Earth science

In this paper, we show with examples that cratons involved in intercontinental collisions in a lower plate position are often affected by orogenic events, leading to the transformation of their margins. In some cases, craton interiors can also be shaped by intense collisional processes, leading to the generation of intracratonic orogenic belts. We propose to call these events "metacratonization" and the resulting lithospheric tract "metacraton". Metacratons can appear similar to typical orogenic belts (i.e. active margin transformed by collisional processes) but are actually sharply different. Their main distinctive characteristics (not all are present in each metacraton) are: (1) absence of pre-collisional events; (2) absence of lithospheric thickening, high-pressure metamorphism being generated by subduction, leading to high gradient in strain and metamorphic intensity; (3) preservation of allochthonous pre-collisional oceanic terranes; (4) abundant postcollisional magmatism associated with shear zones but not with lithospheric thickening; (5) presence of high-temperature-low-pressure metamorphism associated with post-collisional magmatism; (6) intracontinental orogenic belts unrelated to subduction and oceanic basin closures. Reactivation of the rigid but fractured metacratonic lithosphere will cause doming, asthenospheric volcanism emplacement, and mineralizations due to repetitive mineral enrichments. This paper provides several geological cases exemplifying these different metacratonic features in Scandinavia, Sahara, Central Africa and elsewhere. A special focus is given to the Saharan Metacraton because it is where the term "metacraton" originated and it is a vastly expanded tract of continental crust (5,000,000 km 2 ). Metacratonization is a common process in the Earth's history. Considering the metacraton concept in geological studies is crucial for understanding the behavior of cratons and their partial destruction.

The Fodjomekwet-Fotouni shear zone (FFSZ) belongs to the western part of the Central Cameroon Shear
Zone (CCSZ). From the border to the core, the FFSZ is made of: (i) protomylonites, (ii) garnet-sillimanite
mylonites and (iii) garnet-sillimanite ultramylonites. Structural data indicate (1) a N40E mylonitic foliation
trend (strongly dipping toward NE or SW) with strike varying between N34E–78NW at Fotouni
and N52E–61SE at Fodjomekwet; (2) a stretching lineation (plunging toward NE or SW) with best line
varying between 224/4 at Fotouni and 232/10 at Fodjomekwet; (3) sinistral (N–S) and dextral (NE–SW)
kinematic markers, respectively correlated to the D2 and D3 of the CCSZ deformation phases. The presence
of relic sinistral shear markers wrapped by dominant dextral shear markers rendered difficult the
understanding of the FFSZ evolution. Anisotropy of magnetic susceptibility in the FFSZ shows that magnetic
fabrics are characterized by dominant NE–SW and locally N–S to NNE–SSW trending foliation and
lineation. These directions show that mylonitisation was initiated in the N–S direction during the sinistral
syn-D2 shearing, evolved and reoriented toward NNE–SSW and NE–SW between 613 and 590 Ma. The
sinistral shearing event was thereafter followed by a NE–SW trend dextral syn-D3 reactivation of the
N50E fault between 580 and 552 Ma. The sinistral phase seems to have favoured the evolution of fractures
in pull-apart structures. The pull-apart opening of fracture enables the upwelling of magma and the
emplacement of the Fomopéa and the Bandja plutons (FBP). This synkinematic emplacement is witnessed
by the elongated shape and the NE–SW trending direction of these massifs. Kinematic emplacement of
FBP controlled by active shear zone is comparable to syntectonic plutonism in eastern Nigeria and NE
Brazil.

