Sample records for baikal rift zone

  1. Lower crustal intrusions beneath the southern Baikal Rift Zone

    DEFF Research Database (Denmark)

    Nielsen, Christoffer; Thybo, Hans


    The Cenozoic Baikal Rift Zone (BRZ) is situated in south-central Siberia in the suture between the Precambrian Siberian Platform and the Amurian plate. This more than 2000-km long rift zone is composed of several individual basement depressions and half-grabens with the deep Lake Baikal at its...... centre. The BEST (Baikal Explosion Seismic Transect) project acquired a 360-km long, deep seismic, refraction/wide-angle reflection profile in 2002 across southern Lake Baikal. The data from this project is used for identification of large-scale crustal structures and modelling of the seismic velocities...... velocities around the rift structure, except for beneath the rift axis where a distinct 50-80-km wide high-velocity anomaly (7.4-7.6 ± 0.2 km/s) is observed. Reverberant or "ringing" reflections with strong amplitude and low frequency originate from this zone, whereas the lower crust is non...

  2. Arshan palaeoseismic feature of the Tunka fault (Baikal rift zone, Russia) (United States)

    Smekalin, Oleg P.; Shchetnikov, Alexander A.; White, Dustin


    The traditional concept of the rift development of flank depressions in the Baikal rift zone is now doubted in view of some indicators for compression deformations identified by the seismogeological and geodetic methods. Besides, the paleoseismological investigations revealed seismogenic strike-slips and reverse faults in the Tunka fault zone that is a major structure-controlling element of the Tunka rift depression. However, a detailed study of the upslope-facing scarp in the Arshan paleoseismogenic structure zone has shown that its formation might be due to rift mechanism of basin formation. Age estimation has been made for the previously unknown pre-historic earthquake whose epicentral area coincides with the western flank of the Arshan paleoseismogenic structure. Judging from previously determined ages of paleoearthquakes, the mean recurrence period for faulting events on the central Tunka fault is 2780-3440 years.

  3. No Moho uplift below the Baikal Rift Zone

    DEFF Research Database (Denmark)

    Nielsen, Christoffer; Thybo, Hans


    .4-7.6 ± 0.2 km/s), slightly offset to the northeast from the rift axis. We interpret this feature as resulting from mafic intrusions. Their presence may explain the flat Moho by compensation of lower crustal thinning by intrusion of mafic melts. The Pn wave velocities (8.15-8.2 km/s) are normal for the area...


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    N. A. Radziminovich


    Full Text Available The catalog of earthquakes (КR³6.6 which occurred in the Baikal rift zone (BRZ was declastered, and the results are presented in the article. Aftershocks of seismic events (КR³12.5 were determined by the software developed by V.B. Smirnov (Lomonosov Moscow State University with application of the algorithm co-authored by G.M. Molchan and O.E. Dmitrieva. To ensure proper control of the software application, aftershocks were also selected manually. The results of declustering show that aftershocks of the earthquakes (КR³12.5 account for about 25 per cent of all seismic events in the regional catalog. Aftershocks accompanied 90 per cent of all the earthquakes considered as main shocks. Besides, earthquake swarms, including events with КR³11, were identified. The results of this study show that, in the BRZ, the swarms and strong events with aftershocks are not spatially separated, and this conclusion differs from the views of the previous studies that reviewed data from a shorter observation period. Moreover, it is noted that the swarms may consist of several main shocks accompanied by aftershocks. The data accumulated over the last fifty years of instrumental observations support the conclusion made earlier that the swarms in BRZ occur mainly in the north-eastward direction from Lake Baikal and also confirm the trend of a small number of aftershocks accompanying earthquakes in the south-western part of the Baikal rift zone.


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    Alexander V. Pospeev


    Full Text Available The article is aimed at discussion of geological and geophysical aspects of the ‘asthenospheric’ interpretation of the ‘anomalous’ mantle layer that is revealed in the Baikal rift zone by deep seismic sounding (DSS methods. Based on the analysis of the geoelectrical model, estimations of rheological properties, regional geothermal and deep petrological data, it is concluded that the ‘anomalous’ mantle phenomenon should be interpreted within the framework of solid-phase models. It is shown that the actual minimum depth to the top of the asthenosphere is about 60–70 km in the region under study, and temperatures at the surface of the Earth’s mantle varies from 600 to 900 °С. It is most probable that velocities are reduced in the ‘anomalous’ mantle layer due to the presence of hightemperature spinel-pyroxene facies of the mantle rocks.


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    Andrey A. Lukashov


    Full Text Available The morphostructure of the region is a natural result of active geodynamics in the eastern Stanovoe Upland. Extreme seismic conditions become apparent in rare devastating earthquakes (up to 10-11 in the Mercally scale, as well as in frequent slight ones. Seismic events affect topography and produce seismic deformations of different scale and morphology. Areal disturbances (like the New Namarakit Lake in the South-Muya Mountains origin and, more often, local deformations (like destructions of the Kodar ridge rocky saddles or clamms [gorges] opening are evident. Using morphotectonic analysis methods the morphostructural scheme of the Kodar-Udocan section of the Baikal rift zone (perhaps pull-apart basin is done. In our model piedmont and mountain territories are divided in five level groups of blocks. Neotectonic movements’ amplitude is estimated at 5000 m.

  7. Numerical reconstruction of Late-Cenosoic evolution of normal-fault scarps in Baikal Rift Zone (United States)

    Byzov, Leonid; San'kov, Vladimir


    Numerical landscape development modeling has recently become a popular tool in geo-logic and geomorphic investigations. We employed this technique to reconstruct Late-Cenosoic evolution of Baikal Rift Zone mountains. The objects of research were Barguzin Range and Svyatoy Nos Upland. These structures are formed under conditions of crustal extension and bounded by active normal faults. In our experiments we used instruments, engineered by Greg Tucker (University of Colo-rado) - CHILD (Channel-Hillslope Integrated Landscape Development) and 'Bedrock Fault Scarp'. First program allowed constructing the complex landscape model considering tectonic uplift, fluvial and hillslope processes; second program is used for more accurate simulating of triangular facet evolution. In general, our experiments consisted in testing of tectonic parameters, and climatic char-acteristic, erosion and diffusion properties, hydraulic geometry were practically constant except for some special runs. Numerous experiments, with various scenarios of development, showed that Barguzin range and Svyatoy Nos Upland has many common features. These structures characterized by internal differentiation, which appear in height and shape of slopes. At the same time, individual segments of these objects are very similar - this conclusion refers to most developing parts, with pronounced facets and V-shaped valleys. Accordingly modelling, these landscapes are in a steady state and are undergoing a uplift with rate 0,4 mm/yr since Early Pliocene (this solution accords with AFT-dating). Lower segments of Barguzin Range and Svyatoy Nos Upland also have some general fea-tures, but the reasons of such similarity probably are different. In particular, southern segment of Svyatoy Nos Upland, which characterized by relative high slope with very weak incision, may be formed as result very rapid fault movement or catastrophic landslide. On the other hand, a lower segment of Barguzin Range (Ulun segment, for example

  8. Specific features of electric field in the atmosphere and Radon emanations in Tunkin Basin of Baikal rift zone (United States)

    Soloviev, S.; Loktev, D.


    Development of methods for diagnosing local crust encourages finding new ways for preventing hazardous geologic phenomena. Using measurements of several geophysical fields in addition to seismic methods enables to improve the existing methods and increase their reliability. In summer of 2009 and 2010, complex geophysical acquisition company was organized in the Tunkin Basin of the Baikal rift zone in South-Eastern Siberia, that runs 200 km to East-West from the southern tip of Baikal. Stationary observations were carried out in the central part of the Tunkin Basin, at the Geophysical observatory "I" of Institute of Solar-Terrestrial Physics of Siberian Branch of RAS and "II" near the Arshan settlement. Along with observations of microseismic noise and electric field variations in soil, there were performed measurements of electric field strength (Ez) in lowest atmosphere and volumetric activity of natural Radon in subsoil. Meteorological parameters were monitored with the use of DavisVantagePro meteorological stations. The analysis of observations showed that characteristic features of electric field in near-surface atmosphere are majorly defined by complex orography of the place and, consequently, by quickly changing meteorological conditions: thunderstorm activity and other mesometeorological events (with characteristic scale of tens of km and few hours long) in nearby rocks. The results of Ez(t) measurements performed under "good" weather conditions showed that the character of field variations depended on the local time with their maximum in daylight hours and minimum in the night. The analysis of Radon volumetric activity evidenced that its variations are influenced by atmospheric pressure and tides, and such influence is different at points "I" and "II". In particular, the tidal and atmospheric influence on Radon variations is more pronounced at "II" if compared to "I", which can be explained by locations of the registration points. Registration Point "II" is

  9. Two-Dimensional Numerical Modeling of Intracontinental Extension: A Case Study Of the Baikal Rift Formation

    DEFF Research Database (Denmark)

    Yang, H.; Chemia, Zurab; Artemieva, Irina

    The Baikal Rift zone (BRZ) is a narrow ( 10 km) active intra-continental basin, located at the boundary between the Amurian and Eurasian Plates. Although the BRZ is one of the major tectonically active rift zones in the world andit has been a subject of numerous geological...... on topography,basin depth, the structure of the crust, lithosphere thickness, and the location of major tectonic faults. Our goal is to determine the physical models that reproduce reasonably well the ob-served deformation patterns of the BRZ.We perform a systematic analysis of the pa-rameter space in order...

  10. Mantle Flow Across the Baikal Rift Constrained With Integrated Seismic Measurements (United States)

    Lebedev, S.; Meier, T.; van der Hilst, R. D.


    The Baikal Rift is located at the boundary of the stable Siberian Craton and deforming central Mongolia. The origin of the late Cenozoic rifting and volcanism are debated, as is the mantle flow beneath the rift zone. Here we combine new evidence from azimuthally-anisotropic upper-mantle tomography and from a radially-anisotropic inversion of interstation surface-wave dispersion curves with previously published shear-wave-splitting measurements of azimuthal anisotropy across the rift (Gao et al. 1994). While our tomographic model maps isotropic and anisotropic shear-velocity heterogeneity globally, the inversion of interstation phase-velocity measurements produces a single, radially-anisotropic, shear-velocity profile that averages from the rift to 500 km SE of it. The precision and the broad band (8-340 s) of the Rayleigh and Love wave curves ensures high accuracy of the profile. Tomography and shear-wave splitting both give a NW-SE fast direction (perpendicular to the rift) in the vicinity of the rift, changing towards W-E a few hundred kilometers from it. Previously, this has been interpreted as evidence for mantle flow similar to that beneath mid-ocean ridges, with deeper vertical flow directly beneath the rift also proposed. Our radially anisotropic profile, however, shows that while strong anisotropy with SH waves faster than SV waves is present in the thin lithosphere and upper asthenosphere beneath and SE of the rift, no anisotropy is required below 110 km. The tomographic model shows thick cratonic lithosphere north of the rift. These observations suggest that instead of a flow diverging from the rift axis in NW and SE directions, the most likely pattern is the asthenospheric flow in SE direction from beneath the Siberian lithosphere and across the rift. Possible driving forces of the flow are large-scale lithospheric deformation in East Asia and the draining of asthenosphere at W-Pacific subduction zones; a plume beneath the Siberian craton also cannot be

  11. Large mammals from the Upper Neopleistocene reference sections in the Tunka rift valley, southwestern Baikal Region (United States)

    Shchetnikov, A. A.; Klementiev, A. M.; Filinov, I. A.; Semeney, E. Yu.


    This work presents the data on new finds of fossil macrotheriofauna in the reference sections of the Upper Neopleistocene sediments in the Tunka rift valley (southwestern Baikal Region). The osteological material of a number of Late Neopleistocene mammals including extinct species rare for the Baikal region such as Crocuta spelaea, Panthera spelaea, and Spirocerus kiakhtensis (?) was directly dated with a radiocarbon (AMS) method. The obtained 14C data (18000-35000 years) allow one to rejuvenate significantly the upper limit of the common age interval of habitat of these animals in southern part of Eastern Siberia. Cave hyena and spiral-horned antelope lived in the Tunka rift valley in the Baikal region in Late Kargino time (37-24 ka), and cave lion survived the maximum in the Sartan cryochron in the region (21-20 ka). The study of collected paleontological collections provides a basis for selection of independent Kargino (MIS 3) faunal assemblages to use them for regional biostratigraphic analysis of Pleistocene deposits. Radiocarbon age dating of samples allows one to attribute confidently all paleofaunal remains available to the second half of the Late Pleistocene.

  12. Coupled large earthquakes in the Baikal rift system: Response to bifurcations in nonlinear resonance hysteresis

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    Anatoly V. Klyuchevskii


    Full Text Available The current lithospheric geodynamics and tectonophysics in the Baikal rift are discussed in terms of a nonlinear oscillator with dissipation. The nonlinear oscillator model is applicable to the area because stress change shows up as quasi-periodic inharmonic oscillations at rifting attractor structures (RAS. The model is consistent with the space-time patterns of regional seismicity in which coupled large earthquakes, proximal in time but distant in space, may be a response to bifurcations in nonlinear resonance hysteresis in a system of three oscillators corresponding to the rifting attractors. The space-time distribution of coupled MLH > 5.5 events has been stable for the period of instrumental seismicity, with the largest events occurring in pairs, one shortly after another, on two ends of the rift system and with couples of smaller events in the central part of the rift. The event couples appear as peaks of earthquake ‘migration’ rate with an approximately decadal periodicity. Thus the energy accumulated at RAS is released in coupled large events by the mechanism of nonlinear oscillators with dissipation. The new knowledge, with special focus on space-time rifting attractors and bifurcations in a system of nonlinear resonance hysteresis, may be of theoretical and practical value for earthquake prediction issues. Extrapolation of the results into the nearest future indicates the probability of such a bifurcation in the region, i.e., there is growing risk of a pending M ≈ 7 coupled event to happen within a few years.

  13. [Identification of two cyanobacterial strains isolated from the Kotel'nikovskii hot spring of the Baikal rift]. (United States)

    Sorokovnikova, E G; Tikhonova, I V; Belykh, O I; Klimenkov, I V; Likhoshvaĭ, E V


    Two cyanobacterial strains, Pseudanabaena sp. 0411 and Synechococcus sp. 0431, were isolated from a sample collected in the Kotel'nikovskii hot spring of the Baikal rift. According to the results of light and transmission electron microscopy, as well as of the phylogenetic analysis of the 16S rRNA gene, these cyanobacteria were classified as Pseudanabaena sp. nov. and Synechococcus bigranulatus Skuja. The constructed phylogenetic tree shows that the studied strains are positioned in the clades of cyanobacteria isolated from hydrothermal vents of Asia and New Zealand, separately from marine and freshwater members of these genera, including those isolated from Lake Baikal.


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    A. A. Stepashko


    mantle lense (Fig 6, A; it is one of four main tectonical units that compose the basement of the Siberian craton [Mironyuk, Zagruzina, 1983]. As evidenced by the zonal composition of the mantle lense, the centre of the lense is highly dense, and this explains the location of a seismic anomaly there (Fig. 6, B which is determined to a depth of about 50–60 km [Pavlenkova G.A., Pavlenkova N.I., 2006]. The high-velocity root located in this segment of the craton is traced by seismic tomography [Koulakov, Bushenkova, 2010] to a depth of about 600 km (Fig. 7. The southward-stretching edge of the sub-cratonic mantle has played a major role in the evolution of the Central Asian orogenic belt. In the Paleozoic, the position and the configuration of the accretional margin of the Siberian paleocontinent were determined by the hidden boundary of the craton (Fig. 8, A. Along the craton’s boundary, rifting zones of various ages are located, and intrusions are concentrated, which genesis was related to extension settings (Fig. 8, B. The Cenozoic sedimentary basins are located above the hidden edge of the Siberian craton, which gives evidence of involvement of the deep lithospheric structure in the formation of the recent destruction zone. The basin of Lake Baikal is located along the mantle edge of the Siberian craton, and the basin’s crescent shape accentuates the strike of the mantle edge.In the region under study, the wave nature of seismicity is most evidently manifested by the cyclicity of the strongest earthquakes in the Baikal zone (Table 2. Three seismic cycles are distinguished as follows: (1 at the turn of the 20th century (earthquakes in the period from 1885 to 1931, M=6.6–8.2, (2 the middle of the 20th century (earthquakes from 1950 to 1967, M=6.8–8.1, and (3 at the turn of the 21st century (earthquakes from 1991 to 2012, M=6.3–7.3. While moving in the mantle, the deformation front collapses with the craton’s basement, partially releases its energy to the


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    Konstantin Zh. Seminsky


    Full Text Available The subject of comprehensive studies is the underground hydrosphere of the upper crust of the western shoulder of the Baikal rift, being characterized by high tectonic activity in the recent stage of tectogenesis. The studies were focused on the Bayandai – Krestovsky Cape site, considering it as a benchmark for the territory of the Western Pribiakalie (Fig. 1. The available hydrogeological survey database is used to study underground waters circulating at depth of several kilometers. Analyses of deeper waters are conducted on the basis of geophysical data. According to results of initial geological and geophysical studies [Семинский и др., 2010], the crust at the junction of the Siberian crater and the SayanBaikal folded belt is characterized by a hierarchic zoneblock structure (Fig. 2. Regardless of the scale of studies, the territory under study can be divided into sections of two types, that alternate from NW to SE and represent wide highly destructed zones and relatively monolithic blocks of the crust. The Obruchev fault system is distinguished as the main interblock zone (the 2nd hierarchic level in the study area. It represents the 50 km long NW shoulder of the Baikal rift (the1st hierarchic level and includes the Morskaya, Primorskaya and Prikhrebtovaya interplate zones (the 3rd hierarchic level. These zones are traced from depth of dozens of kilometers; at the surface, they are represented by fault structures of the highest hierarchic levels.Specific features of the current zoneblock divisibility of the crust serve as the structural basis for interpreting the materials obtained by hydrogeological studies conducted on the Bayandai – Krestovsky Cape site to research the distribution, mineralization and macrocomponent compositions of waters which represent the subsurface part of the underground lithosphere in the study area. The research is based on analyses of the underground water samples from 46 observation points

  16. Search for ancient microorganisms in Lake Baikal

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    Hunter-Cevera, Jennie C.; Repin, Vladimir E.; Torok, Tamas


    Lake Baikal in Russia, the world's oldest and deepest continental lake lies in south central Siberia, near the border to Mongolia. The lake is 1,643 m deep and has an area of about 46,000 km2. It holds one-fifth of all the terrestrial fresh water on Earth. Lake Baikal occupies the deepest portion of the Baikal Rift Zone. It was formed some 30-45 million years ago. The isolated Lake Baikal ecosystem represents a unique niche in nature based on its historical formation. The microbial diversity present in this environment has not yet been fully harvested or examined for products and processes of commercial interest and value. Thus, the collection of water, soil, and sub-bottom sediment samples was decided to characterize the microbial diversity of the isolated strains and to screen the isolates for their biotechnological value.

  17. Ez-response as a monitor of a Baikal rift fault electrical resistivity: 3D modelling studies

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    I. L. Trofimov


    Full Text Available 3D numerical studies have shown that the vertical voltage above the Baikal deep-water fault is detectable and that respective transfer functions, Ez-responses, are sensitive to the electrical resistivity changes of the fault, i.e. these functions appear actually informative with respect to the resistivity «breath» of the fault. It means that if the fault resistivity changed, conventional electromagnetic instruments would be able to detect this fact by measurement of the vertical electric field, Ez, or the vertical electric voltage just above the fault as well as horizontal magnetic field on the shore. Other electromagnetic field components (Ex, Ey, Hz do not seem to be sensitive to the resistivity changes in such a thin fault (as wide as 500 m. On the other hand, such changes are thought to be able to indicate a change of a stress state in the earthquake preparation zone. Besides, the vertical profile at the bottom of Lake Baikal is suitable for electromagnetic monitoring of the fault electrical resistivity changes. Altogether, the vertical voltage above the deep-water fault might be one of earthquake precursors.

  18. Root zone of a continental rift

    DEFF Research Database (Denmark)

    Kirsch, Moritz; Svenningsen, Olaf


    Mafic magmatic rocks formed between ca. 615 and 560 Ma along the Neoproterozoic margins of Baltica and Laurentia are classically attributed to continental rifting heralding the opening of the Iapetus Ocean. We report new data for the Kebnekaise Intrusive Complex (KIC) exposed in the Seve Nappes i...

  19. How do volcanic rift zones relate to flank instability? Evidence from collapsing rifts at Etna (United States)

    Pepe, Susi; Ruch, Joel; Casu, Francesco; Acocella, Valerio; Neri, Marco; Solaro, Giuseppe; Sansosti, Eugenio


    Volcanic rift zones, characterized by repeated dike emplacements, are expected to delimit the upper portion of unstable flanks at basaltic edifices. However, the relationship between flank instability and rift zone behavior, activity, and location on longer, inter-diking timescales is poorly understood. To characterize the relationship between rift kinematics, dike emplacement and flank instability at Etna, we used long-term (1992-2010) InSAR ground deformation time series, giving unprecedented coverage of the volcano's summit. As snow coverage prevents coherence of the backscattered radar signal, long-term InSAR time series on the summit of seasonally snow-capped volcanoes, such as Mount Etna, are affected by decorrelation, which hinders detection of any summit deformation. To increase the summit coverage, we removed from our Etna dataset all the SAR images possibly affected by snow-related decorrelation phenomena. We then jointly processed ERS data between 1992 and 2010 and ENVISAT data between 2003 and 2010, acquired from both ascending and descending orbits, and computed 204 ascending and 194 descending interferograms. These were inverted by applying the Small BAseline Subset (SBAS) technique (e.g., Pepe et al., 2005) to produce combined ERS-ENVISAT velocity maps and deformation time series. Ascending and descending maps and time series were used to separate vertical and East-West components of on-going displacements. This approach greatly improved the spatial coverage of elevated areas. A spatial comparison with a similar dataset used by Solaro et al. (2010), but limited to 1994-2008, shows an increase of the summit coverage of about 14 km2 in our dataset. The results highlight a general eastward shift of the volcano summit, including the northeast and south rifts. This steady-state eastward movement (1-2 cm/yr) is interrupted or even reversed during transient dike injections. Detailed analysis of the northeast rift shows that only during phases of dike

  20. Geology of the Elephanta Island fault zone, western Indian rifted ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 126; Issue 1. Geology of the Elephanta Island fault zone, western Indian rifted margin, and its significance for understanding the Panvel flexure. Hrishikesh Samant Ashwin Pundalik Joseph D'souza Hetu Sheth Keegan Carmo Lobo Kyle D'souza Vanit Patel. Volume ...


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    K. Zh. Seminsky


    Full Text Available This article discusses the distribution patterns of high-radon groundwater at the southwestern shore of LakeBaikal. This region is a flank of the South Baikalrift basin, characterized by high geodynamic activity and complex fault patterns, without any special geochemical conditions with regard to the content of uranium in the rocks. Based on our observations and measurements, we consolidated the first massive database on radon volume activity (Q in a variety of local water sources. In the Kultuk–Vydrino area, the Q values vary from zero to 81.1 Bq/l, according to the analysis of the water samples from 93 springs, lakes, small streams, wells, and drilled holes. The highest concentrations of radon are discovered in the groundwater samples. Such values are unevenly scattered across the study area. The chain of the maximum Q values trends northwestwards along the LakeBaikalshore. This distribution pattern of radon, as well as the locations of individual water sources with Q>15 Bq/l are predetermined by the structural factor. The paragenetic analysis of faults and joints in the Kultuk–Vydrino area shows that this factor includes both the structure and stages in the development of the regional largest Main Sayan fault zone (the southwestern flank of the South Baikalbasin is a segment of this zone. The water sources with increased concentrations of radon are located in zones with a high density of the 2nd order faults, especially on sites wherein the NW-striking faults cross the transverse faults that have experienced repeated activation. Temperature T is an additional factor influencing the degree of radioactivity in water. A relationship between T and Q is reverse. Water sources with Q>15 Bq/l associated with the 2nd order fault zones may occur also due to a locally lower temperature of groundwater. Our study gives evidence that the southwestern coast ofLake Baikal is promising for finding high-radon water sources. Using such water in balneo

  2. Concentration of strain in a marginal rift zone of the Japan backarc during post-rift compression (United States)

    Sato, H.; Ishiyama, T.; Kato, N.; Abe, S.; Shiraishi, K.; Inaba, M.; Kurashimo, E.; Iwasaki, T.; Van Horne, A.; No, T.; Sato, T.; Kodaira, S.; Matsubara, M.; Takeda, T.; Abe, S.; Kodaira, C.


    Late Cenozoic deformation zones in Japan may be divided into two types: (1) arc-arc collision zones like those of Izu and the Hokkaido axial zone, and (2) reactivated back-arc marginal rift (BMR) systems. A BMR develops during a secondary rifting event that follows the opening of a back-arc basin. It forms close to the volcanic front and distant from the spreading center of the basin. In Japan, a BMR system developed along the Sea of Japan coast following the opening of the Japan Sea. The BMR appears to be the weakest, most deformable part of the arc back-arc system. When active rifting in the marginal basins ended, thermal subsidence, and then mechanical subsidence related to the onset of a compressional stress regime, allowed deposition of up to 5 km of post-rift, deep-marine to fluvial sedimentation. Continued compression produced fault-related folds in the post-rift sediments, in thin-skin style deformation. Shortening reached a maximum in the BMR system compared to other parts of the back-arc, suggesting that it is the weakest part of the entire system. We examined the structure of the BMR system using active source seismic investigation and earthquake tomography. The velocity structure beneath the marginal rift basin shows higher P-wave velocity in the upper mantle/lower crust which suggests significant mafic intrusion and thinning of the upper continental crust. The syn-rift mafic intrusive forms a convex shape, and the boundary between the pre-rift crust and the mafic intrusive dips outward. In the post-rift compressional stress regime, the boundary of the mafic body reactivated as a reverse fault, forming a large-scale wedge thrust and causing further subsidence of the rift basin. The driver of the intense shortening event along the Sea of Japan coast in SW Japan was the arrival of a buoyant young (15 Ma) Shikoku basin at the Nankai Trough. Subduction stalled and the backarc was compressed. As the buoyant basin cooled, subduction resumed, and the rate of

  3. Extending the Rift Zone: evidence from central Botswana (United States)

    van der Meijde, M.; Fadel, I.; Paulssen, H.; Kwadiba, T.


    The 3D crustal and upper mantle structure of Botswana is a major gap in our knowledge about the tectonic evolution of Africa. We will present a new model for crust and upper mantle structure and velocity in which we indicate very strong indications for active rifting in north and central Botswana. Our model is based on data from the NARS Botswana and AfricaArray networks, broadband temporary networks in southern Africa (Botswana, Namibia, South Africa and Zambia). The NARS-Botswana seismic network was established to provide broadband recordings in Botswana, covering one of the least studied regions in the world. It is an area that is for a large part covered by the Kalahari sands but also covers the southwestern most branch of the African Rift under the Okavango delta. The goal is to understand how the rifting process and cratonic provinces influence crustal thickness and couple to the underlying mantle. Crust and upper mantle structure, down to the bottom of the mantle transition zone, will be based on receiver function analysis and surface wave tomography. In the receiver functions, we observe crustal thicknesses between 35 and 46 km, strongly linked to basins and cratons in the region. The central Kalahari part, which has been previously unstudied, showed some anomalous structure, possibly suggesting melt in the lower crust. This lower crustal anomaly is also visible in surface wave tomography models and coincides with the present Botswana earthquake which also suggest an extensional stress regime in central Botswana. Going deeper we see that the mantle transition zone varies in thickness, and sharpness of the bounding discontinuities, suggesting active dynamical processes underneath Botswana.

  4. When Rifts Meet Cratons (United States)

    Chen, W. P.; Ning, J.


    The longevity of cratons and the evolution of rifts are two outstanding issues in continental dynamics. Intriguingly, there are several active cases where the two seemingly antithetical tectonic settings abut each other. In most instances, rifting is not accompanied by widespread destruction of adjacent cratons. In the case of the East African rift system (EARS), the most prominent active rift system in the world, its western branch clearly circumvents the Tanzania craton and continues southward along the narrow Malawi rift. Meanwhile, a broad zone of scattered seismicity associated with normal faulting extends westward for about 1,000 km, as accentuated by the recent earthquake of Mw 6.8 in Botswana. Along the eastern branch of the EARS, the well-defined Kenya rift terminates against the Tanzania craton as a diffuse zone of extension (the northern Tanzania divergence.) Yet, farther southward, a band of concentrated seismicity follows the trace of the Davie ridge off the east coast of Africa for another 1,300 km. Similarly, the Ordos plateau (the western portion of the north China craton, NCC), comparable in size to the Tanzania craton, is straddled by the active Yinchuan and Shanxi rifts on its western and eastern flanks, respectively. Along the edges of the Colorado plateau, the very broad Basin and Range province of extension and the narrow Rio Grande rift surround the stable plateau. Therefore, it seems that rifting is not an effective process to destabilize cratons en masse. Widespread, low-angle detachment faulting and the intrusion of Mesozoic granitic plutons characterize the eastern portion of the NCC, an often-cited example of a craton's demise. Here we propose that these features are the consequence, not the cause of the destruction of the NCC. The exact cause(s) of this destruction process remain enigmatic, as the spatial extent of this event apparently reaches as far north as Lake Baikal.

  5. The Iceland Plate Boundary Zone: Propagating Rifts, Migrating Transforms, and Rift-Parallel Strike-Slip Faults (United States)

    Karson, J. A.


    Unlike most of the Mid-Atlantic Ridge, the North America/Eurasia plate boundary in Iceland lies above sea level where magmatic and tectonic processes can be directly investigated in subaerial exposures. Accordingly, geologic processes in Iceland have long been recognized as possible analogs for seafloor spreading in the submerged parts of the mid-ocean ridge system. Combining existing and new data from across Iceland provides an integrated view of this active, mostly subaerial plate boundary. The broad Iceland plate boundary zone includes segmented rift zones linked by transform fault zones. Rift propagation and transform fault migration away from the Iceland hotspot rearrange the plate boundary configuration resulting in widespread deformation of older crust and reactivation of spreading-related structures. Rift propagation results in block rotations that are accommodated by widespread, rift-parallel, strike-slip faulting. The geometry and kinematics of faulting in Iceland may have implications for spreading processes elsewhere on the mid-ocean ridge system where rift propagation and transform migration occur.

  6. Seismic Investigations of an Accommodation zone in the Northern Rio Grande Rift, New Mexico, USA (United States)

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


    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.

  7. Focused seismicity triggered by flank instability on Kīlauea's Southwest Rift Zone (United States)

    Judson, Josiah; Thelen, Weston A.; Greenfield, Tim; White, Robert S.


    Swarms of earthquakes at the head of the Southwest Rift Zone on Kīlauea Volcano, Hawai´i, reveal an interaction of normal and strike-slip faulting associated with movement of Kīlauea's south flank. A relocated subset of earthquakes between January 2012 and August 2014 are highly focused in space and time at depths that are coincident with the south caldera magma reservoir beneath the southern margin of Kīlauea Caldera. Newly calculated focal mechanisms are dominantly dextral shear with a north-south preferred fault orientation. Two earthquakes within this focused area of seismicity have normal faulting mechanisms, indicating two mechanisms of failure in very close proximity (10's of meters to 100 m). We suggest a model where opening along the Southwest Rift Zone caused by seaward motion of the south flank permits injection of magma and subsequent freezing of a plug, which then fails in a right-lateral strike-slip sense, consistent with the direction of movement of the south flank. The seismicity is concentrated in an area where a constriction occurs between a normal fault and the deeper magma transport system into the Southwest Rift Zone. Although in many ways the Southwest Rift Zone appears analogous to the more active East Rift Zone, the localization of the largest seismicity (>M2.5) within the swarms to a small volume necessitates a different model than has been proposed to explain the lineament outlined by earthquakes along the East Rift Zone.

  8. Dykes and structures of the NE rift of Tenerife, Canary Islands: a record of stabilisation and destabilisation of ocean island rift zones (United States)

    Delcamp, A.; Troll, V. R.; van Wyk de Vries, B.; Carracedo, J. C.; Petronis, M. S.; Pérez-Torrado, F. J.; Deegan, F. M.


    Many oceanic island rift zones are associated with lateral sector collapses, and several models have been proposed to explain this link. The North-East Rift Zone (NERZ) of Tenerife Island, Spain offers an opportunity to explore this relationship, as three successive collapses are located on both sides of the rift. We have carried out a systematic and detailed mapping campaign on the rift zone, including analysis of about 400 dykes. We recorded dyke morphology, thickness, composition, internal textural features and orientation to provide a catalogue of the characteristics of rift zone dykes. Dykes were intruded along the rift, but also radiate from several nodes along the rift and form en échelon sets along the walls of collapse scars. A striking characteristic of the dykes along the collapse scars is that they dip away from rift or embayment axes and are oblique to the collapse walls. This dyke pattern is consistent with the lateral spreading of the sectors long before the collapse events. The slump sides would create the necessary strike-slip movement to promote en échelon dyke patterns. The spreading flank would probably involve a basal decollement. Lateral flank spreading could have been generated by the intense intrusive activity along the rift but sectorial spreading in turn focused intrusive activity and allowed the development of deep intra-volcanic intrusive complexes. With continued magma supply, spreading caused temporary stabilisation of the rift by reducing slopes and relaxing stress. However, as magmatic intrusion persisted, a critical point was reached, beyond which further intrusion led to large-scale flank failure and sector collapse. During the early stages of growth, the rift could have been influenced by regional stress/strain fields and by pre-existing oceanic structures, but its later and mature development probably depended largely on the local volcanic and magmatic stress/strain fields that are effectively controlled by the rift zone growth

  9. High Fluoride and Geothermal Activities In Continental Rift Zones, Ethiopia (United States)

    Weldesenbet, S. F.; Wohnlich, S.


    The Central Main Ethiopian Rift basin is a continental rift system characterized by volcano-tectonic depression endowed with huge geothermal resource and associated natural geochemical changes on groundwater quality. Chemical composition of groundwater in the study area showed a well defined trend along flow from the highland and escarpment to the rift floor aquifer. The low TDS ( 1000 mg/l) Na-HCO3-Cl type in volcano-lacustrine aquifers of the rift floor. High concentrations of fluoride (up to 97.2 mg/l) and arsenic (up to 98μg/l) are recognized feature of groundwaters which occur mostly in the vicinity of the geothermal fields and the rift lakes in the basin. Fluoride and arsenic content of dry volcaniclastic sediments close to these areas are in the range 666-2586mg/kg and 10-13mg/kg respectively. The relationship between fluoride and calcium concentrations in groundwaters showed negative correlation. Near-equilibrium state attained between the mineral fluorite (CaF2) and the majority of fluoride-rich (>30mg/l) thermal groundwater and shallow cold groundwater. This indicated that the equilibrium condition control the high concentration of fluoride in the groundwaters. Whereas undersaturation state of fluorite in some relatively low-fluoride (surface system is simulated with sediment-packed column leached by flowing water and applying temporary interruption of flow during the experiment. The result indicated that a sharp increase of fluoride concentration (up to 58mg/kg) observed in leachates before one pore-volume of water eluted from the column. The concentration of leached fluoride consequently declined with the increased flowing pore-volume of water and finally the lowest concentrations of leached fluoride occurred in the end of the experiment. Flow interruption during column leaching experiment causes a noticeable fluoride concentration perturbation due to the heterogeneity of the sediment.

  10. Fluoride and Geothermal Activities In Continental Rift Zones, Ethiopia (United States)

    Weldesenbet, S. F.


    The Central Main Ethiopian Rift basin is a continental rift system characterized by volcano-tectonic depression endowed with huge geothermal resource and associated natural geochemical changes on groundwater quality. Chemical composition of groundwater in the study area showed a well defined trend along flow from the highland and escarpment to the rift floor aquifer. The low TDS ( 1000 mg/l) Na-HCO3-Cl type in volcano-lacustrine aquifers of the rift floor. High concentrations of fluoride (up to 97.2 mg/l) and arsenic (up to 98μg/l) are recognized feature of groundwaters which occur mostly in the vicinity of the geothermal fields and the rift lakes in the basin. Fluoride and arsenic content of dry volcaniclastic sediments close to these areas are in the range 666-2586mg/kg and 10-13mg/kg respectively. The relationship between fluoride and calcium concentrations in groundwaters showed negative correlation. Near-equilibrium state attained between the mineral fluorite (CaF2) and the majority of fluoride-rich (>30mg/l) thermal groundwater and shallow cold groundwater. This indicated that the equilibrium condition control the high concentration of fluoride in the groundwaters. Whereas undersaturation state of fluorite in some relatively low-fluoride (surface system is simulated with sediment-packed column leached by flowing water and applying temporary interruption of flow during the experiment. The result indicated that a sharp increase of fluoride concentration (up to 58mg/kg) observed in leachates before one pore-volume of water eluted from the column. The concentration of leached fluoride consequently declined with the increased flowing pore-volume of water and finally the lowest concentrations of leached fluoride occurred in the end of the experiment. Flow interruption during column leaching experiment causes a noticeable fluoride concentration perturbation due to the heterogeneity of the sediment.

  11. Investigations into early rift development and geothermal resources in the Pyramid Lake fault zone, Western Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Eisses, A.; Kell, A.; Kent, G.; Driscoll, N. [UCSD; Karlin, R.; Baskin, R. [USGS; Louie, J. [UNR; Pullammanappallil, S. [Optim


    A. K. Eisses, A. M. Kell, G. Kent, N. W. Driscoll, R. E. Karlin, R. L. Baskin, J. N. Louie, S. Pullammanappallil, 2010, Investigations into early rift development and geothermal resources in the Pyramid Lake fault zone, Western Nevada: Abstract T33C-2278 presented at 2010 Fall Meeting, AGU, San Francisco, Calif., 13-17 Dec.

  12. Extension parallel to the rift zone during segmented fault growth: application to the evolution of the NE Atlantic

    Directory of Open Access Journals (Sweden)

    A. Bubeck


    Full Text Available The mechanical interaction of propagating normal faults is known to influence the linkage geometry of first-order faults, and the development of second-order faults and fractures, which transfer displacement within relay zones. Here we use natural examples of growth faults from two active volcanic rift zones (Koa`e, island of Hawai`i, and Krafla, northern Iceland to illustrate the importance of horizontal-plane extension (heave gradients, and associated vertical axis rotations, in evolving continental rift systems. Second-order extension and extensional-shear faults within the relay zones variably resolve components of regional extension, and components of extension and/or shortening parallel to the rift zone, to accommodate the inherently three-dimensional (3-D strains associated with relay zone development and rotation. Such a configuration involves volume increase, which is accommodated at the surface by open fractures; in the subsurface this may be accommodated by veins or dikes oriented obliquely and normal to the rift axis. To consider the scalability of the effects of relay zone rotations, we compare the geometry and kinematics of fault and fracture sets in the Koa`e and Krafla rift zones with data from exhumed contemporaneous fault and dike systems developed within a > 5×104 km2 relay system that developed during formation of the NE Atlantic margins. Based on the findings presented here we propose a new conceptual model for the evolution of segmented continental rift basins on the NE Atlantic margins.

  13. The origin of Mauna Loa's Nīnole Hills: Evidence of rift zone reorganization (United States)

    Zurek, Jeffrey; Williams-Jones, Glyn; Trusdell, Frank A.; Martin, Simon


    In order to identify the origin of Mauna Loa volcano's Nīnole Hills, Bouguer gravity was used to delineate density contrasts within the edifice. Our survey identified two residual anomalies beneath the Southwest Rift Zone (SWRZ) and the Nīnole Hills. The Nīnole Hills anomaly is elongated, striking northeast, and in inversions both anomalies merge at approximately −7 km above sea level. The positive anomaly, modeled as a rock volume of ~1200 km3 beneath the Nīnole Hills, is associated with old eruptive vents. Based on the geologic and geophysical data, we propose that the gravity anomaly under the Nīnole Hills records an early SWRZ orientation, now abandoned due to geologically rapid rift-zone reorganization. Catastrophic submarine landslides from Mauna Loa's western flank are the most likely cause for the concurrent abandonment of the Nīnole Hills section of the SWRZ. Rift zone reorganization induced by mass wasting is likely more common than currently recognized.

  14. Lithospheric low-velocity zones associated with a magmatic segment of the Tanzanian Rift, East Africa (United States)

    Plasman, M.; Tiberi, C.; Ebinger, C.; Gautier, S.; Albaric, J.; Peyrat, S.; Déverchère, J.; Le Gall, B.; Tarits, P.; Roecker, S.; Wambura, F.; Muzuka, A.; Mulibo, G.; Mtelela, K.; Msabi, M.; Kianji, G.; Hautot, S.; Perrot, J.; Gama, R.


    Rifting in a cratonic lithosphere is strongly controlled by several interacting processes including crust/mantle rheology, magmatism, inherited structure and stress regime. In order to better understand how these physical parameters interact, a 2 yr long seismological experiment has been carried out in the North Tanzanian Divergence (NTD), at the southern tip of the eastern magmatic branch of the East African rift, where the southward-propagating continental rift is at its earliest stage. We analyse teleseismic data from 38 broad-band stations ca. 25 km spaced and present here results from their receiver function (RF) analysis. The crustal thickness and Vp/Vs ratio are retrieved over a ca. 200 × 200 km2 area encompassing the South Kenya magmatic rift, the NTD and the Ngorongoro-Kilimanjaro transverse volcanic chain. Cratonic nature of the lithosphere is clearly evinced through thick (up to ca. 40 km) homogeneous crust beneath the rift shoulders. Where rifting is present, Moho rises up to 27 km depth and the crust is strongly layered with clear velocity contrasts in the RF signal. The Vp/Vs ratio reaches its highest values (ca. 1.9) beneath volcanic edifices location and thinner crust, advocating for melting within the crust. We also clearly identify two major low-velocity zones (LVZs) within the NTD, one in the lower crust and the second in the upper part of the mantle. The first one starts at 15-18 km depth and correlates well with recent tomographic models. This LVZ does not always coexist with high Vp/Vs ratio, pleading for a supplementary source of velocity decrease, such as temperature or composition. At a greater depth of ca. 60 km, a mid-lithospheric discontinuity roughly mimics the step-like and symmetrically outward-dipping geometry of the Moho but with a more slanting direction (NE-SW) compared to the NS rift. By comparison with synthetic RF, we estimate the associated velocity reduction to be 8-9 per cent. We relate this interface to melt ponding

  15. Geophysical and geochemical models of the Earth's shields and rift zones

    International Nuclear Information System (INIS)

    Chung, D.H.


    This report summarizes a collection of, synthesis of, and speculation on the geophysical and geochemical models of the earth's stable shields and rift zones. Two basic crustal types, continental and oceanic, and two basic mantle types, stable and unstable, are described. It is pointed out that both the crust and upper mantle play a strongly interactive role with surface geological phenomena ranging from the occurrence of mountains, ocean trenches, oceanic and continental rifts to geographic distributions of earthquakes, faults, and volcanoes. On the composition of the mantle, there is little doubt regarding the view that olivine constitutes a major fraction of the mineralogy of the earth's upper mantle. Studies are suggested to simulate the elasticity and composition of the earth's lower crust and upper mantle

  16. The influence of the Precambrian Mughese Shear Zone structures on strain accommodation in the northern Malawi Rift (United States)

    Dawson, Sam M.; Laó-Dávila, Daniel A.; Atekwana, Estella A.; Abdelsalam, Mohamed G.


    Precambrian shear zones have been recognized as regions that affect the propagation, segmentation, and location of continental rifts. However, it is still unclear how the orientation of these shear zones influence strain accommodation along the rifts. In this study, we investigated the influence of the Mughese Shear Zone (MSZ) on strain accommodation within the young magma-poor Malawi Rift, a seismically-active segment of the Western Branch of the East African Rift System. We used Shuttle Radar Topography Mission (SRTM) Digital Elevation Models (DEM), aeromagnetic data, and mapped mesoscopic-scale structures within the Precambrian MSZ and younger rocks in the Karonga area. We found that in the northern portion of the Karonga Fault Zone, a fault zone that accommodates the majority of extension in this region, one major fault is oriented 32°/59° SE and cuts across the Precambrian foliation that has an orientation of 301°/79° NE. South of the city of Karonga, the Precambrian foliation is sub-vertical and has a strike of 321°. Here, the Karonga fault splays from a main fault with a 2 km damage zone to several distinct E-and W-dipping faults over a 10 km zone that strike in the general direction of the foliation planes of the MSZ. Recent seismicity is distributed within this zone. The faults formed in reactivated foliation planes of the MSZ. The N-striking Karoo rift horsts and grabens and their associated rock formations might have also been reactivated in this area. These relationships suggest that within the northern Malawi Rift, extension was accommodated differently based on the nature and orientation of the pre-existing structures. The orientation of the Precambrian MSZ influences strain accommodation in the Karonga area and has important implications for seismic hazards. We conclude that the Karonga area is an important seismically active zone based on favorably-oriented and reactivated pre-existing structures.

  17. Active seepage and water infiltration in Lake Baikal sediments: new thermal data from TTR-Baikal 2014 (Class@Baikal) (United States)

    Poort, Jeffrey; Khlystov, Oleg M.; Akhmanov, Grigorii G.; Khabuev, Andrei V.; Belousov, Oleg V.


    New thermal data from the sediments of Lake Baikal were collected in July 2014 during the first Training-Through-Research cruise on Lake Baikal (Class@Baikal) organized by MGU and LIN. TTR-Baikal is a comprehensive multidisciplinary program to train students on the field on pertinent scientific topics. The cruise program focused on seafloor sampling, acoustic investigations and heat flow measurements of gas seeps, flares, mud volcanoes, slumps and debris flows, canyons and channels in the coastal proximity. The thermal data were acquired using autonomous temperature sensors on a 3 meter long gravity corer that allowed analysis at the same spot of sediments, pore fluids, hydrates and microbiology. A total of eight thermal measurements were performed in five structures located on the lake floor of the Central Baikal Basin at 333-1530 meter water depths: 3 mud volcanoes (Novosibirsk, Unshuy and Krest), 1 seep site (Seep 13), and one fault outcrop in the Selenga transfer zone. All studied structures show signals of active seepage, water infiltration and/or hydrate dynamics. The strongest thermal gradient has been measured in Seep 13, suggesting a strong upflow of warm fluids similar to the Gorevoy Utes seep. At the three mud volcanoes, hydrate presence have been evidenced and both enhanced and reduced thermal gradients have been observed. This is similar to the hydrate-bearing K-2 mud volcano in Baikal (Poort et al., 2012). A strongly reduced thermal gradient was observed in the Krest mud volcano where the presence of oxidized channels at 30-40 cm under the sediment surface indicate an infiltration of cold lake water. The water infiltration process at hydrate bearing seep sites will be discussed and compared with other seep areas in the world.

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

    Atekwana, E. A.


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

  19. Magmatic Consequences of Failed Rift Zones: Examples from the Eastern Pacific (United States)

    Harpp, K. S.; Wanless, V. D.; Otto, R. H.; Hoernle, K.


    The aseismic Cocos Ridge, one of the most prominent bathymetric features in the eastern Pacific, records ~20 million years of interaction between the Galapagos hotspot and the Galapagos Spreading Center. Two major clusters of seamounts are located along the northern flanks of the ridge, one near the Costa Rican coast and the second around Cocos Island. The Costa Rica and Cocos Seamount Provinces (including Cocos Island) have produced alkalic lavas accompanied by enrichment in incompatible trace elements beyond any observed in the Galapagos Archipelago today or in samples from the crest of the Cocos Ridge. Cocos Island is known to be millions of years younger than the hotspot track on which it lies, and the other seamounts likely share this characteristic. Trace element data determined by ICP-MS from over 90 dredged samples from the ridge and seamounts suggest that the compositions of the lavas are strongly controlled by the history of rift jumping in the region. The lavas are the result of small degrees of melting of a Galapagos plume-like source, predominantly in the garnet stability field. In the case of both seamount fields, their eruption immediately follows the failure of a rift zone at each province's location. Thus we attribute the anomalously young alkalic lavas of the seamount provinces to post-abandonment volcanism following either a ridge jump or rift failure, and not to the direct activity of the Galapagos plume. The seamounts and Cocos Island are instead the result of passive upwelling caused by a major tectonic rearrangement, such that the seamounts are significantly younger than their supporting lithosphere or the hotspot trace. The failed rift tapped mantle that had previously incorporated Galapagos plume material when the lithosphere was produced at the plume-affected GSC. Fundamentally, the hotspot's variable interaction with the Galapagos Spreading Center, coupled with rift failures associated with tectonic rearrangements of the ridge itself may

  20. The latest geodynamics in Asia: Synthesis of data on volcanic evolution, lithosphere motion, and mantle velocities in the Baikal-Mongolian region

    Directory of Open Access Journals (Sweden)

    Sergei Rasskazov


    Full Text Available From a synthesis of data on volcanic evolution, movement of the lithosphere, and mantle velocities in the Baikal-Mongolian region, we propose a comprehensive model for deep dynamics of Asia that assumes an important role of the Gobi, Baikal, and North Transbaikal transition-layer melting anomalies. This layer was distorted by lower-mantle fluxes at the beginning of the latest geodynamic stage (i.e. in the early late Cretaceous due to avalanches of slab material that were stagnated beneath the closed fragments of the Solonker, Ural-Mongolian paleoceans and Mongol-Okhotsk Gulf of Paleo-Pacific. At the latest geodynamic stage, Asia was involved in east–southeast movement, and the Pacific plate moved in the opposite direction with subduction under Asia. The weakened upper mantle region of the Gobi melting anomaly provided a counterflow connected with rollback in the Japan Sea area. These dynamics resulted in the formation of the Honshu-Korea flexure of the Pacific slab. A similar weakened upper mantle region of the North Transbaikal melting anomaly was associated with the formation of the Hokkaido-Amur flexure of the Pacific slab, formed due to progressive pull-down of the slab material into the transition layer in the direction of the Pacific plate and Asia convergence. The early–middle Miocene structural reorganization of the mantle processes in Asia resulted in the development of upper mantle low-velocity domains associated with the development of rifts and orogens. We propose that extension at the Baikal Rift was caused by deviator flowing mantle material, initiated under the moving lithosphere in the Baikal melting anomaly. Contraction at the Hangay orogen was created by facilitation of the tectonic stress transfer from the Indo-Asian interaction zone due to the low-viscosity mantle in the Gobi melting anomaly.

  1. The Baikal Neutrino Telescope

    International Nuclear Information System (INIS)

    Aynutdinov, V. M.; Balkanov, V. A.; Belolaptikov, I. A.; Bezrukov, L. B.; Borschev, D. A.; Budnev, N. M.; Burmistrov, K. V.; Danilchenko, I. A.; Davidov, Ya. I.; Domogatsky, G. V.; Doroshenko, A. A.; Dyachok, A. N.; Dzhilkibaev, Zh.-A. M.; Fialkovsky, S. V.; Gaponenko, O. N.; Golubkov, K. V.; Gress, O. A.; Gress, T. I.; Grishin, O. V.; Klabukov, A. M.


    We review the present status of the Baikal Neutrino Experiment and present results of a search for upward-going atmospheric neutrinos and magnetic monopoles obtained with the detector NT200. The results of a search for very high energy neutrinos are presented and an upper limit on the extraterrestrial diffuse neutrino flux is obtained. We describe the strategy of upgrading the NT200 to NT200+ and creating a detector on the Gigaton scale at Lake Baikal. The first results obtained with the new NT200+ detector as a basic cell of a future Gigaton detector are presented

  2. Geology of the Elephanta Island fault zone, western Indian rifted margin, and its significance for understanding the Panvel flexure (United States)

    Samant, Hrishikesh; Pundalik, Ashwin; D'souza, Joseph; Sheth, Hetu; Lobo, Keegan Carmo; D'souza, Kyle; Patel, Vanit


    The Panvel flexure is a 150-km long tectonic structure, comprising prominently seaward-dipping Deccan flood basalts, on the western Indian rifted margin. Given the active tectonic faulting beneath the Panvel flexure zone inferred from microseismicity, better structural understanding of the region is needed. The geology of Elephanta Island in the Mumbai harbour, famous for the ca. mid-6th century A.D. Hindu rock-cut caves in Deccan basalt (a UNESCO World Heritage site) is poorly known. We describe a previously unreported but well-exposed fault zone on Elephanta Island, consisting of two large faults dipping steeply east-southeast and producing easterly downthrows. Well-developed slickensides and structural measurements indicate oblique slip on both faults. The Elephanta Island fault zone may be the northern extension of the Alibag-Uran fault zone previously described. This and two other known regional faults (Nhava-Sheva and Belpada faults) indicate a progressively eastward step-faulted structure of the Panvel flexure, with the important result that the individual movements were not simply downdip but also oblique-slip and locally even rotational (as at Uran). An interesting problem is the normal faulting, block tectonics and rifting of this region of the crust for which seismological data indicate a normal thickness (up to 41.3 km). A model of asymmetric rifting by simple shear may explain this observation and the consistently landward dips of the rifted margin faults.

  3. Rift zones and magma plumbing system of Piton de la Fournaise volcano: How do they differ from Hawaii and Etna? (United States)

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


    On ocean basaltic volcanoes, magma transfer to the surface proceeds by subvertical ascent from the mantle lithosphere through the oceanic crust and the volcanic edifice, possibly followed by lateral propagation along rift zones. We use a 19-year-long database of volcano-tectonic seismic events together with detailed mapping of the cinder cones and eruptive fissures to determine the geometry and the dynamics of the magma paths intersecting the edifice of Piton de la Fournaise volcano. We show that the overall plumbing system, from about 30 km depth to the surface, is composed of two structural levels that feed distinct types of rift zones. The deep plumbing system is rooted between Piton des Neiges and Piton de la Fournaise volcanoes and has a N30-40 orientation. Above 20 km below sea level (bsl), the main axis switches to a N120 orientation, which permits magma transfer from the lithospheric mantle to the base of the oceanic crust, below the summit of Piton de la Fournaise. The related NW-SE rift zone is 15 km wide, linear, spotted by small to large pyroclastic cones and related lava flows and emits slightly alkaline magmas resulting from high-pressure fractionation of clinopyroxene ± olivine. This rift zone has low magma production rate of ~ 0.5-3.6 × 10- 3 m3s- 1 and an eruption periodicity of around 200 years over the last 30 ka. Seismic data suggest that the long-lasting activity of this rift zone result from regional NNE-SSW extension, which reactivates inherited lithospheric faults by the effect of underplating and/or thermal erosion of the mantle lithosphere. The shallow plumbing system (de la Fournaise. Outer NE and SE rift zones are much less active (~ 4-7.3 × 10- 3 m3s- 1) and extend from inside the Enclos Fouqué caldera to bound the mobile eastern volcano flank. We show that the outer rift zones are almost aseismic and are genetically linked to the seaward flank displacements, whose most recent events where detected in 2004 and 2007. East flank

  4. Lava Flow Morphologies and Structural Features Along the Axis of the South Rift Zone of Loihi Seamount, Hawaii (United States)

    Deemer, J. L.; Kurz, M. D.; Fornari, D. J.


    In an effort to document the morphology of the deep South Rift Zone of the Loihi Seamount, we report new observations collected in 2008 using ROV Jason2 on the R/V Thomas G. Thompson (C. Moyer and K. Edwards, chief scientists). The South Rift Zone extends more than 20 kilometers from 4950 meters depth at its base to Loihi’s summit at 980 meters. To date, there are few studies of the deep Loihi South Rift Zone and this work provides important geologic context for ongoing microbiological studies of Loihi (Fe-Oxidizing Microbial Observatory Project). Existing EM300 multibeam bathymetry provides the broader context necessary for interpreting smaller-scale Loihi South Rift features mapped using Jason2. Three Jason2 dives included continuous low-altitude (indicated by the ubiquitous presence of glassy flows and a complete absence of sediment cover, with the exception of microbial mats in the deepest section (FeMO Deep). Flows are predominantly lobate and pillow types. Pyroclastic deposits are expressed as loose volcanic sand in localized depressions, and are found at depths as great as 4909 meters. Distinct meter-scale flow morphologies were identified and constrained, and this information can be used to determine rudimentary stratigraphic relationships of individual flows. The compilation of lava flow morphologies from the ROV data, in conjunction with along-axis structure, bathymetry, and distribution of talus and pyroclastic deposits, will be presented.

  5. Datasets for mapping pastoralist movement patterns and risk zones of Rift Valley fever occurrence

    Directory of Open Access Journals (Sweden)

    Gladys Mosomtai


    Full Text Available Rift Valley fever (RVF is a zoonotic disease affecting humans and animals. It is caused by RVF virus transmitted primarily by Aedes mosquitoes. The data presented in this article propose environmental layers suitable for mapping RVF vector habitat zones and livestock migratory routes. Using species distribution modelling, we used RVF vector occurrence data sampled along livestock migratory routes to identify suitable vector habitats within the study region which is located in the central and the north-eastern part of Kenya. Eleven herds monitored with GPS collars were used to estimate cattle utilization distribution patterns. We used kernel density estimator to produce utilization contours where the 0.5 percentile represents core grazing areas and the 0.99 percentile represents the entire home range. The home ranges were overlaid on the vector suitability map to identify risks zones for possible RVF exposure. Assimilating high spatial and temporal livestock movement and vector distribution datasets generates new knowledge in understanding RVF epidemiology and generates spatially explicit risk maps. The results can be used to guide vector control and vaccination strategies for better disease control.

  6. Motion in the north Iceland volcanic rift zone accommodated by bookshelf faulting (United States)

    Green, Robert G.; White, Robert S.; Greenfield, Tim


    Along mid-ocean ridges the extending crust is segmented on length scales of 10-1,000km. Where rift segments are offset from one another, motion between segments is accommodated by transform faults that are oriented orthogonally to the main rift axis. Where segments overlap, non-transform offsets with a variety of geometries accommodate shear motions. Here we use micro-seismic data to analyse the geometries of faults at two overlapping rift segments exposed on land in north Iceland. Between the rift segments, we identify a series of faults that are aligned sub-parallel to the orientation of the main rift. These faults slip through left-lateral strike-slip motion. Yet, movement between the overlapping rift segments is through right-lateral motion. Together, these motions induce a clockwise rotation of the faults and intervening crustal blocks in a motion that is consistent with a bookshelf-faulting mechanism, named after its resemblance to a tilting row of books on a shelf. The faults probably reactivated existing crustal weaknesses, such as dyke intrusions, that were originally oriented parallel to the main rift and have since rotated about 15° clockwise. Reactivation of pre-existing, rift-parallel weaknesses contrasts with typical mid-ocean ridge transform faults and is an important illustration of a non-transform offset accommodating shear motion between overlapping rift segments.


    Directory of Open Access Journals (Sweden)

    K. Zh. Seminsky


    Full Text Available This study aimed to provide a systematic overview of water sources in the Baikal region and Transbaikalia by the content of radon (Q and establish regularities in variations of Q values in space and time.We collected and analyzed our evaluations of Q and the available published Q values for many dozens of water sources in the study area (Fig. 1, and reviewed the monitoring data of eight water sources that belong to the Angarsky fault impact zone in Southern Priangarie (Fig. 5. Radon content in water samples was measured in accordance with the standard procedure using a RRA-01M-03 radiometer (sensitivity of at least 1.4∙10–4 s–1∙Bq–1∙m3; maximum allowable relative error of 30 %.Based on the frequency patterns of Q values measured in the Baikal region and Transbaikalia (Fig. 2 and the analysis of the known classifications of the water sources by radioactivity, we propose a uniform regional classification of groundwaters with respect to 222Rn content (Table 1. In seismically active Baikal region, wherein water sources with Q>185 Bq/l are practically lacking, we distinguish the first three groups with the following Q ranges: Group I – Q≤15 Bq/l, Group II – 16≤Q≤99 Bq/l, and Group III – 100≤Q≤184 Bq/l. Most of the water sources sampled in the Baikal region and Transbaikalia belong to Groups I and II, which allows us to recommend an objectively existing value of 100 Bq/l as the level of intervention in the preparation of drinking water in this region, instead of the limit of 60 Bq/l that is now approved in Russia.In order to identify the special patterns of groundwater sources in the Baikal region and Transbaikalia, which belong to different radioactivity groups, we sampled these sources along the transect from Bayanday to Muhorshibir, across the Baikal rift and other large regional tectonic structures (Fig. 4. On a larger scale, we analysed the radon content variability in the groundwater sources within the zones

  8. Class@Baikal: the Endurance of the UNESCO Training-Through-Research Programme (United States)

    Mazzini, A.; Akhmanov, G.; Khlystov, O.; Tokarev, M.; Korost, D. V.; Poort, J.; Fokina, A.; Giliazetdinova, D. R.; Yurchenko, A.; Vodopyanov, S.


    In July 2014, by the initiative of the Moscow State University and Limnological Institute of Russian Academy of Sciences, the first Training-through-Research Class@Baikal was launched in Lake Baikal, Russia. The cruise program focused on seafloor sampling and acoustic investigations of gas seeps, flares, mud volcanoes, slumps and debris flows, canyons and channels in the coastal proximity. A comprehensive multidisciplinary program to train students has been developed to cover sedimentology, fluid geochemistry, biology, geophysics and marine geology in general. Daily lectures were conducted on board by academics presenting pertinent research projects, and cruise planning and preliminary results were discussed with all the scientific crew. A daily blog with updates on the expedition activities, images, and ongoing cruise results, was also completed (i.e. visit the cruise blog: and gave the opportunity to interact with experts as well as attract the interest also of a broader audience. This project is a follow up to the well-established UNESCO Training-through-Research (TTR) Floating University Programme ( that covered large areas on the European and arctic margins since 1991 with 18 research cruises attended by about 1000 BSc, MSc and PhD students from Europe, Asia, Africa and America. The crucial goal of both programmes is the training of new generations of scientists through active research directly on the field. Students can access the collected data and samples for their Master and PhD projects. Typically an extensive set of analyses and data processing is completed in-house and the results and interpretations are presented at post cruise meetings and international conferences. The Baikal lake is 25 million years old rift zone and provides a large variety of active geological features that can be easily reached at daily sailing distance. This represents an extraordinary opportunity to switch and focus

  9. State-of-stress in magmatic rift zones: Predicting the role of surface and subsurface topography (United States)

    Oliva, S. J. C.; Ebinger, C.; Rivalta, E.; Williams, C. A.


    Continental rift zones are segmented along their length by large fault systems that form in response to extensional stresses. Volcanoes and crustal magma chambers cause fundamental changes to the density structure, load the plates, and alter the state-of-stress within the crust, which then dictates fracture orientation. In this study, we develop geodynamic models scaled to a effects of loading on state-of-stress. By modeling varying geometric arrangements, and density contrasts of topographic and subsurface loads, and with reasonable regional extensional forces, the resulting state-of-stress reveals the favored orientation for new intrusions. Although our models are generalized, they allow us to evaluate whether a magmatic system (surface and subsurface) can explain the observed stress rotation, and enable new intrusions, new faults, or fault reactivation with orientations oblique to the main border faults. Our results will improve our understanding of the different factors at play in these extensional regimes, as well as contribute to a better assessment of the hazards in the area.

  10. The post-Mazama northwest rift zone eruption at Newberry Volcano, Oregon (United States)

    McKay, Daniele; Donnelly-Nolan, Julie M.; Jensen, Robert A.; Champion, Duane E.; O'Connor, Jim; Dorsey, Rebecca; Madin, Ian


    The northwest rift zone (NWRZ) eruption took place at Newberry Volcano ~7000 years ago after the volcano was mantled by tephra from the catastrophic eruption that destroyed Mount Mazama and produced the Crater Lake caldera. The NWRZ eruption produced multiple lava flows from a variety of vents including cinder cones, spatter vents, and fissures, possibly in more than one episode. Eruptive behaviors ranged from energetic Strombolian, which produced significant tephra plumes, to low-energy Hawaiian-style. This paper summarizes and in part reinterprets what is known about the eruption and presents information from new and ongoing studies. Total distance spanned by the eruption is 32 km north-south. The northernmost flow of the NWRZ blocked the Deschutes River upstream from the city of Bend, Oregon, and changed the course of the river. Renewed mafic activity in the region, particularly eruptions such as the NWRZ with tephra plumes and multiple lava flows from many vents, would have significant impacts for the residents of Bend and other central Oregon communities.

  11. Landscape dynamics assessment of dry climatic zones on the Baikal-Gobi transect from NDVI time series and field investigations data (United States)

    Sayapina, D. O.; Zharnikova, M. A.; Tsydypov, B. Z.; Sodnomov, B. V.; Garmaev, E. Zh


    Starting in the eighties of the 20th century, the scientists of the Baikal Institute of Nature Management (BINM SB RAS) have been conducting field observations of the Transbaikalia geosystems transformation due to the change of climate and nature management. An utmost importance is placed on the study of a negative response of the land geosystems. This is shown through their deterioration, degradation, and desertification in particular. Through the years of research (1985-2015) in dry areas of the north of Central Asia, the scientists of the BINM SB RAS established a network of key sites for contact monitoring of the status and dynamics of the geosystems and the negative natural-anthropogenic processes along the Baikal-Gobi meridional transect (51-44° N, 105-107° E). The monitoring of the status and dynamics of the vegetation cover of some key sites is conducted by processing and analysis of multitemporal and multispectral Landsat and MODIS Terra imagery. An automatic analysis of the time variation of NDVI and a comparison with the progress of the index in the previous seasons are performed. The landscape indication of the key sites is made on the basis of satellite imagery and complete geobotanical descriptions. Landscape profiles and facies maps with natural boundaries are created.

  12. Trace element and isotope geochemistry of geothermal fluids, East Rift Zone, Kilauea, Hawaii

    Energy Technology Data Exchange (ETDEWEB)

    West, H.B.; Delanoy, G.A.; Thomas, D.M. (Hawaii Univ., Honolulu, HI (United States). Hawaii Inst. of Geophysics); Gerlach, D.C. (Lawrence Livermore National Lab., CA (United States)); Chen, B.; Takahashi, P.; Thomas, D.M. (Hawaii Univ., Honolulu, HI (United States) Evans (Charles) and Associates, Redwood City, CA (United States))


    A research program has been undertaken in an effort to better characterize the composition and the precipitation characteristic of the geothermal fluids produced by the HGP-A geothermal well located on the Kilauea East Rift Zone on the Island of Hawaii. The results of these studies have shown that the chemical composition of the fluids changed over the production life of the well and that the fluids produced were the result of mixing of at least two, and possibly three, source fluids. These source fluids were recognized as: a sea water composition modified by high temperature water-rock reactions; meteoric recharge; and a hydrothermal fluid that had been equilibrated with high temperature reservoir rocks and magmatic volatiles. Although the major alkali and halide elements show clearly increasing trends with time, only a few of the trace transition metals show a similar trend. The rare earth elements, were typically found at low concentrations and appeared to be highly variable with time. Studies of the precipitation characteristics of silica showed that amorphous silica deposition rates were highly sensitive to fluid pH and that increases in fluid pH above about 8.5 could flocculate more than 80% of the suspended colloidal silica in excess of its solubility. Addition of transition metal salts were also found to enhance the recovery fractions of silica from solution. The amorphous silica precipitate was also found to strongly scavenge the alkaline earth and transition metal ions naturally present in the brines; mild acid treatments were shown to be capable of removing substantial fractions of the scavenged metals from the silica flocs yielding a moderately pure gelatinous by-product. Further work on the silica precipitation process is recommended to improve our ability to control silica scaling from high temperature geothermal fluids or to recover a marketable silica by-product from these fluids prior to reinjection.

  13. Trace element and isotope geochemistry of geothermal fluids, East Rift Zone, Kilauea, Hawaii (United States)

    West, H. B.; Delanoy, G. A.; Thomas, D. M.; Gerlach, D. C.; Chen, B.; Takahashi, P.; Thomas, D. M.


    A research program has been undertaken in an effort to better characterize the composition and the precipitation characteristic of the geothermal fluids produced by the HGP-A geothermal well located on the Kilauea East Rift Zone on the island of Hawaii. The results of these studies have shown that the chemical composition of the fluids changed over the production life of the well and that the fluids produced were the result of the mixing of at least two, and possibly three, source fluids. These source fluids were recognized as a sea water composition modified by high temperature water-rock reactions; meteoric recharge; and a hydrothermal fluid that had been equilibriated with high temperature reservoir rocks and magmatic volatiles. Although the major alkali and halide elements show clearly increasing trends with time, only a few of the trace transition metals show a similar trend. The rare earth elements were typically found at low concentrations and appeared to be highly variable with time. Studies of the precipitation characteristics of silica showed that amorphous silica deposition rates were highly sensitive to fluid pH and that increases in fluid pH above about 8.5 could flocculate more than 80 percent of the suspended colloidal silica in excess of its solubility. Addition of transition metal salts were also found to enhance the recovery fractions of silica from solution. The amorphous silica precipitate was also found to strongly scavenge the alkaline earth and transition metal ions naturally present in the brines; mild acid treatments were shown to be capable of removing substantial fractions of the scavenged metals from the silica flocs, yielding a moderately pure gelatinous by-product. Further work on the silica precipitation process is recommended to improve our ability to control silica scaling from high temperature geothermal fluids or to recover a marketable silica by-product from these fluids prior to reinjection.

  14. Crustal Structure Across the Okavango Rift Zone, Botswana: Initial Results From the PRIDE-SEISORZ Active-Source Seismic Profile (United States)

    Canales, J. P.; Moffat, L.; Lizarralde, D.; Laletsang, K.; Harder, S. H.; Kaip, G.; Modisi, M.


