Les travaux menés dès les années 60 dans les formations sédimentaires de la région du Béli n'ont pas permis l'établissement d'une échelle lithostratigraphique. Dans la présente étude, qui s'appuie sur une approche terrain à travers des levés de coupes géologiques et sur des études lithologique, pétrographique et structurale, une triade, ainsi qu'une formation molassique ont été mises en évidence pour la première fois dans cette portion du bassin. Ainsi, à l'instar des formations sédimentaires des bassins de Taoudeni et des Volta, celles de la région du Béli, localisées sur la bordure sud du bassin du Gourma (Nord-Est du Burkina Faso), comportent une association « Tillite-calcaire-silexite » qui a été corrélée à la « triade » du bassin de Taoudeni. L'échelle lithostratigraphique de la région du Béli comprend huit formations. La triade repose sur des grès-quartzites et est surmontée successivement par des shales, des dolomies, un ensemble métamorphique allochtone constitué de phyllades et par la formation molassique. Tout comme les formations carbonatées, certaines roches du complexe silexitique renferment des stromatolites ainsi que des micro-organismes. La déformation panafricaine se matérialise par des plissements, une schistosité et par un réseau de failles. On y reconnaît les phases compressives D1, D3 et D4 des épisodes tectoniques de l'orogenèse panafricaine et on soupçonne une réactivation des fractures au cours du cénozoïque. Les caractéristiques des épisodes tectoniques permettent de distinguer deux unités structurales: l'unité structurale du Nord-Béli (allochtone), caractérisée par une déformation de type ductile et un anchimétamorphisme, est charriée sur l'unité structurale du Sud-Béli (para-autochtone). Celle-ci est marquée par une déformation à dominante cassante, n'a subi aucun métamorphisme et est chevauchant sur le socle éburnéen. La formation silexitique de la triade contient une minéralisation polymétallifère probablement enrichie lors des différents épisodes tectoniques qui ont affecté cette formation. Studies conducted since the 1960s on the sedimentary formations of the Béli region have not permitted the establishment of a lithostratigraphic log for the area. Based on fieldwork involving drafting of cross-sections and lithologic, petrographic and structural studies, a triad and a molasse formation have been described for the first time in this portion of the basin. Therefore, as in the sedimentary formations of the Taoudeni and Volta Basins, the formations in the Béli area, located on the southern edge of the Gourma Basin (northeastern Burkina Faso), include an association of "Tillite-limestone-chert" that is correlated with the "triad" of the Taoudeni Basin. The lithostratigraphic section of the Béli area comprises eight formations. The triad overlays quartzitic sandstones and is covered by shales and dolomite. Above the triad is the metamorphic allochthonous unit composed of phyllites, which are covered by the molassic formation. As in the carbonate formations, some rocks of the cherty complex contain stromatolites as well as micro-organisms. The Pan-African deformation is characterized by folding, schistosity and a fault network. Compressive phases D1, D3 and D4 of the Pan-African orogeny are identified, and we suspect a reactivation of Pan-African fractures during the Cenozoic. The characteristics of the tectonic episodes are utilized to distinguish two structural units: the allochthonous unit of North Béli, characterized by a ductile deformation and an anchi-metamorphism thrust on the para-autochthonous unit of South Béli. The latter is marked by a dominant brittle deformation; it underwent non-metamorphism and is thrust on the Eburnean basement. The cherty formation of the triad contains a polymetalliferous mineralization that was probably enriched during the different tectonic events.

