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Sample records for rift system final

  1. Formation and deformation of hyperextended rift systems: Insights from rift domain mapping in the Bay of Biscay-Pyrenees

    NASA Astrophysics Data System (ADS)

    Tugend, J.; Manatschal, G.; Kusznir, N. J.; Masini, E.; Mohn, G.; Thinon, I.

    2014-07-01

    The Bay of Biscay and the Pyrenees correspond to a Lower Cretaceous rift system including both oceanic and hyperextended rift domains. The transition from preserved oceanic and rift domains in the West to their complete inversion in the East enables us to study the progressive reactivation of a hyperextended rift system. We use seismic interpretation, gravity inversion, and field mapping to identify and map former rift domains and their subsequent reactivation. We propose a new map and sections across the system illustrating the progressive integration of the rift domains into the orogen. This study aims to provide insights on the formation of hyperextended rift systems and discuss their role during reactivation. Two spatially and temporally distinct rift systems can be distinguished: the Bay of Biscay-Parentis and the Pyrenean-Basque-Cantabrian rifts. While the offshore Bay of Biscay represent a former mature oceanic domain, the fossil remnants of hyperextended domains preserved onshore in the Pyrenean-Cantabrian orogen record distributed extensional deformation partitioned between strongly segmented rift basins. Reactivation initiated in the exhumed mantle domain before it affected the hyperthinned domain. Both domains accommodated most of the shortening. The final architecture of the orogen is acquired once the conjugate necking domains became involved in collisional processes. The complex 3-D architecture of the initial rift system may partly explain the heterogeneous reactivation of the overall system. These results have important implications for the formation and reactivation of hyperextended rift systems and for the restoration of the Bay of Biscay and Pyrenean domains.

  2. Cenozoic rifting in the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

  3. Cenozoic rifting in the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  4. The role of inheritance in structuring hyperextended rift systems

    NASA Astrophysics Data System (ADS)

    Manatschal, Gianreto; Lavier, Luc; Chenin, Pauline

    2015-04-01

    A long-standing question in Earth Sciences is related to the importance of inheritance in controlling tectonic processes. In contrast to physical processes that are generally applicable, assessing the role of inheritance suffers from two major problems: firstly, it is difficult to appraise without having insights into the history of a geological system; and secondly all inherited features are not reactivated during subsequent deformation phases. Therefore, the aim of our presentation is to give some conceptual framework about how inheritance may control the architecture and evolution of hyperextended rift systems. We use the term inheritance to refer to the difference between an "ideal" layer-cake type lithosphere and a "real" lithosphere containing heterogeneities and we define 3 types of inheritance, namely structural, compositional and thermal inheritance. Moreover, we assume that the evolution of hyperextended rift systems reflects the interplay between their inheritance (innate/"genetic code") and the physical processes at play (acquired/external factors). Thus, by observing the architecture and evolution of hyperextended rift systems and integrating the physical processes, one my get hints on what may have been the original inheritance of a system. Using this approach, we focus on 3 well-studied rift systems that are the Alpine Tethys, Pyrenean-Bay of Biscay and Iberia-Newfoundland rift systems. For the studied examples we can show that: 1) strain localization on a local scale and during early stages of rifting is controlled by inherited structures and weaknesses 2) the architecture of the necking zone seems to be influenced by the distribution and importance of ductile layers during decoupled deformation and is consequently controlled by the thermal structure and/or the inherited composition of the curst 3) the location of breakup in the 3 examples is not significantly controlled by the inherited structures 4) inherited mantle composition and rift-related mantle processes may control the rheology of the mantle, the magmatic budget, the thermal structure and the localization of final rifting Conversely, the deformation in hyperextended domains is strongly controlled by weak hydrated minerals (e.g. clay, serpentinite) that result form the breakdown of feldspar and olivine due to fluid and reaction assisted deformation and is consequently not inherited but the result of rift induced processes. These key observations show that both inheritance and rift-induced processes play a significant role in the development of magma-poor rift systems and that the role of inheritance may change as the physical conditions vary during the evolving rifting and as rift-induced processes (serpentinization; magma) become more important. Thus, it is not only important to determine the "genetic code" of a rift system, but also to understand how it interacts and evolves during rifting. Understand how far these new ideas and concepts derived from the southern North Atlantic and Alpine Tethys can be translated to other less explored hyperextended rift systems will be one of the challenges of the future research in rifted margins.

  5. Geodynamics of the Shanxi Rift system, China

    NASA Astrophysics Data System (ADS)

    Xu, Xiwei; Ma, Xingyuan

    1992-07-01

    The Pliocene-Quaternary Shanxi Rift system of northern China transsects the domal axis of the Shanxi Highlands and is defined by an S-shaped string of asymmetric basins, extending from Huailai-Yanqing in the north via Taiyuan to Yuncheng in the south. This rift system has a length of about 1200 km and a width of 20-80 km; it is characterized by strong earthquakes. Its central, NNE-trending, transtensional segment forms the main element of the Shanxi Rift system. Basin subsidence commenced during the early Pliocene along NNE oriented master-faults characterized by large strike-slip rates (5.68-7 mm/yr); crustal extension amounts to some 1.4 km; basins are separated by push-up blocks; destructive earthquakes ( M = 7-8) are unevenly distributed. The ENE trending northern and southern branches of the Shanxi Rift system are characterized by orthogonal crustal extension along ENE striking normal faults, amounting to about 8 km; these areas are characterized by a basin-and-range type structural style and weak seismic activity. The Shanxi Rift system developed on a some 40 km thick, thermally cool Precambrian crustal segment that was overprinted during Mesozoic diastrophic events. There is only minor rift-related volcanic activity. The Moho is pulled up by a few kilometers only under the axial rift zone; sub-Moho compressional velocities are in the 8.0-8.1 km/s range. The Shanxi Rift system evolved in response to the build-up of regional stress fields related to the collision of India and Eurasia; its localization involved reactivation of pre-existing fracture systems.

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

    NASA Astrophysics Data System (ADS)

    Klyuchevskii, Anatoly V.

    2014-07-01

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

  7. Strain partitioning in hyper-extended, strongly segmented rift systems: insights from the Cretaceous Bay of Biscay- Pyrenean rift system and comparison with present-day mature rift-transform margins

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Continental margins are often subdivided into transform and volcanic and non-volcanic rifted margins, although, in reality, such end-member type margins do not exist and the distribution of strain and magma leading to lithospheric breakup is more complex. Key questions related to the development of oblique and/or segmented rift-transform margins include the importance of inheritance, the partitioning of deformation in time and space, the interplay between deformation and magmatism, the timing and location of breakup, and the isostatic evolution of these systems during and after final rifting. At present-day continental margins the initial stages associated with the development of highly segmented rift-transform margins are often masked by thick sedimentary sequences and the relation between the rift structures, syn-tectonic sediments and magmatic additions remain poorly understood. Moreover, it looks as if the oceanic transform faults do not develop from transfer or transform faults within continental rifts, suggesting that the continental and oceanic systems are decoupled within the ocean continent transition. In this study we use the Bay of Biscay - Pyrenean system to understand how deformation was distributed in time and space during the evolution of a highly segmented rift-transform system along the Iberian/European plate boundary during Late Jurassic to Mid Cretaceous time. We will show that the rift basins (Parentis, Arzacq-Mauléon, Cantabrian basins) that developed along this embryonic plate boundary record a complex poly-phase deformation history, showing locale evidence for extreme crustal thinning and locally also mantle exhumation. Because these basins are preserved to the west (Bay of Biscay-Parentis), but reactivated and exposed in the east (Pyrenees), the basins and related structures can be studied using geological and geophysical methods. In our presentation we will show new observations and preliminary results that enable discussion about how a segmented rift-transform plate boundary formed in time and space. We will also show that the poly-phase evolution recorded along the European-Iberian plate boundary has important kinematic implications for the pre-breakup evolution that cannot be taken into account by kinematic models based on magnetic anomaly restorations only. These results, combined with those of present day margins, may give some insights on the pre-breakup evolution and processes that are at the origin of highly segmented rift-transform margins as seen in the Equatorial Atlantic.

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

    E-print Network

    Ebinger, Cynthia Joan

    1988-01-01

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

  9. Neotectonic activity along the Shanxi rift system, China

    NASA Astrophysics Data System (ADS)

    Xu, Xiwei; Ma, Xingyuan; Deng, Qidong

    1993-03-01

    The Shanxi rift system is one of the most outstanding Pliocene-Quaternary continental rift systems and strong earthquake belts in China. It extends as a series of en echelon left-stepping asymmetrical half-graben basins on the Shanxi Highlands over a distance of more than 1200 km. It describes a sinous S-shaped curve with a NNE-trending transtensional segment in the middle, and NE-ENE-trending extensional domains on both terminal segments. The latter are characterized by apparently synchronous, high-angle normal faulting, accommodating large vertical and relatively smaller lateral strains (3.5-8.5%), which produces the modern basin and range structure. The rift system has been intermittently active since the Pliocene. Geomorphological, neotectonic and seismic studies indicate that the rift system is at present still developing, as demonstrated by the occurrence of strong destructive historical earthquakes of magnitudes 7-8 and the large slip rates on the NNE-trending transtensional faults in the middle segment. The slip rates of these faults reached 4.9-6.4 mm per year during the Holocene. Geophysical studies show that the rifting occurred in a thickened crust, and no compelling evidence exists for the major thermal event in the mantle uniquely associated with the rifting. The development of the Shanxi rift system is consistent with the regional brittle strain pattern of a right-lateral shear belt and a regional stress field of ENE-WSW compression and NNW-SSE extension of the North China subplate. This structural setting corroborates the hypothesis that the deformation is in response to the escape tectonics caused by the Himalayan indenter from the southwest, and at the same time by the counter-clockwise rotation of the intervening crustal blocks. This provides the mode of formation of the Shanxi rift system.

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

    NASA Astrophysics Data System (ADS)

    Bingham, Robert; Ferraccioli, Fausto

    2014-05-01

    The West Antarctic Rift System (WARS) forms one of the largest continental rift systems on Earth. The WARS is of major significance as it forms the lithospheric cradle for the marine-based and potentially unstable West Antarctic Ice Sheet (WAIS). Seismic refraction, reflection, aeromagnetic, gravity and drilling in the Ross Sea have revealed most of what we know about its structure, tectonic and magmatic patterns and sedimentary basins. Aerogeophysical research and passive seismic networks have considerably extended our knowledge of the WARS and its influence on the overlying WAIS in the Siple Coast and Amundsen Sea Embayment (ASE) regions. The Bellingshausen Sea Embayment region has however remained largely unexplored, and hence the possible extent of the WARS in this sector has remained poorly constrained. Here we use a combination of reconnaissance ground-based and airborne radar observations, airborne gravity, satellite gravity and aeromagnetic data to investigate the WARS in the Bellingshausen Sea Embayment, in the area of the Ferrigno Ice Stream (Bingham et al., 2012, Nature). This region is of high significance, as it one of the main sectors of the WAIS that is currently exhibiting rapid ice loss, thought to be driven primarily by oceanic warming. Assessing geological controls on subice topography and ice dynamics is therefore of prime importance in this part of the WAIS. Ground-based and airborne radar image a subglacial basin beneath the Ferrigno Ice Stream that is up to 1.5 kilometres deep and that connects the ice-sheet interior to the Bellingshausen Sea margin. We interpret this basin as a narrow, glacially overdeepened rift basin that formed at the northwestern tip of the WARS. Satellite gravity data cannot resolve such a narrow rift basin but indicate that the crust beneath the region is likely thinned, lending support to the hypothesis that this area is indeed part of the WARS. Widely-spaced aeromagnetic data image a linear low along the inferred Ferrigno rift, but provide no evidence for high-amplitude aeromagnetic anomalies, typically associated with Cenozoic magmatism within the WARS. However, the reconnaissance character of these data, do not enable us to rule out the presence of magmatism within this part of the rift and cannot disclose the potential greater variability in subglacial geology either. Bingham et al. (2012) proposed the glacially overdeepened Ferrigno rift basins provided major controls for a palaeo-ice stream on the adjacent continental shelf during glacial maxima. The palaeo-ice stream, in turn, eroded the 'Belgica' trough, which today routes warm open ocean water back to the ice front to potentially reinforce dynamic thinning. Dynamic thinning in the Bellingshausen Sea region appears to be steered back to the ice-sheet interior along the Ferrigno rift system. We conclude that detailed aerogeophysical studies of the inferred rift basins that cut across the WAIS margin in the Bellingshausen Sea sector are a high priority to: a) better comprehend the structure and the tectono-magmatic evolution of the WARS and; b) to test the hypothesis that these rifts play a key role in rapidly transmitting oceanic-driven change inland, potentially promoting accelerated ice-sheet instability.

