Les formations à quartzites rubanés ferrugineux des Monts Nimba et du Simandou: des unités empilées tectoniquement, sur un « soubassementplutonique Archéen (craton de Kénéma-Man), lors de l'orogène Éburnéen

Billa, Mario; Feybesse, Jean-Louis; Bronner, Georges; Lerouge, Cathérine; Milési, Jean-Pierre; Traore, Sory; Diaby, Sory

doi:10.1016/s1251-8050(99)80248-1

Cited by 15 publications

(16 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For example, in the Zimbabwe Craton greenstone belts of three different ages are known (Blenkinsop et al, 1997). In support of this view is the work of Rollinson (1999) who showed that there is a major unconformity in some of the stratigraphic sequences of the Sierra Leone supracrustal belts and Billa et al, (1999) who showed that the Nimba and Simandou belts in Guinea, in the east of the area, are unconformable upon older amphibolites indicating at least two episodes of basaltic magmatism.…”

Section: Supracrustal Rocksmentioning

confidence: 97%

“…The Nimba belt (Liberia and Ivory Coast) and the Simandou belt (Guinea) form large supracrustal belts containing thick banded iron formation sequences (Figure 2). The Simandou and Nimba supracrustal belts are known to lie unconformably on older amphibolites and TTG gneisses, of presumed Archaean age (Billa et al, 1999). On the basis of detrital zircon ages the Nimba supracrustal belt is thought to have formed between 2615 and 2250 Ma (Billa et al, 1999), whereas a quartzite from the Simandou succession contains detrital zircons with ages of between 2711 and 2871 Ma, thus constraining its age to younger than 2711 Ma (Thieblemont et al, 2004).…”

Section: Age Constraints On the Supracrustal Beltsmentioning

confidence: 99%

See 1 more Smart Citation

Archaean crustal evolution in West Africa: A new synthesis of the Archaean geology in Sierra Leone, Liberia, Guinea and Ivory Coast

Rollinson

2016

Precambrian Research

View full text Add to dashboard Cite

A new synthesis of the geology and geochronology of the little-known Archaean rocks in Sierra Leone, Liberia, Guinea and Ivory Coast is presented in order to better understand the processes of Archaean crustal evolution in this region, and to attempt to interpret these data in the light of our current understanding of Archaean crustal evolution. In addition, this study seeks to identify those aspects of Archaean crustal evolution which are currently not known in this area and which need to become the subject of future studies, given the economic importance of this region in terms of the mineral deposits hosted in the Archaean rocks. These include greenstone-belt hosted iron ore, lode gold, chromite and columbite-tantalite and younger diamondiferous kimberlites intrusive into Archaean felsic gneisses.The new results show that this cratonic nucleus comprises of four main geological units: 1. The oldest crust is made up of 3.5-3.6 Ga TTG (tonalite-trondjemite-granodiorite) gneisses. These only outcrop in the east of the craton in Guinea but their presence is indicated elsewhere in the central part of the craton though xenocrystic zircon cores in younger rocks. 2. The major rock type found throughout the craton is 3.26-2.85 Ga TTG gneiss. In detail these magmas are thought to have formed in two episodes one between 3.05-3.26 Ga and the other between 2.85-2.96 Ga. The presence of inherited zircons in the younger suite indicate that this event represents the partial reworking of the older gneisses. 3.4 Ga eclogite xenoliths in kimberlite derived from the sub-continental lithospheric mantle are thought to be the restite after the partial melting of a basaltic protolith in the production of the TTG magmas. 3. Supracrustal rocks form linear belts infolded into the TTG gneisses and metamorphosed to amphibolite and granulite grade. They are of different sizes, contain a variety of lithological sequences and may be of several different ages. The larger supracrustal belts in Sierra Leone contain a thick basalt-komatiite sequence derived by the partial melting of two different mantle sources, unconformably overlain by a sedimentary formation. They are seen as an important resource for gold, iron-ore, chromite and columbite-tantalite. 4. A suite of late Archaean granitoids formed by the partial melting of the TTG gneisses in a craton wide deformation-metamorphic-partial melting event at 2800 +/-20 Ma. This thermal event is thought to be responsible for the stabilisation of the craton.This new synthesis highlights major geological and geochronological similarities between the Archaean rocks of Sierra Leone, Liberia, Guinea and Ivory Coast and those in the Reguibat Shield in the northern part of the West African Craton suggesting that the two regions were once more closely related.

show abstract

Section: Supracrustal Rocksmentioning

confidence: 97%

Section: Age Constraints On the Supracrustal Beltsmentioning

confidence: 99%

Archaean crustal evolution in West Africa: A new synthesis of the Archaean geology in Sierra Leone, Liberia, Guinea and Ivory Coast

Rollinson

2016

Precambrian Research

View full text Add to dashboard Cite

show abstract

“…Despite their economic importance, very little work has been published on these supracrustal belts (Rollinson, 2016) and their ages are poorly constrained. In Guinea, metasedimentary rocks from the Nimba and Simandou supracrustal belts contain detrital zircons with ages as young as 2615 Ma (Billa et al, 1999;Thiéblemont et al, 2004). In contrast, some of the supracrustal belts in Sierra Leone are cut by a suite of late Archaean granitoids emplaced at about 2800 Ma (Thiéblemont et al, 2004).…”

Section: Regional Geology Of West Africamentioning

confidence: 99%

“…The Nimba greenstone belt is a 1400 m-thick sequence of metavolcanic and metasedimentary rocks which extends for a total length of 45 km, with 25 km in Liberia and the remainder to the northeast along the border zone of Guinea and Côte d'Ivoire (Berge, 1974). Dating of detrital zircons in quartzite has placed the Nimba greenstone belt as latest Archaean to early Palaeoproterozoic (Billa et al, 1999), the same age as the Simandou belt in Guinea.…”

