U–Pb zircon and microfabric data of (meta) granitoids of western Cameroon: Constraints on the timing of pluton emplacement and deformation in the Pan-African belt of central Africa

Striking characteristics of the western Neoproterozoic belt of Cameroon (NFBC) are the large volume of granitoids and crustal-scale shear zones. New structural and geochronological data from this area are provided to put constraints on the tectonic evolution of this segment of the belt and to make further correlations between major shear zones exposed on both sides of the Atlantic Ocean.

Three different complexes have been identified in the study area: the migmatitic complex of Foumbot (MCF), the metagranitoid complex of Bangwa (BC), and the Batié pluton (BP). The MCF was intruded by the BC, while the BP cuts through the BC. U–Pb zircon dating of metaleucogranite and metagranodiorite of the BC yielded concordant to subconcordant ages of 638 ± 2 Ma and 637 ± 5 Ma, respectively. A concordant U–Pb zircon age of 602 ± 1.4 Ma has been obtained from porphyrogranite of the BP. These ages are interpreted as emplacement ages. Continuous deformation from magmatic to solid-state flow along the BP margins and the (sub)parallelism of the steep solid-state foliation in the BP margins with the foliation in the surrounding BC and MFC suggest synkinematic emplacement of the BP along crustal-scale NNE to ENE-trending strike–slip shear zones. Subhorizontal foliations in migmatitic-gneiss xenoliths found in the BC suggest that the major transcurrent motion was preceded by thrusting.

The new data confirm previous assumptions that the western NFBC is equivalent to parts of the Borborema province of Brazil. There are geochronological correlations between the studied (meta)granitoids and Brasiliano pre- to syn-transcurrent granitoids of the Borborema province.     

Multi-hazard risk mapping and assessment on an active volcano: the GRINP project at Mount Cameroon

To help improve the safety of its population faced with natural disasters, the Cameroon Government, with the support of the French Government, initiated a programme of geological risk analysis and mapping on Mount Cameroon. This active volcano is subject to a variety of hazards: volcanic eruptions, slope instability and earthquakes. Approximately 450,000 people live or work around this volcano, in an area which includes one of Cameroon’s main economic resources. An original methodology was used for obtaining the information to reply to questions raised by the authorities. It involves several stages: identifying the different geological hazard components, defining each phenomenon’s threat matrix by crossing intensity and frequency indices, mapping the hazards, listing and mapping the exposed elements, analysing their respective values in economic, functional and strategic terms, establishing typologies for the different element-at-risk groups and assessing their vulnerability to the various physical pressures produced by the hazard phenomena, and establishing risk maps for each of the major element-at-risk groups (population, infrastructures, vegetation, atmosphere). At the end of the study we were able (a) to identify the main critical points within the area, and (b) provide quantified orders of magnitude concerning the dimensions of the risk by producing a plausible eruption scenario. The results allowed us to put forward a number of recommendations to the Cameroon Government concerning risk prevention and management. The adopted approach corresponds to a first level of response to the authorities. Later developments should make it possible to refine the quality of the methodology.     

L'hétérogénéité du manteau supérieur à l'aplomb du volcan de Nyos (Cameroun) révélée par les enclaves ultrabasiques

Volcanic deposits from the lake Nyos (Cameroon) contain ultrabasic xenoliths: lherzolites, harzburgites and websterites, sometimes containing amphibole. Major and trace element compositions of clinopyroxene and amphibole allow the recognition of an old depletion event followed by two episodes of incompatible-element enrichment. One is high in light rare-earth elements, while the other one is low in these elements, but high in U and Th. Their relative chronology is not yet established. To cite this article: R. Temdjim et al., C. R. Geoscience 336 (2004).     

