Sample records for western eger rift

  1. Bottom to top lithosphere structure and evolution of western Eger Rift (Central Europe)

    Czech Academy of Sciences Publication Activity Database

    Babuška, Vladislav; Fiala, Jiří; Plomerová, Jaroslava


    Roč. 99, č. 4 (2010), s. 891-907 ISSN 1437-3254 R&D Projects: GA ČR GA205/07/1088; GA AV ČR IAA300120709 Institutional research plan: CEZ:AV0Z30120515; CEZ:AV0Z30130516 Keywords : western Bohemian Massif * Eger (Ohře) Rift * lithosphere structure and development * mantle seismic anisotropy Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.980, year: 2010

  2. Tectonic evolution of the Western Eger rift: a tale of two faults (United States)

    Tomasek, Jan; Kley, Jonas; Fischer, Tomáš; Štěpančíková, Petra


    The Eger Rift and Cheb basin in northwestern Bohemia are part of the European Cenozoic Rift System. They are associated with earthquake swarms, voluminous CO2 outgassing and Quaternary mantle-derived volcanism. The Eger Graben, of which the Cheb basin is traditionally considered a subbasin, contains a Cenozoic volcano-sedimentary record no thicker than 500 m. The structure of the extensional system is dominated by two large faults: (1) the ENE-striking Krušné Hory Fault (KHF), which delimits the northwestern shoulder of the Eger rift and has accommodated tilting and uplift of the Erzgebirge, creating a present day elevation difference of 700 m; (2) the NNW-striking Mariánské Lázně Fault (MLF), which is the master fault of the Cheb basin. First-order structural relationships indicate that the MLF has cross-cut the Eger rift at right angle and offset it with dominantly normal sense of motion. These relationships suggest that activity on the MLF was accentuated late in the history of the rift, around early Pliocene time, reflecting a fundamental change of the governing stress field. We aim to constrain, in conjunction with a Czech companion project focussing on tectonic geomorphology and seismology, the tectonic evolution of the two basins, and in particular the kinematics and timing of the Krušné Hory (Erzgebirge) and Mariánské Lázně bounding faults over Late Cenozoic time. This will be done by modelling the subsidence of the basins from stratigraphic and structural data. Rift shoulder uplift, exhumation and fault offsets will be constrained by low-T thermochronology, especially (U-Th)/He on apatite (AHe). 2D cross-sections and restorable structural 3D models will delimit the range of possible fault geometries and constrain the magnitude of fault displacements, their gradients and the deep architecture of the large faults. The Cheb basin forms an approximate semi-ellipse in map view, suggesting it is a half-graben bounded by a listric, WSW-dipping MLF

  3. High-Ti basaltic rocks in the uplifted shoulder of the Ohre (Eger) Rift, western Bohemia/Saxony

    Czech Academy of Sciences Publication Activity Database

    Novák, Jiří Karel; Ulrych, Jaromír; Ackerman, Lukáš; Jelínek, E.; Chadima, Martin; Mizera, Jiří; Řanda, Zdeněk


    Roč. 34, 4/6 (2008), s. 1325145-1325145 ISSN 0161-6951. [International Geological Congress /33./. 06.08.2008-14.08.2008, Oslo] R&D Projects: GA AV ČR IAA300130706 Institutional research plan: CEZ:AV0Z30130516; CEZ:AV0Z10480505 Keywords : high -Ti basalts * Krušné hory/Erzgebirge * Eger Rift * magnetic properties Subject RIV: DB - Geology ; Mineralogy

  4. Isotopically light carbon dioxide in nitrogen rich gases: the gas distribution pattern in the French Massif Central, the Eifel and the western Eger Rift

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    F. H. Weinlich


    Full Text Available Based on characteristics of the distribution pattern of the western Eger Rift spring gases, a distribution pattern is presented for the gases of the French Massif Central. The central parts of these areas with ascending magmatic CO2 are characterised by high gas fluxes, high CO2 contents of up to 99.99 vol% and isotopially heavy CO2. In the peripheries, the decrease of d13C values of CO2 and CO2 contents in the gas phase is compensated by a rise in N2 contents. It can be demonstrated that gas fractionation in contrary to mixtures with isotopically light biogenic or crustal CO2 controls the distribution pattern of gas composition and isotopic composition of CO2 in these spring gases. Dissolution of CO2 results in formation of HCO3 ? causing isotope fractionation of CO2 and an enrichment of N2 in the gas phase. With multiple equilibrations, values of about ?17 ? or lower are obtained. The scale of gas alteration depends on the gas flux and the gas-water ratios respectively and can result in N2-rich gases. Essential for the interpretation are gas flux measurements with mass balances derived for most of the springs. Without such mass balances it is not possible to discriminate between mixture and fractionation. The processes of isotopic and chemical solubility fractionations evidently control the gas distribution pattern in other regions as well.

  5. Drilling into an active mofette: pilot-hole study of the impact of CO2-rich mantle-derived fluids on the geo–bio interaction in the western Eger Rift (Czech Republic

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    R. Bussert


    Full Text Available Microbial life in the continental deep biosphere is closely linked to geodynamic processes, yet this interaction is poorly studied. The Cheb Basin in the western Eger Rift (Czech Republic is an ideal place for such a study because it displays almost permanent seismic activity along active faults with earthquake swarms up to ML 4.5 and intense degassing of mantle-derived CO2 in conduits that show up at the surface in form of mofettes. We hypothesize that microbial life is significantly accelerated in active fault zones and in CO2 conduits, due to increased fluid and substrate flow. To test this hypothesis, pilot hole HJB-1 was drilled in spring 2016 at the major mofette of the Hartoušov mofette field, after extensive pre-drill surveys to optimize the well location. After drilling through a thin caprock-like structure at 78.5 m, a CO2 blowout occurred indicating a CO2 reservoir in the underlying sandy clay. A pumping test revealed the presence of mineral water dominated by Na+, Ca2+, HCO3−, SO42− (Na-Ca-HCO3-SO4 type having a temperature of 18.6 °C and a conductivity of 6760 µS cm−1. The high content of sulfate (1470 mg L−1 is typical of Carlsbad Spa mineral waters. The hole penetrated about 90 m of Cenozoic sediments and reached a final depth of 108.50 m in Palaeozoic schists. Core recovery was about 85 %. The cored sediments are mudstones with minor carbonates, sandstones and lignite coals that were deposited in a lacustrine environment. Deformation structures and alteration features are abundant in the core. Ongoing studies will show if they result from the flow of CO2-rich fluids or not.

  6. Drilling into an active mofette: pilot-hole study of the impact of CO2-rich mantle-derived fluids on the geo-bio interaction in the western Eger Rift (Czech Republic) (United States)

    Bussert, Robert; Kämpf, Horst; Flechsig, Christina; Hesse, Katja; Nickschick, Tobias; Liu, Qi; Umlauft, Josefine; Vylita, Tomáš; Wagner, Dirk; Wonik, Thomas; Estrella Flores, Hortencia; Alawi, Mashal


    Microbial life in the continental deep biosphere is closely linked to geodynamic processes, yet this interaction is poorly studied. The Cheb Basin in the western Eger Rift (Czech Republic) is an ideal place for such a study because it displays almost permanent seismic activity along active faults with earthquake swarms up to ML 4.5 and intense degassing of mantle-derived CO2 in conduits that show up at the surface in form of mofettes. We hypothesize that microbial life is significantly accelerated in active fault zones and in CO2 conduits, due to increased fluid and substrate flow. To test this hypothesis, pilot hole HJB-1 was drilled in spring 2016 at the major mofette of the Hartoušov mofette field, after extensive pre-drill surveys to optimize the well location. After drilling through a thin caprock-like structure at 78.5 m, a CO2 blowout occurred indicating a CO2 reservoir in the underlying sandy clay. A pumping test revealed the presence of mineral water dominated by Na+, Ca2+, HCO3-, SO42- (Na-Ca-HCO3-SO4 type) having a temperature of 18.6 °C and a conductivity of 6760 µS cm-1. The high content of sulfate (1470 mg L-1) is typical of Carlsbad Spa mineral waters. The hole penetrated about 90 m of Cenozoic sediments and reached a final depth of 108.50 m in Palaeozoic schists. Core recovery was about 85 %. The cored sediments are mudstones with minor carbonates, sandstones and lignite coals that were deposited in a lacustrine environment. Deformation structures and alteration features are abundant in the core. Ongoing studies will show if they result from the flow of CO2-rich fluids or not.

  7. Depth-Recursive Tomography Along the Eger Rift Using the S01 Profile Refraction Data: Tested at the KTB Super Drilling Hole, Structural Interpretation Supported by Magnetic, Gravity and Petrophysical Data (United States)

    Novotný, Miroslav; Skácelová, Zuzana; Mrlina, Jan; Mlčoch, Bedřich; Růžek, Bohuslav


    The refraction data from the SUDETES 2003 experiment were used for high-resolution tomography along the profile S01. The S01 profile crosses the zone Erbendorf-Vohenstrauss (ZEV) near the KTB site, then follows the SW-NE oriented Eger Rift in the middle part and continues toward the NE across the Elbe zone and the Sudetic structures as far as the Trans-European Suture Zone. To get the best resolution in the velocity image only the first arrivals of Pg waves with minimum picking errors were used. The previous depth-recursive tomographic method, based on Claerbout’s imaging principle, has been adapted to perform the linearized inversions in iterative mode. This innovative DRTG method (Depth-Recursive Tomography on Grid) uses a regular system of refraction rays covering uniformly the mapped domain. The DRTG iterations yielded a fine-grid velocity model with a required level of RMS travel-time fit and the model roughness. The travel-time residuals, assessed at single depth levels, were used to derive the statistical lateral resolution of “lens-shaped” velocity anomalies. Thus, for the 95% confidence level and 5% anomalies, one can resolve their lateral sizes from 15 to 40 km at the depths from 0 to 20 km. The DRTG tomography succeeded in resolving a significant low-velocity zone (LVZ) bound to the Franconian lineament nearby the KTB site. It is shown that the next optimization of the model best updated during the DRTG iterations tends to a minimum-feature model with sweeping out any LVZs. The velocities derived by the depth-recursive tomography relate to the horizontal directions of wave propagation rather than to the vertical. This was proved at the KTB site where pronounced anisotropic behavior of a steeply tilted metamorphic rock complex of the ZEV unit has been previously determined. Involving a ~7% anisotropy observed for the “slow” axis of symmetry oriented coincidentally in the horizontal SW-NE direction of the S01 profile, the DRTG velocity model

  8. 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 ...

  9. Ambient noise tomography of the western Corinth Rift, Greece (United States)

    Giannopoulos, Dimitrios; Rivet, Diane; Sokos, Efthimios; Deschamps, Anne; Mordret, Aurelien; Lyon-Caen, Hélène; Bernard, Pascal; Paraskevopoulos, Paraskevas; Tselentis, G.-Akis


    Three years of continuous waveform data recorded at 22 stations from the Corinth Rift Laboratory and the Hellenic Unified Seismological Network are used to perform an ambient noise surface wave tomography of the western Corinth Rift. All available vertical component time-series were cross-correlated to extract empirical Rayleigh-wave Green's functions. Group velocity dispersion curves were measured for each station-pair by applying frequency-time analysis and then inverted to build 2-D group velocity maps between 1 and 6 s period. Finally, we locally inverted these velocity maps using a neighbourhood algorithm to assess the 3-D shear-velocity model of the shallow crustal structure of the western Corinth Rift. Across all studied periods the southern coast of the Corinth Gulf is generally imaged as a region of lower velocities compared to the northern coast. At periods up to 3 s, the spatial variation of the group velocities is correlated with the surface geology of the area. Lower velocities are observed in areas where mostly Plio-Quaternary syn-rift sediments are present, such as offshore regions of the rift, the Mornos delta and the largest part of the southern coast. Higher velocities are observed in pre-rift basement structures which are dominated mostly by carbonates. At periods above 3 s, where Rayleigh-waves begin to sense deeper structures below the sediments within the underlying basement, our study highlights the presence of a distinct zone of lower velocities across the southern part of the rift with an elongation in the WNW-ESE direction. The interpretation of this low velocity includes two arguments, the present-day active tectonic regime and the possible involvement of fluids circulation processes at depth within a highly fractured upper crust in the vicinity of the major faults zones. In general, the results demonstrate good agreement with the major geological and tectonic features of the area, as well as with previous local earthquake tomography

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

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    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.

  11. 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

  12. 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.

  13. Permo-Triassic anatexis, continental rifting and the disassembly of western Pangaea (United States)

    Cochrane, Ryan; Spikings, Richard; Gerdes, Axel; Ulianov, Alexey; Mora, Andres; Villagómez, Diego; Putlitz, Benita; Chiaradia, Massimo


    Crustal anatectites are frequently observed along ocean-continent active margins, although their origins are disputed with interpretations varying between rift-related and collisional. We report geochemical, isotopic and geochronological data that define an ~ 1500 km long belt of S-type meta-granites along the Andes of Colombia and Ecuador, which formed during 275-223 Ma. These are accompanied by amphibolitized tholeiitic basaltic dykes that yield concordant zircon U-Pb dates ranging between 240 and 223 Ma. A model is presented which places these rocks within a compressive Permian arc setting that existed during the amalgamation of westernmost Pangaea. Anatexis and mafic intrusion during 240-223 Ma are interpreted to have occurred during continental rifting, which culminated in the formation of oceanic crust and initiated the break-up of western Pangaea. Compression during 275-240 Ma generated small volumes of crustal melting. Rifting during 240-225 Ma was characterized by basaltic underplating, the intrusion of tholeiitic basalts and a peak in crustal melting. Tholeiitic intrusions during 225-216 Ma isotopically resemble depleted mantle and yield no evidence for contamination by continental crust, and we assign this period to the onset of continental drift. Dissected ophiolitic sequences in northern Colombia yield zircon U-Pb dates of 216 Ma. The Permo-Triassic margin of Ecuador and Colombia exhibits close temporal, faunal and geochemical similarities with various crustal blocks that form the basement to parts of Mexico, and thus these may represent the relict conjugate margin to NW Gondwana. The magmatic record of the early disassembly of Pangaea spans ~ 20 Ma (240-216 Ma), and the duration of rifting and rift-drift transition is similar to that documented in Cretaceous-Tertiary rift settings such as the West Iberia-Newfoundland conjugate margins, and the Taupo-Lau-Havre System, where rifting and continental disassembly also occurred over periods lasting ~ 20 Ma.

  14. Thermal and exhumation history of the central Rwenzori Mountains, Western Rift of the East African Rift System, Uganda (United States)

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


    The Rwenzori Mountains (Mtns) in west Uganda are the highest rift mountains on Earth and rise to more than 5,000 m. We apply low-temperature thermochronology (apatite fission-track (AFT) and apatite (U-Th-Sm)/He (AHe) analysis) for tracking the cooling history of the Rwenzori Mtns. Samples from the central and northern Rwenzoris reveal AFT ages between 195.0 (±8.4) Ma and 85.3 (±5.3) Ma, and AHe ages between 210.0 (±6.0) Ma to 24.9 (±0.5) Ma. Modelled time-temperature paths reflect a protracted cooling history with accelerated cooling in Permo-Triassic and Jurassic times, followed by a long period of constant and slow cooling, than succeeded by a renewed accelerated cooling in the Neogene. During the last 10 Ma, differentiated erosion and surface uplift affected the Rwenzori Mtns, with more pronounced uplift along the western flank. The final rock uplift of the Rwenzori Mtns that partly led to the formation of the recent topography must have been fast and in the near past (Pliocene to Pleistocene). Erosion could not compensate for the latest rock uplift, resulting in Oligocene to Miocene AHe ages.

  15. Magmatic constraints on rift development and the uplift of the Rwenzori Mountains in western Uganda (United States)

    Foley, Stephen; Link, Klemens; Tiberindwa, John; Barifaijo, Erasmus


    The northern end of the western branch of the East African rift valley in western Uganda is located at the junction between a Proterozoic belt to the south and continuous Archaean crust of the Congo-Tanzania craton to the north (1). The difficulty of rift propagation through the thick Archaean lithosphere may explain the lack of a connection with the eastern rift branch around Lake Turkana. The >5,000m-high Rwenzori Mountains form a block lodged between two rift arms at this junction (2). The location and composition of Pleistocene to Recent volcanic rocks can be used to constrain models for the uplift of the Rwenzori Mountains that explain uplift by delamination of a lithosphere block beneath the rift (3). Six small volcanic fields are located in the Toro Ankole area east and southeast of Rwenzori; they contain carbonatite either as lava flows or as components in lapilli tuffs, as well as unusual K2O-rich, SiO2-poor melt compositions akin to leucitites and potassic melilitites that increase in importance towards the south. Their major and trace element and Sr-, Nd-, Hf-, and Os-isotope compositions are consistent with a source composed not just of peridotite, but also containing mica- and clinopyroxene-rich ultramafic assemblages (4). The requirement for assemblages of this type is greater than for potassic melilitites and nephelinites further south in the rift, and this agrees with their greater abundance as xenoliths in the lavas of the Toro Ankole area. The xenoliths contain no evidence for metasomatic replacement of pre-existing peridotite minerals, but rather appear to be formed by crystallization as liquidus minerals on the walls of magma channelways within the upper mantle. Some are zoned and contain vein margins, indicating more than one episode of melt infiltration. Re-melting of such assemblages partially meets the geochemical requirements of the volcanics (4) and has been shown to produce melts with similar major element compositions in experiments (5

  16. Mapping hyper-extended rift systems offshore and onshore: insights from the Bay of Biscay- Western Pyrenees (United States)

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


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

  17. 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.

  18. 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

  19. Low-temperature evolution of the Morondava rift shoulder in western Madagascar (United States)

    Giese, Jörg; Seward, Diane; Schreurs, Guido


    Separation of Madagascar from eastern Africa resulted in the development of sedimentary basins covering the west coast of Madagascar. The largest and oldest of these basins, the Morondava basin, is bound to the east by crystalline basement of Precambrian age and stretches into the Mozambique Channel to the west. The evolution of the sedimentary sequence is mainly influenced by (I) a Permo-Triassic continental failed rift (e.g. Clark, 1998), also referred to as the Karroo rift (e.g., Montenat et al., 1996) and (II) the early Jurassic separation of Madagascar from eastern Africa (Geiger et al., 2004). Deposits related to the Karroo rift are restricted to a narrow corridor along the basement-basin contact. The rift locus shifted to the west before final separation and relative southward displacement of Madagascar commenced in early Jurassic times (Geiger et al., 2004). In the central part of the basin, the basement-basin contact features a steep escarpment with an altitude difference of greater than 1000 m from the sedimentary plains to the crystalline basement. Here, apatite fission-track analysis of a series of both basement and sediment samples across the escarpment provides the possibility to study the low temperature evolution of the exhuming Precambrian basement in the rift basin shoulder and the associated thermal evolution of the sedimentary succession. The timing of basement surface exposure is constrained by the stratigraphic ages of the overlying sediments and modelling of the thermal evolution indicates post-depositional thermal overprinting of basement and Karroo age sediments with partial annealing of fission tracks related to burial by Mesozoic sediments. The temperatures of this heating / reheating of the basin shoulder increase towards the west in the presently exposed sequences. The westernmost sample experienced almost complete resetting of the detrital apatite grains. The general younging of the apparent apatite fission-track ages towards the west

  20. Reactivation of a segmented hyper-extended rift system: the example of the Pamplona transfer zone in the western Pyrenees (United States)

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


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

  1. Andesite petrogenesis in a hybrid arc-rift setting: the Western Trans-Mexican Volcanic Belt (United States)

    Gómez-Tuena, A.; Vázquez-Duarte, A.; Díaz-Bravo, B.; Mori, L.


    The western sector of the Mexican subduction zone is characterized by the steep subduction of one of the youngest slabs on the planet (Rivera plate), and by the existence of a continental rift at ~230 km to the north from the trench (the so-called Tepic-Zacoalco rift, TZR), under which the subducted slab is either extremely deep or even absent (>250 km). The volcanic front is located at ~170 km from the trench and contains abundant potassic-alkaline lamprophyres with strong subduction (Ba/Ta= 1600-6000) and garnet signatures (Gd/Yb= 2-8), that have been recently interpreted as influenced by deep K2O-rich slab melts or supercritical fluids (Gómez-Tuena et al., 2011, GCA). In contrast, the most mafic rocks within the TZR are high-Nb, intraplate-like basalts that appear to derive from low extents of melting of a dryer (Ba/Ta= 800-60) and shallower (Gd/Yb= 2-2.5) mantle source. Even though a simple transition from an arc environment to an extensional tectonic regime is apparent when only the most primitive volcanic rocks are taken into account, the scenario becomes more complicated since at least five stratovolcanoes have been erupting typical arc andesites within the TZR over the last million years (San Juan, Sanganguey, Tepetiltic, Ceboruco and Tequila). Surprisingly, true calc-alkaline basalts that could be parental to andesites have not been found, indicating that andesites may have a direct mantle origin. Indeed, mayor and trace element compositions of volcanic rocks from western Mexico arrange in discrete suites with linear trends that are indicative of mixing, but they form sub-parallel arrays that do not converge to a common primitive basaltic melt, and often follow diverging trends in trace element-ratio plots. Melt-crust interactions likely occurred during magma ascent, since the volcanic rocks frequently include xenoliths and disequilibrium textures, but correlations among isotopic compositions and indexes of fractionation are not clearly observed in the

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

    Schneider, Sandra; Hornung, Jens; Hinderer, Matthias


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

  3. Probable existence of a Gondwana transcontinental rift system in western India: Implications in hydrocarbon exploration in Kutch and Saurashtra offshore: A GIS-based approach (United States)

    Mazumder, S.; Tep, Blecy; Pangtey, K. K. S.; Das, K. K.; Mitra, D. S.


    The Gondwanaland assembly rifted dominantly during Late Carboniferous-Early Permian forming several intracratonic rift basins. These rifts were subsequently filled with a thick sequence of continental clastic sediments with minor marine intercalations in early phase. In western part of India, these sediments are recorded in enclaves of Bikaner-Nagaur and Jaisalmer basins in Rajasthan. Facies correlatives of these sediments are observed in a number of basins that were earlier thought to be associated with the western part of India. The present work is a GIS based approach to reconnect those basins to their position during rifting and reconstruct the tectono-sedimentary environment at that time range. 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. Extensions related to the opening of Neo-Tethys led to the formation of a number of cross trends in the rift systems that acted as barriers to marine transgressions from the north as well as disrupted the earlier continuous longitudinal drainage systems. The axis of this rift system is envisaged to pass through present day offshore Kutch and Saurashtra and implies a thick deposit of Late Carboniferous to Early Jurassic sediments in these areas. Based on analogy with other basins associated with this rift system, these sediments may be targeted for hydrocarbon exploration.

  4. 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

  5. Seismic and Gravity Investigations of the Western Espanola Basin, Rio Grande Rift, New Mexico (United States)

    Braile, L. W.; Coldren, B. G.; Baca, A.; Fontana, J.; Olheiser, M.; Ziff, M.; Keske, A.; Rhode, A.; Martin-Short, R.; Allen, W.; Denton, K. M.; Harper, C.; Baldridge, W.; Biehler, S.; Ferguson, J. F.; McPhee, D.; Snelson, C. M.


    The SAGE (Summer of Applied Geophysical Experience) program collected new seismic, gravity, electromagnetic and down-hole temperature data in 2013 in the western Espanola basin of the Rio Grande rift area of northern New Mexico. The location, about 25 km NW of Santa Fe, has been identified as a potential geothermal resources area based on relatively high temperature gradients in drill holes. The SAGE 2013 data collection was part of an integrated geophysical study of the area initiated in 2011. Seismic data consisted of a 4.8 km W to E profile (120 three-component stations in four overlapping deployments, 20 m station spacing, using a Vibroseis source - 20 m spacing for reflection VPs; 800 m spacing for refraction VPs) with both refraction and CMP reflection coverage. About 55,000 seismograms were recorded. The surface conditions (dry unconsolidated sediments) increased surface wave energy and limited the signal-to-noise level of the refraction and reflection arrivals. Utilizing longer source-receiver offsets improved the shot-gather record sections by emphasizing wider angle reflections which are very strong and coherent. The refraction data were modeled with first arrival travel time methods. The reflection data were processed to produce a CMP stacked record section. Strong reflectors from basin-filling sedimentary rocks (mostly Tertiary in age) are visible above reflections from a thin section of Paleozoic rocks and the basement. The lower reflections have an apparent dip to the west of about 12 degrees. Eighty-one new gravity measurements (detailed data at 200 m spacing along the seismic profile, and regional stations) were collected and combined with existing regional data for modeling. Interpretation of the seismic and gravity data was aided by refraction velocities, the existence of a nearby regional seismic reflection profile from industry, and lithologies and well-logs from a deep well. The sedimentary basin interpreted from the seismic and gravity data

  6. 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.

  7. Basement depth and sedimentary infill from deep seismic reflection data at the western tip of the offshore Corinth Rift (United States)

    Beckers, Arnaud; Tripsanas, Efthymios; Hubert-Ferrari, Aurélia; Beck, Christian; Sakellariou, Dimitris


    The Corinth rift is a young continental rift located in central Greece. The active part of the rift forms an E-W striking depression - the Gulf of Corinth - that is the deepest in its central part. Extensive seismic surveys have imaged the basin's basement and allowed to estimate the total extension across most of the Gulf except its western tip. Extension is high in the central part and decreases westward and eastward, as reflected in the present-day bathymetry. Two decades of GPS measurements have shown that the extension rate increases westwards from ~5 to 10-15 mm yr-1, but this is not consistent with the long term pattern. However, no data allowed so far to estimate the basement depth at the western tip of the Gulf, where the geodetic extension rate is the largest. Such data would allow to check the apparent inconsistency between the present rate and the long-term estimates of crustal extension. We present here an unpublished multichannel seismic line dating from 1979 and crossing the western tip of the Gulf of Corinth. The line is 22 km long and strikes WNW-ESE, from the Mornos delta to the West-Channel fault. A Maxipulse source has been used, allowing to image the basement below the synrift sedimentary infill. To the east, a ~1.6 km deep basin is imaged between the southern margin of the Gulf and an inactive south-dipping fault located between the Aigion and the Trizonia faults. The sedimentary infill consists in an alternation between basin-focused bodies made of incoherent reflections and more extensive high-amplitude reflectors. Attributing this alternation to eustatic variations give an age of 300-350 ka to the oldest well imaged deposits. Northwest of the Trizonia fault, the basement is imaged at shallower depth, i.e. ~450 m. The western tip of the seismic line reaches the Mornos delta, close to the northern shoreline. There, the depth to the basement is larger, reaching ~1.2 km. The infill is made of 3 units : on the basement lies a thin unit of

  8. A new alien snail species from the Eger stream, Hungary (Mollusca, Ampullariidae

    Directory of Open Access Journals (Sweden)

    Frisóczki, B.


    Full Text Available Our macrozoobenthon samplings carried out in the Eger stream during 2015–2016 resulted in recording an alien species Marisa cornuarietis (Linneaus, 1758 the giant ramshorn snail which has not been reported so far from outdoorwaters in Hungary. Here we report on collecting several specimens from the urban section of the stream close to the outflow of the Eger thermal spa.

  9. Evidence of Rift Valley fever seroprevalence in the Sahrawi semi-nomadic pastoralist system, Western Sahara. (United States)

    Di Nardo, Antonello; Rossi, Davide; Saleh, Saleh M Lamin; Lejlifa, Saleh M; Hamdi, Sidumu J; Di Gennaro, Annapia; Savini, Giovanni; Thrusfield, Michael V


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

  10. Quantification and restoration of extensional deformation along the Western Iberia and Newfoundland rifted margins (United States)

    Sutra, Emilie; Manatschal, Gianreto; Mohn, Geoffroy; Unternehr, Patrick


    Many recent papers describe the structure of the Iberia and Newfoundland rifted margins; however, none of them propose kinematic restorations of the complete rift system to quantify the amount of extension necessary to exhume mantle and initiate seafloor spreading. In our study, we use two pairs of cross sections considered as conjugate lines: one across the Galicia Bank-Flemish Cap and the other across the Southern Iberia Abyssal Plain-Flemish Pass. Both transects have been imaged by reflection- and refraction-seismic methods and have been drilled during Ocean Drilling Program Legs 103, 149, 173, and 210. Drilling penetrated parts of the rift stratigraphy and the underlying basement. The cross sections can therefore be considered as the best-documented conjugate transects across present-day hyperextended, magma-poor rifted margins. The aim of this paper is threefold: (1) provide a detailed description of the crustal architecture of the two conjugate sections, (2) define the extensional structures and their ages, and (3) quantify the amount of strain and strain rate accommodated along these lines. This paper proposes a quantitative description of extension along the Iberia-Newfoundland rift system and discusses the limitations and problems in quantifying extensional deformation along hyperextended rifted margins.

  11. Gravity anomalies, crustal structure and rift tectonics at the Konkan and Kerala basins, western continental margin of India (United States)

    Dev, Sheena V.; Radhakrishna, M.; Chand, Shyam; Subrahmanyam, C.


    Litho-stratigraphic variation of sedimentary units constructed from seismic sections and gravity anomaly in the Konkan and Kerala basins of the western continental margin of India (WCMI) have been used to model processes such as lithospheric rifting mechanism, its strength, and evolution of flank uplift topography that led to the present-day Western Ghats escarpment. Based on the process-oriented approach, two lithospheric models (necking and magmatic underplating) of evolution of the margin were tested. Both, necking and underplating models suggest an effective elastic thickness (Te) of 5 km and 10 km along Konkan and Kerala basins, respectively and a deep level of necking at 20 km at both basins. Model study suggests that the necking model better explains the observed gravity anomalies in the southern part of the WCMI. A synthesis of these results along with the previously published elastic thickness estimates along the WCMI suggests that a low-to-intermediate strength lithosphere and a deeper level of necking explains the observed flank-uplift topography of the Western Ghats. Process-oriented gravity modelling further suggests that the lateral variations in the lithospheric strength, though not very significant, exist from north to south within a distance of 600 km in the Konkan and Kerala basins along the WCMI at the time of rifting. A comparison with previous Te estimates from coherence analysis along the WCMI indicates that the lithospheric strength did not change appreciably since the time of rifting and it is low both onshore and offshore having a range of 5-15 km.

  12. Geothermal activity at continental rift Citala, Western Mexico, where Lake Chapala is emplaced: past and present (United States)

    Zárate-del Valle, P. F.


    Lake Chapala is a tectonic lake developed on a continental rift named Citala (CRC) which belongs to a tectonically active zone in Western Mexico: the so-called Jalisco continental triple junction. Fossil sinter deposit, thermal spring, hydrothermal (hy) petroleum manifestation and hy alteration halo characterized the Lake Chapala basin. On the SE shore, outcrops a carbonate deposit named ``La Calera" (LC) which consists of a carbonate fossil sinter that measures 2 km in E-W direction and 600 m in N-S direction and overlays andesitic rock. With a thickness of approximately 5 m and a roughly horizontal attitude, the LC is characterized by a two-fold structure: when massive, it is colored in yellow brownish and grey and elsewhere it shows a pseudo-brecciated structure and when banded, yellow and dark millimetre alternated bands can be seen. The LC is marked by vuggy porosity and silica (quartz and chalcedony) vein lets. Under microscope a pseudo-micritic texture is observed; vugs coated by iron oxides, are filled with calcite, and/or quartz, chalcedony and clay minerals. Six samples of LC were analysed (LODC-UParis VI) for their stable isotopes (δ18O and δ13C): From δ13C{PDB} values we have two sets of data: -8.03 to -8.69 ppm that means a no contribution of organic carbon (oc) and -0.35 to -0.75 ppm meaning an important contribution of oc; from δ18O{PDB} values: -8.5 to -10.27 ppm we deduced a deposit in meteoric water with a temperature deposition higher than the surface. The CRC is characterized also by the presence of hydrothermal petroleum (hp): Inside the Chapala and ˜2 km from SE shore (Los Arcos) there are some small spots made of hp which look like islands (bitumen. Thermal springs (ths) occur both inside and outside the lake Chapala: the water in out-shore ths is of carbonate type (69^oC; ˜ 240 mg L-1 [HCO_3]^-; with one exception: the ths at the San Juan Cosalá spa (N shore), which is of sulphate type (64-83^oC; ˜479 mg L-1 [SO_4]-2) and is

  13. Intraplate seismicity along the Gedi Fault in Kachchh rift basin of western India (United States)

    Joshi, Vishwa; Rastogi, B. K.; Kumar, Santosh


    The Kachchh rift basin is located on the western continental margin of India and has a history of experiencing large to moderate intraplate earthquakes with M ≥ 5. During the past two centuries, two large earthquakes of Mw 7.8 (1819) and Mw 7.7 (2001) have occurred in the Kachchh region, the latter with an epicenter near Bhuj. The aftershock activity of the 2001 Bhuj earthquake is still ongoing with migration of seismicity. Initially, epicenters migrated towards the east and northeast within the Kachchh region but, since 2007, it has also migrated to the south. The triggered faults are mostly within 100 km and some up to 200 km distance from the epicentral area of the mainshock. Most of these faults are trending in E-W direction, and some are transverse. It was noticed that some faults generate earthquakes down to the Moho depth whereas some faults show earthquake activity within the upper crustal volume. The Gedi Fault, situated about 50 km northeast of the 2001 mainshock epicenter, triggered the largest earthquake of Mw 5.6 in 2006. We have carried out detailed seismological studies to evaluate the seismic potential of the Gedi Fault. We have relocated 331 earthquakes by HypoDD to improve upon location errors. Further, the relocated events are used to estimate the b value, p value, and fractal correlation dimension Dc of the fault zone. The present study indicates that all the events along the Gedi Fault are shallow in nature, with focal depths less than 20 km. The estimated b value shows that the Gedi aftershock sequence could be classified as Mogi's type 2 sequence, and the p value suggests a relatively slow decay of aftershocks. The fault plane solutions of some selected events of Mw > 3.5 are examined, and activeness of the Gedi Fault is assessed from the results of active fault studies as well as GPS and InSAR results. All these results are critically examined to evaluate the material properties and seismic potential of the Gedi Fault that may be useful

  14. Intraplate seismicity along the Gedi Fault in Kachchh rift basin of western India (United States)

    Joshi, Vishwa; Rastogi, B. K.; Kumar, Santosh


    The Kachchh rift basin is located on the western continental margin of India and has a history of experiencing large to moderate intraplate earthquakes with M ≥ 5. During the past two centuries, two large earthquakes of Mw 7.8 (1819) and Mw 7.7 (2001) have occurred in the Kachchh region, the latter with an epicenter near Bhuj. The aftershock activity of the 2001 Bhuj earthquake is still ongoing with migration of seismicity. Initially, epicenters migrated towards the east and northeast within the Kachchh region but, since 2007, it has also migrated to the south. The triggered faults are mostly within 100 km and some up to 200 km distance from the epicentral area of the mainshock. Most of these faults are trending in E-W direction, and some are transverse. It was noticed that some faults generate earthquakes down to the Moho depth whereas some faults show earthquake activity within the upper crustal volume. The Gedi Fault, situated about 50 km northeast of the 2001 mainshock epicenter, triggered the largest earthquake of Mw 5.6 in 2006. We have carried out detailed seismological studies to evaluate the seismic potential of the Gedi Fault. We have relocated 331 earthquakes by HypoDD to improve upon location errors. Further, the relocated events are used to estimate the b value, p value, and fractal correlation dimension Dc of the fault zone. The present study indicates that all the events along the Gedi Fault are shallow in nature, with focal depths less than 20 km. The estimated b value shows that the Gedi aftershock sequence could be classified as Mogi's type 2 sequence, and the p value suggests a relatively slow decay of aftershocks. The fault plane solutions of some selected events of Mw > 3.5 are examined, and activeness of the Gedi Fault is assessed from the results of active fault studies as well as GPS and InSAR results. All these results are critically examined to evaluate the material properties and seismic potential of the Gedi Fault that may be useful

  15. From rifting to spreading - seismic structure of the rifted western Mariana extinct arc and the ParceVela back-arc basin (United States)

    Grevemeyer, Ingo; Kodaira, Shuichi; Fujie, Gou; Takahashi, Narumi


    The proto Izu-Ogasawara (Bonin)-Mariana (IBM) Island arc was created when subduction of the Pacific plate began during the Eocene. Today, the Kyushu-Palau Ridge (KPR) at the centre of the Philippine Sea and the western Mariana Ridge (WMR) are considered to be a remnant of the proto IBM Island arc. The KPR and WMR were separated when back-arc spreading began at 30 to 29 Ma in the Shikoku Basin and ParceVela Basin (PVB). Volcanic activity along the arcs diminished at 27 Ma and there is little evidence of volcanic activity between 23-17 Ma. Arc volcanism was reactivated at 15 Ma, when the opening of the Shikoku Basin and PVB ceased. At about 5 Ma the Mariana Basin opened, rifting the WMR from the Mariana arc. Here, we report results from the seismic refraction and wide-angle profile MR101c shot in summer of 2003 by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) aboard the RV KAIYO during the cruise KY03-06, extending from the PVB across the WMR and terminating just to the east of the WMR. Along MR101c 46 OBS recorded shots from an airgun array of 12,000 cubic inches (197 litres); 44 OBS provided excellent P-wave data, including arrivals sampling the crust (Pg), the crust/mantle boundary (PmP), the uppermost mantle (Pn) and a deep reflection (PnP) under the WMR. To yield the seismic velocity structure, we used a joint reflection and refraction tomography, revealing the crustal and mantle P-wave velocity structure, the seismic Moho, and a deep-seated reflector. Distinct features are a 14 km thick crust forming the WMR, a high-velocity lower crust in both transition zones to the ParceVela Basin and Mariana Basin, and a reflector at 24 km depth, which shallows to 18 km in the transition zone to the Mariana Basin, perhaps reflecting rifting-related thinning of the entire lithosphere. The deep-reflector, however, did not occur under the PVB. Upper mantle velocity below the WMR is 8 km/s. However, with respect to oceanic crust sampled in the Pacific Basin

  16. Methodology for earthquake rupture rate estimates of fault networks: example for the western Corinth rift, Greece (United States)

    Chartier, Thomas; Scotti, Oona; Lyon-Caen, Hélène; Boiselet, Aurélien


    Modeling the seismic potential of active faults is a fundamental step of probabilistic seismic hazard assessment (PSHA). An accurate estimation of the rate of earthquakes on the faults is necessary in order to obtain the probability of exceedance of a given ground motion. Most PSHA studies consider faults as independent structures and neglect the possibility of multiple faults or fault segments rupturing simultaneously (fault-to-fault, FtF, ruptures). The Uniform California Earthquake Rupture Forecast version 3 (UCERF-3) model takes into account this possibility by considering a system-level approach rather than an individual-fault-level approach using the geological, seismological and geodetical information to invert the earthquake rates. In many places of the world seismological and geodetical information along fault networks is often not well constrained. There is therefore a need to propose a methodology relying on geological information alone to compute earthquake rates of the faults in the network. In the proposed methodology, a simple distance criteria is used to define FtF ruptures and consider single faults or FtF ruptures as an aleatory uncertainty, similarly to UCERF-3. Rates of earthquakes on faults are then computed following two constraints: the magnitude frequency distribution (MFD) of earthquakes in the fault system as a whole must follow an a priori chosen shape and the rate of earthquakes on each fault is determined by the specific slip rate of each segment depending on the possible FtF ruptures. The modeled earthquake rates are then compared to the available independent data (geodetical, seismological and paleoseismological data) in order to weight different hypothesis explored in a logic tree.The methodology is tested on the western Corinth rift (WCR), Greece, where recent advancements have been made in the understanding of the geological slip rates of the complex network of normal faults which are accommodating the ˜ 15 mm yr-1 north

  17. A Permo-Triassic border rift structure within the south-western Bay of Biscay controlling the shape of the Alpine crustal root beneath the Cantabrian Mountains (United States)

    Cadenas, Patricia; Fernández-Viejo, Gabriela; Álvarez-Pulgar, Javier


    The Bay of Biscay-Pyrenean geological system is an inverted hyperextended rift that illustrates in its deep structure the transition between an oceanic underthrusting in the west to a continent-continent collision in the east. We developed a structural analysis of the south-western reactivated rift system, which represents at present-day the western branch of the Cantabrian-Pyrenean collisional chain, including the Cantabrian Mountains onshore and the central and western segments of the North Iberian margin in the southern Bay of Biscay. This passive margin was structured during polyphase Triassic to Lower Cretaceous rifting events and subsequently inverted in the Cenozoic during the Alpine orogeny, when the Cantabrian-Pyrenean realm formed in the Iberian-European plate boundary. The reactivated rift system shows a significant structural variability resulting from the strong segmentation and strain partitioning during the subsequent tectonic events. Thus, it is a natural laboratory to study the constraints imposed by tectonic inheritance in the successive stages of an almost complete orogenic cycle. From the interpretation of offshore geological and geophysical data and the integration of onshore wide-angle results, where Mesozoic fossil remnants are very scarce, we analyzed the crustal structure of the reactivated rift system and mapped the now inverted rift domains. Our results show that the inherited rift architecture controlled the subsequent compressional reactivation of the hyperextended rift system. Of particular interest are the structural variations observed in proximal areas. Offshore, the proximal domain includes classical shallow grabens and half-grabens with low degrees of extension developed during an early Permo-Triassic rift event governed by stretching processes. Its NW-SE distal limit runs parallel to the Cantabrian Fault. Following this trend, a major structure, called Ventaniella fault, has been traditionally mapped onshore, interpreted as a

  18. The sero-epidemiology of Rift Valley fever in people in the Lake Victoria Basin of western Kenya (United States)

    Grossi-Soyster, Elysse Noel; de Glanville, William Anson; Thomas, Lian Francesca; Kariuki, Samuel; Bronsvoort, Barend Mark de Clare; Wamae, Claire Njeri; LaBeaud, Angelle Desiree; Fèvre, Eric Maurice


    Rift Valley fever virus (RVFV) is a zoonotic arbovirus affecting livestock and people. This study was conducted in western Kenya where RVFV outbreaks have not previously been reported. The aims were to document the seroprevalence and risk factors for RVFV antibodies in a community-based sample from western Kenya and compare this with slaughterhouse workers in the same region who are considered a high-risk group for RVFV exposure. The study was conducted in western Kenya between July 2010 and November 2012. Individuals were recruited from randomly selected homesteads and a census of slaughterhouses. Structured questionnaire tools were used to collect information on demographic data, health, and risk factors for zoonotic disease exposure. Indirect ELISA on serum samples determined seropositivity to RVFV. Risk factor analysis for RVFV seropositivity was conducted using multi-level logistic regression. A total of 1861 individuals were sampled in 384 homesteads. The seroprevalence of RVFV in the community was 0.8% (95% CI 0.5–1.3). The variables significantly associated with RVFV seropositivity in the community were increasing age (OR 1.2; 95% CI 1.1–1.4, pslaughterhouse workers were sampled in 84 ruminant slaughterhouses. The seroprevalence of RVFV in slaughterhouse workers was 2.5% (95% CI 1.5–4.2). Being the slaughterman, the person who cuts the animal’s throat (OR 3.5; 95% CI 1.0–12.1, p = 0.047), was significantly associated with RVFV seropositivity. This study investigated and compared the epidemiology of RVFV between community members and slaughterhouse workers in western Kenya. The data demonstrate that slaughtering animals is a risk factor for RVFV seropositivity and that slaughterhouse workers are a high-risk group for RVFV seropositivity in this environment. These risk factors have been previously reported in other studies providing further evidence for RVFV circulation in western Kenya. PMID:28686589

  19. Crustal structure of the rifted volcanic margins and uplifted plateau of Western Yemen from receiver function analysis (United States)

    Ahmed, Abdulhakim; Tiberi, Christel; Leroy, Sylvie; Stuart, Graham W.; Keir, Derek; Sholan, Jamal; Khanbari, Khaled; Al-Ganad, Ismael; Basuyau, Clémence


    We analyse P-wave receiver functions across the western Gulf of Aden and southern Red Sea continental margins in Western Yemen to constrain crustal thickness, internal crustal structure and the bulk seismic velocity characteristics in order to address the role of magmatism, faulting and mechanical crustal thinning during continental breakup. We analyse teleseismic data from 21 stations forming the temporary Young Conjugate Margins Laboratory (YOCMAL) network together with GFZ and Yemeni permanent stations. Analysis of computed receiver functions shows that (1) the thickness of unextended crust on the Yemen plateau is ˜35 km; (2) this thins to ˜22 km in coastal areas and reaches less than 14 km on the Red Sea coast, where presence of a high-velocity lower crust is evident. The average Vp/Vs ratio for the western Yemen Plateau is 1.79, increasing to ˜1.92 near the Red Sea coast and decreasing to 1.68 for those stations located on or near the granitic rocks. Thinning of the crust, and by inference extension, occurs over a ˜130-km-wide transition zone from the Red Sea and Gulf of Aden coasts to the edges of the Yemen plateau. Thinning of continental crust is particularly localized in a <30-km-wide zone near the coastline, spatially co-incident with addition of magmatic underplate to the lower crust, above which on the surface we observe the presence of seaward dipping reflectors (SDRs) and thickened Oligo-Miocene syn-rift basaltic flows. Our results strongly suggest the presence of high-velocity mafic intrusions in the lower crust, which are likely either synrift magmatic intrusion into continental lower crust or alternatively depleted upper mantle underplated to the base of the crust during the eruption of the SDRs. Our results also point towards a regional breakup history in which the onset of rifting was synchronous along the western Gulf of Aden and southern Red Sea volcanic margins followed by a second phase of extension along the Red Sea margin.

  20. Microsatellite and mitochondrial genetic differentiation of Anopheles arabiensis (Diptera: Culicidae) from western Kenya, the Great Rift Valley, and coastal Kenya. (United States)

    Temu, Emmanuel A; Yan, Guiyun


    The population genetic structure of the African malaria vector Anopheles arabiensis from western Kenya, the Great Rift Valley, and coastal Kenya was investigated using 12 microsatellite loci and a partial sequence of mtDNA dehydrogenase gene subunit 5 (ND5). The mean number of alleles and the observed heterozygosity were similar for the mosquito populations from the three regions as revealed by the microsatellite data. A total of 30 polymorphic sites in the ND5 gene defined 39 haplotypes. Six haplotypes were shared among four populations from the three distinct ecological conditions, and they constituted 92% of the total number of individuals sequenced. Mitochondrial haplotype and nucleotide diversity were high. Microsatellite markers within polymorphic inversions revealed a level of genetic differentiation (F(ST) = 0.116) four to seven times higher than markers outside inversions (F(ST) = 0.016) or inside fixed inversions (F(ST) = 0.027). Mitochondrial ND5 gene sequences did not reveal significant genetic differentiation for the same four populations (phi(ST) = -0.008). The contrasts in the level of genetic differentiation between microsatellite markers inside polymorphic inversions, the mitochondrial ND5 gene, and microsatellite markers outside inversions suggest that the level of genetic differentiation in An. arabiensis populations across the Great Rift Valley varies significantly among different areas of the genome. Variations in the degree of genetic differentiation with respect to the chromosomal location of microsatellite markers may result from intrinsic characteristics of the markers, demographic or historic factors affecting these populations, and the possible adaptive significance of chromosomal inversions to climatic conditions.

  1. The sero-epidemiology of Rift Valley fever in people in the Lake Victoria Basin of western Kenya.

    Directory of Open Access Journals (Sweden)

    Elizabeth Anne Jessie Cook


    Full Text Available Rift Valley fever virus (RVFV is a zoonotic arbovirus affecting livestock and people. This study was conducted in western Kenya where RVFV outbreaks have not previously been reported. The aims were to document the seroprevalence and risk factors for RVFV antibodies in a community-based sample from western Kenya and compare this with slaughterhouse workers in the same region who are considered a high-risk group for RVFV exposure. The study was conducted in western Kenya between July 2010 and November 2012. Individuals were recruited from randomly selected homesteads and a census of slaughterhouses. Structured questionnaire tools were used to collect information on demographic data, health, and risk factors for zoonotic disease exposure. Indirect ELISA on serum samples determined seropositivity to RVFV. Risk factor analysis for RVFV seropositivity was conducted using multi-level logistic regression. A total of 1861 individuals were sampled in 384 homesteads. The seroprevalence of RVFV in the community was 0.8% (95% CI 0.5-1.3. The variables significantly associated with RVFV seropositivity in the community were increasing age (OR 1.2; 95% CI 1.1-1.4, p<0.001, and slaughtering cattle at the homestead (OR 3.3; 95% CI 1.0-10.5, p = 0.047. A total of 553 slaughterhouse workers were sampled in 84 ruminant slaughterhouses. The seroprevalence of RVFV in slaughterhouse workers was 2.5% (95% CI 1.5-4.2. Being the slaughterman, the person who cuts the animal's throat (OR 3.5; 95% CI 1.0-12.1, p = 0.047, was significantly associated with RVFV seropositivity. This study investigated and compared the epidemiology of RVFV between community members and slaughterhouse workers in western Kenya. The data demonstrate that slaughtering animals is a risk factor for RVFV seropositivity and that slaughterhouse workers are a high-risk group for RVFV seropositivity in this environment. These risk factors have been previously reported in other studies providing further

  2. Lower Pliensbachian caldera volcanism in high-obliquity rift systems in the western North Patagonian Massif, Argentina (United States)

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


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

  3. Inversions for earthquake focal mechanisms and regional stress in the Kachchh Rift Basin, western India: Tectonic implications (United States)

    Singh, A. P.; Zhao, L.; Kumar, Santsoh; Mishra, Smita


    More than a decade after the 2001 MW 7.7 Bhuj earthquake in western India, aftershocks up to MW 5.0 are still continuing around the rupture zone in the Kachchh Rift Basin. Over the years, some surrounding faults in the region have been activated, and a transverse fault generated an MW 5.1 earthquake in 2012. Most of the earthquakes occur in the lower crust at depths between 15 and 35 km. We have determined focal mechanism solutions of 47 earthquakes (MW 3.2-5.1) that were recorded by a 60-station broadband network during 2007-2014 within an area of 50 km radius of the 2001 main shock. South dipping nodal planes in most of the solutions correlate well with the active faults. The earthquakes near the epicenter of the 2001 main shock primarily show reverse-faulting mechanisms. The surrounding earthquakes in the area, however, show predominantly strike-slip mechanisms. The P axes of the earthquakes mostly oriented in north-south, and the T axes in east-west. However, the orientations of the P and T axes exhibit more complexity near the source area of the main shock. Stress field inversion of the solutions yields a dominant north-south compression, which is consistent with the ambient tectonic stress field owing to the northward movement of the Indian Plate with respect to the Eurasian Plate. The geodetic measurements are in reasonable agreement with our results.

  4. Seismic volcanostratigraphy of the western Indian rifted margin: The pre-Deccan igneous province


    Calvès, Gérôme; Schwab, Anne M.; Huuse, Mads; Clift, Peter D.; Gaina, Carmen; Jolley, David; Tabrez, Ali R.; Inam, Asif


    The Indian Plate has been the focus of intensive research concerning the flood basalts of the Deccan Traps. Here we document a volcanostratigraphic analysis of the offshore segment of the western Indian volcanic large igneous province, between the shoreline and the first magnetic anomaly (An 28 ∼63 Ma). We have mapped the different crustal domains of the NW Indian Ocean from stretched continental crust through to oceanic crust, using seismic reflection and potential field data. Two volcanic s...

  5. Faulting, volcanism, and basin development along the western margin of the southern San Luis Basin segment of the Rio Grande rift, New Mexico and Colorado (United States)

    Turner, K. J.; Thompson, R. A.; Cosca, M. A.; Drenth, B.; Lee, J.; Budahn, J. R.


    The San Luis Basin segment of the northern Rio Grande rift, straddling the Colorado-New Mexico border, is an asymmetrical graben where the major basin-bounding fault is on the east side. In contrast, the west side is a basin-directed dip slope surface cut by north to northwest trending faults with predominantly down-to-southwest displacement. Around 26 Ma, initial rift-related faulting formed broad, shallow basins coincident with basaltic volcanism of the Hinsdale Formation. Later episodes of rifting produced deep and narrow sub-basins generally along the eastern boundary. Basin-fill deposits along the western margin are generally thin. However, in the northern Tusas Mountains, gravity data identifies a small, yet deep, sub-basin that may contain 750 m of basin-filling Los Pinos Formation based on thickness projections derived from mapping. The Los Pinos Formation is overlain by early rift-related Hinsdale Formation basalt flows indicating this sub-basin formed as part of early rifting; the sub-basin may be a southern extension of the Monte Vista graben to the north. The stratigraphic section along the western boundary includes Precambrian basement up to volcanic rocks of the Taos Plateau volcanic field (~5-2Ma). Dips on the early-rift Miocene to Oligocene Hinsdale Formation lavas (3-5 degrees) reflect the cumulative eastward tilting corresponding to continued basin subsidence. Shallower dips (1-2 degrees) on early Pliocene volcanic rocks suggest continued subsidence up to about 3 Ma, or younger. Down-to-southwest faults accommodating eastward tilting are mostly in areas west of Pliocene volcanic rocks; individual faults offset Hinsdale Formation and older rocks by up to 200 m. The few observed faults in the Pliocene volcanic rocks have minor offset. Numerous volcanic vents are in close proximity to the faults along the western boundary. Volcanoes are commonly low to medium relief shield volcanoes with basaltic andesite composition capped by late stage cinder cones

  6. Geology of the Western Part of Los Alamos National Laboratory (TA-3 to TA-16), Rio Grande Rift, New Mexico

    Energy Technology Data Exchange (ETDEWEB)

    C.J.Lewis; A.Lavine; S.L.Reneau; J.N.Gardner; R.Channell; C.W.Criswell


    We present data that elucidate the stratigraphy, geomorphology, and structure in the western part of Los Alamos National Laboratory between Technical Areas 3 and 16 (TA-3 and TA-16). Data include those gathered by geologic mapping of surficial, post-Bandelier Tuff strata, conventional and high-precision geologic mapping and geochemical analysis of cooling units within the Bandelier Tuff, logging of boreholes and a gas pipeline trench, and structural analysis using profiles, cross sections, structure contour maps, and stereographic projections. This work contributes to an improved understanding of the paleoseismic and geomorphic history of the area, which will aid in future seismic hazard evaluations and other investigations. The study area lies at the base of the main, 120-m (400-ft) high escarpment formed by the Pajarito fault, an active fault of the Rio Grande rift that bounds Los Alamos National Laboratory on the west. Subsidiary fracturing, faulting, and folding associated with the Pajarito fault zone extends at least 1,500 m (5,000 ft) to the east of the main Pajarito fault escarpment. Stratigraphic units in the study area include upper units of the Tshirege Member of the early Pleistocene Bandelier Tuff, early Pleistocene alluvial fan deposits that predate incision of canyons on this part of the Pajarito Plateau, and younger Pleistocene and Holocene alluvium and colluvium that postdate drainage incision. We discriminate four sets of structures in the area between TA-3 and TA-16: (a) north-striking faults and folds that mark the main zone of deformation, including a graben in the central part of the study area; (b) north-northwest-striking fractures and rare faults that bound the eastern side of the principal zone of deformation and may be the surface expression of deep-seated faulting; (c) rare northeast-striking structures near the northern limit of the area associated with the southern end of the Rendija Canyon fault; and (d) several small east

  7. 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

  8. Structural style of the Turkana Rift, Kenya

    Energy Technology Data Exchange (ETDEWEB)

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


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

  9. Petrogenesis and tectonic association of rift-related basic Panjal dykes from the northern Indian plate, North-Western Pakistan: evidence of high-Ti basalts analogous to dykes from Tibet (United States)

    Sajid, Muhammad; Andersen, Jens; Arif, Mohammad


    Rift related magmatism during Permian time in the northern margin of Indian plate is represented by basic dykes in several Himalayan terranes including north western Pakistan. The field relations, mineralogy and whole rock geochemistry of these basic dykes reveal significant textural, mineralogical and chemical variation between two major types (a) dolerite and (b) amphibolite. Intra-plate tectonic settings for both rock types have been interpreted on the basis of low Zr/Nb ratios (tectonic restoration of Gondwana indicate the coeval origin for both dykes from distinct mantle source during continental rifting related to formation of the Neotethys Ocean.

