Sample records for rift oblicuo aplicaciones

  1. Frameworks de desarrollo de Aplicaciones -Spring

    E-print Network

    Escolano, Francisco

    Frameworks de desarrollo de Aplicaciones - Spring Índice 1 Presentación en Spring. Este framework de desarrollo de aplicaciones se ha convertido en un completo ecosistema en integración. Finalizaremos con una introducción al desarrollo rápido de aplicaciones con Spring Roo, que nos

  2. APLICACIONES SIG Y SR EN

    E-print Network

    Gilbes, Fernando

    y otra cosa es Puerto Rico #12;COSTA RICA #12;#12;FUENTES DE INFORMACIÓN GEOGRÁFICA IGN (Fotos;MISIÓN CARTA 2005 Cobertura de MASTER 80% cobertura #12;#12;MISIÓN CARTA 2005 Cobertura de fotos 80% cobertura #12;FOTOS CARTA 2005 #12;Posibles Aplicaciones Prevención de desastres Planificación urbana

  3. Rift nucleation, rift propagation and the creation of basement micro-plates within active rifts

    Microsoft Academic Search

    D. Koehn; K. Aanyu; S. Haines; T. Sachau

    2008-01-01

    In this contribution we study the dynamics of rift nucleation and the interaction of propagating rift segments. We use the East African Rift System (EARS) as a case study with special emphasis on the Albertine rift system situated within the western branch of the EARS with the 5000 m high Rwenzori horst, a basement block that was captured by two rift

  4. Rift Valley Fever Virus

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  5. Jornadas sobre Tecnologas y Aplicaciones de

    E-print Network

    Escolano, Francisco

    espaciales para misiones científicas, tecnológicas y de sostenibilidad. 09:30 - 10:00 La Agencia EspacialJornadas sobre Tecnologías y Aplicaciones de las Comunicaciones Espaciales EMPRESA Colaboran-CV APLICACIONES Y TECNOLOGÍAS ESPACIALES EN LA COMUNIDAD VALENCIANA. Instituto Superior de Investigación

  6. Continental rifting: a planetary perspective

    SciTech Connect

    Muehlberger, W.R.

    1985-01-01

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

  7. Evolution of Oblique Rifting on the Main Ethiopian Rift

    NSDL National Science Digital Library

    Giacomo Corti

    Movie showing the evolution of oblique rifting in analogue models (from Corti, 2008, Nature Geosc). Obliquity in this model is 30° (angle between the normal to the rift axis and the direction of extension). Note the two-phase rift evolution with a first phase of boundary fault activity and basin subsidence, followed by activation of en-echelon arranged internal faults obliquely cutting the rift floor.

  8. Rift Valley fever vaccines

    PubMed Central

    Ikegami, Tetsuro; Makino, Shinji

    2009-01-01

    Rift 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 Rift Valley fever. This article summarizes the development of inactivated RVFV vaccine, live attenuated vaccine, and other new generation vaccines. PMID:19837291

  9. Continental rifting - Progress and outlook

    NASA Technical Reports Server (NTRS)

    Baker, B. H.; Morgan, P.

    1981-01-01

    It is noted that in spite of the flood of new data on continental rifts in the last 15 years, there is little consensus about the basic mechanisms and causes of rifting. The remarkable similarities in rift cross sections (shown in a figure), are considered to suggest that the anomalous lithospheric structure of rifts is more dependent on lithosphere properties than the mode of rifting. It is thought that there is a spectrum of rifting processes for which two fundamental mechanisms can be postulated: an active mechanism, whereby thermal energy is transmitted into the lithosphere from the underlying asthenosphere, and a passive mechanism by which mechanical energy is transmitted laterally through the lithosphere as a consequence of plate interactions at a distance. In order to permit the concept of the two fundamentally different mechanisms to be tested, a tentative classification is proposed that divides rifts into two basic categories: active rifting and passive rifting. Here, the magnitude of active rifting will depend on the rate at which lithosphere moves over the thermal source, with rifts being restricted to stationary or slow-moving plates.

  10. East African Rift System

    Microsoft Academic Search

    R. B. McConnell

    1969-01-01

    THE article entitled ``How far does the Rift System extend through Africa ?'' by Fairhead and Girdler1 is of great interest to geologists who are studying the structure of the African Pre-Cambrian platform, because the exact relocation of the epicentres of earthquakes could have great significance if related to known geological features. For example, in addition to the relationships suggested

  11. Rift-flank uplift and rift dynamics, a new perspective

    Microsoft Academic Search

    D. Koehn; T. Sachau; K. Aanyu

    2009-01-01

    In this contribution we present a new model of passive rifting and related rift-flank uplift. The numerical model is based on a lattice spring network coupled with a viscous particle model so that we can simulate visco-elasto-plastic behaviour with dynamic fault development. In our model we show that rift flank uplift can be achieved best when extension in the crust

  12. 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.

  13. Rift Valley fever

    Microsoft Academic Search

    G. H. Gerdes

    2004-01-01

    Summary Rift Valley fever (RVF) is an arthropod-borne viral disease of ruminants, camels and humans. It is also a significant zoonosis which may be encountered as an uncomplicated influenza-like illness, but may also present as a haemorrhagic disease with liver involvement; there may also be ocular or neurological lesions. In animals, RVF may be inapparent in non-pregnant adults, but outbreaks

  14. Baikal Rift Zone: Intracratonic rifting without Moho uplift

    Microsoft Academic Search

    H. Thybo; C. Nielsen; M. Jensen; V. D. Suvorov; E. Perchuc

    2006-01-01

    The Baikal Rift Zone is located in Siberia at the centre of the world's largest continental area. It provies a unique opportunity for studying the processes of ongoing continental rifting in an area with thick cratonic crust. The BEST project (Baikal Explosion Seismic Transects) aims at providing seismic velocity models of the crust and uppermost mantle across and along the

  15. Granular mechanics and rifting

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  17. Short term development of intracontinental rifts, with reference to the late Quaternary of the Rukwa Rift (East African Rift System)

    Microsoft Academic Search

    T. Kjennerud; S. J. Lippard; P. Vanhauwaert

    2001-01-01

    Relatively low-resolution seismic data and high contemporaneous rift topography normally limit quantitative analysis of normal faults in rifts. The availability of a recently collected high-resolution reflection seismic survey in the SE part of the presently active Rukwa Rift (East African Rift System) coupled with high sedimentation rates in the submerged part of the rift makes detailed quantitative analysis possible. High-resolution

  18. Cenozoic rifting in the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  19. Rift basins - Origin, history, and distribution

    NASA Technical Reports Server (NTRS)

    Burke, K. C.

    1985-01-01

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

  20. The East African rift system

    Microsoft Academic Search

    Jean Chorowicz

    2005-01-01

    This overview paper considers the East African rift system (EARS) as an intra-continental ridge system, comprising an axial rift. It describes the structural organization in three branches, the overall morphology, lithospheric cross-sections, the morphotectonics, the main tectonic features—with emphasis on the tension fractures—and volcanism in its relationships with the tectonics. The most characteristic features in the EARS are narrow elongate

  1. Relationships between pre-rift structure and rift architecture in Lakes Tanganyika and Malawi, East Africa

    Microsoft Academic Search

    J. Versfelt; B. R. Rosendahl

    1989-01-01

    Continental rift systems are rips in plates caused by focusing of extensional stresses along some zone. In the same way that tensile cracks in the side of a brick building generally follow the mortar between bricks, rifts initially follow the weakest pathways in the pre-rift materials. There has even been a suggestion that the occurrence of rifts is controlled by

  2. Inversion tectonics during continental rifting: The Turkana Cenozoic rifted zone, northern Kenya

    E-print Network

    Brest, Université de

    Inversion tectonics during continental rifting: The Turkana Cenozoic rifted zone, northern Kenya B of inverted deformation within Miocene-Recent basins of the Turkana rift (northern Kenya) in the eastern: The Turkana Cenozoic rifted zone, northern Kenya, Tectonics, 24, TC2002, doi:10.1029/2004TC001637. 1

  3. Rift valley fever.

    PubMed

    Gerdes, Gertruida H

    2002-11-01

    Rift Valley fever virus is an arthropod-borne Phlebovirus endemic in sub-Saharan Africa. Outbreaks also have occurred in Egypt, Madagascar, and most recently in the Arabian peninsula. Large epizootics occur at irregular intervals in seasons of above-average rainfall with persistent flooding and the appearance of large numbers of floodwater-breeding Aedine mosquitoes. The virus is transmitted transovarially and can remain dormant in mosquito eggs during dry interepizootic periods. Low-level virus circulation occurs in high-rainfall forested areas, although individual cases of the disease rarely are recognized. RVF is characterized by abortion in pregnant animals and a high mortality in newborn lambs, kids, and calves. Susceptibility to disease is related to age and breed, with severe disease occurring in the young of exotic sheep and cattle breeds. RVF is a zoonosis, and human beings experience an influenza-like illness and, more rarely, complications such as encephalitis or retinitis. The virus causes a severe hepatitis, particularly in aborted fetuses and newborn lambs. The disease must be differentiated from other conditions that cause death with hepatitis and jaundice. Both an inactivated and a live attenuated vaccine are available. New-generation vaccines are being tested, because the existing mousebrain-attenuated strain induces fetal teratology or abortion in a percentage of pregnant animals. Diagnosis is based on histopathology or the demonstration of viral antigen or antibody. PMID:12442582

  4. 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).

  5. Hydrocarbon potential of intracratonic rift basins

    SciTech Connect

    Baker, D.G.; Derksen, S.J.

    1984-09-01

    Significant world oil reserves have been added in recent years from rift system. Examples of petroliferous rift basins may be found on nearly every major continent. As our understanding of the mechanisms of sedimentation and structure in rift basins grows, more rift systems will be found. With a few notable exceptions, rifts that have been explored in the past are those that formed along continental margins. These contain marine sediments, and the conditions of source rock, sediment type, depositional environment, and structural style are well-known exploration concepts. Intracratonic rift systems containing continental sediments, and also because of the problems perceived to accompany continental sedimentation. A good modern analog is the East African rift system. Several companies have made significant oil discoveries in different components of the Central African rift system. Average daily production for 1982 from the basins associated with the Benue trough was 107.928 BOPD. In the Abu Gabra rift component, where Marathon is currently exploring, Chevron has drilled approximately 60 wells. Nineteen of these were discoveries and tested an average rate per well of 3,500 BOPD. The Abu Gabra rift may contain up to 10 billion bbl of oil. Research indicates that this type of rift system is present in other areas of the world. Ongoing worldwide exploration has shown that intracratonic rift basins have the potential to make a significant contribution to world oil reserves.

  6. Structural style of the Turkana Rift, Kenya

    SciTech Connect

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

    1988-03-01

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

  7. Cenozoic rift formation in the northern Caribbean

    NASA Technical Reports Server (NTRS)

    Mann, P.; Burke, K.

    1984-01-01

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

  8. The East African Rift System

    Microsoft Academic Search

    R. B. McConnell

    1967-01-01

    Dr McConnell joined the Geological Survey of Tanganyika in 1939 and worked there and in other parts of the African continent during the following eighteen years. He reviews here geological aspects of the East African rift structure which have a bearing on problems of the upper mantle and continental drift.

  9. Parga Chasma: Coronae and Rifting on Venus

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  10. Discontinuous and diachronous evolution of the Main Ethiopian Rift: Implications for development of continental rifts

    Microsoft Academic Search

    K. Keranen; S. L. Klemperer

    2008-01-01

    The Main Ethiopian Rift (MER) is commonly considered the archetypal magma-assisted rift. Tomographic images of upper-mantle upwellings beneath the rift, aligned anisotropy beneath magmatic segments, and pervasive magmatic modification of the crust all indicate the importance of magmatic processes in present-day rift evolution. It has been suggested that this magmatic development is responsible for the straight and continuous path the

  11. The diverging volcanic rift system

    NASA Astrophysics Data System (ADS)

    Tibaldi, A.; Bonali, F. L.; Corazzato, C.

    2014-01-01

    Eruptions and volcano internal growth are mostly fed by dykes. The comprehension of the control factors on dyke paths is fundamental for the assessment of areas prone to vent formation and to the general understanding of how volcanoes work. We analyse an understudied magma path system; field data of nine volcanoes show they have a rectilinear rift zone in the central part passing into fan-arranged dykes at the two opposite volcano flanks. The geological, geomorphological and structural characteristics of these volcanoes and their substrate suggest that the formation of these "diverging rifts" is not specifically linked to substrate lithology and mechanical behaviour. The studied volcanoes have elongation < 0.88 and V > 10 km3 (mostly > 300 km3). Eight volcanoes have the central rift that is normal to the regional tectonic least principal stress (?3reg) and in one case it is sub-perpendicular. Field data have been combined with scaled analogue modelling, suggesting that if the ?3reg is oblique to the volcano elongation axis, dyke geometry in the edifice axial zone is controlled by elongation and thus by local gravity ?3, but dyke strike becomes perpendicular to ?3reg when dykes intrude the more external areas of the volcano. If a dyke is injected under the volcano flanks with slope inclination > 50°, it attains a geometry parallel to the slope. At lower slope inclinations at the edifice terminations, magma paths diverge outwards and crosscut slopes at high angle. Our data are in agreement with the assumption that regional tectonic stresses can affect large volcanoes up to the summit area guiding the development of a rectilinear thoroughgoing rift, both in extensional and transtensional regimes. The diverging pattern takes place due to reorientation of the local stress field guided by topography only when dyke inception localizes laterally respect to the edifice axis.

  12. Rift reactivation and migration during multiphase extension

    NASA Astrophysics Data System (ADS)

    Naliboff, John; Buiter, Susanne J. H.

    2015-07-01

    Passive margins may undergo multiple phases of extension with distinct structural, petrological and sedimentary processes before achieving breakup. Observations of rift axis migration through time may reflect cooling, hardening and subsequent abandonment of the rift axis during either long-term periods of slow extension or periods of tectonic quiescence. Here, we use 2D thermo-mechanical numerical models to examine rift reactivation and migration during multiphase extension where a period of tectonic quiescence separates phases of extension. Our goals are to identify the rheological mechanism(s) controlling rift reactivation versus migration and determine if cooling phases may help explain recent interpretations of passive margin architecture and evolution. Our numerical experiments indicate that the relative integrated brittle strength between the initial rift and surrounding regions, rather than the total integrated strength, largely controls rift reactivation versus migration. The tectonic quiescence (cooling) duration required to induce rift migration ranges between 20 and 60 Myr (minimum bounds). This range reflects variations in extension velocity, magnitude of shear zone healing, crustal rheology and asthenospheric rheology. Reactivated rifts after extensive (>20 Myr) cooling periods in some cases develop asymmetric margins with deformation patterns stepping toward the future rift, such as characterizing most of the Atlantic conjugate margins.

  13. Lithospheric structure of the Rio Grande rift.

    PubMed

    Wilson, David; Aster, Richard; West, Michael; Ni, James; Grand, Steve; Gao, Wei; Baldridge, W Scott; Semken, Steve; Patel, Paresh

    2005-02-24

    A high-resolution, regional passive seismic experiment in the Rio Grande rift region of the southwestern United States has produced new images of upper-mantle velocity structure and crust-mantle topography. Synthesizing these results with geochemical and other geophysical evidence reveals highly symmetric lower-crustal and upper-mantle lithosphere extensional deformation, suggesting a pure-shear rifting mechanism for the Rio Grande rift. Extension in the lower crust is distributed over a region four times the width of the rift's surface expression. Here we propose that the laterally distributed, pure shear extension is a combined effect of low strain rate and a regionally elevated geotherm, possibly abetted by pre-existing lithospheric structures, at the time of rift initiation. Distributed extension in the lower crust and mantle has induced less concentrated vertical mantle upwelling and less vigorous small-scale convection than would have arisen from more localized deformation. This lack of highly focused mantle upwelling may explain a deficit of rift-related volcanics in the Rio Grande rift compared to other major rift systems such as the Kenya rift. PMID:15729338

  14. The origin of along-rift variations in faulting and magmatism in the Ethiopian Rift

    NASA Astrophysics Data System (ADS)

    Keir, Derek; Bastow, Ian D.; Corti, Giacomo; Mazzarini, Francesco; Rooney, Tyrone O.

    2015-03-01

    The geological record at rifts and margins worldwide often reveals considerable 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 Main Ethiopian Rift (MER) in East Africa provides an excellent opportunity to address this dichotomy: 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 volcanic cone density and rift obliquity along strike in the MER. By synthesizing these new data in light of existing geophysical, geochemical, and petrological constraints on magma generation and emplacement, we are able to discriminate between tectonic and mantle geodynamic controls on the geological record of a newly forming magmatic rifted margin. The timing of rift sector development, the three-dimensional focusing of melt, and the ponding of plume material where the rift dramatically narrows each influence igneous intrusion and volcanism along the MER. However, rifting 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.

  15. Magmatic Versus Amagmatic Rifting in the East African Rift System from Pn and Sn Tomography

    NASA Astrophysics Data System (ADS)

    O'Donnell, J. P.; Nyblade, A.

    2014-12-01

    Geodynamic models of rifting currently rely on the mechanism of hot mantle upwelling and decompressional melting to weaken lithospheric rock to the degree that rifting can initiate. However, many rift segments worldwide are apparently amagmatic. The East African Rift System is a prime example, with large sections of the system subaerially amagmatic. We seek to address the question of whether these apparently amagmatic rift segments merely lack a surficial expression of magmatism which exists at depth, or whether rifting is genuinely amagmatic. Based on regional earthquakes recorded by the Tanzania Broadband Seismic Experiment, the Kenya Broadband Seismic Experiment, the AfricaArray East African Seismic Experiment and several permanent GSN stations, we probe for uppermost mantle melt signatures along the East African Rift System using P- and S-wave speed ratios derived from Pn and Sn tomography. Pn- and Sn-velocity models, and their ratio which can be diagnostic of the presence of fluids, will be presented.

  16. Rio Grande rift: problems and perspectives

    SciTech Connect

    Baldridge, W.S.; Olsen, K.H.; Callender, J.F.

    1984-01-01

    Topics and ideas addressed include: (1) the regional extent of the Rio Grande rift; (2) the structure of the crust and upper mantle; (3) whether the evidence for an axile dike in the lower crust is compelling; (4) the nature of faulting and extension in the crust; and (5) the structural and magmatic development of the rift. 88 references, 5 figures.

  17. Evidence of Ancient Rifts Beneath Texas

    NASA Astrophysics Data System (ADS)

    Irie, K.; Velasco, A. A.

    2011-12-01

    Continental rifts are defined as geological features where Earth's lithosphere is pulled away by surface expansion of the Earth. Their physiographic features include linear rift valleys associated with active volcanism. Many rifts fail to split a continent and ancient rifts that failed to split can be found by using seismic waves to image these ancient structures. Using seismic data collected by EarthScope USArray stations in Texas, we calculate teleseismic receiver functions and utilized surface wave dispersion curves to simultaneously invert for the velocity structure beneath each seismic station. With the calculated receiver functions, we generate maps to show preliminary 3-D crust/upper mantle boundary structure, the velocity ratio of P and S waves, and the S-wave velocity structure. We expect to characterize the ancient rift zones that exist in Texas and compare these results with the Rio Grande Rift in New Mexico. The goal for this comparison is to determine whether Rio Grande rift is still active or doomed to be another failed rift.

  18. Stratigraphic Modelling of Continental Rifting

    NASA Astrophysics Data System (ADS)

    Mondy, Luke; Duclaux, Guillaume; Salles, Tristan; Thomas, Charmaine; Rey, Patrice

    2013-04-01

    Interlinks between deformation and sedimentation have long been recognised as an important factor in the evolution of continental rifts and basins development. However, determining the relative impact of tectonic and climatic forcing on the dynamics of these systems remains a major challenge. This problem in part derives from a lack of modelling tools capable of simulated high detailed surface processes within a large scale (spatially and temporally) tectonic setting. To overcome this issue an innovative framework has been designed using two existing numerical forward modelling codes: Underworld, capable of simulating 3D self-consistent tectonic and thermal lithospheric processes, and Tellus, a forward stratigraphic and geomorphic modelling framework dedicated to simulating highly detailed surface dynamics. The coupling framework enables Tellus to use Underworld outputs as internal and boundary conditions, thereby simulating the stratigraphic and geomorphic evolution of a realistic, active tectonic setting. The resulting models can provide high-resolution data on the stratigraphic record, grain-size variations, sediment provenance, fluvial hydrometric, and landscape evolution. Here we illustrate a one-way coupling method between active tectonics and surface processes in an example of 3D oblique rifting. Our coupled model enables us to visualise the distribution of sediment sources and sinks, and their evolution through time. From this we can extract and analyse at each simulation timestep the stratigraphic record anywhere within the model domain. We find that even from a generic oblique rift model, complex fluvial-deltaic and basin filling dynamics emerge. By isolating the tectonic activity from landscape dynamics with this one-way coupling, we are able to investigate the influence of changes in climate or geomorphic parameters on the sedimentary and landscape record. These impacts can be quantified in part via model post-processing to derive both instantaneous and cumulative erosion/sedimentation.

  19. Internet y sus aplicaciones al sector turstico E. Furio -M. Alonso Matilde Alonso Prez

    E-print Network

    Paris-Sud XI, Université de

    Internet y sus aplicaciones al sector turístico E. Furio -M. Alonso - 1 - Matilde Alonso Pérez-00119439,version1-24Dec2006 #12;Internet y sus aplicaciones al sector turístico E. Furio -M. Alonso - 2 - Resumen: El objetivo de este trabajo es analizar las aplicaciones que Internet tiene en el sector

  20. The Effect of Continental Rifting on Lithospheric Fabric: Evidence From the Mid-Continent Rift

    NASA Astrophysics Data System (ADS)

    Ola, O. B.; Frederiksen, A. W.

    2013-12-01

    The Mid-Continent Rift (MCR) is a major feature of the North American continent: a 1.1 Ga rift that failed to develop into an ocean basin. Though the crustal expression of the rift is preserved, it is impossible to determine from crustal evidence the nature of the lithospheric contribution to the rifting process. The installation of teleseismic instrumentation through the Superior Province Rifting Earthscope Experiment (SPREE) is allowing investigation of the lithosphere beneath the MCR, which will help in addressing questions about the initiation, propagation, and failure of the rift structure. We focus on observing the strength and orientation of lithospheric fabric through measurements of the splitting of teleseismic SK(K)S waves at instruments in and near the rift axis, using the method of Silver and Chan (1991) to find the set of parameters that optimally restores linear particle motion. Our results show that the fast direction varies only subtly across the study area, with the exception of localized outliers. The fast direction is close to the direction of absolute plate motion, but shows greater scatter within the MCR itself. Split times show strong variations (from near-zero to 1.5 s), with lower values within the rift; the Nipigon Embayment stands out as a particularly low-anisotropy region. These measurements suggest that the rifting process thinned the lithosphere or reset its fabric, indicating significant lithospheric participation in the rifting process.

  1. The influence of preexisting structure on the evolution of the Cenozoic Malawi rift (East African rift system)

    Microsoft Academic Search

    Uwe Ring

    1994-01-01

    This paper analyzes the importance of preexisting structure for the evolution of the Cenozoic Malawi rift, which constitutes the southernmost part of the western branch of the East African rift system. Kinematic analyses demonstrate that the regional extension direction rotated clockwise from ENE to SE during rifting. Cenozoic rift faults (of dip-, oblique-, and strike-slip character) rejuvenated crustal structures whenever

  2. 3D Dynamics of Oblique Rift Systems: Fault Evolution from Rift to Break-up

    NASA Astrophysics Data System (ADS)

    Brune, S.

    2014-12-01

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

  3. Modelos de estados y transicines: nuevas aplicaciones en contexto mundial

    E-print Network

    Modelos de estados y transiciónes: nuevas aplicaciones en contexto mundial Brandon T. Bestelmeyer predicciones a los encargados Necesitamos sistemas de conocimiento espacial que son fácilmente disponible a los posibles en la vegetación y suelos por cada sitio ecologico · Modelos estado y transición son archivos de

  4. Rapid spatio-temporal variations in rift zone deformation, Corinth rift, Greece

    NASA Astrophysics Data System (ADS)

    Nixon, Casey; McNeill, Lisa; Bull, Jonathan; Henstock, Timothy; Bell, Rebecca; Gawthorpe, Robert; Christodoulou, Dimitris; Kranis, Haris; Ferentinos, George; Papatheodorou, George; Taylor, Brian; Ford, Mary; Sakellariou, Dimitris; Leeder, Mike; Collier, Richard; Goodliffe, Andrew; Sachpazi, Maria

    2015-04-01

    The Gulf of Corinth is a young and highly active rift (<5 Ma) in its initial stages of development. An abundance of marine geophysical data and onshore exposures makes it an ideal case study for investigating early rift and fault development. Using a high resolution chronstratigraphic and rift fault model we investigate along strike variations in the basin development within the rift over the past 1-2 Myr and establishing a history of fault activity on major basin controlling faults, at temporal resolutions of ca. 100 kyr or less. We focus on variations in depocentre development and the distribution of displacement and faulting along and across the rift axis; focussing on the partitioning of deformation between N-dipping and S-dipping faults. The rift basin geometry has a complex history and varies spatially along strike of the rift. We highlight a major change in rift structure ca. 600 ka, changing from a complex rift zone to a uniform asymmetric graben. Syn-rift isochore maps identify two stages that accommodate this change: 1. a switch in rift polarity from a dominant N-thickening depocentre to a dominant S-thickening depocentre between ca. 620-420 ka (a rapid change in rift structure and strain distribution). This change is accommodated by transfer of activity between major faults but also by formation of numerous non-basement cutting small faults. 2. Progressive localization of deformation onto major N-dipping faults on the rift's southern margin. This is characterised by depocentre growth and linkage and increased activity on major N-dipping faults since ~340 ka, with faults becoming kinematically and geometrically linked with almost equal slip rates along strike by ca. 130 ka. Ultimately our results show that the early evolution of a rift fault network can be complex but that a dominant fault set eventually forms even in the earliest stages of rifting. Furthermore a switch in rift polarity is a progressive process with deformation becoming distributed before localizing onto a final dominant fault set, but this process can occur rapidly on a timescale of 100's kyr.

  5. Thermochronological investigation of the timing of rifting and rift segmentation in the Gulf of Suez, Egypt

    NASA Astrophysics Data System (ADS)

    Bosworth, W.; Stockli, D. F.

    2006-12-01

    The Tertiary Gulf of Suez rift system is one of the best-studied continental rift systems and has inspired many fundamental geodynamic models for continental rifting. 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 rift. A critical aspect of constraining the evolution of rifting and rift 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 rifting, lateral rift segmentation, and rift 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 rift integrated with structural data will allow us to directly determine the timing, distribution, and magnitude of extension. The onset of major rifting (~24-19 Ma) in the Gulf of Suez was marked by the development of crustal domino-style tilt blocks and syn-rift 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 rift from the Red Sea rift at an early extensional stage. Apatite (AHe) and zircon (ZHe) (U- Th)/He data were collected from basement and pre-rift 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 basin-ward AHe samples are as young as ~17 Ma, recording continued early to middle Miocene extension in the Gulf of Suez. Detailed thermochronometric dating in progress should yield a more complete picture of the temporal and spatial distribution of extensional faulting in the Gulf of Suez.

  6. Evolution of a rift basin dominated by subaerial deposits: The Guaritas Rift, Early Cambrian, Southern Brazil

    NASA Astrophysics Data System (ADS)

    de Almeida, Renato P.; Janikian, Liliane; Fragoso-Cesar, Antonio Romalino S.; Marconato, André

    2009-05-01

    Most existing models for the evolution of rift basins predict the development of deep-water depositional systems during the stage of greatest tectonic subsidence, when accommodation generation potentially outpaces sedimentation. Despite this, some rift basins do not present deep-water systems, instead being dominated by subaerial deposits. This paper focuses on one of these particular rift basins, the Cambrian Guaritas Rift, Southern Brazil, characterized by more than 1500 m of alluvial and aeolian strata deposited in a 50-km-wide basin. The deposits of the Guaritas Rift can be ascribed to four depositional systems: basin-border alluvial fans, bed-load-dominated ephemeral rivers, mixed-load ephemeral rivers and aeolian dune fields. These four systems are in part coeval and in part succeed each other, forming three stages of basin evolution: (i) Rift Initiation to Early Rift Climax stage, (ii) Mid to Late Rift Climax stage, and (iii) Early Post-Rift stage. The first stage comprises most of the Guaritas Group and is characterized by homogeneous bed-load-dominated river deposits, which do not clearly record the evolution of subsidence rates. The onset of sedimentation of finer-grained deposits occurred as a consequence of a reactivation event that changed the outline of the basin and the distribution of the nearby highlands. This strongly suggests that the capture of the main river system to another depression decreased the sediment supply to the basin. The study of the Guaritas Rift indicates that rift basins in which the sediment supply exceeds the accommodation generation occur as a consequence of moderate subsidence combined with the capture of a major river system to the basin during the initial stages of basin evolution. In these basins, changes in the average discharge of the river system or tectonic modification of the drainage network may be the major control on the stratigraphic architecture.

  7. Surface deformation in volcanic rift zones

    USGS Publications Warehouse

    Pollard, D.D.; Delaney, P.T.; Duffield, W.A.; Endo, E.T.; Okamura, A.T.

    1983-01-01

    The principal conduits for magma transport within rift zones of basaltic volcanoes are steeply dipping dikes, some of which feed fissure eruptions. Elastic displacements accompanying a single dike emplacement elevate the flanks of the rift relative to a central depression. Concomitant normal faulting may transform the depression into a graben thus accentuating the topographic features of the rift. If eruption occurs the characteristic ridge-trough-ridge displacement profile changes to a single ridge, centered at the fissure, and the erupted lava alters the local topography. A well-developed rift zone owes its structure and topography to the integrated effects of many magmatic rifting events. To investigate this process we compute the elastic displacements and stresses in a homogeneous, two-dimensional half-space driven by a pressurized crack that may breach the surface. A derivative graphical method permits one to estimate the three geometric parameters of the dike (height, inclination, and depth-to-center) and the mechanical parameter (driving pressure/rock stiffness) from a smoothly varying displacement profile. Direct comparison of measured and theoretical profiles may be used to estimate these parameters even if inelastic deformation, notably normal faulting, creates discontinuities in the profile. Geological structures (open cracks, normal faults, buckles, and thrust faults) form because of stresses induced by dike emplacement and fissure eruption. Theoretical stress states associated with dilation of a pressurized crack are used to interpret the distribution and orientation of these structures and their role in rift formation. ?? 1983.

  8. The 1974 Ethiopian rift geodimeter survey

    NASA Technical Reports Server (NTRS)

    Mohr, P.

    1977-01-01

    The field techniques and methods of data reduction for five successive geodimeter surveys in the Ethiopian rift valley are enlarged upon, with the considered conclusion that there is progressive accumulation of upper crustal strain, consonant with on-going rift extension. The extension is restricted to the Quaternary volcanotectonic axis of the rift, namely the Wonji fault belt, and is occurring at rates of 3 to 6 mm/yr in the northern sector of the rift valley. Although this concurs with the predictions of platetectonic analysis of the Afar triple junction, it is considered premature to endorse such a concurrence on the basis of only 5 years of observations. This is underlined by the detection of local tectonic contractions and expansions associated with geothermal and gravity anomalies in the central sector of the rift valley. There is a hint of a component of dextral slip along some of the rift-floor fault zones, both from geological evidence and from the strain patterns detected in the present geodetic surveys.

  9. Impact of rheological layering on rift asymmetry

    NASA Astrophysics Data System (ADS)

    Jaquet, Yoann; Schmalholz, Stefan M.; Duretz, Thibault

    2015-04-01

    Although numerous models of rift formation have been proposed, what triggers asymmetry of rifted margins remains unclear. Parametrized material softening is often employed to induce asymmetric fault patterns in numerical models. Here, we use thermo-mechanical finite element models that allow softening via thermal weakening. We investigate the importance of lithosphere rheology and mechanical layering on rift morphology. The numerical code is based on the MILAMIN solver and uses the Triangle mesh generator. Our model configuration consists of a visco-elasto-platic layered lithosphere comprising either (1) only one brittle-ductile transition (in the mantle) or (2) three brittle-ductile transitions (one in the upper crust, one in the lower crust and one in the mantle). We perform then two sets of simulations characterized by low and high extensional strain rates (5*10-15 s-1, 2*10-14 s-1). The results show that the extension of a lithosphere comprising only one brittle-ductile transition produces a symmetric 'neck' type rift. The upper and lower crusts are thinned until the lithospheric mantle is exhumed to the seafloor. A lithosphere containing three brittle-ductile transitions favors strain localization. Shear zones at different horizontal locations and generated in the brittle levels of the lithosphere get connected by the weak ductile layers. The results suggest that rheological layering of the lithosphere can be a reason for the generation of asymmetric rifting and subsequent rift morphology.

  10. Deepening, and repairing, the metabolic rift.

    PubMed

    Schneider, Mindi; McMichael, Philip

    2010-01-01

    This paper critically assesses the metabolic rift as a social, ecological, and historical concept describing the disruption of natural cycles and processes and ruptures in material human-nature relations under capitalism. As a social concept, the metabolic rift presumes that metabolism is understood in relation to the labour process. This conception, however, privileges the organisation of labour to the exclusion of the practice of labour, which we argue challenges its utility for analysing contemporary socio-environmental crises. As an ecological concept, the metabolic rift is based on outmoded understandings of (agro) ecosystems and inadequately describes relations and interactions between labour and ecological processes. Historically, the metabolic rift is integral to debates about the definitions and relations of capitalism, industrialism, and modernity as historical concepts. At the same time, it gives rise to an epistemic rift, insofar as the separation of the natural and social worlds comes to be expressed in social thought and critical theory, which have one-sidedly focused on the social. We argue that a reunification of the social and the ecological, in historical practice and in historical thought, is the key to repairing the metabolic rift, both conceptually and practically. The food sovereignty movement in this respect is exemplary. PMID:20645448

  11. Three-dimensional laboratory modelling of rifting: application to the Baikal Rift, Russia

    E-print Network

    Déverchère, Jacques

    -branch configuration of the Baikal rift system only by introducing a weak zone in the area of Lake Baikal. Such a zone to the tension direction. In nature and in the model, rifting starts in the central branch corresponding to Lake Baikal. The modelling also predicts the formation of a fourth oblique f NS-trending branch to the south

  12. Evolution of the Main Ethiopian Rift in the frame of Afar and Kenya rifts propagation

    Microsoft Academic Search

    Marco Bonini; Giacomo Corti; Fabrizio Innocenti; Piero Manetti; Francesco Mazzarini; Tsegaye Abebe; Zoltan Pecskay

    2005-01-01

    The Main Ethiopian Rift (MER) has a complex structural pattern composed of southern, central, and northern segments. Ages of onset of faulting and volcanism apparently indicate a heterogeneous time-space evolution of the segments, generally referred to as a northward progression of the rifting process. New structural, petrological, and geochronological data have been used to attempt reconciling the evolution of the

  13. Mid-continent rift system: a frontier hydrocarbon province

    SciTech Connect

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

    1984-04-01

    The Mid-continent rift system can be traced by the Mid-continent geophysical anomaly (MGA) from the surface exposure of the Keweenawan Supergroup in the Lake Superior basin southwest in the subsurface through Wisconsin, Minnesota, Iowa, Nebraska, and Kansas. Outcrop and well penetrations of the late rift Keweenawan sedimentary rocks reveal sediments reflecting a characteristic early continental rift clastic sequence, including alluvial fans, deep organic-rich basins, and prograding fluvial plains. Sedimentary basins where these early rift sediments are preserved can be located by upward continuation of the aeromagnetic profiles across the rift trend and by gravity models. Studies of analog continental rifts and aulacogens show that these gravity models should incorporate (1) a deep mafic rift pillow body to create the narrow gravity high of the MGA, and (2) anomalously thick crust to account for the more regional gravity low. Preserved accumulations of rift clastics in central rift positions can then be modeled to explain the small scale notches which are found within the narrow gravity high. Indigenous oil in Keweenawan sediments in the outcrop area and coaly partings in the subsurface penetrations of the Keweenawan clastics support the analogy between these rift sediments and the exceptionally organic-rich sediments of the East African rift. COCORP data across the rift trend in Kansas show layered deep reflectors and large structures. There is demonstrable source, reservoir, and trap potential within the Keweenawan trend, making the Mid-Continent rift system a frontier hydrocarbon province.

  14. Mid-Continent rift system: a frontier hydrocarbon province

    SciTech Connect

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

    1984-04-01

    The Mid-Continent rift system can be traced by the Mid-Continent geophysical anomaly (MGA) from the surface exposure of the Keweenawan Supergroup in the Lake Superior basin southwest in the subsurface through Wisconsin, Minnesota, Iowa, Nebraska, and Kansas. Outcrop and well penetrations of the late rift Keweenawan sedimentary rocks reveal sediments reflecting a characteristic early continental rift clastic sequence, including alluvial fans, deep organic-rich basins, and prograding fluvial plains. Sedimentary basins where these early rift sediments are preserved can be located by upward continuation of the aeromagnetic profiles across the rift trend and by gravity models. Studies of analog continental rifts and aulacogens show that these gravity models should incorporate (1) a deep mafic rift pillow body to create the narrow gravity high of the MGA, and (2) anomalously thick crust to account for the more regional gravity low. Preserved accumulations of rift clastics in central rift positions can then be modeled to explain the small scale notches which are found within the narrow gravity high. Indigenous oil in Keweenawan sediments in the outcrop area and coaly partings in the subsurface penetrations of the Keweenawan clastics support the analogy between these rift sediments and the exceptionally organic-rich sediments of the East African rift. COCORP data across the rift trend in Kansas show layered deep reflectors and large structures. There is demonstrable source, reservoir, and trap potential within the Keweenawan trend, making the Mid-Continent rift system a frontier hydrocarbon province.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  16. Rift initiation with volatiles and magma

    NASA Astrophysics Data System (ADS)

    Ebinger, Cynthia; Muirhead, James; Roecker, Steve; Tiberi, Christel; Muzuka, Alfred; Ferdinand, Rrichard; Mulibo, Gabrile; Kianji, Gladys

    2015-04-01

    Rift initiation in cratonic lithosphere remains an outstanding problem in continental tectonics, but strain and magmatism patterns in youthful sectors of the East African rift provide new insights. Few teleseisms occur in the Eastern rift arm of the East African rift system, except the southernmost sector in northern Tanzania where extension occurs in Archaean lithosphere. The change in seismic energy release occurs over a narrow along-axis zone, and between sectors with and without volcanoes in the central rift valley. Are these differences in strain behavior indicative of along-strike variations in a) rheology; b) strain transfer from border faults to magma intrusion zones; c) dike vs fault slip; and/or d) shallow vs deep magma chambers? We present time-space relations of seismicity recorded on a 38-station array spanning the Kenya-Tanzania border, focal mechanisms for the largest events during those time periods, and compare these to longer-term strain patterns. Lower crustal seismicity occurs along the rift length, including sectors on and off craton, and those with and without central rift valley volcanoes, and we see no clear along-strike variation in seismogenic layer thickness. One explanation for widespread lower crustal seismicity is high gas pressures and volatile migration from active metasomatism of upper mantle and magma degassing, consistent with very high volatile flux along fault zones, and widespread metasomatism of xenoliths. Volatile release and migration may be critical to strength reduction of initially cold, strong cratonic lithosphere. Seismicity patterns indicate strain (and fluid?) transfer from the Manyara border fault to Gelai shield volcano (faulting, diking) via Oldoinyo Lengai volcano. Our focal mechanisms and Global CMTs from an intense fault-dike episode (2007) show a local, temporally stable, rotation from ~E-W extension to NE-SE extension in this linkage zone, consistent with longer term patterns recorded in vent and eruptive chain alignments.

  17. Review article Rift Valley fever virus (Bunyaviridae: Phlebovirus)

    E-print Network

    Paris-Sud XI, Université de

    Review article Rift Valley fever virus (Bunyaviridae: Phlebovirus): an update on pathogenesis Africa (Received 5 February 2010; accepted 21 May 2010) Abstract ­ Rift Valley fever (RVF) virus fever / molecular epidemiology / vector / pathogenesis / diagnostic Table of contents 1. Introduction

  18. Post Rift Thermal Evolution of Extended Lithosphere

    NASA Astrophysics Data System (ADS)

    Cardoso, R. R.; Hamza, V. M.

    2009-12-01

    An improved thermal model of the lithosphere extension is proposed and its influence in the petroleum system in sedimentary basins examined. The new model assumes existence of time dependent variation in the lithosphere thickness during the post-rift period, which was not take account in the formulation of the Mackenzie model (1978). In the present work we assume that the asymptotic growth of the lithosphere thickness, during the post-rift period, may be represented by an asymptotic relation of the type: L(t)=(L/?)+(L-L/?)erf(?*t) where L(t) is lithospheric thickness at post-rift time t, ? the stretching factor as defined in the McKenzie model, erf the error function and ? a suitable scaling constant. According to the above equation the syn-rift value of L is (L/?). For large times the thickness of the lithosphere approaches asymptotically the pre-rift value of L. The value of ? can be determined by calculating the time necessary for the stretched lithosphere (L/?) to return to original thickness. The results of numerical simulations indicate that the heat flux derived from the new model is substantially lower than the values predicted by the McKenzie model (see Figure 1). The new model has been calibrated using available information on evolution of thermal maturity indices for the Santos Basin, situated in the offshore area of southeast Brazil. Heat flow variations during the post stretch period, for the case in which the stretching factor is 2.5.

  19. Anisotropy beneath a highly extended continental rift

    NASA Astrophysics Data System (ADS)

    Eilon, Zachary; Abers, Geoffrey A.; Jin, Ge; Gaherty, James B.

    2014-03-01

    have employed shear wave splitting techniques to image anisotropy beneath the D'Entrecasteaux Islands, in southeastern Papua New Guinea. Our results provide a detailed picture of the extending continent that lies immediately ahead of a propagating mid-ocean ridge tip; we image the transition from continental to oceanic extension. A dense shear wave splitting data set from a 2010 to 2011 passive-source seismic deployment is analyzed using single and multichannel methods. Splitting delay times of 1-1.5 s are observed and fast axes of anisotropy trending N-S, parallel to rifting direction, predominate the results. This trend is linked to lattice-preferred orientation of olivine, primarily in the shallow convecting mantle, driven by up to 200 km of N-S continental extension ahead of the westward-propagating Woodlark Rift. This pattern differs from several other continental rifts that evince rift-strike-parallel fast axes and is evident despite the complex recent tectonic history. We contend that across most of this rift, the unusually high rate and magnitude of extension has been sufficient to produce a regime change to a mid-ocean-ridge-like mantle fabric. Stations in the south of our array show more complex splitting that might be related to melt or to complex inherited structure at the edge of the extended region.

  20. Variation in styles of rifting in the Gulf of California.

    PubMed

    Lizarralde, Daniel; Axen, Gary J; Brown, Hillary E; Fletcher, John M; González-Fernández, Antonio; Harding, Alistair J; Holbrook, W Steven; Kent, Graham M; Paramo, Pedro; Sutherland, Fiona; Umhoefer, Paul J

    2007-07-26

    Constraints on the structure of rifted continental margins and the magmatism resulting from such rifting can help refine our understanding of the strength of the lithosphere, the state of the underlying mantle and the transition from rifting to seafloor spreading. An important structural classification of rifts is by width, with narrow rifts thought to form as necking instabilities (where extension rates outpace thermal diffusion) and wide rifts thought to require a mechanism to inhibit localization, such as lower-crustal flow in high heat-flow settings. Observations of the magmatism that results from rifting range from volcanic margins with two to three times the magmatism predicted from melting models to non-volcanic margins with almost no rift or post-rift magmatism. Such variations in magmatic activity are commonly attributed to variations in mantle temperature. Here we describe results from the PESCADOR seismic experiment in the southern Gulf of California and present crustal-scale images across three rift segments. Over short lateral distances, we observe large differences in rifting style and magmatism--from wide rifting with minor synchronous magmatism to narrow rifting in magmatically robust segments. But many of the factors believed to control structural evolution and magmatism during rifting (extension rate, mantle potential temperature and heat flow) tend to vary over larger length scales. We conclude instead that mantle depletion, rather than low mantle temperature, accounts for the observed wide, magma-poor margins, and that mantle fertility and possibly sedimentary insulation, rather than high mantle temperature, account for the observed robust rift and post-rift magmatism. PMID:17653189

  1. Young rift kinematics in the Tadjoura rift, western Gulf of Aden, Republic of Djibouti

    NASA Astrophysics Data System (ADS)

    Daoud, Mohamed A.; Le Gall, Bernard; Maury, René C.; Rolet, JoëL.; Huchon, Philippe; Guillou, Hervé

    2011-02-01

    The Tadjoura rift forms the westernmost edge of the westerly propagating Sheba ridge, between Arabia and Somalia, as it enters into the Afar depression. From structural and remote sensing data sets, the Tadjoura rift is interpreted as an asymmetrical south facing half-graben, about 40 km wide, dominated by a large boundary fault zone to the north. It is partially filled up by the 1-3 Myr old Gulf Basalts which onlapped the older Somali Basalts along its shallower southern flexural margin. The major and trace element analysis of 78 young onshore lavas allows us to distinguish and map four distinct basaltic types, namely the Gulf, Somali, Goumarre, and Hayyabley Basalts. These results, together with radiometric age data, lead us to propose a revised volcano-stratigraphic sketch of the two exposed Tadjoura rift margins and to discriminate and date several distinct fault networks of this oblique rift. Morphological and statistical analyses of onshore extensional fault populations show marked changes in structural styles along-strike, in a direction parallel to the rift axis. These major fault disturbances are assigned to the arrest of axial fault tip propagation against preexisting discontinuities in the NS-oriented Arta transverse zone. According to our model, the sinistral jump of rifting into the Asal-Ghoubbet rift segment results from structural inheritance, in contrast with the en échelon or transform mechanism of propagation that prevailed along the entire length of the Gulf of Aden extensional system.

  2. Longitudinal evolution of the Suez rift structure (Egypt)

    Microsoft Academic Search

    B. Colletta; P. Le Quellec; J. Letouzey; I. Moretti

    1988-01-01

    A three-dimensional study of the structure of the Suez Rift has been carried out using field and subsurface data in an attempt to determine the role of transverse faults and the longitudinal evolution of the rift. As in most intracontinental rifts, the structure of the Gulf of Suez area is governed by normal faults and tilted blocks, whose crests constitute

  3. REVIEW Open Access Towards a better understanding of Rift Valley

    E-print Network

    Paris-Sud XI, Université de

    REVIEW Open Access Towards a better understanding of Rift Valley fever epidemiology in the south , Matthieu Roger1 and Betty Zumbo7 Abstract Rift Valley fever virus (Phlebovirus, Bunyaviridae be contaminated by close contact with infectious tissues or through mosquito infectious bites. Rift Valley fever

  4. Aedes Mosquito Saliva Modulates Rift Valley Fever Virus Pathogenicity

    E-print Network

    Boyer, Edmond

    Aedes Mosquito Saliva Modulates Rift Valley Fever Virus Pathogenicity Alain Le Coupanec1 , Divya contro^le, Centre IRD de Montpellier, Montpellier, France Abstract Background: Rift Valley fever (RVF of mosquito saliva in the transmission of Rift Valley fever virus (RVFV) has not been investigated. Objective

  5. The Offshore East African Rift System

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Numerous studies have addressed various aspects of the East African Rift system but surprisingly few on the offshore continuation of the south-eastern branch of the rift into the Mozambique Channel. The most prominent article has been published almost 30 years ago by Mougenot et al. (1986) and is based on vintage seismic data. Several studies investigating earthquakes and plate motions from GPS measurements reveal recent deformation along the offshore branch of the East African Rift system. Slip vectors from earthquakes data in Mozambique's offshore basins show a consistent NE direction. Fault plane solutions reveal ~ E-W extensional failure with focal depth clustering around 19 km and 40 km, respectively. Here, we present new evidence for neotectonic deformation derived from modern seismic reflection data and supported by additional geophysical data. The modern rift system obviously reactivates structures from the disintegration of eastern Gondwana. During the Jurassic/Cretaceous opening of the Somali and Mozambique Basins, Madagascar moved southwards along a major shear zone, to its present position. Since the Miocene, parts of the shear zone became reactivated and structurally overprinted by the East African rift system. The Kerimbas Graben offshore northern Mozambique is the most prominent manifestation of recent extensional deformation. Bathymetry data shows that it deepens northwards, with approximately 700 m downthrown on the eastern shoulder. The graben can be subdivided into four subbasins by crosscutting structural lineaments with a NW-SE trend. Together with the N-S striking graben-bounding faults, this resembles a conjugate fault system. In seismic reflection data normal faulting is distinct not only at the earthquake epicenters. The faults cut through the sedimentary successions and typically reach the seafloor, indicating ongoing recent deformation. Reference: Mougenot, D., Recq, M., Virlogeux, P., and Lepvrier, C., 1986, Seaward extension of the East African Rift: Nature, v. 321, p. 599-603

  6. Thermomechanical models of the Rio Grande rift

    SciTech Connect

    Bridwell, R.J.; Anderson, C.A.

    1980-01-01

    Fully two-dimensional, coupled thermochemical solutions of a continental rift and platform are used to model the crust and mantle structure of a hot, buoyant mantle diapir beneath the Rio Grande rift. The thermomechanical model includes both linear and nonlinear laws of the Weertman type relating shear stress and creep strain rate, viscosity which depends on temperature and pressure, and activation energy, temperature-dependent thermal conductivity, temperature-dependent coefficient of thermal expansion, the Boussinesq approximation for thermal bouyancy, material convection using a stress rate that is invariant to rigid rotations, an elastically deformable crust, and a free surface. The model determines the free surface velocities, solid state flow field in the mantle, and viscosity structure of lithosphere and asthenosphere. Regional topography and crustal heat flow are simulated. A suite of symmetric models, assumes continental geotherms on the right and the successively increasing rift geotherms on the left. These models predict an asthenospheric flow field which transfers cold material laterally toward the rift at > 300 km, hot, buoyant material approx. 200 km wide which ascends vertically at rates of 1 km/my between 175 to 325 km, and spreads laterally away from the rift at the base of the lithosphere. Crustal spreading rates are similar to uplift rates. The lithosphere acts as stiff, elastic cap, damping upward motion through decreased velocities of 1 km/10 my and spreading uplift laterally. A parameter study varying material coefficients for the Weertman flow law suggests asthenospheric viscosities of approx. 10/sup 22/ to 10/sup 23/ poise. Similar studies predict crustal viscosities of approx. 10/sup 25/ poise. The buoyant process of mantle flow narrows and concentrates heat transport beneath the rift, increases upward velocity, and broadly arches the lithosphere. 10 figures, 1 table.

  7. Continental Rifting in the Western Ross Sea

    NASA Astrophysics Data System (ADS)

    Davey, F. J.; Cande, S. C.; Stock, J. M.

    2014-12-01

    The Ross Sea forms the north western end of the West Antarctic Rift system, a major continental rift that lies across the western part of Antarctica, and results from rifting during the break-up of Gondwana starting some 180 m.y. ago. In the Ross Sea region, extension comprised a regional thinning associated with the break-up of New Zealand and Australia from Antarctica, and a more focussed extension during the Cenozoic. The last episode of extension, largely from 46 Ma - 25 Ma, formed the Victoria Land Basin (VLB) in the southwest, the Northern Basin (offset from the VLB) in north western Ross Sea and the Adare Basin in the deep ocean to the north. Marine magnetic anomalies associated with the seafloor spreading that formed the Adare Basin, extend continuously onto the continental shelf of the Northern Basin, suggesting that the basin is underlain by oceanic crust, consistent with high gravity anomalies across the continental shelf edge. No seismic data exist for the deeper crust of Northern Basin. The amplitude and gradient of gravity anomalies across the basin limit the depth, density contrast and thickness of the dense body underlying it and are consistent with oceanic crust with steep margins at a depth of about 8 - 10 km. The VLB in contrast shows an extensional thinning of the continental crust. The three basins thus show seafloor spreading in the north, continental rifting at the continental margin, and continental thinning in the south. The pole of rotation for the extension lies to the south of the VLB so the rate of extension increases to the north. In addition, the azimuth of the axis of spreading changes relative to the extension direction, presumably as it followed pre-existing zones of weakness in the Antarctic lithosphere. This leads to a much larger degree of strike slip motion in the Northern Basin rifting that may be a significant factor in the development there of narrow rifting of the continental lithosphere.

  8. Denudation history of the Malawi and Rukwa Rift flanks (East African Rift System) from apatite fission track thermochronology

    Microsoft Academic Search

    Peter Van der Beek; Evelyne Mbede; Paul Andriessen; Damien Delvaux

    1998-01-01

    Thirty apatite fission track ages and 22 track length measurements are presented from samples of basement rocks flanking the Malawi and Rukwa Rifts (East African Rift System) in order to elucidate the thermotectonic history of the rift flanks. The apatite fission track ages fall in the range 30 ± 15 to 296 ± 10 Ma. The relatively short (11.0–13.2 ?m)

  9. Molecular Epidemiology of Rift Valley Fever Virus

    PubMed Central

    Grobbelaar, Antoinette A.; Weyer, Jacqueline; Leman, Patricia A.; Kemp, Alan; Paweska, Janusz T.

    2011-01-01

    Phylogenetic relationships were examined for 198 Rift Valley fever virus isolates and 5 derived strains obtained from various sources in Saudi Arabia and 16 countries in Africa during a 67-year period (1944–2010). A maximum-likelihood tree prepared with sequence data for a 490-nt section of the Gn glycoprotein gene showed that 95 unique sequences sorted into 15 lineages. A 2010 isolate from a patient in South Africa potentially exposed to co-infection with live animal vaccine and wild virus was a reassortant. The potential influence of large-scale use of live animal vaccine on evolution of Rift Valley fever virus is discussed. PMID:22172568

  10. Topside Driven 3D Convection Model of the East African Rift System with Comparison to Observed Rift-Parallel Surface Motions

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    We test the hypothesis of basal shear driven tectonics where rift-parallel surface motions are observed in an active rift of the East African Rift System using a new 3D regional geodynamic model based on the code ASPECT.

  11. 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.

  12. Syn-rift unconformities punctuating the lower-middle Cambrian transition in the Atlas Rift, Morocco

    NASA Astrophysics Data System (ADS)

    Álvaro, J. Javier; Ezzouhairi, Hassan; Clausen, Sébastien; Ribeiro, M. Luisa; Solá, Rita

    2015-04-01

    The Cambrian Tamdroust and Bab n'Ali Volcanic Complexes represent two magmatic episodes developed in the latest Ediacaran-Cambrian Atlas Rift of Morocco. Their rifting pulses were accompanied by accumulation of volcanosedimentary edifices (dominated by effusive lava flows in the former and explosive acidic aprons in the latter) associated with active tilting and uplift. Sealing of their peneplaned horst-and-graben palaeotopographies led to the onset of distinct onlapping geometries and angular discordances capping eroded basements ranging from the Ediacaran Ouarzazate Supergroup to the Cambrian Asrir Formation. Previous interpretations of these discordances as pull-apart or compressive events are revised here and reinterpreted in an extensional (rifting) context associated with active volcanism. The record of erosive unconformities, stratigraphic gaps, condensed beds and onlapping patterns across the traditional "lower-middle Cambrian" (or Cambrian Series 2-3) transition of the Atlas Rift must be taken into consideration for global chronostratigraphic correlation based on their trilobite content.

  13. Volcanic field elongation, vent distribution and tectonic evolution of continental rift: The Main Ethiopian Rift example

    NASA Astrophysics Data System (ADS)

    Mazzarini, Francesco; Le Corvec, Nicolas; Isola, Ilaria; Favalli, Massimiliano

    2015-04-01

    Magmatism and faulting operate in continental rifts and interact at a variety of scales, however their relationship is complex. The African rift, being the best example for both active continental rifting and magmatism, provides the ideal location to study the interplay between the two mechanisms. The Main Ethiopian Rift (MER), which connects the Afar depression in the north with the Turkana depression and Kenya Rift to the south, consists of two distinct systems of normal faults and its floor is scattered with volcanic fields formed by tens to several hundreds monogenetic, generally basaltic, small volcanoes and composite volcanoes and small calderas. The distribution of vents defines the overall shape of the volcanic field. Previous work has shown that the distribution of volcanic vents and the shape of a field are linked to its tectonic environment and its magmatic system. In order to distinguish the impact of each mechanism, we analyzed four volcanic fields located at the boundary between the central and northern MER, three of them (Debre Zeyit, Wonji and Kone) grew in the rift valley and one (Akaki) on the western rift shoulder. The elongation and shape of the fields were analyzed based on their vent distribution using the Principal Component Analysis (PCA), the Vent-to-Vent Distance (VVD), and the two dimensional symmetric Gaussian kernel density estimate methods. We extracted from these methods several parameters characterizing the spatial distribution of points (e.g., eccentricity (e), eigenvector index (evi), angular dispersion (Da)). These parameters allow to define at least three types of shape for volcanic fields: strong elongate (line and ellipse), bimodal/medium elongate (ellipse) and dispersed (circle) shapes. Applied to the natural example, these methods well differentiate each volcanic field. For example, the elongation of the field increases from shoulder to rift axis inversely to the angular dispersion. In addition, the results show that none of the analyzed fields has its shape parallel to the actual trend of youngest and active faulting and volcanism. The alignment analysis shows that the feeders located along the actual rift axis (Wonji and Kone) are parallel to the NNE trend of the youngest fault system. This parallelism decreases as we move to the rift border. Our results suggest that the shape of volcanic fields is controlled mainly by large crustal to lithosphere scale structures (main border faults of the rift) and/or by the Lithosphere-Asthenosphere-Border (LAB) geometry, whereas diking, occurring at shallower levels, is principally controlled by upper crustal stress and strain state.

  14. Structure and kinematics of the Taupo Rift, New Zealand

    NASA Astrophysics Data System (ADS)

    Seebeck, Hannu; Nicol, Andrew; Villamor, Pilar; Ristau, John; Pettinga, Jarg

    2014-06-01

    The structure and kinematics of the continental intra-arc Taupo Rift have been constrained by fault-trace mapping, a large catalogue of focal mechanisms (N = 202) and fault slip striations. The mean extension direction of ~137° is approximately orthogonal to the regional trend of the rift and arc front (? = 84° and 79°, respectively) and to the strike of the underlying subducting Pacific Plate. Bending and rollback of the subduction hinge strongly influence the location, orientation, and extension direction of intra-arc rifting in the North Island. In detail, orthogonal rifting (? = 85-90°) transitions northward to oblique rifting (? = 69-71°) across a paleovertical-axis rotation boundary where rift faults, extension directions, and basement fabric rotate by ~20-25°. Toward the south, extension is orthogonal to normal faults which are parallel to, and reactivate, steeply dipping basement fabric. Basement reactivation facilitates strain partitioning with a portion of margin-parallel motion in the overriding plate mainly accommodated east of the rift by strike-slip faults in the North Island Fault System (NIFS). Toward the north where the rift and NIFS intersect, ~4 mm/yr strike slip is transferred into the rift with net oblique extension accommodating a component of margin-parallel motion. The trend and kinematics of the Taupo Rift are comparable to late Miocene-Pliocene intra-arc rifting in the Taranaki Basin, indicating that the northeast strike of the subducting plate and the southeast extension direction have been uniform since at least 4 Ma.

