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The 60 km-long Pan-African Bape massif intruded in the Adamawa-Yade Archaean block is an excellent case for the study of subduction–collision-related magmatism, its origin by interaction among magmas from various sources, and its bearing on the evolution of the Pan-African orogenic belt in Cameroon. An integrated study including mapping, petrography and geochemistry was carried out on these Ba–Sr rich quartz monzonites, quartz monzodiorites, monzonites, granodiorites (adakites), syenites and micromonzogabbros. The rocks are dominated by plagioclase + alkali feldspars + amphibole + biotite + sphene + opaque minerals + apatite + zircon ± pyroxene ± quartz assemblage. They are I-type, ferroan, metaluminous and belong to high-K calc-alkaline, shoshonitic series. REE patterns form two sets of tight closed and of highly differentiated patterns. The spider diagrams display Th, U, Nb, Ta, Zr and Hf negative and Ba, K, Pb and Sr positive anomalies. High K2O, Ba–Sr and moderate SiO2 contents and the variation of canonical ratios such as Zr/Sm, Zr/Hf, La/Sm, and Sm/Yb, point to multiple origins for the Bape granitoids such as (i) melting of a dehydrated subducting crust (adakites) and/or the metasomatized heterogeneous mantle wedge (spinel– and phlogopite–amphibole–garnet lherzolite), or (ii) the mixing of these liquids (other granitoids). The U–Pb emplacement age (640–603 Ma), coeval with the subduction–collision between the West-African and the Congo cratons, the occurrence of adakites, combined with geophysical data, support that these granitoids are link to the southeast–northwest subduction of the hot Yaounde oceanic crust under the Adamawa-Yade craton, during the Neoproterozoic time.

The Paleocene-Lower Eocene N'kapa Formation has long been considered as an important groundwater and hydrocarbon resource in the eastern edge of the Douala Basin. The present study’s aim is to establish a possible link between the geological nature of this formation and the quality of potential aquifers using Gamma Ray well log, cuttings and outcrops through sedimentology and sequence stratigraphy studies. The results obtained from this study show that: lithofacies are dominated by clays, silts and sands/sandstones; gamma ray electrofacies are funnel-shaped to cylindrical-shaped with some bell-shaped; depositional environments are continental to shallow marine dominated by fluvial and sometimes tidal processes; fluvial channel-fill, tidal channel-fill and delta front bars sands are potential aquifers; sequence stratigraphy analysis reveals two transgressive–regressive cycles of second order (Danian to Selandian and Thanetian to Ypresian), two Highstand System Tracts, one Transgressive System Tract and one Lowstand System Tract; the high-resolution geometry of these sandy/sandstone sedimentary bodies shows that their distribution is linked to the hydrodynamic factors and the topography of the depositional environment. A total of two types of lithological facies of the reservoir levels were defined according to the volume of clay: clean sandstone (0–15%) and low clayey sandstone (15–30%). The gamma ray well log correlation shows that the thickness of the reservoir levels is variable and that the clay content (Vsh%) increases from the NE to the SW. As a result, the best potential aquifers appear to correspond to the fluvial channel-fill sands deposited during the base-level fall of Upper Paleocene age (Lower Thanetian).

The Douala-Buea Region (DBR; 4°–5°N, 9°–10°30′E), a portion of the southern Cameroon passive margin, developed on the Proterozoic granito-gneissic basement and the Cretaceous to Recent volcano-sedimentary cover, was explored in order to evaluate the lithology and tectonics controls on its landscape using the qualitative and quantitative geomorphological analyses based on 30 m resolution Digital Elevation Models (DEM) and field evidences. This area displays an uneven and complex landscape differentiated into four morphological units: Douala, Nkondjock, Kumba and Buea Units. The Douala Unit corresponds to the Coastal Plain and is extended on the Douala-Kribi/Campo sedimentary basin. The Nkondjock Unit represents a middle plateau developed on a Proterozoic granito-gneissic basement. The Kumba Unit matches with the southernmost volcanic Western Cameroon High Plateau. The Buea Unit corresponds to the Mount Cameroon stratovolcano. The relief analysis through mountain-front sinuosity (Smf, 1.19–1.43) and relative relief ratio (Rr, 0.10–2.31) vary from one unit to another. The drainage network analysis including drainage patterns, stepped longitudinal river profiles, the associated morphometric indexes, notably the concavity index (IC, 0.56–0.88), deviation (D, 267–2912 m), basin asymmetry factor (A f, 6.37–42.12), hypsometric integral (HI, 0.10–0.29), valley floor width to valley height ratio (Vf, 0.36–2.75), elongation ratio (Re, 0.30–0.50), watershed slope (S, 6.88–88.88) and stream length gradient index (SL, 0–3332) vary from one basin to another too. These results also show the heterogeneous and uneven DBR landscape controlled by its lithology and active tectonics. The drainage system reveals concave to concavo-convex longitudinal river profile shapes with knick points, asymmetric basins, and fault reactivations, and highlights the tectonics activity that used to occur through the time and their control on the morphology. Together, they document the lithostructural controls on the DBR landscape evolution, extendable in the whole SW Cameroon margin.