Les travaux menés dès les années 60 dans les formations sédimentaires de la région du Béli n'ont pas permis l’établissement d'une échelle lithostratigraphique. Dans la présente étude, qui s'appuie sur une approche terrain à travers des levés de coupes géologiques et sur des études lithologique, pétrographique et structurale, une triade, ainsi qu'une formation molassique ont été mises en évidence pour la première fois dans cette portion du bassin. Ainsi, à l'instar des formations sédimentaires des bassins de Taoudeni et des Volta, celles de la région du Béli, localisées sur la bordure sud du bassin du Gourma (Nord-Est du Burkina Faso), comportent une association « Tillite-calcaire-silexite » qui a été corrélée à la « triade » du bassin de Taoudeni. L’échelle lithostratigraphique de la région du Béli comprend huit formations. La triade repose sur des grès-quartzites et est surmontée successivement par des shales, des dolomies, un ensemble métamorphique allochtone constitué de phyllades et par la formation molassique. Tout comme les formations carbonatées, certaines roches du complexe silexitique renferment des stromatolites ainsi que des micro-organismes. La déformation panafricaine se matérialise par des plissements, une schistosité et par un réseau de failles. On y reconnaît les phases compressives D1, D3 et D4 des épisodes tectoniques de l'orogenèse panafricaine et on soupçonne une réactivation des fractures au cours du cénozoïque. Les caractéristiques des épisodes tectoniques permettent de distinguer deux unités structurales: l'unité structurale du Nord-Béli (allochtone), caractérisée par une déformation de type ductile et un anchimétamorphisme, est charriée sur l'unité structurale du Sud-Béli (para-autochtone). Celle-ci est marquée par une déformation à dominante cassante, n'a subi aucun métamorphisme et est chevauchant sur le socle éburnéen. La formation silexitique de la triade contient une minéralisation polymétallifère probablement enrichie lors des différents épisodes tectoniques qui ont affecté cette formation.

The African part of the Neoproterozoic Aracuai-West Congo orogen forms a more than 1400 km long belt, running from Gabon in the north to Angola in the south, parallel to the South Atlantic coast. It consists of the West Congo fold belt in the west and a largely undeformed sedimentary foreland basin in the east. In the Republic of Congo (Congo Brazzaville) these are known as, respectively, the 'Mayombe fold belt' and the 'Niari basin'. The 'Mayombe fold belt is largely made up of strongly deformed metasedimentary rocks of the Mayombe Supergroup and its reworked granitoid basement complex. The Niari basin comprises the sedimentary strata of the West Congo Supergroup, which contain a unit of diamictite and associated cap-carbonate, related to the Marinoan (ca. 635 Ma) glaciation. In this paper detrital zircon U-Pb data are employed to investigate the relationships between the Mayombe and West Congo Supergroups in Congo Brazzaville, as well as the relationships with similar stratigraphic units in the Democratic Republic of Congo (DR Congo). Unfortunately, major differences in stratigraphical nomenclature exist between Congo Brazzaville and DR Congo which, together with geological differences, complicate comparisons. The terminology used in this paper follows the Congo Brazzaville tradition.U-Pb data have been obtained by LA-ICP-MS on 1674 zircon grains from samples of the Mayombe and West Congo Supergroups (seven and eight samples, respectively). Two of the samples have Palaeoproterozoic ages. The other samples are of Neoproterozoic age. Zircons from the latter fall into four main age groups: Group 1, 500-800 Ma, forming 8% of the total population; Group 2, 900-1200 Ma (29%); Group 3, 1800-2300 Ma (19%); and Group 4, 2500-3100 Ma (31%). Only ca. 13% of the zircons fall outside of these groups.Most zircons of Group 1 (600-800 Ma) are interpreted to have been derived from late Neoproterozoic magmatic arc rocks and syn- to post-collisional granites of the Aracuai orogen in Brazil, since rocks of these ages are rare in the Congo craton to the east. Most of Group 2 zircons have probably been derived from early Neoproterozoic (1000-900 Ma) rhyolitic and granitic rocks exposed in DR Congo. The Palaeoproterozoic and Archaean zircons of Groups 3 and 4 may have been derived both from eastern and western source regions.None of the stratigraphical units beneath the Marinoan diamictite contain the 500-800 Ma zircons of Group 1. This is interpreted to indicate deposition of these units during the earlier Neoproterozoic rift and drift phases in the history of the Aracuai-West Congo orogen, while the strata that do contain Group 1 zircons were deposited during the collisional phases and post-collisional uplift. A significant hiatus is likely to be present beneath the Marinoan diamictite. Based on these results, a revision of the stratigraphy of the Mayombe and West Congo Supergroups is recommended.Three granitoid rocks and two metasedimentary samples from the reworked basement complex have also been investigated, yielding Palaeoproterozoic ages, 2050-2100 Ma for the granites, and Palaeoproterozoic and Archaean detrital zircon ages for the metasedimentary rocks.Sm-Nd isotope data have been obtained on a number of (meta-)argilitic and siltstone samples. All samples yielded Palaeoproterozoic model ages, indicating mixing of sediments of different ages, as also observed in the zircon age distributions. (C) 2015 Elsevier B.V. All rights reserved.

