www.MantlePlumes.org © MantlePlumes.org Magmatism Within Africa: Lithophere Control and Global Tectonics

Since the original concept of plumes as an explanation for intraoceanic volcanism, they have become a popular choice for the cause of intracontinental igneous activity, where the most numerous eruptions, in time and space, are small volume melts in the alkaline igneous-carbonatite-kimberlite range. Such activity is most intense in interior Africa, which has been anorogenic for 550 Ma, with a lithosphere record> 3 Ga. Because continental alkaline magmatism is characteristically repetitive through the same segment of the lithosphere over geologic time, this long record is ideal for defi ning constraints on processes of magma generation. Plume models for African magmatism are numerous and highly divergent, but in the absence of hot spot tracks none can claim the primary attribute of plumes, namely, lithosphere independence. On the contrary, the typical pattern in Africa is that the magmatism is sited on pre-existing structures in the lithosphere, notably rifts and rift intersections. Some have a record of repeated activity over periods of 2 Ga, during which time the African plate has moved long distances over the deep mantle. When the canvas is broadened to other parts of the plate the constraints are multiplied, because with increasing age data it is becoming apparent that in many cases igneous episodes in different provinces are synchronous (Figure 1). Repeated, synchronous magmatism at the same sites across Africa is incompatible with any plume model. As many of the eruptives carry ocean island basalt (OIB) type chemical signatures, it follows that these are not exclusive to plume melting. Petrogenetic options are still further constrained when the African igneous episodes are found to coincide with external, global events. www.MantlePlumes.or