Section: Iron Orementioning

confidence: 99%

A review of the mineral potential of Liberia

Gunn

Dorbor

Mankelow

et al. 2018

Ore Geology Reviews

View full text Add to dashboard Cite

The Republic of Liberia in West Africa is underlain mostly by Precambrian rocks of Archaean (Liberian) age in the west and of Proterozoic (Eburnean) age in the east. By analogy with similar terranes elsewhere in the world, and in West Africa in particular, the geology of Liberia is favourable for the occurrence of deposits of a wide range of metals and industrial minerals, including gold, iron ore, diamonds, base metals, bauxite, manganese, fluorspar, kyanite and phosphate.Known gold deposits, mostly orogenic in style, occur widely and are commonly associated with north-easttrending regional shear zones. Gold mining commenced at the New Liberty deposit in western Liberia in 2015, while significant gold resources have also been identified at several other sites in both Archaean and Proterozoic terranes. Liberia has large resources of itabirite-type iron ores, most of which are located in the Liberian terrane, and was the largest producer in Africa prior to the onset of civil war in 1989. Production of iron ore is currently restricted to a single mine, Yekepa, in the Nimba Range. Other important deposits, some of them previously mined, include Bong, the Western Cluster, Putu and Goe Fantro. There is a long history of alluvial diamond production in western and central Liberia, together with more than 160 known occurrences of kimberlite. Most of the known kimberlites occur in three clusters of small pipes and abundant dykes, located at Kumgbor, Mano Godua and Weasua, close to the border with Sierra Leone. Many of these are considered to be part of a single province that includes Jurassic age diamondiferous kimberlites in Sierra Leone and Guinea.Deposits and occurrences of a wide range of other metals and industrial minerals are also known. Several of these have been worked on a small scale in the past, mainly by artisanal miners, but most are poorly known in detail with sub-surface information available at only a few localities. By comparison with most other countries in West Africa, the geology of Liberia is poorly known and there has been very little systematic exploration carried out for most commodities other than gold, iron ore and diamonds since the 1960s and 1970s. Further detailed field and laboratory investigations using modern techniques are required to properly evaluate the potential for the occurrence of economic deposits of many minerals and metals in a variety of geological settings. Digital geological, geochemical, geophysical and mineral occurrence datasets, including new national airborne geophysical survey data, provide a sound basis for the identification of new exploration targets, but in almost every part of the country there is a need for new and more detailed geological surveys to underpin mineral exploration.

show abstract

“…In the northern, Guinean part the main ridge undulates between 1,200 m asl and 1,762 m asl (Leclerc et al 1955). It consists of banded iron formations (Billa et al 1999), which are of high global economic importance (Berge 1974, Lamotte 1983, Schnell 1987. The presence of Nimba toads and chimpanzees as part of a rich and endemic fauna and flora led to the declaration of the Nimba mountains as a World Heritage Site in Guinea in 1981and Ivory Coast in 1982(UNESCO July 22, 2015/2015.…”

Section: A Short History Of the Taxonomy Of Nimbaphrynoides Occidentalismentioning

confidence: 99%

A review of the reproductive biology of the only known matrotrophic viviparous anuran, the West African Nimba toad, Nimbaphrynoides occidentalis

Sandberger-Loua¹,

Müller²,

Rödel³

2017

ZSE

View full text Add to dashboard Cite

Amphibians, and anurans in particular, show the highest diversity of reproductive modes among tetrapods. Nevertheless, viviparity is scarce in anurans and its occurrence is even more often assumed rather than confirmed. Probably the best studied viviparous amphibian is the Nimba toad, Nimbaphrynoides occidentalis. During more than 40 years of research, the Nimba toad's reproductive morphology, endocrine activity of the ovary as well as the pituitary gland, and to some extent the ecological impact (seasonality, humidity, food availability) on reproduction was examined. Due to the Nimba toad's unique reproductive mode, summaries are usually included in reviews discussing amphibian reproduction and articles on reproductive biology often discuss the exceptional reproductive system of Nimba toads. However, to our knowledge a detailed synthesis, summarising all the different original studies on the toad's reproduction, is so far missing. In this paper we review and summarise all available initial publications, which often have been published in French and/or are difficult to access. A short overview is given of the climatic and environmental conditions experienced by Nimba toads and the key findings supporting a "true" viviparous reproduction with matrotrophy (maternal provision of nutrition during the gestation) and pueriparity (birth of juveniles). Then foetal development (morphological, gonad and pituitary development), and the female (ovary, oviduct, pituitary and their endocrine interactions) and the male reproductive system (testes and pituitary) are reviewed. Finally, the reproductive cycle and its link to the Nimba mountains' seasonality and ecological/ conservation implications are discussed. Key WordsAmphibia development evolution ovary oviduct pueriparity seasonality testes uterus

show abstract

Les formations à quartzites rubanés ferrugineux des Monts Nimba et du Simandou: des unités empilées tectoniquement, sur un « soubassementplutonique Archéen (craton de Kénéma-Man), lors de l'orogène Éburnéen

Cited by 15 publications

References 6 publications

Archaean crustal evolution in West Africa: A new synthesis of the Archaean geology in Sierra Leone, Liberia, Guinea and Ivory Coast

Archaean crustal evolution in West Africa: A new synthesis of the Archaean geology in Sierra Leone, Liberia, Guinea and Ivory Coast

A review of the mineral potential of Liberia

A review of the reproductive biology of the only known matrotrophic viviparous anuran, the West African Nimba toad, Nimbaphrynoides occidentalis

Contact Info

Product

Resources

About