D es travaux paleomagnetiques sont realises sur les formations du Neoproterozoique-Cambrien inferieur de la couverture du craton ouest-africain, dans les bassins du Gourma et des Volta et la partie occidentale de l’Anti-Atlas. L’aimantation est portee essentiellement par la magnetite et l’hematite. Les directions moyennes des sites sont calculees a partir des composantes de hautes temperatures situees entre 500 et 670°C. Deux tests positifs de pli sont obtenus a partir des sites de Tin Dioulaf, dans le bassin du Gourma et d’Ait-Abdallah 2 et 4, dans l’ O uest de l’Anti-Atlas. Les Poles G eomagnetiques Virtuels obtenus a partir des directions moyennes indiquent des basses paleolatitudes qui placent le craton ouest- africain en position subequatoriale au cours de la periode Ediacarien-Cambrien inferieur. Ces resultats consolident l’hypothese de la Terre boule de neige qui place les masses continentales en position subequatoriale a cette epoque.

Le Massif Kabye represente le plus puissant des massifs de la zone de suture de la Chaine Panafricaine des Dahomeyides. Il se definit comme un edifice de nappes granulitiques tectoniquement encaisse dans des unites gneissiques externes et internes. Cette pile de nappes comprend une unite petrographique occidentale, constituee de granulites leucocrates a grenat, denommees « Granulites de Lassa-Soumdina » (GLS), et une unite petrographique orientale, composee de granulites melanocrates a structure metagabbroique, appelees « Granulites de Ketao-Sirka » (GKS). Ces deux unites petrographiques ou series de nappes sont separees par la zone mylonitique de Panalo (ZMP) qui correspond a une zone de charriage majeur et laquelle se superpose un couloir de cisaillement dextre syn-Dn+2. Ces nappes granulitiques comportent des lambeaux de metacumulats pyroxeniques ou rarement plagioclasiques, et de roches ultrabasiques retromorphosees (serpentinites, talcschistes, actinolites et chloritoschistes) soulignant generalement des semelles de nappes. Les microstructures et les parageneses minerales des granulites et des roches associees traduisent une evolution tectono-metamorphique polyphasee : une granulitisation syn-Dn vers 612 Ma (phase de collision) ; une amphibolitisation syn-Dn+1 vers 585 Ma (phase tangentielle ou d’obduction) ; et une retromorphose syn- a post-Dn+2, a facies schiste vert, vers 566 Ma (phase de plissement post-nappe).

