The conference was hosted by the Institute for Geological and Mining Research (IRGM) and was under the sponsorship of both the Ministry of Scientific and Technical Research and UNESCO/IUGS. The meeting was attended by 100 participants from Botswana, Cameroon, Central African Republic, Chad, Denmark, France, Germany and Nigeria.  25 persons (mainly foreign participants) were invited to participate to the field trip.

The opening ceremony was held at Mont Fébé Hotel, Yaoundé and was chaired by Justin Djomatchoua, Permanent Secretary, representing the Minister of Scientific and Technical Research. Three addresses were given: (1) the welcome address by Joseph Victor Hell, Director of the IRGM; (2) the address of Wolfgang Eder, Director of the UNESCO Division of Earth Sciences and Secretary of the International Geological Correlations Programme (IGCP), read on his behalf by H.A.B. Kampunzu (University of Botswana) and; (3) the opening address by Justin Djomatchoua.

After the opening ceremony, the meeting focused on papers presentation covering the geology of central Africa and the neighbouring regions and on the break up of Rodinia and assembly of Gondwana. The selected oral presentations were grouped in three sessions: (1) specialized lectures (4 papers) under the chair of Tchoua Félix (University of Yaoundé-I); (2) regional geology (10 papers) chaired by Kampunzu and; (3) tectonic and applied geology session (6 papers) chaired by Nnange Metuk, Deputy Director of IRGM.

The IGCP-470 first business meeting covered the following points: (1) election of the project leader: S. Félix Toteu was unanimously elected as the leader of the IGCP-470; (2) appointment of national representatives. A number of representatives were nominated and the project leader will continue consultations for the designation of additional national correspondents of the IGCP-470 and; (3) location of the 2003 annual meeting: looking at the political situation in the Central African Republic, participants agreed that consultations must continue to find out if the original plan of holding the 2003 annual meeting in Central Africa Republic can go ahead or suggest an alternative solution to the members.

The five days field trip in southern Cameroon started on December 3 in the morning and ended on December 7 in the afternoon. Southern Cameroon comprises three main geological units: (1) the Archean Ntem complex marking the northern edge of the Congo craton; (2) the Paleoproterozoic Nyong “series” and its extension reworked by the Pan-African belt and; (3) the Neoproterozoic Yaoundé “series” forming the southernmost part of the Pan-African belt thrust onto the Ntem complex.

Archean Ntem Complex

From geochronological data, the Archean crustal evolution can be summarized as follows: (1) formation of greenstone belts prior to 3.0 Ga (mainly from Sm/Nd ages); (2) emplacement of TTG plutonic rocks (3.0 –2.8 Ga), the charnockitic TTG being older (2.9 Ga). This time span corresponds to a major period of crustal accretion and; (3) emplacement of K-rich granitoids (2.6-2.5 Ga) from partial melting of the TTG rocks. The Ntem complex was subsequently more or less affected by the Paleoproterozoic event (2.05 Ga). Several Sm/Nd data suggest a pre-3.0 Ga tectonic and metamorphic history, but this possible existence of a protocrust is still open to additional research.

Paleoproterozoic Nyong “series”

Rock units of the Nyong “series” are: (1) meta-sedimentary and meta-volcano-sedimentary rocks which may correspond to remnants of greenstone belts; they include pyroxene meta-quartzites and meta-arkoses, calc-silicate rocks (garnet-rich amphibolo-pyroxenites and gneisses), Mamelles type Banded Iron Formations, mafic and ultramafic meta-volcanic rocks; (2) migmatitic grey gneisses of TTG composition; (3) syn- to late-tectonic charnockites, augen metadiorites, leucogranites and alkaline syenites. Northward in the orogenic belt, similar lithologies are observed but, with a more important volume of mafic to intermediate rocks.

Geochronological data suggest the following evolution for the Nyong “series”: (1) formation of Paleoproterozoic series (prior to 2.1 Ga) from recycling of Archean crust (dominant process in the Nyong “series”) and from minor newly accreted material; (2) deformation, metamorphism, crustal melting and emplacement of plutonic bodies (including TTG and charnockites) between 2.1 and 2.0 Ga. These rocks were subsequently reworked by the Pan-African orogenic events, especially towards the north. However, there is no consensus about this evolution, the alternative being that the Nyong “series” represent a part of the Ntem complex reactivated at 2.1 Ga

Neoproterozoic Yaoundé “series”

The Yaoundé “series” is an association of metasedimentary (garnet-kyanite, garnet-plagioclase and amphibole-biotite gneisses, micaschists) and metaplutonic (mostly garnet-pyroxene metadiorites) rocks that underwent a regional metamorphism culminating in the granulite facies. The deformation is polyphase, the latest stage corresponding to the southward thrusting of the unit onto the Congo craton. Except for the metamorphism which is well constrained at ca. 620 Ma, the deposition age of the package is still uncertain, but is assumed to be younger than 1.0 Ga. T_DM ages of most of the rocks indicate a mixed source between Paleoproterozoic and Neoproterozoic components. The question still debated is the tectonic position of the “series” (autochthonous or allochthonous on the craton) and the tectonic significance of granulitic rocks (root of a collision zone or intracontinental).

Field trip itinerary

The objectives of the five-day field trip were to present the main geological features of southern Cameroon and to trigger discussions on issues still on debate. For this purpose, some key outcrops easily accessible were selected in the above units.