  10. Turning soil survey data into digital soil maps in the Energy Region Eger Research Model Area (United States)

    Pásztor, László; Dobos, Anna; Kürti, Lívia; Takács, Katalin; Laborczi, Annamária


    Agria-Innoregion Knowledge Centre of the Eszterházy Károly College has carried out targeted basic researches in the field of renewable energy sources and climate change in the framework of TÁMOP-4.2.2.A-11/1/KONV project. The project has covered certain issues, which require the specific knowledge of the soil cover; for example: (i) investigation of quantitative and qualitative characteristics of natural and landscape resources; (ii) determination of local amount and characteristics of renewable energy sources; (iii) natural/environmental risk analysis by surveying the risk factors. The Energy Region Eger Research Model Area consists of 23 villages and is located in North-Hungary, at the Western part of Bükkalja. Bükkalja is a pediment surface with erosional valleys and dense river network. The diverse morphology of this area results diversity in soil types and soil properties as well. There was large-scale (1:10,000 and 1:25,000 scale) soil mappings in this area in the 1960's and 1970's which provided soil maps, but with reduced spatial coverage and not with fully functional thematics. To achive the recent tasks (like planning suitable/optimal land-use system, estimating biomass production and development of agricultural and ecomonic systems in terms of sustainable regional development) new survey was planned and carried out by the staff of the College. To map the soils in the study area 10 to 22 soil profiles were uncovered per settlement in 2013 and 2014. Field work was carried out according to the FAO Guidelines for Soil Description and WRB soil classification system was used for naming soils. According to the general goal of soil mapping the survey data had to be spatially extended to regionalize the collected thematic local knowledge related to soil cover. Firstly three thematic maps were compiled by digital soil mapping methods: thickness of topsoil, genetic soil type and rate of surface erosion. High resolution digital elevation model, Earth

  11. Tectonic block rotation, arc curvature, and back-arc rifting: Insights into these processes in the Mediterranean and the western Pacific

    Energy Technology Data Exchange (ETDEWEB)

    Wallace, L M; Ellis, S [GNS Science, PO Box 30368, Lower Hutt (New Zealand); Mann, P [Institute for Geophysics, University of Texas at Austin, Austin, Texas (United States)], E-mail:


    The fastest modern-day tectonic block rotations on Earth (up to 9 degrees/Myr) occur in the forearcs of convergent plate margins where a transition from collision of a bathymetric high to subduction of normal oceanic crust occurs. GPS techniques have enabled accurate documentation of the kinematics of these rotations, leading us to develop a conceptual model where the change from collision to subduction exerts a torque on microplates within the plate boundary zone, causing them to spin rapidly about an axis at the collision point. We have investigated geophysical and geological data from several active plate boundaries (from the western Pacific and Mediterranean regions) to document a compelling spatial and temporal relationship between the transition from collision to subduction, plate boundary curvature, and rapid tectonic block rotations. In some cases, these microplate rotations can initiate back-arc rifting. We also present numerical modelling results supporting our conceptual model for block rotations at collision/subduction transition. Our results suggest that the rate of microplate rotation depends on the incoming indentor velocity, and can be greatly enhanced by: (1) extensional stresses acting at the subduction interface (possibly due to slab roll back), and (2) a low-viscosity back-arc. Where viscosity of the back-arc is low, forearc microplate rotation dominates. In contrast, tectonic escape of strike-slip fault-bounded microplates is predicted in areas where the back-arc viscosity is high. Previous workers have suggested that the kinematics of the Anatolian block and back-arc rifting in the Aegean are influenced by some combination of forces associated with Arabia/Eurasia collision, and/or subduction (including slab rollback) at the Hellenic trench. Based on previous work from active western Pacific arcs, we propose that the collision of two separate indentors (Arabian promontory in the east, Apulian platform in the west), is a fundamental tectonic

  12. Mineral inclusions in placer zircon from the Ohře (Eger) Graben: New data on „strontiopyrochlore“

    Czech Academy of Sciences Publication Activity Database

    Seifert, W.; Förster, H.-J.; Rhede, D.; Tietz, O.; Ulrych, Jaromír


    Roč. 92, 1/2 (2012), s. 39-53 ISSN 0930-0708 R&D Projects: GA ČR(CZ) GA205/09/1170 Institutional support: RVO:67985831 Keywords : Eger Graben * zircon * "strontiopyrochlore" Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.681, year: 2012

  13. 3D architecture of a complex transcurrent rift system: The example of the Bay of Biscay-Western Pyrenees (United States)

    Jammes, Suzon; Tiberi, Christel; Manatschal, Gianreto


    The Parentis and Arzacq-Mauléon basins located in front of the V-shaped oceanic propagator in the Bay of Biscay present evidence for extreme crustal thinning. In this paper we investigate the 3D structure of these rift basins, based on field observations and the interpretation of seismic data. We compare these results with those obtained from two different and independent inversion methods: first a 3D gravity inversion and second the standard Euler deconvolution. For the Mauléon Basin our results show that the positive gravimetric anomaly identified above its southern margin is the consequence of two shallower high density bodies that are separated by the Pamplona fault and a deeper high density body. The high density bodies can be explained by the presence of mid-crustal and mantle rocks that were exhumed or uplifted at shallower depth during Early Cretaceous rifting before they were reworked and integrated to the Pyrenean chain during compression phase. Also, during this reactivation phase, some slices of the exhumed mid-crustal and mantle rocks were sheared off and were integrated in the present-day thrust belt in the Mauléon basin. For the Parentis Basin we can demonstrate, based on seismic data and gravimetric inversion methods, a decrease in extension from west to east, which is compatible with the V-shape geometry of the overall basin. Along strike, a change in the fault geometry from downward concave top-basement detachment faults to upward concave high-angle faults can be observed eastwards, i.e. towards the termination of the basin. A key structure, controlling the evolution of the Parentis Basin, is the east-west trending Ibis fault. We interpret this fault to have initially formed as a strike slip fault before it was reactivated during later crustal thinning. At present, it forms the limit between an upper plate sag basin to the north and a lower plate sag basin, floored at least locally by a top-basement detachment faults to the south. The strong

  14. Holocene late Pleistocene non-tropical carbonate sediments and tectonic history of the western rift basin margin of the southern Gulf of California (United States)

    Halfar, Jochen; Godinez-Orta, Lucio; Goodfriend, Glenn A.; Mucciarone, David A.; Ingle, James C.; Holden, Peter


    Using high-resolution seismic reflection profiling and dating of (1) shallow marine vibracores and (2) sediments collected from uplifted marine terraces we reconstruct the tectonic history and sediment accumulation patterns of Holocene to late Pleistocene warm-temperate to subtropical carbonates in the southern Gulf of California, Mexico. The study was conducted in the vicinity of La Paz where carbonates form along the fault bounded narrow western shelf of the tectonically active Gulf of California rift basin. The non-tropical nature of the setting is responsible for (1) poor cementation of the bioclastic carbonates, and (2) a composition which is dominated by rhodoliths (coralline red algae), corals and mollusks. Unrimmed carbonate flats forming in small pocket bays and a rhodolith bioherm, which has a surface area of more than 20 km2 and is up to 16 m thick, constitute the major carbonate factories. Holocene carbonate accumulation rates were deduced from seismic and core data and are highest on the rhodolith bioherm (260 cm/ka) and in subtidal zones of pocket bays (210 cm/ka), and lowest on the inner and middle shelf (100 cm/ka). Taken together, rates of carbonate accumulation are intermediate in magnitude between higher rates recorded in fully tropical carbonate settings and lower rates typical of cool-water carbonates. Seismic reflection profiles demonstrate that Isla Espiritu Santo in the center of the study area is a west dipping fault block, which is tectonically influenced by two distinct faults, the La Paz and Espiritu Santo faults. The latter fault accommodates at least 700 m of east-side down normal offset, and forms a steep eastern escarpment leading into the La Paz slope basin. Some of the sediments produced in the shallow carbonate factories of the narrow La Paz shelf are transported across this escarpment and are redeposited in the slope basin at a water depth of 750 m. Uranium-series dates of marine terraces exposed on Isla Espiritu Santo indicate


    Directory of Open Access Journals (Sweden)

    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


    Directory of Open Access Journals (Sweden)

    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

  17. Seismic structure of western Mediterranean back-arc basins and rifted margins - constraints from the Algerian-Balearic and Tyrrhenian Basins (United States)

    Grevemeyer, Ingo; Ranero, Cesar; Sallares, Valenti; Prada, Manel; Booth-Rea, Guillermo; Gallart, Josep; Zitellini, Nevio


    The Western Mediterranean Sea is a natural laboratory to study the processes of continental extension, rifting and back-arc spreading in a convergent setting caused by rollback of fragmented subducting oceanic slabs during the latest phase of consumption of the Tethys ocean, leading to rapid extension in areas characterized by a constant convergence of the African and European Plates since Cretaceous time. Opening of the Algerian-Balearic Basin was governed by a southward and westward retreating slab 21 to 18 Myr and 18 to15 Myr ago, respectively. Opening of the Tyrrhenian Basin was controlled by the retreating Calabrian slab 6 to 2 Myr ago. Yet, little is known about the structure of the rifted margins, back-arc extension and spreading. Here we present results from three onshore/offshore seismic refraction and wide-angle lines and two offshore lines sampling passive continental margins of southeastern Spain and to the south of the Balearic promontory and the structure of the Tyrrhenian Basin to the north of Sicily. Seismic refraction and wide-angle data were acquired in the Algerian-Balearc Basin during a cruise of the German research vessel Meteor in September of 2006 and in the Tyrrhenian Sea aboard the Spanish research vessel Sarmiento de Gamboa in July of 2015. All profiles sampled both continental crust of the margins surrounding the basins and extend roughly 100 km into the Algerian-Balearic and the Tyrrhenian Basins, yielding constraints on the nature of the crust covering the seafloor in the basins and adjacent margins. Crust in the Algerian-Balearic basin is roughly 5-6 km thick and the seismic velocity structure mimics normal oceanic crust with the exception that lower crustal velocity is 24 km under SE Spain and the Balearic Islands, displaying typical features and structure of continental crust. Offshore Sicily, continental crust reaches 22 km. However, the Tyrrhenian Basin indicates a lithosphere with velocities increasing continuously from 3 km/s to

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

    NARCIS (Netherlands)

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

    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

  19. Besshi-type mineral systems in the Palaeoproterozoic Bryah Rift-Basin, Capricorn Orogen, Western Australia: Implications for tectonic setting and geodynamic evolution

    Directory of Open Access Journals (Sweden)

    Franco Pirajno


    Full Text Available In this contribution we use VMS mineral systems in the Bryah rift-basin to constrain the tectonic setting of the widespread mafic and ultramafic magmatism that characterises the rift-basin in question. Two distinct, but temporally closely associated, lithostratigraphic sequences, Narracoota and Karalundi Formations, are discussed. The Karalundi Formation is the main host of VMS mineral systems in the region. The Karalundi Formation consists of turbiditic and immature clastic sediments, which are locally intercalated with basaltic hyaloclastites, dolerites and banded jaspilites. We propose that the basaltic hyaloclastites, dolerites and clastics and jaspilites rocks, form a distinct unit of the Karalundi Formation, named Noonyereena Member. The VMS mineral systems occur near the north-east trending Jenkin Fault and comprise the giant and world-class DeGrussa and the Red Bore deposits. The nature of these deposits and their intimate association with terrigenous clastic rocks and dominantly marine mafic volcanic and subvolcanic rocks, as well as the common development of peperitic margins, are considered indicative of a Besshi-type environment, similar to that of present-day Gulf of California. Our Re-Os age data from a primary pyrite yielded a mean model age of 2012 ± 48 Ma, which coincides (within error with recent published Re-Os data (Hawke et al., 2015 and confirms the timing of the proposed geodynamic evolution. We propose a geodynamic model that attempts to explain the presence of the Narracoota and Karalundi Formations as the result of mantle plume activity, which began with early uplift of continental crust with intraplate volcanism, followed by early stages of rifting with the deposition of the Karalundi Formation (and Noonyereena Member, which led to the formation of Besshi-type VMS deposits. With on-going mantle plume activity and early stages of continental separation, an oceanic plateau was formed and is now represented by mafic

  20. Deposition and alteration of carbonaceous series within a Neotethyan rift at the western boundary of the Arabian plate: The late Permian Um Irna Formation, NW Jordan, a petroleum system

    Energy Technology Data Exchange (ETDEWEB)

    Dill, H.G.; Kus, J. [Federal Institute for Geosciences and Natural Resources, P.O. Box 51 01 53 D-30631 Hannover (Germany); Bechtel, A.; Gratzer, R. [Department of Applied Geosciences and Geophysics, University of Leoben, Peter Tunner Strasse 5, A-8700 Leoben (Austria); Abu Hamad, A.M.B. [Geology Department, University of Jordan, Amman 11942 (Jordan)


    During the late Permian (Kungurian to Kazanian) a Neotethyan rift basin evolved at the western boundary of the Arabian Plate, in what is called today the Dead Sea Valley of western Jordan. The break-up of Pangaea was accompanied by low-sinuosity sandy braided- to meandering-fluvial drainage systems which were fed by the uplift of the Arabian Shield and by poorly aerated swamps and ponds that concentrated plant debris of the Cathaysian floral province in the Um Irna Formation. These proximal wet fan sediments are overlain by a dry fan characterized by extensive reddish floodplain deposits, anastomosing channel systems and paleosols. The wet fan is underlain by Cambrian sandstones. These units serve as the top and bottom seals of the OM-bearing system of the Um Irna Formation. The sedimentary rocks of the OM-bearing Um Irna Formation underwent supergene, diagenetic and epigenetic hydrothermal alteration under an elevated geothermal gradient. The temperature increased from the time of deposition of the wet to the time of deposition of the dry fan and caused remobilization of manganese already pre-concentrated in the Cambrian footwall rocks of the rift basin. The anomalous heat regime may be accounted for as a predecessor stage of the Dead Sea Rift which is still active today. Oil seeps are found along faults and fractures near this deep-seated lineamentary fault zone. The deposition and alteration of the organic matter in this late Permian rift are of great consequence for oil generation in the region. Organic petrographic investigations revealed that organic-rich terrestrial carbonaceous and coal rich sediments of mainly of type III kerogen are dominant in the Um Irna Formation. In addition, aquatic liptinite rich sedimentary input (fresh water lake and/or lacustrine swamp) of type I kerogen is also noted. Coal derived organic matter occurs in the form of coaly particles with ranks from subbituminous A to high volatile bituminous C. Higher plant-derived macerals as

  1. Rio Grande Rift: History of Tectonic Opening and Magmatism (United States)

    van Wijk, J.; Axen, G. J.; Koning, D.


    We describe the mid-Miocene to present opening history of the Rio Grande rift from tectonic subsidence patterns, published Quaternary fault activity, and spatial, temporal and geochemical distributions of volcanism. Rift opening was quite fast until 8 Ma, with tectonic subsidence rates comparable to those of the pre-rupture phase of rifted continent margins, but post-8 Ma rates are slower in all studied localities. Integration of age control reveals that a rift-margin unconformity formed between 8.5 and 3.5 Ma, its exact duration varying depending on location. This partly coincides with uplift of the Ogallala formation in the western Great Plains. The widespread extent of the unconformity suggest that the unconformity records a region-wide dynamic uplift event, possibly resulting from mantle upwelling below the region. This is supported by geoid analyses. The unconformity postdates a change in relative plate motion between the North American and Pacific plates, which may account for the post-8 Ma decrease in subsidence rates. Distribution of Quaternary fault activity is concentrated on the border faults in the northern basins where the rift is in a juvenile stage, but distributed on intra-basin faults further south in the rift where the crust is thinned more. Our analyses show that volcanism in the Rio Grande rift has been of mainly basaltic composition since the Miocene; volcanism during early rifting ranged from basalt to rhyolite. Volcanism has not been evenly distributed in the rift, but concentrated in three large volcanic fields that were located outside of the main rift prior to rift opening, and along the Jemez Lineament which crosses the Rio Grande rift, with sporadic volcanic activity elsewhere. The southern portion of the rift has experienced less volcanic activity than the northern rift, perhaps because it is underlain by fast seismic wave velocity upper mantle that may be linked to colder or compositionally different (Farallon plate subduction related

  2. 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.

  3. 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....

  4. 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

  5. Volcanic field elongation, vent distribution and tectonic evolution of continental rift: The Main Ethiopian Rift example (United States)

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


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

  6. 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

  7. Antecedent rivers and early rifting: a case study from the Plio-Pleistocene Corinth rift, Greece (United States)

    Hemelsdaël, Romain; Ford, Mary; Malartre, Fabrice


    facies distribution throughout the early rift evolution. We show that the length scale of fluvial facies transitions is greater than and therefore not related to fault spacing. First order facies variations instead occur at the scale of the full antecedent fluvial system. Strike-parallel subsidence variations in individual fault blocks represent a second order controlling factor on stratigraphic architecture. As depocentres enlarged through time, sediments progressively filled palaeorelief, and formed a continuous alluvial plain above active faults. There was limited creation of footwall relief and thus no significant consequent drainage system developed. Here, instead of being diverted toward subsiding zones, the drainage system overfilled the whole rift from the onset of faulting. Moreover, the zones of maximum subsidence on individual faults are aligned across strike parallel to the persistent fluvial axis. This implies that long-term sediment loading influenced the growth of normal faults. We conclude that a major antecedent drainage system inherited from the Hellenide mountain belt supplied high volumes of coarse sediment from the onset of faulting in the western Corinth rift (around 4 Ma). These observations demonstrate that antecedent drainage systems can be important in the tectono-sedimentary evolution of rift basins.

  8. 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

  9. Continental Rifts and Resources (United States)

    Stein, Holly J.


    Nearly all resource-forming systems involve upward mobility of fluids and melts. In fact, one of the most effective means of chemically transforming the earth's crust can be readily observed in the rift environment. Imposition of rifting is based on deeper stresses that play out in the crust. At its most fundamental level, rifting transfers heat and fluids to the crust. Heat delivered by fluids aids both in transport of metal and maturation of hydrocarbons. The oxidizing capacity of fluids on their arrival in the deep crust, whether derived from old slabs, depleted upper mantle and/or deeper, more primitive mantle, is a fundamental part of the resource-forming equation. Oxidizing fluids transport some metals and breakdown kerogen, the precursor for oil. Reducing fluids transport a different array of metals. The tendency is to study the resource, not the precursor or the non-economic footprint. In doing so, we lose the opportunity to discover the involvement and significance of initiating processes; for example, externally derived fluids may produce widespread alteration in host rocks, a process that commonly precedes resource deposition. It is these processes that are ultimately the transferable knowledge for successful mineral and hydrocarbon exploration. Further limiting our understanding of process is the tendency to study large, highly complex, and economically successful ore-forming or petroleum systems. In order to understand their construction, however, it is necessary to put equal time toward understanding non-economic systems. It is the non-economic systems that often clearly preserve key processes. The large resource-forming systems are almost always characterized by multiple episodes of hydrothermal overprints, making it difficult if not impossible to clearly discern individual events. Understanding what geologic and geochemical features blocked or arrested the pathway to economic success or, even worse, caused loss of a resource, are critical to

  10. Deep seismic sounding in the Turkana depression, northern Kenya Rift (United States)

    Gajewski, Dirk; Schulte, Andreas; Riaroh, Don; Thybo, Hans


    Existing models of the structure and evolution of the Kenya Rift such as pure shear lithospheric extension, extension by simple shear or rift development by diapiric upwelling of an asthenolith, were based upon surface geology and a few geophysical (mainly gravity and seismic) data sets. Since the knowledge of the lithospheric structure plays an important role to distinguish between these different models, the Kenya Rift International Seismic Project was conducted in 1990 in the area of the Kenya Rift. The project involved a detailed multi-fold refraction wide-angle reflection line in the northern Kenya Rift along the western shore of Lake Turkana which is the most prominent feature of the so-called Turkana depression. Under-water explosions were used as sources and a good signal-to-noise ratio was obtained allowing the identification of arrivals from the crust and upper mantle. The most important result of modelling the data is a crustal thickness of 21 km in the area of Lake Turkana, whereas in the area of the Kenya dome the crustal thickness is 34 km. This points to an extension not previously expected in the northern Kenya Rift. The Moho discontinuity appears as a transition zone in the northern part of the profile, whereas in the southern part it changes to a first-order discontinuity. The largest vertical and lateral heterogeneities are observed in the rift infill displaying basins of varying thickness. The upper and lower crust which are separated by the Conrad discontinuity (the velocity changes from 6.2 to 6.4 km/s here) show very little lateral heterogeneity. The P-wave velocity in the upper mantle was modelled to be 7.7 km/s and thus can be distinguished from that in the southern Kenya Rift, where a velocity of 7.5 km/s was observed. The crustal structure of the graben supports a model of a southerly propagation of the rift.

  11. North America's Midcontinent Rift: when Rift MET Lip (United States)

    Stein, C. A.; Stein, S. A.; Kley, J.; Keller, G. R., Jr.; Bollmann, T. A.; Wolin, E.; Zhang, H.; Frederiksen, A. W.; Ola, K.; Wysession, M. E.; Wiens, D.; Alequabi, G.; Waite, G. P.; Blavascunas, E.; Engelmann, C. A.; Flesch, L. M.; Rooney, T. O.; Moucha, R.; Brown, E.


    Rifts are segmented linear depressions, filled with sedimentary and igneous rocks, that form by extension and often evolve into plate boundaries. Flood basalts, a class of Large Igneous Provinces (LIPs), are broad regions of extensive volcanism due to sublithospheric processes. Typical rifts are not filled with flood basalts, and typical flood basalts are not associated with significant crustal extension and faulting. North America's Midcontinent Rift (MCR) is an unusual combination. Its 3000-km length formed as part of the 1.1 Ga rifting of Amazonia (Precambrian NE South America) from Laurentia (Precambrian North America) and became inactive once seafloor spreading was established, but contains an enormous volume of igneous rocks. MCR volcanics are significantly thicker than other flood basalts, due to deposition in a narrow rift rather than a broad region, giving a rift geometry but a LIP's magma volume. Structural modeling of seismic reflection data shows an initial rift phase where flood basalts filled a fault-controlled extending basin, and a postrift phase where volcanics and sediments were deposited in a thermally subsiding basin without associated faulting. The crust thinned during rifting and rethickened during the postrift phase and later compression, yielding the present thicker crust. The coincidence of a rift and LIP yielded the world's largest deposit of native copper. This combination arose when a new rift associated with continental breakup interacted with a mantle plume or anomalously hot or fertile upper mantle. Integration of diverse data types and models will give insight into questions including how the magma source was related to the rifting, how their interaction operated over a long period of rapid plate motion, why the lithospheric mantle below the MCR differs only slightly from its surroundings, how and why extension, volcanism, and compression varied along the rift arms, and how successful seafloor spreading ended the rift phase. Papers

  12. YORP and Yarkovsky effects in asteroids (1685) Toro, (2100) Ra-Shalom, (3103) Eger, and (161989) Cacus (United States)

    Ďurech, J.; Vokrouhlický, D.; Pravec, P.; Hanuš, J.; Farnocchia, D.; Krugly, Yu. N.; Inasaridze, R. Y.; Ayvazian, V. R.; Fatka, P.; Chiorny, V. G.; Gaftonyuk, N.; Galád, A.; Groom, R.; Hornoch, K.; Kučáková, H.; Kušnirák, P.; Lehký, M.; Kvaratskhelia, O. I.; Masi, G.; Molotov, I. E.; Oey, J.; Pollock, J. T.; Shevchenko, V. G.; Vraštil, J.; Warner, B. D.


    Context. The rotation states of small asteroids are affected by a net torque arising from an anisotropic sunlight reflection and thermal radiation from the asteroids' surfaces. On long timescales, this so-called YORP effect can change asteroid spin directions and their rotation periods. Aims: We analyzed lightcurves of four selected near-Earth asteroids with the aim of detecting secular changes in their rotation rates that are caused by YORP or at least of putting upper limits on such changes. Methods: We use the lightcurve inversion method to model the observed lightcurves and include the change in the rotation rate dω/ dt as a free parameter of optimization. To enlarge the time line of observations and to increase the sensitivity of the method, we collected more than 70 new lightcurves. For asteroids Toro and Cacus, we used thermal infrared data from the WISE spacecraft and estimated their size and thermal inertia by means of a thermophysical model. We also used the currently available optical and radar astrometry of Toro, Ra-Shalom, and Cacus to infer the Yarkovsky effect. Results: We detected a YORP acceleration of dω/ dt = (1.9 ± 0.3) × 10-8 rad d-2 for asteroid Cacus. The current astrometric data set is not sufficient to provide detection of the Yarkovsky effect in this case. For Toro, we have a tentative (2σ) detection of YORP from a significant improvement of the lightcurve fit for a nonzero value of dω/ dt = 3.0 × 10-9 rad d-2. We note an excellent agreement between the observed secular change of the semimajor axis da/ dt and the theoretical expectation for densities in the 2-2.5 g cm-3 range. For asteroid Eger, we confirmed the previously published YORP detection with more data and updated the YORP value to (1.1 ± 0.5) × 10-8 rad d-2. We also updated the shape model of asteroid Ra-Shalom and put an upper limit for the change of the rotation rate to | dω/ dt | ≲ 1.5 × 10-8 rad d-2. Ra-Shalom has a greater than 3σ Yarkovsky detection with a

  13. Tectonic Evolution of the Terceira Rift (Azores) (United States)

    Stratmann, Sjard; Huebscher, Christian; Terrinha, Pedro; Ornelas Marques, Fernando; Weiß, Benedik


    The Azores Plateau is located in the Central Atlantic at the Eurasian, Nubian and North-American plates (RRT) Azores Triple Junction. The Terceira Rift (TR) connects the Mid-Atlantic Ridge with the Gloria Fault, hence establishing a transtensional-transform present day plate boundary between the Eurasian and the Nubian plates. Three volcanic islands arose along the TR, Graciosa, Terceira and Sao Miguel. In the geological past, the plate boundary in the Azores area between the Eurasian and Nubian plates was located further south at the East Azores Fracture Zone. The timing of the plate boundary jump, which marks the onset of rifting along the TR, is heavily disputed. Published ages vary from 36 to 1 Ma. Based on bathymetric data and high-resolution marine 2D multi-channel seismic data acquired during M113 cruise of R/V Meteor in 2014/2015 we discuss the structural evolution of the TR and address the question whether the divergence between both plates is entirely accommodated by the TR. The central TR between São Miguel and Terceira, also known as Hirondelle Basin, is up to 70 km wide. Rifting created two asymmetric graben sections separated by a rift parallel horst. The north-eastern and south-western graben sections are ca. 4 km and 3 km deep, respectively, and the corresponding graben floors are tilted towards the central horst. Volcanic cones emerged on the central horst and rift shoulders. Bright spots in the basin fill deposits indicate fluid flow out of the volcanic basement. The seafloor is displaced by faults which suggest recent fault displacement. In the Eastern Graciosa Basin between Terceira and Graciosa Islands the rift narrows to ca. 40 km and shallows to ca. 3200 m water depth. The central horst is no longer detectable. Instead, a buried normal fault and a small escarpment are observed. Shallow faults and block rotation are less pronounced compared to the basins to the south-east and north-west. The Western Graciosa Basin is about 30 km wide and ca

  14. 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

  15. Probable existence of a Gondwana transcontinental rift system in ...

    Indian Academy of Sciences (India)

    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. Extensions related to the opening of Neo-Tethys led to the formation of a number of ...

  16. Gravity anomalies, crustal structure and rift tectonics at the Konkan ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 121; Issue 3. Gravity anomalies, crustal structure and rift tectonics at the Konkan and Kerala basins, western continental margin of India. Sheena V Dev M Radhakrishna Shyam Chand C Subrahmanyam. Volume 121 Issue 3 June 2012 pp 813-822 ...

  17. Geoelectric structure of northern Cambay rift basin from magnetotelluric data (United States)

    Danda, Nagarjuna; Rao, C. K.; Kumar, Amit


    Broadband and long-period magnetotelluric data were acquired over the northern part of the Cambay rift zone along an east-west profile 200 km in length. The decomposed TE- and TM-mode data were inverted using a 2-D nonlinear conjugate gradient algorithm to obtain the lithospheric structure of the region. A highly conductive ( 1000 S) layer was identified within the Cambay rift zone and interpreted as thick Quaternary and Tertiary sediments. The crustal conductors found in the profile were due to fluid emplacement in the western part, and the presence of fluids and/or interconnected sulfides caused by metamorphic phases in the eastern part. The demarcation of the Cambay rift zone is clearly delineated with a steeply dipping fault on the western margin, whereas the eastern margin of the rift zone gently dips along the NE-SW axis, representing a half-graben structure. A highly resistive body identified outside the rift zone is interpreted as an igneous granitic intrusive complex. Moderately conductive (30-100 Ω-m) zones indicate underplating and the presence of partial melt due to plume-lithosphere interactions.[Figure not available: see fulltext.

  18. Integrated Numerical Model for the East African Rift System: Plume-induced Rifting and Continental Break-up from Lake Malawi to Red Sea (United States)

    Koptev, A.; Leroy, S. D.; Calais, E.; Gerya, T.


    We present numerical experiments that target to reveal the role of active mantle plume, far-field tectonic forces and pre-existing lithospheric heterogeneities in structural development of the East African Rift system (EARS). Starting with models capturing the essential geophysical features of the central and southern parts of the EARS (two «cratonic» bodies (Tanzanian craton and Bangweulu block) embedded into a «normal» surrounding lithosphere) we show that development of the magmatic Eastern branch, the amagmatic Western branch and its southern prolongation (Malawi rift) can be the result of non-uniform splitting of some hot plume material that has been initially seeded underneath the southern part of Tanzanian craton. 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. These models permit us to reproduce observed orientation and relative position of two spreading axes (Red Sea, Gulf of Aden) and rifting (Main Ethiopian rift) one. All are joining at Afar triple junction. Finally, for laterally extended experiment we have used parameters of the best-fit models for the southern and northern segments of the EARS in order to define the position of Kenyan plume and the velocity boundary conditions. This model cover all rifting and spreading structure associated with both Afar and Kenyan plumes: Red Sea Rift and the Aden Ridge to the north of the Afar Triple Junction; Main Ethiopian Rift running to the south that continues as the Kenyan Rift; Western Rift and its southern prolongation corresponding to Malawi rift.We argue that main features of the EARS can be reproduced in a relatively simple context of the interaction between two mantle anomalies corresponding to Afar and Kenyan plumes and pre-stressed rheologically stratified continental lithosphere containing only first-order structural heterogeneities (such as

  19. Cenozoic rifting in the West Antarctic Rift System (United States)

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


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

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

    Hassaan, Mahmoud


    connected with NW,WNW and N-S faults genetically related to volcano-hydrothermal activity associated the Red Sea rifting. At Sherm EL-Sheikh hydrothermal manganese deposit occurs in Oligocene clastics within fault zone. Four iron-manganese-barite mineralization in Esh-Elmellaha plateau are controlled by faults trending NW,NE and nearly E-W intersecting Miocene carbonate rocks. Barite exists disseminated in the ores and as a vein in NW fault. In Shalatee - Halaib district 24 manganese deposits and barite veins with sulphide patches occur within Miocene carbonates distributed along two NW fault planes,trending 240°and 310° and occur in granite and basalt . Uranium -lead-zinc sulfide mineralization occur in Late Proterozoic granite, Late Cretaceous sandstones, and chiefly in Miocene clastic-carbonate-evaporate rocks. The occurrences of uranium- lead-zinc and iron-manganese-barite mineralization have the characteristic features of hypogene cavity filling and replacement deposits correlated with Miocene- Recent Aden volcanic rocks rifting. In western Saudi Arabia barite-lead-zinc mineralization occurs at Lat. 25° 45' and 25° 50'N hosted by Tertiary sediments in limestone nearby basaltic flows and NE-SW fault system. The mineralized hot brines in the Red Sea deeps considered by the author a part of this province. The author considers the constant rifting phases of Pangea and then progressive fragmentation of Western Gondwana during the Late Carboniferous-Lias, Late Jurassic-Early Aptian, Late Aptian - Albian and Late Eocene-Early Miocene and Oligocene-Miocene, responsible for formation of the mineral deposits constituting the M provinces. During these events, rifting, magmatism and hydrothermal activities took place in different peri-continental margins.

  1. Plume-rift interaction in the Deccan volcanic province (United States)

    Sheth, H. C.; Chandrasekharam, D.


    It is widely accepted that the grand volcanic episode of the Deccan in India was a consequence of the passage of the northerly drifting Indian subcontinent over the Réunion starting plume in the Late Cretaceous. This plume also produced the three-rift Cambay triple junction, the three arms being the West Coast graben belt, the Narmada-Tapi rift zone and the Cambay rift. Deccan-related alkalic magmatism both preceded and followed the main tholeiitic phase of ˜ 65 Ma ago by about 3 MY. The uniformly tholeiitic thick basalt sequence of the Western Ghats was derived from direct melting of the plume head, but the tholeiitic-alkalic magmatism of the three rift belts was due to melting of the hydrous lithospheric mantle due to variable amounts of rifting. Any lithospheric loading mechanism for generating post-tholeiite alkalic lavas does not seem feasible for the Deccan; nor can it explain the pre-tholeiite alkaline magmatism in the Deccan. Similarly, conductive heating of the lithosphere by the plume cannot have generated the alkalic melts. Some amount of actual rifting did occur. Direct melt supply from the plume is not necessary for magmatism in the rifts, though it seems to have occurred in some cases. Our documentation of indigenous magmatism for the three rift belts calls into question any attempts at inferring the size of the plume head from synchroneity in geochronologic data alone, and we negate the possibility or necessity of large-distance transport of magmas from the plume through the lithosphere, to feed the rifts. Recent evidence indicates that alkalic magmatism north of the main Deccan outcrop preceded the main tholeiite phase by ˜ 3 MY. The Cambay graben was active 3.5 MY before the main tholeiite phase. As the alkalic complexes at the northern end of this graben are 68.5 Ma in age (so far the oldest well-proven Deccan-related rocks), they are the first expression of the Réunion plume, and the borehole picrites from the triple junction area, until now

  2. Two-and three-dimensional gravity modeling along western ...

    Indian Academy of Sciences (India)

    The western continental margin and the intraplate Narmada-Tapti rifts are primarily covered by Deccan flood basalts. Three-dimensional gravity modeling of +70 mgal Bouguer gravity highs extending in the north-south direction along the western continental margin rift indicates the presence of a subsurface high density, ...

  3. Sensitivity of the East African rift lakes to climate variability (United States)

    Olaka, L.; Trauth, M. H.


    Lakes in the East African Rift have provided excellent proxies to reconstruct past climate changes in the low latitudes. The lakes occupy volcano-tectonic depressions with highly variable climate and hydrological setting, that present a good opportunity to study the climatic and hydrogeological influences on the lake water budget. Previous studies have used lake floor sediments to establish the sensitivity of the East African rift lakes. This study focuses on geomorphology and climate to offer additional or alternative record of lake history that are key to quantifying sensitivity of these lakes as archives to external and internal climatic forcings. By using the published Holocene lake areas and levels, we analyze twelve lakes on the eastern arm of the East African rift; Ziway, Awassa, Turkana, Suguta, Baringo, Nakuru, Elmenteita, Naivasha, Natron, Manyara and compare with Lake Victoria, that occupies the plateau between the east and the western arms of the rift. Using the SRTM data, Hypsometric (area-altitude) analysis has been used to compare the lake basins between latitude 80 North and 30 South. The mean elevation for the lakes, is between 524 and 2262 meters above sea level, the lakes' hypsometric integrals (HI), a measure of landmass volume above the reference plane, vary from 0.31 to 0.76. The aridity index (Ai), defined as Precipitation/ Evapotranspiration, quantifies the water available to a lake, it encompasses land cover and climatic effects. It is lowest (arid) in the basin between the Ethiopian rift and the Kenyan rift and at the southern termination of the Kenyan Rift in the catchments of lake Turkana, Suguta, Baringo and Manyara with values of 0.55, 0.43, 0.43 and 0.5 respectively. And it is highest (wet) in the catchments of, Ziway, Awassa, Nakuru and Naivasha as 1.33,1.03 and 1.2 respectively, which occupy the highest points of the rift. Lake Victoria has an index of 1.42 the highest of these lakes and receives a high precipitation. We use a

  4. 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

  5. Mapping rift domains within an inverted hyperextended rift system: The role of rift inheritance in controlling the present-day structure of the North Iberian margin (Bay of Biscay) (United States)

    Cadenas, Patricia; Fernández-Viejo, Gabriela; Álvarez-Pulgar, Javier; Tugend, Julie; Manatschal, Gianreto; Minshull, Tim


    This study presents a new rift domain map in the central and western North Iberian margin, in the southern Bay of Biscay. This margin was structured during polyphase Triassic to Lower Cretaceous rifting events which led to hyperextension and exhumation and the formation of oceanic crust during a short-lived seafloor spreading period. Extension was halted due to the Alpine convergence between the Iberian and the European plates which led to the formation of the Cantabrian-Pyrenean orogen during the Cenozoic. In the Bay of Biscay, while the northern Biscay margin was slightly inverted, the North Iberian margin, which is at present-day part of the western branch of the Alpine belt together with the Cantabrian Mountains, exhibits several degrees of compressional reactivation. This makes this area a natural laboratory to study the influence of rift inheritance into the inversion of a passive margin. Relying on the interpretation of geological and geophysical data and the integration of wide-angle results, we have mapped five rift domains, corresponding to the proximal, necking, hyperthinned, exhumed mantle, and oceanic domains. One of the main outcomes of this work is the identification of the Asturian Basin as part of a hyperthinned domain bounded to the north by the Le Danois basement high. We interpret Le Danois High as a rift-related crustal block inherited from the margin structure. Our results suggest that the inherited rift architecture controlled the subsequent compressional reactivation. The hyperextended domains within the abyssal plain focused most of the compression resulting in the development of an accretionary wedge and the underthrusting of part of these distal domains beneath the margin. The presence of the Le Danois continental block added complexity, conditioning the inversion undergone by the Asturian Basin. This residual block of less thinned continental crust acted as a local buttress hampering further compressional reactivation within the platform


    African Journals Online (AJOL)

    Department of Geology, University of Dar es Salaam. PO. Box 35052, Dar es Salaam, Tanzania. ABSTRACT ,. 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 ...

  7. Simple shear detachment fault system and marginal grabens in the southernmost Red Sea rift (United States)

    Tesfaye, Samson; Ghebreab, Woldai


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

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

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


    This study is based on a coupled basin infilling study and a landforms analysis of the Lake Albert Rift located at the northern part of the western branch of the East African Rift. The basin infilling study is based on both subsurface data and outcrops analysis. The objective was to (1) obtain an age model based on onshore mammals biozones, (2) to reconstruct the 3D architecture of the rift using sequence stratigraphy correlations and seismic data interpretation, (3) to characterize the deformation and its changes through times and (4) to quantify the accommodation for several time intervals. The infilling essentially consists of isopach fault-bounded units composed of lacustrine deposits wherein were characterized two major unconformities dated at 6.2 Ma (Uppermost Miocene) and 2.7 Ma (Pliocene-Pleistocene boundary), coeval with major subsidence and climatic changes. The landforms analysis is based on the characterization and relative dating (geometrical relationships with volcanism) of Ugandan landforms which consist of stepped planation surfaces (etchplains and peplians) and incised valleys. We here proposed a seven-steps reconstruction of the deformation-erosion-sedimentation relationships of the Lake Albert Basin and its catchments: - 55-45 Ma: formation of laterites corresponding to the African Surface during the very humid period of the Lower-Middle Eocene; - 45-22: stripping of the African Surface in response of the beginning of the East-African Dome uplift and formation of a pediplain which associated base level is the Atlantic Ocean; - 17-2.5 Ma: Initiation of the Lake Albert Basin around 17 Ma and creation of local base levels (Lake Albert, Edward and George) on which three pediplains tend to adapt; - 18 - 16 Ma to 6.2 Ma: "Flexural" stage (subsidence rate: 150-200 m/Ma; sedimentation rate 1.3 km3/Ma between 17 and 12 Ma and 0.6 km3/Ma from 12 to 6 Ma) - depocenters location (southern part of Lake Albert Basin) poorly controlled by fault; - 6.2 Ma to 2

  9. Albertine Rift, Uganda: Deformation-Sedimentation-Erosion relationships (United States)

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


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

  10. Magmatism in rifting and basin formation (United States)

    Thybo, H.


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

  11. Phase relationships and P-T path in NCFMASHTO system of the eclogite from the Tighsi area (Egere terrane, Central Hoggar, Algeria) (United States)

    Doukkari, Sid Ali; Ouzegane, Khadidja; Arab, Amar; Kienast, Jean-Robert; Godard, Gaston; Drareni, Amar; Zetoutou, Souad; Liégeois, Jean-Paul


    The Tighsi area is situated in the northern part of the Egere-Aleksod terrane (Central Hoggar, South of Algeria). The eclogites and the garnet-amphibolites occur as lenses in marble, metapelite and quartzite. The petrological study shows that the high pressure paragenesis is characterized by the assemblage omphacite-garnet-rutile-quartz and epidote. Omphacite contains epidote, rutile and quartz inclusions. Due to the decompression, omphacite is the first mineral to destabilize into very thin symplectites of albite and clinopyroxene poorer of the jadeitic component. The paragenese of the lower pressure is represented by kelyphites and symplectites of amphibole-plagioclase separating garnet from omphacite and quartz. During this evolution, rutile transforms into ilmenite then, in the latest stage sphene replaces ilmenite. The thermodynamic modeling using THERMOCALC has confirmed these textural observations and suggests that the eclogites have experienced three stages of metamorphism. Stage I is the high pressure association, an H2O under-saturated pseudosection adapted to this stage has been constructed in NCFMASHTO system. The association of high pressure corresponds to the field where garnet is in equilibrium with omphacite including epidote-rutile and quartz; The P-T conditions of 19.6 kbar and 694 °C have been estimated using the garnet core compositions. Stage II is the isothermal decompression where the amphibole-plagioclase kelyphites occur at the expense of garnet, omphacite and quartz at 15.5 kbar and 774 °C (conditions estimated using the garnet rim and the plagioclase-amphibole kelyphites compositions). Stage III is the late retrograde evolution; a second pseudosection with H2O in excess has been constructed to model this stage and show the transformation of eclogites into garnet-bearing amphibolites and explains the occurrence of sphene. The P-T conditions of 9.3 kbar and 695 °C have been estimated using the compositions of the plagioclase with the

  12. Thermal state of the Roer Valley Graben, part of the European Cenozoic Rift System

    NARCIS (Netherlands)

    Luijendijk, E.; ter Voorde, M.; van Balen, R.T.; Verweij, H.; Simmelink, E.


    We performed a detailed analysis of the thermal state of the Cenozoic Roer Valley Graben, the north-western branch of the European Cenozoic Rift System, based on a new set of temperature data. We developed a numerical technique for correcting bottom hole temperatures, including an evaluation of the

  13. Thermal state of the Roer Valley Graben, part of the European Cenozoic Rift System

    NARCIS (Netherlands)

    Luijendijk, E.; ter Voorde, M.; van Balen, R.T.; Verweij, H.; Simmelink, E.


    We performed a detailed analysis of the thermal state of the Cenozoic Roer Valley Graben, the north-western branch of the European Cenozoic Rift System, based on a new set of temperature data. We developed a numerical technique for correcting bottom hole temperatures, including an evaluation of the

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

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


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

  15. 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

  16. 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

  17. 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

  18. Pre-existing normal faults have limited control on the rift geometry of the northern North Sea (United States)

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


    Many rifts develop in response to multiphase extension with numerical and physical models suggesting that reactivation of first-phase normal faults and rift-related variations in bulk crustal rheology control the evolution and final geometry of subsequent rifts. However, many natural multiphase rifts are deeply buried and thus poorly exposed in the field and poorly imaged in seismic reflection data, making it difficult to test these models. Here we integrate recent 3D seismic reflection and borehole data across the entire East Shetland Basin, northern North Sea, to constrain the long-term, regional development of this multiphase rift. We document the following key stages of basin development: (i) pre-Triassic to earliest Triassic development of multiple sub-basins controlled by widely distributed, NNW- to NE-trending, east- and west-dipping faults; (ii) Triassic activity on a single major, NE-trending, west-dipping fault located near the basins western margin, and formation of a large half-graben; and (iii) Jurassic development of a large, E-dipping, N- to NE-trending half-graben near the eastern margin of the basin, which was associated with rift narrowing and strain focusing in the Viking Graben. In contrast to previous studies, which argue for two discrete periods of rifting during the Permian-Triassic and Late Jurassic-Early Cretaceous, we find that rifting in the East Shetland Basin was protracted from pre-Triassic to Cretaceous. We find that, during the Jurassic, most pre-Jurassic normal faults were buried and in some cases cross-cut by newly formed faults, with only a few being reactivated. Previously developed faults thus had only a limited control on the evolution and geometry of the later rift. We instead argue that strain migration and rift narrowing was linked to the evolving thermal state of the lithosphere, an interpretation supporting the predictions of lithosphere-scale numerical models. Our study indicates that additional regional studies of

  19. 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

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

    African Journals Online (AJOL)

    Background: Cancer of esophagus is the 9th It is aggressive with poor prognosis especially in its late stage. Cancer of esophagus is geographically unevenly distributed with high incidence found within sharply demarcated geographic confines. Earlier reports from this country indicated relatively high proportion of cases in ...

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

    Indian Academy of Sciences (India)

    ... Madagascar (Storey et al. 1995;. Pande et al. 2001) and at ∼63 Ma between India and Seychelles (Collier et al. 2008; Bhattacharya and Yatheesh 2015). The Panvel flexure in the. ∼65 Ma Deccan flood basalts runs along the. Keywords. Flood volcanism; Deccan traps; Panvel flexure; Mumbai; Elephanta Island; faulting.

  2. Layered Crustal and Mantle Structure and Anisotropy beneath the Afar Depression and Malawi Rift Zone (United States)

    Reed, Cory Alexander

    Although a wealth of geophysical data sets have been acquired within the vicinity of continental rift zones, the mechanisms responsible for the breakup of stable continental lithosphere are ambiguous. Eastern Africa is host to the largest contemporary rift zone on Earth, and is thus the most prominent site with which to investigate the processes which govern the rupture of continental lithosphere. The studies herein represent teleseismic analyses of the velocity and thermomechanical structure of the crust and mantle beneath the Afar Depression and Malawi Rift Zone (MRZ) of the East African Rift System. Within the Afar Depression, the first densely-spaced receiver function investigation of crustal thickness and inferred velocity attenuation across the Tendaho Graben is conducted, and the largest to-date study of the topography of the mantle transition zone (MTZ) beneath NE Africa is provided, which reveals low upper-mantle velocities beneath the Afar concordant with a probable mantle plume traversing the MTZ beneath the western Ethiopian Plateau. In the vicinity of the MRZ, a data set comprised of 35 seismic stations is employed that was deployed over a two year period from mid-2012 to mid-2014, belonging to the SAFARI (Seismic Arrays For African Rift Initiation) experiment. Accordingly, the first MTZ topography and shear wave splitting analyses were conducted in the region. The latter reveals largely plate motion-parallel anisotropy that is locally modulated by lithospheric thickness abnormalities adjacent to the MRZ, while the former reveals normal MTZ thicknesses and shallow discontinuities that support the presence of a thick lithospheric keel within the MRZ region. These evidences strongly argue for the evolution of the MRZ via passive rifting mechanisms absent lower-mantle influences.

  3. Tectono-stratigraphic evolution and crustal architecture of the Orphan Basin during North Atlantic rifting (United States)

    Gouiza, Mohamed; Hall, Jeremy; Welford, J. Kim


    The Orphan Basin is located in the deep offshore of the Newfoundland margin, and it is bounded by the continental shelf to the west, the Grand Banks to the south, and the continental blocks of Orphan Knoll and Flemish Cap to the east. The Orphan Basin formed in Mesozoic time during the opening of the North Atlantic Ocean between eastern Canada and western Iberia-Europe. This work, based on well data and regional seismic reflection profiles across the basin, indicates that the continental crust was affected by several extensional episodes between the Jurassic and the Early Cretaceous, separated by events of uplift and erosion. The preserved tectono-stratigraphic sequences in the basin reveal that deformation initiated in the eastern part of the Orphan Basin in the Jurassic and spread towards the west in the Early Cretaceous, resulting in numerous rift structures filled with a Jurassic-Lower Cretaceous syn-rift succession and overlain by thick Upper Cretaceous to Cenozoic post-rift sediments. The seismic data show an extremely thinned crust (4-16 km thick) underneath the eastern and western parts of the Orphan Basin, forming two sub-basins separated by a wide structural high with a relatively thick crust (17 km thick). Quantifying the crustal architecture in the basin highlights the large discrepancy between brittle extension localized in the upper crust and the overall crustal thinning. This suggests that continental deformation in the Orphan Basin involved, in addition to the documented Jurassic and Early Cretaceous rifting, an earlier brittle rift phase which is unidentifiable in seismic data and a depth-dependent thinning of the crust driven by localized lower crust ductile flow.

  4. 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

  5. Geophysical expression of elements of the Rio Grande rift in the northeast Tusas Mountains - Preliminary interpretations (United States)

    Drenth, Benjamin J.; Turner, Kenzie J.; Thompson, Ren A.; Grauch, V. J.; Cosca, Michael A.; Lee, John


    New interpretations of the nature of the Rio Grande rift and pre-existing rocks in the northeast Tusas Mountains region are derived from new and existing gravity and aeromagnetic data. 12-15 mGal amplitude gravity lows are interpreted to mainly reflect large thicknesses of the upper Oligocene to upper Miocene, syn-rift Los Pinos Formation and possibly significant amounts of the Eocene El Rito Formation. The Broke Off Mountain sub basin, named after the location of its greatest inferred depth, is interpreted to be a ~40 km long and ~13 km wide structure elongated in a northwest trend at the western margin of the San Luis Basin. The sub basin is interpreted to contain a maximum combined thickness of 900-2300 m of the Los Pinos Formation and El Rito Formation, with the Los Pinos Formation constituting the majority of the section. Sub basin age is constrained to be older than 21.6 ± 1.4 Ma, the age of a Hinsdale Formation basalt flow that caps the Los Pinos Formation section at Broke Off Mountain. This age constraint and surface geology indicate a pre- and early-rift age. The structural fabric of the northeast Tusas Mountains region is dominated by northwest-trending normal faults, as indicated by geologic mapping and interpretation of aeromagnetic data. Preliminary analysis of the aeromagnetic data suggests that lineaments, possibly reflecting faulting, trend through volcanic rocks as young as Pliocene in age. If correct, these interpretations challenge commonly held beliefs regarding two stages in the structural style of rifting, where early (Oligocene-Miocene) rifting was characterized by broad, shallow basins bounded by northwest-trending faults and later (Miocene-Pliocene) rifting was characterized by deep, narrow basins bounded by north-trending faults. The Broke Off Mountain sub basin is a counter example of a pre- and early-rift, deep and narrow basin. We hypothesize that the Broke Off Mountain sub basin may represent a southward extension of the Monte Vista

  6. Geothermal resources of rifts: A comparison of the rio grande rift and the salton trough (United States)

    Swanberg, Chandler A.


    The Rio Grande Rift and the Salton Trough are the best developed rift systems in the United States and both share many features common to rifts in general, including geothermal resources. These two rifts have different tectonic and magmatic histories, however, and these differences are reflected in the nature of their geothermal resources. The Salton Trough is a well developed and successful rift. It is the landward extension of the Gulf of California spreading center, which has separated Baja, California, from the remainder of Mexico. Quaternary silicic magmatization has occurred and several of the geothermal resources are associated with recent rhyolitic intrusions. Such resources tend to be high temperature (> 200°C). Greenschist facies metamorphism has been observed in several of the geothermal wells. Localized upper crustal melting is a distinct possibility and there is increasing speculation that very high temperature (> 300°C) geothermal fluids may underlie a large portion of the central trough at depths in excess of 4 km. Low temperature geothermal resources associated with shallow hydrothermal convection are less common and tend to be located on the flanks of the trough or in the Coachella Valley to the north of the zone of active rifting. In contrast, the Rio Grande Rift is less well developed. Recent volcanism consists primarily of mantle-derived basalts, which have not had sufficient residence time within the crust to generate significant crustal melting. The geothermal resources within the Rio Grande Rift do not correlate well with these young basalts. Rather, the quantity of geothermal resources are low temperature (resources are less common and the only discovered example is the Valles Caldera of northern New Mexico ( T = 250-300°C). The deep interiors of the sedimentary basins of the Rio Grande Rift do not appear to be major geothermal exploration targets.

  7. 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

  8. Thermomechanical models of the Rio Grande rift

    Energy Technology Data Exchange (ETDEWEB)

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


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

  9. A finite amplitude necking model of rifting in brittle lithosphere (United States)

    Lin, Jian; Parmentier, E. M.


    We formulate a mechanical model describing the formation of rifts as finite amplitude necking of an elastic-plastic layer overlying a fluid substrate. A perfectly plastic rheology is a continuum description of faulting in rift zones. Two important aspects of rift evolution are illustrated by this model: the evolution of the rift width as extension proceeds and the finite strain that occurs. A region at yield initially develops with a width determined by the thickness of the brittle layer, and the internal deformation within this yield zone is proportional to the topographic slope. As extension proceeds, the surface within the rift subsides, and the width of the subsiding yield zone decreases. At any stage of rifting, material in regions just outside the yield zone is deformed but no longer deforming. The width of these deformed regions increases with increasing extension. Vertical forces due to the mass deficit of the rift depression will flex the elastic layer outside the yield zone, creating flanking uplifts. The external force required to maintain active rifting increases with the amount of lithospheric stretching, indicating that rifting is a quasi-static, stable process. Because the yield zone will revert to elastic behavior if the external force causing extension is removed, the model predicts that the rift depression and flanking uplifts will be preserved after extension stops. Our simple mechanical model demonstrates the inherent relationship among graben formation, lithospheric thinning, and rift shoulder uplift in rift zones.

