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Sample records for africa rift system

  1. Seismic Migration Imaging of the Lithosphere beneath the Afar Rift System, East Africa

    NASA Astrophysics Data System (ADS)

    Lee, T. T. Y.; Chen, C. W.; Rychert, C.; Harmon, N.

    2015-12-01

    The Afar Rift system in east Africa is an ideal natural laboratory for investigating the incipient continental rifting, an essential component of plate tectonics. The Afar Rift is situated at the triple junction of three rifts, namely the southern Red Sea Rift, Gulf of Aden Rift and Main Ethiopian Rift (MER). The ongoing continental rifting at Afar transitions to seafloor spreading toward the southern Red Sea. The tectonic evolution of Afar is thought to be influenced by a mantle plume, but how the plume affects and interacts with the Afar lithosphere remains elusive. In this study, we use array seismic data to produce high-resolution migration images of the Afar lithosphere from scattered teleseismic wavefields to shed light on the lithospheric structure and associated tectonic processes. Our preliminary results indicate the presence of lithospheric seismic discontinuities with depth variation across the Afar region. Beneath the MER axis, we detect a pronounced discontinuity at 55 km depth, characterized by downward fast-to-slow velocity contrast, which appears to abruptly deepen to 75 km depth to the northern flank of MER. This discontinuity may be interpreted as the lithosphere-asthenosphere boundary. Beneath the Ethiopian Plateau, on the other hand, a dipping structure with velocity increase is identified at 70-90 km depth. Further synthesis of observations from seismic tomography, receiver functions, and seismic anisotropy in the Afar region will offer better understanding of tectonic significance of the lithospheric discontinuities.

  2. Surface Wave Analysis of Regional Earthquakes in the Eastern Rift System (Africa)

    NASA Astrophysics Data System (ADS)

    Oliva, S. J. C.; Guidarelli, M.; Ebinger, C. J.; Roecker, S. W.; Tiberi, C.

    2015-12-01

    The Northern Tanzania Divergence (NTD), the youngest part of the East African Rift System, presents the opportunity to obtain insights about the birth and early stages of rifting before it progresses to mature rifting and seafloor spreading. This region is particularly interesting because the Eastern rift splits into three arms in this area and develops in a region of thick and cold lithosphere, amid the Archaean Tanzanian craton and the Proterozoic orogenic belt (the Masai block). We analyzed about two thousand seismic events recorded by the 39 broadband stations of the CRAFTI network during its two-year deployment in the NTD area in 2013 to 2014. We present the results of surface wave tomographic inversion obtained from fundamental-mode Rayleigh waves for short periods (between 4 to 14 seconds). Group velocity dispersion curves obtained via multiple filter analysis are path-averaged and inverted to produce 0.1º x 0.1º nodal grid tomographic maps for discrete periods using a 2D generalization of the Backus and Gilbert method. To quantify our results in terms of S-wave velocity structure the average group velocity dispersion curves are then inverted, using a linearized least-squares inversion scheme, in order to obtain the shear wave velocity structure for the upper 20 km of the crust. Low velocity anomalies are observed in the region 50 km south of Lake Natron, as well as in the area of the Ngorongoro crater. The implications of our results for the local tectonics and the development of the rifting system will be discussed in light of the growing geophysical database from this region.

  3. Mesozoic and early Tertiary rift tectonics in East Africa

    NASA Astrophysics Data System (ADS)

    Bosworth, William

    1992-08-01

    A complex history of crustal extension occurred in east and central Africa during the Mesozoic and early Tertiary. Beginning in the Late Jurassic, this resulted in a large system of rifts, the Central African rift system, that spanned from central Sudan to southern Kenya. Late Jurassic rifting is best documented in the White and Blue Nile rifts of the Sudan, and records east-west extension in half-graben that were connected by large-scale shear zones and pull-apart basins. Early Cretaceous rifting re-activated Jurassic basins and spread to the large South Sudan rifts and Anza rift in Kenya. By the Late Cretaceous, the extension direction shifted to the NE-SW, and the presently observed large-scale rift geometry was established. In the early Tertiary, some Mesozoic basins were again reactivated, while other regions underwent wrench faulting and basin inversion. The large number of basins preserved in the Central African rift system can be used to construct an evolutionary model of continental rift tectonics. Early phases of extension at low strains produced alternating half-graben/accommodation zone geometries similar to those observed in most young and active continental rifts. At higher strains, some border faults were abandoned so that through-going, simpler active fault systems could evolve. This is interpreted as representing a switch from complex, oppositely dipping detachment structures, with strike dimensions of 50-150 km, to regional detachment structures that continue for hundreds of kilometers parallel to the rift. This change in the type of detachment was accompanied by a shift in the position of the subsidence away from the breakaway to a position focused further within the regional upper plate. Non-rotational, high angle, normal faulting dominates in the development of these late basin geometries. Deciphering similar rift basin histories from passive continental margins may, in many cases, exceed the limits of available reflection seismic data. East

  4. Continental rift evolution: From rift initiation to incipient break-up in the Main Ethiopian Rift, East Africa

    NASA Astrophysics Data System (ADS)

    Corti, Giacomo

    2009-09-01

    The Main Ethiopian Rift is a key sector of the East African Rift System that connects the Afar depression, at Red Sea-Gulf of Aden junction, with the Turkana depression and Kenya Rift to the South. It is a magmatic rift that records all the different stages of rift evolution from rift initiation to break-up and incipient oceanic spreading: it is thus an ideal place to analyse the evolution of continental extension, the rupture of lithospheric plates and the dynamics by which distributed continental deformation is progressively focused at oceanic spreading centres. The first tectono-magmatic event related to the Tertiary rifting was the eruption of voluminous flood basalts that apparently occurred in a rather short time interval at around 30 Ma; strong plateau uplift, which resulted in the development of the Ethiopian and Somalian plateaus now surrounding the rift valley, has been suggested to have initiated contemporaneously or shortly after the extensive flood-basalt volcanism, although its exact timing remains controversial. Voluminous volcanism and uplift started prior to the main rifting phases, suggesting a mantle plume influence on the Tertiary deformation in East Africa. Different plume hypothesis have been suggested, with recent models indicating the existence of deep superplume originating at the core-mantle boundary beneath southern Africa, rising in a north-northeastward direction toward eastern Africa, and feeding multiple plume stems in the upper mantle. However, the existence of this whole-mantle feature and its possible connection with Tertiary rifting are highly debated. The main rifting phases started diachronously along the MER in the Mio-Pliocene; rift propagation was not a smooth process but rather a process with punctuated episodes of extension and relative quiescence. Rift location was most probably controlled by the reactivation of a lithospheric-scale pre-Cambrian weakness; the orientation of this weakness (roughly NE-SW) and the Late

  5. Neotectonic faults and stress field in the East African Rift System around the Tanzanian Craton - A contribution to the seismotectonic map of Africa

    NASA Astrophysics Data System (ADS)

    Delvaux, Damien; Macheyeki, Athanas Simon; Fernandes, Rui-Manuel; Ayele, Atalay; Meghraoui, Mustapha

    2015-04-01

    As a contribution to the UNESCO-IUGS IGCP 601 project "Seismotectonics and seismic hazards in Africa" and in preparation of the Seismotectonic Map of Africa, we compiled the neotectonic faults related to the East African Rift System around the Tanzanian craton. The initial aim was to identify and map the potentially active faults. Faults are usually defined as active when they show seismogenic displacement during the last 10,000 to 100,000 years, generally on the basis of paleoseismic investigation. In East Africa, however, very few faults have been studied by paleoseismic techniques and even fewer have known historical seismic activation. To address this issue, we mapped faults that show morphological indications of displacement. We used the SRTM DTM (90 and 30 m when available to us), with artificial shading as basis for identify neotectonic faults, in combination with existing data from geological maps, publications and reports, complemented by our own field observations. Thermal springs often occur along tectonically active faults. We use them to distinguish present-day faulting from other mapped faults as they are in most cases structurally controlled. In parallel, we used also the available focal mechanisms and geological fault-slip data to constrain the stress second-order stress field (at the scale of rift segments) and locally also the third-order stress field (at the local scale). All these elements are combined and compared with existing kinematic models for the East African Rift based on earthquake slip vectors, GPS measurements and geologic indicators. The comparison evidences some local discrepancies between the stress field and the direction of opening, probably due to the interactions between different rift segments, as in the Rukwa rift, Mbeya southern junction between the eastern and western rift branches, and in the Manyara-Natron area.

  6. A Rift Valley fever risk surveillance system for Africa using remotely sensed data: potential for use on other continents.

    PubMed

    Linthicum, Kenneth J; Anyamba, Assaf; Britch, Seth C; Chretien, Jean-Paul; Erickson, Ralph L; Small, Jennifer; Tucker, Compton J; Bennett, Kristine E; Mayer, Richard T; Schmidtmann, Edward T; Andreadis, Theodore G; Anderson, John F; Wilson, William C; Freier, Jerome E; James, Angela M; Miller, Ryan S; Drolet, Barbara S; Miller, Scott N; Tedrow, Christy A; Bailey, Charles L; Strickman, Daniel A; Barnard, Donald R; Clark, Gary G; Zou, Li

    2007-01-01

    The authors developed a monitoring and risk mapping system using normalized difference vegetation index (NDVI) times series data derived from the advanced very high resolution radiometer (AVHRR) instrument on polar orbiting national oceanographic and atmospheric administration (NOAA) satellites to map areas with a potential for a Rift Valley fever (RVF) outbreaks in sub-Saharan Africa. This system is potentially an important tool for local, national and international organisations involved in the prevention and control of animal and human disease, permitting focused and timely implementation of disease control strategies several months before an outbreak. We are currently developing a geographic information system (GIS)-based remotely sensed early warning system for potential RVF vectors in the United States. Forecasts of the potential emergence of mosquito vectors will be disseminated throughout the United States, providing several months' warning in advance of potentially elevated mosquito populations. This would allow timely, targeted implementation of mosquito control, animal quarantine and vaccine strategies to reduce or prevent animal and human disease. PMID:20422546

  7. Early Cretaceous rifts of Western and Central Africa: an overview

    NASA Astrophysics Data System (ADS)

    Guiraud, René; Maurin, Jean-Christophe

    1992-10-01

    The structure and evolution of Early Cretaceous rift basins in Western and Central Africa are described. Two stages of rift development and fracturing have been identified: (1) from Neocomian to Early Aptian roughly E-W and NW trending troughs (Upper Benue, N Cameroon, S Chad, Sudan etc.) opened in response to a submeridian extensional regime in Central Africa while in Western Africa the N-S trending transsaharian fault zone acted as a sinistral wrench; (2) from Middle Aptian to Late Albian large northwest trending troughs (E Niger, Sudan, Sirte, etc.) opened in response to a northeast extensional regime while the Central African fault zone (from Benue to Sudan) exhibited strike-slip movements, generating pull-apart basins. These rift and fracture systems delimit three large blocks within the African plate: a Western block, an Arabian-Nubian block and an Austral block. The Arabian-Nubian block tends to separate from the two other blocks, migrating towards the north during the first stage of basin development and then towards the NE during the second stage. The opening of the Atlantic Ocean was the dominant driving force for the Western and Austral blocks while the Arabian-Nubian block probably moved in response to the opening of the Indian Ocean and to the evolution of the Tethyan margin.

  8. Transition From a Magmatic to a Tectonic Rift System : Seismotectonics of the Eyasi- Manyara Region, Northern Tanzania, East Africa

    NASA Astrophysics Data System (ADS)

    Albaric, J.; Perrot, J.; Deschamps, A.; Deverchere, J.; Wambura, R. F.; Tiberi, C.; Petit, C.; Le Gall, B.; Sue, C.

    2008-12-01

    How a rift system propagates and breaks throughout a cold and thick continental crust remains poorly known. Only few places allow to address the question. In the East African Rift System (EARS), the eastern magma- rich branch abruptly splits into two amagmatic arms (the Eyasi and Manyara faulted systems), south of a E-W volcanic chain (the Ngorongoro-Kilimanjaro transverse volcanic belt), as crossing the Archaean Tanzanian craton margin. We present the first detailed seismotectonic picture of the Eyasi-Manyara rifts where a network of ~25 seismometers was settled from June to November 2007 (SEISMO-TANZ'07 seismological experiment). From the seismicity recorded by the network, we identify active faults and discuss the stress field framework obtained from the inversion of focal mechanisms. We use the determined depth of earthquakes (1) to discuss the crustal structure of the transition zone from a magma-rich to a magma-starved section of the EARS and (2) to further emphasize the rheological control on depth distributions in the EARS (Albaric et al., Tectonophysics, 2008). The stress and strain directions deduced from our work are also used to question recently published kinematics and conceptual models of the EARS (Calais et al., Geol. Soc. London, 2006 ; Le Gall et al., Tectonophysics, 2008).

  9. Gravity study of the Central African Rift system: A model of continental disruption 1. The Ngaoundere and Abu Gabra Rifts

    NASA Astrophysics Data System (ADS)

    Browne, S. E.; Fairhead, J. D.

    1983-05-01

    A regional compilation of published and unpublished gravity data for Central Africa is presented and reveals the presence of a major rift system, called here, the Central African Rift System. It is proposed that the junction area between the Ngaoundere and Abu Gabra rift arms in Western Sudan forms an incipient intraplate, triple-junction with the as yet unfractured, but domally uplifted and volcanically active, Darfur swell. It is only the Darfur swell that shows any similarities to the uplift and rift history of East Africa. The other two rifts arms are considered to be structurally similar to the early stages of passive margin development and thus reflect more closely the initial processes of continental fragmentation than the structures associated with rifting in East Africa.

  10. A Rift Valley Fever Risk Surveillance System in Africa Using Remotely Sensed Data in a GIS: Potential for Use on Other Continents

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a mosquito-borne viral disease with pronounced health and economic impacts to domestic animals and humans in much of sub-Saharan Africa (1). The disease causes high mortality and abortion in domestic animals, and significant morbidity and mortality in humans. RVF epizootic...

  11. Mapping Extensional Structures in the Makgadikgadi Pans, Botswana with remote sensing and aeromagnetic data: Implication for the continuation of the East African Rift System in southern Africa

    NASA Astrophysics Data System (ADS)

    Fetkovich, E. J.; Atekwana, E. A.; Abdelsalam, M. G.; Atekwana, E. A.; Katumwehe, A. B.

    2015-12-01

    We used Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) and aeromagnetic data to map extensional structures in the Makgadikgadi Pans in northeastern Botswana. These pans are a major morphological feature in Southern Africa characterized by the presence of low lying and flat topography with the highest elevation of 945 m. This topography was a result of multiple filling and desiccation of paleo-lakes that accompanied alternation of wetter and dryer climate during the Late Quaternary period. The objective of our study was to map the extent and distribution of normal faults using their morphological expression and magnetic signature, and examine their relationship with paleo-shorelines of the pans. We: (1) Created a hill shade relief map from the SRTM DEM; (2) Extracted regional NW-SE trending topographic profiles across the pans; (3) Constructed displacement profiles for major normal faults; and (4) Created tilt derivative images from the aeromagnetic data. We found that: (1) The northeastern part of the pan is dissected by three morphologically-defined NE-trending normal faults. The along strike continuity of these faults is in the range of 75 and 170 km and they are spaced at ~30 km apart from each other. (2) The topographic profiles suggest that the exposed minimum vertical displacement (EMVD), defined by poorly developed escarpments, is in the range of 0 m and 49 m. (3) The displacement profiles of the faults is characterized by maximum EMVD in the middle of the faults and that it decays towards the fault tips. These faults are also apparent in the aeromagnetic maps where they seem to displace E-W trending Karoo-age dikes. (4) At least the outer paleo-shoreline of the pans is modified by the NE-trending faults. This suggests that the faults are younger than the paleo-shorelines, which is suggested to have been developed between 500 and 100 ka. Traditionally, the southwestern extension of the East African Rift System has been assigned to the

  12. Images of the East Africa Rift System from the Joint Inversion of Body Waves, Surface Waves, and Gravity: Investigating the Role of Magma in Early-Stage Continental Rifting

    NASA Astrophysics Data System (ADS)

    Roecker, S. W.; Ebinger, C. J.; Tiberi, C.; Mulibo, G. D.; Ferdinand-Wambura, R.; Muzuka, A.; Khalfan, M.; Kianji, G.; Gautier, S.; Albaric, J.; Peyrat, S.

    2015-12-01

    With several rift segments at different stages of the rifting cycle, and the last orogenic episode more than 500 Mya, the young (<7 My) Eastern rift system in northern Tanzania and southern Kenya offers an ideal venue to study the role of magma and other fluids in continental rifting. To estimate both the location and volume of magma beneath the rift system, we generated 3D elastic wave images of the crust and uppermost mantle of this region by analyzing data recorded by a local deployment of 40 broad band seismic stations over a period of two years. We jointly inverted P and S wave arrival times from locally recorded earthquakes with Rayleigh wave dispersion curves derived from cross correlating ambient noise. These results were combined with Bouguer gravity anomalies to increase resolution and add constraints. The ambient noise signal appears to be channeled along the axis of the rift system, suggesting a waveguide effect. Tests with synthetic data estimate a spatial resolution in our images on the order of a few km. Our results demonstrate fundamental modifications of continental crustal structure by magmatic processes during the first few My of rift basin development. To first order, our models are dominated by regions of exceptionally low (by 10-20%) shear wavespeed relative to that of average continental crust. To a large extent the wavespeeds mimic the topography, with the slowest shear wave speeds corresponding to the lowest elevations, and tracing out a NE-SW striking region about 20 km wide from the Natron basin in the north to a NW-SE region of similar width beneath the Manyara basin in the south. These low wavespeeds are likely to be a consequence of the presence of magma and other fluids from at least 30 km depth, the limit of depth resolution for this dataset and near the base of the crust (~35 km), and extending to upper crustal levels in some areas. Somewhat surprisingly, a second region of significant low wavespeed beneath the Ngorongoro caldera

  13. The East African rift system

    NASA Astrophysics Data System (ADS)

    Chorowicz, Jean

    2005-10-01

    This overview paper considers the East African rift system (EARS) as an intra-continental ridge system, comprising an axial rift. It describes the structural organization in three branches, the overall morphology, lithospheric cross-sections, the morphotectonics, the main tectonic features—with emphasis on the tension fractures—and volcanism in its relationships with the tectonics. The most characteristic features in the EARS are narrow elongate zones of thinned continental lithosphere related to asthenospheric intrusions in the upper mantle. This hidden part of the rift structure is expressed on the surface by thermal uplift of the rift shoulders. The graben valleys and basins are organized over a major failure in the lithospheric mantle, and in the crust comprise a major border fault, linked in depth to a low angle detachment fault, inducing asymmetric roll-over pattern, eventually accompanied by smaller normal faulting and tilted blocks. Considering the kinematics, divergent movements caused the continent to split along lines of preexisting lithospheric weaknesses marked by ancient tectonic patterns that focus the extensional strain. The hypothesis favored here is SE-ward relative divergent drifting of a not yet well individualized Somalian plate, a model in agreement with the existence of NW-striking transform and transfer zones. The East African rift system comprises a unique succession of graben basins linked and segmented by intracontinental transform, transfer and accommodation zones. In an attempt to make a point on the rift system evolution through time and space, it is clear that the role of plume impacts is determinant. The main phenomenon is formation of domes related to plume effect, weakening the lithosphere and, long after, failure inducing focused upper mantle thinning, asthenospheric intrusion and related thermal uplift of shoulders. The plume that had formed first at around 30 Ma was not in the Afar but likely in Lake Tana region (Ethiopia

  14. Is the Ventersdorp rift system of southern Africa related to a continental collision between the Kaapvaal and Zimbabwe Cratons at 2.64 Ga AGO?

    NASA Technical Reports Server (NTRS)

    Burke, K.; Kidd, W. S. F.; Kusky, T.

    1985-01-01

    Rocks of the Ventersdorp Supergroup were deposited in a system of northeast trending grabens on the Kaapvaal Craton approximately 2.64 Ga ago contemporary with a continental collision between the Kaapvaal and Zimbabwe Cratons. It is suggested that it was this collision that initiated the Ventersdorp rifting. Individual grabens strike at high angles toward the continental collision zone now exposed in the Limpopo Province where late orogenic left-lateral strike-slip faulting and anatectic granites are recognized. The Ventersdorp rift province is related to extension in the Kaapvaal Craton associated with the collision, and some analogy is seen with such rifts as the Shansi and Baikal Systems associated with the current India-Asia continental collision.

  15. Sedimentary deposits in response to rift geometry in Malawi, Africa

    SciTech Connect

    Bishop, M.G. )

    1991-03-01

    Sedimentary deposits of the Malawi continental rift basin are a direct result of topography and tectonics unique to rift structure. Recent models describe rifts as asymmetric half-graben connected in series by transfer of accommodation zones. Half-graben consist of roughly parallel, tilted fault blocks stepping up from the bounding fault zone where maximum subsidence occurs. The rift becomes a local baselevel and depocenter as regional drainage is shed away by the rift shoulders. Most of the sediments are derived locally due to internal drainage of connected basins, individual basins, and individual fault blocks. The patterns of sedimentation and facies associations depend on structural position at both fault block and half-graben scales. Drainage is directed and dammed by tilted fault blocks. Forward-tilted fault blocks form basinward-thickening sediment wedges filled with facies of axial fluvial systems, alluvial fault-scarp fans, and ponded swamp and lake deposits. These deposits are asymmetrically shifted toward the controlling fault and onlap the upthrown side of the block, ordinarily the site of erosion or nondeposition. Rivers entering the lake on back tilted fault blocks form large deltas resulting in basinward fining and thinning sediment wedges. Lacustrine, nearshore, shoreline, and lake shore plain deposits over multiple fault blocks record lake levels, water chemistry, and tectonic episodes. Tectonic movement periodically changes the basin depth, configuration, and baselevel. This movement results in widespread unconformities deposition and reworking of sediments within the rift.

  16. Cenozoic rifting in the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

    Granot, R.; Cande, S. S.; Stock, J. M.; Clayton, R. W.; Davey, F. J.

    2007-12-01

    The West Antarctic Rift System (WARS) experienced two episodes of Cenozoic rifting. Seafloor spreading at the Adare spreading axis, north of the Ross Sea, from Middle Eocene to Late Oligocene time (43 - 26 Ma), was directly linked with motions within the WARS. For this time interval, marine magnetic anomalies within the Adare Basin and structural features within the Ross Sea constrain the motion between East and West Antarctica. During this episode, widespread intrusive activity took place in the continental part of the rift. Subsequent Late Oligocene until present-day (26 - 0 Ma) extension was characterized by a transition to volcanic activity. Yet, the details of extension during this episode have been poorly resolved. We present preliminary results of new seismic reflection and seafloor mapping data acquired on geophysical cruise 07-01 aboard the R/VIB Nathaniel Palmer in the northern part of the rift. Our results suggest that the style of deformation changed from spreading-related faulting into diffuse normal faulting (tilted blocks) that trend NE-SW with little resultant E-W extension. Recent volcanism is distributed throughout but tends to align with the NE-SW trend, into a localized zone. Formation of the Terror Rift, Ross Sea, within the same time frame suggests that the pole of rotation has changed its position, reflecting a change in the relative magnitudes of tensile stresses along the rift. Moreover, this change was accompanied with a sharp decrease of extension rates.

  17. Initiation and development of the Kivu rift segment in Central Africa by reactivating un-favorably oriented structural weaknesses

    NASA Astrophysics Data System (ADS)

    Delvaux, Damien; Smets, Benoît

    2015-04-01

    The Kivu rift region forms the central segment of the western branch of the East African rift system, between the northern termination of the Tanganyika rift and the southern extension of the Edward-George rift. Its structure and geological evolution has been revised in the light of a compilation of existing data on earthquake epicenters, focal depth, focal mechanisms, thermal springs and neotectonic faults. It has long been shown that the link between the Kivu rift basin and the Northern termination of the Tanganyika rift basin forms an accommodation zone in which the Rusizi tectonic depression occupies a central place (Ebinger, 1989). In addition, our compilation suggests that the NNE-trending Kivu rift basin and the N-S northern half of the Tanganyika rift basin initiated as separated, partly overlapping and differently oriented basins. The orientation and development of the Kivu rift basin was controlled by an inferred Mid-Proterozoic crustal shear zone and a Pan-African reverse fault front. It was not optimally oriented with the general (first-order) stress field characterized by roughly E-W extension. In a later stage, the more optimally N-S oriented North Tanganyika basin progressed towards the North and connected to Kivu rift in its middle in a region now occupied by the town of Bukavu. This accommodation zone is marked by Quaternary volcanism, warm thermal springs, frequent and relatively shallow seismicity. The southwestern part of the Kivu rift became progressively abandoned but it is still seismically active and hosts a number of warm thermal springs. This particular architecture influences the present-day stress field. This work is a contribution to the Belgian GeoRisCA project. Ebinger, C.J. 1989. Geometric and kinematic development of border faults and accommodation zones, Kivu-Rusizi Rift, Africa. Tectonics, 8, 117-133

  18. Geophysical studies of the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

    Behrendt, J. C.; Lemasurier, W. E.; Cooper, A. K.; Tessensohn, F.; TréHu, A.; Damaske, D.

    1991-12-01

    and the Byrd Subglacial Basin areas). The near absence of earthquakes in the West Antarctic rift system probably results from a combination of primarily sparse seismograph coverage and, secondarily, suppression of earthquakes by the ice sheet (e.g., Johnston, 1987) and very high seismicity shortly after deglaciation in the Ross Embayment followed by abnormally low seismicity at present (e.g., Muir Wood, 1989). The evidence of high temperatures at shallow depth beneath the Ross Sea continental shelf and adjacent Transantarctic Mountains is supportive of thermal uplift of the mountains associated with lateral heat conduction from the rift and can possibly also explain the volcanism, rifting, and high elevation of the entire rift shoulder to the Ellsworth-Horlick-Whitmore Mountains. We infer that the Gondwana breakup and the West Antarctic rift are part of a continuously propagating rift that started in the Jurassic when Africa separated from East Antarctica (including the failed Jurassic Transantarctic rift). Rifting proceeded clockwise around East Antarctica to the separation of New Zealand and the Campbell Plateau about 85-95 Ma and has continued (with a spreading center jump) to its present location in the Ross Embayment and West Antarctica. The Cenozoic activity of the West Antarctic rift system appears to be continuous in time with rifting in the same area that began only in the late Mesozoic. Although the mechanism for rifting is not completely explained, we suggest a combination of the flexural rigidity model (Stem and ten Brink, 1989) proposed for the Ross Embayment and the thermal plume or hot spot concepts. The propagating rift may have been "captured" by the thermal plume.

  19. The Example of Eastern Africa: the dynamic of Rift Valley fever and tools for monitoring virus activity

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever is a mosquito-borne viral zoonosis that primarily affects animals but also has the capacity to infect humans. Outbreaks of this disease in eastern Africa are closely associated with periods of heavy rainfall and forecasting models and early warning systems have been developed to en...

  20. The Albertine Rift, East Africa: Initial rifting, long-term landscape evolution and final surface uplift

    NASA Astrophysics Data System (ADS)

    Bauer, Friederike U.; Glasmacher, Ulrich A.; Ring, Uwe; Grobe, René W.; Starz, Matthias; Mambo, Vikandy S.

    2013-04-01

    The Albertine Rift and associated Rwenzori Mountains form a striking feature at the north-western portion of the East African Rift System. The Rwenzori Mtns are built up by a dissected Precambrian metamorphic basement block that has been uplifted to heights of more than 5 km. The fundamental subject addressed by this study is the temporal and spatial evolution of the Rwenzori Mtns and adjacent Albertine Rift (western Uganda and Eastern Congo) at different time scales. In order to unlock how and at what time the extreme surface uplift occurred, low-temperature thermochronology methods were applied and combined with thermokinematic modelling. By means of apatite fission-track, apatite and zircon (U-Th-Sm)/He dating, combined with 2D (HeFTy) and 3D (Pecube) thermokinematic modelling different phases of landscape evolution could be determined for the Albertine area, where movements of surface uplift can be traced from Palaeozoic to Neogene times. Since the Palaeozoic several cooling events affected the Albertine area and Rwenzori Mtns, as revealed from samples along the rift shoulders and across the mountain range. Results from low-temperature thermochronology and thermokinematic modelling demonstrate that the Rwenzoris were not exhumed as a coherent block but are composed of distinct decoupled blocks with diverging exhumation histories and block movements along inherited faults. Thus, the evolution of the Rwenzoris was not solely triggered by Neogene rifting; moreover, a Mesozoic topographic Albertine high is conceivable. Since the Miocene renewed rock and surface uplift of distinct blocks with forced movements at the western flank of the Rwenzoris occurred. Rock uplift, thereby, outweighed erosion, resulting in the recent high topography of the Rwenzoris and their asymmetric character. Detrital thermochronology data confirm a Neogene surface uplift and indicate transition of erosional forces in Plio-/Pleistocene times. Thermokinematic modelling, applied to samples

  1. The Pongola structure of southeastern Africa - The world's oldest preserved rift?

    NASA Technical Reports Server (NTRS)

    Burke, K.; Kidd, W. S. F.; Kusky, T. M.

    1985-01-01

    Rocks of the Pongola Supergroup form an elongate belt in the Archean Kaapvaal Craton of southern Africa. Because these rocks exhibit many features that are characteristic of rocks deposited in continental rifts, including rapid lateral variations in thickness and character of sediments, volcanic rocks that are bimodal in silica content, coarse, basement derived conglomerates and thick sequences of shallow water sedimentary facies associations, it is suggested that the Pongola Supergroup was deposited in such a rift. The age of these rocks (approximately 3.0 Ga) makes the Pongola structure the world's oldest well-preserved rift so far recognized, and comparison of the Pongola Rift with other rifts formed more recently in earth history reveals striking similarities, suggesting that the processes that formed this rift were not significantly different from those that form continental rifts today.

  2. Combining detrital geochronology and sedimentology to assess basin development in the Rukwa Rift of the East African Rift System

    NASA Astrophysics Data System (ADS)

    Hilbert-Wolf, Hannah; Roberts, Eric; Mtelela, Cassy; Downie, Bob

    2015-04-01

    We have employed a multifaceted approach to sedimentary provenance analysis in order to assess the timing and magnitude of tectonic events, sedimentation, and landscape development in the Western Branch of the East African Rift System. Our approach, termed 'Sedimentary Triple Dating', integrates: (1) U-Pb dating via LA-ICPMS; (2) fission track; and (3) (U-Th)/He thermochronology of detrital zircon and apatite. We integrate geochronology, thermochronology, and provenance analysis to relate the initiation of rifting events to regional dynamic uplift, sedimentation patterns, and interpret the far-reaching climatic and evolutionary effects of fluctuating rift flank topography in the Rukwa Rift, a segment of the Western Branch. This work provides additional data to support the recent concept of synchronous development of the Western and Eastern branches of the East African Rift System ~25 Ma, and better constrains the age, location and provenance of subsequent rifting and sedimentation events in the Rukwa Rift Basin. Investigation of well cuttings and outcrop samples from the Neogene-Recent Lake Beds Succession in the Rukwa Rift Basin revealed a suite of previously unrecognized tuffaceous deposits at the base of the succession. A population of euhedral, magmatic zircons from a basal Lake Beds tuff and Miocene-Pliocene detrital zircons from well cuttings suggest that Neogene rift reactivation and volcanism began ~9-10 Ma. This timing is consistent with demonstrated rifting in Uganda and Malawi, as well as with the initiation of volcanism in the Rungwe Volcanic Province at the southern end of the Rukwa Rift, and the estimated development of Lake Tanganyika to the north. Moreover, there appear to be a suite of unconformity bounded stratigraphic units that make up the Lower Lake Beds succession, and detrital zircon maximum depositional ages from these units suggests episodic sedimentation in the rift, punctuated by long hiatuses or uplift, rather than steady subsidence and

  3. Intracontinental rift comparisons: Baikal and Rio Grande Rift Systems

    NASA Astrophysics Data System (ADS)

    Lipman, P. W.; Logatchev, N. A.; Zorin, Y. A.; Chapman, C. E.; Kovalenko, V.; Morgan, P.

    Both the Baikal rift in Siberia and the Rio Grande rift in New Mexico, Colorado and Texas are major intracontinental extensional structures of Cenozoic age that affect regions about 1500 km long and several hundred km wide (Figures 1, 2). In the summer of 1988 these rifts were visited by study groups of U.S. and Soviet geoscientists during cooperative field workshops sponsored by the Soviet Academy of Sciences, U.S. National Academy of Sciences, and U.S. Geological Survey.In the Rio Grande region, we spent 2 weeks examining rift features between El Paso, Tex., and Denver, Colo. Particular emphasis was on the sedimentary record of rift evolution, widespread volcanic activity from inception of rifting to the present, geophysical expression of rift features, and relations between rifting and the larger-scale evolution of the North American Cordillera. In the Baikal region, which presents formidable logistic problems for a workshop, we travelled by bus, truck, helicopter, and ship to examine young seismotectonic features, rift-related basalt, and bounding structures of the Siberian craton that influenced rift development (Figure 3).

  4. Gravity-driven structures and rift basin evolution: Rio Muni Basin, offshore equatorial West Africa

    SciTech Connect

    Turner, J.P.

    1995-08-01

    Offshore Equatorial Guinea, west Africa, gravity-driven nappes, more than 1 km thick and 15 km from head to toe, provide key evidence in reconstructing the late synrift: evolution of this part of the South Atlantic margin basin system. Furthermore, Aptian-Cenomanian carbonate and clastic rocks in the nappes` allochthonous hanging walls are attracting interest as a new exploration play in west Africa. The nappes exhibit a range of geometries that suggest they share many of the same deformation processes as thin-skin thrust and linked extensional fault systems. Not only are these structures significant in their own right, representing a rare example of gravity tectonics in the virtual absence of major halokinesis, but their presence may record an other-wise undetectable process active during the transition from a rift basin to a passive continental margin. A review of Equatorial Guinea in its pre-Atlantic configuration, alongside neighboring basins in Brazil (the Sergipe-Alagoas basin) and Gabon, suggests that gravity gliding was sustained by a relatively steep, westward paleoslope promoted by east-ward offset of the locus of thermal uplift from the rift basin (i.e., a simple shear model of basin formation). In contrast to gravity-driven structures in most postrift settings, the Equatorial Guinea nappes developed at the close of the Aptian-Albian synrift episode in response to a growing bathymetric deep caused by rapid subsidence outpacing restricted sedimentation.

  5. Post Rift Evolution of the Indian Margin of Southern Africa

    NASA Astrophysics Data System (ADS)

    Baby, Guillaume; Guillocheau, François; Robin, Cécile; Dall'asta, Massimo

    2016-04-01

    The objective of this study is to discuss the evolution of the South African Plateau along the Indian margin of Southern Africa. Since the classical works of A. du Toit and L.C. King and the improvement of thermochronological methods and numerical models, the question of the uplift of South African Plateau was highly debated with numerous scenarios: early Cretaceous at time of rifting (Van der Beek et al., J.Geophys.Res., 2002), late Cretaceous (Braun et al., Solid Earth, 2014), late Cenozoic (Burke & Gunnell, Geol.Soc.of America, 2008). Limited attention has been paid on the constraints provided by the offshore stratigraphic record of the surrounding margins. The objective of our study is to integrate onshore and offshore data (seismic profiles and industrial wells) to (1) analyse the infill of the whole margin (21°S to 31°S) from its hinterland to the distal deep water basin, (2) to constrain and quantify the vertical movements. We discuss the impact on accommodation and sediments partitioning, and their significance on South African Plateau uplift history. 1. Sedimentary basins of the Indian margin of Southern Africa are related to the break-up of Gondwana during late Jurassic, resulting in rifts and flexural basins. First marine incursions started during early Cretaceous times (oldest marine outcropping sediments are of Barremian age ~128 Ma). The region developed as a normal continental shelf at the Aptian-Albian transition (~113 Ma). 2. The Cretaceous geological history of the basins is characterized by differential uplift and subsidence of the basement, controlled by structures inherited from break up. As example, major early Cretaceous depocenters of the margin are located on the north of Save-Limpopo uplift (Forster, Paleogography, Paleoclimatology, Paleoecology, 1975) showing an eastward drainage pattern, maybe related to a proto Limpopo drainage. Those observations suggest that the escarpment bordering the Bushveld depression is an old relief inherited

  6. Kanda fault: A major seismogenic element west of the Rukwa Rift (Tanzania, East Africa)

    NASA Astrophysics Data System (ADS)

    Vittori, Eutizio; Delvaux, Damien; Kervyn, François

    1997-09-01

    The NW-SE trending Rukwa Rift, part of the East African Rift System, links the approximately N-S oriented Tanganyika and Nyassa (Malawi) depressions. The rift has a complex half-graben structure, generally interpreted as the result of normal and strike-slip faulting. Morphological and structural data (e.g. fault scarps, faceted spurs, tilting of Quaternary continental deposits, volcanism, seismicity) indicate Late Quaternary activity within the rift. In 1910 an earthquake of M = 7.4 (historically the largest felt in Africa) struck the Rukwa region. The epicentre was located near the Kanda fault, which affects the Ufipa plateau, separating the Rukwa depression from the south-Tanganyika basin. The geomorphic expression of the Kanda fault is a prominent fresh-looking scarp more than 180 km long, from Tunduma to north of Sumbawanga, that strikes roughly NW-SE, and dips constantly northeast. No evidence for horizontal slip was observed. Generally, the active faulting affects a very narrow zone, and is only locally distributed over several subparallel scarps. The height of the scarp progressively decreases towards the northwest, from about 40-50 m to a few metres north of Sumbawanga. Faulted lacustrine deposits exposed in a road cut near Kaengesa were dated as 8340 ± 700 and 13 600 ± 1240 radiocarbon years. These low-energy deposits now hang more than 15 m above the present-day valley floor, suggesting rapid uplift during the Holocene. Due to its high rate of activity in very recent times, the Kanda Fault could have produced the 1910 earthquake. Detailed paleoseismological studies are used to characterize its recent history. In addition, the seismic hazard posed by this fault, which crosses the fast growing town of Sumbawanga, must be seriously considered in urban planning.

  7. Mapping Mantle Mixing and the Extent of Superplume Influence Using He-Ne-Ar-CO2-N2 Isotopes: The Case of the East Africa Rift System

    NASA Astrophysics Data System (ADS)

    Hilton, D. R.; Halldorsson, S. A.; Scarsi, P.; Castillo, P.; Abebe, T.; Kulongoski, J. T.

    2014-12-01

    Earth's mantle possesses distinct and variable volatile characteristics as sampled by magmatic activity in different tectonic environments. In general, trace element depleted mid-ocean ridge basalts, with low Sr and Pb isotope values (but high ɛNd and ɛHf), release mantle-derived noble gases characterised by 3He/4He ~8 ± 1RA, (21Ne/22Ne)ex ~0.06 and 40Ar/36Ar ≥ 10,000 with CO2 and N2 having δ13C~-5‰ and δ15N ~-5‰, respectively. In contrast, enriched intraplate lavas possess higher 3He/4He (up to 50RA), lower (21Ne/22Ne)ex ~0.035 and 40Ar/36Ar ≤ 10,000 with generally higher but variable δ13C and δ15N. These isotopic attributes of mantle-derived volatiles can be exploited to map the extent, and mixing characteristics, of enriched (plume) mantle with depleted asthenospheric mantle ± the effects of over-riding lithosphere and/or crust. The East African Rift System (EARS) is superimposed upon two massive plateaux - the Ethiopia and Kenya domes - regarded as geophysical manifestations of a superplume source, a huge thermochemical anomaly originated at the core-mantle boundary and providing dynamic support for the plateaux. We present new volatile isotopic and relative abundance data (on the same samples) for geothermal fluids (He-CO2-N2), lavas (He-Ne-Ar) and xenoliths (He-Ne-Ar-CO2-N2) which provide an unprecedented overview of the distribution of mantle volatiles of the Ethiopia Dome, from the Red Sea via the Afar region and Main Ethiopian Rift (MER) to the Turkana Depression. Notably, peaks in geothermal fluid 3He/4He (16RA) and δ15N (+6.5‰) are coincident within the MER but the maximum δ13C (-0.78‰) lies ~100 km to the south. Highs in 3He/4He (14RA), δ13C (~-1‰) and δ15N (+3.4‰) for mafic crystals occur in the Afar region ~ 500km to the north. We assess the significance of the off-set in these volatile isotope signals, for sampling volatile heterogeneity in the plume source and/or the relative sensitivity of different volatiles to

  8. The onshore northeast Brazilian rift basins: An early Neocomian aborted rift system

    SciTech Connect

    Matos, R. )

    1990-05-01

    Early Cretaceous rift basins of northeastern Brazil illustrate key three-dimensional geometries of intracontinental rift systems, controlled mainly by the basement structures. These basins were formed and then abandoned during the early extension associated with the north-south-propagating separation of South America and Africa. During the early Neocomian, extensional deformation jumped from the easternmost basins (group 1: Sergipe Alagoas and Gabon basins; group 2: Reconcavo, Tucano, and Jatoba basins) to the west, forming a series of northeast-trending intracratonic basins (group 3: Araripe, Rio do Peixe, Iguatu, Malhada Vermelha, Lima Campos, and Potiguar basins). The intracratonic basins of groups 2 and 3 consist of asymmetric half-grabens separated by basement highs, transfer faults, and/or accommodation zones. These basins are typically a few tens of kilometers wide and trend northeast-southwest, roughly perpendicular to the main extension direction during the early Neocomian. Preexisting upper crustal weakness zones, like the dominantly northeast-southwest-trending shear zones of the Brazilian orogeny, controlled the development of intracrustal listric normal faults. Internal transverse structures such as transfer faults (Reconcavo basin and onshore Potiguar basin) and accommodation zones (onshore Potiguar basin and Araripe basin) were also controlled by the local basement structural framework. Transverse megafaults and lithostructural associations controlled the three main rift trends. The megashear zones of Pernanbuco (Brazil)-Ngaundere (Africa) apparently behaved like a huge accommodation zone, balancing extensional deformation along the Reconcavo-Jatoba/Sergipe Alagoas-Gabon trends with simultaneous extension along the Araripe-Potiguar trend. The Sergipe Alagoas-Gabon trend and the Potiguar basin represent the site of continued evolution into a marginal open basin following early Neocomian deformation.

  9. Mantle support of the East African Rift System

    NASA Astrophysics Data System (ADS)

    Lin, S.; van Keken, P. E.; Brandenburg, J. P.; Furman, T.; Bryce, J.

    2007-12-01

    The African Superplume is a region of slow seismic wave velocities in the lower mantle under southern Africa. The uplift, volcanism and rifting that defines the much of eastern and southern Africa suggest a dynamic link between lower mantle dynamics and near-surface processes affecting the African plate. The dynamic link between the lower mantle and the surface, and the structure and dynamics of the upper mantle below the East African Rift System (EARS) remain unclear. As part of a comprehensive geochemical and numerical investigation of basaltic magmatism in the EARS we have modeled the interaction between putative upper mantle plumes and the rifting continental lithosphere. The modeling provides dynamically tested scenarios that explain the observed episodes of Cenozoic volcanism. Results from recent models that provided an explanation for the present day distribution of volcanism (Lin et al., EPSL, 237, 2005) suggest two plumes below Afar and Tanzania whose uplift is influenced by lithospheric topography. In new 3D modeling we provide improved quantification of the mantle involvement in generating EARS volcanism as constrained by the timing of uplift and regional volcanism. The time scales of episodicity of the volcanism observed at Turkana (related to the Tanzania-Kenya plume) since 45 Ma can be explained by deep- seated time-dependent plume activity. We suggest that this time-dependence is due to thermochemical interactions of dense recycled oceanic crust in the thermally hot regions in the African superplume region (Lin and Van Keken, Nature, 436, 2005).

  10. The Offshore East African Rift System

    NASA Astrophysics Data System (ADS)

    Franke, D.; Klimke, J.; Jokat, W.; Stollhofen, H.; Mahanjane, S.

    2014-12-01

    Numerous studies have addressed various aspects of the East African Rift system but surprisingly few on the offshore continuation of the south-eastern branch of the rift into the Mozambique Channel. The most prominent article has been published almost 30 years ago by Mougenot et al. (1986) and is based on vintage seismic data. Several studies investigating earthquakes and plate motions from GPS measurements reveal recent deformation along the offshore branch of the East African Rift system. Slip vectors from earthquakes data in Mozambique's offshore basins show a consistent NE direction. Fault plane solutions reveal ~ E-W extensional failure with focal depth clustering around 19 km and 40 km, respectively. Here, we present new evidence for neotectonic deformation derived from modern seismic reflection data and supported by additional geophysical data. The modern rift system obviously reactivates structures from the disintegration of eastern Gondwana. During the Jurassic/Cretaceous opening of the Somali and Mozambique Basins, Madagascar moved southwards along a major shear zone, to its present position. Since the Miocene, parts of the shear zone became reactivated and structurally overprinted by the East African rift system. The Kerimbas Graben offshore northern Mozambique is the most prominent manifestation of recent extensional deformation. Bathymetry data shows that it deepens northwards, with approximately 700 m downthrown on the eastern shoulder. The graben can be subdivided into four subbasins by crosscutting structural lineaments with a NW-SE trend. Together with the N-S striking graben-bounding faults, this resembles a conjugate fault system. In seismic reflection data normal faulting is distinct not only at the earthquake epicenters. The faults cut through the sedimentary successions and typically reach the seafloor, indicating ongoing recent deformation. Reference: Mougenot, D., Recq, M., Virlogeux, P., and Lepvrier, C., 1986, Seaward extension of the East

  11. Environmental change and Rift Valley fever in eastern Africa: projecting beyond HEALTHY FUTURES.

    PubMed

    Taylor, David; Hagenlocher, Michael; Jones, Anne E; Kienberger, Stefan; Leedale, Joseph; Morse, Andrew P

    2016-01-01

    Outbreaks of Rift Valley fever (RVF), a relatively recently emerged zoonosis endemic to large parts of sub-Saharan Africa that has the potential to spread beyond the continent, have profound health and socio-economic impacts, particularly in communities where resilience is already low. Here output from a new, dynamic disease model [the Liverpool RVF (LRVF) model], driven by downscaled, bias-corrected climate change data from an ensemble of global circulation models from the Inter-Sectoral Impact Model Intercomparison Project run according to two radiative forcing scenarios [representative concentration pathway (RCP)4.5 and RCP8.5], is combined with results of a spatial assessment of social vulnerability to the disease in eastern Africa. The combined approach allowed for analyses of spatial and temporal variations in the risk of RVF to the end of the current century. Results for both scenarios highlight the high-risk of future RVF outbreaks, including in parts of eastern Africa to date unaffected by the disease. The results also highlight the risk of spread from/to countries adjacent to the study area, and possibly farther afield, and the value of considering the geography of future projections of disease risk. Based on the results, there is a clear need to remain vigilant and to invest not only in surveillance and early warning systems, but also in addressing the socio-economic factors that underpin social vulnerability in order to mitigate, effectively, future impacts. PMID:27063733

  12. Along-rift Variations in Deformation and Magmatism in the Ethiopian and Afar Rift Systems

    NASA Astrophysics Data System (ADS)

    Keir, D.; Bastow, I. D.; Corti, G.; Mazzarini, F.; Rooney, T. O.

    2015-12-01

    The geological record at rifts and margins worldwide often reveals along-strike variations in volumes of extruded and intruded igneous rocks. These variations may be the result of asthenospheric heterogeneity, variations in rate, and timing of extension; alternatively, preexisting plate architecture and/or the evolving kinematics of extension during breakup may exert first-order control on magmatism. The Ethiopian and Afar Rift systems provide an excellent opportunity to address this since it exposes, along strike, several sectors of asynchronous rift development from continental rifting in the south to incipient oceanic spreading in the north. Here we perform studies of distribution and style of volcanism and faulting along strike in the MER and Afar. We also incorporate synthesis of geophysical, geochemical, and petrological constraints on magma generation and emplacement in order to discriminate between tectonic and mantle geodynamic controls on the geological record of a newly forming magmatic rift. Along-rift changes in extension by magma intrusion and plate stretching, and the three-dimensional focusing of melt where the rift dramatically narrows each influence igneous intrusion, volcanism and subsidence history. In addition, rift obliquity plays an important role in localizing intrusion into the crust beneath en echelon volcanic segments. Along-strike variations in volumes and types of igneous rocks found at rifted margins thus likely carry information about the development of strain during rifting, as well as the physical state of the convecting mantle at the time of breakup.

  13. 3D Dynamics of Oblique Rift Systems: Fault Evolution from Rift to Break-up

    NASA Astrophysics Data System (ADS)

    Brune, S.

    2014-12-01

    Rift evolution and passive margin formation has been thoroughly investigated using conceptual and numerical models in two dimensions. However, the 2D assumption that the extension direction is perpendicular to the rift trend is often invalid. In fact, the majority of rift systems that lead to continental break-up during the last 150 My involved moderate to high rift obliquity. Yet, the degree to which oblique lithospheric extension affects first-order rift and passive margin properties like surface stress pattern, fault azimuths, and basin geometry, is still not entirely clear. This contribution provides insight in crustal stress patterns and fault orientations by applying a 3D numerical rift model to oblique extensional settings. The presented forward experiments cover the whole spectrum of oblique extension (i.e. rift-orthogonal extension, low obliquity, high obliquity, strike-slip deformation) from initial deformation to breakup. They are conducted using an elasto-visco-plastic finite element model and involve crustal and mantle layers accounting for self-consistent necking of the lithosphere. Even though the model setup is very simple (horizontally layered, no inherited faults), its evolution exhibits a variety of fault orientations that are solely caused by the interaction of far-field stresses with rift-intrinsic buoyancy and strength. Depending on rift obliquity, these orientations involve rift-parallel, extension-orthogonal, and intermediate normal fault directions as well as strike-slip faults. Allowing new insights on fault patterns of the proximal and distal margins, the model shows that individual fault populations are activated in a characteristic multi-phase evolution driven by lateral density variations of the evolving rift system. Model results are in very good agreement with inferences from the well-studied Gulf of Aden and provide testable predictions for other rifts and passive margins worldwide.

  14. Mapping of the major structures of the African rift system

    NASA Technical Reports Server (NTRS)

    Mohr, P. A. (Principal Investigator)

    1972-01-01

    The author has identified the following significant results. ERTS-1 imagery of the African rift system resolves the major Cenozoic faults, zones of warping, and the associated volcanism. It also clearly depicts the crustal grain of the Precambrian rocks where these are exposed. New structural features, or new properties of known features such as greater extent, continuity, linearity, etc., are revealed by the ERTS-1 imagery. This applies to the NE-SW fracture zones in Yemen, the Aswa mylonite zone at the northern end of the Western Rift, the Nandi fault of western Kenya, the arcuate faults of the Elgeyo escarpment in the Gregory rift, and hemi-basins of warped Tertiary lavas on the Red Sea margin of Yemen, matching those of the Ethiopian plateau-Afar margin. A tentative scheme is proposed, relating the effect on the pattern of Cenozoic faulting of the degree of obliquity to Precambrian structural trend. Some ground-mapped lithological boundaries are obscure on ERTS-1 imagery. The present approaches to mapping of Precambrian terrain in Africa may require radical revision with the input of satellite imagery.

  15. The Importance of Magmatic Fluids in Continental Rifting in East Africa

    NASA Astrophysics Data System (ADS)

    Muirhead, J.; Kattenhorn, S. A.; Ebinger, C. J.; Lee, H.; Fischer, T. P.; Roecker, S. W.; Kianji, G.

    2015-12-01

    The breakup of strong continental lithosphere requires more than far-field tectonic forces. Growing evidence for early-stage cratonic rift zones points to the importance of heat, magma and volatile transfer in driving lithospheric strength reduction. The relative contributions of these processes are fundamental to our understanding of continental rifting. We present a synthesis of results from geological, geochemical and geophysical studies in one of the most seismically and volcanically active sectors of the East African Rift (Kenya-Tanzania border) to investigate the role of fluids during early-stage rifting (<10 Ma). Xenolith data indicate that rifting initiated in initially thick lithosphere. Diffuse soil CO2 flux maxima occur in the vicinity of faults, with carbon isotope values exhibiting a mantle-derived signature. These faults feed aligned sets of hydrothermal springs, which have N2-He-Ar relative abundances also indicating a mantle-derived source. Geochemical and surface faulting information are integrated with subsurface imaging and fault kinematic data derived from the 38-station CRAFTI broadband seismic array. Teleseismic and abundant local earthquakes enable assessment of the state-of-stress and b-values as a function of depth. High Vp/Vs ratios and tomographic imaging suggest the presence of fluids in the crust, with high pore fluid pressures driving failure at lower tectonic stress. Together, these cross-disciplinary data provide compelling evidence that early-stage rifting in East Africa is assisted by fluids exsolved from deep magma bodies, some of which are imaged in the lower crust. We assert that the flux of deep magmatic fluids during rift initiation plays a key role in weakening lithosphere and localizing strain. High surface gas fluxes, fault-fed hydrothermal springs and persistent seismicity highlight the East African Rift as the ideal natural laboratory for investigating fluid-driven faulting processes in extensional tectonic environments.

  16. Mapping the Risk of Rift Valley fever re-emergence in Southern Africa using remote sensing data

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever is a viral disease of animals and humans that occurs throughout sub-Saharan Africa, Egypt and the Arabian Peninsula. Outbreaks of the disease are episodic and closely linked to climate variability, especially widespread elevated rainfall that facilitates Rift Valley fever virus tra...

  17. Heat flow in the Keweenawan rift system

    NASA Astrophysics Data System (ADS)

    Perry, C.; Mareschal, J.; Jaupart, C. P.

    2012-12-01

    The emplacement of large volumes of mafic volcanic rocks during the Keweenawan rifting has modified the average crustal composition and affects the present steady state heat flux in the region. We have combined new heat flux measurements in the Superior Province of the Canadian Shield and previously published data to characterize the heat flux field around the Keweenawan rift system. For the Nipigon embayment, North of lake Superior in Ontario, mafic intrusions associated with the Keweenawan rifting have resulted in an increase in the volume of mafic rocks in the crust and caused a very small <3mW m-2 decrease in the mean heat flux. There is a very marked decrease in the heat flux (Δ Q ≈ 20mW m-2) beneath the western half of Lake Superior and to the west. The very low values of the surface heat flux (≈ 22mW m-2 correlate with the maximum Bouguer gravity anomaly. The heat flux at the base of the crust in the Canadian Shield has been determined from surface heat flux, heat production, and crustal stucture to be ≈ 15 mW m-2. In the Keweenawan rift, the surface heat flux is only a few mW m-2 higher than the mantle heat flux, which implies that the contribution of the entire crustal column to the surface heat flux is small and that the crust is exclusively made up of depleted mafic volcanic rocks. In the eastern part and northeast of Lake Superior, there is a marked increase in heat flux that correlates with a lower Bouguer anomaly. Local high heat flux anomalies due to intrusions by felsic rocks are superposed with a long wavelength trend of higher heat flow suggesting a more felsic crustal composition in the eastern part of the Keweenawan rift. Simple models suggest that such a thick dense volcanic pile as accumulated in the Keweenawan rift is almost invariably unstable and that very particular conditions were required for it to stabilize in the crust.

  18. Proterozoic Midcontinent Rift System, an overview

    SciTech Connect

    Kerr, S.D.; Landon, S.M.

    1992-01-01

    The Middle and Late Proterozoic Midcontinent Rift System (MRS) extends across the middle US, from Lake Superior through Wisconsin, Minnesota, Iowa and Nebraska into Kansas on the southwest limb and across upper and lower Michigan on the southeast limb. Exploration for oil and gas generated over 7,000 miles of seismic, a leasehold of near seven million acres, but only three test wells. The initial extension of the MRS was marked by filling with layered basalt. Thickness documented by GLIMPCE suggests crustal separation was nearly achieved. The thick dense basalts and thinned pre-rift crust provide high amplitude gravity anomalies which characterize the rift trend. Extension slowed and eventually ceased, creating a sag phase during which clastic sediments were deposited, including sapropelic shale and siltstone, fluvial sandstones and siltstones, and fluvial/alluvial conglomerates. Tectonic inversion to compressional and transpressional forces occurred late in rift history, possibly during part of the period of clastic fill. The MRS trend is highly segmented, with varied tectonic styles, suggesting complex stress systems in its development. The Nonesuch Formation is marine or lacustrine siltstone and shale containing sufficient organic matter to be an effective source rock for oil and gas. Similar facies have been identified along the extent of the western limb, in the subsurface in Minnesota, Iowa and Kansas. TOC values are as high as 3% and maturity ranges from peak oil to advanced. Surface seeps, fluid inclusions, mud log shows and modeling indicate the potential for multiple episodes of generation. Potential reservoir rocks have been identified and seals are present as lacustrine and fluvial shales and possible evaporites. The MRS remains a relatively unexplored frontier hydrocarbon province with giant field potential in the heart of North America.

  19. The offshore East African Rift System: Structural framework at the toe of a juvenile rift

    NASA Astrophysics Data System (ADS)

    Franke, Dieter; Jokat, Wilfried; Ladage, Stefan; Stollhofen, Harald; Klimke, Jennifer; Lutz, Ruediger; Mahanjane, Estevão. Stefane; Ehrhardt, Axel; Schreckenberger, Bernd

    2015-10-01

    The Cenozoic East African Rift System (EARS) extends from the Red Sea to Mozambique. Here we use seismic reflection and bathymetric data to investigate the tectonic evolution of the offshore branch of the EARS. The data indicate multiple and time transgressive neotectonic deformations along ~800 km of the continental margin of northern Mozambique. We observe a transition from a mature rift basin in the north to a juvenile fault zone in the south. The respective timing of deformation is derived from detailed seismic stratigraphy. In the north, a ~30 km wide and more than 150 km long, N-S striking symmetric graben initiated as half-graben in the late Miocene. Extension accelerated in the Pliocene, causing a continuous conjugate border fault and symmetric rift graben. Coevally, the rift started to propagate southward, which resulted in a present-day ~30 km wide half-graben, approximately 200 km farther south. Since the Pleistocene, the rift has continued to propagate another ~300 km, where the incipient rift is reflected by subrecent small-scale normal faulting. Estimates of the overall brittle extension of the matured rift range between 5 and 12 km, with an along-strike southward decrease of the extension rate. The offshore portion of the EARS evolves magma poor, similar to the onshore western branch. The structural evolution of the offshore EARS is suggested to be related to and controlled by differing inherited lithospheric fabrics. Preexisting fabrics may not only guide and focus extension but also control rift architecture.

  20. Trace element and Sr-Nd-Pb isotope geochemistry of Rungwe Volcanic Province, Tanzania: Implications for a superplume source for East Africa Rift magmatism

    NASA Astrophysics Data System (ADS)

    Castillo, Paterno; Hilton, David; Halldórsson, Sæmundur

    2014-09-01

    The recently discovered high, plume-like 3He/4He ratios at Rungwe Volcanic Province (RVP) in southern Tanzania, similar to those at the Main Ethiopian Rift in Ethiopia, strongly suggest that magmatism associated with continental rifting along the entire East African Rift System (EARS) has a deep mantle contribution (Hilton et al., 2011). New trace element and Sr-Nd-Pb isotopic data for high 3He/4He lavas and tephras from RVP can be explained by binary mixing relationships involving Early Proterozoic (+/- Archaean) lithospheric mantle, present beneath the southern EARS, and a volatile-rich carbonatitic plume with a limited range of compositions and best represented by recent Nyiragongo lavas from the Virunga Volcanic Province also in the Western Rift. Other lavas from the Western Rift and from the southern Kenya Rift can also be explained through mixing between the same endmember components. In contrast, lavas from the northern Kenya and Main Ethiopian rifts can be explained through variable mixing between the same mantle plume material and the Middle to Late Proterozoic lithospheric mantle, present beneath the northern EARS. Thus, we propose that the bulk of EARS magmatism is sourced from mixing among three endmember sources: Early Proterozoic (+/- Archaean) lithospheric mantle, Middle to Late Proterozoic lithospheric mantle and a volatile-rich carbonatitic plume with a limited range of compositions. We propose further that the African Superplume, a large, seismically anomalous feature originating in the lower mantle beneath southern Africa, influences magmatism throughout eastern Africa with magmatism at RVP and Main Ethiopian Rift representing two different heads of a single mantle plume source. This is consistent with a single mantle plume origin of the coupled He-Ne isotopic signatures of mantle-derived xenoliths and/or lavas from all segments of the EARS (Halldorsson et al., 2014).

  1. Persistence of Rift Valley fever virus in East Africa

    NASA Astrophysics Data System (ADS)

    Gachohi, J.; Hansen, F.; Bett, B.; Kitala, P.

    2012-04-01

    Rift Valley fever virus (RVFv) is a mosquito-borne pathogen of livestock, wildlife and humans that causes severe outbreaks in intervals of several years. One of the open questions is how the virus persists between outbreaks. We developed a spatially-explicit, individual-based simulation model of the RVFv transmission dynamics to investigate this question. The model, is based on livestock and mosquito population dynamics. Spatial aspects are explicitly represented by a set of grid cells that represent mosquito breeding sites. A grid cell measures 500 by 500m and the model considers a grid of 100 by 100 grid cells; the model thus operates on the regional scale of 2500km2. Livestock herds move between grid cells, and provide connectivity between the cells. The model is used to explore the spatio-temporal dynamics of RVFv persistence in absence of a wildlife reservoir in an east African semi-arid context. Specifically, the model assesses the importance of local virus persistence in mosquito breeding sites relative to global virus persistence mitigated by movement of hosts. Local persistence is determined by the length of time the virus remains in a mosquito breeding site once introduced. In the model, this is a function of the number of mosquitoes that emerge infected and their lifespan. Global persistence is determined by the level of connectivity between isolated grid cells. Our work gives insights into the ecological and epidemiological conditions under which RVFv persists. The implication for disease surveillance and management are discussed.

  2. The mesoproterozoic midcontinent rift system, Lake Superior region, USA

    USGS Publications Warehouse

    Ojakangas, R.W.; Morey, G.B.; Green, J.C.

    2001-01-01

    Exposures in the Lake Superior region, and associated geophysical evidence, show that a 2000 km-long rift system developed within the North American craton ??? 1109-1087 Ma, the age span of the most of the volcanic rocks. This system is characterized by immense volumes of mafic igneous rocks, mostly subaerial plateau basalts, generated in two major pulses largely by a hot mantle plume. A new ocean basin was nearly formed before rifting ceased, perhaps due to the remote effect of the Grenville continental collision to the east. Broad sagging/subsidence, combined with a system of axial half-grabens separated along the length of the rift by accommodation zones, provided conditions for the accumulation of as much as 20 km of volcanic rocks and as much as 10 km of post-rift clastic sediments, both along the rift axis and in basins flanking a central, post-volcanic horst. Pre-rift mature, quartzose sandstones imply little or no uplift prior to the onset of rift volcanism. Early post-rift red-bed sediments consist almost entirely of intrabasinally derived volcanic sediment deposited in alluvial fan to fluvial settings; the exception is one gray to black carbon-bearing lacustrine(?) unit. This early sedimentation phase was followed by broad crustal sagging and deposition of progressively more mature red-bed, fluvial sediments with an extra-basinal provenance. ?? 2001 Elsevier Science B.V. All rights reserved.

  3. The Mesoproterozoic Midcontinent Rift System, Lake Superior Region, USA

    NASA Astrophysics Data System (ADS)

    Ojakangas, R. W.; Morey, G. B.; Green, J. C.

    2001-06-01

    Exposures in the Lake Superior region, and associated geophysical evidence, show that a 2000 km-long rift system developed within the North American craton ∽1109-1087 Ma, the age span of most of the volcanic rocks. This system is characterized by immense volumes of mafic igneous rocks, mostly subaerial plateau basalts, generated in two major pulses largely by a hot mantle plume. A new ocean basin was nearly formed before rifting ceased, perhaps due to the remote effect of the Grenville continental collision to the east. Broad sagging/subsidence, combined with a system of axial half-grabens separated along the length of the rift by accommodation zones, provided conditions for the accumulation of as much as 20 km of volcanic rocks and as much as 10 km of post-rift clastic sediments, both along the rift axis and in basins flanking a central, post-volcanic horst. Pre-rift mature, quartzose sandstones imply little or no uplift prior to the onset of rift volcanism. Early post-rift red-bed sediments consist almost entirely of intrabasinally derived volcanic sediment deposited in alluvial fan to fluvial settings; the exception is one gray to black carbon-bearing lacustrine(?) unit. This early sedimentation phase was followed by broad crustal sagging and deposition of progressively more mature red-bed, fluvial sediments with an extra-basinal provenance.

  4. Failure was not an option- the Mid-Continent Rift system succeeded

    NASA Astrophysics Data System (ADS)

    Merino, M.; Stein, C. A.; Stein, S. A.; Keller, G. R.; Flesch, L. M.; Jurdy, D. M.

    2013-12-01

    The 1.1 Ga Mid-Continent Rift (MCR) in North America is often viewed as a failed rift formed by isolated midplate volcanism and extension within the ~1.3-~0.98 Ga Grenville orogeny. An alternative view is suggested by analogy with younger and morphologically similar rift systems, whose plate tectonic settings are more easily understood because their surroundings - including seafloor with magnetic anomalies - have not been deformed or destroyed by subsequent collisions and rifting events. In this view, the MCR was part of a larger plate boundary rifting event that resulted in a successful episode of seafloor spreading. This view is motivated by various pieces of evidence. The MCR rifting looks much like rigid plate block motion, such as associated with the West Central African Rift systems formed during the Mesozoic breakup of Africa and South America and the ongoing rifting in the East African Rift region with seafloor spreading in the Gulf of Aden and the Red Sea. This view explains the affinities of the Grenville-age rocks in the central and southern Appalachians to Amazonia rather than Canadian Grenville-age Appalachian rocks. The MCR extends farther to the south than traditionally assumed along the East Continental Gravity High (a buried feature from Ohio to Alabama). This failed portion of the rift system connected to the rift successfully separating Laurentia and Amazonia. The seafloor spreading separating Amazonia from Laurentia may explain the former's relative motion toward Greenland and Baltica. This model is consistent with some of the ~1.1 Ga geological events in Amazonia. A change in the apparent polar wander path for Laurentia during the period of volcanism of the MCR could be attributed to this plate reconfiguration. The extensional phase on the MCR may have ended because motion was taken up by seafloor spreading between Laurentia and Amazonia rather ending due to another continental collision. Later reverse faulting on the MCR normal faults due to

  5. East African Rift Valley, Kenya

    NASA Technical Reports Server (NTRS)

    1990-01-01

    This rare, cloud free view of the East African Rift Valley, Kenya (1.5N, 35.5E) shows a clear view of the Turkwell River Valley, an offshoot of the African REift System. The East African Rift is part of a vast plate fracture which extends from southern Turkey, through the Red Sea, East Africa and into Mozambique. Dark green patches of forests are seen along the rift margin and tea plantations occupy the cooler higher ground.

  6. Rift basins - Origin, history, and distribution

    NASA Technical Reports Server (NTRS)

    Burke, K. C.

    1985-01-01

    Rifts are elongate depressions overlying places where the lithosphere has ruptured in extension. Where filled with sediment they may contain exploitable quantities of oil and gas. Because rits form in a variety of tectonic settings, it is helpful to define the particular tectonic environment in which a specific rift or set of rifts has developed. A useful approach has been to relate that environment to the Wilson Cycle of the opening and the closing of oceans. This appreciation of tectonic setting can help in better understanding of the depositional, structural and thermal history of individual rift systems. The global distribution of rifts can also be related to tectonic environment. For example, rifts associated with continental rupture at a temporary still-stand of a continent over the mantle convective system (rifts like those active in East Africa today) can be distinguished from those associated with continental collision (rifts like the Cenozoic rifts of China).

  7. Epidemiologic and Environmental Risk Factors of Rift Valley Fever in Southern Africa from 2008 to 2011

    PubMed Central

    Glancey, Margaret M.; Linthicum, Kenneth J.

    2015-01-01

    Abstract Background: Rift Valley fever (RVF) outbreaks have been associated with periods of widespread and above-normal rainfall over several months. Knowledge on the environmental factors influencing disease transmission dynamics has provided the basis for developing models to predict RVF outbreaks in Africa. From 2008 to 2011, South Africa experienced the worst wave of RVF outbreaks in almost 40 years. We investigated rainfall-associated environmental factors in southern Africa preceding these outbreaks. Methods: RVF epizootic records obtained from the World Animal Health Information Database (WAHID), documenting livestock species affected, location, and time, were analyzed. Environmental variables including rainfall and satellite-derived normalized difference vegetation index (NDVI) data were collected and assessed in outbreak regions to understand the underlying drivers of the outbreaks. Results: The predominant domestic vertebrate species affected in 2008 and 2009 were cattle, when outbreaks were concentrated in the eastern provinces of South Africa. In 2010 and 2011, outbreaks occurred in the interior and southern provinces affecting over 16,000 sheep. The highest number of cases occurred between January and April but epidemics occurred in different regions every year, moving from the northeast of South Africa toward the southwest with each progressing year. The outbreaks showed a pattern of increased rainfall preceding epizootics ranging from 9 to 152 days; however, NDVI and rainfall were less correlated with the start of the outbreaks than has been observed in eastern Africa. Conclusions: Analyses of the multiyear RVF outbreaks of 2008 to 2011 in South Africa indicated that rainfall, NDVI, and other environmental and geographical factors, such as land use, drainage, and topography, play a role in disease emergence. Current and future investigations into these factors will be able to contribute to improving spatial accuracy of models to map risk areas

  8. Mid-Continent rift system - a frontier hydrocarbon province

    SciTech Connect

    Lee, C.K.; Kerr, S.D. Jr.

    1983-08-01

    Geophysical evidence in the Mid-Continent has led to delineation of a rift system active during the Proterozoic Y Era. The Mid-Continent rift system can be traced by the Mid-Continent gravity high and corresponding aeromagnetic anomaly signature from the surface exposure of the Keweenawan Supergroup in the Lake Superior basin southwest in the subsurface through Wisconsin, Minnesota, Iowa, Nebraska, and Kansas. The aeromagnetic anomaly signature of the rift trend discloses where these sediments have been preserved. Thick accumulations of upper Proterozoic sediments are indicated by both upward continuation of the aeromagnetic profiles across the rift trend and gravity models which incorporate: 1) a deep mafic body to create the narrow gravity high, 2) anomalously thick crust to account for the more regional gravity low, and 3) sedimentary accumulations on the Precambrian surface to explain the small-scale notches which occur within the narrow gravity high. Reflection seismic data are virtually unknown in the rift area; however, data recently acquired by COCORP across the southern end of the feature in Kansas provide evidence of thick stratified sequences in the rift valley. Studies of the East African rift have revealed that the tropical rift valley is an exceptionally fertile environment for deposition and preservation of kerogenous material. The Sirte, Suez, Viking, Dnieper-Donetz, and Tsaidam basins are just a few of the rift basins currently classed as giant producers. The existence of a rift basin trend with thick accumulations of preserved sediments, demonstrably organic rich, introduces the northern Mid-Continent US as a new frontier for hydrocarbon exploration.

  9. Numerical modeling of continental rifting: Implications for the East African Rift system

    NASA Astrophysics Data System (ADS)

    Koptev, Alexander; Burov, Evgueni; Calais, Eric; Leroy, Sylvie; Gerya, Taras; Guillou-Frottier, Laurent; Cloetingh, Sierd

    2016-04-01

    The East African Rift system (EARS) provides a unique system with juxtaposition of two contrasting yet simultaneously formed rift branches, the eastern, magma-rich, and the western, magma-poor, on either side of the old thick Tanzanian craton embedded into younger lithosphere. Here we take advantage of the improvements in our understanding of deep structures, geological evolution and recent kinematics, together with new cutting edge numerical modeling techniques to design a three-dimensional ultra-high resolution viscous plastic thermo-mechanical numerical model that accounts for thermo-rheological structure of the lithosphere and hence captures the essential geophysical features of the central EARS. Based on our experiments, we show that in case of the mantle plume seeded slightly to the northeast of the craton center, the ascending plume material is deflected by the cratonic keel and preferentially channeled along the eastern side of the craton, leading to formation of a large rift zone characterized by important magmatic activity with substantial amounts of melts derived from mantle plume material. This model is in good agreement with the observations in the EARS, as it reproduces the magmatic eastern branch and at the same time, anticlockwise rotation of the craton. However, this experiment does not reproduce the observed strain localization along the western margin of the cratonic bloc. To explain the formation of contrasting magmatic and amagmatic rift branches initiating simultaneously on either side of a non-deforming block as observed in the central EARS, we experimentally explored several scenarios of which three can be retained as specifically pertaining to the EARS: (1) The most trivial first scenario assumes rheologically weak vertical interface simulating the suture zone observed in the geological structure along the western border of the craton; (2) The second scenario involves a second smaller plume initially shifted in SW direction; (3) Finally, a

  10. The role of inheritance in structuring hyperextended rift systems

    NASA Astrophysics Data System (ADS)

    Manatschal, Gianreto; Lavier, Luc; Chenin, Pauline

    2015-04-01

    A long-standing question in Earth Sciences is related to the importance of inheritance in controlling tectonic processes. In contrast to physical processes that are generally applicable, assessing the role of inheritance suffers from two major problems: firstly, it is difficult to appraise without having insights into the history of a geological system; and secondly all inherited features are not reactivated during subsequent deformation phases. Therefore, the aim of our presentation is to give some conceptual framework about how inheritance may control the architecture and evolution of hyperextended rift systems. We use the term inheritance to refer to the difference between an "ideal" layer-cake type lithosphere and a "real" lithosphere containing heterogeneities and we define 3 types of inheritance, namely structural, compositional and thermal inheritance. Moreover, we assume that the evolution of hyperextended rift systems reflects the interplay between their inheritance (innate/"genetic code") and the physical processes at play (acquired/external factors). Thus, by observing the architecture and evolution of hyperextended rift systems and integrating the physical processes, one my get hints on what may have been the original inheritance of a system. Using this approach, we focus on 3 well-studied rift systems that are the Alpine Tethys, Pyrenean-Bay of Biscay and Iberia-Newfoundland rift systems. For the studied examples we can show that: 1) strain localization on a local scale and during early stages of rifting is controlled by inherited structures and weaknesses 2) the architecture of the necking zone seems to be influenced by the distribution and importance of ductile layers during decoupled deformation and is consequently controlled by the thermal structure and/or the inherited composition of the curst 3) the location of breakup in the 3 examples is not significantly controlled by the inherited structures 4) inherited mantle composition and rift

  11. Prediction, Assessment of the Rift Valley fever Activity in East and Southern Africa 2006 - 2008 and Possible Vector Control Strategies

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Historical outbreaks of Rift Valley fever (RVF) since the early 1950s have been associated with cyclical patterns of the El Nino/Southern Oscillation (ENSO) phenomenon which results in elevated and widespread rainfall over the RVF endemic areas of Africa. Using satellite measurements of global and ...

  12. Prediction, Assessment of the Rift Valley Fever Activity in East and Southern Africa 2006 - 2008 and Possible Vector Control Strategies

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Historical episodic outbreaks of Rift Valley fever (RVF) since the early 1950s have been associated with cyclical patterns (El Niño and La Niña) of El Niño Southern Oscillation (ENSO) phenomenon which results in elevated and widespread rainfall over the RVF endemic areas of Africa. Using satellite ...

  13. Facies distributions within contrasting structural components of a rift lake: Lake Tanganyika, Africa

    SciTech Connect

    Soreghan, M.J.; Cohen, A.S. )

    1991-03-01

    Lake Tanganyika is the most widely cited modern analog for interpreting ancient rift lakes; thus, understanding controls on its facies distribution is critical for refining stratigraphic models for rifts. Four recurrent margin types occur along the alternating half-graben structure of the lake: rift axes, platforms, escarpments, and accommodation zones. Data from study sites in the northern part of the lake suggest that predictable facies differences exist between these structural margin types. The rift axis site comprises a low-gradient, clastic (wave/current)-dominated deltaic system, with strong facies asymmetry and minor carbonate accumulations on raised benches. The platform margin site comprises a series of structurally controlled benches over which long, continuous facies tracts occur. Carbonate sands, muds, and shell gravel dominate; clastics are limited to moderate-sized silty deltas and long, narrow shoreface sands. The escarpment margin site is a steep-gradient system along which small ({lt}1 km{sup 2}) fan deltas alternate with cemented talus. The accommodation zone margin sites are also dominated by rugged structural relief, generally small fan deltas, and semicontinuous shoreface sand belts ({gt}5 km) onshore and poorly sorted silts offshore. TOC from fine-grained samples reflects the contrast in margin types. TOC values for the platform and rift axis range from 0.4 - 2.1 wt. % (avg. 1.3%), whereas accommodation zone and escarpment margin values range from 0.5-5.5% (avg. 3.0%). Acid insoluble sulfur shows a similar trend. Although all data are significantly correlated with depth, the relative area of the lake margin above and below the oxicline is directly controlled by the structural style of the lake margin.

  14. Risk factors associated with Rift Valley fever epidemics in South Africa in 2008–11

    PubMed Central

    Métras, Raphaëlle; Jewell, Chris; Porphyre, Thibaud; Thompson, Peter N.; Pfeiffer, Dirk U.; Collins, Lisa M.; White, Richard G.