This paper discusses the geological and geotechnical potentialities of Ntem formations from the Memve’ele dam construction. Stratigraphic formations on the dam site consist from top to bottom sand, silty sand, silty, silty clay, very to moderate weathered rocks with a thickness of about 0.5–3 m above a sound bed rock which are represented by Ntem formations. These rocks have main mineral associations represented by orthopyroxene, clinopyroxene, quartz, plagioclase and garnet, display reaction textures, idiomorphic crystals, straight boundaries between crystals, the iron bearing amphibole, biotite and epidote, quartz ribbons and iron minerals (ilmenite and magnetite) are also present. All these permit to class them from granulite to amphibolite facies metamorphic conditions; therefore they are very hard and appear good for civil applications. The permeability has thickness from 0 to 13 m in the depth with Lugeon values higher than 15 UL. The RQD values are permitted to class these rocks as being moderated to good resistant. These character features which improve their geophysical properties (e.i. hard quality) have permitted that the dam and powerhouse foundations refitting on them. According to geophysical properties and rock mass rating, the rock mass is fair and good and is classified to class II and III. All these indicate that the rock mass is well compacted and sound with sparsely spaced discontinuities. The Ntem formations have uniaxial compressive strength under saturated condition generally higher than 40 Mpa, dry density or specific weight not less than 2.7 g/cm3, low porosity (average from 0.69 to 0.83%), low coefficient of water absorption (average from 0.012 to 0.04%), deformation modulus from 82.3 to 87.86 Gpa, Los Angeles and Micro Deval values are lower than 40% and 20% respectively, swelling risks are very limited with low values (1.07–1.11%) of sulphate, under 4.5% of cement and low values (0–0.07%) obtained during alkali-reaction test. All these have permitted that to obtain concrete aggregate and rip rap by crushing and processing these rocks from quarry during the dam, spillway, powerhouse and road constructions. These results confirm use of these formations during Memve’ele dam constructions.

Gold enrichment and other metals usually occur during fractional crystallization in granitoids. In this study, the spatial analysis of multi-element associations from stream sediments is proposed to identify the characteristics and distributions of lithological units and mineralized pegmatite vein with associated stream sediments in the Lingbim-Zimbi gold field for mineral exploration purposes. The sampling campaign was carried out both on rocks and in exploration wells. Principal component analysis and the phased array approach have allowed distinguishing the chemical elements linked to the mineralized structure from those linked to the geology of the area. Then, two potential gold mineralization phases were identified along with the anomalies observed and the spatial distribution of the elemental associations; the first one being linked to the emplacement of granitoids and the second linked to the formation of the Central Cameroonian Shear Zone (CCSZ) oriented NE-SW.

The north-central Cameroon is located at the northern edge of Archean Congo–Sao Francisco craton and at the east of the West African craton. This area includes various Neoproterozoic to Holocene geological litho-structural units. It corresponds to a juvenile crust resulting from the collision of the above cratons. Geological features associated with the Poli–Ounianga–Kebir heavy gravity line trending NE–SW crosscuts the study area and hosts several deposits, chiefly auriferous and uraniferous ore deposits. Uraniferous bodies are described at the SW and NE sides of the Benue Trough and are related to hydrothermal processes and structural events in Neoproterozoic granitoids of Poli (Cameroon) and Zabili (Chad). Gold ore deposits are found around faulted zones mostly in the Tchollire shear zone. Gravity data derived from the Earth Gravitational Model EGM2008, combining terrestrial, maritime and satellite-derived data, were used to model the crust of the north-central Cameroon. The geophysical filtering enabled to highlight that the most fractured areas with the deepest faults are situated on the positive anomalies of the mineralized volcano-sedimentary belts of Poli and Bibemi. The Benue Trough that crosscuts the volcano-sedimentary belts exposes few structural features due to the weak gravity signal of Cretaceous sedimentary cover. The radially averaged power spectrum analysis brought out the density contrast depths of some geological belts and revealed the Moho discontinuity of the study area at about 24 km depth. This Moho depth is in accordance with the assumption of a thin crust and a mantle upwelling in the study area proposed by previous works. Thus, the presence of geological formations of mantle, crustal and mixed crustal-mantle origin such as mafic rocks as well as calc-alkaline to alkaline granitoid outcropping in the study area may be the consequence of the proximity of the upper mantle to the surface. Moreover, fractures highlighted in this work brought out the crustal permeability in the study area illustrating migratory passages for mantle formations found at the surface. Based on the gravity field analysis, the proposed models of basement in this study provide geological architecture highlighting the presence of more or less dense rocks and hydrothermal fluids migration along faults as key elements for ore deposits formation.

This paper presents the results of engineering investigations used to select a best design for the Memve’ele dam. The selection of Memve’ele dam type has been based on consideration of physical factors such as topography, climate, availability of construction material, geology, geotechnical and foundation conditions and the selection of optima alternative between three dam types. According to these factors, Memve’ele valley is very wide and situated in the warm climate zone with dry and rainy seasons favorable to embankment type dam; the geology reveals very good conditions with Ntem formations and residual deposits as foundation materials and the dam site is not influenced by earthquake; this behavior is confirmed by geotechnical data and further indicates that this site is favorable to a composite dam type (embankment and concrete dams or connecting concrete structures) and the construction materials found within or near the dam site are suitable for usage. These characteristics have contributed retaining three dam types. The alternative of these three dams is a composite dam type option including homogeneous earth dam and rock fill dam with central core link by concrete structures. Engineering geological map and general layout of Memve’ele’s dam highlight the important role plays by engineers. The main dam that is observed actually in the Memve’ele dam site is composed from left to right of left connecting dam section, flushing sluice, main spillway section, riverbed dam section, auxiliary spillway section and right bank dam section.