  10. Molecular Epidemiology of Rift Valley Fever Virus (United States)

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


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

  11. From rift-inherited hyper-extension to orogenesis: De-coding the axial zone of orogenic belts (United States)

    Beltrando, Marco; Manatschal, Gianreto; Mohn, Geoffroy


    The relative role of rift-inherited hyper-extension and subduction/collisional dynamics in establishing the lithostratigraphic associations and overall architecture of orogenic belts has been investigated for the Western Alps. This case study was selected to test existing models involving complex subduction/exhumation dynamics to account for seemingly chaotic mixing of continental crust and serpentinized mantle rocks in high-pressure metamorphic units. The methodology developed to assess the role of rift-inheritance in multiply deformed/metamorphosed tectonometamorphic units stems from recent advances in the understanding of hyper-extended domains in present-day magma-poor rifted margins, where the crustal architecture displays transitional features between typical oceanic and continental domains. In these areas, slivers of hyper-extended continental crust or pre-rift sediments may rest as extensional allochthons upon serpentinized mantle, while syn- and post- rift sediments seal the extension-related lithostratigraphy. Following multi-stage orogeny-related deformation and metamorphism, this rift-related lithostratigraphic architecture can erroneously be ascribed to complex subduction dynamics, partly due to the sliver-like appearance of continental basement. However, the partial preservation of rift-related lithostratigraphic associations may still be assessed by (1) the consistency of the lithostratigraphic architecture over large areas, based on the continuity of key surfaces (i.e. base of early post-rift sediments) across the orogeny-related macro-structures, (2) the presence of clasts of basement rocks in the neighboring meta-sediments, indicating the original proximity of the different lithologies, (3) evidence of brittle deformation in continental basement and ultramafic rocks pre-dating Alpine metamorphism, indicating that they were juxtaposed by fault activity prior to the deposition of post-rift sediments, and (4) the similar Alpine tectono

  12. An attempt to model rift propagation (United States)

    Zwaan, Frank; Schreurs, Guido


    Rift propagation is along-strike growth of an initial small rift structure. Since rift propagation is a major factor in continent-break up (e.g. the opening of the Atlantic) we started a series of models to investigate associated tectonic processes. These analogue models involve either standard extension (continuous along-strike) or scissor-like extension (with an along-strike gradient and a rotation axis). Both the standard and scissor set-ups involve a base of foam and plastic components that transfers distributed extension to the overlying model materials as the model sidewalls are moved apart. The difference between the standard set-up and the scissor set-up is that the sidewalls move apart in a parallel fashion in the former, while in the latter, the sidewalls move around a rotation axis, causing a scissor-like deformation gradient. We use quartz sand layer for the brittle upper crust and a viscous sand/silicone mixture for ductile lower crust (total 8 cm, 1 cm = 5 km). Lines of semi-circular silicone (seeds) on top of the basal viscous layer act as weak zones along deformation focuses because the stronger sand layer on top is thinner and therefore weaker. These 0.75 cm thick seeds are situated at one end of the model (ca. 20 cm long on a model length of 80-90 cm), to initiate a rift structure from which rift propagation could start. Both set-ups encounter the same problems. In contrast with our previous model series (e.g. Zwaan et al., 2016), the seeds cause little localization and almost no rift propagation. Instead, extensional faulting occurs mostly along the sidewalls, especially away from the seeds. Apparently, the models need a seed or weak zone to localize deformation, otherwise the model boundaries provide the weaknesses along which faulting occurs. Tests with lower extension velocities (which should improve rift localization due to lower brittle-ductile coupling) did not improve the results. Neither did the application of a thicker seed (ø up to 1

  13. 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.

  14. 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...

  15. 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. ...

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

    Directory of Open Access Journals (Sweden)

    Paterno R Castillo


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

  17. Numerical modeling of seismicity and geodynamics of the Kachchh rift zone, Gujarat, India (United States)

    Vorobieva, Inessa; Mandal, Prantik; Gorshkov, Alexander


    The numerical block-and-fault model of lithosphere dynamics and seismicity (BAFD) is used to understand crustal motion and features of the observed seismicity in the Kachchh rift zone, Gujarat, Western India. The block-model allows simulating seismicity and geodynamics simultaneously unlike other modeling approaches for studying seismicity or geodynamics. The model structure of Kachchh rift zone is composed of seven major crustal blocks separated by fault planes. Based on the orientation of boundary crustal block movements, we develop a set of numerical experiments to analyze the spatial distribution of earthquakes, frequency-to-magnitude relationships, earthquake focal mechanisms, velocity field, and fault slip rates in the model. The main results of our modeling suggest that an NNW-SSE trending compression is a principal driving force in the Kachchh rift zone that explains basic features of the regional seismicity, direction of block motions, and the presence of an extensional stress regime associated with the Cambay rift zone. Large synthetic events occur on the fault segments associated with the Allah-Bund fault, Katrol hill fault and north Wagad fault which have been causative faults for the 1819 Mw7.7 Allah-Bund, 1956 Mw6.0 Anjar and 2001 Mw7.7 Bhuj earthquakes. The frequency-magnitude distribution for both synthetic seismicity and observed seismicity shows a similar slope. The focal mechanisms of the synthetic events are found to be consistent with those of earthquakes in the region. A special attention has been paid to study long-term and post-seismic deformations. Our results are in a qualitative agreement with the GPS post-seismic observations in the Kachchh rift zone. We infer that the observed seismicity and crustal block motions are a consequence of the dynamics of the entire regional fault and block system rather than that of a single causative fault only.

  18. Surface wave imaging of the weakly extended Malawi Rift from ambient-noise and teleseismic Rayleigh waves from onshore and lake-bottom seismometers (United States)

    Accardo, N. J.; Gaherty, J. B.; Shillington, D. J.; Ebinger, C. J.; Nyblade, A. A.; Mbogoni, G. J.; Chindandali, P. R. N.; Ferdinand, R. W.; Mulibo, G. D.; Kamihanda, G.; Keir, D.; Scholz, C.; Selway, K.; O'Donnell, J. P.; Tepp, G.; Gallacher, R.; Mtelela, K.; Salima, J.; Mruma, A.


    Located at the southernmost sector of the Western Branch of the East African Rift System, the Malawi Rift exemplifies an active, magma-poor, weakly extended continental rift. To investigate the controls on rifting, we image crustal and uppermost mantle structure beneath the region using ambient-noise and teleseismic Rayleigh-wave phase velocities between 9 and 100 s period. Our study includes six lake-bottom seismometers located in Lake Malawi (Nyasa), the first time seismometers have been deployed in any of the African rift lakes. Noise levels in the lake are lower than that of shallow oceanic environments and allow successful application of compliance corrections and instrument orientation determination. Resulting phase-velocity maps reveal slow velocities primarily confined to Lake Malawi at short periods (T thick sediments in the border-fault bounded rift basin. The slowest velocities occur within the Central Basin where Malawi Rift sedimentary strata may overlie older (Permo-Triassic) Karoo group sediments. At longer periods (T > 25 s), a prominent low-velocity anomaly exists beneath the Rungwe Volcanic Province at the northern terminus of the rift basin. Estimates of phase-velocity sensitivity indicates these low velocities occur within the lithospheric mantle and potentially uppermost asthenosphere, suggesting that mantle processes may control the association of volcanic centres and the localization of magmatism. Beneath the main portion of the Malawi Rift, a modest reduction in velocity is also observed at periods sensitive to the crust and upper mantle, but these velocities are much higher than those observed beneath Rungwe.

  19. Straight from the source's mouth; a quantitative study of grain-size export for an entire active rift, the Corinth Rift, central Greece (United States)

    Watkins, Stephen E.; Whittaker, Alexander C.; Bell, Rebecca E.; Brooke, Sam A. S.; McNeill, Lisa C.; Gawthorpe, Robert L.


    The volumes, grain sizes and characteristics of sediment supplied from source catchments fundamentally controls basin stratigraphy. However, to date, few studies have constrained sediment budgets, including grain size, released into an active rift basin at a regional scale. The Gulf of Corinth, central Greece, is one of the most rapidly extending rifts in the world, with geodetic measurements of 5 mm/yr in the East to 15 mm/yr in the West. It has well-constrained climatic and tectonic boundary conditions and bedrock lithologies are well-characterised. It is therefore an ideal natural laboratory to study the grain-size export for a rift. In the field, we visited the river mouths of 49 catchments draining into the Corinth Gulf, which in total drain 83% of the rift. At each site, hydraulic geometries, surface grain-size of channel bars and full-weighted grain-size distributions of river sediment were obtained. The surface grain-size was measured using the Wolman point count method and the full-weighted grain-size distribution of the bedload by in-situ sieving. In total, approximately 17,000 point counts and 3 tonnes of sediment were processed. The grain-size distributions show an overall increase from East to West on the southern coast of the gulf, with largest grain-sizes exported from the Western rift catchments. D84 ranges from 20 to 110 mm, however 50% of D84 grain-sizes are less than 40 mm. Subsequently, we derived the full Holocene sediment budget for the Corinth Gulf by combining our grain size data with catchment sediment fluxes, constrained using the BQART model and calibrated to known Holocene sediment volumes in the basin from seismic data (c.f. Watkins et al., in review). This is the first time such a budget has been derived for the Corinth Rift. Finally, our estimates of sediment budgets and grain sizes were compared to regional uplift constraints, fault distributions, slip rates and lithology to identify the relative importance of these controls on

  20. Spatial and Temporal Evolution of Rift Systems: Implication for the Nature, Kinematics and Timing of the Iberian-European Plate Boundary (United States)

    Tugend, J.; Manatschal, G.; Kusznir, N. J.


    The mechanisms of continental lithosphere deformation that control the formation and evolution of rift systems leading to continental breakup and the creation of divergent plate boundaries represent a long-standing problem in tectonics. Studies conducted in present-day rifted margins and their onshore fossil analogues reveal variable crustal architecture emphasizing the complex spatial and temporal evolution of rift systems. The Bay of Biscay and Pyrenees, at the transition between the Iberian and European plates, correspond to a Late Jurassic to Mid Cretaceous rift system. The transition from preserved oceanic and rift domains to the West to their complete inversion in the East enables the investigation of seismically imaged, drilled and exposed parts of a rift system. We combine observations from seismic reflection data, gravity inversion results and field mapping to identify and map former rift domains from the Bay of Biscay margins to onshore fossil analogues preserved in the Pyrenean orogen. The results of this mapping emphasize the existence of spatially disconnected and strongly segmented rift systems preserved along the paleo Iberian-European plate boundary. Based on their restoration, subsidence and deformation history, we illustrate the evolution of strain partitioning between them and present the implications at the scale of the Iberian-European plate boundary. The deformation history suggested is more complex than previously assumed, highlighting the polyphased evolution of this plate boundary. We propose that the onset of the Late Jurassic to Early Cretaceous rifting was partitioned between a set of distinct left-lateral transtensional rift systems. A plate kinematic reorganization at Aptian-Albian time resulted in the onset of seafloor spreading in the Western Bay of Biscay and extreme crustal and lithosphere thinning in intra-continental rift basins to the east. Finally, the results of this work may provide insights on: (1) processes preceding break

  1. Giant seismites and megablock uplift in the East African Rift: evidence for Late Pleistocene large magnitude earthquakes. (United States)

    Hilbert-Wolf, Hannah Louise; Roberts, Eric M


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

  2. Geometrical analysis of Palesch family chapel in Kľačno, former Gaidel in Western Slovakia.

    Directory of Open Access Journals (Sweden)

    Grúňová Zuzana


    Full Text Available Oval and elliptic spaces are one group of central plans, used mainly in sacral architecture and palaces. Paper deals with geometrical analysis of one of the smaller representatives of the neoclassical sacral architecture with oval plan - Palesch family chapel of Virgin Mary in village Kľačno in Western Slovakia. Oval and elliptic forms are not so often used in Slovak historical architecture and they are almost always connected with foreign influence and knowledge brought form Vienna, Paris, Pest, Eger and other education and praxis localities of the builder or architect. This uncommon oval form used in the small chapel is therefore certainly of interest from the point of view of architecture and geometry.

  3. 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

  4. 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

  5. The MOZART Project - MOZAmbique Rift Tomography (United States)

    Fonseca, J. F.; Chamussa, J. R.; Domingues, A.; Helffrich, G. R.; Fishwick, S.; Ferreira, A. M.; Custodio, S.; Brisbourne, A. M.; Grobbelaar, M.


    Project MOZART (MOZAmbique Rift Tomography) is an ongoing joint effort of Portuguese, Mozambican and British research groups to investigate the geological structure and current tectonic activity of the southernmost tip of the East African Rift System (EARS) through the deployment of a network of 30 broad band seismic stations in Central and Southern Mozambique. In contrast with other stretches of the EARS to the North and with the Kapvaal craton to the West and South, the lithosphere of Mozambique was not previously studied with a dense seismographic deployment on account of past political instability, and many questions remain unanswered with respect to the location and characteristics of the EARS to the south of Tanzania. In recent years, space geodesy revealed the existence of three microplates in and off Mozambique - Victoria, Rovuma, Lwandle - whose borders provide a connection of the EARS to the South West Indian Ridge as required by plate tectonics. However, the picture is still coarse concerning the location of the rift structures. The 2006 M7 Machaze earthquake in Central Mozambique highlighted the current tectonic activity of the region and added a further clue to the location of the continental rift, prompting the MOZART deployment. Besides helping unravel the current tectonics, the project is expected to shed light on the poorly known Mesoproterozoic structure described by Arthur Holmes in 1951 as the Mozambique Belt, and on the mechanisms of transition from stable craton to rifted continental crust, through the development of a tomographic model for the lithosphere. The MOZART network is distributed South of the Zambezi river at average inter-station spaces of the order of 100 km and includes four stations across the border in South Africa. Data exchange was agreed with AfricaArray. The deployment proceeded in two phases in March 2011, and November and December 2011. Decommissioning is foreseen for August 2013. We report preliminary results for this

  6. Initial rifting and long-term landscape evolution of the Albertine Rift in East Africa (United States)

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


    In East Africa, the feedback between tectonic uplift, erosional denudation and associated possible climate changes is being studied by a multidisciplinary research group, 'RiftLink'. The group's focus is the Albertine Rift of the East African Rift System (EARS), and therein rising Rwenzori Mountains that stretch along the border of the D.R. Congo (DRC) and Uganda. Major questions relate to temporal and spatial evolution of the Rwenzori Mountains and surrounding Albertine Rift: is the surface uplift of the Rwenzoris (>5 km) directly linked to rift movements in Neogene times, or was there a topographic high long before [1]. To understand the morphological evolution of an area or landscape, knowledge about phases of (dis-)equilibrium between rock exhumation and rock uplift governed by climatic and tectonic processes is essential. Low-temperature thermochronology, like fission-track and (U-Th-Sm)/He dating on apatite and zircon (AFT, AHe, ZHe) are well established tools to trace rock displacements through the upper crust. And, therefore, provide fundamental information helping to decipher the long-term landscape evolution of an area. Thermokinematic modelling, applied to samples from different parts of the working area allow to better constrain the cooling history and landscape evolution of the Rwenzori Mts as well as surrounding Albertine Rift which will be discussed in the frame of this presentation. Samples taken along and across the Albertine Rift, cover the area around the Rwenzori Mts and the mountain range itself. From thermochronological analyses (AFT, AHe & ZHe) and subsequent thermal modelling a protracted cooling history since Palaeozoic times can be revealed. This allows tracing back the thermal evolution of this area, long before initiation of the EARS, with the latter showing only minor effects on the cooling of the samples. Striking is the distinct cooling pattern within the Rwenzori Mts, where different blocks can be distinguished revealing

  7. Style of rifting and the stages of Pangea breakup (United States)

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


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

  8. Modeling the Sedimentary Infill of Lakes in the East African Rift: A Case Study of Multiple versus Single Rift Basin Segments (United States)

    Zhang, C.; Scholz, C. A.


    The sedimentary basins in the East African Rift are considered excellent modern examples for investigating sedimentary infilling and evolution of extensional systems. Some lakes in the western branch of the rift have formed within single-segment systems, and include Lake Albert and Lake Edward. The largest and oldest lakes developed within multi-segment systems, and these include Lake Tanganyika and Lake Malawi. This research aims to explore processes of erosion and sedimentary infilling of the catchment area in single-segment rift (SSR) and multi-segment rift (MSR) systems. We consider different conditions of regional precipitation and evaporation, and assess the resulting facies architecture through forward modeling, using state-of-the-art commercial basin modeling software. Dionisos is a three-dimensional numerical stratigraphic forward modeling software program, which simulates basin-scale sediment transport based on empirical water- and gravity-driven diffusion equations. It was classically used to quantify the sedimentary architecture and basin infilling of both marine siliciclastic and carbonate environments. However, we apply this approach to continental rift basin environments. In this research, two scenarios are developed, one for a MSR and the other for a SSR. The modeled systems simulate the ratio of drainage area and lake surface area observed in modern Lake Tanganyika and Lake Albert, which are examples of MSRs and SSRs, respectively. The main parameters, such as maximum subsidence rate, water- and gravity-driven diffusion coefficients, rainfall, and evaporation, are approximated using these real-world examples. The results of 5 million year model runs with 50,000 year time steps show that MSRs are characterized by a deep water lake with relatively modest sediment accumulation, while the SSRs are characterized by a nearly overfilled lake with shallow water depths and thick sediment accumulation. The preliminary modeling results conform to the features

  9. Transect across the West Antarctic rift system in the Ross Sea, Antarctica (United States)

    Trey, H.; Cooper, A. K.; Pellis, G.; Della, Vedova B.; Cochrane, G.; Brancolini, Giuliano; Makris, J.


    In 1994, the ACRUP (Antarctic Crustal Profile) project recorded a 670-km-long geophysical transect across the southern Ross Sea to study the velocity and density structure of the crust and uppermost mantle of the West Antarctic rift system. Ray-trace modeling of P- and S-waves recorded on 47 ocean bottom seismograph (OBS) records, with strong seismic arrivals from airgun shots to distances of up to 120 km, show that crustal velocities and geometries vary significantly along the transect. The three major sedimentary basins (early-rift grabens), the Victoria Land Basin, the Central Trough and the Eastern Basin are underlain by highly extended crust and shallow mantle (minimum depth of about 16 km). Beneath the adjacent basement highs, Coulman High and Central High, Moho deepens, and lies at a depth of 21 and 24 km, respectively. Crustal layers have P-wave velocities that range from 5.8 to 7.0 km/s and S-wave velocities from 3.6 to 4.2 km/s. A distinct reflection (PiP) is observed on numerous OBS from an intra-crustal boundary between the upper and lower crust at a depth of about 10 to 12 km. Local zones of high velocities and inferred high densities are observed and modeled in the crust under the axes of the three major sedimentary basins. These zones, which are also marked by positive gravity anomalies, may be places where mafic dikes and sills pervade the crust. We postulate that there has been differential crustal extension across the West Antarctic rift system, with greatest extension beneath the early-rift grabens. The large amount of crustal stretching below the major rift basins may reflect the existence of deep crustal suture zones which initiated in an early stage of the rifting, defined areas of crustal weakness and thereby enhanced stress focussing followed by intense crustal thinning in these areas. The ACRUP data are consistent with the prior concept that most extension and basin down-faulting occurred in the Ross Sea during late Mesozoic time, with

  10. Asymmetric rifting and structures of conjugated margins in the Tyrrhenian Sea (United States)

    Moeller, S.; Grevemeyer, I.; Berndt, C.; Klaeschen, D.; Ranero, C. R.; Sallares, V.; Zitellini, N.


    Stretching and thinning of the continental lithosphere leads to rifting and the formation of passive continental margins. However, there is a discrepancy between horizontal extension by faulting and vertical crustal thinning. Research is ongoing to investigate this relationship. The Tyrrhenian Sea is a young rift basin of Neogene age located in the Western Mediterranean. Here, it is assumed that rifting and opening of the basin commenced in the context of slab rollback during the closing of the Tethys oceanic lithosphere. The advantages of studying rift processes here are the conjugated margins which are very close to each other. We present results of an integrated reflection (MCS) and refraction/wide-angle seismic (WAS) profile crossing the North Tyrrhenian Sea along 41° N. The data of the 240 km geophysical profile were acquired in April and May of 2010 during the MEDOC-Cruise in a two-ship operation with the Spanish and Italian vessels Sarmiento de Gamboa and Urania. The basin is characterized by N-S elongated horst and graben structures indicating that the rifting occured in W-E direction. The depth-migrated MCS section shows a detailed image of the infill of these grabens and reveals buried blocks, normal listric faults and smaller detachments in the brittle upper crust to a depth of 5-6 km. Integrating drilling information of ODP leg 107, we identified Messinian synrift and Plio/Pleistocene postrift sediments to derive the chronological development of the Tyrrhenian Sea. The deep and thick Messinian evaporites near the Sardinian continental margin support the idea that this area marks the origin of rifting, subsidence and initial flooding. A comparison of crustal structures between the Sardinian and Campanian margins reveals significant differences in block size and in sedimentary thickness, which decreases from west to east. The horizontal extension in the West was accommodated by the formation of large horst and graben structures while extension in the

  11. The NE Rift of Tenerife: towards a model on the origin and evolution of ocean island rift


    Delcamp, A.; Troll, V.; S. Wiesmaier; R. Paris; Rodríguez González, A.; Pérez-Torrado, F. J.; Rodríguez Badiola, E.; Guillou, H.; Carracedo, J.C; Fernández-Turiel, J.L. (José Luis)


    The NE Rift of Tenerife is an excellent example of a persistent, recurrent rift, providing important evidence of the origin and dynamics of these major volcanic features. The rift developed in three successive, intense and relatively short eruptive stages (a few hundred ka), separated by longer periods of quiescence or reduced activity: A Miocene stage (7266 ± 156 ka), apparently extending the central Miocene shield of Tenerife towards the Anaga massif; an Upper Pliocene stage (2710 ± 58 ka) ...

  12. Is the Gop rift oceanic? A reevaluation of the Seychelles-India conjugate margins (United States)

    Guan, Huixin; Werner, Philippe; Geoffroy, Laurent


    Gop Rift axis. We propose that the conspicuous buoyant central part of the Gop Rift is likely associated with a continental C-Block as described in a recent paper on conjugated VPMs8, at least in the southern part of the Gop Rift. The crust below the Laxmi basin is probably transitional continental i.e. strongly intruded. West of India and west of the Laxmi Ridge, the transition to the Carlsberg Basin occurs along a clearly-expressed transform fault, not through an extended and thinned continental margin. We reinterpret the whole system based on those observations and propositions, giving some explanations on controversial magnetic anomalies based on similar observations from the southern Atlantic Ocean. 1: Collier et al., 2008. Age of the Seychelles-India break-up. Earth and Planetary Science Letters. 2: Minshull et al., 2008. The relationship between riftingand magmatism in the northeastern Arabian Sea. Nature Geoscience. 3 : Armitage et al., 2010. The importance of rift history for volcanic margin. Nature. 4 : Krishna et al., 2006. Nature of the crust in the Laxmi Basin (14 degrees-20 degrees N), western continental margin of India. Tectonics. 5 : Misra et al., 2015. Repeat ridge jumps and microcontinent separation: insights from NE Arabian Sea. Marine and Petroleum Geology. 6 : Biswas, 1982. Rift basins in the western margin of India and their hydrocarbon prospects. Bull. Am. Assoc. Pet. Geol. 7 : Chatterjee et al., 2013. The longest voyage: Tectonic, magmatic, and paleoclimatic evolution of the Indian plate during its northward flight from Gondwana to Asia. Gondwana Research. 8 : Geoffroy et al., 2015. Volcanic passive margins: anotherway to break up continents. Scientific Reports.

  13. Butterfly Species Richness in Selected West Albertine Rift Forests

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    Patrice Kasangaki


    Full Text Available The butterfly species richness of 17 forests located in the western arm of the Albertine Rift in Uganda was compared using cluster analysis and principal components analysis (PCA to assess similarities among the forests. The objective was to compare the butterfly species richness of the forests. A total of 630 butterfly species were collected in 5 main families. The different species fell into 7 ecological groupings with the closed forest group having the most species and the swamp/wetland group with the fewest number of species. Three clusters were obtained. The first cluster had forests characterized by relatively high altitude and low species richness despite the big area in the case of Rwenzori and being close to the supposed Pleistocene refugium. The second cluster had forests far away from the supposed refugium except Kisangi and moderate species richness with small areas, whereas the third cluster had those forests that were more disturbed, high species richness, and low altitudinal levels with big areas.

  14. af ar rift: discovery of a metallogenic province

    African Journals Online (AJOL)

    Rift Valley has caused hydrothermal activity, which is still active in several sites being investigated for geothermal energy. Extinct geothermal fields are also quite common. The possibility that these geothermal systems, related to the continental rifting, have been and may be ore-forming systems cannot be discarded a priori.

  15. 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

  16. 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 ce...

  17. Lithosphere Response to Intracratonic Rifting: Examples from Europe and Siberia

    DEFF Research Database (Denmark)

    Artemieva, I. M.; Thybo, H.; Herceg, M.


    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...


    African Journals Online (AJOL)


    ABSTRACT. The Tanzanian rift system salt lakes present significant cultural, ecological, recreational and economical values. Beyond the wealth of minerals, resources of these rift salt lakes include unique wildlife, for instance Lesser Flamingo (Phoenicopterus minor) and Cichlids (Alcolapia spp), which adapted chemically ...

  19. 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 ...

  20. New insights into continental rifting from a damage rheology modeling (United States)

    Lyakhovsky, Vladimir; Segev, Amit; Weinberger, Ram; Schattner, Uri


    Previous studies have discussed how tectonic processes could produce relative tension to initiate and propagate rift zones and estimated the magnitude of the rift-driving forces. Both analytic and semi-analytic models as well as numerical simulations assume that the tectonic force required to initiate rifting is available. However, Buck (2004, 2006) estimated the minimum tectonic force to allow passive rifting and concluded that the available forces are probably not large enough for rifting of thick and strong lithosphere in the absence of basaltic magmatism (the "Tectonic Force" Paradox). The integral of the yielding stress needed for rifting over the thickness of the normal or thicker continental lithosphere are well above the available tectonic forces and tectonic rifting cannot happen (Buck, 2006). This conclusion is based on the assumption that the tectonic stress has to overcome simultaneously the yielding stress over the whole lithosphere thickness and ignore gradual weakening of the brittle rocks under long-term loading. In this study we demonstrate that the rifting process under moderate tectonic stretching is feasible due to gradual weakening and "long-term memory" of the heavily fractured brittle rocks, which makes it significantly weaker than the surrounding intact rock. This process provides a possible solution for the tectonic force paradox. We address these questions utilizing 3-D lithosphere-scale numerical simulations of the plate motion and faulting process base on the damage mechanics. The 3-D modeled volume consists of three main lithospheric layers: an upper layer of weak sediments, middle layer of crystalline crust and lower layer of the lithosphere mantle. Results of the modeling demonstrate gradual formation of the rift zone in the continental lithosphere with the flat layered structure. Successive formation of the rift system and associated seismicity pattern strongly depend not only on the applied tectonic force, but also on the healing

  1. 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

  2. Seismicity of the rocky mountains and Rio Grande Rift from the EarthScope Transportable Array and CREST temporary seismic networks, 2008-2010 (United States)

    Nakai, J. S.; Sheehan, A. F.; Bilek, S. L.


    We developed a catalog of small magnitude (ML -0.1 to 4.7) seismicity across Colorado and New Mexico from the EarthScope USArray Transportable Array and CREST (Colorado Rocky Mountains Experiment and Seismic Transects) seismic networks from 2008 to 2010 to characterize active deformation in the Rio Grande Rift. We recorded over 900 earthquakes in the Rio Grande Rift region, not including induced earthquakes and mine blasts, and find that the rift is actively deforming both broadly and in distinct regions. Seismic events that are likely induced, mostly in the Raton Basin, make up 66% of the catalog (1837 earthquakes). Neogene faults in the northern rift in north central Colorado are seismically active in the North Park Basin and northwestern Colorado. The central rift from the San Luis Basin (southern Colorado) to south of the Socorro Magma Body is the most seismically active rift region, and seismicity delineates the deformation in the Colorado Plateau transition zone, which is spatially correlated with volcanic vents, dikes, and faults within the western Jemez Lineament. The eastern Jemez Lineament is nearly aseismic and surrounded by a halo of seismicity culminating in boundaries defined by recent moderate (Mw 3.9 and Mw 3.3) earthquakes. The southern rift is characterized by diffuse seismicity in Texas and Mexico. This study provides an updated seismic catalog built with uniformity in seismometer coverage and low epicentral uncertainties ( 2 km) that allows for regional evaluation of seismicity. During this time period, clusters of seismicity and moderate magnitude earthquakes characterize deformation in a low-strain rate extensional environment.

  3. Neogene deformation in the West Antarctic Rift in the McMurdo Sound region from studies of the ANDRILL and Cape Roberts drill cores (United States)

    Paulsen, T. S.; Wilson, T. J.; Jarrard, R. D.; Millan, C.; Saddler, D.; Läufer, A.; Pierdominici, S.


    Seismic studies indicate that the West Antarctic rift system records at least two distinct periods of Cenozoic rifting (Paleogene and Neogene) within the western Ross Sea. Natural fracture data from ANDRILL and Cape Roberts drill cores are revealing a picture of the geodynamic patterns associated with these rifting episodes. Kinematic indicators along faults recovered in drill cores document dominant normal faulting, although reverse and strike-slip faults are also present. Ongoing studies of mechanically twinned calcite in veins recovered in the drill cores yield predominantly vertical shortening strains with horizontal extension, consistent with a normal fault regime. In the Cape Roberts Project drill core, faults of inferred Oligocene age document a dominant NNE maximum horizontal stress associated with Paleogene rifting within the Victoria Land Basin. The NNE maximum horizontal stress at Cape Roberts is at an oblique angle to Transantarctic Mountain front, and consistent with previous interpretations invoking Cenozoic dextral transtensional shear along the boundary. In the ANDRILL SMS (AND-2A) drill core, faults and veins presumably associated with Neogene rifting document a dominant NNW to NE faulting of an expanded Lower Miocene section, although subsidiary WNW faulting is also present within the upper sections of oriented core. In the ANDRILL MIS (AND-1B) drill core, natural fractures are consistently present through the core below c. 450 mbsf, the estimated depth of the ‘B-clino’ seismic reflector. This is consistent with the presence of seismically-detectable faults below this horizon, which record the major faulting episode associated with Neogene rifting in the Terror Rift. Sedimentary intrusions and steep veins folded by compaction indicate that deformation occurred prior to complete lithification of the strata, suggesting that deformation was at least in part coeval with deposition. Faults and associated veins intersected in the AND-1B drill core

  4. A Blowing Snow Model for Ice Shelf Rifts (United States)

    Leonard, K. C.; Tremblay, L.; Macayeal, D. R.


    Ice melange (a mixture of snow, marine ice, and ice talus) may play various roles in the rates of propagation of iceberg-calving rifts through Antarctic ice shelves. This modeling study examines the role of windblown snow in the formation and maintenance of ice melange in the "nascent rift" in the Ross Ice Shelf (78 08'S, 178 29'W). The rift axis is perpendicular to the regional wind direction, allowing us to employ a two-dimensional blowing snow model. The Piektuk-Tuvaq blowing snow model (Dery and Tremblay, 2004) adapted the Piektuk blowing snow model for use in sea ice environments by including parameterization for open-water leads within the sea ice. This version of the model was used to study the initial conditions of a freshly-opened rift, as the input of blowing snow into the seawater within the rift promotes marine ice formation by cooling and freshening the surface water. We adapted the Piektuk-Tuvaq model both for the local climatic conditions and to incorporate the geometry of the rift, which is 30m deep and 100m wide (far deeper than a lead). We present the evolution of the topography within the rift for two cases. The first is an ice melange composed exclusively of snow and marine ice, the second uses an initial topography including large chunks of ice talus.

  5. Facies, stratal and stacking patterns of syn-rift sequences along present-day and fossil hyperextended rifted margins (United States)

    Ribes, Charlotte; Epin, Marie-Eva; Gillard, Morgane; Chenin, Pauline; Ghienne, Jean-Francois; Manatschal, Gianreto; Karner, Garry D.; Johnson, Christopher A.


    Research on the formation and evolution of deep-water rifted margins has undergone a major paradigm shift in recent years. An increasing number of studies of present-day and fossil rifted margins allows us to identify and characterize the architecture of hyperextended rifted margins. However, at present, little is known about the depositional environments, sedimentary facies and stacking and stratal patterns in syn-rift sequences within these domains. In this context, characterizing and understanding the spatial and temporal evolution of the stratal and stacking patterns is a new challenge. The syn-rift sequence at rifted margins is deposited during the initial stages of stretching to the onset of oceanic accretion and comprises pre-, syn- and post-kinematic deposits along the margin. A difficulty arises from the fact that the observed stratigraphic geometries and facies relationships result from the complex interplay between sediment supply and creation of accommodation, which in turn are controlled by regional synchronous events (i.e. crustal necking and onset of seafloor spreading) and diachronous events (i.e. migration of deformation during rifting, lags in sediment input to the distal margin). These parameters are poorly constrained in hyperextended rift systems. Indeed, the complex structural evolution of hyperextended systems include an evolution from initially distributed to localized extension (i.e. necking) and the development of poly-phase in-sequence and/or out of sequence extensional faulting associated with mantle exhumation and magmatic activity. This multiphase structural evolution can generate complex accommodation patterns over a highly structured top basement but can only be recognized if there is sufficient sediment input to record the events. In our presentation, we show preliminary results for fossil Alpine Tethys margins exposed in the Alps and seismic examples of the present-day deep water rifted margins offshore Australian-Antarctica, East

  6. An epidemiological model of Rift Valley fever

    Directory of Open Access Journals (Sweden)

    Nicole P. Leahy


    Full Text Available We present and explore a novel mathematical model of the epidemiology of Rift Valley Fever (RVF. RVF is an Old World, mosquito-borne disease affecting both livestock and humans. The model is an ordinary differential equation model for two populations of mosquito species, those that can transmit vertically and those that cannot, and for one livestock population. We analyze the model to find the stability of the disease-free equlibrium and test which model parameters affect this stability most significantly. This model is the basis for future research into the predication of future outbreaks in the Old World and the assessment of the threat of introduction into the New World.

  7. 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

  8. 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

  9. A Statistical Model of Rift Valley Fever Activity in Egypt

    National Research Council Canada - National Science Library

    John M. Drake; Ali N. Hassan; John C. Beier


    Rift Valley fever (RVF) is a viral disease of animals and humans and a global public health concern due to its ecological plasticity, adaptivity, and potential for spread to countries with a temperate climate...

  10. Metallogeny of the midcontinent rift system of North America (United States)

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


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

  11. 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.


    The Cretaceous-Tertiary northwest-trending Sirt Basin system, Libya, is a rift/sag basin formed on Pan-African to Paleozoic-aged basement of North Africa. In this study, we investigate the rift-basin architecture and tectonic framework of the western Sirt Basin. Using remote sensed data, supported by borehole data from about 300 deep wells and surface geologic maps, we constructed geological cross sections and surface geology maps. Indication of the relative timing of structures and movement along faults has been determined where possible. Direction statistics for all the interpreted linear features acquired in the study area were calculated and given as a total distribution and then the totals are broken down by the major basin elements of the area. Hundreds of lineaments were recognized. Their lengths, range between a hundred meters up to hundreds of kilometers and the longest of the dominant trends are between N35W-N55W and between N55E-N65E which coincides with Sirt Basin structures. The produced rose diagrams reveal that the majority of the surface linear features in the region have four preferred orientations: N40-50W in the Zallah Trough, N45-55W in the Dur al Abd Trough, N35-55W in the Az Zahrah-Al Hufrah Platform, and in contrast in the Waddan Uplift a N55-65E trend. We recognize six lithostratigraphic sequences (phases) in the area's stratigraphic framework. A Pre-graben (Pre-rift) initiation stage involved the Pre-Cretaceous sediments formed before the main Sirt Basin subsidence. Then followed a Cretaceous to Eocene graben-fill stage that can divided into four structurally-active and structurally-inactive periods, and finally a terminal continental siliciclastics-rich package representing the post-rift stage of the development in post-Eocene time. In general five major fault systems dissect and divide the study area into geomorphological elevated blocks and depressions. Most of the oil fields present in the study area are associated with structural hinge

  12. Tracing the exhumation history of the Rwenzori Mountains, Albertine Rift, Uganda, using low-temperature thermochronology (United States)

    Bauer, Friederike U.; Glasmacher, Ulrich A.; Ring, Uwe; Karl, Markus; Schumann, Andreas; Nagudi, Betty


    The Rwenzori Mtns form a striking feature within the Albertine Rift of the East African Rift System. They are made up of a dissected Precambrian metamorphic basement block reaching heights of more than 5 km. Applying low-temperature thermochronology a complex exhumation history becomes evident, where rock and surface uplift can be traced from Palaeozoic to Neogene times. Fission-track and (U-Th-Sm)/He cooling ages and derived cooling histories allow distinguishing different blocks in the Rwenzori Mtns. In the central part a northern and a southern block are separated by a putative NW-SE trending fault; with the northern block showing distinctly younger apatite fission-track ages (~ 130 Ma) than the southern block (~ 300 Ma). Cooling ages in both blocks do not vary significantly with elevation, despite considerable differences in elevation. Thermal history modelling reflects protracted cooling histories. Modelled t-T paths show decoupled blocks that were relocated separately along distinct fault planes, which reactivated pre-existing structures, inherited from Palaeozoic folding and thrusting. Initial cooling affected the Rwenzori area in Silurian to Devonian times, followed by Mesozoic and Cainozoic cooling events. Pre-Neogene evolution seems to be triggered by tectonic processes like the opening of the Indian Ocean and the south Atlantic. From thermochronological data the formation of a Mesozoic "Albertine high" is conceivable. In Cainozoic times the area was affected by rifting, resulting in differentiated surface uplift. Along the western flank of the Rwenzori Mtns, surface uplift was more pronounced. This is also reflected in their recent topography, formed by accelerated rock uplift in the near past (Pliocene to Pleistocene). Erosion could not compensate for this most recent uplift, resulting in apatite He ages of Oligocene to Miocene age or even older.

  13. 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

    fragments of an active margin'. This chapter uses a panoply of geochronological (U-Pb zircon) and geochemical (Lu-Hf and Sm-Nd isotopes, trace/REEs, and major elements) tools to investigate the origin the major lithostratigraphic units in the Woodlark Rift. Important findings in this chapter include the establishment of a tectonic link between sialic metamorphic rocks in the Woodlark Rift and the remnants of a Late Cretaceous aged bi-modal volcanic province along Australia's northern Queensland coast. This link is important because it identifies another rifted fragment of the former Australian continental margin in Gondwana, and demonstrates the complexity of recognizing the dispersed fragments of active margins. Another important finding of this chapter is that Quaternary aged high silica rhyolites erupted in the western Woodlark Rift have mantle isotopic and geochemical signatures, and are therefore not the extrusive equivalents of partially melted metamorphic rocks found in the lower plates of large metamorphic core complexes. This is important because it signifies that lithospheric rupture has already occurred, despite the fact that mid-ocean ridge basalts are not yet being erupted and there are still topographically prominent metamorphic core complexes in the region. This chapter is not yet published, but is being prepared for submission to Gondwana Research. The third chapter is entitled 'Zircon growth in rapidly evolving plate boundary zones: Evidence from the active Woodlark Rift of Papua New Guinea'. The original purpose of this chapter was simply to use U-Pb dating of zircons from felsic and intermediate gneisses in the Woodlark Rift to understand the history of rocks from (U)HP terranes that don't preserve the (U)HP metamorphic paragenesis. It was soon realized that the types of U-Pb zircon analyses typically performed on a SIMS instrument were going to be insufficient to fully understand the geochemical and geochronological records within zircons from these

  14. 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...

  15. Control of rift asymmetry and segmentation on the thermal architecture of hyperextended rift systems: insights from Pyrenean field observations and numerical modelling (United States)

    Lescoutre, Rodolphe; Tugend, Julie; Brune, Sascha; Manatschal, Gianreto


    Mid-Cretaceous rift basins are exposed in the Pyrenees providing key information on rifted domain formation that is not available at present-day rift system. Substantial paleotemperature and thermochronological data have been collected and published in numerous recent papers. These data show a strong heterogeneity in the distribution of peak temperatures within the Cretaceous rift basins. Locations that experienced relatively high or low temperatures appear to cluster in specific areas along strike. These areas have been interpreted as either reflecting hot and cold conditions during rifting, or alternatively, a change in the polarity of a strongly asymmetric rift systems. In this study, we test if the observed variability of peak temperatures can be explained by segmentation and a change in polarity of an asymmetrical upper/lower plate rift model. To this aim we restore the observed syn- to early post-rift peak temperatures to their paleo-location within sections across the evolving rift system. In the meantime, we conduct numerical models of rift migration leading to asymmetrical extension that are benchmarked with geological and geophysical observations from the Pyrenees. From the models, we extract thermal information at different stages of rifting that are finally compared to the thermal data from the Pyrenean Cretaceous rift basins. This work employs a novel approach by comparing thermal output from numerical modelling with the distribution of peak temperatures and thermal gradient from field data. As such, these results may have substantial implications to further understand the pre-orogenic thermal evolution of the Pyrenean rift system and the role of segmentation. More generally, the results of this work may unravel the role of rift asymmetry and segmentation on the thermal architecture of hyperextended rift basins and margins.

  16. 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.

  17. Baikal rift basement: structure and tectonic evolution

    Energy Technology Data Exchange (ETDEWEB)

    Melnikov, A.I.; Mazukabzov, A.M.; Sklyarov, E.V.; Vasiljev, E.P. (AN SSSR, Irkutsk (Russian Federation). Sibirskij Ehnergeticheskij Inst.)


    The Baikal rift zone in East Siberia has, due to its very long history, starting in the Early Precambrian and continuing into the Cenozoic, an heterogeneous structure. Two major structural elements are distinguished: the Siberian craton and the Sayan-Baikal fold system, which is part of the Central Asian Fold Belt. Within the craton, the following units are recognized: the Early Precambrian metamorphic rocks of the basement, the Vendian-Paleozoic sedimentary cover with superimposed Paleozoic and Mesozoic basins and a reworked margin which is transitional between the craton and the fold belt. The Sayan-Baikal fold system comprises the Barguzin, Tuva-Mongolian and Dzhida terranes. The Barguzin and Tuva-Mongolian terranes are composite, consisting of separate Early Precambrian massifs, volcanic-sedimentary and carbonate Phanerozoic terranes, impregnated by granites. They are thus super-terranes. The oldest units are ophiolites, dated around 1.1 - 1.3 Gy in the Barguzin terrane and 0.9 - 1.1 Gy in the Tuva-Mongolian terrane. They associate with complexes of immature island-arc accretionary wedges of mainly terrigenous or terrigeno-volcanic composition with occasional slices of ophiolite and glaucophane schists. (authors). 68 refs., 12 figs., 2 tabs.

  18. The role of inherited rifted lithospheric structure on middle Cretaceous orogeny and Tertiary-present extension, North American Cordillera (United States)

    Tikoff, Basil; Kelso, Paul; Fayon, Annia; Gaschnig, Richard; Vervoort, Jeff; Stetson-Lee, Tor; Byerly, Ad


    While the Eastern North American margin exhibits evidence of the rifted margin on subsequent deformation, this record is more obscure along the western Cordilleran margin. We recently conducted paleomagnetic and geochronologic analyses along the abrupt, boundary between cratonic North American and accreted terranes in Idaho. In this location, the abrupt boundary is designated by geochemical gradients (Sr, Nd, O) that are spatially coincident with major, regional-scale (western Idaho, Ahsahka) shear zones. The boundary is oriented NS in central-southern Idaho, and then abruptly changes 90° near Orofino, ID, to become EW oriented. Recent paleomagnetic data indicates that 30° clockwise rotation of the entire margin occurred post 85 Ma. Reconstruction of this rotation orients the margins at 060 (transform) and 330 (extensional), parallel to the inferred orientation of the Precambrian rifted margin elsewhere in the US Cordillera. The geometry would cause a structural syntaxis during northward (right-lateral) translation of accreted terranes. Northward terrane motion at 100 Ma result in dextral transpressional kinematics along the 330-oriented western Idaho shear zone and contractional deformation in the EW-oriented Ahsahka shear zone (Cretaceous orientations) in this syntaxis. This middle Cretaceous orogeny occurs at the other major structural syntaxis, south of the Sierra Nevada batholith in southeastern California, as a result of a 100 Ma worldwide plate re-organization. The Idaho syntaxis also acts as a fulcrum for Tertiary-present rotation, explaining the current displacement field in the northern US Cordillera. Overall, the study indicates that the inherited Precambrian rifted margin of the North American Cordillera exhibited a significant influence on subsequent deformation, despite overprinting of abundant magmatism, margin parallel terrane translation, and subsequent rotation.

  19. Active fault systems of the Kivu rift and Virunga volcanic province, and implications for geohazards (United States)

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


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

  20. Strain Localisation at Rift Segment Boundaries: An Example from the Bocana Transfer Zone in Central Baja California, Mexico (United States)

    Seiler, C.; Gleadow, A. J.; Kohn, B. P.


    Rifts are commonly segmented into several hundred kilometre long zones of opposing upper-plate transport direction with boundaries defined by accommodation and transfer zones. A number of such rift segments have been recognized in the northern Gulf of California, a youthful oceanic basin that is currently undergoing the rift-drift transition. However, detailed field studies have so far failed to identify suitable structures that could accommodate the obvious deformation gradients between different rift segments, and the nature of strain transfer at segment boundaries remains enigmatic. The situation is even less clear in central and southern Baja California, where a number of rift segments have been hypothesized but it is unknown whether the intervening segment boundaries facilitate true reversals in the upper-plate transport direction, or whether they simply accommodate differences in the timing, style or magnitude of deformation. The Bocana transfer zone (BTZ) in central Baja California is a linear, WNW-ESE striking structural discontinuity separating two rift segments with different magnitudes and styles of extensional deformation. North of the BTZ, the Libertad fault is part of the Main Gulf Escarpment, which represents the breakaway fault that separates the Gulf of California rift to the east from the relatively stable western portion of the Baja peninsula. The N-striking Libertad escarpment developed during the Late Miocene (~10-8Ma) and exhibits a topographic relief of ca. 1,000m along a strike-length of ca. 50km. Finite displacement decreases from ~1000m in the central fault segment to ~500m further south, where the fault bends SE and merges with the BTZ. In the hanging wall of the Libertad fault, a series of W-tilted horsts are bound along their eastern margins by two moderate-displacement E-dipping normal faults. South of the BTZ, extension was much less than further north, which explains the comparatively subdued relief and generally shallower tilt of

  1. Secular and tidal strain across the Main Ethiopian Rift (United States)

    Bilham, Roger; Bendick, R.; Larson, K.; Mohr, P.; Braun, J.; Tesfaye, S.; Asfaw, L.

    Using a combination of laser ranging and GPS data acquired between 1969 and 1997 we derive a separation velocity for the Somali and Nubian plates in Ethiopia (4.5±1 mm/yr at N108±10E). This vector is orthogonal to the NNE-trending neotectonic axis (Wonji fault belt) of the Ethiopian rift axis. Current rifting is concentrated within a 33-km-wide zone that includes a 7-km-wide belt of late Quaternary faulting where maximum surface strain rates are comparable to those at active plate boundaries (0.1 μstrain/yr). The strain-field suggests that thin (<5 km) elastic crust separates thick continental lithosphere, a geometry quite different from oceanic rifting, and a mechanical configuration that favors the amplification of regional strain. Semidiurnal strain tides, however, as measured by kinematic GPS methods are not amplified along or across the rift, indicating that the rift zone's low rigidity applies only at periods of years.

  2. 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

  3. 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

  4. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Cunningham, A.C.; Armentrout, J.M.; Prebish, M. [Mobil Oil Corp., Dallas, TX (United States)] [and others


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

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

    Energy Technology Data Exchange (ETDEWEB)

    Cunningham, A.C.; Armentrout, J.M.; Prebish, M. (Mobil Oil Corp., Dallas, TX (United States)) (and others)


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

  7. US-Africa collaborative research on incipient continental rift zones (United States)

    Atekwana, E. A.


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

  8. Some characteristics of the seismicity and the stress field in the Panxi rift zone (United States)

    Zheng, Jian-Zhong; Xu, Wen-Yue; Liu, Jin; Zou, Ying


    Some characteristics of the horizontal distribution of the earthquakes, the focus depth distribution, distribution of the earthquakes with time, b-values, fault slip rates and stress field in the Panxi rift zone have been investigated. The results are as follows: (1) Earthquakes with M ⩾ 4.7 occurred mainly along the major faults in the Panxi rift zone. Earthquake activity is greater along the sides of the Panxi rift zone than along its axis. Earthquakes with M ⩾ 6 occurred along the bounding faults of the Panxi rift zone. The small earthquakes exhibit a random distribution. (2) The focal depths along the axis of the Panxi rift zone are shallow (5-20 km), but the focal depths outside the rift zone are deeper (6-40 km). (3) The b-values in the Panxi rift zone are 0.58-0.75. (4) The correlation of the seismicity between the Panxi rift zone and the eastern India-Eurasian collision zone is high. (5) The fault planes in the Panxi rift zone are nearly vertical and strike-slip. The fault slip rates in the Panxi rift zone are 0.13-0.19 cm/yr. (6) The maximum principal compressive stress axis in the Panxi rift zone is nearly horizontal, NNW-SSE in direction. According to the above results, a dynamic model for the aborting process of the Panxi rift zone is suggested.

  9. Western Sufism

    DEFF Research Database (Denmark)

    Sedgwick, Mark

    Western Sufism is sometimes dismissed as a relatively recent "new age" phenomenon, but in this book, Mark Sedgwick argues that it actually has very deep roots, both in the Muslim world and in the West. In fact, although the first significant Western Sufi organization was not established until 1915...... to the internet, Mark Sedgwick demonstrates that the phenomenon of Western Sufism not only draws on centuries of intercultural transfers, but is also part of a long-established relationship between Western thought and Islam that can be productive, not confrontational....

  10. 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

  11. 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, ...

  12. Pediatric Burns at The Rift Valley Provincial General Hospital ...

    African Journals Online (AJOL)

    surgical/female burn ward were eligible. On average the ward admits 680 patients a year out of which 170 pa- tients (25.7 %) are due to pediatric burns. The Hospital attracts patients mostly from low socioeconomic status. Pediatric Burns at The Rift Valley. Provincial General Hospital, Nakuru,. Kenya. Author: Oduor P.R. ...

  13. 3-D Numerical Stratigraphic Forward Modeling of Rifts (United States)

    Lovely, P. J.; Harris, A.; Baumgardner, S. E.; Engelder, T.; Sun, T.; Lyons, R. P.; Granjeon, D.


    Continental rifts are of great interest and relevance to scientists and the general public because they contain numerous depositional environments at relatively compressed spatiotemporal scales, continuous climate records, and hydrocarbon resources. The interaction of climate, sediment routing, and tectonism controls the distribution and continuity of the depositional environments, but these relationships are nonlinear and complex. Conceptual stratigraphic models provide useful insight into facies distribution but are typically qualitative and may not capture the full range of geologically plausible scenarios generated by these interactions. Here, we use a numerical forward stratigraphic model to demonstrate that a deterministic, nonlinear diffusion-based sediment transport model can approximate key tectonostratigraphic processes interpreted from continental rift systems. The sediment transport model acts upon a simple elastic tectonic model that approximates appropriate distributions of subsidence and uplift associated with a schematic fault architecture typical of early stage continental rifting. Comparison of model results to observations of outcrops and the subsurface demonstrates the model's ability to reproduce key tectonostratigraphic features. We also show that such a model may be used to analyze the sensitivity of sand distributions to base-level, sediment, and water flux changes. We present an example analysis with a suite of metrics such as sand thickness, net-to-gross, and mass extraction methods that quantitatively describe the deposits that result from various inputs. This simple sensitivity analysis can be conducted by academic and industry groups to better characterize facies distribution or quantify uncertainties associated with continental rifts.

  14. Fluoride Contamination in Drinking Water in the Rift Valley, Kenya ...

    African Journals Online (AJOL)

    A survey of the amount of Fluoride in ground, potable water in Njoro division, Nakuru district and some parts outside the division was conducted to determine the concentration of Fluoride the residents are consuming through water. This area is situated in the Great Rift Valley of East Africa, which is known to have high levels ...

  15. Three-dimensional frictional plastic strain partitioning during oblique rifting (United States)

    Duclaux, Guillaume; Huismans, Ritske S.; May, Dave


    Throughout the Wilson cycle the obliquity between lithospheric plate motion direction and nascent or existing plate boundaries prompts the development of intricate three-dimensional tectonic systems. Where oblique divergence dominates, as in the vast majority of continental rift and incipient oceanic domains, deformation is typically transtensional and large stretching in the brittle upper crust is primarily achieved by the accumulation of displacement on fault networks of various complexity. In continental rift depressions such faults are initially distributed over tens to hundreds of kilometer-wide regions, which can ultimately stretch and evolve into passive margins. Here, we use high-resolution 3D thermo-mechanical finite element models to investigate the relative timing and distribution of localised frictional plastic deformation in the upper crust during oblique rift development in a simplified layered lithosphere. We vary the orientation of a wide oblique heterogeneous weak zone (representing a pre-existing geologic feature like a past orogenic domain), and test the sensitivity of the shear zones orientation to a range of noise distribution. These models allow us to assess the importance of material heterogeneities for controlling the spatio-temporal shear zones distribution in the upper crust during oblique rifting, and to discuss the underlying controls governing oblique continental breakup.

  16. 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)

  17. 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...

  18. Rift Valley fever Entomology, Ecology, and Outbreak Risk Factors (United States)

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

  19. 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...