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

    SciTech Connect

    Winn, R.D. Jr.; Steinmetz, J.C. (Marathon Oil Co., Littleton, CO (United States)); Kerekgyarto, W.L. (Marathon Oil Co., Houston, TX (United States))

    1993-11-01

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

  16. Tectonic inheritance and continental rift architecture: Numerical and analogue models of the East African Rift system

    NASA Astrophysics Data System (ADS)

    Corti, Giacomo; van Wijk, Jolante; Cloetingh, Sierd; Morley, Chris K.

    2007-12-01

    The western branch of the East African Rift is composed of an arcuate succession of elongate asymmetric basins, which differ in terms of interaction geometry, fault architecture and kinematics, and patterns of uplift/subsidence and erosion/sedimentation. The basins are located within Proterozoic mobile belts at the edge of the strong Tanzanian craton; surface geology suggests that the geometry of these weak zones is an important parameter in controlling rift development and architecture, although other processes have been proposed. In this study, we use lithosphere-scale numerical models and crustal-scale analogue experiments to shed light on the relations between preexisting structures and rift architecture. Results illustrate that on a regional scale, rift localization within the mobile belts at the curved craton's western border results in an arcuate rift system, which implies that under a constant extensional stress field, part of the western branch experienced orthogonal extension and part oblique extension. Largest depocenters are predicted to form mostly orthogonal to the extension direction, and smaller depocenters will form along the oblique parts of the rift. The varying extension direction along the rift zone furthermore results in lengthwise varying rift asymmetry, segmentation characteristics, and border fault architecture (trend, length, and kinematics). Analogue models predict that discrete upper crustal fabrics may influence the location of accommodation zones and control the architecture of extension-related faults at a local scale. Models support that fabric reactivation is responsible for the oblique-slip kinematics on faults and for the development of Z-shaped or arcuate normal faults typically documented in nature.

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

    USGS Publications Warehouse

    Hall, Jerome; Wilson, Terry; Henrys, Stuart

    2007-01-01

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

  18. El diseño experimental y los métodos de Taguchi: Conceptos y aplicaciones en la industria farmacéutica

    Microsoft Academic Search

    Enrique Yacuzzi; Fernando Martín; Hugo M. Quiñones; Matías Popovsky

    2004-01-01

    Los orígenes del diseño experimental se remontan a las primeras décadas del siglo XX, cuando Ronald Fisher introdujo el concepto de aleatorización y el análisis de varianza. En estos últimos años, la teoría y aplicaciones del diseño de experimentos se consolidaron y expandieron y, en varias industrias, las contribuciones de Gen'ichi Taguchi, abrieron el camino de aplicaciones rutinarias. En este

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

    NASA Astrophysics Data System (ADS)

    Hamling, I. J.; Wright, T. J.; Bennati Rassion, L. S.; Calais, E.; Lewi, E.; Pagli, C.

    2010-12-01

    The 60-km-long Dabbahu segment of the Nubia-Arabia plate boundary lies in the Northern Ethiopian region of Afar. In September 2005 a major rifting episode resulted in the injection of a 60-km-long dyke with a maximum thickness of ~8m (e.g. Wright et al., 2006). Subsidence observed at Dabbahu and Gabho volcanoes implied that some of the magma was sourced from shallow reservoirs beneath the volcanoes. Since the September 2005 intrusion, background displacement rates are significantly larger than the average secular divergence between Nubia and Arabia. Furthermore, between June 2006 and July 2009 a further 12 dykes were intruded in the Dabbahu segment, in the vicinity and to the south of Ado'Ale - a dissected, silicic volcanic complex at the centre of the rift segment. Using multiple ascending and descending interferograms, acquired regularly following the onset of rifting, we invert for rift perpendicular and vertical displacement rates around the rift segment. Largest displacement rates are observed around the Ado’ Ale volcanic complex, presumably caused by the accumulation of magma in a shallow (8-10 km) reservoir. Viscoelastic models, consisting of an elastic lid over a viscoelastic half-space, suggest an crustal thickness of ~14 km with an underlying viscosity of 10^18.5 Pa s. However, the presence of multiple magmatic sources around the rift zone cause large residuals between the data and model suggesting that viscoelastic relaxation alone cannot account for the observed deformation

  20. Submarine Thermal Springs on the Galapagos Rift

    Microsoft Academic Search

    John B. Corliss; Jack Dymond; Louis I. Gordon; John M. Edmond; Richard P. von Herzen; Robert D. Ballard; Kenneth Green; David Williams; Arnold Bainbridge; Kathy Crane; Tjeerd H. van Andel

    1979-01-01

    The submarine hydrothermal activity on and near the Galapagos Rift has been explored with the aid of the deep submersible Alvin. Analyses of water samples from hydrothermal vents reveal that hydrothermal activity provides significant or dominant sources and sinks for several components of seawater; studies of conductive and convective heat transfer suggest that two-thirds of the heat lost from new

  1. South Polar Cycloidal Rift on Enceladus

    Microsoft Academic Search

    Terry A. Hurford; R. Greenberg; G. V. Hoppa

    2006-01-01

    Large rifts near the south pole of Enceladus have been observed to be significantly warmer than the surrounding surface (Spencer et al. 2006 Science 311) and are most likely the source of jets of icy particles observed by Cassini (Porco et al. 2006 Science 311). The observed tectonics within the region have been proposed to have formed in response to

  2. Rift Valley Fever, Mayotte, 2007–2008

    PubMed Central

    Giry, Claude; Gabrie, Philippe; Tarantola, Arnaud; Pettinelli, François; Collet, Louis; D’Ortenzio, Eric; Renault, Philippe; Pierre, Vincent

    2009-01-01

    After the 2006–2007 epidemic wave of Rift Valley fever (RVF) in East Africa and its circulation in the Comoros, laboratory case-finding of RVF was conducted in Mayotte from September 2007 through May 2008. Ten recent human RVF cases were detected, which confirms the indigenous transmission of RFV virus in Mayotte. PMID:19331733

  3. Rift Valley fever, Mayotte, 2007-2008.

    PubMed

    Sissoko, Daouda; Giry, Claude; Gabrie, Philippe; Tarantola, Arnaud; Pettinelli, François; Collet, Louis; D'Ortenzio, Eric; Renault, Philippe; Pierre, Vincent

    2009-04-01

    After the 2006-2007 epidemic wave of Rift Valley fever (RVF) in East Africa and its circulation in the Comoros, laboratory case-finding of RVF was conducted in Mayotte from September 2007 through May 2008. Ten recent human RVF cases were detected, which confirms the indigenous transmission of RFV virus in Mayotte. PMID:19331733

  4. Diagnostic approaches for Rift Valley Fever

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Disease outbreaks caused by arthropod-borne animal viruses (arboviruses) resulting in significant livestock and economic losses world-wide appear to be increasing. Rift Valley fever (RVF) virus (RVFV) is an important arbovirus that causes lethal disease in cattle, camels, sheep and goats in Sub-Saha...

  5. Late Paleozoic Rifting in northern Pakistan

    NASA Astrophysics Data System (ADS)

    Pogue, Kevin R.; Dipietro, Joseph A.; Khan, Said Rahim; Hughes, Scott S.; Dilles, John H.; Lawrence, Robert D.

    1992-08-01

    Metasedimentary rocks exposed in the eastern Peshawar basin and the southern Swat region of northern Pakistan provide evidence for late Paleozoic continental rifting. The onset of extensional tectonics in the Early Carboniferous is indicated by north derived clasts in the Jafar Kandao Formation eroded from thermally induced uplifts of parts of the formerly passive margin of Gondwana. Rift highlands were eroded until they were inundated during the Middle Carboniferous. Renewed uplift accompanied the eruption of basaltic lava flows during the Early Permian. Uplift along south dipping, northeast striking normal faults during the Carboniferous was accompanied by alkaline magmatism represented by the Shewa-Shahbazgarhi and Warsak porphyries and Koga syenite. Geochemistry of basaltic flows (now amphibolites) and intrusions associated with Permian uplift is similar to the coeval Panjal volcanics of northwestern India and indicates rift zone magmatism. Postrifting thermal subsidence led to the deposition of Upper Triassic marine carbonate rocks which unconformably overlie the rift basalts. A similar tectonic history in central Afghanistan suggests continuity between the two regions prior to the opening of the Neo-Tethys.

  6. Prediction of a Rift Valley fever Outbreak

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  7. RIFT VALLEY FEVER POTENTIAL, ARABIAN PENINSULA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) was first confirmed outside of Africa in September 2000. This outbreak, which occurred in southwestern coastal Saudi Arabia and neighboring coastal areas of Yemen, followed elevated rainfall levels in nearby highlands which flooded the coastal areas, providing ideal environm...

  8. Longitudinal evolution of Suez rift structure, Egypt

    SciTech Connect

    Colletta, B.; Le Quellec, P.; Letouzey, J.; Moretti, I.

    1988-01-01

    A three-dimensional study of the structure of the Suez Rift has been carried out using field and subsurface data in an attempt to determine the role of transverse faults and the longitudinal evolution of the rift. As in most intracontinental rifts, the structure of the Gulf of Suez area is governed by normal faults and tilted blocks, whose crests constitute the main target of exploratory wells. The fault pattern consists of two major sets of trends: (1) longitudinal faults parallel with the rift axis and created in an extensional regime, trending east-northeast-west-southwest, and (2) transverse faults with north-south to north-northeast-south-southwest dominant trend. The transverse faults are inherited passive discontinuities, whereas most of the longitudinal faults were created during the Neogene in a purely extensional regime. Both sets were simultaneously active, producing a zigzag pattern and rhombic-shaped blocks. The transverse faults can show horizontal strike-slip components and act as relays between major normal faults.

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

    NASA Astrophysics Data System (ADS)

    Park, Munjae; Jung, Haemyeong; Kil, Youngwoo

    2015-04-01

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

  10. Thermal localization as a potential mechanism to rift cratons Gang Lu a,b,

    E-print Network

    Kaus, Boris

    directly adjacent to orogens or rifts (e.g. the east African Rift System, the Baikal RiftThermal localization as a potential mechanism to rift cratons Gang Lu a,b, , Boris J.P. Kaus b and/or high viscosity are insufficient to keep cratons stable. The forma- tion of continental rifts

  11. Variations in Mid-Continent Rift magma volumes consistent with microplate evolution

    E-print Network

    Stein, Seth

    active East African and Baikal rifts, has two major arms meeting in the Lake Superior region. One extends Mid- Continent Rift System shows systematic patterns in magma volume between and along the rift's two as a leaky transform. This view of the rift system's evolution is compatible with the rift being part

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

    NASA Astrophysics Data System (ADS)

    Huismans, Ritske S.

    2015-04-01

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

  13. 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.

  14. Structure of continental rifts: Role of older features and magmatism

    SciTech Connect

    Keller, G.R. [Univ. of Texas, El Paso, TX (United States)

    1996-12-31

    Recent geological and geophysical studies in several continental rifts have begun to shed light on the details of the processes which govern the structural evolution of these important exploration targets. In Kenya and Tanzania, the classic East African rift has been the object of several investigations which reveal that its location follows the boundary (suture ?) between the Tanzanian craton (Archean) and Mozambiquan belt (Proterozoic), The Baikal rift also follows a similar boundary, and the Mid-continent rift of North America appears to do the same. Rifts themselves often act as zones of weakness which are reactivated by younger tectonic regimes. The classic North American example of this effect is the Eocambrian Southern Oklahoma aulacogen which was deformed to create the Anadarko basin and Wichita uplift in the late Paleozoic. The Central basin platform has a similar history although the original rift formed at {approximately}1,100Ma. Integration of geophysical data with petrologic and geochemical data from several rift zones has also provided a new picture of the nature and extent of magmatic modification of the crust. An interesting contradiction is that Phanerozoic rifts, except the Afar region, show little evidence for major magmatic modification of the crust whereas, at least in North America, many Precambrian rifts are associated with very large mafic bodies in the crust. The Kenya rift displays evidence for modification of the lower crust in a two-phase magmatic history, but upper crustal magmatic features are limited to local intrusions associated with volcanoes. In this rift, complex basement structure plays a much more important role than previously realized, and the geophysical signatures of basement structure and magmatism are easy to confuse. If this is also the case in other rifts, additional rift basins remain to be discovered.

  15. Structure of continental rifts: Role of older features and magmatism

    SciTech Connect

    Keller, G.R. (Univ. of Texas, El Paso, TX (United States))

    1996-01-01

    Recent geological and geophysical studies in several continental rifts have begun to shed light on the details of the processes which govern the structural evolution of these important exploration targets. In Kenya and Tanzania, the classic East African rift has been the object of several investigations which reveal that its location follows the boundary (suture ) between the Tanzanian craton (Archean) and Mozambiquan belt (Proterozoic), The Baikal rift also follows a similar boundary, and the Mid-continent rift of North America appears to do the same. Rifts themselves often act as zones of weakness which are reactivated by younger tectonic regimes. The classic North American example of this effect is the Eocambrian Southern Oklahoma aulacogen which was deformed to create the Anadarko basin and Wichita uplift in the late Paleozoic. The Central basin platform has a similar history although the original rift formed at [approximately]1,100Ma. Integration of geophysical data with petrologic and geochemical data from several rift zones has also provided a new picture of the nature and extent of magmatic modification of the crust. An interesting contradiction is that Phanerozoic rifts, except the Afar region, show little evidence for major magmatic modification of the crust whereas, at least in North America, many Precambrian rifts are associated with very large mafic bodies in the crust. The Kenya rift displays evidence for modification of the lower crust in a two-phase magmatic history, but upper crustal magmatic features are limited to local intrusions associated with volcanoes. In this rift, complex basement structure plays a much more important role than previously realized, and the geophysical signatures of basement structure and magmatism are easy to confuse. If this is also the case in other rifts, additional rift basins remain to be discovered.

  16. Forensic investigation of rift-to-drift transitions and volcanic rifted margins birth

    NASA Astrophysics Data System (ADS)

    Meyer, R.; Hertogen, J.

    2008-12-01

    Volcanic rifted margins (VRM) reflect excess magmatism generated during the rift-to-drift transition of a continental rift system evolving into a Mid-Ocean Ridge (MOR). As a result many VRM (e.g. NAIP and CAMP) are recognized as Large Igneous Provinces (LIP). The prominent structural characteristics of VRM are Continental Flood Basalts, High-Velocity Lower Crustal bodies (HVLC) and Seaward Dipping Reflector Sequences (SDRS). However, the causes of these anomalously high eruption rates and magma volumes are presently poorly understood. Controversial issue opinions are based on two competing hypotheses: 1) Mantle plume related mechanisms where the excess magmatism results from elevated mantle temperatures; and 2) Rift induced small scale convection processes causing temperature anomalies and enhancing the mantle rock flux through the melt window. Largely because of difficulties to sample oceanic basement at VRM -due to thick sediment covers- the composition of rift-to-drift transition magmas is generally poorly constrained. We reviewed the geodynamic histories and magma compositions from well known VRM (e.g. NE Australia, E USA, Madagascar) and compared these data with own geochemical data from different NE Atlantic tectono-magmatic VRM zones. These comparisons point to a consistent, general VRM formation model. This model has to explain the primary observation, that geological long periods of extension have been reported -in all investigated VRM areas- prior to the breakup. Extensional far field stress looks to be the main geodynamic cause for continental breakup. Small scale convection during the late phase of a continental rift system is probably the key process generating excess magmatism in LIP related to rift-to-drift transitions.

  17. Tectonics of the South Georgia Rift

    NASA Astrophysics Data System (ADS)

    Heffner, David M.

    Triassic rifting of the supercontinent Pangea left behind numerous basins on what is now the eastern North American margin. The South Georgia Rift (SGR) was thought to be the best preserved of these basins having been capped by thick basalt flows of the Central Atlantic Magmatic Province (CAMP) and later buried beneath the Cretaceous and younger Coastal Plain. Because it is buried beneath the Coastal Plain, the SGR is only known through sparse drilling and geophysical methods. Despite this limited dataset, the SGR is the only one of the eastern North American Triassic basins known to overlie the ancient Alleghanian suture between Laurentia and Gondwana, although it isn't clear what influence this lithospheric weakness played in formation of the rift. The SGR has been variably interpreted as a singular large basin or as isolated sub-basins separated by transfer zones. Transfer zones are rift-transverse structural features that link major faults of rift sub-basins and accommodate differences in extensional strain. Transfer zones have been previously hypothesized to be present in the SGR based on onshore projections of Central Atlantic fracture zones, but observations confirming their existence, such as reversal in sub-basin polarity, have been lacking. Three separate hypotheses are tested related to the SGR: 1) the J-Horizon corresponds everywhere with basalt; 2) transfer zones are an important structural component of the SGR; 3) structural features of the Central Atlantic Ocean are related to transfer zones of the SGR. Reanalysis of existing well and seismic data shows that the extent of the flood basalt in the SGR is restricted and that the J-Horizon coincides with the base of the Coastal Plain. Subsurface mapping reveals reversals in sub-basin polarity, confirming the existence of previously hypothesized transfer zones. Small circle projections of the transfer zones correlate with oceanic features, and Central Atlantic fracture zones project onshore into inferred transfer zones of the SGR. The results of these studies suggest that tectonic inheritance of the Alleghanian suture played an important role in the rifting of Pangea and that tectonic inheritance may be an important process for the formation of an ocean basin.

  18. Evidence for a Nascent Rift in South Sudan: Westward Extension of the East African Rift System?

    NASA Astrophysics Data System (ADS)

    Maceira, M.; Van Wijk, J. W.; Coblentz, D. D.; Modrak, R. T.

    2013-12-01

    Joint inversion of seismic and gravity data of eastern Africa reveals a low seismic wave velocity arm stretching from the southern Main Ethiopian rift westward in an east-west direction that has not been noticed in earlier work. The zone of low velocities is located in the upper mantle and is not overlain by a known structural rift expression. We analyzed the local pattern of seismicity and the stresses in the African plate to interpret this low velocity arm. The zone of low velocities is located within the Central African Fold Belt, which dissects the northern and southern portions of the African continent. It is seismically active with small to intermediate sized earthquakes occurring in the crust. Seven earthquake solutions indicate (oblique) normal faulting and low-angle normal faulting with a NS to NNW-SSE opening direction, as well as strike-slip faulting. This pattern of deformation is typically associated with rifting. The present day stress field in northeastern Africa reveals a tensional state of stress at the location of the low velocity arm with an opening direction that corresponds to the earthquake data. We propose that the South Sudan low velocity zone and seismic center are part of an undeveloped, nascent rift arm. The arm stretches from the East African Rift system westward.

  19. The Pathogenesis of Rift Valley Fever

    PubMed Central

    Ikegami, Tetsuro; Makino, Shinji

    2011-01-01

    Rift Valley fever (RVF) is an emerging zoonotic disease distributed in sub-Saharan African countries and the Arabian Peninsula. The disease is caused by the Rift 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

  20. Rainfall and epizootic Rift Valley fever*

    PubMed Central

    Davies, F. G.; Linthicum, K. J.; James, A. D.

    1985-01-01

    Epizootic Rift Valley fever (RVF) has occurred in Kenya four times over the last 30 years. Widespread, frequent, and persistent rainfall has been a feature of these epizootic periods. A composite statistic, based upon measurements of these rainfall characteristics, is positive during periods of epizootic Rift Valley fever. The heavy rainfall raises the level of the water table in certain areas, flooding the grassland depressions (dambos) that are the habitat of the immature forms of certain ground-pool-breeding mosquitos of the genus Aedes. RVF virus is probably transmitted transovarially in these species, very large numbers of which emerge under these damp conditions. This is when clinical signs of the disease are first seen. PMID:3879206

  1. Crustal structure of central Lake Baikal: Insights into intracontinental rifting

    E-print Network

    ten Brink, Uri S.; Taylor, Michael Halford

    2002-07-16

    Crustal structure of central Lake Baikal: Insights into intracontinental rifting Uri S. ten Brink and Michael H. Taylor1 U.S. Geological Survey, Woods Hole, Massachusetts, USA Received 26 January 2001; revised 15 October 2001; accepted 25 October...; KEYWORDS: Lake Baikal, continental rifts, Newark basin, crustal extension, plate driving forces, seismic velocity structure 1. Introduction [2] Most aspects of the deformation of intracontinental rifts can be explained by a combination of several physical...

  2. Experimental Rift Valley fever in rhesus macaques

    Microsoft Academic Search

    C. J. Peters; D. Jones; R. Trotter; J. Donaldson; J. White; E. Stephen; T. W. Slone

    1988-01-01

    Summary Rift Valley fever (RVF) is a major cause of human morbidity and mortality in endemic areas of sub-Saharan Africa and has the potential to cause epidemic disease in receptive areas world-wide. In this study, a RVF viral isolate from the 1977 Egyptian epidemic (ZH-501) inoculated intravenously into rhesus macaques caused a benign viremic infection in most, but resulted in

  3. Rifted Margins: Building Blocks of Later Collision

    Microsoft Academic Search

    T. Reston; G. Manatschal

    \\u000a Rifted margins develop by the splitting apart of continents and form the trailing edges of ocean basins, to be incorporated\\u000a into collision zones when those basins eventually close. Magma-poor margins are dominated by tectonic processes, including\\u000a crustal extension and thinning, mantle serpentinization and the unroofing of broad expanses of lithospheric mantle. Magma\\u000a rich margins may follow a similar history until

  4. Seismotectonics of Reelfoot rift basement structures

    SciTech Connect

    Dart, R.L.; Swolfs, H.S. (Geological Survey, Denver, CO (United States))

    1993-03-01

    Contour maps of the Precambrian basement surface show major northwest-trending structural features within the boundaries of the northeast-oriented Reelfoot rift. These northwest-trending features, southeast of New Madrid, Missouri, consist of a trough flanked on the northeast by a 2-km-high ridge. These features correlate with similar features on an updated depth-to-magnetic basement map. The boundary between the trough and the ridge slopes gently to the southwest. The upward projection of this boundary into the overlying Paleozoic strata may be expressed on a structure-contour map of the Cambrian rocks. The vertical relief of this boundary on the younger datum is inferred to be about 1 km. This Precambrian trough-ridge structure may correlate with a southwest dipping, west-northwest-striking normal fault inferred by Schwalb (1982) to offset rocks of the Cambrian-Ordovician Knox Megagroup that subcrop at the Paleozoic surface. Schwalb (1982) inferred 1.22 km of vertical relief on this fault near the bootheel of Missouri. The nature and significance of this tectonic-structural boundary is unclear, but at the top of the Precambrian basement rocks, it coincides with the southwestern terminus of the New Madrid seismic zone (NMSZ) near the end of the Blytheville arch in northeastern Arkansas. Since the mid-1970's, when instrumental recording began, some of the earthquakes in the NMSZ having the largest magnitudes occurred in this area. The authors working hypothesis is that this trough-ridge structural boundary may concentrate stress and/or may be a barrier that defines the southwestern limit of the seismically active axial fault zone in the rift. Future study will concentrate on improving the understanding of the influence of rift-bounding faults on the lateral extent of this structure, as well as constructing a tectonic stress model of seismically active rift faults and this trough-ridge structure.

  5. Lake Baikal - A Touchstone for Global Change and Rift Studies

    NSDL National Science Digital Library

    This is a United States Geological Survey (USGS) fact sheet about the Lake Baikal rift system. This site provides a good general overview of this rift system, illustrating its importance to the overall study of plate tectonics. The Lake Baikal rift system is a modern analogue for formation of ancient Atlantic-type continental margins. It tells us the first chapter in the story of how continents separate and ultimately develop into ocean basins like the Atlantic Ocean. Continental rifting is an important component of plate tectonics theory.

  6. Style of rifting and the stages of Pangea breakup

    NASA Astrophysics Data System (ADS)

    Frizon de Lamotte, Dominique; Fourdan, Brendan; Leleu, Sophie; Leparmentier, François; Clarens, Philippe

    2015-05-01

    Pangea results from the progressive amalgamation of continental blocks achieved at 320 Ma. Assuming that the ancient concept of "active" versus "passive" rifting remains pertinent as end-members of more complex processes, we show that the progressive Pangea breakup occurred through a succession of rifting episodes characterized by different tectonic evolutions. A first episode of passive continental rifting during the Upper Carboniferous and Permian led to the formation of the Neo-Tethys Ocean. Then at the beginning of Triassic times, two short episodes of active rifting associated to the Siberian and Emeishan large igneous provinces (LIPs) failed. The true disintegration of Pangea resulted from (1) a Triassic passive rifting leading to the emplacement of the central Atlantic magmatic province (200 Ma) LIP and the subsequent opening of the central Atlantic Ocean during the lowermost Jurassic and from (2) a Lower Jurassic active rifting triggered by the Karoo-Ferrar LIP (183 Ma), which led to the opening of the West Indian Ocean. The same sequence of passive then active rifting is observed during the Lower Cretaceous with, in between, the Parana-Etendeka LIP at 135 Ma. We show that the relationships between the style of rifts and their breakdown or with the type of resulting margins (as magma poor or magma dominated) are not straightforward. Finally, we discuss the respective role of mantle global warming promoted by continental agglomeration and mantle plumes in the weakening of the continental lithosphere and their roles as rifting triggers.

  7. Moho topography beneath the Corinth Rift area (Greece) from inversion of gravity data

    E-print Network

    Demouchy, Sylvie

    Moho topography beneath the Corinth Rift area (Greece) from inversion of gravity data C. Tiberi,1 to Miocene lithospheric instabilities. Key words: boudinage, continental rifts, gravity inversion, Greece

  8. K?lauea's Upper East Rift Zone: A Rift Zone in Name Only

    NASA Astrophysics Data System (ADS)

    Swanson, D. A.; Fiske, R. S.

    2014-12-01

    K?lauea's upper east rift zone (UERZ) extends ~3 km southeastward from the summit caldera to the Koáe fault system, where it starts to bend into the main part of the ENE-trending rift zone. The UERZ lacks a distinct positive gravity anomaly (though coverage is poor) and any evidence of deformation associated with magma intrusion. All ground ruptures—and the Puhimau thermal area—trend ENE, crossing the UERZ at a high angle. Lua Manu, Puhimau, and Kóokóolau craters are the only surface evidence of the UERZ. Yet the UERZ is seismically active, and all magma entering the rest of the rift zone must pass through it. Rather than a rift zone in the traditional sense, with abundant dikes and ground ruptures along its trend, the UERZ cuts across the ENE structural grain and serves only as a connector to the rest of the rift zone, not a locus of dike formation along its length. The UERZ probably developed as a consequence of gradual SSE migration of the active part of the main east rift zone at the trailing edge of the south flank. During migration, a connection to the summit reservoir complex must be maintained; otherwise, the middle and lower east rift zone would starve and magma from K?lauea's summit reservoir complex would have to go elsewhere. Over time, the UERZ lengthened and rotated clockwise to maintain the connection. Near the caldera, the UERZ may be widening westward as the summit reservoir complex migrates southward from the center of the caldera to its present position. A layered stress regime results in the upper 2-3 km mimicking the pervasive ENE structural grain of most of K?lauea, whereas the underlying magmatic part of the UERZ responds to stresses related to SE magma transport. Magma intruding upward from the connector forms a dike that follows the ENE structural grain, as during the 1974 eruption. The active east rift zone has been migrating since ~100 ka, estimated by applying a 700-y extension rate across the Koa'e fault system to the ~6.5 km of migration, and presumably the UERZ connector has been developing during this time.

  9. Mesozoic Rifting in the German North Sea

    NASA Astrophysics Data System (ADS)

    Lutz, R.; Jähne, F.; Arfai, J.

    2013-12-01

    The Central Graben is the southernmost expressions of the Mesozoic North Sea rift system that includes the Viking Graben, Moray Firth-Witch Ground grabens and the Horda-Egersund half graben. In the southern North Sea the Central Graben extends across the Dutch and the German exclusive economic zones. The structure of the Central Graben in German territorial waters was mapped in great detail in 2D and 3D seismic data and the stratigraphy has been constraint by borehole data. We provide a detailed review of the rifting activity in the German North Sea sector both in time and space and the link between rifting and salt movement. Major rifting activity started in the Central Graben during the Late Triassic and peaked during the Late Jurassic when extensive rift grabens formed, further influenced by halokinetic movements. First subsidence in the Central Graben area appears in the Early Triassic. This is documented by thickness variations in the sedimentary strata from the Triassic to the Jurassic. Remarkably thick sediments were deposited during the Late Triassic along the eastern border fault of the Central Graben and in the Late Jurassic sediments accumulated along graben-wide extensional faults and in rim-synclines of salt-structures. A basin inversion commenced in the Late Cretaceous resulting in an erosion of wide portions of Lower Cretaceous rocks or even complete removal in some parts. The area to the east of the Central Graben faced a completely different evolution. In this area major rifting activity initiated already in the Early to Middle Triassic. This is evident from huge packages of Middle Buntsandstein to Muschelkalk (Middle Triassic) sediments in the Horn Graben. Jurassic doming, forming the Mid-North Sea High, resulted in almost complete erosion of Lower and Middle Jurassic sediments in the central German North Sea. Sedimentation continued during the Early and Late Cretaceous. The Glückstadt Graben, which is a structure located farther east has a similar evolution as the Horn Graben with high sediment thicknesses deposited during the Triassic. This indicates that initiation of rifting started in the central German North Sea already during the Early Triassic and subsequently migrated to the west into the Central Graben. Before the Triassic thick layers of Permian rock salt (Upper Rotliegend and Zechstein) were deposited in the Central European Basin System, which spans from the UK across the Netherlands, southern Denmark, Germany, and into Poland. Salt movements resulted in the formation of salt diapirs, salt pillows, salt walls and intrusions into faults. Analyses of rim-synclines of salt diapirs reveals that most of the salt structures inside the German Central Graben had a main phase of growth during the Late Jurassic while the salt structures situated toward the southeast had their main phase of growth during the Triassic. The final products of the project are accessible at www.geopotenzial-nordsee.de/.

  10. ENTRENAMIENTO EN LA PLATAFORMA VIBRATORIA 1. Conocer las aplicaciones reales y saludables de medios de entrenamiento

    E-print Network

    Escolano, Francisco

    1/2 ENTRENAMIENTO EN LA PLATAFORMA VIBRATORIA OBJETIVOS 1. Conocer las aplicaciones reales y de inestabilidad y plataformas vibratorias. 2. Conocer los fundamentos neurofisiológicos explicativos sistemática de programas de entrenamiento con plataformas vibratorias y con dispositivos generadores de

  11. Tectonic inheritance and continental rift architecture: Numerical and analogue models of the East African Rift system

    Microsoft Academic Search

    Giacomo Corti; Jolante van Wijk; Sierd Cloetingh; Chris K. Morley

    2007-01-01

    The western branch of the East African Rift is composed of an arcuate succession of elongate asymmetric basins, which differ in terms of interaction geometry, fault architecture and kinematics, and patterns of uplift\\/subsidence and erosion\\/sedimentation. The basins are located within Proterozoic mobile belts at the edge of the strong Tanzanian craton; surface geology suggests that the geometry of these weak

  12. CDROM Interstation Pn Study Along the Rio Grande Rift

    Microsoft Academic Search

    Lynda A. Lastowka; Anne F. Sheehan

    Upper mantle velocities in the regions of the Rio Grande rift and the Southern Rockies were investigated using Pn waves from the broadband seismic data obtained from the Continen- tal Dynamics - Rocky Mountain (CDROM) experiment. A velocity of 7.8 +\\/- 0.1 km\\/s on the eastern flank of the Rio Grande rift in New Mexico was measured from epicentral dis-

  13. Geophysical studies of the West Antarctic rift system

    USGS Publications Warehouse

    Behrendt, John C.; LeMasurier, W.E.; Cooper, A. K.; Tessensohn, F.; Trehu, A.; Damaske, D.

    1991-01-01

    This paper is an effort to integrate the geophysical research over the West Antarctic rift system over the past three decades, including new data in the Ross Sea area within the concepts of continental rifting developed for other areas during the past decade. The results of aeromagnetic, seismic and gravity survey are discussed. -after Authors

  14. New Vectors of Rift Valley Fever in West Africa

    Microsoft Academic Search

    D. Fontenille; M. Traore-Lamizana; M. Diallo; J. Thonnon; J. P. Digoutte; H. G. Zeller

    1998-01-01

    After an outbreak of Rift Valley fever in Southern Mauritania in 1987, entomologic studies were conducted in a bordering region in Sénégal from 1991 to 1996 to identify the sylvatic vectors of Rift Valley fever virus. The virus was isolated from the floodwater mosquitoes Aedes vexans and Ae. ochraceus. In 1974 and 1983, the virus had been isolated from Ae.

  15. Upper Mantle Pollution during Afar Plume^Continental Rift Interaction

    E-print Network

    Paris-Sud XI, Université de

    Upper Mantle Pollution during Afar Plume^Continental Rift Interaction TYRONE O. ROONEY1 , BARRY B Ethiopian Rift, show systematic mixing relationships involving three distinct mantle sources.The Pb, Sr, Nd the composition of the Afar mantle plume (centered about 206 Pb/204 Pb ¼19·5, 87 Sr/86 Sr ¼ 0·7035, eNd ¼ þ4·6, e

  16. Geodetic constraints on rifting processes in East Africa (Invited)

    Microsoft Academic Search

    E. Calais; D. S. Stamps; L. Bennati; E. Saria; L. M. Flesch; A. M. Freed

    2009-01-01

    Many features in rift zones and passive margins have been successfully explained by stretching models where lithospheric thinning and crustal extension are driven by far-field tectonic stresses. However, recent observations in East Africa show that magma intrusions can accommodate large amounts of strain during the initial stages of continental rifting and prior to significant crustal thinning. We will present a

  17. Ethiopian Rift and Plateaus: Some Volcanic Petrochemical Differences

    Microsoft Academic Search

    P. A. Mohr

    1971-01-01

    Volcanism on the Arabo-Ethiopian swell has accompanied the development of the three traversing spreading zones conjoining at Afar: the Red Sea, Gulf of Aden, and African rift systems. The Red Sea and Gulf of Aden floors are formed by oceanic tholerites, but Afar and the main Ethiopian rift show a wider range of more alkaline volcanics, related to slower crustal

  18. Innovative tephra studies in the East African Rift System

    Microsoft Academic Search

    Giday WoldeGabriel; William K. Hart; Grant Heiken

    2005-01-01

    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,

  19. Understanding the Transition From Continental to Oceanic Rifting in the Northern Ethiopian Rift - the EAGLE Project

    NASA Astrophysics Data System (ADS)

    Stuart, G.

    2003-12-01

    A consortium of UK (Leeds, Leicester, Royal Holloway, Edinburgh,), US (Stanford, UTEP, Penn State,) and Ethiopian (Addis Ababa) universities are exploring the kinematics and dynamics of continental breakup through the Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE), which aims to probe the crust and upper mantle structure between the Main Ethiopian (continental) and Afar (ocean spreading) rifts. EAGLE is a multi-disciplinary study centered around a set of passive and controlled-source seismic experiments, and incorporates additional magnetotelluric, gravity, GPS and petrological studies. The initial Phase I seismic experiment consisted of a deployment of 30 broadband seismometers for a period of 16 months (Oct. 2001 to Jan. 2003) over a 250 km x 250 km area of the rift valley and its uplifted flanks. P- and S-wave tompography from teleseismic traveltime residuals, SKS splitting analyses and receiver functions provide images of crust and deep earth structure. The Phase II seismic experiment consisted of a further 50 broadband instruments for a period of 4 months over a 200 km x 100 km area encompassing 4 magmatic segments in the Main Ethiopian Rift. These recordings have furthered our understanding of the location of active seismicity, fault plane mechanisms and segmentation of rift crustal structure. Phase III consisted of the deployment of a further 1100 seismic instruments during a controlled source seismic project involving 20 shots being fired into one 450 km cross-rift profile (Profile 1), one 450 km axial profile (Profile 2), and a dense 2D array of instruments in a 150 km diameter circle around the profiles1 intersection (Profile 3), all centered on the magmatically active Nazret region. The crust and upper mantle velocity models derived provide estimates of total crustal thinning across the rift, assess the role of basement in the location of major faults and magmatic segments, and determine whether significant underplating takes place. An 18 sounding magnetotelluric profile along the cross rift profile I provides additional constraints on the nature and distribution of crustal heterogeneity, and images melt accumulation zones. New gravity and geodetic information have also been acquired.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    We have employed a multifaceted approach to sedimentary provenance analysis in order to assess the timing and magnitude of tectonic events, sedimentation, and landscape development in the Western Branch of the East African Rift System. Our approach, termed 'Sedimentary Triple Dating', integrates: (1) U-Pb dating via LA-ICPMS; (2) fission track; and (3) (U-Th)/He thermochronology of detrital zircon and apatite. We integrate geochronology, thermochronology, and provenance analysis to relate the initiation of rifting events to regional dynamic uplift, sedimentation patterns, and interpret the far-reaching climatic and evolutionary effects of fluctuating rift flank topography in the Rukwa Rift, a segment of the Western Branch. This work provides additional data to support the recent concept of synchronous development of the Western and Eastern branches of the East African Rift System ~25 Ma, and better constrains the age, location and provenance of subsequent rifting and sedimentation events in the Rukwa Rift Basin. Investigation of well cuttings and outcrop samples from the Neogene-Recent Lake Beds Succession in the Rukwa Rift Basin revealed a suite of previously unrecognized tuffaceous deposits at the base of the succession. A population of euhedral, magmatic zircons from a basal Lake Beds tuff and Miocene-Pliocene detrital zircons from well cuttings suggest that Neogene rift reactivation and volcanism began ~9-10 Ma. This timing is consistent with demonstrated rifting in Uganda and Malawi, as well as with the initiation of volcanism in the Rungwe Volcanic Province at the southern end of the Rukwa Rift, and the estimated development of Lake Tanganyika to the north. Moreover, there appear to be a suite of unconformity bounded stratigraphic units that make up the Lower Lake Beds succession, and detrital zircon maximum depositional ages from these units suggests episodic sedimentation in the rift, punctuated by long hiatuses or uplift, rather than steady subsidence and sedimentation. A distinct, upward-younging trend in detrital zircon populations associated with each stratigraphic interval suggests that volcanism was also episodic through the Late Miocene-Pliocene, and linked to periods of rifting and basin filling. Detrital zircon populations are dominated by Paleoproterozoic grains of the same age as the metamorphic Ubendian Belt that underlies the rift basin and forms the flanks. This provenance, volcaniclastic-dominated sedimentation, and clasts from the rift flanks suggest an internally draining basin and high rift flanks associated with the most recent rifting episode. There are also dominant populations of Neoproterozoic and Mesoproterozoic zircons, likely reworked from the underlying Cretaceous sandstones and derived from younger metamorphic terranes of the Ubendian Belt. Volcanic pulses associated with rifting are responsible for the young magmatic zircons, and suggest the initiation of a late Cenozoic rifting event, further constraining the timing of rifting and basin development in the Western Branch, as well as the timing of landscape change associated with erosion and uplift. Our dates additionally provide important temporal context for the rich vertebrate record described from the East African Rift, illuminating the tectonic backdrop of important large-scale faunal shifts in East Africa.

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

    NASA Astrophysics Data System (ADS)

    Brune, Sascha

    2015-04-01

    Present-day knowledge of rifted margin formation is largely based on 2D seismic lines, 2D conceptual models, and corroborated by 2D numerical experiments. However, the 2D assumption that the extension direction is perpendicular to the rift trend is often invalid. In fact, worldwide more than 75% of all rifted margin segments have been formed under significant obliquity exceeding 20° (angle measured between extension direction and rift trend normal): During formation of the Atlantic Ocean, oblique rifting dominated at the sheared margins of South Africa and Patagonia, the Equatorial Atlantic margins, separation of Greenland and North America, and it played a major role in the protracted rift history of the North East Atlantic. Outside the Atlantic Ocean, oblique rifting occurred during the split between East and West Gondwana, the separation of India and Australia, India and Madagascar, Australia and Antarctica, as well as Arabia and Africa. It is presently observed in the Gulf of California, the Aegean and in the East African Rift. Despite its significance, the degree to which oblique lithospheric extension affects first-order rift and passive margin properties like surface stress pattern, fault azimuths, and basin geometry, is still not entirely clear. This contribution provides insight in crustal stress patterns and fault orientations by applying a 3D numerical rift model to oblique extensional settings. The presented forward experiments cover the whole spectrum of oblique extension (i.e. rift-orthogonal extension, low obliquity, high obliquity, strike-slip deformation) from initial deformation to breakup. They are conducted using an elasto-visco-plastic finite element model and involve crustal and mantle layers accounting for self-consistent necking of the lithosphere. Results are thoroughly compared to previous analogue experiments, which yields many similarities but also distinct differences for late rift stages and for high obliquity. Even though the model setup is very simple (horizontally layered, no inherited faults, constant extension velocity and direction), its evolution exhibits a variety of fault orientations that are solely caused by the three-dimensionality of oblique rift systems. Allowing new insights on fault patterns of the proximal and distal margins, the model shows that individual fault populations are activated in a characteristic multi-phase evolution driven by lateral density variations of the evolving rift system. Moreover, the model depicts strain partitioning between rift-parallel and rift-perpendicular far-field velocity components that are accommodated by strike-slip faults in the rift centre and normal faults at the rift sides, respectively. Oblique extensional systems worldwide differ in many aspects and clearly one suit of models cannot explain all rifted margin structures at the same time. However, the distinct pattern of fault populations discussed in this study and their sequence of activity compares very well to previous studies of the Gulf of Aden and holds implications for many other rifted margins worldwide. Note that in nature, the resulting stress and fault pattern will also be affected by inherited heterogeneities, surface processes, as well as melting and dyke dynamics.

  2. Seismic images of magmatic rifting beneath the western branch of the East African rift

    NASA Astrophysics Data System (ADS)

    Jakovlev, Andrey; Rümpker, Georg; Schmeling, Harro; Koulakov, Ivan; Lindenfeld, Michael; Wallner, Herbert

    2013-11-01

    We have performed a tomographic study using a joint data set that includes local and teleseismic events, recorded by a temporary network in the western branch of the East African rift system. From the travel time residuals, we derive a three-dimensional model of seismic P-wave velocity anomalies for the crust and upper mantle down to a depth of 80 km. Particular attention is paid to the verification of the inversion results by various resolution tests. The results show that the eastern rift shoulder is characterized by relatively high seismic velocities. Lower velocities are obtained beneath the entire length of the rift valley and the Rwenzori Mountains. A prominent feature is observed north-east of the mountain range: here we detected a vertically oriented, cylindrical low-velocity anomaly with maximum amplitudes in the middle crust and the upper mantle lithosphere. We suggest that this anomaly indicates reservoirs of molten material related to the ongoing rifting process within this segment of the rift. Just above this anomaly, at depths between 5 and 16 km, earthquake swarms exist. The observed reduction in P-wave velocity is used to provide constraints on the possible melt content and temperature anomaly in the uppermost mantle. The observed 3-5% P-velocity decrease can be explained by melt fraction up to 2%-3.3% or alternatively by a temperature increase of at least 248 to 376 K and even higher-temperature anomalies are possible if lower ambient temperatures in the reference mantle are assumed. Probably, the two effects act in combination.

  3. Seismic crustal study of the Oslo Rift

    Microsoft Academic Search

    Johannes Tryti; Markvard A. Sellevoll

    1977-01-01

    A seismic refraction investigation across the southern part of the Oslo Rift has been made, based on quarry blasts at three localities. The study shows a three-layered crust with the followingP-wave velocities:\\u000a$$V_{P_{g(av)} } = 6.20 km\\/s, V_{P_b } = 6.60 km\\/s, V_{P^x } = 7.10 km\\/s$$\\u000a.\\u000a$$V_{P_n } $$\\u000a the upper mantleP-wave celocity, is 8.07 km\\/s. The velocity-depth

  4. Exploring the Environment: Rift Valley Fever

    NSDL National Science Digital Library

    Classrooms of the Future/Wheeling Jesuit University

    2005-01-01

    Students will study the nature and transmission of the Rift Valley fever virus to determine ways to prevent an outbreak. This is one of several interdisciplinary problem-based learning modules for high school and middle school students addressing real-world problems in environmental earth science. Teacher pages include module notes, software information, and a teacher-to-teacher message board to share/borrow ideas for planning, facilitating, and assessing information. Situations and very clear instructions are given on how to implement problem-based learning in the classroom.

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

    SciTech Connect

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

    1983-08-01

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

  6. PROPOSAL TITLE Evolution of Rift and Rifted Margin Sedimentary Basins: Numerical Investigation of Tectonics, Sedimentation, and Salt-

    E-print Network

    Beaumont, Christopher

    of Tectonics, Sedimentation, and Salt- Related Structures of the Atlantic Canada Margin and Elsewhere will focus on: crustal deformation during rifting and rift reactivation; salt tectonics induced by thin of salt and the development of finite amplitude salt structures. 3) The role of differential sedimentary

  7. Continental rift structures and dynamics with reference to teleseismic studies of the Rio Grande and East African rifts

    NASA Astrophysics Data System (ADS)

    Davis, Paul M.

    1991-10-01

    Teleseismic travel time residuals measured on 600-1000 km seismic arrays across the Rio Grande and East African rifts provide evidence for upper mantle low velocity zones beneath each rift. We propose that these zones arise from asthenosphere replacing the base of the lithosphere . Refraction studies show thinning of the crust below the rift axes. Regional uplift, which extends for hundreds of kilometers on either side of the axes, is isostatically compensated by negative density contrast at depth. Since the refraction results argue against compensation by crustal thickening, compensation within the upper mantle is suggested. Temperature effects alone do not explain the magnitudes of the reduced velocities. Instead, generation of a few percent of partial melt is the most probable source of the reduction. A passive extensional mechanism is investigated for the Rio Grande rift in which hot asthenosphere intrudes into the lithosphere , raising its temperature and generating moderate melting. It requires less than 1% extension to explain the melting; in contrast, a prodigious 26% would be required to raise the temperature from a pre-rifting continental geotherm to the solidus. Geological estimates based on palinspastic reconstruction find that extension is less than 10% over the uplift zone. A passive mechanism is possible if the pre-rifting lower lithosphere geotherm lies closer to the solidus than the geotherm of a stable continent. This hypothesis is supported by the observed high heat flow in the Rio Grande rift uplift region which, given the long time constant for thermal diffusion, reflects elevated temperatures at depth well before the onset of rifting. The elevated asthenosphere boundary, found teleseismically, lies directly beneath both rifts favoring a "pure shear" over the "simple shear" model of rifting. We propose a model for continental rifting in which the asthenosphere intrudes into dike-like structures in the lithosphere beneath the rift zone. This explains the observed upwarp of the Moho beneath the rift as asthenosphere intrudes the upper mantle and base of the crust. The forces associated with wedging apart of the upper mantle give rise to tensional and compressional stresses in the crust which form the graben and uplifted shoulders, respectively. Mantle xenoliths indicate brittle diking occurs in the upper mantle to depths of 70 km. Furthermore, evidence of asthenospheric intrusion from Neodymium ratios supports the role of asthenospheric advection in the rifting process.

  8. Europan Cycloidal Rift Densities and Io Volcano Distribution: Implications for Tidal Activity

    Microsoft Academic Search

    M. P. Madison; P. R. Stoddard

    2007-01-01

    Previous works have described cycloidal rifts and how they form (Hoppa, 1999), but none have gone into detail on where they occur and what rift density may mean to the system as a whole. In this study, GIS software is used in conjunction with high-resolution images to map cycloidal rifts on Europa's surface. Total lengths of rifts within varying latitudinal\\/longitudinal

  9. Volcanic architecture of the Afar Rift

    NASA Astrophysics Data System (ADS)

    Vye, C.; Smith, K.; Bateson, L.; Jordan, C.

    2010-12-01

    A new approach for rapidly mapping large volcanic areas has enabled identification of the spatial relationship between lava flows at the scale of single eruptive units, and the temporal development of faults associated with continental rifting. This integrated geological mapping approach involving remote sensing and three-dimensional image analysis has been applied to the Afar Region of the African Rift. We analyse topography and surface rock chemistry based false colour Landsat, ASTER and Lidar imagery within an immersive three-dimensional visualisation suite using SocetSet and Geovisionary software. This remote data is ground-proofed by the targeted field studies. This method is proving to be particularly successful in producing a subdivision of basaltic lava flows based on surface features and morphology of flow lobes where chemostratigraphic applications fail to identify individual eruption units. The high-resolution record has facilitated investigations of the style and size of fissure eruptions, their source, the processes affecting synchronous basaltic and felsic volcanic activity, and the style and duration of basaltic lava flow emplacement. The success of this technique is particularly significant when working in areas which are difficult to access, and may be applied in the future within environmentally or logistically challenging regions.

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

    NASA Technical Reports Server (NTRS)

    Frey, H. V.

    1978-01-01

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

  11. Evolution, distribution, and characteristics of rifting in southern Ethiopia

    NASA Astrophysics Data System (ADS)

    Philippon, Melody; Corti, Giacomo; Sani, Federico; Bonini, Marco; Balestrieri, Maria-Laura; Molin, Paola; Willingshofer, Ernst; Sokoutis, Dimitrios; Cloetingh, Sierd

    2014-04-01

    Southern Ethiopia is a key region to understand the evolution of the East African rift system, since it is the area of interaction between the main Ethiopian rift (MER) and the Kenyan rift. However, geological data constraining rift evolution in this remote area are still relatively sparse. In this study the timing, distribution, and style of rifting 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 rift 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 rift-related extension in the area.

  12. Magma-compensated crustal thinning in continental rift zones.

    PubMed

    Thybo, H; Nielsen, C A

    2009-02-12

    Continental rift zones are long, narrow tectonic depressions in the Earth's surface where the entire lithosphere has been modified in extension. Rifting can eventually lead to rupture of the continental lithosphere and creation of new oceanic lithosphere or, alternatively, lead to formation of wide sedimentary basins around failed rift zones. Conventional models of rift zones include three characteristic features: surface manifestation as an elongated topographic trough, Moho shallowing due to crustal thinning, and reduced seismic velocity in the uppermost mantle due to decompression melting or heating from the Earth's interior. Here we demonstrate that only the surface manifestation is observed at the Baikal rift zone, whereas the crustal and mantle characteristics can be ruled out by a new seismic profile across southern Lake Baikal in Siberia. Instead we observe a localized zone in the lower crust which has exceptionally high seismic velocity and is highly reflective. We suggest that the expected Moho uplift was compensated by magmatic intrusion into the lower crust, producing the observed high-velocity zone. This finding demonstrates a previously unknown role for magmatism in rifting processes with significant implications for estimation of stretching factors and modelling of sedimentary basins around failed rift structures. PMID:19212408

  13. Composition of the crust beneath the Kenya rift

    USGS Publications Warehouse

    Mooney, W.D.; Christensen, N.I.

    1994-01-01

    We infer the composition of the crust beneath and on the flanks of the Kenya rift based on a comparison of the KRISP-90 crustal velocity structure with laboratory measurements of compressional-wave velocities of rock samples from Kenya. The rock samples studied, which are representative of the major lithologies exposed in Kenya, include volcanic tuffs and flows (primarily basalts and phonolites), and felsic to intermediate composition gneisses. This comparison indicates that the upper crust (5-12 km depth) consists primarily of quartzo-feldspathic gneisses and schists similar to rocks exposed on the flanks of the rift, whereas the middle crust (12-22 km depth) consists of more mafic, hornblende-rich metamorphic rocks, probably intruded by mafic rocks beneath the rift axis. The lower crust on the flanks of the rift may consist of mafic granulite facies rocks. Along the rift axis, the lower crust varies in thickness from 9 km in the southern rift to only 2-3 km in the north, and has a seismic velocity substantially higher than the samples investigated in this study. The lower crust of the rift probably consists of a crust/mantle mix of high-grade metamorphic rocks, mafic intrusives, and an igneous mafic residuum accreted to the base of the crust during differentiation of a melt derived from the upper mantle. ?? 1994.

  14. Martian canyons and African rifts - Structural comparisons and implications

    NASA Technical Reports Server (NTRS)

    Frey, H.

    1979-01-01

    The resistant parts of the canyon walls of the Martian rift complex Valles Marineris have been used to infer an earlier, less eroded reconstruction of the major troughs. The individual canyons are compared with individual rifts of East Africa. When measured in units of planetary radius, Martian canyons show a distribution of lengths nearly identical to those in Africa, both for individual rifts and for compound rift systems. A common mechanism which scales with planetary radius is suggested. Martian canyons are significantly wider than African rifts. This is consistent with the longstanding idea that rift width is related to crustal thickness: most evidence favors a crust on Mars at least 50% thicker than that of Africa. The overall patterns of the rift systems of Africa and Mars are quite different in that the African systems are composed of numerous small faults with highly variable trend. On Mars the trends are less variable; individual scraps are straighter for longer than on earth. The basement and lithosphere of Mars are inferred to be simple, reflecting a relatively inactive tectonic history prior to the formation of the canyonlands.

  15. Final Rifting and Continental Breakup in the South China Sea

    NASA Astrophysics Data System (ADS)

    Franke, D.; Savva, D.; Pubellier, M. F.; Steuer, S.; Mouly, B.; Auxietre, J. L.; Meresse, F.; Chamot-Rooke, N. R. A.

    2014-12-01

    The magma-poor or intermediate magmatic South China Sea basin shows a triangular shape with a SW pointing apex, which manifests a preceding propagating rift. The earliest phase of rifting started in the Early Paleocene when a Mesozoic convergent margin changed to extension. After about 30 Myrs of rifting, breakup in the major eastern subbasin of the SCS occurred in the Early Oligocene and subsequent breakup of the southwest subbasin took place in the Late Oligocene. Seismic reflection data imaging conjugate crustal sections result in a conceptual model for rift-evolution at conjugate margins in time and space. Distinct are regular undulations in the crust-mantle boundary. Individual rift basins are bounded to crustal blocks by listric normal faults on either side. Moho uplifts are distinct beneath major rift basins, while the Moho is downbended beneath crustal blocks. Most of the basin-bounding faults sole out within the middle crust. At the distal margins, detachment faults are located at a mid-crustal level where a weak zone decouples crust and mantle lithosphere during rifting. The lower crust in contrast is interpreted as being strong. Only in the region within about 50 km from the oceanic domain we suggest that normal faults reach the mantle, enabling potentially a coupling between the crust and the mantle. Here, at the proximal margins detachment fault dip either seaward or landward. Largely symmetric structures result from the initial rifting stage. At the future breakup position either of the rift basin bounding faults subsequently penetrates the entire crust, resulting in asymmetry at this location. However, asymmetric deformation which is controlled by large scale detachment faulting is confined to narrow areas and does not result in a margin-wide simple-shear model. Rather considerable along-margin variations are suggested resulting in alternating "upper and lower plate" margins.

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

    Microsoft Academic Search

    I. J. Hamling; T. J. Wright; L. S. Bennati Rassion; E. Calais; E. Lewi; C. Pagli

    2010-01-01

    The 60-km-long Dabbahu segment of the Nubia-Arabia plate boundary lies in the Northern Ethiopian region of Afar. In September 2005 a major rifting episode resulted in the injection of a 60-km-long dyke with a maximum thickness of ~8m (e.g. Wright et al., 2006). Subsidence observed at Dabbahu and Gabho volcanoes implied that some of the magma was sourced from shallow

  17. 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-related mantle processes may control the rheology of the mantle, the magmatic budget, the thermal structure and the localization of final rifting Conversely, the deformation in hyperextended domains is strongly controlled by weak hydrated minerals (e.g. clay, serpentinite) that result form the breakdown of feldspar and olivine due to fluid and reaction assisted deformation and is consequently not inherited but the result of rift induced processes. These key observations show that both inheritance and rift-induced processes play a significant role in the development of magma-poor rift systems and that the role of inheritance may change as the physical conditions vary during the evolving rifting and as rift-induced processes (serpentinization; magma) become more important. Thus, it is not only important to determine the "genetic code" of a rift system, but also to understand how it interacts and evolves during rifting. Understand how far these new ideas and concepts derived from the southern North Atlantic and Alpine Tethys can be translated to other less explored hyperextended rift systems will be one of the challenges of the future research in rifted margins.

  18. Biogeochemistry of Kenyan Rift Valley Lake Sediments

    NASA Astrophysics Data System (ADS)

    Grewe, Sina; Kallmeyer, Jens

    2013-04-01

    The numerous lakes in the Kenyan Rift Valley show strong hydrochemical differences due to their varying geologic settings. There are freshwater lakes with a low alkalinity like Lake Naivasha on the one hand and very salt-rich lakes with high pH values like Lake Logipi on the other. It is known that the underlying lake sediments are influenced by the lake chemistry and by the microorganisms in the sediment. The aim of this work is to provide a biogeochemical characterization of the lake sediments and to use these data to identify the mechanisms that control lake chemistry and to reconstruct the biogeochemical evolution of each lake. The examined rift lakes were Lakes Logipi and Eight in the Suguta Valley, Lakes Baringo and Bogoria south of the valley, as well as Lakes Naivasha, Oloiden, and Sonachi on the Kenyan Dome. The porewater was analysed for different ions and hydrogen sulphide. Additionally, alkalinity and salinity of the lake water were determined as well as the cell numbers in the sediment, using fluorescent microscopy. The results of the porewater analysis show that the overall chemistry differs considerably between the lakes. In some lakes, concentrations of fluoride, chloride, sulphate, and/or hydrogen sulphide show strong concentration gradients with depth, whereas in other lakes the concentrations show only minor variations. Fluoride is present in all lakes; the lowest concentration is found in Lake Oloiden (60 - 90 mg/l), the highest one in Lake Bogoria (1,025 - 1,930 mg/l). The lakes show also large differences in sulphate concentrations. The values vary between 2 mg/l in Lake Baringo and 15,250 mg/l in Lake Eight. In all cores, sulphate concentration does not change significantly with depth; however, there is a distinct peak in each core, raising the question of synchronicity. As expected, chloride concentrations correlate with total salinity. There is no hydrogen sulphide present in the porewater of Lakes Naivasha, Baringo, and Oloiden, whereas in the other lakes, the hydrogen sulphide concentrations are decreasing with depth. Although in close proximity to each other, the Kenyan Rift Valley lakes offer the unique opportunity to study a wide range of geochemical environments and the associated biogeochemical processes.

  19. Evolution and characteristics of continental rifting: Analog modeling-inspired view and comparison with examples from the East African Rift System

    Microsoft Academic Search

    Giacomo Corti

    The evolution and characteristics of narrow continental rifting are illustrated in this paper through a review of recent lithospheric-scale analog models of continental extension compared with selected examples from the East African Rift System.Rift location is controlled by reactivation of lithospheric-scale pre-existing weaknesses; in these areas, the initial phases of rifting correspond to the activation of few, large-offset boundary faults

  20. Diagnostic approaches for Rift Valley fever.

    PubMed

    Wilson, W C; Weingartl, H M; Drolet, B S; Davé, K; Harpster, M H; Johnson, P A; Faburay, B; Ruder, M G; Richt, J A; McVey, D S

    2013-01-01

    Disease outbreaks caused by arthropod-borne animal viruses (arboviruses) resulting in significant livestock and economic losses world-wide appear to be increasing. Rift Valley fever (RVF) virus is an important arbovirus that causes lethal disease in cattle, camels, sheep and goats in Sub-Saharan Africa. There is concern that this virus could spread because of global warming, increased animal trade or through bioterrorism. This paper discusses the current and developing approaches to diagnosis of RVF. Diagnostic assays are available for RVF, but availability can be limited and there is a need for global harmonization. Continued improvement of standard serological and viral genome amplification approaches, including new embedded/syndromic testing, biosensor, emerging virus detection and characterization technologies is needed. PMID:23689885

  1. Rift Valley Fever, Sudan, 2007 and 2010

    PubMed Central

    Aradaib, Imadeldin E.; Erickson, Bobbie R.; Elageb, Rehab M.; Khristova, Marina L.; Carroll, Serena A.; Elkhidir, Isam M.; Karsany, Mubarak E.; Karrar, AbdelRahim E.; Elbashir, Mustafa I.