This chapter mainly focuses on engineering geology for dam construction from the Memve’ele region in Cameroon. Here, it deals with geotechnical and geological proprieties of both construction and dam foundation materials. This study is done at the aim to ensure that these materials need to be improved and how they have been used during dam construction. Field investigations, borehole information, density and seismic velocity measurements have been used, and results indicate that soil deposits have slightly clay content, mechanically well for dam construction and display a weak thickness layer particularly on the dam site. These conditions suggest that soil materials can be used as construction (cushion, transition layers, etc.) and foundation materials after few amendments. Ntem Formations appear weathered and fractured sometimes, though their mechanical behaviors display a good character for civil applications. However, engineering processes have been used to improve it by GIN (Grouting Intensity Number) methods. These formations have been used as construction (rip rap crushing aggregate, etc.) and dam foundation materials. Thus, this chapter contributes to highlight materials and dam foundation conditions which are crucial criteria encountered in the dam with emphasis on both theoretical study and practical application during dam construction.

New LA–ICP–MS U–Pb zircon ages from the Nyong Complex of southwestern Cameroon—a part of the West Central African Fold Belt—trace Late Mesoarchean (∼2,850 Ma), Middle Palaeoproterozoic (∼2,080 Ma), and Neoproterozoic (∼605 Ma) events: Two meta‐syenites and the protolith of an amphibolite are Late Mesoarchean; two meta‐granodiorites are Middle Palaeoproterozoic; the amphibolite may have recrystallized in the Middle Palaeoproterozoic; all rocks are overprinted by the Neoproterozoic event. Integration with published data shows that our amphibolite sample has one of the oldest amphibolite‐protolith ages (∼2,810 Ma) reported so far. It shares the Middle Palaeoproterozoic metamorphism/recrystallization with other, previously dated amphibolites. An earlier reported metamorphic zircon age (∼2,090 Ma) from eclogite is somewhat older than the regional Middle Palaeoproterozoic metamorphism/recrystallization ages (∼2,040 Ma) reported from amphibolites. Thus, the eclogite–amphibolite ages may date an exhumation process. A published charnockite age, interpreted as an Early Mesoarchean crystallization age, is older than the Late Mesoarchean meta‐syenite and amphibolite‐protolith dates; its Middle Palaeoproterozoic metamorphism/recrystallization age, however, is identical with the meta‐granodiorites and amphibolites. The Neoproterozoic ages demonstrate the regional overprint of the Nyong Complex during this period. Integration of the Nyong Complex ages with published ones from the entire West Central African Fold Belt, and comparison with those from West Africa and South America, support their common origin from the Palaeoproterozoic collision between the Archean Congo and São Francisco shields., (a) South America–Africa fit, showing shields of western Gondwana (modified after Neves et al., 2006). (b) Geological sketch of Cameroon, showing its Archean, Paleo‐, and Neoproterozoic basement and the Cretaceous‐Cenozoic volcano‐sedimentary cover (modified after Castaing et al., 1994; Ngako, Affaton, Nnangue, & Njanko, 2003; Owona, Mvondo Ondoa & Ekodeck, 2013). (c) Geology of the Nyong Complex and related U‐Pb zircon ages. Abbreviations: NEFB – North Equatorial Fold belt, OC – Oubanguide Complex. Published studies: 1 – Toteu et al. (1994), 2 – Lerouge et al. (2006), 3 – Loose & Schenk (2018), 4 – Nkoumbou et al. (2015), and * – present study. (d) Normalized age probability diagrams summarizing the new and published U‐Th‐Pb ages from the West Central African fold belt (including the Nyong Complex), and those from the South American and West African equivalents. Abbreviations: CS – Congo Shield, KS – Kalahari Shield, SFS – São Francisco Shield, TS – Tanzania Shield, WAS – West African Shield. image, German Academic Exchange Service http://dx.doi.org/10.13039/501100001655

