Geophysical evidence for the structure of the crust and upper mantle of the Tanzania Craton and the Gregory Rift Valley
2008. "Geophysical evidence for the structure of the crust and upper mantle of the Tanzania Craton and the Gregory Rift Valley", The Gregory Rift Valley and Neogene—Recent Volcanoes of Northern Tanzania, J. B. Dawson
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The past three decades have seen an upsurge in geophysical fieldwork across the East African Rift Valley in Kenya (KRISP: the Kenya Rift International Seismic Project; Prodehl et al. 1994; Fuchs et al. 1997) and in Ethiopia (Project EAGLE: the Ethiopia Afar Geophysical Lithosphere Experiment; Yirgu et al. 2006). In northern Tanzania, in 1994, A. A. Nyblade and co-workers established an array of broadband receivers in northern Tanzania, the Tanzania Broadband Seismic Experiment, TBSE (Nyblade et al. 1996) that, together with interpretation of earlier commercially acquired data, have provided new insights into the present-day structure of the Tanzania Craton and the Mozambique belt. Although in many experiments data have also been acquired for the Western Rift, attention will be confined in the following section to observations on the northern Tanzania and southern Kenya sectors of the Gregory Rift Valley.
The interpretation of gravity data alone does not give a unique solution because Bouguer anomalies can reflect lateral changes in: (i) the density of the crust; (ii) the density of the upper mantle; (iii) the depth to the crust/mantle interface, the Moho; or (iv) a combination of these possible variables. Gravity measurements can, when combined with data from seismic experiments and measured rock densities, lead to integrated models for the structure of the crust and upper mantle, but it is relevant to discuss here the results obtained by individual disciplines.
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The structure and volcanic activity of the northern Tanzania sector of the Gregory Rift Valley have hitherto been described less than those in Ethiopia and Kenya. This book focuses on northern Tanzania where, although the volcanic area is smaller than those to the north, there are major features such as Kilimanjaro, the highest mountain on the African continent, Ngorongoro, one of the largest calderas on Earth, and Oldoinyo Lengai, the world’s only active carbonatite volcano. Following an account of the discovery and early exploration of the Rift Valley, there are descriptions of the individual volcanoes. These are set within the context of the regional geology and geophysics of the rift valley and in relation to the structural evolution of the rift and its associated sedimentary basins which include Olduvai, an important site in the history of human evolution. The volume concludes with a discussion of the volcanism in relation to the plume-related African Superswell.