| Title | Mantle Influence, Rifting and Magmatism in the East African Rift System (EARS): A Regional View of the Controls on Hydrothermal Activity |
|---|---|
| Authors | Getahun Demissie |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | EARS development, Afar, Main Ethiopian Rift, Kenya Rift, Western Rift, Southwestern EARS branches, plume impact, magmatism, hydrothermal features |
| Abstract | The most energetic hydrothermal features in Africa occur in the EARS region. EARS development is controlled by the magnitude of the in-field extensive stresses, the fabrics of rifting terrains and, during its later stages, by mantle plume impact. The African Superplume has installed an anomalously high subsurface temperature regime in the South-central, Eastern and Northeastern Africa regions. On this background is superimposed an anomalous temperature regime caused by two focused mantle plumes, one rising under Afar and the other from underneath the Tanzanian craton and spreading to the north and west. There is a strong correlation between high energy hydrothermal activity and these two temperature structures. Passive rifting, where the deep seated Superplume drives crustal extension is associated with the occurrence of hydrothermal features which are due to heating of meteoric water by circulation in the upper crust which is itself heated conductively by the tumescent mantle. Active rifting, where the focused plumes are involved in crust mantle interactions, is associated with hydrothermal activity which is attributed to the heating of the upper crust by mass and heat transfer from the upper mantle. To better understand the occurrence and development potentials of the variety of geothermal resources which the surface hydrothermal features may indicate, it is useful to account for the wide diversity in the modes of occurrence and characteristics of the features in the various EARS sectors. This is achieved by viewing the settings and characteristics of the features in light of rifting as an evolutionary continuum, amagmatic during its early stages, and later, engendering magmatism which itself evolves in stages from the initial eruption of primitive effusives to that of evolved volcanic products. Based on this, it is proposed that the above diversity arises from the different modes of hydrothermal fluid heating which prevail during the different stages of the evolving rifting process. |