  11. The Midcontinent rift system in Kansas

    SciTech Connect

    Berendsen, P. . Kansas Geological Survey)

    1993-03-01

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

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

    NASA Astrophysics Data System (ADS)

    Zhang, Xuewei; Scholz, Christopher A.

    2015-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  14. Innovative tephra studies in the East African Rift System

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Technical Reports Server (NTRS)

    Mohr, P. A. (principal investigator)

    1973-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Technical Reports Server (NTRS)

    Mohr, P. A. (principal investigator)

    1972-01-01

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

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

    SciTech Connect

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

    1993-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Rilling, Sarah E.

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

  1. Fluid history in hyper-extended rifted margins: Examples from the fossil Alpine and western Pyrenean rift systems and the present-day Iberia rifted continental margin.

    NASA Astrophysics Data System (ADS)

    Pinto, Victor Hugo; Manatschal, Gianreto; Karpoff, Anne Marie; Masini, Emmanuel; Lemarchand, Damien; Hayman, Nicholas; Trow, Rudolph; Viana, Adriano

    2013-04-01

    The evolution of deep-water, magma-poor rifted margins is intimately linked with complex and polyphase fault structures. These structures, known as detachment faults, are responsible for extreme crustal thinning and mantle exhumation. During the evolution of detachment faults fluid-rock interaction plays an important role, changing the chemical and physical properties of rocks. These processes likely have major implications for the strain localization and structural evolution of the margin. The change in rock chemistry and rheology is best indicated by the breakdown of feldspars and olivine into clay and serpentine minerals and the pervasive cementation and precipitation of quartz along the fault zones. Although the chemical and mineral reactions are well known, it is still unclear to what extent these reactions lead to changes in the overall rheology of the extending lithosphere and how they can affect the thermal evolution of the hyper-extended rifted margins. In order to answer to these questions it is important to understand the origin, timing, pathways and composition of the fluids generated during rifting. Are fluids solely of marine origin or do they have a metamorphic- or mantle-derived component? Can we determine the range of temperature and consequently at what depth these fluids are formed? And can we constrain the age of their migration? These questions can be addressed in the well-known hyper-extended rift systems such as the Alpine Tethys margins exposed in the Alps, the Mauléon basin in the Western Pyrenees and the Deep Iberia margin drilled and seismically imaged offshore Portugal. All of these rift settings show evidence for detachment systems associated with hyper-extension and mantle exhumation. The aim of this ongoing study is to characterize the fluid signature in hyper-extended domain in magma-poor rifted margins. Including different sites with different degrees of compressional and metamorphic overprint enables us to compare results and to define the general importance of fluid systems in the development of hyper-extended rifts systems. The first results show that in all three geological settings fluid percolation can be recognized in fault rocks linked to the detachment systems. Evidence for the presence of fluids comes from the analyses of hydration reactions in fault zones. In the Alps the major and trace elements show a gain in elements typical from mantle rocks (Mg, Ni, Cu, Co, V). In the Pyrenees, microstructural studies show that detachment faulting crossed a range of crustal depths providing constraints on the depths of fluid migration. Future analyses will focus on additional major and trace elements and isotopic ratios (Sr and B) of hydrated rocks recovered from these hyper-extended domains, which will be linked with the temporal and spatial evolution of the major detachment structures.

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

    NASA Astrophysics Data System (ADS)

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

    1992-10-01

    The East Brazilian Rift system (Ebris) constitutes the northern segment of the South Atlantic rift system which developed during the Mesozoic breakup of South America and Africa. Following crustal separation in the Late Aptian, it evolved into a passive continental margin. Along the continental margin six basins are recognized, while three onshore basins form part of an aborted rift. Three continental syn-rift stratigraphic sequences are recognized, spanning Jurassic to Barremian times. The Jurassic (Syn-rift I) and Neocomian (Syn-rift II) phases were most active in the interior rift basins. During the Barremian (Syn-rift III), rift subsidence rates were twice as large as during the Neocomian (Syn-rift II), both in the interior rift and in the marginal rift segments, indicating that rift axis did not migrate from the interior to the marginal setting. Rift magmatism was centered on the southern EBRIS and peaked between 130 and 120 Ma during syn-rift phase II. Rift phase III was followed by a transitional marine, evaporitic megasequence of Aptian age, which directly overlies the rift unconformity and a marine drift megasequence which spans Albian to Recent times. During the Late Cretaceous, sedimentation rates responded to first-order eustatic sea-level fluctuations. Tertiary accelerated sedimentation rates can be related to local clastic supply which filled in spaces inherited from previous starved conditions. Between 60 and 40 Ma, post-rift magmatism, centered on the Abrolhos and Royal Charlotte banks, is probably related to development of a hot spot associated with the Vitória-Trindade Seamount Chain. Although crossing three distinct Precambrian tectono-thermal provinces, ranging from Archean through Late Proterozoic, rift structures follow a general NE trend, subparallel to the principal basement fabric. A NW-SE oriented stress field appears to be compatible with both Neocomian and Barremian phases of crustal extension. Profiles transverse to the rift axis indicate crustal stretching factors ranging between ? = 2.16 and 2.88. In the shallow portions of the rift, surface extension and crustal thinning seem to be compatible; however, in the deep portions of the basins, this relationship could not be tested. Reinterpretation of refraction profiles, north and south of the Walvis-São Paulo Ridge transform, indicates that seafloor spreading, from M3 anomaly to Aptian off Pelotas Basin, was taken up by crustal extension in the São Paulo Plateau. Differences in stretching rates may have been accommodated by extension across the Ponta Grossa Arch. The Early Aptian syn-rift/post-rift transition in the EBRIS marginal basins does not coincide with the onset of the drift phase during the Early Albian. This apparent discrepancy may be explained by a change from distributed margin-wide extension to a focused mode of extension near the future continent/ocean boundary.

  3. Magmatism in rifting and basin formation

    NASA Astrophysics Data System (ADS)

    Thybo, H.

    2008-12-01

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

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

    USGS Publications Warehouse

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

    1992-01-01

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

  5. Tectonomagmatic evolution of the final stages of rifting along the deep conjugate Australian-Antarctic magma-poor rifted margins: Constraints from seismic observations

    NASA Astrophysics Data System (ADS)

    Gillard, Morgane; Autin, Julia; Manatschal, Gianreto; Sauter, Daniel; Munschy, Marc; Schaming, Marc

    2015-04-01

    The processes related to hyperextension, exhumed mantle domains, lithospheric breakup, and formation of first unequivocal oceanic crust at magma-poor rifted margins are yet poorly understood. In this paper, we try to bring new constraints and new ideas about these latest deformation stages by studying the most distal Australian-Antarctic rifted margins. We propose a new interpretation, linking the sedimentary architectures to the nature and type of basement units, including hyperextended crust, exhumed mantle, embryonic, and steady state oceanic crusts. One major implication of our study is that terms like prerift, synrift, and postrift cannot be used in such polyphase settings, which also invalidates the concept of breakup unconformity. Integration and correlation of all available data, particular seismic and potential field data, allows us to propose a new model to explain the evolution of magma-poor distal rifted margins involving multiple and complex detachment systems. We propose that lithospheric breakup occurs after a phase of proto-oceanic crust formation, associated with a substantial magma supply. First steady state oceanic crust may therefore not have been emplaced before ~53.3 Ma corresponding to magnetic anomaly C24. Observations of magma amount and its distribution along the margins highlight a close magma-fault relationship during the development of these margins.

  6. How does the crust thin during final rifting: evidence from the Bernina/Campo domain in the Central Alps (SE-Switzerland and N-Italy)

    NASA Astrophysics Data System (ADS)

    Mohn, G.; Manatschal, G.; Masini, E.; Beltrando, M.; Muntener, O.; Kusznir, N. J.

    2009-12-01

    A long-standing problem in Earth Sciences is to understand how continents break apart to form new oceanic basins. Many of the questions that currently frame ongoing debates about continental break-up are related to the mechanics of extreme lithospheric extension. It is generally accepted that subcontinental mantle is exhumed at magma-poor rifted margins. However, much less attention has been paid to the processes that predate mantle exhumation. An increasing number of observations from magma-poor rifted margins show evidence for extreme crustal thinning to less than 10km without seismic evidence for significant normal faulting. This leads to the question of what structures/processes can explain such major crustal thinning and where and when are they active? The low resolution of the available offshore data and the small number of drill holes in present-day deep water rifted margins make it difficult to answer these questions. A more direct access to the sedimentary record of deep-water rifted margins and the underlying crustal and mantle rocks are exposed in the Alps in Western Europe. Remnants of the ancient Alpine Tethys rifted margins are well exposed and their paleogeographic evolution can be restored reasonably well. We initiated a research project in the Bernina/Campo domain in SE Switzerland, which exposes remnants of the fossil transition between the proximal and the distal/deep Adriatic margin, comparable with the necking zone in present-day magma-poor rifted margins. In the Bernina/Campo domain, primary, i.e. pre-Alpine contacts between sub-continental mantle, lower, middle and upper crustal rocks and pre-, syn- and post-rift sediments are locally preserved, which enables to unravel the structural, petrological and sedimentary evolution during extreme crustal thinning. Our results show that crustal thinning results from the interplay between detachment and decollement systems. The juxtaposition of pre-rift upper crustal rock against mafic lower crustal rocks in the most distal parts of the margin and the omission of the ductile quartzo-feldspatic middle crust in the necking zone suggests that extreme crustal thinning is strongly controlled by the rheological evolution of the extending lithosphere. The timing of extreme crustal thinning is well documented by the exhumation and cooling of mid to lower crustal rocks along low-angle detachment faults and their reworking in the syn-extensional sediments. The results show that the thinning of the continental crust is characterized by a system of conjugate crustal scale detachment systems along which the middle crust is omitted (necking zone). We believe that our results can help to better understanding the extreme thinning of the crust during final rifting as well as to better understand the rheological and isostastatic evolution of hyper-extended rifted margins.