    The PRIDE project aims to understand the processes of continental rift initiation and evolution by analyzing along-axis trends in the southern portion of the East Africa Rift System, from Botswana through Zambia and Malawi. The SEISORZ active-source seismic component of PRIDE focused on the Okavango Rift Zone (ORZ) in northwestern Botswana, with the main goal of imaging the crustal structure across the ORZ. This will allow us to estimate total crustal extension, determine the pattern and amount of thinning, assess the possible presence of melt within the rift zone, and assess the contrasts in crustal blocks across the rift, which closely follows the trend of a fold belt. In November 2014 we conducted a crustal-scale, 450-km-long seismic refraction/wide-angle reflection profile consisting of 19 sources (shots in 30-m-deep boreholes) spaced ~25 km apart from each other, and 900 receivers (IRIS/PASSCAL "Texan" dataloggers and 4.5Hz geophones) with ~500 m spacing. From NW to SE, the profile crosses several tectonic domains: the Congo craton, the Damara metamorphic belt and the Ghanzi-Chobe fold belt where the axis of the ORZ is located, and continues into the Kalahari craton. The record sections display clear crustal refraction (Pg) and wide-angle Moho reflection (PmP) phases for all 17 of the good-quality shots, and a mantle refraction arrival (Pn), with the Pg-PmP-Pn triplication appearing at 175 km offset. There are distinct changes in the traveltime and amplitude of these phases along the transect, and on either side of the axis, that seem to correlate with sharp transitions across tectonic terrains. Initial modeling suggests: (1) the presence of a sedimentary half-graben structure at the rift axis beneath the Okavango delta, bounded to the SE by the Kunyere-Thamalakane fault system; (2) faster crustal Vp in the domains to the NW of the ORZ; and (3) thicker crust (45-50 km) at both ends of the profile within the Congo and Kalahari craton domains than at the ORZ and

  15. Diachronism in the late Neoproterozoic-Cambrian arc-rift transition of North Gondwana: A comparison of Morocco and the Iberian Ossa-Morena Zone (United States)

    Álvaro, J. Javier; Bellido, Félix; Gasquet, Dominique; Pereira, M. Francisco; Quesada, Cecilio; Sánchez-García, Teresa


    In the northwestern border of the West African craton (North Gondwana), a transition from late Neoproterozoic subduction/collision to Cambrian rift processes was recorded in the Anti-Atlas (Morocco) and in the Ossa-Morena Zone (Iberia). Cambrian rifting affected both Pan-African and Cadomian basements in a stepwise and diachronous way. Subsequently, both areas evolved into a syn-rift margin episodically punctuated by uplift and tilting that precluded Furongian sedimentation. A comparison of sedimentary, volcanic and geodynamic evolution is made in the late Neoproterozoic (Pan-African and Cadomian) belts and Cambrian rifts trying to solve the apparent diachronous (SW-NE-trending) propagation of an early Palaeozoic rifting regime that finally led to the opening of the Rheic Ocean.

  16. An inventory survey at the site of the proposed Kilauea Middle East Rift Zone (KMERZ), Well Site No. 2

    Energy Technology Data Exchange (ETDEWEB)

    Kennedy, Joseph


    At the request of True Mid Pacific Geothermal, Archaeological Consultants of Hawaii, Inc. has conducted an inventory survey at the site of the proposed Kilauea Middle East Rift Zone (KMERZ), Well Site No.2, TMK: 1-2-10:3. The Principal Investigator was Joseph Kennedy M.A., assisted by Jacob Kaio, Field Supervisor and field crew Mark Borrello B.A., Michael O'Shaughnessy B.A., and Randy Adric. This report supercedes all previous reports submitted to the Historic Presentation Section of the Department of Land and Natural Resources. In addition to 100% surface coverage of the 400 x 400 foot well pad itself, 100% surface coverage of a substantial buffer zone was also completed. This buffer zone was established by the Department of Land and Natural Resources, Historic Preservation personnel and extends 1000 feet east and west of the well site and 500 feet north and south of the well site.

  17. The Azores - G3 cruise: Multidisciplinary studies from the Azores rift zone to the Great Meteor seamount


    Lourenço, Nuno; Pinto de Abreu, Manuel; Madureira, Pedro; Pinto Ribeiro, Luísa


    During May/June 2007, the Cruise EMEPC/Açores/G3/2007 was sailed aboard the SV Kommandor Jack in the scope of Portuguese Program for the Extension of the Continental Shelf. The Cruise, mainly focused on geological sampling, comprised a 1st leg lasting five days, at the Terceira rift zone and S. Jorge Island flank and a 2nd leg which lasted twenty-four days at the Atlantis, Plato, Hyeres and Great Meteor Seamounts located south of the Azores region, in the Mid-Atlantic Ridge off...

  18. Characterization of tephra from the northwest rift zone eruption, Newberry Volcano, Oregon (United States)

    McKay, D.; Cashman, K. V.; Wallace, P. J.


    The northwest rift zone (NWRZ) eruption was the most recent episode of mafic activity to occur at Newberry Volcano, Oregon, USA. Vents of the NWRZ are aligned along a series of northwest trends extending ~32 km across the northwest and southwest flanks of the volcano. The total volume (DRE) of erupted material is 862 x 106 m3, with individual vents erupting volumes ranging from 0.1 x 106 to 381.9 x 106 m3. Eruption duration is not constrained, but tephra from NWRZ vents was deposited directly on top of 7700 ybp Mazama ash, leading to the interpretation that vents were active simultaneously and the eruptive period represents a large input of mafic magma into the Newberry system. Paleomagnetic work has suggested the eruption spanned a period of decades to a century. Individual vents produced a range of deposits, including large and small scoria cones, spatter cones and ramparts, tephra blankets, and extensive lava flows. These eruptive products suggest that individual eruptive episodes were characterized by eruption styles ranging from the passive effusion of lava to explosive activity. Compositional data for both tephra and lava show considerable variation (ranging from 51.3 to 58.4 wt. % SiO2). If the NWRZ eruption represents input of a single magma batch, some combination of fractionation, assimilation, and/or mixing must have occurred to produce the observed range in compositions. Here we present detailed analysis of tephra clasts collected from NWRZ vents, including whole rock, microphenocryst and glass compositions, and water contents derived from the plagioclase-liquid hygrometer described by Lange et al., 2009. We use these data to constrain the pre-eruptive storage conditions (pressure, temperature, and water content) of magma batches erupted at individual vents. Thermodynamic modeling of geochemical data is used to determine the genetic relationship between these magmas. In addition to petrological and geochemical constraints, we use spatial relationships

  19. Lake Baikal Ecosystem Faces the Threat of Eutrophication

    Directory of Open Access Journals (Sweden)

    Galina I. Kobanova


    Full Text Available Recently there have been reports about large accumulations of algae on the beaches of Lake Baikal, the oldest and deepest freshwater body on earth, near major population centers and in areas with large concentrations of tourists and tourism infrastructure. To evaluate the observations indicating the ongoing process of eutrophication of Lake Baikal, a field study in July 2012 in the two largest bays of Lake Baikal, Barguzinsky and Chivyrkuisky, was organized. The study of phytoplankton using the sedimentary method and quantitative records of accumulations of macrophytes in the surf zone was made. In Chivyrkuisky Bay, we found the massive growth of colorless flagellates and cryptomonads as well as the aggregations of Elodea canadensis along the sandy shoreline (up to 26 kg/m2. Barguzinsky Bay registered abundantly cyanobacterial Anabaena species, cryptomonads, and extremely high biomass of Spirogyra species (up to 70 kg/m3. The results show the presence of local but significant eutrophication of investigated bays. To prevent further extensions of this process in unique ecosystem of Lake Baikal, the detailed study and monitoring of the coastal zone, the identification of the sources of eutrophication, and the development of measures to reduce nutrient inputs in the waters are urgently needed.

  20. Fault zone architecture within Miocene–Pliocene syn-rift sediments ...

    Indian Academy of Sciences (India)

    syn-rift sediments, Northwestern Red Sea, Egypt. Khairy S Zaky. Department of Geology, Minia University, El Minia 61519, Egypt. e-mail: The present study focusses on field description of ...... tectonothermal history of the Arabian–Nubian shield in the Eastern Desert of Egypt: Evidence from fission track.

  1. Yield gaps and resource use across farming zones in the central rift valley of Ethiopia

    NARCIS (Netherlands)

    Getnet, Mezegebu; Ittersum, van Martin; Hengsdijk, Huib; Descheemaeker, Katrien


    In the Central Rift Valley (CRV) of Ethiopia, low productive cereal systems and a declining resource base call for options to increase crop productivity and improve resource use efficiency to meet the growing demand of food. We compiled and analysed a large amount of data from farmers’ fields

  2. Rifting-to-drifting transition of the South China Sea: Moho reflection characteristics in continental-ocean transition zone (United States)

    Wen, Y.; Li, C.


    Dispute remains on the process of continental rifting to subsequent seafloor spreading in the South China Sea (SCS). Several crust-scale multi-channel seismic reflection profiles acquired in the continent-ocean transition zone (COT) of the SCS provide a detailed overview of Moho and deep crustal reflectors and give key information on rifting-to-drifting transition of the area. Moho has strong but discontinuous seismic reflection in COT. These discontinuities are mainly located in the landward side of continent-ocean boundary (COB), and may own to upwelling of lower crustal materials during initial continental extension, leading to numerous volcanic edifices and volcanic ridges. The continental crust in COT shows discontinuous Moho reflections at 11-8.5 s in two-way travel time (twtt), and thins from 18-20.5 km under the uppermost slope to 6-7 km under the lower slope, assuming an average crustal velocity of 6.0 km/s. The oceanic crust has Moho reflections of moderate to high continuity mostly at 1.8-2.2 s twtt below the top of the igneous basement, which means that the crustal thickness excluding sediment layer in COT is 5.4-6.6 km. Subhorizontal Moho reflections are often abruptly interrupted by large seaward dipping normal faults in southern COT but are more continuous compared with the fluctuant and very discontinuous Moho reflections in northern COT. The thickness of thinned continental crust (4.2-4.8 km) is smaller than that of oceanic crust (5.4-6.0 km) near southern COB, indicating that the continental crust has experienced a long period of rifting before seafloor spreading started. The smaller width of northern COT (0-40 km) than in southern COT (0-60 km), and thinner continental crust in southern COT, all indicate that the continental margin rifting and extension was asymmetric. The COT width in the SCS is narrower than that found in other magma-poor continental margins, indicating a swift transition from the final stage of rifting to the inception of

  3. [Rift Valley fever: sporadic infection of French military personnel outside currently recognized epidemic zones]. (United States)

    Durand, J P; Richecoeur, L; Peyrefitte, C; Boutin, J P; Davoust, B; Zeller, H; Bouloy, M; Tolou, H


    For three years the arbovirus surveillance unit of the Tropical Medicine Institute of the French Army Medical Corps (French acronym IMTSSA) in Marseille, France has been investigating causes of benign non-malarial febrile syndromes in French military personnel serving outside mainland France. The methodology used in N'Djamena consisted of sending frozen specimens collected concomitant with viremia, to Marseille for culture. During the rainy season of 2001, specimens were collected from a total of 50 febrile soldiers. Cultures allowed isolation and identification of two strains of Rift Valley virus. The risk of contamination exists not only in the field but also in mainland hospital departments treating infected patients. Routine serological diagnosis for Rift Valley fever must be DISCUSSED for all patients in the field or returning from Africa.

  4. Hydrochemical characterization of complex volcanic aquifers in a continental rifted zone: the Middle Awash basin, Ethiopia (United States)

    Furi, Wakgari; Razack, Moumtaz; Abiye, Tamiru Alemayehu; Kebede, Seifu; Legesse, Dagnachew


    The Middle Awash basin is an arid region in Ethiopia where surface waters are scarce and local communities are dependent on groundwater resources for water supply. The complex hydrogeological system of this basin has been conceptualized. Multivariate statistical analysis of hydrochemical variables and water isotopes were used to study the rock-water interaction, geochemical reaction processes and the hydrological link between aquifers. Groundwaters from aquifers of the high-rainfall plateau bounding the rift are slightly mineralized, as well as depleted in δ18O and δD, and contain 3H above 0.8 TU. This suggests a low degree of rock-water interaction and that groundwater is under recharge from heavy rain that falls on surrounding highlands. On the other hand, groundwaters from aquifers of the rift floor are highly mineralized and show slight enrichment in δ18O and δD with positive oxygen shift, but contain 3H below 0.8 TU. The positive oxygen shift in rift floor groundwaters may be caused by the isotopic exchange of oxygen between groundwater and aquifer materials during rock-water interaction, whereas the low 3H content could be due to the decay of tritium along relatively long flow paths. The approach utilized in this study may be applicable to understanding hydrogeochemical processes in other complex volcanic terrains.

  5. Magmatic architecture of Kilauea's rift zones: A geochemical perspective from historical lavas (1790 A.D. to present) (United States)

    Marske, J. P.; Garcia, M. O.; Pietruszka, A. J.; Rhodes, J. M.; Norman, M. D.; Heaton, D. E.


    Over 220 years of frequent, voluminous (~4.5 km3), and compositionally variable (5-18 wt. % MgO) eruptions at Kilauea's summit, and east (ERZ) and southwest (SWRZ) rift zones provide an excellent opportunity to delineate the volcano's magmatic architecture, and to infer shallow magma storage times. Here, we present new Pb, Sr, and Nd isotopic ratios, and major- and trace-element abundances for 22 historical Kilauea rift lava samples (1790-2010 A.D), which significantly expand our existing data set for this time period. These data allow us to trace the passage of geochemically distinct batches of magma within the volcano. Overall, historical Kilauea rift and summit lavas display overlapping temporal geochemical variations (e.g., K2O/TiO2, Nb/Y, 87Sr/86Sr, and 206Pb/204Pb) indicating that they originated from similar parental magmas for a given time period (i.e., months to years). The exceptions are strongly evolved (20th century Kilauea historical summit lavas (~0.004 year-1). This rapid change indicates these lavas may have partially or completely bypassed the summit reservoir. The MgO-variable (6.7-11.5 wt. %) 1971 and 1974 caldera rim and floor lavas reflect the eruption of stored, moderately evolved magmas from the volcano's summit reservoir that were hydraulically forced to the surface by more mafic magmas that bypassed the summit reservoir. Magma storage times for late 20th century lavas in the ERZ (~12-165 years) are significantly shorter than most previous estimates for Kilauea's summit and middle ERZ (~23-160 years), and lower ERZ (>550 years).

  6. Magma transport and olivine crystallization depths in Kīlauea’s East Rift Zone inferred from experimentally rehomogenized melt inclusions (United States)

    Tuohy, Robin M; Wallace, Paul J.; Loewen, Matthew W; Swanson, Don; Kent, Adam J R


    Concentrations of H2O and CO2 in olivine-hosted melt inclusions can be used to estimate crystallization depths for the olivine host. However, the original dissolved CO2concentration of melt inclusions at the time of trapping can be difficult to measure directly because in many cases substantial CO2 is transferred to shrinkage bubbles that form during post-entrapment cooling and crystallization. To investigate this problem, we heated olivine from the 1959 Kīlauea Iki and 1960 Kapoho (Hawai‘i) eruptions in a 1-atm furnace to temperatures above the melt inclusion trapping temperature to redissolve the CO2 in shrinkage bubbles. The measured CO2 concentrations of the experimentally rehomogenized inclusions (⩽590 ppm for Kīlauea Iki [n=10]; ⩽880 ppm for Kapoho, with one inclusion at 1863 ppm [n=38]) overlap with values for naturally quenched inclusions from the same samples, but experimentally rehomogenized inclusions have higher within-sample median CO2 values than naturally quenched inclusions, indicating at least partial dissolution of CO2 from the vapor bubble during heating. Comparison of our data with predictions from modeling of vapor bubble formation and published Raman data on the density of CO2 in the vapor bubbles suggests that 55-85% of the dissolved CO2 in the melt inclusions at the time of trapping was lost to post-entrapment shrinkage bubbles. Our results combined with the Raman data demonstrate that olivine from the early part of the Kīlauea Iki eruption crystallized at magma was supplied from Kīlauea’s summit magma reservoir (∼2-5 km depth). In contrast, olivine from Kapoho, which was the rift zone extension of the Kīlauea Iki eruption, crystallized over a much wider range of depths (∼1-16 km). The wider depth range requires magma transport during the Kapoho eruption from deep beneath the summit region and/or from deep beneath Kīlauea’s east rift zone. The deeply derived olivine crystals and their host magma mixed with stored

  7. Diffuse CO2 degassing monitoring for the volcanic surveillance of Tenerife North-East Rift Zone (NERZ) volcano, Canary Islands (United States)

    Rodríguez, F.; Thomas, G. E.; Wong, T.; García, E.; Melián, G.; Padron, E.; Asensio-Ramos, M.; Hernández, P. A.; Perez, N. M.


    The North East Rift zone of Tenerife Island (NERZ, 210 km2) is one of the three major volcanic rift-zones of the island. The most recent eruptive activity along the NERZ took place in the 1704-1705 period with eruptions of Siete Fuentes, Fasnia and Arafo volcanoes. Since fumarolic activity is nowadays absent at the NERZ, soil CO2 degassing monitoring represent a potential geochemical tool for its volcanic surveillance. The aim of this study is to report the results of the last CO2 efflux survey performed in June 2017, with 658 sampling sites. In-situ measurements of CO2 efflux from the surface environment of the NERZ were performed by means of a portable non-dispersive infrared spectrophotometer (NDIR) following the accumulation chamber method. To quantify the total CO2 emission, soil CO2 efflux spatial distribution maps were constructed using Sequential Gaussian Simulation (SGS) as interpolation method. The diffuse CO2 emission values ranged between 0 - 41.1 g m-2 d-1. The probability plot technique applied to the data allowed to distinguish two different geochemical populations; background (B) and peak (P) represented by 81.8% and 18.2% of the total data, respectively, with geometric means of 3.9 and 15.0 g m-2 d-1, respectively. The average map constructed with 100 equiprobable simulations showed an emission rate of 1,361±35 t d-1. This value relatively higher than the background average of CO2 emission estimated on 415 t d-1 and slightly higher than the background range of 148 t d-1 (-1σ) and 1,189 t d-1 (+1σ) observed at the NERZ. This study reinforces the importance of performing soil CO2 efflux surveys as an effective surveillance volcanic tool in the NERZ.

  8. Rift Valley fever in a zone potentially occupied by Aedes vexans in Senegal: dynamics and risk mapping

    Directory of Open Access Journals (Sweden)

    Cécile Vignolles


    Full Text Available This paper presents an analysis of the interaction between the various variables associated with Rift Valley fever (RVF such as the mosquito vector, available hosts and rainfall distribution. To that end, the varying zones potentially occupied by mosquitoes (ZPOM, rainfall events and pond dynamics, and the associated exposure of hosts to the RVF virus by Aedes vexans, were analyzed in the Barkedji area of the Ferlo, Senegal, during the 2003 rainy season. Ponds were identified by remote sensing using a high-resolution SPOT-5 satellite image. Additional data on ponds and rainfall events from the Tropical Rainfall Measuring Mission were combined with in-situ entomological and limnimetric measurements, and the localization of vulnerable ruminant hosts (data derived from QuickBird satellite. Since “Ae. vexans productive events” are dependent on the timing of rainfall for their embryogenesis (six days without rain are necessary to trigger hatching, the dynamic spatio-temporal distribution of Ae. vexans density was based on the total rainfall amount and pond dynamics. Detailed ZPOM mapping was obtained on a daily basis and combined with aggressiveness temporal profiles. Risks zones, i.e. zones where hazards and vulnerability are combined, are expressed by the percentages of parks where animals are potentially exposed to mosquito bites. This new approach, simply relying upon rainfall distribution evaluated from space, is meant to contribute to the implementation of a new, operational early warning system for RVF based on environmental risks linked to climatic and environmental conditions.

  9. Fault zone architecture within Miocene–Pliocene syn-rift sediments ...

    Indian Academy of Sciences (India)

    The fault zones are associated with sliver fault blocks, clay smear, segmented faults and fault lenses' structural features. These features are mechanically related to the growth and linkage of the fault arrays. The structural features may represent a neotectonic and indicate that the architecture of the fault zones is developed ...

  10. Fault zone architecture within Miocene–Pliocene syn-rift sediments ...

    Indian Academy of Sciences (India)

    The present study focusses on field description of small normal fault zones in Upper Miocene–Pliocene sedimentary rocks on the northwestern side of the Red Sea, Egypt. The trend of these fault zones is mainly NW–SE. Paleostress analysis of 17 fault planes and slickenlines indicate that the tension direction is NE–SW.

  11. Neotectonic deformation in the transition zone between the Dead Sea Transform and the East Anatolian Fault Zone, Southern Turkey: a palaeomagnetic study of the Karasu Rift Volcanism (United States)

    Tatar, O.; Piper, J. D. A.; Gürsoy, H.; Heimann, A.; Koçbulut, F.


    In southern Turkey ongoing differential impingement of Arabia into the weak Anatolian collisional collage resulting from subduction of the Neotethyan Ocean has produced one of the most complex crustal interactions along the Alpine-Himalayan Orogen. Several major transforms with disputed motions, including the northward extension of the Dead Sea Fault Zone (DSFZ), meet in this region. To evaluate neotectonic motion on the Amanos and East Hatay fault zones considered to be northward extensions of the DSFZ, the palaeomagnetism of volcanic fields in the Karasu Rift between these faults has been studied. Remanence carriers are low-Ti magnetites and all except 5 of 51 basalt lavas have normal polarity. Morphological, polarity and K-Ar evidence show that rift formation occurred largely during the Brunhes chron with volcanism concentrated at 0.66-0.35 Ma and a subsidiary episode at ˜0.25-0.05. Forty-four units of normal polarity yield a mean of D/ I=8.8°/54.7° with inclination identical to the present-day field and declination rotated clockwise by 8.8±4.0°. Within the ˜15-km-wide Hassa sector of the Karasu Rift, the volcanic activity is concentrated between the Amanos and East Hatay faults, both with left lateral motions, which have rotated blocks bounded by NW-SE cross faults in a clockwise sense as the Arabian Block has moved northwestwards. An average lava age of ˜0.5 Ma yields a minimum cumulative slip rate on the system bounding faults of 0.46 cm/year according with the rate deduced from the Africa-Arabia Euler vector and reduced rates of slip on the southern extension of the DSFZ during Plio-Quaternary times. Estimates deduced from offsets of dated lavas flows and morphological features on the Amanos Fault Zone [Tectonophysics 344 (2002) 207] are lower (0.09-0.18 cm/year) probably because they are limited to surface fault breaks and do not embrace the seismogenic crust. Results of this study suggest that most strike slip on the DSFZ is taken up by the Amanos

  12. [Microorganisms of Lake Baikal and Lake Nyasa as indicators of anthropogenic influence: prospects of use in biotechnology]. (United States)

    Verkhozina, V A; Verkhozina, E V; Gonchar, D A; Dedkov, V S; Degtiarev, S Kh; Kusner, Iu S


    Restriction endonucleases (RENs) were detected in 650 microbial strains isolated from water columns and bottom sediments of deep rift lakes, Baikal (Russia) and Nyasa (Southeastern Africa). They enzymes included unique (Fan I, Aca I, and Sse 91) and very rare (Bsi I, and Cci N I) species not typical of aquatic ecosystems. Water columns, deep cores, and bottom sediments of pure areas of the lakes contained no microorganisms with new RENs. Thus, inshore areas of Lake Baikal exposed to anthropogenic influence may contain mutant bacterial strains expressing RENs that have not been described previously.

  13. Receiver Function Imaging of Mantle Transition Zone Discontinuities Beneath the Tanzania Craton and Adjacent Segments of the East African Rift System (United States)

    Sun, Muchen; Liu, Kelly H.; Fu, Xiaofei; Gao, Stephen S.


    The mantle transition zone (MTZ) discontinuities beneath the Tanzania Craton and the Eastern and Western Branches of the East African Rift System are imaged by stacking over 7,100 receiver functions. The mean thickness of the MTZ beneath the Western Branch and Tanzania Craton is about 252 km, which is comparable to the global average and is inconsistent with the existence of present-day thermal upwelling originating from the lower mantle. In contrast, beneath the Eastern Branch, an up to 30 km thinning of the MTZ is observed and is attributable to upwelling of higher temperature materials from either the upper MTZ or the lower mantle. The observations are in agreement with the hypothesis that rifting in Africa is primarily driven by gradients of gravitational potential energy and lateral variations of basal traction force along zones of significant changes of lithospheric thickness such as the edges of the Tanzania Craton.

  14. Near the Lake and around the Lake: Artists and Baikal

    Directory of Open Access Journals (Sweden)

    Marina Tkacheva


    Full Text Available The article considers several aspects of how Lake Baikal influences artists’ work:Baikal as a theme for painting and exhibiting;Creative events at Baikal;Baikal as a place where artists live;Half-amateur paintings for sale.

  15. Hydrogeological Modelling of the Geothermal Waters of Alaşehir in the Continental Rift Zone of the Gediz, Western Anatolia, Turkey (United States)

    Ӧzgür, Nevzat; Bostancı, Yesim; Anilır Yürük, Ezgi


    In western Anatolia, Turkey, the continental rift zones of the Büyük Menderes, Küçük Menderes and Gediz were formed by extensional tectonic features striking E-W generally and representing a great number of active geothermal systems, epithermal mineralizations and volcanic rocks from Middle Miocene to recent. The geothermal waters are associated with the faults which strike preferentially NW-SE and NE-SW and locate diagonal to general strike of the rift zones of the Menderes Massif. These NW-SE and NE-SW striking faults were probably generated by compressional tectonic regimes which leads to the deformation of uplift between two extensional rift zones in the Menderes Massif. The one of these rift zones is Gediz which is distinguished by a great number of geothermal waters such as Alaşehir, Kurşunlu, Çamurlu, Pamukkale and Urganlı. The geothermal waters of Alaşehir form the biggest potential in the rift zone of Gediz with a capacity of about 100 to 200 MWe. Geologically, the gneisses from the basement rocks in the study area which are overlain by an Paleozoic to Mesozoic intercalation of mica schists, quartzites and marbles, a Miocene intercalation of conglomerates, sandstones and clay stones and Plio-Quaternary intercalation of conglomerates, sandstones and clay stones discordantly. In the study area, Paleozoic to Mesozoic quartzites and marbles form the reservoir rocks hydrogeologically. The geothermal waters anions with Na+K>Ca>Mg dominant cations and HCO3>Cl> dominant anions are of Na-HCO3 type and can be considered as partial equilibrated waters. According to the results of geochemical thermometers, the reservoir temperatures area of about 185°C in accordance with measured reservoir temperatures. Stabile isotopes of δ18O versus δ2H of geothermal waters of Alaşehir deviate from the meteoric water line showing an intensive water-rock interaction under high temperature conditions. These data are well correlated with the results of the

  16. Seventeen years of monitoring diffuse CO2 emission from the Tenerife North-West Rift Zone (NWRZ) volcano, Canary Islands (United States)

    Padilla, Germán D.; Evans, Bethany J.; Provis, Aaron R.; Asensio, María; Alonso, Mar; Calvo, David; Hernández, Pedro; Pérez, Nemesio M.


    Tenerife together and Gran Canaria are the central islands of the Canarian archipelago, which have developed a central volcanic complex characterized by the eruption of differentiated magmas. Tenerife is the largest of the Canary Islands (2100 km2) and at present, the North-West Rift-Zone (NWRZ) is one of the most active volcanic structures of the three volcanic rift-zone of the island, which has hosted two historical eruptions (Arenas Negras in 1706 and Chinyero in 1909). In order to monitor the volcanic activity of NWRZ, since the year 2000, 49 soil CO2 efflux surveys have been performed at NWRZ (more than 300 observation sites each one) to evaluate the temporal an spatial variations of CO2 efflux and their relationships with the volcanic-seismic activity. Measurements were performed in accordance with the accumulation chamber method. Spatial distribution maps were constructed following the sequential Gaussian simulation (sGs) procedure. To quantify the total CO2 emission from the studied area, 100 simulations for each survey have been performed. We report herein the results of the last diffuse CO2 efflux surveys at the NWRZ undertaken in July and October 2016 to constrain the total CO2 output from the studied area. During July and October 2016 surveys, soil CO2 efflux values ranged from non-detectable up to 32.4 and 53.7 g m-2 d-1, respectively. The total diffuse CO2 output released to atmosphere were estimated at 255 ± 9 and 338 ± 18 t d-1, respectively, values higher than the background CO2 emission estimated on 144 t d-1. Since 2000, soil CO2 efflux values have ranged from non-detectable up to 141 g m-2 d-1, with the highest values measured in May 2005 whereas total CO2 output ranged between 52 and 867 t d-1. Long-term variations in the total CO2 output have shown a temporal correlation with the onsets of seismic activity at Tenerife, supporting unrest of the volcanic system, as is also suggested by anomalous seismic activity recorded in the studied area

  17. Rift brittle deformation of SE-Brazilian continental margin: Kinematic analysis of onshore structures relative to the transfer and accommodation zones of southern Campos Basin (United States)

    Savastano, Vítor Lamy Mesiano; Schmitt, Renata da Silva; Araújo, Mário Neto Cavalcanti de; Inocêncio, Leonardo Campos


    High-resolution drone-supported mapping and traditional field work were used to refine the hierarchy and kinematics of rift-related faults in the basement rocks and Early Cretaceous mafic dikes onshore of the Campos Basin, SE-Brazil. Two sets of structures were identified. The most significant fault set is NE-SW oriented with predominantly normal displacement. At mesoscale, this fault set is arranged in a rhombic pattern, interpreted here as a breached relay ramp system. The rhombic pattern is a penetrative fabric from the thin-section to regional scale. The second-order set of structures is an E-W/ESE-WNW system of normal faults with sinistral component. These E-W structures are oriented parallel with regional intrabasinal transfer zones associated with the earliest stages of Campos Basin's rift system. The crosscutting relationship between the two fault sets and tholeiitic dikes implies that the NE-SW fault set is the older feature, but remained active until the final stages of rifting in this region as the second-order fault set is older than the tholeiitic dikes. Paleostresses estimated from fault slip inversion method indicated that extension was originally NW-SE, with formation of the E-W transfer, followed by ESE-WNW oblique opening associated with a relay ramp system and related accommodation zones.

  18. The Baikal Neutrino Project: Present and perspective

    Energy Technology Data Exchange (ETDEWEB)

    Aynutdinov, V.; Avrorin, A.; Balkanov, V. [Institute for Nuclear Research, Moscow (Russian Federation); Belolaptikov, I. [Joint Institute for Nuclear Research, Dubna (Russian Federation); Bogorodsky, D. [Applied Physics Institute of Irkutsk State University, Gagarin blvd. 20, 1, Karl Marx Street, Irkutsk 664003 (Russian Federation); Budnev, N., E-mail: nbudnev@api.isu.r [Applied Physics Institute of Irkutsk State University, Gagarin blvd. 20, 1, Karl Marx Street, Irkutsk 664003 (Russian Federation); Danilchenko, I.; Domogatsky, G.; Doroshenko, A. [Institute for Nuclear Research, Moscow (Russian Federation); Dyachok, A. [Applied Physics Institute of Irkutsk State University, Gagarin blvd. 20, 1, Karl Marx Street, Irkutsk 664003 (Russian Federation); Dzhilkibaev, Zh.-A. [Institute for Nuclear Research, Moscow (Russian Federation); Fialkovsky, S. [Nizhni Novgorod State Technical University, Nizhni Novgorod (Russian Federation); Gaponenko, O. [Institute for Nuclear Research, Moscow (Russian Federation); Golubkov, K. [Joint Institute for Nuclear Research, Dubna (Russian Federation); Gress, O.; Gress, T.; Grishin, O. [Applied Physics Institute of Irkutsk State University, Gagarin blvd. 20, 1, Karl Marx Street, Irkutsk 664003 (Russian Federation); Klabukov, A. [Institute for Nuclear Research, Moscow (Russian Federation); Klimov, A. [Kurchatov Institute, Moscow (Russian Federation); Kochanov, A. [Applied Physics Institute of Irkutsk State University, Gagarin blvd. 20, 1, Karl Marx Street, Irkutsk 664003 (Russian Federation)


    The first stage Baikal Neutrino Telescope NT200 has been operating since 1998 and was upgraded to the 10 Mton detector NT200+ in 2005. The preparation towards a development of a km{sup 3}-scale detector in Lake Baikal is currently a central activity point. As an important milestone a km{sup 3}-prototype Cherenkov string, based on completely new technology, was installed in 2008 and has been successfully operating together with NT200+. It was upgraded in April 2009. Also, we review the status of high-energy acoustic neutrino detection activities in Lake Baikal.

  19. Archaeology in the Kilauea East Rift Zone: Part 1, Land-use model and research design, Kapoho, Kamaili and Kilauea Geothermal Subzones, Puna District, Hawaii Island

    Energy Technology Data Exchange (ETDEWEB)

    Burtchard, G.C.; Moblo, P. [International Archaeological Research Inst., Inc., Honolulu, HI (United States)


    The Puna Geothermal Resource Subzones (GRS) project area encompasses approximately 22,000 acres centered on the Kilauea East Rift Zone in Puna District, Hawaii Island. The area is divided into three subzones proposed for geothermal power development -- Kilauea Middle East Rift, Kamaili and Kapoho GRS. Throughout the time of human occupation, eruptive episodes along the rift have maintained a dynamic landscape. Periodic volcanic events, for example, have changed the coastline configuration, altered patterns of agriculturally suitable sediments, and created an assortment of periodically active, periodically quiescent, volcanic hazards. Because of the active character of the rift zone, then, the area`s occupants have always been obliged to organize their use of the landscape to accommodate a dynamic mosaic of lava flow types and ages. While the specific configuration of settlements and agricultural areas necessarily changed in response to volcanic events, it is possible to anticipate general patterns in the manner in which populations used the landscape through time. This research design offers a model that predicts the spatial results of long-term land-use patterns and relates them to the character of the archaeological record of that use. In essence, the environmental/land-use model developed here predicts that highest population levels, and hence the greatest abundance and complexity of identifiable prehistoric remains, tended to cluster near the coast at places that maximized access to productive fisheries and agricultural soils. With the possible exception of a few inland settlements, the density of archaeological remains expected to decrease with distance from the coastline. The pattern is generally supported in the regions existing ethnohistoric and archaeological record.

  20. Fleeing to Fault Zones: Incorporating Syrian Refugees into Earthquake Risk Analysis along the East Anatolian and Dead Sea Rift Fault Zones (United States)

    Wilson, B.; Paradise, T. R.


    The influx of millions of Syrian refugees into Turkey has rapidly changed the population distribution along the Dead Sea Rift and East Anatolian Fault zones. In contrast to other countries in the Middle East where refugees are accommodated in camp environments, the majority of displaced individuals in Turkey are integrated into cities, towns, and villages—placing stress on urban settings and increasing potential exposure to strong shaking. Yet, displaced populations are not traditionally captured in data sources used in earthquake risk analysis or loss estimations. Accordingly, we present a district-level analysis assessing the spatial overlap of earthquake hazards and refugee locations in southeastern Turkey to determine how migration patterns are altering seismic risk in the region. Using migration estimates from the U.S. Humanitarian Information Unit, we create three district-level population scenarios that combine official population statistics, refugee camp populations, and low, median, and high bounds for integrated refugee populations. We perform probabilistic seismic hazard analysis alongside these population scenarios to map spatial variations in seismic risk between 2011 and late 2015. Our results show a significant relative southward increase of seismic risk for this period due to refugee migration. Additionally, we calculate earthquake fatalities for simulated earthquakes using a semi-empirical loss estimation technique to determine degree of under-estimation resulting from forgoing migration data in loss modeling. We find that including refugee populations increased casualties by 11-12% using median population estimates, and upwards of 20% using high population estimates. These results communicate the ongoing importance of placing environmental hazards in their appropriate regional and temporal context which unites physical, political, cultural, and socio-economic landscapes. Keywords: Earthquakes, Hazards, Loss-Estimation, Syrian Crisis, Migration

  1. The Summerville Formation: Evidence for a sub-horizontal stratigraphic sequence below the post-rift unconformity in the Middleton Place Summerville Seismic Zone (United States)

    Getz, Joseph Edward

    The Middleton Place Summerville Seismic Zone (MPSSZ) near Summerville, South Carolina was the site of renewed extensive investigation, beginning in the 1970's, for the source of the 1886 Charleston earthquake. Reactivation of faults associated with a putative fault-bounded Triassic rift basin through analysis of seismic reflection, seismic refraction, and well data has since become the favored interpretation for the source of MPSSZ seismicity. Critical to this interpretation is the association of continental redbed sedimentary rocks with Triassic basins identified throughout the North American Atlantic margin. Reanalysis of 18 seismic reflection profiles and 25 seismic refraction profiles within the MPSSZ suggests that the red beds found here are a thin, sub-horizontal, regionally extensive, generally unbroken subsurface stratigraphic sequence distinct from the sedimentary architecture observed in analog Triassic rift systems. In addition, this sequence appears to unconformably overly a structural depression (the Jedberg basin) previously interpreted as a Triassic rift basin in the vicinity of the MPSSZ. In addition to the geometries observed on seismic reflection profiles, seismic refraction velocities ranging from 4.2 to 6.1 km/s can be correlated with (1) Jurassic basalt flows, (2) the newly proposed Summerville Formation, and (3) the Basement (B) sequences respectively. The current study maps the Summerville red bed section and its bounding reflectors. In addition to mapping the regional extent of the newly proposed Summerville Formation, refraction velocities and changes in reflection character, the lateral extent of the basalt flows can be changed to a more localized flow rather than a regionally extensive flow of which was previously thought. Reanalysis of data in the MPSSZ suggests that the area may not be part of the Triassic South Georgia Rift system due to the sub-horizontal geometry of the red bed reflections, the apparent lack of faulting, and their

  2. A shifting rift—Geophysical insights into the evolution of Rio Grande rift margins and the Embudo transfer zone near Taos, New Mexico (United States)

    Grauch, V.J.S.; Bauer, Paul W.; Drenth, Benjamin J.; Kelson, Keith I.


    We present a detailed example of how a subbasin develops adjacent to a transfer zone in the Rio Grande rift. The Embudo transfer zone in the Rio Grande rift is considered one of the classic examples and has been used as the inspiration for several theoretical models. Despite this attention, the history of its development into a major rift structure is poorly known along its northern extent near Taos, New Mexico. Geologic evidence for all but its young rift history is concealed under Quaternary cover. We focus on understanding the pre-Quaternary evidence that is in the subsurface by integrating diverse pieces of geologic and geophysical information. As a result, we present a substantively new understanding of the tectonic configuration and evolution of the northern extent of the Embudo fault and its adjacent subbasin.We integrate geophysical, borehole, and geologic information to interpret the subsurface configuration of the rift margins formed by the Embudo and Sangre de Cristo faults and the geometry of the subbasin within the Taos embayment. Key features interpreted include (1) an imperfect D-shaped subbasin that slopes to the east and southeast, with the deepest point ∼2 km below the valley floor located northwest of Taos at ∼36° 26′N latitude and 105° 37′W longitude; (2) a concealed Embudo fault system that extends as much as 7 km wider than is mapped at the surface, wherein fault strands disrupt or truncate flows of Pliocene Servilleta Basalt and step down into the subbasin with a minimum of 1.8 km of vertical displacement; and (3) a similar, wider than expected (5–7 km) zone of stepped, west-down normal faults associated with the Sangre de Cristo range front fault.From the geophysical interpretations and subsurface models, we infer relations between faulting and flows of Pliocene Servilleta Basalt and older, buried basaltic rocks that, combined with geologic mapping, suggest a revised rift history involving shifts in the locus of fault activity as

  3. Olivine-liquid relations of lava erupted by Kilauea volcano from 1994 to 1998: Implications for shallow magmatic processes associated with the ongoing east-rift-zone eruption (United States)

    Thornber, C.R.


    From 1994 through 1998, the eruption of Ki??lauea, in Hawai'i, was dominated by steady-state effusion at Pu'u 'O??'??o that was briefly disrupted by an eruption 4 km uprift at Np??au Crater on January 30, 1997. In this paper, I describe the systematic relations of whole-rock, glass, olivine, and olivine-inclusion compositions of lava samples collected throughout this interval. This suite comprises vent samples and tube-contained flows collected at variable distances from the vent. The glass composition of tube lava varies systematically with distance and allows for the "vent-correction" of glass thermometry and olivine-liquid KD as a function of tube-transport distance. Combined olivine-liquid data for vent samples and "vent-corrected" lava-tube samples are used to document pre-eruptive magmatic conditions. KD values determined for matrix glasses and forsterite cores define three types of olivine phenocrysts: type A (in equilibrium with host glass), type B (Mg-rich relative to host glass) and type C (Mg-poor relative to host glass). All three types of olivine have a cognate association with melts that are present within the shallow magmatic plumbing system during this interval. During steady-state eruptive activity, the compositions of whole-rock, glass and most olivine phenocrysts (type A) all vary sympathetically over time and as influenced by changes of magmatic pressure within the summit-rift-zone plumbing system. Type-A olivine is interpreted as having grown during passage from the summit magmachamber along the east-rift-zone conduit. Type-B olivine (high Fo) is consistent with equilibrium crystallization from bulk-rock compositions and is likely to have grown within the summit magma-chamber. Lower-temperature, fractionated lava was erupted during non-steady state activity of the Na??pau Crater eruption. Type-A and type-B olivine-liquid relations indicate that this lava is a mixture of rift-stored and summit-derived magmas. Post-Na??pau lava (at Pu'u 'O?? 'o

  4. Archaeology in the Kilauea East Rift Zone: Part 2, A preliminary sample survey, Kapoho, Kamaili and Kilauea geothermal subzones, Puna District, Hawaii island

    Energy Technology Data Exchange (ETDEWEB)

    Sweeney, M.T.K.; Burtchard, G.C. [International Archaeological Research Inst., Inc., Honolulu, HI (United States)


    This report describes a preliminary sample inventory and offers an initial evaluation of settlement and land-use patterns for the Geothermal Resources Subzones (GRS) area, located in Puna District on the island of Hawaii. The report is the second of a two part project dealing with archaeology of the Puna GRS area -- or more generally, the Kilauea East Rift Zone. In the first phase of the project, a long-term land-use model and inventory research design was developed for the GRS area and Puna District generally. That report is available under separate cover as Archaeology in the Kilauea East Rift Zone, Part I: Land-Use Model and Research Design. The present report gives results of a limited cultural resource survey built on research design recommendations. It offers a preliminary evaluation of modeled land-use expectations and offers recommendations for continuing research into Puna`s rich cultural heritage. The present survey was conducted under the auspices of the United States Department of Energy, and subcontracted to International Archaeological Research Institute, Inc. (IARII) by Martin Marietta Energy Systems, Inc. The purpose of the archaeological work is to contribute toward the preparation of an environmental impact statement by identifying cultural materials which could be impacted through completion of the proposed Hawaii Geothermal Project.

  5. High-resolution seismic survey for the characterization of planned PIER-ICDP fluid-monitoring sites in the Eger Rift zone (United States)

    Simon, H.; Buske, S.


    The Eger Rift zone (Czech Republic) is a intra-continental non-volcanic region and is characterized by outstanding geodynamic activities, which result in earthquake swarms and significant CO2 emanations. Because fluid-induced stress can trigger earthquake swarms, both natural phenomena are probably related to each other. The epicentres of the earthquake swarms cluster at the northern edge of the Cheb Basin. Although the location of the cluster coincides with the major Mariánské-Lázně Fault Zone (MLFZ) the strike of the focal plane indicates another fault zone, the N-S trending Počátky-Plesná Zone (PPZ). Isotopic analysis of the CO2-rich fluids revealed a significant portion of upper mantle derived components, hence a magmatic fluid source in the upper mantle was postulated. Because of these phenomena, the Eger Rift area is a unique site for interdisciplinary drilling programs to study the fluid-earthquake interaction. The ICDP project PIER (Probing of Intra-continental magmatic activity: drilling the Eger Rift) will set up an observatory, consisting of five monitoring boreholes. In preparation for the drilling, the goal of the seismic survey is the characterization of the projected fluid-monitoring drill site at the CO2 degassing mofette field near Hartoušov. This will be achieved by a 6 km long profile with dense source and receiver spacing. The W-E trending profile will cross the proposed drill site and the surface traces of MLFZ and PPZ. The outcome of the seismic survey will be a high-resolution structural image of potential reflectors related to these fault zones. This will be achieved by the application of advanced pre-stack depth migration methods and a detailed P-wave velocity distribution of the area obtained from first arrival tomography. During interpretation of the seismic data, a geoelectrical resistivity model, acquired along the same profile line, will provide important constraints, especially with respect to fluid pathways.

  6. The Northeast Brazilian Rift System (United States)

    de Matos, Renato M. Darros


    The northeast Brazilian rift basins provide important data critical to the understanding of continental rifting processes associated with the opening of the South Atlantic. These basins represent the locus of intersection of the Southern and Equatorial branches and some basins yield substantial chronostratigraphic data that constrain the temporal and spatial interaction of the rift phases. Similar data are not found in its counterpart in Africa, especially for the Neocomian. These Early Cretaceous rift basins of northeast Brazil illustrate key three-dimensional geometries of intracontinental rift systems, mainly controlled by the basement structural framework. During the main rift phase (Syn-rift II, Neocomian-early Barremian) extensional deformation was distributed over three main rift axes: (1) the Gabon-Sergipe Alagoas (GSA) trend, (2) the Recôncavo-Tucano-Jatobá (RTJ) trend and (3) the Cariri-Potiguar (CP) trend. During this phase, extensional deformation jumped west from the easternmost basins (GSA trend) to a series of NE trending intracratonic basins (RTJ and CP trends), characterized by a set of asymmetric half grabens separated by basement highs, transfer faults, and/or accommodation zones. These basins are typically a few tens of kilometers wide and trend NE-SW, roughly perpendicular to the main extension direction during the Neocomian. Preexisting upper crustal weakness zones, like the dominantly NE-SW trending shear zones of the Brazilian/Pan-African orogeny, controlled the development of intracrustal listric normal faults. Internal transverse structures such as transfer faults and accommodation zones were also controlled by the local basement structural framework. The megashear zones of Pernambuco (Brazil) and Ngaundere (Africa) seem to have behaved like a huge accommodation zone, accommodating extensional deformation along the RTJ/GSA trends with simultaneous extension along the CP trend. During the late Barremian (Syn-rift phase III), a significant

  7. Silica-scaled chrysophytes of Lake Baikal

    Directory of Open Access Journals (Sweden)

    A. Yu. Bessudova


    Full Text Available The list of silica-scaled chrysophytes of Lake Baikal has been enlarged using electron microscopy. It has been supplemented with 12 species and 2 forms. Spiniferomonas takahashii has been observed for the first time in the water bodies of Russia. According to our data, the list of silica-scaled chrysophytes of Lake Baikal includes 25 species and intra-species taxa: Chrysosphaerella – 3, Paraphysomonas – 2, Clathromonas – 1, Spiniferomonas – 7, Mallomonas – 8 and Synura – 4. We have also analyzed their seasonal dynamics and observed algal species that are dominant in spring, summer and autumn.

  8. The 1170 and 1202 CE Dead Sea Rift earthquakes and long-term magnitude distribution of the Dead Sea Fault zone (United States)

    Hough, S.E.; Avni, R.


    In combination with the historical record, paleoseismic investigations have provided a record of large earthquakes in the Dead Sea Rift that extends back over 1500 years. Analysis of macroseismic effects can help refine magnitude estimates for large historical events. In this study we consider the detailed intensity distributions for two large events, in 1170 CE and 1202 CE, as determined from careful reinterpretation of available historical accounts, using the 1927 Jericho earthquake as a guide in their interpretation. In the absence of an intensity attenuation relationship for the Dead Sea region, we use the 1927 Jericho earthquake to develop a preliminary relationship based on a modification of the relationships developed in other regions. Using this relation, we estimate M7.6 for the 1202 earthquake and M6.6 for the 1170 earthquake. The uncertainties for both estimates are large and difficult to quantify with precision. The large uncertainties illustrate the critical need to develop a regional intensity attenuation relation. We further consider the distribution of magnitudes in the historic record and show that it is consistent with a b-value distribution with a b-value of 1. Considering the entire Dead Sea Rift zone, we show that the seismic moment release rate over the past 1500 years is sufficient, within the uncertainties of the data, to account for the plate tectonic strain rate along the plate boundary. The results reveal that an earthquake of M7.8 is expected within the zone on average every 1000 years. ?? 2011 Science From Israel/LPPLtd.


    Directory of Open Access Journals (Sweden)

    K. Zh. Seminsky


    Full Text Available The zone-block structure of the lithosphere is represented by a hierarchically organized pattern of stable blocks and mobile zones which border such blocks and contain highly dislocated geological medium (Fig. 1. Today, different specialists adhere to different concepts of blocks and zones, which are two main elements of the lithosphere structure. Differences are most significant in determinations of ‘interblock zones’ that are named as deformation / destructive / contact / mobile / fracture zones etc. due to their diversity in different conditions of deformation. One of the most effective approaches to studying the zone-block structure of the lithosphere is a combination of geological and geophysical studies of interblock zones tectonic features on various scales, which can make it possible to reveal the most common patterns of the interblock zones, general regularities of their development and relationships between the interblock zones.The main objectives of our study were (1 to identify the zone-block structure of the crust in the southern regions of East Siberia from tectonophysical analysis of geological and geophysical surveys conducted on four different scales along the 500 km long Shertoy-Krasny Chikoy transect crossing the marginal segment of the Siberian block, the Baikal rift and the Transbaikalian block (Fig. 2; (2 to clarify structural features of the central part of the Baikal rift (representing the tectonic type of interblock extension zone by applying new research methods, such as radon emanation survey, to the Shertoy-Krasny Chikoy transect and using the previously applied methods, such as magnetotelluric sounding, on a smaller scale; and (3 to study manifestation of interblock zones of various ranks in different geological and geophysical fields, to reveal common specific features of their structural patterns for the upper crust, and to establish regularities of hierarchic and spatial relationships between the interblock

  10. Receiver function imaging of mantle transition zone discontinuities beneath the Tanzania Craton and the Eastern and Western Branches of the East African Rift System (United States)

    Sun, M.; Liu, K. H.; Fu, X.; Gao, S. S.


    To investigate the mechanism of initiation and development of the Eastern African Rifting System (EARS) circumfluent the Tanzania Craton (TC), over 7,100 P-to-S radial receiver functions (RFs) recorded by 87 broadband seismic stations are stacked to map the topography of mantle transition zone (MTZ) discontinuities beneath the TC and the Eastern and Western Branches of the EARS. After time-depth conversion using the 1-D IASP91 Earth model, the resulting 410 km (d410) and 660 km (d660) discontinuity apparent depths are found to be greater than the global averages beneath the whole study area, implying slower than normal upper mantle velocities. The mean thickness of the MTZ beneath the Western Branch and TC is about 252 km, which is comparable to the global average and is inconsistent with the existence of present-day thermal upwelling originating from the lower mantle. In contrast, beneath the Eastern Branch, an 30 km thinning of the MTZ is observed from an up to 50 km and 20 km apparent depression of the d410 and d660, respectively. On the basis of previous seismic tomographic results and empirical relationships between velocity and thermal anomalies, we propose that the most plausible explanation for the observations beneath the volcanic Eastern Branch is the existence of a low-velocity layer extending from the surface to the upper MTZ, probably caused by decompression partial melting associated with continental rifting. The observations are in general agreement with an upper mantle origin for the initiation and development of both the Western and Eastern Branches of the EARS beneath the study area.

  11. [Genome similarity of Baikal omul and sig]. (United States)

    Bychenko, O S; Sukhanova, L V; Ukolova, S S; Skvortsov, T A; Potapov, V K; Azhikina, T L; Sverdlov, E D


    Two members of the Baikal sig family, a lake sig (Coregonus lavaretus baicalensis Dybovsky) and omul (C. autumnalis migratorius Georgi), are close relatives that diverged from the same ancestor 10-20 thousand years ago. In this work, we studied genomic polymorphism of these two fish species. The method of subtraction hybridization (SH) did not reveal the presence of extended sequences in the sig genome and their absence in the omul genome. All the fragments found by SH corresponded to polymorphous noncoding genome regions varying in mononucleotide substitutions and short deletions. Many of them are mapped close to genes of the immune system and have regions identical to the Tc-1-like transposons abundant among fish, whose transcription activity may affect the expression of adjacent genes. Thus, we showed for the first time that genetic differences between Baikal sig family members are extremely small and cannot be revealed by the SH method. This is another endorsement of the hypothesis on the close relationship between Baikal sig and omul and their evolutionarily recent divergence from a common ancestor.

  12. Onshore-offshore evidence for periodic post-rift shear reversal along the Pernambuco Fracture Zone, NE Brazil (United States)

    Balsamo, Fabrizio; Nestola, Yago; Storti, Fabrizio; Nogueira, Cézar; Bezerra, Hilario F. R.


    Oceanic facture zones are among the most evident bathymetric features of seafloors. They include transform faults that connect adjacent mid-ocean ridge segments and accommodate opposite spreading directions. According to the plate tectonics theory, only the latter are tectonically active. Recent onshore and offshore evidence in the Antarctic plate sector facing Australia suggest, conversely, that oceanic fracture zones can transfer shear into the plate interior. In this contribution we illustrate the results of a research project performed in the NE Brazilian passive margin, where the seismic activity is clustered along major crustal-scale, long-lived shear zones, thus resembling the Antarctic case. In particular, we performed a detailed study of the offshore pattern of seafloor age domains on both sides of the Pernambuco Fracture Zone (PFZ), which indicates non-uniform spreading rates on the two lithospheric lanes separated by the PFZ. The differential spreading rate, calculated in 8 age provinces from Upper Cretaceous to Present, varies between 1.3 and 8.8 mm/yr and periodically switched from right-lateral to left-lateral excess transform shear along the PFZ. Five major inversions were found, including a Tortonian inversion from right-lateral to left-lateral excess shear, consistently with structural data acquired in Miocene to Quaternary sediments along the PFZ. We discuss the impact of our findings in the current plate tectonic theory framework.

  13. Two-stage rifting of Zealandia-Australia-Antarctica: Evidence from 40Ar/39Ar thermochronometry of the Sisters shear zone, Stewart Island, New Zealand (United States)

    Kula, Joseph; Tulloch, Andy; Spell, Terry L.; Wells, Michael L.


    The Sisters shear zone is a newly discovered Late Cretaceous detachment fault system exposed for 40 km along the southeast coast of Stewart Island, southernmost New Zealand. Footwall rocks consist of variably deformed ca. 310 and 105 Ma granites that range from undeformed to protomylonite, mylonite, and ultramylonite. The hanging wall includes non-marine conglomerate and brittley deformed granite. K-feldspar thermochronometry of the footwall indicates moderately rapid cooling (20 30 C°/m.y.) due to tectonic denudation over the interval ca. 89 82 Ma. Return to slow cooling at 82 Ma coincides with the age of the oldest seafloor adjacent to the Campbell Plateau and reflects the mechanical transition from continental extension to lithospheric rupture and formation of the Pacific-Antarctic Ridge. Our findings support a two-stage rift model for continental breakup of this part of the Gondwana margin. Stage one (ca. 101 88 Ma) is the northward propagation of continental extension and the Tasman Ridge as recorded in mylonite dredged from the Ross Sea and the Paparoa core complex. Stage two (ca. 89 82 Ma) is extension between the Campbell Plateau and West Antarctica leading to formation of the Pacific-Antarctic Ridge.

  14. The East African rift system (United States)

    Chorowicz, Jean


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

  15. Oblique reactivation of lithosphere-scale lineaments controls rift physiography - the upper-crustal expression of the Sorgenfrei-Tornquist Zone, offshore southern Norway (United States)

    Phillips, Thomas B.; Jackson, Christopher A.-L.; Bell, Rebecca E.; Duffy, Oliver B.


    Pre-existing structures within sub-crustal lithosphere may localise stresses during subsequent tectonic events, resulting in complex fault systems at upper-crustal levels. As these sub-crustal structures are difficult to resolve at great depths, the evolution of kinematically and perhaps geometrically linked upper-crustal fault populations can offer insights into their deformation history, including when and how they reactivate and accommodate stresses during later tectonic events. In this study, we use borehole-constrained 2-D and 3-D seismic reflection data to investigate the structural development of the Farsund Basin, offshore southern Norway. We use throw-length (T-x) analysis and fault displacement backstripping techniques to determine the geometric and kinematic evolution of N-S- and E-W-striking upper-crustal fault populations during the multiphase evolution of the Farsund Basin. N-S-striking faults were active during the Triassic, prior to a period of sinistral strike-slip activity along E-W-striking faults during the Early Jurassic, which represented a hitherto undocumented phase of activity in this area. These E-W-striking upper-crustal faults are later obliquely reactivated under a dextral stress regime during the Early Cretaceous, with new faults also propagating away from pre-existing ones, representing a switch to a predominantly dextral sense of motion. The E-W faults within the Farsund Basin are interpreted to extend through the crust to the Moho and link with the Sorgenfrei-Tornquist Zone, a lithosphere-scale lineament, identified within the sub-crustal lithosphere, that extends > 1000 km across central Europe. Based on this geometric linkage, we infer that the E-W-striking faults represent the upper-crustal component of the Sorgenfrei-Tornquist Zone and that the Sorgenfrei-Tornquist Zone represents a long-lived lithosphere-scale lineament that is periodically reactivated throughout its protracted geological history. The upper-crustal component of

  16. The effect of bloom of filamentous green algae on the reproduction of yellowfin sculpin Cottocomephorus grewingkii (Dybowski, 1874) (Cottoidae) during ecological crisis in Lake Baikal. (United States)

    Khanaev, I V; Dzyuba, E V; Kravtsova, L S; Grachev, M A


    In shallow water areas of open Lake Baikal, filamentous green alga of the genus Spirogyra grows abundantly. Together with alga of the genus Ulothrix, it forms algal mats. According to our observations from 2010 to 2013, the spawning habitat conditions for the yellowfin sculpin Cottocomephorus grewingkii (Dybowski, 1874) (Cottidae) proved to be significantly disturbed in the littoral zone of Listvennichnyi Bay (southern Baikal), which, in turn, reduced the number of egg layings. With a 100% projective cover of the floor and a high density of green filamentous algae, the shallow-water stony substrate becomes completely inaccessible for spawning of the August population.

  17. Mapping of zones potentially occupied by Aedes vexans and Culex poicilipes mosquitoes, the main vectors of Rift Valley fever in Senegal

    Directory of Open Access Journals (Sweden)

    Yves M. Tourre


    Full Text Available A necessary condition for Rift Valley fever (RVF emergence is the presence of Aedes (Aedimorphus vexans and Culex (Culex poicilipes mosquitoes carrying the arbovirus and responsible for the infection. This paper presents a detailed mapping in the Sahelian region of Senegal of zones potentially occupied by these mosquitoes (ZPOMs whose population density is directly linked to ecozones in the vicinity of small ponds. The vectors habitats and breeding sites have been characterized through an integrated approach combining remote sensing technology, geographical information systems, geographical positioning systems and field observations for proper geo-referencing. From five SPOT-5 images (~10 m spatial resolution with appropriate channels, a meridional composite transect of 290 x 60 km was first constructed at the height of the summer monsoon. Subsequent ZPOMs covered major ecozones from north to south with different hydrological environments and different patterns pond distributions. It was found that an overall area of 12,817 ha ± 10% (about 0.8% of the transect is occupied by ponds with an average ZPOM 17 times larger than this (212,813 ha ± 10% or about 14% of the transect. By comparing the very humid year of 2003 with 2006 which had just below normal rainfall, the ZPOMs inter-annual variability was analyzed in a sandy-clayey ecozone with an important hydrofossil riverbed within the Ferlo region of Senegal. Very probably contributing to an increased abundance of vectors by the end of August 2003, it was shown that the aggregate pond area was already about 22 times larger than in August 2006, corresponding to an approximately five times larger total ZPOM. The results show the importance of pin-pointing small ponds (sizes down to 0.1 ha and their geographical distribution in order to assess animal exposure to the RVF vectors.

  18. Is the Proterozoic Ladoga Rift (SE Baltic Shield) a rift?

    DEFF Research Database (Denmark)

    Artemieva, Irina; Shulgin, Alexey


    , and geophysical characteristics typical of continental rifts in general and demonstrate that, except for magmatic and, perhaps, some gravity signature, the Lake Ladoga region lacks any other rift features. We also compare the geophysical data from the Lake Ladoga region with similar in age Midcontinent and Valday......) supercontinent, which led to magma intrusions as a series of mafic dykes along lithosphere weakness zones and ponding of small magma pockets within the cratonic lithosphere. Consequent magma cooling and its partial transition to eclogite facies could have led to the formation of a series of basement depressions...

  19. Spatial and temporal variations of diffuse CO_{2} degassing at the Tenerife North-South Rift Zone (NSRZ) volcano (Canary Islands) during the period 2002-2016 (United States)

    Rodríguez, Fátima; McCollum, John J. K.; Orland, Elijah D. M.; Barrancos, José; Padilla, Germán D.; Calvo, David; Amonte, Cecilia; Pérez, Nemesio M.


    Subaerial volcanic activity on Tenerife (2034 km2), the largest island of the Canary archipelago, started 14 My ago and 4 volcanic eruptions have occurred in historical times during the last 300 years. The main volcano-structural and geomorphological features of Tenerife are (i) the central volcanic complex, nowadays formed by Las Cañadas caldera, a volcanic depression measuring 16×9 km that resulted from multiple vertical collapses and partially filled by post-caldera volcanic products and (ii) the triple junction-shaped rift system, formed by numerous aligned monogenetic cones. Up to 297 mafic monogenetic cones have been recognized on Tenerife, and they represent the most common eruptive activity occurring on the island during the last 1 My (Dóniz et al., 2008). The North-South Rift Zone (NSRZ) of Tenerife comprises at least 139 cones. The main structural characteristic of the NSRZ of the island is an apparent absence of a distinct ridge, and a fan shaped distribution of monogenetic cones. Since there are currently no visible gas emissions at the NSRZ, diffuse degassing surveys have become an important geochemical tool for the surveillance of this volcanic system. Five diffuse CO2 degassing surveys have been carried out at NSRZ of Tenerife since 2002, the last one in the summer period of 2016, to evaluate the spatio-temporal variations of CO2 degassing as a volcanic surveillance tool for the NSRZ of Tenerife. At each survey, around 600 sampling sites were selected to cover homogenously the study area (325 km2) using the accumulation chamber method. The diffuse CO2 output ranged from 78 to 707 t/d in the study period, with the highest emission rate measured in 2015. The backgroung emission rate was estimated in 300 t/d. The last results the soil CO2 efflux values ranged from non-detectable up to 24.7 g m-2 d-1. The spatial distribution map, constructed following the sequential Gaussian simulation (sGs) procedure, showed the highest CO2 values as multiple

  20. The ability of microbial community of Lake Baikal bottom sediments associated with gas discharge to carry out the transformation of organic matter under thermobaric conditions

    Directory of Open Access Journals (Sweden)

    Sergei Viktorovich Bukin


    Full Text Available The ability to compare the composition and metabolic potential of microbial communities inhabiting the subsurface sediment in geographically distinct locations is one of the keys to understanding the evolution and function of the subsurface biosphere. Prospective areas for study of the subsurface biosphere are the sites of hydrocarbon discharges on the bottom of the Lake Baikal rift, where ascending fluxes of gas-saturated fluids and oil from deep layers of bottom sediments seep into near-surface sediment. The samples of surface sediments collected in the area of the Posolskaya Bank methane seep were cultured for 17 months under thermobaric conditions (80°С, 5 MPa with the addition of complementary organic substrate, and a different composition for the gas phase. After incubation, the presence of intact cells of microorganisms, organic matter transformation and the formation of oil biomarkers was confirmed in the samples, with the addition of Baikalian diatom alga Synedra acus detritus, and gas mixture СH4:H2:CO2. Taxonomic assignment of the 16S rRNA sequence data indicates that the predominant sequences in the enrichment were Sphingomonas (55.3%, Solirubrobacter (27.5% and Arthrobacter (16.6%. At the same time, in heat-killed sediment and in sediment without any additional substrates, which were cultivated in a CH4 atmosphere, no geochemical changes were detected, nor the presence of intact cells and 16S rRNA sequences of Bacteria and Archaea. This data may suggest that the decomposition of organic matter under culturing conditions could be performed by microorganisms from low-temperature sediment layers. One possible explanation of this phenomenon is migration of the representatives of the deep thermophilic community through fault zones in the near surface sediment layers, together with gas-bearing fluids.

  1. Continental Rifts (United States)

    Rosendahl, B. R.

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

  2. Climate-Induced Mortality of Siberian Pine and Fir in the Lake Baikal Watershed, Siberia (United States)

    Kharuk, Viacheslav I.; Im, Sergei T.; Petrova, IIya A.; Golyukov, Alexei S.; Ranson, Kenneth J.; Yagunov, Mikhail N.


    Siberian pine (Pinus sibirica) and fir (Abies sibirica) (so called "dark needle conifers", DNC) showed decreased radial growth increment within the Lake Baikal watershed since the 1980s with increasing mortality recorded since the year 2000. Tree ring width was strongly correlated with vapor pressure deficit, aridity and root zone moisture. Water stress from droughts made trees more susceptible to insect attacks causing mortality in about 10% of DNC stands within the Lake Baikal watershed. Within Siberia DNC mortality increased in the southern part of the DNC range. Biogeographically, tree mortality was located within the DNC - forest-steppes transition. Tree mortality was significantly correlated with drought and soil moisture anomalies. Within the interior of the DNC range mortality occurred within relief features with high water stress risk (i.e., steep convex south facing slopes with shallow well-drained soils). In general, DNC mortality in Siberia was induced by increased aridity and severe drought (inciting factors) in synergy with biotic attacks (contributing factor). In future climate scenarios with predicted increase in aridity DNC could be eliminated from the southern part of its current range and will be replaced by drought-resistant conifers and broadleaf species (e.g., Larix sibirica, Pinus silvestris, and Betula pubescence).

  3. Structural evolution of the Kilombero rift basin in central Tanzania ...

    African Journals Online (AJOL)

    Detailed geological and structural investigations at the northwestern scarp of the Cenozoic Kilombero Rift allow the drawing of its structural evolution and establishment of stress conditions that prevailed at the different deformational episodes at this rift zone. The structure, where the northwestern scarp of the Cenozoic ...

  4. Canine distemper virus in Lake Baikal seals (Phoca sibirica).

    NARCIS (Netherlands)

    L.V. Mamaev; I.K.G. Visser (Ilona); S.I. Belikov; N.N. Denikina; T.C. Harder (Timm); L. Goatley; B. Rima; B. Edginton; A.D.M.E. Osterhaus (Albert); T. Barrett (Thomas)


    textabstractThe virus epizootic which resulted in significant mortality in Siberian seals (Phoca sibirica) in Lake Baikal during 1987/88 was caused by canine distemper virus. Sequence analysis of the virus glycoprotein genes revealed that it was most closely related to recent European field isolates

  5. Cyanobacterial bloom in the world largest freshwater lake Baikal (United States)

    Namsaraev, Zorigto; Melnikova, Anna; Ivanov, Vasiliy; Komova, Anastasia; Teslyuk, Anton


    Lake Baikal is a UNESCO World Heritage Site and holds 20% of the world’s freshwater reserves. On July 26, 2016, a cyanobacterial bloom of a green colour a few kilometers in size with a bad odor was discovered by local people in the Barguzinsky Bay on the eastern shore of Lake Baikal. Our study showed very high concentration of chlorophyll a (41.7 g/m3) in the sample of bloom. We found that the bloom was dominated by a nitrogen-fixing heterocystous cyanobacteria of the genus Dolichospermum. The mass accumulation of cyanobacteria in the lake water with an extremely high chlorophyll a concentration can be explained by a combination of several factors: the discharge of biologicaly-available nutrients, including phosphorus, into the water of Lake Baikal; low wind speed and weak water mixing; buoyant cyanobacterial cells on the lake surface, which drifted towards the eastern coast, where the maximum concentration of chlorophyll a was recorded. In the center of the Barguzinsky Bay and in the open part of Lake Baikal, according to satellite data, the chlorophyll a concentration is several orders of magnitude lower than at the shoreline.


    Directory of Open Access Journals (Sweden)

    R. M. Lobatskaya


    Full Text Available The article reviews specific features of its fault-block structure of the Baikal-Yenisei fault in view of safe operations of nuclear energy facilities in the Krasnoyarsk region, Russia. The fault is located at the junction of the Siberian platform and the West Siberian plate. Velocities of neotectonic movements in the fault zone and adjacent territories are estimated from data on the current positions of fluvial terraces of the Yenisei river valley, peneplanation planes varying in ages and erosional incision depths. It is revealed that maximum gradients of recent movement velocities vary not higher than 10–8 to 10–9. Average velocities of relative displacements amount to 0.1–0.2 mm per year for intra-fault blocks bounded by regional faults and do not exceed 0.02–0.03 mm per year for intra-fault blocks bordered by local faults. There are grounds to conclude that recent geodynamic activity in the zone of the Baikal-Yenisei fault zone is weak and thus does not affect the safety of nuclear energy facilities operating in the region, including FGUP GKhK (Mining and Chemical Combine.

  7. Flux and genesis of CO2 degassing from volcanic-geothermal fields of Gulu-Yadong rift in the Lhasa terrane, South Tibet: Constraints on characteristics of deep carbon cycle in the India-Asia continent subduction zone (United States)

    Zhang, Lihong; Guo, Zhengfu; Sano, Yuji; Zhang, Maoliang; Sun, Yutao; Cheng, Zhihui; Yang, Tsanyao Frank


    Gulu-Yadong rift (GYR) is the longest extensional, NE-SW-trending rift in the Himalayas and Lhasa terrane of South Tibet. Many volcanic-geothermal fields (VGFs), which comprise intense hot springs, steaming fissures, geysers and soil micro-seepage, are distributed in the GYR, making it ideal area for studying deep carbon emissions in the India-Asia continent subduction zone. As for the northern segment of GYR in the Lhasa terrane, its total flux and genesis of CO2 emissions are poorly understood. Following accumulation chamber method, soil CO2 flux survey has been carried out in VGFs (i.e., Jidaguo, Ningzhong, Sanglai, Tuoma and Yuzhai from south to north) of the northern segment of GYR. Total soil CO2 output of the northern GYR is about 1.50 × 107 t a-1, which is attributed to biogenic and volcanic-geothermal source. Geochemical characteristics of the volcanic-geothermal gases (including CO2 and He) of the northern GYR indicate their significant mantle-derived affinities. Combined with previous petrogeochemical and geophysical data, our He-C isotope modeling calculation results show that (1) excess mantle-derived 3He reflects degassing of volatiles related with partial melts from enriched mantle wedge induced by northward subduction of the Indian lithosphere, and (2) the crust-mantle interaction can provide continuous heat and materials for the overlying volcanic-geothermal system, in which magma-derived volatiles are inferred to experience significant crustal contamination during their migration to the surface.

  8. Organic matter degradation in Lake Baikal - a sediment trap study

    DEFF Research Database (Denmark)

    Schubert, Carsten J.; Niggemann, Jutta; Lomstein, Bente Aagaard

    Lake Baikal offers a unique opportunity to study water column processes in a freshwater system with conditions similar to oceanic systems, e. g. great water depth and oxygenated water column. Investigations on sediment trap material provide information on the early stages of organic matter...... degradation in the water column. Sediment trap material from 18 different water depths has been analysed for bulk organic matter parameters, including organic carbon and nitrogen isotopic compositions, chlorin concentrations, and Chlorin Indices [1]. Detailed studies focused on the concentration...... and composition of amino acids and fatty acids. The extent of organic matter degradation in the water column of Lake Baikal is reflected in the fluxes of total organic carbon, chlorins, amino acids, and fatty acids at different water depths. In line with earlier studies in marine systems, the labile compounds...