Zoning in: The contributions of buyam–sellams to constructing Cameroon’s wild food zone

Studies of forests in Africa employ the term zone to denote a particular type of forested area. This limited usage speaks to a need for human geographers to pay more attention to elaborating and engaging with the concept of the zone. This article shows why human geography should pay the ‘zone’ more attention. Using Cameroon’s humid forest zone (HFZ) as a case study, the article focuses on how conceptual elaboration of the ‘zone’ can inform analyses of the food product trade in Cameroon. This trade is organized around various types of buyers and sellers (or buyam–sellam in pidgin), and offers a wide variety of wild products to Cameroon’s urban food consumers, including fruits and vegetables, game meat, condiments, medicinal plants, and fibers. Drawing on fieldwork surveys, interviews and focus groups in twenty-four markets of 203 buyam–sellams and 197 of their customers during the wet and dry seasons, this article analyzes narratives about Cameroon’s wild food zone. It ultimately shows what scholarly attention to the ‘zone’ offers in this case that other spatial concepts do not.     

Geochemistry of peridotite and granite xenoliths during the early stage of weathering in the Nyos volcanic region (NW Cameroon): Implications for PGE exploration

Peridotite and granite xenoliths, in the early stage of weathering, occur in the Nyos volcanic region (NW Cameroon). Geochemical data shows that peridotites are marked by high concentrations of MgO (42.30 wt.%, with SiO₂/MgO ∼ 1), chromium (2100 ppm), nickel (2100 ppm) and cobalt (104 ppm), as well as by low lanthanide contents (ΣREE: 7.41 ppm). Granites display SiO₂ contents (70–73 wt.%), and are mostly peraluminous (1.40 > A/CNK < 1.6). They are also characterized by low contents in chromium (<24 ppm), nickel (ranging from 6 to 15 ppm) and cobalt (ranging from 3 to 6 ppm). Granites possess high lanthanide contents (ΣREE varying between 248.00 and 463.00 ppm), particularly in light lanthanides (LREE/HREE ratios ranging from 21 to 32). The chondrite-normalized patterns of the studied xenoliths are characterized by: (i) LREE enrichments in both rock types; (ii) negative Eu anomalies ([Eu/Eu*] ranging from 0.45 to 0.64) and weak positive Ce anomalies ([Ce/Ce*] ranging from 1.06 to 1.46) in granites. The weathering process provokes a remobilization of several trace elements notably light lanthanides.The geochemical survey of Platinum-Group Elements (PGE) done in these rocks in the early stage of weathering shows that PGE contents are less than 7 ppb in the peridotites. The highly concentrated elements are ruthenium (6.26 ppb) and platinum (5.53 ppb). The total PGE content is 14.57 ppb. These concentrations normalized with respect to chondrites display a flat spectrum from iridium to platinum. PGE contents in the granites are below detection limit except for two samples (LNY01 and LNY02) whose platinum content is close to 0.23 ppb.     

Producing hybrid forests in the Congo Basin: A political ecology of the landscape approach to conservation

Environmental conservation is increasingly operated through partnerships among state, private, and civil society actors, yet little is known empirically about how such collectives function and with what livelihood and governance outcomes. The landscape approach to conservation (known also as the ecosystem approach) is one such hybrid governance platform. Implemented worldwide over the past decade by international NGOs, the landscape approach employs the ‘ecosystem principles’ of the Convention on Biological Diversity (CBD). In spite of its prominence as a conservation and development strategy, little political ecology scholarship has considered the landscape approach. This article offers a case study of a conservation landscape in the Congo Basin, the Tri-National de la Sangha (TNS), which connects tropical forests in Cameroon, Republic of Congo, and Central African Republic. Led by NGOs, the TNS has since 2001 relied on partnerships among logging companies, safari hunters, the state, and local communities. Although the landscape approach purports to facilitate re-negotiations of user rights, resource access patterns in the TNS appear to have molded to pre-existing power relations. Rather than incorporating local concerns and capabilities into management, local knowledge is discredited and livelihoods are marginalized. As a result, management occurs through spatially-demarcated zones, contrasting the fluidity of interactions among diverse groups: both human (loggers, hunter-gatherers, safari guides, NGOs) and non-human (trees, elephants). These findings are situated within a burgeoning literature on neoliberal environmental governance, and suggest that ensuring ecologically and socially positive outcomes will require careful and iterative attention to linkages between ecological processes and evolving power dynamics.