The Western Branch of the East African Rift : A Review of Tectonics , Volcanology and Geothermal Activity (original) (raw)
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The geology and geothermal activity of the East African Rift
2014
The East Africa Rift System is a classical continental rift system associated with the world-wide mid ocean rift systems. The rift extends from the Red Sea – Afar triple junction through Ethiopian highlands, Kenya, Tanzania and Malawi to Mozambique in the south. The western branch passes through Uganda, DRC and Rwanda while the nascent south-western branch runs through Luangwa and Kariba rifts in Zambia into Botswana. The volcanic and tectonic activity in the rift started about 30 million years ago and in the eastern branch the activity involved faulting and eruption of large volumes of mafic and silicic lavas and pyroclastics. The western branch, typified by paucity of volcanism, is younger and dominated by faulting that has created deep basins currently filled with lakes and sediments. Geothermal activity in the rift is manifested by the occurrences of Quaternary volcanoes, hot springs, fumaroles, boiling pools, hot and steaming grounds, geysers and sulphur deposits. The manifesta...
The Geothermal Activity of the East African Rift
2007
The East Africa Rift System is a classical continental rift system associated with the world-wide mid ocean rift systems. The rift extends from the Red Sea – Afar triple junction through Ethiopian highlands, Kenya, Tanzania and Malawi to Mozambique in the south. The western branch passes through Uganda, DRC and Rwanda while the nascent south-western branch runs through Luangwa and Kariba rifts in Zambia into Botswana. The volcanic and tectonic activity in the rift started about 30 million years ago and in the eastern branch the activity involved faulting and eruption of large volumes of mafic and silicic lavas and pyroclastics. The western branch, typified by paucity of volcanism, is younger and dominated by faulting that has created deep basins currently filled with lakes and sediments. Geothermal activity in the rift is manifested by the occurrences of Quaternary volcanoes, hotsprings, fumaroles, boiling pools, hot and steaming grounds, geysers and sulphur deposits. The manifestat...
The Geology and geothermal activity of the East Africal Rift system
2013
The East Africa Rift System is a classical continental rift system associated with the worldwide mid ocean rift systems. The rift extends from the Red Sea-Afar triple junction through Ethiopian highlands, Kenya, Tanzania and Malawi to Mozambique in the south. The western branch passes through Uganda, DRC and Rwanda while the nascent southwestern branch runs through Luangwa and Kariba rifts in Zambia into Botswana. The volcanic and tectonic activity in the rift started about 30 million years ago and in the eastern branch the activity involved faulting and eruption of large volumes of mafic and silicic lavas and pyroclastics. The western branch, typified by paucity of volcanism, is younger and dominated by faulting that has created deep basins currently filled with lakes and sediments. Geothermal activity in the rift is manifested by the occurrences of Quaternary volcanoes, hot springs, fumaroles, boiling pools, hot and steaming grounds, geysers and sulphur deposits. The manifestations are abundant and stronger in the eastern branch that encompasses Afar, Ethiopian and Kenya rifts while in the western branch, the activity is subdued and occurs largely as hot springs and fumaroles. Detailed and reconnaissance studies of geothermal potential in Eastern Africa indicates that the region has potential of over 15,000MW e .
EAST AFRICAN RIFT SYSTEM -AN OVERVIEW
The main characteristics of the East African Rift System are outlined from selected references. The difference between the Eastern Rift with high volcanicity on two domal uplifts as against the Western Rift of restricted volcanism, but sediment and lake filled grabens is pointed out. This is also evident from the earthquake activity: Large earthquakes occur in the Western Rift, whereas earthquake swarms of mosty microseismic activity characterize the Eastern Rift. The difference is significant for the geothermal potential of the region. The high temperature geothermal systems are closely related to volcanic centres. High volcanoes are not easily accessible for developing geothermal reservoirs in their roots. But hot outflows at lower ground near to them may prove significant, however, of lower temperature. By mapping a volcanic system as a whole and defining a related fissure swarm of faults and eruptive fissures, local concentration of high activity may show up as possible geothermal targets.
Geology and the geothermal systems of the southern segment of the Kenya Rift
2003
The Kenya Rift is part of the East African Rift system, which is an active continental divergent zone. The Southern segment of the Kenya Rift Valley is a unique petrographic province comprising of at least four Quaternary to Recent volcanic complexes namely Suswa, Longonot, Olkaria, and Eburru. Although these volcanoes are located only about 40 km from each other, the eruptive products show marked compositional contrasts, requiring differences in magmatic processes. The rocks are characterised by subalkaline/peralkaline trachyte and/or peralkaline rhyolite volcanism with basalts being confined to eruption sites between individual centres. The segment of the Kenya Rift has anomalously high heat flow due to shallow intrusions. Active geothermal systems are associated with the volcanic centres. This paper summarizes the geology of the southern segment of the Kenya Rift and discusses reasons that indicate greater geothermal potential for Olkaria and Eburru and promising geothermal poten...
