Cameroon: consequences for the Eburnean–Transamazonian belt of NE Brazil and Central Africa

International audienceThe Nyong Group of the NW corner of the Congo craton is a metasedimentary and metaplutonic rock unit that underwent a high-grade tectono-metamorphic event at ∼2050 Ma associated with charnockite formation. However, the age of the sedimentation and associated plutonism was not known. In view of this, the unit was considered to be part of the Archean Congo craton reactivated during a Paleoproterozoic or a Pan-African orogeny. Such interpretation was widely supported by the persistence of Archean inheritance revealed by Nd isotope data on whole rocks and U–Pb on zircons. New SHRIMP analyses on detrital zircons from metasediments (BIF, orthopyroxene gneiss and garnet gneiss) yield Mesoarchean to Paleoproterozoic ages, with the youngest zircon at 2423 ± 4 Ma, thus giving the maximum deposition age for the Nyong Group. Data on a metagranodiorite at Bonguen and a metasyenite at Lolodorf yield emplacement ages of 2066 ± 4 Ma and 2055 ± 5 Ma respectively, with Archean inheritance (2836 ± 11 Ma) for the metasyenite. The syntectonic emplacement of these plutonic rocks is supported by the age of 2044 ± 9 Ma obtained on the Bienkop charnockite, associated with Eburnean high-grade metamorphism which continued probably up to 1985 ± 8 Ma. These new data permit correlation of the Nyong rocks with the Paleoproterozoic of NE Brazil and the discussion of the source provenance of detritus for the Nyong Group. Finally, it is proposed that the West Central African Belt (WCAB) in southern Cameroon, Gabon, Congo and Angola represents a segment of the Eburnean–Transamazonian orogeny that resulted from the convergence and collision between the São Francisco-Nigerian Shield block and a former Congo megacraton

Shrimp U-Pb zircon age evidence for Paleoproterozoic sedimentation and 2.05 Ga syntectonic plutonism in the Nyong Group, South Western Cameroon: consequences for the Eburnean-Transamazonian belt of NE Brazil and Central Africa

The Nyong Group of the NW corner of the Congo craton is a metasedimentary and metaplutonic rock unit that underwent a high-grade tectono-metamorphic event at ∼2050 Ma associated with charnockite formation. However, the age of the sedimentation and asso

Geochronology and correlations in the Central African Fold Belt along the northern edge of the Congo Craton: New insights from U-Pb dating of zircons from Cameroon, Central African Republic, and south-western Chad

International audienceThe Central African Fold Belt (CAFB) is the least well-known of all major Pan African belts. Here, we present new geochronologic work carried out in several critical areas of western Central African Republic, the region standing between northern Cameroon and southwestern Chad, and southern Cameroon. Our results allow us to: (1) clarify the regional extension of the Congo Craton in SE Cameroon and in the SW Central African Republic; (2) demonstrate that the units thrust along the northern edge of the Congo Craton from Cameroon to the Central African Republic are comparable in nature and in age; (3) better constrain the limits and described better the role of the Adamawa-Yadé crustal block during the Pan-African pre-collisional and collisional events in relation to the Congo Craton and the Yaoundé-Yangana nappe units to the South, and to the Poli-Leré magmatic arc to the North and; (4) clarify some of the elements of correlation with NE Brazil. Overall, a model involving two subduction zones is proposed to explain the evolution of the Pan-African belt north of the Congo Craton. The main steps include; (1) break-up and basin development from the early Tonian to at least 620 Ma on the northern edge of the Congo Craton, and on both the southern and the northern edges of the Adamawa-Yadé Block, concomitantly with the development of the Poli-Leré arc in northern Cameroon and Chad; (2) pre-tectonic plutonism in all domains since c. 800 Ma with culmination between 650 and 620 Ma; (3) collisional events starting around 620 Ma with metamorphism reaching the granulite facies at c. 600 Ma in all the domains; (4) nappe tectonics with thrusting of the Yaoundé-Yangana units onto the Congo Craton, accretion of the Poli-Leré arc to Adamawa-Yadé Block, and widespread syntectonic magmatism (600–580 Ma) with emplacement partly controlled by transcurrent regional shear zones, and emplacement of post-tectonic granitoids (c. 550 Ma) in both Adamawa-Yadé block and Poli-Leré magmatic arc. Collisional and post-collisional (620–550 Ma) events were synchronous along the entire belt from Central Africa to Brazil