The biotite granite of Dschang composing of quartz, feldspar and biotite, is a haplogranite I-type calc-alkaline granitoid. It is weakly peraluminous with a ferroan affinity and exhibits fractionated feature. This granite was generated at the minimum temperature and pressure of crystallization of 650°C/4 Kb. Its emplacement is syn-central Cameroon shear zone like most of post-collisional granitoids of the Pan-African fold belt in central Africa, and it displays N-S to NNE-SSW magmatic foliation dipping 30° to 60° towards W or WNW. The evolution of the major elements shows a generalized decrease correlation trends look firstly like fractional crystallization. The depleted Sr content related to decreasing Al 2 O 3 and CaO concentrations, indicate the role played by plagioclase during differentiation. The trace elements normalized to the primitive mantle, show negative anomalies out of Nb, Ta, Sr and Ti, and positive anomalies out of Ba, Rb, Th, comparable with those of the continental crust. The isotopic data Sr-Nd are rather homogeneous suggesting a single source for the biotite granite of Dschang. Ɛ Nd600Ma (-16 to-18) and T DM (1.9 to 2.1 Ga) confirm the formation of the magma of the biotite granite of Dschang starting from an old Paleoproterozoic crust by partial melting around 600 Ma. This melting which seems to have spread in the area and at several levels of the continental lithosphere, hence magmas were mixing throughout their evolution, considering the diversity of the granites and their sources, is certainly caused by great movements along CCSZ, at the post-collisional period of Pan-African orogenesis in central Africa.

Major and trace element data were used to constrain the nature and origin of the Bitkine gabbro-diorite magma.The gabbro-diorites of Bitkine within the Guera Massif, and associated microgranular enclaves consist of plagioclase, k-feldspar, clinopyroxene, amphibole, biotite and quartz. Gabbro-diorites and enclaves are basic to intermediate rocks. They are high-K magnesian calc-alkaline with shoshonite affinity. ΣREE range from 132 to 436 ppm in gabbro-diorites, while they are from 134 to 207 ppm in enclaves. LREE are weakly enriched compared to HREE (La/Yb)N = (12.23 -41.40) and (6.20-31.86) respectively in gabbro-diorites and enclaves. These rocks show a weak negative anomaly in europium (Eu/Eu* = 0.78-1.07). They are rich in Ba and Sr, and show negative anomalies in Nb, Ta and Ti. The Nb/Ta, Rb/Cs and Ba/Nb ratios of the Bitkine gabbro-diorites and their enclaves indicate that they are derived from mantle magma modified by subducted fluids. This magma during its evolution by fracti...

Major and trace element geochemistry have been used to unravel the tectonic setting, source rock composition, and depositional environment of sedimentary rocks in the Mamfe formation. Field studies reveal both sub tabular and tabular outcrops indicating a post tectonic sedimentary activity for the subtabualar outcrops. Major element geochemistry reveals a moderate to high proportion (50-75wt %) of silica for the analyzed samples. New discriminant diagrams constructed for usage of adjusted major elements shows samples plotting on collision, arc and rift. Another discriminant plot for adjusted major element combined with trace elements shows samples plotting on active and passive tectonic setting.  Ratios of highly immobile trace elements such as Cr/Th, Th/Sc, Th/Co, and La/Sc conclude a felsic source rock for the studied rocks of the Mamfe formation. Trace elements ratios for redox conditions and marine-continental discrimination such as Ni/Co, U/Th, V/Cr, Th/U, and Y/Ho show that th...

The Fotouni volcanic rocks outcrop within mylonitic corridor, in the southern domain of the continental part of Cameroon Line (CL). The NE-SW shape display by these volcanic rocks within the mylonitic corridor is an uncommon case along the CL. Field and petrographic data and spaces image analysis were performed in order to understand the NE-SW shape display by these rocks. Geochemical data display two distinct volcanic compositional groups: alkaline lavas and transitional lavas. Alkaline series ranges in composition from basanite, basalt to hawaiite and transitional series range from basalt, trachy-basalt to basaltic trachy-andesite. Field investigations show that the Fotouni, Fangam, Song and Mbeng basalts outcrops as NE-SW trending prismatic dykes which displaying well differentiated vertical tetragonal, pentagonal and hexagonal prisms within the Fotouni-Kekem shear zone (FFSZ). The overall NE-SW orientation of hills, where these prisms outcrop suggests the tectonic control on the...