    2015-01-01

    Rift Valley fever (RVF) is a zoonotic and vector-borne disease, mainly present in Africa, which represents a threat to human health, animal health and production. South Africa has experienced three major RVF epidemics (1950–51, 1973–75 and 2008–11). Due to data scarcity, no previous study has quantified risk factors associated with RVF epidemics in animals in South Africa. Using the 2008–11 epidemic datasets, a retrospective longitudinal study was conducted to identify and quantify spatial and temporal environmental factors associated with RVF incidence. Cox regressions with a Besag model to account for the spatial effects were fitted to the data. Coefficients were estimated by Bayesian inference using integrated nested Laplace approximation. An increase in vegetation density was the most important risk factor until 2010. In 2010, increased temperature was the major risk factor. In 2011, after the large 2010 epidemic wave, these associations were reversed, potentially confounded by immunity in animals, probably resulting from earlier infection and vaccination. Both vegetation density and temperature should be considered together in the development of risk management strategies. However, the crucial need for improved access to data on population at risk, animal movements and vaccine use is highlighted to improve model predictions. PMID:25804974

  15. Has Rift Valley fever virus evolved with increasing severity in human populations in East Africa?

    PubMed Central

    Baba, Marycelin; Masiga, Daniel K; Sang, Rosemary; Villinger, Jandouwe

    2016-01-01

    Rift Valley fever (RVF) outbreaks have occurred across eastern Africa from 1912 to 2010 approximately every 4–15 years, most of which have not been accompanied by significant epidemics in human populations. However, human epidemics during RVF outbreaks in eastern Africa have involved 478 deaths in 1998, 1107 reported cases with 350 deaths from 2006 to 2007 and 1174 cases with 241 deaths in 2008. We review the history of RVF outbreaks in eastern Africa to identify the epidemiological factors that could have influenced its increasing severity in humans. Diverse ecological factors influence outbreak frequency, whereas virus evolution has a greater impact on its virulence in hosts. Several factors could have influenced the lack of information on RVF in humans during earlier outbreaks, but the explosive nature of human RVF epidemics in recent years mirrors the evolutionary trend of the virus. Comparisons between isolates from different outbreaks have revealed an accumulation of genetic mutations and genomic reassortments that have diversified RVF virus genomes over several decades. The threat to humans posed by the diversified RVF virus strains increases the potential public health and socioeconomic impacts of future outbreaks. Understanding the shifting RVF epidemiology as determined by its evolution is key to developing new strategies for outbreak mitigation and prevention of future human RVF casualties. PMID:27329846

  16. Has Rift Valley fever virus evolved with increasing severity in human populations in East Africa?

    PubMed

    Baba, Marycelin; Masiga, Daniel K; Sang, Rosemary; Villinger, Jandouwe

    2016-01-01

    Rift Valley fever (RVF) outbreaks have occurred across eastern Africa from 1912 to 2010 approximately every 4-15 years, most of which have not been accompanied by significant epidemics in human populations. However, human epidemics during RVF outbreaks in eastern Africa have involved 478 deaths in 1998, 1107 reported cases with 350 deaths from 2006 to 2007 and 1174 cases with 241 deaths in 2008. We review the history of RVF outbreaks in eastern Africa to identify the epidemiological factors that could have influenced its increasing severity in humans. Diverse ecological factors influence outbreak frequency, whereas virus evolution has a greater impact on its virulence in hosts. Several factors could have influenced the lack of information on RVF in humans during earlier outbreaks, but the explosive nature of human RVF epidemics in recent years mirrors the evolutionary trend of the virus. Comparisons between isolates from different outbreaks have revealed an accumulation of genetic mutations and genomic reassortments that have diversified RVF virus genomes over several decades. The threat to humans posed by the diversified RVF virus strains increases the potential public health and socioeconomic impacts of future outbreaks. Understanding the shifting RVF epidemiology as determined by its evolution is key to developing new strategies for outbreak mitigation and prevention of future human RVF casualties. PMID:27329846

  17. Risk factors associated with Rift Valley fever epidemics in South Africa in 2008-11.

    PubMed

    Métras, Raphaëlle; Jewell, Chris; Porphyre, Thibaud; Thompson, Peter N; Pfeiffer, Dirk U; Collins, Lisa M; White, Richard G

    2015-01-01

    Rift Valley fever (RVF) is a zoonotic and vector-borne disease, mainly present in Africa, which represents a threat to human health, animal health and production. South Africa has experienced three major RVF epidemics (1950-51, 1973-75 and 2008-11). Due to data scarcity, no previous study has quantified risk factors associated with RVF epidemics in animals in South Africa. Using the 2008-11 epidemic datasets, a retrospective longitudinal study was conducted to identify and quantify spatial and temporal environmental factors associated with RVF incidence. Cox regressions with a Besag model to account for the spatial effects were fitted to the data. Coefficients were estimated by Bayesian inference using integrated nested Laplace approximation. An increase in vegetation density was the most important risk factor until 2010. In 2010, increased temperature was the major risk factor. In 2011, after the large 2010 epidemic wave, these associations were reversed, potentially confounded by immunity in animals, probably resulting from earlier infection and vaccination. Both vegetation density and temperature should be considered together in the development of risk management strategies. However, the crucial need for improved access to data on population at risk, animal movements and vaccine use is highlighted to improve model predictions. PMID:25804974

  18. Geophysical glimpses into the Ferrigno Rift at the northwestern tip of the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

    Bingham, Robert; Ferraccioli, Fausto

    2014-05-01

    The West Antarctic Rift System (WARS) forms one of the largest continental rift systems on Earth. The WARS is of major significance as it forms the lithospheric cradle for the marine-based and potentially unstable West Antarctic Ice Sheet (WAIS). Seismic refraction, reflection, aeromagnetic, gravity and drilling in the Ross Sea have revealed most of what we know about its structure, tectonic and magmatic patterns and sedimentary basins. Aerogeophysical research and passive seismic networks have considerably extended our knowledge of the WARS and its influence on the overlying WAIS in the Siple Coast and Amundsen Sea Embayment (ASE) regions. The Bellingshausen Sea Embayment region has however remained largely unexplored, and hence the possible extent of the WARS in this sector has remained poorly constrained. Here we use a combination of reconnaissance ground-based and airborne radar observations, airborne gravity, satellite gravity and aeromagnetic data to investigate the WARS in the Bellingshausen Sea Embayment, in the area of the Ferrigno Ice Stream (Bingham et al., 2012, Nature). This region is of high significance, as it one of the main sectors of the WAIS that is currently exhibiting rapid ice loss, thought to be driven primarily by oceanic warming. Assessing geological controls on subice topography and ice dynamics is therefore of prime importance in this part of the WAIS. Ground-based and airborne radar image a subglacial basin beneath the Ferrigno Ice Stream that is up to 1.5 kilometres deep and that connects the ice-sheet interior to the Bellingshausen Sea margin. We interpret this basin as a narrow, glacially overdeepened rift basin that formed at the northwestern tip of the WARS. Satellite gravity data cannot resolve such a narrow rift basin but indicate that the crust beneath the region is likely thinned, lending support to the hypothesis that this area is indeed part of the WARS. Widely-spaced aeromagnetic data image a linear low along the inferred

  19. Cenozoic extension in the Kenya Rift from low-temperature thermochronology: Links to diachronous spatiotemporal evolution of rifting in East Africa

    NASA Astrophysics Data System (ADS)

    Torres Acosta, Verónica; Bande, Alejandro; Sobel, Edward R.; Parra, Mauricio; Schildgen, Taylor F.; Stuart, Finlay; Strecker, Manfred R.

    2015-12-01

    The cooling history of rift shoulders and the subsidence history of rift basins are cornerstones for reconstructing the morphotectonic evolution of extensional geodynamic provinces, assessing their role in paleoenvironmental changes and evaluating the resource potential of their basin fills. Our apatite fission track and zircon (U-Th)/He data from the Samburu Hills and the Elgeyo Escarpment in the northern and central sectors of the Kenya Rift indicate a broadly consistent thermal evolution of both regions. Results of thermal modeling support a three-phased thermal history since the early Paleocene. The first phase (~65-50 Ma) was characterized by rapid cooling of the rift shoulders and may be coeval with faulting and sedimentation in the Anza Rift basin, now located in the subsurface of the Turkana depression and areas to the east in northern Kenya. In the second phase, very slow cooling or slight reheating occurred between ~45 and 15 Ma as a result of either stable surface conditions, very slow exhumation, or subsidence. The third phase comprised renewed rapid cooling starting at ~15 Ma. This final cooling represents the most recent stage of rifting, which followed widespread flood-phonolite emplacement and has shaped the present-day landscape through rift shoulder uplift, faulting, basin filling, protracted volcanism, and erosion. When compared with thermochronologic and geologic data from other sectors of the East African Rift System, extension appears to be diachronous, spatially disparate, and partly overlapping, likely driven by interactions between mantle-driven processes and crustal heterogeneities, rather than the previously suggested north-south migrating influence of a mantle plume.

  20. Mantle Anisotropy, Collisional Rifts and the Magmatic Evolution of Southern Africa: Old (Mantle) Fabric Never Dies.

    NASA Astrophysics Data System (ADS)

    Silver, P. G.; Fouch, M.; Gao, S.; Schmitz, M.

    2003-12-01

    The observed seismic anisotropy of the southern African mantle, made possible by data from the Southern African Seismic Experiment, provides important constraints on modes of mantle deformation beneath this ancient continent. We find that the mantle anisotropy is dominated by deformational events in Archean times occurring within the lithosphere, and can thus be used to assess the mantle's role in the tectonic evolution of this region. The pattern of mantle anisotropy derived from shear wave splitting observations reveals two noteworthy characteristics. First, there is a spatially continuous arc of mantle anisotropy extending from the western Kaapvaal and Zimbabwe Cratons to the northeastern Kaapvaal. All along the arc, the splitting fast polarization direction, φ , is subparallel to the trend of the arc. Given the crust/mantle chronology associated with these regions, the anisotropy likely represents deformation that occurred at ca. 2.9 to 2.7 Ga during collisional accretion of both the western Kimberley and northern Pietersburg blocks onto the ca. 3.2 Ga eastern shield of the Kaapvaal, with accretion on the northern ramparts of the Kaapvaal ultimately culminating in the Neo-Archean Limpopo orogen. Second, there is mantle anisotropy closely associated with the Great Dyke with values of φ parallel to the Dyke, just north of and distinct from this arc of anisotropy. We present evidence that the mantle fabric that generates seismic anisotropy also constitutes preexisting structure in the mantle that is subsequently reactivated, much like the more commonly cited reactivation of crustal structures. In particular, we argue that the Neo-Archean collision imparted a mechanical anisotropy to the mantle that controlled the subsequent magmatic history of cratonic southern Africa (old fabric never dies!). Study of mechanical anisotropy of olivine aggregates suggests that failure is most likely parallel to the olivine b-plane, which for transcurrent deformation is a vertical

  1. Sismotectonics in the western branch of the East African Rift System

    NASA Astrophysics Data System (ADS)

    Delvaux, Damien; Kervyn, François; Mulumba, Jean-Luc; Kipata, Louis; Sebagenzi, Stanislas; Mavonga, Georges; Macheyeki, Athanas; Temu, Elly Bryan

    2013-04-01

    The western branch of the East African rift system is known of its particular seismic activity with larger magnitude (up to Ms 7.3) and more frequent destructive earthquakes than in the eastern branch. As a contribution to the IGCP 601 project Seismotectonic Map of Africa, we compiled the known active faults, thermal springs and historical seismicity in Central Africa. Using the rich archives of the Royal Museum for Central Africa, publications and own field observations, we present a compilation of available data relative to the current seismotectonic activity along the western branch of the East African rift system, in DRC, Rwanda, Burundi and Tanzania. Neotectonic activity related to the western rift branch is in general well expressed and relatively well studied in the eastern flank of this rift branch, in Uganda, Rwanda, Burundi and Tanzania. In contrast, the western flank of this rift branch, largely exposed in the DRC, has attracted less attention. However, data collected during the colonial times show significant sismotectonic activity in East DRC, not only in the western flank of the western rift branch, but extending far westwards up to the margin of the Congo basin. In particular, our predecessors paid a special attention to the mapping and description of thermal springs, noticing that they are often controlled by active faults. In addition, the operators of the relatively dense network of meteorological stations installed in the DRC, Rwanda and Burundi also recorded were with variable level of completeness and detail the earthquakes that they could felt. This provides a rich database that is used to complete the existing knowledge on historical seismicity. An important effort has still to be paid to identify and map potentially active fault due to poor field accessibility, tropical climate weathering and vegetation coverage. The main problem in the compilation of active fault data is that very few of them have been investigated by paleoseismic trenching

  2. The Midcontinent rift system in Kansas

    SciTech Connect

    Berendsen, P. . Kansas Geological Survey)

    1993-03-01

    A sequence of rift-related mafic volcanic rocks, volcanoclastic-, and clastic sedimentary rocks are recognized in cuttings and cores from about seventy wells in Kansas. The age (1,097.5 Ma) for gabbro in the Poersch [number sign]1 well in northern Kansas, as well as the general petrographic characteristics of the sedimentary rocks throughout the area favors a correlation with established Keweenawan stratigraphy in the Lake Superior region. Rift-related northeast-trending faults and older northwest-trending faults divide the area up into a number of orthogonal fault blocks or basins. Depending upon the tectonic history of the individual basin all or part of the Keweenawan section may be preserved. It is believed that large amounts of Keweenawan clastic sedimentary rock were eroded from the nemaha uplift east of the central graben of the rift and transported in an easterly direction. Prior to deposition of Paleozoic rocks the area was peneplaned. Correlation of various stratigraphic units over any distance is complicated by tectonic activity occurring at several times during the Precambrian and Paleozoic. Stratabound or stratiform deposits can occur both in the Precambrian as well as the overlying Paleozoic rocks. The possibility of massive sulfides to occur in the mafic intrusive rocks must not be excluded. In the core from the Poersch [number sign]1 well sulfides are recognized in gabbroic sills or dikes. Dark, fissile shale, similar to the Nonesuch Shale in the [number sign]1--4 Finn well averages 0.75% organic carbon. Thermal maturation within the rift probably ranges from within the oil window to over maturity.

  3. Post-rift unroofing of the NW Africa passive continental margin during the Central Atlantic opening

    NASA Astrophysics Data System (ADS)

    Ghorbal, B.; Bertotti, G.; Andriessen, P. A. M.

    2009-04-01

    Many passive margins considered as being stable for long times, show however late uplift and exhumation at regional scale as assessed by low temperature geochronometry. A large amount of Lower Cretaceous terrigeneous sediments laid down in most of basins along the NW Africa continental margins indicate that a major episode of erosion occurred during early post-rift period in the Central Atlantic. AFT and (U-Th)/He dating performed, along a roughly >500 km N-S transect, on pre-Mesozoic basement rocks from Western Meseta to the Anti-Atlas (Morocco, NW Africa) document a fully unexpected widespread unroofing during the Middle-Late Jurassic to early Late Cretaceous, with AFT and (U-Th)/He ages ranging respectively between 120-170Ma and 115-165Ma. A well documented age cluster of 140±20Ma measured for the Moroccan Meseta, Atlas domains and Anti-Atlas belt designates those domains as potentially being the source areas of the detritic sediments considering the proximity of the depositional basins. Absence of major fault separating the Anti-Atlas from the rest of the Western African Craton during the Mesozoic suggests the unroofing region to extend further in Morocco, as far south as the Reguibat (Mauritania) or even New Guinea, documented by our investigation, and perhaps even further when confirmed by additional AFT and AHe data.

  4. History of the development of the East African Rift System: A series of interpreted maps through time

    NASA Astrophysics Data System (ADS)

    Macgregor, Duncan

    2015-01-01

    This review paper presents a series of time reconstruction maps of the 'East African Rift System' ('EARS'), illustrating the progressive development of fault trends, subsidence, volcanism and topography. These maps build on previous basin specific interpretations and integrate released data from recent petroleum drilling. N-S trending EARS rifting commenced in the petroliferous South Lokichar Basin of northern Kenya in the Late Eocene to Oligocene, though there seem to be few further deep rifts of this age other than those immediately adjoining it. At various times during the Mid-Late Miocene, a series of small rifts and depressions formed between Ethiopia and Malawi, heralding the main regional rift subsidence phase and further rift propagation in the Plio-Pleistocene. A wide variation is thus seen in the ages of initiation of EARS basins, though the majority of fault activity, structural growth, subsidence, and associated uplift of East Africa seem to have occurred in the last 5-9 Ma, and particularly in the last 1-2 Ma. These perceptions are key to our understanding of the influence of the diverse tectonic histories on the petroleum prospectivity of undrilled basins.

  5. Strain accommodation by slow slip and dyking in a youthful continental rift, East Africa.

    PubMed

    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, Benoît; Stamps, D Sarah; Wauthier, Christelle

    2008-12-11

    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. PMID:19079058

  6. Recent outbreaks of rift valley Fever in East Africa and the middle East.

    PubMed

    Himeidan, Yousif E; Kweka, Eliningaya J; Mahgoub, Mostafa M; El Rayah, El Amin; Ouma, Johnson O

    2014-01-01

    Rift Valley fever (RVF) is an important neglected, emerging, mosquito-borne disease with severe negative impact on human and animal health. Mosquitoes in the Aedes genus have been considered as the reservoir, as well as vectors, since their transovarially infected eggs withstand desiccation and larvae hatch when in contact with water. However, different mosquito species serve as epizootic/epidemic vectors of RVF, creating a complex epidemiologic pattern in East Africa. The recent RVF outbreaks in Somalia (2006-2007), Kenya (2006-2007), Tanzania (2007), and Sudan (2007-2008) showed extension to districts, which were not involved before. These outbreaks also demonstrated the changing epidemiology of the disease from being originally associated with livestock, to a seemingly highly virulent form infecting humans and causing considerably high-fatality rates. The amount of rainfall is considered to be the main factor initiating RVF outbreaks. The interaction between rainfall and local environment, i.e., type of soil, livestock, and human determine the space-time clustering of RVF outbreaks. Contact with animals or their products was the most dominant risk factor to transfer the infection to humans. Uncontrolled movement of livestock during an outbreak is responsible for introducing RVF to new areas. For example, the virus that caused the Saudi Arabia outbreak in 2000 was found to be the same strain that caused the 1997-98 outbreaks in East Africa. A strategy that involves active surveillance with effective case management and diagnosis for humans and identifying target areas for animal vaccination, restriction on animal movements outside the affected areas, identifying breeding sites, and targeted intensive mosquito control programs has been shown to succeed in limiting the effect of RVF outbreak and curb the spread of the disease from the onset. PMID:25340047

  7. Recent Outbreaks of Rift Valley Fever in East Africa and the Middle East

    PubMed Central

    Himeidan, Yousif E.; Kweka, Eliningaya J.; Mahgoub, Mostafa M.; El Rayah, El Amin; Ouma, Johnson O.

    2014-01-01

    Rift Valley fever (RVF) is an important neglected, emerging, mosquito-borne disease with severe negative impact on human and animal health. Mosquitoes in the Aedes genus have been considered as the reservoir, as well as vectors, since their transovarially infected eggs withstand desiccation and larvae hatch when in contact with water. However, different mosquito species serve as epizootic/epidemic vectors of RVF, creating a complex epidemiologic pattern in East Africa. The recent RVF outbreaks in Somalia (2006–2007), Kenya (2006–2007), Tanzania (2007), and Sudan (2007–2008) showed extension to districts, which were not involved before. These outbreaks also demonstrated the changing epidemiology of the disease from being originally associated with livestock, to a seemingly highly virulent form infecting humans and causing considerably high-fatality rates. The amount of rainfall is considered to be the main factor initiating RVF outbreaks. The interaction between rainfall and local environment, i.e., type of soil, livestock, and human determine the space-time clustering of RVF outbreaks. Contact with animals or their products was the most dominant risk factor to transfer the infection to humans. Uncontrolled movement of livestock during an outbreak is responsible for introducing RVF to new areas. For example, the virus that caused the Saudi Arabia outbreak in 2000 was found to be the same strain that caused the 1997–98 outbreaks in East Africa. A strategy that involves active surveillance with effective case management and diagnosis for humans and identifying target areas for animal vaccination, restriction on animal movements outside the affected areas, identifying breeding sites, and targeted intensive mosquito control programs has been shown to succeed in limiting the effect of RVF outbreak and curb the spread of the disease from the onset. PMID:25340047

  8. Rifting, Volcanism, and the Geochemical Character of the Mantle Beneath the West Antarctic Rift System (Invited)

    NASA Astrophysics Data System (ADS)

    Mukasa, S. B.; Aviado, K. B.; Rilling-Hall, S.; Bryce, J. G.; Cabato, J.

    2013-12-01

    The West Antarctic Rift System (WARS) is one of the largest extensional alkali volcanic provinces on Earth, but the mechanisms responsible for generating the massive amounts of its associated magmatism remain controversial. The failure of both passive and active decompression melting models to adequately explain the observed lava volumes has prompted debate about the relative roles of thermal plume-related melting and ancient subduction-related flux melting. 40Ar/39Ar dating and geochemical analyses of the lavas, as well as volatile and trace-element determinations of olivine-hosted melt inclusions shed light on the relationship between rifting and volcanism, and also improve our understanding of the geochemical character of the mantle beneath the WARS. Results show that the magmatism post-dates the main phase of extension along the Terror Rift within the WARS, which supports a decompression-melting model without the benefit of a significant thermal anomaly. However, the observed large magma volumes seem to require a volatile-fluxed mantle, a notion supported by a long history of subduction (>500 Myr) along the paleo-Pacific margin of Gondwana. In fact, the legacy of that subduction may manifest itself in the high H2O concentrations of olivine-hosted melt inclusions (up to 3 wt% in preliminary results from ion probe measurements). The major oxide compositions of lavas in the WARS are best matched to experimental melts of garnet pyroxenite and carbonated peridotite sources. The Pb and Nd isotopic systems are decoupled from each other, suggesting removal of fluid-mobile elements from the mantle source possibly during the long history of subduction along this Gondwana margin. Extremely unradiogenic 187Os/188Os ranging to as low as 0.1081 × 0.0001 hints at the involvement of lithospheric components in generation of magmas in the WARS.

  9. Prebreakup geology of the Gulf of Mexico-Caribbean: Its relation to Triassic and Jurassic rift systems of the region

    NASA Astrophysics Data System (ADS)

    Bartok, Peter

    1993-01-01

    A review of the prebreakup geology of west central Pangea, comprising northern South America, the Gulf of Mexico, and West Africa, combined with a study of the Mesozoic rift trends of the region confirms a relation between the rift systems and the underlying older grain of deformation. The prebreakup analysis focuses attention on the Precambrian, early Paleozoic, and late Paleozoic tectonic events affecting the region and assumes a Pindell fit. Two late Precambrian orogenic belts are observed in west central Pangea. Along the northern South American margin and Yucatan a paleo northeast trending Pan-African aged fold belt is documented. A second system is observed along West Africa extending from the High Atlas to the Mauritanides and Rockelides. Similar aged orogenies in the Appalachians are compared. During the late Paleozoic, renewed orogenic activity, associated with the Gondwana-Laurentia suture, affected large segments of west central Pangea. The general trend of the system is northeast-southwest and essentially parallels the Guayana craton and West African and eastern North American cratons. Mesozoic rifling closely followed either the Precambrian trends or the late Paleozoic orogenic belt. The Triassic component focused along the western portions of the Gulf of Mexico continuing into eastern Mexico and western South America. The Jurassic rift trend followed along the separation between Yucatan and northern South America. At Lake Maracaibo the Jurassic rift system eventually overlaps the Triassic rifts. The Jurassic rift resulted in the "Hispanic Corridor" that permitted Tethyan and Pacific marine faunas to mix at a time when the Gulf of Mexico underwent continental sedimentation.

  10. Innovative tephra studies in the East African Rift System

    NASA Astrophysics Data System (ADS)

    WoldeGabriel, Giday; Hart, William K.; Heiken, Grant

    Geosciences investigations form the foundation for paleoanthropological research in the East African Rift System. However, innovative applications of tephra studies for constraining spatial and temporal relations of diverse geological processes, biostratigraphic records, and paleoenvironmental conditions within the East African Rift System were fueled by paleoanthropological investigations into the origin and evolution of hominids and material culture. Tephra is a collective, size-independent term used for any material ejected during an explosive volcanic eruption.The East African Rift System has become a magnet for paleoanthropological research ever since the discovery of the first hominids at Olduvai Gorge, in Tanzania, in the 1950s [Leakey et al., 1961]. Currently, numerous multidisciplinary scientific teams from academic institutions in the United States and Western Europe make annual pilgrimages for a couple of months to conduct paleoanthropological field research in the fossil-rich sedimentary deposits of the East African Rift System in Ethiopia, Kenya, and Tanzania. The field expedition consists of geological, paleontological, archaeological, and paleoenvironmental investigations.

  11. Risk assessment of the introduction of Rift Valley fever from the Horn of Africa to Yemen via legal trade of small ruminants.

    PubMed

    Abdo-Salem, Shaif; Waret-Szkuta, Agnès; Roger, François; Olive, Marie-Marie; Saeed, Khalid; Chevalier, Véronique

    2011-02-01

    Rift Valley fever (RVF) is a mosquito-borne viral zoonosis of increasing global importance. Occurring since 1930 across Africa, it was detected for the first time in Saudi Arabia and Yemen in September 2000, leading to human deaths and major losses in livestock populations. Assuming the virus has not survived in Yemen or has been circulating at a low level, authors qualitatively assessed the likelihood of "re-introduction" of RVF into Yemen through the legal importation of small ruminants from the Horn of Africa. The overall probability of introduction was assessed very low to medium, increasing during festival periods and higher when considering a direct transmission exposure as compared to a vectorial transmission exposure. The uncertainty was considered to be medium underlining important gaps in information that need to be fulfilled in the region. Options to reduce the risk are proposed and discussed, including possible improvements of the current Yemeni quarantine system. PMID:20967567

  12. DoD-GEIS Rift Valley Fever Monitoring and Prediction System as a Tool for Defense and US Diplomacy

    NASA Technical Reports Server (NTRS)

    Anyamba, Assaf; Tucker, Compton J.; Linthicum, Kenneth J.; Witt, Clara J.; Gaydos, Joel C.; Russell, Kevin L.

    2011-01-01

    Over the last 10 years the Armed Forces Health Surveillance Center's Global Emerging Infections Surveillance and Response System (GEIS) partnering with NASA'S Goddard Space Flight Center and USDA's USDA-Center for Medical, Agricultural & Veterinary Entomology established and have operated the Rift Valley fever Monitoring and Prediction System to monitor, predict and assess the risk of Rift Valley fever outbreaks and other vector-borne diseases over Africa and the Middle East. This system is built on legacy DoD basic research conducted by Walter Reed Army Institute of Research overseas laboratory (US Army Medical Research Unit-Kenya) and the operational satellite environmental monitoring by NASA GSFC. Over the last 10 years of operation the system has predicted outbreaks of Rift Valley fever in the Horn of Africa, Sudan, South Africa and Mauritania. The ability to predict an outbreak several months before it occurs provides early warning to protect deployed forces, enhance public health in concerned countries and is a valuable tool use.d by the State Department in US Diplomacy. At the international level the system has been used by the Food and Agricultural Organization (FAD) and the World Health Organization (WHO) to support their monitoring, surveillance and response programs in the livestock sector and human health. This project is a successful testament of leveraging resources of different federal agencies to achieve objectives of force health protection, health and diplomacy.

  13. Differential opening of the Central and South Atlantic Oceans and the opening of the West African rift system

    NASA Astrophysics Data System (ADS)

    Fairhead, J. D.; Binks, R. M.

    1991-02-01

    Plate tectonic studies of the development of the Central and South Atlantic Oceans using Seasat and Geosat altimeter and magnetic anomaly isochron data now provide quantitative models of seafloor spreading through time. Such models enable an initial assessment of the differential opening between these two oceanic basins to be determined. The Equatorial Atlantic is an integral part of this oceanic rifting process, allowing stresses arising from the differential opening to be dissipated into both the Caribbean and Africa along its northern and southern boundaries respectively. The tectonic model for the West African rift system, based on geological and geophysical studies, shows a series of strike-slip fault zones diverging into Africa from the Gulf of Guinea and dissipating their shear movement into the development of extensional basins orientated perpendicular to these faults zones. The development of the West African rift system was contemporaneous with the early opening of the South Atlantic, continued to develop well after the final breakup of South America from Africa and did not cease until the late Cretaceous when there was a major phase of basin inversion and deformation. Santonian ( ~ 80 Ma) deformation across the Benue Trough (Nigeria) is broadly contemporaneous with dextral shear reactivation of the central African fracture system which, in turn resulted in renewed extension in the Sudan basins during the late Cretaceous and early Tertiary. This paper illustrates the close linkage in both time and space between the history of the African rift basins and the opening of the Atlantic. Both exhibit distinct phases of evolution with the rift basins developing in direct response to the differential opening between the Central and South Atlantic in order to dissipate stresses generated by this opening. The Mesozoic tectonic model proposed is therefore one of an intimate interaction between oceanic and continental tectonics.

  14. Deltas of the Lake Malawi rift, east Africa: Seismic expression and exploration implications

    SciTech Connect

    Scholz, C.A.

    1995-11-01

    High-resolution, air-gun-sourced seismic reflection surveys over the offshore regions of five river deltas in Lake Malawi in the East African rift system reveal considerable variability in acoustic facies and stratigraphic architecture. This variability can largely be attributed to the influences of different structural settings, and to a lesser degree to high-amplitude (100-400 m) and high-frequency (1000 to 100,000 yr) fluctuations in lake level. Deltas on flexural and axial margins in the rift lake show well-developed progradational geometries. In contrast, a delta on a steep, accommodation zone margin distributes coarse sediments over a broad depositional apron, rather than concentrating sediment in discrete progradational lobes as on the other deltas. A large border fault margin river delta displays the most complex tectonic and stratigraphic architecture of all the deltas studied. It contains several delta-associated facies, including prograding clinoform packages, fan deltas stacked against a boundary fault, and extensive subaqueous fans. Flexural margin lowstand deltas may be the most prospective for hydrocarbon exploration due to their large, internally well-organized, progradational lobes and their close proximity to deep-water, high total organic carbon lacustrine source facies.

  15. Fault Growth and Propagation and its Effect on Surficial Processes within the Incipient Okavango Rift Zone, Northwest Botswana, Africa (Invited)

    NASA Astrophysics Data System (ADS)

    Atekwana, E. A.

    2010-12-01

    The Okavango Rift Zone (ORZ) is suggested to be a zone of incipient continental rifting occuring at the distal end of the southwestern branch of the East African Rift System (EARS), therefore providing a unique opportunity to investigate neotectonic processes during the early stages of rifting. We used geophysical (aeromagnetic, magnetotelluric), Shuttle Radar Tomography Mission, Digital Elevation Model (SRTM-DEM), and sedimentological data to characterize the growth and propagation of faults associated with continental extension in the ORZ, and to elucidate the interplay between neotectonics and surficial processes. The results suggest that: (1) fault growth occurs by along axis linkage of fault segments, (2) an immature border fault is developing through the process of “Fault Piracy” by fault-linkages between major fault systems, (3) significant discrepancies exits between the height of fault scarps and the throws across the faults compared to their lengths in the basement, (4) utilization of preexisting zones of weakness allowed the development of very long faults (> 25-100 km) at a very early stage of continental rifting, explaining the apparent paradox between the fault length versus throw for this young rift, (5) active faults are characterized by conductive anomalies resulting from fluids, whereas, inactive faults show no conductivity anomaly; and 6) sedimentlogical data reveal a major perturbation in lake sedimentation between 41 ka and 27 ka. The sedimentation perturbation is attributed to faulting associated with the rifting and may have resulted in the alteration of hydrology forming the modern day Okavango delta. We infer that this time period may represent the age of the latest rift reactivation and fault growth and propagation within the ORZ.

  16. Deep crustal earthquakes in North Tanzania, East Africa: Interplay between tectonic and magmatic processes in an incipient rift

    NASA Astrophysics Data System (ADS)

    Albaric, Julie; Déverchère, Jacques; Perrot, Julie; Jakovlev, Andrey; Deschamps, Anne

    2014-02-01

    In this study, we explore the origin of lower crustal seismicity and the factors controlling rift propagation using seismological data recorded within the youngest part of the East African Rift System, the North Tanzanian Divergence (NTD). Most earthquakes below Lake Manyara occur at depth ranging between 20 and 40 km and have a swarm-like distribution. Focal mechanisms of 26 events indicate a combination of strike-slip and normal faulting involving Archaean basement structures and forming a relay zone. The derived local stress regime is transtensive and the minimum principal stress is oriented N110°E. Crustal seismic tomography reveals low-velocity anomalies below the rifted basins in the NTD, interpreted as localized thermomechanical perturbations promoting fluid release and subsequent seismicity in the lower crust. SKS splitting analysis in the NTD indicates seismic anisotropy beneath 17 stations most likely due to aligned magma lenses and/or dikes beneath the rift and to the lithospheric fabrics. Our results favor a strain pattern intermediate between purely mechanical and purely magmatic. We suggest that melt products arising from a large asthenospheric thermal anomaly enhance lithospheric weakening and facilitate faulting and creeping on critically oriented inherited structures of the Precambrian lower crust. Although the crust is unlikely weakened at a point comparable to other parts of the East African Rift System, this deep-seated thermomechanical process is efficient enough to allow slow rift propagation within the eastern Tanzanian cratonic edge.

  17. Hydrothermal vents in Lake Tanganyika, East African, Rift system

    NASA Astrophysics Data System (ADS)

    Tiercelin, Jean-Jacques; Pflumio, Catherine; Castrec, Maryse; Boulégue, Jacques; Gente, Pascal; Rolet, Joël; Coussement, Christophe; Stetter, Karl O.; Huber, Robert; Buku, Sony; Mifundu, Wafula

    1993-06-01

    Sublacustrine hydrothermal vents with associated massive sulfides were discovered during April 1987 at Pemba and Cape Banza on the Zaire side of the northern basin of Lake Tanganyika, East African Rift system. New investigations by a team of ten scuba divers during the multinational (France, Zaire, Germany, and Burundi) TANGANYDRO expedition (August-October 1991) found hydrothermal vents down to a depth of 46 m along north-trending active faults bounding the Tanganyika rift on the western side. Temperatures from 53 to 103 °C were measured in hydrothermal fluids and sediments. Veins of massive sulfides 1-10 cm thick (pyrite and marcasite banding) were found associated with vents at the Pemba site. At Cape Banza,active vents are characterized by 1-70-cm-high aragonite chimneys, and there are microcrystalline pyrite coatings on the walls of hydrothermal pipes. Hydrothermal fluid end members show distinctive compositions at the two sites. The Pemba end member is a NaHCO3-enriched fluid similar to the NaHCO3 thermal fluids from lakes Magadi and Bogoria in the eastern branch off the rift. The Cape Banza end member is a solution enriched in NaCl. Such brines may have a deep-seated basement origin, as do the Uvinza NaCl brines on the eastern flank of the Tanganyika basin. Geothermometric calculations have yielded temperatures of fluid-rock interaction off 219 and 179 °C in the Pemba and Cape Banza systems, respectively. Abundant white or reddish-brown microbial colonies resembling Beggiatoa mats were found surrounding the active vents. Thermal fluid circulation is permitted by opening of cracks related to 130 °N normal-dextral faults that intersect the north- south major rift trend. The source of heat for such hydrothermal systems may relate to the existence of magmatic bodies under the rift, which is suggested by the isotopic composition of carbon dioxide released at Pemba and Cape Banza.

  18. Clastic rocks associated with the Midcontinent rift system in Iowa

    USGS Publications Warehouse

    Anderson, Raymond R.; McKay, Robert M.

    1997-01-01

    The Middle Proterozoic Midcontinent Rift System (MRS) of North America is a failed rift that formed in response to region-wide stresses about 1,100 Ma. In Iowa, the MRS is buried beneath 2,200?3,500 ft of Paleozoic and Mesozoic sedimentary rocks and Quaternary glaciogenic deposits. An extremely large volume of sediments was deposited within basins associated with the rift at several stages during its development. Although the uplift of a rift-axial horst resulted in the erosional removal of most of these clastic rocks from the central region of the MRS in Iowa, thick sequences are preserved in a series of horst-bounding basins. Recent studies incorporating petrographic analysis, geophysical modeling, and other analytical procedures have led to the establishment of a preliminary stratigraphy for these clastic rocks and interpretations of basin geometries. This information has allowed the refinement of existing theories and history of MRS formation in Iowa. Additionally, drill samples previously interpreted as indicating the existence of early Paleozoic basins overlying the Proterozoic MRS basins were re-examined. Samples previously interpreted as deep-lying Paleozoic rocks are now known to have caved from upper levels of the drillhole and were out of stratigraphic position. No deep Paleozoic basins exist in this area. These investigations led to the development of petrographic parameters useful in differentiating the Proterozoic MRS Red clastics from Paleozoic clastic rocks having similar lithologies.

  19. A common mantle plume source beneath the entire East African Rift System revealed by coupled helium-neon systematics

    NASA Astrophysics Data System (ADS)

    Halldórsson, Sæmundur A.; Hilton, David R.; Scarsi, Paolo; Abebe, Tsegaye; Hopp, Jens

    2014-04-01

    We report combined He-Ne-Ar isotope data of mantle-derived xenoliths and/or lavas from all segments of the East Africa Rift System (EARS). Plume-like helium isotope (3He/4He) ratios (i.e., greater than the depleted MORB mantle (DMM) range of 8 ± 1RA) are restricted to the Ethiopia Rift and Rungwe, the southernmost volcanic province of the Western Rift. In contrast, neon isotope trends reveal the presence of an ubiquitous solar (plume-like) Ne component throughout the EARS, with (21Ne/22Ne)EX values (where (21Ne/22Ne)EX is the air-corrected 21Ne/22Ne ratio extrapolated to Ne-B) as low as 0.034, close to that of solar Ne-B (0.031). Coupling (21Ne/22Ne)EX with 4He/3He ratios indicates that all samples can be explained by admixture between a single mantle plume source, common to the entire rift, and either a DMM or subcontinental lithospheric mantle source. Additionally, we show that the entire sample suite is characterized by low 3He/22NeS ratios (mostly < 0.2)—a feature characteristic of oceanic hot spots such as Iceland. We propose that the origin of these unique noble gas signatures is the deeply rooted African Superplume which influences magmatism throughout eastern Africa. We argue that the Ethiopia and Kenya domes represent two different heads of this common mantle plume source.

  20. The uppermost mantle shear wave velocity structure of eastern Africa from Rayleigh wave tomography: constraints on rift evolution

    NASA Astrophysics Data System (ADS)

    O'Donnell, J. P.; Adams, A.; Nyblade, A. A.; Mulibo, G. D.; Tugume, F.

    2013-08-01

    An expanded model of the 3-D shear wave velocity structure of the uppermost mantle beneath eastern Africa has been developed using earthquakes recorded by the AfricaArray East African Seismic Experiment in conjunction with data from permanent stations and previously deployed temporary stations. The combined data set comprises 331 earthquakes recorded on a total of 95 seismic stations spanning Kenya, Uganda, Tanzania, Zambia and Malawi. In this study, data from 149 earthquakes were used to determine fundamental-mode Rayleigh wave phase velocities at periods ranging from 20 to 182 s using the two-plane wave method, and then combined with the similarly processed published measurements and inverted for a 3-D shear wave velocity model of the uppermost mantle. New features in the model include (1) a low-velocity region in western Zambia, (2) a high-velocity region in eastern Zambia, (3) a low-velocity region in eastern Tanzania and (4) low-velocity regions beneath the Lake Malawi rift. When considered in conjunction with mapped seismicity, these results support a secondary western rift branch striking southwestwards from Lake Tanganyika, likely exploiting the relatively weak lithosphere of the southern Kibaran Belt between the Bangweulu Block and the Congo Craton. We estimate a lithospheric thickness of ˜150-200 km for the substantial fast shear wave anomaly imaged in eastern Zambia, which may be a southward subsurface extension of the Bangweulu Block. The low-velocity region in eastern Tanzania suggests that the eastern rift branch trends southeastwards offshore eastern Tanzania coincident with the purported location of the northern margin of the proposed Ruvuma microplate. Pronounced velocity lows along the Lake Malawi rift are found beneath the northern and southern ends of the lake, but not beneath the central portion of the lake.

  1. Application of knowledge-driven spatial modelling approaches and uncertainty management to a study of Rift Valley fever in Africa

    PubMed Central

    Clements, Archie CA; Pfeiffer, Dirk U; Martin, Vincent

    2006-01-01

    Background There are few studies that have investigated uncertainties surrounding the scientific community's knowledge of the geographical distribution of major animal diseases. This is particularly relevant to Rift Valley fever (RVF), a zoonotic disease causing destructive outbreaks in livestock and man, as the geographical range of the disease is widening to involve previously unaffected regions. In the current study we investigate the application of methods developed in the decision sciences: multiple criteria decision making using weighted linear combination and ordered weighted averages, and Dempster-Shafer theory, implemented within the geographical information system IDRISI, to obtain a greater understanding of uncertainty related to the geographical distribution of RVF. The focus is on presenting alternate methods where extensive field data are not available and traditional, model-based approaches to disease mapping are impossible to conduct. Results Using a compensatory multiple criteria decision making model based on weighted linear combination, most of sub-Saharan Africa was suitable for endemic circulation of RVF. In contrast, areas where rivers and lakes traversed semi-arid regions, such as those bordering the Sahara, were highly suitable for RVF epidemics and wet, tropical areas of central Africa had low suitability. Using a moderately non-compensatory model based on ordered weighted averages, the areas considered suitable for endemic and epidemic RVF were more restricted. Varying the relative weights of the different factors in the models did not affect suitability estimates to a large degree, but variations in model structure had a large impact on our suitability estimates. Our Dempster-Shafer analysis supported the belief that a range of semi-arid areas were suitable for RVF epidemics and the plausibility that many other areas of the continent were suitable. Areas where high levels of uncertainty were highlighted included the Ethiopian Highlands

  2. Lake level change and total water discharge in East Africa Rift Valley from satellite-based observations

    NASA Astrophysics Data System (ADS)

    Hassan, Ayman A.; Jin, Shuanggen

    2014-06-01

    The measurement of total basin water discharge is important for understanding the hydrological and climatologic issues related to the water and energy cycles. Climatic extreme events are normal climatic occurrences in Africa. For example, extensive droughts are regular features in the last few decades in parts of East Africa, which suffers from a lack of in situ observations as well as a lack of regional hydrological models. In this study, multi-disciplinary different types of space-borne observations and global hydrological models are used to study total water discharge in the Great Rift Valley of East Africa (i.e. Lakes Victoria, Tanganyika, and Malawi) from January 2003 to December 2012. The data include the following: (1) total water storage (TWS) variations from Gravity Recovery and Climate Experiment (GRACE), (2) the lake level variations from Satellite Alimetric data, (3) rainfall from Tropical Rainfall Measurement Mission (TRMM) products, (4) soil moisture from WaterGAP Global Hydrology Model (WGHM), and (5) water fluxes from Global Land Data Assimilation System (GLDAS). Results show that a significant decline in the average lake level is found for all of the three lakes between 2003 and 2006. GRACE TWS variations of the whole basin area show the same pattern of variation as the average lake level variations estimated from Altimetric data. The TWS in the basin area of Lakes Victoria and Malawi is governed by the surface water stored in each lake itself, while for Lake Tanganyika, it is governed by both surface water and the soil moisture content in the basin area. Furthermore, the effect of rainfall on TWS is also studied. A phase lag of ~ 2 months is found between TRMM rainfall and GRACE TWS (generally, rainfall precedes the GRACE TWS) for the three lakes. In addition, the regional evapotranspiration ET is estimated from the water balance equation using GRACE land-water solutions, rainfall data from TRMM and runoff values obtained as a fraction of rainfall

  3. Sediment infill within rift basins: Facies distribution and effects of deformation: Examples from the Kenya and Tanganyika Rifts, East Africa

    SciTech Connect

    Tiercelin, J.J.; Lezzar, K.E. ); Richert, J.P. )

    1994-07-01

    Oil is known from lacustrine basins of the east African rift. The geology of such basins is complex and different depending on location in the eastern and western branches. The western branch has little volcanism, leading to long-lived basins, such as Lake Tanganyika, whereas a large quantity of volcanics results in the eastern branch characterized by ephemeral basins, as the Baringo-Bogoria basin in Kenya. The Baringo-Bogoria basin is a north-south half graben formed in the middle Pleistocene and presently occupied by the hypersaline Lake Bogoria and the freshwater Lake Baringo. Lake Bogoria is fed by hot springs and ephemeral streams controlled by grid faults bounding the basin to the west. The sedimentary fill is formed by cycles of organic oozes having a good petroleum potential and evaporites. On the other hand, and as a consequence of the grid faults, Lake Baringo is fed by permanent streams bringing into the basin large quantities of terrigenous sediments. Lake Tanganyika is a meromictic lake 1470 m deep and 700 km long, of middle Miocene age. It is subdivided into seven asymmetric half grabens separated by transverse ridges. The sedimentary fill is thick and formed by organic oozes having a very good petroleum potential. In contrast to Bogoria, the lateral distribution of organic matter is characterized by considerable heterogeneity due to the existence of structural blocks or to redepositional processes.

  4. Crust and Mantle Structure of a Closed Rift System from the Superior Province Rifting Earthscope Experiment (SPREE) (Invited)

    NASA Astrophysics Data System (ADS)

    van der Lee, S.; Wolin, E.; Bollmann, T. A.; Tekverk, K.

    2013-12-01

    The existence of the 1.1 Ga Mid-continent Rift System (MRS) in the Great Lakes region of North America is well known on account of its prominent gravity and magnetic anomalies. These elongated anomalies are associated with dense igneous rocks, which surface in sparse outcrops and are imaged in a handful of active source profiles. Part of the MRS cuts across the Archean Superior Craton while other parts cut through at least three different Proterozoic terranes, though there are indications that offsets between rift segments, such as the Belle Plaine Fault, may follow pre-existing terrane boundaries. The total volume of igneous rock imaged in active source data is consistently estimated as at least one million km3, which is enough for a sea floor of the size of the current Gulf of California, or five times the size of Lake Baikal. However, cessation of rifting and closure of the rift uplifted the igneous rocks along the axes, causing lateral gravity gradients of 150 mgal over 50 km between the gravity high above the uplifted igneous rift axis and the low above the sediment deposits in the original rift flanks. Our seismic experiment (SPREE) covers an area around a one thousand km long segment of the MRS. A long, interrupted line of stations follows the rift axis, another line cuts across this high gravity gradient, yet another line cuts across the Belle Plaine rift axis offset, and a TA-like station group north of Lake Superior complements surrounding Transportable Array coverage. The Superior Province Rifting Earthscope Flexible Array (FA) Experiment (SPREE) has been running for two years with a data return of over 96%. Preliminary SPREE and other analyses show puzzling low velocities along the rift axis and complex Moho structure beneath thickened crust. Other crustal features include a large diversity of sediments, from soggy Quaternary mud through meta-sedimentary Proterozoic rocks. At the time of writing we are quantifying the effects of this complex geological

  5. The complex post-rift evolution of the South Atlantic margin, South Africa: new insights from joint inversion of apatite (U-Th)/He and fission track thermochronometry.

    NASA Astrophysics Data System (ADS)

    Wildman, Mark; Brown, Roderick; Persano, Cristina; Beucher, Romain; Stuart, Finlay

    2013-04-01

    The continental edge of southwestern Africa has long been seen as a type example of a high elevation passive margin, with its characteristic topography forming during or shortly after rifting (c. 130 Ma). Recent work along the South Atlantic passive margin has highlighted the importance of interactions between rift-tectonics, mantle flow and dynamic topography on controlling margin evolution, however, the temporal relationship between these processes is still poorly understood. There is now increasing evidence from satellite imagery, onshore field observations (e.g. Viola et al., 2012) and offshore sedimentary basin analysis (e.g. Hirsch et al., 2010) that suggests that these processes have resulted in a much more complex structural and thermal history along the margin than previously thought. A critical step towards developing a better understanding of the post-rift evolution of this margin is to quantify the surface response (i.e. uplift and erosion) to these major structural and thermal events. Apatite fission track analysis (AFTA) has been used world-wide as a powerful means of extracting quantitative constraints on the timing and rate of major episodes of onshore denudation. Previous AFTA studies in SW Africa have identified two distinct cooling events occurred during early and late Cretaceous, respectively. However, in places AFT ages vary significantly over relatively short distances and this has been interpreted to indicate local differential erosion levels controlled by tectonic displacements related to fault reactivation. A limitation of the AFT system is that it is sensitive to a temperature range of c. 120-60°C and therefore is unable to evaluate the magnitude of denudation episodes where the amounts are less than c. 1.5-2 km. So while the Cretaceous history of erosion is well established from existing AFTA data, the details of the timing and amount of erosion occurring during the Cenozoic remain relatively poorly constrained. The apatite (U

  6. Evolution of the Lake Victoria basin in the context of coeval rift initiation in East Africa: a 3D numerical model approach

    NASA Astrophysics Data System (ADS)

    Wichura, Henry; Quinteros, Javier; Melnick, Daniel; Brune, Sascha; Schwanghart, Wolfgang; Strecker, Manfred R.

    2015-04-01

    Over the last four years sedimentologic and thermochronologic studies in the western and eastern branches of the Cenozoic East African Rift System (EARS) have supported the notion of a broadly contemporaneous onset of normal faulting and rift-basin formation in both segments. These studies support previous interpretations based on geophysical investigations from which an onset of rifting during the Paleogene had been postulated. In light of these studies we explore the evolution of the Lake Victoria basin, a shallow, unfaulted sedimentary basin centered between both branches of the EARS and located in the interior of the East African Plateau (EAP). We quantify the fluvial catchment evolution of the Lake Victoria basin and assess the topographic response of African crust to the onset of rifting in both branches. Furthermore, we evaluate and localize the nature of strain and flexural rift-flank uplift in both branches. We use a 3D numerical forward model that includes nonlinear temperature- and stress-dependent elasto-visco-plastic rheology. The model is able to reproduce the flexural response of variably thick lithosphere to rift-related deformation processes such as lithospheric thinning and asthenospheric upwelling. The model domain covers the entire EAP and integrates extensional processes in a heterogeneous, yet cold and thick cratonic block (Archean Tanzania craton), which is surrounded by mechanically weaker Proterozoic mobile belts, which are characterized by thinner lithosphere ("thin spots"). The lower limits of the craton (170 km) and the mobile belts (120 km) are simulated by different depths of the 1300 °C lithosphere-asthenosphere boundary. We assume a constant extension rate of 4 mm/a throughout the entire simulation of 30 Ma and neglect the effect of dynamic topography and magmatism. Even though the model setup is very simple and the resolution is not high enough to calculate realistic rift-flank uplift, it intriguingly reveals important topographic

  7. Decision-support tool for prevention and control of Rift Valley fever epizootics in the Greater Horn of Africa.

    PubMed

    2010-08-01

    In East Africa, Rift Valley fever (RVF) usually occurs as explosive epizootics with prolonged inter-epidemic periods on the order of 8 to 10 years. The episodic nature of the disease and the rapid evolution of outbreaks create special challenges for its mitigation and control. Following the events of the 2006 and 2007 RVF outbreak in East Africa, decision-makers assembled their collective experiences in the form of a risk-based decision support tool to help guide responses in future emergencies. The premise of the tool is that a series of natural events are indicative of the increasing risk of an outbreak and that actions should be matched to this evolving risk profile. In this manner, investment in prevention and control can be qualitatively optimized. The decision support tool is a living document written through stakeholder input. This publication captures the current tool as an example of risk-based decision support. PMID:20682910

  8. Benue trough and the mid-African rift system

    SciTech Connect

    Thomas, D.

    1996-01-29

    Large areas of the Anambra and Gongola basins have distinct petroleum exploration problems: a geologically persistent high geothermal gradient that promoted Cretaceous source rock maturation into the gas phase very early on; intrusive lead-zinc mineralization veins attributed to the Senonian igneous and folding event; and meteoric water-flushing along the periphery of the basins. From preliminary analysis, these basins have to be considered high risk for the discovery of commercial oil accumulations. On the other hand, the petroleum potential of the Bornu basins seems favorable. This Nigerian northernmost rift basin continues into the Kanem basin of western Chad, which has proven oil accumulations in Coniacian deltaic sands. Cretaceous paleofacies is considered to be relatively continuous throughout both basins. Paleo-geothermal history is also considered to be similar, although some igneous activity is recorded in the Bornu basin (Senonian?). There is a very real possibility of kerogen-rich non-marine basal Albo-Aptian basin fill lacustrine source rocks, as found in the Doba basin, could be present in the deepest sections of the Nigerian rift basins. Due to the depths involved, no well is expected to penetrate the incipient graben-fill stage sequences; however, possible oil migration from these tectono-stratigraphic units would certainly enhance the petroleum potential of cooler sections of the rift system. As opposed to interpreted thermogenic gas which seems to be prevalent in the Anambra basin.

  9. Ouachita trough: Part of a Cambrian failed rift system

    NASA Astrophysics Data System (ADS)

    Lowe, Donald R.

    1985-11-01

    Pre-flysch (Cambrian-Mississippian) strata of the Ouachita Mountains of Arkansas and Oklahoma include two main sandstone lithofacies: (1) a craton-derived lithofacies made up largely of mature medium- to coarse-grained quartzose and carbonate detritus and, in some units, sediment eroded from exposed basement rocks and (2) an orogen-derived facies made up mainly of fine-grained quartzose sedimentary and metasedimentary debris and possibly, in lower units, a volcaniclastic component. Paleocurrent and distribution patterns indicate that detritus of facies I in the Benton uplift was derived from north and detritus of facies II throughout the Ouachitas was derived from south and east of the depositional basin. Overall sedimentological results suggest that the Ouachita trough was a relatively narrow, two-sided basin throughout most and probably all of its existence and never formed the southern margin of the North American craton. Regional comparisons suggest that it was one of several basins, including the Southern Oklahoma aulacogen, Reelfoot Rift, Illinois Basin, and Rome trough, that formed as a Cambrian failed rift system 150 to 250 m.y. after initial rifting along the Appalachian margin of the North American craton.

  10. Hydrothermal vents is Lake Tanganyika, East African Rift system

    SciTech Connect

    Tiercelin, J.J.; Pflumio, C.; Castrec, M.

    1993-06-01

    Sublacustrine hydrothermal vents with associated massive sulfides were discovered during April 1987 at Pemba and Cape Banza on the Zaire side of the northern basin of Lake Tanganyika, East African Rift system. New investigations by a team of ten scuba divers during the multinational (France, Zaire, Germany, and Burundi) TANGANYDRO expedition (August-October 1991) found hydrothermal vents down to a depth of 46 m along north-trending active faults bounding the Tanganyika rift on the western side. Temperatures from 53 to 103 {degrees}C were measured in hydrothermal fluids and sediments. Veins of massive sulfides 1-10 cm thick (pyrite and marcasite banding) were found associated with vents at the Pemba site. At Cape Banza, active vents are characterized by 1-70-cm-high aragonite chimneys, and there are microcrystalline pyrite coatings on the walls of hydrothermal pipes. Hydrothermal fluid end members show distinctive compositions at the two sites. The Pemba end member is a NaHCO{sub 3}-enriched fluid similar to the NaHCO{sub 3} thermal fluids form lakes Magadi and Bogoria in the eastern branch of the rift. The Cape Banza end member is a solution enriched in NaCl. Such brines may have a deep-seated basement origin, as do the Uvinza NaCl brines on the eastern flank of the Tanganyika basin. Geothermometric calculations have yielded temperatures of fluid-rock interaction of 219 and 179 {degrees}C in the Pemba and Cape Banza systems, respectively. Abundant white or reddish-brown microbial colonies resembling Beggiatoa mats were found surrounding the active vents. Thermal fluid circulation is permitted by opening of cracks related to 130{degrees}N normal-dextral faults that intersect the north-south major rift trend. The sources of heat for such hydrothermal systems may relate to the existence of magmatic bodies under the rift, which is suggested by the isotopic composition of carbon dioxide released at Pemba and Cape Banza. 21 refs., 2 figs.

  11. Active fault systems of the Kivu rift and Virunga volcanic province, and implications for geohazards

    NASA Astrophysics Data System (ADS)

    Zal, H. J.; Ebinger, C. J.; Wood, D. J.; Scholz, C. A.; d'Oreye, N.; Carn, S. A.; Rutagarama, U.

    2013-12-01

    H Zal, C Ebinger, D. Wood, C. Scholz, N. d'Oreye, S. Carn, U. Rutagarama The weakly magmatic Western rift system, East Africa, is marked by fault-bounded basins filled by freshwater lakes that record tectonic and climatic signals. One of the smallest of the African Great Lakes, Lake Kivu, represents a unique geohazard owing to the warm, saline bottom waters that are saturated in methane, as well as two of the most active volcanoes in Africa that effectively dam the northern end of the lake. Yet, the dynamics of the basin system and the role of magmatism were only loosely constrained prior to new field and laboratory studies in Rwanda. In this work, we curated, merged, and analyzed historical and digital data sets, including spectral analyses of merged Shuttle Radar Topography Mission topography and high resolution CHIRP bathymetry calibrated by previously mapped fault locations along the margins and beneath the lake. We quantitatively compare these fault maps with the time-space distribution of earthquakes located using data from a temporary array along the northern sector of Lake Kivu, as well as space-based geodetic data. During 2012, seismicity rates were highest beneath Nyiragongo volcano, where a range of low frequency (1-3 s peak frequency) to tectonic earthquakes were located. Swarms of low-frequency earthquakes correspond to periods of elevated gas emissions, as detected by Ozone Monitoring Instrument (OMI). Earthquake swarms also occur beneath Karisimbi and Nyamuragira volcanoes. A migrating swarm of earthquakes in May 2012 suggests a sill intrusion at the DR Congo-Rwanda border. We delineate two fault sets: SW-NE, and sub-N-S. Excluding the volcano-tectonic earthquakes, most of the earthquakes are located along subsurface projections of steep border faults, and intrabasinal faults calibrated by seismic reflection data. Small magnitude earthquakes also occur beneath the uplifted rift flanks. Time-space variations in seismicity patterns provide a baseline

  12. Discussion on final rifting evolution and breakup : insights from the Mid Norwegian - North East Greenland rifted system

    NASA Astrophysics Data System (ADS)

    Peron-Pinvidic, Gwenn; Terje Osmundsen, Per

    2016-04-01

    In terms of rifted margin studies, the characteristics of the distal and outer domains are among the today's most debated questions. The architecture and composition of deep margins are rarely well constrained and hence little understood. Except from in a handful number of cases (eg. Iberia-Newfoundland, Southern Australia, Red Sea), basement samples are not available to decipher between the various interpretations allowed by geophysical models. No consensus has been reached on the basement composition, tectonic structures, sedimentary geometries or magmatic content. The result is that non-unique end-member interpretations and models are still proposed in the literature. So, although these domains mark the connection between continents and oceans, and thus correspond to unique stages in the Earth's lithospheric life cycle, their spatial and temporal evolution are still unresolved. The Norwegian-Greenland Sea rift system represents an exceptional laboratory to work on questions related to rifting, rifted margin formation and sedimentary basin evolution. It has been extensively studied for decades by both the academic and the industry communities. The proven and expected oil and gas potentials led to the methodical acquisition of world-class geophysical datasets, which permit the detailed research and thorough testing of concepts at local and regional scales. This contribution is issued from a three years project funded by ExxonMobil aiming at better understanding the crustal-scale nature and evolution of the Norwegian-Greenland Sea. The idea was to take advantage of the data availability on this specific rift system to investigate further the full crustal conjugate scale history of rifting, confronting the various available datasets. In this contribution, we will review the possible structural and sedimentary geometries of the distal margin, and their connection to the oceanic domain. We will discuss the definition of 'breakup' and introduce a first order conceptual

  13. Pre-breakup geology of the Gulf of Mexico-Caribbean: Its relation to Triassic and Jurassic rift systems of the region

    SciTech Connect

    Bartok, P. )

    1993-02-01

    A review of the pre-breakup geology of west-central Pangea, comprised of northern South America, Gulf of Mexico and West Africa, combined with a study of the Mesozoic rift trends of the region confirms a relation between the rift systems and the underlying older grain of deformation. The pre-breakup analysis focuses attention on the Precambrian, Early Paleozoic and Late Paleozoic tectonic events affecting the region and assumes a Pindell fit. Two Late Precambrian orogenic belts are observed in the west central Pangea. Along the northern South American margin and Yucatan a paleo northeast trending Pan-African aged fold belt is documented. A second system is observed along West Africa extending from the High Atlas to the Mauritanides and Rockelides. During the Late Paleozoic, renewed orogenic activity, associated with the Gondwana/Laurentia suture, affected large segments of west central Pangea. The general trend of the system is northeast-southwest and essentially parallels the Gyayana Shield, West African, and eastern North American cratons. Mesozoic rifting closely followed either the Precambrian trends or the Late Paleozoic orogenic belt. The Triassic component focuses along the western portions of the Gulf of Mexico continuing into eastern Mexico and western South America. The Jurassic rift trend followed along the separation between Yucatan and northern South America. At Lake Maracaibo the Jurassic rift system eventually overlaps the Triassic rifts. The Jurassic rift resulted in the [open quotes]Hispanic Corridor[close quotes] that permitted Tethyan and Pacific marine faunas to mix at a time when the Gulf of Mexico underwent continental sedimentation.

  14. How Closed are Closed Lakes in Rifts? Significance of Hydraulic Gradients for the Budgets of Paleo-Lakes in East Africa

    NASA Astrophysics Data System (ADS)

    Olaka, L. A.

    2015-12-01

    The hydrogeology of rift lakes is complex due to the potential influence of faults and porous volcanic and volcanoclastic media on groundwater flow. We conducted a comprehensive study that integrated geological and hydrogeological data as well as the application of a linear decay model to estimate the groundwater flow between the two of the best-studied lake systems in East Africa, the adjacent Lakes Naivasha and Nakuru- Elmenteita in the Central Kenya Rift. Whereas both lake basins host relatively shallow lakes today, paleo-shorelines and sediments suggest >100 m deep lakes during a wetter climate during the Early Holocene during the so-called African Humid Period. Stable isotope data show variations form highly depleted to more enriched d18O waters. The linear-reservoir depletion model simulates the decline of the Early Holocene lakes in both basins to the modern levels. The altitude difference of ca. 100 m of both paleo-lake levels enables us to estimate the duration of the groundwater decline and the connectivity of the two basins via the Eburru/Gilgil barrier. The results suggest a decline of the groundwater levels during ca. 5 kyrs if there is no recharge, and between 2-2.7 kyrs based on the modern recharge of 0.52 m/yr as the end members of the delay time introduced by subsurface water flow to the hydrology of the lake system. The latter value suggests that ca. 40.95 cubic kilometres of water flowed from Lake Naivasha to Nakuru- Elmenteita at maximum lake level in the Early Holocene following the hydraulic gradient concurrent to the topographic slope. The unexpectedly large volume, more than half of the volume of the paleo-Lake Naivasha during the Early Holocene, emphasizes the importance of groundwater in hydrological modelling of paleo-lakes in rifts. Moreover, the subsurface connectivity of rift lakes also causes a significant lag time to the system introducing a nonlinear component to the system that has to be considered while interpreting paleo

  15. Modelling Rift Valley fever (RVF) disease vector habitats using active and passive remote sensing systems

    NASA Technical Reports Server (NTRS)

    Ambrosia, Vincent G.; Linthicum, K. G.; Bailey, C. L.; Sebesta, P.

    1989-01-01

    The NASA Ames Ecosystem Science and Technology Branch and the U.S. Army Medical Research Institute of Infectious Diseases are conducting research to detect Rift Valley fever (RVF) vector habitats in eastern Africa using active and passive remote-sensing. The normalized difference vegetation index (NDVI) calculated from Landsat TM and SPOT data is used to characterize the vegetation common to the Aedes mosquito. Relationships have been found between the highest NDVI and the 'dambo' habitat areas near Riuru, Kenya on both wet and dry data. High NDVI values, when combined with the vegetation classifications, are clearly related to the areas of vector habitats. SAR data have been proposed for use during the rainy season when optical systems are of minimal use and the short frequency and duration of the optimum RVF mosquito habitat conditions necessitate rapid evaluation of the vegetation/moisture conditions; only then can disease potential be stemmed and eradication efforts initiated.

  16. The Lake Albert Rift (uganda, East African Rift System): Deformation, Basin and Relief Evolution Since 17 Ma

    NASA Astrophysics Data System (ADS)

    Brendan, Simon; François, Guillocheau; Cécile, Robin; Olivier, Dauteuil; Thierry, Nalpas; Martin, Pickford; Brigitte, Senut; Philippe, Lays; Philippe, Bourges; Martine, Bez

    2016-04-01

    .5 Ma: Rift stage 1 (subsidence rate: > 500m/Ma up to 600-800 m/Ma; sedimentation rate: 2.4 km3/Ma) - Rifting climax; - 2.5-0.4 Ma: uplift of the Ruwenzori Mountains and shifting from an alluvial system to a network of bedrock river incision - Rift Stage 2 (subsidence rate: 450 to 250 m/Ma; sedimentation rate: 1.5 km3/Ma); - 0.4-0 Ma: long wavelength downwarping of the Tanzanian Craton, initiation of the Lake Victoria trough, drainage network inversion and uplift of the present-day Ugandan escarpment (normal faulting motion of the border faults) with formation of perched valleys associated to the Lower Pleistocene (2.5-0.4 Ma) rivers network. At larger scale, comparison of the Lake Albert Rift evolution with the data available in the basins of both eastern and western branches of the East African Rift System shows that most of the sedimentary basins experienced the same geometrical evolution from large basins with limited fault controls during Late Miocene to narrow true rift in Late Pleistocene (e.g. Northern and Central Kenyan Basins), in agreement with the volcanism distribution, large (width >100 km) during the Miocene times, narrower (width x10 km) from Late Pliocene to Pleistocene times and today limited to narrow rifts.

  17. Geochronological and geochemical assessment of Cenozoic volcanism from the Terror Rift region of the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

    Rilling, Sarah E.

    The work presented in this dissertation explains results from three different methods to determine the relation between tectonism and rift-related volcanism in the Terror Rift region of the West Antarctic Rift System (WARS). Alkaline lavas from seven submarine features, Beaufort Island and Franklin Islands, and several locations near Mt Melbourne were dated by 40Ar/39Ar geochronology and analyzed for elemental and isotopic chemical signatures. Each chapter addresses a different aspect of the hypothesis that the presence of volatiles, primarily H2O or CO2, in the magma source has led to anomalously high volumes of magmatism after rift-related decompressional melting rather than requiring an active mantle plume source. Chapter 2 provides the temporal framework, illustrating that the sampled features range in age from 6.7 Ma to 89 ka, post-dating the main Miocene age phase of Terror Rift extension. Chapter 3 illustrates the traditional enriched elemental and isotopic chemical signatures to support the overall homogeneity of these lavas and previously analyzed areas of the WARS. This chapter also provides a new model for the generation of the Pb isotopic signatures consistent with a history of metasomatism in the magma source. Chapter 4 provides an entirely new chemical dataset for the WARS. The first platinum group element (PGE) abundances and extremely unradiogenic Os isotopic signatures of Cenozoic lavas from Antarctica provide the strongest evidence of melting contributions from a lithospheric mantle source. The combined results from these three studies consistently support the original hypothesis of this dissertation. New evidence suggests that WARS related lavas are not related to a mantle plume(s) as previously proposed. Instead, they are generated by passive, decompressional melting of a source, likely a combination of the asthenospheric and lithospheric mantle, which has undergone previous melting events and metasomatism.

  18. Rift Valley fever virus infection in African Buffalo (Syncerus caffer) herds in rural South Africa: Evidence of interepidemic transmission

    USGS Publications Warehouse

    LaBeaud, A.D.; Cross, P.C.; Getz, W.M.; Glinka, A.; King, C.H.

    2011-01-01

    Rift Valley fever virus (RVFV) is an emerging biodefense pathogen that poses significant threats to human and livestock health. To date, the interepidemic reservoirs of RVFV are not well defined. In a longitudinal survey of infectious diseases among African buffalo during 2000-2006, 550 buffalo were tested for antibodies against RVFV in 820 capture events in 302 georeferenced locations in Kruger National Park, South Africa. Overall, 115 buffalo (21%) were seropositive. Seroprevalence of RVFV was highest (32%) in the first study year, and decreased progressively in subsequent years, but had no detectable impact on survival. Nine (7%) of 126 resampled, initially seronegative animals seroconverted during periods outside any reported regional RVFV outbreaks. Seroconversions for RVFV were detected in significant temporal clusters during 2001-2003 and in 2004. These findings highlight the potential importance of wildlife as reservoirs for RVFV and interepidemic RVFV transmission in perpetuating regional RVFV transmission risk. Copyright ?? 2011 by The American Society of Tropical Medicine and Hygiene.

  19. Seismic hazard assessment of the Kivu rift segment based on a new sismo-tectonic zonation model (Western Branch of the East African Rift system)

    NASA Astrophysics Data System (ADS)

    Havenith, Hans-Balder; Delvaux, Damien

    2015-04-01

    In the frame of the Belgian GeoRisCA multi-risk assessment project focused on the Kivu and Northern Tanganyika Region, a seismic hazard map has been produced for this area. It is based on a on a recently re-compiled catalogue using various local and global earthquake catalogues. The use of macroseismic epicenters determined from felt earthquakes allowed to extend the time-range back to the beginning of the 20th century, thus spanning about 100 years. The magnitudes have been homogenized to Mw and the coherence of the catalogue has been checked and validated. The seismo-tectonic zonation includes 10 seismic source areas that have been defined on the basis of the regional geological structure, neotectonic fault systems, basin architecture and distribution of earthquake epicenters. The seismic catalogue was filtered by removing obvious aftershocks and Gutenberg-Richter Laws were determined for each zone. On the basis of this seismo-tectonic information and existing attenuation laws that had been established by Twesigomwe (1997) and Mavonga et al. (2007) for this area, seismic hazard has been computed with the Crisis 2012 (Ordaz et al., 2012) software. The outputs of this assessment clearly show higher PGA values (for 475 years return period) along the Rift than the previous estimates by Twesigomwe (1997) and Mavonga (2007) while the same attenuation laws had been used. The main reason for these higher PGA values is likely to be related to the more detailed zonation of the Rift structure marked by a strong gradient of the seismicity from outside the rift zone to the inside. Mavonga, T. (2007). An estimate of the attenuation relationship for the strong ground motion in the Kivu Province, Western Rift Valley of Africa. Physics of the Earth and Planetary Interiors 62, 13-21. Ordaz M, Martinelli F, Aguilar A, Arboleda J, Meletti C, D'Amico V. (2012). CRISIS 2012, Program for computing seismic hazard. Instituto de Ingeniería, Universidad Nacional Autónoma de M

  20. The Corinth Rift Laboratory, Greece (CRL) : A Multidisciplinary Near Fault Observatory (NFO) on a Fast Rifting System

    NASA Astrophysics Data System (ADS)

    Bernard, P.; Lyon-Caen, H.; Deschamps, A.; Briole, P.; Lambotte, S.; Ford, M.; Scotti, O.; Beck, C.; Hubert-Ferrari, A.; Boiselet, A.; Godano, M.; Matrullo, E.; Meyer, N.; Albini, P.; Elias, P.; Nercessian, A.; Katsonopoulou, D.; Papadimitriou, P.; Voulgaris, N.; Kapetanidis, V.; Sokos, E.; Serpetsidaki, A.; el Arem, S.; Dublanchet, P.; Duverger, C.; Makropoulos, K.; Tselentis, A.

    2014-12-01

    The western rift of Corinth (Greece) is one of the most active tectonic structures of the euro-mediterranean area. Its NS opening rate is 1.5 cm/yr ( strain rate of 10-6/yr) results into a high microseismicity level and a few destructive, M>6 earthquakes per century, activating a system of mostly north dipping normal faults. Since 2001, monitoring arrays of the European Corinth Rift Laboratory (CRL, www.crlab.eu) allowed to better track the mechanical processes at work, with short period and broad band seismometers, cGPS, borehole strainmeters, EM stations, …). The recent (300 kyr) tectonic history has been revealed by onland (uplifted fan deltas and terraces) and offshore geological studies (mapping, shallow seismic, coring), showing a fast evolution of the normal fault system. The microseismicity, dominated by swarms lasting from days to months, mostly clusters in a layer 1 to 3 km thick, between 6 and 9 km in depth, dipping towards north, on which most faults are rooting. The diffusion of the microseismicity suggests its triggering by pore pressure transients, with no or barely detected strain. Despite a large proportion of multiplets, true repeaters seem seldom, suggesting a minor contribution of creep in their triggering, although transient or steady creep is clearly detected on the shallow part of some majors faults. The microseismic layer may thus be an immature, downward growing detachment, and the dominant rifting mechanism might be a mode I, anelastic strain beneath the rift axis , for which a mechanical model is under development. Paleoseismological (trenching, paleoshorelines, turbidites), archeological and historical studies completed the catalogues of instrumental seismicity, motivating attempts of time dependent hazard assessment. The Near Fault Observatory of CRL is thus a multidisciplinary research infrastructure aiming at a better understanding and modeling of multiscale, coupled seismic/aseismic processes on fault systems.

  1. Volcanic water flows could have flooded Ganymede's planetary rift system

    SciTech Connect

    Allison, M.L.; Clifford, S.M.

    1985-01-01

    Global expansion on Ganymede of only 1 or 2% created a planetary rift system which was resurfaced over a significant period of the planet's history creating bright, grooved terrain. The most reasonable model entails flooding of grabens by water or slush magmas which rose to the surface along normal faults in the rift system. Various models exist for the origin of the water magmas including isostatic rise of freezing ice I or diapirs of unstable ice III. A model considering the heat balance at the surface of an ice-covered water flow is constructed with the simplifying assumption that both laminar flow and a solid ice cover are achieved relatively soon after eruption. The ice cover will thicken until the underlying flowing water is entirely frozen. Energy into the system comes from solar radiation and the latent heat of freezing. Energy lost will be by evaporative and radiative cooling at the ice surface and by conduction into the substratum. Solving the heat balance allows a prediction for the volume of magma that can flood the surface. For example a flow 5 m thick will take tens of days to freeze, so that discharge rates equal to that of average terrestrial basalt flows could flood relatively large areas of the surface before freezing. Volcanic flooding is therefore a physically viable mechanism for the origin of bright terrain. During freezing the water/ice volume increases, lifting and fracturing the ice cover. These fractures may localize continued tectonic forces producing large displacements and creating the present grooved terrain.

  2. Beta Regio rift system on Venus: Geologic interpretation of Magellan images

    NASA Technical Reports Server (NTRS)

    Nikishin, A. M.; Bobina, N. N.; Borozdin, V. K.; Burba, G. A.

    1993-01-01

    Magellan SAR images and altimetric data were used to produce a new geologic map of the Northern part of Beta Regio within the frames of C1-30N279 mapsheet. It was part of our contributions into C1-formate geologic mapping efforts. The original map is at 1:8,000,000 scale. The rift structures are typical for Beta Regio on Venus. There are many large uplifted tessera areas on Beta upland. They occupy areas of higher topography. These tessera are partly burried by younger volcanic cover of plain material. These observations show that Beta upland was formed mainly due to lithospheric tectonical uplifting, and only partly was constructed by volcanic activity. A number of rift valleis traverse Beta upland and spread to the surrounding lowlands. The largest rift crosses Beta N to S. Typical width of rifts is 40 to 160 km. Rift valleis in this region are structurally represented by crustal grabens and half-grabens. There are symmetrical and asymmetrical rifts. A lot of them have shoulder uplifts with the relative high up to 0.5-1 km and width 40 to 60 km. Preliminary analysis of the largest rift valley structural cross-sections leads to the conclusion that it originated due to a 5-10 percent crustal extension. The prominent shield volcano - Theia Mons - is located at the center of Beta rift system. It could be considered as the surface manifestation of the upper mantle hot spot. Most of the rift belts are located radially to Theia Mons. The set of these data leads to conclusion that Beta rift system has an 'active-passive' origin. It was formed due to the regional tectonic lithospheric extension. Rifting was accelerated by the upper mantle hot spot located under the center of passive extension (under Beta Regio).

  3. NW Africa post-rift tectonics: fieldwork constraints from an "unfitting" anticline in west Morocco

    NASA Astrophysics Data System (ADS)

    Fernández-Blanco, David; Gouiza, Mohamed

    2015-04-01

    The evolution of the Moroccan Atlantic rifted margin is marked by a period of abnormal and excessive early post-rift subsidence during the Late Jurassic-Early Cretaceous affecting the proximal coastal basins, the continental shelf and the distal deep basins, which acted coevally to km-scale uplift and erosion of large domains to the east. The tectonics of the uplift event are still unclear, as it took place 30 to 50 Myr after lithospheric breakup between Morocco and Nova Scotia and prior to the Atlas/Alpine contraction, which gave rise to the Atlas and the Rif mountain belts. The Essaouira-Haha basin, located on the coastal plain of the Atlantic rifted margin of Morocco, and bounded by two uplifted Paleozoic basement highs (i.e. the Massif Ancien of Marrakech, to the east, and the Jebilet, to the northeast), is an ideal location to investigate the tectonic processes that might have triggered these vertical movements. Although most of the deformation observed in the basin is classically attributed to Upper Cretaceous halokinesis and Neogene Atlas contraction, recent works have shown the existence of contractional structures. We carry out a structural analysis of the Jbel Amsittene Anticline, located in the middle of the Essaouira-Haha basin to investigate the tectonics of its formation and its relationship with the above-mentioned exhumation. We show structural field data along several cross-sections transecting the anticline, and characterize a salt-cored fault propagation fold verging north, with a Triassic salt acting as a detachment plane. Regional kinematic indicators and structures show overall NNW-SSE to NNE-SSW shortening and active tectonics during the postrift phase, as indicated by syn-tectonic wedges seen for the Late Jurassic to Early Cretaceous period. These facts discard the "salt-drives-tectonics" theory to let "tectonic-drives-salt" one to rise, and point to factors other than small-cell mantle convection acting during the evolution of the Moroccan

  4. The role of magmatic processes in strain localization from rift onset to rupture in East Africa and the Red Sea (Invited)

    NASA Astrophysics Data System (ADS)

    Ebinger, C. J.; Lindsey, N.; Cote, D. M.; Keir, D.; Ayele, A.; Tiberi, C.

