Extreme source heterogeneity and complex contamination patterns along the Cameroon Volcanic Line: New geochemical data from the Bamoun plateau

We investigated mafic and felsic volcanic rocks from the Bamoun plateau, a magmatic province located north of Mount Cameroon, in the continental part of the Cameroon Volcanic Line (CVL). Basalts and dacites were probably emplaced more than 40 Ma ago, while basanites represent very young volcanic eruptions. Among the basalts, some of them have suffered crustal contamination during their uprise through the continental crust, and their primary trace element and isotopic compositions have been slightly modified. The formation of the dacites was also accompanied by some crustal contamination. Non-contaminated rocks show that the oldest magmas are transitional basalts formed by relatively high degrees of partial melting of a moderately enriched mantle source, probably containing pyroxenites. Recent basanites were produced by very low partial melting degrees of an enriched mantle source with HIMU composition, but different from the source of the nearby Mount Cameroon lavas. The mantle beneath the CVL is thus very heterogeneous, and the tendency towards more alkaline mafic-ultramafic compositions in the youngest volcanic manifestations along the CVL seems to be a general feature of all CVL

Geoheritage of the volcanic landscapes of Foumbot-Kouomboum region, Noun Plain, Cameroon: Geomorphological features and assessment of geomorphosites

This study was carried out in the Foumbot-Kouomboum region (Noun Plain, Cameroon Volcanic Line), with the main objective of presenting (i) the geomorphological characteristics of the volcanic landforms and (ii) the inventory and evaluation of the main geomorphosites in the Foumbot-Kouomboum region. All the geomorphosites selected in this study are of volcanic origin and include four crater lakes (Monoun Lake, Mfouet Lake, Negop-Ghang Lake, Ngouondam Lake) and four Strombolian cones (Mfomben, Chapchap, Makwet, North-Njitande). Most of these volcanic geomorphosites are accessible and have volcanic features that highlight the geological significance of this region, warranting national and international recognition. These volcanic landscapes have relatively high scientific and additional values. The integrity of many of the selected geomorphosites is preserved and they are representative of the regional geomorphology. Some artisanal and industrial quarries, as well as agro-pastoral activities, tend to degrade certain geomorphosites that currently lack legal protection. The results of the inventory and evaluation of the selected geomorphosites show that they have enormous geotourism, educational and cultural potential that can be studied in depth with the aim of creating an UNESCO Global Geopark. Therefore, it is highly recommended to implement geoconservation policies for these geomorphosites. This will help to safeguard and enhance the natural beauty and unique volcanic landscapes they possess

Petrogenesis and geodynamic environment of the Recent pyroclastic deposits from Baïgom and Petpenoun volcanoes of the Noun Plain, Cameroon Volcanic Line, Central Africa

This study presents petrography, mineral chemistry, whole-rock major and trace elemental systematics for Recent pyroclastic deposits from volcanic edifices of Baïgom and Petpenoun, located in the Noun Plain graben along the Cameroon Volcanic Line (CVL), Central Africa, to better understanding their petrogenesis and geodynamic environment. The samples are mainly ash, lapilli and scoria, belonging to two different magmatic series: an alkaline series and a sub-alkaline series. Petrographic and mineralogical evidence in alkaline samples show a common crystallizing mineral assemblage of olivine, clinopyroxene and/or plagioclase, scattered in a fine-grained to glassy matrix. Clinopyroxene occurs in variable sizes, and includes megacrysts, which show either little or strong zonation, and thus represent different processes. The large, unzoned crystals provide clear evidence for prolonged magma chamber processes involving high and near-constant melt/Clinopyroxene ratios. The megacryst abundances are interpreted as crystal accumulation. The thermobarometry results in alkaline samples provide temperatures of 1188–1267 °C and pressure estimates in the range of 10.3–23.8 kbar. All the Recent pyroclastic deposits display high (La/Yb)N (11.20–20.35) and (Tb/Yb)N ratios (1.93–2.64), suggesting that their parental magmas originated from partial melting in the garnet-bearing mantle zone, at a depth > 80 km. The near-constant Ce/Y (3.14–3.76) and the higher Zr/Nb (5.85–10.71) ratios in sub-alkaline lava samples adequately fit with derivation of the magmas from a melt column extending across the garnet-spinel transition zone. Our results suggest two distinct origins for Recent pyroclastic samples from volcanic edifices of Baïgom and Petpenoun and imply an underlying heterogeneous mantle source beneath the CVL