The Nlonako anorogenic complex (NAC) is located in the south western part of the Cameroon Line and is superposed on the N50E section of the central Cameroon shear zone. It is suggested to be a ring complex of 10 km diameter which was emplaced as sill intrusive body during the Tertiary. In order to do characterize the Nlonako complex shape and characterize the tectonic history in the study area and surrounding, spatial technology (Landsat 8 ETM+ and SRTM images) were used for geological mapping and structural reconstruction based on lineament analysis. Data extracted from Landsat 8 ETM and SRTM images show a sub-circular shape for the NAC and the superposition of field and petrographic data from our previous research works confirm the fact that the NAC is a ring or annular complex slightly elongated NNE-SSW, thus it is known as the Nlonako ring complex (NRC). Map of lineament synthesis and the SRTM image of the study area display NE-SW, NW-SE and N-S trend structures. (1) The dominan...

The present study focuses on the use of feldspars from Batie granites (West-Cameroon) as a fluxing agent in ceramic applications, in order to reduce the energy cost of brick manufacture. Three alluvial clays were collected in the field using an auger and the feldspar sample was collected by hammering. Mineralogical, physical and geochemical analysis of alluvial clays samples were carried out, as well as the microscopy analysis of feldspar. The specimen of fired bricks was formulated with different proportions of feldspar (0%, 10%, 15%, 20%, and 25%) and calcined respectively at 750 °C, 850 °C, 950 °C and 1050 °C in an electric furnace. The physical analysis of the clay material showed a well graded granulometry composed of 3% gravel, 10% coarse sand, 23% fine sand, 13% silt and 51% clay. Thin section microscopic analysis revealed essentially perthites. The mineralogical analysis obtained by XRD on total powder shows that the alluvial clays are composed essentially of: 55.8% of total...

Widikum and its surroundings (North-West Cameroon) are covered with basalts, granites and gneisses. Construction companies use these rocks extensively and indiscriminately for structural loading, pavements, wall cladding as cobblestone and masonry stones. The suitability of these rocks and their petrographic (outcrops mode, structure, color, mineralogical composition and crystals size), physical and geomechanical (specific density, bulk density, Los Angeles abrasion test, and Aggregates crushing test) properties evaluation becomes important for their aforementioned applications. The aim of this study is to characterize on the petrographic and geomechanical level, basalts, granites and gneisses of the locality of Widikum and its surroundings for their use as construction materials. Concerning the petrographical point, granites and gneisses are rich in quartz, feldspar, plagioclase, biotite, amphibole and accessory minerals like opaque minerals and zircon. On the other hand, basalts are ferro-magnesians rich in olivine, pyroxene and opaque minerals. Plagioclase is also a main constituent mineral of this geological formation. On the physical and geomechanical properties, despite their extension on the field, granites have satisfactory density; but, they are least resistant according to the Los Angeles abrasion values. However, basalts are one of the geological formations which are the least extended on the field. They are most dense with the satisfactory to excellent Los Angeles abrasion values. Concerning the gneissic formation, its density and Los Angeles abrasion values are satisfactory. Generally, the aggregates crushing values of studied geological formations attest that they are satisfactory to excellent apart from those of coarse grainy granites. In view of the foregoing, basalts have the best geomechanical qualities and could be used as constituent of construction materials.