    2013-01-01

    To elucidate whether Rift Valley fever virus (RVFV) diversity in Sudan resulted from multiple introductions or from acquired changes over time from 1 introduction event, we generated complete genome sequences from RVFV strains detected during the 2007 and 2010 outbreaks. Phylogenetic analyses of small, medium, and large RNA segment sequences indicated several genetic RVFV variants were circulating in Sudan, which all grouped into Kenya-1 or Kenya-2 sublineages from the 2006–2008 eastern Africa epizootic. Bayesian analysis of sequence differences estimated that diversity among the 2007 and 2010 Sudan RVFV variants shared a most recent common ancestor circa 1996. The data suggest multiple introductions of RVFV into Sudan as part of sweeping epizootics from eastern Africa. The sequences indicate recent movement of RVFV and support the need for surveillance to recognize when and where RVFV circulates between epidemics, which can make data from prediction tools easier to interpret and preventive measures easier to direct toward high-risk areas. PMID:23347790

  2. Regional magnetic anomaly constraints on continental rifting

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.

    1985-01-01

    Radially polarized MAGSAT anomalies of North and South America, Europe, Africa, India, Australia and Antarctica demonstrate remarkably detailed correlation of regional magnetic lithospheric sources across rifted margins when plotted on a reconstruction of Pangea. These major magnetic features apparently preserve their integrity until a superimposed metamorphoric event alters the magnitude and pattern of the anomalies. The longevity of continental scale magnetic anomalies contrasts markedly with that of regional gravity anomalies which tend to reflect predominantly isostatic adjustments associated with neo-tectonism. First observed as a result of NASA's magnetic satellite programs, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans. Accordingly, satellite magnetic observations provide a further tool for investigating continental drift to compliment other lines of evidence in paleoclimatology, paleontology, paleomagnetism, and studies of the radiometric ages and geometric fit of the continents.

  3. Teleseismic body wave tomography within a highly extended continental rift: the Woodlark Rift, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Eilon, Z.; Abers, G. A.; Jin, G.; Kim, Y.; Gaherty, J. B.

    2013-12-01

    The Woodlark Rift, Papua New Guinea, has been a region of westward-propagating continental extension for 6-8 Ma, grading westward from seafloor spreading to newly thinned continent. The D'Entrecasteaux Islands (DIs) lie immediately to the west of the youngest spreading centres in continental crust that has undergone 140-190 km of extension. These islands are dominated by metamorphic core complexes (MCCs) containing 5-6 Ma ultra-high pressure (UHP) coesite-eclogite exhumed at ~20 mm/yr coeval with extension. An array of 31 PASSCAL broadband seismometers and 8 broadband OBSs was installed around the region from 2010-2011 to investigate the thinned continent close to the onset of seafloor spreading. We present results of a teleseismic P- and S- wave tomography study that images the mantle beneath the rapidly extending continent. Preliminary observations include strong azimuthal dependence of differential travel times, indicating significant lateral velocity variations and inferred thermal gradients. Using Ps receiver functions and SsPmP reflections, we estimate variations in Moho depth to correct for the crustal effect on travel times. We observe large (>1s) travel time delays beneath the DIs in both P and S arrivals, while stations on the Trobriand Islands and Papuan Peninsula exhibit travel time deficits of 1-2 s. This indicates that lithosphere is thinnest beneath the DIs, along the axis of the rift, in agreement with the location of Quaternary volcanism and consistent with results from surface waves [Ge et al., AGU2013 abstract] and a previous, lower-resolution tomographic study nearby. There is also evidence for moderately thinned lithosphere in the basin immediately south of the DIs. We have previously established strong, spreading-parallel anisotropy from SKS splitting caused by mantle olivine fabric beneath the DIs and the Trobriand Platform, inferred to represent asthenospheric flow in response to rifting. Detailed tomography will reveal how thinning of mantle lithosphere varies with depth and distance from the rift axis, and possibly other features related to UHP exhumation. We anticipate an improved understanding of the kinematics of lithospheric thinning, and the transition in deep structure between rifted continent and adjacent spreading centers. Differential teleseismic P-wave travel times from cross-correlation of 192 earthquakes between March 2010 and August 2011, with crustal correction applied assuming Vp_crust = 6.2 km/s. Delay times at each station are plotted by back azimuth.

  4. Sociocultural and Economic Dimensions of Rift Valley Fever

    PubMed Central

    Muga, Geoffrey Otieno; Onyango-Ouma, Washington; Sang, Rosemary; Affognon, Hippolyte

    2015-01-01

    Health researchers have advocated for a cross-disciplinary approach to the study and prevention of infectious zoonotic diseases, such as Rift Valley Fever. It is believed that this approach can help bring out the social determinants and effects of the zoonotic diseases for the design of appropriate interventions and public health policy. A comprehensive literature review using a systematic search strategy was undertaken to explore the sociocultural and economic factors that influence the transmission and spread of Rift Valley Fever. Although the findings reveal a paucity of social research on Rift Valley Fever, they suggest that livestock sacrificial rituals, food preparation and consumption practices, gender roles, and inadequate resource base for public institutions are the key factors that influence the transmission. It is concluded that there is need for cross-disciplinary studies to increase the understanding of Rift Valley Fever and facilitate appropriate and timely response and mitigation measures. PMID:25688166

  5. Sociocultural and economic dimensions of Rift Valley fever.

    PubMed

    Muga, Geoffrey Otieno; Onyango-Ouma, Washington; Sang, Rosemary; Affognon, Hippolyte

    2015-04-01

    Health researchers have advocated for a cross-disciplinary approach to the study and prevention of infectious zoonotic diseases, such as Rift Valley Fever. It is believed that this approach can help bring out the social determinants and effects of the zoonotic diseases for the design of appropriate interventions and public health policy. A comprehensive literature review using a systematic search strategy was undertaken to explore the sociocultural and economic factors that influence the transmission and spread of Rift Valley Fever. Although the findings reveal a paucity of social research on Rift Valley Fever, they suggest that livestock sacrificial rituals, food preparation and consumption practices, gender roles, and inadequate resource base for public institutions are the key factors that influence the transmission. It is concluded that there is need for cross-disciplinary studies to increase the understanding of Rift Valley Fever and facilitate appropriate and timely response and mitigation measures. PMID:25688166

  6. Structure and Evolution of the Kenya Rift Valley

    Microsoft Academic Search

    B. H. Baker; J. Wohlenberg

    1971-01-01

    Geological evidence makes possible a reconstruction of events since Miocene times, with about 10 km of crustal separation and the pressure beneath the central rift of an upward intrusion from the mantle.

  7. Remote Sensing for Biodiversity Conservation of the Albertine Rift

    E-print Network

    Wang, Y.Q. "Yeqiao"

    183 10 Remote Sensing for Biodiversity Conservation of the Albertine Rift in Eastern Africa Samuel of biodiversity conservation is understanding how environmental factors influence species abundance 2003). The rapidly developing field of remote sensing has been invaluable to biodiversity conservation

  8. Thermal and mechanical development of the East African Rift System

    E-print Network

    Ebinger, Cynthia Joan

    1988-01-01

    The deep basins, uplifted flanks, and volcanoes of the Western and Kenya rift systems have developed along the western and eastern margins of the 1300 km-wide East African plateau. Structural patterns deduced from field, ...

  9. Arc abandonment as a cause for passive continental rifting: Comparison of the Jurassic Mexican Borderland rift and the Cenozoic Rio Grande rift

    NASA Astrophysics Data System (ADS)

    Lawton, Timothy F.; McMillan, Nancy J.

    1999-09-01

    Two rift systems, one of late Mesozoic age and the other of Tertiary age, in the southern Cordillera of North America formed along the inner flanks of former continental arcs. Both rift systems were initiated when arc magmatism abandoned its former inboard extent as a result of retrograde motion of the subducted slab. Similarities in stratigraphy and geochemistry preceding and during crustal extension of each rift system suggest a three-phase magmatic-depositional model for the formation of passive continental rifts above a foundering subducted slab. Continental arc magmatism associated with normal subduction weakens the continental crust during phase 1. Phase 2 involves incipient retrograde motion of the slab, or slab foundering, initiating mantle return into the wedge-shaped volume between slab and overlying continental lithosphere. This causes crustal extension, lithospheric melting, and deposition of conglomerate in nascent rift basins stratigraphically above and adjacent to the extinguished arc. Caldera-related silicic volcanism defines an ignimbrite flare-up, accompanied by extrusion of lithosphere-derived basalt. Mafic volcanism, block faulting, and extensional sedimentary-basin formation continue after the end of silicic volcanism. During phase 3, decompression partial melting of convecting asthenosphere creates basalts with ocean-island chemical affinities intercalated with alluvial or marine sedimentary rocks in extensional basins.

  10. Crustal structure of central Lake Baikal: Insights into intracontinental rifting

    USGS Publications Warehouse

    ten Brink, U.S.; Taylor, M.H.

    2002-01-01

    The Cenozoic rift system of Baikal, located in the interior of the largest continental mass on Earth, is thought to represent a potential analog of the early stage of breakup of supercontinents. We present a detailed P wave velocity structure of the crust and sediments beneath the Central Basin, the deepest basin in the Baikal rift system. The structure is characterized by a Moho depth of 39-42.5 km; an 8-km-thick, laterally continuous high-velocity (7.05-7.4 km/s) lower crust, normal upper mantle velocity (8 km/s), a sedimentary section reaching maximum depths of 9 km, and a gradual increase of sediment velocity with depth. We interpret the high-velocity lower crust to be part of the Siberian Platform that was not thinned or altered significantly during rifting. In comparison to published results from the Siberian Platform, Moho under the basin is elevated by <3 km. On the basis of these results we propose that the basin was formed by upper crustal extension, possibly reactivating structures in an ancient fold-and-thrust belt. The extent and location of upper mantle extension are not revealed by our data, and it may be offset from the rift. We believe that the Baikal rift structure is similar in many respects to the Mesozoic Atlantic rift system, the precursor to the formation of the North Atlantic Ocean. We also propose that the Central Baikal rift evolved by episodic fault propagation and basin enlargement, rather than by two-stage rift evolution as is commonly assumed.

  11. TDRS satellite over African Rift Valley, Kenya, Africa

    NASA Technical Reports Server (NTRS)

    1983-01-01

    This post deploy view of a TDRS satellite shows a segment of the African Rift Valley near Lake Baringo, Kenya, Africa (3.0S, 36.0E). The African Rift Valley system is a geologic fault having its origins in southern Turkey, through the near east forming the bed of the Jordan River, Gulf of Aqaba, the Red Sea and down through east Africa. The line of lakes and valleys of east Africa are the result of the faulting activity.

  12. Results of GPS Observations Across the Kenya Rift Valley

    NASA Astrophysics Data System (ADS)

    Hunja, W.; Kasahara, M.; Takahashi, H.; Kamamia, M.; Tanaka, H.; Miyazaki, K.; Suzuki, A.; Tanaka, K.

    2001-12-01

    Since Feb 1998, GPS measurements have been carried out across the Kenya Rift Valley for the purpose of studying crustal dynamics associated with continental rifting within the East African Rift System. A network comprising of seven stations was established and has been observed periodically for the last three years. Originally, two of the stations were intended to be on a continuously operating mode, while the rest would be occupied on a temporal basis, at least twice to three times per year. However due to unmitigated operational problems there are some large data gaps for the two continuously operating stations. Past geophysical methods have confirmed the East African Rift to be an active divergent boundary. In this study, we present results from the ongoing GPS measurements carried out to determine the current spreading rate across the Kenya Rift. Three main baselines, Malindi-Eldoret, Malindi-KISM and Eldoret-KISM and a combination of other shorter lines were analyzed using ionosphere free double differenced data. Our results indicate some significant length changes of between 2-10mm/yr aligned_@in an East-West direction in two of the baselines. Despite the intermittent data outages, the results obtained so far presents a good pointer to the current dynamics within the Kenya Rift System.

  13. Elevated, passive continental margins: Not rift shoulders, but expressions of episodic, post-rift burial and exhumation

    NASA Astrophysics Data System (ADS)

    Japsen, Peter; Chalmers, James A.; Green, Paul F.; Bonow, Johan M.

    2012-06-01

    Many studies of elevated, passive continental margins (EPCMs) assume that their characteristic, large-scale morphology with high-level plateaux and deeply incised valleys has persisted since rifting and crustal separation, and that the absence of post-rift sediments is evidence of non-deposition. The high mountains in West Greenland, however, expose evidence of km-scale, post-rift subsidence, and recent studies showed that typical EPCM morphology with elevated plateaux formed c. 50 Myr after breakup through a process of uplift and dissection of a regional, post-rift erosion surface. Since the West Greenland margin shares all the morphological characteristics of EPCMs, the results from West Greenland lead us to question the common assumption that EPCMs have remained high since the onset of continental separation. We present published evidence of post-rift burial followed by uplift and exhumation from a number of EPCMs and their adjacent basins to support the notion that EPCMs are not permanent highs and that their morphology is unrelated to rifting and continental breakup. Geodynamic models that explain EPCMs as permanent highs since the time of rifting require either no lithospheric mantle extension below extending crust or effective elastic thicknesses > 100 km. Such models are, however, not consistent with the subsidence history inferred from actual rifts and their margins. Geodynamic models using low elastic thicknesses and a much more uniform distribution of strain within the lithosphere are more consistent with observations of early post-rift behaviour, but some additional process is needed to uplift the margins later. We suggest that EPCMs represent anticlinal, lithospheric folds formed under compression where an abrupt change in crustal or lithospheric thickness occurs between cratons and rift basins. We propose that EPCMs are expressions of episodes of post-rift burial followed by compression-induced uplift and exhumation; one episode of uplift results in erosion of the region to produce a low-relief surface near the level of the adjacent, opening ocean, and a second (or more) episode(s) raises the plateau to its present elevation, after which the plateau is dissected by fluvial and possibly glacial erosion.

  14. Rifts in the tectonic structure of East Antarctica

    NASA Astrophysics Data System (ADS)

    Golynsky, Dmitry; Golynsky, Alexander

    2010-05-01

    It was established that riftogenic and/or large linear tectonic structures in East Antarctica are distributed with a steady regularity with average distance between them about 650 km. All these structures (13) represent objects of undoubted scientific and practical interest and might be considered as immediate objects for conducting integrated geological and geophysical investigations. Analysis and generalization of the RADARSAT satellite system imagery and radio-echosounding survey data collected in the eastern part of Princess Elizabeth Land allow us to distinguish spatial boundaries of previously unknown continental rift system that was proposed to name Gaussberg (Golynsky & Golynsky, 2007). The rift is about 500 km long, and taking into consideration its western continuation in the form of short (fragmented) faults, may exceed 700 km. The elevation difference between depressions and horsts reaches 3 km. The rift structure consists of two sub-parallel depressions separated by segmented horst-like rises (escarpments). Deep depressions within the rift reach more than 800 m bsl near the West Ice Shelf and within the central graben occupied by the Phillipi Glacier. The width of the Gaussberg Rift system varies from 60 km in the south-western area to 150 km near the West Ice Shelf. The Gaussberg rift is considered as a part of the Lambert rift system, which has a complicated structure clearly recognized over both the continent and also its margin. The Gaussberg rift probably exploited a weak zone between the Proterozoic mobile belt and the Archaean Vestfold-Rauer cratonic block. Supposedly it initiated at the turn of Jurassic and Permian epoch or a little bit earlier as in case of the Lambert rift where the Permian graben formation with coal-bearing deposits predetermined the subsequent development of submeridional rift zone. The Gaussberg and also the Scott rift developed in the Queen Marie Land, may be considered as continuations of the Mahanadi Valley rift and coal-bearing basins in the Rajmahal Hills of East India, respectively, in the Antarctic continent. These structures can also be considered as major drainage feeders of terrigenous sediments onto the Davis Sea continental margin. Preliminary analysis of the RADARSAT imagery shows that the Denman Glacier occupies a linear fault system (> 400 km), whereas southward continuation of the Scott Glacier area represents a continuous system of horsts that bound a wide central depression.The Scott Glacier together with graben-like structures hidden by ice and with the graben of Lake Vostok may represent an extensive rift system developed as a result of large-scale pre-breakup extension of Gondwana. We speculate that the Gaussberg rift may be considered as a hypothetical accommodation zone of the Carboniferous-Permian intracontinental rift along 4000 km of the west Australian and east Indian margins, which filled with thick Permian-Triassic sediment including alluvial coals.

  15. Isotopic and geochemical evidence for a heterogeneous mantle plume origin of the Virunga volcanics, Western rift, East African Rift system

    Microsoft Academic Search

    Ramananda Chakrabarti; Asish R. Basu; Alba P. Santo; Dario Tedesco; Orlando Vaselli

    2009-01-01

    Virunga volcanics in the western rift of the East African Rift system (EARS) show silica-undersaturated, ultra-alkaline, alkalic-mafic compositions. The two active Virunga volcanoes, Nyiragongo and Nyamuragira, are 15 km apart. Nyiragongo shows unusual compositions not seen globally and has the lowest recorded viscosity among terrestrial magmas while Nyamuragira is unusually effusive. These volcanoes occur along the fringes of a topographic uplift

  16. Geodynamic models of the Wilson Cycle: From rifts to mountains to rifts

    NASA Astrophysics Data System (ADS)

    Buiter, Susanne; Tetreault, Joya; Torsvik, Trond

    2015-04-01

    The Wilson Cycle theory that oceans close and reopen along the former suture is a fundamental concept in plate tectonics. The theory suggests that subduction initiates at a passive margin, closing the ocean, and that future continental extension localises at the ensuing collision zone. Each stage of the Wilson Cycle will therefore be characterised by inherited structural and thermal heterogeneities. Here we investigate the role of Wilson Cycle inheritance by considering the influence of (1) passive margin structure on continental collision and (2) collision zones on passive margin formation. Passive margins may be preferred locations for subduction initiation because inherited faults and areas of exhumed serpentinized mantle may weaken a margin enough to localise shortening. If subduction initiates at a passive margin, the shape and structure of the passive margins will affect future continental collision. Our review of present-day passive margins along the Atlantic and Indian Oceans reveals that most passive margins are located on former collision zones. Continental break-up occurs on relatively young sutures, such as Morocco-Nova Scotia, and on very old sutures, such as the Greenland-Labrador and East Antarctica-Australia systems. This implies that it is not always post-collisional collapse that initiates the extensional phase of a Wilson Cycle. We highlight the impact of collision zone inheritance on continental extension and rifted margin architecture. We show numerical experiments of one Wilson Cycle of subduction, collision, and extension. Subduction initiates at a tapered passive margin. Closure of a 60 Ma ocean leads to continental collision and slab break-off, followed by some tens of kilometres of slab eduction. Mantle flow above the sinking detached slab enhances deformation in the rift area. The resulting rift exposes not only continental crust, but also subduction-related sediments and oceanic crust remnants. Renewed subduction in the post-collision phase is enabled by lithosphere delamination and slab rollback, leading to back-arc extension in a style similar to the Tyrrhenian Sea.

  17. Tectonostratigraphic development of the Interior Sudan rifts, Central Africa

    NASA Astrophysics Data System (ADS)

    McHargue, Tim R.; Heidrick, Tom L.; Livingston, Jack E.

    1992-10-01

    In the Muglad, Melut and Blue Nile rift basins of Interior Sudan three major episodes of rifting, concomitant subsidence and nonmarine/nonvolcanic sedimentation are recognized. These three rifting cycles, which spanned 140 to 95 Ma (Fl), 95 to 65 Ma (F2), and 65 to 30 Ma (F3), resulted in the accumulation of up to 5400, 4200 and 5400 m of sediments, respectively. In the Muglad Basin, the best known and largest of the Sudan rift basins, each rifting cycle consists of (1) a basal sandstone unit (at least near rift margins), that is followed by (2) an upward coarsening section of lacustrine shale grading through marginal lacustrine mudstone and sandstone into fluvial mudstone and sandstone, and (3) a capping blanket of fluvial and alluvial sandstone. The shale-dominated portions of these cycles were deposited in a closed-drainage basin during active faulting. The fluvial and alluvial blanket sands were deposited in an open-drainage basin during the thermal sag phase following each tectonic cycle. The Early Cretaceous F1 intracontinental rifts of Interior Sudan were linked to major rifts/spreading centres in the Proto-South Atlantic by the dextral WSW-trending Central African Shear Zone and to the Indian Ocean via the NW-trending Anza rift in Kenya. In the Muglad Basin, F1 deformation involved high strain rates, rapid syn-rift crustal stretching and subsidence, and the formation of deep, fault-bounded tensional and transtensional pull-apart basins. During the F2 and F3 deformations, the rates of subsidence and stretching were much lower and were focused within smaller geographic areas. Structural elements include asymmetric half-grabens and less common full-grabens with central highs. The three superimposed tectonic episodes resulted in the subsidence of NNW- to NW-trending rift sub-basins; this gave rise to a wide variety of normal fault geometries, displacements, and growth histories. Planar domino-style and listric normal F1 fault arrays are modeled. The rotated F1 basement blocks typically are asymmetric and low-standing, and favour NE-directed growth and material transport. The F2 and F3 normal faults, which have both NE- and SW-directed polarities, often are listric and decouple younger syn-rift strata from older F1 rotated and locked planar basement faults. Palinspastic restorations and forward modeling of three regional cross-sections suggest that F1 faults account for 65-80% of total crustal extension. Stretching factors across the Interior Sudan rifts vary between 1.25 and 1.40. This range is considered to be a minimum since restored sections do not cross F3 depocenters. Total crustal extension across the Muglad plus the Melut rift basins exceeds 75 km.

  18. Groundwater origin and flow dynamics in active rift systems - A multi-isotope approach in the Main Ethiopian Rift

    NASA Astrophysics Data System (ADS)

    Bretzler, Anja; Osenbrück, Karsten; Gloaguen, Richard; Ruprecht, Janina S.; Kebede, Seifu; Stadler, Susanne

    2011-05-01

    SummaryThis study aims to investigate groundwater recharge and flow patterns in tectonically active rift systems, exemplified by a case study in the Main Ethiopian Rift. The chosen approach includes the investigation of hydrochemical parameters and environmental isotopes ( 3H, ? 2H, ? 18O, ? 13C-DIC, 14C-DIC, 87Sr/ 86Sr). Apparent groundwater ages were determined by radiocarbon dating after correction of 14C-DIC using a modified ? 13C-mixing model and further validation using geochemical modelling with NETPATH. Hydrochemical and isotopic data indicate an evolutionary trend existing from the escarpments towards the Rift floor. Groundwater evolves from tritium-containing and hence recently recharged Ca-HCO 3-type water on the escarpments to tritium-free Na-HCO 3 groundwater dominating deep Rift floor aquifers. Correspondingly, rising pH and HCO3- values coupled with increasingly enriched ? 13C signatures point to hydrochemical evolution of DIC and beginning dilution of the carbon isotope signature by other carbon sources, related to a diffuse influx of mantle CO 2 into the groundwater system. Especially thermal groundwater sampled near the most recent fault zones in the Fantale/Beseka region displays clear influence of mantle CO 2 and increased water-rock interaction, indicated by a shift in ? 13C and 87Sr/ 86Sr signatures. The calculation of apparent groundwater ages revealed an age increase of deep groundwater from the escarpments to the Rift floor, complying with hydrochemical evolution. Within the Rift, samples show a relatively uniform distribution of apparent 14C ages of ˜1800 to ˜2800 years, with the expected down-gradient aging trend lacking, contradicting the predominant intra-rift groundwater flow described in existing transect-based models of groundwater flow. By combining hydrochemical and new isotopic data with knowledge of the structural geology of the Rift, we improve the existing groundwater flow model and propose a new conceptual model by identifying flow paths both transversal and longitudinal to the main Rift axis, the latter being strongly controlled by faulted and tilted blocks on the escarpment steps. The connection between groundwater flow and fault direction make this model applicable to other active rift systems with similar structural settings.

  19. APLICACIONES A LA ECOLOGA DE LA AGREGACIN APROXIMADA DE VARIABLES EN SISTEMAS DINMICOS DISCRETOS

    E-print Network

    modelos con varias escalas de tiempo. La agregación aproximada de sistemas consiste en definir a partir deAPLICACIONES A LA ECOLOGÍA DE LA AGREGACIÓN APROXIMADA DE VARIABLES EN SISTEMAS DINÁMICOS DISCRETOS de variables permiten reducir el número de variables de un sistema dinámico, dando lugar a otro

  20. Despeses de personal. PDI numerari APLICACIONS DOTACIONS 120.00 121.01 121.02

    E-print Network

    Oro, Daniel

    Despeses de personal. PDI numerari APLICACIONS DOTACIONS 120.00 121.01 121.02 pagues extres(2) C.287,74 TOTAL PARCIAL PDI 29.232.815,68 QUOTA PATRONAL INTERINS 160.00 207.140,01 TOTAL GLOBAL 29.439.955,69 C

  1. Despeses de personal. PDI numerari APLICACIONS DOTACIONS 120.00 121.01 121.02

    E-print Network

    Oro, Daniel

    Despeses de personal. PDI numerari APLICACIONS DOTACIONS 120.00 121.01 121.02 pagues extres(2) C.628,58 TOTAL PARCIAL PDI 29.222.203,10 QUOTA PATRONAL INTERINS 160.00 218.013,47 TOTAL GLOBAL 29.440.216,57 C

  2. [Rift Valley fever virus: evolution in progress].

    PubMed

    Tolou, H; Plumet, S; Leparc-Goffart, I; Couissinier-Paris, P

    2009-06-01

    Several viruses now circulating in tropical zones around the globe are potential threats for ever-increasing human populations even in temperate zones that have long remained unaffected. The mechanisms underlying transport and transmission, which can be enhanced by human activity, can be even stronger in zones where factors needed to support development of these viruses, i.e., hosts, reservoirs and vectors, are already present. This possibility has been illustrated by dengue virus, and now by the rapid spread of the Chikungunya virus on Reunion Island in 2005 and then in Italy in 2007. The spreading of Chikungunya virus despite its mild reputation had a major unexpected impact. It showed that the evolution of the virus, whether a cause or consequence of observed events, could be determinant. The risk of extension of more pathogenic viruses due to similar mechanisms must be considered as a possibility. In this regard the Rift Valley fever virus, that already involves a large area and has a major reservoir, is one of the viruses that deserves close surveillance. PMID:19702138

  3. Field Studies of Geothermal Reservoirs Rio Grande Rift, New Mexico

    SciTech Connect

    James C Witcher

    2002-07-30

    The Rio Grande rift provides an excellent field laboratory to study the nature of geothermal systems in an extensional environment. Much of the geologic complexity that is found in the Basin and Range is absent because the rift is located on cratonic crust with a thin and well-characterized Phanerozoic stratigraphy and tectonic history. On the other hand, the Neogene thermo-tectonic history of the rift has many parallels with the Basin and Range to the west. The geology of the southern Rio Grande rift is among the best characterized of any rift system in the world. Also, most geologic maps for the region are rather unique in that detailed analyses of Quaternary stratigraphic and surficial unit are added in concert with the details of bedrock geology. Pleistocene to Holocene entrenchment of the Rio Grande and tributaries unroofs the alteration signatures and permeability attributes of paleo outflow plumes and upflow zones, associated with present-day, but hidden or ''blind,'' hydrothermal systems at Rincon and San Diego Mountain.

  4. CDROM interstation Pn study along the Rio Grande rift

    NASA Astrophysics Data System (ADS)

    Lastowka, Lynda A.; Sheehan, Anne F.

    Upper mantle velocities in the regions of the Rio Grande rift and the Southern Rockies were investigated using Pn waves from the broadband seismic data obtained from the Continental Dynamics-Rocky Mountain (CDROM) experiment. A velocity of 7.8+/-0.1 km/s on the eastern flank of the Rio Grande rift in New Mexico was measured from epicentral distance vs. travel time data for ten Pn measurements from a south-western New Mexico earthquake that was in-plane with the southern CDROM line. Thirty-two interstation Pn measurements were made using eight western United States earthquakes. Using these measurements another bulk velocity estimate was made by solving for the best-fit velocity for inter-station distances and travel times; this method also shows that the upper mantle beneath the Rio Grande rift has a slow velocity of 7.8+/- 0.1 km/s. This low velocity is consistent with the high heat flow in the Rio Grande rift area and the evidence of modern rifting. Individual measurements made in the north end of the southern Rocky Mountains are near the global average Pn value of 8.1 km/s.

  5. Upper-mantle seismic structure in a region of incipient continental breakup: northern Ethiopian rift

    Microsoft Academic Search

    Ian D. Bastow; Graham W. Stuart; J-Michael Kendall; Cynthia J. Ebinger

    2005-01-01

    SUMMARY The northern Ethiopian rift forms the third arm of the Red Sea, Gulf of Aden triple junction, and marks the transition from continental rifting in the East African rift to incipient oceanic spread- ing in Afar. We determine the P- and S-wave velocity structure beneath the northern Ethiopian rift using independent tomographic inversion of P- and S-wave relative arrival-time

  6. A comparison of rift-zone tectonics in Iceland and Hawaii

    Microsoft Academic Search

    Allan M Rubin

    1990-01-01

    Observations of eroded volcanic rift zones indicate that dikes in Iceland are typically several times thicker than those in Hawaii. Geodetic and seismic observations of active rifts, however, suggest that dike heights in the two regions are similar. Provided the elastic properties of the rift zones are the same, this implies that dikes are intruded with higher driving pressures (magma

  7. Geodetic measurements of rifting associated with a seismo-volcanic crisis in afar

    Microsoft Academic Search

    J. C. Ruegg; M. Kasser; J. C. Lepine; A. Tarantola

    1979-01-01

    The resurvey of both a geodetic network and a levelling line, soon after a seismotectonic crisis which occured inside the subaerial rift of Asal--Ghoubbet in Afar, shows an horizontal extension of about 2 m and a vertical movement up to 70 cm. These movements showed clearly the mechanism of rifting in a setting similar to a typical oceanic rift valley.

  8. Relative Timing of CAMP, Rifting, Continental Breakup, and Basin Inversion: Tectonic Significance

    E-print Network

    Olsen, Paul E.

    1 Relative Timing of CAMP, Rifting, Continental Breakup, and Basin Inversion: Tectonic Significance in eastern North America provides a temporal benchmark for assessing the relative timing of rifting, drift, and geochronological data favor a diachronous rift-drift transition (seafloor spreading began earlier in the south

  9. Transtensional Rifting in the Late Proto-Gulf of California Near Bahía Kino, Sonora, México

    Microsoft Academic Search

    S. E. Bennett; M. E. Oskin; R. J. Dorsey

    2009-01-01

    We investigate the role of obliquity in continental rupture from the example of the Gulf of California rift. Focused transtensional strain adjacent to strike-slip faults, ubiquitous in oblique rifts, may act as a catalyst for lithospheric rupture. To test this hypothesis we completed detailed structural mapping, fault kinematic analysis, basin analysis, and paleomagnetism of pre- and syn-rift volcanic and sedimentary

  10. An Unexpected Recurrent Transmission of Rift Valley Fever Virus in Cattle in a Temperate and Mountainous

    E-print Network

    Paris-Sud XI, Université de

    An Unexpected Recurrent Transmission of Rift Valley Fever Virus in Cattle in a Temperate States of America Abstract Rift Valley fever is an acute, zoonotic viral disease of domestic ruminants­2009. The goal of the present study was to evaluate the point prevalence of antibodies against Rift Valley Fever

  11. Host Alternation Is Necessary to Maintain the Genome Stability of Rift Valley Fever Virus

    E-print Network

    Paris-Sud XI, Université de

    Host Alternation Is Necessary to Maintain the Genome Stability of Rift Valley Fever Virus Sara evolution. To test this hypothesis, we used Rift Valley fever virus (RVFV), an arbovirus that can Is Necessary to Maintain the Genome Stability of Rift Valley Fever Virus. PLoS Negl Trop Dis 5(5): e1156. doi

  12. A Fusion-Inhibiting Peptide against Rift Valley Fever Virus Inhibits Multiple, Diverse Viruses

    E-print Network

    A Fusion-Inhibiting Peptide against Rift Valley Fever Virus Inhibits Multiple, Diverse Viruses (Class I, II, and III) based on the protein sequence and structure. For Rift Valley fever virus (RVFV KW, Taylor SL, et al. (2013) A Fusion-Inhibiting Peptide against Rift Valley Fever Virus Inhibits

  13. Recent seismicity of the East African Rift system and its implications

    Microsoft Academic Search

    Fekadu Kebede; Ota Kulhánek

    1991-01-01

    The seismicity of the East African Rift system and southern Red Sea is studied here. Location of earthquake epicenters in East Africa shows that there is a seismicity gap in space and time between the Main Ethiopian Rift system and the eastern rift. However, distribution of earthquake epicenters together with the energy mapping suggest a continuity of seismic activity or

  14. Significant crustal thinning beneath the Baikal rift zone: New constraints from receiver function analysis

    E-print Network

    Gao, Stephen Shangxing

    is a major feature of typical continental rifts such as the East African (EAR) and Rio Grande (RGR) rifts of more than 10 km has been observed in the Rio Grande [Wilson et al., 2003] and East African [Prodehl et, still remain as debated issues. [3] The BRZ (Figure 1) is a 1800 km long system of rift depressions

  15. From hyper-extended rifts to orogens: the example of the Mauléon rift basin in the Western Pyrenees (SW France)

    NASA Astrophysics Data System (ADS)

    Masini, E.; Manatschal, G.; Tugend, J.

    2011-12-01

    An integral part of plate tectonic theory is that the fate of rifted margins is to be accreted into mountain belts. Thus, rift-related inheritance is an essential parameter controlling the evolution and architecture of collisional orogens. Although this link is well accepted, rift inheritance is often ignored. The Pyrenees, located along the Iberian and European plate boundary, can be considered as one of the best places to study the reactivation of former rift structures. In this orogen the Late Cretaceous and Tertiary convergence overprints a Late Jurassic to Lower Cretaceous complex intracontinental rift system related to the opening of the North Atlantic. During the rifting, several strongly subsiding basins developed in the axis of the Pyrenees showing evidence of extreme crustal extension and even locale mantle exhumation to the seafloor. Although the exact age and kinematics of rifting is still debated, these structures have an important impact in the subsequent orogenic overprint. In our presentation we discuss the example of the Mauléon basin, which escaped from the most pervasive deformations because of its specific location at the interface between the western termination of the chain and the Bay of Biscay oceanic realm. Detailed mapping combined with seismic reflection, gravity data and industry wells enabled to determine the 3D rift architecture of the Mauléon basin. Two major diachronous detachment systems can be mapped and followed through space. The Southern Mauléon Detachment (SMD) develops first, starts to thin the crust and floors the Southern Mauléon sub-Basin (SMB). The second, the Northern Mauléon Detachment (SMD) is younger and controls the final crustal thinning and mantle exhumation to the north. Both constitute the whole Mauléon basin. Like at the scale of the overall Pyrenees, the reactivation of the Mauléon Basin increases progressively from west to east, which enables to document the progressive reactivation of an aborted hyper-extended rift system. In our presentation, we discuss the compressional reactivation of the rift structures by the study of dip sections across the basin, from weakly reactivated sections in the west to strongly reactivated sections in the east. Comparing the sections, it results that the compression reactivated the rift structures (mainly the detachment faults) and that this reactivation occurred in 2 steps. It corresponds to the reactivation through time of the NMB before the SMB. This evolution is in line with an early proto-subduction of the hyper-extended domain beneath the European plate whereas the NMB sediments are wedged, folded and thrust onto the Iberia and Europe margins ("thin-skin" tectonics). The second step occurs when the deformation started to migrate southward resulting in the formation of the axial Pyrenees nappe stack (thick-skin tectonics). These results suggest that the inherited rift structures strongly controlled the initial convergence. Future work will revisit the more reactivated Albian basins throughout the chain to investigate how far the results from western Pyrenees can be used to understand the Central and Eastern Pyrenees. Moreover, this field-oriented study can serve as an example of how rift structures may control style and timing of orogenic processes.

  16. A groundwater convection model for Rio Grande rift geothermal resources

    NASA Technical Reports Server (NTRS)

    Morgan, P.; Harder, V.; Daggett, P. H.; Swanberg, C. A.

    1981-01-01

    It has been proposed that forced convection, driven by normal groundwater flow through the interconnected basins of the Rio Grande rift is the primary source mechanism for the numerous geothermal anomalies along the rift. A test of this concept using an analytical model indicates that significant forced convection must occur in the basins even if permeabilities are as low as 50-200 millidarcies at a depth of 2 km. Where groundwater flow is constricted at the discharge areas of the basins forced convection can locally increase the gradient to a level where free convection also occurs, generating surface heat flow anomalies 5-15 times background. A compilation of groundwater data for the rift basins shows a strong correlation between constrictions in groundwater flow and hot springs and geothermal anomalies, giving strong circumstantial support to the convection model.

  17. The First Prediction of a Rift Valley Fever Outbreak

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

  18. US-Africa collaborative research on incipient continental rift zones

    NASA Astrophysics Data System (ADS)

    Atekwana, E. A.

    2007-12-01

    Since 1999, we have been conducting research in Botswana in collaboration with colleagues at the University of Botswana (UB). Recently, we have expanded our research activities to include the University of Zambia (UNZA). The goal of the collaborative efforts center on investigating geologic processes operating during the initial stages of continental extension. During student training, US students partner with peers from UB and UNZA to conduct field-based research within a multi-disciplinary framework focused on investigating the interplay between neotectonics and surficial processes due to rifting. The student projects are designed to: 1) assess the role of pre-existing structures on rift basin development; 2) determine fault kinematics and direction of rift extension; 3) characterize the geometry of the basins; 4) assess current models for fault growth and propagation and linkage to form border faults; 5) investigate environmental change information preserved in rift basin sediments; 6) determine how magma below the rift basin affects surface water chemical properties; and 7) develop tectonic and geologic models for the evolution of rift basins during the incipient stages of continental extension. Our goal is to provide is to improve research and education in developing countries while providing talented and motivated US students with hands-on field research experience in near surface geophysical surveying, field geologic mapping, GPS mapping, and geochemical and hydrogeologic techniques necessary for addressing basic research questions in the geosciences, as well as resources exploration (e.g., hydrocarbon, water resources, mineral, geothermal, etc.). Our US students acquire an enriching cultural experience, make personal contacts, and build relationships that will form the core of future international research collaborations. At the same time, project activities introduce the African students to state-of the art geophysical equipment and research methodologies that will result in capacity building in the African nations involved. In this presentation, we will provide our perspective on both the opportunities provided and challenges faced while conducting basic research in sub-Saharan Africa.

  19. Magnetotelluric pilot study in the Rio Grande Rift, southwest USA

    NASA Astrophysics Data System (ADS)

    Feucht, D. W.; Bedrosian, P. A.; Sheehan, A. F.

    2012-12-01

    A magnetotelluric (MT) pilot study consisting of approximately 25 stations distributed in and around the Rio Grande Rift of the southwest United States was carried out in the summer of 2012. Both broadband (100 Hz to 1000 s) and long-period (up to 10 000 s) MT data were collected across two profiles that run perpendicular to the rift axis near Denver, Colorado and Taos, New Mexico, respectively. Time-domain EM data was also collected at each site to account for galvanic distortion in the near-surface. The tectonic forces and rheologic properties behind the initiation and propagation of the rift are poorly understood. Surface mapping of volcanism, normal faulting and sedimentary basins reveals a narrow band of crustal deformation confined to a region in close proximity to the rift axis while geophysical results suggest that deformation is distributed across a much broader and deeper region of the lithosphere. In particular, seismic tomography shows low seismic wave speeds into the lower crust and upper mantle. The magnetotelluric technique is a well-proven passive electromagnetic method that allows for the detection of apparent resistivity at a wide range of depth scales. Complimenting the seismic results with MT data will provide important new information on the geologic and geophysical properties that control the rifting process in this low-strain rate environment. Properties to which the MT method is particular sensitive include temperature, fluid content, and mineral alteration. Preliminary results from this most recent survey are encouraging, showing good data quality up to 10 000 s. In an important precursor to full 2D modeling, the magnetotelluric phase tensor has been used to assess the dimensionality of the electrical resistivity structure at depth. This pilot study provides proof of concept for a much larger magnetotelluric experiment planned to take place in the Rio Grande Rift in 2013.

  20. Intermittent upwelling of asthenosphere beneath the Gregory Rift, Kenya

    SciTech Connect

    Tatsumi, Yoshiyuki (Univ. of Tasmania (Australia) Kyoto Univ. (Japan)); Kimura, Nobukazu (Kyoto Univ. (Japan)); Itaya, Tetsumaru (Okayama Univ. of Science (Japan)); Koyaguchi, Takehiro (Kumamoto Univ. (Japan)); Suwa, Kanenori (Nagoya Univ. (Japan))

    1991-06-01

    K-Ar dates and chemical compositions of basalts in the Gregory Rift, Kenya, demonstrate marked secular variation of lava chemistry. Two magmatic cycles characterized by incompatible element relative depletion are recognized; both occurring immediately after the peak of basaltic volcanism and coeval with both trachyte/phonolite volcanism and domal uplift of the region. These cycles may be attributed to increasing degree of partial melting of mantle source material in association with thinning of the lithosphere by thermal erosion through contact with hot upwelling asthenospheric mantle. Cyclic variation in asthenosphere upwelling may be considered an important controlling process in the evolution of the Gregory Rift.

  1. Continental rifting and the origin of Beta Regio, Venus

    NASA Technical Reports Server (NTRS)

    Mcgill, G. E.; Steenstrup, S. J.; Barton, C.; Ford, P. G.

    1981-01-01

    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 rift systems on earth. This interpretation is consistent with the commonly quoted analogy between the East African rift system 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.

  2. 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

  3. Active transsection faults in rift transfer zones: evidence for complex stress fields and implications for crustal fragmentation processes in the western branch of the East African Rift

    Microsoft Academic Search

    D. Koehn; M. Lindenfeld; G. Rümpker; K. Aanyu; S. Haines; C. W. Passchier; T. Sachau

    2010-01-01

    New structural and seismologic evidence from the Rwenzori Mountains, Uganda, indicate that continental rifts can capture and\\u000a rotate fragments of the lithosphere while rift segments interact, in a manner analogous to the interaction of small-scale\\u000a fractures. The Rwenzori Mountains are a basement block within the western branch of the East African Rift System that is located\\u000a at the intersection of

  4. Spatial variation of primordial 3He in crustal fluids along the East-African Rift system (the Ethiopian and the Kenya Rift section)

    Microsoft Academic Search

    E. Griesshaber; S. Weise; G. Darling

    1994-01-01

    (3)He\\/(4)He compositions are presented for groundwater samples from the Ethiopian segment of the East-Afrikan Rift and from its northern extension, the adjacent Afar region (Djibuti). Helium isotope data are compared to those obtained previously from the Gregory Rift, south of Ethiopia. The distribution pattern of mantle-derived volatiles along the entire East-African-Rift (-from south Kenya to Djibuti-) is discussed and their

  5. Seismic tomography of continental rifts revisited: from relative to absolute heterogeneities

    NASA Astrophysics Data System (ADS)

    Achauer, Ulrich; Masson, Frédéric

    2002-11-01

    Tomographic images for four major continental rift zones, namely the southern Rhine Graben (SRG, Germany/France), the Gregory rift (Kenya) which is the central part of the East African rift system, the Rio Grande rift (RGR) in the United States and the Lake Baikal rift zone (LBR) in Russia have been revisited by calculating and comparing absolute velocity models. The four rifts exhibit strong structural differences in the uppermost mantle down to more than 300-km depth, suggesting major differences in their geodynamic evolution albeit their similarity in age and similar surface expression. The comparative analysis suggests that tomographic images of rift zones can be used to characterize continental rifts, once the corrections to obtain absolute velocities have been carried out. Our results suggest that while the Kenya and the Rio Grande rift may be considered active with large upwelling plumes being the main controlling factor in the evolution, the southern Rhine Graben and the Lake Baikal rift are more likely passive rifts, where complex regional stress fields and inherited structures play the governing role in the evolution.

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

    PubMed

    Calais, Eric; d'Oreye, Nicolas; Albaric, Julie; Deschamps, Anne; Delvaux, Damien; Déverchère, Jacques; Ebinger, Cynthia; Ferdinand, Richard W; Kervyn, François; Macheyeki, Athanas S; Oyen, Anneleen; Perrot, Julie; Saria, Elifuraha; Smets, Benoît; Stamps, D Sarah; Wauthier, Christelle

    2008-12-11

    Continental rifts begin and develop through repeated episodes of faulting and magmatism, but strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented. In highly evolved rifts, tensile stresses from far-field plate motions accumulate over decades before being released during relatively short time intervals by faulting and magmatic intrusions. These rifting crises are rarely observed in thick lithosphere during the initial stages of rifting. Here we show that most of the strain during the July-August 2007 seismic crisis in the weakly extended Natron rift, Tanzania, was released aseismically. Deformation was achieved by slow slip on a normal fault that promoted subsequent dyke intrusion by stress unclamping. This event provides compelling evidence for strain accommodation by magma intrusion, in addition to slip along normal faults, during the initial stages of continental rifting and before significant crustal thinning. PMID:19079058

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

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

    USGS Publications Warehouse

    Hayes, Gavin; 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.

  9. Mending the Rift between Academic and Vocational Education.

    ERIC Educational Resources Information Center

    Douglas, Ann M.

    1992-01-01

    The rift between academic and vocational education has been magnified by the physical isolation of vocational facilities. Vocational educators must abandon their apologetic soapboxes to help parents and students realize the vocational nature of almost all education. Dialogue is essential. Teachers must assume responsibility for educating all…

  10. Seismic monitoring of the Olkaria Geothermal area, Kenya Rift valley

    Microsoft Academic Search

    Silas M. Simiyu; G. Randy Keller

    2000-01-01

    Seismic monitoring of the Olkaria Geothermal area in the southern Rift Valley region of Kenya has been carried out since 1985. The initial purpose of this effort was to determine the background level of seismicity before full exploitation of the geothermal resource was started. This monitoring began with one seismic station. However, since May 1996, a seismic network comprising six

  11. Crustal structure of central Lake Baikal: Insights into intracontinental rifting

    E-print Network

    ten Brink, Uri S.

    of Baikal, located in the interior of the largest continental mass on Earth, is thought to represent. The structure is characterized by a Moho depth of 39­42.5 km; an 8-km-thick, laterally continuous high rifting. In comparison to published results from the Siberian Platform, Moho under the basin is elevated

  12. ORIGINAL PAPER Separation of rifting and lithospheric folding signatures

    E-print Network

    Vallée, Martin

    Mediterranean Sea and the Bohemian Massif; (2) long-wavelength lithospheric folds striking NE and located of the pre- Mesozoic basement and of the Moho. We derive the respective timing of rifting and folding from sedimentary accumulation curves computed for selected locations of the Upper Rhine Graben. From

  13. Monitoring Volcanic Gases on Kilauea's East Rift Zone

    USGS Multimedia Gallery

    Hawaiian Volcano Observatory Geochemist Jeff Sutton and CSAV international volcanology students visit a continuous gas monitoring site on Kilauea's east rift zone during field studies portion of the summer training course. Instrumentation at this site measures ambient concentration of noxious sulfur...

  14. Monitoring Volcanic Gases on Kilauea's East Rift Zone II

    USGS Multimedia Gallery

    Hawaiian Volcano Observatory Geochemist Jeff Sutton and CSAV international volcanology students visit a continuous gas monitoring site on Kilauea's east rift zone during field studies portion of the summer training course. Instrumentation at this site measures ambient concentration of noxious su...

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

    Microsoft Academic Search

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

    1993-01-01

    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

  16. Rift Valley fever: an uninvited zoonosis in the Arabian peninsula

    Microsoft Academic Search

    Hanan H Balkhy; Ziad A Memish

    2003-01-01

    Rift Valley fever (RVF) is an acute viral disease, affecting mainly livestock but also humans. The virus is transmitted to humans through mosquito bites or by exposure to blood and bodily fluids. Drinking raw, unpasteurized milk from infected animals can also transmit RVF. Routine vaccination of livestock in Africa has been prohibitively expensive, leading to endemicity of RVF in most

  17. Rift Valley Fever Overview and Recent Developments at USDA

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  18. Geodetic constraints on rifting processes in East Africa (Invited)

    NASA Astrophysics Data System (ADS)

    Calais, E.; Stamps, D. S.; Bennati, L.; Saria, E.; Flesch, L. M.; Freed, A. M.

    2009-12-01

    Many features in rift zones and passive margins have been successfully explained by stretching models where lithospheric thinning and crustal extension are driven by far-field tectonic stresses. However, recent observations in East Africa show that magma intrusions can accommodate large amounts of strain during the initial stages of continental rifting and prior to significant crustal thinning. We will present a large-scale kinematic model for the East African Rift derived from space geodetic observations, earthquake slip vectors, transform azimuths, and spreading rates that includes three subplates (Victoria, Rovuma, and Lwandle) between Nubia and Somalia, with total opening increasing from ~1 mm/yr in southern Mozambique to 7 mm/yr in northern Ethiopia. We will use regional-scale geodetic results to show that far-field plate divergence in East Africa can involve a significant amount of strain accommodation by magma intrusions. We will argue that contributions other than tectonic forces are required to overcome the strength of the continental lithosphere and to initiate and sustain rifting in East Africa.

  19. Post-rifting relaxation in the Afar region, Ethiopia

    Microsoft Academic Search

    Scott L. Nooner; Laura Bennati; Eric Calais; W. Roger Buck; Ian J. Hamling; Tim J. Wright; Elias Lewi

    2009-01-01

    Crustal accretion at divergent plate boundaries typically occurs via the periodic intrusion of dikes, but their emplacement and the associated deformation are rarely observed. The few existing observations at subaerial rifts show that these diking events are followed by a decadal-scale period with extension rates faster than the secular divergent plate motion. This transient accelerated deformation has been explained by

  20. 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.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  3. Forecast and Outbreak of Rift valley fever in Sudan, 2007

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Background Rift Valley fever (RVF) outbreaks occur during heavy rainfall in various sub-Saharan countries including Kenya, Somalia, and Tanzania and more recently in Saudi Arabia and Yemen. Given the wide geographic and ecological range of RVF virus, it is necessary to monitor large areas for condit...

  4. Masirah Graben, Oman: A hidden Cretaceous rift basin

    Microsoft Academic Search

    W. H. Beauchamp; A. C. Ries; M. P. Coward

    1995-01-01

    Reflection seismic data, well data, geochemical data, and surface geology suggest that a Cretaceous rift basin exists beneath the thrusted allochthonous sedimentary sequence of the Masirah graben, Oman. The Masirah graben is located east of the Huqf uplift, parallel to the southern coast of Oman. The eastern side of the northeast-trending Huqf anticlinorium is bounded by an extensional fault system

  5. Geochemical Overview of the East African Rift System

    Microsoft Academic Search

    T. Furman

    2003-01-01

    Mafic volcanics of the East African Rift System (EARS) record a protracted history of continental extension that is linked to mantle plume activity. The modern EARS traverses two post-Miocene topographic domes separated by a region of polyphase extension in northern Kenya and southern Ethiopia. Basaltic magmatism commenced ˜45 Ma in this highly extended region, while the onset of plume-related activity

  6. Mantle support of the East African Rift System

    Microsoft Academic Search

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

    2007-01-01

    The African Superplume is a region of slow seismic wave velocities in the lower mantle under southern Africa. The uplift, volcanism and rifting that defines the much of eastern and southern Africa suggest a dynamic link between lower mantle dynamics and near-surface processes affecting the African plate. The dynamic link between the lower mantle and the surface, and the structure

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

    Microsoft Academic Search

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

    1993-01-01

    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

  8. The role of structural inheritance in continental rifting

    NASA Astrophysics Data System (ADS)

    Buiter, Susanne; Tetreault, Joya

    2015-04-01

    In nature we observe that passive margins tend to originate on continental collision zones. This is not surprising as continents are long-lived and therefore have undergone multiple deformation phases, producing many regions with inherited structures. Collision zones can act as intrinsic rift-localizers for several reasons: rifting at a suture may be initiated by extensional collapse of the orogen, the thicker crustal root of orogens and their associated increase in heat producing elements makes orogens thermally weak, and inherited thrust faults form large-scale heterogeneities. When investigating continental extension geodynamically, numerical experiments often simplify such inheritance and start from laterally homogeneous crustal layers with a prescribed inhomogeneity that initiates deformation. These inhomogeneities represent thermal or structural remnants from previous deformation phases and are imposed as a thermal anomaly, a variation in Moho geometry, or an inherited weak region. However, imposed initial heterogeneities do not fully capture the structural and thermal complexities of continental sutures. Here we present 2-D numerical experiments that investigate the role of inherited crustal structures in continental rifting and passive margin formation. We first examine a series of experiments in which we explicitly prescribe collisional structures in the initial setup, such as increased Moho depth and inherited thrust faults. Different prescribed collisional structures result in different rift to break-up durations, crustal shear zone patterns, and margin symmetry. Our second series of experiments actually creates an inherited collision zone through subduction and closure of an ocean. We use this set-up to investigate how extension localizes on a former continental collision zone. Passive margin architecture strongly depends on the duration of post-collision thermal equilibration time, with a long pause between collision and initiation of extension producing wide, faulted margins that take long to break-up. We find that the two approaches of prescribing or creating a suture zone to initiate a continental rift result in different dynamics of the crust and mantle, thereby impacting rift geometry, rift to break-up duration and exhumation of subduction-related sediments and oceanic crust.

  9. The Porcupine Basin: from rifting to continental breakup

    NASA Astrophysics Data System (ADS)

    Reston, Timothy; Gaw, Viola; Klaeschen, Dirk; McDermott, Ken

    2015-04-01

    Southwest of Ireland, the Porcupine Basin is characterized by axial stretching factors that increase southward to values greater than six and typical of rifted margins. As such, the basin can be regarded as a natural laboratory to investigate the evolution and symmetry of rifting leading towards continental separation and breakup, and in particular the processes of mantle serpentinisation, and the onset of detachment faulting. We have processed through to prestack depth migration a series of E-W profiles crossing the basin at different axial stretching factors and linked by a N-S profile running close to the rift axis. Our results constrain the structure of the basin and have implications for the evolution of rifted margins. In the north at a latitude of 52.25N, no clear detachment is imaged, although faults do appear to cut down into the mantle, so that serpentinisation may have started. Further south (51.75N), a bright re?ection (here named P) cuts down to the west from the base of the sedimentary section, is overlain by small fault blocks and appears to represent a detachment fault. P may in part follow the top of partially serpentinized mantle: this interpretation is consistent with gravity modelling, with numerical models of crustal embrittlement and mantle serpentinization during extension and with wide-angle data (see posters of Prada and of Watremez). Furthermore, P closely resembles the S re?ection west of Iberia, where such serpentinites are well documented. P develops where the crust was thinned to less than 3 km during rifting, again similar to S. Although overall the basin remains symmetrical, the consistent westward structural dip of the detachment implies that, at high stretching factors, extension became asymmetric. Analysis of the depth sections suggests that the detachment may have been active as a rolling hinge rooting at low-angle beneath the Porcupine Bank, consistent with the presence of a footwall of serpentinites. This requires very weak fault rocks, such as serpentinites. Reconstructions suggest that the detachment developed after the onset of serpentinisation and thus represents late stage of faulting within a complex polyphase rift history. Farther south still, a N-S running profile shows that P cuts up to form the top of the basement, and locally forms the top of what we interpret as exhumed mantle, since buried by postrift sediments. Thus detachment here appear to have been both responsible for the late-stage extension of the crust and the unroofing of the mantle. The same processes are likely to have occurred at magma poor rifted margins.

  10. Rifting, landsliding and magmatic variability in the Canary Islands

    NASA Astrophysics Data System (ADS)

    Carracedo, J. C.; Troll, V. R.; Guillou, H.; Badiola, E. R.; Pérez-Torrado, F. J.; Wiesmaier, S.; Delcamp, A.; Gonzalez, A. R.

    2009-04-01

    Rifts, probably the most influential structures in the geology of the Canary Islands, may also be responsible for the development of central felsic volcanoes, which are consistently nested in the collapse basins of the massive lateral collapses found in the Canaries. Three main types of post-collapse volcanism have been observed, particularly in the western Canaries: 1. Collapses followed by relatively scant, non-differentiated volcanism inside the collapse depression (El Golfo, El Hierro; La Orotava and Güímar, Tenerife), 2. those with important, although short-lasting (tens of thousands of years), post-collapse activity including felsic (phonolitic, trachytic) central volcanism (Bejenado, La Palma; Vallehermoso, La Gomera), and 3. those with very important, long-lasting (>100 kyr) post-collapse activity, evolving from primitive to felsic magmatism, eventually resulting in very high stratovolcanoes (Teide, Tenerife). Three consecutive sector collapses (Micheque, Güímar and La Orotava) mass-wasted the flanks of in the NE rift of Tenerife after intense and concentrated eruptive activity, particularly from about 1.10 Ma to 0.96 Ma, with periods of growth up to 15-25 m/kyr. Volcanic activity completely filled the Micheque collapse, evolving from basaltic to differentiated trachytic eruptions. Conversely, nested volcanism was less abundant in the Güímar and La Orotava collapses. This requires two fundamentally different scenarios which may be a function of active versus passive flank collapse trigger mechanisms: 1. The collapse occurs as a result of one of these short but intense intrusive-eruptive periods and probably triggered by concurring extensional stresses at the rifts (rift push), or 2. the giant landslide is derived only from gravitational instability. In the first scenario, the collapse of the flank of the rift may disrupt an established fissural feeding system that rapidly fills the collapse basin. Due to its disruption and the progressive new overburden of dense basaltic and ankaramitic lavas, the plumbing system increasingly favours shallow emplacement of new magma batches and subsequent differentiation, leading to intermediate and felsic nested eruptions. In contrast, a pure gravitational collapse will unload the edifice and allow for a limited amount of dense and primitive magma to erupt that may otherwise have been stored and solidified at depth, e.g. in upper mantle underplating zones. Rifts and their collapse may therefore act as an important factor in providing petrologic variability to oceanic volcanoes. Ad contrarium, it can be argued that felsic nested volcanoes in the Canaries frequently form because giant landslides provide the particular conditions required for primitive rift magmas to differentiate.

  11. Seismic structure of the uppermost mantle beneath the Kenya rift

    USGS Publications Warehouse

    Keller, Gordon R.; Mechie, J.; Braile, L.W.; Mooney, W.D.; Prodehl, C.