  9. Diversity of Bacterial Photosymbionts in Lubomirskiidae Sponges from Lake Baikal


    Kulakova, Nina V.; Denikina, Natalia N.; Belikov, Sergei I.


    Sponges are permanent benthos residents which establish complex associations with a variety of microorganisms that raise interest in the nature of sponge-symbionts interactions. A molecular approach, based on the identification of the 16S rRNA and ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit genes, was applied to investigate diversity and phylogeny of bacterial phototrophs associated with four species of Lubomirskiidae in Lake Baikal. The phylogeny inferred from both genes sh...


    Directory of Open Access Journals (Sweden)

    Konstantin Lidin


    Full Text Available Walk 14 DOWN THE CIRCUM-BAIKAL RAILWAYSketch Redesign of the Sverdlovsky Market in Irkutsk "Glazkovo Shopping Arcade"Church of Sts. Apostles Peter and Pavel in Irkutsk – a Rare Monument of Architecture in PribaikalieRedesign of the Church of Sts. Peter and Pavel in IrkutskSt. Nicholas and St. Innokenty Temple in IrkutskRedesign of St. Nicholas and St. Innokenty ChurchRailway Station BuildingProjects of the Railway Station and the Hotel Facilities

  11. Haemoragisk Rift Valley Fever

    DEFF Research Database (Denmark)

    Fabiansen, Christian; Thybo, Søren


    A case of fatal hemorrhagic Rift Valley fever during an epidemic in Kenya's North Eastern Province in January 2007 is described.......A case of fatal hemorrhagic Rift Valley fever during an epidemic in Kenya's North Eastern Province in January 2007 is described....

  12. Dinoflagellates associated with freshwater sponges from the ancient lake baikal. (United States)

    Annenkova, Natalia V; Lavrov, Dennis V; Belikov, Sergey I


    Dinoflagellates are a diverse group of protists that are common in both marine and freshwater environments. While the biology of marine dinoflagellates has been the focus of several recent studies, their freshwater relatives remain little-investigated. In the present study we explore the diversity of dinoflagellates in Lake Baikal by identifying and analyzing dinoflagellate sequences for 18S rDNA and ITS-2 from total DNA extracted from three species of endemic Baikalian sponges (Baikalospongia intermedia,Baikalospongia rectaand Lubomirskia incrustans). Phylogenetic analyses of these sequences revealed extensive dinoflagellate diversity in Lake Baikal. We found two groups of sequences clustering within the order Suessiales, known for its symbiotic relationships with various invertebrates. Thus they may be regarded as potential symbionts of Baikalian sponges. In addition,Gyrodinium helveticum, representatives from the genus Gymnodinium, dinoflagellates close to the family Pfiesteriaceae, and a few dinoflagellates without definite affiliation were detected. No pronounced difference in the distribution of dinoflagellates among the studied sponges was found, except for the absence of the Piscinoodinium-like dinoflagellates inL. incrustans. To the best of our knowledge, this is the first study of the diversity of dinoflagellates in freshwater sponges, the first systematic investigation of dinoflagellate molecular diversity in Lake Baikal and the first finding of members of the order Suessiales as symbionts of freshwater invertebrates. Copyright © 2010 Elsevier GmbH. All rights reserved.

  13. Seismic structure of the central US crust and upper mantle: Uniqueness of the Reelfoot Rift (United States)

    Pollitz, Fred; Mooney, Walter D.


    Using seismic surface waves recorded with Earthscope's Transportable Array, we apply surface wave imaging to determine 3D seismic velocity in the crust and uppermost mantle. Our images span several Proterozoic and early Cambrian rift zones (Mid-Continent Rift, Rough Creek Graben—Rome trough, Birmingham trough, Southern Oklahoma Aulacogen, and Reelfoot Rift). While ancient rifts are generally associated with low crustal velocity because of the presence of thick sedimentary sequences, the Reelfoot Rift is unique in its association with low mantle seismic velocity. Its mantle low-velocity zone (LVZ) is exceptionally pronounced and extends down to at least 200 km depth. This LVZ is of variable width, being relatively narrow (∼50km">∼50km wide) within the northern Reelfoot Rift, which hosts the New Madrid Seismic Zone (NMSZ). We hypothesize that this mantle volume is weaker than its surroundings and that the Reelfoot Rift consequently has relatively low elastic plate thickness, which would tend to concentrate tectonic stress within this zone. No other intraplate ancient rift zone is known to be associated with such a deep mantle low-velocity anomaly, which suggests that the NMSZ is more susceptible to external stress perturbations than other ancient rift zones.

  14. Structural inheritance, segmentation, and rift localization in the Gulf of Aden oblique rift (United States)

    Bellahsen, Nicolas; Leroy, Sylvie; Autin, Julia; d'Acremont, Elia; Razin, Philippe; Husson, Laurent; Pik, Raphael; Watremez, Louise; Baurion, Celine; Beslier, Marie-Odile; Khanbari, Khaled; Ahmed, Abdulhakim


    The structural evolution of the Gulf of Aden passive margins was controlled by its oblique divergence kinematics, inherited structures, and the Afar hot spot. The rifting between Arabia and Somalia started at 35 Ma just before the hot spot paroxysm (at 30Ma) and lasted until 18Ma, when oceanic spreading started. Fieldwork suggests that rift parallel normal faults initiated in the (future) distal margins, after a first stage of distributed rifting, and witness the rift localization, as confirmed by 4-layer analogue models. These faults arise either from crust or lithosphere scale buoyancy forces that are strongly controlled by the mantle temperature under the influence of the Afar hot spot. This implies a transition from a distributed mode to a localized one, sharper, both in space and time, in the West (close to the hot spot) than in the East (far away from the hot spot). In this framework, first order transform F.Z. are here (re-) defined by the fact that they deform continental crust. In the Gulf of Aden, as well as in other continental margins, it appears that these F.Z. are often, if not always, located at continental transfer or "transform" fault zones. Our detailed field-study of an offshore transfer fault zone in the southeastern Gulf of Aden (Socotra Island) shows that these structures are long-lived since early rifting until post rift times. During the early rifting, they are inherited structures reactivated as oblique normal faults before accommodating strike-slip motion. During the Ocean-Continent Transition (OCT) formation ("post syn-rift" times), a significant uplift occurred in the transfer fault zone footwall as shown by stratigraphic and LT thermochronology data. Second order transform F.Z. are defined as deforming only the OCT, thus initiated at the moment of its formation. In the western Gulf of Aden, the hot spot provoked a rift localization strongly oblique to the divergence and, as a consequence, several second order transform F.Z. formed (as

  15. Acoustic Search for High Energy Neutrinos in Lake Baikal: Status and Perspectives

    Directory of Open Access Journals (Sweden)

    Budnev N.M.


    Full Text Available The status and perspectives of the feasibility study to detect high energy cosmic neutrinos acoustically in Lake Baikal is presented. The concept of on acoustic array as a part of the Baikal Gigaton Volume Neutrino Telescope GVD based on results of simulation and background measurements is described.

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

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


    With several rift segments at different stages of the rifting cycle, and the last orogenic episode more than 500 Mya, the young (Ngorongoro caldera appears to be physically cut off from the magma beneath the main part of the rift zone by a relatively thin (< 10 km) wide zone of higher shear wave speeds that lies along the western edge of the fault-bounded rift. The narrow ridge of higher velocity lower crustal material may be a consequence of flexural uplift of the rift flank in response to stretching of strong, cratonic lithosphere.

  17. The mesoproterozoic midcontinent rift system, Lake Superior region, USA (United States)

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


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

  18. Crustal-scale recycling in caldera complexes and rift zones along the Yellowstone hotspot track: O and Hf isotopic evidence in diverse zircons from voluminous rhyolites of the Picabo volcanic field, Idaho (United States)

    Drew, Dana L.; Bindeman, Ilya N.; Watts, Kathryn E.; Schmitt, Axel K.; Fu, Bin; McCurry, Michael


    followed by rapid batch assembly prior to eruption. However, due to the greater abundance of low-δ18O rhyolites at Picabo, the eruptive framework may reflect an intertwined history of caldera collapse and coeval Basin and Range rifting and hydrothermal alteration. We speculate that the source rocks with pre-existing low-δ18O alteration may be related to: (1) deeply buried and unexposed older deposits of Picabo-age or Twin Falls-age low-δ18O volcanics; and/or (2) regionally-abundant late Eocene Challis volcanics, which were hydrothermally altered near the surface prior to or during peak Picabo magmatism. Basin and Range extension, specifically the formation of metamorphic core complexes exposed in the region, could have facilitated the generation of low-δ18O magmas by exhuming heated rocks and creating the large water-rock ratios necessary for shallow hydrothermal alteration of tectonically (rift zones) and volcanically (calderas) buried volcanic rocks. These interpretations highlight the major processes by which supereruptive volumes of magma are generated in the SRP, mechanisms applicable to producing rhyolites worldwide that are facilitated by plume driven volcanism and extensional tectonics.

  19. The prototyping/early construction phase of the BAIKAL-GVD project

    Energy Technology Data Exchange (ETDEWEB)

    Avrorin, A.D.; Avrorin, A.V.; Aynutdinov, V.M. [Institute for Nuclear Research, 60th October Anniversary pr. 7a, Moscow 117312 (Russian Federation); Bannasch, R. [EvoLogics GmbH, Berlin (Germany); Belolaptikov, I.A. [Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Bogorodsky, D.Yu. [Irkutsk State University, Irkutsk 664003 (Russian Federation); Brudanin, V.B. [Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Budnev, N.M. [Irkutsk State University, Irkutsk 664003 (Russian Federation); Danilchenko, I.A.; Domogatsky, G.V.; Doroshenko, A.A. [Institute for Nuclear Research, 60th October Anniversary pr. 7a, Moscow 117312 (Russian Federation); Dyachok, A.N. [Irkutsk State University, Irkutsk 664003 (Russian Federation); Dzhilkibaev, Zh-A.M., E-mail: [Institute for Nuclear Research, 60th October Anniversary pr. 7a, Moscow 117312 (Russian Federation); Fialkovsky, S.V. [Nizhni Novgorod State Technical University, Nizhni Novgorod 603950 (Russian Federation); Gafarov, A.R. [Irkutsk State University, Irkutsk 664003 (Russian Federation); Gaponenko, O.N.; Golubkov, K.V. [Institute for Nuclear Research, 60th October Anniversary pr. 7a, Moscow 117312 (Russian Federation); Gress, T.I. [Irkutsk State University, Irkutsk 664003 (Russian Federation); Honz, Z. [Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Kebkal, K.G. [EvoLogics GmbH, Berlin (Germany); and others


    The prototyping phase of the BAIKAL-GVD project has been started in April 2011 with the deployment of a three string engineering array which comprises all basic elements and systems of the Gigaton Volume Detector (GVD) in Lake Baikal. In April 2012 the version of engineering array which comprises the first full-scale string of the GVD demonstration cluster had been deployed and operated during 2012. The first stage of the GVD-cluster which consists of three strings was deployed in April 2013. We review the prototyping phase of the BAIKAL-GVD project and describe the configuration and design of the 2013 engineering array.

  20. Argon systematics of neutron irradiated submarine basalt glasses from the deep south rift zone of Loihi seamount and the {sup 40}Ar/{sup 36}Ar ratio of the Hawaiian plume source

    Energy Technology Data Exchange (ETDEWEB)

    Trieloff, M.; Falter, M. [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Jessberger, E.K. [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany)]|[Muenster Univ. (Germany). Inst. fuer Planetologie


    Submarine basalt glasses from Loihi seamount dredged at the southern rift zone between 3 and 5 km depth were studied. These glasses contain neon with the highest {sup 20}Ne/{sup 22}Ne ratios measured so far in submarine volcanics and constrain a well defined correlation line in a Ne-3-isotope plot (Valbracht et al., 1997). Within this study that focussed on argon isotopes an increased resolution regarding temperature and crushing steps was used: High {sup 40}Ar/{sup 36}Ar ratios at intermediate temperatures and in several crushing steps were measured which are related to argon from vesicle populations containing the most pristine mantle signature. This argon is highly improbable to be related to olivine phenocrysts and a possible contamination by MORB type noble gases. Our best constraint on the argon isotopic composition of the Loihi glasses is {sup 40}Ar/{sup 36}Ar=6590{+-}840, providing a lower limit of >5750 for the Hawaiian lower mantle source, further attesting its partially degassed nature concerning primordial noble gases. The argon distribution in the investigated Loihi glasses shows characteristic features very similar to MORB glasses. The isotopic composition of vesicle argon released by crushing covers the complete range between the atmospheric and the mantle endmember. In low vesicularity glasses mantle argon shows a nearly perfect correlation with the glass dissolved, neutron induced argon isotopes in the course of stepheating, while in glasses of higher vesicularity mantle argon partitioned into the vesicles. This is independently confirmed by the comparison of the argon yield by crushing and heating. On the other hand, the stepheating release pattern of the atmospheric component does hardly correlate with glass dissolved argon, independent on vesicularity. A significant fraction of the atmospheric contaminant is related to vesicles and pyroxene microlites, and is moreover associated with microdefects or, alternatively, is inhomogeneously distributed

  1. The role of pre-existing Precambrian lithospheric structures in the development of Rukwa Rift basin in the Western Branch of East African Rift System, SW Tanzania (United States)

    Lemna, Obeid; Stephenson, Randell; Cornwell, David


    Continental rifts are inter-connected groups of half-grabens bordered by steep escarpments formed by border fault displacement. They often follow the pre-existing zones of weakness and/or tectonic boundaries diverging around the craton. In some areas it has been observed that border fault segmentation and rift basin asymmetry shows little or no correlation with basement structures, raising the possibility that continental rift development may in some cases at least be linked to deeper-seated lithospheric structures. The influence of pre-existing/inherited lithospheric structure remains a question for study in unravelling the evolution of continental rifts. The Rukwa Rift Basin is a northwest trending half-graben developed along the trend of the Paleoproterozoic Ubendian belt in southwest Tanzania. This belt is a linear, NW-SE trending orogenic belt in western Tanzania. It is part of a larger Paleoproterozoic orogenic belt, developed around the west and south-western margin of the Archaean Tanzanian craton. This belt is characterised by a consistent NW-trending fabric and by the presence of large shear zones that persist along the whole of the belt. As such, it offers the opportunity to examine the role of pre-existing Precambrian structures on the development of the Rukwa Rift. Digital Elevation Models (DEMs) extracted from Shuttle Radar Topography Mission (SRTM) and aeromagnetic data are used in this study. The results suggest that the orientation and geometry of Rukwa Rift basin has been influenced by the structural grains of the Paleoproterozoic Ubendian belt. Pre-existing structures within the Paleoproterozoic terrains facilitated the strain localisation within border faults that exploited the existence of inherited lithospheric heterogeneity. The southern border fault of the rift has been influenced by the NW-trending Mugese shear zone (MSZ). This shear zone has prominent NW-trending pre-existing structures in the form of transcurrent shear fabric and zones of

  2. The geology and geophysics of the Oslo rift (United States)

    Ruder, M. E.


    The regional geology and geophysical characteristics of the Oslo graben are reviewed. The graben is part of a Permian age failed continental rift. Alkali olivine, tholefitic, and monzonitic intrusives as well as basaltic lavas outline the extent of the graben. Geophysical evidence indicates that rifting activity covered a much greater area in Skagerrak Sea as well as the Paleozoic time, possibly including the northern Skagerrak Sea as well as the Oslo graben itself. Much of the surficial geologic characteristics in the southern part of the rift have since been eroded or covered by sedimentation. Geophysical data reveal a gravity maximum along the strike of the Oslo graben, local emplacements of magnetic material throughout the Skagerrak and the graben, and a slight mantle upward beneath the rift zone. Petrologic and geophysical maps which depict regional structure are included in the text. An extensive bibliography of pertinent literature published in English between 1960 and 1980 is also provided.

  3. Long-Term and Ontogenetic Patterns of Heavy Metal Contamination in Lake Baikal Seals (Pusa sibirica). (United States)

    Ozersky, Ted; Pastukhov, Mikhail V; Poste, Amanda E; Deng, Xiu Y; Moore, Marianne V


    Little is known about the history of heavy metal pollution of Russia's Lake Baikal, one of the world's largest lakes and a home to numerous endemic species, including the Baikal Seal, Pusa sibirica. We investigated the history of heavy metal (V, Cu, Zn, Cd, Hg, Tl, Pb, U) pollution in Lake Baikal seals over the past 8 decades. C and N stable isotope analysis (SIA) and laser-ablation ICP-MS of seal teeth were used to examine changes in feeding ecology, heavy metal levels associated with life history events and long-term variation in metal exposure. SIA did not suggest large changes in the feeding ecology of Baikal seals over the past 80 years. LA-ICP-MS analyses revealed element-specific ontogenetic variability in metal concentrations, likely related to maternal transfer, changes in food sources and starvation. Hg and Cd levels in seals varied significantly across the time series, with concentrations peaking in the 1960s - 1970s but then declining to contemporary levels similar to those observed in the 1930s and 1940s. Trends in atmospheric emissions of Hg suggest that local sources as well as emissions from eastern Russia and Europe may be important contributors of Hg to Lake Baikal and that, despite the size of Lake Baikal, its food web appears to respond rapidly to changing inputs of contaminants.

  4. Rift-drift transition in the Dangerous Grounds, South China Sea (United States)

    Peng, Xi; Shen, Chuanbo; Mei, Lianfu; Zhao, Zhigang; Xie, Xiaojun


    The South China Sea (SCS) has a long record of rifting before and after subsequent seafloor spreading, affecting the wide continent of the Dangerous Grounds, and its scissor-shape opening manner results in the rifting structures that vary along this margin. Some 2000 km of regional multichannel seismic data combined with borehole and dredge data are interpreted to analyze the multistage rifting process, structural architecture and dynamic evolution across the entire Dangerous Grounds. Key sequence boundaries above the Cenozoic basement are identified and classified into the breakup unconformity and the rift end unconformity, which consist of the rift-related unconformities. Reflector T70 in the east of the Dangerous Grounds represents the breakup unconformity, which is likely corresponding to the spreading of the East Subbasin. T60 formed on the top of carbonate platform is time equivalent to the spreading of the Southwest Subbasin, marking the breakup unconformity of the central Dangerous Grounds. The termination of the spreading of the SCS is manifested by the rift end unconformity of T50 in the southwest and the final rift occurring in the northwest of the Dangerous Grounds is postponed to the rift end unconformity of T40. On the basis of the stratigraphic and structural analysis, distinct segments in the structural architecture of the syn-rift units and the ages of rift-drift transition show obvious change from the proximal zone to the distal zone. Three domains, which are the Reed Bank-Palawan Rift domain, the Dangerous Grounds Central Detachment domain and Nam Con Son Exhumation domain, reflect the propagation of the margin rifting developed initially by grabens formed by high angle faults, then large half-grabens controlled by listric faults and detachments and finally rotated fault blocks in the hyper-extended upper crust associated with missing lower crust or exhumed mantle revealing a migration and stepwise rifting process in the south margin of the SCS.

  5. Contrasted continental rifting via plume-craton interaction: Applications to Central East African Rift

    Directory of Open Access Journals (Sweden)

    Alexander Koptev


    Full Text Available The East African Rift system (EARS provides a unique system with the juxtaposition of two contrasting yet simultaneously formed rift branches, the eastern, magma-rich, and the western, magma-poor, on either sides of the old thick Tanzanian craton embedded in a younger lithosphere. Data on the pre-rift, syn-rift and post-rift far-field volcanic and tectonic activity show that the EARS formed in the context of the interaction between a deep mantle plume and a horizontally and vertically heterogeneous lithosphere under far-field tectonic extension. We bring quantitative insights into this evolution by implementing high-resolution 3D thermo-mechanical numerical deformation models of a lithosphere of realistic rheology. The models focus on the central part of the EARS. We explore scenarios of plume-lithosphere interaction with plumes of various size and initial position rising beneath a tectonically pre-stretched lithosphere. We test the impact of the inherited rheological discontinuities (suture zones along the craton borders, of the rheological structure, of lithosphere plate thickness variations, and of physical and mechanical contrasts between the craton and the embedding lithosphere. Our experiments indicate that the ascending plume material is deflected by the cratonic keel and preferentially channeled along one of its sides, leading to the formation of a large rift zone along the eastern side of the craton, with significant magmatic activity and substantial melt amount derived from the mantle plume material. We show that the observed asymmetry of the central EARS, with coeval amagmatic (western and magmatic (eastern branches, can be explained by the splitting of warm material rising from a broad plume head whose initial position is slightly shifted to the eastern side of the craton. In that case, neither a mechanical weakness of the contact between the craton and the embedding lithosphere nor the presence of second plume are required to

  6. Consequences of Rift Propagation for Spreading in Thick Oceanic Crust in Iceland (United States)

    Karson, J. A.


    Iceland has long been considered a natural laboratory for processes related to seafloor spreading, including propagating rifts, migrating transforms and rotating microplates. The thick, hot, weak crust and subaerial processes of Iceland result in variations on the themes developed along more typical parts of the global MOR system. Compared to most other parts of the MOR, Icelandic rift zones and transform faults are wider and more complex. Rift zones are defined by overlapping arrays of volcanic/tectonic spreading segments as much as 50 km wide. The most active rift zones propagate N and S away from the Iceland hot spot causing migration of transform faults. A trail of crust deformed by bookshelf faulting forms in their wakes. Dead or dying transform strands are truncated along pseudofaults that define propagation rates close to the full spreading rate of ~20 mm/yr. Pseudofaults are blurred by spreading across wide rift zones and laterally extensive subaerial lava flows. Propagation, with decreasing spreading toward the propagator tips causes rotation of crustal blocks on both sides of the active rift zones. The blocks deform internally by the widespread reactivation of spreading-related faults and zones of weakness along dike margins. The sense of slip on these rift-parallel strike-slip faults is inconsistent with transform-fault deformation. These various deformation features as well as subaxial subsidence that accommodate the thickening of the volcanic upper crustal units are probably confined to the brittle, seismogenic, upper 10 km of the crust. At least beneath the active rift zones, the upper crust is probably decoupled from hot, mechanically weak middle and lower gabbroic crust resulting in a broad plate boundary zone between the diverging lithosphere plates. Similar processes may occur at other types of propagating spreading centers and magmatic rifts.

  7. Search for acoustic effects from extensive atmospheric showers in Baikal

    International Nuclear Information System (INIS)

    Lyashuk, V.I.; Novikov, E.G.


    The search for acoustic effects from showers by means of hydrophones was realized in a trigger scheme of recording sound files when atmospheric showers were detected by the scintillation installation. A method of peaks and noncoincidences was proposed to search for weak sound sources. The algorithm of the method is amplitude independent. Processing of a great body of data (obtained for different geometries, different noise background during three expeditions to Baikal) allows one to indicate the closely analogous phenomena at the instant of time of expected sound signals from showers. In spite of their low power, the effects appear in the different hydrophones and have similar time distributions, which points to the detection of the acoustic effects

  8. Diversity of Bacterial Photosymbionts in Lubomirskiidae Sponges from Lake Baikal

    Directory of Open Access Journals (Sweden)

    Nina V. Kulakova


    Full Text Available Sponges are permanent benthos residents which establish complex associations with a variety of microorganisms that raise interest in the nature of sponge-symbionts interactions. A molecular approach, based on the identification of the 16S rRNA and ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit genes, was applied to investigate diversity and phylogeny of bacterial phototrophs associated with four species of Lubomirskiidae in Lake Baikal. The phylogeny inferred from both genes showed three main clusters of Synechococcus associated with Baikalian sponges. One of the clusters belonged to the cosmopolitan Synechococcus rubescens group and the two other were not related to any of the assigned phylogenetic groups but placed as sister clusters to S. rubescens. These results expanded the understanding of freshwater sponge-associated photoautotroph diversity and suggested that the three phylogenetic groups of Synechococcus are common photosynthetic symbionts in Lubomirskiidae sponges.

  9. Dike intrusions during rifting episodes obey scaling relationships similar to earthquakes (United States)

    L., Passarelli; E., Rivalta; A., Shuler


    As continental rifts evolve towards mid-ocean ridges, strain is accommodated by repeated episodes of faulting and magmatism. Discrete rifting episodes have been observed along two subaerial divergent plate boundaries, the Krafla segment of the Northern Volcanic Rift Zone in Iceland and the Manda-Hararo segment of the Red Sea Rift in Ethiopia. In both cases, the initial and largest dike intrusion was followed by a series of smaller intrusions. By performing a statistical analysis of these rifting episodes, we demonstrate that dike intrusions obey scaling relationships similar to earthquakes. We find that the dimensions of dike intrusions obey a power law analogous to the Gutenberg-Richter relation, and the long-term release of geodetic moment is governed by a relationship consistent with the Omori law. Due to the effects of magma supply, the timing of secondary dike intrusions differs from that of the aftershocks. This work provides evidence of self-similarity in the rifting process. PMID:24469260

  10. Kinematics of the South Atlantic rift (United States)

    Heine, C.; Zoethout, J.; Müller, R. D.


    The South Atlantic rift basin evolved as a branch of a large Jurassic-Cretaceous intraplate rift zone between the African and South American plates during the final break-up of western Gondwana. While the relative motions between South America and Africa for post-break-up times are well resolved, many issues pertaining to the fit reconstruction and particularly the relation between kinematics and lithosphere dynamics during pre-break-up remain unclear in currently published plate models. We have compiled and assimilated data from these intraplated rifts and constructed a revised plate kinematic model for the pre-break-up evolution of the South Atlantic. Based on structural restoration of the conjugate South Atlantic margins and intracontinental rift basins in Africa and South America, we achieve a tight-fit reconstruction which eliminates the need for previously inferred large intracontinental shear zones, in particular in Patagonian South America. By quantitatively accounting for crustal deformation in the Central and West African Rift Zones, we have been able to indirectly construct the kinematic history of the pre-break-up evolution of the conjugate west African-Brazilian margins. Our model suggests a causal link between changes in extension direction and velocity during continental extension and the generation of marginal structures such as the enigmatic pre-salt sag basin and the São Paulo High. We model an initial E-W-directed extension between South America and Africa (fixed in present-day position) at very low extensional velocities from 140 Ma until late Hauterivian times (≈126 Ma) when rift activity along in the equatorial Atlantic domain started to increase significantly. During this initial ≈14 Myr-long stretching episode the pre-salt basin width on the conjugate Brazilian and west African margins is generated. An intermediate stage between ≈126 Ma and base Aptian is characterised by strain localisation, rapid lithospheric weakening in the

  11. Rift Valley fever vaccines


    Ikegami, Tetsuro; Makino, Shinji


    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 human...

  12. Thermal Preference Ranges Correlate with Stable Signals of Universal Stress Markers in Lake Baikal Endemic and Holarctic Amphipods.

    Directory of Open Access Journals (Sweden)

    Denis Axenov-Gribanov

    Full Text Available Temperature is the most pervasive abiotic environmental factor for aquatic organisms. Fluctuations in temperature range lead to changes in metabolic performance. Here, we aimed to identify whether surpassing the thermal preference zones is correlated with shifts in universal cellular stress markers of protein integrity, responses to oxidative stress and lactate content, as indicators of anaerobic metabolism. Exposure of the Lake Baikal endemic amphipod species Eulimnogammarus verrucosus (Gerstfeldt, 1858, Ommatogammarus flavus (Dybowski, 1874 and of the Holarctic amphipod Gammarus lacustris Sars 1863 (Amphipoda, Crustacea to increasing temperatures resulted in elevated heat shock protein 70 (Hsp70 and lactate content, elevated antioxidant enzyme activities (i.e., catalase and peroxidase, and reduced lactate dehydrogenase and glutathione S-transferase activities. Thus, the zone of stability (absence of any significant changes of the studied molecular and biochemical markers correlated with the behaviorally preferred temperatures. We conclude that the thermal behavioral responses of the studied amphipods are directly related to metabolic processes at the cellular level. Thus, the determined thermal ranges may possibly correspond to the thermal optima. This relationship between species-specific behavioral reactions and stress response metabolism may have significant ecological consequences that result in a thermal zone-specific distribution (i.e., depths, feed spectrum, etc. of species. As a consequence, by separating species with different temperature preferences, interspecific competition is reduced, which, in turn, increases a species' Darwinian fitness in its environment.

  13. Tracing the sources of PCDD/Fs and PCBs in Lake Baikal

    Energy Technology Data Exchange (ETDEWEB)

    Mamontov, A.A.; Mamontova, E.A.; Tarasova, E.N.; McLachlan, M.S.


    Lake Baikal is a unique freshwater ecosystem that has been declared a UNESCO World Heritage Site. It contains high levels of PCBs, and Baikal seal were recently found to have PCDD/F concentrations comparable to those in the Baltic Sea. In this work fish and soil were analyzed to trace the sources of these compounds to the lake. The fish samples indicated that the PCDD/F and PCB contamination of Lake Baikal does not originate from background inputs and that the contamination increases from north to south. The soil inventory was determined at 34 sites around Lake Baikal and in the Angara River valley. For the PCDD/Fs and most PCBs, the soil inventory is a good approximation of the cumulative atmospheric deposition. It varied over a factor of 1,000, with the highest levels in Usol'ye Sibirskoe, a city 110 km north of the southwestern tip of the lake in the highly industrialized Angara River valley, and the lowest values in the pristine areas to the northeast of the lake. A continuous decrease in the soil inventory was observed moving from Usol'ye S. up the Angara River valley to Lake Baikal and from there northeastward along the lake.

  14. Lithospheric drip magmatism and magma-assisted rifting: a case study in the Western Rift, East Africa (United States)

    Pitcavage, E.; Furman, T.; Nelson, W. R.


    The East African Rift System (EARS) is earth's largest continental divergent boundary and an unparalleled natural laboratory for understanding magmatism related to successful continental rifting. Classic views of continental rifting suggest that faulting and extension are facilitated by ascending magmas that weaken the lithosphere thermally and structurally within basin-bounding accommodation zones. In the EARS Western Rift (WR), many volcanic fields are not aligned along rift-bounding faults, and magma compositions lack evidence for asthenospheric inputs expected along lithosphere-penetrating fault systems. We note that compositional input from the Cenozoic Afar mantle plume is not recognized convincingly in WR mafic alkaline lavas1. Rather, magma compositions demonstrate significant input from anciently metasomatized sub-continental lithospheric mantle (SCLM). Destabilization and foundering of metasomatized SCLM has an increasingly recognized role in continental magmatism worldwide, producing volatile-rich, alkaline volcanics when drips of foundered SCLM devolatilize and melt on descent. This magmatism can lead to faulting: the lithospheric thinning that results from this process may play a role in physical aspects of rifting, contrasting with faulting facilitated by asthenospheric melts. Geochemical and geophysical evidence indicates that drip magmatism has occurred in several EARS provinces, including Turkana, Chyulu Hills, and in Afar2 where it is geographically coincident with successful rifting. We present bulk geochemical data that suggest drip melting of metasomatized SCLM is occurring in several WR volcanic fields. We focus on Bufumbira (Uganda), where mafic lavas are derived from garnet+phlogopite+amphibole+zircon-bearing pyroxenite, indicating a deep metasomatized SCLM source. Isotopic and trace element data suggest that extent of melting increased with depth of melting, a signature of lithospheric drip. We propose that drip magmatism is an important

  15. Along-axis transition between narrow and wide rifts: Insights from 3D numerical experiments (United States)

    Koptev, Alexander; Calais, Eric; Burov, Evgueni; Leroy, Sylvie; Gerya, Taras


    Based on performed high-resolution rheologically consistent three-dimensional thermo-mechanical numerical models, we show that there is a significant difference in the influence of the rheological profile on rifting style in the case of dominant active (plume-activated) rifting compared to dominant passive (far-field tectonic stresses) rifting. Narrow rifting, conventionally attributed to cold strong lithosphere in passive rifting mode, may develop in weak hot ultra-stretched lithosphere during active rifting, after plume impingement on a tectonically pre-stressed lithosphere. In that case, initially ultra-wide small-amplitude rift patterns focus, in a few Myr, in large-scale faults that form a narrow rift. Also, wide rifting may develop during ultra-slow spreading of strong lithosphere, and "switch" to the narrow rifting upon plume impingement. For further understanding the mechanisms behind the interactions between the mantle plume and far-field stresses in case of realistic horizontally heterogeneous lithosphere, we have tested our models on the case of the central East African Rift system (EARS). The EARS south of the Ethiopian Rift Valley bifurcates in two branches (eastern, magma-rich and western, magma-poor) surrounding the strong Tanzanian craton. Broad zones of low seismic velocity observed throughout the upper mantle beneath the central part of the EARS are consistent with the spreading of a deep mantle plume. The extensional features and topographic expression of the Eastern rift varies significantly north-southward: in northern Kenya the area of deformation is very wide (some 150-250 km in E-W direction), to the south the rift narrows to 60-70 km, yet further to the south this localized deformation widens again. Here we investigate this transition between localized and wide rifting using thermo-mechanical numerical modeling that couples, in a dynamic sense, the rise of the upper mantle material with the deformation of the African lithosphere below the

  16. Initiation and development of the Kivu rift segment in Central Africa by reactivating un-favorably oriented structural weaknesses (United States)

    Delvaux, Damien; Smets, Benoît


    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

  17. Paleomagnetic evidence for vertical-axis rotations of crustal blocks in the Woodlark Rift, SE Papua New Guinea: Miocene to present-day kinematics in one of the world's most rapidly extending plate boundary zones (United States)

    Cairns, Elizabeth A.; Little, Timothy A.; Turner, Gillian M.; Wallace, Laura M.; Ellis, Susan


    The continental Woodlark Rift, in SE Papua New Guinea lies west of a propagating oceanic spreading center in the Woodlark Basin and is currently one of few places on Earth where active continental breakup is thought to be occurring. Here north-south extension is localized on a few major normal faults. We determined characteristic remanent magnetization (ChRM) components from demagnetization profiles of >300 individual specimens. From these, 157 components contribute to paleomagnetic directions for six formations. We compare Early Miocene (˜20 Ma) to Late Pliocene (3.0 ± 0.5) ChRM mean directions, at four localities, with contemporaneous expected field directions corresponding to the Australian Plate. Time-varying finite rotations from Cape Vogel Peninsula (28-12°) suggest anticlockwise rotation had begun by ˜15 Ma. This rotation may have been accompanied by rifting, ˜7 Ma earlier than previously inferred. Furthermore, that early extension may have occurred south of the present rift, and that deformation later migrated north of the Peninsula. Pliocene vertical-axis rotations are consistent with GPS-determined plate motions, suggesting that contemporary rift kinematics were established by ˜3 Ma. Finite anticlockwise rotation (10.1 ± 7.6°) in the Amphlett Islands is accordant with seafloor spreading in the Woodlark Basin, suggesting this locality has seen the full Woodlark plate motion since 3 Ma. Clockwise rotation of the Goodenough Bay Block (-6.5 ± 11.2°) since the Late Miocene has accomplished transfer of deformation between major extensional corridors, and an especially rapid local rotation (-16.3 ± 9.5°) in NW Normanby Island may suggest an incipient dextral transfer fault.

  18. Overview of geology and tectonic evolution of the Baikal-Tuva area. (United States)

    Gladkochub, Dmitry; Donskaya, Tatiana


    This chapter provides the results of geological investigations of the main tectonic units of the Baikal-Tuva region (southwestern part of Siberia) during the last decades: the ancient Siberian craton and adjacent areas of the Central Asian Orogenic belt. In the framework of these main units we describe small-scale blocks (terranes) with focus on details of their inner structure and evolution through time. As well as describing the geology and tectonics of the area studied, we give an overview of underwater sediments, neotectonics, and some phenomena of history and development of the Baikal, Khubsugul, Chargytai, and Tore-Chol Lakes basins of the Baikal-Tuva region. It is suggested that these lakes' evolution was controlled by neotectonic processes, modern seismic activity, and global climate changes.

  19. The isolation and characterization of actinobacteria from dominant benthic macroinvertebrates endemic to Lake Baikal. (United States)

    Axenov-Gribanov, Denis; Rebets, Yuriy; Tokovenko, Bogdan; Voytsekhovskaya, Irina; Timofeyev, Maxim; Luzhetskyy, Andriy


    The high demand for new antibacterials fosters the isolation of new biologically active compounds producing actinobacteria. Here, we report the isolation and initial characterization of cultured actinobacteria from dominant benthic organisms' communities of Lake Baikal. Twenty-five distinct strains were obtained from 5 species of Baikal endemic macroinvertebrates of amphipods, freshwater sponges, turbellaria worms, and insects (caddisfly larvae). The 16S ribosomal RNA (rRNA)-based phylogenic analysis of obtained strains showed their affiliation to Streptomyces, Nocardia, Pseudonocardia, Micromonospora, Aeromicrobium, and Agromyces genera, revealing the diversity of actinobacteria associated with the benthic organisms of Lake Baikal. The biological activity assays showed that 24 out of 25 strains are producing compounds active against at least one of the test cultures used, including Gram-negative bacteria and Candida albicans. Complete dereplication of secondary metabolite profiles of two isolated strains led to identification of only few known compounds, while the majority of detected metabolites are not listed in existing antibiotic databases.

  20. Uranium distribution in Baikal sediments using SSNTD method for paleoclimate reconstruction

    CERN Document Server

    Zhmodik, S M; Nemirovskaya, N A; Zhatnuev, N S


    First data on local distribution of uranium in the core of Lake Baikal floor sediments (Academician ridge, VER-95-2, St 3 BC, 53 deg. 113'12'N/108 deg. 25'01'E) are presented in this paper. They have been obtained using (n,f)-radiography. Various forms of U-occurrence in floor sediments are shown, i.e. evenly disseminated, associated with clayey and diatomaceous components; micro- and macroinclusions of uranium bearing minerals - microlocations with uranium content 10-50 times higher than U-concentrations associated with clayey and diatomaceous components. Relative and absolute U-concentration can be determined for every mineral. Signs of various order periodicity of U-distribution in the core of Lake Baikal floor sediments have been found. Using (n,f)-radiography method of the study of Baikal floor sediment permits gathering of new information that can be used at paleoclimate reconstruction.

  1. Next-generation Geotectonic Data Analysis: Using pyGPlates to quantify Rift Obliquity during Supercontinent Dispersal (United States)

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


    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

  2. ALVIN-SeaBeam studies of the Sumisu Rift, Izu-Bonin arc (United States)

    Taylor, B.; Brown, G.; Fryer, P.; Gill, J. B.; Hochstaedter, A. G.; Hotta, H.; Langmuir, C. H.; Leinen, M.; Nishimura, A.; Urabe, T.


    Bimodal volcanism, normal faulting, rapid sedimentation, and hydrothermal circulation characterize the rifting of the Izu-Bonin arc at 31°N. Analysis of the zigzag pattern, in plan view, of the normal faults that bound Sumisu Rift indicates that the extension direction (080° ± 10°) is orthogonal to the regional trend of the volcanic front. Normal faults divide the rift into an inner rift on the arc side, which is the locus for maximum subsidence and sedimentation, and an outer rift further west. Transfer zones that link opposing master faults and/or rift flank uplifts further subdivide the rift into three segments along strike. Volcanism is concentrated along the ENE-trending transfer zone which separates the northern and central rift segments. The differential motion across the zone is accommodated by interdigitating north-trending normal faults rather than by ENE-trending oblique-slip faults. Volcanism in the outer rift has built 50-700 m high edifices without summit craters whereas in the inner rift it has formed two multi-vent en echelon ridges (the largest is 600 m high and 16 km long). The volcanism is dominantly basaltic, with compositions reflecting mantle sources little influenced by arc components. An elongate rhyolite dome and low-temperature hydrothermal deposits occur at the en echelon step in the larger ridge, which is located at the intersection of the transfer zone with the inner rift. The chimneys, veins, and crusts are composed of silica, barite and iron oxide, and are of similar composition to the ferruginous chert that mantles the Kuroko deposits. A 1.2-km transect of seven ALVIN heat flow measurements at 30°48.5'N showed that the inner-rift-bounding faults may serve as water recharge zones, but that they are not necessarily areas of focussed hydrothermal outflow, which instead occurs through the thick basin sediments. The rift basin and arc margin sediments are probably dominated by permeable rhyolitic pumice and ash erupted from submarine

  3. Magma genesis by rifting of oceanic lithosphere above anomalous mantle: Terceira Rift, Azores (United States)

    Beier, Christoph; Haase, Karsten M.; Abouchami, Wafa; Krienitz, Marc-S.; Hauff, Folkmar


    The Terceira Rift formed relatively recently (˜1 Ma ago) by rifting of the old oceanic lithosphere of the Azores Plateau and is currently spreading at a rate of 2-4mm/a. Together with the Mid-Atlantic Ridge, the Terceira Rift forms a triple junction that separates the Eurasian, African, and American Plates. Four volcanic systems (São Miguel, João de Castro, Terceira, Graciosa), three of which are islands, are distinguished along the axis and are separated by deep avolcanic basins similar to other ultraslow spreading centers. The major element, trace element and Sr-Nd-Pb isotope geochemistry of submarine and subaerial lavas display large along-axis variations. Major and trace element modeling suggests melting in the garnet stability field at smaller degrees of partial melting at the easternmost volcanic system (São Miguel) compared to the central and western volcanoes, which appear to be characterized by slightly higher melting degrees in the spinel/garnet transition zone. The degrees of partial melting at the Terceira Rift are slightly lower than at other ultraslow mid-ocean ridge spreading axes (Southwest Indian Ridge, Gakkel Ridge) and occur at greater depths as a result of the melting anomaly beneath the Azores. The combined interaction of a high obliquity, very slow spreading rates, and a thick preexisting lithosphere along the axis probably prevents the formation and eruption of larger amounts of melt along the Terceira Rift. However, the presence of ocean islands requires a relatively stable melting anomaly over relatively long periods of time. The trace element and Sr-Nd-Pb isotopes display individual binary mixing arrays for each volcanic system and thus provide additional evidence for focused magmatism with no (or very limited) melt or source interaction between the volcanic systems. The westernmost mantle sources beneath Graciosa and the most radiogenic lavas from the neighboring Mid-Atlantic Ridge suggest a mantle flow from Graciosa toward the Mid

  4. Phanerozoic Rifting Phases And Mineral Deposits (United States)

    Hassaan, Mahmoud


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

  5. Mid-Continent Rift: Rift, LIP, or Both? (United States)

    Stein, C. A.; Stein, S. A.; Kley, J.; Hindle, D.; Keller, G. R., Jr.


    North America's Midcontinent Rift (MCR) is traditionally considered to have formed by midplate extension and volcanism ~1.1 Ga that ended due to compression from the Grenville orogeny, the ~1.3 - ~0.98 Ga assembly of Amazonia (Precambrian northeast South America), Laurentia (Precambrian North America), and other continents into the supercontinent of Rodinia. We find that a more plausible scenario is that it formed as part of the rifting of Amazonia from Laurentia and became inactive once seafloor spreading was established. The MCR has aspects both of a continental rift - a segmented linear depression filled with sedimentary and igneous rocks - and a large igneous province (LIP). Comparison of areas and volumes for a range of continental LIPS shows that the MCR volcanic rocks are significantly thicker than the others. The MCR flood basalts have steeper dips and thicker overlying sediments than other continental flood basalts, and were deposited in a subsiding basin after most extension ended, indicating that they are better viewed as post-rift than syn-rift rocks. Hence we view the MCR as a LIP deposited in crust weakened by rifting, and thus first a rift and then a LIP.

  6. The Age of Rift-Related Basalts in East Antarctica (United States)

    Leitchenkov, G. L.; Belyatsky, B. V.; Kaminsky, V. D.


    The Lambert Rift, which is a large intracontinental rift zone in East Antarctica, developed over a long period of geological time, beginning from the Late Paleozoic, and its evolution was accompanied by magmatic activity. The latest manifestation of magmatism is eruption of alkaline olivine-leucite basalts on the western side of the Lambert Rift; Rb-Sr dating referred its time to the Middle Eocene, although its genesis remained vague. In order to solve this problem, we found geochronometer minerals in basaltic samples and 68 apatite grains appeared to be suitable for analysis. Their ages and ages of host basalts, determined by the U-Pb local method on the SIMS SHRIMP-II, were significantly different (323 ± 31 Ma) from those assumed earlier. This age corresponds to the earliest stage of crustal extension in East Antarctica and to most of Gondwana. The new data crucially change the ideas about the evolution of Lambert Rift and demonstrate the ambiguity of K-Ar dates of the alkali effusive formed under long-term rifting.

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

    Energy Technology Data Exchange (ETDEWEB)

    James C Witcher


    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.

  8. Current ecosystem processes in steppe near Lake Baikal (United States)

    Vanteeva, Julia


    The steppes and forest steppes complexes of Priol'khonie at the Lake Baikal (southern Siberia, Russia) were studied in this research. Recreational activity has a significant impact on the Priol'khonie region. During soviet time this area was actively used for agriculture. Nowadays, this territory is the part of Pribaikalskyi National Park and special protection is needed. As the landscapes satisfy different human demands there are many land-management conflicts. The specific climate and soil conditions and human activity lead to erosion processes on study area. Sediment loads are transferred into the Lake Baikal and cause water pollution. Consequently, vegetation cover and phytomass play an important role for regulating hydrological processes in the ecosystems. The process of phytomass formation and its proactive role playing on sedimentation and mitigate silt detaching by rill and inter-rill erosion are considered in the research as important indicators of the ecosystem functions for steppe landscapes. These indicators were studied for the different land cover types identified on the area because the study area has a large variety of steppe and forest steppe complexes, differing in the form of relief, soil types, vegetation species composition and degree of land degradation. The fieldwork was conducted in the study area in the July and August of 2013. Thirty-two experimental sites (10 x 10 m) which characterized different types of ecosystem were established. The level of landscape degradation was estimated. The method of clipping was used for the valuation of above-ground herbaceous phytomass. The phytomass of tree stands was calculated using the volume-conversion rates for forest-steppe complexes. For the quantification of transferred silt by inter-rill erosion in different conditions (vegetation, slope, soil type, anthropogenic load) a portable rainfall simulator was created with taking into account the characteristics of the study area. The aboveground

  9. Sensitivity of the Baikal neutrino telescope NT-200 to point sources of very high energy neutrinos

    International Nuclear Information System (INIS)

    Krabi, J.; Spiering, C.; Bugaev, E.V.; Klimushin, S.I.


    The sensitivity of the deep underwater muon and neutrino detector 'NT-200' in lake Baikal to point sources of extraterrestrial neutrinos is calculated. Results are given for different assumptions on the neutrino source spectrum and the reconstruction capabilities of the detector. (orig.)

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

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


    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

  11. Groundwater origin and flow along selected transects in Ethiopian rift volcanic aquifers (United States)

    Kebede, Seifu; Travi, Yves; Asrat, Asfawossen; Alemayehu, Tamiru; Ayenew, Tenalem; Tessema, Zenaw


    The disruption of lithologies by cross-cutting faults and the variability in volcanic structures make the hydrogeology of the rifted volcanic terrain in Ethiopia very complex. Along two transects, selected due to their hydrogeologic characteristics, groundwater flow, depth of circulation and geochemical evolution have been conceptualized. The groundwater flow continuity between the high rainfall plateau bounding the rift and the rift valley aquifers depends principally on the nature of the bounding faults. Up to 50% of recharge to the rift aquifers comes from the plateau as groundwater inflow where the rift is cross cut by transverse fault zones. Recharge from the mountains is found to be insignificant where the rift is bounded by marginal grabens; channel loss and local precipitation are the principal sources of recharge to the rift aquifers in such cases. At a regional scale, there is a clear zonation in the geochemical compositions of groundwaters, the result of aquifer matrix composition differences. The environmental isotope results show that the majority of the aquifers contain modern groundwaters. In a few localities, particularly in thermal groundwaters representing deeper circulation, palaeo-groundwaters have been identified. Deeper groundwaters in the rift floor have a uniform 14C age ranging between 2,300 and 3,000 years.


    Directory of Open Access Journals (Sweden)

    E. N. Sutyrina


    Full Text Available The surface temperature of the water and the characteristics of the ice cover are important parameters of the state of the ecosystem of the lake and one of the most important indicators that allow us to identify climate change. Dimensions of Lake Baikal with an area of 31.7 thousand sq. kilometers make it reasonable to use the data of satellite remote sensing to study the characteristics of its ice-thermal regime. The purpose of this investigation was to study the features of the spatiotemporal distribution of the parameters of the ice-thermal regime of Lake Baikal using AVHRR (Advanced Very High Resolution Radiometer radiometer data for the period of 1998-2016.The paper describes the developed approach to mapping the stages of melting and destruction of the snow-ice cover on Baikal Lake in the spring and the method for mapping the surface temperature of the lake in an ice-free period according to AVHRR data. Samples of compiled schematic maps of the ice situation and of temperature distribution on the lake surface are given. Based on the obtained cartographic materials, the specificity of ice disappearance of the water areas of the Southern, Central and Northern basins of Lake Baikal has been studied. And it was found that the interannual fluctuations in the timing of the ice disappearance on the given water areas are in antiphase with the interannual fluctuations in the value of the Arctic Oscillation Index. Schematic temperature maps were used to study the intra-annual and interannual variability in the temperature distribution of Lake Baikal’s surface and it was revealed that the greatest interannual variability of temperature on its surface is observed in August, which is characterized by the maximum warming of the surface of the water body. Also, the contribution of several significant factors to the formation of temperature fields on the surface of Lake Baikal was estimated. 

  13. Stress perturbation associated with the Amazonas and other ancient continental rifts (United States)

    Zoback, M.L.; Richardson, R.M.


    rift case, because the observed stress rotation only weakly constrains the ratio of the regional horizontal stress difference to the rift-normal compression to be between 0.25 and 1.0, our analysis is inconclusive because the resultant normalized horizontal shear stress may be reduced (for ratios >0.5) or enhanced (for ratios Amazonas rift. A rift-normal stress associated with the seismically active New Madrid ancient rift may be sufficient to rotate the horizontal stress field consistent with strike-slip faults parallel to the axis of the rift, although this results in a 20-40% reduction in the local horizontal shear stress within the seismic zone. Sparse stress data in the vicinity of the seismically quiescent Midcontinent rift of the central United States suggest a stress state similar to that of New Madrid, with the local horizontal shear stress potentially reduced by as much as 60%. Thus the markedly different levels of seismic activity associated with these two subparallel ancient rifts is probably due to other factors than stress perturbations due to dense rift pillows. The modeling and analysis here demonstrate that rift-normal compressive stresses are a significant source of stress acting on the lithosphere and that in some cases may be a contributing factor to the association of intraplate seismicity with old zones of continental extension.

  14. How sedimentation affects rift segment interaction during oblique extension: a 4D analogue modelling study (United States)

    Zwaan, Frank; Schreurs, Guido; Adam, Jürgen


    During the early stages of rifting, rift segments may form along non-continuous and/or offset pre-existing weaknesses. It is important to understand how these initial rift segments interact and connect to form a continuous rift system. Previous modelling of rift interaction structures has shown the dominant influence of oblique extension, promoting rift segment linkage (e.g. Zwaan et al., 2016) and eventual continent break-up (Brune et al., 2012). However, these studies did not incorporate sedimentation, which can have important implications for rift evolution (e.g. Bialas and Buck, 2009). Here we present a series of analogue model experiments investigating the influence of sedimentation on rift interaction structures under oblique extension conditions. Our set-up involves a base of compressed foam and plexiglass that forces distributed extension in the overlying analogue materials when the model sidewalls move apart. A sand layer simulates the brittle upper crust and a viscous sand/silicone mixture the ductile lower crust. One of the underlying base plates can move laterally allowing oblique extension. Right-stepping offset and disconnected lines of silicone (seeds) on top of the basal viscous serve as inherited structures since the strong sand cover is locally thinner. We apply syn-rift sediments by filling in the developing rift and transfer zone basins with sand at fixed time steps. Models are run either with sedimentation or without to allow comparison. The first results suggest that the gross structures are similar with or without sedimentation. As seen by Zwaan et al. (2016), dextral oblique extension promotes rift linkage because rift propagation aligns itself perpendicular to the extension direction. This causes the rift segments to grow towards each other and to establish a continuous rift structure. However, the structures within the rift segments show quite different behaviour when sedimentation is applied. The extra sediment loading in the rift basin

  15. New and rare findings of lignicolous lichen species for the Southern Siberia from the Baikal nature reserve

    Directory of Open Access Journals (Sweden)

    I. N. Urbanavichene


    Full Text Available Based on field trips between 2009–2014, rare and noteworthy lichens from the Baikal Nature Reserve (Baikal nature reserve, Khamar-Daban ridge are described. These are mostly lignicolous lichens growing on wood and bark of Abies sibirica and Pinus sibirica, such as Absconditella lignicola, Strangospora moriformis, Trapeliopsis gelatinosa, T. viridescens. Trapeliopsis pseudogranulosa is new for Siberia, Lepraria jackii – new for South Siberia.

  16. Sm-Nd age of ultrabasite-basite massifs of east part of Baikal-Mujya ophiolite belt

    International Nuclear Information System (INIS)

    Izokh, A.Eh.; Gibsher, A.S.; Zhuravlev, D.Z.; Balykin, P.A.


    Two stratified ultrabasite-basite massifs of the Urals mountains were selected for isotope-geochemical studies. The intrusives, related to plutonic members of the island-arc associations, were used for dating. The Sm-Nd method indicated that one more belt, namely the Vend belt, is taking shape in the Baikal-Mujya tectonic collage alongside with the later Riphean (pre-Baikal) episubconduction belt of stratified intrusives [ru

  17. Structural interpretation of El Hierro (Canary Islands) rifts system from gravity inversion modelling (United States)

    Sainz-Maza, S.; Montesinos, F. G.; Martí, J.; Arnoso, J.; Calvo, M.; Borreguero, A.


    Recent volcanism in El Hierro Island is mostly concentrated along three elongated and narrow zones which converge at the center of the island. These zones with extensive volcanism have been identified as rift zones. The presence of similar structures is common in many volcanic oceanic islands, so understanding their origin, dynamics and structure is important to conduct hazard assessment in such environments. There is still not consensus on the origin of the El Hierro rift zones, having been associated with mantle uplift or interpreted as resulting from gravitational spreading and flank instability. To further understand the internal structure and origin of the El Hierro rift systems, starting from the previous gravity studies, we developed a new 3D gravity inversion model for its shallower layers, gathering a detailed picture of this part of the island, which has permitted a new interpretation about these rifts. Previous models already identified a main central magma accumulation zone and several shallower high density bodies. The new model allows a better resolution of the pathways that connect both levels and the surface. Our results do not point to any correspondence between the upper parts of these pathways and the rift identified at the surface. Non-clear evidence of progression toward deeper parts into the volcanic system is shown, so we interpret them as very shallow structures, probably originated by local extensional stresses derived from gravitational loading and flank instability, which are used to facilitate the lateral transport of magma when it arrives close to the surface.

  18. The evolution of the western rift area of the Fimbul Ice Shelf, Antarctica

    Directory of Open Access Journals (Sweden)

    A. Humbert


    Full Text Available This paper studies the evolution of a zone in the Fimbul Ice Shelf that is characterised by large crevasses and rifts west of Jutulstraumen, an outlet glacier flowing into Fimbulisen. High-resolution radar imagery and radio echo sounding data were used to study the surface and internal structure of this rift area and to define zones of similar characteristics. The western rift area is dominated by two factors: a small ice rumple that leads to basal crevasses and disturbs the homogeneity of the ice, and a zone with fibre-like blocks. Downstream of the rumple we found down-welling of internal layers and local thinning, which we explain as a result of basal crevasses due to the basal drag at the ice rumple. North of Ahlmannryggen the ice loses its lateral constraint and forms individual blocks, which are deformed like fibres under shear, where the ice stream merges with slower moving ice masses of the western side. There, the ice loses its integrity, which initiates the western rift system. The velocity difference between the slow moving western part and the fast moving extension of Jutulstraumen produces shear stress that causes the rifts to form tails and expand them to the major rifts of up to 30 km length.

  19. 3D numerical simulations of multiphase continental rifting (United States)

    Naliboff, J.; Glerum, A.; Brune, S.


    Observations of rifted margin architecture suggest continental breakup occurs through multiple phases of extension with distinct styles of deformation. The initial rifting stages are often characterized by slow extension rates and distributed normal faulting in the upper crust decoupled from deformation in the lower crust and mantle lithosphere. Further rifting marks a transition to higher extension rates and coupling between the crust and mantle lithosphere, with deformation typically focused along large-scale detachment faults. Significantly, recent detailed reconstructions and high-resolution 2D numerical simulations suggest that rather than remaining focused on a single long-lived detachment fault, deformation in this phase may progress toward lithospheric breakup through a complex process of fault interaction and development. The numerical simulations also suggest that an initial phase of distributed normal faulting can play a key role in the development of these complex fault networks and the resulting finite deformation patterns. Motivated by these findings, we will present 3D numerical simulations of continental rifting that examine the role of temporal increases in extension velocity on rifted margin structure. The numerical simulations are developed with the massively parallel finite-element code ASPECT. While originally designed to model mantle convection using advanced solvers and adaptive mesh refinement techniques, ASPECT has been extended to model visco-plastic deformation that combines a Drucker Prager yield criterion with non-linear dislocation and diffusion creep. To promote deformation localization, the internal friction angle and cohesion weaken as a function of accumulated plastic strain. Rather than prescribing a single zone of weakness to initiate deformation, an initial random perturbation of the plastic strain field combined with rapid strain weakening produces distributed normal faulting at relatively slow rates of extension in both 2D and

  20. Transcriptome-based phylogeny of endemic Lake Baikal amphipod species flock: fast speciation accompanied by frequent episodes of positive selection. (United States)

    Naumenko, Sergey A; Logacheva, Maria D; Popova, Nina V; Klepikova, Anna V; Penin, Aleksey A; Bazykin, Georgii A; Etingova, Anna E; Mugue, Nikolai S; Kondrashov, Alexey S; Yampolsky, Lev Y


    Endemic species flocks inhabiting ancient lakes, oceanic islands and other long-lived isolated habitats are often interpreted as adaptive radiations. Yet molecular evidence for directional selection during species flocks radiation is scarce. Using partial transcriptomes of 64 species of Lake Baikal (Siberia, Russia) endemic amphipods and two nonendemic outgroups, we report a revised phylogeny of this species flock and analyse evidence for positive selection within the endemic lineages. We confirm two independent invasions of amphipods into Baikal and demonstrate that several morphological features of Baikal amphipods, such as body armour and reduction in appendages and sensory organs, evolved in several lineages in parallel. Radiation of Baikal amphipods has been characterized by short phylogenetic branches and frequent episodes of positive selection which tended to be more frequent in the early phase of the second invasion of amphipods into Baikal when the most intensive diversification occurred. Notably, signatures of positive selection are frequent in genes encoding mitochondrial membrane proteins with electron transfer chain and ATP synthesis functionality. In particular, subunits of both the membrane and substrate-level ATP synthases show evidence of positive selection in the plankton species Macrohectopus branickii, possibly indicating adaptation to active plankton lifestyle and to survival under conditions of low temperature and high hydrostatic pressures known to affect membranes functioning. Other functional categories represented among genes likely to be under positive selection include Ca-binding muscle-related proteins, possibly indicating adaptation to Ca-deficient low mineralization Baikal waters. © 2016 John Wiley & Sons Ltd.

  1. ALVIN investigation of an active propagating rift system, Galapagos 95.5° W (United States)

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


    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.

  2. Tectonic Evolution of the Rift Basins in the Northeastern Brazilian Region (United States)

    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.

  3. Preliminary results of the first scientific Drilling on Lake Baikal, Buguldeika site, southeastern Siberia (United States)

    Williams, Douglas F.; Colman, S.; Grachev, M.; Hearn, P.; Horie, Shoji; Kawai, T.; Kuzmin, Mikhail I.; Logachov, N.; Antipin, V.; Bardardinov, A.; Bucharov, A.; Fialkov, V.; Gorigljad, A.; Tomilov, B.; Khakhaev, B.N.; Kochikov, S.; Logachev, N.; Pevzner, L.A.; Karabanov, E.B.; Mats, V.; Baranova, E.; Khlystov, O.; Khrachenko, E.; Shimaraeva, M.; Stolbova, E.; Efremova, S.; Gvozdkov, A.; Kravchinski, A.; Peck, J.; Fileva, T.; Kashik, S.; Khramtsova, T.; Kalashnikova, I.; Rasskazova, T.; Tatarnikova, V.; Yuretich, Richard; Mazilov, V.; Takemura, K.; Bobrov, V.; Gunicheva, T.; Haraguchi, H.; Ito, S.; Kocho, T.; Markova, M.; Pampura, V.; Proidakova, O.; Ishiwatari, R.; Sawatari, H.; Takeuchi, A.; Toyoda, K.; Vorobieva, S.; Ikeda, A.; Marui, A.; Nakamura, T.; Ogura, K.; Ohta, Takeshi; King, J.; Sakai, H.; Yokoyama, T.; Hayashida, A.; Bezrukova, E.; Fowell, S.; Fujii, N.; Letunova, P.; Misharina, V.; Miyoshi, N.; Chernyaeva, G.; Ignatova, I.; Likhoshvai, E.; Granina, L.; Levina, O.; Dolgikh, P.; Lazo, F.; Lutskaia, N.; Orem, W.; Wada, E.; Yamada, K.; Yamada, S.; Callander, E.; Golobokoval, L.; Shanks, W. C. Pat; Dorofeeva, R.; Duchkov, A.


    The Baikal Drilling Project (BDP) is a multinational effort to investigate the paleoclimatic history and tectonic evolution of the Baikal sedimentary basin during the Late Neogene. In March 1993 the Baikal drilling system was successfuly deployed from a barge frozen into position over a topographic high, termed the Buguldeika saddle, in the southern basin of Lake Baikal. The BDP-93 scientific team, made up of Russian, American and Japanese scientists, successfully recovered the first long (>100 m) hydraulic piston cores from two holes in 354 m of water. High quality cores of 98 m (Hole 1) and 102 m (Hole 2), representing sedimentation over the last 500,000 years, were collected in 78 mm diameter plastic liners with an average recovery of 72% and 90%, respectively. Magnetic susceptibility logging reveals an excellent hole-to-hole correlation. In this report the scientific team describes the preliminary analytical results from BDP-93 hole 1 cores. Radiocarbon dating by accelerator mass spectrometry provides an accurate chronology for the upper portion of Hole 1. Detailed lithologic characteristics, rock magnetic properties and inorganic element distributions show a significant change to the depositional environment occuring at 50 m subbottom depth, approximately 250,000 BP. This change may be due to uplift and rotation of the horst block in the Buguldeika saddle. The sedimentary section above 50 m is pelitic with varve-like laminae, whereas the section below 50 m contains a high proportion of sand and gravel horizons often organized into turbidite sequences. Accordingly, high resolution seismic records reveal a change in sonic velocity at this depth. It is inferred that sedimentation prior to 250 ka BP was from the west via the Buguldeika river system. After 250 ka BP the Buguldeika saddle reflects an increase in hemipelagic sediments admixed with fine-grained material from the Selenga River drainage basin, east of Lake Baikal. Variations in the spore

  4. The regional structure of the Red Sea Rift revised (United States)

    Augustin, Nico; van der Zwan, Froukje M.; Devey, Colin W.; Brandsdóttir, Bryndís


    The Red Sea Rift has, for decades, been considered a text book example of how young ocean basins form and mature. Nevertheless, most studies of submarine processes in the Red Sea were previously based on sparse data (mostly obtained between the late 1960's and 1980's) collected at very low resolution. This low resolution, combined with large gaps between individual datasets, required large interpolations when developing geological models. Thus, these models generally considered the Red Sea Rift a special case of young ocean basement formation, dividing it from North to South into three zones: a continental thinning zone, a "transition zone" and a fully developed spreading zone. All these zones are imagined, in most of the models, to be separated by large transform faults, potentially starting and ending on the African and Arabian continental shields. However, no consensus between models e.g. about the locations (or even the existence) of major faults, the nature of the transition zone or the extent of oceanic crust in the Red Sea Rift has been reached. Recently, high resolution bathymetry revealed detailed seafloor morphology as never seen before from the Red Sea, very comparable to other (ultra)slow spreading mid-ocean ridges such as the Gakkel Ridge, the Mid-Atlantic Ridge and SW-Indian Ridge, changing the overall picture of the Red Sea significantly. New discoveries about the extent, movement and physical properties of submarine salt deposits led to the Red Sea Rift being linked to the young Aptian-age South Atlantic. Extensive crosscutting transform faults are not evident in the modern bathymetry data, neither in teleseismic nor vertical gravity gradient data and comparisons to Gakkel Ridge and the SW-Indian Ridge suggest that the Red Sea is much simpler in terms of structural geology than was previously thought. Complicated tectonic models do not appear necessary and there appears to be large areas of oceanic crust under the Red Sea salt blankets. Based on

  5. A global census of continental rift activity since 250 Ma reveals a missing element of the deep carbon cycle (United States)

    Brune, Sascha; Williams, Simon; Müller, Dietmar


    The deep carbon cycle connects CO2 concentrations within the atmosphere to the vast carbon reservoir in Earth's mantle: subducted lithosphere carries carbon into the mantle, while extensional plate boundaries and arc volcanoes release it back to Earth's surface. The length of plate boundaries thereby exerts first-order control on global CO2 fluxes on geological time scales. Here we provide a global census of rift length from the Triassic to present day, combining a new plate reconstruction analysis technique with data from the geological rift record. We find that the most extensive rift phase during the fragmentation of Pangea occurred in the Jurassic/Early Cretaceous with extension along the South Atlantic (9700 km) and North Atlantic rifts (9100 km), within East Gondwana (8500 km), the failed African rift systems (4900 km), and between Australia and Antarctica (3700 km). The combined extent of these and other rift systems amounts to more than 50.000 km of simultaneously active continental rifts. During the Late Cretaceous, in the aftermath of this massive rift episode, the global rift length dropped by 60% to 20.000 km. We further show that a second pronounced rift episode starts in the Eocene with global rift lengths of up to 30.000 km. It is well-accepted that volcanoes at plate boundaries release large amounts of CO2 from the Earth's interior. Recent work, however, highlights the importance of deep-cutting faults and diffuse degassing on CO2 emissions in the East African Rift, which appear to be comparable to CO2 release rates at mid-ocean ridges worldwide. Upscaling measured CO2 fluxes from East Africa to all concurrently active global rift zones with due caution, we compute the first-order history of cumulative rift-related CO2 degassing rates for the last 250 Myr. We demonstrate that rift-related CO2 release in the Early Cretaceous may have reached 400% of present-day rates. In first-order agreement with paleo-atmospheric CO2 concentrations from proxy

  6. Seismic hazard of the Kivu rift (western branch, East African Rift system): new neotectonic map and seismotectonic zonation model (United States)

    Delvaux, Damien; Mulumba, Jean-Luc; Sebagenzi Mwene Ntabwoba, Stanislas; Fiama Bondo, Silvanos; Kervyn, François; Havenith, Hans-Balder


    The first detailed probabilistic seismic hazard assessment has been performed for the Kivu and northern Tanganyika rift region in Central Africa. This region, which forms the central part of the Western Rift Branch, is one of the most seismically active part of the East African rift system. It was already integrated in large scale seismic hazard assessments, but here we defined a finer zonation model with 7 different zones representing the lateral variation of the geological and geophysical setting across the region. In order to build the new zonation model, we compiled homogeneous cross-border geological, neotectonic and sismotectonic maps over the central part of East D.R. Congo, SW Uganda, Rwanda, Burundi and NW Tanzania and defined a new neotectonic sheme. The seismic risk assessment is based on a new earthquake catalogue, compiled on the basis of various local and global earthquake catalogues. The use of macroseismic epicenters determined from felt earthquakes allowed to extend the time-range back to the beginning of the 20th century, spanning 126 years, with 1068 events. The magnitudes have been homogenized to Mw and aftershocks removed. From this initial catalogue, a catalogue of 359 events from 1956 to 2015 and with M > 4.4 has been extracted for the seismic hazard assessment. The seismotectonic zonation includes 7 seismic source areas that have been defined on the basis of the regional geological structure, neotectonic fault systems, basin architecture and distribution of thermal springs and earthquake epicenters. The Gutenberg-Richter seismic hazard parameters were determined using both the least square linear fit and the maximum likelihood method (Kijko & Smit aue program). Seismic hazard maps have been computed with the Crisis 2012 software using 3 different attenuation laws. We obtained higher PGA values (475 years return period) for the Kivu rift region than the previous estimates (Delvaux et al., 2016). They vary laterally in function of the tectonic

  7. Fault kinematics and tectonic stress in the seismically active Manyara Dodoma Rift segment in Central Tanzania Implications for the East African Rift (United States)

    Macheyeki, Athanas S.; Delvaux, Damien; De Batist, Marc; Mruma, Abdulkarim


    The Eastern Branch of the East African Rift System is well known in Ethiopia (Main Ethiopian Rift) and Kenya (Kenya or Gregory Rift) and is usually considered to fade away southwards in the North Tanzanian Divergence, where it splits into the Eyasi, Manyara and Pangani segments. Further towards the south, rift structures are more weakly expressed and this area has not attracted much attention since the mapping and exploratory works of the 1950s. In November 4, 2002, an earthquake of magnitude Mb = 5.5 struck Dodoma, the capital city of Tanzania. Analysis of modern digital relief, seismological and geological data reveals that ongoing tectonic deformation is presently affecting a broad N-S trending belt, extending southward from the North Tanzanian Divergence to the region of Dodoma, forming the proposed "Manyara-Dodoma Rift segment". North of Arusha-Ngorongoro line, the rift is confined to a narrow belt (Natron graben in Tanzania) and south of it, it broadens into a wide deformation zone which includes both the Eyasi and Manyara grabens. The two-stage rifting model proposed for Kenya and North Tanzania also applies to the Manyara-Dodoma Rift segment. In a first stage, large, well-expressed topographic and volcanogenic structures were initiated in the Natron, Eyasi and Manyara grabens during the Late Miocene to Pliocene. From the Middle Pleistocene onwards, deformations related to the second rifting stage propagated southwards to the Dodoma region. These young structures have still limited morphological expressions compared to the structures formed during the first stage. However, they appear to be tectonically active as shown by the high concentration of moderate earthquakes into earthquake swarms, the distribution of He-bearing thermal springs, the morphological freshness of the fault scarps, and the presence of open surface fractures. Fault kinematic and paleostress analysis of geological fault data in basement rocks along the active fault lines show that recent

  8. Authigenic rhodochrosite from a gas hydrate-bearing structure in Lake Baikal (United States)

    Krylov, Alexey A.; Hachikubo, Akihiro; Minami, Hirotsugu; Pogodaeva, Tatyana V.; Zemskaya, Tamara I.; Krzhizhanovskaya, Mariya G.; Poort, Jeffrey; Khlystov, Oleg M.