  20. East Antarctic rifting triggers uplift of the Gamburtsev Mountains. (United States)

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


    The Gamburtsev Subglacial Mountains are the least understood tectonic feature on Earth, because they are completely hidden beneath the East Antarctic Ice Sheet. Their high elevation and youthful Alpine topography, combined with their location on the East Antarctic craton, creates a paradox that has puzzled researchers since the mountains were discovered in 1958. The preservation of Alpine topography in the Gamburtsevs may reflect extremely low long-term erosion rates beneath the ice sheet, but the mountains' origin remains problematic. Here we present the first comprehensive view of the crustal architecture and uplift mechanisms for the Gamburtsevs, derived from radar, gravity and magnetic data. The geophysical data define a 2,500-km-long rift system in East Antarctica surrounding the Gamburtsevs, and a thick crustal root beneath the range. We propose that the root formed during the Proterozoic assembly of interior East Antarctica (possibly about 1 Gyr ago), was preserved as in some old orogens and was rejuvenated during much later Permian (roughly 250 Myr ago) and Cretaceous (roughly 100 Myr ago) rifting. Much like East Africa, the interior of East Antarctica is a mosaic of Precambrian provinces affected by rifting processes. Our models show that the combination of rift-flank uplift, root buoyancy and the isostatic response to fluvial and glacial erosion explains the high elevation and relief of the Gamburtsevs. The evolution of the Gamburtsevs demonstrates that rifting and preserved orogenic roots can produce broad regions of high topography in continental interiors without significantly modifying the underlying Precambrian lithosphere. © 2011 Macmillan Publishers Limited. All rights reserved

  1. Magma ascent and emplacement in a continental rift setting: lessons from alkaline complexes in active and ancient rift zones (United States)

    Hutchison, William; Lloyd, Ryan; Birhanu, Yelebe; Biggs, Juliet; Mather, Tamsin; Pyle, David; Lewi, Elias; Yirgu, Gezahgen; Finch, Adrian


    A key feature of continental rift evolution is the development of large chemically-evolved alkaline magmatic systems in the shallow crust. At active alkaline systems, for example in the East African Rift, the volcanic complexes pose significant hazards to local populations but can also sustain major geothermal resources. In ancient rifts, for example the Gardar province in Southern Greenland, these alkaline magma bodies can host some of the world's largest rare element deposits in resources such as rare earths, niobium and tantalum. Despite their significance, there are major uncertainties about how such magmas are emplaced, the mechanisms that trigger eruptions and the magmatic and hydrothermal processes that generate geothermal and mineral resources. Here we compare observations from active caldera volcanoes in the Ethiopian Rift with compositionally equivalent ancient (1300-1100 Ma) plutonic systems in the Gardar Rift province (Greenland). In the Ethiopian Rift Valley we use InSAR and GPS data to evaluate the temporal and spatial evolution of ground deformation at Aluto and Corbetti calderas. We show that unrest at Aluto is characterized by short (3-6 month) accelerating uplift pulses likely caused by magmatic fluid intrusion at 5 km. At Corbetti, uplift is steady ( 6.6 cm/yr) and sustained over many years with analytical source models suggesting deformation is linked to sill intrusion at depths of 7 km. To evaluate the validity of these contrasting deformation mechanisms (i.e. magmatic fluid intrusion and sill emplacement) we carried out extensive field, structural and geochemical analysis in the roof zones of two alkaline plutons (Ilímaussaq and Motzfeldt) in Greenland. Our results show that the volatile contents (F, Cl, OH and S) of these magmas were exceptionally high and that there is evidence for ponding of magmatic fluids in the roof zone of the magma reservoir. We also identified extensive sill networks at the contact between the magma reservoir and the

  2. The timing of uplift, volcanism, and rifting peripheral to the Red Sea: A case for passive rifting? (United States)

    Bohannon, Robert G.; Naeser, Charles W.; Schmidt, Dwight L.; Zimmermann, Robert A.


    Prior to the formation of the Red Sea the northeastern Afro/Arabian continent had low relief and was largely below sea level from the Late Cretaceous to the early Oligocene. The events leading to the formation of the Red Sea followed the sequence (1) alkaline volcanism and rifting beginning about 30-32 Ma affecting a narrow linear zone in the continent, (2) rotational block faulting and detachment faulting, well underway by 25 Ma, (3) gabbro and diorite magmatism, andesite to rhyolite volcanism, and fine-grained nonmarine sedimentation in the rift between 20 and 25 Ma, (4) fine-grained marine sedimentation in the rift as the early shelves started to subside in the middle Miocene, and (5) uplift of the adjacent continents (about 3 km) and subsidence of the shelves (about 4 km) between 13.8 and 5 Ma. The youth of the uplift is suggested by 44 fission track dates on apatites from rocks of the Proterozoic Arabian Shield that range in age from 13.8 to 568 Ma. The youngest of these ages, coupled with the present high relief along the Arabian escarpment and published heat flow measurements, indicate that 2.5-4 km uplift has occurred in the last 13.8 m.y. The sequence volcanism/rifting followed by uplift leads to our adoption of a passive mantle model for rift origin. Models that require uplift to create the rift are rejected, because of the late uplift. We advocate a model of lithospheric extension caused by two-dimensional plate stress over those requiring tractional drag at the base of the lithosphere caused by vigorous flow in the asthenosphere. It is acknowledged that traction models could explain the observed data, but they imply a rigid, static lithosphere and seem to require a link between the direction of flow in the asthenosphere and plate motions. Neither requirement is necessary in the extension model. The rift starts with mechanical extension in a narrow zone of lithosphere between 25-32 Ma in our model. The thinned lithosphere is replaced by upwelling

  3. Petrogenesis of lamprophyres from Chhota Udepur area, Narmada rift zone, and its relation to Deccan magmatism (United States)

    Chalapathi Rao, N. V.; Dharma Rao, C. V.; Das, Sanjay


    Geological setting, petrology and geochemistry of a new find of lamprophyre dykes, intruding the Precambrian basement gneisses from the Chhota Udepur area, Narmada rift zone, Western India, are presented. Of the three lamprophyre dykes, two of them display E-W trend paralleling that of the Narmada rift, extend up to ˜2.5 km in length and constitute the longest yet recorded lamprophyre dykes from the Indian shield. The Chhota Udepur lamprophyres (CUL) show several overlapping mineralogical and geochemical characteristic features displayed by alkaline- and calc-alkaline lamprophyres and hence it is not straight forward to pigeon-hole them in existing lamprophyre classification schemes. They are porphyritic-panidiomorphic with euhedral to sub-hedral phenocrysts and microphenocrysts of olivine (Fo 78.33-78.42 Fa 21.24-21.37), diopsidic augite to titaniferous augite (Wo 54.83-59.03 En 36.75-41.36 Fs 0.1-5.66), biotite and amphibole (kaersutite). Feldspar (orthoclase perthite and plagioclase) is essentially confined to the groundmass along with accessory phases such as apatite and spinel (ti-magnetite). Rare carbonate ocelli are also present. In terms of major element geochemistry the CUL are nepeheline-normative and predominantly sodic (Na 2O > K 2O); yet their K 2O and SiO 2 contents are sufficiently high to signal traits of calc-alkaline lamprophyres. On the other hand, the CUL exclude negative spikes at Nb-Ta which are considered to be a characteristic of subduction-related (calc-alkaline) magmas, are highly evolved (Mg#: 27.82-55.45), enriched in incompatible trace elements (high La/Nb, Zr/Nb) and have fractionated REE distribution patterns (La/Yb N ratios: 35-44). Post-emplacement alteration and crustal contamination have had little influence on their geochemistry. Th/Yb, Ta/Yb, Nb/U and Ce/Pb ratios of the CUL imply an OIB type-enriched mantle source, similar to that displayed by other Deccan-related lamprophyres. A metasomatised (enriched) garnet lherzolite

  4. Geochronological and geochemical assessment of Cenozoic volcanism from the Terror Rift region of the West Antarctic Rift System (United States)

    Rilling, Sarah E.

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


    Directory of Open Access Journals (Sweden)

    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.

  6. Post-rift unroofing of the NW Africa passive continental margin during the Central Atlantic opening (United States)

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


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

  7. Comparative riftology: insights from crustal structure into the evolution of continental rifts and passive continental margins (United States)

    Kley, Jonas; Stein, Carol; Stein, Seth; Keller, Randy; Wysession, Michael; Frederiksen, Andrew


    Continental rifts evolve to seafloor spreading and are preserved in passive margins, or fail and remain as fossil features in continents. Rifts at different stages give insight into these different evolutionary paths. Of particular interest is how volcanic passive margins evolve. These features are characterized by sequences of volcanic rocks yielding magnetic anomalies landward of and sometimes larger than the oldest spreading anomalies. Seaward-dipping reflectors (SDR) occur in stretched continental crust landward of the oldest oceanic crust and are underplated by high-velocity lower crustal bodies. How and when these features form remains unclear. Insights are given by the Midcontinent Rift (MCR), formed by 1.1 Ga rifting of Amazonia from Laurentia, that failed once seafloor spreading was established elsewhere. MCR volcanics are much thicker than other continental flood basalts, due to deposition in a narrow rift rather than a broad region, giving a rift's geometry but a LIP's magma volume. The MCR provides a snapshot of the deposition of a thick highly magnetized volcanic section during rifting. Surface exposures and seismic-reflection data in and near Lake Superior show a rift basin filled by inward-dipping flood basalt layers. Had the rift evolved to seafloor spreading, the basin would have split into two sets of volcanics with opposite-facing SDRs, each with a strong magnetic anomaly. Because the rift formed as a series of alternating half-grabens, structural asymmetries between conjugate margins can naturally occur. Hence the MCR shows that many features form prior to breakup. Because the MCR was massively inverted by regional compression long after it failed and was uplifted, its structure is better known than failed rifts that incurred lesser degrees of inversion. It provides an end member for the evolution of actively extending rifts, characterized by upwelling mantle and negative gravity anomalies, in contrast to failed and inverted rifts without

  8. The formation of the south-eastern part of the Dniepr-Donets Basin: 2-D forward and reverse syn-rift and post-rift modelling.

    NARCIS (Netherlands)

    Stovba, S.M.; Maystrenko, Yu.; Stephenson, R.A.; Kusznir, N.J.


    Forward and reverse modelling of structure and stratigraphy has been used to investigate the syn-rift (Late Devonian) and early post-rift (Carboniferous) evolution of the south-eastern part of the Dniepr-Donets Basin (DDB). Modelling was carried out with and without taking into consideration the

  9. No Moho uplift below the Baikal Rift Zone

    DEFF Research Database (Denmark)

    Nielsen, Christoffer; Thybo, Hans


    The late Cenozoic Baikal Rift Zone (BRZ) in southern Siberia is composed of several individual topographic depressions and half grabens with the deep Lake Baikal at its center. We have modeled the seismic velocity structure of the crust and uppermost mantle along a 360 km long profile of the Baikal.......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...

  10. Crustal structure on the northeastern flank of the Kenya rift (United States)

    Prodehl, C.; Jacob, A. W. B.; Thybo, H.; Dindi, E.; Stangl, R.


    The KRISP flank line E converges with the Kenya rift at an angle of about 45° and is approximately parallel to the older Anza graben to the north. The depth to the basement is almost zero along the entire onshore part of the profile with higher velocities at the southeastern end indicative of extensive Precambrian gabbroic intrusions in the upper crust. The Moho shallows steadily from about 35 km at the southeastern end of the profile to about 24 km under Lake Turkana. Even though the Moho rises fairly steadily, there is significant heterogeneity in the crust above it. This shows that the extension is unevenly distributed between the upper and the lower crust. The Moho is laminated and variably reflective. Compared to the KRISP cross-line D further south, the crust is unexpectedly thin and shows extension increasing in a northerly direction. This extension is probably not associated with the Anza and Kenya rifting but with the profile's position on the slope of the Kenya dome. The indications are that there is a relatively abrupt change to a 20-km Moho depth near the Lake Turkana Central shotpoint. This change to a mid-rift crustal thickness occurs not at the postulated margin at the southeastern shore of Lake Turkana but at least 50 km further to the northwest. We suggest that the position of this margin may need to be redefined. The P n velocity is quite high at 8.1 km/s. This may indicate either a cold upper mantle or anisotropy. An upper-mantle reflector has been identified between 15 and 20 km below the Moho. It dips gently away from the rift.

  11. 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.

  12. Geophysical exploration of the Boku geothermal area, Central Ethiopian Rift

    Energy Technology Data Exchange (ETDEWEB)

    Abiye, Tamiru A. [School of Geosciences, Faculty of Science, University of the Witwatersrand, Private Bag X3, P.O. Box Wits, 2050 Johannesburg (South Africa); Tigistu Haile [Department of Geology and Geophysics, Addis Ababa University, P.O. Box 1176, Addis Ababa (Ethiopia)


    The Boku central volcano is located within the axial zone of the Central Ethiopian Rift near the town of Nazareth, Ethiopia. An integrated geophysical survey involving thermal, magnetic, electrical and gravimetric methods has been carried out over the Boku geothermal area in order to understand the circulation of fluids in the subsurface, and to localize the 'hot spot' providing heat to the downward migrating groundwaters before they return to the surface. The aim of the investigations was to reconstruct the geometry of the aquifers and the fluid flow paths in the Boku geothermal system, the country's least studied. Geological studies show that it taps heat from the shallow acidic Quaternary volcanic rocks of the Rift floor. The aquifer system is hosted in Quaternary Rift floor ignimbrites that are intensively fractured and receive regional meteoric water recharge from the adjacent escarpment and locally from precipitation and the Awash River. Geophysical surveys have mapped Quaternary faults that are the major geologic structures that allow the ascent of the hotter fluids towards the surface, as well as the cold-water recharge of the geothermal system. The shallow aquifers are mapped, preferred borehole sites for the extraction of thermal fluids are delineated and the depths to deeper thermal aquifers are estimated. (author)

  13. Basement rift control on oil production in eastern Kansas

    Energy Technology Data Exchange (ETDEWEB)

    Gustavson, J.B.


    Improved understanding of the central North American rift system (CNARS) offers a new interpretation of the basement structure in certain parts of the Mid-Continent. In eastern Kansas, basement structure can be shown to control oil production from some producing fields. Structural control includes rotated blocks along faults created by horst and graben tectonics typically associated with rift zones. A distinctive gravity signature, the Mid-Continent geophysical anomaly (MGA) is related directly to the CNARS and provides good data for interpretation of the basement structure. Some oil fields can be correlated directly with gravity-interpreted basement structure. Aeromagnetic and Landsat information, combined with the gravity data, further define exploration targets along the general trend of basement features. Migration of thermally matured hydrocarbons into pre-Pennsylvanian, rift generated traps in the ancestral north Kansas basin is postulated. The Nemaha ridge subsequently divided that basin into two smaller basins, the present Salina and Forest City basins. Several exploration targets could exist in this area, with the Arbuckle, Simpson, and Viola units being primary targets. The source of hydrocarbons also may lie in the deep but distant Anadorko basin. An additional totally untested hydrocarbons potential exists in the deep Precambrian/Cambrian sedimentary subbasins created along the flanks of the CNARS. Recent data points to sedimentary columns with depths of approximately 15,000 ft (4500 m) which might be hosts to gas reserves similar to the Rome trough potential of the Appalachian region.

  14. 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

  15. Subsidence History, Seismic Stratigraphy and Crustal Structure of Western Musandam Peninsula (United States)

    Watts, A. B.; Ali, M.; Aidarbayev, S.; Searle, M. P.


    Seismic reflection profiles and deep exploratory well data have been used to determine the tectonic subsidence and uplift history of the Mesozoic rifted margin, late Cretaceous fold-thrust belt, Oligocene-Miocene culmination and foreland basins of the western margin of Musandam Peninsula. Seismic stratigraphy of regional seismic profiles show that the subsurface architecture of the western side of the Musandam Peninsula can be divided into six main sequences: (1) Late Permian-Jurassic rifted margin sequence (2) Early Cretaceous to Cenomanian shelf carbonates, (3) Late Cretaceous Aruma foreland basin sequence (4) Early-mid Cenozoic Pabdeh foreland basin sequence (5) Late Cenozoic and (6) a sequence above the Late Pliocene unconformity which marks the final continental collision expressed along the Zagros Fold Belt in Iran. In addition, the seismic profiles captured multiple west-verging and east-dipping thrust faults associated with frontal deformation of the major Hagab thrust, which causes repetition of stratigraphic layers. The majority of fault tip lines terminate within the Pabdeh Group below the mid-Miocene unconformity, which marks the timing of the end of the Musandam culmination. Backstripping of biostratigraphic data from seventeen exploration wells suggest two phases of rifting and two phases of uplift. The tectonic subsidence and uplift history at the wells can be explained by a model in which the margin developed by uniform depth extension with an initial age of rifting of 260 Ma and duration of 7 Ma and a final age of rifting of 185 Ma and a rift duration of 10 Ma. The initial rifting phase is interpreted as a result of continental breakup and opening of the Neo-Tethys Ocean, while the final rifting is attributed to final continental break-up of Gondwana and opening of the Indian Ocean. The combined effect of the two rifting events has been to thin the Arabian crust to 24-26 km. Tectonic subsidence curves indicate that the two compressional uplift

  16. Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa (United States)

    Minissale, A.; Corti, G.; Tassi, F.; Darrah, T. H.; Vaselli, O.; Montanari, D.; Montegrossi, G.; Yirgu, G.; Selmo, E.; Teclu, A.


    In this study, the occurrence, chemical composition, origin and geothermal significance of thermal springs and fumaroles naturally discharging in the area located north of the Lake Abaya (western margin of the Main Ethiopian Rift, East Africa) are reviewed in relation with recent tectonics. All thermal springs showed a dominantly Na-HCO3 composition, consistent with observations dating from at least 1972, and most of them displayed a narrow range of δD and δ18O isotopic compositions for water similar to regional meteoric origins. These observations suggest that water-rock interaction processes occur in all aquifers and dominate the contributions of water that actively circulate within thermal fluids, and also suggest a similar elevation of groundwater recharge throughout the study area. Most of the thermal springs are dominated by a CO2-rich gas phase and discharge along the active faults bordering the western edge of the Main Ethiopian Rift valley. The δ13C values of CO2 and the 3He/4He isotopic ratios are consistent with the presence of mantle-derived fluids similar to what is observed in many other areas along the kinematically active African Rift, especially within Ethiopia. The application of geothermometric techniques in the liquid and the gas phases suggests the presence of a deep reservoir in which the fluids equilibrated at a maximum temperature of approximately 180 °C. Additionally, the presence of fumaroles at boiling temperatures and water/mud boiling pools in several places suggests that the geothermal reservoir is positioned at a relatively shallow depth and likely located in the western side of the study area. The analysis of data collected throughout time reveals that the waters of Lake Abaya have experienced an increase in salinity of 20% paralleled contemporaneously with a decrease in pH and δ18O and δD of water in the last 40 years; these changes do not appear to be related to climate change-induced increases in temperature or evaporation

  17. Isotopic evidence for evolution of sub-continental mantle during Red Sea rifting (United States)

    Pallister, John S.; Hegner, Ernst


    Tertiary igneous rocks from near Al Lith, Saudi Arabia are alkaline to subalkaline and bimodal in composition, and document early and late rift volcanism (≥30 Ma to ~20 Ma, 11 Ma and 3 Ma) in the central part of the Red Sea rift. Isotopic and trace-element data from twenty-five samples are presented and used to characterize basalt sources in the early rift.

  18. 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

  19. 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

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

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


    The breakup of the Gondwana supercontinent resulted in the formation of the Central Mozambique passive margin as Africa and Antarctica were separated during the mid-Jurassic period. The identification of magnetic anomalies in the Mozambique Basin and Riiser Larsen Sea means that post-oceanisation plate kinematics are well-constrained. Unresolved questions remain, however, regarding the initial fit, continental breakup process, and the first relative movements of Africa and Antarctica. This study uses high quality multi-channel seismic reflection profiles in an effort to identify the major crustal domains in the Angoche and Beira regions of the Central Mozambique margin. This work is part of the integrated pluri-disciplinary PAMELA project*. Our results show that the Central Mozambique passive margin is characterised by intense but localised magmatic activity, evidenced by the existence of seaward dipping reflectors (SDR) in the Angoche region, as well as magmatic sills and volcanoclastic material which mark the Beira High. The Angoche region is defined by a faulted upper-continental crust, with the possible exhumation of lower crustal material forming an extended ocean-continent transition (OCT). The profiles studied across the Beira high reveal an offshore continental fragment, which is overlain by a pre-rift sedimentary unit likely to belong to the Karoo Group. Faulting of the crust and overlying sedimentary unit reveals that the Beira High has recorded several phases of deformation. The combination of our seismic interpretation with existing geophysical and geological results have allowed us to propose a breakup model which supports the idea that the Central Mozambique margin was affected by polyphase rifting. The analysis of both along-dip and along-strike profiles shows that the Beira High initially experienced extension in a direction approximately parallel to the Mozambique coastline onshore of the Beira High. Our results suggest that the Beira High results

  1. Postspreading rifting in the Adare Basin, Antarctica: Regional tectonic consequences (United States)

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


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

  2. Seismic hazard in the DRC and Western Rift Valley of Africa

    CSIR Research Space (South Africa)

    Mavonga, T


    Full Text Available September 1992. The main shock claimed 11 lives, 109 people were seriously injured, and more than 2000 families were left homeless. However, the relationship between the surface structures and deeper features needs to be determined in order to establish...


    Directory of Open Access Journals (Sweden)



    Full Text Available Marine Jurassic sediments (Bajocian-Tithonian of the Kachchh Basin were deposited in a ramp setting. Except during the Middle and Late Bathonian, when a carbonate regime became established, the fill of the basin consists predominantly of siliciclastics. The sediments represent environments that range from coastal plains (rivers and associated flood plains with caliche nodules, deltas, brackish water lagoons, nearshore sand and iron-oolite bars of the inner ramp, generally situated above fair-weather wave-base, to the middle ramp influenced by storm-waves and by storm-generated currents, and finally to the outer ramp which is characterised by low energy, fine-grained sediments. Changes in relative sea level produced a cyclic sedimentation pattern. The rich benthic fauna of macroinvertebrates is dominated by bivalves, followed by brachiopods, gastropods, corals, serpulids, and sponges. The analysis of 370 statistical samples and more than 27, 000 specimens produced more than 40 benthic associations and assemblages. They show a relationship to several environmental parameters, two of which, salinity and climate, are briefly discussed. The spatial distribution of the facies and biota is outlined for two time slices, the Bathonian and the Callovian-Oxfordian, respectively.

  4. 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.

  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. 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 (water at recharge area in the highlands and escarpments evolve progressively into Ca-Na-HCO3 and Na-Ca-HCO3 type waters along the rift ward groundwater flow paths. These waters finally appear as moderate TDS (mean 960mg/l) Na-HCO3 type and as high 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 (waters indicated a dilution by cold waters. Laboratory batch leaching experiments showed that fast dissolution of fluoride from the sediment samples suddenly leached into the interacting water at the first one hour and then remain stable throughout the experiment. The concentrations of leached fluoride from the hot spring deposits, the lacustrine sediments, and the pyroclastic rock are usually low (1% of the total or less than the content in the sediment or rock) but

  7. 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 (water at recharge area in the highlands and escarpments evolve progressively into Ca-Na-HCO3 and Na-Ca-HCO3 type waters along the rift ward groundwater flow paths. These waters finally appear as moderate TDS (mean 960mg/l) Na-HCO3 type and as high 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 (waters indicated a dilution by cold waters. Laboratory batch leaching experiments showed that fast dissolution of fluoride from the sediment samples suddenly leached into the interacting water at the first one hour and then remain stable throughout the experiment. The concentrations of leached fluoride from the hot spring deposits, the lacustrine sediments, and the pyroclastic rock are usually low (1% of the total or less than the content in the sediment or rock) but

  8. Crustal and lithospheric thinning beneath the seismogenic Kachchh rift zone, Gujarat (India): Its implications toward the generation of the 2001 Bhuj earthquake sequence (United States)

    Mandal, Prantik


    A high-resolution passive seismic experiment in the Kachchh rift zone of the western India has produced an excellent dataset of several thousands teleseismic events. From this network, 500 good teleseismic events recorded at 14 mobile broadband sites are used to estimate receiver functions (for the 30-310° back-azimuth ranges), which show a positive phase at 4.5-6.1 s delay time and a strong negative phase at 8.0-11.0 s. These phases have been modeled by a velocity increase at Moho (i.e. 34-43 km) and a velocity decrease at 62-92 km depth. The estimation of crustal and lithospheric thicknesses using the inversion of stacked radial receiver functions led to the delineation of a marked thinning of 3-7 km in crustal thickness and 6-14 km in lithospheric thickness beneath the central rift zone relative to the surrounding un-rifted parts of the Kachchh rift zone. On an average, the Kachchh region is characterized by a thin lithosphere of 75.9 ± 5.9 km. The marked velocity decrease associated with the lithosphere-asthenoshere boundary (LAB), observed over an area of 120 km × 80 km, and the isotropic study of xenoliths from Kachchh provides evidence for local asthenospheric updoming with pockets of partial melts of CO 2 rich lherzolite beneath the Kachchh seismic zone that might have caused by rifting episode (at 88 Ma) and the associated Deccan thermal-plume interaction (at 65 Ma) episodes. Thus, the coincidence of the area of the major aftershock activity and the Moho as well as asthenospheric upwarping beneath the central Kachchh rift zone suggests that these pockets of CO 2-rich lherzolite partial melts could perhaps provide a high input of volatiles containing CO 2 into the lower crust, which might contribute significantly in the seismo-genesis of continued aftershock activity in the region. It is also inferred that large stresses in the denser and stronger lower crust (at 14-34 km depths) induced by ongoing Banni upliftment, crustal intrusive, marked lateral

  9. Unravelling the long-term cooling history of the northern Pyrenees from rifting-to-orogenic evolution (United States)

    Vacherat, Arnaud; Mouthereau, Frédéric; Pik, Raphaël; Bellahsen, Nicolas; Gautheron, Cécile; Bernet, Matthias; Tibari, Bouchaib; Pinna, Rosella; Daudet, Maxime; Radal, Julien


    Providing constraints on the temporal and spatial evolution of shortening in collision zones is key to reconstruct past plate motion. There are increasing evidences that the pre-orogenic architecture of the continental margins controls the development of continental accretion and therefore may be responsible for changes in the timing and rate of thrusting in collisional orogens. How this affect the thermal/exhumational record in the orogens is however little documented. Here, we study the northern Pyrenees (Ariège, Central North-Pyrenean Zone) that is exposed on the retro-wedge side of the orogen. This region developed in the vicinity of a domain that recorded hyper-extension and mantle exhumation and therefore potentially recorded the transition from rifting to collision. Apatite fission-track data from the granitic massifs of the Arize and Trois-Seigneurs Massifs indicate that collision-related exhumation started in the Early Eocene and lasted until Miocene. However, there are only scarce constraints on the former thermal history as there is not enough data from higher temperature thermochronometers. To gain a better resolution of the cooling/exhumation history from rift to mature collisional stage, we provide interpretations from new in-situ apatite and zircon fission-track and (U-Th-Sm)/He from the Arize and Trois Seigneurs massif. During extension, the studied granite recorded spatially variable thermal histories depending on the original rift-related architecture of the massifs. We show that the southern side of the Arize and 3S massif recorded significant cooling at 130-115 Ma from temperatures of 300-350°C, in agreement with RSCM temperatures obtained from the surrounding folded Mesozoic units. The northern sides recorded heating with subsidence. The massifs were rapidly cooled and exhumed between 50 and 35 Ma. Onset of convergence is only recorded in the hot basins as contraction resulted in ductile deformation. In this study, we show that the rift

  10. Sedimentology and paleoenvironments of a new fossiliferous late Miocene-Pliocene sedimentary succession in the Rukwa Rift Basin, Tanzania (United States)

    Mtelela, Cassy; Roberts, Eric M.; Hilbert-Wolf, Hannah L.; Downie, Robert; Hendrix, Marc S.; O'Connor, Patrick M.; Stevens, Nancy J.


    This paper presents a detailed sedimentologic investigation of a newly identified, fossiliferous Late Neogene sedimentary succession in the Rukwa Rift Basin, southwestern Tanzania. This synrift deposit is a rare and significant new example of a fossiliferous succession of this age in the Western Branch of East Africa Rift System. The unit, informally termed the lower Lake Beds succession, is late Miocene to Pliocene in age based on cross-cutting relationships, preliminary biostratigraphy, and U-Pb geochronology. An angular unconformity separates the lower Lake Beds from underlying Cretaceous and Oligocene strata. Deposition was controlled by rapid generation of accommodation space and increased sediment supply associated with late Cenozoic tectonic reactivation of the Rukwa Rift and synchronous initiation of the Rungwe Volcanic Centre. The lower Lake Beds, which have thus far only been identified in three localities throughout the Rukwa Rift Basin, are characterized by two discrete lithologic members (herein A and B). The lower Member A is a volcanic-rich succession composed mostly of devitrified volcanic tuffs, and volcaniclastic mudstones and sandstones with minor conglomerates. The upper Member B is a siliciclastic-dominated succession of conglomerates, sandstones, mudstones and minor volcanic tuffs. Detailed facies analysis of the lower Lake Beds reveals various distinctive depositional environments that can be grouped into three categories: 1) alluvial fan; 2) fluvial channel; and 3) flood basin environments, characterized by volcanoclastic-filled lakes and ponds, abandoned channel-fills and pedogenically modified floodplains. Member A represents a shallow lacustrine setting filled by tuffaceous sediments, which grade up into a system of alluvial fans and high-energy, proximal gravel-bed braided rivers. An unconformity marks the contact between the two members. Member B shows an upward transition from a high-energy, gravel-bed braided river system to a sandy

  11. Evolution of the Lake Victoria basin in the context of coeval rift initiation in East Africa: a 3D numerical model approach (United States)

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


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

  12. Escape tectonism in the Gulf of Thailand: Paleogene left-lateral pull-apart rifting in the Vietnamese part of the Malay Basin

    DEFF Research Database (Denmark)

    Fyhn, Michael B.W.; Boldreel, Lars Ole; Nielsen, Lars H


    The Malay Basin represents one of the largest rift basins of SE Asia. Based on a comprehensive 2-D seismic database tied to wells covering mainly Vietnamese acreage, the evolution of the Vietnamese part of the basin is outlined and a new tectonic model is proposed for the development of the basin...... the west and was probably related to coeval extension in the western part of the Gulf of Thailand. Neogene extension culminated before the Pliocene, although faults in places remains active. Late Neogene basin inversion has been attributed to c. 70 km of right-lateral movement across major c. N...

  13. 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

  14. 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.

  15. 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.

  16. New structural/tectonical model and its implication on hydrological thinking and groundwater management - the Lake Tiberias, Jordan Rift Valley (United States)

    Inbar, Nimrod; Magri, Fabien; Yellin-Dror, Annat; Rosenthal, Eliahu; Möller, Peter; Siebert, Christian; Guttman, Josef


    Lake Tiberias is a fresh water lake located at the Kinneret basin which is approximately 30 km long and 10 km wide. It comprises a link in the chain of pull-apart basins that characterizes the structure of the conspicuous Jordan Rift Valley (JRV). The basin surface is about 200 m below mean sea level (msl) and basin-fill attains a thickness of up to 8 km. Until recently, studies focused mainly on the upper strata of basin fill. Consequently, a complete three dimensional geological model, including clear view of the tectonic framework at the Kinneret Basin was incomplete. This situation imposes great difficulty in understanding the local hydrological system and as consequence enforce constrains on groundwater management of the regional aquifers that flows towards the lake. A recently proposed structural/tectonical model (Inbar, 2012) enables revaluation of several geohydrological aspects at Sea of Galilee and its surroundings and a new hydrological model based on those findings aims to clarify those aspects with relation to groundwater management. The deep-seated stratigraphical units were seismically studied at the Kinnarot Valley (southern part of Kinneret basin) where sufficient information is available (Inbar, 2012). This study shows the subsidence and northwestward tilting of the basin floor (pre-rift formations) and the flow of thick Late Miocene salt accumulation accordingly. Furthermore, shallower seismic data, collected at the lake itself, shows a suspected salt dome close to the western boundary fault of the basin (Resnikov et al., 2004). Salt flow is now suggested to be a substantial factor in the tectonic play. At the lake surroundings there are several springs and boreholes where brine immerges from an estimated depth of about 2-3 kilometers. Significant differences in brine characteristics raised questions regarding the location of brine traps, flow mechanism and the mixture process between the fresh water and the brine. However, the effect of the

  17. Post-rift deformation of the Red Sea Arabian margin (United States)

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


    Starting from the Oligocene, the Red Sea rift nucleated within the composite Neoproterozoic Arabian-Nubian shield. After about 30 Ma-long history of continental lithosphere thinning and magmatism, the first pulse of oceanic spreading occurred at around 4.6 Ma at the triple junction of Africa, Arabia, and Danakil plate boundaries and propagated southward separating Danakil and Arabia plates. Ocean floor spreading between Arabia and Africa started later, at about 3 Ma and propagated northward (Schettino et al., 2016). Nowadays the northern part of the Red Sea is characterised by isolated oceanic deeps or a thinned continental lithosphere. Here we investigate the deformation of thinned continental margins that develops as a consequence of the continental lithosphere break-up induced by the progressive oceanisation. This deformation consists of a system of transcurrent and reverse faults that accommodate the anelastic relaxation of the extended margins. Inversion and shortening tectonics along the rifted margins as a consequence of the formation of a new segment of ocean ridge was already documented in the Atlantic margin of North America (e.g. Schlische et al. 2003). We present preliminary structural data obtained along the north-central portion of the Arabian rifted margin of the Red Sea. We explored NE-SW trending lineaments within the Arabian margin that are the inland continuation of transform boundaries between segments of the oceanic ridge. We found brittle fault zones whose kinematics is consistent with a post-rift inversion. Along the southernmost transcurrent fault (Ad Damm fault) of the central portion of the Red Sea we found evidence of dextral movement. Along the northernmost transcurrent fault, which intersects the Harrat Lunayyir, structures indicate dextral movement. At the inland termination of this fault the evidence of dextral movement are weaker and NW-SE trending reverse faults outcrop. Between these two faults we found other dextral transcurrent

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

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


    The state of stress in the vicinity of old continental rifts is examined to investigate the possibility that crustal structure associated with ancient rifts (specifically a dense rift pillow in the lower crust) may modify substantially the regional stress field. Both shallow (2.0-2.6 km depth) breakout data and deep (20-45 km depth) crustal earthquake focal mechanisms indicate a N to NNE maximum horizontal compression in the vicinity of the Paleozoic Amazonas rift in central Brazil. This compressive stress direction is nearly perpendicular to the rift structure and represents a ???75?? rotation relative to a regional E-W compressive stress direction in the South American plate. Elastic two-dimensional finite element models of the density structure associated with the Amazonas rift (as inferred from independent gravity modeling) indicate that elastic support of this dense feature would generate horizontal rift-normal compressional stresses between 60 and 120 MPa, with values of 80-100 MPa probably most representative of the overall structure. The observed ???75?? stress rotation constrains the ratio of the regional horizontal stress difference to the rift-normal compressive stress to be between 0.25 and 1.0, suggesting that this rift-normal stress may be from 1 to 4 times larger than the regional horizontal stress difference. A general expression for the modification of the normalized local horizontal shear stress (relative to the regional horizontal shear stress) shows that the same ratio of the rift-normal compression relative to the regional horizontal stress difference, which controls the amount of stress rotation, also determines whether the superposed stress increases or decreases the local maximum horizontal shear stress. The potential for fault reactivation of ancient continental rifts in general is analyzed considering both the local stress rotation and modification of horizontal shear stress for both thrust and strike-slip stress regimes. In the Amazonas

  19. Phylogeography of Rift Valley Fever virus in Africa reveals multiple introductions in Senegal and Mauritania.

    Directory of Open Access Journals (Sweden)

    P O Ly Soumaré

    Full Text Available Rift Valley Fever (RVF virus (Family Bunyaviridae is an arthropod-borne RNA virus that infects primarily domestic ruminants and occasionally humans. RVF epizootics are characterized by numerous abortions and mortality among young animals. In humans, the illness is usually characterized by a mild self-limited febrile illness, which could progress to more serious complications. RVF virus is widespread and endemic in many regions of Africa. In Western Africa, several outbreaks have been reported since 1987 when the first major one occurred at the frontier of Senegal and Mauritania. Aiming to evaluate the spreading and molecular epidemiology in these countries, RVFV isolates from 1944 to 2008 obtained from 18 localities in Senegal and Mauritania and 15 other countries were investigated. Our results suggest that a more intense viral activity possibly took place during the last century compared to the recent past and that at least 5 introductions of RVFV took place in Senegal and Mauritania from distant African regions. Moreover, Barkedji in Senegal was possibly a hub associated with the three distinct entries of RVFV in West Africa.

  20. Climate Influence on Emerging Risk Areas for Rift Valley Fever Epidemics in Tanzania. (United States)

    Mweya, Clement N; Mboera, Leonard E G; Kimera, Sharadhuli I


    Rift Valley Fever (RVF) is a climate-related arboviral infection of animals and humans. Climate is thought to represent a threat toward emerging risk areas for RVF epidemics globally. The objective of this study was to evaluate influence of climate on distribution of suitable breeding habitats for Culex pipiens complex, potential mosquito vector responsible for transmission and distribution of disease epidemics risk areas in Tanzania. We used ecological niche models to estimate potential distribution of disease risk areas based on vectors and disease co-occurrence data approach. Climatic variables for the current and future scenarios were used as model inputs. Changes in mosquito vectors' habitat suitability in relation to disease risk areas were estimated. We used partial receiver operating characteristic and the area under the curves approach to evaluate model predictive performance and significance. Habitat suitability for Cx. pipiens complex indicated broad-scale potential for change and shift in the distribution of the vectors and disease for both 2020 and 2050 climatic scenarios. Risk areas indicated more intensification in the areas surrounding Lake Victoria and northeastern part of the country through 2050 climate scenario. Models show higher probability of emerging risk areas spreading toward the western parts of Tanzania from northeastern areas and decrease in the southern part of the country. Results presented here identified sites for consideration to guide surveillance and control interventions to reduce risk of RVF disease epidemics in Tanzania. A collaborative approach is recommended to develop and adapt climate-related disease control and prevention strategies.

  1. Paleofluid-flow circulation within a Triassic rift basin: Evidence from oil inclusions and thermal histories (United States)

    Tseng, H.-Y.; Burruss, R.C.; Onstott, T.C.; Omar, G.


    The migration of subsurface fluid flow within continental rift basins has been increasingly recognized to significantly affect the thermal history of sediments and petroleum formation. To gain insight into these paleofluid flow effects, the thermal history of the Taylorsville basin in Virginia was reconstructed from fluid-inclusion studies, apatite fission-track data, and vitrinite reflectance data. Models of thermal history indicate that the basin was buried to the thermal maximum at 200 Ma; a cooling event followed during which the eastern side of the basin cooled earlier and faster than the western side, suggesting that there was a differential uplift and topographically driven fluid flow. This hypothesis is supported by analyses of secondary oil and aqueous inclusions trapped in calcite and quartz veins during the uplift stage. Gas chromatograms of inclusion oils exhibit variable but extensive depletion of light molecular-weight hydrocarbons. The relative abundance of n-alkanes, petrographic observations, and the geological data indicate that the alteration process on these inclusion oils was probably neither phase separation nor biodegradation, but water washing. Water:oil ratios necessary to produce the observed alteration are much greater than 10000:1. These exceedingly high ratios are consistent with the migration of inclusion oils along with fluid flow during the early stages of basin evolution. The results provide significant evidence about the role of a subsurface flow system in modifying the temperature structure of the basin and the composition of petroleum generated within the basin.

  2. Lithology and temperature: How key mantle variables control rift volcanism (United States)

    Shorttle, O.; Hoggard, M.; Matthews, S.; Maclennan, J.


    Continental rifting is often associated with extensive magmatic activity, emplacing millions of cubic kilometres of basalt and triggering environmental change. The lasting geological record of this volcanic catastrophism are the large igneous provinces found at the margins of many continents and abrupt extinctions in the fossil record, most strikingly that found at the Permo-Triassic boundary. Rather than being considered purely a passive plate tectonic phenomenon, these episodes are frequently explained by the involvement of mantle plumes, upwellings of mantle rock made buoyant by their high temperatures. However, there has been debate over the relative role of the mantle's temperature and composition in generating the large volumes of magma involved in rift and intra-plate volcanism, and even when the mantle is inferred to be hot, this has been variously attributed to mantle plumes or continental insulation effects. To help resolve these uncertainties we have combined geochemical, geophysical and modelling results in a two stage approach: Firstly, we have investigated how mantle composition and temperature contribute to melting beneath Iceland, the present day manifestation of the mantle plume implicated in the 54Ma break up of the North Atlantic. By considering both the igneous crustal production on Iceland and the chemistry of its basalts we have been able to place stringent constraints on the viable temperature and lithology of the Icelandic mantle. Although a >100°C excess temperature is required to generate Iceland's thick igneous crust, geochemistry also indicates that pyroxenite comprises 10% of its source. Therefore, the dynamics of rifting on Iceland are modulated both by thermal and compositional mantle anomalies. Secondly, we have performed a global assessment of the mantle's post break-up thermal history to determine the amplitude and longevity of continental insulation in driving excess volcanism. Using seismically constrained igneous crustal

  3. Molecular Epidemiology and Emergence of Rift Valley Fever

    Directory of Open Access Journals (Sweden)

    Sall AA


    Full Text Available Rift Valley fever (RVF is a mosquito-borne viral disease which manifested itself during recent epidemics and revealed its significant potential of emergence. Studies on molecular epidemiology undertaken to better understand the factors leading to RVF emergence, have confirmed the mode of circulation of the virus and highlithted probable risks and obstacles for prevention and control. As for several other viral agents, molecular epidemiology is becoming a useful tool in the study of the emergence of RVF as a serious infectious disease.

  4. Magmatism on rift flanks : Insights from ambient noise phase velocity in Afar region

    NARCIS (Netherlands)

    Korostelev, F.; Weemstra, C.; Leroy, S.; Boschi, L.; Keir, D.; Ren, Y.; Molinari, I.; Ahmed, A.; Stuart, G.W.; Rolandone, F.; Khanbari, K.; Hammond, J.O.S.; Kendall, M.K.; Doubre, C.; Al Ganad, I.; Goitom, B.; Ayele, A.


    During the breakup of continents in magmatic settings, the extension of the rift valley is commonly assumed to initially occur by border faulting and progressively migrate in space and time toward the spreading axis. Magmatic processes near the rift flanks are commonly ignored. We present phase

  5. Permo-Triassic intraplate magmatism and rifting in Eurasia: implications for mantle dynamics.

    NARCIS (Netherlands)

    Nikishin, A.M.; Ziegler, P.A.; Abbott, D.; Brunet, M.F.; Cloetingh, S.A.P.L.


    At the transition from the Permian to the Triassic, Eurasia was the site of voluminous flood-basalt extrusion and rifting. Major flood-basalt provinces occur in the Tunguska, Taymyr, Kuznetsk, Verkhoyansk - Vilyuy and Pechora areas, as well as in the South Chinese Emeishen area. Contemporaneous rift

  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. Kinematic and thermal evolution of the Moroccan rifted continental margin: Doukkala-High Atlas transect (United States)

    Gouiza, M.; Bertotti, G.; Hafid, M.; Cloetingh, S.


    The Atlantic passive margin of Morocco developed during Mesozoic times in association with the opening of the Central Atlantic and the Alpine Tethys. Extensional basins formed along the future continental margin and in the Atlas rift system. In Alpine times, this system was inverted to form the High and Middle Atlas fold-and-thrust belts. To provide a quantitative kinematic analysis of the evolution of the rifted margin, we present a crustal section crossing the Atlantic margin in the region of the Doukkala Basin, the Meseta and the Atlas system. We construct a post-rift upper crustal section compensating for Tertiary to present vertical movements and horizontal deformations, and we conduct numerical modeling to test quantitative relations between amounts and distribution of thinning and related vertical movements. Rifting along the transect began in the Late Triassic and ended with the appearance of oceanic crust at 175 Ma. Subsidence, possibly related to crustal thinning, continued in the Atlas rift in the Middle Jurassic. The numerical models confirm that the margin experienced a polyphase rifting history. The lithosphere along the transect preserved some strength throughout rifting with the Effective Elastic Thickness corresponding to an isotherm of 450°C. A mid-crustal level of necking of 15 km characterized the pre-rift lithosphere.

  8. Investigation of Fault Systems Controlling Breakup and Deposition in the Galicia Rift Margin (United States)

    Alexanian, A.; Sawyer, D. S.; Gray, G. G.; Shillington, D. J.; Davy, R. G.; Minshull, T. A.; Reston, T. J.; Morgan, J.


    The Galicia Margin offshore of Spain represents a magma-poor end member of rifting systems. The development of these systems can be understood by imaging the subsurface distribution of crust and upper mantle. The Galicia Margin has been studied extensively with seismic data, and the research cruise R/V Marcus Langseth 1307 collected 3D seismic data along this margin. The dataset includes a 68 by 20 kilometer box in the Deep Galicia Basin and a 110 kilometer x 600 meter 3D swath to the west. Through selective Prestack Depth Migration (PSDM), seismic interpretation, and structural restoration of one of the swaths, one can gain insight into the different fault regimes and depositional history of the margin. PSDM is an important tool to image the subsurface and model the velocities present. Ray based tomography is used to create a migration velocity model that will allow depth migration to faithfully focus the seismic data and send reflection events to their correct location in space. We chose to process Western Extension 1 (WE1), which partially overlaps the 3D box and extends it to the west. This line captures the transition from a crustal necking region to hyperextended crust to exhumed mantle. The eastern 150 kilometers of the line was processed using a 3D Kirchoff algorithm. Its velocity model utilizes reflection tomography in the sediments, and we used forward modeling to minimize residual move out on strong events in the basement. The western 20 kilometer long segment was previously undiscovered due to a lack of geometric control while shots were being recorded. These data were processed using a 2D Kirchoff algorithm using the vessel's navigation systems to estimate source and receiver locations. In this study we found a velocity inversion in the sediment, evidence suggesting a large deposition of synrift sediment in the crustal blocks, and the locations of continental crust and mantle.

  9. Late Jurassic – early Cretaceous inversion of rift structures, and linkage of petroleum system elements across post-rift unconformity, U.S. Chukchi Shelf, arctic Alaska (United States)

    Houseknecht, David W.; Connors, Christopher D.


    Basin evolution of the U.S. Chukchi shelf involved multiple phases, including Late Devonian–Permian rifting, Permian–Early Jurassic sagging, Late Jurassic–Neocomian inversion, and Cretaceous–Cenozoic foreland-basin development. The focus of ongoing exploration is a petroleum system that includes sag-phase source rocks; inversion-phase reservoir rocks; structure spanning the rift, sag, and inversion phases; and hydrocarbon generation during the foreland-basin phase.

  10. 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.

  11. 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

  12. 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.

  13. Characteristics of seismicity in Eritrea (2011-2012): Implications for rifting dynamics (United States)

    Goitom, B.; Hammond, J. O. S.; Kendal, M. J.; Ogubazghi, G.; Keir, D.; Ayele, A.; Illsley-Kemp, F.


    Eritrea hosts the final stages of on-land East-African rifting, yet questions remain about how rifting transits from the Afar Depression to the Red Sea. In this study, we use data from recent deployments of 6 broadband seismometers in Eritrea together with deployments in Ethiopia to locate seismicity and determine the current focus of strain. Over 1000 events have been located with local magnitudes 0.7-5.0. A significant period of seismicity was observed on 1 July 2012 around Nabro volcano and is associated with the biggest event of mL 5 preceded by 33 events in the previous two days. It may be related to magma movement below Nabro. Other significant seismicity was observed on 25 December 2011 and is correlated with an earthquake of mL 4.2 and associated with 13 other events on the same day. This event is located around Hayli Gubbi and Ale Bagu volcanoes and could be related to the activities around these volcanoes. We use double difference relocations to improve accuracy and show two main clusters of seismicity, one oriented NW-SE in the Bada-Alid axis along the north-western boundary of the Danakil microplate and the other NE-SW, following the trend of the Biddu-Nabro volcanic complex. Our new estimates of seismicity demarcate the boundary between the Nubian, Somalian, and Danakil Microplate and suggest that the Danakil microplate may be broken in two along the Biddu-Nabro Volcanic complex. We estimate b-values for the different clusters of events and show that close to the major border faults near Massawa, average b-values are lower (0.65) than that found near the volcanic centres (1.2 - Bada-Alid, 0.81 - Biddu-Nabro). This may indicate that the stress is less in the volcanic regions and the seismicity is due to movement of magma fluids and strain is accommodated by the injection of magma. In contrast the earthquakes around Massawa occur in relatively stronger rocks suggesting strain may be accommodated by movement on larger faults.

  14. An Epidemiological Model of Rift Valley Fever with Spatial Dynamics

    Directory of Open Access Journals (Sweden)

    Tianchan Niu


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

  15. 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

  16. Structural inheritance versus magmatic weakening: What controls the style of deformation at rift segment boundaries in the Gulf of California, Mexico? (United States)

    Seiler, Christian; Gleadow, Andrew; Kohn, Barry


    Rifts are commonly segmented into several hundred kilometre long zones of opposing upper-plate transport direction with boundaries defined by accommodation and transfer zones. A number of such rift segments have been recognized in the Gulf of California, a youthful oceanic basin that is currently undergoing the rift-drift transition. However, detailed field studies have so far failed to identify suitable structures that could accommodate the obvious deformation gradients between different rift segments, and the nature of strain transfer at segment boundaries remains enigmatic. The Bocana transfer zone (BTZ) in central Baja California is a linear, WNW striking structural discontinuity separating two rift segments with different magnitudes and styles of extensional deformation. North of the BTZ, the Libertad fault is part of the Main Gulf Escarpment, which represents the breakaway fault that separates the Gulf of California rift to the east from the relatively stable western portion of the Baja peninsula. The N-striking Libertad escarpment developed during the Late Miocene (~10-8Ma) and exhibits a topographic relief of ca. 1,000m along a strike-length of ca. 50km. Finite displacement decreases from ~1000m in the central fault segment to ~500m further south, where the fault bends SE and merges with the BTZ. In the hanging wall of the Libertad fault, a series of W-tilted horsts are bound along their eastern margins by two moderate-displacement E-dipping normal faults. South of the BTZ, extension was much less than further north, which explains the comparatively subdued relief and generally shallower tilt of pre-rift strata in this area. The BTZ itself is characterized by two en echelon WNW-ESE striking dextral-oblique transfer faults with a significant down-to-the-NNE extensional component. Strain is transferred from the Libertad breakaway fault onto the transfer faults over a distance of >20km through a network of interacting normal, oblique and strike-slip faults

  17. Geochemistry of Woranso-Mille Pliocene basalts from west-central Afar, Ethiopia: Implications for mantle source characteristics and rift evolution (United States)

    Alene, Mulugeta; Hart, William K.; Saylor, Beverly Z.; Deino, Alan; Mertzman, Stanley; Haile-Selassie, Yohannes; Gibert, Luis B.


    The Woranso-Mille (WORMIL) area in the west-central Afar, Ethiopia, contains several Pliocene basalt flows, tuffs, and fossiliferous volcaniclastic beds. We present whole-rock major- and trace-element data including REE, and Sr-Nd-Pb isotope ratios from these basalts to characterize the geochemistry, constrain petrogenetic processes, and infer mantle sources. Six basalt groups are distinguished stratigraphically and geochemically within the interval from 3.8 to 3 Ma. The elemental and isotopic data show intra- and inter-group variations derived primarily from source heterogeneity and polybaric crystallization ± crustal inputs. The combined Sr-Nd-Pb isotope data indicate the involvement of three main reservoirs: the Afar plume, depleted mantle, and enriched continental lithosphere (mantle ± crust). Trace element patterns and ratios further indicate the basalts were generated from spinel-dominated shallow melting, consistent with significantly thinned Pliocene lithosphere in western Afar. The on-land continuation of the Aden rift into western Afar during the Pliocene is reexamined in the context of the new geochemistry and age constraints of the WORMIL basalts. The new data reinforce previous interpretations that progressive rifting and transformation of the continental lithosphere to oceanic lithosphere allows for increasing asthenospheric inputs through time as the continental lithosphere is thinned.

  18. Gondwana breakup via double-saloon-door rifting and seafloor spreading in a backarc basin during subduction rollback (United States)

    Martin, A. K.


    A model has been developed where two arc-parallel rifts propagate in opposite directions from an initial central location during backarc seafloor spreading and subduction rollback. The resultant geometry causes pairs of terranes to simultaneously rotate clockwise and counterclockwise like the motion of double-saloon-doors about their hinges. As movement proceeds and the two terranes rotate, a gap begins to extend between them, where a third rift initiates and propagates in the opposite direction to subduction rollback. Observations from the Oligocene to Recent Western Mediterranean, the Miocene to Recent Carpathians, the Miocene to Recent Aegean and the Oligocene to Recent Caribbean point to a two-stage process. Initially, pairs of terranes comprising a pre-existing retro-arc fold thrust belt and magmatic arc rotate about poles and accrete to adjacent continents. Terrane docking reduces the width of the subduction zone, leading to a second phase during which subduction to strike-slip transitions initiate. The clockwise rotated terrane is caught up in a dextral strike-slip zone, whereas the counterclockwise rotated terrane is entrained in a sinistral strike-slip fault system. The likely driving force is a pair of rotational torques caused by slab sinking and rollback of a curved subduction hingeline. By analogy with the above model, a revised five-stage Early Jurassic to Early Cretaceous Gondwana dispersal model is proposed in which three plates always separate about a single triple rift or triple junction in the Weddell Sea area. Seven features are considered diagnostic of double-saloon-door rifting and seafloor spreading: earliest movement involves clockwise and counterclockwise rotations of the Falkland Islands Block and the Ellsworth Whitmore Terrane respectively; terranes comprise areas of a pre-existing retro-arc fold thrust belt (the Permo-Triassic Gondwanide Orogeny) attached to an accretionary wedge/magmatic arc; the Falklands Islands Block is initially

  19. Long-term coupling and feedbacks between surface processes and tectonics during rifting (United States)

    Theunissen, Thomas; Huismans, Ritske S.


    Whereas significant efforts have been made to understand the relationship between mountain building and surfaces processes, limited research has been done on the relationship between surface processes and extensional tectonics. Here we present high-resolution 2-D coupled tectonic-surface processes modeling of extensional basin formation. The main aim is to find out how erosion and deposition affect the deformation in extensional systems. We test the combined effects of crustal rheology and varying surface process efficiency (erodibility, sea level) on structural style of rift and passive margin formation. The results show that both erosion of rift flank areas and basin deposition enhance localization of crustal deformation. Frictional-plastic extensional shear zones accumulate more deformation during a longer period of time, and loading of offshore basins can generate crustal ductile flow. In extreme cases sediment deposition delays lithospheric rupture. These mechanisms are enhanced when fluvial erosion, transport and deposition are efficient. We show that removal of mass from rift flanks and sedimentary loading in the basin area provide a first order feedback with tectonic deformation and control on rifted margin tectonic-morphology. However, surface processes do not change the first order structural style of rifting, which is largely controlled by crustal rheology. Rift escarpment morphology is function of paleo-topography and sea level. Variation of strain localization in natural rift systems correlates with the observed behavior and suggests similar feedbacks as demonstrated by the forward numerical models.

  20. Upper mantle seismic anisotropy in the intra-continental Kachchh rift zone, Gujarat, India (United States)

    Mandal, Prantik


    Shear wave splitting study of 411 SKS/SKKS phases covering backazimuth range of 13 ° to 305 ° recorded by 12 broadband stations in the Kachchh rift has led to estimates of fast axis orientations and splitting times for 118 good measurements. The average vector mean of fast axis orientation (86 ± 14 °) corresponds to the E-W axis of the Kachchh rift and the delay time (~ 1.6 s) is attributed to the ~ 184 km-thick upper mantle layer with 4% anisotropy. The anisotropic character observed for the Kachchh rift (KR) is comparable to other continental rifts and these are related to the high-temperature, lattice-preferred orientation fabric of olivine, inherited from the mantle flows. The source of the rift-axis parallel anisotropy is traced to the rift-parallel flows within the 76 ± 6 km-thick lithosphere. Additionally, the rift-parallel pockets of partial melts also induce anisotropy within the asthenosphere. Both these are inherited from the plume-lithosphere interaction during the Deccan/Reunion plume episode (~ 65 Ma).