South of Bafia (Cameroon), the Pan-African Yoro-Yangben massif is emplaced in the Adamawa-Yade block, an archaean-paleoprotrozoic micro-continent that detached from the Congo craton during the early Neoproterozoic. This emplacement within a micro-continent raises the problematic of its (i) origin either by the melting of a subducted slab and the mantle wedge, or by the melting of the base of a thick crust or both, and (ii) bearing on the evolution of the Pan-African orogeny in Cameroon. Granodiorites, quartz monzonites, quartz diorites and adamellites occur as massive bodies crosscut by dykes of gabbros and granites. The texture varies progressively from granular bands at the core of the massif to foliated texture towards the border. Mineralogical composition is constant in all the rock types (Am+Bt+Pl+Kfs+Qtz+Op+Sph+Zrn+Ap), except the adamellites which are amphibole-free. Chemically, these potassic rocks are either magnesian and metaluminous, or ferroan and peraluminous. Quartz diorites, granodiorites and granites are High-K calc-alkaline whereas quartz monzonites, adamellites and gabbros are shoshonitic. Most incompatible elements (e.g. Nb, Zr) show an erratic variation with increasing silica contents. Granites rare earth elements (REE) patterns are highly fractionated with a positive Eu anomaly (Eu/Eu* = 2.50–2.04) compared to less fractionated REE patterns of adamellites, quartz monzonites, and granodiorites. The negative anomalies in U, Nb, Ta and Ti shown by gabbros, quartz diorites, quartz monzonites and granodiorites spider diagrams as Th, K, Pb, Zr and Hf positive anomalies for the adamellites and granites patterns are consistent with magmas derived from a subduction setting. The low 87Sr/86Sr(600) initial ratio (0.697–0.706) and eNdi values (−0.82706- 1.03707) of the rocks plot in the mantle array. However, a wide variation of the 87Sr/86Sr ratio values with constant eNdi suggests an enrichment in radiogenic 87Sr likely from an old crust displaying high Rb/Sr ratio. The variations of the La/Yb, Y/Nb and Zr/Nb ratios preclude the fractional crystallization process. Moreover, these characteristics, combined with the erratic (Zr, Nb) suggest particular magmatic sources and complex fusion processes to the Yoro-Yangben heterogeneous granitoids. The lower range of Ba/Nb values (130–135) and the occurrence of shoshonitic magmas likely point to the melting of an oceanic slab; while the higher range (225–230) indicates a blend of melts from oceanic slab and the associated sediments. Granite compositions are similar to melting liquids of metagreywackes. La/Sm and Sm/Yb ratios in gabbros, quartz monzonites and quartz diorite indicate an origin by a batch melting of phlogopite-amphibole-garnet lherzolite, whereas granodiorites and adamellites parent magmas may have originated from a batch melting of a metasomatized spinel lherzolite. Whole rock Sm-Nd and Rb-Sr results yield a unique age of 600 Ma, assigned to the collision time between the West-African and the Congo cratons. Thus, the Yoro-Yangben intrusion is part of the numerous Pan-African granitoids in Cameroon, South of Chad and East of Nigeria.

Shuttle Radar Topography Mission (SRTM) - 3 data for Digital Elevation Model through morphometric analyses of the Sanaga, Nyong and Kelle watersheds and landform were correlated with field survey in a Geographical Information System (GIS) model in the Edea-Eseka Region in SW Cameroon; erected on Paleo-to Neoproterozoic crystallophyllian rock types, Cretaceous to Recent sedimentary formations later affected by reactivated and neotectonic faults. This study that aimed to evaluate the lithology, tectonic and climate interactions on operating processes and landform characteristics based on the morphometric parameters of watersheds. Parameters vary from one watershed to another establishing one to three controls. The density drainage (0.05–0.29), the constant of channel maintenance (3.5–19.47) and the drainage pattern; outlines the lithological, the tectonic and the climate controls of the morphology. The Bifurcation ratio (2–5.25), the mean bifurcation ratio (3.67–4.09), the relative relief ratio (0.21–0.27), the watershed slope (5.75–9.35) and the watershed deviation (105–507); highlights the lithostructural controls of the morphology; whilst the wandering ratio (1.54–2.12) individualises both, the structural and climate controls. The stream number (370–2473) and the stream length ratio (0.57–1.91), the elongation ratio (0.47–0.55), the circularity ratio (0.25–0.29), fitness ratio (0.56–0.63), dissection index (0.91–0.99), the concavity index (−0.1-0.56), the hypsometric integral (0.45–0.49) and the stepped longitudinal length profiles, establishes the dominant tectonic controls of the morphology; while the rho coefficient (0.34–0.43) and drainage texture (1.91–4.75) displays the lithological control of the morphology and; the drainage intensity (1.76–7.62) and the length overland flow (1.75–9.74) typified the climate control of the morphology. The Edea-Eseka Region uplift rejuvenates old watershed each time they evolve to equilibrium because of lithological variations, neotectonics, differential erosion and climate variations; overriding its morphology. This geodynamic and climatic control of morphometric processes in the SW Cameroon can be extended to the whole of Central Africa and in Equatorial Regions that display similar evolutions.

The Nyong Complex and the Yaounde Group represent two crustal sequences of West Gondwana in Cameroon. We use U-Pb zircon geochronology on meta-sedimentary rocks to analyze their depositional age, provenance, and age of the high-grade metamorphic overprint. Due to the undoubtedly Precambrian age of these rocks, we also pursue questions regarding the veiling of the provenance signal by subsequent overprints, the diversity of the sources, and the role of crustal reworking in such an old setting. Although both the Nyong and the Yaounde meta-sedimentary rocks were strongly affected by the Pan-African orogeny, Discordia analysis and the evaluation of remnant concordant zircons allow addressing these classic provenance questions with the LA-ICP-MS U-Pb zircon technique. We show that the Nyong Complex meta-sedimentary rocks likely have a 2.2 Ga depositional age (∼Rhyacian, early-middle Paleoproterozoic) and were locally sourced from the Meso-Neoarchean Congo Shield (∼2.8 Ga); they were overprinted during the Paleoproterozoic Eburnean orogeny (∼2.2–2.0 Ga). The Yaounde Group meta-sedimentary rocks likely have a