    Early diagenetic carbonates are rare in Lake Baikal. Siderite (Fe carbonate) concretions in the sediments were discovered only recently. Here, we discuss the first finding of rhodochrosite concretions (Mn carbonate) discovered in the near-bottom sediments of the gas hydrate-bearing seepage structure St. Petersburg-2 in the deep water environment of the Central Baikal Basin. The crystal lattice of rhodochrosite contains iron and calcium substituting to manganese. Based on pore water geochemistry and of δ 13C values of rhodochrosite (- 23.3 and - 29.4‰), carbon dioxide (+ 3.8 to - 16.1‰) and methane (- 63.2 to - 67.8‰), we show that carbonate crystallization most likely occurred during microbial anaerobic oxidation of organic matter, and that part of the oxygen making up the rhodochrosite seems to be derived from the 18O-rich water released from dissociating gas hydrates.

  9. Phylogenetic diversity of T4-like bacteriophages in Lake Baikal, East Siberia. (United States)

    Butina, Tatyana Vladimirovna; Belykh, Olga I; Maksimenko, Svetlana Yu; Belikov, Sergey I


    Among the tailed phages, the myoviruses, those with contractile tails, are widespread and diverse. An important component of the Myoviridae family is the genus 'T4-like viruses'. The present study was aimed at elucidating the molecular diversity of T4-type bacteriophages in Lake Baikal by partial sequencing of g23 genes of T4-type bacteriophages. Our study revealed that the g23 gene sequences investigated were highly diverse and different from those of T4-like bacteriophages and from g23 clones obtained from different environments. Phylogenetic analysis showed that all g23 fragments from Lake Baikal, except for the one sequence, were more closely related to marine T4 cyanophages and to previously described subgroups of uncultured T4 phages from marine and rice field environments.

  10. Characterization of expandable clay minerals in Lake Baikal sediments by thermal dehydration and cation exchange

    Czech Academy of Sciences Publication Activity Database

    Grygar, Tomáš; Bezdička, Petr; Hradil, David; Hrušková, Michaela; Novotná, Kateřina; Kadlec, Jaroslav; Pruner, Petr; Oberhansli, H.


    Roč. 53, č. 4 (2005), s. 389-400 ISSN 0009-8604 R&D Projects: GA AV ČR(CZ) IAA3032401 Grant - others:European Commission(XE) EVK2-2000-00057 Institutional research plan: CEZ:AV0Z40320502 Keywords : cation exchange capacity * Lake Baikal * Lake Sediments Subject RIV: CA - Inorganic Chemistry Impact factor: 1.364, year: 2005

  11. Trends in dynamics of forest upper boundary in high mountains of northern Baikal area

    Directory of Open Access Journals (Sweden)

    V. I. Voronin


    Full Text Available Studies of spatial-temporal variability of the upper boundary of the forest on the north-western coast of Lake Baikal (Baikal and Upper Angara Ridges are performed on the base of the analysis of forests renewal processes and of the dynamics of larch radial increment in the ecotone of the forest upper boundary and out of it. The presence of a large amount of well-developed uplands and circuses with considerable heights drops in the structure of mountain system favours formation of interrupted boundary between forest and subgoltsy belt. The timber stand of the upper forest boundary in the studied area is represented by Daurian larch. Three tree-ring chronologies of larch are obtained. The longest chronology is obtained for mountain taiga belt of Baikal Ridge and is as long as 460 years. Since 1980ies, a sustainable trend of increase of radial trees growth is observed. It is observed the most distinctly in trees of the upper forest boundary on the Baikal Ridge. There is advancing of trees species into subgoltsy belt and into mountain tundra, which depends, respectively, on slopes heights, exposition and tilting, on sites of growth of concrete cenoses. Modern peculiarity of the vegetation of the studied area is presence of abundant viable larch undergrowth (from 2–3 to 25 y.o. and fir in the ecotone of upper forest boundary and in subgoltsy belt, as well as appearing of single specimens of spruce. Main undergrowth mass (2/3 is presented by trees aged in average 15–25 y.o., i.e., they appeared in late 1980ies. Due to increase of snow cover thickness in winter, the trees young growth obtained great protection from freezing resulting in the increase of ability of young growth to live up to elder age.

  12. Stratified distribution of nutrients and extremophile biota within freshwater ice covering the surface of Lake Baikal. (United States)

    Bondarenko, Nina A; Belykh, Olga I; Golobokova, Ludmila P; Artemyeva, Olga V; Logacheva, Natalia F; Tikhonova, Irina V; Lipko, Irina A; Kostornova, Tatyana Ya; Parfenova, Valentina V; Khodzher, Tamara V; Ahn, Tae-Seok; Zo, Young-Gun


    Biological entities and gradients of selected chemicals within the seemingly barren ice layers covering Lake Baikal were investigated. Ice cores 40-68 cm long were obtained from in shore and offshore sites of Southern Lake Baikal during the cold period of a year (March-April) in 2007 and 2008. In microscopic observations of the melted ice, both algae and bacteria were found in considerable numbers (>10(3) cells/L and >10(4) cells/ml, respectively). Among all organisms found, diatom was generally the most predominant taxon in the ice. Interestingly, both planktonic and benthic algae were present in considerable numbers (2-4×10(4) cells/L). Dominant phototrophic picoplankton were comprised of small green algae of various taxa and cyanobacteria of Synechococcus and Cyanobium. The bacterial community consisted mostly of short rod and cocci cells, either free-living or aggregated. Large numbers of yeast-like cells and actinomycete mycelium were also observed. Concentrations of silica, phosphorus, and nitrate were low by an order of magnitude where biota was abundant. The profile of the ice could be interpreted as vertical stratification of nutrients and biomass due to biological activities. Therefore, the organisms in the ice were regarded to maintain high activity while thriving under freezing conditions. Based on the results, it was concluded that the freshwater ice covering the surface of Lake Baikal is considerably populated by extremophilic microorganisms that actively metabolize and form a detritus food chain in the unique large freshwater ecosystem of Lake Baikal.

  13. Paleomagnetic record from lake Baikal sediments: Geomagnetic reversals excursion and relative paleointensity data

    Czech Academy of Sciences Publication Activity Database

    Pruner, Petr; Kadlec, Jaroslav; Schnabl, Petr; Šlechta, Stanislav; Chadima, Martin


    Roč. 34, Spec. (2004), s. 112-113 ISSN 1335-2806. [Paleo, Rock and Environmental Magnetism. Castle /9./. Tatranská Javorina, 27.06.2004-03.07.2004] Grant - others:EVK(XE) Project CONTINENT EC Project EVK 2-2000-00057 Institutional research plan: CEZ:AV0Z3013912 Keywords : magnetostratigraphy * geomagnetic excursions * Lake Baikal Subject RIV: DB - Geology ; Mineralogy

  14. Microplate rotation in northeast Brazil during South Atlantic rifting: Analogies with the Sinai microplate (United States)

    Szatmari, Peter; Milani, Edison J.


    The Early Cretaceous northeast Brazilian Sergipe microplate, formed at the northern end of the South Atlantic rift between South America and Africa, closely resembles the modern Sinai microplate at the northern end of the Red Sea in size, shape, and relative motion. Both formed where east-northeast trending transverse shear zones arrested northward rift propagation, causing the Tucano-Recôncavo and Gulf of Suez rifts to fail and be replaced by northeast-trending leaky transforms (Sergipe-Alagoas and Dead Sea transforms) as the new paths of continental breakup. Bordered by the failed rift, the leaky transform, and the transverse shear zone, both microplates were rotated counterclockwise by drag along their eastern transform margins. Rotation thrust the edge of the Sergipe microplate over part of its northern border, creating the Arcoverde thrust wedge. The northwest-trending Vaza-Barris fault sheared the microplate, transferring the rift and evaporite sequence from the Sergipe-Alagoas to the Gabon continental margin. In Albian time, heating of the lithosphere in the Cabo igneous province near Recife permitted the South Atlantic rift to propagate across the Arcoverde thrust wedge, completing continental breakup.


    Directory of Open Access Journals (Sweden)

    Victoria Nikolaevna Lavrikova


    Full Text Available Goal. The article looks at the topical issue of youth labour market. It should be noted that young people experience considerable difficulties when entering into the labour market due to their age as well as social, psychological and professional characteristics. The author introduces the definition of the labour market, looks at how deeply the issue has been researched and detects core characteristics and factors present on the Russian youth labour market. The goal of the study is to analyse youth labour market as applied to Trans-Baikal Territory. Materials and/or Methods. Study of statistical information provided by Trans-Baikal Territorial Government Statistical Service and the Ministry of Labour and Social Security was used as the research method. Results. As the result of the research the author has provided main characteristics and indicators of youth labour market in Trans-Baikal Territory (labour force participation rate among young people, the rate of employed young people based on their education, employment and unemployment rates. Main reasons for youth unemployment and the most popular professions among young people have also been analysed and specified. Conclusion. The author concludes that main characteristics of the regional youth labour market specified by the International Labour Organization should be utilized more comprehensively.

  16. Accumulation features and temporal trends of PCDDs, PCDFs and PCBs in Baikal seals (Pusa sibirica)

    Energy Technology Data Exchange (ETDEWEB)

    Imaeda, Daisuke [Center for Marine Environmental Studies (CMES), Ehime University, Bunkyo-cho 2-5, Matsuyama 790-8577 (Japan); Kunisue, Tatsuya [Center for Marine Environmental Studies (CMES), Ehime University, Bunkyo-cho 2-5, Matsuyama 790-8577 (Japan); Wadsworth Center, New York State Department of Health, Empire State Plaza, P.O. Box 509, Albany, NY 12201-0509 (United States); Ochi, Yoko; Iwata, Hisato; Tsydenova, Oyuna; Takahashi, Shin [Center for Marine Environmental Studies (CMES), Ehime University, Bunkyo-cho 2-5, Matsuyama 790-8577 (Japan); Amano, Masao [Department of Animal Sciences, Teikyo University of Science and Technology, 2525 Yatsusawa Uenohara-shi, Yamanashi 409-0193 (Japan); Petrov, Evgeny A. [The Eastern-Siberian Scientific and Production Fisheries Center, ' VOSTSIBRYBCENTER' , Ulan-Ude, Buryatia 670034 (Russian Federation); Batoev, Valeriy B. [Baikal Institute of Nature Management, Siberian Branch of Russian Academy of Sciences, Ulan-Ude, Buryatia 670047 (Russian Federation); Tanabe, Shinsuke [Baikal Institute of Nature Management, Siberian Branch of Russian Academy of Sciences, Ulan-Ude, Buryatia 670047 (Russian Federation)], E-mail:


    This study investigated the accumulation features and temporal trends of PCDD/Fs, dioxin-like PCBs (DL-PCBs) and non-dioxin-like PCBs (NDL-PCBs) in the blubber of Baikal seals collected in 1992 and 2005. DL-PCBs (480-3600 ng/g) and NDL-PCBs (980-35,000 ng/g) were dominant contaminants. Concentrations of PCDDs and PCBs in males were significantly higher than in females. In males, age-dependent accumulation was observed for PCDDs, mono-ortho PCBs and NDL-PCBs. PCDFs and non-ortho PCBs showed no such trends, implying that exposure of seals to these contaminants has been decreasing in recent years. No decreasing temporal trend was observed for PCDDs, mono-ortho PCBs and NDL-PCBs, suggesting that Baikal seals are still exposed to PCDDs and PCBs. TEQs of PCDDs and mono-ortho PCBs in seals collected in 2005 accounted for 62-77% of total TEQs. The TEQ levels in 40% of the specimens exceeded the threshold level for immunosuppression observed in harbor seals (209 pg/g). - Concentrations of PCDDs and PCBs remain high in Baikal seals.

  17. The rise and fall of plankton: long-term changes in the vertical distribution of algae and grazers in Lake Baikal, Siberia.

    Directory of Open Access Journals (Sweden)

    Stephanie E Hampton

    Full Text Available Both surface water temperatures and the intensity of thermal stratification have increased recently in large lakes throughout the world. Such physical changes can be accompanied by shifts in plankton community structure, including changes in relative abundances and depth distributions. Here we analyzed 45 years of data from Lake Baikal, the world's oldest, deepest, and most voluminous lake, to assess long-term trends in the depth distribution of pelagic phytoplankton and zooplankton. Surface water temperatures in Lake Baikal increased steadily between 1955 and 2000, resulting in a stronger thermal gradient within the top 50 m of the water column. In conjunction with these physical changes our analyses reveal significant shifts in the daytime depth distribution of important phytoplankton and zooplankton groups. The relatively heavy diatoms, which often rely on mixing to remain suspended in the photic zone, shifted downward in the water column by 1.90 m y(-1, while the depths of other phytoplankton groups did not change significantly. Over the same time span the density-weighted average depth of most major zooplankton groups, including cladocerans, rotifers, and immature copepods, exhibited rapid shifts toward shallower positions (0.57-0.75 m y(-1. As a result of these depth changes the vertical overlap between herbivorous copepods (Epischura baikalensis and their algal food appears to have increased through time while that for cladocerans decreased. We hypothesize that warming surface waters and reduced mixing caused these ecological changes. Future studies should examine how changes in the vertical distribution of plankton might impact energy flow in this lake and others.

  18. ethiopian rift and adjacent highlands

    African Journals Online (AJOL)

    ABSTRACT: Remotely sensed thermal-infrared spectral data can be used to derive surface temperature of any object if the optical and thermal properties are known. In this study 1M band six has been used to assess the spatial variability of the kinetic temperature of the central Ethiopian rift lakes and adjacent highlands.

  19. Activation of preexisting transverse structures in an evolving magmatic rift in East Africa (United States)

    Muirhead, J. D.; Kattenhorn, S. A.


    Inherited crustal weaknesses have long been recognized as important factors in strain localization and basin development in the East African Rift System (EARS). However, the timing and kinematics (e.g., sense of slip) of transverse (rift-oblique) faults that exploit these weaknesses are debated, and thus the roles of inherited weaknesses at different stages of rift basin evolution are often overlooked. The mechanics of transverse faulting were addressed through an analysis of the Kordjya fault of the Magadi basin (Kenya Rift). Fault kinematics were investigated from field and remote-sensing data collected on fault and joint systems. Our analysis indicates that the Kordjya fault consists of a complex system of predominantly NNE-striking, rift-parallel fault segments that collectively form a NNW-trending array of en echelon faults. The transverse Kordjya fault therefore reactivated existing rift-parallel faults in ∼1 Ma lavas as oblique-normal faults with a component of sinistral shear. In all, these fault motions accommodate dip-slip on an underlying transverse structure that exploits the Aswa basement shear zone. This study shows that transverse faults may be activated through a complex interplay among magma-assisted strain localization, preexisting structures, and local stress rotations. Rather than forming during rift initiation, transverse structures can develop after the establishment of pervasive rift-parallel fault systems, and may exhibit dip-slip kinematics when activated from local stress rotations. The Kordjya fault is shown here to form a kinematic linkage that transfers strain to a newly developing center of concentrated magmatism and normal faulting. It is concluded that recently activated transverse faults not only reveal the effects of inherited basement weaknesses on fault development, but also provide important clues regarding developing magmatic and tectonic systems as young continental rift basins evolve.

  20. Seismic hazard assessment of the Kivu rift segment based on a new seismotectonic zonation model (western branch, East African Rift system) (United States)

    Delvaux, Damien; Mulumba, Jean-Luc; Sebagenzi, Mwene Ntabwoba Stanislas; Bondo, Silvanos Fiama; Kervyn, François; Havenith, Hans-Balder


    In the frame of the Belgian GeoRisCA multi-risk assessment project focusing on the Kivu and northern Tanganyika rift region in Central Africa, a new probabilistic seismic hazard assessment has been performed for the Kivu rift segment in the central part of the western branch of the East African rift system. As the geological and tectonic setting of this region is incompletely known, especially the part lying in the Democratic Republic of the Congo, we compiled homogeneous cross-border tectonic and neotectonic maps. The seismic risk assessment is based on a new earthquake catalogue based on the ISC reviewed earthquake catalogue and supplemented by other local catalogues and new macroseismic epicenter data spanning 126 years, with 1068 events. The magnitudes have been homogenized to Mw and aftershocks removed. The final catalogue used for the seismic hazard assessment spans 60 years, from 1955 to 2015, with 359 events and a magnitude of completeness of 4.4. The seismotectonic zonation into 7 seismic source areas was done on the basis of the regional geological structure, neotectonic fault systems, basin architecture and distribution of thermal springs and earthquake epicenters. The Gutenberg-Richter seismic hazard parameters were determined by the least square linear fit and the maximum likelihood method. Seismic hazard maps have been computed using existing attenuation laws with the Crisis 2012 software. We obtained higher PGA values (475 years return period) for the Kivu rift region than the previous estimates. They also vary laterally in function of the tectonic setting, with the lowest value in the volcanically active Virunga - Rutshuru zone, highest in the currently non-volcanic parts of Lake Kivu, Rusizi valley and North Tanganyika rift zone, and intermediate in the regions flanking the axial rift zone.

  1. Evolution of the East African Rift System With Special Emphasis on the Central Rift of Kenya: A new Model

    International Nuclear Information System (INIS)

    Nyambok, I.O.


    The East African rift system has been of immense interest to geoscientist since its first account was given by Gregory (1896). Several recent views have followed, showing continuing interest in its evolution Baker et al. 19971; Baker et al. 1972; Baker and Wohlenberg 1971; McConnell 1972; Nyabok 1983; Williams and Truckle 1980; Williams, MacDonald and Leat 1983). This interest is being refueled by modern views which are emerging from our better understanding of plate tectonic processes. The major tectonic events took place during the Miocene and late Pliocene with the attendant volcanism which continued into the late Pleistocene. The late Pleistocene volcanism provided the heat source for the long on-going geothermal activity in the rift zone

  2. Tectonic inheritance in the development of the Kivu - north Tanganyika rift segment of the East African Rift System: role of pre-existing structures of Precambrian to early Palaeozoic origin. (United States)

    Delvaux, Damien; Fiama Bondo, Silvanos; Ganza Bamulezi, Gloire


    The present architecture of the junction between the Kivu rift basin and the north Tanganyika rift basin is that of a typical accommodation zone trough the Ruzizi depression. However, this structure appeared only late in the development of the Western branch of the East African Rift System and is the result of a strong control by pre-existing structures of Precambrian to early Palaeozoic origin. In the frame of a seismic hazard assessment of the Kivu rift region, we (Delvaux et al., 2016) constructed homogeneous geological, structural and neotectonic maps cross the five countries of this region, mapped the pre-rift, early rift and Late Quaternary faults and compiled the existing knowledge on thermal springs (assumed to be diagnostic of current tectonic activity along faults). We also produced also a new catalogue of historical and instrumental seismicity and defined the seismotectonic characteristics (stress field, depth of faulting) using published focal mechanism data. Rifting in this region started at about 11 Ma by initial doming and extensive fissural basaltic volcanism along normal faults sub-parallel to the axis of the future rift valley, as a consequence of the divergence between the Nubia and the Victoria plate. In a later stage, starting around 8-7 Ma, extension localized along a series of major border faults individualizing the subsiding tectonic basins from the uplifting rift shoulders, while lava evolved towards alkali basaltic composition until 2.6 Ma. During this stage, initial Kivu rift valley was extending linearly in a SSW direction, much further than its the actual termination at Bukavu, into the Mwenga-Kamituga graben, up to Namoya. The SW extremity of this graben was linked via a long oblique transfer zone to the central part of Lake Tanganyika, itself reactivating an older ductile-brittle shear zone. In the late Quaternary-early Holocene, volcanism migrated towards the center of the basin, with the development of the Virunga volcanic massif

  3. Colorado Basin Structure and Rifting, Argentine passive margin (United States)

    Autin, Julia; Scheck-Wenderoth, Magdalena; Loegering, Markus; Anka, Zahie; Vallejo, Eduardo; Rodriguez, Jorge; Marchal, Denis; Reichert, Christian; di Primio, Rolando


    The Argentine margin presents a strong segmentation with considerable strike-slip movements along the fracture zones. We focus on the volcanic segment (between the Salado and Colorado transfer zones), which is characterized by seaward dipping reflectors (SDR) all along the ocean-continent transition [e.g. Franke et al., 2006; Gladczenko et al., 1997; Hinz et al., 1999]. The segment is structured by E-W trending basins, which differs from the South African margin basins and cannot be explained by classical models of rifting. Thus the study of the relationship between the basins and the Argentine margin itself will allow the understanding of their contemporary development. Moreover the comparison of the conjugate margins suggests a particular evolution of rifting and break-up. We firstly focus on the Colorado Basin, which is thought to be the conjugate of the well studied Orange Basin [Hirsch et al., 2009] at the South African margin [e.g. Franke et al., 2006]. This work presents results of a combined approach using seismic interpretation and structural, isostatic and thermal modelling highlighting the structure of the crust. The seismic interpretation shows two rift-related discordances: one intra syn-rift and the break-up unconformity. The overlying sediments of the sag phase are less deformed (no sedimentary wedges) and accumulated before the generation of oceanic crust. The axis of the Colorado Basin trends E-W in the western part, where the deepest pre-rift series are preserved. In contrast, the basin axis turns to a NW-SE direction in its eastern part, where mainly post-rift sediments accumulated. The most distal part reaches the margin slope and opens into the oceanic basin. The general basin direction is almost orthogonal to the present-day margin trend. The most frequent hypothesis explaining this geometry is that the Colorado Basin is an aborted rift resulting from a previous RRR triple junction [e.g. Franke et al., 2002]. The structural interpretation

  4. Late Paleogene rifting along the Malay Peninsula thickened crust (United States)

    Sautter, Benjamin; Pubellier, Manuel; Jousselin, Pierre; Dattilo, Paolo; Kerdraon, Yannick; Choong, Chee Meng; Menier, David


    Sedimentary basins often develop above internal zones of former orogenic belts. We hereafter consider the Malay Peninsula (Western Sunda) as a crustal high separating two regions of stretched continental crust; the Andaman/Malacca basins in the western side and the Thai/Malay basins in the east. Several stages of rifting have been documented thanks to extensive geophysical exploration. However, little is known on the correlation between offshore rifted basins and the onshore continental core. In this paper, we explore through mapping and seismic data, how these structures reactivate pre-existing Mesozoic basement heterogeneities. The continental core appears to be relatively undeformed after the Triassic Indosinian orogeny. The thick crustal mega-horst is bounded by complex shear zones (Ranong, Klong Marui and Main Range Batholith Fault Zones) initiated during the Late Cretaceous/Early Paleogene during a thick-skin transpressional deformation and later reactivated in the Late Paleogene. The extension is localized on the sides of this crustal backbone along a strip where earlier Late Cretaceous deformation is well expressed. To the west, the continental shelf is underlain by three major crustal steps which correspond to wide crustal-scale tilted blocks bounded by deep rooted counter regional normal faults (Mergui Basin). To the east, some pronounced rift systems are also present, with large tilted blocks (Western Thai, Songkhla and Chumphon basins) which may reflect large crustal boudins. In the central domain, the extension is limited to isolated narrow N-S half grabens developed on a thick continental crust, controlled by shallow rooted normal faults, which develop often at the contact between granitoids and the host-rocks. The outer limits of the areas affected by the crustal boudinage mark the boundary towards the large and deeper Andaman basin in the west and the Malay and Pattani basins in the east. At a regional scale, the rifted basins resemble N-S en

  5. The Geomorphometrics of the Rio Grande Rift: The role of tectonics, climate, and erosional processes in forming the Rio Grande river (United States)

    Berry, M. A.; van Wijk, J.; Emry, E.; Axen, G. J.; Coblentz, D. D.


    Geomorphometrics provides a powerful tool for quantifying the topographic fabric of a landscape and can help with correlating surface features with underlying dynamic processes. Here we use a suite of geomorphometric metrics (including the topographic power spectra, fabric orientation/organization) to compare and contrast the geomorphology of two of the world's major rifts, the Rio Grande Rift (RGR) in western US and the East Africa Rift (EAR). The motivation for this study is the observation of fundamental differences between the characteristics of the intra-rift river drainage for the two rifts. The RGR consists of a series of NS trending rift basins, connected by accommodation or transfer zones. The Rio Grande river developed in the late Neogene, and follows these rift segments from the San Luis basin in Colorado to the Gulf of Mexico. Before the river system formed, basins are thought to have formed internally draining systems, characterized by shallow playa lakes. This is in contrast with lakes in the Tanganyika and Malawi rifts of the East African Rift that are deep and have existed for >5 My. We investigate the role of climate, tectonics and erosional processes in the formation of the through-going Rio Grande river. This occurred around the time of a slowing down of rift opening ( 10 Ma), but also climatic changes in the southwestern U.S. have been described for the late Neogene. To model our hypothesis, a tectonics and surface transport code TISC (Transport, Isostasy, Surface Transport, Climate) was used to evaluate the dynamics of a series of proto-rift basins and their connecting accommodation zones. Basin infill and drainage system development are studied as a result of varying sediment budgets, climate variables, and rift opening rate.

  6. A fugacity model for source determination of the Lake Baikal region pollution with polychlorinated Biphenyls

    Energy Technology Data Exchange (ETDEWEB)

    Sofiev, M. [Finnish Meteorological Inst., Helsinki (Finland); Galperin, M.; Maslyaev, A. [Inst. of Program Systems, Pereslavl-Zalesskiy (Russian Federation); McLachlan, M. [Stockholm Univ. (Sweden); Wania, F. [Toronto Univ. (Canada)


    PCBs were discovered in the Lake Baikal ecosystem by Malakhov et al. and Bobovnikova et al. A follow up to the initial study showed no decrease over 1981-1989 4, in contrast to what has been observed in other water bodies in the industrialised world. Further studies also showed the contamination in pinnipeds to be among the highest measured anywhere. Above studies and other data suggested a presence of a strong local PCB source (or several ones), which has had a widespread adverse effect for the whole region. To locate the source, Mamontov et al. collected samples from 34 sites over the region, the analysis of which showed a gradient of a factor of 1000, with the lowest concentrations at the north-east of Lake Baikal and the highest concentrations close to the city of Usolye Sibirskoye, a centre of the chemical industry in the Angara River valley. A continuous decrease in the soil contamination was observed along the path from Usolye Sibirskoye up the Angara River valley to Lake Baikal and from there north-eastward along the lake. These results indicate that there was (and perhaps still is) a major source of PCBs in the Usolye area, from where the PCBs are dispersed over the region. However, various obstacles prevent direct observations of potential sources. Therefore, a mathematical modelling approach was adopted in a currently ongoing INTAS project aiming to shed some more light on this problem. The model principles, setup and the results of the first experiments are presented in the current paper.

  7. Lower Crustal Seismicity, Volatiles, and Evolving Strain Fields During the Initial Stages of Cratonic Rifting (United States)

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


    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.

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

    Directory of Open Access Journals (Sweden)

    Alessandro eTibaldi


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

  9. A new species of Astragalus (Fabaceae from west coast of Baikal Lake (Irkutsk Oblast

    Directory of Open Access Journals (Sweden)

    N. V. Stepantsova


    Full Text Available A new species, Astragalus rytyensis Stepantsova (Fabaceae, growing on the west coast of the lake Baikal, is described. Morphological differences from related taxa – A. versicolor Pall., A. austrosibiricus Schischk., and A. inopinatus Boriss., are discussed and uncertain position of the new species in the system of the genus is emphasized which is intermediate between subg. Phaca (L. Bunge sect. Hemiphaca Bunge and subg. Cercidothrix Bunge sect. Onobrychium Bunge. Ecological and phonological features of A. rytyensis are reported and chromosome numbers of the new (2n = 6x = 48 and related species are counted.

  10. [Differential expression of DTSsa4 Tc1-like transposons in closely related populations of Baikal ciscoes]. (United States)

    Bychenko, O S; Sukhanova, L V; Azhikina, T L; Sverdlov, E D


    Two representatives of Baikal ciscoes - lake cisco and omul - diverged from a common ancestor as recently as 10-20 thousand years ago. We have found an increasing expression level of DTSsa4 Tc1-like DNA transposons in cisco and omul brains. The mapping of the sequences of these transposons from Salmo salar and Danio rerio genomes has shown that in some cases, these transposons are located in the 5' and 3' regions, as well as in the promoter regions of various genes. Probably, Tc1-like transposons affect the activity of neighboring genes, providing the adaptive divergence of the cisco population.

  11. [Telomere length and phylogenetic relationship of Baikal and Siberian planarians (Turbellaria, Tricladida)]. (United States)

    Koroleva, A G; Evtushenko, E V; Timoshkin, O A; Vershinin, A V; Kiril'chik, S V


    Dynamics of the telomeric DNA (tDNA) and the phylogeny of the Baikal and Siberian planarians have been studied based on the analysis of the 18S rDNA and beta-actin gene fragments. A relationship between tDNA and the planarians size has been demonstrated. Giant planarians with a minor exception have longer tDNA than little planarians. Phylogenetic affinity between the species that have the stretched tracks of tDNA, big size and similar habitats may indicate possible role of tDNA in the development of the indefinite regenerative capacity of planarians.

  12. Cultivated bacteria from the sub-ice algae-bacterial communities of Lake Baikal

    Directory of Open Access Journals (Sweden)

    M. V. Bashenkhaeva


    Full Text Available A collection of pure cultures isolated from the sub-ice algae-bacterial communities inhabiting the lower ice surface of Lake Baikal was obtained. The differences in morphology of the cultured bacteria and their enzymatic activities were revealed by the methods of classical microbiology. The taxonomic affiliation of several cultures was determined by the 16S rRNA gene sequencing. They belong to the genera Pseudomonas putida, P. psychrophila, Methylobacterium extorquens, Rhodococcus aerolatus, Brevundimonas aurantiaca, B. vesicularis, Sphingomonas subarctica, Roseomonas frigidaqua, and Janthinobacterium lividum. These taxa are adapted to low-temperature environments.

  13. Geodynamic modelling of the rift-drift transition: Application to the Red Sea (United States)

    Fierro, E.; Schettino, A.; Capitanio, F. A.; Ranalli, G.


    The onset of oceanic accretion after a rifting phase is generally accompanied by an initial fast pulse of spreading in the case of volcanic margins, such that the effective spreading rate exceeds the relative far-field velocity between the two plates for a short time interval. This pulse has been attributed to edge-driven convention (EDC), although our numerical modelling shows that the shear stress at the base of the lithosphere cannot exceed 1 MPa. In general, we have developed a 2D numerical model of the mantle instabilities during the rifting phase, in order to determine the geodynamic conditions at the rift-drift transition. The model was tested using Underworld II software, variable rheological parameters, and temperature and stress-dependent viscosity. Our results show an increase of strain rates at the top of the lithosphere with the lithosphere thickness as well as with the initial width of the margin up to 300 km. Beyond this value, the influence of the initial rift width can be neglected. An interesting outcome of the numerical model is the existence of an axial zone characterized by higher strain rates, which is flanked by two low-strain stripes. As a consequence, the model suggests the existence of an area of syn-rift compression within the rift valley. Regarding the post-rift phase, we propose that at the onset of a seafloor spreading, a phase of transient creep allows the release of the strain energy accumulated in the mantle lithosphere during the rifting phase, through anelastic relaxation. Then, the conjugated margins would be subject to post-rift contraction and eventually to tectonic inversion of the rift structures. To explore the tenability of this model, we introduce an anelastic component in the lithosphere rheology, assuming both the classical linear Kelvin-Voigt rheology and a non-linear Kelvin model. The non-linear model predicts viable relaxation times ( 1-2Myrs) to explain the post-rift tectonic inversion observed along the Arabian

  14. Rift systems in the southern North Atlantic: why did some fail and others not? (United States)

    Nirrengarten, M.; Manatschal, G.; Tugend, J.; Kusznir, N. J.; Sauter, D.


    Orphan, Rockall, Porcupine, Parentis and Pyrenean Basins are failed rift systems surrounding the southern North Atlantic Ocean. The failure or succeessing of a rift system is intimately linked to the question of what controls lithospheric breakup and what keeps oceanic spreading alive. Extension rates and the thermal structure are usually the main parameters invoked. However, between the rifts that succeeded and those that failed, the relative control and relative importance of these parameters is not clear. Cessation of driving forces, strain hardening or competition between concurrent rifts are hypotheses often used to explain rift failure. In this work, we aim to analyze the influence of far field forces on the abandon of rift systems in the southern North Atlantic domain using plate kinematic modeling. A new reconstruction approach that integrates the spatio-temporal evolution of rifted basins has been developed. The plate modeling is based on the definition, mapping and restoration of rift domains using 3D gravity inversions methods that provide crustal thickness maps. The kinematic description of each rift system enables us to discuss the local rift evolution relative to the far field kinematic framework. The resulting model shows a strong segmentation of the different rift systems during extreme crustal thinning that are crosscut by V-shape propagators linked to the exhumation of mantle and emplacement of first oceanic crust. The northward propagating lithospheric breakup of the southern North Atlantic may be partly triggered and channeled by extreme lithospheric thinning. However, at Aptian-Albian time, the northward propagating lithospheric breakup diverts and is partitioned along a transtensional system resulting in the abandon of the Orphan and Rockall basins. The change in the propagation direction may be related to a local strain weakening along existing/inherited transfer zones and/or, alternatively, to a more global plate reorganization. The

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

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


    heads measured in 72 wells. To account for the incomplete knowledge of the aquifer system several model set-ups differing in the number of transmissivity zones as well as in the implementation of fault zones, rivers, and model boundaries were evaluated using information criteria. The general pattern of the hydraulic-head distribution resulting from the plausible model set-ups agrees reasonably well with that obtained from the observations. Likewise the simulated baseflow is similar (though slightly higher) to that obtained by baseflow separation from measured discharge. The estimated transmissivity increases from the highland (in the order of 10-100 m²/day) toward the rift floor (in the order of 100-1000 m²/day). Although the rift-floor aquifers are mainly (65%) supplied by recharge from precipitation, groundwater flow from the highland (mountain block recharge) is found to provide a significant contribution (35%). At present, less than 1% of the groundwater flow is abstracted by pumping wells, suggesting a high potential for groundwater development both in the highland and the rift floor. With regard to the rift floor, potential effects of climate change on groundwater resources deserve further investigation, as the hydrological model suggests a high sensitivity of groundwater recharge to changes of precipitation and air temperature particularly within this part of the watershed.

  16. [Effect of different calcium hypochlorite concentrations on the survival of potentially pathogenic microorganisms isolated from Baikal Lake]. (United States)

    Parfenova, V V; Kravchenko, O S; Pavlova, O N; Suslova, M Iu; Bedoshvili, E D


    The survival rate of bacteria of the genera Pseudomonas and Enterococcus isolated from Baikal Lake, exposed to different concentration of calcium hypochlorite used as a main agent for drinking water disinfection, was studied. Experimental studies have shown that chlorination was imperfect as this method is not always effective against Enterococci.

  17. Comparative analysis of four active compounds of Baikal skullcap and its classical TCM prescriptions according to different clinical curative effects

    Directory of Open Access Journals (Sweden)

    Guang-Wei Zhu


    Full Text Available Objective: A sensitive HPLC-DAD detection method was established for the comparative analysis of the four active compounds (including baicalin, baicalein, wogonoside and wogonin of Baikal Skullcap and its classical TCM prescriptions according to different clinical curative effects. And analyze the relationship between compatibility of medicines, content and clinical curative effect.

  18. Tectonic Geomorphology and Geodynamics of Rifting: Goodenough Basin, Papua New Guinea (United States)

    Collier, R. E.


    Variations in deformation style are evident along the rift axis of the Woodlark Basin and Papuan Peninsula, where oceanic rifting is propagating westward into a more distributed zone of continental lithospheric extension. The Goodenough Basin lies west of the westernmost segment of the Woodlark oceanic spreading zone. To its north lie the D'Entrecasteaux Islands, metamorphic core complexes rapidly uplifted through the Late Tertiary due to a combination of continental extension and density contrasts within the continental crust. To its south lies the Papuan Peninsula, the southern rift margin, the structural geometry of which has not been characterized previously. Analysis of SRTM digital elevation data together with fieldwork in March 2006 has allowed basic mapping of rift-bounding normal faults, with offset fault segments having lengths of up to 60 km. Geomorphic features such as linear range fronts with faceted spurs, tilted hangingwall surfaces and linear footwall drainage basins typify an immature and active rift margin. Fault traces are however buried beneath rapidly accumulating colluvial soils in this zone of tropical weathering and largely basaltic and gabbroic pre-rift lithologies. Footwall-derived, deltaic coarse clastics are uplifted and exposed in transfer zones between fault segments. These deposits, previously described as tectonically folded, show dip variations that may be explained as low-angle topset fluviatile conglomerates and angle-of-repose grain flow and mass flow conglomerates of Gilbert-type delta foresets. Staircases of offlapping depositional terraces are inferred to be the product of forced regression due to Late Quaternary footwall uplift superimposed upon Late Pleistocene glacio-eustatic fluctuations. Away from loci of coarse clastic input, raised terraces and platforms of coral and carbonate detritus occur, with raised notches evidencing continued Holocene uplift. Instrumentally recorded seismicity within the Goodenough Basin has been

  19. Nuclear free zone

    International Nuclear Information System (INIS)

    Christoffel, T.


    Health professionals have played a leading role in alerting and educating the public regarding the danger of nuclear war which has been described as the last epidemic our civilization will know. Having convinced most people that the use of nuclear weapons would mean intolerable consequences, groups such as Physicians for Social Responsibility have focused on the second critical question how likely is it that these weapons will be used? The oultlook is grim. This article describes the nuclear free zone movement, explores relevant legal questions, and shows how the political potential of nuclear free zones threatens to open a deep rift in the American constitutional system

  20. Relationships and bioaccumulation of chemical elements in the Baikal seal (Phoca sibirica)

    Energy Technology Data Exchange (ETDEWEB)

    Ciesielski, Tomasz [Department of Food Sciences, Medical University of Gdansk, ul. Hallera 107, 80-416 Gdansk (Poland); Pastukhov, Mikhail V. [Institute of Geochemistry, Siberian Branch of the Russian Academy of Science, Irkutsk 664033 (Russian Federation); Fodor, Peter [Department of Applied Chemistry, Faculty of Food Science, Szent Istvan University, Villanyi ut. 29-43, Budapest, H-1118 (Hungary); Bertenyi, Zsuzsanna [Department of Applied Chemistry, Faculty of Food Science, Szent Istvan University, Villanyi ut. 29-43, Budapest, H-1118 (Hungary); Namiesnik, Jacek [Department of Analytical Chemistry, Chemical Faculty, Gdansk University of Technology, ul. Narutowicza 11/12, 80-952 Gdansk (Poland); Szefer, Piotr [Department of Food Sciences, Medical University of Gdansk, ul. Hallera 107, 80-416 Gdansk (Poland)]. E-mail:


    Concentrations of Al, Ba, Cd, Cu, Fe, Mn, Mo, Si, Sr, Zn, Ca, K, Mg, Na and P in the livers of Baikal seal, plankton, zoobenthos, and fish, constituting the food sources for the seals, were determined by ICP-MS and ICP-AES. The accumulation of elements in the liver of seals, affected by internal and external (environmental) factors, was assessed by multidimensional (ANOVA, FA) and correlation analyses. FA has enabled identification of abiotic and biotic factors responsible for the accumulation of elements in the livers of Baikal seals. Significant influence of sex and development stage of the seals analysed on hepatic concentrations of some elements was found. The observed differences in element concentrations between pups, males and females could be attributable to the reproductive cycle of this species. ANOVA showed differences in concentrations of Fe, Zn, Cu and Cd in seals from the three separate basins of the lake. BMFs suggest biomagnification of Fe and Zn in the fish-seal trophic link. - Biomagnification may be occurring in the fish-seal trophic link.

  1. Evolution of the hydro-climate system in the Lake Baikal basin (United States)

    Törnqvist, Rebecka; Jarsjö, Jerker; Pietroń, Jan; Bring, Arvid; Rogberg, Peter; Asokan, Shilpa M.; Destouni, Georgia


    Climatic changes can profoundly alter hydrological conditions in river basins. Lake Baikal is the deepest and largest freshwater reservoir on Earth, and has a unique ecosystem with numerous endemic animal and plant species. We here identify long-term historical (1938-2009) and projected future hydro-climatic trends in the Selenga River Basin, which is the largest sub-basin (>60% inflow) of Lake Baikal. Our analysis is based on long-term river monitoring and historical hydro-climatic observation data, as well as ensemble mean and 22 individual model results of the Coupled Model Intercomparison Project, Phase 5 (CMIP5). Study of the latter considers a historical period (from 1961) and projections for 2010-2039 and 2070-2099. Observations show almost twice as fast warming as the global average during the period 1938-2009. Decreased intra-annual variability of river discharge over this period indicates basin-scale permafrost degradation. CMIP5 ensemble projections show further future warming, implying continued permafrost thaw. Modelling of runoff change, however, is highly uncertain, with many models (64%) and their ensemble mean failing to reproduce historical behaviour, and with indicated future increase being small relative to the large differences among individual model results.

  2. Long-term changes in the hydroclimatic characteristics in the Baikal region (United States)

    Voropay, N. N.; Kichigina, N. V.


    Since the end of the 19th century, global air temperature has been increasing. The period after 1976 is called the period of the most intensive warming. In Russia, the average annual air temperature rises at a rate of + 0.43 ° C / 10 years. The change of precipitation over the last 50-60 years on average in Russia is not significant. In the Baikal region, precipitation increase during the warm period (10-11%) and decrease during the cold period (4%). It is reflected on hydrological regime and the factors of river flow formation. The regional features of the hydrological regime dynamics of the Baikal region against the background of climate change are considered. Groups of the rivers with similar alternations of low water and high-water periods are allocated. Trends in runoff are analyzed. The increase in air temperature leads to intra annual redistribution of river flow. The majority of statistically significant trends of river run off are observed during the cold period of year.

  3. Rift Valley fever outbreak, southern Mauritania, 2012. (United States)

    Sow, Abdourahmane; Faye, Ousmane; Ba, Yamar; Ba, Hampathé; Diallo, Diawo; Faye, Oumar; Loucoubar, Cheikh; Boushab, Mohamed; Barry, Yahya; Diallo, Mawlouth; Sall, Amadou Alpha


    After a period of heavy rainfall, an outbreak of Rift Valley fever occurred in southern Mauritania during September-November 2012. A total of 41 human cases were confirmed, including 13 deaths, and 12 Rift Valley fever virus strains were isolated. Moudjeria and Temchecket Departments were the most affected areas.

  4. Boundary separating the seismically active reelfoot rift from the sparsely seismic Rough Creek graben, Kentucky and Illinois (United States)

    Wheeler, R.L.


    The Reelfoot rift is the most active of six Iapetan rifts and grabens in central and eastern North America. In contrast, the Rough Creek graben is one of the least active, being seismically indistinguishable from the central craton of North America. Yet the rift and graben adjoin. Hazard assessment in the rift and graben would be aided by identification of a boundary between them. Changes in the strikes of single large faults, the location of a Cambrian transfer zone, and the geographic extent of alkaline igneous rocks provide three independent estimates of the location of a structural boundary between the rift and the graben. The boundary trends north-northwest through the northeastern part of the Fluorspar Area Fault Complex of Kentucky and Illinois, and has no obvious surface expression. The boundary involves the largest faults, which are the most likely to penetrate to hypocentral depths, and the boundary coincides with the geographic change from abundant seismicity in the rift to sparse seismicity in the graben. Because the structural boundary was defined by geologic variables that are expected to be causally associated with seismicity, it may continue to bound the Reelfoot rift seismicity in the future.

  5. The main features of the interaction of mantle magmas with granulite complexes of the lower crust and their relationship with granitic melts (exemplified by the Early Caledonides of the West Baikal Region, Russia) (United States)

    Vladimirov, Alexandr; Khromykh, Sergei; Mekhonoshin, Alexei; Volkova, Nina; Travin, Alexei; Mikheev, Evgeny; Vladimirova, Anna


    Granulite complexes occurring in the Early Caledonian southern folded framing of the Siberian Craton are deeply eroded fragments of the Vendian-Early Paleozoic accretionary prism, which is an indicator of the early stages of the Paleo-Asian Ocean (Gladkochub et al., 2010). The main feature of the granulite complexes is a wide development of gabbro-pyroxenites composing tectonic plates, synmetamorphic intrusive bodies, and numerous disintegrated fragments (boudins and enclaves), immersed in a metamorphic matrix. The volume of basites reaches 5-10 %, which allows us to consider mantle magmatism as a heat source for the granulite metamorphism. The most studied polygon is Chernorud granulite zone, which is a part of the Olkhon metamorphic terrane, West Baikal Region. Just this polygon was used for considering the problems of interaction of mantle magmas with lower crust granulite complexes and their relationship with granitic melts. The Chernorud Zone is a typical example of the accretionary prism with a predominance of metabasalts (70-80 %), subordinate amounts of marbles, quartzites and metapelites that have been subjected to granulite facies metamorphism and viscoelastic flow of rock masses. Study of two-pyroxene granulites (metabasalts) and garnet-sillimanite gneisses (metapelites) allows us to estimate P-T metamorphic conditions (P = 7.7-8.6 kbar, T = 770-820°C) and their U-Pb metamorphic age (530-500 Ma). Metabasalts correspond in their geochemistry to the island-arc tholeiitic series (Volkova et al., 2010; Gladkochub et al., 2010). Sin-metamorphic gabbro-pyroxenites formed in two stages: 1) Chernorud complex - tectonic slices and body's exhumed from deep earth crust levels (10-12 kb) and composed of arc tholeiitic series rocks (age T ≥ 500 Ma); 2) Ulan-Khargana complex - supply magmatic canals and fragmented tabular intrusions. This rocks composition corresponds to subalkaline petrochemical series (OIB) and U/Pb age is equal to 485±10 Ma (Travin et al., 2009

  6. Off-axis volcano-tectonic activity during continental rifting: Insights from the transversal Goba-Bonga lineament, Main Ethiopian Rift (East Africa) (United States)

    Corti, Giacomo; Sani, Federico; Agostini, Samuele; Philippon, Melody; Sokoutis, Dimitrios; Willingshofer, Ernst


    The Main Ethiopian Rift, East Africa, is characterized by the presence of major, enigmatic structures which strike approximately orthogonal to the trend of the rift valley. These structures are marked by important deformation and magmatic activity in an off-axis position in the plateaus surrounding the rift. In this study, we present new structural data based on a remote and field analysis, complemented with analogue modelling experiments, and new geochemical analysis of volcanic rocks sampled in different portions of one of these transversal structures: the Goba-Bonga volcano-tectonic lineament (GBVL). This integrated analysis shows that the GBVL is associated with roughly E-W-trending prominent volcano-tectonic activity affecting the western plateau. Within the rift floor, the approximately E-W alignment of Awasa and Corbetti calderas likely represent expressions of the GBVL. Conversely, no tectonic or volcanic features of similar (E-W) orientation have been recognized on the eastern plateau. Analogue modelling suggests that the volcano-tectonic features of the GBVL have probably been controlled by the presence of a roughly E-W striking pre-existing discontinuity beneath the western plateau, which did not extend beneath the eastern plateau. Geochemical analysis supports this interpretation and indicates that, although magmas have the same sub-lithospheric mantle source, limited differences in magma evolution displayed by products found along the GBVL may be ascribed to the different tectonic framework to the west, to the east, and in the axial zone of the rift. These results support the importance of the heterogeneous nature of the lithosphere and the spatial variations of its structure in controlling the architecture of continental rifts and the distribution of the related volcano-tectonic activity.

  7. Neotectonics of the Roer Valley Rift System, the Netherlands.

    NARCIS (Netherlands)

    Houtgast, R.F.; van Balen, R.T.


    The Roer Valley Rift System (RVRS) is located in the southern part of the Netherlands and adjacent parts of Germany and Belgium. The last rifting episode of the RVRS started in the Late Oligocene and is still ongoing. The present-day seismic activity in the rift system is part of that last rifting

  8. Seasonal Dynamics of Stress Proteins in Leaves of Medicinal Plants in a Natural Environment of Irkutsk and on the Shores of the Lake Baikal

    Directory of Open Access Journals (Sweden)

    M.A. Zhivetiev


    Full Text Available We study leafs of five plant species, growing in Irkutsk city and on the southeastern shore of Lake Baikal. These species are Achillea asiatica Serg., Taraxacum officinale Wigg., Plantago major L., Veronica chamaedrys L. and Alchemilla subcrenata Buser. In its leafs we identify some types of stress-induced proteins. In autumn, the accumulation of stress proteins in leafs of plants both from shores of Lake Baikal and from Irkutsk have been registered.

  9. Polyphase Rifting and Breakup of the Central Mozambique Margin (United States)

    Senkans, Andrew; Leroy, Sylvie; d'Acremont, Elia; Castilla, Raymi


    from strike-slip deformation localised along a proposed crustal weakness, represented by the Lurio-Pebane shear zone. A more north-south oriented extension is recorded by the continental breakup and oceanisation. A failed rift is initially formed between the Beira High and the African continent followed by the successful rifting of its southern margin. This study proposes a segmentation of the Central Mozambique margin, with oceanisation first occurring in the Angoche segment. The formation of the first oceanic crust in the Beira segment followed, likely delayed by the formation and failure of the northern Beira High rift. *The PAMELA project (PAssive Margin Exploration Laboratories) is a scientific project led by Ifremer and TOTAL in collaboration with Université Rennes 1, Université Pierre and Marie Curie, Université de Bretagne Occidentale, CNRS and IFPEN.

  10. From continental to oceanic rifting in the Gulf of California (United States)

    Ferrari, Luca; Bonini, Marco; Martín, Arturo


    The continental margin of northwestern Mexico is the youngest example of the transition from a convergent plate boundary to an oblique divergent margin that formed the Gulf of California rift. Subduction of the Farallon oceanic plate during the Cenozoic progressively brought the East Pacific Rise (EPR) toward the North America trench. In this process increasingly younger and buoyant oceanic lithosphere entered the subduction zone until subduction ended just before most of the EPR could collide with the North America continental lithosphere. The EPR segments bounding the unsubducted parts of the Farallón plate remnants (Guadalupe and Magdalena microplates) also ceased spreading (Lonsdale, 1991) and a belt of the North American plate (California and Baja California Peninsula) became coupled with the Pacific Plate and started moving northwestward forming the modern Gulf of California oblique rift (Nicholson et al., 1994; Bohannon and Parsons, 1995). The timing of the change from plate convergence to oblique divergence off western Mexico has been constrained at the middle Miocene (15-12.5 Ma) by ocean floor morphology and magnetic anomalies as well as plate tectonic reconstructions (Atwater and Severinghaus, 1989; Stock and Hodges, 1989; Lonsdale, 1991), although the onset of transtensional deformation and the amount of right lateral displacement within the Gulf region are still being studied (Oskin et al., 2001; Fletcher et al., 2007; Bennett and Oskin, 2014). Other aspects of the formation of the Gulf of California remain not well understood. At present the Gulf of California straddles the transition from continental transtension in the north to oceanic spreading in the south. Seismic reflection-refraction data indicate asymmetric continent-ocean transition across conjugate margins of rift segments (González-Fernández et al., 2005; Lizarralde et al., 2007; Miller and Lizarralde, 2013; Martín-Barajas et al., 2013). The asymmetry may be related to crustal

  11. Strike-slip tectonics during rift linkage (United States)

    Pagli, C.; Yun, S. H.; Ebinger, C.; Keir, D.; Wang, H.


    The kinematics of triple junction linkage and the initiation of transforms in magmatic rifts remain debated. Strain patterns from the Afar triple junction provide tests of current models of how rifts grow to link in area of incipient oceanic spreading. Here we present a combined analysis of seismicity, InSAR and GPS derived strain rate maps to reveal that the plate boundary deformation in Afar is accommodated primarily by extensional tectonics in the Red Sea and Gulf of Aden rifts, and does not require large rotations about vertical axes (bookshelf faulting). Additionally, models of stress changes and seismicity induced by recent dykes in one sector of the Afar triple junction provide poor fit to the observed strike-slip earthquakes. Instead we explain these patterns as rift-perpendicular shearing at the tips of spreading rifts where extensional strains terminate against less stretched lithosphere. Our results demonstrate that rift-perpendicular strike-slip faulting between rift segments achieves plate boundary linkage during incipient seafloor spreading.

  12. Faunal communities at sites of gas- and oil-bearing fluids in Lake Baikal (United States)

    Zemskaya, Tamara I.; Sitnikova, Tatiana Y.; Kiyashko, Sergei I.; Kalmychkov, Gennady V.; Pogodaeva, Tatiana V.; Mekhanikova, Irina V.; Naumova, Tatiana V.; Shubenkova, Olga V.; Chernitsina, Svetlana M.; Kotsar, Oleg V.; Chernyaev, Evgeny S.; Khlystov, Oleg M.


    Macro- and meiofaunal communities were examined at four geomorphologically distinct sites with different gas- and oil-bearing fluid characteristics in the northern, central and southern basins of Lake Baikal. All sites had elevated concentrations of bicarbonate, nitrate, sulphate and chloride ions in pore fluids, with highest values at the Frolikha vent. Elevated levels of iron ions were found in pore waters of the St. Petersburg methane seep and the Gorevoy Utes oil seep. The chemical composition of pore waters at the Malenky mud volcano was similar to that reported in earlier work. Consistent with published data, the Frolikha vent (northern basin) and the St. Petersburg methane seep (central basin) were characterised by methane of mixed genesis (thermogenic + biogenic), whereas the methane source was mainly thermogenic at the Gorevoy Utes oil seep (central basin) and biogenic at the Malenky mud volcano (southern basin). In contrast to marine seep ecosystems, the macrofauna was dominated only by amphipods, giant planarians and oligochaetes, whereas bivalves were absent; the meiofauna was similar to its marine counterpart, being dominated by nematodes, cyclops, harpacticoids and ostracods. A statistically significant positive relationship was revealed between faunal abundance and the availability of bacterial mats on seep sediments. Moreover, ANOVA tests showed significant increases in both meiozoobenthic and macrozoobenthic densities at "hot spot" vent/seep sites relative to discharge-free reference sites. The isotopic composition of carbon and nitrogen at various trophic levels of these benthic vent/seep communities was found to differ markedly from that reported by earlier studies for the pelagic and other benthic food webs in Lake Baikal. As in marine seeps, the macrofauna had variable isotopic signatures. Light δ13C and δ15N values suggest the utilization of chemosynthetically fixed and/or methane-derived organic matter. By contrast, the heavy δ13C

  13. Diurnal behavior of the carbon dioxide flux and change in the isotopic ratio δ13C in surface and near-bottom water in littoral of Lake Baikal (United States)

    Panchenko, Mikhail V.; Domysheva, Valentina M.; Padalko, Natalia L.; Chernikov, Eugenii V.; Prazdnichnykh, Maxim I.; Tumakov, Alexander G.; Pestunov, Dmitrii A.


    Lake Baikal is one of the unique natural environments in Siberia which, to a large extent, affects the state of the nature in this region. The processes of gas exchange in the "water-atmosphere" system have been studied in Lake Baikal since 2002. The main purpose of the integrated investigations of exchange of carbon-containing gases in the water-atmosphere system in Lake Baikal is to study the contribution of physical, chemical, and biological components of the process and their interrelation with the intensity and rhythms of the fluxes. In 2013, the integrated measurements in the littoral area of Baikal were complemented with studies of the diurnal dynamics of isotopic ratio δ 13C in the surface and near-bottom water, which were not yet performed in Baikal before. In this work, we analyze first results of the joint analysis of RO2 fluxes in the "atmosphere - water surface" system and δ 13C, obtained in August 2013 in the littoral area of South Baikal. It is shown that d13C markedly increases in the surface waters at daylight time. In nighttime period, there takes place a reverse process, when δ 13C of the surface water approaches δ 13C, which is recorded for near-bottom water.

  14. Permafrost as an additional driving factor for the extreme fire event in the boreal Baikal region in 2003 (United States)

    Forkel, M.; Thonicke, K.; Beer, C.; Cramer, W.; Bartalev, S.; Schmullius, C.


    Wildfires are a natural and important element in the functioning of boreal forests. However, in some years, fires with extreme spread and severity occur. Such severe fires degrade the forest, affect human values, emit huge amount of carbon and aerosols and alter the land surface albedo. Usually, wind, slope, and dry conditions have been recognized as factors determining fire spread. In the Baikal region, 127,000 km2 burned in 2003, while the annual average burned area is approx. 8100 km2. In average years, 16% of the burned area occurred in the continuous permafrost zone but in 2003, 33% of these burned areas coincide with the existence of permanently frozen grounds. Permafrost and the associated upper active layer, which thaws during summer and refreezes during winter, is an important supply for soil moisture in boreal ecosystems. This leads to the question if permafrost hydrology is a potential additional driving factor for extreme fire events in boreal forests. Using temperature and precipitation data, we calculated the Nesterov index as indicator for fire weather conditions. Further, we used satellite observations of burned area and surface moisture, a digital elevation model, a land cover and a permafrost map to evaluate drivers for the temporal dynamic and spatial variability of surface moisture conditions and burned area in spring 2003. On the basis of time series decomposition, we separated the effect of drivers for fire activity on different time scales. We next computed cross-correlations to identify potential time lags between weather conditions, surface moisture and fire activity. Finally, we assessed the predictive capability of different combinations of driving variables for surface moisture conditions and burned area using multivariate spatial-temporal regression models. The results from this study demonstrate that permafrost in larch-dominated ecosystems regulates the inter-annual variability of surface moisture and thus increases the inter

  15. Improving physical health international students enrolled in a technical college in Baikal region

    Directory of Open Access Journals (Sweden)

    M.M. Kolokoltsev


    Full Text Available Purpose : to improve the physical health of foreign students enrolled in a technical college Baikal region using an extended motor mode. Material : in the experiment participated 57 students attending the training of South-East Asia, 74 - from Central Asia and 455 - Slavs, natives of the Irkutsk region. Results : it was found poor fitness and low functional performance among foreign students. For this purpose they had used advanced motoring. It included, besides training curriculum additional group activities in the form of sports, participating in sports events and guided independent study physical education. Conclusion : the end of follow foreign students involved in the extended motor mode, significantly outperform their peers engaged on normal functional parameters (heart rate, a test with 20 squats, the recovery time after exercise, dynamometry hands, breath tests, adaptive capacity as well as motor qualities.

  16. [Length and structure of telomeric DNA in three species of Baikal gastropods (Caenogastropoda: Hydrobioidea: Benedictiidae)]. (United States)

    Koroleva, A G; Evtushenko, E V; Maximova, N V; Vershinin, A V; Sintnikova, T Y; Kirilchik, S V


    The structure of telomeric repeat (TTAGGG)n was determined and the length of telomeric DNA (tDNA) was measured in three species of gastropods from the family Benedictiidae that are endemic to Lake Baikal. Fluorescence in situ hybridization (FISH) confirmed the localization of a telomeric repeat at the chromosome ends. The sizes of tDNA in "giant" eurybathic, psammo-pelobiontic species Benedictia fragilis and shallow water litho-psammobiontic species B. baicalensis with medium shell sizes were similar (16 ± 2.9 and 15 ± 2.1 kb, respectively), but they had a greater length than that of the shallow water spongio-litobiontic species Kobeltocochlea martensiana with small shells (10.5 ± 1.5 kb). We discuss tendencies in age-related changes in tDNA length in snails and a possible mechanism for maintaining tDNA size in ontogeny.

  17. Experimental Paper. Intrapopulation variability of flavonoid content in roots of Baikal skullcap (Scutellaria baicalensis Georgi

    Directory of Open Access Journals (Sweden)

    Kosakowska Olga


    Full Text Available Introduction: Baikal skullcap (Scutellaria baicalensis Georgi is an important medicinal plant, indigenous to Asia. Due to a wide range of pharmacological activities, its roots has been used for ages in Traditional Chinese Medicine. Recently, the species has become an object of interest of Western medicine, as well. Objective: The aim of the study was to determine the variability of Baikal skullcap population originated from Mongolia and cultivated in Poland, in terms of content and composition of flavonoids in the roots. Methods: The objects of the study were 15 individual plants, selected within examined population and cloned in order to obtain a sufficient amount of raw material. The total content of flavonoids in roots was determined according to Polish Pharmacopeia 6th. The qualitative analysis of flavonoids was carried out using HPLC, Shimadzu chromatograph. Results: The dry mass of roots ranged from 25.88 to 56.14 g × plant-1. The total content of flavonoids (expressed as a quercetin equivalent varied between 0.17 and 0.52% dry matter (DM. Nine compounds were detected within the group, with oroxylin A 7-Oglucuronide (346.90-1063.00 mg × 100 g-1 DM as a dominant, which differentiated investigated clones at the highest degree (CV=0.27. Baicalin (391.40-942.00 mg × 100 g-1 DM, wogonoside (324.00-641.10 mg × 100 g-1 DM and hesperetine 7-O-glucoside (163.00-346.32 mg × 100 g-1 DM were also present in a considerable amounts. Clone 7 was distinguished by the highest content of all investigated compounds, except wogonin and oroxylin A 7-O-glucuronide. Conclusions: Results obtained in present study show a high variability within Baical skullcap investigated population in respect of flavonoid compounds detected in roots. Thus, the results may be used in future investigations concerning the selection and breeding of this species.


    Directory of Open Access Journals (Sweden)

    Hidetoshi Naganawa


    Full Text Available Lake Gusinoe is the largest water body in the Buryat Republic (South Siberia, Russia and still the only source of both drinking and industrial water supply. All the wastewater is thrown away into the same lake. Most of the tributaries, concentrated on the western lakeshore, disappear into the coarse deposits of alluvial fans soon after they emerge from the mountains. Anthropogenic impacts on the lake ecosystem increased during the 20th century. The biggest environmental polluters are the Gusinoozersk coal mine, the Kholboldzhinsky opencut coal mine, and the Gusinoozersk State Regional Power Plant (Gusinoozersk SRPP. The Gusinoozersk SRPP takes a large amount of freshwater from the Zagustai River, the longest influent of Lake Gusinoe, to produce hot water and steam for the turbines. The warm wastewater is discharged back into the lake. As a result of this, an unfrozen patch of water measuring about 2 km2 is formed on the lake in winter, and the water temperature in the upper layer is 13–14°C higher than the lower ones. Some chemical components (e.g., sulfate, phenol, iron ions of both the lake water and surface/groundwater of the Lake Gusinoe Basin are with constant excess of the maximum allowable concentration (MAC. The Gusinoozersk SRPP is also the main air polluter. Now Lake Gusinoe is constantly polluted and in the state of degradation. Lake Gusinoe might be possible one of the largest pollution sources in the Baikal region, because the connecting transboundary Selenga River is the main inflow of Lake Baikal

  19. Plate Speed-up and Deceleration during Continental Rifting: Insights from Global 2D Mantle Convection Models. (United States)

    Brune, S.; Ulvrova, M.; Williams, S.


    The surface of the Earth is divided into a jigsaw of tectonic plates, some carrrying continents that disperse and aggregate through time, forming transient supercontinents like Pangea and Rodinia. Here, we study continental rifting using large-scale numerical simulations with self-consistent evolution of plate boundaries, where continental break-up emerges spontaneously due to slab pull, basal drag and trench suction forces.We use the StagYY convection code employing a visco-plastic rheology in a spherical annulus geometry. We consider an incompressible mantle under the Boussinesq approximation that is basally and internally heated.We show that continental separation follows a characteristic evolution with three distinctive phases: (1) A pre-rift phase that typically lasts for several hundreds of millions of years with tectonic quiescence in the suture and extensional stresses that are slowly building up. (2) A rift phase that further divides into a slow rift period of several tens of millions of years where stresses continuously increase followed by a rift acceleration period featuring an abrupt stress drop within several millions of years. The speed-up takes place before lithospheric break-up and therefore affects the structural architecture of the rifted margins. (3) The drifting phase with initially high divergence rates persists over tens of millions of years until the system adjust to new conditions and the spreading typically slows down.By illustrating the geodynamic connection between subduction dynamics and rift evolution, our results allow new interpretations of plate tectonic reconstructions. Rift acceleration within the second phase of rifting is compensated by enhanced convergence rates at subduction zones. This model outcome predicts enhanced subduction velocities, e.g. between North America and the Farallon plate during Central Atlantic rifting 200 My ago, or closure of potential back-arc basins such as in the proto-Andean ranges of South America

  20. The major tectonic boundaries of the Northern Red Sea rift, Egypt derived from geophysical data analysis (United States)

    Saleh, Salah; Pamukçu, Oya; Brimich, Ladislav


    In the present study, we have attempted to map the plate boundary between Arabia and Africa at the Northern Red Sea rift region including the Suez rift, Gulf of Aqaba-Dead Sea transform and southeastern Mediterranean region by using gravity data analysis. In the boundary analysis method which was used; low-pass filtered gravity anomalies of the Northern Red Sea rift region were computed. Different crustal types and thicknesses, sediment thicknesses and different heat flow anomalies were evaluated. According to the results, there are six subzones (crustal blocks) separated from each other by tectonic plate boundaries and/or lineaments. It seems that these tectonic boundaries reveal complex structural lineaments, which are mostly influenced by a predominant set of NNW-SSE to NW-SE trending lineaments bordering the Red Sea and Suez rift regions. On the other side, the E-W and N-S to NNE-SSW trended lineaments bordering the South-eastern Mediterranean, Northern Sinai and Aqaba-Dead Sea transform regions, respectively. The analysis of the low pass filtered Bouguer anomaly maps reveals that the positive regional anomaly over both the Red Sea rift and South-eastern Mediterranean basin subzones are considered to be caused by the high density of the oceanic crust and/or the anomalous upper mantle structures beneath these regions whereas, the broad medium anomalies along the western half of Central Sinai with the Suez rift and the Eastern Desert subzones are attributed to low-density sediments of the Suez rift and/or the thick upper continental crustal thickness below these zones. There are observable negative anomalies over the Northern Arabia subzone, particularly in the areas covered by Cenozoic volcanics. These negative anomalies may be attributed to both the low densities of the surface volcanics and/or to a very thick upper continental crust. On the contrary, the negative anomaly which belongs to the Gulf of Aqaba-Dead Sea transform zone is due to crustal thickening

  1. Geology of the Elephanta Island fault zone, western Indian rifted ...

    Indian Academy of Sciences (India)

    distinct faults ∼70 m apart. The inner (western) fault (figure 4a, b) is best observed at the south- western top edge of the quarry. It has an overall. N25. ◦. E trend, and a steep ... Mumbai harbour, with parts of Nhava–Sheva port immedi- ately to the east ... to and parallel with the fault surface; view looking down along the fault ...

  2. Geology of the Elephanta Island fault zone, western Indian rifted ...

    Indian Academy of Sciences (India)

    Panel (e) shows a hand-held red bole specimen with slickenlines. Small white arrows indicate two of the steps on the .... groups based on their morphology, namely 'V' or crescentic markings, steps, fractures, trains ..... evolution of the deep ocean basins adjoining the west- ern continental margin of India – a proposed model ...

  3. Mitochondrial and nuclear DNA phylogeography of Thymallus spp (grayling) provides evidence of ice-age mediated environmental perturbations in the world's oldest body of fresh water, Lake Baikal. (United States)

    Koskinen, Mikko T; Knizhin, Igor; Primmer, Craig R; Schlötterer, Christian; Weiss, Steven


    Theories on the hydrological history of Lake Baikal, the world's oldest and deepest body of freshwater, and its surrounding great rivers, are currently based solely on geological evidence and are conflicting. Baikal is inhabited by numerous zoogeographical enigmas but their high level of endemism has hindered phylogeographic inferences. We provide a biological perspective of the region's palaeo-hydrological development based on the demographic and genealogical history of the widespread Thymallus spp. (grayling). Phylogenetic reconstruction reveals that old lineages of grayling (pre-Pleistocene) currently inhabit the Enisey, Lena and Amur River basins. For Lake Baikal however, we conclude that a mid-Pleistocene colonization (110000-450000 years ago) of an unoccupied niche has occurred. Population genetic inferences support an Enisey-Angara river route of colonization into Baikal, corresponding to the cataclysmic palaeo-hydrological event that led to the formation of the lake's only contemporary outlet, and a subsequent range expansion several thousand kilometres into the uppermost reaches of the Selenga River basin. The evolutionary history of Lake Baikal grayling is congruent with the controversial hypothesis of repeated glaciation. However, considering the extraordinary levels of endemism and proposed Miocene or Oligocene coalescence of other faunal lineages, a less profound but equally consequential cycle of environmental perturbations may have taken place. Bi-parentally inherited microsatellite DNA loci supported the phylogenetic relationships of Thymallus spp. and the geographical expansion of Baikal grayling strikingly well. A Markov Chain Monte Carlo modelling approach suggested severe contemporary population decline during the last century, possibly reflecting the influence of an uncontrolled fishery on this treasured ecosystem. These complementary pictures of the demographic history of grayling underscore the breadth of historical inquiry that can be

  4. Orbit-related long-term climate cycles revealed in a 12-Myr continental record from Lake Baikal. (United States)

    Kashiwaya, K; Ochiai, S; Sakai, H; Kawai, T


    Quaternary records of climate change from terrestrial sources, such as lake sediments and aeolian sediments, in general agree well with marine records. But continuous records that cover more than the past one million years were essentially unavailable until recently, when the high-sedimentation-rate site of Lake Baikal was exploited. Because of its location in the middle latitudes, Lake Baikal is highly sensitive to insolation changes and the entire lake remained uncovered by ice sheets throughout the Pleistocene epoch, making it a valuable archive for past climate. Here we examine long sediment cores from Lake Baikal that cover the past 12 million years. Our record reveals a gradual cooling of the Asian continental interior, with some fluctuations. Spectral analyses reveal periods of about 400 kyr, 600 kyr and 1,000 kyr, which may correspond to Milankovitch periods (reflecting orbital cycles). Our results indicate that changes in insolation were closely related to long-term environmental variations in the deep continental interior, over the past 12 million years.

