Using seismic data to interpret the mechanism for Cenozoic volcanism beneath Ross Island, Antarctica and the Cameroon volcanic line, West Africa

Seismic data from Antarctica and Cameroon have been used to image the seismic structure of the upper mantle beneath Ross Island, the Transantarctic Mountains, and West Antarctica and Cameroon, West Africa. In Antarctica, results from a receiver function analysis of the mantle transition zone discontinuities do not show a thermal anomaly at these depths, and consequently the upper-mantle thermal anomaly imaged in regional tomography models beneath Ross Island does not appear to extend to >400km depth. This result suggests that the mechanism for the formation of the Transantarctic Mountains is not related to a deep-seated plume and that Cenozoic volcanism in the area is due to a thermal anomaly localized in the upper 300km of the mantle. In Cameroon, the P and S wave velocity structure of the upper mantle and transition zone discontinuities, imaged using body wave tomography and receiver function analysis, reveal a linear, low velocity anomaly in the upper mantle that extends to at least 300km but does not extend to mantle transition zone depths. Temperatures within the anomalous mantle, inferred from the tomographic models, are ∼280--560K higher than normal. These results suggest that the Cameroon Volcanic Line is caused by a linear, tabular thermal upwelling in the mantle, possibly related to eddy-flow edge-convection induced by temperature differences between colder and thicker lithosphere of the Archean Congo Craton and the thinner lithosphere of the Proterozoic mobile belt north of the craton. The results of this study are not consistent with the formation of the Cameroon Volcanic Line by a plume or decompression melting associated with thinned lithosphere.