Thermal and mechanical development of the East African Rift System
1988
The deep basins, uplifted flanks, and volcanoes of the Western and Kenya rift systems have developed along the western and eastern margins of the 1300 km-wide East African plateau. Structural patterns deduced from field, Landsat, and geophysical studies in the Western rift reveal a series of asymmetric basins bounded by approximately 100 kmlong segments of the border fault system. These basins are linked by oblique-slip and strike-slip faults cross-cutting the rift valley. Faults bounding the Kenya and Western rift valleys delineate two north-south-trending, 40-75 km wide zones of crustal extension, and little or no crustal thinning has occurred beneath the uplifted flanks or the central plateau. In the Western rift, volcanism in Late Miocene time began prior to or concurrent with basinal subsidence, followed by rift flank uplift. Individual extensional basins developed diachronously, and basinal propagation may give rise to the along-axis segmentation of the rift valley. The coherence between gravity and topography data indicates that the mechanical lithosphere beneath the two rift valleys has been weakened relative to the central plateau and adjacent cratonic regions. Gravity and topography data at wavelengths corresponding to the overcompensated East African plateau can be explained by density variations within the upper mantle that are dynamically maintained.
Advances in the Geothermal Exploration of the East Africa Rift System
2019
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 cou...
2016
The workshop was funded by ARGeo-UNEP and ICEIDA and organized at the request of countries of the western branch of East African Rift System (EARS) arising from poor results from previous geothermal projects. The main objectives of the workshop were to discuss the geologic setting and conditions that support the development of geothermal systems in the countries of the western branch of East African Rift System (EARS). Further, the workshop was geared to understanding the occurrence, nature and characteristics of the geothermal systems in the western branch and to discuss the appropriate exploration methods. Some of the key findings were that it is likely that medium to high temperature geothermal systems exist at several localities within the western EARS and that majority of the systems can be described by fault controlled model. It is believed that some localities that are associated with volcanoes may have magmatic geothermal systems. It was recommended that exploration of fract...
Seismic images of magmatic rifting beneath the western branch of the East African rift
Geochemistry, Geophysics, Geosystems, 2013
1] We have performed a tomographic study using a joint data set that includes local and teleseismic events, recorded by a temporary network in the western branch of the East African rift system. From the travel time residuals, we derive a three-dimensional model of seismic P-wave velocity anomalies for the crust and upper mantle down to a depth of 80 km. Particular attention is paid to the verification of the inversion results by various resolution tests. The results show that the eastern rift shoulder is characterized by relatively high seismic velocities. Lower velocities are obtained beneath the entire length of the rift valley and the Rwenzori Mountains. A prominent feature is observed north-east of the mountain range: here we detected a vertically oriented, cylindrical low-velocity anomaly with maximum amplitudes in the middle crust and the upper mantle lithosphere. We suggest that this anomaly indicates reservoirs of molten material related to the ongoing rifting process within this segment of the rift. Just above this anomaly, at depths between 5 and 16 km, earthquake swarms exist. The observed reduction in P-wave velocity is used to provide constraints on the possible melt content and temperature anomaly in the uppermost mantle. The observed 3-5% P-velocity decrease can be explained by melt fraction up to 2%-3.3% or alternatively by a temperature increase of at least 248 to 376 K and even higher-temperature anomalies are possible if lower ambient temperatures in the reference mantle are assumed. Probably, the two effects act in combination.
Overview of Geothermal Resource Utilization in the East African Rift System
2011
The Great East African Rift System (EARS) is one of the major tectonic structures of the earth that extends for about 6500 km from the Middle East (Dead Sea-Jordan Valley) in the North to Mozambique in the south. This system consists of three main arms: the Red Sea Rift; the Gulf of Aden Rift; and the East African Rift which develops through Eritrea, Ethiopia, Kenya, Tanzania, Zambia, Malawi and northern Mozambique floored by a thinned continental crust. The EARS is composed of two rift trends; the eastern and western branches. The western branch develops from Uganda throughout lake Tanganyika, where it joins the Eastern branch, following the border between Rwanda and Zaire. The western branch is, however, much less active in terms of tectonics and volcanism although both branches are seismically and tectonically active today. The East African Rift is one of the most important zones of the world where the heat energy of the interior of the Earth escapes to the surface in the form of...