  1. Rift-to-collision transition recorded by tectonothermal evolution of the northern Pyrenees (United States)

    Vacherat, Arnaud; Mouthereau, Frédéric; Pik, Raphaël.; Bellahsen, Nicolas; Gautheron, Cécile; Bernet, Matthias; Daudet, Maxime; Balansa, Jocelyn; Tibari, Bouchaib; Pinna Jamme, Rosella; Radal, Julien


    The impact of rift-related processes on tectonic and thermal evolution of collisional orogens is poorly documented. Here, we study the northern Pyrenees, a region that has preserved a geological record of the transition from rifting to collision. Using modeling of new low-temperature thermochronological data, including fission track and (U-Th)/He on apatite and zircon, we propose a temporal reconstruction of the inversion of the European rifted margin. Our data confirm that rifting and related cooling started in the Late Paleozoic-Triassic. Throughout the Jurassic and Early Cretaceous the European margin recorded slow heating during postrift subdsidence. Modeling of thermochronological data allows distinguishing subsidence and denudation controlled by south dipping normal faults in granitic massifs that reflect a second episode of crustal thinning at 130-110 Ma. Following onset of convergence at 83 Ma, shortening accumulated into the weak and hot Albian-Cenomanian rift basins floored by both hyperextended continental crust and exhumed subcontinental mantle. The lack of cooling during this initial stage of convergence is explained by the persistence of a high geothermal gradient. The onset of exhumation-related cooling is recognized in the whole Pyrenean region at 50-35 Ma. This timing reveals that the main phase of mountain building started when hyperextended rift basins closed and collision between proximal domains of the rifted margin occurred.

  2. Crustal thickness and Moho sharpness beneath the Midcontinent rift from receiver functions

    Directory of Open Access Journals (Sweden)

    Moikwathai Moidaki


    Full Text Available The Mesoproterozoic Midcontinent rift (MCR in the central US is an approximately 2000 km long, 100 km wide structure from Kansas to Michigan. During the 20-40 million years of rifting, a thick (up to 20 km layer of basaltic lava was deposited in the rift valleys. Quantifying the effects of the rifting and associated volcanic eruptions on the structure and composition of the crust and mantle beneath the MCR is important for the understanding of the evolution of continental lithosphere. In this study we measure the crustal thickness (H, and the sharpness of the Moho (R at about 24 portable and permanent stations in Iowa, Kansas, and South Dakota by stacking Pto- S converted waves (PmS and their multiples (PPmS and PSmS. Under the assumption that the crustal mean velocity in the study area is the same as the IASP91 earth model, we find a significantly thickened crust beneath the MCR of about 53 km. The crustal Vp/Vs ratios increases from about 1.80 off rift to as large as 1.95 within the rift, which corresponds to an increase of Poisson’s ratio from 0.28 to 0.32, suggesting a more mafic crust beneath the MCR. The R measurements are spatially variable and are relatively small in the vicinity of the MCR, indicating the disturbance of the original sharp Moho by the rifting and magmatic intrusion and volcanic eruption.

  3. Using the salt tectonics as a proxy to reveal post-rift active crustal tectonics: The example of the Eastern Sardinian margin (United States)

    Lymer, Gaël; Vendeville, Bruno; Gaullier, Virginie; Chanier, Frank; Gaillard, Morgane


    The Western Tyrrhenian Basin, Mediterranean Sea, is a fascinating basin in terms of interactions between crustal tectonics, salt tectonics and sedimentation. The METYSS (Messinian Event in the Tyrrhenian from Seismic Study) project is based on 2100 km of HR seismic data acquired in 2009 and 2011 along the Eastern Sardinian margin. The main aim is to study the Messinian Salinity Crisis (MSC) in the Western Tyrrhenian Basin, but we also investigate the thinning processes of the continental crust and the timing of crustal vertical motions across this complex domain. Our first results allowed us to map the MSC seismic markers and to better constrain the timing of the rifting, which ended before the MSC across the upper and middle parts of the margin. We also evidenced that crustal activity persisted long after the end of rifting. This has been particularly observed on the upper margin, where several normal faults and a surprising compressional structure were recently active. In this study we investigate the middle margin, the Cornaglia Terrace, where the Mobile Unit (MU, mobile Messinian salt) accumulated during the MSC and acts as a décollement. Our goal is to ascertain whether or not crustal tectonics existed after the pre-MSC rift. This is a challenge where the MU is thick, because potential basement deformations could be first accommodated by the MU and therefore would not find any expression in the supra-salt layers (Upper Unit, UU and Plio-Quaternary, PQ). However our investigations clearly reveal interactions between crustal and salt tectonics along the margin. We thus evidence gravity gliding of the salt and its brittle sedimentary cover along basement slopes generated by the post-MSC tilting of some basement blocks bounded by crustal normal faults, formerly due to the rifting. Another intriguing structure also got our interest. It corresponds to a wedge-shaped of MU located in a narrow N-S half graben bounded to the west by a major, east-verging, crustal

  4. 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.

  5. Exploring virtual reality technology and the Oculus Rift for the examination of digital pathology slides. (United States)

    Farahani, Navid; Post, Robert; Duboy, Jon; Ahmed, Ishtiaque; Kolowitz, Brian J; Krinchai, Teppituk; Monaco, Sara E; Fine, Jeffrey L; Hartman, Douglas J; Pantanowitz, Liron


    Digital slides obtained from whole slide imaging (WSI) platforms are typically viewed in two dimensions using desktop personal computer monitors or more recently on mobile devices. To the best of our knowledge, we are not aware of any studies viewing digital pathology slides in a virtual reality (VR) environment. VR technology enables users to be artificially immersed in and interact with a computer-simulated world. Oculus Rift is among the world's first consumer-targeted VR headsets, intended primarily for enhanced gaming. Our aim was to explore the use of the Oculus Rift for examining digital pathology slides in a VR environment. An Oculus Rift Development Kit 2 (DK2) was connected to a 64-bit computer running Virtual Desktop software. Glass slides from twenty randomly selected lymph node cases (ten with benign and ten malignant diagnoses) were digitized using a WSI scanner. Three pathologists reviewed these digital slides on a 27-inch 5K display and with the Oculus Rift after a 2-week washout period. Recorded endpoints included concordance of final diagnoses and time required to examine slides. The pathologists also rated their ease of navigation, image quality, and diagnostic confidence for both modalities. There was 90% diagnostic concordance when reviewing WSI using a 5K display and Oculus Rift. The time required to examine digital pathology slides on the 5K display averaged 39 s (range 10-120 s), compared to 62 s with the Oculus Rift (range 15-270 s). All pathologists confirmed that digital pathology slides were easily viewable in a VR environment. The ratings for image quality and diagnostic confidence were higher when using the 5K display. Using the Oculus Rift DK2 to view and navigate pathology whole slide images in a virtual environment is feasible for diagnostic purposes. However, image resolution using the Oculus Rift device was limited. Interactive VR technologies such as the Oculus Rift are novel tools that may be of use in digital pathology.

  6. Integrated Analysis of Environment, Cattle and Human Serological Data: Risks and Mechanisms of Transmission of Rift Valley Fever in Madagascar.

    Directory of Open Access Journals (Sweden)

    Marie-Marie Olive


    Full Text Available Rift Valley fever (RVF is a vector-borne disease affecting ruminants and humans. Madagascar was heavily affected by RVF in 2008-2009, with evidence of a large and heterogeneous spread of the disease. The identification of at-risk environments is essential to optimize the available resources by targeting RVF surveillance in Madagascar. Herein, the objectives of our study were: (i to identify the environmental factors and areas favorable to RVF transmission to both cattle and human and (ii to identify human behaviors favoring human infections in Malagasy contexts.First, we characterized the environments of Malagasy communes using a Multiple Factor Analysis (MFA. Then, we analyzed cattle and human serological data collected at national level using Generalized Linear Mixed Models, with the individual serological status (cattle or human as the response, and MFA factors, as well as other potential risk factors (cattle density, human behavior as explanatory variables. Cattle and human seroprevalence rates were positively associated to humid environments (p<0.001. Areas with high cattle density were at risk (p<0.01; OR = 2.6. Furthermore, our analysis showed that frequent contact with raw milk contributed to explain human infection (OR = 1.6. Finally, our study highlighted the eastern-coast, western and north-western parts as high-risk areas for RVF transmission in cattle.Our integrated approach analyzing environmental, cattle and human datasets allow us to bring new insight on RVF transmission patterns in Madagascar. The association between cattle seroprevalence, humid environments and high cattle density suggests that concomitant vectorial and direct transmissions are critical to maintain RVF enzootic transmission. Additionally, in the at-risk humid environment of the western, north-western and the eastern-coast areas, suitable to Culex and Anopheles mosquitoes, vectorial transmission probably occurs in both cattle and human. The relative contribution

  7. 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

  8. Triassic rift-related sedimentary basins in northern Chile (24° 29°S) (United States)

    Suarez, M.; Bell, C. M.


    Triassic rocks in northern Chile (latitude 24°-29°S) include marine and continental rift-related sedimentary deposits, associated with basaltic, andesitic, and silicic volcanic rocks. Five main successions include the deposits of two marine basins (Profeta and San Félix) separated by three continental basins (Cifuncho, La Ternera, and La Coipa). The marine strata include turbidites and debris flow deposits interpreted as coarse-grained fan-delta sediments. The continental sediments include lacustrine fan delta, open lake, braided river, alluvial fan, and sabkha deposits. The widespread fan-delta systems (both marine and lacustrine), together with abrupt lateral and vertical facies discontinuities and large-scale depositional cycles, are indicative of rift-controlled sedimentation. The associated magmatic activity indicates that this rifting was the product of subduction-related extension or strike-slip movement on the active plate margin. Triassic rifting was followed in Late Triassic to Early Jurassic times by widespread thermotectonic subsidence.

  9. Data-driven modeling to assess receptivity for Rift Valley Fever virus

    National Research Council Canada - National Science Library

    Barker, Christopher M; Niu, Tianchan; Reisen, William K; Hartley, David M


    Rift Valley Fever virus (RVFV) is an enzootic virus that causes extensive morbidity and mortality in domestic ruminants in Africa, and it has shown the potential to invade other areas such as the Arabian Peninsula...

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

    National Research Council Canada - National Science Library

    Xue, Ling; Cohnstaedt, Lee W; Scott, H Morgan; Scoglio, Caterina


    .... In the event Rift Valley fever virus is introduced to the United States or other non-endemic areas, understanding the potential patterns of spread and the areas at risk based on disease vectors...

  11. Data-Driven Modeling to Assess Receptivity for Rift Valley Fever Virus: e2515

    National Research Council Canada - National Science Library

    Christopher M Barker; Tianchan Niu; William K Reisen; David M Hartley


      Rift Valley Fever virus (RVFV) is an enzootic virus that causes extensive morbidity and mortality in domestic ruminants in Africa, and it has shown the potential to invade other areas such as the Arabian Peninsula...

  12. Inflation rates, rifts, and bands in a pāhoehoe sheet flow (United States)

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


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

  13. Micrometre-scale deformation observations reveal fundamental controls on geological rifting. (United States)

    Thun, Johannes; Lokmer, Ivan; Bean, Christopher J; Eibl, Eva P S; Bergsson, Bergur H; Braiden, Aoife


    Many of the world's largest volcanic eruptions are associated with geological rifting where major fractures open at the Earth's surface, yet fundamental controls on the near-surface response to the rifting process are lacking. New high resolution observations gleaned from seismometer data during the 2014 Bárðarbunga basaltic dyke intrusion in Iceland allow us unprecedented access to the associated graben formation process on both sub-second and micrometre scales. We find that what appears as quasi steady-state near-surface rifting on lower resolution GPS observation comprises discrete staccato-like deformation steps as the upper crust unzips through repetitive low magnitude (MW earthquakes, demonstrating that the uppermost crust in the rift zone is exceptionally weak.

  14. Landform development in a zone of active Gedi Fault, Eastern Kachchh rift basin, India (United States)

    Kothyari, Girish Ch.; Rastogi, B. K.; Morthekai, P.; Dumka, Rakesh K.


    An earthquake of 2006 Mw 5.7 occurred along east-west trending Gedi Fault (GF) to the north of the Kachchh rift basin in western India which had the epicenter in the Wagad upland, which is approximately 60 km northeast of the 2001 Mw 7.7 earthquake site (or epicenter). Development of an active fault scarp, shifting of a river channel, offsetting of streams and uplift of the ground indicate that the terrain is undergoing active deformation. Based on detailed field investigations, three major faults that control uplifts have been identified in the GF zone. These uplifts were developed in a step-over zone of the GF, and formed due to compressive force generated by left-lateral motion within the segmented blocks. In the present research, a terrace sequence along the north flowing Karaswali river in a tectonically active GF zone has been investigated. Reconstructions based on geomorphology and terrace stratigraphy supported by optical chronology suggest that the fluvial aggradation in the Wagad area was initiated during the strengthening (at ~ 8 ka) and declining (~ 4 ka) of the Indian Summer Monsoon (ISM). The presence of younger valley fill sediments which are dated ~ 1 ka is ascribed to a short lived phase of renewed strengthening of ISM before present day aridity. Based on terrace morphology two major phases of enhanced uplift have been estimated. The older uplift event dated to 8 ka is represented by the Tertiary bedrock surfaces which accommodated the onset of valley-fill aggradation. The younger event of enhanced uplift dated to 4 ka was responsible for the incision of the older valley fill sediments and the Tertiary bedrock. These ages suggest that the average rate of uplift ranges from 0.3 to 1.1 mm/yr during the last 9 ka implying active nature of the area.

  15. 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

  16. The magmatic budget of Atlantic type rifted margins: is it related to inheritance? (United States)

    Manatschal, Gianreto; Tugend, Julia; Picazo, Suzanne; Müntener, Othmar


    In the past, Atlantic type rifted margins were either classified as volcanic or non-volcanic. An increasing number of high quality reflection and refraction seismic surveys and drill hole data show a divergent style of margin architecture and an evolution in which the quantity and distribution of syn-rift magmatism is variable, independently of the amount of extension. Overgeneralized classifications and models assuming simple relations between magmatic and extensional systems are thus inappropriate to describe the formation of rifted margins. More recent studies show that the magmatic evolution of rifted margins is complex and cannot be characterized based on the volume of observed magma alone. On the one hand, so-called "non-volcanic" margins are not necessarily amagmatic, as shown by the results of ODP drilling along the Iberia-Newfoundland rifted margins. On the other hand, magma-rich margins, such as the Norwegian, NW Australian or the Namibia rifted margins show evidence for hyper-extension prior to breakup. These observations suggest that the magmatic budget does not only depend on extension rates but also on the composition and temperature of the decompressing mantle. Moreover, the fact that the magmatic budget may change very abruptly along strike and across the margin is difficult to reconcile with the occurrence of plumes or other deep-seated large-scale mantle phenomena only. These overall observations result in questions on how magmatic and tectonic processes are interacting during rifting and lithospheric breakup and on how far inheritance may control the magmatic budget during rifting. In our presentation we will review results from the South and North Atlantic and the Alpine Tethys domain and will discuss the structural and magmatic evolution of so-called magma-rich and magma-poor rifted margins. In particular, we will try to define when, where and how much magma forms during rifting and lithospheric breakup. The key questions that we aim to address

  17. Breaking the paradigm at magma-poor and magma-rich rifted margins (United States)

    Tugend, Julie; Manatschal, Gianreto; Gillard, Morgane; Nirrengarten, Michael; Epin, Marie-Eva; Sauter, Daniel; Autin, Julia; Harkin, Caroline; Kusznir, Nick


    Rifted margins used to be classified into volcanic or non-volcanic passive margins. Because magmatism is evidenced even in so-called 'non-volcanic' settings, this terminology was later adjusted to magma-poor and magma-rich rifted margins. This classification represents a simplification into end-member magmatic types depending on the magmatic budget related to rifting and/or breakup processes. New observations derived from higher quality geophysical data sets and drill-hole data revealed the great diversity of rifted margin architecture and highly variable distribution of rift-related and/or breakup related magmatism. Recent studies suggest that rifted margins have a more complex tectono-magmatic evolution than previously assumed and cannot be characterized based on the observed volume of magma alone. In this study, we present seismic observations from 2D high resolution long-offset deep reflection seismic profiles across the East-Indian and South-Atlantic rifted margins. We aim to compare structural similarities between rifted margins with different magmatic budgets. We apply a systematic seismic interpretation approach to describe and characterize the first-order architecture and magmatic budget of our case examples. The identification of magmatic additions based on seismic observations only is indeed not unequivocal, in spite of the high-resolution dataset. Interpretations are related to large uncertainties in particular at ocean-continent transitions (i.e. outer highs) where most of the magmatism seems to be located. For each line, we present three different interpretations based on offshore and/or onshore field analogues. These interpretations illustrate scenarios for the nature of the outer highs that we believe are geologically meaningful and reasonable, and imply different magmatic budgets at breakup. Based on these interpretations we discuss different mechanisms for lithospheric breakup involving either a gradual or more instantaneous process independently

  18. Teleseismic Investigations of the Malawi and Luangwa Rift Zones: Ongoing Observations From the SAFARI Experiment (United States)

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


    In order to evaluate the influence of crustal and mantle heterogeneities upon the initiation of the Malawi rift zone (MRZ) and reactivation of the Zambian Luangwa rift zone (LRZ) subject to Cenozoic plate boundary stress fields and mantle buoyancy forces, we installed and operated 33 Seismic Arrays For African Rift Initiation (SAFARI) three-component broadband seismic stations in Malawi, Mozambique, and Zambia from 2012 to 2014. During the twenty-four month acquisition period, nearly 6200 radial receiver functions (RFs) were recorded. Stations situated within the MRZ, either along the coastal plains or within the Shire Graben toward the south, report an average crustal thickness of 42 km relative to approximately 46 km observed at stations located along the rift flanks. This implies the juvenile MRZ is characterized by a stretching factor not exceeding 1.1. Meanwhile, P-to-S velocity ratios within the MRZ increase from 1.71 to 1.82 in southernmost Malawi, indicating a substantial modification of the crust during Recent rifting. Time-series stacking of approximately 5500 RFs recorded by the SAFARI and 44 neighboring network stations reveals an apparent uplift of 10 to 15 km along both the 410- and 660-km mantle transition zone (MTZ) discontinuities beneath the MRZ and LRZ which, coupled with an apparently normal 250-km MTZ thickness, implies a first-order high-velocity contribution from thickened lithosphere. Preliminary manual checking of SAFARI shear-wave splitting (SWS) measurements provides roughly 650 high-quality XKS phases following a component re-orientation to correct station misalignments. Regional azimuthal variations in SWS fast orientations are observed, from rift-parallel in the vicinity of the LRZ to rift-oblique in the MRZ. A major 60° rotation in the fast orientation occurs at approximately 31°E, possibly resulting from the modulation of mantle flow around a relatively thick lithospheric keel situated between the two rift zones.

  19. Imaging the midcontinent rift beneath Lake Superior using large aperture seismic data (United States)

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


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

  20. Basement structure and its influence on the structural configuration of the northern North Sea rift (United States)

    Fazlikhani, Hamed; Fossen, Haakon; Gawthorpe, Robert L.; Faleide, Jan Inge; Bell, Rebecca E.


    The northern North Sea rift basin developed on a heterogeneous crust comprising structures inherited from the Caledonian orogeny and Devonian postorogenic extension. Integrating two-dimensional regional seismic reflection data and information from basement wells, we investigate the prerift structural configuration in the northern North Sea rift. Three seismic facies have been defined below the base rift surface: (1) relatively low-amplitude and low-frequency reflections, interpreted as pre-Caledonian metasediments, Caledonian nappes, and/or Devonian clastic sediments; (2) packages of high-amplitude dipping reflections (>500 ms thick), interpreted as basement shear zones; and (3) medium-amplitude and high-frequency reflections interpreted as less sheared crystalline basement of Proterozoic and Paleozoic (Caledonian) origin. Some zones of Seismic Facies 2 can be linked to onshore Devonian shear zones, whereas others are restricted to the offshore rift area. Interpreted offshore shear zones dip S, ESE, and WNW in contrast to W to NW dipping shear zones onshore West Norway. Our results indicate that Devonian strain and ductile deformation was distributed throughout the Caledonian orogenic belt from central South Norway to the Shetland Platform. Most of the Devonian basins related to this extension are, however, removed by erosion during subsequent exhumation. Basement shear zones reactivated during the rifting and locally control the location and geometry of rift depocenters, e.g., in the Stord and East Shetland basins. Prerift structures with present-day dips >15° were reactivated, although some of the basement shear zones are displaced by rift faults regardless of their orientation relative to rift extension direction.

  1. Using the virtual reality device Oculus Rift for neuropsychological assessment of visual processing capabilities. (United States)

    Foerster, Rebecca M; Poth, Christian H; Behler, Christian; Botsch, Mario; Schneider, Werner X


    Neuropsychological assessment of human visual processing capabilities strongly depends on visual testing conditions including room lighting, stimuli, and viewing-distance. This limits standardization, threatens reliability, and prevents the assessment of core visual functions such as visual processing speed. Increasingly available virtual reality devices allow to address these problems. One such device is the portable, light-weight, and easy-to-use Oculus Rift. It is head-mounted and covers the entire visual field, thereby shielding and standardizing the visual stimulation. A fundamental prerequisite to use Oculus Rift for neuropsychological assessment is sufficient test-retest reliability. Here, we compare the test-retest reliabilities of Bundesen's visual processing components (visual processing speed, threshold of conscious perception, capacity of visual working memory) as measured with Oculus Rift and a standard CRT computer screen. Our results show that Oculus Rift allows to measure the processing components as reliably as the standard CRT. This means that Oculus Rift is applicable for standardized and reliable assessment and diagnosis of elementary cognitive functions in laboratory and clinical settings. Oculus Rift thus provides the opportunity to compare visual processing components between individuals and institutions and to establish statistical norm distributions.

  2. Structure and genetic mechanisms of the Precambrian rifts of the East-European Platform in Russia by integrated study of seismic, gravity, and magnetic data (United States)

    Kostyuchenko, S. L.; Egorkin, A. V.; Solodilov, L. N.


    Integrated models of the deep structure and origin of rifts located within the Russian portion of the East-European Platform have been developed from recent DSS results, new gravity and magnetic modelling, and geological and older geophysical data acquired over the last 50 years. The Mezen rift province, the Middle-Russian rift, the Valday rift, the Pachelma rift, and the rifts within the Pre-Caspian depression were studied. All of these rifts were affected by extension and filled with syn-rift sediments at different times through the Riphean (1650-650 Ma). Post-rift sedimentary basins developed from the end of the Neoproterozoic until the Cenozoic. The models indicate that the crustal structure and genesis of the individual rifts are different. The Mezen rift province was formed under a condition of limited extension of the continental crust. The McKenzie pure strain mechanism is acceptable for lithosphere extension in the Middle-Russian rift. The Wernicke model best expresses the Valday and Pachelma rifts. The rift process in the Pre-Caspian area is explained in terms of large-scale sliding apart of lithospheric plates, and approached the stage of development of oceanic crust.

  3. Morphometric and magmatic evolution at the Boset-Bericha Volcanic Complex in the Main Ethiopian Rift (United States)

    Siegburg, Melanie; Gernon, Thomas; Bull, Jonathan; Keir, Derek; Taylor, Rex; Nixon, Casey; Abebe, Bekele; Ayele, Atalay


    Tectono-magmatic interactions are an intrinsic feature of continental rifting and break up in the Main Ethiopian Rift (MER). The Boset-Bericha volcanic complex (BBVC) is one of the largest stratovolcanoes in the MER (with a total area of ˜870 km2), with volcanism largely occurring over the last ˜2 Myr. Despite the fact that 4 million people live within 100 km of the volcano, little is known about its eruptive history and how the volcanic system interacts with rift valley tectonics. Here, we present a detailed relative eruption chronology combined with morphometric analyses of different elements of the volcanic complex and petrological analyses to constrain morphometric and magmatic evolution at the BBVC. Additionally, tectonic activity has been characterised around the BBVC, all based on field observations and mapping using high-resolution digital elevation data. The BBVC consists of the Gudda Volcano and the younger Bericha Volcano, two silicic eruption centres located along the NNE-SSW trending rift axis. The fault population predominantly comprises distributed extensional faults parallel to the rift axis, as well as localised discrete faults with displacements of up to 50 m in the rift centre, and up to 200 m in the NE-SW trending border fault system. Multiple cones, craters and fissure systems are also oriented parallel to the rift axis, i.e. perpendicular to the minimum compressive stress. The eruption history of BBVC can be differentiated into 5 main eruption stages, subdivided into at least 12 eruptive phases with a total of 128 mappable lava flows. Crosscutting relationships of lava flows provide a relative chronology of the eruptive history of the BBVC, starting with pre-BBVC rift floor basalts, pre-caldera and caldera activity, three post-caldera phases at the Gudda Volcano and two phases forming the Bericha Volcano. At least four fissure eruption phases occurred along the rift axis temporally in between the main eruptive phases. Morphometric analyses

  4. Deformation derived from GPS geodesy associated with Bárðarbunga 2014 rifting event in Iceland

    KAUST Repository

    Ofeigsson, Benedikt Gunnar


    On August 16, 2014 an intense seismic swarm started below the eastern part of Bárðarbunga Caldera in the north-western corner of Vatnajökull ice-cap, Iceland, marking the onset of the first rifting event in Iceland since the Krafla fires (1975-1984). The migration of the seismicity was corroborated by ground deformation in areas outside the ice cap and on nunataks within the ice cap suggesting a lateral propagation of magma, from the Bárðabunga system. The sesimicity migrated out of the caldera forming a dyke with roughly three segments, changing direction each time until August 28 when the migration stopped around 10 km south of Askja Volcano, eventually leading to a short lived eruption in Holuhraun north of Dyngjujökull. A second fissure eruption started in Holuhraun on August 31 which is still ongoing at the time of this writing. In the months prior to the onset of the activity, subtle signs of inflation where observed on continuous GPS sites around the Bárðarbunga indicating a volume increase in the roots of the volcanic system. When the activity started on August 16, the deformation pattern indicated a simultaneous deflation centered within the caldera and a lateral growth of a dyke also reflected in the migration of seismicity along segments of variable strike. A maximum widening of 1.3 m occurred between stations on opposite sides of the dyke spaced 25 km apart. Significant movements where detected on GPS site more then 80 km away from the tip of dyke. Displacements indicated the fastest rate of widening at any time in the most distal segment of the dyke throughout its evolution. After the dyke stopped propagating, the inflation continued, decaying exponentialy with time. On September 4, five days into the second fissure eruption, the movements associated with the dyke where no longer significant. As the fissure eruption continues, a slowly decaying contraction is observed around the Bárðarbunga central volcano, both shown in the piston like

  5. Spatial and Temporal Population Genetics at Deep-Sea Hydrothermal Vents Along the East Pacific Rise and Galapagos Rift (United States)


    Pacific Rise and Galapagos Rift by Abigail Jean Fusaro September 2008 20081117239 50? 𔃼-101 REPORT DOCUMENTATION PAGE 1. REPORT NO. MIT/WHOI...Pacific Rise and Galapagos Rift 5. Report Date September 2008 6. ?. uthor(s) . Abigail Jean husaro 8. Performing Organization...2008. Spatial and Temporal Population Genetics at Deep-Sea Hydrothermal Vents Along the East Pacific Rise and Galapagos Rift. Ph.D. Thesis. MITAVHOI

  6. The case for nearly continuous extension of the West Antarctic Rift System, 105-25 Ma (Invited) (United States)

    Wilson, D. S.; Luyendyk, B. P.


    It is a common perception that extension in the West Antarctic Rift System (WARS) was a two-phase process, with a Cretaceous phase ending when the Campbell Plateau rifted from West Antarctica (~80 Ma), and a mid-Cenozoic phase synchronous with sea floor spreading in the Adare trough (~45-25 Ma). Several lines of evidence indicate that significant extension probably occurred in the intervening 80-45 Ma interval. The strongest evidence comes from subsidence rates on the Central High and Coulman High structures in the central-western Ross Sea, where DSDP Site 270 and other areas with shallow basement have subsided 1 km or more since Oligocene time. With sediment load, these subsidence rates are reasonable for thermal subsidence resulting from extension with a stretching factor of about 2.0-2.5 at about 50-70 Ma, but are hard to reconcile with an extension age around 90 Ma. The seismic velocity structure of the WARS inferred from global surface-wave dispersion is similar to that of oceanic lithosphere of age 40-60 Ma [Ritzwoller et al., 2001 JGR]. Geometric relations of sea floor between Adare Trough and Iselen Bank, northwest Ross Sea, suggest sea floor spreading of about 130 km during early Cenozoic, before the Adare Trough spreading episode started. Numerous cooling ages in the Transantarctic Mountains in the range of 55-45 Ma [Fitzgerald, 1992 Tectonics; Miller et al., 2010 Tectonics] support the interpretation of significant extension prior to 45 Ma. Present crustal thickness of about 22 km near DSDP Site 270 [Trey et al., 1999 Tectonophysics] suggests a pre-extension crustal thickness exceeding 50 km. A simple overall interpretation follows that the WARS has a tectonic history similar to the Basin and Range of western North America: a thick-crust orogenic highland extended for many tens of million years. The main difference between the WARS and the Basin and Range is the post-tectonic cooling and subsidence in the WARS.

  7. Continuous cratonic crust between the Congo and Tanzania blocks in western Uganda (United States)

    Link, Klemens; Koehn, Daniel; Barth, Matthias G.; Tiberindwa, John V.; Barifaijo, Erasmus; Aanyu, Kevin; Foley, Stephen F.


    Western Uganda is a key region for understanding the development of the western branch of the East African rift system and its interaction with pre-existing cratonic lithosphere. It is also the site of the topographically anomalous Rwenzori Mountains, which attain altitudes of >5000 m within the rift. New structural and geochronological data indicate that western Uganda south and east of the Rwenzori Mountains consists of a WSW to ENE trending fold and thrust belt emplaced by thick-skinned tectonics that thrust several slices of Proterozoic and Archaean units onto the craton from the south. The presence of Archaean units within the thrust stack is supported by new Laser-ICP-MS U-Pb age determinations (2637-2584 Ma) on zircons from the Rwenzori foothills. Repetition of the Paleoproterozoic units is confirmed by mapping the internal stratigraphy where a basal quartzite can be used as marker layer, and discrete thrust units show distinct metamorphic grades. The thrust belt is partially unconformably covered by a Neoproterozoic nappe correlated with the Kibaran orogenic belt. Even though conglomerates mark the bottom of the Kibaran unit, intensive brittle fault zones and pseudotachylites disprove an autochthonous position. The composition of volcanics in the Toro-Ankole field of western Uganda can be explained by the persistence of a cratonic lithosphere root beneath the northwardly thrusted Archaean and Palaeoproterozoic rocks of westernmost Uganda. Volcanic geochemistry indicates thinning of the lithosphere from >140 km beneath Toro-Ankole to ca. 80 km beneath the Virunga volcanic field about 150 km to the south. We conclude that the western branch of the East African rift system was initiated in an area of thinner lithosphere with Palaeoproterozoic cover in the Virunga area and has propagated northwards where it now abuts against thick cratonic lithosphere covered by a thrust belt consisting of gneisses, metasediments and metavolcanics of Neoarchaean to Proterozoic

  8. Onshore and offshore apatite fission-track dating from the southern Gulf of California: Insights into the time-space evolution of the rifting (United States)

    Balestrieri, Maria Laura; Ferrari, Luca; Bonini, Marco; Duque-Trujillo, Jose; Cerca, Mariano; Moratti, Giovanna; Corti, Giacomo


    We present the results of a apatite fission-track (AFT) study on intrusive rocks in the southern Gulf of California, sampled along the eastern margin of Baja California Sur (western rift margin), as well as from islands and submerged rifted blocks within the Gulf of California, and from the conjugate Mexican margin (Nayarit state). For most of the samples U-Pb zircon and 40Ar-39Ar mineral ages were already available (Duque-Trujillo et al., 2015). Coupled with the new AFT data these ages provide a more complete information on cooling after emplacement. Our samples span a wide range of ages between 5.5 ± 1.1 and 73.7 ± 5.8 Ma, and show a general spatial distribution, with late Miocene AFT ages (about 6 Ma) aligned roughly NW-SE along a narrow offshore belt, parallel to Baja California Peninsula, separating older ages on both sides. This pattern suggests that in Late Miocene, deformation due to plate transtension focused at the eastern rheological boundary of the Baja California block. Some Early Miocene AFT ages onshore Baja California could be related to plutons emplaced at shallow depths and thermal resetting associated with the onset of volcanism at 19 Ma in this part of the Peninsula. On the other hand, an early extensional event similar to that documented in the eastern Gulf cannot be ruled out in the westernmost Baja California.

  9. Seismicity and S-wave velocity structure of the crust and the upper mantle in the Baikal rift and adjacent regions (United States)

    Seredkina, Alena; Kozhevnikov, Vladimir; Melnikova, Valentina; Solovey, Oksana


    Correlations between seismicity, seismotectonic deformation (STD) field and velocity structure of the crust and the upper mantle in the Baikal rift and the adjacent areas of the Siberian platform and the Mongol-Okhotsk fold belt have been investigated. The 3D S-wave velocity structure up to the depths of 500 km has been modeled using a representative sample of Rayleigh wave group velocity dispersion curves (about 3200 paths) at periods from 10 to 250 s. The STD pattern has been reconstructed from mechanisms of large earthquakes, and is in good agreement with GPS and structural data. Analysis of the results has shown that most of large shallow earthquakes fall in regions of low S-wave velocities in the uppermost mantle (western Mongolia and areas of recent mountain building in southern Siberia) and in zones of their relatively high lateral variations (northeastern flank of the Baikal rift). In the first case the dominant STD regime is compression manifested in a mixture of thrust and strike-slip deformations. In the second case we observe a general predominance of extension.

  10. Sustaining without Changing: The Metabolic Rift of Certified Organic Farming

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    Julius Alexander McGee


    Full Text Available Many proponents of organic farming claim that it is a sustainable alternative to conventional agriculture due to its reliance on natural agro-inputs, such as manure based fertilizers and organic pesticides. However, in this analysis we argue that although particular organic farming practices clearly benefit ecosystems and human consumers, the social context in which some organic farms develop, limit the potential environmental benefits of organic agriculture. Specifically, we argue that certified organic farming’s increased reliance on agro-inputs, such as organic fertilizers and pesticides, reduces its ability to decrease global water pollution. We review recent research that demonstrates the environmental consequences of specific organic practices, as well as literature showing that global organic farming is increasing its reliance on agro-inputs, and contend that organic farming has its own metabolic rift with natural water systems similar to conventional agriculture. We use a fixed-effects panel regression model to explore how recent rises in certified organic farmland correlate to water pollution (measured as biochemical oxygen demand. Our findings indicate that increases in the proportion of organic farmland over time increases water pollution. We conclude that this may be a result of organic farms increasing their reliance on non-farm agro-inputs, such as fertilizers.

  11. The North Galactic Pole Rift and the Local Hot Bubble (United States)

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


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

  12. Middle Stone Age starch acquisition in the Niassa Rift, Mozambique (United States)

    Mercader, Julio; Bennett, Tim; Raja, Mussa


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

  13. A dynamic, climate-driven model of Rift Valley fever

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    Joseph Leedale


    Full Text Available Outbreaks of Rift Valley fever (RVF in eastern Africa have previously occurred following specific rainfall dynamics and flooding events that appear to support the emergence of large numbers of mosquito vectors. As such, transmission of the virus is considered to be sensitive to environmental conditions and therefore changes in climate can impact the spatiotemporal dynamics of epizootic vulnerability. Epidemiological information describing the methods and parameters of RVF transmission and its dependence on climatic factors are used to develop a new spatio-temporal mathematical model that simulates these dynamics and can predict the impact of changes in climate. The Liverpool RVF (LRVF model is a new dynamic, process-based model driven by climate data that provides a predictive output of geographical changes in RVF outbreak susceptibility as a result of the climate and local livestock immunity. This description of the multi-disciplinary process of model development is accessible to mathematicians, epidemiological modellers and climate scientists, uniting dynamic mathematical modelling, empirical parameterisation and state-of-the-art climate information.

  14. An Assembly Model of Rift Valley Fever Virus (United States)

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


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

  15. An assembly model of Rift Valley fever virus

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    Mirabela eRusu


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

  16. Stress Rotation in the Kachchh Rift Zone, Gujarat, India (United States)

    Mandal, Prantik


    Double difference relocations of the 1402 Kachchh events (2001 2006) clearly delineate two fault zones viz. south-dipping North Wagad fault (NWF) and almost vertical Gedi fault (GF). The relocated focal depths delineate a marked variation of 4 and 7 km in the brittle-ductile transition depths beneath GF and NWF, respectively. The focal mechanism solutions of 464 aftershocks (using 8 12 first motions) show that the focal mechanisms ranged between pure reverse and pure strike-slip except for a few pure dip-slip solutions. The stress inversions performed for five rectangular zones across the Kachchh rift reveal both clockwise and anticlockwise rotation (7 32°) in the σ1 orientation within the rupture zone, favoring a heterogeneous stress regime with an average N-S fault normal compression. This rotation may be attributed to the presence of crustal mafic intrusives (5 35 km depth) in the rupture zone of the 2001 Bhuj main shock. Results suggest a relatively homogeneous stress regime in the GF zone favoring strike-slip motion, with a fault normal N-S compression.

  17. 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

  18. Re-orientation of the extension direction and pure extensional faulting at oblique rift margins: Comparison between the Main Ethiopian Rift and laboratory experiments

    NARCIS (Netherlands)

    Corti, G.; Philippon, M.|info:eu-repo/dai/nl/370818636; Sani, F.; Keir, D.; Kidane, T.


    In this study, we draw on a unique combination of well-resolved fault-slip data and earthquake focal mechanisms to constrain spatial variations in style of faulting in the obliquely extending Main Ethiopian Rift, East Africa. These data show that both boundary and internal faults - oblique and


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    V. V. Chashchin


    Full Text Available The article provides data on the structure of the Paleoproterozoic intercontinental Imandra-Varzuga rifting structure (IVS and compositions of intrusive formations typical of the early stage of the IVS development and associated mineral resources. IVS is located in the central part of the Kola region. Its length is about 350 km, and its width varies from 10 km at the flanks to 50 km in the central part. IVS contains an association of the sedimentary-volcanic, intrusive and dyke complexes. It is a part of a large igneous Paleoproterozoic province of the Fennoscandian Shield spreading for a huge area (about 1 million km2, which probably reflects the settings of the head part of the mantle plume. Two age groups of layered intrusions were associated with the initial stage of the IVS development. The layered intrusions of the Fedorovo-Pansky and Monchegorsk complexes (about 2.50 Ga are confined to the northern flank and the western closure of IVS, while intrusions of the Imandra complex (about 2.45 Ga are located at the southern flank of IVS. Intrusions of older complexes are composed of rock series from dunite to gabbro and anorthosites (Monchegorsk complex and from orthopyroxenite to gabbro and anorthosites (Fedorovo-Pansky complex. Some intrusions of this complexes reveal features of multiphase ones. The younger Imandra complex intrusions (about 2.45 Ga are stratified from orthopyroxenite to ferrogabbro. Their important feature is comagmatical connection with volcanites. All the intrusive complexes have the boninite-like mantle origin enriched by lithophyle components. Rocks of these two complexеs with different age have specific geochemical characteristics. In the rocks of the Monchegorsk and Fedorovo-Pansky complexes, the accumulation of REE clearly depends on the basicity of the rocks, the spectrum of REE is non-fractionated and ‘flat’, and the Eu positive anomaly is slightly manifested. In the rocks of the Imandra complex, the level of


    Directory of Open Access Journals (Sweden)

    V. V. Chashchin


    Full Text Available The article provides data on the structure of the Paleoproterozoic intercontinental Imandra-Varzuga rifting structure (IVS and compositions of intrusive formations typical of the early stage of the IVS development and associated mineral resources. IVS is located in the central part of the Kola region. Its length is about 350 km, and its width varies from 10 km at the flanks to 50 km in the central part. IVS contains an association of the sedimentary-volcanic, intrusive and dyke complexes. It is a part of a large igneous Paleoproterozoic province of the Fennoscandian Shield spreading for a huge area (about 1 million km2, which probably reflects the settings of the head part of the mantle plume. Two age groups of layered intrusions were associated with the initial stage of the IVS development. The layered intrusions of the Fedorovo-Pansky and Monchegorsk complexes (about 2.50 Ga are confined to the northern flank and the western closure of IVS, while intrusions of the Imandra complex (about 2.45 Ga are located at the southern flank of IVS. Intrusions of older complexes are composed of rock series from dunite to gabbro and anorthosites (Monchegorsk complex and from orthopyroxenite to gabbro and anorthosites (Fedorovo-Pansky complex. Some intrusions of this complexes reveal features of multiphase ones. The younger Imandra complex intrusions (about 2.45 Ga are stratified from orthopyroxenite to ferrogabbro. Their important feature is comagmatical connection with volcanites. All the intrusive complexes have the boninite-like mantle origin enriched by lithophyle components. Rocks of these two complexеs with different age have specific geochemical characteristics. In the rocks of the Monchegorsk and Fedorovo-Pansky complexes, the accumulation of REE clearly depends on the basicity of the rocks, the spectrum of REE is non-fractionated and ‘flat’, and the Eu positive anomaly is slightly manifested. In the rocks of the Imandra complex, the level of

  1. Synthesis and tectonic interpretation of the westernmost Paleozoic Variscan orogen in southern Mexico: From rifted Rheic margin to active Pacific margin (United States)

    Keppie, J. Duncan; Dostal, Jaroslav; Murphy, J. Brendan; Nance, R. Damian


    origin along the southern margin of the Rheic Ocean. Latest Devonian-Permian deposition was synchronous with Mississippian extrusion of the HP rocks into the upper plate during extensional deformation. The HP Cambro-Orodivician rift-shelf rocks are inferred to have originated in the forearc region of the upper plate that was removed by subduction erosion, carried down the subduction channel, and then extruded into the upper plate in the middle of the Mixteca terrane. The presence of arc-related rocks in the HP assemblage suggests that the arc complex was also removed, whereas the MORB rocks may have been derived from the subducting slab. Detrital zircons in the Carboniferous rocks of both the Mixteca and Oaxaquia terranes contain Devonian detrital zircons and volcanic clasts that are inferred to have come from the removed Devonian arc on the western margin of the Mixteca terrane and/or from exhumed HP rocks. During the Permian, arc-related intrusions in both the Mixteca and Oaxaquia terranes were accompanied by dextral transtensional deformation and deposition of clastic rocks containing Permian detrital zircons and carbonates in periarc, pull-apart basins. Empirical relationships between the dip of the Benioff zone and the widths of arc and forearc indicate that the Permian trench lay beneath the eastern edge of the Mesozoic Guerrero terrane.

  2. Crustal Deformation Field Around Rift Zone In Southeastern Afar Derived From Jers-1/in-sar (United States)

    Ozawa, T.; Nogi, Y.; Shibuya, K.

    Afar is one of the major active rift zones recognized on the ground and located around the triple junction of Arabia, Somalia and Nubian plates. Afar is one of the major rift zones recognized on the ground. The crustal deformation of Afar has been deduced from paleomagnetism, geology and seismology by many scientists. The current crustal deformation must be detected by geodetic measurements. Ruegg et al. (J. Geophys. Res., 1984) showed the crustal deformation across the Asal-Ghoubbet rift with rate of about 60 mm/yr extension derived from triangulation and trilateration. Walpersdorf et al. (J. Geodyn., 1999) show the opening between South Djibouti and Yemen with rate of 16 mm/yr by GPS surveys. Denser observations are required for detailed crustal deformation, however it is difficult to construct such observation network because of harsh environment. The geodetic application of remote sensing is useful in this region, and we apply JERS-1 SAR interferometry in southeastern Afar, which is one of the most active deformation area. In this study, we use six SAR scenes observed from 1996/5/20 to 1997/5/7, and generate five interferograms; these repeat cycles are 88 (2 pairs), 176, 264, 352 days. First, we generate the digital elevation model (DEM) from two 88 repeat cycle pairs applying the multiple pass SAR interferometry method by Kwok and Fahnestock (IEEE Trans. Geosci. Remote Sensing, 1996). Next, the topographic fringes of all pairs are removed using the DEM. The crustal deformation derived from SAR interferometry increases with expanding repeat cycle. Finally, the velocity field is estimated by fitting to linear trend for each pixel. The spreading rate of Asal-Ghoubbet rift derived from SAR interferometry is good agreement with that by Ruegg et al. (J. Geophys. Res., 1984). We can see the crustal deformation with the subsidence sense in the west of Asal-Ghoubbet rift. This suggests that the extension is distinguished in this area. The subsidence sense deformation

  3. Crustal and lithospheric structure of the west Antarctic Rift System from geophysical investigations: A review (United States)

    Behrendt, John C.


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

  4. Exploring virtual reality technology and the Oculus Rift for the examination of digital pathology slides

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    Navid Farahani


    Full Text Available Background: Digital slides obtained from whole slide imaging (WSI platforms are typically viewed in two dimensions using desktop personal computer monitors or more recently on mobile devices. To the best of our knowledge, we are not aware of any studies viewing digital pathology slides in a virtual reality (VR environment. VR technology enables users to be artificially immersed in and interact with a computer-simulated world. Oculus Rift is among the world′s first consumer-targeted VR headsets, intended primarily for enhanced gaming. Our aim was to explore the use of the Oculus Rift for examining digital pathology slides in a VR environment. Methods: An Oculus Rift Development Kit 2 (DK2 was connected to a 64-bit computer running Virtual Desktop software. Glass slides from twenty randomly selected lymph node cases (ten with benign and ten malignant diagnoses were digitized using a WSI scanner. Three pathologists reviewed these digital slides on a 27-inch 5K display and with the Oculus Rift after a 2-week washout period. Recorded endpoints included concordance of final diagnoses and time required to examine slides. The pathologists also rated their ease of navigation, image quality, and diagnostic confidence for both modalities. Results: There was 90% diagnostic concordance when reviewing WSI using a 5K display and Oculus Rift. The time required to examine digital pathology slides on the 5K display averaged 39 s (range 10-120 s, compared to 62 s with the Oculus Rift (range 15-270 s. All pathologists confirmed that digital pathology slides were easily viewable in a VR environment. The ratings for image quality and diagnostic confidence were higher when using the 5K display. Conclusion: Using the Oculus Rift DK2 to view and navigate pathology whole slide images in a virtual environment is feasible for diagnostic purposes. However, image resolution using the Oculus Rift device was limited. Interactive VR technologies such as the Oculus Rift are

  5. Geometry and kinematics of the Triassic rift basin in Jameson Land (East Greenland) (United States)

    Guarnieri, Pierpaolo; Brethes, Anaïs.; Rasmussen, Thorkild M.


    The Triassic rift basin along the east Greenland margin described in this paper is represented by NE-SW trending basins and highs segmented by NW-SE trending transfer zones. Coarse-grained sediments along the eastern side of Jameson Land are shown to be hosted in half-graben structures belonging to the Carlsberg Fjord Basin that is bounded by NW dipping normal faults mapped and described after fieldwork in the Klitdal area in Liverpool Land. New aeromagnetic and electromagnetic data together with new drill cores allow the reinterpretation of available seismic lines showing the continuation of the Triassic rift basin toward the SW where it is buried under the Upper Triassic postrift sediments and the Jurassic successions of the Jameson Land Basin. The N-S trending Liverpool Land, interpreted as the boundary block of the Triassic basin, is shown to represent a structural high inherited from the Late Carboniferous tectonics and faulted during the Triassic rifting. The Carlsberg Fjord Basin and the Klitdal Fault System described in this paper should be seen as analogues to the Helgeland Basin in the Norwegian offshore that is bounded by the Ylvingen Fault Zone and to the Papa and West of Shetlands Basins that are bounded by the Spine Fault. The Triassic rift zone and transfer faults on both conjugate margins show a straightforward correlation with the trends of the initial spreading line and fracture zones of the northeast Atlantic indicating a possible inheritance of the Triassic rifting.

  6. 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.

  7. Strain partitioning evolution and segmentation in hyperextended rift systems: insights from the Bay of Biscay and Pyrenees (United States)

    Tugend, Julie; Manatschal, Gianreto; Kusznir, Nick J.


    The understanding of the formation of hyper-extended domains has greatly benefited from combined studies at present-day and fossil rift systems preserved in collisional orogens. However, even though domains of extreme crustal and lithosphere thinning have been increasingly recognized, the spatial and temporal evolution of their tectonic processes remains poorly constrained. The Bay of Biscay and Pyrenees correspond to a Late Jurassic to Mid Cretaceous rift system including both oceanic and hyper-extended rift domains. The transition from preserved oceanic and rift domains to the West to their complete inversion in the East provide simultaneous access to seismically imaged and exposed parts of a hyper-extended rift system. We combine seismic interpretations and gravity inversion results with field mapping to identify and map former rift domains from the Bay of Biscay margins to their fossil analogues preserved in the Pyrenean orogen. This onshore/offshore map of the rift systems enables us to investigate the spatial and temporal evolution and the strain distribution related to the formation of a strongly segmented rift system preserved at the transition between the European and Iberian plate boundary. The restoration of the hyper-extended domains reveals the occurrence of spatially disconnected rift systems separated by weakly thinned continental ribbons (e.g. Landes High, Ebro block). While the offshore Bay of Biscay represent a former mature oceanic domain, the fossil remnants of hyper-extended domains preserved onshore in the Pyrenean-Cantabrian orogen record distributed extensional deformation partitioned between strongly segmented rift basins (e.g. Basque-Cantabrian, Arzacq-Mauléon basins). Rift system segmentation controls lateral variations of architecture and may be partly inherited from the pre-rift structuration. The relative timing of hyper-extensional processes is diachronous between the different rift systems recording the polyphased evolution of the

  8. P-Wave Velocity Tomography from Local Earthquakes in Western Mexico (United States)

    Ochoa-Chávez, Juan A.; Escudero, Christian R.; Núñez-Cornú, Francisco J.; Bandy, William L.


    In western Mexico, the subduction of the Rivera and Cocos plates beneath the North America plate has deformed and fragmented the overriding plate, forming several structural rifts and crustal blocks. To obtain a reliable subsurface image of the continental crust and uppermost mantle in this complex area, we used P-wave arrivals of local earthquakes along with the Fast Marching Method tomography technique. We followed an inversion scheme consisting of (1) the use of a high-quality earthquake catalog and corrected phase picks, (2) the selection of earthquakes using a maximum location error threshold, (3) the estimation of an improved 1-D reference velocity model, and (4) the use of checkerboard testing to determine the optimum configuration of the velocity nodes and inversion parameters. Surprisingly, the tomography results show a very simple δVp distribution that can be described as being controlled by geologic structures formed during two stages of the separation of the Rivera and Cocos plates. The earlier period represents the initial stages of the separation of the Rivera and Cocos plates beneath western Mexico; the later period represents the more advanced stage of rifting where the Rivera and Cocos plates had separated sufficiently to allow melt to accumulate below the Colima Volcanic complex. During the earlier period (14 or 10-1.6 Ma), NE-SW-oriented structures/lineaments (such as the Southern Colima Rift) were formed as the two plates separated. During the second period (1.6 Ma to the present), the deformation is attributed to magma, generated within and above the tear zone between the Rivera and Cocos plates, rising beneath the region of the Colima Volcanic Complex. The rising magma fractured the overlying crust, forming a classic triple-rift junction geometry. This triple-rift system is confined to the mid- to lower crust perhaps indicating that this rifting process is still in an early stage. This fracturing, along with fluid circulation and associated

  9. Quaternary perpotassic magmatism in Uganda (Toro-Ankole Volcanic Province): age assessment and significance for magmatic evolution along the East African Rift (United States)

    Boven, A.; Pasteels, P.; Punzalan, L. E.; Yamba, T. K.; Musisi, J. H.


    The Toro-Ankole volcanics in the northern sector of the Western Branch of the East African Rift are generally assumed to be of Quaternary age. New field observations and comparative KAr and ArAr analyses on whole rock samples and phenocrysts of perpotassic lavas reveal the presence of excess Ar and led to the conclusion that apparently no volcanics have been erupted prior to 50 ka. The present geochronological data, compared with previous ones for the Virunga and South Kivu volcanic fields, suggest that a Late Quaternary pulse of volcanic activity occured in the three areas, with the emission of perpotassic, mildly potassic or sodic alkaline magmas. The genetic implications of such a synchronous activity with wide compositional variation are briefly discussed with respect to basement age and assumed lithosphere characteristics.

  10. Post Rift Evolution of the Indian Margin of Southern Africa (United States)

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


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

  11. Innate Immune Response to Rift Valley Fever Virus in Goats (United States)

    Nfon, Charles K.; Marszal, Peter; Zhang, Shunzhen; Weingartl, Hana M.


    Rift Valley fever (RVF), a re-emerging mosquito-borne disease of ruminants and man, was endemic in Africa but spread to Saudi Arabia and Yemen, meaning it could spread even further. Little is known about innate and cell-mediated immunity to RVF virus (RVFV) in ruminants, which is knowledge required for adequate vaccine trials. We therefore studied these aspects in experimentally infected goats. We also compared RVFV grown in an insect cell-line and that grown in a mammalian cell-line for differences in the course of infection. Goats developed viremia one day post infection (DPI), which lasted three to four days and some goats had transient fever coinciding with peak viremia. Up to 4% of peripheral blood mononuclear cells (PBMCs) were positive for RVFV. Monocytes and dendritic cells in PBMCs declined possibly from being directly infected with virus as suggested by in vitro exposure. Infected goats produced serum IFN-γ, IL-12 and other proinflammatory cytokines but not IFN-α. Despite the lack of IFN-α, innate immunity via the IL-12 to IFN-γ circuit possibly contributed to early protection against RVFV since neutralising antibodies were detected after viremia had cleared. The course of infection with insect cell-derived RVFV (IN-RVFV) appeared to be different from mammalian cell-derived RVFV (MAM-RVFV), with the former attaining peak viremia faster, inducing fever and profoundly affecting specific immune cell subpopulations. This indicated possible differences in infections of ruminants acquired from mosquito bites relative to those due to contact with infectious material from other animals. These differences need to be considered when testing RVF vaccines in laboratory settings. PMID:22545170

  12. Response to Rift Valley Fever in Tanzania: Challenges and Opportunities. (United States)

    Fyumagwa, Robert D; Ezekiel, Mangi J; Nyaki, Athanas; Mdaki, Maulid L; Katale, Zablon B; Moshiro, Candida; Keyyu, Julius D


    Rift Valley Fever (RVF) is an arthropod borne viral disease affecting livestock (cattle, sheep, goats and camels), wildlife and humans caused by Phlebovirus. The disease occurs in periodic cycles of 4-15 years associated with flooding from unusually high precipitations in many flood-prone habitats. Aedes and Culex spp and other mosquito species are important epidemic vectors. Because of poor living conditions and lack of knowledge on the pathogenesis of RVF, nomadic pastoralists and agro-pastoralists are at high risk of contracting the disease during epidemics. RVF is a professional hazard for health and livestock workers because of poor biosafety measures in routine activities including lack of proper Personal Protective Equipment (PPE). Direct exposure to infected animals can occur during handling and slaughter or through veterinary and obstetric procedures or handling of specimens in laboratory. The episodic nature of the disease creates special challenges for its mitigation and control and many of the epidemics happen when the governments are not prepared and have limited resource to contain the disease at source. Since its first description in 1930s Tanzania has recorded six epidemics, three of which were after independence in 1961. However, the 2007 epidemic was the most notable and wide spread with fatal human cases among pastoralists and agro-pastoralists concurrent with high livestock mortality. Given all the knowledge that exist on the epidemiology of the disease, still the 2006/2007 epidemic occurred when the government of Tanzania was not prepared to contain the disease at source. This paper reviews the epidemiology, reporting and outbreak-investigation, public awareness, preparedness plans and policy as well as challenges for its control in Tanzania.

