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Sample records for african rift system

  1. 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.

  2. Kinematics and Dynamics of Observed Along-Rift Surface Motions in the East African Rift System

    NASA Astrophysics Data System (ADS)

    Stamps, D. S.; Bangerth, W.; Hager, B. H.; Kreemer, C.; Saria, E.

    2015-12-01

    Geodetic observations of Nubian and Somalian plate interiors measure ~E-W divergence across the East African Rift System (EARS), which, in the absence of slab pull forces, is driven by shallow, lithospheric buoyancy and mantle shear tractions. Previous studies indicate the former drives E-W divergence a with minimal role of basal shear. In addition to E-W extension, an increasing number of Global Navigation Satellite System (GNSS) stations within the deforming zones of the EARS detect an along-rift component of motion that is inconsistent with our current understanding of the EARS. In this work we investigate the kinematics and dynamics of these along-rift motions. We first calculate a strain rate and velocity field by fitting bi-cubic Bessel splines to new and existing GNSS observations. We resolve regions of localized compression and transtension within individual rifts that are corroborated by independent seismic and geologic observations. In a second step we test the competing roles of shallow topographic stresses and sub-lithospheric basal shear stresses acting beneath individual rifts where we observe along-rift surface motions using the finite element code ASPECT to solve for Stokes flow in a 3D regional geodynamic model. We compare predicted surface motions and mantle flow directions from our geodynamic simulations with our new continuous deformation model based on GNSS observations. Our work indicates topside driven upper mantle flow directions correspond with anomalous along-rift surface motions in several key locations, but our modeled rheological structure impedes basal shear stresses (<1-3 MPa) from driving surface deformation where we observe along-rift surface motions. This work suggests along-rift surface motions are decoupled from asthenospheric flow.

  3. 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.

  4. 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. ERTS-1 imagery of the African rift system has already proved of great value in structural geological studies. One of the interesting megastructures expressed on the imagery occurs some 40 km east of the eastern margin of the main Ethiopian rift, in Arussi province, and extending between latitude 71/2 and 81/4 deg N. The Badda-Encuolo ridge proves to have been a line of major Tertiary volcanism and probably supplied the thick Trap Series flood basalt sequence exposed farther east in the canyons of the Webi Shebeli drainage system. The ridge itself was built up by the waning activity of the Sagatu line of volcanism. Serendipitious has been the discovery on Mt. Badda of several deeply glaciated valleys, many of which show clearly on the ERTS-1 imagery. It seems that Mt. Badda was one of the most important glacial centers in eastern Africa during the Pleistocene. Three major late-Tertiary trachytic centers lie between the Badda-Encuolo ridge and the rift valley. The relationships of these three volcanoes to each other and to the rift faulting is revealed for the first time by the ERTS-1 imagery, as is the form of the cladera of Baltata and the crater of Chilalo.

  5. 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

  6. 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.

  7. Geochemical evidence for pre- and syn-rifting lithospheric foundering in the East African Rift System

    NASA Astrophysics Data System (ADS)

    Nelson, W. R.; Furman, T.; Elkins-Tanton, L. T.

    2015-12-01

    The East African Rift System (EARS) is the archetypal active continental rift. The rift branches cut through the elevated Ethiopian and Kenyan domes and are accompanied by a >40 Myr volcanic record. This record is often used to understand changing mantle dynamics, but this approach is complicated by the diversity of spatio-temporally constrained, geochemically unique volcanic provinces. Various sources have been invoked to explain the geochemical variability across the EARS (e.g. mantle plume(s), both enriched and depleted mantle, metasomatized or pyroxenitic lithosphere, continental crust). Mantle contributions are often assessed assuming adiabatic melting of mostly peridotitic material due to extension or an upwelling thermal plume. However, metasomatized lithospheric mantle does not behave like fertile or depleted peridotite mantle, so this model must be modified. Metasomatic lithologies (e.g. pyroxenite) are unstable compared to neighboring peridotite and can founder into the underlying asthenosphere via ductile dripping. As such a drip descends, the easily fusible metasomatized lithospheric mantle heats conductively and melts at increasing T and P; the subsequent volcanic products in turn record this drip magmatism. We re-evaluated existing data of major mafic volcanic episodes throughout the EARS to investigate potential evidence for lithospheric drip foundering that may be an essential part of the rifting process. The data demonstrate clearly that lithospheric drip melting played an important role in pre-flood basalt volcanism in Turkana (>35 Ma), high-Ti "mantle plume-derived" flood basalts and picrites (HT2) from NW Ethiopia (~30 Ma), Miocene shield volcanism on the E Ethiopian Plateau and in Turkana (22-26 Ma), and Quaternary volcanism in Virunga (Western Rift) and Chyulu Hills (Eastern Rift). In contrast, there is no evidence for drip melting in "lithosphere-derived" flood basalts (LT) from NW Ethiopia, Miocene volcanism in S Ethiopia, or Quaternary

  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. 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.

  10. Magmatic lithospheric heating and weakening during continental rifting: A simple scaling law, a 2-D thermomechanical rifting model and the East African Rift System

    NASA Astrophysics Data System (ADS)

    Schmeling, Harro; Wallner, Herbert

    2012-08-01

    Continental rifting is accompanied by lithospheric thinning and decompressional melting. After extraction, melt is intruded at shallower depth thereby heating and weakening the lithosphere. In a feedback mechanism this weakening may assist rifting and melt production. A one-dimensional kinematic lithospheric thinning model is developed including decompressional melting and intrusional magma deposition. The intrusional heating effect is determined as a function of thinning rate and amount, melting parameters, potential temperature, and the depth range of emplacement. The temperature increases approximately proportionally to the square root of the thinning rate and to the square of the supersolidus potential temperature. Simple scaling laws are derived allowing predicting these effects and the surface heat flux for arbitrary scenarios. Two-dimensional thermomechanical extension models are carried out for a multicomponent (crust-mantle) two-phase (melt-matrix) system with a rheology based on laboratory data including magmatic weakening. In good agreement with the 1-D kinematic models it is found that the lithosphere may heat up by several 100 K. This heating enhances viscous weakening by one order of magnitude or more. In a feedback mechanism rifting is dynamically enforced, leading to a significant increase of rift induced melt generation. Including the effect of lateral focusing of magma toward the rift axis the laws are applied to different segments of the East African Rift System. The amount of intrusional heating increases with maturity of the rift from O(10 K) to up to 200 K or 400 K at the Afar Rift depending on the depth range of the magmatic emplacement.

  11. Tomography of the East African Rift System in Mozambique

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Unlike the majority of the East African Rift, the Mozambique region has not been deeply studied, not only due to political instabilities but also because of the difficult access to its most interior regions. An earthquake with M7 occurred in Machaze in 2006, which triggered the investigation of this particular region. The MOZART project (funded by FCT, Lisbon) installed a temporary seismic network, with a total of 30 broadband stations from the SEIS-UK pool, from April 2011 to July 2013. Preliminary locations of the seismicity were estimated with the data recorded from April 2011 to July 2012. A total of 307 earthquakes were located, with ML magnitudes ranging from 0.9 to 3.9. We observe a linear northeast-southwest distribution of the seismicity that seems associated to the Inhaminga fault. The seismicity has an extension of ~300km reaching the Machaze earthquake area. The northeast sector of the seismicity shows a good correlation with the topography, tracing the Urema rift valley. In order to obtain an initial velocity model of the region, the ambient noise method is used. This method is applied to the entire data set available and two additional stations of the AfricaARRAY project. Ambient noise surface wave tomography is possible by computing cross-correlations between all pairs of stations and measuring the group velocities for all interstation paths. With this approach we obtain Rayleigh wave group velocity dispersion curves in the period range from 3 to 50 seconds. Group velocity maps are calculated for several periods and allowing a geological and tectonic interpretation. In order to extend the investigation to longer wave periods and thus probe both the crust and upper mantle, we apply a recent implementation of the surface-wave two-station method (teleseismic interferometry - Meier el al 2004) to augment our dataset with Rayleigh wave phase velocities curves in a broad period range. Using this method we expect to be able to explore the lithosphere

  12. Post-Pan-African tectonic evolution of South Malawi in relation to the Karroo and recent East African rift systems

    NASA Astrophysics Data System (ADS)

    Castaing, C.

    1991-05-01

    Structural studies conducted in the Lengwe and Mwabvi Karroo basins and in the basement in South Malawi, using regional maps and published data extended to cover Southeast Africa, serve to propose a series of geodynamic reconstructions which reveal the persistence of an extensional tectonic regime, the minimum stress σ3 of which has varied through time. The period of Karroo rifting and the tholeiitic and alkaline magmatism which terminated it, were controlled by NW-SE extension, which resulted in the creation of roughly NE-SW troughs articulated by the Tanganyika-Malawi and Zambesi pre-transform systems. These were NW-SE sinistral-slip systems with directions of movement dipping slightly to the Southeast, which enabled the Mwanza fault to play an important role in the evolution of the Karroo basins of the Shire Valley. The Cretaceous was a transition period between the Karroo rifting and the formation of the Recent East African Rift System. Extension was NE-SW, with some evidence for a local compressional episode in the Lengwe basin. Beginning in the Cenozoic, the extension once more became NW-SE and controlled the evolution in transtension of the Recent East African Rift System. This history highlights the major role of transverse faults systems dominated by strike-slip motion in the evolution and perpetuation of the continental rift systems. These faults are of a greater geological persistence than the normal faults bounding the grabens, especially when they are located on major basement anisotropies.

  13. 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.

  14. Current kinematics and dynamics of Africa and the East African Rift System

    NASA Astrophysics Data System (ADS)

    Stamps, D. S.; Flesch, L. M.; Calais, E.; Ghosh, A.

    2014-06-01

    Although the East African Rift System (EARS) is an archetype continental rift, the forces driving its evolution remain debated. Some contend buoyancy forces arising from gravitational potential energy (GPE) gradients within the lithosphere drive rifting. Others argue for a major role of the diverging mantle flow associated with the African Superplume. Here we quantify the forces driving present-day continental rifting in East Africa by (1) solving the depth averaged 3-D force balance equations for 3-D deviatoric stress associated with GPE, (2) inverting for a stress field boundary condition that we interpret as originating from large-scale mantle tractions, (3) calculating dynamic velocities due to lithospheric buoyancy forces, lateral viscosity variations, and velocity boundary conditions, and (4) calculating dynamic velocities that result from the stress response of horizontal mantle tractions acting on a viscous lithosphere in Africa and surroundings. We find deviatoric stress associated with lithospheric GPE gradients are ˜8-20 MPa in EARS, and the minimum deviatoric stress resulting from basal shear is ˜1.6 MPa along the EARS. Our dynamic velocity calculations confirm that a force contribution from GPE gradients alone is sufficient to drive Nubia-Somalia divergence and that additional forcing from horizontal mantle tractions overestimates surface kinematics. Stresses from GPE gradients appear sufficient to sustain present-day rifting in East Africa; however, they are lower than the vertically integrated strength of the lithosphere along most of the EARS. This indicates additional processes are required to initiate rupture of continental lithosphere, but once it is initiated, lithospheric buoyancy forces are enough to maintain rifting.

  15. 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

  16. 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.

  17. Historical volcanism and the state of stress in the East African Rift System

    NASA Astrophysics Data System (ADS)

    Wadge, Geoffrey; Biggs, Juliet; Lloyd, Ryan; Kendall, Michael

    2016-09-01

    Crustal extension at the East African Rift System (EARS) should, as a tectonic ideal, involve a stress field in which the direction of minimum horizontal stress is perpendicular to the rift. A volcano in such a setting should produce dykes and fissures parallel to the rift. How closely do the volcanoes of the EARS follow this? We answer this question by studying the 21 volcanoes that have erupted historically (since about 1800) and find that 7 match the (approximate) geometrical ideal. At the other 14 volcanoes the orientation of the eruptive fissures/dykes and/or the axes of the host rift segments are oblique to the ideal values. To explain the eruptions at these volcanoes we invoke local (non-plate tectonic) variations of the stress field caused by: crustal heterogeneities and anisotropies (dominated by NW structures in the Protoerozoic basement), transfer zone tectonics at the ends of offset rift segments, gravitational loading by the volcanic edifice (typically those with 1-2 km relief) and magmatic pressure in central reservoirs. We find that the more oblique volcanoes tend to have large edifices, large eruptive volumes and evolved and mixed magmas capable of explosive behaviour. Nine of the volcanoes have calderas of varying ellipticity, 6 of which are large, reservoir-collapse types mainly elongated across rift (e.g. Kone) and 3 are smaller, elongated parallel to the rift and contain active lava lakes (e.g. Erta Ale), suggesting different mechanisms of formation and stress fields. Nyamuragira is the only EARS volcano with enough sufficiently well-documented eruptions to infer its long-term dynamic behaviour. Eruptions within 7 km of the volcano are of relatively short duration (<100 days), but eruptions with more distal fissures tend to have greater obliquity and longer durations, indicating a changing stress field away from the volcano. There were major changes in long-term magma extrusion rates in 1977 (and perhaps in 2002) due to major along-rift dyking

  18. 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

  19. European Cenozoic rift system

    NASA Astrophysics Data System (ADS)

    Ziegler, Peter A.

    1992-07-01

    The European Cenozoic rift system extends from the coast of the North Sea to the Mediterranean over a distance of some 1100 km; it finds its southern prolongation in the Valencia Trough and a Plio-Pleistocene volcanic chain crossing the Atlas ranges. Development of this mega-rift was paralleled by orogenic activity in the Alps and Pyrenees. Major rift domes, accompanied by subsidence reversal of their axial grabens, developed 20-40 Ma after beginning of rifting. Uplift of the Rhenish Shield is related to progressive thermal lithospheric thinning; the Vosges-Black Forest and the Massif Central domes are probably underlain by asthenoliths emplaced at the crust/mantle boundary. Evolution of this rift system, is thought to be governed by the interaction of the Eurasian and African plates and by early phases of a plate-boundary reorganization that may lead to the break-up of the present continent assembly.

  20. The East African rift system in the light of KRISP 90

    USGS Publications Warehouse

    Keller, Gordon R.; Prodehl, C.; Mechie, J.; Fuchs, K.; Khan, M.A.; Maguire, Peter K.H.; Mooney, W.D.; Achauer, U.; Davis, P.M.; Meyer, R.P.; Braile, L.W.; Nyambok, I.O.; Thompson, G.A.

    1994-01-01

    On the basis of a test experiment in 1985 (KRISP 85) an integrated seismic-refraction/teleseismic survey (KRISP 90) was undertaken to study the deep structure beneath the Kenya rift down to depths of 100-150 km. This paper summarizes the highlights of KRISP 90 as reported in this volume and discusses their broad implications as well as the structure of the Kenya rift in the general framework of other continental rifts. Major scientific goals of this phase of KRISP were to reveal the detailed crustal and upper mantle structure under the Kenya rift, to study the relationship between mantle updoming and the development of sedimentary basins and other shallow structures within the rift, to understand the role of the Kenya rift within the Afro-Arabian rift system and within a global perspective and to elucidate fundamental questions such as the mode and mechanism of continental rifting. The KRISP results clearly demonstrate that the Kenya rift is associated with sharply defined lithospheric thinning and very low upper mantle velocities down to depths of over 150 km. In the south-central portion of the rift, the lithospheric mantle has been thinned much more than the crust. To the north, high-velocity layers detected in the upper mantle appear to require the presence of anistropy in the form of the alignment of olivine crystals. Major axial variations in structure were also discovered, which correlate very well with variations in the amount of extension, the physiographic width of the rift valley, the regional topography and the regional gravity anomalies. Similar relationships are particularly well documented in the Rio Grande rift. To the extent that truly comparable data sets are available, the Kenya rift shares many features with other rift zones. For example, crustal structure under the Kenya, Rio Grande and Baikal rifts and the Rhine Graben is generally symmetrically centered on the rift valleys. However, the Kenya rift is distinctive, but not unique, in terms of

  1. Modeling fault kinematics, segment interaction and transfer zone geometry as a function of pre-existing fabrics: the Albertine rift, East African Rift System.

    NASA Astrophysics Data System (ADS)

    Aanyu, Kevin; Koehn, Daniel

    2010-05-01

    This study focuses on the development of the Rwenzori Mountains, an uplift horst block within the northern-most segment of the western branch of the East African Rift System (EARS). Attention is drawn to the role of pre-existing crustal weaknesses left behind by Proterozoic mobile belts that pass around cratonic Archean shields namely the Tanzanian Craton to the southeast and the Congo craton to the northwest. We study how the southward propagating sub-segment of the rift that contains Lake Albert to the north interacts with the northward propagating sub-segment that contains the lakes Edward and George and how this interaction produces the structural geometries observed within and around the Rwenzori horst block. Analogue experiments are used to simulate behavior of the upper crust with pre-cut rubber strips of varying overstep/overlap, placed oblique and/or orthogonal to the extension vector. The points of connection to the basal sheet present velocity discontinuities to localize deformation below the sand. Surface geometry of the developing rifts and section cuts are used to study the kinematics that result from the given boundary conditions. In general we try to model two parallel rifts that propagate towards each other and interact. Results show that greater overstep of rifts produces an oblique shear-dominated transfer zone with deep grabens (max.7.0km) in the adjoining segments. Smaller overlap ends in extension-dominated transfer, offset rift segments without oblique transfer faults to join two adjacent rift arms and produces moderately deep grabens (max.4.6km). When overlap doubles the overstep (SbR5), rifts propagate sub-orthogonal to the extension direction in a rotation-dominated transfer and form shallow valleys (max.2.9km). Whether a block like the Rwenzori Mountains is captured and rotates, depends on the overlap/overstep ratio where the rotation direction of a captured block is determined by the sense of overlap (right- or left-lateral). Fault

  2. The East African Rift System and the impact of orographic changes on regional climate and the resulting aridification

    NASA Astrophysics Data System (ADS)

    Sommerfeld, Anja; Prömmel, Kerstin; Cubasch, Ulrich

    2016-09-01

    Several proxy data indicate an aridification of the East African climate during the Neogene, which might be influenced by the orographic changes of the East African Rift System (EARS) induced by tectonic forcing during the last 20 million years. To investigate the impact of the orography and especially of the rifts, the regional climate model CCLM is used, covering the EARS with Lake Victoria in the centre of the model domain. CCLM is driven by the ERA-Interim reanalysis and applied with a double-nesting method resulting in a very high spatial resolution of 7 km. The resolution clearly shows the shoulders and rifts of the western and eastern branch of the EARS and the Rwenzoris within the western branch. To analyse the orographic influence on climate, a new technique of modifying the orography is used in this sensitivity study. The shoulders of the branches are lowered and the rifts are elevated, resulting in a smoothed orography structure with less altitude difference between the shoulders and rifts. The changes in 2 m-temperature are very local and associated with the changes in the orography. The vertically integrated moisture transport is characterised by less vortices, and its zonal component is increased over the branches. The resulting amount of precipitation is mainly decreased west of the western branch and increased in the rift of the western branch. In the eastern branch, however, the changes in the amount of precipitation are not significant. The changes in the precipitation and temperature patterns lead to a shift of biomes towards a vegetation coverage characterised by more humid conditions in the northern part of the model domain and more arid conditions in the South. Thus, the aridification found in the proxy data can be attributed to the orographic changes of the rifts only in the northern model domain.

  3. 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

  4. 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

  5. Evolution of the western East African Rift System reflected in provenance changes of Miocene to Pleistocene synrift sediments (Albertine Rift, Uganda)

    NASA Astrophysics Data System (ADS)

    Schneider, Sandra; Hornung, Jens; Hinderer, Matthias

    2016-08-01

    Miocene to Pleistocene synrift sediments in the Albertine Graben reflect the complex geodynamic evolution in the Western branch of the East African Rift System. In this study we focus on the provenance of these siliciclastic deposits to identify sediment sources and supply paths with the ultimate goal to reconstruct the exhumation history of different tectonic blocks during prolonged rifting, with specific focus on the uplift of the Rwenzori Mountains in Uganda. We present framework and heavy mineral petrographic data combined with varietal studies of detrital garnet and rutile, based on logged sediment sections on the Ugandan side of Lake Albert (Kisegi-Nyabusosi area). The analyzed sedimentary units have a feldspatho-quartzose composition and distinct variations in heavy mineral assemblages and mineral chemical composition indicating two provenance changes. The Miocene part of the stratigraphy is dominated by garnet, zircon, tourmaline and rutile, whereas Pliocene to Pleistocene sediment yields high amounts of less stable amphibole and epidote. An abrupt switch in heavy mineral assemblages occurs during the early Pliocene ( 5.5-5.0 Ma) and clearly postdates the formation of Palaeolake Obweruka at 8 Ma. Provenance signatures point to major sediment supply from the northeast and subsequently from the southeast. We interpret this first shift as transition from the pre-rift to the syn-rift stage. In this scenario, formation of Palaeolake Obweruka is due to higher humidity in the upper Miocene, rather than forced rifting. A second change of sediment composition is documented by mineral geochemistry and coincides with fragmentation of Palaeolake Obweruka starting at 2.5 Ma. Detrital garnet in sediment of Miocene to Pliocene age is rich in pyrope and almandine and calculated Zr-in-rutile temperatures range between 550 and 950 °C. In contrast, garnet occurring in Pleistocene sediment (Nyabusosi Formation) has a higher spessartine component and rutile thermometry is

  6. 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

  7. 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

  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. Anomalous seafloor mounds in the northern Natal Valley, southwest Indian Ocean: Implications for the East African Rift System

    NASA Astrophysics Data System (ADS)

    Wiles, Errol; Green, Andrew; Watkeys, Mike; Jokat, Wilfried; Krocker, Ralph

    2014-09-01

    The Natal Valley (southwest Indian Ocean) has a complicated and protracted opening history, as has the surrounding southwest Indian Ocean. Recently collected multibeam swath bathymetry and 3.5 kHz seismic data from the Natal Valley reveal anomalous seafloor mounds in the northern Natal Valley. The significance, of these domes, as recorders of the geological history of the Natal Valley and SE African Margin has been overlooked with little attempt made to identify their origin, evolution or tectonic significance. This paper aims to describe these features from a morphological perspective and to use their occurrence as a means to better understand the geological and oceanographic evolution of this basin. The seafloor mounds are distinct in both shallow seismic and morphological character from the surrounding seafloor of the Natal Valley. Between 25 km and 31 km long, and 16 km and 18 km wide, these features rise some 400 m above the sedimentary deposits that have filled in the Natal Valley. Such macro-scale features have not previously been described from the Natal Valley or from other passive margins globally. They are not the result of bottom water circulation, salt tectonics; rather, igneous activity is favoured as the origin for these anomalous seafloor features. We propose a hypothesis that the anomalous seafloor mounds observed in the Natal Valley are related to igneous activity associated with the EARS. The complicated opening history and antecedent geology, coupled with the southward propagation of the East African Rift System creates a unique setting where continental rift associated features have been developed in a marine setting.

  10. Minimal Role of Basal Shear Tractions in Driving Nubia-Somalia Divergence Across the East African Rift System

    NASA Astrophysics Data System (ADS)

    Stamps, D. S.; Calais, E.; Iaffaldano, G.; Flesch, L. M.

    2012-12-01

    The Nubian and Somalian plates actively diverge along the topographically high, ~5000 km long East African Rift System (EARS). As no major subduction zones bound Africa, one can assume that the forces driving the Nubia-Somalia plate system result primarily from mantle buoyancies and lateral variation in lithospheric gravitational potential energy. Images from seismic tomography and convection models suggest active mantle flow beneath Africa. However, the contribution from large-scale convection to the force balance driving plate divergence across the EARS remains in question. In this work we investigate the impact of mantle shear tractions on the dynamics of Nubia-Somalia divergence across the EARS. We compare surface motions inferred from GPS observations with strain rates and velocities predicted from dynamic models where basal shear stresses are (1) derived from forward mantle circulation models and (2) inferred from stress field boundary conditions that balance buoyancy forces in the African lithosphere. Upper mantle anisotropy derived from seismic observations beneath Africa provide independent constraints for the latter. Preliminary results suggest that basal shear tractions play a minor role in the dynamics of Nubia-Somalia divergence along the EARS. This result implies mantle-lithosphere decoupling, possibly promoted by a low viscosity asthenosphere. We corroborate the robustness of our results with estimates of upper mantle viscosity based on local upper mantle temperature estimates and rheological parameters obtained from laboratory experiments.

  11. 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

  12. 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

  13. Influence of pre-existing fabrics on fault kinematics and rift geometry of interacting segments: Analogue models based on the Albertine Rift (Uganda), Western Branch-East African Rift System

    NASA Astrophysics Data System (ADS)

    Aanyu, K.; Koehn, D.

    2011-02-01

    This study aims at showing how far pre-existing crustal weaknesses left behind by Proterozoic mobile belts, that pass around cratonic Archean shields (Tanzania Craton to the southeast and Congo Craton to the northwest), control the geometry of the Albertine Rift. Focus is laid on the development of the Lake Albert and Lake Edward/George sub-segments and between them the greatly uplifted Rwenzori Mountains, a horst block located within the rift and whose highest peak rises to >5000 m above mean sea level. In particular we study how the southward propagating Lake Albert sub-segment to the north interacts with the northward propagating Lake Edward/George sub-segment south of it, and how this interaction produces the structures and geometry observed in this section of the western branch of the East African Rift, especially within and around the Rwenzori horst. We simulate behaviour of the upper crust by conducting sandbox analogue experiments in which pre-cut rubber strips of varying overstep/overlap connected to a basal sheet and oriented oblique and/or orthogonal to the extension vector, are placed below the sand-pack. The points of connection present velocity discontinuities to localise deformation, while the rubber strips represent ductile domain affected by older mobile belts. From fault geometry of developing rift segments in plan view and section cuts, we study kinematics resulting from a given set of boundary conditions, and results are compared with the natural scenario. Three different basal model-configurations are used to simulate two parallel rifts that propagate towards each other and interact. Wider overstep (model SbR3) produces an oblique transfer zone with deep grabens (max. 7.0 km) in the adjoining segments. Smaller overlap (model SbR4) ends in offset rift segments without oblique transfer faults to join the two, and produces moderately deep grabens (max. 4.6 km). When overlap doubles the overstep (model SbR5), rifts propagate sub-orthogonal to the

  14. Spatio-temporal trends in normal-fault segmentation recorded by low-temperature thermochronology: Livingstone fault scarp, Malawi Rift, East African Rift System

    NASA Astrophysics Data System (ADS)

    Mortimer, Estelle; Kirstein, Linda A.; Stuart, Finlay M.; Strecker, Manfred R.

    2016-12-01

    The evolution of through-going normal-fault arrays from initial nucleation to growth and subsequent interaction and mechanical linkage is well documented in many extensional provinces. Over time, these processes lead to predictable spatial and temporal variations in the amount and rate of displacement accumulated along strike of individual fault segments, which should be manifested in the patterns of footwall exhumation. Here, we investigate the along-strike and vertical distribution of low-temperature apatite (U-Th)/He (AHe) cooling ages along the bounding fault system, the Livingstone fault, of the Karonga Basin of the northern Malawi Rift. The fault evolution and linkage from rift initiation to the present day has been previously constrained through investigations of the hanging wall basin fill. The new cooling ages from the footwall of the Livingstone fault can be related to the adjacent depocentre evolution and across a relay zone between two palaeo-fault segments. Our data are complimented by published apatite fission-track (AFT) data and reveal significant variation in rock cooling history along-strike: the centre of the footwall yields younger cooling ages than the former tips of earlier fault segments that are now linked. This suggests that low-temperature thermochronology can detect fault interactions along strike. That these former segment boundaries are preserved within exhumed footwall rocks is a function of the relatively recent linkage of the system. Our study highlights that changes in AHe (and potentially AFT) ages associated with the along-strike displacement profile can occur over relatively short horizontal distances (of a few kilometres). This is fundamentally important in the assessment of the vertical cooling history of footwalls in extensional systems: temporal differences in the rate of tectonically driven exhumation at a given location along fault strike may be of greater importance in controlling changes in rates of vertical exhumation

  15. 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; 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.

  16. Experimental Rift Valley fever in West African Dwarf sheep.

    PubMed

    Fagbami, A H; Tomori, O; Fabiyi, A; Isoun, T T

    1975-05-01

    West African Dwarf sheep were challenged with a low mouse brain-passaged Rift Valley fever virus (Ib-AR 55172) isolated from Nigeria. Viraemia, mild febrile reaction and neutralising antibodies were demonstrated in inoculated animals.

  17. 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

  18. Petroleum geology of Cretaceous-Tertiary rift basins in Niger, Chad, and Central African Republic

    SciTech Connect

    Genik, G.J. )

    1993-08-01

    This overview of the petroleum geology of rift basins in Niger, Chad, and Central African Republic (CAR) is based on exploration work by Exxon and partners in the years 1969-1991. The work included 50,000 km of modern reflection seismic, 53 exploration wells, 1,000,000 km[sup 2] of aeromagnetic coverage, and about 10,500 km of gravity profiles. The results outline ten Cretaceous and Tertiary rift basins, which constitute a major part of the West and Central African rift system (WCARS). The rift basins derive from a multiphased geologic history dating from the Pan-African (approximately 750-550 Ma) to the Holocene. WCARS in the study area is divided into the West African rift subsystem (WAS) and the Central African rift subsystem (WAS) and the Central African rift subsystem (CAS). WAS basins in Niger and Chad are chiefly extensional, and are filled by up to 13,000 m of Lower Cretaceous to Holocene continental and marine clastics. The basins contain five oil (19-43[degrees]API) and two oil and gas accumulations in Upper Cretaceous and Eocene sandstone reservoirs. The hydrocarbons are sourced and sealed by Upper Cretaceous and Eocene marine and lacustrine shales. The most common structural styles and hydrocarbon traps usually are associated with normal fault blocks. CAS rift basins in Chad and CAR are extensional and transtensional, and are filled by up to 7500 m of chiefly Lower Cretaceous continental clastics. The basins contain eight oil (15-39[degrees]API) and one oil and gas discovery in Lower and Upper Cretaceous sandstone reservoirs. The hydrocarbons are sourced by Lower Cretaceous shales and sealed by interbedded lacustrine and flood-plain shales. Structural styles range from simple fault blocks through complex flower structures. The main hydrocarbon traps are in contractional anticlines. Geological conditions favor the discovery of potentially commercial volumes of oil in WCARS basins, of Niger, Chad and CAR. 108 refs., 24 figs., 4 tabs.

  19. 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

  20. 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.

  1. 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

  2. The life cycle of continental rifting as a focus for U.S.-African scientific collaboration

    NASA Astrophysics Data System (ADS)

    Abdelsalam, Mohamed G.; Atekwana, Estella A.; Keller, G. Randy; Klemperer, Simon L.

    2004-11-01

    The East African Rift System (EARS) provides the unique opportunity found nowhere else on Earth, to investigate extensional processes from incipient rifting in the Okavango Delta, Botswana, to continental breakup and creation of proto-oceanic basins 3000 km to the north in the Afar Depression in Ethiopia, Eritrea, and Djibouti.The study of continental rifts is of great interest because they represent the initial stages of continental breakup and passive margin development, they are sites for large-scale sediment accumulation, and their geomorphology may have controlled human evolution in the past and localizes geologic hazards in the present. But there is little research that provides insights into the linkage between broad geodynamic processes and the life cycle of continental rifts: We do not know why some rifts evolve into mid-ocean ridges whereas others abort their evolution to become aulacogens. Numerous studies of the EARS and other continental rifts have significantly increased our understanding of rifting processes, but we particularly lack studies of the embryonic stages of rift creation and the last stages of extension when continental breakup occurs.

  3. 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.

  4. Geophysical evidence of Cretaceous volcanics in Logone Birni Basin (Northern Cameroon), Central Africa, and consequences for the West and Central African Rift System

    NASA Astrophysics Data System (ADS)

    Loule, Jean-Pierre; Pospisil, Lubomil

    2013-01-01

    Detailed analyses and interpretation realized by combining existing 2D reflection seismic and Gravity/Magnetic data of the Logone Birni Basin (LBB) in the West and Central African Rift System (WCAS) have revealed the distribution of the main buried volcanic bodies as well as their relationships with the structural and tectonic evolution of this basin. The volcanic activity in the LBB is restricted to the Cretaceous period. Three main volcanic episodes are identified and are associated to the Neocomian, Late Albian and Cenomanian-Turonian rifting phases respectively. The volcanic bodies within the Lower Cretaceous are either lying directly on basement or are mainly interbedded with the contemporaneous sediments whereas the Upper Cretaceous bodies are morphologically expressed in the forms of dykes and sills. The volcanic activity was more intense in the western region of the central LBB (Zina sub-basin) along the Cameroon-Nigeria border whereas it was scanty and scattered in the other parts of the basin. The main volcanic dykes are found on the flanks of the major faults bounding basement horsts or in crestal positions in association with syndepositional faults. Although WCAS is associated with large amount of crustal extension and minor volcanism, the intense volcanic activity observed in LBB during the Cretaceous suggests that the intrusive zone during this period was confined to the basement beneath the study area flanked respectively to the north, south and southwest by the Lake Chad, Poli and Chum triple junctions. Tensional stresses generated by this localized domal uplift accounts for most of the observed tectonic structures where major faults transected the entire lithosphere, thus providing conduits for magma migration.

  5. Passive rifting of thick lithosphere in the southern East African Rift: Evidence from mantle transition zone discontinuity topography

    NASA Astrophysics Data System (ADS)

    Reed, Cory A.; Liu, Kelly H.; Chindandali, Patrick R. N.; Massingue, Belarmino; Mdala, Hassan; Mutamina, Daniel; Yu, Youqiang; Gao, Stephen S.

    2016-11-01

    To investigate the mechanisms for the initiation and early-stage evolution of the nonvolcanic southernmost segments of the East African Rift System (EARS), we installed and operated 35 broadband seismic stations across the Malawi and Luangwa rift zones over a 2 year period from mid-2012 to mid-2014. Stacking of over 1900 high-quality receiver functions provides the first regional-scale image of the 410 and 660 km seismic discontinuities bounding the mantle transition zone (MTZ) within the vicinity of the rift zones. When a 1-D standard Earth model is used for time-depth conversion, a normal MTZ thickness of 250 km is found beneath most of the study area. In addition, the apparent depths of both discontinuities are shallower than normal with a maximum apparent uplift of 20 km, suggesting widespread upper mantle high-velocity anomalies. These findings suggest that it is unlikely for a low-velocity province to reside within the upper mantle or MTZ beneath the nonvolcanic southern EARS. They also support the existence of relatively thick and strong lithosphere corresponding to the widest section of the Malawi rift zone, an observation that is consistent with strain localization models and fault polarity and geometry observations. We postulate that the Malawi rift is driven primarily by passive extension within the lithosphere attributed to the divergent rotation of the Rovuma microplate relative to the Nubian plate, and that contributions of thermal upwelling from the lower mantle are insignificant in the initiation and early-stage development of rift zones in southern Africa.

  6. 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

  7. Venus: Geology of Beta Regio rift system

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    Beta Regio is characterized by the existence of rift structures. We compiled new geologic maps of Beta Regio according to Magellan data. There are many large uplifted tesserae on beta upland. These tesserae are partly buried by younger volcanic cover. We can conclude, using these observations, that Beta upland formed mainly due to lithospheric tectonic uplifting and was only partly constructed by volcanism. Theia Mons is the center of the Beta rift system. Many rift belts are distributed radially to Theia Mons. Typical widths of rifts are 40-160 km. Rift valleys are structurally represented by crustal grabens or half-grabens. There are symmetrical and asymmetrical rifts. Many rifts have shoulder uplifts up to 0.5-1 km high and 40-60 km wide. Preliminary analysis for rift valley structural cross sections lead to the conclusion that rifts originated due to 5-10 percent crustal extension. Many rifts traverse Beta upland and spread to the surrounding lowlands. We can assume because of these data that Beta rift system has an active-passive origin. It formed due to regional tectonic lithospheric extension. Rifting was accelerated by upper-mantle hot spot origination under the center of passive extension (under the Beta Regio).

  8. Upper mantle structure of the Congo Craton and the East African Rift from full wave ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Emry, E.; Shen, Y.; Nyblade, A.; Bao, X.; Flinders, A. F.

    2015-12-01

    The relationship between lithospheric structure, mantle flow, and continental rifting along the East African Rift is the subject of ongoing discussion. The upper mantle beneath the Main Ethiopian Rift and the East African Rift farther south has been seismically imaged following the deployment of several temporary regional arrays. However, due to uneven distribution of seismic arrays, key questions regarding a connection between these upper mantle anomalies at the Turkana Depression and the effect that the thick Congo Craton has on diverting upwelling material towards the East African Rift are poorly resolved. We use overlapping records from several temporary and permanent broadband seismic arrays (1980-2014) located throughout the African continent and surrounding regions in order to image the upper mantle beneath the East African Rift and the Congo Craton where regional seismic arrays have not been deployed. We do this by seismic ambient noise tomography using the recently developed frequency-time normalization (FTN) method to extract empirical Green's functions (EGFs) at periods of 7-250 seconds. We cross correlate the normalized continuous records and stack them to obtain EGFs for each temporally coincident station-station pair. We simulate wave propagation through a spherical Earth using a finite-difference method, measure phase delay times between synthetics and EGFs, and invert them for velocity perturbations with 3D Rayleigh wave sensitivity kernels. We will present results from full-wave ambient noise inversions that illuminate upper mantle structure throughout the continent, with particular focus on the Congo Craton and northern sections of the East African Rift System.

  9. Present-day kinematics of the East African Rift

    NASA Astrophysics Data System (ADS)

    Saria, E.; Calais, E.; Stamps, D. S.; Delvaux, D.; Hartnady, C. J. H.

    2014-04-01

    The East African Rift (EAR) is a type locale for investigating the processes that drive continental rifting and breakup. The current kinematics of this ~5000 km long divergent plate boundary between the Nubia and Somalia plates is starting to be unraveled thanks to a recent augmentation of space geodetic data in Africa. Here we use a new data set combining episodic GPS measurements with continuous measurements on the Nubian, Somalian, and Antarctic plates, together with earthquake slip vector directions and geologic indicators along the Southwest Indian Ridge to update the present-day kinematics of the EAR. We use geological and seismological data to determine the main rift faults and solve for rigid block rotations while accounting for elastic strain accumulation on locked active faults. We find that the data are best fit with a model that includes three microplates embedded within the EAR, between Nubia and Somalia (Victoria, Rovuma, and Lwandle), consistent with previous findings but with slower extension rates. We find that earthquake slip vectors provide information that is consistent with the GPS velocities and helps to significantly reduce uncertainties of plate angular velocity estimates. We also find that 3.16 Myr MORVEL average spreading rates along the Southwest Indian Ridge are systematically faster than prediction from GPS data alone. This likely indicates that outward displacement along the SWIR is larger than the default value used in the MORVEL plate motion model.

  10. Turbidite systems of lacustrine rift basins: Examples from the Lake Kivu and Lake Albert rifts, East Africa

    NASA Astrophysics Data System (ADS)

    Zhang, Xuewei; Scholz, Christopher A.

    2015-07-01

    The Holocene turbidite systems of Lake Kivu and the Pliocene turbidite systems of Lake Albert in the East African Rift were examined using high-resolution 2-D and 3-D seismic reflection data and sediment core information. Based on investigations of seismic facies and lithofacies, several key turbidity-flow depositional elements were observed, including channels, overbank levees with sediment waves, and depositional lobes. Analyses of the sources of the recent and ancient turbidite systems in these two extensional basins suggest that flood-induced hyperpycnal flows are important triggers of turbidity currents in lacustrine rift basins. From source to sink, sediment dispersal, facies distribution, and depositional thickness of the turbidite systems are strongly influenced by rift topography. The Lake Kivu and Lake Albert rifts serve as excellent analogues for understanding the sedimentary patterns of lacustrine turbidites in extensional basins.

  11. 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.

  12. The evolving contribution of border faults and intra-rift faults in early-stage East African rifts: insights from the Natron (Tanzania) and Magadi (Kenya) basins

    NASA Astrophysics Data System (ADS)

    Muirhead, J.; Kattenhorn, S. A.; Dindi, E.; Gama, R.

    2013-12-01

    In the early stages of continental rifting, East African Rift (EAR) basins are conventionally depicted as asymmetric basins bounded on one side by a ~100 km-long border fault. As rifting progresses, strain concentrates into the rift center, producing intra-rift faults. The timing and nature of the transition from border fault to intra-rift-dominated strain accommodation is unclear. Our study focuses on this transitional phase of continental rifting by exploring the spatial and temporal evolution of faulting in the Natron (border fault initiation at ~3 Ma) and Magadi (~7 Ma) basins of northern Tanzania and southern Kenya, respectively. We compare the morphologies and activity histories of faults in each basin using field observations and remote sensing in order to address the relative contributions of border faults and intra-rift faults to crustal strain accommodation as rifting progresses. The ~500 m-high border fault along the western margin of the Natron basin is steep compared to many border faults in the eastern branch of the EAR, indicating limited scarp degradation by mass wasting. Locally, the escarpment shows open fissures and young scarps 10s of meters high and a few kilometers long, implying ongoing border fault activity in this young rift. However, intra-rift faults within ~1 Ma lavas are greatly eroded and fresh scarps are typically absent, implying long recurrence intervals between slip events. Rift-normal topographic profiles across the Natron basin show the lowest elevations in the lake-filled basin adjacent to the border fault, where a number of hydrothermal springs along the border fault system expel water into the lake. In contrast to Natron, a ~1600 m high, densely vegetated, border fault escarpment along the western edge of the Magadi basin is highly degraded; we were unable to identify evidence of recent rupturing. Rift-normal elevation profiles indicate the focus of strain has migrated away from the border fault into the rift center, where

  13. Analogies Between the East African Rift Around the Tanzania Craton and the Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Montesi, L. G.

    2013-12-01

    Continental rifts and oceanic spreading centers both accommodate plate divergence but their morphologies are often quite different. Yet, ultraslow spreading centers, especially the Southwest Indian ridge at the 9 to 16°E area (SWIR), present good analogies for the East African Rift (EAR), including localized volcanism, avolcanic segments, and a continuous but not straight rift axis. The archetypal oceanic spreading center features transform offsets. Volcanism is continuous along the ridge axis and is most vigorous at the center of spreading segments. By contrast, continental rifts do not feature transform offsets. The orientation of the rift can change along strike. Several rift segments are purely tectonic, with relatively isolated volcanic centers. The EAR around the Tanzania Craton clearly shows this kind of morphology. Ultraslow spreading centers share many of these features. The SWIR, in particular, displays dramatic changes in orientation, with volcanism localized at the junction between segments of different obliquity. Melt production and transport are controlled by the effective spreading rate, a combination of plate divergence velocity and rift obliquity. Ultraslow spreading center all have an effective spreading rate less than 13 mm/yr. At that speed the thickness of the thermal boundary layer is similar to the depth from which magma can be effectively extracted, opening the possibility for long-distance transport of magma along axis without extraction. Volcanic centers correspond to the location where the magma transport system first encounters a tectonically damaged zone that enables extraction to the surface. The effective velocity of the EAR in the Kenya dome is less than 4mm/yr firmly on par with ultraslow ridges. In fact, to generate magma by mantle upwelling at such a slow opening rate requires a higher mantle temperature or fertility than in the oceanic domain. Both opening rate and effective velocity increase northward along the Eastern branch

  14. Seismicity Patterns and Magmatic Processes in the Rwenzori Region, East-African Rift

    NASA Astrophysics Data System (ADS)

    Lindenfeld, M.; Rumpker, G.; Schmeling, H.; Wallner, H.

    2010-12-01

    The 5000m high Rwenzori Mountains are situated within the western branch of the East African Rift System (EARS), at the border between Uganda and the Democratic Republic of Congo. They represent a basement block located within the rift valley whose origin and relation to the evolution of the EARS are highly puzzling. During a recent seismological campaign we located more than 800 earthquakes per month with magnitudes ranging from 0.5 to 5.1. Vertical sections across the northern parts of the Rwenzoris show, that west of the mountains (towards the rift valley) the focal depths range from 10 to 20 km, whereas the hypocentres go as deep as 30 km on the eastern side. This is in good agreement with Moho-depths derived from receiver functions and implies that all of these events are located within the crust. However, about 30 km east of the northern mountain ridge we located a cluster of 7 events that exhibit an anomalous depth of about 60 km. We can confidently locate these earthquakes within the mantle lithosphere beneath the rift. The existence of earthquakes at this depth is enigmatic, especially within a rifting regime were one expects hot and weak material relatively close to the surface. We think that these events are possibly related to the evolution of the Rwenzori Mountains. A recent hypothesis to explain the extreme uplift of the Rwenzori Mountains is rift induced delamination (RID) of mantle lithosphere. Here we show that the RID-process is indeed capable of explaining the seismic energy release in the mantle. However, in view of the specific hypocentral location of the event cluster, magmatic impregnation processes associated with dyke propagation into the mantle lithosphere may be a more realistic cause for seismic radiation at the observed depth. Crustal earthquakes northeast of the Rwenzori area are relocated with a double-difference algorithm to improve the spatial resolution of seismicity pattern. Several event clusters in the vicinity of the Fort

  15. Giant Seismites and Megablock Uplift in the East African Rift: Evidence for Late Pleistocene Large Magnitude Earthquakes

    PubMed Central

    Hilbert-Wolf, Hannah Louise; Roberts, Eric M.

    2015-01-01

    In lieu of comprehensive instrumental seismic monitoring, short historical records, and limited fault trench investigations for many seismically active areas, the sedimentary record provides important archives of seismicity in the form of preserved horizons of soft-sediment deformation features, termed seismites. Here we report on extensive seismites in the Late Quaternary-Recent (≤ ~ 28,000 years BP) alluvial and lacustrine strata of the Rukwa Rift Basin, a segment of the Western Branch of the East African Rift System. We document examples of the most highly deformed sediments in shallow, subsurface strata close to the regional capital of Mbeya, Tanzania. This includes a remarkable, clastic ‘megablock complex’ that preserves remobilized sediment below vertically displaced blocks of intact strata (megablocks), some in excess of 20 m-wide. Documentation of these seismites expands the database of seismogenic sedimentary structures, and attests to large magnitude, Late Pleistocene-Recent earthquakes along the Western Branch of the East African Rift System. Understanding how seismicity deforms near-surface sediments is critical for predicting and preparing for modern seismic hazards, especially along the East African Rift and other tectonically active, developing regions. PMID:26042601

  16. Giant seismites and megablock uplift in the East African Rift: evidence for Late Pleistocene large magnitude earthquakes.

    PubMed

    Hilbert-Wolf, Hannah Louise; Roberts, Eric M

    2015-01-01

    In lieu of comprehensive instrumental seismic monitoring, short historical records, and limited fault trench investigations for many seismically active areas, the sedimentary record provides important archives of seismicity in the form of preserved horizons of soft-sediment deformation features, termed seismites. Here we report on extensive seismites in the Late Quaternary-Recent (≤ ~ 28,000 years BP) alluvial and lacustrine strata of the Rukwa Rift Basin, a segment of the Western Branch of the East African Rift System. We document examples of the most highly deformed sediments in shallow, subsurface strata close to the regional capital of Mbeya, Tanzania. This includes a remarkable, clastic 'megablock complex' that preserves remobilized sediment below vertically displaced blocks of intact strata (megablocks), some in excess of 20 m-wide. Documentation of these seismites expands the database of seismogenic sedimentary structures, and attests to large magnitude, Late Pleistocene-Recent earthquakes along the Western Branch of the East African Rift System. Understanding how seismicity deforms near-surface sediments is critical for predicting and preparing for modern seismic hazards, especially along the East African Rift and other tectonically active, developing regions.

  17. 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.

  18. Chow Bahir rift: A “failed” rift in southern Ethiopia

    NASA Astrophysics Data System (ADS)

    W-Gabriel, Giday; Aronson, James L.

    1987-05-01

    The Chow Bahir rift system is a major graben in a 300-km-broad rift zone recognized in southern Ethiopia between the Kenyan and Ethiopian domes where the East African rift is not well defined. An extinct (failed) rift discovered along the Omo Canyon to the north and on strike with the Chow Bahir rift ceased activity about 4 m.y. ago. Chow Bahir is in a younger stage of abandonment as the main Ethiopian rift propagates south into this region.

  19. 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.

  20. 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

    The West Antarctic rift system extends over a 3000 × 750 km, largely ice covered area from the Ross Sea to the base of the Antarctic Peninsula, comparable in area to the Basin and Range and the East African rift system. A spectacular rift shoulder scarp along which peaks reach 4-5 km maximum elevation marks one flank and extends from northern Victoria Land-Queen Maud Mountains to the Ellsworth-Whitmore-Horlick Mountains. The rift shoulder has maximum present physiographic relief of 5 km in the Ross Embayment and 7 km in the Ellsworth Mountains-Byrd Subglacial Basin area. The Transantarctic Mountains part of the rift shoulder (and probably the entire shoulder) has been interpreted as 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. The rift system is characterized by bimodal alkaline volcanic rocks ranging from at least Oligocene to the present. These are exposed asymmetrically along the rift flanks and at the south end of the Antarctic Peninsula. The trend of the Jurassic tholeiites (Ferrar dolerites, Kirkpatric basalts) marking the Jurassic Transantarctic rift is coincident with exposures of 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 continuously (including the Dufek intrusion) along the lower- elevation (1-2 km) section of Transantarctic Mountains to the Weddell Sea. Widely spaced aeromagnetic profiles in West Antarctica indicate the absence of Cenozoic volcanic rocks in the ice covered part of the Whitmore-Ellsworth-Mountain block and suggest their widespread occurrence beneath the western part of the ice sheet overlying the Byrd Subglacial Basin. A German Federal Institute for Geosciences and Natural Resources (BGR)-U.S. Geological Survey (USGS) aeromagnetic

  1. Assessment of conventional oil resources of the East African Rift Province, East Africa, 2016

    USGS Publications Warehouse

    Brownfield, Michael E.; Schenk, Christopher J.; Klett, Timothy R.; Mercier, Tracey J.; Gaswirth, Stephanie B.; Marra, Kristen R.; Finn, Thomas M.; Le, Phuong A.; Leathers-Miller, Heidi M.

    2017-03-27

    Using a geology-based assessment methodology, the U.S. Geological Survey estimated undiscovered, technically recoverable mean conventional resources of 13.4 billion barrels of oil and 4.6 trillion cubic feet of gas in the East African Rift Province of east Africa.

  2. 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...

  3. 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.

  4. The role of inherited crustal structures and magmatism in the development of rift segments: Insights from the Kivu basin, western branch of the East African Rift

    NASA Astrophysics Data System (ADS)

    Smets, Benoît; Delvaux, Damien; Ross, Kelly Ann; Poppe, Sam; Kervyn, Matthieu; d'Oreye, Nicolas; Kervyn, François

    2016-06-01

    The study of rift basin's morphology can provide good insights into geological features influencing the development of rift valleys and the distribution of volcanism. The Kivu rift segment represents the central section of the western branch of the East African Rift and displays morphological characteristics contrasting with other rift segments. Differences and contradictions between several structural maps of the Kivu rift make it difficult to interpret the local geodynamic setting. In the present work, we use topographic and bathymetric data to map active fault networks and study the geomorphology of the Kivu basin. This relief-based fault lineament mapping appears as a good complement for field mapping or mapping using seismic reflection profiles. Results suggest that rifting reactivated NE-SW oriented structures probably related to the Precambrian basement, creating transfer zones and influencing the location and distribution of volcanism. Both volcanic provinces, north and south of the Kivu basin, extend into Lake Kivu and are connected to each other with a series of eruptive vents along the western rift escarpment. The complex morphology of this rift basin, characterized by a double synthetic half-graben structure, might result from the combined action of normal faulting, magmatic underplating, volcanism and erosion processes.

  5. Topographic and Structural Analysis of Devana Chasma, Venus: A Propagating Rift System

    NASA Astrophysics Data System (ADS)

    Kiefer, W. S.; Swafford, L. C.

    2003-12-01

    Devana Chasma is a rift system on Venus that formed due to extensional stresses from the Beta Regio and Phoebe Regio mantle plumes. Devana has often been compared to the East African Rift system on Earth. Here, we focus on the portion of Devana in the lowland plains between Beta and Phoebe, 20 North - 4 South, a distance of 2500 km. Over this region, Devana is typically 150 to 250 km wide. Recent gravity modeling (Kiefer and Peterson, Geophys. Res. Lett., Jan. 2003) demonstrated that most of this segment of the rift is presently underlain by hot, low density mantle material. The rift has a 600 km lateral offset near 8 North latitude, where the gravity results show no evidence for hot mantle. This lead Kiefer and Peterson to propose that Devana is actually two propagating rifts, one propagating southward from Beta Regio and the other propagating northward from Phoebe Regio. As a test of this hypothesis, we have examined the detailed structural geology of this section of the rift using topographic profiles and radar imagery from the Magellan mission. We constructed a series of topographic transects spaced at approximately 50 km intervals along the rift and measured the average flank height and the maximum rift depth. We measured the total vertical offset along faulted surfaces and converted this to horizontal extension assuming a characteristic normal fault dip of 60 degrees. Plots of these quantities as a function of distance along the rift reveals several characteristic zones. Average flank height has maximum values near the edges of Beta Regio (3.5 km) and Phoebe Regio (2.75 km) and decreases rapidly as the rift crosses the intervening plains. This is consistent with the rift forming due to thermal anomalies centered at Beta and Phoebe. The virtual absence of elevated rift flanks in the offset region near 8 North is consistent with the absence of hot mantle in this region, as inferred from the gravity model. The horizontal extension decreases strongly with

  6. Morphotectonics of the Tunka rift and its bordering mountains in the Baikal rift system, Russia

    NASA Astrophysics Data System (ADS)

    Shchetnikov, Alexander

    2016-11-01

    The Tunka section of the Baikal rift system presents a uniform alternation of the following neostructural forms: tilted horsts and asymmetrical block uplifts on the northern flank; the central system of the rift valleys; and the arched uplift of the southern flank. This is a standard set of morphostructural elements for the Baikal rift system. The main morphological feature of the Tunka rift is the strong inclination of its floor, ranging from 900 m to 200 km in general elevation above Lake Baikal. Such traits of recent geodynamics as volcanism, thermal activity, and seismicity are also different from other parts of the rift zone. All of these features of the Tunka rift are related to the deep structure of the rift zone. The peculiarities of the neotectonic structure of the Tunka rift, which are clearly expressed morphologically as is typical of the Baikal rift system, as well as its unique features are in accordance with deep geodynamic processes of the region. On the other hand, the development of the rift basin structures of the southwestern area near Baikal is complicated by inversion deformations. Local uplifts followed by deformations of the basin sedimentary cover and inverted morphostructures expressed in relief are fixed against the background of the general subsidence of blocks of the pre-Cenozoic basement grabens. The Tunka rift has repeatedly experienced inversion deformations throughout its history. The last wave of such deformations involved the southwestern region near Baikal in the second half of the late Pleistocene. During the Quaternary, the positive component prevailed in the whole range of vertical movements of the inter-rift and interbasin blocks; since the late Neogene, these structures have experienced a slow but steady uplift, accompanied by their extension at the expense of the bordering basins. The remote influence of the India-Asia collision on the formation of the southwestern section of the Baikal rift system is very significant and

  7. Rifting Attractor Structures in the Baikal Rift System: Location and Effects

    NASA Astrophysics Data System (ADS)

    Klyuchevskii, Anatoly V.

    2014-07-01

    The current geodynamics and tectonophysics of the Baikal rift system (BRS) as recorded in lithospheric stress and strain are discussed in the context of self organization of nonlinear dissipative dynamic systems and nonlinear media. The regional strain field inferred from instrumental seismic moment and fault radius data for almost 70,000 MLH ⩾ 2.0 events of 1968 through 1994 shows a complex pattern with zones of high strain anisotropy in the central part and both flanks of the rift system (the South Baikal, Hovsgöl, and Muya rift basins, respectively). The three zones of local strain anisotropy highs coincide with domains of predominantly vertical stress where earthquakes of different magnitudes are mostly of normal slip geometry. Pulse-like reversals of principal stresses in the high-strain domains appear to be nonlinear responses of the system to subcrustal processes. In this respect, the BRS lithosphere is interpreted in terms of the self organization theory as a geological dissipative system. Correspondingly, the domains of high strain anisotropy and stress change, called rifting attractor structures (RAS), are the driving forces of its evolution. The location and nonlinear dynamics of the rifting attractors have controlled lithospheric stress and strain of the rift system over the period of observations, and the same scenario may have been valid also in the Mesozoic-Cenozoic rifting history. The suggested model of a positive-feedback (fire-like) evolution of nonlinear dynamical systems with rifting attractors opens a new perspective on the current geodynamics and tectonophysics of the Baikal rift system.

  8. Petroleum geology of rift basins in Niger, Chad, and the Central African Republic

    SciTech Connect

    Genik, G.J. )

    1991-03-01

    Ten Cretaceous-Tertiary rift basins in Niger, Chad, and the Central African Republic (C.A.R.) are defined and the petroleum geology is overviewed. This paper is based on proprietary exploration results derived from more than 1 million km{sup 2} of aeromagnetics, 10,520 line km of gravity profiles, 49,721 km of reflection seismic, and 50 exploration wells. The data were acquired by Exxon with partners Shell, Chevron, Elf, Conoco, Texaco, and Amax Oil Gas, Inc., during the years 1969-1989. In Niger and Chad, the West African rift subsystem includes the extensional basins of Termit, Tefidet, Tenere, Grein/Kafra, N'Djel Edji, and Bongor. These rift basins contain up to 15,000 m of Cretaceous to Cenozoic continental and marine clastics. Key exploration elements are Tertiary and Cretaceous fluvial to tidal sandstone reservoirs, Tertiary and Cretaceous marine to lacustrine shale source rocks, and seals, with traps in normal fault blocks and anticlinal closures. There are six oil discoveries in the Termit basin. In Chad and the C.A.R., the Central African rift subsystem incorporates the extensional Doba and transtensional Doseo and Salamat basins flanking the Borogop dextral wrench fault. These basins contain up to 7,500 m of chiefly Cretaceous continental clastics. Key exploration elements are Lower and Upper Cretaceous fluvial to lacustrine sandstone reservoirs, Lower Cretaceous lacustrine shale source rocks, lacustrine to flood plain shale and mudstone seals, with traps in mainly faulted anticlinal closures. There are six oil discoveries in the Doba basin and three in the Doseo basin. The studied petroleum geology in the rifts of Niger, Chad, and the C.A.R. indicates that potentially commercial volumes of oil remain to be discovered.

  9. Petroleum geology of rift basins in Niger, Chad, and Central African Republic

    SciTech Connect

    Genik, G.J. )

    1991-08-01

    Ten Cretaceous-Tertiary rift basins in Niger, Chad and the Central African Republic (C.A.R.) are defined and the petroleum geology is overviewed based on proprietary exploration results derived from more than one million km{sup 2} of aeromagnetics, 10,520 line-km of gravity profiles, 49,721 km of reflection seismic, and 50 exploration wells. The data were acquired by Exxon with partners Shell, Chevron, Elf, Conoco, Texaco, and Amax Oil Gas During 1969-1989. In Niger and Chad, the West African rift subsystem includes the extensional basins of Termit, Tefidet, Tenere, Grein/Kafra, N'Djel Edji, and Bongor. These rift basins contain up to 15,000 m of Cretaceous to Cenozoic continental and marine clastics. Key exploration elements are Tertiary and Cretaceous fluvial to tidal sandstone reservoirs, Tertiary and Cretaceous marine to lacustrine shale source rocks and seals, with traps in normal fault blocks and anticlinal closures. There have been six oil discoveries in the Termit basin. In C.A.R., the Central African rift subsystem incorporates the extensional Doba and transtensional Doseo and Salamat basins flanking the Borogop dextral wrench fault. These basins contain up to 7,500 m of chiefly Cretaceous continental clastics. key exploration elements are Lower and Upper Cretaceous fluvial to lacustrine sandstone reservoirs, Lower Cretaceous lacustrine shale source rocks, lacustrine to flood-plain shale and mudstone seals, with traps in mainly faulted anticlinal closures. There have been six oil discoveries in the Doba basin and three in the Doseo basin. The studied petroleum geology in the rifts of Niger, Chad, and C.A.R. indicates that potentially commercial volumes of oil remain to be discovered.

  10. A new brachypterous scarab species, Orphnus longicornis (Coleoptera: Scarabaeidae: Orphninae), from the East African Rift.

    PubMed

    Frolov, Andrey; Akhmetova, Lilia

    2015-11-05

    The Afrotropical Region is the center of the diversity of the scarab beetle genus Orphnus MacLeay, 1819 (Coleoptera: Scarabaeidae: Orphninae), with 94 species occurring from Sahel in the north to Little Karoo in the south (Paulian, 1948; Petrovitz, 1971; Frolov, 2008). The East African Rift is one of the richest regions of the Afrotropics housing more than 20 species of Orphnus (Paulian, 1948; Frolov, 2013), most of which are endemic to this region. Yet the scarab beetle fauna of the East African Rift, and especially the Eastern Arc Mountains, is still inadequately studied. Examination of the material housed in the Museum of Natural History of Humboldt-Universität, Berlin, Germany (ZMHUB), revealed a series of brachypterous Orphnus beetles belonging to an undescribed species. The new species is described and illustrated below.

  11. Plate kinematics of the Afro-Arabian Rift System with emphasis on the Afar Depression, Ethiopia

    NASA Astrophysics Data System (ADS)

    Bottenberg, Helen Carrie

    This work utilizes the Four-Dimensional Plates (4DPlates) software, and Differential Interferometric Synthetic Aperture Radar (DInSAR) to examine plate-scale, regional-scale and local-scale kinematics of the Afro-Arabian Rift System with emphasis on the Afar Depression in Ethiopia. First, the 4DPlates is used to restore the Red Sea, the Gulf of Aden, the Afar Depression and the Main Ethiopian Rift to development of a new model that adopts two poles of rotation for Arabia. Second, the 4DPlates is used to model regional-scale and local-scale kinematics within the Afar Depression. Most plate reconstruction models of the Afro-Arabian Rift System relies on considering the Afar Depression as a typical rift-rift-rift triple junction where the Arabian, Somali and Nubian (African) plates are separating by the Red Sea, the Gulf of Aden and the Main Ethiopian Rift suggesting the presence of "sharp and rigid" plate boundaries. However, at the regional-scale the Afar kinematics are more complex due to stepping of the Red Sea propagator and the Gulf of Aden propagator onto Afar as well as the presence of the Danakil, Ali Sabieh and East Central Block "micro-plates". This study incorporates the motion of these micro-plates into the regional-scale model and defined the plate boundary between the Arabian and the African plates within Afar as likely a diffused zone of extensional strain within the East Central Block. Third, DInSAR technology is used to create ascending and descending differential interferograms from the Envisat Advanced Synthetic Aperture Radar (ASAR) C-Band data for the East Central Block to image active crustal deformation related to extensional tectonics and volcanism. Results of the DInSAR study indicate no strong strain localization but rather a diffused pattern of deformation across the entire East Central Block.