    2010-12-01

    The continental rift zones of East Africa, Red Sea, and Gulf of Aden are sites of mechanical stretching and heating of the lithosphere in response to regional plate pulling forces and dynamic upwelling(s) within the underlying mantle. In the East African and the southern Red Sea rifts magmatism accompanied initial faulting and plateau uplift, and magma intrusion continues to accommodate deformation in many sectors, including the deeply rooted Tanzanian craton. The surface volcanism is often spectacularly evident, but the intrusion of magma in the form of dikes and sills that do not reach Earth’s surface is far more difficult to detect. The aims of our data synthesis and modeling studies are to recognize and quantify the contribution of magmatism to plate boundary deformation within one geodynamic province: the uplifted plateaux above the African superplume province. The intense and ongoing dike intrusions that commenced in 2005 in the southernmost Red Sea rift in Afar proved an eye-opener, and alerted geoscientists to the attendant seismic and volcanic hazards within active rift zones. Recent dike intrusions in the East African and Red Sea rifts provide some constraints on the time and length scales of diking processes. Current strain distributions estimated from cumulative seismic and geodetic moment release (Lindsey et al., this session) indicate predominantly aseismic deformation, even near small volume volcanoes. We compare and contrast observations of strain and volcanism with thermo-mechanical properties of the plate to predict zones of subsurface magma intrusion and possible metasomatic modification of the mantle lithosphere.

  5. Earthquakes along the East African Rift System: A multiscale, system-wide perspective

    NASA Astrophysics Data System (ADS)

    Yang, Zhaohui; Chen, Wang-Ping

    2010-12-01

    On the basis of a comprehensive data set of precisely determined depths of 121 large to moderate-sized earthquakes along and near the entire East African Rift System (EARS), there are three distinct patterns in focal depths which seem to correlate with progressive stages in the development of the largest active rift in the world. First, away from both ends of the western, younger branch of the EARS, very large (Mw ≥ 7) earthquakes occurred in the top 15 km of the crust where surficial expressions of rifting are yet to appear. Curiously, there are unusually deep aftershocks reaching down to 35 ± 3 km. Second, under well-developed but amagmatic rift segments, focal depths show a bimodal distribution, with peaks centered near depths of about 15 ± 5 km and 35 ± 5 km. This pattern is present both under the main axis of the EARS, where rift zone have lengths approaching 1000 km, and beneath rift units 10 times shorter in length. Underside reflections off the Moho indicate that at least part of the second peak in seismicity is due to mantle earthquakes down to 44 ± 4 km, attesting to high differential stress in the mantle lithosphere which is capable of accumulating seismogenic, elastic strain (the "jelly sandwich" rheology). Third, beneath magmatic segments of well-developed rifts, seismicity is largely confined to the upper 15 km of the crust as observed previously, akin to the pattern along mid-ocean ridges where plastic flow due to high temperature inhibits accumulation of shear stress deep in the lithosphere.

  6. Continental rift jumps

    NASA Astrophysics Data System (ADS)

    Wood, Charles A.

    1983-05-01

    Continental rift jumps, analogous to jumps of oceanic spreading ridges, are here proposed to be common. Good examples exist in Iceland and Afar (both transitional from ridge to rift jumps), West Africa (Benue Trough and Cameroon Volcanic Line), and Kenya. Indeed, the Kenya rift appears to have jumped c. 100 km eastward c. 10 m.y. ago and is currently jumping further to the east. Possible jumps exist in the Baikal rift, the Limagne-Bresse rift pair, and parallel to ancient continental margins (e.g., the Triassic basins of the eastern U.S. to Baltimore Canyon and Georges Bank). Continental rifts jump distances that are approximately equal to local lithosphere thickness, suggesting that jumped rifts are controlled by lithosphere fracturing, but there appears to be no reason for the fracturing except migration of hot spots.

  7. Rift Valley Fever Virus

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever virus (RVFV) is a mosquito-transmitted virus or arbovirus that is endemic in sub-Saharan Africa. In the last decade, Rift Valley fever (RVF) outbreaks have resulted in loss of human and animal life, as well as had significant economic impact. The disease in livestock is primarily a...

  8. Forecast and Validation of the Rift Valley fever outbreak in East Africa: 2006-2007

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Background The instantaneous occurrence of El Nino / Southern Oscillation (ENSO) warm events and anomalous warming of the equatorial western Indian Ocean (WIO) are associated with elevated and widespread rainfall over East Africa. Such, sustained, heavy rainfall in East is associated with the emerg...

  9. ALVIN investigation of an active propagating rift system, Galapagos 95.5° W

    USGS Publications Warehouse

    Hey, R.N.; Sinton, J.M.; Kleinrock, M.C.; Yonover, R.N.; MacDonald, K.C.; Miller, S.P.; Searle, R.C.; Christie, D.M.; Atwater, T.M.; Sleep, N.H.; Johnson, H. Paul; Neal, C.A.

    1992-01-01

    ALVIN investigations have defined the fine-scale structural and volcanic patterns produced by active rift and spreading center propagation and failure near 95.5° W on the Galapagos spreading center. Behind the initial lithospheric rifting, which is propagating nearly due west at about 50 km m.y.−1, a triangular block of preexisting lithosphere is being stretched and fractured, with some recent volcanism along curving fissures. A well-organized seafloor spreading center, an extensively faulted and fissured volcanic ridge, develops ~ 10 km (~ 200,000 years) behind the tectonic rift tip. Regional variations in the chemical compositions of the youngest lavas collected during this program contrast with those encompassing the entire 3 m.y. of propagation history for this region. A maximum in degree of magmatic differentiation occurs about 9 km behind the propagating rift tip, in a region of diffuse rifting. The propagating spreading center shows a gentle gradient in magmatic differentiation culminating at the SW-curving spreading center tip. Except for the doomed rift, which is in a constructional phase, tectonic activity also dominates over volcanic activity along the failing spreading system. In contrast to the propagating rift, failing rift lavas show a highly restricted range of compositions consistent with derivation from a declining upwelling zone accompanying rift failure. The lithosphere transferred from the Cocos to the Nazca plate by this propagator is extensively faulted and characterized by ubiquitous talus in one of the most tectonically disrupted areas of seafloor known. The pseudofault scarps, where the preexisting lithosphere was rifted apart, appear to include both normal and propagator lavas and are thus more lithologically complex than previously thought. Biological communities, probably vestimentiferan tubeworms, occur near the top of the outer pseudofault scarp, although no hydrothermal venting was observed.

  10. The Kinematic Puzzle of the Gulf of California Rift system

    NASA Astrophysics Data System (ADS)

    Stock, J. M.

    2007-05-01

    Extensive recent studies of the Gulf of California greatly advanced our understanding of the kinematics of this Pacific-North America plate boundary rift and its crustal structure. However, some kinematic discrepancies that need to be resolved, particularly for the time interval 12-6 Ma, after subduction had stopped but possibly before major opening began in the northern Gulf basins. Correlation of pyroclastic flow deposits across the Upper Delfin Basin segment (Oskin et al., 2001 and subsequent papers) indicates that virtually all of the opening between the coastlines in this segment (from San Felipe/Puertecitos in Baja California to the W side of Tiburon Island) occurred since ~6.1 Ma producing ~250 km of opening of the marine basin. This implies that the crust in the basin should have been brought into the region since ca. 6 Ma, perhaps by production of new igneous crust or remobilization of continental crust to fill the ~250-km gap. The total amount of post-6 Ma opening in the rift, including the onland deformation, is consistent with expected Pacific-North America displacement determined from the global plate circuit since 6 Ma, and it is also consistent with the slip history of the southern San Andreas fault. A smaller amount of motion (tens of kms) can be identified geologically post-12.5 Ma and pre-6 Ma. However, this is not sufficient to match the plate circuit results, which seem to require several hundred more km of Pacific-North America plate motion at this latitude between 12 Ma and 6 Ma. This motion has to have been located elsewhere, not between the modern marine basin boundaries. The Pliocene basin history of the Gulf has varied from place to place, as the loci of extension moved around in the rift system Similar variations in late Miocene time could explain this discrepancy, with abandoned extensional or strike-slip fault systems elsewhere, perhaps in the Sonoran coastal plain. However, further geological and geophysical work is needed to

  11. The Okavango Dike Swarm (ODS) of Northern Botswana: Was it associated with a failed Rift System?

    NASA Astrophysics Data System (ADS)

    LePera, Alan; Atekwana, Estella; Abdelsalam, Mohamed

    2014-05-01

    Dikes and dike swarms often play a significant role in the initiation and extension of rift zones. The giant ODS in northern Botswana, Africa represents a Jurassic aged (~180Ma) thermo-tectonic event which developed during the initial lithospheric weakening phase of Gondwana. Detailed investigations of the mafic dike swarm over the last four decades have provided insights into its age, shape, orientation, and chemistry but have thus far been limited in addressing the crustal structure below the swarm. Historically, the ODS has been interpreted as a failed rift arm based on its association with the Bouvet Hotspot and geometric relationship with two other prominent dike swarms. More recent studies suggest instead that the ODS was emplaced along a preexisting Precambrian basement fabric. Accordingly, the origin of the swarm still remains a matter of debate. The objectives of this study were: (1) determine the role of crustal heterogeneities on the emplacement of the dikes, (2) determine variations in crustal thickness below the ODS and geographically related Okavango Rift Zone (ORZ), a zone of incipient rifting and (3) determine along-strike variations in Curie Point Depth (CPD) below the swarm. We used high resolution aeromagnetic data and applied mathematical filters to enhance structures associated with the swarm's oblique geometry. Crustal thicknesses were estimated using the radial average power spectrum method, applied to 1.2km spatial resolution gravity data. 3D inversions were used to map the magnetic basement and determine the depth to the base of the swarm. Our results showed: (1) There were no apparent basement structures with the same 110° orientation as the ODS. (2) Crustal thickness below the swarm ranges from 39 to 45km with an average of 42± 3km, comparable with thicknesses derived from the Southern African Seismic Experiment (SASE). In contrast, crustal thickness below the ORZ is 9 to 16km thinner than the surrounding blocks. (3) The magnetic

  12. Coupling Vector-host Dynamics with Weather Geography and Mitigation Measures to Model Rift Valley Fever in Africa

    PubMed Central

    McMahon, B.H.; Manore, C.A.; Hyman, J.M.; LaBute, M.X.; Fair, J.M.

    2015-01-01

    We present and characterize a multi-host epidemic model of Rift Valley fever (RVF) virus in East Africa with geographic spread on a network, rule-based mitigation measures, and mosquito infection and population dynamics. Susceptible populations are depleted by disease and vaccination and are replenished with the birth of new animals. We observe that the severity of the epidemics is strongly correlated with the duration of the rainy season and that even severe epidemics are abruptly terminated when the rain stops. Because naturally acquired herd immunity is established, total mortality across 25 years is relatively insensitive to many mitigation approaches. Strong reductions in cattle mortality are expected, however, with sufficient reduction in population densities of either vectors or susceptible (ie. unvaccinated) hosts. A better understanding of RVF epidemiology would result from serology surveys to quantify the importance of herd immunity in epidemic control, and sequencing of virus from representative animals to quantify the realative importance of transportation and local reservoirs in nucleating yearly epidemics. Our results suggest that an effective multi-layered mitigation strategy would include vector control, movement control, and vaccination of young animals yearly, even in the absence of expected rainfall. PMID:25892858

  13. A preliminary evaluation of the DDT contamination of sediments in lakes Natron and Bogoria (Eastern Rift Valley, Africa).

    PubMed

    Bettinetti, Roberta; Quadroni, Silvia; Crosa, Giuseppe; Harper, David; Dickie, Jennifer; Kyalo, Margaret; Mavuti, Kenneth; Galassi, Silvana

    2011-06-01

    Dichlorodiphenyltrichloroethane (DDT) is still used in Africa for the indoor control of malaria and it may represent a potential hazard for wildlife. The littoral sediments of two alkaline-saline lakes, Natron (Tanzania) and Bogoria (Kenya), in the Eastern Rift Valley, supporting large populations of lesser flamingos (Phoeniconaias minor), were analysed for DDT residues. Physical-chemical analyses (temperature, conductivity, pH and dissolved oxygen) were also performed on the water of the two lakes and in the tributaries of Lake Natron, to evaluate the influence of the environmental variables on pollutant occurrence. At Lake Natron, around 1 km from the sediment collection sites, tree leaves of Acacia tortilis were also collected. The main metabolite found in all sediment samples was pp'DDE, whilst equal concentrations of pp'DDT and pp'DDE were measured in acacia leaves. The levels of DDTs measured in the sediments were within 5.9-30.9 ng g(-1) d.w., reaching the maximum value in a tributary of Lake Natron. On the whole, the contamination of Lake Natron and Lake Bogoria basins seems to be quite moderate. Nevertheless, the pp'DDE/pp'DDT ratio equals 1 in the Acacia tortilis leaves, which makes one suppose that the input of the parent compound was rather recent and could have been from aerial transport or dust from relatively close-by old pesticides storage sites. PMID:21809777

  14. Simple shear detachment fault system and marginal grabens in the southernmost Red Sea rift

    NASA Astrophysics Data System (ADS)

    Tesfaye, Samson; Ghebreab, Woldai

    2013-11-01

    The NNW-SSE oriented Red Sea rift, which separates the African and Arabian plates, bifurcates southwards into two parallel branches, southeastern and southern, collectively referred to as the southernmost Red Sea rift. The southern branch forms the magmatically and seismo-tectonically active Afar rift, while the less active southeastern branch connects the Red Sea to the Gulf of Aden through the strait of Bab el Mandeb. The Afar rift is characterized by lateral heterogeneities in crustal thickness, and along-strike variation in extension. The Danakil horst, a counterclockwise rotating, narrow sliver of coherent continental relic, stands between the two rift branches. The western margin of the Afar rift is marked by a series of N-S aligned right-lateral-stepping and seismo-tectonically active marginal grabens. The tectonic configuration of the parallel rift branches, the alignment of the marginal grabens, and the Danakil horst are linked to the initial mode of stretching of the continental crust and its progressive deformation that led to the breakup of the once contiguous African-Arabian plates. We attribute the initial stretching of the continental crust to a simple shear ramp-flat detachment fault geometry where the marginal grabens mark the breakaway zone. The rift basins represent the ramps and the Danakil horst corresponds to the flat in the detachment fault system. As extension progressed, pure shear deformation dominated and overprinted the initial low-angle detachment fault system. Magmatic activity continues to play an integral part in extensional deformation in the southernmost Red Sea rift.

  15. East Antarctic Rift Systems - key to understanding of Gondwana break-up

    NASA Astrophysics Data System (ADS)

    Golynsky, D. A.; Golynsky, A. V.

    2012-04-01

    The results of analysis of radio-echo sounding surveys, the RADARSAT satellite data, magnetic and gravity information give evidence that East Antarctica contains 13 riftogenic systems and/or large linear tectonic structures. Among known and suggested rifts of East Antarctica the Lambert rift has a pivotal position and it manifests oneself as symmetry axis. Six additional systems are revealed on both sides of it and any one of them possesses special features in geologic and geomorphologic aspects. In most cases they inherited the anisotropy of long-lived cratonic blocks. Riftogenic and/or large linear tectonic structures along the East Antarctica coastal regions are distributed with a steady regularity with average distance between them about 650 km. For six (7) structures from 13 (Lambert, Jutulstraumen-Pencksökket, Vestfjella, Mellor-Slessor (Bailey), Wilkes Basin, Gaussberg (?) and Rennick) there is a distinct spatial coupling with trough complexes of the Beacon Supergroup and their subsequent reactivation in Late Jurassic - Permian time when the East Gondwana started break-up. Rift system of the Lambert-Amery Glaciers and Prydz Bay is related to Mesozoic extension events and it inherited structures of Paleozoic grabens. The total length of the rift system exceeds 4000 km of the same scale as largest the World rift belts. The length of the western branch of the Lambert rift that includes the Mellor rift and graben-like structures of the Bailey and Slessor glaciers exceeds 2300 km. Results of radio-echo sounding investigation of the subglacial Aurora Basin allow to suggest that this large basin of sub-meridian extension is underlain by an extensive (> 1000 km) riftogenic structure that is running towards the Transantarctic Mountains where it forms a triple junction with the eastern branch of the Lambert rift and structures of the Wilkes Basin. It is hereby proposed that Aurora-Scott rift is formed by complex system of sub-parallel depressions divided by

  16. Martian canyons and African rifts: Structural comparisons and implications

    NASA Technical Reports Server (NTRS)

    Frey, H. V.

    1978-01-01

    The resistant parts of the canyon walls of the Martian rift complex Valled Marineris were used to infer an earlier, less eroded reconstruction of the major roughs. The individual canyons were then compared with individual rifts of East Africa. When measured in units of planetary radius, Martian canyons show a distribution of lengths nearly identical to those in Africa, both for individual rifts and for compound rift systems. A common mechanism which scales with planetary radius is suggested. Martian canyons are significantly wider than African rifts. The overall pattern of the rift systems of Africa and Mars are quite different in that the African systems are composed of numerous small faults with highly variable trend. On Mars the trends are less variable; individual scarps are straighter for longer than on earth. This is probably due to the difference in tectonic histories of the two planets: the complex history of the earth and the resulting complicated basement structures influence the development of new rifts. The basement and lithosphere of Mars are inferred to be simple, reflecting a relatively inactive tectonic history prior to the formation of the canyonlands.

  17. Prediction, assessment of the Rift Valley fever activity in East and Southern Africa 2006-2008 and possible vector control strategies.

    PubMed

    Anyamba, Assaf; Linthicum, Kenneth J; Small, Jennifer; Britch, Seth C; Pak, Edwin; de La Rocque, Stephane; Formenty, Pierre; Hightower, Allen W; Breiman, Robert F; Chretien, Jean-Paul; Tucker, Compton J; Schnabel, David; Sang, Rosemary; Haagsma, Karl; Latham, Mark; Lewandowski, Henry B; Magdi, Salih Osman; Mohamed, Mohamed Ally; Nguku, Patrick M; Reynes, Jean-Marc; Swanepoel, Robert

    2010-08-01

    Historical outbreaks of Rift Valley fever (RVF) since the early 1950s have been associated with cyclical patterns of the El Niño/Southern Oscillation (ENSO) phenomenon, which results in elevated and widespread rainfall over the RVF endemic areas of Africa. Using satellite measurements of global and regional elevated sea surface temperatures, elevated rainfall, and satellite derived-normalized difference vegetation index data, we predicted with lead times of 2-4 months areas where outbreaks of RVF in humans and animals were expected and occurred in the Horn of Africa, Sudan, and Southern Africa at different time periods from September 2006 to March 2008. Predictions were confirmed by entomological field investigations of virus activity and by reported cases of RVF in human and livestock populations. This represents the first series of prospective predictions of RVF outbreaks and provides a baseline for improved early warning, control, response planning, and mitigation into the future. PMID:20682905

  18. Prediction, Assessment of the Rift Valley Fever Activity in East and Southern Africa 2006–2008 and Possible Vector Control Strategies

    PubMed Central

    Anyamba, Assaf; Linthicum, Kenneth J.; Small, Jennifer; Britch, Seth C.; Pak, Edwin; de La Rocque, Stephane; Formenty, Pierre; Hightower, Allen W.; Breiman, Robert F.; Chretien, Jean-Paul; Tucker, Compton J.; Schnabel, David; Sang, Rosemary; Haagsma, Karl; Latham, Mark; Lewandowski, Henry B.; Magdi, Salih Osman; Mohamed, Mohamed Ally; Nguku, Patrick M.; Reynes, Jean-Marc; Swanepoel, Robert

    2010-01-01

    Historical outbreaks of Rift Valley fever (RVF) since the early 1950s have been associated with cyclical patterns of the El Niño/Southern Oscillation (ENSO) phenomenon, which results in elevated and widespread rainfall over the RVF endemic areas of Africa. Using satellite measurements of global and regional elevated sea surface temperatures, elevated rainfall, and satellite derived-normalized difference vegetation index data, we predicted with lead times of 2–4 months areas where outbreaks of RVF in humans and animals were expected and occurred in the Horn of Africa, Sudan, and Southern Africa at different time periods from September 2006 to March 2008. Predictions were confirmed by entomological field investigations of virus activity and by reported cases of RVF in human and livestock populations. This represents the first series of prospective predictions of RVF outbreaks and provides a baseline for improved early warning, control, response planning, and mitigation into the future. PMID:20682905

  19. CASERTZ aeromagnetic data reveal late Cenozoic flood basalts (?) in the West Antarctic rift system

    USGS Publications Warehouse

    Behrendt, John C.

    1994-01-01

    The late Cenozoic volcanic and tectonic activity of the enigmatic West Antarctic rift system, the least understood of the great active continental rifts, has been suggested to be plume driven. In 1991-1992, as part of the CASERTZ (Corridor Aerogeophysics of the Southeast Ross Transect Zone) program, an ~25 000 km aeromagnetic survey over the ice-covered Byrd subglacial basin shows magnetic "texture' critical to interpretations of the underlying extended volcanic terrane. The aeromagnetic data reveal numerous semicircular anomalies ~100-1100 nT in amplitude, interpreted as having volcanic sources at the base of the ice sheet; they are concentrated along north-trending magnetic lineations interpreted as rift fabric. The CASERTZ aeromagnetic results, combined with >100 000 km of widely spaced aeromagnetic profiles, indicate at least 106 km3 of probable late Cenozoic volcanic rock (flood basalt?) in the West Antarctic rift beneath the ice sheet and Ross Ice Shelf. -from Authors

  20. Structural geology of the African rift system: Summary of new data from ERTS-1 imagery. [Precambrian influence

    NASA Technical Reports Server (NTRS)

    Mohr, P. A.

    1974-01-01

    ERTS imagery reveals for the first time the structural pattern of the African rift system as a whole. The strong influence of Precambrian structures on this pattern is clearly evident, especially along zones of cataclastic deformation, but the rift pattern is seen to be ultimately independent in origin and nature from Precambrian tectonism. Continuity of rift structures from one swell to another is noted. The widening of the Gregory rift as its northern end reflects an underlying Precambrian structural divergence, and is not a consequence of reaching the swell margin. Although the Western Rift is now proven to terminate at the Aswa Mylonite Zone, in southern Sudan, lineaments extend northeastwards from Lake Albert to the Eastern Rift at Lake Stefanie. The importance of en-echelon structures in the African rifts is seen to have been exaggerated.

  1. The Lithosphere of The East African Rift System: Insights From Three-Dimensional Density Modelling

    NASA Astrophysics Data System (ADS)

    Woldetinsae, G.; Götze, H. J.

    2004-12-01

    We use the gravity data that cover the large part of the Afro-Arabian rift system, the eastern branch (Ethiopia-Afar and northern Kenya), in order to produce a regional density model. In an earlier work the new and old gravity data were compiled, evaluated and homogenised using a consistent data reduction procedures. Three basic constraints widely spaced over a 1500 km rift length have been generated between 1969 and 2003 by an international consortium with information from isostatic models, global tomography, geological, geochemical evidences, and petrological and experimental results. These are integrated and applied to the model to constrain upper and lower crustal structures underneath the Rift and Plateau areas. New crustal thickness estimations (Dugda et al., 2004 in press) and inferences from recent velocity models along the axis of the Main Ethiopian Rift (Keller et al., 2004) are added to the density model. Thirty parallel planes cutting across the entire plateau region and Rift system (Afar-Ethiopia-Kenya) are interactively modelled using a starting geometry that invoke asthenospheric upwelling. Densities for the upper crust are calculated using Nafe Drake method, averaged from earlier interpretation and measured ones from the Geological Survey of Ethiopia database (e.g. Geothermal project, GSE petrophysical laboratory, pers. communication). Densities for lower crust are estimated using the approach by Sobolov and Babyko (1994). We used also lower crustal densities calculated by (Simyu and Keller, 1997) for the northern part of Kenya rift. The preliminary model offers a possibility to quantify depth, thickness and volumes of different geological interfaces and bodies. As for example, the estimation of the volume of volcanic constructs on the western plateau of Ethiopia is relatively larger than the eastern plateau. The load map derived from the model indicated maximum crustal loads at the crust/mantle interface (ca. 40km) on the eastern and western flanks

  2. Common host-derived chemicals increase catches of disease-transmitting mosquitoes and can improve early warning systems for rift valley fever virus

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF), a mosquito-borne zoonosis, is a major public health problem in sub-Saharan Africa. The emergence and re-emergence of the disease in the last 20 years especially in East Africa, poses a looming health threat which is likely to spread to beyond Africa. This threat is exacerbat...

  3. Littoral sedimentation of rift lakes: an illustrated overview from the modern to Pliocene Lake Turkana (East African Rift System, Kenya)

    NASA Astrophysics Data System (ADS)

    Schuster, Mathieu; Nutz, Alexis

    2015-04-01

    Existing depositional models for rift lakes can be summarized as clastics transported by axial and lateral rivers, then distributed by fan-deltas and/or deltas into a standing water body which is dominated by settling of fine particles, and experiencing occasional coarser underflows. Even if known from paleolakes and modern lakes, reworking of clastics by alongshore drift, waves and storms are rarely considered in depositional models. However, if we consider the lake Turkana Basin (East African Rift System, Kenya) it is obvious that this vision is incomplete. Three representative time slices are considered here: the modern Lake Turkana, the Megalake Turkana which developed thanks to the African Humid Period (Holocene), and the Plio-Pleistocene highstand episodes of paleolake Turkana (Nachukui, Shungura and Koobi Fora Formations, Omo Group). First, remarkable clastic morphosedimentary structures such as beach ridges, spits, washover fans, lagoons, or wave-dominated deltas are very well developed along the shoreline of modern lake Turkana, suggesting strong hydrodynamics responsible for a major reworking of the fluvial-derived clastics all along the littoral zone (longshore and cross-shore transport) of the lake. Similarly, past hydrodynamics are recorded from prominent raised beach ridges and spits, well-preserved all around the lake, above its present water-level (~360 m asl) and up to ~455 m. These large-scale clastic morphosedimentary structures also record the maximum extent of Megalake Turkana during the African Humid Period, as well as its subsequent regression forced by the end of the Holocene climatic optimum. Several hundreds of meters of fluvial-deltaic-lacustrine deposits spanning the Pliocene-Pleistocene are exposed in the Turkana basin thanks to tectonic faulting. These deposits are world famous for their paleontological and archeological content that documents the very early story of Mankind. They also preserve several paleolake highstand episodes with

  4. Basement control in the development of the early cretaceous West and Central African rift system

    NASA Astrophysics Data System (ADS)

    Maurin, Jean-Christophe; Guiraud, René

    1993-12-01

    The structural framework of the Precambrian basement of the West and Central African Rift System (WCARS) is described in order to examine the role of ancient structures in the development of this Early Cretaceous rift system. Basement structures are represented in the region by large Pan-African mobile belts (built at ca. 600 Ma) surrounding the > 2 Ga West African, Congo and Sao Francisco cratons. Except for the small Gao trough (eastern Mali) located near the contact nappe of the Pan-African Iforas suture zone along the edge of the West African craton, the entire WCARS is located within the internal domains of the Pan-African mobile belts. Within these domains, two main structural features occur as the main basement control of the WCARS: (1) an extensive network of near vertical shear zones which trend north-south through the Congo, Brazil, Nigeria, Niger and Algeria, and roughly east-west through northeastern Brazil and Central Africa. The shear zones correspond to intra-continental strike-slip faults which accompanied the oblique collision between the West African, Congo, and Sao Francisco cratons during the Late Proterozoic; (2) a steep metamorphic NW-SE-trending belt which corresponds to a pre-Pan-African (ca. 730 Ma) ophiolitic suture zone along the eastern edge of the Trans-Saharian mobile belt. The post-Pan-African magmatic and tectonic evolution of the basement is also described in order to examine the state of the lithosphere prior to the break-up which occurred in the earliest Cretaceous. After the Pan-African thermo-tectonic event, the basement of the WCARS experienced a long period of intra-plate magmatic activity. This widespread magmatism in part relates to the activity of intra-plate hotspots which have controlled relative uplift, subsidence and occasionally block faulting. During the Paleozoic and the early Mesozoic, this tectonic activity was restricted to west of the Hoggar, west of Aïr and northern Cameroon. During the Late Jurassic

  5. AIDS Infects Education Systems in Africa

    ERIC Educational Resources Information Center

    Keller, Bess

    2005-01-01

    The AIDS pandemic raging across sub-Saharan Africa does not stop with personal carnage. It also threatens whole systems, including what is arguably the most critical for the region's future--education. Where rates of HIV infection are high, as they are in much of southern and eastern Africa, experts warn, the effects on social stability and…

  6. Combining hydrologic and groundwater modelling to characterize a regional aquifer system within a rift setting (Gidabo River Basin, Main Ethiopian Rift)

    NASA Astrophysics Data System (ADS)

    Birk, Steffen; Mechal, Abraham; Wagner, Thomas; Dietzel, Martin; Leis, Albrecht; Winkler, Gerfried; Mogessie, Aberra

    2016-04-01

    The development of groundwater resources within the Ethiopian Rift is complicated by the strong physiographic contrasts between the rift floor and the highland and by the manifold hydrogeological setting composed of volcanic rocks of different type and age that are intersected by numerous faults. Hydrogeochemical and isotope data from various regions within the Ethiopian Rift suggest that the aquifers within the semi-arid rift floor receive a significant contribution of groundwater flow from the humid highland. For example, the major ion composition of groundwater samples from Gidabo River Basin (3302 km²) in the southern part of the Main Ethiopian Rift reveals a mixing trend from the highland toward the rift floor; moreover, the stable isotopes of water, deuterium and O-18, of the rift-floor samples indicate a component recharged in the highland. This work aims to assess if the hydrological and hydrogeological data available for Gidabo River Basin is consistent with these findings and to characterize the regional aquifer system within the rift setting. For this purpose, a two-step approach is employed: First, the semi-distributed hydrological model SWAT is used to obtain an estimate of the spatial and temporal distribution of groundwater recharge within the watershed; second, the numerical groundwater flow model MODFLOW is employed to infer aquifer properties and groundwater flow components. The hydrological model was calibrated and validated using discharge data from three stream gauging stations within the watershed (Mechal et al., Journal of Hydrology: Regional Studies, 2015, doi:10.1016/j.ejrh.2015.09.001). The resulting recharge distribution exhibits a strong decrease from the highland, where the mean annual recharge amounts to several hundred millimetres, to the rift floor, where annual recharge largely is around 100 mm and below. Using this recharge distribution as input, a two-dimensional steady-state groundwater flow model was calibrated to hydraulic

  7. Rift systems on Venus: An assessment of mechanical and thermal models

    NASA Technical Reports Server (NTRS)

    Solomon, S. C.; Head, J. W.

    1985-01-01

    The formation and distribution of major tectonic features on Venus are closely linked to the dominant mechanism of lithospheric heat loss. Among the most spectacular and extensive of the major tectonic features on Venus are the Chasmata, deep linear valleys generally interpreted to be the products of lithospheric extension and rifting. Systems of chasmata and related features can be traced along several tectonic zones up to 20,000 km in linear extent. Mechanical and thermal models for terrestrial continental-rifting are applied to the rift systems of Venus. The models are tested against known topographic and tectonic characteristics of Venus chasmata as well as independent information on the physical properties of the Venus crust and lithosphere.

  8. The hydrothermal system associated with the Kilauea East Rift Zone, Hawaii

    SciTech Connect

    Thomas, D.M.; Conrad, M.E.

    1997-12-31

    During the last twenty years drilling and fluid production on the Kilauea East Rift Zone (KERZ) has shown that an active hydrothermal system is associated with much of the rift. Well logging and fluid geochemistry indicate that reservoir temperatures exceed 360 C but are highly variable. Although neither well testing nor pressure decline data have clearly demonstrated the lateral limits of the reservoir, divergent fluid compositions over short distances suggest that the larger hydrothermal system is strongly compartmentalized across the rift zone. The chemical compositions of production fluids indicate that recharge is derived from ocean water and meteoric recharge and isotopic data suggest that the latter may be derived from subsurface inflow from the flanks of Mauna Loa.

  9. Continental rifting: a planetary perspective

    SciTech Connect

    Muehlberger, W.R.

    1985-01-01

    The only inner planet that has abundant evidence of regional extension, and the consequent generation of rifts in the earth. The absence of plate motion on the other inner planets limits their rifts to localized bulges or subsidence areas. The rifting of oceanic lithosphere is seldom preserved in the geological record. Thus, such rifting must be inferred via plate tectonic interpretation: if there is rifting, then there must be subduction whose results are commonly well preserved. Modern continental rifts are found in many tectonic settings: continental breakup, extension transverse to collisional stresses, or wide regions of nearly uniform extension. Recognition of these settings in older rocks becomes more difficult the farther back in geologic time you travel. Rift basin fillings typically show rapid lateral and vertical facies and thickness changes, bimodal volcanism, and distinctive rift-drift sequences. Proterozoic rifts and aulacogens are well-documented in North America; ex. Keweenawan, western margin of Labrador fold belt, Belt-Uinta and the Wopmay-Athapuscow regions. Documented Archean rifts are rare. In Quebec, the truncated margin of the Minto craton bounded on the south by a 2.8 Ga greenstone belt implies an earlier rift event. The oldest proposed rift dated at 3.0 Ga contains the Pongola Supergroup in southeastern Africa. The presence of Archean dikes demonstrates a rigid crust and andesites as old as 3.5 Ga imply plate tectonics and thus, at least, oceanic rifting.

  10. Where is the West Antarctic Rift System in the Amundsen Sea and Bellingshausen Sea sectors?

    NASA Astrophysics Data System (ADS)

    Gohl, Karsten; Kalberg, Thomas; Eagles, Graeme; Dziadek, Ricarda; Kaul, Norbert; Spiegel, Cornelia; Lindow, Julia

    2015-04-01

    The West Antarctic Rift System (WARS) is one of the largest continental rifts globally, but its lateral extent, distribution of local rifts, timing of rifting phases, and mantle processes are still largely enigmatic. It has been presumed that the rift and its crustal extensional processes have widely controlled the history and development of West Antarctic glaciation with an ice sheet of which most is presently based at sub-marine level and which is, therefore, likely to be highly sensitive to ocean warming. While the western domain of the WARS in the Ross Sea has been studied in some detail, only recently have various geophysical and geochemical/thermochronological analyses revealed indications for its eastern extent in the Amundsen Sea and Bellingshausen Sea sectors of the South Pacific realm. The current model, based on these studies and additional data, suggests that the WARS activity included tectonic translateral, transtensional and extensional processes from the Amundsen Sea Embayment to the Bellingshausen Sea region of the southern Antarctic Peninsula. We present the range of existing hypotheses regarding the extent of the eastern WARS as well as published and yet unpublished data that support a conceptual WARS model for the eastern West Antarctica with implications for glacial onset and developments.

  11. Rift border system: The interplay between tectonics and sedimentation in the Reconcavo basin, northeastern Brazil

    SciTech Connect

    Magnavita, L.P.; Silva, T.F. da

    1995-11-01

    A geometric and depositional model is proposed to explain the tectonic and sedimentary evolution of the main border of the Reconcavo basin. The architecture of the rift margin is characterized by a rift border system constituted by (1) a master fault, (2) a step, and (3) a clastic wedge. This footwall-derived clastic wedge is interpreted as alluvial fans and fan deltas composed of conglomerates that interfinger with hanging-wall strata. The analysis of the vertical distribution of coarse-grained components of this wedge suggests that its composition is geographically controlled, and no regular inverted stratigraphy is commonly described for this type of succession. During an initial lacustrine phase, turbidites accumulated farther from and parallel to the rift margin. The mapping of marker beds that bound these lacustrine turbidite deposits may be used to infer major periods of clastic influx and, therefore, to correlate with periods of fault-related subsidence or climatic fluctuations in the depositional basin and erosion of the sediment source area. Periods of limited back-faulting and basin expansion toward the main border are distinguished through patterns of progradation and aggradation indicating progressive retreat of the rift border and younging; in the footwall direction. The overall evolution of the rift border seems to be related to extension, block rotation, hanging-wall subsidence, and footwall uplift associated with the initial master fault, with limited propagation of faults away from the basin into the footwall.

  12. Earthquakes and Geological Structures of the St. Lawrence Rift System

    NASA Astrophysics Data System (ADS)

    Lamontagne, M.; Ranalli, G.

    2013-12-01

    The St. Lawrence Rift System (SLRS), which includes the Ottawa-Bonnechère and Saguenay grabens, is located well inside the North American plate. Most historic and the some 350 earthquakes recorded yearly occur in three main seismically active zones, namely Charlevoix (CSZ), Western Quebec (WQSZ), and Lower St. Lawrence (LSLSZ)). Outside these areas, most of the Canadian Shield and bordering regions have had a very low level of earthquake activity. In the SLRS, moderate to large earthquakes (Moment magnitude (M) 5.5 to M 7) are known to have occurred since 1663 causing landslides and damage mostly to unreinforced masonry elements of buildings located on ground capable of amplifying ground motions. Most earthquakes in these seismic zones share common characteristics such as mid- to upper crustal focal depths, no known surface ruptures and proximity to SLRS faults. Variations also exist such as vast seismically-active region (WQSZ and LSLSZ), presence of a large water body (CSZ and LSLSZ), and absence of SLRS faults near concentration of earthquakes (WQSZ). The CSZ is the best studied seismic zone and there, earthquakes occur in the Canadian Shield, mostly in a 30 X 85 km rectangle elongated along the trend of the St. Lawrence River with local variations in focal depth distribution. Faults related to the SLRS and to a meteor impact structure exist and earthquakes occur along the SLRS faults as well as in between these faults. Overall, the SLRS faults are probably reactivated by the larger earthquakes (M ≥ 4.5) of the 20th century (CSZ in 1925; WQCSZ in 1935 and 1944; Saguenay in 1988) for which we have focal mechanisms. We propose that caution be exercised when linking historical events that have uncertain epicentres with SLRS faults. Similarly, SLRS faults should not be necessarily considered to be the reactivated structures for most small to moderate earthquakes (M < 4.5). A good example of this is the earthquakes of the WQSZ that tend to concentrate in a well

  13. Seismicity of the Earth 1900-2013 East African Rift

    USGS Publications Warehouse

    Hayes, Gavin P.; Jones, Eric S.; Stadler, Timothy J.; Barnhart, William D.; McNamara, Daniel E.; Benz, Harley M.; Furlong, Kevin P.; Villaseñor, Antonio

    2014-01-01

    Rifting in East Africa is not all coeval; volcanism and faulting have been an ongoing phenomenon on the continent since the Eocene (~45 Ma). The rifting began in northern East Africa, and led to the separation of the Nubia (Africa) and Arabia plates in the Red Sea and Gulf of Aden, and in the Lake Turkana area at the Kenya-Ethiopia border. A Paleogene mantle superplume beneath East Africa caused extension within the Nubia plate, as well as a first order topographic high known as the African superswell which now includes most of the eastern and southern sectors of the Nubia plate. Widespread volcanism erupted onto much of the rising plateau in Ethiopia during the Eocene-Oligocene (45–29 Ma), with chains of volcanoes forming along the rift separating Africa and Arabia. Since the initiation of rifting in northeastern Africa, the system has propagated over 3,000 km to the south and southwest, and it experiences seismicity as a direct result of the extension and active magmatism.

  14. Ambient Noise Tomography of the East African Rift System in Mozambique

    NASA Astrophysics Data System (ADS)

    Domingues, A.; Chamussa, J.; Silveira, G. M.; Custodio, S.; Lebedev, S.; Chang, S.; Ferreira, A. M.; Fonseca, J. F.

    2013-12-01

    A wide range of studies has shown that the cross-correlation of ambient noise can provide an estimate of the Greens functions between pairs of stations. Project MOZART (funded by FCT, Lisbon, PI J. Fonseca) deployed 30 broadband (120s) seismic stations from the SEIS-UK Pool in Central Mozambique and NE South Africa, with the purpose of studying the East African Rift System (EARS) in Mozambique. We applied the Ambient Noise Tomography (ANT) method to broadband seismic data recorded from March 2011 until July 2012. Cross-correlations were computed between all pairs of stations, and from these we obtained Rayleigh wave group velocity dispersion curves for all interstation paths, in the period range from 3 to 50 seconds. We tested various approaches for pre-processing the ambient noise data regarding time-domain and spectral normalisation, as well as the use of phase cross-correlations. Moreover, we examined the robustness of our dispersion maps by splitting our dataset into various sub-sets of Green's functions with similar paths and by quantifying the differences between the dispersion maps obtained from the various sub-sets of data. We find that while the geographical distribution of the group velocity anomalies is well constrained, the amplitudes of the anomalies are slightly less robust. We performed a three-dimensional inversion to obtain the S-wave velocity of the crust and upper mantle. In addition, our preliminary results show a good correlation between the Rayleigh wave group velocity and the geology of Mozambique. In order to extend the investigation to longer periods and, thus, to be able to look into the lithosphere-asthenosphere depth range in the upper mantle, we apply a recent implementation of the surface-wave two-station method (teleseismic interferometry) and augment our dataset with Rayleigh wave phase velocities curves in broad period ranges.

  15. The Midcontinent rift system and the Precambrian basement in southern Michigan

    SciTech Connect

    Smith, W.A. . Dept. of Geology)

    1994-04-01

    The Precambrian basement within Michigan consists of at least three provinces, each characterized by distinctive potential field anomalies: (1) the Eastern Granite-Rhyolite Province (EGRP) in the south, (2) the Grenville Province in the southeast and (3) the Penokean Province to the north. Also located within the basement is the Mid-Michigan rift (MMR), which is the eastern arm of the Midcontinent rift system (MRS). Southwest and parallel to the MMR is a series of linear positive gravity anomalies which has been referred to as the Ft. Wayne rift (FWR) and the Southwest Michigan Anomaly (SWMA). The EGRP, which is characterized by undeformed and unmetamorphosed rhyolite to dacite and epizonal granites, was emplaced ca. 1510--1450 Ma. However, the EGRP may be comprised of several terranes of varying extent and origin based on analysis of potential field data and rock and mineral ages. The MMR and the FWR/SWMA are characterized by linear arrays of positive magnetic and gravity anomalies, which are probably due to thick accumulations of mafic igneous rocks within the rifts. The extent and trends of the FWR/SWMA have been largely inferred from geophysical data with a presumption of the age of about 1,100 Ma. The continuation of the MMR southward into Ohio and Kentucky as a sequence of gravity highs is questionable and needs further resolution. The FWR/SWMA may be part of the East Continent Rift Basin (ECRB). The ECRB, which is a large complex of related rift basins of Keweenawan age (1300 --1100 Ma), may be an extension of the MRS but it is not physically continuous with it. The ECRB lies to the west of the Grenville Front and extends at least from northwest Ohio to central Kentucky. Extensions of the ECRB north and south are speculative.

  16. The development of the East African Rift system in north-central Kenya

    NASA Astrophysics Data System (ADS)

    Hackman, B. D.; Charsley, T. J.; Key, R. M.; Wilkinson, A. F.

    1990-11-01

    Between 1980 and 1986 geological surveying to produce maps on a scale of 1:250,000 was completed over an area of over 100,000 km 2 in north-central Kenya, bounded by the Equator, the Ethiopian border and longitudes 36° and 38 °E. The Gregory Rift, much of which has the structure of an asymmetric half-graben, is the most prominent component of the Cenozoic multiple rift system which extends up to 200 km to the east and for about 100 km to the west, forming the Kenya dome. On the eastern shoulder and fringes two en echelon arrays of late Tertiary to Quaternary multicentre shields can be recognized: to the south is the Aberdares-Mount Kenya-Nyambeni Range chain and, to the north the clusters of Mount Kulal, Asie, Huri Hills and Marsabit, with plateau lavas and fissure vents south of Marsabit in the Laisamis area. The Gregory Rift terminates at the southern end of Lake Turkana. Further north the rift system splays: the arcuate Kinu Sogo fault zone forms an offset link with the central Ethiopian Rift system. In the rifts of north-central Kenya volcanism, sedimentation and extensional tectonics commenced and have been continuous since the late Oligocene. Throughout this period the Elgeyo Fault acted as a major bounding fault. A comparative study of the northern and eastern fringes of the Kenya dome with the axial graben reinforces the impression of regional E-W asymmetry. Deviations from the essential N-trend of the Gregory Rift reflect structural weaknesses in the underlying Proterozoic basement, the Mozambique Orogenic Belt: thus south of Lake Baringo the swing to the southeast parallels the axes of the ca. 620 Ma phase folds. Secondary faults associated with this flexure have created a "shark tooth" array, an expression of en echelon offsets of the eastern margin of the Gregory Rift in a transtensional stress regime: hinge zones where major faults intersect on the eastern shoulder feature intense box faulting and ramp structures which have counterparts in the rift

  17. The uppermost mantle beneath the Kenya dome and relation to melting, rifting and uplift in East Africa

    NASA Astrophysics Data System (ADS)

    Davis, Paul M.; Slack, Philip D.

    2002-04-01

    We compare new results on S-wave delays and P wave tomography to characterize the rising limb and melt zone of an inferred mantle convection cell beneath the Kenya dome. These results are extended to the Nyiragongo and Ethiopia domes using long wavelength gravity and topography. We suggest that the east African rift results from separation of deeper mantle upwelling into three currents that impinge on and erode the base of the lithosphere. Their thermal buoyancy drives the domal uplift, whereas brittle failure of the upper lithosphere forms the rift grabens.

  18. Characterising East Antarctic Lithosphere and its Rift Systems using Gravity Inversion

    NASA Astrophysics Data System (ADS)

    Vaughan, Alan P. M.; Kusznir, Nick J.; Ferraccioli, Fausto; Leat, Phil T.; Jordan, Tom A. R. M.; Purucker, Michael E.; Golynsky, A. V. Sasha; Rogozhina, Irina

    2013-04-01

    Since the International Geophysical Year (1957), a view has prevailed that East Antarctica has a relatively homogeneous lithospheric structure, consisting of a craton-like mosaic of Precambrian terranes, stable since the Pan-African orogeny ~500 million years ago (e.g. Ferracioli et al. 2011). Recent recognition of a continental-scale rift system cutting the East Antarctic interior has crystallised an alternative view of much more recent geological activity with important implications. The newly defined East Antarctic Rift System (EARS) (Ferraccioli et al. 2011) appears to extend from at least the South Pole to the continental margin at the Lambert Rift, a distance of 2500 km. This is comparable in scale to the well-studied East African rift system. New analysis of RadarSat data by Golynsky & Golynsky (2009) indicates that further rift zones may form widely distributed extension zones within the continent. A pilot study (Vaughan et al. 2012), using a newly developed gravity inversion technique (Chappell & Kusznir 2008) with existing public domain satellite data, shows distinct crustal thickness provinces with overall high average thickness separated by thinner, possibly rifted, crust. Understanding the nature of crustal thickness in East Antarctica is critical because: 1) this is poorly known along the ocean-continent transition, but is necessary to improve the plate reconstruction fit between Antarctica, Australia and India in Gondwana, which will also better define how and when these continents separated; 2) lateral variation in crustal thickness can be used to test supercontinent reconstructions and assess the effects of crystalline basement architecture and mechanical properties on rifting; 3) rift zone trajectories through East Antarctica will define the geometry of zones of crustal and lithospheric thinning at plate-scale; 4) it is not clear why or when the crust of East Antarctica became so thick and elevated, but knowing this can be used to test models of

  19. Forecasting the Temporal and Spatial Distribution of a Rift Valley fever Outbreak in East Africa: 2006-2007

    Technology Transfer Automated Retrieval System (TEKTRAN)

    El Niño/Southern Oscillation (ENSO) related climate anomalies have been shown to have a direct impact on Rift Valley fever (RVF) disease outbreaks. Knowledge of the links between ENSO driven climate anomalies and RVF can allow us to provide improved long range forecasts of an epidemic or epizootic. ...

  20. Morphotectonic evolution of two depressions at the southern border of the Baikal rift system

    NASA Astrophysics Data System (ADS)

    Vogt, Henri; Vogt, Thea

    2007-05-01

    Detailed study of two dry depressions in the Baikal rift system: the E-W Khoito Ghol-Tunka-Bistraya depression and the SW-NE Gusinoje-Ivolga depression, aims to provide a better understanding of tectonic control on the intershoulder relief evolution after the rift opened. Both depressions are grabens and both feature a suite of 10-20 km-wide basins alternating with more or less massive highs. Field and laboratory analysis shows that this pattern is of recent tectonic origin and that local breaking-up and subsidence followed the general sinking which originally formed the grabens. The subsidence belts seem to have gradually shifted north and northeastwards. Geomorphological analysis reveals that in both depressions the highs are remnants of a former pediment which was broken up. The young basins display numerous relevant hydrographic anomalies of the secondary channels and a general water-logging. They also suggest that the subsidence belts have gradually shifted north-and northeastwards. In the Gusinoje-Ivolga depression evidence was found of a Plio-Pleistocene river course, parallel to the Selenga river, which was later dismantled by the breaking-up. This depression, parallel to the Baikal rift and belonging to the Mesozoic system of grabens in the Caledonian fold belt, seems to have been included into the general system of rifts during the Pliocene tectonic phase. As for the main hydrographic axes, the Selenga river was set on a Palaeogene-age planation surface before the first tectonic phase and kept its original course. The Irkut river flowed in the Khoito Gol-Tunka-Bistraya depression after the first tectonic phase and was not affected by the later breaking-up. In contrast, the secondary drainage network is largely discordant. Despite their different geotectonic contexts, the two depressions show a similar development of relief pattern ,which poses the question of the style of rift dynamics after the main Pliocene tectonic phase.

  1. Mapping of the major structures of the African rift system

    NASA Technical Reports Server (NTRS)

    Mohr, P. A. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. Lake Tara lies within a previously recognized asymmetric graben situated on the Ethiopian plateau and about 250 km west of the plateau-Afar margin. ERTS-1 imagery confirms the stronger deformation of the western side of the Tara graben, with intense faulting and some associated monoclinal mapping extending between latitudes 12 deg and 14 deg N, and lying close to meridian 37 deg E. The zone of deformation is gently arcuate in plan, trending NNE in the south NNW in the north. In the north, the Quaternary faulting dies out in the alluvial plains of the Takazze Valley; in the south the faulting appears to die out in coincidence with a large erosional escapement trending S30W from Lake Tara to precisely latitude 11 deg N. This escapement aligns with the massive NE-SW escapement of western Simien, northeast of Lake Tara, and may represent erosional recession from major faulting and tilting much older than that of the superimposed, obliquely trending Tara graben. A 30 km diameter circular feature has been identified from the ERTS-1 imagery of the Tara graben, centered on 13 deg 05 min N, 37 deg 20 min E. ERTS-1 imagery further shows that the Tara graben and its associated young volcanics have no direct connection with the Red Sea or Ethiopian rift valley.

  2. Tectonic development of the SW Arabian Plate margin within the central Arabian flank of the Red Sea rift system

    NASA Astrophysics Data System (ADS)

    Szymanski, E.; Stockli, D. F.; Johnson, P. R.; Kattan, F. H.; Cosca, M. A.

    2009-12-01

    The Red Sea rift system is a prime example of continental rifting and has contributed significantly to our understanding of the geologic processes that manage the rupture of continental lithosphere. Using a combined geo- and thermochronometric approach, we explore the modes and mechanisms of rift margin development by studying Red Sea rift-related geologic products along the central Saudi Arabian flank of the rift system, north of Jeddah. We use apatite and zircon (U-Th)/He thermochronometry and whole-rock 40Ar/39Ar dating of basalt to define the spatiotemporal relationship between rift flank extensional structures and rift-related harrat volcanism. This technical approach permits the reconstruction of the tectonic margin from early rift architecture, to strain distribution during progressive rifting, and through subsequent whole-scale modifications of the rift flank due to thermal and isostatic factors. Constraints on the dynamics of rift flank deformation are achieved through the collection of geologic samples along long-baseline thermochronometric transects that traverse the entire Arabian shield from the coastal escarpment to the inland Paleozoic sedimentary cover sequences. Long-baseline transects resolve the timing of rift flank uplift and reveal the pattern of lithospheric modification during the rupturing of continental lithosphere. Locally, short-baseline elevation transects map the footwall exhumation of major normal faults that delineate both the modern rift margin and inland extensional basins such as the NW-trending Hamd-Jizil basin, a prominent syn-extensional basin comprised of two distinct half-grabens (Jizil and Hamd) located NW of Medina. Diffuse lithospheric extension during the Oligo-Miocene affected a widespread area well inboard from the modern rift margin; samples from footwall blocks that bound the inland Jizil and Hamd half-grabens yield apatite (U-Th)/He cooling ages of 14.7 ± 0.9 Ma and 24.5 ± 1.5 Ma, respectively. The mid-Miocene age

  3. Some characteristics of aftershock sequences of major earthquakes from 1994 to 2002 in the Kivu province, Western Rift Valley of Africa

    NASA Astrophysics Data System (ADS)

    Mavonga, Tuluka

    2007-07-01

    The temporal and spatial distribution of the aftershock sequences of the Ruwenzori (February 5, 1994, Mb (5.8)), Masisi (April 29, 1995, Mb (5.1)) and Kalehe (October 24, 2002, Mb (5.9)) earthquakes have been studied. It has been found that most of the aftershocks of the Ruwenzori earthquake are located on the eastern flank of the main escarpment and those of the Masisi earthquake are confined to the northwest of Lake Kivu margin where earthquake occurrence of swarm-type was normally observed. The Kalehe earthquake occurred in the central part of Lake Kivu and it was the largest earthquake observed in the Lake Kivu basin since 1900. The rate of decrease in aftershock activity with the time has shown that the p-value for Ruwenzori and Masisi earthquake equals 0.6, somehow smaller than that found in other geotectonic zones where p is close to 1. The p-value of the Kalehe earthquake is a normal value equal to 1. From an area delimited by spatial distribution of aftershocks, the linear dimension of the fault was estimated. The fault area determined in this study correlates well with those of previous studies which occurred in the Western Rift Valley of Africa including the Tanganyika and Upemba Rift.

  4. Anatomy of a river drainage reversal in the Neogene Kivu Nile Rift

    NASA Astrophysics Data System (ADS)

    Holzförster, F.; Schmidt, U.

    2007-07-01

    The Neogene geological history of East Africa is characterised by the doming and extension in the course of development of the East African Rift System with its eastern and western branches. In the centre of the Western Rift Rise Rwanda is situated on Proterozoic basement rocks exposed in the strongly uplifted eastern rift shoulder of the Kivu-Nile Rift segment, where clastic sedimentation is largely restricted to the rift axis itself. A small, volcanically and tectonically controlled depository in northwestern Rwanda preserved the only Neogene sediments known from the extremely uplifted rift shoulder. Those (?)Pliocene to Pleistocene/Holocene fluvio-lacustrine muds and sands of the Palaeo-Nyabarongo River record the influence of Virunga volcanism on the major drainage reversal that affected East Africa in the Plio-/Pleistocene, when the originally rift-parallel upper Nile drainage system became diverted to the East in order to enter the Nile system via Lake Victoria. Sedimentary facies development, heavy mineral distributions and palaeobiological controls, including hominid artefacts, signal a short time interval of <300-350 ka to complete this major event for the sediment supply system of the Kivu-Nile Rift segment.

  5. How strong ist the impact of changing topography of the East African Rift System on regional climate?

    NASA Astrophysics Data System (ADS)

    Prömmel, Kerstin; Kaspar, Frank; Cubasch, Ulrich

    2010-05-01

    The evolution of the East African Rift System (EARS) leads to a topography change at the surface and the impact of this change on climate in this region can easily be analysed with climate models. In the present study both global and regional climate models are applied. The global climate model is the coupled atmosphere ocean general circulation model ECHO-G and the regional climate model is the non-hydrostatic CLM, which is the climate version of the numerical weather prediction model of the German Meterorological Service. At the lateral boundaries the regional model is driven by the simulations performed with the global model. Different topographical situations representing possible conditions in the past, are simulated with the global and the regional climate model. One assumption affects only the highest peaks of the EARS south of the Turkana Channel by reducing them to 1200 m. The other assumptions affect a much larger area covering the whole of Southern and Eastern Africa. Over this region topography is reduced by 25%, 50%, 75% and 95%. These different topography reductions have an impact on circulation and therefore also on moisture transport. This leads to changes in the precipitation patterns over Africa. One strong effect is the decrease in orographic precipitation windward of the mountains. Wetter conditions can be found over the east coast of Africa, where moisture is transported from the Indian Ocean farther into the continent due to the lower barrier. Both global and regional models show similar results on the continental scale, however the results of the regional model are much more detailed due to the higher horizontal resolution (50 km) compared to the global model (~350 km).

  6. Sedimentary budgets of the Tanzania coastal basin and implications for uplift history of the East African rift system

    NASA Astrophysics Data System (ADS)

    Said, Aymen; Moder, Christoph; Clark, Stuart; Abdelmalak, Mohamed Mansour

    2015-11-01

    Data from 23 wells were used to quantify the sedimentary budgets in the Tanzania coastal basin in order to unravel the uplift chronology of the sourcing area located in the East African Rift System. We quantified the siliciclastic sedimentary volumes preserved in the Tanzania coastal basin corrected for compaction and in situ (e.g., carbonates) production. We found that the drainage areas, which supplied sediments to this basin, were eroded in four episodes: (1) during the middle Jurassic, (2) during the Campanian-Palaeocene, (3) during the middle Eocene and (4) during the Miocene. Three of these high erosion and sedimentation periods are more likely related to uplift events in the East African Rift System and earlier rift shoulders and plume uplifts. Indeed, rapid cooling in the rift system and high denudation rates in the sediment source area are coeval with these recorded pulses. However, the middle Eocene pulse was synchronous with a fall in the sea level, a climatic change and slow cooling of the rift flanks and thus seems more likely due to climatic and eustatic variations. We show that the rift shoulders of the East African rift system have inherited their present relief from at least three epeirogenic uplift pulses of middle Jurassic, Campanian-Palaeocene, and Miocene ages.

  7. Mapping hyper-extended rift systems offshore and onshore: insights from the Bay of Biscay- Western Pyrenees

    NASA Astrophysics Data System (ADS)

    Tugend, Julie; Manatschal, Gianreto; Kusznir, Nicolas J.; Masini, Emmanuel; Thinon, Isabelle

    2013-04-01

    Research conducted at present-day passive continental margins shows more varied crustal architectures than previously assumed. New seismic data together with drill-holes have revealed the occurrence of extremely thinned continental crust in the distal part of the margin as well as exhumed serpentinised sub-continental mantle oceanwards. In addition the understanding of the formation of hyper-extended rift systems has also greatly benefited from the study of onshore analogs preserved in mountain belts. The Bay of Biscay and Western Pyrenees correspond to a Lower Cretaceous rift system leading to the development of hyper-extended domains and ultimately oceanic crust in the Bay of Biscay. This domain represents one of the best natural laboratories to study the formation processes and evolution of hyper-extended domains. During late Cretaceous compression, these rifted domains were inverted resulting in the present-day Pyrenean mountain belt. In this contribution, we present a new paleogeographic map of the Bay of Biscay-Pyrenean rift system. We integrate results from previous works and new work using different mapping methods to distinguish distinctive crustal domains related to hyper-extended systems both offshore and onshore. We combine seismic interpretations with gravity anomaly inversion and residual depth anomaly analysis to distinguish the different crustal domains across the offshore margin. Onshore, we use an innovative approach based on observations from present-day rifted margin architecture associated with classical field work to map the former hyper-extended domains. Another outcome of this work is the creation of a crustal thickness map using gravity inversion linking offshore and onshore domains from the Bay of Biscay to that of the Western-Pyrenees. This multidisciplinary approach enables us to investigate the spatial and temporal evolution of the Bay of Biscay rift system with the aim of better understanding the formation of hyper-extended domains

  8. Rift Valley Fever Review

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a disease of animals and humans that occurs in Africa and the Arabian Peninsula. A Phlebovirus in the family Bunyaviridae causes the disease that is transmitted by mosquitoes. Epidemics occur during years of unusually heavy rainfall that assessment models are being develo...

  9. [Epidemiology of Rift Valley fever in western Africa. I. Serologic survey in domestic ruminants of Burkina Faso].

    PubMed

    Akakpo, A J; Some, M J; Bornarel, P; Jouan, A; Gonzalez, J P

    1989-01-01

    A serosurvey of Rift valley fever virus infection has been conducted among 2,410 domestic ruminants (sheep, goats and cattle) from Burkina Faso in 1985, 1986 and 1987. An active circulation of virus was demonstrated and 26.7% of the total animal tested had Rift valley fever virus reacting antibodies. An epizootic was demonstrated retrospectively for 1987 and appears to correspond to the RVF outbreak observed in the same type of sahelian environment during the same year in Mauritania. Analogous ecoclimatic and environmental risk factors are discussed. Others phleboviruses such as Arumowot, Gordil, Saint-Floris, Gabek Forest and Odrenisrou seem to be active in some areas but no evidence of pathogenesis for domestic ruminants was demonstrated. PMID:2766443

  10. Fault Orientations at Obliquely Rifted Margins: Where? When? Why?

    NASA Astrophysics Data System (ADS)

    Brune, Sascha

    2015-04-01

    Present-day knowledge of rifted margin formation is largely based on 2D seismic lines, 2D conceptual models, and corroborated by 2D numerical experiments. However, the 2D assumption that the extension direction is perpendicular to the rift trend is often invalid. In fact, worldwide more than 75% of all rifted margin segments have been formed under significant obliquity exceeding 20° (angle measured between extension direction and rift trend normal): During formation of the Atlantic Ocean, oblique rifting dominated at the sheared margins of South Africa and Patagonia, the Equatorial Atlantic margins, separation of Greenland and North America, and it played a major role in the protracted rift history of the North East Atlantic. Outside the Atlantic Ocean, oblique rifting occurred during the split between East and West Gondwana, the separation of India and Australia, India and Madagascar, Australia and Antarctica, as well as Arabia and Africa. It is presently observed in the Gulf of California, the Aegean and in the East African Rift. Despite its significance, the degree to which oblique lithospheric extension affects first-order rift and passive margin properties like surface stress pattern, fault azimuths, and basin geometry, is still not entirely clear. This contribution provides insight in crustal stress patterns and fault orientations by applying a 3D numerical rift model to oblique extensional settings. The presented forward experiments cover the whole spectrum of oblique extension (i.e. rift-orthogonal extension, low obliquity, high obliquity, strike-slip deformation) from initial deformation to breakup. They are conducted using an elasto-visco-plastic finite element model and involve crustal and mantle layers accounting for self-consistent necking of the lithosphere. Results are thoroughly compared to previous analogue experiments, which yields many similarities but also distinct differences for late rift stages and for high obliquity. Even though the model

  11. Characterising Antarctic and Southern Ocean Lithosphere with Magnetic and Gravity Imaging of East Antarctic Rift Systems

    NASA Astrophysics Data System (ADS)

    Vaughan, A. P.; Kusznir, N. J.; Ferraccioli, F.; Jordan, T. A.; Purucker, M. E.; Golynsky, A. V.; Rogozhina, I.

    2012-12-01

    Since the International Geophysical Year (1957), a view has prevailed that the lithospheric structure of East Antarctica is relatively homogeneous, forming a geological block of largely cratonic nature, consisting of a mosaic of Precambrian terranes, stable since the Pan-African orogeny ~500 million years ago. Recent recognition of a continental-scale rift system cutting the East Antarctic interior indicates that this is incorrect, and has crystallised an alternative view of much more recent geological activity with important implications for tectonic reconstructions and controls on ice sheet formation and stability. The newly defined East Antarctic Rift System appears to extend from at least the South Pole to the continental margin at the Lambert Rift, a distance of 2500 km. This is comparable in scale to the well-studied East African rift system. New analysis of RadarSat data pioneered by Golynsky & Golynsky indicates that further rift zones may extend the East Antarctic Rift System into widely distributed extension zones within the continent. We have carried out a pilot study, using a newly developed gravity inversion technique with existing public domain satellite data, which shows that East Antarctica consists of distinct crustal thickness provinces with anomalously thick areas separated by thin, possibly rifted crust and overall high average thickness. Understanding the nature of crustal thickness in East Antarctica is critical because: 1) Better understanding of crustal thickness in Antarctica, especially along the ocean-continent transition (OCT), will make it possible to improve the plate reconstruction fit between Antarctica, Australia and India in Gondwana and also refine constraints on how and when these continents separated; 2) crustal thickness provinces can be used to aid supercontinent reconstructions and provide new assessments of the influence of basement architecture and mechanical properties on rifting processes; 3) tracking rift zones through

  12. Diachronous Growth of Normal Fault Systems in Multiphase Rift Basins: Structural Evolution of the East Shetland Basin, Northern North Sea

    NASA Astrophysics Data System (ADS)

    Claringbould, Johan S.; Bell, Rebecca E.; A-L. Jackson, Christopher; Gawthorpe, Robert L.; Odinsen, Tore

    2015-04-01

    Our ability to determine the structural evolution and interaction of fault systems (kinematically linked group of faults that are in the km to 10s of km scale) within a rift basin is typically limited by the spatial extent and temporal resolution of the available data and methods used. Physical and numerical models provide predictions on how fault systems nucleate, grow and interact, but these models need to be tested with natural examples. Although field studies and individual 3D seismic surveys can provide a detailed structural evolution of individual fault systems, they are often spatially limited and cannot be used examine the interaction of fault systems throughout the entire basin. In contrast, regional subsurface studies, commonly conducted on widely spaced 2D seismic surveys, are able to capture the general structural evolution of a rift basin, but lack the spatial and temporal detail. Moreover, these studies typically describe the structural evolution of rifts as comprising multiple discrete tectonic stages (i.e. pre-, syn- and post-rift). This simplified approach does not, however, consider that the timing of activity can be strongly diachronous along and between faults that form part of a kinematically linked system within a rift basin. This study focuses on the East Shetland Basin (ESB), a multiphase rift basin located on the western margin of the North Viking Graben, northern North Sea. Most previous studies suggest the basin evolved in response to two discrete phases of extension in the Permian-Triassic and Middle-Late Jurassic, with the overall geometry of the latter rift to be the result of selective reactivation of faults associated with the former rift. Gradually eastwards thickening intra-rift strata (deposited between two rift phases) that form wedges between and within fault blocks have led to two strongly contrasting tectonic interpretations: (i) Early-Middle Jurassic differential thermal subsidence after Permian-Triassic rifting; or (ii

  13. Rheological variations across an active rift system -- results from lithosphere-scale 3D gravity and thermal models of the Kenya Rift

    NASA Astrophysics Data System (ADS)

    Meeßen, Christian; Sippel, Judith; Cacace, Mauro; Scheck-Wenderoth, Magdalena; Fishwick, Stewart; Heine, Christian; Strecker, Manfred R.

    2015-04-01

    Due to its tectono-volcanic activity and economic (geothermal and petroleum) potential, the eastern branch of the East African Rift System (EARS) is one of the best studied extensional systems worldwide and an important natural laboratory for the development of geodynamic concepts on rifting and nascent continental break-up. The Kenya Rift, an integral part of the eastern branch of the EARS, has formed in the area of weak Proterozoic crust of the Mozambique mobile belt adjacent to the rheologically stronger Archean Tanzania craton. To assess the variations in lithospheric strength between different tectonic domains and their influence on the tectonic evolution of the region, we developed a set of structural, density, thermal and rheological 3D models. For these models we integrated multi-disciplinary information, such as published geological field data, sediment thicknesses, well information, existing structural models, seismic refraction and reflection data, seismic tomography, gravity and heat-flow data. Our main approach focused on combined 3D isostatic and gravity modelling. The resulting lithosphere-scale 3D density model provides new insights into the depth distribution of the crust-mantle boundary and thickness variations of different crustal density domains. The latter further facilitate interpretations of variations of lithologies and related physical rock properties. By considering lithology-dependent heat production and thermal conductivity, we calculate the conductive thermal field across the region of the greater Kenya Rift. Finally, the assessed variations in lithology and temperature allow deriving differences in the integrated strength of the lithosphere across the different tectonic domains.

  14. What role does crustal heterogeneity play on continental break-up; the interplay of a foldbelt, rift system and ocean basin in the South Atlantic

    NASA Astrophysics Data System (ADS)

    Paton, Douglas; Mortimer, Estelle; Hodgson, Neil

    2015-04-01

    Although extensively studied, two key questions remain unanswered regarding the evolution of the southern South Atlantic. Firstly, where is the Cape Foldbelt (CFB) in offshore South Africa? The CFB is part of the broader Gonwanian Orogeny that prior to South Atlantic rifting continued into the Ventana Foldbelt of Argentina but to date its location in the offshore part of South Africa remains enigmatic. Secondly, the conjugate rift basin to South Africa is the Colorado Basin in Argentina but why does it trend east-west despite its perpendicular orientation to the Atlantic spreading ridge? Current plate models and structural understands cannot explain these fundamental questions. We use newly acquired deep reflection seismic data in the Orange Basin, South Africa, to develop a new structural model for the southern South Atlantic. We characterise the geometry of the Cape Foldbelt onshore and for the first time correlate it into the offshore. We show that it has a north-south trend immediately to the north of the Cape Peninsula but then has a syntaxis (Garies syntaxis) that results in a change to an east-west orientation. This forms the missing jigsaw piece of the Atlantic reconstruction as this is directly beside the restored Colorado Basin. When considered within the pre-break up structural configuration our observations imply that prior to the main phase of Atlantic rifting in the Mezosoic there was significant variation in crustal geometry incorporating the Orange Basin of South Africa, the Colorado Basin and the Gariep Belt of Namibia. These faults were active during Gondwana rifting, but the Colorado rift failed resulting in the present day location of the South Atlantic. Not only do our results improve our understanding of the evolution of the South Atlantic ocean, they highlight the importance of differentiating between early rift evolution and strain localisation during the subsequent rift phase prior to seafloor spreading.

  15. Nature of the Mantle Sources and Bearing on Tectonic Evolution in the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

    Mukasa, S. B.; Rilling-Hall, S.; Marcano, M. C.; Wilson, T. J.; Lawver, L. A.; LeMasurier, W. E.

    2012-12-01

    We collected samples from subaerial lava flows and dredged some Neogene basanitic lavas from seven volcanic edifices in the Ross Sea, Antarctica - a part of the West Antarctic Rift System (WARS) and one of the world's largest alkaline magmatic provinces - for a study aimed at two principal objectives: (1) Geochemical interrogation of the most primitive magmatic rocks to try and understand the nature of the seismically abnormal mantle domain recently identified beneath the shoulder of the Transantarctic Mountains (TAM), the Ross Sea Embayment and Marie Byrd Land; and (2) Using 40Ar/39Ar geochronology to establish a temporal link between magmatism and tectonism, particularly in the Terror Rift. We have attempted to answer the questions of whether magmatism is due to a hot mantle or wet mantle, and whether rifting in the area triggered magmatic activity or vice versa. Results show that the area does not have an age-progressive hotspot track, and the magmatism post-dates the main phase of extension along the Terror Rift within the WARS, which supports a decompression-melting model without the benefit of a significant thermal anomaly. In fact, preliminary volatile measurements on olivine-hosted melt inclusions have yielded water concentrations in excess of 2 wt%, indicating that flux melting was an important complementary process to decompression melting. The major oxide compositions of lavas in the WARS are best matched to experimental melts of carbonated peridotite, though garnet pyroxenite can also be a minor source. The Pb and Nd isotopic systems are decoupled from each other, suggesting removal of fluid-mobile elements from the mantle source possibly during the long history of subduction along the Paleo-Pacific margin of Gondwana. Extremely unradiogenic 187Os/188Os ranging to as low as 0.1081 ± 0.0001 hints at the involvement of lithospheric components in generation of magmas in the WARS.

  16. South Africa's School Infrastructure Performance Indicator System

    ERIC Educational Resources Information Center

    Gibberd, Jeremy

    2007-01-01

    While some South African schools have excellent infrastructure, others lack basic services such as water and sanitation. This article describes the school infrastructure performance indicator system (SIPIS) in South Africa. The project offers an approach that can address both the urgent provision of basic services as well as support the…

  17. Combining Hydrology and Mosquito Population Models to Identify the Drivers of Rift Valley Fever Emergence in Semi-Arid Regions of West Africa

    PubMed Central

    Soti, Valérie; Tran, Annelise; Degenne, Pascal; Chevalier, Véronique; Lo Seen, Danny; Thiongane, Yaya; Diallo, Mawlouth; Guégan, Jean-François; Fontenille, Didier

    2012-01-01

    Background Rift Valley fever (RVF) is a vector-borne viral zoonosis of increasing global importance. RVF virus (RVFV) is transmitted either through exposure to infected animals or through bites from different species of infected mosquitoes, mainly of Aedes and Culex genera. These mosquitoes are very sensitive to environmental conditions, which may determine their presence, biology, and abundance. In East Africa, RVF outbreaks are known to be closely associated with heavy rainfall events, unlike in the semi-arid regions of West Africa where the drivers of RVF emergence remain poorly understood. The assumed importance of temporary ponds and rainfall temporal distribution therefore needs to be investigated. Methodology/Principal Findings A hydrological model is combined with a mosquito population model to predict the abundance of the two main mosquito species (Aedes vexans and Culex poicilipes) involved in RVFV transmission in Senegal. The study area is an agropastoral zone located in the Ferlo Valley, characterized by a dense network of temporary water ponds which constitute mosquito breeding sites. The hydrological model uses daily rainfall as input to simulate variations of pond surface areas. The mosquito population model is mechanistic, considers both aquatic and adult stages and is driven by pond dynamics. Once validated using hydrological and entomological field data, the model was used to simulate the abundance dynamics of the two mosquito species over a 43-year period (1961–2003). We analysed the predicted dynamics of mosquito populations with regards to the years of main outbreaks. The results showed that the main RVF outbreaks occurred during years with simultaneous high abundances of both species. Conclusion/Significance Our study provides for the first time a mechanistic insight on RVFV transmission in West Africa. It highlights the complementary roles of Aedes vexans and Culex poicilipes mosquitoes in virus transmission, and recommends the

  18. Mode of rifting in magmatic-rich setting: Tectono-magmatic evolution of the Central Afar rift system

    NASA Astrophysics Data System (ADS)

    Stab, Martin; Bellahsen, Nicolas; Pik, Raphaël; Leroy, Sylvie; Ayalew, Dereje

    2014-05-01

    Observation of deep structures related to break-up processes at volcanic passive margins (VPM) is often a troublesome exercise: thick pre- to syn-breakup seaward-dipping reflectors (SDR) usually mask the continent-ocean boundary and hide the syn-rift tectonic structures that accommodate crustal stretching and thinning. Some of the current challenges are about clarifying 1) if tectonic stretching fits the observed thinning and 2) what is the effect of continuous magma supply and re-thickening of the crust during extension from a rheological point of view? The Afar region in Ethiopia is an ideal natural laboratory to address those questions, as it is a highly magmatic rift that is probably close enough to breakup to present some characteristics of VPM. Moreover, the structures related to rifting since Oligocene are out-cropping, onshore and well preserved. In this contribution, we present new structural field data and lavas (U-Th/He) datings along a cross-section from the Ethiopian Plateau, through the marginal graben down to the Manda-Hararo active rift axis. We mapped continent-ward normal fault array affecting highly tilted trapp series unconformably overlain by tilted Miocene (25-7 Ma) acid series. The main extensional and necking/thinning event took place during the end of this Miocene magmatic episode. It is itself overlain by flat lying Pliocene series, including the Stratoid. Balanced cross-sections of those areas allow us to constrain a surface stretching factor of about 2.1-2.9. Those findings have the following implications: - High beta factor constrained from field observations is at odd with thinning factor of ~1.3 predicted by seismic and gravimetric studies. We propose that the continental crust in Central Afar has been re-thickened by the emplacement of underplated magma and SDR. - The deformation in Central Afar appears to be largely distributed through space and time. It has been accommodated in a 200-300 km wide strip being a diffuse incipient

  19. Orthorhombic faults system at the onset of the Late Mesozoic-Cenozoic Barents Sea rifting

    NASA Astrophysics Data System (ADS)

    Collanega, Luca; Breda, Anna; Massironi, Matteo

    2016-04-01

    The structures of the Late Mesozoic/Cenozoic Barents Sea rifting have been investigated with multichannel 3D seismics, covering an area of 7700 sqKm in the Hoop Fault Complex, a transitional area between the platform and the marginal basins. The main structural lineaments have been mapped in a time domain 3D surface and their activity ranges have been constrained through the sin-sedimentary thickness variations detected in time-thickness maps. Two main fault systems have been identified: an orthorhombic fault system consisting of two fault sets trending almost perpendicularly one to the other (WNW-ESE and NNE-SSW) and a graben/half-graben system, elongated approximately N-S in the central part of the study area. While the graben/half-graben system can be explained through the theory of Anderson, this landmark theory fails to explain the simultaneous activity of the two fault sets of the orthorhombic system. So far, the models that can better explain orthorhombic fault arrangements are the slip model by Reches (Reches, 1978; Reches, 1983; Reches and Dieterich, 1983) and the odd-axis model by Krantz (Krantz, 1988). However, these models are not definitive and a strong quest to better understand polymodal faulting is actual (Healy et al., 2015). In the study area, the presence of both a classical Andersonian and an orthorhombic system indicates that these models are not alternative but are both effective and necessary to explain faulting in different circumstances. Indeed, the Andersonian plain strain and the orthorhombic deformation have affected different part of the succession during different phases of the rifting. In particular, the orthorhombic system has affected only the Late Mesozoic-Cenozoic interval of the succession and it was the main active system during the initial phase of the rifting. On the other hand, the graben/half-graben system has affected the whole sedimentary succession, with an increasing activity during the development of the rifting. It has

  20. The Rwenzori Mountains, a Palaeoproterozoic crustal shear belt crossing the Albertine rift system

    NASA Astrophysics Data System (ADS)

    Koehn, D.; Link, K.; Sachau, T.; Passchier, C. W.; Aanyu, K.; Spikings, A.; Harbinson, R.

