Search

Hangloa granitoids form part of the wide range calc-alkaline Pan-African granitic suites within the Adamawa Yade Domain (AYD) in Cameroon. There are several reports on metaluminous granitoids within this domain. The peraluminous suite has been locally reported and their petrogenesis is not fully understood. Petrography and whole-rock geochemistry were used to study the petrogenesis/formation of granitic rocks within this area. The results show that the granitoids are composed of quartzo-feldspathic, made up of granites, monzonites and quartz monzonites which were intruded in the Paleoproterozoic orthogneissic basement. The major and trace element compositions show that they are high-K calc-alkaline to shoshonites, with S-type affinity. The molar ratio A/CNK is > 1.1, while the ratio of CaO + Na2O/Al2O3 is generally < 1 making them strongly peraluminous. The REE shows enrichment in the LREE over the HREE, with (La/Yb)N varying from 11.9 to 53.32, (Dy/Yb)N from 0.77 to 2.13 and moderately negative Eu anomaly ((Eu/Eu*)N range from 0.42 to 0.93). Most granite samples show depletion in P, with CaO/Na2O < 0.3 and Rb/Sr ≤ 1 indicative of clay-poor metapelitic source, while the others show clay-rich metagreywackes sources. The strong peraluminosity, S-type affinity, high Ba/Sr, Ba/Rb and low Rb/Sr indicate they are crustal-derived. The compositional variation might be induced by the partial melting of different source materials followed by fractional crystallization of the granitic magma. The source nature requires fragments of Paleoproterozoic metasedimentary and metaigneous rocks derived from the collision between the north-central Cameroon block and the Congo Craton during the Pan-African. Article highlights: This study investigates the occurrence of strongly peraluminous granitic rocks within the Hangloa area. The lithologies consist of granites, monzonites and quartz monzonites hosted within orthogneissic basement. The mineralogy show very weak clues in support of their peraluminosity except for the presence of kyanite in some of the granites. Major elements characteristics shows A/CNK > 1.1, CaO + Na2O/Al2O3 < 1 indicating their high aluminium saturation and upper crustal source. However the presence of mafic enclaves within the granitoids indicates partial mixing with mafic mantle material. Major oxides correlate negative correlation with significant scattering with SiO2, while LRRE are relatively enriched over the HREE indicating crystal fractionation. However, the scattering suggest internal compositional variations. The show rock chemical features indicative of multiple sources of magma for the Hangloa granitoids. Granites show CaO/Na2O < 0.3, depleted P and Rb/Sr < 1 indicating a metapelitic source, poor in clay. The monzonites and quartz monzonite are enriched in P with CaO/Na2O > 0.3, Rb/Sr > 1 characteristic of clay-rich sources. The Y + Nb content versus Rb show that they were derived from a volcanic arc setting common with upper crustal magmas along subduction environments. [ABSTRACT FROM AUTHOR]

