his study presents the first and detail field investigations of exposed deposits at proximal sections of the Barombi Mbo Maar (BMM), NE Mt Cameroon, with the aim of documenting its past activity, providing insight on the stratigraphic distribution, depositional process, and evolution of the eruptive sequences during its formation. Field evidence reveals that the BMM deposit is about 126m thick, of which about 20m is buried lowermost under the lake level and covered by vegetation. Based on variation in pyroclastic facies within the deposit, it can be divided into three main stratigraphic units: U 1 , U 2 and U 3 . Interpretation of these features indicates that U 1 consists of alternating lapilli-ash-lapilli beds series, in which fallout derived individual lapilli-rich beds are demarcated by surges deposits made up of thin, fine-grained and consolidated ash-beds that are well-defined, well-sorted and laterally continuous in outcrop scale. U 2 , a pyroclastic fall-derived unit, shows crudely lenticular stratified scoriaceous layers, in which many fluidal and spindle bombs-rich lapilli-beds are separated by very thin, coarse-vesiculatedash-beds, overlain by a mantle xenolith-and accidental lithic-rich explosive breccia, and massive lapilli tuff and lapillistone. U 3 displays a series of surges and pyroclastic fall layers. Emplacement processes were largely controlled by fallout deposition and turbulent diluted pyroclastic density currents under "dry" and "wet" conditions. The eruptive activity evolved in a series of initial phreatic eruptions, which gradually became phreatomagmatic, followed by a phreato-Strombolian and a violent phreatomagmatic fragmentation. A relatively long-time break, demonstrated by a paleosol between U 2 and U 3 , would have permitted the feeding of the root zone or the prominent crater by the water that sustained the next eruptive episode, dominated by subsequent phreatomagmatic eruptions. These preliminary results require complementary studies, such as geochemistry, for a better understanding of the changes in the eruptive styles, and to develop more constraints on the maar's polygenetic origin.

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ICP-MS U-Pb zircon ages from the Nyong Complex of southwestern Cameroona 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 amphiboliteprotolith 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 metagranodiorites 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.

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