  7. Lacustrine system evolution during early rifting: El Castellar Formation (Galve sub-basin, Central Iberian Chain)

    NASA Astrophysics Data System (ADS)

    Meléndez, Nieves; Liesa, Carlos L.; Soria, Ana R.; Meléndez, Alfonso

    2009-12-01

    A detailed sedimentological study of the first synrift deposits recorded in the Galve sub-basin of NE Spain during the Early Cretaceous aided in the reconstruction of climatic and tectonic influences. The El Castellar Formation is composed of siliciclastics and carbonates (unit 1), claystones, gypsum, and carbonates (unit 2), and marls and limestones (unit 3). Unit 1 facies formed in alluvial and palustrine plains, a local alluvial fan, and low-energy shallow lake subenvironments. Low-energy lacustrine facies characterised unit 2. In contrast, palustrine, low- and high-energy lake facies were identified for unit 3. The spatial and temporal distribution of lithofacies representing the several environments were used to propose a general lacustrine system evolution from isolated ponds and marshes, to low-energy shallow lakes, and finally to an extensive, high-energy lake. Lake evolution is related to changes in the subsidence pattern, from local- to basin-scale subsidence, which was ultimately related to the transition from the initial rift to rift climax stage. Shallowing-upwards lacustrine successions have been interpreted as climatically forced and linked to sediment and water supply. Both tectonics and climate determined the change from an overfilled to a balanced-fill lake-basin through time.

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

    NASA Technical Reports Server (NTRS)

    Mohr, P. A.

    1974-01-01

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

  9. Investigation of rifting processes in the Rio Grande Rift using data from an unusually large earthquake swarm. Final report, October 1, 1992--September 30, 1993

    SciTech Connect

    Sanford, A.; Balch, R.; Hartse, H.; House, L.

    1995-03-01

    Because the Rio Grande Rift is one of the best seismically instrumented rift zones in the world, studying its seismicity provides an exceptional opportunity to elucidate the active tectonic processes within continental rifts. Beginning on 29 November 1989, a 15 square km region near Bernardo, NM, produced the strongest and longest lasting sequence of earthquakes in the rift in 54 years. Our research focuses on the Bernardo swarm which occurred 40 km north of Socorro, New Mexico in the axial region of the central Rio Grande rift. Important characteristics concerning hypocenters, fault mechanisms, and seismogenic zones are discussed.

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

    USGS Publications Warehouse

    Behrendt, John C.

    1994-01-01

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

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

    USGS Publications Warehouse

    Qiang, J.; McCabe, P.J.

    1998-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Schuster, Mathieu; Nutz, Alexis

    2015-04-01

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

  13. Strain partitioning evolution and segmentation in hyperextended rift systems: insights from the Bay of Biscay and Pyrenees

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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 European - Iberian plate boundary. Based on the subsidence and deformation history, we propose a scenario illustrating the strain partitioning evolution between the different rift systems. The results of this work may provide insights on the spatial and temporal evolution of the embryonic stages of other segmented rifted continental margins.

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

    SciTech Connect

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

    1995-11-01

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

  15. 563Studinger et al.--Airborne geophysical mapping of the West Antarctic Rift System Mesozoic and Cenozoic extensional tectonics of the West Antarctic Rift

    E-print Network

    Studinger, Michael

    and Cenozoic extensional tectonics of the West Antarctic Rift System from high-resolution airborne geophysical shoulder close to the Whitmore Mountains block might have been reactivated during regional Cenozoic right Byrd Land (Fig. 1). In contrast, models of the Mesozoic and Cenozoic evolution of the region between

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

    NASA Astrophysics Data System (ADS)

    Lamontagne, M.; Ranalli, G.

    2013-12-01

    The St. Lawrence Rift System (SLRS), which includes the Ottawa-Bonnechère and Saguenay grabens, is located well inside the North American plate. Most historic and the some 350 earthquakes recorded yearly occur in three main seismically active zones, namely Charlevoix (CSZ), Western Quebec (WQSZ), and Lower St. Lawrence (LSLSZ)). Outside these areas, most of the Canadian Shield and bordering regions have had a very low level of earthquake activity. In the SLRS, moderate to large earthquakes (Moment magnitude (M) 5.5 to M 7) are known to have occurred since 1663 causing landslides and damage mostly to unreinforced masonry elements of buildings located on ground capable of amplifying ground motions. Most earthquakes in these seismic zones share common characteristics such as mid- to upper crustal focal depths, no known surface ruptures and proximity to SLRS faults. Variations also exist such as vast seismically-active region (WQSZ and LSLSZ), presence of a large water body (CSZ and LSLSZ), and absence of SLRS faults near concentration of earthquakes (WQSZ). The CSZ is the best studied seismic zone and there, earthquakes occur in the Canadian Shield, mostly in a 30 X 85 km rectangle elongated along the trend of the St. Lawrence River with local variations in focal depth distribution. Faults related to the SLRS and to a meteor impact structure exist and earthquakes occur along the SLRS faults as well as in between these faults. Overall, the SLRS faults are probably reactivated by the larger earthquakes (M ? 4.5) of the 20th century (CSZ in 1925; WQCSZ in 1935 and 1944; Saguenay in 1988) for which we have focal mechanisms. We propose that caution be exercised when linking historical events that have uncertain epicentres with SLRS faults. Similarly, SLRS faults should not be necessarily considered to be the reactivated structures for most small to moderate earthquakes (M < 4.5). A good example of this is the earthquakes of the WQSZ that tend to concentrate in a well-defined NW-SE alignment with no obvious geological control, except perhaps, a hypothetical hotspot track. Two local factors can lead to the occurrence of SLRS earthquakes: weak faults or enhanced stress levels. We propose that local conditions, concentrated in a few seismic zones, can alter these factors and lead to the occurrence of earthquakes, especially those with M < 4.5. At a continent-wide scale, the correlation between the SLRS and earthquakes is appealing. We suggest, however, that pre-existing faults related to the SLRS do not explain all features of the seismicity. Seismicity is concentrated in more active areas, some with conspicuous normal faults and some with suspected weakening mechanisms such as intense pre-fracturing (e.g. due to a meteorite impact), the passage over a hot spot, or the presence of intrusions and lateral crustal density variations.

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

    SciTech Connect

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

    1994-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1990-11-01

    Between 1980 and 1986 geological surveying to produce maps on a scale of 1:250,000 was completed over an area of over 100,000 km 2 in north-central Kenya, bounded by the Equator, the Ethiopian border and longitudes 36° and 38 °E. The Gregory Rift, much of which has the structure of an asymmetric half-graben, is the most prominent component of the Cenozoic multiple rift system which extends up to 200 km to the east and for about 100 km to the west, forming the Kenya dome. On the eastern shoulder and fringes two en echelon arrays of late Tertiary to Quaternary multicentre shields can be recognized: to the south is the Aberdares-Mount Kenya-Nyambeni Range chain and, to the north the clusters of Mount Kulal, Asie, Huri Hills and Marsabit, with plateau lavas and fissure vents south of Marsabit in the Laisamis area. The Gregory Rift terminates at the southern end of Lake Turkana. Further north the rift system splays: the arcuate Kinu Sogo fault zone forms an offset link with the central Ethiopian Rift system. In the rifts of north-central Kenya volcanism, sedimentation and extensional tectonics commenced and have been continuous since the late Oligocene. Throughout this period the Elgeyo Fault acted as a major bounding fault. A comparative study of the northern and eastern fringes of the Kenya dome with the axial graben reinforces the impression of regional E-W asymmetry. Deviations from the essential N-trend of the Gregory Rift reflect structural weaknesses in the underlying Proterozoic basement, the Mozambique Orogenic Belt: thus south of Lake Baringo the swing to the southeast parallels the axes of the ca. 620 Ma phase folds. Secondary faults associated with this flexure have created a "shark tooth" array, an expression of en echelon offsets of the eastern margin of the Gregory Rift in a transtensional stress regime: hinge zones where major faults intersect on the eastern shoulder feature intense box faulting and ramp structures which have counterparts in the rift system in southern Ethiopia. The NE- and ENE-trending fissures of the eastern fringes of the Kenya dome, notably in the Meru-Nyambeni areaand in the Huri and Marsabit shields, parallel late orogenic structures dated at around 580-480 Ma. Alkaline trends characterize the petrochemistry of the Cenozoic volcanics: In the Gregory Rift, voluminous Miocene alkali basalts, associated with hawaiite/mugearite lavas, define a trend culminating in the Miocene flood phonolites of the eastern shoulderand in the trachyphonolites, trachytes and peralkaline rhyolites, with associated pyroclastics, in central volcanoes such as Korosi, Paka and Silali. Such trends may manifest in the products of a single volcanic centre, also regionally on a broadly cyclic basis. On the eastern flanks of the Kenya dome the flood phonolites are less evident, but the same alkaline trends dominate the lava sequences, supplemented by nephelinitic extrusives in parts of the Nyambeni Range and in the Laisamis area. Results from recent seismicity surveys in the Laisamis area indicate that crustal extension may be currently active on the eastern fringes of the Kenya dome, but manifest at greater depths than in the axial Gregory Rift-Lake Turkana zone: a correlation is suggested with the ultra-alkaline petrochemistry of some of the eastern multicentre shields.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    Since the International Geophysical Year (1957), a view has prevailed that East Antarctica has a relatively homogeneous lithospheric structure, consisting of a craton-like mosaic of Precambrian terranes, stable since the Pan-African orogeny ~500 million years ago (e.g. Ferracioli et al. 2011). Recent recognition of a continental-scale rift system cutting the East Antarctic interior has crystallised an alternative view of much more recent geological activity with important implications. The newly defined East Antarctic Rift System (EARS) (Ferraccioli et al. 2011) appears to extend from at least the South Pole to the continental margin at the Lambert Rift, a distance of 2500 km. This is comparable in scale to the well-studied East African rift system. New analysis of RadarSat data by Golynsky & Golynsky (2009) indicates that further rift zones may form widely distributed extension zones within the continent. A pilot study (Vaughan et al. 2012), using a newly developed gravity inversion technique (Chappell & Kusznir 2008) with existing public domain satellite data, shows distinct crustal thickness provinces with overall high average thickness separated by thinner, possibly rifted, crust. Understanding the nature of crustal thickness in East Antarctica is critical because: 1) this is poorly known along the ocean-continent transition, but is necessary to improve the plate reconstruction fit between Antarctica, Australia and India in Gondwana, which will also better define how and when these continents separated; 2) lateral variation in crustal thickness can be used to test supercontinent reconstructions and assess the effects of crystalline basement architecture and mechanical properties on rifting; 3) rift zone trajectories through East Antarctica will define the geometry of zones of crustal and lithospheric thinning at plate-scale; 4) it is not clear why or when the crust of East Antarctica became so thick and elevated, but knowing this can be used to test models of Cenozoic ice sheet formation and stability. References Chappell, A.R. & Kusznir, N.J. 2008. Three-dimensional gravity inversion for Moho depth at rifted continental margins incorporating a lithosphere thermal gravity anomaly correction. Geophysical Journal International, 174 (1), 1-13. Ferraccioli, F., Finn, C.A., Jordan, T.A., Bell, R.E., Anderson, L.M. & Damaske, D. 2011. East Antarctic rifting triggers uplift of the Gamburtsev Mountains Nature, 479, 388-392. Golynsky, A.V. & Golynsky, D.A. 2009. Rifts in the tectonic structure of East Antarctica (in Russian). Russian Earth Science Research in Antarctica, 2, 132-162. Vaughan, A.P.M., Kusznir, N.J., Ferraccioli, F. & Jordan, T.A.R.M. 2012. Regional heat-flow prediction for Antarctica using gravity inversion mapping of crustal thickness and lithosphere thinning. Geophysical Research Abstracts, 14, EGU2012-8095.

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

    NASA Astrophysics Data System (ADS)

    Balanyuk, I.; Dmitrievsky, A.