  5. Endemic Lake Baikal sponges from deep water. 1: Potential cryptic speciation and discovery of living species known only from fossils. (United States)

    Itskovich, Valeria B; Kaluzhnaya, Oxana V; Veynberg, Elena; Erpenbeck, Dirk


    We revealed new deep-water species and cryptic speciation within freshwater sponges of the endemic family Lubomirskiidae (Porifera; Demospongiae; Spongillina) based on molecular and spicule morphology analyses of ITS and CO1 mtDNA. Lubomirskiidae contains a group of closely related species which are a dominant component of the benthos in Lake Baikal, the world's deepest and most ancient lake. Spicule morphology was similar between two Recent samples and species only known previously from fossils in Late Pliocene (3.2-2.8 mya) sediments. Despite the morphological similarity with the cosmopolitan family Spongillidae, molecular analysis of ITS sequences has reliably assigned these species to Lubomirskiidae. This not only indicates that species identification of freshwater fossil sponge spicules should be made with caution, but also suggests that the structure of megascleres may not be a reliable character for interpretations of paleoclimatic reconstructions for the Baikal region. Our results do not support the current classification of Lubomirskiidae into its morphologically defined genera and species, suggesting a strong discrepancy between molecular and morphological variation in Baikalian sponges. This present contribution is the first part of a study on the phylogenetic relationships of the Lake Baikal deep water sponge fauna.

  6. The structures, stratigraphy and evolution of the Gulf of Corinth rift, Greece (United States)

    Taylor, Brian; Weiss, Jonathan R.; Goodliffe, Andrew M.; Sachpazi, Maria; Laigle, Mireille; Hirn, Alfred


    gradually rotate from 090-120° in the basement and early rift to 090-100° in the latest rift, reflecting a ˜10° rotation of the opening direction to the 005° presently measured by GPS. The sediments include a (locally >1.5-km-) thick, early-rift section, and a late-rift section (also locally >1.5-km-thick) that we subdivide into three sequences and correlate with seven 100-ka glacio-eustatic cycles. The Gulf depocentre has deepened through time (currently >700 mbsl) as subsidence has outpaced sedimentation. We measure the minimum total horizontal extension across the central and eastern Gulf as varying along strike between 4 and 10 km, and estimate full values of 6-11 km. The rift evolution is strongly influenced by the inherited basement fabric. The regional NNW structural fabric of the Hellenic nappes changes orientation to ESE in the Parnassos terrane, facilitating the focused north-south extension observed offshore there. The basement-penetrating faults lose seismic reflectivity above the 4-14-km-deep seismogenic zone. Multiple generations and dips of normal faults, some cross-cutting, accommodate extension beneath the GoC, including low-angle (15-20°) interfaces in the basement nappes. The thermally cool forearc setting and cross-orogen structures unaccompanied by magmatism make this rift a poor analogue and unlikely precursor for metamorphic core complex formation.

  7. Drought vulnerability drives land-use and land cover changes in the Rift Valley dry lands of Ethiopia

    NARCIS (Netherlands)

    Biazin, B.; Sterk, G.|info:eu-repo/dai/nl/157276465


    The Ethiopian Rift Valley is a dry land zone where for a long time pastoral communities have made their living from acacia-based woodlands. But many pastoralists have changed from a pastoral way of life to mixed farming over time. The aim of this study was to evaluate land-use and land cover (LULC)

  8. Geodynamics of rift-plume interaction in Iceland as constrained by new 40Ar/ 39Ar and in situ U-Pb zircon ages (United States)

    Martin, E.; Paquette, J. L.; Bosse, V.; Ruffet, G.; Tiepolo, M.; Sigmarsson, O.


    The interaction between a rift zone and a mantle plume leads to exceptional situations in Iceland where the island is 1.5 wider than expected, given the North-Atlantic spreading rate. In order to give a better idea of the timeframe of this evolution, we present 32 new 40Ar/ 39Ar and in-situ U-Pb dating on zircon from 16 volcanic systems located from the west to east coasts of Iceland. The North Iceland Rift Zone (NIRZ) was initiated at least 12 Ma ago. Furthermore, during these last 12 Ma, the NIRZ half spreading rate was between 0.7 and 1.2 cm/yr and it propagated to the south at a rate of 1.0-1.2 cm/yr. The excess width of Iceland can thus not be explained by faster spreading rate in the past. Here we discuss a model that explains the ~ 200 km 'excess' of crust, taking into account the eastward relocation of the rift zone and corresponding older crustal capture over the course of Iceland's geological history. The most recent rift relocation is dated at approximately 6 Ma at Snæfellsnes Peninsula in the west, whereas the oldest volcanic systems (15-13 Ma) from the extreme north east of Iceland were most likely generated at the Kolbeinsey ridge north of Iceland rather than in the NIRZ itself. The need for rift relocations and crustal capture to explain the width of Iceland strongly suggests that during rift-plume interaction the mantle plume plays an active role. It forces the active rift zone to be frequently relocated by rift jumps above its center leaving inactive rift zones as older synclines in the geological record. This result in an eastward position of the rift zone in Iceland relative to the North Atlantic ridge, and it can be predicted that in a few tens of millions of years the Mid-Atlantic ridge and the Icelandic plume may become decoupled.

  9. Crustal structure of the southern Okinawa Trough: Symmetrical rifting, submarine volcano, and potential mantle accretion in the continental back-arc basin (United States)

    Arai, Ryuta; Kodaira, Shuichi; Yuka, Kaiho; Takahashi, Tsutomu; Miura, Seiichi; Kaneda, Yoshiyuki


    Back-arc basins are a primary target to understand lithospheric evolution in extension associated with plate subduction. Most of the currently active back-arc basins formed in intraoceanic settings and host well-developed spreading centers where seafloor spreading has occurred. However, rift structure at its initial stage, a key to understand how the continental lithosphere starts to break in a magma-rich back-arc setting, is poorly documented. Here we present seismological evidence for structure of the southern Okinawa Trough, an active rift zone behind the Ryukyu subduction zone. We find that the southern Okinawa Trough exhibits an almost symmetric rift system across the rift axis (Yaeyama Rift) and that the sedimentary layers are highly cut by inward dipping normal faults. The rift structure also accompanies a narrow (2-7 km wide) on-axis intrusion resulted from passive upwelling of magma. On the other hand, an active submarine volcano is located 10 km away from the rift axis. The P wave velocity (Vp) model derived from seismic refraction data suggests that the crust has been significantly thinned from the original 25 km thick arc crust and the thinnest part with 12 km thickness occurs directly beneath the rift axis. The velocity model also reveals that there exists a thick layer with Vp of 6.5-7.2 km/s at lower crustal levels and may indicate that mantle materials accreted at the bottom of the crust during the crustal stretching. The abrupt crustal thinning and the velocity-depth profile suggest that the southern Okinawa Trough is at a transitional stage from continental rifting to seafloor spreading.

  10. Mindoro: a rifted microcontinent in collision with the Philippines volcanic arc; basin evolution and hydrocarbon potential (United States)

    Bird, P. R.; Quinton, N. A.; Beeson, M. N.; Bristow, C.

    The Mindoro area is the easternmost part of the Palawan-Mindoro microcontinent which rifted away from the South China margin during the Early Oligocene. Sea floor spreading carried it southwards until the Late Miocene, when collision with the Philippines Arc in the east, and other terranes to the south began. This paper considers the collision tectonics which operated at the eastern end of the microcontinent, which resulted in the inversion and thrusting of its rifted margin. These processes are documented by seismic data and field outcrop. The syn- and post-rift sedimentary sequences contain prospective source and reservoir intervals. Subsequent burial and deformation have resulted in the generation of hydrocarbons, as proved by the existence of several oil seeps on Mindoro Island, and by hydrocarbon shows recorded in offshore exploration wells. The structural history of the area since the Eocene is divided into four phases: Syn-Rift:Early Eocene-Mid-OligoceneDrift:Late Oligocene-Mid-MioceneCollision:Mid-Late Miocenetranspression:Latest Miocene-Present The unconformities which separate these stratigraphic sequences can be identified on seismic data. The sequences show characteristic differences in stratigraphy and structure, which control their prospectivity. The Syn-Rift Sequence consists of non-marine arkosic sandstones at the base, becoming marine towards the top and including platform and reefal limestones. The Drift Sequence records an overall regression, beginning with the deposition of marine shales, sandstones and detrital limestones and passes upwards into deltaic sands, shales and coals. This sequence contains reservoir quality sandstones and several potential source horizons. On Mindoro Island, the Collision/Transpression Sequence interval is dominated by coarse clastics derived from the uplifted collision zone. In offshore areas to the south and west, away from the collision zone with the arc, a more uniform blanket of parallel bedded shale and

  11. Land use changing and land use optimization of Lake Baikal basin on the example of two key areas (United States)

    Solodyankina, S.


    Lake Baikal contains roughly 20% of the world's unfrozen surface fresh water. It was declared a UNESCO World Heritage Site in 1996. Today levels of urbanization and economic stress on environmental resources is increasing on the shorts of the lake Baikal. The potential of economic development (industry, local tourism, and mining) of the Severobaykalsky and Sludyansky districts is rather high although they are characterized not only by beneficial features for local economy but also by considerable disadvantages for nature of this world valuable territory. This investigation show human-caused landscape changes during economic development of the two key areas in Baikal water catchment basin during 10 years (point of reference is 2000 year). Key areas are 1) the Baikalo-Patomskoe highland in the north of the Baikal catchment basin (Severobaykalsky district, Republic of Buryatia); 2) Khamar-Daban mountain system in the south of the Baikal catchment basin (Sludyansky districy, Irkutsk region). Since 2000 year land use of the territory has changed. Areas of agriculture were reduced but recreation activity on the bank of the lake was increased. Methods of GIS analysis and local statistic analysis of landscape characteristic were used. Nature, rural and urban areas ratio are estimated. Vegetation and soil condition assessment were made. The essence of this research is in helping to make decisions linked to upcoming problems: situation identification, evaluation and forecasting of the potential landscape condition, optimization of land use, mitigation of impact and mapping of territories and nature resources which have a high ecological value or endangered by industrial impact. For this purpose landscape maps of the territories on the base of the remote sensing information and field investigations were created. They used to calculate potential landscape functions of the territory without taking into account present impact of anthropogenic actions. Land use maps for years

  12. Influence of the inherited lithospheric structure on the interaction between the Kenyan and Ethiopian rifts across the Turkana depression: analog and numerical models (United States)

    Corti, Giacomo; Brune, Sascha; Ranalli, Giorgio


    Rifting processes result from the application of extensional stresses to a pre-deformed, and thus already structured, anisotropic lithosphere; consequently, the pre-rift lithospheric rheological structure and its along-axis variations play a major role in controlling the evolution and architecture of continental rifts. The East African Rift is a classic example of this process. The rift system developed within a region that has experienced several deformation events, which have given rise to significant variations in the rheological structure of the lithosphere. These variations -in turn- have played a major role on rift evolution, as clearly testified by the localisation and propagation of major rift segments within weak Proterozoic mobile belts surrounding cratonic areas. Linkage and mechanical interaction between adjacent rift segments typically occurred in correspondence to transverse pre-existing fabrics, where structurally complex areas (transfer zones) allowed significant along-axis variations in subsidence of grabens and elevation of uplifted flanks. One of these complex areas is the Turkana depression where the Ethiopian and Kenyan rifts interact. The region is characterised by anomalous morphology and distribution of deformation with respect to the rift valleys in Kenya and Ethiopia. In this work we investigate whether these anomalies result from the presence of a pre-existing Mesozoic graben, transverse to the trend of the rift valleys and characterized by thin crust and lithosphere. To this aim, we integrate crustal-scale, isothermal analog experiments with lithospheric-scale, thermo-mechanical numerical models. The two different methodologies generate very similar results, reproducing the along-axis transition from narrow rift valleys in Ethiopia/Kenya to a distributed deformation within the Turkana depression. Modeling results indicate that this variation results from the inherited distribution of lithospheric strength and -in particular- from the

  13. Insights into Rift Initiation, Evolution, and Failure from North America's Midcontinent Rift (United States)

    Stein, C. A.; Stein, S.; Elling, R. P.; Keller, G. R.; Kley, J.; Wysession, M. E.


    Recent studies of the Midcontinent Rift (MCR) near Lake Superior give insights into how some rifts start, evolve, and fail because the rift-filling volcanic and sedimentary rocks are exposed at the surface and well imaged by deep seismic reflection and gravity data. The MCR was traditionally considered to have formed by midplate extension and volcanism 1.1 Ga that ended due to compression from the Grenville orogeny, the 1.3 - 0.98 Ga assembly of Amazonia (Precambrian northeast South America), Laurentia (Precambrian North America), and other continents into the supercontinent of Rodinia. We find that a more plausible scenario is that the MCR formed as part of the rifting of Amazonia from Laurentia and became inactive once seafloor spreading was established. A cusp in Laurentia's apparent polar wander path just before the onset of MCR volcanism likely reflects the rifting. Such cusps have been observed elsewhere when continents separate and a new ocean forms between the two fragments. New analyses also find that the MCR's failure did not result from Grenville compression. This view is consistent with the observation that many intracontinental rifts form and fail as part of plate boundary reorganizations. Present-day continental extension in the East African Rift and seafloor spreading in the Red Sea and Gulf of Aden form a classic three-arm rift geometry as Africa splits into Nubia, Somalia, and Arabia. The West Central African Rift system formed during the Mesozoic breakup of Africa and South America and became inactive once full seafloor spreading was established on the Mid-Atlantic Ridge. An important feature of the MCR is that it is has aspects both of a continental rift - a segmented linear depression filled with sedimentary and igneous rocks - and a large igneous province (LIP). We view it as a LIP deposited in crust weakened by rifting, and thus first a rift and then a LIP. The MCR exhibits many key features of volcanic passive margins: seaward dipping

  14. Small HSPs molecular weights as new indication to the hypothesis of segregated status of thermophilic relict Gmelinoides fasciatus among baikal and palearctic amphipods

    Directory of Open Access Journals (Sweden)

    Timofeyev M.A.


    Full Text Available Among the great diverse of Baikal fauna of amphipods (more than 350 species and subspecies Gmelinoides fasciatus (Stebbing 1899 takes the special place. It is characterized by a high morphological variability and wide thermal-adaptive possibilities. By common opinion G. fasciatus is a thermophilic relict segregated from other Baikal temperature sensitive amphipods' fauna. In present study we tested hypothesis of segregated status of G. fasciatus among some Baikal and some Palearctic amphipods using of heat-shock proteins’ (HSP molecular weight as comparative biomarkers. We used heat-shock proteins (HSP from two families: HSP70 and small HSP (sHSP immunochemically related to α-crystalline. 15 species of Baikal amphipods from different genera and families and 2 Palearctic species from genus Gammarus were tested. It was shown, that molecular weights of HSP70 were the same in all investigated species and corresponds close to 70 kD. In the contrast, the molecular weights of sHSP in G. fasciatus was 37 kD and differed from all other species, in which molecular weights of sHSP were 35 kD. In sum, this study showed that sHSPs molecular weights may relate to evolutional differences between the close related species. Additionally, obtained data can be taken as new indication of segregated status of thermophilic relict G. fasciatus which linked with its phylogenetic history in Lake Baikal.

  15. How inheritance, geochemical and geophysical properties of the lithospheric mantle influence rift development and subsequent collision (United States)

    Picazo, Suzanne; Chenin, Pauline; Müntener, Othmar; Manatschal, Gianreto; Karner, Garry; Johnson, Christopher


    In magma-poor rifted margins, the rift structures, width of necking zones and overall geometry are controlled by the heterogeneities of geochemical and geophysical properties of the crust and mantle. In this presentation we focus on the mantle heterogeneities and their major implications on the closure of a hyper-extended rifted system. In our study, we review the clinopyroxene and spinel major element composition from the Liguria-Piemonte domain, the Pyrenean domain, the Dinarides and Hellenides ophiolites and the Iberia-Newfoundland rifted margins (Picazo et al, 2016). It would seem that during an extensional cycle i.e., from post-orogenic collapse to polyphase rifting to seafloor spreading, the mineral compositions of mantle peridotites are systematically modified. The initially heterogeneous subcontinental mantle cpx (inherited mantle type 1) equilibrated in the spinel peridotite field and is too enriched in Na2O and Al2O3 to be a residue of syn-rift melting. The heterogeneous inherited subcontinental mantle becomes progressively homogenized due to impregnation by MORB-type melts (refertilized mantle-type 2) during extensional thinning of the lithosphere. At this stage, cpx equilibrate with plagioclase and display lower Na2O and Al2O3 and high Cr2O3 contents. The system might evolve into breakup and oceanization (mantle type 3) i.e., self-sustained steady-state seafloor spreading. The different mantle-types are present in various reconstructed sections of magma-poor margins and display a systematic spatial distribution from mantle type 1 to 3 going oceanwards in Western and Central Europe. We estimated the density of the three identified mantle types using idealized modal peridotite compositions using the algorithm by Hacker et al, (2003). The density of the refertilized plagioclase peridotite is predicted to be lower than that of inherited subcontinental and depleted oceanic mantle. This has some interesting consequences on the reactivation of rifted margins

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

    Directory of Open Access Journals (Sweden)

    Geoffrey Wadge


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

  17. Rifting kinematics along the Arabian Margin, Red Sea (United States)

    Pierantoni, Pietro Paolo; Schettino, Antonio; Zanoni, Davide; Rasul, Najeeb


    The Red Sea represents a young basin floored by oceanic, transitional, or thinned continental crust that formed between Nubia and Arabia. According to most authors, rifting between Nubia and Arabia started in the late Oligocene ( 27 Ma) and it is still in progress in the northern part of the Red Sea at latitudes greater than 24°N. Conversely, the area south of 20.3°N displays a linear spreading ridge extending as south as 14.8°N, which formed in the early Pliocene (the first pulse of sea floor spreading occurred during chron C3n.2n, 4.62 Ma). A transition zone (between 24°N and 20.3°N, present-day coordinates) exists between the northern and the southern sectors, characterized by a segmented spreading center that started forming at 2.58 Ma (chron 2A, late Pliocene) in the southernmost area and propagated northwards. Some authors suggest that the present-day NE-SW spreading directions can be extended back to the early Miocene. However, we are going to show, on the basis of geological evidence from the Arabian margin, that at least two phases of rifting, characterized by distinct extension directions, are necessary to explain the observed structural pattern of deformation in a wide area extending from 28°N to 20°N. At present, there is no magnetic evidence for the existence of a linear spreading center in the northern Red Sea at latitudes higher than 24°N. In this area, the syn-rift pattern of deformation along the Arabian margin is only partly coherent with the present day NE-SW sea floor spreading directions and with the observed trend of fracture zones in the Red Sea. In fact, an older set of rift structures was found during 3 field trips performed along the northern and central Red Sea Arabian margin (2015-2016), suggesting the existence of an earlier rifting stage characterized by N-S trending strike-slip faults and E-W normal faults. The objective of the field trips was to investigate the hypothesis that an early phase of N-S extension and formation of

  18. Genome analysis of Rift Valley fever virus, Mayotte. (United States)

    Cêtre-Sossah, Catherine; Zeller, Hervé; Grandadam, Marc; Caro, Valérie; Pettinelli, François; Bouloy, Michèle; Cardinale, Eric; Albina, Emmanuel


    As further confirmation of a first human case of Rift Valley fever in 2007 in Comoros, we isolated Rift Valley fever virus in suspected human cases. These viruses are genetically closely linked to the 2006-2007 isolates from Kenya.

  19. A joint inversion for shear velocity and anisotropy: the Woodlark Rift, Papua New Guinea (United States)

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


    Trade-offs between velocity and anisotropy heterogeneity complicate the interpretation of differential traveltime data and have the potential to bias isotropic tomographic models. By constructing a simple parametrisation to describe an elastic tensor with hexagonal symmetry, we find analytic solutions to the Christoffel equations in terms of fast and slow horizontal velocities that allow us to simultaneously invert differential traveltime data and splitting data from teleseismic S arrivals to recover 3-D velocity and anisotropy structure. This technique provides a constraint on the depth-extent of shallow anisotropy, otherwise absent from interpretations based on SKS splitting alone. This approach is well suited to the young Woodlark Rift, where previous studies have found strong velocity variation and substantial SKS splitting in a continental rift with relatively simple geometry. This study images a low-velocity rift axis with ≤4 per cent spreading-parallel anisotropy at 50-100 km depth that separates regions of pre-existing lithospheric fabric, indicating the synchronous development of extensional crystallographic preferred orientation and lithospheric thinning. A high-velocity slab fragment north of the rift axis is associated with strike-parallel anisotropic fast axes, similar to that seen in the shallow mantle of some subduction zones. In addition to the insights provided by the anisotropy structure, the improvement in fit to the differential traveltime data demonstrates the merit to a joint inversion that accounts for anisotropy.

  20. Proterozoic rifting and major unconformities in Rajasthan, and their implications for uranium mineralisation

    International Nuclear Information System (INIS)

    Sinha-Roy, S.


    Evolution of the Precambrian terrain in Rajasthan has taken place via crustal consolidation of the basement at ca. 2.9 Ga, its cratonisation at ca. 2.5 Ga, through protracted tectonostratigraphic evolution of the Proterozoic cover sequences, following repeated rifting and Wilson cycles in the Aravalli and Delhi foldbelts. Consequently, the Proterozoic rift basins are characterised by growth faults and pull-aparts, and multitier volcanose dimentary sequences that contain a number of unconformities and stratigraphic breaks. The Archaean basement of the Mewar terrain that witnessed end-Archaean K-magmatism and ductile shearing, led to the creation of a possible uranium province, namely uranium enriched basement. This province acted as the source of remobilised uranium and its concentration at suitable multilevel structural and stratigraphic traps within the Proterozoic rift basins to give rise to unconformity-related syngenetic uranium mineralisation. Late Neoproterozoic to Pan-African tectonothermal reworking of the basement rocks produced fracture zones and caused Na-metasomatism giving rise to albitite-related uranium mineralisation. Based on an analysis of Proterozoic rift kinematics and lithofacies characteristics, five possible uranium-enriched stratigraphic horizons have been identified in the Aravalli and its equivalent sequences as well as in the North Delhi foldbelt sequences. From a regional synthesis, ten possible uranium metallogenic events, spanning ca. 2.5-0.5 Ga, are recognised in Rajasthan. These uranium events have predictive value for delineation of target areas for exploration. (author)

  1. Submarine thermal springs on the Galapagos Rift (United States)

    Corliss, J.B.; Dymond, J.; Gordon, L.I.; Edmond, J.M.; Von Herzen, R. P.; Ballard, Richard D.; Green, K.; Williams, D.; Bainbridge, A.; Crane, K.; Van Andel, T. H.


    The submarine hydrothermal activity on and near the Galápagos 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 oceanic lithosphere at the Galápagos Rift in the first million years may be vented from thermal springs, predominantly along the axial ridge within the rift valley. The vent areas are populated by animal communities. They appear to utilize chemosynthesis by sulfur-oxidizing bacteria to derive their entire energy supply from reactions between the seawater and the rocks at high temperatures, rather than photosynthesis

  2. The lakes of the Jordan Rift Valley

    International Nuclear Information System (INIS)

    Gat, J.R.


    This paper presents a summary of the proceedings of a workshop on the Lakes of the Jordan Rift Valley that was held in conjunction with the CRP on The Use of Isotope Techniques in Lake Dynamics Investigations. The paper presents a review of the geological, hydrogeological and physical limnological setting of the lakes in the Jordan Rift Valley, Lake Hula, Lake Kinneret and the Dead Sea. This is complemented by a description of the isotope hydrology of the system that includes the use of a wide range of isotopes: oxygen-18, deuterium, tritium, carbon-14, carbon-13, chlorine isotopes, boron-11 and helium-3/4. Environmental isotope aspects of the salt balances of the lakes, their palaeolimnology and biogeochemical tracers are also presented. The scope of application of isotopic tracers is very broad and provides a clear insight into many aspects of the physical, chemical and biological limnology of the Rift Valley Lakes. (author)

  3. Magma genesis by rifting of oceanic lithosphere above anomalous mantle: Terceira Rift, Azores


    Beier, C.; Haase, K. M.; Abouchami, W.; Krienitz, M-S.; Hauff, Folkmar


    [1] The Terceira Rift formed relatively recently (∼1 Ma ago) by rifting of the old oceanic lithosphere of the Azores Plateau and is currently spreading at a rate of 2–4mm/a. Together with the Mid-Atlantic Ridge, the Terceira Rift forms a triple junction that separates the Eurasian, African, and American Plates. Four volcanic systems (São Miguel, João de Castro, Terceira, Graciosa), three of which are islands, are distinguished along the axis and are separated by deep avolcanic basins similar ...

  4. Subsidence History of the Rukwa Rift in South West Tanzania ...

    African Journals Online (AJOL)

    The variation in subsidence rate during rift basin development is a good indication for the Geodynamic history of a sedimentary basin. The sedimentary section of Ivuna Well is herein used to explain the structural evolution of Rukwa Basin within the Western Rift of the East African Rift System. The sedimentary record of ...

  5. Pyrogenic Transformations of the Baikal Lake Forests. Retrospective and Contemporary Issues

    Directory of Open Access Journals (Sweden)

    M. D. Yevdokimenko


    Full Text Available In the forests of the Baikal Lake basin annual fire activity historically has been higher as compared to surrounding forest areas due to specific climatic conditions and altitude-controlled vegetation structure. The regional forests, predominantly light coniferous, develop under a high or, in dry years, extreme-fire-activity regime. Common pine and larch tree stands of fire origin are periodically thinned by fire. The productivity of the fire-intact parts of such stands decreases as a result of fire-caused soil condition disturbances. In extreme fire years, large fires cover landscapes and lead to irreversible forest ecosystem degradation and, hence, to local deforestation. In the past, forest fire activity and area burned increased with increasing use of the regional forests beginning with hunting, wood extraction by dwellers of local settlements, Trans-Siberian Rail Road building and, finally, industrial-scale logging. In 1970–1980, the regional fire situation was successfully controlled due to improvements of forest use and protection. However, the recently relaxed forest economy standards have resulted in loss of the progress achieved.

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

    Schuster, Mathieu; Nutz, Alexis


    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

  7. Transfer fault earthquake in compressionally reactivated back-arc failed rift: 1948 Fukui earthquake (M7.1), Japan (United States)

    Ishiyama, Tatsuya; Kato, Naoko; Sato, Hiroshi; Koshiya, Shin


    Back-arc rift structures in many subduction zones are recognized as mechanically and thermally weak zones that possibly play important roles in strain accommodation at later post-rift stages within the overriding plates. In case of Miocene back-arc failed rift structures in the Sea of Japan in the Eurasian-Pacific subduction system, the mechanical contrasts between the crustal thrust wedges of the pre-rift continental crust and high velocity lower crust have fundamentally controlled the styles of post-rift, Quaternary active deformation (Ishiyama et al. 2016). In this study, we show a possibility that strike-slip M>7 devastating earthquakes in this region have been gregion enerated by reactivation of transfer faults highly oblique to the rift axes. The 1948 Fukui earthquake (M7.1), onshore shallow seismic event with a strike-slip faulting mechanism (Kanamori, 1973), resulted in more than 3,500 causalities and destructive damages on the infrastructures. While geophysical analyses on geodetic measurements based on leveling and triangulation networks clearly show coseismic left-lateral fault slip on a NNW striking vertical fault plane beneath the Fukui plain (Sagiya, 1999), no evidence for coseismic surface rupture has been identified based on both post-earthquake intensive fieldwork and recent reexamination of stereopair interpretations using 1/3,000 aerial photographs taken in 1948 (Togo et al., 2000). To find recognizable fault-related structures that deform Neogene basin fill sediments, we collected new 9.6-km-long high-resolution seismic reflection data across the geodetically estimated fault plane and adjacent subparallel active strike slip faults, using 925 offline recorders and Envirovib truck as a seismic source. A depth-converted section to 1.5 km depth contains discontinuous seismic reflectors correlated to Miocene volcaniclastic deposits and depression of the overlying Plio-Pleistocene sediments above the geodetically determined fault plane. We interpreted

  8. Stratigraphy, Structure and Tectonics of the Eyjafjarðaráll Rift, Abandoned Southern Segment of the Kolbeinsey Ridge, North Iceland (United States)

    Brandsdottir, B.; Karson, J. A.; Magnúsdóttir, S.; Detrick, B.; Driscoll, N. W.


    The multi-branched plate boundary across Iceland is made up of divergent and oblique rifts, and transform zones, characterized by entwined extensional and transform tectonics. The Tjörnes Fracture Zone (TFZ) is a complex transform linking the northern rift zone (NVZ) on land with the offshore Kolbeinsey Ridge. The TFZ lacks a clear topographic expression typical of oceanic fracture zones. The transform zone is roughly 150 km long (E-W) by 50-75 km wide (N-S) with three N-S trending pull-apart basins bounded by a complex array of normal and oblique-slip faults. The offshore extension of the NVZ, the Grímsey Oblique Rift, is composed of several active volcanic systems with N-S trending fissure swarms, including the Skjálfandadjúp Basin (SB). The magma-starved southern extension of the KR, the 80 km NS and 15-20 EW Eyjafjarðaráll Rift (ER), is made up of dominantly normal faults merging southwards with a system of right-lateral strike-slip faults with vertical displacement up to 15 m in the Húsavík Flatey Fault Zone (HFFZ). The northern ER is a 500-700 m deep asymmetric rift, framed by normal faults with 20-25 m vertical displacement, To the south, transform movement associated with the HFFZ has created a NW- striking pull-apart basin with frequent earthquake swarms. Details of the tectonic framework of the ER are documented in a compilation of data from aerial photos, satellite images, field mapping, multibeam bathymetry, high-resolution seismic reflection surveys (Chirp) and seismicity. The TFZ rift basins contain post-glacial sediments of variable thickness. Strata in the western ER and SB basins dip steeply E along the normal faults, towards the deepest part of the rift. The eastern side of the ER and SB basins differ considerably from the western side, with near-vertical faults. Correlation of Chirp reflection data and tephrachronology from a sediment core reveal major rifting episodes between 10-12.1 kyrs BP activating both the Eyjafjarðaráll and Skj

  9. Syn-rift unconformities punctuating the lower-middle Cambrian transition in the Atlas Rift, Morocco (United States)

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


    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.

  10. Geochemical and 40Ar/39Ar constraints on the evolution of volcanism in the Woodlark Rift, Papua New Guinea (United States)

    Catalano, Joseph P.

    The tectonic mechanisms producing Pliocene to active volcanism in eastern Papua New Guinea (PNG) have been debated for decades. In order to assess mechanisms that produce volcanism in the Woodlark Rift, we evaluate the evolution of volcanism in eastern PNG using 40Ar/39Ar thermochronology and whole rock geochemistry. Active volcanism in southeastern Papua New Guinea occurs on the Papuan Peninsula (Mt. Lamington, Mt. Victory and Waiwa), in the Woodlark Rift (Dobu Island, SE Goodenough Island, and Western Fergusson Island), and in the Woodlark Basin. In the Woodlark Basin, seafloor spreading is active and decompression melting of the upper mantle is producing basaltic magmatism. However, the cause of Pliocene and younger volcanism in the Woodlark Rift is controversial. Two hypotheses for the tectonic setting have been proposed to explain Pliocene and younger volcanism in the Woodlark Rift: (1) southward subduction of Solomon Sea lithosphere beneath eastern PNG at the Trobriand Tough and (2) decompression melting of mantle, previously modified by subduction, as the lithosphere undergoes extension associated with the opening of the Woodlark Basin. A comparison of 40Ar/39Ar ages with high field strength element (HFSE) concentrations in primary magmas indicates that HFSE concentrations correlate with age in the Woodlark rift. These data support the hypothesis that Pliocene to active volcanism in the Woodlark Rise and D'Entrecasteaux Islands results from decompression melting of a relict mantle wedge. The subduction zone geochemical signatures (negative HFSE anomalies) in Woodlark Rift lavas younger than 4 m.y. are a relict from older subduction beneath eastern Papua, likely in the middle Miocene. As the lithosphere is extended ahead of the tip of the westward propagating seafloor spreading center in the Woodlark Basin, the composition of volcanism is inherited from prior arc magmatism (via flux melting) and through time evolves toward magmatism associated with a rifting

  11. 3D Numerical Rift Modeling with Application to the East African Rift System (United States)

    Glerum, A.; Brune, S.; Naliboff, J.


    As key components of plate tectonics, continental rifting and the formation of passive margins have been extensively studied with both analogue models and numerical techniques. Only recently however, technical advances have enabled numerical investigations into rift evolution in three dimensions, as is actually required for including those processes that cause rift-parallel variability, such as structural inheritance and oblique extension (Brune 2016). We use the massively parallel finite element code ASPECT (Kronbichler et al. 2012; Heister et al. 2017) to investigate rift evolution. ASPECT's adaptive mesh refinement enables us to focus resolution on the regions of interest (i.e. the rift center), while leaving other areas such as the asthenospheric mantle at coarse resolution, leading to kilometer-scale local mesh resolution in 3D. Furthermore, we implemented plastic and viscous strain weakening of the nonlinear viscoplastic rheology required to develop asymmetric rift geometries (e.g. Huismans and Beaumont 2003). Additionally created plugins to ASPECT allow us to specify initial temperature and composition conditions based on geophysical data (e.g. LITHO1.0, Pasyanos et al. 2014) or to prescribe more general along-strike variation in the initial strain seeding the rift. Employing the above functionality, we construct regional models of the East African Rift System (EARS), the world's largest currently active rift. As the EARS is characterized by both orthogonal and oblique rift sections, multi-phase extension histories as well as magmatic and a-magmatic branches (e.g. Chorowicz 2005; Ebinger and Scholz 2011), it constitutes an extensive natural laboratory for our research into the 3D nature of continental rifting. References:Brune, S. (2016), in Plate boundaries and natural hazards, AGU Geophysical Monograph 219, J. C. Duarte and W. P. Schellart (Eds.). Chorowicz, J. (2005). J. Afr. Earth Sci., 43, 379-410. Ebinger, C. and Scholz, C. A. (2011), in Tectonics of

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


    Álvaro, J. Javier; Ezzouhairi, Hassan; Clausen, Sébastien; Ribeiro, Maria Luísa; Solá, Ana Rita


    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 geometrie...

  13. Cratonic roots and lower crustal seismicity: Investigating the role of deep intrusion in the Western rift, Africa (United States)

    Drooff, C.; Ebinger, C. J.; Lavayssiere, A.; Keir, D.; Oliva, S. J.; Tepp, G.; Gallacher, R. J.


    Improved seismic imaging beneath the African continent reveals lateral variations in lithospheric thickness, and crustal structure, complementing a growing crust and mantle xenolith data base. Border fault systems in the active cratonic rifts of East Africa are characterized by lower crustal seismicity, both in magmatic sectors and weakly magmatic sectors, providing constraints on crustal rheology and, in some areas, magmatic fluid migration. We report new seismicity data from magmatic and weakly magmatic sectors of the East African rift zone, and place the work in the context of independent geophysical and geochemical studies to models for strain localization during early rifting stages. Specifically, multidisciplinary studies in the Magadi Natron rift sectors reveal volumetrically large magmatic CO2 degassing along border faults with seismicity along projections of surface dips to the lower crust. The magmatic CO2 degassing and high Vp/Vs ratios and reflectivity of the lower crust implies that the border fault serves a conduit between the lower crustal underplating and the atmospheric. Crustal xenoliths in the Eastern rift sector indicate a granulitic lower crust, which is relatively weak in the presence of fluids, arguing against a strong lower crust. Within magmatic sectors, seismic, structural, and geochemistry results indicate that frequent lower crustal earthquakes are promoted by elevated pore pressures from volatile degassing along border faults, and hydraulic fracture around the margins of magma bodies. Within some weakly magmatic sectors, lower crustal earthquakes also occur along projections of border faults to the lower crust (>30 km), and they are prevalent in areas with high Vp/Vs in the lower crust. Within the southern Tanganyika rift, focal mechanisms are predominantly normal with steep nodal planes. Our comparative studies suggest that pervasive metasomatism above a mantle plume, and melt extraction in thin zones between cratonic roots, lead to

  14. Sediment Dispersal on the Topset of a Tectonically Active Shelf-edge Delta: an Interplay Between Sediment Supply and Subsidence, as Demonstrated for the Selenga River, Lake Baikal, Russia (United States)

    Nittrouer, J. A.; Dong, T. Y.


    The Selenga River delta (Lake Baikal, Russia), located adjacent to an active rift margin and filling the world's deepest lake, represents one of the few examples of a modern shelf-edge system. Research into sediment dispersal on the Selenga delta was undertaken with the aim of linking topset morphodynamics and sediment accumulation patterns with the production of stratigraphy. The subaerial delta is constructed of three active lobes that receive varying amounts of water and sediment, distributed among a nine-order bifurcating channel network. Data from multiple expeditions include bathymetric and water-discharge measurements, side-scan images of the bed and banks, sediment samples, and bankline composition (including sediment type and vegetation). This information is analyzed to evaluate spatial variability in: 1. channel geometry, 2. boundary shear stress, 3. bedform size, and 4. bed sediment composition. The delta possesses downstream sediment fining, whereby median channel bed size decreases by two orders of magnitude over thirty kilometers, from a predominantly gravel and sand mixture near the delta apex to silt and fine sand at the lake interface. The location of gravel termination among distributary channels coincides with a reduction in sediment-transport capacity, as assessed by measurements of boundary shear stress. Interestingly, backwater hydrodynamics, which operate as important influences on bed grain size for many deltas, is not a major influence on the Selenga system. Instead, a non-linear downstream decrease in boundary shear stress arises due to partitioning of water among the bifurcating channel network. As has been documented in previous studies, gravel and coarse sand are absent on the delta foreset and bottomset (i.e., the rift axis), despite a continuous sediment feed from upstream that should provide the supply necessary to increase bed slope and enhance transport capacity over the delta. To reconcile this discrepancy, a tectonic timescale is

  15. Rift Valley fever, Mayotte, 2007-2008. (United States)

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


    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.

  16. Groundwater links between Kenyan Rift Valley lakes


    Becht, Robert; Mwango, Fred; Muno, Fred Amstrong


    The series of lakes in the bottom of the Kenyan Rift valley are fed by rivers and springs. Based on the water balance, the relative positions determining the regional groundwater flow systems and the analysis of natural isotopes it can be shown that groundwater flows from lake Naivasha to lake Magadi, Elementeita, Nakuru and Bogoria.

  17. Molecular Rift: Virtual Reality for Drug Designers. (United States)

    Norrby, Magnus; Grebner, Christoph; Eriksson, Joakim; Boström, Jonas


    Recent advances in interaction design have created new ways to use computers. One example is the ability to create enhanced 3D environments that simulate physical presence in the real world--a virtual reality. This is relevant to drug discovery since molecular models are frequently used to obtain deeper understandings of, say, ligand-protein complexes. We have developed a tool (Molecular Rift), which creates a virtual reality environment steered with hand movements. Oculus Rift, a head-mounted display, is used to create the virtual settings. The program is controlled by gesture-recognition, using the gaming sensor MS Kinect v2, eliminating the need for standard input devices. The Open Babel toolkit was integrated to provide access to powerful cheminformatics functions. Molecular Rift was developed with a focus on usability, including iterative test-group evaluations. We conclude with reflections on virtual reality's future capabilities in chemistry and education. Molecular Rift is open source and can be downloaded from GitHub.

  18. Reemergence of Rift Valley fever, Mauritania, 2010. (United States)

    Faye, Ousmane; Ba, Hampathé; Ba, Yamar; Freire, Caio C M; Faye, Oumar; Ndiaye, Oumar; Elgady, Isselmou O; Zanotto, Paolo M A; Diallo, Mawlouth; Sall, Amadou A


    A Rift Valley fever (RVF) outbreak in humans and animals occurred in Mauritania in 2010. Thirty cases of RVF in humans and 3 deaths were identified. RVFV isolates were recovered from humans, camels, sheep, goats, and Culex antennatus mosquitoes. Phylogenetic analysis of isolates indicated a virus origin from western Africa.

  19. Unexpected Rift Valley fever outbreak, northern Mauritania. (United States)

    El Mamy, Ahmed B O; Baba, Mohamed Ould; Barry, Yahya; Isselmou, Katia; Dia, Mamadou L; El Kory, Mohamed O B; Diop, Mariam; Lo, Modou Moustapha; Thiongane, Yaya; Bengoumi, Mohammed; Puech, Lilian; Plee, Ludovic; Claes, Filip; de La Rocque, Stephane; Doumbia, Baba


    During September-October 2010, an unprecedented outbreak of Rift Valley fever was reported in the northern Sahelian region of Mauritania after exceptionally heavy rainfall. Camels probably played a central role in the local amplification of the virus. We describe the main clinical signs (hemorrhagic fever, icterus, and nervous symptoms) observed during the outbreak.

  20. Rift Valley fever: A neglected zoonotic disease? (United States)

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

  1. Rift Valley Fever, Mayotte, 2007–2008 (United States)

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


    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

  2. Rifte Guaritas basin compartmentation in Camaqua

    International Nuclear Information System (INIS)

    Preissler, A; Rolim, S; Philipp, R.


    The study contributes to the knowledge of the tectonic evolution of the Guaritas rift basin in Camaqua. Were used aero magnetic geophysical data for modeling the geometry and the depth of the structures and geological units. The research was supported in processing and interpretation of Aster images (EOS-Terra), which were extracted from geophysical models and digital image

  3. Episodic kinematics in continental rifts modulated by changes in mantle melt fraction (United States)

    Lamb, Simon; Moore, James D. P.; Smith, Euan; Stern, Tim


    Oceanic crust is created by the extraction of molten rock from underlying mantle at the seafloor ‘spreading centres’ found between diverging tectonic plates. Modelling studies have suggested that mantle melting can occur through decompression as the mantle flows upwards beneath spreading centres, but direct observation of this process is difficult beneath the oceans. Continental rifts, however—which are also associated with mantle melt production—are amenable to detailed measurements of their short-term kinematics using geodetic techniques. Here we show that such data can provide evidence for an upwelling mantle flow, as well as information on the dimensions and timescale of mantle melting. For North Island, New Zealand, around ten years of campaign and continuous GPS measurements in the continental rift system known as the Taupo volcanic zone reveal that it is extending at a rate of 6-15 millimetres per year. However, a roughly 70-kilometre-long segment of the rift axis is associated with strong horizontal contraction and rapid subsidence, and is flanked by regions of extension and uplift. These features fit a simple model that involves flexure of an elastic upper crust, which is pulled downwards or pushed upwards along the rift axis by a driving force located at a depth greater than 15 kilometres. We propose that flexure is caused by melt-induced episodic changes in the vertical flow forces that are generated by upwelling mantle beneath the rift axis, triggering a transient lower-crustal flow. A drop in the melt fraction owing to melt extraction raises the mantle flow viscosity and drives subsidence, whereas melt accumulation reduces viscosity and allows uplift—processes that are also likely to occur in oceanic spreading centres.

  4. Rifting Thick Lithosphere - Canning Basin, Western Australia (United States)

    Czarnota, Karol; White, Nicky


    The subsidence histories and architecture of most, but not all, rift basins are elegantly explained by extension of ~120 km thick lithosphere followed by thermal re-thickening of the lithospheric mantle to its pre-rift thickness. Although this well-established model underpins most basin analysis, it is unclear whether the model explains the subsidence of rift basins developed over substantially thick lithosphere (as imaged by seismic tomography beneath substantial portions of the continents). The Canning Basin of Western Australia is an example where a rift basin putatively overlies lithosphere ≥180 km thick, imaged using shear wave tomography. Subsidence modelling in this study shows that the entire subsidence history of the account for the observed subsidence, at standard crustal densities, the lithospheric mantle is required to be depleted in density by 50-70 kg m-3, which is in line with estimates derived from modelling rare-earth element concentrations of the ~20 Ma lamproites and global isostatic considerations. Together, these results suggest that thick lithosphere thinned to > 120 km is thermally stable and is not accompanied by post-rift thermal subsidence driven by thermal re-thickening of the lithospheric mantle. Our results show that variations in lithospheric thickness place a fundamental control on basin architecture. The discrepancy between estimates of lithospheric thickness derived from subsidence data for the western Canning Basin and those derived from shear wave tomography suggests that the latter technique currently is limited in its ability to resolve lithospheric thickness variations at horizontal half-wavelength scales of <300 km.

  5. A bottom-driven mechanism for distributed faulting: Insights from the Gulf of California Rift (United States)

    Persaud, P.; Tan, E.; Choi, E.; Contreras, J.; Lavier, L. L.


    findings motivate a suite of 3D models of the early plate boundary evolution in the Gulf, and highlight the importance of local stress field perturbations as a mechanism for broadening the deformation zone in other regions such as the Basin and Range, Rio Grande Rift and Malawi Rift.

  6. Primary production and microbial activity in the euphotic zone of Lake Baikal (Southern Basin) during late winter

    Czech Academy of Sciences Publication Activity Database

    Straškrábová, Viera; Izmest’yeva, L. R.; Maksimova, E. A.; Fietz, S.; Nedoma, Jiří; Borovec, Jakub; Kobanova, G. I.; Shchetinina, E. V.; Pislegina, E. V.


    Roč. 46, 1-4 (2005), s. 57-73 ISSN 0921-8181 Grant - others:EU(XE) CONTINENT EVK2-2000-0057 Institutional research plan: CEZ:AV0Z6017912 Keywords : primary production * bacterial production * microbial loop Subject RIV: DA - Hydrology ; Limnology Impact factor: 2.223, year: 2005

  7. Asymmetric rifting, breakup and magmatism across conjugate margin pairs: insights from Newfoundland to Ireland (United States)

    Peace, Alexander L.; Welford, J. Kim; Foulger, Gillian R.; McCaffrey, Ken J. W.


    Continental extension, subsequent rifting and eventual breakup result in the development of passive margins with transitional crust between extended continental crust and newly created oceanic crust. Globally, passive margins are typically classified as either magma-rich or magma-poor. Despite this simple classification, magma-poor margins like the West Orphan Basin, offshore Newfoundland, do exhibit some evidence of localized magmatism, as magmatism to some extent invariably accompanies all continental breakup. For example, on the Newfoundland margin, a small volcanic province has been interpreted near the termination of the Charlie Gibbs Fracture Zone, whereas on the conjugate Irish margin within the Rockall Basin, magmatism appears to be more widespread and has been documented both in the north and in the south. The broader region over which volcanism has been identified on the Irish margin is suggestive of magmatic asymmetry across this conjugate margin pair and this may have direct implications for the mechanisms governing the nature of rifting and breakup. Possible causes of the magmatic asymmetry include asymmetric rifting (simple shear), post-breakup thermal anomalies in the mantle, or pre-existing compositional zones in the crust that predispose one of the margins to more melting than its conjugate. A greater understanding of the mechanisms leading to conjugate margin asymmetry will enhance our fundamental understanding of rifting processes and will also reduce hydrocarbon exploration risk by better characterizing the structural and thermal evolution of hydrocarbon bearing basins on magma-poor margins where evidence of localized magmatism exists. Here, the latest results of a conjugate margin study of the Newfoundland-Ireland pair utilizing seismic interpretation integrated with other geological and geophysical datasets are presented. Our analysis has begun to reveal the nature and timing of rift-related magmatism and the degree to which magmatic asymmetry

  8. Geometry of the neoproterozoic and paleozoic rift margin of western Laurentia: Implications for mineral deposit settings (United States)

    Lund, K.


    The U.S. and Canadian Cordilleran miogeocline evolved during several phases of Cryogenian-Devonian intracontinental rifting that formed the western mangin of Laurentia. Recent field and dating studies across central Idaho and northern Nevada result in identification of two segments of the rift margin. Resulting interpretations of rift geometry in the northern U.S. Cordillera are compatible with interpretations of northwest- striking asymmetric extensional segments subdivided by northeast-striking transform and transfer segments. The new interpretation permits integration of miogeoclinal segments along the length of the western North American Cordillera. For the U.S. Cordillera, miogeoclinal segments include the St. Mary-Moyie transform, eastern Washington- eastern Idaho upper-plate margin, Snake River transfer, Nevada-Utah lower-plate margin, and Mina transfer. The rift is orthogonal to most older basement domains, but the location of the transform-transfer zones suggests control of them by basement domain boundaries. The zigzag geometry of reentrants and promontories along the rift is paralleled by salients and recesses in younger thrust belts and by segmentation of younger extensional domains. Likewise, transform transfer zones localized subsequent transcurrent structures and igneous activity. Sediment-hosted mineral deposits trace the same zigzag geometry along the margin. Sedimentary exhalative (sedex) Zn-Pb-Ag ??Au and barite mineral deposits formed in continental-slope rocks during the Late Devonian-Mississippian and to a lesser degree, during the Cambrian-Early Ordovician. Such deposits formed during episodes of renewed extension along miogeoclinal segments. Carbonate-hosted Mississippi Valley- type (MVT) Zn-Pb deposits formed in structurally reactivated continental shelf rocks during the Late Devonian-Mississippian and Mesozoic due to reactivation of preexisting structures. The distribution and abundance of sedex and MVT deposits are controlled by the

  9. Specifics of fire-preventing arrangements in the forests of Baikal region

    Directory of Open Access Journals (Sweden)

    M. D. Evdokimenko


    Full Text Available Fire risk in major forest types and concomitant vegetation complexes across all altitudinal belts has been analyzed. High fire risk in woodlands is determined by domination of light needle coniferous stands in their structure and specific climate with continuous spring-summer droughts. Thus, the risk of landscape wildfires is high. The most drastic situations occur in very dry years of climatic cycles during forest pyrogenic anomalies when fire spreads across the main landscapes in several nature areas. Current fire-frequency is incompatible with high biosphere status of nature complex of Lake Baikal as an object of the World nature heritage. Extensive forest exploitation is unacceptable as well. Fire-prevention measures in the area require modernization. According to the results of many years of comparative studies of fire risk in phytocenoses with different species composition and structure of tree layers, the techniques of making fire stopping barriers were developed. The scheme of dividing the managed forests into isolated cells separated by special obstacles and fire-resistant forest borders combined with commonly used fire barriers is suggested. Fire-resistant barriers should be formed on both sides of main roads, passing through the intensively exploited woodlands dominating with common pine Pinus sylvestris L., Siberian stone pine Pinus sibirica Du Tour, Siberian spruce Picea obovata Ledeb., and Siberian fir Abies sibirica Ledeb. tree species. Such barriers are intended to stop the fire front of crown fires. The barrier width is determined by the cell order. The barriers are bordered with clearings with scarified soil strips of 3–4 meters in width. Trees and shrubs damaged in the process are removed during clutter cleaning. In places where the barrier passes through coniferous tree stands longitudinal corridors with scarified soil strips every 20–30 meters should be made. Reforestation and thinning are supposed to be combined with


    Directory of Open Access Journals (Sweden)

    V. Yu. Timofeev


    Full Text Available Modern methods for determination of gravity values make it possible to obtain measurements with the accuracy up to 10–9 from g0 of the normal value (up to 1 microgal = 10 m/sec2. While all the systematic and periodic effects are excluded, a question is raised about stability of the gravity field of the Earth over time. Changes of the altitude (the Earth’s radius with time can be estimated with an accuracy of 0.1 mm by modern space geodetic techniques, such as VLBI method. Our experiments for evaluation of stability of the gravity values over the past decades are based on the data obtained by Russian and foreign observatories using absolute ballistic laser gravimeters. The results put a limit of 10–10 per year to changes of the Earth’s radius. These estimations can be useful for testing hypotheses in tectonics.Measurements of non-tidal variations of gravity (Δg, which were obtained from 1992 to 2012 at the Talaya seismic station (located in the south-western part of the Baikal region, are interpreted together with GPS observation data. At the Talaya seismic station, the linear component of gravity variations corresponds to changes in the elevation of this site. The correlation coefficient is close to the normal value of the vertical gradient of gravity. At this site, coseismic gravity variations at the time of the Kultuk earthquake (27 August 2008, Mw=6.3 were caused by a combined effect of the change of the site’s elevation and deformation of the crust. Our estimations of the coseismic effects are consistent with results obtained by modeling based on the available seismic data.

  11. Drift dives and prolonged surfacing periods in Baikal seals: resting strategies in open waters? (United States)

    Watanabe, Yuuki Y; Baranov, Eugene A; Miyazaki, Nobuyuki


    Many pinnipeds frequently rest on land or ice, but some species remain in open waters for weeks or months, raising the question of how they rest. A unique type of dive, called drift dives, has been reported for several pinnipeds with suggested functions of rest, food processing and predator avoidance. Prolonged surfacing periods have also been observed in captive seals and are thought to aid food processing. However, information from other species in a different environment would be required to better understand the nature and function of this behavior. In this study, we attached multi-sensor tags to Baikal seals Pusa sibirica, a rare, freshwater species that has no aquatic predators and few resting grounds during the ice-free season. The seals exhibited repeated drift dives (mean depth, 116 m; duration, 10.1 min) in the daytime and prolonged periods at the surface (mean duration, 1.3 h) mainly around dawn. Drift dives and prolonged surfacing periods were temporally associated and observed between a series of foraging dives, suggesting a similar function, i.e. a combination of resting and food processing. The maximum durations of both drift and foraging dives were 15.4 min, close to the aerobic dive limit of this species; therefore, metabolic rates might not be significantly depressed during drift dives, further supporting the function of food processing rather than purely resting. Our results also show that drift diving can occur in a predator-free environment, and thus predator avoidance is not a general explanation of drift dives in pinnipeds. © 2015. Published by The Company of Biologists Ltd.

  12. Commercial helium reserves, continental rifting and volcanism (United States)

    Ballentine, C. J.; Barry, P. H.; Hillegonds, D.; Fontijn, K.; Bluett, J.; Abraham-James, T.; Danabalan, D.; Gluyas, J.; Brennwald, M. S.; Pluess, B.; Seneshens, D.; Sherwood Lollar, B.


    Helium has many industrial applications, but notably provides the unique cooling medium for superconducting magnets in medical MRI scanners and high energy beam lines. In 2013 the global supply chainfailed to meet demand causing significant concern - the `Liquid Helium Crisis' [1]. The 2017 closure of Quatar borders, a major helium supplier, is likely to further disrupt helium supply, and accentuates the urgent need to diversify supply. Helium is found in very few natural gas reservoirs that have focused 4He produced by the dispersed decay (a-particle) of U and Th in the crust. We show here, using the example of the Rukwa section of the Tanzanian East African Rift, how continental rifting and local volcanism provides the combination of processes required to generate helium reserves. The ancient continental crust provides the source of 4He. Rifting and associated magmatism provides the tectonic and thermal mechanism to mobilise deep fluid circulation, focusing flow to the near surface along major basement faults. Helium-rich springs in the Tanzanian Great Rift Valley were first identified in the 1950's[2]. The isotopic compositions and major element chemistry of the gases from springs and seeps are consistent with their release from the crystalline basement during rifting [3]. Within the Rukwa Rift Valley, helium seeps occur in the vicinity of trapping structures that have the potential to store significant reserves of helium [3]. Soil gas surveys over 6 prospective trapping structures (1m depth, n=1486) show helium anomalies in 5 out of the 6 at levels similar to those observed over a known helium-rich gas reservoir at 1200m depth (7% He - Harley Dome, Utah). Detailed macroseep gas compositions collected over two days (n=17) at one site allows us to distinguish shallow gas contributions and shows the deep gas to contain between 8-10% helium, significantly increasing resource estimates based on uncorrected values (1.8-4.2%)[2,3]. The remainder of the deep gas is

  13. The life cycle of continental rifts: Numerical models of plate tectonics and mantle convection. (United States)

    Ulvrova, Martina; Brune, Sascha; Williams, Simon


    Plate tectonic processes and mantle convection form a self-organized system whose surface expression is characterized by repeated Wilson cycles. Conventional numerical models often capture only specific aspects of plate-mantle interaction, due to imposed lateral boundary conditions or simplified rheologies. Here we study continental rift evolution using a 2D spherical annulus geometry that does not require lateral boundary conditions. Instead, continental extension is driven self-consistently by slab pull, basal drag and trench suction forces. We use the numerical code StagYY to solve equations of conservation of mass, momentum and energy and transport of material properties. This code is capable of computing mantle convection with self-consistently generated Earth-like plate tectonics using a pseudo-plastic rheology. Our models involve an incompressible mantle under the Boussinesq approximation with internal heat sources and basal heating. Due to the 2D setup, our models allow for a comparably high resolution of 10 km at the mantle surface and 15 km at the core mantle boundary. Viscosity variations range over 7 orders of magnitude. We find that the causes for rift initiation are often related to subduction dynamics. Some rifts initiate due to increasing slab pull, others because of developing trench suction force, for instance by closure of an intra-oceanic back-arc basin. In agreement with natural settings, our models reproduce rifts forming in both young and old collision zones. Our experiments show that rift dynamics follow a characteristic evolution, which is independent of the specific setting: (1) continental rifts initiate during tens of million of years at low extension rates (few millimetres per year) (2) the extension velocity increases during less than 10 million years up to several tens of millimetres per year. This speed-up takes place before lithospheric break-up and affects the structural architecture of rifted margins. (3) high divergence rates

  14. Magnetostratigraphy of the Lake Baikal sediments: A unique record of 8.4 Ma of continuous sedimentation in the continental environment (United States)

    Kravchinsky, Vadim A.


    Lake Baikal sedimentary records in general and magnetostratigraphy in particular have already enormously contributed in the global context to evaluate environmental and climatic changes in the deep continental setting. The Baikal Drilling Project (BDP) has become a world leader in pioneering recovery of extremely long (several hundred meters) lacustrine sediment sequences from deep water. This has made it possible, for the first time, to obtain a continental archive with the same chronostratigraphic integrity as marine records to address critical questions of the last eight million years. It explains why the amount of publications on Lake Baikal sedimentary and magnetic records can be compared to the number of papers for the Oceanic Drilling Program. The unique continuity of the Lake Baikal deep drilled cores - short piston cores and deep drilled cores - of 1993, 1996, and 1998 enables one to reconstruct reliably the geomagnetic polarity chrons and a number of the shorter geomagnetic events. Data from three very long cores allows a comparison to the geomagnetic polarity time scale (GPTS) and detailed records of geomagnetic events in the last 8.4 Ma. A refined age model, supported by 10Be dates, provides constraints for the short geomagnetic events. Some geomagnetic events are correlated with geomagnetic excursions already discussed in the literature; others are identified for the first time and may need future confirmation.

  15. The comparison of biogenic silica, Br and Nd distributions in the sediments of Lake Baikal as proxies of changing paleoclimates of the last 480 kyr

    International Nuclear Information System (INIS)

    Phedorin, M.A.; Goldberg, E.L.; Grachev, M.A.; Levina, O.L.; Khlystov, O.M.; Dolbnya, I.P.


    The paper presents a comparison of the profiles of biogenic silica (BiSi), Br and Nd in the first 20 m of the BDP-96-2 core of sediments of Lake Baikal obtained on top of the underwater Akademichesky Ridge. The concentrations of the two elements mentioned were measured by X-ray fluorescent analysis with synchrotron radiation (SR-XFA) at 10 cm intervals. Br correlates positively, and Nd negatively with BiSi. Spectral analysis of the profiles revealed the 100, 41, 23 and 19 kyr major external forcing periods. We studied the elemental composition of extant diatom algae of Lake Baikal in order to find out whether any elements are bound by them specifically. SR-XFA revealed, among others that Br is accumulated by extant diatom algae of Lake Baikal, presumably due to incorporation into their organic matter. Br can be regarded as a new proxy of the paleo-productivity of Lake Baikal. The paper also considers arguments suggesting that the first 2 m of sediment are missing in the BDP-96-2 core

  16. Influence of long-distance climate teleconnection on seasonality of water temperature in the world's largest lake--Lake Baikal, Siberia.

    Directory of Open Access Journals (Sweden)

    Stephen L Katz

    Full Text Available Large-scale climate change is superimposed on interacting patterns of climate variability that fluctuate on numerous temporal and spatial scales--elements of which, such as seasonal timing, may have important impacts on local and regional ecosystem forcing. Lake Baikal in Siberia is not only the world's largest and most biologically diverse lake, but it has exceptionally strong seasonal structure in ecosystem dynamics that may be dramatically affected by fluctuations in seasonal timing. We applied time-frequency analysis to a near-continuous, 58-year record of water temperature from Lake Baikal to examine how seasonality in the lake has fluctuated over the past half century and to infer underlying mechanisms. On decadal scales, the timing of seasonal onset strongly corresponds with deviation in the zonal wind intensity as described by length of day (LOD; on shorter scales, these temperature patterns shift in concert with the El Nino-Southern Oscillation (ENSO. Importantly, the connection between ENSO and Lake Baikal is gated by the cool and warm periods of the Pacific Decadal Oscillation (PDO. Large-scale climatic phenomena affecting Siberia are apparent in Lake Baikal surface water temperature data, dynamics resulting from jet stream and storm track variability in central Asia and across the Northern Hemisphere.

  17. Fluids circulation during the Miocene rifting of the Penedès half-graben, NE Iberian Peninsula (United States)

    Baqués, Vinyet; Travé, Anna; Cantarero, Irene


    The Penedès half-graben, located in the north-western part of the Mediterranean, is a NE-SW oriented basin generated during the Miocene rifting. This graben is bounded to the northwest by the SE-dipping Vallès-Penedès fault, which places the Mesozoic rocks in contact with the Miocene basin-fill. The basin is filled with an up to 4 km thick succession of sediments divided into three lithostratigraphic units. From base to top: (1) a lower continental complex, (2) a continental to marine complex and (3) an upper continental complex. These units are covered by Pliocene deposits which onlap a Messinian regional erosive surface. The structural features within the Penedès half-graben allow defining three deformational phases during the Miocene rifting. The first, during the syn-rift, two successive stages of NE-SW normal faults were formed. The second, during the early post-rift, one stage of NE-SW normal faults and one minor compression phase with a dextral directional developed. The third, during the late post-rift, two successive stages of N-S trending extensional fractures (faults and joints) and one minor compression with a sinistral component developed. The fractures related to the syn-rift stage acted as conduits for meteoric fluids both, in the phreatic and in the vadose zone. During the early post-rift, Fe2+- rich fluids precipitated oxides along the NE-SW fault planes. The dextral directional faults served as conduits for meteoric fluids which reequilibrated totally the marine Miocene host rocks under the phreatic environment. The late post-rift stage was characterized by marine fluids upflowing through the N-S fractures, probably derived from the Miocene marine interval, which mixed with meteoric fluids producing dolomitization. The second set of N-S fractures served as conduits for meteoric fluids characterised by δ13C-depleted soil-derived CO2 attributed to precipitation in the vadose zone. The change from phreatic to vadose meteoric environment and the

  18. Lithospheric rheological heterogeneity across an intraplate rift basin (Linfen Basin, North China) constrained from magnetotelluric data: Implications for seismicity and rift evolution (United States)

    Yin, Yaotian; Jin, Sheng; Wei, Wenbo; Ye, Gaofeng; Jing, Jian'en; Zhang, Letian; Dong, Hao; Xie, Chengliang; Liang, Hongda


    We take the Linfen Basin, which is the most active segment of the Cenozoic intraplate Shanxi Rift, as an example, showing how to use magnetotelluric data to constrain lithospheric rheological heterogeneities of intraplate tectonic zones. Electrical resistivity models, combined with previous rheological numerical simulation, show a good correlation between resistivity and rheological strength, indicating the mechanisms of enhanced conductivity could also be reasons of reduced viscosity. The crust beneath the Linfen Basin shows overall stratified features in both electrical resistivity and rheology. The uppermost crustal conductive layer is dominated by friction sliding-type brittle fracturing. The high-resistivity mid-crust is inferred to be high-viscosity metamorphic basement being intersected by deep fault. The plastic lower crust show significantly high-conductivity feature. Seismicity appears to be controlled by crustal rheological heterogeneity. Micro-earthquakes mainly distribute at the brittle-ductile transition zones as indicated by high- to low-resistivity interfaces or the high pore pressure fault zones while the epicenters of two giant destructive historical earthquakes occur within the high-resistivity and therefore high-strength blocks near the inferred rheological interfaces. The lithosphere-scale lateral rheological heterogeneity along the profile can also be illustrated. The crust and upper mantle beneath the Ordos Block, Lüliang Mountains and Taihang Mountains are of high rheological strength as indicated by large-scale high-resistivity zones while a significant high-conductivity, lithosphere-scale weak zone exists beneath the eastern margin of the Linfen Basin. According to previous geodynamic modeling works, we suggest that this kind of lateral rheological heterogeneity may play an essential role for providing driving force for the formation and evolution of the Shanxi Rift, regional lithospheric deformation and earthquake activities under the

  19. Seasonal variation of persistent organochlorine accumulation in birds from Lake Baikal, Russia, and the role of the south Asian region as a source of pollution for wintering migrants. (United States)

    Kunisue, Tatsuya; Minh, Tu Binh; Fukuda, Kayo; Watanabe, Mafumi; Tanabe, Shinsuke; Titenko, Alexei M


    Concentrations of persistent organochlorines (OCs) such as polychlorinated biphenyls (PCBs), DDT and its metabolites (DDTs), hexachlorocyclohexane isomers (HCHs), and chlordane compounds (CHLs) were determined in whole body soft tissue homogenates and in muscles of resident and migratory birds collected from Lake Baikal, Russia. The residue pattern in both resident and migratory birds was in the following order: PCBs > DDTs > HCHs > CHLs. OC concentrations in migratory birds varied, depending on the feeding habit. The maximum levels of OCs were found in piscivores, followed by insectivores, omnivores, and herbivores. OC residue levels in Lake Baikal birds were lower than those in the Great Lakes region as well as in other lakes in Europe and Japan. Concentrations of HCHs and DDTs in most of the migratory birds collected in the spring were higher than for those collected in the autumn, indicating a notable accumulation in wintering grounds. Compilation and analysis of the available data in fish and birds from Asia suggested that the tropical and subtropical regions in south Asian countries may be a source of pollution for the wintering accumulation of migratory birds from Lake Baikal. Relatively higher compositions of alpha- and gamma-HCH in total HCHs, p,p'-DDT in total DOTs were observed in some migratory species, indicating recent exposure to HCHs and DDTs in Lake Baikal or wintering areas. PCB isomer patterns were different between residents and migrants, with the predominance of lower chlorinated congeners in migratory species, suggesting recent PCB accumulation in stopover sites during wintering. TEQ concentrations of toxic non- and mono-ortho coplanar PCBs in common terns from Lake Baikal were comparable to those reported in some species from Japan, the United States, and Europe. Relative contributions of non-ortho coplanar congeners to toxic equivalents (TEQs) were predominant, in which CB-126 accounted for the highest toxicity contribution. Estimated TEQ

  20. Plume-induced continental break-up from Red Sea to Lake Malawi: 3D numerical models of the East African Rift System (United States)

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


    We use numerical thermo-mechanical experiments in order to analyze the role of active mantle plume, far-field tectonic stresses and pre-existing lithospheric heterogeneities in structural development of the East African Rift system (EARS). It is commonly assumed that the Cenozoic rifts have avoided the cratons and follow the mobile belts which serve as the weakest pathways within the non-uniform material structured during pre-rift stages. Structural control of the pre-existing heterogeneities within the Proterozoic belts at the scale of individual faults or rifts has been demonstrated as well. However, the results of our numerical experiments show that the formation of two rift zones on opposite sides of a thick lithosphere segment can be explained without appealing to pre-imposed heterogeneities at the crustal level. These models have provided a unified physical framework to understand the development of the Eastern branch, the Western branch and its southern prolongation by the Malawi rift around thicker lithosphere of the Tanzanian and Bangweulu cratons as a result of the interaction between pre-stressed continental lithosphere and single mantle plume anomaly corresponding to the Kenyan plume. The second series of experiments has been designed in order to investigate northern segment of the EARS where Afro-Arabian plate separation is supposed to be related with the impact of Afar mantle plume. We demonstrate that whereas relatively simple linear rift structures are preferred in case of uni-directional extension, more complex rifting patterns combining one or several ridge-ridge-ridge triple junctions can form in response to bi-directional extensional far-field stresses. In particular, our models suggest that Afar triple junction represents an end-member mode of plume-induced bi-directional rifting combining asymmetrical northward traction and symmetrical EW extension of similar magnitudes. The presence of pre-existing linear weak zones appears to be not

  1. Evidence for cross rift structural controls on deformation and seismicity at a continental rift caldera (United States)

    Lloyd, Ryan; Biggs, Juliet; Wilks, Matthew; Nowacki, Andy; Kendall, J.-Michael; Ayele, Atalay; Lewi, Elias; Eysteinsson, Hjálmar


    In continental rifts structural heterogeneities, such as pre-existing faults and foliations, are thought to influence shallow crustal processes, particularly the formation of rift faults, magma reservoirs and surface volcanism. We focus on the Corbetti caldera, in the southern central Main Ethiopian Rift. We measure the surface deformation between 22nd June 2007 and 25th March 2009 using ALOS and ENVISAT SAR interferograms and observe a semi-circular pattern of deformation bounded by a sharp linear feature cross-cutting the caldera, coincident with the caldera long axis. The signal reverses in sign but is not seasonal: from June to December 2007 the region south of this structure moves upwards 3 cm relative to the north, while from December 2007 until November 2008 it subsides by 2 cm. Comparison of data taken from two different satellite look directions show that the displacement is primarily vertical. We discuss potential mechanisms and conclude that this deformation is associated with pressure changes within a shallow (Analysis of the distribution of post-caldera vents and cones inside the caldera shows their locations are statistically consistent with this fault structure, indicating that the fault has also controlled the migration of magma from a reservoir to the surface over tens of thousands of years. Spatial patterns of seismicity are consistent with a cross-rift structure that extents outside the caldera and to a depth of ∼30 km, and patterns of seismic anisotropy suggests stress partitioning occurs across the structure. We discuss the possible nature of this structure, and conclude that it is most likely associated with the Goba-Bonga lineament, which cross-cuts and pre-dates the current rift. Our observations show that pre-rift structures play an important role in magma transport and shallow hydrothermal processes, and therefore they should not be neglected when discussing these processes.

  2. The evolution of magma during continental rifting: New constraints from the isotopic and trace element signatures of silicic magmas from Ethiopian volcanoes (United States)

    Hutchison, William; Mather, Tamsin A.; Pyle, David M.; Boyce, Adrian J.; Gleeson, Matthew L. M.; Yirgu, Gezahegn; Blundy, Jon D.; Ferguson, David J.; Vye-Brown, Charlotte; Millar, Ian L.; Sims, Kenneth W. W.; Finch, Adrian A.


