Browsing by Author "Delvaux, Damien"

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    Fault Kinematics and Tectonic Stress in the Seismically Active Manyara–Dodoma Rift Segment in Central Tanzania – Implications for the East African Rift
    (2008-02) Macheyeki, Athanas S.; Delvaux, Damien; Batista, Marc De; Mruma, Abdulkarim H.
    The Eastern Branch of the East African Rift System is well known in Ethiopia (Main Ethiopian Rift) and Kenya (Kenya or Gregory Rift) and is usually considered to fade away southwards in the North Tanzanian Divergence, where it splits into the Eyasi, Manyara and Pangani segments. Further towards the south, rift structures are more weakly expressed and this area has not attracted much attention since the mapping and exploratory works of the 1950s. In November 4, 2002, an earthquake of magnitude Mb = 5.5 struck Dodoma, the capital city of Tanzania. Analysis of modern digital relief, seismological and geological data reveals that ongoing tectonic deformation is presently affecting a broad N–S trending belt, extending southward from the North Tanzanian Divergence to the region of Dodoma, forming the proposed “Manyara–Dodoma Rift segment”. North of Arusha–Ngorongoro line, the rift is confined to a narrow belt (Natron graben in Tanzania) and south of it, it broadens into a wide deformation zone which includes both the Eyasi and Manyara grabens. The two-stage rifting model proposed for Kenya and North Tanzania also applies to the Manyara–Dodoma Rift segment. In a first stage, large, well-expressed topographic and volcanogenic structures were initiated in the Natron, Eyasi and Manyara grabens during the Late Miocene to Pliocene. From the Middle Pleistocene onwards, deformations related to the second rifting stage propagated southwards to the Dodoma region. These young structures have still limited morphological expressions compared to the structures formed during the first stage. However, they appear to be tectonically active as shown by the high concentration of moderate earthquakes into earthquake swarms, the distribution of He-bearing thermal springs, the morphological freshness of the fault scarps, and the presence of open surface fractures. Fault kinematic and paleostress analysis of geological fault data in basement rocks along the active fault lines show that recent faults often reactivate older fault systems that were formed under E–W to NW–SE horizontal compression, compatible with late Pan-African tectonics. The present-day stress inverted from earthquake focal mechanisms shows that the Manyara–Dodoma Rift segment is presently subjected to an extensional stress field with a N080°E direction of horizontal principal extension. Under this stress field, the rift develops by: (1) reactivation of the pre-existing tectonic planes of weakness, and (2) progressive development of a new fault system in a more N–S trend by the linkage of existing rift faults. This process started about 1.2 Ma ago and is still ongoing.
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    Major Pan-African Imprints in the Ubendian Belt of SW Tanzania
    (1992) Theunissen, K.; Lenoir, J. L.; Liégeois, J. P.; Delvaux, Damien; Mruma, Abdulkarim H.
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    Quaternary Ostracodes and Molluscs from the Rukwa Basin (Tanzania) and Their Evolutionary and Paleobiogeographic Implications
    (Elsevier, 2013) Cohen, Andrew S.; Van Bocxlaerb, Bert; Todd, Jonathan A.; McGlue, Michael; Michel, Ellinor; Nkotagu, Hudson H.; Groveg, A.T.; Delvaux, Damien
    Much of the spectacular biodiversity of the African Great Lakes is endemic to single lake basins so that the margins of these basins or their lakes coincide with biogeographic boundaries. Longstanding debate surrounds the evolution of these endemic species, the stability of bioprovinces, and the exchange of faunas between them over geologic time as the rift developed. Because these debates are currently unsettled, we are uncertain of how much existing distribution patterns are determined by modern hydrological barriers versus reflecting past history. This study reports on late Quaternary fossils from the Rukwa Basin and integrates geological and paleoecological data to explore faunal exchange between freshwater bioprovinces, in particular with Lake Tanganyika. Lake Rukwa's water level showed large fluctuations over the last 25 ky, and for most of this period the lake contained large habitat diversity, with different species assemblages and taphonomic controls along its northern and southern shores. Comparison of fossil and modern invertebrate assemblages suggests faunal persistence through the Last Glacial Maximum, but with an extirpation event that occurred in the last 5 ky. Some of the molluscs and ostracodes studied here are closely related to taxa (or part of clades) that are currently endemic to Lake Tanganyika, but others testify to wider and perhaps older faunal exchanges between the Rukwa bioprovince and those of Lake Malawi and the Upper Congo (in particular Lake Mweru). The Rukwa Basin has a long history of rifting and lacustrine conditions and, at least temporarily, its ecosystems appear to have functioned as satellites to Lake Tanganyika in which intralacustrine speciation occurred. Paleontological studies of the Rukwa faunas are particularly relevant because of the basin's important role in the late Cenozoic biogeography of tropical Africa, and because many of the molecular traces potentially revealing this history would have been erased in the late Holocene extirpation.