    2009-04-01

    All the Barents Sea deposits are situated in the epicenter on active geodynamic development of the Barents Sea rift and, most important, over the zone of listric faults intersection, which consist a knot system over the mantle diapir. This is confirmed by prospecting seismology. Intrusion of hot mantle matter with further cooling down of abnormal lense might be a possible cause of appearance and evolution of ultradeep depressions. A high "seismic stratification" of the lower crust (nearly reaching the basement surface) at time scale about 8 sec. is typical for the inner, the deepest part of the depression. Supposing the "seismic stratified" lower crust correspond to "basalt" layer, this area is nearly upper crust ("granitic-gneiss") free. This fact confurmes conception on development of "granite free gaps" in the depression basement. Thick blocks of "seismically transparent" upper crust corresponding to the "granitic-gneiss" layer are marked out within Kolsk-Kanin monocline. An abrupt thickness decrease and appearance of "stratified" areas takes place at the southern edge of the depression. A filling of the over-rift sag with sediments, revival of the faults and their effect on the filtration processes and gas hydrates formation took place in the South Barents Sea depression. Repeating activation of the fault blocks in the basement, especially during late Jurassic - early Cretaceous period contributed to formation of the structures related to the greatest deposits of the South Barents Sea depression. An extended field acoustic data collected in the Barents Sea led to understanding of general fundamental problems for all Arctic Seas and, first of all, the problem of Quaternary glaciations. An analysis of Eurasian-Arctic continental margin shows correspondence between the rift systems of the shelf with those of the ocean. This relation can be observed by an example of the central Arctic region. All the rift systems underlying the sediment basin are expressed in the sea bed relief as spacious and extensive graben valleys burnished by lobes. The rift structures and the sediment cover are connected by the systems of transversal (or oblique) faults. A study of the regional geologic structure of basins affords believing in the very complicated inner riftogenic structure of the base and the lower part of the sediment cover, which is represented by a combination of grabens and horsts bound by the same tectonic border in the form of high amplitude fault zones, and have a very high density of fault-fractured tectonics. In the same time, a branching of the rift structures related to rounding of large solid blocks of the crust, represented by Archaean or Baikal base prominences, takes place. Their frequent structural connection with the continental paleo-rift structures is ascertained, but the shelf rift system are not their straight prolongation and separated by base thresholds concealed under the sediment cover or by bulkheads expressed even in the modern relief. Filling of over rift flexure by sediments, revival of faults and their impact on flow processes and gas hydrate formation in under sea bed sediments have occurred in the South Barents depression. Geodynamic development of the Barents sea rift not only played a substantial role in formation of as unique fields as Shtokman, Prirazlomnoe and others, but created prerequisites for possible gas outbursts into near-surface sediments of the Barents Sea that could result, in some cases, in gas hydrate formation. Periodic activation of basic fault blocks, especially in late Jurassic - early Cretaceous time significantly contributed to formation of the structures related to the greatest fields of South Barents depression. The information on geodynamic development of the region, thermal convection and modern sedimentation enable assessment of the real potentiality for underwater works in the region, potential gas hydrates resources, and will help to assign a strategy of prospecting work, to range the known

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  3. Tomography of the East African Rift System in Mozambique

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  4. Geodynamic modeling of the Mid-Continental Rift System: Is a mantle plume required?

    NASA Astrophysics Data System (ADS)

    Moucha, R.; Rooney, T. O.; Stein, S. A.; Brown, E.

    2013-12-01

    The Mid-Continent Rift System (MCRS) is a 2000-km long trace of a massive igneous event that nearly split North America 1.1 billion years ago. The MCRS offers a snapshot of continental rifting and rift failure. The rift started, evolved, and terminated via a complex and not-yet-understood interplay of mantle dynamics, magmatism, and extension. In particular, details of the processes surrounding melt formation and the associated depletion of the lithospheric mantle, and re-thickening of the extended crust remain poorly constrained. To help unravel the complex history of the MCRS, we present a new geodynamic model for late Proterozoic rifting and compare a number of different extension scenarios in an effort to answer the following question: can the volume of magmas preserved in the MCRS be explained by extensional processes in the absence of a thermo-chemical mantle plume anomaly? In the late Proterozoic, inherently higher mantle potential temperatures may have permitted rifting at lower stress levels and favored more melt formation. Therefore, the inferred volume of magma in the MCRS may not have required a plume. To explore this idea, we compare models for the evolution of a rift under different ambient mantle temperatures and radiogenic heating conditions, i.e. Phanerozoic vs. Proterozoic, and in the absence or presence of a thermal-chemical plume. Our geodynamic model of the MCRS includes a temperature dependent visco-elasto-plastic rheology in the presence of partial melt that is dynamically determined according to given rock-type, pressure and temperature. The models include a 'sticky air' layer to mimic a free surface that is coupled to a surface processes model to account for erosion and sedimentation. The numerical method we use is based on the primitive variable particle-in-cell finite-difference method developed by Taras Gerya and others (e.g. Gerya, 2010). The advantage of this approach is that specific material properties are inherently traced through time negating the need for numerous high-resolution grids. Moreover, melt-extraction and the formation of a crust along with depletion and fertilization are also easily tracked.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Our ability to determine the structural evolution and interaction of fault systems (kinematically linked group of faults that are in the km to 10s of km scale) within a rift basin is typically limited by the spatial extent and temporal resolution of the available data and methods used. Physical and numerical models provide predictions on how fault systems nucleate, grow and interact, but these models need to be tested with natural examples. Although field studies and individual 3D seismic surveys can provide a detailed structural evolution of individual fault systems, they are often spatially limited and cannot be used examine the interaction of fault systems throughout the entire basin. In contrast, regional subsurface studies, commonly conducted on widely spaced 2D seismic surveys, are able to capture the general structural evolution of a rift basin, but lack the spatial and temporal detail. Moreover, these studies typically describe the structural evolution of rifts as comprising multiple discrete tectonic stages (i.e. pre-, syn- and post-rift). This simplified approach does not, however, consider that the timing of activity can be strongly diachronous along and between faults that form part of a kinematically linked system within a rift basin. This study focuses on the East Shetland Basin (ESB), a multiphase rift basin located on the western margin of the North Viking Graben, northern North Sea. Most previous studies suggest the basin evolved in response to two discrete phases of extension in the Permian-Triassic and Middle-Late Jurassic, with the overall geometry of the latter rift to be the result of selective reactivation of faults associated with the former rift. Gradually eastwards thickening intra-rift strata (deposited between two rift phases) that form wedges between and within fault blocks have led to two strongly contrasting tectonic interpretations: (i) Early-Middle Jurassic differential thermal subsidence after Permian-Triassic rifting; or (ii) Triassic syn-rift activity on west-dipping faults. Our analysis of regional 2D and basin-wide 3D 'mega-merge' seismic reflection data calibrated by wells allow us to re-evaluate the pre-Triassic-to-Cretaceous structural evolution of the ESB. Our results suggest that pre-Triassic extension was accommodated by diachronous growth of NW-SE-to-NE-SW-striking faults that dipped either to the east or the west. In the NW of the ESB, Triassic syn-rift deposits are observed along large (>20 km long), NE-SW-striking faults. Elsewhere in the basin, post-rift deposits gradually thicken eastward, suggesting differential Triassic post-rift thermal subsidence with its axis to the east of the ESB. Subsequent Early-to-Middle Jurassic deposits thicken eastward across large N-S striking faults, suggesting syn-depositional fault growth. Our observations suggest that, rather than forming in response to discrete periods of extension separated by periods of tectonic quiescence, the ESB witnessed diachronous fault system evolution with faults showing polyphase activity, cross-cutting relationships, and protracted growth from the pre-Triassic to Middle-Late Jurassic. The results of this work reveal the complex structural evolution of rifts, highlight the power of 3D mega-merge seismic reflection data, and demonstrate that the conventional rift package nomenclature of pre-, syn-, and post-rift is difficult to apply at the basin-scale.

  6. Tectonic and sediment supply control of deep rift lake turbidite systems: Lake Baikal, Russia

    USGS Publications Warehouse

    Nelson, C.H.; Karabanov, E.B.; Colman, Steven M.; Escutia, C.

    1999-01-01

    Tectonically influenced half-graben morphology controls the amount and type of sediment supply and consequent type of late Quaternary turbidite systems developed in the active rift basins of Lake Baikal, Russia. Steep border fault slopes (footwall) on the northwest sides of half-graben basins provide a limited supply of coarser grained clastic material to multiple small fan deltas. These multiple sediment sources in turn laterally feed small (65 km) axially fed elongate mud-rich fans sourced by regional exterior drainage of the Selenga River that supplies large quantities of silt. Basin plain turbidites in the center of the linear basins and axial channels that are controlled by rift-parallel faults are fed from, and interfinger with, aprons and fans. The predictability of the turbidite systems in Lake Baikal provides the best example yet studied of how tectonics and sediment supply interact to control the development of a wide variety of coeval turbidite systems on a single basin floor.

  7. Keweenaw hot spot: Geophysical evidence for a 1. 1 Ga mantle plume beneath the Midcontinent Rift System

    SciTech Connect

    Hutchinson, D.R. ); White, R.S. ); Cannon, W.F.; Schulz, K.J. )

    1990-07-10

    The Proterozoic Midcontinent Rift System of North America is remarkably similar to Phanerozoic rifted continental margins and flood basalt provinces. Like the younger analogues, the volcanism within this older rift can be explained by decompression melting and rapid extrusion of igneous material during lithospheric extension above a broad, asthenospheric, thermal anomaly which the authors call the Keweenaw hot spot. Great Lakes International Multidisciplinary Program on Crustal evolution seismic reflection profiles constrain end-member models of melt thickness and stretching factors, which yield an inferred mantle potential temperature of 1,500-1,570C during rifting. Combined gravity modeling and subsidence calculations are consistent with stretching factors that reached 3 or 4 before rifting ceased, and much of the lower crust beneath the rift consists of relatively high density intruded or underplated synrift igneous material. The isotopic signature of Keweenawan volcanic rocks, presented in a companion paper by Nicholson and Shirey (this issue), is consistent with the model of passive rifting above an asthenospheric mantle plume.

  8. Transect across the West Antarctic rift system in the Ross Sea, Antarctica

    USGS Publications Warehouse

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

    1999-01-01

    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 relatively small extension, concentrated in the western half of the Ross Sea, during Cenozoic time.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  11. On the geotectonic nature of the Fen-Wei rift system

    NASA Astrophysics Data System (ADS)

    Guoda, Chen

    1987-11-01

    The Fen-Wei rift system, 1200 km long and 10-100 km wide, is situated in the northern part of East China, following a zigzag path trending NNE-SSW. It cuts the Shanxi-Shaanxi Plateau (average altitude 2 km) reaching depths of 5-6 km, and is filled with Cenozoic sediments (thickness 3-4 km). Accompanying the mainly vertical displacement of the marginal fault zones, the rift system extends laterally up to 7 km (greatest in the southern part). Earthquakes with foci 10-30 km deep are frequent; M = 8. Eruptions mainly of alkaline basalts took place 24 times in the Cenozoic. Heat flow appears to be rather high as marked by 17 hot springs. Negative Bouguer anomalies are dominant, reaching a maximum of -200 mGal. The crust is 38 km thick on average, 2-4 km thinner than that of the marginal uplift zones. Possibly a mantle arched belt exists below. In the upper mantle, Vp = 7.95 km/ s. Originally the rift system was part of the broad ancient China platform. In the Early Jurassic, the latter underwent activation and became the North China diwa (geodepression) region . In the Cenozoic, the Fen-Wei rift system formed as a result of contraction of the crust in this region combined with creeping of asthenospheric material. It may be referred to the crevice type of post-platform continental rift zones in E.E. Milanovsky's classification. The term "diwa" is derived from Chinese words meaning geodepression, being a special kind of intermountain-structural basins occurring mostly on the ancient platform region, filled chiefly with mollasoid sediments. A diwa region is marked with high relief and by basins, diwa as negative units intercalated with ranges as positive units called "geodomes". It is a post-platform mobile region, the third geotectonic element of the continental crust besides géosynclinal and platform regions, proposed by the author in 1959 (Chen, 1959, 1960b, 1965, 1980, etc). Its synonym is "activated region" proposed by the author in 1956, because it is formed by the activation of the platform (Chen 1956, 1960a).