A barium bearing phlogopite (celsian) has been found for the first time within the charnockitic and tonalitic suites that compose Archean mineral belt in Cameroon. Electron microprobe analyses of these phlogopites are reported and contain moderate contents of BaO (0.42–1.26 wt. %) and up to 5.95 wt. % TiO2. Micas are Mg-rich and their compositions indicate phlogopites rich-meroxenes. Phlogopites from Memve'ele are characterized by a nearly horizontal trend of increasing total aluminium (2.494–2.931 a.p.f.u.) and relatively constant Fe/(Fe + Mg) suggesting contributions of aluminous supracrustal material to the magmas by anatexis or assimilation. Compositions of the barium titanium bearing phlogopite vary systematically according to rock types. It seems that the substitution scheme include Ba + Al + VI (Mg, Fe)2+ + 2 IVSi = K + Si + VITi + 2IVAl was dominant in the Memve'ele area thus, this scheme has made easy incorporation of Ba into phlogopite structure. The binary diagram of aluminium vs. titanium shows that phlogopites from the Memve'ele area have been formed by the same metasomatic mechanism as phlogopites from Canary Island xenoliths and Mezitler andesites but Ba enrichment of phlogopites from the Memve'ele area implies an early Ba-metasomatism contrary to those from Mezitler. The estimated temperature of the studied phlogopites indicated mainly two groups: (1) temperature range from 662 to 688 °C (average 676 °C) for phlogopite grains with High Mg# in the trondhjemite sample and (2) temperatures with interval limits from 757 to 800 °C (average 777.07 °C) for remnant phlogopites; reflecting primary and late crystallization respectively from slightly to highly oxidized magma (−17.30 to −13.87 Kbars). The geothermal gradient with average temperatures are 35.57–53.360 °C/Km and 30.95–46.42 °C/Km corresponding to 14.56–21.84 Km and 14.56–30.58 Km depth of below crust respectively. The crystallizing melt is enriched in Ba emanated from sea water at medium and high temperatures, low and high fugacity and high water fugacity generated Ba-bearing phlogopite grains both in trondhjemite samples (S13W6) and remaining granitoids during partial melting of the mantle. The phlogopite grains with low Mg# in S13W6 sample have more Ba than all remain phlogopites. The presence of high Ba contents in these phlogopite grains can be explained by (1) the admixture of residual and new Ba rich melts or (2) the presence of both low Mg and Mn contents in the octahedral site that generate a large interlayer site which accommodate more Ba or (3) both mechanisms are displayed to crystallize these phlogopite grains. Thus Ba rich phlogopites occur in the fresh granitoids depending only on early magmatic processes or hydrothermal alteration at high temperature. Contents of titanium are only controlled by temperature during phlogopite crystallizations. Moreover, igneous phlogopites are used as metallogenic indicator. The study is useful to the exploration efforts for barium ore and shows that the Ba-rich parent granitoids can produce Ba-rich soils which can be potential economic interest for Cameroon.

The Mesoarchean crust of the plutonic belt of the Memve'ele area lies in the southwestern part of the Ntem Complex (NTC), Cameroon. Emplacement of these rocks resulted from both gravity and tectonic driven vertical flow perpendicular to the direction of shortening at the time of partial melting and magmatic accretion. Such deformation patterns suggest the occurrence of a long-lived hot orogen and may explain a nearly isobaric retrograde pressure-temperature (P-T) path recorded within high-T, low- to medium-P metamorphic rocks. However, in the Memve'ele shear zone (MSZ), a metamorphic gradient runs from granulite to green-schist facies. Structural analysis reveals four continuous ductile deformations. The first stage is characterized by the emplacement of dome and basin structures, the second stage is marked by coeval diapiric movements and a transpressional shear zone, the third stage is marked by both transpressional and lateral flow regimes, and the last stage is marked by horizontal constrictional strain. These features indicate that the Mesoarchean crust is affected by a long-lived horizontal shortening deformation (D1-D3) coeval with vertical movements in which concentric cleavages occur around domes. Thus, the studied area can be considered as exemplifying an “Early Earth” style tectonics. The structural patterns in the MSZ contain zone of high-strain rocks belonging to the deep and shallow/mid crusts that have recorded transpressional tectonics. The compressional strain regime in which results coeval steep to shallow dipping structural features and “dome and basin” geometries associated to MSZ activities contributed to maintaining a stable crustal thickness in the Memve'ele area during Mesoarchean orogeny.

During the night of November 18 to 19, 2016, many stormy cells are not very mobile organized on the east of the southern plateau of Cameroon and dumped up to 260 mm of rain in 4 hours. Occurring on a relatively saturated soil, these rains caused strong floods of Kadey and Doumé. The floods were particularly damaging in the city of Batouri, where a subdivision was submerged by the Boumbé (tributary of the Sangha) with water heights in the houses reaching 1.75 m, despite the presence of a dam allowing clipping floods upstream of the basin. In this article, we present the results of the analysis of the postevent survey generated on this event with flow rates estimated on 15 sections of ungauged subbasins. These flows are then compared with those obtained from other recent postevent survey and those estimated by various regional estimations. The inventory of heavy rains around Batouri during the period 1970-2016 has led to the revision of current development standards in the region, which seem to underestimate rainfall and infrequent flows.