  13. Rift Valley fever: Real or perceived threat for Zambia?

    Directory of Open Access Journals (Sweden)

    George Dautu


    Full Text Available Rift Valley fever (RVF in Zambia was first reported in 1974 during an epizootic of cattle and sheep that occurred in parts of Central, Southern and Copperbelt Provinces. In 1990, the disease was documented in nine districts of the provinces of Zambia. In the last two decades, there have been no reports of RVF. This long period without reported clinical disease raises questions as to whether RVF is a current or just a perceived threat. To address this question, World Organisation for Animal Health (OIE disease occurrence data on RVF for the period 2005−2010 in the Southern Africa Development Community (SADC was analysed. From the analysis, it was evident that most countries that share a common border with Zambia had reported at least one occurrence of the disease during the period under review. Due to the absence of natural physical barriers between Zambia and most of her neighbours, informal livestock trade and movements is a ubiquitous reality. Analysis of the rainfall patterns also showed that Zambia received rains sufficient to support a mosquito population large enough for high risk of RVF transmission. The evidence of disease occurrence in nearby countries coupled with animal movement, and environmental risk suggests that RVF is a serious threat to Zambia. In conclusion, the current occurrence of RVF in Zambia is unclear, but there are sufficient indications that the magnitude of the circulating infection is such that capacity building in disease surveillance and courses on recognition of the disease for field staff is recommended. Given the zoonotic potential of RVF, these measures are also a prerequisite for accurate assessment of the disease burden in humans.

  14. The 2007 Rift Valley Fever Outbreak in Sudan (United States)

    Hassan, Osama Ahmed; Ahlm, Clas; Sang, Rosemary; Evander, Magnus


    Rift Valley fever (RVF) is a neglected, emerging, mosquito-borne disease with severe negative impact on human and animal health and economy. RVF is caused by RVF virus (RVFV) affecting humans and a wide range of animals. The virus is transmitted through bites from mosquitoes and exposure to viremic blood, body fluids, or tissues of infected animals. During 2007 a large RVF outbreak occurred in Sudan with a total of 747 confirmed human cases including 230 deaths (case fatality 30.8%); although it has been estimated 75,000 were infected. It was most severe in White Nile, El Gezira, and Sennar states near to the White Nile and the Blue Nile Rivers. Notably, RVF was not demonstrated in livestock until after the human cases appeared and unfortunately, there are no records or reports of the number of affected animals or deaths. Ideally, animals should serve as sentinels to prevent loss of human life, but the situation here was reversed. Animal contact seemed to be the most dominant risk factor followed by animal products and mosquito bites. The Sudan outbreak followed an unusually heavy rainfall in the country with severe flooding and previous studies on RVF in Sudan suggest that RVFV is endemic in parts of Sudan. An RVF outbreak results in human disease, but also large economic loss with an impact beyond the immediate influence on the directly affected agricultural producers. The outbreak emphasizes the need for collaboration between veterinary and health authorities, entomologists, environmental specialists, and biologists, as the best strategy towards the prevention and control of RVF. PMID:21980543

  15. Age and isotopic marks of K-rich Manning Massif trachybasalts: an evidence for Lambert-Amery rift-system initiation (East Antarctica) (United States)

    Leitchenkov, German; Belyatsky, Boris; Lepekhina, Elena; Antonov, Anton; Krymsky, Robert; Andronikov, Alex; Sergeev, Sergey


    Volcanic rocks from the Manning Massif, which is situated in the western flank of the Paleozoic-Late Mesozoic Lambert Rift (East Antarctica), belong to a rare type of alkaline magmatism within the Precambrian East Antarctic Craton. K-rich olivine trachybasalts compose some flows resting upon a surface of Precambrian granulite terrain, each flow of 2.5-7 m in thickness and total section not less than 30 m. Each flow sequence comprises of glassy chilled base with vitroporphyritic texture, fine-plated vesicular basalt with interstitial texture, massive fine-grained basalt with porphyritic microlitic texture, amigdaloidal aphanitic basalt with poikilophytic texture, and vesicular mandelstone of slag crust with vitroporphyritic texture [Andronikov et al., 1998]. Rb-Sr and K-Ar isotopic age of this eruption was estimated as 40-50 Ma and the main reason for this Cenozoic continental volcanism was supposed the post-rift tectonic activity [Andronikov et al., 1998]. But the isotopic characteristics of these trachybasalts are very similar to those obtained for the part of spinel lherzolite and spinel-garnet lherzolite xenoliths from the Mesozoic alkaline picrite of the adjacent Jetty Peninsula region. That could be evidence of the trachybasalt mantle source in long-lived enriched upper mantle beneath the region, either under the lowermost levels of spinel lherzolite facies or on the highest levels of garnet lherzolite facies conditions. To reveal tectonic position of these enigmatic volcanics, we have studied 16 samples from different parts of basaltic flows for U-Pb geochronology and Pb-Sr-Nd-Os isotopic characteristics. U-Pb SIMS SHRIMP-II analysis was performed for 68 apatite grains from 5 samples. All obtained data-points are approximated by discordia line (MSWD=1.6) on Tera-Wasserburg diagram, corresponding to the age of 346±46 Ma. Common Pb isotope composition of these apatites differs from the model by increased 206Pb/204Pb (19.8) and 207Pb/204Pb (18.3) that means the

  16. 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...... and geophysical studies, the geodynamic origin and evolution of the BRZ is still debated. We applytwo-dimensional finite difference code to model the lithosphere-scale de-formation in several locations across the strike of the Baikal Rift zone. The model se-tup takes an advantage of regional geophysical models...... 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...

  17. Characteristics of Dengying Fm sedimentary sequence in the central–western Sichuan Basin and their controlling effect on gas accumulation

    Directory of Open Access Journals (Sweden)

    Long Wen


    Full Text Available A large gas reservoir in the Sinian Dengying Fm was recently discovered in Anyue area, central Sichuan Basin. In order to promote the oil and gas exploration in this area, it is of great significance to sustainably deepen the analysis on its high-quality reservoir distribution and source-reservoir assemblage. In this paper, a series of studies were performed on the sequence frameworks and sedimentary filling evolution characteristics of the Dengying Fm in central–western Sichuan Basin, and their controlling effects on the reservoir development and distribution and source-reservoir assemblage during its sedimentation. It is shown that the Deyang–Anyue paleo-rift is, on the whole, distributed in a NW direction, and is morphologically wide and steep in the north, but narrow and gentle in the south. There are two rift boundaries of the second and fourth members of Dengying Fm (Deng 2 Member and Deng 4 Member, respectively. The rift of Deng 2 Member is distributed in the shape of “U” in Deyang–Neijiang area. Dengying Fm is divided into four third-order sequences (SQ1–SQ4. In SQ3 of Gaoshiti–Moxi area, central Sichuan Basin, a complete sedimentation reflection structure of transgressive overlap and regressive progradation can be identified with early–middle Deng 4 Member platform margin. The paleo-rift was in embryo before the sedimentation of Sinian, so the sedimentary filling and lithofacies distribution of the Sinian were influenced by the inherited activities of pre-Sinian rifts. The favorable distribution zones of high-quality reservoirs are located at the rift margins of Deng 2 and Deng 4 Members that were formed respectively during the SQ2 and SQ4 and the platform margin of early Deng 4 Member that was formed during the SQ3. A laterally connected source-reservoir assemblage occurs at the margins of Deng 2 and Deng 4 Members around the Lower Cambrian source rocks of the paleo-rift. The northwestward extending margin zone along

  18. Tertiary rifting and its related structural development of the southern offshore Korea (United States)

    Sunwoo, Don


    Analysis of regional multi-channel seismic data integrated with exploratory wells has helped to investigate the structural and stratigraphic evolution of the southern offshore Korea. The northeast-southwest trending Taiwan Sinzi Fold Belt separates the area into two regions, the northern East China Sea Shelf Basin and the northern Okinawa Trough, with different structural features. The northern East China Sea Shelf Basin is characterized by Hupijiao Rise and Oligocene and late Miocene folded structures, whereas no uplifted and folded structures exist in the northern Okinawa Trough. However, the basement structure in both regions is much similar. The structure is characterized by a series of half-grabens and tilted fault blocks bounded by listric faults associated with rifting activity. These structures are more distinct in the northern Okinawa Trough. Rifting and extension in the northern East China Sea Shelf Basin, probably initiated in the Paleogene, resulted in a series of grabens and half-grabens. In the late Oligocene, the area west of the Hupijiao Rise experienced compressional tectonism and subsequent erosion flattened the area. In the early Miocene, extension and rifting resumed and the Hupijiao Rise uplifted locally. A second phase of compression, probably triggered by changes in plate motions caused large-scale uplift and folding in the eastern part of the area during the late Miocene. Subsequent erosion leveled the area including the Taiwan Sinzi Fold Belt, resulting in a significant regional unconformity. In contrast, the rifting and extension in the northern Okinawa Trough probably began in late Miocene and continued until early Pleistocene. The most active rifting occurred during early Pliocene and the rifting seems to become weaker during late Pliocene and early Pleistocene. The late Miocene unconformity that eroded the Taiwan Sinzi Fold Belt forms a conformable surface in the northern Okinawa Trough

  19. Very early rift sedimentation in the Turkana depression (EARS, Kenya): example of the Topernawi Formation (United States)

    Nutz, A.; Ragon, T.; Schuster, M.; Ghienne, J. F.


    Sedimentation associated with very early phase of continental rifting remains poorly understood as related deposits lie at deepest part of basins and rarely outcrop at the surface. However, understanding of these sediments are essential first to better-constrain early extensional phase and second in term of potential resources. The Turkana depression is a rift system active since the Paleogene, which makes the connection between Kenyan and Ethiopian domes. The southern area consists of four asymmetrical and juxtaposed grabens: the Lokichar, Turkwell, Kerio and South Lake Basin, which have been intensively documented through oil exploration. The northern part is structured into a single asymmetrical graben, the North Lake basin, less-known even oil exploration started. In this contribution, a sedimentary system preserved on the rift shoulder of the North Lake Basin is presented. Referred to as the Topernawi Fm, it is interpreted as recording the earliest phase of Cenozoic rifting in the area. The Topernawi Fm delineates a relic sedimentary basin of limited extension (3 - 5 km). Boundaries of the basin are inherited from basement structures, more precisely from the reactivation during Late Oligocene to Early Miocene of a previous transfer zone producing N40-50° border faults. Basin fills is up to 80 m thick and includes first alluvial fan associated with the reactivation of these faults and then braided fluvial deposits from axial system. Above, several volcanic events recurrently emplaced pyroclastic deposits, repeatedly reworked by fluvial channels. Subsequently, N-S trend faulting cut the Topernawi system during the development of the North Lake Basin and led to its partial preservation over the present-day rift shoulder. Geological maps, structural sections across Topernawi basin and sedimentary facies are presented. An integrated model is proposed to illustrate the basin evolution. Implications for rifting in Northern Turkana depression are discussed.

  20. Three-dimensional Aquila Rift: magnetized H I arch anchored by molecular complex (United States)

    Sofue, Yoshiaki; Nakanishi, Hiroyuki


    Three-dimensional structure of the Aquila Rift of magnetized neutral gas is investigated by analysing H I and CO line data. The projected distance on the Galactic plane of the H I arch of the Aquila Rift is r⊥ ˜ 250 pc from the Sun. The H I arch emerges at l ˜ 30°, reaches to altitudes as high as ˜500 pc above the plane at l ˜ 350°, and returns to the disc at l ˜ 270°. The extent of arch at positive latitudes is ˜1 kpc and the width is ˜100 pc. The eastern root is associated with the giant molecular cloud complex, which is the main body of the optically defined Aquila Rift. The H I and molecular masses of the Rift are estimated to be M_{H I}˜ 1.4{×} 10^5 M_{⊙} and M_H_2˜ 3{×} 10^5 M_{⊙}. Gravitational energies to lift the gases to their heights are E_{grav: H I}˜ 1.4{×} 10^{51} erg and E_{grav: H_2}˜ 0.3{×} 10^{51} erg, respectively. Magnetic field is aligned along the H I arch of the Rift, and the strength is measured to be B ˜ 10 μG using Faraday rotation measures of extragalactic radio sources. The magnetic energy is estimated to be Emag ˜ 1.2 × 1051 erg. A possible mechanism of formation of the Aquila Rift is proposed in terms of interstellar magnetic inflation by a sinusoidal Parker instability of wavelength of ˜2.5 kpc and amplitude ˜500 pc.

  1. Toward self-consistent tectono-magmatic numerical model of rift-to-ridge transition (United States)

    Gerya, Taras; Bercovici, David; Liao, Jie


    Natural data from modern and ancient lithospheric extension systems suggest three-dimensional (3D) character of deformation and complex relationship between magmatism and tectonics during the entire rift-to-ridge transition. Therefore, self-consistent high-resolution 3D magmatic-thermomechanical numerical approaches stand as a minimum complexity requirement for modeling and understanding of this transition. Here we present results from our new high-resolution 3D finite-difference marker-in-cell rift-to-ridge models, which account for magmatic accretion of the crust and use non-linear strain-weakened visco-plastic rheology of rocks that couples brittle/plastic failure and ductile damage caused by grain size reduction. Numerical experiments suggest that nucleation of rifting and ridge-transform patterns are decoupled in both space and time. At intermediate stages, two patterns can coexist and interact, which triggers development of detachment faults, failed rift arms, hyper-extended margins and oblique proto-transforms. En echelon rift patterns typically develop in the brittle upper-middle crust whereas proto-ridge and proto-transform structures nucleate in the lithospheric mantle. These deep proto-structures propagate upward, inter-connect and rotate toward a mature orthogonal ridge-transform patterns on the timescale of millions years during incipient thermal-magmatic accretion of the new oceanic-like lithosphere. Ductile damage of the extending lithospheric mantle caused by grain size reduction assisted by Zenner pinning plays critical role in rift-to-ridge transition by stabilizing detachment faults and transform structures. Numerical results compare well with observations from incipient spreading regions and passive continental margins.

  2. 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.

  3. Soils, slopes and source rocks: Application of a soil chemistry model to nutrient delivery to rift lakes (United States)

    Harris, Nicholas B.; Tucker, Gregory E.


    The topographic evolution of rift basins may be critical to the deposition of lacustrine source rocks such as the organic-rich Lower Cretaceous shales of the South Atlantic margin. Soils have been proposed as a key link between topography and source rock deposition by providing nutrients for the algae growth in rift lakes. Decreasing topographic relief from active rift to late rift has several effects on soils: soils become thicker and finer, erosion of dead surface and soil organic matter decreases, and the fractionation of precipitation between runoff and infiltration may favor increased infiltration. This hypothesis is tested by application of CENTURY, a complex box model that simulates transfer of nutrients within soil pools. The model is first applied to a rainforest soil, with several parameters individually varied. Infiltration experiments show that the concentrations of C, N and P in groundwater decrease rapidly as infiltration decreases, whether due to increased slope or to decreased precipitation. Increased erosion of surface plant litter and topsoil results in substantially decreased nutrient concentrations in groundwater. Increased sand content in soil causes an increase in nutrient concentration. We integrate these variables in analyzing topographic swathes from the Rio Grande Rift, comparing the southern part of the rift, where topography is relatively old and reduced, to the northern rift. C and P concentrations in groundwater increase as slope gradient decreases, resulting in substantially larger C and P concentrations in groundwater in the southern rift than the northern rift. Nitrogen concentrations in groundwater depends on whether infiltration varies as a function of slope gradient; in experiments where the fraction of infiltrated precipitation decreased with increasing slope, N concentrations was also substantially higher in the southern rift; but in experiments where that fraction was held constant, N concentrations was lower in the southern

  4. Integrated Analysis of Environment, Cattle and Human Serological Data: Risks and Mechanisms of Transmission of Rift Valley Fever in Madagascar. (United States)

    Olive, Marie-Marie; Chevalier, Véronique; Grosbois, Vladimir; Tran, Annelise; Andriamandimby, Soa-Fy; Durand, Benoit; Ravalohery, Jean-Pierre; Andriamamonjy, Seta; Rakotomanana, Fanjasoa; Rogier, Christophe; Heraud, Jean-Michel


    Rift Valley fever (RVF) is a vector-borne disease affecting ruminants and humans. Madagascar was heavily affected by RVF in 2008-2009, with evidence of a large and heterogeneous spread of the disease. The identification of at-risk environments is essential to optimize the available resources by targeting RVF surveillance in Madagascar. Herein, the objectives of our study were: (i) to identify the environmental factors and areas favorable to RVF transmission to both cattle and human and (ii) to identify human behaviors favoring human infections in Malagasy contexts. First, we characterized the environments of Malagasy communes using a Multiple Factor Analysis (MFA). Then, we analyzed cattle and human serological data collected at national level using Generalized Linear Mixed Models, with the individual serological status (cattle or human) as the response, and MFA factors, as well as other potential risk factors (cattle density, human behavior) as explanatory variables. Cattle and human seroprevalence rates were positively associated to humid environments (ptransmission in cattle. Our integrated approach analyzing environmental, cattle and human datasets allow us to bring new insight on RVF transmission patterns in Madagascar. The association between cattle seroprevalence, humid environments and high cattle density suggests that concomitant vectorial and direct transmissions are critical to maintain RVF enzootic transmission. Additionally, in the at-risk humid environment of the western, north-western and the eastern-coast areas, suitable to Culex and Anopheles mosquitoes, vectorial transmission probably occurs in both cattle and human. The relative contribution of vectorial or direct transmissions could be further assessed by mathematic modelling.

  5. The distribution of volcanism in the Beta-Atla-Themis region of Venus: Its relationship to rifting and implications for global tectonic regimes (United States)

    Airey, M. W.; Mather, T. A.; Pyle, D. M.; Ghail, R. C.


    A new analysis of the spatial relationships between volcanic features and rifts on Venus provides new constraints on models of planetary evolution. We developed a new database of volcanic features for the Beta-Atla-Themis (BAT) region and used nearest neighbor measurements to determine relationships between different types of volcanic features and the rifts. Nearest neighbor analysis shows that all the dome-type and corona-type subpopulations tend to cluster. Rift associations were inferred from the deviation of a feature's population distribution (as a function of distance from rift) from that of a random population. Dome-type features in general have no discernible relationship with rifts. Most corona-type features have a strong association with rifts, with intermediate and large volcanoes also tending to occur close to or on rifts. Shield fields, on the other hand, tend to occur away from rifts. Our new evidence supports classifications of rifts on Venus into different types, possibly by age, with a shift from globally dispersed (more uniform) volcanism toward the more rift-focused distribution, which suggests a shift in tectonic regime. Our observations are consistent with recent models proposing the evolution of Venus from a stagnant lid regime to a subcrustal spreading regime. We also present evidence for a failed rift on Venus and note that this process may be analogous, albeit on a larger scale, to a proposed model for the evolution of the East African rift system.

  6. Comparison of hydrothermal activity between the Adriatic and the Red Sea rift margins (United States)

    Ball, Philip; Incerpi, Nicolò; Birkle, Peter; Lacsamana, Elizabeth; Manatschal, Gianreto; Agar, Susan; Zhang, Shuo; Borsato, Ron


    Detailed field studies, and access to high-quality seismic reflection and refraction data have led to an improved understanding of the architecture and evolution of magma poor and magma rich margins. Associated with the spatial-temporal evolution of the rift, it is evident that there are evolving, extensive, fluid-rock interactions due to the infiltration of fluids within the sediment, basement and lithospheric mantle. Key questions therefore arise: What are the different fluid-rock reactions that can be typed to different geodynamic stages of the rift evolution? What are their compositions and how do they interact with their environment (basement, sediments, evaporites, hydrosphere, and magmatism)? What are the implications for the evolution of the margin rheology, thermal structure, depositional environments/organic matter maturity, and reservoir quality? The Adriatic paleo-rifted margin is preserved in both SE Switzerland and northern Italy. The field exposures provide a unique opportunity to study the fluid flow history of a hyperextended magma poor extensional margin. Analysis of breccias, cement veins and replacement minerals reveal that the margin records a complex, long-lasting history of dolomitization, calcification and silicification during the Jurassic rifting. The Red Sea by contrast is a young rifted margin. It differs from the paleo-Adriatic margin by several characteristics: volcanism is more evident, and syn-tectonic sediments, including evaporites (halite and anhydrite) are thicker. Several core and fluid samples are available from both onshore and offshore wells, which reveal rift-related hydrothermal alteration. In addition, we find evidence for the presence of an extreme dynamic hydraulic system with infiltration of surface water into sub-salt units during Late Pleistocene. In this study we present results from petrographic and geochemical analysis of basement and sedimentary rocks from Adriatic field-derived samples and core/subsurface fluid

  7. 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

  8. Force Required to Breakup a Continent: Implications on Rifting Localization and Migration (United States)

    Svartman Dias, A. E.; Lavier, L. L.; Hayman, N. W.


    The maximum force from ridge push available is about 5 TN/m, lower than that required by 2D and 3D numerical experiments to rift the lithosphere in the absence of magmatic input. We carry out 2D numerical experiments without any magmatic input to study the extensional force necessary to start a rift basin and to breakup a continent. We assume a range of initial temperature structure, crust and mantle initial thicknesses and composition. In a first step, we use velocity boundary conditions (1cm/yr) and we monitor the force necessary to breakup the continent. Results can be classified in two groups according to the amount of force needed to rift through time: (1) The initial force builds up rapidly to 12-20 TN/m within 0.4-1.0 Myr. This is followed by an exponential decrease due to early strain localization and lithospheric weakening. The force is value of 3-5 TN/m from 0.4 Myr to 10 Myr, when strain starts localizing. The constant force through time reflects lithosphere strengthening and migration of the deformation. This rift migration forms a wide basin (> 250 km wide) that may evolve to form very asymmetric conjugate margins. Breakup occurs 18 Myr after the onset of rifting or later. This second group corresponds to experiments with initial Tmoho > 650 km and crustal thicknesses ≥ 35 km. High bending stresses result in upper crust brittle failure and on enhancement of lower crust lateral flow. Interaction between ductile failure in the lower crust and brittle failure in the upper crust controls the migration of the deformation. In a second step, we repeat the same experiments applying a constant extensional force ≤ 5 TN/m to test whether and how the limited ridge push force naturally available can rift and breakup a continent. We then compare our results to the evolution of aborted rifts and to along strike variations in rifted magins such as the South Atlantic.

  9. Kinematics of the Ethiopian Rift and Absolute motion of Africa and Somalia Plates (United States)

    Muluneh, A. A.; Cuffaro, M.; Doglioni, C.


    The Ethiopian Rift (ER), in the northern part of East African Rift System (EARS), forms a boundary zone accommodating differential motion between Africa and Somalia Plates. Its orientation was influenced by the inherited Pan-African collisional system and related lithospheric fabric. We present the kinematics of ER derived from compilation of geodetic velocities, focal mechanism inversions, structural data analysis, and construction of geological profiles. GPS velocity field shows a systematic eastward magnitude increase in NE direction in the central ER. In the same region, incremental extensional strain axes recorded by earthquake focal mechanism and fault slip inversion show ≈N1000E orientation. This deviation between GPS velocity trajectories and orientation of incremental extensional strain is developed due to left lateral transtensional deformation. This interpretation is consistent with the en-échelon pattern of tensional and transtensional faults, the distribution of the volcanic centers, and the asymmetry of the rift itself. Small amount of vertical axis blocks rotation, sinistral strike slip faults and dyke intrusions in the rift accommodate the transtensional deformation. We analyzed the kinematics of ER relative to Deep and Shallow Hot Spot Reference Frames (HSRF). Comparison between the two reference frames shows different kinematics in ER and also Africa and Somalia plate motion both in magnitude and direction. Plate spreading direction in shallow HSRF (i.e. the source of the plumes locates in the asthenosphere) and the trend of ER deviate by about 27°. Shearing and extension across the plate boundary zone contribute both to the style of deformation and overall kinematics in the rift. We conclude that the observed long wavelength kinematics and tectonics are consequences of faster SW ward motion of Africa than Somalia in the shallow HSRF. This reference frame seems more consistent with the geophysical and geological constraints in the Rift. The

  10. Lithological Influences on Occurrence of High-Fluoride Waters in The Central Kenya Rift (United States)

    Olaka, L. A.; Musolff, A.; Mulch, A.; Olago, D.; Odada, E. O.


    Within the East African rift, groundwater recharge results from the complex interplay of geology, land cover, geomorphology, climate and on going volcano-tectonic processes across a broad range of spatial and temporal scales. The interrelationships between these factors create complex patterns of water availability, reliability and quality. The hydrochemical evolution of the waters is further complex due to the different climatic regimes and geothermal processes going on in this area. High fluoridic waters within the rift have been reported by few studies, while dental fluorosis is high among the inhabitants of the rift. The natural sources of fluoride in waters can be from weathering of fluorine bearing minerals in rocks, volcanic or fumarolic activities. Fluoride concentration in water depends on a number of factors including pH, temperature, time of water-rock formation contact and geochemical processes. Knowledge of the sources and dispersion of fluoride in both surface and groundwaters within the central Kenya rift and seasonal variations between wet and dry seasons is still poor. The Central Kenya rift is marked by active tectonics, volcanic activity and fumarolic activity, the rocks are majorly volcanics: rhyolites, tuffs, basalts, phonolites, ashes and agglomerates some are highly fractured. Major NW-SE faults bound the rift escarpment while the rift floor is marked by N-S striking faults We combine petrographic, hydrochemistry and structural information to determine the sources and enrichment pathways of high fluoridic waters within the Naivasha catchment. A total of 120 water samples for both the dry season (January-February2012) and after wet season (June-July 2013) from springs, rivers, lakes, hand dug wells, fumaroles and boreholes within the Naivasha catchment are collected and analysed for fluoride, physicochemical parameters and stable isotopes (δ2 H, δ18 O) in order to determine the origin and evolution of the waters. Additionally, 30 soil and

  11. Origin of the Eastern Mediterranean: Neo-Tethys Rifting Along a Cryptic Cadomian Suture with Afro-Arabia (United States)

    Avigad, D.; Abbo, A.; Gerdes, A.


    The East Mediterranean is a land-locked basin, a remnant of Neo-Tethys. It was formed in the Permo-Triassic as a result of the drift of the Tauride block from the Afro-Arabian margin of Gondwana. Herein we show that rather than being a genuine Afro-Arabia crustal fragment, the Tauride block is underlain by a Late Neoproterozoic Cadomian basement, which differs significantly from the Neoproterozoic "Pan-African" basement of NE Africa from which it was detached. Resembling other Cadomian terranes of Western Europe, the Tauride basement is chiefly a greywacke succession deposited in a mid to late Ediacaran back-arc basin formed on the periphery of Afro-Arabia, above the southward subducting proto-Tethys. The back-arc region was deformed and metamorphosed to various degrees and intruded by latest Ediacaran-Cambrian granites and volcanics during the Cadomian orogeny. Unlike the protracted (ca .300 m.y.) Neoproterozoic crustal evolution recorded in Afro-Arabia, the Cadomian basement of the Taurides evolved briefly, over ca. 50 m.y. We show that the entire cycle of sedimentation, metamorphism and magmatism in the Tauribe basement took place in the late Ediacaran-Cambrian and lagged after Neoproterozoic Pan-African orogeny and igneous activity in Afro-Arabia. The Cadomian orogeny had accreted the Taurides, and adjoining peri-Gandwana Cadomian terranes, with an already-consolidated Afro-Arabian continent. Permo-Triassic rifting of the East Mediterranean occurred close to the transition between these two domains. Rifting has thus been inherited from, and superimposed on late Ediacaran structures formed in front of the current Afro-Arabia margin of Gondwana during Cadomian orogeny. The boundary between the Cadomian edifice and the Pan-African crust of Afro-Arabia appears to lie nowadays on the southern margin of the Mediterranean, extending from Morocco in the west to Arabia in the east. Hence, the continental margin of the East Mediterranean, including in the Levant basin

  12. The role of pre-existing Precambrian structures in rift evolution: The Albertine and Rhino grabens, Uganda (United States)

    Katumwehe, Andrew B.; Abdelsalam, Mohamed G.; Atekwana, Estella A.


    We integrated Shuttle Radar Topography Mission (SRTM) Digital Elevation Models (DEM), airborne magnetic, radiometric and three-dimensional Full Tensor Gravity Gradiometry (3D-FTG) data to investigate the role of Precambrian structures in the evolution of the largely amagmatic Miocene-Recent aged Albertine and Rhino grabens in Uganda. These grabens represent the northern segment of the Western Branch of the East African Rift System (EARS). The two NE-trending grabens are connected by a right-stepping transfer zone and they extend within the Archean-Paleoproterozoic Northeast Congo block which represents the northeastern extension of the Congo craton. Our results show the following and highlight the importance of pre-existing structures in the evolution of continental rift systems: (1) The NE-extent of the Albertine full-graben is controlled by NE-trending Precambrian fabric and the graben terminates at its northeastern end when it encounters a multiply folded Precambrian basement terrain with poorly-developed NW-trending structural grain. Additionally, the northeastern termination of the Albertine graben coincides with the presence of NW-trending right-stepping high-density bodies within the Precambrian terrain. (2) The transfer zone between the Albertine and Rhino grabens is controlled by NE-trending Precambrian structures which might have facilitated the development of relay ramp faults. (3) Strain localization within the better-developed southeastern border fault of the Rhino half-graben is facilitated by the presence of Precambrian structures better aligned in a NE-direction in the southeastern part of the basin compared to its northwestern part. (4) Further to the northeast, the Rhino graben is segmented and transitions into a narrower ENE-trending half-graben with a better-developed border fault on its northwestern side. This segmentation coincides with the presence of N-trending Precambrian structures. (5) The Rhino graben terminates farther northeast against

  13. Rift Valley fever: current challenges and future prospects

    Directory of Open Access Journals (Sweden)

    Himeidan YE


    Full Text Available Yousif E Himeidan Vector Control Unit, Africa Technical Research Centre, Vector Health International, Arusha, Tanzania Abstract: Rift Valley fever (RVF is a zoonotic, mosquito-borne viral disease that affects human health and causes significant losses in the livestock industry. Recent outbreaks have led to severe human infections with high mortality rates. There are many challenges to applying effective preventive and control measures, including weak infrastructure of health facilities, lack of capacity and support systems for field logistics and communication, access to global expert organizations, and insufficient information on the epidemiological and reservoir status of the RVF virus. The health systems in East African countries are underdeveloped, with gaps in adaptability to new, more accurate and rapid techniques, and well-trained staff that affect their capacity to monitor and evaluate the disease. Surveillance and response systems are inadequate in providing accurate information in a timely manner for decision making to deal with the scope of interrupting the disease transmission by applying mass animal vaccination, and other preventive measures at the early stage of an outbreak. The historical vaccines are unsuitable for use in newborn and gestating livestock, and the recent ones require a booster and annual revaccination. Future live-attenuated RVF vaccines should possess lower safety concerns regardless of the physiologic state of the animal, and provide rapid and long-term immunity after a single dose of vaccination. In the absence of an effective vaccination program, prevention and control measures must be immediately undertaken after an alert is generated. These measures include enforcing and adapting standard protocols for animal trade and movement, extensive vector control, safe disposal of infected animals, and modification of human–animal contact behavior. Directing control efforts on farmers and workers who deal with

  14. Middle to late cenozoic magmatism of the southeastern Colorado plateau and central Rio Grande rift (New Mexico and Arizona, U.S.A.) : a model for continental rifting (United States)

    Baldridge, W.S.; Perry, F.V.; Vaniman, D.T.; Nealey, L.D.; Leavy, B.D.; Laughlin, A.W.; Kyle, P.; Bartov, Y.; Steinitz, G.; Gladney, E.S.


    The region of the present Rio Grande rift and southeastern Colorado Plateau underwent lithospheric extension during middle to late Cenozoic deformation affecting the entire southwestern U.S. Lithospheric mantle was disrupted, and in many regions displaced or replaced by asthenospheric mantle at depths from which basaltic magmas were derived and erupted to the surface. Study of the igneous rocks erupted or intruded during this deformation yields insights into processes of magmatism associated with extension of continental lithosphere. Magmatic rocks associated with an early (late Oligocene-early Miocene) ductile phase of extension are dominantly basaltic andesites and related, calc-alkaline intermediate to silicic derivative rocks. Mafic magmas were probably derived from isotopically "enriched" lithospheric mantle. Igneous rocks associated with a later (middle Miocene-Holocene), more brittle phase of extension include widespread basaltic rocks and localized central volcanoes of intermediate to silicic composition. Isotopic compositions of mafic rocks, which include both tholeiitic and alkalic basalts, correlate strongly with tectonic setting and lithospheric structure. Basalts erupted in areas of greatest crustal extension, such as the central and southern rift and Basin and Range province, were derived from isotopically "depleted" (correlated with "asthenospheric") mantle. Also, isotopic compositions of Pliocene to Holocene basalts are slightly more depleted than those of Miocene basalts, suggesting that subcrustal lithospheric mantle was thinned during late Miocene extension. Intermediate rocks of the central volcanoes formed by a complex combination of processes, probably dominated by fractional crystallization and by assimilation of upper and lower crust in isolated, small magma chambers. The petrologic, geochemical, and isotopic data are compatible with a model, derived first from geophysical data, whereby lithosphere is thinned beneath the central rift and

  15. Seismic stratigraphy of rift basins: techniques, methods and its application in the Reconcavo Basin; Sismoestratigrafia de bacias rifte: tecnicas, metodos e sua aplicacao na Bacia do Reconcavo

    Energy Technology Data Exchange (ETDEWEB)

    Kuchle, Juliano [Universidade Federal do Rio Grande do Sul (UFRGS). Inst. de Geociencias. Programa de Pos-Graduacao em Geociencias (Brazil)], e-mail:; Scherer, Claiton Marlon dos Santos [Universidade Federal do Rio Grande do Sul (UFRGS). Inst. de Geociencias. Dept. de Paleontologia e Estratigrafia (Brazil)], e-mail:


    This paper aims a proposal of interpretation and seismic stratigraphy systematic mapping of rift basins based on genetic concepts, as offered by the basic development of the Sequence Stratigraphy - the temporal interpretation of units based on concepts derived from variables and observable in depositional trends. So, rift basins are controlled by specifically variables and its relationships, which results in theoretical evolutional models. Those theoretical models are detailed as depositional trends denominated stacking patterns. Thus, from the stacking patterns, it is able to establish the inverse way analysis, picturing evolutional models and controlling variables. The main objective of this paper is the migration of the genetic tectonic-stratigraphic model of rift basins to the seismic platform, supported by the key-concepts of the seismic stratigraphy. This analysis is based on the recognition of seismic stratigraphic units which composes the tectonic system tracts - basic units of the framework, and these system tracts are formed by specific stacking patterns for each portion of the half Graben. As those stacking patterns reflect changes in the accommodation, stratigraphic surfaces and strata termination patterns are established. Therefore, a whole conceptual basis of seismic stratigraphy recognition and mapping is proposed, as well as a time determination of evolutional models in chronostratigraphic diagrams (Wheeler charts), to supply a useful tectonic-stratigraphic framework to hydrocarbon exploration. (author)

  16. Analysis of Adoption Spell of Hybrid Maize in the Central Rift Valley ...

    African Journals Online (AJOL)

    This paper estimates farm household level determinants of the speed of adoption of hybrid maize in the central rift valley of Ethiopia in the framework of the dynamic time on cross-sectional data. Descriptive statistics and duration model were used to study the objectives of the study. The results from descriptive analysis ...

  17. Petroleum systems in rift basins – a collective approach in South-east Asian basins.

    NARCIS (Netherlands)

    Doust, H.; Sumner, D.


    This paper synthesizes some of the main conclusions reached in a recent regional review of the Tertiary basins of Southeast Asia, carried out by Shell. Four distinctive types of petroleum systems, correlating with the four main stages of basin evolution (early to late syn-rift and early to late

  18. Broad accommodation of rift-related extension recorded by dyke intrusion in Saudi Arabia

    KAUST Repository

    Pallister, John S.


    The extensive harrat lava province of Arabia formed during the past 30 million years in response to Red Sea rifting and mantle upwelling. The area was regarded as seismically quiet, but between April and June 2009 a swarm of more than 30,000 earthquakes struck one of the lava fields in the province, Harrat Lunayyir, northwest Saudi Arabia. Concerned that larger damaging earthquakes might occur, the Saudi Arabian government evacuated 40,000 people from the region. Here we use geologic, geodetic and seismic data to show that the earthquake swarm resulted from magmatic dyke intrusion. We document a surface fault rupture that is 8 km long with 91 cm of offset. Surface deformation is best modelled by the shallow intrusion of a north-west trending dyke that is about 10 km long. Seismic waves generated during the earthquakes exhibit overlapping very low- and high-frequency components. We interpret the low frequencies to represent intrusion of magma and the high frequencies to represent fracturing of the crystalline basement rocks. Rather than extension being accommodated entirely by the central Red Sea rift axis, we suggest that the broad deformation observed in Harrat Lunayyir indicates that rift margins can remain as active sites of extension throughout rifting. Our analyses allowed us to forecast the likelihood of a future eruption or large earthquake in the region and informed the decisions made by the Saudi Arabian government to return the evacuees. © 2010 Macmillan Publishers Limited. All rights reserved.

  19. Petrology of rift-related basalts at Bombay High waters, Arabian Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Karisiddaiah, S.M.; Iyer, S.D.

    .39% and FeO super(t) 11.79 to 15.5%. The iron enrichment and the low Mg numbers suggest derivation of these basalts from extensive fractional crystallisation. These basalts are compositionally similar to rift related basaltic rocks associated with the opening...

  20. A Systematic Scoping Study of the Socio-Economic Impact of Rift Valley Fever

    NARCIS (Netherlands)

    Peyre, M.; Chevalier, V.; Abdo-Salem, S.; Velthuis, A.; Antoine-Moussiaux, N.; Thiry, E.; Roger, F.


    Rift Valley fever (RVF) is a severe mosquito-borne disease affecting humans and domestic ruminants. RVF virus has been reported in most African countries, as well as in the Arabic Peninsula. This paper reviews the different types of socio-economic impact induced by RVF disease and the attempts to

  1. Hydrogeological aspects of fault zones on various scales in the Roer Valley Rift System.

    NARCIS (Netherlands)

    Bense, V.F.; van Balen, R.T.


    The impact of faults on the groundwater flow system in the Roer Valley Rift System (RVRS) is demonstrated with examples from outcrop scale to regional scale. Faults in the RVRS can form strong barriers to horizontal groundwater flow as well as enhanced vertical groundwater flow paths at the same

  2. Water Hyacinth in the Rift Valley Water Bodies of Ethiopia: Its Distribution, Socioeconomic Importance and Management

    NARCIS (Netherlands)

    Firehun, Y.; Struik, P.C.; Lantinga, E.A.; Taye, T.


    A survey was conducted in the Rift Valley water bodies of Ethiopia from 2009 to 2011 to (i) determine the prevalence, agro-ecological distribution and sources of infestation of water hyacinth, (ii) investigate the socio-economic impact of water hyacinth, and (iii) assess changes in its

  3. Management of water hyacinth (Eichhornia crassipes [Mart.] Solms) using bioagents in the Rift Valley of Ethiopia

    NARCIS (Netherlands)

    Gebregiorgis, Firehun Yirefu


    This thesis presents a study on management of water hyacinth (Eichhornia crassipes [Mart.] Solms) using insects and fungal pathogens as bioagents. The main goal was to develop an effective biocontrol strategy for water hyacinth in the Rift Valley of Ethiopia. To this end, a field survey was

  4. Rift Valley Fever Risk Map Model and Seroprevalence in Selected Wild Ungulates and Camels from Kenya

    NARCIS (Netherlands)

    Britch, S.C.; Binepal, Y.S.; Ruder, M.G.; Kariithi, H.M.; Linthicum, K.J.; Anyamba, A.; Small, J.L.; Tucker, C.J.; Ateya, L.O.; Oriko, A.A.; Gacheru, S.; Wilson, W.C.


    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

  5. Rift Valley Fever Virus Growth Curve Kinetics in Cattle and Sheep Peripheral Blood Monocyte Derived Macrophages (United States)

    Rift Valley fever virus (RVFV), is a mosquito-borne, zoonotic pathogen within genus Phlebovirus, family Bunyaviridae that typically causes outbreaks in sub-Saharan Africa and recently spread to the Arabian Peninsula. In ruminants, RVFV infections cause mass abortion and high mortality rates in neona...

  6. 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

  7. Identifying rift zones on volcanoes: an example from La Réunion island, Indian Ocean (United States)

    Bonali, Fabio Luca; Corazzato, Claudia; Tibaldi, Alessandro


    We describe a methodology for identifying complex rift zones on recent or active volcanoes, where structures hidden by recent deposits and logistical conditions might prevent carrying out detailed fieldwork. La Réunion island was chosen as a test-site. We used georeferenced topographic maps, aerial photos and digital terrain models to perform a statistical analysis of several morphometric parameters of pyroclastic cones. This provides a great deal of geometric information that can help in distinguishing the localisation and orientation of buried magma-feeding fractures, which constitute the surface expression of rift zones. It also allowed the construction of a complete GIS database of the pyroclastic cones. La Réunion is a perfect example where past and active volcanic rift zones are mostly expressed by clusters of monogenic centres. The data has been validated in the field and compared and integrated with the distribution and geometry of dyke swarms. Results show the presence of several main and secondary rift segments of different ages, locations and orientations, whose origin is discussed considering regional tectonics, local geomorphology, and volcano deformation.

  8. Assessment of conventional oil resources of the East African Rift Province, East Africa, 2016 (United States)

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


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

  9. The rift-like structure and asymmetry of the Dead Sea Fault

    NARCIS (Netherlands)

    Smit, J.H.W.; Brun, J.P.; Cloetingh, S.A.P.L.; Ben-Avraham, Z.


    Whereas the Dead Sea Fault is a major continental transform, active since ca. 13-18 Ma ago, it has a rift-like morphology along its southern part. It has been argued that this results from a transtensional component active since 5 Ma ago, due to a regional plate kinematics change. We present the

  10. Pesticide use practices among smallholder vegetable farmers in Ethiopian Central Rift Valley

    NARCIS (Netherlands)

    Mengistie, B.T.; Mol, A.P.J.; Oosterveer, P.J.M.


    Pesticide use is a common practice to control pests and diseases in vegetable cultivation, but often at the expense of the environment and human health. This article studies pesticide-buying and use practices among smallholder vegetable farmers in the Central Rift Valley of Ethiopia, using a

  11. Long-distance impact of Iceland plume on Norway’s rifted margin

    National Research Council Canada - National Science Library

    Alexander Koptev; Sierd Cloetingh; Evgueni Burov; Thomas François; Taras Gerya


    ... from the Iceland mantle plume has been the norm in the geological past. In the Northern Atlantic the Iceland plume has a strong long-distance impact on intraplate deformation affecting both onshore and offshore parts of Norway’s rifted margin...


    DEFF Research Database (Denmark)

    Schiffer, Christian; Petersen, Kenni Dinesen

    during extension and form structures within the lower crust. The numerical model is consistent with the observation that passive margins often show dipping sub-Moho structures that are commonly interpreted as remnants of subducted crust emplaced during pre-rift compressional phases of the Wilson cycle...

  13. Spatial distribution of non-clinical Rift Valley fever viral activity in ...

    African Journals Online (AJOL)

    Rift Valley fever (RVF) is an acute zoonotic viral disease of domestic ruminants in mainland Africa and Madagascar. The disease may exist in non-clinical form in apparently health animals. This study was designed to investigate the existence and spatial distribution of non-clinical form of RVF virus (RVFV) activity in wild and ...

  14. Four-segmented Rift Valley fever virus induces sterile immunity in sheep after a single vaccination

    NARCIS (Netherlands)

    Wichgers Schreur, P.J.; Kant-Eenbergen, H.C.M.; Keulen, van L.J.M.; Moormann, R.J.M.; Kortekaas, J.A.


    Rift Valley fever virus (RVFV), a mosquito-borne virus in the Bunyaviridae family, causes recurrent outbreaks with severe disease in ruminants and occasionally humans. The virus comprises a segmented genome consisting of a small (S), medium (M) and large (L) RNA segment of negative polarity. The

  15. Broad accommodation of rift-related extension recorded by dyke intrusion in Saudi Arabia (United States)

    Pallister, J.S.; McCausland, W.A.; Jonsson, Sigurjon; Lu, Z.; Zahran, H.M.; El, Hadidy S.; Aburukbah, A.; Stewart, I.C.F.; Lundgren, P.R.; White, R.A.; Moufti, M.R.H.


    The extensive harrat lava province of Arabia formed during the past 30 million years in response to Red Sea rifting and mantle upwelling. The area was regarded as seismically quiet, but between April and June 2009 a swarm of more than 30,000 earthquakes struck one of the lava fields in the province, Harrat Lunayyir, northwest Saudi Arabia. Concerned that larger damaging earthquakes might occur, the Saudi Arabian government evacuated 40,000 people from the region. Here we use geologic, geodetic and seismic data to show that the earthquake swarm resulted from magmatic dyke intrusion. We document a surface fault rupture that is 8 km long with 91 cm of offset. Surface deformation is best modelled by the shallow intrusion of a north-west trending dyke that is about 10 km long. Seismic waves generated during the earthquakes exhibit overlapping very low- and high-frequency components. We interpret the low frequencies to represent intrusion of magma and the high frequencies to represent fracturing of the crystalline basement rocks. Rather than extension being accommodated entirely by the central Red Sea rift axis, we suggest that the broad deformation observed in Harrat Lunayyir indicates that rift margins can remain as active sites of extension throughout rifting. Our analyses allowed us to forecast the likelihood of a future eruption or large earthquake in the region and informed the decisions made by the Saudi Arabian government to return the evacuees.

  16. Feedbacks of lithosphere dynamics and environmental change of the Cenozoic West Antarctic Rift System.

    NARCIS (Netherlands)

    van der Wateren, F.M.; Cloetingh, S.A.P.L.


    This special issue of Global and Planetary Change contains 11 contributions dealing with various aspects of the Cenozoic West Antarctic Rift System. During the last two decades, investigations of the interplay of tectonics and climate greatly improved understanding of Cenozoic global change. Major

  17. Strain distribution across magmatic margins during the breakup stage: Seismicity patterns in the Afar rift zone (United States)

    Brown, C.; Ebinger, C. J.; Belachew, M.; Gregg, T.; Keir, D.; Ayele, A.; Aronovitz, A.; Campbell, E.


    Fault patterns record the strain history along passive continental margins, but geochronological constraints are, in general, too sparse to evaluate these patterns in 3D. The Afar depression in Ethiopia provides a unique setting to evaluate the time and space relations between faulting and magmatism across an incipient passive margin that formed above a mantle plume. The margin comprises a high elevation flood basalt province with thick, underplated continental crust, a narrow fault-line escarpment underlain by stretched and intruded crust, and a broad zone of highly intruded, mafic crust lying near sealevel. We analyze fault and seismicity patterns across and along the length of the Afar rift zone to determine the spatial distribution of strain during the final stages of continental breakup, and its relation to active magmatism and dike intrusions. Seismicity data include historic data and 2005-2007 data from the collaborative US-UK-Ethiopia Afar Geodynamics Project that includes the 2005-present Dabbahu rift episode. Earthquake epicenters cluster within discrete, 50 km-long magmatic segments that lack any fault linkage. Swarms also cluster along the fault-line scarp between the unstretched and highly stretched Afar rift zone; these earthquakes may signal release of stresses generated by large lateral density contrasts. We compare Coulomb static stress models with focal mechanisms and fault kinematics to discriminate between segmented magma intrusion and crank- arm models for the central Afar rift zone.

  18. Exploring determinants of farmers' investments in land management in the Central Rift Valley of Ethiopia

    NARCIS (Netherlands)

    Adimassu Teferi, Z.; Kessler, A.; Hengsdijk, H.


    Land degradation, especially water erosion and nutrient depletion, seriously affects agricultural production in the Central Rift Valley of Ethiopia. Farmers' investments to conserve their land are until now however quite limited. The objective of this study is to identify the major factors that

  19. Pathology Review of Two New Rift Valley Fever Virus Ruminant Models (United States)

    Rift Valley fever virus (RVFV), is a mosquito-borne, zoonotic pathogen within genus Phlebovirus, family Bunyaviridae that typically causes outbreaks in sub-Saharan Africa and recently spread to the Arabian Peninsula. In ruminants, RVFV infections cause mass abortion and high mortality rates in neona...

  20. Sero-surveillance of Rift Valley fever in sheep and goat flocks in ...

    African Journals Online (AJOL)

    The surveillance of Rift Valley Fever (RVF) was carried out in the risk areas of Kenya by monitoring free range/migratory and sedentary farm sheep and goat herds for antibodies to RVF virus (RVFV). A total of 986 serum samples were collected and analyzed from farms in Molo, (where no outbreaks has ever been previously ...

  1. 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

  2. The rift architecture and extensional tectonics of the South China Sea (United States)

    Cameselle, Alejandra L.; Ranero, César R.; Barckhausen, Udo; Franke, Dieter


    Non-volcanic rifted continental margins are classically described as the product of lithospheric stretching and breakup leading to mantle exhumation, and subsequent seafloor spreading. However, recent studies question this model and indicate a wider range of structural evolutions, that challenge the existing model (e.g. Australia-Antarctic Rift System (Direen et al. 2007, 2011); the Tyrrhenian basin (Prada et al., 2014) or the South China Sea (Cameselle et al. 2015)). Rifting in the South China Sea developed from a series of extensional events, from early Eocene to Late Oligocene, resulting in a V-shape oceanic basin affected by the occurrence of several spreading centers, ridges, transform faults and post-spreading volcanism. In recent years, this marginal basin - the largest in East Asia - has increasingly become one of the key sites for the study of rifting and continental break-up. Its relative small size - compared to many classic, Atlantic-type continental margin settings - allows to easily match conjugated rifted margins and its relative youth promotes the preservation of its original nature. To examine the rifting evolution of the South China Sea, we have reprocessed with modern algorithms multichannel seismic profiles acquired during Sonne49 and BGR84 cruises across the three major subbasins: NW, SW and East subbasins. State-of-the-art of processing techniques have been used to increase the signal to noise ratio, including Tau-P and Wiener predictive deconvolution, multiple attenuation by both radon filtering and wave-equation-based surface-related multiple elimination (SRME) and time migration. To complement seismic interpretation, available vintage multichannel seismic data have been reprocessed with a post-stack flow, including Wiener deconvolution, FK-filtering, space and time variant band-pass filter and time migration. The improving quality of the seismic images shows a range of features including post-rift and syn-rift sediments, the structure of

  3. 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

  4. Sediment flux dynamics as fingerprints of catchment rehabilitation: The case of western Rift Valley escarpment of northern Ethiopia (United States)

    Asfaha, Tesfaalem G.; Frankl, Amaury; Haile, Mitiku; Zenebe, Amanuel; Nyssen, Jan


    Variability in supply and entrainment of stream bedload particles during storm events is an important hydrogeomorphologic response of steep mountain streams to land management in their catchments. Because of difficulties in its measurement and absence of accurate measuring equipment, bedload transport in mountain streams is, however, poorly understood. This study focuses on analyzing bedload supply and entrainment in 11 streams of sloping (27-65%) catchments (0.4-25 km2) in northern Ethiopia, which have experienced severe deforestation and degradation processes until the first half of the 1980s and considerable rehabilitation thereafter. Field measurements of the median diameter of the 10 coarsest bedload particles (Max10) moved in each event (n = 332) and stream bed particle sampling were carried out in three rainy seasons (2012-2014). Event peak discharges were calculated from daily measurements by 11 crest stage gauges using Manning's equation. Percentages of land cover classes in the catchments were detected from high resolution (0.6 m) Google Earth imagery (1 February, 2014). Morphometric characteristics of the catchments were computed from an ASTER digital elevation model and topographic maps. Hydraulic competence analysis for entrainment of the average Max10 was carried out using peak discharge, stream power, and critical shear stress approaches. The supply of Max10 was positively related to scar density on the surrounding slopes (R2 = 0.50, p < 0.05) and catchment area (R2 = 0.36, p < 0.05) while negatively related with total forest cover (R2 = 0.63, p < 0.05) or vegetation cover (R2 = 0.58, p < 0.05). A multiple regression analysis showed that 98% of the variability in Max10 is explained by scar density and catchment area. Entrainment of Max10 was positively related to peak discharge (Qp) (R2 = 0.60, p < 0.01), stream power (Ω) (R2 = 0.71, p < 0.01), Strickler's roughness (Sn) (R2 = 0.86, p < 0.01), and critical shear stress (τc) with reference to D50 (r50) (R2 = 0.96, p < 0.01), and with reference to D84 (r84) (R2 = 0.93, p < 0.01). The relationships between event Max10 and event Qp in each catchment were also used to extrapolate the peak discharges that would have prevailed in the first half of the 1980s, and the results showed huge reductions in peak discharges (p < 0.01) as a result of the reforestation interventions. Overall, this study demonstrates that (i) the supply of bedload in steep tropical mountains is determined negatively by forest or vegetation cover and positively by the presence of scar networks in the sloping parts of the catchments and catchment size; (ii) entrainment of the coarsest bedload particles is determined positively by peak discharge, stream power, stream bed roughness, and most strongly by critical shear stress; and (iii) in steep mountain streams where direct measurement of bedload movement is difficult, yet simple in situ measurement of the coarsest bedload particles (Max10) supplied and entrained in each event helps for understanding the dynamics of sediment flux in relation to catchment rehabilitation.

  5. Prevalence of anaemia in patients attending an outpatient clinic in western Rift Valley in Kenya during a low malaria season. (United States)

    Carter, J Y; Lema, O E; Mukunza, H K; Varia, H N; Munyere, A S; Watkins, W M; Watkins, K M


    To assess the prevalence of anaemia in outpatients attending a rural health clinic in an area of seasonal malaria, during the low transmission season. Haemoglobin estimation and blood slide examination for malaria parasites were performed on 280 consecutive patients attending outpatient curative services at Entasopia Health Centre, Kajiado District, Kenya, between April-May 1996. Anaemia was defined according to World Health Organisation guidelines for age, sex and pregnancy status. In all groups except adult males, more than half of the patients tested had haemoglobin values below the lower reference limits, suggesting that anaemia is widely present in this population even during the low malaria season. Only 5% of patients were positive for Plasmodium falciparum malaria. Peripheral blood film examination suggested iron deficiency as the major cause of anaemia. Further studies to define the underlying causes of anaemia and to develop community strategies to prevent anaemia are required. The association between fever and anaemia and the use of pallor to diagnose anaemia, are discussed.

  6. The Overthrust Belt of Western North America

    Energy Technology Data Exchange (ETDEWEB)

    Verrall, P.