  12. Melt globules as micro-magmachambers: Extreme fractionation in peralkaline nephelinite at Nyiragongo, East African Rift

    NASA Astrophysics Data System (ADS)

    Andersen, Tom; Elburg, Marlina; Erambert, Muriel

    2014-05-01

    Highly peralkaline leucite nephelinite from the active volcano Nyiragongo in the Virunga province of the East African Rift contains globules of iron- and volatile-rich, highly peralkaline silicate glass with (Na+K)/Al up to 18, which has formed as a late differentiate of less peralkaline precursors, probably by fractional crystallization at a shallow level in the volcanic system. Several uncommon minerals coexist with this glass (kalsilite, kirschsteinite, chlorbartonite, götzenite, delhayelite, zirconian cuspidine, rare alkali-barium minerals), while combeite is a near-solidus mineral. Low-variance mineral assemblages define a cooling trend from eruptive temperatures ≥980 ºC to the solidus of extremely peralkaline residual liquids at 600 ºC. Oxygen fugacities well below the QFM buffer (QFM-2 to-3) persisted throughout the magmatic crystallization stage. The oxygen fugacity increased to QFM+1 or higher during the final stage of postmagmatic recrystallization. Highly alkaline, volatile-rich minerals such as delhayelite, götzenite and cuspidine were stabilized by a combination of high peralkalinity and elevated activity of chlorine and fluorine; these conditions persisted to sub-solidus temperatures. The exotic mineralogy in these melt globules is similar to mineral assemblages in agpaitic nepheline syenites. The crystallization hisotory of these globules may be an analogue to fractionation processes in large, agpaitic intrusions (e.g. Ilímaussaq, Greenland), including the interplay of the controlling factors peralkalinity, oxygen- and volatile fugacity.

  13. Extreme peralkalinity in delhayelite- and andremeyerite-bearing nephelinite from Nyiragongo volcano, East African Rift

    NASA Astrophysics Data System (ADS)

    Andersen, Tom; Elburg, Marlina A.; Erambert, Muriel

    2014-10-01

    Highly peralkaline leucite nephelinite from the active volcano Nyiragongo in the Virunga province of the East African Rift contains globules of iron- and volatile-rich, highly peralkaline silicate glass with (Na + K)/Al up to 18 which has formed as a late differentiate of less peralkaline precursors, probably by fractional crystallization at a shallow level in the volcanic system. A number of uncommon minerals coexist with this glass (kalsilite, kirschsteinite, chlorbartonite, götzenite, delhayelite, umbrianite, zirconian cuspidine, andremeyerite (BaFe2Si2O7), other Ba-Fe-Ti silicate minerals, and unnamed alkali-barium phosphate and Zr-Nb-Ti silicate minerals). These minerals are members of late magmatic assemblages that have survived sub-solidus recrystallization. Combeite occurs as a near-solidus mineral. Low-variance mineral assemblages in Nyiragongo nephelinite define a cooling trend from eruptive temperatures ≥ 980 °C to the solidus of extremely peralkaline residual liquids at ca. 600 °C, followed by sub-solidus recrystallization and metasomatism down to ca. 500 °C. Oxygen fugacity well below the QFM buffer (QFM-2 to -3) persisted throughout the magmatic crystallization stage, but increased to above QFM during the final stage of postmagmatic recrystallization. Highly alkaline, volatile-rich minerals such as delhayelite, götzenite and cuspidine were stabilized by a combination of high peralkalinity and elevated activity of chlorine and fluorine; these conditions persisted to sub-solidus temperatures.

  14. Thick lithosphere, deep crustal earthquakes and no melt: a triple challenge to understanding extension in the western branch of the East African Rift

    NASA Astrophysics Data System (ADS)

    O'Donnell, J. P.; Selway, K.; Nyblade, A. A.; Brazier, R. A.; Tahir, N. El; Durrheim, R. J.

    2016-02-01

    rift system. Stresses arising from the gravitational force related to the uplift of the East African Plateau provide only one-eighth of the minimum stress necessary to produce observed lower crustal earthquakes in the western branch. We expect that some of this disparity may be accounted for by considering smaller scale bending stresses and dynamic feedbacks between brittle and elastic deformation and between faulting, topography and weathering that are not currently included in models of the East African Rift.

  15. Small-scale thermal upwellings under the northern East African Rift from S travel time tomography

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    There is a long-standing debate over how many and what types of plumes underlie the East African Rift and whether they do or do not drive its extension and consequent magmatism and seismicity. Here we present a new tomographic study of relative teleseismic S and SKS residuals that expands the resolution from previous regional studies below the northern East African Rift to image structure from the surface to the base of the transition zone. The images reveal two low-velocity clusters, below Afar and west of the Main Ethiopian Rift, that extend throughout the upper mantle and comprise several smaller-scale (about 100 km diameter), low-velocity features. These structures support those of our recent P tomographic study below the region. The relative magnitude of S to P residuals is around 3.5, which is consistent with a predominantly thermal nature of the anomalies. The S and P velocity anomalies in the low-velocity clusters can be explained by similar excess temperatures in the range of 100-200°C, consistent with temperatures inferred from other seismic, geochemical, and petrological studies. Somewhat stronger VS anomalies below Afar than west of the Main Ethiopian Rift may include an expression of volatiles and/or melt in this region. These results, together with a comparison with previous larger-scale tomographic models, indicate that these structures are likely small-scale upwellings with mild excess temperatures, rising from a regional thermal boundary layer at the base of the upper mantle.

  16. Planation surfaces as a record of medium to large wavelength deformation: the example of the Lake Albert Rift (Uganda) on the East African Dome

    NASA Astrophysics Data System (ADS)

    Brendan, Simon; François, Guillocheau; Cécile, Robin; Jean, Braun; Olivier, Dauteuil; Massimo, Dall'Asta

    2016-04-01

    African relief is characterized by planation surfaces, some of them of continental scale. These surfaces are slightly deformed according to different wavelengths (x10 km; x100 km, x1000 km) which record both mantle dynamics (very long wavelength, x 1000 km) and lithosphere deformation (long wavelength deformation, x 100 km). Different types of these planation surfaces are recognized: - Etchplains capped by iron-duricrust which correspond to erosional nearly flat weathered surfaces resulting from the growth of laterites under warm and humid conditions. - Pediments which define mechanical erosional surfaces with concave or rectilinear profiles delimited by upslope scarps connected upstream with the upper landforms. We here focused on the Lake Albert Rift at the northern termination of the western branch of the East African Rift System of which the two branches are surimposed on the East-African Dome. Different wavelengths of deformation were characterized based on the 3D mapping of stepped planation surfaces: (1) very long wavelength deformations resulting from the uplift of the East African Dome; (2) long wavelength deformations resulting from the opening of the eastern branch and (3) medium wavelength deformations represented by the uplift of rift shoulders like the Rwenzori Mountains. The paleo-landscape reconstruction of Uganda shows the existence of four generations of landforms dated according to their geometrical relationships with volcanic rocks. A four stepped evolution of the Ugandan landforms is proposed: • 70 - 22 Ma: generation of two weathered planation surfaces (etchplain Uw and Iw). The upper one (Uw) records a very humid period culminating at time of the Early Eocene Climatic Optimum (70-45 Ma). It corresponds to the African Surface. A first uplift of the East African Dome generates a second lower planation surface (Iw) connected to the Atlantic Ocean base level; • 17-2.7 Ma: planation of large pediplains connected to the local base level induced

  17. 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.

  18. Comparative sequence stratigraphy of low-latitude versus high-latitude lacustrine rift basins: Seismic data examples from the East African and Baikal rifts

    USGS Publications Warehouse

    Scholz, C.A.; Moore, T.C.; Hutchinson, D.R.; Golmshtok, A. Ja; Klitgord, Kim D.; Kurotchkin, A.G.

    1998-01-01

    Lakes Baikal, Malawi and Tanganyika are the world's three largest rift valley lakes and are the classic modem examples of lacustrine rift basins. All the rift lakes are segmented into half-graben basins, and seismic reflection datasets reveal how this segmentation controls the filling of the rift basins through time. In the early stages of rifting, basins are fed primarily by flexural margin and axial margin drainage systems. At the climax of syn-rift sedimentation, however, when the basins are deeply subsided, almost all the margins are walled off by rift shoulder uplifts, and sediment flux into the basins is concentrated at accommodation zone and axial margin river deltas. Flexural margin unconformities are commonplace in the tropical lakes but less so in high-latitude Lake Baikal. Lake levels are extremely dynamic in the tropical lakes and in low-latitude systems in general because of the predominance of evaporation in the hydrologic cycle in those systems. Evaporation is minimized in relation to inflow in the high-latitude Lake Baikal and in most high-latitude systems, and consequently, major sequence boundaries tend to be tectonically controlled in that type of system. The acoustic stratigraphies of the tropical lakes are dominated by high-frequency and high-amplitude lake level shifts, whereas in high-latitude Lake Baikal, stratigraphic cycles are dominated by tectonism and sediment-supply variations.

  19. Kinematics and dynamics of Nubia-Somalia divergence along the East African rift

    NASA Astrophysics Data System (ADS)

    Stamps, Dorothy Sarah

    Continental rifting is fundamental to the theory of plate tectonics, yet the force balance driving Earth's largest continental rift system, the East African Rift (EAR), remains debated. The EAR actively diverges the Nubian and Somalian plates spanning ˜5000 km N-S from the Red Sea to the Southwest Indian Ridge and ˜3000 km NW-SE from eastern Congo to eastern Madagascar. Previous studies suggest either lithospheric buoyancy forces or horizontal tractions dominate the force balance acting to rupture East Africa. In this work, we investigate the large-scale dynamics of Nubia-Somalia divergence along the EAR driving present-day kinematics. Because Africa is largely surrounded by spreading ridges, we assume plate-plate interactions are minimal and that the major driving forces are gradients in gravitational potential energy (GPE), which includes the effect of vertical mantle tractions, and horizontal basal tractions arising from viscous coupling to horizontal mantle flow. We quantify a continuous strain rate and velocity field based on kinematic models, an updated GPS velocity solution, and the style of earthquake focal mechanisms, which we use as an observational constraint on surface deformation. We solve the 3D force balance equations and calculate vertically averaged deviatoric stress for a 100 km thick lithosphere constrained by the CRUST2.0 crustal density and thickness model. By comparing vertically integrated deviatoric stress with integrated lithospheric strength we demonstrate forces arising from gradients in gravitational potential energy are insufficient to rupture strong lithosphere, hence weakening mechanisms are required to initiate continental rupture. The next step involves inverting for a stress field boundary condition that is the long-wavelength minimum energy deviatoric stress field required to best-fit the style of our continuous strain rate field in addition to deviatoric stress from gradients in GPE. We infer the stress field boundary condition

  20. Evolution of the SW African passive continental margin during the post-rift phase

    NASA Astrophysics Data System (ADS)

    Dressel, Ingo; Scheck-Wenderoth, Magdalena; Götze, Hans-Jürgen; Reichert, Christian

    2014-05-01

    The tectonic evolution of the SW African margin and the breakup of the South Atlantic Ocean are still under debate. Furthermore, there are economic interests in terms of hydrocarbon resources. In particular, the understanding of the subsidence history at the SW African passive continental margin can help to investigate the evolution of this margin. For this reason, we aim to reconstruct paleotopographies for three time steps during the post-rift phase (112 Ma to present day). These three time steps are: Cretaceous-Tertiary boundary (67 Ma), Cenomanian-Turonian boundary (93 Ma) and start post-rift (112 Ma). We use a recent regional scale 3D structural model (Maystrenko et al., 2013) as base for our subsidence analysis. This model includes the upper mantle, the crystalline crust, four sedimentary units as well as the water column. The sedimentary units comprise sediments of the (1) Cenozoic, (2) base Turonian-base Cenozoic, (3) base Aptian-base Turonian and (4) pre-Aptian sediments. Therefore, our subsidence reconstruction has the particular advantage that we include as much present day information as possible. In order to reconstruct paleotopographies we calculate the subsidence components separately. On the one hand we determine the thermal subsidence due to cooling of the lithosphere. On the other hand, the load induced subsidence exerted by the preserved sedimentary cover is calculated by applying a backstripping method which considers local isostatic rebound and decompaction. Both the amount of thermal subsidence and the amount of load induced subsidence are then subtracted from the total subsidence which is nowadays observed. Subtracting these individual subsidence components leads to the paleotopographies. The paleotopographies provide information about the long-term behavior of the margin area since the beginning of the post-rift phase. Moreover, the paleotopographies provide the opportunity to estimate vertical movements which have occurred during the post-rift

  1. 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

  2. Crustal and lithospheric structure of the west Antarctic Rift System from geophysical investigations: a review

    USGS Publications Warehouse

    Behrendt, John C.

    1999-01-01

    The active West Antarctic Rift System, which extends from the continental shelf of the Ross Sea, beneath the Ross Ice Shelf and the West Antarctic Ice Sheet, is comparable in size to the Basin and Range in North America, or the East African rift systems. Geophysical surveys (primarily marine seismic and aeromagnetic combined with radar ice sounding) have extended the information provided by sparse geologic exposures and a few drill holes over the ice and sea covered area. Rift basins developed in the early Cretaceous accompanied by the major extension of the region. Tectonic activity has continued episodically in the Cenozoic to the present, including major uplift of the Transantarctic Mountains. The West Antarctic ice sheet, and the late Cenozoic volcanic activity in the West Antarctic Rift System, through which it flows, have been coeval since at least Miocene time. The rift is characterized by sparse exposures of late Cenozoic alkaline volcanic rocks extending from northern Victoria Land throughout Marie Byrd Land. The aeromagnetic interpretations indicate the presence of > 5 x 105 km2 (> 106 km3) of probable late Cenozoic volcanic rocks (and associated subvolcanic intrusions) in the West Antarctic rift. This great volume with such limited exposures is explained by glacial removal of the associated late Cenozoic volcanic edifices (probably hyaloclastite debris) concomitantly with their subglacial eruption. Large offset seismic investigations in the Ross Sea and on the Ross Ice Shelf indicate a ~ 17-24-km-thick, extended continental crust. Gravity data suggest that this extended crust of similar thickness probably underlies the Ross Ice Shelf and Byrd Subglacial Basin. Various authors have estimated maximum late Cretaceous-present crustal extension in the West Antarctic rift area from 255-350 km based on balancing crustal thickness. Plate reconstruction allowed < 50 km of Tertiary extension. However, paleomagnetic measurements suggested about 1000 km of post

  3. The seismotectonics of Southeastern Tanzania: Implications for the propagation of the eastern branch of the East African Rift

    NASA Astrophysics Data System (ADS)

    Mulibo, Gabriel D.; Nyblade, Andrew A.

    2016-04-01

    Seismicity patterns and focal mechanisms in southeastern Tanzania, determined from data recorded on temporary and permanent AfricaArray seismic stations, have been used to investigate the propagation direction of the Eastern branch of the East African Rift System southward from the Northern Tanzania Divergence Zone (NTDZ). Within the NTDZ, the rift zone is defined by three segments, the Eyasi segment to the west, the Manyara segment in the middle, and the Pangani segment to the east. Results show that most of the seismicity (~ 75%) extends to the south of the Manyara segment along the eastern margin of the Tanzania Craton, and at ~ 6-7° S latitude trends to the SE along the northern boundary of the Ruvuma microplate, connecting with a N-S zone of seismicity offshore southern Tanzania and Mozambique. A lesser amount of seismicity (~ 25%) is found extending from the SE corner of the Tanzania Craton at ~ 6-7° S latitude southwards towards Lake Nyasa. This finding supports a model of rift propagation via the Manyara segment to the southeast of the Tanzania Craton along the northern boundary of the Ruvuma microplate. However, given the limited duration of the seismic recordings used in this study, the possibility of another zone of extension developing to the south towards Lake Nyasa (Malawi) cannot be ruled out. Focal mechanisms along the boundary between the Victoria and the Ruvuma microplates and offshore southeastern Tanzania show a combination of normal and strike slip faulting indicating mainly extension with some sinistral motion, consistent with the mapped geologic faults and a clockwise rotation of the Ruvuma microplate.

  4. Regional 3D Numerical Modeling of the Lithosphere-Mantle System: Implications for Continental Rift-Parallel Surface Velocities

    NASA Astrophysics Data System (ADS)

    Stamps, S.; Bangerth, W.; Hager, B. H.

    2014-12-01

    The East African Rift System (EARS) is an active divergent plate boundary with slow, approximately E-W extension rates ranging from <1-6 mm/yr. Previous work using thin-sheet modeling indicates lithospheric buoyancy dominates the force balance driving large-scale Nubia-Somalia divergence, however GPS observations within the Western Branch of the EARS show along-rift motions that contradict this simple model. Here, we test the role of mantle flow at the rift-scale using our new, regional 3D numerical model based on the open-source code ASPECT. We define a thermal lithosphere with thicknesses that are systematically changed for generic models or based on geophysical constraints in the Western branch (e.g. melting depths, xenoliths, seismic tomography). Preliminary results suggest existing variations in lithospheric thicknesses along-rift in the Western Branch can drive upper mantle flow that is consistent with geodetic observations.

  5. 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

  6. Latitudinal Hydrologic Variability Along the East African Rift, Over the Past 200 Kyr

    NASA Astrophysics Data System (ADS)

    Scholz, C. A.

    2014-12-01

    Within the deep sediments of the large lakes of Africa's Great Rift Valley are continuous environmental records of remarkable antiquity and fidelity. Not only do stratigraphic sections from these basins extend back millions of years, many of the intervals represented contain high-resolution material of decadal resolution or better. East African lake basins remain sparsely sampled however, with only a few long and continuous records available. Our ability to image the lakes using seismic reflection methods greatly exceeds our opportunities for coring and drilling however; assessing stratal relationships observed in the geophysical data permits powerful inferences about past hydrologic changes. With intensive hydrocarbon exploration work underway in East Africa, industry well data can also help constrain and ground truth basin histories. Substantial spatio-temporal hydrologic variability is observed in East African basins over the past 200 kyr. Paleohydrological changes in the late Pleistocene and early Holocene are now well constrained in the northern hemisphere East African topics, with widespread aridity and in some cases lake desiccation observed during Heinrich Event 1. A climate recovery followed in the northern hemisphere East African tropics, with the early Holocene African Humid Period a time of positive water balance across most of the rift valley. The paleohydrology of southern hemisphere tropical East Africa is more equivocal, for instance with negligible draw-down of Lake Malawi at HE1. Whereas these late Pleistocene events represent substantial climate reorganizations, severe droughts during the middle-late Pleistocene (150-65 kyr BP) were far more intense, and produced much more severe drawdowns of Lakes Malawi and Tanganyika. Scientific drill cores, kullenberg cores, and extensive seismic reflection data sets from Lakes Malawi and Tanganyika provide indisputable evidence for lowstands of -500m and -600 m respectively. Climate changes that lowered the

  7. The Rift Valley of African Plate in Elasto-Plastic Creeping over Magma Motion

    NASA Astrophysics Data System (ADS)

    Nakamura, Shigehisa

    2016-04-01

    This is a brief note to a problem on the Rift Valley in the eastern Africa. It is said that this valley was formed in an age 20,000,000 years before present though the valley is yet continuing to move eastward at an annual rate of about 5 cm/year in a geographical trend. Adding to some of the scientists tell that the separation threat of the easternAfrica from the mother land of the Africa under the effect of African crust motion over the magma. However, it is now geological understanding that the land of the Africa has been kept its basic coastal configulation in geographic pattern since the time more than 20,000,000 years before present. Sothat, it is hard to consider the above noted African land separation by part could be in the next age in a time scale of 20,000,000 years. As far as, we concern the geographic data obtaoned by the ground based survey of the African typical mountain peaks, the highest mountain peak 5885m (in 1980) is for Kilimanjaro, Kibo Peak though one of the scientific almanacs tells us its peak height as 5890m (in 2009). As for the Mount Kenia, the peak height is as 5199m (in 1980) and 5200m(in 2009). At a glance, it looks to be a trend in altimetry of the African typical mountain. Now, what trends are noted for the peak heights could be taken to suggesting the geological activity on the earth surface to maintain in a spherical shape approximately on the orbit around the Sun. In these several ten years, the digitizing of the data has been promoted even for the topographic patterns on the earth though its time scaling is extremely short comparing to the geological time scaling. Now, it should be found what is effective to monitor any trends of the African crust in motion as well as variations of the mountain peaks.

  8. Istopically Defined Source Reservoirs of Primitive Magmas in the East African Rift.

    NASA Astrophysics Data System (ADS)

    Rooney, T. O.; Furman, T.; Hanan, B.

    2005-12-01

    Extension within the East African Rift is a function of the interaction between plume-driven uplift and far-field stresses associated with plate tectonic processes. Geochemical and isotopic investigation of primitive basalts from the Main Ethiopian Rift (MER) reveals systematic spatial variations in the contributions from distinct and identifiable source reservoirs that, in turn help identify the mechanisms by which along-axis rifting has progressed. The Sr-Nd-Pb isotopic characteristics of MER basalts can be described by a three-component mixing model involving the long-lived Afar plume, a depleted mantle component similar to the source region for Gulf of Aden MORB from east of 48° E and a reservoir that is likely lithospheric (sub-continental mantle lithosphere, magmatic underplate or lower crust). Quaternary basalts in the central MER exhibit a systematic decrease in plume influence southward from 9.5° N to 8° N, i.e., away from the modern surface expression of the Afar plume in Djibouti and Erta 'Ale. The composition of the Afar plume component is comparable to the "C" mantle reservoir. This southward decrease in plume influence is coupled with an increase in the influence of the lithospheric and depleted mantle components. Linear arrays observed within Pb-Pb isotopic space at each eruptive center require distinctive ratio of lithospheric + depleted mantle components mixing with variable amounts of the "C"-like plume component. This isotopic evidence suggests the depleted mantle and lithosphere mixed prior to the generation of the recent magmas. To the south, the Sr-Nd-Pb isotopic compositions of Turkana (Kenya) rift basalts record a mix of a similar "C"-like plume component and a fourth HIMU-like source component. Low 3He/4He values observed in the HIMU-dominated lavas from Turkana contrast with the higher ratios found in basalts associated with the "C"-like Afar plume. Further analysis of "C"-HIMU lavas at Turkana is required to fully constrain the He

  9. Deriving spatial patterns from a novel database of volcanic rock geochemistry in the Virunga Volcanic Province, East African Rift

    NASA Astrophysics Data System (ADS)

    Poppe, Sam; Barette, Florian; Smets, Benoît; Benbakkar, Mhammed; Kervyn, Matthieu

    2016-04-01

    The Virunga Volcanic Province (VVP) is situated within the western branch of the East-African Rift. The geochemistry and petrology of its' volcanic products has been studied extensively in a fragmented manner. They represent a unique collection of silica-undersaturated, ultra-alkaline and ultra-potassic compositions, displaying marked geochemical variations over the area occupied by the VVP. We present a novel spatially-explicit database of existing whole-rock geochemical analyses of the VVP volcanics, compiled from international publications, (post-)colonial scientific reports and PhD theses. In the database, a total of 703 geochemical analyses of whole-rock samples collected from the 1950s until recently have been characterised with a geographical location, eruption source location, analytical results and uncertainty estimates for each of these categories. Comparative box plots and Kruskal-Wallis H tests on subsets of analyses with contrasting ages or analytical methods suggest that the overall database accuracy is consistent. We demonstrate how statistical techniques such as Principal Component Analysis (PCA) and subsequent cluster analysis allow the identification of clusters of samples with similar major-element compositions. The spatial patterns represented by the contrasting clusters show that both the historically active volcanoes represent compositional clusters which can be identified based on their contrasted silica and alkali contents. Furthermore, two sample clusters are interpreted to represent the most primitive, deep magma source within the VVP, different from the shallow magma reservoirs that feed the eight dominant large volcanoes. The samples from these two clusters systematically originate from locations which 1. are distal compared to the eight large volcanoes and 2. mostly coincide with the surface expressions of rift faults or NE-SW-oriented inherited Precambrian structures which were reactivated during rifting. The lava from the Mugogo

  10. Metallogeny of the midcontinent rift system of North America

    USGS Publications Warehouse

    Nicholson, S.W.; Cannon, W.F.; Schulz, K.J.

    1992-01-01

    The 1.1 Ga Midcontinent rift system of North America is one of the world's major continental rifts and hosts a variety of mineral deposits. The rocks and mineral deposits of this 2000 km long rift are exposed only in the Lake Superior region. In the Lake Superior region, the rift cuts across Precambrian basement terranes ranging in age from ??? 1850 Ma to more than 3500 Ma. Where exposed, the rift consists of widespread tholeiitic basalt flows with local interlayered rhyolite and clastic sedimentary rocks. Beneath the center of Lake Superior the volcanic and sedimentary rocks are more than 30 km deep as shown by recent seismic reflection profiles. This region hosts two major classes of mineral deposits, magmatic and hydrothermal. All important mineral production in this region has come from hydrothermal deposits. Rift-related hydrothermal deposits include four main types: (1) native copper deposits in basalts and interflow sediments; (2) sediment-hosted copper sulfide and native copper; (3) copper sulfide veins and lodes hosted by rift-related volcanic and sedimentary rocks; and (4) polymetallic (five-element) veins in the surrounding Archean country rocks. The scarcity of sulfur within the rift rocks resulted in the formation of very large deposits of native metals. Where hydrothermal sulfides occur (i.e., shale-hosted copper sulfides), the source of sulfur was local sedimentary rocks. Magmatic deposits have locally supported exploration and minor production, but most are subeconomic presently. These deposits occur in intrusions exposed near the margins of the rift and include CuNiPGE and TiFe (V) in the Duluth Complex, U-REE-Nb in small carbonatites, and breccia pipes resulting from local hydrothermal activity around small felsic intrusions. Mineralization associated with some magmatic bodies resulted from the concentration of incompatible elements during fractional crystallization. Most of the sulfide deposits in intrusions, however, contain sulfur derived from

  11. The diagenesis of continental (Karoo-Tertiary?) siliciclastics from an East African rift valley (Rukwa-Tukuyu area), Tanzania

    NASA Astrophysics Data System (ADS)

    Dypvik, Henning; Nesteby, Helge

    1992-07-01

    The diagenetic history of the Karoo and Jurassic/Tertiary beds of East African rift valleys is related to the tectonic activity and sedimentary evolution of the rift valley area. In the Karoo beds early diagenetic calcite and hematite formation are succeeded by mechanical compaction and minor quartz, kaolinite and calcite precipitation. Renewed tectonic activity (possible half-graben formation) and exposure of the Karoo beds in Jurassic/Tertiary time resulted in alluvial fan deposition (the Red Sandstone Group) and associated fresh-water flushing, caliche formation and hematite precipitation. Late diagenetic precipitation of potash feldspar and feldspar leaching were the final controls on the porosity and permeability development of the sediments.

  12. Shaded Relief with Height as Color, Virunga and Nyiragongo Volcanoes and the East African Rift

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Volcanic, tectonic, erosional and sedimentary landforms are all evident in this comparison of two elevation models of a region along the East African Rift at Lake Kivu. The area shown covers parts of Congo, Rwanda and Uganda.

    These two images show exactly the same area. The image on the left was created using the best global topographic data set previously available, the U.S. Geological Survey's GTOPO30. In contrast, the much more detailed image on the right was generated with data from the Shuttle Radar Topography Mission, which collected enough measurements to map 80 percent of Earth's landmass at this level of precision. Elevation is color coded, progressing from green at the lower elevations through yellow to brown at the higher elevations. A false sun in the northwest (upper left) creates topographic shading.

    Lake Kivu is shown as black in the Shuttle Radar Topography Mission version (southwest corner). It lies within the East African Rift, an elongated tectonic pull-apart depression in Earth's crust. The rift extends to the northeast as a smooth lava- and sediment-filled trough. Two volcanic complexes are seen in the rift. The one closer to the lake is the Nyiragongo volcano, which erupted in January 2002, sending lava toward the lake shore and through the city of Goma. East of the rift, even more volcanoes are seen. These are the Virunga volcano chain, which is the home of the endangered mountain gorillas. Note that the terrain surrounding the volcanoes is much smoother than the eroding mountains that cover most of this view, such that topography alone is a good indicator of the extent of the lava flows. But this clear only at the higher spatial resolution of the shuttle mission's data set.

    For some parts of the globe, Shuttle Radar Topography Mission measurements are 30 times more precise than previously available topographical information, according to NASA scientists. Mission data will be a welcome resource for national and local governments

  13. 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

  14. 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.

  15. Rift Valley Fever Virus Circulating among Ruminants, Mosquitoes and Humans in the Central African Republic

    PubMed Central

    Nakouné, Emmanuel; Kamgang, Basile; Berthet, Nicolas; Manirakiza, Alexandre; Kazanji, Mirdad

    2016-01-01

    Background Rift Valley fever virus (RVFV) causes a viral zoonosis, with discontinuous epizootics and sporadic epidemics, essentially in East Africa. Infection with this virus causes severe illness and abortion in sheep, goats, and cattle as well as other domestic animals. Humans can also be exposed through close contact with infectious tissues or by bites from infected mosquitoes, primarily of the Aedes and Culex genuses. Although the cycle of RVFV infection in savannah regions is well documented, its distribution in forest areas in central Africa has been poorly investigated. Methodology/Principal Findings To evaluate current circulation of RVFV among livestock and humans living in the Central African Republic (CAR), blood samples were collected from sheep, cattle, and goats and from people at risk, such as stock breeders and workers in slaughterhouses and livestock markets. The samples were tested for anti-RVFV immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies. We also sequenced the complete genomes of two local strains, one isolated in 1969 from mosquitoes and one isolated in 1985 from humans living in forested areas. The 1271 animals sampled comprised 727 cattle, 325 sheep, and 219 goats at three sites. The overall seroprevalence of anti-RVFV IgM antibodies was 1.9% and that of IgG antibodies was 8.6%. IgM antibodies were found only during the rainy season, but the frequency of IgG antibodies did not differ significantly by season. No evidence of recent RVFV infection was found in 335 people considered at risk; however, 16.7% had evidence of past infection. Comparison of the nucleotide sequences of the strains isolated in the CAR with those isolated in other African countries showed that they belonged to the East/Central African cluster. Conclusion and significance This study confirms current circulation of RVFV in CAR. Further studies are needed to determine the potential vectors involved and the virus reservoirs. PMID:27760144

  16. Early-stage rifting in the southwest East African Rift: Insights from new reflection seismic data from Lakes Tanganyika and Malawi (Nyasa)

    NASA Astrophysics Data System (ADS)

    Scholz, C. A.; Wood, D. A.; Shillington, D. J.; McCartney, T.; Accardo, N. J.

    2015-12-01

    The western branch of the East African Rift is characterized by modest amounts of mainly amagmatic extension; deeply-subsided, fault-controlled basins; and large-magnitude, deep seismicity. Lakes Tanganyika and Malawi are two of the world's largest lakes, with maximum water depths of 1450 and 700 m respectively. Newly acquired seismic reflection data, along with newly reprocessed legacy data reveal thick sedimentary sections, in excess of 5 km in some localities. The 1980's vintage legacy data from Project PROBE have been reprocessed through pre-stack depth migration in Lake Tanganyika, and similar reprocessing of legacy data from Lake Malawi is forthcoming. New high-fold and large-source commercial and academic data have recently been collected in southern Lake Tanganyika, and in the northern and central basins of Lake Malawi as part of the 2015 SEGMeNT project. In the case of Lake Tanganyika, new data indicate the presence of older sediment packages that underlie previously identified "pre-rift" basement (the "Nyanja Event"). These episodes of sedimentation and extension may substantially predate the modern lake. These deep stratal reflections are absent in many localites, possibly on account of attenuation of the acoustic signal. However in one area of southern Lake Tanganyika, the newly-observed deep strata extend axially for ~70 km, likely representing deposits from a discrete paleolake. The high-amplitude Nyanja Event is interpreted as the onset of late-Cenozoic rifting, and the changing character of the overlying depositional sequences reflects increasing relief in the rift valley, as well as the variability of fluvial inputs, and the intermittent connectivity of upstream lake catchments. Earlier Tanganyika sequences are dominated by shallow lake and fluvial-lacustrine facies, whereas later sequences are characterized by extensive gravity flow deposition in deep water, and pronounced erosion and incision in shallow water depths and on littoral platforms. The

  17. Discovery of sublacustrine hydrothermal activity and associated massive sulfides and hydrocarbons in the north Tanganyika trough, East African Rift

    SciTech Connect

    Tiercelin, J.J.; Mondeguer, A. ); Thouin, C. ); Kalala, T. )

    1989-11-01

    Massive sulfides and carbonate mineral deposits associated with sublacustrine thermal springs were recently discovered along the Zaire side of the north Tanganyika trough, western branch of the East African Rift. This hydrothermal activity, investigated by scuba diving at a maximum depth of 20 m, is located at the intersection of major north-south normal faults and northwest-southeast faults belonging to the Tanganyika-Rukwa-Malawi (TRM) strike-slip fault zone. The preliminary results presented here come from analyses of sulfide deposits, hydrothermal fluids, and associated hydrocarbons that result from geothermal activity in this part of the East African Rift filled by a thick pile of sediment, the north Tanganyika trough.

  18. 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.

  19. Petroleum system of the Shelf Rift Basin, East China Sea

    SciTech Connect

    Cunningham, A.C.; Armentrout, J.M.; Prebish, M.

    1996-12-31

    The Tertiary section of the Oujioang and Quiontang Depressions of the East China Sea Basin consists of at least eight rift-related depositional sequences identified seismically by regionally significant onlap and truncation surfaces. These sequences are calibrated by several wells including the Wenzhou 6-1-1 permitting extrapolation of petroleum system elements using seismic facies analysis. Gas and condensate correlated to non-marine source rocks and reservoired in sandstone at the Pinghu field to the north of the study area provides an known petroleum system analogue. In the Shelf Rift Basin, synrift high-amplitude parallel reflections within the graben axes correlate with coaly siltstone strata and are interpreted as coastal plain and possibly lacustrine facies with source rock potential. Synrift clinoform seismic facies prograding from the northwest footwall correlate with non-marine to marginal marine conglomerate, sandstone and siltstone, and are interpreted as possible delta or fan-delta facies with reservoir potential although porosity and permeability is low within the Wenzhou 6-1-1 well. Post-rift thermal sag sequences are characterized by parallel and relatively continuous seismic reflections and locally developed clinoform packages. These facies correlate with porous and permeable marine sandstone and siltstone. Shales of potential sealing capacity occur within marine flooding intervals of both the synrift and post-rift sequences. Traps consist of differentially rotated synrift fill, and post-rift inversion anticlines. Major exploration risk factors include migration from the synrift coaly source rocks to the post-rift porous and permeable sandstones, and seismic imaging and drilling problems associated with extensive Tertiary igneous intrusions.

  20. Petroleum system of the Shelf Rift Basin, East China Sea

    SciTech Connect

    Cunningham, A.C.; Armentrout, J.M.; Prebish, M. )

    1996-01-01

    The Tertiary section of the Oujioang and Quiontang Depressions of the East China Sea Basin consists of at least eight rift-related depositional sequences identified seismically by regionally significant onlap and truncation surfaces. These sequences are calibrated by several wells including the Wenzhou 6-1-1 permitting extrapolation of petroleum system elements using seismic facies analysis. Gas and condensate correlated to non-marine source rocks and reservoired in sandstone at the Pinghu field to the north of the study area provides an known petroleum system analogue. In the Shelf Rift Basin, synrift high-amplitude parallel reflections within the graben axes correlate with coaly siltstone strata and are interpreted as coastal plain and possibly lacustrine facies with source rock potential. Synrift clinoform seismic facies prograding from the northwest footwall correlate with non-marine to marginal marine conglomerate, sandstone and siltstone, and are interpreted as possible delta or fan-delta facies with reservoir potential although porosity and permeability is low within the Wenzhou 6-1-1 well. Post-rift thermal sag sequences are characterized by parallel and relatively continuous seismic reflections and locally developed clinoform packages. These facies correlate with porous and permeable marine sandstone and siltstone. Shales of potential sealing capacity occur within marine flooding intervals of both the synrift and post-rift sequences. Traps consist of differentially rotated synrift fill, and post-rift inversion anticlines. Major exploration risk factors include migration from the synrift coaly source rocks to the post-rift porous and permeable sandstones, and seismic imaging and drilling problems associated with extensive Tertiary igneous intrusions.

  1. U-series Chronology of volcanoes in the Central Kenya Peralkaline Province, East African Rift

    NASA Astrophysics Data System (ADS)

    Negron, L. M.; Ma, L.; Deino, A.; Anthony, E. Y.

    2012-12-01

    We are studying the East African Rift System (EARS) in the Central Kenya Peralkaline Province (CKPP), and specifically the young volcanoes Mt. Suswa, Longonot, and Menengai. Ar dates by Al Deino on K-feldspar phenocrysts show a strong correlation between older Ar ages and decreasing 230Th/232Th, which we interpret to reflect the age of eruption. This system has been the subject of recent research done by several UTEP alumni including Antony Wamalwa using potential field and magnetotelluric (MT) data to identify and characterize fractures and hydrothermal fluids. Also research on geochemical modeling done by John White, Vanessa Espejel and Peter Omenda led to the hypothesis of possible disequilibrium in these young, mainly obsidian samples in their post eruptive history. A pilot study of 8 samples, (also including W-2a USGS standard and a blank) establish the correlation that was seen between the ages found by Deino along with the 230/232Th ratios. All 8 samples from Mt. Suswa showed a 234U/238U ratio of (1) which indicates secular equilibrium or unity and that these are very fresh samples with no post-eruptive decay or leaching of U isotopes. The pilot set was comprised of four samples from the ring-trench group (RTG) with ages ranging from 7ka-present, two samples from the post-caldera stage ranging from 31-10ka, one sample from the syn-caldera stage dated at 41ka, and one sample from the pre-caldera stage dated at 112ka. The young RTG had a 230/232Th fractionation ratio of 0.8 ranging to the older pre-caldera stage with a 230/232Th ratio of 0.6. From this current data and research of 14C ages by Nick Rogers, the data from Longonot volcano was also similar to the 230/232Th ratio we found. Rogers' data places Longonot volcano ages to be no more than 20ka with the youngest samples also roughly around 0.8 disequilibrium. These strong correlations between the pilot study done for Mt. Suswa, 40Ar ages by Deino, along with 14C ages from Rogers have led to the

  2. 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.

  3. Volcanic activities in the Southern part of East African rift initiation: Melilitites and nephelinites from the Manyara Basin (North Tanzania rift axis)

    NASA Astrophysics Data System (ADS)

    Baudouin, Celine; Parat, Fleurice; Tiberi, Christel; Gautier, Stéphanie; Peyrat, Sophie

    2016-04-01

    The East African Rift exposes different stages of plate boundary extension, from the initiation of the rift (North (N) Tanzania) to oceanic accretion (Afar). The N Tanzania rift-axis (north-south (S) trend) is divided into 2 different volcanic and seismic activities: (1) the Natron basin (N) with shallow seismicity and intense volcanism and (2) the Manyara basin (S) with deep crustal earthquakes and sparse volcanism. The Natron basin is characterized by extinct volcanoes (2 Ma-0.75 Ma) and active volcano (Oldoinyo Lengai) and a link between seismicity and volcanism has been observed during the Oldoinyo Lengai crisis in 2007. In the S part of the N Tanzanian rift, volcanoes erupted in the Manyara basin between 0.4 and 0.9 Ma. In this study, we used geochemical signature of magmas and deep fluids that percolate into the lithosphere beneath Manyara basin, to define the compositions of magmas and fluids at depth beneath the S part of the N Tanzania rift, compare to the Natron basin and place constrain on the volcanic and seismic activities. The Manyara basin has distinct volcanic activities with mafic magmas as melilitites (Labait) and Mg-nephelinites (carbonatite, Kwaraha), and more differentiated magmas as Mg-poor nephelinites (Hanang). Melilitites and Mg-nephelinites are primary magmas with olivine, clinopyroxene (cpx), and phlogopite recording high-pressure crystallization environment, (melilitites >4 GPa and Mg-nephelinites>1 GPa) with high volatile contents (whole rock: 0.7-4.6 wt% CO2, 0.1-0.3 wt% F and 0.1 wt% Cl). FTIR analyses of olivine constrained the water content of Labait and Kwaraha magmas at 0.1 and 0.4 wt% H2O, respectively. Geochemical modelling suggests that mafic magmas result from a low degree of partial melting (1-2%) of a peridotitic source with garnet and phlogopite (high Tb/Yb (>0.6) and Rb/Sr (0.03-0.12) ratio). Mg-poor nephelinites from Hanang volcano crystallized cpx, Ti-garnet, and nepheline as phenocrysts. Magmas result from fractional

  4. Aerosolized Rift Valley Fever Virus Causes Fatal Encephalitis in African Green Monkeys and Common Marmosets

    PubMed Central

    Hartman, Amy L.; Powell, Diana S.; Bethel, Laura M.; Caroline, Amy L.; Schmid, Richard J.; Oury, Tim

    2013-01-01

    Rift Valley fever (RVF) is a veterinary and human disease in Africa and the Middle East. The causative agent, RVF virus (RVFV), can be naturally transmitted by mosquito, direct contact, or aerosol. We sought to develop a nonhuman primate (NHP) model of severe RVF in humans to better understand the pathogenesis of RVF and to use for evaluation of medical countermeasures. NHP from four different species were exposed to aerosols containing RVFV. Both cynomolgus and rhesus macaques developed mild fevers after inhalation of RVFV, but no other clinical signs were noted and no macaque succumbed to RVFV infection. In contrast, both marmosets and African green monkeys (AGM) proved susceptible to aerosolized RVF virus. Fever onset was earlier with the marmosets and had a biphasic pattern similar to what has been reported in humans. Beginning around day 8 to day 10 postexposure, clinical signs consistent with encephalitis were noted in both AGM and marmosets; animals of both species succumbed between days 9 and 11 postexposure. Marmosets were susceptible to lower doses of RVFV than AGM. Histological examination confirmed viral meningoencephalitis in both species. Hematological analyses indicated a drop in platelet counts in both AGM and marmosets suggestive of thrombosis, as well as leukocytosis that consisted mostly of granulocytes. Both AGM and marmosets would serve as useful models of aerosol infection with RVFV. PMID:24335307

  5. Hydrothermal petroleum from lacustrine sedimentary organic matter in the East African Rift.

    PubMed

    Simoneit, B R; Aboul-Kassim, T A; Tiercelin, J J

    2000-03-01

    Cape Kalamba oil seeps occur at the south end of the Ubwari Peninsula, at the intersection of faults controlling the morphology of the northern basin of the Tanganyika Rift, East Africa. Oil samples collected at the surface of the lake 3-4 km offshore from Cape Kalamba have been studied. The aliphatic hydrocarbon and biomarker compositions, with the absence of the typical suite of polynuclear aromatic hydrocarbons, indicate an origin from hydrothermal alteration of immature microbial biomass in the sediments. These data show a similarity between a tar sample from the beach and the petroleum from the oil seeps, and confirm that the source of these oils is from organic matter consisting mainly of bacterial and degraded algal biomass, altered by hydrothermal activity. The compositions also demonstrate a < 200 degrees C temperature for formation/generation of this hydrothermal petroleum, similar to the fluid temperature identified for the Pemba hydrothermal site located 150 km north of Cape Kalamba. The 14C age of 25.6 ka B.P. obtained for the tar ball suggests that Pleistocene lake sediments could be the source rock. Hydrothermal generation may have occurred slightly before 25 ka B.P., during a dry climatic environment, when the lake level was lower than today. These results also suggest that the Cape Kalamba hydrothermal activity did not occur in connection with an increased flux of meteoric water, higher water tables and lake levels as demonstrated in the Kenya Rift and for the Pemba site. Hydrothermal petroleum formation is a facile process also in continental rift systems and should be considered in exploration for energy resources in such locales.

  6. 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.

  7. Nocardiopsis mwathae sp. nov., isolated from the haloalkaline Lake Elmenteita in the African Rift Valley.

    PubMed

    Akhwale, Juliah Khayeli; Göker, Markus; Rohde, Manfred; Schumann, Peter; Boga, Hamadi Iddi; Klenk, Hans-Peter

    2016-03-01

    During a screening for novel and biotechnologically useful bacteria in haloalkaline lakes, strain No.156(T) was isolated from a sediment sample from lake Elmenteita in the African Rift Valley and studied by a polyphasic taxonomic approach. The strain was observed to form yellow aerial and substrate mycelia; optimal growth was found to be at 30-35 °C in salt concentrations of 6-9 % (w/v) and at pH 7-9. The DNA G+C content of the novel strain was 71 mol%. Analysis of 16S rRNA sequences indicated that the isolate belongs to the genus Nocardiopsis with sequence similarities below 98 % to the type strains of all other representatives of the genus. Mycolic acids were not detected in whole cell methanolysates. The peptidoglycan was found to contain meso-diaminopimelic acid as the diamino acid with no diagnostic sugars. The main polar lipids were identified as phosphatidylmethylethanolamine, phosphatidylcholine, phosphatidylglycerol and phosphatidylinositol but no diphosphatidylglycerol. The predominant menaquinones were MK-11(H8), MK-11(H6), MK-10(H8) and MK-10(H6). Cellular fatty acids were found to consist of saturated and monounsaturated iso- and anteiso-branched acids with 16-18 C-length, tuberculostearic acid (Me18:0), and straight-chain saturated (16:0, 18:0) acids. These characteristics match those of the genus Nocardiopsis. Based on 16S rRNA gene sequence analysis and phenotypic characteristics, a novel species with the name Nocardiopsis mwathae is proposed. The type strain is No.156(T) (=DSM 46659(T) = CECT 8552(T)). The INSDC accession number for the 16S rRNA gene sequence of strain No.156(T) is KF976731.

  8. Implications of new gravity data for Baikal Rift zone structure

    NASA Technical Reports Server (NTRS)

    Ruppel, C.; Kogan, M. G.; Mcnutt, M. K.

    1993-01-01

    Newly available, 2D Bouguer gravity anomaly data from the Baikal Rift zone, Siberia, indicate that this discrete, intracontinental rift system is regionally compensated by an elastic plate about 50 km thick. However, spectral and spatial domain analyses and isostatic anomaly calculations show that simple elastic plate theory does not offer an adequate explanation for compensation in the rift zone, probably because of significant lateral variations in plate strength and the presence of subsurface loads. Our results and other geophysical observations support the interpretation that the Baikal Rift zone is colder than either the East African or Rio Grande rift.

  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. Constraining the Composition of the Subcontinental Lithospheric Mantle Beneath the East African Rift: FTIR Analysis of Water in Spinel Peridotite Mantle Xenoliths

    NASA Technical Reports Server (NTRS)

    Erickson, Stephanie Gwen; Nelson, Wendy R.; Peslier, Anne H.; Snow, Jonathan E.

    2014-01-01

    The East African Rift System was initiated by the impingement of the Afar mantle plume on the base of the non-cratonic continental lithosphere (assembled during the Pan-African Orogeny), producing over 300,000 kmof continental flood basalts approx.30 Ma ago. The contribution of the subcontinental lithospheric mantle (SCLM) to this voluminous period of volcanism is implied based on basaltic geochemical and isotopic data. However, the role of percolating melts on the SCLM composition is less clear. Metasomatism is capable of hybridizing or overprinting the geochemical signature of the SCLM. In addition, models suggest that adding fluids to lithospheric mantle affects its stability. We investigated the nature of the SCLM using Fourier transform infrared spectrometry (FTIR) to measure water content in mantle xenoliths entrained in young (1 Ma) basaltic lavas from the Ethiopian volcanic province. The mantle xenoliths consist dominantly of spinel lherzolites and are composed of nominally anhydrous minerals, which can contain trace water as H in mineral defects. Eleven mantle xenoliths come from the Injibara-Gojam region and two from the Mega-Sidamo region. Water abundances of olivines in six samples are 1-5ppm H2O while the rest are below the limit of detection (<0.5 ppm H2O); orthopyroxene and clinopyroxene contain 80-238 and 111-340 ppm wt H2O, respectively. Two xenoliths have higher water contents - a websterite (470 ppm) and dunite (229 ppm), consistent with involvement of ascending melts. The low water content of the upper SCLM beneath Ethiopia is as dry as the oceanic mantle except for small domains represented by percolating melts. Consequently, rifting of the East African lithosphere may not have been facilitated by a hydrated upper mantle.

  11. Studies on Rift Valley fever in some African murids (Rodentia: Muridae).

    PubMed Central

    Swanepoel, R.; Blackburn, N. K.; Efstratiou, S.; Condy, J. B.

    1978-01-01

    Brains, spleens and livers of 2214 murids, 27 shrews and 7 dormice, trapped at 7 sites in Rhodesia, were tested in 277 pools for the presence of Rift Valley Fever virus. There were no isolations of Rift Valley Fever, but 69 isolations of an unidentified virus were obtained. Sixteen out of 867 sera had low-titre haemagglutination-inhibition activity against Rift Valley Fever antigen, but only one out of 1260 sera had neutralizing antibody. The evidence suggests that murids fail to encounter infection in nature and are unlikely to play a role in circulation and dissemination of Rift Valley Fever virus. Four out of seven widely distributed species of muried, Rhabdomys pumilio, Saccostomys campestris, Aethomys chrysophilus and Lemniscomys griselda, were shown to be capable of circulating amounts of virus likely to be infective for mosquitoes. PMID:632561

  12. Studies on Rift Valley fever in some African murids (Rodentia: Muridae).

    PubMed

    Swanepoel, R; Blackburn, N K; Efstratiou, S; Condy, J B

    1978-04-01

    Brains, spleens and livers of 2214 murids, 27 shrews and 7 dormice, trapped at 7 sites in Rhodesia, were tested in 277 pools for the presence of Rift Valley Fever virus. There were no isolations of Rift Valley Fever, but 69 isolations of an unidentified virus were obtained. Sixteen out of 867 sera had low-titre haemagglutination-inhibition activity against Rift Valley Fever antigen, but only one out of 1260 sera had neutralizing antibody. The evidence suggests that murids fail to encounter infection in nature and are unlikely to play a role in circulation and dissemination of Rift Valley Fever virus. Four out of seven widely distributed species of muried, Rhabdomys pumilio, Saccostomys campestris, Aethomys chrysophilus and Lemniscomys griselda, were shown to be capable of circulating amounts of virus likely to be infective for mosquitoes.

  13. 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.

    2016-09-01

    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

  14. 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

  15. Holocene phreatomagmatic eruptions alongside the densely populated northern shoreline of Lake Kivu, East African Rift: timing and hazard implications

    NASA Astrophysics Data System (ADS)

    Poppe, Sam; Smets, Benoît; Fontijn, Karen; Rukeza, Montfort Bagalwa; De Marie Fikiri Migabo, Antoine; Milungu, Albert Kyambikwa; Namogo, Didier Birimwiragi; Kervyn, François; Kervyn, Matthieu

    2016-11-01

    The Virunga Volcanic Province (VVP) represents the most active zone of volcanism in the western branch of the East African Rift System. While the VVP's two historically active volcanoes, Nyamulagira and Nyiragongo, have built scoria cones and lava flows in the adjacent lava fields, several small phreatomagmatic eruptive centers lie along Lake Kivu's northern shoreline, highlighting the potential for explosive magma-water interaction. Their presence in the densely urbanized Sake-Goma-Gisenyi area necessitates an assessment of their eruptive mechanisms and chronology. Some of these eruptive centers possess multiple vents, and depositional contacts suggest distinct eruptive phases within a single structure. Depositional facies range from polymict tuff breccia to tuff and loose lapilli, often impacted by blocks and volcanic bombs. Along with the presence of dilute pyroclastic density current (PDC) deposits, indicators of magma-water interaction include the presence of fine palagonitized ash, ash aggregates, cross-bedding, and ballistic impact sags. We estimate that at least 15 phreatomagmatic eruptions occurred in the Holocene, during which Lake Kivu rose to its current water level. Radiocarbon dates of five paleosols in the top of volcanic tuff deposits range between ˜2500 and ˜150 cal. year bp and suggest centennial- to millennial-scale recurrence of phreatomagmatic activity. A vast part of the currently urbanized zone on the northern shoreline of Lake Kivu was most likely impacted by products from phreatomagmatic activity, including PDC events, during the Late Holocene, highlighting the need to consider explosive magma-water interaction as a potential scenario in future risk assessments.

  16. 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.

  17. How many rifts are there in West Africa?

    NASA Astrophysics Data System (ADS)

    Freeth, S. J.

    1984-02-01

    The West African Rift System has, for the last ten years, been thought to consist of five interconnected rifts extending from the Gulf of Guinea deep into the heart of Africa. Careful re-examination of the geophysical evidence makes it quite clear that there are only three interconnected rifts in West Africa; the Lower Benue Rift which extends to the northeast from the Gulf of Guinea to a triple junction near Chum, and the Gongola and Yola Rifts which extend to the north and east, respectively, from the Chum triple junction. These three rifts opened during the earlier part of the Mesozoic and were subsequently filled with Cretaceous sediments. The evidence for two further rifts, the Ati Rift and the Fort Archambault Rift which were thought to extend to the northeast and southeast, respectively, from a triple junction at the eastern end of the Yola Rift, does not stand up to re-examination. The "Ati Rift" was thought to follow a major linear positive gravity anomaly which had been mapped beneath the Quaternary sediments of the Chad Basin. The main gravity anomaly is separated from the Yola Rift by over 300 km and is probably due to a linear body of basic volcanic or volcano-clastic rocks associated with a suture of Pan-African age. Within the gap, between the main anomaly and the Yola Rift, there are three localised positive anomalies which relate to a gabbro of Precambrian age, a band of dense meta-sediments within the Basement Complex and an acid igneous complex of Palaeogene age. The anomaly as a whole is therefore a sequence of unrelated anomalies, none of which are due to features of Mesozoic age. The "Fort Archambault Rift" was thought to follow a major linear negative gravity anomaly which has been mapped beneath the Quaternary sediments of the Chad Basin. To a large extent the negative anomaly overlies the fosse de Baké-Birao (Baké-Birao Basin) which is itself part of a far larger structure that extends, parallel to the southern margin of the West African

  18. Seismological investigation of the Okavango Rift, Botswana

    NASA Astrophysics Data System (ADS)

    Yu, Youqiang

    The mechanisms of rifting have been intensively investigated using geological and geophysical techniques beneath mature rift zones. However, current understanding on the earliest stages of rifting is seriously limited. Here we employ recently archived data from 17 broadband seismic stations traversing northern Botswana to conduct the first shear wave splitting and mantle transition zone (MTZ) studies within the Okavango Rift Zone (ORZ). The ORZ is an incipient continental rift situated at the terminal of the southwestern branch of the East African Rift System. The resulting normal MTZ thickness and consistently rift-parallel fast polarizations imply an absence of significant thermal anomalies in the upper mantle, ruling out the role of mantle plumes in the initiation of the ORZ. The observed anisotropy beneath the ORZ and adjacent areas is mainly attributed to the relative movement between the lithosphere and asthenosphere with regional contributions from fabrics in the lithosphere and flow deflection by the bottom of the lithosphere. Our observations imply that the initiation and development of the ORZ can be initiated following a passive mode from the consequences of relative movements between the South African block and the rest of the African plate along a zone of lithospheric weakness between the Congo and Kalahari cratons. In addition, an approach was developed to effectively remove the near surface reverberations in the resulting receiver functions, decipher the P-to-S converted phases associated with the Moho discontinuity, and thus resolve sub-sediment crustal structure beneath stations sitting on a low-velocity sedimentary layer.

  19. Regional assessment of lake ecological states using Landsat: A classification scheme for alkaline-saline, flamingo lakes in the East African Rift Valley

    NASA Astrophysics Data System (ADS)

    Tebbs, E. J.; Remedios, J. J.; Avery, S. T.; Rowland, C. S.; Harper, D. M.

    2015-08-01

    In situ reflectance measurements and Landsat satellite imagery were combined to develop an optical classification scheme for alkaline-saline lakes in the Eastern Rift Valley. The classification allows the ecological state and consequent value, in this case to Lesser Flamingos, to be determined using Landsat satellite imagery. Lesser Flamingos depend on a network of 15 alkaline-saline lakes in East African Rift Valley, where they feed by filtering cyanobacteria and benthic diatoms from the lakes' waters. The classification developed here was based on a decision tree which used the reflectance in Landsat ETM+ bands 2-4 to assign one of six classes: low phytoplankton biomass; suspended sediment-dominated; microphytobenthos; high cyanobacterial biomass; cyanobacterial scum and bleached cyanobacterial scum. The classification accuracy was 77% when verified against in situ measurements. Classified imagery and timeseries were produced for selected lakes, which show the different ecological behaviours of these complex systems. The results have highlighted the importance to flamingos of the food resources offered by the extremely remote Lake Logipi. This study has demonstrated the potential of high spatial resolution, low spectral resolution sensors for providing ecologically valuable information at a regional scale, for alkaline-saline lakes and similar hypereutrophic inland waters.

  20. Sedimentology of rift climax deep water systems; Lower Rudeis Formation, Hammam Faraun Fault Block, Suez Rift, Egypt

    NASA Astrophysics Data System (ADS)

    Leppard, Christopher W.; Gawthorpe, Rob L.

    2006-09-01

    In most marine rift basins, subsidence outpaces sedimentation during rift climax times. Typically this results in sediment-starved hangingwall depocentres dominated by deep-marine mudstones, with subordinate local development of coarser clastics in the immediate hangingwall derived from restricted catchments on the immediate footwall scarp. To highlight the spatial variability of rift climax facies and the controls upon them, we have investigated the detailed three-dimensional geometry and facies relationships of the extremely well exposed Miocene, rift climax Lower Rudeis Formation in the immediate hangingwall to the Thal Fault Zone, Suez Rift, Egypt. Detailed sedimentological analyses allows the Lower Rudeis Formation to be divided into two contemporaneous depositional systems, (1) a laterally continuous slope system comprising, hangingwall restricted (< 250 m wide) slope apron, slope slumps, fault scarp degradation complex and laterally extensive lower slope-to-basinal siltstones, and (2) a localized submarine fan complex up to 1 km wide and extending at least 2 km basinward of the fault zone. Interpretation of individual facies, facies relationships and their spatial variability indicate that deposition in the immediate hangingwall to the Thal Fault occurred via a range of submarine concentrated density flows, surge-like turbidity flows, mass wasting and hemipelagic processes. Major controls on the spatial variability and stratigraphic architecture of the depositional systems identified reflect the influence of the steep footwall physiography, accommodation and drainage evolution associated with the growth of the Thal Fault. The under-filled nature of the hangingwall depocentre combined with the steep footwall gradient result in a steep fault-controlled basin margin characterised by either slope bypass or erosion, with limited coastal plain or shelf area. Sediment supply to the slope apron deposits is controlled in part by the evolution and size of small

  1. Quantifying the morphometric variability of monogenetic cones in volcanic fields: the Virunga Volcanic Province, East African Rift

    NASA Astrophysics Data System (ADS)

    Poppe, Sam; Grosse, Pablo; Barette, Florian; Smets, Benoît; Albino, Fabien; Kervyn, François; Kervyn, Matthieu

    2016-04-01

    Volcanic cone fields are generally made up of tens to hundreds of monogenetic cones, sometimes related to larger polygenetic edifices, which can exhibit a wide range of morphologies and degrees of preservation. The Virunga Volcanic Province (VVP) developed itself in a transfer zone which separates two rift segments (i.e. Edward and Kivu rift) within the western branch of the East-African Rift. As the result of volcanic activity related to this tectonic regime of continental extension, the VVP hosts eight large polygenetic volcanoes, surrounded by over 500 monogenetic cones and eruptive fissures, scattered over the vast VVP lava flow fields. Some cones lack any obvious geo-structural link to a specific Virunga volcano. Using recent high-resolution satellite images (SPOT, Pléiades) and a newly created 5-m-resolution digital elevation model (TanDEM-X), we have mapped and classified all monogenetic cones and eruptive fissures of the VVP. We analysed the orientation of all mapped eruptive fissures and, using the MORVOLC program, we calculated a set of morphometric parameters to highlight systematic spatial variations in size or morphometric ratios of the cones. Based upon morphological indicators, we classified the satellite cones into 4 categories: 1. Simple cones with one closed-rim crater; 2. Breached cones with one open-rim crater; 3. Complex cones with two or more interconnected craters and overlapping cones; 4. Other edifices without a distinguishable crater or cone shape (e.g. spatter mounds and levees along eruptive fissures). The results show that cones are distributed in clusters and along alignments, in some cases parallel with the regional tectonic orientations. Contrasts in the volumes of cones positioned on the rift shoulders compared to those located on the rift valley floor can possibly be attributed to contrasts in continental crust thickness. Furthermore, higher average cone slopes in the East-VVP (Bufumbira zone) and central-VVP cone clusters suggest

  2. 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.

  3. Rift-wide correlation of 1.1 Ga Midcontinent rift system basalts: Implications for multiple mantle sources during rift development

    USGS Publications Warehouse

    Nicholson, S.W.; Shirey, S.B.; Schulz, K.J.; Green, J.C.

    1997-01-01

    Magmatism that accompanied the 1.1 Ga Midcontinent rift system (MRS) is attributed to the upwelling and decompression melting of a mantle plume beneath North America. Five distinctive flood-basalt compositions are recognized in the rift-related basalt succession along the south shore of western Lake Superior, based on stratigraphically correlated major element, trace element, and Nd isotopic analyses. These distinctive compositions can be correlated with equivalent basalt types in comparable stratigraphic positions in other MRS localities around western Lake Superior. Four of these compositions are also recognized at Mamainse Point more than 200 km away in eastern Lake Superior. These regionally correlative basalt compositions provide the basis for determining the sequential contribution of various mantle sources to flood-basalt magmatism during rift development, extending a model originally developed for eastern Lake Superior. In this refined model, the earliest basalts were derived from small degrees of partial melting at great depth of an enriched, ocean-island-type plume mantle source (??Nd(1100) value of about 0), followed by magmas representing melts from this plume source and interaction with another mantle source, most likely continental lithospheric mantle (??Nd(1100) < 0). The relative contribution of this second mantle source diminished with time as larger degree partial melts of the plume became the dominant source for the voluminous younger basalts (??Nd(1100) value of about 0). Towards the end of magmatism, mixtures of melts from the plume and a depleted asthenospheric mantle source became dominant (??Nd(1100) = 0 to +3).

  4. 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

  5. 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.

  6. Rift Valley fever virus infection in African buffalo (Syncerus caffer) herds in rural South Africa: evidence of interepidemic transmission.

    PubMed

    LaBeaud, A Desirée; Cross, Paul C; Getz, Wayne M; Glinka, Allison; King, Charles H

    2011-04-01

    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.

  7. The Ngorongoro Volcanic Highland and its relationships to volcanic deposits at Olduvai Gorge and East African Rift volcanism.

    PubMed

    Mollel, Godwin F; Swisher, Carl C

    2012-08-01

    The Ngorongoro Volcanic Highland (NVH), situated adjacent and to the east of Olduvai Gorge in northern Tanzania, is the source of the immense quantities of lava, ignimbrite, air fall ash, and volcaniclastic debris that occur interbedded in the Plio-Pleistocene sedimentary deposits in the Laetoli and Olduvai areas. These volcanics have proven crucial to unraveling stratigraphic correlations, the age of these successions, the archaeological and paleontological remains, as well as the source materials from which the bulk of the stone tools were manufactured. The NVH towers some 2,000 m above the Olduvai and Laetoli landscapes, affecting local climate, run-off, and providing varying elevation - climate controlled ecosystem, habitats, and riparian corridors extending into the Olduvai and Laetoli lowlands. The NVH also plays a crucial role in addressing the genesis and history of East African Rift (EAR) magmatism in northern Tanzania. In this contribution, we provide age and petrochemical compositions of the major NVH centers: Lemagurut, basalt to benmorite, 2.4-2.2 Ma; Satiman, tephrite to phonolite, 4.6-3.5 Ma; Oldeani, basalt to trachyandesite, 1.6-1.5 Ma; Ngorongoro, basalt to rhyolite, 2.3-2.0 Ma; Olmoti, basalt to trachyte, 2.0-1.8 Ma; Embagai, nephelinite to phonolite, 1.2-0.6 Ma; and Engelosin, phonolite, 3-2.7 Ma. We then discuss how these correlate in time and composition with volcanics preserved at Olduvai Gorge. Finally, we place this into context with our current understanding as to the eruptive history of the NVH and relationship to East African Rift volcanism.