Geomorphological component of volcanic geoheritage of Kouoptamo, Cameroon Volcanic Line: Geoconservation and perspectives for geotourism industry

This study was conducted in Kouoptamo, located in the Noun Plain in Western Cameroon, with the main objective of inventorying and evaluating the geological heritage, and promoting the protection and geoconservation of geosites, and their use in geotourism development. Geosites in the region include dammed lakes (Petpenoun lakes), maars (Sanka Ndoumkain Maar, Tchoua Maar), scoria cones (Nkoambeng, Kechuentim, Ngouen volcanoes), a dome (Njigoumbé Dome) and a managed natural area (Petponoun Domain). Most geosites have a high scientific, aesthetic and educational value. The method used for the inventory and assessment of geosites in this work is according to Reynard, et al. (2016), which is more suitable for geological heritage on a regional scale. The scientific value in this method is composed of four criteria, namely rarity, representativeness, integrity and palaeogeographical interest. Each of these criteria is evaluated independently by a numerical score ranging from 0 (nil) to 1 (very high) in intervals of 0.25. The overall average scientific value of the Kouoptamo geosites is 0.77. Nkoambeng Volcano has the highest scientific value (0.88), followed by Tchoua Maar, Sanka Ndoumkain Maar, Njigoumbé Dome and Ngouen Volcano, all of which score 0.81, while Kechuentim Volcano and Petpenoun Domain score 0.75 and 0.69, respectively. The integrity of several of these geosites is preserved, mainly the Petpenoun lakes, the Tchoua Maar, and the Sanka Ndoumkain Maar. Geosites such as Sanka Ndoumkain Maar, Tchoua Maar, Njigoumbé Dome and the Nkoambeng, Kechuentim, and Ngouen volcanoes are representative of the regional geomorphology. Artisanal quarries (Nkoambeng Volcano) and industrial quarries (Njigoumbé Dome), as well as agro-pastoral activities, tend to degrade these geosites, which in general do not benefit from any legal protection. It is strongly recommended that geoconservation policies be adopted for these geosites, in order to preserve and develop these sites for their considerable geotourism potential while taking into account the current resource and land usage to find an optimum, sustainable strategy

Assessment of shear zone-derived quartz from the Etam area, southwest Cameroon as potential high-purity quartz resource : petrography, geochemistry and technological studies

This study focuses on the evaluation of the high-purity quartz (HPQ) potential of a shear zone-hosted hydrothermal and metamorphic quartz deposit in Etam, southwest Cameroon. The shear zone quartz-rich rock is monomineralic and consists of both milky and translucent varieties. The combination of ICP-MS and LA-ICP-MS analytical techniques was used to assess the chemical purity of both quartz varieties. These compositional analyses show that all quartz samples have SiO2 content of 98.46–99.75 wt% with very low concentrations of all the other elements. Translucent quartz when compared to the milky quartz variety shows low concentration of most of the elements including the following principal impurities: Al (mean 107 µg g−1), Ca (mean 27.85 µg g−1) and Fe (mean 26.05 µg g−1). Bubble generation in the samples after flame fusion over a silica plate was assessed to test the suitability of the quartz in industrial uses. The results obtained from the chemical analyses and bubble formation tests indicate that all the samples investigated do not meet the HPQ requirement. However, the translucent quartz shows characteristics of medium-purity quartz and can produce silica glass for some industrial manufacturing even without further purification. In this study, the fluid inclusions in the samples were examined as this bears information on the economic viability of the deposit and provides clues on the genesis of the quartz vein. Also tiny mineral inclusions within individual quartz grains were identified by SEM–EDS. The results of these studies show that the deposit is probably of metamorphic origin marked by crystal-plastic deformation in quartz grains. The veins were later modified by hydrothermal fluid input. The results also indicate that the majority of impurities are likely hosted by fluid inclusions and thus the quartz can be upgraded to HPQ after purification by suitable methods24CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQNão temThis paper is part of ongoing Ph.D. thesis by the first author. This work has been financially supported by the Ministry of Higher Education, Cameroon, through the Special Allocation for the Modernization of Research (SAMR) granted to the first author. Authors thank the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) for the financial support. We highly appreciate the support of Prof. Nzenti Jean Paul who suggested constructive revisions to the various versions of the manuscript. The incisive comments of two anonymous reviewers and the Editor are much appreciate