    1994-01-01

    A major goal of the Kenya Rift International Seismic Project (KRISP) 1990 experiment was the determination of deep lithospheric structure. In the refraction/wide-angle reflection part of the KRISP effort, the experiment was designed to obtain arrivals to distances in excess of 400 km. Phases from interfaces within the mantle were recorded from many shotpoints, and by design, the best data were obtained along the axial profile. Reflected arrivals from two thin (< 10 km), high-velocity layers were observed along this profile and a refracted arrival was observed from the upper high-velocity layer. These mantle phases were observed on record sections from four axial profile shotpoints so overlapping and reversed coverage was obtained. Both high-velocity layers are deepest beneath Lake Turkana and become more shallow southward as the apex of the Kenya dome is approached. The first layer has a velocity of 8.05-8.15 km/s, is at a depth of about 45 km beneath Lake Turkana, and is observed at depths of about 40 km to the south before it disappears near the base of the crust. The deeper layer has velocities ranging from 7.7 to 7.8 km/s in the south to about 8.3 km/s in the north, has a similar dip as the upper one, and is found at depths of 60-65 km. Mantle arrivals outside the rift valley appear to correlate with this layer. The large amounts of extrusive volcanics associated with the rift suggest compositional anomalies as an explanation for the observed velocity structure. However, the effects of the large heat anomaly associated with the rift indicate that composition alone cannot explain the high-velocity layers observed. These layers require some anisotropy probably due to the preferred orientation of olivine crystals. The seismic model is consistent with hot mantle material rising beneath the Kenya dome in the southern Kenya rift and north-dipping shearing along the rift axis near the base of the lithosphere beneath the northern Kenya rift. This implies lithosphere thickening towards the north and is consistent with a thermal thinning of the lithosphere from below in the south changing to thinning of the lithosphere due to stretching in the north. ?? 1994.

  12. 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).

  13. Thermal Evolution of Continental Rifting in Corsica (France)

    NASA Astrophysics Data System (ADS)

    Seymour, N. M.; Stockli, D. F.; Beltrando, M.; Smye, A.

    2014-12-01

    Present thermal evolution models for continental rifting are based on pure-shear extension (McKenzie 1978), in which crustal and mantle strain is co-located and all rocks cool throughout rifting. However, the multi-phase rift model of Lavier and Manatschal (2006) accommodates lithospheric extension via spatially offset crustal and mantle strains, producing depth-dependent thinning and exhumation of lithospheric mantle. Significant reheating of the upper plate is a natural consequence of this model. We seek to constrain the temperature-time history of the upper-plate Tethyan margin preserved in Corsica to discriminate between the two thermal models. A record of the conditions and timing of reheating is preserved in the age and trace element compositions of metamorphic zircon overgrowths. Zircon from the hanging wall and footwall of the Jurassic-age Belli Piani shear zone (Beltrando et al 2013) were depth-profiled for both U-Pb and trace element concentrations via LA-ICP-MS split streaming. Across both sides of the shear zone, U-Pb ages show a strong population of 275-300 Ma grains. However, a subset of footwall grains show 165-210 Ma overgrowths. These ages indicate that the margin reached temperature conditions sufficient for zircon saturation and subsequent zircon growth. These lower crustal findings are consistent with prior observations made within the sedimentary succession, which records rapid thermal uplift, karstification, and subsequent drowning of Triassic dolostones contemporaneous with the opening of the Alpine Tethys (Decarlis and Lualdis 2008). Ti-in-zircon thermometry yields temperatures of ~720°C in the hanging wall and ~830°C in the footwall. This is consistent with the appearance of overgrowths, and provides further support that the Belli Piani shear zone was active during Jurassic rifting. Collectively, these data point directly to a rift-coeval reheating event that affected the entire crustal pile and lend support to the multi-stage Lavier and Manatschal model.

  14. Crustal structure beneath the Kenya Rift from axial profile data

    USGS Publications Warehouse

    Mechie, J.; Keller, Gordon R.; Prodehl, C.; Gaciri, S.; Braile, L.W.; Mooney, W.D.; Gajewski, D.; Sandmeier, K.-J.

    1994-01-01

    Modelling of the KRISP 90 axial line data shows that major crustal thinning occurs along the axis of the Kenya Rift from Moho depths of 35 km in the south beneath the Kenya Dome in the vicinity of Lake Naivasha to 20 km in the north beneath Lake Turkana. Low Pn velocities of 7.5-7.7 km/s are found beneath the whole of the axial line. The results indicate that crustal extension increases to the north and that the low Pn velocities are probably caused by magma (partial melt) rising from below and being trapped in the uppermost kilometres of the mantle. Along the axial line, the rift infill consisting of volcanics and a minor amount of sediments varies in thickness from zero where Precambrian crystalline basement highs occur to 5-6 km beneath the lakes Turkana and Naivasha. Analysis of the Pg phase shows that the upper crystalline crust has velocities of 6.1-6.3 km/s. Bearing in mind the Cainozoic volcanism associated with the rift, these velocities most probably represent Precambrian basement intruded by small amounts of igneous material. The boundary between the upper and lower crusts occurs at about 10 km depth beneath the northern part of the rift and 15 km depth beneath the southern part of the rift. The upper part of the lower crust has velocities of 6.4-6.5 km/s. The basal crustal layer which varies in thickness from a maximum of 2 km in the north to around 9 km in the south has a velocity of about 6.8 km/s. ?? 1994.

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

    NASA Astrophysics Data System (ADS)

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

    1993-06-01

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

  16. Galapagos Rift at 86°W: 3. Sheet flows, collapse pits, and lava lakes of the rift valley

    Microsoft Academic Search

    Robert D. Ballard; Robin T. Holcomb; Tjeerd H. van Andel

    1979-01-01

    It has long been known that pillow basalts are a dominant feature of oceanic volcanism on midocean ridges. Recent studies in the Cayman Trough, East Pacific Rise, and Galapagos Rift valley have shown that sheet flows are also an important component, especially on ridges with intermediate and fast opening rates. This paper describes the surface forms of such sheet flows

  17. The origin of high bicarbonate and fluoride concentrations in waters of the Main Ethiopian Rift Valley, East African Rift system

    Microsoft Academic Search

    Berhanu Gizaw

    1996-01-01

    Thermal waters in the Main Ethiopian Rift Valley are characterized by high Na, bicarbonate and fluoride concentrations, and near-neutral to alkaline pH. Sodium, bicarbonate and fluoride are positively correlated in the waters. The principal reason for the bicarbonate in the area is the high rate of carbon dioxide outgassing. This, combined with acid volcanics, geothermal heating, low Ca and low

  18. Orphan Basin: Multiple `Failed' Rifting During Early Opening of the North Atlantic.

    NASA Astrophysics Data System (ADS)

    Skogseid, J.; Barnwell, A.; Aarseth, E. S.; Alsgaard, P. C.; Briseid, H. C.; Zwach, C.

    2004-05-01

    New seismic data from the Orphan Basin, offshore Newfoundland, Canada, allowed interpretation of a shallow Moho beneath almost the entire basin. Two semi-parallel `central rift zones', characterized by particularly thin crust, indicate that sea-floor spreading may have been initiated. The stratigraphic relationships indicate that the first episode of rifting took place from Triassic trough Jurassic time, eventually creating a deep rift trough close to the Flemish Cap, whereas a second episode of Early Cretaceous rifting established a new rift zone along the northwestern flank of the Jurassic basin. The total duration of rifting concurs with the suggested duration of rifting from published plate tectonic models for the Newfoundland-Iberia separation (e.g. Plates Project), but put new constraints on the early opening of the Rockall Trough off Britain. Both Orphan Basin rift zones demonstrate an unusual degree of crustal thinning over broad areas towards the northeast, rapidly narrowing southwestwards. The Jurassic `central rift zone' is partly associated with a significant Bouguer gravity anomaly indicating isostatically uncompensated shallow mantle. Despite the fact that the crust is thinned down to only 4 km locally, no igneous rocks are inferred from the seismic data. We suggest that the slow rifting has caused significantly higher thinning of the crust than of the mantle, and thus caused more syn-rift subsidence than in a uniform stretching scenario. From a rifted margin point of view it is intriguing that the Jurassic rift zone was abandoned and that subsequent lithospheric deformation created a Cretaceous rift zone side by side the older one. From a plate tectonic view, however, the tectonic evolution of the Orphan Basin nicely fits with a successively westward stepping between rift zones west of Britain. The Porcupine Basin, for example, appears to link up with the Jurassic Orphan Basin; whereas the Rockall Trough at that time formed a continuous structure with the Cretaceous Orphan Basin. The most spectacular feature related to the Cretaceous rift zone is the extreme extension seen on individual upper crustal fault blocks. Up to 20 km heave on the main bounding fault can be mapped out over a length of c.100kms. To the northeast the rift is very broad and igneous rocks may exist along a symmetric central `graben', whereas the rift zone rapidly narrows south-westward, making an almost 90 degree bend and dying out into just one deep and narrow trough.

  19. Aerosol and Cloud Microphysical Characteristics of Rifts and Gradients in Maritime Stratocumulus Clouds

    NASA Technical Reports Server (NTRS)

    Sharon, Tarah M.; Albrecht, Bruce A.; Jonsson, Haflidi H.; Minnis, Patrick; Khaiyer, Mandana M.; Van Reken, Timothy; Seinfeld, John; Flagan, Rick

    2008-01-01

    A cloud rift is characterized as a large-scale, persistent area of broken, low reflectivity stratocumulus clouds usually surrounded by a solid deck of stratocumulus. A rift observed off the coast of Monterey Bay, California on 16 July 1999 was studied to compare the aerosol and cloud microphysical properties in the rift with those of the surrounding solid stratus deck. Variables measured from an instrumented aircraft included temperature, water vapor, and cloud liquid water. These measurements characterized the thermodynamic properties of the solid deck and rift areas. Microphysical measurements made included aerosol, cloud drop and drizzle drop concentrations and cloud condensation nuclei (CCN) concentrations. The microphysical characteristics in a solid stratus deck differ substantially from those of a broken, cellular rift where cloud droplet concentrations are a factor of 2 lower than those in the solid cloud. Further, CCN concentrations were found to be about 3 times greater in the solid cloud area compared with those in the rift and aerosol concentrations showed a similar difference as well. Although drizzle was observed near cloud top in parts of the solid stratus cloud, the largest drizzle rates were associated with the broken clouds within the rift area. In addition to marked differences in particle concentrations, evidence of a mesoscale circulation near the solid cloud rift boundary is presented. This mesoscale circulation provides a mechanism for maintaining a rift, but further study is required to understand the initiation of a rift and the conditions that may cause it to fill.

  20. Fault evolution in the Potiguar rift termination, Equatorial margin of Brazil

    NASA Astrophysics Data System (ADS)

    de Castro, D. L.; Bezerra, F. H. R.

    2014-10-01

    The transform shearing between South American and African plates in the Cretaceous generated a series of sedimentary basins on both plate margins. In this study, we use gravity, aeromagnetic, and resistivity surveys to identify fault architecture and to analyse the evolution of the eastern Equatorial margin of Brazil. Our study area is the southern onshore termination of the Potiguar rift, which is an aborted NE-trending rift arm developed during the breakup of Pangea. The Potiguar rift is a Neocomian structure located in the intersection of the Equatorial and western South Atlantic and is composed of a series of NE-trending horsts and grabens. This study reveals new grabens in the Potiguar rift and indicates that stretching in the southern rift termination created a WNW-trending, 10 km wide and ~40 km long right-lateral strike-slip fault zone. This zone encompasses at least eight depocenters, which are bounded by a left-stepping, en-echelon system of NW- to EW-striking normal faults. These depocenters form grabens up to 1200 m deep with a rhomb-shaped geometry, which are filled with rift sedimentary units and capped by post-rift sedimentary sequences. The evolution of the rift termination is consistent with the right-lateral shearing of the Equatorial margin in the Cretaceous and occurs not only at the rift termination, but also as isolated structures away from the main rift.

  1. Rift zone reorganization through flank instability in ocean island volcanoes: an example from Tenerife, Canary Islands

    NASA Astrophysics Data System (ADS)

    Walter, T. R.; Troll, V. R.; Cailleau, B.; Belousov, A.; Schmincke, H.-U.; Amelung, F.; Bogaard, P.

    2005-04-01

    The relationship between rift zones and flank instability in ocean island volcanoes is often inferred but rarely documented. Our field data, aerial image analysis, and 40Ar/39Ar chronology from Anaga basaltic shield volcano on Tenerife, Canary Islands, support a rift zone—flank instability relationship. A single rift zone dominated the early stage of the Anaga edifice (~6-4.5 Ma). Destabilization of the northern sector led to partial seaward collapse at about ~4.5 Ma, resulting in a giant landslide. The remnant highly fractured northern flank is part of the destabilized sector. A curved rift zone developed within and around this unstable sector between 4.5 and 3.5 Ma. Induced by the dilatation of the curved rift, a further rift-arm developed to the south, generating a three-armed rift system. This evolutionary sequence is supported by elastic dislocation models that illustrate how a curved rift zone accelerates flank instability on one side of a rift, and facilitates dike intrusions on the opposite side. Our study demonstrates a feedback relationship between flank instability and intrusive development, a scenario probably common in ocean island volcanoes. We therefore propose that ocean island rift zones represent geologically unsteady structures that migrate and reorganize in response to volcano flank instability.

  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. Seismic studies of the East African Rift System and the Tibetan Plateau: Implications for the rheology of lithosphere and the evolution of rifts in continents

    Microsoft Academic Search

    Zhaohui Yang

    2009-01-01

    This dissertation investigates rheology of the continental lithosphere and evolution of continental rifts using earthquake source parameters, precisely determined from waveforms and travel-times in two target regions. First, I investigate the distribution of focal depths for earthquakes that occurred along the East African Rift System (EARS), using both new results of this study and reports from the literature. Three different

  4. Albertine Rift, Uganda: Deformation-Sedimentation-Erosion relationships

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    The Albertine Rift is the northern part of the western branch of the East African Rift that runs over a distance of around 2000 km from Lake Albert in the north to Lake Malawi in the south. Lake Albert Basin is assumed to be a classical half-graben initiated around 12 Ma and oriented NNW-SSW, with a major northwesterly bounding fault - the Bunia fault - located along the western Congolese shoreline (Ebinger, 1989; Pickford & al., 1993). The aim of this study is to understand the relationships between deformation, erosion, and sedimentation of the rift through time by restoring (1) the timing and amplitude of vertical movements (subsidence, uplift), (2) the geometry and paleo-environmental evolution (including climate) of the sedimentary infilling and (3) the geomorphological evolution of the surrounding area and associated erosion budget. Seismic data and outcrops studies suggest a much more complex history than previously described. (1) The age model, mainly based on mammal fossils (Pickford et al., 1993; Van Damme and Pickford, 2003), is debated, but the early stage of the rift is probably Middle Miocene. (2) No half-graben geometry has been characterized: the infilling consists of juxtaposed tabular compartments with sharp thicknesses variations along bounding faults, in response of either low rate extensional or combined strike-slip/extensional movements. The following onshore-offshore evolution is proposed: - Middle Miocene (~ 13 Ma) to Late Miocene (?): rifting 1 - differential subsidence along N60° faults - major deepening from fluvio-deltaic to deep lacustrine environments (maximum flooding at 8 Ma) - uplift, erosion and reworking of weathered profiles - first generation of pediments. - Late Miocene (?) to Late Pliocene (~ 3 Ma): quiescence phase - homogenous subsidence - lacustrine clays interbedded with sandy flood-lobes - uplift, erosion and reworking of ferruginous laterite (iron duricrusts) - second generation of pediments. - Late Pliocene (~ 3Ma) to Early Pleistocene (~ 2 Ma): rifting 2 - major uplift and growth of the Ruwenzori Mountains (5000 m of elevation) - differential subsidence - deltaic to wave-dominated coast (shoreface) sandy deposits - pediments degradation by fluvial erosion. - Middle-Late Pleistocene: late regional uplift and tilting - drainage inversion and present-day scarp formation.

  5. Radial Anisotropy beneath the Main Ethiopian Rift and Afar Depression

    NASA Astrophysics Data System (ADS)

    Accardo, N. J.; Gaherty, J. B.; Jin, G.; Shillington, D. J.

    2014-12-01

    The Main Ethiopian Rift (MER) and Afar uniquely capture the final stages of transition from continental rifting in the broader East African Rift System 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 rift 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 rift 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 anisotropy. The pronounced changes in the depth extent of slow velocities and strength of anisotropy interpreted to be associated with asthenosphere may reflect variations in the distribution and magnitude of temperature anomalies/melt between continental rifting in the MER and incipient, hot-spot influenced seafloor spreading in Afar.

  6. 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 the amount of volcanism. This volcanic activity would suggest large-scale modification of the crust by magmatism. Although there is evidence of underplating in the form of a relatively high-velocity lower crustal layer, there are no major seismic velocity anomalies in the middle and upper crust which would suggest pervasive magmatism. This apparent lack of major modification is an enigma which requires further study. ?? 1994.

  7. Distributed Nubia-Somalia relative motion and dike intrusion in the Main Ethiopian Rift

    NASA Astrophysics Data System (ADS)

    Bendick, R.; McClusky, S.; Bilham, R.; Asfaw, L.; Klemperer, S.

    2006-04-01

    The Main Ethiopian Rift (MER) in central Ethiopia extended in the rift-normal direction at a mean rate of 4.0 +/- 0.9 mm yr-1 (1?) during the period 1992-2003, nearly a factor of two slower than the opening rate estimated from global plate motion inversions. Rift opening near a geodetic array during this period was accommodated by a single dike injection event in 1993, spatially coincident with active magmatic segments, probably triggered by observed seismicity. Following dike injection, the crust in the rift relaxed as a layered medium, with a ~15-km-thick elastic lid over a viscous half space of 1018 Pa s. Diking, rather than normal faulting on rift-bounding faults, appears to be the predominant mechanism of extension in the MER, explaining the very low regional rates of moment release. The length scale and temporal behaviour of surface displacements require viscoelastic rheology in the rift.

  8. Novel approaches to develop Rift Valley fever vaccines

    PubMed Central

    Indran, Sabarish V.; Ikegami, Tetsuro

    2012-01-01

    Rift Valley fever (RVF) is endemic to sub-Saharan Africa, and has spread into Madagascar, Egypt, Saudi Arabia, and Yemen. Rift Valley fever virus (RVFV) of the family Bunyaviridae, genus Phlebovirus causes hemorrhagic fever, neurological disorders or blindness in humans, and high rate abortion and fetal malformation in ruminants. RVFV is classified as a Category A Priority pathogen and overlap select agent by CDC/USDA due to its potential impact on public health and agriculture. There is a gap in the safety and immunogenicity in traditional RVF vaccines; the formalin-inactivated RVFV vaccine TSI-GSD-200 requires three doses for protection, and the live-attenuated Smithburn vaccine has a risk to cause abortion and fetal malformation in pregnant ruminants. In this review, problems of traditional vaccines and the safety and efficacy of recently reported novel RVF candidate vaccines including subunit vaccines, virus vector, and replicons are discussed. PMID:23112960

  9. Rift Valley Fever in Small Ruminants, Senegal, 2003

    PubMed Central

    Lancelot, Renaud; Thiongane, Yaya; Sall, Baba; Diaité, Amadou; Mondet, Bernard

    2005-01-01

    During the 2003 rainy season, the clinical and serologic incidence of Rift Valley fever was assessed in small ruminant herds living around temporary ponds located in the semi-arid region of the Ferlo, Senegal. No outbreak was detected by the surveillance system. Serologic incidence was estimated at 2.9% (95% confidence interval 1.0–8.7) and occurred in 5 of 7 ponds with large variations in the observed incidence rate (0%–20.3%). The location of ponds in the Ferlo Valley and small ponds were correlated with higher serologic incidence (p = 0.0005 and p = 0.005, respectively). Rift Valley fever surveillance should be improved to allow early detection of virus activity. Ruminant vaccination programs should be prepared to confront the foreseeable higher risks for future epidemics of this disease. PMID:16318720

  10. Rifting, rotation, detachment faulting, and sedimentation: Miocene evolution of the southern California margin

    SciTech Connect

    Bachman, S.B.; Crouch, J.K. (Crouch, Bachman, and Associates, Inc., Santa Barbara, CA (USA))

    1990-05-01

    The evolution of the Los Angeles and adjacent offshore Santa Monica and San Pedro basins of southern California began during the earliest Miocene. The basins formed as the result of rifting and subsequent large scale rotation of segments within a preexisting Mesozoic-Paleogene forearc basin. Clockwise rotation (less than 90{degree}) of the outer two-thirds of this fore-arc basin during the early and middle Miocene moved these once north-trending forearc strata into an east-west trend (the modern Transverse Ranges). The eastern margin of the initial rift remains in its original location and is best documented from outcrop and subsurface data in the San Joaquin Hills. What was once the western margin of the rift has been rotated to a position north of the rift, along the southern Santa Monica Mountains. The early Miocene Vaqueros sandstones. which that are entirely shallow-marine and thousands of feet thick provide evidence for initial subsidence of the rift. Widening of the rift and separation of the Santa Monica Mountains and the San Joaquin Hills in the early and middle Miocene was accompanied by detachment faulting and volcanism along the rift margins. These detachment faults can be documented in the subsurface of the San Joaquin Hills and in outcrop in the Santa Monica Mountains. A unique aspect of this inner borderland rift is the rapid uplift, exposure, erosion, and then subsidence of high pressure/temperature metamorphic basement blocks (Catalina schist) within the rift itself. These basement rocks were buried 20 to 30 km beneath the ancestral fore arc prior to rifting. They were uplifted, perhaps due to thermal effects, during pervasive early and middle Miocene volcanism within the rift. Evidence of these dramatic events is provided by the distinctive San Onofre breccia deposit exposed along the margins of the rift.

  11. Faulting of the lithosphere during extension and related rift-flank uplift: a numerical study

    Microsoft Academic Search

    Till Sachau; Daniel Koehn

    2010-01-01

    In this contribution, we present a new model of passive rifting and related rift-flank uplift. The numerical model is based\\u000a on a lattice spring network coupled with a viscous particle model so that we can simulate visco-elasto-plastic behaviour with\\u000a dynamic fault development. In our model, we show that rift-flank uplift can be achieved best when extension in the crust is

  12. A model for Iapetan rifting of Laurentia based on Neoproterozoic dikes and related rocks

    USGS Publications Warehouse

    Burton, William C.; Southworth, Scott

    2010-01-01

    Geologic evidence of the Neoproterozoic rifting of Laurentia during breakup of Rodinia is recorded in basement massifs of the cratonic margin by dike swarms, volcanic and plutonic rocks, and rift-related clastic sedimentary sequences. The spatial and temporal distribution of these geologic features varies both within and between the massifs but preserves evidence concerning the timing and nature of rifting. The most salient features include: (1) a rift-related magmatic event recorded in the French Broad massif and the southern and central Shenandoah massif that is distinctly older than that recorded in the northern Shenandoah massif and northward; (2) felsic volcanic centers at the north ends of both French Broad and Shenandoah massifs accompanied by dike swarms; (3) differences in volume between massifs of cover-sequence volcanic rocks and rift-related clastic rocks; and (4) WNW orientation of the Grenville dike swarm in contrast to the predominately NE orientation of other Neoproterozoic dikes. Previously proposed rifting mechanisms to explain these features include rift-transform and plume–triple-junction systems. The rift-transform system best explains features 1, 2, and 3, listed here, and we propose that it represents the dominant rifting mechanism for most of the Laurentian margin. To explain feature 4, as well as magmatic ages and geochemical trends in the Northern Appalachians, we propose that a plume–triple-junction system evolved into the rift-transform system. A ca. 600 Ma mantle plume centered east of the Sutton Mountains generated the radial dike swarm of the Adirondack massif and the Grenville dike swarm, and a collocated triple junction generated the northern part of the rift-transform system. An eastern branch of this system produced the Long Range dike swarm in Newfoundland, and a subsequent western branch produced the ca. 554 Ma Tibbit Hill volcanics and the ca. 550 Ma rift-related magmatism of Newfoundland.

  13. Stratigraphic and structural evolution of the Selenga Delta Accommodation Zone, Lake Baikal Rift, Siberia

    Microsoft Academic Search

    C. A. Scholz; D. R. Hutchinson

    2000-01-01

    Seismic reflection profiles from the Lake Baikal Rift reveal extensive details about the sediment thickness, structural geometry\\u000a and history of extensional deformation and syn-rift sedimentation in this classic continental rift. The Selenga River is the\\u000a largest single source of terrigenous input into Lake Baikal, and its large delta sits astride the major accommodation zone\\u000a between the Central and South basins

  14. Distributed Nubia-Somalia relative motion and dike intrusion in the Main Ethiopian Rift

    Microsoft Academic Search

    R. Bendick; S. McClusky; R. Bilham; L. Asfaw; S. Klemperer

    2006-01-01

    The Main Ethiopian Rift (MER) in central Ethiopia extended in the rift-normal direction at a mean rate of 4.0 +\\/- 0.9 mm yr-1 (1sigma) during the period 1992-2003, nearly a factor of two slower than the opening rate estimated from global plate motion inversions. Rift opening near a geodetic array during this period was accommodated by a single dike injection

  15. Extension across the Laptev Sea continental rifts constrained by gravity modeling

    NASA Astrophysics Data System (ADS)

    Mazur, S.; Campbell, S.; Green, C.; Bouatmani, R.

    2015-03-01

    The Laptev Shelf is the area where the Gakkel Ridge, an active oceanic spreading axis, approaches a continental edge, causing a specific structural style dominated by extensive rift structures. From the latest Cretaceous to the Pliocene, extension exerted on the Laptev Shelf created there several deep subsided rifts and high-standing basement blocks. To understand syn-rift basin geometries and sediment supply relationships across the Laptev Shelf, accurate extension estimates are essential. Therefore, we used 2-D gravity modeling and 3-D gravity inversion to constrain the amount of crustal stretching across the North America-Eurasia plate boundary in the Laptev Shelf. The latest Cretaceous-Cenozoic extension in that area is partitioned among two rift zones, the Laptev Rift System and the New Siberian Rift. These rifts were both overprinted on the Eurasian margin that had been stretched by 190-250 km before the Late Cretaceous. While the Laptev Rift System, connected to the Gakkel Ridge, reveals increasing extension toward the shelf edge (190-380 km), the New Siberian Rift is characterized by approximately uniform stretching along strike (110-125 km). The architecture of the Laptev Rift System shows that the finite extension of about 500 km is sufficient to entirely eliminate crystalline continental crust. In the most stretched rift segment, continental mantle is exhumed at the base of the Late Mesozoic basement. The example of the Laptev Rift System shows that extension driven by divergent plate movement is a sufficient cause to produce almost complete continental breakup without an increased heat input from the asthenospheric mantle.

  16. Seismic Investigations of an Accommodation zone in the Northern Rio Grande Rift, New Mexico, USA

    NASA Astrophysics Data System (ADS)

    Baldridge, W. S.; Valdes, J.; Nedorub, O.; Phrampus, B.; Braile, L. W.; Ferguson, J. F.; Benage, M. C.; Litherland, M.

    2010-12-01

    Seismic reflection and refraction data acquired in the Rio Grande rift near Santa Fe, New Mexico, in 2009 and 2010 by the SAGE (Summer of Applied Geophysical Experience) program imaged the La Bajada fault (LBF) and strata offset across the associated, perpendicular Budagher fault (BF). The LBF is a major basin-bounding normal fault, offset down to the west; the smaller BF is an extensional fault that breaks the hanging wall ramp of the LBF. We chose this area because it is in a structurally complex region of the rift, comprising a small sub-basin and plunging relay ramps, where north-trending, en echelon basin-bounding faults (including the LBF) transfer crustal extension laterally between the larger Española (to north) and Albuquerque rift basins. Our data help determine the precise location and geometry of the poorly exposed LBF, which, near the survey location, offsets the rift margin vertically about 3,000 m. When integrated with industry reflection data and other SAGE seismic, gravity, and magnetotelluric surveys, we are able to map differences in offset and extension laterally (especially southward) along the fault. We interpret only about 200 m of normal offset across the BF. Our continuing work helps define multiple structural elements, partly buried by syn-rift basin-filling sedimentary rocks, of a complex intra-rift accommodation zone. We are also able to discriminate pre-Eocene (Laramide) from post-Miocene (rift) structures. Our data help determine the amount of vertical offset of pre-rift strata across structural elements of the accommodation zone, and depth and geometry of basin fill. A goal is to infer the kinematic development of this margin of the rift, linkages among faults, growth history, and possible pre-rift structural controls. This information will be potentially useful for evaluation of resources, including oil and/or gas in pre-rift strata and ground water in Late Miocene to Holocene rift-filling units.

  17. Erosion of Terrestrial Rift Flank Topography: A Quantitative Study

    NASA Technical Reports Server (NTRS)

    Weissel, Jeffrey K.

    1999-01-01

    Many rifted or passive continental margins feature a seaward-facing erosional escarpment which abruptly demarcates deeply weathered, low relief, interior uplands from a deeply incised, high relief coastal zone. It is generally accepted that these escarpments originate at the time of continental rifting and propagate inland through the elevated rift flank topography at rates on the order of 1 km/Myr over the course of a margin's history. Considering the length of passive margins worldwide and an average rift flank plateau height of several hundred meters, it is clear that sediment eroded from passive margins is an important component of the mass flux from continents to oceans through geologic time. The overall goal of the research reported here is to develop a quantitative understanding of the kinematics of escarpment propagation across passive margins and the underlying geological processes responsible for this behavior. Plateau-bounding escarpments in general exhibit two basic forms depending on the direction of surface water drainage on the plateau interior relative to the escarpment. Where surface water flows away from the escarpment, the escarpment takes the form of subdued embayments and promontories, such that its overall trend remains fairly straight as it evolves with time. Where upland streams flow across the escarpment, it takes the form of dramatic, narrow gorges whose heads appear to propagate up the plateau drainage systems as large-scale knickpoints. From work on the Colorado Plateau, Schmidt (1987) noted that the Colorado River is located much closer to the Grand Canyon's south rim, a drainage divide escarpment, than to the north rim, which is a gorge-like escarpment. The main implication is that the gorge-like form might be associated with higher long-term average erosion rates compared to the drainage divide escarpment type.

  18. Rifted continental margins: The case for depth-dependent extension

    NASA Astrophysics Data System (ADS)

    Huismans, Ritske S.; Beaumont, Christopher

    2014-12-01

    Even though many basic properties of non-volcanic rifted margins are predicted by uniform extension of the lithosphere, uniform extension fails to explain other important characteristics. Particularly significant discrepancies are observed at: 1) the Iberia-Newfoundland conjugate margins (Type I), where large tracts of continental mantle lithosphere are exposed at the seafloor, and at 2) ultra-wide central South Atlantic margins (Type II) where continental crust spans wide regions below which it appears that lower crust and mantle lithosphere were removed. Neither corresponds to uniform extension in which crust and mantle thin by the same factor. Instead, either the crust or mantle lithosphere has been preferentially removed during extension. We show that the Type I and II styles are respectively reproduced by dynamical numerical lithospheric stretching models (Models I-A/C and II-A/C) that undergo depth-dependent extension. In this notation A and C imply underplating of the rift zone during rifting by asthenosphere and lower cratonic lithosphere, respectively. We also present results for models with a weak upper crust and strong lower crust, Models III-A/C, to show that lower crust can also be removed from beneath the rift zone by horizontal advection with the mantle lithosphere. From the model results we infer that these Type I, II, and III margin styles are controlled by the strength of the mid/lower crust, which determines the amount of decoupling between upper and lower lithosphere during extension and the excision of crust or mantle. We also predict the styles of sedimentary basins that form on these margins as a test of the concepts presented.

  19. Rifted Continental Margins: The Case for Depth-Dependent Extension

    NASA Astrophysics Data System (ADS)

    Huismans, Ritske S.; Beaumont, Christopher

    2015-04-01

    Even though many basic properties of non-volcanic rifted margins are predicted by uniform extension of the lithosphere, uniform extension fails to explain other important characteristics. Particularly significant discrepancies are observed at: 1) the Iberia-Newfoundland conjugate margins (Type I), where large tracts of continental mantle lithosphere are exposed at the seafloor, and at; 2) ultra-wide central South Atlantic margins (Type II) where continental crust spans wide regions below which it appears that lower crust and mantle lithosphere were removed. Neither corresponds to uniform extension in which crust and mantle thin by the same factor. Instead, either the crust or mantle lithosphere has been preferentially removed during extension. We show that the Type I and II styles are respectively reproduced by dynamical numerical lithospheric stretching models (Models I-A/C and II-A/C) that undergo depth-dependent extension. In this notation A and C imply underplating of the rift zone during rifting by asthenosphere and lower cratonic lithosphere, respectively. We also present results for models with a weak upper crust and strong lower crust, Models III-A/C, to show that lower crust can also be removed from beneath the rift zone by horizontal advection with the mantle lithosphere. From the model results we infer that these Types I, II, and III margin styles are controlled by the strength of the mid/lower crust, which determines the amount of decoupling between upper and lower lithosphere during extension and the excision of crust or mantle. We also predict the styles of sedimentary basins that form on these margins as a test of the concepts presented.

  20. Seismic Evidence for an Active Southern Rio Grande Rift

    NASA Astrophysics Data System (ADS)

    Thompson, L. E.; Velasco, A. A.

    2010-12-01

    Competing models exist to explain what caused the Earth’s crust to spread apart 29 million years ago to create a region known today as the Rio Grande Rift (RGR). The RGR extends from central Colorado through New Mexico to northern Mexico, near El Paso. A growing body of evidence shows that geologic activity still occurs in the RGR, with a continuation of faulting, seismicity and a small widening rate. We map of the seismic velocity structure and crustal thickness using data from the Rio Grande Rift Seismic TRAnsect (RISTRA) experiment and the EarthScope Transportable Array (USArray) dataset. In addition to the data we collected from the RISTRA experiment and USArray dataset, we also acquired receiver functions from the EarthScope Automatic Receiver Survey (EARS) website (http://www.earthscope.org/data) and waveform data from the Incorporated Research Institutes for Seismology (IRIS) Data Management Center (DMC). In particular, we requested seismograms from the IRIS DMC database where we acquired teleseismic events from Jan 2000 to Dec 2009. This includes 7,259 seismic events with a minimum magnitude of 5.5 and 106,389 continuous waveforms. This data was preprocessed (merged, rotated) using a program called Standing Order of Data (SOD). We computed receiver functions and receiver function stacks for all data in the Southern Rio Grande Rift (SRGR). We map the crustal thickness, seismic velocity, and mantle structure to better determine the nature of tectonic activity that is presently taking place and further investigate the regional extension of the Southern Rio Grande Rift (SRGR). Here we present results of the crustal and velocity structure using the kriging interpolation scheme and interpret our results in relation to southern RGR deformation and extension.

  1. The Sagatu Ridge dike swarm, Ethiopian rift margin. [tectonic evolution

    NASA Technical Reports Server (NTRS)

    Mohr, P. A.; Potter, E. C.

    1976-01-01

    A swarm of dikes forms the core of the Sagatu Ridge, a 70-km-long topographic feature elevated to more than 4000 m above sea level and 1500 m above the level of the Eastern (Somalian) plateau. The ridge trends NNE and lies about 50 km east of the northeasterly trending rift-valley margin. Intrusion of the dikes and buildup of the flood-lava pile, largely hawaiitic but with trachyte preponderant in the final stages, occurred during the late Pliocene-early Pleistocene and may have been contemporaneous with downwarping of the protorift trough to the west. The ensuing faulting that formed the present rift margin, however, bypassed the ridge. The peculiar situation and orientation of the Sagatu Ridge, and its temporary existence as a line of crustal extension and voluminous magmatism, are considered related to a powerful structural control by a major line of Precambrian crustal weakness, well exposed further south. Transverse rift structures of unknown type appear to have limited the development of the ridge to the north and south.

  2. Post-rifting relaxation in the Afar region, Ethiopia

    NASA Astrophysics Data System (ADS)

    Nooner, Scott L.; Bennati, Laura; Calais, Eric; Buck, W. Roger; Hamling, Ian J.; Wright, Tim J.; Lewi, Elias

    2009-11-01

    Crustal accretion at divergent plate boundaries typically occurs via the periodic intrusion of dikes, but their emplacement and the associated deformation are rarely observed. The few existing observations at subaerial rifts show that these diking events are followed by a decadal-scale period with extension rates faster than the secular divergent plate motion. This transient accelerated deformation has been explained by continued subsurface magma injection or by relaxation, in the viscoelastic mantle, of the stress changes imparted by dike opening. For the first time, GPS measurements were collected within a few months of a rifting event at a major plate boundary, the September 2005, 60 km-long dike intrusion in the Dabbahu segment, Afar, Ethiopia. Extension rates for the first 3 years greatly exceed the plate motion (Nubia-Arabia) secular divergence rate, even at sites located more than 60 km from the rift axis. Here we show that these observations are consistent with stress relaxation in a viscoelastic upper mantle with a viscosity of about 5 × 1018 Pa·s overlain by a 12-14 km-thick elastic crust. The alternative model of continued diking requires continuous opening well below the Moho and is therefore unlikely. Instead, magma injection in Afar since June 2006 has taken the form of smaller discrete diking events, tapping into a mid-crustal melt reservoir under the segment center.

  3. Seismological constraints on lithospheric structure beneath rifted margins

    NASA Astrophysics Data System (ADS)

    Fishwick, Stewart

    2014-05-01

    There is considerable variation in both topography and crustal architecture along passive margins worldwide. However, the variations in lithospheric mantle structure are less well studied. This is, perhaps, in part due to the technical challenge for offshore-onshore passive seismology and also the lower resolution obtained in most mantle studies, particularly when compared to detailed imaging of the crust available from reflection seismology. The available large scale observations of mantle structure (predominately from surface waves), and crustal structure (from receiver functions) for the continental region adjacent to the margins are reviewed. Results for Africa and Australia show clear correlations between the mantle structure and the present day topography of the margin, and this relationship is explored from a worldwide perspective. Seismic studies can also provide information on lithospheric thickness at the margin, which can be used as an additional constraint for the thermal modelling of basin structure. In this case the limitations include the depth resolution of the method, and the particular proxy used to extract a lithospheric thickness estimate from a seismic model. Perhaps most importantly, is to remember that these seismological observations tell us only the existing structure. The challenge remains how to decipher whether the present structures relate to inherited pre-rift architecture; to alteration of lithospheric mantle during rifting, or to much later post rift changes associated with separate tectonic events.

  4. Rifting and early tectonic evolution of the equatorial Atlantic

    SciTech Connect

    Szatmari, P.; Zanotto, O.; Francolin, J.; Wolff, S.

    1985-01-01

    The Equatorial Atlantic forms a giant transform connecting the Central and the South Atlantic between northwest Africa and Brazil. Improved onshore mapping and offshore seismic and drilling by Petrobras permitted the differentiation of the following phases in the tectonic evolution of the Equatorial Atlantic: (1) Basaltic volcanism along the eastern and southern margins of the Guyanan Shield during Triassic-Jurassic time as North America separated from Gondwana. (2) During Early Cretaceous time, clockwise rotation of South America caused rifting east of Fortaleza and compression and arching of the basement further west. Subsequently, the rift propagated westward along the whole length of the Equatorial Atlantic. (3) From Albian time on, there has been right-lateral divergent movement between northwest Africa and South America. (4) This movement was interrupted by intense compression in the Late Cretaceous resulting from convergence between southwest Europe and Africa, causing shortening and southward thrusting of the rift sequence. This compression was alleviated by left-lateral movement along the intracontinental Sobral transform.

  5. Rift flank segmentation, basin initiation and propagation: a neotectonic example from Lake Baikal

    USGS Publications Warehouse

    Agar, S.M.; Klitgord, Kim D.

    1995-01-01

    New surficial data (field, Landsat TM and topography) define morpho-tectonic domains and rift flank segmentation in the Ol'khon region of the Central Baikal rift. Deformation, drainage and depositional patterns indicate a change in the locus of active extension that may relate to a recent (rift with concomitant shifts in depocentres. Within the hanging wall of the new western border fault, distinct segments control the location of drainage paths and syn-rift deposits. Morphology, sediment thicknesses and fault scarp amplitude indicate that a segmented rift flank graben has propagated southwards along the rift flank and is still actively fragmenting. These surficial data are used to constrain a model for the time-dependent topographic variations during progressive subsidence along a rift flank, involving the transfer of footwall units to hanging-wall domains. Rapid changes in border fault footwall relief in this model are associated with change in the active border fault location with widespread mass-wasting. The model shows that time-dependent histories need to be integrated with flexural uplift models for active normal faults. The active, syn-rift depositional systems of the Ol'khon region provide a valuable analogue for the early evolution of continental margins and the structural controls on syn-rift hydrocarbon sources and reservoirs.

  6. Understanding Along-strike Variations in Extension and Magmatism in Active Rifts: Discontinuous Structure Along the Main Ethiopian Rift

    Microsoft Academic Search

    K. M. Keranen; S. L. Klemperer

    2006-01-01

    A compilation of recent geophysical and geological data reveals a discontinuity in the structure of the Main Ethiopian Rift (MER) at ~8.5°N. Recent wide-angle seismic data (from the 2003 EAGLE project) recorded along the axis of the MER show a rapid increase of crustal thickness from c. 26 km in the NE to c. 40 km in the SW at

  7. Two mantle plumes beneath the East African rift system: Sr, Nd and Pb isotope evidence from Kenya Rift basalts

    Microsoft Academic Search

    Nick Rogers; Ray Macdonald; J. Godfrey Fitton; Rhiannon George; Martin Smith; Barbara Barreiro

    2000-01-01

    Major and trace element and radiogenic isotope ratios (Sr, Nd and Pb) are presented for a suite of Neogene to Recent basalts (MgO>4 wt%) from the axial regions of the Kenya Rift. Samples have compositions ranging from hypersthene-normative basalt through alkali basalt to basanite and are a subset of a larger database in which compositions extend to nephelinite. A broadly

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

    SciTech Connect

    Tiercelin, J.J. [Universite de Bretagne Occidentale, Brest (France)] [Universite de Bretagne Occidentale, Brest (France); Pflumio, C.; Castrec, M. [Universite Paris VI, Paris (France)] [and others] [Universite Paris VI, Paris (France); and others

    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.

  9. The Chukchi Borderland: a Sediment-starved Rifted Continental Margin

    NASA Astrophysics Data System (ADS)

    Hutchinson, D. R.; Houseknecht, D.; Mosher, D. C.; Hart, P. E.; Jackson, H. R.; Lebedeva-Ivanova, N. N.; Shimeld, J.; Chian, D.

    2013-12-01

    The origin and geologic structure of the Chukchi Borderland region, approximately 650 by 400 km in size, has been the subject of speculation since the earliest ice island research groups discovered its existence more than 60 years ago. Multichannel seismic reflection and refraction data acquired between 2007 and 2011, together with legacy seismic data show fragments of high-standing basement (continental) horsts. The structure is draped with less than a kilometer of sediment. Between the high-standing blocks are deep grabens with locally tilted but mostly flat-lying deposits generally only 1-2 km thick. Northwind Escarpment, along the eastern boundary of the Borderland, is a 600-km-long fault adjacent to the deeply subsided and hyper-extended crust of the Canada Basin to the east. The long, linear, sub-parallel orientation of the major structures (including Northwind Escarpment) is consistent with transtensional deformation of the Borderland. The general paucity of thick sediments indicates a sediment-starved environment. Both the North Chukchi Basin on the west and an unnamed deeply buried valley east on the Beaufort margin provide sediment-routing conduits through which sediment by-passed the Borderland throughout much of the Cretaceous history of the growing Brooks Range to the south. Canada Basin deposits also show strata thicken towards the southwest, suggesting sediment influx via the deeply buried valley on the Beaufort margin. On the northeastern side of the Canada Basin, the region is underlain by horst and graben structures with orientations similar to the Chukchi Borderland, but the intervening valleys are filled with as much as two km of sediment and the entire feature is buried beneath another 2 km of post-rift sediment. The similarity of structural styles on both sides of the Canada Basin suggests that this style of transtensional rifting could have been widespread during the early extension of this part of the Arctic and perhaps the Chukchi Borderland and parts of the Canadian Arctic Archipelago margin were conjugates prior to rifting. Seismic data also show that volcanism associated with the High-Arctic Large Igneous Province to the north has intruded or flowed over the northern parts of the Borderland. The Chukchi Borderland, because of its lack of sedimentary cover, offers a unique window into the early rifting history of the Canada Basin and the transition from rifted to hyper-extended continental crust.

  10. Postspreading rifting in the Adare Basin, Antarctica: Regional tectonic consequences

    NASA Astrophysics Data System (ADS)

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

    2010-08-01

    Extension during the middle Cenozoic (43-26 Ma) in the north end of the West Antarctic rift system (WARS) is well constrained by seafloor magnetic anomalies formed at the extinct Adare spreading axis. Kinematic solutions for this time interval suggest a southward decrease in relative motion between East and West Antarctica. Here we present multichannel seismic reflection and seafloor mapping data acquired within and near the Adare Basin on a recent geophysical cruise. We have traced the ANTOSTRAT seismic stratigraphic framework from the northwest Ross Sea into the Adare Basin, verified and tied to DSDP drill sites 273 and 274. Our results reveal three distinct periods of tectonic activity. An early localized deformational event took place close to the cessation of seafloor spreading in the Adare Basin (˜24 Ma). It reactivated a few normal faults and initiated the formation of the Adare Trough. A prominent pulse of rifting in the early Miocene (˜17 Ma) resulted in normal faulting that initiated tilted blocks. The overall trend of structures was NE-SW, linking the event with the activity outside the basin. It resulted in major uplift of the Adare Trough and marks the last extensional phase of the Adare Basin. Recent volcanic vents (Pliocene to present day) tend to align with the early Miocene structures and the on-land Hallett volcanic province. This latest phase of tectonic activity also involves near-vertical normal faulting (still active in places) with negligible horizontal consequences. The early Miocene extensional event found within the Adare Basin does not require a change in the relative motion between East and West Antarctica. However, the lack of subsequent rifting within the Adare Basin coupled with the formation of the Terror Rift and an on-land and subice extension within the WARS require a pronounced change in the kinematics of the rift. These observations indicate that extension increased southward, therefore suggesting that a major change in relative plate motion took place in the middle Miocene. The late Miocene pole of rotation might have been located north of the Adare Basin, with opposite opening sign compared to the Eocene-Oligocene pole.

  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. Seismicity within a propagating ice shelf rift: the relationship between icequake locations and ice shelf structure

    USGS Publications Warehouse

    Heeszel, David S.; Fricker, Helen A.; Bassis, Jeremy N.; O'Neel, Shad; Walter, Fabian

    2014-01-01

    Iceberg calving is a dominant mass loss mechanism for Antarctic ice shelves, second only to basal melting. An important known process involved in calving is the initiation and propagation of through-penetrating fractures called rifts; however, the mechanisms controlling rift propagation remain poorly understood. To investigate the mechanics of ice-shelf rifting, we analyzed seismicity associated with a propagating rift tip on the Amery Ice Shelf, using data collected during the Austral summers of 2004-2007. We investigated seismicity associated with fracture propagation using a suite of passive seismological techniques including icequake locations, back projection, and moment tensor inversion. We confirm previous results that show that seismicity is characterized by periods of relative quiescence punctuated by swarms of intense seismicity of one to three hours. However, even during periods of quiescence, we find significant seismic deformation around the rift tip. Moment tensors, calculated for a subset of the largest icequakes (MW?>?-2.0) located near the rift tip, show steeply dipping fault planes, horizontal or shallowly plunging stress orientations, and often have a significant volumetric component. They also reveal that much of the observed seismicity is limited to the upper 50?m of the ice shelf. This suggests a complex system of deformation that involves the propagating rift, the region behind the rift tip, and a system of rift-transverse crevasses. Small-scale variations in the mechanical structure of the ice shelf, especially rift-transverse crevasses and accreted marine ice, play an important role in modulating the rate and location of seismicity associated with propagating ice shelf rifts.

  13. RIFT-BASIN STRUCTURE AND ITS INFLUENCE ON SEDIMENTARY SYSTEMS MARTHA OLIVER WITHJACK AND ROY W. SCHLISCHE

    E-print Network

    ; strike-slip and reverse faults; and extensional fault-displacement, fault-propagation, forced, and fault-bend with associated fault-bend folds. In Type 2 rift basins, contractional activity before rifting produced low faults, and contractional fault-bend and fault-propagation folds. Structures within rift basins affect

  14. A structural analysis of the Midcontinent Rift in Michigan, based on a fault array analysis utilizing slickenside

    Microsoft Academic Search

    K. M. Witthuhn; C. Teyssier

    1992-01-01

    The Midcontinent Rift is a 1.1 billion year old crustal structure which has been defined primarily on the basis of geophysical studies. It displays evidence of both rifting and subsequent closure. Many studies have examined the rift from a petrologic view but few have examined it in any detail from a structural geological viewpoint. This paper examines the structural aspects

  15. Culex pipiens, an Experimental Efficient Vector of West Nile and Rift Valley Fever Viruses in the Maghreb Region

    E-print Network

    Paris-Sud XI, Université de

    Culex pipiens, an Experimental Efficient Vector of West Nile and Rift Valley Fever Viruses fever (WNF) and Rift Valley fever (RVF) are emerging diseases causing epidemics outside their natural birds as amplifying hosts, and horses and humans as accidental dead-end hosts. Rift Valley fever virus

  16. New K-Ar age determinations of Kilimanjaro volcano in the North Tanzanian diverging rift, East Africa.

    E-print Network

    Paris-Sud XI, Université de

    insu-00304458,version1-23Jul2008 #12;1. Introduction The Eastern Branch of the East African Rift System local stress field. Keywords: Kilimanjaro, East African Rift, K-Ar dating, volcanic history, Tanzania 2New K-Ar age determinations of Kilimanjaro volcano in the North Tanzanian diverging rift, East

  17. Asthenospheric flow and origin of volcanism in the Baikal Rift area Sergei Lebedev a,, Thomas Meier b

    E-print Network

    Utrecht, Universiteit

    ,9] and for high-volume volcanism such as in the East African rift system [10,11]. A more common kindAsthenospheric flow and origin of volcanism in the Baikal Rift area Sergei Lebedev a,, Thomas Meier King Abstract The origin of low-volume, hotspot-like volcanism often observed in continental rift areas

  18. Inflation along Kilauea's Southwest Rift Zone in 2006 David Myer a,

    E-print Network

    Sandwell, David T.

    Inflation along Kilauea's Southwest Rift Zone in 2006 David Myer a, , David Sandwell a , Benjamin results showing the first crustal inflation along the southwest rift zone at Kilauea volcano in over 20, and after inflation shows that a swarm of shallow earthquakes (zb5 km) signaled the beginning of the uplift

  19. Evidence of Active Rifts in The Southwest United States Using Geophysical Inversion of Seismic Data

    NASA Astrophysics Data System (ADS)

    Celis, S. H.; Velasco, A. A.; Gonzalez-Huizar, H.; Sosa, A.

    2013-05-01

    A continental rift is a linear zone where the lithosphere has become thinner due to extensional forces associated with plate tectonic. Many of these rifts are still active, such as the East Africa rift, while others appear to be failed rifts. We investigate the southern section of the Rio Grande Rift using seismic data collected by USArray stations, and extend the analysis into Texas to investigate the differences between active and failed rifts. We collect multiple geophysical data sets, including receiver functions, surface waves, and teleseismic P- and S- wave travel times, and perform a joint inversion to determine 1-D S-wave velocity structure. This joint inversion is based on constrained optimization that introduces a structural constraint over the inversion model. From the 1-D models, we interpolate layers of the S-wave velocity to create a 3-D velocity model. These results will allow us to analyze and locate any possible active or failed rifts and make a correlation with data from the Rio Grande rift.

  20. The origin and geologic evolution of the East Continent Rift Basin

    SciTech Connect

    Drahovzal, J.A. (Univ. of Kentucky, Lexington, KY (United States). Kentucky Geological Survey)

    1992-01-01

    The East Continent Rift Basin (ECRB) is a newly recognized, dominantly sedimentary-volcanic Proterozoic rift basin that apparently represents the southern extension of the Keweenawan Midcontinent Rift. The ECRB extends from central Michigan at least as far south as south-central Kentucky. The inferred age of the rift fill is approximately 1,000 Ma. Evidence supporting a rift origin for the ECRB includes: interbedding of continental flood basalts and felsic volcanics with siliciclastics; sedimentary fill consisting of distal, arid-climate alluvial fan sediments that lack metamorphic lithologies; close proximity and similar lithologic succession to the Keweenawan rift-fill rocks of the Michigan Basin; and inferred marginal block faulting of Granite-Rhyolite Province rocks near the western edge of the ECRB. ECRB evolution is interpreted as follows: (1) formation of Granite-Rhyolite Province rocks (1,500--1,340 Ma); (2) Keweenawan crustal extension and rifting with development of central mafic complexes, emplacement of volcanic rocks, and deposition of siliciclastic fill from eroded marginal Granite-Rhyolite Province tilted fault blocks (ca 1,000 Ma); (3) overthrusting of the Grenville allochthon and associated foreland thrusting and folding of the rift sequence rocks together with deposition of foreland basin sediments (975---890 Ma); (4) Late Proterozoic erosional removal of the foreland basin sediments and interpreted wrench faulting along the Grenville Front (post-975 to pre-570 Ma); and (5) tectonic inversion, with the ECRB area remaining relatively high during major cambrian subsidence in central Kentucky (590--510 Ma).

  1. Lattice-particle simulation of stress patterns in a Rwenzori-type rift transfer zone

    Microsoft Academic Search

    Till Sachau; Daniel Koehn; Cees Passchier

    2011-01-01

    A new 3D spring lattice computer model has been developed and used to calculate the stress-field in the vicinity of a rift transfer zone. The numerical setup is based on the Rwenzori block, a transfer zone in the Western Branch of the East African Rift Valley. The study has two closely related, yet independent aims: primarily to gain insight into

  2. Connection of the Panama fracture zone with the Galapagos rift zone, eastern tropical Pacific

    Microsoft Academic Search

    Paul J. Grim

    1970-01-01

    Magnetic data recently collected in the eastern tropical Pacific confirm that the Galapagos rift zone is connected to the Panama fracture zone by a short north-south fracture zone (the Ecuador fracture zone) and a short east-west center of sea floor spreading (the Costa Rica rift zone). These features were found approximately in the locations predicted by Molnar and Sykes from

  3. Crustal and uppermost mantle structure in the central U.S. encompassing the Midcontinent Rift

    E-print Network

    Mojzsis, Stephen J.

    the MCR, but there is a gradient Moho in the northern part of the rift and a sharp Moho in the south as to the nature and origin of the rift system [Stein et al., 2011]. [3] Figure 1 outlines the location-air gravity high defines its location (see 40 mGal anomaly contour in Figure 1b), but it divides further

  4. Contour mapping of relic structures in the Precambrian basement of the Reelfoot rift, North American midcontinent

    Microsoft Academic Search

    Richard L. Dart; Henri S. Swolfs

    1998-01-01

    A new contour map of the basement of the Reelfoot rift constructed from drill hole and seismic reflection data shows the general surface configuration as well as several major and minor structural features. The major features are two asymmetric intrarift basins, bounded by three structural highs, and the rift margins. The basins are oriented normal to the northeast trend of

  5. Fracture populations on the Reykjanes Peninsula, Iceland: Comparison with experimental clay models of oblique rifting

    E-print Network

    in the center of the zone of active volcanism. Along the margin, fractures are long, highly segmented extension to the trend of the plate boundary (rift axis). In the center of the zone of active volcanism, fractures of the rift zone. Scaled experimental models of oblique extension predict a significant change in fracture

  6. Jurassic carbonate facies of the Central and Eastern High Atlas rift, Morocco

    Microsoft Academic Search

    John Warme

    The present Central and Eastern High Atlas mountains of southern Morocco represent a short-lived Mesozoic rift, 500 × 100 km, associated with an ancient fracture zone between the Saharan Craton to the south and the smaller microplate mesetas to the north. A continental rift opened in the Upper Triassic, accumulating redbeds, evaporites and basalts. Marine carbonate deposits were initiated abruptly

  7. Rifting processes in the centre of Siberia revealed by BEST (Baikal Explosion Seismic Transects)

    Microsoft Academic Search

    C. A. Nielsen; H. Thybo; M. M. Jensen; A. Ross; V. D. Suvorov; A. Emanov; V. Seleznev; G. Tatkov; E. Perchuc; E. Gazcynski

    2003-01-01

    The Baikal Rift Zone is located in Siberia at the centre of the world's largest continental area. It offers a unique opportunity for studying the processes of intra-cratonic rifting. The BEST project (Baikal Explosion Seismic Transects) comprises two deep seismic profiles at the southern end of Lake Baikal. The field project was carried out in October 2002 after a pilot

  8. Baikal Seismic Experiment (base), Probing Lower Crustal Reflectivity Around The Baikal Rift

    Microsoft Academic Search

    H. Thybo; M.-B. Jensen; A. Ross; V. Suvorov; A. Emanov; V. Seleznev; G. Tatkov; E. Perchuc

    2002-01-01

    The Baikal Seismic Experiment aims at studying crustal structure of the Baikal Rift Zone by deep seismic profiling along profiles around the southern Lake Baikal and the Tunka depression. In September 2001, data were acquired along two profiles: (1) a 350 km long, NS-trending profile across the rift zone from Kyahta at the Mongolian border to Cheremhovo, and (2) a

  9. 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.

  10. Insights into rifting from shear wave splitting and receiver functions: an example from Ethiopia

    Microsoft Academic Search

    Atalay Ayele; Graham Stuart; J.-Michael Kendall

    2004-01-01

    Seismic anisotropy beneath broad-band stations in the vicinity of the East African rift are compared with those on stable cratonic parts of Africa and Arabia. Such measurements offer potential constraints on rift processes, absolute plate motions (APM) and tectonic structure. New SKS shear wave splitting parameters are analysed beneath the broad-band stations of FURI and AAE (Ethiopia), BGCA (Central African

  11. Melt-induced seismic anisotropy and magma assisted rifting in Ethiopia: Evidence from surface waves

    Microsoft Academic Search

    I. D. Bastow; S. Pilidou; J.-M. Kendall; G. W. Stuart

    2010-01-01

    The East African rift in Ethiopia is unique worldwide because it captures the final stages of transition from continental rifting to seafloor spreading. A recent study there has shown that magma intrusion plays an important role during the final stages of continental breakup, but the mechanism by which it is incorporated into the extending plate remains ambiguous: wide-angle seismic data

  12. Compositional Similarities between Hot Mineral Springs in the Jordan and Suez Rift Valleys

    Microsoft Academic Search

    Emanuel Mazor

    1968-01-01

    THE chemical composition of the Hammam Farun hot spring (72° C) in the Suez Rift Valley has been found to be almost identical to that of the Tiberias Hot Springs (60° C) in the Jordan Rift Valley (Figs. 1 and 2 and Table 1). This finding is of vital importance in the evaluation and sorting out of various hypotheses that

  13. Geometry and scaling relations of a population of very small rift-related normal faults

    E-print Network

    Geometry and scaling relations of a population of very small rift-related normal faults Roy W normal faults within the Solite Quarry of the Dan River rift basin range in length from a few millimetres to a few metres and are possibly the smallest visible faults studied to date. Displacement is greatest

  14. A SAP30 Complex Inhibits IFN-b Expression in Rift Valley Fever Virus Infected Cells

    E-print Network

    Paris-Sud XI, Université de

    A SAP30 Complex Inhibits IFN-b Expression in Rift Valley Fever Virus Infected Cells Nicolas Le May1, Institut Pasteur, Paris, France Rift Valley fever virus (RVFV) nonstructural protein NSs acts as the major Valley Fever Virus infected cells. PLoS Pathog 4(1): e13. doi:10.1371/journal.ppat.0040013 Introduction

  15. Rift Valley Fever in Humans and Animals in Mayotte, an Endemic Situation?

    E-print Network

    Paris-Sud XI, Université de

    Rift Valley Fever in Humans and Animals in Mayotte, an Endemic Situation? Tinne Lernout1 *. , Eric on Arboviruses and Viral Haemorrhagic fevers, Institut Pasteur, Paris, France, 5 Laboratory of the Hospital revealed that Rift Valley Fever virus (RVFV) has been circulating on Mayotte for at least several years

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  17. A hierarchical network approach for modeling Rift Valley fever epidemics with applications in North America

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a vector-borne zoonotic disease which causes high morbidity and mortality in livestock. In the event Rift Valley fever virus is introduced to the United States or other non-endemic areas, understanding the potential patterns of spread and the areas at risk based on disease...