Among the greatest challenges of Sub-Saharan Africa is the need for more crop production for supplying the increasing demand of its growing population. For this purpose, knowledge on soil resources and their agricultural potentials is important for defining proper and appropriate land use and management. We thus investigated on the status of soil fertility in Tombel area, in order to produce such knowledge through understanding and monitoring the impact of physicochemical properties of soil. Diverse analyses performed on various datasets demonstrated the direct impact of physicochemical properties of soil and derived soil fertility parameters on major constraints for plant growth and optimal crop production such as water retention capacity, roots development, soils aeration, nutrients availability, nutrients abundance and cations balance. Based on physicochemical soil properties, fertility parameters and Soil Quality Index (SQI), four soil fertility classes were identified in the area: (i) very good fertility soils (66 km 2) that corresponds to Dystric Vitric Andosols (Melanic) above 500m asl; (ii) good fertility soils (506 km 2), grouping Dystric Vitric Andosols (Melanic) below 500m asl and Leptic Fragic Umbrisols; (iii) fairly good fertile soils (787 km 2) including Dystric Fragic Cambisols (Humic), Rhodic Acrisols (Cutanic Humic), Fragic Umbrisols (Arenic), and Mollic Ferralsols (Eutric Humic); (iv) poorly fertile soils (375 km 2) including Umbric Andosols (Fragic) and Umbric Pisoplinthic Plinthosols (Haplic Dystric). The principal indicators controlling soil quality in the Tombel area as derived from ANOVA and PCA analyses, are: Ca, Mg, pH water, organic matter (OM), available P, total Nitrogen and CEC. Four of the seven indicators (Ca, pH, OM, P) were also identified as important indicators for assessing the fertility status of the different soils groups in the Tombel area.

Mineralogical transformations and microstructures during the firing alluvial clays from Monoun plain were studied. The firing of clays was carried out in the temperature range from 800 to 1150?C. Minerals transformation was investigated by X-ray diffraction, polarize stereomicroscopy and scanning electron microscopy (SEM). In the raw materials, typical assemblages with quartz, kaolinite, goethite, anatase, hematite, gibbsite and feldspar were observed. Many neoformed mineral phases were identified with the reaction products including mullite, cristobalite, spinel, amorphous phase which occurred in the high temperature (1050-1150?C) in the fired bricks. The quartz phenocrist with some microlites oxides embedded in few mesostasis glass have been illustrated at 950?C by stereomicroscopy analysis. At 1150?C, the vitreous matrix has embedded phenocrist of quartz and other relic minerals. The best temperature for fired alluvial clay brick was discovered between 1050-1150?C.

The present study focuses on the use of feldspars from Batie granites (West-Cameroon) as a fluxing agent in ceramic applications, in order to reduce the energy cost of brick manufacture. Three alluvial clays were collected in the field using an auger and the feldspar sample was collected by hammering. Mineralogical, physical and geochemical analysis of alluvial clays samples were carried out, as well as the microscopy analysis of feldspar. The specimen of fired bricks was formulated with different proportions of feldspar (0%, 10%, 15%, 20%, and 25%) and calcined respectively at 750 °C, 850 °C, 950 °C and 1050 °C in an electric furnace. The physical analysis of the clay material showed a well graded granulometry composed of 3% gravel, 10% coarse sand, 23% fine sand, 13% silt and 51% clay. Thin section microscopic analysis revealed essentially perthites. The mineralogical analysis obtained by XRD on total powder shows that the alluvial clays are composed essentially of: 55.8% of total...

This work concerns the mineralogical, physico-chemical characterization and ceramic properties of the Babouantou clay materials (lower area of the Western flank of the Bana volcano-plutonic complex). Four samples of clayey materials were collected from wells in Nguieu and Batchieu localities precisely from the illuvial and elluvial horizons (BE1, BE2, BE3 and BE4). Mineralogical analysis showed that they are made of relictual minerals (quartz and feldspar), clays mineral (kaolinite), weathering minerals (illite), hydroxides (gibbsite) and oxyhydroxydes (goethite). The chemistry shows a silico-aluminous character with moderate iron (Fe 2 O 3) content and small quantities of alkali (Na 2 O, K 2 O) and alkaline earth metals (CaO). It is poor in organic matter (< 1%). The physical parameters display a continuous and wide spread granulometry with variable plasticity (5-13). The ceramic tests conducted on fired bricks at 900°, 1000°, 1100°C respectively, presented some standard physico...