The analysis of structural markers collected from the petrostrutural units of Parakou-Nikki, in Northeast Benin, indicates that the Pan-African remobilization or rejuvenation (600 ± 50 Ma) of the Benino-Nigerian Metacraton consits of a wide migmatization accompanied by five tectogenetic phases (Dn–Dn+4). The Dn phase is penecontemporaneous with the collision between the Benino-Nigerian shield and the oriental margin of the West-African Craton. This phase is associated with the granulitization or migmatization episode, and materialized by the Sn foliation on which the Dn+1 deformation markers (major Pan-African structuring phase in the Dahomeyide orogenic belt) are superimposed. Thus, the Sn+1 plane and the Ln+1 lineations indicate a perfect transposition of the Sn plane and a syn-Dn paragenesis remobilization in the syn-Dn+1 amphibolite facies retromorphosis. The strong resumption of the main foliation (Sn+1) corresponds to the Dn+2 deformation phase. The latter, associated with a second retromorphosis, is materialized by Pn+2 folds, with submeridian to NE–SW axes, and by a Sn+2 foliation or strain-slip cleavage. It is also the phase of emplacement of the Kandi mega-shear zone associated with the development of Cn+2 dextral shear plane very generalized over all the petrostructural units of Parakou–Nikki. At a large scale, the Dn+3 phase is expressed as Pn+3 kilometric synform and antiform structures with NE–SW to ENE–WSW trending axes. This Dn+3 phase can be considered as a transpression responsible for the development of the Cn+3 sinistral shear plane and flat shear structures displaying a westward overlapping. It ends with a fracturing episode materialized by strike-slip fault systems defining a main stress σ1 trending ESE–WNW to SE–NW. The late Dn+4 phase only corresponds to conjugated strike-slip faults which resulted from a major SE–NW to SSE–NNW compression.

•A depositional model for post-Marinoan cap carbonates is proposed.•Cap carbonates are interpreted to have deposited in peritidal environments.•A south-westward migration of the carbonate factory though time is evidenced.•The top of cap carbonates is a diachronous surface.

Despite recent works on the Schisto-calcaire Group of the West-Congolian Supergroup in Central Africa, Neoproterozoic Cap Carbonate have not been well documented in the Niari-Nyanga basin that extends from Gabon to Angola. The couplet “Cap Carbonate (SCIa) and Upper Diamictite”, that is a marker of the “Snowball Earth event” was studied in 5 sections from the Niari-Nyanga basin and in one section from the external zone of the Mayombe folded belt (MFB). Our paper presents a high-resolution data set based on results from petrography, geochemistry, mineralogy and stable isotope studies performed on Cap Carbonate samples. The estimation of the illite crystallinity indexes indicates different degrees of post-sedimentary transformations evolving from deep diagenesis in the syncline basin to an epimetamorphism in the external zone of the MFB. Thin-sections of rocks sampled in this latter section display metamorphic features materialized by recrystallization of minerals in a S1 cleavage plane. Despite such an observation, all our samples clearly show preservation of primary petrographic structures such as biolaminations, fenestrae and peloids. Geochemical data leads us to highlight that the Cap Carbonate is composed by a variety of carbonate types. These results support the fact that the Cap Carbonate was derived from a combination of biological and chemical processes: organomineralization and chemical precipitation from supersaturated solutions, with a negligible impact of post-depositional transformations. For all the studied sections, stable isotope profiles display a drop in δ13C values, from about −2.6‰ to −4‰, associated with δ18O values ranging from −6‰ to −10‰. Moreover, the similarity of the isotopic profiles of the studied Cap Carbonate (from the Niari-Nyanga basin and the MFB) and the close fit to the expected Neoproterozoic δ13C and δ18O seawater values constitute a strong indication of a weak impact of a diagenetic to epimetamorphic evolution on the carbon isotopic signature of the SCIa Cap Carbonate. In the light of this data set, our isotopic records must be considered as a reliable tracer of the Marinoan Glaciation within the West-Congolian Supergroup.

Post-sedimentary transformations have masked or completely obliterated the structures and textures of Precambrian carbonate rocks. Therefore, methods of classification of the carbonate rocks founded on the observation of primary structures or textural characteristics are ill-adapted. Consequently, only certain geochemical classification methods allow us to distinguish the various rock-types in the case of Neoproterozoic carbonates. After presenting the most suitable geochemical classifications, we propose a new classification into 14 groups based on a regular ternary diagram with computerized data input. For each sample of carbonate rock, analysis of calcium and magnesium contents allows us to calculate the input data for our diagram i.e. the percentages of Calcite, Dolomite and Insoluble Residue. To automate the application of this diagram, input parameters are created in a descriptive file "Roches.ternaires.txt" using an option called "Ternaires" in the "Diagrammes" software developed by Roland Simler. Thirty cap carbonates of Africa are used to validate this new method.