  18. Case History Seismic signal penetration beneath post-rift sills on the

    E-print Network

    Shillington, Donna J.

    Case History Seismic signal penetration beneath post-rift sills on the Newfoundland rifted margin that the transparency of "transitional" crust arises from poor signal penetration. In principle, the high the top of basement.We interpret these observations as evidence that signal penetration is compar- atively

  19. Heterogeneity and Reservoir Quality of Yabus and Samaa Formations, Agordeed Field, Melut Rift Basin, Sudan

    Microsoft Academic Search

    Amani Badi; Omer Ali; Abdalla Farwa; Osman Abdullatif

    2010-01-01

    The Tertiary Yabus and Samaa Formations occur within the Melut Rift basin of interior Sudan which is regionally linked to the central and west African rift system. Yabus and Samaa Formations in Agordeed oil field are ones of the most productive oil reservoirs in Melut basin and are composed of sandstones and mudstones lithofacies that differ in size and length

  20. Modeling suggests that oblique extension facilitates rifting and continental break-up

    E-print Network

    Kaus, Boris

    Modeling suggests that oblique extension facilitates rifting and continental break-up Sascha Brune; accepted 5 June 2012; published 2 August 2012. [1] In many cases the initial stage of continental break-up was and is associated with oblique rifting. That includes break-up in the Southern and Equatorial Atlantic, separation

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

    Microsoft Academic Search

    Zhaohui Yang; Wang-Ping Chen

    2010-01-01

    On the basis of a comprehensive data set of precisely determined depths of 121 large to moderate-sized earthquakes along and near the entire East African Rift System (EARS), there are three distinct patterns in focal depths which seem to correlate with progressive stages in the development of the largest active rift in the world. First, away from both ends of

  2. Geochemical evidence of mantle reservoir evolution during progressive rifting along the western Afar margin

    E-print Network

    Paris-Sud XI, Université de

    junction, where the Red Sea, Gulf of Aden and African Rift System extension zones converge, is a pivotalGeochemical evidence of mantle reservoir evolution during progressive rifting along the western Sciences, Michigan State University, East Lansing, MI 48824, USA b Tonagharraun, Corrandulla, Co. Galway

  3. Earthquakes along the East African Rift System: A multi-scale, continent-wide perspective

    Microsoft Academic Search

    Z. Yang; W. Chen

    2009-01-01

    Based on a comprehensive dataset of precisely determined depths of 121 large to moderate-sized earthquakes along and near the entire East African Rift system (EARS), there are three distinct patterns in focal depths which seem to reflect progressive stages in the development of the largest active rift in the world. First, away from both ends of the western, younger branch

  4. East African Rift System (EARS) Plume Structure: Insights from Quaternary Mafic Lavas of Turkana, Kenya

    Microsoft Academic Search

    TANYA FURMAN; JULIA G. BRYCE; JEFFREY KARSON; ANNAMARIA IOTTI

    2004-01-01

    Quaternary mafic lavas from Lake Turkana (northern Kenya) provide information on processes operating beneath the East African Rift in an area of anomalous lithospheric and crustal thinning. Inferred depths of melting beneath Turkana (15---20km) are shal- lower than those recorded elsewhere along the rift, consistent with the anomalously thin crustal section. The mafic lavas have elevated incompatible trace element contents

  5. Next-generation Geotectonic Data Analysis: Using pyGPlates to quantify Rift Obliquity during Supercontinent Dispersal

    NASA Astrophysics Data System (ADS)

    Butterworth, Nathaniel; Brune, Sascha; Williams, Simon; Müller, Dietmar

    2015-04-01

    Fragmentation of a supercontinent by rifting is an integral part of plate tectonics, yet the dynamics that govern the success or failure of individual rift systems are still unclear. Recently, analytical and thermo-mechanical modelling has suggested that obliquely activated rifts are mechanically favoured over orthogonal rift systems. Hence, where two rift zones compete, the more oblique rift proceeds to break-up while the less oblique one stalls and becomes an aulacogen. This implies that the orientation and shape of individual rift systems affects the relative motion of Earth's continents during supercontinent break-up. We test this hypothesis using the latest global plate tectonic reconstructions for the past 200 million years. The analysis is performed using pyGPlates, a recently developed Python library that allows script-based access to the plate reconstruction software GPlates. We quantify rift obliquity, extension velocity and their temporal evolution for all small-scale rift segments that constituted a major rift system during the last 200 million years. Boundaries between continental and oceanic crust (COBs) mark the end of rifting and the beginning of sea floor spreading, which is why we use a global set of updated COBs in order to pinpoint continental break-up and as a proxy for the local trend of former rift systems. Analysing the entire length of all rift systems during the last 200 My, we find a mean obliquity of ~40° (measured as the angle between extension direction and local rift trend normal), with a standard deviation of 25°. More than 75% of all rift segments exceeded an obliquity of 20° highlighting the fact that oblique rifting is the rule, not the exception. More specifically, East and West Gondwana split along the East African coast with a mean obliquity of 45°. While rifting of the central and southern South Atlantic segment involved a low obliquity of 10°, the Equatorial Atlantic opened under a high angle of 60°. The separation of Australia and Antarctica involved a protracted extension history involving two stages with ~25° prior to 100 Ma followed by more than 50° obliquity. In many cases both obliquity and extension velocity increase during rift evolution (e.g. South Atlantic, India-Antarctica, Australia-Antarctica, Gulf of California), suggesting an underlying geodynamic correlation. Considering that most conceptual models of rift evolution assume 2D deformation, we here quantify the degree to which 2D rift models are globally applicable, and highlight the importance of 3D models where oblique rifting is the dominant mode of deformation.

  6. Rifting and Post-Rift Reactivation of The Eastern Sardinian Margin (Western Tyrrhenian Back-Arc Basin) Evidenced by the Messinian Salinity Crisis Markers and Salt Tectonics

    NASA Astrophysics Data System (ADS)

    Gaullier, V.; Chanier, F.; Vendeville, B.; Lymer, G.; Lofi, J.; Sage, F.; Maillard, A.; Thinon, I.

    2014-12-01

    The Eastern Sardinian margin formed during the opening of the Tyrrhenian Sea, a back-arc basin created by continental rifting and oceanic spreading related to the eastward migrating Apennine subduction system from middle Miocene to Pliocene times. We carried out the "METYSS" project aiming at better understanding the Miocene-Pliocene relationships between crustal tectonics and salt tectonics in this key-area, where rifting is pro parte coeval with the Messinian Salinity Crisis (MSC, 5.96-5.33 Ma) and Messinian salt décollement creates thin-skinned tectonics. Thereby, we use the MSC seismic markers and the deformation of viscous salt and its brittle overburden as proxies to better delineate the timing of rifting and post-rift reactivation, and especially to quantifying vertical and horizontal movements. Our mapping of the Messinian Erosion Surface and of Messinian Upper and Mobile Units shows that a rifted basin already existed by the Messinian times, revealing a major pre-MSC rifting episode across the entire domain. Because salt tectonics can create fan-shaped geometries in sediments, syn-rift deposits have to be carefully re-examined in order to decipher the effects of crustal tectonics (rifting) and salt tectonics. Our data surprisingly showed that there are no clues for Messinian syn-rift sediments along the East-Sardinia Basin and Cornaglia Terrace, hence no evidence for rifting after Late Tortonian times. Nevertheless, widespread deformation occurred during the Pliocene and is attributed to post-rift reactivation. Some Pliocene vertical movements have been evidenced by discovering localized gravity gliding of the salt and its Late Messinian (UU) and Early Pliocene overburden. To the South, crustal-scale southward tilting triggered along-strike gravity gliding of salt and cover recorded by upslope extension and downslope shortening. To the North, East of the Baronie Ridge, there was some post-salt crustal activity along a narrow N-S basement trough, bounded by crustal faults. The salt geometry would suggest that nothing happened after Messinian times, but some structural features (confirmed by analogue modelling) show that basement fault slip was accommodated by lateral salt flow, which thinned upslope and inflated downslope, while the overlying sediments remained sub-horizontal.

  7. Rift flank uplift and thermal evolution of an intracratonic rift basin (eastern Canada) determined by combined apatite and zircon (U-Th)/He thermochronology

    NASA Astrophysics Data System (ADS)

    Hardie, Rebecca; Schneider, David; Metcalf, James; Flowers, Rebecca

    2015-04-01

    As a significant portion of the world's oil reserves are retrieved from rift systems, a better understanding of the timing of thermal evolution and burial history of these systems will increase the potential for the discovery of hydrocarbon-bearing rifts. The Ottawa Embayment of the St. Lawrence Platform of eastern Canada is a reactivated intracratonic rift basin related to the opening of the Iapetus Ocean at ca. 620-570 Ma, followed by the formation of the well-developed continental passive margin. Siliciclastic sediments derived from the adjacent uplifted Neoproterozoic Grenville basement provide the basin fill material. Apatite and zircon (U-Th)/He thermochronology allows for low-temperature analysis across the exposed crystalline rift flank into the synrift sedimentary sequence to resolve the unroofing, burial and subsidence history of the region. Samples were collected along a ~250 km NE-SW transect, oblique to the axis of the rift, from Mont-Tremblant, Québec (~900 m) to the central axis of the Paleozoic rift in the Southern Ontario Lowlands (~300 m). Targets included Neoproterozoic metamorphic rocks of the Grenville Province along the rift flank and basinal Cambro-Ordovician Potsdam Group. Samples from the rift flank yield zircon ages from ca. 650 Ma to ca. 560 Ma and apatite ages from ca. 290 Ma to ca. 190 Ma, with a weak positive correlation between age and grain size. Zircon ages demonstrate a strong negative correlation with radiation damage: as eU increases, age decreases. By incorporating (U-Th)/He ages with regional constraints in the thermal modelling program HeFTy, viable temperature time paths for the region can be determined. Through inverse and forward modeling, preliminary rift flank (U-Th)/He ages correspond to post-Grenville cooling with <4 km of post-Carboniferous burial. The data define slow and long episodes of syn- to post-rift cooling with rates between 0.4 and 0.1 °C/Ma. (U-Th)/He dating of samples along the full-length of the transect will resolve thermal changes in the basin-orogen system and improve our understanding of the rift related history of the region.

  8. APLICACION DE LA LEY Y "AUTORIDAD DEL Este simple artculo de revista, producto de muchas horas en el campo

    E-print Network

    INCAE APLICACION DE LA LEY Y "AUTORIDAD DEL RECURSO" Este simple artículo de revista, producto de muchas horas en el campo registrando interacciones entre guardaparques y visitantes, describe una técnica Oficina de Manejo de Tierras y el Servicio de Parques Nacionales de ese país, así como por muchas agencias

  9. Stratigraphy, structure, and extent of the East Continent Rift Basin

    SciTech Connect

    Wickstrom, L.H. (Cincinnati Arch Consortium and Ohio Geological Survey, Columbus, OH (United States))

    1992-01-01

    The proven existence of pre-Mt. Simon sedimentary rocks named the Middle Run Formation in southwestern Ohio led to the establishment of the Cincinnati Arch Consortium, a joint industry-government partnership to investigate the areal extent, nature, and origin of this new unit. Utilizing available well, seismic, and potential-field data, the consortium has shown that the Middle Run was deposited in a Precambrian rift basin, named the East Continent Rift Basin (ECRB). These data indicate the ECRB assemblage consists of a large folded and faulted wedge of interlayered volcanic and sedimentary rocks, unconformably overlain by Cambrian strata. This wedge is estimated to be thickest (up to about 22,000 feet) on the western edge, where it is in fault contact with Grenville Province rocks. To the west, the ECRB may extend as far as central Illinois and postdates the Precambrian Granite-Rhyolite Province rocks. The contact between the ECRB and this older province appears to be in part an angular unconformity and in part block faulted. The northern limit of this basin was not encountered in the study area; this may indicate a connection with the Midcontinent Rift in Michigan. In central Kentucky, the boundary conditions are more complex. It appears that the ECRB is constricted between a large block of the Granite-Rhyolite Province to the west and the Grenville Front on the east. Large Cambrian extensional structures (Rough Creek Graben and Rome Trough) were overprinted on the Granite-Rhyolite and Grenville Provinces. The ECRB may have acted as a stable block between these Cambrian features. The relationships of the ECRB to overlying Paleozoic features may be profound. Indeed, the ECRB may prove to be the reason for the very existence of the Cincinnati and Kankakee Arches.

  10. Graben formation during the Bárðarbunga rifting event in central Iceland

    NASA Astrophysics Data System (ADS)

    Ruch, Joël; Jónsson, Sigurjón; Wang, Teng; Xu, Wenbin; Trippanera, Daniele

    2015-04-01

    On the 16th of August 2014, an intense seismic swarm was detected at the Bárðarbunga caldera (central Iceland), which migrated to the east and then to the northeast during the following days. The swarm, highlighting magma propagation pathway from the caldera, migrated laterally during the following two weeks over 40 km. By the end of August, a volcanic eruption had started along a north-south oriented fissure located ~45 km from the caldera. Here we focus on the near-field deformation related to the dike emplacement in the shallow crust, which generated in few days an 8 km long by 0.8 km wide graben (depression) structure. The new graben extends from the northern edge of the Vatnajökull glacier and to the north to the eruptive fissure. We analyze the temporal evolution of the graben by integrating structural mapping using multiple acquisitions of TerraSAR-X amplitude radar images, InSAR and ground-truth data with GPS and structural measurements. Pixel-offset tracking of radar amplitude images shows clearly the graben subsidence, directly above the intrusion pathway, of up to 6 meters in the satellite line-of-sight direction. We installed a GPS profile of 15 points across the graben in October 2014 and measured its depth up to 8 meters, relative to the flanks of the graben. Field structural observations show graben collapse structures that typically accompany dike intrusions, with two tilted blocks dipping toward the graben axis, bordered by two normal faults. Extensive fractures at the center of the graben and at the graben edges show a cumulative extension of ~8 meters. The formation of the graben was also accompanied by strong seismic activity locally, constraining the time frame period of the main graben formation subsidence. Our results show a rare case of a graben formation captured from space and from ground observations. Such structures are the dominant features along rift zones, however, their formation remain poorly understood. The results also provide information about transient deformation occurring along rift zones, suggesting that rapid dike intrusions modify the topography permanently in only a few days. This supports that rift morphologies are primarily generated during rifting events rather than by long-term regional tectonic processes.

  11. Seismic investigation of the southern Rio Grande Rift

    NASA Astrophysics Data System (ADS)

    Thompson, Lennox E.

    Competing models exist to explain what caused the Earth's crust to spread apart 29 million years ago to create a region known today as the Rio Grande Rift (RGR). The RGR extends from central Colorado through New Mexico to northern Mexico, near El Paso. The RGR has different geologic features that distinguish it from most other valleys (e.g., the RGR was not cut by a river nor does a river branch upstream). A growing body of evidence shows that geologic activity still occurs in the RGR, with a continuation of faulting, seismicity and widening at a small rate of about 0.3 mm/yr (Woodward , 1977). We map of the seismic velocity structure and crustal thickness using data from the Rio Grande Rift Seismic TRAnsect (RISTRA) experiment and the EarthScope Transportable Array (USArray) dataset. In addition to the data we collected from the RISTRA experiment and USArray dataset, we also acquired receiver functions from the EarthScope Automatic Receiver Survey (EARS) website (http://www.earthscope.org/data) and waveform data from the Incorporated Research Institutes for Seismology (IRIS) Data Management Center (DMC). We requested seismograms from the IRIS DMC database where we acquired teleseismic events from Jan 2000 to Dec 2009. This includes 7,259 seismic events with a minimum magnitude of 5.5 and 106,389 continuous waveforms. This data was preprocessed (merged, rotated) using a program called Standing Order of Data (SOD). The RISTRA experiment and the USArray were designed to image crust and mantle structures by computing receiver functions for all data in the Southern Rio Grande Rift (SRGR). We map the crustal thickness, seismic velocity, and mantle structure for the sole purpose to better determine the nature of tectonic activity that is presently taking place and further investigate the regional extension of the Southern Rio Grande Rift (SRGR). Here we present preliminary results of the crustal and velocity structure using the kriging interpolation scheme seem stable and we are now able to clearly observe certain patterns we can use to interpret the southern RGR deformation and extension.

  12. Crustal structure and tectonic evolution of the anza rift, northern Kenya

    NASA Astrophysics Data System (ADS)

    Greene, L. C.; Richards, D. R.; Johnson, R. A.

    1991-10-01

    The Anza trough is a Mesozoic rift located in northern Kenya that appears to be the failed third arm of a paleo-triple junction which allowed the separation of Madagascar from Africa during the Jurassic. The rift is oriented NW-SE and its tectonic evolution is related to that of the Mesozoic southern Sudan rift system. We analyzed seismic and gravity data from the southwestern side of the Anza rift including the Chalbi Desert to gain a better understanding of rift structure. Gravity data delineate the main rift basins as well as a small sub-basin on the southwest side of the main rift. Normal faulting evident on the NW end of a 42-km-long, NW-SE oriented Vibroseis® profile, marks the western boundary of the sub-basin. This sub-basin is offset from the trend of the main Anza trough; the western boundary may be a complex fault zone accommodating a change in direction of the main rift trend. Gravity values increase to the NW in the faulted area, suggesting shallowing of basement. A strong NW-dipping reflection from 0.5 s to almost 3 s is interpreted as a pre- to mid-Cretaceous unconformity. The configuration of the unconformity and the normal faulting strongly resembles the half-graben geometry imaged in the East African Rift. Numerous discontinuous reflections can be seen deeper in the section between 6 and 9 s, but a distinct reflection Moho cannot be interpreted with certainty. In addition to seismic and gravity data, regional geologic and well data lead us to conclude that there are probably Jurassic marine sediments in the bottom of the Anza rift.

  13. Fault evolution in the Potiguar rift termination, equatorial margin of Brazil

    NASA Astrophysics Data System (ADS)

    de Castro, D. L.; Bezerra, F. H. R.

    2015-02-01

    The transform shearing between South American and African plates in the Cretaceous generated a series of sedimentary basins on both plate margins. In this study, we use gravity, aeromagnetic, and resistivity surveys to identify architecture of fault systems and to analyze the evolution of the eastern equatorial margin of Brazil. Our study area is the southern onshore termination of the Potiguar rift, which is an aborted NE-trending rift arm developed during the breakup of Pangea. The 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 rift 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 rift and indicates that stretching in the southern rift termination created a WNW-trending, 10 km wide, and ~ 40 km long right-lateral strike-slip fault zone. This zone encompasses at least eight depocenters, which are bounded by a left-stepping, en echelon system of NW-SE- to NS-striking normal faults. These depocenters form grabens up to 1200 m deep with a rhomb-shaped geometry, which are filled with rift sedimentary units and capped by postrift sedimentary sequences. The evolution of the rift termination is consistent with the right-lateral shearing of the equatorial margin in the Cretaceous and occurs not only at the rift termination but also as isolated structures away from the main rift. 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 rift geometry.

  14. Relative timing of CAMP, rifting, continental breakup, and basin inversion: Tectonic significance

    NASA Astrophysics Data System (ADS)

    Schlische, Roy W.; Withjack, Martha Oliver; Olsen, Paul E.

    Short-duration CAMP magmatic activity at ˜200 Ma in eastern North America provides a temporal benchmark for assessing the relative timing of rifting, drifting, and basin inversion. In the southeastern United States, rifting ceased and shortening/inversion began before CAMP magmatism. In the northeastern United States and southeastern Canada, rifting continued during and after CAMP magmatism. Rifting ceased in the northeastern United States and southeastern Canada by the early Middle Jurassic, after CAMP magmatic activity. Shortening/inversion occurred in southeastern Canada before or during the Early Cretaceous. The available geological, geophysical, and geochronological data favor a diachronous rift-drift transition (seafloor spreading began earlier in the south) rather than the traditional synchronous rift-drift transition along the entire central North Atlantic margin. In this scenario, there are two magmatic pulses. The first includes CAMP and the formation of seaward-dipping reflectors (SDR's) near the continent-ocean boundary during the rift-drift transition along the southern margin segment. The second, younger magmatic pulse is associated with the formation of SDR's during the rift-drift transition along the northern margin segment. We believe that the widespread magmatism and shortening/inversion in eastern North America are related to active asthenospheric upwelling that culminated during the rift-drift transition. Inversion is a common feature along many volcanic passive margins and is associated with a change in the strain state from extension at a high angle to the margin during rifting to shortening at a high angle to the margin during drifting. The presence of dikes oriented at a high angle to the trend of the margin (e.g., the dike swarms in the southeastern United States, southeastern Greenland, offshore northwest Europe, and South America) may reflect this change in strain state associated with inversion.

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

    USGS Publications Warehouse

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

    1992-01-01

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

  16. Tectonic Evolution of the Rift Basins in the Northeastern Brazilian Region

    NASA Astrophysics Data System (ADS)

    Mohriak, Webster U.; Bassetto, Marcelo; Vieira, Ines S.

    The transition from onshore failed rifts to offshore sedimentary basins along divergent continental margins is discussed on the basis of a regional, multidisciplinary integration of deep seismic reflection profiling, potential fied methods, geological data, and tectonic analysis. The following themes are addressed: a) the geologic evolution of the onshore and offshore rift systems of the Brazilian northeastern margin; b) the potential field methods response to the deep crustal structures; c) the seismic expression of major structural features in the rifts and within the continental and oceanic crusts; d) a possible geodynamic model for the evolution of the rift system; and e) analogies with a number of failed rifts and passive margin systems in the North Atlantic. The sedimentary basins in northeastern Brazil include a series of asymmetric grabens, such as the onshore Recôncavo-Tucano-Jatobá rift system (RTJ) and the offshore Jacuípe-Sergipe-Alagoas basins (JSA). Pre-rift sediments include Paleozoic to Jurassic/Early Cretaceous sediments deposited above a basement that includes Archean rocks to Late Proterozoic metasediments. The main rift phase (Neocomian to Barremian) terminated in the onshore rifts with fluvial deposits above a major regional unconformity. No further sedimentation is observed in the Recôncavo and Tucano basins, in a marked contrast to the geodynamic evolution of the Sergipe Basin, which is characterized by renewed phases of basement-involved faulting from Aptian to Early Albian, followed by a thermal phase of subsidence. The overall picture of two branches of a rift system, with different geodynamic evolution following the inception of oceanic crust, may be associated with a regional lithospheric extension during the Neocomian, first distributed over a wide region, and subsequently, focussing along a deeper mantle weak zone, local of a later plate rupture.

  17. Spatial variation of primordial 3-He in crustal fluids along the East-African Rift system (the Ethiopian and the Kenya Rift section)

    NASA Technical Reports Server (NTRS)

    Griesshaber, E.; Weise, S.; Darling, G.

    1994-01-01

    (3)He/(4)He compositions are presented for groundwater samples from the Ethiopian segment of the East-Afrikan Rift and from its northern extension, the adjacent Afar region (Djibuti). Helium isotope data are compared to those obtained previously from the Gregory Rift, south of Ethiopia. The distribution pattern of mantle-derived volatiles along the entire East-African-Rift (-from south Kenya to Djibuti-) is discussed and their sources are identified. Helium isotope ratios (R) for samples from the Ethiopian part of the Rift range from 6.3 to 16.0 times the atmospheric ratio (Ra=1.4 x 10(exp -6) and thus show together with a MOR component a considerable hotspot helium component. These mantle helium concentrations are comparable to those observed in groundwaters and volcanic rocks from the Afar plume region in Djibuti. Here R/Ra values range from 9 to 13 times the atmospheric composition, with mantle-derived helium concentrations being higher than at spreading ocean ridges. R/Ra values from Ethiopia and Djibuti are entirely different from those observed in groundwaters at the southerly extending Gregory Rift in Kenya, where R/Ra values scatter between 0.5 and 6. At the northernmost part of the Gregory Rift, close to Ethiopia mantle helium contents are slightly higher, with R/Ra-values varying between 6.5 and 8.0.

  18. RECONNAISSANCE ASSESSMENT OF CO2 SEQUESTRATION POTENTIAL IN THE TRIASSIC AGE RIFT BASIN TREND OF SOUTH CAROLINA, GEORGIA, AND NORTHERN FLORIDA

    Microsoft Academic Search

    G. Blount; M. Millings

    2011-01-01

    A reconnaissance assessment of the carbon dioxide (CO) sequestration potential within the Triassic age rift trend sediments of South Carolina, Georgia and the northern Florida Rift trend was performed for the Office of Fossil Energy, National Energy Technology Laboratory (NETL). This rift trend also extends into eastern Alabama, and has been termed the South Georgia Rift by previous authors, but

  19. Thermal and exhumation history of the central Rwenzori Mountains, Western Rift of the East African Rift System, Uganda

    Microsoft Academic Search

    F. U. Bauer; U. A. Glasmacher; U. Ring; A. Schumann; B. Nagudi

    2010-01-01

    The Rwenzori Mountains (Mtns) in west Uganda are the highest rift mountains on Earth and rise to more than 5,000 m. We apply\\u000a low-temperature thermochronology (apatite fission-track (AFT) and apatite (U–Th–Sm)\\/He (AHe) analysis) for tracking the cooling\\u000a history of the Rwenzori Mtns. Samples from the central and northern Rwenzoris reveal AFT ages between 195.0 (±8.4) Ma and\\u000a 85.3 (±5.3) Ma, and

  20. Construction and destruction of a volcanic island developed inside an oceanic rift: Graciosa Island, Terceira Rift, Azores

    NASA Astrophysics Data System (ADS)

    Sibrant, A. L. R.; Marques, F. O.; Hildenbrand, A.

    2014-09-01

    There is a great lack of knowledge regarding the evolution of islands inside active oceanic rifts, in particular the meaning of the different evolutionary steps. Therefore, we conducted an investigation in Graciosa Island, which lies at the northwestern end of the Terceira Rift in the Azores Triple Junction, with the objective of constraining the evolution of the island in terms of volcanic growth and mass wasting, in particular the meaning and age of the destruction events. From digital elevation model (DEM) analysis, stratigraphic and tectonic observations, K/Ar dating on key samples, and available bathymetry and gravity data, we propose that Graciosa comprises five main volcanic complexes separated by major unconformities related to large scale mass wasting: (1) The older volcanic edifice (Serra das Fontes Complex) grew until ca. 700 ka, and was affected by a major flank collapse towards the southwest, which removed the whole SW flank, the summit and a part of the NE flank. (2) The Baía do Filipe Complex developed between at least 472 ka and 433 ka in two different ways: in the SW (presently offshore) as a main volcano, and in the NE unconformably over the sub-aerial remnants of the Serra das Fontes Complex, as secondary volcanic edifices. (3) The Baía do Filipe Complex was affected by a major flank collapse towards the SW, again removing most of the edifice. (4) The remnants of the Baía do Filipe Complex were covered in unconformity by the Serra Dormida Complex between ca. 330 and 300 ka, which in turn was unconformably covered by the younger Basaltic Cover Complex between ca. 300 ka and 214 ka. These two units were affected by a third major sector collapse that removed the whole western flank, the summit and part of the eastern flank of the Serra Dormida and Basaltic Cover complexes. (5) Despite the relatively young age of Graciosa, the collapse scars are not well preserved, and not active anymore. (6) A central-type volcano has been growing since at least 60 ka at the southeastern end of the island, inside the scar left by a fourth sector collapse towards the SE, which affected most previous complexes. Contemporaneously, parasitic strombolian cones formed all over the island. Despite the location of Graciosa inside the active Terceira Rift, the new data indicate that the evolution of the island has been driven by a competition between volcano growth and repeated destruction by catastrophic sector collapses, rather than by slow incremental faulting associated with the tectonics of the rift.

  1. Determination and implication of Lower Crustal Bodies in the Møre rifted margin (offshore Norway)

    NASA Astrophysics Data System (ADS)

    Nirrengarten, Michael; Gernigon, Laurent; Manatschal, Gianreto

    2014-05-01

    The Møre margin is the result of a long period of rifting events influenced by different tectonic processes. The last extension phase of the Møre margin was accompanied by the onset of massive magmatic activity leading to the emplacement of seaward dipping reflector sequences (SDRS). However the previous events were probably characterized by a smaller amount of magmatism, like for a classic magma poor rifted margin. Several refraction studies across the Møre rifted margin have also revealed the occurrence of high velocity lower crustal bodies (LCB) under the distal SDRS wedge but also in more proximal positions of the margin (e.g. Kvarven et al., 2012). The nature, age and location of these LCBs are still questionable and represent key and primary parameters to understand the tectonic and crustal evolution of the volcanic rifted margin. Nature, age and geometry of these LCBs have major implications on the rheological and thermal evolution of the rift/margin system. In light of 2D potential field modelling combined with reflection and refraction seismic data, we reinvestigated the crustal nature of the Møre volcanic rifted margin and adjacent Jan Mayen corridor. In the proximal domain of the Møre volcanic rifted margin, our study shows that the LCBs most likely represent inherited crustal bodies and are not necessarily made of rift-related serpentinised mantle as previously proposed. In the distal margin, our preferred interpretation suggests that the outer LCBs are still made of relics of pre-rift lower continental crustal rocks, more or less intruded and/or underplated by Tertiary magmatic rocks. The seismic, magnetic and gravity data do not easily support large scale exhumation of serpentinised mantle in the inner and outer parts of the Møre Basin. Our model suggests that the Møre rift system evolved through a significant Late Jurassic-Cretaceous thinning phase. This rift episode led to a thin continental crust with pre rift lower crustal rocks but without perennial domains of exhumed and serpentinised mantle. This significant extensional event preceded a Late Cretaceous-Early Tertiary rift episode which is characterised by different and independent magmatic and lithospheric processes leading to breakup (e.g. diking and lithospheric plumbing).

  2. An epidemiological model of Rift Valley fever with spatial dynamics.

    PubMed

    Niu, Tianchan; Gaff, Holly D; Papelis, Yiannis E; Hartley, David M

    2012-01-01

    As a category A agent in the Center for Disease Control bioterrorism list, Rift Valley fever (RVF) is considered a major threat to the United States (USA). Should the pathogen be intentionally or unintentionally introduced to the continental USA, there is tremendous potential for economic damages due to loss of livestock, trade restrictions, and subsequent food supply chain disruptions. We have incorporated the effects of space into a mathematical model of RVF in order to study the dynamics of the pathogen spread as affected by the movement of humans, livestock, and mosquitoes. The model accounts for the horizontal transmission of Rift Valley fever virus (RVFV) between two mosquito and one livestock species, and mother-to-offspring transmission of virus in one of the mosquito species. Space effects are introduced by dividing geographic space into smaller patches and considering the patch-to-patch movement of species. For each patch, a system of ordinary differential equations models fractions of populations susceptible to, incubating, infectious with, or immune to RVFV. The main contribution of this work is a methodology for analyzing the likelihood of pathogen establishment should an introduction occur into an area devoid of RVF. Examples are provided for general and specific cases to illustrate the methodology. PMID:22924058

  3. Correlation of geophysical datasets in rifted margin studies

    NASA Astrophysics Data System (ADS)

    Peron-Pinvidic, Gwenn; Terje Osmundsen, Per; Ebbing, Jörg

    2015-04-01

    A robust interpretation protocol for defining offshore rifted margin architecture includes interpretation of seismic reflection data supplemented by refraction and/or potential field modeling. In combination, this workflow is believed to provide better constraints on sedimentary, basement and Moho geometries at depth and/or the presence of magmatic material. Interpretation of the new generation of long-offset seismic reflection data shows that conflicts may arise between structural observations made from high-resolution seismic reflection profiles and a simple translation of density and velocity values into specific rock-types. We illustrate variations over this topic using three type-examples from the Mid-Norwegian rifted system. We show, for instance, that dense sediments wrongly interpreted as crystalline basement, can lead to incorrect mapping of the top of basement and thus to a wrong distribution of crustal and sedimentary material in the margin. This would directly impact margin restoration exercises, modeled plate kinematics and basin analyses. Our examples show that, in the absence of a seismic reflection dataset with good local coverage and high resolution, interpretation of potential field and/or velocity models in terms of structures or lithologies should be handled with care in order to avoid misunderstanding of the margin's tectonic and stratigraphic evolution.

  4. Lithospheric cross sections of the European Cenozoic rift system

    NASA Astrophysics Data System (ADS)

    Prodehl, C.; Mueller, St.; Glahn, A.; Gutscher, M.; Haak, V.

    1992-07-01

    The lithospheric structure of the European Cenozoic rift system ( ECRIS) is presented in transects through the southern Rhine Graben and the Rhenish Massif/Hessen depression, emphasizing the geophysical structure of the lithosphere based on seismic refraction/reflection investigations, teleseismic tomography, electromagnetic depth-sounding models, and gravity, aeromagnetic, earthquake, uplift/subsidence and heat flow data. The rift is clearly expressed in the Rhine Graben, but is not evident at the surface in the area of the Rhenish Massif where its existence is indicated by seismicity. It is characterized by abnormal crustal and upper-mantle structures which vary considerably in horizontal direction. For example, under the Rhine Graben the crust is thinned to 25 km, but at 40 km depth anomalously high velocities are observed. In contrast, beneath the Rhenish Massif the crust is thickened to 35-37 km and under its eastern part a high-velocity thin upper-mantle slice is seen at 30 km depth within the lower crust which, towards the Hessen depression, is gradually replaced by normal Variscan mantle with the Moho near 30 km depth. Under the western part of the Rhenish Massif P- and S-wave velocities are reduced below 50 km depth which is not seen east of the Rhine river. Under the Rhine Graben the existence of a low-velocity upper mantle above 100 km cannot be generalized, but is restricted to confined regions.

  5. Young Stellar Object Candidates in the Aquila Rift Region

    NASA Astrophysics Data System (ADS)

    Zhang, Miao-miao; Wang, Hong-chi; Stecklum, B.

    2010-10-01

    Using the 2m telescope of the Turingia State Observatory at Tauten-berg (TLS), imaging observations in 3 wavebands (H ?, R and I) are performed in the 16 fields in the Aquila Rift region. The observed fields cover about 7 square degrees. Excluding the 3 fields with unqualified data, the photometrical analysis is made for the remaining 13 fields, from which point sources are identified, and finally 7 H ? emission-line star candidates are identified by color-color diagrams. The 7 candidates are located in five fields. Three of them are located near the Galactic plane, while the galactic latitudes of the rest are greater than 4°. The 2 M ASS counterparts of the point sources are identified, and the properties of the 7 H ? emission-line star candidates are further analyzed by using the two-color diagrams. It is found that the near-infrared radiation from these H ? emission-line star candidates has no obvious infrared excess, one of them even falls on the main-sequence branch. This indicates that the H ?-emissive young stellar objects (YSOs) are not always accompanied with the infrared excess, and that the results of the H ? emission line observation and the infrared excess observation are mutually supplemented. If the 7 H ? emission-line star candidates are regarded as YSO candidates, then the number of YSOs in the Aquila Rift region is quite small. The further confirmation of these candidates needs subsequent spectral observations.

  6. 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.

  7. Lattice-particle simulation of stress patterns in a Rwenzori-type rift transfer zone

    NASA Astrophysics Data System (ADS)

    Sachau, Till; Koehn, Daniel; Passchier, Cees

    2011-11-01

    A new 3D spring lattice computer model has been developed and used to calculate the stress-field in the vicinity of a rift transfer zone. The numerical setup is based on the Rwenzori block, a transfer zone in the Western Branch of the East African Rift Valley. The study has two closely related, yet independent aims: primarily to gain insight into the pattern and the causes of the stress field in the Rwenzori area. The second aim is the evaluation of the model itself, based on a comparison of the model results with local geological structures. The simulations calculate the stress in the brittle part of the crust, at the topographic surface and at a depth of 10 km. The model does therefore not rely on the rate of the continental extension, but only on the amount. The generated stress maps display the maximum and minimum principal normal stress. The stress is calculated for a total extension of 7.5 km, a value based on common estimates for the local rift extension. The local stress field is created by the interplay of the plate driven far-field stress and the mechanics of the rift system. The propagation of the rift system leads thus to stress rotations and to characteristic stress patterns. An important mechanism is lithospheric bending caused by rift flank uplift, which reverses the far field stress in rift vicinity. The stress-field resulting from the simulations explains several previously unexplained structural features encountered in the Rwenzori block.

  8. Long-term cooling history of the Albertine Rift: new evidence from the western rift shoulder, D.R. Congo

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    To determine the long-term landscape evolution of the Albertine Rift in East Africa, low-temperature thermochronology was applied and the cooling history constrained using thermal history modelling. Acquired results reveal (1) "old" cooling ages, with predominantly Devonian to Carboniferous apatite fission-track ages, Ordovician to Silurian zircon (U-Th)/He ages and Jurassic to Cretaceous apatite (U-Th-Sm)/He ages; (2) protracted cooling histories of the western rift shoulder with major phases of exhumation in mid-Palaeozoic and Palaeogene to Neogene times; (3) low Palaeozoic and Neogene erosion rates. This indicates a long residence time of the analysed samples in the uppermost crust, with the current landscape surface at a near-surface position for hundreds of million years. Apatite He cooling ages and thermal history models indicate moderate reheating in Jurassic to Cretaceous times. Together with the cooling age distribution, a possible Albertine high with a distinct relief can be inferred that might have been a source area for the Congo Basin.

  9. Transition From Rift to Drift at Obliquely Divergent Continental Rifts: the Paired Rio Muni (W Africa) and NE Brazilian Margins

    NASA Astrophysics Data System (ADS)

    Turner, J. P.; Green, P. F.; Wilson, P. G.; Westbrook, G. K.; Lawrence, S.

    2005-12-01

    We develop a synoptic model for the breakup and drift of a major sheared continental margin system: the Rio Muni basin and its NE Brazilian counterpart. It relates the evolution of crustal structure determined from seismic interpretation (including gravity-modelling of the deep-imaging PROBE dataset) to the cooling history of this margin system yielded from thermal history data (mainly apatite fission track analysis - AFTAr - and vitrinite reflectance data). Shear margins initiate as a leaky transform fracture system accommodating the oblique (i.e. non-orthogonal) divergence of opposing rifted continental margins. As such, the transition from continental breakup (i.e. rupture) to continental drift (i.e. ocean opening) at shear margins exhibits significant differences from that of the much better understood normally divergent rifts, where the spreading vector is normal to the strike of the opposing rift margins. For example, unlike at normally divergent rifts, continental breakup and drift are separate episodes in the early evolution of shear margins. In Rio Muni-NE Brazil, they are recorded by separate breakup and drift unconformities spanning a 15-20Ma. interval, the time taken for the ocean ridge to traverse the length of the margin before a continuous arm of oceanic crust separated Rio Muni from its Brazilian counterpart. In the Rio Muni basin, the c.70km-wide Ascension Fracture Zone (AFZ) exhibits oblique-slip faulting and synrift half-graben formation that accommodated oblique extension during the period leading up to and immediately following whole-lithosphere failure and continental breakup 117Ma. Gravity-modelling of PROBE seismic profiles reveals a land-locked precursor oceanic basin that preceded full ocean opening and which subsequently was stranded on the African margin. Its existence supports the idea of multiple rift suture lines accommodating episodic breakup and it emphasizes the significance of separate breakup and drift episodes at shear margins. Oblique extension is recorded also by strike- and oblique-slip fault geometry within the AFZ and buckling of Aptian synrift rocks in response to block rotation and local transpression. Principal cooling episodes affecting both margins identified from the AFTAr occurred in the Mid-Cretaceous 110-90Ma., following a period of high heatflow during which the geothermal gradient was more than twice that of the present day 25°C/km gradient, and 45-35Ma. coinciding with a major change in the pole of rotation at Chron 34 some 84Ma. Additional cooling episodes between 85-75Ma. and 10-2Ma. are restricted to the African side. Given that this margin system underwent breakup some 117Ma., it appears that thermal equilibrium was maintained throughout the initial breakup meaning that no significant uplift and erosion is recorded by the thermal history data during this period. Instead, Mid-Cretaceous cooling is interpreted as a response to the influence of i) the c.105Ma. St Helena Plume and ii) transpressional shortening and inversion that accompanied the breakup to drift period.

  10. An integrated geophysical analysis of the upper crust of the southern Kenya rift

    NASA Astrophysics Data System (ADS)

    Simiyu, Silas M.; Keller, G. Randy

    2001-12-01

    Previous interpretations of seismic data collected by the Kenya Rift International Seismic Project (KRISP) experiments indicate the presence of crustal thickening within the rift valley area beneath the Kenya dome, an uplift centred on the southern part of the Kenya rift. North of the dome, these interpretations show thinning of the crust and an increase in crustal extension. To the south near the Kenya/Tanzania border, crustal thinning associated with the rift is modest. Our study was aimed at further investigating crustal structure from this dome southwards via a detailed analysis focused on upper crustal structure. We used results from surface geological mapping, drill hole data from water wells and geothermal exploration wells, KRISP 85 seismic data for a profile across the rift, KRISP 85 and 90 seismic data for a profile along the rift axis and KRISP 94 seismic data for a profile crossing southernmost Kenya to constrain gravity modelling and construction of integrated models of crustal structure. Our integrated analysis produced the following results concerning the structure and evolution of the southern Kenya rift: (1) the graben master faults are consistently located along the western margin of the rift valley, and there is no evidence for half-graben polarity reversals for a distance of about 300km (2) there is no axial (north-south) crustal symmetry with respect to the apex of the Kenya dome, and the crustal thickness may be as much related to pre-rift crustal type and thickness as it is to crustal thickening and modification by magmatic processes; (3) the pre-existing lithospheric contrast between the Archaean and Proterozoic basement terranes played a significant role in the location and structural geometry of the rift; (4) south of latitude 1°S, low velocities and densities observed under the western flank of the rift probably represent reworked Archaean Tanzanian craton; (5) magmatic modification of the upper crust is modest except near the major Quaternary volcanic centres that produce a series of isolated axial gravity highs; (6) the other element of the axial gravity high is an intrarift horst block that extends along the axis of most of the rift valley.

  11. Basin evolution and the distribution of strain within the Gulf of Corinth rift

    NASA Astrophysics Data System (ADS)

    Bell, Rebecca; McNeill, Lisa; Nixon, Casey; Henstock, Timothy; Bull, Jonathan; Christodoulou, Dimitris; Papatheodorou, George; Taylor, Brian; Ferentinos, George; Sakellariou, Dimitris; Lykousis, Vasilis; Sachpazi, Maria; Ford, Mary; Goodliffe, Andrew; Leeder, Mike; Gawthorpe, Robert; Collier, Richard; Clements, Benjamin

    2013-04-01

    The Gulf of Corinth is a classic young active continental rift initiating <5 Ma and with current extension rates up to 15 mm/yr. The modern rift (ca. 1-2 Myr old) has been studied extensively both onshore and offshore. In this paper we bring together the results of study of the offshore rift with existing onshore data to generate a model for how the modern rift has tectonically evolved, how strain is distributed across and along the rift, how slip on individual major faults controlling rift basin subsidence has changed over relatively short timescales (e.g. <0.5 Myr) and how extension in the upper crust through fault displacement compares with whole crustal extension over the history of the rift. The results indicate that the rift stratigraphy is divided into two units (pre- and post- ca. 0.5Ma). The two units indicate markedly different rift basin geometry during these two time periods. Two separated depocentres 20-50 km long were created controlled by N- and S-dipping faults before ca. 0.5 Ma, while since ca. 0.5 Ma a single depocentre (80 km long) has been controlled by several connected N-dipping faults, with maximum subsidence focused between the two older depocentres. Thus isolated but nearby faults can persist for timescales ca. 1 Ma and form major basins before becoming linked. There is a general evolution towards a dominance of N-dipping faults; however, in the western Gulf strain is distributed across several active N- and S-dipping faults throughout rift history, producing a more complex basin geometry. Examination of extension at a larger spatial and temporal scale suggests that uniform pure shear extension without the need for a significant N-S dipping detachment fault is a viable extension mechanism for at least the western rift where constraints are greater. These results also indicate that the present day strain distribution indicated by GPS data cannot have persisted over the lifetime of the modern rift. We are now building on these studies by performing a major data integration exercise of all available seismic reflection (both conventional and high resolution, digital and analogue) and bathymetric data within the Gulf. This integrated dataset will allow us to refine and improve the syn-rift chronostratigraphic model (based on sequence stratigraphic interpretation) for the Gulf, to correlate this stratigraphic interpretation throughout the Gulf, and to interpret the rift fault network at a much great level of detail than before. We will use these results to refine locations of proposed ocean drilling boreholes which may ultimately provide critical absolute chronological and environmental information. In addition the results will allow us to develop models of rift fault activity, growth and interaction, a detailed history of rift evolution in time and space, and identify the roles of tectonics and climate on sediment flux into the rift and landscape development.

  12. Geodetic determination of plate velocity vector in the Ethiopia Rift

    NASA Astrophysics Data System (ADS)

    Boku, E.; Teklemariam, E.; Rivalta, E.

    2011-12-01

    The Red sea, Gulf of Aden and the Main Ethiopian rift form a triple junction in the Afar Region. Although the East African Rift, the divergent plate boundary between Nubian and Somalia, is often cited as a modern archetype for rifting and continental breakup, its current kinematics is the least known of all major plate boundaries. Moreover, geodetic datum in such tectonically active area is subject to distortion that increases with time. Therefore, a close study of the positions and velocities of reference stations in such tectonic active areas is necessary, if one wants to have high precise geodetic measurement for any developmental activity. In this study phase and pseudo-range GPS measurements were processed to derive the daily solutions of positions in reference to the ITRF05. This solution from 8 continuous stations in Ethiopia, with a length of 0.75 to 2.67 years, is then combined into a cumulative solution with position and velocity estimates. Here a method that combines GPS observation data from 2007 to 2009 to estimate time-dependent motion of stations in a region of active deformation is implemented. First, observations were analysed separately to produce loosely constrained estimates of station positions and coordinate system parameters which are then combined with appropriate constraints to estimate velocities and co-seismic displacements. The result archived gives a good insight about the velocity at which the three major plates, namely the Nubian, Arabian and Somalia plates are moving with respect to each other. The study shows the relative velocity between Nubia and Somalia plates with 4.6±0.3 mm/yr. While, the Nubia and Arabia plates are moving with 33±0.15mm/yr.Moreover; positions of stations are computed with high precession for any future reference purpose. Due to short duration of measurements at some stations further observation are recommended to compute positions and velocity fields after all stations have data at least for two years time. Key words: GPS, Space geodesy, ITRF05, Deformation

  13. Formation of hyperextended rifted margins: Insights from flexural isostatic structural-stratigraphic modeling and observations from present-day rifted margins

    NASA Astrophysics Data System (ADS)

    Mohn, Geoffroy; Kusznir, Nick; Manatschal, Gianreto

    2014-05-01

    The understanding of how continental lithosphere extends, thins and ruptures leading to the formation of a new divergent plate boundary represent a fundamental question in Earth Sciences. In particular the mechanisms controlling the extreme pre-breakup stretching and thinning of the continental crust and lithosphere, documented at many present-day rifted margins, are still poorly known. Many questions remain of the fundamental processes controlling the extensional deformation of the continental crust and lithosphere, including fault geometries and their evolution in space and time, the occurrence of decoupling horizons within the continental crust and the importance of depth-dependent lithosphere thinning processes. We investigate the control of these key factors on continental crust and lithosphere thinning processes by combining seismic reflection and drill-hole observations from present-day Iberia-Newfoundland rifted margins with flexural isostatic forward tectonic and stratigraphic modeling. These observations made at present-day rifted margins constrain the input parameters used in the flexural isostatic forward modeling. At the same time, the forward tectonic and stratigraphic modeling provides validation of the interpretation of the seismic reflection data. Through this modeling, we produce isostatically and thermally balanced sections reproducing the geometries observed along the Iberia-Newfoundland rifted margins. Our results suggest that crustal and lithospheric thinning results from the combination of both pure- and simple-shear deformation. The model predicts the critical role of intra-crustal decoupling horizons confirming the importance of depth-dependent thinning through polyphased rifting events.

  14. Effect of depleted continental lithosphere counterflow and inherited crustal weakness on rifting of the continental lithosphere: General results

    NASA Astrophysics Data System (ADS)

    Beaumont, Christopher; Ings, Steven J.

    2012-08-01

    Some non-volcanic rifted continental margins differ from the predictions of uniform lithospheric extension in two significant ways, namely: 1) large tracts of continental mantle lithosphere are exposed at the seafloor or are inferred to have been emplaced beneath the outer regions of the margin; 2) rifting evolves from distributed extension with multiple rifts to terminal focused rifting. These characteristics are explained by depth-dependent extension. We investigate this type of deformation using 2D upper-mantle-scale dynamical finite element models of rifting that include: 1) lithospheric counterflow, the gravitationally driven lateral flow of depleted lower lithosphere during rifting, as a mechanism for underplating and exhuming continental mantle, and; 2) inherited crustal weak zones that cause initially distributed syn-rift extension. Depleted lower lithosphere (compositionally less dense than sublithospheric mantle by 50-80 kg m-3, with a moderately 'dry' olivine rheology) efficiently flows laterally thereby exhuming zones of continental mantle lithosphere that are respectively up to 90 and 140 km wide. Inherited crustal weak zones that are offset from the main central rift axis can be reactivated as offset rift basins. Extension in these basins depends on their proximity to the central rift and the ease with which crust decouples from mantle: narrow (<50 km) basins when crust does not decouple, and longer-lived wider basins for moderate decoupling. For weak crust that readily decouples during depth-dependent extension, the offset rift basins may remain active throughout rifting, giving rise to highly allochthonous crustal terranes that are translated toward and over the central rift axis.

  15. [Severe hemorrhagic form of Rift Valley Fever in Mauritania].

    PubMed

    Boushab, M B; Savadogo, M; Sow, M S; Fall-Malick, F Z; Seydi, M

    2015-03-01

    We report three severe cases of hemorrhagic form of Rift Valley Fever which have been observed in the Hospital of Aïoun (two cases) and in the regional hospital of Tidjikdja (one case). The disease manifested itself by an infectious syndrome, an early infectious syndrome (on the second day) with onset of hemorrhagic complications and disorder of consciousness ranging from an agitation to deep coma. The biological examinations showed a severe anemia. Multiple organ failures were also observed. Of the three patients treated one died. Therefore, the management of both suspected and confirmed cases must be initiated as soon as possible in order to control organ damages and prevent fatality. There is no specific treatment. The importance of the epidemiological survey must be emphasized to avoid outbreaks and control any epidemic due to this virus. PMID:25925806

  16. Decision making environment on Rift Valley fever in Ferlo (Senegal).

    PubMed

    Bouba, Fanta; Bah, Alassane; Cambier, Christophe; Ndiaye, Samba; Ndione, Jacques-André; Teisseire, Maguelonne

    2014-09-01

    The Rift Valley fever (RVF), which first appeared in Kenya in 1912, is an anthropozoonosis widespread in tropical areas. In Senegal, it is particularly felt in the Ferlo area where a strong presence of ponds shared by humans, cattle and vectors is noted. As part of the studies carried out on the environmental factors which favour its start and propagation, the focus of this paper is put on the decision making process to evaluate the impacts, the interactions and to make RVF monitoring easier. The present paper proposes a model based on data mining techniques and dedicated to trade experts. This model integrates all the involved data and the results of the analyses made on the characteristics of the surrounding ponds. This approach presents some advantage in revealing the relationship between environmental factors and RVF transmission vectors for space-time epidemiology monitoring purpose. PMID:25107274

  17. Arc rifting of the Carolina terrane in northwestern South Carolina

    SciTech Connect

    Dennis, A.J. (Univ. of South Carolina, Aiken (USA)); Shervais, J.W. (Univ. of South Carolina, Columbia (USA))

    1991-03-01

    Recent mapping and whole-rock geochemistry studies demonstrate that mafic metavolcanic rocks found along the boundary between the exotic Carolina terrane and the Inner Piedmont formed in a subduction-related volcanic arc and do not represent the Iapetan suture. Mafic metavolcanic rocks are spatially and genetically related to zoned mafic-ultramafic intrusive complexes. These rocks are similar to those found in other ancient and modern volcanic island arcs where ankaramites and picrites are well known, and they are locally associated with zoned complexes, e.g., Sierra Foothills-Klamath Mountains of the western U.S. Cordillera. The authors propose that prior to accretion to Laurentia in the early to middle Paleozoic, the Carolina arc terrane underwent an episode of intra-arc rifting which allowed primitive arc magmas to ascend and erupt without significant crystal fractionation or lithospheric assimilation. This interpretation may help resolve some stratigraphic problems in the eastern part of the Carolina terrane (Caroline slate belt).

  18. Volcaniclastic alluvial fan sedimentation, northern Rio Grande rift

    SciTech Connect

    McPherson, J.G.; Waresback, D.B.; Self, S.

    1986-05-01

    The Pliocene Puye Formation is a well-exposed, volcanogenic, alluvial fan sequence 150+ m thick, representing a range of volcaniclastic deposits (proximal, medial, and distal) that may be generated in response to long-lived, multicompositional (basaltic to rhyolitic) volcanism in a rift setting. The deposits are a composite of eruptives (effusives and pyroclastics) and epiclastics (reworked primary volcanics). An almost complete record of source-area volcanics (style, intensity, and composition) is preserved in the volcaniclastic fan deposits, as sedimentation rates were high and basinal subsidence was continuous because of concomitant rift downfaulting. At least eight silicic, primary airfall beds are interstratified through the fan deposits and provide a reliable stratigraphic control for establishing vertical and lateral lithofacies correlations. Proximal (inner fan) lithofacies include voluminous block-and-ash deposits that have downfan facies equivalents as pyroclastic flows and mudflows. Other proximal facies include very coarse clast-bearing debris flows, boulder-rich stream-channel and hyperconcentrated flood-flow deposits, and minor sheet-flood sequences. Medial (midfan) deposits display the greatest variability in lithofacies and provide details of the rate and intensity of volcanism by means of a distinctive vertical lithofacies assemblage: a basal plinian layer, stacked debris flows, and stacked mudflows, capped by a fluvial reworking phase of interstratified stream-channel and sheetflood deposits. Debris flows (clast and matrix rich), mudflows, and hyperconcentrated flood-flow deposits are abundant; the latter show evidence of transformation to mudflows with increasing transport distance, as they incorporate added fines (ash). Sheetflood deposits increase in number and thickness at the expense of stream-channel deposits.

  19. Molecular biology and genetic diversity of Rift Valley fever virus

    PubMed Central

    Ikegami, Tetsuro

    2013-01-01

    Rift Valley fever virus (RVFV), a member of the family Bunyaviridae, genus Phlebovirus, is the causative agent of Rift Valley fever (RVF), a mosquito-borne disease of ruminant animals and humans. The generation of a large sequence database has facilitated studies of the evolution and spread of the virus. Bayesian analyses indicate that currently circulating strains of RVFV are descended from an ancestral species that emerged from a natural reservoir in Africa when large-scale cattle and sheep farming were introduced during the 19th century. Viruses descended from multiple lineages persist in that region, through infection of reservoir animals and vertical transmission in mosquitoes, emerging in years of heavy rainfall to cause epizootics and epidemics. On a number of occasions, viruses from these lineages have been transported outside the enzootic region through the movement of infected animals or mosquitoes, triggering outbreaks in countries such as Egypt, Saudi Arabia, Mauritania and Madagascar, where RVF had not previously been seen. Such viruses could potentially become established in their new environments through infection of wild and domestic ruminants and other animals and vertical transmission in local mosquito species. Despite their extensive geographic dispersion, all strains of RVFV remain closely related at the nucleotide and amino acid level. The high degree of conservation of genes encoding the virion surface glycoproteins suggests that a single vaccine should protect against all currently circulating RVFV strains. Similarly, preservation of the sequence of the RNA-dependent RNA polymerase across viral lineages implies that antiviral drugs targeting the enzyme should be effective against all strains. Researchers should be encouraged to collect additional RVFV isolates and perform whole-genome sequencing and phylogenetic analysis, so as to enhance our understanding of the continuing evolution of this important virus. This review forms part of a series of invited papers in Antiviral Research on the genetic diversity of emerging viruses. PMID:22710362

  20. Generation of continental rifts, basins, and swells by lithosphere instabilities

    NASA Astrophysics Data System (ADS)

    Fourel, LoïC.; Milelli, Laura; Jaupart, Claude; Limare, Angela

    2013-06-01

    Continents may be affected simultaneously by rifting, uplift, volcanic activity, and basin formation in several different locations, suggesting a common driving mechanism that is intrinsic to continents. We describe a new type of convective instability at the base of the lithosphere that leads to a remarkable spatial pattern at the scale of an entire continent. We carried out fluid mechanics laboratory experiments on buoyant blocks of finite size that became unstable due to cooling from above. Dynamical behavior depends on three dimensionless numbers, a Rayleigh number for the unstable block, a buoyancy number that scales the intrinsic density contrast to the thermal one, and the aspect ratio of the block. Within the block, instability develops in two different ways in an outer annulus and in an interior region. In the outer annulus, upwellings and downwellings take the form of periodically spaced radial spokes. The interior region hosts the more familiar convective pattern of polygonal cells. In geological conditions, such instabilities should manifest themselves as linear rifts striking at a right angle to the continent-ocean boundary and an array of domal uplifts, volcanic swells, and basins in the continental interior. Simple scaling laws for the dimensions and spacings of the convective structures are derived. For the subcontinental lithospheric mantle, these dimensions take values in the 500-1000 km range, close to geological examples. The large intrinsic buoyancy of Archean lithospheric roots prevents this type of instability, which explains why the widespread volcanic activity that currently affects Western Africa is confined to post-Archean domains.

