This memoir has attempted to give an account of the present knowledge of this part of the Gregory Rift, but should be regarded as an interim report. Like most reviews, it has served to identify areas that would benefit from further research. Some are listed below.
The eastern margin of the Tanzania craton is buried to the east of the mapped surface contact between it and the Mozambique fold belt. As noted in Chapter 3, there is now evidence that Archaean and Neoproterozoic rocks exist intermixed with the rocks of the Mozambique Belt, well to the east of the mapped contact. Seismic traverses across the Maasai Block would be highly desirable to determine whether the eastern extent of the craton can be ascertained, and whether there might be any coincidence between its extent and the identified geophysical properties of the Maasai Block suggesting that it might be a discrete terrain.
Investigations into the structure and history of the Tanzanian mantle by means of xenolith studies are still at an early stage. Some xenoliths, such as those at Lashaine and Pello Hill, contain micas, whereas others (e.g. at Olmani) contain monazite. Dating these phases could shed new light on the timing of the upper mantle metasomatism. The age and isotopic characteristics of the host rocks of the xenoliths (mainly olivine melilitites and nephelinites) need investigation to find out whether the metasomatism and magmatism are linked. For example, are the helium isotope characteristics of xenoliths imposed by the host magmas during transportation?
Figures & Tables
The Gregory Rift Valley and Neogene—Recent Volcanoes of Northern Tanzania
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.