  8. The Thermal History of the East African Rift Lakes Region Since the Last Glacial Maximum Using TEX86 Paleothermometry

    NASA Astrophysics Data System (ADS)

    Berke, M. A.; Johnson, T. C.; Werne, J. P.; Schouten, S.; Sinninghe Damsté, J. S.

    2008-12-01

    We present preliminary results from a study using the TEX86 temperature proxy from sediments of East African Rift Lakes (including Lakes Turkana, Albert, and Malawi) to reconstruct the thermal history of tropical Africa for the last ~ 20,000 years at a subcentennial to multicentennial resolution. The TEX86 proxy, based on tetraether membrane lipids produced by lacustrine Crenarchaeota, has been shown to be successful at recording lake surface temperatures of some large lakes, including Lakes Malawi and Tanganyika, while providing unreasonable surface temperatures for lakes that receive a large input of soil material. The East African Rift Lakes are climatically sensitive, with the majority of water loss due to evaporation rather than outflow. Thus, they are useful for paleoclimate studies, being sensitive to even small changes in aridity. Temperature records from the northern and central basins of Lake Malawi agree well and fall within modern surface lake temperatures. A 2.5°C cooling is evident during the Younger Dryas in the northern basin record, with no response seen in the central basin. We are currently investigating mechanisms to explain why both records show a gradual cooling of 3°C during the late Holocene. Lake Albert shows an intriguing two-step cooling during the Younger Dryas, reaching temperatures 2.5°C lower than temperatures preceding or following this interval. The temperature record of Lake Turkana shows an interesting ~ 500 year cyclicity of low temperatures punctuated by abrupt warming events. Lakes Turkana and Albert show TEX86 paleotemperatures considerably lower (8°C cooler in Lake Albert and ~ 4°C cooler in Lake Turkana) than modern surface water temperatures. Although these records appear to fall in the range of temporal variability, these temperature discrepancies may indicate varying Crenarcheotal populations between lakes or other influencing factors.

  9. Tectonics and stratigraphy of the East Brazil Rift system: an overview

    NASA Astrophysics Data System (ADS)

    Hung Kiang Chang; Kowsmann, Renato Oscar; Figueiredo, Antonio Manuel Ferreira; Bender, AndréAdriano

    1992-10-01

    The East Brazilian Rift system (Ebris) constitutes the northern segment of the South Atlantic rift system which developed during the Mesozoic breakup of South America and Africa. Following crustal separation in the Late Aptian, it evolved into a passive continental margin. Along the continental margin six basins are recognized, while three onshore basins form part of an aborted rift. Three continental syn-rift stratigraphic sequences are recognized, spanning Jurassic to Barremian times. The Jurassic (Syn-rift I) and Neocomian (Syn-rift II) phases were most active in the interior rift basins. During the Barremian (Syn-rift III), rift subsidence rates were twice as large as during the Neocomian (Syn-rift II), both in the interior rift and in the marginal rift segments, indicating that rift axis did not migrate from the interior to the marginal setting. Rift magmatism was centered on the southern EBRIS and peaked between 130 and 120 Ma during syn-rift phase II. Rift phase III was followed by a transitional marine, evaporitic megasequence of Aptian age, which directly overlies the rift unconformity and a marine drift megasequence which spans Albian to Recent times. During the Late Cretaceous, sedimentation rates responded to first-order eustatic sea-level fluctuations. Tertiary accelerated sedimentation rates can be related to local clastic supply which filled in spaces inherited from previous starved conditions. Between 60 and 40 Ma, post-rift magmatism, centered on the Abrolhos and Royal Charlotte banks, is probably related to development of a hot spot associated with the Vitória-Trindade Seamount Chain. Although crossing three distinct Precambrian tectono-thermal provinces, ranging from Archean through Late Proterozoic, rift structures follow a general NE trend, subparallel to the principal basement fabric. A NW-SE oriented stress field appears to be compatible with both Neocomian and Barremian phases of crustal extension. Profiles transverse to the rift axis

  10. 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

  11. 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).

  12. 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.

  13. 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

  14. 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, Norman 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.

  15. A methodology to track temporal dynamics and rainfall thresholds of landslide processes in the East African Rift

    NASA Astrophysics Data System (ADS)

    Monsieurs, Elise; Jacobs, Liesbet; Kervyn, François; Kirschbaum, Dalia; d'Oreye, Nicolas; Derauw, Dominique; Kervyn, Matthieu; Nobile, Adriano; Trefois, Philippe; Dewitte, Olivier

    2015-04-01

    The East African rift valley is a major tectonic feature that shapes Central Africa and defines linear-shaped lowlands between highland ranges due to the action of geologic faults associated to earthquakes and volcanism. The region of interest, covering the Virunga Volcanic Province in eastern DRC, western Rwanda and Burundi, and southwest Uganda, is threatened by a rare combination of several types of geohazards, while it is also one of the most densely populated region of Africa. These geohazards can globally be classified as seismic, volcanic and landslide hazards. Landslides, include a wide range of ground movements, such as rock falls, deep failure of slopes and shallow debris flows. Landslides are possibly the most important geohazard in terms of recurring impact on the populations, causing fatalities every year and resulting in structural and functional damage to infrastructure and private properties, as well as serious disruptions of the organization of societies. Many landslides are observed each year in the whole region, and their occurrence is clearly linked to complex topographic, lithologic and vegetation signatures coupled with heavy rainfall events, which is the main triggering factor. The source mechanisms underlying landslide triggering and dynamics in the region of interest are still poorly understood, even though in recent years, some progress has been made towards appropriate data collection. Taking into account difficulties of field accessibility, we present a methodology to study landslide processes by multi-scale and multi-sensor remote sensing data from very high to low resolution (Pléiades, TRMM, CosmoSkyMed, Sentinel). The research will address the evolution over time of such data combined with other earth observations (seismic ground based networks, catalogues, rain gauge networks, GPS surveying, field observations) to detect and study landslide occurrence, dynamics and evolution. This research aims to get insights into the rainfall

  16. 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

  17. Influence of heterogeneities within the lithosphere on the deformation pattern of continental rift systems.

    NASA Astrophysics Data System (ADS)

    Philippon, Melody; Thieulot, Cedric; van Wijk, Jolante; Sokoutis, Dimitrios; Willingshofer, Ernst; Cloetingh, Sierd

    2013-04-01

    Understanding how heterogeneities within the lithosphere influence the deformation pattern in continental rifts still remains a challenge and is of real importance to constrain continental break-up. We have selected the Main Ethiopian Rift in East Africa and the Rio Grande Rift in the south-western U.S. These two rifts are perfect natural laboratories to investigate the effect of inherited as they share similar structural characteristics but develop above different kinds of lithosphere-scale heterogeneities. From a structural point of view both rifts show similar length (1000km), width (50 to 70 km) and asymmetry. The Main Ethiopian rift is the NE-SW trending plate boundary between the Nubian and Somalian plates that has been developing for the past 11 Ma above a palaeo-Proterozoic lithospheric-scale weak zone re-heated by the Afar hotspot, whereas the Rio Grande Rift is the eastern "boundary" of the Basin & Range system which has been developing for the past 30 Ma in the frame of a westward-retreating Farallon subduction zone. However, the Rio Grande Rift shows evidence of low angle normal faulting whereas the Main Ethiopian Rift shows steeply dipping (with a mean close to 70°) normal faults. The Main Ethiopian Rift shows larger volume of erupted lavas than the Rio Grande Rift. Combined with a structural analyses of both rifts, we present here a series of 2D cross sections numerical models that allow better understanding of the influence of initial heterogeneities such as 1) the rheological state of the crust; 2) the presence of a crustal-scale to lithospheric-scale discrete weak or strong zone, 3) the effects of the presence of magma. We illustrate that rheological boundaries are not reactivated if the rheological contrast it too high, which is the case of the Rio Grande Rift that developed to the east of the North American Craton within thinned lithosphere. We also illustrate that the width of the weak zone do no have any influence on the exhumation of the

  18. 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.

  19. Overview of African petroleum systems

    SciTech Connect

    Perrodon, A. )

    1993-07-12

    Bordered by two large, still spreading oceans and subjected to tensional forces for more than 200 million years, continental Africa has now reached its largest surface expression ever. With a total sedimentary area of 15 million sq km distributed in about 80 basins, Africa possesses and produces circa 10% of the world's oil and 7% of the gas. More than 95% of these hydrocarbons are concentrated in seven petroleum provinces, ruled by three great petroleum systems that in turn are tightly controlled and determined by the geodynamic characteristics of the basins. From a stratigraphic standpoint, these three petroleum systems belong to three geological time periods: Silurian, Cretaceous, and Oligo-Miocene. Generally the Silurian system occurs in Saharan sag basins, the Cretaceous-Eocene systems in a continental rift complex of western and equatorial Africa, and the Cenozoic in two deltaic basins. The Upper Paleozoic and Jurassic, so rich in other continents, here play but a very minor part. The paper describes the Silurian system, the Cretaceous-Eocene system, and the Tertiary system.

  20. Petrology of combeite- and götzenite-bearing nephelinite at Nyiragongo, Virunga Volcanic Province in the East African Rift

    NASA Astrophysics Data System (ADS)

    Andersen, Tom; Elburg, Marlina; Erambert, Muriel

    2012-11-01

    The lavas and pyroclastic rocks of Nyiragongo volcano (East African Rift) range in composition from olivine melilitite to nephelinite and minor alkali olivine basalt, and include rare examples of strongly peralkaline combeite nephelinite. In peralkaline nephelinites at Nyiragongo, titanium is hosted in mineral assemblages with Ti-bearing magnetite ± perovskite ± Ti-rich clinopyroxene ± götzenite. Combeite and götzenite occur as groundmass minerals in holocrystalline melilite nephelinite, which also carries kirschsteinite (replacing melilite phenocrysts), recrystallized nepheline + kalsilite phenocryst aggregates and a range of late accessory minerals including delhayelite. The compositions of coexisting nepheline and kalsilite in phenocryst aggregates and groundmass suggest a crystallization temperature of ca. 600 °C for the götzenite- and combeite bearing mineral assemblages. The textural features of the rock agree with an origin of holocrystalline nephelinite (with or without götzenite and combeite) by recrystallization of glass-bearing, nepheline-kalsilite and melilite porphyritic peralkaline nephelinite due to thermal metamorphism and metasomatism within the volcanic edifice. A chemographic analysis of the Ti-bearing mineral assemblages of götzenite-bearing and götzenite-free peralkaline nephelinite suggests that götzenite is stabilized by elevated fluorine activity combined with moderately high (for nephelinite) silica activity. At increasing peralkalinity, götzenite is likely to break down to perovskite-bearing mineral assemblages coexisting with combeite.

  1. The Hominin Sites and Paleolakes Drilling Project: inferring the environmental context of human evolution from eastern African rift lake deposits

    NASA Astrophysics Data System (ADS)

    Cohen, A.; Campisano, C.; Arrowsmith, R.; Asrat, A.; Behrensmeyer, A. K.; Deino, A.; Feibel, C.; Hill, A.; Johnson, R.; Kingston, J.; Lamb, H.; Lowenstein, T.; Noren, A.; Olago, D.; Owen, R. B.; Potts, R.; Reed, K.; Renaut, R.; Schäbitz, F.; Tiercelin, J.-J.; Trauth, M. H.; Wynn, J.; Ivory, S.; Brady, K.; O'Grady, R.; Rodysill, J.; Githiri, J.; Russell, J.; Foerster, V.; Dommain, R.; Rucina, S.; Deocampo, D.; Russell, J.; Billingsley, A.; Beck, C.; Dorenbeck, G.; Dullo, L.; Feary, D.; Garello, D.; Gromig, R.; Johnson, T.; Junginger, A.; Karanja, M.; Kimburi, E.; Mbuthia, A.; McCartney, T.; McNulty, E.; Muiruri, V.; Nambiro, E.; Negash, E. W.; Njagi, D.; Wilson, J. N.; Rabideaux, N.; Raub, T.; Sier, M. J.; Smith, P.; Urban, J.; Warren, M.; Yadeta, M.; Yost, C.; Zinaye, B.

    2016-02-01

    The role that climate and environmental history may have played in influencing human evolution has been the focus of considerable interest and controversy among paleoanthropologists for decades. Prior attempts to understand the environmental history side of this equation have centered around the study of outcrop sediments and fossils adjacent to where fossil hominins (ancestors or close relatives of modern humans) are found, or from the study of deep sea drill cores. However, outcrop sediments are often highly weathered and thus are unsuitable for some types of paleoclimatic records, and deep sea core records come from long distances away from the actual fossil and stone tool remains. The Hominin Sites and Paleolakes Drilling Project (HSPDP) was developed to address these issues. The project has focused its efforts on the eastern African Rift Valley, where much of the evidence for early hominins has been recovered. We have collected about 2 km of sediment drill core from six basins in Kenya and Ethiopia, in lake deposits immediately adjacent to important fossil hominin and archaeological sites. Collectively these cores cover in time many of the key transitions and critical intervals in human evolutionary history over the last 4 Ma, such as the earliest stone tools, the origin of our own genus Homo, and the earliest anatomically modern Homo sapiens. Here we document the initial field, physical property, and core description results of the 2012-2014 HSPDP coring campaign.

  2. 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

  3. 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

  4. Rift Valley fever among domestic animals in the recent West African outbreak.

    PubMed

    Ksiazek, T G; Jouan, A; Meegan, J M; Le Guenno, B; Wilson, M L; Peters, C J; Digoutte, J P; Guillaud, M; Merzoug, N O; Touray, E M

    1989-01-01

    Severe haemorrhagic disease among the human population of the Senegal River Basin brought the Rift Valley fever virus (RVFV) outbreak of 1987 to the attention of science. As in previous RVFV outbreaks, local herdsmen reported a high incidence of abortion and disease in their livestock. Serum samples were obtained from domestic animal populations from areas near Rosso, the best studied focus of human infection, as well as other areas distant from known human disease. Among animals from the area of high incidence of human disease, antibody prevalence was as high as 85%, with approximately 80% of the sera positive for both RVFV IgG- and viral-specific IgM antibodies. In contrast, human populations in the same area had lower RVFV antibody prevalences, 40% or less, with 90% also being IgM-positive. Sera from livestock in coastal areas 280 km south of the epidemic area were negative for RVFV antibodies. Thus, the detection of RVFV specific IgG and IgM antibodies provided evidence of recent disease activity without the requirement to establish pre-disease antibody levels in populations or individuals and without viral isolation. Subsequently, detection of modest levels of IgG and IgM in the Ferlo region, 130 km south of the Senegal River flood plain, established that RVFV transmission also occurred in another area of the basin. Similar serological testing of domestic ungulates in The Gambia, 340 km south of Rosso, demonstrated antibody prevalence consistent with a lower level of recent transmission of RVFV, i.e., 24% IgG-positive with 6% of the positive sera also having RVFV-specific IgM.

  5. Genetic features of petroleum systems in rift basins of eastern China

    USGS Publications Warehouse

    Qiang, J.; McCabe, P.J.

    1998-01-01

    Most oil-bearing basins in eastern China are Mesozoic-Cenozoic continental rifts which have played a habitat for oil and gas in China. Investigation of the petroleum systems may give a better understanding of the oil and gas habitats in these basins. Of the essential elements of the petroleum system, the source rock is the most important in rift basins. However, rift tectonic evolution controls all the essential elements and processes nevessary for a petroleum system. A four stage evolution model is suggested for the controls in the rift basin. A rift basin may consist of sub-basins, depressions, sub-depressions, and major, moderate, and minor uplifts. A depression or sub-depression has its own depocentre (mainly occupied by source rock) and all kinds of lacustrine sediments, and thus has all the essential elements of a petroleum system. However, only those depressions or sub-depressions which are rich in organic matter and deeply buried to generate oil and gas form petroleum systems. Immature oil, another characteristic, complicates the petroleum system in the rift basins. Three types of oil and gas habitats are described as a result of this analysis of the petroleum systems of the 26 largest oil and gas fields discovered in eastern China rift basins: uplifts between oil source centres are the most prospective areas for oil and gas accumulations, slopes connecting oil source centres and uplifts are the second, and the third type is subtle traps in the soil source centre.Most oil-bearing basins in eastern China are Mesozoic-Cenozoic continental rifts which have played a habitat for oil and gas in China. Investigation of the petroleum systems may give a better understanding of the oil and gas habitats in these basins. Of the essential elements of the petroleum system, the source rock is the most important in rift basins. However, rift tectonic evolution controls all the essential elements and processes necessary for a petroleum system. A four stage evolution model

  6. Convection pattern and stress system under the African plate

    NASA Technical Reports Server (NTRS)

    Liu, H.-S.

    1977-01-01

    Studies on tectonic forces from satellite-derived gravity data have revealed a subcrustal stress system which provides a unifying mechanism for uplift, depression, rifting, plate motion and ore formation in Africa. The subcrustal stresses are due to mantle convection. Seismicity, volcanicity and kimberlite magmatism in Africa and the development of the African tectonic and magnetic features are explained in terms of this single stress system. The tensional stress fields in the crust exerted by the upwelling mantle flows are shown to be regions of structural kinship characterized by major concentration of mineral deposits. It is probable that the space techniques are capable of detecting and determining the tectonic forces in the crust of Africa.

  7. Comparative pathogenicity and antigenic cross-reactivity of Rift Valley fever and other African phleboviruses in sheep.

    PubMed Central

    Swanepoel, R.; Struthers, J. K.; Erasmus, M. J.; Shepherd, S. P.; McGillivray, G. M.; Shepherd, A. J.; Hummitzsch, D. E.; Erasmus, B. J.; Barnard, B. J.

    1986-01-01

    Homologous and heterologous haemagglutination-inhibition (HAI), complement-fixation (CF), immunodiffusion (ID) and mouse neutralization tests were performed with the Lunyo (LUN) and a Zimbabwean strain of Rift Valley fever (RVF) virus, the prototype and a South African strain of Arumowot (AMT) virus and prototype strains of Gordil (GOR), Saint-Floris (SAF) and Gabek Forest (GF) viruses, using immune mouse ascitic fluids prepared against these viruses. Reactions of identity occurred in all tests between LUN and the Zimbabwean strains of RVF and between the two strains of AMT virus. Otherwise, cross-reactions occurred between all the phleboviruses in HAI tests, while reactions in CF, ID and neutralization tests were monospecific for virus serotypes, except that weak cross-reaction occurred between GOR and SAF viruses in CF and ID tests. Four sheep infected subcutaneously with the Zimbabwean strain of RVF virus developed transient fever, viraemia, leucopaenia, relative thrombocytopaenia, haemoconcentration and raised serum enzyme levels, which indicated that the sheep had developed necrotic hepatitis. Disseminated focal necrotic hepatitis was confirmed in a sheep killed for examination on day 4 post-infection. The other three sheep recovered uneventfully after only mild depression and anorexia. Groups of three sheep infected with SAF, GOR, AMT and GF viruses had no demonstrable viraemia or other sign of infection or illness, except that the sheep infected with AMT developed mild fever lasting less than 24 h. Antibody responses were monitored at intervals over a period of 24 weeks in all sheep by homologous and heterologous HAI, CF and cell culture neutralization (CPENT) tests. Homologous antibody responses were marked in the RVF-infected sheep and their sera cross-reacted strongly in HAI tests with antigens of the other viruses. The sera of the RVF-infected sheep cross-reacted less markedly in CF and CPENT tests. Homologous antibody responses were poor in all the

  8. 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

  9. Analysis of surveillance systems in place in European Mediterranean countries for West Nile virus (WNV) and Rift Valley fever (RVF).

    PubMed

    Cito, F; Narcisi, V; Danzetta, M L; Iannetti, S; Sabatino, D D; Bruno, R; Carvelli, A; Atzeni, M; Sauro, F; Calistri, P

    2013-11-01

    West Nile virus (WNV) and Rift Valley fever virus (RVFV) represent an important group of viral agents responsible for vector-borne zoonotic diseases constituting an emerging sanitary threat for the Mediterranean Basin and the neighbouring countries. WNV infection is present in several Mediterranean countries, whereas RVF has never been introduced into Europe, but it is considered a major threat for North African countries. Being vector-borne diseases, they cannot be prevented only through an animal trade control policy. Several approaches are used for the surveillance of WNV and RVFV. With the aim of assessing the surveillance systems in place in Mediterranean countries, two disease-specific questionnaires (WNV, RVFV) have been prepared and submitted to Public Health and Veterinary Authorities of six EU countries. This study presents the information gathered through the questionnaires and describes some critical points in the prevention and surveillance of these diseases as emerged by the answers received.

  10. Structural geometry and evolution of the Dead Sea-Jordan rift system as deduced from new subsurface data

    NASA Astrophysics Data System (ADS)

    Kashai, E. L.; Croker, P. F.

    1987-09-01

    Analysis of deep drilling data and seismic reflection surveys obtained in recent years permit establishment of a tectonic model of the Dead Sea-Jordan rift system that is in part conformable with some of the many, often controversial, theories on this subject, but which also introduces new information negating some concepts that are widely accepted in the literature. The Dead Sea-Jordan rift system is not a tensional graben between two parallel sets of faults, but instead can be best defined as a sinistral transform connecting an incipient oceanic ridge—the Red Sea—with an upthrusted collision zone, the Taurus range. The shear is caused by the opening of the Red Sea and the motion of the Arabian sub-plate away from the African plate. The shearing occurs along a largely south-north trending, slightly arcuate Une, consisting of a series of en echelon left-stepping left-lateral strike-slip master faults of varying lengths. These faults characteristically die out to the north by bending outward (northeast), and the movement is taken up by the strike-slip faults to the left (i.e. to the west). Where overlap of the two faults occurs, very narrow and very deep grabens have evolved, in places the width being equal to the depth. The narrowness of these grabens is dictated by the closeness of the overlapping segments of the successive strike-slip faults. This feature points to the probability that the en echelon strike-slip faults have a common root zone at great depth. These grabens are not typical "leaky" pull-aparts in that they have no gravimetric, magnetic or heat flow anomalies; nor are they closed on all four sides by large faults. Their northern ends are characterized by gradually rising graben floors without major diagonal cross faults. The Dead Sea-Jordan rift system sensu stricto extends over a distance of 420 km, from the northern shore of the Gulf of Elat to the northern margin of the Hula Valley. Southward, it is connected with the Red Sea along the Gulf of

  11. 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

  12. Oligocene Termite Nests with In Situ Fungus Gardens from the Rukwa Rift Basin, Tanzania, Support a Paleogene African Origin for Insect Agriculture.

    PubMed

    Roberts, Eric M; Todd, Christopher N; Aanen, Duur K; Nobre, Tânia; Hilbert-Wolf, Hannah L; O'Connor, Patrick M; Tapanila, Leif; Mtelela, Cassy; Stevens, Nancy J

    2016-01-01

    Based on molecular dating, the origin of insect agriculture is hypothesized to have taken place independently in three clades of fungus-farming insects: the termites, ants or ambrosia beetles during the Paleogene (66-24 Ma). Yet, definitive fossil evidence of fungus-growing behavior has been elusive, with no unequivocal records prior to the late Miocene (7-10 Ma). Here we report fossil evidence of insect agriculture in the form of fossil fungus gardens, preserved within 25 Ma termite nests from southwestern Tanzania. Using these well-dated fossil fungus gardens, we have recalibrated molecular divergence estimates for the origins of termite agriculture to around 31 Ma, lending support to hypotheses suggesting an African Paleogene origin for termite-fungus symbiosis; perhaps coinciding with rift initiation and changes in the African landscape.

  13. Oligocene Termite Nests with In Situ Fungus Gardens from the Rukwa Rift Basin, Tanzania, Support a Paleogene African Origin for Insect Agriculture

    PubMed Central

    Roberts, Eric M.; Todd, Christopher N.; Aanen, Duur K.; Nobre, Tânia; Hilbert-Wolf, Hannah L.; O’Connor, Patrick M.; Tapanila, Leif; Mtelela, Cassy; Stevens, Nancy J.

    2016-01-01

    Based on molecular dating, the origin of insect agriculture is hypothesized to have taken place independently in three clades of fungus-farming insects: the termites, ants or ambrosia beetles during the Paleogene (66–24 Ma). Yet, definitive fossil evidence of fungus-growing behavior has been elusive, with no unequivocal records prior to the late Miocene (7–10 Ma). Here we report fossil evidence of insect agriculture in the form of fossil fungus gardens, preserved within 25 Ma termite nests from southwestern Tanzania. Using these well-dated fossil fungus gardens, we have recalibrated molecular divergence estimates for the origins of termite agriculture to around 31 Ma, lending support to hypotheses suggesting an African Paleogene origin for termite-fungus symbiosis; perhaps coinciding with rift initiation and changes in the African landscape. PMID:27333288

  14. 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.

  15. 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.

  16. 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.

  17. Short-lived increase in erosion during the African Humid Period: Evidence from the northern Kenya Rift

    NASA Astrophysics Data System (ADS)

    Garcin, Yannick; Schildgen, Taylor F.; Torres Acosta, Verónica; Melnick, Daniel; Guillemoteau, Julien; Willenbring, Jane; Strecker, Manfred R.

    2017-02-01

    The African Humid Period (AHP) between ∼15 and 5.5 cal. kyr BP caused major environmental change in East Africa, including filling of the Suguta Valley in the northern Kenya Rift with an extensive (∼2150 km2), deep (∼300 m) lake. Interfingering fluvio-lacustrine deposits of the Baragoi paleo-delta provide insights into the lake-level history and how erosion rates changed during this time, as revealed by delta-volume estimates and the concentration of cosmogenic 10Be in fluvial sand. Erosion rates derived from delta-volume estimates range from 0.019 to 0.03 mm yr-1. 10Be-derived paleo-erosion rates at ∼11.8 cal. kyr BP ranged from 0.035 to 0.086 mm yr-1, and were 2.7 to 6.6 times faster than at present. In contrast, at ∼8.7 cal. kyr BP, erosion rates were only 1.8 times faster than at present. Because 10Be-derived erosion rates integrate over several millennia, we modeled the erosion-rate history that best explains the 10Be data using established non-linear equations that describe in situ cosmogenic isotope production and decay. Two models with different temporal constraints (15-6.7 and 12-6.7 kyr) suggest erosion rates that were ∼25 to ∼300 times higher than the initial erosion rate (pre-delta formation). That pulse of high erosion rates was short (∼4 kyr or less) and must have been followed by a rapid decrease in rates while climate remained humid to reach the modern 10Be-based erosion rate of ∼0.013 mm yr-1. Our simulations also flag the two highest 10Be-derived erosion rates at ∼11.8 kyr BP related to non-uniform catchment erosion. These changes in erosion rates and processes during the AHP may reflect a strong increase in precipitation, runoff, and erosivity at the arid-to-humid transition either at ∼15 or ∼12 cal. kyr BP, before the landscape stabilized again, possibly due to increased soil production and denser vegetation.

  18. Extension and Basin Evolution of the East Kivu Graben, Rwanda, East African Rift: Results of New Multichannel Seismic Reflection Imaging

    NASA Astrophysics Data System (ADS)

    Scholz, C. A.; Zhang, X.; Wood, D.; Mburu, D.

    2012-12-01

    The East Kivu Graben resides within the eastern part of Lake Kivu, the highest Great Lake in the western branch of the East African Rift. The lake is more than 440 m deep in the East Kivu Basin, with a catchment comprised of Precambrian metasedimentary rocks and late-Cenozoic volcanics. Lake Kivu is renowned for its uniquely stratified water column, which is charged with considerable quantities of dissolved CO2 and methane, the former due to magmatic degassing. In February and March 2012 514 km of single- and multi-channel seismic reflection data were acquired in the Rwandan waters of Lake Kivu. The 24-fold multichannel seismic data were acquired aboard a modular research vessel, using a 600 m-long hydrophone streamer and single 40 cubic inch airgun. Extension in the East Kivu basin is largely accommodated along a major N-S striking, east-dipping boundary fault observed along the eastern edge of Iwawa Island, and extending for ~40 km along the length of the basin. Numerous intrabasinal normal faults occur to the east of the boundary fault, commonly displacing the lake floor and controlling the location of modern sublacustrine channels. The deepest sedimentary reflections observed on the new MCS data are 1.2-1.5 km below lake floor, near the center of the basin and boundary fault. Crystalline basement is not observed in these deepest areas however, suggesting the presence of a substantial sedimentary section below the imaged strata. Stratal surfaces dip steeply to the west over large areas of the half-graben basin. An acoustically transparent seismic sequence up to ~25 m thick is observed at the lake floor, which overlies a pronounced erosional unconformity over much of the basin. Some intrabasinal normal faults are draped by and do not penetrate the upper sequences, indicating several generations of fault activity in the basin. The late-Pleistocene exposure surface likely correlates to the previous lake level low stage that persisted prior to volcanic damming by

  19. Chemistry and chronology of magmatic processes, Central Kenya Peralkaline province, East African Rift

    NASA Astrophysics Data System (ADS)

    Anthony, E.; Deino, A. L.; White, J. C.; Omenda, P. A.

    2014-12-01

    We report here a synthesis of the geochemistry of magma evolution correlated with 40Ar/39Ar, 14 C, and U-series chronology for volcanoes in the Central Kenya Peralkaline Province (CKPP). The volcanic centers - Menengai, Eburru, Olkaria, Longonot, and Suswa - are at the apex of the Kenya Dome, and consist of trachyte, phonolite, comendite, and pantellerite. These volcanic centers are within the graben of the EARS and are characterized by a shield-building phase followed by caldera collapse and subsequent post-caldera eruptions. Geochemical modeling demonstrates that the magmas are the result of fractional crystallization of alkali basaltic magmas and magma mixing. Longonot and Suswa have the most chronologic data -14 C, Ar/Ar and U-series - and they show that the youngest eruptions have 230 Th/232Th of 0.8, which was inherited from the magma system prior to eruption. Subsequent changes in 230 Th/232 Th are due to post-eruptive decay of 230 Th and correlate well with 14 C and Ar/Ar.

  20. 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.

  1. Initial Results of Scientific Drilling on Lake Malawi, East African Rift

    NASA Astrophysics Data System (ADS)

    Scholz, C. A.; Johnson, T. C.; King, J.; Cohen, A. S.; Lyons, R. P.; Kalindekafe, L.; Forman, S. L.; McHargue, L. R.; Singer, B. S.

    2005-12-01

    Lake Malawi is one of the largest and oldest lakes in the southern hemisphere and in the tropical latitudes, measuring more than 580 km in length, with a maximum depth of 700 m, and with an estimated age of more than 7 Ma. The lake water column is anoxic below 200 m, thus preserving an extensive record of laminated (varved) sediments. The lake's hydrologic budget is hypersensitive to minor changes in precipitation:evaporation, and signals of lake level and limnologic change respond markedly to regional climate variations. During February-March 2005 a scientific drilling program was conducted on the deep, open waters of Lake Malawi, using a converted local fuel barge outfitted with a deep-water-capable geotechnical drilling rig, a portable dynamic positioning system, and a suite of sampling tools designed for deep lake coring. A total of 623 m of core was recovered in seven holes at two sites on the lake. The high-resolution North Basin site (water depth 359 m) was triple-cored, providing redundant sampling of the sedimentary section representing the past ~75-100 kyr; the Central Basin deep site (592 m water depth) was double cored over the period of the past ~200 kyr, and single-cored to 380 m, covering perhaps 1.5 million years. The North Basin high-resolution site targeted a hemipelagic sequence, which in core samples consists of alternating zones of laminated and homogenous silty mud. At the base of these cores we observe well-sorted medium-grained shoreface sand deposits, that we interpret to be a transgressive surface deposited following a severe (500 m) lake lowstand. Density, magnetic susceptibility, TOC, and C/N profiles closely follow lithologic changes, and correspond to periods of enhanced or diminished productivity and dramatically varying lake level. Initial dating of the North Basin site (total core length 38 m) is underway using a combination of Radiocarbon, Tephra Ar-Ar, and Optically-Stimulated Luminescence methods, and initial results indicate a

  2. 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.

  3. Twenty-five years of geodetic measurements along the Tadjoura-Asal rift system, Djibouti, East Africa

    NASA Astrophysics Data System (ADS)

    Vigny, Christophe; de Chabalier, Jean-Bernard; Ruegg, Jean-Claude; Huchon, Philippe; Feigl, Kurt L.; Cattin, Rodolphe; Asfaw, Laike; Kanbari, Khaled

    2007-06-01

    Since most of Tadjoura-Asal rift system sits on dry land in the Afar depression near the triple junction between the Arabia, Somalia, and Nubia plates, it is an ideal natural laboratory for studying rifting processes. We analyze these processes in light of a time series of geodetic measurements from 1978 through 2003. The surveys used triangulation (1973), trilateration (1973, 1979, and 1981-1986), leveling (1973, 1979, 1984-1985, and 2000), and the Global Positioning System (GPS, in 1991, 1993, 1995, 1997, 1999, 2001, and 2003). A network of about 30 GPS sites covers the Republic of Djibouti. Additional points were also measured in Yemen and Ethiopia. Stations lying in the Danakil block have almost the same velocity as Arabian plate, indicating that opening near the southern tip of the Red Sea is almost totally accommodated in the Afar depression. Inside Djibouti, the Asal-Ghoubbet rift system accommodates 16 ± 1 mm/yr of opening perpendicular to the rift axis and exhibits a pronounced asymmetry with essentially null deformation on its southwestern side and significant deformation on its northeastern side. This rate, slightly higher than the large-scale Arabia-Somalia motion (13 ± 1 mm/yr), suggests transient variations associated with relaxation processes following the Asal-Ghoubbet seismovolcanic sequence of 1978. Inside the rift, the deformation pattern exhibits a clear two-dimensional pattern. Along the rift axis, the rate decreases to the northwest, suggesting propagation in the same direction. Perpendicular to the rift axis, the focus of the opening is clearly shifted to the northeast, relative to the topographic rift axis, in the "Petit Rift," a rift-in-rift structure, containing most of the active faults and the seismicity. Vertical motions, measured by differential leveling, show the same asymmetric pattern with a bulge of the northeastern shoulder. Although the inner floor of the rift is subsiding with respect to the shoulders, all sites within the

  4. Impact of geodynamic development of the Barents Sea deep rift on evolving petroleum systems

    NASA Astrophysics Data System (ADS)

    Balanyuk, I.; Dmitrievsky, A.

    2009-04-01

    All the Barents Sea deposits are situated in the epicenter on active geodynamic development of the Barents Sea rift and, most important, over the zone of listric faults intersection, which consist a knot system over the mantle diapir. This is confirmed by prospecting seismology. Intrusion of hot mantle matter with further cooling down of abnormal lense might be a possible cause of appearance and evolution of ultradeep depressions. A high "seismic stratification" of the lower crust (nearly reaching the basement surface) at time scale about 8 sec. is typical for the inner, the deepest part of the depression. Supposing the "seismic stratified" lower crust correspond to "basalt" layer, this area is nearly upper crust ("granitic-gneiss") free. This fact confurmes conception on development of "granite free gaps" in the depression basement. Thick blocks of "seismically transparent" upper crust corresponding to the "granitic-gneiss" layer are marked out within Kolsk-Kanin monocline. An abrupt thickness decrease and appearance of "stratified" areas takes place at the southern edge of the depression. A filling of the over-rift sag with sediments, revival of the faults and their effect on the filtration processes and gas hydrates formation took place in the South Barents Sea depression. Repeating activation of the fault blocks in the basement, especially during late Jurassic - early Cretaceous period contributed to formation of the structures related to the greatest deposits of the South Barents Sea depression. An extended field acoustic data collected in the Barents Sea led to understanding of general fundamental problems for all Arctic Seas and, first of all, the problem of Quaternary glaciations. An analysis of Eurasian-Arctic continental margin shows correspondence between the rift systems of the shelf with those of the ocean. This relation can be observed by an example of the central Arctic region. All the rift systems underlying the sediment basin are expressed in the

  5. Revised Eocene-Oligocene kinematics for the West Antarctic rift system

    NASA Astrophysics Data System (ADS)

    Granot, R.; Cande, S. C.; Stock, J. M.; Damaske, D.