  1. Epidemiological study of Rift Valley fever virus in Kigoma, Tanzania.

    PubMed

    Kifaro, Emmanuel G; Nkangaga, Japhet; Joshua, Gradson; Sallu, Raphael; Yongolo, Mmeta; Dautu, George; Kasanga, Christopher J

    2014-01-01

    Rift Valley fever virus (RVFV) is an acute, zoonotic viral disease caused by a Phlebovirus, which belongs to the Bunyaviridae family. Among livestock, outbreaks of the disease are economically devastating. They are often characterised by large, sweeping abortion storms and have significant mortality in adult livestock. The aim of the current study was to investigate RVFV infection in the Kigoma region, which is nestled under the hills of the western arm of the Great Rift Valley on the edge of Lake Tanganyika, Tanzania. A region-wide serosurvey was conducted on non-vaccinated small ruminants (sheep and goats, n = 411). Sera samples were tested for the presence of anti-RVFV antibodies and viral antigen, using commercial enzyme-linked immunosorbent assay and reverse transcriptase polymerase chain reaction, respectively. The overall past infections were detected in 22 of the 411 animals, 5.4% (Confidence Interval (CI) 95% = 3.5% - 8.1%). The Kigoma rural area recorded the higher seroprevalence of 12.0% (CI 95% = 7.3% - 18.3%; p < 0.0001), followed by Kibondo at 2.3% (CI 95% = 0.5% - 6.5%; p > 0.05) and the Kasulu district at 0.8% (CI 95% = 0.0% - 4.2%; p > 0.05). The prevalence was 12.5% and 4.7% for sheep and goats, respectively. Reverse transcriptase polymerase chain reaction results indicated that only eight samples were found to be positive (n = 63). This study has confirmed, for the first time, the presence of the RVFV in the Kigoma region four years after the 2007 epizootic in Tanzania. The study further suggests that the virus activity exists during the inter-epizootic period, even in regions with no history of RVFV. PMID:25005550

  2. Active Tectonics In The Rukwa Rift (sw Tanzania): A Study of The Potential For Large Earthquakes In A Continental Rift.

    NASA Astrophysics Data System (ADS)

    Kervyn, F.

    The Rukwa rift is a deep sedimentary basin that is considered as a tectonic trans- fer zone between the Tanganyika and the Malawi troughs. The tectonic evolution of the depression is controlled by the reactivation of proterozoic structures and started with the deposition of the permo-triasic Karoo sediments. In the southeast, the rift is divided into two facing half graben separated by a Precambrian horst, whereas its northwestern part has a more symmetrical graben structure. Although most of the vertical displacement is accommodated by the Lupa eastern boundary fault, onshore shallow seismic profiles have confirmed the co-occurrence of intrabasin synthetic- and strike-slip faults within the sub surface sediments. Both normal and dextral strike-slip movement are indeed observed in the basin in response to the E-W to WNW-SSE ex- tension. The region has a moderate seismic activity and the earthquakes magnitude is generally below M 6.5. However, a M 7.4 earthquake occurred in the Rukwa region in 1910 but its exact location remains uncertain. The current research aimed at the identi- fication of active faults within the recent deposits of the basin by the combination in a GIS of radar interferometric data with topographical and geological maps, geophysical data, and field observations. Radar interferometry (InSAR) was found to be especially suitable for DEM computation in low relief areas where available topographic data are limited in accuracy. Numerous topographic lineaments were observed on InSAR DEM, and follow two main directions, both oblique to the main NW-SE trend of the rift. On the one hand, the GIS analysis confirms that the observed lineaments corre- spond to real natural alignment such like the drainage for example, and are therefore not related to atmospheric artefacts. On the other hand, the field observations revealed that in most cases, the topographic lineaments are very subtle and difficult to identify. However, direct correlations with tectonic structures (faults, fissures, ...) were recog- nized in some places. From the satellite imagery, the northwestern part of the basin is marked by the succession of paleo-shorelines evidencing the lake level fluctuations. The highest level was dated to 10.000 yrs BP, when the Rukwa was supposed to flow into lake Tanganyika. The corresponding shoreline is cut by a fault, ~ 40 km long, striking NNW-SSE, evidenced on the InSAR DEM and confirmed by the LANDSAT and ASTER optical imagery. Although a possible strike-slip component, the 5 to 10 1 meters of vertical offset from one to the other side of the fault would yield to a slip rate of 0.5 U 1mm/yr. 2

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

    NASA Astrophysics Data System (ADS)

    Schuster, Mathieu; Nutz, Alexis

    2015-04-01

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

  4. Style of extensional tectonism during rifting, Red Sea and Gulf of Aden

    USGS Publications Warehouse

    Bohannon, R.G.

    1989-01-01

    Geologic and geophysical studies from the Arabian continental margin in the southern Red Sea and LANDSAT analysis of the northern Somalia margin in the Gulf of Aden suggest that the early continental rifts were long narrow features that formed by extension on closely spaced normal faults above moderate- to shallow-dipping detachments with break-away zones defining one rift flank and root zones under the opposing rift flank. The rift flanks presently form the opposing continental margins across each ocean basin. The detachment on the Arabian margin dips gently to the west, with a breakaway zone now eroded above the deeply dissected terrain of the Arabian escarpment. A model is proposed in which upper crustal breakup occurs on large detachment faults that have a distinct polarity. -from Author

  5. Inflation rates, rifts, and bands in a p?hoehoe sheet flow

    USGS Publications Warehouse

    Hoblitt, Richard P.; Orr, Tim R.; Heliker, Christina; Denlinger, Roger P.; Hon, Ken; Cervelli, Peter F.

    2012-01-01

    The margins of sheet flows—p?hoehoe lavas emplaced on surfaces sloping Inflation and rift-band formation is probably cyclic, because the pattern we observed suggests episodic or crude cyclic behavior. Furthermore, some inflation rifts contain numerous bands whose spacing and general appearances are remarkably similar. We propose a conceptual model wherein the inferred cyclicity is due to the competition between the fluid pressure in the flow's liquid core and the tensile strength of the viscoelastic layer where it is weakest—in inflation rifts. The viscoelastic layer consists of lava that has cooled to temperatures between 800 and 1070 °C. This layer is the key parameter in our model because, in its absence, rift banding and stepwise changes in the flow height would not occur.

  6. Monitoring recent crustal movements in the Kenya rift valley by global positioning system (GPS) — a proposal

    NASA Astrophysics Data System (ADS)

    Rostom, R. S.

    There is evidence that the Kenya Rift is active. 1990 witnessed the execution of the Kenya Rift International Seismic Project to study the deep structure of the Kenya Rift. Yet there is no actual measurement of the rate of its spreading. Estimation based on volumes of volcanic rocks extruded over a given period has led to a wide range of estimates (0.2-2 mm/a). There is a need to establish geometrically the real spreading rate at present. The new technology (Global Positioning System) in its precise mode gives a promise to solve the problem. A preliminary network is proposed to consist of 4 points on each of the Rift walls. The logistics of site location, configuration of the network, observation method, frequency, etc. are discussed. The project requires international cooperation for execution.

  7. Workshop on The Rio Grande Rift: Crustal Modeling and Applications of Remote Sensing

    NASA Technical Reports Server (NTRS)

    Blanchard, D. P. (editor)

    1980-01-01

    The elements of a program that could address significant earth science problems by combining remote sensing and traditional geological, geophysical, and geochemical approaches were addressed. Specific areas and tasks related to the Rio Grande Rift are discussed.

  8. A Cycloid-like Rift Near Enceladus' South Pole: Europa-style Production by Tidal Stress

    Microsoft Academic Search

    T. A. Hurford; P. Helfenstein; R. Greenberg; G. V. Hoppa

    2007-01-01

    One prominent rift on Enceladus' south pole consists of arcuate segments, resembling the shape of cycloidal cracks on Europa. We explore the possibility that a similar mechanism may have caused the cracking on Enceladus as on Europa.

  9. 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

  10. Controls on strain localisation in the Middle to Late Jurassic North Sea rift system 

    E-print Network

    Gill, Caroline E

    2005-01-01

    Extensional fault propagation and linkage play an important role in the structural and sedimentological development of rift basins. In this study, use of 85,000km² 3D seismic data provides a new and unique opportunity ...

  11. Coupling volcanism and tectonics along divergent plate boundaries: collapsed rifts from Central Afar, Ethiopia

    Microsoft Academic Search

    Valerio Acocella

    2010-01-01

    Magma along divergent plate boundaries is erupted from fissures or vents from central volcanoes, with limited impact on rift architecture. Here I summarize the geological and structural features accompanying the eruption of part of a km-thick volcanic sequence (\\

  12. A kinematic model for the East African Rift D. Sarah Stamps,1

    E-print Network

    Nocquet, Jean-Mathieu

    A kinematic model for the East African Rift D. Sarah Stamps,1 Eric Calais,1 Elifuraha Saria,2 Chris blocks. Citation: Stamps, D. S., E. Calais, E. Saria, C. Hartnady, J.-M. Nocquet, C. J. Ebinger, and R. M

  13. Heat flow in the Nipigon arm of the Keweenawan rift, northwestern Ontario, Canada

    E-print Network

    Long, Bernard

    by Keweenawan diabase sills. It has been interpreted as a failed arm of the ca. 1100 Ma Keweenawan rift. Six new diabase sills ca. 1109 Ma [Davis and Sutcliffe, 1985; Sutcliffe, 1991]. Prior to the Keweenawan event

  14. Evidence for asymmetric nonvolcanic rifting and slow incipient oceanic accretion from seismic reflection data

    E-print Network

    Shillington, Donna J.

    -hinge faults. Although we cannot definitively discriminate between these possibilities, seismic reflectionEvidence for asymmetric nonvolcanic rifting and slow incipient oceanic accretion from seismic. [1] Prestack depth migrations of seismic reflection data collected around the Ocean Drilling Program

  15. Early growth of Kohala volcano and formation of long Hawaiian rift zones

    USGS Publications Warehouse

    Lipman, P.W.; Calvert, A.T.

    2011-01-01

    Transitional-composition pillow basalts from the toe of the Hilo Ridge, collected from outcrop by submersible, have yielded the oldest ages known from the Island of Hawaii: 1138 ?? 34 to 1159 ?? 33 ka. Hilo Ridge has long been interpreted as a submarine rift zone of Mauna Kea, but the new ages validate proposals that it is the distal east rift zone of Kohala, the oldest subaerial volcano on the island. These ages constrain the inception of tholeiitic volcanism at Kohala, provide the first measured duration of tholeiitic shield building (???870 k.y.) for any Hawaiian volcano, and show that this 125-km-long rift zone developed to near-total length during early growth of Kohala. Long eastern-trending rift zones of Hawaiian volcanoes may follow fractures in oceanic crust activated by arching of the Hawaiian Swell in front of the propagating hotspot. ?? 2011 Geological Society of America.

  16. Three-Dimensional (3D) Structure of the Malawi Rift from Remote Sensing and Geophysics Data

    NASA Astrophysics Data System (ADS)

    Salmi, Haifa S. Al; Abdelsalam, Mohamed G.

    2014-05-01

    The Malawi rift is a Cenozoic aged rift representing the southernmost segment of the Western Branch of the East African Rift System (EARS). This rift extends over 900 km from the Rungwe volcanic province (Tanzania) in the north to the Urema graben (Mozambique) to the south, with an average width of 50km. It traverses a complex array of Proterozoic orogenic belts of different ages and Permo-Triassic (Karoo) and cretaceous graben systems. The rift's depth is between 3 to 5km partitioned between the topographic escarpment and the sediments fill. The basin's subsidence reflects accumulation of sediments and rift flank uplift. Regardless of its importance in understanding rift tectonics, especially in Africa, the three-dimensional (3D) geometry of the rift is not fully understood. This research presents results from detailed analysis of Digital Elevation Model (DEM) extracted from the Shuttle Radar Topography Mission (SRTM) data to map surface morphological expressions of the entire basin. These results are compared with available seismic data to provide along-strike and at depth variation of the geometry of the border fault systems, nature of rift segmentation and alternation of the polarity of half-grabens, and the partitioning of displacement between exposed and sub-surface border faults. Our results show the following: (1) Surface expression of border faults show that, unlike the typical half-graben en-echelon rift model, where half-graben segments with opposite polarity are linked together through accommodation zones indicative of soft linkage, the Malawi rift shows along-strike segmentation by changing geometry from half-graben to full graben geometry. A half-graben with specific polarity passes through a full-graben geometry before giving place to a half-graben with the opposite polarity. The length of half-gaben and graben segments becomes shorter as the rift progresses from north to south, and this is accompanied by a decrease in displacement within border faults. This geometry is indicative of the propagation of border faults through hard linkage. (2) The continuation of border faults at the subsurface show patterns consistent with those observed at the surface. At the sub-surface, the general trend of rift segmentation, formation of full grabens at the end of each segment, and the decreases in the length of the segments from north to south is consistent with observations at the surface. This suggests the homogeneity of strain accommodation throughout the depth of border faults. (3) Zones of segmentation of the Malawi rift coincide with regions where the pre-existing structures (both the Proterozoic basement and the Karoo grabens) are at high angle to the trend of the rift whereas well-developed border faults of the basin coincides with N-trending pre-existing structures sub-parallel to the rift.

  17. Dynamics of ice shelf rift propagation and iceberg calving inferred from geodetic and seismic observations

    E-print Network

    Bassis, Jeremy N.

    2007-01-01

    the rift obtained from a satellite laser altimeter (ICESat).Laser Altimeter System (GLAS) onboard the Ice, Cloud and land Elevation Satellite (Laser Altimeter System (GLAS) on the Ice, Cloud and land Elevation Satellite (

  18. Predicting the Introduction and Transmission of Rift Valley Fever Virus in the United States 

    E-print Network

    Golnar, Andrew John

    2014-12-09

    Rift Valley fever virus (RVFV) is a mosquito-borne virus in the family Bunyaviridae that has spread throughout continental Africa to Madagascar and the Arabian Peninsula. The establishment of RVFV in North America would ...

  19. Origin of three-armed rifts in volcanic islands: the case of El Hierro (Canary Islands)

    NASA Astrophysics Data System (ADS)

    Galindo Jiménez, Inés; Becerril Carretero, Laura; Martí Molist, Joan; Gudmundsson, Agust

    2015-04-01

    Rifts zones in volcanic oceanic islands are common structures that have been explained through several theories/models. However, despite all these models it is as yet unclear whether it is the intense intrusive activity or the sector collapses that actually control the structural evolution and geometry of oceanic-island rift zones. Here we provide a new hypothesis to explain the origin and characteristics of the feeding system of oceanic-island rift zones based on the analysis of more than 1700 surface, subsurface (water galleries), and submarine structural data from El Hierro (Canary Islands). El Hierro's geological structure is primarily controlled by a three-armed rift-zone, the arms striking NE, WSW and S. Between the rift axes there are three valleys formed during huge landslides: El Golfo, El Julan, and Las Playas. Our results show: (1) a predominant NE-SW strike of structural elements, which coincides with the main regional trend of the Canary Archipelago as a whole; (2) a clear radial strike distribution of structural elements for the whole volcanic edifice (including submarine flanks) with respect to the centre of the island; (3) that the rift zones are mainly subaerial structures and do not propagate through the submarine edifice; (4) that it is only in the NE rift that structures have a general strike similar to that of the rift as a whole, and; (5) that in the W and S rifts there is not clear main direction, showing the structural elements in the W rift a fan distribution coinciding with the general radial pattern in the island as a whole. Based on these data, we suggest that the radial-striking structures reflect comparatively uniform stress fields that operated during the constructive episodes, mainly conditioned by the combination of overburden pressure, gravitational spreading, and magma-induced stresses. By contrast, in the shallower parts of the edifice, that is, the NE-SW, N-S and WNW-ESE-striking structures, reflect local stress fields related to the formation of mega-landslides and mask the general radial pattern. Thus, the rift zones on El Hierro are shallow structures that commonly capture and divert ascending magma towards different parts of the island but do not condition magma ascent at depth.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  1. Imaging the midcontinent rift beneath Lake Superior using large aperture seismic data

    USGS Publications Warehouse

    Trehu, Anne M.; Morel-a-l'Huissier, Patrick; Meyer, R.; Hajnal, Z.; Karl, J.; Mereu, R. F.; Sexton, J.; Shay, J.; Chan, W. K.; Epili, D.; Jefferson, T.; Shih, X. R.; Wendling, S.; Milkereit, B.; Green, A.; Hutchinson, Deborah R.

    1991-01-01

    We present a detailed velocity model across the 1.1 billion year old Midcontinent Rift System (MRS) in central Lake Superior. The model was derived primarily from onshore-offshore large-aperture seismic and gravity data. High velocities obtained within a highly reflective half-graben that was imaged on coincident seismic reflection data demonstrate the dominantly mafic composition of the graben fill and constrain its total thickness to be at least 30km. Strong wide-angle reflections are observed from the lower crust and Moho, indicating that the crust is thickest (55–60km) beneath the axis of the graben. The total crustal thickness decreases rapidly to about 40 km beneath the south shore of the lake and decreases more gradually to the north. Above the Moho is a high-velocity lower crust interpreted to result from syn-rift basaltic intrusion into and/or underplating beneath the Archean lower crust. The lower crust is thickest beneath the axis of the main rift half-graben. A second region of thick lower crust is found approximately 100km north of the axis of the rift beneath a smaller half graben that is interpreted to reflect an earlier stage of rifting. The crustal model presented here resembles recent models of some passive continental margins and is in marked contrast to many models of both active and extinct Phanerozoic continental rift zones. It demonstrates that the Moho is a dynamic feature, since the pre-rift Moho is probably within or above the high-velocity lower crust, whereas the post-rift Moho is defined as the base of this layer. In the absence of major tectonic activity, however, the Moho is very stable, since the large, abrupt variations in crustal thickness beneath the MRS have been preserved for at least a billion years.

  2. On rates and styles of late volcanism and rifting on Venus

    NASA Astrophysics Data System (ADS)

    Basilevsky, Alexander T.; Head, James W.

    2002-06-01

    We investigated the possibility of significant variations in the rates and styles of volcanism and rifting during the time postdating the formation of regional plains on Venus. We analyzed the age relations of all known impact craters >=30 km in diameter (183 craters) with the neighboring geologic units. Of these we selected 164 craters which were superposed on regional plains and determined if post-regional-plains (PRP) volcanics and/or PRP rift structures were present in the crater vicinity and if these craters postdated the volcanics and rift structures or predated them. In 53 cases it was possible to determine these relations. On the basis of these relationships, it was found that the general rates of volcanism and rifting during PRP time were close to constant or at least had no drastic changes. This implies a significant change in the rates of volcanism and rifting in the vicinity of the boundary between PRP time and the preceding time, which is marked by the formation of the global wrinkle-ridge network. It was also found that (1) the role of rift-associated volcanism during PRP time was close to constant or slightly decreasing, (2) the role of corona-related volcanism was noticeably decreasing, and (3) the role of noncorona, hot spot volcanism was proportionally increasing. The latter changes may be due to thickening of the lithosphere during PRP time. The results imply also that at most if not all places where PRP rifting occurred, the rift-associated fracturing, when started, continued for a significant part of PRP time. Our conclusions are valid both (1) for the case of a globally synchronous transition from emplacement of regional plains to the PRP regime and (2) for the case of such a transition occurring at different times in different areas of Venus.

  3. Rifting to drifting transition of the Southwest Subbasin of the South China Sea

    NASA Astrophysics Data System (ADS)

    Song, Taoran; Li, Chun-Feng

    2015-03-01

    Continental rupturing process and related dynamics on the onset of seafloor spreading remain poorly understood in the opening of the South China Sea. To constrain the timing and cause of major tectonic events, we focus on the rifting-to-drifting transition of the Southwest Subbasin, which has very wide extended continental margins. By carefully interpreting rifting structures and carbonate platforms and reefs, we distinguished two major unconformities, i.e., the breakup unconformity (BRU) and the mid-Miocene unconformity, in the two conjugate margins of the Southwest Subbasin. The age of the BRU in our study area is near the Oligocene/Miocene boundary (~23 Ma). Pre-stack depth migration of a recently acquired multichannel reflection seismic profile reveals complex structures and strong lateral velocity variations associated with a 3.5 km thick syn-rifting sequence developed right at the continent-ocean boundary (COB) of the Southwest Subbasin. This syn-rifting sequence is bounded landwards by a large seaward dipping fault, and tapers out seawards. An erosional truncation, which represents the mid-Miocene unconformity landwards but the older breakup unconformity on the seaward side, occurred at the top of this sequence. The overall transitional deformation style from the rifting to drifting suggests a successive episode of rifting, faulting, compression, tilting, and erosion at the COB during the crustal thinning and mantle upwelling. Localized thick syn-rifting deposition and early deposition beneath the BRU in the oceanic domain exist only at the seaward concave part of the COB, indicating discrete rifting and seafloor spreading prior to the buildup of a unified spreading center for the entire subbasin.

  4. Geodetic observations of the ongoing Dabbahu rifting episode: new dyke intrusions in 2006 and 2007

    Microsoft Academic Search

    Ian J. Hamling; Atalay Ayele; Laura Bennati; Eric Calais; Cynthia J. Ebinger; Derek Keir; Elias Lewi; Tim J. Wright; Gezahegn Yirgu

    2009-01-01

    A 60-km-long dyke intruded the Dabbahu segment of the Nubia-Arabia Plate boundary (Afar, Ethiopia) in 2005 September, marking the beginning of an ongoing rifting episode. We have monitored the continuing activity using Satellite Radar Interferometry (InSAR) and with data from Global Positioning System (GPS) instruments and seismometers deployed around the rift in response to the initial intrusion. These data show

  5. Deformation during the 1975-1984 Krafla rifting crisis, NE Iceland, measured from historical optical imagery

    NASA Astrophysics Data System (ADS)

    Hollingsworth, James; Leprince, SéBastien; Ayoub, FrançOis; Avouac, Jean-Philippe

    2012-11-01

    We measure the displacement field resulting from the 1975-1984 Krafla rifting crisis, NE Iceland, using optical image correlation. Images are processed using the COSI-Corr software package. Surface extension is accommodated on normal faults and fissures which bound the rift zone, in response to dike injection at depth. Correlation of declassified KH-9 spy and SPOT5 satellite images reveals extension between 1977-2002 (2.5 m average opening over 80 km), while correlation of aerial photos between 1957-1990 provide measurements of the total extension (average 4.3 m opening over 80 km). Our results show ˜8 m of opening immediately north of Krafla caldera, decreasing to 3-4 m at the northern end of the rift. Correlation of aerial photos from 1957-1976 reveal a bi-modal pattern of opening along the rift during the early crisis, which may indicate either two different magma sources located at either end of the rift zone (a similar pattern of opening was observed in the 2005 Afar rift crisis in East Africa), or variations in rock strength along the rift. Our results provide new information on how past dike injection events accommodate long-term plate spreading, as well as providing more details on the Krafla rift crisis. This study also highlights the potential of optical image correlation using inexpensive declassified spy satellite and aerial photos to measure deformation of the Earth's surface going back many decades, thus providing a new tool for measuring Earth surface dynamics, e.g. glaciers, landsliding, coastal erosion, volcano monitoring and earthquake studies, when InSAR and GPS data are not available.

  6. LARGE-SCALE VARIATION IN LITHOSPHERIC STRUCTURE ALONG AND ACROSS THE KENYA RIFT

    Microsoft Academic Search

    C PRODEHL; J MECHIE; W KAMINSKI; K FUCHS; C GROSSE; H HOFFMANN; R STANGL; R STELLRECHT; MA KHAN; PKH MAGUIRE; W KIRK; GR KELLER; A GITHUI; M BAKER; W MOONEY; E CRILEY; J LUETGERT; B JACOB; H THYBO; M DEMARTIN; S SCARASCIA; A HIRN; I NYAMBOK; S GACIRI; J PATEL; E DINDI; DH GRIFFITHS; RF KING; AE MUSSETT; LW BRAILE; G THOMPSON; K OLSEN; S HARDER; R VEES; D GAJEWSKI; A SCHULTE; J OBEL; F MWANGO; J MUKINYA; D RIAROH

    1991-01-01

    THE Kenya rift is one of the classic examples of a continental rift\\u000a zone: models for its evolution range from extension of the lithosphere\\u000a by pure shear 1, through extension by simple shear 2, to diapiric\\u000a upwelling of an asthenolith 3. Following a pilot study in 1985 4, the\\u000a present work involved the shooting of three seismic refraction and\\u000a wide-angle

  7. Precambrian lithospheric controls on the development of the East African rift system

    Microsoft Academic Search

    Andrew A. Nyblade; Richard A. Brazier

    2002-01-01

    We propose a new kinematic framework for the East African rift system linking the development of the Eastern and Western rifts via stress transmission across the Archean Tanzania craton. The proposal is based on three observations. (1) A new map of uppermost-mantle P-wave velocities beneath Tanzania, in combination with the results of other seismic, gravity, heat-flow, and xenolith studies, reveals

  8. The Historic and Future Roles of Magmatism and Underplate Beneath the Northern Main Ethiopian Rift

    NASA Astrophysics Data System (ADS)

    Cornwell, D. G.; England, R. W.; Maguire, P. K.; Stuart, G. W.

    2006-12-01

    The magmatic Northern Main Ethiopian Rift (NMER) is believed to represent the transitional stage between continental and oceanic rifting, with recent studies from the Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE) project concluding that magmatic processes dominate the rifting. 133 broadband seismometers were deployed in three separate arrays across the NMER at a spacing of between 5 and 30 km and receiver functions have been analyzed using H-? stacking, forward modelling and inversion techniques. H-? stacking results reveal a consistent V_p/V_s ratio of 1.75--1.80 and Moho depth of 38--40 km along 125 km of the south-eastern rift flank. Beneath the rift valley, the V_p/V_s ratios rise to over 1.90 with the Moho depth thinning to 30--35 km. The average crustal V_p/V_s ratio varies between 1.80 and 2.00 to the north-west of the rift. A lower crustal or upper mantle layer is confirmed beneath the north-western rift flank from the observation of a double P- to S-wave conversion, as identified by seismic refraction and interpreted as underplate. This layer thins from ~15 km to less than 10 km from NW to SE into the rift and is likely to have a V_p/V_s ratio of between 1.75 and 1.95. Beneath this layer, evidence for an upper mantle discontinuity exists, that shallows into the rift. These results, together with further receiver function analyses, indicate that significant magma has been added to the base of the crust and throughout the crust on the north-western rift flank and throughout the crust beneath the rift valley. It is unlikely that magma has been added beneath the south-eastern rift flank. The maximum crustal thinning and surface expression of the present-day rifting occur at the location where the underplate layer is at its thinnest or where there is no evidence for its existence. This may indicate that the underplate emplacement phase occurred and strengthened the crust beneath the Ethiopian Plateau and rifting followed by magmatic processes exploited the relatively thin and weak crust (aided by a pre-existing lithospheric suture or weak zone). The receiver function results are combined with and compared to shear-wave splitting, gravity, seismic tomography and controlled-source seismic results to build a 3D model of the location, volume, nature and emplacement history of magmatic addition to the base of the crust beneath the Ethiopian Plateau. We examine how this underplate layer affects the current magmatically-driven rifting in the NMER in terms of crustal thinning, recent magmatic addition throughout the whole crust and upper mantle partial melting.

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

    NASA Astrophysics Data System (ADS)

    Delvaux, Damien; Smets, Benoît

    2015-04-01

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

  10. Extreme uplift of the Rwenzori Mountains in the East African Rift, Uganda: Structural framework and possible role of glaciations

    Microsoft Academic Search

    Uwe Ring

    2008-01-01

    The >5-km-high Rwenzori Mountains in the East African Rift form a promontory on the rift shoulder and are an extreme expression of rift-mountain uplift. This study reports the pattern and the kinematics of major faults in the Rwenzori region. The fault pattern is characterized by a first set of N\\/NNE-striking normal faults that are offset by mainly NE- to E-striking

  11. Upper crustal structure in the vicinity of Lake Magadi in the Kenya Rift Valley region

    NASA Astrophysics Data System (ADS)

    Simiyu, Silas M.; Randy Keller, G.

    1998-11-01

    In 1994, the Kenya Rift International Seismic Project (KRISP) conducted a large-scale seismic experiment which extended across southern Kenya from Lake Victoria to the Indian Ocean. One major goal of the KRISP 94 effort was to determine the upper crustal structure of the southern Kenya Rift Valley near Lake Magadi. Thus in this area, the seismic refraction experiment was designed to obtain better resolution of shallow structures by employing a shorter seismic station spacing (1.5 km). In this study, these seismic data were used simultaneously with surface geology, drill hole data and gravity measurements to construct a relatively detailed model of the upper crust in the Lake Magadi region. This integrated analysis provided several significant results. At Lake Magadi, the rift floor is covered by low density-low velocity (2400 kg m -3 and 4.2 km s -1) sediments and volcanics that form a complex, asymmetric graben whose deepest portion (about 3.5 km) is found adjacent to the Nguruman Escarpment master fault to the west. This basin is about 2.0 km deep along its eastern margin and is divided into two sub-basins by a horst that runs along its axis, creating a localised gravity high. This simple structure was sufficient to produce the observed geophysical anomalies, so no pervasive magmatic modification of the upper crust was required. Beneath the rift basin, a 4 km thick layer, with relatively low velocities and densities, was found to extend from the eastern rift valley margin across the western rift flank to the vicinity of the Oloololo Scarp. This basement layer, with an average velocity of 5.6 km s -1 and a density of 2600 kg m -3, is intetpreted to represent a combination of quartzites and rocks fractured by the Neoproterozoic (Pan-African) collision of the Mozambique Belt and Tanzania Craton. Although Proterozoic rocks of the Mozambique Belt outcrop on both sides of the rift valley, the velocities, densities and thicknesses of the layers constituting the crystalline upper crust on the western rift flank are less than those on the eastern flank and similar to values found within the Tanzania Craton elsewhere. This suggests that the two rift flanks are located in different structural regimes (craton and mobile belt) with rifting having been localised along the boundary between them. From a deep crustal perspective, this boundary appears to be the western margin of the Mozambique Belt terrane, although rocks of this belt are found at the surface further west.

  12. The Baikal rift zone: the effect of mantle plumes on older structure

    NASA Astrophysics Data System (ADS)

    Zorin, Yu. A.; Turutanov, E. Kh.; Mordvinova, V. V.; Kozhevnikov, V. M.; Yanovskaya, T. B.; Treussov, A. V.

    2003-08-01

    The main chain of SW-NE-striking Cenozoic half-grabens of the Baikal rift zone (BRZ) follows the frontal parts of Early Paleozoic thrusts, which have northwestern and northern vergency. Most of the large rift half-grabens are bounded by normal faults at the northwestern and northern sides. We suggest that the rift basins were formed as a result of transformation of ancient thrusts into normal listric faults during Cenozoic extension. Seismic velocities in the uppermost mantle beneath the whole rift zone are less than those in the mantle beneath the platform. This suggests thinning of the lithosphere under the rift zone by asthenosphere upwarp. The geometry of this upwarp and the southeastward spread of its material control the crustal extension in the rift zone. This NW-SE extension cannot be blocked by SW-NE compression generated by pressure from the Indian lithospheric block against Central Asia. The geochemical and isotopic data from Late Cenozoic volcanics suggest that the hot material in the asthenospheric upwarp is probably provided by mantle plumes. To distinguish and locate these plumes, we use regional isostatic gravity anomalies, calculated under the assumption that topography is only partially compensated by Moho depth variations. Variations of the lithosphere-asthenosphere discontinuity depth play a significant role in isostatic compensation. We construct three-dimensional gravity models of the plume tails. The results of this analysis of the gravity field are in agreement with the seismic data: the group velocities of long-period Rayleigh waves are reduced in the areas where most of the recognized plumes are located, and azimuthal seismic anisotropy shows that these plumes influence the flow directions in the mantle above their tails. The Baikal rift formation, like the Kenya, Rio Grande, and Rhine continental rifts [Achauer, U., Granet, M., 1997. Complexity of continental rifts as revealed by seismic tomography and gravity modeling. In: Jacob, A.W.B., Delvaux, D., Khan, M.A. (Eds.), Lithosphere Structure, Evolution and Sedimentation in Continental Rifts. Proceedings of the IGCP 400 Meeting, Dublin, March 20-22, 1997. Institute of Advanced Studies, Dublin, pp. 161-171], is controlled by the three following factors: (i) mantle plumes, (ii) older (prerift) linear lithosphere structures favorably positioned relative to the plumes, and (iii) favorable orientation of the far-field forces.

  13. The Role of Rift Obliquity in Formation of the Gulf of California

    NASA Astrophysics Data System (ADS)

    Bennett, Scott Edmund Kelsey

    The Gulf of California illustrates how highly oblique rift geometries, where transform faults are kinematically linked to large-offset normal faults in adjacent pull-apart basins, enhance the ability of continental lithosphere to rupture and, ultimately, hasten the formation of new oceanic basins. The Gulf of California rift has accommodated oblique divergence of the Pacific and North America tectonic plates in northwestern Mexico since Miocene time. Due to its infancy, the rifted margins of the Gulf of California preserve a rare onshore record of early continental break-up processes from which to investigate the role of rift obliquity in strain localization. Using new high-precision paleomagnetic vectors from tectonically stable sites in north-central Baja California, I compile a paleomagnetic transect of Miocene ignimbrites across northern Baja California and Sonora that reveals the timing and distribution of dextral shear associated with inception of this oblique rift. I integrate detailed geologic mapping, basin analysis, and geochronology of pre-rift and syn-rift volcanic units to determine the timing of fault activity on Isla Tiburon, a proximal onshore exposure of the rifted North America margin, adjacent to the axis of the Gulf of California. The onset of strike-slip faulting on Isla Tiburon, ca. 8 - 7 Ma, was synchronous with the onset of transform faulting along a significant length of the nascent plate boundary within the rift. This tectonic transition coincides with a clockwise azimuthal shift in Pacific-North America relative motion that increased rift obliquity. I constrain the earliest marine conditions on southwest Isla Tiburon to ca. 6.4 - 6.0 Ma, coincident with a regional latest Miocene marine incursion in the northern proto-Gulf of California. This event likely flooded a narrow, incipient topographic depression along a ˜650 km-long portion of the latest Miocene plate boundary and corresponds in time and space with formation of a newly-constrained ˜50-100 kilometer-wide transtensional belt of focused strike-slip faulting, basin formation, and rotating crustal blocks. This proto-Gulf of California shear zone, embedded within the wider Mexican Basin and Range extensional province and connected to the San Andreas fault in southern California, hosted subsequent localization of the plate boundary and rupture of the continental lithosphere.

  14. Three-Dimensional Modelling of Rift Basin Evolution

    NASA Astrophysics Data System (ADS)

    Longshaw, S. M.; Finch, E.; Turner, M.; Gawthorpe, R. L.

    2009-12-01

    Numerical simulation of faulting is gaining interest, typically utilising the Discrete Element Modelling (DEM) technique. As computational power increases, so does the ability to run larger and more complex experiments. This research aims to explore rift basin evolution, with emphasis placed on the interaction of multiple faults as they evolve. Importance is placed on the technical aspects of implementing a complex and large DEM, specifically parallelism and whether currently popular software libraries known as physics engines can be a useful tool in their development. The technique employed is a variation of Mora and Place’s Lattice-Solid Model (1994). We use a 3D block of spheres, initially packed into a defined volume, interconnected using spring-damper structures. Elemental position is controlled throughout the simulation using Newtonian physics, while underlying plate movement is introduced by applying a specific force to each element. The spring-damper components provide a compressive force in the system, restricting each element to its neighbours, until the point the spring-damper has reached a pre-defined maximum extension, at which point it breaks resulting in a fault. Physical calculations are performed using using a publically available engine. The technical implementation of a physics engine is markedly more advanced than that found in many DEM codes used to date, specifically that of the collision detection system, which is implemented as a broad and then narrow phase process, which is solved as a Linear Complementarity Problem. In order to make use of large, distributed computing resources, a method by which to split the DEM into smaller sub-DEMs and then calculate each on an individual CPU has been defined. Typically results are accurate to within four decimal places compared to idealised values; this is comparable to other integration techniques such as Verlet or RK4. Through splitting the model and using multiple instances of a physics engine, it has been possible to limit the scale of simulation to available computing hardware, rather than software libraries. Extension of the crust results in an initial phase of a large number of small faults over which extensional strain is accommodated. As extension progresses, these faults are noted to either link to become larger structures or become inactive and passively rotated in the hanging-wall and footwalls of neighbouring structures. This does not mean, however, that they cannot be reactivated later during rift development. As deformation within the system reaches the rift climax phase, extension is focused on a small number of large faults within the basin. The timing, location, linkage and strain accommodated by these structures is determined during extension and examined as it progresses in three-dimensions. It can also be concluded that using a physics engine in the design of a geological DEM can be beneficial for development time, speed of execution and ensuring physical correctness. Model splitting provides a neat and scalable method by which to distribute computation of a large DEM over multiple CPUs and memory resources.

  15. 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-asthenosphere depth range beneath Mozambique.

  16. The Corinth Rift Laboratory (CRL) strainmeters: calibration and data analysis

    NASA Astrophysics Data System (ADS)

    Canitano, A.; Bernard, P.; Linde, A. T.; Sacks, S. I.; Boudin, F.

    2010-12-01

    The Gulf of Corinth (Greece) is one of the most seismic regions in Europe, producing some strong earthquakes in the decades, 1 to 1.5 cm/yr of north-south extension, and frequent seismic swarms. This structure is a 110 km long, N110E oriented graben bounded by systems of very recent normal faults. The Corinth Rift Laboratory (CRL) project is concentrated in the western part of the rift, around the city of Aigion, where instrumental seismicity and strain rate is highest. The CRL Network is made up about fifteen seismic stations as well as tiltmeters, strainmeters or GPS in order to study the local seismicity, and to observe and model the short and long term mechanics of the normal fault system. The instrumental seismicity in the Aigion zone clearly shows a strong concentration of small earthquakes between 5 and 10 km. In order to study slow transient deformation,two borehole strainmeters have been installed in the area (Trizonia, Monasteraki). We focus here on the one installed in the Trizonia island, which is continuously recording the horizontal strain at 150 m depth with a short term resolution better than 10-9. The dominant signal is the earth and sea tidal effects (few 10-7 strain), this one is modulated by the mechanical effects of the free oscillations of the Gulf with periods between 8 and 40 min. The barometric pressure fluctuations acts in combination with the mean sea level variation at longer periods and both effects are not independant. The comparison between the strain data and the two forcing signals exhibits a non zero phase delay of the sea-level which is increasing with period. We estimate a transfer function after few correlation iterations for each forcing signal but the physical interpretation of the sea-level function is still unclear. As the strainmeter is at 150 m depth, below the shoreline, a sea water percolation on land would increase the effect of sea level fluctuation, and be more efficient at longer periods. The dilatometer response to crustal sources, made possible recently through the record of the coseismic strain steps of the 2010, M=5.3 local events, shows a fast relaxation (hours). This suggests poor coupling to the rock, due to cementation problems. The sensor would then act dominantly as a pore pressure sensor. Taking into account the related transfer function, together with the one of the external signals, allow us to study accurately the residual signal in order to find slow transient signatures, especially during the reported seismic swarms. We also present here the first analysis of the Monasteraki strainmeter records after correction of the fast long term drift (10-7/day).

  17. 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.

  18. Lower Crustal Seismicity, Volatiles, and Evolving Strain Fields During the Initial Stages of Cratonic Rifting

    NASA Astrophysics Data System (ADS)

    Lambert, C.; Muirhead, J.; Ebinger, C. J.; Tiberi, C.; Roecker, S. W.; Ferdinand-Wambura, R.; Kianji, G.; Mulibo, G. D.

    2014-12-01

    The volcanically active East African rift system 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 rifting in cratonic lithosphere. Our 38-station broadband network spans all or parts of fault-bounded rift 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 rift. 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 rift 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 rift basins, and (3) a far-field ESE-WNW extensional stress regime. We explore the spatial correlation between zones of intense degassing along fault systems and seismicity, and examine the influence of high gas pressures on lower and upper crustal seismicity in this youthful cratonic rift zone.

  19. Traces of extension in continental lithosphere: Towards a seismic image of the Mid-Continent Rift

    NASA Astrophysics Data System (ADS)

    Frederiksen, A. W.; Bollmann, T. A.; Darbyshire, F. A.; Jurdy, D. M.; Revenaugh, J.; Stein, S. A.; van der Lee, S.; Wiens, D. A.; Wysession, M. E.

    2012-12-01

    The centre of the North American continent preserves tectonic events ranging from the Archean to the Proterozoic. One major late-stage event was the failed Mid-Continent Rift (MCR), a ca. 1.1 Ga episode of extension and magmatism along a ca. 2000 km path through the Great Lakes and environs. The rifting process never reached the point of developing an ocean basin, and so the MCR presumably preserves a snapshot of the rifting process at both crustal and lithospheric levels. The in-progress Superior Province Rifting Earthscope Experiment (SPREE) is a major multi-institution deployment of Earthscope Flexible Array instruments designed to augment the Transportable Array deployment as it crosses the MCR, both by extending coverage into Canada along the north shore of Lake Superior, and by concentrating a dense deployment of instruments along and across the terrestrial portion of the MCR in Minnesota and Wisconsin. Multiple seismic imaging techniques will be then used to obtain crustal and lithospheric images of the MCR, and so examine questions regarding the origin, propagation, and failure of the rift, and its relationship to the contemporaneous Grenville orogen. Though SPREE itself is in its early stages, some novel work has been done with pre-SPREE data. Notably, we present new tomographic and shear-wave splitting constraints on the region immediately west of the MCR. New results include delineation of the southern and western limits of the anomalous Western Superior lithosphere, which may have been particularly resistant to rifting; a novel low-velocity channel striking WNW-ESE beneath Minnesota and the Dakotas, which may represent an unrecognized failed branch of the MCR; and very weak lithospheric fabric beneath the unusual Minnesota River Valley terrane, which may reflect rifting-related disruption of previously-existing fabric, or a different tectonic origin to the remainder of the Superior. We will also present some preliminary travel-time and splitting results from early-stage SPREE data.

  20. Seismic anisotropy of the lithosphere/asthenosphere system beneath the Rwenzori region of the Albertine Rift

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    Shear-wave splitting measurements from local and teleseismic earthquakes are used to investigate the seismic anisotropy in the upper mantle beneath the Rwenzori region of the East African Rift system. At most stations, shear-wave splitting parameters obtained from individual earthquakes exhibit only minor variations with backazimuth. We therefore employ a joint inversion of SKS waveforms to derive hypothetical one-layer parameters. The corresponding fast polarizations are generally rift parallel and the average delay time is about 1 s. Shear phases from local events within the crust are characterized by an average delay time of 0.04 s. Delay times from local mantle earthquakes are in the range of 0.2 s. This observation suggests that the dominant source region for seismic anisotropy beneath the rift is located within the mantle. We use finite-frequency waveform modeling to test different models of anisotropy within the lithosphere/asthenosphere system of the rift. The results show that the rift-parallel fast polarizations are consistent with horizontal transverse isotropy (HTI anisotropy) caused by rift-parallel magmatic intrusions or lenses located within the lithospheric mantle—as it would be expected during the early stages of continental rifting. Furthermore, the short-scale spatial variations in the fast polarizations observed in the southern part of the study area can be explained by effects due to sedimentary basins of low isotropic velocity in combination with a shift in the orientation of anisotropic fabrics in the upper mantle. A uniform anisotropic layer in relation to large-scale asthenospheric mantle flow is less consistent with the observed splitting parameters.

  1. Evolution of stratigraphic sequences in multisegmented continental rift basins: Comparison of computer models with the basins of the East African rift system

    Microsoft Academic Search

    Juan Contreras; Christopher H. Scholz

    This article presents a series of numerical simulations of the strati- graphic evolution of continental rift basins. We model the geomor- phic and tectonic processes acting in this depositional environment, which contrasts with the traditional approach of modeling the set- tling of sediments, especially in marine clastic basins. What is new in our model is that it can simulate the

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

    Microsoft Academic Search

    Kevin Aanyu; Daniel Koehn

    2010-01-01

    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

  3. Rifting-to-drifting transition of the South China Sea: early Cenozoic syn-rifting deposition imaged with prestack depth migration

    NASA Astrophysics Data System (ADS)

    Song, T.; Li, C.; Li, J.

    2012-12-01

    One of the major unsolved questions of the opening of the South China Sea (SCS) is its opening sequences and episodes. It has been suggested, for example, that the opening of the East and Northwest Sub-basins predated, or at least synchronized with, that of the Southwest Sub-basin, a model contrasting with some others in which an earlier opening in the Southwest Sub-basin is preferred. Difficulties in understanding the perplexing relationships between different sub-basins are often compounded by contradicting evidences leading to different interpretations. Here we carry out pre-stack depth migration of a recently acquired multichannel reflection seismic profile from the Southwest Sub-basin of the SCS in order to reveal complicated subsurface structures and strong lateral velocity variations associated with a thick syn-rifting sequence on the southern margin of the Southwest Sub-basin. Combined with gravimetric and magnetic inversion and modeling, this depth section helps us understand the complicated transitional processes from continental rifting to seafloor spreading. This syn-rifting sequence is found to be extremely thick, over 2 seconds in two-way travel time, and is located directly within the continent-ocean transition zone. It is bounded landwards by a seaward dipping fault, and tapers out seaward. The top of this sequence is an erosional truncation, representing mainly the Oligocene-Miocene unconformity landward but slightly an older unconformity on the seaward side. Stronger erosions of this sequence are found toward the ocean basin. The sequence itself is severely faulted by a group of seaward dipping faults developed mainly within the sequence. The overall deformation style suggests a successive episode of rifting, faulting, compression, tilting, and erosion, prior to seafloor spreading. Integrating information from gravity anomalies and seismic velocities, we interpret that this sequence represents a syn-rifting sequence developed during a long period of rifting in the Southwest Sub-basin prior to the inception of seafloor spreading. The initial rifting in the Southwest Sub-basin appears to be no later, if not earlier, than in the East Sub-basin. Initial seafloor spreading incurred significant shortening, erosion, inversion, and fault tilting.

  4. The North Galactic Pole Rift and the Local Hot Bubble

    NASA Astrophysics Data System (ADS)

    Snowden, S. L.; Koutroumpa, D.; Kuntz, K. D.; Lallement, R.; Puspitarini, L.

    2015-06-01

    The North Galactic Pole Rift (NGPR) is one of the few distinct neutral hydrogen clouds at high Galactic latitudes that have well-defined distances. It is located at the edge of the Local Cavity (LC) and provides an important test case for understanding the Local Hot Bubble (LHB), the presumed location for the hot diffuse plasma responsible for much of the observed 1/4 keV emission originating in the solar neighborhood. Using data from the ROSAT All-Sky Survey and the Planck reddening map, we find the path length within the LC (LHB plus Complex of Local Interstellar Clouds) to be 98 ± 27 pc, in excellent agreement with the distance to the NGPR of 98 ± 6 pc. In addition, we examine another 14 directions that are distributed over the sky where the LC wall is apparently optically thick at 1/4 keV. We find that the data in these directions are also consistent with the LHB model and a uniform emissivity plasma filling most of the LC.

  5. A statistical model of Rift Valley fever activity in Egypt

    PubMed Central

    Hassan, Ali N.; Beier, John C.

    2014-01-01

    Rift Valley fever (RVF) is a viral disease of animals and humans and a global public health concern due to its ecological plasticity, adaptivity, and potential for spread to countries with a temperate climate. In many places, outbreaks are episodic and linked to climatic, hydrologic, and socioeconomic factors. Although outbreaks of RVF have occurred in Egypt since 1977, attempts to identify risk factors have been limited. Using a statistical learning approach (lasso-regularized generalized linear model), we tested the hypotheses that outbreaks in Egypt are linked to (1) River Nile conditions that create a mosquito vector habitat, (2) entomologic conditions favorable to transmission, (3) socio-economic factors (Islamic festival of Greater Bairam), and (4) recent history of transmission activity. Evidence was found for effects of rainfall and river discharge and recent history of transmission activity. There was no evidence for an effect of Greater Bairam. The model predicted RVF activity correctly in 351 of 358 months (98.0%). This is the first study to statistically identify risk factors for RVF outbreaks in a region of unstable transmission. PMID:24581353

  6. An Assembly Model of Rift Valley Fever Virus

    PubMed Central

    Rusu, Mirabela; Bonneau, Richard; Holbrook, Michael R.; Watowich, Stanley J.; Birmanns, Stefan; Wriggers, Willy; Freiberg, Alexander N.

    2012-01-01

    Rift Valley fever virus (RVFV) is a bunyavirus endemic to Africa and the Arabian Peninsula that infects humans and livestock. The virus encodes two glycoproteins, Gn and Gc, which represent the major structural antigens and are responsible for host cell receptor binding and fusion. Both glycoproteins are organized on the virus surface as cylindrical hollow spikes that cluster into distinct capsomers with the overall assembly exhibiting an icosahedral symmetry. Currently, no experimental three-dimensional structure for any entire bunyavirus glycoprotein is available. Using fold recognition, we generated molecular models for both RVFV glycoproteins and found significant structural matches between the RVFV Gn protein and the influenza virus hemagglutinin protein and a separate match between RVFV Gc protein and Sindbis virus envelope protein E1. Using these models, the potential interaction and arrangement of both glycoproteins in the RVFV particle was analyzed, by modeling their placement within the cryo-electron microscopy density map of RVFV. We identified four possible arrangements of the glycoproteins in the virion envelope. Each assembly model proposes that the ectodomain of Gn forms the majority of the protruding capsomer and that Gc is involved in formation of the capsomer base. Furthermore, Gc is suggested to facilitate intercapsomer connections. The proposed arrangement of the two glycoproteins on the RVFV surface is similar to that described for the alphavirus E1-E2 proteins. Our models will provide guidance to better understand the assembly process of phleboviruses and such structural studies can also contribute to the design of targeted antivirals. PMID:22837754

  7. Climate Change Affects the East African Rift Valley Lakes

    NASA Astrophysics Data System (ADS)

    O'Reilly, C. M.; Plisnier, P.; Cohen, A. S.

    2004-12-01

    Over the last 100 years, air temperatures in eastern African have been warming consistent with the global average temperature increase. This has led to warmer water temperatures in the East African Rift Valley lakes, increasing the stability of the water column. Subsequently, there has been a reduction in the upwelling of deep nutrient-rich waters that are the primary source of nutrients for most of these lakes. There were decreases in surface water N and P and increases in the Si:P ratio over the past 70 years for Lakes Malawi, Tanganyika, Edward, and Albert. The lower nutrient concentrations in the surface waters were associated with reduced algal biomass and increased water clarity. The consistent, regional-scale changes among these lakes provide strong evidence that climate warming may be having a large negative affect on these unique tropical lakes. A decrease in primary productivity of 20% has been indicated for Lake Tanganyika, which would be associated with a 30% decrease in fisheries yields. The human implications of such subtle, but progressive, environmental changes are potentially dire in this densely populated region of the world, where these large lakes are an important nutritional and economic resource.

  8. Observations on rift valley fever virus and vaccines in Egypt

    PubMed Central

    2011-01-01

    Rift Valley Fever virus (RVFV, genus: Phlebovirus, family: Bunyaviridae), is an arbovirus which causes significant morbidity and mortality in animals and humans. RVFV was introduced for the first time in Egypt in 1977. In endemic areas, the insect vector control and vaccination is considering appropriate measures if applied properly and the used vaccine is completely safe and the vaccination programs cover all the susceptible animals. Egypt is importing livestock and camels from the African Horn & the Sudan for human consumption. The imported livestock and camels were usually not vaccinated against RVFV. But in rare occasions, the imported livestock were vaccinated but with unknown date of vaccination and the unvaccinated control contacts were unavailable for laboratory investigations. Also, large number of the imported livestock and camels are often escaped slaughtering for breeding which led to the spread of new strains of FMD and the introduction of RVFV from the enzootic African countries. This article provide general picture about the present situation of RVFV in Egypt to help in controlling this important disease. PMID:22152149

  9. Middle Stone Age starch acquisition in the Niassa Rift, Mozambique

    NASA Astrophysics Data System (ADS)

    Mercader, Julio; Bennett, Tim; Raja, Mussa

    2008-09-01

    The quest for direct lines of evidence for Paleolithic plant consumption during the African Middle Stone Age has led scientists to study residues and use-wear on flaked stone tools. Past work has established lithic function through multiple lines of evidence and the spatial breakdown of use-wear and microscopic traces on tool surfaces. This paper focuses on the quantitative analysis of starch assemblages and the botanical identification of grains from flake and core tools to learn about human ecology of carbohydrate use around the Niassa woodlands, in the Mozambican Rift. The processing of starchy plant parts is deduced from the occurrence of starch assemblages that presumably got attached to stone tool surfaces by actions associated with extractive or culinary activities. Specifically, we investigate starch grains from stone tools recently excavated in northern Mozambique at the site of Mikuyu; which presumably spans the middle to late Pleistocene and represents similar sites found along the Malawi/Niassa corridor that links East, Southern, and Central Africa. Starch was extracted and processed with a diverse tool kit consisting of scrapers, cores, points, flakes, and other kinds of tools. The microbotanical data suggests consumption of seeds, legumes, caryopses, piths, underground storage organs, nuts, and mesocarps from more than a dozen families. Our data suggest a great antiquity for starch use in Africa as well as an expanded diet and intensification.

  10. Lacustrine deposits in rifted deep basins of Yellow Sea

    SciTech Connect

    Han, J.H.

    1985-02-01

    The central Yellow Sea is a typical intracratonic rifted basin that consists of 4 major depressions bounded by aligned listric faults along horst blocks of uplifted basement (Kunsan, West Kunsan, Yellow Sea sub-basins, and Central Trough). The depressions are half grabens caused by pull-apart extensional stresses. Core analysis and micropaleotologic study indicate that more than 5 km of lacustrine sediments were accumulated in the central part of the West Kunsan basin. Two distinctive sedimentary successions are recognized in the core descriptions: alternation of reddish-brown siltstones and sandstones containing evaporites and marlstones, and an overlying progradational sequence including minor limestone beds in the lower part of the sequence. The progradational sequence is interpreted as lacustrine deltaic deposits. Abundant palynofloral occurrence of freshwater green algae, Pediastrum, and absence of marine fauna such as dinoflagellates are also supporting evidence for a lacustrine environment. The lithofacies and tectonic framework of the Yellow Sea are very similar to those of Cretaceous lacustrine sediments of the Korea Peninsula onshore and Pohai coastal basin in China.

  11. Rift Valley fever virus infection in golden Syrian hamsters.

    PubMed

    Scharton, Dionna; Van Wettere, Arnaud J; Bailey, Kevin W; Vest, Zachary; Westover, Jonna B; Siddharthan, Venkatraman; Gowen, Brian B

    2015-01-01

    Rift Valley fever virus (RVFV) is a formidable pathogen that causes severe disease and abortion in a variety of livestock species and a range of disease in humans that includes hemorrhagic fever, fulminant hepatitis, encephalitis and blindness. The natural transmission cycle involves mosquito vectors, but exposure can also occur through contact with infected fluids and tissues. The lack of approved antiviral therapies and vaccines for human use underlies the importance of small animal models for proof-of-concept efficacy studies. Several mouse and rat models of RVFV infection have been well characterized and provide useful systems for the study of certain aspects of pathogenesis, as well as antiviral drug and vaccine development. However, certain host-directed therapeutics may not act on mouse or rat pathways. Here, we describe the natural history of disease in golden Syrian hamsters challenged subcutaneously with the pathogenic ZH501 strain of RVFV. Peracute disease resulted in rapid lethality within 2 to 3 days of RVFV challenge. High titer viremia and substantial viral loads were observed in most tissues examined; however, histopathology and immunostaining for RVFV antigen were largely restricted to the liver. Acute hepatocellular necrosis associated with a strong presence of viral antigen in the hepatocytes indicates that fulminant hepatitis is the likely cause of mortality. Further studies to assess the susceptibility and disease progression following respiratory route exposure are warranted. The use of the hamsters to model RVFV infection is suitable for early stage antiviral drug and vaccine development studies. PMID:25607955

  12. Observations on rift valley fever virus and vaccines in Egypt.

    PubMed

    Ahmed Kamal, Samia

    2011-01-01

    Rift Valley Fever virus (RVFV, genus: Phlebovirus, family: Bunyaviridae), is an arbovirus which causes significant morbidity and mortality in animals and humans. RVFV was introduced for the first time in Egypt in 1977. In endemic areas, the insect vector control and vaccination is considering appropriate measures if applied properly and the used vaccine is completely safe and the vaccination programs cover all the susceptible animals. Egypt is importing livestock and camels from the African Horn & the Sudan for human consumption. The imported livestock and camels were usually not vaccinated against RVFV. But in rare occasions, the imported livestock were vaccinated but with unknown date of vaccination and the unvaccinated control contacts were unavailable for laboratory investigations. Also, large number of the imported livestock and camels are often escaped slaughtering for breeding which led to the spread of new strains of FMD and the introduction of RVFV from the enzootic African countries. This article provide general picture about the present situation of RVFV in Egypt to help in controlling this important disease. PMID:22152149

  13. Rift Valley fever: an uninvited zoonosis in the Arabian peninsula.

    PubMed

    Balkhy, Hanan H; Memish, Ziad A

    2003-02-01

    Rift Valley fever (RVF) is an acute viral disease, affecting mainly livestock but also humans. The virus is transmitted to humans through mosquito bites or by exposure to blood and bodily fluids. Drinking raw, unpasteurized milk from infected animals can also transmit RVF. Routine vaccination of livestock in Africa has been prohibitively expensive, leading to endemicity of RVF in most African countries. Reports in September 2000 first documented RVF occurring outside of Africa in the Kingdom of Saudi Arabia and Yemen. Prior to this outbreak, the potential for RVF spread into the Arabian Peninsula had already been exemplified by a 1977 Egyptian epidemic. This appearance of RVF outside the African Continent might be related to importation of infected animals from Africa. In the most recent outbreak patients presented with a febrile haemorrhagic syndrome accompanied by liver and renal dysfunction. By the end of the outbreak, April 2001 statistics from the Saudi Ministry of Health documented a total of 882 confirmed cases with 124 deaths. Both the severity of disease and the relatively high 14% death rate might be a consequence of underreporting of less severe disease. Travellers to endemic areas may be at risk of acquiring the disease if exposed to animals or their body fluids directly or through mosquito bites. Special education regarding both modes of transmission and the geographical distribution of this disease needs to be given to travellers at risk. PMID:12615379

  14. Climate-disease connections: Rift Valley Fever in Kenya

    NASA Technical Reports Server (NTRS)

    Anyamba, A.; Linthicum, K. J.; Tucker, C. J.

    2001-01-01

    All known Rift Valley fever(RVF) outbreaks in Kenya from 1950 to 1998 followed periods of abnormally high rainfall. On an interannual scale, periods of above normal rainfall in East Africa are associated with the warm phase of the El Nino/Southern Oscillation (ENSO) phenomenon. Anomalous rainfall floods mosquito-breeding habitats called dambos, which contain transovarially infected mosquito eggs. The eggs hatch Aedes mosquitoes that transmit the RVF virus preferentially to livestock and to humans as well. Analysis of historical data on RVF outbreaks and indicators of ENSO (including Pacific and Indian Ocean sea surface temperatures and the Southern Oscillation Index) indicates that more than three quarters of the RVF outbreaks have occurred during warm ENSO event periods. Mapping of ecological conditions using satellite normalized difference vegetation index (NDVI) data show that areas where outbreaks have occurred during the satellite recording period (1981-1998) show anomalous positive departures in vegetation greenness, an indicator of above-normal precipitation. This is particularly observed in arid areas of East Africa, which are predominantly impacted by this disease. These results indicate a close association between interannual climate variability and RVF outbreaks in Kenya.