    Magma plays a vital role in the break-up of continental lithosphere. However, significant uncertainty remains about how magma-crust interactions and melt evolution vary during the development of a rift system. Ethiopia captures the transition from continental rifting to incipient sea-floor spreading and has witnessed the eruption of large volumes of silicic volcanic rocks across the region over ∼45 Ma. The petrogenesis of these silicic rocks sheds light on the role of magmatism in rift development, by providing information on crustal interactions, melt fluxes and magmatic differentiation. We report new trace element and Sr-Nd-O isotopic data for volcanic rocks, glasses and minerals along and across active segments of the Main Ethiopian (MER) and Afar Rifts. Most δ18 O data for mineral and glass separates from these active rift zones fall within the bounds of modelled fractional crystallization trajectories from basaltic parent magmas (i.e., 5.5-6.5‰) with scant evidence for assimilation of Pan-African Precambrian crustal material (δ18 O of 7-18‰). Radiogenic isotopes (εNd = 0.92- 6.52; 87Sr/86Sr = 0.7037-0.7072) and incompatible trace element ratios (Rb/Nb Pan-African crust. However, there are important regional variations in melt evolution revealed by incompatible elements (e.g., Th and Zr) and peralkalinity (molar Na2 O +K2 O /Al2O3). The most chemically-evolved peralkaline compositions are associated with the MER volcanoes (Aluto, Gedemsa and Kone) and an off-axis volcano of the Afar Rift (Badi). On-axis silicic volcanoes of the Afar Rift (e.g., Dabbahu) generate less-evolved melts. While at Erta Ale, the most mature rift setting, peralkaline magmas are rare. We find that melt evolution is enhanced in less mature continental rifts (where parental magmas are of transitional rather than tholeiitic composition) and regions of low magma flux (due to reduced mantle melt productivity or where crustal structure inhibits magma ascent). This has important

  3. Seismicity of the Earth 1900-2013 East African Rift (United States)

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


    The East African Rift system (EARS) is a 3,000-km-long Cenozoic age continental rift extending from the Afar triple junction, between the horn of Africa and the Middle East, to western Mozambique. Sectors of active extension occur from the Indian Ocean, west to Botswana and the Democratic Republic of the Congo (DRC). It is the only rift system in the world that is active on a continent-wide scale, providing geologists with a view of how continental rifts develop over time into oceanic spreading centers like the Mid-Atlantic Ridge.

  4. From continental platform towards rifting of the Tisza Unit in the Late Triassic to Early Cretaceous (United States)

    Császár, Géza; Szinger, Balázs; Piros, Olga


    The Upper Triassic-Lower Cretaceous successions of the Transdanubian part of the Mecsek and Villány- Bihor Zones of the Tisza Unit have been studied from the lithological, lithostratigraphical, sedimentological, microfossil and microfacies points of view in order to correlate and interpret the significant differences between them and to draw a conclusion about their geological and paleogeographical history. After an overview of the paleogeographical reconstructions of the broader area, the succession of the Mecsek and Villány-Bihor Zones and the debated Máriakéménd-Bár Range are introduced. Until the end of the Middle Triassic the study area acted as an entity. The first fundamental difference between the two zones can be recognized in the Late Triassic when marine carbonates were replaced by thick fluvial siliciclastics in the Mecsek Zone, while it is represented only by small, local lenses with a few and thin dolostone intercalations in the Villány Zone. The Mecsek Zone is bordered southward by one of the large listric faults to the north of which very thick siliciclastics developed in the Early to Middle Jurassic, whereas it is highly lacunose in the larger western part of the Villány-Bihor Zone. The break at the base is subaerial, higher in the succession it is shallow submarine. The sediment is silty, occasionally sandy crinoidal limestone of late Early Jurassic or even Middle Jurassic in age. The Upper Jurassic in the Mecsek Zone is composed of deep-water cherty limestone while in the Villány Zone it became a thick, shallowing pelagic limestone with reworked patch reef fragments. It is clear evidence that the Mecsek Zone had a thinned continental crust thanks to the nearby rift zone while in the Villány Zone the crust remained thick. The actualized version of the Plašienka's paleogeographical model (Plašienka 2000) is introduced

  5. The crust and mantle beneath the Siberian provinces: a preliminary model based on new receiver function analysis

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Artemieva, Irina; Thybo, Hans


    The new receiver function (RF) study complements the existing seismic data on the crustal and upper mantle structure at the margins of the Siberian craton and the West Siberian Basin. So far, RF studies of Siberia have been largely restricted to the Baikal rift zone (Gao et al., 2004; Liu and Gao...

  6. Variable styles of rifting expressed in crustal structure across three rift segments of the Gulf of California (United States)

    Lizarralde, D. D.; Axen, G. J.; Brown, H. E.; Fletcher, J. M.; Fernandez, A. G.; Harding, A. J.; Holbrook, W. S.; Kent, G. M.; Paramo, P.; Sutherland, F. H.; Umhoefer, P. J.


    We present a summary of results from a crustal-scale seismic experiment conducted in the southern Gulf of California. This experiment, the PESCADOR experiment, imaged crustal structure across three rift segments, the Alarcon, Guaymas, and San José del Cabo to Puerto Vallarta (Cabo-PV) segments, using seismic refraction/wide-angle reflection data acquired with airgun sources and recorded by closely spaced (10-15 km) ocean-bottom seismometers (OBSs). The imaged crustal structure reveals a surprisingly large variation in rifting style and magmatism between these segments: the Alarcon segment is a wide rift with apparently little syn-rift magmatism; the Guaymas segment is a narrow, magmatically robust rift; and the Cabo-PV segment is a narrow, magmatically "normal" rift. Our explanation for the observed variability is non-traditional in that we do not invoke mantle temperature, the factor commonly invoked to explain end-member volcanic and non-volcanic rifted margins, as the source of the considerable, though non-end-member variability we observe. Instead, we invoke mantle depletion related to pre-rift arc volcanism to account for observed wide, magma-poor rifting and mantle fertility and possibly the influence of sediments to account for robust rift and post-rift magmatism. These factors may commonly vary over small lateral spatial scales in regions that have transitioned from convergent to extensional tectonics, as is the case for the Gulf of California and many other rifts. Our hypothesis suggests that substantial lateral variability may exist within the uppermost mantle beneath the Gulf of California today, and it is hoped that ongoing efforts to image upper mantle structure here will provide tests for this hypothesis.

  7. Late Paleozoic low-angle southward-dipping thrust in the Züünharaa area, Mongolia: tectonic implications for the geological structures in the Sayan-Baikal and Hangai-Daur belts (United States)

    Onon, Gantumur; Tsukada, Kazuhiro


    The Central Asian Orogenic Belt (CAOB) is key to understanding the Paleozoic-Mesozoic geodynamics of Eurasian continent. The geological structure of the Middle-to-Late Paleozoic rock units in the North Mongolia-West Transbaikal region is critical in revealing development process of CAOB. The region is largely comprised of rocks from the continental affinity and accretionary complexes which form the Sayan-Baikal (SB) and Hangai-Daur (HD) belts. This paper describes the lithology, stratigraphy, geological structure, and U-Pb age of the rocks in the Züünharaa area, which is located within the Haraa terrane of the HD belt in Mongolia. We identified a regional low-angle southward-dipping thrust in this area. The tectonic implication of the low-angle south-dipping thrust is discussed within the North Mongolia-West Transbaikal region. The study area exposes metamorphosed clastic rocks of the Haraa Group intruded by Ordovician-Silurian granitic rocks, Devonian felsic volcanic rocks of the Ulaan Öndör Formation, and Visean clastic rocks of the Örmögtei Formation in ascending order. The Haraa Group, granitic rock, and Ulaan Öndör Formation are cut by the low-angle southward-dipping thrust throughout this area. The rocks along the thrust are fractured to form cataclasite zone up to 40 m wide. The thrust includes granite-rhyolite clast of 450-420 Ma, and is unconformably covered by Visean Örmögtei Formation. Therefore, thrusting occurred after Ordovician-Silurian and before Visean. Late Paleozoic low-angle southward-dipping thrusts, similar to the present study, are widely distributed in the Haraa terrane of the Hangai-Daur belt and in terranes of the Sayan-Baikal belt. Whereas, the contemporaneous southeast-verging composite folds and northward-dipping thrusts are developed in the accretionary complexes, which are exposed at south of the Haraa terrane. These contrasting structures suggest a couple of "landward-verging" and "oceanward-verging" structures and may

  8. Thermal and Crustal Structure Beneath the Northern Segment of the Western Brach of the East African Rift System: Constraints from Gravity and Magnetic Data (United States)

    Katumwehe, A. B.; Atekwana, E. A.; Abdelsalam, M. G.; Mickus, K. L.; Ngalamo, J. G.


    We used two-dimensional (2D) radially averaged power spectral analysis and 2D forward modeling of aeromagnetic and satellite gravity data to investigate the thermal and crustal structure beneath the Albertine-Rhino graben and the Edward-George rift in order to understand controls on strain localization during rift initiation. These extensional structures are separated by the 5 km high Rwenzori Mountains (RM) and represent the northern segment of the magma-poor Western Branch (WB) of the East African Rift System (EARS). The northern part of the Albertine-Rhino graben is non-volcanic and extends within the Mesoproterozoic Madi-Igisi fold belt between the Archean North Uganda terrane in the east and the West Nile block to the west. The southwestern part of the Albertine-Rhino graben and the Edward-George rift contain volcanic exposures and extend within the Paleoproterozoic Rwenzori and Kibara-Karagwe-Ankole orogenic belts. Previous seismic and magenetotelluric data has suggested magma assisted rifting in the Edward-George rifts and southern Albertine rift. We found shallow Curie Point Depths ( 19-22±1 km), elevated heat flow ( 62-79±0.2 mWm-2) and thin crust ( 24-32 km) consistent with previous seismic receiver function data beneath the Edward-George rift and the Rwenzori Mountains. Both the crustal thickness and thermal anomaly exhibit a strong gradient, attenuating to the north beneath the Albertine-Rhino graben. Additionally, the 2D forward models suggest consistent crustal thinning beneath the Rwenzori Mountains, the Edward-George rifts and the entire axis of the Albertine-Rhino rifts. We propose that strain localization was facilitated by sub-continental lithospheric mantle delamination beneath the Edward-George rift and the Rwenzori Mountains that resulted in rapid uplift. This was accompanied by mantle melting that produced the Toro-Ankole volcanic field. The presence of the Madi-Igisi "suture zone" assisted the northeastward migration of the mantle fluids

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

    Havenith, Hans-Balder; Delvaux, Damien


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

  10. A Middle-Upper Miocene fluvial-lacustrine rift sequence in the Song Ba Rift, Vietnam

    DEFF Research Database (Denmark)

    Lars H., Nielsen; Henrik I., Petersen; Nguyen D., Dau


    The small Neogene Krong Pa graben is situated within the continental Song Ba Rift, which is bounded by strike-slip faults that were reactivated as extensional faults in Middle Miocene time. The 500 m thick graben-fill shows an overall depositional development reflecting the structural evolution, ...

  11. The upper mantle structure of the central Rio Grande rift region from teleseismic P and S wave travel time delays and attenuation (United States)

    Slack, P.D.; Davis, P.M.; Baldridge, W.S.; Olsen, K.H.; Glahn, A.; Achauer, U.; Spence, W.


    The lithosphere beneath a continental rift should be significantly modified due to extension. To image the lithosphere beneath the Rio Grande rift (RGR), we analyzed teleseismic travel time delays of both P and S wave arrivals and solved for the attenuation of P and S waves for four seismic experiments spanning the Rio Grande rift. Two tomographic inversions of the P wave travel time data are given: an Aki-Christofferson-Husebye (ACH) block model inversion and a downward projection inversion. The tomographic inversions reveal a NE-SW to NNE-SSW trending feature at depths of 35 to 145 km with a velocity reduction of 7 to 8% relative to mantle velocities beneath the Great Plains. This region correlates with the transition zone between the Colorado Plateau and the Rio Grande rift and is bounded on the NW by the Jemez lineament, a N52??E trending zone of late Miocene to Holocene volcanism. S wave delays plotted against P wave delays are fit with a straight line giving a slope of 3.0??0.4. This correlation and the absolute velocity reduction imply that temperatures in the lithosphere are close to the solidus, consistent with, but not requiring, the presence of partial melt in the mantle beneath the Rio Grande rift. The attenuation data could imply the presence of partial melt. We compare our results with other geophysical and geologic data. We propose that any north-south trending thermal (velocity) anomaly that may have existed in the upper mantle during earlier (Oligocene to late Miocene) phases of rifting and that may have correlated with the axis of the rift has diminished with time and has been overprinted with more recent structure. The anomalously low-velocity body presently underlying the transition zone between the core of the Colorado Plateau and the rift may reflect processes resulting from the modern (Pliocene to present) regional stress field (oriented WNW-ESE), possibly heralding future extension across the Jemez lineament and transition zone.

  12. Tectono-thermal modeling of Cenozoic multiple rift episodes in the Bohai Bay Basin, eastern China and its geodynamic implications (United States)

    Liu, Qiongying; He, Lijuan; Chen, Lichun


    The Bohai Bay Basin (BBB) is the largest Cenozoic rifted basin in eastern China, which exhibited a multi-episodic behavior. A 2D multi-episodic finite extension model is employed to estimate the stretching factor and strain rate for each rift episode along six seismic profiles. The modeling is based on a reconstruction of pre-rift crustal and lithospheric thicknesses, and is calibrated with the present-day heat flow and Moho depth. The pre-rift thicknesses of the crust and lithosphere are determined to be 34-39 and 80-105 km. The stretching factors range from 1.28 to 1.97, with a peak in the middle-to-late Eocene during which the average strain rate reached 1.1 × 10- 15 s- 1. Our analyses show that the centers of stretching migrated generally from south to north and from west to east during the Cenozoic. The results also indicate an inverse relationship between variations of the average strain rate and the relative motion rate between Pacific plate and Eurasian plate. Combining the results of the previous studies with ours, we infer that the changing subduction rate of the Pacific plate accompanied by episodic eastward retreat of the subduction zone plays important roles in the episodic extension of the BBB and eastward migration of the centers of stretching.

  13. Monitoring of the Syrian rift valley using radon technique

    International Nuclear Information System (INIS)

    Al-Hilal, M.; Al-Ali, A.; Jubeli, Y.


    Groundwater radon data were recorded once every two months from six monitoring sites of the Syrian rift valley during the year 1996. Radon samples were measured from deep artesian wells and from continuously-flowing springs that are distributed along this most active seismic zone in Syria. The available data were integrated with previously measured groundwater radon data from the same stations in order to estimate the range of normal radon fluctuations in the region. The estimation of such range may enable the separation between usual groundwater radon variations from other outliers which may indicate possible tectonic activities or earthquake hazards in the study area. Periodical radon measurements based on two months intervals and long distance between sampling stations does not enable us to trust with high level of confidence the connection between radon values and any possible earth dynamics. Therefore, shorter measuring time with closer monitoring sites are highly recommended to achieve the optimum advantage of such application. (Author). 8 Figs., 2 Tabs., 10 Refs

  14. Baikal test stand modifications for liquid metal and gas fill operations for TOPAZ II space power acceptance test (United States)

    Schrieber, Christopher A.; Peterson, Earl; Sinkevich, Valery G.; Vdovin, Boris


    The Thermionic System Evaluation Test (TSET) facility, part of the TOPAZ International Program, in Albuquerque is currently testing Russian TOPAZ II space power systems (Wold 1993). The TOPAZ International Program has received six TOPAZ II Space Nuclear Power Reactors. Two of these reactors (Eh-43 and Eh-44) are considered ``flight quality.'' A considerable transfer of technology has occurred during the preparations for acceptance testing of the Eh-43 and Eh-44 TOPAZ II reactors. Eh-43 and Eh-44 are new systems that require the coolant loop and gas cavities to be filled and have not undergone any testing. In comparison to the tests performed on the V-71 and Ya-21u systems, the future operations with the flight units Eh-43 and Eh-44 will require expansion of the Baikal Test Stand's capabilities.

  15. [The Great Rift Valley. Parasitological results]. (United States)

    Nozais, J P


    East Africa is separated from the continent by the Great Rift Valley which was created at the end of the secondary era limiting then the East Africa under-continent with peculiar fauna and flora features. A several million years long isolation, during the tertiary era, seems to explain that a certain number of protozoan and helminthic diseases present peculiar clinical, epidemiological, therapeutical and parasitological features. The occurrence of those peculiar strains tends to indicate that in this region, for example, the resistance of P. falciparum to amino-4-quinolines is a regional feature which should not largely expand to the rest of the African continent.

  16. Rifts, orogens, cratons, and global tectonics: Introduction

    Directory of Open Access Journals (Sweden)

    S. V. Rasskazov


    Full Text Available A key role in developing the Earth theory is played by comparative studies of orogens, rifts, and platforms in the equatorial, middle and high latitudes of Asia and the adjacent Arctic regions. The modern shape of the planet’s triaxial asymmetrical cardioid ellipsoid results from its latest (Late Phanerozoic geodynamic evolution that began in Arctic and then commenced in Asia. At this stage, mechanisms of the lithosphere extension and compression, combined with extension, were launched in Arctic and Asia, respectively. The special issue of Geodynamics & Tectonophysics presents papers on this topic.

  17. Prevalence of Rift Valley Fever among ruminants, Mayotte. (United States)

    Cêtre-Sossah, Catherine; Pédarrieu, Aurélie; Guis, Hélène; Defernez, Cédric; Bouloy, Michèle; Favre, Jacques; Girard, Sébastien; Cardinale, Eric; Albina, Emmanuel


    Rift Valley fever threatens human and animal health. After a human case was confirmed in Comoros in 2007, 4 serosurveys among ruminants in Mayotte suggested that Rift Valley fever virus had been circulating at low levels since 2004, although no clinical cases occurred in animals. Entomologic and ecologic studies will help determine outbreak potential.

  18. Rift Valley fever potential mosquito vectors and their infection status ...

    African Journals Online (AJOL)

    Background: Rift Valley fever (RVF) is a mosquito-borne viral zoonotic disease. Rift Valley fever virus (RVFV) has been isolated from more than 40 species of mosquitoes from eight genera. This study was conducted to determine the abundance of potential mosquito vectors and their RVFV infection status in Ngorongoro ...

  19. Salt Lakes of the African Rift System: A Valuable Research ...

    African Journals Online (AJOL)

    Salt Lakes of the African Rift System: A Valuable Research Opportunity for Insight into Nature's Concenrtated Multi-Electrolyte Science. JYN Philip, DMS Mosha. Abstract. The Tanzanian rift system salt lakes present significant cultural, ecological, recreational and economical values. Beyond the wealth of minerals, resources ...

  20. Rift Valley Fever Outbreak in Livestock, Mozambique, 2014 (United States)

    Coetzee, Peter; Mubemba, Benjamin; Nhambirre, Ofélia; Neves, Luis; Coetzer, J.A.W.; Venter, Estelle H.


    In early 2014, abortions and death of ruminants were reported on farms in Maputo and Gaza Provinces, Mozambique. Serologic analysis and quantitative and conventional reverse transcription PCR confirmed the presence of Rift Valley fever virus. The viruses belonged to lineage C, which is prevalent among Rift Valley fever viruses in southern Africa. PMID:27869589

  1. Esophageal cancer in north rift valley of western Kenya | Wakhisi ...

    African Journals Online (AJOL)

    Esophageal cancer in north rift valley of western Kenya. ... Our finding also contrast with an earlier reported study that indicated that Rift Valley is a low prevalence area for this type of cancer. The mean age ... This may lead to identification of molecular biomarkers to be used in future for the early detection of this neoplasm.

  2. Transfer/transform relationships in continental rifts and margins and their control on syn- and post-rift denudation: the case of the southeastern Gulf of Aden, Socotra Island, Yemen (United States)

    Pik, Raphael; Bellahsen, Nicolas; Leroy, Sylvie; Denele, Yoann; Razin, Philippe; Ahmed, Abdulhakim; Khanbari, Khaled


    Transfer zones are ubiquist features in continental rifts and margins, as well as transform faults in oceanic lithosphere. Here, we present the structural study of such a structure (the Hadibo Transfer Zone, HTZ) from the southeastern Gulf of Aden, in Socotra Island, Yemen. There, from field data, the HTZ is interpreted as being reactivated, obliquely to divergence, since early rifting stages. Then, from a short review of transfer/transform fault zone geometries worldwide, we derive a classification in terms of relative importance (1st, 2nd, 3rd order), geometry, and location. We suggest that the HTZ is a 1st order transfer fault zone as it controls the initiation of a 1st order oceanic transform fault zone. We then investigate the denudation history of the region surrounding the HTZ in order to highlight the interplay of normal and transfer/transform tectonic structures in the course of rift evolution. Samples belong from two distinct East and West domains of the Socotra Island, separated by the (HTZ). Tectonic denudation started during the Priabonian-Rupelian along flat normal faults and removed all the overlying sedimentary formations, allowing basement exhumation up to the surface (~ 1.2 - 1.6 km of exhumation). Forward t-T modelling of the data requires a slightly earlier date and shorter period for development of rifting in the E-Socotra domain (38 - 34 Ma), compared to the W-Socotra domain (34 - 25 Ma), which suggests that the HTZ was already active at that time. A second major event of basement cooling and exhumation (additional ~ 0.7 - 1 km), starting at about ~ 20 Ma, has only been recorded on the E-Socotra domain. This second denudation phase significantly post-dates local rifting period but appears synchronous with Ocean Continent Transition (OCT: 20 - 17.6 Ma). This late syn-OCT uplift is maximum close to the HTZ, in the wedge of hangingwall delimited by this transfer system and the steep north-dipping normal faults that accommodated the vertical

  3. Burying dogs in ancient Cis-Baikal, Siberia: temporal trends and relationships with human diet and subsistence practices.

    Directory of Open Access Journals (Sweden)

    Robert J Losey

    Full Text Available The first objective of this study is to examine temporal patterns in ancient dog burials in the Lake Baikal region of Eastern Siberia. The second objective is to determine if the practice of dog burial here can be correlated with patterns in human subsistence practices, in particular a reliance on terrestrial mammals. Direct radiocarbon dating of a suite of the region's dog remains indicates that these animals were given burial only during periods in which human burials were common. Dog burials of any kind were most common during the Early Neolithic (∼7-8000 B.P., and rare during all other time periods. Further, only foraging groups seem to have buried canids in this region, as pastoralist habitation sites and cemeteries generally lack dog interments, with the exception of sacrificed animals. Stable carbon and nitrogen isotope data indicate that dogs were only buried where and when human diets were relatively rich in aquatic foods, which here most likely included river and lake fish and Baikal seal (Phoca sibirica. Generally, human and dog diets appear to have been similar across the study subregions, and this is important for interpreting their radiocarbon dates, and comparing them to those obtained on the region's human remains, both of which likely carry a freshwater old carbon bias. Slight offsets were observed in the isotope values of dogs and humans in our samples, particularly where both have diets rich in aquatic fauna. This may result from dietary differences between people and their dogs, perhaps due to consuming fish of different sizes, or even different tissues from the same aquatic fauna. This paper also provides a first glimpse of the DNA of ancient canids in Northeast Asia.

  4. Burying dogs in ancient Cis-Baikal, Siberia: temporal trends and relationships with human diet and subsistence practices. (United States)

    Losey, Robert J; Garvie-Lok, Sandra; Leonard, Jennifer A; Katzenberg, M Anne; Germonpré, Mietje; Nomokonova, Tatiana; Sablin, Mikhail V; Goriunova, Olga I; Berdnikova, Natalia E; Savel'ev, Nikolai A


    The first objective of this study is to examine temporal patterns in ancient dog burials in the Lake Baikal region of Eastern Siberia. The second objective is to determine if the practice of dog burial here can be correlated with patterns in human subsistence practices, in particular a reliance on terrestrial mammals. Direct radiocarbon dating of a suite of the region's dog remains indicates that these animals were given burial only during periods in which human burials were common. Dog burials of any kind were most common during the Early Neolithic (∼7-8000 B.P.), and rare during all other time periods. Further, only foraging groups seem to have buried canids in this region, as pastoralist habitation sites and cemeteries generally lack dog interments, with the exception of sacrificed animals. Stable carbon and nitrogen isotope data indicate that dogs were only buried where and when human diets were relatively rich in aquatic foods, which here most likely included river and lake fish and Baikal seal (Phoca sibirica). Generally, human and dog diets appear to have been similar across the study subregions, and this is important for interpreting their radiocarbon dates, and comparing them to those obtained on the region's human remains, both of which likely carry a freshwater old carbon bias. Slight offsets were observed in the isotope values of dogs and humans in our samples, particularly where both have diets rich in aquatic fauna. This may result from dietary differences between people and their dogs, perhaps due to consuming fish of different sizes, or even different tissues from the same aquatic fauna. This paper also provides a first glimpse of the DNA of ancient canids in Northeast Asia.

  5. a system approach to the long term forecasting of the climat data in baikal region (United States)

    Abasov, N.; Berezhnykh, T.


    The Angara river running from Baikal with a cascade of hydropower plants built on it plays a peculiar role in economy of the region. With view of high variability of water inflow into the rivers and lakes (long-term low water periods and catastrophic floods) that is due to climatic peculiarities of the water resource formation, a long-term forecasting is developed and applied for risk decreasing at hydropower plants. Methodology and methods of long-term forecasting of natural-climatic processes employs some ideas of the research schools by Academician I.P.Druzhinin and Prof. A.P.Reznikhov and consists in detailed investigation of cause-effect relations, finding out physical analogs and their application to formalized methods of long-term forecasting. They are divided into qualitative (background method; method of analogs based on solar activity), probabilistic and approximative methods (analog-similarity relations; discrete-continuous model). These forecasting methods have been implemented in the form of analytical aids of the information-forecasting software "GIPSAR" that provides for some elements of artificial intelligence. Background forecasts of the runoff of the Ob, the Yenisei, the Angara Rivers in the south of Siberia are based on space-time regularities that were revealed on taking account of the phase shifts in occurrence of secular maxima and minima on integral-difference curves of many-year hydrological processes in objects compared. Solar activity plays an essential role in investigations of global variations of climatic processes. Its consideration in the method of superimposed epochs has allowed a conclusion to be made on the higher probability of the low-water period in the actual inflow to Lake Baikal that takes place on the increasing branch of solar activity of its 11-year cycle. The higher probability of a high-water period is observed on the decreasing branch of solar activity from the 2nd to the 5th year after its maximum. Probabilistic method

  6. Combining detrital geochronology and sedimentology to assess basin development in the Rukwa Rift of the East African Rift System (United States)

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


    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

  7. Fault Orientations at Obliquely Rifted Margins: Where? When? Why? (United States)

    Brune, Sascha


    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

  8. Between Lake Baikal and the Baltic Sea: genomic history of the gateway to Europe. (United States)

    Triska, Petr; Chekanov, Nikolay; Stepanov, Vadim; Khusnutdinova, Elza K; Kumar, Ganesh Prasad Arun; Akhmetova, Vita; Babalyan, Konstantin; Boulygina, Eugenia; Kharkov, Vladimir; Gubina, Marina; Khidiyatova, Irina; Khitrinskaya, Irina; Khrameeva, Ekaterina E; Khusainova, Rita; Konovalova, Natalia; Litvinov, Sergey; Marusin, Andrey; Mazur, Alexandr M; Puzyrev, Valery; Ivanoshchuk, Dinara; Spiridonova, Maria; Teslyuk, Anton; Tsygankova, Svetlana; Triska, Martin; Trofimova, Natalya; Vajda, Edward; Balanovsky, Oleg; Baranova, Ancha; Skryabin, Konstantin; Tatarinova, Tatiana V; Prokhortchouk, Egor


    The history of human populations occupying the plains and mountain ridges separating Europe from Asia has been eventful, as these natural obstacles were crossed westward by multiple waves of Turkic and Uralic-speaking migrants as well as eastward by Europeans. Unfortunately, the material records of history of this region are not dense enough to reconstruct details of population history. These considerations stimulate growing interest to obtain a genetic picture of the demographic history of migrations and admixture in Northern Eurasia. We genotyped and analyzed 1076 individuals from 30 populations with geographical coverage spanning from Baltic Sea to Baikal Lake. Our dense sampling allowed us to describe in detail the population structure, provide insight into genomic history of numerous European and Asian populations, and significantly increase quantity of genetic data available for modern populations in region of North Eurasia. Our study doubles the amount of genome-wide profiles available for this region. We detected unusually high amount of shared identical-by-descent (IBD) genomic segments between several Siberian populations, such as Khanty and Ket, providing evidence of genetic relatedness across vast geographic distances and between speakers of different language families. Additionally, we observed excessive IBD sharing between Khanty and Bashkir, a group of Turkic speakers from Southern Urals region. While adding some weight to the "Finno-Ugric" origin of Bashkir, our studies highlighted that the Bashkir genepool lacks the main "core", being a multi-layered amalgamation of Turkic, Ugric, Finnish and Indo-European contributions, which points at intricacy of genetic interface between Turkic and Uralic populations. Comparison of the genetic structure of Siberian ethnicities and the geography of the region they inhabit point at existence of the "Great Siberian Vortex" directing genetic exchanges in populations across the Siberian part of Asia. Slavic speakers

  9. Proterozoic orogenic belts and rifting of Indian cratons: Geophysical constraints

    Directory of Open Access Journals (Sweden)

    D.C. Mishra


    Full Text Available The Aravalli–Delhi and Satpura Mobile Belts (ADMB and SMB and the Eastern Ghat Mobile Belt (EGMB in India form major Proterozoic mobile belts with adjoining cratons and contemporary basins. The most convincing features of the ADMB and the SMB have been the crustal layers dipping from both sides in opposite directions, crustal thickening (∼45 km and high density and high conductivity rocks in upper/lower crust associated with faults/thrusts. These observations indicate convergence while domal type reflectors in the lower crust suggest an extensional rifting phase. In case of the SMB, even the remnant of the subducting slab characterized by high conductive and low density slab in lithospheric mantle up to ∼120 km across the Purna–Godavari river faults has been traced which may be caused by fluids due to metamorphism. Subduction related intrusives of the SMB south of it and the ADMB west of it suggest N–S and E–W directed convergence and subduction during Meso–Neoproterozoic convergence. The simultaneous E–W convergence between the Bundelkhand craton and Marwar craton (Western Rajasthan across the ADMB and the N–S convergence between the Bundelkhand craton and the Bhandara and Dharwar cratons across the SMB suggest that the forces of convergence might have been in a NE–SW direction with E–W and N–S components in the two cases, respectively. This explains the arcuate shaped collision zone of the ADMB and the SMB which are connected in their western part. The Eastern Ghat Mobile Belt (EGMB also shows signatures of E–W directed Meso–Neoproterozoic convergence with East Antarctica similar to ADMB in north India. Foreland basins such as Vindhyan (ADMB–SMB, and Kurnool (EGMB Supergroups of rocks were formed during this convergence. Older rocks such as Aravalli (ADMB, Mahakoshal–Bijawar (SMB, and Cuddapah (EGMB Supergroups of rocks with several basic/ultrabasic intrusives along these mobile belts, plausibly formed during

  10. Structural pattern at the northwestern sector of the Tepic-Zacoalco rift and tectonic implications for the Jalisco block, western Mexico (United States)

    Urrutia-Fucugauchi, Jaime; González-Morán, Tomás


    Analysis of the aeromagnetic anomalies over the northwestern sector of the Tepic-Zacoalco rift documents a NE-SW pattern of lineaments that are perpendicular to the inferred NW-SE boundary between the Jalisco block and the Sierra Madre Occidental. The boundary lies within the central sector of the Tepic-Zacoalco rift immediately north of the Ceboruco and Tepetiltic stratovolcanoes and extends up to the San Juan stratovolcano, where it intersects the NE-SW magnetic anomaly lineament that runs toward the Pacific coast (which intersects two volcanic centers). This N35°E lineament separates the central rift zone of low amplitude mainly negative anomalies (except those positive anomalies over the stratovolcanoes) from the zone to the north and west characterized by high amplitude positive long wavelength anomalies. The NE-SW lineament is parallel to the western sector of the Ameca graben and the offshore Bahia de Banderas graben and to the structural features of the Punta Mita peninsula at the Pacific coast, and thus seems to form part of a regional NE-SW pattern oblique to the proposed westward or northwestward motion of the Jalisco block. The orientation of this regional structural pattern at the northern end of the Tepic-Zacoalco rift seems consistent with proposed dominant SW-directed extension along the rift during the Pliocene and Quaternary, rather than with NW-SE lateral strike-slip faulting. The orthogonal pattern that characterizes the northernmost boundary of the Tepic-Zacoalco rift is oblique to the pattern observed in the Grande de Santiago river (which conforms the northern limit of the rift) and for the central-eastern sectors of the Ameca graben (south of the rift). This spatial arrangement of major lineaments and structural elements points to a complex tectonic history for the region that includes the rifting of the Gulf of California and margin deformation due to plate convergence and kinematic re-organization events, and which may have resulted in

  11. [Phototrophic microorganisms in the symbiotic communities of Baikal sponges: Diversity of psbA gene (encoding D1 protein of photosystem II) sequences]. (United States)

    Kaluzhnaya, O V; Itskovich, V B


    The psbA gene, which encodes a major photosystem II protein (protein II or D1), is a marker for the presence of phototrophic organisms in water communities. We have pioneered the use of this marker for studying the diversity of phototrophic microflora of freshwater invertebrates. The object of the study is the microbial associations accompanying the endemic Baikal sponge Baikalospongia intermedia and the surrounding aquatic microbial community. Analysis of the psbA gene sequences in the examined microbiomes demonstrates the presence of various phototrophic groups, such as Cyanobacteria, Chlorophyta, Heterokonta, Haptophyta, and Ochrophyta algae, as well as cyanophages. A total of 35 unique psbA gene sequences have been distinguished in the microbial communities of the endemic sponge B. intermedia and 32 unique sequences in the water community surrounding the sponge. These data demonstrate the involvement of sponge symbiotic communities in the accumulation of primary production and carbon cycle in the Lake Baikal ecosystem.

  12. Seismic structure of the Rivera subduction zone - the MARS experiment (United States)

    Grand, S. P.; Yang, T.; Sudharja, S.; Wilson, D.; Guzman Speziale, M.; Gomez Gonzalez, J.; Leon-Soto, G.; Ni, J.; Dominguez Reyes, T.


    The subduction zone of western Mexico is a unique region on Earth where microplate capture and overriding plate disruption are occurring today. The small Rivera plate is subducting beneath western most Mexico primarily beneath Jalisco state while to the east it is the Cocos plate that is subducting. Above the Rivera plate the Jalisco block of Mexico is bounded by the north trending Colima Rift and the northwest trending Tepic-Chapala Rift and may form a microplate in its own right. Magmatism is present throughout the region and is unusual for a subduction zone in that geochemical analyses indicate an ocean island basalt component to some of the lavas. Also, Colima volcano is offset trenchward from other volcanoes in the Mexican Volcanic Belt. Little is known of the subducting Rivera plate geometry due to the paucity of seismicity within the plate yet the geometry of the Rivera and Cocos plates at depth are likely critical for understanding the tectonic evolution of western Mexico. The MARS (MApping the Rivera Subduction zone) project consists of the deployment of 50 broadband seismometers covering the Jalisco block from the coast to the Tepic-Chapala rift in the north and about 150 km to the west of the Colima rift. The instruments were deployed in January, 2006 and will be removed in June, 2007. The goal of the project is to seismically image the subducting Rivera and Cocos plates at depth as well as the mantle wedge above the plates. A number of different analyses of MARS data are underway including teleseismic tomography, receiver function analysis, and shear wave splitting analysis. The preliminary tomography results clearly show both subducting plates with a sharp change in dip to the east of the Colima rift probably indicating a tear between the two plates along a trend more eastward than the trend of the rift. The images also show extremely slow shallow mantle velocities beneath the Tepic-Chapala rift but not beneath the Colima rift. Receiver functions

  13. Groundwater fluoride enrichment in an active rift setting: Central Kenya Rift case study

    Energy Technology Data Exchange (ETDEWEB)

    Olaka, Lydia A., E-mail: [Department of Geology, University of Nairobi, P.O Box 30197, Nairobi (Kenya); Wilke, Franziska D.H. [Geoforschungs Zentrum, Telegrafenberg, 14473 Potsdam (Germany); Olago, Daniel O.; Odada, Eric O. [Department of Geology, University of Nairobi, P.O Box 30197, Nairobi (Kenya); Mulch, Andreas [Senckenberg Biodiversity and Climate Research Centre, Senckenberganlage 25, 60325 Frankfurt (Germany); Institut für Geowissenschaften, Goethe Universität Frankfurt, Altenhöferallee 1, 60438 Frankfurt (Germany); Musolff, Andreas [UFZ-Helmholtz-Centre for Environmental Research, Department of Hydrogeology, Permoserstr. 15, 04318 Leipzig (Germany)


    Groundwater is used extensively in the Central Kenya Rift for domestic and agricultural demands. In these active rift settings groundwater can exhibit high fluoride levels. In order to address water security and reduce human exposure to high fluoride in drinking water, knowledge of the source and geochemical processes of enrichment are required. A study was therefore carried out within the Naivasha catchment (Kenya) to understand the genesis, enrichment and seasonal variations of fluoride in the groundwater. Rocks, rain, surface and groundwater sources were sampled for hydrogeochemical and isotopic investigations, the data was statistically and geospatially analyzed. Water sources have variable fluoride concentrations between 0.02–75 mg/L. 73% exceed the health limit (1.5 mg/L) in both dry and wet seasons. F{sup −} concentrations in rivers are lower (0.2–9.2 mg/L) than groundwater (0.09 to 43.6 mg/L) while saline lake waters have the highest concentrations (0.27–75 mg/L). The higher values are confined to elevations below 2000 masl. Oxygen (δ{sup 18}O) and hydrogen (δD) isotopic values range from − 6.2 to + 5.8‰ and − 31.3 to + 33.3‰, respectively, they are also highly variable in the rift floor where they attain maximum values. Fluoride base levels in the precursor vitreous volcanic rocks are higher (between 3750–6000 ppm) in minerals such as cordierite and muscovite while secondary minerals like illite and kaolinite have lower remnant fluoride (< 1000 ppm). Thus, geochemical F{sup −} enrichment in regional groundwater is mainly due to a) rock alteration, i.e. through long residence times and natural discharge and/or enhanced leakages of deep seated geothermal water reservoirs, b) secondary concentration fortification of natural reservoirs through evaporation, through reduced recharge and/or enhanced abstraction and c) through additional enrichment of fluoride after volcanic emissions. The findings are useful to help improve water management

  14. Joint observations of the dynamics of atmospheric aerosol by means of aerosol and Doppler lidars on the coast of Lake Baikal (United States)

    Kokhanenko, G. P.; Smalikho, I. N.; Balin, Yu. S.; Banakh, V. A.; Klemasheva, M. G.; Novoselov, M. M.; Rudi, Yu. A.; Penner, I. E.; Sukharev, A. A.; Falits, A. V.; Chen, W.-N.


    Observations of the aerosol atmosphere by means of the "LOSA-M2" aerosol Raman lidar and the "Stream Line" pulsed coherent Doppler lidar were carried out in August 2014 near village Boyarsk (Baikal Lake coast). The wind field and its impact on the stratification and dynamics of the aerosol layers in the lower troposphere were studied under various synoptic conditions. The data of simultaneous observations of wave-like motions in the boundary layer of the troposphere by two lidars are presented.

  15. Blood levels of polychlorinated biphenyls and their hydroxylated metabolites in Baikal seals (Pusa sibirica): emphasis on interspecies comparison, gender difference and association with blood thyroid hormone levels. (United States)

    Imaeda, Daisuke; Nomiyama, Kei; Kunisue, Tatsuya; Iwata, Hisato; Tsydenova, Oyuna; Amano, Masao; Petrov, Evgeny A; Batoev, Valeriy B; Tanabe, Shinsuke


    We have previously demonstrated that Baikal seals (Pusa sibirica) are still being exposed to polychlorinated biphenyls (PCBs), and the population is at risk. In the present study, we measured the residue levels of PCBs and their hydroxylated metabolites (OH-PCBs) in the blood of Baikal seals and assessed the impact of OH-PCBs on the thyroid function. Blood concentrations of PCBs and OH-PCBs were in the range of 2.8-130 ng g(-1)wet wt. and 0.71-4.6 ng g(-1)wetwt., respectively. Concentrations of higher-chlorinated OH-PCBs (hexa- to octa-PCBs) were more than 70% to total OH-PCB concentrations, indicating Baikal seals are mostly risked by higher-chlorinated OH-PCBs. High levels of 4OH-CB146 and 4OH-CB187 and low levels of 4OH-CB107/4'OH-CB108 found in Baikal seals were different from those in other phocidae species, suggesting the unique drug-metabolizing enzyme activities and/or contamination sources in this species. Concentrations of some OH-PCBs in males were significantly higher than those in females. These results suggest that these isomers may be preferentially transferred from mother to pup via cord blood. However, concentrations of almost all the isomers were not significantly correlated with the levels of blood total T3 and T4, implying less impact of PCB-related compounds on the thyroid hormone circulation. Copyright © 2014 Elsevier Ltd. All rights reserved.

  16. Uppermost mantle (Pn) velocity model for the Afar region, Ethiopia: an insight into rifting processes (United States)

    Stork, A. L.; Stuart, G. W.; Henderson, C. M.; Keir, D.; Hammond, J. O. S.


    The Afar Depression, Ethiopia, offers unique opportunities to study the transition from continental rifting to oceanic spreading because the process is occurring onland. Using traveltime tomography and data from a temporary seismic deployment, we describe the first regional study of uppermost mantle P-wave velocities (VPn). We find two separate low VPn zones (as low as 7.2 km s-1) beneath regions of localized thinned crust in northern Afar, indicating the existence of high temperatures and, potentially, partial melt. The zones are beneath and off-axis from, contemporary crustal magma intrusions in active magmatic segments, the Dabbahu-Manda-Hararo and Erta'Ale segments. This suggests that these intrusions can be fed by off-axis delivery of melt in the uppermost mantle and that discrete areas of mantle upwelling and partial melting, thought to characterize segmentation of the uppermost mantle at seafloor spreading centres, are initiated during the final stages of break-up.

  17. Style of extensional tectonism during rifting, Red Sea and Gulf of Aden (United States)

    Bohannon, R. G.

    Models describing the development of the Red Sea and the Gulf of Aden, prior to the present periods of sea-floor spreading, include those that use block faulting on steep normal faults, uniform diffuse shear in continental crust, simple shear on large detachment faults that cut the entire lithosphere, combinations involving detachment faults/ductile deformation/plutonic inflation, and ones that minimize the role of mechanical extension in favor of an earlier stage of sea-floor spreading. 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. The Arabian detachment projects westward to middle crustal levels beneath the sediment of the southern Red Sea coastal plain. Strata in the upper plate dip as steeply as 60° to the west, and the beds are repeated by numerous planar and listric normal faults that dip to the east. Most of the faults truncate downward at the detachment. Thus, the upper plate is highly extended and the rocks in its eastern part have been translated about 20 km westward and 21/2- to 5-km downward relative to the rest of Arabia. A prominent detachment surface, with a north dip, is evident in northernmost Somalia where it breaks away north of the Somalian escarpment in an otherwise undeformed section of cratonic strata of Jurassic to Eocene age. The upper plate of the Somalian detachment consists of a highly faulted collage of the cratonic

  18. Geochemical and geochronological constraints on the origin and evolution of rocks in the active Woodlark Rift of Papua New Guinea (United States)

    Zirakparvar, Nasser Alexander

    Tectonically active regions provide important natural laboratories to glean information that is applicable to developing a better understanding of the geologic record. One such area of the World is Papua New Guinea, much of which is situated in an active and transient plate boundary zone. The focus of this PhD research is to develop a better understanding of rocks in the active Woodlark Rift, situated in Papua New Guinea's southernmost reaches. In this region, rifting and lithospheric rupture is occurring within a former subduction complex where there is a history of continental subduction and (U)HP metamorphism. The lithostratigraphic units exposed in the Woodlark Rift provide an opportunity to better understand the records of plate boundary processes at many scales from micron-sized domains within individual minerals to regional geological relationships. This thesis is composed of three chapters that are independent of one another but are all related to the overall goal of developing a better understanding of the record of plate boundary processes in the rocks currently exposed in the Woodlark Rift. The first chapter, published in its entirety in Earth and Planetary Science Letters (2011 v. 309, p. 56 - 66), is entitled 'Lu-Hf garnet geochronology applied to plate boundary zones: Insights from the (U)HP terrane exhumed within the Woodlark Rift'. This chapter focuses on the use of the Lu-Hf isotopic system to date garnets in the Woodlark Rift. Major findings of this study are that some of the rocks in the Woodlark Rift preserve a Lu-Hf garnet isotopic record of initial metamorphism and continental subduction occurring in the Late Mesozoic, whereas others only preserve a record of tectonic processes related to lithospheric rupture during the initiation of rifting in the Late Cenozoic. The second chapter is entitled 'Geochemical and geochronological constraints on the origin of rocks in the active Woodlark Rift of Papua New Guinea: Recognizing the dispersed

  19. Regional magnetic anomaly constraints on continental rifting (United States)

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


    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.

  20. Diagnostic approaches for Rift Valley fever. (United States)

    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


    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.

  1. Rift Valley Fever, Sudan, 2007 and 2010 (United States)

    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.


    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. SHRIMP U-Pb dating of recurrent Cryogenian and Late Cambrian-Early Ordovician alkalic magmatism in central Idaho: Implications for Rodinian rift tectonics (United States)

    Lund, K.; Aleinikoff, J.N.; Evans, K.V.; duBray, E.A.; deWitt, E.H.; Unruh, D.M.


    Composite alkalic plutonic suites and tuffaceous diamictite, although discontinuously exposed across central Idaho in roof pendants and inliers within the Idaho batholith and Challis volcanic-plutonic complex, define the >200-km-long northwest-aligned Big Creek-Beaverhead belt. Sensitive highresolution ion microprobe (SHRIMP) U-Pb zircon dates on these igneous rocks provide direct evidence for the orientation and location of the Neoproterozoic-Paleozoic western Laurentian rift margin in the northern U.S. Cordillera. Dating delimits two discrete magmatic pulses at ca. 665-650 Ma and 500-485 Ma at the western and eastern ends, respectively, of this belt. Together with the nearby 685 Ma volcanic rocks of the Edwardsburg Formation, there is a 200 Ma history of recurrent extensional magmatic pulses along the belt. A similar history of recurrent uplift is reflected in the stratigraphic record of the associated miogeoclinal and cratonal platform basins, suggesting that the Big Creek-Beaverhead belt originated as a border fault during continental rift events. The magmatic belt is paired with the recurrently emergent Lemhi Arch and narrow miogeoclinal facies belts and it lies inboard of a northwest-striking narrow zone of thinned continental crust. These features define a northeast-extending upper-plate extensional system between southeast Washington and southeast Idaho that formed a segment of the Neoproterozoic-Paleozoic miogeocline. This segment was flanked on the north by the St. Mary-Moyie transform zone (south of a narrow southern Canadian upper-plate margin) and on the south by the Snake River transfer zone (north of a broad Great Basin lower-plate margin). These are the central segments of a zigzagshaped Cordilleran rift system of alternating northwest-striking extensional zones offset by northeast-striking transfers and transforms. The data substantiate polyphase rift and continental separation events that included (1) pre-and syn-Windermere rifting, (2) Windermere

  3. The centuries-old and thousand- year oscillations of uranium distribution in the Lake Baikal sediments, according to the neutron-fission (n,f)-autoradiography (United States)

    Kirichenko, Ivan; Zhmodik, Sergey; Belyanin, Dmitriy; Khlistov, Oleg


    The trace elements local distribution data, particularly (U, P, Br, Mo, BiSi et. all) in a lake and oceans bottom sediments reflects the conditions of those sediments formation, and correlates with changes in paleoclimatic conditions. In papers [Colman et all, 1995; Goldberg et all, 2000, etc.] established that the concentrations of some elements contained in the bottom sediments of Lake Baikal, in particular BiSi, Sr / Ba, Sr / Rb, Ti, U et al., reflect changes in insolation caused by periodic oscillations parameters Earth's orbit (Milankovitch cycles). At the same time, a bottom sediments of the largest continental lake (Lake Baikal), can keep a record of changes less periodicity. Our research focuses on the study of the spatial distribution of uranium with high resolution in the bottom sediments of Lake Baikal. The purpose of this research is determination the centure-old and thousand- old year oscillations in the concentration of uranium in the sediments of Lake Baikal. Fragments of the lake sediment columns taken from the axial part of the Akademicheskiy Ridge in Lake Baikal (stations coordinates St -8 (53 32'15"N 107 56'25"E); - and St11 - (53 33'51"N 108 00'05"E) were studied using complex of local analysis methods, such as: n, f - and n, β-autoradiography, SEM. The distributions of uranium and phosphorus in the authigenic component of sediments along the whole columns length (with the resolution of 10 micron which corresponds to the time resolution of about six months) have been studied by the autoradiography method. Statistical data analysis (Fourier and wavelet analysis) were used for detection oscillations in the uranium concentration Three main different factors of concentrators were established for uranium and phosphorus in the sediments of the Academic mountain range:1) sedimentation, 2) nutrient,3) diagenetic. The periodicity (range from 100 to 1,000 years), in the distribution of authigenic uranium in the sediment column were identified by

  4. Hydrothermal Petroleum in Active Continental Rift: Lake Chapala, Western Mexico, Initial Results. (United States)

    Zarate-del Valle, P. F.; Simoneit, B. R.; Ramirez-Sanchez, H. U.


    Lake Chapala in western Mexico is located partially in the Citala Rift, which belongs to the well-known neotectonic Jalisco continental triple junction. The region is characterized by active volcanism (Ceboruco, Volcan de Fuego), tectonic (1995 earthquake, M=8, 40-50 mm to SW) and hydrothermal (San Juan Cosala & Villa Corona spas and La Calera sinter deposit) activities. Hydrothermal petroleum has been described in active continental rift (East African Rift) and marine spreading zones (Guaymas Basin, Gulf of California). In 1868 the Mexican local press reported that manifestations of bitumen were appearing in front of the Columba Cap on the mid south shore of Lake Chapala. This bitumen is linked to the lake bottom and when the water level decreases sufficiently it is possible to access these tar bodies as islands. Because of these manifestations the Mexican oil company (PEMEX) drilled an exploration well (2,348m) at Tizapan El Alto without success. Hydrothermal activity is evident in the tar island zone as three in-shore thermal springs (26.8 m depth, 48.5° C, pH 7.8 and oriented N-S). The preliminary analyses by GC-MS of the tar from these islands indicate hydrothermal petroleum derived from lake sedimentary organic matter, generated at low temperatures (150° -200° C). The tars contain no n-alkanes, no PAH or other aromatics, but a major UCM of branched and cyclic hydrocarbons and mature biomarkers derived from lacustrine biota. The biomarkers consist of mainly 17α (H),21β (H)-hopanes ranging from C27 to C34 (no C28), gammacerane, tricyclic terpanes (C20-C26), carotane and its cracking products, and drimanes (C14-C16). The biomarker composition indicates an organic matter source from bacteria and algae, typical of lacustrine ecosystems. 14C dating of samples from two tar islands yielded ages exceeding 40 kyrs, i.e., old carbon from hydrothermal/tectonic remobilization of bitumen from deeper horizons to the surface. The occurrence of hydrothermal petroleum in

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

    KAUST Repository

    Ruch, Joel


    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

  6. Lithospheric discontinuities beneath the U.S. Midcontinent - signatures of Proterozoic terrane accretion and failed rifting (United States)

    Chen, Chen; Gilbert, Hersh; Fischer, Karen M.; Andronicos, Christopher L.; Pavlis, Gary L.; Hamburger, Michael W.; Marshak, Stephen; Larson, Timothy; Yang, Xiaotao


    Seismic discontinuities between the Moho and the inferred lithosphere-asthenosphere boundary (LAB) are known as mid-lithospheric discontinuities (MLDs) and have been ascribed to a variety of phenomena that are critical to understanding lithospheric growth and evolution. In this study, we used S-to-P converted waves recorded by the USArray Transportable Array and the OIINK (Ozarks-Illinois-Indiana-Kentucky) Flexible Array to investigate lithospheric structure beneath the central U.S. This region, a portion of North America's cratonic platform, provides an opportunity to explore how terrane accretion, cratonization, and subsequent rifting may have influenced lithospheric structure. The 3D common conversion point (CCP) volume produced by stacking back-projected Sp receiver functions reveals a general absence of negative converted phases at the depths of the LAB across much of the central U.S. This observation suggests a gradual velocity decrease between the lithosphere and asthenosphere. Within the lithosphere, the CCP stacks display negative arrivals at depths between 65 km and 125 km. We interpret these as MLDs resulting from the top of a layer of crystallized melts (sill-like igneous intrusions) or otherwise chemically modified lithosphere that is enriched in water and/or hydrous minerals. Chemical modification in this manner would cause a weak layer in the lithosphere that marks the MLDs. The depth and amplitude of negative MLD phases vary significantly both within and between the physiographic provinces of the midcontinent. Double, or overlapping, MLDs can be seen along Precambrian terrane boundaries and appear to result from stacked or imbricated lithospheric blocks. A prominent negative Sp phase can be clearly identified at 80 km depth within the Reelfoot Rift. This arrival aligns with the top of a zone of low shear-wave velocities, which suggests that it marks an unusually shallow seismic LAB for the midcontinent. This boundary would correspond to the top of a

  7. Along strike behavior of the Tizi n' Firest fault during the Lower Jurassic rifting (Central High Atlas Carbonate basin, Morocco) (United States)

    Sarih, S.; Quiquerez, A.; Allemand, P.; Garcia, J. P.; El Hariri, K.


    The purpose of this study is to document the along-strike early syn-rift history of the Lower Jurassic Carbonate basin of the Central High Atlas (Morocco) by combining sedimentological observations and high-resolution biostratigraphy. Six sections, each from the Sinemurian to the Upper Pliensbachian, were investigated along a 75 km-long transect at the hanging wall of a major fault of the Lower Jurassic Basin (i.e. the Tizi n' Firest fault). Depositional geometries of the early syn-rift deposits were reconstructed from the correlation between eight main timelines dated by biochronological markers for a time span covering about 6 Ma. Depocentre migration was examined and accommodation rates were calculated at the sub-zone timescale to discuss the along-strike-fault behavior of the Lower Jurassic basin formation. The early stages of extension are marked by contrasted along-strike variations in depositional geometry thickness, depocentre migration and accommodation rates, leading to the growth of three independent sub-basins (i.e. western, central, and eastern), ranging in size from 30 to 50 km, and displaying three contrasted tectono-sedimentary histories. Our results suggest that, during the early rifting phase, tectonic activity was not a continuous and progressive process evolving towards a rift climax stage, but rather a series of acceleration periods that alternated with periods of much reduced activity. The length of active fault segments is estimated at about 15-20 km, with a lifespan of a few ammonite sub-zones (> 2-3 Ma).

  8. Along-Axis Structure and Crustal Construction Processes of Spreading Segments in Iceland: Implications for Magmatic Rifts (United States)

    Siler, D. L.; Karson, J. A.


    Magmatic rift systems are composed of discrete spreading segments defined by morphologic, structural, and volcanic features that vary systematically along strike. In Iceland, structural features mapped in the glaciated and exhumed Miocene age upper crust correlate with analogous features in the seismically and volcanically active neovolcanic zone. Integrating information from both the active rift zones and ancient crust provides a three-dimensional perspective of crustal structure and the volcanic and tectonic processes that construct crust along spreading segments. Crustal exposures in the Skagi region of northern Iceland reveal significant along-strike variations in geologic structure. The upper crust at exhumed magmatic centers (segment centers) is characterized by a variety of intrusive rocks, high-temperature hydrothermal alteration, and geologic evidence for kilometer-scale subsidence. In contrast, the upper crust along segment limbs, which extend along strike from magmatic centers, is characterized by thick sections of gently dipping lava flows, cut by varying proportions of subvertical dikes. This structure implies relatively minor upper crustal subsidence and lateral dike intrusion. The differing modes of subsidence beneath segment centers and segment limbs require along-axis mass redistribution in the underlying upper, middle, and lower crust during crustal construction. This along-axis material transport is accomplished through lateral dike intrusion in the upper crust and by along-axis flow of magmatic to high-temperature solid-state gabbroic material in the middle and lower crust. These processes, inferred from outcrop evidence in Skagi, are consistent with processes inferred to be important during active rifting in Iceland and at analogous magmatic oceanic and continental rifts.

  9. Seismicity associated with magmatism, faulting and hydrothermal circulation at Aluto Volcano, Main Ethiopian Rift (United States)

    Wilks, Matthew; Kendall, J.-Michael; Nowacki, Andy; Biggs, Juliet; Wookey, James; Birhanu, Yelebe; Ayele, Atalay; Bedada, Tulu


    The silicic volcanic centres of the Main Ethiopian Rift (MER) play a central role in facilitating continental rifting. Many of these volcanoes host geothermal resources and are located in heavily populated regions. InSAR studies have shown several are deforming, but regional seismic networks have detected little seismicity. A local network of 12 seismometers was deployed at Aluto Volcano from 2012 to 2014, and detected 2142 earthquakes within a 24-month period. We locate the events using a 1D velocity model that exploits a regional model and information from geothermal boreholes and calculate local magnitudes, b-values and focal mechanisms. Event depths generally range from the near surface to 15 km with most of the seismicity clustering in the upper 2 km. A significant amount of seismicity follows the Artu Jawa Fault Zone, which trends in alignment with the Wonji Fault Belt, NNE-SSW and is consistent with previous studies of strain localisation in the MER. Focal mechanisms are mostly normal in style, with the mean T-axes congruent to the orientation of extension in the rift at this latitude. Some show relatively small left-lateral strike-slip components and are likely associated with the reactivation of NE-ENE structures at the southern tip of the Aluto-Gedemsa segment. Events range from - 0.40 to 2.98 in magnitude and we calculate an overall b-value of 1.40 ± 0.14. This relatively elevated value suggests fluid-induced seismicity that is particularly evident in the shallow hydrothermal reservoir and above it. Subdividing our observations according to depth identifies distinct regions beneath the volcanic edifice: a shallow zone (- 2-0 km) of high seismicity and high b-values that corresponds to the hydrothermal system and is influenced by a high fluid saturation and circulation; a relatively aseismic zone (0-2 km) with low b-values that is impermeable to ascending volatiles; a region of increased fluid-induced seismicity (2-9 km) that is driven by magmatic

  10. Is the Okavango Delta the terminus of the East African Rift System? Towards a new geodynamic model: Geodetic study and geophysical review (United States)

    Pastier, Anne-Morwenn; Dauteuil, Olivier; Murray-Hudson, Michael; Moreau, Frédérique; Walpersdorf, Andrea; Makati, Kaelo


    The Okavango Graben (OG) has been considered as the terminus of the southwestern branch of the East African Rift System (EARS) since the 1970s based on fault morphology and early seismic and geophysical data. Thus it has been assumed to be an incipient rifting zone, analogous to the early stage of mature rifts in the EARS. Recent geodetic data and geophysical studies in the area bring new insights into the local crust and lithosphere, mantle activity and fault activity. In this study, we computed the velocities for three permanent GPS stations surrounding the graben and undertook a review of the new geophysical data available for the area. The northern and southern blocks of the graben show an exclusively low strike-slip displacement rate of about 1mm/year, revealing the transtensional nature of this basin. The seismic record of central and southern Africa was found to be instrumentally biased for the events recorded before 2004 and the OG may not represent the most seismically active area in Botswana anymore. Moreover, no significant lithosphere and crustal thinning is found in the tectonic structure nor any strong negative Bouguer anomaly and surface heat flux. Thus the OG does not match the classical model for a rifting zone. We propose a new geodynamic model for the deformation observed west of the EARS based on accommodation of far-field deformation due to the differential extension rates of the EARS and the displacement of the Kalahari craton relative to the Nubian plate.

  11. Low lower crustal velocity across Ethiopia: Is the Main Ethiopian Rift a narrow rift in a hot craton? (United States)

    Keranen, K.M.; Klemperer, S.L.; Julia, J.; Lawrence, J. F.; Nyblade, A.A.


    [1] The Main Ethiopian Rift (MER) is a classic narrow rift that developed in hot, weak lithosphere, not in the initially cold, thick, and strong lithosphere that would be predicted by common models of rift mode formation. Our new 1-D seismic velocity profiles from Rayleigh wave/receiver function joint inversion across the MER and the Ethiopian Plateau indicate that hot lower crust and upper mantle are present throughout the broad region affected by Oligocene flood basalt volcanism, including both the present rift and the adjacent Ethiopian Plateau hundreds of kilometers from the rift valley. The region of hot lithosphere closely corresponds to the region of flood basalt volcanism, and we interpret that the volcanism and thermal perturbation were jointly caused by impingement of the Afar plume head. Across the affected region, Vs is 3.6-3.8 km/s in the lowermost crust and ???4.3 km/s in the uppermost mantle, both ??0.3 km/s lower than in the eastern and western branches of the East African Rift System to the south. We interpret the low Vs in the lower crust and upper mantle as indicative of hot lithosphere with partial melt. Our results lead to a hybrid rift mode, in which the brittle upper crust has developed as a narrow rift along the Neoproterozoic suture between East and West Gondwana, while at depth lithospheric deformation is distributed over the broad region (??400 km wide) thermally perturbed by the broad thermal upwelling associated with the Afar plume head. Development of both the East African Rift System to the south (in cold, strong lithosphere) and the MER to the north (in hot, weak lithosphere) as narrow rifts, despite their vastly different initial thermal states and depth-integrated lithospheric strength, indicates that common models of rift mode formation that focus only on temperature, thickness, and vertical strength profiles do not apply to these classic continental rifts. Instead, inherited structure and associated lithospheric weaknesses are

  12. Temporal Constraints on Continental Rifting and the Exhumation of Pliocene Eclogites, SE Papua New Guinea (United States)

    Waggoner, A. G.; Baldwin, S. L.; Webb, L. E.; Little, T. A.; Fitzgerald, P. G.


    The youngest known HP-UHP rocks on Earth have been exhumed in the footwalls of the metamorphic core complexes (MCCs) of Goodenough and Fergusson Islands within the active Woodlark rift of southeast Papua New Guinea. What can the felsic and intermediate gneisses found in the lower plate of these metamorphic core complexes tell us about the thermal evolution of these HP-UHP rocks? Also, how does their exhumation during rifting temporally relate with the sea-floor spreading history of the Woodlark Basin? Ion-microprobe U-Pb zircon, 40Ar/39Ar amphibole, phengite, biotite, and K-feldspar analyses were performed on gneisses collected from the ductile shear zones of the MCCs of Goodenough and Fergusson Islands. The application of a broad range of thermochronometers permits the detailed determination of the thermal histories of these rocks from eclogite-facies conditions to their exhumation to middle and upper crustal levels. U-Pb zircon data from these lower plate gneisses indicate a period of zircon growth concordant with the timing of eclogite facies metamorphism as previously determined in mafic eclogites. This younger population of zircon occurs as rims on cores; the cores yield ages that range in age from Paleocene to Permian. These older ages indicate an inherited component likely reflecting the nature of the protolith of these gneisses. However, the abundance and degree of this inherited component is highly variable from sample to sample. New 40Ar/39Ar data from samples collected from the northern range-bounding Wakonai shear zone and the core of Goodenough Island MCC indicate rapid cooling of these rocks as recorded by Ar closure in amphibole, phengite, biotite, and K-feldspar (~500 to ~150 °C) at ~2-1.5 Ma. Samples from along the northern range front of the Goodenough MCC indicate a southeastward younging trend that parallels the active Wakonai normal fault from the northwest end of the island to the center of the island. However, no age gradient is apparent

  13. Ice Shelf Rift Time-Lapse Photography, Antarctica, Version 1 (United States)

    National Aeronautics and Space Administration — From November 2004 to March 2005, on the Ross Ice Shelf, Antarctica, an automated "web cam" was operated on the southward facing lip of a large ice-shelf rift to...

  14. Amagmatic Lithospheric Rifting as Expressed in the Red Sea (Invited) (United States)

    Cochran, J. R.


    The Red Sea is an active analog for the rifting that produced most of the non-magmatic passive continental margins of the Atlantic and Indian Oceans. Specifically, it cuts through old (Pre-Cambrian) lithosphere well away from other plate boundaries and rifting is within 30° of orthogonal to the trend of the rift. Observations in the Red Sea therefore provide insights that can be applied to older, relict non-magmatic margins Although rifting in the Red Sea has been basically amagmatic, magmatism at two crucial times was important in defining the location of the rift and of initiating active extension and rifting. The onset of rifting was preceded by massive volcanism in Ethiopia and southern Yemen. The major volume of lava was erupted over a short period from 31-29.5 Ma. This event appears to have defined the location of the triple junction between the Red Sea, Gulf of Aden and Ethiopian rifts. Although rifting along the Gulf of Aden may have initiated at the time of the Afar volcanism, this magmatic episode was not accompanied by significant extension in the region that was to become the Red Sea and there is no sign of continuing extension in the Red Sea beginning at that time. The onset of rifting and extension in the Red Sea immediately follows a massive episode of dike intrusion that occurred over a short period of time at 24-21 Ma. Diking extended for 1700 km along the entire length of the Red Sea with no discernable temporal pattern. The diking event coincides with deposition of the first clearly syn-rift sediments at locations from the Gulf of Suez to Eritrea as well as the beginning of uplift and denudation. The diking event may have enabled rifting and extension in the Red Sea. There is no evidence of additional volcanism within the Red Sea rift from 21 Ma to the initiation of seafloor spreading. Seismic reflection and potential field data from the northern Red Sea show that large, rotated fault blocks of continental crust underlie the basin. Rifting is

  15. Sociocultural and economic dimensions of Rift Valley fever. (United States)

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


    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. © The American Society of Tropical Medicine and Hygiene.

  16. The post-Variscan development of the British Isles within a regional transfer zone influenced by orogenesis (United States)

    Peacock, D. C. P.


    The break-up of Pangaea after the Variscan Orogeny included rifting extending southwards from the Barents Sea via the Norwegian-Greenland Rift and into the North Sea, and northwards from the Central Atlantic. These two major rift systems interacted to form an approximately 1200-km-wide transfer zone across the British Isles, where a complex network of basins developed during the Mesozoic. Fault patterns were commonly controlled by reactivation of Precambrian, Caledonian and Variscan structures. The two main rift systems were unable to breach this regional transfer zone, where the crust had been thickened by the Caledonian and Variscan orogenies, until the Eocene. Breaching did not occur down the North Sea and through the English Channel because of Alpine contraction in NW Europe. Instead, breaching occurred around the west of Ireland and NW Scotland, so the British Isles remained connected to Europe rather than to the North American Plate.

  17. Stress-associated synchronization and desynchronization in geologic and biologic systems (United States)

    Kluchevsky, A. V.; Kluchevskaya, A. A.


    Variations in the annual numbers of representative earthquakes in three areas and six districts of the Baikal rift zone in 1964-2002 were subjected to correlation analysis. Episodes of significant correlations of shock flow rates were found against the background of chaotic seismic activity. They followed the rearrangements (catastrophes) of stresses in the lithosphere, which are also stressing factors for the whole rift geodynamic system. The episode of the late 1970s-early 1980s was particularly long and showed the maximum correlation. Therefore, it can be considered the principal event in seismic process synchronization in the Baikal Rift Zone. The same approach to data analysis revealed similar synchronization and desynchronization phenomena in the behavior of Baikalian turbellaria when they deviated from homeostasis as a result of illumination, which is a stress for this biologic system. Possible reasons for the behavior of biologic and geodynamic systems are discussed in terms of the synergetic concept of phenomena in living and nonliving nature.

  18. Rotation, narrowing and preferential reactivation of brittle structures during oblique rifting (United States)

    Huismans, R. S.; Duclaux, G.; May, D.


    Occurrence of multiple faults populations with contrasting orientations in oblique continental rifts and passive margins has long sparked debate about relative timing of deformation events and tectonic interpretations. Here, we use high-resolution three-dimensional thermo-mechanical numerical modeling to characterize the evolution of the structural style associated with moderately oblique rifting in the continental lithosphere. Automatic analysis of the distribution of active extensional shears at the surface of the model demonstrates a characteristic deformation sequence. We show that upon localization, Phase 1 wide oblique en-échelon grabens develop, limited by extensional shears oriented orthogonal to σ3. Subsequent widening of the grabens is accompanied by a progressive rotation of the Phase 1 extensional shears that become sub-orthogonal the plate motion direction. Phase 2 is marked by narrowing of active deformation resulting from thinning of the continental lithosphere and development of a second-generation of extensional shears. During Phase 2 deformation localizes both on plate motion direction-orthogonal structures that reactivate rotated Phase 1 shears, and on new oblique structures orthogonal to σ3. Finally, Phase 3 consists in the oblique rupture of the continental lithosphere and produces an oceanic domain where oblique ridge segments are linked with highly oblique accommodation zones. We conclude that while new structures form normal to σ3 in an oblique rift, progressive rotation and long-term reactivation of Phase 1 structures promotes orthorhombic fault systems, critical to accommodate upper crustal extension and control oblique passive margin architecture. The distribution, orientation, and evolution of frictional-plastic structures observed in our models is remarkably similar to documented fault populations in the Gulf of Aden conjugate passive margins, which developed in moderately oblique extensional settings.

  19. From rifting to subduction: the role of inheritance in the Wilson Cycle (United States)

    Beaussier, Stéphane; Gerya, Taras; Burg, Jean-Pierre


    The Wilson Cycle entails that oceans close and reopen. This cycle is a fundamental principle in plate tectonics, inferring continuity from divergence to convergence and that continental rifting takes place along former suture zones. This view questions the role of inherited structures at each stage of the Wilson Cycle. Using the 3D thermo-mechanical code, I3ELVIS (Gerya and Yuen 2007) we present a high-resolution continuous model of the Wilson cycle from continental rifting, breakup and oceanic spreading to convergence and spontaneous subduction initiation. Therefore, all lateral and longitudinal structures of the lithospheres are generated self-consistently and are consequences of the initial continental structure, tectono-magmatic inheritance and material rheology. In the models, subduction systematically initiates off-ridge and is controlled by the convergence-induced swelling of the ridge. Geometry and dynamics of the developing off-ridge subduction is controlled by four main factors: (1) the obliquity of the ridge with respect to the convergence direction; (2) fluid-induced weakening of the oceanic crust; (3) irregularity of ridge and margins inherited from rifting and spreading; (4) strain localization at transform faults formed during ocean floor spreading. Further convergence can lead to obduction of the oceanic crust and segments of ridge after the oceanic lithosphere is entrained into subduction. We show that the main parameters controlling the occurrence and geometry of obducted ophiolite are the convergence rate and the inherited structure of the passive margins and ridge. Our numerical experiments results show the essential role played by inheritance during the Wilson Cycle and are consistent with nature observations such as the tectonic history of the Oman subduction-obduction system. REFERENCES Gerya, T. V., and D. A. Yuen. 2007: "Robust Characteristics Method for Modelling Multiphase Visco-Elasto-Plastic Thermo-Mechanical Problems, Physics of the

  20. Du Lac de Geneve au Lac Baikal: deux metropoles en construction

    Directory of Open Access Journals (Sweden)

    Guy Mettan


    centres de recherche et de haute technologie.3 promouvoir la region comme un ensemble coherent et solidaire tant aupres des autorites federales, des autres regions du pays que vis-a-vis de l'etranger. La promotion economique, la vision politique, le developpement des infrastructures, le tourisme doivent faire l'objet d'une communication commune car les etrangers ne font pas tres bien la difference entre les divers elements qui composent la region. Un label commun a ainsi ete cree sou l'appellation de Lake Geneva Region.4 L'equilibre entre les partenaires doit etre respecte. On ne rapproche pas des villes comme on fusion des entreprises. Pour reussir, les objectifs doivent etre partages et chacun doit etre respecte. C'est pour cela que de tels rapprochement consomment beaucoup de temps, d'energie et exigent de la patience. C'est tres long d'apprendre a voir ce qui unit plutot que ce qui separe. C'est ainsi que toutes les tentatives de rapprochement entre Geneve et Lausanne ont, pendant des decennies, echoue parce que beaucoup de riches habitants du canton de Vaud viennent travailler a Geneve mais paient les impots dans le canton de Vaud selon le droit national, ce que Geneve trouve injuste car c'est elle qui doit financer les infrastructures publiques. Desormais, on a decide de laisser le probleme en suspens pour s'attaquer seulement aux projets communs, que chacun peut financer de facon equitable.Voila en quelques mots, l'etat d'avancement de la metropole lemanique. Le projet avance, des habitudes de collaboration sont prises. En Suisse, a cause de la complexite des procedures democratiques, les changements sont tres lents. Il est donc possible d'aller plus vite. Mais a condition de respecter les quatre principes enonces plus haut. Dans cette perspective, je souhaite donc bonne chance a la future megapole Irkutsk-Baikal!