The Bangui magnetic anomaly (BMA) is the largest lithospheric magnetic field anomaly on Earth at low latitudes. Previous studies investigated its geological source using constraints from satellite and ground magnetic field measurements, as well as from surface magnetic susceptibility measurements on rocks from the Panafrican Mobile Belt Zone (PMBZ). Here we combine magnetic field data modelling and rock magnetic property measurements (susceptibility and natural remanent magnetization, NRM) on many samples from this PMBZ and the surrounding formations. It reveals that NRM is a significant component of the total magnetization (Mt) of the BMA source, which reaches 4.3 A/m with maximum thicknesses of 38 and 54 km beneath the western and eastern parts of the BMA. Only the isolated and relatively thin banded iron formations and some migmatites show such Mt values. Thus we suggest that the thick BMA source may be composed either by overlapped slices of such metamorphic rocks, or by an iron-rich mafic source, or by a combination of these two geological structures. (C) 2013 Elsevier B.V. All rights reserved.

In northern Togo, the Aledjo Mountains represent a NE-SW to ENE-WSW trending segment of the Pan-African Dahomeyide orogen. This mainly quartzitic topography belongs to the external zone of the belt and, more precisely, to the eastern assemblage of the Atacora Structural Unit. It corresponds to a ruiniform landscape which resulted from an erosive sculpturing that started at the end of the Pan-African tectogenesis within the Dahomeyide Belt, at about 550 Ma. A first interpretation of these spectacular sculptures attributed their great variety to predisposition factors related to the petrographic heterogeneity of the quartzites and to the Pan-African tectogenesis. With reference to these genetic factors, the Aledjo quartzitic ruins are subdivided into two morphostructural groups related either to a combination of folding and erosion or fracturing and erosion. Moreover, the Aledjo ruiniform landscape may be considered as an attractive touristic target which can contribute to regional economic development in northern Togo. Keywords: Quartzitic Ruins, Aledjo Montains, Dahomeyide, Northern Togo, Morphogenesis

The Kekem shoshonitic gabbro-norite association is part of the high-K calc-alkaline (HKCA) post-collisional magmatism, a major feature of the Pan-African Belt in Cameroon. LA-ICP-MS U-Pb zircon analyses provide an age of 576 +/- 4 Ma for the Kekem complex. This age is interpreted as dating the emplacement of the massif during the waning stage of the Pan-African orogeny. The latter is related to dextral movements along the Central Cameroon Shear Zone (CCSZ).The REE patterns display enriched LREE (La-N/Yb-N = 14.2-23.5) while HREE present a nearly flat profile (Dy-N/Yb-N = 1.3-1.7), and the La/Sm and Sm/Yb ratios led to propose that the Kekem gabbro-norites have been derived from the partial melting of a garnet-spinel lherzolite mantle source. The negative Nb-Ta and Ti anomalies and the positive Pb anomalies indicate that this mantle source was modified by contribution of a subduction-related material. The low Ce/Pb (2.6-10.4) and Th/Yb ratios associated to high Ba/La ratios, indicate that source enrichment could be related to slab derived fluids. As a whole, the Kekem geochemical features suggest that primary gabbro-noritic magmas derived from a subduction-modified mantle source (metasomatised lithospheric mantle). Moderately high Sr-86/Sr-87 initial ratios (0.7068-0.7082), low epsilon(Nd) (-5 to -9) and old Nd T-DM model ages (1.6-1.8 Ga) are interpreted to result from contamination of Neoproterozoic mantle by the Paleoproterozoic crust.The ca. 576 Ma movements along the CCSZ are related to a Neoproterozoic metacratonization of the northern margin of the Congo craton during the Pan-African orogeny. This metacratonization led to vertical planar lithospheric delamination along lithospheric transcurrent faults, asthenospheric uprise and partial melting of the Paleoproterozoic lithospheric mantle. (c) 2013 Elsevier Ltd. All rights reserved.