    The Overthrust Belt extends for 5000 mi (8000 km) from the Brooks Range in Alaska to the Sierra Madre Oriental in Mexico. It consists of northeastward vergent thrust and fold structures involving late Precambrian to early Tertiary sedimentary section. These sediments represent deposition off the western rift margin, formed in late Precambrian time, of the North American Precambrian craton. The northeastward thrusting continued throughout the Mesozoic as a response to the convergence of the East Pacific Plate with the North American Plate. This convergence resulted in subduction beneath the North American Plate except at the northwest end (the Brooks Range) where the result was obduction. Convergence ceased when the west edge of the East Pacific Plate reached the subduction zone. The sedimentary section involved in the Thrust Belt contains good Devonian to Cretaceous hydrocarbon source rocks, and Ordovician to traps related to the thrusting (simple thrust sheets, imbricate thrust sheets, folded thrust sheets, step anticlines, footwall cutoffs, footwall anticlines, etc.). Field methods involved in exploration for hydrocarbons include field geological mapping, remote sensing (aerial photography and Landsat imagery), various seismic refraction and seismic reflection techniques (including modern detailed three dimension surveys) and potential field methods such as gravity and magnetic surveying. Studies of the field data include paleontology, source rock and hydrocarbon migration studies, structural and stratigraphic analyses, and the processing of geophysical data. This work has succeeded in two major areas: the Western Canadian Rocky Mountain Foothills, a major gas province producing mainly from Paleozoic reservoirs; and the Wyoming-Idaho-Utah portion of the thrust belt, also a major gas producer from Paleozoic reservoirs and, in addition, a major oil producer from the Jurassic Nugget Sandstone.

  7. The stress shadow induced by the 1975-1984 Krafla rifting episode

    KAUST Repository

    Maccaferri, F.


    It has been posited that the 1975–1984 Krafla rifting episode in northern Iceland was responsible for a significant drop in the rate of earthquakes along the Húsavík-Flatey Fault (HFF), a transform fault that had previously been the source of several magnitude 6–7 earthquakes. This compelling case of the existence of a stress shadow has never been studied in detail, and the implications of such a stress shadow remain an open question. According to rate-state models, intense stress shadows cause tens of years of low seismicity rate followed by a faster recovery phase of rate increase. Here, we compare the long-term predictions from a Coulomb stress model of the rifting episode with seismological observations from the SIL catalog (1995–2011) in northern Iceland. In the analyzed time frame, we find that the rift-induced stress shadow coincides with the eastern half of the fault where the observed seismicity rates are found to be significantly lower than expected, given the historical earthquake activity there. We also find that the seismicity rates on the central part of the HFF increased significantly in the last 17 years, with the seismicity progressively recovering from west to east. Our observations confirm that rate-state theory successfully describes the long-term seismic rate variation during the reloading phase of a fault invested by a negative Coulomb stress. Coincident with this recovery, we find that the b-value of the frequency-magnitude distribution changed significantly over time. We conclude that the rift-induced stress shadow not only decreased the seismic rate on the eastern part of the HFF but also temporarily modified how the system releases seismic energy, with more large magnitude events in proportion to small ones. This behavior is currently being overturned, as rift-induced locking is now being compensated by tectonic forcing.

  8. 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.

  9. Assessing the Threat of Amphibian Chytrid Fungus in the Albertine Rift: Past, Present and Future.

    Directory of Open Access Journals (Sweden)

    Tracie A Seimon

    Full Text Available Batrachochytrium dendrobatidis (Bd, the cause of chytridiomycosis, is a pathogenic fungus that is found worldwide and is a major contributor to amphibian declines and extinctions. We report results of a comprehensive effort to assess the distribution and threat of Bd in one of the Earth's most important biodiversity hotspots, the Albertine Rift in central Africa. In herpetological surveys conducted between 2010 and 2014, 1018 skin swabs from 17 amphibian genera in 39 sites across the Albertine Rift were tested for Bd by PCR. Overall, 19.5% of amphibians tested positive from all sites combined. Skin tissue samples from 163 amphibians were examined histologically; of these two had superficial epidermal intracorneal fungal colonization and lesions consistent with the disease chytridiomycosis. One amphibian was found dead during the surveys, and all others encountered appeared healthy. We found no evidence for Bd-induced mortality events, a finding consistent with other studies. To gain a historical perspective about Bd in the Albertine Rift, skin swabs from 232 museum-archived amphibians collected as voucher specimens from 1925-1994 were tested for Bd. Of these, one sample was positive; an Itombwe River frog (Phrynobatrachus asper collected in 1950 in the Itombwe highlands. This finding represents the earliest record of Bd in the Democratic Republic of Congo. We modeled the distribution of Bd in the Albertine Rift using MaxEnt software, and trained our model for improved predictability. Our model predicts that Bd is currently widespread across the Albertine Rift, with moderate habitat suitability extending into the lowlands. Under climatic modeling scenarios our model predicts that optimal habitat suitability of Bd will decrease causing a major range contraction of the fungus by 2080. Our baseline data and modeling predictions are important for comparative studies, especially if significant changes in amphibian health status or climactic conditions

  10. Neoproterozoic rift basins and their control on the development of hydrocarbon source rocks in the Tarim Basin, NW China (United States)

    Zhu, Guang-You; Ren, Rong; Chen, Fei-Ran; Li, Ting-Ting; Chen, Yong-Quan


    The Proterozoic is demonstrated to be an important period for global petroleum systems. Few exploration breakthroughs, however, have been obtained on the system in the Tarim Basin, NW China. Outcrop, drilling, and seismic data are integrated in this paper to focus on the Neoproterozoic rift basins and related hydrocarbon source rocks in the Tarim Basin. The basin consists of Cryogenian to Ediacaran rifts showing a distribution of N-S differentiation. Compared to the Cryogenian basins, those of the Ediacaran are characterized by deposits in small thickness and wide distribution. Thus, the rifts have a typical dual structure, namely the Cryogenian rifting and Ediacaran depression phases that reveal distinct structural and sedimentary characteristics. The Cryogenian rifting basins are dominated by a series of grabens or half grabens, which have a wedge-shaped rapid filling structure. The basins evolved into Ediacaran depression when the rifting and magmatic activities diminished, and extensive overlapping sedimentation occurred. The distributions of the source rocks are controlled by the Neoproterozoic rifts as follows. The present outcrops lie mostly at the margins of the Cryogenian rifting basins where the rapid deposition dominates and the argillaceous rocks have low total organic carbon (TOC) contents; however, the source rocks with high TOC contents should develop in the center of the basins. The Ediacaran source rocks formed in deep water environment of the stable depressions evolving from the previous rifting basins, and are thus more widespread in the Tarim Basin. The confirmation of the Cryogenian to Ediacaran source rocks would open up a new field for the deep hydrocarbon exploration in the Tarim Basin.

  11. From Rifting of a volcanic province to Oceanic Spreading in the Andaman Sea, South-East Asia. (United States)

    Jourdain, A.; Singh, S. C.; Klinger, Y.


    The Andaman Sea is an enigmatic feature in the Indian Ocean region. It contains the volcanic provinces of Alcock and Sewell Rises and an active spreading center. The recent rifting in the Andaman Sea initiated 4.5 Ma ago, rifting the Alcock and Seawell Rises that were formed by extensive volcanism between 23-16 Ma. The spreading started with a full spreading rate of 1.6 cm/yr and increased to 3.8 cm/yr in the last 2.5 Ma. We have access to high-resolution deep seismic reflection data crossing the whole spreading center from the rifted volcanic provinces to the spreading center. The data show the whole oceanic crust up to the Moho. The Andaman Sea is covered with a thick pile of sediments that record the tectonic history of the rift system up to the spreading axis, allowing to decipher the whole process from rifting to spreading for the first time. We see a very rapid phase of transition from the rifting of the rises to the spreading in less than 20 km. Then a succession of at least 7 half-grabens is well recorded by the sediments on both sides of the spreading center. These half grabens are separated by outward tilted low angle detachment faults, which form the base of steeply dipping normal faults due to stretching. These low angle faults seem to connect with axial magma chambers that control evolution of the rift valley. We find that new detachment faults develop every 350,000 years, forming a new rift valley. The images of active normal faults within the central rift valley allow us to quantify the formation of oceanic crust by tectonic versus magmatic processes.

  12. Rift processes and crustal structure of the Amundsen Sea Embayment, West Antarctica, from 3D potential field modelling (United States)

    Kalberg, Thomas; Gohl, Karsten; Eagles, Graeme; Spiegel, Cornelia


    The Amundsen Sea Embayment of West Antarctica is of particular interest as it provides critical geological boundary conditions in better understanding the dynamic behavior of the West Antarctic Ice Sheet, which is undergoing rapid ice loss in the Amundsen Sea sector. One of the highly debated hypothesis is whether this region has been affected by the West Antarctic Rift System, which is one of the largest in the world and the dominating tectonic feature in West Antarctica. Previous geophysical studies suggested an eastward continuation of this rift system into the Amundsen Sea Embayment. This geophysical study of the Amundsen Sea Embayment presents a compilation of data collected during two RV Polarstern expeditions in the Amundsen Sea Embayment of West Antarctica in 2006 and 2010. Bathymetry and satellite-derived gravity data of the Amundsen Sea Embayment complete the dataset. Our 3-D gravity and magnetic models of the lithospheric architecture and development of this Pacific margin improve previous interpretations from 2-D models of the region. The crust-mantle boundary beneath the continental rise and shelf is between 14 and 29 km deep. The imaged basement structure can be related to rift basins within the Amundsen Sea Embayment, some of which can be interpreted as products of the Cretaceous rift and break-up phase and some as products of later propagation of the West Antarctic Rift System into the region. An estimate of the flexural rigidity of the lithosphere reveals a thin elastic thickness in the eastern embayment which increases towards the west. The results are comparable to estimates in other rift systems such as the Basin and Range province or the East African Rift. Based on these results, we infer an arm of the West Antarctic Rift System is superposed on a distributed Cretaceous rift province in the Amundsen Sea Embayment. Finally, the embayment was affected by magmatism from discrete sources along the Pacific margin of West Antarctica in the Cenozoic.

  13. Long Wavelenth Subsidence of Western Europe during Late Eocene-Oligocene (38-23 Ma): Mantle Dynamic Effect? (United States)

    Guillocheau, Francois; Robin, Cécile; Bessin, Paul


    Western Europe (France, southern Britain, southern Belgium, western Germany) is subsiding during Late Eocene to Oligocene (38-23 Ma) as suggested by the growth of numerous small sedimentary basins mainly filled by lacustrine deposits with some brackish to marine deposits. This large-scale subsidence is coeval with the early stage of the so-called Oligocene rifts (in fact Late Bartonian to Rupelian): Lower Rhinegraben, Bresse, Limagnes. The subsiding domain extends from Cornwall to the Rhine Graben including the Armorican Massif, the southern Paris Basin, the northern Aquitaine Basin, the French Central Massif, the Ardennes-Eifel… This subsidence occurred at a period of global sea level fall and then an eustatic component cannot explain (1) the accommodation space creation and (2) the marine floding with a paroxysm during Early Oligocene times (Armorican Massif, ?Ardennes, French Massif central). This marine flooding also indicate that the relief of the Hercynian basement was less elevated and smoother than today. Some of those small "basins" were interpreted as little rifts, but new mapping (e.g. Puy-en-Velay or Forez Plain in the French Massif central) or new geophysical data (e.g. Rennes Basin in the Armorican massif) suggest that no faults control those basins or that they result from post-depositional collapses. This long wavelength subsidence is at the scale of the mantle dynamic. Possible mantle mechanisms and the relationships with the "Oligocene" rifts and the North Sea inversion will be discussed.

  14. InSAR Time Series to Characterize Landslide Ground Deformations in a Tropical Urban Environment: Focus on Bukavu, East African Rift System (RD Congo). (United States)

    Nobile, A.; d'Oreye, N.; Monsieurs, E.; Dewitte, O.; Kervyn, F.


    The western branch of the East African Rift System, in Central Africa, is a region naturally prone to landslides due to factors such as heavy rainfall, tectonic activity and steep topography. In addition, sensibility to slope instability is expected to increase in the future in response to increasing demographic pressure and land use/land cover changes. The Rift flanks west of Lake Kivu (DRC) are one of the Congolese regions most affected by landslides. Although heavy rainfall periods and earthquakes are the main triggering factors, nothing is known on their potential role on the current dynamics of existing landslides Here we used InSAR time series to monitor ground deformations associated to large slow-moving landslides that continuously affect highly populated slopes in the city of Bukavu (DRC). Bukavu is located within the Rift, on the southern shore of Lake Kivu, in a tropical environment. Using >100 Cosmo-SkyMed SAR images, acquired between March 2015 and June 2016 with a mean revisiting time of 8 days per orbit (ascending and descending), we produce displacement-rate maps and ground deformation time series using different techniques: Persistent Scatter (PS), Small Baseline Subset (SBAS) and Multidimensional Small Baseline Subsets (MSBAS). The three techniques provides similar results in areas with relatively small displacements (few mm per months). However, in areas where displacements are much higher and where coherence is lost by traditional techniques, MSBAS, that process concurrently the two satellite orbits improving temporal resolution, is more efficient. It allows to measure higher ground deformation rates by keeping the coherence. For one specific landslide where intense field mapping was done, the results show clearly the pattern of the deformations that divides the landslide in blocks that move with different velocity (up to 20 cm/yr). This pattern is consistent with field observations and possibly related to the anthropic activity. Furthermore

  15. Tectonic stress evolution in the Pan-African Lufilian Arc and its foreland (Katanga, DRC): orogenic bending, late orogenic extensional collapse and transition to rifting (United States)

    Kipata, M. L.; Delvaux, D.; Sebagenzi, M. N.; Cailteux, J.; Sintubin, M.


    Between the paroxysm of the Lufilian orogeny at ~ 550 Ma and the late Neogene to Quaternary development of the south-western branch of the East African rift system, the tectonic evolution of the Lufilian Arc and Kundelungu foreland in the Katanga region of the Democratic Republic of Congo remains poorly unknown although it caused important Cu-dominated mineral remobilizations leading to world-class ore deposits. This long period is essentially characterized by brittle tectonic deformations that have been investigated by field studies in open mines spread over the entire arc and foreland. Paleostress tensors were computed for a database of 1450 fault-slip data by interactive stress tensor inversion and data subset separation, and the relative succession of 8 brittle deformation events established. The oldest brittle structures observed are related to the Lufilian brittle compressional climax (stage 1). They have been re-oriented during the orogenic bending that led to the arcuate shape of the belt. Unfolding the stress directions from the first stage allows to reconstruct a consistent NE-SW direction of compression for this stage. Constrictional deformation occurred in the central part of the arc, probably during orogenic bending (Stage 2). After the orogenic bending, a sequence of 3 deformation stages marks the progressive onset of late-orogenic extension: strike-slip deformations (stages 3-4) and late-orogenic arc-parallel extension (stage 5). It is proposed that these 3 stages correspond to orogenic collapse. In early Mesozoic, NW-SE compression was induced by a transpressional inversion, interpreted as induced by far-field stresses generated at the southern active margin of Gondwana (stage 6). Since then, this region was affected by rift-related extension, successively in a NE-SW direction (stage 7, Tanganyika trend) and NW-SE direction (stage 8, Moero trend).

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

    Loule, Jean-Pierre; Pospisil, Lubomil


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

  17. Western Australia energy system

    Energy Technology Data Exchange (ETDEWEB)

    Peter Scaife; Andre Urfer; Phil Brown; Aaron Cottrell; Jason Nunn; Louis Wibberley


    The study aims to assess present and future energy supply in Western Australia, and incorporates requests made by Wesfarmers, Griffin Energy, Western Power and the Department of Industry and Resources in October 2003 to include a number of hypothetical energy futures.

  18. Subsidence history, crustal structure and evolution of the Nogal Rift, Northern Somalia (United States)

    Ali, M. Y.; Watts, A. B.


    Seismic reflection profile, gravity anomaly, and biostratigraphic data from deep exploration wells have been used to determine the tectonic subsidence, structure and evolution of the Nogal basin, Northern Somalia, one of a number of ENE-WSW trending early Mesozoic rifts that formed prior to opening of the Gulf of Aden. Backstripping of biostratigraphic data at the Nogal-1 and Kali-1 wells provides new constraints on the age of rifting, and the amount of crustal and mantle extension. The tectonic subsidence and uplift history at the wells can be generally explained as a consequence of two, possibly three, major rifting events. The first event initiated in the Late Jurassic (~156 Ma) and lasted for ~10 Myr. We interpret the rift as a late stage event associated with the break-up of Gondwana and the separation of Africa and Madagascar. The second event initiated in the Late Cretaceous (~80 Ma) and lasted for ~20 Myr. This event probably correlates with a rapid increase in spreading rate on the ridges separating the African and Indian and African and Antarctica plates and a contemporaneous slowing down of Africa's plate motion. The backstripped tectonic subsidence data can be explained by a multi-rift extensional model with a stretching factor, β, in the range 1.17-1.38. The third and most recent event occurred in the Oligocene (~32 Ma) and lasted for ~10 Myr. This rift only developed at the centre of the basin close to Nogal-1 well, and is related to the opening of the Gulf of Aden. The amount of crustal thinning inferred at the Kali-1 well is consistent with the results of Process-Oriented Gravity and Flexure (POGM) modelling, assuming an elastic thickness of ~30 km. The thinning at the Nogal-1 well, however, is greater by ~ 7 km than predicted suggesting that the basin may be locally underplated by magmatic material. Irrespective, POGM suggests the transition between thick crust beneath Northern Somalia to thin crust beneath the Indian Ocean forms a ~500 km wide

  19. 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

  20. Internal Structure of the Extinct Skagi-Hunafloi Rift Zone and Implications for Magmatic Construction (United States)

    Siler, D. L.; Karson, J. A.; Varga, R. J.; Horst, A. J.


    Structural relief ~1.5 km of basaltic crust on the eastern flank of the now-extinct Skagi-Hunafloi rift zone (active between 8 and 4 Ma) is exposed in two mountain ranges bounding the glacially excavated Vatnsdalur in northwestern Iceland. This area reveals both the along- and across-strike variations within an abandoned Tertiary rift zone. Regionally the rift zone is characterized by a "flexure zone" with basaltic lavas that dip 5-10° westward, toward the rift axis. Superimposed on this structure is a bowl-shaped depression at least 800 m deep and ~5 km in diameter in which lava flows dip as much as 50° inward. The lowest package of lavas associated with the depression are basaltic and minor rhyolitic flows (7.62±0.32 Ma), which are at least 400 m thick and have been tectonically rotated during subsidence, as indicated by field relationships and preliminary paleomagnetic data. Overlying these tilted, pre-subsidence flows are syn-subsidence basaltic lavas, which are at least 150 m thick and breccias all of which thicken toward the center of the depression. Overlying the syn- subsidence flows is a ~250 m thick basaltic lens (6.98±0.32 Ma). Ages and thicknesses of units associated with the depression roughly constrain the local subsidence rates at ~1 km/my. Just to the west, gabbroic to granophyric intrusions and hydrothermally altered igneous rocks and breccias mark a dissected volcanic center. Dense (cone?) sheet swarms dip radially inward. This entire assemblage is overlain by gently dipping basaltic to rhyolitic lavas showing that magmatic construction did not result in generation of high relief. Crustal thickening was accommodated by subsidence and backfilling near the depression and by basaltic to minor rhyolitic sheet intrusions over a broader surrounding area. Folding of the pre-subsidence lavas was likely accommodated by slip on steeply dipping fractures and within flow top breccia units. Focused subaxial subsidence in rift zones may result from

  1. Using osmium isotopes to explore the link between alkaline lavas and metasomatized mantle in the Western Branch, Uganda (United States)

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


    The subcontinental lithospheric mantle (SCLM) is foundational to understanding the construction, destruction, and division of tectonic plates. Tectonic processes both directly and indirectly influence the lithosphere's thermal, physical and mineralogical properties. Mantle melting and melt/fluid percolation cause fundamental changes to the lithosphere that affect its composition and stability. Specifically, metasomatism by silicate melts and hydrous/carbonated fluids can create lithologies (i.e. pyroxenites) that are denser, more fusible, and less viscous than adjacent peridotite. The resulting density instabilities may lead to lithospheric erosion, topographic uplift and even continental rifting. We explore the link between metasomatized SCLM and mafic volcanism in the Ugandan portion of the Western Branch of the East African Rift System using Re-Os isotopes from both alkaline mafic lavas and pyroxenite mantle xenoliths. The lavas record age-corrected 187Os/188Os that range from 0.1421 to 0.2105, which is more radiogenic than primitive mantle. These data demonstrate that many of the lavas were derived from a metasomatized mantle source though a few have experienced crustal contamination. Mantle xenoliths also record a wide range of 187Os abundances. One peridotite xenolith has a mildly radiogenic signature (187Os/188Os = 0.1342) whereas the pyroxenites span a wide range of 187Os/188Os ratios (0.1270-0.5052). Based on these data, we conclude that the lavas were derived from metasomatized SCLM. Some of the SCLM was sampled by mantle xenoliths but, as a whole, the SCLM is more heterogeneous than the lavas suggest. The widespread, metasomatized SCLM readily contributed to melt generation both in situ as well as during foundering via lithospheric drip (Furman et al., 2016). The SCLM-derived volcanism occurred prior to and during Western Rift extension, suggesting that the metasomatized SCLM played a vital role in rift development

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

    Rostom, R. S.

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

  3. A Hierarchical Network Approach for Modeling Rift Valley Fever Epidemics with Applications in North America: e62049

    National Research Council Canada - National Science Library

    Ling Xue; Lee W Cohnstaedt; H Morgan Scott; Caterina Scoglio


    .... In the event Rift Valley fever virus is introduced to the United States or other non-endemic areas, understanding the potential patterns of spread and the areas at risk based on disease vectors...

  4. Identification of suitable areas for the occurrence of Rift Valley fever outbreaks in Spain using a multiple criteria decision framework. (United States)

    Sánchez-Vizcaíno, Fernando; Martínez-López, Beatriz; Sánchez-Vizcaíno, José Manuel


    Rift Valley fever (RVF) is a mosquito-borne viral disease that may produce a considerable impact on the economy in affected countries. In the last decades, the geographic distribution of RVF virus has increased including most of the countries in Africa, Arabia Saudi and Yemen. This situation has raised the concerns regarding its potential introduction in the European Union (EU) countries where the high number of susceptible species and competent vectors may contribute to the spread of the disease and challenge its rapid control. Thus, the identification of the areas and time periods with highest suitability for RVF outbreak occurrence would be useful for improving the early detection and rapid response of the disease into free countries. The objective of this study was to identify suitable areas for the occurrence of RVF outbreaks in Spain using a multiple criteria decision making model based on weighted linear combination of factors in geographical information systems (GIS). To the best of the author's knowledge this is the first comprehensive GIS-based framework that provides risk maps for RVF suitability in an EU country. Spanish zones with the highest suitability for RVF were concentrated in the regions of Extremadura, south-western Castile and Leon, eastern Galicia, Asturias, Cantabria, Basque Country, northern-central and southern region of Andalusia and in the Balearic Islands. October and May were the most suitable months for RVF outbreak occurrence. Methods and results presented here may be useful to target risk-based surveillance strategies and to more cost-effectively control potential RVFV incursions into Spain. Copyright © 2013 Elsevier B.V. All rights reserved.

  5. Comparison of the rift and post-rift architecture of conjugated salt and salt-free basins offshore Brazil and Angola/Namibia, South Atlantic (United States)

    Strozyk, Frank; Back, Stefan; Kukla, Peter A.


    This study presents a regional comparison between selected 2D seismic transects from large, conjugated salt and salt-free basins offshore southern Brazil (Campos Basin, Santos Basin, Pelotas Basin) and southwest Africa (Kwanza Basin, northern and southern Namibe Basin, Walvis Basin). Tectonic-stratigraphic interpretation of the main rift and post-rift units, free-air gravity data and flexural isostatic backstripping were used for a comprehensive basin-to-basin documentation of key mechanisms controlling the present-day differences in conjugated and neighbouring South Atlantic basins. A significant variation in the tectonic-sedimentary architecture along-strike at each margin and between the conjugated basins across the South Atlantic reflects major differences in (1) the structural configuration of each margin segment at transitional phase between rifting and breakup, as emphasized in the highly asymmetric settings of the large Santos salt basin and the conjugated, salt-free southern Namibe Basin, (2) the post-breakup subsidence and uplift history of the respective margin segment, which caused major differences for example between the Campos and Espirito Santo basins and the conjugated northern Namibe and Kwanza basins, (3) variations in the quantity and distribution of post-breakup margin sediments, which led to major differences in the subsidence history and the related present-day basin architecture, for example in the initially rather symmetric, siliciclastic Pelotas and Walvis basins, and (4) the deposition of Aptian evaporites in the large rift and sag basin provinces north of the Rio Grande Rise and Walvis Ridge, highly contrasting the siliciclastic basins along the margin segments south of the ridges. The resulting present-day architecture of the basins can be generally classified as (i) moderately symmetric, salt-free, and magma-rich in the northern part of the southern segment, (i) highly asymmetric, salt-bearing and magma-poor vs. salt-free and magma

  6. Thermo-mechanical modeling of continental rift evolution over mantle upwelling in presence of far-field stresses (United States)

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


    We conducted fully-coupled high resolution rheologically consistent 3D thermo-mechanical numerical models to investigate the processes of mantle-lithosphere interaction (MLI) in presence of preexisting far-field tectonic stresses. MLI-induced topography exhibits strongly asymmetric small-scale 3D features, such as rifts, flexural flank uplifts and complex faults structures. This suggests a dominant role of continental rheological structure and intra-plate stresses in controlling continental rifting and break-up processes above mantle upwelling while reconciling the passive (far-field tectonic stresses) versus active (plume-activated) rift concepts as our experiments show both processes in action. We tested different experiments by varying two principal controlling parameters: 1) horizontal extension velocity and 2) Moho temperature used as simplified indicator of the thermal and rheological lithosphere layering. An increase in the applied extension expectedly gives less localized deformation at lithospheric scale: the growth of external velocity from 1.5 mm/years to 6 mm/years leads to enlargement of the rift zones from 75-175 km to 150-425 km width. On the contrary, increasing of the lithospheric geotherm has an opposite effect leading to narrowing of the rift zone: the change of the Moho isotherm from 600°C to 800°C causes diminution of the rift width from 175-425 km to 75-150 km. Some of these finding are contra-intuitive in terms of usual assumptions. The models refer to strongly non-linear impact of far-field extension rates on timing of break-up processes. Experiments with relatively fast far-field extension (6 mm/years) show intensive normal fault localization in crust and uppermost mantle above the plume head at 15-20 Myrs after the onset of the experiment. When plume head material reaches the bottom of the continental crust (at 25 Myrs), the latter is rapidly ruptured (break-up time (from 60 to 70 Myrs depending on initial isotherm at the crust bottom

  7. Basement - Cover decoupling and progressive exhumation of metamorphic sediments at hot rifted margin. Insights from the Northeastern Pyrenean analog (United States)

    Clerc, Camille; Lagabrielle, Yves; Labaume, Pierre; Ringenbach, Jean-Claude; Vauchez, Alain; Nalpas, Thierry; Bousquet, Romain; Ballard, Jean-François; Lahfid, Abdeltif; Fourcade, Serge


    We compile field data collected along the eastern part of the North Pyrenean Zone (NPZ) to point to a tectonic evolution under peculiar thermal conditions applying to the basin sediments in relation with the opening of the Cretaceous Pyrenean rift. Based on this compilation, we show that when thinning of the continental crust increased, isotherms moved closer to the surface with the result that the brittle-ductile transition propagated upward and reached sediments deposited at the early stage of the basin opening. During the continental breakup, the pre-rift Mesozoic cover was efficiently decoupled from the Paleozoic basement along the Triassic evaporite level and underwent drastic ductile thinning and boudinage. We suggest that the upper Albian and upper Cretaceous flysches acted as a blanket allowing temperature increase in the mobile pre-rift cover. Finally, we show that continuous spreading of the basin floor triggered the exhumation of the metamorphic, ductily sheared pre-rift cover, thus contributing to the progressive thinning of the sedimentary pile. In a second step, we investigate the detailed geological records of such a hot regime evolution along a reference-section of the eastern NPZ. We propose a balanced restoration from the Mouthoumet basement massif (north) to the Boucheville Albian basin (south). This section shows a north to south increase in the HT Pyrenean imprint from almost no metamorphic recrystallization to more than 600 °C in the pre- and syn-rift sediments. From this reconstruction, we propose a scenario of tectonic thinning involving the exhumation of the pre-rift cover by the activation of various detachment surfaces at different levels in the sedimentary pile. In a third step, examination of the architecture of current distal passive margin domains provides confident comparison between the Pyrenean case and modern analogs. Finally, we propose a general evolutionary model for the pre-rift sequence of the Northeastern Pyrenean rifted

  8. Seroprevalence of Sheep and Goat Pox, Peste Des Petits Ruminants and Rift Valley Fever in Saudi Arabia


    Hani Boshra; Thang Truong; Shawn Babiuk; Maged Gomaa Hemida


    Sheep and goat pox, peste des petits ruminants and Rift Valley fever are important diseases of small ruminant livestock. Sheep and goat pox, along with peste des petits ruminants, are endemic throughout most of Africa, Asia and the Middle East. Whereas Rift Valley fever is endemic in Africa, outbreaks in the Middle East have been reported over the past decade, including the Arabian Peninsula. Saudi Arabia is a major importer of livestock, and understanding the prevalence of these viral infect...

  9. Evolution of the broadly rifted zone in southern Ethiopia through gravitational collapse and extension of dynamic topography (United States)

    Emishaw, Luelseged; Laó-Dávila, Daniel A.; Abdelsalam, Mohamed G.; Atekwana, Estella A.; Gao, Stephen S.


    The Broadly Rifted Zone (BRZ) is a 315 km wide zone of extension in southern Ethiopia. It is located between the Southern Main Ethiopian Rift and the Eastern Branch of the East African Rift System (EARS) represented by the Kenya-Turkana Rift. The BRZ is characterized by NE-trending ridges and valleys superimposed on regionally uplifted ( 2 km average elevation) terrain. Previous studies proposed that the BRZ is an overlap zone resulted from northward propagation of the Kenya-Turkana Rift and southward propagation of the Southern Main Ethiopian Rift. To understand the relationship between the BRZ's extensional style and its crustal and upper mantle structures, this work first estimated the Moho depth using the two-dimensional (2D) radially-averaged power spectral analysis of the World Gravity Map. Verification of these results was accomplished through lithospheric-scale 2D forward gravity models along E-W profiles. This work found that the Moho topography beneath the BRZ depicts a dome-like shape with a minimum depth of 27 km in the center of the dome. This work proposes that the Moho doming, crustal arching underlying the BRZ and associated topographic uplift are the result of asthenospheric mantle upwelling beneath the BRZ. This upwelling changed to a NE-directed lateral mantle flow at shallower depth. This is supported by seismic tomography imaging which shows slow S-wave velocity anomaly at lithospheric depth of 75 km to 150 km stretching in a NE-SW direction from beneath the BRZ to the Afar Depression. This work proposes that the asthenospheric upwelling created gravitationally unstable dynamic topography that triggered extensional gravitational collapse leading to the formation of the BRZ as a wide rift within the narrow rift segments of the EARS.

  10. History of the development of the East African Rift System: A series of interpreted maps through time (United States)

    Macgregor, Duncan


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

  11. The distribution and hydrogeological controls of fluoride in the groundwater of central Ethiopian rift and adjacent highlands (United States)

    Ayenew, Tenalem


    Occurrence of fluoride (F) in groundwater has drawn worldwide attention, since it has considerable impact on human health. In Ethiopia high concentrations of F in groundwaters used for community water supply have resulted in extensive dental and skeletal fluorosis. As a part of a broader study, the distribution of F in groundwater has been investigated, and compared with bedrock geology and pertinent hydrochemical variables. The result indicates extreme spatial variations. High F concentration is often associated with active and sub-active regional thermal fields and acidic volcanics within high temperature rift floor. Variations in F can also be related to changes in calcium concentration resulting from dissolution of calcium minerals and mixing with waters of different chemical composition originated from variable hydrogeological environment across the rift valley. The concentration of F dramatically declines from the rift towards the highlands with the exception of scattered points associated with thermal springs confined in local volcanic centers. There are also interactions of F-rich alkaline lakes and the surrounding groundwater. Meteoric waters recharging volcanic aquifers become enriched with respect to F along the groundwater flow path from highland recharge areas to rift discharge areas. Locally wells drilled along large rift faults acting as conduits of fresh highland waters show relatively lower F. These areas are likely to be possible sources of better quality waters within the rift. The result of this study has important implications on site selection for water well drilling.

  12. CineGlobe Film Festival, Wednesday programme with Science Story Telling Hackathon and Oculus Rift

    CERN Multimedia

    Marcelloni De Oliveira, Claudia


    Besides the short-film competitions, the second day of 2015 CineGlobe included a Soirée Oculus Rift with the public launch of the “Storytelling Science” Hackathon. CineGlobe and Festival Tous Ecrans joined forces to launch the “Storytelling Science” hackathon, in collaboration with Tribeca Film Institute and LIFT Conference. The keynote speech was given by renowned filmmaker and transmedia creator Michel Reihlac, who spoke about the role of interactive and immersive storytelling techniques in cinematic narrative. By placing the viewer in the center of the story, these new technologies are profoundly changing the way we tell stories. Michel Reilhac designs innovative story based experiences, using digital platforms (cinema, tv, mobile, tablets, …) and real life events. His creative approach to storytelling ambitions to offer viewers/ participants a unique opportunity for an immersive, participatory and interactive experience. During the evening, Oculus Rift virtual reality headsets were available to...

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

    Scholz, C.A.; Hutchinson, D.R.


    Seismic reflection profiles from the Lake Baikal Rift reveal extensive details about the sediment thickness, structural geometry and history of extensional deformation and syn-rift sedimentation in this classic continental rift. The Selenga River is the largest single source of terrigenous input into Lake Baikal, and its large delta sits astride the major accommodation zone between the Central and South basins of the lake. Incorporating one of the world's largest lacustrine deltas, this depositional system is a classic example of the influence of rift basin structural segmentation on a major continental drainage. More than 3700 km of deep basin-scale multi-channel seismic reflection (MCS) data were acquired during the 1989 Russian and the 1992 Russian–American field programs. The seismic data image most of the sedimentary section, including pre-rift basement in several localities. The MCS data reveal that the broad bathymetric saddle between these two major half-graben basins is underlain by a complex of severely deformed basement blocks, and is not simply a consequence of long-term deltaic deposition. Maximum sediment thickness is estimated to be more than 9 km in some areas around the Selenga Delta. Detailed stratigraphic analyses of the Selenga area MCS data suggest that modes of deposition have shifted markedly during the history of the delta. The present mode of gravity- and mass-flow sedimentation that dominates the northern and southern parts of the modern delta, as well as the pronounced bathymetric relief in the area, are relatively recent developments in the history of the Lake Baikal Rift. Several episodes of major delta progradation, each extending far across the modern rift, can be documented in the MCS data. The stratigraphic framework defined by these prograding deltaic sequences can be used to constrain the structural as well as depositional evolution of this part of the Baikal Rift. An age model has been established for this stratigraphy, by

  14. Animal movements in the Kenya Rift and evidence for the earliest ambush hunting by hominins (United States)

    Kübler, Simon; Owenga, Peter; Reynolds, Sally C.; Rucina, Stephen M.; King, Geoffrey C. P.


    Animal movements in the Kenya Rift Valley today are influenced by a combination of topography and trace nutrient distribution. These patterns would have been the same in the past when hominins inhabited the area. We use this approach to create a landscape reconstruction of Olorgesailie, a key site in the East African Rift with abundant evidence of large-mammal butchery between ~1.2 and ~0.5 Ma BP. The site location in relation to limited animal routes through the area show that hominins were aware of animal movements and used the location for ambush hunting during the Lower to Middle Pleistocene. These features explain the importance of Olorgesailie as a preferred location of repeated hominin activity through multiple changes in climate and local environmental conditions, and provide insights into the cognitive and hunting abilities of Homo erectus while indicating that their activities at the site were aimed at hunting, rather than scavenging.

  15. Protection of sheep against Rift Valley fever virus and sheep poxvirus with a recombinant capripoxvirus vaccine. (United States)

    Soi, Reuben K; Rurangirwa, Fred R; McGuire, Travis C; Rwambo, Paul M; DeMartini, James C; Crawford, Timothy B


    Rift Valley fever (RVF) is an epizootic viral disease of sheep that can be transmitted from sheep to humans, particularly by contact with aborted fetuses. A capripoxvirus (CPV) recombinant virus (rKS1/RVFV) was developed, which expressed the Rift Valley fever virus (RVFV) Gn and Gc glycoproteins. These expressed glycoproteins had the correct size and reacted with monoclonal antibodies (MAb) to native glycoproteins. Mice vaccinated with rKS1/RVFV were protected against RVFV challenge. Sheep vaccinated with rKS1/RVFV twice developed neutralizing antibodies and were significantly protected against RVFV and sheep poxvirus challenge. These findings further document the value of CPV recombinants as ruminant vaccine vectors and support the inclusion of RVFV genes encoding glycoproteins in multivalent recombinant vaccines to be used where RVF occurs.

  16. Protection of Sheep against Rift Valley Fever Virus and Sheep Poxvirus with a Recombinant Capripoxvirus Vaccine▿ (United States)

    Soi, Reuben K.; Rurangirwa, Fred R.; McGuire, Travis C.; Rwambo, Paul M.; DeMartini, James C.; Crawford, Timothy B.


    Rift Valley fever (RVF) is an epizootic viral disease of sheep that can be transmitted from sheep to humans, particularly by contact with aborted fetuses. A capripoxvirus (CPV) recombinant virus (rKS1/RVFV) was developed, which expressed the Rift Valley fever virus (RVFV) Gn and Gc glycoproteins. These expressed glycoproteins had the correct size and reacted with monoclonal antibodies (MAb) to native glycoproteins. Mice vaccinated with rKS1/RVFV were protected against RVFV challenge. Sheep vaccinated with rKS1/RVFV twice developed neutralizing antibodies and were significantly protected against RVFV and sheep poxvirus challenge. These findings further document the value of CPV recombinants as ruminant vaccine vectors and support the inclusion of RVFV genes encoding glycoproteins in multivalent recombinant vaccines to be used where RVF occurs. PMID:20876822

  17. Serological surveillance studies confirm the Rift Valley fever virus free status in South Korea. (United States)

    Kim, Hyun Joo; Park, Jee-Yong; Jeoung, Hye-Young; Yeh, Jung-Yong; Cho, Yun-Sang; Choi, Jeong-Soo; Lee, Ji-Youn; Cho, In-Soo; Yoo, Han-Sang


    Rift Valley fever is a mosquito-borne zoonotic disease of domestic ruminants. This disease causes abortions in pregnant animals, and it has a high mortality rate in newborn animals. Recently, a Rift Valley fever virus (RVFV) outbreak in the Arabian Peninsula increased its potential spread to new regions worldwide. In non-endemic or disease-free countries, early detection and surveillance are important for preventing the introduction of RVFV. In this study, a serological surveillance was conducted to detect antibodies against RVFV. A total of 2382 serum samples from goats and cattle were randomly collected from nine areas in South Korea from 2011 to 2013. These samples were tested for antibodies against RVFV, using commercial ELISA kits. None of the goats and cattle were positive for antibodies against RVFV. This finding suggests that this disease is not present in South Korea, and furthermore presents the evidence of the RVFV-free status of this country.

  18. The lifecycle of caldera-forming volcanoes in the Main Ethiopian Rift: insights from Aluto volcano (United States)

    Mather, T. A.; Hutchison, W.; Yirgu, G.; Biggs, J.; Cohen, B. E.; Barfod, D. N.; Lewi, E.; Pyle, D. M.


    The silicic peralkaline volcanoes of the East African Rift are some of the least studied and yet potentially most dangerous volcanoes in the world. We present the first detailed account of the eruptive history of Aluto, a restless silicic volcano located in the Main Ethiopian Rift, using new constraints from fieldwork, remote sensing, 40Ar/39Ar geochronology and geochemistry. Prior to the growth of the Aluto volcanic complex (before 500 ka) the region was characterized by a significant period of fault development and mafic fissure eruptions. The earliest volcanism at Aluto built up a trachytic complex over 8 km in diameter. Aluto then underwent large-volume ignimbrite eruptions at ca. 300 ka developing a ~42 km2 collapse structure. After a hiatus of ~250 kyr, a phase of post-caldera volcanism began. Since ca. 60 ka, highly-evolved peralkaline rhyolite lavas, ignimbrites and pumice fall deposits have erupted from vents across the complex. The age of the youngest volcanism is not well known. Geochemical modelling is consistent with rhyolite genesis from protracted fractionation (>80 %) of typical 'rift basalt'. Based on the field stratigraphy and the number, style and volume of recent eruptions we suggest that silicic eruptions occur at an average rate of 1 per 1000 years, and that future eruptions of Aluto will involve explosive emplacement of localised pumice cones and effusive obsidian coulees of volumes between 1-100 × 106 m3. Comparisons with other caldera volcanoes in this section of the rift suggest that there may be parallels between Aluto's behaviour and that of other volcanic centres, both in terms of the volcanic 'lifecycle', and broad timings of caldera collapse events.

  19. Geochemistry of Peralkaline Melts at Kone Volcanic Complex, Main Ethiopian Rift (United States)

    Iddon, F. E.; Edmonds, M.; Jackson, C.; Hutchison, W.; Mather, T. A.; Fontijn, K.; Pyle, D. M.


    The East Africa rift system (EARS) is the archetypal example of continental rifting, with the Main Ethiopian rift (MER) segment offering a unique opportunity to examine the dynamics of peralkaline magmas; the development of central volcanoes; melt distribution and transport in the crust; the volatile budgets of rift magmas and their implications for the formation of ore deposits. The alkali- and halogen-rich magmas of the MER differ from their calc-alkaline counterparts in other settings due to their lower viscosities and higher volatile contents, which have important implications for magma transport, reservoir dynamics and eruptive hazards. The high halogen contents of the magmas give rise to halogen-rich vapor which has the capacity to transport and concentrate metals and REE. The Kone Volcanic complex is one of the lesser studied Quaternary peralkaline centres, located on the axial portion of the MER. It comprises two superimposed calderas, surrounded by ignimbrite deposits and unwelded felsic pyroclastic material, small basaltic vents and rhyolitic domes. Unusually for the central volcanoes of the MER, the caldera has refilled with basaltic lava, not pyroclastic material. We use whole rock and micro-analysis to characterize a range of Kone tephras, glasses, crystal phases and melt inclusions in terms of major, trace and volatile element abundances, alongside detailed textural analysis using QEMSCAN and SEM. The whole rock geochemistry reflects the clear peralkaline nature of the suite, with a distinct compositional gap between 50 wt% and 65 wt% SiO2, controlled largely by fractional crystallization. Trace element systematics illustrate that trachytes entrain alkali feldspars, with the crystal cargo of the entire suite reflecting the structure of the magma reservoir at depth, with liquid-rich lenses and regions of syenitic mush. Melt inclusion geochemistry allows reconstruction of complex, multiphase differentiation processes and the exsolution of both a vapor

  20. Early Pleistocene lake formation and hominin origins in the Turkana-Omo rift (United States)

    Lepre, Christopher J.


    Prior research has correlated the formation of Plio-Pleistocene lakes in East Africa to global/regional climate changes and interpreted the lacustrine basins as significant settings of hominin evolution. Paleo-Lake Lorenyang from the Turkana-Omo rift is important to these issues, as its marginal deposits contain some of, if not the earliest currently known specimens of Acheulian stone tools and African Homo erectus. Magnetostratigraphic and sedimentological evidence indicates that the oldest preserved paleo-Lake Lorenyang deposits are dated at 2.148-2.128 Ma and derive from the NW Turkana basin, predating those from the Omo basin by ˜100 kyr and the NE Turkana basin by ˜190 kyr. Apparently, the lake expanded asynchronously in the rift, potentially due to a volcano-tectonic influence on the location of drainage networks, depositional slopes, or topographic elevation differences within and between the basins at the time of flooding. The onset of the lake temporally coincides with the eruption of basalt lava flows dated to 2.2-2.0 Ma that blocked the southeast outlet of the Turkana basin. This provides a plausible mechanism for hydrologic closure and lacustrine basin formation through volcano-tectonic impounding. It also points to a non-climatic cause for the initial formation of paleo-Lake Lorenyang at ˜2.14 Ma. First appearances for African H. erectus (˜1.87 Ma) and Acheulian tools (˜1.76 Ma) in the Turkana-Omo rift postdate the lake's initial formation by about 270 kyr and 380 kyr, respectively. Such timing differences contrast with studies that correlate all three to the 400-kyr-eccentricity maximum at 1.8 Ma. Although the Turkana-Omo rift is just one example, it does provide alternative insights to views that link climate, hominin evolution, and lake formation in East Africa.

  1. Andean deformation and rift inversion, eastern edge of Cordillera Oriental (Guateque Medina area), Colombia (United States)

    Branquet, Y.; Cheilletz, A.; Cobbold, P. R.; Baby, P.; Laumonier, B.; Giuliani, G.


    In the Guateque-Medina area, Paleozoic basement and Mesozoic rift basins have been uplifted and exhumed during the Andean orogeny (12 Ma to present). Surface exposures and subsurface data constrain the deformation style and the rift geometry. We have mapped a regional transect and restored a cross section. We have also reconciled existing stratigraphic data, from cordillera, foothills and foreland basin, and have added new data of our own. In Early Cretaceous shales, there is evidence for fault-controlled sedimentation. A brecciated evaporitic layer, which is locally emerald bearing, has acted as a regional detachment. The underlying basement, composed of Paleozoic sediments, crops out as the Quetame Massif. It was uplifted during the Andean orogeny on a series of high-angle reverse faults. The main SE-verging Tesalia fault has resulted from Andean reactivation of an Early Cretaceous normal fault, which bounded a half-rift. A series of NW-verging back-thrusts may have resulted from Andean reactivation of Paleozoic faults. Between the back-thrusts and the Tesalia fault is a basement pop-up. It may be part of a flower structure, because components of right-lateral slip have been identified. These are attributed to eastward subduction of the Nazca plate beneath South America. In general, the style and timing of Andean deformation in the Guateque-Medina area are compatible with the plate tectonic setting of the northern Andes.

  2. Magmatic architecture within a rift segment: Articulate axial magma storage at Erta Ale volcano, Ethiopia (United States)

    Xu, Wenbin; Rivalta, Eleonora; Li, Xing


    Understanding the magmatic systems beneath rift volcanoes provides insights into the deeper processes associated with rift architecture and development. At the slow spreading Erta Ale segment (Afar, Ethiopia) transition from continental rifting to seafloor spreading is ongoing on land. A lava lake has been documented since the twentieth century at the summit of the Erta Ale volcano and acts as an indicator of the pressure of its magma reservoir. However, the structure of the plumbing system of the volcano feeding such persistent active lava lake and the mechanisms controlling the architecture of magma storage remain unclear. Here, we combine high-resolution satellite optical imagery and radar interferometry (InSAR) to infer the shape, location and orientation of the conduits feeding the 2017 Erta Ale eruption. We show that the lava lake was rooted in a vertical dike-shaped reservoir that had been inflating prior to the eruption. The magma was subsequently transferred into a shallower feeder dike. We also find a shallow, horizontal magma lens elongated along axis inflating beneath the volcano during the later period of the eruption. Edifice stress modeling suggests the hydraulically connected system of horizontal and vertical thin magmatic bodies able to open and close are arranged spatially according to stresses induced by loading and unloading due to topographic changes. Our combined approach may provide new constraints on the organization of magma plumbing systems beneath volcanoes in continental and marine settings.

  3. A satellite magnetic perspective of subduction zones, large igneous provinces, rifts, and diffuse plate boundary zones (United States)

    Purucker, M. E.; Whaler, K. A.


    Large and intermediate-scale tectonic features such as subduction zones, large igneous provinces, rifts, and diffuse plate boundary zones are often seen to have a magnetic signature visible from the perspective of near-Earth magnetic field satellites such as CHAMP and Orsted. Why do these tectonic features have a magnetic signature, while others do not? A new model of the lithospheric field (MF-6, Maus et al., 2008) extending to spherical harmonic degree 120 (333 km wavelength) has been used to evaluate the magnetic state of the lithosphere under the assumption that the magnetization is either induced (with a seismic starting model), or remanent (with a minimum norm approach). Some of the features identified from these images include the Tethyan and NE Siberian diffuse plate boundary zones, the Red Sea rift, and Cretaceous rift basins developed on the West African shield. Almost without exception, subduction zones exhibit a magnetic signature, as do many large igneous provinces. In this talk we discuss some of the new insights this magnetic perspective provides, and speculate on the controls which determine whether tectonic features will be expressed magnetically.

  4. Effect of 3D boundary conditions on rift propagation or failure to break. (United States)

    Le Pourhiet, Laetitia; Watremez, Louise; Delescluse, Matthias


    Oblique rift segments are generally modelled using two type of set-ups. The first one consist of off-set weak notches which are pulled in a cylindrical manner, the second one consist at pulling obliquely on wide weak zone inside which a system of en-echellon grabben can develop. These two set up produce diverging segments of constant age and younger oblique segments which localise after some delays which depends on the offset of the diverging segments and the rheology of the lithosphere. In this study, we propose a different set-up which consist at seeding only one diverging weak segments and at letting the continental rupture propagate through the model in order to assess 1/ how 3D boundary conditions affect the speed on propagation of the continental break-up and 2/ how the structure that form at the front of the propagating break-up affect the propagation it-self. We find that a cylindrical boundary condition or extension in the direction of propagation favour very rapid continental break-up propagation, narrow rift zones and extremely linear diverging segments. On the contrary, when a slight compression is applied in the direction of rift propagation. The propagation is slow and might even stop completely. This slow down in propagation results in an increase of pre-breakup structuration of the margins and can even cause segmentation of final spreading. The numerical models are finally compared to natural examples from the Atlantic and the South China Sea.

  5. Rifting and magmatism associated with the South America and Africa break-up

    Energy Technology Data Exchange (ETDEWEB)

    Thomaz Filho, Antonio; Cesero, Pedro de [Universidade do Estado, Rio de Janeiro, RJ (Brazil). Faculdade de Geologia; Mizusaki, Ana Maria Pimentel [Rio Grande do Sul Univ., Porto Alegre, RS (Brazil). Inst. de Geociencias; Milani, Edison Jose [PETROBRAS, Rio de Janeiro, RJ (Brazil)


    Based on about 380 K/Ar dating of basic and alkaline magmatic rocks from Brazilian sedimentary basins and the argentinean Atlantic margin it is possible to interpret the evolution of the rifting that caused the South America and Africa break-up. This process started in the Triassic and took place northwestward of the Foz do Amazonas basin, on the equatorial Brazilian continental margin, and reached the San Julian and North Malvinas basins, in the southern portion of South America. From this latter up to the Espirito Santo Basin, rifting took place between the Jurassic and Neocomian whereas transcurrence caused by clockwise rotation of South America on the equatorial margin generated the Potiguar Basin. The available information suggests that the final break-up of Africa and South America occurred along the eastern Brazilian margin, between the Cumuruxatiba/Mucuri and Pernambuco basins, during the Cenomanian/Turonian. The resistance offered by the Sao Luis/West African and Sao Francisco/Congo cratons promoted the huge magnetic manifestations which occur in the Brazilian paleozoic intracratonic basins (Acre, Solimoes, Amazonas, Paranaiba and Parana basins) as well as in the interior Tacutu Rift. Hot spots turned out during the drift phase, as registered by the Mecejana (CE)/Rocas Atoll/Fernando de Noronha Archipelago Alignment and Pocos de Caldas/Cabo Frio Alkaline Rocks Alignment that persists up to Vitoria/Trindade Chain. (author)

  6. Tectonics and sedimentation of the central sector of the Santo Onofre rift, north Minas Gerais, Brazil

    Directory of Open Access Journals (Sweden)

    Alice Fernanda Costa


    Full Text Available ABSTRACT: The Santo Onofre Group registers the filling of a Tonian, intracontinental paleo-rift that developed along the northern and central Espinhaço regions. This paper examines this unit in the central Espinhaço region with stratigraphic analysis and U-Pb geochronology, reviewing and dividing into the Canatiba and Rio Peixe Bravo Formations, which include the Barrinha Member. The Canatiba Formation mainly comprises carbon-rich mudstones that were deposited through low-density turbidity flows that alternated with sediment settling under anoxic conditions. The Rio Peixe Bravo Formation consists of a succession of sandstones and minor mudstones, which were deposited through low- to high-density turbidity flows. The Barrinha Member mainly consists of conglomerates and is related to channelized debris flows. Detrital zircon grains show maximum depositional ages of 930 ± 33 Ma and around 865 Ma for the Canatiba and Rio Peixe Bravo Formations, respectively. We interpret the Santo Onofre rifting to be relative younger than that for the Sítio Novo Group and to be a precursor stage of the glacial and post-glacial rift-to-passive margin-related sequences of the Macaúbas Group. The lithostratigraphic term “Macaúbas Supergroup” would be of better use to accommodate the unconformity-bounded Tonian sequences that were related to the Rodinia breakup in the Congo-São Francisco paleocontinent.

  7. Silvics of western redcedar (United States)

    Raymond J. Boyd


    Western redcedar (Thuja plicata) is one of the most important commercial species in the Pacific Northwest, Alaska, and British Columbia. Local common names include giant arborvitae, canoe cedar, shinglewood, Pacific redcedar, giant cedar, arborvitae, and cedar (24).

  8. Circulation of Surface Water And Groundwater. Geophysical approach (electrical tomography). Western Haouz plain. Western Morocco (United States)

    ibtissam, Chouikri; Mandour Abdennabi, El; Mohammed, Jeffal; Mahjoub, Himi; Rochdane, Samia; Karroum, Morad; Elgettafi, Mohammed; Casas, Albert


    The Western Haouz plain and the Mejjate plain constitute a vast alluvial plain of about 2800 km2. The area is located between 30 and 80 km south-west of Marrakech city and it is characterized by a semi-arid climate. The morphology of the plain is known by a flat topography, monotone and it is drained by three wadis: Nfis wadi, Assif El Mal wadi and Chichaoua wadi. The compilation of Geological, Geophysical and hydrogeological data shows that the Western Haouz plain is divided into two parts, it is a synclinal form separated by Marmouta horst and Guemassa horst. In the southern part, the Mejjate syncline is subsiding and shows a several formations from the shales of the Paleozoic to the alluvium of the quaternary. In the northern part, the syncline is less developed and it is formed by the conglomerates of the Mio-Pliocene and the alluvium of the Quaternary. The gravity map established shows positive anomalies due to the outcrop of the basement, and negative anomalies in the subsiding basins. Hydrogeologically, the geometry of the reservoirs and the groundwater circulation are controlled by geology (Rifts, flexure, anticline and syncline). The southern part of the plain between the Marmouta anticline and the piedmont of the High Atlas Mountains shows two aquifers; the unconfined aquifer housed in thick formations of Quaternary and Mio-Pliocene; and the confined aquifer housed in dolomitic limestones of the Cenomanian-Turonian. The confined aquifer is fed at the northern flank of the High Atlas showing karts morphology and high cliff of limestone slab of the Turonian. The outlet of the deep confined aquifer is shown by Abainou source with a variation between 300 and 600 l/s south of the Marmouta anticline and constitutes a barrier for the deep waters flow circulations.