The Edea-Eseka region (EER), a portion of West African Margin located in SW Cameroon between 3°30′—4°00′ N and 10°00′—10°55′ E and submitted to equatorial climate since early Miocene is used here as a proxy for climatic conditions. Geomorphological analysis based on morphometric parameters computed from DEM (30 m) combined with geological maps and field observations were used to constrain geomorphic evolution and landscape adjustment to tectonic processes in this humid zone. Three types of geomorphic indices reflecting specially patterns of differential uplift, those efficient in detecting tilting, and those revealing interactions between erosion and tectonics. - The obtained results show that lithological boundaries and base level controls on landscape are very limited. Tectonic processes, peculiarly uplift induced by faults or tilting at local scale and by mantle dynamics at large scale coupled with climate condition, represent the main factors that drove the geomorphic evolution of this area discriminating three main morphotectonic provinces different by their geomorphic characteristics, uplift and degree of incision. There are, from West to East: (1) the coastal province (CP), deeply incised and built on Douala-Kribi/Campo basin ( - Several geomorphic indices used to evaluate tectonic activities and their average the index of relative active tectonics (IAT) show that tectonic activity differs from one province to another and within each province. Generally, it increases from coast (coastal province) to hinterland (UP). EER are represented by classes 2 and 3 of IAT indicating moderate to high active tectonics. Class 1 revealing the highest tectonic activity, occurs exclusively in the UP. Class 2 corresponding to high tectonic activity happens largely in the south of the IP along the Nyong Fault and the UP where relief are particularly high. Class 3 indicates the moderate relative tectonic in the IP. Class 4 mainly takes place in tectonically low to inactive Douala-Kribi/Campo basin, except along the South part of Sanaga Fault. The development and the evolution of Edea-Eseka region landscape is then acted by a dominant high-uplift rate in SW Cameroon. This tectonic activity apparently incompatible with the passive margin context is however realistic in this area, on one hand justified by the numerous reactivations over time of faults crossing the region that generate earthquakes in some places and on the other hand, by the activity of the Cameroon Volcanic Line, and particularly that of the Mount Cameroon located near the study area. It appears at the end that, due to mantle dynamics, the EER has been rejuvenated under the tectonics and climate forcings, returning to a transient stage of its geomorphic evolution.

V. Ngako and E. Njonfang addressed in their comment an interesting and debated issue about the collision geodynamics of the Pan-African Central African Orogenic Belt (CAOB) in Cameroon. However, the reason for this comment is still not clear to us since it mainly deals with issues far away from the scope of our study, namely, the pre-collisional set up of the belt. The comment raises two main points – the reworking process during plate collision and the Pan-African strain pattern – not discussed in our paper for the simple reason that it was not our goal and because our data set does not even allow such discussion. Having said that, the comment gives us the opportunity to clarify our view on the nature of the Adamawa-Yade domain (Central Cameroon) and the early evolution of the CAOB. We will successively discuss two other points raised in the comment: (1) our Fig. 12 depicting a possible pre-collisional configuration at the northern and southern margin of the Congo craton in the Early Neoproterozoic, and (2) the nature and extent of the Adamawa-Yade domain.

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New field observations, ages and geochemical data are presented for the Adamawa-Yade domain, forming part of Central African Orogenic Belt in Cameroon. This belt delineates the northern margin of the Congo craton and is part of the Braziliano/Pan-African orogenic system, which was formed during amalgamation of the West Gondwana continent at the end of the Neoproterozoic. U–Pb dating indicates that the protoliths of some orthogneisses from the Adamawa-Yade domain were emplaced during three distinct periods. Tonalite-Trondhjemite-Granodiorite (TTG) suites in the Makenene area intruded at ca. 3.0–2.5 Ga, and were affected by partial melting at ca. 2.08–2.07 Ga, during the Eburnean orogeny, and by a magmatic event with a metamorphic overprint at 0.64–0.61 Ga, during the Pan-African orogeny. A dioritic orthogneiss from the Maham area, north of Makenene, was emplaced at 2.07 Ga and also reworked at 0.62–0.61 Ga. The youngest granitic orthogneisses, sampled in the vicinity of Bafia, Bep and Ngaa-Bape, yield intrusion ages of 0.64–0.63 Ga. Some of these Neoproterozoic plutonic rocks show shoshonitic affinity and reveal eNd (630 Ma) values ranging from −1.2 to −6.9 (1.7 > T DM > 1.1 Ga), and 87 Sr/ 86 Sr initial ratios of 0.706 and 0.704, providing evidence for crustal reworking during the Pan-African collision. The isotopic geochemical characteristics provide evidence that potassic magmas result from the interaction between the Archaean TTG continental crust and magmas derived from a mantle enriched in silica and incompatible elements during subduction underneath a continental margin. The Bafia group appears as a complex geological entity comprised of an Archaean/Palaeoproterozoic basement and its Neoproterozoic sedimentary cover, both deformed and recrystallized at ca. 0.61 Ga. The crustal evolution of the Adamawa-Yade domain is very similar to that inferred for the northern margin of the Congo craton (the Ntem complex and Nyong series). This and the sedimentary record suggest that the Adamawa-Yade domain represents an Archaean/Palaeoproterozoic microcontinent, which was detached from the northern margin of the Congo craton in the early Neoproterozoic, but became re-accreted together with the Mayo Kebbi (magmatic) arc during the Pan-African orogeny.