L’ensemble lithostructural de Nikki, au NE-Bénin, appartient à la zone interne de la chaîne panafricaine des Dahomeyides. Il correspond à un complexe réunissant des faciès d’orthogneiss granodioritiques, des migmatites et quelques intrusions granitiques associées. Les microstructures analysées, pour la première fois, dans ces ensembles lithologiques permettent de reconstruire cinq phases de déformation marquant la remobilisation panafricaine du bouclier bénino-nigérian. Cette tectogenèse débute avec le développement de la foliation Sn associée à la phase de collision (Dn) entre le bouclier bénino-nigérian et la marge orientale du craton ouest-africain. La foliation principale (Sn+1) est attribuée à la phase majeure Dn+1 qui induit la transposition du plan Sn et la refonte des paragenèses syn- Dn dans les conditions du faciès amphibolite. La phase de déformation Dn+2 est surtout matérialisée par le plan de cisaillement dextre Cn+2 assez pénétratif à l’échelle de l’affleurement. La phase de déformation Dn+3 se traduit par la superposition d’un plan de cisaillement senestre Cn+3. Les marqueurs de déformation cassante composent deux systèmes de familles de décrochements attribués aux épisodes tardi-Dn+3 et syn-Dn+4. Ces systèmes de décrochements indiquent des axes de paléocontraintes de compression majeure respectivement ESE-WNW et SENW à SSE – NNW.Mots clés : Bénin, Panafricain, Dahomeyides, zone interne, microstructures

The Kabye and Kpaza Massifs correspond to two main granulitic suites in the suture zone of the Pan-African Dahomeyide orogenic belt, in northern Togo. The Kabye Massif is composed of an important west verging nappe pile subdivided into two petrographic units. The nappes in its western petrographic unit are made up of leucocratic garnetbearing granulites defined as the “Lassa-Soumdina Granulites” (GLS). The eastern petrographic unit consists of mela-nocratic granulites, with metagabbroic structures, called the “Ketao-Sirka Granulites” (GKS). These two petrographic units are separated by the Panalo Mylonitic Zone (ZMP). This major west verging zone includes a syn-Dn + 2 dextral shear contact. The Kpaza Massif comprises nappes of melanocratic granulites (GKM), comparable to the GKS of the Kabye Massif. All these granulitic nappes include boudins of pyroxenites or meta-anorthosites, and ultramafic rocks represented by serpentinites, talcschists, actinolite- and chlorite-schists which generally mark thrust soles. The GLS nappes are thrust over the Kara-Niamtougou orthogneissic unit (UKN) which is considered as the easternmost structural unit of the Dahomeyide external zone. On the other hand, the GKS nappes underlie those of the Binah meta-volcano sedimentary Complex (CB) which belongs to the Dahomeyide internal zone. As regards the Kpaza Massif, it occurs as a geologic window tectonically enclosed in the Mono Complex nappes (CM) corresponding to the southern part of the CB. The organization of the Kabye and Kpaza Massifs, as west verging nappe piles, and their relationships with the surrounding structural units express the tangential and folding tectonics that structured the Pan-African belt in northern Togo. The microstructures and mineral parageneses of the granulites and associated rocks in these two massifs indicate a polyphase tectono-metamorphic evolution: a syn-Dn granulitization (collision phase); a syn-Dn + 1 amphibolitization (obduction or tangential phase); and a syn- to post-Dn + 2 greenschist facies retrogressive metamorphism (post-nappe folding phase).