The present study focuses on the use of feldspars from Batie granites (West-Cameroon) as a fluxing agent in ceramic applications, in order to reduce the energy cost of brick manufacture. Three alluvial clays were collected in the field using an auger and the feldspar sample was collected by hammering. Mineralogical, physical and geochemical analysis of alluvial clays samples were carried out, as well as the microscopy analysis of feldspar. The specimen of fired bricks was formulated with different proportions of feldspar (0%, 10%, 15%, 20%, and 25%) and calcined respectively at 750 °C, 850 °C, 950 °C and 1050 °C in an electric furnace. The physical analysis of the clay material showed a well graded granulometry composed of 3% gravel, 10% coarse sand, 23% fine sand, 13% silt and 51% clay. Thin section microscopic analysis revealed essentially perthites. The mineralogical analysis obtained by XRD on total powder shows that the alluvial clays are composed essentially of: 55.8% of total...

Widikum and its surroundings (North-West Cameroon) are covered with basalts, granites and gneisses. Construction companies use these rocks extensively and indiscriminately for structural loading, pavements, wall cladding as cobblestone and masonry stones. The suitability of these rocks and their petrographic (outcrops mode, structure, color, mineralogical composition and crystals size), physical and geomechanical (specific density, bulk density, Los Angeles abrasion test, and Aggregates crushing test) properties evaluation becomes important for their aforementioned applications. The aim of this study is to characterize on the petrographic and geomechanical level, basalts, granites and gneisses of the locality of Widikum and its surroundings for their use as construction materials. Concerning the petrographical point, granites and gneisses are rich in quartz, feldspar, plagioclase, biotite, amphibole and accessory minerals like opaque minerals and zircon. On the other hand, basalts are ferro-magnesians rich in olivine, pyroxene and opaque minerals. Plagioclase is also a main constituent mineral of this geological formation. On the physical and geomechanical properties, despite their extension on the field, granites have satisfactory density; but, they are least resistant according to the Los Angeles abrasion values. However, basalts are one of the geological formations which are the least extended on the field. They are most dense with the satisfactory to excellent Los Angeles abrasion values. Concerning the gneissic formation, its density and Los Angeles abrasion values are satisfactory. Generally, the aggregates crushing values of studied geological formations attest that they are satisfactory to excellent apart from those of coarse grainy granites. In view of the foregoing, basalts have the best geomechanical qualities and could be used as constituent of construction materials.

The objective of this paper is to estimate water seepage from the upper reservoir of Azad pumped storage power plant, based on combined geotechnical investigations and geostatistical methods. In order to select the optimum water tightening alternative, such as clay blanket, concrete cover (or concrete lining), geomembrane, asphalt cover, etc., estimation of water seepage from the reservoir is essential. Six exploratory boreholes were drilled at the pumped storage reservoir area and permeability tests (Lugeon tests) were conducted in all of them. Records at the boreholes have been considered as the main source for seepage calculations. Due to expansion of upper reservoir and a few boreholes, distribution of permeability and permeability changes in the reservoir area is not an indicator for reservoir. In this research using geostatistical method (Kriging), Lugeon values have been estimated for walls of reservoir. According to correspondence between estimated permeability distribution and geological conditions, the estimated values are acceptable. In addition, results show that in about 60% of tests, permeability is very high and potential of water seepage is very dangerous. Afterward, seepage was estimated for reservoir by using both analytical (Vedernikov method) and numerical method. Results from both methods are very close together and the average seepage is around 280,000 m 3 /day according to analytical and numerical results. Regarding results and general geological considerations, seepage is concentrated at fault zones. Results show that using appropriate permeability distribution, the estimated values of water seepage are acceptable and reliable. Due to the high amount of water seepage and economical value of water in this region, water tightening is necessary.