  9. A missing element of the deep carbon cycle: CO2 degassing estimates from rift length analysis during Pangea fragmentation (United States)

    Brune, S.; Williams, S.; Müller, D.


    The deep carbon cycle connects CO2 within the atmosphere and oceans to the vast CO2 reservoir in Earth's mantle: subducted lithosphere carries CO2 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 worldwide census of extensional plate boundary length from the Triassic to present day, in one million year time intervals, using a novel analysis technique (Brune et al. 2016, Nature, doi:10.1038/nature18319). The most extensive rift phase during the fragmentation of Pangea occurred in the Cretaceous with extension along the South Atlantic (9700 km) and North Atlantic rifts (9100 km), within East Gondwana (8500 km), and the failed African rift systems (4900 km). The combined extent of these and several smaller rifts amounts to more than 30.000 km of simultaneously active continental rifting. It is well-accepted that volcanoes at plate boundaries release large amounts of CO2 from the Earth's interior. Recent work, however, revealed the importance of deep-cutting faults and diffuse degassing on CO2 emissions in the East African rift (Lee et al. 2016, Nature Geoscience, doi: 10.1038/ngeo2622). Upscaling these measured CO2 fluxes to all concurrently active global rift zones, we compute first-order estimates of total rift-related CO2 degassing rates for the last 240 Myr. Our results show that rift-related CO2 release rates may have reached 600 Mt/yr in the Early Cretaceous, while Cenozoic rates rarely exceeded 200 Mt/yr. By comparison, present-day estimates of CO2 release at mid-ocean ridges range between 53 and 97 Mt/yr. We suggest that rift-related degassing during supercontinental breakup played a major role in maintaining high atmospheric CO2 concentrations through Mesozoic times, which exceeded Quaternary values by 400%.

  10. Variations in the reflectivity of the moho transition zone beneath the Midcontinent Rift System of North America: results from true amplitude analysis of GLIMPCE data (United States)

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


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

  11. Wetlands as a Record of Climate Change and Hydrological Response in Arid Rift Settings (United States)

    Ashley, G. M.


    Of all the terrestrial depositional settings, rift basins typically provide the greatest accommodation space, and consequently have some of the longest records of continental sedimentation. Lake deposits were the only rift component studied for records of long-term climatic change and for testing hypotheses of orbital forcing. Recently, the continuing quest for the paleontological and cultural records of human origins entombed in the sedimentary rocks of the East African Rift System raised questions concerning hydrologic and biologic response to climatic change. Additional issues are the impact of climate on paleolandscapes and the environmental stresses that might have affected human evolution. Other important indicators of rift hydrology, such as springs and wetlands are now emerging as viable records of climate change. Rift valley basins are shallow, hydrologically closed systems that are responsive to shifts in climate, and specifically sensitive to changes in the hydrologic budget (P-ET). Long term wet-dry cycles in the low latitudes are thought to be astronomically controlled, i.e. Milankovitch precession cycles (19-23 ka). In the tropics, precipitation (P) varies with changes in solar insolation which fluctuates plant remains (e.g. roots, stems) pollen, phytoliths, diatoms, root casts, charcoal, carbonate and manganese-rich nodules, as well as copious evidence of bioturbation (plants and invertebrates to large vertebrate trampling). Older (Pleistocene) deposits that retain little original organic matter and plant remains are generally silicified, but otherwise the record is similar to modern wetlands. Records from Olduvai Gorge (1.85-1.75 Ma) contain springs and wetlands associated with stone tools. On shorter time-frames, a drought occurred during the Medieval Warm Period (MWP) and higher rainfall in East Africa during the Little Ice Age (700 BP) led to higher lake levels of Lake Naivasha and Lake Turkana (Mohamed et al. 1995; Verschuren et al. 2000) and

  12. QLg tomography in Gujarat, Western India (United States)

    Aggarwal, Sandeep Kumar; Khan, Prosanta Kumar


    We propose a novel Lg attenuation tomography model (QLg tomography) for the state of Gujarat, Western India, using earthquake data recorded by the Gujarat Seismic Network, operated by the Institute of Seismological Research in Gandhinagar. The waveform dataset consist of 400 3-component recordings, produced by 60 earthquakes with magnitude (ML) spanning from 3.6 to 5.1, recorded at 60 seismic stations having epicentral distances spanning between 200 and 500 km. Spectral amplitude decays for Lg wave displacement were obtained by generalized inversion at 17 frequencies spanning between 0.9 and 9 Hz. Lg wave propagation efficiency was measured by Lg/Pn spectral ratio categorizing as efficient ratio ≥6 for 86%, intermediate ratio of 3-6 for 10% and inefficient ratio Gujarat. Average power-law attenuation relationship obtained for Gujarat as QLg(f) = 234f0.64, which corresponds to high attenuation in comparison to peninsular India shield region and other several regions around the world. QLg tomography resolves the highly attenuating crust of extremely fractured Saurashtra region and tectonically active Kachchh region. The Gujarat average attenuation is also lying in between them. The low attenuation in Cambay and Narmada rift basins and extremely low attenuation in patch of Surendranagar area is identified. This study is the first attempt and can be utilized as pivotal criteria for scenario hazard assessment, as maximum hazard has been reported in highly attenuating tectonically active Kachchh region and in low attenuating Cambay, Narmada and Surendranagar regions. The site and source terms are also obtained along with the QLg inversion. The estimated site responses are comparable with observed local geological condition and agree with the previously reported site amplifications at the same sites. The source terms are comparable with local magnitude estimated from Network. The Mw (Lg) is nearly equivalent to ML (GSN) and the slight differences are noted for larger

  13. Tectono-magmatic evolution of the younger Gardar southern rift, South Greenland

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    Brian G.J. Upton


    Full Text Available The 1300–1140 Ma Gardar period in South Greenland involved continental rifting, sedimentation and alkaline magmatism. The latest magmatism was located along two parallel rift zones, Isortoq–Nunarsuit in the north and the Tuttutooq–Ilimmaasaq–Narsarsuaq zone in the south addressed here. The intrusive rocks crystallised at a depth of <4 km and are essentially undisturbed by later events. Magmatism in the southern zone began with the emplacement of two giant, ≤800 m wide dykes and involved intrusion of transitional olivine basaltic, high Al/Ca magmas crystallising to troctolitic gabbros. These relatively reduced magmas evolved through marked iron enrichment to alkaline salic differentiates. In the Older giant dyke complex, undersaturated augite syenites grade into sodalite foyaite. The larger, c. 1163 Ma Younger giant dyke complex (YGDC mainly consists of structureless troctolite with localised developments of layered cumulates. A layered pluton (Klokkenis considered to be coeval and presumably comagmatic with the YGDC. At the unconformitybetween the Ketilidian basement and Gardar rift deposits, the YGDC expanded into a gabbroic lopolith. Its magma may represent a sample from a great, underplated mafic magma reservoir, parental to all the salic alkaline rocks in the southern rift. The bulk of these are silica undersaturated; oversaturated differentiates are probably products of combined fractional crystallisation and crustalassimilation.A major dyke swarm 1–15 km broad was intruded during declining crustal extension, with decreasing dyke widths and increasing differentiation over time. Intersection of the dyke swarm and E–W-trending sinistral faults controlled the emplacement of at least three central complexes (Narssaq, South Qôroq and early Igdlerfigssalik. Three post-extensional complexes (Tugtutôq,Ilímaussaq and late Igdlerfigssalik along the former rift mark the end of magmatism at c. 1140 Ma. The latter two complexes have

  14. East Antarctic intraplate earthquakes recorded by the AGAP/GAMSEIS temporary seismic array delineate possible ancient rift (United States)

    Lough, A. C.; Wiens, D.; Nyblade, A.


    East Antarctica is primarily a stable craton and thus little deformation as is seen in geodetic observations. Although Antarctica was once thought to be aseismic, small events have been detected teleseismically. In 2009 the AGAP/GAMSEIS project operated a network of 26 broadband seismic stations that recorded 27 seismic events (ML 1.74-3.43) The majority of events are 10-30 km deep indicating a tecontic origin. Most events occur beneath subglacial topographic depressions that border the Gamburtsev Subglacial Mountains (GSM). 16 events follow a linear chain of depressions between the GSM and the Vostok Subglacial Highlands (VSH) that link the Polar Subglacial Basin to the Lambert Graben. This particular feature was identified as an ancient 'rift' by Ferraccioli et al. (2011). Gravity data in the 'rift' is distinct from surrounding areas with high Bouger and low free air gravity anomalies in the 'rift', in contrast to the GSM and VSH (Ferraccioli et al., 2011). The `rift' is embedded in the seismically fast East Antarctic cratonic mantle (Heeszel et al., 2013), but it shows a narrow region of lower velocities (Lloyd et al., 2013) and has thinner continental crust (Hansen et al., 2010) than surrounding regions. The feature potentially represents a terrain boundary between the Mawson and Crohn cratons (Boger, 2011) or could be a failed continental rift. One year of data cannot fully constrain the underlying cause of the seismicity. To further characterize the tectonics we calculate first motion double couple focal mechanisms for events showing impulsive body wave arrivals and good azimuthal station coverage. Preliminary results show the majority of fault plane solutions are extensional with fault planes that orient parallel or subparallel to the strike of the 'rift'. We compute synthetic waveforms to further test the robustness of our fault plane solutions. We propose the events are intraplate earthquakes located in zones of weakness associated with a failed

  15. Rift systems of the Russian Eastern Arctic shelf and Arctic deep water basins: link between geological history and geodynamics

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    A. M. Nikishin


    Full Text Available In our study, we have developed a new tectonic scheme of the Arctic Ocean, which is based mainly on seismic profiles obtained in the Arctic-2011, Arctic-2012 and Arctic-2014 Projects implemented in Russia. Having interpreted many seismic profiles, we propose a new seismic stratigraphy of the Arctic Ocean. Our main conclusions are drawn from the interpretation of the seismic profiles and the analysis of the regional geological data. The results of our study show that rift systems within the Laptev, the East Siberian and the Chukchi Seas were formed not earlier than Aptian. The geological structure of the Eurasian, Podvodnikov, Toll and Makarov Basins is described in this paper. Having synthesized all the available data on the study area, we propose the following model of the geological history of the Arctic Ocean: 1. The Canada Basin formed till the Aptian (probably, during Hauterivian-Barremian time. 2. During the Aptian-Albian, large-scale tectonic and magmatic events took place, including plume magmatism in the area of the De Long Islands, Mendeleev Ridge and other regions. Continental rifting started after the completion of the Verkhoyansk-Chukotka orogenу, and rifting occurred on the shelf of the Laptev, East Siberian, North Chukchi and South Chukchi basins, and the Chukchi Plateau; simultaneously, continental rifting started in the Podvodnikov and Toll basins. 3. Perhaps the Late Cretaceous rifting continued in the Podvodnikov and Toll basins. 4. At the end of the Late Cretaceous and Paleocene, the Makarov basin was formed by rifting, although local spreading of oceanic crust during its formation cannot be excluded. 5. The Eurasian Basin started to open in the Early Eocene. We, of course, accept that our model of the geological history of the Arctic Ocean, being preliminary and debatable, may need further refining. In this paper, we have shown a link between the continental rift systems on the shelf and the formation history of the Arctic

  16. Making it and breaking it in the Midwest: Continental assembly and rifting from modeling of EarthScope magnetotelluric data (United States)

    Bedrosian, Paul A.


    A three-dimensional lithospheric-scale resistivity model of the North American mid-continent has been estimated based upon EarthScope magnetotelluric data. Details of the resistivity model are discussed in relation to lithospheric sutures, defined primarily from aeromagnetic and geochronologic data, which record the southward growth of the Laurentian margin in the Proterozoic. The resistivity signature of the 1.1 Ga Mid-continent Rift System is examined in detail, in particular as relates to rift geometry, extent, and segmentation. An unrecognized expanse of (concealed) Proterozoic deltaic deposits in Kansas is identified and speculated to result from axial drainage along the southwest rift arm akin to the Rio Grande delta which drains multiple rift basins. A prominent conductor traces out Cambrian rifting in Arkansas, Missouri, Tennessee, and Kentucky; this linear conductor has not been imaged before and suggests that the Cambrian rift system may have been more extensive than previously thought. The highest conductivity within the mid-continent is imaged in Minnesota, Michigan, and Wisconsin where it is coincident with Paleoproterozoic metasedimentary rocks. The high conductivity is attributed to metallic sulfides, and in some cases, graphite. The former is a potential source of sulfur for multiple mineral deposits types, occurrences of which are found throughout the region. Finally, the imprint left within the mantle following the 1.1 Ga rifting event is examined. Variations in lithospheric mantle conductivity are observed and are interpreted to reflect variations in water content (depleted versus metasomatized mantle) imprinted upon the mantle by the Keweenawan mantle plume.

  17. Tectonic evolution of Western Patagonia and hydrocarbon habitats

    Energy Technology Data Exchange (ETDEWEB)

    Urien, C.M. (Urien Associates, Buenos Aires (Argentina))


    In Devonian times, Western Patagonia was a Pericratonic Foreland basin. The rift-like, faulted platform underwent several marine transgressions-regressions related to tectonic episodes occurring mainly from Hercynian to Andean (Pyrenaic) times that modified the extension and nature of sedimentation in the region, due to the evolution of the Pacific Plate and Margin, and the accretion of successive acidic magmatic arcs. The marine sequences that flooded Patagonia, uneven in extension, shifted from North to South in accordance with differential subsidence in this margin, particularly in the three main sedimentary embayments: Neuquen, San Jorge and Magellan-Malvinas. Transversal ridges, following ancestral transtensional features, rejuvenated during the Atlantic opening separate these embayments. Marine sequences evolved into restricted circulation oxygen poor seas, whose organic matter rich sediments originated hydrocarbon source rocks, identified in the three most important basinal complexes of Patagonia. The beginning of the Andean Orogeny and the emplacement of the Andean Batholith, hindered the Pacific marine presence in western Patagonian basins. Subsequently, an Eastern elongated region-wide subsidence allowed the accumulation of molasse-like sequences over most foredeep sediments in the region, creating several hydrocarbons habitats grouped as follows: Neuquen: Proven: Liassic-Aptian; Potential: Triassic; San Jorge: Proven: U. Jurassic-L. Cretaceous; Unproven: L. Paleozoic-L. Jurassic; Magellan/Malvinas: Proven: L. Cretaceous; Unproven: Jurassic-U. Cretaceous During Laramic time, Atlantic highstand sea levels flooded a great part of Extra Andean Patagonia, while the Andean Chain started rising with an active magmatic arc.

  18. Western blot analysis. (United States)

    Hirano, Seishiro


    Electrophoresis and the following western blot analysis are indispensable to investigate biochemical changes in cells and tissues exposed to nanoparticles or nanomaterials. Proteins should be extracted from the cells and tissues using a proper method, especially when phosphorylated proteins are to be detected. It is important to select a good blocking agent and an appropriate pair of primary and peroxidase-tagged secondary antibodies to obtain good results in western blot analysis. One thing that may be specific to nanomaterials, and that you should keep in mind, is that some proteins may be adsorbed on the surface of particulate nanomaterials. In this chapter the whole process of western blot analysis, from sample preparation to quantitative measurement of target proteins, is described.

  19. Architecture and temporal variations of a terrestrial CO2 degassing site using electric resistivity tomography and selfpotential

    Czech Academy of Sciences Publication Activity Database

    Nickschick, T.; Flechsig, C.; Meinel, C.; Mrlina, Jan; Kämpf, H.


    Roč. 106, č. 8 (2017), s. 2915-2926 ISSN 1437-3254 Institutional support: RVO:67985530 Keywords : Eger rift * ERT * CO2 gax flux * Cheb Basin * mofettes Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.283, year: 2016

  20. Madagascar's escape from Africa: A high-resolution plate reconstruction for the Western Somali Basin and implications for supercontinent dispersal (United States)

    Phethean, Jordan J. J.; Kalnins, Lara M.; van Hunen, Jeroen; Biffi, Paolo G.; Davies, Richard J.; McCaffrey, Ken J. W.


    Accurate reconstructions of the dispersal of supercontinent blocks are essential for testing continental breakup models. Here, we provide a new plate tectonic reconstruction of the opening of the Western Somali Basin during the breakup of East and West Gondwana. The model is constrained by a new comprehensive set of spreading lineaments, detected in this heavily sedimented basin using a novel technique based on directional derivatives of free-air gravity anomalies. Vertical gravity gradient and free-air gravity anomaly maps also enable the detection of extinct mid-ocean ridge segments, which can be directly compared to several previous ocean magnetic anomaly interpretations of the Western Somali Basin. The best matching interpretations have basin symmetry around the M0 anomaly; these are then used to temporally constrain our plate tectonic reconstruction. The reconstruction supports a tight fit for Gondwana fragments prior to breakup, and predicts that the continent-ocean transform margin lies along the Rovuma Basin, not along the Davie Fracture Zone (DFZ) as commonly thought. According to our reconstruction, the DFZ represents a major ocean-ocean fracture zone formed by the coalescence of several smaller fracture zones during evolving plate motions as Madagascar drifted southwards, and offshore Tanzania is an obliquely rifted, rather than transform, margin. New seismic reflection evidence for oceanic crust inboard of the DFZ strongly supports these conclusions. Our results provide important new constraints on the still enigmatic driving mechanism of continental rifting, the nature of the lithosphere in the Western Somali Basin, and its resource potential.

  1. Neotectonics along the Turkana Rift (North Kenya) from river network analysis, remote sensing and reflection seismic data (United States)

    Vetel, W.; Le Gall, B.; Tiercelin, J.-J.


    The NS-trending Turkana Rift (North Kenya) cuts through a N140^oE transverse depressed zone between the Kenyan and Ethiopian domes. It forms a 200 km-long rift segment of the East African Rift System, centered on the Turkana Lake. In this region, widespread rifting occurred during the Oligocene to Mio-Pliocene and opened large NS-trending hemigrabens imaged by seismics to the West of the Turkana Lake. Because the Turkana rifted zone is a low and poorly contrasted topographic area, it is difficult to draw the trace of the active rift, in contrast with 1) the narrow (20 km-wide) N10^o-trending axial trough forming the Suguta valley to the South, and 2) the Chew Bahir faulted basin to the North. Despite a semi-arid climate, the Turkana area shows a dense and widely-distributed river drainage network dominated by the Turkwell, Kerio and Omo first-order rivers. The entire stream pattern has been extracted from Landsat satellite images and then analyzed in terms of drainage anomalies. Major anomalies have been recognized at various scales and assigned to active tectonics. The direct correlation between surface data and the deep structures imaged on seismics allows to precise the inherited (Oligo-Miocene) or newly-formed origin of the active deformation. Evidence for neotectonics are observed along 1) a large-scale transverse (EW) fault rooting at depth along a steep basement discontinuity (Turkwell), 2) a rift-parallel (NS) fault zone probably emplaced during Plio-Pleistocene and actually bounding the Napedet volcanic plateau to the West, and 3) over a round-shaped uplifted zone caused by inversion tectonics (Kalabata). Structural interpretation of offshore high-resolution seismics from Lake Turkana illustrates the existence of recent deformation and also helps complete the overall neotectonic framework of the Turkana rift zone. Finally, this study leads us to regard the Turkana area as a broad (ca. 100 km wide) zone of diffuse extension where active deformation is

  2. Seismic stratigraphy of the western South Korea Plateau, East Sea: implications for tectonic history and sequence development during back-arc evolution (United States)

    Kwon, Y. K.; Yoon, S. H.; Chough, S. K.


    The western South Korea Plateau in the East Sea (Sea of Japan) is occupied by rifted continental fragments formed in association with the early phase of back-arc opening. The present study focuses on the seismic stratigraphy of the sedimentary succession and the underlying acoustic basement in this region, based on closely spaced multichannel seismic reflection profiles. The sedimentary succession occurs mainly within a series of subparallel basement troughs (grabens or half grabens) bounded by faulted continental blocks (horsts) or volcanic ridges, and commonly floored by extrusive volcanic rocks showing hyperbolic reflectors. These features are strongly suggestive of continental rifting accompanied by normal faulting, volcanic activity and high rates of basin subsidence. The sedimentary succession can be subdivided into four seismic units. Unit 1 is characterized by short and irregular high-amplitude reflectors and interpreted as a syn-rift deposit consisting of a non-marine volcanics/sediment complex in topographic lows. Units 2 and 3 formed in an open marine environment during the Middle Miocene to Early Pliocene, characterized by an onlap-fill and later draping marine sedimentary succession dominantly composed of hemipelagic sediments and turbidites with frequent intercalation of mass-flow deposits. Along the western margin of the plateau, these units were deformed under a compressional regime in the Early Pliocene, associated with the back-arc closing phase. Unit 4 (deposited since the Early Pliocene) comprises hemipelagic sediments and turbidites with evidence of sporadic slides/slumps.

  3. The importance of microearthquakes in crustal extension of an active rift: A case study from New Zealand (United States)

    Mouslopoulou, Vasiliki; Hristopulos, Dionissios T.; Nicol, Andrew; Walsh, John J.; Bannister, Stephen


    The amount of extension accommodated in active rifts by earthquakes that do not rupture the ground surface (e.g., Rift in New Zealand over a period of 49 months, has been used to quantify the proportion of extension produced by small to moderate sized earthquakes. Analysis shows that the extension rate across the rift due to the MES is 2.4±0.7 mm/yr (at 1σ standard deviation), an average extension rate for small to moderate magnitude earthquakes which also prevailed during the preceding 28 years (1977-2004) and represents up to ~30% of the total contemporary deformation recorded across the north Taupo Rift by GPS (15 ± 5 mm/yr). The bulk of the MES (94%) occurred at depths of 1.5 to 6.5 km and may not be observed in geological datasets (e.g., as displacements of the ground- or near-surface horizons). Small-scale faulting associated with microseismicity may thus record strains not measured by geological datasets and constitute an important component of the ~3-10 mm/yr disparity between geological and GPS rates of extension across the Taupo Rift.

  4. Continentward-dipping detachment fault system and asymmetric rift structure of the Baiyun Sag, northern South China Sea (United States)

    Zhou, Zhichao; Mei, Lianfu; Liu, Jun; Zheng, Jinyun; Chen, Liang; Hao, Shihao


    The rift architecture and deep crustal structure of the distal margin at the mid-northern margin of the South China Sea have been previously investigated by using deep seismic reflection profiles. However, one fundamental recurring problem in the debate is the extensional fault system and rift structure of the hyperextended rift basins (Baiyun Sag and Liwan Sag) within the distal margin because of the limited amount of seismic data. Based on new 3D seismic survey data and 2D seismic reflection profiles, we observe an array of fault blocks in the Baiyun Sag, which were tilted towards the ocean by extensional faulting. The extensional faults consistently dip towards the continent. Beneath the tilted fault blocks and extensional faults, a low-angle, high-amplitude and continuous reflection has been interpreted as the master detachment surface that controls the extension process. During rifting, the continentward-dipping normal faults evolved in a sequence from south to north, generating the asymmetric rift structure of the Baiyun Sag. The Baiyun Sag is separated from the oceanic domain by a series of structural highs that were uplifted by magmatic activity in response to the continental breakup at 33 Ma and a ridge jump to the south at 26-24 Ma. Therefore, we propose that magmatism played a significant role in the continental extension and final breakup in the South China Sea.

  5. Crustal and mantle structure and anisotropy beneath the incipient segments of the East African Rift System: Preliminary results from the ongoing SAFARI (United States)

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


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

  6. Extension velocity partitioning, rheological crust-mantle and intra-crustal decoupling and tectonically inherited structures: consequences for continental rifting dynamics. (United States)

    Wang, Kun; Mezri, Leila; Burov, Evgueni; Le Pourhiet, Laetitia


    We implemented series of systematic thermo-mechanical numerical models testing the importance of the rheological structure and extension rate partitioning for continental rift evolution. It is generally assumed that styles of continental rifting are mainly conditioned by the initial integrated strength of the lithosphere. For example, strong plates are expected to undergo extension in narrow rifting mode, while weak lithospheres would stretch in wide rifting mode. However, we show that this classification is largely insufficient because the notion of the integrated strength ignores the internal rheological structure of the lithosphere that may include several zones of crust-mantle or upper-crust-intermediate (etc) crust decoupling. As well, orogenic crusts characterizing most common sites of continental extension may exhibit inverted lithological sequences, with stronger and denser formerly lower crustal units on top of weaker and lighter upper crustal units. This all may result in the appearance of sharp rheological strength gradients and presence of decoupling zones, which may lead to substantially different evolution of the rift system. Indeed, strong jump-like contrasts in the mechanical properties result in mechanical instabilities while mechanical decoupling between the competent layers results in overall drop of the flexural strength of the system and may also lead to important horizontal flow of the ductile material. In particular, the commonly inferred concept of level of necking (that assumes the existence of a stationary horizontal stretching level during rifting) looses its sense if necking occurs at several distinct levels. In this case, due to different mechanical strength of the rheological layers, several necking levels develop and switch from one depth to another resulting in step-like variations of rifting style and accelerations/decelerations of subsidence during the active phase of rifting. During the post-rifting phase, initially decoupled

  7. 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

  8. New insights into volcanism and tectonics in the Red Sea Rift (United States)

    van der Zwan, Froukje M.; Augustin, Nico; Devey, Colin W.; Bantan, Rashad; Kwasnitschka, Tom


    The Red Sea is one of the few places on Earth where rifting and splitting of a continent by the formation of an ocean basin is presently occurring. Continental rifting takes place in the northernmost Red Sea and ocean floor is continuously created from at least 23°N to the vicinity of the strait of Bab al-Mandab in the south. Here we present a unique collection of recent continuous multibeam bathymetric datasets with a spatial acoustic resolution of 15-30 m from the Thetis Deep at 23°N to the RSR at 16.5°N together with new volcanic sampling over the Red Sea Rift (RSR). This enables us to study in detail the bathymetry of volcanic structures formed during the creation of this young ocean and the relationship between extension and volcanism allows us to make an extensive interpretation of the structural, tectonic, magmatic and sedimentary evolution of the RSR. Even though the central graben of the RSR is widely covered by sediments and Miocene evaporites north of 20°N (Augustin et al. 2012), the open parts of the rift valley show a wide range of volcanic activity and tectonic features over 700 km of mapped ridge axis. Numerous volcanoes (flat top volcanoes, submarine equivalents of Venusian pancake domes and lava shields) and ridges of hummocky volcanics are scattered all along the RSR. In addition the Red Sea Rift displays typical features of a slow spreading ridge where the slowest spreading, northern section of the Red Sea is strongly tectonically dominated with distinct basins and a strong horst and graben structure with locally very large volcanic edifices. The largest submarine volcano yet observed in the RSR is the Hatiba Mons volcano, previously not recognized as a volcanic edifice. In the south, where the spreading rates are greatest, large basins are not present and instead axial highs are observed as the result of higher recent volcanic activity. The geochemistry of basalts from sampled volcanoes display MORB signatures with no sign of continental

  9. Western Indian Ocean

    African Journals Online (AJOL)

    Western Indian Ocean. II: The sandfish Holothuria scabra (ja'éger, 1833). Richard Rasolofonirina”, Devaraien Vai'tilingon“, Igor Eeckhaut"3 and Michel jangouxm”. IInstitut Halieurique et des Sciences Marines, Universite' de Toliara, BP 141, Toliara 601, Madagascar;. 2Labarrataire de Biologie Marine (CP 160/15), ...

  10. The western blot (United States)

    Western blotting is a technique that involves the separation of proteins by gel electrophoresis, their blotting or transfer to a membrane, and selective immunodetection of an immobilized antigen. This is an important and routine method for protein analysis that depends on the specificity of antibod...

  11. Red Sea rift-related Quseir basalts, central Eastern Desert, Egypt: Petrogenesis and tectonic processes (United States)

    Farahat, Esam S.; Ali, Shehata; Hauzenberger, Christoph


    Mineral and whole-rock chemistry of Red Sea rift-related Tertiary basalts from south Quseir city, central Eastern Desert of Egypt is presented to investigate their petrogenesis and relationship to tectonic processes. The south Quseir basalts (SQB) are classified as high-Ti (TiO2 >2 wt.%) subalkaline transitional lava emplaced in an anorogenic tectonic setting. Their Mg# varies from 48 to 53 indicating the evolved nature of the SQB. Pearce element ratios suggest that the SQB magmas evolved via fractional crystallization of olivine + clinopyroxene ± plagioclase, but the absence of Eu anomalies argues against significant plagioclase fractionation. Clinopyroxene compositions provide evidence for polybaric fractionation of the parental mafic magmas. Estimated temperatures of crystallization are 1015 to 1207 °C for clinopyroxene and 1076 to 1155 °C for plagioclase. These values are interpreted to result from early stage crystallization of clinopyroxene followed by concurrent crystallization of clinopyroxene and plagioclase. The incompatible trace element signatures of the SQB (La/Ba = 0.08-0.10 and La/Nb = 0.89-1.04) are comparable to those of ocean island basalts (OIB) generated from an asthenospheric mantle source unaffected by subduction components. Modeling calculations indicate that the SQB primary magmas were derived from 4-5% partial melting of a garnet-bearing lherzolite mantle source. The NE Egyptian basaltic volcanism is spatially and temporally related to Red Sea rifting and to the local E-W striking faults, confirming a relationship to tectonic activity. Our results suggest that the extensional regime associated with Red Sea rifting controlled the generation of the Egyptian basalts, likely as a result of passive upwelling of asthenospheric mantle.

  12. Hot Spot Induced Cenozoic Volcanism in the Upper Rajang Valley, Sarawak - Is Borneo Rifting? (United States)

    Taib, N.


    The Upper Rajang Valley covers a large area in the northern interior of the island of Borneo, in the Malaysian state of Sarawak . It is underlain by the Cretaceous to Late Eocene deep to shallow marine sediments of the Rajang Group. Within this area are several Cenozoic volcanic edifices, which to date have been sparsely studied. Two distinct episodes of volcanism are recognized - the first, dated early Eocene, consists of K-rich basalts, and is represented by the Bukit Mersing volcanics, which were erupted conformably onto deep water turbidites of the Rajang Group. The second, far more extensive, is dated Pliocene to Quaternary, and is bimodal, consisting mainly of early dacite and rhyodacite tuffs, with a smaller amount of later basalt, forming several volcanic plateaus and massifs (Hose Mountains, Usun Apau, Linau-Balui, Nieuwenhuis Mountains and others). They lie unconformably over pre-Miocene sediments, the Linau-Balui basalts having been erupted onto Quaternary river terraces. Mantle-normalized REE and incompatible trace element spider plots reveal that the Bukit Mersing basalts have geochemical affinity with Oceanic Island Basalts (OIB) and rift basalts, being enriched in LREEs and Most Incompatible Elements, and no Eu anomaly. Preliminary trace element data for several basalt samples from Usun Apau also show Oceanic Island/Rift affinity. Bimodal volcanism is most often associated with rift environments. Efforts are being made to radiometrically date the volcanics, in part to determine the possibility of future eruptions. The Upper Rajang Valley is remote, covered in tropical rainforest and is very sparsely populated. At this time, there is no information concerning signs of imminent volcanism, such as hot springs and microseismicity.

  13. Tectonoestratigraphic and Thermal Models of the Tiburon and Wagner Basins, northern Gulf of California Rift System (United States)

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


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

  14. 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

  15. Creating global comparative analyses of tectonic rifts, monogenetic volcanism and inverted relief (United States)

    van Wyk de Vries, Benjamin


    I have been all around the world, and to other planets and have travelled from the present to the Archaean and back to seek out the most significant tectonic rifts, monogenetic volcanoes and examples of inverted relief. I have done this to provide a broad foundation of the comparative analysis for the Chaîne des Puys - Limagne fault nomination to UNESCO world Heritage. This would have been an impossible task, if not for the cooperation of the scientific community and for Google Earth, Google Maps and academic search engines. In preparing global comparisons of geological features, these quite recently developed tools provide a powerful way to find and describe geological features. The ability to do scientific crowd sourcing, rapidly discussing with colleagues about features, allows large numbers of areas to be checked and the open GIS tools (such as Google Earth) allow a standardised description. Search engines also allow the literature on areas to be checked and compared. I will present a comparative study of rifts of the world, monogenetic volcanic field and inverted relief, integrated to analyse the full geological system represented by the Chaîne des Puys - Limagne fault. The analysis confirms that the site is an exceptional example of the first steps of continental drift in a mountain rift setting, and that this is necessarily seen through the combined landscape of tectonic, volcanic and geomorphic features. The analysis goes further to deepen the understanding of geological systems and stresses the need for more study on geological heritage using such a global and broad systems approach.

  16. Miocene rifting in the Los Angeles basin: Evidence from the Puente Hills half-graben, volcanic rocks, and P-wave tomography (United States)

    Bjorklund, Tom; Burke, Kevin; Zhou, Hua-Wei; Yeats, Robert S.


    Formation of the Puente Hills half-graben in the northeastern Los Angeles basin and eruption of the Glendora and El Modeno Volcanics (16 14 Ma) help to define the timing of extension in the basin. Normal faulting on the proto-Whittier fault ca. 14 Ma established the Puente Hills half-graben, in which sedimentary strata accumulated between ca. 14 and 10 Ma and into which diabase sills intruded. North-South contraction began to invert the Puente Hills half-graben ca. 7 Ma, leading to formation of the Puente Hills anticline and the Whittier fault. Our high-resolution three-dimensional P-wave velocity model shows two anomalous higher velocity (6.63 km/s) bodies at depths between 9 and 18 km, which we attribute to dioritic plutons named here for Whittier Narrows and El Modeno. The stocklike Whittier Narrows pluton could have been a source for the Glendora Volcanics and the diabase sills in the Puente Hills half-graben. The sill-shaped El Modeno pluton was a likely source for the El Modeno Volcanics. The northwesterly alignment of the plutons may mark the location of the northeastern Los Angeles basin rift boundary, which is associated with the clockwise rotation of the western Transverse Ranges. Three active faults, the Elysian Park blind thrust, the Puente Hills blind thrust, and the Whittier fault, converge on the Whittier Narrows pluton, which may have played a role in their location and segmentation.

  17. The genus Atheris (Serpentes: Viperidae) in East Africa: phylogeny and the role of rifting and climate in shaping the current pattern of species diversity. (United States)

    Menegon, M; Loader, S P; Marsden, S J; Branch, W R; Davenport, T R B; Ursenbacher, S


    Past climatic and tectonic events are believed to have strongly influenced species diversity in the Eastern Afromontane Biodiversity Hotspot. We investigated the phylogenetic relationships and historical biogeography of the East African genus Atheris (Serpentes: Viperidae), and explored temporal and spatial relationships between Atheris species across Africa, and the impact of palaeoclimatic fluctuations and tectonic movements on cladogenesis of the genus. Using mitochondrial sequence data, the phylogeny of East African species of Atheris shows congruent temporal patterns that link diversification to major tectonic and aridification events within East Africa over the last 15million years (my). Our results are consistent with a scenario of a delayed direct west-east colonisation of the Eastern Arc Mountains of Atheris by the formation of the western rift. Based on the phylogenetic patterns, this terrestrial, forest-associated genus has dispersed into East Africa across a divided route, on both west-southeasterly and west-northeasterly directions (a C-shaped route). Cladogenesis in the Eastern Arc Mountains and Southern Highlands of Tanzania corresponds to late Miocene and Plio-Pleistocene climatic shifts. Taxonomically, our data confirmed the monophyly of Atheris as currently defined, and reveal four major East African clades, three of which occur in discrete mountain ranges. Possible cryptic taxa are identified in the Atheris rungweensis and A. ceratophora clades. Copyright © 2014 Elsevier Inc. All rights reserved.

  18. 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

  19. 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

  20. Multiple rifting and alkaline magmatism in southern India during Paleoproterozoic and Neoproterozoic (United States)

    Renjith, M. L.; Santosh, M.; Satyanarayanan, M.; Rao, D. V. Subba; Tang, Li


    The Southern Granulite Terrane (SGT) in India preserves the history of tectonothermal events ranging from Paleoarchean to latest Neoproterozoic-Cambrian. Here we investigate alkaline magmatism possibly associated with rifting events in Paleoproterozoic and Neoproterozoic based on petrological, geochemical and zircon U-Pb and Lu-Hf isotopic studies on the alkaline complexes of Korangani (KGAC) and Kambamettu (KAC) in the Madurai Block of SGT. The mica pyroxenite which represents the first intrusive phase at KGAC crystallized from a mildly alkaline hydrous magma derived from a metasomatized mantle. The younger shoshonitic syenite was emplaced at 2533 ± 16 Ma, carries mafic microgranular enclaves, and shows trace-elements ratios consistent with magma mixing trend, and zircon εHf(t) values display mixed positive and negative values - 2.6 to 3.6 suggesting the mixing of adakite-like felsic crustal melt and non-adakitic mantle derived melt. In KAC, four distinct magmatic intrusions are identified: i) quartz-monzonite (emplaced at 2498 ± 16 Ma), an ultrapotassic adakitic rock derived from a carbonated alkali-rich lower crustal source with negative zircons εHf(t) values in zircon (- 8.0 to - 0.8); Y/Nb (> 1.2) and Th/Ce (0.03-0.8) ratios; lower Ni (peralkaline syenite rock (emplaced at 608 ± 6 Ma) with strong adakitic signature, low MgO (zircon εHf(t) values (- 30.3 to - 27.3) and trough of Zr-Hf in spidergrams suggesting a carbonated alkali-rich garnet-bearing crustal source. The geochemical features and petrogenetic considerations of the felsic shoshonitic-ultrapotassic adakite-like rocks (syenite, quartz monzonite), mica-pyroxenites and carbonatite reveal rift-related extensional tectonic settings with magma sources involving both mantle and crustal components during Paleoproterozoic. The late Neoproterozoic shoshonitic adakite-like syenite from KAC also formed in a rift-related setting. In both cases, intracontinental rifting associated with post

  1. Gas-oil fluids in the formation of travertines in the Baikal rift zone (United States)

    Tatarinov, A. A.; Yalovik, L. I.; Shumilova, T. G.; Kanakin, S. V.


    Active participation of gas-oil fluids in the processes of mineral formation and petrogenesis in travertines of the Arshan and Garga hot springs is substantiated. The parageneses of the products of pyrolytic decomposition and oxidation of the gas-oil components of hydrothermal fluids (amorphous bitumen, graphite-like CM, and graphite) with different genetic groups of minerals crystallized in a wide range of P-T conditions were established. Travertines of the Baikal rift zone were formed from multicomponent hydrous-gas-oil fluids by the following basic mechanisms of mineral formation: chemogenic, biogenic, cavitation, fluid pyrometamorphism, and pyrolysis.

  2. Rift in Antarctic Glacier: a Unique Chance to Study Ice Shelf Retreat (United States)

    Howat, Ian M.; Jezek, Ken; Studinger, Michael; Macgregor, Joseph A.; Paden, John; Floricioiu, Dana; Russell, Rob; Linkswiler, Matt; Dominguez, Roseanne T.


    It happened again, but this time it was caught in the act. During the last week of September 2011 a large transverse rift developed across thefloating terminus of West Antarcticas PineIsland Glacier, less than 5 years after its lastlarge calving event, in 2007 (Figure 1). PineIsland Glaciers retreat has accelerated substantiallyin the past 2 decades, and it is nowlosing 50 gigatons of ice per year, or roughly 25 of Antarcticas total annual contributionto sea level rise [Rignot et al., 2008]. The glaciers recent accelerated retreat is likely triggered by ocean warming and increased submarine melting. As such, it is of significant interest to glaciologists and of heightened societal relevance.

  3. Western USA groundwater drilling (United States)

    Jasechko, S.; Perrone, D.


    Groundwater in the western US supplies 40% of the water used for irrigated agriculture, and provides drinking water to individuals living in rural regions distal to perennial rivers. Unfortunately, current groundwater use is not sustainable in a number of key food producing regions. While substantial attention has been devoted to mapping groundwater depletion rates across the western US, the response of groundwater users via well drilling to changing land uses, water demands, pump and drilling technologies, pollution vulnerabilities, and economic conditions remains unknown. Here we analyze millions of recorded groundwater drilling events in the western US that span years 1850 to 2015. We show that groundwater wells are being drilled deeper in some, but not all, regions where groundwater levels are declining. Groundwater wells are generally deeper in arid and mountainous regions characterized by deep water tables (e.g., unconfined alluvial and fractured bedrock aquifers), and in regions that have productive aquifers with high water quality deep under the ground (e.g., confined sedimentary aquifers). Further, we relate water quality and groundwater drilling depths in 40 major aquifer systems across the western US. We show that there is substantial room for improvement to the existing 2-D continental-scale assessments of domestic well water vulnerability to pollution if one considers the depth that the domestic well is screened in addition to pollutant loading, surficial geology, and vertical groundwater flow rates. These new continental-scale maps can be used to (i) better assess economic, water quality, and water balance limitations to groundwater usage, (ii) steer domestic well drilling into productive strata bearing clean and protected groundwater resources, and (iii) assess groundwater management schemes across the western US.

  4. Seroprevalence of Sheep and Goat Pox, Peste Des Petits Ruminants and Rift Valley Fever in Saudi Arabia.

    Directory of Open Access Journals (Sweden)

    Hani Boshra

    Full Text Available Sheep and goat pox, peste des petits ruminants and Rift Valley fever are important diseases of small ruminant livestock. Sheep and goat pox, along with peste des petits ruminants, are endemic throughout most of Africa, Asia and the Middle East. Whereas Rift Valley fever is endemic in Africa, outbreaks in the Middle East have been reported over the past decade, including the Arabian Peninsula. Saudi Arabia is a major importer of livestock, and understanding the prevalence of these viral infections would be useful for disease control. In this study, sera from sheep and goats were collected from 3 regions in Saudi Arabia. They were evaluated for antibodies specific to sheep and goat pox, peste des petits ruminants and Rift Valley fever by virus neutralization assays. To the best of our knowledge, this is the first study to evaluate the seroprevalence of these viruses in sheep and goats.

  5. Seroprevalence of Sheep and Goat Pox, Peste Des Petits Ruminants and Rift Valley Fever in Saudi Arabia. (United States)

    Boshra, Hani; Truong, Thang; Babiuk, Shawn; Hemida, Maged Gomaa


    Sheep and goat pox, peste des petits ruminants and Rift Valley fever are important diseases of small ruminant livestock. Sheep and goat pox, along with peste des petits ruminants, are endemic throughout most of Africa, Asia and the Middle East. Whereas Rift Valley fever is endemic in Africa, outbreaks in the Middle East have been reported over the past decade, including the Arabian Peninsula. Saudi Arabia is a major importer of livestock, and understanding the prevalence of these viral infections would be useful for disease control. In this study, sera from sheep and goats were collected from 3 regions in Saudi Arabia. They were evaluated for antibodies specific to sheep and goat pox, peste des petits ruminants and Rift Valley fever by virus neutralization assays. To the best of our knowledge, this is the first study to evaluate the seroprevalence of these viruses in sheep and goats.


    Directory of Open Access Journals (Sweden)

    Sergey V. Rasskazov


    Full Text Available N.A. Florensov and N.A. Logatchev pioneered development of fundamental concepts of the structure and evolution of the Baikal system of rift basins. At the turn to the 21st century, in view of the wide availability of scientific research data on the Cenozoic continental rift zones located in Eurasia, Africa and North America, and taking into account the application of new research methods and options to process and analyze huge amounts of geological and geophysical data, a priority was comprehensive modeling of rifting from its origin to the current period of time. This scientific challenge was addressed by the research team under the leadership of N.A. Logachev.

  7. The Ellsworth terrane, coastal Maine: Geochronology, geochemistry, and Nd-Pb isotopic composition - Implications for the rifting of Ganderia (United States)

    Schulz, K.J.; Stewart, D.B.; Tucker, R.D.; Pollock, J.C.; Ayuso, R.A.


    The Ellsworth terrane is one of a number of fault-bounded blocks that occur along the eastern margin of Ganderia, the western-most of the peri-Gondwanan domains in the northern Appalachians that were accreted to Laurentia in the Paleozoic. Geologic relations, detrital zircon ages, and basalt geochemistry suggest that the Ellsworth terrane is part of Ganderia and not an exotic terrane. In the Penobscot Bay area of coastal Maine, the Ellsworth terrane is dominantly composed of bimodal basalt-rhyolite volcanic sequences of the Ellsworth Schist and unconformably overlying Castine Volcanics. We use new U-Pb zircon geochronology, geochemistry, and Nd and Pb isotopes for these volcanic sequences to constrain the petrogenetic history and paleotectonic setting of the Ellsworth terrane and its relationship with Ganderia. U-Pb zircon geochronology for rhyolites indicates that both the Ellsworth Schist (508.6 ?? 0.8 Ma) and overlying Castine Volcanics (503.5 ?? 2.5 Ma) are Middle Cambrian in age. Two tholefitic basalt types are recognized. Type Tb-1 basalt, present as pillowed and massive lava flows and as sills in both units, has depleted La and Ce ([La/Nd]N = 0.53-0.87) values, flat heavy rare earth element (REE) values, and no positive Th or negative Ta anomalies on primitive mantle-normalized diagrams. In contrast, type Th-2 basalt, present only in the Castine Volcanics, has stightly enriched LREE ([La/Yb]N = 1.42-2.92) values and no Th or Th anomalies. Both basalt types have strongly positive ??Nd (500) values (Th-1 = +7.9-+8.6; Th-2 = +5.6-+7.0) and relatively enriched Pb isotopic compositions (206Ph/204Pb = 18.037-19.784; 207/204Pb = 15.531-15.660; 2088Pb/204Pb = 37.810-38.817). The basalts have compositions transitional between recent normal and enriched mid-ocean-ridge basalt, and they were probably derived by partial melting of compositionatly heterogeneous asthenosphenc mantle. Two types of rhyolite also are present. Type R-1 rhyolite, which mostly occurs as tuffs

  8. Interactions between propagating rifts and pre-existing linear rheological heterogeneities: insights from 3D analogue experiments of rotational extension (United States)

    Molnar, Nicolas; Cruden, Alexander


    Propagating rifts are a natural consequence of lithospheric plates that diverge with respect to each other about a pole of rotation. This process of "unzipping" is common in the geological record, but how rifts interact with pre-existing structures (i.e., with a non-homogeneous lithosphere) as they propagate is poorly understood. Here we report on a series of lithospheric-scale three-dimensional analogue experiments of rotational extension with in-built, variably oriented linear weak zones in the lithospheric mantle, designed to investigate the role that inherited structural or thermal weaknesses play in the localisation of strain and rifting. Surface strain and dynamic topography in the analogue models are quantified by high-resolution particle imaging velocimetry and digital photogrammetry, which allows us to characterise the spatio-temporal evolution of deformation as a function of the orientation of the linear heterogeneities in great detail. The results show that the presence of a linear zone of weakness oriented at low angles with respect to the rift axis (i.e., favourably oriented) produces strain localisation in narrow domains, which enhances the "unzipping" process prior to continental break up. Strong strain partitioning is observed when the linear heterogeneity is oriented at high angles with respect to the rift axis (i.e., unfavourably oriented). In these experiments, early sub-parallel V-shaped basins propagate towards the pole of rotation until they are abandoned and strain is transferred entirely to structures developed in the vicinity of the strongly oblique weak lithosphere zone boundary. The modelling also provides insights on how propagating rift branches that penetrate the weak linear zone boundary are aborted when strain is relayed onto structures that develop in rheologically weaker areas. The experimental results are summarised in terms of their evolution, patterns of strain localisation, and dynamic topography as a function of the

  9. Physics-based and statistical earthquake forecasting in a continental rift zone: the case study of Corinth Gulf (Greece) (United States)

    Segou, Margarita


    I perform a retrospective forecast experiment in the most rapid extensive continental rift worldwide, the western Corinth Gulf (wCG, Greece), aiming to predict shallow seismicity (depth evaluate the forecasts for six months following the 1995 M = 6.4 Aigio earthquake using log-likelihood performance metrics. For the ETAS realizations, I use seismic events with magnitude M ≥ 2.5 within daily update intervals to enhance their predictive power. For assessing the role of background seismicity, I implement a stochastic reconstruction (aka declustering) aiming to answer whether M > 4.5 earthquakes correspond to spontaneous events and identify, if possible, different triggering characteristics between aftershock sequences and swarm-type seismicity periods. I find that: (1) ETAS models outperform CRS models in most time intervals achieving very low rejection ratio RN = 6 per cent, when I test their efficiency to forecast the total number of events inside the study area, (2) the best rejection ratio for CRS models reaches RN = 17 per cent, when I use varying target depths and receiver plane geometry, (3) 75 per cent of the 1995 Aigio aftershocks that occurred within the first month can be explained by static stress changes, (4) highly variable performance on behalf of both statistical and physical models is suggested by large confidence intervals of information gain per earthquake and (5) generic ETAS models can adequately predict the temporal evolution of seismicity during swarms. Furthermore, stochastic reconstruction of seismicity makes possible the identification of different triggering processes between specific seismic crises (2001, 2003-04, 2006-07) and the 1995 aftershock sequence. I find that: (1) seismic events with M ≥ 5.0 are not a part of a preceding earthquake cascade, since they are characterized by high probability being a background event (average Pback > 0.8) and (2) triggered seismicity within swarms is characterized by lower event productivity when

  10. 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

  11. Serological evidence for the circulation of Rift Valley Fever Virus in domestic small ruminants in Southern Gabon


    Maganga, G. D.; Ndong, A. L. A.; Okouyi, C. S. M.; Mandanda, S. M.; N'Dilimabaka, N.; Pinto, A.; Agossou, E.; Cossic, B.; Akue, J. P.; Leroy, Eric


    Rift Valley fever (RVF) is a zoonotic disease, which caused several epidemics in humans in many countries of Africa. Using an inhibition enzyme-linked immunosorbent assay (ELISA), real-time reverse transcription PCR, and nested one-step reverse transcription PCR, we conducted a cross-sectional study in populations of sheep and goats from the Mongo County in 2014 to determine the circulation of the Rift Valley fever virus (RVFV) in small ruminants from this area. From a total of 201 small rumi...

  12. Volcanic facies analysis of a subaqueous basalt lava-flow complex at Hruškovec, NW Croatia — Evidence of advanced rifting in the Tethyan domain (United States)

    Palinkaš, Ladislav A.; Bermanec, Vladimir; Borojević Šoštarić, Sibila; Kolar-Jurkovšek, Tea; Palinkaš, Sabina Strmić; Molnar, Ferenc; Kniewald, Goran


    The Hru\\vskovec quarry of basaltoid rocks is situated on the northwestern slopes of Mt. Kalnik, within the Zagorje-Mid-Transdanubian zone, a part of the North-western Dinarides. The basaltoids are inter-bedded with radiolarites of the Middle and Upper Triassic age (Langobardian, Carnian-Norian). Spilites, altered diabases and meta-basalts form part of Triassic volcanic-sedimentary sequence, made of sandstones, shales, micritic limestone, altered vitric tuffs and radiolarian cherts, incorporated tectonically into the Jurassic-Cretaceous mélange. The architecture of the 2 km long and 100 m high pile of the extrusive basaltoid rocks is interpreted as a subaqueous basaltic lava flow. The presented research deals with a variety of volcanic facies of the subaqueous basaltic lava flow, which consists of several facial units: 1. Coherent pillow lavas, with massive core; the bending rims around the massive core, 30-50 cm thick, are dissected by polygonal columnar joints radiating from the pillow centres; 2. Closely packed pillows; densely packed and contorted pillows due to emplacement accommodation, clearly younging upward; 3. Pillow fragment breccia; clast supported, matrix poor, monomict breccia, formed proximal to the axis of the extrusion; 4. Isolated pillow breccia; matrix supported, clast poor breccia, made of lava pipes and tubes, within a matrix of fine-grained sideromelan granules and shards; 5. Pyjama-style pillows; spherical, decimetre to meter size pillow lava balls, grown and chilled in isostatic state (i.e. in a state of diminished density contrast) within water-soaked sediments, named after peculiar alternating basaltic shelves inside the sphere, which are encrusted with white secondary minerals; 6. Peperite and peperitic hyaloclastites; blocky and globular peperites developed at the contact of soft, wet sediment and hot intruding magma. Discovery of peperite and peperitic hyaloclastites within the Triassic radiolarian cherts, shales, and micritic

  13. Insights into the crustal structure and magmatic evolution of the High and Western Plateau of the Manihiki Plateau, Central Pacific (United States)

    Hochmuth, Katharina; Gohl, Karsten; Uenzelmann-Neben, Gabriele


    The Manihiki Plateau is a Large Igneous Province (LIP) located in the Central Pacific. It is assumed, that the formation of the Manihiki Plateau took place during the early Cretaceous in multiple volcanic stages as part of the "Super-LIP" Ontong-Java-Nui. The plateau consists of several sub-plateaus of which the Western Plateau und High Plateau are the largest. In addressing the plateau's magmatic evolutionary history, one of the key questions is whether all sub-plateaus experienced the same magmatic history or if distinct phases of igneous or tectonic processes led to its fragmentation. During the RV Sonne cruise SO-224 in 2012; we collected two deep crustal seismic refraction/wide-angle reflection lines, crossing the two main sub-plateaus. Modeling of P- and S-wave phases reveals the different crustal nature of both sub-plateaus. On the High Plateau, the 20 km thick crust is divided into four seismic units, interpreted to range from basaltic composition in the uppermost crust to peridotitic composition in the middle and lower crust. The Western Plateau on the other hand shows multiple rift structures and no indications of basalt flows. With a maximum of 17 km crustal thickness, the Western Plateau is also thinner than the High Plateau. The upper basement layers show relatively low P-wave velocities (3.0 - 5.0 km/s), which infers that on the Western Plateau these layers consist of volcanoclastic and carbonatic rocks rather than basaltic flow units. Later volcanic stages may be restricted to the High Plateau with a possible eastward trend in the center of volcanic activity. Extensive secondary volcanism does not seem to have occurred on the Western Plateau, and its later deformation is mainly caused by tectonic extension and rifting.

  14. Western Military Culture and Counterinsurgency:

    African Journals Online (AJOL)


    that industrial Western military culture negatively influenced the ability to wage .... revolution occurred when Western troops started to pay attention to local support for ... The fourth principle is the priority of the fight against the insurgents'.

  15. Gujarat, Western India (United States)


    Extremely high sediment loads are delivered to the Arabian Sea along the coast of Pakistan (upper left) and western India. In the case of the Indus River (far upper left) this sedimentation, containing large quantities of desert sand, combines with wave action to create a large sand-bar like delta. In the arid environment, the delta lacks much vegetation, but contains numerous mangrove-lined channels. This true-color image from May 2001 shows the transition from India's arid northwest to the wetter regions farther south along the coast. The increase in vegetation along the coast is brought about by the moisture trapping effect of the Western Ghats Mountain Range that runs north-south along the coast. Heavy sediment is visible in the Gulf of Kachchh (north) and the Gulf of Khambhat(south), which surround the Gujarat Peninsula.