    2013-01-01

    Abstract<p label="1">Past plate motion between East and West Antarctica along the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> had important regional and global implications. Although extensively studied, the kinematics of the <span class="hlt">rift</span> during Eocene-Oligocene time still remains elusive. Based on a recent detailed aeromagnetic survey from the Adare and Northern Basins, located in the northwestern Ross Sea, we present the first well-constrained kinematic model with four rotations for Anomalies 12o, 13o, 16y, and 18o (26.5-40.13 Ma). These rotation poles form a cluster suggesting a stable sense of motion during that period of time. The poles are located close to the central part of the <span class="hlt">rift</span> implying that the local motion varied from extension in the western Ross Sea sector (Adare Basin, Northern Basin, and Victoria Land Basin) to dextral transcurrent motion in the Ross Ice Shelf and to oblique convergence in the eastern end of the <span class="hlt">rift</span> zone. The results confirm previous estimates of 95 km of extension in the Victoria Land Basin.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4250055','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4250055"><span id="translatedtitle">Statistical Modeling of the Abundance of Vectors of West <span class="hlt">African</span> <span class="hlt">Rift</span> Valley Fever in Barkédji, Senegal</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Talla, Cheikh; Diallo, Diawo; Dia, Ibrahima; Ba, Yamar; Ndione, Jacques-André; Sall, Amadou Alpha; Morse, Andy; Diop, Aliou; Diallo, Mawlouth</p> <p>2014-01-01</p> <p><span class="hlt">Rift</span> Valley fever is an emerging mosquito-borne disease that represents a threat to human and animal health. The exophilic and exophagic behavior of the two main vector in West Africa (Aedes vexans and Culex poicilipes), adverse events post-vaccination, and lack of treatment, render ineffective the disease control. Therefore it is essential to develop an information <span class="hlt">system</span> that facilitates decision-making and the implementation of adaptation strategies. In East Africa, RVF outbreaks are linked with abnormally high rainfall, and can be predicted up to 5 months in advance by modeling approaches using climatic and environmental parameters. However, the application of these models in West Africa remains unsatisfactory due to a lack of data for animal and human cases and differences in the dynamics of the disease emergence and the vector species involved in transmission. Models have been proposed for West Africa but they were restricted to rainfall impact analysis without a spatial dimension. In this study, we developed a mixed Bayesian statistical model to evaluate the effects of climatic and ecological determinants on the spatiotemporal dynamics of the two main vectors. Adult mosquito abundance data were generated from July to December every fortnight in 2005–2006 at 79 sites, including temporary ponds, bare soils, shrubby savannah, wooded savannah, steppes, and villages in the Barkédji area. The results demonstrate the importance of environmental factors and weather conditions for predicting mosquito abundance. The rainfall and minimum temperature were positively correlated with the abundance of Cx. poicilipes, whereas the maximum temperature had negative effects. The rainfall was negatively correlated with the abundance of Ae. vexans. After combining land cover classes, weather conditions, and vector abundance, our model was used to predict the areas and periods with the highest risks of vector pressure. This information could support decision-making to improve</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25437856','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25437856"><span id="translatedtitle">Statistical modeling of the abundance of vectors of West <span class="hlt">African</span> <span class="hlt">Rift</span> Valley fever in Barkédji, Senegal.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Talla, Cheikh; Diallo, Diawo; Dia, Ibrahima; Ba, Yamar; Ndione, Jacques-André; Sall, Amadou Alpha; Morse, Andy; Diop, Aliou; Diallo, Mawlouth</p> <p>2014-01-01</p> <p><span class="hlt">Rift</span> Valley fever is an emerging mosquito-borne disease that represents a threat to human and animal health. The exophilic and exophagic behavior of the two main vector in West Africa (Aedes vexans and Culex poicilipes), adverse events post-vaccination, and lack of treatment, render ineffective the disease control. Therefore it is essential to develop an information <span class="hlt">system</span> that facilitates decision-making and the implementation of adaptation strategies. In East Africa, RVF outbreaks are linked with abnormally high rainfall, and can be predicted up to 5 months in advance by modeling approaches using climatic and environmental parameters. However, the application of these models in West Africa remains unsatisfactory due to a lack of data for animal and human cases and differences in the dynamics of the disease emergence and the vector species involved in transmission. Models have been proposed for West Africa but they were restricted to rainfall impact analysis without a spatial dimension. In this study, we developed a mixed Bayesian statistical model to evaluate the effects of climatic and ecological determinants on the spatiotemporal dynamics of the two main vectors. Adult mosquito abundance data were generated from July to December every fortnight in 2005-2006 at 79 sites, including temporary ponds, bare soils, shrubby savannah, wooded savannah, steppes, and villages in the Barkédji area. The results demonstrate the importance of environmental factors and weather conditions for predicting mosquito abundance. The rainfall and minimum temperature were positively correlated with the abundance of Cx. poicilipes, whereas the maximum temperature had negative effects. The rainfall was negatively correlated with the abundance of Ae. vexans. After combining land cover classes, weather conditions, and vector abundance, our model was used to predict the areas and periods with the highest risks of vector pressure. This information could support decision-making to improve RVF</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMPP33D1274D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMPP33D1274D"><span id="translatedtitle">The Olorgesailie Drilling Project (ODP): a high-resolution drill core record from a hominin site in the East <span class="hlt">African</span> <span class="hlt">Rift</span> Valley</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dommain, R.; Potts, R.; Behrensmeyer, A. K.; Deino, A. L.</p> <p>2014-12-01</p> <p>The East <span class="hlt">African</span> <span class="hlt">rift</span> valley contains an outstanding record of hominin fossils that document human evolution over the Plio-Pleistocene when the global and regional climate and the <span class="hlt">rift</span> valley itself changed markedly. The sediments of fossil localities typically provide, however, only short time windows into past climatic and environmental conditions. Continuous, long-term terrestrial records are now becoming available through core drilling to help elucidate the paleoenvironmental context of human evolution. Here we present a 500,000 year long high-resolution drill core record obtained from a key fossil and archeological site - the Olorgesailie Basin in the southern Kenya <span class="hlt">Rift</span> Valley, well known for its sequence of archeological and faunal sites for the past 1.2 million years. In 2012 two drill cores (54 and 166 m long) were collected in the Koora Plain just south of Mt. Olorgesailie as part of the Olorgesailie Drilling Project (ODP) to establish a detailed climate and ecological record associated with the last evidence of Homo erectus in Africa, the oldest transition of Acheulean to Middle Stone Age technology, and large mammal species turnover, all of which are documented in the Olorgesailie excavations. The cores were sampled at the National Lacustrine Core Facility. More than 140 samples of tephra and trachytic basement lavas have led to high-precision 40Ar/39Ar dating. The cores are being analyzed for a suite of paleoclimatic and paleoecological proxies such as diatoms, pollen, fungal spores, phytoliths, ostracodes, carbonate isotopes, leaf wax biomarkers, charcoal, and clay mineralogy. Sedimentological analyses, including lithological descriptions, microscopic smear slide analysis (242 samples), and grain-size analysis, reveal a highly variable sedimentary sequence of deep lake phases with laminated sediments, diatomites, shallow lake and near shore phases, fluvial deposits, paleosols, interspersed carbonate layers, and abundant volcanic ash deposits. Magnetic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.430....1Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.430....1Y"><span id="translatedtitle">Seismic anisotropy beneath the incipient Okavango <span class="hlt">rift</span>: Implications for <span class="hlt">rifting</span> initiation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yu, Youqiang; Gao, Stephen S.; Moidaki, Moikwathai; Reed, Cory A.; Liu, Kelly H.</p> <p>2015-11-01</p> <p>This study represents the first shear-wave splitting investigation of the Okavango <span class="hlt">rift</span> zone (ORZ), an incipient continental <span class="hlt">rift</span> belonging to the East <span class="hlt">African</span> <span class="hlt">rift</span> <span class="hlt">system</span> in northern Botswana. Analysis of broadband seismic data recorded along a 750 km long profile of 22 stations traversing the ORZ and adjacent Congo and Kalahari cratons and several Precambrian orogenic zones reveals dominantly NE-SW fast orientations, which are parallel to both the absolute plate motion direction (based on the NNR-NUVEL-1A model) and the trend of most tectonic boundaries, including that of the ORZ. Spatial coherence analysis of the splitting parameters and correspondence between the observed fast orientations and the trend of tectonic features indicate that the main source of observed anisotropy is most likely in the upper asthenosphere, probably due to simple shear associated with the relative movement of the lithosphere against the asthenosphere. The presence of consistently <span class="hlt">rift</span>-parallel fast orientations and normal splitting times in the ORZ and most parts of southern Africa implies that neither an upper mantle plume nor small-scale convection is the dominant source for <span class="hlt">rift</span> initiation and development. The first shear-wave splitting measurements in the vicinity of the ORZ favor a model in which continental <span class="hlt">rifting</span> develops in response to intra-plate relative movement of continental blocks along zones of weakness produced by ancient tectonic events.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeoJI.198..414A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeoJI.198..414A"><span id="translatedtitle">Upper mantle seismic anisotropy beneath the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> and surrounding region from shear wave splitting analysis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p>2014-07-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span> (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 <span class="hlt">African</span> <span class="hlt">rift</span> <span class="hlt">system</span> and <span class="hlt">rifts</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70021879','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70021879"><span id="translatedtitle">Tectonic and sediment supply control of deep <span class="hlt">rift</span> lake turbidite <span class="hlt">systems</span>: Lake Baikal, Russia</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Nelson, C.H.; Karabanov, E.B.; Colman, Steven M.; Escutia, C.</p> <p>1999-01-01</p> <p>Tectonically influenced half-graben morphology controls the amount and type of sediment supply and consequent type of late Quaternary turbidite <span class="hlt">systems</span> developed in the active <span class="hlt">rift</span> basins of Lake Baikal, Russia. Steep border fault slopes (footwall) on the northwest sides of half-graben basins provide a limited supply of coarser grained clastic material to multiple small fan deltas. These multiple sediment sources in turn laterally feed small (65 km) axially fed elongate mud-rich fans sourced by regional exterior drainage of the Selenga River that supplies large quantities of silt. Basin plain turbidites in the center of the linear basins and axial channels that are controlled by <span class="hlt">rift</span>-parallel faults are fed from, and interfinger with, aprons and fans. The predictability of the turbidite <span class="hlt">systems</span> in Lake Baikal provides the best example yet studied of how tectonics and sediment supply interact to control the development of a wide variety of coeval turbidite <span class="hlt">systems</span> on a single basin floor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014SolED...6.2885D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014SolED...6.2885D"><span id="translatedtitle">Fault evolution in the Potiguar <span class="hlt">rift</span> termination, Equatorial margin of Brazil</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>de Castro, D. L.; Bezerra, F. H. R.</p> <p>2014-10-01</p> <p>The transform shearing between South American and <span class="hlt">African</span> 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 <span class="hlt">rift</span>, which is an aborted NE-trending <span class="hlt">rift</span> arm developed during the breakup of Pangea. The Potiguar <span class="hlt">rift</span> 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 <span class="hlt">rift</span> and indicates that stretching in the southern <span class="hlt">rift</span> 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 <span class="hlt">system</span> 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 <span class="hlt">rift</span> sedimentary units and capped by post-<span class="hlt">rift</span> sedimentary sequences. The evolution of the <span class="hlt">rift</span> termination is consistent with the right-lateral shearing of the Equatorial margin in the Cretaceous and occurs not only at the <span class="hlt">rift</span> termination, but also as isolated structures away from the main <span class="hlt">rift</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V51A4730M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V51A4730M"><span id="translatedtitle">The Timing of Early Magmatism and Extension in the Southern East <span class="hlt">African</span> <span class="hlt">Rift</span>: Tracking Geochemical Source Variability with 40Ar/39Ar Geochronology at the Rungwe Volcanic Province, SW Tanzania</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mesko, G. T.; Class, C.; Maqway, M. D.; Boniface, N.; Manya, S.; Hemming, S. R.</p> <p>2014-12-01</p> <p>The Rungwe Volcanic Province is the southernmost expression of volcanism in the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>. Rungwe magmatism is focused in a transfer zone between two weakly extended <span class="hlt">rift</span> segments, unlike more developed <span class="hlt">rifts</span> where magmatism occurs along segment axes (e.g. mid-ocean ridges). Rungwe was selected as the site of the multinational SEGMeNT project, an integrated geophysical, geochronological and geochemical study to determine the role of magmatism during early stage continental <span class="hlt">rifting</span>. Argon geochronology is underway for an extensive collection of Rungwe volcanic rocks to date the eruptive sequence with emphasis on the oldest events. The age and location of the earliest events remains contested, but is critical to evaluating the relationship between magmatism and extension. Dated samples are further analyzed to model the geochemistry and isotopic signature of each melt's source and define it as lithospheric, asthenospheric, or plume. Given the goals, the geochronology focuses on mafic lavas most likely to preserve the geochemical signature of the mantle source. Groundmass was prepared and analyzed at the LDEO AGES lab. Twelve preliminary dates yield ages from 8.5 to 5.7Ma, consistent with prior results, supporting an eruptive episode concurrent with tectonic activity on the Malawi and Rukwa border faults (Ebinger et al., JGR 1989; 1993). Three additional samples yield ages from 18.51 to 17.6 Ma, consistent with the 18.6 ±1.0 Ma age obtained by Rasskazov et al. (Russ. Geology & Geophys. 2003). This eruptive episode is spatially limited to phonolite domes in the Usangu Basin and a mafic lava flow on the uplifted Mbeya Block. These eruptions predate the current tectonic extensional structure, suggesting magmatism predates extension, or that the two are not highly interdependent. No Rungwe samples dated yet can be the source of the of 26Ma carbonatitic tuffs in the nearby Songwe River Basin sequence (Roberts et al., Nature Geoscience 2012). Isochron ages</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.4428B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.4428B"><span id="translatedtitle">Next-generation Geotectonic Data Analysis: Using pyGPlates to quantify <span class="hlt">Rift</span> Obliquity during Supercontinent Dispersal</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Butterworth, Nathaniel; Brune, Sascha; Williams, Simon; Müller, Dietmar</p> <p>2015-04-01</p> <p>Fragmentation of a supercontinent by <span class="hlt">rifting</span> is an integral part of plate tectonics, yet the dynamics that govern the success or failure of individual <span class="hlt">rift</span> <span class="hlt">systems</span> are still unclear. Recently, analytical and thermo-mechanical modelling has suggested that obliquely activated <span class="hlt">rifts</span> are mechanically favoured over orthogonal <span class="hlt">rift</span> <span class="hlt">systems</span>. Hence, where two <span class="hlt">rift</span> zones compete, the more oblique <span class="hlt">rift</span> proceeds to break-up while the less oblique one stalls and becomes an aulacogen. This implies that the orientation and shape of individual <span class="hlt">rift</span> <span class="hlt">systems</span> 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 <span class="hlt">rift</span> obliquity, extension velocity and their temporal evolution for all small-scale <span class="hlt">rift</span> segments that constituted a major <span class="hlt">rift</span> <span class="hlt">system</span> during the last 200 million years. Boundaries between continental and oceanic crust (COBs) mark the end of <span class="hlt">rifting</span> 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 <span class="hlt">rift</span> <span class="hlt">systems</span>. Analysing the entire length of all <span class="hlt">rift</span> <span class="hlt">systems</span> during the last 200 My, we find a mean obliquity of ~40° (measured as the angle between extension direction and local <span class="hlt">rift</span> trend normal), with a standard deviation of 25°. More than 75% of all <span class="hlt">rift</span> segments exceeded an obliquity of 20° highlighting the fact that oblique <span class="hlt">rifting</span> is the rule, not the exception. More specifically, East and West Gondwana split along the East <span class="hlt">African</span> coast with a mean obliquity of 45°. While <span class="hlt">rifting</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.5869C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.5869C"><span id="translatedtitle">Diachronous Growth of Normal Fault <span class="hlt">Systems</span> in Multiphase <span class="hlt">Rift</span> Basins: Structural Evolution of the East Shetland Basin, Northern North Sea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Claringbould, Johan S.; Bell, Rebecca E.; A-L. Jackson, Christopher; Gawthorpe, Robert L.; Odinsen, Tore</p> <p>2015-04-01</p> <p>Our ability to determine the structural evolution and interaction of fault <span class="hlt">systems</span> (kinematically linked group of faults that are in the km to 10s of km scale) within a <span class="hlt">rift</span> 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 <span class="hlt">systems</span> 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 <span class="hlt">systems</span>, they are often spatially limited and cannot be used examine the interaction of fault <span class="hlt">systems</span> 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 <span class="hlt">rift</span> basin, but lack the spatial and temporal detail. Moreover, these studies typically describe the structural evolution of <span class="hlt">rifts</span> as comprising multiple discrete tectonic stages (i.e. pre-, syn- and post-<span class="hlt">rift</span>). 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 <span class="hlt">system</span> within a <span class="hlt">rift</span> basin. This study focuses on the East Shetland Basin (ESB), a multiphase <span class="hlt">rift</span> 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 <span class="hlt">rift</span> to be the result of selective reactivation of faults associated with the former <span class="hlt">rift</span>. Gradually eastwards thickening intra-<span class="hlt">rift</span> strata (deposited between two <span class="hlt">rift</span> 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 <span class="hlt">rifting</span>; or (ii</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70021976','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70021976"><span id="translatedtitle">Transect across the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> in the Ross Sea, Antarctica</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Trey, H.; Cooper, A. K.; Pellis, G.; Della, Vedova B.; Cochrane, G.; Brancolini, Giuliano; Makris, J.</p> <p>1999-01-01</p> <p>In 1994, the ACRUP (Antarctic Crustal Profile) project recorded a 670-km-long geophysical transect across the southern Ross Sea to study the velocity and density structure of the crust and uppermost mantle of the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>. Ray-trace modeling of P- and S-waves recorded on 47 ocean bottom seismograph (OBS) records, with strong seismic arrivals from airgun shots to distances of up to 120 km, show that crustal velocities and geometries vary significantly along the transect. The three major sedimentary basins (early-<span class="hlt">rift</span> grabens), the Victoria Land Basin, the Central Trough and the Eastern Basin are underlain by highly extended crust and shallow mantle (minimum depth of about 16 km). Beneath the adjacent basement highs, Coulman High and Central High, Moho deepens, and lies at a depth of 21 and 24 km, respectively. Crustal layers have P-wave velocities that range from 5.8 to 7.0 km/s and S-wave velocities from 3.6 to 4.2 km/s. A distinct reflection (PiP) is observed on numerous OBS from an intra-crustal boundary between the upper and lower crust at a depth of about 10 to 12 km. Local zones of high velocities and inferred high densities are observed and modeled in the crust under the axes of the three major sedimentary basins. These zones, which are also marked by positive gravity anomalies, may be places where mafic dikes and sills pervade the crust. We postulate that there has been differential crustal extension across the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, with greatest extension beneath the early-<span class="hlt">rift</span> grabens. The large amount of crustal stretching below the major <span class="hlt">rift</span> basins may reflect the existence of deep crustal suture zones which initiated in an early stage of the <span class="hlt">rifting</span>, defined areas of crustal weakness and thereby enhanced stress focussing followed by intense crustal thinning in these areas. The ACRUP data are consistent with the prior concept that most extension and basin down-faulting occurred in the Ross Sea during late Mesozoic time, with</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996E%26PSL.144..505S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996E%26PSL.144..505S"><span id="translatedtitle">Helium isotope ratios in Ethiopian <span class="hlt">Rift</span> basalts</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scarsi, P.; Craig, H.</p> <p>1996-11-01</p> <p>Helium isotope ratios were measured in olivine and pyroxene phenocrysts from basalts of the Ethiopian <span class="hlt">Rift</span> Valley and Afar Depression between 6° and 15°N and 37° and 43°E. 3He/4He ratios range from 6 to 17 times the atmospheric value (RA = 1.4 × 10-6), that is, from ratios less than typical MORB (depleted mantle) helium (R/RA= 8 ± 1) to ratios similar to high-3He hotspots and to the Yellowstone hotspot (R/RA= 16.5). The high 3He/4He ratios occur all along the Ethiopian <span class="hlt">Rift</span> and well up into the Afar Depression, with a maximum value of 17.0 RA at 8°N in the <span class="hlt">Rift</span> Axis and a high value of 14.2 RA in the central Tat'Ali sector of the Afar Depression. The ratios decrease to MORB-like values near the edge of the Red Sea, and to sub-MORB ratios (5-6 RA) at the northern end of the <span class="hlt">Rift</span> (Zula Peninsula) and at the southern end, at lakes Abaya and Chamo. The Ethiopian <span class="hlt">Rift</span> provides the only continental hotspot terrain in which helium isotope ratios can be compared in detail between volcanic lavas and associated geothermal and volcanic gases, a primary motivation for this work. Comparison with our previously measured ratios in fluids and gases (range 2-15 RA) shows excellent agreement in the areas sampled for both lavas and fluids, and indicates that high-temperature volcanic fluids can be used for establishing helium isotope signatures in such terrains. The high-3He values in both fluids and basalts show that a Primitive Mantle (PM) component is required and that a Lower Mantle High-3He plume is strongly involved as a driving force in the <span class="hlt">rifting</span> process of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5456203','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5456203"><span id="translatedtitle">Keweenaw hot spot: Geophysical evidence for a 1. 1 Ga mantle plume beneath the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hutchinson, D.R. ); White, R.S. ); Cannon, W.F.; Schulz, K.J. )</p> <p>1990-07-10</p> <p>The Proterozoic Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> of North America is remarkably similar to Phanerozoic <span class="hlt">rifted</span> continental margins and flood basalt provinces. Like the younger analogues, the volcanism within this older <span class="hlt">rift</span> can be explained by decompression melting and rapid extrusion of igneous material during lithospheric extension above a broad, asthenospheric, thermal anomaly which the authors call the Keweenaw hot spot. Great Lakes International Multidisciplinary Program on Crustal evolution seismic reflection profiles constrain end-member models of melt thickness and stretching factors, which yield an inferred mantle potential temperature of 1,500-1,570C during <span class="hlt">rifting</span>. Combined gravity modeling and subsidence calculations are consistent with stretching factors that reached 3 or 4 before <span class="hlt">rifting</span> ceased, and much of the lower crust beneath the <span class="hlt">rift</span> consists of relatively high density intruded or underplated synrift igneous material. The isotopic signature of Keweenawan volcanic rocks, presented in a companion paper by Nicholson and Shirey (this issue), is consistent with the model of passive <span class="hlt">rifting</span> above an asthenospheric mantle plume.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1715136M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1715136M"><span id="translatedtitle">Volcanic field elongation, vent distribution and tectonic evolution of continental <span class="hlt">rift</span>: The Main Ethiopian <span class="hlt">Rift</span> example</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mazzarini, Francesco; Le Corvec, Nicolas; Isola, Ilaria; Favalli, Massimiliano</p> <p>2015-04-01</p> <p>Magmatism and faulting operate in continental <span class="hlt">rifts</span> and interact at a variety of scales, however their relationship is complex. The <span class="hlt">African</span> <span class="hlt">rift</span>, being the best example for both active continental <span class="hlt">rifting</span> and magmatism, provides the ideal location to study the interplay between the two mechanisms. The Main Ethiopian <span class="hlt">Rift</span> (MER), which connects the Afar depression in the north with the Turkana depression and Kenya <span class="hlt">Rift</span> to the south, consists of two distinct <span class="hlt">systems</span> 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 <span class="hlt">system</span>. 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 <span class="hlt">rift</span> valley and one (Akaki) on the western <span class="hlt">rift</span> 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 <span class="hlt">rift</span> axis inversely to the angular dispersion. In addition, the results show that none of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tecto..34.2399L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tecto..34.2399L"><span id="translatedtitle">Hierarchical segmentation of the Malawi <span class="hlt">Rift</span>: The influence of inherited lithospheric heterogeneity and kinematics in the evolution of continental <span class="hlt">rifts</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Laó-Dávila, Daniel A.; Al-Salmi, Haifa S.; Abdelsalam, Mohamed G.; Atekwana, Estella A.</p> <p>2015-12-01</p> <p>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 <span class="hlt">rifts</span>. We focused on the Cenozoic Malawi <span class="hlt">Rift</span>, which represents the southern extension of the Western Branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>. This north trending <span class="hlt">rift</span> traverses Precambrian and Paleozoic-Mesozoic structures of different orientations. We found that the <span class="hlt">rift</span> can be hierarchically divided into first-order and second-order segments. In the first-order segmentation, we divided the <span class="hlt">rift</span> into Northern, Central, and Southern sections. In its Northern Section, the <span class="hlt">rift</span> 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 <span class="hlt">rift</span> extent. We propose that the lack of inherited lithospheric heterogeneity favoring extension localization resulted in the development of the <span class="hlt">rift</span> 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 <span class="hlt">Rift</span> during its opening resulting from extension.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Tecto..33..485P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Tecto..33..485P"><span id="translatedtitle">Evolution, distribution, and characteristics of <span class="hlt">rifting</span> in southern Ethiopia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Philippon, Melody; Corti, Giacomo; Sani, Federico; Bonini, Marco; Balestrieri, Maria-Laura; Molin, Paola; Willingshofer, Ernst; Sokoutis, Dimitrios; Cloetingh, Sierd</p> <p>2014-04-01</p> <p>Southern Ethiopia is a key region to understand the evolution of the East <span class="hlt">African</span> <span class="hlt">rift</span> <span class="hlt">system</span>, since it is the area of interaction between the main Ethiopian <span class="hlt">rift</span> (MER) and the Kenyan <span class="hlt">rift</span>. However, geological data constraining <span class="hlt">rift</span> evolution in this remote area are still relatively sparse. In this study the timing, distribution, and style of <span class="hlt">rifting</span> in southern Ethiopia are constrained by new structural, geochronological, and geomorphological data. The border faults in the area are roughly parallel to preexisting basement fabrics and are progressively more oblique with respect to the regional Nubia-Somalia motion proceeding southward. Kinematic indicators along these faults are mainly dip slip, pointing to a progressive rotation of the computed direction of extension toward the south. Radiocarbon data indicate post 30 ka faulting at both western and eastern margins of the MER with limited axial deformation. Similarly, geomorphological data suggest recent fault activity along the western margins of the basins composing the Gofa Province and in the Chew Bahir basin. This supports that interaction between the MER and the Kenyan <span class="hlt">rift</span> in southern Ethiopia occurs in a 200 km wide zone of ongoing deformation. Fault-related exhumation at ~10-12 Ma in the Gofa Province, as constrained by new apatite fission track data, occurred later than the ~20 Ma basement exhumation of the Chew Bahir basin, thus pointing to a northward propagation of the Kenyan <span class="hlt">rift</span>-related extension in the area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25788592','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25788592"><span id="translatedtitle">Enemies and turncoats: bovine tuberculosis exposes pathogenic potential of <span class="hlt">Rift</span> Valley fever virus in a common host, <span class="hlt">African</span> buffalo (Syncerus caffer).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Beechler, B R; Manore, C A; Reininghaus, B; O'Neal, D; Gorsich, E E; Ezenwa, V O; Jolles, A E</p> <p>2015-04-22</p> <p>The ubiquity and importance of parasite co-infections in populations of free-living animals is beginning to be recognized, but few studies have demonstrated differential fitness effects of single infection versus co-infection in free-living populations. We investigated interactions between the emerging bacterial disease bovine tuberculosis (BTB) and the previously existing viral disease <span class="hlt">Rift</span> Valley fever (RVF) in a competent reservoir host, <span class="hlt">African</span> buffalo, combining data from a natural outbreak of RVF in captive buffalo at a buffalo breeding facility in 2008 with data collected from a neighbouring free-living herd of <span class="hlt">African</span> buffalo in Kruger National Park. RVF infection was twice as likely in individual BTB+ buffalo as in BTB- buffalo, which, according to a mathematical model, may increase RVF outbreak size at the population level. In addition, co-infection was associated with a far higher rate of fetal abortion than other infection states. Immune interactions between BTB and RVF may underlie both of these interactions, since animals with BTB had decreased innate immunity and increased pro-inflammatory immune responses. This study is one of the first to demonstrate how the consequences of emerging infections extend beyond direct effects on host health, potentially altering the dynamics and fitness effects of infectious diseases that had previously existed in the ecosystem on free-ranging wildlife populations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/262596','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/262596"><span id="translatedtitle">Clinical, virological and serological response of the West <span class="hlt">African</span> dwarf sheep to experimental infection with different strains of <span class="hlt">Rift</span> Valley fever virus.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tomori, O</p> <p>1979-03-01</p> <p>West <span class="hlt">African</span> dwarf sheep were inoculated with three different strains of <span class="hlt">Rift</span> Valley fever virus (RVFV). Using infective mouse serum as the source of virus classical RVFV disease characterised by sudden onset, a sharp but transient febrile response, viraemia, abortions and the development of specific RVFV antibodies in surviving animals was observed. The severity of clinical response was, however, dependent on the strain of virus used, with animals inoculated with Smithburn's neuroadapted strain showing a milder response than those inoculated with either the Nigerian or Lunyo strain. The inoculation of sheep with RVFV infective mouse brain material of the three different strains resulted in a mild febrile response with low level viraemia. Immune sera from sheep inoculated with both the Nigerian and Smithburn's neurotropic strains did not neutralise the Lunyo virus strain in a mouse intracerebral neutralisation test; the reverse, however, was not the case. The findings indicate that the West <span class="hlt">African</span> dwarf sheep is highly susceptible to RVFV infection and that previous reports of only a mild clinical response following inoculation with the Nigerian strain were due to infective mouse brain rather than infective mouse serum.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T43C2693M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T43C2693M"><span id="translatedtitle">Nature of the Mantle Sources and Bearing on Tectonic Evolution in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mukasa, S. B.; Rilling-Hall, S.; Marcano, M. C.; Wilson, T. J.; Lawver, L. A.; LeMasurier, W. E.</p> <p>2012-12-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span> (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 <span class="hlt">Rift</span>. We have attempted to answer the questions of whether magmatism is due to a hot mantle or wet mantle, and whether <span class="hlt">rifting</span> 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 <span class="hlt">Rift</span> 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 <span class="hlt">systems</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70034427','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70034427"><span id="translatedtitle">Low lower crustal velocity across Ethiopia: Is the Main Ethiopian <span class="hlt">Rift</span> a narrow <span class="hlt">rift</span> in a hot craton?</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Keranen, K.M.; Klemperer, S.L.; Julia, J.; Lawrence, J. F.; Nyblade, A.A.</p> <p>2009-01-01</p> <p>[1] The Main Ethiopian <span class="hlt">Rift</span> (MER) is a classic narrow <span class="hlt">rift</span> that developed in hot, weak lithosphere, not in the initially cold, thick, and strong lithosphere that would be predicted by common models of <span class="hlt">rift</span> 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 <span class="hlt">rift</span> and the adjacent Ethiopian Plateau hundreds of kilometers from the <span class="hlt">rift</span> 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 <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> 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 <span class="hlt">rift</span> mode, in which the brittle upper crust has developed as a narrow <span class="hlt">rift</span> 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 <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> to the south (in cold, strong lithosphere) and the MER to the north (in hot, weak lithosphere) as narrow <span class="hlt">rifts</span>, despite their vastly different initial thermal states and depth-integrated lithospheric strength, indicates that common models of <span class="hlt">rift</span> mode formation that focus only on temperature, thickness, and vertical strength profiles do not apply to these classic continental <span class="hlt">rifts</span>. Instead, inherited structure and associated lithospheric weaknesses are</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21507967','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21507967"><span id="translatedtitle">Genetic evidence for <span class="hlt">Rift</span> Valley fever outbreaks in Madagascar resulting from virus introductions from the East <span class="hlt">African</span> mainland rather than enzootic maintenance.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Carroll, Serena A; Reynes, Jean-Marc; Khristova, Marina L; Andriamandimby, Soa Fy; Rollin, Pierre E; Nichol, Stuart T</p> <p>2011-07-01</p> <p><span class="hlt">Rift</span> Valley fever virus (RVFV), a mosquito-borne phlebovirus, has been detected in Madagascar since 1979, with occasional outbreaks. In 2008 to 2009, a large RVFV outbreak was detected in Malagasy livestock and humans during two successive rainy seasons. To determine whether cases were due to enzootic maintenance of the virus within Madagascar or to importation from the East <span class="hlt">African</span> mainland, nine RVFV whole genomic sequences were generated for viruses from the 1991 and 2008 Malagasy outbreaks. Bayesian coalescent analyses of available whole S, M, and L segment sequences were used to estimate the time to the most recent common ancestor for the RVFVs. The 1979 Madagascar isolate shared a common ancestor with strains on the mainland around 1972. The 1991 Madagascar isolates were in a clade distinct from that of the 1979 isolate and shared a common ancestor around 1987. Finally, the 2008 Madagascar viruses were embedded within a large clade of RVFVs from the 2006-2007 outbreak in East Africa and shared a common ancestor around 2003 to 2004. These results suggest that the most recent Madagascar outbreak was caused by a virus likely arriving in the country some time between 2003 and 2008 and that this outbreak may be an extension of the 2006-2007 East <span class="hlt">African</span> outbreak. Clustering of the Malagasy sequences into subclades indicates that the viruses have continued to evolve during their short-term circulation within the country. These data are consistent with the notion that RVFV outbreaks in Madagascar result not from emergence from enzootic cycles within the country but from recurrent virus introductions from the East <span class="hlt">African</span> mainland.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19810056997&hterms=Continental+Drift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DContinental%2BDrift','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19810056997&hterms=Continental+Drift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DContinental%2BDrift"><span id="translatedtitle">Continental <span class="hlt">rifting</span> and the origin of Beta Regio, Venus</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mcgill, G. E.; Steenstrup, S. J.; Barton, C.; Ford, P. G.</p> <p>1981-01-01</p> <p>Topographic maps based on Pioneer Venus altimetry suggest that Beta Regio, an elevated feature centered at 27 deg N, 282 deg E, is analogous to domes associated with continental <span class="hlt">rift</span> <span class="hlt">systems</span> on earth. This interpretation is consistent with the commonly quoted analogy between the East <span class="hlt">African</span> <span class="hlt">rift</span> <span class="hlt">system</span> and the topography of the region from Beta Regio southward to Phoebe Regio. If Beta Regio is a dome, major structural uplift of the crust of Venus is implied, suggesting a more dynamic upper mantle than would be the case if Beta Regio were simply a large volcanic construct.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1814331C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1814331C"><span id="translatedtitle">Orthorhombic faults <span class="hlt">system</span> at the onset of the Late Mesozoic-Cenozoic Barents Sea <span class="hlt">rifting</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Collanega, Luca; Breda, Anna; Massironi, Matteo</p> <p>2016-04-01</p> <p>The structures of the Late Mesozoic/Cenozoic Barents Sea <span class="hlt">rifting</span> 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 <span class="hlt">systems</span> have been identified: an orthorhombic fault <span class="hlt">system</span> consisting of two fault sets trending almost perpendicularly one to the other (WNW-ESE and NNE-SSW) and a graben/half-graben <span class="hlt">system</span>, elongated approximately N-S in the central part of the study area. While the graben/half-graben <span class="hlt">system</span> 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 <span class="hlt">system</span>. 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 <span class="hlt">system</span> 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 <span class="hlt">rifting</span>. In particular, the orthorhombic <span class="hlt">system</span> has affected only the Late Mesozoic-Cenozoic interval of the succession and it was the main active <span class="hlt">system</span> during the initial phase of the <span class="hlt">rifting</span>. On the other hand, the graben/half-graben <span class="hlt">system</span> has affected the whole sedimentary succession, with an increasing activity during the development of the <span class="hlt">rifting</span>. It has</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1614484S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1614484S"><span id="translatedtitle">Mode of <span class="hlt">rifting</span> in magmatic-rich setting: Tectono-magmatic evolution of the Central Afar <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stab, Martin; Bellahsen, Nicolas; Pik, Raphaël; Leroy, Sylvie; Ayalew, Dereje</p> <p>2014-05-01</p> <p>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-<span class="hlt">rift</span> 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 <span class="hlt">rift</span> that is probably close enough to breakup to present some characteristics of VPM. Moreover, the structures related to <span class="hlt">rifting</span> 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 <span class="hlt">rift</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFM.U13A..05S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFM.U13A..05S"><span id="translatedtitle">Understanding Chad Basin Evolution Since Miocene: Climate and Vegetation Simulations, Roles of Orbital Parameters and East <span class="hlt">African</span> <span class="hlt">Rift</span>.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sepulchre, P.; Ramstein, G.; Krinner, G.; Schuster, M.; Fluteau, F.; Kageyama, M.; Tiercelin, J.; Vignaud, P.; Brunet, M.</p> <p>2004-12-01</p> <p>Since the discovery of the earliest hominid known, Chad basin is a major place to study paleoclimates and hominid evolution. This discovery implies to re-evaluate the "East Side Story" paradigm for early hominids. To achieve this goal, we have performed numerical simulations to quantify the climatic and vegetation response of the <span class="hlt">Rift</span> Uplift. We used a zoomed (144 X 108) AGCM (LMDz from IPSL). On the one hand, offline continental biosphere model (ORCHIDEE) has been used to simulate the vegetation response over western and eastern parts of the <span class="hlt">rift</span>. On the other hand, since geomorphologic evidences have shown that from Upper Miocene to mid-Holocene Lake Chad had known several level oscillations leading to a huge lake known as Mega Lake Chad (MLC), we also ran atmospheric simulations to demonstrate, with boundary conditions at 6 000 BP, that orbital forcing allowed the existence of a MLC. Volume and surface of the lake have been calculated using an adapted lake model. These simulations have shown that the ITCZ shift induced by the mid-Holocene orbital parameters drives the existence of a MegaChad. Our model result having been tested successfully for the last occurrence of the MLC, we will apply it to Upper Miocene accounting for topographic changes, in order to reconstruct as accurately as possible the first hominids environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.4444B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.4444B"><span id="translatedtitle">Fault Orientations at Obliquely <span class="hlt">Rifted</span> Margins: Where? When? Why?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brune, Sascha</p> <p>2015-04-01</p> <p>Present-day knowledge of <span class="hlt">rifted</span> 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 <span class="hlt">rift</span> trend is often invalid. In fact, worldwide more than 75% of all <span class="hlt">rifted</span> margin segments have been formed under significant obliquity exceeding 20° (angle measured between extension direction and <span class="hlt">rift</span> trend normal): During formation of the Atlantic Ocean, oblique <span class="hlt">rifting</span> 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 <span class="hlt">rift</span> history of the North East Atlantic. Outside the Atlantic Ocean, oblique <span class="hlt">rifting</span> 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 <span class="hlt">African</span> <span class="hlt">Rift</span>. Despite its significance, the degree to which oblique lithospheric extension affects first-order <span class="hlt">rift</span> 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 <span class="hlt">rift</span> model to oblique extensional settings. The presented forward experiments cover the whole spectrum of oblique extension (i.e. <span class="hlt">rift</span>-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 <span class="hlt">rift</span> stages and for high obliquity. Even though the model</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007JAESc..29..722Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007JAESc..29..722Z"><span id="translatedtitle">Structure and geochronology of the southern Xainza-Dinggye <span class="hlt">rift</span> and its relationship to the south Tibetan detachment <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Jinjiang; Guo, Lei</p> <p>2007-03-01</p> <p>The Xainza-Dinggye <span class="hlt">rift</span> is one of several north-south trending <span class="hlt">rifts</span> in central and southern Tibet created by Cenozoic east-west extension during Indo-Asian convergence. The southern part of the <span class="hlt">rift</span> cuts through the Tethyan and High Himalayas. In the Tethyan Himalaya, this <span class="hlt">rift</span> consists of an early domal structure and a late normal fault developed during the progressive deformation. The dome is cored by leucogranitic plutons that intruded during extension. Muscovite 40Ar/ 39Ar ages of the mylonitic leucogranite indicate that extension in the Tethyan Himalaya began at ˜8 Ma or before. In the High Himalaya, the <span class="hlt">rift</span> is controlled by a normal fault dipping to the southeast. This fault has a structural constitution similar to a detachment fault. Its lower block is made up of mylonitic High Himalayan gneiss, intruded by early mylonitic leucogranite sills and late less-deformed biotite-bearing leucogranite dikes. Mica 40Ar/ 39Ar ages of these leucogranites and the retrograded metamorphosed gneiss of the lower block range from ˜13 to ˜10 Ma. In the study area, the south Tibetan detachment <span class="hlt">system</span> (STDS) is a ductile shear zone composed of mylonitic leucogranite that is intruded by less-deformed leucogranite and overlain by low grade metamorphic rocks. Mica 40Ar/ 39Ar ages of leucogranites in the shear zone and schist from the detachment hanging wall indicate a protracted deformation history of the STDS from ˜19 to ˜13 Ma. The Xainza-Dinggye <span class="hlt">rift</span> is younger than the STDS because it offsets the STDS; this north-south trending <span class="hlt">rift</span> belongs to a different tectonic <span class="hlt">system</span> from the east-west striking STDS, and may be caused by geological process related to India-Asia convergence. This temporal and spatial relationship of the STDS to the <span class="hlt">rift</span> may indicate an important change in tectonic regime at ˜13 Ma in the building of the plateau.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25686252','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25686252"><span id="translatedtitle">Seroprevalence of <span class="hlt">Rift</span> Valley fever and lumpy skin disease in <span class="hlt">African</span> buffalo (Syncerus caffer) in the Kruger National Park and Hluhluwe-iMfolozi Park, South Africa.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fagbo, Shamsudeen; Coetzer, Jacobus A W; Venter, Estelle H</p> <p>2014-10-16</p> <p><span class="hlt">Rift</span> Valley fever and lumpy skin disease are transboundary viral diseases endemic in Africa and some parts of the Middle East, but with increasing potential for global emergence. Wild ruminants, such as the <span class="hlt">African</span> buffalo (Syncerus caffer), are thought to play a role in the epidemiology of these diseases. This study sought to expand the understanding of the role of buffalo in the maintenance of <span class="hlt">Rift</span> Valley fever virus (RVFV) and lumpy skin disease virus (LSDV) by determining seroprevalence to these viruses during an inter-epidemic period. Buffaloes from the Kruger National Park (n = 138) and Hluhluwe-iMfolozi Park (n = 110) in South Africa were sampled and tested for immunoglobulin G (IgG) and neutralising antibodies against LSDV and RVFV using an indirect enzyme-linked immunosorbent assay (I-ELISA) and the serum neutralisation test (SNT). The I-ELISA for LSDV and RVFV detected IgG antibodies in 70 of 248 (28.2%) and 15 of 248 (6.1%) buffaloes, respectively. Using the SNT, LSDV and RVFV neutralising antibodies were found in 5 of 66 (7.6%) and 12 of 57 (21.1%), respectively, of samples tested. The RVFV I-ELISA and SNT results correlated well with previously reported results. Of the 12 SNT RVFV-positive sera, three (25.0%) had very high SNT titres of 1:640. Neutralising antibody titres of more than 1:80 were found in 80.0% of the positive sera tested. The LSDV SNT results did not correlate with results obtained by the I-ELISA and neutralising antibody titres detected were low, with the highest (1:20) recorded in only two buffaloes, whilst 11 buffaloes (4.4%) had evidence of co-infection with both viruses. Results obtained in this study complement other reports suggesting a role for buffaloes in the epidemiology of these diseases during inter-epidemic periods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFM.T11A1232P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFM.T11A1232P"><span id="translatedtitle">Neogene-Quaternary Volcanic Alignments in the Transantarctic Mountains and West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> of Southern Victoria Land, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Paulsen, T. S.; Wilson, T. J.</p> <p>2004-12-01</p> <p>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 <span class="hlt">rift</span>-flank uplift to offshore localities within the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>. We are mapping volcanic vent patterns in the province to detect alignments indicative of stress/strain patterns during <span class="hlt">rift</span> 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 <span class="hlt">rift</span> margin, and results obtained so far within the <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span>, 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 <span class="hlt">rift</span> flank and the <span class="hlt">rift</span> <span class="hlt">system</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T51G3008G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T51G3008G"><span id="translatedtitle">Seismological Investigations of Crustal and Mantle Structures Beneath the Incipient Okavango <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gao, S. S.; Yu, Y.; Liu, K. H.; Reed, C. A.; Moidaki, M.; Mickus, K. L.; Atekwana, E. A.</p> <p>2015-12-01</p> <p><span class="hlt">Rifting</span> plays a significant role in the evolution of sedimentary basins. However, our current understandings on <span class="hlt">rifting</span> mechanisms are mostly based on studies of mature <span class="hlt">rifts</span>. Here we report results from the first teleseismic investigations of the incipient Okavango <span class="hlt">rift</span> zone (ORZ), which is located at the southwestern terminal of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> in northern Botswana. Data used in the study were recorded by the 17 broadband seismic stations deployed along a NW-SE profile traversing the ORZ with a recording duration of 2 years starting in the summer of 2012. Receiver function and shear wave splitting techniques have been employed to explore upper mantle thermal anomalies and anisotropy. The resulting dominantly absolute plate motion-parallel fast polarization orientations and normal mantle transition zone thickness ruled out the possible existence of one or more mantle plumes in the upper mantle or mantle transition zone beneath the ORZ. The Moho beneath the Okavango <span class="hlt">rift</span> zone is uplifted by 4-5 km and is symmetric with regard to the <span class="hlt">rift</span> axis, favoring a pure shear model of early-stage continental extension. The observations favor a passive model for <span class="hlt">rift</span> initiation in which <span class="hlt">rifts</span> develop inside ancient orogenic zones as the result of relative movements between Archean cratonic blocks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUSM.T43B..07A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUSM.T43B..07A"><span id="translatedtitle">Structural Evolution of the Incipient Okavango <span class="hlt">Rift</span> Zone, NW Botswana</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Atekwana, E. A.; Kinabo, B. D.; Modisi, M. P.; Hogan, J. P.; Wheaton, D. D.</p> <p>2005-05-01</p> <p>Studies of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) and other continental <span class="hlt">rifts</span> have significantly improved our understanding of <span class="hlt">rifting</span> processes; however, we particularly lack studies of the embryonic stages of <span class="hlt">rift</span> creation. The Okavango <span class="hlt">Rift</span> Zone (ORZ), NW Botswana is one of few places worldwide where one can study the early stages of continental extension prior to the accumulation of significant amounts of sediments, volcanism, and multiphase deformation that obscure the investigation of these early time processes in more evolved continental <span class="hlt">rift</span> zones. In this study, gravity and aeromagnetic data have been used to examine the initiation and development of the nascent ORZ. The Okavango basin in NW Botswana is located at the southern tip of the southwestern branch of the EARS. The <span class="hlt">rift</span> is hosted within the Proterozoic fold and thrust belt of the Ghanzi-Chobe formation. Our objectives include (1) assessing the role of pre-existing structures on the development of <span class="hlt">rift</span> faults and basin architecture, (2) Examining fault linkage patterns and boarder fault development, and (3) determining the shallow subsurface basin geometry. Aeromagnetic data from the ORZ suggest two main structural trends: 1) northeast-southwest (030- 070o) and 2) northwest - southeast (290 - 320o). The 030- 070o structures occur within the <span class="hlt">rift</span> zone and throughout the surrounding basement. They form the main bounding fault <span class="hlt">system</span> of this incipient <span class="hlt">rift</span>. The NE - SW orientations of <span class="hlt">rift</span> faults mirror the fold axes and foliation of the basement rocks, suggesting that the basement fabric played an important role in localizing the development of faults within the stress regime present during the initiation of this <span class="hlt">rift</span>. Additionally, the greatest throw (~400- ~700 m) occurs along the Kunyere (NW dipping) and Tsau faults (SE dipping), defining a full graben as observed on gravity models. This differs from the half-graben model typical of most continental <span class="hlt">rift</span> zones. Thus, it appears the basin geometry was</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T13A2512A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T13A2512A"><span id="translatedtitle">Melt generation in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>: the volatile legacy of Gondwana subduction?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aviado, K.; Rilling-Hall, S.; Mukasa, S. B.; Bryce, J. G.; Cabato, J.</p> <p>2013-12-01</p> <p>The West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (WARS) represents one of the largest extensional alkali volcanic provinces on Earth, yet the mechanisms responsible for driving <span class="hlt">rift</span>-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 <span class="hlt">rifting</span> 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 <span class="hlt">Rift</span>, 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Geote..50..223S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Geote..50..223S"><span id="translatedtitle">Spatial instability of the <span class="hlt">rift</span> in the St. Paul multifault transform fracture <span class="hlt">system</span>, Atlantic Ocean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sokolov, S. Yu.; Zaraiskaya, Yu. A.; Mazarovich, A. O.; Efimov, V. N.; Sokolov, N. S.</p> <p>2016-05-01</p> <p>The structure of the acoustic basement of the eastern part of the St. Paul multifault transform fracture <span class="hlt">system</span> hosts <span class="hlt">rift</span> 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 <span class="hlt">rift</span> segments, which jumped according to redistribution of stresses. The St. Paul <span class="hlt">system</span> is characterized by straightening of the transform transition between two remote segments of the Mid-Atlantic Ridge (MAR). The eastern part of the <span class="hlt">system</span> 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 <span class="hlt">system</span> continue to the north for 120 km from the active segments of the St. Paul <span class="hlt">system</span>. Currently seismically active segments of the spreading <span class="hlt">system</span> 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 <span class="hlt">system</span> is a specific type of oceanic strike-slip faults.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.2814A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.2814A"><span id="translatedtitle">Differentiating climatic- and tectonic-controlled lake margin in <span class="hlt">rift</span> <span class="hlt">system</span>: example of the Plio-Quaternary Nachukui Formation, Turkana depression, Kenya</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Alexis, Nutz; Mathieu, Schuster; Abdoulaye, Balde; Jean-Loup, Rubino</p> <p>2016-04-01</p> <p>The Turkana Depression is part of the eastern branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>. This area consists of several Oligo-Pliocene north-south oriented half-grabens that connect the Ethiopian and Kenyan <span class="hlt">rift</span> valleys. Exposed on the west side of the Lake Turkana, the Nachukui Formation represents a Plio-Quaternary syn-<span class="hlt">rift</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007QSRv...26.1771H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007QSRv...26.1771H"><span id="translatedtitle">Anatomy of a river drainage reversal in the Neogene Kivu Nile <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Holzförster, F.; Schmidt, U.</p> <p>2007-07-01</p> <p>The Neogene geological history of East Africa is characterised by the doming and extension in the course of development of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> with its eastern and western branches. In the centre of the Western <span class="hlt">Rift</span> Rise Rwanda is situated on Proterozoic basement rocks exposed in the strongly uplifted eastern <span class="hlt">rift</span> shoulder of the Kivu-Nile <span class="hlt">Rift</span> segment, where clastic sedimentation is largely restricted to the <span class="hlt">rift</span> axis itself. A small, volcanically and tectonically controlled depository in northwestern Rwanda preserved the only Neogene sediments known from the extremely uplifted <span class="hlt">rift</span> 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 <span class="hlt">rift</span>-parallel upper Nile drainage <span class="hlt">system</span> became diverted to the East in order to enter the Nile <span class="hlt">system</span> 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 <span class="hlt">system</span> of the Kivu-Nile <span class="hlt">Rift</span> segment.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.6390D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.6390D"><span id="translatedtitle">Initiation and development of the Kivu <span class="hlt">rift</span> segment in Central Africa by reactivating un-favorably oriented structural weaknesses</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Delvaux, Damien; Smets, Benoît</p> <p>2015-04-01</p> <p>The Kivu <span class="hlt">rift</span> region forms the central segment of the western branch of the East <span class="hlt">African</span> <span class="hlt">rift</span> <span class="hlt">system</span>, between the northern termination of the Tanganyika <span class="hlt">rift</span> and the southern extension of the Edward-George <span class="hlt">rift</span>. 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 <span class="hlt">rift</span> basin and the Northern termination of the Tanganyika <span class="hlt">rift</span> 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 <span class="hlt">rift</span> basin and the N-S northern half of the Tanganyika <span class="hlt">rift</span> basin initiated as separated, partly overlapping and differently oriented basins. The orientation and development of the Kivu <span class="hlt">rift</span> basin was controlled by an inferred Mid-Proterozoic crustal shear zone and a Pan-<span class="hlt">African</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">Rift</span>, Africa. Tectonics, 8, 117-133</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T11C4571C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T11C4571C"><span id="translatedtitle">Tectonoestratigraphic and Thermal Models of the Tiburon and Wagner Basins, northern Gulf of California <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Contreras, J.; Ramirez Zerpa, N. A.; Negrete-Aranda, R.</p> <p>2014-12-01</p> <p>The northern Gulf of California <span class="hlt">Rift</span> <span class="hlt">System</span> 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 <span class="hlt">system</span>, 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 <span class="hlt">rift</span> 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 <span class="hlt">Rift</span> <span class="hlt">System</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5872335','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5872335"><span id="translatedtitle">Age relationships for magmatic units of Mid-Continent <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Van Schmus, W.R.</p> <p>1989-03-01</p> <p>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 <span class="hlt">rift</span> magmatism there may be distinctly younger than that in the Lake Superior region, and that development of the <span class="hlt">rift</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28210894','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28210894"><span id="translatedtitle">Expansion of sugarcane monoculture: associated impacts and management measures in the semi-arid East <span class="hlt">African</span> <span class="hlt">Rift</span> Valley, Ethiopia.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Beza, Solomon A; Assen, Mohammed A</p> <p>2017-03-01</p> <p>The study examined the expansion of sugarcane monoculture over the period 1957-2010 and its implications for land degradation and land management measures in the semi-arid northern Main Ethiopian <span class="hlt">Rift</span> Valley. It used multi-scale and multi-temporal imageries aided by qualitative surveying to investigate the dynamics of land use and cover changes. The study applied both a pixel-based supervised classification and feature extraction methods at subclass levels and merged them into major compatible and comparable land use and cover groups. The results indicated a substantial transformation in the landscape over 53 years (1957-2010), which is attributed to expansion of sugarcane plantation, saline lake water, and smallholder farmland and settlements. The land use and cover changes culminated in reduction of native vegetation cover and biodiversity loss, encroachment of non-native species, and occurrence of soil salinity. Major causes that justify the changes include (1) macro-economic changes and policy shifts towards agricultural development, (2) change in underground hydrology, (3) population growth, and (4) sedentarization of the traditional pastoral community. Proper measures should aim at addressing the trade-off between economic development and environmental sustainability. Moreover, management opportunities should base on the understanding of socioeconomic and biophysical settings and balance the sustenance of the local people and ecological function of the area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70015574','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70015574"><span id="translatedtitle">Mineralization potential along the trend of the Keweenawan- age Central North American <span class="hlt">Rift</span> <span class="hlt">System</span> in Iowa, Nebraska, and Kansas</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Berendsen, P.</p> <p>1989-01-01</p> <p>The tectonic and sedimentary environment of the Central North American <span class="hlt">Rift</span> <span class="hlt">System</span> (CNARS) provides an excellent setting for major mineral deposits. Major north-northeast-trending high-angle normal or reverse faults and northwest-trending transcurrent fault <span class="hlt">systems</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> as a whole remains largely unexplored.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T13F..03R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T13F..03R"><span id="translatedtitle">Feedback between magmatic, tectonic and glacial processes in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rocchi, S.</p> <p>2010-12-01</p> <p>The western Ross Sea coast of the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> (WARS) is littered with mid-Eocene to Present alkaline plutons, dike swarms and volcanoes. The mafic igneous products have OIB-HIMU signature, similar to basalts associated with long-lived hotspot tracks, pointing to the possible occurrence of one or more mantle plumes active during the Cenozoic or the Mesozoic. However, He and Pb isotope data suggest alternative views, with a rather shallow magma source not involving deep, undegassed mantle, and affected by a metasomatic episode as young as hundred(s) of million years, an order of magnitude less than typically invoked for mantle plume sources. A shallow <span class="hlt">rift</span>-driving mechanism is supported also by the geometric relationships between magma emplacement and regional <span class="hlt">rift</span>-related fault <span class="hlt">systems</span>. Further, these faults were active coeval with magma emplacement, as demonstrated by the age of a fault-generated pseudotachylyte (34 Ma) and by apatite fission track thermochronology. In a wider perspective, these faults are in striking continuity with Southern Ocean fracture zones, and mantle tomography depicts a low-velocity anomaly of linear (not circular) shape overlapping the belt of these fracture zones. The lack of firm evidence for plume activity is thus at odds with a clear link between large-scale tectonic features and magma emplacement, supporting this three-stage model. (1) The WARS Late Cretaceous amagmatic extension led to metasomatism of the sublithospheric mantle, later rheologically incorporated into the lithosphere. (2) During Eocene-Oligocene times, craton-ward mantle flow under the thinned WARS heated up the mantle at the edge of the Antarctic lithosphere. In mid Eocene, the differential velocity across Southern Ocean fracture zones reactivated Paleozoic translithospheric discontinuities in northern Victoria Land as intraplate dextral strike-slip fault <span class="hlt">systems</span>, promoting local mantle decompression melting and rise of magmas in plutons and dike</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4672236','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4672236"><span id="translatedtitle">Serological Evidence of <span class="hlt">Rift</span> Valley Fever Virus Circulation in Domestic Cattle and <span class="hlt">African</span> Buffalo in Northern Botswana (2010–2011)</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Jori, Ferran; Alexander, Kathleen A.; Mokopasetso, Mokganedi; Munstermann, Suzanne; Moagabo, Keabetswe; Paweska, Janusz T.</p> <p>2015-01-01</p> <p><span class="hlt">Rift</span> Valley fever (RVF) is endemic in many countries in Sub-Saharan Africa and is responsible for severe outbreaks in livestock characterized by a sudden onset of abortions and high neonatal mortality. During the last decade, several outbreaks have occurred in Southern Africa, with a very limited number of cases reported in Botswana. To date, published information on the occurrence of RVF in wild and domestic animals from Botswana is very scarce and outdated, despite being critical to national and regional disease control. To address this gap, 863 cattle and 150 buffalo sampled at the interface between livestock areas and the Chobe National Park (CNP) and the Okavango Delta (OD) were screened for the presence of RVF virus (RVFV) neutralizing antibodies. Antibodies were detected in 5.7% (n = 863), 95% confidence intervals (CI) (4.3–7.5%) of cattle and 12.7% (n = 150), 95% CI (7.8–19.5%) of buffalo samples. The overall prevalence was significantly higher (p = 0.0016) for buffalo [12.7%] than for cattle [5.7%]. Equally, when comparing RVF seroprevalence in both wildlife areas for all pooled bovid species, it was significantly higher in CNP than in OD (9.5 vs. 4%, respectively; p = 0.0004). Our data provide the first evidence of wide circulation of RVFV in both buffalo and cattle populations in Northern Botswana and highlight the need for further epidemiological and ecological investigations on RVF at the wildlife–livestock–human interface in this region. PMID:26664990</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5993676','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5993676"><span id="translatedtitle">Stratigraphy of Mid-Continent <span class="hlt">rift</span> <span class="hlt">system</span> in Kansas as revealed by recent exploration wells</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Newell, K.D.; Berendsen, P.; Watney, W.L.; Doveton, J.H.; Steeples, D.</p> <p>1989-03-01</p> <p>The Texaco 1 Poersch well in Kansas (11,300 ft TD) was the first significant exploration test of the Mid-Continent <span class="hlt">Rift</span> <span class="hlt">System</span> (MRS). An upper succession of <span class="hlt">rift</span>-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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.6498G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.6498G"><span id="translatedtitle">Post-<span class="hlt">rift</span> uplift, paleorelief and sedimentary fluxes: the case example of the <span class="hlt">African</span> margin of the South Atlantic</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guillocheau, F.; Dauteuil, O.</p> <p>2012-04-01</p> <p>Several attempts have been made to identify different paleosurfaces since the classical works of Lester King (1942, 1949) at the scale of Africa. Thermochronologists and river geomorphologists criticized this approach. This criticism mainly concerned the age of the surfaces, that were (1) poorly constraints and (2) a king of catechism on which all studies must refer. Nevertheless, those planation surfaces exist and are key features of the present-day morphology of Africa. In details, real planation surfaces are (1) no more than two or three and (2) can be deformed and then merged together. Those surfaces are incised by large smooth valleys, called pediments or glacis (with some semantic differences between English and French-speaking geomorphologists). Those pediments formed a pre-network of rivers, later re-incised by the present-day incised narrow valleys. Those different morphological structures can be dated using (1) their merge with sedimentary basins, (2) their relationship with the different types of dated weathering periods and (3) their relationships with volcanism. They also can be used as a proxy of the deformation based on the differences of elevation of the planations surfaces or on the shape of the pediments. From the Orange River to the Cameroon Volcanic Line, including the Congo Cuvette, two planations surfaces were identified (the Bauxitic or <span class="hlt">African</span> surface, the intermediate surface), at least two generations of pediment valleys and the present-day incised valley network. The <span class="hlt">African</span> surface is of Late Paleocene to Middle Eocene age with a climax during this last period and two major periods of uplift can be identified and mapped (1) Late Eocene-Early Oligocene and (2) Lower Miocene. Most of the relief is fossil since that period, excepted in the Angola Mountains were deformations are active during Plio-Pleistocene times. Those uplifts of smoother, most of the time weathered, relief than today, had important consequences on the petrology and the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985Tecto...4..497S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985Tecto...4..497S"><span id="translatedtitle">The Najd Fault <span class="hlt">System</span>, Saudi Arabia and Egypt: a Late Precambrian <span class="hlt">Rift</span>-Related Transform <span class="hlt">System</span>?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stern, Robert J.</p> <p>1985-08-01</p> <p>The Najd Fault <span class="hlt">System</span> is a complex set of left-lateral strike-slip faults and ductile shear zones that strike NW-SE across the Precambrian of Arabia and Egypt. This <span class="hlt">system</span> was developed during the interval 540-620 Ma. It is up to 400 km wide with an exposed length of 1100 km; inferred buried extensions of the Najd give it a total length of 2000 km. It is the best exposed and may be the largest pre-Mesozoic zone of transcurrent faulting on earth. Previous models for the Najd Fault <span class="hlt">System</span> suggest it formed as a result of a major Late Precambrian continent-continent collision. This model is not preferred here because (1) the lack of evidence for a pre-Late Precambrian continent to the east of the Najd Fault <span class="hlt">System</span>; (2) the difference between the orientation of the Najd Fault <span class="hlt">System</span> and that predicted by slip-line theory; (3) the younger age of Najd movements compared with that of collisional sutures in the Arabian Shield; and (4) lack of evidence for wide-spread crustal uplift that would be expected to accompany collision. A new model for the origin of the Najd Fault <span class="hlt">System</span> accounts for each of these objections: The Najd Fault <span class="hlt">System</span> formed in response to a broad zone of NW-SE directed crustal extension that accompanied juvenile continental crustal formation in northernmost Afro-Arabia. This model also accounts for the following observations: (1) Strands of the Najd parallel the direction of extension in the North Eastern Desert of Egypt and Sinai; (2) the timing of the principal <span class="hlt">rifting</span> movements (ca. 575-600 Ma) overlap with those of the Najd (ca. 560-620 Ma); (3) in spite of observation (2), the Najd Fault <span class="hlt">System</span> is not recognized in northernmost Afro-Arabia; instead the Najd deformation becomes increasingly ductile and these zones are more commonly intruded by sheared and foliated granites as the principal zone of extension is approached. The Najd Fault <span class="hlt">System</span> thus represents a set of continental transforms developed in response to a major episode of Late</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://onlinelibrary.wiley.com/doi/10.1029/91JB02572/abstract','USGSPUBS'); return false;" href="http://onlinelibrary.wiley.com/doi/10.1029/91JB02572/abstract"><span id="translatedtitle">Variations in the reflectivity of the moho transition zone beneath the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> of North America: results from true amplitude analysis of GLIMPCE data</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hutchinson, Deborah R.; Lee, Myung W.; Behrendt, John C.; Cannon, William F.; Green, Adrian</p> <p>1992-01-01</p> <p>True amplitude processing of The Great Lakes International Multidisciplinary Program on Crustal Evolution seismic reflection data from the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> of North America shows large differences in the reflectivity of the Moho transition zone beneath the axial <span class="hlt">rift</span>, beneath the <span class="hlt">rift</span> flanks, and outside of the <span class="hlt">rift</span>. The Moho reflection from the axial <span class="hlt">rift</span> has a discontinuous, diffractive character marginally stronger (several decibels) than an otherwise transparent lower crust and upper mantle. Beneath the axial <span class="hlt">rift</span>, Moho is interpreted to be a synrift igneous feature. Beneath the <span class="hlt">rift</span> 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 <span class="hlt">rift</span>. 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 (<span class="hlt">rift</span> flanks) and not where they are extreme (axial <span class="hlt">rift</span>). 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5930257','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5930257"><span id="translatedtitle">Continental <span class="hlt">rifts</span> and mineral resources</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Burke, K. . Geosciences Dept.)</p> <p>1992-01-01</p> <p>Continental <span class="hlt">rifts</span> are widespread and range in age from the present to 3 b.y. Individual <span class="hlt">rifts</span> may form parts of complex <span class="hlt">systems</span> as in E. Africa and the Basin and Range. <span class="hlt">Rifts</span> have originated in diverse environments such as arc-crests, sites of continental collision, collapsing mountain belts and on continents at rest over the mantle circulation pattern. Continental <span class="hlt">rift</span> resources can be classified by depth of origin: For example, in the Great Dike, Norilsk and Mwadui magma from the mantle is the host. At shallower depths continental crust partly melted above mafic magma hosts ore (Climax, Henderson). <span class="hlt">Rift</span> volcanics are linked to local hydrothermal <span class="hlt">systems</span> and to extensive zeolite deposits (Basin and Range, East Africa). Copper (Zambia, Belt), zinc (Red Dog) and lead ores (Benue) are related to hydrothermal <span class="hlt">systems</span> which involve hot rock and water flow through both pre-<span class="hlt">rift</span> basement and sedimentary and volcanic <span class="hlt">rift</span> fill. Economically significant sediments in <span class="hlt">rifts</span> include coals (the Gondwana of Inida), marine evaporites (Lou Ann of the Gulf of Mexico) and non-marine evaporites (East Africa). Oil and gas in <span class="hlt">rifts</span> relate to a variety of source, reservoir and trap relations (North Sea, Libya), but <span class="hlt">rift</span>-lake sediment sources are important (Sung Liao, Bo Hai, Mina, Cabinda). Some ancient iron ores (Hammersley) may have formed in <span class="hlt">rift</span> lakes but Algoman ores and greenstone belt mineral deposits in general are linked to oceanic and island arc environments. To the extent that continental environments are represented in such areas as the Archean of the Superior and Slave they are Andean Arc environments which today have locally <span class="hlt">rifted</span> crests (Ecuador, N. Peru). The Pongola, on Kaapvaal craton may, on the other hand represent the world's oldest preserved, little deformed, continental <span class="hlt">rift</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMDI11B2583N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMDI11B2583N"><span id="translatedtitle">Mid-lithospheric Discontinuity Beneath the Malawi <span class="hlt">Rift</span>, Deduced from Gravity Studies and its Relation to the <span class="hlt">Rifting</span> Process.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Njinju, E. A.; Atekwana, E. A.; Mickus, K. L.; Abdelsalam, M. G.; Atekwana, E. A.; Laó-Dávila, D. A.</p> <p>2015-12-01</p> <p>The World Gravity Map satellite gravity data were used to investigate the lithospheric structure beneath the Cenozoic-age Malawi <span class="hlt">Rift</span> which forms the southern extension of the Western Branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>. 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 <span class="hlt">rift</span> 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 <span class="hlt">Rift</span>, there is no pattern of N-S elongated crustal thinning following the surface expression of the Malawi <span class="hlt">Rift</span>. With the exception of a north-central region of crustal thinning (< 35 km), most of the southern part of the <span class="hlt">rift</span> is underlain by thick crust (~40‒44 km). Different from the Moho, the MLD is shallower beneath the axis of the Malawi <span class="hlt">Rift</span> 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 <span class="hlt">rift</span> nucleation. The availability of satellite gravity worldwide makes gravity a promising technique for determining the MLD globally.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T31C4635D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T31C4635D"><span id="translatedtitle">Syn-<span class="hlt">Rift</span> <span class="hlt">Systems</span> of East Godavari Sub Basin: Its Evolution and Hydrocarbon Prospectivity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dash, J., Jr.; Zaman, B.