| Abstract |
We review results of geological, geochemical and geophysical investigations carried out within the frame of recent geothermal surveys in the East African Rift System (EARS). In particular, we focus on three of the most important geothermal fields namely Alalobeda (Ethiopia), Menengai (Kenya) and Ilwalilo-Kilambo (Tanzania). These fields well represent the different structural, volcanological and hydrogeological realms that may be encountered in EARS. Alalobeda and Menengai are examples of two possible geothermal play types of the Eastern Branch of EARS. The former is a fault-leakage-controlled geothermal system, located in a half-graben structure, where the heat source is likely diffuse, deep-seated magmatism, associated to the lithosphere thinning that regionally affects this area. The reservoir temperature of this water-dominated system ranges from 185 to 225 °C. The Menengai geothermal field can be classified as a convection-dominated magmatic play-type, where the heat source could be a magmatic intrusion (syenitic), located beneath the caldera. A shallow, liquid-dominated reservoir (with temperatures of 150-190 °C) and intermediate-deep reservoir, hosting steam and liquid (with temperatures of 230-340 °C) were detected. The Ilwalilo-Kilambo field is geothermal system located in a half-graben realm, in which the ascending groundwater flow is controlled by the main regional fault. Reservoir temperatures are of about 110-140 °C and the source of heat is provided by the elevated mantle. |