This work presents an interpretation of gravity data derived from the Earth Gravitational Model EGM2008 in the Center north Cameroon and a correlation with previous tectonic geological and mining studies. EGM2008 Model provides high spatial resolution gravitational data integrating land, airborne, maritime gravity data, as well as satellite altimetry data. Significant similarities are underlined through Bouguer anomaly maps deduced from EGM2008 and land gravity data according to shape, orientation, and amplitude of anomalies. Furthermore, the statistical analysis of both datasets gives means of −38.25 and −38.21 mGal as well as standard deviations of 12.30 and 12.42 for EGM2008 and land data, respectively. Regional geological formations are largely interpreted and identified on EGM2008 Bouguer anomaly map. We applied regional/residual separation filtering, upward continuation and horizontal gradient methods to investigate the subsurface structure. Some known geological lineaments are highlighted such as Poli and Koum faults and Tchollire shear zone, while new ones are revealed. This work brings out main regional feature known as Poli-Ounianga-Kebir gravity heavy line trending SW-NE which contains uraniferous and auriferous deposits located along the same direction. This paper presents a coherent correlation between positive gravity anomalies, faults, and mineral indices in the Center-North Cameroon (Central Africa Fold belt), and thus brings new evidences of the efficiency of Earth Gravitational Model EGM2008 for structural investigation and mining exploration.

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.

The foliations, lineations, fold axes trajectories and shear zones kinematics vary from the Archean Ntem and Paleoproterozoic Nyong complexes to Neoproterozoic Oubanguide complex. The S1, S2 and S3 typified foliations are folded in F2, F3 and F4 cartographic folds equivalent to thrust slices while the L1, L2 and L3 lineations are oriented SSE-NNW, west-east and sub-north-south in the above complexes, respectively. Both, the foliations and lineations confirm the transport top-to-the east of the Nyong nappe onto the Congo craton during the Eburnean orogeny under amphibolitic conditions and as the transport top-to-the SSE of the Yaounde nappe onto the Ntem and Nyong complexes during the Pan-African event under granulitic to green schist conditions. The paleostress of fault and shear zones display crustal thinning and horizontal extension oriented east-west, NW-SE and sub-north-south in the Ntem, Nyong and Oubanguide complexes. All these tectonic features, completed by north-south and east-west cross sections, demonstrate litho-chrono-stratigraphical, structural and angular discordances between the three complexes.

Garnet-bearing micaschists and paragneisses of the Yaounde Group in the Pan-African Central African Orogenic Belt in Cameroon underwent a polyphase structural evolution with the deformation stages D1–D2, D3 and D4. The garnet-bearing assemblages crystallized in course of the deformation stage D1–D2 which led to the formation of the regional main foliation S2. In XCa–XMg coordinates one can distinguish several zonation trends in the garnet porphyroblasts. Zonation trends with increasing XMg and variably decreasing XCa signalize a garnet growth during prograde metamorphism. Intermineral microstructures provided criteria for local equilibria and a structurally controlled application of geothermobarometers based on cation exchange and net transfer reactions. The syndeformational P–T path sections calculated from cores and rims of garnets in individual samples partly overlap and align along clockwise P–T trends. The P–T evolution started at ∼450 °C/7 kbar, passed high-pressure conditions at 11–12 kbar at variable temperatures (600–700 °C) and involved a marked decompression toward 6–7 kbar at high temperatures (700–750 °C). Th–U–Pb dating of metamorphic monazite by electron microprobe (EMP-CHIME method) in eight samples revealed a single period of crystallization between 613 ± 33 Ma and 586 ± 15 Ma. The EMP-monazite age populations between 613 ± 33 Ma enclosed in garnet and 605 ± 12 Ma in the matrix apparently bracket the high temperature–intermediate pressure stage at the end of the prograde P–T path. The younger monazites crystallized still at amphibolite-facies conditions during subsequent retrogression. The Pan-African overall clockwise P–T evolution in the Yaounde Group with its syndeformational high pressure stages and marked pressure variations is typical of the parts of orogens which underwent contractional crustal thickening by stacking of nappe units during continental collision and/or during subduction-related accretionary processes.

The Kombe-II area belongs to the southern part of the Cameroonian Panafrican belt. It is made up of different gneisses, amphibolites and quartzites of the Bafia Group. This volcano-sedimentary rock sequence became polyphasely deformed and metamorphosed during the Panafrican orogeny. It was thrust in SSW-ward direction, parallel to the L2 stretching lineation, over the Congo Craton. Zircon morphology and 207Pb/206Pb evaporation ages (2289–2351 Ma) show that the gneissic metasediments contain detritus of Paleoproterozoic plutonic rocks. In addition to existing data, our zircon ages and Nd model ages (generally in the range of 2.4–3.4 Ga) indicate that the sedimentary sequence derived from material which was added to the crust between the Archean and the Mesoproterozoic era. A garnet-amphibole paragneiss, however, has a Nd model age of 1.5 Ga demonstrating the contribution of younger mafic material in the sediment source. Our results strengthen earlier suggestions that NE Brazil and Central Africa followed the same evolution during the Proterozoic.