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Macgregor, Duncan

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    The West Antarctic Rift System (WARS) represents one of the largest extensional alkali volcanic provinces on Earth, yet the mechanisms responsible for driving rift-related magmatism remain controversial. The failure of both passive and active models of decompression melting to explain adequately the observed volume of volcanism has prompted debate about the relative roles of thermal plume-related melting and ancient subduction-related flux melting. The latter is supported by roughly 500 Ma of subduction along the paleo-Pacific margin of Gondwana, although both processes are capable of producing the broad seismic anomaly imaged beneath most of the Southern Ocean. Olivine-hosted melt inclusions from basanitic lavas provide a means to evaluate the volatile budget of the mantle responsible for active rifting beneath the WARS. We present H2O, CO2, F, S and Cl concentrations determined by SIMS and major oxide compositions by EMPA for olivine-hosted melt inclusions from lavas erupted in Northern Victoria Land (NVL) and Marie Byrd Land (MBL). The melt inclusions are largely basanitic in composition (4.05 - 17.09 wt % MgO, 37.86 - 45.89 wt % SiO2, and 1.20 - 5.30 wt % Na2O), and exhibit water contents ranging from 0.5 up to 3 wt % that are positively correlated with Cl and F. Coupling between Cl and H2O indicates metasomatic enrichment by subduction-related fluids produced during dehydration reactions; coupling between H2O and F, which is more highly retained in subducting slabs, may be related to partial melting of slab remnants [1]. Application of source lithology filters [2] to whole rock major oxide data shows that primitive lavas (MgO wt % >7) from the Terror Rift, considered the locus of on-going tectonomagmatic activity, have transitioned from a pyroxenite source to a volatilized peridotite source over the past ~4 Ma. Integrating the volatile data with the modeled characteristics of source lithologies suggests that partial melting of lithosphere modified by subduction processes is the source of pyroxenite and volatiles in the mantle beneath the present-day rift. The earliest magmatic activity preferentially removed the most readily fusible components from the mantle, resulting in transition to a metasomatized peridotite source over time. [1] Straub & Layne, 2003, GCA; [2] Herzberg & Asimow, 2008, G3; [3] Rilling et al., 2009, JGR.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Sommerfeld, Anja; Prömmel, Kerstin; Cubasch, Ulrich

    2014-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Domingues, Ana; Custódio, Susana; Chamussa, José; Silveira, Graça; Chang, Sung-Joon; Lebedev, Sergei; Ferreira, Ana; Fonseca, João

    2014-05-01

    Project MOZART - MOZAmbique Rift Tomography (funded by FCT, Lisbon) deployed a total of 30 temporary broadband seismic stations from the SEIS-UK Pool in central and south Mozambique and in NE South Africa. The purpose of this project is the study of the East African Rift System (EARS) in Mozambique. We estimated preliminary locations with the data recorded from April 2011 to July 2012. A total of 307 earthquakes were located, with ML magnitudes ranging from 0.9 to 3.9. We observe a linear northeast-southwest distribution of the seismicity that seems associated to the Inhaminga fault. The seismicity in the northeast sector correlates well with the topography, tracing the Urema rift valley. The seismicity extends to ~300km, reaching the M7 2006 Machaze earthquake area. In order to obtain an initial velocity model of the region, we applied the ambient noise method to the MOZART data and two additional stations from AfricaARRAY. Cross-correlations were computed between all pairs of stations, and we obtained Rayleigh wave group velocity dispersion curves for all interstation paths, in the period range from 3 to 50 seconds. The geographical distribution of the group velocity anomalies is in good agreement with the geology map of Mozambique, having lower group velocities in sedimentary basins areas and higher velocities in cratonic regions. We also observe two main regions with different velocities that may indicate a structure not proposed in previous studies. We perform a three-dimensional inversion to obtain the S-wave velocity of the crust and upper mantle, and in order to extend the investigation to longer periods we apply a recent implementation of the surface-wave two-station method (teleseismic interferometry), while augmenting our dataset with Rayleigh wave phase velocities curves in broad period ranges. In this way we expect to be able to look into the lithosphere-asthenosphere depth range.

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

    SciTech Connect

    Van Schmus, W.R.

    1989-03-01

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

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

    USGS Publications Warehouse

    Berendsen, P.

    1989-01-01

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

  1. Rift basins - Origin, history, and distribution

    NASA Technical Reports Server (NTRS)

    Burke, K. C.

    1985-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Fabbi, Simone; Santantonio, Massimo

    2012-12-01

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

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

    SciTech Connect

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

    1989-03-01

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

  4. East African Rift Valley, Kenya

    NASA Technical Reports Server (NTRS)

    1990-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Koehn, D.; Sachau, T.; Aanyu, K.

    2009-04-01

    In this contribution we present a new model of passive rifting and related rift-flank uplift. The numerical model is based on a lattice spring network coupled with a viscous particle model so that we can simulate visco-elasto-plastic behaviour with dynamic fault development. In our model we show that rift flank uplift can be achieved best when extension in the crust is localized and the lower crust is strong so that major rift faults transsect the whole crust. Uplift of rift flanks follows a smooth function whereas down-throw in the rift basin takes place in steps. The geometry of the developing faults has also an influence on the uplift, in this case displacement along major rift faults produces higher flanks than distributed displacement on many faults. Our model also shows that the relative elastic thickness of the crust has only a minor influence on the uplift since fault depth and elastic thickness are not independent. In addition we show with a second set of simulations and analytically that a strain misfit between the upper and lower boundaries of a stretched crust leads to an active uplift driven by elastic forces. We compare the numerical simulations, the analytical solution and real surface data from the Albertine rift in the East African Rift System and show that our new model can reproduce realistic features. Our two-layer beam model with strain misfit can also explain why a thick crust in the simulations can have an even higher rift flank than a thin crust even though the thin crust topography has a higher curvature. We discuss the implications of our simulations for real rift systems and for the current theory of rift flank uplift.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    On ocean basaltic volcanoes, magma transfer to the surface proceeds by subvertical ascent from the mantle lithosphere through the oceanic crust and the volcanic edifice, possibly followed by lateral propagation along rift zones. We use a 19-year-long database of volcano-tectonic seismic events together with detailed mapping of the cinder cones and eruptive fissures to determine the geometry and the dynamics of the magma paths intersecting the edifice of Piton de la Fournaise volcano. We show that the overall plumbing system, from about 30 km depth to the surface, is composed of two structural levels that feed distinct types of rift zones. The deep plumbing system is rooted between Piton des Neiges and Piton de la Fournaise volcanoes and has a N30-40 orientation. Above 20 km below sea level (bsl), the main axis switches to a N120 orientation, which permits magma transfer from the lithospheric mantle to the base of the oceanic crust, below the summit of Piton de la Fournaise. The related NW-SE rift zone is 15 km wide, linear, spotted by small to large pyroclastic cones and related lava flows and emits slightly alkaline magmas resulting from high-pressure fractionation of clinopyroxene ± olivine. This rift zone has low magma production rate of ~ 0.5-3.6 × 10- 3 m3s- 1 and an eruption periodicity of around 200 years over the last 30 ka. Seismic data suggest that the long-lasting activity of this rift zone result from regional NNE-SSW extension, which reactivates inherited lithospheric faults by the effect of underplating and/or thermal erosion of the mantle lithosphere. The shallow plumbing system (< 11 km bsl) connects the base of the crust with the Central Cone. It is separated from the deep plumbing system by a relatively large aseismic zone between 8 and 11 km bsl, which may represent a deep storage level of magma. The shallow plumbing system feeds frequent, short-lived summit and flank (NE and SE flanks) eruptions along summit and outer rift zones, respectively. Summit rift zones are very active (~ 0.1-0.25 m3s- 1), short (2-3 km), and present an orthogonal pattern confined to the central active cone of Piton de la Fournaise. Outer NE and SE rift zones are much less active (~ 4-7.3 × 10- 3 m3s- 1) and extend from inside the Enclos Fouqué caldera to bound the mobile eastern volcano flank. We show that the outer rift zones are almost aseismic and are genetically linked to the seaward flank displacements, whose most recent events where detected in 2004 and 2007. East flank sliding is itself triggered by shallow (< 2 km depth) sill intrusions. We propose that the subvertical magma intrusions along the perpendicular summit rift zones, sill intrusions, and subsequent magma injections along the outer rift zones are controlled by cycles of stress permutations. We thus tentatively propose that as for Piton de la Fournaise, the regional stress field acting on Etna and Hawaiian volcanoes is an important parameter in the control of the magma transfer along their deep plumbing system whereas the dynamics of their summit system is governed by shallow stress variations (above 5-10 km bsl) due to edifice deformation and magma transfers.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

    LePera, Alan; Atekwana, Estella; Abdelsalam, Mohamed

    2014-05-01

    Dikes and dike swarms often play a significant role in the initiation and extension of rift zones. The giant ODS in northern Botswana, Africa represents a Jurassic aged (~180Ma) thermo-tectonic event which developed during the initial lithospheric weakening phase of Gondwana. Detailed investigations of the mafic dike swarm over the last four decades have provided insights into its age, shape, orientation, and chemistry but have thus far been limited in addressing the crustal structure below the swarm. Historically, the ODS has been interpreted as a failed rift arm based on its association with the Bouvet Hotspot and geometric relationship with two other prominent dike swarms. More recent studies suggest instead that the ODS was emplaced along a preexisting Precambrian basement fabric. Accordingly, the origin of the swarm still remains a matter of debate. The objectives of this study were: (1) determine the role of crustal heterogeneities on the emplacement of the dikes, (2) determine variations in crustal thickness below the ODS and geographically related Okavango Rift Zone (ORZ), a zone of incipient rifting and (3) determine along-strike variations in Curie Point Depth (CPD) below the swarm. We used high resolution aeromagnetic data and applied mathematical filters to enhance structures associated with the swarm's oblique geometry. Crustal thicknesses were estimated using the radial average power spectrum method, applied to 1.2km spatial resolution gravity data. 3D inversions were used to map the magnetic basement and determine the depth to the base of the swarm. Our results showed: (1) There were no apparent basement structures with the same 110° orientation as the ODS. (2) Crustal thickness below the swarm ranges from 39 to 45km with an average of 42± 3km, comparable with thicknesses derived from the Southern African Seismic Experiment (SASE). In contrast, crustal thickness below the ORZ is 9 to 16km thinner than the surrounding blocks. (3) The magnetic basement extends to a depth of about 24km and is segmented into a number of along-strike magnetic bodies. The lack of significant crustal thinning below the ODS and poor relationship with the Precambrian basement fabric suggests either the ODS was not associated with a failed rift system or the remnants of the crustal disturbance have since been modified to depict a normal continental crust. The along-strike magnetic bodies conceivably represent mid-crustal feeder chambers, similar to those found in modern extensional environments such as Afar, or magma pooling zones developed along Proterozoic discontinuities. Due to the relative inconsistency of the magnetic anomaly below the swarm we speculate that a majority of the dikes are confined to the upper 5-10km of the crust. The ODS is thus interpreted to be a magma enhanced fissure network emplaced within the upper crust during an extensive period of regional tension induced by a continental wide upwelling of the asthenosphere caused by thermal incubation of the mantle.

  9. Nonlinear geodynamics of the Baikal rift system: An evolution scenario with triple equilibrium bifurcation

    NASA Astrophysics Data System (ADS)

    Klyuchevskii, Anatoly V.