</p> <p>2014-12-01</p> <p>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 <span class="hlt">rift</span> <span class="hlt">systems</span>. <span class="hlt">Rift</span> 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-<span class="hlt">rift</span> 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 <span class="hlt">systems</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JGeo...49...19K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JGeo...49...19K"><span id="translatedtitle">Nonlinear geodynamics of the Baikal <span class="hlt">rift</span> <span class="hlt">system</span>: An evolution scenario with triple equilibrium bifurcation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Klyuchevskii, Anatoly V.</p> <p>2010-01-01</p> <p>This is an attempt to analyze the current lithospheric stress pattern in the Baikal <span class="hlt">rift</span> in terms of nonlinear dynamics as an open self-organizing <span class="hlt">system</span> in order to gain more insights into the general laws of regional seismicity. According to the suggested approach, the stress pattern inferred from seismic moments of 70,000 MLH ≥ 2.0 events that occurred in the region between 1968 and 1994 is presented as a phase portrait in the phase spaces of the seismic moments. The obtained phase portrait of the <span class="hlt">system</span> evolution fits well a scenario with triple equilibrium bifurcation where stress bifurcations account for the frequency of M > 5.5 earthquakes. Extrapolation of the results into the nearest future indicates probability of such a bifurcation (a catastrophe of stress), i.e., there is growing risk that M ≈ 7 events may happen in the region within a few years.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JVGR..303..112M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JVGR..303..112M"><span id="translatedtitle"><span class="hlt">Rift</span> zones and magma plumbing <span class="hlt">system</span> of Piton de la Fournaise volcano: How do they differ from Hawaii and Etna?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Michon, Laurent; Ferrazzini, Valérie; Di Muro, Andrea; Villeneuve, Nicolas; Famin, Vincent</p> <p>2015-09-01</p> <p>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 <span class="hlt">rift</span> 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 <span class="hlt">system</span>, from about 30 km depth to the surface, is composed of two structural levels that feed distinct types of <span class="hlt">rift</span> zones. The deep plumbing <span class="hlt">system</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">system</span> (< 11 km bsl) connects the base of the crust with the Central Cone. It is separated from the deep plumbing <span class="hlt">system</span> by a relatively large aseismic zone between 8 and 11 km bsl, which may represent a deep storage level of magma. The shallow plumbing <span class="hlt">system</span> feeds frequent, short-lived summit and flank (NE and SE flanks) eruptions along summit and outer <span class="hlt">rift</span> zones, respectively</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850053973&hterms=origin+crude+oil&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dorigin%2Bcrude%2Boil','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850053973&hterms=origin+crude+oil&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dorigin%2Bcrude%2Boil"><span id="translatedtitle"><span class="hlt">Rift</span> basins - Origin, history, and distribution</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burke, K. C.</p> <p>1985-01-01</p> <p><span class="hlt">Rifts</span> 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 <span class="hlt">rift</span> or set of <span class="hlt">rifts</span> 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 <span class="hlt">rift</span> <span class="hlt">systems</span>. The global distribution of <span class="hlt">rifts</span> can also be related to tectonic environment. For example, <span class="hlt">rifts</span> associated with continental rupture at a temporary still-stand of a continent over the mantle convective <span class="hlt">system</span> (<span class="hlt">rifts</span> like those active in East Africa today) can be distinguished from those associated with continental collision (<span class="hlt">rifts</span> like the Cenozoic <span class="hlt">rifts</span> of China).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005IJEaS..94..594Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005IJEaS..94..594Z"><span id="translatedtitle">Evolution of the lithosphere in the area of the Rhine <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ziegler, P. A.; Dèzes, P.</p> <p>2005-09-01</p> <p>The Rhine <span class="hlt">Rift</span> <span class="hlt">System</span> (RRS) forms part of the European Cenozoic <span class="hlt">Rift</span> <span class="hlt">System</span> (ECRIS) and transects the Variscan Orogen, Permo-Carboniferous troughs and Late Permian to Mesozoic thermal sag basins. Crustal and lithospheric thicknesses range in the RRS area between 24 36 km and 50 120 km, respectively. We discuss processes controlling the transformation of the orogenically destabilised Variscan lithosphere into an end-Mesozoic stabilised cratonic lithosphere, as well as its renewed destabilisation during the Cenozoic development of ECRIS. By end-Westphalian times, the major sutures of the Variscan Orogen were associated with 45 60 km deep crustal roots. During the Stephanian-Early Permian, regional exhumation of the Variscides was controlled by their wrench deformation, detachment of subducted lithospheric slabs, asthenospheric upwelling and thermal thinning of the mantle-lithosphere. By late Early Permian times, when asthenospheric temperatures returned to ambient levels, lithospheric thicknesses ranged between 40 km and 80 km, whilst the thickness of the crust was reduced to 28 35 km in response to its regional erosional and local tectonic unroofing and the interaction of mantle-derived melts with its basal parts. Re-equilibration of the lithosphere-asthenosphere <span class="hlt">system</span> governed the subsidence of Late Permian-Mesozoic thermal sag basins that covered much of the RRS area. By end-Cretaceous times, lithospheric thicknesses had increased to 100 120 km. Paleocene mantle plumes caused renewed thermal weakening of the lithosphere. Starting in the late Eocene, ECRIS evolved in the Pyrenean and Alpine foreland by passive <span class="hlt">rifting</span> under a collision-related north-directed compressional stress field. Following end-Oligocene consolidation of the Pyrenees, west- and northwest-directed stresses originating in the Alps controlled further development of ECRIS. The RRS remained active until the Present, whilst the southern branch of ECRIS aborted in the early Miocene. Extensional</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGeo..102...24E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGeo..102...24E"><span id="translatedtitle">Modeling along-axis variations in fault architecture in the Main Ethiopian <span class="hlt">Rift</span>: Implications for Nubia-Somalia kinematics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Erbello, Asfaw; Corti, Giacomo; Agostini, Andrea; Sani, Federico; Kidane, Tesfaye; Buccianti, Antonella</p> <p>2016-12-01</p> <p>In this contribution, analogue modeling is used to provide new insights into the Nubia-Somalia kinematics responsible for development and evolution of the Main Ethiopian <span class="hlt">Rift</span> (MER), at the northern termination of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">system</span>. In particular, we performed new crustal-scale, brittle models to analyze the along-strike variations in fault architecture in the MER and their relations with the <span class="hlt">rift</span> trend, plate motion and the resulting Miocene-recent kinematics of <span class="hlt">rifting</span>. The models reproduced the overall geometry of the ∼600 km-long MER with its along-strike variation in orientation to test different hypothesis proposed to explain <span class="hlt">rift</span> evolution. Analysis of model results in terms of statistics of fault length and orientation, as well as deformation architecture, and its comparison with the MER suggest that models of two-phase <span class="hlt">rifting</span> (with a first phase of NW-SE extension followed by E-W <span class="hlt">rifting</span>) or constant NW-SE extension, as well as models of constant ENE-WSW <span class="hlt">rifting</span> are not able to reproduce the fault architecture observed in nature. Model results suggest instead that the <span class="hlt">rift</span> has likely developed under a constant, post-11 Ma extension oriented roughly ESE-WNW (N97.5°E), consistent with recent plate kinematics models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.6511K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.6511K"><span id="translatedtitle">Along-axis transition between narrow and wide <span class="hlt">rifts</span>: Insights from 3D numerical experiments</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koptev, Alexander; Calais, Eric; Burov, Evgueni; Leroy, Sylvie; Gerya, Taras</p> <p>2016-04-01</p> <p>Based on performed high-resolution rheologically consistent three-dimensional thermo-mechanical numerical models, we show that there is a significant difference in the influence of the rheological profile on <span class="hlt">rifting</span> style in the case of dominant active (plume-activated) <span class="hlt">rifting</span> compared to dominant passive (far-field tectonic stresses) <span class="hlt">rifting</span>. Narrow <span class="hlt">rifting</span>, conventionally attributed to cold strong lithosphere in passive <span class="hlt">rifting</span> mode, may develop in weak hot ultra-stretched lithosphere during active <span class="hlt">rifting</span>, after plume impingement on a tectonically pre-stressed lithosphere. In that case, initially ultra-wide small-amplitude <span class="hlt">rift</span> patterns focus, in a few Myr, in large-scale faults that form a narrow <span class="hlt">rift</span>. Also, wide <span class="hlt">rifting</span> may develop during ultra-slow spreading of strong lithosphere, and "switch" to the narrow <span class="hlt">rifting</span> upon plume impingement. For further understanding the mechanisms behind the interactions between the mantle plume and far-field stresses in case of realistic horizontally heterogeneous lithosphere, we have tested our models on the case of the central East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">system</span> (EARS). The EARS south of the Ethiopian <span class="hlt">Rift</span> Valley bifurcates in two branches (eastern, magma-rich and western, magma-poor) surrounding the strong Tanzanian craton. Broad zones of low seismic velocity observed throughout the upper mantle beneath the central part of the EARS are consistent with the spreading of a deep mantle plume. The extensional features and topographic expression of the Eastern <span class="hlt">rift</span> varies significantly north-southward: in northern Kenya the area of deformation is very wide (some 150-250 km in E-W direction), to the south the <span class="hlt">rift</span> narrows to 60-70 km, yet further to the south this localized deformation widens again. Here we investigate this transition between localized and wide <span class="hlt">rifting</span> using thermo-mechanical numerical modeling that couples, in a dynamic sense, the rise of the upper mantle material with the deformation of the <span class="hlt">African</span> lithosphere below the</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.4941A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.4941A"><span id="translatedtitle">Götzenite- and combeite-bearing mineral assemblages in peralkaline nephelinite at Nyiragongo, East <span class="hlt">African</span> <span class="hlt">Rift</span>: Recrystallization around a degassing alkaline magma chamber</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andersen, T.; Elburg, M.; Erambert, M.</p> <p>2012-04-01</p> <p>In most igneous rocks, the high field strength elements (HFSE) titanium and zirconium reside in minerals such as ilmenite, titanite, zircon and baddelyite. In some highly peralkaline igneous rocks (agpaitic nepheline syenite, elpidite granite) these minerals are not stable, and the HFSE form complex, Na-, Ca- and volatile bearing silicate minerals. The central crater of Nyiragongo volcano in the East <span class="hlt">African</span> <span class="hlt">Rift</span> has a semi-permanent lava lake which may be regarded as a high-level magma chamber open to the atmosphere. The lavas and pyroclastic rocks of Nyiragongo range in composition from olivine melilitite to nephelinite and minor alkali olivine basalt. The nephelinites range from metaluminous to peralkaline compositions, including strongly peralkaline combeite nephelinite. In fresh peralkaline nephelinite, titanium is hosted in different minerals or mineral assemblages with titanomagnetite ± perovskite ± Ti-rich clinopyroxene, but in some holocrystalline, thermally metamorphosed nephelinites, götzenite (ideally Na2Ca5Ti(Si2O7)2F4) is the main Ti-bearing mineral. Götzenite is stable with combeite (Na2Ca2Si3O9), diopside and kirschsteinite, which replace primary magmatic minerals and glassy groundmass. The compositions of coexisting nepheline and kalsilite suggest recrystallization temperatures between 500 and 600 °C. A chemographic analysis of the sub-solidus mineral assemblages of götzenite-bearing and götzenite-free peralkaline nephelinite suggests that götzenite is stabilized by elevated fluorine activity combined with moderately high (for nephelinite) silica activity. At increasing peralkalinity, götzenite is likely to break down to perovskite-bearing mineral assemblages coexisting with combeite. The presence of götzenite- and combeite-bearing nephelinite at Nyiragongo is due to the influence of fluorine-rich fluids degassing from magma stored in the lava lake.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GGG....17.3008H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GGG....17.3008H"><span id="translatedtitle">Causes of unrest at silicic calderas in the East <span class="hlt">African</span> <span class="hlt">Rift</span>: New constraints from InSAR and soil-gas chemistry at Aluto volcano, Ethiopia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hutchison, William; Biggs, Juliet; Mather, Tamsin A.; Pyle, David M.; Lewi, Elias; Yirgu, Gezahegn; Caliro, Stefano; Chiodini, Giovanni; Clor, Laura E.; Fischer, Tobias P.</p> <p>2016-08-01</p> <p>Restless silicic calderas present major geological hazards, and yet many also host significant untapped geothermal resources. In East Africa, this poses a major challenge, although the calderas are largely unmonitored their geothermal resources could provide substantial economic benefits to the region. Understanding what causes unrest at these volcanoes is vital for weighing up the opportunities against the potential risks. Here we bring together new field and remote sensing observations to evaluate causes of ground deformation at Aluto, a restless silicic volcano located in the Main Ethiopian <span class="hlt">Rift</span> (MER). Interferometric Synthetic Aperture Radar (InSAR) data reveal the temporal and spatial characteristics of a ground deformation episode that took place between 2008 and 2010. Deformation time series reveal pulses of accelerating uplift that transition to gradual long-term subsidence, and analytical models support inflation source depths of ˜5 km. Gases escaping along the major fault zone of Aluto show high CO2 flux, and a clear magmatic carbon signature (CO2-δ13C of -4.2‰ to -4.5‰). This provides compelling evidence that the magmatic and hydrothermal reservoirs of the complex are physically connected. We suggest that a coupled magmatic-hydrothermal <span class="hlt">system</span> can explain the uplift-subsidence signals. We hypothesize that magmatic fluid injection and/or intrusion in the cap of the magmatic reservoir drives edifice-wide inflation while subsequent deflation is related to magmatic degassing and depressurization of the hydrothermal <span class="hlt">system</span>. These new constraints on the plumbing of Aluto yield important insights into the behavior of <span class="hlt">rift</span> volcanic <span class="hlt">systems</span> and will be crucial for interpreting future patterns of unrest.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009IJEaS..98.1809B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009IJEaS..98.1809B"><span id="translatedtitle">Geochemistry of basement rocks from SE Kenya and NE Tanzania: indications for <span class="hlt">rifting</span> and early Pan-<span class="hlt">African</span> subduction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bauernhofer, A. H.; Hauzenberger, C. A.; Wallbrecher, E.; Muhongo, S.; Hoinkes, G.; Mogessie, A.; Opiyo-Akech, N.; Tenczer, V.</p> <p>2009-12-01</p> <p>Amphibolites and orthogneisses from the Taita Hills-Galana River area (SE Kenya) indicate their broad geological-tectonic setting. There are groups of subduction-related rocks which show characteristic REE (rare earth element) patterns and enrichment or varying concentrations of HFS (high field strength) elements. The groups can be assigned to tectonostratigraphic domains marked by different structural styles (e.g., thrust- or strike slip dominated). Tholeiitic gneisses, often emerging as folded and isolated (ridge-shaped) leucocratic bodies, belong to a group of rocks located between the thrust- and strike-slip domain. Compared to calc-alkaline gneisses of the area they contain more mafic inclusions and have lower LIL (large ionic lithophile), HFS and light REE values. These gneisses have chemical characteristics of M-type granitoids of oceanic island arc signature. Intrusion ages of ~955-845 Ma determined for these rocks suggest early Pan-<span class="hlt">African</span> subduction. Mafic to ultramafic rocks from the Pare mountains of NE Tanzania show evidence of ophiolitic cumulates, subduction settings were also observed for the granulite areas in central and southern Tanzania. Together with the widespread arc settings documented in the Arabian-Nubian Shield, the presented data supports the continuation of an island-continental arc range across Kenya-Tanzania to Mozambique.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1254465','SCIGOV-DOEDE'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1254465"><span id="translatedtitle">Hawaii <span class="hlt">Rifts</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/dataexplorer">DOE Data Explorer</a></p> <p>Nicole Lautze</p> <p>2015-01-01</p> <p><span class="hlt">Rifts</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70014173','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70014173"><span id="translatedtitle">The Goodman swell: a lithospheric flexure caused by crustal loading along the Midcontinent <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Peterman, Z.E.; Sims, P.K.</p> <p>1988-01-01</p> <p>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 <span class="hlt">rift</span> <span class="hlt">system</span> (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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910031351&hterms=rainy+season&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Drainy%2Bseason','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910031351&hterms=rainy+season&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Drainy%2Bseason"><span id="translatedtitle">Modelling <span class="hlt">Rift</span> Valley fever (RVF) disease vector habitats using active and passive remote sensing <span class="hlt">systems</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ambrosia, Vincent G.; Linthicum, K. G.; Bailey, C. L.; Sebesta, P.</p> <p>1989-01-01</p> <p>The NASA Ames Ecosystem Science and Technology Branch and the U.S. Army Medical Research Institute of Infectious Diseases are conducting research to detect <span class="hlt">Rift</span> 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 <span class="hlt">systems</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19198772','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19198772"><span id="translatedtitle">Tectonics of the baikal <span class="hlt">rift</span> deduced from volcanism and sedimentation: a review oriented to the Baikal and Hovsgol lake <span class="hlt">systems</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ivanov, Alexei V; Demonterova, Elena I</p> <p>2009-01-01</p> <p>As known from inland sedimentary records, boreholes, and geophysical data, the initiation of the Baikal <span class="hlt">rift</span> basins began as early as the Eocene. Dating of volcanic rocks on the <span class="hlt">rift</span> 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 <span class="hlt">rifting</span> 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 <span class="hlt">rift</span> propagation from the historical center towards the wings of the <span class="hlt">rift</span> <span class="hlt">system</span>. <span class="hlt">Rifting</span> 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 <span class="hlt">rifting</span>. 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SolE....6..185D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SolE....6..185D"><span id="translatedtitle">Fault evolution in the Potiguar <span class="hlt">rift</span> termination, equatorial margin of Brazil</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>de Castro, D. L.; Bezerra, F. H. R.</p> <p>2015-02-01</p> <p>The transform shearing between South American and <span class="hlt">African</span> 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 architecture of fault <span class="hlt">systems</span> and to analyze the evolution of the eastern equatorial margin of Brazil. Our study area is the southern onshore termination of the Potiguar <span class="hlt">rift</span>, which is an aborted NE-trending <span class="hlt">rift</span> arm developed during the breakup of Pangea. The basin is located along the NNE margin of South America that faces the main transform zone that separates the North and the South Atlantic. The Potiguar <span class="hlt">rift</span> is a Neocomian structure located at 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 <span class="hlt">rift</span> and indicates that stretching in the southern <span class="hlt">rift</span> 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 <span class="hlt">system</span> of NW-SE- to NS-striking normal faults. These depocenters form grabens up to 1200 m deep with a rhomb-shaped geometry, which are filled with <span class="hlt">rift</span> sedimentary units and capped by postrift sedimentary sequences. The evolution of the <span class="hlt">rift</span> termination is consistent with the right-lateral shearing of the equatorial margin in the Cretaceous and occurs not only at the <span class="hlt">rift</span> termination but also as isolated structures away from the main <span class="hlt">rift</span>. This study indicates that the strike-slip shearing between two plates propagated to the interior of one of these plates, where faults with similar orientation, kinematics, geometry, and timing of the major transform are observed. These faults also influence <span class="hlt">rift</span> geometry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoJI.201..505L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoJI.201..505L"><span id="translatedtitle">Stress pattern of the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>, North China, inferred from the inversion of new focal mechanisms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Bin; Atakan, Kuvvet; Sørensen, Mathilde Bøttger; Havskov, Jens</p> <p>2015-05-01</p> <p>Earthquake focal mechanisms of the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>, North China, are investigated for the time period 1965-April 2014. A total of 143 focal mechanisms of ML ≥ 3.0 earthquakes were compiled. Among them, 105 solutions are newly determined in this study by combining the P-wave first motions and full waveform inversion, and 38 solutions are from available published data. Stress tensor inversion was then performed based on the new database. The results show that most solutions in the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span> exhibit normal or strike-slip faulting, and the regional stress field is transtensional and dominated by NNW-SSE extension. This correlates well with results from GPS data, geological field observations and levelling measurements across the faults. Heterogeneity exists in the regional stress field, as indicated by individual stress tensor inversions conducted for five subzones. While the minimum stress axis (σ3) appears to be consistent and stable, the orientations, especially the plunges, of the maximum and intermediate stresses (σ1 and σ2) vary significantly along the strike of the different subzones. Based on our results and combining multidisciplinary observations from geological surveys, GPS and cross-fault monitoring, a kinematic model is proposed for the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>, in which the <span class="hlt">rift</span> is situated between two opposite rotating crustal blocks, exhibiting a transtensional stress regimes. This model illustrates the present-day stress field and its correlation to the regional tectonics, as well as the current crustal deformation of the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>. Results obtained in this study, may help to understand the geodynamics, neotectonic activity, active seismicity and potential seismic hazard in this region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.V31A2103T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V31A2103T"><span id="translatedtitle"><span class="hlt">Rifting</span> process of the Izu-Ogasawara-Mariana arc-backarc <span class="hlt">system</span> inferred from active source seismic studies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Takahashi, N.; Kodaira, S.; Miura, S.; Sato, T.; Yamashita, M.; No, T.; Takizawa, K.; Kaiho, Y.; Kaneda, Y.</p> <p>2008-12-01</p> <p>The Izu-Ogasawara-Mariana (IBM) arc-backarc <span class="hlt">system</span> has continued the crustal growth through crustal thickening by magmatic activities and crustal thinning by backarc opening. Tatsumi et al (2008) proposed petrological crustal growth model started from basaltic magmas rising from the slab, and showed the consistency with the seismic velocity model. Although crustal growth by the crustal thickening are modeled, crustal structural change by the backarc opening are not still unknown yet. The Shikoku Basin and Parece Vela Basin were formed by the backarc opening during approximately 15-30 Ma. Since 6 Ma, the Mariana Trough has opened and the stage already moved to spreading process from <span class="hlt">rifting</span> process. In the northern Izu-Ogasawara arc, the Sumisu <span class="hlt">rift</span> is in the initial <span class="hlt">rifting</span> stage. Therefore, understanding of the crustal change by the backarc opening from <span class="hlt">rifting</span> to spreading is indispensable to know the crustal growth of whole Izu-Ogasawara-Mariana island arc. Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has carried out seismic studies using a multichannel reflection survey <span class="hlt">system</span> and ocean bottom seismographs (OBSs) around the IBM arc since 2003 (Takahashi et al., 2007; Kodaira et al., 2007; Takahashi et al., 2008; Kodaira et al., 2008). We already obtained eight P-wave velocity models across the IBM arc and these structures record the crustal structural change during the backarc opening process from the <span class="hlt">rifting</span> stage to the spreading stage. As the results, we identified characteristics of the crustal structural change accompanied with backarc opening as follows. (1) Beneath the initial <span class="hlt">rifting</span> stage without normal faults, for example, in the northern tip of the Mariana Trough, crustal thickening are identified. (2) Beneath the initial <span class="hlt">rifting</span> stage with normal faults, for example, in the Sumisu <span class="hlt">Rift</span>, the crustal thickness is almost similar to that beneath the volcanic front. Although an existence of the crust-mantle transition layer with</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMPP21A2221G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMPP21A2221G"><span id="translatedtitle">Constraining the Thermal History of the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> with Clumped Isotopes and Organic Thermal Maturity Indices</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gallagher, T. M.; Sheldon, N. D.; Mauk, J. L.; Gueneli, N.; Brocks, J. J.</p> <p>2015-12-01</p> <p>The Mesoproterozoic (~1.1 Ga) North American Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> (MRS) has been of widespread interest to researchers studying its economic mineral deposits, continental <span class="hlt">rifting</span> 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 <span class="hlt">rift</span>. 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GPC...111..174J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GPC...111..174J"><span id="translatedtitle">Hydrological constraints of paleo-Lake Suguta in the Northern Kenya <span class="hlt">Rift</span> during the <span class="hlt">African</span> Humid Period (15-5 ka BP)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Junginger, Annett; Trauth, Martin H.</p> <p>2013-12-01</p> <p>During the <span class="hlt">African</span> Humid Period (AHP, 15-5 ka BP) an almost 300 m deep paleo-lake covering 2200 km2 developed in the Suguta Valley, in the Northern Kenya <span class="hlt">Rift</span>. Data from lacustrine sediments and paleo-shorelines indicate that a large paleo-lake already existed by 13.9 ka BP, and record rapid water level fluctuations of up to 100 m within periods of 100 years or less, and a final lowstand at the end of the AHP (5 ka BP). We used a hydro-balance model to assess the abruptness of these water level fluctuations and identify their causes. We observed that fluctuations within the AHP were caused by abrupt changes in precipitation of 26-40%. Despite the absence of continuous lacustrine data documenting the onset of the AHP in the Suguta Valley, we conclude from the hydro-balance model that only an abrupt onset to the AHP, prior to 14.8 ka BP, could have led to high water levels recorded. The modeling results suggest that the sudden increase in rainfall was the direct consequence of an eastward migration of the Congo Air Boundary (CAB), caused by an enhanced atmospheric pressure gradient between East Africa and southern Asia during a northern hemisphere (NH) summer insolation maximum. In contrast, the end of the AHP must have been gradual despite an abrupt change in the source of precipitation when a decreasing pressure gradient between Asia and Africa prevented the CAB from reaching the study area. This abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during September-October. This change would have meant that the only rain source was the Intertropical Convergence Zone (ITCZ), which would have carried a greater amount of moisture during the short rainy season thus slowing the fall in water level over a period of about 1000 years in association with the reduction in insolation. The results of this study provide an indication of the amount of time available for humans in north-eastern Africa to adapt</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.4381L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.4381L"><span id="translatedtitle">Geomorphometric reconstruction of post-eruptive surfaces of the Virunga Volcanic Province (East <span class="hlt">African</span> <span class="hlt">Rift</span>), constraint of erosion ratio and relative chronology</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lahitte, Pierre; Poppe, Sam; Kervyn, Matthieu</p> <p>2016-04-01</p> <p>Quaternary volcanic landforms result from a complex evolution, involving volcanic constructional events and destructive ones by collapses and long-term erosion. Quantification, by morphometric approaches, of the evolution through time of the volcano shape allows the estimation of relative ages between volcanoes sharing the same climate and eruptive conditions. We apply such method to six volcanoes of the Virunga Volcanic Province in the western branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> Valley that still has rare geochronological constraints. As they have comparable sizes, volcanic history and erupted products, these edifices may have undergone comparable conditions of erosion which justify the deduction of relative chronology from their erosion pattern. Our GIS-based geomorphometric approach, the SHAPEVOLC algorithm, quantifies erupted or dismantled volumes by numerically modeling topographies resulting from the eruptive construction of each volcano. Constraining points are selected by analyses of morphometric properties of each cell of the current DEM, as the loci where the altitude is still representative of the un-eroded volcanic surfaces. A primary elevation surface is firstly adjusted to these constraining points by modeling a first-order pseudo-radial surface defined by: 1. the curve best fitting the concave-upwards volcano profile; 2. the location and elevation of the volcano summit; and 3. the possible eccentricity and azimuth parameters that allow to stretch and contract contours to adjust the shape of the model to the elliptically-shaped surface of the volcano. A second-order surface is next computed by local adjustment of the first-order surface to the constraining points to obtain the definitive primary elevation surface of the considered volcanic construct. Amount of erosion is obtained by summing the difference in elevation between reconstructed surfaces and current ones that allows to establish relative ages of volcanoes. For the 6 studied Virunga volcanoes</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015CoMP..169...46H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015CoMP..169...46H"><span id="translatedtitle">Melt inclusion evidence for CO2-rich melts beneath the western branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span>: implications for long-term storage of volatiles in the deep lithospheric mantle</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hudgins, T. R.; Mukasa, S. B.; Simon, A. C.; Moore, G.; Barifaijo, E.</p> <p>2015-05-01</p> <p>We present new major element, trace element, and volatile (H2O, CO2, S, F, and Cl) concentrations of olivine-hosted melt inclusions from five high-K, low-silica basanites from the western branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> and use these data to investigate the generation of H2O- and CO2-rich melts at up to ~150 km depth. Measured H2O and CO2 concentrations reach ~2.5 and ~1 wt%, respectively, representing some of the highest CO2 concentrations measured in a melt inclusion to date. These measurements represent direct evidence of the high CO2 and H2O concentrations required to generate high-K alkaline lavas, and the CO2 that has been previously inferred to be necessary for the low mantle potential temperatures in the area. Ratios of CO2/Nb, CO2/Ba, and CO2/Cl are used to estimate an initial melt CO2 concentration of 5-12 wt%. The measured CO2 concentrations are consistent with CO2 solubilities determined by molecular dynamics calculations and high-pressure experiments for melt generation at 3-6 GPa; the depth of melting suggested by previous studies in the area. These melt inclusions measurements represent direct evidence for the presence of H2O- and CO2-rich melts in the deep upper mantle that have been proposed based on experimental and seismic evidence. Primitive-mantle normalized trace element patterns more closely resemble those found in subduction settings rather than ocean island basalt, and ratios of slab fluid tracers such as Li/Dy and B/Be indicate that the measured volatile abundances may be related to Neoproterozoic subduction during the assembly of Gondwana, implying the storage of volatiles in the mantle by subduction-related metasomatism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110023310','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110023310"><span id="translatedtitle">DoD-GEIS <span class="hlt">Rift</span> Valley Fever Monitoring and Prediction <span class="hlt">System</span> as a Tool for Defense and US Diplomacy</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Anyamba, Assaf; Tucker, Compton J.; Linthicum, Kenneth J.; Witt, Clara J.; Gaydos, Joel C.; Russell, Kevin L.</p> <p>2011-01-01</p> <p>Over the last 10 years the Armed Forces Health Surveillance Center's Global Emerging Infections Surveillance and Response <span class="hlt">System</span> (GEIS) partnering with NASA'S Goddard Space Flight Center and USDA's USDA-Center for Medical, Agricultural & Veterinary Entomology established and have operated the <span class="hlt">Rift</span> Valley fever Monitoring and Prediction <span class="hlt">System</span> to monitor, predict and assess the risk of <span class="hlt">Rift</span> Valley fever outbreaks and other vector-borne diseases over Africa and the Middle East. This <span class="hlt">system</span> 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 <span class="hlt">system</span> has predicted outbreaks of <span class="hlt">Rift</span> 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 <span class="hlt">system</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1611128D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1611128D"><span id="translatedtitle">Groundwater dynamics in the complex aquifer <span class="hlt">system</span> of Gidabo River Basin, southern Main Ethiopian <span class="hlt">Rift</span>: Evidences from hydrochemistry and isotope hydrology</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Degu, Abraham; Birk, Steffen; Dietzel, Martin; Winkler, Gerfried; Moggessie, Aberra</p> <p>2014-05-01</p> <p>Located in the tectonically active Main Ethiopian <span class="hlt">Rift</span> <span class="hlt">system</span>, the Gidabo River Basin in Ethiopia has a complex hydrogeological setting. The strong physiographic variation from highland to <span class="hlt">rift</span> 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 <span class="hlt">rift</span> floor aquifers. δ18O and δD composition of groundwater show a general progressive enrichment from the highland to the <span class="hlt">rift</span> floor, except in thermal and deep <span class="hlt">rift</span> floor aquifers. Relatively the thermal and deep <span class="hlt">rift</span> 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 <span class="hlt">system</span>. 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 <span class="hlt">rift</span>, hydrochemical and isotopic data we propose a conceptual groundwater flow model by characterizing flow paths to the main <span class="hlt">rift</span> axis. The connection between groundwater flow and the impact of faults make this model applicable to other active <span class="hlt">rift</span> <span class="hlt">systems</span> with similar</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.V33C2649A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V33C2649A"><span id="translatedtitle">Open <span class="hlt">system</span> evolution of trachyte and phonolite magmas from the East Africa <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Anthony, E. Y.; Espejel, V.</p> <p>2011-12-01</p> <p>The Quaternary Suswa volcanic <span class="hlt">system</span> consists of a large shield volcano that developed two nested summit calderas and erupted metaluminous to peralkaline trachyte and phonolite lavas and tuffs. Suswa is adjacent to the Greater Olkaria Volcanic Center, Longonot, Eburru, and Menengai volcanic <span class="hlt">systems</span>, which erupted trachyte, comendite, and pantellerite. These volcanoes comprise the Central Kenya Peralkaline Province and are the site of active geothermal energy production and exploration. Mafic to intermediate lavas (Elementieta, Ndabibi, and Lolonito-Akira-Tandamara volcanic fields) lie in the <span class="hlt">rift</span> floor between the shield volcanoes and occur as components of mixed magmas within the complexes. Suswa includes two suites of trachyte-phonolite lavas and tuffs. The first suite (C1) consists of lavas that built the original shield volcano and lavas and tuffs related to the formation of the first caldera; the second suite (C2) consists of lavas and tuffs erupted during and after the formation of the second caldera. Trachyte-carbonate immiscibility has been recorded in C1 ash flow units. The lavas and tuffs of the C2 suite are generally less peralkaline and more silica undersaturated than those of the C1 suite and did not share a common parental magma. Geochemical modeling precludes fractional crystallization as the sole process for Suswa magmas. Instead, assimilation of syenitic material (probably the crystal mush left over from C1 fractional crystallization), resorption, and mixing between the mafic to intermediate lavas satellite to the shield volcanoes have contributed to the composition and eruptive style of these volcanoes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Tectp.632...21M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Tectp.632...21M"><span id="translatedtitle">Left-lateral transtension along the Ethiopian <span class="hlt">Rift</span> and constrains on the mantle-reference plate motions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muluneh, Ameha A.; Cuffaro, Marco; Doglioni, Carlo</p> <p>2014-09-01</p> <p>We present the kinematics of the Ethiopian <span class="hlt">Rift</span>, in the northern part of East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>, derived from compilation of geodetic velocities, focal mechanism inversions, structural data analysis and geological profiles. In the central Ethiopian <span class="hlt">Rift</span>, the GPS velocity field shows a systematic magnitude increase in ENE direction, and the incremental extensional strain axes recorded by earthquake focal mechanisms and fault slip inversion show ≈ N100°E orientation. This deviation between direction of GPS velocity vectors and orientation of incremental extensional strain is developed due to left lateral transtensional deformation along the NE-SW trending segment of the <span class="hlt">rift</span>. This interpretation is consistent with the en-échelon pattern of tensional and transtensional faults, plus the distribution of the volcanic centers, and the asymmetry of the <span class="hlt">rift</span> itself. We analyzed the kinematics of the Ethiopian <span class="hlt">Rift</span> also relative to the mantle comparing the results in the deep and shallow hotspot reference frames. While the oblique orientation of the <span class="hlt">rift</span> was controlled by the pre-existing lithospheric fabric, the two reference frames predict different kinematics of Africa and Somalia plates along the <span class="hlt">rift</span> itself, both in magnitude and direction, and with respect to the mantle. However, the observed kinematics and tectonics along the <span class="hlt">rift</span> are more consistent with a faster WSW-ward motion of Africa than Somalia observed in the shallow hotspot framework. The faster WSW motion of Africa with respect to Somalia plate is inferred to be due to the lower viscosity in the top asthenosphere (LVZ-low-velocity zone) beneath Africa. These findings have significant implication for the evolution of continental <span class="hlt">rifting</span> in transtensional settings and provide evidence for the kinematics of the Ethiopian <span class="hlt">Rift</span> in the context of the Africa-Somalia plate interaction in the mantle reference frame.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010IJEaS..99.1663B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010IJEaS..99.1663B"><span id="translatedtitle">Stable isotope variation in tooth enamel from Neogene hippopotamids: monitor of meso and global climate and <span class="hlt">rift</span> dynamics on the Albertine <span class="hlt">Rift</span>, Uganda</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brachert, Thomas Christian; Brügmann, Gerhard B.; Mertz, Dieter F.; Kullmer, Ottmar; Schrenk, Friedemann; Jacob, Dorrit E.; Ssemmanda, Immaculate; Taubald, Heinrich</p> <p>2010-10-01</p> <p>The Neogene was a period of long-term global cooling and increasing climatic variability. Variations in <span class="hlt">African</span>-Asian monsoon intensity over the last 7 Ma have been deduced from patterns of eolian dust export into the Indian Ocean and Mediterranean Sea as well as from lake level records in the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS). However, lake <span class="hlt">systems</span> not only depend on rainfall patterns, but also on the size and physiography of river catchment areas. This study is based on stable isotope proxy data (18O/16O, 13C/12C) from tooth enamel of hippopotamids (Mammalia) and aims in unravelling long-term climate and watershed dynamics that control the evolution of palaeolake <span class="hlt">systems</span> in the western branch of the EARS (Lake Albert, Uganda) during the Late Neogene (7.5 Ma to recent). Having no dietary preferences with respect to wooded (C3) versus grassland (C4) vegetation, these territorial, water-dependant mammals are particularly useful for palaeoclimate analyses. As inhabitants of lakes and rivers, hippopotamid tooth enamel isotope data document mesoclimates of topographic depressions, such as the <span class="hlt">rift</span> valleys and, therefore, changes in relative valley depth instead of exclusively global climate changes. Consequently, we ascribe a synchronous maximum in 18O/16O and 13C/12C composition of hippopotamid enamel centred around 1.5-2.5 Ma to maximum aridity and/or maximum hydrological isolation of the <span class="hlt">rift</span> floor from <span class="hlt">rift</span>-external river catchment areas in response to the combined effects of <span class="hlt">rift</span> shoulder uplift and subsidence of the <span class="hlt">rift</span> valley floor. Structural rearrangements by ~2.5 Ma within the northern segment of the Albertine <span class="hlt">Rift</span> are well constrained by reversals in river flow, cannibalisation of catchments, biogeographic turnover and uplift of the Rwenzori horst. However, a growing rain shadow is not obvious in 18O/16O signatures of the hippopotamid teeth of the Albertine <span class="hlt">Rift</span>. According to our interpretation, this is the result of the overriding effect of evaporation on 18</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26640665','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26640665"><span id="translatedtitle">Evolution along the Great <span class="hlt">Rift</span> Valley: phenotypic and genetic differentiation of East <span class="hlt">African</span> white-eyes (Aves, Zosteropidae).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Habel, Jan Christian; Borghesio, Luca; Newmark, William D; Day, Julia J; Lens, Luc; Husemann, Martin; Ulrich, Werner</p> <p>2015-11-01</p> <p>The moist and cool cloud forests of East Africa represent a network of isolated habitats that are separated by dry and warm lowland savannah, offering an opportunity to investigate how strikingly different selective regimes affect species diversification. Here, we used the passerine genus Zosterops (white-eyes) from this region as our model <span class="hlt">system</span>. Species of the genus occur in contrasting distribution settings, with geographical mountain isolation driving diversification, and savannah interconnectivity preventing differentiation. We analyze (1) patterns of phenotypic and genetic differentiation in high- and lowland species (different distribution settings), (2) investigate the potential effects of natural selection and temporal and spatial isolation (evolutionary drivers), and (3) critically review the taxonomy of this species complex. We found strong phenotypic and genetic differentiation among and within the three focal species, both in the highland species complex and in the lowland taxa. Altitude was a stronger predictor of phenotypic patterns than the current taxonomic classification. We found longitudinal and latitudinal phenotypic gradients for all three species. Furthermore, wing length and body weight were significantly correlated with altitude and habitat type in the highland species Z. poliogaster. Genetic and phenotypic divergence showed contrasting inter- and intraspecific structures. We suggest that the evolution of phenotypic characters is mainly driven by natural selection due to differences in the two macro-habitats, cloud forest and savannah. In contrast, patterns of neutral genetic variation appear to be rather driven by geographical isolation of the respective mountain massifs. Populations of the Z. poliogaster complex, as well as Z. senegalensis and Z. abyssinicus, are not monophyletic based on microsatellite data and have higher levels of intraspecific differentiation compared to the currently accepted species.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatGe...9..145L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatGe...9..145L"><span id="translatedtitle">Massive and prolonged deep carbon emissions associated with continental <span class="hlt">rifting</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Hyunwoo; Muirhead, James D.; Fischer, Tobias P.; Ebinger, Cynthia J.; Kattenhorn, Simon A.; Sharp, Zachary D.; Kianji, Gladys</p> <p>2016-02-01</p> <p>Carbon from Earth’s interior is thought to be released to the atmosphere mostly via degassing of CO2 from active volcanoes. CO2 can also escape along faults away from active volcanic centres, but such tectonic degassing is poorly constrained. Here we use measurements of diffuse soil CO2, combined with carbon isotopic analyses to quantify the flux of CO2 through fault <span class="hlt">systems</span> away from active volcanoes in the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">system</span>. We find that about 4 Mt yr-1 of mantle-derived CO2 is released in the Magadi-Natron Basin, at the border between Kenya and Tanzania. Seismicity at depths of 15-30 km implies that extensional faults in this region may penetrate the lower crust. We therefore suggest that CO2 is transferred from upper-mantle or lower-crustal magma bodies along these deep faults. Extrapolation of our measurements to the entire Eastern <span class="hlt">rift</span> of the <span class="hlt">rift</span> <span class="hlt">system</span> implies a CO2 flux on the order of tens of megatonnes per year, comparable to emissions from the entire mid-ocean ridge <span class="hlt">system</span> of 53-97 Mt yr-1. We conclude that widespread continental <span class="hlt">rifting</span> and super-continent breakup could produce massive, long-term CO2 emissions and contribute to prolonged greenhouse conditions like those of the Cretaceous.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3695L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3695L"><span id="translatedtitle">Stress Pattern of the Shanxi <span class="hlt">Rift</span> <span class="hlt">System</span>, North China, Inferred from the Inversion of New Focal Mechanisms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Bin; Sørensen, Mathilde; Atakan, Kuvvet; Havskov, Jens</p> <p>2015-04-01</p> <p>The Shanxi <span class="hlt">rift</span> <span class="hlt">system</span> is one of the most outstanding intra-plate transtensional fault zones in the North China block. Earthquake focal mechanisms of the <span class="hlt">rift</span> <span class="hlt">system</span> are investigated for the time period 1965 - Apr. 2014. A total of 143 focal mechanisms of ML ≥ 3.0 earthquakes were compiled. Among them, 105 solutions are newly determined by combining the P-wave first motions and full waveform inversion, and 38 solutions are from available published data. Stress tensor inversion was then performed based on the new database. The results show that most solutions exhibit normal or strike-slip faulting, and the regional stress field is transtensional and dominated by NNW-SSE extension. This correlates well with results from GPS data, geological field observations and leveling measurements across the faults. Heterogeneity exists in the regional stress field, as indicated by individual stress tensor inversions conducted for five subzones. While the minimum stress axis (σ3) appears to be consistent and stable, the orientations, especially the plunges, of the maximum and intermediate stresses (σ1 and σ2) vary significantly among the different subzones. Based on our results and combining multidisciplinary observations from geological surveys, GPS and cross-fault monitoring, a kinematic model is proposed, in which the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span> is situated between two opposite rotating blocks, exhibiting a transtensional stress regime. This model illustrates the present-day stress field and its correlation with the regional tectonics, as well as the current crustal deformation of the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>. Results obtained in this study, may help to understand the geodynamics, neotectonic activity, active seismicity and potential seismic hazard in this region of North China.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.V34B..07D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V34B..07D"><span id="translatedtitle">Crystallization, Fluid Exsolution, and Eruption of Extremely Volatile-rich Silicate Magma at Oldoinyo Lengai Volcano, East <span class="hlt">African</span> <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>de Moor, J.; Fischer, T. P.; King, P. L.; Hervig, R. L.; Hilton, D. R.</p> <p>2011-12-01</p> <p>, however CO2/Nb ratios are much lower than depleted upper mantle values indicating that the magma experienced prior exsolution of C-rich fluid. The MI display a trend of decreasing H2O and increasing CO2 with evolution of the melt. This trend is interpreted to reflect crystallization-driven melt evolution in a stream of C-rich fluid percolating from deeper in the magma <span class="hlt">system</span>. Melt evolution to higher alkali and lower SiO2 contents resulted in less polymerized melt compositions and increasing CO2 solubility, whereas H2O was partitioned into the fluid phase. Crystallization and degassing of H2O led to increasing magma viscosity, which ultimately inhibited gas-magma separation and triggered the explosive eruption. Once the viscous apex of the magma chamber was expelled then quiescent degassing and NC effusion were able to resume. [1] Klaudius, J., and Keller, J. (2006) Lithos, 91: 173-190. [2] Dawson, J.B., et al. (1995) IAVCEI Proc. in Volc., 4: 70-86. [3] Mitchell, R.H. (2009) Contrib. Min. Pet.,158: 589-598.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010Tectp.488....7A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010Tectp.488....7A"><span id="translatedtitle">On the geodynamics of the Aegean <span class="hlt">rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Agostini, Samuele; Doglioni, Carlo; Innocenti, Fabrizio; Manetti, Piero; Tonarini, Sonia</p> <p>2010-06-01</p> <p>The Aegean <span class="hlt">rift</span> is considered to be either a classic backarc basin, or the result of the westward escape of Anatolia, or the effect of a gravitational collapse of an over-thickened lithosphere. Here these models are questioned. We alternatively present a number of geodynamic and magmatic constraints suggesting a simple model for the genesis of the extension as being related to the differential advancement of the upper lithosphere over a heterogeneous lower <span class="hlt">African</span> plate. The Greek microplate overrides the Ionian oceanic segment of the <span class="hlt">African</span> plate faster than the Anatolian microplate over the thicker Levantine more continental segment. This setting is evidenced by GPS-velocity gradient in the hangingwall of the Hellenic-Cyprus subduction <span class="hlt">system</span> and requires a zone of <span class="hlt">rifting</span> splitting the hangingwall into two microplates. This mechanism is unrelated to the replacement of retreated slab by the asthenosphere as typically occurs in the backarc of west-directed subduction zones. The supposed greater dehydration of the Ionian segment of the slab is providing a larger amount of fluids into the low velocity channel at the top of the asthenosphere, allowing a faster decoupling between the Greek microplate and the underlying mantle with respect to the Anatolian microplate. Slab ruptures associated with the differential retreat controlled by the inherited lithospheric heterogeneities in the lower plate and the proposed upwelling of the mantle suggested by global circulation models would explain the occurrence and coexistence of slab-related and slab-unrelated magmatism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12413108','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12413108"><span id="translatedtitle"><span class="hlt">African</span> American teens and the neo-juvenile justice <span class="hlt">system</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rozie-Battle, Judith L</p> <p>2002-01-01</p> <p><span class="hlt">African</span> American youth continue to be overrepresented in the juvenile justice <span class="hlt">system</span>. As a result of the current political environment and the perceived increase in crime among young people, the nation has moved away from rehabilitation and toward harsher treatment of delinquents. The <span class="hlt">African</span> American community must encourage policy makers and community leaders to continue to address the disproportionate representation of <span class="hlt">African</span> American youth in the <span class="hlt">system</span>. Current policing and prosecutorial policies must also be examined and challenged to end the perception of an unjust <span class="hlt">system</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994GeoRu..83..689E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994GeoRu..83..689E"><span id="translatedtitle">Multiple episodes of <span class="hlt">rifting</span> in Central and East Africa: A re-evaluation of gravity data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ebinger, C. J.; Ibrahim, A.</p> <p>1994-12-01</p> <p>A compilation of new and existing gravity data, as well as geophysical and geological data, is used to assess the cumulative effects of multiple <span class="hlt">rifting</span> episodes on crustal and upper mantle density structures beneath the Uganda-Kenya-Ethiopia-Sudan border region. This compilation includes new gravity and geological data collected in 1990 in south-western Ethiopia. Variations in the trends and amplitudes of Bouguer gravity anomalies reveal three overlapping <span class="hlt">rift</span> <span class="hlt">systems</span>: Mesozoic, Paleogene and Miocene-Recent. Each of these <span class="hlt">rift</span> <span class="hlt">systems</span> is a number of 40 100 km long sedimentary basins, and each <span class="hlt">system</span> is approximately 1000 km long. The Bouguer anomaly patterns indicate that the Ethiopian and East <span class="hlt">African</span> plateaux and corresponding gravity anomalies are discrete tectonic features. Models of structural and gravity profiles of two basins (Omo and Chew Bahir basins) suggest that pre-Oligocene (Cretaceous?) strata underlie 3 km or more of Neogene-Recent strata within the northern Kenya <span class="hlt">rift</span>, and that more than 2 km of Neogene-Recent strata underlie parts of the southern Main Ethiopian <span class="hlt">rift</span>. The superposition of perhaps three <span class="hlt">rifting</span> episodes in the Lake Turkana (Omo) region has led to 90% crustal thinning (β ≈ 2).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017HydJ...25..519M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017HydJ...25..519M"><span id="translatedtitle">Groundwater flow dynamics in the complex aquifer <span class="hlt">system</span> of Gidabo River Basin (Ethiopian <span class="hlt">Rift</span>): a multi-proxy approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mechal, Abraham; Birk, Steffen; Dietzel, Martin; Leis, Albrecht; Winkler, Gerfried; Mogessie, Aberra; Kebede, Seifu</p> <p>2017-03-01</p> <p>Hydrochemical and isotope data in conjunction with hydraulic head and spring discharge observations were used to characterize the regional groundwater flow dynamics and the role of the tectonic setting in the Gidabo River Basin, Ethiopian <span class="hlt">Rift</span>. Both groundwater levels and hydrochemical and isotopic data indicate groundwater flow from the major recharge area in the highland and escarpment into deep <span class="hlt">rift</span> floor aquifers, suggesting a deep regional flow <span class="hlt">system</span> can be distinguished from the shallow local aquifers. The δ18O and δ2H values of deep thermal (≥30 °C) groundwater are depleted relative to the shallow (<60 m below ground level) groundwater in the <span class="hlt">rift</span> floor. Based on the δ18O values, the thermal groundwater is found to be recharged in the highland around 2,600 m a.s.l. and on average mixed with a proportion of 30 % shallow groundwater. While most groundwater samples display diluted solutions, δ13C data of dissolved inorganic carbon reveal that locally the thermal groundwater near fault zones is loaded with mantle CO2, which enhances silicate weathering and leads to anomalously high total dissolved solids (2,000-2,320 mg/l) and fluoride concentrations (6-15 mg/l) exceeding the recommended guideline value. The faults are generally found to act as complex conduit leaky barrier <span class="hlt">systems</span> favoring vertical mixing processes. Normal faults dipping to the west appear to facilitate movement of groundwater into deeper aquifers and towards the <span class="hlt">rift</span> floor, whereas those dipping to the east tend to act as leaky barriers perpendicular to the fault but enable preferential flow parallel to the fault plane.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MsT..........2N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MsT..........2N"><span id="translatedtitle">Crustal and sub-continental lithospheric mantle decoupling beneath the Malawi <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Njinju, Emmanuel Atem</p> <p></p> <p>We analyzed satellite gravity and aeromagnetic data using the two-dimensional (2D) power-density spectrum technique to investigate the lithospheric and thermal structure beneath the magma-starved Malawi <span class="hlt">Rift</span>, which forms the southern extension of the Western Branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>. We observed: (1) lack of consistent pattern of crustal thinning and elevated heat flow along the surface expression of the <span class="hlt">rift</span>. Beneath the Rungwe Volcanic Province (RVP) in the north, the crustal thickness ranges between 40 and 45 km and varies between 35 and 40 km along the entire length of the <span class="hlt">rift</span>. (2) shallow lithosphere-asthenosphere boundary (LAB) elevated to ˜64 km beneath the entire length of the <span class="hlt">rift</span> and deeper than 100 km beneath the surrounding Precambrian terranes reaching in places ˜124 km. (3) localized zones of high heat flow (70-75 mWm-2) beneath the RVP, and the central and southern parts of the <span class="hlt">rift</span>. The central and southern thermal anomalies are due to the presence of uranium deposits in the Karoo sedimentary rocks. We interpret the crustal thickness heterogeneity to have been inherited from pre-existing lithospheric stretching, while strain during the extension of the Malawi <span class="hlt">Rift</span> is preferentially localized in the sub-continental lithospheric mantle (SCLM). Our interpretation is supported by 2D forward modeling of the gravity data showing uniform stretching of the SCLM by a factor of 1.5 to 1.8 beneath the entire length of the <span class="hlt">rift</span>. Our results indicate decoupling of the crust from the SCLM during the early stages of the development of the Malawi <span class="hlt">Rift</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4176798','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4176798"><span id="translatedtitle"><span class="hlt">African</span> Americans, hypertension and the renin angiotensin <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Williams, Sandra F; Nicholas, Susanne B; Vaziri, Nosratola D; Norris, Keith C</p> <p>2014-01-01</p> <p><span class="hlt">African</span> Americans have exceptionally high rates of hypertension and hypertension related complications. It is commonly reported that the blood pressure lowering efficacy of renin angiotensin <span class="hlt">system</span> (RAS) inhibitors is attenuated in <span class="hlt">African</span> Americans due to a greater likelihood of having a low renin profile. Therefore these agents are often not recommended as initial therapy in <span class="hlt">African</span> Americans with hypertension. However, the high prevalence of comorbid conditions, such as diabetes, cardiovascular and chronic kidney disease makes treatment with RAS inhibitors more compelling. Despite lower circulating renin levels and a less significant fall in blood pressure in response to RAS inhibitors in <span class="hlt">African</span> Americans, numerous clinical trials support the efficacy of RAS inhibitors to improve clinical outcomes in this population, especially in those with hypertension and risk factors for cardiovascular and related diseases. Here, we discuss the rationale of RAS blockade as part of a comprehensive approach to attenuate the high rates of premature morbidity and mortality associated with hypertension among <span class="hlt">African</span> Americans. PMID:25276290</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.6029E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.6029E"><span id="translatedtitle">Characterization of basement highs in hyper-extended <span class="hlt">rift</span> <span class="hlt">systems</span>: examples from the Err nappe, SE Switzerland.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Epin, Marie-Eva; Manatschal, Gianreto; Haupert, Isabelle; Decarlis, Alessandro</p> <p>2015-04-01</p> <p>Despite of the fact that many studies investigated magma-poor <span class="hlt">rifted</span> margins, there are still open questions that are related to the nature of basement highs and the timing and processes related to their formation. While these questions are difficult to answer at present-day margins due to the lack of drill hole data, field analogues provide important insights and enable to find some answers to these questions. This is particularly true for the Err nappe in southeastern Switzerland, which is one of the world's few exposed and preserved <span class="hlt">rift</span>-related hyper-extended domains. This nappe preserves a <span class="hlt">rift</span> related extensional detachment <span class="hlt">system</span> that is exposed over more than 200km2, characterized by distinctive black gouges and green cataclasites and preserving the relation to its hanging wall and footwall rocks and the pre-, syn-, and post-tectonic sediments. The aim of our study was to investigate the 3D architecture of the detachment <span class="hlt">system</span> based on detailed mapping of this structure north and south of the Julier valley between Bivio and San Moritz in Central Grisons, SE Switzerland. Our results show the lateral variation of the morphology of the major detachment fault and its relation to extensional allochthons and the pre-, syn- and post-tectonic sediments. The main observation is that the architecture of the detachment <span class="hlt">system</span> changes over very short distance across the Julier valley. While in the north the detachment is overlain by an allochthonous block (e.g. the Bardella block), to the south this block disappears and the detachment fault is exhumed at the seafloor. The mapping of the syn-tectonic sediments show that they are thick in the north and get thinner to the south where they are locally absent and the post-<span class="hlt">rift</span> sediments directly overlie the detachment <span class="hlt">system</span>. Furthermore the syn-tectonic sediments are locally characterized by basement clasts. These relationships suggest a rapid change from a domain where the detachment is overlain by allochthons and thick</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70027062','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70027062"><span id="translatedtitle">A hydrogeologic model of stratiform copper mineralization in the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span>, Northern Michigan, USA</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Swenson, J.B.; Person, M.; Raffensperger, J.P.; Cannon, W.F.; Woodruff, L.G.; Berndt, M.E.</p> <p>2004-01-01</p> <p>This paper presents a suite of two-dimensional mathematical models of basin-scale groundwater flow and heat transfer for the middle Proterozoic Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span>. 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 <span class="hlt">systems</span> 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 <span class="hlt">systems</span> did not produce focused discharge in the vicinity of the White Pine ore district.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1989PEPI...58...52Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1989PEPI...58...52Z"><span id="translatedtitle">Recent seismic activity of the Kivu Province, Western <span class="hlt">Rift</span> Valley of Africa</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zana, N.; Kamba, M.; Katsongo, S.; Janssen, Th.</p> <p>1989-11-01</p> <p>The Kivu Province is located at the junction between the well-defined Ruzizi Valley to the south and the Lake Amin Trough to the north. In this zone, the <span class="hlt">Rift</span> Valley is characterized by the highest uplift and by complex dislocations of the crust, accompanied by the most intensive volcanism of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>. In this paper, we show the recent state of the seismic activity of this zone in connection with the seismic activity generated by the volcanoes Nyiragongo and Nyamuragira. The pattern of cumulative energy release by these volcanoes shows a steplike increase that is believed to be a precursor of volcanic eruptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/7036216','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/7036216"><span id="translatedtitle">Probing the processes and products of an ancient continental crustal rupture: Scientific drillng into the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hinz, W.J.</p> <p>1988-01-01</p> <p>Geochemical and geophysical investigations over the past decade suggest a laterally as well radially heterogeneous upper mantle. The sources of this variability are mantle dynamics and interactions with the crust. The opportunities to sample these variations directly are limited within continental regions. However, the basalts of the Midcontinent <span class="hlt">Rift</span> (MCR) <span class="hlt">System</span> of North America are particularly attractive for studying subcontinental mantle. The MCR is an 1100 Ma paleorift that extends for more than 2000 km across the North American midcontinent. Drill holes into the MCR to obtain samples of the basalt can be located to answer critical questions regarding the origin and evolution of this aborted Precambrian <span class="hlt">rift</span>. Outcrops of the MCR rocks occur only in the Lake Superior region, and the rocks that crop out are restricted largely to the margins of the structure and the upper part of the stratigraphic section. Available drill holes are shallow and poorly distributed for scientific purposes and provide only limited samples for analysis. Many sites along the <span class="hlt">rift</span> have been pinpointed where holes of 5 km or less in depth can be drilled to sample the Proterozoic (Keweenawan) igneous rocks of the <span class="hlt">rift</span>. In September, 1987, approximately 90 geoscientists from North America and Europe met in Duluth, Minnesota, for a workshop. The goals of the workshop were to define the scientific objectives of drilling the MCR and to develop a plan for achieving these objectives. As a result of the workshop and subsequent deliberations, we proposed a multi-year, multi-hole program of drilling and related scientific investigation of the MCR utilizing shallow to intermediate depth holes. 18 refs. 5 figs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tecto..34.2367T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tecto..34.2367T"><span id="translatedtitle">Cenozoic extension in the Kenya <span class="hlt">Rift</span> from low-temperature thermochronology: Links to diachronous spatiotemporal evolution of <span class="hlt">rifting</span> in East Africa</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Torres Acosta, Verónica; Bande, Alejandro; Sobel, Edward R.; Parra, Mauricio; Schildgen, Taylor F.; Stuart, Finlay; Strecker, Manfred R.</p> <p>2015-12-01</p> <p>The cooling history of <span class="hlt">rift</span> shoulders and the subsidence history of <span class="hlt">rift</span> 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 <span class="hlt">Rift</span> 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 <span class="hlt">rift</span> shoulders and may be coeval with faulting and sedimentation in the Anza <span class="hlt">Rift</span> 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 <span class="hlt">rifting</span>, which followed widespread flood-phonolite emplacement and has shaped the present-day landscape through <span class="hlt">rift</span> shoulder uplift, faulting, basin filling, protracted volcanism, and erosion. When compared with thermochronologic and geologic data from other sectors of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T53B4674B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T53B4674B"><span id="translatedtitle"><span class="hlt">Rift</span> Fault Geometry and Distribution in Layered Basaltic Rocks: A Comparison Between the Koa'e (Hawai'i) and Krafla (Iceland) Fault <span class="hlt">Systems</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bubeck, A.; Walker, R. J.; MacLeod, C. J.; Imber, J.</p> <p>2014-12-01</p> <p>Fault <span class="hlt">systems</span> within incipient <span class="hlt">rifts</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> fault <span class="hlt">system</span> on the south flank of Kilauea Volcano on Hawaii's Big Island, and the Krafla <span class="hlt">rift</span> <span class="hlt">system</span>, Iceland, to investigate the evolution of segmented <span class="hlt">rift</span> fault <span class="hlt">systems</span> in layered basalts, formed at low confining pressures. Extension in the Koa'e <span class="hlt">system</span> 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 <span class="hlt">system</span> 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 <span class="hlt">systems</span> 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 <span class="hlt">rift</span> zones.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.6614I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.6614I"><span id="translatedtitle">Hydrogeological structure of a seafloor hydrothermal <span class="hlt">system</span> related to backarc <span class="hlt">rifting</span> in a continental margin setting</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ishibashi, Jun-ichiro</p> <p>2016-04-01</p> <p>Seafloor hydrothermal <span class="hlt">systems</span> in the Okinawa Trough backarc basin are considered as related to backarc <span class="hlt">rifting</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.V24B..06L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.V24B..06L"><span id="translatedtitle">Patterns of Volcanism Associated With Oligocene to Recent Dome Uplift, West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Le Masurier, W. E.</p> <p>2005-12-01</p> <p>The Marie Byrd Land dome lies on the Pacific coast of the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>. It is a structural dome defined by elevations of a low-relief erosion surface that is exposed in fault- block nunataks. The dome has roughly 3000 m of structural relief and is about 800 km in diameter.The growth of the dome has been closely associated with two rather unusual patterns of volcanic activity that provide keys to the timing and rate of uplift. (1) The ages of basaltic rocks that rest on the erosion surface become systematically older with increasing elevation of the surface, e.g. 6.27 Ma at 600 m elevation, 27 Ma at 2700 m, etc., suggesting that uplift began around 27 Ma and continued to 6 Ma at roughly 100m/m.y. (2) The oldest of 18 felsic shield volcanoes formed around 19 Ma at the dome crest. The remaining felsic volcanoes become systematically younger toward the distal flanks of the dome, along linear, fault-controlled, N-S and E-W chains. Late Pleistocene (active) volcanoes lie at the north, south, east, and west margins of the dome, suggesting that uplift proceeded systematically from 19 Ma to the present by centrifugal extension of relict fractures during uplift, accompanied by the rise of felsic magmas from crustal reservoirs. Teleseismic studies (Winberry and Anandakrishnan, 2004) show that the crust has been thinned over the dome crest, and that the dome is supported by low density mantle. Tomographic images near the dome (Sieminski, et al., 2003) show a low velocity column extending down to the transition zone. The Antarctic plate has been stationary at least since the Eocene. In the apparent absence of a mechanism driven by plate tectonics, it is reasonable to infer that mantle plume activity has produced these spatial and temporal patterns of volcanism focused around dome uplift, rather than the more familiar linear volcanic chains associated with moving plates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..11.5475Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..11.5475Z"><span id="translatedtitle">Land - Ocean Climate Linkages and the Human Evolution - New ICDP and IODP Drilling Initiatives in the East <span class="hlt">African</span> <span class="hlt">Rift</span> Valley and SW Indian Ocean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zahn, R.; Feibel, C.; Co-Pis, Icdp/Iodp</p> <p>2009-04-01</p> <p>, and Interocean Exchanges"; IODP ref. no. 702-full) aims at deciphering the late Neogene ocean history of the SW Indian Ocean. SAFARI specifically targets the Agulhas Current in the SW Indian Ocean that constitutes the strongest western boundary current in the southern hemisphere oceans. The Current transports warm and saline surface waters from the tropical Indian Ocean to the southern tip of Africa. Exchanges with the atmosphere influence eastern and southern <span class="hlt">African</span> climates including individual weather <span class="hlt">systems</span> such as extra-tropical cyclone formation in the region and rainfall patterns. Ocean models further suggest the "leakage" of Agulhas water around South Africa into the Atlantic potentially modulates the Atlantic meridional overturning circulation (MOC) with consequences for climate globally. The SAFARI drilling initiative aims to retrieve a suite of long drill cores along the southeast <span class="hlt">African</span> margin and in the Indian-Atlantic ocean gateway. SAFARI will shed light on the history of Agulhas Current warm water transports along the southeast <span class="hlt">African</span> margin during the late Neogene and its linking with ocean-climate developments. Specific objectives of SAFARI are to test (1) the sensitivity of the Agulhas Current to changing climates of the Plio/Pleistocene, including upstream forcing linked with equatorial Indian Ocean changes and Indonesian Throughflow; (2) the Current's influence on eastern and southern Africa climates, including rain fall patterns and vegetation changes; (3) buoyancy transfer to the Atlantic by Agulhas leakage around southern Africa, and (4) the contribution of variable Agulhas Leakage to shifts of the Atlantic MOC during episodes of major ocean and climate reorganizations of the past 5 Ma. These studies will provide insight into the Current's influence on eastern and southern <span class="hlt">African</span> terrestrial climates, including its possible impact on the late Neogene evolution of large mammals including hominids. The ICDP and IODP drilling campaigns will</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008cosp...37..636D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008cosp...37..636D"><span id="translatedtitle">Using of Remote Sensing Techniques for Monitoring the Earthquakes Activities Along the Northern Part of the Syrian <span class="hlt">Rift</span> <span class="hlt">System</span> (LEFT-LATERAL),SYRIA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dalati, Moutaz</p> <p></p> <p>Earthquake mitigation can be achieved with a better knowledge of a region's infra-and substructures. High resolution Remote Sensing data can play a significant role to implement Geological mapping and it is essential to learn about the tectonic setting of a region. It is an effective method to identify active faults from different sources of Remote Sensing and compare the capability of some satellite sensors in active faults survey. In this paper, it was discussed a few digital image processing approaches to be used for enhancement and feature extraction related to faults. Those methods include band ratio, filtering and texture statistics . The experimental results show that multi-spectral images have great potentials in large scale active faults investigation. It has also got satisfied results when deal with invisible faults. Active Faults have distinct features in satellite images. Usually, there are obvious straight lines, circular structures and other distinct patterns along the faults locations. Remotely Sensed imagery Landsat ETM and SPOT XS /PAN are often used in active faults mapping. Moderate and high resolution satellite images are the best choice, because in low resolution images, the faults features may not be visible in most cases. The area under study is located Northwest of Syria that is part of one of the very active deformation belt on the Earth today. This area and the western part of Syria are located along the great <span class="hlt">rift</span> <span class="hlt">system</span> (Left-Lateral or <span class="hlt">African</span>- Syrian <span class="hlt">Rift</span> <span class="hlt">System</span>). Those areas are tectonically active and caused a lot of seismically events. The AL-Ghab graben complex is situated within this wide area of Cenozoic deformation. The <span class="hlt">system</span> formed, initially, as a result of the break up of the Arabian plate from the <span class="hlt">African</span> plate. This action indicates that these sites are active and in a continual movement. In addition to that, the statistic analysis of Thematic Mapper data and the features from a digital elevation model ( DEM )produced from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MarGR..36..263K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MarGR..36..263K"><span id="translatedtitle"><span class="hlt">Rift</span> processes and crustal structure of the Amundsen Sea Embayment, West Antarctica, from 3D potential field modelling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kalberg, Thomas; Gohl, Karsten; Eagles, Graeme; Spiegel, Cornelia</p> <p>2015-12-01</p> <p>The Amundsen Sea Embayment of West Antarctica is of particular interest as it provides critical geological boundary conditions in better understanding the dynamic behavior of the West Antarctic Ice Sheet, which is undergoing rapid ice loss in the Amundsen Sea sector. One of the highly debated hypothesis is whether this region has been affected by the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>, which is one of the largest in the world and the dominating tectonic feature in West Antarctica. Previous geophysical studies suggested an eastward continuation of this <span class="hlt">rift</span> <span class="hlt">system</span> into the Amundsen Sea Embayment. This geophysical study of the Amundsen Sea Embayment presents a compilation of data collected during two RV Polarstern expeditions in the Amundsen Sea Embayment of West Antarctica in 2006 and 2010. Bathymetry and satellite-derived gravity data of the Amundsen Sea Embayment complete the dataset. Our 3-D gravity and magnetic models of the lithospheric architecture and development of this Pacific margin improve previous interpretations from 2-D models of the region. The crust-mantle boundary beneath the continental rise and shelf is between 14 and 29 km deep. The imaged basement structure can be related to <span class="hlt">rift</span> basins within the Amundsen Sea Embayment, some of which can be interpreted as products of the Cretaceous <span class="hlt">rift</span> and break-up phase and some as products of later propagation of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> into the region. An estimate of the flexural rigidity of the lithosphere reveals a thin elastic thickness in the eastern embayment which increases towards the west. The results are comparable to estimates in other <span class="hlt">rift</span> <span class="hlt">systems</span> such as the Basin and Range province or the East <span class="hlt">African</span> <span class="hlt">Rift</span>. Based on these results, we infer an arm of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> is superposed on a distributed Cretaceous <span class="hlt">rift</span> province in the Amundsen Sea Embayment. Finally, the embayment was affected by magmatism from discrete sources along the Pacific margin of West Antarctica in the Cenozoic.