  1. Tectonic history along the South Gabon Basin: Anomalous early post-rift subsidence

    International Nuclear Information System (INIS)

    Dupre, Stephanie; Bertotti, Giovanni; Cloetingh, Sierd


    An integrated study of the South Gabon Margin (South Atlantic) based on reflection seismic and well data has been performed to quantify tectonic activity. A regional profile crossing the entire basin together with subsidence analysis, highlights important aspects of the post-rift history. The most striking event in the margin evolution appears to be the anomalous extra subsidence during the early post-rift period characterized by high sedimentation rates, equivalent to one third of the syn-rift subsidence. Although the presence of evaporite layers restricts knowledge of the underlying structures essentially composed of pre-rift and syn-rift sequences, the outcome of this post-rift tectonic study has strong implications for the rifting history. The early post-rift subsidence patterns can be related to a high thermal anomaly during the early rifting thermal state of the lithosphere. These findings are highly relevant for petroleum system studies and have implications for hydrocarbon generation. (author)

  2. Pre-existing oblique transfer zones and transfer/transform relationships in continental margins: New insights from the southeastern Gulf of Aden, Socotra Island, Yemen (United States)

    Bellahsen, N.; Leroy, S.; Autin, J.; Razin, P.; d'Acremont, E.; Sloan, H.; Pik, R.; Ahmed, A.; Khanbari, K.


    Transfer zones are ubiquitous features in continental rifts and margins, as are transform faults in oceanic lithosphere. Here, we present a structural study of the Hadibo Transfer Zone (HTZ), located in Socotra Island (Yemen) in the southeastern Gulf of Aden. There, we interpret this continental transfer fault zone to represent a reactivated pre-existing structure. Its trend is oblique to the direction of divergence and it has been active from the early up to the latest stages of rifting. One of the main oceanic fracture zones (FZ), the Hadibo-Sharbithat FZ, is aligned with and appears to be an extension of the HTZ and is probably genetically linked to it. Comparing this setting with observations from other Afro-Arabian rifts as well as with passive margins worldwide, it appears that many continental transfer zones are reactivated pre-existing structures, oblique to divergence. We therefore establish a classification system for oceanic FZ based upon their relationship with syn-rift structures. Type 1 FZ form at syn-rift structures and are late syn-rift to early syn-OCT. Type 2 FZ form during the OCT formation and Type 3 FZ form within the oceanic domain, after the oceanic spreading onset. The latter are controlled by far-field forces, magmatic processes, spreading rates, and oceanic crust rheology.

  3. New Geodetic Results from the Hauraki Rift: Slow Continental Rifting Oblique to Subduction, North Island, New Zealand (United States)

    Pickle, R. C.; Eccles, J. D.; Hreinsdottir, S.; Palmer, N.; Rowland, J. V.


    The Hauraki Rift, an active but slow-deforming narrow intra-continental rift in northern New Zealand paradoxically strikes nearly normal to the Pacific-Australian oblique subduction boundary 300+ km to the southeast. Both the driving mechanism and quantitative details of the rift's current activity are unknown. Past GPS/GNSS geodetic surveying in the area has been coarse and erratic (e.g. single 8-hour surveys in 1995). In 2015 and again in 2016 a 37 station network of existing benchmarks around the rift was measured with the aim of gaining better insight into deformation in the region. We find that it is primarily extensional ( 0.9 mm/yr) with a small portion of right-lateral shearing ( 0.1 mm/yr) relative to a fixed Australian plate in ITRF2008. Closer to the plate boundary, the oblique westward subduction of the Pacific plate generates a strong clockwise angular strain signature in the over-riding plate; this same angular stress field is the simplest explanation for the Hauraki Rift's axis-perpendicular strain and in consistent with previous geophysical observations. Additionally, several short wavelength dislocations between our velocity solutions hint at the existence of undocumented active faults which will have implications to the seismic hazard to Auckland, New Zealand's largest city, located just 50km west of the rift.

  4. Thermochronological response to rifting and subduction in the Corsica-Sardinia block (United States)

    Malusà, Marco Giovanni; Danišík, Martin; Kuhlemann, Joachim


    The linkage between deep-seated tectonic processes and surface processes provides a key to investigate the geological evolution of complex plate boundaries starting from the analysis of low-temperature geochronological systems. Here, we integrate published thermochronological data from Corsica (Danišík et al., 2007) with a new multi-thermochronological dataset (i.e., zircon and apatite fission track (ZFT and AFT), and apatite (U-Th)/He (AHe) data) from Sardinia, in order to tackle the Western Mediterranean tectonic issue and constrain the problematic transition in space and time between the opposite-dipping Alpine (European) and Apenninic (Adriatic) subductions. Mesozoic AFT ages (169-201 Ma) and AHe ages (133-204 Ma), found on mountain ridges of central Sardinia and on the eastern coast of the island, indicate that rocks now exposed at the surface have resided since Jurassic times at very shallow depth, i.e., above the partial annealing zone of the AFT system (~60-110°C) or even above the partial retention zone of the AHe system (~40-80°C). The observed age pattern and track length distributions are consistent with those predicted after rising of isothermal surfaces during rifting and subsequent thermal relaxation after continental break-up. We demonstrate that the crustal sections now exposed in central and eastern Sardinia were originally located closer to the Tethyan rift axis than crustal sections exposed in NW Sardinia and Corsica, pointing to a NNE trend for the continental crust isopachs of the northern Tethyan margin (ENE before Corsica-Sardinia rotation), with burial depth progressively increasing from SE to NW. In Alpine Corsica, the low-T geochronological evidence of Jurassic rifting was largely obliterated by Cenozoic metamorphism, but it is still recognized in high-T systems. AFT and AHe ages set after Tethyan rifting but not thermally affected by Neogene backarc extension, define a SE-NW trend of decreasing ages from southern Sardinia to northern

  5. A Middle-Upper Miocene fluvial-lacustrine rift sequence in the Song Ba Rift, Vietnam

    DEFF Research Database (Denmark)

    Lars H., Nielsen; Henrik I., Petersen; Nguyen D., Dau


    The small Neogene Krong Pa graben is situated within the continental Song Ba Rift, which is bounded by strike-slip faults that were reactivated as extensional faults in Middle Miocene time. The 500 m thick graben-fill shows an overall depositional development reflecting the structural evolution...... development sedimentation rate outpaced the formation of accommodation space and fluvial activity increased again. During periods when the general sedimentation rate was in balance with the creation of accommodation space the environment changed frequently between lake deposition and intermittent vigorous...

  6. Voluminous lava flow from Axial Seamount's south rift constrains extension rate on northern Vance Segment (United States)

    Le Saout, M.; Clague, D. A.; Paduan, J. B.


    Axial Seamount is characterized by a robust magma supply resulting from the interaction between the Cobb hotspot and the Juan de Fuca Ridge. During the last two decades, magmatic activity was focused within the summit caldera and upper and middle portions of the two rift zones, with eruptions in 1998, 2011, and 2015. However, the distal ends of both rift zones have experienced numerous eruptions in the past. The most voluminous flows are located near the extreme ends, greater than 40 kilometers from the caldera. Where Axial's South Rift Zone overlaps with the Vance Segment of the Juan de Fuca Ridge, the 2015 MBARI expedition mapped 16 km2 of the seafloor with our AUV, and collected 33 rocks and 33 sediment cores during two ROV dives. The data were used to confirm the boundaries of an extensive flow tentatively identified using modern ship based bathymetry. This flow is 18 km wide and 6 km long for a total surface area of 63 km2. The flow is modified by superficial ( 5 m deep) and deep (25 to 45 m deep) subsidence pits, with the deepest pits giving an indication of the minimum thickness of the flow. The maximum thickness of 100 m is measured at the margins of the flow. We thus estimate a volume between 2.5 and 6 km3, making this flow the most voluminous known on the global mid ocean ridge system. The minimum volume is equivalent to the present volume of the summit caldera. Radiocarbon ages of foraminifera from the basal sections of sediment cores suggest that this flow is 1000 years old. This flow travelled east and partially filled the axial valley of the adjacent Vance Segment. Since emplacement, this part of the flow has experienced deformation by fissures and faults aligned with the trend of the Vance Segment. The horizontal extension across these features allows us to estimate a local deformation rate of 3 cm/yr of tectonic extension on the northern end of Vance Segment during the last 1000 years.

  7. Basement control in the development of the early cretaceous West and Central African rift system (United States)

    Maurin, Jean-Christophe; Guiraud, René


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

  8. Tectonic characteristics and structural styles of a continental rifted basin: Revelation from deep seismic reflection profiles

    Directory of Open Access Journals (Sweden)

    Yuan Li


    Full Text Available The Fushan Depression is a half-graben rifted sub-basin located in the southeast of the Beibuwan Basin, South China Sea. The Paleogene Liushagang sequence is the main hydrocarbon-bearing stratigraphic unit in the sub-basin. Using three-dimensional (3-D seismic data and logging data over the sub-basin, we analyzed structural styles and sedimentary characteristics of the Liushagang sequence. Five types of structural styles were defined: ancient horst, traditional slope, flexure slope-break, faulted slope-break and multiple-stage faults slope, and interpretations for positions, background and development formations of each structural style were discussed. Structural framework across the sub-basin reveals that the most remarkable tectonic setting is represented by the central transfer zone (CTZ which divides the sub-basin into two independent depressions, and two kinds of sequence architectures are summarized: (i the western multi-stage faults slope; (ii the eastern flexure slope break belt. Combined with regional stress field of the Fushan Depression, we got plane combinations of the faults, and finally built up plan distribution maps of structural system for main sequence. Also, we discussed the controlling factors mainly focused on subsidence history and background tectonic activities such as volcanic activity and earthquakes. The analysis of structural styles and tectonic evolution provides strong theoretical support for future prospecting in the Fushan sub-basin and other similar rifted basins of the Beibuwan Basin in South China Sea.

  9. Transition From a Magmatic to a Tectonic Rift System : Seismotectonics of the Eyasi- Manyara Region, Northern Tanzania, East Africa (United States)

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


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

  10. Fracture-zone tectonics at Zabargad Island, Red Sea (Egypt) (United States)

    Marshak, Stephen; Bonatti, Enrico; Brueckner, Hannes; Paulsen, Timothy


    Zabargad Island, which lies along the western margin of the Red Sea rift, is a remarkable place because it provides fresh exposures of undepleted mantle peridotite. How this peridotite came to be exposed on Zabargad remains unclear. Our field mapping indicates that most of the contacts between peridotite and the adjacent bodies of Pan-African gneiss and Cretaceous(?) Zabargad Formation on the island are now high-angle brittle faults. Zabargad Formation strata have been complexly folded, partly in response to this faulting. Overall, the array of high-angle faults and associated folds on the island resembles those found in cross-rift transfer zones. We suggest, therefore, that the Zabargad fracture zone, a band of submarine escarpments on the floor of the Red Sea north of the island, crosses Zabargad Island and has actively resolved differential movement between the central Red Sea rift and the northern Red Sea rift. The final stage of uplift that brought the unusual peridotite to the earth's surface is related to shallow crustal transpression, which may have inverted an earlier transtensional regime.

  11. The Tethys Rifting of the Valencia Trough Basin (United States)

    Viñas, Marina; Ranero, César R.; Cameselle, Alejandra L.


    The western Mediterranean submarine realm is composed of several basin inferred to be formed by a common geodynamic process: upper plate extension during slab rollback of a retreating subduction zone. Although the time evolution of the geometry of the trenches is debated, all models assume that basins opened sequentially from NW (Gulf of Lions) towards the SE (Ligurian-Provençal and later Tyrrhenian basins) and SW (Valencia Trough and later Algerian-South Balearic and Alboran Basin) as trenches migrated. Basin opening history is key to reconstruct kinematics of slab retreat preferred in each model. However, the deep structure of basins is inadequately known due to the paucity of modern wide-angle and multichannel reflection seismic studies across entire systems, and absence of deep drilling in the deep-water regions of the basins, as a result, much of the opening evolution is inferred from indirect evidence. In the Valencia Trough Basin (VTB), drilling and vintage seismic data provide good knowledge of the shallow geology of the basin. However, crustal-scale information across the entire VTB has been limited to two studies (Figure 1): One in the late 80's (Valsis experiment) with three Expanded Spread Profiles that yielded local 1D velocity/depth models used to constrain 2D gravity modeling, and a few multichannel seismic profiles along the Iberian shelf and across segments of the basin. A second study in the early 90's (ESCI experiment) collected a low-resolution deep-penetration multichannel seismic reflection profile across the basin and a coincident wide-angle seismic line with numerous land stations in Iberia but a handful of widely-spaced Ocean Bottom Seismometers. In the absence of modern detailed crustal structure, the origin and evolution of the VTB is still debated. Industry multichannel seismic reflection profiles cover the SW segment of the VTB. This is a region where the basin sea floor is comparatively shallower and has numerous industry wells

  12. Rift architecture and evolution: The Sirt Basin, Libya: The influence of basement fabrics and oblique tectonics (United States)

    Abdunaser, K. M.; McCaffrey, K. J. W.


    zones and adjoining highs. Late Eocene rocks exposed in the western part of the basin exhibit a complex network of branching segmented normal and strike-slip faults, generally with a NNW-SSE structural orientations. Many surface structural features have been interpreted from satellite images which confirm sinistral strike-slip kinematics. Relay ramp structures, numerous elongate asymmetric synclines associated with shallow west limbs and steeper dipping east limbs are developed in the hangingwalls adjacent to west downthrowing normal faults. These structural patterns reflect Cretaceous/Tertiary extensional tectonics with additional control by underlying pre-existing Pan-African basement fabrics and ENE-WSW trending Hercynian structures. We relate the Sirt Basin rift development as exemplified in our study area to the break-up of Gondwana represented by the structural evolution of the West-Central African rift system, and the South and Central Atlantic, the Tethys and the Indian Oceans.

  13. Elemental composition of peat organic matter as an indicator of trophic conditions of marsh ecosystems in the south of the Baikal region (United States)

    Tarasova, E. N.; Bezrukova, E. V.; Mamontova, E. A.; Mamontov, A. A.; Kuzmin, M. I.


    Based on measurements of the concentrations of C, N, P, and chlorophyll- a, as well as on palynological analysis of the core Vdr 2011 of peaty sediments from the Vydrinaya River along the southern coast of Lake Baikal, the geochemical characteristics of eutrophy were compared to pollen indices of changes in the environment and the mode of marsh ecosystem transformations into various trophic states was specified. It was shown that geochemical parameters of the changes in the environment may be considered as the characteristics of trophic conditions in ecosystems in the course of paleo-reconstructions.

  14. Orogenic structural inheritance and rifted passive margin formation (United States)

    Salazar Mora, Claudio A.; Huismans, Ritske S.


    Structural inheritance is related to mechanical weaknesses in the lithosphere due to previous tectonic events, e.g. rifting, subduction and collision. The North and South Atlantic rifted passive margins that formed during the breakup of Western Gondwana, are parallel to the older Caledonide and the Brasiliano-Pan-African orogenic belts. In the South Atlantic, 'old' mantle lithospheric fabric resulting from crystallographic preferred orientation of olivine is suggested to play a role during rifted margin formation (Tommasi and Vauchez, 2001). Magnetometric and gravimetric mapping of onshore structures in the Camamu and Almada basins suggest that extensional faults are controlled by two different directions of inherited older Brasiliano structures in the upper lithosphere (Ferreira et al., 2009). In the South Atlantic Campos Basin, 3D seismic data indicate that inherited basement structures provide a first order control on basin structure (Fetter, 2009). Here we investigate the role of structural inheritance on the formation of rifted passive margins with high-resolution 2D thermo-mechanical numerical experiments. The numerical domain is 1200 km long and 600 km deep and represents the lithosphere and the sublithospheric mantle. Model experiments were carried out by creating self-consistent orogenic inheritance where a first phase of orogen formation is followed by extension. We focus in particular on the role of varying amount of orogenic shortening, crustal rheology, contrasting styles of orogen formation on rifted margin style, and the time delay between orogeny and subsequent rifted passive formation. Model results are compared to contrasting structural styles of rifted passive margin formation as observed in the South Atlantic. Ferreira, T.S., Caixeta, J.M., Lima, F.D., 2009. Basement control in Camamu and Almada rift basins. Boletim de Geociências da Petrobrás 17, 69-88. Fetter, M., 2009. The role of basement tectonic reactivation on the structural evolution

  15. Role of the Tectonic inheritance on multi-phased rifting of the Sperchios Basin (Greece), north-western boundary of the Aegean Plate (United States)

    Chanier, Frank; Ferriere, Jacky; Averbuch, Olivier; Gaullier, Virginie; Graveleau, Fabien


    The Aegean plate is characterized by active extension, mainly occurring during the Pliocene to the Quaternary. This extensional deformation is considered as the upper plate response to the rollback of the northward subducting African slab. In Central Greece, it has led to the formation of large rifted basins, such as the Corinth Rift or the Sperchios basin. Both are experiencing active tectonics, as seismicity and morphotectonic analysis demonstrate. In this study, we focus on the East-West Sperchios basin, which has developed obliquely across a major NW-SE thrust zone separating the internal and external zones of the Hellenides mountain range. This range has developed since the late Jurassic, with the obduction of the Maliac Ocean, up to the Eocene times, with the collision of the External Zones. The Frontal Thrust of the internal Hellenides constitutes a major discontinuity within the crust, which may have influenced the development of the Sperchios basin. Our field investigations indicate that the southern boundary of the Sperchios rifted basin shows several large E-W to NW-SE normal faults that accommodate km-scale offsets. Our fault plane analysis showed a variety of fault orientations, all with dip-slip slicken-slides. It suggests at least two major episodes of extension, starting with a NE-SW direction in the Pliocene and then followed by a N-S direction. The latter is still active today and confirmed by geodetic studies and by earthquakes focal mechanisms. The early NE-SW episode of extension (mainly Pliocene in age) is expressed in the field by low-angle normal faults, dipping 20 to 30° northeastward, more or less parallel to the Frontal thrust of the Internal Hellenides. These low-angle normal faults are separating the platform limestones of the external zones from the upper tectonic units of the internal zones. We suggest that these low-angle normal faults are corresponding to the earlier stage of rifting and that they are rooted in the major thrust

  16. Morpho-functional differences at tissue level in some radents of arid zone: common vole and laboratory mouse C57B1 differing in radioresistance

    International Nuclear Information System (INIS)

    Popova, M.F.; Bulyakova, N.V


    An assumption is made, that mechanisms of physiological regenration of the investigation tissues in rodents of arid zones, located in different continents, differ in principle. Physiological regeneration in Rhombomys opimus and meriones unguiculatis inhabiting the Kara Kum desert and the Baikal region mainly occurs in the results of intracellular repair and in Dipodomus merriamy from Mexican Sonora desert - to a great extent by way of intensive cell division and replacement of cellular populations by other ones. The reason for the different detected lies most probably in different ways of evolution of these animals

  17. Volcanic Zone, New Zealand

    Directory of Open Access Journals (Sweden)

    Graham J. Weir


    Full Text Available A conceptual model of the Taupo Volcanic Zone (TVZ is developed, to a depth of 25 km, formed from three constant density layers. The upper layer is formed from eruption products. A constant rate of eruption is assumed, which eventually implies a constant rate of extension, and a constant rate of volumetric creation in the middle and bottom layers. Tectonic extension creates volume which can accomodate magmatic intrusions. Spreading models assume this volume is distributed throughout the whole region, perhaps in vertical dykes, whereas rifting models assume the upper crust is thinned and the volume created lies under this upper crust. Bounds on the heat flow from such magmatic intrusions are calculated. Heat flow calculations are performed and some examples are provided which match the present total heat output from the TVZ of about 4200 MW, but these either have extension rates greater than the low values of about 8 ± 4 mm/a being reported from GPS measurements, or else consider extension rates in the TVZ to have varied over time.

  18. Slip history of the La Cruz fault: Development of a late Miocene transform in response to increased rift obliquity in the northern Gulf of California (United States)

    Bennett, Scott E. K.; Oskin, Michael E.; Iriondo, Alexander; Kunk, Michael J.


    The Gulf of California rift has accommodated oblique divergence of the Pacific and North America plates in northwestern México since Miocene time. Due to its infancy, its rifted margins preserve a rare onshore record of early continental break-up processes and an opportunity to investigate the role of rift obliquity in strain localization. We map rift-related structures and syn-tectonic basins on southern Isla Tiburón, a proximal onshore exposure of the rifted North America margin. We integrate analysis and geochronology of syn-tectonic sedimentary basins and mapping of crosscutting relationships to characterize the style and timing of fault activity. On southern Isla Tiburón, an early phase of extension initiated between 19-17 Ma and 12.2 Ma. Subsequently, these normal faults and related basins were cut by the La Cruz strike-slip fault and buried by deposits of the La Cruz basin, an elongate, fault-controlled trough coextensive with the La Cruz fault. Crosscutting relationships show that the NW-striking La Cruz fault accrued 5 ± 2 km of dextral slip 8-4 Ma. The La Cruz fault and parallel Tiburón transform were kinematically linked to detachment faulting that accommodated latest Miocene to Pliocene oblique opening of the offshore Upper Tiburón pull-apart basin. The onset of strike-slip faulting on Isla Tiburón was synchronous with the 8-6 Ma onset of transform faulting and basin formation along > 1000 km of the reconstructed Pacific-North America plate boundary. This transition coincides with the commencement of a clockwise azimuthal shift in Pacific-North America relative plate motion that increased the obliquity of the Gulf of California rift and formed the Gulf of California shear zone. The record from the proto-Gulf of California illustrates how highly oblique rift geometries, where transform faults are kinematically linked to pull-apart basins, enhance the ability of continental lithosphere to rupture and, ultimately, hasten the formation of new oceanic

  19. Constrictional strain during oblique rifting: A record from transtensional basins in the Gulf Extensional Province (United States)

    Seiler, C.; Quigley, M.; Fletcher, J. M.


    Oblique opening of the Gulf of California provides a unique opportunity to study the mode of deformation in transtensional rift systems. Sedimentation in rifted basins is primarily controlled by the characteristics of the basin-bounding fault and the available sediment supply, and can thus be used as a proxy to understand tectonic processes during oblique shear. Transtensional basins are generally seen as composites between rift and pull-apart basins, with facies distributions that are controlled by interacting normal and strike-slip faults. Yet, transtensional shear may also be accommodated by more distributed constrictional strain that is not localised along fault zones. The Santa Rosa basin, located in the Sierra San Felipe of northern Baja California, is one of a series of transtensional syn-rift basins along the oblique-divergent plate boundary of the northern Gulf of California. The basin represents an asymmetric half-graben in the hanging wall of the Santa Rosa detachment, a low-angle normal fault with ~4-5km of E- to SE-directed displacement. The basin-fill dips NW into the detachment and displays form lines that mimic the corrugations of the detachment. The basin is broadly sigmoidal in shape, is truncated in the south by a dextral transfer zone and pinches out against the hanging wall basement in the north. The syn-rift stratigraphy is dominated by a sequence of alluvial fans shed from the hanging wall and footwall that interfinger with fine grained playa deposits. Stratigraphic analysis reveals systematic basin-scale variations in facies distributions, both along and across the axis of the basin. In a transverse direction, the basin-fill records a fining-upward cycle from conglomerate at the base to alternating sandstone-mudstone in the depocentre, which in turn interfingers with the proximal fault-scarp facies of the Santa Rosa detachment. Facies patterns also vary parallel to the basin axis even though finite displacement on the detachment was

  20. Spatio-temporal trends in normal-fault segmentation recorded by low-temperature thermochronology: Livingstone fault scarp, Malawi Rift, East African Rift System (United States)

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


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

  1. rift sediments, Northwestern Red Sea, Egypt

    Indian Academy of Sciences (India)


    Fault zones may have important implications for fluid flow in the earth's shallow crust as they commonly act as ... block, segmented faults, fault lenses and clay smears represents the main structural features within the ..... Permeability can be reduced as much as seven orders of magnitude due to the incorporation of clay in ...

  2. Tectonics and sedimentology of post-rift anomalous vertical movements: the rifted margin of Morocco (United States)

    Bertotti, Giovanni; Charton, Remi; Luber, Tim; Arantegui, Angel; Redfern, Jonathan


    Roughly 15 years ago it was discovered that substantial parts of the Morocco passive continental margin experienced km-scale, post-rift exhumation. It was predicted that the sands resulting from the associated erosion would be present in the offshore and potentially form hydrocarbon reservoirs. At the same time, anomalous post-rift vertical movements have been documented in various localities of the world and rifted continental margins are at present exciting objects of research. Following intense research efforts the knowledge of the kinematics of vertical movements and their implications for sedimentary systems is increasing. The low-T geochronology initially limited to the classical Meseta-Massif Ancien de Marrakech transect has been expanded reaching the Reguibate Massif to the S and covering, possibly more importantly, one transect in E-W direction along the Anti Atlas. Exhumation occurred along two dominant trends. In N-S direction a several hundred-kilometers long exhuming domain developed roughly parallel to the Atlantic margin. Changes in magnitude and timing of exhumation are observed along this elevated domain associated with E-W trending undulations. The timing of main stage of upward movement of E-W trending highs seems to be Late Jurassic-Early Cretaceous in the Meseta and High Atlas and somewhat older, Early to Middle Jurassic, in the Anti-Atlas and Reguibate. The discovery of E-W trending highs and lows has major implication for sediment distribution and dispersal. At the large scale, it means that the drainage basins were smaller than initially predicted. This seems to be compatible with the paucity of sands encountered by recent exploration wells drilled offshore Morocco. At the scale of several kilometers, W-E trending anticlines and synclines developed in a generally subsiding coastal environment. These folds often had an expression at the sea floor documented by ravinement surfaces and (Jurassic) reef build-ups on top of the anticlines

  3. Lithosphere Response to Intracratonic Rifting: Examples from Europe and Siberia

    DEFF Research Database (Denmark)

    Artemieva, I. M.; Thybo, H.; Herceg, M.


    is based on critically assessed results from various seismic studies, including reflection and refraction profiles and receiver function studies. We also use global shear-wave tomography models, gravity constraints based on GOCE data, and thermal models for the lithosphere to speculate on thermo......Several cratons have experienced a significant modification of their crustal and mantle lithosphere structure during Phanerozoic large-scale lithosphere-mantle interactions. In Eurasia, the most prominent examples include the Dniepre-Donets rift in the East European craton, the Oslo graben...... of basaltic magmas and consequently in a change in mantle density and seismic velocities. Although kimberlite magmatism is commonly not considered as a rifting events, its deep causes may be similar to the mantle-driven rifting and, as a consequence, modification of mantle density and velocity structure may...

  4. The First Prediction of a Rift Valley Fever Outbreak (United States)

    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.


    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.

  5. Orientations of Pre-existing Structures along the Scarp of the Bilila-Mtakataka Fault in the Central Malawi Rift. (United States)

    Elifritz, E. A.; Johnson, S.; Beresh, S. C. M.; Mendez, K.; Mynatt, W. G.; Mayle, M.; Laó-Dávila, D. A.; Atekwana, E. A.; Chindandali, P. R. N.; Chisenga, C.; Gondwe, S.; Mkumbwa, M.; Kalindekafe, L.; Kalaguluka, D.; Salima, J.


    The NW-SE Bilila-Mtakataka Fault is suggested to be 100 km in length and is located in the Malawi Rift, a portion of the magma-poor Western Branch of the East African Rift System. This fault is exposed south of Lake Malawi and occurs close to the epicenter of the 1989 6.2 magnitude Salima Earthquake. Moreover, it traverses rocks with inherited Precambrian fabrics that may control the modern rifting process. The effect of the orientation of the pre-existing fabric on the formation of this potentially seismogenic fault has not been well studied. In this project, we measured the older foliations, dikes, and joints in addition to younger faults and striations to understand how the active faulting of the Bilila-Mtakataka Fault is affected by the older fabric. The Fault is divided into 5 segments and 4 linkage zones. All four linkage zones were studied in detail and a Brunton compass was used to determine orientations of structures. The linkage zone between segments 1 and 2 occurs between a regional WNW-ESE joint and the border fault, which is identified by a zig-zag pattern in SRTM data. Precambrian gneiss is cut by oblique steeply-dipping faults in this area. Striations and layer offsets suggest both right-lateral and normal components. This segment strikes NE-SW, in contrast with the NW-SE average strike of the entire fault. The foliations, faults, dikes, and joints collected in this area strike NE-SW, therefore running parallel to the segment. The last 3 southern linkage zones all strike NW-SE and the linkage zone between segment 3 and 4 has a steep dip angle. Dip angles of structures vary from segment to segment, having a wide range of results. Nonetheless, all four linkage zones show structures striking parallel to its segment direction. The results show that pre-existing meso-scale and regional structures and faults strike parallel to the fault scarp. The parallelism of the structures suggest that they serve as planes of weakness, controlling the localization of

  6. Assessing the diversity of the g23 gene of T4-like bacteriophages from Lake Baikal with high-throughput sequencing. (United States)

    Potapov, Sergey; Belykh, Olga; Krasnopeev, Andrey; Gladkikh, Anna; Kabilov, Marsel; Tupikin, Aleksey; Butina, Tatyana


    Based on second generation sequencing (MiSeq platform, Illumina), we determined the genetic diversity of T4-like bacteriophages of the family Myoviridae by analysing fragments of the major capsid protein gene g23 in the plankton of Lake Baikal. The sampling depth in our study was significantly higher than in those obtained by the Sanger method before. We obtained 33 701 sequences of the g23 gene fragments, 141 operational taxonomic units (OTUs) of which were identified. 86 OTUs (60.9%) had the closest relatives from lakes Bourget and Annecy, and 28 OTUs (19.8%) had the highest identity with the Baikal g23 clones, which had been previously identified in the northern and southern basins of the lake by the Sanger method. The remaining OTUs were similar to the clones from other ecosystems. We showed a high genetic diversity of T4-type bacteriophages and a genetic difference with the phage communities from other ecosystems. © FEMS 2017. All rights reserved. For permissions, please e-mail:

  7. [The molecular genetic typification of planarians in the genus Bdellocephala (Dendrocoelidae, Tricladida, Turbellaria) from Lake Baikal with an assessment of their species diversity]. (United States)

    Kuznedelov, K D; Novikova, O A; Naumova, T V


    Baikal planaria from genus Bdellocephala were typified using rDNA locus coding 5'--end domain of 18S ribosome RNA. Five colour forms of 24 possible variants that differ in diapason 0-1.3% of genotype were determined by comparative analysis of nucleotide sequences. The authors use back colour--one of the most variable and typical character in the given group--to collect material for investigation. It allows to minimize the size of investigation sample and at the same time to cover maximum variability of Bdellocephala. One of the positive result of molecular typification of colour forms was a discovery of unique individuals that belong to new species. Karyological analysis of colour forms shows variations in chromosome numbers that divide planaria into 3 groups (2n = 20, 24, 26). Comparative analysis of morphological and ecological characters and karyotypes of some forms united by the same genotype allows to distinguish them as separate species. Criteria of modern phenetic system of Baikal planaria are discussed.

  8. Imprint of salt tectonics on subsidence patterns during rift to post-rift transition: The Central High Atlas case study (United States)

    Moragas, Mar; Vergés, Jaume; Saura, Eduard; Diego Martín-Martín, Juan; Messager, Grégoire; Hunt, David William


    During Mesozoic time, the extensional basin of the Central High Atlas in Morocco underwent two consecutive rifting events: Permo-Triassic and Early-Middle Jurassic in age. However, a review of the literature reveals that the precise timing of the Early-Middle Jurassic rift and post-rift transition varies depending of the analysed area. The discrepancy about rifting ages is associated with the general lack of normal faulting cutting post-Lower Jurassic strata and the presence of significant salt diapiric activity during Early and Middle Jurassic in the central part of the basin. To evaluate the influence on subsidence patterns of the interaction between both extensional and salt tectonics, we present new subsidence data from diverse paleogeographic and tectonic settings of the Central High Atlas rift basin. From the periphery of the basin, the Djebel Bou Dahar platform-basin system corresponds to a shallow carbonate platform developed on top of a basement high, controlled and bounded by normal faults. The results of the subsidence analysis show long-term and low-rate of tectonic and total subsidence (0.06 and 0.08 mmyr-1 respectively). The roughly parallel evolution of both total and tectonic subsidence curves indicates the tectonic influence of the platform-basin system, as corroborated by the syndepositional fault activity of the outcropping Sinemurian-Pliensbachian normal faults. Contrarily, the rift axis is characterised by the presence of diapiric salt ridges and minibasins as in the Tazoult-Amezraï area and Imilchil diapiric province. Comparison between subsidence curves from the SE flank of the Tazoult salt wall and from Amezraï minibasin centre shows that, from Pliensbachian to Aalenian, the tectonic and total subsidence rates of the Amezraï minibasin (between 0.17-0.32 mmyr-1 and 0.38-0.98 mmyr-1) are two-fold their equivalent rates in the Tazoult salt wall. Amezraï minibasin values are in agreement with the values from Imilchil minibasins (tectonic and

  9. Morphology and kinematics of the rifted margin of West Antarctica in relation to separation from Zealandia and Bellingshausen plate motion (United States)

    Wobbe, F.; Gohl, K.; Chambord, A.; Sutherland, R.


    The final breakup of Gondwana occurred during Late Cretaceous time as rifted continental crust of New Zealand separated from West Antarctica. Geophysical data acquired using R/V Polarstern constrain the structure and age of Antarctica's rifted oceanic margin. The Marie Byrd Land sector resembles a typical magma-poor margin with a narrow steep slope and a 145 km wide continent-ocean transition zone (COTZ). Our transect modelled from gravity and seismic reflection data indicates initial continental crust of thickness 24 km that was stretched 90 km. The Bellingshausen sector, east of the Antipodes Fault, is broad and complex with abundant evidence for later volcanism. The COTZ is ~670 km wide and substantial uncertainty remains as to the nature of crust within the COTZ. Extension estimates fall in the range of 106-304 km for this sector. Seafloor magnetic anomalies adjacent to the Marie Byrd Land sector at the longitude of the Pahemo Fracture Zone indicate a full-spreading rate during c33-c31 (80-68 Myr) of 60 mm/yr, increasing to 74 mm/yr at c27 (62 Myr), and then dropping to 22 mm/yr by c22 (50 Myr). Spreading rates were lower to the west. Extrapolation towards the continental margin indicates that initial oceanic crust formation was at ~c34y (84 Myr). The high extension rate of 30-60 mm/yr during the initial margin formation is consistent with the relatively sharp and symmetrical margin morphology, but subsequent motion of the Bellingshausen plate relative to Antarctica was slow and complex, and modified the rift morphology through migrating deformation and volcanic centres to create a broad and complex COTZ.

  10. Analysis of thyroid hormones in serum of Baikal seals and humans by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and immunoassay methods: application of the LC-MS/MS method to wildlife tissues. (United States)

    Kunisue, Tatsuya; Eguchi, Akifumi; Iwata, Hisato; Tanabe, Shinsuke; Kannan, Kurunthachalam


    Thyroid hormones (THs) are essential for the regulation of growth and development in both humans and wildlife. Until recently, TH concentrations in the tissues of animals have been examined by immunoassay (IA) methods. IA methods are sensitive, but for TH analysis, they are compromised by a lack of adequate specificity. In this study, we determined the concentrations of six THs, L-thyroxine (T(4)), 3,3',5-triiodo-L-thyronine (T(3)), 3,3',5'-triiodo-L-thyronine (rT(3)), 3,5-diiodo-L-thyronine (3,5-T(2)), 3,3'-diiodo-L-thyronine (3,3'-T(2)), and 3-iodo-L-thyronine (3-T(1)), in the serum of humans (n = 79) and wild Baikal seals (n = 37), by isotope ([(13)C(6)]-T(4))-dilution liquid chromatography (LC)-tandem mass spectrometry (MS/MS), and compared the TH levels with those measured by an electrochemiluminescent immunoassay (ECLIA) method. T(3) and T(4) were detected in all serum samples of both humans and Baikal seals, whereas T(1), 3,3'-T(2), and 3,5-T(2) were below the limit of detection (LOD). rT(3) was detected in Baikal seal sera at concentrations higher than T(3) in 28 seal samples, indicating an anomaly in deiodinase activity in Baikal seals. In humans, regression analyses of TH concentrations, measured by ECLIA and LC-MS/MS methods, showed significant correlations for T(4) (r = 0.852) and T(3) (r = 0.676; after removal of a serum sample with abnormal T(3) levels). In Baikal seals, a low correlation coefficient (r = 0.466) for T(4) levels and no correlation for T(3) levels (p = 0.093) were found between ECLIA and LC-MS/MS methods. These results suggest that interference by a nonspecific reaction against anti-T(3) and anti-T(4) antibodies used in the ECLIA can contribute to inaccuracies in TH measurement in Baikal seals. When the relationship between concentrations of THs in sera and dioxin-like toxic equivalents in blubber samples of Baikal seals (n = 19) was examined, a significantly negative correlation was found for serum T(4) levels measured by the LC

  11. Imaging rifting at the lithospheric scale in the northern East African Rift using S-to-P receiver functions (United States)

    Lavayssiere, A.; Rychert, C.; Harmon, N.; Keir, D.; Hammond, J. O. S.; Kendall, J. M.; Leroy, S. D.; Doubre, C.


    The lithosphere is modified during rifting by a combination of mechanical stretching, heating and potentially partial melt. We image the crust and upper mantle discontinuity structure beneath the northern East African Rift System (EARS), a unique tectonically active continental rift exposing along strike the transition from continental rifting in the Main Ethiopian rift (MER) to incipient seafloor spreading in Afar and the Red Sea. S-to-P receiver functions from 182 stations across the northern EARS were generated from 3688 high quality waveforms using a multitaper technique and then migrated to depth using a regional velocity model. Waveform modelling of data stacked in large conversion point bins confirms the depth and strength of imaged discontinuities. We image the Moho at 29.6±4.7 km depth beneath the Ethiopian plateaux with a variability in depth that is possibly due to lower crustal intrusions. The crust is 27.3±3.9 km thick in the MER and thinner in northern Afar, 17.5±0.7 km. The model requires a 3±1.2% reduction in shear velocity with increasing depth at 68.5±1.5 km beneath the Ethiopian plateaux, consistent with the lithosphere-asthenosphere boundary (LAB). We do not resolve a LAB beneath Afar and the MER. This is likely associated with partial melt near the base of the lithosphere, reducing the velocity contrast between the melt-intruded lithosphere and the partially molten asthenosphere. We identify a 4.5±0.7% increase in velocity with depth at 91±3 km beneath the MER. This change in velocity is consistent with the onset of melting found by previous receiver functions and petrology studies. Our results provide independent constraints on the depth of melt production in the asthenosphere and suggest melt percolation through the base of the lithosphere beneath the northernmost East African rift.

  12. Linking deep earth to surface processes in the Woodlark Rift of Papua New Guinea; a framework for understanding (U)HP exhumation globally (United States)

    Baldwin, S.; Fitzgerald, P. G.; Bermudez, M. A.; Webb, L. E.; Moucha, R.; Miller, S. R.; Catalano, J. P.; Zirakparvar, N. A.


    During the Cenozoic the leading edge of the AUS plate was subducted northwards beneath the forearc of oceanic island arc(s), during its north-northeast passage over a complexly structured mantle. Sediments and basalts were metamorphosed under (U)HP conditions to form blueschists and eclogites, and lower-grade metamorphic rocks that are now exposed throughout New Guinea, primarily south of, and structurally beneath, obducted ophiolites. In the Woodlark Rift the youngest (2-8 Ma) (U)HP rocks on Earth were exhumed from mantle depths (>90 km) at plate tectonic rates (1-4 cm yr-1) west of the active Woodlark Basin seafloor spreading center rift tip. How these (U)HP rocks were exhumed is the focus of an ongoing collaborative multidisciplinary project which aims to understand linkages between deep earth, plate tectonic, and surface processes in the Woodlark Rift. Since the Late Miocene, a regionally extensive subduction complex was exhumed on the southern-rifted margin of the Woodlark Basin (Pocklington Rise), and in the lower plates of the D'Entrecasteaux, Misima, and Dayman dome metamorphic core complexes. Late Miocene-to-Pliocene metamorphism of sediments and basalts preceded diachronous exhumation from east to west, in the same direction as rift propagation. In contrast the northern-rifted margin (Woodlark Rise) comprises mid-Miocene to Pliocene volcanic flows and pyroclastic material ranging in composition from basalt to rhyolite, with capping limestone. The age of volcanic rocks on the northern-rifted margin also youngs from east to west. Pliocene to active syn-rift volcanism on the Woodlark Rise and in the D'Entrecasteaux Islands is synchronous with (U)HP exhumation, and results from decompression melting of a relict mantle wedge. As lithospheric extension proceeds, volcanic compositions evolve from subduction zone geochemical signatures (i.e., negative HFSE anomalies) toward E-MORB. Preliminary mantle convection models investigate large-scale background mantle

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

    Energy Technology Data Exchange (ETDEWEB)

    Beauchamp, W.H. [Cornell Univ., Ithaca, NY (United States); Ries, A.C. [Ries-Coward Associates Ltd., Caversham (United Kingdom); Coward, M.P. [Imperial College, London (United Kingdom)] [and others


    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 that is downthrown to the southeast, forming the western edge of the Masirah graben. This graben is limited to the east by a large wedge of sea floor sediments and oceanic crust, that is stacked as imbricate thrusts. These sediments/ophiolites were obducted onto the southern margin of the Arabian plate during the collision of the Indian/Afghan plates at the end of the Cretaceous. Most of the Masirah graben is covered by an allochthonous sedimentary sequence, which is complexly folded and deformed above a detachment. This complexly deformed sequence contrasts sharply with what is believed to be a rift sequence below the ophiolites. The sedimentary sequence in the Masirah graben was stable until further rifting of the Arabian Sea/Gulf of Aden in the late Tertiary, resulting in reactivation of earlier rift-associated faults. Wells drilled in the Masirah graben in the south penetrated reservoir quality rocks in the Lower Cretaceous Natih and Shuaiba carbonates. Analyses of oil extracted from Infracambrian sedimentary rocks penetrated by these wells suggest an origin from a Mesozoic source rock.

  14. Pediatric Burns at The Rift Valley Provincial General Hospital ...

    African Journals Online (AJOL)

    Aim To determine the etiology and outcome of pediatric burns (0-12 years). Design A retrospective study of burn victims hospitalized at the Rift Valley Provincial General Hospital, Nakuru, Kenya from April 2004 to March 2007. Method Charts of all children hospitalized for burn injury were reviewed for patient demographics, ...

  15. Comparison of sampling techniques for Rift Valley Fever virus ...

    African Journals Online (AJOL)

    We investigated mosquito sampling techniques with two types of traps and attractants at different time for trapping potential vectors for Rift Valley Fever virus. The study was conducted in six villages in Ngorongoro district in Tanzania from September to October 2012. A total of 1814 mosquitoes were collected, of which 738 ...

  16. Epidemiology of gastrointestinal helminthiasis of rift valley goats ...

    African Journals Online (AJOL)

    The prevalence, mean intensity, relative density of helminth species and the effects of environmental factors, sex and maturity of host on seasonal dynamics in relative density of helminthes ova in Rift Valley goats were investigated from July 1997 to June 1998. Ten nematode and three cestode species were identified.

  17. Defluoridation of Ethiopian Rift Valley Region water using reverse ...

    African Journals Online (AJOL)

    Defluoridation of Ethiopian Rift Valley Region (ERVR) raw ground water using reverse osmosis (RO) membranes was studied. Four RO membranes CA995PlE, HR98PP, LFC and ESPA delivered by DSS and Hydranautics were investigated for the retention of fluoride in fluoride water. All four membranes were observed to ...

  18. Impact of Global Climate on Rift Valley Fever Disease Outbreaks (United States)

    Rift Valley fever is a viral disease of animals and humans in Africa and the Middle East that is transmitted by mosquitoes. Since the virus was first isolated in Kenya in 1930 it has caused significant impact to animal and human health and national economies, and it is of concern to the internationa...

  19. Probable existence of a Gondwana transcontinental rift system in ...

    Indian Academy of Sciences (India)

    S Mazumder


    Aug 31, 2017 ... Permian rifts in the East African countries of. South Africa, Kenya, Tanzania and Mozambique are mostly referred to as the Karoo System. South Africa: In the main Karoo Basin in South. Africa (figure 5), the Karoo sequence (figure 2) is subdivided into Dwyka Series (Late Carbonif- erous), Ecca Series (Early ...

  20. One health approach to Rift Valley fever vaccine development

    NARCIS (Netherlands)

    Kortekaas, J.A.


    Since its discovery in the 1930s, Rift Valley fever virus (RVFV) spread across the African continent and invaded the Arabian Peninsula and several islands off the coast of Southeast Africa. The virus causes recurrent outbreaks in these regions, and its continued spread is of global concern.

  1. Outbreak of Rift Valley fever affecting veterinarians and farmers in ...

    African Journals Online (AJOL)

    Background. During 2008, Rift Valley fever (RVF) virus re-emerged in South Africa as focal outbreaks in several provinces. Aims. To investigate an outbreak affecting cattle farmers and farm workers, and the staff and students of a veterinary school, assess the prevalence of infection during the outbreak, document the clinical ...

  2. Efficacy of three candidate Rift Valley fever vaccines in sheep

    NARCIS (Netherlands)

    Kortekaas, J.; Antonis, A.F.G.; Kant, J.; Vloet, R.P.M.; Vogel, A.; Oreshkova, N.D.; de Boer, S.M.; Bosch, B.J.; Moormann, R.J.M.


    Rift Valley fever virus (RVFV) is a mosquito-transmitted Bunyavirus that causes high morbidity and mortality among ruminants and humans. The virus is endemic to the African continent and the Arabian Peninsula and continues to spread into new areas. The explosive nature of RVF outbreaks requires that

  3. Rift Valley fever potential mosquito vectors and their infection status ...

    African Journals Online (AJOL)

    conducted to determine the abundance of potential mosquito vectors and their RVFV infection status in. Ngorongoro District ... Rift Valley fever (RVF) is an acute febrile arthropod-borne viral zoonotic disease of mainly human ..... A.S., Rollin, P.E., Swanepoel, R., Ksiazek, T.G. & Nichol, S.T. (2002) Genetic analysis of viruses.

  4. Mapping of the major structures of the African rift system (United States)

    Mohr, P. A. (Principal Investigator)


    The author has identified the following significant results. The new fault map of the main Ethiopian rift, based on aerial photo compilations, generally agrees well with the maps produced from ERTS-1 imagery. Characteristically, the ERTS-1 imagery shows some of the major faults to be more extensive than realized from ground studies, though due to the angle of sun illumination some east-facing fault scarps are not easily discernible on the imagery. The Corbetti caldera, shows up surprisingly poor on the imagery, and is shown to be an adjunct to an older, larger caldera now occupied by Lakes Awassa and Shallo. The lithological boundaries mapped by De Paola in the rift are difficult to discern on the ERTS-1 imagery. On the Somalian plateau, east of the rift, a denuded caldera has been identified as the source of much of the lavas of the Batu Mountains. Further south, ERTS-1 imagery amplifies the structural and lithological mapping of the Precambrian rocks of the Shakisso-Arero area, and of the Kenya-Ethiopia border region. For the first time with some certainty, it is now possible to say that on the evidence of the ERTS-1 imagery, the Western Rift does not continue northeast beyond the Sudan-Uganda border, and is thus not to be sought in western Ethiopia.

  5. Probable existence of a Gondwana transcontinental rift system in ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 126; Issue 6 ... The study indicates a rift system spanning from Arabian plate in the north and extending to southern part of Africa that passes through Indus basin, western part of India and Madagascar, and existed from Late Carboniferous to Early Jurassic.

  6. The Reconcavo Basin reservoirs in transition of the pre-rift and rift phases: new discussion; Os reservatorios da Bacia do Reconcavo na transicao das fases pre-rift e rift: nova discussao

    Energy Technology Data Exchange (ETDEWEB)

    Romao, Felipe [Queiroz Galvao Perfuracoes S.A., Rio de Janeiro, RJ (Brazil); Borghi, Leonardo [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil)


    The facies analysis of the stratigraphic interval represented by Sergi, Itaparica, and Agua Grande formations (Brotas and Santo Amaro groups) of Reconcavo basin was guided by cores description of the well 1-CAL-1-BA (Caldeirao 1), located in the Northwestern part of the Reconcavo Basin. Sedimentary facies (lithofacies) were described and grouped into four facies association interpreted as fluvial (upper Sergi Fm.), fluvial-lacustrine (Itaparica Fm.), and fluvial-eolian (Agua Grande Fm.) depositional systems; also, forced-regression erosive surfaces (unconformities) and transgressive ones were identified. The analysis of these results points that the upper Sergi Fm. would have subsided as consequence of the early rifting of the basin, creating space for the formation of shallow lake (Itaparica Fm.). This ancient lake undergone several forced regressions due to a continuous early tectonism (rifting), responsible by the sand input into the lake, in a coarsening up cycle topped by the expressive fluvio-eolian system of the Agua Grande Fm. Each forced regression smaller cycle is capped by lake flooding shales. Above this major CU cycle, the intensification of tectonic event subsided the basin and created a deep lake (Candeias Fm.) - the Rift Phase. So, the initial rifting would not have started during a 'Candeias time', but by earlier, in a less intense way. It must be stressed that this interpretation was based solely in only one well, but it's important to keep this new idea in mind for revision or new studies on this interval. (author)

  7. Gravity anomalies, crustal structure and rift tectonics at the Konkan ...

    Indian Academy of Sciences (India)

    trolled by the mode of extension and thinning of continental lithosphere during its formation. Stud- ies on the evolution of passive margins therefore facilitate to understand the genetic link between tectonics, geomorphology and sedimentation. The. Western Continental Margin of India (WCMI) has evolved through rifting and ...

  8. Occurrence of rift valley fever (RVF) in Dodoma region, Tanzania ...

    African Journals Online (AJOL)

    Rift Valley Fever (RVF) is a peracute or acute febrile zoonotic mosquito-borne viral disease affecting wildlife, domestic animals and occasionally humans. It occurs after heavy rains and ... While waiting for the results the patients were treated for malaria and/or meningitis based on visual/ clinical signs. However, most of the ...


    African Journals Online (AJOL)


    Philip and Mosha - Salt Lakes of the African Rift System … 2 development of newer models for a clear understanding of the governing equilibria. Chemical speciation, the new equilibria and processes such as pH, pKa's buffer capacities, the extreme aggressive chemical environment and adaptive mechanisms evolved by ...

  10. Forecast and Outbreak of Rift valley fever in Sudan, 2007 (United States)

    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...

  11. Perched Lava Pond Complex on South Rift of Axial Volcano Revealed in AUV Mapping (United States)

    Paduan, J. B.; Clague, D. A.; Caress, D. W.; Thomas, H. J.


    -like structures and jumbled sheet flows on the floors suggest the eruption was on-going when the ponds emptied. 14C-dating of foraminifera from basal sediments on the pond floors gives a minimum age for the ponds of ~1500 years, which is older than any of the surface flows in Axial's summit caldera. Limu o Pele was abundant. Glass contents of the recovered lavas are 7.6 to 8.0 wt% MgO with few exceptions, and other than being plagioclase-phyric, the chemistry is similar to the majority of lavas at the summit. Lava samples from the floors of several ponds have a few tenths of a weight percent lower MgO than the nearby levees, suggesting the pond's molten interior or resupplied lavas had some time to cool. The varying levee rim heights and abundance of ponds in the vicinity suggest this type of activity occurred many times in this area, but it is an unusual eruption style for mid-ocean ridges. Another lava pond complex with even higher levees occurs on the north rift of Axial Volcano. Formation of these ponds requires long-lived, steady, moderate-eruption-rate lava effusion on nearly horizontal seafloor and may occur only on deep distal rift zones of central volcanoes.

  12. Clastic Sediment Dispersal in Rifted Margins, an Example From the Swiss Alps (United States)

    Galster, Federico; Stockli, Daniel


    temperatures above 700°C are drastically reduced and the input of rutile from mafic sources as well as a Permo-Triassic population is observed. This trend marks the compartmentalization of the European margin in sub-basins, the emergence and rapid unroofing of local sources and the progressive reduction and eventual disconnection from far-field sources. However, eventually this period leads to the creation of new sediment dispersal pathways tapping into very far-field sources, as deduced from the Cretaceous DR record. In particular, Aptian to Cenomanian ("Gault") sedimentary strata in the Helvetic, North Penninic, and Briançonnais domains show remarkable similarities, incl. the reappearance of abundant Mid-Proterozoic zircons and the appearance, for the first time in the system, of Paleoproterozoic (1.8-2 Ga) rutiles. This trend marks the general subsidence of the rifted margin and the instauration of strong longitudinal currents. The appearance of abundant Paleoproterozoic rutile in central Europe, whose basement has been formed and repeatedly metamorphosed during the late Proterozoic and the Paleozoic, suggests a source located to the east of the Tornquist-Teisseyre zone, in the basement of the East European platform and a direct connection through E-W currents between the Outer Carpathians and the Central Alps.

  13. Heat Flow Budget of the Gulf of California Rift: Preliminary Results of a High Resolution Survey Across the Wagner Basin (United States)

    Negrete-Aranda, R.; Neumann, F.; Harris, R. N.; Contreras, J.; Gonzalez-Fernandez, A.; Sclater, J. G.


    The thermal regime exerts a primary control on rift dynamics and mode of extension for continental lithosphere. We present three heat-flow profiles across the southern terminus of the Cerro Prieto fault, in the northern Gulf of California. The longest profile is 42 km and has a measurement spacing of 1 km that spans the hanging-wall block (Wagner basin) and the footwall block of that fault. Measurements were taken with a 6.5 m long Fielax, violin-bow probe. Most measurements are of good quality, i.e., the probe fully penetrated sediments and measurements were stable enough to perform reliable inversion for heat flow and thermal properties. However, it was necessary to perform numerous corrections due to environmental phenomena related the copious sedimentation in the area, and seasonal changes in water temperature. Our measurements indicate the total throughput across the central rift and its east shoulder is 15 KW/m per meter of rift length. More important, heat flow values cluster in three distinct spatial groups: (i) heat flow in the well sedimented depocenter of the Wagner basin is approximately 200 mW/m2; (ii) the footwall block heat-flow is approximately 400 mW/m2; and (iii) heat flow across the fault zone is very high, up to 5,000 mW/m2. Our interpretation is that the former value represents the background conductive heat flow in the rift whereas heat flow across the fault represents advective heat transport by hydrothermal fluids. The high heat flow in the footwall block of the Cerro Prieto fault might be result of both conductive and advective heat transfer by fluid seepage from the basin. These data provide evidence that fluids from deep magma bodies transported along faults assist rifting in the northern Gulf of California. We are exploring how fluids may play a role in weakening the lithosphere and help localizing/delocalizing strain along major transforms and numerous normal faults observed in the area.

  14. Kinematics of the entire East African Rift from GPS velocities (United States)

    Floyd, M.; King, R. W.


    Through a collaborative effort of the GeoPRISMS East Africa Rift GPS Working Group, we have collected and collated all of the publicly available continuous and survey-mode data for the entire rift system between 1994 and 2017 and processed these data as part of a larger velocity solution for Africa, Arabia and western Eurasia. We present here our velocity solution encompassing the major bounding plates and intervening terranes along the East African Rift from the Red Sea to the Malawi Rift and adjacent regions for GPS sites with data spans of at least 2.4 years, and north and east velocity uncertainties less than 1.5 mm/yr. To obtain realistic uncertainties for the velocity estimates, we attempted at each stage of the analysis to account for the character of the noise: During phase processing, we used an elevation-dependent weighting based on the phase residuals for each station; we then examined each position time series, removing outliers and reweighting appropriately to account for the white noise component of the errors; and e accounted for temporal correlations by estimating an equivalent random-walk magnitude for each continuous site and applying the median value (0.5 mm/√yr) to all survey-mode sites. We rigorously estimate relative rotation rates of Nubia, by choosing subset of well-determined sites such that the effective weights of western, northeastern and southern Africa were roughly equivalent, and Somalia, for which the estimate is dominated by three sites (MALI, RCMN, SEY1) whose uncertainties are a factor of 2-3 smaller than those of the other sites. For both plates, the weighted root-mean-square of the velocity residuals is 0.5 mm/yr. Our unified velocity solution provides a geodetic framework and constraints on the continental-scale kinematics of surface motions as well as more local effects both within and outside of the rift structures. Specific focus areas with denser coverage than previous fields include the Danakil block, the Afar Rift, the

  15. The Porcupine Basin: from rifting to continental breakup (United States)

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


    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 reflection (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 reflection 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

  16. The influence of inherited structures on magmatic and amagmatic processes in the East African Rift. (United States)

    Biggs, J.; Lloyd, R.; Hodge, M.; Robertson, E.; Wilks, M.; Fagereng, A.; Kendall, J. M.; Mdala, H. S.; Lewi, E.; Ayele, A.


    The idea that crustal heterogeneities, particularly inherited structures, influence the initiation and evolution of continental rifts is not new, but now modern techniques allow us to explore these controls from a fresh perspective, over a range of lengthscales, timescales and depths. In amagmatic rifts, I will demonstrate that deep fault structure is controlled by the stress orientation during the earliest phase of rifting, while the surface expression exploits near-surface weaknesses. I will show that pre-existing structures control the storage and orientation of deeper magma reservoirs in magmatic rifts, while the tectonic stress regime controls intra-rift faulting and shallow magmatism and stresses related to surface loading and cycles of inflation and deflation dominate at volcanic edifices. Finally, I will show how cross-rift structures influence short-term processes such as deformation and seismicity. I will illustrate the talk throughout using examples from along the East African Rift, including Malawi, Tanzania, Kenya and Ethiopia.

  17. Active Magmatic Underplating in Western Eger Rift, Central Europe (United States)

    Hrubcová, Pavla; Geissler, Wolfram H.; Bräuer, Karin; Vavryčuk, Václav; Tomek, Čestmír.; Kämpf, Horst


    The Eger Rift is an active element of the European Cenozoic Rift System associated with intense Cenozoic intraplate alkaline volcanism and system of sedimentary basins. The intracontinental Cheb Basin at its western part displays geodynamic activity with fluid emanations, persistent seismicity, Cenozoic volcanism, and neotectonic crustal movements at the intersections of major intraplate faults. In this paper, we study detailed geometry of the crust/mantle boundary and its possible origin in the western Eger Rift. We review existing seismic and seismological studies, provide new interpretation of the reflection profile 9HR, and supplement it by new results from local seismicity. We identify significant lateral variations of the high-velocity lower crust and relate them to the distribution and chemical status of mantle-derived fluids and to xenolith studies from corresponding depths. New interpretation based on combined seismic and isotope study points to a local-scale magmatic emplacement at the base of the continental crust within a new rift environment. This concept of magmatic underplating is supported by detecting two types of the lower crust: a high-velocity lower crust with pronounced reflectivity and a high-velocity reflection-free lower crust. The character of the underplated material enables to differentiate timing and tectonic setting of two episodes with different times of origin of underplating events. The lower crust with high reflectivity evidences magmatic underplating west of the Eger Rift of the Late Variscan age. The reflection-free lower crust together with a strong reflector at its top at depths of 28-30 km forms a magma body indicating magmatic underplating of the late Cenozoic (middle and upper Miocene) to recent. Spatial and temporal relations to recent geodynamic processes suggest active magmatic underplating in the intracontinental setting.

  18. Results of the monitoring of the Steppe Eagle population in Trans-Baikal Territory (Zabaikalsky Kray in 2015, Russia

    Directory of Open Access Journals (Sweden)

    Anna N. Barashkova


    Full Text Available Ornithological survey was carried out in July–August 2015 in steppe areas of Russian part of Dauria (Trans-Baikal Territory, or Zabaikalsky Krai in the frames of monitoring the population of the Steppe Eagle (Aquila nipalensis. Research was conducted at 13 study sites in 10 administrative districts of the region, including 11 study sites which were surveyed repeatedly (after first survey in 2010. A total of 57 nesting territories with 95 nest structures were identified in 2010 and 2015 together. Additionally adult birds were recorded in 24 points but nests were not found. In 2015 we checked 35 of 40 nesting territories that were identified in 2010 while other 35 nesting territories (including 17 ones with nest structures are localized for the first time. A total of 27 nestlings and fledglings (1.4±0.5 nestlings and fledglings produced per successful nest in 19 nests were recorded during the 2015 survey. In 2010, the status of Steppe Eagle in Dauria was assessed as extremely unfavorable. The main population characteristics had not essentially changed to 2015. Actual average nesting density slightly increased but still is close to 1 pair per 100 km2. An average distance between neighbor active nests in Dauria is unexpectedly long as comparing with such figures in other regions of the Steppe Eagle nesting. More than a half of potentially available nesting territories remain unoccupied, and the share of unoccupied nesting territories almost did not change. The productivity of successful nests (average brood size remains low – on average 1.4±0.5 fledglings and nestlings per successful nest in 2015. The negative factors such as power lines that are dangerous for birds and steppe wild fires are still acting. More than 40 % of all the nesting territories were affected by fires in 2015; the nest structures were completely burnt at 17% of the known nesting territories visited in 2015. Meanwhile the following positive trends can be noted: the

  19. Mantle convection patterns reveal the enigma of the Red Sea rifting (United States)

    Petrunin, Alexey; Kaban, Mikhail; El Khrepy, Sami; Al-Arifi, Nassir


    Initiation and further development of the Red Sea rift (RSR) is usually associated with the Afar plume at the Oligocene-Miocene separating the Arabian plate from the rest of the continent. Usually, the RSR is divided into three parts with different geological, tectonic and geophysical characteristics, but the nature of this partitioning is still debatable. To understand origin and driving forces responsible for the tectonic partitioning of the RSR, we have developed a global mantle convection model based on the refined density model and viscosity distribution derived from tectonic, rheological and seismic data. The global density model of the upper mantle is refined for the Middle East based on the high-resolution 3D model (Kaban et al., 2016). This model based on a joint inversion of the residual gravity and residual topography provides much better constraints on the 3D density structure compared to the global model based on seismic tomography. The refined density model and the viscosity distribution based on a homologous temperature approach provide an initial setup for further numerical calculations. The present-day snapshot of the mantle convection is calculated by using the code ProSpher 3D that allows for strong lateral variations of viscosity (Petrunin et al., 2013). The setup includes weak plate boundaries, while the measured GPS velocities are used to constrain the solution. The resulting mantle flow patterns show clear distinctions among the mantle flow patterns below the three parts of the RSR. According to the modeling results, tectonics of the southern part of the Red Sea is mainly determined by the Afar plume and the Ethiopian rift opening. It is characterized by a divergent mantle flow, which is connected to the East African Rift activity. The rising mantle flow is traced down to the transition zone and continues in the lower mantle for a few thousand kilometers south-west of Afar. The hot mantle anomaly below the central part of the RSR can be

  20. Petrological and Geochemical characterization of central Chihuahua basalts: a possible local sign of rifting activity (United States)

    Espejel-Garcia, V. V.; Garcia-Rascon, M.; Villalobos-Aragon, A.; Morton-Bermea, O.


    The central part of the mexican state, Chihuahua, is the oriental border of the Sierra Madre Occidental (silicic large igneous province), which consist of series of ignimbrites divided into two volcanic groups of andesites and rhyolites. In the central region of Chihuahua, the volcanic rocks are now part of the Basin and Range, allowing the presence of mafic rocks in the lower areas. The study area is located approximately 200 km to the NW of Chihuahua city near to La Guajolota town, in the Namiquipa County. There are at least 5 outcrops of basalts to the west of the road, named Puerto de Lopez, Malpaises, El Tascate, Quebrada Honda, and Carrizalio, respectively. These outcrops have only been previously described by the Mexican Geologic Survey (SGM) as thin basaltic flows, with vesicles filled with quartz, and phenocrystals of labradorite, andesine, oligoclase and olivine. Petrologically, the basalts present different textures, from small phenocrysts of plagioclase in a very fine matrix to large, zoned and sometimes broken phenocrysts of plagioclase in a coarser matrix. All samples have olivine in an advanced state of alteration, iddingsite. The geochemical analyses report that these basaltic flows contain characteristics of rift basalts. The rocks have a normative olivine values from 5.78 to 27.26 and nepheline values from 0 to 2.34. In the TAS diagram the samples straddle the join between basalt and trachy-basalt, reflecting a high K2O content. The Mg# average is 0.297, a value that suggests that the basalts do not come from a primitive magma. The basalts have high values of Ba (945-1334 ppm), Cu (54-147 ppm), and Zn (123-615 ppm). The contents of Rb (23-57 ppm), Sr (659-810 ppm), Y (26-33 ppm), Zr (148-217 ppm) and Cr (79-98 ppm) are characteristics of rift basalts. Using discrimination diagrams, the basalts plot in the field of within plate, supporting the rifting origin. Outcrops of other basalts, at about 80 to 100 km to the east of the study area, Lomas El

  1. Persistent C3 vegetation accompanied Plio-Pleistocene hominin evolution in the Malawi Rift (Chiwondo Beds, Malawi). (United States)

    Lüdecke, Tina; Schrenk, Friedemann; Thiemeyer, Heinrich; Kullmer, Ottmar; Bromage, Timothy G; Sandrock, Oliver; Fiebig, Jens; Mulch, Andreas


    The development of East African savannas is crucial for the origin and evolution of early hominins. These ecosystems, however, vary widely in their fraction of woody cover and today range from closed woodland to open grassland savanna. Here, we present the first Plio-Pleistocene long-term carbon isotope (δ(13)C) record from pedogenic carbonate and Suidae teeth in the southern East African Rift (EAR). These δ(13)C data from the Chiwondo and Chitimwe Beds (Karonga Basin, Northern Malawi) represent a southern hemisphere record in the EAR, a key region for reconstructing vegetation patterns in today's Zambezian Savanna, and permit correlation with data on the evolution and migration of early hominins in today's Somali-Masai Endemic Zone. The sediments along the northwestern shore of Lake Malawi contain fossils attributed to Homo rudolfensis and Paranthropus boisei. The associated hominin localities (Uraha, Malema) are situated between the well-known hominin bearing sites of the Somali-Masai Endemic Zone in the Eastern Rift and the Highveld Grassland in southern Africa, and fill an important geographical gap for hominin research. Persistent δ(13)C values around -9‰ from pedogenic carbonate and suid enamel covering the last ∼4.3 Ma indicate a C3-dominated closed environment with regional patches of C4-grasslands in the Karonga Basin. The overall fraction of woody cover of 60-70% reflects significantly higher canopy density in the Malawi Rift than the Eastern Rift through time. The discrepancy between the two savanna types originated in the Late Pliocene, when the Somali-Masai ecosystem started to show increasing evidence for open, C4-dominated landscapes. Based on the Malawi δ(13)C data, the evolution of savanna ecosystems in Eastern Africa followed different patterns along the north-south extent of the EAR. The appearance of C4-grasses is considered a driver of evolutionary faunal shifts, but despite the difference of ecosystem evolution in the north, similar

  2. Rift Valley Fever Risk Map Model and Seroprevalence in Selected Wild Ungulates and Camels from Kenya (United States)

    Britch, Seth C.; Binepal, Yatinder S.; Ruder, Mark G.; Kariithi, Henry M.; Linthicum, Kenneth J.; Anyamba, Assaf; Small, Jennifer L.; Tucker, Compton J.; Ateya, Leonard O.; Oriko, Abuu A.; hide


    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 on key environmental indicators that precede Rift Valley fever (RVF) epizootics and epidemics. Although the timing and locations of human case data from the 2006-2007 RVF outbreak in Kenya have been compared to risk zones flagged by the model, seroprevalence of RVF antibodies in wildlife has not yet been analyzed in light of temporal and spatial predictions of RVF activity. Primarily wild ungulate serum samples from periods before, during, and after the 2006-2007 RVF epizootic were analyzed for the presence of RVFV IgM and/or IgG antibody. Results show an increase in RVF seropositivity from samples collected in 2007 (31.8%), compared to antibody prevalence observed from 2000-2006 (3.3%). After the epizootic, average RVF seropositivity diminished to 5% in samples collected from 2008-2009. Overlaying maps of modeled RVF risk assessments with sampling locations indicated positive RVF serology in several species of wild ungulate in or near areas flagged as being at risk for RVF. Our results establish the need to continue and expand sero-surveillance of wildlife species Kenya and elsewhere in the Horn of Africa to further calibrate and improve the RVF risk model, and better understand the dynamics of RVFV transmission.

  3. Structure of the la VELA Offshore Basin, Western Venezuela: AN Obliquely-Opening Rift Basin Within the South America-Caribbean Strike-Slip Plate Boundary (United States)

    Blanco, J. M.; Mann, P.