    2015-04-01

    This contribution discusses the development of the Palaeoproterozoic Buganda-Toro belt in the Rwenzori Mountains and its influence on the western part of the East African Rift System in Uganda. The Buganda-Toro belt is composed of several thick-skinned nappes consisting of Archaean Gneisses and Palaeoproterozoic cover units that are thrusted northwards. The high Rwenzori Mountains are located in the frontal unit of this belt with retrograde greenschist facies gneisses towards the north, which are unconformably overlain by metasediments and amphibolites. Towards the south, the metasediments are overthrust by the next migmatitic gneiss unit that belongs to a crustal-scale nappe. The southwards dipping metasedimentary and volcanic sequence in the high Rwenzori Mountains shows an inverse metamorphic grade with greenschist facies conditions in the north and amphibolite facies conditions in the south. Early D1 deformation structures are overgrown by cordierite, which in turn grows into D2 deformation, representing the major northwards directed thrusting event. We argue that the inverse metamorphic gradient develops because higher grade rocks are exhumed in the footwall of a crustal-scale nappe, whereas the exhumation decreases towards the north away from the nappe leading to a decrease in metamorphic grade. The D2 deformation event is followed by a D3 E-W compression, a D4 with the development of steep shear zones with a NNE-SSW and SSE-NNW trend including the large Nyamwamba shear followed by a local D5 retrograde event and D6 brittle reverse faulting. The Palaeoproterozoic Buganda-Toro belt is relatively stiff and crosses the NNE-SSW running rift system exactly at the node where the highest peaks of the Rwenzori Mountains are situated and where the Lake George rift terminates towards the north. Orientation of brittle and ductile fabrics show some similarities indicating that the cross-cutting Buganda-Toro belt influenced rift propagation and brittle fault development

  1. Neogene-Quaternary Volcanic Alignments in the Transantarctic Mountains and West Antarctic Rift System of Southern Victoria Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Paulsen, T. S.; Wilson, T. J.

    2004-12-01

    Neogene-Quaternary volcanism in southern Victoria Land, Antarctica, produced the Erebus Volcanic Province, a suite of alkaline volcanic rocks that extend from the Transantarctic Mountains rift-flank uplift to offshore localities within the West Antarctic rift system. We are mapping volcanic vent patterns in the province to detect alignments indicative of stress/strain patterns during rift evolution. In the southern sector of the Erebus Volcanic Province in the Royal Society Range Block of the Transantarctic Mountains, mapping shows that elliptical scoria cones, fissures, dikes, and linear vent arrays define volcanic alignments that have a dominant NNE trend, with subsidiary WNW trends. Age data for the alignments suggest that this pattern persisted from 14.6 to 0.25 Ma. We are currently completing mapping along an east-west transect crossing the rift margin, and results obtained so far within the rift region indicate a similar pattern of alignments. On the northern flank of Mount Morning, a large volcano just to the east of the Royal Society Range, elliptical scoria cones and linear vent arrays define volcanic alignments that have a dominant NE trend, with a subsidiary NNW trend. Available age data suggest that many of these cone alignments may be of Quaternary age. At Brown Peninsula, further east from the rift flank, cone alignments trend NNE and available ages range from 2 to 3 Ma. To the east of Brown Peninsula, cone alignments trend NW at Black Island, but are of uncertain age; age data on Black Island range from 11 to 3.4 Ma. At White Island, the farthest east into the rift, cone alignments trend NNE and available age data suggest volcanism as young as 0.2 Ma. Although some differences in cone alignment trends are apparent between the rift flank and the rift system across our transect, both regions appear to be dominated by NE trending alignments, which implies a WNW to NW minimum horizontal stress (Shmin) direction. This is oblique to the ENE Shmin Cape

  2. Melt generation in the West Antarctic Rift System: the volatile legacy of Gondwana subduction?

    NASA Astrophysics Data System (ADS)

    Aviado, K.; Rilling-Hall, S.; Mukasa, S. B.; Bryce, J. G.; Cabato, J.

    2013-12-01

    The West Antarctic Rift System (WARS) represents one of the largest extensional alkali volcanic provinces on Earth, yet the mechanisms responsible for driving rift-related magmatism remain controversial. The failure of both passive and active models of decompression melting to explain adequately the observed volume of volcanism has prompted debate about the relative roles of thermal plume-related melting and ancient subduction-related flux melting. The latter is supported by roughly 500 Ma of subduction along the paleo-Pacific margin of Gondwana, although both processes are capable of producing the broad seismic anomaly imaged beneath most of the Southern Ocean. Olivine-hosted melt inclusions from basanitic lavas provide a means to evaluate the volatile budget of the mantle responsible for active rifting beneath the WARS. We present H2O, CO2, F, S and Cl concentrations determined by SIMS and major oxide compositions by EMPA for olivine-hosted melt inclusions from lavas erupted in Northern Victoria Land (NVL) and Marie Byrd Land (MBL). The melt inclusions are largely basanitic in composition (4.05 - 17.09 wt % MgO, 37.86 - 45.89 wt % SiO2, and 1.20 - 5.30 wt % Na2O), and exhibit water contents ranging from 0.5 up to 3 wt % that are positively correlated with Cl and F. Coupling between Cl and H2O indicates metasomatic enrichment by subduction-related fluids produced during dehydration reactions; coupling between H2O and F, which is more highly retained in subducting slabs, may be related to partial melting of slab remnants [1]. Application of source lithology filters [2] to whole rock major oxide data shows that primitive lavas (MgO wt % >7) from the Terror Rift, considered the locus of on-going tectonomagmatic activity, have transitioned from a pyroxenite source to a volatilized peridotite source over the past ~4 Ma. Integrating the volatile data with the modeled characteristics of source lithologies suggests that partial melting of lithosphere modified by

  3. Kinematics and Dynamics of the Kivu Rift System from Seismic Anisotropy, Seismicity, and Structural Analyses

    NASA Astrophysics Data System (ADS)

    Zal, H. J.; Wood, D. A.; Ebinger, C. J.; Scholz, C. A.; d'Oreye, N.; Carn, S. A.; Rutagarama, U.

    2014-12-01

    The westward-tilted Kivu rift in East Africa is bounded by the ~100 km-long, seismically active West Kivu border fault, and dammed at its northern end by flows from the Virunga Volcanic Province. Earlier work delineated faults along the basin margins, but little was known of active faults beneath Lake Kivu, and the lithospheric structure was unexplored. The aims of this study are to determine the kinematics of normal faults and their relation to pre-existing basement structures; to examine the locations of earthquakes with respect to faults in order to delineate zones of active faulting; to evaluate models for the modification of lithosphere by extension and mantle plume processes using seismic shear wave splitting measurements; and to evaluate the role of volcanic loading within the Virunga volcanic province on the evolution of the Kivu basin. We determine rift fault and volcanic fissure locations and orientations using merged high-resolution CHIRP bathymetric and Space Radar Topography Mission data. The majority of faults in the northern sector strike NNE, whereas NE faults are equally important in the southern basin, marking the Kivu-Rusizi accommodation zone. Seismic data was acquired from an 8-station array deployed between March 2012 and April 2013. Although the majority of earthquakes beneath the rift (excluding the active volcanoes) occur at depths of 8-20 km, unusually shallow earthquakes (2-4 km) are located along submerged faults within the East Kivu basin and suggest high pore pressures within the upper crust. Using simple elastic plate flexure model calculations we estimate the maximum deflection of the plate to be ~7 km, using an effective elastic thickness of ~7.5 km. We propose that the rapid subsidence of the ~400 m deep northern Kivu basin occurred in response to volcanic construction. We evaluate models for the modification of lithosphere using shear wave splitting measurements. Splitting results with backazimuths ranging from 88˚ - 98˚ and 240

  4. Seismic anisotropy of the lithosphere/asthenosphere system beneath the Rwenzori region of the East-African Rift

    NASA Astrophysics Data System (ADS)

    Homuth, Benjamin; Löbl, Ulrike; Batte, Arthur; Link, Klemens; Kasereka, Celestine; Rümpker, Georg

    2014-05-01

    We present results from a temporary seismic network of 32 broad-band stations located around the Rwenzori region of the Albertine rift at the border between Uganda and DR Congo. The study aims to constrain seismic anisotropy and mantle deformation processes in relation to the formation of the rift zone. Shear-wave splitting measurements from local and teleseismic earthquakes are used to investigate the seismic anisotropy in the crust and upper mantle beneath the Rwenzori region. At most stations, shear-wave splitting parameters obtained from individual earthquakes exhibit only minor variations with backazimuth. We therefore employ a joint inversion of SKS waveforms to derive hypothetical one-layer parameters. The corresponding fast polarizations are generally rift-parallel and the average delay time is about 1 s. On the other hand, shear phases from local events within the crust are characterized by a bimodal pattern of fast polarizations and an average delay time of 0.04 s. This observation suggests that the dominant source region for seismic anisotropy beneath the rift is located within the mantle. We use finite-frequency waveform modeling to test different models of anisotropy within the lithosphere/asthenosphere system of the rift. The results show that the rift-parallel fast polarizations are consistent with HTI anisotropy caused by rift-parallel magmatic intrusions or lenses located within the lithospheric mantle - as it would be expected during the early stages of continental rifting. Furthermore, the short-scale spatial variations in the fast polarizations observed in the southern part of the study area can be explained by effects due to sedimentary basins of low isotropic velocity in combination with a shift in the orientation of anisotropic fabrics in the upper mantle. A uniform anisotropic layer in relation to large-scale asthenospheric mantle flow is less consistent with the observed splitting parameters.

  5. Spatial instability of the rift in the St. Paul multifault transform fracture system, Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Sokolov, S. Yu.; Zaraiskaya, Yu. A.; Mazarovich, A. O.; Efimov, V. N.; Sokolov, N. S.

    2016-05-01

    The structure of the acoustic basement of the eastern part of the St. Paul multifault transform fracture system hosts rift paleovalleys and a paleonodal depression that mismatch the position of the currently active zones. This displacement zone, which is composed of five fault troughs, is unstable in terms of the position of the rift segments, which jumped according to redistribution of stresses. The St. Paul system is characterized by straightening of the transform transition between two remote segments of the Mid-Atlantic Ridge (MAR). The eastern part of the system contains anomalous bright-spot-like reflectors on the flattened basement, which is a result of atypical magmatism, that forms the standard ridge relief of the acoustic basement. Deformations of the acoustic basement have a presedimentation character. The present-day deformations with lower amplitude in comparison to the basement are accompanied by acoustic brightening of the sedimentary sequence. The axial Bouguer anomalies in the east of the system continue to the north for 120 km from the active segments of the St. Paul system. Currently seismically active segments of the spreading system are characterized by increasing amplitudes of the E-W displacement along the fault troughs. Cross-correlation of the lengths of the active structural elements of the MAR zone (segments of the ridge and transform fracture zones of displacement) indicates that, statistically, the multifault transform fracture system is a specific type of oceanic strike-slip faults.

  6. Rifting of Continental Interiors: Some New Geophysical Data and Interpretations

    NASA Astrophysics Data System (ADS)

    Keller, G. R.

    2005-12-01

    Rifting is one of the major processes that affect the evolution of the continents. This process sometimes leads to continental breakup and the formation of new oceans, but more often does not. This is presumably due to extension not progressing sufficiently to form a new plate margin resulting in a structure, which remains isolated in an intra-plate environment. The Southern Oklahoma aulacogen is such a feature, and the continental portion of the East African rift system may be a modern example. As more detailed geophysical and geological studies of rifts have become available in recent years, a complex picture of rift structure and evolution has emerged. Global patterns that reveal the connections between lithospheric structure (deep and shallow), magmatism (amount and style), amount of extension, uplift, and older structures remain elusive. However, our geophysical studies of modern and paleo rifts in North America, East Africa, and Europe makes it possible to make some general observations: 1). Magmatism in rifts is modest without the presence of a (pre-existing?) thermal anomaly in the mantle. 2). Magmatic modification of the crust takes many forms which probably depend on the nature of older structures present and the state of the lithosphere when rifting is initiated (i.e. cold vs. hot; fertility), 3) There is no clear relation between amount of extension and the amount of magmatic modification of the crust. 4) Brittle deformation in the upper crustal is complex, often asymmetrical and older features often play important roles in focusing deformation. However on a lithospheric scale, rift structure is usually symmetrical. 5) A better understanding of rift processes is emerging as we achieve higher levels of integration of a wide variety of geoscience data.

  7. Tectonoestratigraphic and Thermal Models of the Tiburon and Wagner Basins, northern Gulf of California Rift System

    NASA Astrophysics Data System (ADS)

    Contreras, J.; Ramirez Zerpa, N. A.; Negrete-Aranda, R.

    2014-12-01

    The northern Gulf of California Rift System consist sofa series faults that accommodate both normal and strike-slip motion. The faults formed a series of half-greens filled with more than 7 km of siliciclastic suc­cessions. Here, we present tectonostratigraphic and heat flow models for the Tiburón basin, in the southern part of the system, and the Wag­ner basin in the north. The models are constrained by two-dimensional seis­mic lines and by two deep boreholes drilled by PEMEX­-PEP. Analysis of the seismic lines and models' results show that: (i) subsidence of the basins is controlled by high-angle normal faults and by flow of the lower crust, (ii) basins share a common history, and (iii) there are significant differences in the way brittle strain was partitioned in the basins, a feature frequently observed in rift basins. On one hand, the bounding faults of the Tiburón basin have a nested geometry and became active following a west-to-east sequence of activation. The Tiburon half-graben was formed by two pulses of fault activity. One took place during the protogulf extensional phase in the Miocene and the other during the opening of Gulf of California in the Pleistocene. On the other hand, the Wagner basin is the result of two fault generations. During the late-to middle Miocene, the west-dipping Cerro Prieto and San Felipe faults formed a domino array. Then, during the Pleistocene the Consag and Wagner faults dissected the hanging-wall of the Cerro Prieto fault forming the modern Wagner basin. Thermal modeling of the deep borehole temperatures suggests that the heat flow in these basins in the order of 110 mW/m2 which is in agreement with superficial heat flow measurements in the northern Gulf of California Rift System.

  8. Multiple mantle upwellings beneath the Northern East-African Rift System from relative P- and S-wave traveltime tomography

    NASA Astrophysics Data System (ADS)

    Civiero, Chiara; Hammond, James; Goes, Saskia; Fishwick, Stewart; Ahmed, Abdulhakim; Ayele, Atalay; Doubre, Cecile; Goitom, Berhe; Keir, Derek; Kendall, Mike; Leroy, Sylvie; Ogubazghi, Ghebrebrhan; Rumpker, Georg; Stuart, Graham

    2015-04-01

    Mantle plumes have been invoked as the likely cause of East African Rift volcanism and extension. However, the nature of mantle upwelling is debated, with proposed configurations ranging from a single broad plume, the African Superplume, connected to the LLSVP beneath Southern Africa, to one or more distinct lower-mantle sources along the rift. We present a new relative travel-time tomography model that images detailed P- and S- wave velocities from P,S and SKS phases below the northern East-African, Red Sea and Gulf of Aden rift. Data comes from stations that cover the area from Tanzania to Saudi Arabia. The aperture of the integrated dataset allows us to image for the first time structures of ~100 km length scale down to depths of 900 km beneath this region. Our images provide evidence of at least two low-velocity structures with a diameter of ~200 km that continue through the transition zone and into the lower mantle: the first extends to at least 900 km beneath Afar, and a second reaching at least 750 km depth just west of the Main Ethiopian Rift, a region with off-rift volcanism. Taking into account seismic sensitivity to temperature and thermally controlled phase boundary topography, we interpret these features as multiple focused upwellings from below the transition zone with excess temperatures of 100±50 K. The scale of the upwellings is smaller than any of the previously proposed lower mantle plume sources. This suggests the ponding or flow of deep-plume material below the transition zone may be spawning smaller upper-mantle upwellings.

  9. Evidence of rift valley fever seroprevalence in the Sahrawi semi-nomadic pastoralist system, Western Sahara

    PubMed Central

    2014-01-01

    Background The increasing global importance of Rift Valley fever (RVF) is clearly demonstrated by its geographical expansion. The presence of a wide range of host and vector species, and the epidemiological characteristics of RVF, have led to concerns that epidemics will continue to occur in previously unaffected regions of Africa. The proximity of the Sahrawi territories of Western Sahara to endemic countries, such as Mauritania, Senegal, and Mali with periodic isolation of virus and serological evidence of RVF, and the intensive livestock trade in the region results in a serious risk of RVF spread in the Sahrawi territories, and potentially from there to the Maghreb and beyond. A sero-epidemiological survey was conducted in the Saharawi territories between March and April 2008 to investigate the possible presence of the RVF virus (RVFV) and associated risk factors. A two-stage cluster sampling design was used, incorporating 23 sampling sites. Results A total of 982 serum samples was collected from 461 sheep, 463 goats and 58 camels. Eleven samples (0.97%) tested positive for IgG against the RVFV. There were clusters of high seroprevalence located mostly in the Tifariti (7.69%) and Mehaires (7.14%) regions, with the Tifariti event having been found in one single flock (4/26 positive animals). Goats and older animals were at a significantly increased risk being seropositive (p = 0.007 and p = 0.007, respectively). Conclusion The results suggest potential RVF activity in the study area, where intense livestock movement and trade with neighbouring countries might be considered as a primary determinant in the spread of the disease. The importance of a continuous field investigation is reinforced, in light of the risk of RVF expansion to historically unaffected regions of Africa. PMID:24758592

  10. Disjunct distributions of freshwater snails testify to a central role of the Congo system in shaping biogeographical patterns in Africa

    PubMed Central

    2014-01-01

    Background The formation of the East African Rift System has decisively influenced the distribution and evolution of tropical Africa’s biota by altering climate conditions, by creating basins for large long-lived lakes, and by affecting the catchment and drainage directions of river systems. However, it remains unclear how rifting affected the biogeographical patterns of freshwater biota through time on a continental scale, which is further complicated by the scarcity of molecular data from the largest African river system, the Congo. Results We study these biogeographical patterns using a fossil-calibrated multi-locus phylogeny of the gastropod family Viviparidae. This group allows reconstructing drainage patterns exceptionally well because it disperses very poorly in the absence of existing freshwater connections. Our phylogeny covers localities from major drainage basins of tropical Africa and reveals highly disjunct sister-group relationships between (a) the endemic viviparids of Lake Malawi and populations from the Middle Congo as well as between (b) the Victoria region and the Okavango/Upper Zambezi area. Conclusions The current study testifies to repeated disruptions of the distribution of the Viviparidae during the formation of the East African Rift System, and to a central role of the Congo River system for the distribution of the continent’s freshwater fauna during the late Cenozoic. By integrating our results with previous findings on palaeohydrographical connections, we provide a spatially and temporarily explicit model of historical freshwater biogeography in tropical Africa. Finally, we review similarities and differences in patterns of vertebrate and invertebrate dispersal. Amongst others we argue that the closest relatives of present day viviparids in Lake Malawi are living in the Middle Congo River, thus shedding new light on the origin of the endemic fauna of this rift lake. PMID:24597925

  11. Communications satellite system for Africa

    NASA Astrophysics Data System (ADS)

    Kriegl, W.; Laufenberg, W.

    1980-09-01

    Earlier established requirement estimations were improved upon by contacting African administrations and organizations. An enormous demand is shown to exist for telephony and teletype services in rural areas. It is shown that educational television broadcasting should be realized in the current African transport and communications decade (1978-1987). Radio broadcasting is proposed in order to overcome illiteracy and to improve educational levels. The technical and commercial feasibility of the system is provided by computer simulations which demonstrate how the required objectives can be fulfilled in conjunction with ground networks.

  12. Age relationships for magmatic units of Mid-Continent rift system

    SciTech Connect

    Van Schmus, W.R.

    1989-03-01

    K-Ar ages ranging from about 600 to 1000 Ma have recently been reported for gabbro and basalt recovered from the Texaco 1 Poersch well in Kansas. This has prompted suggestions that rift magmatism there may be distinctly younger than that in the Lake Superior region, and that development of the rift may have lasted several hundred million years. Review of ages from Keweenawan volcanic and plutonic rocks in the Lake Superior region shows that the best results are obtained from U-Pb analyses of zircon and baddeleyite; recent published results range from 1087 to 1108 Ma, with uncertainties on individual ages of /plus minus/ 4 m.y. This finding is consistent with earlier reported U-Pb zircon results. Virtually all other techniques are susceptible to geologic error and generally yield ages of significant less than 1100 Ma. The reliability decreases approximately in the sequence Rb-Sr (whole rock), K-Ar (biotite), Ar/sup 39/-Ar/sup 40/ (whole rock), K-Ar (whole rock), with fresh, coarse-grained plutonic rocks yielding older ages than altered, fine-grained volcanic rocks. K-Ar data on altered, fine-grained mafic rocks, therefore, are very poor indicators of original crystallization ages. Since the rocks from the Texaco 1 Poersch well are fine grained and slightly to moderately altered, their true ages are probably substantially older than 800-900 Ma. Interpretations based on the K-Ar ages from this well are ill advised; tectonic interpretation of the Mid-Continent rift system must wait for more accurate results. Several possibilities exist for obtaining more reliable ages from samples of the Poersch well and other, older wells in the region. These studies are in progress, and any available results will be presented.

  13. Seismic Anisotropy of the Lithosphere/Asthenosphere System Beneath the Rwenzori Region of the East-African Rift

    NASA Astrophysics Data System (ADS)

    Homuth, B.; Löbl, U.; Batte, A.; Link, K.; Kasereka, C.; Rumpker, G.

    2014-12-01

    We present results from a temporary seismic network of 32 broad-band stations located around the Rwenzori region of the Albertine rift at the border between Uganda and DR Congo. The study aims to constrain seismic anisotropy and mantle deformation processes in relation to the formation of the rift zone. Shear-wave splitting measurements from local and teleseismic earthquakes are used to investigate the seismic anisotropy in the crust and upper mantle beneath the Rwenzori region. At most stations, shear-wave splitting parameters obtained from individual earthquakes exhibit only minor variations with backazimuth. We therefore employ a joint inversion of SKS waveforms to derive hypothetical one-layer parameters. The corresponding fast polarizations are generally rift-parallel and the average delay time is about 1 s. On the other hand, shear phases from local events within the crust are characterized by an average delay time of 0.04 s. This observation suggests that the dominant source region for seismic anisotropy beneath the rift is located within the mantle. We use finite-frequency waveform modeling to test different models of anisotropy within the lithosphere/asthenosphere system of the rift. The results show that the rift-parallel fast polarizations are consistent with HTI anisotropy caused by magmatic intrusions or lenses located within the lithospheric mantle - as it would be expected during the early stages of continental rifting. Furthermore, the short-scale spatial variations in the fast polarizations observed in the southern part of the study area can be explained by effects due to sedimentary basins of low isotropic velocity in combination with a shift in the orientation of anisotropic fabrics in the upper mantle. A uniform anisotropic layer in relation to large-scale asthenospheric mantle flow is less consistent with the observed splitting parameters.

  14. Footwall progradation in syn-rift carbonate platform-slope systems (Early Jurassic, Northern Apennines, Italy)

    NASA Astrophysics Data System (ADS)

    Fabbi, Simone; Santantonio, Massimo

    2012-12-01

    The so-called Umbria-Marche Domain of Northern Apennines represents a vast depositional system, also stretching across the Adriatic Sea subsurface, that was characterized by dominantly pelagic sedimentation through most of its Jurassic to Oligocene/Early Miocene history. The pelagic succession is underlain by Hettangian shallow-water carbonates (Calcare Massiccio Fm.), constituting a regional carbonate platform that was subjected to tectonic extension due to rifting of the Adria/African Plate in the earliest Jurassic. While tectonic subsidence of the hangingwalls drove the drowning of the platform around the Hettangian/Sinemurian boundary, the production of benthic carbonate on footwall blocks continued parallel to faulting, through a sequence of facies that was abruptly terminated by drowning and development of condensed pelagites in the early Pliensbachian. By then rifting had ceased, so that the Pliensbachian to Early Cretaceous hangingwall deposits represent a post-rift basin-fill succession onlapping the tectonically-generated escarpment margins of the highs. During the early phases of syndepositional faulting, the carbonate factories of footwall blocks were still temporarily able to fill part of the accommodation space produced by the normal faults by prograding into the incipient basins. In this paper we describe for the first time a relatively low-angle (< 10°) clinoform bed package documenting such an ephemeral phase of lateral growth of a carbonate factory. The clinoforms are sigmoidal, and form low-relief (maximum 5-7 m) bodies representing a shallow-water slope that was productive due to development of a Lithocodium-dominated factory. Continued faulting and hangingwall subsidence then decoupled the slope from the platform top, halting the growth of clinoforms and causing the platform margin to switch from accretionary to bypass mode as the pre-rift substrate became exposed along a submarine fault escarpment. The downfaulted clinoform slope was then

  15. Mineralization potential along the trend of the Keweenawan- age Central North American Rift System in Iowa, Nebraska, and Kansas

    USGS Publications Warehouse

    Berendsen, P.

    1989-01-01

    The tectonic and sedimentary environment of the Central North American Rift System (CNARS) provides an excellent setting for major mineral deposits. Major north-northeast-trending high-angle normal or reverse faults and northwest-trending transcurrent fault systems may exercise control over ore forming processes. Gabbro and basalt are the dominant igneous rock types. Carbonatite and kimberlite occur in Nebraska and Kansas. Concentrations of Cu, Ni, Co, Ti, Au, Ag and PG minerals are known to occur in this setting. Arkosic sandstone, siltstone, shale, and minor carbonate units occur on top of the rift basalts and in flanking basins where they may reach thicknesses of 10 km (6 miles). The potential for stratiform or unconformity-related metalliferous deposits should be considered. The rift as a whole remains largely unexplored.

  16. Detection and Response for Rift Valley fever

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever is a viral disease that impacts domestic livestock and humans in Africa and the Middle East, and poses a threat to military operations in these areas. We describe a Rift Valley fever Risk Monitoring website, and its ability to predict risk of disease temporally and spatially. We al...

  17. Stratigraphy of Mid-Continent rift system in Kansas as revealed by recent exploration wells

    SciTech Connect

    Newell, K.D.; Berendsen, P.; Watney, W.L.; Doveton, J.H.; Steeples, D.

    1989-03-01

    The Texaco 1 Poersch well in Kansas (11,300 ft TD) was the first significant exploration test of the Mid-Continent Rift System (MRS). An upper succession of rift-related rocks (2846-7429 ft) contains approximately 90% mafic igneous rocks with minor pegmatites and 10% oxidized siltstone and arkose. Arkose and subarkose with minor siltstone and shale make up 90% of a lower succession (7429 ft to TD). The remaining lower succession is composed of mafic igneous rocks. Mafic rocks are typically alkali basalts. Individual flows (detected by presence of amygdules, interflow sediments, compositional differences, and oxidized zones) range in thickness from 20 to 250 ft. Sedimentary rocks in the lower succession are divided into three sequences, each 1000-2000 ft thick. The sequences overlie relatively thin mafic flows or intrusives. Each sequence is generally composed of fining-upward units (50-150 ft thick) attributed to episodic movement and erosion of fault blocks in alluvial fan-dominated sedimentary environments. Shales and siltstones are too oxidized to be viable petroleum source rocks, but gray shale with approximately 0.5% total organic carbon was found in the MRS by the 1-4 Finn well, 21 mi to the northeast. Geologic examination of several shallower Precambrian tests holes near 1 Poersch shows considerable variability in sedimentary and tectonic settings along the MRS. Correlation between wells in Kansas and exposed areas of the MRS is still problematic. Additional wells will be necessary to better understand its hydrocarbon potential.

  18. Regional paleogeographic evolution of west Africa: Implications for hydrocarbon exploration

    SciTech Connect

    Hempton, M.R.; Rosen, M.A.; Coughlin, R.M.; Scardina, A.D.; Hagen, E.S.; Nordstrom, P.J. )

    1991-03-01

    New paleogeographic reconstructions of west African continental margins provide a regional framework to contrast differences in hydrocarbon habitat and tectonostratigraphic style. Five regional provinces are delineated: (1) Northwest Africa margin from mauritania to Sierra Leone, (2) Transform margin from Liberia to Benin, (3) Niger delta of Nigeria, Cameroon, and Equatorial Guinea, (4) South Atlantic Salt basin margin from Cameroon to Angola, and (5) Southwest Africa margin of Namibia and South Africa. Computer-constrained paleogeographic reconstructions based on exploration data depict the separation of west Africa from South and North America during the Late Triassic to the present along three rift systems. In northwest Africa rifting began in the Late Triassic associated with the opening of the Central Atlantic. In southwest Africa rifting began between the southern tips of Africa and South America in the Early Cretaceous (Valanginian) and propagated northward to the Benue Trough, a broad zone of left-lateral shear and extensional basins that began to open in the Aptian. Between these two rift systems, the Transform margin rift system initiated in the Early Cretaceous (Barremain) as a wrench-fault dominated eastward extension of the Proto-Caribbean ocean that propagated to the Benue Trough by the middle Albian. The most important variables affecting the tectonostratigraphic and hydrocarbon evolution of the west African margins include (1) the geometry, kinematics, and duration of rifting; (2) distribution of rift basins relative to paleoclimate zones (which affects the deposition of lacustrine source rocks and evaporites while influencing the type and quantity of sediment derived from land); (3) sea-level fluctuations; and (4) distribution of deltaic and turbiditic depocenters.

  19. Reactivation of a segmented hyper-extended rift system: the example of the Pamplona transfer zone in the western Pyrenees

    NASA Astrophysics Data System (ADS)

    Lescoutre, Rodolphe; Schaeffer, Frédéric; Masini, Emmanuel; Manatschal, Gianreto

    2016-04-01

    Numerous studies have revealed the importance of rift-inheritance on the formation of orogens but little consideration was given to rift segmentation and the role of transfer zones on the architecture of mountain chains. Indeed, structural mapping of passive margins pointed out the occurrence of a strong variability in the rift architecture along the margin when crossing through peculiar features that represent transfer zones. These transfer zones are generally oriented in the extension direction and relay the deformation between rift segments. The aim of this study is twofold: 1) characterize and define the Pamplona fault system as well as the structures and architecture of the basins bounding this major paleo-transfer fault located in the Western Pyrenees, and 2) understand its role during the subsequent Pyrenean convergence. The influence of the Pamplona fault system on the structuration of the Mauléon basin to the northeast and the Basque-Cantabrian basin to the southwest is substantial as expressed by their large offset and the occurrence of exhumed deep crustal and mantle rocks flooring the two basins. On the one hand, field work in the Labourd Massif and the western termination of the Mauléon basin enabled to describe faults and their relations to sedimentary sequences. This work also allowed describing the formation and reactivation of faults according to their orientation and their activity with respect to key markers (pre-Trias and post-Cenomanian). A strong relationship between rift architecture (proximal to distal domains) and structural inheritance is suggested. On the other hand, preliminary results from fieldwork, literature compilation and new tomographic imaging enable to determine the role and the history of the Pamplona fault system during Late Cretaceous compression. A significant work of this starting PhD project will be to determine the rift structures that have been reactivated and to assess their influence on the final architecture of the

  20. Geoscience Methods Lead to Paleo-anthropological Discoveries in Afar Rift, Ethiopia

    NASA Astrophysics Data System (ADS)

    WoldeGabriel, Giday; Renne, Paul R.; Hart, William K.; Ambrose, Stanley; Asfaw, Berhane; White, Tim D.

    2004-07-01

    With few exceptions, most of the hominid evolutionary record in Africa is closely associated with the East African Rift System. The exceptions are the South African and Chadian hominids collected from the southern and west-central parts of the continent, respectively. The Middle Awash region stands alone as the most prolific paleoanthropological area ever discovered (Figure 1). Its paleontological record has yielded over 13,000 vertebrate fossils, including several hominid taxa, ranging in age from 5.8 Ma to the present. The uniqueness of the Middle Awash hominid sites lies in their occurrence within long, > 6 Ma volcanic and sedimentary stratigraphic records. The Middle Awash region has yielded the longest hominid record yet available. The region is characterized by distinct geologic features related to a volcanic and tectonic transition zone between the continental Main Ethiopian and the proto-oceanic Afar Rifts. The rift floor is wider-200 km-than other parts of the East African Rift (Figure 1). Moreover, its Quaternary axial rift zone is wide and asymetrically located close to the western margin. The fossil assemblages and the lithostratigraphic records suggest that volcanic and tectonic activities within the broad rift floor and the adjacent rift margins were intense and episodic during the late Neogene rift evolution.

  1. Variations in the reflectivity of the moho transition zone beneath the Midcontinent Rift System of North America: results from true amplitude analysis of GLIMPCE data

    USGS Publications Warehouse

    Hutchinson, Deborah R.; Lee, Myung W.; Behrendt, John C.; Cannon, William F.; Green, Adrian

    1992-01-01

    True amplitude processing of The Great Lakes International Multidisciplinary Program on Crustal Evolution seismic reflection data from the Midcontinent Rift System of North America shows large differences in the reflectivity of the Moho transition zone beneath the axial rift, beneath the rift flanks, and outside of the rift. The Moho reflection from the axial rift has a discontinuous, diffractive character marginally stronger (several decibels) than an otherwise transparent lower crust and upper mantle. Beneath the axial rift, Moho is interpreted to be a synrift igneous feature. Beneath the rift flanks, the reflectivity of the Moho transition is generally well developed with two identifiable boundaries, although in places it is weakly reflective to nonreflective, similar to Moho outside the rift. The two boundaries are interpreted as the base of essentially intact, although stretched, prerift Archean crust (upper boundary) and new synrift Moho 1-2 s (6-7 km) deeper (lower boundary). Beneath the rift flanks, the layered reflection Moho transition results from the preexisting crustal composition and fabric modified by synrift igneous processes and extensional tectonic/metamorphic processes. The geologic evidence for extensive basaltic magmatism in the rift is the basis for interpreting the Moho signature as a Keweenawan structure that has been preserved for 1.1 b.y. Extension and magmatism appear to enhance reflectivity in the lower crust and Moho transition zone only where stretching factors are moderate (rift flanks) and not where they are extreme (axial rift). This leads to the prediction that the reflectivity across analogous volcanic passive continental margins should be greatest beneath the moderately stretched continental shelves and should decrease towards the ocean-continent boundary.

  2. Sedimentology and depositional environments of the Red Sandstone Group, Rukwa Rift Basin, southwestern Tanzania: New insight into Cretaceous and Paleogene terrestrial ecosystems and tectonics in sub-equatorial Africa

    NASA Astrophysics Data System (ADS)

    Roberts, Eric M.; O'Connor, Patrick M.; Stevens, Nancy J.; Gottfried, Michael D.; Jinnah, Zubair A.; Ngasala, Sifael; Choh, Adeline M.; Armstrong, Richard A.

    2010-05-01

    The Red Sandstone Group (RSG) in the Rukwa Rift Basin of southwestern Tanzania represents one of the only well-exposed, fossiliferous Cretaceous-Paleogene continental sedimentary sequences in sub-equatorial Africa. The significance of the RSG for reconstructing the paleoenvironmental and paleoclimatic history of African ecosystems during these critical time periods has been obfuscated by long-standing confusion and debate over the age of the deposits. Detailed stratigraphic, sedimentologic, and paleontologic investigations of the RSG conducted between 2002 and 2008 have produced a wealth of new fossil discoveries and data on lithofacies, alluvial architecture, sedimentary provenance, clay mineralogy and geochronology that resolve the long-standing debate over the age of these deposits. This study confirms the existence of an extensive middle Cretaceous sequence, herein named the Galula Formation, and subdivided into the Mtuka and Namba members. Moreover, we document the existence of a previously unrecognized late Paleogene continental sequence termed the Nsungwe Formation, which is divided into the Utengule and Songwe members. The Galula Formation represents a 600-3000 m thick sequence of amalgamated, braided fluvial deposits that were deposited across a large braidplain system via multiple parallel channels that had their source in the highlands of Malawi and Zambia. The middle Cretaceous Dinosaur Beds of Malawi are hypothesized to be at least partially correlative with the Galula Formation, and represent proximal deposits of this large, northwest flowing, trunk stream system. A moderately diverse terrestrial vertebrate fauna, including multiple species of dinosaurs, crocodyliforms, turtles, fishes and mammals have been recovered, along with a sparse aquatic molluscan fauna. Lithofacies and clay mineralogy indicate that Cretaceous paleoclimate ameliorated during deposition of the Galula Formation, transitioning from tropical semi-arid to tropical humid conditions

  3. Syn-Rift Systems of East Godavari Sub Basin: Its Evolution and Hydrocarbon Prospectivity

    NASA Astrophysics Data System (ADS)

    Dash, J., Jr.; Zaman, B.

    2014-12-01

    Krishna Godavari (K.G.) basin is a passive margin basin developed along the Eastern coast of India. This basin has a polyhistoric evolution with multiple rift systems. Rift basin exploration has provided the oil and gas industry with almost one third of discovered global hydrocarbon resources. Understanding synrift sequences, their evolution, depositional styles and hydrocarbon prospectivity has become important with recent discovery of the wells, G-4-6,YS-AF and KG-8 in the K.G. offshore basin. The East Godavari subbasin is a hydrocarbon producing basin from synrift and pre-rift sediments, and hence this was selected as the study area for this research. The study has been carried out by utilizing data of around 58 wells (w1-w58) drilled in the study area 25 of which are hydrocarbon bearing with organic thickness varying from 200 m to 600 m. Age data generated by palaentology and palynology studies have been utilized for calibration of key well logs to differentiate between formations within prerift and synrift sediments. The electrologs of wells like resistivity, gamma ray, neutron, density and sonic logs have been utilized for correlation of different formations in all the drilled wells. The individual thicknesses of sand, shale and coal in the formations have been calculated and tabulated. For Golapalli formation, the isopach and isolith maps were generated which revealed that there were four depocentres with input from the north direction. Schematic geological cross sections were prepared using the well data and seismic data to understand the facies variation across the basin. The sedimentological and petrophysical analysis reports and electro log suites were referred to decipher the environment of deposition, the reservoir characteristics, and play types. The geochemical reports [w4 (Tmax)= 455-468 °C; w1 (Tmax) = 467-514 °C; w4(VRO)= 0.65-0.85; w1(VRO)= 0.83-1.13] revealed the source facies, its maturation and migration timings i.e. the petroleum systems

  4. Metasomatized lithospheric mantle beneath Turkana depression in southern Ethiopia (the East Africa Rift): geochemical and Sr-Nd-Pb isotopic characteristics

    NASA Astrophysics Data System (ADS)

    Meshesha, Daniel; Shinjo, Ryuichi; Matsumura, Risa; Chekol, Takele

    2011-11-01

    Mantle xenoliths entrained in Quaternary alkaline basalts from the Turkana Depression in southern Ethiopia (the East Africa Rift) were studied for their geochemical and Sr-Nd-Pb isotopic compositions to constrain the evolution of the lithosphere. The investigated mantle xenoliths are spinel lherzolites in composition with a protogranular texture. They can be classified into two types: anhydrous and hydrous spinel lherzolites; the latter group characterized by the occurrences of pargasite and phlogopite. The compositions of whole-rock basaltic component (CaO = 3.8-5.6 wt%, Al2O3 = 2.5-4.1 wt%, and MgO = 34.7-38.1 wt%), spinel (Cr# = 0.062-0.117, Al2O3 = 59.0-64.4 wt%) and clinopyroxene (Mg# = 88.4-91.7, Al2O3 = 5.2-6.7 wt%) indicate that the lherzolites are fertile and have not experienced significant partial melting. Both types are characterized by depleted 87Sr/86Sr (0.70180-0.70295) and high 143Nd/144Nd (0.51299-0.51348) with wide ranges of 206Pb/204Pb (17.86-19.68) isotopic compositions. The variations of geochemical and isotopic compositions can be explained by silicate metasomatism induced by different degree of magma infiltrations from ascending mantle plume. The thermobarometric estimations suggest that the spinel lherzolites were derived from depths of 50-70 km (15.6-22.2 kb) and entrained in the alkaline magma at 847-1,052°C. Most of the spinel lherzolites from this study record an elevated geotherm (60-90 mW/m2) that is related to the presence of rising mantle plume in an active tectonic setting. Sm-Nd isotopic systematic gives a mean TDM model age of 0.95 Ga, interpreted as the minimum depletion age of the subcontinental lithosphere beneath the region.

  5. The stratigraphic architecture of hyper-extended rift systems: A field perspective from Aps, Pyrenees and Baja-California

    NASA Astrophysics Data System (ADS)

    Masini, Emmanuel; Manatschal, Gianreto; Tugend, Julie; Mohn, Geoffroy; Robin, Cécile; Geoffroy, Laurent; Unternehr, Patrick

    2013-04-01

    The discovery of hyper-extended domains in deep water rifted margins challenged the classical view of the evolution of rift systems leading to continental breakup. In these hyper-extended domains, rift basins occur over less than 10km thick extended continental crust or exhumed subcontinental mantle. Neither their imaged stratigraphic architecture and drilled facies nor the subsidence history can be explained by classical McKenzie-type rift models. Studies performed on off- and on-shore examples demonstrate the importance of tectonic exhumation by detachment faulting. However, despite their apparent widespread occurrence in present-day rifted margins, the overall tectono-sedimentary evolution of these systems remains poorly understood. In this study we review and compare key multi-scale observations from 3 different hyper-extended rift systems. 1) The first example, in the Western Pyrenees, corresponds to a complete sediment-rich Cretaceous hyper-extended rift system that can be investigated. 2) The second example in the Swiss Alps, gives the access to supra-detachment sedimentary evolution in a sediment-starved context. 3) The last example exposed in Baja California Sur, shows supra-detachment sedimentary evolution in sediment-rich and shallow water environment. Based on these studies in three different settings, we conclude that the basins forming in the lower and upper plate position respective to detachment fault polarity develop as two different types of basins. Lower plate basins develop over top-basement detachment systems and discontinuous pieces of pre-rift strata (extensional allochthons). In this setting, the sequential development of low-angle detachment systems implies the creation of new real estate crust (new seafloor surfaces) and a complex syn-rift stratigraphic architecture. Through this domain, the deposition of syn- and post-tectonic sediments above exhumation surfaces are diachronous along stretching direction illustrating relative migration of

  6. Attractor structures of riftogenesis in the lithosphere of Baikal Rift System

    NASA Astrophysics Data System (ADS)

    Klyuchevskii, A. V.

    2011-03-01

    The study results of modern geodynamics and tectonophysics of the lithosphere of Baikal Rift System (BRS) are generalized. By the data on radii of dislocations, three areas of maximal strain-strength anisotropy of the medium are distinguished, while analysis of seismic moments of earthquakes has showed that in these parts of the lithosphere mostly dip-slip fault-causing quakes of various energy classes take place; i.e., riftogenesis processes dominate. Within the framework of the theory of nonlinear dissipative dynamical systems, these areas are classified as attractor structures of riftogenesis (ASR). ASRs are located in the central part and in the flanks of the BRS, and they form nonlinearity and instability of modern geodynamical and tectonophysical processes in the lithosphere, which are manifested in seismicity of the Baikal Region and Mongolia.

  7. Rift zones and magma plumbing system of Piton de la Fournaise volcano: How do they differ from Hawaii and Etna?

    NASA Astrophysics Data System (ADS)

    Michon, Laurent; Ferrazzini, Valérie; Di Muro, Andrea; Villeneuve, Nicolas; Famin, Vincent

    2015-09-01

    On ocean basaltic volcanoes, magma transfer to the surface proceeds by subvertical ascent from the mantle lithosphere through the oceanic crust and the volcanic edifice, possibly followed by lateral propagation along rift zones. We use a 19-year-long database of volcano-tectonic seismic events together with detailed mapping of the cinder cones and eruptive fissures to determine the geometry and the dynamics of the magma paths intersecting the edifice of Piton de la Fournaise volcano. We show that the overall plumbing system, from about 30 km depth to the surface, is composed of two structural levels that feed distinct types of rift zones. The deep plumbing system is rooted between Piton des Neiges and Piton de la Fournaise volcanoes and has a N30-40 orientation. Above 20 km below sea level (bsl), the main axis switches to a N120 orientation, which permits magma transfer from the lithospheric mantle to the base of the oceanic crust, below the summit of Piton de la Fournaise. The related NW-SE rift zone is 15 km wide, linear, spotted by small to large pyroclastic cones and related lava flows and emits slightly alkaline magmas resulting from high-pressure fractionation of clinopyroxene ± olivine. This rift zone has low magma production rate of ~ 0.5-3.6 × 10- 3 m3s- 1 and an eruption periodicity of around 200 years over the last 30 ka. Seismic data suggest that the long-lasting activity of this rift zone result from regional NNE-SSW extension, which reactivates inherited lithospheric faults by the effect of underplating and/or thermal erosion of the mantle lithosphere. The shallow plumbing system (< 11 km bsl) connects the base of the crust with the Central Cone. It is separated from the deep plumbing system by a relatively large aseismic zone between 8 and 11 km bsl, which may represent a deep storage level of magma. The shallow plumbing system feeds frequent, short-lived summit and flank (NE and SE flanks) eruptions along summit and outer rift zones, respectively

  8. Crustal and mantle structure and anisotropy beneath the incipient segments of the East African Rift System: Preliminary results from the ongoing SAFARI

    NASA Astrophysics Data System (ADS)

    Yu, Y.; Reed, C. A.; Gao, S. S.; Liu, K. H.; Massinque, B.; Mdala, H. S.; moidaki, M.; Mutamina, D. M.; Atekwana, E. A.; Ingate, S. F.; Reusch, A.; Barstow, N.

    2013-12-01

    Despite the vast wealth of research conducted toward understanding processes associated with continental rifting, the extent of our knowledge is derived primarily from studies focused on mature rift systems, such as the well-developed portions of the East African Rift System (EARS) north of Lake Malawi. To explore the dynamics of early rift evolution, the SAFARI (Seismic Arrays for African Rift Initiation) team deployed 50 PASSCAL broadband seismic stations across the Malawi, Luangwa, and Okavango rifts of the EARS during the summer of 2012. The cumulative length of the profiles is about 2500 km and the planned recording duration is 2 years. Here we present the preliminary results of systematic analyses of data obtained from the first year of acquisition for all 50 stations. A total of 446 high-quality shear-wave splitting measurements using PKS, SKKS, and SKS phases from 84 teleseismic events were used to constrain fast polarization directions and splitting times throughout the region. The Malawi and Okavango rifts are characterized by mostly NE trending fast directions with a mean splitting time of about 1 s. The fast directions on the west side of the Luangwa Rift Zone are parallel to the rift valley, and those on the east side are more N-S oriented. Stacking of approximately 1900 radial receiver functions reveals significant spatial variations of both crustal thickness and the ratio of crustal P and S wave velocities, as well as the thickness of the mantle transition zone. Stations situated within the Malawi rift demonstrate a southward increase in observed crustal thickness, which is consistent with the hypothesis that the Malawi rift originated at the northern end of the rift system and propagated southward. Both the Okavango and Luangwa rifts are associated with thinned crust and increased Vp/Vs, although additional data is required at some stations to enhance the reliability of the observations. Teleseismic P-wave travel-time residuals show a delay of about

  9. Hawaii Rifts

    SciTech Connect

    Nicole Lautze

    2015-01-01

    Rifts mapped through reviewing the location of dikes and vents on the USGS 2007 Geologic Map of the State of Hawaii, as well as our assessment of topography, and, to a small extent, gravity data. Data is in shapefile format.

  10. The Goodman swell: a lithospheric flexure caused by crustal loading along the Midcontinent rift system

    USGS Publications Warehouse

    Peterman, Z.E.; Sims, P.K.

    1988-01-01

    Rb-Sr biotite ages of Archean and Early to Middle Proterozoic crystalline rocks in northern Wisconsin and adjacent Upper Peninsula of Michigan describe a regionally systematic pattern related to differential uplift. An "age low' occurs in northern Wisconsin where values range from 1070-1172 Ma for rocks with crystallization ages of 1760 to 1865 Ma. These values overlap with the main episode of mafic igneous activity (1090 to 1120 Ma) along the Midcontinent rift system (MRS). We interpret these low biotite ages as registering closure due to cooling below the 300??C isotherm as a consequence of uplift and rapid erosion of an area that we are informally naming the Goodman swell. We interpret the swell to be a forebulge imposed on an elastic crust by loading of mafic igneous rocks along and within the axis of the MRS. -from Authors

  11. Exploring Crustal Structure and Mantle Seismic Anisotropy Associated with the Incipient Southern and Southwestern Branches of the East African Rift System

    NASA Astrophysics Data System (ADS)

    Yu, Y.; Reed, C. A.; Gao, S. S.; Liu, K. H.; Massinque, B.; Mdala, H. S.; Chindandali, P. R. N.; Moidaki, M.; Mutamina, D. M.

    2014-12-01

    In spite of numerous geoscientific studies, the mechanisms responsible for the initiation and development of continental rifts are still poorly understood. The key information required to constrain various geodynamic models on rift initiation can be derived from the crust/mantle structure and anisotropy beneath incipient rifts such as the Southern and Southwestern branches of the East African Rift System. As part of a National Science Foundation funded interdisciplinary project, 50 PASSCAL broadband seismic stations were deployed across the Malawi, Luangwa, and Okavango rift zones from the summer of 2012 to the summer of 2014. Preliminary results from these 50 SAFARI (Seismic Arrays for African Rift Initiation) and adjacent stations are presented utilizing shear-wave splitting (SWS) and P-S receiver function techniques. 1109 pairs of high-quality SWS measurements, consisting of fast polarization orientations and splitting times, have been obtained from a total of 361 seismic events. The results demonstrate dominantly NE-SW fast orientations throughout Botswana as well as along the northwestern flank of the Luangwa rift valley. Meanwhile, fast orientations beneath the eastern Luangwa rift flank rotate from NNW to NNE along the western border of the Malawi rift. Stations located alongside the western Malawi rift border faults yield ENE fast orientations, with stations situated in Mozambique exhibiting more E-W orientations. In the northern extent of the study region, fast orientations parallel the trend of the Rukwa and Usangu rift basins. Receiver function results reveal that, relative to the adjacent Pan-African mobile belts, the Luangwa rift zone has a thin (30 to 35 km) crust. The crustal thickness within the Okavango rift basin is highly variable. Preliminary findings indicate a northeastward thinning along the southeast Okavango border fault system congruent with decreasing extension toward the southwest. The Vp/Vs measurements in the Okavango basin are roughly

  12. Two Plumes Beneath the East African Rift System: a Geochemical Investigation into Possible Interactions in Ethiopia

    NASA Astrophysics Data System (ADS)

    Nelson, W. R.; Furman, T.; van Keken, P. E.; Lin, S.

    2007-12-01

    East African Rift System magmatism began over 40 my ago and has continued through the present. Numerical models have determined two plumes are necessary to create the spatial and temporal distribution of volcanism. Geochemical data support the presence of two chemically distinct plumes initially located beneath the Afar Depression (NE Ethiopia) and the Turkana Depression (SW Ethiopia/N Kenya). The timing and eruptive of the Afar and Kenya plumes are also distinct. While there is growing evidence to support the existence of two dynamically and chemically distinct plumes beneath the East African Rift System, the interactions between them remain unclear. Our study focuses on the geochemistry of mafic shield lavas from three locations on the eastern flank of the Ethiopian plateau. These lavas are spatially located between the surface manifestation of the Afar and Kenya plumes. The majority of the lava is alkaline and has experienced varying degrees of olivine and pyroxene fractionation. The northernmost lavas (9°10'N) are transitional and display the most fractionation. Primitive mantle melts were generated at depths near the fertile mantle garnet-spinel transition zone and deeper (80-100km) and are free of metasomatic influence. Minor HREE depletions also support derivation of melts from a garnet-bearing source. Lavas with lithospheric influence are generated from shallower depths and show minor amphibole influence. Overall, geochemical data show the lavas in this study closely resemble those from various episodes of Kenya plume magmatism with modifications attributed to lithospheric contamination. This interpretation is consistent with current numerical models suggesting episodic northward movement of Kenya plume magmas along the lithosphere-asthenosphere boundary. The data imply that the Kenya plume has a much larger spatial influence and therefore a larger geodynamic influence in the EARS than previously recognized.

  13. Rift propagation

    NASA Technical Reports Server (NTRS)

    Parmentier, E. M.; Schubert, G.

    1989-01-01

    A model for rift propagation which treats the rift as a crack in an elastic plate which is filled from beneath by upwelling viscous asthenosphere as it lengthens and opens. Growth of the crack is driven by either remotely applied forces or the pressure of buoyant asthenosphere in the crack and is resisted by viscous stresses associated with filling the crack. The model predicts a time for a rift to form which depends primarily on the driving stress and asthenosphere viscosity. For a driving stress on the order of 10 MPa, as expected from the topography of rifted swells, the development of rifts over times of a few Myr requires an asthenosphere viscosity of 10 to the 16th Pa s (10 to the 17th poise). This viscosity, which is several orders of magnitude less than values determined by postglacial rebound and at least one order of magnitude less than that inferred for spreading center propagation, may reflect a high temperature or large amount of partial melting in the mantle beneath a rifted swell.

  14. Geochemical evidence of mantle reservoir evolution during progressive rifting

    NASA Astrophysics Data System (ADS)

    Rooney, T. O.; Mohr, P.; Dosso, L.; Hall, C. M.

    2010-12-01

    The Afar region in East Africa, which represents the triple junction of three well-exposed Cenozoic rift systems, is a pivotal domain in the study of rift evolution. The western margin of Afar, defined by a wide transitional region from plateau to rift floor, developed in response to the rifting of the Red Sea commencing shortly after the eruption of the ~31-29 Ma Ethiopian-Yemen flood basalts. The Oligocene lava sequence which covers this rift margin was fed from intensive diking. The dikes and the block-faulting and monoclinal warping that followed provide an opportunity to probe the geochemical reservoirs preserved in the magmatic record and the development of the rifting processes. Argon geochronology reveals that dikes along the western Afar margin span the entire history of rift evolution from the initial Oligocene flood basalt event to the development of focused zones of intrusion in rift marginal basins. Major and trace element, and isotopic results (Sr-Nd-Pb-Hf) from these dikes demonstrate temporal geochemical heterogeneity defined by variable contributions from the Afar plume, depleted mantle and African lithosphere, consistent with studies of Quaternary basalts from the Ethiopian Rift. On a broader scale our results show that as the western Afar margin matures, the initially significant contribution from the Afar plume wanes in favor of shallow asthenospheric and lithospheric reservoirs. The early dikes, which are coincident with the initial weakening of the lithosphere in a magma-assisted rifting model, geochemically resemble the widespread plume-derived flood basalts and shields that constitute the Ethiopian Plateau. Subsequent diking is characterized by a lesser role for the Afar plume and greater contributions from the African lithosphere and depleted mantle. During the terminal stage of dike emplacement, where focused magmatic intrusion accommodated extension, a more significant fraction is derived from the depleted mantle and less of a

  15. Structure of backarc inner rifts as a weakest zone of arc-backarc system: a case study of the Sea of Japan

    NASA Astrophysics Data System (ADS)

    Sato, Hiroshi; Ishiyama, Tasuya; Kato, Naoko; Abe, Susumu; Saito, Hideo; Shiraishi, Kazuya; Abe, Shiori; Iwasaki, Takaya; Inaba, Mitsuru; No, Tetsuo; Sato, Takeshi; Kodaira, Shuichi; Takeda, Tetsuya; Matsubara, Makoto; Kodaira, Chihiro

    2015-04-01

    compression, the boundary of rock units reactivated as reverse faults, commonly forming a large-scale wedge thrust and produced subsidence of rift basin under compressional stress regime. Large amount of convergence of overriding plate is accommodated along the inner rift, suggesting that it is a weakest zone in whole arc-backarc system. The convergence between young (15 Ma) Shikoku basin and SW Japan arc produced intense shortening along the inner failed rift along the Sea of Japan coast. After the onset of subduction along the Nankai trough, the fold-and-thrust belt was covered by Pliocene marine sediment. Before the 2011 off-Tohoku earthquake (M9), several damaging earthquakes occurred along the backarc fold-and-thrust belt. These represents that a weak backarc inner rift is very sensitive for the stress produce by the subduction interface.

  16. East Antarctic rifting triggers uplift of the Gamburtsev Mountains.

    PubMed

    Ferraccioli, Fausto; Finn, Carol A; Jordan, Tom A; Bell, Robin E; Anderson, Lester M; Damaske, Detlef

    2011-11-17

    The Gamburtsev Subglacial Mountains are the least understood tectonic feature on Earth, because they are completely hidden beneath the East Antarctic Ice Sheet. Their high elevation and youthful Alpine topography, combined with their location on the East Antarctic craton, creates a paradox that has puzzled researchers since the mountains were discovered in 1958. The preservation of Alpine topography in the Gamburtsevs may reflect extremely low long-term erosion rates beneath the ice sheet, but the mountains' origin remains problematic. Here we present the first comprehensive view of the crustal architecture and uplift mechanisms for the Gamburtsevs, derived from radar, gravity and magnetic data. The geophysical data define a 2,500-km-long rift system in East Antarctica surrounding the Gamburtsevs, and a thick crustal root beneath the range. We propose that the root formed during the Proterozoic assembly of interior East Antarctica (possibly about 1 Gyr ago), was preserved as in some old orogens and was rejuvenated during much later Permian (roughly 250 Myr ago) and Cretaceous (roughly 100 Myr ago) rifting. Much like East Africa, the interior of East Antarctica is a mosaic of Precambrian provinces affected by rifting processes. Our models show that the combination of rift-flank uplift, root buoyancy and the isostatic response to fluvial and glacial erosion explains the high elevation and relief of the Gamburtsevs. The evolution of the Gamburtsevs demonstrates that rifting and preserved orogenic roots can produce broad regions of high topography in continental interiors without significantly modifying the underlying Precambrian lithosphere. PMID:22094700

  17. An investigation into an outbreak of Rift Valley fever on a cattle farm in Bela-Bela, South Africa, in 2008.

    PubMed

    Mapaco, Lourenço P; Coetzer, Jacobus A W; Paweska, Janusz T; Venter, Estelle H

    2012-01-01

    In 2008, a suspected outbreak of Rift Valley fever (RVF) was reported on a farm in the Bela-Bela area, Limpopo Province, South Africa. Seven calves died on the affected dairy farm, where no RVF vaccination programme was practised. No apparent clinical disease was reported in the other 300 cattle (33 calves included) or 200 sheep on the farm. During the outbreak, blood samples from 77.7% (233/300) of the cattle and 36.5% (73/200) of the sheep were collected on the affected farm and 55 blood samples were taken from cattle on a neighbouring farm. Eight weeks later, 78% of the cattle (234/300) and 42.5% of the sheep (85/200) were bled on the affected farm only. All sera were tested by an Immunoglobulin M (IgM)-capture Enzymelinked immunosorbent assay (ELISA) and by an indirect Immunoglobulin G (IgG) ELISA. Selected IgM-positive (n = 14), IgG-positive (n = 23) and samples negative for both IgM and IgG-specific antibodies against RVF virus (n = 19) were tested using the serum neutralisation test (SNT). Sera from IgM-positive (n = 14) and negative (n = 20) animals were also tested by a TaqMan polymerase chain reaction (PCR). On the affected farm, 7% (16/233) of the cattle were IgM-positive and 13.7% (32/233) IgG-positive at the first bleed and 2% were IgM-positive at the second bleed, whilst the number of cattle positive for IgG-specific antibodies increased by 21.3% compared with the first bleed. Only 1.4% of sheep were positive for both IgM and IgG antibodies at the first collection; at the second bleed, IgM-positive cases decreased to 1.2%, whilst IgG-positive cases increased to 2.4%. Whilst no IgM-positive cattle were found on the neighbouring farm, 5.5% of cattle were IgG-positive. The SNT confirmed most of the ELISA results, whilst PCR results were all negative. Although serology results indicated virus circulation on both farms, the negative PCR results demonstrated that the animals were not viraemic at the time they were sampled. The movement of infected mosquito

  18. Modeling the distribution of the West Nile and Rift Valley Fever vector Culex pipiens in arid and semi-arid regions of the Middle East and North Africa

    PubMed Central

    2014-01-01

    Background The Middle East North Africa (MENA) region is under continuous threat of the re-emergence of West Nile virus (WNV) and Rift Valley Fever virus (RVF), two pathogens transmitted by the vector species Culex pipiens. Predicting areas at high risk for disease transmission requires an accurate model of vector distribution, however, most Cx. pipiens distribution modeling has been confined to temperate, forested habitats. Modeling species distributions across a heterogeneous landscape structure requires a flexible modeling method to capture variation in mosquito response to predictors as well as occurrence data points taken from a sufficient range of habitat types. Methods We used presence-only data from Egypt and Lebanon to model the population distribution of Cx. pipiens across a portion of the MENA that also encompasses Jordan, Syria, and Israel. Models were created with a set of environmental predictors including bioclimatic data, human population density, hydrological data, and vegetation indices, and built using maximum entropy (Maxent) and boosted regression tree (BRT) methods. Models were created with and without the inclusion of human population density. Results Predictions of Maxent and BRT models were strongly correlated in habitats with high probability of occurrence (Pearson’s r = 0.774, r = 0.734), and more moderately correlated when predicting into regions that exceeded the range of the training data (r = 0.666,r = 0.558). All models agreed in predicting high probability of occupancy around major urban areas, along the banks of the Nile, the valleys of Israel, Lebanon, and Jordan, and southwestern Saudi Arabia. The most powerful predictors of Cx. pipiens habitat were human population density (60.6% Maxent models, 34.9% BRT models) and the seasonality of the enhanced vegetation index (EVI) (44.7% Maxent, 16.3% BRT). Maxent models tended to be dominated by a single predictor. Areas of high probability corresponded with sites of

  19. Prediction of a Rift Valley fever Outbreak

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Using satellite measurements to detect elevated sea surface temperatures (SSTs) and subsequent elevated normalized difference vegetation index (NDVI) data in Africa, we predicted an outbreak of Rift Valley fever (RVF) in humans and animals in the Horn of Africa during September 2006-May 2007. We det...

  20. Constraining the Thermal History of the Midcontinent Rift System with Clumped Isotopes and Organic Thermal Maturity Indices

    NASA Astrophysics Data System (ADS)

    Gallagher, T. M.; Sheldon, N. D.; Mauk, J. L.; Gueneli, N.; Brocks, J. J.

    2015-12-01

    The Mesoproterozoic (~1.1 Ga) North American Midcontinent Rift System (MRS) has been of widespread interest to researchers studying its economic mineral deposits, continental rifting processes, and the evolution of early terrestrial life and environments. For their age, the MRS rocks are well preserved and have not been deeply buried, yet a thorough understanding of the regional thermal history is necessary to constrain the processes that emplaced the mineral deposits and how post-burial alteration may have affected various paleo-records. To understand the thermal history of the MRS better, this study presents carbonate clumped isotope (Δ47) temperatures from deposits on the north and south sides of the rift. Due to the age of these deposits and known post-depositional processes, uncertainties exist about whether the clumped isotope signature has been reset. To test this, three generations of calcite were analyzed from the Nonesuch Fm. from the White Pine mine in Michigan including: sedimentary limestone beds, early diagenetic carbonate nodules, and hydrothermal calcite veins associated with the emplacement of copper mineralization. Clumped isotope temperatures from the White Pine mine range from 84 to 131°C, with a hydrothermal vein producing the hottest temperature. The clumped isotope temperature range for samples throughout the rift expands to 41-134°C. The hottest temperatures are associated with areas of known copper mineralization, whereas the coolest temperatures are found on the northern arm of the rift in Minnesota, far from known basin-bounding faults. Our hottest temperatures are broadly consistent with preexisting maximum thermal temperature estimates based on clay mineralogy, fluid inclusions, and organic geochemistry data. Clumped isotope results will also be compared to new hydrocarbon maturity data from the Nonesuch Fm., which suggest that bitumen maturities consistently fall within the early oil window across Michigan and Wisconsin.

  1. Gravity study of the Central African Rift system: a model of continental disruption 2. The Darfur domal uplift and associated Cainozoic volcanism

    NASA Astrophysics Data System (ADS)

    Bermingham, P. M.; Fairhead, J. D.; Stuart, G. W.

    1983-05-01

    Gravity studies of the Darfur uplift, Western Sudan, show it to be associated with a circular negative Bouguer anomaly, 50 mGal in amplitude and 700 km across. A three-dimensional model interpretation of the Darfur anomaly, using constraints deduced from geophysical studies of similar but more evolved Kenya and Ethiopia domes, suggests either a low-density laccolithic body at mid-lithospheric depth (~ 60 km) or a thinned lithosphere with emplacement at high level of low-density asthenospheric material. The regional setting of the Darfur uplift is described in terms of it being an integral part of the Central African Rift System which is shown to be broadly equivalent to the early to middle Miocene stage in the development of the Afro-Arabian Rift System. Comparisons between these rift systems suggest that extensional tectonics and passive rifting, resulting in the subsiding sedimentary rift basins associated with the Ngaoundere, Abu Gabra, Red Sea and Gulf of Aden rifts, are more typical of the early stage development of passive continental margins than the active domal uplift and development of rifted features associated with the Darfur, Kenya and Ethiopia domes.

  2. Africa.

    ERIC Educational Resources Information Center

    Happel, Sue; Loeb, Joyce

    Although the activities in this unit are designed primarily for students in the intermediate grades, the document's text, illustrations, and bibliographic references are suitable for anyone interested in learning about Africa. Following a brief introduction and map work, the document is arranged into six sections. Section 1 traces Africa's history…

  3. Africa.

    ERIC Educational Resources Information Center

    Martz, Carlton

    2001-01-01

    This publication explores issues related to Africa. It examines the U.S. response to the Barbary pirate states (Morocco, Algiers, Tunis, Tripoli) in the early 19th century; the current AIDS crisis in Africa; and 14th century Mali and other Islamic lands through the eyes of Ibn Battuta, who traveled throughout the Muslim world. Each article…

  4. Rapid spatiotemporal variations in rift structure during development of the Corinth Rift, central Greece

    NASA Astrophysics Data System (ADS)

    Nixon, Casey W.; McNeill, Lisa C.; Bull, Jonathan M.; Bell, Rebecca E.; Gawthorpe, Robert L.; Henstock, Timothy J.; Christodoulou, Dimitris; Ford, Mary; Taylor, Brian; Sakellariou, Dimitris; Ferentinos, George; Papatheodorou, George; Leeder, Mike R.; Collier, Richard E. LI.; Goodliffe, Andrew M.; Sachpazi, Maria; Kranis, Haralambos

    2016-05-01

    The Corinth Rift, central Greece, enables analysis of early rift development as it is young (<5 Ma) and highly active and its full history is recorded at high resolution by sedimentary systems. A complete compilation of marine geophysical data, complemented by onshore data, is used to develop a high-resolution chronostratigraphy and detailed fault history for the offshore Corinth Rift, integrating interpretations and reconciling previous discrepancies. Rift migration and localization of deformation have been significant within the rift since inception. Over the last circa 2 Myr the rift transitioned from a spatially complex rift to a uniform asymmetric rift, but this transition did not occur synchronously along strike. Isochore maps at circa 100 kyr intervals illustrate a change in fault polarity within the short interval circa 620-340 ka, characterized by progressive transfer of activity from major south dipping faults to north dipping faults and southward migration of discrete depocenters at ~30 m/kyr. Since circa 340 ka there has been localization and linkage of the dominant north dipping border fault system along the southern rift margin, demonstrated by lateral growth of discrete depocenters at ~40 m/kyr. A single central depocenter formed by circa 130 ka, indicating full fault linkage. These results indicate that rift localization is progressive (not instantaneous) and can be synchronous once a rift border fault system is established. This study illustrates that development processes within young rifts occur at 100 kyr timescales, including rapid changes in rift symmetry and growth and linkage of major rift faults.

  5. He-Ne-Ar isotope studies of mafic volcanic rocks and mantle xenoliths from the East African Rift System - contrasting isotope signals in different rift branches

    NASA Astrophysics Data System (ADS)

    Halldorsson, S. A.; Hilton, D. R.; Scarsi, P.; Abebe, T.; Massi, K. M.; Barry, P. H.; Fischer, T. P.; de Moor, J.; Rudnick, R. L.

    2010-12-01

    Helium isotope studies of the East African Rift System (EARS) suggest the involvement of a deep mantle plume(s) beneath the northern (Ethiopian) segment [1-3]. The highest 3He/4He (RA) signatures found to date show a close association with the greatest magma volumes erupted since the Early Cenozoic in the region. While the helium isotope characteristics are well established in the Ethiopia-Afar region, Ne and Ar systematics remain poorly constrained. Using a combined He-Ne-Ar isotope approach, our aim is to determine the regional extent of the influence of the Afar plume and to distinguish between subcontinental lithospheric mantle (SCLM) and/or a possible second mantle plume sources located to the south of the Turkana Depression. Xenoliths and mafic lavas from N-Tanzania display a limited range in He isotopes (5-7 RA) with exceptions at Arusha (7.8RA) and Labait (8.7RA), through 7.1-8.7 RA in N-Kenya and S-Ethiopia, to 14.3 RA in the Main Ethiopian Rift and Afar, spanning nearly the entire range of previously reported values. The mean 3He/4He ratio from of lavas and xenoliths from N-Tanzania is remarkably close to the global average of 6.1±0.9 (RA) for continental xenoliths and basalts, thought to represent the SCLM [4]. Thus far, only MORB-like values of 7.3-8.3 RA have been found in volcanics of the Western rift. Initial Ne isotope data reveal the presence of a solar-like Ne component in xenoliths from the Ethiopia-Afar region, with extrapolated 21Ne/22Neex ratios of 0.0365 (assuming Ne-B = 12.5). This trend overlaps that of the Loihi-Kilauea line (L-K). Interestingly, a xenolith from N-Tanzania has a 21Ne/22Neex ratio of 0.0415, falling on a trajectory intermediate between MORB and L-K. The highest 40Ar/36Ar ratio obtained on phenocrysts/xenoliths to date is 1510. The generally low 3He/4He ratios of N-Tanzania likely result from different mixing proportions of asthenospheric sources with lithospheric material, the latter having developed lower 3He/4He ratios

  6. Melt Distribution in the Ethiopian Rift System: Constraints From Seismic Observations and Finite-Frequency Modelling

    NASA Astrophysics Data System (ADS)

    Angus, D.; Hammond, J. O.; Kendall, J.; Wookey, J.

    2008-12-01

    As part of the Ethiopian Afar Geoscientific Lithospheric Experiment (EAGLE) 79 seismic stations were deployed, for up to 18 months, in the Main Ethiopian Rift (MER). Many indicators of melt were observed leading to the idea that magma was driving the rifting process in this region. Some of the best evidence for melt came from observations of anisotropy in studies of surface waves and shear-wave splitting. The shear- wave splitting shows fast directions which change abruptly from being rift parallel on the rift flanks to magmatic-segment parallel in the rift valley. This was interpreted in terms of melt-induced anisotropy. The abrupt change in splitting parameters over small lateral distances suggests that the source of anisotropy is shallow. To further constrain the location of the anisotropy and study the ability of shear-wave splitting to identify sharp lateral changes in anisotropy, we model finite-frequency waveforms for a suite of model representations of the rift zone. This allows us to determine the lateral and vertical extent of the melt-induced anisotropy. The results show how a simple model with two regimes of anisotropy can explain the variability across the rift, in both delay time and shear-wave polarization, over short length scales of the order 20- 40 km. Our models have enabled us to constrain the anisotropic characteristics beneath the MER. Our best model has a 9% anisotropy on the western rift margin, with fast directions of 30°, a 100 km wide rift zone with fast direction of 20° inside the rift zone and with 9% anisotropy close to the western margin, 7% elsewhere, and 7% anisotropy on the eastern margin with fast directions of 30°. In all regions of the model we constrain anisotropy to begin at a depth of 90 km. The depth of anisotropy co-incides with the proposed depth of melt initiation beneath the region, based on geochemistry. Also the elevated splitting beneath the western margin supports evidence of low velocities and highly conductive

  7. Groundwater dynamics in the complex aquifer system of Gidabo River Basin, southern Main Ethiopian Rift: Evidences from hydrochemistry and isotope hydrology

    NASA Astrophysics Data System (ADS)

    Degu, Abraham; Birk, Steffen; Dietzel, Martin; Winkler, Gerfried; Moggessie, Aberra

    2014-05-01

    Located in the tectonically active Main Ethiopian Rift system, the Gidabo River Basin in Ethiopia has a complex hydrogeological setting. The strong physiographic variation from highland to rift floor, variability in volcanic structures and disruption of lithologies by cross-cutting faults contribute for their complex nature of hydrogeology in the area. Until now, the groundwater dynamics and the impact of the tectonic setting on groundwater flow in this region are not well understood, though the local population heavily depends on groundwater as the major water supply. A combined approach based on hydrochemical and isotopic data was applied to investigate the regional flow dynamics of the groundwater and the impact of tectonic setting. Groundwater evolves from slightly mineralized Ca-Mg-HCO3 on the highland to highly mineralized Na-HCO3 dominating type in the deep rift floor aquifers. δ18O and δD composition of groundwater show a general progressive enrichment from the highland to the rift floor, except in thermal and deep rift floor aquifers. Relatively the thermal and deep rift floor aquifers are depleted and show similar signature to the groundwaters of highland, indicating groundwater inflow from the highland. Correspondingly, rising HCO3 and increasingly enriched signatures of δ 13C points to hydrochemical evolution of DIC and diffuse influx of mantle CO2 into the groundwater system. Thermal springs gushing out along some of the fault zones, specifically in the vicinity of Dilla town, display clear influence of mantle CO2 and are an indication of the role of the faults acting as a conduit for deep circulating thermal water to the surface. By considering the known geological structures of the rift, hydrochemical and isotopic data we propose a conceptual groundwater flow model by characterizing flow paths to the main rift axis. The connection between groundwater flow and the impact of faults make this model applicable to other active rift systems with similar

  8. Uplift of Africa as a potential cause for Neogene intensification of the Benguela upwelling system

    NASA Astrophysics Data System (ADS)

    Jung, Gerlinde; Prange, Matthias; Schulz, Michael

    2014-10-01

    The Benguela Current, located off the west coast of southern Africa, is tied to a highly productive upwelling system. Over the past 12 million years, the current has cooled, and upwelling has intensified. These changes have been variously linked to atmospheric and oceanic changes associated with the glaciation of Antarctica and global cooling, the closure of the Central American Seaway or the further restriction of the Indonesian Seaway. The upwelling intensification also occurred during a period of substantial uplift of the African continent. Here we use a coupled ocean-atmosphere general circulation model to test the effect of African uplift on Benguela upwelling. In our simulations, uplift in the East African Rift system and in southern and southwestern Africa induces an intensification of coastal low-level winds, which leads to increased oceanic upwelling of cool subsurface waters. We compare the effect of African uplift with the simulated impact of the Central American Seaway closure, Indonesian Throughflow restriction and Antarctic glaciation, and find that African uplift has at least an equally strong influence as each of the three other factors. We therefore conclude that African uplift was an important factor in driving the cooling and strengthening of the Benguela Current and coastal upwelling during the late Miocene and Pliocene epochs.

  9. Interaction between transform faults and rift systems: a combined field and experimental approach

    NASA Astrophysics Data System (ADS)

    Tibaldi, Alessandro; Bonali, Fabio; Pasquaré Mariotto, Federico

    2016-04-01

    We present a detailed field structural survey of the area of interaction between the active NW-striking transform Husavik-Flatey Fault (HFF) and the N-S Theystareykir Fissure Swarm (TFS), in North Iceland, integrated by analogue scaled models. Field data contribute to a better understanding of how transform faults work, at a much higher detail than classical marine geophysical studies. Analogue experiments are conducted to analyse the fracture patterns resulting from different possible cases where transform faulting accompanies or postpones the rift motions; different tectonic block configurations are also considered. West of the intersection between the transform fault (HFF) and the rift zone (TFS), the former splays with a gradual bending giving rise to a leading extensional imbricate fan. The westernmost structure of the rift, the N-S Gudfinnugja Fault (GF), is divided into two segments: the southern segment makes a junction with the HFF and is part of the imbricate fan; north of the junction instead, the northern GF appears right-laterally offset by about 20 m. Southeast of the junction, along the possible prolongation of the HFF across the TFS, the strike of the rift faults rotates in an anticlockwise direction, attaining a NNW-SSE orientation. Moreover, the TFS faults north of the HFF prolongation are fewer and have smaller offsets than those located to the south. Through the comparison between the structural data collected in the field at the HFF-TFS connection zone and a set of scaled experiments, we confirm a prolongation of the HFF through the rift, although here the transform fault has a much lower slip-rate than west of the junction. Our data suggest that transform fault terminations may be more complex than previously known, and propagate across a rift through a modification of the rift pattern.

  10. Quantifying the Temporal and Spatial Response of Channel Steepness to Changes in Rift Basin Architecture

    NASA Astrophysics Data System (ADS)

    Robinson, Scott M.

    Quantifying the temporal and spatial evolution of active continental rifts contributes to our understanding of fault system evolution and seismic hazards. Rift systems also preserve robust paleoenvironmental records and are often characterized by strong climatic gradients that can be used to examine feedbacks between climate and tectonics. In this thesis, I quantify the spatial and temporal history of rift flank uplift by analyzing bedrock river channel profiles along footwall escarpments in the Malawi segment of the East Africa Rift. This work addresses questions that are widely applicable to continental rift settings: (1) Is rift-flank uplift sufficiently described by theoretical elliptical along-fault displacement patterns? (2) Do orographic climate patterns induced by rift topography affect rift-flank uplift or morphology? (3) How do uplift patterns along rift flanks vary over geologic timescales? In Malawi, 100-km-long border faults of alternating polarity bound half-graben sedimentary basins containing up to 4km of basin fill and water depths up to 700m. Orographically driven precipitation produces climatic gradients along footwall escarpments resulting in mean annual rainfall that varies spatially from 800 to 2500 mm. Temporal oscillations in climate have also resulted in lake lowstands 500 m below the modern shoreline. I examine bedrock river profiles crossing the Livingstone and Usisya Border Faults in northern Malawi using the channel steepness index (Ksn) to assess importance of these conditions on rift flank evolution. River profiles reveal a consistent transient pattern that likely preserves a temporal record of slip and erosion along the entire border fault system. These profiles and other topographic observations, along with known modern and paleoenvironmental conditions, can be used to interpret a complete history of rift flank development from the onset of rifting to present. I interpret the morphology of the upland landscape to preserve the onset

  11. Oil source rocks in lacustrine sequences from Tertiary grabens, western Mediterranean rift system, northeast Spain

    SciTech Connect

    Anadon, P.; Cawley, S.J.; Julia, R.