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850056208&hterms=Cenozoic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DCenozoic','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850056208&hterms=Cenozoic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DCenozoic"><span id="translatedtitle">Cenozoic <span class="hlt">rift</span> formation in the northern Caribbean</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mann, P.; Burke, K.</p> <p>1984-01-01</p> <p><span class="hlt">Rifts</span> 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 <span class="hlt">rifts</span> 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 <span class="hlt">rifts</span> become progressively younger westward; (2) a two-phase subsidence history in a <span class="hlt">rift</span> exposed by upthrusting in Jamaica; (3) the absence of <span class="hlt">rifts</span> east of Jamaica; and (4) the observation that removal of 1400 km of strike-slip displacement on the Cayman Trough fault <span class="hlt">system</span> places the Paleogene <span class="hlt">rifts</span> of Jamaica in an active area of extension south of Yucatan where the <span class="hlt">rifts</span> of Honduras and Guatemala are forming today.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.4244Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.4244Z"><span id="translatedtitle">How oblique extension and structural inheritance control <span class="hlt">rift</span> segment linkage: Insights from 4D analogue models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zwaan, Frank; Schreurs, Guido</p> <p>2016-04-01</p> <p>INTRODUCTION During the early stages of <span class="hlt">rifting</span>, <span class="hlt">rift</span> segments may form along non-continuous and/or offset pre-existing weaknesses. It is important to understand how these initial <span class="hlt">rift</span> segments interact and connect to form a continuous <span class="hlt">rift</span> <span class="hlt">system</span>. A previous study of ours (Zwaan et al., in prep) investigated the influence of dextral oblique extension and <span class="hlt">rift</span> offset on <span class="hlt">rift</span> interaction. Here we elaborate upon our previous work by using analogue models to assess the added effects of 1) sinistral oblique extension as observed along the East <span class="hlt">African</span> <span class="hlt">Rift</span> and 2) the geometry of linked and non-linked inherited structures. METHODS Our set-up involves a base of foam and plexiglass that forces distributed extension in the overlying model materials: a sand layer for the brittle upper crust and a viscous sand/silicone mixture for ductile lower crust. A mobile base plate allows lateral motion for oblique extension. We create inherited structures, along which <span class="hlt">rift</span> segments develop, with right-stepping offset lines of silicone (seeds) on top of the basal viscous layer. These seeds can be connected by an additional weak seed that represents a secondary inherited structural grain (model series 1) or disconnected and laterally discontinuous (over/underlap, model series 2). Selected models are run in an X-ray computer topographer (CT) to reveal the 3D evolution of internal structures with time that can be quantified with particle image velocitmetry (PIV) techniques. RESULTS Models in both series show that <span class="hlt">rift</span> segments initially form along the main seeds and then generally propagate approximately perpendicular to the extension direction: with orthogonal extension they propagate in a parallel fashion, dextral oblique extension causes them to grow towards each other and connect, while with sinistral oblique extension they grow away from each other. However, sinistral oblique extension can also promote <span class="hlt">rift</span> linkage through an oblique- or strike-slip zone oriented almost parallel to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T51H..06F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T51H..06F"><span id="translatedtitle">The MOZART Project - MOZAmbique <span class="hlt">Rift</span> Tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fonseca, J. F.; Chamussa, J. R.; Domingues, A.; Helffrich, G. R.; Fishwick, S.; Ferreira, A. M.; Custodio, S.; Brisbourne, A. M.; Grobbelaar, M.</p> <p>2012-12-01</p> <p>Project MOZART (MOZAmbique <span class="hlt">Rift</span> Tomography) is an ongoing joint effort of Portuguese, Mozambican and British research groups to investigate the geological structure and current tectonic activity of the southernmost tip of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) through the deployment of a network of 30 broad band seismic stations in Central and Southern Mozambique. In contrast with other stretches of the EARS to the North and with the Kapvaal craton to the West and South, the lithosphere of Mozambique was not previously studied with a dense seismographic deployment on account of past political instability, and many questions remain unanswered with respect to the location and characteristics of the EARS to the south of Tanzania. In recent years, space geodesy revealed the existence of three microplates in and off Mozambique - Victoria, Rovuma, Lwandle - whose borders provide a connection of the EARS to the South West Indian Ridge as required by plate tectonics. However, the picture is still coarse concerning the location of the <span class="hlt">rift</span> structures. The 2006 M7 Machaze earthquake in Central Mozambique highlighted the current tectonic activity of the region and added a further clue to the location of the continental <span class="hlt">rift</span>, prompting the MOZART deployment. Besides helping unravel the current tectonics, the project is expected to shed light on the poorly known Mesoproterozoic structure described by Arthur Holmes in 1951 as the Mozambique Belt, and on the mechanisms of transition from stable craton to <span class="hlt">rifted</span> continental crust, through the development of a tomographic model for the lithosphere. The MOZART network is distributed South of the Zambezi river at average inter-station spaces of the order of 100 km and includes four stations across the border in South Africa. Data exchange was agreed with AfricaArray. The deployment proceeded in two phases in March 2011, and November and December 2011. Decommissioning is foreseen for August 2013. We report preliminary results for this</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JAfES.121..136H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JAfES.121..136H"><span id="translatedtitle"><span class="hlt">Rift</span>-related active fault-<span class="hlt">system</span> and a direction of maximum horizontal stress in the Cairo-Suez district, northeastern Egypt: A new approach from EMR-Technique and Cerescope data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hagag, Wael; Obermeyer, Hennes</p> <p>2016-09-01</p> <p>An active fault <span class="hlt">system</span> has been detected along the Cairo-Suez district in northeastern Egypt, applying the EMR-Technique using Cerescope. The E-W (old Mediterranean) and NW-SE (Red Sea-Gulf of Suez) fault-trends are estimated to have ongoing activity. Horizontal EMR-measurements indicate a NW to NNW orientation as a maximum horizontal stress direction (σ1), whereas an E-W orientation to has a secondary tendency. A simplified stress map for the Cairo-Suez district is constructed from the horizontal stress data measured at about 20 locations within the district. The mapped stresses will contribute to the stress data of the Cairo-Suez region on the world stress map (WSM). The present study results indicate rejuvenation of the inherited Mesozoic E-W oriented and Oligocene-Miocene <span class="hlt">rift</span>-related NW-SE oriented faults. The transfer of <span class="hlt">rift</span>-related deformation from Red Sea-Gulf of Suez region, which is currently undergoing an extensional stress regime in NE to NNE direction, would explain a seismotectonic activity of the Cairo-Suez district. These results are consistent with a present day NNW oriented compressional stresses attributed to a convergence between the <span class="hlt">African</span> and Eurasian plates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMDI24A..04H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMDI24A..04H"><span id="translatedtitle">Mapping Mantle Mixing and the Extent of Superplume Influence Using He-Ne-Ar-CO2-N2 Isotopes: The Case of the East Africa <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hilton, D. R.; Halldorsson, S. A.; Scarsi, P.; Castillo, P.; Abebe, T.; Kulongoski, J. T.</p> <p>2014-12-01</p> <p>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 <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> (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 <span class="hlt">Rift</span> (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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70020527','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70020527"><span id="translatedtitle">The provenance and chemical variation of sandstones associated with the Mid-continent <span class="hlt">Rift</span> <span class="hlt">System</span>, U.S.A.</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Cullers, R.L.; Berendsen, P.</p> <p>1998-01-01</p> <p>Sandstones along the northern portion of the Precambrian Mid-continent <span class="hlt">Rift</span> <span class="hlt">System</span> (MRS) have been petrographically and chemically analyzed for major elements and a variety of trace elements, including the REE. After the initial extrusion of the abundant basalts along the MRS, dominantly volcaniclastic sandstones of the Oronto Group were deposited. These volcaniclastic sandstones are covered by quartzose and subarkosic sandstones of the Bayfield Group. Thus the sandstones of the Oronto Group were derived from previously extruded basalts, whereas, the sandstones of the Bayfield Group were derived from Precambrian granitic gneisses located on the <span class="hlt">rift</span> flanks. The chemical variation of these sandstones closely reflects the changing detrital modes with time. The elemental composition of the sandstones confirms the source lithologies suggested by the mineralogy and clasts. The Oronto Group sandstones contain lower ratios of elements concentrated in silicic source rocks (La or Th) relative to elements concentrated in basic source rocks (Co, Cr, or Sc) than the Bayfield Group. Also, the average size of the negative Eu anomaly of the sandstones of the Oronto Group is significantly less (Eu/Eu* mean ?? standard deviation = 0.79 ?? 0.13) than that of the Bayfield Group (mean + standard deviation = 0.57 ?? 0.09), also suggesting a more basic source for the former than the latter. Mixing models of elemental ratios give added insight as to the evolution of the <span class="hlt">rift</span>. These models suggest that the volcanistic sandstones of the lower portion of the Oronto Group are derived from about 80 to 90 percent basalt and 10 to 20 percent granitoids. The rest of the Oronto Group and the lower to middle portion of the Bayfield Group could have formed by mixing of about 30 to 60 percent basalt and 40 to 70 percent granitoids. The upper portion of the Bayfield Group is likely derived from 80 to 100 percent granitoids and zero to 20 percent basalt.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JAfES..57..345K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JAfES..57..345K"><span id="translatedtitle">Active fault segments as potential earthquake sources: Inferences from integrated geophysical mapping of the Magadi fault <span class="hlt">system</span>, southern Kenya <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kuria, Z. N.; Woldai, T.; van der Meer, F. D.; Barongo, J. O.</p> <p>2010-06-01</p> <p> uplifted, heavily fractured and deformed basin to the north (highly disturbed magnetic signatures) characteristic of on going active <span class="hlt">rifting</span>; and a refined architecture of the asymmetry graben to the south with an intrarift horst, whose western graben is 4 km deep and eastern graben is much deeper (9 km), with a zone of significant break in magnetic signatures at that depth, interpreted as source of the hot springs south of Lake Magadi (a location confirmed near surface by ground magnetic and resistivity data sets). The magnetic sources to the north are shallow at 15 km depth compared to 22 km to the south. The loss of magnetism to the north is probably due to increased heat as a result of magmatic intrusion supporting active <span class="hlt">rifting</span> model. Conclusively, the integrated approach employed in this research confirms that fault <span class="hlt">system</span> delineated to the north is actively deforming under E-W normal extension and is a potential earthquake source probably related to magmatic intrusion, while the presence of fluids within the south fault zone reduce intensity of faulting activity and explains lack of earthquakes in a continental <span class="hlt">rift</span> setting.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050176001','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050176001"><span id="translatedtitle">Parga Chasma: Coronae and <span class="hlt">Rifting</span> on Venus</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smrekar, S. E.; Stofan, E. R.; Buck, W. R.; Martin, P.</p> <p>2005-01-01</p> <p>The majority of coronae (quasicircular volcano-tectonic features) are found along <span class="hlt">rifts</span> or fracture belts, and the majority of <span class="hlt">rifts</span> have coronae [e.g. 1,2]. However, the relationship between coronae and <span class="hlt">rifts</span> remains unclear [3-6]. There is evidence that coronae can form before, after, or synchronously with <span class="hlt">rifts</span> [3,4]. The extensional fractures in the <span class="hlt">rift</span> zones have been proposed to be a result of broad scale upwelling and traction on the lower lithosphere [7]. However, not all <span class="hlt">rift</span> <span class="hlt">systems</span> have a significant positive geoid anomaly, as would be expected for an upwelling site [8]. This could be explained if the <span class="hlt">rifts</span> lacking anomalies are no longer active. Coronae are generally accepted to be sites of local upwelling [e.g. 1], but the observed <span class="hlt">rifting</span> 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 <span class="hlt">rifts</span> 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 <span class="hlt">rifts</span>. 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].</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=Defending+AND+National+AND+Interest&id=ED266067','ERIC'); return false;" href="http://eric.ed.gov/?q=Defending+AND+National+AND+Interest&id=ED266067"><span id="translatedtitle">The Fundamentals of an <span class="hlt">African</span> American Value <span class="hlt">System</span>.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Alexander, E. Curtis</p> <p></p> <p>The Nguzo Saba or "Seven Principles of Blackness" provide the fundamental basis for the development of an <span class="hlt">African</span> America value <span class="hlt">system</span> that is based on the cultural and historical particularisms of being Black in an American society that devalues Black efficacy and Black people. The fundamentals of this value <span class="hlt">system</span>, foundational to the Kwanzaa…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=meagre&pg=2&id=EJ131895','ERIC'); return false;" href="http://eric.ed.gov/?q=meagre&pg=2&id=EJ131895"><span id="translatedtitle">Welfare <span class="hlt">Systems</span> and <span class="hlt">African</span>-Americans: Historical Notes</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Nicholson, Rosetta</p> <p>1975-01-01</p> <p>An historical discussion of the relationship of American welfare <span class="hlt">systems</span> to <span class="hlt">African</span>-Americans, stating that Europeans, primarily from England, reluctantly established meagre, inhumane welfare <span class="hlt">systems</span> based on seventeenth century English philosophy and tradition for members of their own nationality group after more than two centuries of poverty in…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2007/1047/kp/kp09/of2007-1047kp09.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2007/1047/kp/kp09/of2007-1047kp09.pdf"><span id="translatedtitle">Tectonics of the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>: new light on the history and dynamics of distributed intracontinental extension</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Siddoway, C.S.</p> <p>2007-01-01</p> <p>The West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> (WARS) is the product of multiple stages of intracontinental deformation from Jurassic to Present. The Cretaceous <span class="hlt">rifting</span> 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 <span class="hlt">system</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T24B..06L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T24B..06L"><span id="translatedtitle">Stress Pattern of the Shanxi <span class="hlt">Rift</span> <span class="hlt">System</span>, North China, Inferred from the Inversion of New Focal Mechanisms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, B.; Atakan, K.; Sorensen, M. B.; Havskov, J.</p> <p>2014-12-01</p> <p>Earthquake focal mechanisms of the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>, North China, are investigated for the time period 1965 - Apr. 2014. A total of 143 focal mechanisms of ML ≥ 3.0 earthquakes were compiled. Among them, 105 solutions are newly determined by combining the P-wave first motions and full waveform inversion, and 38 solutions are from available published data. Stress tensor inversion was then performed based on the new database. The results show that most solutions exhibit normal or strike-slip faulting, and the regional stress field is characterized by a stable, dominating NNW-SSE extension and an ENE-WSW compression. This correlates well with results from GPS data, geological field observations and leveling measurements across the faults. Heterogeneity exists in the regional stress field, as indicated by individual stress tensor inversions conducted for five subzones. While the minimum stress axis (σ3) appears to be consistent and stable, the orientations, especially the plunges, of the maximum and intermediate stresses (σ1 and σ2) vary significantly among the different subzones. Based on our results and combining multidisciplinary observations from geological surveys, GPS and cross-fault monitoring, a kinematic model is proposed, to illustrate the present-day stress field and its correlation with the regional tectonics, as well as the current crustal deformation of the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>. Results obtained in this study, may help to understand the geodynamics, neotectonic activity, active seismicity and potential seismic hazard in this region of North China.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Tectp.688...65J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Tectp.688...65J"><span id="translatedtitle">Jurassic failed <span class="hlt">rift</span> <span class="hlt">system</span> below the Filchner-Ronne-Shelf, Antarctica: New evidence from geophysical data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jokat, Wilfried; Herter, Ulrich</p> <p>2016-10-01</p> <p>During the austral summer of 1994/95, reasonable ice conditions in the Weddell Sea allowed the acquisition of new high quality seismic refraction data parallel to the Filchner-Ronne Ice Shelf (FRS), Antarctica. Although pack ice conditions resulted in some data gaps, the final velocity-depth/2D-density models cover the entire FRS in E-W direction using all available deep seismic data/picks from this remote area. The velocity-depth model shows a sedimentary basin with a thickness up to 12 km and a large velocity inversion in the lowermost sedimentary unit. The crustal thickness reaches a maximum of 40 km along the basin's margins in the Antarctic Peninsula and East Antarctica. In the central shelf area, numerous interfering seismic phases occur from the crust-mantle boundary at decreasing distances indicating a thinning of the crust. Here, the modelled velocities and densities reveal a thickness of 20 km for the igneous crust. This corridor of overthickened oceanic or close to oceanic crust is 160 km wide. The corridor is characterized by weak, but in general continuous magnetic anomalies, which we interpret as isochrons developed during the <span class="hlt">rifting</span> or the initial formation of oceanic crust. If the crustal composition represents an old stripe of oceanic crust, a minimum estimate for the early formation of the oceanic crust is 145/148 Ma (Late Jurassic). However, based on the velocity of <span class="hlt">rift</span> propagation during the initial opening of the adjacent Weddell Sea the oceanic crust is likely to have formed around 160 Ma. The onset of <span class="hlt">rifting</span> and development of a thick igneous crust can be related to stresses developed between the interior and the southwestern paleo-Pacific subduction margin of the fragmenting Gondwana supercontinent in combination with additional melt supply from a deeper mantle source that arrived and spread in the period 183-155 Ma.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70016810','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70016810"><span id="translatedtitle">Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> and a speculation on possible climate forcing</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Behrendt, John C.; Cooper, A.</p> <p>1991-01-01</p> <p>The Cenozoic West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span> and waxing and waning of the Antarctic ice sheet beginning about earliest Oligocene time. -from Authors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850066340&hterms=Continental+Drift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DContinental%2BDrift','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850066340&hterms=Continental+Drift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DContinental%2BDrift"><span id="translatedtitle">Is the Ventersdorp <span class="hlt">rift</span> <span class="hlt">system</span> of southern Africa related to a continental collision between the Kaapvaal and Zimbabwe Cratons at 2.64 Ga AGO?</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burke, K.; Kidd, W. S. F.; Kusky, T.</p> <p>1985-01-01</p> <p>Rocks of the Ventersdorp Supergroup were deposited in a <span class="hlt">system</span> 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 <span class="hlt">rifting</span>. 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 <span class="hlt">rift</span> province is related to extension in the Kaapvaal Craton associated with the collision, and some analogy is seen with such <span class="hlt">rifts</span> as the Shansi and Baikal <span class="hlt">Systems</span> associated with the current India-Asia continental collision.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tectp.663..177D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tectp.663..177D"><span id="translatedtitle">The inverted Triassic <span class="hlt">rift</span> of the Marrakech High Atlas: A reappraisal of basin geometries and faulting histories</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Domènech, Mireia; Teixell, Antonio; Babault, Julien; Arboleya, Maria-Luisa</p> <p>2015-11-01</p> <p>The High Atlas of Morocco is an aborted <span class="hlt">rift</span> developed during the Triassic-Jurassic and moderately inverted during the Cenozoic. The Marrakech High Atlas, with large exposures of basement and Triassic early syn-<span class="hlt">rift</span> deposits, is ideal to investigate the geometries of the deepest parts of a <span class="hlt">rift</span>, constituting a good analogue for pre-salt domains. It allows unraveling geometries and kinematics of the extensional and compressional structures and the influence that they exert over one another. A detailed structural study of the main Triassic basins and basin-margin faults of the Marrakech High Atlas shows that only a few <span class="hlt">rift</span> faults were reactivated during the Cenozoic compressional stage in contrast to previous interpretations, and emphasizes that fault reactivation cannot be taken for granted in inverted <span class="hlt">rift</span> <span class="hlt">systems</span>. Preserved extensional features demonstrate a dominant dip-slip opening kinematics with strike-slip playing a minor role, at variance to models proposing a major strike-slip component along the main basin-bounding faults, including faults belonging to the Tizi n'Test fault zone. A new Middle Triassic paleogeographic reconstruction shows that the Marrakech High Atlas was a narrow and segmented orthogonal <span class="hlt">rift</span> (sub-perpendicular to the main regional extension direction which was ~ NW-SE), in contrast to the central and eastern segments of the Atlas <span class="hlt">rift</span> which developed obliquely. This difference in orientation is attributed to the indented Ouzellarh Precambrian salient, part of the West <span class="hlt">African</span> Craton, which deflected the general <span class="hlt">rift</span> trend in the area evidencing the major role of inherited lithospheric anisotropies in <span class="hlt">rift</span> direction and evolution. As for the Cenozoic inversion, total orogenic shortening is moderate (~ 16%) and appears accommodated by basement-involved large-scale folding, and by newly formed shortcut and by-pass thrusting, with rare left-lateral strike-slip indicators. Triassic faults commonly acted as buttresses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21295425','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21295425"><span id="translatedtitle">[<span class="hlt">Rift</span> Valley fever].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pépin, M</p> <p>2011-06-01</p> <p><span class="hlt">Rift</span> Valley Fever (RVF) is a zoonotic arbovirosis. Among animals, it mainly affects ruminants, causing abortions in gravid females and mortality among young animals. In humans, RVF virus infection is usually asymptomatic or characterized by a moderate fever. However, in 1 to 3% of cases, more severe forms of the disease (hepatitis, encephalitis, retinitis, hemorrhagic fever) can lead to the death of infected individuals or to major sequels. The RVF virus (Bunyaviridae, genus Phlebovirus) was identified for the first time in the 1930s in Kenya. It then spread over almost all <span class="hlt">African</span> countries, sometimes causing major epizootics/epidemics. In 2000, the virus was carried out of Africa, in the Middle East Arabian Peninsula. In 2007-2008, Eastern-<span class="hlt">African</span> countries, including Madagascar, reported significant episodes of RVF virus, this was also the case for the Comoros archipelago and the French island of Mayotte. This ability to spread associated with many vectors, including in Europe, and high viral loads in infected animals led the health authorities worldwide to warn about the potential emergence of RVF virus in areas with a temperate climate. The awareness has increased in recent years with climate changes, which may possibly modify the vector distribution and competence, and prompted many RVF virus-free countries to better prepare for a potential implantation of RVF.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28235305','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28235305"><span id="translatedtitle">Seroprevalence of <span class="hlt">Rift</span> Valley fever and lumpy skin disease in <span class="hlt">African</span> buffalo (<i>Syncerus caffer</i>) in the Kruger National Park and Hluhluwe-iMfolozi Park, South Africa.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fagbo, Shamsudeen; Coetzer, Jacobus A W; Venter, Estelle H</p> <p>2014-10-16</p> <p><span class="hlt">Rift</span> Valley fever and lumpy skin disease are transboundary viral diseases endemic in Africa and some parts of the Middle East, but with increasing potential for global emergence. Wild ruminants, such as the <span class="hlt">African</span> buffalo (Syncerus caffer), are thought to play a role in the epidemiology of these diseases. This study sought to expand the understanding of the role of buffalo in the maintenance of <span class="hlt">Rift</span> Valley fever virus (RVFV) and lumpy skin disease virus (LSDV) by determining seroprevalence to these viruses during an inter-epidemic period. Buffaloes from the Kruger National Park (n = 138) and Hluhluwe-iMfolozi Park (n = 110) in South Africa were sampled and tested for immunoglobulin G (IgG) and neutralising antibodies against LSDV and RVFV using an indirect enzyme-linked immunosorbent assay (I-ELISA) and the serum neutralisation test (SNT). The I-ELISA for LSDV and RVFV detected IgG antibodies in 70 of 248 (28.2%) and 15 of 248 (6.1%) buffaloes, respectively. Using the SNT, LSDV and RVFV neutralising antibodies were found in 5 of 66 (7.6%) and 12 of 57 (21.1%), respectively, of samples tested. The RVFV I-ELISA and SNT results correlated well with previously reported results. Of the 12 SNT RVFV-positive sera, three (25.0%) had very high SNT titres of 1:640. Neutralising antibody titres of more than 1:80 were found in 80.0% of the positive sera tested. The LSDV SNT results did not correlate with results obtained by the I-ELISA and neutralising antibody titres detected were low, with the highest (1:20) recorded in only two buffaloes, whilst 11 buffaloes (4.4%) had evidence of co-infection with both viruses. Results obtained in this study complement other reports suggesting a role for buffaloes in the epidemiology of these diseases during inter-epidemic periods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T53B4678L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T53B4678L"><span id="translatedtitle">Lower Crustal Seismicity, Volatiles, and Evolving Strain Fields During the Initial Stages of Cratonic <span class="hlt">Rifting</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lambert, C.; Muirhead, J.; Ebinger, C. J.; Tiberi, C.; Roecker, S. W.; Ferdinand-Wambura, R.; Kianji, G.; Mulibo, G. D.</p> <p>2014-12-01</p> <p>The volcanically active East <span class="hlt">African</span> <span class="hlt">rift</span> <span class="hlt">system</span> in southern Kenya and northern Tanzania transects thick cratonic lithosphere, and comprises several basins characterized by deep crustal seismicity. The US-French-Tanzania-Kenya CRAFTI project aims to understand the role of magma and volatile movement during the initiation and evolution of <span class="hlt">rifting</span> in cratonic lithosphere. Our 38-station broadband network spans all or parts of fault-bounded <span class="hlt">rift</span> segments, enabling comparison of lithospheric structure, fault kinematics, and seismogenic layer thickness with age and proximity to the deeply rooted Archaen craton. Seismicity levels are high in all basins, but we find profound differences in seismogenic layer thickness along the length of the <span class="hlt">rift</span>. Seismicity in the Manyara basin occurs almost exclusively within the lower crust, and in spatial clusters that have been active since 1990. In contrast, seismicity in the ~ 5 My older Magadi basin is localized in the upper crust, and the long border fault bounding the west side of the basin is seismically inactive. Between these two basins lies the Natron <span class="hlt">rift</span> segment, which shows seismicity between ~ 20 and ~2 km depth, and high concentrations at Oldoinyo Lengai and Gelai volcanoes. Older volcanoes on the uplifted western flank (e.g., Ngorongoro) experience swarms of activity, suggesting that active magmatism and degassing are widespread. Focal mechanisms of the frequent earthquakes recorded across the array are spatially variable, and indicate a stress field strongly influenced by (1) Holocene volcanoes, (2) mechanical interactions between adjacent <span class="hlt">rift</span> basins, and (3) a far-field ESE-WNW extensional stress regime. We explore the spatial correlation between zones of intense degassing along fault <span class="hlt">systems</span> and seismicity, and examine the influence of high gas pressures on lower and upper crustal seismicity in this youthful cratonic <span class="hlt">rift</span> zone.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015DokES.465.1191S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015DokES.465.1191S"><span id="translatedtitle">Modern fault formation in the Earth's crust of the Baikal <span class="hlt">rift</span> <span class="hlt">system</span> according to the data on the mechanisms of earthquake sources</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>San'kov, V. A.; Dobrynina, A. A.</p> <p>2015-11-01</p> <p>The spatial characteristics of seismotectonic deformations and the most likely fracture planes in the earthquake sources of the Baikal <span class="hlt">rift</span> <span class="hlt">system</span> (BRS) are determined using the method of cataclastic analysis of fractures [1]. It is shown that extension conditions with a strike of modern fractures parallel to the <span class="hlt">rift</span>-controlling faults are dominant in the central zone and in most of the NE flank of the BRS. The flat average dip of fractures in the earthquake sources of the main fault zones for some <span class="hlt">rift</span> depressions allow a suggestion about the flattening of faults in the middle crust. The antithetic faults are steeper. The BRS flanks are characterized by dominant shear deformations and more diverse morphogenetic faults in the earthquake sources (strike-slip faults, reversed faults, and normal faults). The modern faults at the BRS flanks weakly inherit the neotectonic structure.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeCoA.102...65R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeCoA.102...65R"><span id="translatedtitle">Geochemical evidence of mantle reservoir evolution during progressive <span class="hlt">rifting</span> along the western Afar margin</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rooney, Tyrone O.; Mohr, Paul; Dosso, Laure; Hall, Chris</p> <p>2013-02-01</p> <p>The Afar triple junction, where the Red Sea, Gulf of Aden and <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> extension zones converge, is a pivotal domain for the study of continental-to-oceanic <span class="hlt">rift</span> evolution. The western margin of Afar forms the southernmost sector of the western margin of the Red Sea <span class="hlt">rift</span> where that margin enters the Ethiopian flood basalt province. Tectonism and volcanism at the triple junction had commenced by ˜31 Ma with crustal fissuring, diking and voluminous eruption of the Ethiopian-Yemen flood basalt pile. The dikes which fed the Oligocene-Quaternary lava sequence covering the western Afar <span class="hlt">rift</span> margin provide an opportunity to probe the geochemical reservoirs associated with the evolution of a still active continental margin. 40Ar/39Ar geochronology reveals that the western Afar margin dikes span the entire history of <span class="hlt">rift</span> evolution from the initial Oligocene flood basalt event to the development of focused zones of intrusion in <span class="hlt">rift</span> marginal basins. Major element, trace element and isotopic (Sr-Nd-Pb-Hf) data demonstrate temporal geochemical heterogeneities resulting from variable contributions from the Afar plume, depleted asthenospheric mantle, and <span class="hlt">African</span> lithosphere. The various dikes erupted between 31 Ma and 22 Ma all share isotopic signatures attesting to a contribution from the Afar plume, indicating this initial period in the evolution of the Afar margin was one of magma-assisted weakening of the lithosphere. From 22 Ma to 12 Ma, however, diffuse diking during continued evolution of the <span class="hlt">rift</span> margin facilitated ascent of magmas in which depleted mantle and lithospheric sources predominated, though contributions from the Afar plume persisted. After 10 Ma, magmatic intrusion migrated eastwards towards the Afar <span class="hlt">rift</span> floor, with an increasing fraction of the magmas derived from depleted mantle with less of a lithospheric signature. The dikes of the western Afar margin reveal that magma generation processes during the evolution of this continental <span class="hlt">rift</span> margin</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.5707S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.5707S"><span id="translatedtitle">Trends and variability of East <span class="hlt">African</span> rainfall and its relationship to the Mascarene High pressure <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Seregina, Larisa; Pinto, Joaquim G.; Fink, Andreas H.; Ermert, Volker</p> <p>2016-04-01</p> <p>In the recent decades, East Africa needs to deal with strong fluctuations in seasonal rainfall including precipitation extremes. In context of climate change, such extremes can become more frequent in the future. However, regional climate projections are uncertain about the future development of seasonal precipitation in the region. Rainfall regimes over East Africa are influenced by multiple factors, including two monsoon <span class="hlt">systems</span>, several convergence zones and the <span class="hlt">Rift</span> Valley lakes. In addition, local conditions, like topography, modulate the large-scale rainfall pattern. East <span class="hlt">African</span> rainfall variability is also influenced by various teleconnections like the Indian Ocean Zonal Mode and El Niño Southern Oscillation. The study of past climate variability in East Africa requires sufficient observational data coverage in the region. As East Africa does not have a dense observational network of meteorological stations, satellite rainfall observations gain on importance in studies on climate variability in the region. The specific aim of the present study is the analysis of historic data from weather stations in East Africa (Kenya, Tanzania, Ruanda and Uganda), the use of gridded satellite products, and three-dimensional atmospheric reanalysis (e.g., ERA-Interim) to quantify climate variability in the recent past and to understand its causes. Climate variability and trends, including changes in extreme events, are evaluated using ETCCDI climate change and standardized precipitation indices. These climate indices are determined in order to investigate the variability of rainfall and its trends with the focus on recent decades. For seasonal trend analysis, an independent and non-calendaric rainfall onset criterion is introduced. In the follow-up, statistical and dynamical analyses are conducted to quantify the local impact of Mascarene High as a part of the Subtropical High Pressure Ridge on East <span class="hlt">African</span> seasonal rainfall. Possible connections to pertinent large</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70019000','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70019000"><span id="translatedtitle">Patterns of late Cenozoic volcanic and tectonic activity in the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> revealed by aeromagnetic surveys</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Behrendt, John C.; Saltus, R.; Damaske, D.; McCafferty, A.; Finn, C.A.; Blankenship, D.; Bell, R.E.</p> <p>1996-01-01</p> <p>Aeromagnetic surveys, spaced ???5 km, over widely separated areas of the largely ice- and sea-covered West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, reveal similar patterns of 100- to 1700-nT, shallow-source magnetic anomalies interpreted as evidence of extensive late Cenozoic volcanism. We use the aeromagnetic data to extend the volcanic <span class="hlt">rift</span> interpretation over West Antarctica starting with anomalies over (1) exposures of highly magnetic, late Cenozoic volcanic rocks several kilometers thick in the McMurdo-Ross Island area and elsewhere; continuing through (2) volcanoes and subvolcanic intrusions directly beneath the Ross Sea continental shelf defined by marine magnetic and seismic reflection data and aeromagnetic data and (3) volcanic structures interpreted beneath the Ross Ice Shelf partly controlled by seismic reflection determinations of seafloor depth to (4) an area of similar magnetic pattern over the West Antarctic Ice Sheet (400 km from the nearest exposed volcanic rock), where interpretations of late Cenozoic volcanic rocks at the base of the ice are controlled in part by radar ice sounding. North trending magnetic <span class="hlt">rift</span> fabric in the Ross Sea-Ross Ice Shelf and Corridor Aerogeophysics of the Southeast Ross Transect Zone (CASERTZ) areas, revealed by the aeromagnetic surveys, is probably a reactivation of older <span class="hlt">rift</span> trends (late Mesozoic?) and is superimposed on still older crosscutting structural trends revealed by magnetic terrace maps calculated from horizontal gradient of pseudogravity. Longwavelength (???100-km wide) magnetic terraces from sources within the subvolcanic basement cross the detailed survey areas. One of these extends across the Ross Sea survey from the front of the Transantarctic Mountains with an east-southeast trend crossing the north trending <span class="hlt">rift</span> fabric. The Ross Sea-Ross Ice Shelf survey area is characterized by highly magnetic northern and southern zones which are separated by magnetically defined faults from a more moderately magnetic central zone</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ESASP.740E.168L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ESASP.740E.168L"><span id="translatedtitle">Developing a Satellite Based Automatic <span class="hlt">System</span> for Crop Monitoring: Kenya's Great <span class="hlt">Rift</span> Valley, A Case Study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lucciani, Roberto; Laneve, Giovanni; Jahjah, Munzer; Mito, Collins</p> <p>2016-08-01</p> <p>The crop growth stage represents essential information for agricultural areas management. In this study we investigate the feasibility of a tool based on remotely sensed satellite (Landsat 8) imagery, capable of automatically classify crop fields and how much resolution enhancement based on pan-sharpening techniques and phenological information extraction, useful to create decision rules that allow to identify semantic class to assign to an object, can effectively support the classification process. Moreover we investigate the opportunity to extract vegetation health status information from remotely sensed assessment of the equivalent water thickness (EWT). Our case study is the Kenya's Great <span class="hlt">Rift</span> valley, in this area a ground truth campaign was conducted during August 2015 in order to collect crop fields GPS measurements, leaf area index (LAI) and chlorophyll samples.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997Tecto..16..425O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997Tecto..16..425O"><span id="translatedtitle">A shortened intraplate <span class="hlt">rift</span> <span class="hlt">system</span> in the Proterozoic Mount Isa terrane, NW Queensland, Australia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>O'Dea, Mark G.; Lister, Gordon S.; Betts, Peter G.; Pound, Katherine S.</p> <p>1997-06-01</p> <p>The Leichhardt River Fault Trough of the Mount Isa terrane developed a complex extensional architecture between approximately 1800 and 1600 Ma, forming the underlying template upon which compressional structures were superimposed during the 1590 to 1500 Ma Isan Orogeny. Basin-fill material accumulated during at least five multiphase periods of <span class="hlt">rifting</span> and associated postrift subsidence forming a stacked succession of unconformity-bounded sequences. Initial E-W extension was associated with a massive magmatic event. Half graben greater than 50 km in width and of alternating asymmetry localized the extrusion of up to 4 km of continental tholeiites. Thereafter a period of N-S extension resulted in southward tapering north tilted half graben in which synrift basaltic and siliciclastic strata accumulated. N-S extension was followed by regional postrift subsidence and the deposition of a laterally continuous quartzite-carbonate package. A multiphase period of E-W to NW-SE extension ensued during which time two unconformity-bounded sequences accumulated. The stratal architectures of these sequences are strongly asymmetric in cross section, exhibiting a pronounced rotational thickening toward the east, consistent with their deposition in the hanging walls of east dipping tilt blocks between 15 and 40 km in width. Finally, a period of N-S extension resulted in the development of E-W trending F1 drag synclines in the highest level cover rocks. The association of angular unconformities and block-bounding faults, E-W trending synclines and E-W striking faults, and the unique internal fold geometries of fault blocks suggest that many fault-bounded blocks originated as coherent structural entities during <span class="hlt">rifting</span> and continued to act as such during subsequent shortening.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010PhDT........19T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010PhDT........19T"><span id="translatedtitle">Using remote sensing, ecological niche modeling, and Geographic Information <span class="hlt">Systems</span> for <span class="hlt">Rift</span> Valley fever risk assessment in the United States</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tedrow, Christine Atkins</p> <p></p> <p>The primary goal in this study was to explore remote sensing, ecological niche modeling, and Geographic Information <span class="hlt">Systems</span> (GIS) as aids in predicting candidate <span class="hlt">Rift</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JAESc.135..257Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JAESc.135..257Z"><span id="translatedtitle">Contemporary kinematics of the Ordos block, North China and its adjacent <span class="hlt">rift</span> <span class="hlt">systems</span> constrained by dense GPS observations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhao, Bin; Zhang, Caihong; Wang, Dongzhen; Huang, Yong; Tan, Kai; Du, Ruilin; Liu, Jingnan</p> <p>2017-03-01</p> <p>The detailed kinematic pattern of the Ordos block, North China and its surrounding <span class="hlt">rift</span> <span class="hlt">systems</span> remains uncertain, mainly due to the low signal-to-noise ratio of the Global Positioning <span class="hlt">System</span> (GPS) velocity data and the lack of GPS stations in this region. In this study, we have obtained a new and dense velocity field by processing GPS data primarily collected from the Crustal Motion Observation Network of China and from other GPS networks between 1998 and 2014. The GPS velocities within the Ordos block can be interpreted as counterclockwise rotation of the block about the Euler pole with respect to the Eurasia plate. Velocity profiles across the graben-bounding faults show relatively rapid right-lateral strike-slip motion along the Yinchuan graben, with a rate of 0.8-2.6 mm/a from north to south. In addition, a right-lateral slip rate of 1.1-1.6 mm/a is estimated along the central segment of the Shanxi <span class="hlt">rift</span>. However, strike-slip motion is not detected along the northern and southern margins of the Ordos block. Conversely, significant extension motion is detected across the northwestern corner of the block, with a value of 1.6 mm/a, and along the northern segment of the Shanxi <span class="hlt">rift</span>, where an extensional rate of 1.3-1.7 mm/a is measured. Both the Daihai and Datong basins are experiencing crustal extension. On the southwestern margin of the block, deformation across the compressional zone of the Liupanshan range is subtle; however, the far-field shorting rate is as high as 3.0 mm/a, implying that this region is experiencing ongoing compression. The results reveal that present-day fault slip occurs mainly along the block bounding faults, with the exception of faults along the northern and southern margins of the block. These results provide new insights into the nature of tectonic deformation around the Ordos block, and are useful for assessing the seismic activity in this region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T32C..01A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T32C..01A"><span id="translatedtitle">Fault Growth and Propagation and its Effect on Surficial Processes within the Incipient Okavango <span class="hlt">Rift</span> Zone, Northwest Botswana, Africa (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Atekwana, E. A.</p> <p>2010-12-01</p> <p>The Okavango <span class="hlt">Rift</span> Zone (ORZ) is suggested to be a zone of incipient continental <span class="hlt">rifting</span> occuring at the distal end of the southwestern branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS), therefore providing a unique opportunity to investigate neotectonic processes during the early stages of <span class="hlt">rifting</span>. 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 <span class="hlt">systems</span>, (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 <span class="hlt">rifting</span>, explaining the apparent paradox between the fault length versus throw for this young <span class="hlt">rift</span>, (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 <span class="hlt">rifting</span> 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 <span class="hlt">rift</span> reactivation and fault growth and propagation within the ORZ.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoJI.203.1642L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoJI.203.1642L"><span id="translatedtitle">Coulomb stress evolution in the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>, North China, since 1303 associated with coseismic, post-seismic and interseismic deformation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Bin; Sørensen, Mathilde Bøttger; Atakan, Kuvvet</p> <p>2015-12-01</p> <p>The Shanxi <span class="hlt">rift</span> <span class="hlt">system</span> is one of the most active intraplate tectonic zones in the North China Block, resulting in devastating seismicity. Since 1303, the <span class="hlt">rift</span> has experienced fifteen Ms ≥ 6.5 earthquakes. Aiming at a better understanding of Coulomb stress evolution and its relationship with the seismicity in the <span class="hlt">rift</span> <span class="hlt">system</span>, 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 <span class="hlt">rift</span> <span class="hlt">system</span>. 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 <span class="hlt">rift</span> <span class="hlt">system</span>, the Linfen basin, southern and northern Taiyuan basin, Xinding basin and the north part of the <span class="hlt">rift</span> <span class="hlt">system</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span> and thus help guiding earthquake risk mitigation efforts in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70032593','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70032593"><span id="translatedtitle">Mercury isotopic composition of hydrothermal <span class="hlt">systems</span> in the Yellowstone Plateau volcanic field and Guaymas Basin sea-floor <span class="hlt">rift</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Sherman, L.S.; Blum, J.D.; Nordstrom, D.K.; McCleskey, R.B.; Barkay, T.; Vetriani, C.</p> <p>2009-01-01</p> <p>To characterize mercury (Hg) isotopes and isotopic fractionation in hydrothermal <span class="hlt">systems</span> 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 <span class="hlt">rift</span>. These samples provide an initial indication of the variability in Hg isotopic composition among marine and continental hydrothermal <span class="hlt">systems</span> 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 <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T21A2516M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T21A2516M"><span id="translatedtitle">Kinematics of the Ethiopian <span class="hlt">Rift</span> and Absolute motion of Africa and Somalia Plates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muluneh, A. A.; Cuffaro, M.; Doglioni, C.</p> <p>2013-12-01</p> <p>The Ethiopian <span class="hlt">Rift</span> (ER), in the northern part of East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS), forms a boundary zone accommodating differential motion between Africa and Somalia Plates. Its orientation was influenced by the inherited Pan-<span class="hlt">African</span> collisional <span class="hlt">system</span> and related lithospheric fabric. We present the kinematics of ER derived from compilation of geodetic velocities, focal mechanism inversions, structural data analysis, and construction of geological profiles. GPS velocity field shows a systematic eastward magnitude increase in NE direction in the central ER. In the same region, incremental extensional strain axes recorded by earthquake focal mechanism and fault slip inversion show ≈N1000E orientation. This deviation between GPS velocity trajectories and orientation of incremental extensional strain is developed due to left lateral transtensional deformation. This interpretation is consistent with the en-échelon pattern of tensional and transtensional faults, the distribution of the volcanic centers, and the asymmetry of the <span class="hlt">rift</span> itself. Small amount of vertical axis blocks rotation, sinistral strike slip faults and dyke intrusions in the <span class="hlt">rift</span> accommodate the transtensional deformation. We analyzed the kinematics of ER relative to Deep and Shallow Hot Spot Reference Frames (HSRF). Comparison between the two reference frames shows different kinematics in ER and also Africa and Somalia plate motion both in magnitude and direction. Plate spreading direction in shallow HSRF (i.e. the source of the plumes locates in the asthenosphere) and the trend of ER deviate by about 27°. Shearing and extension across the plate boundary zone contribute both to the style of deformation and overall kinematics in the <span class="hlt">rift</span>. We conclude that the observed long wavelength kinematics and tectonics are consequences of faster SW ward motion of Africa than Somalia in the shallow HSRF. This reference frame seems more consistent with the geophysical and geological constraints in the <span class="hlt">Rift</span>. The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5130219','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5130219"><span id="translatedtitle">Paleoseismologic studies of the Pajarito fault <span class="hlt">system</span>, western margin of the Rio Grande <span class="hlt">rift</span> near Los Alamos, NM</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kelson, K.I. ); Hemphill-Haley, M.A.; Wong, I.G. ); Gardner, J.N.; Reneau, S.L. )</p> <p>1993-04-01</p> <p>As in much of the Basin and Range province, low levels of historical seismicity in the Rio Grande <span class="hlt">rift</span> (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 <span class="hlt">system</span> (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 <span class="hlt">rift</span> margin near Taos.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JGRB..119.8267H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRB..119.8267H"><span id="translatedtitle">Seismicity and subsidence following the 2011 Nabro eruption, Eritrea: Insights into the plumbing <span class="hlt">system</span> of an off-<span class="hlt">rift</span> volcano</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hamlyn, Joanna E.; Keir, Derek; Wright, Tim J.; Neuberg, Jürgen W.; Goitom, Berhe; Hammond, James O. S.; Pagli, Carolina; Oppenheimer, Clive; Kendall, J.-Michael; Grandin, Raphaël.</p> <p>2014-11-01</p> <p>Nabro volcano, situated to the east of the Afar <span class="hlt">Rift</span> Zone, erupted on 12 June 2011. Eruptions at such off-<span class="hlt">rift</span> volcanoes are infrequent, and consequently, the plumbing <span class="hlt">systems</span> are poorly understood. We present posteruption Synthetic Aperture Radar (SAR) images from the TerraSAR-X satellite and posteruption continuous seismic activity from a local seismic array. Interferometric analysis of SAR data, reveals a circular, 12 km wide, signal subsiding at ˜200 mm/yr. We inverted for the best fit Mogi source finding a 4 ± 1 × 107 m3/yr volume decrease at 7 ± 1 km depth. Between 31 August and 7 October 2011, we located 658 and relocated 456 earthquakes with local magnitudes between -0.4 and 4.5. Seismicity beneath the SE edge of Nabro at 11 km depth is likely associated with high strain rates from deep magma flow into the modeled reservoir. This suggests that magma is supplied through a narrow conduit and then stored at ˜7 km depth. We interpret seismicity at 4-6 km depth as brittle fracturing above the inferred magma reservoir. Focal mechanisms delineate a thrust fault striking NE-SW and dipping 45° to the SE across the caldera floor. We propose that the crustal response is to slip on this fault which crosscuts the caldera rather than to deform on ring faults. The NE-SW fault plane is not associated with measurable surface deformation, indicating that it does not contribute much to the caldera deformation. We show that subsidence of the caldera is controlled by magma chamber processes rather than fault slip.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Tectp.699..213E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Tectp.699..213E"><span id="translatedtitle">Evolution of the broadly <span class="hlt">rifted</span> zone in southern Ethiopia through gravitational collapse and extension of dynamic topography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Emishaw, Luelseged; Laó-Dávila, Daniel A.; Abdelsalam, Mohamed G.; Atekwana, Estella A.; Gao, Stephen S.</p> <p>2017-03-01</p> <p>The Broadly <span class="hlt">Rifted</span> Zone (BRZ) is a 315 km wide zone of extension in southern Ethiopia. It is located between the Southern Main Ethiopian <span class="hlt">Rift</span> and the Eastern Branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) represented by the Kenya-Turkana <span class="hlt">Rift</span>. The BRZ is characterized by NE-trending ridges and valleys superimposed on regionally uplifted ( 2 km average elevation) terrain. Previous studies proposed that the BRZ is an overlap zone resulted from northward propagation of the Kenya-Turkana <span class="hlt">Rift</span> and southward propagation of the Southern Main Ethiopian <span class="hlt">Rift</span>. To understand the relationship between the BRZ's extensional style and its crustal and upper mantle structures, this work first estimated the Moho depth using the two-dimensional (2D) radially-averaged power spectral analysis of the World Gravity Map. Verification of these results was accomplished through lithospheric-scale 2D forward gravity models along E-W profiles. This work found that the Moho topography beneath the BRZ depicts a dome-like shape with a minimum depth of 27 km in the center of the dome. This work proposes that the Moho doming, crustal arching underlying the BRZ and associated topographic uplift are the result of asthenospheric mantle upwelling beneath the BRZ. This upwelling changed to a NE-directed lateral mantle flow at shallower depth. This is supported by seismic tomography imaging which shows slow S-wave velocity anomaly at lithospheric depth of 75 km to 150 km stretching in a NE-SW direction from beneath the BRZ to the Afar Depression. This work proposes that the asthenospheric upwelling created gravitationally unstable dynamic topography that triggered extensional gravitational collapse leading to the formation of the BRZ as a wide <span class="hlt">rift</span> within the narrow <span class="hlt">rift</span> segments of the EARS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002SedG..147...13O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002SedG..147...13O"><span id="translatedtitle">The 1.1-Ga Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span>, central North America: sedimentology of two deep boreholes, Lake Superior region</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ojakangas, Richard W.; Dickas, Albert B.</p> <p>2002-03-01</p> <p>The Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> (MRS) of central North America is a 1.1-Ga, 2500-km long structural feature that has been interpreted as a triple-junction <span class="hlt">rift</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70015106','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70015106"><span id="translatedtitle">Mechanical response of the south flank of kilauea volcano, hawaii, to intrusive events along the <span class="hlt">rift</span> <span class="hlt">systems</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Dvorak, J.J.; Okamura, A.T.; English, T.T.; Koyanagi, R.Y.; Nakata, J.S.; Sako, M.K.; Tanigawa, W.T.; Yamashita, K.M.</p> <p>1986-01-01</p> <p>Increased earthquake activity and compression of the south flank of Kilauea volcano, Hawaii, have been recognized by previous investigators to accompany <span class="hlt">rift</span> intrusions. We further detail the temporal and spatial changes in earthquake rates and ground strain along the south flank induced by six major <span class="hlt">rift</span> intrusions which occurred between December 1971 and January 1981. The seismic response of the south flank to individual <span class="hlt">rift</span> 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 <span class="hlt">rift</span> intrusions and eruptions. Emplacement of an intrusion at a depth greater than about 4 km, such as the June 1982 southwest <span class="hlt">rift</span> 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-<span class="hlt">rift</span> 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 <span class="hlt">rift</span> earthquakes. ?? 1986.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5657215','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5657215"><span id="translatedtitle">Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> and a speculation on possible climate forcing</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Behrendt, J.C. ); Cooper, A. )</p> <p>1991-04-01</p> <p>The Cenzoic West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, 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 <span class="hlt">rift</span>-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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span> and waxing and waning of the Antarctic ice sheet beginning about earliest Oligocene time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007JAfES..48..125K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007JAfES..48..125K"><span id="translatedtitle">Early structural development of the Okavango <span class="hlt">rift</span> zone, NW Botswana</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kinabo, B. D.; Atekwana, E. A.; Hogan, J. P.; Modisi, M. P.; Wheaton, D. D.; Kampunzu, A. B.</p> <p>2007-06-01</p> <p>Aeromagnetic and gravity data collected across the Okavango <span class="hlt">rift</span> zone, northwest Botswana are used to map the distribution of faults, provide insights into the two-dimensional shallow subsurface geometry of the <span class="hlt">rift</span>, and evaluate models for basin formation as well as the role of pre-existing basement fabric on the development of this nascent continental <span class="hlt">rift</span>. The structural fabric (fold axes and foliation) of the Proterozoic basement terrane is clearly imaged on both gravity and magnetic maps. The strike of <span class="hlt">rift</span>-related faults (030-050° in the north and 060-070° in the south) parallels fold axes and the prominent foliation directions of the basement rocks. These pre-existing fabrics and structures represent a significant strength anisotropy that controlled the orientation of younger brittle faults within the stress regime present during initiation of this <span class="hlt">rift</span>. Northwest dipping faults consistently exhibit greater displacements than southeast dipping faults, suggesting a developing half-graben geometry for this <span class="hlt">rift</span> zone. However, the absence of fully developed half-grabens along this <span class="hlt">rift</span> zone suggests that the border fault <span class="hlt">system</span> is not fully developed consistent with the infancy of <span class="hlt">rifting</span>. Three en-echelon northeast trending depocenters coincide with structural grabens that define the Okavango <span class="hlt">rift</span> zone. Along the southeastern boundary of the <span class="hlt">rift</span>, developing border faults define a 50 km wide zone of subsidence within a larger 150 km wide zone of extension forming a <span class="hlt">rift-in-rift</span> structure. We infer from this observation that the localization of strain resulting from extension is occurring mostly along the southeastern boundary where the border fault <span class="hlt">system</span> is being initiated, underscoring the important role of border faults in accommodating strain even during this early stage of <span class="hlt">rift</span> development. We conclude that incipient <span class="hlt">rift</span> zones may provide critical insights into the development of <span class="hlt">rift</span> basins during the earliest stages of continental <span class="hlt">rifting</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/ED477778.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED477778.pdf"><span id="translatedtitle">Summary and Final Recommendations of the University <span class="hlt">System</span> of Georgia's <span class="hlt">African</span>-American Male Initiative.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Georgia Univ. System, Atlanta. Board of Regents.</p> <p></p> <p>In 2000, the University <span class="hlt">System</span> of Georgia (USG) verified that USG institutions enrolled a low percentage of <span class="hlt">African</span> American males in comparison with the percentage of <span class="hlt">African</span> American males in the state's population. In 2001, the USG developed a special funding initiative to conduct a study of barriers to the participation of <span class="hlt">African</span> American…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4003290','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4003290"><span id="translatedtitle">Evidence of <span class="hlt">rift</span> valley fever seroprevalence in the Sahrawi semi-nomadic pastoralist <span class="hlt">system</span>, Western Sahara</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p></p> <p>2014-01-01</p> <p>Background The increasing global importance of <span class="hlt">Rift</span> 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</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T13C4665S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T13C4665S"><span id="translatedtitle">Earthquake Rupture Forecast of M>= 6 for the Corinth <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scotti, O.; Boiselet, A.; Lyon-Caen, H.; Albini, P.; Bernard, P.; Briole, P.; Ford, M.; Lambotte, S.; Matrullo, E.; Rovida, A.; Satriano, C.</p> <p>2014-12-01</p> <p>Fourteen years of multidisciplinary observations and data collection in the Western Corinth <span class="hlt">Rift</span> (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<Mw<4.5), delineating steep and low-angle (blind) active fault geometries between 4 and ~10 km depth; GPS velocity vectors, indicating that most of the N-S extension rate (16 mm/y) is limited to the width of the WCR; recent historical seismicity investigations, that have led to important reassessments of magnitudes and locations of M>=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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T43A4678A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T43A4678A"><span id="translatedtitle">Radial Anisotropy beneath the Main Ethiopian <span class="hlt">Rift</span> and Afar Depression</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Accardo, N. J.; Gaherty, J. B.; Jin, G.; Shillington, D. J.</p> <p>2014-12-01</p> <p>The Main Ethiopian <span class="hlt">Rift</span> (MER) and Afar uniquely capture the final stages of transition from continental <span class="hlt">rifting</span> in the broader East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> to incipient seafloor spreading above a mantle hotspot. Studies of the region increasingly point to magmatism as a controlling factor on continental extension. However, the character and depth extent of these melt products remain contentious. Radial anisotropy derived from surface waves provides a unique diagnostic constraint on the presence of oriented melt pockets versus broader oriented anisotropic fabrics. This study investigates the thermal and radially anisotropic structure beneath the broader MER and Afar to resolve the magmatic character of the region and ultimately to understand the role of magmatism in present day <span class="hlt">rift</span> development. We utilize 104 stations from 4 collocated arrays in the MER/Afar region to constrain radial anisotropy within the upper mantle via the inversion of Love- and Rayleigh-wave observations between 25 and 100 s period. We employ a multi-channel cross-correlation algorithm to obtain inter-station phase and amplitude information. The multi-channel phase observations are inverted for dynamic phase velocity across the array, which are then corrected for focusing and multipathing using the amplitude observations via Helmholtz tomography. We jointly invert Love- and Rayleigh-wave structural phase velocity measurements employing crustal constraints from co-located active source experiments to obtain estimates of Vsv and Vsh between 50 - 170 km depth. Preliminary results readily reveal the distinct shear velocity structure beneath the MER and Afar. Within the MER, shear velocity structure suggests pronounced low velocities accompanied by strong anisotropy between 80 - 140 km depth beneath the western Ethiopian plateau and <span class="hlt">rift</span> valley. Within Afar, shear velocity structure is more varied with the slowest velocities found at shallow depths (less than 70 km depth), accompanied by weak</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Tecto..35.2863S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Tecto..35.2863S"><span id="translatedtitle">Thermochronometric evidence for diffuse extension and two-phase <span class="hlt">rifting</span> within the Central Arabian Margin of the Red Sea <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Szymanski, E.; Stockli, D. F.; Johnson, P. R.; Hager, C.</p> <p>2016-12-01</p> <p>Numerical time-temperature models derived from a 2-D network of apatite and zircon (U-Th)/He ages reveal a three-stage thermotectonic history for the central Arabian <span class="hlt">rift</span> flank (CARF) of the Red Sea <span class="hlt">Rift</span> (RSR) <span class="hlt">system</span>. The pre-<span class="hlt">rift</span> Arabian-Nubian Shield existed as part of a passive Paleo-Tethyan margin until a widespread tectonic event at 350 Ma exhumed the proto-CARF to mid-to-upper crustal structural levels. After remaining thermally stable through the Mesozoic, the first phase of RSR extension began with a distinct <span class="hlt">rift</span> pulse at 23 Ma when fault blocks across a 150 km wide area were exhumed along a diffuse set of <span class="hlt">rift</span>-parallel faults from an average pre-<span class="hlt">rift</span> flank depth of 1.7 ± 0.8 km. This <span class="hlt">rift</span> onset age is mirrored in thermochronometric and sequence stratigraphic analyses elsewhere along the Red Sea Nubian and Arabian margins, confirming that <span class="hlt">rifting</span> occurred concomitantly along the full Red Sea-Gulf of Suez <span class="hlt">rift</span> <span class="hlt">system</span>. Diffuse lithospheric extension lasted for 8 Myr before a second <span class="hlt">rift</span> pulse at 15 Ma, coincident with regional stress realignment, transferred active faulting basinward toward the modern RSR axial trough. CARF time-temperature models indicate that the prevalent <span class="hlt">rift</span> style during both RSR extensional phases was one of localized, structurally controlled block faulting and contemporaneous dike injection, not wholesale <span class="hlt">rift</span> flank uplift.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1713633R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1713633R"><span id="translatedtitle">Receiver function imaging of the lithosphere-asthenosphere boundary and melt beneath the Afar <span class="hlt">Rift</span> in comparison to other <span class="hlt">systems</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rychert, Catherine A.; Harmon, Nicholas</p> <p>2015-04-01</p> <p>Heating, melting, and stretching destroy continents at volcanic <span class="hlt">rifts</span>. Mantle plumes are often invoked to thermally weaken the continental lithosphere and accommodate <span class="hlt">rifting</span> 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 <span class="hlt">rifting</span>. S-to-p (Sp) imaging beneath the Afar <span class="hlt">Rift</span> 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 <span class="hlt">Rift</span> vs. its complete absence beneath the <span class="hlt">rift</span>. Instead, a strong velocity increase with depth at ~75 km depth is imaged. Beneath the <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S41B2733K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S41B2733K"><span id="translatedtitle">Crustal Structure beneath the Rwenzori Region of the Albertine <span class="hlt">Rift</span> using Ambient-Noise Tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kaviani, A.; Paul, A.; Rumpker, G.</p> <p>2015-12-01</p> <p>In this study we investigate the crustal structure beneath the Rwenzori region by analyzing a 1-year ambient-noise data set recorded by a network of 33 broadband seismic stations that have operated between September 2009 and August 2011. The Rwenzori region, located between the Democratic Republic of Congo and Uganda, is part of the western (Albertine) branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS). The region of study is situated between the Albert <span class="hlt">Rift</span> and the Edward <span class="hlt">Rift</span> segments and covers an area of approximately 120 km by 50 km. The main objective of the seismological experiment was to address the questions of the uplift of the Rwenzori Mountains in an extensional regime and the absence of a crustal root beneath the mountain range. Any model proposed to address these questions requires the knowledge of the structure of the Rwenzori horst and surrounding <span class="hlt">rift</span> shoulders. Previous results from local travel-time tomography revealed the presence of low-velocity anomalies in the upper crust beneath the mountain range relative to higher velocities in the surrounding shoulders. However, since the stations used in the previous study only covered the northern part of the region, the resolution of the models proposed by the body-wave tomography was very low beneath the Rwenzori Mountains. Hence, the limits of the Rwenzori horst at depth relative to the <span class="hlt">rift</span> shoulders are still poorly known. The main objective of our ambient-noise tomography (ANT) is to provide an explanation for the building of Rwenzori Mountains. Due to the small aperture of the seismological network, we are mainly interested in the shallow crustal structure including the boundaries between the central Rwenzori horst and the surrounding <span class="hlt">rift</span> shoulders as well as the variations in the thickness of the sedimentary basins. We expect that the ANT images will be able to delineate the boundaries between the main tectonic features including the limits of the Rwenzori horst at depth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JSAES..56....1B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JSAES..56....1B"><span id="translatedtitle">Lower Pliensbachian caldera volcanism in high-obliquity <span class="hlt">rift</span> <span class="hlt">systems</span> in the western North Patagonian Massif, Argentina</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Benedini, Leonardo; Gregori, Daniel; Strazzere, Leonardo; Falco, Juan I.; Dristas, Jorge A.</p> <p>2014-12-01</p> <p>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 <span class="hlt">system</span>; 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 <span class="hlt">system</span>; 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 <span class="hlt">rift</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T11C2906Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T11C2906Z"><span id="translatedtitle">Crustal Structure in the area of the North American Mid-Continent <span class="hlt">Rift</span> <span class="hlt">System</span> from P-wave Receiver Functions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p>2015-12-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span> (MRS). The Superior Province <span class="hlt">Rifting</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T13F..08W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T13F..08W"><span id="translatedtitle">The case for nearly continuous extension of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>, 105-25 Ma (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wilson, D. S.; Luyendyk, B. P.</p> <p>2010-12-01</p> <p>It is a common perception that extension in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (WARS) was a two-phase process, with a Cretaceous phase ending when the Campbell Plateau <span class="hlt">rifted</span> from West Antarctica (~80 Ma), and a mid-Cenozoic phase synchronous with sea floor spreading in the Adare trough (~45-25 Ma). Several lines of evidence indicate that significant extension probably occurred in the intervening 80-45 Ma interval. The strongest evidence comes from subsidence rates on the Central High and Coulman High structures in the central-western Ross Sea, where DSDP Site 270 and other areas with shallow basement have subsided 1 km or more since Oligocene time. With sediment load, these subsidence rates are reasonable for thermal subsidence resulting from extension with a stretching factor of about 2.0-2.5 at about 50-70 Ma, but are hard to reconcile with an extension age around 90 Ma. The seismic velocity structure of the WARS inferred from global surface-wave dispersion is similar to that of oceanic lithosphere of age 40-60 Ma [Ritzwoller et al., 2001 JGR]. Geometric relations of sea floor between Adare Trough and Iselen Bank, northwest Ross Sea, suggest sea floor spreading of about 130 km during early Cenozoic, before the Adare Trough spreading episode started. Numerous cooling ages in the Transantarctic Mountains in the range of 55-45 Ma [Fitzgerald, 1992 Tectonics; Miller et al., 2010 Tectonics] support the interpretation of significant extension prior to 45 Ma. Present crustal thickness of about 22 km near DSDP Site 270 [Trey et al., 1999 Tectonophysics] suggests a pre-extension crustal thickness exceeding 50 km. A simple overall interpretation follows that the WARS has a tectonic history similar to the Basin and Range of western North America: a thick-crust orogenic highland extended for many tens of million years. The main difference between the WARS and the Basin and Range is the post-tectonic cooling and subsidence in the WARS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010IJEaS..99.1511W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010IJEaS..99.1511W"><span id="translatedtitle"><span class="hlt">Rift</span> induced delamination of mantle lithosphere and crustal uplift: a new mechanism for explaining Rwenzori Mountains' extreme elevation?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wallner, Herbert; Schmeling, Harro</p> <p>2010-10-01</p> <p>With heights of 4-5 km, the topography of Rwenzori Mountains, a large horst of old crustal rocks located inside a young passive <span class="hlt">rift</span> <span class="hlt">system</span>, poses the question “Why are the Rwenzori Mountains so high?”. The Cenozoic Western <span class="hlt">Rift</span> branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> is situated within the Late Proterozoic mobile belts between the Archean Tanzania Craton and Congo Craton. The special geological setting of the massif at a <span class="hlt">rift</span> node encircled by the ends of the northern Western <span class="hlt">Rift</span> segments of Lake Albert and Lake Edward suggests that the mechanism responsible for the high elevation of the Rwenzoris is related to the <span class="hlt">rifting</span> process. Our hypothesis is based on the propagation of the <span class="hlt">rift</span> tips, surrounding the stiff old lithosphere at Rwenzori region, thereby triggering the delamination of the cold and dense mantle lithosphere (ML) root by reducing viscosity and strength of the undermost lower crust. As a result, this unloading induces fast isostatic pop-up of the less dense crustal Rwenzori block. We term this RID—“ <span class="hlt">rift</span> induced delamination of Mantle Lithosphere”. The physical consistency of the RID hypothesis is tested numerically. Viscous flow of 2D models is approximated by a Finite Difference Method with markers in an Eulerian formulation. The equations of conservation of mass, momentum and energy are solved for a multi-component <span class="hlt">system</span>. Based on laboratory data of appropriate rock samples, a temperature-, pressure- and stress-dependent rheology is assumed. Assuming a simple starting model with a locally heated ML, the ML block between the weakened zones becomes unstable and sinks into the asthenosphere, while the overlying continental crust rises up. Thus, RID seems to be a viable mechanism to explain geodynamically the extreme uplift. Important conditions are a thermal anomaly within the ML, a ductile lower crust with visco-plastic rheology allowing significant strength reduction and lateral density variations. The special situation of a two</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5237275','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5237275"><span id="translatedtitle">Off-axis volcanism in the Gregory <span class="hlt">rift</span>, east Africa: implications for models of continental <span class="hlt">rifting</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bosworth, W.</p> <p>1987-05-01</p> <p>The largest volcanic centers of the Gregory <span class="hlt">rift</span> occur in two belts located 100 to 150 km east and west of the axis of the <span class="hlt">rift</span> valley. These off-axis volcanic belts include the highest peaks on the continent of Africa and are interpreted to lie above the intersection of low-angle detachment <span class="hlt">systems</span> with the base of a regionally thinned lithosphere. These detachment <span class="hlt">systems</span> are manifested at the surface as a series of breakaway zones and regional bounding faults that produce subbasins with half-graben form. The asymmetry of subbasins alternates along the <span class="hlt">rift</span> axis, indicating that the polarity of the underlying active detachment <span class="hlt">systems</span> also reverses. The detachments are separated laterally by regional oblique-slip accommodation zones typified by wrench-style tectonism. Off-axis from the <span class="hlt">rift</span>, the detachments are inferred to merge along strike as they cut to the base of the lithosphere. This results in irregular but persistent paired zones of volcanism and lithospheric thinning off-axis from the <span class="hlt">rift</span> proper. The development of major volcanic cones such as Mount Kilimanjaro may be controlled by the interaction of leaky accommodation zones with the regions of structurally thinned lithosphere. The central Kenya hot spot has produced the anomalous quantities of volcanic material that fills the Gregory <span class="hlt">rift</span> and probably enhances the off-axis volcanism but does not directly control its location. The model proposed here for tectonic controls of volcanism in the Gregory <span class="hlt">rift</span> may be applicable to Phanerozoic continental <span class="hlt">rifts</span> in general.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=African+AND+Trade+AND+Policy&id=EJ805462','ERIC'); return false;" href="http://eric.ed.gov/?q=African+AND+Trade+AND+Policy&id=EJ805462"><span id="translatedtitle">Trade in Educational Services: Reflections on the <span class="hlt">African</span> and South <span class="hlt">African</span> Higher Education <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Sehoole, Chika Trevor</p> <p>2004-01-01</p> <p>This article discusses and analyses the emergence of globalisation and its impact on developments within the <span class="hlt">African</span> continent. Africa's response at a regional level through the New Partnership for Africa's Development and at a subregional level through the Southern <span class="hlt">African</span> Development Community's "Protocol on Education" come under…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.T31D0486B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.T31D0486B"><span id="translatedtitle">Thermochronological investigation of the timing of <span class="hlt">rifting</span> and <span class="hlt">rift</span> segmentation in the Gulf of Suez, Egypt</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bosworth, W.; Stockli, D. F.