    2010-01-01

    This is an attempt to analyze the current lithospheric stress pattern in the Baikal rift in terms of nonlinear dynamics as an open self-organizing system in order to gain more insights into the general laws of regional seismicity. According to the suggested approach, the stress pattern inferred from seismic moments of 70,000 MLH ? 2.0 events that occurred in the region between 1968 and 1994 is presented as a phase portrait in the phase spaces of the seismic moments. The obtained phase portrait of the system evolution fits well a scenario with triple equilibrium bifurcation where stress bifurcations account for the frequency of M > 5.5 earthquakes. Extrapolation of the results into the nearest future indicates probability of such a bifurcation (a catastrophe of stress), i.e., there is growing risk that M ? 7 events may happen in the region within a few years.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    In spite of numerous geoscientific studies, the mechanisms responsible for the initiation and development of continental rifts are still poorly understood. The key information required to constrain various geodynamic models on rift initiation can be derived from the crust/mantle structure and anisotropy beneath incipient rifts such as the Southern and Southwestern branches of the East African Rift System. As part of a National Science Foundation funded interdisciplinary project, 50 PASSCAL broadband seismic stations were deployed across the Malawi, Luangwa, and Okavango rift zones from the summer of 2012 to the summer of 2014. Preliminary results from these 50 SAFARI (Seismic Arrays for African Rift Initiation) and adjacent stations are presented utilizing shear-wave splitting (SWS) and P-S receiver function techniques. 1109 pairs of high-quality SWS measurements, consisting of fast polarization orientations and splitting times, have been obtained from a total of 361 seismic events. The results demonstrate dominantly NE-SW fast orientations throughout Botswana as well as along the northwestern flank of the Luangwa rift valley. Meanwhile, fast orientations beneath the eastern Luangwa rift flank rotate from NNW to NNE along the western border of the Malawi rift. Stations located alongside the western Malawi rift border faults yield ENE fast orientations, with stations situated in Mozambique exhibiting more E-W orientations. In the northern extent of the study region, fast orientations parallel the trend of the Rukwa and Usangu rift basins. Receiver function results reveal that, relative to the adjacent Pan-African mobile belts, the Luangwa rift zone has a thin (30 to 35 km) crust. The crustal thickness within the Okavango rift basin is highly variable. Preliminary findings indicate a northeastward thinning along the southeast Okavango border fault system congruent with decreasing extension toward the southwest. The Vp/Vs measurements in the Okavango basin are roughly 1.75 on average, suggesting an unmodified crustal composition, while those of the Luangwa and southern Malawi rift zones are relatively high, probably suggesting ancient or ongoing magmatic emplacement. The Pan-African mobile belts enveloping the rift zones are mostly characterized by more felsic and thicker crust.

  11. Development of Magma Reservoirs during the Final Stages of Rifting - the Role of the Continental Lithosphere in Magma Genesis in the Afar Depression

    NASA Astrophysics Data System (ADS)

    Rooney, T. O.; Yirgu, G.; Dosso, L.

    2012-12-01

    The Afar depression, which lies at the intersection of the East African Rift system, the Red Sea and Gulf of Aden, is a key target in understanding the transition from continental rifting to oceanic spreading. Critical to this transition is thinning of the lithospheric mantle and the commencement of dominantly asthenospheric decompression melting. Lithospheric stretching and elevated mantle potential temperatures have facilitated melt production and these magmatic products may be used to probe conditions of melt generation beneath the Afar depression. Quaternary basalts in the region exhibit an array of trace element characteristics that extend from enriched to somewhat depleted. The more trace element enriched samples share similar characteristics to basalts from the Main Ethiopian Rift, interpreted to represent a mixture of asthenospheric and lithospheric reservoirs. However, a subset of basalts from the Afar depression exhibits a distinctive depletion in the most incompatible trace elements, Ti, K, and P. These Afar depression depleted basalts (ADDB) have no correlative within the Ethiopian Rift and are distinguished from regional MORB suites by radiogenic Pb and Sr values. The ADDB suite have Pb isotopes that overlap with the least radiogenic end of the Main Ethiopian rift array, but display more radiogenic Nd isotopes. The ?Hf- ?Nd values of the ADDB suite fall in a tight cluster substantially above the mantle array. The isotopic characteristics of the ADDB suite cannot be explained by melting of existing inferred asthenospheric or lithospheric reservoirs. Alternatively, we suggest the ADDB suite is the result of melting at shallow levels in the lithospheric mantle. Advanced lithospheric thinning within the Afar depression has exposed this shallow reservoir to melt generation. In less extended regions, such as in the Ethiopian rift, thicker lithospheric mantle prevents melt generation within this shallow lithospheric mantle reservoir, consistent with the restricted occurrence of the ADDB suite to the Afar depression. Thus, in addition to asthenospheric decompression melting, the lithospheric mantle is contributing to melt production within the Afar depression. When combined with enriched trace element and isotopic values for other basalts in the Afar depression, our data indicate a wide array of potential melt sources in the region that includes the Afar plume, continental lithosphere and ambient asthenosphere. These data have significant implications for existing interpretations that link low-velocity seismic anomalies to melt derived from oceanic-ridge style decompression melting of the ambient asthenosphere beneath the Afar depression. Instead, the continued presence and melting of the continental lithosphere dictates that the Afar depression remains a transitional structure between a continental rift and an oceanic spreading center.

  12. Rift propagation

    NASA Technical Reports Server (NTRS)

    Parmentier, E. M.; Schubert, G.

    1989-01-01

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

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

    PubMed

    Ivanov, Alexei V; Demonterova, Elena I

    2009-01-01

    As known from inland sedimentary records, boreholes, and geophysical data, the initiation of the Baikal rift basins began as early as the Eocene. Dating of volcanic rocks on the rift shoulders indicates that volcanism started later, in the Early Miocene or probably in the Late Oligocene. Prominent tectonic uplift took place at about 20 Ma, but information (from both sediments and volcanics) on the initial stage of the rifting is scarce and incomplete. A comprehensive record of sedimentation derived from two stacked boreholes drilled at the submerged Akademichesky ridge indicates that the deep freshwater Lake Baikal existed for at least 8.4 Ma, while the exact formation of the lake in its roughly present-day shape and volume is unknown. Four important events of tectonic/environmental changes at about approximately 7, approximately 5, approximately 2.5, and approximately 0.1 Ma are seen in that record. The first event probably corresponds to a stage of rift propagation from the historical center towards the wings of the rift system. Rifting in the Hovsgol area was initiated at about this time. The event of ~5 Ma is a likely candidate for the boundary between slow and fast stages of rifting. It is reflected in a drastic change of sedimentation rate due to isolation of the Akademichesky ridge from the central and northern Lake Baikal basins. The youngest event of 0.1 Ma is reflected by the (87)0Sr/ (86)Sr ratio increase in Lake Baikal waters and probably related to an increasing rate of mountain growth (and hence erosion) resulting from glacial rebounding. The latter is responsible for the reorganization of the outflow pattern with the termination of the paleo-Manzurka outlet and the formation of the Angara outlet. The event of approximately 2.5 Ma is reflected in the decrease of the (87)Sr/(86)Sr and Na/Al ratios in Lake Baikal waters. We suggest that it is associated with a decrease of the dust load due to a reorganization of the atmospheric circulations in Mainland Asia. All these tectonic and climatic events could (and actually did) influence the biota of Lake Baikal. The Hovsgol rift basin was shaped to its recent form between 5.5 and 0.4 Ma. However, freshwater Lake Hovsgol appeared only in the latest pre-Holocene time as a result of meltwater inflow and increase of atmospheric precipitations during the Bølling-Allerød warming. Prior to this, a significantly smaller, saline outflow-free precursor of Lake Hovsgol existed. It explains why two, now connected, lakes of similar water chemistry within similar climatic and tectonic conditions differ so much in their biodiversity. PMID:19198772

  14. Observations From Fieldwork and (U-Th)/He Thermochronologic Study of the Central Arabian Flank of the Red Sea Rift System

    NASA Astrophysics Data System (ADS)

    Szymanski, E.; Stockli, D. F.; Johnson, P. R.; Kattan, F. H.; Al Shammari, A.

    2007-12-01

    Improvement in our modeling of continental lithosphere rupturing and rifting dynamics requires an absolute understanding of the temporal and spatial strain distribution throughout an entire rift system. This statement holds especially true for our understanding of Red Sea rift system dynamics. However, critical geologic data used to determine the tectonic evolution of the Red Sea rift system come mainly from the Gulf of Suez and the Egyptian and Yemeni margins of the Red Sea while the rift flanks in Sudan and Saudi Arabia have remained largely unstudied. This study aims to fill that information gap by focusing on the development of extensional structures and rift-related Tertiary basaltic volcanism along the central Saudi Arabian rift flank. Traditional structural analyses, coupled with thermochronometric techniques, are used to elucidate the temporal and spatial evolution of strain markers manifested by structurally-controlled extensional basins that parallel the trend of the main Red Sea rift. Constraints on the dynamics of rift flank deformation are achieved through the collection of long-baseline thermochronometric transects that traverse the entire Arabian shield and short-baseline transects that resolve the thermal evolution of individual normal faults that bound inland basins. The variation in sampling resolution is a comprehensive method that allows tectonic study at different scales; long-baseline transects aim to resolve the timing and kinematics of rift flank uplift and exhumation while short-baseline transects address issues well inboard from the modern rift margin such as structural control on pre- and syn-rift stratigraphy. Structural field analyses have shown that the NW-SE trend of inland basin-bounding faults is strongly coincident with the trend of pre-existing crustal fabrics produced by the Late Proterozoic Najd Fault System. Furthermore, the magnitude of normal fault activation along these heterogeneities controlled the geometry of inland basins. Preliminary (U- Th)/He apatite analysis of samples from both short- and long-baseline transects reveal a temporally dichotomous and spatially complex cooling history for the central rift flank that includes active footwall exhumation approximately 130 km inland from the rift margin during the Middle Miocene.

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

    USGS Publications Warehouse

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

    1988-01-01

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

  16. On abrupt transpression to transtension transition in the South Baikal rift system (Tunka - South Baikal segment)

    NASA Astrophysics Data System (ADS)

    Sankov, Vladimir; Parfeevets, Anna; Lukhnev, Andrey; Miroshnitchenko, Andrey; Ashurkov, Sergey; Sankov, Alexey; Usynin, Leonid; Eskin, Alexander; Bryzhak, Evgeny

    2013-04-01

    This work addresses to relation of transpression and extension stress-strain conditions in intracontinental rift system. In our investigation we use a new structural, shallow geophysics, GPS geodetic data and paleostress reconstructions. The surroundings of southern tip of Siberian platform is the region of three Late Cenozoic structures conjugation: sublatitudinal Obruchev fault (OF) controlling the northern boundary of the South Baikal basin, NW trending Main Sayan fault (MSF) as the strike-slip boundary between Siberian platform and East Sayan block and WNW trending eastern segment of Tunka fault (TF) as part of the Tunka basins system northern boundary. A new evidences of superposition of compression and extension fault structures were revealed near the southern extremity of Baikal lake. We've find a very close vicinity of Late Pleistocene - Holocene strike-slip, thrust and normal faulting in the MSF and OF junction zone. The on-land Holocene normal faulting can be considered as secondary fault paragenesis within the main strike-slip zone (Sankov et al., 2009). Active strike-slip, thrust and reverse faulting characterize the MSF and TF junction zone. The transpression conditions are replaced very sharply by transtension and extension ones in eastern direction from zone of structures conjugation - the active normal faulting is dominated within the South Baikal basin. The Bystraya rift basin located in the west shows the tectonic inversion since Middle Pleistocene as a result of the strike-slip movements partitioning between TF and MSF and inset of edition compression stress. The active strike-slip and intrabasin extension conditions are dominated father to the west in Tunka basin. The results of our GPS measurements show the present day convergence and east movements of Khamar-Daban block and eastern Tunka basins relative to Siberian platform along MSF and TF with NE-SW shortening domination. The clear NW-SE divergence across Baikal basin is documented. Holocene and present-day left lateral relative motions of about 3 mm/yr (Sankov et al., 2004) between of Siberian platform and its mounting frame are accommodated along south-eastern segment of MSF. We consider two main factors of sharp transition between transpression and transtension to extension conditions in Tunka-South Baikal segment of Baikal rift system. The first one is the influence of geometry of southern tip of Siberian platform as a first order ancient lithosphere heterogeneity in agreement with (Petit et al., 1996). The second factor is the interaction in this region of two tectonic forces driving the Cenozoic geodynamics. The initial opening of the Tunka and South Baikal basins since Oligocene time as well as father Baikal rift system development caused by long lived asthenosphere flow along NW-SE direction (Sankov et al., 2011). The addition NE-SW compression started during Pliocene (Parfeevets, Sankov, 2006) as the result of the Hindustan and Eurasia convergence. The former caused transpression deformations and clockwise horizontal block rotations along south-western boundary of the platform with their SE movements to the "free space" opened by the divergence of Siberian platform and Transbaikal block (Sankov et al., 2002, 2005).