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    Quaternary Ostracodes and Molluscs from the Rukwa Basin (Tanzania) and their Evolutionary and Paleobiogeographic Implications
    (2013-12) Cohen, Andrew S.; Bocxlaerb, Bert V.; Toddc, Jonathan A.; McGlued, Michael; Michele, Ellinor; Nkotagu, Hudson H.; Groveg, A.T.; Delvaux, Damien
    Much of the spectacular biodiversity of the African Great Lakes is endemic to single lake basins so that the margins of these basins or their lakes coincide with biogeographic boundaries. Longstanding debate surrounds the evolution of these endemic species, the stability of bioprovinces, and the exchange of faunas between them over geologic time as the rift developed. Because these debates are currently unsettled, we are uncertain of how much existing distribution patterns are determined by modern hydrological barriers versus reflecting past history. This study reports on late Quaternary fossils from the Rukwa Basin and integrates geological and paleoecological data to explore faunal exchange between freshwater bioprovinces, in particular with Lake Tanganyika. Lake Rukwa's water level showed large fluctuations over the last 25 ky, and for most of this period the lake contained large habitat diversity, with different species assemblages and taphonomic controls along its northern and southern shores. Comparison of fossil and modern invertebrate assemblages suggests faunal persistence through the Last Glacial Maximum, but with an extirpation event that occurred in the last 5 ky. Some of the molluscs and ostracodes studied here are closely related to taxa (or part of clades) that are currently endemic to Lake Tanganyika, but others testify to wider and perhaps older faunal exchanges between the Rukwa bioprovince and those of Lake Malawi and the Upper Congo (in particular Lake Mweru). The Rukwa Basin has a long history of rifting and lacustrine conditions and, at least temporarily, its ecosystems appear to have functioned as satellites to Lake Tanganyika in which intralacustrine speciation occurred. Paleontological studies of the Rukwa faunas are particularly relevant because of the basin's important role in the late Cenozoic biogeography of tropical Africa, and because many of the molecular traces potentially revealing this history would have been erased in the late Holocene extirpation.
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    Quaternary Ostracodes and Molluscs from the Rukwa Basin (Tanzania) and their Evolutionary and Paleobiogeographic Implications
    (2013-09) Bert Van Bocxlaer; Cohen, Andrew S.; Bocxlaer, Bert V.; Todd, Jonathan A.; McGlue, Michael; Michel, Ellinor; Nkotagu, Hudson H.; Groveg, A.T.; Delvaux, Damien
    Much of the spectacular biodiversity of the African Great Lakes is endemic to single lake basins so that the margins of these basins or their lakes coincide with biogeographic boundaries. Longstanding debate surrounds the evolution of these endemic species, the stability of bioprovinces, and the exchange of faunas between them over geologic time as the rift developed. Because these debates are currently unsettled, we are uncertain of how much existing distribution patterns are determined by modern hydrological barriers versus reflecting past history. This study reports on late Quaternary fossils from the Rukwa Basin and integrates geological and paleoecological data to explore faunal exchange between freshwater bioprovinces, in particular with Lake Tanganyika. Lake Rukwa's water level showed large fluctuations over the last 25 ky, and for most of this period the lake contained large habitat diversity, with different species assemblages and taphonomic controls along its northern and southern shores. Comparison of fossil and modern invertebrate assemblages suggests faunal persistence through the Last Glacial Maximum, but with an extirpation event that occurred in the last 5 ky. Some of the molluscs and ostracodes studied here are closely related to taxa (or part of clades) that are currently endemic to Lake Tanganyika, but others testify to wider and perhaps older faunal exchanges between the Rukwa bioprovince and those of Lake Malawi and the Upper Congo (in particular Lake Mweru). The Rukwa Basin has a long history of rifting and lacustrine conditions and, at least temporarily, its ecosystems appear to have functioned as satellites to Lake Tanganyika in which intralacustrine speciation occurred. Paleontological studies of the Rukwa faunas are particularly relevant because of the basin's important role in the late Cenozoic biogeography of tropical Africa, and because many of the molecular traces potentially revealing this history would have been erased in the late Holocene extirpation.
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    Strain Accommodation by Slow Slip and Dyking in a Youthful Continental Rift, East Africa
    (2008) Calais, Eric; d’Oreye, Nicolas; Albaric, Julie; Deschamps, Anne; Delvaux, Damien; Déverchère, Jacques; Ebinger, Cynthia; Ferdinand, Richard W.; Kervyn, François; Macheyeki, Athanas S.; Oyen, Anneleen; Perrot, Julie; Saria, Elifuraha; Smets, Benoit; Stamps, Sarah D.; Wauthier, Christelle
    Continental rifts begin and develop through repeated episodes of faulting and magmatism, but strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented. In highly evolved rifts, tensile stresses from far-field plate motions accumulate over decades before being released during relatively short time intervals by faulting and magmatic intrusions. These rifting crises are rarely observed in thick lithosphere during the initial stages of rifting. Here we show that most of the strain during the July-August 2007 seismic crisis in the weakly extended Natron rift, Tanzania, was released aseismically. Deformation was achieved by slow slip on a normal fault that promoted subsequent dyke intrusion by stress unclamping. This event provides compelling evidence for strain accommodation by magma intrusion, in addition to slip along normal faults, during the initial stages of continental rifting and before significant crustal thinning.