| Title | Geology of Extensional –TYPE Geothermal Systems in Uganda |
|---|---|
| Authors | A. Rusoke |
| Year | 2020 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | deep circulation, magmatic, amagmatic, extension-type geothermal systems |
| Abstract | Geothermal systems in East Africa are either magmatic or amagmatic/extensional-type systems. Magmatic driven systems rely on shallow magma chambers as their heat source for example in Ethiopia and Kenya while the extensional-type systems are associated with deep seated magma chambers. This clear distinction is highlighted in the subsurface temperature differences seen in the western and eastern branches of the East African Rift System. Most of Uganda’s geothermal systems are non-magmatic deep-circulation/extensional-type systems similar to the Great Basin in the USA and Western Turkey. In many respects, they typify other fault-controlled geothermal systems that are driven by deep circulation of ground waters. At these rift fault-bounded geothermal systems, fluid movement is controlled by the permeable rift fault zone that bounds the rift valley. During the rift formation in Uganda; there was extension, fracturing and thinning of the crust causing the mantle to become elevated which results in areas of elevated heat fluxes that are exploration targets for geothermal resources. The heat that drives these amagmatic systems is believed to result from active/extensional tectonics that permit the deep circulation of meteoric fluids through high angle faults and elevated heat flow that raises the temperature of fluids to 150˚C and above. The 3He/4He ratios of geothermal fluids from fault-bounded Kibiro Geothermal systems were measured to determine if a mantle signature was present, a value of 0.2 RA was obtained (Kato ,2018) therefore no signature was indicated. The fact that the Kibiro prospect area is not proximal to young volcanic/magmatic rocks and the absence of the mantle signature, supports the presence of extensional-type system. Soil gas and gas flux measurements have indicated high permeability concealed fault-bounded geothermal systems at Kibiro, Buranga and Panyimur areas. During exploration studies in Uganda, the exploration targets are at the points where the escarpment and the basin intersect, this is believed to be the location of the rift bounding faults controlling the up flow of geothermal fluids. |