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    A backarc inner rift is formed after a major opening of backarc basin near a volcanic front away from the spreading center of a major backarc basin. An obvious example is the inner rift along the Izu-Bonin arc. Similar inner rift zones have been developed along the Sea of Japan coast of Honshu island, Japan. NE and SW Japan arcs experienced strong shortening after the Miocene backarc rifting. The amount of shortening shows its maximum along the backarc inner rifts, forming a fold-and-thrust of thick post-rift sediments over all the structure of backarc. The rift structure has been investigated by onshore-offshore deep seismic reflection/wide-angle reflection surveys. We got continuous onshore-offshore image using ocean bottom cable and collected offshore seismic reflection data using two ships to obtain large offset data in the difficult area for towing a long streamer cable. The velocity structure beneath the rift basin was deduced by refraction tomography in the upper curst and earthquake tomography in the deeper part. It demonstrates larger P-wave velocity in upper mantle and lower crust, suggesting a large amount of mafic intrusion and thinning of upper continental crust. The deeper seismicity in the lower crust beneath the rift basin accords well to the mafic intrusive rocks. Syn-rift volcanism was bimodal, comprising a reflective unit of mafic rocks around the rift axis and a non-reflective unit of felsic rocks near the margins of the basins. Once rifting ended, thermal subsidence, and subsequently, mechanical subsidence related to the onset of the compressional regime, allowed deposition of up to 5 km of post-rift, deep marine to fluvial sedimentation. Continued compression produced fault-related folds in the post-rift sediments, characterized by thin-skin style of deformation. The syn-rift mafic intrusion in the crust forms convex shape and the boundary between pre-rift crust and mafic intrusive shows outward dipping surface. Due to the post rift compression, the boundary of rock units reactivated as reverse faults, commonly forming a large-scale wedge thrust and produced subsidence of rift basin under compressional stress regime. Large amount of convergence of overriding plate is accommodated along the inner rift, suggesting that it is a weakest zone in whole arc-backarc system. The convergence between young (15 Ma) Shikoku basin and SW Japan arc produced intense shortening along the inner failed rift along the Sea of Japan coast. After the onset of subduction along the Nankai trough, the fold-and-thrust belt was covered by Pliocene marine sediment. Before the 2011 off-Tohoku earthquake (M9), several damaging earthquakes occurred along the backarc fold-and-thrust belt. These represents that a weak backarc inner rift is very sensitive for the stress produce by the subduction interface.

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  1. Stress Pattern of the Shanxi Rift System, North China, Inferred from the Inversion of New Focal Mechanisms

    NASA Astrophysics Data System (ADS)

    Li, Bin; Sørensen, Mathilde; Atakan, Kuvvet; Havskov, Jens

    2015-04-01

    The Shanxi rift system is one of the most outstanding intra-plate transtensional fault zones in the North China block. Earthquake focal mechanisms of the rift system are investigated for the time period 1965 - Apr. 2014. A total of 143 focal mechanisms of ML ? 3.0 earthquakes were compiled. Among them, 105 solutions are newly determined by combining the P-wave first motions and full waveform inversion, and 38 solutions are from available published data. Stress tensor inversion was then performed based on the new database. The results show that most solutions exhibit normal or strike-slip faulting, and the regional stress field is transtensional and dominated by NNW-SSE extension. This correlates well with results from GPS data, geological field observations and leveling measurements across the faults. Heterogeneity exists in the regional stress field, as indicated by individual stress tensor inversions conducted for five subzones. While the minimum stress axis (?3) appears to be consistent and stable, the orientations, especially the plunges, of the maximum and intermediate stresses (?1 and ?2) vary significantly among the different subzones. Based on our results and combining multidisciplinary observations from geological surveys, GPS and cross-fault monitoring, a kinematic model is proposed, in which the Shanxi rift system is situated between two opposite rotating blocks, exhibiting a transtensional stress regime. This model illustrates the present-day stress field and its correlation with the regional tectonics, as well as the current crustal deformation of the Shanxi rift system. Results obtained in this study, may help to understand the geodynamics, neotectonic activity, active seismicity and potential seismic hazard in this region of North China.

  2. Open system evolution of trachyte and phonolite magmas from the East Africa Rift

    NASA Astrophysics Data System (ADS)

    Anthony, E. Y.; Espejel, V.

    2011-12-01

    The Quaternary Suswa volcanic system consists of a large shield volcano that developed two nested summit calderas and erupted metaluminous to peralkaline trachyte and phonolite lavas and tuffs. Suswa is adjacent to the Greater Olkaria Volcanic Center, Longonot, Eburru, and Menengai volcanic systems, which erupted trachyte, comendite, and pantellerite. These volcanoes comprise the Central Kenya Peralkaline Province and are the site of active geothermal energy production and exploration. Mafic to intermediate lavas (Elementieta, Ndabibi, and Lolonito-Akira-Tandamara volcanic fields) lie in the rift floor between the shield volcanoes and occur as components of mixed magmas within the complexes. Suswa includes two suites of trachyte-phonolite lavas and tuffs. The first suite (C1) consists of lavas that built the original shield volcano and lavas and tuffs related to the formation of the first caldera; the second suite (C2) consists of lavas and tuffs erupted during and after the formation of the second caldera. Trachyte-carbonate immiscibility has been recorded in C1 ash flow units. The lavas and tuffs of the C2 suite are generally less peralkaline and more silica undersaturated than those of the C1 suite and did not share a common parental magma. Geochemical modeling precludes fractional crystallization as the sole process for Suswa magmas. Instead, assimilation of syenitic material (probably the crystal mush left over from C1 fractional crystallization), resorption, and mixing between the mafic to intermediate lavas satellite to the shield volcanoes have contributed to the composition and eruptive style of these volcanoes.

  3. Rio Grande rift: An overview

    NASA Astrophysics Data System (ADS)

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

    1987-11-01

    The Rio Grande rift of the southwestern United States is one of the world's principal continental rift systems. It extends as a series of asymmetrical grabens from central Colorado, through New Mexico, to Presidio, Texas, and Chihuahua, Mexico—a distance of more than 1000 km. Although the Rio Grande rift is closely related in timing and structural style to the contiguous Basin and Range extensional province, the two can be distinguished by a variety of geological and geophysical signatures. Rifts (both oceanic and continental) can be defined as elongate depressions overlying places where the entire lithosphere has ruptured in extension. The lithosphere of the Rio Grande rift conforms to this definition, in that: (1) the crust is moderately thinned—Moho depths range from about 45 km under the flanks to about 33 km beneath the rift axis. (2) anomalously low P n velocities (7.6-7.8 km s -1) beneath the rift and a long wavelength gravity low suggest that the asthenosphere is in contact with the base of the crust. The P-velocity is abnormally low (6.4-6.5 km s -1) in the lower half of the crust beneath the rift, suggesting high crustal temperatures. However, associated seismic and volcanologic data indicate the sub-rift lower crust is not dominated by a massive composite mafic intrusion such as is sometimes inferred for the East African rifts. Seismic and magnetotelluric data suggest the presence of a thin (< 1 km) sill-like contemporary midcrustal magma body which may perhaps extend intermittently along much of the length of the rift. Seismic and structural studies indicate a dominant horizontal fabric in the upper and middle crust. The brittle-ductile transition is at depths -15 km except for the major volcanic fields, where it rises to 2-3 km. Structural development of the rift occurred mainly during two time intervals: the early phase beginning at -30 Ma. and lasting 10-12 m.y., and the late phase extending from -10 to 3 Ma. The early phase involved extensive low-angle normal faulting throughout the rift region which was subsequently offset by high-angle normal faulting during the later deformational event. Volcanism of the Rio Grande rift is minor compared to some other continental rifts. Most of the volcanism is basaltic and occurred less than about 5 m.y. ago. Compositions range from alkalic to tholeiitic, with no unique spatial or temporal pattern. Magmas were probably derived from a variety of depths, indicating an unintegrated heat source with only local melting. Basaltic andesites and related calc-alkaline rocks erupted in the southern rift between about 30 and 18 m.y. ago were not uniquely related to the rifting process. Rather, the thermal pulse which generated these magmas was part of the previous, subduction-related event. Our interpretation of existing data concerning the evolution of the Rio Grande rift does not fit either simple active or passive "end-member" models. In particular, there is no compelling evidence for a major thermal event in the mantle uniquely associated with rifting. Yet heat—inherited from the immediately-preceding deformational regime—was certainly a critical factor in, and was probably a necessary condition for, rifting.

  4. Anatomy of a rift system: Triassic-Jurassic basins of eastern North America

    SciTech Connect

    Schlische, R.W. ); Olsen, P.E. )

    1991-03-01

    Basins containing the early Mesozoic Newark Supergroup formed during the incipient rifting of Pangaea. The basins are characterized by the following: (1) The border fault systems (BFS) represent reactivated older faults. (2) A regionally persistent northwest-southeast to west-northeast-east-southeast extension direction reactivated northeast- to north-striking structures as predominantly normal dip-slip faults. (3) The half-grabens are lozenge-shaped basins in which subsidence-fault slip was greatest at or near the center of the BFS and decreased to zero toward either end. (4) Transverse folds in the hanging walls immediately adjacent to the BFS formed as a result of higher-frequency variations in subsidence. (5) Subsidence also decreased in a direction perpendicular to the BFS. (6) Intrabasinal faults are overwhelmingly synthetic and predominantly post-depositional. (7) Younger strata progressively onlap prerift rocks of the hanging wall block; this indicates that the basins grew both in width and length as they filled. (8) In all basins initial sedimentation was fluvial, reflecting an oversupply of sediment with respect to basin capacity. (9) Sediments were derived largely from the hanging wall block, which sloped toward the basin, and from streams that entered the basin axially; a direct footwall source was minor, owing to footwall uplift. (10) In strike-slip-dominated basins, subsidence was considerably less than in dip-slip basins, and mosaics of strike- and dip-slip faults are common.