  15. Persistence of Rift Valley fever virus in East Africa

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  16. Constraints on the magmatic plumbing system of the Dabbahu rift (Afar, Ethiopia) from InSAR and GPS.

    NASA Astrophysics Data System (ADS)

    Wright, T. J.; Calais, E.; Biggs, J.; Lewi, E.; Hamling, I.; Ebinger, C. J.

    2006-12-01

    The 60-km-long Dabbahu segment of Nubia-Arabia plate boundary the experienced a major rifting episode in September 2005 when 2.5~km3 of magma was injected in the upper 10~km of the crust along a dike with a maximum thickness of 8~m (Wright et al., 2006). Subsidence around Dabbahu and Gabho volcanoes, at the northern end of the rift segment, suggests that at least 20% of the injected magma came from shallow magma chambers, 3-5~km beneath these volcanoes. This volume estimate could rise significantly if the magma contains a significant volatile fraction and is highly compressible. However, it is probable that additional, deep magma reservoirs injected magma directly into the dike during the rifting episode. To investigate the magmatic plumbing system around the rift segment, we have created interferograms showing the pre- and post-diking deformation around the Dabbahu rift segment, and analysed cGPS data collected from 10 instruments installed around the rift segment in January 2006. We show that Gabho experienced at least three inflation events prior to the 2005 diking episode, suggesting episodic recharge of the magma chamber beneath Gabho. Furthermore, time series of post-rifting interferograms, and cGPS data, show that Gabho has been inflating extremely rapidly since September 2005, and that Dabbahu, after an initial period of deflation, is now also inflating. A broad area of post-diking subsidence south of the rift segment suggests magma may be flowing towards the rift segment at sub-crustal levels. An additional dyke injection occurred in June 2006 near the centre of the rift segment, without subsidence at Dabbahu and Gabho, implying an additional magmatic source. We will present the latest geodetic data from the Dabbahu rift segment, and simple models of the magmatic plumbing system.

  17. Left-lateral transtension along the Ethiopian Rift and constrains on the mantle-reference plate motions

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    We present the kinematics of the Ethiopian Rift, in the northern part of East African Rift System, derived from compilation of geodetic velocities, focal mechanism inversions, structural data analysis and geological profiles. In the central Ethiopian Rift, 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 rift. 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 rift itself. We analyzed the kinematics of the Ethiopian Rift also relative to the mantle comparing the results in the deep and shallow hotspot reference frames. While the oblique orientation of the rift was controlled by the pre-existing lithospheric fabric, the two reference frames predict different kinematics of Africa and Somalia plates along the rift itself, both in magnitude and direction, and with respect to the mantle. However, the observed kinematics and tectonics along the rift 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 rifting in transtensional settings and provide evidence for the kinematics of the Ethiopian Rift in the context of the Africa-Somalia plate interaction in the mantle reference frame.

  18. A multidisciplinary study of the final episode of the Manda Hararo dyke sequence, Ethiopia, and implications for trends in volcanism during the rifting cycle

    E-print Network

    Barnie, T. D.; Keir, D.; Hamling, I.; Hofmann, B.; Belachew, M.; Carn, S.; Eastwell, D.; Hammond, J. O. S.; Ayele, A.; Oppenheimer, C.; Wright, T.

    2015-01-01

    The sequence of dyke intrusions between 2005 and 2010 in the Manda Hararo rift segment, Ethiopia, provided an opportunity to test conceptual models of continental rifting. Based on trends up to dyke 13 in the sequence, it was anticipated that...

  19. Exhumation, rift-flank uplift, and the thermal evolution of the Rwenzori Mountains determined by combined (U-Th)/He and U-Pb thermochronometry

    E-print Network

    MacPhee, Daniel

    2006-01-01

    Rising over 5 km along the border of Uganda and the Democratic Republic of the Congo, the Rwenzori Mountains represent an extreme example of basement rift-flank uplift in the western branch of the East African Rift, a ...

  20. ENAM: A community seismic experiment targeting rifting processes and post-rift evolution of the Mid Atlantic US margin

    NASA Astrophysics Data System (ADS)

    Van Avendonk, H. J.; Magnani, M. B.; Shillington, D. J.; Gaherty, J. B.; Hornbach, M. J.; Dugan, B.; Long, M. D.; Lizarralde, D.; Becel, A.; Benoit, M. H.; Harder, S. H.; Wagner, L. S.; Christeson, G. L.

    2014-12-01

    The continental margins of the eastern United States formed in the Early Jurassic after the breakup of supercontinent Pangea. The relationship between the timing of this rift episode and the occurrence of offshore magmatism, which is expressed in the East Coast Magnetic Anomaly, is still unknown. The possible influence of magmatism and existing lithospheric structure on the rifting processes along margin of the eastern U.S. was one of the motivations to conduct a large-scale community seismic experiment in the Eastern North America (ENAM) GeoPRISMS focus site. In addition, there is also a clear need for better high-resolution seismic data with shallow penetration on this margin to better understand the geological setting of submarine landslides. The ENAM community seismic experiment is a project in which a team of scientists will gather both active-source and earthquake seismic data in the vicinity of Cape Hatteras on a 500 km wide section of the margin offshore North Carolina and Virginia. The timing of data acquisition in 2014 and 2015 facilitates leveraging of other geophysical data acquisition programs such as Earthscope's Transportable Array and the USGS marine seismic investigation of the continental shelf. In April of 2014, 30 broadband ocean-bottom seismometers were deployed on the shelf, slope and abyssal plain of the study site. These instruments will record earthquakes for one year, which will help future seismic imaging of the deeper lithosphere beneath the margin. In September and October of 2014, regional marine seismic reflection and refraction data will be gathered with the seismic vessel R/V Marcus Langseth, and airgun shots will also be recorded on land to provide data coverage across the shoreline. Last, in the summer of 2015, a land explosion seismic refraction study will provide constraints on the crustal structure in the adjacent coastal plain of North Carolina and Virginia. All seismic data will be distributed to the community through IRIS/DMC and the LDEO/UTIG Seismic data center. Two workshops are planned for 2015, where new users get an opportunity to engage in basic processing and analysis of the new data set.

  1. Complexities in rift initiation and development within the Iceland Plateau, North-Atlantic.

    NASA Astrophysics Data System (ADS)

    Brandsdóttir, Bryndís; Hooft, Emilie; Mjelde, Rolf; Murai, Yoshio

    2015-04-01

    Spreading north of Iceland has been complex since the break-up of the North Atlantic in late Paleocene-early Eocene. Magnetic anomalies within the Iceland Plateau, west of the Ægir Ridge and along the Greenland-Iceland-Faeroe Ridge are irregular, formed by plate boundary complexities at breakup, branched accretion zones, westward rifting relocations, and large overlapping rifts. The 700 km long KRISE7 seismic refraction/reflection and gravity profile, straddles 66.5°N, between the Kolbeinsey and Ægir Ridges, crossing the three physiographic provinces that characterize this region: the Iceland Shelf, Iceland Plateau and Norway Basin. On the basis of crustal thickness and velocity structure, combined with older seismic reflection profiles and drill cores, these provinces correspond to three individual spreading rifts that were active at different time periods. The deep, fan shaped Norway basin was formed during the initial opening of the Atlantic by spreading at the now extinct Ægir Ridge. The oldest crust in the western Norway Basin has thickness 8-10 km and this thins to 4-5 km at the Ægir Ridge reflecting the progressive abandonment of spreading at this rift axis. The eastern Iceland Plateau was the locus of an extinct spreading center, which was segmented and overlapped the Ægir Ridge by 300 km. Spreading on the Iceland Plateau rift occurred simultaneously with that on the Ægir Ridge prior to 26 Ma, when the Kolbeinsey Ridge was initiated by a westward rift jump. The Iceland Plateau rift formed by rifting along the continent-ocean transition at the former central E-Greenland margin, associated with the formation of the Jan Mayen Ridge. Lower crustal domes and corresponding gravity highs across the Iceland Plateau mark the location of the extinct rift axis. The crust at the Iceland Plateau rift is thicker (12-15 km) that that at the conjugate Ægir Ridge and formed under active upwelling conditions (normal lower crustal velocities), which we attribute to the influence of the Iceland plume. The overlapping geometry of the Ægir and Iceland Plateau rift, led to progressive south to north abandonment of spreading on the Ægir Ridge. Rifting at the Kolbeinsey Ridge in the last 26 Ma formed the shallowest physiographic province, the Iceland Shelf. Initiation of the Kolbeinsey Ridge is recorded in very thick crust (24-28 km) at the eastern Iceland Shelf, due to significant increase in melt flux (active, plume driven upwelling) which caused the spreading axis to jump from the Iceland Plateau to the new Kolbeinsey ridge. Magmatism at the new Kolbeinsey Ridge was also associated with unusual large amounts of extrusive volcanism as recorded by an extremely thick (6 km) layer of low velocities in this region. As the Iceland plume approached the Mid-Atlantic ridge from the west, three separate spreading centers formed - each progressively further west. Magma from the plume generated new zones of weakness at the continent-ocean boundary and thus facilitated new spreading rifts. The plume influence is documented in thicker crust as each successive spreading center was initiated.

  2. Intrusion of Oceanic-type Basaltic Melts Precedes Continental Break up in the Red Sea Rift

    NASA Astrophysics Data System (ADS)

    Bonatti, Enrico; Ligi, Marco; Ronca, Sara; Seyler, Monique; Bosworth, William; Cipriani, Anna

    2013-04-01

    The role of magmatism in continental rifting and break up and in the birth of a new ocean are not well understood. Continental break up can take place with intense and voluminous volcanism, as in the Southern Red Sea/Afar Rift, or in a relatively amagmatic mode, as in the Mesozoic Iberian Atlantic rift. Studies of gabbros from the Brothers and Zabargad islands suggest that continental break up in the northern Red Sea, a relatively non-volcanic rift, is preceded by intrusion of oceanic-type basaltic melts that crystallize at progressively shallower crustal depths as rifting progresses towards continental break-up. A seismic reflection profile running across the central part of the southern Thetis basin, shows a ~5 km wide reflector ~1.25 s below the axial neovolcanic zone. We interpret it as marking the roof of a magma chamber or melt lens, similar to those identified below several mid-ocean ridges. Assuming a 4.5 km/s acoustic velocity for the upper oceanic crust at Thetis, this reflector is ~3.5 km below the seafloor. The presence of a few kilometers deep subrift magma chamber soon after the initiation of oceanic spreading implies the crystallization of lower oceanic crust intrusives as a last step in a sequence of basaltic melt intrusion from pre-oceanic continental rifting to oceanic spreading. Thus, oceanic crust accretion in the Red Sea rift starts at depth before continental break up, emplacement of oceanic basalt at the sea floor, and development of Vine-Matthews magnetic anomalies, pointing to a rift model, where the lower continental lithosphere has been replaced by upwelling asthenosphere before continental rupturing. This model would imply depth-dependent extension due to decoupling between the upper and lower lithosphere with mantle-lithosphere-necking breakup before crustal-necking breakup. This mode of initial oceanic crust accretion may have been common in Mesozoic Atlantic-type rifts, in addition to wider, amagmatic, Iberian-type continent-ocean zones of transition.

  3. Continued dyking in the Dabbuhu Rift segment, Afar, Ethiopia, from radar interferometry.

    NASA Astrophysics Data System (ADS)

    Hamling, I. J.; Keir, D.; Ayele, A.; Calais, E.; Ebinger, C.; Lewi, E.; Yirgu, G.; Wright, T.

    2007-12-01

    The 60-km-long Dabbahu segment of the Nubia-Arabia plate boundary lies in the Northern Ethiopian region of Afar. In September 2005 a major rifting episode resulted in the injection of a 60-km-long dyke with a maximum thickness of ~8m (Wright et al., 2006). Subsidence observed at Dabbahu and Gabho volcanoes implied that some of the magma was sourced from shallow reservoirs beneath the volcanoes. Using a combination of satellite interferometry, GPS and seismicity we aim to monitor the ongoing deformation in the Dabbahu rift segment. Interferograms in the following months show only isolated deformation around the volcanoes and around the centre of the Dabbahu rift segment. However, in June 2006, intense deformation is observed along a rift parallel, 10 km long zone extending north of Ado"Ale, which is a volcanic complex located in the middle of the rift segment. Modelling of radar interferometry (InSAR) data indicates the injection of a ~2 m thick, ~10 km long dyke, with deformation spatially coincident with seismicity (Keir et al., this session). Since June 2006 a further 5 dyke intrusions have been detected using InSAR - in July, September and December of 2006 and in January and August of 2007. Elastic modelling of InSAR data suggests that a ~2 m thick, ~9 km long dyke was intruded in July 2006 followed by a ~2 m thick, ~8 km long dyke in September, neither dyke reached the surface and both dykes were confined to the upper 10 -12 km of the crust. Preliminary results suggest similar styles of intrusion for the December 2006 and January 2007 dykes. A fissural basaltic eruption occurred with the August 2007 deformation showing that the dyke reached the surface. . All dykes since June 2006 are south of the Ado Ale complex - a rifted silicic centre in the middle of the rift segment. InSAR and GPS show no deflation at either of the volcanoes at the northern end of the segment implying an alternate source is feeding the ongoing intrusions. We do not observe surface subsidence associated with any source region, and thus require a deep source (> ~ 8 km) and suggest that this is located near the centre of the rift segment. The apparent migration sequences seen so far appear to be similar to those seen in Iceland during the 1975-1984 Krafla rifting episode, and we anticipate further dyking episodes and eruptions over the next few years.

  4. Force Required to Breakup a Continent: Implications on Rifting Localization and Migration

    NASA Astrophysics Data System (ADS)

    Svartman Dias, A. E.; Lavier, L. L.; Hayman, N. W.

    2014-12-01

    The maximum force from ridge push available is about 5 TN/m, lower than that required by 2D and 3D numerical experiments to rift the lithosphere in the absence of magmatic input. We carry out 2D numerical experiments without any magmatic input to study the extensional force necessary to start a rift basin and to breakup a continent. We assume a range of initial temperature structure, crust and mantle initial thicknesses and composition. In a first step, we use velocity boundary conditions (1cm/yr) and we monitor the force necessary to breakup the continent. Results can be classified in two groups according to the amount of force needed to rift through time: (1) The initial force builds up rapidly to 12-20 TN/m within 0.4-1.0 Myr. This is followed by an exponential decrease due to early strain localization and lithospheric weakening. The force is < 5TN/m after 4.4-7.0 Myr of extension. Continental breakup occurs approximately 10 Myr after the onset of extension forming narrow conjugate margins. This group encompasses experiments with initial Tmoho < 650oC and crustal thicknesses ? 35 km, where crust and mantle deformation are coupled from the early stages of rifting. (2) The initial build-up is more discrete, from < 3 TN/m to 4-6.5 TN/m in the first 0.1 Myr, followed by a decrease to a nearly constant value of 3-5 TN/m from 0.4 Myr to 10 Myr, when strain starts localizing. The constant force through time reflects lithosphere strengthening and migration of the deformation. This rift migration forms a wide basin (> 250 km wide) that may evolve to form very asymmetric conjugate margins. Breakup occurs 18 Myr after the onset of rifting or later. This second group corresponds to experiments with initial Tmoho > 650 km and crustal thicknesses ? 35 km. High bending stresses result in upper crust brittle failure and on enhancement of lower crust lateral flow. Interaction between ductile failure in the lower crust and brittle failure in the upper crust controls the migration of the deformation. In a second step, we repeat the same experiments applying a constant extensional force ? 5 TN/m to test whether and how the limited ridge push force naturally available can rift and breakup a continent. We then compare our results to the evolution of aborted rifts and to along strike variations in rifted magins such as the South Atlantic.

  5. Role of ductile strain localization in the lithospheric mantle on continental rifting

    NASA Astrophysics Data System (ADS)

    Gueydan, Frédéric; Precigout, Jacques

    2014-05-01

    The strength of the lithospheric mantle controls the mode of lithosphere deformation: the presence or absence of a high strength brittle mantle respectively leads to localized or distributed rifting. However, first order geophysical data question the existence of such a brittle mantle. Here we use 2-D finite-element large strain modelling to quantify the impact of a ductile localizing mantle - instead of brittle - in triggering continental rifting. As a novelty, the mantle rheology considers the effect of grain boundary sliding during strain-induced grain size reduction, which may promote a significant strength drop and subsequent strain localization at low mantle temperature (< 700-800° C). Our results reveal that such ductile localizing mantle implies varying modes of continental rifting that mainly depend on both the amount of weakening in the ductile mantle and the strength of the lower ductile crust. A medium to strong lower crust implies coupling between the upper crust and ductile localizing mantle, yielding to narrow continental rifting. In contrast, a weak lower crust implies decoupling between the upper crust and ductile localizing mantle, giving rise to a switch from distributed faulting at incipient strain to localized faulting at large strain. Ductile strain localization in the lithospheric mantle is therefore sufficient to trigger continental rifting, although a critical amount of weakening is required. Such ductile localizing mantle provides a relevant geological and mechanical alternative to the brittle mantle. It moreover provides a wider variety of modes of upper crustal faulting that are commonly observed in nature.

  6. Cenozoic thermal, mechanical and tectonic evolution of the Rio Grande rift

    NASA Technical Reports Server (NTRS)

    Morgan, P.; Seager, W. R.; Golombek, M. P.

    1986-01-01

    Two areas of New Mexico which exhibit complex but similar Cenozoic histories of extensional tectonism are analyzed. The first study area is the Basin and Range province and southern Rio Gande rift in southern New Mexico; the second study area is the central Rio Grande rift in central and northern New Mexico, the southern San Luis basin, the Espanola basin, and the Albuquerque basin. Two phases of extension were identified: the first phase which began in mid-Oligocene was characterized by local high-strain extension events, low-angle faulting, and the development of broad, shallow basins, all indicating an approximately NE-SW + or - 25 deg extension direction; the later phase which occurred primarily in the late Miocene, was characterized by synchronous, high-angle faulting, resulting in large vertical strains which produced the modern Rio Grande rift morphology. Extension direction was approximately E-W. Geotherms were estimated and lithospheric strength curves were calculated for these two phases of extension. A high geotherm was deduced for the early phase resulting in a shallow crustal brittle transition, and insignificant mantle strength. The lithosphere subsequently cooled, resulting in a significant zone of mantle strength beneath the Moho. It is concluded that the interrelationship among regional and local prerifting, synrifting, and postrifting events in the Rio Grande rift attests to the fact that the rifting (in the region studied) should be considered in the context of other geologic events.

  7. Crustal structure of the Southern Rio Grande rift determined from seismic refraction profiling

    NASA Technical Reports Server (NTRS)

    Sinno, Y. A.; Keller, G. R.; Harder, S. H.; Daggett, P. H.; Morgan, P.

    1986-01-01

    As part of a major cooperative seismic experiment, a series of seismic refraction profiles have been recorded in south-central New Mexico with the goal of determining the crustal structure in the southern Rio Grande rift. The data gathered greatly expand the seismic data base in the area, and consist of three interlocking regional profiles: a reversed E-W line across the rift, an unreversed N-S axial line, and an unreversed SW-SE line. The reversed E-W line shows no significant dip along the Moho (32 km thick crust) and a 7.7 km/s Pn velocity. Results from the N-S axial line and the NW-SE line indicate an apparent Pn velocity of 7.95 km/s and significant dip along the Moho with crustal thinning toward the south and southeast. When interpreted together, these data indicate a crustal thinning in the southern rift of 4-6 km with respect to the northern rift and the adjacent Basin and Range province, and establish the regional Pn velocity to be approximately 7.7 km/s. These results suggest that the Rio Grande rift can be identified as a crustal feature separate and distinct from the Basin and Range province.

  8. Sedimentologic and tectonic patterns in Dead Sea rift and their application to hydrocarbon exploration

    SciTech Connect

    Eshet, Y.; Robbins, E.I.

    1986-05-01

    The Dead Sea rift was produced primarily by sinistral strike-slip movement that offset many prominent geologic features along its 600-km length, from the Red Sea to the Lebanon Mountains. Unique structural patterns such as pull-apart basins arranged en echelon show that east-west extension and compression also occurred. The sedimentologic history includes deposits of Miocene lacustrine and continental clastic sediments, Pliocene lagoonal evaporites from a marine tongue, and Pleistocene peat in the north with various clastic and chemical sediments derived from narrow, closed lakes in the south. The southern sediments were penetrated by the rising Sedom salt diapir. Recent sedimentologic features include alluvial fans along the rift margins that are being dissected during the winter by runoff. At the eastern rift margin, sands are being offset by active faults. The Dead Sea, a remnant of an earlier lake, is halite saturated and is precipitating carbonates, sulfates, and halite. Tar sands and asphalt seeps in marginal outcrops, oil and gas shows in cores, and the huge Sedom salt body have attracted hydrocarbon exploration to the Dead Sea area. Hydrocarbons may originate from (1) Senonian oil shales that occur both east and west of the rift, or (2) older (Permian-Triassic.) reservoirs that have undergone hydrologic changes brought on by rift-valley formation. An exploration model is being tested to evaluate the possibility of oil being generated by deep circulation of heavy, organic matter-rich brines along fault boundaries.

  9. 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.

  10. Geodynamic modelling of non-volcanic rifted margins: sedimentation process and effects

    NASA Astrophysics Data System (ADS)

    Andres-Martinez, Miguel; Perez-Gussinye, Marta; Phipps Morgan, Jason; Armitage, John; Monteiro da Silva, Rafael

    2014-05-01

    Non-volcanic rifted margins (NVRMs) are characterized by an anomalous lack of magmatism and a wide continental-ocean transition which has been interpreted as an expanse of exhumed and serpentinized mantle. NVRMs are represented all over the world as in Labrador Sea, Southeast Australia, Newfoundland, and West Iberian Margin (WIM), where a serpentinized peridotite ridge is found. Erosion and sedimentation are surficial processes that redistribute material along the margins, changing the forces along the margin and affecting its thermal structure. In order to study coupled mantle dynamics and sedimentation processes during rifting, we used a modified version of the dynamic 2D code MILAMIN (Dabrowski et al. 2008). Our modified version includes a free surface together with a free-surface stabilization algorithm to generate stable topographies, strain softening to simulate faulting, serpentinization, magmatism, erosion and sedimentation. Erosion and sedimentation algorithm is based on diffusion and transport equations in 1D. The code allow us to investigate how sedimentation process conditions the architecture of the margins during rifting and in which magnitude the width of the margins and the height of the rift shoulders are affected by surficial processes. Furthermore, we can study how sediments influence the temperature distribution and evolution and, ultimately, the rheology of the crust during rifting. We are also working on modelling sedimentation with high resolution meshes to try to reproduce break-up uncomformities and to study the thermal evolution of the sediments.

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

    SciTech Connect

    Magnavita, L.P.; Silva, T.F. da [Petrobras/E & P - BA, Bahia (Brazil)

    1995-11-01

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

  12. Kinematics of the asal rift (djibouti) determined from the deformation of fieale volcano.

    PubMed

    De Chabalier, J B; Avouac, J P

    1994-09-16

    Because of its subaerial exposure the Asal rift segment provides an exceptional opportunity to quantify the deformation field of an active rift and assess the contribution of tectonics and volcanism to rifting processes. The present topography of the Asal rift results from the tectonic dismemberment during the last 100,000 years of a large central volcanic edifice that formed astride the rift zone 300,000 to 100,000 years ago. Three-dimensional deformation of this volcano has been quantified from the combined analysis of the topography and geology. The analysis indicates that spreading at 17 to 29 millimeters per year in a N40 degrees +/- 5 degrees E direction accounts for most of the separation between Arabia and Somalia. The small topographic subsidence relative to extension suggests that tectonic thinning of the crust has been balanced by injection and underplating of magmatic material of near crustal density. The methodology developed in this study could also be applied to quantify deformation in relatively inaccessible areas where the main available information is topography or bathymetry. PMID:17770894

  13. Rift migration explains continental margin asymmetry and crustal hyper-extension.

    PubMed

    Brune, Sascha; Heine, Christian; Pérez-Gussinyé, Marta; Sobolev, Stephan V

    2014-01-01

    When continents break apart, continental crust and lithosphere are thinned until break-up is achieved and an oceanic basin is formed. The most remarkable and least understood structures associated with this process are up to 200 km wide areas of hyper-extended continental crust, which are partitioned between conjugate margins with pronounced asymmetry. Here we show, using high-resolution thermo-mechanical modelling, that hyper-extended crust and margin asymmetry are produced by steady state rift migration. We demonstrate that rift migration is accomplished by sequential, oceanward-younging, upper crustal faults, and is balanced through lower crustal flow. Constraining our model with a new South Atlantic plate reconstruction, we demonstrate that larger extension velocities may account for southward increasing width and asymmetry of these conjugate magma-poor margins. Our model challenges conventional ideas of rifted margin evolution, as it implies that during rift migration large amounts of material are transferred from one side of the rift zone to the other. PMID:24905463

  14. Acheron Fossae, Mars: A Martian rift observed by the High Resolution Stereo Camera (HRSC)

    NASA Astrophysics Data System (ADS)

    Kronberg, P.; Hauber, E.; Masson, P.; Neukum, G.; HRSC Co-Investigator Team

    Several large extensional tectonic structures on Mars have been described as possible analogues to terrestrial continental rifts. With few exceptions (e.g., Hauber and Kronberg, 2001), however, there was no detailed description of the rifts, partly because there was no accurate topographic information available. The HRSC on the Mars Express mission began to acquire high-resolution stereo colour images in January 2004. Orbits 37 and 143 in January and February 2004 covered large parts of the Acheron Fossae north of Olympus Mons, respectively. We constructed a Digital Elevation Model (DEM) and registered orthoimages in colour. Our preliminary analysis shows that several rift-like surface features can be identified at Acheron Fossae. We see some large horst and graben structures, the latter being filled with a relatively dark and smooth material. This material is smooth and seems to have been subject to viscous flow. In places, its distribution is obviously controlled by sun exposure, so it may be related to climatic processes. The extensional structures are situated on a topographical high. The graben shoulders are elevated, and this may be the result of rift flank uplift. At least one small, conical volcano can be distinguished. We measured fault offsets in the DEM, and obtain a minimum extension of 3.5 km across the Acheron Fossae system. The actual value is probably higher, since the graben filling obscures the actual vertical offset. Our preliminary conclusion is that the Acheron Fossae are indeed comparable to a terrestrial continental rift.

  15. Cretaceous intracontinental rifting and post-rift inversion in NE Brazil: Insights from the Rio do Peixe Basin

    NASA Astrophysics Data System (ADS)

    Nogueira, Francisco C. C.; Marques, Fernando O.; Bezerra, Francisco H. R.; de Castro, David L.; Fuck, Reinhardt A.

    2015-03-01

    The breakup of Pangea in the Mesozoic placed the South American and African plates under horizontal extension, which triggered rifting and the formation of intracontinental basins in NE Brazil. The subsequent geodynamic evolution changed the forces acting upon the South American plate because of the simultaneous development of the Mid-Atlantic Ridge (MAR) and the Andes. The problem we address in this work is the effect of the changing stress field on intracontinental deformation in NE Brazil, and we used the intracontinental Rio do Peixe Basin (RPB) as case study. We used remote sensing, shuttle radar topography, geophysical data, and detailed structural geology to address this problem. Based on the integrated analysis of brittle deformation within the basin, at the basin boundaries, and in the host basement, we conclude the following: (1) In the Cretaceous, the Rio do Peixe Basin formed from an approximately NW-SE tension, as deduced from brittle deformation in sedimentary rocks within the RPB and bounding master faults. (2) Subsequently, the maximum compressive stress that acted upon the study area shifted from vertical to horizontal, and was oriented approximately ENE-WSW. The new compressive stress field inverted the RPB, which is recorded in the basin at all scales. (3) The inversion of the RPB is consistent with the stress field imposed by the MAR push (to the west) and the Andean push (to the east), which have kept the South American plate under ENE-WSW horizontal compression since the late Cretaceous.

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

    SciTech Connect

    Tiercelin, J.J.; Lezzar, K.E. (Universite de Bretagne Occidentale, Brest (France)); Richert, J.P. (Elf Aquitaine, Pau (France))

    1994-07-01

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

  17. Effects of initial weakness on rift architecture S. DYKSTERHUIS1, P. REY1, R. D. MU LLER1 & L. MORESI2

    E-print Network

    Müller, Dietmar

    rift mode, exempli- fied by the East African System, extensional defor- mation localizes alongEffects of initial weakness on rift architecture S. DYKSTERHUIS1, P. REY1, R. D. MU¨ LLER1 & L controlling rift architecture, using both computational and laboratory methods. Here, we examine the effects

  18. The structure of the cross-cutting volcanic chain of Northern Tanzania and its relation to the East African rift system

    Microsoft Academic Search

    J. D. Fairhead

    1980-01-01

    The WSW---ENE chain of Cenozoic volcanoes in northern Tanzania lies tangental to and on the southeastern flank of the Kenya dome and represents a major cross-cutting feature of the Eastern Rift System dividing areas of the rift that are tectonically distinctly different. These tectonic differences are reflected in the nature of the rift's faulting, volcanism, seismicity and geothermal activity. To

  19. Crustal structure in Ethiopia and Kenya from receiver function analysis: Implications for rift development in eastern Africa

    Microsoft Academic Search

    Mulugeta T. Dugda; Andrew A. Nyblade; Jordi Julia; Charles A. Langston; Charles J. Ammon; Silas Simiyu

    2005-01-01

    Crustal structure in Kenya and Ethiopia has been investigated using receiver function analysis of broadband seismic data to determine the extent to which the Cenozoic rifting and magmatism has modified the thickness and composition of the Proterozoic crust in which the East African rift system developed. Data for this study come from broadband seismic experiments conducted in Ethiopia between 2000

  20. The distribution of basaltic volcanism on Tenerife, Canary Islands: Implications on the origin and dynamics of the rift systems

    Microsoft Academic Search

    A. Geyer; J. Martí

    2010-01-01

    One of the most characteristic features of volcanic islands is the existence of rift zones defined commonly as orientated eruptive fissures or parallel rows of elongate cinder cones and dyke swarms. Occasionally, these rifts can appear at the birth of the volcanic island and persist until the last episodes of its constructions, controlling the form and structure of the island

  1. Geophys. 1. Inl. (1994) 118, 159-180 Moho and lower crustal reflectivity beneath a young rift basin

    E-print Network

    Watts, A. B. "Tony"

    1994-01-01

    Geophys. 1. Inl. (1994) 118, 159-180 Moho and lower crustal reflectivity beneath a young rift basin present new images of the lower crust and Moho beneath the Valencia Trough-a young rift basin profiles. The Moho, which was previously only seen intermittently, can now be confidently traced throughout

  2. No Moho uplift below the Baikal Rift Zone: Evidence from a seismic refraction profile across southern Lake Baikal

    Microsoft Academic Search

    Christoffer Nielsen; H. Thybo

    2009-01-01

    The late Cenozoic Baikal Rift Zone (BRZ) in southern Siberia is composed of several individual topographic depressions and half grabens with the deep Lake Baikal at its center. We have modeled the seismic velocity structure of the crust and uppermost mantle along a 360 km long profile of the Baikal Explosion Seismic Transects (BEST) project across the rift zone in

  3. Physics of the Earth and Planetary Interiors 158 (2006) 174189 Texture of mantle lithosphere along the Dead Sea Rift

    E-print Network

    2006-01-01

    the Dead Sea Rift: Recently imposed or inherited? Vadim Levina,, Alissa Henzaa, Jeffrey Parkb, Arthur the trace of the Dead Sea Rift (DSR), owing to a combination of present day and ancient tectonics. Using.V. All rights reserved. Keywords: Anisotropy, Lithosphere, Upper mantle, Body waves 1. Introduction

  4. 3D architecture of a complex transcurrent rift system: The example of the Bay of BiscayWestern Pyrenees

    E-print Network

    Demouchy, Sylvie

    3D architecture of a complex transcurrent rift system: The example of the Bay of Biscay 19 April 2010 Available online 24 April 2010 Keywords: 3D structure of rifted basins Gravimetric inversion Seismic interpretation Bay of Biscay Western Pyrenees The Parentis and Arzacq­Mauléon basins

  5. Along-margin variations of magmatism at volcanic passive margins: Numerical models of continental extension with rift propagation barriers

    NASA Astrophysics Data System (ADS)

    Koopmann, Hannes; Brune, Sascha; Franke, Dieter; Breuer, Sonja

    2015-04-01

    Seaward-dipping reflectors (SDRs) constitute a first-order feature of volcanic rifted margins and are imaged in seismic reflection profiles of the North and South Atlantic. Recent studies describe distinct along-strike variations in the distribution of SDRs, where abundance of volcanic material could be spatially linked to transfer fault systems. These segmented the propagating rift that later developed into the ocean, and are interpreted as rift propagation barriers. Here we present 3d numerical forward models of a segmented rift system suggesting a causal link between segment boundaries and magmatic volume variations. Our results explain along-strike variations in magmatism by significant rift-parallel mantle flow across segment boundaries. This rift-parallel flow is caused by a lateral pressure gradient between sequentially opening segments. The along-strike flow of hot material near the segment boundary leads to elevated temperature and thus decompression melting if compared to the segment interior. This takes place without enhancing crustal thinning near the transfer zones and generates peaks in overall pre-break-up melt volumes. We conclude that delayed rift propagation at inherited structures can play an important part in enhancing and localizing volcanic activity by controlling the mantle flow beneath the rift axis.

  6. The Influence of Mantle Petrology on Basin Subsidence During Rifting Nina S.C. Simon & Yuri Y. Podladchikov

    E-print Network

    Simon, Nina

    The Influence of Mantle Petrology on Basin Subsidence During Rifting Nina S.C. Simon & Yuri Y-spinel and spinel plagioclase transitions in the lithospheric mantle have the most profound effect on uplift/subsidence- rift subsidence recorded in the basin is directly proportional to the total amount of plagioclase

  7. Genetic Analysis of Viruses Associated with Emergence of Rift Valley Fever in Saudi Arabia and Yemen, 2000-01

    Microsoft Academic Search

    Trevor Shoemaker; Carla Boulianne; Martin J. Vincent; Linda Pezzanite; Mohammed M. Al-Qahtani; Yagub Al-Mazrou; Ali S. Khan; Pierre E. Rollin; Robert Swanepoel; Thomas G. Ksiazek; Stuart T. Nichol

    The first confirmed Rift Valley fever outbreak outside Africa was reported in September 2000, in the Ara- bian Peninsula. As of February 2001, a total of 884 hospitalized patients were identified in Saudi Arabia, with 124 deaths. In Yemen, 1,087 cases were estimated to have occurred, with 121 deaths. Laboratory diagnosis of Rift Valley fever virus (RVFV) infections included virus

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

    Microsoft Academic Search

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

    2007-01-01

    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,

  9. Inverse models of gravity data from the Red Sea-Aden-East African rifts triple junction zone

    Microsoft Academic Search

    Christel Tiberi; Cynthia Ebinger; Valérie Ballu; Graham Stuart; Befekadu Oluma

    2005-01-01

    The combined effects of stretching and magmatism permanently modify crustal structure in continental rifts and volcanic passive margins. The Red Sea-Gulf of Aden-Ethiopian rift triple junction zone provides a unique opportunity to examine incipient volcanic margin formation above or near an asthenospheric upwelling. We use gravity inversions and forward modelling to examine lateral variations in crust and upper mantle structure

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  11. Tectonic Control on Hydrocarbon Accumulation in the IntraContinental Albertine Graben of the East African Rift System

    Microsoft Academic Search

    Dozith Abeinomugisha; Robert Kasande

    The Albertine Graben is a Tertiary intra-continental rift that developed on the Precambrian orogenic belt of the African Craton. It forms the northern termination of the Western arm of the East African Rift System (EARS) (Figure 1). It stretches from the border between Uganda and Sudan in the north, to Lake Edward in the south. The available geological and geophysical

  12. Depth distribution of earthquakes in the Baikal rift system and its implications for the rheology of the lithosphere

    E-print Network

    Déverchère, Jacques

    Depth distribution of earthquakes in the Baikal rift system and its implications for the rheology controlled by a close station and located within the extensional domain of the Baikal rift system) can match, where the crust is supposed to be ductile, in a way very similar to what is found in the East African

  13. Soils, slopes and source rocks: Application of a soil chemistry model to nutrient delivery to rift lakes

    NASA Astrophysics Data System (ADS)

    Harris, Nicholas B.; Tucker, Gregory E.

    2015-06-01

    The topographic evolution of rift basins may be critical to the deposition of lacustrine source rocks such as the organic-rich Lower Cretaceous shales of the South Atlantic margin. Soils have been proposed as a key link between topography and source rock deposition by providing nutrients for the algae growth in rift lakes. Decreasing topographic relief from active rift to late rift has several effects on soils: soils become thicker and finer, erosion of dead surface and soil organic matter decreases, and the fractionation of precipitation between runoff and infiltration may favor increased infiltration. This hypothesis is tested by application of CENTURY, a complex box model that simulates transfer of nutrients within soil pools. The model is first applied to a rainforest soil, with several parameters individually varied. Infiltration experiments show that the concentrations of C, N and P in groundwater decrease rapidly as infiltration decreases, whether due to increased slope or to decreased precipitation. Increased erosion of surface plant litter and topsoil results in substantially decreased nutrient concentrations in groundwater. Increased sand content in soil causes an increase in nutrient concentration. We integrate these variables in analyzing topographic swathes from the Rio Grande Rift, comparing the southern part of the rift, where topography is relatively old and reduced, to the northern rift. C and P concentrations in groundwater increase as slope gradient decreases, resulting in substantially larger C and P concentrations in groundwater in the southern rift than the northern rift. Nitrogen concentrations in groundwater depends on whether infiltration varies as a function of slope gradient; in experiments where the fraction of infiltrated precipitation decreased with increasing slope, N concentrations was also substantially higher in the southern rift; but in experiments where that fraction was held constant, N concentrations was lower in the southern rift. These simulations demonstrate that evolving topography during rift development can significantly influence nutrient concentrations in groundwater and, if these nutrients flow into rift lakes and stimulate organic productivity, account for the deposition of rich oil-prone source rocks in late rift stages.

  14. 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 rift system show uplift at rates varying from 0 to 10 mm/yr with respect to a far-field reference outside the rift.

  15. 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

    Microsoft Academic Search

    K. Aanyu; D. Koehn

    2011-01-01

    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

  16. GPS Constraints on the Spatial Distribution of Extension in the Ethiopian Highlands and Main Ethiopian Rift

    NASA Astrophysics Data System (ADS)

    Amere, Y. B.; Bendick, R. O.; Fisseha, S.; Lewi, E.; Reilinger, R. E.; King, R. W.; Kianji, G.

    2014-12-01

    27 campaign and 17 continuous GPS sites spanning the Ethiopian Highlands, Main Ethiopian Rift (MER), and Somali Platform in Ethiopia and Eritrea were measured for varying durations between 1995 and 2014. Velocities at these sites show that present day strain in NE Africa is not localized only in the Afar depression and MER system. Rather, velocities as high as 6 mm/yr relative to stable Nubia occur in the central Ethiopian highlands west of the rift bounding faults; the northern and southern Ethiopian highlands host velocities as high as 3 mm/yr. These approach the magnitude of Nubia-Somalia spreading accommodated within the rift itself of 6 + 1 mm/yr with an azimuth of N770E. The combination of distributed low strain rate deformation contiguous with higher strain rate plate boundary deformation is similar to that expressed in other tectonically active continental settings like Basin and Range and Tibetan Plateau.Keywords: deformation, localized, distributed, strain, stable Nubia.

  17. Evidence for a seismogenic upper mantle and lower crust in the Baikal rift

    SciTech Connect

    Deverchere, J.; Houdry, F. (Univ. Paris 6 (France)); Diament, M. (Inst. de Physique du Globe, Paris (France)); Solonenko, N.V.; Solonenko, A.V. (Inst. of the Earth's Crust, Irkutsk (USSR))

    1991-06-01

    The high level seismicity of the Baikal rift zone and its spatial distribution in dense swarms and belts provide an opportunity to study the seismogenic behavior of a continental lithosphere submitted to extension in an early stage. Using data from a regional seismological network, the authors analyze a significantly large set of events from an earthquake swarm located east of the nearly aseismic northern Baikal lake. They find that at least 10% of the well-constrained events are located in the lower crust or the uppermost mantle. The fault plane solutions of earthquakes within the crust define a NW-SE extensional stress regime perpendicular to the rift axis. Results confirm the idea that zones of continental extension may exhibit significant rigidity. The authors propose to infer a migration of deformation from the northern Baikal lake to an initially stronger part of the lithosphere, i.e. the Barguzin rift and its extension to the east.

  18. Interplay of phosphogenesis and hydrothermalism in the latest Ediacaran rift of the High Atlas, Morocco

    NASA Astrophysics Data System (ADS)

    Álvaro, J. Javier; Subías, Ignacio

    2011-01-01

    Two dissolution surfaces, capped by phosphatic crusts that contain up to 40 wt.% of P 2O 5, are well exposed in the latest Ediacaran Tabia Member (Adoudou Formation) of the Ouneïn region, High Atlas. Both the Tabia dolostones and capping phosphorites are crosscut by several generations of synsedimentary faults, fissures, and hydrothermal dikes hosting Cu ore bodies, in a scenario of down-faulted blocks. Stratigraphic and facies relationships suggest the preservation of a major pulse of intra-cratonic rifting, responsible for the development of an unstable carbonate platform subjected to sharp uplift and tilting perturbations and dissolution processes, associated with hydrothermal dike-swarm injection. The whole framework is sealed with the Tamjout Bed (Tifnout Member), which marks the end of abundant regional tilting (syn-rift phase) and the beginning of a thermal subsidence-dominated regime (post-rift phase) in the Moroccan margin of West Gondwana.

  19. The Mesozoic rift basins of eastern North America: Potential reservoir or Explorationist's folly

    SciTech Connect

    Pyron, A.

    1991-08-01

    Mesozoic rift basins are found on the East Coast of North America from Georgia to Nova Scotia. The basins formed as a result of extensional activity associated with the breakup of Pangaea. The internal geometry of the basins includes a depositional sequence ranging from coarse fanglomerates to fine-grained siltstones and argillites. Since these Mesozoic rift basins were first studied, they have not been considered to be likely spots for hydrocarbon accumulations. Recently, geologists have reconsidered these Mesozoic basins and have developed a more synergistic approach that suggests that many of these rift basins might be suitable targets for exploration. By analogy, these Mesozoic basins are correlative to similar basins in northwestern Africa, where significant reserved of oil and natural gas have been developed. The similarity between the productive basins in northwestern Africa and the Mesozoic basins of North America and their proximity to major markets provides sufficient rationale to further investigate these basins.

  20. Shear source multiazimuth near- and far-offset vertical seismic profiles, Asal Rift, Republic of Djibouti

    SciTech Connect

    Hirn, A.; Magnier, S.A. (Institut de Physique du Globe, Paris (France))

    1992-12-10

    A three-component borehole seismic data set obtained in the Asal rift zone shows that azimuthal anisotropy may be present with the fast propagation direction aligned with the present-day rift axis. This is seen on the near- and far-offset vertical seismic profile (VSP) data from the two source points lying parallel to the rift axis. The third orthogonal source point gives propagation times characteristic of near-horizontal paths along the detected slow direction. The reflected VSP wave field contains both P and S energy. The main P and S reflections correlate well and correspond to thin clay and siltstone layers interspersed within the lava flow series. Some evidence exists for a change with depth of the amount or direction of the anisotropy found in the uppermost 400 m.

  1. Episodic rifting of phanerozoic rocks in the Victoria Land basin, Western Ross Sea, Antarctica

    USGS Publications Warehouse

    Cooper, A. K.; Davey, F.J.

    1985-01-01

    Multichannel seismic-reflection data show that the Victoria Land basin, unlike other sedimentary basins in the Ross Sea, includes a rift-depression 15 to 25 kilometers wide that parallels the Transantarctic Mountains and contains up to 12 kilometers of possible Paleozoic to Holocene age sedimentary rocks. An unconformity separates the previously identified Cenozoic sedimentary section from the underlying strata of possible Mesozoic and Paleozoic age. Late Cenozoic volcanic rocks intrude into the entire section along the eastern flank of the basin. The Victoria Land basin is probably part of a more extensive rift system that has been active episodically since Paleozoic time. Inferred rifting and basin subsidence during Mesozoic and Cenozoic time may be associated with regional crustal extension and uplift of the nearby Transantarctic Mountains.

  2. Geodetic measurement of horizontal deformation across the Rio Grande rift near Socorro, New Mexico.

    USGS Publications Warehouse

    Savage, J.C.; Lisowski, M.; Prescott, W.H.; Sanford, A.R.

    1980-01-01

    Trilateration surveys of a geodetic network across the Rio Grande rift near Socorro, New Mexico, in 1972, 73, 76 and 79 have failed to detect any significant strain accumulation. The surveys place an upper bound (95% confidence limit) of 1 mm/a (a = years) on EW spreading across the rift in 1972-79. There is marginal evidence from triangulation for an episode of EW spreading across the rift within the interval 1954-72. The trilateration network lies on the S flank of an uplift caused by magma intrusion into a midcrustal sill during this century according to Reilinger and Oliver. The horizontal deformation induced by sill inflation is sufficiently small that continued uplift during 1972-79 cannot be excluded by the observed absence of significant horizontal deformation.-Authors

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    The Red Sea rift system is a prime example of continental rifting and has contributed significantly to our understanding of the geologic processes that manage the rupture of continental lithosphere. Using a combined geo- and thermochronometric approach, we explore the modes and mechanisms of rift margin development by studying Red Sea rift-related geologic products along the central Saudi Arabian flank of the rift system, north of Jeddah. We use apatite and zircon (U-Th)/He thermochronometry and whole-rock 40Ar/39Ar dating of basalt to define the spatiotemporal relationship between rift flank extensional structures and rift-related harrat volcanism. This technical approach permits the reconstruction of the tectonic margin from early rift architecture, to strain distribution during progressive rifting, and through subsequent whole-scale modifications of the rift flank due to thermal and isostatic factors. Constraints on the dynamics of rift flank deformation are achieved through the collection of geologic samples along long-baseline thermochronometric transects that traverse the entire Arabian shield from the coastal escarpment to the inland Paleozoic sedimentary cover sequences. Long-baseline transects resolve the timing of rift flank uplift and reveal the pattern of lithospheric modification during the rupturing of continental lithosphere. Locally, short-baseline elevation transects map the footwall exhumation of major normal faults that delineate both the modern rift margin and inland extensional basins such as the NW-trending Hamd-Jizil basin, a prominent syn-extensional basin comprised of two distinct half-grabens (Jizil and Hamd) located NW of Medina. Diffuse lithospheric extension during the Oligo-Miocene affected a widespread area well inboard from the modern rift margin; samples from footwall blocks that bound the inland Jizil and Hamd half-grabens yield apatite (U-Th)/He cooling ages of 14.7 ± 0.9 Ma and 24.5 ± 1.5 Ma, respectively. The mid-Miocene age is doubly-significant since it reveals not only a Red Sea rift signal 140 km inboard from the modern border fault complex but also underscores the importance of fault reactivation during progressive rifting since the Jizil half-graben is structurally delineated by faults formed within the Neoproterozoic Najd shear zone fabric. Oligo-Miocene apatite (U-Th)/He ages from Jabal Radwa, a pluton exhumed within the border fault complex, show that rift flank exhumation and extensional faulting occurred within the central portion of the Arabian rift flank penecontemporaneous to faulting in the Hamd-Jizil half-graben system. Within the rift flank fault systems, an absence of footwall exhumation ages younger than ~13 Ma confirms that major extensional faulting migrated basin-ward in the middle Miocene during a time of rift reorganization and the establishment of the Dead Sea-Gulf of Aqaba transform. However, minor deepening of the inland Hamd-Jizil basin continued through the late Miocene as relatively young, basin-internal faults cut 17 Ma - 10 Ma basalt flows from harrat Khaybar that had blanketed the region.

  4. Late Miocene - Pliocene rifting in west-central Tibet: Evidence from (U-Th)/He thermochronology of the North Lunggar Rift

    NASA Astrophysics Data System (ADS)

    Sundell, K. E.; Taylor, M. H.; Stockli, D. F.; Kapp, P. A.; Styron, R. H.; Liu, D.; Ding, L.

    2010-12-01

    The deformation style in southern Tibet is dominated by constriction, as most of the significant deformation observed is related to kinematically linked north-trending rifts and v-shaped conjugate strike-slip fault systems accommodating coeval north-south contraction and east-west stretching. Estimates for the onset of east-west extension vary from the middle to late Miocene, but the precise timing is debated, and spatial coverage of timing constraints across Tibet remains sparse. The North Lunggar Rift is located in west-central Tibet, and is an example of an active north-trending rift accommodating east-west extension. The north-trending rift valley is ~60 km long, and is bounded on its west side by an east-dipping low-angle (< 40°) normal fault (detachment). The north-trending North Lunggar Range is ~70 km long and 30 km at its widest. The detachment footwall consists of Paleozoic-Mesozoic sedimentary rocks and variably deformed Miocene granites and gneisses. The hanging wall is dominantly Cretaceous volcanic rocks. The adjacent rift basin fill is comprised of Paleogene (?) sedimentary rocks showing a change in stratigraphy from older fine-grained lacustrine rocks to younger fluvial conglomerates. The detachment is inactive at the surface, as it is unconformably overlain by glacial moraines and cobble to boulder conglomerates. The active locus of extension is located approximately 5 - 6 km east of the range front in the hanging wall valley, as indicated by scarp forming faults with up to 40 meters of throw. Here, we present apatite and zircon (U-Th)/He thermochronological data from detachment parallel and perpendicular transects, in the context of fault geometry, fault kinematics, and petrographic data. Results show an along-strike variation in cooling age with the oldest ages in the north of the rift and the youngest ages to the south. The youngest cooling ages translate to the highest exhumation and detachment slip-rates, which are proximal to the greatest relief of the range and a drainage divide in the hanging wall basin. Results from detachment perpendicular transects into the footwall yield elevation invariant ages between 5 - 3 Ma indicating rapid exhumation during this time with exhumation rates varying between 1.2 - 2.1 mm/yr. Additional application of higher temperature thermochronometers and thermal modeling will provide the necessary information to determine the precise timing for the onset of extension, which when compared to prior studies, will determine if there are spatial and temporal differences for the onset of extension across southern Tibet.

  5. Four thousand years of seismicity along the Dead Sea Rift

    NASA Astrophysics Data System (ADS)

    Ben-Menahem, Ari

    1991-11-01

    A study of major earthquake occurrence along the Dead Sea transform (35.5°-36.5° E; 27.2°-37.5° N) during the past four millenia has been attempted. Geological, archaeological, biblical, historical, and seismological evidence were integrated in an effort to quantify the space-time distribution of seismicity in the said province. The overall earthquake activity in the conterminous Near East indicates a stable pattern and appeared to have been stationary over the examined time window. About 110 earthquakes in the magnitude range 6.7 ? ML ? 8.3 affected the area during the past 2500 years. Of these, 42 originated along the Dead Sea fault system itself, while 68 were imported from the Helenic-Cyprian arcs and the Anatolian-Elburz-Zagros fault systems. These events were responsible for the repeated destruction of many cultural centers. In the Dead Sea region proper, the major seismic activity since 2100 B.C.E. (Before Christian Era), has been confined to the vicinity of its eastern shore with extremal seismicity at its southern tip near the prehistorical site of Bab-a-Dara'a (31° 15'N, 35° 32'E). This may constitute the first solid evidence that the Biblical "cities of the Plain" (Sodom, Gommorah, etc.) were located there. Recent studies of earthquake deformations in the Lisan deposits near Bab-a-Dara'a, agree with our findings. At the present time, a magnitude 6¾ earthquake is pending at the northern edge of the Levant rift, with its average recurrence interval (83 years) exceeded by one standard deviation (32 years).

  6. Innate Immune Response to Rift Valley Fever Virus in Goats

    PubMed Central

    Nfon, Charles K.; Marszal, Peter; Zhang, Shunzhen; Weingartl, Hana M.

    2012-01-01

    Rift Valley fever (RVF), a re-emerging mosquito-borne disease of ruminants and man, was endemic in Africa but spread to Saudi Arabia and Yemen, meaning it could spread even further. Little is known about innate and cell-mediated immunity to RVF virus (RVFV) in ruminants, which is knowledge required for adequate vaccine trials. We therefore studied these aspects in experimentally infected goats. We also compared RVFV grown in an insect cell-line and that grown in a mammalian cell-line for differences in the course of infection. Goats developed viremia one day post infection (DPI), which lasted three to four days and some goats had transient fever coinciding with peak viremia. Up to 4% of peripheral blood mononuclear cells (PBMCs) were positive for RVFV. Monocytes and dendritic cells in PBMCs declined possibly from being directly infected with virus as suggested by in vitro exposure. Infected goats produced serum IFN-?, IL-12 and other proinflammatory cytokines but not IFN-?. Despite the lack of IFN-?, innate immunity via the IL-12 to IFN-? circuit possibly contributed to early protection against RVFV since neutralising antibodies were detected after viremia had cleared. The course of infection with insect cell-derived RVFV (IN-RVFV) appeared to be different from mammalian cell-derived RVFV (MAM-RVFV), with the former attaining peak viremia faster, inducing fever and profoundly affecting specific immune cell subpopulations. This indicated possible differences in infections of ruminants acquired from mosquito bites relative to those due to contact with infectious material from other animals. These differences need to be considered when testing RVF vaccines in laboratory settings. PMID:22545170

  7. Sedimentary fill of 1100 Ma mid-continent rift system

    SciTech Connect

    Ojakangas, R.W.

    1986-05-01

    In the Lake Superior region, four sequences of sedimentary rocks reflect the tectonic-sedimentary framework before, during, and after the magmatic event that resulted in 10,000 m of dominantly basaltic volcanic rocks and large layered gabbroic intrusions. The oldest sequence includes four geographically separated, thin (100 m) pre-volcanic, white to pink, quartzose sandstone units that were deposited in braided alluvial plain-lacustrine environments within the shallow basin that was the initial manifestation of rifting. The second sedimentary sequence consists of immature sediment, largely derived from the volcanic sequence and deposited in alluvial fan, fluvial, and lacustrine environments during intervals between extrusive episodes. These red silty to conglomeratic units range from a few centimeters to hundreds of meters in thickness. The Oronto Group and the younger Bayfield Group and their equivalents are post-volcanic, dominantly red-bed sequences of siltstone, sandstone, and conglomerate, deposited in alluvial fan, fluvial, and lacustrine environments within the elongate basin. The Oronto Group (600 m) includes the Copper Harbor Conglomerate, the Nonesuch Shale (gray, carbonaceous, pyritiferous, and cupriferous argillaceous siltstone) and the Freda Sandstone. The Bayfield Group (2100 m) includes the Orienta Sandstone, the Devils Island Sandstone (100 m of orthoquartzite), and the Chequamegon Sandstone. Whereas volcanic detritus is dominant in most of the Oronto Group and the equivalent Solor Church Formation, extrabasinal granitic detritus dominants in the Bayfield Group and its equivalents (Fond de Lac Formation, Hinckley Sandstone, and Jacobsville Sandstone). Paleocurrent data indicate a general basinward transport of sediment during deposition of the four sequences, 1100 Ma(.) to 950 Ma(.).

  8. Evaporation Estimation of Rift Valley Lakes: Comparison of Models

    PubMed Central

    Melesse, Assefa M.; Abtew, Wossenu; Dessalegne, Tibebe

    2009-01-01

    Evapotranspiration (ET) accounts for a substantial amount of the water flux in the arid and semi-arid regions of the World. Accurate estimation of ET has been a challenge for hydrologists, mainly because of the spatiotemporal variability of the environmental and physical parameters governing the latent heat flux. In addition, most available ET models depend on intensive meteorological information for ET estimation. Such data are not available at the desired spatial and temporal scales in less developed and remote parts of the world. This limitation has necessitated the development of simple models that are less data intensive and provide ET estimates with acceptable level of accuracy. Remote sensing approach can also be applied to large areas where meteorological data are not available and field scale data collection is costly, time consuming and difficult. In areas like the Rift Valley regions of Ethiopia, the applicability of the Simple Method (Abtew Method) of lake evaporation estimation and surface energy balance approach using remote sensing was studied. The Simple Method and a remote sensing-based lake evaporation estimates were compared to the Penman, Energy balance, Pan, Radiation and Complementary Relationship Lake Evaporation (CRLE) methods applied in the region. Results indicate a good correspondence of the models outputs to that of the above methods. Comparison of the 1986 and 2000 monthly lake ET from the Landsat images to the Simple and Penman Methods show that the remote sensing and surface energy balance approach is promising for large scale applications to understand the spatial variation of the latent heat flux. PMID:22303142

  9. A cluster of outflows in the Vulpecula Rift

    NASA Astrophysics Data System (ADS)

    Mottram, J. C.; Brunt, C. M.

    2012-02-01

    We present 12CO, 13CO and C18O (J=3-2) observations of a new cluster of outflows in the Vulpecula Rift with HARP on the James Clerk Maxwell Telescope (JCMT). The mass associated with the outflows, measured using the 12CO HARP observations and assuming a distance to the region of 2.3 kpc, is 129 M?, while the mass associated with the dense gas from C18O observations is 458 M? and the associated sub-millimeter (sub-mm) core has a mass of 327 ± 112 M? independently determined from Bolocam 1.1-mm data. The outflow-to-core mass ratio is therefore ˜0.4, making this region one of the most efficient observed thus far with more than an order of magnitude more mass in the outflow than would be expected based on previous results. The kinetic energy associated with the flows, 94 × 1045 erg, is enough to drive the turbulence in the local clump, and potentially unbind the local region altogether. The detection of SiO (J=8-7) emission towards the outflows indicates that the flow is still active, and not simply a fossil flow. We also model the spectral energy distributions (SEDs) of the four young stellar objects (YSOs) associated with the molecular material, finding them all to be of mid to early B spectral type. The energetic nature of the outflows and significant reservoir of cold dust detected in the sub-mm suggest that these intermediate mass YSOs will continue to accrete and become massive, rather than reach the main sequence at their current mass.

  10. The Corinth Rift Laboratory (Greece): What Can Micro-Seismicity Reveal?

    NASA Astrophysics Data System (ADS)

    Lambotte, S.; Matrullo, E.; Satriano, C.; Lyon-Caen, H.; Bernard, P.; Deschamps, A.