    Bathymetric, gravity and magnetic maps show that the east-west trend of the Cretaceous Great Arc of the Caribbean in the Leeward Antilles islands is transected by an en echelon series of obliquely-sheared rift basins that show right-lateral offsets ranging from 20 to 40 km. The basins are 75-100 km in length and 20-30 km in width and are composed of sub-parallel, oblique slip normal faults that define deep, bathymetric channels that bound the larger islands of the Leeward Antilles including Aruba, Curacao and Bonaire. A single basin of similar orientation and structure, the Urumaco basin, is present to the southwest in the Gulf of Venezuela. We mapped structures and sedimentation in the La Vela rift basin using a 3D seismic data volume recorded down to 6 seconds TWT. The basin can be mapped from the Falcon coast where it is correlative with the right-lateral Adicora fault mapped onshore, and its submarine extension. To the southeast of the 3D survey area, previous workers have mapped a 70-km-wide zone of northeast-striking, oblique, right-lateral faults, some with apparent right-lateral offsets of the coastline. On seismic data, the faults vary in dip from 45 to 60 degrees and exhibit maximum vertical offsets of 600 m. The La Vela and other obliquely-opening rifts accommodate right-lateral shear with linkages to intervening, east-west-striking right-lateral faults like the Adicora. The zone of oblique rifts is restricted to the trend of the Great Arc of the Caribbean and may reflect the susceptiblity of this granitic basement to active shearing. The age of onset for the basins known from previous studies on the Leeward Antilles is early Miocene. As most of these faults occur offshore their potential to generate damaging earthquakes in the densely populated Leeward Antilles is not known.

  4. Late Miocene-Pleistocene evolution of a Rio Grande rift subbasin, Sunshine Valley-Costilla Plain, San Luis Basin, New Mexico and Colorado (United States)

    Ruleman, C.A.; Thompson, R.A.; Shroba, R.R.; Anderson, M.; Drenth, B.J.; Rotzien, J.; Lyon, J.


    The Sunshine Valley-Costilla Plain, a structural subbasin of the greater San Luis Basin of the northern Rio Grande rift, is bounded to the north and south by the San Luis Hills and the Red River fault zone, respectively. Surficial mapping, neotectonic investigations, geochronology, and geophysics demonstrate that the structural, volcanic, and geomorphic evolution of the basin involves the intermingling of climatic cycles and spatially and temporally varying tectonic activity of the Rio Grande rift system. Tectonic activity has transferred between range-bounding and intrabasin faults creating relict landforms of higher tectonic-activity rates along the mountain-piedmont junction. Pliocene–Pleistocene average long-term slip rates along the southern Sangre de Cristo fault zone range between 0.1 and 0.2 mm/year with late Pleistocene slip rates approximately half (0.06 mm/year) of the longer Quaternary slip rate. During the late Pleistocene, climatic influences have been dominant over tectonic influences on mountain-front geomorphic processes. Geomorphic evidence suggests that this once-closed subbasin was integrated into the Rio Grande prior to the integration of the once-closed northern San Luis Basin, north of the San Luis Hills, Colorado; however, deep canyon incision, north of the Red River and south of the San Luis Hills, initiated relatively coeval to the integration of the northern San Luis Basin.Long-term projections of slip rates applied to a 1.6 km basin depth defined from geophysical modeling suggests that rifting initiated within this subbasin between 20 and 10 Ma. Geologic mapping and geophysical interpretations reveal a complex network of northwest-, northeast-, and north-south–trending faults. Northwest- and northeast-trending faults show dual polarity and are crosscut by north-south– trending faults. This structural model possibly provides an analog for how some intracontinental rift structures evolve through time.

  5. A Geodetic Strain Rate Model for the East African Rift System. (United States)

    Stamps, D S; Saria, E; Kreemer, C


    Here we describe the new Sub-Saharan Africa Geodetic Strain Rate Model v.1.0 (SSA-GSRM v.1.0), which provides fundamental constraints on long-term tectonic deformation in the region and an improved seismic hazards assessment in Sub-Saharan Africa. Sub-Saharan Africa encompasses the East African Rift System, the active divergent plate boundary between the Nubian and Somalian plates, where strain is largely accommodated along the boundaries of three subplates. We develop an improved geodetic strain rate field for sub-Saharan Africa that incorporates 1) an expanded geodetic velocity field, 2) redefined regions of deforming zones guided by seismicity distribution, and 3) updated constraints on block rotations. SSA-GSRM v.1.0 spans longitudes 22° to 55.5° and latitudes -52° to 20° with 0.25° (longitude) by 0.2° (latitude) spacing. For plates/sub-plates, we assign rigid block rotations as constraints on the strain rate calculation that is determined by fitting bicubic Bessel splines to a new geodetic velocity solution for an interpolated velocity gradient tensor field. We derive strain rates, velocities, and vorticity rates from the velocity gradient tensor field. A comparison with the Global Geodetic Strain Rate model v2.1 reveals regions of previously unresolved spatial heterogeneities in geodetic strain rate distribution, which indicates zones of elevated seismic risk.

  6. Integrated Remote Sensing and Geophysical Investigations of the Geodynamic Activities at Lake Magadi, Southern Kenyan Rift

    Directory of Open Access Journals (Sweden)

    Akinola Adesuji Komolafe


    Full Text Available The tectonic lineaments and thermal structure of Lake Magadi, southern Kenyan rift system, were investigated using ASTER data and geophysical methods. Five N-S faults close to known hot springs were identified for geoelectric ground investigation. Aeromagnetic data were employed to further probe faults at greater depths and determine the Curie-point depth. Results indicate a funnel-shaped fluid-filled (mostly saline hydrothermal zone with relatively low resistivity values of less than 1 Ω-m, separated by resistive structures to the west and east, to a depth of 75 m along the resistivity profiles. There was evidence of saline hydrothermal fluid flow toward the surface through the fault splays. The observed faults extend from the surface to a depth of 7.5 km and are probably the ones that bound the graben laterally. They serve as major conduits for the upward heat flux in the study area. The aeromagnetics spectral analysis also revealed heat source emplacement at a depth of about 12 km. The relative shallowness implies a high geothermal gradient evidenced in the surface manifestations of hot springs along the lake margins. Correlation of the heat source with the hypocenters showed that the seismogenetic zone exists directly above the magmatic intrusion, forming the commencement of geodynamic activities.

  7. Hypothesis for Cretaceous rifting of east Gondwana caused by subducted slab capture (United States)

    Luyendyk, Bruce P.


    In the process of subducted slab capture, a spreading ridge approaches subparallel to a subduction zone following the trailing edge of a downgoing plate. Eventually the downgoing plate is too young and small to subduct, and spreading stops. The spreading ridge stalls many tens of kilometres outboard of the subduction zone. The subducted plate welds to the outboard plate across the dormant spreading center and is captured by it. The captured plate then acquires the motion of the plate it welded to. In the southwest Pacific the Pacific-Phoenix ridge approached the east Gondwana margin as the Phoenix plate subducted beneath New Zealand, the Chatham Rise and Campbell Plateau, the Lord Howe Rise (collectively, Zealandia), and Marie Byrd Land in Cretaceous time. Spreading and subduction shut down here between 110 and 105 Ma, and some sections of the Phoenix plate became welded to (captured by) the Pacific plate. Pacific plate northward motion began in Aptian time, pulling the captured subducted microplates with it. This movement exerted a basal traction on the overlying east Gondwana margin and resulted in extension of Zealandia and Marie Byrd Land. Continued Pacific northward motion rifted Zealandia from Marie Byrd Land at about 85 Ma.

  8. Thermomechanical Controls on the Success and Failure of Continental Rift Systems (United States)

    Brune, S.


    Studies of long-term continental rift evolution are often biased towards rifts that succeed in breaking the continent like the North Atlantic, South China Sea, or South Atlantic rifts. However there are many prominent rift systems on Earth where activity stopped before the formation of a new ocean basin such as the North Sea, the West and Central African Rifts, or the West Antarctic Rift System. The factors controlling the success and failure of rifts can be divided in two groups: (1) Intrinsic processes - for instance frictional weakening, lithospheric thinning, shear heating or the strain-dependent growth of rift strength by replacing weak crust with strong mantle. (2) External processes - such as a change of plate divergence rate, the waning of a far-field driving force, or the arrival of a mantle plume. Here I use numerical and analytical modeling to investigate the role of these processes for the success and failure of rift systems. These models show that a change of plate divergence rate under constant force extension is controlled by the non-linearity of lithospheric materials. For successful rifts, a strong increase in divergence velocity can be expected to take place within few million years, a prediction that agrees with independent plate tectonic reconstructions of major Mesozoic and Cenozoic ocean-forming rift systems. Another model prediction is that oblique rifting is mechanically favored over orthogonal rifting, which means that simultaneous deformation within neighboring rift systems of different obliquity and otherwise identical properties will lead to success and failure of the more and less oblique rift, respectively. This can be exemplified by the Cretaceous activity within the Equatorial Atlantic and the West African Rifts that lead to the formation of a highly oblique oceanic spreading center and the failure of the West African Rift System. While in nature the circumstances of rift success or failure may be manifold, simplified numerical and

  9. Decade-centenary resolution records of climate changes in East Siberia from elements in the bottom sediments of lake Baikal for the last 150 kyr

    International Nuclear Information System (INIS)

    Goldberg, E.L.; Phedorin, M.A.; Chebykin, E.P.; Zolotarev, K.B; Zhuchenko, N.A.


    High-resolution scanning Synchrotron Radiation X-ray Fluorescence Analysis (SRXFA) was applied to investigate the downcore distribution of elements in the sediments from Lake Baikal (East Siberia). The obtained multi-element time series reveal the presence of abrupt climate shifts in East Siberia which were synchronous with the abrupt warming events in the North Atlantic and Greenland (Dansgaard-Oeschges events (D/O) during the last ice age 24-75 kyr BP. We show here the set of climatic indicators reveals all globally known climate changes from dry and cool or glacial climates to humid and warm ones, which were recorded in Northern Atlantic and East Siberia both on the orbital and millennial time scales during the last 150 kyr

  10. Sound Zones

    DEFF Research Database (Denmark)

    Møller, Martin Bo; Olsen, Martin


    Sound zones, i.e. spatially confined regions of individual audio content, can be created by appropriate filtering of the desired audio signals reproduced by an array of loudspeakers. The challenge of designing filters for sound zones is twofold: First, the filtered responses should generate...... an acoustic separation between the control regions. Secondly, the pre- and post-ringing as well as spectral deterioration introduced by the filters should be minimized. The tradeoff between acoustic separation and filter ringing is the focus of this paper. A weighted L2-norm penalty is introduced in the sound...

  11. Hotspots trails below Arabia and the Horn of Africa: new insight about the initiation of the Red Sea rift (United States)

    de Gouveia, Sophie Vicente; Besse, Jean; Frizon de Lamotte, Dominique; Greff-Lefftz, Marianne; Gueydan, Frédéric; Lescanne, Marc; Leparmentier, François


    The past trajectories followed by three present-day hotspots, Afar, East-Africa and Lake-Victoria were computed using a hotspot reference frame. The tracks are most of time situated under continental crust, which is known to strongly filter surface plume activity. We thus look for surface markers of their ancient existence, such as volcanism, doming, geochemistry and finally by a compilation of heat flow data issued from petroleum wells. Hence, the East-Africa hotspot is episodically warranted up to at least 110 Ma, the Afar one to about 90 Ma and the Lake-Victoria hotspot activity appears more recent and is attested until the Cenozoic. According to the hotspot trajectories, two important issues are addressed. Firstly, the Afar hotspot was situated 1000 km on the north-east of the Ethiopian-Yemen traps at 32 Ma, too far to be responsible for it. The trigger was most probably the East-Africa hotspot situated at the right location at that time. Secondly, we address the question of the Arabian Plate formation as the result of the coeval opening of both the Gulf of Aden and the Red Sea in a context characterized by extensional forces linked to the Neo-Tethys slab-pull: (1) the Gulf of Aden overlaps on inherited Mesozoic extensional basin between two weak zones, the Carlsberg ridge's end and a hotspot heated area; while (2) the Red Sea develops on the previous hotspot track location suggesting a causal relationship between a thermal weakening of the lithosphere and the rift initiation. To test this idea, we performed a numerical simulation in order to describe the lithosphere strength evolution when exposed to a hotspot heating combined with tectonic forces along the East-Africa hotspot track from 110 Ma until the beginning of the rifting at early Oligocene time. Preliminary results suggest that the Red Sea rift was compelled to evolve in a specific area pre-weakened by a hotspot impact.

  12. Evolution of Kilauea Volcano's shallow magmatic plumbing system: a geochemical perspective from historical rift lavas (1790-present) (United States)

    Marske, J. P.; Garcia, M. O.; Pietruszka, A. J.; Rhodes, J. M.; Norman, M. D.; Heaton, D. E.


    Over 200 years of frequent, voluminous (~4.3 km3), and compositionally variable (5-18 wt. % MgO) eruptions at Kilauea’s summit, and east (ERZ) and southwest (SWRZ) rift zones provide an excellent opportunity to delineate its magmatic architecture, and to infer shallow magma storage times. Pb, Sr, and Nd isotopic ratios, and major- and trace-element abundances of historical Kilauea rift lavas (1790-2010 A.D.) display systematic temporal variations that allow us to trace the passage of geochemically distinct batches of magma within the volcano. Overall, historical Kilauea rift and summit lavas display overlapping temporal geochemical variations (e.g., K2O/TiO2, Nb/Y, 87Sr/86Sr, and 206Pb/204Pb) indicating that they originated from similar parental magmas for a given time period (i.e., months to years). The exceptions are strongly evolved (20th century Kilauea historical summit lavas (~0.004 year-1). This rapid change indicates these lavas may have partially or completely bypassed the summit reservoir. The MgO-variable (6.7-11.5 wt. %) 1971 and 1974 caldera rim and floor lavas reflect the eruption of stored, moderately evolved magmas from the volcano’s summit reservoir that were hydraulically forced to the surface by more mafic magmas that also bypassed the summit reservoir. Magma storage times for late 20th century lavas in the ERZ (~12-165 years) are significantly shorter than most previous estimates for Kilauea’s summit and middle ERZ (~23-160 years), lower ERZ (>550 years), and the interconnected volume beneath the volcano (~100-3000 years).

  13. Fault-Magma Interactions during Early Continental Rifting: Seismicity of the Magadi-Natron-Manyara basins, Africa (United States)

    Weinstein, A.; Oliva, S. J.; Ebinger, C.; Aman, M.; Lambert, C.; Roecker, S. W.; Tiberi, C.; Muirhead, J.


    Although magmatism may occur during the earliest stages of continental rifting, its role in strain accommodation remains weakly constrained by largely 2D studies. We analyze seismicity data from a 13-month, 39-station broadband seismic array to determine the role of magma intrusion on state-of-stress and strain localization, and their along-strike variations. Precise earthquake locations using cluster analyses and a new 3D velocity model reveal lower crustal earthquakes along projections of steep border faults that degas CO2. Seismicity forms several disks interpreted as sills at 6-10 km below a monogenetic cone field. The sills overlie a lower crustal magma chamber that may feed eruptions at Oldoinyo Lengai volcano. After determining a new ML scaling relation, we determine a b-value of 0.87 ± 0.03. Focal mechanisms for 66 earthquakes, and a longer time period of relocated earthquakes from global arrays reveal an along-axis stress rotation of 50 o ( N150 oE) in the magmatically active zone. Using Kostrov summation of local and teleseismic mechanisms, we find opening directions of N122ºE and N92ºE north and south of the magmatically active zone. The stress rotation facilitates strain transfer from border fault systems, the locus of early stage deformation, to the zone of magma intrusion in the central rift. Our seismic, structural, and geochemistry results indicate that frequent lower crustal earthquakes are promoted by elevated pore pressures from volatile degassing along border faults, and hydraulic fracture around the margins of magma bodies. Earthquakes are largely driven by stress state around inflating magma bodies, and more dike intrusions with surface faulting, eruptions, and earthquakes are expected.

  14. Re-Emergence of Rift Valley Fever in Madagascar

    Centers for Disease Control (CDC) Podcasts


    This podcast describes the re-emergence of Rift Valley Fever in Madagascar during two rainy seasons in 2008 and 2009. CDC epidemiologist Dr. Pierre Rollin discusses what researchers learned about the outbreak and about infections in the larger population in Madagascar.  Created: 5/27/2010 by National Center for Emerging and Zoonotic Infectious Diseases (NCEZID).   Date Released: 5/27/2010.

  15. Eradicating tsetse from the Southern Rift Valley of Ethiopia

    International Nuclear Information System (INIS)


    Farming activities in Ethiopia, as in much of sub-Saharan Africa, are restricted by the presence of tsetse flies (Glossina spp.). These carry the livestock and human disease, trypanosomosis, which severely affects agricultural production and human well-being. In collaboration with the Ethiopian authorities, the International Atomic Energy Agency is sponsoring a Sterile Insect Technique (SIT) programme to eradicate tsetse from the Southern Rift Valley of Ethiopia. (IAEA)

  16. Quantitative reconstruction of the last interglacial vegetation and climate based on the pollen record from Lake Baikal, Russia

    Energy Technology Data Exchange (ETDEWEB)

    Tarasov, P. [Free University, Institute of Geological Sciences, Palaeontology Department, Berlin (Germany); Granoszewski, W. [Polish Geological Institute, Carpathian Branch, Krakow (Poland); Bezrukova, E.; Abzaeva, A. [Siberian Branch Russian Academy of Sciences, Institute of Geochemistry, Irkutsk (Russian Federation); Brewer, S. [CEREGE CNRS/University P. Cezanne, UMR 6635, BP80, Aix-en-Provence (France); Nita, M. [University of Silesia, Faculty of Earth Sciences, Sosnowiec (Poland); Oberhaensli, H. [GeoForschungsZentrum, Potsdam (Germany)


    Changes in mean temperature of the coldest (T{sub c}) and warmest month (T{sub w}), annual precipitation (P{sub ann}) and moisture index ({alpha}) were reconstructed from a continuous pollen record from Lake Baikal, Russia. The pollen sequence CON01-603-2 (53 57'N, 108 54'E) was recovered from a 386 m water depth in the Continent Ridge and dated to ca. 130-114.8 ky BP. This time interval covers the complete last interglacial (LI), corresponding to MIS 5e. Results of pollen analysis and pollen-based quantitative biome reconstruction show pronounced changes in the regional vegetation throughout the record. Shrubby tundra covered the area at the beginning of MIS 5e (ca. 130-128 ky), consistent with the end of the Middle Pleistocene glaciation. The late glacial climate was characterised by low winter and summer temperatures (T{sub c}{proportional_to} -38 to -35 C and T{sub w}{proportional_to}11-13 C) and low annual precipitation (P{sub ann}{proportional_to}300 mm). However, the wide spread of tundra vegetation suggests rather moist environments associated with low temperatures and evaporation (reconstructed {alpha}{proportional_to}1). Tundra was replaced by boreal conifer forest (taiga) by ca. 128 ky BP, suggesting a transition to the interglacial. Taiga-dominant phase lasted until ca. 117.4 ky BP, e.g. about 10 ky. The most favourable climate conditions occurred during the first half of the LI. P{sub ann} reached 500 mm soon after 128 ky BP. However, temperature changed more gradually. Maximum values of T{sub c}{proportional_to} -20 C and T{sub w}{proportional_to}16-17 C are reconstructed from about 126 ky BP. Conditions became gradually colder after ca. 121 ky BP. T{sub c} dropped to {proportional_to} -27 C and T{sub w} to {proportional_to}15 C by 119.5 ky BP. The reconstructed increase in continentality was accompanied by a decrease in P{sub ann} to {proportional_to}400-420 mm. However, the climate was still humid enough ({alpha}{proportional_to}0.9) to

  17. Correlation of Plio Pleistocene Tephra in Ethiopian and Kenyan rift basins: Temporal calibration of geological features and hominid fossil records (United States)

    WoldeGabriel, Giday; Hart, William K.; Katoh, Shigehiro; Beyene, Yonas; Suwa, Gen


    The 200-m-thick fossiliferous Konso Formation and overlying terrace deposits, which crop out at the end of the southern sector of the Main Ethiopian Rift (MER), contain more than 30 distal tephra layers. Local and regional tephra correlations of more than 20 tephra units were established using major and trace element data of discrete and purified bulk glass samples within the Konso study area. Eleven correlative marker tuffs were recognized in stratigraphic sections of both the Konso Formation and the Omo-Turkana Basin sediments in southern Ethiopia and northern Kenya. The Turoha, Hope, Ivory, Bright White, and Boleshe Tuffs in the Konso Formation, and the Upper White Tuff in the overlying terrace deposits are securely correlated with the KBS, Akait, Lokapetamoi, Chari, Lower Nariokotome, and Silbo Tuffs of the Omo-Turkana Basin, using least mobile major elements (CaO, Fe 2O 3*, and TiO 2) and geochronology. Preliminary correlations are also suggested between the Konso Formation distal tephra and proximal units of the Quaternary caldera-forming silicic centers in the central sector of the MER. The strongly peralkaline tuffs of the Konso Formation are compositionally similar to proximal eruptions mostly located along the Quaternary axial rift zone of the southern, central, and northern sectors of the MER. The tephra correlation provides information about the temporal and spatial features of the volcanic and tectonic processes recorded in the evolving basins. Thickness and sedimentation rate were determined for both the Konso Formation and the Omo-Turkana Basin sections, measured between the Turoha (=KBS; 1.91 ± 0.03 Ma) and the Bright White (=Chari; 1.40 ± 0.02 Ma) Tuffs. Although the lithostratigraphic sequence at the Konso study area is younger, sedimentation rate within the Konso Formation was comparable to that of the Koobi Fora Formation, higher in the Nachukui Formation, and lower in the Shungura Formation. Local and regional differences in thickness and

  18. Latest Miocene transtensional rifting of northeast Isla Tiburón, eastern margin of the Gulf of California (United States)

    Bennett, Scott E. K.; Oskin, Michael E.; Iriondo, Alexander


    Details about the timing and kinematics of rifting are crucial to understand the conditions that led to strain localization, continental rupture, and formation of the Gulf of California ocean basin. We integrate detailed geologic and structural mapping, basin analysis, and geochronology to characterize transtensional rifting on northeastern Isla Tiburón, a proximal onshore exposure of the rifted North America margin, adjacent to the axis of the Gulf of California. Slip on the Kunkaak normal fault tilted its hanging wall down-to-the-east 70° and formed the non-marine Tecomate basin, deposited across a 20° angular unconformity. From 7.1-6.4 Ma, the hanging wall tilted at 35 ± 5°/Myr, while non-marine sandstone and conglomerate accumulated at 1.4 ± 0.2 mm/yr. At least 1.8 ± 0.1 km of sediments and pyroclastic deposits accumulated in the Tecomate basin concurrent with clockwise vertical-axis block rotation and 2.8 km of total dip-slip motion on the Kunkaak fault. Linear extrapolation of tilting and sedimentation rates suggests that faulting and basin deposition initiated 7.6-7.4 Ma, but an older history involving initially slower rates is permissible. The Kunkaak fault and Tecomate basin are truncated by NW-striking, dextral-oblique structures, including the Yawassag fault, which accrued > 8 km of post-6.4 Ma dextral displacement. The Coastal Sonora fault zone on mainland Sonora, which accrued several tens of kilometers of late Miocene dextral offset, continues to the northwest, across northeastern Isla Tiburón and offshore into the Gulf of California. The establishment of rapid, latest Miocene transtension in the Coastal Sonora fault zone was synchronous with the 8-7 Ma onset of transform faulting and basin formation along the nascent Pacific-North America plate boundary throughout northwestern Mexico and southern California. Plate boundary strain localized into this Gulf of California shear zone, a narrow transtensional belt that subsequently hosted the

  19. A Fusion-Inhibiting Peptide against Rift Valley Fever Virus Inhibits Multiple, Diverse Viruses (United States)


    This entry is mediated by a viral fusion protein. Here, we synthesized peptides based on the Rift Valley fever virus (RVFV) fusion protein stem...attenuation of Rift Valley fever virus as a method for vaccine development. J Gen Virol 66 (Pt 10): 2271–2277. 28. Spik K, Shurtleff A, McElroy AK, Guttieri MC...Hooper JW, et al. (2006) Immunogenicity of combination DNA vaccines for Rift Valley fever virus, tick- borne encephalitis virus, Hantaan virus, and

  20. La dorsal NE de Tenerife: hacia un modelo del origen y evolución de los rifts de islas oceánicas

    Directory of Open Access Journals (Sweden)

    Delcamp, A.


    primordial, plume-related fractures acting throughout the entire growth of the islands. Basaltic volcanism forms the bulk of the islands and rift zones. However, collapses of the flanks of the rifts disrupt their established fissural feeding system, frequently favouring magma accumulation and residence at shallow emplacements, leading to differentiation of magmas, and intermediate to felsic nested eruptions. Rifts and their collapse may therefore act as an important factor in providing petrological variability to oceanic volcanoes. Conversely, the possibility exists that the presence of important felsic volcanism may indicate lateral collapses in oceanic shields and ridge-like volcanoes, even if they are concealed by post-collapse volcanism or partially mass-wasted by erosion.El Rift NE de Tenerife, conocido localmente como la Dorsal de La Esperanza, es un excelente ejem plo de un rift persistente y recurrente. Su estudio ha aportado evidencias significativas del origen y diná mica de este tipo de estructuras volcánicas. Los rifts son posiblemente las estructuras más relevantes en la geología de las islas volcánicas oceánicas: 1. Controlan, tal vez desde su inicio, la construcción de los edificios insulares; 2. Son elementos sustanciales en la configuración (forma y topografía de estas islas; 3. Dan origen a sus principales formas del relieve y el paisaje; 4. Al concentrar la actividad eruptiva, son asimismo estructuras cruciales en la distribución del riesgo volcánico; 5. Condicionan la distribución de recursos naturales básicos, como el agua subterránea. En las Canarias están muy bien representados tanto los rifts típicos de los estadios juveniles de desarrollo en escudo, como los más tardíos, correspondientes a las fases de rejuvenecimiento post-ero sivo. El Rift NE es un buen ejemplo de este último tipo de rifts. El Rift NE se ha desarrollado en tres etapas diferentes separadas por periodos más largos de quiescencia o actividad reducida. La primera

  1. The role of magmatic loads and rift jumps in generating seaward dipping reflectors on volcanic rifted margins (United States)

    Buck, W. Roger


    The largest volcanic constructs on Earth are the seismically imaged seaward dipping reflector (SDR) units found offshore of many rifted continental margins, including most that border the Atlantic Ocean. Whether their formation requires large magnitude (i.e. 10 s of km) of normal fault slip or results from the deflection of the lithosphere by the weight of volcanic flows is controversial. Though there is evidence for faulting associated with some SDRs, this paper considers the range of structures that can be produced by magmatic and volcanic loading alone. To do this an idealized mechanical model for the construction of rift-related volcanic flow structures is developed. Dikes open as plates move away from the center of a model rift and volcanic flows fill the depression produced by the load caused by dike solidification. The thin elastic plate flexure approximation allows a closed form description of the shape of both the contacts between flows and between the flows and underlying dikes. The model depends on two independent parameters: the flexure parameter, α, and the maximum isostatically supported extrusive layer thickness, w0. For reasonable values of these parameters the model reproduces the observed down-dip thickening of flows and the range of reflector dip angles. A numerical scheme using the analytic results allows simulation of the effect of temporal changes in the locus of magmatic spreading as well as changes in the amount of volcanic infill. Either jumps in the location of the center of diking or periods with no volcanism result in separate units or "packages" of model SDRs, in which the flow-dike contact dips landward, consistent with observations previously attributed only to listric normal fault offset. When jumps in the spreading center are small (i.e. less than α) they result in thicker, narrower volcanic units on one side of a rift compared to those on the other side. This is similar to the asymmetric distributions of volcanic packages seen

  2. Crust and upper mantle structure associated with extension in the Woodlark Rift, Papua New Guinea from Rayleigh-wave tomography (United States)

    Jin, Ge; Gaherty, James B.; Abers, Geoffery A.; Kim, Younghee; Eilon, Zachary; Buck, W. Roger


    The Woodlark seafloor spreading center is propagating westward into the Australian plate near the D'Entrecasteaux Islands (DI), Papua New Guinea, generating an active transition zone from continental rifting to seafloor spreading. From March 2010 to July 2011, we deployed 31 on-shore and 8 offshore broadband seismic stations around the DI region, to explore the dynamic processes of the lithosphere extension and the exhumation of the high-pressure terranes exposed on those islands. We measure the multiband (10-60 s) Rayleigh-wave phase velocities from both ambient noise and earthquake signals. These measurements are then inverted for a three-dimensional shear-velocity model for the crust and upper mantle. The results indicate that the lithosphere extension is localized near the rift axis beneath the DI, with a shear-velocity structure in the upper mantle that is similar to mid-ocean ridges. Beneath the Kiribisi Basin west of DI, an ultraslow shear-velocity anomaly (˜4.0 km/s) is observed at shallow mantle depth (30-60 km), which can be interpreted either by the presence of excess partial melt due to slow melt extraction, or by the existence of felsic crustal material buried to mantle depth and not yet exhumed.

  3. Fluid flow and permeabilities in basement fault zones (United States)

    Hollinsworth, Allan; Koehn, Daniel


    Fault zones are important sites for crustal fluid flow, specifically where they cross-cut low permeability host rocks such as granites and gneisses. Fluids migrating through fault zones can cause rheology changes, mineral precipitation and pore space closure, and may alter the physical and chemical properties of the host rock and deformation products. It is therefore essential to consider the evolution of permeability in fault zones at a range of pressure-temperature conditions to understand fluid migration throughout a fault's history, and how fluid-rock interaction modifies permeability and rheological characteristics. Field localities in the Rwenzori Mountains, western Uganda and the Outer Hebrides, north-west Scotland, have been selected for field work and sample collection. Here Archaean-age TTG gneisses have been faulted within the upper 15km of the crust and have experienced fluid ingress. The Rwenzori Mountains are an anomalously uplifted horst-block located in a transfer zone in the western rift of the East African Rift System. The north-western ridge is characterised by a tectonically simple western flank, where the partially mineralised Bwamba Fault has detached from the Congo craton. Mineralisation is associated with hydrothermal fluids heated by a thermal body beneath the Semliki rift, and has resulted in substantial iron oxide precipitation within porous cataclasites. Non-mineralised faults further north contain foliated gouges and show evidence of leaking fluids. These faults serve as an analogue for faults associated with the Lake Albert oil and gas prospects. The Outer Hebrides Fault Zone (OHFZ) was largely active during the Caledonian Orogeny (ca. 430-400 Ma) at a deeper crustal level than the Ugandan rift faults. Initial dry conditions were followed by fluid ingress during deformation that controlled its rheological behaviour. The transition also altered the existing permeability. The OHFZ is a natural laboratory in which to study brittle fault

  4. Abrupt plate acceleration through oblique rifting: Geodynamic aspects of Gulf of California evolution (United States)

    Brune, S.


    The Gulf of California formed by oblique divergence across the Pacific-North America plate boundary. This presentation combines numerical forward modeling and plate tectonic reconstructions in order to address 2 important aspects of rift dynamics: (1) Plate motions during continental rifting are decisively controlled by the non-linear decay of rift strength. This conclusion is based on a recent plate-kinematic analysis of post-Pangea rift systems (Central Atlantic, South Atlantic, Iberia/Newfoundland, Australia/Antarctica, North Atlantic, South China Sea). In all cases, continental rifting starts with a slow phase followed by an abrupt acceleration within a few My introducing a fast rift phase. Numerical forward modeling with force boundary conditions shows that the two-phase velocity behavior and the rapid speed-up during rifting are intrinsic features of continental rupture that can be robustly inferred for different crust and mantle rheologies. (2) Rift strength depends on the obliquity of the rift system: the force required to maintain a given rift velocity can be computed from simple analytical and more realistic numerical models alike, and both modeling approaches demonstrate that less force is required to perpetuate oblique extension. The reason is that plastic yielding requires a smaller plate boundary force when extension is oblique to the rift trend. Comparing strike slip and pure extension end-member scenarios, it can be shown that about 50% less force is required to deform the lithosphere under strike-slip. This result implies that rift systems involving significant obliquity are mechanically preferred. These two aspects shed new light on the underlying geodynamic causes of Gulf of California rift history. Continental extension is thought to have started in Late Eocene/Oligocene times as part of the southern Basin and Range Province and evolved in a protracted history at low extension rate (≤15 mm/yr). However, with a direction change in Baja

  5. Analysis of the pre-rift/rifte transition interval (Serraria and Barra de Itiuba formations) from the Sergipe-Alagoas basin; Analise da secao de transicao pre-rifte/rifte (formacoes Serraria e Barra de Itiuba) da Bacia Sergipe-Alagoas

    Energy Technology Data Exchange (ETDEWEB)

    Barreiro, C.B.; Mizusaki, A.M.P. [Rio Grande do Sul Univ., Porto Alegre, RS (Brazil)]. E-mail:;; Garcia, A.J.V. [Universidade do Vale do Rio dos Sinos (UNISINOS), Sao Leopoldo, RS (Brazil)]. E-mail:


    The pre-rift/rift transition is represented by the Serraria and Barra de Itiuba formations. This interval was analyzed through qualitative and quantitative descriptions of cores, electric log analysis and studies of outcropping sections. The integration of surface and subsurface data allowed the stratigraphic characterization of sandstone bodies in the pre-rift/rift. These sandstones bodies were deposited by fluvial braided, lacustrine and deltaic systems (delta plain, delta front and pro delta). The sedimentary deposits characterized in the Serraria Formation are of channel, flooding of the fluvial system and eolic. The upper interval of this formation is characterized by to coarse medium-grained sandstones identified as the Caioba Sandstone. The Barra de Itiuba Formation contains lake, pro delta, frontal bar, distributary mouth, crevasse and distributary channel deposits. The sandstone units were specifically characterized in terms of their potential reservoir quality, and they were characterized the reservoirs R1 (good to medium quality) and Caioba (good quality) from the pre-rift phase, and reservoirs R2 (medium quality) and R3 (medium to good quality) from the rift phase. The reservoirs from pre-rift phase phase show the better reservoirs quality potential of the pre-rift/rift transition in the Sergipe-Alagoas Basin. (author)

  6. Tectonics and stratigraphy of the East Brazil Rift system: an overview (United States)

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


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

  7. Coastal zone

    International Nuclear Information System (INIS)


    The report entitled Climate Change Impacts and Adaptation : A Canadian Perspective, presents a summary of research regarding the impacts of climate change on key sectors over the past five years as it relates to Canada. This chapter on the coastal zone focuses on the impact of climate change on Canada's marine and Great Lakes coasts with tips on how to deal with the impacts associated with climate change in sensitive environments. This report is aimed at the sectors that will be most affected by adaptation decisions in the coastal zone, including fisheries, tourism, transportation and water resources. The impact of climate change in the coastal zone may include changes in water levels, wave patterns, storm surges, and thickness of seasonal ice cover. The Intergovernmental Panel on Climate Change projects global average sea level will rise between 9 and 88 centimetres between 1990 to 2100, but not all areas of Canada will experience the same rate of future sea level change. The main physical impact would be shoreline change that could result in a range of biophysical and socio-economic impacts, some beneficial, some negative. The report focuses on issues related to infrastructure and communities in coastal regions. It is noted that appropriate human adaptation will play a vital role in reducing the extent of potential impacts by decreasing the vulnerability of average zone to climate change. The 3 main trends in coastal adaptation include: (1) increase in soft protection, retreat and accommodation, (2) reliance on technology such as geographic information systems to manage information, and (3) awareness of the need for coastal adaptation that is appropriate for local conditions. 61 refs., 7 figs

  8. Correlation Analysis of NINO3.4 SST and Inland Lake Level Variations Monitored with Satellite Altimetry: Case Studies of Lakes Hongze, Khanka, La-ang, Ulungur, Issyk-kul and Baikal

    Directory of Open Access Journals (Sweden)

    Jinyun Guo


    Full Text Available Climate change can sometimes be reflected in variations in lake levels, thus understanding variations in lake levels and their relationship to climate change plays an important role in studying climate change. In this study, about 10 years of Topex/Poseidon (T/P altimetric data and 6 years of Jason-1 data were used to compute time series of level variations of six lakes in the Central and East Asia. The study sites were Hongze, La-ang, Ulungur, Khanka, Issyk-kul and Baikal Lakes. Time series of level variations were analyzed by means of the wavelet spectrum for inter-annual (between 2 to 4 years, annual and semiannual signals. Since 2000, water level variations of Issyk-kul, Ulungur and Khanka lakes were larger than those of Baikal and Hongze. Correlations between the NINO3.4 sea surface temperature (SST and the level variations of the six lakes were analyzed. For Baikal and Khanka Lakes, the correlations were significant (+0.3834 and +0.3334 for 3 - 5 months after the occurrence of ENSO, while the correlation for La-ang Lake was the weakest (< 0.1, indicating that ENSO showed a lag influence on variation in lake levels in the Central and East Asia.

  9. Upper crustal structure of the northern part of the Bohemian ­Massif in ­rel­ation­ t­o geological, potential field data and new deep seismic data (Eger/Ohře Rift, Central Europe)

    Czech Academy of Sciences Publication Activity Database

    Skácelová, Z.; Mlčoch, B.; Novotný, Miroslav; Mrlina, Jan


    Roč. 39, č. 1 (2011), s. 1-18 ISSN 0303-4534 R&D Projects: GA AV ČR IAA300460602; GA MŽP SB/630/3/02 Institutional research plan: CEZ:AV0Z30120515 Keywords : upper crustal structure * Bohemian Massif * Eger/Ohře Rift * Saxothuringian Zone * Teplá-Barrandian Unit * Moldanubian Zone Subject RIV: DC - Siesmology, Volcanology, Earth Structure

  10. China's first intermediate resolution multi-channel seismic survey in the northern Victoria Land Basin and Terror Rift, Ross Sea, Antarctica (United States)

    Shen, Zhongyan; Gao, Jinyao; Zhang, Tao; Wang, Wei; Ding, Weifeng; Zhang, Sheng


    The West Antarctic Rift System (WARS) represents one of the largest active continental rift systems on Earth and is less well known than other rift systems because it is largely covered by thick ice. The Terror Rift (TR), superimposing on the Victoria Land Basin (VLB) in the western Ross Sea, is identified as the most recent deformational zone of the WARS, thus will provide knowledge of the active deformation process of the WARS. The structure and kinematics of the TR is under debate. Originally, the TR was thought to consist of two parts: the Discovery Graben and the magmatically-intruded Lee Arch. New denser seismic grid in the middle and southern segments of the TR revealed a different structure of the Lee Arch while the northern segment of the TR is not well studied. The glacial history of the VLB/TR region is another attractive issue to the geologists since this area records the behavior information of EAIS and WAIS. In the southern part of the VLB, especially in the McMurdo Sound, the framework of the glacial history is well established after several deep cores which recovery the whole stratigraphic sequences since the onset of the glaciation. However, the glacial history of the northern part of the VLB/TR is less well studied and here we emphasize its importance because the northern part of the VLB/TR is a link between the well-studied southern VLB and the sediment-well-preserved Northern Basin. During the 32nd Chinese National Antarctic Research Expedition, on the board of the RV XueLong, we collected intermediate resolution multi-channel seismic reflection data in the northern VLB/TR. These data will establish new constraints on the timing of deformation, structure and kinematics of the TR, and the history of the EAIS and WAIS.

  11. Influence of rifting episodes on seismic and volcanic activity in the southern Red Sea region (United States)

    Viltres, Renier; Ruch, Joël; Doubre, Cécile; Reilinger, Rob; Ogubazghi, Ghebrebrhan; Jónsson, Sigurjón


    Rifting episodes cause large changes to the state of stress in the surrounding crust, both instantaneously (elastic stress transfer) and in the years following the episodes (viscoelastic stress transfer), and can significantly influence occurrence of future earthquakes and volcanic eruptions. Here we report on a new project that aims at studying the stress impact of rifting episodes and focuses on the southern Red Sea, Afar and Gulf of Aden region, which has seen a significant increase in rifting activity during the past decade. The Afar rift system experienced a major rifting episode (Dabbahu segment) in 2005-2010 and the southern Red Sea also appears to have had one, indicated by three volcanic eruptions in 2007, 2011-12, and 2013 (the first in the area in over a century), accompanied by several seismic swarms. In addition, Gulf of Aden had an exceptionally strong seismic swarm activity starting in late 2010 that was associated with intrusion of magma in a separate rifting episode. To explore the influence of these recent rifting episodes in the region we will use new geodetic observations, seismicity analysis and modeling. We have analyzed new GPS data collected in Eritrea, in Afar, and in southern Saudi Arabia. Comparisons with older surveys has not only resulted in better GPS velocities for the observed sites, but also revealed changes to velocities at some sites influenced by the rifting activity. We use the results along with seismic data to better constrain the timing, magnitude and duration of the rifting activity in the region. We will then apply elastic and visco-elastic stress transfer modeling to assess the associated stress changes, in particular at locations where volcanic eruptions or intrusions have occurred or where significant seismicity has been detected. The project should provide new information about the impact rifting events and episodes can have on regional volcanic and earthquake activity and how rifting episodes may influence one another.


    Directory of Open Access Journals (Sweden)

    S. V. Rasskazov


    .5 mkg/l concentrations of uranium (components from the Medlyanka river and Kultuchnaya river, respectively. The U abundances reflect relatively reduced conditions in group 1 and more oxidized in group 2. The higher (234U/238U in the surface water with intermediate concentrations of uranium (0.009–0.500 mkg/l may indicate the admixture of a groundwater component (Fig. 3. Figure 4 shows relations between surface water and groundwater components in the Kultuk polygon in terms of U content. In Figure 5, the field of data points of U and Sr isotope ratios in groundwater from the Kultuk polygon is contoured by curved lines that meet with each other at compositions corresponding to the end members E (87Sr/86Sr=0.7205, 234U/238U=1.0 and NE (87Sr/86Sr=0.70534, 234U/238U=3.3. Uranium ratios of the former and the latter components show equilibrium and the most nonequilibrium compositions, respectively. The field is characteristic of water samples from the rocks of the southern suture zone of the Siberian craton. Shift of the data points of water from stations 26 and 1310 to the right of this data field (i.e. with relative increasing 87Sr/86Sr is due to lateral transition from the rocks of the suture zone to the Archean rocks of the Sharyzhalgai block (Fig. 6. The isotope systematics of uranium and strontium in the strongly nonequilibrium uranium segment is supplemented by the systematics of uranium in (234U/238U vs. 1/U diagram (Fig. 7. The U composition in water from station 40 reflects a combination of processes that take place at station 27 (i.e. in the central part of the deformation system and at station 38 (i.e. at its periphery. Approximately equal contents of uranium at the three above‐mentioned stations may reflect similar oxidization levels of the medium. In the Southern Baikal basin, the Irkutsk Seismic Station recorded an earthquake of class 11.2 on 08 January 2013 [Map…, 2013]. The earthquake epicentre was located near Listvyanka settlement (51.85° N, 105°16

  13. Fylla Bank: structure and evolution of a normal-to-shear rifted margin in the northern Labrador Sea

    DEFF Research Database (Denmark)

    Døssing, Arne


    . Combined with an interpreted interplay between normal stresses in the Labrador Sea and oblique‐shear stresses in the Davis Strait, this resulted in a very complex structural‐tectonic evolution and the formation of several distinct structural styles. The seismic interpretations are supported by maps......Cenozoic seafloor spreading between Greenland and North America is generally considered a major right‐stepping ridge‐transform‐ridge system between NW–SE trending spreading ridge segments in the Labrador Sea and Baffin Bay. The ridges were linked by N–S/NNE–SSW trending transform motions...... in the Davis Strait, in particular expressed by the ∼1000‐km‐long Ungava Fault Zone. Fylla Bank, part of the southern West Greenland continental margin, is located in the northernmost Labrador Sea at the transition between the normal and shear rifting regimes of the Labrador Sea and Davis Strait. As such...

  14. Continental basement inheritance and multiscale rifted ocean margin architectures: case studies from the N Atlantic-Greenland region (Invited) (United States)

    Holdsworth, R. E.; Wilson, R.; McCaffrey, K. J.; Imber, J.; Jones, R.


    It is widely believed that pre-existing basement structures significantly influence the development of rifts in both intracontinental and margin settings, but this hypothesis remains to be tested in many areas.We first investigate how fault reactivation controls the distribution and growth of individual faults in the post-breakup cover sequence of the Norwegian margin. We then use a combined onshore and offshore approach to address the wider problem of how intraplate basement structures control subsequent regional-scale fault patterns and kinematics. The influence of pre-existing, rift-related normal faults upon the early stages of fault growth in the post-breakup cover sequence is well illustrated offshore in the Vøring basin. Here Maastrichtian to Palaeocene age rift-related normal faults on the Nyk High were blanketed by Plio-Pleistocene sediments, which are cut locally by small (maximum throw directly above points of maximum throw or offsets along underlying rift-related faults, which therefore clearly control the location and architecture of later structures. Both upward and downward fault propagation from basement to cover and vice versa are recognised during this reactivation. Elastic interactions between en-echelon fault segments situated above basement heterogeneities are likely to promote the rapid growth of reactivated fault systems. Basement structures are often oriented significantly oblique to later rifting directions and can lead to transtensional deformation patterns. The Davis Strait of West Greenland contains the Ungava transform fault zone, which separates the failed spreading centres of the Labrador Sea and Baffin Bay. Detailed onshore studies of fault patterns and kinematics, at regional to outcrop scales, reveal the key roles played by two main transtensional fault systems. An older system of N-S trending en echelon normal faults bound a series of deep sedimentary basins of mid- upper-Cretaceous age that are linked by ESE-trending normal

  15. Fault-magma interactions during early continental rifting: Seismicity of the Magadi-Natron-Manyara basins, Africa (United States)

    Weinstein, A.; Oliva, S. J.; Ebinger, C. J.; Roecker, S.; Tiberi, C.; Aman, M.; Lambert, C.; Witkin, E.; Albaric, J.; Gautier, S.; Peyrat, S.; Muirhead, J. D.; Muzuka, A. N. N.; Mulibo, G.; Kianji, G.; Ferdinand-Wambura, R.; Msabi, M.; Rodzianko, A.; Hadfield, R.; Illsley-Kemp, F.; Fischer, T. P.


    Although magmatism may occur during the earliest stages of continental rifting, its role in strain accommodation remains weakly constrained by largely 2-D studies. We analyze seismicity data from a 13 month, 39-station broadband seismic array to determine the role of magma intrusion on state-of-stress and strain localization, and their along-strike variations. Precise earthquake locations using cluster analyses and a new 3-D velocity model reveal lower crustal earthquakes beneath the central basins and along projections of steep border faults that degas CO2. Seismicity forms several disks interpreted as sills at 6-10 km below a monogenetic cone field. The sills overlie a lower crustal magma chamber that may feed eruptions at Oldoinyo Lengai volcano. After determining a new ML scaling relation, we determine a b-value of 0.87 ± 0.03. Focal mechanisms for 65 earthquakes, and 13 from a catalogue prior to our array reveal an along-axis stress rotation of ˜60° in the magmatically active zone. New and prior mechanisms show predominantly normal slip along steep nodal planes, with extension directions ˜N90°E north and south of an active volcanic chain consistent with geodetic data, and ˜N150°E in the volcanic chain. The stress rotation facilitates strain transfer from border fault systems, the locus of early-stage deformation, to the zone of magma intrusion in the central rift. Our seismic, structural, and geochemistry results indicate that frequent lower crustal earthquakes are promoted by elevated pore pressures from volatile degassing along border faults, and hydraulic fracture around the margins of magma bodies. Results indicate that earthquakes are largely driven by stress state around inflating magma bodies.

  16. Emplacement of ultramafic-carbonatite intrusions along reactivated North American mid-continent rift structures (United States)

    Shavers, Ethan J.; Ghulam, Abduwasit; Encarnacion, John; Hartling, Sean


    Understanding the various emplacement pathways of ultramafic‑carbonatite intrusive complexes and mapping of their global distribution are in an early stage. Discerning the pattern of their emplacement can reveal information about earth's dynamics and guide exploration for associated economic deposits. Here we apply multiple spatial analysis methods and synthetic aperture radar (SAR) data to assess the correlation between outcrops of ultramafic‑carbonatite intrusives and regional craton-scale fractures and assign targets for further exploration. Kernel density cluster, two-point azimuth, and the Fry method two-dimension spatial analyses are applied to 58 known outcrops of intrusives in the Avon Volcanic District (AVD), southeast Missouri USA. The results of the spatial analysis show linear trends among the outcrops with three primary orientations: northwest, northeast, and east-west and a strong correlation with regional fault zones. SAR data processing and analysis guided by the spatial results reveals rhombic lineament patterns with sides that parallel the northwest-northeast emplacement patterns of the AVD. These rhombic structures are related to possible extensional stepover duplexes, likely formed during Precambrian North American plate rifting along transfer faults. Reactivation of the Precambrian structures during high angle dip slip and wrench faulting that was penecontemporaneous with emplacement of the AVD in the Devonian likely provided pathways for the mantle-derived intrusives. These findings can guide exploration efforts and help us understand the emplacement of a unique intracontinental intrusive complex.

  17. Rifts of deeply eroded Hawaiian basaltic shields: a structural analog for large Martian volcanoes

    International Nuclear Information System (INIS)

    Knight, M.D.; Walker, G.P.L.; Mouginis-Mark, P.J.; Rowland, S.K.


    Recently derived morphologic evidence suggests that intrusive events have not only influenced the growth of young shield volcanoes on Mars but also the distribution of volatiles surrounding these volcanoes: in addition to rift zones and flank eruptions on Arsia Mons and Pavonis Mons, melt water channels were identified to the northwest of Hecates Tholus, to the south of Hadriaca Patera, and to the SE of Olympus Mons. Melt water release could be the surface expression of tectonic deformation of the region or, potentially, intrusive events associated with dike emplacement from each of these volcanoes. In this study the structural properties of Hawaiian shield volcanoes were studied where subaerial erosion has removed a sufficient amount of the surface to enable a direct investigation of the internal structure of the volcanoes. The field investigation of dike morphology and magma flow characteristics for several volcanoes in Hawaii is reported. A comprehensive investigation was made of the Koolau dike complex that passes through the summit caldera. A study of two other dissected Hawaiian volcanoes, namely Waianae and East Molokai, was commenced. The goal is not only to understand the emplacement process and magma flow within these terrestrial dikes, but also to explore the possible role that intrusive events may have played in volcano growth and the distribution of melt water release on Mars

  18. REE partitioning between apatite and melt in a peralkaline volcanic suite, Kenya Rift Valley (United States)

    Macdonald, R.; Baginski, B.; Belkin, H.E.; Dzierzanowski, P.; Jezak, L.


    Electron microprobe analyses are presented for fluorapatite phenocrysts from a benmoreite-peralkaline rhyolite volcanic suite from the Kenya Rift Valley. The rocks have previously been well characterized petrographically and their crystallization conditions are reasonably well known. The REE contents in the M site increase towards the rhyolites, with a maximum britholite component of ~35 mol.%. Chondrite-normalized REE patterns are rather flat between La and Sm and then decrease towards Yb. Sodium and Fe occupy up to 1% and 4%, respectively, of the M site. The major coupled substitution is REE3+ + Si4+ ??? Ca2+ + P5+. The substitution REE3+ + Na+ ??? 2Ca2+ has been of minor importance. The relatively large Fe contents were perhaps facilitated by the low fo2 conditions of crystallization. Zoning is ubiquitous and resulted from both fractional crystallization and magma mixing. Apatites in some rhyolites are relatively Y-depleted, perhaps reflecting crystallization from melts which had precipitated zircon. Mineral/glass (melt) ratios for two rhyolites are unusually high, with maxima at Sm (762, 1123). ?? 2008 The Mineralogical Society.

  19. A Cenozoic diffuse alkaline magmatic province (DAMP) in the southwest Pacific without rift or plume origin (United States)

    Finn, Carol A.; Müller, R. Dietmar; Panter, Kurt S.


    Common geological, geochemical, and geophysical characteristics of continental fragments of East Gondwana and adjacent oceanic lithosphere define a long-lived, low-volume, diffuse alkaline magmatic province (DAMP) encompassing the easternmost part of the Indo-Australian Plate, West Antarctica, and the southwest portion of the Pacific Plate. A key to generating the Cenozoic magmatism is the combination of metasomatized lithosphere underlain by mantle at only slightly elevated temperatures, in contrast to large igneous provinces where mantle temperatures are presumed to be high. The SW Pacific DAMP magmatism has been conjecturally linked to rifting, strike-slip faulting, mantle plumes, or hundreds of hot spots, but all of these associations have flaws. We suggest instead that sudden detachment and sinking of subducted slabs in the late Cretaceous induced Rayleigh-Taylor instabilities along the former Gondwana margin that in turn triggered lateral and vertical flow of warm Pacific mantle. The interaction of the warm mantle with metasomatized subcontinental lithosphere that characterizes much of the SW Pacific DAMP concentrates magmatism along zones of weakness. The model may also provide a mechanism for warming south Pacific mantle and resulting Cenozoic alkaline magmatism, where the oceanic areas are characterized primarily, but not exclusively, by short-lived hot spot tracks not readily explained by conventional mantle plume theory. This proposed south Pacific DAMP is much larger and longer-lived than previously considered.

  20. Normal-Faulting in Madagascar: Another Round of Continental Rifting? (United States)

    Wysession, M. E.; Pratt, M. J.; Tsiriandrimanana, R.; Andriampenomanana Ny Ony, F. S. T.; Nyblade, A.; Durrheim, R. J.; Tilmann, F. J.; Rumpker, G.; Rambolamanana, G.; Aleqabi, G. I.; Shore, P.


    Analyses of seismicity and seismic structure within Madagascar suggest the current occurrence of crustal extension, which may be related to continental rifting associated with a diffuse boundary between the Somalia and Lwandle tectonic plates. Madagascar has participated in two major rifting events as part of the break-up of Gondwana: the break-away of Greater India (Madagascar, India, the Seychelles) away from mainland Africa during the Jurassic and the break-away of India from Madagascar during the Cretaceous. Seismic activity and the structures obtained from it, using data from the 2-year (2011-2013) MACOMO project, suggest that this break-up may not be finished, and that continental rifts may be developing again. There are fairly high levels of intraplate seismicity within Madagascar: over 800 events located during the 22 months of the deployment. For comparison, a 2-year deployment of seismometers within the upper Midwest of the U.S. yielded just 12 intraplate earthquakes. While the Madagascar seismicity occurs across the island, it is strongly concentrated in the central region, where Cenozoic volcanism has occurred through the Holocene, and earthquakes align along N-S-trending lineations associated with N-S-trending pull-apart graben structures. The thickness of the crust is still >40 km in this region, but it is underlain by a large low-velocity structure within the lithosphere and asthenosphere that is observed in our studies of surface-wave, body-wave, and Pn-phase tomography. Normal faulting is not observed everywhere on the island, however; seismicity in the north is largely strike-slip, and seismicity in the south appears to be largely reverse faulting. Several studies have suggested that the diffuse boundary between the Somalia and Lwandle plates runs roughly E-W across Madagascar. Extensional faulting seems to predominate only within central Madagascar, likely associated with the current volcanic activity, which also appears to be associated with the

  1. Restriction of Rift Valley Fever Virus Virulence in Mosquito Cells

    Directory of Open Access Journals (Sweden)

    Sonja R. Gerrard


    Full Text Available Arboviruses are maintained in a natural cycle that requires blood-sucking arthropod and vertebrate hosts. Arboviruses are believed to persistently infect their arthropod host without overt pathology and cause acute infection with viremia in their vertebrate host. We have focused on elucidating how a specific arbovirus, Rift Valley fever (RVF virus, causes cytopathic effect in cells derived from vertebrates and non-cytopathic infection in cells derived from arthropods. We demonstrate that the vertebrate virulence factor, NSs, is functional in arthropod cells but is expressed at significantly lower levels in infected arthropod versus infected vertebrate cells.

  2. A Surface Wave's View of the Mid-Continent Rift (United States)

    Foster, A. E.; Darbyshire, F. A.; Schaeffer, A. J.


    The presence of the Mid-Continent Rift (MCR), a 1.1Ga failed rift in central North America, raises many questions. We address the following: what lasting effects has it had on the continental lithosphere? Though many studies have looked at the area with a variety of data types, the combination of USArray Transportable Array stations to the south, permanent and temporary Canadian stations to the north, and SPREE stations in strategic locations crossing the rift provide a new opportunity for a regional surface-wave study. We select 80 stations with roughly 200 km spacing, resulting in dense path coverage of a broad area centered on the MCR. We use teleseismic data for all earthquakes from January 2005-August 2016 with a magnitude greater than 6.0, amounting to over 1200 events, and we make Rayleigh wave two-station dispersion measurements for all station pairs with suitable event-station geometry. We invert these measurements for anisotropic phase-velocity maps at periods of 20-200 s, yielding information not only on the wave speed but also the current fabric of the lithosphere, a complicated record of strain from formation, through modification from orogeny, attempted rifting, and hotspot interaction, to present day plate motion. We observe a clear signature of the MCR at short (20-25 s) periods, with the slowest phase-velocity anomaly in the region aligning with the strongest gravity anomaly. At increasing periods, and thus greater depths, this slowest anomaly shifts to beneath the center of Lake Superior (30-40 s). Eventually, it appears to merge with a slow anomaly to the north associated with the Nipigon Embayment, and contrasts sharply with an adjacent fast anomaly in the western Superior Province. In our preliminary anisotropy results, we observe weak anisotropy at the latitude of the MCR and to the south, whereas to the north of the MCR we find strong anisotropy. This is similar to the spatial variations in magnitude of delay times from shear-wave splitting

  3. Opening of the Central Atlantic Ocean: Implications for Geometric Rifting and Asymmetric Initial Seafloor Spreading after Continental Breakup (United States)

    Klingelhoefer, F.; Biari, Y.; Sahabi, M.; Funck, T.; Benabdellouahed, M.; Schnabel, M.; Reichert, C. J.; Gutscher, M. A.; Bronner, A.; Austin, J. A., Jr.


    The structure of conjugate passive margins provides information about rifting styles, the initial phases of the opening of an ocean and the formation of its associated sedimentary basins. The study of the deep structure of conjugate passive continental margins combined with precise plate kinematic reconstructions can provide constraints on the mechanisms of rifting and formation of initial oceanic crust. In this study the Central Atlantic conjugate margins are compared, based on compilation of wide-angle seismic profiles from the NW-Africa Nova Scotian and US passive margins. Plate cinematic reconstructions were used to place the profiles in the position at opening and at the M25 magnetic anomaly. The patterns of volcanism, crustal thickness, geometry, and seismic velocities in the transition zone. suggest symmetric rifting followed by asymmetric oceanic crustal accretion. Conjugate profiles in the southern Central Atlantic image differences in the continental crustal thickness. While profiles on the eastern US margin are characterized by thick layers of magmatic underplating, no such underplate was imaged along the NW-African continental margin. It has been proposed that these volcanic products form part of the CAMP (Central Atlantic Magmatic Province). In the north, two wide-angle seismic profiles acquired in exactly conjugate positions show that the crustal geometry of the unthinned continental crust and the necking zone are nearly symmetric. A region including seismic velocities too high to be explained by either continental or oceanic crust is imaged along the Nova Scotia margin off Eastern Canada, corresponding on the African side to an oceanic crust with slightly elevated velocities. These might result from asymmetric spreading creating seafloor by faulting the existing lithosphere on the Canadian side and the emplacement of magmatic oceanic crust including pockets of serpentinite on the Moroccan margin. A slightly elevated crustal thickness along the

  4. An eco-health approach to Rift Valley Fever control among ...

    International Development Research Centre (IDRC) Digital Library (Canada)

    Rift Valley Fever is a severe mosquito-transmitted disease that infects humans, livestock, and wildlife. In addition, humans may contract the disease through contact with infected animals. Rift Valley Fever has spread across Africa and beyond, and outbreaks are increasing in frequency and scale, seemingly connected to ...

  5. Mouse model for the Rift Valley fever virus MP12 strain infection (United States)

    Rift Valley fever virus (RVFV), a Category A pathogen and select agent, is the causative agent of Rift Valley fever. To date, no fully licensed vaccine is available in the U.S. for human or animal use and effective antiviral drugs have not been identified. The RVFV MP12 strain is conditionally licen...

  6. Crustal structure and rift tectonics across the Cauvery–Palar basin ...

    Indian Academy of Sciences (India)

    The Cauvery–Palar basin is a major peri-cratonic rift basin located along the Eastern Continental Margin of India (ECMI) that had formed during the rift-drift events associated with the breakup of eastern Gondwanaland (mainly India–Sri Lanka–East Antarctica). In the present study, we carry out an integrated analysis of the ...

  7. An eco-health approach to Rift Valley Fever control among ...

    International Development Research Centre (IDRC) Digital Library (Canada)


    Aug 17, 2016 ... Rift Valley Fever is a severe mosquito-transmitted disease that infects humans, livestock, and wildlife. In addition, humans may contract the disease through contact with infected animals. Rift Valley Fever has spread across Africa and beyond, and outbreaks are increasing in frequency and scale, seemingly ...

  8. The life cycle of continental rifting as a focus for U.S.-African scientific collaboration (United States)

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


    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.

  9. Seismic imaging of the geodynamic activity at the western Eger rift in central Europe

    Czech Academy of Sciences Publication Activity Database

    Mullick, N.; Buske, S.; Hrubcová, Pavla; Růžek, Bohuslav; Shapiro, S.; Wigger, P.; Fischer, T.

    647-648, 19 April (2015), s. 105-111 ISSN 0040-1951 R&D Projects: GA ČR GA13-08971S Institutional support: RVO:67985530 Keywords : European Cenozoic Rift System * Eger Rift * West Bohemian Massif Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.650, year: 2015

  10. Electrical Conductance Map for the Kachchh Rift Basin: Constraint on Tectonic Evolution and Seismotectonic Implications (United States)

    Subba Rao, P. B. V.; Arora, B. R.; Singh, A. K.


    Geomagnetic field variations recorded by an array of magnetometers spread across the Kachchh Rift basin are reduced to a set of induction arrows as a diagnostic of lateral electrical conductivity variations. A non-uniform thin-sheet electrical conductance model is developed to account for the salient induction patterns. It indicates that the imaged conductivity anomalies can be related to the sediment-filled structural lows in between the fault bounded uplifts. It is suggested that sagging structural lows preserved the marine sediments deposited during the Mesozoic sea transgression and later developed into first order embayment basins for the deposition of sediments in association with Late Eocene transgression. Depth integrated electrical conductance helped in mapping two depo-centres: along the ENE-WSW trending Banni half-Graben bounded by the Kachchh Main fault on the south and, second, along the Vinjan depression formed in response to the subsidence between the Vigodi fault and westward extension of the Katrol Hill fault together with the westward bending of the Median High. Presence of metamorphosed graphite schist clasts in shale dominated Mesozoic sequence and/or thin films of carbon resulting from the thermal influence of Deccan activity on Carbonate-rich formations can account for the high electrical conductivity anomalies seen in the depo-centres of thick Mesozoic and Tertiary sediments. Additionally two high conductivity zones are imaged encompassing a block defined by the 2001 Bhuj earthquake and its aftershocks. In agreement with gravity, magnetic and seismic velocity signatures, aqueous fluids released by recrystallizing magmatic bodies intruded in association with Deccan trap activity account for mapped high conductivity zones. High fluid pressure in such a fractured domain, surrounding the intruded magmatic plugs, perturb the regional stress concentrations to produce frequent and low magnitude aftershocks in the shallow section of the epicentral

  11. Application of synchrotron X-ray fluorescent analysis to studies of the records of paleoclimates of Eurasia stored in the sediments of Lake Baikal and Lake Teletskoye

    International Nuclear Information System (INIS)

    Goldberg, E.L.; Grachev, M.A.; Phedorin, M.A.; Kalugin, I.A.; Khlystov, O.M.; Mezentsev, S.N.; Azarova, I.N.; Vorobyeva, S.S.; Zheleznyakova, T.O.; Kulipanov, G.N.; Kondratyev, V.I.; Miginsky, E.G.; Tsukanov, V.M.; Zolotarev, K.V.; Trunova, V.A.; Kolmogorov, Yu.P.; Bobrov, V.A.


    Multi-element SRXRF of sediments of Lake Baikal (East Siberia) with samples taken at 10 cm intervals from a core spanning the last 250 ky revealed nine peaks of 'warm' signals like Sr/Ba(Rb,Cs) and U/Th corresponding to Oceanic Isotope Stages 1,3,5a,5c,5e,7 and 9, and six peaks of 'cold correlator' corresponding to OIS 2,4,5d,6 and 8. A slab (1500-2200 mm below the sediment surface) taken from another core was studied by scanning SRXRF. This interval corresponds to the Siberian Karga interstadial (OIS3, 24-58 ky BP). It hosted two peaks of diatom algae frustulles, indicators of warmer climates. The scanning was performed at a temporal resolution of ca. 50 yr. Ratios of concentrations like Sr/Rb(Ba,Cs,Ti,Fe) (Nucl. Instr. and Meth. A 448(1-2) (2000) 384; Nucl. Instr. and Meth. A 448 (1-2) (2000) 400) appeared to be more sensitive proxies of warm climates, compared to total diatoms, and revealed at least six pronounced cycles of abrupt warming and cooling episodes, each lasting a few millennia. These fluctuations may reflect a response of the catchment basin of the Lake Baikal to abrupt global climate cycles recorded in the ice of Greenland and in the sediments of North Atlantic (Nature 364 (1993) 142; Science 278 (1997) 1257; Science 288 (2000) 128). SRXRF applied to the sediments of Lake Teletskoye (West Siberia, Altai Mountains) of the last 600 yr provided a temporal resolution of 1.2-1.8 yr. The profiles of a few elements like K, Ca, Ti, Fe, V revealed oscillations with a periodicity of 9.4 yr over the time interval between years 1400 and 1600. Oscillations faded out after the cooling of 1600-1700 (The Maunder interval). Periodic oscillations between years 1400 and 1600 seem to correspond to periodic changes in the height of oceanic tides (9 yr (PNAS 94 (1997) 8321; PNAS 97 (2000) 3814)) rather than to the solar activity cycles (periodicity of 11 yr)

  12. Oblique rift opening revealed by reoccurring magma injection in central Iceland

    KAUST Repository

    Ruch, Joel


    Extension deficit builds up over centuries at divergent plate boundaries and is recurrently removed during rifting events, accompanied by magma intrusions and transient metre-scale deformation. However, information on transient near-field deformation has rarely been captured, hindering progress in understanding rifting mechanisms and evolution. Here we show new evidence of oblique rift opening during a rifting event influenced by pre-existing fractures and two centuries of extension deficit accumulation. This event originated from the Bárðarbunga caldera and led to the largest basaltic eruption in Iceland in >200 years. The results show that the opening was initially accompanied by left-lateral shear that ceased with increasing opening. Our results imply that pre-existing fractures play a key role in controlling oblique rift opening at divergent plate boundaries.

  13. Rift Valley fever virus seroprevalence in human rural populations of Gabon.

    Directory of Open Access Journals (Sweden)

    Xavier Pourrut

    Full Text Available BACKGROUND: Rift Valley fever (RVF is a mosquito-borne viral zoonosis caused by a phlebovirus and transmitted by Aedes mosquitoes. Humans can also be infected through direct contact with blood (aerosols or tissues (placenta, stillborn of infected animals. Although severe clinical cases can be observed, infection with RVF virus (RVFV in humans is, in most cases, asymptomatic or causes a febrile illness without serious symptoms. In small ruminants RVFV mainly causes abortion and neonatal death. The distribution of RVFV has been well documented in many African countries, particularly in the north (Egypt, Sudan, east (Kenya, Tanzania, Somalia, west (Senegal, Mauritania and south (South Africa, but also in the Indian Ocean (Madagascar, Mayotte and the Arabian Peninsula. In contrast, the prevalence of RVFV has rarely been investigated in central African countries. METHODOLOGY/PRINCIPAL FINDINGS: We therefore conducted a large serological survey of rural populations in Gabon, involving 4,323 individuals from 212 randomly selected villages (10.3% of all Gabonese villages. RVFV-specific IgG was found in a total of 145 individuals (3.3% suggesting the wide circulation of Rift Valley fever virus in Gabon. The seroprevalence was significantly higher in the lakes region than in forest and savannas zones, with respective rates of 8.3%, 2.9% and 2.2%. In the lakes region, RVFV-specific IgG was significantly more prevalent in males than in females (respectively 12.8% and 3.8% and the seroprevalence increased gradually with age in males but not in females. CONCLUSIONS/SIGNIFICANCE: Although RVFV was suggested to circulate at a relatively high level in Gabon, no outbreaks or even isolated cases have been documented in the country. The higher prevalence in the lakes region is likely to be driven by specific ecologic conditions favorable to certain mosquito vector species. Males may be more at risk of infection than females because they spend more time farming and

  14. The origin of thermal waters in the northeastern part of the Eger Rift, Czech Republic

    International Nuclear Information System (INIS)

    Dupalová, Tereza; Sracek, Ondra; Vencelides, Zbyněk; Žák, Karel


    An investigation of the thermal waters in the Ústí nad Labem area in the northeastern part of the Eger Rift has been carried out, with the principal objective of determining their origin. Waters from geothermal reservoirs in the aquifers of the Bohemian Cretaceous Basin (BCB) from depths of 240 to 616 m are exploited here. For comparison, thermal waters of the adjacent Teplice Spa area were also incorporated into the study. Results based on water chemistry and isotopes indicate mixing of groundwater from aquifers of the BCB with groundwater derived from underlying crystalline rocks of the Erzgebirge Mts. Unlike thermal waters in Děčín, which are of Ca–HCO 3 type, there are two types of thermal waters in Ústí nad Labem, Na–HCO 3 –Cl–SO 4 type with high TDS values and Na–Ca–HCO 3 –SO 4 type with low TDS values. Carbon isotope data, speciation calculations, and inverse geochemical modeling suggest a significant input of endogenous CO 2 at Ústí nad Labem in the case of high TDS groundwaters. Besides CO 2 input, both silicate dissolution and cation exchange coupled with dissolution of carbonates may explain the origin of high TDS thermal waters equally well. This is a consequence of similar δ 13 C and 14 C values in endogenous CO 2 and carbonates (both sources have 14 C of 0 pmc, endogenous CO 2 δ 13 C around −3‰, carbonates in the range from −5‰ to +3‰ V-PDB). The source of Cl − seems to be relict brine formed in Tertiary lakes, which infiltrated into the deep rift zone and is being flushed out. The difference between high and low TDS groundwaters in Ústí nad Labem is caused by location of the high mineralization groundwater wells in CO 2 emanation centers linked to channel-like conduits. This results in high dissolution rates of minerals and in different δ 13 C(DIC) and 14 C(DIC) fingerprints. A combined δ 34 S and δ 18 O study of dissolved SO 4 indicates multiple SO 4 sources, involving SO 4 from relict brines and oxidation

  15. The wide-angle seismic image of a compl