GEOPHYSICAL EVIDENCE FOR METACRATONIZATON OF THE NORTHERN EDGE OF THE CONGO CRATON IN CAMEROON

We used the World Gravity Map (2012) satellite gravity data to investigate the transition between the Archean Congo craton in the south and the Neoproterozoic Pan-African Oubanguides orogenic belt to the north in Cameroon. The Oubanguides orogenic belt constitutes, from northwest to southeast, the West Cameroon domain, the Adamawa-Yade domain, and the Yaoundé domain. The Yaoundé domain represents the suture zone between the Congo craton and terranes of the Oubanguides orogenic belt. We used Bouguer gravity anomaly map and its derivatives to identify different anomalies in the region. We also used two-dimensional (2D) power density spectrum analysis and 2D forward modeling of the gravity data to estimate the Moho depth and to image the lithospheric structure associated with the craton and the orogenic belt. We found that: (1) the Congo craton, the Yaoundé domain, the southeastern part of the West Cameroon domain, and the northern part of the Adamawa-Yade domain are characterized by low gravity anomaly. (2) the southern part of the Adamawa-Yade domain is marked by a pronounced E-W trending high gravity anomaly. (3) the crust is thicker beneath the Congo Craton, the Yaoundé domain, and the southern part of the Adamawa-Yade domain, reaching 44 km in some places. Our estimations of the Moho depths are in good agreement with previous results obtained from gravity and passive seismic studies. (4) the 2D forward model suggests the presence of a denser lower crust material beneath the southern part of the Adamawa-Yade domain. We suggest that this material might be due to densification through metacratonization processes of an under-thrust portion of the Congo craton beneath the Oubanguides orogenic belt that accompanied Neoproterozoic collision. This suggestion is in good agreement with geological and geochemical observations indicating the northern edge of the Congo craton had undergone metacratonization during Neoproterozoic orogenic event. Our suggestion is also in good agreement with geological, geochemical and geophysical observations showing that the margins of some cratons Worldwide have been decratonized due to subduction processes. Our work highlights the importance of potential field geophysical data in aiding future studies aimed at understanding processes leading to the destruction of stable cratons.