The Rio del Rey sub-basin belonging to the Cretaceous–Cenozoic coastal basins of Cameroon is studied with geochemistry (major and trace elements) associated to mineralogy, palynology and petrography. One dominant facies (calcareous shales/siltstones/claystones) occurs in the Cretaceous series and two others (calcareous fine- to coarse-grained sandstones and calcareous claystones/shales in the Paleocene series. Ratios of LREE/HREE (9.27–24.23), Cr/Th (2.24–12.60), Th/Sc (0.54–6.10), Eu/Eu* (> 1 on PAAS normalized and ˂ 1 on Chondrite normalized), Al2O3/TiO2 (10.42–112.93) plotted in the Ce vs. La/Yb, Zr vs.TiO2 and La/Sc vs.Th/Co diagrams indicate that the sediments derivate from felsic rocks associated with subordinate intermediate composition to mafic igneous rocks. CIA (Chemical Index of Alteration, 61.69–92.76), PIA (Plagioclase to Index of Alteration; 62.16–99.47) and K2O/Na2O ratios (0.08–22.13) suggest that the source rocks have experienced low to high weathering (during the Paleocene), high chemical weathering (at the Campanian–Maastrichtian transition) and moderate to high chemical weathering (during the Cenomanian). The Zr/Sc vs. Th/Sc diagram of sample groups reveals that the Paleocene coarse-grained sediments have higher zircon content. Al/Si ratios, low in the coarse-grained (0.04–0.06) and high in the fine-grained (0.2–0.58) sediments, behavior of Al/Si vs. CIA and some elemental concentrations, such as Zr, Hf, Ca, K, and Na, suggest that the geochemical composition is controlled by grain sizes. The petrographic and X-ray diffraction results point early to mesodiagenesis effects and an important role of sea level change on the environments of sedimentation. These latter vary from marginal to shallow marine during the Cretaceous and fluctuated between shallow marine/lagoonal and brackish/littoral settings during the Paleocene according to facies analysis and palynology, with marine species such as Dinopterygium cladoides and continental species such as Classopollis sp. The SiO2 vs. Al2O3 + K2O + Na2O plot suggests that a predominant semi-arid to arid climate with periodically semi-humid periods was the rule during the Paleocene, The Arc-Rift-Collision, with two sets of high and low-silica rocks and SiO2 vs. K2O/Na2O diagrams, indicates a Collisional or Active Continental Margin tectonic as also recorded in the Cretaceous and Paleocene deposits in the Douala coastal sub-basin and in the Cretaceous Campo coastal sub-basin in Cameroon. These tectonic events could reflect the Precambrian basement history linked to the Neoproterozoic orogeny. The geological history of the Rio del Rey sub-basin is similar to those of Nigerian and Brazilian East costal basins, with local variations of the sea level changes on both sides of the Atlantic Ocean and the sediments distribution which is related to the source rock lithology. [ABSTRACT FROM AUTHOR]

Ngaye area belongs to the Adamawa-Yadé domain (AYD) of the Central African Fold Belt (CAFB) in Cameroon. It is underlain by gneisses and amphibolites intruded by a variety of granitoids including granites and granodiorites. Petrographic, mineralogical and bulk-rock geochemical analyses were applied to assess the characteristics, petrogenesis and tectonic settings of these formations. Gneisses and amphibolites are characterized by a heterogranular granoblastic texture and a weakly to well-developed foliation. The granodiorites are characterized by high SiO2 (65.32 to 69.04 wt%) and K2O/Na2O < 1, with Mg-number (Mg#) of 23.44 to 43.67. They display affinities to calc-alkaline, peraluminous to metaluminous, magnesian I-type granites. Granite samples display higher SiO2 contents (69.62–81.04 wt%) with wide ranges of K2O/Na2O (0.44–4.72) and Mg# (5.85–41.16). These granites are classified mostly as ferroan, calc-alkaline, peraluminous, I-type granites. Comparable features were observed in the Hawal Massif granitoids in the eastern Nigeria and in the Ngoura-Moyto granitoids of south-central Chad. The chondrite-normalized REE patterns of the studied granitoids are weakly to strongly fractionated, with negative to weak positive Eu anomalies (Eu/Eu* = 0.28–1.36) for granodiorites and mostly positive Eu anomalies (Eu/Eu* = 1.54–5.78) for granites. In primitive mantle-normalized multi-element diagrams, all granitoids show enrichment in LILE relative to HFSE and display positive Ba, K and Pb, and negative Nb, Ta, Ti and P anomalies. The gneisses show high and variable contents in SiO2 (48.78–68.17 wt%), Al2O3 (13.06–18.03 wt%), and moderate Mg# (35.41 to 59.99). Their REE patterns are weakly to strongly fractionated ((La/Yb)N ≈ 3–168) and exhibit negative and positive Eu anomalies (Eu/Eu* = 0.59−2.05). Amphibolites display lower SiO2 (48.13–50.84 wt%) and Al2O3 (13.53–15.37 wt%), with Mg# ranging from 34.38 to 58.18. Their REE patterns are weakly fractionated ((La/Yb)N ≈ 3–5) with no Eu anomalies. Both gneiss and amphibolite samples are marked by troughs of Ta and P, and peaks of K, Pb and Nd on the primitive-mantle normalized spidergrams, suggesting that they were derived from the same source. Petrological and geochemical characteristics show that the Ngaye granitoids emplaced in a volcanic arc subduction-related environment, from partial melting of metabasaltic, metatonalitic and metagreywacke source rocks, under hydrous conditions. The Ngaye amphibolites display geochemical features of island arc basalt with MORB-like signature, continental forearc setting with calc-alkaline signature and syn-orogenic environment, implying an overall arc environment for the Ngaye formations. [ABSTRACT FROM AUTHOR]