    1988-08-01

    Lacustrine sequences, 100-250 m thick, containing oil-prone, organic-rich mudstones (ORM) are exposed in five Tertiary basins in northeastern Spain. They were deposited in small lacustrine basins (up to 50 km/sup 2/) that developed in grabens of the western Mediterranean rift system. ORMs from the Rubielos basin comprise laminated gray mudstones with interbedded rhythmite intervals (up to 2.5 m thick) formed by couplets of organic- and carbonate-rich laminae (< 1 mm thick). In marginal zones, ORMs (up to 10 m thick) alternate with lean, bioturbated green marls (up to 5 m thick). ORMs (Rock-Eval yields /approximately/ 40 kg/MT, HI /approximately/ 850 mg HC/g TOC) had a dominant waxy terrestrial plant input, with significant and variable algal/bacterial input. ORMs in these basins are immature for petroleum generation. Larger lacustrine basins similar to those described above, in more appropriate burial/thermal situations, can be envisioned as zones of potential interest for lacustrine oil exploration in the western Mediterranean.

  12. Syn-rift, syn-glacial and syn-orogenic sedimentary mélanges as indicators of tectonic and palaeoclimatic evolution of the Lufilian Belt, Neoproterozoic-Lower Palaeozoic of Central Africa

    NASA Astrophysics Data System (ADS)

    Wendorff, Marek

    2010-05-01

    The Lufilian belt is an important segment of the Neoproterozoic-Lower Palaeozoic orogenic network within southern and central Africa. It deforms a sedimentary suite of the Katanga Supergroup (880-500 Ma). Mélange occurrences, traditionally called the Katangan breccias/megabreccias, are a prominent feature of the belt architecture. Some mélange bodies reach thickness of 2000 m and contain huge blocks of Katangan rocks. They were previously considered as tectonic mélanges ("friction breccias") marking regional decollement zones related to thrusting during the Pan-African orogenesis. However, these fragmental rocks were recently shown to be of sedimentary origin. They form two regionally extensive olistostrome bodies and one glaciogenic unit. The main lines of evidence for the olistostrome genesis are following: (1) lack of pervasive shearing that would point to tectonic fragmentation; (2) textures and structures diagnostic for subaqueous sediment gravity flows ranging from debris flows to turbidites; (3) roundness and provenance of clasts, and lateral facies gradients implying erosion, abrasion and unroofing of the Katangan source rocks elevated in the source areas; (4) lower boundaries of fragmental bodies are not tectonic but stratigraphic; (5) injections of unconsolidated conglomeratic matrix filling open joints in allochthonous blocks embedded in olistostrome lithosomes. The oldest mélange is a disorganised to locally organised syn rift olistostrome complex with olistoliths reaching 5 metres across. The clasts were derived from the uplifted rift margin and redeposition resulted from mass-wasting (rockfalls producing sedimentary breccias), sliding of solitary blocks, and pebbly to cobbly debris flows. The succeeding glaciogenic mélange complex originated during the Grand Conglomerat glaciation (correlative to the Sturtian glacial). It consists of disorganised clast-in-matrix facies that resulted from glacial erosion of the uplifted rift margin and

  13. Structural style of the Turkana Rift, Kenya

    SciTech Connect

    Dunkelman, T.J.; Karson, J.A.; Rosendahl, B.R.

    1988-03-01

    Multifold seismic reflection and geologic mapping in part of the eastern branch of the East African Rift system of northern Kenya reveal a major rift structure containing at least 3 km of Neogene sediment fill beneath Lake Turkana. This includes a series of half-graben basins, with centrally located quaternary volcanic centers, which are linked end-to-end by structural accommodation zones. Whereas the geometry of rifting is similar to that of the nonvolcanic western branch of the East African Rift system, the Turkana half-grabens are much smaller and may reflect extension of a thinner lithosphere or development of more closely spaced fracture patterns during rift evolution, or both.

  14. Cretaceous paleogeography of Africa

    SciTech Connect

    Hulver, M.L.; Ziegler, A.M.; Rowley, D.B.; Sahagian, D.

    1986-05-01

    Five stage-length maps (Valanginian, Aptian, Cenomanian, Coniacian, and Maestrichtian) of Africa integrate topography/bathymetry, lithofacies, tectonics, and climatically sensitive sediments. These reconstructions differ from currently available maps in their level of detail and accuracy, and in that computer routines were developed to plot all aspects of the maps, including lithofacies patterns. Bathymetric contours were determined from community paleoecology and from thermal subsidence models of the newly opening Atlantic and Indian oceans. Topographic contours have been estimated from uplift models of rift shoulders, as well as from the erosion and sedimentation record of both the internal and marginal basins. The uplift of rift shoulders from Nigeria to Sudan is suggested by the extensive Nubian and equivalent sandstones across north Africa. This Benue-Ngaoundere-Abu Gabra rift system approximately paralleled the paleoequator, and its shoulders must have experienced the high rainfall normally associated with the intertropical convergence zone (ITCZ). In fact, these mountains would have served as a high level heat source, and would have pinned the ITCZ to their summits. Such a system tends to reduce seasonal excursions of the ITCZ, and may have influenced the high biological productivity represented by the oil source rocks of the Arabian peninsula. These sources also lie on the equator and could have resulted from a shelf incursion of the equatorial divergence zone, which is controlled by the ITCZ.

  15. Complex seismicity patterns in the Rwenzori region: insights to rifting processes at the Albertine Rift.

    NASA Astrophysics Data System (ADS)

    Lindenfeld, M.; Rümpker, G.; Wölbern, I.; Batte, A. G.; Schumann, A.

    2012-04-01

    Numerous seismological studies in East Africa have focused on the northern and eastern branches of the East African Rift System (EARS). However, the seismic activity along the western branch is much more pronounced. Here, the Rwenzori Mountains are located within the Albertine rift valley, at the border between Uganda and D.R. Congo. During a seismic monitoring campaign between February 2006 and September 2007 we have recorded more than 800 earthquakes per month in the Rwenzori area. The earthquake distribution is highly heterogeneous. The majority of located events lie within faults zones to the East and West of the Rwenzoris with the highest seismic activity observed in the northeastern area, were the mountains are in contact with the rift shoulders. The hypocentral depth distribution peaks at 16 km depth and extends down to the Moho which was found at 20 - 32 km depths by teleseismic receiver functions. Local magnitudes range from -0.5 to 5.1 with a b-value of 1.1. Fault plane solutions of 304 events were derived from P-polarities and SV/P amplitude ratios. More than 70% of the source mechanisms exhibit normal faulting. T-axis trends are highly uniform and oriented WNW-ESE, which is perpendicular to the rift axis and in good agreement with kinematic rift models. The area of highest seismic activity NE of the Rwenzoris is characterized by the occurrence of several earthquake clusters in 5 -20 km depth. They have stable positions throughout time and form elongated pipes with 1-2 km diameter and vertical extensions of 3-5 km. From petrological considerations we presume that these earthquake swarms are triggered by fluids and gasses which originate from a magmatic source below the crust. The existence of a magmatic source within the lithosphere is supported by the detection of a shear-wave velocity reduction in 55-80 km depth from receiver-function analysis and the location of mantle earthquakes at about 60 km. We interpret these observations as indication for an

  16. A hydrogeologic model of stratiform copper mineralization in the Midcontinent Rift System, Northern Michigan, USA

    USGS Publications Warehouse

    Swenson, J.B.; Person, M.; Raffensperger, J.P.; Cannon, W.F.; Woodruff, L.G.; Berndt, M.E.

    2004-01-01

    This paper presents a suite of two-dimensional mathematical models of basin-scale groundwater flow and heat transfer for the middle Proterozoic Midcontinent Rift System. The models were used to assess the hydrodynamic driving mechanisms responsible for main-stage stratiform copper mineralization of the basal Nonesuch Formation during the post-volcanic/pre-compressional phase of basin evolution. Results suggest that compaction of the basal aquifer (Copper Harbor Formation), in response to mechanical loading during deposition of the overlying Freda Sandstone, generated a pulse of marginward-directed, compaction-driven discharge of cupriferous brines from within the basal aquifer. The timing of this pulse is consistent with the radiometric dates for the timing of mineralization. Thinning of the basal aquifer near White Pine, Michigan, enhanced stratiform copper mineralization. Focused upward leakage of copper-laden brines into the lowermost facies of the pyrite-rich Nonesuch Formation resulted in copper sulfide mineralization in response to a change in oxidation state. Economic-grade mineralization within the White Pine ore district is a consequence of intense focusing of compaction-driven discharge, and corresponding amplification of leakage into the basal Nonesuch Formation, where the basal aquifer thins dramatically atop the Porcupine Mountains volcanic structure. Equilibrium geochemical modeling and mass-balance calculations support this conclusion. We also assessed whether topography and density-driven flow systems could have caused ore genesis at White Pine. Topography-driven flow associated with the Ottawan orogeny was discounted because it post-dates main-stage ore genesis and because recent seismic interpretations of basin inversion indicates that basin geometry would not be conductive to ore genesis. Density-driven flow systems did not produce focused discharge in the vicinity of the White Pine ore district.

  17. Fluvial systems response to rift margin tectonics: Makhtesh Ramon area, southern Israel

    NASA Astrophysics Data System (ADS)

    Ben-David, Ram; Eyal, Yehuda; Zilberman, Ezra; Bowman, Dan

    2002-06-01

    The geomorphic evolution of Makhtesh Ramon, a feather-shaped erosional valley, and the Nahal Neqarot drainage system to the south occurred largely in response to tectonic activity along the Dead Sea Rift and its western shoulder. Remnants of Miocene clastic sediments (Hazeva Formation) deposited on an erosional peneplain that formed over this area during the Oligocene epoch provide a datum plane for reconstructing subsequent fluvial evolution. These clastic remnants are presently located on the shoulders of Makhtesh Ramon at various elevations. The peneplain truncating the Makhtesh Ramon block has been tilted 0.7% northeastward since the Pliocene epoch (post-Hazeva Formation), whereas that of the Neqarot syncline, south of the Ramon, has been tilted 1.2%. The elliptical exposure of friable Lower Cretaceous sandstone, exposed in the core of the truncated Ramon structure, governed the development of a new ENE directed (riftward) drainage system through capture of streams that previously drained toward the Mediterranean Sea to the northwest. Incised fluvial gaps in the southern rim of Makhtesh Ramon and alluvial fan relicts within Makhtesh Ramon attest to original drainage into the Makhtesh from the south. Remnants of the Plio-Pleistocene Arava Conglomerate on the eastern end of the Neqarot syncline contain clasts from rocks exposed within Makhtesh Ramon, also indicating that streams flowed into the Makhtesh from the southern Neqarot block through the western gaps, then turning eastward and exiting the Makhtesh via the next (Sha'ar-Ramon) gap to the east. Further down-faulting of the Neqarot block during Mid-Late Pleistocene time led to westward retreat of the Neqarot valley and capture of the last stream flowing northward into the Ramon, leaving the modern Makhtesh Ramon isolated from the southern drainage system.

  18. Kinematics of Rift-Parallel Deformation Along the Rukwa Rift, Western Branch, and Main Ethiopian Rift

    NASA Astrophysics Data System (ADS)

    Stamps, D.; Koehn, D.; Burke, K. C.; d'Oreye, N.; Saria, E.; Xu, R.

    2013-12-01

    The East African Rift System spans N-S ~5000 km and currently experiences E-W extension. Previous kinematic studies of the EARS delineated 3 relatively rigid sub-plates (Victoria, Rovuma, and Lwandle) between the Nubian and Somalian plates. GPS observations of these block interiors confirm the rigid plate model, but we also detect a systematic along-rift deformation pattern at GPS stations located within rift zones bounding the western Victoria block and continuing north between the Nubian and Somalian plates. Here we present a kinematic model of present-day rift-parallel deformation along the Western branch, Rukwa Rift, and Main Ethiopian Rift constrained by a new GPS solution, earthquake slip vectors, and mapped active fault structures. We test the roles of block rotation, elastic deformation, and anelastic deformation by varying block geometry, fault slip distribution parameters, estimating permanent strain rate, and scoring each model with GPS observations. We also explore how the present-day deformation patterns relate to longer-term paleostress indicators. Observations of slickensides and offsets in seismic reflection profiles in the northern Western branch (Albertine rift) indicate a change from ~NNE trending normal faulting to include strike-slip motion within the past 7 My that may be related to previously studied stress changes in the Turkana rift. Preliminary results from the kinematic modeling demonstrate simple elastic strain accumulation on major border faults cannot explain an observed systematic northward component in GPS velocities relative to the Victoria block and the Nubian plate.

  19. Sedimentation and reservoir distribution related to a tilted block system in the Sardinia Oligocene-Miocene rift (Italy)

    SciTech Connect

    Tremolieres, P.; Cherchi, A.; Eschard, R.; De Graciansky, P.C.; Montadert, L.

    1988-08-01

    In the western Mediterranean basin lies a rift system about 250 km long and 50 km wide and its infilling outcrop (central Sardinia). Seismic reflection surveys show its offshore extension. Block tilting started during the late Oligocene and lasted during Aquitanian-early Burdigalian time. Two main fault trends, with synthetic and antithetic throws, define the more-or-less collapsed blocks. This morphology guided the transit and trapping of sediments. The sedimentation started in a continental environment then, since the Chattian, in marine conditions. In the central part, the series can reach a thickness of 2,000 m. The basement composition and the volcanics products related to the main fault motion controlled the nature of the synrift deposits. According to their location in the rift context, the tilted blocks trap either continental deposits or marine siliciclastic or carbonate deposits. In the deeper part of the graben, sands were redeposited by gravity flows into the basinal marls. The younger prerift deposits are from Eocene to early Oligocene age and locally comprise thick coal layers. Postrift deposits, mainly marls, sealed the blocks and synrift sedimentary bodies. In middle and late Miocene time some faults were reactivated during compressional events. Then, a quaternary extensional phase created the Campidano graben, filled with about 1,000 m of sediments superimposed on the Oligocene-Miocene rift.

  20. Tag team tectonics: mantle upwelling and lithospheric heterogeneity ally to rift continents (Invited)

    NASA Astrophysics Data System (ADS)

    Nelson, W. R.; Furman, T.

    2013-12-01

    The configuration of continents we know today is the result of several billion years of active Wilson Cycle tectonics. The rifting of continents and subsequent development of ocean basins is an integral part of long-term planetary-scale recycling processes. The products of this process can be seen globally, and the East African Rift System (EARS) provides a unique view of extensional processes that actively divide a continent. Taken together with the adjoining Red Sea and Gulf of Aden, the EARS has experienced over 40 Ma of volcanism and ~30 Ma of extension. While early (pre-rift) volcanism in the region is attributed to mantle plume activity, much of the subsequent volcanism occurs synchronously with continental rifting. Numerous studies indicate that extension and magmatism are correlated: extension leads to decompression melting while magmatism accommodates further extension (e.g. Stein et al., 1997; Buck 2004; Corti 2012). Evaluation of the entire EARS reveals significant geochemical patterns - both spatial and temporal - in the volcanic products. Compositional variations are tied directly to the melt source(s), which changes over time. These variations can be characterized broadly by region: the Ethiopian plateau and Turkana Depression, the Kenya Rift, and the Western Rift. In the Ethiopian plateau, early flood basalt volcanism is dominated by mantle plume contributions with variable input from lherzolitic mantle lithosphere. Subsequent alkaline shield volcanism flanking the juvenile Main Ethiopian Rift records the same plume component as well as contributions from a hydrous peridotitic lithosphere. The hydrous lithosphere does not contribute indefinitely. Instead, young (< 2 Ma) volcanism taps a combination of the mantle plume and anhydrous depleted lithospheric mantle. In contrast, volcanism in the Kenya Rift and the Western Rift are derived dominantly from metasomatized lithospheric mantle rather than mantle plume material. These rifts lie in the mobile

  1. Tectonics of the baikal rift deduced from volcanism and sedimentation: a review oriented to the Baikal and Hovsgol lake systems.

    PubMed

    Ivanov, Alexei V; Demonterova, Elena I

    2009-01-01

    As known from inland sedimentary records, boreholes, and geophysical data, the initiation of the Baikal rift basins began as early as the Eocene. Dating of volcanic rocks on the rift shoulders indicates that volcanism started later, in the Early Miocene or probably in the Late Oligocene. Prominent tectonic uplift took place at about 20 Ma, but information (from both sediments and volcanics) on the initial stage of the rifting is scarce and incomplete. A comprehensive record of sedimentation derived from two stacked boreholes drilled at the submerged Akademichesky ridge indicates that the deep freshwater Lake Baikal existed for at least 8.4 Ma, while the exact formation of the lake in its roughly present-day shape and volume is unknown. Four important events of tectonic/environmental changes at about approximately 7, approximately 5, approximately 2.5, and approximately 0.1 Ma are seen in that record. The first event probably corresponds to a stage of rift propagation from the historical center towards the wings of the rift system. Rifting in the Hovsgol area was initiated at about this time. The event of ~5 Ma is a likely candidate for the boundary between slow and fast stages of rifting. It is reflected in a drastic change of sedimentation rate due to isolation of the Akademichesky ridge from the central and northern Lake Baikal basins. The youngest event of 0.1 Ma is reflected by the (87)0Sr/ (86)Sr ratio increase in Lake Baikal waters and probably related to an increasing rate of mountain growth (and hence erosion) resulting from glacial rebounding. The latter is responsible for the reorganization of the outflow pattern with the termination of the paleo-Manzurka outlet and the formation of the Angara outlet. The event of approximately 2.5 Ma is reflected in the decrease of the (87)Sr/(86)Sr and Na/Al ratios in Lake Baikal waters. We suggest that it is associated with a decrease of the dust load due to a reorganization of the atmospheric circulations in Mainland

  2. Rio Grande rift: An overview

    NASA Astrophysics Data System (ADS)

    Olsen, Kenneth H.; Scott Baldridge, W.; Callender, Jonathan F.

    1987-11-01

    The Rio Grande rift of the southwestern United States is one of the world's principal continental rift systems. It extends as a series of asymmetrical grabens from central Colorado, through New Mexico, to Presidio, Texas, and Chihuahua, Mexico—a distance of more than 1000 km. Although the Rio Grande rift is closely related in timing and structural style to the contiguous Basin and Range extensional province, the two can be distinguished by a variety of geological and geophysical signatures. Rifts (both oceanic and continental) can be defined as elongate depressions overlying places where the entire lithosphere has ruptured in extension. The lithosphere of the Rio Grande rift conforms to this definition, in that: (1) the crust is moderately thinned—Moho depths range from about 45 km under the flanks to about 33 km beneath the rift axis. (2) anomalously low P n velocities (7.6-7.8 km s -1) beneath the rift and a long wavelength gravity low suggest that the asthenosphere is in contact with the base of the crust. The P-velocity is abnormally low (6.4-6.5 km s -1) in the lower half of the crust beneath the rift, suggesting high crustal temperatures. However, associated seismic and volcanologic data indicate the sub-rift lower crust is not dominated by a massive composite mafic intrusion such as is sometimes inferred for the East African rifts. Seismic and magnetotelluric data suggest the presence of a thin (< 1 km) sill-like contemporary midcrustal magma body which may perhaps extend intermittently along much of the length of the rift. Seismic and structural studies indicate a dominant horizontal fabric in the upper and middle crust. The brittle-ductile transition is at depths -15 km except for the major volcanic fields, where it rises to 2-3 km. Structural development of the rift occurred mainly during two time intervals: the early phase beginning at -30 Ma. and lasting 10-12 m.y., and the late phase extending from -10 to 3 Ma. The early phase involved extensive

  3. New Insights into the Transition From Magmatic to Tectonic Rifting

    NASA Astrophysics Data System (ADS)

    Bialas, R. W.; Buck, W. R.; Qin, R.

    2008-12-01

    Magma plays a major role in the development of many rifts and continental margins. This is particularly clear for some of the more recent continental rifts including the Afro-Arabian Rift System and the breakup of South America from Africa. We are interested in how magma, injected as dikes, may lead to weakening of the lithosphere so that rifting can proceed even if the supply of magma wanes. We use a hybrid numerical model to simulate the effect of dike injection on continental lithopsheric rifting. We have developed a numerical diking simulation where the key diking parameters controlling the input of magma are the magma chamber size, minimum diking interval, and maximum tectonic force. The model includes a 2D finite difference code (FLAC) for tracking long- term stress build-up and strain in a viscoelastic-plactic model lithosphere. A boundary element code is used to simulate the effect of short-duration dike intrusion events that are specified to occur periodically at the center of the model region. The stresses from the finite difference code are applied to the boundary element code to calculate how much a dike opens as a function of depth. If a dike is generated, basaltic-density magma is "injected" into the finite difference model based on the distribution of dike opening obtained from the boundary element code. Diking thermally weakens the lithosphere and changes the lithospheric density structure, both weakening the lithosphere and reduce the force difference needed to continue extension. Varying the diking interval and magma chamber size, changes the rates magma input and lithospheric weakening. The maximum tectonic force effects the rate of magma injection, total magmatic extension, and hence, the timing of the transition from magmatic to tectonic extension. With normal lithospheric thicknesses and thermal structure, this transition may require as little as 3-5 km of magmatic extension before the onset of tectonic rifting.

  4. Planning for Rift Valley fever virus: use of geographical information systems to estimate the human health threat of white-tailed deer (Odocoileus virginianus)-related transmission.

    PubMed

    Kakani, Sravan; LaBeaud, A Desirée; King, Charles H

    2010-11-01

    Rift Valley fever (RVF) virus is a mosquito-borne phlebovirus of the Bunyaviridae family that causes frequent outbreaks of severe animal and human disease in sub-Saharan Africa, Egypt and the Arabian Peninsula. Based on its many known competent vectors, its potential for transmission via aerosolization, and its progressive spread from East Africa to neighbouring regions, RVF is considered a high-priority, emerging health threat for humans, livestock and wildlife in all parts of the world. Introduction of West Nile virus to North America has shown the potential for "exotic" viral pathogens to become embedded in local ecological systems. While RVF is known to infect and amplify within domestic livestock, such as taurine cattle, sheep and goats, if RVF virus is accidentally or intentionally introduced into North America, an important unknown factor will be the role of local wildlife in the maintenance or propagation of virus transmission. We examined the potential impact of RVF transmission via white-tailed deer (Odocoileus virginianus) in a typical north-eastern United States urban-suburban landscape, where livestock are rare but where these potentially susceptible, ungulate wildlife are highly abundant. Model results, based on overlap of mosquito, human and projected deer densities, indicate that a significant proportion (497/1186 km(2), i.e. 42%) of the urban and peri-urban landscape could be affected by RVF transmission during the late summer months. Deer population losses, either by intervention for herd reduction or by RVF-related mortality, would substantially reduce these likely transmission zones to 53.1 km(2), i.e. by 89%. PMID:21080319

  5. Investigating the Influence of Pre-Existing Basement Structures on the Propagation of the Malawi Rift using SRTM, RADARSAT, and Aeromagnetic Data

    NASA Astrophysics Data System (ADS)

    Robertson, K.; Atekwana, E. A.; Abdelsalam, M. G.; Laó-Dávila, D. A.

    2015-12-01

    The Malawi rift is a Neogene, amagmatic rift located where the Western Branch of the East Africa Rift System (EARS) terminates. In more mature rifts, magmatism is frequently recognized as a driving factor in rift propagation; however, the amagmatic nature of the Malawi rift permits investigation into the relationship between pre-existing structures and current rift propagation, without the influence of magmatism. To map surface structures, we used Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) and RADARSAT imagery over southern Malawi. To process the SRTM data, we applied edge enhancing filters and derivatives, and extracted topographic profiles to examine scarp height and minimum vertical exposed displacement. We mapped morphologically-defined structures by filtering the RADARSAT imagery using an enhanced lee filter to reduce noise and a Laplacian filter for edge enhancement. To examine Precambrian basement structures, we filtered aeromagnetic data using vertical and horizontal derivatives, tilt derivative, and analytic signal to create magnetic anomaly maps. Surface mapping indicated three primary trends in the southern Malawi rift: NW-SE (dominant), NE-SW, both of which are most likely the remnants of Mesozoic Karoo rifting, and a NNE-SSW trend seen in Neogene rifting. The Precambrian basement structural mapping also reveals three primary trends: WNW-ESE, NE-SW, and NW-SE. Ductile deformation causes the dominant basement fabric to change, switching polarity as the rift propagated southward from NE-SW orientation to NW-SE and WNW-ESE orientations, and back to a NE-SW orientation. In general, the surficial structures follow this trend. In some areas, however, the more recent rifting cut across pre-existing basement structures, possibly due to rheological heterogeneities or selective strain partitioning. Nonetheless, pre-existing basement structures played a critical role in strain localization and fault propagation in Malawi. However

  6. Common host-derived chemicals increase catches of disease-transmitting mosquitoes and can improve early warning systems for Rift Valley fever virus.

    PubMed

    Tchouassi, David P; Sang, Rosemary; Sole, Catherine L; Bastos, Armanda D S; Teal, Peter E A; Borgemeister, Christian; Torto, Baldwyn

    2013-01-01

    Rift Valley fever (RVF), a mosquito-borne zoonosis, is a major public health and veterinary problem in sub-Saharan Africa. Surveillance to monitor mosquito populations during the inter-epidemic period (IEP) and viral activity in these vectors is critical to informing public health decisions for early warning and control of the disease. Using a combination of field bioassays, electrophysiological and chemical analyses we demonstrated that skin-derived aldehydes (heptanal, octanal, nonanal, decanal) common to RVF virus (RVFV) hosts including sheep, cow, donkey, goat and human serve as potent attractants for RVFV mosquito vectors. Furthermore, a blend formulated from the four aldehydes and combined with CO(2)-baited CDC trap without a light bulb doubled to tripled trap captures compared to control traps baited with CO(2) alone. Our results reveal that (a) because of the commonality of the host chemical signature required for attraction, the host-vector interaction appears to favor the mosquito vector allowing it to find and opportunistically feed on a wide range of mammalian hosts of the disease, and (b) the sensitivity, specificity and superiority of this trapping system offers the potential for its wider use in surveillance programs for RVFV mosquito vectors especially during the IEP. PMID:23326620

  7. Common Host-Derived Chemicals Increase Catches of Disease-Transmitting Mosquitoes and Can Improve Early Warning Systems for Rift Valley Fever Virus

    PubMed Central

    Tchouassi, David P.; Sang, Rosemary; Sole, Catherine L.; Bastos, Armanda D. S.; Teal, Peter E. A.; Borgemeister, Christian; Torto, Baldwyn

    2013-01-01

    Rift Valley fever (RVF), a mosquito-borne zoonosis, is a major public health and veterinary problem in sub-Saharan Africa. Surveillance to monitor mosquito populations during the inter-epidemic period (IEP) and viral activity in these vectors is critical to informing public health decisions for early warning and control of the disease. Using a combination of field bioassays, electrophysiological and chemical analyses we demonstrated that skin-derived aldehydes (heptanal, octanal, nonanal, decanal) common to RVF virus (RVFV) hosts including sheep, cow, donkey, goat and human serve as potent attractants for RVFV mosquito vectors. Furthermore, a blend formulated from the four aldehydes and combined with CO2-baited CDC trap without a light bulb doubled to tripled trap captures compared to control traps baited with CO2 alone. Our results reveal that (a) because of the commonality of the host chemical signature required for attraction, the host-vector interaction appears to favor the mosquito vector allowing it to find and opportunistically feed on a wide range of mammalian hosts of the disease, and (b) the sensitivity, specificity and superiority of this trapping system offers the potential for its wider use in surveillance programs for RVFV mosquito vectors especially during the IEP. PMID:23326620

  8. Evolution of bimodal volcanism in Gona, Ethiopia: geochemical associations and geodynamic implications for the East African Rift System

    NASA Astrophysics Data System (ADS)

    Ghosh, N.; Basu, A. R.; Gregory, R. T.; Richards, I.; Quade, J.; Ebinger, C. J.

    2013-12-01

    The East African rift system in Ethiopia formed in the Earth's youngest flood basalt province, and provides a natural laboratory to study the geochemistry of bimodal volcanism and its implications for plume-derived magmatism, mantle-lithosphere interactions and evolution of continental rifts from plate extension to rupture. Our geochemical studies of the ~6 Ma to recent eruptive products from Gona within the Afar Rift Zone are understood in context of crustal and upper mantle seismic imaging studies that provide constraints on spatial variations. Geochemical (major element, trace element and isotope) analyses of basalts and rhyolitic tuff from Gona indicate a common magma source for these bimodal volcanics. Light rare earth elements (LREEs) are enriched with a strong negative Eu anomaly and a positive Ce anomaly in some of the silicic volcanic rocks. We observe strong depletions in Sr and higher concentrations of Zr, Hf, Th, Nb and Ta. We hypothesize that the silicic rocks may be residues from a plume-derived enriched magma source, following partial melting with fractional crystallization of plagioclase at shallow magma chambers. The absence of Nb-Ta anomaly shows no crustal assimilation by magmas. Sr isotopes, in conjunction with Nd and Pb isotopes and a strong Ce anomaly could reflect interaction of the parent magma with a deep saline aquifer or brine. Nd isotopic ratios (ɛNd = 1.9 to 4.6) show similarity of the silicic tuffs and basalts in their isotopic compositions except for some ~6 Ma lavas showing MORB-like values (ɛNd = 5 to 8.7) that suggest involvement of the asthenosphere with the plume source. Except for one basaltic tuff, the whole rock oxygen isotopic ratios of the Gona basalts range from +5.8‰ to +7.9‰, higher than the δ values for typical MORB, +5.7. The oxygen isotopes in whole rocks from the rhyolite tuffs vary from 14.6‰ to 20.9‰ while their Sr isotope ratios <0.706, indicative of post-depositional low T alteration of these silicic

  9. Arabidopsis thaliana plants expressing Rift Valley fever virus antigens: Mice exhibit systemic immune responses as the result of oral administration of the transgenic plants.

    PubMed

    Kalbina, Irina; Lagerqvist, Nina; Moiane, Bélisario; Ahlm, Clas; Andersson, Sören; Strid, Åke; Falk, Kerstin I

    2016-11-01

    The zoonotic Rift Valley fever virus affects livestock and humans in Africa and on the Arabian Peninsula. The economic impact of this pathogen due to livestock losses, as well as its relevance to public health, underscores the importance of developing effective and easily distributed vaccines. Vaccines that can be delivered orally are of particular interest. Here, we report the expression in transformed plants (Arabidopsis thaliana) of Rift Valley fever virus antigens. The antigens used in this study were the N protein and a deletion mutant of the Gn glycoprotein. Transformed lines were analysed for specific mRNA and protein content by RT-PCR and Western blotting, respectively. Furthermore, the plant-expressed antigens were evaluated for their immunogenicity in mice fed the transgenic plants. After oral intake of fresh transgenic plant material, a proportion of the mice elicited specific IgG antibody responses, as compared to the control animals that were fed wild-type plants and of which none sero-converted. Thus, we show that transgenic plants can be readily used to express and produce Rift Valley Fever virus proteins, and that the plants are immunogenic when given orally to mice. These are promising findings and provide a basis for further studies on edible plant vaccines against the Rift Valley fever virus. PMID:27402440

  10. GLIMPCE Seismic reflection evidence of deep-crustal and upper-mantle intrusions and magmatic underplating associated with the Midcontinent Rift system of North America

    USGS Publications Warehouse

    Behrendt, John C.; Hutchinson, D.R.; Lee, M.; Thornber, C.R.; Trehu, A.; Cannon, W.; Green, A.

    1990-01-01

    Deep-crustal and Moho reflections, recorded on vertical incidence and wide angle ocean bottom Seismometer (OBS) data in the 1986 GLIMPCE (Great Lakes International Multidisciplinary Program on Crustal Evolution) experiment, provide evidence for magmatic underplating and intrusions within the lower crust and upper mantle contemporaneous with crustal extension in the Midcontinent Rift system at 1100 Ma. The rift fill consists of 20-30 km (7-10 s) of basalt flows, secondary syn-rift volcaniclastic and post-basalt sedimentary rock. Moho reflections recorded in Lake Superior over the Midcontinent Rift system have times from 14-18 s (about 46 km to as great as 58 km) in contrast to times of about 11-13 s (about 36-42 km crustal thickness) beneath the surrounding Great Lakes. The Seismically complex deep-crust to mantle transition zone (30-60 km) in north-central Lake Superior, which is 100 km wider than the rift half-graben, reflects the complicated products of tectonic and magmatic interaction of lower-crustal and mantle components during evolution or shutdown of the aborted Midcontinent Rift. In effect, mantle was changed into crust by lowering Seismic velocity (through intrusion of lower density magmatic rocks) and increasing Moho (about 8.1 km s-1 depth. ?? 1990.

  11. Rift Fault Geometry and Distribution in Layered Basaltic Rocks: A Comparison Between the Koa'e (Hawai'i) and Krafla (Iceland) Fault Systems

    NASA Astrophysics Data System (ADS)

    Bubeck, A.; Walker, R. J.; MacLeod, C. J.; Imber, J.

    2014-12-01

    Fault systems within incipient rifts that cut basaltic rocks comprise an array of fine-scale structures, including networks of fractures and small displacement (<15 m) faults that accommodate regional extension. These zones of damaged rock have mechanical and physical properties distinct from the surrounding intact host rock. As the rift system evolves this early-formed damage can be reactivated, and influence the distribution and growth of new fractures. Constraining the role of this inter-fault deformation in rift zone development is therefore important to characterizing the regional distribution of extensional strains, and the evolving physical and fluid flow properties of the host rock. Here we use high resolution field and remote mapping of the Koa'e insipient rift fault system on the south flank of Kilauea Volcano on Hawaii's Big Island, and the Krafla rift system, Iceland, to investigate the evolution of segmented rift fault systems in layered basalts, formed at low confining pressures. Extension in the Koa'e system is accommodated dominantly by interaction of zones of opening-mode fractures and areas of surface flexure rather than surface-breaching normal faults, which is attributed to gravitational collapse of Kilauea. Extension in the Krafla system is localised on segmented, large displacement (>20 m) normal faults, the development of which may have been controlled by dyke emplacement. Preliminary comparison between the Koa'e and Krafla systems suggests that strain rate and/or the effective stress path plays a primary role in controlling the geometry, characteristics, and distribution of major faults, and the scale and distribution of secondary (oblique) brittle structures within rift zones.

  12. Hydrogeological structure of a seafloor hydrothermal system related to backarc rifting in a continental margin setting

    NASA Astrophysics Data System (ADS)

    Ishibashi, Jun-ichiro

    2016-04-01

    Seafloor hydrothermal systems in the Okinawa Trough backarc basin are considered as related to backarc rifting in a continental margin setting. Since the seafloor is dominantly covered with felsic volcaniclastic material and/or terrigenous sediment, hydrothermal circulation is expected to be distributed within sediment layers of significantly high porosity. Deep drilling through an active hydrothermal field at the Iheya North Knoll in the middle Okinawa Trough during IODP Expedition 331 provided a unique opportunity to directly access the subseafloor. While sedimentation along the slopes of the knoll was dominated by volcanic clasts of tubular pumice, intense hydrothermal alteration was recognized in the vicinity of the hydrothermal center even at very shallow depths. Detailed mineralogical and geochemical studies of hydrothermal clay minerals in the altered sediment suggest that the prevalent alteration is attributed to laterally extensive fluid intrusion and occupation within the sediment layer. Onboard measurements of physical properties of the obtained sediment revealed drastic changes of the porosity caused by hydrothermal interactions. While unaltered sediment showed porosity higher than 70%, the porosity drastically decreased in the layer of anhydrite formation. On the other hand, the porosity remained high (~50%) in the layer of only chlorite alteration. Cap rock formation caused by anhydrite precipitation would inhibit the ascent of high temperature fluids to the seafloor. Moreover, an interbedded nature of pelagic mud units and matrix-free pumice deposits may prompt formation of a tightly layered architecture of aquifers and aquicludes. This sediment architecture should be highly conducive to lateral flow pseudo-parallel to the surface topography. Occurrence of sphalerite-rich sulfides was recognized as associated with detrital and altered sediment, suggesting mineralization related to subsurface chemical processes. Moreover, the vertical profiles of

  13. Miocene Onset of Extension in the Turkana Depression, Kenya: Implications for the Geodynamic Evolution of the East African Rift System

    NASA Astrophysics Data System (ADS)

    Boone, S.; Gleadow, A. J. W.; Kohn, B. P.; Seiler, C.

    2015-12-01

    The Paleogene-Recent East African Rift System (EARS) is the foremost modern example of continental rifting, providing much of our understanding of the early stages of continental breakup. The EARS traverses two regions of crustal uplift, the Ethiopian and East African Domes, separated by the Turkana Depression. This wide region of subdued topography coincides with the NW-SE trend of the Jurassic-Paleogene Anza Rift. Opinions on the fundamental geodynamic driver for EARS rifting are divided, however, principally between models involving migrating plume(s) and a single elongated 'superplume'. While competing models have similar topographic outcomes, they predict different morphotectonic evolutions for the Turkana Depression. Models inferring southward plume-migration imply that the plume must have passed below the Turkana Depression during the Paleogene, in order to have migrated to the East African Dome by the Miocene. The possible temporal denudational response to such plume activity is testable using low temperature thermochronology. We present apatite fission track (AFT) and (U-Th)/He (AHe), and zircon (U-Th)/He (ZHe) data from the Lapurr Range, an uplifted Precambrian basement block in northern Turkana. Low radiation damage ZHe results displaying an age range of ~70-210 Ma, and combined with stratigraphic evidence, suggest ~4-6 km of Jurassic-Early Cretaceous denudation, probably associated with early Anza Rift tectonism. AFT ages of ~9-15 Ma imply subsequent burial beneath no more than ~4 km of overburden, thus preserving the Jurassic-Cretaceous ZHe ages. Together with AFT results, AHe data (~3-19 Ma) support ~2-4 km of Miocene-Pliocene uplift of the Lapurr Range in the footwall of the E-dipping Lapurr normal fault. Miocene AFT and AHe ages are interpreted to reflect the initiation of the EARS in the Turkana Depression. If extension is associated with plume activity, then upwelling in the Turkana region is unlikely to have started prior to the Miocene, much

  14. Cenozoic rift formation in the northern Caribbean

    NASA Technical Reports Server (NTRS)

    Mann, P.; Burke, K.

    1984-01-01

    Rifts form in many different tectonic environments where the lithosphere is put into extension. An outline is provided of the distribution, orientation, and relative ages of 16 Cenozoic rifts along the northern edge of the Caribbean plate and it is suggested that these structures formed successively by localized extension as the Caribbean plate moved eastward past a continental promontory of North America. Evidence leading to this conclusion includes (1) recognition that the rifts become progressively younger westward; (2) a two-phase subsidence history in a rift exposed by upthrusting in Jamaica; (3) the absence of rifts east of Jamaica; and (4) the observation that removal of 1400 km of strike-slip displacement on the Cayman Trough fault system places the Paleogene rifts of Jamaica in an active area of extension south of Yucatan where the rifts of Honduras and Guatemala are forming today.

  15. Paleoseismology and Fault Interactions of the Pajarito Fault System, Rio Grande Rift, New Mexico

    NASA Astrophysics Data System (ADS)

    Gardner, J. N.; Lewis, C. J.; Lavine, A.; Reneau, S. L.; Schultz, E. S.

    2006-12-01

    The Pajarito fault system is the local active boundary fault of the Rio Grande rift in the vicinity of Los Alamos, New Mexico. Detailed geologic and geomorphic mapping, and displacement-length profiles, reveal a complex pattern of structural deformation that suggests interaction and connective growth among the principal faults in the system (Pajarito, Rendija Canyon, Guaje Mountain, and Santa Clara faults, totaling ~55 km in length). At the surface, the Pajarito fault is not a single shear surface but a complex zone of deformation with considerable lateral variation in structural style from south to north. In the area of detailed mapping, the Pajarito fault is a broad zone of distributed deformation: at the southwest corner of the area, structure is dominated by a large monocline, but small faults and monoclines span a breadth of about 2 km with about 125 m of displacement in the last 1.2 million years; at the west central part of the area, the Pajarito fault is expressed as mainly a large normal fault with smaller faults spread across about 1 km with about 80 m of displacement in the last 1.2 million years; and, in the northwestern part of the area, structure is again dominated by a large monocline with normal faulting in a zone about 1.5 km wide with about 65 m of displacement in the last 1.2 million years. These along-strike variations in the deformation of the Pajarito fault suggest that in most places the tip of the master fault does not break the surface; instead, most of what can be observed is subsidiary structure. The implication of the complex structure and styles of deformation in the fault is that it severely complicates paleoseismic exploration for hazard analyses because different subsidiary structures rupture in different seismic events; no individual structure can be identified with even a near- complete paleoseismic record. Additionally, surface rupture hazards must be associated with broad zones instead of individual faults. Seven paleoseismic

  16. Multiple mantle upwellings in the transition zone beneath the northern East-African Rift system from relative P-wave travel-time tomography

    NASA Astrophysics Data System (ADS)

    Civiero, Chiara; Hammond, James O. S.; Goes, Saskia; Fishwick, Stewart; Ahmed, Abdulhakim; Ayele, Atalay; Doubre, Cecile; Goitom, Berhe; Keir, Derek; Kendall, J.-Michael; Leroy, Sylvie; Ogubazghi, Ghebrebrhan; Rümpker, Georg; Stuart, Graham W.

    2015-09-01

    Mantle plumes and consequent plate extension have been invoked as the likely cause of East African Rift volcanism. However, the nature of mantle upwelling is debated, with proposed configurations ranging from a single broad plume connected to the large low-shear-velocity province beneath Southern Africa, the so-called African Superplume, to multiple lower-mantle sources along the rift. We present a new P-wave travel-time tomography model below the northern East-African, Red Sea, and Gulf of Aden rifts and surrounding areas. Data are from stations that span an area from Madagascar to Saudi Arabia. The aperture of the integrated data set allows us to image structures of ˜100 km length-scale down to depths of 700-800 km beneath the study region. Our images provide evidence of two clusters of low-velocity structures consisting of features with diameter of 100-200 km that extend through the transition zone, the first beneath Afar and a second just west of the Main Ethiopian Rift, a region with off-rift volcanism. Considering seismic sensitivity to temperature, we interpret these features as upwellings with excess temperatures of 100 ± 50 K. The scale of the upwellings is smaller than expected for lower mantle plume sources. This, together with the change in pattern of the low-velocity anomalies across the base of the transition zone, suggests that ponding or flow of deep-plume material below the transition zone may be spawning these upper mantle upwellings. This article was corrected on 28 SEP 2015. See the end of the full text for details.

  17. Volcano deformation in central Main Ethiopian Rift system (Aluto Volcano) inferred from continuous GPS and dynamic gravity observations

    NASA Astrophysics Data System (ADS)

    Birhanu, Yelebe; Biggs, Juliet; Gottsmann, Joachim; Lewi, Elias; Lloyd, Ryan; Bekele, Berhanu

    2016-04-01

    Silicic volcanic centres in the rift systems frequently experience unrest indicating long-term activity in the underlying magmatic system, but it is difficult to distinguish the contributions of hydrothermal fluids, magma or gasses. Aluto volcano which is located in the central MER system is situated between the Lakes Ziway and Langano in the north and south respectively. Continuous GPS installed from April 2013 to October 2015 shows subsidence initially, with the largest subsidence observed in the eastern part of the caldera (2 cm/yr). InSAR observations from TerraSAR-X show a radially-symmetric pattern of long-term subsidence. Dynamic gravity surveys carried out in October 2014 and 2015 showed that there is a net mass loss in the western and central part of the caldera and mass gain in the eastern and southern part of the caldera, with a sharp gradient between the two. This complex spatial pattern of gravity change is significantly different to the simple pattern of deformation indicating multiple sources of pressure and mass change exist within the caldera. We explain the ratio of gravity to height change (dg/dh) throughout the volcano by considering cooling and crystallisation of magma body, draining and precipitation of hydrothermal fluids and changes in the water table and lake levels. Keywords: volcano deformation, dynamic gravity, continental rift

  18. Crustal Structure of and near the North American Mid-continent Rift System from Receiver Function Studies

    NASA Astrophysics Data System (ADS)

    Zhang, H.; van der Lee, S.; Wolin, E.; Bollmann, T. A.; Revenaugh, J.; Aleqabi, G. I.; Wiens, D. A.; Frederiksen, A. W.; Darbyshire, F. A.

    2014-12-01

    The more than 1000-km-long main branch of the mid-continent rift system (MRS) near Lake Superior and the Minnesota-Wisconsin border nearly took North America apart, but ceased rifting soon after it began. Thermal and magmatic events and subsidence- related sedimentary processes significantly changed the structure of the upper crust across and along the MRS. To map the depth extent and lateral changes in deep lithospheric structure related to the MRS, we estimated and studied receiver functions (RFs) from 82 SPREE (Superior Province Rifting EarthScope Experiment) broadband seismic stations and seven EarthScope Transportable Array stations. We inverted the RFs for depths of seismic-velocity discontinuities and shear-velocity structure of the crust. The RFs for each station are derived from the deconvolution of the radial component with the vertical component in the time domain (Ammon et al., 1991). Using a relatively high corner frequency in the deconvolution passband helps us resolve multiple layers within the crust. The most prominent feature of the RFs is the P-to-S wave converted at the Moho (Fig. 1), which reflects the contrast in rock properties between the lower crust and upper mantle. This Moho-generated P-to-S converted wave is very clear in RFs for stations outside of the MRS. Inside the MRS, the RFs are more ambiguous and suggestive of a basal crustal layer with shear velocities in between typical lower crust and upper mantle values. There is more variation among the RFs for stations within the MRS than among stations outside of the MRS.

  19. Stable isotope-based Plio-Pleistocene ecosystem reconstruction of some of the earliest hominid fossil sites in the East African Rift System (Chiwondo Beds, N Malawi)

    NASA Astrophysics Data System (ADS)

    Lüdecke, Tina; Thiemeyer, Heinrich; Schrenk, Friedemann; Mulch, Andreas

    2014-05-01

    The isotope geochemistry of pedogenic carbonate and fossil herbivore enamel is a powerful tool to reconstruct paleoenvironmental conditions in particular when climate change plays a key role in the evolution of ecosystems. Here, we present the first Plio-Pleistocene long-term carbon (δ13C), oxygen (δ18O) and clumped isotope (Δ47) records from pedogenic carbonate and herbivore teeth in the Malawi Rift. These data represent an important southern hemisphere record in the East African Rift System (EARS), a key region for reconstructing vegetation patterns in today's Zambezian Savanna and correlation with data on the evolution and migration of early hominids across the Inter-Tropical Convergence Zone. As our study site is situated between the well-known hominid-bearing sites of eastern and southern Africa in the Somali-Masai Endemic Zone and Highveld Grassland it fills an important geographical gap for early hominid research. 5.0 to 0.6 Ma fluviatile and lacustrine deposits of the Chiwondo Beds (NE shore of Lake Malawi) comprise abundant pedogenic carbonate and remains of a diverse fauna dominated by large terrestrial mammals. These sediments are also home to two hominid fossil remains, a mandible of Homo rudolfensis and a maxillary fragment of Paranthropus boisei, both dated around 2.4 Ma. The Chiwondo Beds therefore document early co-existence of these two species. We evaluate δ13C data from fossil enamel of different suid, bovid, and equid species and contrast these with δ13C and δ18O values of pedogenic carbonate. We complement the latter with clumped isotope soil temperature data. Results of almost 800 pedogenic carbonate samples from over 20 sections consistently average δ13C = -8.5 ‰ over the past 5 Ma with no significant short-term δ13C excursions or long-term trends. The data from molar tooth enamel of nine individual suids of the genera Metridiochoerus, Notochoerus and Nyanzachoerus support these findings with average δ13C = -10.0 ‰. The absence

  20. RIFT VALLEY FEVER VIRUS: AN EMERGING THREAT TO WILDLIFE, LIVESTOCK, AND HUMANS IN THE U.S. - A REVIEW OF ISSUES AND CONCERNS, AND A GIS EARLY WARNING SYSTEM FOR RVF VECTORS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) virus is a mosquito-borne zoonotic hemorrhagic disease that causes 100% abortions in ungulates such as cattle, sheep, and goats, and is often fatal to young animals. Though currently confined mainly to Africa this disease could be introduced into the U.S. and spread via mosq...

  1. A REVIEW OF ISSUES AND CONCERNS OF RIFT VALLEY FEVER VIRUS, A POTENTIAL EMERGING THREAT TO LIVESTOCK, WILDLIFE, AND HUMANS IN THE U.S., AND A GIS EARLY WARNING SYSTEM FOR RVF VECTORS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) virus is a mosquito-borne zoonotic hemorrhagic disease that causes 100% abortions in ungulates such as cattle, sheep, and goats, and is often fatal to young animals. Though currently confined mainly to Africa this disease could be introduced into the U.S. and spread via mosq...

  2. Continental Rifts

    NASA Astrophysics Data System (ADS)

    Rosendahl, B. R.

    Continental Rifts, edited by A. M. Quennell, is a new member of the Benchmark Papers in Geology Series, edited in toto by R. W. Fairbridge. In this series the individual volume editors peruse the literature on a given topic, select a few dozen papers of ostensibly benchmark quality, and then reorder them in some sensible fashion. Some of the original papers are republished intact, but many are chopped into “McNuggets™” of information. Depending upon the volume editor, the chopping process can range from a butchering job to careful and prudent pruning. The collecting, sifting, and reorganizing tasks are, of course, equally editor-sensitive. The end product of this series is something akin to a set of Reader's Digest of Geology.

  3. Tectonics of the West Antarctic rift system: new light on the history and dynamics of distributed intracontinental extension

    USGS Publications Warehouse

    Siddoway, C.S.

    2007-01-01

    The West Antarctic rift system (WARS) is the product of multiple stages of intracontinental deformation from Jurassic to Present. The Cretaceous rifting phase accomplished >100 percent extension across the Ross Sea and central West Antarctica, and is widely perceived as a product of pure shear extension orthogonal to the Transantarctic Mountains that led to breakup and opening of the Southern Ocean between West Antarctica and New Zealand. New structural, petrological, and geochronological data from Marie Byrd Land reveal aspects of the kinematics, thermal history, and chronology of the Cretaceous intracontinental extension phase that cannot be readily explained by a single progressive event. Elevated temperatures in "Lachlan-type" crust caused extensive crustal melting and mid-crustal flow within a dextral transcurrent strain environment, leading to rapid extension and locally to exhumation and rapid cooling of a migmatite dome and detachment footwall structures. Peak metamorphism and onset of crustal flow that brought about WARS extension between 105 Ma and 90 Ma is kinematically, temporally, and spatially linked to the active convergent margin system of East Gondwana. West Antarctica-New Zealand breakup is distinguished as a separate event at 83-70 Ma, from the standpoint of kinematics and thermal evolution

  4. Parga Chasma: Coronae and Rifting on Venus

    NASA Technical Reports Server (NTRS)

    Smrekar, S. E.; Stofan, E. R.; Buck, W. R.; Martin, P.

    2005-01-01

    The majority of coronae (quasicircular volcano-tectonic features) are found along rifts or fracture belts, and the majority of rifts have coronae [e.g. 1,2]. However, the relationship between coronae and rifts remains unclear [3-6]. There is evidence that coronae can form before, after, or synchronously with rifts [3,4]. The extensional fractures in the rift zones have been proposed to be a result of broad scale upwelling and traction on the lower lithosphere [7]. However, not all rift systems have a significant positive geoid anomaly, as would be expected for an upwelling site [8]. This could be explained if the rifts lacking anomalies are no longer active. Coronae are generally accepted to be sites of local upwelling [e.g. 1], but the observed rifting is frequently not radial to the coronae and extends well beyond the coronae into the surrounding plains. Thus the question remains as to whether the rifts represent regional extension, perhaps driven by mantle tractions, or if the coronae themselves create local thinning and extension of the lithosphere. In the first case, a regional extension model should be consistent with the observed characteristics of the rifts. In the latter case, a model of lithospheric loading and fracturing would be more appropriate. A good analogy may be the propagation of oceanic intraplate volcanoes [9].

  5. Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic West Antarctic rift system and a speculation on possible climate forcing

    USGS Publications Warehouse

    Behrendt, John C.; Cooper, A.

    1991-01-01

    The Cenozoic West Antarctic rift system, characterized by Cenozoic bimodal alkalic volcanic rocks, extends over a largely ice-covered area, from the Ross Sea nearly to the Bellingshausen Sea. Various lines of evidence lead to the following interpretation: the transantarctic Mountains part of the rift shoulder (and probably the entire shoulder) has been rising since about 60 Ma, at episodic rates of ~1 km/m.y., most recently since mid-Pliocene Time, rather than continuously at the mean rate of 100 m/m.y. Uplift rates vary along the scarp, which is cut by transverse faults. It is speculated that this uplift may have climatically forced the advance of the Antarctic ice sheet since the most recent warm period. A possible synergistic relation is suggested between episodic tectonism, mountain uplift, and volcanism in the Cenozoic West Antarctic rift system and waxing and waning of the Antarctic ice sheet beginning about earliest Oligocene time. -from Authors

  6. Magmatism in rifting and basin formation

    NASA Astrophysics Data System (ADS)

    Thybo, H.

    2008-12-01

    Whether heating and magmatism cause rifting or rifting processes cause magmatic activity is highly debated. The stretching factor in rift zones can be estimated as the relation between the initial and the final crustal thickness provided that the magmatic addition to the crust is insignificant. Recent research demonstrates substantial magmatic intrusion into the crust in the form of sill like structures in the lowest crust in the presently active Kenya and Baikal rift zones and the DonBas palaeo-rift zone in Ukraine. This result may be surprising as the Kenya Rift is associated with large amounts of volcanic products, whereas the Baikal Rift shows very little volcanism. Identification of large amounts of magmatic intrusion into the crust has strong implications for estimation of stretching factor, which in the case of Baikal Rift Zone is around 1.7 but direct estimation gives a value of 1.3-1.4 if the magmatic addition is not taken into account. This may indicate that much more stretching has taken place on rift systems than hitherto believed. Wide sedimentary basins may form around aborted rifts due to loading of the lithosphere by sedimentary and volcanic in-fill of the rift. This type of subsidence will create wide basins without faulting. The Norwegian- Danish basin in the North Sea area also has subsided gradually during the Triassic without faulting, but only few rift structures have been identified below the Triassic sequences. We have identified several mafic intrusions in the form of large batholiths, typically more than 100 km long, 20-40 km wide and 20 km thick. The associated heating would have lifted the surface by about 2 km, which may have been eroded before cooling. The subsequent contraction due to solidification and cooling would create subsidence in a geometry similar to basins that developed by loading. These new aspects of magmatism will be discussed with regard to rifting and basin formation.

  7. Rift Valley fever: A neglected zoonotic disease?

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a serious viral disease of animals and humans in Africa and the Middle East that is transmitted by mosquitoes. First isolated in Kenya during an outbreak in 1930, subsequent outbreaks have had a significant impact on animal and human health, as well as national economies. ...

  8. East Antarctic rifting triggers uplift of the Gamburtsev Mountains

    USGS Publications Warehouse

    Ferraccioli, F.; Finn, Carol A.; Jordan, Tom A.; Bell, Robin E.; Anderson, Lester M.; Damaske, Detlef

    2011-01-01

    The Gamburtsev Subglacial Mountains are the least understood tectonic feature on Earth, because they are completely hidden beneath the East Antarctic Ice Sheet. Their high elevation and youthful Alpine topography, combined with their location on the East Antarctic craton, creates a paradox that has puzzled researchers since the mountains were discovered in 1958. The preservation of Alpine topography in the Gamburtsevs may reflect extremely low long-term erosion rates beneath the ice sheet, but the mountains’ origin remains problematic. Here we present the first comprehensive view of the crustal architecture and uplift mechanisms for the Gamburtsevs, derived from radar, gravity and magnetic data. The geophysical data define a 2,500-km-long rift system in East Antarctica surrounding the Gamburtsevs, and a thick crustal root beneath the range. We propose that the root formed during the Proterozoic assembly of interior East Antarctica (possibly about 1 Gyr ago), was preserved as in some old orogens and was rejuvenated during much later Permian (roughly 250 Myr ago) and Cretaceous (roughly 100 Myr ago) rifting. Much like East Africa, the interior of East Antarctica is a mosaic of Precambrian provinces affected by rifting processes. Our models show that the combination of rift-flank uplift, root buoyancy and the isostatic response to fluvial and glacial erosion explains the high elevation and relief of the Gamburtsevs. The evolution of the Gamburtsevs demonstrates that rifting and preserved orogenic roots can produce broad regions of high topography in continental interiors without significantly modifying the underlying Precambrian lithosphere.

  9. A Review of New and Anticipated High-Resolution Paleoclimate Records from the East African Rift System and Their Implications for Hominin Evolution and Demography

    NASA Astrophysics Data System (ADS)

    Cohen, A. S.

    2014-12-01

    Our understanding of Late Tertiary/Quaternary climate and environmental history in East Africa has, to date, largely been based on outcrop and marine drill core records. Although these records have proven extremely valuable both in reconstructing environmental change and placing human evolution in an environmental context, their quality is limited by resolution, continuity, uncertainties about superposition and outcrop weathering. To address this problem, long drill core records from extant ancient lakes and lake beds are being collected by several research groups. Long cores (up to 100s of m.) from basin depocenters in both the western and eastern rifts are now available spanning nearly the entire latitudinal range of the East Africa Rift. This network of core records, especially when coupled with outcrop data, is providing an opportunity to compare the nature of important global climate transitions (especially glacial/interglacial events and precessional cycles) across the continent, thereby documenting regional heterogeneity in African climate history. Understanding this heterogeneity is critical for realistically evaluating competing hypotheses of environmental forcing of human evolution, and especially ideas about the dispersal of anatomically modern humans out of Africa in the early Late Pleistocene. In particular, understanding the hydrological and paleoecological history of biogeographic corridors linking eastern Africa, the Nile River Valley and the Levant is likely to be vastly improved through comparative analysis of these new drill cores over the next few years. Because we do not a priori know the primary forcing factors affecting this environmental history, it will essential to develop the best possible age models, employing multiple and novel geochronometric tools to make these comparisons.

  10. Inter-Rifting and Inter-Seismic Strain Accumulation in a Propagating Ridge System: A Geodetic Study from South Iceland

    NASA Astrophysics Data System (ADS)

    Travis, M. E.; La Femina, P. C.; Geirsson, H.

    2012-12-01

    The Mid-Atlantic Ridge, a slow spreading (~19 mm/yr) mid-ocean ridge boundary between the North American and Eurasian plates, is exposed subaerially in Iceland as the result of ridge-hotspot interaction. Plate spreading in Iceland is accommodated along neovolcanic zones comprised of central volcanoes and their fissure swarms. In south Iceland plate motion is partitioned between the Western Volcanic Zone (WVZ) and Eastern Volcanic Zone (EVZ). The EVZ is propagating to the southwest, while the WVZ is dying out from the northeast. Plate motion across both systems has been accommodated by repeated rifting events and fissure eruptions. In this study we investigate whether the WVZ is active and accumulating strain, and how strain is partitioned between the WVZ and EVZ. We also test how strain is accumulating along fissure swarms within the EVZ (i.e. is strain accumulation localized to one fissure swarm, or are multiple systems active?). We use GPS data and elastic block models run using the program DEFNODE to investigate these issues. GPS data are processed using the GIPSY-OASIS II software, and have been truncated to the 2000.5-2011 time period to avoid co-seismic displacement from the two June 2000 South Iceland Seismic Zone earthquakes. We also truncate the time series for sites within 20 km of Eyjafjallajökull to the beginning of 2010 to eliminate deformation associated with the March 2010 eruption of that volcano. We correct for co-seismic displacement from the two May 2008 SISZ earthquakes, inflation at Hekla volcano and the horizontal component of glacial isostatic rebound (GIA). Our best-fit model for inter-rifting and inter-seismic elastic strain accumulation suggests 80-90% of spreading is accommodated in the EVZ with the other 10-20% accommodated by the WVZ. The best-fit location of the EVZ is between Veidivotn and Lakigigar in an area of no Holocene volcanic activity. We suggest the WVZ is only active at Hengill and its associated fissure swarm. Geologic and

  11. Constraining the thermal and erosional evolution of the Rwenzori Mtns, Albertine Rift, by detrital thermochronology

    NASA Astrophysics Data System (ADS)

    Bauer, F. U.; Roller, S.; Grobe, R. W.; Glasmacher, U. A.; Hinderer, M.; Ring, U.; Mambo, V. S.

    2012-04-01

    In East Africa, the feedback between tectonic uplift, erosional denudation and associated possible climate changes is being studied by a multidisciplinary research group, 'RiftLink'. The group's focus is the Albertine Rift of the East African Rift System, and therein rising Rwenzori Mountains that stretch along the border of Uganda and Eastern D.R. Congo. Data from low-temperature thermochronology analysis of hardrocks comprising apatite fission-track (AFT), zircon and apatite (U-Th-Sm)/He dating (ZHe, AHe) and thermal modelling point to a prolonged cooling history with differentiated exhumation in Neogene times. The final rock uplift in Plio- to Pleistocene times, thereby, was very fast that the erosion could not keep pace [1]. In order to narrow the final exhumation stage detrital thermochronology has proven to be very useful. Therefore, sedimentary successions of the Albertine Rift valley in western Uganda and Eastern D.R. Congo were sampled to perform AFT, ZHe and AHe dating of detrital sediments. In the frame of the presentation we will present first results from the detrital thermochronology study of the Albertine Rift and will discuss its implications for the landscape evolution of this area.

  12. A new tectono-sedimentary model for Cretaceous mixed nonmarine-marine oil-prone Komombo Rift, South Egypt

    NASA Astrophysics Data System (ADS)

    Selim, S. S.

    2016-07-01

    The Komombo Basin is a recently discovered mixed nonmarine-marine, petroliferous basin of Cretaceous age in South Egypt. It is an asymmetrical half graben, synchronous with the Neothys opening and filled with up to 4 km of continental to open marine strata ranging from Early to Late Cretaceous. Despite its great relevance, no detailed sedimentological study concerning this basin has been carried out to date. Here, we present an integrated approach to the borehole and core data, as well as unique outcrop sections to construct a new detailed sedimentological interpretation on depositional systems, controls on basin evolution, basin configuration and regional tectonic setting. Seven depositional systems were recognized: (I) a fluvial fan system, (II) a braidplain system, (III) a siliciclastic lacustrine system, (IV) a lacustrine/lagoonal system, (V) a fluvial-estuarine system, (VI) a tidally affected delta, and (VII) an open marine system. The Komombo Basin evolution can be compartmentalized into three main rifting phases: the Berriasian-Early Barremian, Late Barremian, and Aptian-Albian. The first and third rifting phases are comparable with the rifting phases reported for several basins in North and Central Africa. The second rifting phase represents a transitional event between the other two phases. The first three depositional systems consist mainly of continental siliciclastics and are dominant in the Berriasian-Early Barremian and Late Barremian rifting phases. The lacustrine/lagoon and fluvial-estuarine systems correspond to the Aptian-Albian rifting phase, while the Campanian-Maastrichtian open-shelf deposits represents the post-rift stage.

  13. Using remote sensing, ecological niche modeling, and Geographic Information Systems for Rift Valley fever risk assessment in the United States

    NASA Astrophysics Data System (ADS)

    Tedrow, Christine Atkins

    The primary goal in this study was to explore remote sensing, ecological niche modeling, and Geographic Information Systems (GIS) as aids in predicting candidate Rift Valley fever (RVF) competent vector abundance and distribution in Virginia, and as means of estimating where risk of establishment in mosquitoes and risk of transmission to human populations would be greatest in Virginia. A second goal in this study was to determine whether the remotely-sensed Normalized Difference Vegetation Index (NDVI) can be used as a proxy variable of local conditions for the development of mosquitoes to predict mosquito species distribution and abundance in Virginia. As part of this study, a mosquito surveillance database was compiled to archive the historical patterns of mosquito species abundance in Virginia. In addition, linkages between mosquito density and local environmental and climatic patterns were spatially and temporally examined. The present study affirms the potential role of remote sensing imagery for species distribution prediction, and it demonstrates that ecological niche modeling is a valuable predictive tool to analyze the distributions of populations. The MaxEnt ecological niche modeling program was used to model predicted ranges for potential RVF competent vectors in Virginia. The MaxEnt model was shown to be robust, and the candidate RVF competent vector predicted distribution map is presented. The Normalized Difference Vegetation Index (NDVI) was found to be the most useful environmental-climatic variable to predict mosquito species distribution and abundance in Virginia. However, these results indicate that a more robust prediction is obtained by including other environmental-climatic factors correlated to mosquito densities (e.g., temperature, precipitation, elevation) with NDVI. The present study demonstrates that remote sensing and GIS can be used with ecological niche and risk modeling methods to estimate risk of virus establishment in mosquitoes and

  14. Upper mantle seismic anisotropy beneath the West Antarctic Rift System and surrounding region from shear wave splitting analysis

    NASA Astrophysics Data System (ADS)

    Accardo, Natalie J.; Wiens, Douglas A.; Hernandez, Stephen; Aster, Richard C.; Nyblade, Andrew; Huerta, Audrey; Anandakrishnan, Sridhar; Wilson, Terry; Heeszel, David S.; Dalziel, Ian W. D.

    2014-07-01

    We constrain azimuthal anisotropy in the West Antarctic upper mantle using shear wave splitting parameters obtained from teleseismic SKS, SKKS and PKS phases recorded at 37 broad-band seismometres deployed by the POLENET/ANET project. We use an eigenvalue technique to linearize the rotated and shifted shear wave horizontal particle motions and determine the fast direction and delay time for each arrival. High-quality measurements are stacked to determine the best fitting splitting parameters for each station. Overall, fast anisotropic directions are oriented at large angles to the direction of Antarctic absolute plate motion in both hotspot and no-net-rotation frameworks, showing that the anisotropy does not result from shear due to plate motion over the mantle. Further, the West Antarctic directions are substantially different from those of East Antarctica, indicating that anisotropy across the continent reflects multiple mantle regimes. We suggest that the observed anisotropy along the central Transantarctic Mountains (TAM) and adjacent West Antarctic Rift System (WARS), one of the largest zones of extended continental crust on Earth, results from asthenospheric mantle strain associated with the final pulse of western WARS extension in the late Miocene. Strong and consistent anisotropy throughout the WARS indicate fast axes subparallel to the inferred extension direction, a result unlike reports from the East African rift system and rifts within the Basin and Range, which show much greater variation. We contend that ductile shearing rather than magmatic intrusion may have been the controlling mechanism for accumulation and retention of such coherent, widespread anisotropic fabric. Splitting beneath the Marie Byrd Land Dome (MBL) is weaker than that observed elsewhere within the WARS, but shows a consistent fast direction, possibly representative of anisotropy that has been `frozen-in' to remnant thicker lithosphere. Fast directions observed inland from the

  15. Coulomb stress evolution in the Shanxi rift system, North China, since 1303 associated with coseismic, post-seismic and interseismic deformation

    NASA Astrophysics Data System (ADS)

    Li, Bin; Sørensen, Mathilde Bøttger; Atakan, Kuvvet

    2015-12-01

    The Shanxi rift system is one of the most active intraplate tectonic zones in the North China Block, resulting in devastating seismicity. Since 1303, the rift has experienced fifteen Ms ≥ 6.5 earthquakes. Aiming at a better understanding of Coulomb stress evolution and its relationship with the seismicity in the rift system, we investigated the Coulomb stress changes due to coseismic slip and post-seismic relaxation processes following strong earthquakes as well as the interseismic tectonic loading since the 1303 Hongdong Ms = 8.0 earthquake. Our calculation applies a specified regional medium model, takes the gravity effect into account and uses the fault geometry of the next event as the receiver fault in a given calculation. Our results show that nine out of 12 Ms ≥ 6.5 earthquakes since the 1303 Hongdong earthquake and more than 82 per cent of small-medium instrumental events after the 1989 Datong-Yanggao Ms = 6.1 earthquake fall into the total stress increased areas. Our results also reveal the different roles of the coseismic, post-seismic and interseismic Coulomb stress changes in the earthquake triggering process in the Shanxi rift system. In a short period after a strong event, the stress field changes are dominated by coseismic Coulomb stress due to sudden slip of the ruptured fault, while in the long term, the stress field is mainly dominated by the accumulation of interseismic tectonic loading. Post-seismic stress changes play an important role by further modifying the distribution of stress and therefore cannot be ignored. Based on the current stress status in the Shanxi rift system, the Linfen basin, southern and northern Taiyuan basin, Xinding basin and the north part of the rift system are identified as the most likely locations of large events in the future. The results of this study can provide important clues for the further understanding of seismic hazard in the Shanxi rift system and thus help guiding earthquake risk mitigation efforts in

  16. Mercury isotopic composition of hydrothermal systems in the Yellowstone Plateau volcanic field and Guaymas Basin sea-floor rift

    USGS Publications Warehouse

    Sherman, L.S.; Blum, J.D.; Nordstrom, D.K.; McCleskey, R.B.; Barkay, T.; Vetriani, C.

    2009-01-01

    To characterize mercury (Hg) isotopes and isotopic fractionation in hydrothermal systems we analyzed fluid and precipitate samples from hot springs in the Yellowstone Plateau volcanic field and vent chimney samples from the Guaymas Basin sea-floor rift. These samples provide an initial indication of the variability in Hg isotopic composition among marine and continental hydrothermal systems that are controlled predominantly by mantle-derived magmas. Fluid samples from Ojo Caliente hot spring in Yellowstone range in δ202Hg from - 1.02‰ to 0.58‰ (± 0.11‰, 2SD) and solid precipitate samples from Guaymas Basin range in δ202Hg from - 0.37‰ to - 0.01‰ (± 0.14‰, 2SD). Fluid samples from Ojo Caliente display mass-dependent fractionation (MDF) of Hg from the vent (δ202Hg = 0.10‰ ± 0.11‰, 2SD) to the end of the outflow channel (&delta202Hg = 0.58‰ ± 0.11‰, 2SD) in conjunction with a decrease in Hg concentration from 46.6pg/g to 20.0pg/g. Although a small amount of Hg is lost from the fluids due to co-precipitation with siliceous sinter, we infer that the majority of the observed MDF and Hg loss from waters in Ojo Caliente is due to volatilization of Hg0(aq) to Hg0(g) and the preferential loss of Hg with a lower δ202Hg value to the atmosphere. A small amount of mass-independent fractionation (MIF) was observed in all samples from Ojo Caliente (Δ199Hg = 0.13‰ ±1 0.06‰, 2SD) but no significant MIF was measured in the sea-floor rift samples from Guaymas Basin. This study demonstrates that several different hydrothermal processes fractionate Hg isotopes and that Hg isotopes may be used to better understand these processes.

  17. STS-57 Earth observation of Lake Victoria, Africa

    NASA Technical Reports Server (NTRS)

    1993-01-01

    STS-57 Earth observation taken aboard Endeavour, Orbiter Vehicle (OV) 105, is of Africa's Lake Victoria, which sits in the middle of the East African Rift Valley System.Lake Victoria is a major resource in eastern Africa, especially to the countries bordering the lake -- Uganda, Kenya and Tanzania. Typical summer indicators in equatorial Africa -- puffy clouds over land mass and clear skies over the lakes -- are in the view. Lake Albert in the western section of the Rift Valley and Lake Turkana in the eastern section can be seen to the west and east of Lake Victoria, respectively. Most of the other features on the right are obscured by clouds. NASA scientists studying the STS-57 Earth photography point out that the wide perspective of this scene gives a sense of the three-dimensional profile of the whole rift system. The scientists cite the way in which the component valleys of the rift system ramp up to Lake Victoria on either side.

  18. A new vertebrate fauna from the Cretaceous Red Sandstone Group, Rukwa Rift Basin, Southwestern Tanzania

    NASA Astrophysics Data System (ADS)

    O'Connor, Patrick M.; Gottfried, Michael D.; Stevens, Nancy J.; Roberts, Eric M.; Ngasala, Sifa; Kapilima, Saidi; Chami, Remigius

    2006-03-01

    The Rukwa Rift Basin Project was initiated to conduct exploratory field paleontology in poorly sampled terrestrial strata in southern and western Tanzania. Here we report the discovery of a series of new fossiliferous localities from Red Sandstone Group deposits in the Rukwa Rift Basin. These localities contain a diverse Cretaceous terrestrial/freshwater vertebrate fauna that consists of members of several major clades, including fishes, turtles, crocodyliforms, dinosaurs and mammals. Expeditions conducted in the austral summers of 2002-05 have identified numerous fossil-bearing localities, with specimens ranging from isolated elements to semi-articulated sauropod and theropod dinosaurs. Notable among the finds are the most complete mammal specimen recovered from the Cretaceous of continental Africa, megaloolithid dinosaur eggshell, and both theropod and sauropod dinosaurs. Given the scarcity of Cretaceous terrestrial faunas from sub-equatorial Africa, this portion of the East Africa Rift System holds great promise for providing new paleontological data that will contribute to testing and refining a number of biogeographic hypotheses that have been advanced to explain Gondwanan vertebrate distributions in the latter half of the Mesozoic.

  19. Quantitative challenges to our understanding of the tectonostratigraphic evolution of rift basin systems

    NASA Astrophysics Data System (ADS)

    Olsen, P. E.; Kent, D. V.

    2012-12-01

    Pervasive orbitally-paced lake level cycles combined with magnetic polarity stratigraphy in central Pangean early Mesozoic rift basins provide a thus far unique and very large-scale quantitative basis for observing patterns of basin fill and comparisons with other basins. The 32 Myr accumulation rate history of the Newark basin is segmented into intervals lasting millions of years with virtually no change in the long-term accumulation rate (at the 400-kyr-scale), and the transitions between segments are abrupt and apparently basin-wide. This is startling, because the basin geometry was, and is, a half graben - triangular in cross section and dish-shaped in along-strike section. The long periods of time with virtually no change is challenging given a simple model of basin growth (1), suggesting some kind of compensation in sediment input for the increasing surface of the area of the basin through time. Perhaps even more challenging are observations based on magnetic polarity stratigraphy and the cyclicity, that basins distributed over a huge area of central Pangea (~700,000 km2) show parallel and correlative quantitative changes in accumulation rate with those of the Newark basin. The synchronous changes in the accumulation rate in these basins suggests a very large-scale linkage, the only plausible mechanism for which would seem to be at the plate-tectonic scale, perhaps involving extension rates. Together, we can speculate that some kind of balance between extension rates, basin accommodation space and perhaps regional drainage basin size might have been in operation The most dramatic accumulation rate change in the basins' histories occurred close to, and perhaps causally related to, the Triassic-Jurassic boundary and end-Triassic extinction. The Newark basin, for example exhibits a 4-to-5-fold increase in accumulation rate during the emplacement of the brief (<1 Myr) and aerially massive Central Atlantic Magmatic Province (CAMP) beginning at 201.5 Ma, the only

  20. Intracontinental rifting and inversion: Missour basin and Atlas Mountains, Morocco

    SciTech Connect

    Beauchamp, W.; Barazangi, M.; Demnati, A.; Alji, M.E.

    1996-09-01

    The intracontinental High and Middle Atlas mountain belts in Morocco intersect to form the southern and western margins of the Missour basin, an intermontane basin formed as a result of the uplift and inversion of the Mesozoic Atlas paleorifts. These rifts were areas where the crust was greatly attenuated and more subject to deformation in response to nearby plate boundary tectonics. Data from observations based on seismic reflection profiles and wells over the Missour basin for hydrocarbon exploration and field mapping were used to understand the basin evolution, structural styles, and inversion timing of the nearby Atlas Mountains. Hercynian and Mesozoic normal faults were reactivated into high-angle reverse and thrust faults in the Mesozoic during the Jurassic, Early Cretaceous (early Alpine phase), and the Paleogene (late Alpine phase). The reactivation of synrift normal faults of the paleo-Atlas rifts inverted previous half grabens into anticlinal structures, with the axis of the half graben centered below the axis of the inverted anticline. The resulting inverted fold geometries are controlled by the geometries of the extensional planar or listric faults. The Atlas paleorift system is one of the largest rift systems in Africa. Little hydrocarbon exploration has occurred within the Atlas Mountains and the margins of the paleo-Atlas rift system. Inversion of synrift structures can lead to both the destruction and preservation of synrift traps and the creation of new hydrocarbon traps. The study of the effects of inversion in the Missour basin may lead to the discovery of footwall subthrust hydrocarbon traps in the Mesozoic sedimentary sequence of the Atlas Mountains.

  1. Paleoseismologic studies of the Pajarito fault system, western margin of the Rio Grande rift near Los Alamos, NM

    SciTech Connect

    Kelson, K.I. ); Hemphill-Haley, M.A.; Wong, I.G. ); Gardner, J.N.; Reneau, S.L. )

    1993-04-01

    As in much of the Basin and Range province, low levels of historical seismicity in the Rio Grande rift (RGR) are inconsistent with abundant geologic evidence for large-magnitude, late Pleistocene and Holocene earthquakes. Recent trenching and surficial mapping along the 40-km-long, north-trending Pajarito fault system (PFS) near Los Alamos provide evidence for multiple surface-rupture events during the late Pleistocene and Holocene. Near Los Alamos, the Pajarito fault (PAF) exhibits an east-facing scarp up to 120 m high that has had at least four surface-rupture events in the past few hundred thousand years. Four trenches across the base of the highest, easternmost fault scarp show that the most-recent rupture occurred prior to about 9 ka, and possible prior to deposition of the 100- to 150-ka El Cajete Pumice. The long-term (post-1.1 Ma) slip rate on the PAF is about 0.1 mm/yr. The down-to-the-west Rendija Canyon (RCF) and Guaje Mountain (GMF) faults both have had at least two surface ruptures since the middle Pleistocene, including most-recent events at about 7.4 ka along the RCF and about 4 to 6 ka along the GMF. Slickensides and other indirect evidence suggest right-oblique normal slip on the RCF and GMF. Long-term (post-1.1 Ma) slip rates on these two faults are approximately an order of magnitude less than that on the PAF. Based on the observed spatial and temporal variations in activity, the subparallel PAF, RCF, and GMF apparently act as independent seismic sources, although they are located only about 1 to 3 km apart. Nevertheless, the average recurrence interval for faults within the PFS is probably comparable to intervals of 10[sup 4] yr estimated along the eastern rift margin near Taos.