The itinerary of the first part of day one focused on typical rock types of the Yaoundé series (granulitic metadiorites and metasedimentary rocks) in quarries in the Yaoundé city (Ngoa Ekelle and Meyon Meyeme). The second part of the day was devoted to the cross-section Yaoundé-Bangoua to study Paleoproterozoic remnants in the Pan-African belt (migmatitic gneisses at Makene in particular) and document the relationship between Pan-African migmatization, granite emplacement and shear zones.

During the second day, a cross-section from Yaoundé to Ebolowa allowed the observation, at Mbalmayo, of structures associated with thrusting of the Pan-African belt onto the Ntem Complex, and representative lithologies of the Ntem complex (e.g. Soo tonalite, Ngoulemakong and Ebolowa charnokites, septa of metasedimentary rocks within the charnockite at Mbondo village).

Day three was devoted to a cross-section from Ebolowa to Mboumnyebel across the Ntem complex, the Paleoproterozoic Nyong “series” and the Neoproterozoic Yaoundé “series”. Emphasis was on metasedimentary and TTG rocks of the Nyong “series”  and on the mylonitic sole between the Nyong and Yaoundé “series”  at Pouth Kelle village.

Day four allowed the observation of uncompletely charnockitised Paleoproterozoic rocks at Edéa, Bienkop and of the porphyritic granitoids along the Edéa-Kribi road.

Day 5, the end of the field trip, was devoted to outcrops of Paleoproterozoic rocks at the Lobé falls and of Neoproterozoic syenites at Rocher du Loup. It was also the opportunity to relax on the Rocher du Loup beach while holding the last business and review meeting to round up the trip.

During this field trip, samples were collected by different teams for petrographic, geochemical and geochronological studies with the objective to solve some of the problems raised by intense and fruitful field discussions which were focussed on the following points: (1) the problem of the root of the Pan-African nappe of Yaoundé; (2) the origin of the Paleoproterozoic terranes, their deformation and metamorphism (both in the Nyong “series”   and in the Pan African belt) during both Eburnean and Pan-African orogenies; (3) the metamorphic evolution (P-T-t path) for the three major critical tectono-metamorphic periods (ca 2.9, 2.1 and 0.6 Ga) for this region; (4) the necessity of carrying out more geochemical investigations, particularly on the Paleoproterozoic rocks and on the Pan-African granitoids; (5)  the kinematics during the emplacement of the granites; (6) the definition of some metallogenic guides in relation with the shear zones and the nappe tectonics in both southern and central Cameroon; (7) the correlation of Meso and early Neoproterozoic rocks in Cameroon, Central Africa Republic and Congo and; (8) the paleo-climatic aspects during the Neoproterozoic and early-Paleozoic in connexion with the “Snowball Earth” hypothesis.

These discussions led to the constitution of research teams to focus on the following points: (1) tectonic and metamorphic studies; (2) intensification of geochemical studies; (3) development of paleomagnetic studies on specific targets; (4) development of Anisotropy of Magnetic Susceptibility (AMS); (5) use of isotopic studies to track the metallogenic evolution during the Pan-African orogeny; (6) geochronological studies on specific targets and; (7) development of the GIS database to update the geological and tectonic map of central Africa.  Beyond these discussions, it appeared that the geological mapping is very poor in central African countries. Thus, there is a strong and urgent need to set up an efficient regional program of remote sensing and geophysical air survey combining aeromagnetics, airborne gravity and radiometric.

2003 IGCP 470 annual meeting

The next annual meeting will be held in December 2003 in Central Africa Republic (Bangui) and will be hosted by the University of Bangui In 2002, several participants were concerned with the political situation in that country and a debate was engaged for alternative solutions among which Nigeria, Chad or a meeting in Chad and cross section in both Chad and northern Cameroon. However, at the end of the meeting, participants did not reach a definitive conclusion. The leader of the project was asked to continue consultations on this point. In any case, it was decided to plan a short field trip in Central Africa Republic as soon as possible. Moloto (CAR) and Milesi (BRGM France) were kindly asked to see how this can be organized.

IGCP-470 National correspondents
The following were nominated IGCP-470 national correspondents in their respective countries:

Botswana: H.A.B. Kampunzu, University of Botswana
Brazil: A. Franscisco da Silva Filho, University of Pernambucu.
Central Africa Republic: A. Malibangar, University of Bangui
Chad: J.C. Doumnang, University of Djaména
Denmark: H. Stendal, Geological Survey of Denmark and Greenland
France: J.P. Milesi (BRGM) for the Survey/Industry; Anne Nédélec (Paul-Sabatier University, Toulouse) for Universities;
Germany: J. Tait, Ludwig-Maximilians-University
Nigeria: B. Ekwueme, University of Calabar
USA: W.R. Van Schmus, University of Kansas

Consultations are still ongoing for the remaining countries.

Web site of the project
Jenny Tait  (Germany) kindly offered to prepare a Web site for the IGCP-470. All participants were asked to provide her with data.

Acknowledgements and vote of thanks

The participants unanimously thanked J.V. Hell, IRGM Director, who joined the trip on the last day at Kribi, for the financial and logistic support provided by Cameroon and especially the institute to support the organization of the field conference. They also congratulated the organising committee for a job well done.

Leader of the IGCP-470
Centre for Geological and Mining Research (CRGM)
B.P. 333, Garoua, Cameroon

e-mail: sftoteu@yahoo.fr, or crgm@iccnet.cm