The westernmost part of the Pan-African (c. 600 Ma) Dahomeyide orogen in Togo and Benin consists of a complex stack of thrust sheets, mainly composed of Palaeoproterozoic ('Eburnean', c. 2000 Ma) granitoid rocks and younger volcanic and metasedimentary successions. This thrust stack comprises the suture between the West-African craton and the Benino-Nigerian province to the east. This eastern province consists largely of migmatites, supracrustals and granitoid rocks. Rb-Sr and Sm-Nd isotope data for four granites from the western domain confirm the Palaeoproterozoic age of these rocks found by earlier studies. One of these granites yielded a zircon U-Pb age of c. 2060 Ma. Twenty samples from the eastern region yield Rb-Sr and Sm-Nd data indicating that both migmatites and granitoid rocks are of Neoproterozoic (Pan-African) age. Zircon U-Pb data on six of these samples yielded ages ranging from c. 650 to c. 550 Ma. Suggestions that parts of the migmatites might be of Eburnean age could not be confirmed. The Neoproterozoic granitoid rocks may represent a Pan-African arc overlying an eastward dipping subduction zone, and Sm-Nd data indicate that they contain significant proportions of older crustal material. Age probability diagrams for detrital zircons from three metasedimentary rocks (one from Nigeria) and one S-type quartz diorite from the eastern region show prominent peaks at c. 1900 Ma and 2400-2200 Ma. A provenance of the zircons from sources in the Borborema province in NE Brazil or lateral equivalents thereof is suggested. A few Neoproterozoic zircons are present in three of the samples. On the basis of Th/U ratios a distinction can be made between Neoproterozoic zircons of metamorphic and detrital origin. The zircon age probability diagram of a quartzite from northern Benin exhibits one peak, at c.1900 Ma, different from the other metasedimentary samples. This quartzite might be correlated with sedimentary strata of the Volta basin that overlie the Eburnean basement in Ghana. Togo and Burkina Faso. Correlation of the rocks in the study area with those in the Borborema province is discussed. (C) 2011 Elsevier B.V. All rights reserved.

The end of the Neogene in the emerged part of the Togolese coastal basin corresponds to a sandy–argillaceous complex of continental appearance devoid of marine fauna and generally attributed to the “Continental terminal” in the neighboring West-African basins. Although the Neogene/Quaternary boundary is identified in this sandy–argillaceous complex in most of the boreholes studied and also in field sections, the lack of precise dating data especially paleontological evidence makes the definition of this boundary difficult. In the present state of knowledge, this boundary merges with an erosional paleosurface which coincides with the erosional discordance that separates the two units composing the sandy–argillaceous complex of the “Continental terminal” in this basin. The two units are the Kpogame pebble bearing formation which corresponds to “Continental terminal sensu stricto” (upper Miocene–Pliocene) and the “Formation de la Terre de barre” of Quaternary age. Future investigations will allow a more accurate determination of the Neogene/Quaternary boundary in this basin.

Three meta-igneous bodies from the Yaounde Group have been analyzed for their petrography, geochemistry, and 207Pb/206Pb zircon ages. According to their geochemical patterns, they represent meta-diorites. The meta-plutonites yielded identical zircon ages with a mean of 624 ± 2 Ma interpreted as their intrusion age. This age is in agreement with previously published zircon ages of meta-diorites from the Yaounde Group. The meta-diorites derived mainly from crustal rocks with minor contribution from mantle material. The 87Rb/86Sr isochron ages of one meta-diorite sample and three meta-sedimentary host rocks are significantly younger than the obtained intrusion age. Therefore, they are not related to igneous processes. 87Rb/86Sr isochron ages differ from sample to sample (599 ± 3, 572 ± 4, 554 ± 5, 540 ± 5 Ma) yielding the oldest Neoproterozoic age (~600 Ma) for a paragneiss sample at a more northern location. The youngest Rb/Sr isochron age (~540 Ma) was obtained for a mica schist sample at a more southern location closer to the border of the Congo Craton. The 87Rb/86Sr whole rock-biotite ages are interpreted as cooling ages related to transpressional processes during exhumation. Therefore, several discrete metamorphic events related to the exhumation of the Yaounde Group were dated. It could be shown by Rb/Sr dating for the first time that these late tectonic processes occurred earlier at more distant northern locations of the Yaounde Group and lasted at least until early Cambrian (~540 Ma) more closely to the border of the Congo Craton.