The deformation history of the Neoproterozoic Central African Orogenic Belt in southern Cameroon is well recorded in the low- to high-grade rocks outcropping in the area around Yaoundé. The fabrics in these rocks are consistent with two main ductile deformation events D1 and D2. D1 predated emplacement of calc-alkaline dioritic bodies and caused the formation of nappes that resulted in high-pressure granulite metamorphism of soft sediments. A strong overprinting of these nappes during D2 symmetric extension, probably associated with large-scale foliation boudinage and (or) gneissic doming and intense magmatic underplating, gave rise to regional flat-lying fabrics. The latter were further buckled by D3 and D4 folding phases defining a vertical constriction occurring with a major east–west to NW–SE shortening direction. The corresponding F3 and F4 folds trend north–south to NE–SW and east–west to NW–SE, respectively, and represent the main regional strain patterns. Based on the east–west to NW–SE maximum shortening orientation indicated by F3 folds, it is proposed that the nappe-stacking phase D1 occurred in the same direction. The deformation history in the area can thus be described as corresponding principally to alternating east–west to NW–SE contractions and north–south to NE–SW orogenic-parallel extensions. At the regional scale, this could be due to the Transaharan east–west collisional system.

The ductile deformation in the paragneissic bed of Mvog-Betsi in the north-eastern part of Yaounde (Cameroon) appears to be intensive and may be traduced by a high shear rate (more than 10%). Some marker subjects that may quantify this strain are observed. Those are elliptical quartz and feldspar, and folds. The study of elliptical markers shows their preferential orientation. The initial rate Ri of the markers before the strain approaches 3.76, and the harmonic value of Rf is between 1.51 and 1.71. Main orientation Of of strain’s ellipse from the direction of stretching in actual position is situated between -10 and -19. The strain’s rate RS is comprised between 1.1 and 1.7. The orientation OS of the strain’s ellipse is situated between N10E and N20E. The rate of shortening varies between 20% and 75%.

Increased cost associated with the used of high quality materials have led to the need for local soils to be used in civil engineering works. In this paper, geo-chemical approaches coupled with conventional geotechnical techniques has been used to investigate vertical and lateral peculiar engineering index properties (EIP) of micaschist derived soils from Mfou, Central-Cameroon for their uses in road construction. The X-ray diffraction (XRD) analysis conducted on the soils indicated the absence of swelling clays. The main mineral phases were quartz, kaolinite, goethite, magnetite and chlorite. Geo-chemical results show that the investigated soils are “true laterites” made up of 41 wt.% of Fe2O3, 35 wt.% of SiO2, 21 wt.% of Al2O3, 1.17 wt.% of K2O and 0.05 wt.% of CaO. The results of geotechnical tests suggest that the upper clayey layer (UCL) and bottom mottled clayey layer (MCL) of the weathering profiles are poorly graded soils with EIP (fines particles (FP) of 61 and 63%, plasticity index (PI) of 30 and 31%, Californian Bearing Ratio (CBR) at 95% of 21 and 19%), which do not allow their use as raw materials in road construction whereas, intermediate nodular layer (INL) are well graded soils having EIP (FP of 26%, PI of 26% and CBR of 39%) that meet the specification required for sub-base materials for light traffic roads. The relatively high sesquioxyde present in these residual soils may act as cementing agent, thereby making the compacted soils relatively brittle. The direct shear test results show that the soils have high bearing capacity (cohesion of 62 Kpa and 27.2° angle of internal friction) making them to be useful in slope stability and shallow foundation design. The comparison of the studied soils with some lateritic soils in Sub-Saharan Africa indicates that i) genesis and climatic conditions are potentials factors that influence EIP of lateritic soils, ii) lateritic soils developed under semi-arid conditions exhibits EIP better than those developed under tropicaland sub-tropical conditions.

The Paleoproterozoic is characterised by a global-scale period of crust formation, extensive mafic to granitic magmatism, crustal reworking and intracrustal partial melting. Since a dramatic strength drop is associated with the presence of melt in crystallising or melting rocks, Paleoproterozoic continental deformation is thought to have been largely accommodated by shearing of high-grade gneisses and syntectonic granitoids. The Paleoproterozoic Nyong complex, which is made up of volumetrically dominant granitoids, metapelites and granitic gneisses, quartzites and banded iron formations; has been affected by the Eburnean/Transamazonian polyphase ductile and brittle deformation responsible of S1/2 foliation and S2 schistosity, L2 stretching and mineral lineations, F3 meso- and large-scale folds, S2/C3 structures and faults. Its shear zone strain anisotropies represent a natural laboratory to study the effect of crystal plastic deformation of felsic minerals and amphibole as predicted by numerical experiments and tectonic models. This paper describes the geometry of the deformation and focus on microstructural evidence of dynamic recrystallization features that were active under granulite conditions (>800 °C, >8.5 Kbar). These thermal conditions can be extended in similar Proterozoic worldwide shear zones.