Upper Mantle Structure Beneath the Cameroon Volcanic Line From Preliminary Body-wave Tomography

The Cameroon Volcanic Line (CVL) is a 1600 km feature traversing both continental Cameroon in west Africa and the offshore islands of Bioko (part of Equitorial Guinea), Sao Tome and Principe, and Annobon (also part of Equitorial Guinea). The CVL is a fairly linear feature, suggestive of the movement of the African plate over a stationary hotspot, but the volcanic rock ages of the CVL range from 42 Ma to the present (with present volcanism occurring in the center of the line at Mt. Cameroon), contrary to what would be expected from a stationary hot spot. Several hypotheses have been proposed for the formation of the CVL. One suggestion is that the line is the result of a localized mantle convection cell resulting from edge flow from the nearby Congo Craton to the southeast. Another possibility is that there may be a plume that is rising to the surface along of previously weakened linear zone. In this scenario, the magma may rise sporadically to the surface at different points along the line thereby explaining the apparent lack of age progression. The Cameroon Seismic Experiment has been deployed in Cameroon since January 2005, with 8 stations active the first year and an additional 24 stations installed in January 2006. The data from the 32 broadband seismometers is currently being used for a body-wave tomography study to study the upper mantle structure beneath Cameroon. Preliminary results from a P wave travel time tomography will be presented and used to evaluate possible models for the origin of the Cameroon Volcanic Line.