  2. Basement Structure Controls on the Evolution and Geometry of Rift Systems - Insights from Offshore S. Norway using 3D Seismic Data

    NASA Astrophysics Data System (ADS)

    Phillips, Thomas; Jackson, Christopher; Bell, Rebecca; Duffy, Oliver; Fossen, Haakon

    2015-04-01

    Rift basins form within lithosphere containing a range of heterogeneities, such as thin-skinned thrust belts and larger scale structures such as thick-skinned shear zones or crustal sutures. How the presence and reactivation of these structures during later rift events affect the geometry and evolution of rifts remains poorly understood as they are not typically well imaged on seismic data. The main reasons for this are that crystalline basement is often buried beneath thick sedimentary successions and contains small impedance contrasts. Furthermore, larger, crustal-scale, lineaments and sutures may not be imaged at all on seismic data due to their large scale and depth. In this study, we use borehole-constrained 2D and 3D seismic reflection data located around the Egersund and Farsund Basins, offshore south Norway. In both areas, crystalline basement is exceptionally well-imaged on typical 2D and 3D reflection data due to large impedance contrasts within a highly heterogeneous, shallow basement. This allows us to map a series of intrabasement reflections and overlying rift systems. Within the Egersund area, two main types of intrabasement structure are identified and mapped: i) thin (100 m), shallowly dipping (0-10°W) reflections showing a ramp-flat geometry; and ii) thick (1-1.5 km), low angle (c. 30°W) structures comprising of packages of reflections. These structures correlate along-strike northwards to Caledonian orogeny related structures mapped onshore Norway. The thin structures are interpreted as thin-skinned Caledonian thrusts, whereas the thicker structures represent thick-skinned Devonian shear zones formed through orogenic collapse of the Caledonides. Through seismic-stratigraphic analysis of the cover, we document multiple stages of extensional reactivation along these structures during Devonian, Permian-Triassic and Late Jurassic-Early Cretaceous extension followed by reverse reactivation during Late Cretaceous compression. The Farsund Basin is

  3. The 1.1-Ga Midcontinent Rift System, central North America: sedimentology of two deep boreholes, Lake Superior region

    NASA Astrophysics Data System (ADS)

    Ojakangas, Richard W.; Dickas, Albert B.

    2002-03-01

    The Midcontinent Rift System (MRS) of central North America is a 1.1-Ga, 2500-km long structural feature that has been interpreted as a triple-junction rift developed over a mantle plume. As much as 20 km of subaerial lava flows, mainly flood basalts, are overlain by as much as 10 km of sedimentary rocks that are mostly continental fluvial red beds. This rock sequence, known as the Keweenawan Supergroup, has been penetrated by a few deep boreholes in the search for petroleum. In this paper, two deep boreholes in the Upper Peninsula of Michigan are described in detail for the first time. Both the Amoco Production #1-29R test, herein referred to as the St. Amour well, and the nearby Hickey Creek well drilled by Cleveland Cliffs Mining Services, were 100% cored. The former is 7238 ft (2410 m) deep and the latter is 5345 ft (1780 m) deep. The entirety of the stratigraphic succession of the Hickey Creek core correlates very well with the upper portion of the St. Amour core, as determined by core description and point-counting of 43 thin sections selected out of 100 studied thin sections. Two Lower Paleozoic units and two Keweenawan red bed units—the Jacobsville Sandstone and the underlying Freda Sandstone—are described. The Jacobsville is largely a feldspatholithic sandstone and the Freda is largely a lithofeldspathic sandstone. Below the Freda, the remaining footage of the St. Amour core consists of a thick quartzose sandstone unit that overlies a heterogenous unit of intercalated red bed units of conglomerate, sandstone, siltstone, and shale; black shale; individual basalt flows; and a basal ignimbritic rhyolite. This lower portion of the St. Amour core presents an enigma, as it correlates very poorly with other key boreholes located to the west and southwest. While a black shale sequence is similar to the petroleum-bearing Nonesuch Formation farther west, there is no conglomerate unit to correlate with the Copper Harbor Conglomerate. Other key boreholes are

  4. Mechanical response of the south flank of kilauea volcano, hawaii, to intrusive events along the rift systems

    USGS Publications Warehouse

    Dvorak, J.J.; Okamura, A.T.; English, T.T.; Koyanagi, R.Y.; Nakata, J.S.; Sako, M.K.; Tanigawa, W.T.; Yamashita, K.M.

    1986-01-01

    Increased earthquake activity and compression of the south flank of Kilauea volcano, Hawaii, have been recognized by previous investigators to accompany rift intrusions. We further detail the temporal and spatial changes in earthquake rates and ground strain along the south flank induced by six major rift intrusions which occurred between December 1971 and January 1981. The seismic response of the south flank to individual rift intrusions is immediate; the increased rate of earthquake activity lasts from 1 to 4 weeks. Horizontal strain measurements indicate that compression of the south flank usually accompanies rift intrusions and eruptions. Emplacement of an intrusion at a depth greater than about 4 km, such as the June 1982 southwest rift intrusion, however, results in a slight extension of the subaerial portion of the south flank. Horizontal strain measurements along the south flank are used to locate the January 1983 east-rift intrusion, which resulted in eruptive activity. The intrusion is modeled as a vertical rectangular sheet with constant displacement perpendicular to the plane of the sheet. This model suggests that the intrusive body that compressed the south flank in January 1983 extended from the surface to about 2.4 km depth, and was aligned along a strike of N66??E. The intrusion is approximately 11 km in length, extended beyond the January 1983 eruptive fissures, which are 8 km in length and is contained within the 14-km-long region of shallow rift earthquakes. ?? 1986.

  5. Mapping of the major structures of the African rift system using ERTS-1

    NASA Technical Reports Server (NTRS)

    Mohr, P. A. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. The structural margin of western Afar with the Ethiopian plateau is marked by a rather wide zone of crustal deformation. ERTS-1 imagery has now permitted a more precise mapping of the structures of this marginal zone, and in particular of the discontinuous marginal graben. The tectonic style of the graben is different in the north from the south, and in the latter region the graben is discordant with the regional tectonic trend. The structural margin of the southern Afar with the Somalian plateau is formed, in the western sector, by a remarkable series of fault-zone splays. Afar-plateau boundary fault-zones successively curve northeast and then NNE to become Afar floor fault-zones, with a distance of about 25 km separating successive turnoffs. The transition from Ethiopian rift to Gulf of Aden tread faulting along this margin is fascinatingly complex. A simplistic crustal thinning model is not adequate to explain all observed structural features of the Afar margins.

  6. Stratigraphy and rifting history of the Mesozoic-Cenozoic Anza rift, Kenya

    SciTech Connect

    Winn, R.D. Jr.; Steinmetz, J.C. ); Kerekgyarto, W.L. )

    1993-11-01

    Lithological and compositional relationships, thicknesses, and palynological data from drilling cuttings from five wells in the Anza rift, Kenya, indicate active rifting during the Late Cretaceous and Eocene-Oligocene. The earlier rifting possibly started in the Santonian-Coniacian, primarily occurred in the Campanian, and probably extended into the Maastrichtian. Anza rift sedimentation was in lacustrine, lacustrine-deltaic, fluvial, and flood-basin environments. Inferred synrift intervals in wells are shalier, thicker, more compositionally immature, and more poorly sorted than Lower Cretaceous ( )-lower Upper Cretaceous and upper Oligocene( )-Miocene interrift deposits. Synrift sandstone is mostly feldspathic or arkosic wacke. Sandstone deposited in the Anza basin during nonrift periods is mostly quartz arenite, and is coarser and has a high proportion of probable fluvial deposits relative to other facies. Volcanic debris is absent in sedimentary strata older than Pliocene-Holocene, although small Cretaceous intrusions are present in the basin. Cretaceous sandstone is cemented in places by laumontite, possibly recording Campanian extension. Early Cretaceous history of the Anza basin is poorly known because of the limited strata sampled; Jurassic units were not reached. Cretaceous rifting in the Anza basin was synchronous with rifting in Sudan and with the breakup and separation of South America and Africa; these events likely were related. Eocene-Oligocene extension in the Anza basin reflects different stresses. The transition from active rifting to passive subsidence in the Anza basin at the end of the Neogene, in turn, records a reconfigured response of east African plates to stresses and is correlated with formation of the East Africa rift.

  7. Southern Africa Validation of NASA's Earth Observing System (SAVE EOS)

    NASA Technical Reports Server (NTRS)

    Privette, Jeffrey L.

    2000-01-01

    Southern Africa Validation of EOS (SAVE) is 4-year, multidisciplinary effort to validate operational and experimental products from Terra-the flagship satellite of NASA's Earth Observing System (EOS). At test sites from Zambia to South Africa, we are measuring soil, vegetation and atmospheric parameters over a range of ecosystems for comparison with products from Terra, Landsat 7, AVHRR and SeaWiFS. The data are also employed to parameterize and improve vegetation process models. Fixed-point and mobile "transect" sampling are used to collect the ground data. These are extrapolated over larger areas with fine-resolution multispectral imagery. We describe the sites, infrastructure, and measurement strategies developed underSAVE, as well as initial results from our participation in the first Intensive Field Campaign of SAFARI 2000. We also describe SAVE's role in the Kalahari Transect Campaign (February/March 2000) in Zambia and Botswana.

  8. Phanerozoic Rifting Phases And Mineral Deposits

    NASA Astrophysics Data System (ADS)

    Hassaan, Mahmoud

    2016-04-01

    In North Africa occur Mediterranean and Red Sea metallogenic provinces. In each province distribute 47 iron- manganese- barite and lead-zinc deposits with tectonic-structural control. The author presents in this paper aspects of position of these deposits in the two provinces with Phanerozoic rifting . The Mediterranean Province belongs to two epochs, Hercynian and Alpine. The Hercynian Epoch manganese deposits in only Moroccoa- Algeria belong to Paleozoic tectonic zones and Proterozoic volcanics. The Alpine Epoch iron-manganese deposits are of post-orogenic exhalative-sedimentary origin. Manganese deposits in southern Morocco occur in Kabil-Rief quartz-chalcedony veins controlled by faults in andesitic sheets and in bedded pelitic tuffs, strata-form lenses and ore veins, in Precambrian schist and in Triassic and Cretaceous dolomites. Disseminated manganese with quartz and barite and effusive hydrothermal veins are hosted in Paleocene volcanics. Manganese deposits in Algeria are limited and unrecorded in Tunisia. Strata-form iron deposits in Atlas Heights are widespread in sub-rift zone among Jurassic sediments inter-bedding volcanic rocks. In Algeria, Group Beni-Saf iron deposits are localized along the Mediterranean coast in terrigenous and carbonate rocks of Jurassic, Cretaceous and Eocene age within faults and bedding planes. In Morocco strata-form hydrothermal lead-zinc deposits occur in contact zone of Tertiary andesite inter-bedding Cambrian shale, Lias dolomites and Eocene andesite. In both Algeria and Tunisia metasomatic Pb-Zn veins occur in Campanian - Maastrichtian carbonates, Triassic breccia, Jurassic limestone, Paleocene sandstones and limestone and Neogene conglomerates and sandstones. The Red Sea metallogenic province belongs to the Late Tertiary-Miocene times. In Wadi Araba hydrothermal iron-manganese deposits occur in Cretaceous sediments within 320°and 310 NW faults related to Tertiary basalt. Um-Bogma iron-manganese deposits are closely

  9. Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic West Antarctic rift system and a speculation on possible climate forcing

    SciTech Connect

    Behrendt, J.C. ); Cooper, A. )

    1991-04-01

    The Cenzoic West Antarctic rift system, characterized by Cenozoic bimodal alkalic volcanic rocks, extends over a largely ice-covered area, from the Ross Sea nearly to the Bellingshausen Sea. It is bounded on one side by a spectacular 4-to 5-km-high rift-shoulder scarp (maximum bedrock relief 5 to 7 km) from northern Victoria Land-Queen Maud Mountains to the Ellsworth-Whitmore-Horlick Mountains. Jurassic tholeiites crop out with the late Cenozoic volcanic rocks along the section of the Transantarctic Mountains from northern Victoria Land to the Horlick Mountains. The Cenozoic rift shoulder diverges here from the Jurassic tholeiite trend, and the tholeiites are exposed discontinuously along the lower elevation (1-2 km) section of the Transantarctic Mountains to the Weddell Sea. Various lines of evidence, no one of which is independently conclusive, lead the authors (as others have also suggested) to interpret the following. The Transantarctic Mountains part of the rift shoulder (and probably the entire shoulder) has been rising since about 60 Ma, at episodic rates of {approximately}1 km/m.y., most recently since mid-Pliocene time, rather than continuously at the mean rate of 100m/m.y. Uplift rates vary along the scarp, which is cut by transverse faults. The authors speculate that this uplift may have climatically forced the advance of the Antarctic ice sheet since the most recent warm period. They suggest a possible synergistic relation between episodic tectonism, mountain uplift, and volcanism in the Cenozoic West Antarctic rift system and waxing and waning of the Antarctic ice sheet beginning about earliest Oligocene time.

  10. Earthquake Rupture Forecast of M>= 6 for the Corinth Rift System

    NASA Astrophysics Data System (ADS)

    Scotti, O.; Boiselet, A.; Lyon-Caen, H.; Albini, P.; Bernard, P.; Briole, P.; Ford, M.; Lambotte, S.; Matrullo, E.; Rovida, A.; Satriano, C.

    2014-12-01

    Fourteen years of multidisciplinary observations and data collection in the Western Corinth Rift (WCR) near-fault observatory have been recently synthesized (Boiselet, Ph.D. 2014) for the purpose of providing earthquake rupture forecasts (ERF) of M>=6 in WCR. The main contribution of this work consisted in paving the road towards the development of a "community-based" fault model reflecting the level of knowledge gathered thus far by the WCR working group. The most relevant available data used for this exercise are: - onshore/offshore fault traces, based on geological and high-resolution seismics, revealing a complex network of E-W striking, ~10 km long fault segments; microseismicity recorded by a dense network ( > 60000 events; 1.5=5 19th century events and a few paleoseismological investigations, allowing to consider time-dependent ERF. B-value estimates are found to be catalogue-dependent (WCR, homogenized NOA+Thessaloniki, SHARE), which may call for a potential break in scaling relationship. Furthermore, observed discrepancies between seismicity rates assumed for the modeled faults and those expected from GPS deformation rates call for the presence of aseismic deformation. Uncertainty in the ERF resulting from the lack of precise knowledge concerning both, fault geometries and seismic slip rates, is quantified through a logic tree exploration. Median and precentile predictions are then compared to ERF assuming a uniform seismicity rate in the WCR region. The issues raised by this work will be discussed in the light of seismic hazard assessment.

  11. Granular mechanics and rifting

    NASA Astrophysics Data System (ADS)

    Reber, Jacqueline E.; Hayman, Nicholas W.; Lavier, Luc L.

    2013-04-01

    Numerical models have proved useful in the interpretation of seismic-scale images of rifted margins. In an effort to both test and further illuminate predictions of numerical models, workers have made some strides using map-scale field relations, microstructures, and strain analyses. Yet, fundamental predictions of modeling and tectonic restorations are not able to capture critical observations. For example, many models and interpretations call on continuous faults with restorable kinematic histories. In contrast, s-reflectors and other interpreted shear fabrics in the middle crust tend to be discontinuous and non-planar across a margin. Additionally, most rift-evolution models and interpretations call on end-member ductile flow laws over a range of mechanical and thermal conditions. In contrast, field observations have found that a range of "brittle" fault rocks (e.g., cataclasites and breccias) form in the deeper crust. Similarly, upper crustal materials in deep basins and fault zones can deform through both distributed and localized deformation. Altogether, there appears to be reason to bring a new perspective to aspects of the structural evolution of rifted margins. A granular mechanics approach to crustal deformation studies has several important strengths. Granular materials efficiently localize shear and exhibit a range of stick-slip behaviors, including quasi-viscous rheological responses. These behaviors emerge in discrete element models, analog-materials experiments, and natural and engineered systems regardless of the specific micromechanical flow law. Yet, strictly speaking, granular deformation occurs via failure of frictional contacts between elastic grains. Here, we explore how to relate granular-mechanics models to mesoscale (outcrop) structural evolution, in turn providing insight into basin- and margin- scale evolution. At this stage we are focusing on analog-materials experiments and micro-to-mesoscale observations linking theoretical predictions

  12. North Sinai-Levant rift-transform continental margin

    SciTech Connect

    Ressetar, R.; Schamel, S.; Travis, C.J.

    1985-01-01

    The passive continental margin of northern Egypt and the Levant coast formed during the Early mesozoic as the relatively small Anatolia plate broke away from northern Africa. The oceanic basin of the eastern Mediterranean and the unusual right-angle bend in the North Sinai-Levant shelf margin are both products of plate separation along a rift-transform fracture system, the south arm of Tethys. The north-south trending Levant transform margin is considerably narrower than the east-west trending rift margin of northern Egypt. Both exhibit similar facies and depositional histories through the mid-Tertiary. Analysis of subsurface data and published reports of the regional stratigraphy point to a three-stage tectonic evolution of this passive margin. The Triassic through mid-Cretaceous was marked by crustal breakup followed by rapid rotational subsidence of the shelf margins about hinge lines located just south and east of the present shorelines. Reef carbonates localized on the shelf edge separated a deep marine basin to the north from a deltaic-shallow marine platform to the south and east. In the Late Cretaceous-Early Tertiary, inversion of earlier formed half-grabens produced broad anticlinal upwarps of the Syrian Arc on the shelf margin that locally influenced facies patterns. The episode of inversion corresponds with the onset of northward subduction of the Africa plate beneath southern Asia. Beginning in the Oligocene and continuing to the present, there has been renewed subsidence of the North Sinai shelf margin beneath thick, outward building clastic wedges. The source of this large volume of sediment is the updomed and erosionally stripped margins of the Suez-Red Sea Rift and the redirected Nile River.

  13. Application of P- and S-receiver functions to investigate crustal and upper mantle structures beneath the Albertine branch of the East African Rift System

    NASA Astrophysics Data System (ADS)

    Gummert, Michael; Lindenfeld, Michael; Wölbern, Ingo; Rümpker, Georg; Kasereka, Celestin; Batte, Arthur

    2014-05-01

    The Rwenzori region at the border between Uganda and the Democratic Republic of Congo is part of the western (Albertine) branch of the East African Rift System (EARS). The region is characterized by a horst structure, the Rwenzori Mountains, reaching elevations of more than 5 km and covering an area of about 120 km by 50 km. The unusual location of the mountain range, between two segments of the Albertine rift, suggests complex structures of the crust and the upper mantle below. In our study, we employ P- and S-receiver functions in order to investigate the corresponding discontinuities of the lithosphere-asthenosphere system. The analyses are based on recordings from a dense network of 33 seismic broadband stations operating in the region for a period of nearly two years, from September 2009 until August 2011. The crustal thickness is analysed by using P-receiver functions and the grid search method of Zhu & Kanamori (2000) which involves the stacking of amplitudes of direct converted (Ps) and multiple phases (PpPs and PpSs) originating from the Moho. The method of S-receiver functions is more effective in analysing deeper discontinuities of the upper mantle, such as the lithosphere-asthenosphere boundary (LAB). The latter method also has the advantage that the interfering influence of multiple phases from shallower discontinuities is avoided. To simplify the analysis of the S-receiver functions, we use an automatic procedure to determine incidence angles used in the rotation from the ZNE system to the ray-centered LQT system. We apply this approach to confirm and significantly extend results from the study of Wölbern et al. (2012), which provided evidence for an intra-lithospheric discontinuity at depths between 54 km and 104 km and the LAB between 135 km and 210 km. Our results provide evidence for significant variations of crustal thickness beneath the region. The Moho depth varies between 20 km beneath the rift valley and 39 km beneath the adjacent rift

  14. Exploring for geothermal resource in a dormant volcanic system: The Haleakala Southwest Rift Zone, Maui, Hawai'i

    NASA Astrophysics Data System (ADS)

    Martini, B. A.; Lewicki, J. L.; Kennedy, B. M.; Lide, C.; Oppliger, G.; Drakos, P. S.

    2011-12-01

    Suites of new geophysical and geochemical surveys provide compelling evidence for geothermal resource at the Haleakala Southwest Rift Zone (HSWRZ) on Maui Island, Hawai'i. Ground-based gravity (~400 stations) coupled with heli-borne magnetics (~1500 line kilometers) define both deep and shallow fractures/faults while also delineating potentially widespread subsurface hydrothermal alteration on the lower flanks (below approximately 1800 feet a.s.l.). Multi-level, upward continuation calculations and 2-D gravity and magnetic modeling provide information on source depths, but lack of lithologic information leaves ambiguity in the estimates. Lithology and physical property data from future drilling will improve these interpretations. Additionally, several well-defined gravity lows (possibly vent zones) lie coincident with magnetic highs suggesting the presence of dike intrusions at depth; a potentially young source of heat for a modern geothermal system. Soil CO2 fluxes were measured along transects across geophysically-defined faults and fractures as well as young cinder cones along the HSWRZ; a weak anomalous flux signal was observed at one young cinder cone location. Dissolved inorganic carbon concentrations and δ13C compositions and 3He/4He values measured in several shallow groundwater samples indicate addition of magmatic CO2 and He to the groundwater system. The general lack of observed magmatic surface CO2 signals on the HSWRZ is therefore likely due to a combination of groundwater 'scrubbing' of CO2 and relatively high biogenic surface CO2 fluxes that mask magmatic CO2. Similar surveys at the Puna geothermal field on the Kilauea Lower East Rift Zone (KLERZ) also showed a lack of surface CO2 flux signals attributed to a magmatic source, while aqueous geochemistry indicated contribution of magmatic CO2 and He to shallow groundwaters at both Maui and Puna. As magma has been intercepted in geothermal drilling at the Puna field, the lack of measured surface CO2

  15. Mesozoic fault reactivation along the St. Lawrence Rift System as constrained by (U-Th/He) thermochronology

    NASA Astrophysics Data System (ADS)

    Bouvier, L.; Pinti, D. L.; Tremblay, A.; Minarik, W. G.; Roden-Tice, M. K.; Pik, R.

    2011-12-01

    The Saint Lawrence Rift System (SLRS) is a half-graben, extending for 1000 km along St. Lawrence River valley. Late Proterozoic-Early Paleozoic faults of the graben form the contact with the metamorphic Grenvillian basement to the northwest and extend under the Paleozoic sedimentary sequences of the St. Lawrence Lowlands to the southeast. The SLRS is the second most seismically active area in Canada, but the causes of this activity remain unclear. Reactivation of the SLRS is believed to have occurred along Late Proterozoic to Early Paleozoic normal faults related to the opening of the Iapetus Ocean. The absence of strata younger than the Ordovician makes difficult to determine when the faults reactivated after the Ordovician. Field relations between the normal faults bordering the SLRS and those produced by the Charlevoix impact crater suggest a reactivation of the rift younger than the Devonian, the estimated age of the impact. Apatite (U-Th)/He thermochronology is an adequate tool to recognize thermal events related to fault movements. A thermochronology study was then started along three transects across the SLRS, from Québec up to Charlevoix. Apatites were extracted and separated from five granitic to charnockitic gneisses and an amphibolite of Grenvillian age. The samples were exposed on hanging wall and footwall of the Montmorency and Saint-Laurent faults at three different locations along the SLRS. For precision and accuracy, each of the six samples was analyzed for radiogenic 4He and U-Th contents at least twice. Apatite grains were isolated by heavy liquids and magnetic separation. For each sample, ten apatite grains were selected under optical microscope and inserted into Pt capsules. Particular care was taken to isolate apatite free of mineral and fluid inclusions. Indeed, SEM investigations showed that some inclusions are U-rich monazite, which is a supplementary source of 4He to be avoided. The 4He content was determined by using a static noble gas

  16. Influence of Neoproterozoic tectonic fabric on the origin of the Potiguar Basin, northeastern Brazil and its links with West Africa based on gravity and magnetic data

    NASA Astrophysics Data System (ADS)

    de Castro, David Lopes; Bezerra, Francisco H. R.; Sousa, Maria O. L.; Fuck, Reinhardt A.

    2012-03-01

    The Potiguar Basin is a ˜6,000 m thick aborted NE-trending rift that was formed during the Cretaceous in the continental margin of northeastern Brazil. Its ˜E-W-trending offshore faults form part of the successful continental margin rift that evolved into the South Atlantic Ocean. The region represents one of the most significant pre-Pangea breakup piercing points between eastern South America and West Africa. We used gravity, aeromagnetic, and geological data to assess the role of reactivated Precambrian shear zones and major terrain boundaries in the development of the Potiguar Basin from the Cretaceous to the Cenozoic. We also looked for possible links between these structures in northeastern Brazil and their continuation in West Africa. Our results indicate that the major fault systems of the Potiguar Basin were superimposed on the Precambrian fabric. Both gravity and magnetic maps show lineaments related to the shear zones and major terrain boundaries in the Precambrian crystalline basement, which also characterize the architecture of the rift. For example, the Carnaubais fault, the master fault of the rift system, represents the reactivation of the Portalegre shear zone, the major tectonic boundary between Precambrian terrains in the crystalline basement. In addition, part of the Moho topography is controlled by these shear zones and developed during the period of main rift extension in the Neocomian. The shear zones bounding the Potiguar rift system continue in West Africa around and underneath the Benue Basin, where fault reactivation also took place.

  17. Receiver function imaging of the lithosphere-asthenosphere boundary and melt beneath the Afar Rift in comparison to other systems

    NASA Astrophysics Data System (ADS)

    Rychert, Catherine A.; Harmon, Nicholas

    2015-04-01

    Heating, melting, and stretching destroy continents at volcanic rifts. Mantle plumes are often invoked to thermally weaken the continental lithosphere and accommodate rifting through the influx of magma. However the relative effects of mechanical stretching vs. melt infiltration and weakening are not well quantified during the evolution of rifting. S-to-p (Sp) imaging beneath the Afar Rift provides additional constraints. We use two methodologies to investigate structure and locate robust features: 1) binning by conversion point and then simultaneous deconvolution in the frequency domain, and 2) extended multitaper followed by migration and stacking. We image a lithosphere-asthenosphere boundary at ~75 km beneath the flank of the Afar Rift vs. its complete absence beneath the rift. Instead, a strong velocity increase with depth at ~75 km depth is imaged. Beneath the rift axis waveform modeling suggests the lack of a mantle lithosphere with a velocity increase at ~75 km depth. Geodynamic models that include high melt retention and suppress thermal convection easily match the required velocity-depth profile, the velocity increase arising from a drop in melt percentage at the onset of decompression melting. Whereas, models with conservative melt retention that include thermal buoyancy effects cannot reproduce the strong velocity increase. The shallow depth of the onset of melting is consistent with a mantle potential temperature = 1350 - 1400°C, i.e., typical for adiabatic decompression melting. Trace element signatures and geochemical modeling have been used to argue for a thick lithosphere beneath the rift and slightly higher mantle potential temperatures ~1450°C, although overall, given modeling assumptions, the results are not in disagreement. Therefore, although a plume initially destroyed the mantle lithosphere, its influence directly beneath Afar today is not strong. Volcanism continues via adiabatic decompression melting assisted by strong melt buoyancy

  18. Geochemistry of 24 Ma Basalts from Northeast Egypt: Implications for Small-Scale Convection Beneath the East African Rift System

    NASA Astrophysics Data System (ADS)

    Endress, C. A.; Furman, T.; Ali Abu El-Rus, M.

    2009-12-01

    Basalts ~24 Ma in the Cairo-Suez and Fayyum districts of NE Egypt represent the youngest and northernmost lavas potentially associated with the initiation of rifting of the Red Sea. The age of these basalts corresponds to a time period of significant regional magmatism that occurred subsequent to emplacement of 30 Ma flood basalts attributed to the Afar Plume in Ethiopia and Yemen. Beginning ~28 Ma, widespread magmatism occurred across supra-equatorial Africa in Hoggar (Algeria), Tibesti (Chad), Darfur (Sudan), Turkana (Kenya) and Samalat, Bahariya, Quesir and the Sinai Peninsula (Egypt) (e.g. Allegre et al., 1981; Meneisy, 1990; Baldridge et al., 1991; Wilson and Guiraud, 1992; Furman et al., 2006; Lucassen et al., 2008). Available geochemical and isotopic data indicate that Hoggar and Darfur basalts are similar to Turkana lavas, although no direct link between the N African lavas and the Kenya Plume has been made. New geochemical data on the NE Egyptian basalts provide insight into the thermochemical, isotopic, and mineralogical characteristics of the mantle beneath the region in which they were emplaced. The basalts are subalkaline with OIB-like incompatible trace element abundances and homogeneous major element, trace element and isotopic geochemistry. They display relatively flat ITE patterns, with notable positive Pb and negative P anomalies. Isotopic (143Nd/144Nd = 0.51274-0.51285, 87Sr/86Sr = 0.7049-0.7050) and trace element signatures (Ce/Pb = 16-22, Ba/Nb = 9-14, and La/Nb = 0.9-1.0) are consistent with melting of a sub-lithospheric source that has been slightly contaminated by continental crust during ascent and emplacement. The Pb isotopic ratios (206Pb/204Pb = 18.53-18.62, 207Pb/204Pb = 15.59-15.64, and 208Pb/204Pb = 38.80-39.00) in the Egyptian basalts are close to the range of those found in the 30 Ma Ethiopian flood basalts, which are distinct from the more highly radiogenic, high-μ type signature seen in basalts from Turkana, Darfur, and Hoggar

  19. Lower Pliensbachian caldera volcanism in high-obliquity rift systems in the western North Patagonian Massif, Argentina

    NASA Astrophysics Data System (ADS)

    Benedini, Leonardo; Gregori, Daniel; Strazzere, Leonardo; Falco, Juan I.; Dristas, Jorge A.

    2014-12-01

    In the Cerro Carro Quebrado and Cerro Catri Cura area, located at the border between the Neuquén Basin and the North Patagonian Massif, the Garamilla Formation is composed of four volcanic stages: 1) andesitic lava-flows related to the beginning of the volcanic system; 2) basal massive lithic breccias that represent the caldera collapse; 3) voluminous, coarse-crystal rich massive lava-like ignimbrites related to multiple, steady eruptions that represent the principal infill of the system; and, finally 4) domes, dykes, lava flows, and lava domes of rhyolitic composition indicative of a post-collapse stage. The analysis of the regional and local structures, as well as, the architectures of the volcanic facies, indicates the existence of a highly oblique rift, with its principal extensional strain in an NNE-SSW direction (˜N10°). The analyzed rocks are mainly high-potassium dacites and rhyolites with trace and RE elements contents of an intraplate signature. The age of these rocks (189 ± 0.76 Ma) agree well with other volcanic sequences of the western North Patagonian Massif, as well as, the Neuquén Basin, indicating that Pliensbachian magmatism was widespread in both regions. The age is also coincident with phase 1 of volcanism of the eastern North Patagonia Massif (188-178 Ma) represented by ignimbrites, domes, and pyroclastic rocks of the Marifil Complex, related to intraplate magmatism.

  20. A Strong Stress Shadow Effect of the 2004 M=9.2 Sumatra-Andaman Earthquake on the Andaman Sea Transform-Rift System 250 km Away

    NASA Astrophysics Data System (ADS)

    Sevilgen, V.; Stein, R. S.

    2010-12-01

    The 26 December 2004 earthquake ruptured a 1,300-km section of the Sunda megathrust. A transform-rift back-arc system accommodates most of the trench-parallel component of the highly oblique subduction. We used the NEIC earthquake catalog at its M≥4.7 completeness level since 1999, and at M≥4.8 since 1975, to examine the seismicity rate along the transform-rift system. We also combined teleseismic double-difference earthquake relocations from Pesicek et al (JGR, 2010) with Global CMT mechanisms, to more accurately associate focal mechanisms with their fault systems. We find a strong drop in seismicity rate along the Andaman Sea transform system east of the northern end of the 2004 rupture zone. This occurs immediately following the Sumatra-Andaman mainshock and persists to this day. The rate drop is associated with strike-slip mechanisms only; along the portions of the rift system with normal-faulting mechanisms, the seismicity rate increased. We calculate that the Sagaing-West Andaman transform in this region was subjected to a static Coulomb stress drop of 0.25 bar (for an assumed fault friction of 0.4), whereas the rift segments sustained stress increases greater than 1 bar. Both of these calculations are in accord with the observations. Because of the large distance between the megathrust source and the back-arc receiver faults, the imparted stresses are insensitive to the unknown details of the megathrust slip and geometry; because the 2004 slip is so large, the imparted stresses are nevertheless substantial 200-300 km east of the trench, where the seismicity rate changes are observed. Thus, the seismicity shutdown associated with the 2004 earthquake stress shadow furnishes an important test of the static Coulomb stress triggering hypothesis.

  1. Teleseismic P-wave Delay Time Tomography of the southern Superior Province and Midcontinent Rift System (MRS) Region

    NASA Astrophysics Data System (ADS)

    Bollmann, T. A.; van der Lee, S.; Frederiksen, A. W.; Wolin, E.; Aleqabi, G. I.; Revenaugh, J.; Wiens, D. A.; Darbyshire, F. A.

    2014-12-01

    The Superior Province Rifting Earthscope Experiment (SPREE) and the northern midwest footprint of USArray's Transportable Array recorded continuous ground motion for a period of 2.5 years. From around 400 M>5.5 teleseismic earthquakes recorded at 337 stations, we measured body wave delay times for 255 of these earthquakes. The P wave delays are accumulated over more than 45 thousand wave paths with turning points in the lower mantle. We combine these delay times with a similar number delay times used in previous tomographic studies of the study region. The latter delay times stem from fewer stations, including Polaris and CNSN stations, and nearly a thousand earthquakes. We combine these two sets of delay times to image the three-dimensional distribution of seismic velocity variations beneath the southern Superior Province and surrounding provinces. This combined data coverage is illustrated in the accompanying figure for a total number of 447 stations . The coverage and the combined delays form the best configuration yet to image the three-dimensional distribution of seismic P and S-wave velocity variations beneath the southern Superior and surrounding provinces. Closely spaced stations (~12 km) along and across the MRS provide higher resolving power for lithospheric structure beneath the rift system. Conforming to expectations that the entire region is underlain by thick, cool lithosphere, a mean delay of -.55 +/- .54 s. This is very similar to the mean delays -.6s +/- .37s measured for this region before 2012. Event corrections range from -.2 +/-.54 s and correlate with tectonics for 80% of the earthquakes. An inversion of these nearly one hundred thousand P and around thirty thousand S-wave delay times for high-resolution P and S-wave velocity structure, respectively, does not show structures that are obviously related to the crustal signature of the MRS. None of structures imaged, align with or have a similar shape to the high Mid-continent Gravity Anomaly

  2. Crustal Structure in the area of the North American Mid-Continent Rift System from P-wave Receiver Functions

    NASA Astrophysics Data System (ADS)

    Zhang, H.; van der Lee, S.; Wolin, E.; Bollmann, T. A.; Revenaugh, J.; Wiens, D. A.; Wysession, M. E.; Aleqabi, G. I.; Frederiksen, A. W.; Darbyshire, F. A.; Stein, S. A.; Jurdy, D. M.

    2015-12-01

    The Mid-continent Geophysical Anomaly (MGA) represents the largest gravity anomaly in the North American continental interior, its strongest portion stretching from Iowa to Lake Superior, and is the direct result of 1.1 Ga deposition and uplift of volcanic rocks in the Mid-continent Rift System (MRS). The Superior Province Rifting Earthscope Experiment (SPREE) collected broadband seismic data around this prominent portion of the MGA for 2.5 years from 82 seismic stations, simultaneously with about 30 Transportable Array (TA) stations in the region. To image crustal structure around the MGA, we analyzed the P-wave trains of 119 teleseismic earthquakes at these stations using the time-domain iterative-deconvolution method of Ligorria and Ammon (1999), the waveform-fitting method of Van der Meijde et al. (2003), and the H-κ stacking method of Zhu and
Kanamori (2000). Our aim was to resolve intra-crustal layering and Moho characteristics. Despite considerable noise related to station installation constraints, we find that outside of the MGA, the Moho is sharp and relatively flat, both beneath the Archean Superior Province as well as beneath the Proterozoic terranes to its south. This Moho produces consistent P to S converted phases in the analyzed receiver functions. Receiver functions show much more complexity along the MGA, where P to S converted phases from the Moho are much weaker and more variable with azimuth and epicentral distance. Similar results have been found in Iowa by French et al. (2009). For many stations along the MGA, multiple weak S phases arrive around the time expected for the Moho-converted phase. In addition, strong P-to-S converted phases are observed from the base of shallow sedimentary layers. The base of the sedimentary layer is fairly shallow outside of the MGA, thickens near the flanks where gravity anomalies are low and shallows again in the center where the gravity peaks. We conclude that the Moho is not a strong feature of the MRS

  3. 40Ar/ 39Ar dating constraints on the high-angle normal faulting along the southern segment of the Tan-Lu fault system: An implication for the onset of eastern China rift-systems

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Zhou, Su

    2009-01-01

    High-angle normal faulting in eastern China was an important tectonic process responsible for the rifting of the eastern Asian continental margin. Along the southern segment of the Tan-Lu fault system, part of the eastern China rift-system, 55-70° east-dipping normal faults are the oldest structures within this rift-system. Chlorite, pseudotachylite, and fault breccia are found in fault zones, which are characterized by microstructures and syn-deformation chlorite minerals aligned parallel to a down-dip stretching lineation. 40Ar/ 39Ar dating of syn-deformation chlorite and K-feldspar from the fault gouge zone yields cooling ages of ˜75-70 Ma, interpreted as the timing of slip along the normal faults. This age is older than that of opening of the Japanese sea and back-arc extension in the west Pacific, but similar to the onset of the Indo-Asian (soft?) collision.

  4. African Indigenous Knowledge Systems and Relevance of Higher Education in South Africa

    ERIC Educational Resources Information Center

    Kaya, Hassan O.; Seleti, Yonah N.

    2013-01-01

    The higher education system in Africa and South Africa in particular, is still too academic and distant from the developmental challenges of African local communities. The integration of African indigenous knowledge systems (AIKS) into the higher educational system could improve its relevance. This is due to the holistic, community-based nature…

  5. Parameters influencing the location and characteristics of volcanic eruptions in a youthful extensional setting: Insights from the Virunga Volcanic Province, in the Western Branch of the East African Rift System

    NASA Astrophysics Data System (ADS)

    Smets, Benoît; d'Oreye, Nicolas; Kervyn, Matthieu; Kervyn, François

    2016-04-01

    The East African Rift System (EARS) is often mentioned as the modern archetype for rifting and continental break-up (Calais et al., 2006, GSL Special Publication 259), showing the complex interaction between rift faults, magmatism and pre-existing structures of the basement. Volcanism in the EARS is characterized by very active volcanoes, several of them being among the most active on Earth (Wright et al., 2015, GRL 42). Such intense volcanic activity provides useful information to study the relationship between rifting, magmatism and volcanism. This is the case of the Virunga Volcanic Province (VVP) located in the central part of the Western Branch of the EARS, which hosts two of the most active African volcanoes, namely Nyiragongo and Nyamulagira. Despite the intense eruptive activity in the VVP, the spatial distribution of volcanism and its relationship with the extensional setting remain little known. Here we present a study of the interaction between tectonics, magmatism and volcanism at the scale of the Kivu rift section, where the VVP is located, and at the scale of a volcano, by studying the dense historical eruptive activity of Nyamulagira. Both the complex Precambrian basement and magmatism appear to contribute to the development of the Kivu rift. The presence of transfer zones north and south of the Lake Kivu rift basin favoured the development of volcanic provinces at these locations. Rift faults, including reactivated Precambrian structures influenced the location of volcanism within the volcanic provinces and the rift basin. At a more local scale, the historical eruptive activity of Nyamulagira highlights that, once a composite volcano developed, the gravitational stress field induced by edifice loading becomes the main parameter that influence the location, duration and lava volume of eruptions.

  6. Structure of the central Terror Rift, western Ross Sea, Antarctica

    USGS Publications Warehouse

    Hall, Jerome; Wilson, Terry; Henrys, Stuart

    2007-01-01

    The Terror Rift is a zone of post-middle Miocene faulting and volcanism along the western margin of the West Antarctic Rift System. A new seismic data set from NSF geophysical cruise NBP04-01, integrated with the previous dataset to provide higher spatial resolution, has been interpreted in this study in order to improve understanding of the architecture and history of the Terror Rift. The Terror Rift contains two components, a structurally-controlled rollover anticlinal arch intruded by younger volcanic bodies and an associated synclinal basin. Offsets and trend changes in fault patterns have been identified, coincident with shifts in the location of depocenters that define rift sub-basins, indicating that the Terror Rift is segmented by transverse structures. Multiple phases of faulting all post-date 17 Ma, including faults cutting the seafloor surface, indicating Neogene rifting and possible modern activity.

  7. Crustal structure and kinematics of the TAMMAR propagating rift system on the Mid-Atlantic Ridge from seismic refraction and satellite altimetry gravity

    NASA Astrophysics Data System (ADS)

    Kahle, Richard L.; Tilmann, Frederik; Grevemeyer, Ingo

    2016-06-01

    The TAMMAR segment of the Mid-Atlantic Ridge forms a classic propagating system centred about two degrees south of the Kane Fracture Zone. The segment is propagating to the south at a rate of 14 mm/yr, 15 % faster than the half-spreading rate. Here we use seismic refraction data across the propagating rift, sheared zone and failed rift to investigate the crustal structure of the system. Inversion of the seismic data agrees remarkably well with crustal thicknesses determined from gravity modelling. We show that the crust is thickened beneath the highly magmatic propagating rift, reaching a maximum thickness of almost 8 km along the seismic line and an inferred (from gravity) thickness of about 9 km at its centre. In contrast, the crust in the sheared zone is mostly 4.5-6.5 km thick, averaging over 1 km thinner than normal oceanic crust, and reaching a minimum thickness of only 3.5 km in its NW corner. Along the seismic line it reaches a minimum thickness of under 5 km. The PmP reflection beneath the sheared zone and failed rift is very weak or absent, suggesting serpentinisation beneath the Moho, and thus effective transport of water through the sheared zone crust. We ascribe this increased porosity in the sheared zone to extensive fracturing and faulting during deformation. We show that a bookshelf-faulting kinematic model predicts significantly more crustal thinning than is observed, suggesting that an additional mechanism of deformation is required. We therefore propose that deformation is partitioned between bookshelf faulting and simple shear, with no more than 60 % taken up by bookshelf faulting.

  8. Crustal structure and kinematics of the TAMMAR propagating rift system on the Mid-Atlantic Ridge from seismic refraction and satellite altimetry gravity

    NASA Astrophysics Data System (ADS)

    Kahle, Richard L.; Tilmann, Frederik; Grevemeyer, Ingo

    2016-08-01

    The TAMMAR segment of the Mid-Atlantic Ridge forms a classic propagating system centred about two degrees south of the Kane Fracture Zone. The segment is propagating to the south at a rate of 14 mm yr-1, 15 per cent faster than the half-spreading rate. Here, we use seismic refraction data across the propagating rift, sheared zone and failed rift to investigate the crustal structure of the system. Inversion of the seismic data agrees remarkably well with crustal thicknesses determined from gravity modelling. We show that the crust is thickened beneath the highly magmatic propagating rift, reaching a maximum thickness of almost 8 km along the seismic line and an inferred (from gravity) thickness of about 9 km at its centre. In contrast, the crust in the sheared zone is mostly 4.5-6.5 km thick, averaging over 1 km thinner than normal oceanic crust, and reaching a minimum thickness of only 3.5 km in its NW corner. Along the seismic line, it reaches a minimum thickness of under 5 km. The PmP reflection beneath the sheared zone and failed rift is very weak or absent, suggesting serpentinisation beneath the Moho, and thus effective transport of water through the sheared zone crust. We ascribe this increased porosity in the sheared zone to extensive fracturing and faulting during deformation. We show that a bookshelf-faulting kinematic model predicts significantly more crustal thinning than is observed, suggesting that an additional mechanism of deformation is required. We therefore propose that deformation is partitioned between bookshelf faulting and simple shear, with no more than 60 per cent taken up by bookshelf faulting.

  9. Imaging the lithosphere of rifted passive margins using waveform tomography: North Atlantic, South Atlantic and beyond

    NASA Astrophysics Data System (ADS)

    Lebedev, Sergei; Schaeffer, Andrew; Celli, Nicolas Luca

    2016-04-01

    Lateral variations in seismic velocities in the upper mantle reflect variations in the temperature of the rocks at depth. Seismic tomography thus provides a proxy for lateral changes in the temperature and thickness of the lithosphere. It can map the deep boundaries between tectonic blocks with different properties and age of the lithosphere. Our 3D tomographic models of the upper mantle and the crust at the Atlantic and global scales are constrained by an unprecedentedly large global dataset of broadband waveform fits (over one million seismograms) and provide improved resolution of the lithosphere, compared to other available models. The most prominent high-velocity anomalies, seen down to 150-200 km depths, indicate the cold, thick, stable mantle lithosphere beneath Precambrian cratons, including those in North America, Greenland, northern and eastern Europe, Africa and South America. The dominant, large-scale, low-velocity feature is the global system of mid-ocean ridges, with broader low-velocity regions near hotspots, including Iceland. Currently active continental rifts show highly variable expression in the upper mantle, from pronounced low velocities to weak anomalies; this correlates with the amount of magmatism within the rift zone. Rifted passive margins have typically undergone cooling since the rifting and show more subtle variations in their seismic-velocity structure. Their thermal structure and evolution, however, are also shaped by 3D geodynamic processes since their formation, including cooling by the adjacent cratonic blocks inland and heating by warm oceanic asthenosphere.

  10. Incipient continental rifting: Insights from the Okavango Rift Zone, northwestern Botswana

    NASA Astrophysics Data System (ADS)

    Kinabo, Baraka Damas

    In this dissertation aeromagnetic, gravity, and Shuttle Radar Topography Mission Digital Elevation Model (SRTM DEM) data from the Okavango Rift Zone in northwest Botswana are used to map the distribution of rift and basement structures. The distribution of these structures provide useful insights into the early stages of continental rifting. The objectives of this study are (1) assessing the role of pre-existing structures on rift basin development, (2) characterizing the geometry of the nascent rift basins, (3) documenting fault growth and propagation patterns, and (4) investigating the border fault development. Potential field data especially aeromagnetic data are used to map out structures in the sediment covered basement, whereas SRTM DEM data express the surface morphology of the structures. The azimuth of rift faults parallel the orientation of the fold axes and the prominent foliation directions of the basement rocks. This indicates that pre-existing structures in the basement influenced the development of the rift structures. NE dipping faults consistently exhibit greater displacements than SE dipping faults, suggesting a developing half-graben geometry. Individual faults grow by along axis linkage of small segments that develop from soft linkage (under lapping to overlapping segments) to hard linkage (hooking, fused segments). Major rifts faults are also linking through transfer zones by the process of "fault piracy" to establish an immature border fault system. The relationships between scam heights and vertical throws reveal that the young and active faults are located outside the rift while the faults with no recent activities are in the middle suggesting that the rift is also growing in width. This study demonstrates the utility of potential field data and SRTM DEM to provide a 3-D view of incipient continental rifting processes such as fault growth and propagation.

  11. Torque exerted on the side of crustal blocks controls the kinematics of Ethiopian Rift

    NASA Astrophysics Data System (ADS)

    Muluneh, Ameha A.; Kidane, Tesfaye; Cuffaro, Marco; Doglioni, Carlo

    2016-04-01

    Plate tectonic stress at active plate boundary can arises from 1) a torque applied on the side of lithospheric blocks and 2) a torque at the base of the lithosphere due to the flow of the underlying mantle. In this paper we use a simple force balance analysis to compare side and basal shear stresses and their contribution in driving kinematics and deformation in the Ethiopian Rift (ER), in the northern part of the East African Rift System (EARS). Assuming the constraints of the ER given by the dimension of the lithospheric blocks, the strain rate, the viscosity of the low velocity zone (LVZ) and the depth of the brittle-ductile transition zone, the lateral torque is several orders of magnitude higher than the basal torque. The minor contribution of basal torque might be due to low viscosity in the LVZ. Both Africa and Somalia plates are moving to the "west" relative to the mantle and there are not slabs that can justify this pull and consequent motion. Therefore, we invoke that westerly oriented tidal torque on Africa and Somalia plates in providing the necessary side torque in the region. This plate motion predicts significant sinistral transtension along the ER and rift parallel strike-slip faulting similar to the estimated angular velocity vector for tectonic blocks and GPS observations. Vertical axis block rotations are observed in areas where the lithospheric mantle is removed and strain is widely distributed.

  12. Iowa portion of rift trend hosts wildcats

    SciTech Connect

    McCaslin, J.C.

    1984-05-07

    Definite signs point to an exploratory effort beginning at the far southwestern end of Iowa's Keweenawan rift - a new frontier for oil and gas hunters. This new round of wildcatting is located on the Midcontinent rift trend, a major geological feature extending to great depths under parts of Michigan, Wisconsin, Minnesota (the Keweenawan rift system), Iowa, Nebraska, Missouri, and Kansas. Recent reports hint that leasing is underway in Minnesota, with interest developing in Iowa, Missouri, and Nebraska sectors. Geophysical evidence has led to the delineation of a rift system active during the Proterozoic Y era. Geologists have traced this system by the Midcontinent gravity high and corresponding aeromagnetic signature from the surface exposure of the Keweenawan supergroup in the Lake Superior basin southwest in the subsurface through the northern Midcontinent states.

  13. Cenozoic rift tectonics of the Japan Sea

    SciTech Connect

    Kimura, K.

    1988-08-01

    The Japan Sea is one of the back-arc basins in trench-arc systems bordering the western Pacific. Recent paleomagnetic works suggest the Japan Sea opened during early to middle Miocene. Radiometric and microfossil ages of the Cenozoic onland sequences in the Japanese Islands elucidate the rift tectonics of the Japan Sea. The rifting history is summarized as follows: nonmarine volcanic formations of prerift stage before 50 Ma, rift-onset unconformity at 40 Ma, nonmarine volcanic formations of synrift stage 20-33 Ma, breakup unconformity 19 Ma showing the opening of the Japan Sea, marine volcanic and sedimentary formations of synrift stage 14.5-18 Ma, beginning of regional subsidence 14.5 Ma corresponding to the end of the Japan Sea opening, marine sedimentary formations of postdrift stage after 14.5 Ma. Rifting is not limited to the synrift stage but is continued to the syndrift stage. Rifting led to a horst-and-graben structure. Thus, the Cenozoic onland sequences in the Japanese Islands are suited for a study of rift tectonics because the sequences were subaerially exposed by the late Miocene-Holocene island-arc tectonics. Rift tectonics cannot be studied as easily in most Atlantic-type passive margins.

  14. A top to bottom lithospheric study of Africa and Arabia

    NASA Astrophysics Data System (ADS)

    Pasyanos, Michael E.; Nyblade, Andrew A.

    2007-11-01

    We study the lithospheric structure of Africa, Arabia and adjacent oceanic regions with fundamental-mode surface waves over a broad period range. Including group velocities with periods shorter than 35 s allows us to examine shallower features than previous studies of the whole continent. In the process, we have developed a crustal thickness map of Africa. Main features include crustal thickness increases under the West African, Congo, and Kalahari cratons. We find crustal thinning under Mesozoic and Cenozoic rifts, including the Benue Trough, Red Sea, and East, Central, and West African rift systems, along with less abrupt crustal thickness changes at passive continental margins. We also find crustal thickness differences in North Africa between the West African Craton and East Saharan Shield. Crustal shear wave velocities are generally faster in oceanic regions and cratons, and slower in more recent crust and in active and remnant orogenic regions. Deeper structure, related to the thickness of cratons and modern rifting, is generally consistent with previous work. Under cratons we find thick lithosphere and fast upper mantle velocities, while under rifts we find thinned lithosphere and slower upper mantle velocities. However, we also find the lack of a thick cratonic keel beneath the central portion of the Congo Craton. There are no consistent effects in areas classified as hotspots, indicating that there seem to be numerous origins for these features. Finally, it appears that the African Superswell, which is responsible for high elevation and uplift over large portions of Africa, has had a significantly different impact (as indicated by features such as temperature, time of influence, etc.) in the north and the south. This is consistent with episodic activity at shallow depths, which is well-expressed in northeastern Africa and Arabia today.

  15. Understanding the thermal and tectonic evolution of Marie Byrd Land from a reanalysis of airborne geophysical data in the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

    Quartini, E.; Powell, E. M.; Richter, T.; Damiani, T.; Burris, S. G.; Young, D. A.; Blankenship, D. D.

    2013-12-01

    The West Antarctic Rift System (WARS) is a region characterized by a significant topographic range, a complex tectonic history, and active subglacial volcanism. Those elements exert a large influence on the stability of the West Antarctic Ice Sheet, which flows within the cradle-shaped rift system and is currently grounded well below sea level. This potentially unstable configuration is the motivation for gaining a better understanding of the ice sheet boundary conditions dictated by rift evolution and how they impact the ice flow. In this study we focus on characterizing the distribution of and transition between sedimentary basins and inferred geothermal heat flux from the flanks to the floor of the rift system. We do so through analysis of gravity data both for sources within the deep lithosphere and near surface targets in the crust. A compilation of gravity datasets over West and Central Antarctica and the analysis thereof is presented. In particular we use gravity data collected during several airborne geophysical surveys: CASERTZ (1994-1997), SOAR/WMB (1997-1998), AGASEA (2004-2005), ICEBRIDGE (2008-2011), and GIMBLE (2012-2013). New processing and data reduction methodologies are applied to the older gravity surveys to improve the high frequency signal content and to make these surveys compatible with modern works (i.e. AGASEA, ICEBRIDGE, GIMBLE). The high frequency signal provides better resolution of small-scale features within survey blocks but long-wavelength integrity is retained by registering the airborne free-air disturbance within those blocks to the gravity disturbance derived from the GOCE global satellite gravity field. This allows for consistent long wavelength interpretation across the merged surveys and provides improved gravity analysis of the deep lithosphere while retaining the capacity to study smaller scale features. A crustal model for the area is produced using the Bouguer anomaly and spectral analyses of the Bouguer anomaly and free

  16. Rift valley fever in the US: Commerce networks, climate, and susceptible vector and host populations

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a mosquito-borne hemorrhagic viral disease with substantial negative impacts on public and animal health in its endemic range of sub-Saharan Africa. Rift Valley fever virus (RVFV) could enter the United States and lead to widespread morbidity and mortality in humans, domes...

  17. A network-based meta-population approach to model Rift Valley fever epidemics

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever virus (RVFV) has been expanding its geographical distribution with important implications for both human and animal health. The emergence of Rift Valley fever (RVF) in the Middle East, and its continuing presence in many areas of Africa, has negatively impacted both medical and vet...

  18. Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland.

    PubMed

    Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S; Ófeigsson, Benedikt G; Heimisson, Elías Rafn; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Gudmundsson, Gunnar B; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T; Högnadóttir, Thórdís; Fridriksdóttir, Hildur María; Hensch, Martin; Einarsson, Páll; Magnússon, Eyjólfur; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert S; Ágústsdóttir, Thorbjörg; Greenfield, Tim; Green, Robert G; Hjartardóttir, Ásta Rut; Pedersen, Rikke; Bennett, Richard A; Geirsson, Halldór; La Femina, Peter C; Björnsson, Helgi; Pálsson, Finnur; Sturkell, Erik; Bean, Christopher J; Möllhoff, Martin; Braiden, Aoife K; Eibl, Eva P S

    2015-01-01

    Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long. Previous models of rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens, or magma flowing vertically into dykes from an underlying source, with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Bárðarbunga volcanic system grew laterally for more than 45 kilometres at a variable rate, with topography influencing the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred primarily over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning System (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bárðarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of magnitude M > 5 earthquakes. Dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries. PMID:25517098

  19. The Role of Rift Obliquity During Pangea Fragmentation

    NASA Astrophysics Data System (ADS)

    Brune, S.; Butterworth, N. P.; Williams, S.; Müller, D.

    2014-12-01

    Does supercontinent break-up follow specific laws? What parameters control the success and the failure of rift systems? Recent analytical and geodynamic modeling suggests that oblique rifting is energetically preferred over orthogonal rifting. This implies that during rift competition, highly oblique branches proceed to break-up while less oblique ones become inactive. These models predict that the relative motion of Earth's continents during supercontinent break-up is affected by the orientation and shape of individual rift systems. Here, we test this hypothesis based on latest plate tectonic reconstructions. Using PyGPlates, a recently developed Python library that allows script-based access to the plate reconstruction software GPlates, we quantify rift obliquity, extension velocity and their temporal evolution for continent-scale rift systems of the past 200 Myr. Indeed we find that many rift systems contributing to Pangea fragmentation involved strong rift obliquity. East and West Gondwana for instance split along the East African coast with a mean obliquity of 55° (measured as the angle between local rift trend normal and extension direction). While formation of the central and southern South Atlantic segment involved a low obliquity of 10°, the Equatorial Atlantic opened under a high angle of 60°. Rifting between Australia and Antarctica involved two stages with 25° prior to 100 Ma followed by 50° obliquity and distinct increase of extension velocity. Analyzing the entire passive margin system that formed during Pangea breakup, we find a mean obliquity of 40°, with a standard deviation of 20°. Hence 50% of these margins formed with an angle of 40° or more. Considering that many conceptual models of rifting and passive margin formation assume 2D deformation, our study quantifies the degree to which such 2D models are globally applicable, and highlights the importance of 3D models where oblique rifting is the dominant mode of deformation.

  20. Atlantic marginal basins of Africa

    SciTech Connect

    Moore, G.T.

    1988-02-01

    The over 10,000-km long Atlantic margin of Africa is divisible into thirty basins or segments of the margin that collectively contain over 18.6 x 10/sup 6/ km/sup 3/ of syn-breakup and post-breakup sediments. Twenty of these basins contain a sufficiently thick volume of sediments to be considered prospects. These basins lie, at least partially, within the 200 m isobath. The distribution of source rocks is broad enough to give potential to each of these basins. The sedimentation patterns, tectonics, and timing of events differ from basin to basin and are related directly to the margin's complex history. Two spreading modes exist: rift and transform. Rifting dates from Late Triassic-Early Jurassic in the northwest to Early Cretaceous south of the Niger Delta. A complex transform fault system separated these two margins. Deep-water communication between the two basins became established in the middle Cretaceous. This Mesozoic-Cenozoic cycle of rifting and seafloor spreading has segmented the margin and where observable, basins tend to be bounded by these segments.

  1. Basin Analysis and Petroleum System Characterisation of Western Bredasdorp Basin, Southern Offshore of South Africa: Insights from a 3d Crust-Scale Basin Model - (Phase 1)

    NASA Astrophysics Data System (ADS)

    Sonibare, W. A.; Scheck-Wenderoth, M.; Sippel, J.; Mikeš, D.

    2012-04-01

    In recent years, construction of 3D geological models and their subsequent upscaling for reservoir simulation has become an important tool within the oil industry for managing hydrocarbon reservoirs and increasing recovery rate. Incorporating petroleum system elements (i.e. source, reservoir and trap) into these models is a relatively new concept that seems very promising to play/prospect risk assessment and reservoir characterisation alike. However, yet to be fully integrated into this multi-disciplinary modelling approach are the qualitative and quantitative impacts of crust-scale basin dynamics on the observed basin-fill architecture and geometries. The focus of this study i.e. Western Bredasdorp Basin constitutes the extreme western section of the larger Bredasdorp sub-basin, which is the westernmost depocentre of the four southern Africa offshore sub-basins (others being Pletmos, Gamtoos and Algoa). These basins, which appear to be initiated by volcanically influenced continental rifting and break-up related to passive margin evolution (during the Mid-Late Jurassic to latest Valanginian), remain previously unstudied for crust-scale basin margin evolution, and particularly in terms of relating deep crustal processes to depo-system reconstruction and petroleum system evolution. Seismic interpretation of 42 2D seismic-reflection profiles forms the basis for maps of 6 stratigraphic horizons which record the syn-rift to post-rift (i.e. early drift and late drift to present-day seafloor) successions. In addition to this established seismic markers, high quality seismic profiles have shown evidence for a pre-rift sequence (i.e. older than Late Jurassic >130 Ma). The first goal of this study is the construction of a 3D gravity-constrained, crust-scale basin model from integration of seismics, well data and cores. This basin model is constructed using GMS (in-house GFZ Geo-Modelling Software) while testing its consistency with the gravity field is performed using IGMAS

  2. Contemporary surface ruptures in the zone of the Baikal-Mondy fault (Baikal rift system): dynamics of formation and origin

    NASA Astrophysics Data System (ADS)

    Sankov, Vladimir; Sankov, Aleksei; Lebedeva, Marina; Ashurkov, Sergey; Parfeevets, Anna

    2014-05-01

    Sublatitudinal Baikal-Mondy (Tunka) left-lateral strike-slip fault accommodates North Mongolia submeridional rift basins opening (Darkhad and Khubsugul). It is the connecting link between the central and south-western parts of the Baikal rift system. We investigated the present-day activity of faulting on southern border of Mondy basin, which is due to their position at the junction of east-west trending active faults of the Baikal-Mondy fault system with submeridional structures of Khubsugul basin. The investigated area is characterized by high seismic activity. The epicenter of one of the strongest Mondy earthquake 1950 (Mw = 7.0) is located within the Mondy basin. Reconstruction of Late Cenozoic tectonic stress field shows a predominance of strike-slip deformation regime with NW-SE direction of the minimum compression axis and NE-SW direction of the maximum compression axis, which correlates with the present-day stress field derived from the data on earthquake focal mechanisms. On the top of the southern shoulder of Mondy basin a series of extended NE trending surface ruptures that cut the crust of weathering and bedrock across the local watershed were discovered. The rupture length reaches 180 m, width ruptures bedrock reaches 0.6 m. In the bedrock tectonic microfractures of NW and NE directions are dominated, but the NW trending surface ruptures are not observed. In the area of contemporary ruptures the geodetic measurements were carried out in the period 2009-2013. The results of processing the measurement data on the local testing ground showed that most divergent baselines undergoes extension with maximum values reaching 30 mm/year. The block experienced elongation in all directions, but the morphology of ruptures suggests that the main direction of stretching is NW-SE. The intensity of cracks opening decreases markedly with time. According to eyewitnesses known that active crack opening at about 100 mm/year started 4 years before Kultuk earthquake (27

  3. TerraSAR-X high-resolution radar remote sensing: an operational warning system for Rift Valley fever risk.

    PubMed

    Vignolles, Cécile; Tourre, Yves M; Mora, Oscar; Imanache, Laurent; Lafaye, Murielle

    2010-11-01

    In the vicinity of the Barkedji village (in the Ferlo region of Senegal), the abundance and aggressiveness of the vector mosquitoes for Rift Valley fever (RVF) are strongly linked to rainfall events and associated ponds dynamics. Initially, these results were obtained from spectral analysis of high-resolution (~10 m) Spot-5 images, but, as a part of the French AdaptFVR project, identification of the free water dynamics within ponds was made with the new high-resolution (down to 3-meter pixels), Synthetic Aperture Radar satellite (TerraSAR-X) produced by Infoterra GmbH, Friedrichshafen/Potsdam, Germany. During summer 2008, within a 30 x 50 km radar image, it was found that identified free water fell well within the footprints of ponds localized by optical data (i.e. Spot-5 images), which increased the confidence in this new and complementary remote sensing technique. Moreover, by using near real-time rainfall data from the Tropical Rainfall Measuring Mission (TRMM), NASA/JAXA joint mission, the filling-up and flushing-out rates of the ponds can be accurately determined. The latter allows for a precise, spatio-temporal mapping of the zones potentially occupied by mosquitoes capable of revealing the variability of pond surfaces. The risk for RVF infection of gathered bovines and small ruminants (~1 park/km(2)) can thus be assessed. This new operational approach (which is independent of weather conditions) is an important development in the mapping of risk components (i.e. hazards plus vulnerability) related to RVF transmission during the summer monsoon, thus contributing to a RVF early warning system. PMID:21080318

  4. Rift Valley Fever Virus Nonstructural Protein NSs Promotes Viral RNA Replication and Transcription in a Minigenome System

    PubMed Central

    Ikegami, Tetsuro; Peters, C. J.; Makino, Shinji

    2005-01-01

    Rift Valley fever virus (RVFV), which belongs to the genus Phlebovirus, family Bunyaviridae, has a tripartite negative-strand genome (S, M, and L segments) and is an important mosquito-borne pathogen for domestic animals and humans. We established an RVFV T7 RNA polymerase-driven minigenome system in which T7 RNA polymerase from an expression plasmid drove expression of RNA transcripts for viral proteins and minigenome RNA transcripts carrying a reporter gene between both termini of the M RNA segment in 293T cells. Like other viruses of the Bunyaviridae family, replication and transcription of the RVFV minigenome required expression of viral N and L proteins. Unexpectedly, the coexpression of an RVFV nonstructural protein, NSs, with N and L proteins resulted in a significant enhancement of minigenome RNA replication. Coexpression of NSs protein with N and L proteins also enhanced minigenome mRNA transcription in the cells expressing viral-sense minigenome RNA transcripts. NSs protein expression increased the RNA replication of minigenomes that originated from S and L RNA segments. Enhancement of minigenome RNA synthesis by NSs protein occurred in cells lacking alpha/beta interferon (IFN-α/β) genes, indicating that the effect of NSs protein on minigenome RNA replication was unrelated to a putative NSs protein-induced inhibition of IFN-α/β production. Our finding that RVFV NSs protein augmented minigenome RNA synthesis was in sharp contrast to reports that Bunyamwera virus (genus Bunyavirus) NSs protein inhibits viral minigenome RNA synthesis, suggesting that RVFV NSs protein and Bunyamwera virus NSs protein have distinctly different biological roles in viral RNA synthesis. PMID:15827175

  5. Paleomagnetism and paleointensity of Mid-Continental Rift System basalts at Silver Mountain and Sturgeon River Falls (Upper Michigan)

    NASA Astrophysics Data System (ADS)

    Kulakov, E.; Piispa, E. J.; Laird, M. S.; Smirnov, A. V.; Diehl, J. F.

    2009-12-01

    Paleomagnetic and paleointensity data from Precambrian rocks are of great importance for understanding the early geodynamo and tectonic evolution of the Earth. We will present results from a rock magnetic and paleomagnetic investigation of basaltic lava flow sequences at Silver Mountain and Sturgeon River Falls in Upper Michigan. While the Silver Mountain and Sturgeon River Falls lava flows have not been radiometrically dated, these rocks have been assigned to the Siemens Creek Volcanics, the lowermost member of ~1.1 Ga Powder Mill Group (PMG). The PMG represents one of the oldest volcanic units associated with the Mid-Continental Rift System (MCRS). We sampled 13 lava flows from the Silver Mountain and two lava flows from the Sturgeon River Falls exposures (a minimum of 15 cores per flow were taken). Paleomagnetic directions were determined from detailed thermal and/or alternating field demagnetization preceded by an initial low-temperature (liquid nitrogen) demagnetization. Most specimens revealed a single- or a two-component remanent magnetization. At both locations, the characteristic remanent magnetization (ChRM) has a reversed direction with very steep inclination similar to that found in other rocks representing the early stages of MCRS. Our magnetic hysteresis measurements, unblocking temperature spectra, and scanning electron microscopy analyses suggest low-Ti, pseudosingle-domain titanomagnetite as the principal magnetic carrier in these rocks. For paleointensity determinations, we applied the multispecimen parallel differential pTRM method. These data add to the Precambrian paleointensity database which otherwise remains limited because of alteration and other factors hampering the applicability of conventional Thellier double-heating method.

  6. Pristine Rhyolite Glass Melt Inclusions in Quartz Phenocrysts From the 1.1 Ga Midcontinent Rift System, Keweenaw Peninsula, Michigan

    NASA Astrophysics Data System (ADS)

    Student, J. J.; Wark, D. A.; Mutchler, S. R.; Bodnar, R. J.

    2006-12-01

    Pristine rhyolite glass from the Proterozoic eon is rarely reported in the literature. Glass-bearing melt inclusions (MI) have been identified in quartz phenocrysts from rhyolite cobbles found in rift related conglomerates within the Portage Lake Volcanics (PLV) near Calumet, Michigan. The rhyolites represent an aspect of mantle plume related bi-modal magmatism that is contemporaneous with the 1.1 Ga Midcontinent Rift System (MRS). Previous studies classified felsic rocks from the PLV into two types, one that is similar to Icelandic rhyolites (Type I) and another similar to Cenozoic topaz rhyolites (Type II). The MRS rhyolite magmas are thought to have been at high temperatures (900-1100 °C) and low water contents prior to eruption. Low-grade burial metamorphism and hydrothermal alteration has affected some rocks in the region. The MI in this study have been categorized based on their phase assemblages and preservation history. Type 1 MI contain clear glass and a shrinkage bubble, Type 2 contain clear glass, a shrinkage bubble and 1 or more, coarser grained (> 3 um) crystals, and Type 3 MI are totally devitrified or otherwise breached. The MI range in size from 1 to over 200 um in diameter and have a negative hexagonal bi-pyramidal morphology. Major element oxide compositions (75.4-SiO2, 0.09-TiO2, 11.3-Al2O3, 2.2-FeO, 0.04- MnO, 0.06-MgO, 0.84-CaO, 5.9-K2O and 2.85-Na2O in wt %) determined by EPMA for Type 1 MI are similar to whole rock compositions reported for rhyolites in the MRS. The water contents of MI are low, as evidenced by the high totals (98.67 wt %) from the EPMA and the fact that a water peak was not observed during Raman analysis (indicating that the MI contain less than 1 wt % H2O). LA-ICPMS analysis for additional trace elements (Cu, Rb, Sr, Zr, Nb, Cs, Ba, La, Ce, Eu, Yb, Ta, Th and U) were preformed on both Type 1 and Type 2 MI. Discrimination based on Ba/Rb and Ba/Th indicate that the MI are most similar to the Type II rhyolites in the region

  7. East African Rift

    NASA Technical Reports Server (NTRS)

    2008-01-01

    Places where the earth's crust has formed deep fissures and the plates have begun to move apart develop rift structures in which elongate blocks have subsided relative to the blocks on either side. The East African Rift is a world-famous example of such rifting. It is characterized by 1) topographic deep valleys in the rift zone, 2) sheer escarpments along the faulted walls of the rift zone, 3) a chain of lakes within the rift, most of the lakes highly saline due to evaporation in the hot temperatures characteristic of climates near the equator, 4) voluminous amounts of volcanic rocks that have flowed from faults along the sides of the rift, and 5) volcanic cones where magma flow was most intense. This example in Kenya displays most of these features near Lake Begoria.

    The image was acquired December 18, 2002, covers an area of 40.5 x 32 km, and is located at 0.1 degrees north latitude, 36.1 degrees east longitude.

    The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

  8. Differentiating climatic- and tectonic-controlled lake margin in rift system: example of the Plio-Quaternary Nachukui Formation, Turkana depression, Kenya

    NASA Astrophysics Data System (ADS)

    Alexis, Nutz; Mathieu, Schuster; Abdoulaye, Balde; Jean-Loup, Rubino

    2016-04-01

    The Turkana Depression is part of the eastern branch of the East African Rift System. This area consists of several Oligo-Pliocene north-south oriented half-grabens that connect the Ethiopian and Kenyan rift valleys. Exposed on the west side of the Lake Turkana, the Nachukui Formation represents a Plio-Quaternary syn-rift succession mainly outcropping near the border fault of the North Lake basin. This Formation consists of a > 700 m thick fluvial-deltaic-lacustrine sediments deposited in this area between 4.2 and 0.5 Ma. In this contribution, we present preliminary results from the investigation of the complete succession based on field geology. Facies description and sequence analyses are provided focusing on lake margin evolution through time and deciphering their controlling factors. Two main types of facies association can be distinguished in the Nachukui Fm and reveal two main types of lake margins that alternatively developed in the Turkana basin. Type-1 is characterized by thick conglomeratic proximal alluvial fan fining laterally from the border fault to the central portion of the lake to gravelly distal alluvial fan. Conglomerate and gravel beds display recurrent wave reworking (ripples, clasts sorting, open-work), as well as intercalated shells placer and stromatolites beds. Laterally, facies rapidly grade to offshore siliciclastic muds. These facies are interpreted as aggrading and prograding coarse fan deltas that entered directly in the lake. Their subaqueous parts were then affected by waves and allowed the development of shell placers and stromatolite reefs. This facies association is generally included in thick packages representing long-term prograding trends of several hundred thousand years duration (> 500 ka). Type-2 is characterized by poorly developed alluvial fan near the border fault, rapidly grading laterally to a fluvial plain and then to well-developed wave-dominated coast (beaches, washover fans, coastal wedges), finally connected to

  9. InSAR observations of post-rifting deformation around the Dabbahu rift segment, Afar, Ethiopia

    NASA Astrophysics Data System (ADS)

    Hamling, Ian J.; Wright, Tim J.; Calais, Eric; Lewi, Elias; Fukahata, Yukitoshi

    2014-04-01

    Increased displacement rates have been observed following manylarge earthquakes and magmatic events. Although an order of magnitude smaller than the displacements associated with the main event, the post-seismic or post-rifting deformation may continue for years to decades after the initial earthquake or dyke intrusion. Due to the rare occurrence of subaerial rifting events, there are very few observations to constrain models of post-rifting deformation. In 2005 September, a 60-km-long dyke was intruded along the Dabbahu segment of the Nubia-Arabia Plate boundary (Afar, Ethiopia), marking the beginning of an ongoing rifting episode. Continued activity has been monitored using satellite radar interferometry and data from global positioning system instruments deployed around the rift in response to the initial intrusion. Using multiple satellite passes, we are able to separate the rift perpendicular and vertical displacement fields around the Dabbahu segment. Rift perpendicular and vertical rates of up to 180 and 240 mm yr-1, respectively. Here, we show that models of viscoelastic relaxation alone are insufficient to reproduce the observed deformation field and that a large portion of the observed signal is related to the movement of magma within the rift segment. Our models suggest upper mantle viscosities of 1018-19 Pa s overlain by an elastic crust of between 15 and 30 km. To fit the observations, inflation and deflation of magma chambers in the centre of the rift and to the south east of the rift axis is required at rates of ˜0.13 and -0.08 km3 yr-1.

  10. A Top to Bottom Lithospheric Study of Africa and Arabia

    SciTech Connect

    Pasyanos, M

    2006-10-31

    We study the lithospheric structure of Africa, Arabia and adjacent oceanic regions with fundamental-mode surface waves over a wide period range. Including short period group velocities allows us to examine shallower features than previous studies of the whole continent. In the process, we have developed a crustal thickness map of Africa. Main features include crustal thickness increases under the West African, Congo, and Kalahari cratons. We find crustal thinning under Mesozoic and Cenozoic rifts, including the Benue Trough, Red Sea, and East, Central, and West African rift systems. Crustal shear wave velocities are generally faster in oceanic regions and cratons, and slower in more recent crust and in active and formerly active orogenic regions. Deeper structure, related to the thickness of cratons and modern rifting, is generally consistent with previous work. Under cratons we find thick lithosphere and fast upper mantle velocities, while under rifts we find thinned lithosphere and slower upper mantle velocities. There are no consistent effects in areas classified as hotspots, indicating that there seem to be numerous origins for these features. Finally, it appears that the African Superswell has had a significantly different impact in the north and the south, indicating specifics of the feature (temperature, time of influence, etc.) to be dissimilar between the two regions. Factoring in other information, it is likely that the southern portion has been active in the past, but that shallow activity is currently limited to the northern portion of the superswell.

  11. Petrofabrics of olivine in a rift axis and rift shoulder and their implications for seismic anisotropy beneath the Rio Grande rift

    NASA Astrophysics Data System (ADS)

    Park, Munjae; Jung, Haemyeong; Kil, Youngwoo

    2015-04-01

    Mantle-derived xenoliths associated with continental rifting can provide important information about the mantle structure and the physicochemical properties of deformation processes in the upper mantle. Metasomatized spinel peridotites from Adam's Diggings (AD) at a rift shoulder and Elephant Butte (EB) at a rift axis in the Rio Grande rift (RGR) were investigated to understand the deformation processes and seismic anisotropy occurring in the upper mantle. As determined through analysis of the lattice preferred orientation (LPO) of olivine by using a scanning electron microscope equipped with electron backscatter diffraction (SEM/EBSD), AD peridotites exhibited C-type LPO of olivine indicating a dominant slip system of (100)[001] at the rift shoulder, whereas EB peridotites exhibited A-type LPO indicating a dominant slip system of (010)[100] at the rift axis. Both geochemical data and microstructural observations indicate that the localized mantle enrichment processes, including melts with hydrous fluids, controlled multiple mantle metasomatisms and deformation of rocks under wet conditions (with olivine C-type LPO) at the rift shoulder (AD), whereas mantle depletion by decompression partial melting caused deformation of rocks under dry conditions (with olivine A-type LPO) at the rift axis (EB). These observations provide evidence for localized hydration and physicochemical heterogeneity of the upper mantle in the Rio Grande rift (RGR) zone. Seismic anisotropy observed beneath this zone can be attributed to the transtensional rupture, such as inhomogeneous stretching, and the petrofabrics of olivine beneath the study area.