</p> <p>2006-12-01</p> <p>The Tertiary Gulf of Suez <span class="hlt">rift</span> <span class="hlt">system</span> is one of the best-studied continental <span class="hlt">rift</span> <span class="hlt">systems</span> and has inspired many fundamental geodynamic models for continental <span class="hlt">rifting</span>. However, our limited knowledge of how extensional strain is spatially and temporally distributed has made it difficult to adequately evaluate models for the dynamic evolution of this <span class="hlt">rift</span>. A critical aspect of constraining the evolution of <span class="hlt">rifting</span> and <span class="hlt">rift</span> segmentation in the Gulf of Suez involves acquiring reliable geochronological constraints on extensional faulting. This study has commenced a systematic investigation of the timing and spatial distribution of <span class="hlt">rifting</span>, lateral <span class="hlt">rift</span> segmentation, and <span class="hlt">rift</span> localization within the Gulf of Suez, Egypt, employing apatite and zircon (U-Th)/He thermochronometry. (U-Th)/He thermochronometric analysis of sample transects from exhumed fault blocks within the <span class="hlt">rift</span> integrated with structural data will allow us to directly determine the timing, distribution, and magnitude of extension. The onset of major <span class="hlt">rifting</span> (~24-19 Ma) in the Gulf of Suez was marked by the development of crustal domino-style tilt blocks and syn-<span class="hlt">rift</span> deposition of the late Oligocene non-marine Abu Zenima Fm and non-marine to restricted marine Nukhul Fm. Development of the Gulf of Aqaba-Dead Sea transform cut off the <span class="hlt">rift</span> from the Red Sea <span class="hlt">rift</span> at an early extensional stage. Apatite (AHe) and zircon (ZHe) (U- Th)/He data were collected from basement and pre-<span class="hlt">rift</span> sedimentary sample transects from the central and southern Sinai Peninsula portion and the Gebel El Zeit area in the southern Gulf of Suez as well as from basement samples from selected drill cores off Gebel El Zeit. Preliminary data exhibit partially reset ages trending as old as ~70 Ma (AHe) and ~450 Ma (ZHe) from shallower structural levels (Proterozoic basement and Phanerozoic cover sequence). Structurally deeper samples yield abundant AHe ages of ~22-24 Ma, indicative of rapid cooling and exhumation during the early Miocene. More</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JVGR..327..208R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JVGR..327..208R"><span id="translatedtitle">Diffuse degassing at Longonot volcano, Kenya: Implications for CO2 flux in continental <span class="hlt">rifts</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Robertson, Elspeth; Biggs, Juliet; Edmonds, Marie; Clor, Laura; Fischer, Tobias P.; Vye-Brown, Charlotte; Kianji, Gladys; Koros, Wesley; Kandie, Risper</p> <p>2016-11-01</p> <p>Magma movement, fault structures and hydrothermal <span class="hlt">systems</span> influence volatile emissions at <span class="hlt">rift</span> volcanoes. Longonot is a Quaternary caldera volcano located in the southern Kenyan <span class="hlt">Rift</span>, where regional extension controls recent shallow magma ascent. Here we report the results of a soil carbon dioxide (CO2) survey in the vicinity of Longonot volcano, as well as fumarolic gas compositions and carbon isotope data. The total non-biogenic CO2 degassing is estimated at < 300 kg d- 1, and is largely controlled by crater faults and fractures close to the summit. Thus, recent volcanic structures, rather than regional tectonics, control fluid pathways and degassing. Fumarolic gases are characterised by a narrow range in carbon isotope ratios (δ13C), from - 4.7‰ to - 6.4‰ (vs. PDB) suggesting a magmatic origin with minor contributions from biogenic CO2. Comparison with other degassing measurements in the East <span class="hlt">African</span> <span class="hlt">Rift</span> shows that records of historical eruptions or unrest do not correspond directly to the magnitude of CO2 flux from volcanic centres, which may instead reflect the current size and characteristics of the subsurface magma reservoir. Interestingly, the integrated CO2 flux from faulted <span class="hlt">rift</span> basins is reported to be an order of magnitude higher than that from any of the volcanic centres for which CO2 surveys have so far been reported.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5594528','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5594528"><span id="translatedtitle">Stratigraphy and <span class="hlt">rifting</span> history of the Mesozoic-Cenozoic Anza <span class="hlt">rift</span>, Kenya</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Winn, R.D. Jr.; Steinmetz, J.C. ); Kerekgyarto, W.L. )</p> <p>1993-11-01</p> <p>Lithological and compositional relationships, thicknesses, and palynological data from drilling cuttings from five wells in the Anza <span class="hlt">rift</span>, Kenya, indicate active <span class="hlt">rifting</span> during the Late Cretaceous and Eocene-Oligocene. The earlier <span class="hlt">rifting</span> possibly started in the Santonian-Coniacian, primarily occurred in the Campanian, and probably extended into the Maastrichtian. Anza <span class="hlt">rift</span> 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 <span class="hlt">rifting</span> in the Anza basin was synchronous with <span class="hlt">rifting</span> 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 <span class="hlt">rifting</span> to passive subsidence in the Anza basin at the end of the Neogene, in turn, records a reconfigured response of east <span class="hlt">African</span> plates to stresses and is correlated with formation of the East Africa <span class="hlt">rift</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2007/1047/srp/srp108/of2007-1047srp108.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2007/1047/srp/srp108/of2007-1047srp108.pdf"><span id="translatedtitle">Structure of the central Terror <span class="hlt">Rift</span>, western Ross Sea, Antarctica</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hall, Jerome; Wilson, Terry; Henrys, Stuart</p> <p>2007-01-01</p> <p>The Terror <span class="hlt">Rift</span> is a zone of post-middle Miocene faulting and volcanism along the western margin of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>. 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 <span class="hlt">Rift</span>. The Terror <span class="hlt">Rift</span> 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 <span class="hlt">rift</span> sub-basins, indicating that the Terror <span class="hlt">Rift</span> is segmented by transverse structures. Multiple phases of faulting all post-date 17 Ma, including faults cutting the seafloor surface, indicating Neogene <span class="hlt">rifting</span> and possible modern activity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007PhDT.......218K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007PhDT.......218K"><span id="translatedtitle">Incipient continental <span class="hlt">rifting</span>: Insights from the Okavango <span class="hlt">Rift</span> Zone, northwestern Botswana</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kinabo, Baraka Damas</p> <p></p> <p>In this dissertation aeromagnetic, gravity, and Shuttle Radar Topography Mission Digital Elevation Model (SRTM DEM) data from the Okavango <span class="hlt">Rift</span> Zone in northwest Botswana are used to map the distribution of <span class="hlt">rift</span> and basement structures. The distribution of these structures provide useful insights into the early stages of continental <span class="hlt">rifting</span>. The objectives of this study are (1) assessing the role of pre-existing structures on <span class="hlt">rift</span> basin development, (2) characterizing the geometry of the nascent <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rifts</span> faults are also linking through transfer zones by the process of "fault piracy" to establish an immature border fault <span class="hlt">system</span>. The relationships between scam heights and vertical throws reveal that the young and active faults are located outside the <span class="hlt">rift</span> while the faults with no recent activities are in the middle suggesting that the <span class="hlt">rift</span> 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 <span class="hlt">rifting</span> processes such as fault growth and propagation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.206.1382K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.206.1382K"><span id="translatedtitle">Crustal structure and kinematics of the TAMMAR propagating <span class="hlt">rift</span> <span class="hlt">system</span> on the Mid-Atlantic Ridge from seismic refraction and satellite altimetry gravity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kahle, Richard L.; Tilmann, Frederik; Grevemeyer, Ingo</p> <p>2016-08-01</p> <p>The TAMMAR segment of the Mid-Atlantic Ridge forms a classic propagating <span class="hlt">system</span> 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 <span class="hlt">rift</span>, sheared zone and failed <span class="hlt">rift</span> to investigate the crustal structure of the <span class="hlt">system</span>. 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 <span class="hlt">rift</span>, 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 <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5840034','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5840034"><span id="translatedtitle">Cenozoic <span class="hlt">rift</span> tectonics of the Japan Sea</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kimura, K.</p> <p>1988-08-01</p> <p>The Japan Sea is one of the back-arc basins in trench-arc <span class="hlt">systems</span> 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 <span class="hlt">rift</span> tectonics of the Japan Sea. The <span class="hlt">rifting</span> history is summarized as follows: nonmarine volcanic formations of prerift stage before 50 Ma, <span class="hlt">rift</span>-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. <span class="hlt">Rifting</span> is not limited to the synrift stage but is continued to the syndrift stage. <span class="hlt">Rifting</span> led to a horst-and-graben structure. Thus, the Cenozoic onland sequences in the Japanese Islands are suited for a study of <span class="hlt">rift</span> tectonics because the sequences were subaerially exposed by the late Miocene-Holocene island-arc tectonics. <span class="hlt">Rift</span> tectonics cannot be studied as easily in most Atlantic-type passive margins.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007JGRE..112.9007F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007JGRE..112.9007F"><span id="translatedtitle">Oblique <span class="hlt">rifting</span> at Tempe Fossae, Mars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fernández, Carlos; Anguita, Francisco</p> <p>2007-09-01</p> <p>This work shows the results of a structural study of the faults observed at the Tempe <span class="hlt">Rift</span> (northeastern Tharsis region), Mars. A new, detailed map of faults and fault <span class="hlt">systems</span> was used to geometrically characterize the fracture architecture of the Tempe <span class="hlt">Rift</span> and to measure fault length, displacement, and spacing data, to analyze the spatial distribution of fault centroids, and to investigate the fractal nature of fault trace maps. A comparison with analog models and the use of conventional techniques of fault population analysis show that the Tempe <span class="hlt">Rift</span> was most probably generated under sinistral oblique-<span class="hlt">rifting</span> processes, which highlights the importance of the presence of inherited fractures in the tectonic evolution of the Noachian crust. The angle between the extension direction and the <span class="hlt">rift</span> axis varies along the Tempe <span class="hlt">Rift</span>, ranging from 50°-60° at its central southern part to 66°-88° to the southwest. Fault scaling relationships are similar to those found at mid-ocean ridges on Earth with exponential fault length-frequency distributions. Localized, inhomogeneous deformation generated weakly interacting faults, spanning the entire thickness of the mechanical layer. This thickness decreased from southwest to northeast along the <span class="hlt">rift</span>, along with distance from the central part of the Tharsis dome.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950035266&hterms=Seamounts&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DSeamounts','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950035266&hterms=Seamounts&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DSeamounts"><span id="translatedtitle">The <span class="hlt">African</span> superswell</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nyblade, Andrew A.; Robinson, Scott W.</p> <p>1994-01-01</p> <p>Maps of residual bathymetry in the ocean basins around the <span class="hlt">African</span> continent reveal a broad bathymetric swell in the southeastern Atlantic Ocean with an amplitude of about 500 m. We propose that this region of anomalously shallow bathymetry, together with the contiguous eastern and southern <span class="hlt">African</span> plateaus, form a superswell which we refer to as the <span class="hlt">African</span> superswell. The origin of the <span class="hlt">African</span> superswell is uncertain. However, <span class="hlt">rifting</span> and volcanism in eastern Africa, as well as heat flow measurements in southern Africa and the southeastern Atlantic Ocean, suggest that the superswell may be attributed, at least in part, to heating of the lithosphere.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=Africa&pg=6&id=EJ1017665','ERIC'); return false;" href="http://eric.ed.gov/?q=Africa&pg=6&id=EJ1017665"><span id="translatedtitle"><span class="hlt">African</span> Indigenous Knowledge <span class="hlt">Systems</span> and Relevance of Higher Education in South Africa</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Kaya, Hassan O.; Seleti, Yonah N.</p> <p>2013-01-01</p> <p>The higher education <span class="hlt">system</span> in Africa and South Africa in particular, is still too academic and distant from the developmental challenges of <span class="hlt">African</span> local communities. The integration of <span class="hlt">African</span> indigenous knowledge <span class="hlt">systems</span> (AIKS) into the higher educational <span class="hlt">system</span> could improve its relevance. This is due to the holistic, community-based nature…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/publication/?seqNo115=314037','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/publication/?seqNo115=314037"><span id="translatedtitle"><span class="hlt">Rift</span> Valley Fever Virus</span></a></p> <p><a target="_blank" href="http://www.ars.usda.gov/services/TekTran.htm">Technology Transfer Automated Retrieval System (TEKTRAN)</a></p> <p></p> <p></p> <p><span class="hlt">Rift</span> Valley fever virus (RVFV) is a mosquito-transmitted virus or arbovirus that is endemic in sub-Saharan Africa. In the last decade, <span class="hlt">Rift</span> 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...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T24C..06D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T24C..06D"><span id="translatedtitle">GPS Velocity Field at the Western Tip of the Aden Ridge ; Implications for <span class="hlt">Rifting</span> and the Arabia-Somalia-Nubia Triple Junction Dynamics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Doubre, C.; Socquet, A.; Masson, F.; Cressot, C.; Mohamed, K.; Vigny, C.; Ruegg, J.</p> <p>2010-12-01</p> <p>Due to the presence of magma and a complex thermal structure, the dynamics of divergent plate boundaries are complicated, with microseismicity (ML<4) contributing very little to the total moment release. For the last 35 years several geodetic campaigns have been conducted at the western tip of the Aden Ridge propagating on land into Afar (Republic of Djibouti). The first segment above water, the Asal <span class="hlt">Rift</span>, experienced a seismo-volcanic event in 1978, which was the first <span class="hlt">rifting</span> episode, along with the 1978-1985 Icelandic Krafla event, to be monitored by terrestrial geodetic measurements. These measurements revealed the opening of two 1-2 m-wide dykes in the <span class="hlt">rift</span> inner floor. Since then, terrestrial and spatial geodetic monitoring shows that the <span class="hlt">rift</span> kept opening, during the post-<span class="hlt">rifting</span> period, at a rate largely exceeding the plates’ motions. This significant opening rate is decreasing with time to tend, three decades after the <span class="hlt">rifting</span> event, to the far-field opening rate. We present here the results of the GPS measurements of a 45 site network covering the Tadjoura-Asal <span class="hlt">Rift</span> <span class="hlt">System</span>, previously made every two years from 1995 to 2003, and repeated in 2010. The calculated 1999-2010 horizontal velocity field is very homogeneous with a quasi-constant N045° direction with respect to Somalia and a regular increase from the southern to the northern margin of the Asal <span class="hlt">Rift</span> clearly controlled by a few normal faults, and reaching a maximum of 12.5 mm/yr. A non-negligible part of the Arabia-Somalia divergent movement (1 to 2 mm/yr) is observed south of this <span class="hlt">rift</span>, which sheds light on the role of the active normal faults bounding the asymmetrical Gaggadé Basin and therefore brings important constraints on the location of the Red Sea Ridge-Aden Ridge-East <span class="hlt">African</span> <span class="hlt">Rift</span> triple junction. Since the last 2003 campaign, the lack of micro-seismicity within the Asal <span class="hlt">Rift</span> seems to be associated with a ˜2 mm/yr decrease of the opening rate deduced from the GPS time series analysis</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T13A2514Q','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T13A2514Q"><span id="translatedtitle">Understanding the thermal and tectonic evolution of Marie Byrd Land from a reanalysis of airborne geophysical data in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Quartini, E.; Powell, E. M.; Richter, T.; Damiani, T.; Burris, S. G.; Young, D. A.; Blankenship, D. D.</p> <p>2013-12-01</p> <p>The West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (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 <span class="hlt">rift</span> <span class="hlt">system</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span>. 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25517098','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25517098"><span id="translatedtitle">Segmented lateral dyke growth in a <span class="hlt">rifting</span> event at Bárðarbunga volcanic <span class="hlt">system</span>, Iceland.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>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</p> <p>2015-01-08</p> <p>Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long. Previous models of <span class="hlt">rifting</span> 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 <span class="hlt">system</span> 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 <span class="hlt">System</span> (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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Natur.517..191S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Natur.517..191S"><span id="translatedtitle">Segmented lateral dyke growth in a <span class="hlt">rifting</span> event at Bárðarbunga volcanic <span class="hlt">system</span>, Iceland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p>2015-01-01</p> <p>Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long. Previous models of <span class="hlt">rifting</span> 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 <span class="hlt">system</span> 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 <span class="hlt">System</span> (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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1710322S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1710322S"><span id="translatedtitle">Segmented lateral dyke growth in a <span class="hlt">rifting</span> event at Bárðarbunga volcanic <span class="hlt">system</span>, Iceland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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; Ágústsdóttir, Thorbjörg; Björnsson, Helgi; Bean, Christopher J.</p> <p>2015-04-01</p> <p>Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of km long. Previous models of <span class="hlt">rifting</span> events indicate either a 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. We show how a recent segmented dyke intrusion in the Bárðarbunga volcanic <span class="hlt">system</span>, 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 deformation mapped by Global Positioning <span class="hlt">System</span> (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 a magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of M>5 earthquakes. The 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T53C..05B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T53C..05B"><span id="translatedtitle">How Mountains Become <span class="hlt">Rifts</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Buiter, S. J.; Tetreault, J. L.</p> <p>2015-12-01</p> <p><span class="hlt">Rifting</span> often initiates on former continental collision zones. For example, the present-day passive margins of the Atlantic and Indian Oceans formed after continental break-up occurred on relatively young and very old sutures, such as Morocco-Nova Scotia and East Antarctica-Australia, respectively. <span class="hlt">Rifts</span> may localize on former collision zones for several reasons: orogens are thermally weak because of the increase in heat producing elements in their thicker crustal root, the inherited thrust faults form large-scale heterogeneities, and in the case of young sutures, extensional collapse of the orogen may help initiate <span class="hlt">rifting</span>. We highlight the impact of collision zone inheritance on continental extension and <span class="hlt">rifted</span> margin architecture using numerical experiments. We first explicitly prescribe collisional structures in the initial setup, such as increased crustal thickness and inherited thrust faults. Varying the prescribed structures results in different <span class="hlt">rift</span> to break-up durations and margin widths. Our second series of experiments creates a collision zone through subduction and closure of an ocean. We confirm that post-collisional collapse is not a sufficient trigger for continental <span class="hlt">rifting</span> and that a change in regional plate motions is required. When extension occurs, the weak former subduction interface and the elevated temperatures in the crustal nappe stack work in tandem as the main deformation localizers for continental <span class="hlt">rifting</span>. Our experiments show that different approaches of initiating a continental <span class="hlt">rift</span> result in different dynamics of the crust and mantle, thereby impacting <span class="hlt">rift</span> geometry, <span class="hlt">rift</span> to break-up duration, and exhumation of subduction-related sediments and oceanic crust.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFMGP11A0732K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFMGP11A0732K"><span id="translatedtitle">Paleomagnetism and paleointensity of Mid-Continental <span class="hlt">Rift</span> <span class="hlt">System</span> basalts at Silver Mountain and Sturgeon River Falls (Upper Michigan)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kulakov, E.; Piispa, E. J.; Laird, M. S.; Smirnov, A. V.; Diehl, J. F.</p> <p>2009-12-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span> (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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21080318','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21080318"><span id="translatedtitle">TerraSAR-X high-resolution radar remote sensing: an operational warning <span class="hlt">system</span> for <span class="hlt">Rift</span> Valley fever risk.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Vignolles, Cécile; Tourre, Yves M; Mora, Oscar; Imanache, Laurent; Lafaye, Murielle</p> <p>2010-11-01</p> <p>In the vicinity of the Barkedji village (in the Ferlo region of Senegal), the abundance and aggressiveness of the vector mosquitoes for <span class="hlt">Rift</span> 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 <span class="hlt">system</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21714111','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21714111"><span id="translatedtitle">Volumetric analysis of the <span class="hlt">African</span> elephant ventricular <span class="hlt">system</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Maskeo, Busisiwe C; Spocter, Muhammed A; Haagensen, Mark; Manger, Paul R</p> <p>2011-08-01</p> <p>This study used magnetic resonance imaging (MRI) to determine the volume of the ventricular <span class="hlt">system</span> in the brain of three adult male <span class="hlt">African</span> elephants (Loxodonta africana). The ventricular <span class="hlt">system</span> of the elephant has a volume of ∼240 mL, an order of magnitude larger than that seen in the adult human. Despite this large size, allometric analysis indicates that the volume of the ventricles in the elephant is what one would expect for a mammal with an ∼5 kg brain. Interestingly, our comparison with other mammals revealed that primates appear to have small relative ventricular volumes, and that megachiropterans and microchiropterans follow different scaling rules when comparing ventricular volume to brain mass indicating separate phylogenetic histories. The current study provides context for one aspect of the elephant brain in the broader picture of mammalian brain evolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://gcsproceedings.sepmonline.org/content/gcs034/1/SEC27.abstract','USGSPUBS'); return false;" href="http://gcsproceedings.sepmonline.org/content/gcs034/1/SEC27.abstract"><span id="translatedtitle">Late Jurassic – early Cretaceous inversion of <span class="hlt">rift</span> structures, and linkage of petroleum <span class="hlt">system</span> elements across post-<span class="hlt">rift</span> unconformity, U.S. Chukchi Shelf, arctic Alaska</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Houseknecht, David W.; Connors, Christopher D.</p> <p>2015-01-01</p> <p>Oil-prone source rocks, reservoir-quality sandstone, migration pathways, and structural closure are linked intimately across the Jurassic unconformity, which reflects inversion. Thus, all these key petroleum <span class="hlt">systems</span> elements were in place when Triassic source rocks entered the oil generation window during Cretaceous–Cenozoic stratigraphic burial.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002AGUFM.T11D1281D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002AGUFM.T11D1281D"><span id="translatedtitle">Mantle Flow, Dynamic Topography and <span class="hlt">Rift</span>-Flank Uplift of Arabia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Daradich, A. L.; Mitrovica, J. X.; Pysklywec, R. N.; Willett, S. D.</p> <p>2002-12-01</p> <p>The Red Sea is flanked by highlands. To the east, the Arabian platform is broadly tilted along an axis that runs parallel to the sea, and the long tail of high topography has been described as a classic example of `<span class="hlt">rift</span>-flank uplift' [Wernicke, 1985]. A suite of thermal and mechanical effects have been invoked to derive generic mechanisms for flank uplift and these have been applied, with varying levels of success, to the Arabian case. We propose that dynamic topography supported by large scale mantle flow beneath the Africa-Arabia <span class="hlt">system</span> contributes significantly to the observed pattern of Arabian <span class="hlt">rift</span>-flank uplift. Seismic tomographic images indicate the existence of large scale (anomalously slow) heterogeneity originating from the deep mantle under southern Africa and, apparently, connecting to more shallow structure beneath the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">system</span> and the Arabian plate. We predict Arabian topography driven by viscous stresses associated with this buoyant megastructure. We first convert velocity anomalies given by the seismic S-wave model S20RTS [Ritsema et al., 1999] to density anomalies using standard scaling profiles, and then input these into a 2-D mantle convection model. Normal stresses derived from the flow models are then used to compute associated profiles of surface (`dynamic') topography. These profiles reconcile the observed topography of the Arabian platform and they provide an explanation for the distinct geometry of <span class="hlt">rift</span>-flank uplift across the two sides of the Red Sea. Our calculations do not preclude a contribution to topography from previously described thermal and/or mechanical effects; however, they indicate that future analyses of <span class="hlt">rift</span>-flank uplift should consider the potential contribution from large scale mantle flow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6747539','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6747539"><span id="translatedtitle">Volcanism at <span class="hlt">rifts</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>White, R.S.; McKenzie, D.P.</p> <p>1989-07-01</p> <p>The earth's outer shell <span class="hlt">rifts</span> continuously, stretching and splitting both on the ocean's floor and on continents. Every 30 million years or so the <span class="hlt">rifting</span> becomes cataclysmic, releasing continent-size floods of magma. This paper explains that the same mechanism is at work in both cases, the difference being in the slightly hotter temperature of the parent mantle for spectacular volcanic outbursts. Two kinds of evidence are described: quantitative descriptions of rock melting and a wide range of observations made on the <span class="hlt">rifted</span> edges of continents and in the oceans that have opened between them.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.8501G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.8501G"><span id="translatedtitle">Tectono-Sedimentary Analysis of <span class="hlt">Rift</span> Basins: Insights from the Corinth <span class="hlt">Rift</span>, Greece</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gawthorpe, Robert; Ford, Mary</p> <p>2015-04-01</p> <p>Existing models for the tectono-sedimentary evolution of <span class="hlt">rift</span> basins are strongly linked the growth and linkage of normal fault segments and localization of fault activity. Early stages of faulting (<span class="hlt">rift</span> 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 (<span class="hlt">rift</span> 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 <span class="hlt">rift</span> basins, but recent work has suggested that pre-existing structures, normal fault interaction with pre-<span class="hlt">rift</span> salt and antecedent drainage <span class="hlt">systems</span> significantly alter this initiation-to-climax perspective of <span class="hlt">rift</span> basin development. The E-W-striking, Pliocene-Pleistocene Corinth <span class="hlt">rift</span>, central Greece, is an excellent natural laboratory for studying the tectono-sedimentary evolution of <span class="hlt">rift</span> basins due to its young age, excellent onshore exposure of syn-<span class="hlt">rift</span> structure and stratigraphy and extensive offshore seismic data. The <span class="hlt">rift</span> 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 <span class="hlt">rift</span>. High topography and large antecedent drainage <span class="hlt">systems</span>, focused along palaeovalleys, provided high sediment flux to NE-flowing alluvial <span class="hlt">systems</span> that overfilled early-<span class="hlt">rift</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70016402','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70016402"><span id="translatedtitle">Large-scale variation in lithospheric structure along and across the Kenya <span class="hlt">rift</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Prodehl, C.; Mechie, J.; Kaminski, W.; Fuchs, K.; Grosse, C.; Hoffmann, H.; Stangl, R.; Stellrecht, R.; Khan, M.A.; Maguire, Peter K.H.; Kirk, W.; Keller, Gordon R.; Githui, A.; Baker, M.; Mooney, W.; Criley, E.; Luetgert, J.; Jacob, B.; Thybo, H.; Demartin, M.; Scarascia, S.; Hirn, A.; Bowman, J.R.; Nyambok, I.; Gaciri, S.; Patel, J.; Dindi, E.; Griffiths, D.H.; King, R.F.; Mussett, A.E.; Braile, L.W.; Thompson, G.; Olsen, K.; Harder, S.; Vees, R.; Gajewski, D.; Schulte, A.; Obel, J.; Mwango, F.; Mukinya, J.; Riaroh, D.</p> <p>1991-01-01</p> <p>The Kenya <span class="hlt">rift</span> is one of the classic examples of a continental <span class="hlt">rift</span> zone: models for its evolution range from extension of the lithosphere by pure shear1, through extension by simple shear2, to diapiric upwelling of an asthenolith3. Following a pilot study in 19854, the present work involved the shooting of three seismic refraction and wide-angle reflection profiles along the axis, across the margins, and on the northeastern flank of the <span class="hlt">rift</span> (Fig. 1). These lines were intended to reconcile the different crustal thickness estimates for the northern and southern parts of the <span class="hlt">rift</span>4-6 and to reveal the structure across the <span class="hlt">rift</span>, including that beneath the flanks. The data, presented here, reveal significant lateral variations in structure both along and across the <span class="hlt">rift</span>. The crust thins along the <span class="hlt">rift</span> axis from 35 km in the south to 20 km in the north; there are abrupt changes in Mono depth and uppermost-mantle seismic velocity across the <span class="hlt">rift</span> margins, and crustal thickening across the boundary between the Archaean craton and Pan<span class="hlt">African</span> orogenic belt immediately west of the <span class="hlt">rift</span>. These results suggest that thickened crust may have controlled the <span class="hlt">rift</span>'s location, that there is a decrease in extension from north to south, and that the upper mantle immediately beneath the <span class="hlt">rift</span> may contain reservoirs of magma generated at greater depth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20841717','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20841717"><span id="translatedtitle">Monitoring diseases across borders: <span class="hlt">African</span> regional integrative information <span class="hlt">systems</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Simbini, Tungamirirai; Foster, Rosemary; Nesara, Paul; Hullin Lucay Cossio, Carola</p> <p>2010-01-01</p> <p>In <span class="hlt">African</span> countries, communicable diseases remain the chief cause of a heavy disease burden. Regional economic, political and social integration bring new challenges in the management of these diseases, many of which are treatable. Information Communication Technology (ICT) applied through electronic health <span class="hlt">systems</span> has the potential to strengthen healthcare service delivery and disease surveillance within these countries. This paper discusses the importance of well-defined e-Health strategies within countries and, in addition, proposes that countries within regions collaborate in planning for health information exchange across borders. It is suggested that particular attention be paid to technical and data standards enabling interoperability, and also to issues of security, patient privacy and governance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6185385','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6185385"><span id="translatedtitle">Oil exploration in nonmarine <span class="hlt">rift</span> basins of interior Sudan</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Schull, T.J.</p> <p>1984-04-01</p> <p>In early 1975 Chevron Overseas Petroleum Inc. commenced a major petroleum exploration effort in previously unexplored interior Sudan. With the complete cooperation of the Sudanese Government, Chevron has acquired a vast amount of geologic and geophysical data during the past 9 years. These data include extensive aeromagnetic and gravity surveys, 25,000 mi (40,200 km) of seismic data, and the results of 66 wells. This information has defined several large <span class="hlt">rift</span> basins which are now recognized as a major part of the Central <span class="hlt">African</span> <span class="hlt">rift</span> <span class="hlt">system</span>. The sedimentary basins of interior Sudan are characterized by thick Cretaceous and Tertiary nonmarine clastic sequences. Over 35,000 ft (10,600 m) of sediment have been deposited in the deepest trough, and extensive basinal areas are underlain by more than 20,000 ft (6100 m) of sediment. The depositional sequence includes thick lacustrine shales and claystones, flood plain claystones, and lacustrine, fluvial, and alluvial sandstones and conglomerates. Those lacustrine claystones which were deposited in an anoxic environment provide oil-prone source rocks. Reservoir sandstones have been found in a wide variety of nonmarine sandstone facies. The extensional tectonism which formed these basins began in the Early Cretaceous. Movement along major fault trends continued intermittently into the Miocene. This deformation resulted in a complex structural history which led to the formation of several deep fault-bounded troughs, major interbasin high trends, and complex basin flanks. This tectonism has created a wide variety of structures, many of which have become effective hydrocarbon traps.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMED23A3482S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMED23A3482S"><span id="translatedtitle">Using Lake Superior Parks to Present the Midcontinent <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stein, C. A.; Stein, S. A.; Blavascunas, E.</p> <p>2014-12-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span> (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 <span class="hlt">African</span> <span class="hlt">Rift</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005GeoJI.161..707S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005GeoJI.161..707S"><span id="translatedtitle">An updated global earthquake catalogue for stable continental regions: reassessing the correlation with ancient <span class="hlt">rifts</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schulte, Saskia M.; Mooney, Walter D.</p> <p>2005-06-01</p> <p>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 <span class="hlt">rifts</span>, we assess the correlation of intraplate seismicity with ancient <span class="hlt">rifts</span> on a global scale. Each tectonic event is put into one of five categories based on location: (i) interior <span class="hlt">rifts</span>/taphrogens, (ii) <span class="hlt">rifted</span> continental margins, (iii) non-<span class="hlt">rifted</span> crust, (iv) possible interior <span class="hlt">rifts</span> and (v) possible <span class="hlt">rifted</span> margins. We find that approximately 27 per cent of all events are classified as interior <span class="hlt">rifts</span> (i), 25 per cent are <span class="hlt">rifted</span> continental margins (ii), 36 per cent are within non-<span class="hlt">rifted</span> crust (iii) and 12 per cent (iv and v) remain uncertain. Thus, over half (52 per cent) of all events are associated with <span class="hlt">rifted</span> crust, although within the continental interiors (i.e. away from continental margins), non-<span class="hlt">rifted</span> crust has experienced more earthquakes than interior <span class="hlt">rifts</span>. 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 <span class="hlt">rifts</span> (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 <span class="hlt">rifts</span>/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 <span class="hlt">rifts</span>/taphrogens that have experienced the largest earthquakes, seismicity within the Kutch <span class="hlt">rift</span>, India, and the East China <span class="hlt">rift</span> <span class="hlt">system</span>, may be controlled by diffuse plate boundary deformation more than by the presence</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70029536','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70029536"><span id="translatedtitle">An updated global earthquake catalogue for stable continental regions: Reassessing the correlation with ancient <span class="hlt">rifts</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Schulte, S.M.; Mooney, W.D.</p> <p>2005-01-01</p> <p>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 <span class="hlt">rifts</span>, we assess the correlation of intraplate seismicity with ancient <span class="hlt">rifts</span> on a global scale. Each tectonic event is put into one of five categories based on location: (i) interior <span class="hlt">rifts</span>/taphrogens, (ii) <span class="hlt">rifted</span> continental margins, (iii) non-<span class="hlt">rifted</span> crust, (iv) possible interior <span class="hlt">rifts</span> and (v) possible <span class="hlt">rifted</span> margins. We find that approximately 27 per cent of all events are classified as interior <span class="hlt">rifts</span> (i), 25 per cent are <span class="hlt">rifted</span> continental margins (ii), 36 per cent are within non-<span class="hlt">rifted</span> crust (iii) and 12 per cent (iv and v) remain uncertain. Thus, over half (52 per cent) of all events are associated with <span class="hlt">rifted</span> crust, although within the continental interiors (i.e. away from continental margins), non-<span class="hlt">rifted</span> crust has experienced more earthquakes than interior <span class="hlt">rifts</span>. 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 <span class="hlt">rifts</span> (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 <span class="hlt">rifts</span>/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 <span class="hlt">rifts</span>/taphrogens that have experienced the largest earthquakes, seismicity within the Kutch <span class="hlt">rift</span>, India, and the East China <span class="hlt">rift</span> <span class="hlt">system</span>, may be controlled by diffuse plate boundary deformation more than by the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012Litho.152...84W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012Litho.152...84W"><span id="translatedtitle">Open <span class="hlt">System</span> evolution of peralkaline trachyte and phonolite from the Suswa volcano, Kenya <span class="hlt">rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>White, John Charles; Espejel-García, Vanessa V.; Anthony, Elizabeth Y.; Omenda, Peter</p> <p>2012-11-01</p> <p>Suswa is the southernmost volcanic center in the Central Kenya Peralkaline Province (CKPP) and represents the only salic center to have erupted significant volumes of peralkaline silica-undersaturated lavas and tuffs (trachyte, nepheline trachyte and phonolite). The eruptive products of Suswa can be clearly divided into two series, which correspond closely to the volcano's eruptive history. The earlier series (C1) includes lavas and tuffs that built the initial shield volcano (pre-caldera, unit S1) and erupted during the first caldera collapse (syn-caldera, units S2-S5); these rocks are dominated by peralkaline, silica-saturated to mildly under-saturated trachyte. The later series (C2) includes lavas and tuffs that erupted within the caldera structure following the initial collapse (post-caldera, units S6-S7) and during the creation of a second smaller, nested caldera and central "island block" (ring trench group, RTG, unit S8); these rocks are dominated by peralkaline phonolite. In this study, we combine mineralogical evidence with the results of major-element, trace-element, and thermodynamic modelling to propose a complex model for the origin of the Suswa volcano. From these results we conclude that C1 is the result of protracted fractional crystallization of a fairly "dry" alkali basalt (< 1 wt.% H2O) under relatively high pressure (400 MPa) and low oxygen fugacity (FMQ to FMQ-1). Although C1 appears to be primarily the result of closed <span class="hlt">system</span> processes, a variety of open <span class="hlt">system</span> processes are responsible for C2. We propose that crystallization of C1 trachyte resulted in the formation of a syenitic residue, which was assimilated (Ma/Mc = 0.1) during a later stage of recharge and differentiation of alkali basalt to produce post-caldera ne-trachyte. Post-caldera (S6-7) phonolites were in turn the result of fractional crystallization of this ne-trachyte. RTG phonolites, however, are the result of feldspar resorption prompted perhaps by magma recharge as evidenced</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=development+AND+theory&pg=3&id=EJ961835','ERIC'); return false;" href="http://eric.ed.gov/?q=development+AND+theory&pg=3&id=EJ961835"><span id="translatedtitle">Understanding <span class="hlt">African</span> American Adolescents' Identity Development: A Relational Developmental <span class="hlt">Systems</span> Perspective</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Brittian, Aerika S.</p> <p>2012-01-01</p> <p>This article examines the development of <span class="hlt">African</span> American adolescents' identity using a relational developmental <span class="hlt">systems</span> theory framework, which led to the expectation that identity development is linked to both the reduction of risk behaviors and the promotion of <span class="hlt">African</span> American adolescents' healthy development. Different personological theories…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=homelessness&pg=6&id=EJ1103188','ERIC'); return false;" href="http://eric.ed.gov/?q=homelessness&pg=6&id=EJ1103188"><span id="translatedtitle">Unheard and Unseen: How Housing Insecure <span class="hlt">African</span> American Adolescents Experience the Education <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Ellis, Addie Lucille; Geller, Kathy D.</p> <p>2016-01-01</p> <p>This narrative study is based on stories told by <span class="hlt">African</span> American adolescents experiencing homelessness. It offers insights into their lived experiences and describes the challenges faced in negotiating the urban education <span class="hlt">system</span>. <span class="hlt">African</span> American youth are disproportionately represented in the adolescent homeless demographic. "Unheard and…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA....10300H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA....10300H"><span id="translatedtitle">The Thaumasia "<span class="hlt">rift</span>", Mars - is it a <span class="hlt">rift</span>?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hauber, E.; Kronberg, P.</p> <p>2003-04-01</p> <p>We describe the morphology of a large and complex graben structure in western Thaumasia which was often ascribed to <span class="hlt">rifting</span> by previous authors (the Thaumasia "<span class="hlt">rift</span>" or TR). We consider possible fault geometries, determine extension, and discuss shortly possible models for its origin. The TR is characterized by a strong (half)graben asymmetry. The master fault <span class="hlt">system</span> changes from the western border in the northern part to the eastern border in the southern part (at ˜21^oS). Several profiles across the TR display features that might indicate a listric master fault, including an overall halfgraben geometry, tilted blocks, and a curvature of the hanging wall which is characteristic of a rollover. For a listric fault, the depth D to a detachment can be determined from the surficial fault dip (α), the tilt of the graben floor (θ), and the vertical offset (d). We measure a scarp height d of ˜2000 m and floor tilts θ between 0.9^o and 2.7^o. For α = 60^o, we obtain values of D between ˜33 km and ˜67 km (θ = 2.0^o and 1.0^o). Interestingly, these values correspond very well with recent estimations of the thickness of the elastic lithosphere T_e in S-Tharsis, as given by Zuber et al. (2000): Valles Marineris ˜60 km, Solis Planum ˜35 km. A listric W-dipping master fault in the middle and southern part of the TR might indicate gravitational gliding of an unstable part of the outward verging fold-and-thrust plateau margin towards W, i.e., toward the foreland of Thaumasia. However, slip along planar faults can also produce tilted graben floors and hanging wall flexure, so the observed morphology does not allow any firm statement about the fault geometry. Extension (assuming planar fault planes) was determined using the vertical displacement at faults. In the N, most of the extension occurred along a few major faults. In the S, it has been distributed among many smaller faults. Extension is 0.5 to 4.5 km (strain 1 to 3%). This is much less than 10 km, as previously</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3111045','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3111045"><span id="translatedtitle">The Pathogenesis of <span class="hlt">Rift</span> Valley Fever</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ikegami, Tetsuro; Makino, Shinji</p> <p>2011-01-01</p> <p><span class="hlt">Rift</span> Valley fever (RVF) is an emerging zoonotic disease distributed in sub-Saharan <span class="hlt">African</span> countries and the Arabian Peninsula. The disease is caused by the <span class="hlt">Rift</span> Valley fever virus (RVFV) of the family Bunyaviridae and the genus Phlebovirus. The virus is transmitted by mosquitoes, and virus replication in domestic ruminant results in high rates of mortality and abortion. RVFV infection in humans usually causes a self-limiting, acute and febrile illness; however, a small number of cases progress to neurological disorders, partial or complete blindness, hemorrhagic fever, or thrombosis. This review describes the pathology of RVF in human patients and several animal models, and summarizes the role of viral virulence factors and host factors that affect RVFV pathogenesis. PMID:21666766</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21666766','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21666766"><span id="translatedtitle">The pathogenesis of <span class="hlt">Rift</span> Valley fever.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ikegami, Tetsuro; Makino, Shinji</p> <p>2011-05-01</p> <p><span class="hlt">Rift</span> Valley fever (RVF) is an emerging zoonotic disease distributed in sub-Saharan <span class="hlt">African</span> countries and the Arabian Peninsula. The disease is caused by the <span class="hlt">Rift</span> Valley fever virus (RVFV) of the family Bunyaviridae and the genus Phlebovirus. The virus is transmitted by mosquitoes, and virus replication in domestic ruminant results in high rates of mortality and abortion. RVFV infection in humans usually causes a self-limiting, acute and febrile illness; however, a small number of cases progress to neurological disorders, partial or complete blindness, hemorrhagic fever, or thrombosis. This review describes the pathology of RVF in human patients and several animal models, and summarizes the role of viral virulence factors and host factors that affect RVFV pathogenesis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA.....8758V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA.....8758V"><span id="translatedtitle">Neotectonics along the Turkana <span class="hlt">Rift</span> (North Kenya) from river network analysis, remote sensing and reflection seismic data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vetel, W.; Le Gall, B.; Tiercelin, J.-J.</p> <p>2003-04-01</p> <p>The NS-trending Turkana <span class="hlt">Rift</span> (North Kenya) cuts through a N140^oE transverse depressed zone between the Kenyan and Ethiopian domes. It forms a 200 km-long <span class="hlt">rift</span> segment of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>, centered on the Turkana Lake. In this region, widespread <span class="hlt">rifting</span> occurred during the Oligocene to Mio-Pliocene and opened large NS-trending hemigrabens imaged by seismics to the West of the Turkana Lake. Because the Turkana <span class="hlt">rifted</span> zone is a low and poorly contrasted topographic area, it is difficult to draw the trace of the active <span class="hlt">rift</span>, in contrast with 1) the narrow (20 km-wide) N10^o-trending axial trough forming the Suguta valley to the South, and 2) the Chew Bahir faulted basin to the North. Despite a semi-arid climate, the Turkana area shows a dense and widely-distributed river drainage network dominated by the Turkwell, Kerio and Omo first-order rivers. The entire stream pattern has been extracted from Landsat satellite images and then analyzed in terms of drainage anomalies. Major anomalies have been recognized at various scales and assigned to active tectonics. The direct correlation between surface data and the deep structures imaged on seismics allows to precise the inherited (Oligo-Miocene) or newly-formed origin of the active deformation. Evidence for neotectonics are observed along 1) a large-scale transverse (EW) fault rooting at depth along a steep basement discontinuity (Turkwell), 2) a <span class="hlt">rift</span>-parallel (NS) fault zone probably emplaced during Plio-Pleistocene and actually bounding the Napedet volcanic plateau to the West, and 3) over a round-shaped uplifted zone caused by inversion tectonics (Kalabata). Structural interpretation of offshore high-resolution seismics from Lake Turkana illustrates the existence of recent deformation and also helps complete the overall neotectonic framework of the Turkana <span class="hlt">rift</span> zone. Finally, this study leads us to regard the Turkana area as a broad (ca. 100 km wide) zone of diffuse extension where active deformation is</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/EJ963743.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/EJ963743.pdf"><span id="translatedtitle">Indigenous <span class="hlt">Systems</span> within the <span class="hlt">African</span>-American Community</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Marbley, Aretha Faye; Rouson, Leon</p> <p>2011-01-01</p> <p>For the <span class="hlt">African</span>-American family, life ain't been no crystal stair. The <span class="hlt">African</span>-American family has trotted for over 400 years through a wilderness of racism, poverty, discrimination of all kinds, crossing seas of monsters and forests of demons. Yet, despite the numerous obstacles and attacks that society has mounted against it since slavery, the…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JAfES..77...41W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JAfES..77...41W"><span id="translatedtitle">The role of tephra studies in <span class="hlt">African</span> paleoanthropology as exemplified by the Sidi Hakoma Tuff</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>WoldeGabriel, Giday; Endale, Tamrat; White, Tim D.; Thouveny, Nicolas; Hart, William K.; Renne, Paul R.; Asfaw, Berhane</p> <p>2013-01-01</p> <p>Beginning in the 1960s, geological and paleoanthropological exploration of the Ethiopian <span class="hlt">rift</span> <span class="hlt">system</span>'s basins have led to the discovery and assembly of the most comprehensive record of human biological and technological change during the last 6 million years. The hominid fossils, including partial skeletons, were primarily discovered in the Afar <span class="hlt">Rift</span>, the Main Ethiopian <span class="hlt">Rift</span>, and in the Omo Basin of the broadly <span class="hlt">rifted</span> zone of SW Ethiopia. The paleoanthropological research areas within the SW Afar <span class="hlt">Rift</span> that have yielded many diverse hominid species and the oldest stone tools are, from north to south, Woranso-Mille (aff. Ardipithecus and Au. afarensis), Hadar (Au. afarensis, Homo sp.), Dikika (Au. afarensis), Gona (Ar. kadabba, Ar. ramidus, H. erectus, and oldest stone tools), Middle Awash (Ar. kadabba, Ar. ramidus, Au. anamensis, Au. afarensis, Au. garhi, H. erectus, H. rhodesiensis, H. sapiens idaltu, and the oldest paleo-butchery locality), and Galili (Au. afarensis). Additional hominid remains were discovered at Melka Kunture on the banks of the Awash River near its source along the western margin of the central part of the Main Ethiopian <span class="hlt">Rift</span> (H. erectus), at Konso (H. erectus and A. boisei), and at the southern end of the MER, and in the Omo Basin (Au. anamensis, Au. afarensis, Au. aethiopicus, Au. boisei, H. habilis, and H. erectus). Distal and sometimes proximal tephra units interbedded within fossilifeous sedimentary deposits have become key elements in this work by providing chronological and correlative control and depositional contexts. Several regional tephra markers have been identified within the northern half of the eastern <span class="hlt">African</span> <span class="hlt">rift</span> valley in Ethiopia and Kenya, and in marine sediments of the Gulf of Aden <span class="hlt">Rift</span> and the NW Indian Ocean. Out of the many regional tephra stratigraphic markers that range in age from the early Pliocene (3.97 Ma) to the late Pleistocene (0.16 Ma), the Sidi Hakoma Tuff (SHT) has been more widely identified and thoroughly</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011Tecto..30.1002D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011Tecto..30.1002D"><span id="translatedtitle">Young <span class="hlt">rift</span> kinematics in the Tadjoura <span class="hlt">rift</span>, western Gulf of Aden, Republic of Djibouti</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Daoud, Mohamed A.; Le Gall, Bernard; Maury, René C.; Rolet, JoëL.; Huchon, Philippe; Guillou, Hervé</p> <p>2011-02-01</p> <p>The Tadjoura <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> margins and to discriminate and date several distinct fault networks of this oblique <span class="hlt">rift</span>. Morphological and statistical analyses of onshore extensional fault populations show marked changes in structural styles along-strike, in a direction parallel to the <span class="hlt">rift</span> 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 <span class="hlt">rifting</span> into the Asal-Ghoubbet <span class="hlt">rift</span> 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 <span class="hlt">system</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1986Tecto...5..279S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1986Tecto...5..279S"><span id="translatedtitle">Continental <span class="hlt">Rifting</span> and Transform Faulting Along the Jurassic Transantarctic <span class="hlt">Rift</span>, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schmidt, Dwight L.; Rowley, Peter D.</p> <p>1986-04-01</p> <p>The Transantarctic <span class="hlt">rift</span>, an extensional continental <span class="hlt">rift</span> valley, formed between East and West Antarctica during latest Early and Middle Jurassic time and is represented today by the high Transantarctic Mountains, which contain large volumes of continental flood basalt, diabase, and gabbro. Transantarctic <span class="hlt">rifting</span> marked the beginning of the breakup of Gondwanaland; it was contiguous and synchronous with continental <span class="hlt">rifting</span> between East Antarctica-India and Africa as represented by the continental basalt and diabase of Queen Maud Land and the Karroo of southern Africa. During Late Jurassic time, about 150 Ma or slightly earlier, East and West Gondwanaland separated and new oceanic crust of the earliest Indian Ocean formed between East Antarctica-India and Africa. If, as assumed, West Antarctica and South America remained fixed through a tip-to-tip join between the Antarctic Peninsula and Tierra del Fuego, then this seafloor spreading required major right-lateral transform faulting of 500 to 1000 km on the Transantarctic <span class="hlt">rift</span> <span class="hlt">system</span> between East and West Antarctica. The Transantarctic Mountains were elevated at about the same time in Late Jurassic; such uplifts are characteristic of active <span class="hlt">rift</span> margins worldwide. During Cenozoic time, extensional block faulting, independent of the Jurassic <span class="hlt">rifting</span>, further disrupted large areas of West Antarctica. During the same time, the Transantarctic Mountains were further uplifted.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JAfES..65...61B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JAfES..65...61B"><span id="translatedtitle">Geometry and faults tectonic activity of the Okavango <span class="hlt">Rift</span> Zone, Botswana: Evidence from magnetotelluric and electrical resistivity tomography imaging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bufford, Kelsey Mosley; Atekwana, Estella A.; Abdelsalam, Mohamed G.; Shemang, Elijah; Atekwana, Eliot A.; Mickus, Kevin; Moidaki, Moikwathai; Modisi, Motsoptse P.; Molwalefhe, Loago</p> <p>2012-04-01</p> <p>We used Magnetotelluric (MT) and Electrical Resistivity Tomography (ERT) to investigate the geometry and nature of faults activity of the Okavango <span class="hlt">Rift</span> Zone (ORZ) in Botswana, an incipient <span class="hlt">rift</span> at the southern tip of the Southwestern Branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>. The ORZ forms a subtle topographic depression filled with Quaternary lacustrine and fluvio-deltaic sediments and is bounded by NE-trending normal faults that are more prominent in the southeastern portion of the <span class="hlt">rift</span> basin. An MT model from a regional (˜140 km) NW-SE trending MT transect shows that much of the <span class="hlt">rift</span> basin is underlain by a broad asymmetrical low resistivity anomaly that slopes gently (˜1°) from NW to SE reaching a depth of ˜300 m. This anomaly suggests that faults in the southeastern part of the <span class="hlt">rift</span> form a NW-dipping border fault zone and that the lacustrine and fluvio-deltaic sediments contain brackish to saline water filling the broad half-graben structure. Furthermore, MT and ERT models from detailed (4-13 km long) MT transects and resistivity profiles show that one border fault (Thamalakane) and two within-basin faults (Lecha and Tsau) in the southeastern part of the ORZ are characterized by a localized high conductivity anomaly while another border fault (Kunyere) lacks such an anomaly. These localized anomalies are attributed to channelized fresh surface water and saline groundwater percolating through these faults forming "fault zone conductors" and suggest actively displacing faults. The lack of a "fault zone conductor" in the Kunyere fault is interpreted as indicating diminishing displacement on this fault, and that strain was transferred to the Thamalakane fault further to the east. The fluids provide lubricant for the ORZ faults, hence preventing infrequent large magnitude earthquakes, but favoring frequent micro-seismicity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27178456','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27178456"><span id="translatedtitle">Kantis: A new Australopithecus site on the shoulders of the <span class="hlt">Rift</span> Valley near Nairobi, Kenya.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mbua, Emma; Kusaka, Soichiro; Kunimatsu, Yutaka; Geraads, Denis; Sawada, Yoshihiro; Brown, Francis H; Sakai, Tetsuya; Boisserie, Jean-Renaud; Saneyoshi, Mototaka; Omuombo, Christine; Muteti, Samuel; Hirata, Takafumi; Hayashida, Akira; Iwano, Hideki; Danhara, Tohru; Bobe, René; Jicha, Brian; Nakatsukasa, Masato</p> <p>2016-05-01</p> <p>Most Plio-Pleistocene sites in the Gregory <span class="hlt">Rift</span> Valley that have yielded abundant fossil hominins lie on the <span class="hlt">Rift</span> Valley floor. Here we report a new Pliocene site, Kantis, on the shoulder of the Gregory <span class="hlt">Rift</span> Valley, which extends the geographical range of Australopithecus afarensis to the highlands of Kenya. This species, known from sites in Ethiopia, Tanzania, and possibly Kenya, is believed to be adapted to a wide spectrum of habitats, from open grassland to woodland. The Kantis fauna is generally similar to that reported from other contemporaneous A. afarensis sites on the <span class="hlt">Rift</span> Valley floor. However, its faunal composition and stable carbon isotopic data from dental enamel suggest a stronger C4 environment than that present at those sites. Although the Gregory <span class="hlt">Rift</span> Valley has been the focus of paleontologists' attention for many years, surveys of the <span class="hlt">Rift</span> shoulder may provide new perspective on <span class="hlt">African</span> Pliocene mammal and hominin evolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GGG....16.4344A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GGG....16.4344A"><span id="translatedtitle">Submarine and subaerial lavas in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>: Temporal record of shifting magma source components from the lithosphere and asthenosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aviado, Kimberly B.; Rilling-Hall, Sarah; Bryce, Julia G.; Mukasa, Samuel B.</p> <p>2015-12-01</p> <p>The petrogenesis of Cenozoic alkaline magmas in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (WARS) remains controversial, with competing models highlighting the roles of decompression melting due to passive <span class="hlt">rifting</span>, active plume upwelling in the asthenosphere, and flux melting of a lithospheric mantle metasomatized by subduction. In this study, seamounts sampled in the Terror <span class="hlt">Rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T43H..04E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T43H..04E"><span id="translatedtitle">Crustal Strain Patterns in Magmatic and Amagmatic Early Stage <span class="hlt">Rifts</span>: Border Faults, Magma Intrusion, and Volatiles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ebinger, C. J.; Keir, D.; Roecker, S. W.; Tiberi, C.; Aman, M.; Weinstein, A.; Lambert, C.; Drooff, C.; Oliva, S. J. C.; Peterson, K.; Bourke, J. R.; Rodzianko, A.; Gallacher, R. J.; Lavayssiere, A.; Shillington, D. J.; Khalfan, M.; Mulibo, G. D.; Ferdinand-Wambura, R.; Palardy, A.; Albaric, J.; Gautier, S.; Muirhead, J.; Lee, H.</p> <p>2015-12-01</p> <p><span class="hlt">Rift</span> initiation in thick, strong continental lithosphere challenges current models of continental lithospheric deformation, in part owing to gaps in our knowledge of strain patterns in the lower crust. New geophysical, geochemical, and structural data sets from youthful magmatic (Magadi-Natron, Kivu), weakly magmatic (Malawi, Manyara), and amagmatic (Tanganyika) sectors of the cratonic East <span class="hlt">African</span> <span class="hlt">rift</span> <span class="hlt">system</span> provide new insights into the distribution of brittle strain, magma intrusion and storage, and time-averaged deformation. We compare and contrast time-space relations, seismogenic layer thickness variations, and fault kinematics using earthquakes recorded on local arrays and teleseisms in sectors of the Western and Eastern <span class="hlt">rifts</span>, including the Natron-Manyara basins that developed in Archaean lithosphere. Lower crustal seismicity occurs in both the Western and Eastern <span class="hlt">rifts</span>, including sectors on and off craton, and those with and without central <span class="hlt">rift</span> volcanoes. In amagmatic sectors, lower crustal strain is accommodated by slip along relatively steep border faults, with oblique-slip faults linking opposing border faults that penetrate to different crustal levels. In magmatic sectors, seismicity spans surface to lower crust beneath both border faults and eruptive centers, with earthquake swarms around magma bodies. Our focal mechanisms and Global CMTs from a 2007 fault-dike episode show a local rotation from ~E-W extension to NE-SE extension in this linkage zone, consistent with time-averaged strain recorded in vent and eruptive chain alignments. These patterns suggest that strain localization via widespread magma intrusion can occur during the first 5 My of <span class="hlt">rifting</span> in originally thick lithosphere. Lower crustal seismicity in magmatic sectors may be caused by high gas pressures and volatile migration from active metasomatism and magma degassing, consistent with high CO2 flux along fault zones, and widespread metasomatism of xenoliths. Volatile release and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992CoMP..111...24Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992CoMP..111...24Z"><span id="translatedtitle">Four- and five-phase peridotites from a continental <span class="hlt">rift</span> <span class="hlt">system</span>: evidence for upper mantle uplift and cooling at the Ross Sea margin (Antarctica)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zipfel, J.; Wörner, G.</p> <p>1992-06-01</p> <p>Upper mantle plagioclase+spinel- and spinel-peridotite xenoliths occur in basanitic and tephritic lavas of the 2.7 my to Recent Mt. Melbourne Volcanic Field (Antarctica). This field belongs to the Cenozoic McMurdo volcanic group which is located between the deep western trough of the Ross Sea <span class="hlt">rift</span> <span class="hlt">system</span> and the uplifted <span class="hlt">rift</span> shoulder of the Transantarctic Mountains. Our samples cover the transition zone between <span class="hlt">rift</span> and shoulder. We examined texture and composition of plagioclase+spinel and normal spinel peridotites and determined temperatures and pressures of formation using the internally consistent Ca-ol/cpx and 2px-thermobarometer of Köhler and Brey (1990) and Brey and Köhler (1990). Distinct calcium distribution patterns in olivines correspond to three different petrographic textures: type ELZ have equigranular textures, and low calcium concentrations of 60 ppm in the olivine cores which are strongly zoned to 200 ppm in their rims. Type PLH are protogranular to porphyroclastic and have low and homogeneous calcium contents in the range of 120 to 200 ppm. Type EHH peridotites are equigranular and have olivines with high and homogeneous calcium values of 467 485 ppm. The application of the 2 px-thermometer give rim temperatures of 800 to 860 °C for Type ELZ, 900 to 1080 °C for type PLH and 1030 to 1050 °C for type EHH. Pressures of 13 to 17 kb calculated with the Ca-ol/epx-barometer for EHH peridotites are consistent with the Ross <span class="hlt">Rift</span> geotherm. For the other two types, this barometer yields unreasonable high pressures exceeding 30 kb for both, plagioclase-bearing and ‘normal’ spinel-peridotites. This indicates disequilibrium and continued calcium-loss from the olivines during cooling below the closure temperature for the 2 px-thermometer. Inversion of the Ca-in-olivine-barometer into a thermometer and application to core compositions of ELZ olivines (60 ppm) suggests that cooling occurred to temperatures of ca. 580 °C. Based on petrographical and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Litho.212...16T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Litho.212...16T"><span id="translatedtitle">Petrogenesis of the Ni-Cu-PGE sulfide-bearing Tamarack Intrusive Complex, Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span>, Minnesota</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Taranovic, Valentina; Ripley, Edward M.; Li, Chusi; Rossell, Dean</p> <p>2015-01-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span> (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 <span class="hlt">system</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4522541','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4522541"><span id="translatedtitle">Regional view of a Trans-<span class="hlt">African</span> Drainage <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Abdelkareem, Mohamed; El-Baz, Farouk</p> <p>2014-01-01</p> <p>Despite the arid to hyperarid climate of the Great Sahara of North Africa, pluvial climates dominated the region. Radar data shed some light on the postulated Trans-<span class="hlt">African</span> Drainage <span class="hlt">System</span> and its relationship to active and inactive tributaries of the Nile basin. Interpretations of recent elevation data confirm a source of the river water from the Red Sea highlands did not connect the Atlantic Ocean across Tushka basin, highlands of Uwinate and Darfur, and Chad basin, but northward to the ancestral Nile Delta. Elements of topography and climate were considered. They show that the former segments of the Nile closely mirror present-day tributaries of the Nile basin in drainage geometry, landscape, and climate. A rainfall data interpolation scenario revealed that this basin received concurrent runoff from both flanks such as Gabgaba-Allaqi to the east and Tushka basin to the west, similar to present-day Sobat and White Nile tributaries, respectively. Overall the western tributaries such as those of Tushka basin and Howar lead to the Nile, which was (and still is) the biggest river <span class="hlt">system</span> in Africa. PMID:26257941</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.T11B1865F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.T11B1865F"><span id="translatedtitle">Low-Temperature Constraints on the Evolution of Metamorphic Core Complexes of the Woodlark <span class="hlt">Rift</span> <span class="hlt">System</span>, Southeastern Papua New Guinea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fitzgerald, P. G.; Baldwin, S. L.; Miller, S. R.; Perry, S. E.; Webb, L. E.; Little, T. A.</p> <p>2008-12-01</p> <p>Subduction of the Woodlark microplate at the New Britain trench is driving seafloor spreading in the Woodlark Basin and, to the west of the basin, extension of continental crust in the Woodlark <span class="hlt">rift</span>. Seafloor spreading in the Woodlark Basin initiated in the east by ~6 Ma, after which it has propagated westward. To the west, in the Woodlark <span class="hlt">rift</span>, one of the most rapidly extending places on earth, exhumation has been locally both profound and rapid (cm/yr rates). In the NW part of the D'Entrecasteaux Islands, HP and UHP rocks have been unroofed from depths ≥90 km in the last 2-8 Ma. As part of a multidisciplinary study to understand the tectonic evolution of this region and to constrain how <span class="hlt">rifting</span> is exhuming the world's youngest HP/UHP rocks, low temperature thermochronology is being applied to the metamorphic core complexes of the D'Entrecasteaux Islands, as well as to continental fragments along the <span class="hlt">rifted</span> conjugate margins of the oceanic Woodlark Basin farther to the east. Within the Woodlark Basin and Woodlark <span class="hlt">rift</span>, apatite fission track (AFT) ages generally decrease from east to west, from ~7.5 Ma in the lower plate of the Misima metamorphic core complex, to ~3 Ma at Moresby Seamount, to between ca. 1.5 and 0.5 Ma in the D'Entrecasteaux Islands. Precision of AFT ages is poor because of low [U] and hence very few tracks are present. There is considerable variation amongst apatite (U-Th)/He (AHe) single-grain ages but not with respect to [eU], indicating that the radiation damage trapping model is likely not responsible for the observed single grain age distribution. Because of the extremely rapid cooling, anomalous older apparent AHe ages are likely due to external 4He implantation from adjacent minerals. We report ranges of minimum AHe ages as these have been shown to be reliably closer to actual AHe ages. AHe single grain ages decrease from east to west, from 3-6 Ma at Misima Island, although AHe ages may be younger on the western end of the island, to</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5013381','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5013381"><span id="translatedtitle">I too, am America: a review of research on <span class="hlt">systemic</span> lupus erythematosus in <span class="hlt">African</span>-Americans</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Williams, Edith M; Bruner, Larisa; Adkins, Alyssa; Vrana, Caroline; Logan, Ayaba; Kamen, Diane; Oates, James C</p> <p>2016-01-01</p> <p><span class="hlt">Systemic</span> lupus erythematosus (SLE) is a multi-organ autoimmune disorder that can cause significant morbidity and mortality. A large body of evidence has shown that <span class="hlt">African</span>-Americans experience the disease more severely than other racial-ethnic groups. Relevant literature for the years 2000 to August 2015 were obtained from systematic searches of PubMed, Scopus, and the EBSCOHost platform that includes MEDLINE, CINAHL, etc. to evaluate research focused on SLE in <span class="hlt">African</span>-Americans. Thirty-six of the 1502 articles were classified according to their level of evidence. The systematic review of the literature reported a wide range of adverse outcomes in <span class="hlt">African</span>-American SLE patients and risk factors observed in other mono and multi-ethnic investigations. Studies limited to <span class="hlt">African</span>-Americans with SLE identified novel methods for more precise ascertainment of risk and observed novel findings that hadn't been previously reported in <span class="hlt">African</span>-Americans with SLE. Both environmental and genetic studies included in this review have highlighted unique <span class="hlt">African</span>-American populations in an attempt to isolate risk attributable to <span class="hlt">African</span> ancestry and observed increased genetic influence on overall disease in this cohort. The review also revealed emerging research in areas of quality of life, race-tailored interventions, and self-management. This review reemphasizes the importance of additional studies to better elucidate the natural history of SLE in <span class="hlt">African</span>-Americans and optimize therapeutic strategies for those who are identified as being at high risk. PMID:27651918</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27651918','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27651918"><span id="translatedtitle">I too, am America: a review of research on <span class="hlt">systemic</span> lupus erythematosus in <span class="hlt">African</span>-Americans.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Williams, Edith M; Bruner, Larisa; Adkins, Alyssa; Vrana, Caroline; Logan, Ayaba; Kamen, Diane; Oates, James C</p> <p>2016-01-01</p> <p><span class="hlt">Systemic</span> lupus erythematosus (SLE) is a multi-organ autoimmune disorder that can cause significant morbidity and mortality. A large body of evidence has shown that <span class="hlt">African</span>-Americans experience the disease more severely than other racial-ethnic groups. Relevant literature for the years 2000 to August 2015 were obtained from systematic searches of PubMed, Scopus, and the EBSCOHost platform that includes MEDLINE, CINAHL, etc. to evaluate research focused on SLE in <span class="hlt">African</span>-Americans. Thirty-six of the 1502 articles were classified according to their level of evidence. The systematic review of the literature reported a wide range of adverse outcomes in <span class="hlt">African</span>-American SLE patients and risk factors observed in other mono and multi-ethnic investigations. Studies limited to <span class="hlt">African</span>-Americans with SLE identified novel methods for more precise ascertainment of risk and observed novel findings that hadn't been previously reported in <span class="hlt">African</span>-Americans with SLE. Both environmental and genetic studies included in this review have highlighted unique <span class="hlt">African</span>-American populations in an attempt to isolate risk attributable to <span class="hlt">African</span> ancestry and observed increased genetic influence on overall disease in this cohort. The review also revealed emerging research in areas of quality of life, race-tailored interventions, and self-management. This review reemphasizes the importance of additional studies to better elucidate the natural history of SLE in <span class="hlt">African</span>-Americans and optimize therapeutic strategies for those who are identified as being at high risk.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5171905','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5171905"><span id="translatedtitle">Simple reverse genetics <span class="hlt">systems</span> for Asian and <span class="hlt">African</span> Zika viruses</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Atieh, Thérèse; Baronti, Cécile; de Lamballerie, Xavier; Nougairède, Antoine</p> <p>2016-01-01</p> <p>Zika virus (ZIKV), a typical example of a re‐emerging pathogen, recently caused large outbreaks in Pacific islands and the Americas, associated with congenital diseases and neurological complications. Deciphering the natural history, ecology and pathophysiology of this mosquito-borne pathogen requires effective reverse genetics tools. In the current study, using the bacterium-free ‘Infectious Subgenomic Amplicons’ (ISA) method, we generated and made available to the scientific community via the non-profit European Virus Archive collection, two simple and performing reverse genetics <span class="hlt">systems</span> for ZIKV. One is based on an Asian ZIKV strain belonging to the outbreak lineage (French Polynesia 2013). The second was designed from the sequence of a low-passaged ZIKV <span class="hlt">African</span> strain (Dakar 1984). Using the ISA procedure, we derived wild-type and a variety of specifically engineered ZIKVs in days (intra- and inter-lineage chimeras). Since they are based on low-passaged ZIKV strains, these engineered viruses provide ideal tools to study the effect of genetic changes observed in different evolutionary time-scales of ZIKV as well as pathophysiology of ZIKV infections. PMID:27991555</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1813153M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1813153M"><span id="translatedtitle">Exploring the contrasts between fast and slow <span class="hlt">rifting</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Morgan, Jason P.; de Monserrat, Albert; White, Lloyd; Hall, Robert</p> <p>2016-04-01</p> <p>Researchers are now finding that extension sometimes occurs at rates much faster than the mean rates observed in the development of passive margins. Examples of rapid and ultra-rapid extension are found in several locations in Eastern Indonesia. This includes in northern and central Sulawesi as well as in eastern- and westernmost New Guinea. The periods of extension are associated with sedimentary basin growth as well as phases of crustal melting and rapid uplift. This is recorded through seismic imagery of basins offshore Sulawesi and New Guinea as well as through new field studies of the onshore geology in these regions. A growing body of new geochronological and biostratigraphic data provide some control on the rates of processes, indicating that rates of extension are typically at least twice as fast and potentially an order of magnitude faster than the fastest rates applied for more commonly studied <span class="hlt">rift</span> settings (e.g. Atlantic opening, East <span class="hlt">African</span> <span class="hlt">Rift</span>, Australia-Antarctica opening). Here we explore a suite of experiments more appropriate for <span class="hlt">rifting</span> episodes in Eastern Indonesia, and compare the evolution of these 'fast' (20-100 mm/year full rate) <span class="hlt">rifting</span> models to experiments with the same crustal geometries <span class="hlt">rifting</span> at ~5-20 mm/year. In particular, we explore to what depths hot lower crust and mantle can be exhumed by fast <span class="hlt">rifting</span>, and whether we can produce the p-T-t paths implied by recent onshore geological studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014ERL.....9j5008R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014ERL.....9j5008R"><span id="translatedtitle">Reducing uncertainty in nitrogen budgets for <span class="hlt">African</span> livestock <span class="hlt">systems</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rufino, M. C.; Brandt, P.; Herrero, M.; Butterbach-Bahl, K.</p> <p>2014-10-01</p> <p>Livestock is poorly represented in N budgets for the <span class="hlt">African</span> continent although some studies have examined livestock-related N flows at different levels. Livestock plays an important role in N cycling and therefore on N budgets including livestock-related flows. This study reviews the literature on N budgets for Africa to identify factors contributing to uncertainties. Livestock densities are usually modelled because of the lack of observational spatial data. Even though feed availability and quality varies across seasons, most studies use constant livestock excretion rates, and excreta are usually assumed to be uniformly distributed onto the land. Major uncertainties originate in the fraction of manure managed, and emission factors which may not reflect the situation of Africa. N budgets use coarse assumptions on production, availability, and use of crop residues as livestock feed. No flows between croplands-livestock and rangelands reflect the lack of data. Joint efforts are needed for spatial data collection of livestock data, crowdsourcing appears to be a promising option. The focus of the assessment of N budgets must go beyond croplands to include livestock and crop-livestock flows. We propose a nested <span class="hlt">systems</span> definition of livestock <span class="hlt">systems</span> to link local, regional level, and continental level and to increase the usefulness of point measurements of N losses. Scientists working at all levels should generate data to calibrate process-based models. Measurements in the field should not only concentrate on greenhouse gas emissions, but need to include crop and livestock production measurements, soil stock changes and other N loss pathways such as leaching, run-off and volatilization to assess management practices and trade-offs. Compared to the research done in other continents on N flows in livestock <span class="hlt">systems</span>, there are few data for Africa, and therefore concerted effort will be needed to generate sufficient data for modelling.