We present a new analysis of the lithospheric architecture of Africa, and its evolution from ca. 3.6 Ga to the present. Upper-lithosphere domains , generated or reworked in different time periods, have been delineated by integrating regional tectonics and geochronology with geophysical data (magnetic, gravity, and seismic). The origins and evolution of lower-lithosphere domains are interpreted from a high-resolution global shear-wave tomographic model, using thermal/compositional modeling and xenolith/xenocryst data from volcanic rocks. These data are integrated to map the distribution of ancient highly depleted subcontinental lithospheric mantle (SCLM), zones of younger or strongly modified SCLM and zones of active mantle upwelling, and to relate these to the evolution of the upper lithosphere domains. The lithospheric architecture of Africa consists of several Archean cratons and smaller cratonic fragments, stitched together and flanked by younger fold belts; the continental assembly as we see it has only existed since lower Paleozoic time. The larger cratons are underlain by geochemically depleted, rigid, and mechanically robust SCLM; these cratonic roots have steep sides, extending in some cases to ≥300-km depth. Beneath smaller cratons (e.g., Kaapvaal) extensive refertilization has reduced the lateral and vertical extent of strongly depleted SCLM. Some cratonic roots extend ≥300 km into the Atlantic Ocean, suggesting that the upper lithosphere may detach during continental breakup, leaving fragments of SCLM scattered in the ocean basin. The cratonic margins, and some intracratonic domain boundaries, have played a major role in the tectonics of Africa. They have repeatedly focused ascending magmas, leading to refertilization and weakening of the SCLM. These boundaries have localized successive cycles of extension, rifting, and renewed accretion; the ongoing development of the East Africa Rift and its branches is only the latest stage in this process. The less depleted SCLM that underlies some accretionary belts may have been generated in Archean time, and repeatedly refertilized by the passage of magmas during younger tectonic events. Our analysis indicates that originally Archean SCLM is far more extensive beneath Africa than previously recognized, and implies that post-Archean SCLM rarely survives the collision/accretion process. Where continental crust and SCLM have remained connected, there is a strong linkage between the tectonic evolution of the crust and the composition and modification of its underlying SCLM.

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The lithospheric architecture of Africa: Seismic tomography, mantle petrology, and tectonic evolution

A full-plate global reconstruction of the Neoproterozoic

New U–Pb and Sm–Nd data from north-central Cameroon and its bearing on the pre-Pan African history of central Africa

The Pan-African belt in central Africa has benefited from the many petrographic, structural, and geochronological studies in the recent years that have improved our understanding of the belt. However, those studies have also produced various and often divergent evolutionary models for the belt, some of which do not even involve well-defined cratons. Following a review of the available data in Cameroon, we propose a model of continentcontinent collision that involved the Congo craton and the north-central Cameroon active margin showing Archean to Paleoproterozoic inheritances. This model is based, among others, on (i) the prominent role of the Congo craton as demonstrated by the regional extension of external nappes on its northern edge and the concomitant exhumation of the 620 Ma granulitic rocks believed to have formed at the root of the collision zone, and (ii) the late development of a strike slip fault system in central Cameroon as the result of horizontal movement following the multistage collision....

Geodynamic evolution of the Pan-African belt in central Africa with special reference to Cameroon

The Congo (CC) and the Sao Francisco (SFC) cratons were joined at about 2.05 Ga; northern parts of Palaeoproterozoic basement subsequently underwent extension at about 1 Ga, forming intracratonic basins. Neoproterozoic metasedimentary rocks in these basins yield detrital zircons as young as 630 Ma. The Brasiliano and Pan-African (c. 620- 580 Ma) assembly of West Gondwana extensively altered this system. The Sergipano domain occurs north of the SFC, and the comparable Yaoundedomain occurs north of the CC. Crust north of the Sergipano domain com- prises the Pernambuco- Alagoas (PEAL) domain. The NE- SW-striking Tchollire ´ -Banyo fault in Cameroon may extend southwestwards between the PEAL and Sergipano domains, defining northern limits of abundant SFC/CC basement. The Adamawa -Yadedomain in Africa does not appear to extend into Brazil. The Transverse domain of Brazil is a collage of Palaeoproterozoic crustal blocks, the 1.0 Ga Cariris Velhos orogen (CVO), late Neoproterozoic basins, and Brasi- liano granites. The CVO extends ENE for more than 700 km in Brazil, but eastern continuation into Africa has not been identified. North of the Transverse domain contiguous c. 2.15 Ga gneisses comprise basement of Rio Grande do Norte and Cearadomains, which continue eastwards into western Nigeria and western Sahara.

Proterozoic links between the Borborema Province, NE Brazil, and the Central African Fold Belt

Des analyses U-Pb sur zircons et Sm-Nd sur roches totales ont ete effectuees sur les metasediments et les metaplutonites qui affleurent en septa au sein des granitoides panafricains du Centre-Nord Cameroun. Les resultats montrent que ces roches appartiennent a un socle paleo-Proterozoique (2 100 Ma) repris dans l'orogenese panafricaine et qu'elles derivent du demantelement ou de la fusion d'une croute archeenne. Les analyses Sm-Nd sur les granatoides panafricains montrent qu'ils derivent de la fusion de ce socle

Preliminary U-Pb and Sm-Nd geochronologic data on the North-Central Cameroon : contribution of an Archean and paleo-Proterozoic crust to the edification of an active domain of the Pan-African orogeny

A. Michard

Papers

New U–Pb and Sm–Nd data from north-central Cameroon and its bearing on the pre-Pan African history of central Africa

Preliminary U-Pb and Sm-Nd geochronologic data on the North-Central Cameroon : contribution of an Archean and paleo-Proterozoic crust to the edification of an active domain of the Pan-African orogeny