  12. Tectono-Sedimentary Analysis of Rift Basins: Insights from the Corinth Rift, Greece

    NASA Astrophysics Data System (ADS)

    Gawthorpe, Robert; Ford, Mary

    2015-04-01

    Existing models for the tectono-sedimentary evolution of rift basins are strongly linked the growth and linkage of normal fault segments and localization of fault activity. Early stages of faulting (rift initiation phase) are characterized by distributed, short, low displacement fault segments, subdued fault-related topography and small depocentres within which sedimentation keeps pace with subsidence. Following linkage and displacement localization (rift climax phase), deformation if focused onto major, crustal-scale fault zones with kilometre-scale displacement. These major faults generate pronounced tilted fault-block topography, with subsidence rates that outpace sedimentation causing a pronounced change to deep-water deposition. Such models have been successful in helping to understand the gross structural and sedimentary evolution of rift basins, but recent work has suggested that pre-existing structures, normal fault interaction with pre-rift salt and antecedent drainage systems significantly alter this initiation-to-climax perspective of rift basin development. The E-W-striking, Pliocene-Pleistocene Corinth rift, central Greece, is an excellent natural laboratory for studying the tectono-sedimentary evolution of rift basins due to its young age, excellent onshore exposure of syn-rift structure and stratigraphy and extensive offshore seismic data. The rift cuts across the NW-SE-striking Hellenide mountain belt and has migrated northward and westward during its evolution. The Hellenide mountain belt significantly influences topography and drainage in the west of the rift. High topography and large antecedent drainage systems, focused along palaeovalleys, provided high sediment flux to NE-flowing alluvial systems that overfilled early-rift depocentres. Further east, away from the main antecedent drainage networks, contemporaneous deposits comprise deep-lacustrine turbidite channel and lobe complexes and basinal marls. Thus the stratigraphic expression within

  13. Westward drift, rift asymmetry and continental uplift

    NASA Astrophysics Data System (ADS)

    Doglioni, C.; Carminati, E.; Bonatti, E.

    2003-04-01

    Although not predicted by classic plate tectonics theory, the topography of ocean ridges and rifts show a distinct asymmetry, when depth is plotted both vs. distance from the ridge and square root of the age of the oceanic crust. The eastern sides of the East Pacific Rise, of the mid Atlantic ridge, of the NW Indian ridge are in average more elevated than the conjugate flank to the west and eastern sides show slower subsidence rates. A similar asymmetry can be observed across the Red Sea and Baikal rifts. We suggest that depleted and lighter asthenosphere generated by partial melting below the ocean ridges shifts 'eastward' relative to the lithosphere, determining a density deficit below the eastern flank. The 'eastward' migration of the lighter Atlantic asthenosphere under the African continent, could eventually have contributed to the anomalous post-rift uplift of Africa and explain the anomalously higher topography of Africa with respect to other continents. This model suggests that the 'westward' drift of the lithosphere relative to the underlying mantle might be a global phenomenon and not just a mean delay.

  14. Controls on (anomalous) topography in rifted margin settings

    NASA Astrophysics Data System (ADS)

    Huismans, Ritske S.

    2015-04-01

    Contrasting end members of volcanic and non-volcanic passive margin formation show a large variability in basin shape and structure, subsidence history, and associated topographic evolution of the onshore rifted margins. The large range of structural style and associated topography of these systems imply a strong variability in the underlying thermo-mechanical conditions at the time of rifting. Rift - passive margin styles ranging from narrow to ultra wide are explained using forward numerical models with varying rheological structure, with strong crust lithosphere leading to narrow rift formation associated with highly elevated rift shoulders and conversely weak crust lithosphere resulting in highly stretched wide rifted conjugate margins and little flank morphology. In some cases rifted margins appear to indicate the formation of anomalous post rift topography. A number of mechanisms including small-scale convective removal of the lower lithosphere, lithosphere counter-flow, and dynamic topography, have been invoked to explain the anomalous topography. Forward numerical models are used to predict the magnitude and characteristic topography associated with each of these mechanisms and to evaluate their potential for explaining these apparent anomalous characteristics of rifts and rifted margins.

  15. The First Prediction of a Rift Valley Fever Outbreak

    NASA Technical Reports Server (NTRS)

    Anyamba, Assaf; Chretien, Jean-Paul; Small, Jennifer; Tucker, Compton J.; Formenty, Pierre; Richardson, Jason H.; Britch, Seth C.; Schnabel, David C.; Erickson, Ralph L.; Linthicum, Kenneth J.

    2009-01-01

    El Nino/Southern Oscillation (ENSO) related anomalies were analyzed using a combination of satellite measurements of elevated sea surface temperatures, and subsequent elevated rainfall and satellite derived normalized difference vegetation index data. A Rift Valley fever risk mapping model using these climate data predicted areas where outbreaks of Rift Valley fever in humans and animals were expected and occurred in the Horn of Africa from December 2006 to May 2007. The predictions were subsequently confirmed by entomological and epidemiological field investigations of virus activity in the areas identified as at risk. Accurate spatial and temporal predictions of disease activity, as it occurred first in southern Somalia and then through much of Kenya before affecting northern Tanzania, provided a 2 to 6 week period of warning for the Horn of Africa that facilitated disease outbreak response and mitigation activities. This is the first prospective prediction of a Rift Valley fever outbreak.

  16. Rift Valley Fever (RVF)

    MedlinePlus

    ... Outbreak resources, VHF information for specific groups, virus ecology, references... RVF Distribution Map Rift Valley Fever Transmission ... Outbreaks Outbreak Summaries RVF Distribution Map Resources Virus Ecology File Formats Help: How do I view different ...

  17. Low-temperature evolution of the Morondava rift basin shoulder in western Madagascar: An apatite fission track study

    NASA Astrophysics Data System (ADS)

    Giese, JöRg; Seward, Diane; Schreurs, Guido

    2012-04-01

    The evolution of the rift shoulder and the sedimentary sequence of the Morondava basin in western Madagascar was mainly influenced by a Permo-Triassic continental failed rift (Karroo rift), and the early Jurassic separation of Madagascar from Africa. Karroo deposits are restricted to a narrow corridor along the basement-basin contact and parts of this contact feature a steep escarpment. Here, apatite fission track (AFT) analysis of a series of both basement and sediment samples across the escarpment reveals the low-temperature evolution of the exhuming Precambrian basement in the rift basin shoulder and the associated thermal evolution of the sedimentary succession. Seven basement and four Karroo sediment samples yield apparent AFT ages between ˜330 and ˜215 Ma and ˜260 and ˜95 Ma, respectively. Partially annealed fission tracks and thermal modeling indicate post-depositional thermal overprinting of both basement and Karroo sediment. Rocks presently exposed in the rift shoulder indicate temperatures of >60°C associated with this reheating whereby the westernmost sample in the sedimentary plain experienced almost complete resetting of the detrital apatite grains at temperatures of about ˜90-100°C. The younging of AFT ages westward indicates activity of faults, re-activating inherited Precambrian structures during Karroo sedimentation. Furthermore, our data suggest onset of final cooling/exhumation linked to (1) the end of Madagascar's drift southward relative to Africa during the Early Cretaceous, (2) activity of the Marion hot spot and associated Late Cretaceous break-up between Madagascar and India, and (3) the collision of India with Eurasia and subsequent re-organization of spreading systems in the Indian Ocean.

  18. Rift Valley fever Entomology, Ecology, and Outbreak Risk Factors

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a mosquito-borne zoonotic disease of domestic ruminants and humans in Africa. The disease is most severe in cattle, sheep, and goats, and it causes high mortality in young animals and abortion in adults. Exotic aanimal breeds from areas where RVF is not endemic tend to be ...

  19. Rift Valley Fever Overview and Recent Developments at USDA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a mosquito-borne viral disease with significant health and economic impacts to domestic animals and humans in much of sub-Saharan Africa. Human infections are believed to occur mainly from mosquito bites and from infectious aerosols. The available strategies for protection...

  20. Predicting the Next Outbreak of Rift Valley Fever (RVF)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a mosquito-borne zoonotic disease of domestic ruminants in Africa. The disease is most severe in cattle, sheep, and goats, and it causes high mortality in young animals and abortion in adults. Exotic aanimal breeds from areas where RVF is not endemic tend to be more suscep...

  1. Potential for Rift Valley to be Introduced into North America

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a mosquito-borne zoonotic disease of domestic ruminants in Africa. The disease is most severe in cattle, sheep, and goats, causing mortality in young animals and abortion in adults. Human infection causes significant morbidity and mortality. RVF occurs in sub-Saharan Afri...

  2. Potential Effects of Rift Valley Fever in the United States

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever virus (RVFV) has been the cause of disease outbreaks throughout Africa and the Arabian Peninsula, and the infection often results in heavy economic costs through loss of livestock. If RVFV, which is common to select agent lists of the US Department of Health and Human Services and ...

  3. Using Lake Superior Parks to Present the Midcontinent Rift

    NASA Astrophysics Data System (ADS)

    Stein, C. A.; Stein, S. A.; Blavascunas, E.

    2014-12-01

    Some of the Midwest's most spectacular scenery occurs near Lake Superior, in places like Pictured Rocks and Apostle Islands National Lakeshores, Isle Royale National Park, Interstate Park, and Porcupine Mountains State Park. These landscapes provide an enormous, but underutilized opportunity for park interpreters and educators to explain some of the most exciting concepts of modern geology. A crucial aspect of doing this is recognizing that many of the rocks and landforms in individual parks are pieces of a huge regional structure. This structure, called the Midcontinent Rift System (MCRS), is a 1.1 billion year old 3000 km (2000 mile) long scar along which the North American continent started to tear apart, just as Africa is splitting today along the East African Rift, but for some reason failed to form a new ocean. Drawing on our experience as researchers and teachers studying the MCRS (Steins) and as an interpreter at Isle Royale National Park (Blavascunas), we seek to give interpreters a brief introduction to MCRS to help them present information about what geologists know already and what they are learning from continuing research. Our goal is to help interpreters visualize how what they see at a specific site fits into an exciting regional picture spanning much of the Midwest.

  4. An updated global earthquake catalogue for stable continental regions: reassessing the correlation with ancient rifts

    NASA Astrophysics Data System (ADS)

    Schulte, Saskia M.; Mooney, Walter D.

    2005-06-01

    We present an updated global earthquake catalogue for stable continental regions (SCRs; i.e. intraplate earthquakes) that is available on the Internet. Our database contains information on location, magnitude, seismic moment and focal mechanisms for over 1300 M (moment magnitude) >= 4.5 historic and instrumentally recorded crustal events. Using this updated earthquake database in combination with a recently published global catalogue of rifts, we assess the correlation of intraplate seismicity with ancient rifts on a global scale. Each tectonic event is put into one of five categories based on location: (i) interior rifts/taphrogens, (ii) rifted continental margins, (iii) non-rifted crust, (iv) possible interior rifts and (v) possible rifted margins. We find that approximately 27 per cent of all events are classified as interior rifts (i), 25 per cent are rifted continental margins (ii), 36 per cent are within non-rifted crust (iii) and 12 per cent (iv and v) remain uncertain. Thus, over half (52 per cent) of all events are associated with rifted crust, although within the continental interiors (i.e. away from continental margins), non-rifted crust has experienced more earthquakes than interior rifts. No major change in distribution is found if only large (M>= 6.0) earthquakes are considered. The largest events (M>= 7.0) however, have occurred predominantly within rifts (50 per cent) and continental margins (43 per cent). Intraplate seismicity is not distributed evenly. Instead several zones of concentrated seismicity seem to exist. This is especially true for interior rifts/taphrogens, where a total of only 12 regions are responsible for 74 per cent of all events and as much as 98 per cent of all seismic moment released in that category. Of the four rifts/taphrogens that have experienced the largest earthquakes, seismicity within the Kutch rift, India, and the East China rift system, may be controlled by diffuse plate boundary deformation more than by the presence

  5. An updated global earthquake catalogue for stable continental regions: Reassessing the correlation with ancient rifts

    USGS Publications Warehouse

    Schulte, S.M.; Mooney, W.D.

    2005-01-01

    We present an updated global earthquake catalogue for stable continental regions (SCRs; i.e. intraplate earthquakes) that is available on the Internet. Our database contains information on location, magnitude, seismic moment and focal mechanisms for over 1300 M (moment magnitude) ??? 4.5 historic and instrumentally recorded crustal events. Using this updated earthquake database in combination with a recently published global catalogue of rifts, we assess the correlation of intraplate seismicity with ancient rifts on a global scale. Each tectonic event is put into one of five categories based on location: (i) interior rifts/taphrogens, (ii) rifted continental margins, (iii) non-rifted crust, (iv) possible interior rifts and (v) possible rifted margins. We find that approximately 27 per cent of all events are classified as interior rifts (i), 25 per cent are rifted continental margins (ii), 36 per cent are within non-rifted crust (iii) and 12 per cent (iv and v) remain uncertain. Thus, over half (52 per cent) of all events are associated with rifted crust, although within the continental interiors (i.e. away from continental margins), non-rifted crust has experienced more earthquakes than interior rifts. No major change in distribution is found if only large (M ??? 6.0) earthquakes are considered. The largest events (M ??? 7.0) however, have occurred predominantly within rifts (50 per cent) and continental margins (43 per cent). Intraplate seismicity is not distributed evenly. Instead several zones of concentrated seismicity seem to exist. This is especially true for interior rifts/taphrogens, where a total of only 12 regions are responsible for 74 per cent of all events and as much as 98 per cent of all seismic moment released in that category. Of the four rifts/taphrogens that have experienced the largest earthquakes, seismicity within the Kutch rift, India, and the East China rift system, may be controlled by diffuse plate boundary deformation more than by the

  6. A recombinant Rift Valley fever virus glycoprotein subunit vaccine confers full protection against Rift Valley fever challenge in sheep

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever virus (RVFV) is a mosquito-borne zoonotic pathogen causing disease outbreaks in Africa and the Arabian Peninsula. The virus has great potential for transboundary spread due to the presence of competent vectors in non-endemic areas. There is currently no fully licensed vaccine suita...

  7. The Precambrian crustal structure of East Africa

    NASA Astrophysics Data System (ADS)

    Tugume, Fred Alex

    In this thesis, the Precambrian crustal structure of East African is investigated along with the crustal structures of three Cenozoic rift basins located in the western branch of the East African Rift System (EARS). In the first part of the thesis, P-wave receiver functions are modeled using the H-k method to obtain new insights about the bulk composition and thickness of the crust for Precambrian terrains throughout East Africa. The average crustal thickness for all but one of the terrains is between 37 and 39 km. An exception is the Ubendian terrain, which has an average crustal thickness 42 km. In all terrains, the average Poisson's ratio is similar, ranging from 0.25 to 0.26, indicating a bulk crustal composition that is felsic to intermediate. The main finding of this study is that crustal structure is similar across all terrains, which span more than 4.0 Ga of earth history. There is no discernable difference in the crustal thicknesses and Poisson's ratios between the Archean and Proterozoic terrains, or between the Proterozoic terrains, unlike the variability in Precambrian crustal structure found in many other continents. In the second part of the thesis, a joint inversion of Rayleigh wave phase and group velocities and receiver functions was used to investigate the shear wave velocity structure of the crust and uppermost mantle beneath the Precambrian terrains of East Africa. In comparison with other areas of similar age in southern and western Africa where the same joint inversion method has been applied, I find that while there is little difference in the mean shear wave velocities for the entire crust across all of the Precambrian terrains, and also few differences in the thickness of the crust, there exists substantial variability in lower crustal structure. This variability is reflected primarily in the thickness of the lower crustal layers with shear wave velocities ≥ 4.0 km/s. This variability is found both within terrains of the same age (i

  8. Volatiles and subduction-recycled lithologies in the petrogenesis of Cenozoic alkaline magmatism in the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

    Aviado, K.; Rilling-Hall, S.; Mukasa, S. B.; Bryce, J. G.; Fahnestock, M. F.

    2015-12-01

    In the West Antarctic Rift System (WARS), the failure of both passive and active models of decompression melting to explain unusually voluminous Cenozoic volcanism has prompted debate about the roles of thermal plume-related melting and ancient subduction-related flux melting. The latter is supported by ~500 Ma of subduction along the paleo-Pacific margin of Gondwana[1], a process capable of generating easily fusible, volatile-rich lithologies and producing the broad seismic low-velocity anomaly imaged beneath the Southern Ocean[2]. We present new geochemical information from submarine lavas in the Ross Sea and subaerial lavas from Franklin Island, Beaufort Island, and Mt. Melbourne in Northern Victoria Land (NVL) supportive of an evolving fluxed mantle source. Lavas exhibit ocean island basalt (OIB)-like trace element signatures and isotopic affinities for the C/FOZO mantle endmember consistent with subduction processing of recycled ocean lithosphere. Lava major-oxide compositions suggest multiple recycled source components, including pyroxenite (associated with older lavas), amphibole-rich metasomes, and volatilized peridotite (associated with the youngest lavas). In-situ analyses of olivine-hosted melt inclusions (MIs) from a subset of host lavas confirm high H2O and CO2 ranging up to 2.94 wt % and 4657 ppm, respectively. MIs exhibit OIB-like trace element compositions and Ba/Rb and Rb/Sr consistent with melting in the presence of hydrated, amphibole-bearing lithosphere[3,4]. We interpret these observations as evidence that ongoing tectonomagmatic activity in the WARS is facilitated by melting of subduction-modified mantle generated by 550 - 100 Ma Gondwana subduction. Following radiogenic ingrowth in high-µ (U/Pb) domains, Cenozoic extension triggered decompression melting of easily fusible, hydrated metasomes and volatilized mantle. This multistage magma model attempts to reconcile geochemical observations with increasing geophysical evidence that the seismic

  9. Young rift kinematics in the Tadjoura rift, western Gulf of Aden, Republic of Djibouti

    NASA Astrophysics Data System (ADS)

    Daoud, Mohamed A.; Le Gall, Bernard; Maury, René C.; Rolet, JoëL.; Huchon, Philippe; Guillou, Hervé

    2011-02-01

    The Tadjoura rift forms the westernmost edge of the westerly propagating Sheba ridge, between Arabia and Somalia, as it enters into the Afar depression. From structural and remote sensing data sets, the Tadjoura rift is interpreted as an asymmetrical south facing half-graben, about 40 km wide, dominated by a large boundary fault zone to the north. It is partially filled up by the 1-3 Myr old Gulf Basalts which onlapped the older Somali Basalts along its shallower southern flexural margin. The major and trace element analysis of 78 young onshore lavas allows us to distinguish and map four distinct basaltic types, namely the Gulf, Somali, Goumarre, and Hayyabley Basalts. These results, together with radiometric age data, lead us to propose a revised volcano-stratigraphic sketch of the two exposed Tadjoura rift margins and to discriminate and date several distinct fault networks of this oblique rift. Morphological and statistical analyses of onshore extensional fault populations show marked changes in structural styles along-strike, in a direction parallel to the rift axis. These major fault disturbances are assigned to the arrest of axial fault tip propagation against preexisting discontinuities in the NS-oriented Arta transverse zone. According to our model, the sinistral jump of rifting into the Asal-Ghoubbet rift segment results from structural inheritance, in contrast with the en échelon or transform mechanism of propagation that prevailed along the entire length of the Gulf of Aden extensional system.

  10. Submarine and subaerial lavas in the West Antarctic Rift System: Temporal record of shifting magma source components from the lithosphere and asthenosphere

    NASA Astrophysics Data System (ADS)

    Aviado, Kimberly B.; Rilling-Hall, Sarah; Bryce, Julia G.; Mukasa, Samuel B.

    2015-12-01

    The petrogenesis of Cenozoic alkaline magmas in the West Antarctic Rift System (WARS) remains controversial, with competing models highlighting the roles of decompression melting due to passive rifting, active plume upwelling in the asthenosphere, and flux melting of a lithospheric mantle metasomatized by subduction. In this study, seamounts sampled in the Terror Rift region of the Ross Sea provide the first geochemical information from submarine lavas in the Ross Embayment in order to evaluate melting models. Together with subaerial samples from Franklin Island, Beaufort Island, and Mt. Melbourne in Northern Victoria Land (NVL), these Ross Sea lavas exhibit ocean island basalt (OIB)-like trace element signatures and isotopic affinities for the C or FOZO mantle endmember. Major-oxide compositions are consistent with the presence of multiple recycled lithologies in the mantle source region(s), including pyroxenite and volatile-rich lithologies such as amphibole-bearing, metasomatized peridotite. We interpret these observations as evidence that ongoing tectonomagmatic activity in the WARS is facilitated by melting of subduction-modified mantle generated during 550-100 Ma subduction along the paleo-Pacific margin of Gondwana. Following ingrowth of radiogenic daughter isotopes in high-µ (U/Pb) domains, Cenozoic extension triggered decompression melting of easily fusible, hydrated metasomes. This multistage magma generation model attempts to reconcile geochemical observations with increasing geophysical evidence that the broad seismic low-velocity anomaly imaged beneath West Antarctica and most of the Southern Ocean may be in part a compositional structure inherited from previous active margin tectonics.

  11. The drainage of Africa since the Cretaceous

    NASA Astrophysics Data System (ADS)

    Goudie, Andrew S.

    2005-04-01

    Much of the drainage of Africa is relatively youthful. Many of its major rivers have shown substantial changes in their courses since the break up of Gondwanaland in the Cretaceous. In addition, many of the rivers have distinctive morphological characteristics such as inland deltas, cataracts and elbows of capture. Tectonic and climatic changes, including the development of the East African Rift System and the aridification of the Quaternary, help to explain the nature of these rivers. The history of the Saharan rivers, the Niger, the Nile, the Congo, the Cunene, the Zambezi, the Limpopo and the Orange, is reviewed.

  12. Petrogenesis of the Ni-Cu-PGE sulfide-bearing Tamarack Intrusive Complex, Midcontinent Rift System, Minnesota

    NASA Astrophysics Data System (ADS)

    Taranovic, Valentina; Ripley, Edward M.; Li, Chusi; Rossell, Dean

    2015-01-01

    The Tamarack Intrusive Complex (TIC, 1105.6 ± 1.2 Ma) in NE Minnesota, was emplaced during the early stages of the development of the Midcontinent Rift System (MRS, "Early Stage": 1110-1106 Ma). Country rocks of the TIC are those of the Paleoproterozoic Thomson Formation, part of the Animikie Group including sulfide-bearing metasedimentary black shale. The magmatic system is composed of at least two principal mafic-ultramafic intrusive sequences: the sulfide-barren Bowl Intrusion in the south and the "dike" area intrusions in the north which host Ni-Cu-Platinum Group Elements (PGE) mineralization with up to 2.33% Ni, 1.24% Cu, 0.34 g/t Pt, 0.23 g/t Pd and 0.18 g/t Au. Two distinct intrusive units in the "dike" area are the CGO (coarse-grained olivine-bearing) Intrusion, a sub-vertical dike-like body, and the overlying sub-horizontal FGO (fine-grained olivine-bearing) Intrusion. Both intrusions comprise peridotite, feldspathic peridotite, feldspathic pyroxenite, melatroctolite and melagabbro. Massive sulfides are volumetrically minor and mainly occur as lenses emplaced into the country rocks associated with both intrusions. Semi-massive (net-textured) sulfides are distributed at the core of the CGO Intrusion, surrounded by a halo of the disseminated sulfides. Disseminated sulfides also occur in lenses along the base of the FGO Intrusion. Olivine compositions in the CGO Intrusion are between Fo89 and Fo82 and in the FGO Intrusion from Fo84 to Fo82. TIC intrusions have more primitive olivine compositions than that of olivine in the sheet-like intrusions in the Duluth Complex (below Fo70), as well as olivine from the smaller, conduit-related, Eagle and East Eagle Intrusions in Northern Michigan (Fo86 to Fo75). The FeO/MgO ratios of the CGO and FGO Intrusion parental magmas, inferred from olivine compositions, are similar to those of picritic basalts erupted during the early stages of the MRS formation. Trace element ratios differ slightly from other intrusions in the

  13. New data on seismic wave attenuation in the lithosphere and upper mantle of the northeastern flank of the Baikal rift system

    NASA Astrophysics Data System (ADS)

    Dobrynina, A. A.; Sankov, V. A.; Chechelnitsky, V. V.

    2016-05-01

    The investigation data on seismic wave attenuation in the lithosphere and upper mantle of the northeastern flank of the Baikal rift system obtained with a seismic coda envelope and sliding window are considered. Eleven local districts were described by one-dimensional attenuation models characterized by alternation of high and low attenuation layers, which are consistent with the results obtained previously by Yu.F. Kopnichev for the southwestern flank of the Baikal rift system [9]. The subcrust of the lithosphere contains a thin layer with high attenuation of seismic waves likely related to higher heterogeneity (fragmentation) and occurrence of fluids. The lithosphere basement depth varies from 100-120 km in the west within the Baikal folded area to 120-140 km in the east within the Siberian Platform. It is concluded that there are two asthenosphere layers. Based on specific features of the lithosphere and upper mantle structure, it can be assumed that they were subject to gradual modification involving fluidization processes and partial melting in the Late Cenozoic extension under the influence of distant tectogenesis sources.

  14. Inheritance and refertilization of Upper Mantle rocks in Alpine type orogens and rift systems: what and why

    NASA Astrophysics Data System (ADS)

    Muntener, O.

    2015-12-01

    Mantle peridotites and their serpentinized counterparts from ocean-continent transition zones (OCT's) and (ultra-) slow spreading ridges question a series of 'common beliefs' that have been applied to understand Alpine-type collisional orogens in the framework of the ophiolite concept. I will show that inherited mantle signatures play a key role for the interpretation of ophiolites, and similar processes are relevant for present-day passive margins. Field data and petrology demonstrates that ancient, thermally undisturbed, pyroxenite-veined subcontinental mantle formed parts of the ocean floor next to thinned continental crust. These heterogeneities might comprise an ancient subduction component. Mantle upwelling and decompression melting during rifting forms partial melts that enter a thick conductive lithospheric mantle and inevitably leads to freezing of the melt and refertilization of the lithospheric mantle. Mafic bodies (gabbros, basalts) are small and discontinous. The abundance of plagioclase peridotites in the Alpine ophiolites and elswhere along rifted margins are interpreted as recorders of refertilization processes related to thinning and exhumation of mantle lithosphere. Similar features are found (ultra-) slow spreading ridges. Another important result is the discovery of extremely refractory Nd-isotopic compositions with highly radiogenic 147Sm/144Nd, which indicates that partial melting processes and Jurassic magmatism in the Western Tethys are locally decoupled. Although the isotopic variability along ridges is generally explained by mantle heterogeneities such as pyroxenites, an alternative is that these depleted domains represent snapshots of melting processes that are related to Permian and/or even older crust forming processes, and during the most recent decompression they were unffected by (further) melting. Similarly, refractory rocks from rifted margins and (ultra-) slow spreading ridges have been interpreted to represent ancient melting

  15. Upper Devonian depositional system of Bel'kov Island (New Siberian Islands): An intracontinental rift or a continental margin?

    NASA Astrophysics Data System (ADS)

    Danukalova, M. K.; Kuzmichev, A. B.; Aristov, V. A.

    2014-09-01

    The archipelago of New Siberian Islands situated on the northeastern continental shelf of Eurasia is considered a part of an exotic terrane that collided with Siberia in the Early Cretaceous. Bel'kov Island is located close to the inferred western boundary of this terrane and thus should demonstrate attributes of its localization at the margin of the Paleozoic oceanic basin. The Upper Devonian section on Bel'kov Island is a continuous sequence of deepwater terrigenous rocks, which indicates a tendency toward deepening of the basin previously revealed on adjacent Kotel'ny Island. The lowermost Upper Devonian unit on Bel'kov Island is represented by thin Domanik-like strata resting on the Middle Devonian carbonate platform. The main body of the Upper Devonian sequence, more than 4 km in total thickness, is made up of gravity-flow sediments including turbidites, clay and block diamictites, and olistostromes in the upper part of the section, which accumulated at the slope of the basin or its rise. At many levels, these sediments have been redeposited by along-slope currents. The uppermost unit of organogenic limestone is evidence for compensation of the trough. According to conodont assemblages, the deepwater terrigenous rocks were deposited from the early Frasnian to the early Tournaisian. This time is known for extensive rifting in the eastern Siberian Platform. The data obtained allowed us to reconstruct a NNW-trending Late Devonian rift basin on the Laptev Sea shelf similar to other rifts at the eastern margin of the Siberian Platform.

  16. Antecedent rivers and early rifting: a case study from the Plio-Pleistocene Corinth rift, Greece

    NASA Astrophysics Data System (ADS)

    Hemelsdaël, Romain; Ford, Mary; Malartre, Fabrice

    2016-04-01

    Models of early rifting present syn-rift sedimentation as the direct response to the development of normal fault systems where footwall-derived drainage supplies alluvial to lacustrine sediments into hangingwall depocentres. These models often include antecedent rivers, diverted into active depocentres and with little impact on facies distributions. However, antecedent rivers can supply a high volume of sediment from the onset of rifting. What are the interactions between major antecedent rivers and a growing normal fault system? What are the implications for alluvial stratigraphy and facies distributions in early rifts? These questions are investigated by studying a Plio-Pleistocene fluvial succession on the southern margin of the Corinth rift (Greece). In the northern Peloponnese, early syn-rift deposits are preserved in a series of uplifted E-W normal fault blocks (10-15 km long, 3-7 km wide). Detailed sedimentary logging and high resolution mapping of the syn-rift succession (400 to 1300 m thick) define the architecture of the early rift alluvial system. Magnetostratigraphy and biostratigraphic markers are used to date and correlate the fluvial succession within and between fault blocks. The age of the succession is between 4.0 and 1.8 Ma. We present a new tectonostratigraphic model for early rift basins based on our reconstructions. The early rift depositional system was established across a series of narrow normal fault blocks. Palaeocurrent data show that the alluvial basin was supplied by one major sediment entry point. A low sinuosity braided river system flowed over 15 to 30 km to the NE. Facies evolved downstream from coarse conglomerates to fined-grained fluvial deposits. Other minor sediment entry points supply linked and isolated depocentres. The main river system terminated eastward where it built stacked small deltas into a shallow lake (5 to 15 m deep) that occupied the central Corinth rift. The main fluvial axis remained constant and controlled

  17. Distribution of fault activity in the early stages of continental breakup: an analysis of faults and volcanic products of the Natron Basin, East African Rift, Tanzania

    NASA Astrophysics Data System (ADS)

    Muirhead, J. D.; Kattenhorn, S. A.

    2012-12-01

    Recent magmatic-tectonic crises in Ethiopia (e.g. 2005 Dabbahu rifting episode, Afar) have informed our understanding of the spatial and temporal distribution of strain in magmatic rifts transitioning to sea-floor spreading. However, the evolving contributions of magmatic and tectonic processes during the initial stages of rifting, is a subject of ongoing debate. The <5 Ma northern Tanzania and southern Kenya sectors of the East Africa Rift provide ideal locations to address this problem. We present preliminary findings from an investigation of fault structures utilizing aerial photography and satellite imagery of the ~35 km wide Natron rift-basin in northern Tanzania. Broad-scale structural mapping will be supplemented by field observations and 40Ar-39Ar dating of lava flows cut by faults to address three major aspects of magma-assisted rifting: (1) the relative timing of activity between the border fault and smaller faults distributed across the width of the rift; (2) time-averaged slip rates along rift-zone faults; and (3) the spatial distribution of faults and volcanic products, and their relative contributions to strain accommodation. Preliminary field observations suggest that the ~500 m high border fault system along the western edge of the Natron basin is either inactive or has experienced a reduced slip rate and higher recurrence interval between surface-breaking events, as evidence by a lack of recent surface-rupture along the main fault escarpments. An exception is an isolated, ~2 km-long segment of the Natron border fault, which is located in close proximity (< 5km) to the active Oldoinyo Lengai volcano. Here, ~10 m of seemingly recent throw is observed in volcaniclastic deposits. The proximity of the fault segment to Oldoinyo Lengai volcano and the localized distribution of fault-slip are consistent with magma-assisted faulting. Faults observed within the Natron basin and on the flanks of Gelai volcano, located on the eastern side of the rift, have

  18. Investing in health systems for universal health coverage in Africa

    PubMed Central

    2014-01-01

    adopt the 2014 Luanda Commitment on UHC in Africa as their long-term vision and back it with sound policies and plans with clearly engrained road maps for strengthening national health systems and addressing the social determinants of health. PMID:25345988

  19. The Astronomy of Africa's Health Systems Literature During the MDG Era: Where Are the Systems Clusters?

    PubMed

    Phillips, James F; Sheff, Mallory; Boyer, Christopher B

    2015-09-01

    Growing international concern about the need for improved health systems in Africa has catalyzed an expansion of the health systems literature. This review applies a bibliometric procedure to analyze the acceleration of scientific writing on this theme. We focus on research published during the Millennium Development Goal (MDG) era between 1990 and 2014, reporting findings from a systematic review of a database comprised of 17,655 articles about health systems themes from sub-Saharan African countries or subregions. Using bibliometric tools for co-word textual analysis, we analyzed the incidence and associations of keywords and phrases to generate and visualize topical foci on health systems as clusters of themes, much in the manner that astronomers represent groupings of stars as galaxies of celestial entities. The association of keywords defines their relative position, with the size of images weighted by the relative frequency of terms. Sets of associated keywords are arrayed as stars that cluster as "galaxies" of concepts in the knowledge universe represented by health systems research from sub-Saharan Africa. Results show that health systems research is dominated by literature on diseases and categorical systems research topics, rather than on systems science that cuts across diseases or specific systemic themes. Systems research is highly developed in South Africa but relatively uncommon elsewhere in the region. "Black holes" are identified by searching for terms in our keyword library related to terms in widely cited reviews of health systems. Results identify several themes that are unexpectedly uncommon in the country-specific health systems literature. This includes research on the processes of achieving systems change, the health impact of systems strengthening, processes that explain the systems determinants of health outcomes, or systematic study of organizational dysfunction and ways to improve system performance. Research quantifying the relationship

  20. Development of Enzyme-Linked Immunosorbent Assays Using Expressed Proteins of Rift Valley Fever Virus

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever virus (RVFV) is a member of the genus Phlebovirus, family Bunyaviridae that can cause severe disease in both humans and animals. The disease is enzootic in sub-Saharan Africa and RVFV epidemics/epizootics occur periodically, primarily in eastern and southern Africa. Since the virus...

  1. Terrestrial heat flow in east and southern Africa

    NASA Astrophysics Data System (ADS)

    Nyblade, Andrew A.; Pollack, Henry N.; Jones, D. L.; Podmore, Francis; Mushayandebvu, Martin

    1990-10-01

    -skinned thrusting of the Mozambique Belt over the Tanzania Cratonic margin, (3) by lateral heat transfer from beneath the rift flanks into the rifts, or (4) by lower mantle heat flow beneath all of eastern Africa prior to the Cenozoic development of the East African rift system.

  2. Rift initiation with volatiles and magma

    NASA Astrophysics Data System (ADS)

    Ebinger, Cynthia; Muirhead, James; Roecker, Steve; Tiberi, Christel; Muzuka, Alfred; Ferdinand, Rrichard; Mulibo, Gabrile; Kianji, Gladys

    2015-04-01

    Rift initiation in cratonic lithosphere remains an outstanding problem in continental tectonics, but strain and magmatism patterns in youthful sectors of the East African rift provide new insights. Few teleseisms occur in the Eastern rift arm of the East African rift system, except the southernmost sector in northern Tanzania where extension occurs in Archaean lithosphere. The change in seismic energy release occurs over a narrow along-axis zone, and between sectors with and without volcanoes in the central rift valley. Are these differences in strain behavior indicative of along-strike variations in a) rheology; b) strain transfer from border faults to magma intrusion zones; c) dike vs fault slip; and/or d) shallow vs deep magma chambers? We present time-space relations of seismicity recorded on a 38-station array spanning the Kenya-Tanzania border, focal mechanisms for the largest events during those time periods, and compare these to longer-term strain patterns. Lower crustal seismicity occurs along the rift length, including sectors on and off craton, and those with and without central rift valley volcanoes, and we see no clear along-strike variation in seismogenic layer thickness. One explanation for widespread lower crustal seismicity is high gas pressures and volatile migration from active metasomatism of upper mantle and magma degassing, consistent with very high volatile flux along fault zones, and widespread metasomatism of xenoliths. Volatile release and migration may be critical to strength reduction of initially cold, strong cratonic lithosphere. Seismicity patterns indicate strain (and fluid?) transfer from the Manyara border fault to Gelai shield volcano (faulting, diking) via Oldoinyo Lengai volcano. Our focal mechanisms and Global CMTs from an intense fault-dike episode (2007) show a local, temporally stable, rotation from ~E-W extension to NE-SE extension in this linkage zone, consistent with longer term patterns recorded in vent and eruptive

  3. Structural and stratigraphic evolution of the Anza rift, Kenya

    NASA Astrophysics Data System (ADS)

    Bosworth, William; Morley, Chris K.

    1994-09-01

    The Anza rift is a large, multi-phase continental rift basin that links the Lamu embayment of southern Kenya with the South Sudan rifts. Extension and deposition of syn-rift sediments are known to have commenced by the Neocomian. Aptian-Albian strata have, thus far, not been encountered during limited drilling campaigns and, in at least one well, are replaced by a significant unconformity. Widespread rifting occurred during the Cenomanian to Maastrichtian, and continued into the Early Tertiary. Marine waters appear to have reached the central Anza rift in the Cenomanian, and a second marine incursion may have occurred during the Campanian. As no wells have yet reached basement in the basinal deeps, the possibility exists that the Anza rift may have initiated in the Late Jurassic, in conjunction with extension to the south in the Lamu embayment and to the north in the Blue Nile rift of Sudan. Structural and stratigraphic evolution in the Anza rift followed a pattern that has now been inferred in several rift settings. Early phases of extension were accommodated by moderately dipping faults that produced large stratal rotations. Sedimentary environments were dominantly fluvial, with associated small lakes and dune fields. Volcanic activity is documented for the early Neocomian, but its extent is unknown. This initial style of deformation and sedimentation may have continued through several of the earliest pulses of rifting. By the Late Cretaceous, a new system of steeply dipping faults was established, that produced a deep basin without significant rotation of strata in the north, and only minor rotation in the south. This basin geometry favored the establishment of large, deep lakes, which occasionally were connected to the sea. The older basins were partly cannibalized during the sedimentary in-filling of these successor basins. Early Senonian volcanism was encountered in one well, and reflection seismic evidence suggests that one or more thick, regionally

  4. Volcanic field elongation, vent distribution and tectonic evolution of continental rift: The Main Ethiopian Rift example

    NASA Astrophysics Data System (ADS)

    Mazzarini, Francesco; Le Corvec, Nicolas; Isola, Ilaria; Favalli, Massimiliano

    2015-04-01

    Magmatism and faulting operate in continental rifts and interact at a variety of scales, however their relationship is complex. The African rift, being the best example for both active continental rifting and magmatism, provides the ideal location to study the interplay between the two mechanisms. The Main Ethiopian Rift (MER), which connects the Afar depression in the north with the Turkana depression and Kenya Rift to the south, consists of two distinct systems of normal faults and its floor is scattered with volcanic fields formed by tens to several hundreds monogenetic, generally basaltic, small volcanoes and composite volcanoes and small calderas. The distribution of vents defines the overall shape of the volcanic field. Previous work has shown that the distribution of volcanic vents and the shape of a field are linked to its tectonic environment and its magmatic system. In order to distinguish the impact of each mechanism, we analyzed four volcanic fields located at the boundary between the central and northern MER, three of them (Debre Zeyit, Wonji and Kone) grew in the rift valley and one (Akaki) on the western rift shoulder. The elongation and shape of the fields were analyzed based on their vent distribution using the Principal Component Analysis (PCA), the Vent-to-Vent Distance (VVD), and the two dimensional symmetric Gaussian kernel density estimate methods. We extracted from these methods several parameters characterizing the spatial distribution of points (e.g., eccentricity (e), eigenvector index (evi), angular dispersion (Da)). These parameters allow to define at least three types of shape for volcanic fields: strong elongate (line and ellipse), bimodal/medium elongate (ellipse) and dispersed (circle) shapes. Applied to the natural example, these methods well differentiate each volcanic field. For example, the elongation of the field increases from shoulder to rift axis inversely to the angular dispersion. In addition, the results show that none of

  5. Investment in South Africa: A Challenge to Schools of Social Work.

    ERIC Educational Resources Information Center

    Brunson, Paul M.

    1980-01-01

    Points out the rift between the non-discrimination ethic of social workers and the apartheid policy in South Africa. University corporate investments in South Africa are questioned, especially those from universities with graduate schools of social work. (LAB)

  6. Geochemistry of hypabyssal rocks of the Midcontinent Rift system in Minnesota, and implications for a Keweenawan magmatic ``family tree``

    SciTech Connect

    Jerde, E.A.

    1998-11-01

    The hypabyssal rocks associated with the Keweenawan (1.1 Ga) Midcontinent Rift along the Minnesota shore of Lake Superior are a distinct suite within the rock associations of this region. These rocks are found predominantly as ophitic diabase dikes and sills of various sizes, ranging from a few meters to several hundred meters across. Chilled margins were sampled and analyzed by neutron activation analysis and microprobe fused-bead techniques for bulk chemistry. Mineral compositions were obtained by electron microprobe. Variations in composition were found that are consistent with fractionation. Major-element modeling of fractionation indicates that the majority of the hypabyssal rocks formed at moderate pressures ({approximately}6 kbar), although a number show evidence of fractionation at near-surface levels, and some deeper ({approximately}10 kbar). Resorption features seen in plagioclase phenocrysts are evidence for magmatic evolution at varying levels in the crust. It is possible to relate the varied hypabyssal rocks to a single primary parent through polybaric fractionation. This parent is a high-Al primitive olivine tholeiite--a magma composition common among the volcanic rocks associated with the Midcontinent Rift. Trace-element modeling with this same parent composition yields results consistent with the formation of some hypabyssal rocks as products of a periodically tapped and replenished, constantly fractionating magma chamber, which can decouple the behavior of major and trace elements.

  7. InSAR and GPS measurements along the Kivu segment of the East African Rift System during the 2011-2012 Nyamulagira volcanic eruption.

    NASA Astrophysics Data System (ADS)

    Nobile, Adriano; Geirsson, Halldor; Smets, Benoît; d'Oreye, Nicolas; Kervyn, François

    2016-04-01

    Along the East African Rift System (EARS), magma intrusions represent a major component in continental rifting. When these intrusions reach the surface, they cause volcanic eruptions. This is the case of the last flank eruption of Nyamulagira, which occurred from November 6 2011 to April 2012. Nyamulagira is an active shield volcano with a central caldera, located in the eastern part of the Democratic Republic of Congo, along the Kivu segment of the East African Rift System. From 1948 to 2012, Nyamulagira mostly showed a particular eruptive cycle with 1) classical short-lived (i.e., 20-30 days) flank eruptions, sometimes accompanied with intracrateral activity, which occurred every 1-4 years on average, and 2) less frequent long-lived (i.e., several months) eruptions usually emitting larger volumes of lava that take place at larger distance (>8 km) from the central caldera. The 2011-2012 Nyamulagira eruption is of that second type. Here we used InSAR data from different satellite (Envisat, Cosmo SkyMed, TerraSAR-X and RADARSAT) to measure pre-, co and post-eruptive ground displacement associated with the Nyamulagira 2011-2012 eruption. Results suggest that a magma intrusion preceded by two days the eruption. This intrusion corresponded to the migration of magma from a shallow reservoir (~3km) below the caldera to the two eruptive fissures located ~11 km ENE of the central edifice. Available seismic data are in agreement with InSAR results showing increased seismic activity since November 4 2011, with long- and short-period earthquakes swarms. Using analytical models we invert the measured ground displacements during the first co-eruptive month to evaluate the deformation source parameters and the mechanism of magma emplacement for this eruption. GPS data from permanent stations in the KivuGNet network are used to constrain the temporal evolution of the eruption and evaluate far-field deformation, while the InSAR data is more sensitive to the near-field deformation

  8. Structure and kinematics of the Taupo Rift, New Zealand

    NASA Astrophysics Data System (ADS)

    Seebeck, Hannu; Nicol, Andrew; Villamor, Pilar; Ristau, John; Pettinga, Jarg

    2014-06-01

    The structure and kinematics of the continental intra-arc Taupo Rift have been constrained by fault-trace mapping, a large catalogue of focal mechanisms (N = 202) and fault slip striations. The mean extension direction of ~137° is approximately orthogonal to the regional trend of the rift and arc front (α = 84° and 79°, respectively) and to the strike of the underlying subducting Pacific Plate. Bending and rollback of the subduction hinge strongly influence the location, orientation, and extension direction of intra-arc rifting in the North Island. In detail, orthogonal rifting (α = 85-90°) transitions northward to oblique rifting (α = 69-71°) across a paleovertical-axis rotation boundary where rift faults, extension directions, and basement fabric rotate by ~20-25°. Toward the south, extension is orthogonal to normal faults which are parallel to, and reactivate, steeply dipping basement fabric. Basement reactivation facilitates strain partitioning with a portion of margin-parallel motion in the overriding plate mainly accommodated east of the rift by strike-slip faults in the North Island Fault System (NIFS). Toward the north where the rift and NIFS intersect, ~4 mm/yr strike slip is transferred into the rift with net oblique extension accommodating a component of margin-parallel motion. The trend and kinematics of the Taupo Rift are comparable to late Miocene-Pliocene intra-arc rifting in the Taranaki Basin, indicating that the northeast strike of the subducting plate and the southeast extension direction have been uniform since at least 4 Ma.

  9. Continental rifting - Progress and outlook

    NASA Technical Reports Server (NTRS)

    Baker, B. H.; Morgan, P.

    1981-01-01

    It is noted that in spite of the flood of new data on continental rifts in the last 15 years, there is little consensus about the basic mechanisms and causes of rifting. The remarkable similarities in rift cross sections (shown in a figure), are considered to suggest that the anomalous lithospheric structure of rifts is more dependent on lithosphere properties than the mode of rifting. It is thought that there is a spectrum of rifting processes for which two fundamental mechanisms can be postulated: an active mechanism, whereby thermal energy is transmitted into the lithosphere from the underlying asthenosphere, and a passive mechanism by which mechanical energy is transmitted laterally through the lithosphere as a consequence of plate interactions at a distance. In order to permit the concept of the two fundamentally different mechanisms to be tested, a tentative classification is proposed that divides rifts into two basic categories: active rifting and passive rifting. Here, the magnitude of active rifting will depend on the rate at which lithosphere moves over the thermal source, with rifts being restricted to stationary or slow-moving plates.

  10. Rift Valley Fever Virus Encephalitis Is Associated with an Ineffective Systemic Immune Response and Activated T Cell Infiltration into the CNS in an Immunocompetent Mouse Model

    PubMed Central

    Dodd, Kimberly A.; McElroy, Anita K.; Jones, Tara L.; Zaki, Sherif R.; Nichol, Stuart T.; Spiropoulou, Christina F.

    2014-01-01

    Background Rift Valley fever virus (RVFV) causes outbreaks of severe disease in livestock and humans throughout Africa and the Arabian Peninsula. In people, RVFV generally causes a self-limiting febrile illness but in a subset of individuals, it progresses to more serious disease. One manifestation is a delayed-onset encephalitis that can be fatal or leave the afflicted with long-term neurologic sequelae. In order to design targeted interventions, the basic pathogenesis of RVFV encephalitis must be better understood. Methodology/Principal Findings To characterize the host immune responses and viral kinetics associated with fatal and nonfatal infections, mice were infected with an attenuated RVFV lacking NSs (ΔNSs) that causes lethal disease only when administered intranasally (IN). Following IN infection, C57BL/6 mice developed severe neurologic disease and succumbed 7–9 days post-infection. In contrast, inoculation of ΔNSs virus subcutaneously in the footpad (FP) resulted in a subclinical infection characterized by a robust immune response with rapid antibody production and strong T cell responses. IN-inoculated mice had delayed antibody responses and failed to clear virus from the periphery. Severe neurological signs and obtundation characterized end stage-disease in IN-inoculated mice, and within the CNS, the development of peak virus RNA loads coincided with strong proinflammatory responses and infiltration of activated T cells. Interestingly, depletion of T cells did not significantly alter survival, suggesting that neurologic disease is not a by-product of an aberrant immune response. Conclusions/Significance Comparison of fatal (IN-inoculated) and nonfatal (FP-inoculated) ΔNSs RVFV infections in the mouse model highlighted the role of the host immune response in controlling viral replication and therefore determining clinical outcome. There was no evidence to suggest that neurologic disease is immune-mediated in RVFV infection. These results provide

  11. Human Dispersals Along the African Rift Valley in the Late Quaternary

    NASA Astrophysics Data System (ADS)

    Tryon, C. A.; Faith, J. T.; Peppe, D. J.

    2014-12-01

    Climate- and tectonic-driven environmental dynamics of the East African Rift System (EARS) during the Quaternary played an important role in the demographic history of early Homo sapiens, including expansions of modern humans across and out of Africa. Human forager population size, geographic range, and behaviors such as hunting strategies and residential mobility likely varied in response to changes in the local and regional environment. Throughout the Quaternary, floral and faunal change was linked at least in part to variations in moisture availability, temperature, and atmospheric CO2, which in addition to uplift and faulting, contributed to the expansion and contraction of a number of large lakes that served as biogeographic barriers to many taxa. This is particularly clear for the Lake Victoria basin, where biogeographic, geological, and paleontological evidence documents repeated expansion and contraction of the ranges of species in response to lake level and vegetation change. Across much of eastern Africa, the topography of the rift facilitated north-south dispersals, the timing of which may have depended in part on the expansion and contraction of the equatorial forest belt. Dispersal potential likely increased during the more arid periods of the late Quaternary, when the roles of lakes and forests as dispersal barriers was reduced and the extent of low net primary productivity dry grasslands increased, the latter requiring large home ranges for human foragers, conditions suitable for range expansions within H. sapiens.

  12. North America's Midcontinent Rift: when Rift MET Lip

    NASA Astrophysics Data System (ADS)

    Stein, C. A.; Stein, S. A.; Kley, J.; Keller, G. R., Jr.; Bollmann, T. A.; Wolin, E.; Zhang, H.; Frederiksen, A. W.; Ola, K.; Wysession, M. E.; Wiens, D.; Alequabi, G.; Waite, G. P.; Blavascunas, E.; Engelmann, C. A.; Flesch, L. M.; Rooney, T. O.; Moucha, R.; Brown, E.

    2015-12-01

    Rifts are segmented linear depressions, filled with sedimentary and igneous rocks, that form by extension and often evolve into plate boundaries. Flood basalts, a class of Large Igneous Provinces (LIPs), are broad regions of extensive volcanism due to sublithospheric processes. Typical rifts are not filled with flood basalts, and typical flood basalts are not associated with significant crustal extension and faulting. North America's Midcontinent Rift (MCR) is an unusual combination. Its 3000-km length formed as part of the 1.1 Ga rifting of Amazonia (Precambrian NE South America) from Laurentia (Precambrian North America) and became inactive once seafloor spreading was established, but contains an enormous volume of igneous rocks. MCR volcanics are significantly thicker than other flood basalts, due to deposition in a narrow rift rather than a broad region, giving a rift geometry but a LIP's magma volume. Structural modeling of seismic reflection data shows an initial rift phase where flood basalts filled a fault-controlled extending basin, and a postrift phase where volcanics and sediments were deposited in a thermally subsiding basin without associated faulting. The crust thinned during rifting and rethickened during the postrift phase and later compression, yielding the present thicker crust. The coincidence of a rift and LIP yielded the world's largest deposit of native copper. This combination arose when a new rift associated with continental breakup interacted with a mantle plume or anomalously hot or fertile upper mantle. Integration of diverse data types and models will give insight into questions including how the magma source was related to the rifting, how their interaction operated over a long period of rapid plate motion, why the lithospheric mantle below the MCR differs only slightly from its surroundings, how and why extension, volcanism, and compression varied along the rift arms, and how successful seafloor spreading ended the rift phase. Papers

  13. A Way Forward: Emerging Perspectives on a National Quality Assurance System for South Africa.

    ERIC Educational Resources Information Center

    Kotecha, P.; Luckett, K.

    2000-01-01

    The final paper in this theme issue summarizes concerns related to establishing a national quality assurance system for institutions of higher education in South Africa. Proposes a three-phase approach to establishing a national quality assurance system to include: (1) evaluation of existing institutional self-evaluation systems; (2) establishment…

  14. How sensitive are sediment routing systems to tectonics and climate? A comparison of sediment fluxes and depositional volumes in the Corinth rift, Greece, over the past 130 ky

    NASA Astrophysics Data System (ADS)

    Watkins, Stephen E.; Whittaker, Alexander C.; Bell, Rebecca E.; McNeill, Lisa C.; Gawthorpe, Robert L.

    2016-04-01

    Sediment supply is a fundamental control on the stratigraphic record. However, a key question is the extent to which tectonics and climate affect sediment fluxes in time and space. To address this question estimates of sediment fluxes must be compared with measured sediment volumes within a closed basin. The Corinth rift in Greece is one of the most actively extending rift basins on Earth, with modern day extension rates of up to 15 mm/yr. The Gulf of Corinth is a closed system and has periodically become a lake during marine lowstands over at least the last 400,000 ky. We have estimated suspended sediment fluxes through time for rivers draining into the Gulf of Corinth using an empirically-derived BQART method. WorldClim climate data, palaeoclimate models and palaeoclimate proxies were used to estimate discharges and temperatures over the last 130 ky. We used high-resolution 2D seismic surveys to interpret the 12 ky highstand, 70 ky lowstand and 130 ky highstand horizons to derive actual basin sedimentary volumes to compare with our sediment input flux estimates. Our results estimate integrated Holocene sediment fluxes into the Gulf of Corinth to be 19 km3 and we constrain how they vary spatially around the Gulf. This number compares exceptionally well with Holocene basin deposit volumes measured from seismic data (30 km3). We estimate sediment fluxes during the last glacial maximum to be significantly lower than the Holocene, likely driven by lower mean annual temperatures. Our results demonstrate that sediment routing systems and sediment export to the Gulf of Corinth is sensitive to glacial-interglacial climate changes from the late Pleistocene to recent.

  15. Deformation rates and localization of an active fault system in relation with rheological and frictional slip properties: The Corinth Rift case

    NASA Astrophysics Data System (ADS)

    El Arem, S.; Lyon-Caen, H.; Bernard, P.; Garaud, J. D.; Rolandone, F.; Briole, P.

    2012-04-01

    The Gulf of Corinth in Greece has attracted increasing attention because of its seismically active complex fault system and considerable seismic hazard. It is one of the most active extensional regions in the Mediterranean area. However, there are still open questions concerning the role and the geometry of the numerous active faults bordering the basin, as well as the mechanisms governing the seismicity. The Corinth Rift Laboratory (CRL http://crlab.eu) project is based on the cooperation of various European institutions that merge their efforts to study fault mechanics and related hazards in this natural laboratory with 10 destructive earthquakes per century (Magnitude > 6), among which 4 in the selected region of CRL. This active rift continues to open over 10-12 Km of width at a rate of 1:5 cm=yr. Most of the faults of the investigated area are in their latest part of cycle, so that the probability of at least one moderate to large earthquake (Magnitude = 6 to 6:7) is very high within a few decades. In the first part of this work, two-dimensional finite element models of a fault system is considered to estimate the effects of the crust rheological parameters on the stress distribution, the horizontal and vertical deformation in the vicinity of the faults, and the plastic deformation localization. We consider elasto-visco-plastic rheology with a power law viscosity for dislocation creep modelling and the Drucker-Prager yield criterion for plasticity. We investigate the rheological properties of the crust and examine their compatibility with both horizontal and vertical GPS observations recorded during campaigns conducted in the last twenty years. The second part is devoted to simulations involving rate and slip history friction laws for earthquake occurence prediction and seismogenic depth approximation. The case of a single fault is examined first, then two active faults are considered to highlight the effect of their interactions on the seismic cycle

  16. Evolution of the East African rift: Drip magmatism, lithospheric thinning and mafic volcanism

    NASA Astrophysics Data System (ADS)

    Furman, Tanya; Nelson, Wendy R.; Elkins-Tanton, Linda T.

    2016-07-01

    The origin of the Ethiopian-Yemeni Oligocene flood basalt province is widely interpreted as representing mafic volcanism associated with the Afar mantle plume head, with minor contributions from the lithospheric mantle. We reinterpret the geochemical compositions of primitive Oligocene basalts and picrites as requiring a far more significant contribution from the metasomatized subcontinental lithospheric mantle than has been recognized previously. This region displays the fingerprints of mantle plume and lithospheric drip magmatism as predicted from numerical models. Metasomatized mantle lithosphere is not dynamically stable, and heating above the upwelling Afar plume caused metasomatized lithosphere with a significant pyroxenite component to drip into the asthenosphere and melt. This process generated the HT2 lavas observed today in restricted portions of Ethiopia and Yemen now separated by the Red Sea, suggesting a fundamental link between drip magmatism and the onset of rifting. Coeval HT1 and LT lavas, in contrast, were not generated by drip melting but instead originated from shallower, dominantly anhydrous peridotite. Looking more broadly across the East African Rift System in time and space, geochemical data support small volume volcanic events in Turkana (N. Kenya), Chyulu Hills (S. Kenya) and the Virunga province (Western Rift) to be derived ultimately from drip melting. The removal of the gravitationally unstable, metasomatized portion of the subcontinental lithospheric mantle via dripping is correlated in each case with periods of rapid uplift. The combined influence of thermo-mechanically thinned lithosphere and the Afar plume together thus controlled the locus of continental rift initiation between Africa and Arabia and provide dynamic support for the Ethiopian plateau.

  17. Gas isotopic signatures (He, C, and Ar) in the Lake Kivu region (western branch of the East African rift system): Geodynamic and volcanological implications

    NASA Astrophysics Data System (ADS)

    Tedesco, D.; Tassi, F.; Vaselli, O.; Poreda, R. J.; Darrah, T.; Cuoco, E.; Yalire, M. M.

    2010-01-01

    On 17 January 2002, the city of Goma was partly destroyed by two of the several lava flows erupted from a roughly N-S oriented fracture system opened along the southern flank of Mount Nyiragongo (Democratic Republic of Congo), in the western branch of the East African rift system. A humanitarian and scientific response was promptly organized by international, governmental, and nongovernmental agencies coordinated by the United Nations and the European Union. Among the different scientific projects undertaken to study the mechanisms triggering this and possible future eruptions, we focused on the isotopic (He, C, and Ar) analysis of the magmatic-hydrothermal and cold gas discharges related to the Nyiragongo volcanic system, the Kivu and Virunga region. The studied area includes the Nyiragongo volcano, its surroundings, and peripheral areas inside and outside the rift. They have been subdivided into seven regions characterized by distinct 3He/4He (expressed as R/Rair) ratios and/or δ13C-CO2 values. The Nyiragongo summit crater fumaroles, whose R/Rair and δ13C-CO2 values are up to 8.73 and from -3.5‰ to -4.0‰ VPDB, respectively, show a clear mantle, mid-ocean ridge basalt (MORB)-like contribution. Similar mantle-like He isotopic values (6.5-8.3 R/Rair) are also found in CO2-rich gas emanations (mazukus) along the northern shoreline of Lake Kivu main basin, whereas the 13δC-CO2 values range from -5.3‰ to -6.8‰ VPDB. The mantle influence progressively decreases in (1) dissolved gases of Lake Kivu (2.6-5.5 R/Rair) and (2) the distal gas discharges within and outside the two sides of the rift (from 0.1 to 1.7 R/Rair). Similarly, δ13C-CO2 ratios of the peripheral gas emissions are lighter (from -5.9‰ to -11.6‰ VPDB) than those of the crater fumaroles. Therefore, the spatial distribution of He and C signatures in the Lake Kivu region is mainly produced by mixing of mantle-related (e.g., Nyiragongo crater fumaroles and/or mazukus gases) and crustal-related (e

  18. Single-cycle replicable Rift Valley fever virus mutants as safe vaccine candidates.

    PubMed

    Terasaki, Kaori; Tercero, Breanna R; Makino, Shinji

    2016-05-01

    Rift Valley fever virus (RVFV) is an arbovirus circulating between ruminants and mosquitoes to maintain its enzootic cycle. Humans are infected with RVFV through mosquito bites or direct contact with materials of infected animals. The virus causes Rift Valley fever (RVF), which was first recognized in the Great Rift Valley of Kenya in 1931. RVF is characterized by a febrile illness resulting in a high rate of abortions in ruminants and an acute febrile illness, followed by fatal hemorrhagic fever and encephalitis in humans. Initially, the virus was restricted to the eastern region of Africa, but the disease has now spread to southern and western Africa, as well as outside of the African continent, e.g., Madagascar, Saudi Arabia and Yemen. There is a serious concern that the virus may spread to other areas, such as North America and Europe. As vaccination is an effective tool to control RVFV epidemics, formalin-inactivated vaccines and live-attenuated RVFV vaccines have been used in endemic areas. The formalin-inactivated vaccines require boosters for effective protection, whereas the live-attenuated vaccines enable the induction of protective immunity by a single vaccination. However, the use of live-attenuated RVFV vaccines for large human populations having a varied health status is of concern, because of these vaccines' residual neuro-invasiveness and neurovirulence. Recently, novel vaccine candidates have been developed using replication-defective RVFV that can undergo only a single round of replication in infected cells. The single-cycle replicable RVFV does not cause systemic infection in immunized hosts, but enables the conferring of protective immunity. This review summarizes the properties of various RVFV vaccines and recent progress on the development of the single-cycle replicable RVFV vaccines. PMID:26022573

  19. Advanced Fire Information System - A real time fire information system for Africa

    NASA Astrophysics Data System (ADS)

    Frost, P. E.; Roy, D. P.

    2012-12-01

    The Council for Scientific and Industrial Research (CSIR) lead by the Meraka Institute and supported by the South African National Space Agency (SANSA) developed the Advanced Fire Information System (AFIS) to provide near real time fire information to a variety of operational and science fire users including disaster managers, fire fighters, farmers and forest managers located across Southern and Eastern Africa. The AFIS combines satellite data with ground based observations and statistics and distributes the information via mobile phone technology. The system was launched in 2004, and Eskom (South Africa' and Africa's largest power utility) quickly became the biggest user and today more than 300 Eskom line managers and support staff receive cell phone and email fire alert messages whenever a wildfire is within 2km of any of the 28 000km of Eskom electricity transmission lines. The AFIS uses Earth observation satellites from NASA and Europe to detect possible actively burning fires and their fire radiative power (FRP). The polar orbiting MODIS Terra and Aqua satellites provide data at around 10am, 15pm, 22am and 3am daily, while the European Geostationary MSG satellite provides 15 minute updates at lower spatial resolution. The AFIS processing system ingests the raw satellite data and within minutes of the satellite overpass generates fire location and FRP based fire intensity information. The AFIS and new functionality are presented including an incident report and permiting system that can be used to differentiate between prescribed burns and uncontrolled wild fires, and the provision of other information including 5-day fire danger forecasts, vegetation curing information and historical burned area maps. A new AFIS mobile application for IOS and Android devices as well as a fire reporting tool are showcased that enable both the dissemination and alerting of fire information and enable user upload of geo tagged photographs and on the fly creation of fire reports

  20. Forensic investigation of rift-to-drift transitions and volcanic rifted margins birth

    NASA Astrophysics Data System (ADS)

    Meyer, R.; Hertogen, J.

    2008-12-01

    Volcanic rifted margins (VRM) reflect excess magmatism generated during the rift-to-drift transition of a continental rift system evolving into a Mid-Ocean Ridge (MOR). As a result many VRM (e.g. NAIP and CAMP) are recognized as Large Igneous Provinces (LIP). The prominent structural characteristics of VRM are Continental Flood Basalts, High-Velocity Lower Crustal bodies (HVLC) and Seaward Dipping Reflector Sequences (SDRS). However, the causes of these anomalously high eruption rates and magma volumes are presently poorly understood. Controversial issue opinions are based on two competing hypotheses: 1) Mantle plume related mechanisms where the excess magmatism results from elevated mantle temperatures; and 2) Rift induced small scale convection processes causing temperature anomalies and enhancing the mantle rock flux through the melt window. Largely because of difficulties to sample oceanic basement at VRM -due to thick sediment covers- the composition of rift-to-drift transition magmas is generally poorly constrained. We reviewed the geodynamic histories and magma compositions from well known VRM (e.g. NE Australia, E USA, Madagascar) and compared these data with own geochemical data from different NE Atlantic tectono-magmatic VRM zones. These comparisons point to a consistent, general VRM formation model. This model has to explain the primary observation, that geological long periods of extension have been reported -in all investigated VRM areas- prior to the breakup. Extensional far field stress looks to be the main geodynamic cause for continental breakup. Small scale convection during the late phase of a continental rift system is probably the key process generating excess magmatism in LIP related to rift-to-drift transitions.

  1. Insights into extensional processes during magma assisted rifting: Evidence from aligned scoria cones

    NASA Astrophysics Data System (ADS)

    Rooney, Tyrone O.; Bastow, Ian D.; Keir, Derek

    2011-04-01

    Mechanical and magmatic processes exert first-order control on the architecture and evolution of rifts. As a continental rift develops towards a new oceanic spreading centre, extension that is initially accommodated in a broad zone of faulting and ductile stretching must transition towards a narrow zone of focused magmatic intrusion. The Main Ethiopian Rift (MER), part of the East African Rift System, is an ideal location to study this transition because it captures rifting processes during continental breakup. In this contribution we synthesise geochemical data from scoria cones in the Wonji Fault Belt (WFB) and Silti-Debre Zeyit Fault Zone (SDFZ) in the MER to provide new constraints on the development of mantle melting columns and magmatic plumbing systems since the onset of rifting. We utilize the extensive geophysical and geochemical databases, collected in the Ethiopian Rift, to show that geochemical evidence of heterogeneity in the depth of the mantle melting column which produced Quaternary rift basalts correlates with lithospheric structure. When combined with existing observations of asymmetry across the rift in terms of depth of melting column and magmatic plumbing systems, it is evident that the mechanical structure of the rift, defined during the initial stages of breakup, has played a dominant role in the initial development of magma assisted rifting in the MER. Surface structures and crustal-scale geophysical studies have suggested the WFB is analogous to a sea-floor spreading centre. However, the geochemical characteristics of rift basalts are consistent with mantle tomography that shows no evidence beneath the MER for passive magmatic upwelling beneath discrete rift segments as is observed in the ocean basins. Collectively, the Ethiopian data show that the distribution of mantle melts during the initiation of magma assisted rifting is fundamentally influenced by lithospheric structures formed during earlier syn-rift stretching.

  2. The GLIMPCE seismic experiment: Onshore refraction and wide-angle reflection observations from a fan line over the Lake Superior Midcontinent Rift System

    NASA Astrophysics Data System (ADS)

    Epili, Duryodhan; Mereu, Robert F.

    The 1986 GLIMPCE experiment (Great Lakes International Multidisciplinary Program for Crustal Evolution) was a combined on-ship seismic reflection and onshore seismic refraction experiment designed to determine the structure of the crust beneath the Great Lakes. The main tectonic targets of interest were the Midcontinent Rift System, the Grenville Front, the Penokean and Huronian Fold Belts and the Michipicoten Greenstone Belt. The source of the seismic energy came from a large air gun array fired at closely spaced intervals (50-350 m) over several long lines (150-350 km) crossing the lakes. Major participants of this experiment were the Geological Survey of Canada, the United States Geological Survey and a number of universities and research institutes on both sides of the border. The University of Western Ontario (UWO) collected data at five separate land stations using portable seismic refraction instruments. In this paper we present the results of a fan profile which was recorded from a UWO station on Michipicoten Island for the N-S line A which crossed the axis of the Lake Superior Synclinal Basin. The azimuth and distance ranges for this profile were 237 to 321 degrees and 120 to 170 km respectively. Detailed observations of the record sections show that p. is not a simple arrival but forms a rather complex pattern of irregular multiple arrivals. The wide-angle PmP reflection signals from the Moho are strong and well obilerved only for the shots fired near the ends of the line. The signals from the middle of the profile arrive relatively late and form very weak complex wave trains. These results indicate that the Moho in that area is probably greatly disrupted and gives added support to the rift theory for the structure under the lake. The observations also support the results of earlier crustal studies of Lake Superior which showed that the crust under the eastern part of the lake was exceedingly thick.

  3. The Use of SDMs in Developing E-Learning Systems in South Africa

    ERIC Educational Resources Information Center

    Taylor, Estelle; van Aswegen, Kobus; Huisman, Magda

    2014-01-01

    The main focus of this study is to determine if systems development methodologies (SDMs) are being utilised in the development of electronic learning systems in South Africa. Electronic learning, or e-learning, is being employed to educate millions of learners, students and employees around the world and it is a critical component of modern…

  4. Depositional and tectonic framework of the rift basins of Lake Baikal from multichannel seismic data

    USGS Publications Warehouse

    Hutchinson, D.R.; Golmshtok, A.J.; Zonenshain, L.P.; Moore, T.C.; Scholz, C.A.; Klitgord, Kim D.

    1992-01-01

    Recent multichannel seismic reflection data from Lake Baikal, located in a large, active, continental rift in central Asia, image three major stratigraphic units totalling 3.5 to 7.5 km thick in four subbasins. A major change in rift deposition and faulting between the oldest and middle-rift units probably corresponds to the change from slow to fast rifting. A brief comparison of the basins of Lake Baikal with those of the East African rift system highlights differences in structural style that can be explained by differences in age and evolution of the surrounding basement rocks. -from Authors

  5. At the tip of a propagating rift - The offshore East African Rift

    NASA Astrophysics Data System (ADS)

    Franke, Dieter; Jokat, Wilfried; Ladage, Stefan; Stollhofen, Harald; Klimke, Jennifer; Lutz, Ruediger; Mahanjane, Stefane; Ehrhardt, Axel; Schreckenberger, Bernd

    2016-04-01

    Numerous studies have addressed various aspects of the East African Rift system (EARS) but surprisingly few the offshore continuation of the south-eastern branch of the rift into the Mozambique Channel. Here, we present new evidence for neotectonic deformation derived from modern seismic reflection data and supported by additional geophysical data. The Kerimbas Graben offshore northern Mozambique is the most prominent manifestation of sub-recent extensional deformation. The seismic reflection data reveals that recent normal faulting often utilizes preexisting, deeply buried half-graben structures which likely are related to the formation of the Somali Basin. The ~30 km wide and ~150 km long symmetric graben is in a stage where the linkage of scattered normal faults already did happen, resulting in increased displacement and accommodation of most of the extension across the basin. However, deep earthquakes below the rift indicate a strong and still preserved lithospheric mantle. Extension is becoming diffuse where an onshore suture, subdividing the northern from the southern metamorphic basement onshore Mozambique, is closest to the offshore rift. It appears likely that this suture is the origin for the variation in rifting style, indicating that mantle fabric resulting from a Cambrian collision has been preserved as mechanical anisotropy of the lithospheric mantle. Further south the rift focuses in an about 30 km wide half-graben. An important finding is that the entire offshore branch of the EARS lacks significant volcanism. Along the offshore EARS there are only negligible indications for recent volcanism in the reflection seismic data such as sills and dikes. Apparently the "Comoros mantle plume" (French and Romanowicz, 2015) has a very minor influence on the progressive extensional deformation along the northern Mozambique continental margin, leading eventually to breakup sometimes in the future. Combining structural with earthquake data reveals that the magma

  6. The Midcontinent Rift and Grenville connection

    SciTech Connect

    Cambray, F.W.; Fujita, K. . Dept. of Geological Sciences)

    1994-04-01

    The Mid-Proterozoic, Midcontinent Rift System (MRS) is delineated by an inverted U shaped gravity and magnetic anomaly. It terminates in southeast Michigan but a less continuous series of anomalies and sediments, the Eastcontinent Rift occur on a north-south line through Ohio and Kentucky. The geometry allows for a north-south opening, the Lake Superior section being orthogonal to opening, the western arm transtensional and the north-south trending eastern arm a transform boundary offset by pull-apart basins. The opening and closing of the rift overlaps in time with the Grenville Orogeny. Grenville age rocks can also be found in the Llano uplift of Texas. The authors propose a model to explain the temporal and geographic association of the opening and closing of the MRS with the Grenville Orogeny that involves irregular suturing between two continental masses. Initiation of Grenville suturing, associated with south dipping subduction, in the northeast and in the Llano area of Texas would leave portion of unclosed ocean in between. Tensional stresses in the continental crust adjacent to the oceanic remnant could lead to its fragmentation and the formation of the MRS. The remaining oceanic lithosphere would eventually subduct, limiting the opening of the MRS. Continued convergence of the plates would induce compressional stresses thus accounting for the deformation of the MRS. An analogy is made with more recent opening of the Red Sea, Gulf of Aden Rift System in association with irregular collision along the Zagros-Bitlis Sutures.

  7. The application of geographical information systems to important public health problems in Africa

    PubMed Central

    Tanser, Frank C; le Sueur, David

    2002-01-01

    Africa is generally held to be in crisis, and the quality of life for the majority of the continent's inhabitants has been declining in both relative and absolute terms. In addition, the majority of the world's disease burden is realised in Africa. Geographical information systems (GIS) technology, therefore, is a tool of great inherent potential for health research and management in Africa. The spatial modelling capacity offered by GIS is directly applicable to understanding the spatial variation of disease, and its relationship to environmental factors and the health care system. Whilst there have been numerous critiques of the application of GIS technology to developed world health problems it has been less clear whether the technology is both applicable and sustainable in an African setting. If the potential for GIS to contribute to health research and planning in Africa is to be properly evaluated then the technology must be applicable to the most pressing health problems in the continent. We briefly outline the work undertaken in HIV, malaria and tuberculosis (diseases of significant public health impact and contrasting modes of transmission), outline GIS trends relevant to Africa and describe some of the obstacles to the sustainable implementation of GIS. We discuss types of viable GIS applications and conclude with a discussion of the types of African health problems of particular relevance to the application of GIS. PMID:12537589

  8. Hierarchical segmentation of the Malawi Rift: The influence of inherited lithospheric heterogeneity and kinematics in the evolution of continental rifts

    NASA Astrophysics Data System (ADS)

    Laó-Dávila, Daniel A.; Al-Salmi, Haifa S.; Abdelsalam, Mohamed G.; Atekwana, Estella A.

    2015-12-01

    We used detailed analysis of Shuttle Radar Topography Mission-digital elevation model and observations from aeromagnetic data to examine the influence of inherited lithospheric heterogeneity and kinematics in the segmentation of largely amagmatic continental rifts. We focused on the Cenozoic Malawi Rift, which represents the southern extension of the Western Branch of the East African Rift System. This north trending rift traverses Precambrian and Paleozoic-Mesozoic structures of different orientations. We found that the rift can be hierarchically divided into first-order and second-order segments. In the first-order segmentation, we divided the rift into Northern, Central, and Southern sections. In its Northern Section, the rift follows Paleoproterozoic and Neoproterozoic terrains with structural grain that favored the localization of extension within well-developed border faults. The Central Section occurs within Mesoproterozoic-Neoproterozoic terrain with regional structures oblique to the rift extent. We propose that the lack of inherited lithospheric heterogeneity favoring extension localization resulted in the development of the rift in this section as a shallow graben with undeveloped border faults. In the Southern Section, Mesoproterozoic-Neoproterozoic rocks were reactivated and developed the border faults. In the second-order segmentation, only observed in the Northern Section, we divided the section into five segments that approximate four half-grabens/asymmetrical grabens with alternating polarities. The change of polarity coincides with flip-over full-grabens occurring within overlap zones associated with ~150 km long alternating border faults segments. The inherited lithospheric heterogeneity played the major role in facilitating the segmentation of the Malawi Rift during its opening resulting from extension.

  9. Magmatic Processes Beneath the East African Rift System (EARS): Insights From Melt Inclusions in Lavas of Turkana, Kenya

    NASA Astrophysics Data System (ADS)

    Waters, C. L.; Bryce, J. G.; Furman, T.

    2004-05-01

    The EARS is an ideal site to study the magmatic processes relevant to continental basaltic volcanism. Within the EARS, the Turkana Depression exhibits maximum extension and crustal thinning [1, 2]. Whole rock elemental and isotopic analyses of Turkana lavas demonstrate heterogeneity that is unlikely due to crustal assimilation during magma transport or storage and is instead attributed to mixing between mantle sources (plume and lithosphere) [3]. In other sites of continental basaltic volcanism, compositional studies of olivine-hosted melt inclusions (MIs) lend perspective on magma chamber processing and source diversity (e.g., [4,5]). MIs hosted in primitive olivine (ol) phenocrysts often sample numerous, discrete melts that existed prior to melt aggregation and homogenization within the continental lithosphere. Thus, ol-hosted MIs from Turkana may also provide insight into magmatic processes beneath continental rifts. Furthermore, Turkana lavas afford an unusual opportunity to study MIs that are likely unaffected by crustal assimilation and provide direct evidence of mantle heterogeneity. We present major element compositional data on ol-hosted MIs from a suite of lavas from the Turkana Depression. To test for geographical control on source heterogeneity beneath the Turkana Rift, analyses in progress encompass basaltic lavas that have been sampled from South and Central Islands and the Barrier. Olivine-hosted MIs in a South Island transitional basalt (MgO= 14.10 wt%, K2O/TiO2= 0.37, K2O/P2O5= 2.08; data from [3]) are dominantly alkaline in composition. Incompatible element ratios between MIs in separate, primitive ol grains (Fo= 83.8-86.7) display significant variability (K2O/TiO2= 0.32-0.63, K2O/P2O5= 1.02-4.36). Also, primitive ol grains (e.g., Fo= 86.2) host multiple MIs that consistently display similar incompatible element variability (e.g., K2O/TiO2= 0.33-0.59, K2O/P2O5=1.27-2.04). These data suggest that melt homogenization occurs at relatively shallow

  10. Recent rift-related volcanism in Afar, Ethiopia

    NASA Astrophysics Data System (ADS)

    Ferguson, David J.; Barnie, Talfan D.; Pyle, David M.; Oppenheimer, Clive; Yirgu, Gezahegn; Lewi, Elias; Kidane, Tesfaye; Carn, Simon; Hamling, Ian

    2010-04-01

    Rift zones are the most common magmatic environment on Earth. However opportunities to observe active rifting are rare, and consequently the volcanological characteristics of rift systems are not well understood. An ongoing phase of magmatic rifting along a section of the Red Sea system in Afar, Ethiopia, presents an exceptional opportunity to constrain relationships between volcanism and crustal growth. Here, by integrating analyses of satellite images (i.e. MODIS, OMI, ASTER, and ALI) with field observations, we characterise two recent (August 2007 and June 2009) basaltic fissure eruptions in Afar and evaluate the role and significance of volcanism in the rifting process. Both events were brief (36-72 h) and erupted 4.4-18 × 10 6 m 3 of lava from a fissure system 4-6.5 km in length. Data from the spaceborne Ozone Monitoring Instrument (OMI) suggests total SO 2 emissions for each eruption of 26 ± 5 kt (2007) and 34 ± 7 kt (2009), consistent with complete degassing of the erupted magma volumes. Using geodetic models for the intrusive activity in Afar we estimate the partitioning of magma between intrusive and extrusive components, up to July 2009, to be ˜ 180:1. Comparing the first-order volcanic characteristics and the intrusive-extrusive volume balance for the Afar volcanism with data from the 1975-1984 Krafla rifting cycle (Iceland) suggests that the volcanic flux in Afar will rise significantly over the next few years as the stresses are increasingly relieved by dyking, and subsequent dykes are able to propagate more easily to the surface. As a consequence, basaltic fissure eruptions in this section of the Afar rift will become of increasing large magnitude as the rifting event matures over the next 5-10 yr. Using available models of magmatic rifting we forecast the likely size and location of future eruptions in Afar.