Petrographical, geochemical, and geochronological data obtained from Ngaye high‐grade metasedimentary rocks have contributed to determine the provenance, nature, and evolutionary history of the Adamawa‐Yadé Domain from the Archean to Pan‐African events. The rocks are migmatites formed after TTG and granitic crusts were reworked by partial melting at T = 683–994°C. Geochemical features, for example, low Rb/Sr ratio (0.03–0.53), high Cr/V, and Cr/Th ratios (9.91–100.75; 28.41–686.15), respectively, indicate that these samples were derived predominantly from a mafic crust source. The primordial mantle‐normalized spidergrams are characterized by negative Nb‐Ta anomalies, suggesting melting of crustal rocks. REE fractionation shown (La/Yb)N = 8.48–197.89) indicate melting of crustal source rocks (meta‐TTGs). Low Hf and Zr contents (0.95–5.65 ppm and 23–262.85 ppm, respectively), low Sr/Y ratios (9.17–200.65), and a positive correlation between Th/Sc and Zr/Sc, point to crustal reworking. U–Pb ages on detrital zircon in tonalitic and granodioritic gneisses indicate contribution of Mesoarchean and Paleoproterozoic sources and suggest a maximum deposition age during the Early Paleoproterozoic for their magmatic protoliths. Magmatic zircon grains of granodiorite, with a round shape, Th/U ratio values ranging from 0.02 to 1.23, and an oscillatory zonation yield post emplacement metamorphic ages at 2,077 Ma. The lower intercept ages obtained in this study, match the tectonic reworking of the crust during the Pan‐African event associated with partial melting due probably to regional‐scale shear zone activities and magmatic accretion of juvenile magmas. [ABSTRACT FROM AUTHOR]

Abstract: The Méiganga area is located in the central part of the Panafrican belt of Cameroon. This region is underlain by a granitic and gneissic basement, crosscut, and covered by basaltic and phonolitic rocks. To the southwest of Méiganga, the pyroxene-and-amphibole-bearing gneiss shows the geochemical characteristics of Archean TTG (tonalite—trondhjemite—granodiorite) associations. The studied samples show LREE enrichment relative to the HREE (LaN/YbN =7–28). This pattern of the REE, particularly the concentration of Y and Yb allowed us to consider some samples as derived from an Archean crust. Cathodoluminescence pictures of zircon crystals from the gneiss reveal magmatic oscillatory zoning with inherited cores. Age determinations employing the 207Pb/206Pb single-zircon evaporation method yielded Late Archean (∼2.6Ga) to Palaeoproterozoic (∼1.7Ga) ages. Ages around 2.0Ga are interpreted to be close to the crystallization age, while the older ages might represent mixing ages, i.e., mixtures between a Palaeoproterozoic magmatic domain and an inherited Archean core. This study discusses the imprints of Archean crust inheritances on the pyroxene–amphibole-bearing gneisses of the Méiganga area. [Copyright &y& Elsevier]