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JAfES.116....1M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JAfES.116....1M"><span id="translatedtitle">Torque exerted on the side of crustal blocks controls the kinematics of Ethiopian <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muluneh, Ameha A.; Kidane, Tesfaye; Cuffaro, Marco; Doglioni, Carlo</p> <p>2016-04-01</p> <p>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 <span class="hlt">Rift</span> (ER), in the northern part of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> (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 <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2764559','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2764559"><span id="translatedtitle"><span class="hlt">Rift</span> Valley fever vaccines</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ikegami, Tetsuro; Makino, Shinji</p> <p>2009-01-01</p> <p><span class="hlt">Rift</span> Valley fever virus (RVFV), which belongs to the genus Phlebovirus, family Bunyaviridae, is a negative-stranded RNA virus carrying a tripartite RNA genome. RVFV is transmitted by mosquitoes and causes large outbreaks among ruminants and humans in Africa and the Arabian Peninsula. Human patients develop an acute febrile illness, followed by a fatal hemorrhagic fever, encephalitis or ocular diseases, whereas ruminants experience abortions during outbreak. Effective vaccination of both humans and ruminants is the best approach to control <span class="hlt">Rift</span> Valley fever. This article summarizes the development of inactivated RVFV vaccine, live attenuated vaccine, and other new generation vaccines. PMID:19837291</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/316236','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/316236"><span id="translatedtitle">Geochemistry of hypabyssal rocks of the Midcontinent <span class="hlt">Rift</span> <span class="hlt">system</span> in Minnesota, and implications for a Keweenawan magmatic ``family tree``</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Jerde, E.A.</p> <p>1998-11-01</p> <p>The hypabyssal rocks associated with the Keweenawan (1.1 Ga) Midcontinent <span class="hlt">Rift</span> 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 <span class="hlt">Rift</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5589281','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5589281"><span id="translatedtitle"><span class="hlt">African</span> oil plays</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Clifford, A.J. )</p> <p>1989-09-01</p> <p>The vast continent of Africa hosts over eight sedimentary basins, covering approximately half its total area. Of these basins, only 82% have entered a mature exploration phase, 9% have had little or no exploration at all. Since oil was first discovered in Africa during the mid-1950s, old play concepts continue to bear fruit, for example in Egypt and Nigeria, while new play concepts promise to become more important, such as in Algeria, Angola, Chad, Egypt, Gabon, and Sudan. The most exciting developments of recent years in <span class="hlt">African</span> oil exploration are: (1) the Gamba/Dentale play, onshore Gabon; (2) the Pinda play, offshore Angola; (3) the Lucula/Toca play, offshore Cabinda; (4) the Metlaoui play, offshore Libya/Tunisia; (5) the mid-Cretaceous sand play, Chad/Sudan; and (6) the TAG-I/F6 play, onshore Algeria. Examples of these plays are illustrated along with some of the more traditional oil plays. Where are the future oil plays likely to develop No doubt, the Saharan basins of Algeria and Libya will feature strongly, also the presalt of Equatorial West Africa, the Central <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> and, more speculatively, offshore Ethiopia and Namibia, and onshore Madagascar, Mozambique, and Tanzania.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/421110','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/421110"><span id="translatedtitle">South Atlantic sag basins: new petroleum <span class="hlt">system</span> components</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Henry, S.G. Mohriak, W.U.; Mello, M.R.</p> <p>1996-08-01</p> <p>Newly discovered pre-salt source rocks, reservoirs and seals need to be included as components to the petroleum <span class="hlt">systems</span> of both sides of the South Atlantic. These new components lie between the pre-salt <span class="hlt">rift</span> strata and the Aptian salt layers, forming large, post-<span class="hlt">rift</span>, thermal subsidence sag basins. These are differentiated from the older <span class="hlt">rift</span> basins by the lack of syn-<span class="hlt">rift</span> faulting and a reflector geometry that is parallel to the base salt regional unconformity rather than to the Precambrian basement. These basins are observed in deep water regions overlying areas where both the mantle and the crust have been involved in the extension. This mantle involvement creates post-<span class="hlt">rift</span> subsiding depocenters in which deposition is continuous while proximal <span class="hlt">rift</span>-phase troughs with little or no mantle involvement are bypassed and failed to accumulate potential source rocks during anoxic times. These features have been recognized in both West <span class="hlt">African</span> Kwanza Basin and in the East Brasil <span class="hlt">Rift</span> <span class="hlt">systems</span>. The pre-salt source rocks that are in the West <span class="hlt">African</span> sag basins were deposited in lacustrine brackish to saline water environment and are geochemically distinct from the older, syn-<span class="hlt">rift</span> fresh to brackish water lakes, as well as from younger, post-salt marine anoxic environments of the drift phase. Geochemical analyses of the source rocks and their oils have shown a developing source rock <span class="hlt">system</span> evolving from isolated deep <span class="hlt">rift</span> lakes to shallow saline lakes, and culminating with the infill of the sag basin by large saline lakes to a marginally marine restricted gulf. Sag basin source rocks may be important in the South Atlantic petroleum <span class="hlt">system</span> by charging deep-water prospects where syn-<span class="hlt">rift</span> source rocks are overmature and the post-salt sequences are immature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3408716','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3408716"><span id="translatedtitle">The Impact of the Geologic History and Paleoclimate on the Diversification of East <span class="hlt">African</span> Cichlids</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Danley, Patrick D.; Husemann, Martin; Ding, Baoqing; DiPietro, Lyndsay M.; Beverly, Emily J.; Peppe, Daniel J.</p> <p>2012-01-01</p> <p>The cichlid fishes of the East <span class="hlt">African</span> Great Lakes are the largest extant vertebrate radiation identified to date. These lakes and their surrounding waters support over 2,000 species of cichlid fish, many of which are descended from a single common ancestor within the past 10 Ma. The extraordinary East <span class="hlt">African</span> cichlid diversity is intricately linked to the highly variable geologic and paleoclimatic history of this region. Greater than 10 Ma, the western arm of the East <span class="hlt">African</span> <span class="hlt">rift</span> <span class="hlt">system</span> began to separate, thereby creating a series of <span class="hlt">rift</span> basins that would come to contain several water bodies, including the extremely deep Lakes Tanganyika and Malawi. Uplifting associated with this <span class="hlt">rifting</span> backponded many rivers and created the extremely large, but shallow Lake Victoria. Since their creation, the size, shape, and existence of these lakes have changed dramatically which has, in turn, significantly influenced the evolutionary history of the lakes' cichlids. This paper reviews the geologic history and paleoclimate of the East <span class="hlt">African</span> Great Lakes and the impact of these forces on the region's endemic cichlid flocks. PMID:22888465</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22888465','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22888465"><span id="translatedtitle">The impact of the geologic history and paleoclimate on the diversification of East <span class="hlt">african</span> cichlids.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Danley, Patrick D; Husemann, Martin; Ding, Baoqing; Dipietro, Lyndsay M; Beverly, Emily J; Peppe, Daniel J</p> <p>2012-01-01</p> <p>The cichlid fishes of the East <span class="hlt">African</span> Great Lakes are the largest extant vertebrate radiation identified to date. These lakes and their surrounding waters support over 2,000 species of cichlid fish, many of which are descended from a single common ancestor within the past 10 Ma. The extraordinary East <span class="hlt">African</span> cichlid diversity is intricately linked to the highly variable geologic and paleoclimatic history of this region. Greater than 10 Ma, the western arm of the East <span class="hlt">African</span> <span class="hlt">rift</span> <span class="hlt">system</span> began to separate, thereby creating a series of <span class="hlt">rift</span> basins that would come to contain several water bodies, including the extremely deep Lakes Tanganyika and Malawi. Uplifting associated with this <span class="hlt">rifting</span> backponded many rivers and created the extremely large, but shallow Lake Victoria. Since their creation, the size, shape, and existence of these lakes have changed dramatically which has, in turn, significantly influenced the evolutionary history of the lakes' cichlids. This paper reviews the geologic history and paleoclimate of the East <span class="hlt">African</span> Great Lakes and the impact of these forces on the region's endemic cichlid flocks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5067589','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5067589"><span id="translatedtitle">Depositional <span class="hlt">systems</span> in the lower Cretaceous Morro Do Chaves and Coqueiro Seco formations, and their relationship to petroleum accumulations, middle <span class="hlt">rift</span> sequence, Sergipe-Alagoas Basin, Brazil</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>de Figueiredo, A.M.F.</p> <p>1981-01-01</p> <p>In the Sergipe-Alagoas Basin, northeast coast of Brazil, the Lower Cretaceous lacustrine, middle <span class="hlt">rift</span> sequence is composed of the Morro do Chaves and Coqueiro Seco Formations. Subsurface analysis permitted recognition and mapping of four principal types of depositional environments: Morro do Chaves carbonate platform, and Coqueiro Seco fluvial-deltaic, fan delta, and slope <span class="hlt">systems</span>. Morro do Chaves lacustrine carbonate sediments were deposited in positive areas flanking the principal point sources (rivers), and are composed of high energy limestones. Contemporaneous deep-water euxinic and bituminous lacustrine shales were deposited under starved basin conditions. Sublacustrine canyon excavation attested to the presence of a destructional slope episode. Coqueiro Seco fluvial-deltaic and fan delta facies display high sand/shale ratios and blocky to massive E-log patterns; slope facies display serrate to digitate E-log patterns and is less sandy. Delta plain channel-fill facies and coarse-grained meanderbelt fluvial facies are dominant in fluvial-deltaic <span class="hlt">systems</span> of the Alagoas Sub-basin; and proximal to medial conglomerates and coarse conglomeratic sandstones are dominant facies in fan delta <span class="hlt">systems</span> of the Rio Sao Francisco Sub-basin. Slope facies are composed of sublacustrine fans formed by fine- to medium-grained sandstones enveloped by subbituminous shales, and lacustrine limestones. Coqueiro Seco coarse clastic <span class="hlt">systems</span> prograded across the basin and buried Morro do Chaves carbonate platforms in response to cyclic tectonic pulses related to <span class="hlt">rift</span> development. Evaluation of petroleum occurrences in relationship to defined depositional <span class="hlt">systems</span> permitted recognition of several types of plays characterized by unique structural and stratigraphic relationships exhibited by reservoirs, source beds and structure. The Coqueiro Seco slope play, formed by updip pinchout of turbidite fans, is judged the most promising in the sequence.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=North+AND+American+AND+plate&id=EJ394260','ERIC'); return false;" href="http://eric.ed.gov/?q=North+AND+American+AND+plate&id=EJ394260"><span id="translatedtitle">Volcanism at <span class="hlt">Rifts</span>.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>White, Robert S.; McKenzie, Dan P.</p> <p>1989-01-01</p> <p>Investigates the nature of catastrophic volcanism and the <span class="hlt">rifting</span> process. Describes two kinds of evidence: quantitative descriptions of rock melting and a wide range of observations. Discusses examples of continent growth in the North Atlantic, India and the Seychelles islands, and the South Atlantic. (YP)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3520439','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3520439"><span id="translatedtitle">Understanding <span class="hlt">African</span> American Adolescents’ Identity Development: A Relational Developmental <span class="hlt">Systems</span> Perspective</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Brittian, Aerika S.</p> <p>2012-01-01</p> <p>This article examines the development of <span class="hlt">African</span> American adolescents’ identity using a relational developmental <span class="hlt">systems</span> theory framework, which led to the expectation that identity development is linked to both the reduction of risk behaviors and the promotion of <span class="hlt">African</span> American adolescents’ healthy development. Different personological theories of identity development were discussed, including Erikson’s theory of psychosocial development and Marcia’s theory of identity statuses. Developmental <span class="hlt">systems</span> theory was used to further the literature on <span class="hlt">African</span> American adolescents’ identity development, by integrating various views of identity development as they pertain to these youth. Furthermore, the formation of many aspects of identity may be an important coping and resilience process for such youth. In addition, directions for future research are discussed, including a consideration of the complexity of diversity that exists within the <span class="hlt">African</span> American adolescent population, and a call for more longitudinal assessments of identity development is presented. PMID:23243325</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19810063492&hterms=continental+divide&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcontinental%2Bdivide','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19810063492&hterms=continental+divide&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcontinental%2Bdivide"><span id="translatedtitle">Continental <span class="hlt">rifting</span> - Progress and outlook</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Baker, B. H.; Morgan, P.</p> <p>1981-01-01</p> <p>It is noted that in spite of the flood of new data on continental <span class="hlt">rifts</span> in the last 15 years, there is little consensus about the basic mechanisms and causes of <span class="hlt">rifting</span>. The remarkable similarities in <span class="hlt">rift</span> cross sections (shown in a figure), are considered to suggest that the anomalous lithospheric structure of <span class="hlt">rifts</span> is more dependent on lithosphere properties than the mode of <span class="hlt">rifting</span>. It is thought that there is a spectrum of <span class="hlt">rifting</span> 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 <span class="hlt">rifts</span> into two basic categories: active <span class="hlt">rifting</span> and passive <span class="hlt">rifting</span>. Here, the magnitude of active <span class="hlt">rifting</span> will depend on the rate at which lithosphere moves over the thermal source, with <span class="hlt">rifts</span> being restricted to stationary or slow-moving plates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5454347','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5454347"><span id="translatedtitle">Continental <span class="hlt">rifting</span> - Progress and outlook</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Baker, B.H.; Morgan, P.</p> <p>1981-07-21</p> <p>It is noted that in spite of the flood of new data on continental <span class="hlt">rifts</span> in the last 15 years, there is little consensus about the basic mechanisms and causes of <span class="hlt">rifting</span>. The remarkable similarities in <span class="hlt">rift</span> cross sections (shown in a figure), are considered to suggest that the anomalous lithospheric structure of <span class="hlt">rifts</span> is more dependent on lithosphere properties than the mode of <span class="hlt">rifting</span>. It is thought that there is a spectrum of <span class="hlt">rifting</span> 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 <span class="hlt">rifts</span> into two basic categories: active <span class="hlt">rifting</span> and passive <span class="hlt">rifting</span>. Here, the magnitude of active <span class="hlt">rifting</span> will depend on the rate at which lithosphere moves over the thermal source, with <span class="hlt">rifts</span> being restricted to stationary or slow-moving plates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T13G..02L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T13G..02L"><span id="translatedtitle">Gas Geochemistry of Volcanic and Geothermal Areas in the Kenya <span class="hlt">Rift</span>: Implications for the Role of Fluids in Continental <span class="hlt">Rifting</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, H.; Fischer, T. P.; Ranka, L. S.; Onguso, B.; Kanda, I.; Opiyo-Akech, N.; Sharp, Z. D.; Hilton, D. R.; Kattenhorn, S. A.; Muirhead, J.</p> <p>2013-12-01</p> <p>The East <span class="hlt">African</span> <span class="hlt">Rift</span> (EAR) is an active continental <span class="hlt">rift</span> and ideal to investigate the processes of <span class="hlt">rift</span> initiation and the breaking apart of continental lithosphere. Mantle and crust-derived fluids may play a pivotal role in both magmatism and faulting in the EAR. For instance, large quantities of mantle-derived volatiles are emitted at Oldoinyo Lengai volcano [1, 2]. Throughout the EAR, CO2-dominated volatile fluxes are prevalent [3, 4] and often associated with faults (i.e. Rungwe area, Tanzania, [5, 6]). The purpose of this study is to examine the relationship between volcanism, faulting and the volatile compositions, focusing on the central and southern Kenyan and northern Tanzanian section of the EAR. We report our analysis results for samples obtained during a 2013 field season in Kenya. Gases were sampled at fumaroles and geothermal plants in caldera volcanoes (T=83.1-120.2°C) and springs (T=40-79.6°C and pH 8.5-10) located near volcanoes, intra-<span class="hlt">rift</span> faults, and a transverse fault (the Kordjya fault, a key fluid source in the Magadi <span class="hlt">rift</span>) by 4N-NaOH solution-filled and empty Giggenbach bottles. Headspace gases were analyzed by a Gas Chromatograph and a Quadrupole Mass Spectrometer at the University of New Mexico. Both N2/Ar and N2/He ratios of all gases (35.38-205.31 and 142.92-564,272, respectively) range between air saturated water (ASW, 40 and ≥150,000) and MORB (100-200 and 40-50). In addition, an N2-Ar-He ternary diagram supports that the gases are produced by two component (mantle and air) mixing. Gases in the empty bottles from volcanoes and springs have N2 (90.88-895.99 mmom/mol), CO2 (2.47-681.21 mmom/mol), CH4 (0-214.78 mmom/mol), O2 (4.47-131.12 mmom/mol), H2 (0-35.78 mmom/mol), Ar (0.15-10.65 mmom/mol), He (0-2.21 mmom/mol), and CO (0-0.08 mmom/mol). Although some of the samples show an atmospheric component, CO2 is a major component in most samples, indicating both volcanoes and springs are emitting CO2. Gases from volcanoes are enriched in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA592038','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA592038"><span id="translatedtitle">Genome-Wide Association Study in <span class="hlt">African</span>-Americans with <span class="hlt">Systemic</span> Lupus Erythematosus</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2013-09-01</p> <p>Americans with <span class="hlt">Systemic</span> Lupus Erythematosus PRINCIPAL INVESTIGATOR: John Harley, M.D., Ph.D...September 2012 – 31 August 2013 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Genome-Wide Association Study in <span class="hlt">African</span>-Americans with <span class="hlt">Systemic</span> Lupus ...SUPPLEMENTARY NOTES 14. ABSTRACT <span class="hlt">Systemic</span> lupus erythematosus ( lupus ) is a potentially deadly <span class="hlt">systemic</span> autoimmune disease that disproportionately</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/ED125949.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED125949.pdf"><span id="translatedtitle"><span class="hlt">African</span> Educational <span class="hlt">Systems</span>: A Comparative Approach. Edu 510.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Watson, Rose T.</p> <p></p> <p>This course of study for college students is about educational development in tropical Africa, or Africa south of the Sahara, excluding North Africa and the Republic of South Africa. The major goals of the course are to help students gain knowledge about the educational policies and practices of <span class="hlt">African</span> countries under the rule of Belgium,…</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.3148B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.3148B"><span id="translatedtitle">Mesoclimatic imprints on palaeoclimate records from <span class="hlt">rift</span> graben sediments: Implications from stable and radiogenic isotope data from mammalian tooth enamel</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brachert, Thomas; Brügmann, Gerhard; Mertz, Dieter F.; Kullmer, Ottmar; Schrenk, Friedemann; Ssemmanda, Immaculate; Taubald, Herbert</p> <p>2010-05-01</p> <p>The Neogene of East Africa is regarded as a period of long-term increasing aridity. It has been proposed that this is the result of a cooling of Indian Ocean surface waters or is caused by tectonic processes leading to the updoming of East Africa. However, mesoclimatic effects induced by the dynamics of the formation of <span class="hlt">rifts</span> involving uplift of the <span class="hlt">rift</span> shoulder and subsidence of the <span class="hlt">rift</span> valley have been largely neglected so far. We have studied mesoclimatic variability by monitoring the evolution of the Albertine <span class="hlt">Rift</span> (western branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>) for the last 7 Ma using the tooth enamel of hippopotamids (Mammalia) as environmental archive. These non-migratory, water-dependant terrestrial mammals are particularly useful for palaeoclimate reconstructions because they have no dietary preferences with respect to C3 - C4 vegetation. By inhabiting lakes and rivers, Hippopotamids document mesoclimates of topographic depressions such as <span class="hlt">rift</span> valleys and, therefore, changes of relative valley depth rather than entirely global climate changes. Average stable isotope compositions of oxygen and carbon were obtained from transects along drill cores through enamel. The Sr isotopic composition was determined by laser ablation multi-collector ICP-MS (Nu Plasma). 13C/12C isotope values in enamel imply the presence of pure C3 browsers (delta 13C < -9 per mil VPDB) from 7.0 to 3.0 Ma and pure C4 grazers (delta 13C > -1 per mil VPDB) from 2.3 to 1.0 Ma. This suggests a spread of grasslands during a maximum in aridity from 2.3 to 1.0 Ma. 18O/16O shows a systematic increase from values of -4.5 at 7.0 Ma to +1.4 per mil (delta 18O VPDB) 2.0 Ma ago. The Sr isotopic composition also increases systematically from 0.713 to 0.717 during this time period. This parallel evolution of 18O/16O and 87Sr/86Sr being climate and water provenance proxies, respectively, is interpreted in terms of <span class="hlt">rift</span> shoulder uplift/subsidence of the <span class="hlt">rift</span> valley floor. The oxygen isotopic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.2376L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.2376L"><span id="translatedtitle">New insights into continental <span class="hlt">rifting</span> from a damage rheology modeling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lyakhovsky, Vladimir; Segev, Amit; Weinberger, Ram; Schattner, Uri</p> <p>2010-05-01</p> <p>Previous studies have discussed how tectonic processes could produce relative tension to initiate and propagate <span class="hlt">rift</span> zones and estimated the magnitude of the <span class="hlt">rift</span>-driving forces. Both analytic and semi-analytic models as well as numerical simulations assume that the tectonic force required to initiate <span class="hlt">rifting</span> is available. However, Buck (2004, 2006) estimated the minimum tectonic force to allow passive <span class="hlt">rifting</span> and concluded that the available forces are probably not large enough for <span class="hlt">rifting</span> of thick and strong lithosphere in the absence of basaltic magmatism (the "Tectonic Force" Paradox). The integral of the yielding stress needed for <span class="hlt">rifting</span> over the thickness of the normal or thicker continental lithosphere are well above the available tectonic forces and tectonic <span class="hlt">rifting</span> cannot happen (Buck, 2006). This conclusion is based on the assumption that the tectonic stress has to overcome simultaneously the yielding stress over the whole lithosphere thickness and ignore gradual weakening of the brittle rocks under long-term loading. In this study we demonstrate that the <span class="hlt">rifting</span> process under moderate tectonic stretching is feasible due to gradual weakening and "long-term memory" of the heavily fractured brittle rocks, which makes it significantly weaker than the surrounding intact rock. This process provides a possible solution for the tectonic force paradox. We address these questions utilizing 3-D lithosphere-scale numerical simulations of the plate motion and faulting process base on the damage mechanics. The 3-D modeled volume consists of three main lithospheric layers: an upper layer of weak sediments, middle layer of crystalline crust and lower layer of the lithosphere mantle. Results of the modeling demonstrate gradual formation of the <span class="hlt">rift</span> zone in the continental lithosphere with the flat layered structure. Successive formation of the <span class="hlt">rift</span> <span class="hlt">system</span> and associated seismicity pattern strongly depend not only on the applied tectonic force, but also on the healing</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.T43A1976M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.T43A1976M"><span id="translatedtitle">Forensic investigation of <span class="hlt">rift</span>-to-drift transitions and volcanic <span class="hlt">rifted</span> margins birth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Meyer, R.; Hertogen, J.</p> <p>2008-12-01</p> <p>Volcanic <span class="hlt">rifted</span> margins (VRM) reflect excess magmatism generated during the <span class="hlt">rift</span>-to-drift transition of a continental <span class="hlt">rift</span> <span class="hlt">system</span> 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) <span class="hlt">Rift</span> 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 <span class="hlt">rift</span>-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 <span class="hlt">rift</span> <span class="hlt">system</span> is probably the key process generating excess magmatism in LIP related to <span class="hlt">rift</span>-to-drift transitions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5787109','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5787109"><span id="translatedtitle"><span class="hlt">African</span> sedimentary basins - Tectonic controls on prospectivity</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bunter, M.A.G.; Crossley, R.; Hammill, M.; Jones, P.W.; Morgan, R.K.; Needham, D.T.; Spaargaren, F.A. )</p> <p>1991-03-01</p> <p>An important prerequisite for the evaluation of any sedimentary basin is the understanding of its regional tectonic setting. This is especially so in the underexplored regions of Africa. The majority of <span class="hlt">African</span> sedimentary basins developed in an extensional setting although some have undergone subsequent compressional or transpressional deformation. The geometry and evolution of these basins is often influenced by basement structure. The extensional phase of basin development controls not only the distribution of syn-<span class="hlt">rift</span> sediments but also the magnitude of post-<span class="hlt">rift</span> regional subsidence and the preservation or removal of pre-<span class="hlt">rift</span> sediments. This has important consequences for exploration models of syn-<span class="hlt">rift</span> and pre-<span class="hlt">rift</span> source rocks and reservoirs. Post-<span class="hlt">rift</span> basin inversion and uplift provide crucial controls on the preservation of mature source rocks and quality of reservoirs. The distribution, nature, timing, and possible mechanisms of this uplift in Africa will be addressed. The hydrocarbon prospectivity of <span class="hlt">African</span> basis appears to be highly variable although the limited exploration of some regions makes the exact extent of this variability unclear. Basins considered potentially prospective range from late Precambrian to Tertiary in age. The various tectonic controls outlined above, and criteria for the evaluation of underexplored areas, will be demonstrated by reference to basins studied by The Robertson Group. Examples described include basins from Bagon, Angola, Namibia, East Africa, Tertiary <span class="hlt">Rift</span> and Karoo <span class="hlt">Rifts</span>, and North Africa (Sudan, Egypt, Algeria, and Morocco).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1989GMS....51...93E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1989GMS....51...93E"><span id="translatedtitle">The GLIMPCE seismic experiment: Onshore refraction and wide-angle reflection observations from a fan line over the Lake Superior Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Epili, Duryodhan; Mereu, Robert F.</p> <p></p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span>, 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 <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24589097','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24589097"><span id="translatedtitle">A geographical information <span class="hlt">system</span>-based multicriteria evaluation to map areas at risk for <span class="hlt">Rift</span> Valley fever vector-borne transmission in Italy.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tran, A; Ippoliti, C; Balenghien, T; Conte, A; Gely, M; Calistri, P; Goffredo, M; Baldet, T; Chevalier, V</p> <p>2013-11-01</p> <p><span class="hlt">Rift</span> Valley fever (RVF) is a severe mosquito-borne disease that is caused by a Phlebovirus (Bunyaviridae) and affects domestic ruminants and humans. Recently, its distribution widened, threatening Europe. The probability of the introduction and large-scale spread of <span class="hlt">Rift</span> Valley fever virus (RVFV) in Europe is low, but localized RVF outbreaks may occur in areas where populations of ruminants and potential vectors are present. In this study, we assumed the introduction of the virus into Italy and focused on the risk of vector-borne transmission of RVFV to three main European potential hosts (cattle, sheep and goats). Five main potential mosquito vectors belonging to the Culex and Aedes genera that are present in Italy were identified in a literature review. We first modelled the geographical distribution of these five species based on expert knowledge and using land cover as a proxy of mosquito presence. The mosquito distribution maps were compared with field mosquito collections from Italy to validate the model. Next, the risk of RVFV transmission was modelled using a multicriteria evaluation (MCE) approach, integrating expert knowledge and the results of a literature review on host sensitivity and vector competence, feeding behaviour and abundance. A sensitivity analysis was performed to assess the robustness of the results with respect to expert choices. The resulting maps include (i) five maps of the vector distribution, (ii) a map of suitable areas for vector-borne transmission of RVFV and (iii) a map of the risk of RVFV vector-borne transmission to sensitive hosts given a viral introduction. Good agreement was found between the modelled presence probability and the observed presence or absence of each vector species. The resulting RVF risk map highlighted strong spatial heterogeneity and could be used to target surveillance. In conclusion, the geographical information <span class="hlt">system</span> (GIS)-based MCE served as a valuable framework and a flexible tool for mapping the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23163047','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23163047"><span id="translatedtitle">[<span class="hlt">Rift</span> valley fever].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Markin, V A; Pantiukhov, V B; Markov, V I; Bondarev, V P</p> <p>2012-01-01</p> <p>In the last quarter of century virus of <span class="hlt">Rift</span> valley fever (RVF) sharply extended its distribution by moving from Africa to Asia and evolving from low- to high pathogenic for humans causing severe hemorrhagic disease, practically equaling in this respect with some members ofa group of extremely dangerous pathogens. Morbidity and epidemics of RVF are analyzed. Evolution of epidemic development of the infection is examined. Necessity of development of means and methods for diagnostics, prophylaxis and therapy of RVF is underlined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.7626G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.7626G"><span id="translatedtitle">The Eastern Sardinian Margin (Tyrrhenian Sea, Western Mediterranean) : a key area to study the <span class="hlt">rifting</span> and post-breakup evolution of a back-arc passive continental margin</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gaullier, Virginie; Chanier, Frank; Vendeville, Bruno; Maillard, Agnès; Thinon, Isabelle; Graveleau, Fabien; Lofi, Johanna; Sage, Françoise</p> <p>2016-04-01</p> <p>The Eastern Sardinian passive continental margin formed during the opening of the Tyrrhenian Sea, which is a back-arc basin created by continental <span class="hlt">rifting</span> and oceanic spreading related to the eastward migrating Apennine subduction <span class="hlt">system</span> (middle Miocene to Pliocene). Up to now, <span class="hlt">rifting</span> in this key area was considered to be pro parte coeval with the Messinian Salinity Crisis (MSC, 5.96-5.32 Ma). We use the MSC seismic markers and the deformation of viscous salt and its brittle overburden as proxies to better delineate the timing of <span class="hlt">rifting</span> and post-<span class="hlt">rift</span> reactivation, and especially to quantify vertical and horizontal movements. On this young, highly-segmented margin, the Messinian Erosion Surface and the Upper and Mobile Units are systematically associated, respectively, to basement highs and deeper basins, showing that a <span class="hlt">rifted</span> deep-sea domain already existed by Messinian times, therefore a major pre-MSC <span class="hlt">rifting</span> episode occurred across the entire domain. Data show that there are no signs of Messinian syn-<span class="hlt">rift</span> sediments, hence no evidence for <span class="hlt">rifting</span> after Late Tortonian times. Moreover, because salt tectonics creates fan-shaped geometries in sediments, syn-<span class="hlt">rift</span> deposits have to be carefully re-examined to distinguish the effects of crustal tectonics (<span class="hlt">rifting</span>) and salt tectonics. We also precise that <span class="hlt">rifting</span> is clearly diachronous from the upper margin (East-Sardinia Basin) to the lower margin (Cornaglia Terrace) with two unconformities, attributed respectively to the necking and to the lithospheric breakup unconformities. The onshore part of the upper margin has been recently investigated in order to characterize the large crustal faults affecting the Mesozoic series (geometry, kinematics and chronology) and to decipher the role of the structural inheritance and of the early <span class="hlt">rifting</span>. Seaward, we also try to constrain the architecture and timing of the continent-ocean transition, between the hyper-extended continental crust and the first oceanic crust. Widespread</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhDT.......202K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhDT.......202K"><span id="translatedtitle">The role of pre-existing Precambrian structures and thermal anomaly in <span class="hlt">rift</span> initiation and evolution-the Albertine and Rhino Grabens in Uganda</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Katumwehe, Andrew Bushekwire</p> <p></p> <p>We integrated Shuttle Radar Topography Mission Digital Elevation Models, airborne magnetic, radiometric, three-dimensional Full Tensor Gravity Gradiometry and Satellite gravity data to investigate the role of Precambrian structures in the evolution of the amagmatic Albertine-Rhino Grabens. The northern part of the Albertine-Rhino Graben extends within Mesoproterozoic Madi-Igisi fold belt wedged between two cratonic blocks. The southwestern part of the Albertine-Rhino Graben and the Edward-George <span class="hlt">Rift</span> (EGR) extends within the Rwenzori and Kibara-Karagwe-Ankole orogenic belts. These extensional structures are separated by the ˜5 km high Rwenzori Mountains and represent the northern segment of the Western Branch of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span>. No expression of surface volcanic activities is observed within the Albertine-Rhino Graben except the Toro-Ankole (TAVF) volcanic fields that are found within the EGR. Our results suggest that: (1) Strain localization, strain transfer, <span class="hlt">rift</span> segmentation as well as <span class="hlt">rift</span> termination against the Aswa Shear Zone (ASZ) as due to the presence of different Precambrian structures. (2) The ASZ extent is ˜550 km in Uganda and South Sudan with a wider (˜50 km) deformation belt and its evolution was due to E-W to NE-SW oblique collision between East and West Gondwana with strain localized at the boundary between the Saharan Metacraton and the Northern Uganda Terrane. (3) <span class="hlt">Rift</span> initiation in the Albertine-Rhino Graben is associated with a thermal structure that shows shallow CPD and high heat flow beneath the EGR and TAVF. We observed a localized thin crust beneath the Rwenzori Mountains, the western Albertine border fault, EGR and TAVF due to the removal of sub-continental lithospheric mantle as a result of delamination. The northward migration of the mantle fluids within lithospheric scale Madi-Igisi Fold and Thrust Belt facilitated strain localization during Albertine-Rhino <span class="hlt">rift</span> initiation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850029005&hterms=DALI&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DDALI','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850029005&hterms=DALI&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DDALI"><span id="translatedtitle">Venus - Volcanism and <span class="hlt">rift</span> formation in Beta Regio</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Campbell, D. B.; Harmon, J. K.; Hine, A. A.; Head, J. W.</p> <p>1984-01-01</p> <p>A new high-resolution radar image of Beta Regio, a Venus highland area, confirms the presence of a major tectonic <span class="hlt">rift</span> <span class="hlt">system</span> and associated volcanic activity. The lack of identifiable impact craters, together with the apparent superposition of the Theia Mons volcanic structure on the <span class="hlt">rift</span> <span class="hlt">system</span>, suggest that at least some of the volcanic activity occurred in relatively recent geologic time. The presence of topographically similar highland areas elsewhere on Venus (Aphrodite Terra, Dali Chasma, and Diana Chasma) suggests that <span class="hlt">rifting</span> and volcanism are significant processes on Venus.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JAfES.100..203A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JAfES.100..203A"><span id="translatedtitle"><span class="hlt">Rift</span> architecture and evolution: The Sirt Basin, Libya: The influence of basement fabrics and oblique tectonics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Abdunaser, K. M.; McCaffrey, K. J. W.</p> <p>2014-12-01</p> <p>The Cretaceous-Tertiary northwest-trending Sirt Basin <span class="hlt">system</span>, Libya, is a <span class="hlt">rift</span>/sag basin formed on Pan-<span class="hlt">African</span> to Paleozoic-aged basement of North Africa. In this study, we investigate the <span class="hlt">rift</span>-basin architecture and tectonic framework of the western Sirt Basin. Using remote sensed data, supported by borehole data from about 300 deep wells and surface geologic maps, we constructed geological cross sections and surface geology maps. Indication of the relative timing of structures and movement along faults has been determined where possible. Direction statistics for all the interpreted linear features acquired in the study area were calculated and given as a total distribution and then the totals are broken down by the major basin elements of the area. Hundreds of lineaments were recognized. Their lengths, range between a hundred meters up to hundreds of kilometers and the longest of the dominant trends are between N35W-N55W and between N55E-N65E which coincides with Sirt Basin structures. The produced rose diagrams reveal that the majority of the surface linear features in the region have four preferred orientations: N40-50W in the Zallah Trough, N45-55W in the Dur al Abd Trough, N35-55W in the Az Zahrah-Al Hufrah Platform, and in contrast in the Waddan Uplift a N55-65E trend. We recognize six lithostratigraphic sequences (phases) in the area's stratigraphic framework. A Pre-graben (Pre-<span class="hlt">rift</span>) initiation stage involved the Pre-Cretaceous sediments formed before the main Sirt Basin subsidence. Then followed a Cretaceous to Eocene graben-fill stage that can divided into four structurally-active and structurally-inactive periods, and finally a terminal continental siliciclastics-rich package representing the post-<span class="hlt">rift</span> stage of the development in post-Eocene time. In general five major fault <span class="hlt">systems</span> dissect and divide the study area into geomorphological elevated blocks and depressions. Most of the oil fields present in the study area are associated with structural hinge</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoRL..4312423S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoRL..4312423S"><span id="translatedtitle">New insights into magma plumbing along <span class="hlt">rift</span> <span class="hlt">systems</span> from detailed observations of eruptive behavior at Axial volcano</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sigmundsson, Freysteinn</p> <p>2016-12-01</p> <p>The magma reservoir in geophysical volcano plumbing models is often modeled as a simple geometric volume, filled with magma of uniform properties. However, the constraints on reservoir size and magma properties in volcano roots are typically indirect and poor. Axial Seamount, a volcano at a depth of about 1500 m on the Juan de Fuca mid-oceanic ridge in the Pacific Ocean, has both high-resolution seismic images of its subsurface magma and detailed results from monitoring of its most recent eruption and associated seismicity and ground deformation. The 2015 eruption at Axial Seamount is the best monitored submarine eruption so far because of observations made possible by the Ocean Observatories Initiative, and seismic imaging of magma at this volcano is better than in most other environments because of advanced analysis of extensive seismic reflection profiling at sea and the relatively simple volcano structure. This allows new understanding compared to findings from earlier observations from monitored <span class="hlt">rifting</span> episodes on land. Geophysical magma plumbing models, in general, may need to allow for more complexities, namely, spatial heterogeneities in magma composition, melt content, and location of major volume changes within a single magma dominated crustal volume during eruptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/7141016','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/7141016"><span id="translatedtitle">The Midcontinent <span class="hlt">Rift</span> and Grenville connection</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cambray, F.W.; Fujita, K. . Dept. of Geological Sciences)</p> <p>1994-04-01</p> <p>The Mid-Proterozoic, Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> (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 <span class="hlt">Rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">Rift</span> <span class="hlt">System</span> in association with irregular collision along the Zagros-Bitlis Sutures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=Social+AND+support+AND+social+AND+networks+AND+older+AND+adults&pg=5&id=EJ828678','ERIC'); return false;" href="http://eric.ed.gov/?q=Social+AND+support+AND+social+AND+networks+AND+older+AND+adults&pg=5&id=EJ828678"><span id="translatedtitle"><span class="hlt">Systems</span> of Social Support in Families Who Care for Dependent <span class="hlt">African</span> American Elders</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Williams, Sharon Wallace; Dilworth-Anderson, Peggye</p> <p>2002-01-01</p> <p>Purpose: This study examined connections (linking, compensatory, or none) between three <span class="hlt">systems</span> of social support (informal, church, and formal). Predictors of each <span class="hlt">system</span> were also examined. Design and Methods: A community sample of 187 caregivers who provided care to older <span class="hlt">African</span> American participants in the Duke Established Populations for…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T13A4608M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T13A4608M"><span id="translatedtitle">Lithospheric Decoupling and Rotations: Hints from Ethiopian <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muluneh, A. A.; Cuffaro, M.; Doglioni, C.; Kidane, T.</p> <p>2014-12-01</p> <p>Plates move relative to the mantle because some torques are acting on them. The shear in the low-velocity zone (LVZ) at the base of the lithosphere is the expression of these torques. The decoupling is allowed by the low viscosity in the LVZ, which is likely few orders of magnitudes lower than previously estimated. The viscosity value in the LVZ controls the degree of coupling/decoupling between the lithosphere and the underlying mantle. Lateral variations in viscosity within the LVZ may explain the velocity gradient among tectonic plates as the one determining the Ethiopian <span class="hlt">Rift</span> (ER) separating Africa from Somalia. While it remains not fully understood the mechanisms of the torques acting on the lithosphere (thermally driven mantle convection or the combination of mantle convection with astronomical forces such as the Earth's rotation and tidal drag), the stresses are transmitted across the different mechanical layers (e.g., the brittle upper crust, down to the viscous-plastic ductile lower crust and upper mantle). Differential basal shear traction at the base of the lithosphere beneath the two sides of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) is assumed to drive and sustain <span class="hlt">rifting</span>. In our analysis, the differential torques acting on the lithospheric/crustal blocks drive kinematics and block rotations. Since, ER involves the whole lithosphere, we do not expect large amount of rotation. Rotation can be the result of the whole plate motion on the sphere moving along the tectonic equator, or the second order sub-rotation of a single plate. Further rotation may occur along oblique plate boundaries (e.g., left lateral transtensional setting at the ER). Small amount of vertical axis rotation of blocks in northern ER could be related to the presence of local, shallower decollement layers. Shallow brittle-ductile transition (BDT) zone and differential tilting of crustal blocks in the northern ER could hint a possibility of detachment surface between the flow in the lower</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17935755','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17935755"><span id="translatedtitle">Astronomically forced climate change in the Kenyan <span class="hlt">Rift</span> Valley 2.7-2.55 Ma: implications for the evolution of early hominin ecosystems.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kingston, John D; Deino, Alan L; Edgar, Robert K; Hill, Andrew</p> <p>2007-11-01</p> <p>Global climate change, linked to astronomical forcing factors, has been implicated in faunal evolutionary change in equatorial Africa, including the origin and diversification of hominin lineages. Empirical terrestrial data demonstrating that orbital forcing has a significant effect, or is detectable, at early hominin sites in equatorial continental interiors during the Pliocene, however, remain limited. Sedimentation patterns in the Baringo Basin within the Central Kenyan <span class="hlt">Rift</span> Valley between ca. 2.7 and 2.55 Ma, controlled by climatic factors, provide a detailed paleoenvironmental record spanning 35 fossil vertebrate localities, including three hominin sites. The succession includes a sequence of diatomites that record rhythmic cycling of major freshwater lake <span class="hlt">systems</span> consistent with approximately 23-kyr Milankovitch precessional periodicity. The temporal framework of shifting precipitation patterns, relative to Pliocene insolation curves, implicate <span class="hlt">African</span> monsoonal climatic control and indicate that climatic fluctuations in <span class="hlt">Rift</span> Valley ecosystems were paced by global climatic change documented in marine cores. These data provide direct evidence of orbitally mediated environmental change at Pliocene <span class="hlt">Rift</span> Valley hominin fossil localities, providing a unique opportunity to assess the evolutionary effect of short-term climatic flux on late Pliocene East <span class="hlt">African</span> terrestrial communities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70155923','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70155923"><span id="translatedtitle">Examination of the Reelfoot <span class="hlt">Rift</span> Petroleum <span class="hlt">System</span>, south-central United States, and the elements that remain for potential exploration and development</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Coleman, James; Pratt, Thomas L.</p> <p>2016-01-01</p> <p>No production has been established in the Reel-foot <span class="hlt">rift</span>. 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 <span class="hlt">rift</span> basin. Structural uplift and faulting within the Reelfoot <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFM.U13A..03A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFM.U13A..03A"><span id="translatedtitle">Wetlands as a Record of Climate Change and Hydrological Response in Arid <span class="hlt">Rift</span> Settings</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ashley, G. M.</p> <p>2004-12-01</p> <p>Of all the terrestrial depositional settings, <span class="hlt">rift</span> basins typically provide the greatest accommodation space, and consequently have some of the longest records of continental sedimentation. Lake deposits were the only <span class="hlt">rift</span> component studied for records of long-term climatic change and for testing hypotheses of orbital forcing. Recently, the continuing quest for the paleontological and cultural records of human origins entombed in the sedimentary rocks of the East <span class="hlt">African</span> <span class="hlt">Rift</span> <span class="hlt">System</span> raised questions concerning hydrologic and biologic response to climatic change. Additional issues are the impact of climate on paleolandscapes and the environmental stresses that might have affected human evolution. Other important indicators of <span class="hlt">rift</span> hydrology, such as springs and wetlands are now emerging as viable records of climate change. <span class="hlt">Rift</span> valley basins are shallow, hydrologically closed <span class="hlt">systems</span> that are responsive to shifts in climate, and specifically sensitive to changes in the hydrologic budget (P-ET). Long term wet-dry cycles in the low latitudes are thought to be astronomically controlled, i.e. Milankovitch precession cycles (19-23 ka). In the tropics, precipitation (P) varies with changes in solar insolation which fluctuates <8-10 % over a cycle. Stronger insolation drives stronger summer monsoon maxima increasing P. Mean annual temperatures are high, but evapo-transpiration, ET (~ 2500 mm/yr) varies little. Consequently, during wetter periods regional groundwater reservoirs enlarge, the water table rises and springs and wetlands increase in number and in size compared to drier periods. Lake levels are known to fluctuate in response to change in hydrologic budget and wetlands appear to respond similarly. Springs and groundwater-fed wetlands are common, however the sources and sustainability of water or what geologic factors lead to the formation and longevity of wetlands is not well established. It appears that rainfall is trapped on topographic highs (<span class="hlt">rift</span> fault blocks</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Tectp.693..239Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Tectp.693..239Z"><span id="translatedtitle">Insights into the effects of oblique extension on continental <span class="hlt">rift</span> interaction from 3D analogue and numerical models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zwaan, Frank; Schreurs, Guido; Naliboff, John; Buiter, Susanne J. H.</p> <p>2016-12-01</p> <p>Continental <span class="hlt">rifts</span> often develop from linkage of distinct <span class="hlt">rift</span> segments under varying degrees of extension obliquity. These <span class="hlt">rift</span> segments arise from <span class="hlt">rift</span> initiation at non-aligned crustal heterogeneities and need to interact to develop a full-scale <span class="hlt">rift</span> <span class="hlt">system</span>. Here, we test the effects of 1) oblique extension and 2) initial heterogeneity (seed) offset on continental <span class="hlt">rift</span> interaction with the use of an improved analogue model set-up. X-ray computer tomography (CT) techniques are used to analyse the 3D models through time and the results are compared with additional numerical models and natural examples. The experimental results reveal that increasing extension obliquity strongly changes <span class="hlt">rift</span> segment structures from wide <span class="hlt">rifts</span> in orthogonal settings to narrower <span class="hlt">rifts</span> with oblique internal structures under oblique extension conditions to narrow strike-slip dominated <span class="hlt">systems</span> towards the strike-slip domain. We also find that both decreasing seed offset and increasing extension obliquity promote hard linkage of <span class="hlt">rift</span> segments through the formation of continuous <span class="hlt">rift</span> boundary faults at the surface. (Initial) soft linkage through the formation of relay ramps is more likely when seed offset increases or extension is more orthogonal. Rather than linking at depth, the <span class="hlt">rift</span> boundary faults curve around each other at depth and merge towards the surface to form a continuous trough. Orthogonal extension promotes the formation of intra-<span class="hlt">rift</span> horsts, which may provide hydrocarbon traps in nature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800004300','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800004300"><span id="translatedtitle">A photovoltaic power <span class="hlt">system</span> in the remote <span class="hlt">African</span> village of Tangaye, Upper Volta</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bifano, W. J.; Ratajczak, A. F.; Martz, J. E.</p> <p>1979-01-01</p> <p>A photovoltaic (PV) <span class="hlt">system</span> powering a grain mill and a water pump was installed in the remote West <span class="hlt">African</span> village of Tangaye, Upper Volta. Village characteristics as well as <span class="hlt">system</span> design, hardware, installation and operation to date are described. The PV <span class="hlt">system</span> cost is discussed. A baseline socio-economic study performed and a follow-up study is planned to determine the impact of the <span class="hlt">system</span> on the villagers.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26373290','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26373290"><span id="translatedtitle">Chronic <span class="hlt">Systemic</span> Immune Dysfunction in <span class="hlt">African</span>-Americans with Small Vessel-Type Ischemic Stroke.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Brown, Candice M; Bushnell, Cheryl D; Samsa, Gregory P; Goldstein, Larry B; Colton, Carol A</p> <p>2015-12-01</p> <p>The incidence of small vessel-type (lacunar) ischemic strokes is greater in <span class="hlt">African</span>-Americans compared to whites. The chronic inflammatory changes that result from lacunar stroke are poorly understood. To elucidate these changes, we measured serum inflammatory and thrombotic biomarkers in <span class="hlt">African</span>-Americans at least 6 weeks post-stroke compared to control individuals. Cases were <span class="hlt">African</span>-Americans with lacunar stroke (n = 30), and controls were age-matched <span class="hlt">African</span>-Americans with no history of stroke or other major neurologic disease (n = 37). Blood was obtained >6 weeks post-stroke and was analyzed for inflammatory biomarkers. Freshly isolated peripheral blood mononuclear cells were stimulated with lipopolysaccharide (LPS) to assess immune responsiveness in a subset of cases (n = 5) and controls (n = 4). After adjustment for covariates, the pro-inflammatory biomarkers, soluble vascular cadherin adhesion molecule-1 (sVCAM-1) and thrombin anti-thrombin (TAT), were independently associated with lacunar stroke. Immune responsiveness to LPS challenge was abnormal in cases compared to controls. <span class="hlt">African</span>-Americans with lacunar stroke had elevated blood levels of VCAM-1 and TAT and an abnormal response to acute immune challenge >6 weeks post-stroke, suggesting a chronically compromised <span class="hlt">systemic</span> inflammatory response.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21082471','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21082471"><span id="translatedtitle">Ideological schisms about HIV/AIDS helping <span class="hlt">systems</span> in the <span class="hlt">African</span> American community, with an emphasis on women.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fairfax, Colita Nichols</p> <p>2010-10-01</p> <p>This article is an initial exploration about the impact of ideological beliefs on helping services in the <span class="hlt">African</span> American community. Newly infected HIV/AIDS cases place <span class="hlt">African</span> Americans at 45% of such new cases, with <span class="hlt">African</span> American women becoming infected at a rate 18 times that of Whites. Yet, helping services that are organic to <span class="hlt">African</span> American women should be stronger through a discussion of cultural beliefs held in the community, where the genesis of helping services exists. Values and beliefs should be at the center of community partnerships, public media strategies, generalist-practice curricula in macro-level <span class="hlt">systems</span>, and creating more space for relationship dialogue between <span class="hlt">African</span> American men and women, which includes gender and racial distortions. Given the exponentially high numbers of HIV/AIDS cases in the <span class="hlt">African</span> American community, a more earnest examination of values and beliefs is warranted.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.8908S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.8908S"><span id="translatedtitle">Orogenic structural inheritance and <span class="hlt">rifted</span> passive margin formation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Salazar Mora, Claudio A.; Huismans, Ritske S.</p> <p>2016-04-01</p> <p>Structural inheritance is related to mechanical weaknesses in the lithosphere due to previous tectonic events, e.g. <span class="hlt">rifting</span>, subduction and collision. The North and South Atlantic <span class="hlt">rifted</span> passive margins that formed during the breakup of Western Gondwana, are parallel to the older Caledonide and the Brasiliano-Pan-<span class="hlt">African</span> orogenic belts. In the South Atlantic, 'old' mantle lithospheric fabric resulting from crystallographic preferred orientation of olivine is suggested to play a role during <span class="hlt">rifted</span> margin formation (Tommasi and Vauchez, 2001). Magnetometric and gravimetric mapping of onshore structures in the Camamu and Almada basins suggest that extensional faults are controlled by two different directions of inherited older Brasiliano structures in the upper lithosphere (Ferreira et al., 2009). In the South Atlantic Campos Basin, 3D seismic data indicate that inherited basement structures provide a first order control on basin structure (Fetter, 2009). Here we investigate the role of structural inheritance on the formation of <span class="hlt">rifted</span> passive margins with high-resolution 2D thermo-mechanical numerical experiments. The numerical domain is 1200 km long and 600 km deep and represents the lithosphere and the sublithospheric mantle. Model experiments were carried out by creating self-consistent orogenic inheritance where a first phase of orogen formation is followed by extension. We focus in particular on the role of varying amount of orogenic shortening, crustal rheology, contrasting styles of orogen formation on <span class="hlt">rifted</span> margin style, and the time delay between orogeny and subsequent <span class="hlt">rifted</span> passive formation. Model results are compared to contrasting structural styles of <span class="hlt">rifted</span> passive margin formation as observed in the South Atlantic. Ferreira, T.S., Caixeta, J.M., Lima, F.D., 2009. Basement control in Camamu and Almada <span class="hlt">rift</span> basins. Boletim de Geociências da Petrobrás 17, 69-88. Fetter, M., 2009. The role of basement tectonic reactivation on the structural evolution</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/10842028','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/10842028"><span id="translatedtitle">A study on ten short tandem repeat <span class="hlt">systems</span>: <span class="hlt">African</span> immigrant and Spanish population data.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gamero, J J; Romero, J L; Gonzalez, J L; Arufe, M I; Cuesta, M I; Corte-Real, F; Carvalho, M; Anjos, M J; Vieira, D N; Vide, M C</p> <p>2000-06-05</p> <p>This work presents the results obtained from a genetic-population study for the D1S1656 <span class="hlt">system</span> in the population of Southwest Spain (Huelva, Cádiz and Sevilla), Spaniards of Caucasian origin from North Africa (Ceuta), as well as in the black Central West <span class="hlt">African</span> and Moroccan immigrant populations in Spain. The results of a study of the autochtonous population of the Canary Islands (n=138), and immigrant Central West <span class="hlt">African</span> populations in Spain (n=132), obtained for nine short tandem repeat (STR) loci (D3S1358, VWA, FGA, D8S1179, D21S11, D18S51, D5S818, D13S317, D7S820), as well as the amelogenin locus, all contained in Profiler Plus (Perkin-Elmer) PCR amplification kits, are also presented. Except for the FGA and VWA data on immigrant Central West <span class="hlt">African</span> populations in Spain, no deviations from the Hardy-Weinberg equilibrium were detected.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910056245&hterms=The_Gulf_of_California&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DThe_Gulf_of_California','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910056245&hterms=The_Gulf_of_California&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DThe_Gulf_of_California"><span id="translatedtitle">Age constraints for the present fault configuration in the Imperial Valley, California - Evidence for northwestward propagation of the Gulf of California <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Larsen, Shawn; Reilinger, Robert</p> <p>1991-01-01</p> <p>Releveling and other geophysical data for the Imperial Valley of southern California suggest the northern section of the Imperial-Brawley fault <span class="hlt">system</span>, 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 <span class="hlt">rift</span> <span class="hlt">system</span> into the North American continent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1810436S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1810436S"><span id="translatedtitle">Exploiting the outcome of FUTUREVOLC: The 2014-2015 <span class="hlt">rifting</span> event, effusive eruption and gradual caldera collapse at Bardarbunga volcanic <span class="hlt">system</span>, Iceland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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</p> <p>2016-04-01</p> <p>Activity in the Bardarbunga volcanic <span class="hlt">system</span> 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 <span class="hlt">rifting</span> 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 <span class="hlt">system</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900012177','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900012177"><span id="translatedtitle">Age constraints for the present fault configuration in the Imperial Valley, California: Evidence for northwestward propagation of the Gulf of California <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Larsen, Shawn; Reilinger, Robert</p> <p>1990-01-01</p> <p>Releveling and other geophysical data for the Imperial Valley of southern California suggest the northern section of the Imperial-Brawley fault <span class="hlt">system</span>, 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 <span class="hlt">rift</span> <span class="hlt">system</span> into the North American continent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=zambia&pg=7&id=EJ878298','ERIC'); return false;" href="http://eric.ed.gov/?q=zambia&pg=7&id=EJ878298"><span id="translatedtitle">Variations in Reading Achievement across 14 Southern <span class="hlt">African</span> School <span class="hlt">Systems</span>: Which Factors Matter?</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Hungi, Njora; Thuku, Florence W.</p> <p>2010-01-01</p> <p>In this study the authors employed a multilevel analysis procedure in order to examine the pupil and school levels factors that contributed to variation in reading achievement among Grade 6 primary school pupils in 14 southern <span class="hlt">African</span> school <span class="hlt">systems</span> (Botswana, Kenya, Lesotho, Malawi, Mauritius, Mozambique, Namibia, Seychelles, South Africa,…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=science+AND+attitude+AND+inventory&id=EJ679771','ERIC'); return false;" href="http://eric.ed.gov/?q=science+AND+attitude+AND+inventory&id=EJ679771"><span id="translatedtitle">The Effects of <span class="hlt">Systemic</span> Reform on Urban, <span class="hlt">African</span> American Fifth Grade Students' Attitudes toward Science.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Weinburgh, Molly H.</p> <p>2003-01-01</p> <p>Investigates the effectiveness of a local <span class="hlt">systemic</span> change grant on 5th grade urban <span class="hlt">African</span> American students' attitudes toward science. Measures students' attitudes by using the modified Attitude Toward Science Inventory (mATSI). Indicates a significant main effect for the program and for school but not for gender. Examines school characteristics…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=registration&pg=5&id=ED541088','ERIC'); return false;" href="http://eric.ed.gov/?q=registration&pg=5&id=ED541088"><span id="translatedtitle">Late Registration and <span class="hlt">African</span> American Males' Academic Performance in a Suburban Community College <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>McWaine, Wendell Lamar, II</p> <p>2012-01-01</p> <p>The purpose of this study was to determine if there was a relationship between registration status and the persistence, end-of-semester GPA, and course success for <span class="hlt">African</span> American males in a suburban community college <span class="hlt">system</span>. This study also sought to determine if there was a difference between the persistence, end-of-semester GPA, and course…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=quality+AND+management+AND+system&pg=2&id=EJ692506','ERIC'); return false;" href="http://eric.ed.gov/?q=quality+AND+management+AND+system&pg=2&id=EJ692506"><span id="translatedtitle">New Controls and Accountability for South <span class="hlt">African</span> Teachers and Schools: The Integrated Quality Management <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Weber, Everard</p> <p>2005-01-01</p> <p>This article analyses the Integrated Quality Management <span class="hlt">System</span> (IQMS), an agreement reached in 2003 between the South <span class="hlt">African</span> Education Department and the major teacher organisations in the country by using discourse analysis. The IQMS was scheduled to be implemented in public schools in 2004. Three discursive tensions are identified and…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=technology+AND+acceptance+AND+model+AND+university&pg=5&id=EJ976019','ERIC'); return false;" href="http://eric.ed.gov/?q=technology+AND+acceptance+AND+model+AND+university&pg=5&id=EJ976019"><span id="translatedtitle">Drivers of Learning Management <span class="hlt">System</span> Use in a South <span class="hlt">African</span> Open and Distance Learning Institution</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Venter, Peet; van Rensburg, Mari Jansen; Davis, Annemarie</p> <p>2012-01-01</p> <p>The study on which this article reports examined the determinants of usage of an online learning management <span class="hlt">system</span> (LMS) by fourth level business students at a South <span class="hlt">African</span> open and distance learning university using an extension of the widely used technology acceptance model (TAM) as a theoretical basis. A survey was conducted among students at…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19940007574&hterms=fallout&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dfallout','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19940007574&hterms=fallout&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dfallout"><span id="translatedtitle">Estimation of age of Dali-Ganis <span class="hlt">rifting</span> and associated volcanic activity, Venus</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Basilevsky, A. T.</p> <p>1993-01-01</p> <p>This paper deals with the estimation of age for the Dali and Ganis Chasma <span class="hlt">rift</span> zones and their associated volcanism based on photogeologic analysis of stratigraphic relations of <span class="hlt">rift</span>-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 <span class="hlt">system</span> of <span class="hlt">rift</span> zones contained within eastern Aphrodite and Atla Regio which is a significant component of Venus tectonics. The <span class="hlt">rifts</span> of this <span class="hlt">system</span> are fracture belts which dissect typical Venusian plains with rare islands of tessera terrain. The <span class="hlt">rift</span> zone <span class="hlt">system</span> consists of several segments following each other (Diane, Dali, Ganis) and forming the major <span class="hlt">rift</span> zone line, about 10,000 km long, which has junctions with several other <span class="hlt">rift</span> zones, including Parga Chasma <span class="hlt">Rift</span>. The junctions are usually locations of <span class="hlt">rift</span>-associated volcanism in the form of volcanic edifices (Maat and Ozza Montes) or plain-forming flows flooding some areas within the <span class="hlt">rift</span> zones and the adjacent plains.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012GGG....13.1012L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012GGG....13.1012L"><span id="translatedtitle">Deformation and seismicity associated with continental <span class="hlt">rift</span> zones propagating toward continental margins</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lyakhovsky, V.; Segev, A.; Schattner, U.; Weinberger, R.</p> <p>2012-01-01</p> <p>We study the propagation of a continental <span class="hlt">rift</span> and its interaction with a continental margin utilizing a 3-D lithospheric model with a seismogenic crust governed by a damage rheology. A long-standing problem in <span class="hlt">rift</span>-mechanics, known as thetectonic force paradox, is that the magnitude of the tectonic forces required for <span class="hlt">rifting</span> are not large enough in the absence of basaltic magmatism. Our modeling results demonstrate that under moderate <span class="hlt">rift</span>-driving tectonic forces the <span class="hlt">rift</span> propagation is feasible even in the absence of magmatism. This is due to gradual weakening and "long-term memory" of fractured rocks that lead to a significantly lower yielding stress than that of the surrounding intact rocks. We show that the style, rate and the associated seismicity pattern of the <span class="hlt">rift</span> zone formation in the continental lithosphere depend not only on the applied tectonic forces, but also on the rate of healing. Accounting for the memory effect provides a feasible solution for thetectonic force paradox. Our modeling results also demonstrate how the lithosphere structure affects the geometry of the propagating <span class="hlt">rift</span> <span class="hlt">system</span> toward a continental margin. Thinning of the crystalline crust leads to a decrease in the propagation rate and possibly to <span class="hlt">rift</span> termination across the margin. In such a case, a new fault <span class="hlt">system</span> is created perpendicular to the direction of the <span class="hlt">rift</span> propagation. These results reveal that the local lithosphere structure is one of the key factors controlling the geometry of the evolving <span class="hlt">rift</span> <span class="hlt">system</span> and seismicity pattern.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5307136','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5307136"><span id="translatedtitle"><span class="hlt">African</span> Ancestry Gradient Is Associated with Lower <span class="hlt">Systemic</span> F2-Isoprostane Levels</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Annor, Francis; Okosun, Ike; Gower, Barbara A.</p> <p>2017-01-01</p> <p>Context. Low levels of <span class="hlt">systemic</span> F2-isoprostanes (F2-IsoP) increase the risk of diabetes and weight gain and were found in <span class="hlt">African</span> Americans. Low F2-IsoPs could reflect an unfavorable metabolic characteristic, namely, slow mitochondrial metabolism in individuals with <span class="hlt">African</span> ancestry. Objective. To examine differences in plasma F2-IsoPs in three groups with a priori different proportion of <span class="hlt">African</span> ancestry: non-Hispanic Whites (NHWs), US-born <span class="hlt">African</span> Americans (AAs), and West <span class="hlt">African</span> immigrants (WAI). Design. Cross-sectional study. Setting. Georgia residents recruited from church communities. Participants. 218 males and females 25–74 years of age, who are self-identified as NHW (n = 83), AA (n = 56), or WAI (n = 79). Main Outcome Measure(s). Plasma F2-IsoPs quantified by gas chromatography-mass spectrometry. Results. After adjustment for age, gender, obesity, and other comorbidities, WAI had lower levels of plasma F2-IsoP than AA (beta-coefficient = −9.8, p < 0.001) and AA had lower levels than NHW (beta-coefficient = −30.3, p < 0.001). Similarly, among healthy nonobese participants, F2-IsoP levels were lowest among WAI, followed by AA, and the highest levels were among NHW. Conclusion. Plasma F2-IsoPs are inversely associated with <span class="hlt">African</span> ancestry gradient. Additional studies are required to test whether optimization of <span class="hlt">systemic</span> F2-IsoP levels can serve as means to improve race-specific lifestyle and pharmacological intervention targeted to obesity prevention and treatment. PMID:28250893</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T31B2875S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T31B2875S"><span id="translatedtitle">Concentration of strain in a marginal <span class="hlt">rift</span> zone of the Japan backarc during post-<span class="hlt">rift</span> compression</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sato, H.; Ishiyama, T.; Kato, N.; Abe, S.; Shiraishi, K.; Inaba, M.; Kurashimo, E.; Iwasaki, T.; Van Horne, A.; No, T.; Sato, T.; Kodaira, S.; Matsubara, M.; Takeda, T.; Abe, S.; Kodaira, C.</p> <p>2015-12-01</p> <p>Late Cenozoic deformation zones in Japan may be divided into two types: (1) arc-arc collision zones like those of Izu and the Hokkaido axial zone, and (2) reactivated back-arc marginal <span class="hlt">rift</span> (BMR) <span class="hlt">systems</span>. A BMR develops during a secondary <span class="hlt">rifting</span> event that follows the opening of a back-arc basin. It forms close to the volcanic front and distant from the spreading center of the basin. In Japan, a BMR <span class="hlt">system</span> developed along the Sea of Japan coast following the opening of the Japan Sea. The BMR appears to be the weakest, most deformable part of the arc back-arc <span class="hlt">system</span>. When active <span class="hlt">rifting</span> in the marginal basins ended, thermal subsidence, and then mechanical subsidence related to the onset of a compressional stress regime, allowed deposition of up to 5 km of post-<span class="hlt">rift</span>, deep-marine to fluvial sedimentation. Continued compression produced fault-related folds in the post-<span class="hlt">rift</span> sediments, in thin-skin style deformation. Shortening reached a maximum in the BMR <span class="hlt">system</span> compared to other parts of the back-arc, suggesting that it is the weakest part of the entire <span class="hlt">system</span>. We examined the structure of the BMR <span class="hlt">system</span> using active source seismic investigation and earthquake tomography. The velocity structure beneath the marginal <span class="hlt">rift</span> basin shows higher P-wave velocity in the upper mantle/lower crust which suggests significant mafic intrusion and thinning of the upper continental crust. The syn-<span class="hlt">rift</span> mafic intrusive forms a convex shape, and the boundary between the pre-<span class="hlt">rift</span> crust and the mafic intrusive dips outward. In the post-<span class="hlt">rift</span> compressional stress regime, the boundary of the mafic body reactivated as a reverse fault, forming a large-scale wedge thrust and causing further subsidence of the <span class="hlt">rift</span> basin. The driver of the intense shortening event along the Sea of Japan coast in SW Japan was the arrival of a buoyant young (15 Ma) Shikoku basin at the Nankai Trough. Subduction stalled and the backarc was compressed. As the buoyant basin cooled, subduction resumed, and the rate of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=inventory+AND+system+AND+accounting&id=ED516272','ERIC'); return false;" href="http://eric.ed.gov/?q=inventory+AND+system+AND+accounting&id=ED516272"><span id="translatedtitle">An Exploration of the Leadership Style Preferences among <span class="hlt">African</span> American Women Administrators of the 1890 Cooperative Extension <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Campbell, Shelvy L.</p> <p>2010-01-01</p> <p>The purpose of this mixed-methods study was to identify and explore the leadership style preferences among current <span class="hlt">African</span> American Administrators of the 1890 Land-Grant Cooperative Extension <span class="hlt">system</span>. The population used in this study was <span class="hlt">African</span> American women administrators from eighteen mostly southern states. The researcher used a…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70024528','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70024528"><span id="translatedtitle">Crustal structure of central Lake Baikal: Insights into intracontinental <span class="hlt">rifting</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>ten Brink, U.S.; Taylor, M.H.</p> <p>2002-01-01</p> <p>The Cenozoic <span class="hlt">rift</span> <span class="hlt">system</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span>. 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 <span class="hlt">rifting</span>. 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 <span class="hlt">rift</span>. We believe that the Baikal <span class="hlt">rift</span> structure is similar in many respects to the Mesozoic Atlantic <span class="hlt">rift</span> <span class="hlt">system</span>, the precursor to the formation of the North Atlantic Ocean. We also propose that the Central Baikal <span class="hlt">rift</span> evolved by episodic fault propagation and basin enlargement, rather than by two-stage <span class="hlt">rift</span> evolution as is commonly assumed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1980JGR....85.3647H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1980JGR....85.3647H"><span id="translatedtitle">Propagating <span class="hlt">rifts</span> on midocean ridges</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hey, Richard; Duennebier, Frederick K.; Morgan, W. Jason</p> <p>1980-07-01</p> <p>Spreading center jumps identified west of the Galapagos Islands near 95°W occur in a pattern consistent with the propagating <span class="hlt">rift</span> hypothesis. A new <span class="hlt">rift</span> is gradually breaking through the Cocos plate. Each successive jump is slightly longer than the preceding jump. The new spreading center grows at a new azimuth toward the west as the old one dies. The jumps are a manifestation of <span class="hlt">rift</span> propagation. We extend the analysis of propagating <span class="hlt">rifts</span> to the case of continuous propagation and predict patterns of magnetic anomalies and bathymetry consistent with the observed patterns. In particular, we correctly predict the trends of fossil spreading centers and V patterns of magnetic anomaly offsets required by the propagating <span class="hlt">rift</span> hypothesis. Similar V patterns have been observed on many other spreading centers and have been interpreted in various ways. The propagating <span class="hlt">rift</span> hypothesis appears to offer a simple explanation, consistent with rigid plate tectonics, for each of these patterns. This hypothesis may also have important implications for continental <span class="hlt">rifting</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.7015D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.7015D"><span id="translatedtitle">Orbital forcing on West <span class="hlt">African</span> monsoon <span class="hlt">system</span> revealed by KZai 02 pollen record spectral analysis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dalibard, Mathieu; Popescu, Speranta-Maria; Pittet, Bernard; Fernandez, Vincent; Marsset, Tania; Droz, Laurence; Suc, Jea