  11. Examination of the Reelfoot Rift Petroleum System, south-central United States, and the elements that remain for potential exploration and development

    USGS Publications Warehouse

    Coleman, James; Pratt, Thomas L.

    2016-01-01

    No production has been established in the Reel-foot rift. However, at least nine of 22 exploratory wells have reported petroleum shows, mainly gas shows with some asphalt or solid hydrocarbon residue. Regional seismic profiling shows the presence of two large inversion structures (Blytheville arch and Pascola arch). The Blytheville arch is marked by a core of structurally thickened Elvins Shale, whereas the Pascola arch reflects the structural uplift of a portion of the entire rift basin. Structural uplift and faulting within the Reelfoot rift since the late Paleozoic appear to have disrupted older conventional hydrocarbon traps and likely spilled any potential conventional petroleum accumulations. The remaining potential resources within the Reelfoot rift are likely shale gas accumulations within the Elvins Shale; however, reservoir continuity and porosity as well as pervasive faulting appear to be significant future challenges for explorers and drillers.

  12. Evolutionary model of the oblique rift basins- Central African Rifts

    NASA Astrophysics Data System (ADS)

    Yang, Kenn-Ming; Cheng, I.-Wen; Wu, Jong-Chang

    2016-04-01

    The geometry of oblique-rifting basin is strongly related with the angle (α) between the trend of rift and that of regional major extensional stress. The main purpose of this study is to investigate characteristics of geometry and kinematics of structure and tectono-stratigraphy during basin evolution of Central African Rifts (CAS). In this study, we simulated the formation of oblique-rifting basin with Particle Flow Code 3-Dimensions-(PFC 3D) and compared the simulation results with the tectonic settings of a series of basin in CAS. CAS started to develop in Early Cretaceous (130Ma) and lasted until the Late Cretaceous (85Ma-80Ma). The following collision between the African and Eurasian plates imposed compressional stress on CAS and folded the strata in the rift basins. Although the characteristics of rift basin formation remain controversial, palinspastic sections constructed in this study show that, in the Early Cretaceous, the rift basins are mainly characterized by normal faults and half-grabens. In the Late Cretaceous, the morphology of the rift basins was altered by large-scaled tectonic compression with the active Borogop Fault of regional scale. Also, en echelon trend of normal faults in the basins were measured and the angles between the trend with that of the rift axes of each basin were demonstrated, indicating that the development of CAS was affected by the regional extensional stress with a dextral component during the rifting process and, therefore, the rift basins were formed by oblique-rifting. In this study, we simulated the oblique-rifting basin model of various α with Particle Flow Code 3-Dimensions-(PFC 3D). The main theory of PFC 3D is based on the Discrete Element Method (DEM), in which parameters are applied to every particle in the models. We applied forces acting on both sides of rift axis, which α are 45°, 60°, 75° and 90° respectively, to simulate basin formation under oblique-rifting process. The study results of simulation

  13. Hydrothermal flow systems in the Midcontinent Rift: Oxygen and hydrogen isotopic studies of the North Shore Volcanic Group and related hypabyssal sills, Minnesota

    SciTech Connect

    Park, Y.R.; Ripley, E.M.

    1999-06-01

    Rift-related lavas of the North Shore Volcanic Group (NSVG) are intruded by plutonic rocks of the Duluth Complex along the unconformity between the NSVG and the underlying Proterozoic metasedimentary rocks (Animikie Group) and Archean volcano-sedimentary and plutonic rocks. Heat associated with the emplacement of the mafic intrusions generated fluid flow in the overlying plateau lavas. {delta}{sup 18}O values for whole rocks from the NSVG and hypabyssal sills range from 5.5 to 17.7{per_thousand} and 5.3 to 11.5{per_thousand}, respectively, and most values are higher than those considered normal for basaltic rocks (5.4 to 6.0{per_thousand}). In general, there is a positive correlation between whole rock {delta}{sup 18}O and water content, which suggests that elevated {delta}{sup 18}O values are related primarily to secondary mineral growth and isotopic exchange during hydrothermal alteration and metamorphism. {delta}{sup 18}O{sub H{sub 2}O} values computed from amygdule-filling minerals such as smectite, chlorite, and epidote found in low- to high-temperature metamorphic zones range from {approximately}{minus}1 to 6{per_thousand} with an average value of {approximately}3{per_thousand}. Smectite in the lower-grade zones gives computed {delta}D{sub H{sub 2}O} values between {minus}26 and {minus}83{per_thousand}, whereas epidote in the higher-grade zones gives {delta}D{sub H{sub 2}O} values of {minus}15 to 6{per_thousand}. Fluid isotopic compositions computed from epidote and smectite values are suggestive of the involvement of at least two fluids during the early stages of amygdule filling. Fluid {delta}D and {delta}{sup 18}O values determined from epidote at the higher metamorphic grades indicate that seawater dominated the deeper portions of the system where greenschist facies assemblages and elevated {delta}{sup 18}O values were produced in flow interiors, as well as margins. Smectite isotopic compositions suggest that meteoric water was predominant in the

  14. Wetlands as a Record of Climate Change and Hydrological Response in Arid Rift Settings

    NASA Astrophysics Data System (ADS)

    Ashley, G. M.

    2004-12-01

    and volcanoes). This meteoric water infiltrates quickly through porous volcanic rocks and is stored in aquifers and released slowly. As a component of the rift hydrologic system, wetlands appear to be reliable indicators of rainfall fluctuations on both Milankovitch and sub-Milankovitch time scales. Wetland sediments are commoner in the geologic record during times of higher rainfall and are less common during drier periods. Modern arid rift wetland records are peats and organic-rich clay deposits that contain eolian-transported mineral matter, plant remains (e.g. roots, stems) pollen, phytoliths, diatoms, root casts, charcoal, carbonate and manganese-rich nodules, as well as copious evidence of bioturbation (plants and invertebrates to large vertebrate trampling). Older (Pleistocene) deposits that retain little original organic matter and plant remains are generally silicified, but otherwise the record is similar to modern wetlands. Records from Olduvai Gorge (1.85-1.75 Ma) contain springs and wetlands associated with stone tools. On shorter time-frames, a drought occurred during the Medieval Warm Period (MWP) and higher rainfall in East Africa during the Little Ice Age (700 BP) led to higher lake levels of Lake Naivasha and Lake Turkana (Mohamed et al. 1995; Verschuren et al. 2000) and the simultaneous initiation and expansion of Loboi Swamp in Baringo-Bogoria basin (Ashley et al. 2004). Therefore, a wetland as an indicator of climate change even on millennial-scale cycles is a viable option to lakes as paleoclimatic indicators in arid, low-latitude continental settings. Groundwater reservoirs provide a perennial water source for plants and animals (including hominins) in what might otherwise be a parched environment.

  15. Seismic tomography of continental rifts revisited: from relative to absolute heterogeneities

    NASA Astrophysics Data System (ADS)

    Achauer, Ulrich; Masson, Frédéric

    2002-11-01

    Tomographic images for four major continental rift zones, namely the southern Rhine Graben (SRG, Germany/France), the Gregory rift (Kenya) which is the central part of the East African rift system, the Rio Grande rift (RGR) in the United States and the Lake Baikal rift zone (LBR) in Russia have been revisited by calculating and comparing absolute velocity models. The four rifts exhibit strong structural differences in the uppermost mantle down to more than 300-km depth, suggesting major differences in their geodynamic evolution albeit their similarity in age and similar surface expression. The comparative analysis suggests that tomographic images of rift zones can be used to characterize continental rifts, once the corrections to obtain absolute velocities have been carried out. Our results suggest that while the Kenya and the Rio Grande rift may be considered active with large upwelling plumes being the main controlling factor in the evolution, the southern Rhine Graben and the Lake Baikal rift are more likely passive rifts, where complex regional stress fields and inherited structures play the governing role in the evolution.

  16. Education for All in South Africa: Developing a National System for Quality Assurance.

    ERIC Educational Resources Information Center

    Smith, William J.; Ngoma-Maema, Wendy Yolisa

    2003-01-01

    Draws on international research, policy, and practice relevant to quality assurance systems to analyze the development of a national framework for educational quality assurance in South Africa. Describes an emerging framework for quality assurance that encompasses evaluation of student achievement, quality audits and reviews, program and service…

  17. Systemic Evaluation of Advisory Services to Family Farms in West Africa

    ERIC Educational Resources Information Center

    Faure, Guy; Rebuffel, Pierre; Violas, Dominique

    2011-01-01

    In West Africa, advisory services for family farms have been promoted to better address producers' needs. The paper aims to show that these services can be understood as a system whose functioning is strongly determined by the financing mechanisms, the governance mechanisms put in place, the quality of human resources delivering advice, and the…

  18. Surface analogue outcrops of deep fractured basement reservoirs in extensional geological settings. Examples within active rift system (Uganda) and proximal passive margin (Morocco).

    NASA Astrophysics Data System (ADS)

    Walter, Bastien; Géraud, Yves; Diraison, Marc

    2014-05-01

    structures). Two field cases, located in Morocco and Uganda, allow us to investigate basement complexes at different stages of an extension process and give us analog geological data of similar fractured basement reservoirs. Border faults and associated fracture networks of an active rifting system propagated in Proterozoic basement rocks are analyzed in the Albertine rift system in Uganda. Brittle structures developed along a proximal passive margin of the Atlantic domain are analyzed in Proterozoic basements rocks in Western Anti-Atlas in Morocco.

  19. Exploiting the outcome of FUTUREVOLC: The 2014-2015 rifting event, effusive eruption and gradual caldera collapse at Bardarbunga volcanic system, Iceland

    NASA Astrophysics Data System (ADS)

    Sigmundsson, Freysteinn; Vogfjord, Kristin S.; Gudmundson, Magnus T.; Ofeigsson, Benedikt G.; Dumont, Stéphanie; Parks, Michelle; Jonsdottir, Kristin; Hooper, Andrew; Hreinsdottir, Sigrun; Rafn Heimisson, Elias; White, Robert; Agustsdottir, Thorbjorg; Bean, Chris; Loughlin, Susan C.; Petur Heidarsson, Einar; Barsotti, Sara; Roberts, Matthew; Ripepe, Maurizio; Ilyinskaya, Evgenia; Consortium, Futurevolc

    2016-04-01

    Activity in the Bardarbunga volcanic system in Iceland 2014-2015 included major lava eruption (~1.5 km3) and gradual caldera collapse (~66 m), connected by a 50-km-long laterally injected dyke that formed mostly over 2-4 weeks after onset of activity on 16 August 2014. This rifting event is the main magmatic activity studied by the FUTUREVOLC project, a 3.5 year, 26-partner project funded by FP7 Environment Programme of the European Commission, addressing topic "Long-term monitoring experiment in geologically active regions of Europe prone to natural hazards: the Supersite concept. The project end is 31 March 2016 and it had aims to (i) establish an innovative volcano monitoring system and strategy, (ii) develop new methods for near real-time integration of multi-parametric datasets, (iii) apply a seamless transdisciplinary approach to further scientific understanding of magmatic processes, and (iv) to improve delivery, quality and timeliness of transdisciplinary information from monitoring scientists to civil protection. A review will be presented on how FUTUREVOLC has contributed to the response and study of the Bardarbunga activity and other events in Iceland during the project period.

  20. Age constraints for the present fault configuration in the Imperial Valley, California - Evidence for northwestward propagation of the Gulf of California rift system

    NASA Technical Reports Server (NTRS)

    Larsen, Shawn; Reilinger, Robert

    1991-01-01

    Releveling and other geophysical data for the Imperial Valley of southern California suggest the northern section of the Imperial-Brawley fault system, which includes the Mesquite Basin and Brawley Seismic Zone, is much younger than the 4 to 5 million year age of the valley itself. A minimum age of 3000 years is calculated for the northern segment of the Imperial fault from correlations between surface topography and geodetically observed seismic/interseismic vertical movements. Calculations of a maximum age of 80,000 years is based upon displacements in the crystalline basement along the Imperial fault, inferred from seismic refraction surveys. This young age supports recent interpretations of heat flow measurements, which also suggest that the current patterns of seismicity and faults in the Imperial Valley are not long lived. The current fault geometry and basement morphology suggest northwestward growth of the Imperial fault and migration of the Brawley Seismic Zone. It is suggested that this migration is a manifestation of the propagation of the Gulf of California rift system into the North American continent.

  1. Age constraints for the present fault configuration in the Imperial Valley, California: Evidence for northwestward propagation of the Gulf of California rift system

    NASA Technical Reports Server (NTRS)

    Larsen, Shawn; Reilinger, Robert

    1990-01-01

    Releveling and other geophysical data for the Imperial Valley of southern California suggest the northern section of the Imperial-Brawley fault system, which includes the Mesquite Basin and Brawley Seismic Zone, is much younger than the 4 to 5 million year age of the valley itself. A minimum age of 3000 years is calculated for the northern segment of the Imperial fault from correlations between surface topography and geodetically observed seismic/interseismic vertical movements. Calculations of a maximum age of 80,000 years is based upon displacements in the crystalline basement along the Imperial fault, inferred from seismic refraction surveys. This young age supports recent interpretations of heat flow measurements, which also suggest that the current patterns of seismicity and faults in the Imperial Valley are not long lived. The current fault geometry and basement morphology suggest northwestward growth of the Imperial fault and migration of the Brawley Seismic Zone. It is suggested that this migration is a manifestation of the propagation of the Gulf of California rift system into the North American continent.

  2. Learning Management System Success: Increasing Learning Management System Usage in Higher Education in Sub-Saharan Africa

    ERIC Educational Resources Information Center

    Mtebe, Joel S.

    2015-01-01

    Learning Management Systems (LMS) have been widely adopted by higher education institutions globally for over a decade. Institutions in sub-Saharan Africa now spend a significant proportion of their limited resources on installing and maintaining these systems. This expenditure continues to increase, raising questions as to whether LMS in these…

  3. Gravity and magnetic joint modeling of the Potiguar Rift Basin (NE Brazil): Basement control during Neocomian extension and deformation

    NASA Astrophysics Data System (ADS)

    Lopes de Castro, David

    2011-03-01

    A 2.5D gravity and magnetic investigation was conducted along five transects across the Potiguar Basin in the Borborema Province, NE Brazil. The objective of the study is to model the internal architecture of this intracontinental rift basin, which represents the interaction between the heterogeneous Precambrian basement and the Neocomian extensional tectonics, which led to the South Atlantic opening. Joint modeling of the gravity and magnetic data was constrained by Euler deconvolution results, seismic data, well logs and geologic mapping. This integrated approach allowed to determine the rift architecture that is inserted in a complex tectonic and structural framework. Results from joint modeling show that a series of asymmetric half-grabens is oriented in the NE-SW direction and controlled by a system of normal faults with throw greater than 5.5 km. High-density and low-magnetized material constitutes the footwall and intrarift horsts. These supracrustal heterogeneities in association with preexisting shear zones probably guided the Mesozoic rifting process in NE Brazil. Their composition seems to be related to metamorphic rocks of the Proterozoic basement, as suggested by gravity and magnetic anomalies and the geology of the exposed basement. Our interpretation is supported by geophysical studies carried out in the Benue Trough, the counterpart of the Potiguar Basin in West Africa.

  4. The Eagle and East Eagle sulfide ore-bearing mafic-ultramafic intrusions in the Midcontinent Rift System, upper Michigan: Geochronology and petrologic evolution

    NASA Astrophysics Data System (ADS)

    Ding, Xin; Li, Chusi; Ripley, Edward M.; Rossell, Dean; Kamo, Sandra

    2010-03-01

    The Eagle and East Eagle intrusions are small, subvertical dike-like mafic-ultramafic bodies that cut Proterozoic sedimentary strata in the Baraga Basin in northern Michigan. The Eagle intrusion hosts a newly discovered magmatic Ni-Cu-PGE deposit. The nearby East Eagle intrusion also contains sulfide mineralization, but the extent of this mineralization has yet to be determined by further drilling. Both intrusions contain olivine-bearing rocks such as feldspathic peridotite, melatroctolite, and olivine melagabbro. Sulfide accumulations range from disseminated at both Eagle and East Eagle to semimassive and massive at Eagle. U-Pb baddeleyite dating gives a crystallization age of 1107.2 ± 5.7 Ma for the Eagle intrusion, coeval with eruption of picritic basalts at the base of the volcanic succession in the Midcontinent Rift System (MRS). The Fo contents of olivine cores in the Eagle and East Eagle intrusions vary between 75 and 85 mol %, higher than those of olivine in larger layered intrusions in the MRS such as the Duluth Complex. The FeO/MgO ratios and Al2O3 contents of the parental magmas for the Eagle and East Eagle intrusions inferred from olivine and spinel compositions are similar to those of picritic basalts in the base of the MRS volcanic succession. These petrochemical data suggest that the Eagle and East Eagle intrusions are the intrusive equivalents of high-MgO basalts that erupted in the early stages of continental magmatism associated with the development of the rift. Variations in mineral compositions and incompatible trace element ratios suggest that at least three major pulses of magmas were involved in the formation of low-sulfide rocks in the Eagle intrusion. Lower Fo contents of olivine associated with semimassive sulfides as compared to that of olivine in low-sulfide rocks suggest that the magma associated with the semimassive sulfide was more fractionated than the parental magmas of the low-sulfide rocks in the Eagle intrusion. Accumulation of

  5. Estimation of age of Dali-Ganis rifting and associated volcanic activity, Venus

    NASA Technical Reports Server (NTRS)

    Basilevsky, A. T.

    1993-01-01

    This paper deals with the estimation of age for the Dali and Ganis Chasma rift zones and their associated volcanism based on photogeologic analysis of stratigraphic relations of rift-associated features with impact craters which have associated features indicative of their age. The features are radar-dark and parabolic, and they are believed to be mantles of debris derived from fallout of the craters' ejecta. They are thought to be among the youngest features on the Venusian surface, so their 'parent' craters must also be very young, evidently among the youngest 10 percent of Venus' crater population. Dali Chasma and Ganis Chasma are a part of a system of rift zones contained within eastern Aphrodite and Atla Regio which is a significant component of Venus tectonics. The rifts of this system are fracture belts which dissect typical Venusian plains with rare islands of tessera terrain. The rift zone system consists of several segments following each other (Diane, Dali, Ganis) and forming the major rift zone line, about 10,000 km long, which has junctions with several other rift zones, including Parga Chasma Rift. The junctions are usually locations of rift-associated volcanism in the form of volcanic edifices (Maat and Ozza Montes) or plain-forming flows flooding some areas within the rift zones and the adjacent plains.

  6. Regional magnetic anomaly constraints on continental rifting

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.

    1985-01-01

    Radially polarized MAGSAT anomalies of North and South America, Europe, Africa, India, Australia and Antarctica demonstrate remarkably detailed correlation of regional magnetic lithospheric sources across rifted margins when plotted on a reconstruction of Pangea. These major magnetic features apparently preserve their integrity until a superimposed metamorphoric event alters the magnitude and pattern of the anomalies. The longevity of continental scale magnetic anomalies contrasts markedly with that of regional gravity anomalies which tend to reflect predominantly isostatic adjustments associated with neo-tectonism. First observed as a result of NASA's magnetic satellite programs, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans. Accordingly, satellite magnetic observations provide a further tool for investigating continental drift to compliment other lines of evidence in paleoclimatology, paleontology, paleomagnetism, and studies of the radiometric ages and geometric fit of the continents.

  7. Low lower crustal velocity across Ethiopia: Is the Main Ethiopian Rift a narrow rift in a hot craton?

    USGS Publications Warehouse

    Keranen, K.M.; Klemperer, S.L.; Julia, J.; Lawrence, J. F.; Nyblade, A.A.

    2009-01-01

    [1] The Main Ethiopian Rift (MER) is a classic narrow rift that developed in hot, weak lithosphere, not in the initially cold, thick, and strong lithosphere that would be predicted by common models of rift mode formation. Our new 1-D seismic velocity profiles from Rayleigh wave/receiver function joint inversion across the MER and the Ethiopian Plateau indicate that hot lower crust and upper mantle are present throughout the broad region affected by Oligocene flood basalt volcanism, including both the present rift and the adjacent Ethiopian Plateau hundreds of kilometers from the rift valley. The region of hot lithosphere closely corresponds to the region of flood basalt volcanism, and we interpret that the volcanism and thermal perturbation were jointly caused by impingement of the Afar plume head. Across the affected region, Vs is 3.6-3.8 km/s in the lowermost crust and ???4.3 km/s in the uppermost mantle, both ??0.3 km/s lower than in the eastern and western branches of the East African Rift System to the south. We interpret the low Vs in the lower crust and upper mantle as indicative of hot lithosphere with partial melt. Our results lead to a hybrid rift mode, in which the brittle upper crust has developed as a narrow rift along the Neoproterozoic suture between East and West Gondwana, while at depth lithospheric deformation is distributed over the broad region (??400 km wide) thermally perturbed by the broad thermal upwelling associated with the Afar plume head. Development of both the East African Rift System to the south (in cold, strong lithosphere) and the MER to the north (in hot, weak lithosphere) as narrow rifts, despite their vastly different initial thermal states and depth-integrated lithospheric strength, indicates that common models of rift mode formation that focus only on temperature, thickness, and vertical strength profiles do not apply to these classic continental rifts. Instead, inherited structure and associated lithospheric weaknesses are

  8. Mean state and kinematic properties of mesoscale convective systems over West Africa

    NASA Astrophysics Data System (ADS)

    Ogungbenro, Stephen B.; Ajayi, V. O.; Adefolalu, D. O.

    2016-04-01

    A 17-year (1984 to 2000) dataset of brightness temperature (T b) was employed to study the spatial and temporal scales of mesoscale convective systems (MCS) over West Africa. The kinematic properties of MCS were tested using wind products. A threshold brightness temperature (T b) of ≤213 K and spatial coverage specifications of more than 5000 km2 were used as two set criteria for initiating MCS tracking. MCS occurrences vary in seasons and locations over West Africa, and their activities vary with different weather zones. They can appear at any time of the day, but this study revealed a significant preference for early morning hours and night hours over continental West Africa. The well-organized systems occur between July and September in the Sahel, and between May and September in the Savanna band. MCS activities in the Gulf of Guinea peak between March and April, while the Savanna and Sahel zones peak between June and August. The produced annual atlas gives a spatial account of areas of MCS dominance in West Africa. The presence of African Easterly Jet (AEJ) and Tropical Easterly Jet (TEJ), and deep monsoon depth all characterize an environment where MCS thrive. Kinematic study of a typical MCS reveals that the monsoon depth increases at the passage of MCS, with cyclonic vorticity dominating from the surface to 300 hpa while anticyclonic vorticity was observed around 200 hpa, and this confirms the importance of low level convergence and upper level divergence as the major requirements for storm mobilization and maintenance.

  9. Kīlauea's Upper East Rift Zone: A Rift Zone in Name Only

    NASA Astrophysics Data System (ADS)

    Swanson, D. A.; Fiske, R. S.

    2014-12-01

    Kīlauea's upper east rift zone (UERZ) extends ~3 km southeastward from the summit caldera to the Koáe fault system, where it starts to bend into the main part of the ENE-trending rift zone. The UERZ lacks a distinct positive gravity anomaly (though coverage is poor) and any evidence of deformation associated with magma intrusion. All ground ruptures—and the Puhimau thermal area—trend ENE, crossing the UERZ at a high angle. Lua Manu, Puhimau, and Kóokóolau craters are the only surface evidence of the UERZ. Yet the UERZ is seismically active, and all magma entering the rest of the rift zone must pass through it. Rather than a rift zone in the traditional sense, with abundant dikes and ground ruptures along its trend, the UERZ cuts across the ENE structural grain and serves only as a connector to the rest of the rift zone, not a locus of dike formation along its length. The UERZ probably developed as a consequence of gradual SSE migration of the active part of the main east rift zone at the trailing edge of the south flank. During migration, a connection to the summit reservoir complex must be maintained; otherwise, the middle and lower east rift zone would starve and magma from Kīlauea's summit reservoir complex would have to go elsewhere. Over time, the UERZ lengthened and rotated clockwise to maintain the connection. Near the caldera, the UERZ may be widening westward as the summit reservoir complex migrates southward from the center of the caldera to its present position. A layered stress regime results in the upper 2-3 km mimicking the pervasive ENE structural grain of most of Kīlauea, whereas the underlying magmatic part of the UERZ responds to stresses related to SE magma transport. Magma intruding upward from the connector forms a dike that follows the ENE structural grain, as during the 1974 eruption. The active east rift zone has been migrating since ~100 ka, estimated by applying a 700-y extension rate across the Koa'e fault system to the ~6.5 km

  10. Anomalous deep earthquakes beneath the East African Rift: evidence for rift induced delamination of the lithosphere?

    NASA Astrophysics Data System (ADS)

    Lindenfeld, Michael; Rümpker, Georg; Schmeling, Harro; Wallner, Herbert

    2010-05-01

    The over 5000 m high Rwenzori Mountains are situated within the western branch of the East African Rift System, at the border between Uganda and the Democratic Republic of Congo. They represent a basement block within the rift valley whose origin and relation to the evolution of the EARS are highly puzzling. During 2006/2007 a network of 27 seismological stations was operated in this area to investigate crustal and upper mantle structure in conjunction with local seismicity. The data analysis revealed unexpectedly high microseismic activity. On average more than 800 events per month could be located with magnitudes ranging from 0.5 to 5.1. Hypocentral depths go as deep as 30 km with a pronounced concentration of activity at a depth of about 15 km. This presentation focuses on a cluster of seven earthquakes that were located at anomalous depths between 53 and 60 km. According to our present knowledge these are the deepest events so far observed within the EARS and the African Plate. Their origin might be connected to magmatic intrusions. However, the existence of earthquakes at this depth is enigmatic, especially within a rifting regime were one expects hot and weak material close to the surface, which is not capable of seismogenic deformation. We think that these events are closely related to the evolution of the Rwenzoris. A recent hypothesis to explain the extreme uplift of the Rwenzori Mountains is rift induced delamination (RID) of mantle lithosphere that is captured between two approaching rift segments. By numerical modelling we show that the RID-process is also able to bring material that is cold and brittle enough to release seismic energy into greater depth. Therefore the RID-mechanism gives a consistent explanation for the detected deep events as well as for the uplift of a mountain block in a rift setting.

  11. Corruption in health-care systems and its effect on cancer care in Africa.

    PubMed

    Mostert, Saskia; Njuguna, Festus; Olbara, Gilbert; Sindano, Solomon; Sitaresmi, Mei Neni; Supriyadi, Eddy; Kaspers, Gertjan

    2015-08-01

    At the government, hospital, and health-care provider level, corruption plays a major role in health-care systems in Africa. The returns on health investments of international financial institutions, health organisations, and donors might be very low when mismanagement and dysfunctional structures of health-care systems are not addressed. More funding might even aggravate corruption. We discuss corruption and its effects on cancer care within the African health-care system in a sociocultural context. The contribution of high-income countries in stimulating corruption is also described. Corrupt African governments cannot be expected to take the initiative to eradicate corruption. Therefore, international financial institutions, health organisations, and financial donors should use their power to demand policy reforms of health-care systems in Africa troubled by the issue of corruption. These modifications will ameliorate the access and quality of cancer care for patients across the continent, and ultimately improve the outcome of health care to all patients. PMID:26248847

  12. 3D object-oriented image analysis in 3D geophysical modelling: Analysing the central part of the East African Rift System

    NASA Astrophysics Data System (ADS)

    Fadel, I.; van der Meijde, M.; Kerle, N.; Lauritsen, N.

    2015-03-01

    Non-uniqueness of satellite gravity interpretation has traditionally been reduced by using a priori information from seismic tomography models. This reduction in the non-uniqueness has been based on velocity-density conversion formulas or user interpretation of the 3D subsurface structures (objects) based on the seismic tomography models and then forward modelling these objects. However, this form of object-based approach has been done without a standardized methodology on how to extract the subsurface structures from the 3D models. In this research, a 3D object-oriented image analysis (3D OOA) approach was implemented to extract the 3D subsurface structures from geophysical data. The approach was applied on a 3D shear wave seismic tomography model of the central part of the East African Rift System. Subsequently, the extracted 3D objects from the tomography model were reconstructed in the 3D interactive modelling environment IGMAS+, and their density contrast values were calculated using an object-based inversion technique to calculate the forward signal of the objects and compare it with the measured satellite gravity. Thus, a new object-based approach was implemented to interpret and extract the 3D subsurface objects from 3D geophysical data. We also introduce a new approach to constrain the interpretation of the satellite gravity measurements that can be applied using any 3D geophysical model.

  13. Seasonal drought forecast system for food-insecure regions of East Africa

    NASA Astrophysics Data System (ADS)

    Shukla, Shraddhanand; McNally, Amy; Husak, Greg; Funk, Chris

    2014-05-01

    In East Africa, agriculture is mostly rainfed and hence sensitive to interannual rainfall variability, and the increasing food and water demands of a growing population place further stresses on the water resources of this region. Skillful seasonal agricultural drought forecasts for this region can inform timely water and agricultural management decisions, support the proper allocation of the region's water resources, and help mitigate socio-economic losses. Here we describe the development and implementation of a seasonal drought forecast system that is being used for providing seasonal outlooks of agricultural drought in East Africa. We present a test case of the evaluation and applicability of this system for March-April-May growing season over equatorial East Africa (latitude 20 south to 80 North and 360 E to 460E) that encompasses one of the most food insecure and climatically and socio-economically vulnerable regions in East Africa. This region experienced famine as recently as in 2011. The system described here combines advanced satellite and re-analysis as well as station-based long term and real-time observations (e.g. NASA's TRMM, Infra-red remote sensing, Climate Forecast System Reanalysis), state-of-the-art dynamical climate forecast system (NCEP's Climate Forecast System Verison-2) and large scale land surface models (e.g. Variable Infiltration Capacity, NASA's Land Information System) to provide forecasts of seasonal rainfall, soil moisture and Water Requirement Satisfaction Index (WRSI) throughout the season - with an emphasis on times when water is the most critical: start of season/planting and the mid-season/crop reproductive phase. Based on the hindcast assessment of this system, we demonstrate the value of this approach to the US Agency for International Development (USAID)'s efforts to mitigate future losses of lives and economic losses by allowing a proactive approach of drought management that includes early warning and timely action.

  14. Introduction - Processes of continental rifting

    NASA Technical Reports Server (NTRS)

    Morgan, P.; Baker, B. H.

    1983-01-01

    It is thought likely that thermal thinning and/or diapirism can cause the extensional stress required for rifting. The rifting, however, will not occur unless the regional tectonic regime permits the sides of the rift to diverge. Whereas passive plate extension could cause rifting in isolation, the extension and rifting are likely to be localized where the lithosphere is weakest over an existing thermal anomaly. In those cases where asthenospheric diapirism occurs, which is essentially a response to thinning of the lithosphere by thermal thinning or plate extension, the effects of diapirism may completely mask the initiating mechanism. It is believed that anomalous heat transfer into the lithosphere, diapirism, and magmatism must all figure in rifting, along with a deviatoric stress field that will permit extension in a developing rift. Even though the models are useful in permitting idealized processes to be quantified and tested, better knowledge of lithosphere properties is considered necessary, in particular knowledge of mantle viscosity and its temperature dependence.

  15. Crustal structure of central Lake Baikal: Insights into intracontinental rifting

    USGS Publications Warehouse

    ten Brink, U.S.; Taylor, M.H.

    2002-01-01

    The Cenozoic rift system of Baikal, located in the interior of the largest continental mass on Earth, is thought to represent a potential analog of the early stage of breakup of supercontinents. We present a detailed P wave velocity structure of the crust and sediments beneath the Central Basin, the deepest basin in the Baikal rift system. The structure is characterized by a Moho depth of 39-42.5 km; an 8-km-thick, laterally continuous high-velocity (7.05-7.4 km/s) lower crust, normal upper mantle velocity (8 km/s), a sedimentary section reaching maximum depths of 9 km, and a gradual increase of sediment velocity with depth. We interpret the high-velocity lower crust to be part of the Siberian Platform that was not thinned or altered significantly during rifting. In comparison to published results from the Siberian Platform, Moho under the basin is elevated by <3 km. On the basis of these results we propose that the basin was formed by upper crustal extension, possibly reactivating structures in an ancient fold-and-thrust belt. The extent and location of upper mantle extension are not revealed by our data, and it may be offset from the rift. We believe that the Baikal rift structure is similar in many respects to the Mesozoic Atlantic rift system, the precursor to the formation of the North Atlantic Ocean. We also propose that the Central Baikal rift evolved by episodic fault propagation and basin enlargement, rather than by two-stage rift evolution as is commonly assumed.

  16. Next-generation Geotectonic Data Analysis: Using pyGPlates to quantify Rift Obliquity during Supercontinent Dispersal

    NASA Astrophysics Data System (ADS)

    Butterworth, Nathaniel; Brune, Sascha; Williams, Simon; Müller, Dietmar

    2015-04-01

    Fragmentation of a supercontinent by rifting is an integral part of plate tectonics, yet the dynamics that govern the success or failure of individual rift systems are still unclear. Recently, analytical and thermo-mechanical modelling has suggested that obliquely activated rifts are mechanically favoured over orthogonal rift systems. Hence, where two rift zones compete, the more oblique rift proceeds to break-up while the less oblique one stalls and becomes an aulacogen. This implies that the orientation and shape of individual rift systems affects the relative motion of Earth's continents during supercontinent break-up. We test this hypothesis using the latest global plate tectonic reconstructions for the past 200 million years. The analysis is performed using pyGPlates, a recently developed Python library that allows script-based access to the plate reconstruction software GPlates. We quantify rift obliquity, extension velocity and their temporal evolution for all small-scale rift segments that constituted a major rift system during the last 200 million years. Boundaries between continental and oceanic crust (COBs) mark the end of rifting and the beginning of sea floor spreading, which is why we use a global set of updated COBs in order to pinpoint continental break-up and as a proxy for the local trend of former rift systems. Analysing the entire length of all rift systems during the last 200 My, we find a mean obliquity of ~40° (measured as the angle between extension direction and local rift trend normal), with a standard deviation of 25°. More than 75% of all rift segments exceeded an obliquity of 20° highlighting the fact that oblique rifting is the rule, not the exception. More specifically, East and West Gondwana split along the East African coast with a mean obliquity of 45°. While rifting of the central and southern South Atlantic segment involved a low obliquity of 10°, the Equatorial Atlantic opened under a high angle of 60°. The separation of

  17. Crustal Structure Across the Okavango Rift Zone, Botswana: Initial Results From the PRIDE-SEISORZ Active-Source Seismic Profile

    NASA Astrophysics Data System (ADS)

    Canales, J. P.; Moffat, L.; Lizarralde, D.; Laletsang, K.; Harder, S. H.; Kaip, G.; Modisi, M.

    2015-12-01

    The PRIDE project aims to understand the processes of continental rift initiation and evolution by analyzing along-axis trends in the southern portion of the East Africa Rift System, from Botswana through Zambia and Malawi. The SEISORZ active-source seismic component of PRIDE focused on the Okavango Rift Zone (ORZ) in northwestern Botswana, with the main goal of imaging the crustal structure across the ORZ. This will allow us to estimate total crustal extension, determine the pattern and amount of thinning, assess the possible presence of melt within the rift zone, and assess the contrasts in crustal blocks across the rift, which closely follows the trend of a fold belt. In November 2014 we conducted a crustal-scale, 450-km-long seismic refraction/wide-angle reflection profile consisting of 19 sources (shots in 30-m-deep boreholes) spaced ~25 km apart from each other, and 900 receivers (IRIS/PASSCAL "Texan" dataloggers and 4.5Hz geophones) with ~500 m spacing. From NW to SE, the profile crosses several tectonic domains: the Congo craton, the Damara metamorphic belt and the Ghanzi-Chobe fold belt where the axis of the ORZ is located, and continues into the Kalahari craton. The record sections display clear crustal refraction (Pg) and wide-angle Moho reflection (PmP) phases for all 17 of the good-quality shots, and a mantle refraction arrival (Pn), with the Pg-PmP-Pn triplication appearing at 175 km offset. There are distinct changes in the traveltime and amplitude of these phases along the transect, and on either side of the axis, that seem to correlate with sharp transitions across tectonic terrains. Initial modeling suggests: (1) the presence of a sedimentary half-graben structure at the rift axis beneath the Okavango delta, bounded to the SE by the Kunyere-Thamalakane fault system; (2) faster crustal Vp in the domains to the NW of the ORZ; and (3) thicker crust (45-50 km) at both ends of the profile within the Congo and Kalahari craton domains than at the ORZ and

  18. A model for Iapetan rifting of Laurentia based on Neoproterozoic dikes and related rocks

    USGS Publications Warehouse

    Burton, William C.; Southworth, Scott

    2010-01-01

    Geologic evidence of the Neoproterozoic rifting of Laurentia during breakup of Rodinia is recorded in basement massifs of the cratonic margin by dike swarms, volcanic and plutonic rocks, and rift-related clastic sedimentary sequences. The spatial and temporal distribution of these geologic features varies both within and between the massifs but preserves evidence concerning the timing and nature of rifting. The most salient features include: (1) a rift-related magmatic event recorded in the French Broad massif and the southern and central Shenandoah massif that is distinctly older than that recorded in the northern Shenandoah massif and northward; (2) felsic volcanic centers at the north ends of both French Broad and Shenandoah massifs accompanied by dike swarms; (3) differences in volume between massifs of cover-sequence volcanic rocks and rift-related clastic rocks; and (4) WNW orientation of the Grenville dike swarm in contrast to the predominately NE orientation of other Neoproterozoic dikes. Previously proposed rifting mechanisms to explain these features include rift-transform and plume–triple-junction systems. The rift-transform system best explains features 1, 2, and 3, listed here, and we propose that it represents the dominant rifting mechanism for most of the Laurentian margin. To explain feature 4, as well as magmatic ages and geochemical trends in the Northern Appalachians, we propose that a plume–triple-junction system evolved into the rift-transform system. A ca. 600 Ma mantle plume centered east of the Sutton Mountains generated the radial dike swarm of the Adirondack massif and the Grenville dike swarm, and a collocated triple junction generated the northern part of the rift-transform system. An eastern branch of this system produced the Long Range dike swarm in Newfoundland, and a subsequent western branch produced the ca. 554 Ma Tibbit Hill volcanics and the ca. 550 Ma rift-related magmatism of Newfoundland.

  19. Rift zone reorganization through flank instability in ocean island volcanoes: an example from Tenerife, Canary Islands

    NASA Astrophysics Data System (ADS)

    Walter, T. R.; Troll, V. R.; Cailleau, B.; Belousov, A.; Schmincke, H.-U.; Amelung, F.; Bogaard, P.

    2005-04-01

    The relationship between rift zones and flank instability in ocean island volcanoes is often inferred but rarely documented. Our field data, aerial image analysis, and 40Ar/39Ar chronology from Anaga basaltic shield volcano on Tenerife, Canary Islands, support a rift zone—flank instability relationship. A single rift zone dominated the early stage of the Anaga edifice (~6-4.5 Ma). Destabilization of the northern sector led to partial seaward collapse at about ~4.5 Ma, resulting in a giant landslide. The remnant highly fractured northern flank is part of the destabilized sector. A curved rift zone developed within and around this unstable sector between 4.5 and 3.5 Ma. Induced by the dilatation of the curved rift, a further rift-arm developed to the south, generating a three-armed rift system. This evolutionary sequence is supported by elastic dislocation models that illustrate how a curved rift zone accelerates flank instability on one side of a rift, and facilitates dike intrusions on the opposite side. Our study demonstrates a feedback relationship between flank instability and intrusive development, a scenario probably common in ocean island volcanoes. We therefore propose that ocean island rift zones represent geologically unsteady structures that migrate and reorganize in response to volcano flank instability.

  20. Fault evolution in the Potiguar rift termination, Equatorial margin of Brazil

    NASA Astrophysics Data System (ADS)

    de Castro, D. L.; Bezerra, F. H. R.

    2014-10-01

    The transform shearing between South American and African plates in the Cretaceous generated a series of sedimentary basins on both plate margins. In this study, we use gravity, aeromagnetic, and resistivity surveys to identify fault architecture and to analyse the evolution of the eastern Equatorial margin of Brazil. Our study area is the southern onshore termination of the Potiguar rift, which is an aborted NE-trending rift arm developed during the breakup of Pangea. The Potiguar rift is a Neocomian structure located in the intersection of the Equatorial and western South Atlantic and is composed of a series of NE-trending horsts and grabens. This study reveals new grabens in the Potiguar rift and indicates that stretching in the southern rift termination created a WNW-trending, 10 km wide and ~40 km long right-lateral strike-slip fault zone. This zone encompasses at least eight depocenters, which are bounded by a left-stepping, en-echelon system of NW- to EW-striking normal faults. These depocenters form grabens up to 1200 m deep with a rhomb-shaped geometry, which are filled with rift sedimentary units and capped by post-rift sedimentary sequences. The evolution of the rift termination is consistent with the right-lateral shearing of the Equatorial margin in the Cretaceous and occurs not only at the rift termination, but also as isolated structures away from the main rift.

  1. Os, Nd, O and S isotope constraints on country rock contamination in the conduit-related Eagle Cu-Ni-(PGE) deposit, Midcontinent Rift System, Upper Michigan

    NASA Astrophysics Data System (ADS)

    Ding, Xin; Ripley, Edward M.; Shirey, Steven B.; Li, Chusi

    2012-07-01

    The Eagle Cu-Ni-(PGE) deposit is hosted by mafic to ultramafic intrusive rocks associated with the Marquette-Baraga dike swarm in northern Michigan. Sulfide mineralization formed in a conduit system during early stages in the development of the ∼1.1 Ga Midcontinent Rift System. The conduit environment represents a prime location for melt-rock interaction. In order to better assess the extent of country rock contamination in the Eagle system, a combined trace element, Nd, Os, O and S isotope study of country rocks, sulfide-bearing igneous rocks and massive sulfide was undertaken. Both the Eagle and the weakly mineralized East Eagle intrusion show trace element patterns that are similar to those of picritic basalts that formed during early stages of rift development. The trace element, Os, Nd, and O isotopic values of the igneous rocks are consistent with <5% of bulk contamination by Paleoproterozoic and Archean country rocks. Both the Re-Os and Sm-Nd system provide isochrons that are in agreement with the 1107 Ma U-Pb baddeleyite age of the intrusive rocks. Calculated γOs(1100) and εNd(1100) values for the magmas are +34 and -2. δ18O values of pyroxene in feldspathic pyroxenite range from 6.5‰ to 6.6‰ and provide the only indication that bulk contamination may locally have exceeded 20%. Sulfur isotopic values of disseminated and massive sulfide in the Eagle intrusion range from 0.3‰ to 4.6‰. The δ34S values are much lower than those that characterize most of the country rocks, but could still be indicative of a contribution of S from country rocks of up to ∼50%. Δ33S values of the disseminated and massive sulfides range from -0.10‰ to 0.09‰ indicating a source in Paleoproterozoic country rocks. Semi-massive sulfide in the Eagle deposit has δ34S values between 2.2‰ and 5.3‰, and Δ33S values show a broad range between -0.86‰ and 0.86‰ indicating a major contribution from an Archean source. Isotopic data from the Eagle deposit strongly

  2. The Mesozoic rift basins of eastern North America: Potential reservoir or Explorationist's folly

    SciTech Connect

    Pyron, A.

    1991-08-01

    Mesozoic rift basins are found on the East Coast of North America from Georgia to Nova Scotia. The basins formed as a result of extensional activity associated with the breakup of Pangaea. The internal geometry of the basins includes a depositional sequence ranging from coarse fanglomerates to fine-grained siltstones and argillites. Since these Mesozoic rift basins were first studied, they have not been considered to be likely spots for hydrocarbon accumulations. Recently, geologists have reconsidered these Mesozoic basins and have developed a more synergistic approach that suggests that many of these rift basins might be suitable targets for exploration. By analogy, these Mesozoic basins are correlative to similar basins in northwestern Africa, where significant reserved of oil and natural gas have been developed. The similarity between the productive basins in northwestern Africa and the Mesozoic basins of North America and their proximity to major markets provides sufficient rationale to further investigate these basins.

  3. Contribution of the FUTUREVOLC project to the study of segmented lateral dyke growth in the 2014 rifting event at Bárðarbunga volcanic system, Iceland

    NASA Astrophysics Data System (ADS)

    Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S.; Ófeigsson, Benedikt; Rafn Heimisson, Elías; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Guðmundsson, Gunnar B.; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T.; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert S.; Ágústsdóttir, Thorbjörg; Björnsson, Helgi; Bean, Christopher J.

    2015-04-01

    The FUTUREVOLC project (a 26-partner project funded by FP7 Environment Programme of the European Commission, addressing topic "Long-term monitoring experiment in geologically active regions of Europe prone to natural hazards: the Supersite concept) set aims to (i) establish an innovative volcano monitoring system and strategy, (ii) develop new methods for near real-time integration of multi-parametric datasets, (iii) apply a seamless transdisciplinary approach to further scientific understanding of magmatic processes, and (iv) to improve delivery, quality and timeliness of transdisciplinary information from monitoring scientists to civil protection. The project duration is 1 October 2012 - 31 March 2016. Unrest and volcanic activity since August 2014 at one of the focus areas of the project in Iceland, at the Bárðarbunga volcanic system, near the middle of the project duration, has offered unique opportunities for this project. On 16 August 2014 an intense seismic swarm started in Bárðarbunga, the beginning of a major volcano-tectonic rifting event forming over 45 km long dyke extending from the caldera to Holuhraun lava field outside the northern margin of Vatnajökull. A large basaltic, effusive fissure eruption began in Holuhraun on 31 August which had by January formed a lava field with a volume in excess of one cubic kilometre. We document how the FUTUREVOLC project has contributed to the study and response to the subsurface dyke formation, through increased seismic and geodetic coverage and joint interpreation of the data. The dyke intrusion in the Bárðarbunga volcanic system, grew laterally for over 45 km at a variable rate, with an influence of topography on the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred over 14 days, was revealed by propagating seismicity, ground

  4. Digital Learning Management Systems in Africa: Myths and Realities

    ERIC Educational Resources Information Center

    Unwin, Tim; Kleessen, Beate; Hollow, David; Williams, James B.; Oloo, Leonard Mware; Alwala, John; Mutimucuio, Inocente; Eduardo, Feliciana; Muianga, Xavier

    2010-01-01

    This paper reports on a survey of 358 respondents across 25 African countries into their usage of learning management systems. It concludes that while there are some enthusiastic advocates of such systems, the reality is that most African educators as yet have little knowledge about, or interest in, their usage. There remain very considerable…

  5. Vector Competence of Selected African Mosquito (Diptera: Culicidae) Species for Rift Valley Fever Virus

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Outbreaks of Rift Valley fever (RVF) in Egypt, Yemen, and Saudi Arabia have indicated the potential for this disease to spread from its enzootic areas in sub-Saharan Africa. Because little is known about the potential for most African mosquito species to transmit RVF virus (RVFV), we conducted stud...

  6. CURRENT ISSUES AND CONCERNS REGARDING RIFT VALLEY FEVER, AN EMERGING VIRUS THREAT

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) virus is a mosquito-borne zoonotic hemorrhagic disease that causes 100% abortions in cattle, sheep, and goats and is often fatal to young animals. Though currently confined mainly to Africa this disease could be introduced into the U.S. and spread via mosquitoes at least as ...

  7. New Diagnostic Tools for Detecting Rift Valley Fever (RVF) and other Arboviruses

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The outbreak of West Nile virus in the United Sates and the recent outbreak of Rift Valley fever (RVF) virus in East Africa have highlighted the need for validated early detection tools for arthropod-borne animal diseases. The Arthropod-Borne Animal Diseases Research Laboratory (ABADRL) has been inv...

  8. Comparison of Rift Valley fever virus replication in North American livestock and wildlife cell lines

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever virus (RVFV) causes outbreaks of endemic disease across Africa and the Arabian Peninsula, resulting in high morbidity and mortality among young domestic livestock, frequent abortions in pregnant animals, and potentially severe or fatal disease in humans. The possibility of RVFV spr...

  9. Evaluation of lamb and calf responses to Rift Valley fever MP-12 vaccination

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is an important viral disease of animals and humans in Africa and the Middle East that is transmitted by mosquitoes. The disease is of concern to international agricultural and public health communities. The RVF MP-12 strain has been the most safety tested attenuated vaccine ...

  10. One Health –One World Approaches to Detection and Control of Rift Valley Fever

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a disease of animals and humans that occurs in Africa and the Arabian Peninsula. A Phlebovirus in the family Bunyaviridae causes the disease that is transmitted by mosquitoes. Epidemics occur during years of unusually heavy rainfall that assessment models are being develop...

  11. Current Status on the Development of Operator Safe Diagnostic Tools for Rift Valley Fever

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a disease of animals and humans that occurs in Africa and the Arabian Peninsula. It is caused by a Phlebovirus in the family Bunyaviridae. Mosquito-borne epidemics occur during years of unusually heavy rainfall. Domestic cattle, sheep and goats are highly susceptible to...

  12. A Glycoprotein Subunit Vaccine Elicits a Strong Rift Valley Fever Virus Neutralizing Antibody Response in Sheep

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever virus (RVFV), a member of the Bunyaviridae family, is a mosquito-borne zoonotic pathogen that causes serious morbidity and mortality in livestock and humans. The recent spread of the virus beyond its traditional endemic boundaries in Africa to the Arabian Peninsula coupled with the...

  13. Blood Meal Analysis of Mosquitoes Involved in a Rift Valley fever Outbreak

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Background: Rift Valley fever (RVF) is a zoonosis of domestic ruminants in Africa. Bloodfed mosquitoes collected during the 2006-2007 RVF outbreak in Kenya were analyzed to determine the virus infection status and animal source of the bloodmeals. Bloodmeals from individual mosquito abdomens were sc...

  14. Rift Valley fever risk map model and seroprevalence in selected wild ungulates and camels from Kenya

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Since the first isolation of Rift Valley fever virus (RVFV) in the 1930s, there have been multiple epizootics and epidemics in animals and humans in sub-Saharan Africa. Prospective climate-based models have recently been developed that flag areas at risk of RVFV transmission in endemic regions based...

  15. Rift Valley Fever Virus Control: Integration of Virus, Host and Vector Studies

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a disease of animals and humans that occurs in Africa and the Arabian Peninsula. It is caused by a Phlebovirus in the family Bunyaviridae. Mosquito-borne epizootics occur during years of unusually heavy rainfall. Domestic cattle, sheep and goats are highly susceptible to i...

  16. Potential for stable flies and house flies (Diptera: Muscidae) to transmit Rift Valley fever virus

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF), a disease of ruminants and humans, has been responsible for large outbreaks in Africa that have resulted in hundreds of thousands of human infections and major economic disruption due to loss of livestock and to trade restrictions. As indicated by the rapid spread of West N...

  17. Improving regional health care in West Africa using current space systems and technology

    NASA Technical Reports Server (NTRS)

    Jemison, Mae C.; Thomas, J. Segun

    1992-01-01

    This paper discusses the issues involved with establishing an integrated satellite health network in West Africa based on currently available technology. The system proposed makes use of a central national facility capable of transmitting and receiving voice/data and video signals from the entire country. Regional, field and local facilities provide timely epidemiologic information, sharing of medical expertise through telemedical consultations, enhance optimized resource distribution and build a framework for telecommunications for the entire country.

  18. Improving regional health care in West Africa using current space systems and technology

    NASA Technical Reports Server (NTRS)

    Jemison, Mae C.; Thomas, J. S.

    1992-01-01

    This paper discusses the issues involved with establishing an integrated satellite health network in West Africa based on currently available technology. The system proposed makes use of a central national facility capable of transmitting and receiving voice/data and video signals from the entire country. Regional, field and local facilities provides timely epidemiologic information, sharing of medical expertise through telemedical consultations, enhances optimized resource distribution and builds a framework for telecommunications for the entire country.

  19. Recent geodynamics and evolution of the Moma rift, Northeast Asia.

    NASA Astrophysics Data System (ADS)

    Imaev, V. S.; Imaeva, L. P.; Kozmin, B. M.; Fujita, K. S.; Mackey, K. G.

    2009-04-01

    The Cenozoic Moma rift system is a major tectonic feature in northeast Russia. It is composed of a series of basins (Selennyakh, Kyrin,Lower Moma,Upper Moma,etc.) filled with up to one km thick and bounded by the Chersky Range (up to 3100 m high) on the southwest and the Moma Range (up to 2400 m high) on the northeast. Northeast of the Moma Range is the Indigirka-Zyryanka foreland basin, composed of thick, up to 2.5 km, Eocene, Oligocene, and Miocene coal-bearing sequences, while on the southwestern side of the Chersky Range there are a number of piedmont basins (Tuostakh, Upper Adycha, Derbeke, etc.) containing up to several hundred meters of Miocene and Oligocene coal-bearing deposits. Despite considerable study over the past half-century, there is considerable debate over the origin, present-day tectonics, and evolution of the Moma rift system. The Cenozoic deposits of the basins generally become younger from northwest to southeast with the exception of the Seimchan-Buyunda basin. In the northeast, fan-shaped coal-bearing basins (e.g., Nenneli, Olzhoi, Selennyakh, Uyandina, Tommot, and others) are filled with Miocene to Pliocene deposits, while basins in the southeast (e.g., Taskan) are filled with Neogene sediments. The Seimchan-Buyunda basin, however, has sediments of Oligocene age. The Moma rift system is reflected a major step in the gravity field, presumably separating denser rocks of the Kolyma-Omolon superterrain from somewhat less dense rocks of the Verkhoyansk fold belt (margin of the North Asian Craton). Analysis of travel-times of Pn and Pg waves from local earthquakes indicates an area of thinned crust (30-35 km) southwest of the Moma rift system, extending as a "tongue" from the Lena River delta and the Laptev Sea to the upper part of the Kolyma River, as compared to 40-45 km in the surrounding areas. This region of thinned crust also coincides with a region of high heat flow values measured in boreholes of the Chersky Range (up to 88 mW/m2). Hot

  20. Extension across the Laptev Sea continental rifts constrained by gravity modeling

    NASA Astrophysics Data System (ADS)

    Mazur, S.; Campbell, S.; Green, C.; Bouatmani, R.

    2015-03-01

    The Laptev Shelf is the area where the Gakkel Ridge, an active oceanic spreading axis, approaches a continental edge, causing a specific structural style dominated by extensive rift structures. From the latest Cretaceous to the Pliocene, extension exerted on the Laptev Shelf created there several deep subsided rifts and high-standing basement blocks. To understand syn-rift basin geometries and sediment supply relationships across the Laptev Shelf, accurate extension estimates are essential. Therefore, we used 2-D gravity modeling and 3-D gravity inversion to constrain the amount of crustal stretching across the North America-Eurasia plate boundary in the Laptev Shelf. The latest Cretaceous-Cenozoic extension in that area is partitioned among two rift zones, the Laptev Rift System and the New Siberian Rift. These rifts were both overprinted on the Eurasian margin that had been stretched by 190-250 km before the Late Cretaceous. While the Laptev Rift System, connected to the Gakkel Ridge, reveals increasing extension toward the shelf edge (190-380 km), the New Siberian Rift is characterized by approximately uniform stretching along strike (110-125 km). The architecture of the Laptev Rift System shows that the finite extension of about 500 km is sufficient to entirely eliminate crystalline continental crust. In the most stretched rift segment, continental mantle is exhumed at the base of the Late Mesozoic basement. The example of the Laptev Rift System shows that extension driven by divergent plate movement is a sufficient cause to produce almost complete continental breakup without an increased heat input from the asthenospheric mantle.

  1. Relationship of coronae, regional plains and rift zones on Venus

    NASA Astrophysics Data System (ADS)

    Krassilnikov, A. S.; Kostama, V.-P.; Aittola, M.; Guseva, E. N.; Cherkashina, O. S.

    2012-08-01

    Coronae and rifts are the most prominent volcano-tectonic features on the surface of Venus. Coronae are large radial-concentric structures with diameters of 100 to over 1000 km. They have varied topographical shapes, radial and concentric fracturing and compressional tectonic structures are common for their annuli. Massive volcanism is also connected with some of the structures. Coronae are interpreted to be the result of updoming and fracturing on the surface due to interaction of mantle diapirs with the lithosphere and its subsequent gravitational relaxation. According to Stofan et al. (2001), two types of coronae are observed: type 1 - coronae that have annuli of concentric ridges and/or fractures (407 structures), and type 2 that have similar characteristics to type 1 but lack a complete annulus of ridges and fractures (107 structures). We analyzed 20% of this coronae population (we chose each fifth structure from the Stofan et al. (2001) catalog; 82 coronae of type 1 and 22 coronae of type 2, in total 104 coronae) for the (1) spatial distribution of rift structures and time relationship of rift zones activity with time of regional volcanic plains emplacement, and (2) tectonics, volcanism, age relative to regional plains and relationship with rifts. Two different age groups of rifts on Venus were mapped at the scale 1:50 000 000: old rifts that predate and young rifts that postdate regional plains. Most of young rifts inherit strikes of old rifts and old rifts are reworked by them. This may be evidence of rift-produced uplift zones that were probably mostly stable during both types of rifts formation. Evolution of distribution of rift systems with time (decreasing of distribution and localization of rift zones) imply thickening of the lithosphere with time. Coronae-producing mantle diapirism and uplift of mantle material in rift zones are not well correlated at least in time in most cases, because majority of coronae (77%) of both types has no genetic

  2. Contribution of Transverse Structures, Magma, and Crustal Fluids to Continental Rift Evolution: The East African Rift in Southern Kenya

    NASA Astrophysics Data System (ADS)

    Kattenhorn, S. A.; Muirhead, J.; Dindi, E.; Fischer, T. P.; Lee, H.; Ebinger, C. J.

    2013-12-01

    The Magadi rift in southern Kenya formed at ~7 Ma within Proterozoic rocks of the Mozambique orogenic belt, parallel to its contact with the Archean Tanzania craton. The rift is bounded to the west by the ~1600-m-high Nguruman border fault. The rift center is intensely dissected by normal faults, most of which offset ~1.4-0.8 Ma lavas. Current E-W extensional velocities are ~2-4 mm/yr. Published crustal tomography models from the rift center show narrow high velocity zones in the upper crust, interpreted as cooled magma intrusions. Local, surface-wave, and SKS-splitting measurements show a rift-parallel anisotropy interpreted to be the result of aligned melt zones in the lithosphere. Our field observations suggest that recent fault activity is concentrated at the rift center, consistent with the location of the 1998 seismic swarm that was associated with an inferred diking event. Fault zones are pervasively mineralized by calcite, likely from CO2-rich fluids. A system of fault-fed springs provides the sole fluid input for Lake Magadi in the deepest part of the basin. Many of these springs emanate from the Kordjya fault, a 50-km-long, NW-SE striking, transverse structure connecting a portion of the border fault system (the NW-oriented Lengitoto fault) to the current locus of strain and magmatism at the rift center. Sampled springs are warm (44.4°C) and alkaline (pH=10). Dissolved gas data (mainly N2-Ar-He) suggests two-component mixing (mantle and air), possibly indicating that fluids are delivered into the fault zone from deep sources, consistent with a dominant role of magmatism to the focusing of strain at the rift center. The Kordjya fault has developed prominent fault scarps (~150 m high) despite being oblique to the dominant ~N-S fault fabric, and has utilized an en echelon alignment of N-S faults to accommodate its motion. These N-S faults show evidence of sinistral-oblique motion and imply a bookshelf style of faulting to accommodate dextral-oblique motion

  3. Geochemistry of East African Rift basalts: An overview

    NASA Astrophysics Data System (ADS)

    Furman, Tanya

    2007-06-01

    Mafic lavas erupted along the East African Rift System from the Afar triangle in northern Ethiopia to the Rungwe province in southern Tanzania display a wide range of geochemical and isotopic compositions that reflect heterogeneity in both source and process. In areas with the lowest degree of crustal extension (the Western and Southern Kenya Rifts) primitive lavas record the greatest extent of lithospheric melting, manifest in elevated abundances of incompatible elements and highly radiogenic Sr-Nd-Pb isotopic compositions. Where prolonged extension has removed most or all of the mantle lithosphere (the Turkana and Northern Kenya Rifts), a larger role for sub-lithospheric processes is indicated. At intermediate degrees of extension (the Main Ethiopian Rift) both lithospheric and sub-lithospheric contributions are observed, and crustal assimilation occurs in some cases. Despite the wide compositional range of African Rift basalts, a restricted number of source domains contribute to magmatism throughout the area. These individual domains are: (1) the subcontinental mantle lithosphere; (2) a plume source with high-μ Sr-Nd-Pb-He isotopic affinities, present in all areas within and south of the Turkana Depression; and (3) a plume source with isotopic signatures analogous to those observed in some ocean islands, including high 3He/ 4He values, present throughout the Ethiopian Rift and the Afar region. The two plume sources may both be derived from the South African Superplume, which is likely to be a compositionally heterogeneous feature of the lower mantle.

  4. P Wave Velocity Structure Beneath the Baikal Rift Axis

    NASA Astrophysics Data System (ADS)

    Brazier, R. A.; Nyblade, A. A.; Boman, E. C.

    2001-12-01

    Over 100 p wave travel times from the 1500 km en echelon Baikal Rift system are used in this study.The events range 3 to 13 degrees from Talaya, Russia (TLY) along the axis of southwest northeast trending rift in East Siberia. A Herglotz Wiechert inversion of these events resolved a crust of 6.4 km/s and a gradient in the mantle starting at 35 km depth and 7.7 km/s down to 200 km depth and 8.2 km/s. This is compatible with Gao et al,1994 cross sectional structure which cuts the rift at about 400km from TLY. The Baikal Rift hosts the deepest lake and is the most seismically active rift in the world. It is one of the few continental rifts, it separates the Siberian craton and the Syan-Baikal mobile fold belt. Two events, the March 21 1999 magnitude 5.7 earthquake 638 km from TLY and the November 13th 1995 magnitude 5.9 earthquake 863 km from TLY were modeled for there PnL wave structure using the discrete wavenumber method and the Harvard CMT solutions with adjusted depths from p-pP times. The PnL signals match well. A genetic algorithm will used to perturb the velocity structure and compare to a selection of the events between 3 and 13 degrees many will require moment tensor solutions.

  5. An economic comparison of typical dairy farming systems in South Africa, Morocco, Uganda and Cameroon.

    PubMed

    Ndambi, Oghaiki Asaah; Hemme, Torsten

    2009-08-01

    Population growth, urbanisation and increased per capita milk consumption are main reasons for recent increasing milk demand in Africa. Due to globalisation, it is important to know how competitive various production systems are, especially as most governments promote local production and disfavour dairy imports. The TIPI-CAL (Technology Impact, Policy Impact Calculations model) was used to analyse and compare costs and returns of predominant dairy farming systems in South Africa, Morocco, Uganda and Cameroon. Results show that, as farms grew larger in size, family resources (especially land and labour) became insufficient and there was need for their acquisition from external sources. Though extensive dairy farming systems had the lowest cost of milk production (<20 US-$ per 100 kg milk), their input productivities and milk yields were lower, leading to very low net cash returns from dairying. Large intensive farms in South Africa had relatively low costs (<30 US-$ per 100 kg milk) and a high Return on Investment (ROI) due to a higher efficiency of input utilisation. It was concluded that, intensification of dairy farming and simultaneously increasing the scale of production will greatly increase productivity of farm inputs, thus recommended for development of the dairy sector in African countries. PMID:19082756

  6. Evidence for integrating eye health into primary health care in Africa: a health systems strengthening approach

    PubMed Central

    2013-01-01

    Background The impact of unmet eye care needs in sub-Saharan Africa is compounded by barriers to accessing eye care, limited engagement with communities, a shortage of appropriately skilled health personnel, and inadequate support from health systems. The renewed focus on primary health care has led to support for greater integration of eye health into national health systems. The aim of this paper is to demonstrate available evidence of integration of eye health into primary health care in sub-Saharan Africa from a health systems strengthening perspective. Methods A scoping review method was used to gather and assess information from published literature, reviews, WHO policy documents and examples of eye and health care interventions in sub-Saharan Africa. Findings were compiled using a health systems strengthening framework. Results Limited information is available about eye health from a health systems strengthening approach. Particular components of the health systems framework lacking evidence are service delivery, equipment and supplies, financing, leadership and governance. There is some information to support interventions to strengthen human resources at all levels, partnerships and community participation; but little evidence showing their successful application to improve quality of care and access to comprehensive eye health services at the primary health level, and referral to other levels for specialist eye care. Conclusion Evidence of integration of eye health into primary health care is currently weak, particularly when applying a health systems framework. A realignment of eye health in the primary health care agenda will require context specific planning and a holistic approach, with careful attention to each of the health system components and to the public health system as a whole. Documentation and evaluation of existing projects are required, as are pilot projects of systematic approaches to interventions and application of best practices

  7. RIFT VALLEY FEVER: PREPARING FOR POTENTIAL NEW MOSQUITO-BORNE DISEASES IN THE U.S. WITH A VECTOR SURVEILLANCE SYSTEM

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In this symposium we have discussed four diseases that are emerging threats in the U.S., and it may be concluded that in our best defense knowing the vector is as important as knowing the disease. Rift Valley fever, Dengue, and JEE are but a few of the many emerging diseases that we can prepare for...

  8. An automated GIS/remotely sensed early warning system to detect elevated populations of vectors of Rift Valley fever, a mosquito-borne emerging virus threat

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Mosquito transmitted infectious diseases, like eastern equine encephalitis (EEE), Rift Valley fever (RVF), and West Nile virus (WNV), pose an international threat to animal and human health. An introduction of RVF into the U.S. would severely impact wild ungulate populations and the beef and dairy ...

  9. Crustal Structure of the Ethiopian Rift and Adjacent Plateaus: Results of new integrated interpretation

    NASA Astrophysics Data System (ADS)

    Tadesse, K.; Keller, G. R.

    2006-12-01

    The Ethiopian rift is the large part of the East African Rift system, which represents an incipient divergent plate boundary. This important structure provides excellent opportunities to study the transition from continental to oceanic. As a result, geophysical data are becoming increasingly available but some results are contradictory. We used a newly enhanced gravity database and seismic information to produce an integrated interpretation of the crustal structure beneath the Ethiopian rift and the adjacent plateaus. Wide regions have been covered to assess the regional structures including the Kenyan and Ethiopian rifts and the area covered by the Ethiopian flood basalt. Broad negative Bouguer gravity anomalies are delineated over the Ethiopian Plateaus and the Kenyan dome. Residual gravity anomalies, which parallel the major border faults clearly highlight the segregation between the plateaus and the rift valleys. Results of other filtering techniques have clearly revealed individual volcanic centers within the rift valleys. Positive gravity anomalies outside the rift valleys may be associated with older structures, shield volcanoes, or structures that are related to the initiation and propagation of rifting. A long axial profile from the central part of Kenya to the Afar triple junction has been modeled to investigate along-axis crustal variation of the East African rift system, with emphasis on the Ethiopian rift. This modeling has been constrained using seismic refraction data from the Ethiopian Afar Geoscientific Lithospheric Experiment (EAGLE) and Kenya Rift International Seismic Project (KRISP) results. We are able to see a thin crust (~26 km) in the Afar triangle with a gradual thickening (~40 km) southwards towards the Main Central Ethiopian rift (MER). The crust thickness decreases towards Turkana rift (~22 km), and increases again towards the central eastern rift section in Kenya. Our profile model across the MER has revealed that the eastern rift

  10. Mid-lithospheric Discontinuity Beneath the Malawi Rift, Deduced from Gravity Studies and its Relation to the Rifting Process.

    NASA Astrophysics Data System (ADS)

    Njinju, E. A.; Atekwana, E. A.; Mickus, K. L.; Abdelsalam, M. G.; Atekwana, E. A.; Laó-Dávila, D. A.

    2015-12-01

    The World Gravity Map satellite gravity data were used to investigate the lithospheric structure beneath the Cenozoic-age Malawi Rift which forms the southern extension of the Western Branch of the East African Rift System. An analysis of the data using two-dimensional (2D) power spectrum methods indicates the two distinctive discontinuities at depths of 31‒44 km and 64‒124 km as defined by the two steepest slopes of the power spectrum curves. The shallower discontinuity corresponds to the crust-mantle boundary (Moho) and compares well with Moho depth determined from passive seismic studies. To understand the source of the deeper discontinuity, we applied the 2D power spectrum analysis to other rift segments of the Western Branch as well as regions with stable continental lithospheres where the lithospheric structure is well constrained through passive seismic studies. We found that the deeper discontinuity corresponds to a mid-lithospheric discontinuity (MLD), which is known to exist globally at depths between 60‒150 km and as determined by passive seismic studies. Our results show that beneath the Malawi Rift, there is no pattern of N-S elongated crustal thinning following the surface expression of the Malawi Rift. With the exception of a north-central region of crustal thinning (< 35 km), most of the southern part of the rift is underlain by thick crust (~40‒44 km). Different from the Moho, the MLD is shallower beneath the axis of the Malawi Rift forming a N-S trending zone with depths of 64‒80 km, showing a broad and gentle topography. We interpret the MLD as representing a sharp density contrast resulting from metasomatized lithosphere due to lateral migration along mobile belts of hot mantle melt or fluids from a distant plume and not from an ascending asthenosphere. These fluids weaken the lithosphere enhancing rift nucleation. The availability of satellite gravity worldwide makes gravity a promising technique for determining the MLD globally.

  11. Chalcophile element (Ni, Cu, PGE, and Au) variations in the Tamarack magmatic sulfide deposit in the Midcontinent Rift System: implications for dynamic ore-forming processes

    NASA Astrophysics Data System (ADS)

    Taranovic, Valentina; Ripley, Edward M.; Li, Chusi; Rossell, Dean

    2016-03-01

    The Tamarack magmatic sulfide deposit is hosted by the Tamarack Intrusive Complex (1105.6 ± 1.2 Ma) in the Midcontinent Rift System. The most important sulfide mineralization in the Complex occurs in the northern part, which consists of two separate intrusive units: an early funnel-shaped layered peridotite body containing relatively fine-grained olivine (referred to as the FGO Intrusion) at the top, and a late gabbro-troctolite-peridotite dike-like body containing relatively coarse-grained olivine (referred to as the CGO Intrusion) at the bottom. Disseminated, net-textured, and massive sulfides occur in the base of the FGO Intrusion as well as in the upper part of the CGO Intrusion. The widest part of the CGO Intrusion also hosts a large semi-massive (net-textured) sulfide ore body locally surrounded by disseminated sulfide mineralization. Small massive sulfide veins occur in the footwall of the FGO Intrusion and in the wall rocks of the CGO dike. The sulfide mineralization is predominantly composed of pyrrhotite, pentlandite, and chalcopyrite, plus minor magnetite. Pyrrhotite containing the highest Ni and Co contents occurs in the FGO disseminated sulfides and in the CGO semi-massive sulfide ores, respectively. The most important platinum-group minerals associated with the base metal sulfides are sperrylite (PtAs2), sudburyite (PdSb), and michenerite (PdBiTe). Nickel shows a strong positive correlation with S in all types of sulfide mineralization, and Cu shows a strong positive correlation with S in the disseminated sulfide mineralization. At a given S content, the concentrations of Pt, Pd, and Au in the CGO disseminated sulfides are significantly higher than those in the FGO disseminated sulfides. The semi-massive sulfide ores are characterized by significantly higher IPGE (Ir, Os, Ru, and Rh) concentrations than most of the massive sulfide ores. With few exceptions, all of the various textural types of sulfide mineralization collectively show a good positive

  12. Description of photovoltaic village power systems in the United States and Africa

    NASA Technical Reports Server (NTRS)

    Ratajczak, A. F.; Bifano, W. J.

    1979-01-01

    Photovoltaic power systems in remote villages in the United States and Africa are described. These projects were undertaken to demonstrate that existing photovoltaic system technology is capable of providing electrical power for basic domestic services for the millions of small, remote communities in both developed and developing countries. One system is located in the Papago Indian Village of Schuchuli in southwest Arizona (U. S.) and became operational 16 December 1978. The other system is located in Tangaye, a rural village in Upper Volta, Africa. It became operational 1 March 1979. The Schuchuli system has a 3.5 kW (peak) solar array which provides electric power for village water pumping, a refrigerator for each family, lights in the village buildings, and a community washing machine and sewing machine. The 1.8 kW (peak) Tangaye system provides power for community water pumping, flour milling and lights in the milling building. These are both stand-alone systems (i.e., no back-up power source) which are being operated and maintained by local personnel. Both systems are instrumented. Systems operations are being monitored by NASA to measure design adequacy and to refine designs for future systems.

  13. The Intraplate Earthquakes of SE Africa

    NASA Astrophysics Data System (ADS)

    Fonseca, J. F. B. D.; Domingues, A.

    2014-12-01

    Southeast Africa is a region of complex tectonic inheritance, combining early Archean cratonic blocks - the Zimbabwe and Kaapvaal cratons - and several collision belts ranging in age from ~2.6Ga (Limpopo Belt) to the Pan-African Orogeny, 800-500 Ma ago (Zambezi Belt, Mozambique Belt). Mesozoic rifting was the last tectonic event to leave an imprint in the lithosphere of the region. Tertiary deformation is mild and related to the extensional regime of the East African Rift System (EARS) further north. Instrumental seismology started in Johannesburg in 1910 (Saunders et al., 2008). Ambraseys and Adams (1991) conducted a reappraisal of the seismicity of Sub-Saharan Africa from 1900 to 1930, and the compilations by Krige and Maree (1948) and Gutenberg and F. Richter (1949) are main sources for the two subsequent decades. The available data can be considered complete since 1900 for magnitudes above M6 (Ambraseys and Adams, 1991), although major epicentral errors are likely to affect the early decades. Earthquakes above this threshold in the region to the south of Lake Malawi and to the east of the Okavango Rift are reported in 1919 (MS6.5, NE South Africa), 1932 (MS6.8, Natal Bay), 1940 (MS6.2, SE Mozambique), 1951 (MS6.0, Central Mozambique), 1957 (M6.0, Central Mozambique), again in 1957 (M6.2, Central Mozambique), 1958 (M6.0, Southern Zimbabwe), 1959 (M6.1, Southern Zambia) and 2006 (M7.0, Central Mozambique). The four M>6 earthquakes from 1957 to 1959 configure a cluster in time, followed by a shutdown (at M>6) that was to last nearly five decades. While a coincidence is unlikely, a causal link is challenged by the large spatial scatter of about 500 km. However, the fact that the four earthquakes occurred on the border of the Zimbabwe craton may provide a clue to the mechanism promoting the clustering. We combine these data with recent seismicity results (Fonseca et al., 2014) to discuss possible factors controlling the seismotectonics of the region.

  14. Magmatic expression of lithospheric thinning across continental rifts

    NASA Astrophysics Data System (ADS)

    Thompson, R. N.; Gibson, S. A.

    1994-05-01

    Studies of magmatism associated with continental rifting have traditionally focused only on volcanism within the downfaulted axial zone and along its immediate flanks. Teleseismic travel-time delay studies during the last decade have confirmed the results of earlier gravity surveys of rifted areas, showing that thinning at the base of the continental lithosphere occurs throughout a zone up to about 10 times wider than the physiographic expression of the rift. It is, therefore, logical to consider rifting-related magmatism on the same scale. Potential sources of mafic magmas in rift zones are the thinned subcontinental lithospheric mantle (SCLM), the convecting mantle beneath the continental plate and mixtures of the two. Detailed elemental and radiogenic isotope geochemical studies show that, during the initial extension of continental rifts, the associated mafic magmatism tends to be: (1) relatively sodic and from predominantly convecting mantle sources at the rift axis; (2) relatively potassic and from predominantly lithospheric mantle sources at the margins of the thinned-plate zone. This underlying geochemical pattern is obscured in many instances by such processes as crustal contamination and magma mixing within open-system reservoirs. The mafic ultrapotassic component that provides a distinctive input to SCLM-source magmas appears to be largely fusible at temperatures well below the dry solidus of SCLM; so that, in some cases, prolonged magmatism at a site causes removal of most or all of the potassic lithosphere-source melt (as mafic ultrapotassic magmas or as a contribution to mixed-source melts) without destruction of that lithosphere segment as a geophysically defined unit. Such a zone of refractory lithosphere permits subsequent, recognisable, convecting mantle source melts to penetrate it and reach the surface. These principles are illustrated by discussion of the Neogene-Quaternary magmatism of the Rio Grande, East African, Rhine and Baikal rifts, in

  15. Special People in Routine Health Information Systems Implementation in South Africa.

    PubMed

    Hanmer, Lyn A; Nicol, Edward

    2015-01-01

    An analysis of roles and decision making structures to facilitate routine health information system (RHIS) implementation and use in public health facilities in South Africa identified a wide range of stakeholders in these processes. Two broad categories of RHIS 'special people' are analysed, i.e. leaders (administrative and/or clinical) and bridgers/support staff. In addition to health system personnel with specific responsibility for RHIS, users with an interest in effective use of RHIS and RHIS outputs, and staff of external