    2014-12-01

    In the framework of the Corinth Rift Laboratory, the seismic activity in the western part of the rift is monitored since 2000 by a network of 15 three-component stations (CRLNET). It is characterized by several instrumental and historical large earthquakes with magnitude larger than 5.5, and numerous active swarms. More than 12 years of seismicity (about 100,000 events) that covers seven orders of magnitude of seismic moment Mo (1010 - 1017 Nm) is available. The detailed analysis of the whole seismicity brings insights into the geometry of faults at depth, the nature and the structure of the active zone at 6-8 km depth previously interpreted as a possible detachment, and more generally into the rifting process and mechanical processes at various space-time scales. For this purpose, we identified multiplets and precisely relocated the seismicity using double difference techniques. The seismicity exhibits a complex structure, strongly varying along the rift axis. We will present some specific structures of the seismicity and swarms. The spatio-temporal evolution of earthquake sequences, which repeatedly occur in specific sub-areas of the fault segments, and the relationship with the distribution of the elastic/anelastic structure, the VP/VS ratio and physical properties of the micro-earthquakes (such as seismic moment, static stress-drop, corner frequency and source size) provide important insights on the presence and the role of fluids during the generation of fractures. The variability of the stress release would suggest, in fact, the presence of heterogeneities in the friction distribution and fluid pressure, and normal stress and elastic properties variability in the fault zone. Finally, according with seismic and geodetic observations, we proposed a new mechanical model for the rifting process in this region, implying a non-elastic, mostly aseismic uniform NS opening below the rift axis, coupled with the downwards growth of a yet unmature detachment.

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

    SciTech Connect

    Smith, W.A. (Western Michigan Univ., Kalamazoo, MI (United States). 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.

  12. A Joint Inversion for Velocity and Anisotropy Structure Beneath a Highly Extended Continental Rift

    NASA Astrophysics Data System (ADS)

    Eilon, Z.; Abers, G. A.; Gaherty, J. B.; Jin, G.

    2014-12-01

    We jointly invert body wave travel times for anisotropy and velocity variations within the Woodlark Rift, Papua New Guinea, one of the youngest (?6Ma) and most highly-extended (?190km) continental rifts known. We use data from the CDPapua passive seismic array deployed around the D'Entrecasteaux Islands; these islands lie within the maximally-thinned continental crust at the centre of the rift and host the world's youngest (5 - 7 Ma) UHP rocks. We have previously used SK(K)S splitting to identify strong anisotropy within this rift, with fast axis orientated parallel to extension, roughly N-S. Consistency of splitting direction across station, back azimuth and method of analysis indicates a simple anisotropic fabric beneath much of this region. Consequently, we simplify the anisotropic inversion by solving for perturbations to N-S and E-W shear velocities at each node. This work builds on our previous isotropic tomographic study by resolving tradeoffs between anisotropy and velocity heterogeneities. We cross-correlate shear wave arrivals separately on N-S and E-W components, using the Christoffel equations to show that the travel times of these orthogonal quasi-shear pulses distinctly record the fast and slow velocities within our model. We invert these data for velocities on an irregular mesh, using a finite frequency approach with a first fresnel zone approximation. Preliminary results identify the locus of the rift beneath the D'Entrecasteaux Islands, and demonstrate that substantial anisotropy is present beneath the region of major extension. This anisotropy is co-located with low seismic velocities that indicate almost total removal of lithosphere, consistent with gravity fitting. Therefore, we ascribe the anisotropy within the rift to LPO of highly sheared asthenospheric mantle as a result of the large magnitude of extension.

  13. Stratigraphy, Structure, and Ore Deposits of the Southern Limb of the Midcontinent Rift System

    NSDL National Science Digital Library

    T. Bornhorst

    This site features an overview of the Midcontinent Rift system of North America, an area that extends for more than 2000 km northeasterly from Kansas, through the Lake Superior region, and then southeasterly through lower Michigan. This summary of the stratigraphy, structure, and mineralization of rift rocks provides an overview of the geologic history in northern Wisconsin and upper Michigan. Separate sections describe the tectonic history and structural features of the area, the stratigraphy of volcanic and sedimentary deposits, and the mineralization that produced rich copper and silver deposits. Information is supported by numerous citations while maps and diagrams help illustrate the concepts.

  14. Orogenic bending around a rigid Proterozoic magmatic rift beneath the Central Appalachian Mountains

    NASA Astrophysics Data System (ADS)

    Benoit, Margaret H.; Ebinger, Cynthia; Crampton, Melanie

    2014-09-01

    The transition zone between the modern northern and southern Appalachian Mountains is located in Pennsylvania, where the structural orientation of the fold-and-thrust belt changes from north-south to east-west, and the orogeny narrows significantly. Vintage studies of wide-angle reflection and temporary broadband seismic data suggest that the crust beneath the ?8 km of foreland basin sequences was thickened and heavily intruded around the margins of and beneath a failed Neoproterozoic rift. We use receiver function analysis of broadband seismic data recorded by additional and permanent stations, along with forward and inverse modeling of Bouguer gravity data to constrain the geometry and depth extent of mafic intrusion and underplating in the rift, as well as the role of this Proterozoic heterogeneity on the location and geometry of the curvature of the Appalachian orogen. The receiver function analyses suggest that the crust is ?47-49 km thick beneath the ancient rift, about 5-7 km thicker than the surrounding area. Inverse models of gravity data indicate that the ?300 km-long zone of thickened, high density crust is bounded on both the NW and SE sides by steep contacts; its shorter NE and SW margins are also steep contacts interpreted as crustal-scale faults. Forward modeling of the gravity data, constrained by the receiver function crustal thickness estimates, sparse seismic reflection data and Euler deconvolution solutions, implies that the Proterozoic rift has been heavily intruded as well as thickened by a 7-10 km mafic underplate. Its margins appear to have been sheared along NE-striking fault zones that parallel Appalachian thrust sheet transport directions. These combined results suggest that the mid- and lower-crust of the Proterozoic rift was enriched with pyroxene, which strengthened the crust locally and localized compressional strain along its margins during the North American-African collision. Compressional strain in the pre-Appalachian crystalline crust to the southwest and northeast of the Proterozoic rift may have been more distributed, leading to the formation of oblique-slip faults orthogonal to the axes of folds, and leading to the curvature in the Pennsylvania salient. Additionally, the thrust sheets are stacked most thickly in front of the rift, suggesting that the rift served as a backstop during collision.

  15. Fracture and Damage Mechanics of Marginal Weakening and Rifting in Pine Island Glacier Ice Shelf

    NASA Astrophysics Data System (ADS)

    Borstad, C. P.; Rignot, E. J.; Larour, E. Y.

    2013-12-01

    The southern ice shelf of Pine Island Glacier has experienced at least seven major tabular calving events since 1973. The most recent calving in July 2013 was the culmination of a rift that initiated further upstream than any in the observational record. Here, we apply fracture and damage mechanics to analyze the pattern, location, and relationship between marginal weakening and rifting over time for the ice shelf. We compute spatially variable maps of ice rigidity for the years 1996 and 2007 using an inverse control method implemented in the Ice Sheet System Model (ISSM). We derive a new theoretical relation for the creep of a damaged ice shelf and use this relation, combined with an analytical temperature calculation for the ice shelf, to partition the inverted rigidity into solutions for damage and backstress for the ice shelf. We find that damage in the shear margins has increased in magnitude and spatial extent over time, in agreement with the amount of marginal weakening necessary for analytical centerline velocity calculations to be consistent with observations. We apply Linear Elastic Fracture Mechanics (LEFM) to analyze the conditions under which rifts originate in the ice shelf. All rifts observed over the last 40 years have been located adjacent to or downstream of an ice rumple located along the northern shear margin of the ice shelf. Prior to 2001, the rifts appeared to initiate in the center of the ice shelf and propagate symmetrically outward and transverse to the flow. Since 2001, however, the rifts have initiated from existing marginal fractures in the wake of the ice rumple. This change in behavior is explained by the loss of buttressing from the ice rumple as the ice upstream has thinned and weakened. Simple LEFM considerations predict that rifts may form more frequently in the future, as propagating a fracture from the edge of a plate is easier, for a given stress, than from the middle. Furthermore, given the reduced buttressing near the front of the ice shelf, future rifts are increasingly likely to originate further upstream than observed previously.

  16. Recent seismic activity of the Kivu Province, Western Rift Valley of Africa

    NASA Astrophysics Data System (ADS)

    Zana, N.; Kamba, M.; Katsongo, S.; Janssen, Th.

    1989-11-01

    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 Rift Valley is characterized by the highest uplift and by complex dislocations of the crust, accompanied by the most intensive volcanism of the East African Rift System. 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.

  17. Brief Communication: Newly developing rift in Larsen C Ice Shelf presents significant risk to stability

    NASA Astrophysics Data System (ADS)

    Jansen, D.; Luckman, A. J.; Cook, A.; Bevan, S.; Kulessa, B.; Hubbard, B.; Holland, P. R.

    2015-06-01

    An established rift in the Larsen C Ice Shelf, formerly constrained by a suture zone containing marine ice, grew rapidly during 2014 and is likely in the near future to generate the largest calving event since the 1980s and result in a new minimum area for the ice shelf. Here we investigate the recent development of the rift, quantify the projected calving event and, using a numerical model, assess its likely impact on ice shelf stability. We find that the ice front is at risk of becoming unstable when the anticipated calving event occurs.

  18. Influence of the mechanical coupling and inherited strength variations on the geometry of continental rifts.

    NASA Astrophysics Data System (ADS)

    Philippon, Melody; van Delft, Pim; van Winden, Matthijs; Zamuroviç, Dejan; Sokoutis, Dimitrios; Willingshofer, Ernst; Cloetingh, Sierd

    2013-04-01

    The geometry of continental rifts is strongly controlled by the rheology of the lithosphere at the onset of rifting. This initial geometry will further control the development of ocean spreading centers and the structure of adjacent passive margins. Therefore, understanding the influence of coupling between the different layers of the lithosphere with and without laterally variable strength in the crust is key when investigating continental rifts. In this study we infer the influence of coupling in the crust on the rift geometry by means of crustal scale analogue experiments, where we characterize the response of the crust to deformation in terms of the strength ratio between brittle and ductile crust. The degree of coupling has been varied for setups containing or not a pre-existing weak zone. To allow a better description of the geometry obtained in our models, some key observations such as: a) the degree of tilting of the blocks, b) the total width of the graben, c) the displacement along the main fault and d) the distribution of thinning in the lower crust are monitored. Models containing a weak zone are compared to natural examples of the inherited Mozambique Ocean suture zones (MOSZ) in the Red Sea rift. The modelling results suggest that deformation is not a-priori localized within pre-existing weak zones unless the coupling between the brittle and the ductile crust is high. With respect to the MOSZ, we infer that: (1) Jurassic NW-SE trending grabens developed parallel to but not within the MOSZ and hence reflect a low degree of coupling whereas (2) Eocene rifting in the Red Sea occurred under coupled conditions as deformation strongly focused within the MOSZ. Models without weak zone shows that large-scale detachment faults can also form within a highly coupled crust, which is at variance to the common perception that detachment faulting demands strong decoupling. Our findings shed light on natural rift systems, which show a wide range of geometries that vary from grabens bounded by high angle normal faults (analogue to the geometry of the Upper Rhine Graben & North Sea Central graben) to listric faults rooting on a basal detachment defining a more asymmetric system (similar to the geometry of the golf of Corinth rift).

  19. Continental rifting and porphyry-molybdenum occurrences in the oslo region, Norway

    NASA Astrophysics Data System (ADS)

    Schönwandt, H. K.; Petersen, J. S.

    1983-05-01

    The overall structure of the Oslo rift-system can be viewed as the result of interference between a N-S trending Permian fault system and a regional NE-SW trending, Precambrian shear-zone. The rift system comprises four mutually opposed horst and graben structures in a centrosymmetrical arrangement. Igneous activity occurred only in two en echelon segments, both of which possess a notable symmetric distribution of rocks and structures around the central axis of the rift system. The axial zone is occupied by Cambro-Silurian sediments which have been intruded by major granite bodies. Extensive lava-plateaus occur on each side of this axial zone. The adjacent zones contain the most prominent cauldrons of province. Further away from the axis follows a zone of batholitic intrusions, emplaced as composite diapirs and plutonic ring complexes. Hornfelsed sediments and volcanics in narrow bands occur at the lateral borders of the province, possibly preserved as the result of marginal tectonics associated with batholith emplacement. The formation of the Oslo Rift system apparently reflects a passive continental rifting which was gradually succeeded by considerable igneous activity. Important porphyry-molybdenum mineralization in the Oslo region is associated with shallow level magmatism in the Glitrevann and Hurdal areas. The porphyry-Mo mineralization in these prospects have several evolutionary features in common: (1) an initial period of effusive eruptions of pyroclastic flows followed by (2) the formation of large-scale ring structures, partly accompanied by peripheral syenite-granite intrusions; (3) the emplacement of a multiple intrusive, central stock of sub-alkaline granite composition which is terminated by (4) the injection of a highly differentiated aplogranite-granophyre, closely associated with the development of the mineralizing hydrothermal porphyry system. Molybdenum mineralization of the Oslo province is closely associated with highly differentiated alkali granites which possess striking similarities to Mo-related granites of the Colorado Mo-province and evolved Rapakivi- or A-type granites, usually considered to be typically associated with bimodal magmatism of crustal extension and continental rifts. The discovery of significant porphyry-Mo mineralization in the Oslo rift associated with Permian igneous rocks draws attention to the possible economic potential of rift structures elsewhere.

  20. Fractal nature and scaling of normal faults, Rio Grande rift, NM: Implications for growth and strain

    SciTech Connect

    Carter, K.E.

    1994-09-01

    In this paper I introduce a suite of Quaternary normal faults from within an active continental rift and characterize the nature of the relationship between fault dimensions. I address the statistical and geological significance of the fractal analysis used in that characterization and discuss the tectonic implications. Specifically, I suggest (1) scaling laws for a previously unanalyzed population of young normal faults in rift environment; (2) implications for fault growth models in this area, in particular, addressing self-similar growth implied from the population; and (3) estimates for the total strain in this part of the basin, considering the contribution of small to unobserved faults.

  1. Deformation during the 1975-84 Krafla rifting crisis, NE Iceland, measured by optical image correlation

    NASA Astrophysics Data System (ADS)

    Hollingsworth, J.; Leprince, S.; Avouac, J.; Ayoub, F.

    2011-12-01

    In this study we combine results from optical image correlation of SPOT, KH-9 spy satellite and aerial photos, EDM data and high resolution topographic data to better constrain the 3D deformation associated with the 1975-84 Krafla rifting crisis, NE Iceland. Inversion of the various geodetic datasets yields new volumes for the amount of material injected into the crust during this rifting crisis. Correlation of aerial photos from 1957 and 1990 for the middle section of the 2 km-wide Krafla fissure swarm, along with DEM differencing of their respective 1957 and 1990 DEM's (extracted using photogrammetric techniques), provides constraints on the full 3D displacement field spanning the entire rifting period. Elastic dislocation modeling of this displacement data is then used to determine the geometry of faulting and diking in the crust. In contrast to leveling data from the northern end of the fissure swarm (Rubin, et al., 1988), we find that dikes do not extend into the upper 1-2 km, where extension is accommodated primarily by faulting in the fissure swarm. Dislocation modeling of a 4 m-wide dike injected between 2 km and 6 km in the crust produces a maximum surface strain which reaches the elastic yield limit for rock (derived from laboratory experiments of deformed granite) at two points spanning a 2 km-wide zone above the dike, and which corresponds with the location of the major rift-bounding faults of the Krafla fissure swarm. If dikes extend nearer to the surface, the predicted fissure zone width would be correspondingly smaller (consistent with the southern-end of the fissure swarm), while deeper diking produces a wider fissure swarm (consistent with the northern-end of the fissure swarm). The apparent northward increase in depth of diking is consistent with the flexural effects of rift-margin topography (Behn, et al., 2006); increased flexure in the south, where the Krafla caldera is located, results in the promotion of shallow diking, where as subdued topography in the north promotes deeper diking. Correlation of aerial photos between 1957 and 1976 (during the early stages of the rifting crisis) indicate 2 m extension, which is localized on faults along the northern end of the fissure swarm. No fault slip occurs in the central section of the fissure swarm during the same period, suggesting extension in the north during the early stages of rifting may result from dike injections sourced from the north (possibly offshore), rather than the Krafla caldera to the south. A similar variation in magmatic source region was also observed during the 2005-2009 Afar rifting crisis in East Africa.

  2. The Proterozoic Ladoga rift (SE Baltic shield): Linking mantle dynamics to supercontinent cycle and regional tectonics

    NASA Astrophysics Data System (ADS)

    Artemieva, Irina; Shulgin, Alexey

    2015-04-01

    Mesoproterozoic mafic magmatism at the southern part of the Baltic Shield (the Lake Ladoga region) is conventionally ascribed to epicratonic rifting. The region hosts a series of mafic dykes and sills of Mesoproterozoic ages, including a ca. 1.53-1.46 Ga sheet-like gabbro-dolerite sills and the Salmi plateau-basalts from the Lake Ladoga region. Based on chiefly geochemical data, the region is conventionally interpreted as an intracratonic Ladoga rift (graben). We question the validity of this geodynamic interpretation by analyzing regional geophysical data (crustal structure, heat flow, Bouguer gravity anomalies, magnetic anomalies, and mantle Vs velocities). Our analysis of characteristics of continental rifts demonstrates that: 1. the topography of the region lacks a linear horst-graben structure typical of modern rifts, however this feature might have been lost by surface erosion; 2. the crust has neither shallow Moho, nor magmatic high-velocity underplated material, and thus is not typical of continental rifts; 3. weakly negative Bouguer gravity anomalies, especially by comparison with adjacent "background" anomalies suggest the presence of high-density material at shallow, near-Moho depths; however, the shape of the anomaly is rounded rather than linear, and may not attest to the paleorifting event; 4. seismic velocities in the upper mantle show a possible weak low-Pn anomaly near Lake Ladoga, and strong positive (+5+7%) Vs anomaly at 75-125 km depth to the NE of the lake, but not in the region of Mesoproterozoic mafic magmatism; 5. no thermal anomaly or lithosphere thickness anomaly is currently present in the lithosphere of the region, which instead is marked by extremely low heat flow; however, given the age of magmatism any thermal anomaly may have long ceased and thus its absence does not disprove rifting origin of magmatism; 6. the absence of linear magnetic anomalies which are preserved in other paleorifts provides strong evidence that this region has not been affected by rifting. We conclude that a mechanism other than rifting is responsible for Mesoproterozoic mafic magmatism at the southern part of the Baltic Shield and propose that magma intrusion associated with deformation along the margins of Nuna (Columbia) supercontinent, and its transformation to eclogite facies, locally speeded by fluids, produced a highly heterogeneous density structure of the lithosphere.

  3. Ground motion and tectonics in the Terceira Island: Tectonomagmatic interactions in an oceanic rift (Terceira Rift, Azores Triple Junction)

    NASA Astrophysics Data System (ADS)

    Marques, F. O.; Catalão, J.; Hildenbrand, A.; Madureira, P.

    2015-05-01

    The interpretation of high-resolution topography/bathymetry, GPS and InSAR data, and detailed structural geology indicate that: (1) Terceira developed at the intersection of two major volcano-tectonic lineaments: WNW-ESE (local TR's direction) and NNW-SSE (submarine chain of volcanoes, here firstly recognised and coined Terceira Seamount Chain). (2) Terceira is affected by four main fault systems: the ca. N165° (normal faults dipping to east and west, mostly across the middle of the island), the N140° (normal faults mostly making up the Lajes Graben), the N110° (faults with oblique striations - normal dextral, making up the main volcanic lineament), and the more subtle N70° (the transform direction related to the Nubia/Eurasia plate boundary). Seismicity, GPS data and faults displacing the topography indicate that all systems are active. (3) The whole island is subsiding at a rate of ca. 5 mm/yr, as attested by both GPS and InSAR data, which is exceptionally high for the Azores islands. Common explanations like thermal contraction, or bending of the lithosphere, or magmatic processes, or collapse of the island under its own weight likely cannot justify the observed subsidence rate. The estimated average of TR's subsidence rate is also not enough, therefore we conclude that the measured 5 mm/yr can be a peak. (4) The fault geometry and kinematics are consistent with the current direction of maximum extension in the Azores (ca. N65°), and the rotation of Nubia relative to Eurasia. (5) Given that the NE shoulder of the Lajes Graben is moving upwards at 5 mm/yr and sits directly on the TR's NE shoulder, we conclude that the TR's shoulder is moving up, most likely as a result of the elastic rebound associated with rifting. The elastic rebound in both NE and SW TR's shoulders is most likely responsible for the observed ridge morphology all along the TR.

  4. Analysis of Proterozoic rifting and subsequent subsidence of the Central Congo Basin

    NASA Astrophysics Data System (ADS)

    Kadima Kabongo, Etienne; Sebagenzi Mwene Ntabwoba, Stanislas; Lucazeau, Francis

    2010-05-01

    The Central Basin (or Cuvette Centrale) of Congo is a late-Proterozoic to Recent basin covering near one million km2 with up to 9 km of sediment. Its subsidence has been related to a preexisting failed rift (Daly et al, 1992), whose origin, geometry and structure remain largely unknown. Here we present a combined analysis of subsidence and gravity that provides new lines of evidence for a rift origin. Although the dataset for the Central Basin is poor and has not been improved for a long time (only four deep wells with depths between 1856 and 4666 meters and 33 seismic lines covering 2900 km), it is sufficient for the first order characteristics. The analysis of wells data reveals that the long term subsidence (~450 m.y.) and present-day surface heat flow (~40 mWm-2) are both characteristic of a 250 km thick thermal lithosphere. This is consistent with the Archean age of the craton but not with thermal reworking during Paleozoic as hypothesized by Artemieva (2006). From the seismic lines, we can derive a 3D geometrical basin model divided into three different units defined by two major uncomformities. Each layer is assigned an average density value inferred from geophysical logs and then gravity effect is determined and subtracted from the observed gravity anomalies. The residual map shows a positive SE-NW elongated structure that can be related to a possible rift prior to basin subsidence. In order to determine the associated crustal structure, we simply assumed that the post-rift subsidence is flexural and that the rift isostasy is governed by a depth of necking. The procedure involves first flexural backstripping of sediments assuming a given Equivalent Elastic Thickness EET and then determination of the crustal thickness assuming a given depth of necking DON. EET and DON are varied in order to obtain the minimum misfit between predicted and observed gravity. The best results are obtained for EET = 100 km, DON = 10 km and an initial crust thickness of 35 km. The thinning factor within the rift is 1.75-2.00, which is comparable with modern rift such as Baikal (Poort et al, 1998) or East African Rift (Mechie, 1994). The modeled EET is high (100 km) but comparable with estimated values from Bouguer gravity / topography coherence analysis (Pérez-Gussinyé et al, 2009) for that area. Such a large strength value is consistent with a 250 km thick and cold thermal lithosphere. Finally, the depth of necking DON=10 km is shallow but mostly representative of the strength conditions during rifting as for modern rifts. The hidden rift below Central Basin is in the continuity of neo Proterozoic geological structures, the Bushimay supergroup to the South-East and the the Liki-Bembien group to the North-West, while a satellite structure is connecting to the Sangha aulacogen.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    Microsoft Academic Search

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

    2010-01-01

    Helium isotope studies of the East African Rift System (EARS) suggest the involvement of a deep mantle plume(s) beneath the northern (Ethiopian) segment [1-3]. The highest 3He\\/4He (RA) signatures found to date show a close association with the greatest magma volumes erupted since the Early Cenozoic in the region. While the helium isotope characteristics are well established in the Ethiopia-Afar

  7. Tectonomagmatic evolution of the final stages of rifting along the deep conjugate Australian-Antarctic magma-poor rifted margins: Constraints from seismic observations

    NASA Astrophysics Data System (ADS)

    Gillard, Morgane; Autin, Julia; Manatschal, Gianreto; Sauter, Daniel; Munschy, Marc; Schaming, Marc

    2015-04-01

    The processes related to hyperextension, exhumed mantle domains, lithospheric breakup, and formation of first unequivocal oceanic crust at magma-poor rifted margins are yet poorly understood. In this paper, we try to bring new constraints and new ideas about these latest deformation stages by studying the most distal Australian-Antarctic rifted margins. We propose a new interpretation, linking the sedimentary architectures to the nature and type of basement units, including hyperextended crust, exhumed mantle, embryonic, and steady state oceanic crusts. One major implication of our study is that terms like prerift, synrift, and postrift cannot be used in such polyphase settings, which also invalidates the concept of breakup unconformity. Integration and correlation of all available data, particular seismic and potential field data, allows us to propose a new model to explain the evolution of magma-poor distal rifted margins involving multiple and complex detachment systems. We propose that lithospheric breakup occurs after a phase of proto-oceanic crust formation, associated with a substantial magma supply. First steady state oceanic crust may therefore not have been emplaced before ~53.3 Ma corresponding to magnetic anomaly C24. Observations of magma amount and its distribution along the margins highlight a close magma-fault relationship during the development of these margins.

  8. The transition from craton to rift in south eastern Africa: Preliminary surface wave tomography from the MOZambique Rift Tomography (MOZART) project

    NASA Astrophysics Data System (ADS)

    Fishwick, S.; Domingues, A.; Fonseca, J. F.; Chamussa, J. R.; Helffrich, G. R.; Grobbelaar, M.

    2012-12-01

    We present preliminary results from the MOZART (Mozambique Rift Tomography) experiment in the context of the transition from the old and cold lithosphere associated with the Kalahari Craton, to the continental lithosphere associated with the southern tip of the East African Rift System (EARS) in Mozambique. The initial stage of surface wave data recorded on the network of 30 broadband seismic stations deployed in 2011 are incorporated into an earlier continental scale tomographic model of Africa (Fishwick, 2010). These data provide a significant increase in potential resolution of upper mantle velocities, in a region where there has previously been little knowledge of the detailed lithospheric structure. Furthermore they allow a better comparison with the velocities observed beneath the Kaapvaal Craton where data from the dense network of seismometers deployed in the earlier Southern Africa Seismic Experiment (SASE) have already been included in the regional tomography. From the new tomographic models we investigate the lateral gradients in seismic velocity at upper mantle depths of 75-250km in order to place better constraints on the thermal and/or chemical transitions from the craton to the rift. In order to test the reliability of these estimates of the velocity gradient we compare different parameterisations and regularisations, but also investigate to what degree the addition of new data to the tomographic model alters the estimated velocities. The regional tomographic model produced will provide a useful new reference model for more detailed inter-station and array tomography when project MOZART is completed in mid-2013.

  9. Deformation modelling of the 2014 Bárðarbunga rifting event in Iceland

    NASA Astrophysics Data System (ADS)

    Hooper, Andrew; Sigmundsson, Freysteinn; Hreinsdóttir, Sigrún; Heimisson, Elías; Ófeigsson, Benedikt; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Drouin, Vincent; Árnadóttir, Thóra; Vogfjörd, Kristín; Jónsdóttir, Kristín; Fridriksdóttir, Hildur; Hensch, Martin

    2015-04-01

    Between 16 August and 31 August 2014 a dike propagated from Bárðarbunga caldera, which culminated in an eruption at Holuhraun that is still ongoing at the time of writing. Previous models of other rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens, or magma flowing vertically into dykes from an underlying source, with the role of topography on the evolution of lateral dykes not clear. Our modelling shows how the segmented dyke intrusion in the Bárðarbunga volcanic system grew laterally for more than 45 kilometres at a variable rate, with topography influencing the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke propagation path is not simple, comprising many segments with differing orientations. We modelled the dyke propagation using deformation data from InSAR and GPS. Initial modelling of the dyke, with no a priori constraints on position, strike or dip, show the deformation data require the dyke to be approximately vertical and line up with the seismicity. We therefore fixed the dip to be vertical and the lateral position of the dyke to coincide with the earthquake locations. We modelled the dyke as a series of rectangular patches and estimated the opening and slip on each patch for each day between 16 August and 6 September. The results suggest that most of the magma injected into the dyke is shallower than the seismicity, which mostly spans the depth range from 5 to 8 km below sea level. Where constraints from InSAR and GPS are good, significant opening is all shallower than 5 km, and opening is up to 6 m. The total volume intruded into the dyke by 28 August was 0.48-0.51 km3. We also modelled the expected propagation direction of the dyke considering the regional stress field and the spatially-variable overburden. We find that our model agrees well with the actual propagation path as indicated by the seismicity.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Our ability to determine the structural evolution and interaction of fault systems (kinematically linked group of faults that are in the km to 10s of km scale) within a rift basin is typically limited by the spatial extent and temporal resolution of the available data and methods used. Physical and numerical models provide predictions on how fault systems nucleate, grow and interact, but these models need to be tested with natural examples. Although field studies and individual 3D seismic surveys can provide a detailed structural evolution of individual fault systems, they are often spatially limited and cannot be used examine the interaction of fault systems throughout the entire basin. In contrast, regional subsurface studies, commonly conducted on widely spaced 2D seismic surveys, are able to capture the general structural evolution of a rift basin, but lack the spatial and temporal detail. Moreover, these studies typically describe the structural evolution of rifts as comprising multiple discrete tectonic stages (i.e. pre-, syn- and post-rift). This simplified approach does not, however, consider that the timing of activity can be strongly diachronous along and between faults that form part of a kinematically linked system within a rift basin. This study focuses on the East Shetland Basin (ESB), a multiphase rift basin located on the western margin of the North Viking Graben, northern North Sea. Most previous studies suggest the basin evolved in response to two discrete phases of extension in the Permian-Triassic and Middle-Late Jurassic, with the overall geometry of the latter rift to be the result of selective reactivation of faults associated with the former rift. Gradually eastwards thickening intra-rift strata (deposited between two rift phases) that form wedges between and within fault blocks have led to two strongly contrasting tectonic interpretations: (i) Early-Middle Jurassic differential thermal subsidence after Permian-Triassic rifting; or (ii) Triassic syn-rift activity on west-dipping faults. Our analysis of regional 2D and basin-wide 3D 'mega-merge' seismic reflection data calibrated by wells allow us to re-evaluate the pre-Triassic-to-Cretaceous structural evolution of the ESB. Our results suggest that pre-Triassic extension was accommodated by diachronous growth of NW-SE-to-NE-SW-striking faults that dipped either to the east or the west. In the NW of the ESB, Triassic syn-rift deposits are observed along large (>20 km long), NE-SW-striking faults. Elsewhere in the basin, post-rift deposits gradually thicken eastward, suggesting differential Triassic post-rift thermal subsidence with its axis to the east of the ESB. Subsequent Early-to-Middle Jurassic deposits thicken eastward across large N-S striking faults, suggesting syn-depositional fault growth. Our observations suggest that, rather than forming in response to discrete periods of extension separated by periods of tectonic quiescence, the ESB witnessed diachronous fault system evolution with faults showing polyphase activity, cross-cutting relationships, and protracted growth from the pre-Triassic to Middle-Late Jurassic. The results of this work reveal the complex structural evolution of rifts, highlight the power of 3D mega-merge seismic reflection data, and demonstrate that the conventional rift package nomenclature of pre-, syn-, and post-rift is difficult to apply at the basin-scale.

  11. Propagated rifting in the Southwest Sub-basin, South China Sea: Insights from 3D analogue modeling

    NASA Astrophysics Data System (ADS)

    Ding, Weiwei; Li, Jiabiao

    2015-04-01

    Most of earth scientists agree that the South China Sea is a rifted marginal sea in the western Pacific. How and when the South China Sea rifted has long been a puzzling question and still debated, especially in the Southwest Sub-basin (SWSB). Analog modeling remains one of the useful tools for testing rift model and process. Here we present and discuss a series of analog modeling experiments designed to investigate the rifting process of the SWSB. Convincing geophysical data were compiled to provide truthful constraints to test the experimental results and interpretations. The results show that rigid tectonic blocks existed in the continental margin, such as the Zhongsha Islands and the Reed Bank, and played an important role in shaping up the continent-ocean boundary (COB) and the coupling between the crust and mantle. Our data suggest that the initial thermal condition and rheologial stratification of the lithosphere under the South China Sea controlled the rifting process of the SWSB. The first-stage seafloor spreading has weakened the lithosphere surrounding the East Sub-basin, and the extension was centered on the deep troughs between the rigid blocks. Rifting bagan in these deep troughs in the east part of the SWSB, and the break-up occurred in localized areas between the rigid blocks. The V-shaped configuration of the SWSB also argues for a propagated rifting model.

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

    USGS Publications Warehouse

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

    1986-01-01

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

  13. Geodynamic significance of the TRM segment in the East African Rift: active tectonics and paleostress in western Tanzania

    NASA Astrophysics Data System (ADS)

    Delvaux, D.; Kervyn, F.; Macheyeki, A. S.; Temu, E. B.

    2012-04-01

    The Tanganyika-Rukwa-Malawi (TRM) rift segment in western Tanzania is a key sector for understanding the opening dynamics of the East African rift system (EARS). In an oblique opening model, it is considered as a dextral transfer fault zone that accommodates the general opening of the EARS in a NW-SE direction. In an orthogonal opening model, it accommodates pure dip-slip normal faulting with extension orthogonal to the rift segments and a general E-W extension for the entire EARS. We investigated the active tectonic architecture and paleostress evolution of the Ufipa plateau and adjacent Rukwa basin and in order to define their geodynamic role in the development of the EARS and highlight their pre-rift brittle tectonic history. The active fault architecture, fault-kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the TRM segment. Two pre-rift brittle events are evidenced. An older brittle thrusting is related to the interaction between the Bangweulu block and the Tanzanian craton during the late Pan-African (early Paleozoic). It was followed by a transpressional inversion during the early Mesozoic. This inversion stage caused dextral strike-slip faulting along the fault systems that now control the major rift structures. It has been erroneously interpreted as related to the late Cenozoic EARS which instead is characterized by pure normal faulting.

  14. Verificaci'on autom'atica de sistemas de razonamiento \\Lambda (aplicaci'on a la ense~nanza de la Inteligencia Artificial)

    E-print Network

    Reina, José Luis Ruiz

    . Una detallada informaci'on del sistema se puede encontrar en [2] y [3]. 2.1 La l'ogica computacionalVerificaci'on autom'atica de sistemas de razonamiento \\Lambda (aplicaci'on a la ense~nanza de la En este art'iculo proponemos el uso de sistemas de demostraci'on autom'atica como herramienta pr

  15. Buried Rift Zones and Seamounts in Hawaii: Implications for Volcano Tectonics

    Microsoft Academic Search

    J. K. Morgan; C. A. Zelt; P. G. Okubo

    2005-01-01

    As volcanoes grow, they deform due to their own weight and ongoing magmatic intrusions. For example, Kilauea's south flank is moving seaward ~10 cm\\/yr, apparently pushed by dike injection along rift zones and\\/or gravitational spreading. Offshore, Kilauea's south flank has developed a broad bench, attributed to overthrusting at the toe of the mobile flank. Mauna Loa's southeastern flank is much

  16. Crustal structure of the northern Nova Scotia rifted continental margin (eastern Canada)

    Microsoft Academic Search

    Thomas Funck; H. Ruth Jackson; Keith E. Louden; Sonya A. Dehler; Yue Wu

    2004-01-01

    The Nova Scotia continental margin off eastern Canada marks a transition from a volcanic to a nonvolcanic style of rifting. The northern (nonvolcanic) segment of the margin was studied by a 490-km-long refraction seismic line with dense air gun shots, coincident with previous deep reflection profiles. A P wave velocity model was developed from forward and inverse modeling of the

  17. Evidence of mass failure in the Hess Deep Rift from multi-resolutional bathymetry data

    E-print Network

    Shillington, Donna J.

    Evidence of mass failure in the Hess Deep Rift from multi-resolutional bathymetry data Vicki Lynn online 17 April 2013 Communicated by D.J.W. Piper Keywords: Hess Deep Bathymetry Mass failure New regional swath and near-bottom bathymetric data provide constraints on shallow structures at the Hess Deep

  18. Evolution of magma-poor continental margins from rifting to seafloor spreading.

    PubMed

    Whitmarsh, R B; Manatschal, G; Minshull, T A

    2001-09-13

    The rifting of continents involves faulting (tectonism) and magmatism, which reflect the strain-rate and temperature dependent processes of solid-state deformation and decompression melting within the Earth. Most models of this rifting have treated tectonism and magmatism separately, and few numerical simulations have attempted to include continental break-up and melting, let alone describe how continental rifting evolves into seafloor spreading. Models of this evolution conventionally juxtapose continental and oceanic crust. Here we present observations that support the existence of a zone of exhumed continental mantle, several tens of kilometres wide, between oceanic and continental crust on continental margins where magma-poor rifting has taken place. We present geophysical and geological observations from the west Iberia margin, and geological mapping of margins of the former Tethys ocean now exposed in the Alps. We use these complementary findings to propose a conceptual model that focuses on the final stage of continental extension and break-up, and the creation of a zone of exhumed continental mantle that evolves oceanward into seafloor spreading. We conclude that the evolving stress and thermal fields are constrained by a rising and narrowing ridge of asthenospheric mantle, and that magmatism and rates of extension systematically increase oceanward. PMID:11557977

  19. Rift Valley Fever: International Coordinated Efforts from Early Warning to Rapid Responses

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Scientists at the USDA, ARS, Arthropod-Borne Animal Diseases Research Laboratory (ABADRL) initiated research to develop operator-safe, rapid diagnostic tests and develop large animal models for both virulent and vaccine strains of Rift Valley Fever (RVF). The ABADRL currently does not have biologica...

  20. Slipped deformation bands: A new type of cataclastic deformation bands in Western Sinai, Suez rift, Egypt

    E-print Network

    Fossen, Haakon

    is described. Slip surface development is normally constrained to the eventual brittle failure of a deformationSlipped deformation bands: A new type of cataclastic deformation bands in Western Sinai, Suez rift August 2008 Keywords: Deformation bands Cataclasis Fault Porous sandstone a b s t r a c t A type

  1. Crustal structure of the Newfoundland rifted continental margin from constrained 3-D gravity inversion

    Microsoft Academic Search

    J. Kim Welford; Jeremy Hall

    2007-01-01

    The rifting history of the Atlantic continental margin of Newfoundland is very complex and so far has been investigated at the crustal scale primarily with the use of 2-D seismic surveys. While informative, the results generated from these surveys cannot easily be interpreted in a regional sense due to their sparse sampling of the margin. A 3-D gravity inversion of

  2. Propagation of rifting along the Arabia-Somalia plate boundary The Gulfs of Aden and Tadjoura

    Microsoft Academic Search

    Isabelle Manighetti; Paul Tapponnier; Vincent Courtillot; Sylvie Gruszow; Pierre-Yves Gillot

    1997-01-01

    The localization and propagation of rifting between Arabia and Somalia are investigated by assessing the deformation geometry and kinematics at different scales between the eastern Gulf of Aden and the Gulf of Tadjoura, using bathymetric, magnetic, seismological, and structural evidence. Large-scale, southwestward propagation of the Aden ridge, markedly oblique to the Arabia-Somalia relative motion vector, began about 30 Myr ago

  3. Master1RservoirsGologiquesDynamiquedesBassins-MichelSranne Cratonic Basins: Michigan Basin -> old rift ???

    E-print Network

    Demouchy, Sylvie

    of Figure 21.4 West Siberian Basin depth to Moho map (contour lines are in kilometers). Location of oil/gas fields and seismic profiles is shown for reference. (Depth to Moho map is modified after Kovylin, 1985&al,inRoberts&Bally,2012 Early Permian rifting Moho depth => crustal thinning Tertiary Tur-Maast Apt-Cen Neoc U.Jur Tr

  4. Predicting OCT Location and Continental Extension for North Atlantic Rifted Margins Using Gravity Inversion

    Microsoft Academic Search

    A. Alvey; N. J. Kusznir

    2007-01-01

    Gravity inversion incorporating a lithosphere thermal gravity anomaly correction has been used to determine Moho depth, crustal basement thickness and lithosphere thinning factor for ~50 2D regional profiles across North Atlantic rifted margins including Labrador Sea, Baffin Bay, Iberian - Newfoundland and Norwegian - Greenland conjugate margins. Sediment thickness derived from seismic refraction\\/reflection data has been included in the gravity

  5. Upper Proterozoic rift-related rocks in the Pensacola Mountains, Antarctica: Precursors to supercontinent breakup?

    Microsoft Academic Search

    Bryan C. Storey; Tony Alabaster; David I. M. Macdonald; Ian L. Millar; Robert J. Pankhurst; Ian W. D. Dalziel

    1992-01-01

    Sedimentological and structural studies in the Pensacola Mountains, Antarctica, suggest that upper Precambrian clastic sedimentary rocks of the Patuxent Formation and associated bimodal volcanic rocks formed in an intracontinental rift setting. The turbidites of the Patuxent Formation are part of a large depositional system, derived from a continental source. Interbedded pillow basalts and basaltic sills have trace and rare earth

  6. Lena Trough (Arctic Ocean): Active mantle exhumation on a continental rifted margin

    Microsoft Academic Search

    J. E. Snow; E. Hellebrand; A. von der Handt; F. Nauret

    2007-01-01

    Lena Trough is the northern continuation of the Mid-Atlantic Ridge through Fram Strait and into the Arctic Ocean. The rifting of Lena Trough began in the Miocene, and significantly, is the final and the most recent event in the separation of the North American from the Eurasian continent. Lena Trough was mapped in 1999, 2001 and 2004 by PFS Polarstern

  7. Lena Trough (Arctic Ocean): Active mantle exhumation on a continental rifted margin

    Microsoft Academic Search

    J. E. Snow; E. Hellebrand; A. von der Handt; F. Nauret

    2004-01-01

    Lena Trough is the northern continuation of the Mid-Atlantic Ridge through Fram Strait and into the Arctic Ocean. The rifting of Lena Trough began in the Miocene, and significantly, is the final and the most recent event in the separation of the North American from the Eurasian continent. Lena Trough was mapped in 1999, 2001 and 2004 by PFS Polarstern

  8. The Tethyan plume: geochemical diversity of Middle Permian basalts from the Oman rifted margin

    E-print Network

    Demouchy, Sylvie

    The Tethyan plume: geochemical diversity of Middle Permian basalts from the Oman rifted margin H in the Saih Hatat tectonic window. They consist predominantly of pillowed basaltic flows among which three trace element contents, and a large range of eNdi values. Group 1 basalts are associated with distal

  9. Topography and Tectonics at the Intersections of Fracture Zones with Central Rifts

    Microsoft Academic Search

    Norman H. Sleep; Shawn Biehler

    1970-01-01

    Deep troughs with up to 2 km of relief occur at intersections of fracture zones with the central rift of mid-ocean ridges. The cause of these depressions may be the loss of hydraulic head due to the viscosity of the material that upwells passively at ridges to produce a new sea floor. At such intersections the transform fault truncates the

  10. New Diagnostic Tools for Detecting Rift Valley Fever (RVF) and other Arboviruses

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The outbreak of West Nile virus in the United Sates and the recent outbreak of Rift Valley fever (RVF) virus in East Africa have highlighted the need for validated early detection tools for arthropod-borne animal diseases. The Arthropod-Borne Animal Diseases Research Laboratory (ABADRL) has been inv...

  11. Geologic controls of hydrothermal activity in the Mid-Atlantic Ridge rift valley: Tectonics and volcanics

    Microsoft Academic Search

    Ginger L. Eberhart; Peter A. Rona; Jose Honnorez

    1988-01-01

    The rift valley at three widely separated sites along the Mid-Atlantic Ridge is characterized using geological and geophysical data. An analysis of bottom photographs and fine-scale bathymetry indicates that each study area has a unique detailed geology and structure. Spreading rates are apparently asymmetric at each site. Relationships between tectonic and volcanic structure and hydrothermal activity show that various stages

  12. Rifting process and thermal evolution of the continental margin of Eastern Canada determined from subsidence curves

    Microsoft Academic Search

    L. Royden; C. E. Keen

    1980-01-01

    The subsidence history of the Nova Scotia and Labrador shelves, determined from deep exploratory well data, indicates that these regions underwent extension during rifting in the Early Jurassic and Late Cretaceous, respectively, and have since subsided passively due to conductive cooling of the lithosphere. The timing of the extension process is consistent with the ages of oldest sea floor adjacent

  13. Lava Flow From Fissure Eruption on Kilauea Volcano's East Rift Zone

    USGS Multimedia Gallery

    A new fissure eruption in September 2011 on the east flank of Pu‘u ‘?‘? on K?lauea Volcano's east rift zone reminds us of the need to be aware of our ever-changing volcanic environment on Hawai‘i Island. The fissure—the source of the lava flow—is sh...

  14. Seismic velocity structure of the rifted margin of the eastern Grand Banks of Newfoundland, Canada

    E-print Network

    Shillington, Donna J.

    ocean bottom seismometers (OBSs). At the landward side, we imaged a crustal thickness of 27 kmSeismic velocity structure of the rifted margin of the eastern Grand Banks of Newfoundland, Canada seismic velocity profile of the crust of the eastern margin of the Grand Banks of Newfoundland, Canada

  15. 3D Graph Visualization with the Oculus Rift Virtual Graph Reality

    E-print Network

    Wismath, Stephen

    3D Graph Visualization with the Oculus Rift Virtual Graph Reality Farshad Barahimi, Stephen Wismath, possibly with a stereographic effect such as shutter glasses, or anaglyphically, · displayed in a virtual reality environment such as a CAVE, or · printed as a physical model with a 3D printer. Early studies

  16. Rifting Oligocne en Languedoc: Un modle d'extension de couverture

    E-print Network

    Demouchy, Sylvie

    - Conclusions La déformation extensive aboutissant à la formation de la marge continentale du Golfe du Lion en'effondrement de la couverture vers la marge continentale amincie du Golfe du Lion ; la déformation de couverture d'épaisseur ? L'évolution post-rift de la marge du Golfe du Lion comprend une subsidence d

  17. Rift Valley fever risk map model and seroprevalence in selected wild ungulates and camels from Kenya

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Since the first isolation of Rift Valley fever virus (RVFV) in the 1930s, there have been multiple epizootics and epidemics in animals and humans in sub-Saharan Africa. Prospective climate-based models have recently been developed that flag areas at risk of RVFV transmission in endemic regions based...

  18. Rift Valley fever ocular manifestations: observations during the 1977 epidemic in Egypt

    Microsoft Academic Search

    A L Siam; J M Meegan; K F Gharbawi

    1980-01-01

    Ocular manifestations resulting from Rift Valley fever (RVF) virus infection were studied during an extensive RVF epidemic in Egypt during 1977. Colour photography and fluorescein angiography of 7 serologically diagnosed patients showed the commonest manifestations to be macular, paramacular, and\\/or extramacular retinal lesions, often occurring bilaterally. Haemorrhage and oedema were frequently associated with the lesions, and vasculitis, retinitis, and vascular

  19. Generation and transmission of Rift Valley fever viral reassortants by the mosquito Culex pipiens

    Microsoft Academic Search

    M. J. Turell; Jean-Francois Saluzzo; Ralph F. Tammariello; Jonathan F. Smith

    1990-01-01

    Reassortant viruses containing heterologous S and M genomic RNA segments were obtained from both mosquito and vertebrate hosts that had been co- infected with Egyptian and Senegalese strains of Rift Valley fever (RVF) virus. The origin of the S and M RNA segments in each plaque-cloned virus was determined with monoclonal antibodies capable of differentiating the nucleocapsid protein (S segment

  20. Pathogenesis of Rift Valley fever in rhesus monkeys: role of interferon response

    Microsoft Academic Search

    J. C. Morrill; G. B. Jennings; A. J. Johnson; T. M. Cosgriff; P. H. Gibbs; C. J. Peters

    1990-01-01

    Summary Rhesus monkeys inoculated intravenously with Rift Valley fever (RVF) virus presented clinical disease syndromes similar to human cases of RVF. All 17 infected monkeys had high-titered viremias but disease ranged from clinically inapparent to death. Three (18%) RVF virus-infected monkeys developed signs of hemorrhagic fever characterized by epistaxis, petechial to purpuric cutaneous lesions, anorexia, and vomiting prior to death.

  1. Characterization of the Golgi Retention Motif of Rift Valley Fever Virus GN Glycoprotein

    Microsoft Academic Search

    Sonja R. Gerrard; Stuart T. Nichol

    2002-01-01

    As Rift Valley fever (RVF) virus, and probably all members of the family Bunyaviridae, matures in the Golgi apparatus, the targeting of the virus glycoproteins to the Golgi apparatus plays a pivotal role in the virus replication cycle. No consensus Golgi localization motif appears to be shared among the glycoproteins of these viruses. The viruses of the family Bunyaviridae synthesize

  2. TFIIH Transcription Factor, a Target for the Rift Valley Hemorrhagic Fever Virus

    Microsoft Academic Search

    Nicolas Le May; Sandy Dubaele; Luca Proietti De Santis; Agnès Billecocq; Michèle Bouloy; Jean-Marc Egly

    2004-01-01

    The Rift Valley fever virus (RVFV) is the causative agent of fatal hemorrhagic fever in humans and acute hepatitis in ruminants. We found that infection by RVFV leads to a rapid and drastic suppression of host cellular RNA synthesis that parallels a decrease of the TFIIH transcription factor cellular concentration. Using yeast two hybrid system, recombinant technology, and confocal microscopy,

  3. Genetic Evidence for an Interferon-Antagonistic Function of Rift Valley Fever Virus Nonstructural Protein NSs

    Microsoft Academic Search

    MICHELE BOULOY; CHRISTIAN JANZEN; PIERRE VIALAT; HUOT KHUN; JOVAN PAVLOVIC; MICHEL HUERRE; OTTO HALLER

    2001-01-01

    Rift Valley fever virus (RVFV), a phlebovirus of the family Bunyaviridae, is a major public health threat in Egypt and sub-Saharan Africa. The viral and host cellular factors that contribute to RVFV virulence and pathogenicity are still poorly understood. All pathogenic RVFV strains direct the synthesis of a nonstructural phosphoprotein (NSs) that is encoded by the smallest (S) segment of

  4. Variability of the NSS protein among Rift Valley fever virus isolates

    Microsoft Academic Search

    A. A. Sall; A. Zanotto; H. G. Zeller; J. P. Digoutte; Y. Thiongane; M. Bouloy

    1997-01-01

    Eighteen strains of Rift Valley fever (RVF) virus collected over a period of 38 years and isolated from diverse localities in Africa and from various hosts (human, animal and arthropod) were investi- gated by RT-PCR followed by sequencing of the NSS protein coding region. This region was chosen to analyse variability because, in contrast to the N protein, the NSS

  5. Detection of Rift Valley fever virus in mosquitoes by RT-PCR

    Microsoft Academic Search

    M. S. Ibrahim; M. J. Turell; F. K. Knauert; R. S. Lofts

    1997-01-01

    A reverse transcriptase-polymerase chain reaction (RT-PCR) assay to detect Rift Valley fever (RVF) virus RNA in experimentally infected mosquitoes was developed. The specificity of the assay was evaluated with three other phleboviruses; sandfly fever Sicilian (Sabin), sandfly fever Naples (Sabin) and Punta Toro (MSP 3) viruses. The relative sensitivity of the assay, determined by using RVF virus RNA extracted from

  6. Modes of continental rifting as a function of ductile strain localization in the lithospheric mantle

    E-print Network

    Paris-Sud XI, Université de

    mantle Frédéric GUEYDAN (1) and Jacques PRÉCIGOUT (2) (1) Géosciences Montpellier, Université Montpellier mantle controls the mode of lithosphere deformation. In extension, the presence or absence of a high strength brittle mantle respectively leads to localized or distributed rifting. However, first order

  7. Post-rifting relaxation processes in the Afar region (Ethiopia) from geodetic measurements and numerical modeling

    Microsoft Academic Search

    L. Bennati; E. Calais; A. M. Freed; I. J. Hamling; T. J. Wright; E. Lewi; S. L. Nooner; W. R. Buck

    2009-01-01

    In September 2005, a 60km-long dike intrusion took place at the Dabbahu rift, Afar, Ethiopia, at the boundary between the Nubian and Danakil plates. Since this major event, 12 new intrusions have affected the central and southern parts of the 2005 dike. Time series from continuous GPS stations outside of volcanoes show a combination of discrete diking events and quasi

  8. Capturing magma intrusion and faulting processes during continental rupture: seismicity of the Dabbahu (Afar) rift

    Microsoft Academic Search

    C. J. Ebinger; D. Keir; A. Ayele; E. Calais; T. J. Wright; M. Belachew; J. O. S. Hammond; E. Campbell; W. R. Buck

    2008-01-01

    Continental rupture models emphasize the role of faults in extensional strain accommodation; extension by dyke intrusion is commonly overlooked. A major rifting episode that began in 2005 September in the Afar depression of Ethiopia provides an opportunity to examine strain accommodation in a zone of incipient plate rupture. Earthquakes recorded on a temporary seismic array (2005 October to 2006 April),

  9. The Salton Seismic Imaging Project (SSIP): Rift Processes and Earthquake Hazards in the Salton Trough (Invited)

    Microsoft Academic Search

    J. A. Hole; J. M. Stock; G. S. Fuis; M. J. Rymer; J. M. Murphy; R. R. Sickler; C. J. Criley; M. Goldman; R. D. Catchings; J. W. Ricketts; A. Gonzalez-Fernandez; N. Driscoll; G. Kent; A. J. Harding; S. L. Klemperer

    2009-01-01

    The Salton Seismic Imaging Project (SSIP) and coordinated projects will acquire seismic data in and across the Salton Trough in southern California and northern Mexico, including the Coachella, Imperial, and Mexicali Valleys. These projects address both rifting processes at the northern end of the Gulf of California extensional province and earthquake hazards at the southern end of the San Andreas

  10. Thermal imprint of rift-related processes in orogens as recorded in the Pyrenees

    NASA Astrophysics Data System (ADS)

    Vacherat, A.; Mouthereau, F.; Pik, R.; Bernet, M.; Gautheron, C.; Masini, E.; Le Pourhiet, L.; Tibari, B.; Lahfid, A.

    2014-12-01

    The extent to which heat recorded in orogens reflects thermal conditions inherited from previous rift-related processes is still debated and poorly documented. As a case study, we examine the Mauléon basin in the north-western Pyrenees that experienced both extreme crustal thinning and tectonic inversion within a period of ?30 Myrs. To constrain the time-temperature history of the basin in such a scenario, we provide new detrital zircon fission-track and (U-Th-Sm)/He thermochronology data. The role of rift-related processes in subsequent collision is captured by inverse modeling of our thermochronological data, using relationships between zircon (U-Th-Sm)/He ages and uranium content, combined with thermo-kinematic models of a rift-orogen cycle. We show that the basin recorded significant heating at about 100 Ma characterized by high geothermal gradients (?80 °C/km). Our thermo-kinematic modeling and geological constraints support the view that subcontinental lithospheric mantle was exhumed at that time below the Mauléon basin. Such a high geothermal gradient lasted 30 Myr after onset of convergence at ?83 Ma and was relaxed during the collision phase from ?50 Ma. This study suggests that heat needed for ductile shortening during convergence, is primarily inherited from extension rather than being only related to tectonic and/or sedimentary burial. This should have strong implications on tectonic reconstructions in many collision belts that resulted from inversion of hyper-extended rift basins.

  11. Utility of Antibody Avidity for Rift Valley Fever Virus Vaccine Potency and Immunogenicity Studies

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Disease outbreaks caused by arthropod-borne animal viruses (arboviruses) resulting in significant livestock and economic losses world-wide appear to be increasing. Rift Valley fever (RVF) virus is an important arbovirus that causes lethal disease in cattle, camels, sheep and goats in sub-Saharan Afr...

  12. Late Jurassic rifting along the Australian North West Shelf: margin geometry and spreading ridge

    E-print Network

    Müller, Dietmar

    for the evolution of the North West Shelf for the early stages after the breakup. The main difference between the Argo Abyssal Plain in the east and the Wharton Basin/ Christmas Island area in the west, the GascoyneLate Jurassic rifting along the Australian North West Shelf: margin geometry and spreading ridge

  13. On rates and styles of late volcanism and rifting on Venus Alexander T. Basilevsky

    E-print Network

    Head III, James William

    On rates and styles of late volcanism and rifting on Venus Alexander T. Basilevsky Vernadsky the formation of regional plains on Venus. We analyzed the age relations of all known impact craters !30 km of such a transition occurring at different times in different areas of Venus. INDEX TERMS: 6295 Planetology: Solar

  14. A Wide-Angle Seismic Profile Across the Jordan-Dead Sea Rift (Transform)

    NASA Astrophysics Data System (ADS)

    Abu-Ayyash, K.; Ben-Avraham, Z.; Mechie, J.; Weber, M.

    2000-12-01

    As part of the DESERT 2000 project a seismic wide-angle reflection / refraction (WRR) experiment was completed for the first time across the Jordan-Dead Sea Rift (Transform). The NW-SE trending 260 km long profile, which passed through Palestine, Israel and Jordan, crossed the rift in the Arava valley about 70 km south of the southern end of the Dead Sea. During the experiment 13 shots, including two quarry blasts, were recorded by 99 three-component instruments spaced 1-4.5 km apart along the whole length of the profile and 125 vertical component geophone groups with 100 m spacing along a 12.5 km long section of the profile in the Arava valley. Both the P- and S-wavefields were successfully recorded. First results will be presented. The results will provide a picture of the P- and S-velocity structures across the rift and together with older mainly N-S trending seismic wide-angle profiles in the region will constrain models of the formation of the Jordan-Dead Sea Rift (Transform).

  15. Development of Enzyme-Linked Immunosorbent Assays Using Expressed Proteins of Rift Valley Fever Virus

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever virus (RVFV) is a member of the genus Phlebovirus, family Bunyaviridae that can cause severe disease in both humans and animals. The disease is enzootic in sub-Saharan Africa and RVFV epidemics/epizootics occur periodically, primarily in eastern and southern Africa. Since the virus...

  16. CURRENT ISSUES AND CONCERNS REGARDING RIFT VALLEY FEVER, AN EMERGING VIRUS THREAT

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  17. Study of selected events in the Baikal rift zone in a seismic discrimination context. Technical report

    Microsoft Academic Search

    P. A. Sobel; D. H. Von Seggern; E. I. Sweetser; D. W. Rivers

    1977-01-01

    Six events from the Baikal rift zone occurring from 1971 to 1975 were examined in a seismic discrimination context. Seismograms from ALPA, LASA, NORSAR, the HGLP, the WWSSN, and the SRO stations were studied for source mechanism, Ms-mb, corner frequency, pP, complexity, and spectral ratio. All the Baikal events can be identified as earthquakes except the November 5, 1976, event

  18. NEAR REAL-TIME SURVEILLANCE FOR RIFT VALLEY FEVER IN AFRICA AND THE ARABIAN PENINSULA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) virus causes severe disease, abortion, and death in domestic animals in Africa and Arabia. Humans are infected by both Aedes and Culex species mosquitoes, which maintain enzootic and epizootic transmission, respectively, or through exposure to infected animal tissue. Outbrea...

  19. Potential for stable flies and house flies (Diptera: Muscidae) to transmit Rift Valley fever virus

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF), a disease of ruminants and humans, has been responsible for large outbreaks in Africa that have resulted in hundreds of thousands of human infections and major economic disruption due to loss of livestock and to trade restrictions. As indicated by the rapid spread of West N...

  20. SATELLITE-BASED RIFT VALLEY FEVER FORECASTS PREDICT A LARGE YELLOW FEVER EPIDEMIC IN SUDAN, 2005

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sustained, heavy East African rainfall is associated with Aedes spp. breeding in Kenyan grasslands and Rift Valley Fever (RVF) epidemics. Validated RVF forecasts use satellite measurements of vegetation greenness (which increases after heavy rains) and other eco-climate indicators. These models may ...