  5. Characterization of basement highs in hyper-extended rift systems: examples from the Err nappe, SE Switzerland.

    NASA Astrophysics Data System (ADS)

    Epin, Marie-Eva; Manatschal, Gianreto; Haupert, Isabelle; Decarlis, Alessandro

    2015-04-01

    Despite of the fact that many studies investigated magma-poor rifted margins, there are still open questions that are related to the nature of basement highs and the timing and processes related to their formation. While these questions are difficult to answer at present-day margins due to the lack of drill hole data, field analogues provide important insights and enable to find some answers to these questions. This is particularly true for the Err nappe in southeastern Switzerland, which is one of the world's few exposed and preserved rift-related hyper-extended domains. This nappe preserves a rift related extensional detachment system that is exposed over more than 200km2, characterized by distinctive black gouges and green cataclasites and preserving the relation to its hanging wall and footwall rocks and the pre-, syn-, and post-tectonic sediments. The aim of our study was to investigate the 3D architecture of the detachment system based on detailed mapping of this structure north and south of the Julier valley between Bivio and San Moritz in Central Grisons, SE Switzerland. Our results show the lateral variation of the morphology of the major detachment fault and its relation to extensional allochthons and the pre-, syn- and post-tectonic sediments. The main observation is that the architecture of the detachment system changes over very short distance across the Julier valley. While in the north the detachment is overlain by an allochthonous block (e.g. the Bardella block), to the south this block disappears and the detachment fault is exhumed at the seafloor. The mapping of the syn-tectonic sediments show that they are thick in the north and get thinner to the south where they are locally absent and the post-rift sediments directly overlie the detachment system. Furthermore the syn-tectonic sediments are locally characterized by basement clasts. These relationships suggest a rapid change from a domain where the detachment is overlain by allochthons and thick syn-tectonic sediments to a domain where the detachment is exposed. The lack of syn-rift sediments and the prominent hiatus suggest that the detachment formed a basement high south of the Julier valley. The overall observations are reminiscent of either a core-complex type structure or a lateral ramp of a detachment fault marking the lateral transition from a hanging wall to a footwall controlled topography. In our presentation we will expose the field relationships and will discuss the tectonic processes and the timing of these structures as well as discuss the nature of the structure controlling the observed 3D geometry of the detachment system.

  6. Cenozoic rift formation in the northern Caribbean

    NASA Technical Reports Server (NTRS)

    Mann, P.; Burke, K.

    1984-01-01

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

  7. Analogy between natural gas found in lakes of rift valley system of east Africa and its allied gas in Japan

    SciTech Connect

    Fukuta, O.

    1984-09-01

    The Afar triangle in northeastern Ethiopia is where the Red Sea rift, the Carlsberg Ridge of the Indian Ocean, and the Rift Valley system of east Africa meet. In 1979, J. Welhan and H. Craig reported that hydrothermal vents at 21/sup 0/N, on the East Pacific Rise, are discharging turbid waters. Mixtures of the plumes with ambient seawater contain significant amounts of dissolved H/sub 2/ and CH/sub 4/ as well as mantel-derived /sup 3/He-rich helium. The /sup 3/He//sup 4/He ratios of rock samples obtained earlier by J. Lupton and H. Craig from the Mid-Oceanic Ridge, including the Mid-Atlantic Ridge and the east Pacific Rise, are extremely high at an almost constant value of (1.3 +/- 0.2) x 10/sup -5/, which they defined as the MOR-type helium. However, the deep brines of the Red Sea contain about 1,000 times more methane than normal seawater does, according to Gold and Soter in 1980. Much evidence leads us to believe that large amounts of /sup 3/He-rich helium-bearing natural gas have been gushing out in many places of the Rift Valley of east Africa for a long time. In 1980, Gold and Soter stated that Lake Kivu, which occupies part of the East African rift valley, contains 50 million tons of dissolved methane for which there is no adequate microbial source. The Japanese Islands began to separate from the Asian continent during the early Miocene. The early Miocene was characterized by intensive volcanic activity that produced large amounts of pyroclastics and other volcanic rocks, generally called green tuff in Japan. It has been suggested that oil and gas in green tuff is derived from the upper mantle.

  8. Seismic and aseismic deformation along the East African Rift System from a reanalysis of the GPS velocity field of Africa

    NASA Astrophysics Data System (ADS)

    Déprez, Aline; Doubre, Cécile; Masson, Frédéric; Ulrich, Patrice

    2013-06-01

    The improvement of the geodetic coverage within the African Plate over the last decade together with an extended GPS position time-series allows improved accuracy in determining the velocity field than prior geodetic studies. Using this new velocity field of the whole African continent, the best model proposed here remains consistent with previous studies including the existence of two small plates along the East African Rift System (EARS, Victoria and Rovuma). We focus specifically on the velocities along this plate boundary by estimating both the geodetic and the seismic moment rate. Whereas we use a scalar form of the Kostrov relation to calculate the geodetic moment rate, the seismic moment rate is obtained by integrating the cumulative truncated Gutenberg-Richter earthquake distribution of local events in the 39-yr-long worldwide catalogue, using a maximum likelihood method. This statistical method allows us to take into account the probable incompleteness of the existing catalogue and to assume the seismic moment rate calculated from this short catalogue to be representative of the long-term seismic deformation. The comparison of geodetic and seismic energy release sheds light on the variations of mechanical behaviour related to intracontinental extension along the EARS. The southward increase, observed along the rift, of the proportion of geodetic moment seismically accommodated suggests a significant control of the thermal structure associated with different states of rifting evolution.

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

    USGS Publications Warehouse

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

    2004-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Corti, Giacomo

    2009-09-01

    The Main Ethiopian Rift is a key sector of the East African Rift System that connects the Afar depression, at Red Sea-Gulf of Aden junction, with the Turkana depression and Kenya Rift to the South. It is a magmatic rift that records all the different stages of rift evolution from rift initiation to break-up and incipient oceanic spreading: it is thus an ideal place to analyse the evolution of continental extension, the rupture of lithospheric plates and the dynamics by which distributed continental deformation is progressively focused at oceanic spreading centres. The first tectono-magmatic event related to the Tertiary rifting was the eruption of voluminous flood basalts that apparently occurred in a rather short time interval at around 30 Ma; strong plateau uplift, which resulted in the development of the Ethiopian and Somalian plateaus now surrounding the rift valley, has been suggested to have initiated contemporaneously or shortly after the extensive flood-basalt volcanism, although its exact timing remains controversial. Voluminous volcanism and uplift started prior to the main rifting phases, suggesting a mantle plume influence on the Tertiary deformation in East Africa. Different plume hypothesis have been suggested, with recent models indicating the existence of deep superplume originating at the core-mantle boundary beneath southern Africa, rising in a north-northeastward direction toward eastern Africa, and feeding multiple plume stems in the upper mantle. However, the existence of this whole-mantle feature and its possible connection with Tertiary rifting are highly debated. The main rifting phases started diachronously along the MER in the Mio-Pliocene; rift propagation was not a smooth process but rather a process with punctuated episodes of extension and relative quiescence. Rift location was most probably controlled by the reactivation of a lithospheric-scale pre-Cambrian weakness; the orientation of this weakness (roughly NE-SW) and the Late Pliocene (post 3.2 Ma)-recent extensional stress field generated by relative motion between Nubia and Somalia plates (roughly ESE-WNW) suggest that oblique rifting conditions have controlled rift evolution. However, it is still unclear if these kinematical boundary conditions have remained steady since the initial stages of rifting or the kinematics has changed during the Late Pliocene or at the Pliocene-Pleistocene boundary. Analysis of geological-geophysical data suggests that continental rifting in the MER evolved in two different phases. An early (Mio-Pliocene) continental rifting stage was characterised by displacement along large boundary faults, subsidence of rift depression with local development of deep (up to 5 km) asymmetric basins and diffuse magmatic activity. In this initial phase, magmatism encompassed the whole rift, with volcanic activity affecting the rift depression, the major boundary faults and limited portions of the rift shoulders (off-axis volcanism). Progressive extension led to the second (Pleistocene) rifting stage, characterised by a riftward narrowing of the volcano-tectonic activity. In this phase, the main boundary faults were deactivated and extensional deformation was accommodated by dense swarms of faults (Wonji segments) in the thinned rift depression. The progressive thinning of the continental lithosphere under constant, prolonged oblique rifting conditions controlled this migration of deformation, possibly in tandem with the weakening related to magmatic processes and/or a change in rift kinematics. Owing to the oblique rifting conditions, the fault swarms obliquely cut the rift floor and were characterised by a typical right-stepping arrangement. Ascending magmas were focused by the Wonji segments, with eruption of magmas at surface preferentially occurring along the oblique faults. As soon as the volcano-tectonic activity was localised within Wonji segments, a strong feedback between deformation and magmatism developed: the thinned lithosphere was strongly modified by the extensive magma intrusion and extension was facilitated

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

    PubMed

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S.; Ófeigsson, Benedikt; Rafn Heimisson, Elías; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Guðmundsson, Gunnar B.; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T.; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert; Ágústsdóttir, Thorbjörg; Björnsson, Helgi; Bean, Christopher J.

    2015-04-01

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

  13. The Magma Plumbing System of Dabbahu and Gabho volcanoes (Afar rift, Ethiopia) from InSAR, GPS and Seismicity data

    NASA Astrophysics Data System (ADS)

    Wright, T. J.; Ayele, A.; Belachew, M.; Bennati, L.; Calais, E.; Ebinger, C. J.; Hamling, I. J.; Keir, D.; Lewi, E.; Pagli, C.; Yirgu, G.

    2008-12-01

    In September 2005, a 60-km-long dike, up to 8 meters thick, was intruded into the Dabbahu rift segment, a nascent seafloor spreading center on the Nubia-Arabia plate boundary in the Afar Depression of Northern Ethiopia. Localized subsidence of 2-3 meters at Dabbahu and Gabho, measured by InSAR, indicated that some of the intrusion was fed from shallow magma chambers beneath Dabbahu and Gabho volcanoes, two centers of focused silicic volcanism at the northern end of the rift segment. An array of 9 seismometers recorded seismicity from October 2005 to April 2006 -- three were located in the area between Dabbahu and Gabho, where an explosive, rhyolite eruption took place on 26 September 2005. Ten continuously-recording GPS receivers were installed in January 2006, including one on the flanks of Dabbahu and one on Gabho. In addition, Envisat was programmed to acquire SAR data on every overpass since September 2005, enabling us to build time series of recent deformation. The data show that: (i) Gabho began to uplift aseismically in November/December 2005. Uplift was most rapid initially, with 25 cm in the first six months, and continued until summer 2007. Since then it has been stable. (ii) The southern flank of Dabbahu began subsiding immediately after the main dyke intruded, continuing until ~March 2006, and reaching a maximum of ~10 cm. This occurred above a band of seismicity that dips to the north beneath Dabbahu. (iii) The center of Dabbahu began to uplift in ~March 2006, and has continued steadily for at least 2 years. The total uplift (by July 2008) was ~50 cm. Seismicity in the first six months was concentrated at 3 km depth beneath the uplifting area. (iv) Gabho and Dabbahu did not subside during the dyke injections that have occurred in the southern half of the rift segment since 2005 (nine by July 2008). Despite the remarkably similar behavior to the Krafla system in Iceland, which underwent a rifting episode from 1975 to 1984, these observations require a more complex magma plumbing system. In contrast to the single inferred shallow chamber beneath Krafla, multiple magmatic sources are required in the Dabbahu rift.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    The East African rift system in Ethiopia formed in the Earth's youngest flood basalt province, and provides a natural laboratory to study the geochemistry of bimodal volcanism and its implications for plume-derived magmatism, mantle-lithosphere interactions and evolution of continental rifts from plate extension to rupture. Our geochemical studies of the ~6 Ma to recent eruptive products from Gona within the Afar Rift Zone are understood in context of crustal and upper mantle seismic imaging studies that provide constraints on spatial variations. Geochemical (major element, trace element and isotope) analyses of basalts and rhyolitic tuff from Gona indicate a common magma source for these bimodal volcanics. Light rare earth elements (LREEs) are enriched with a strong negative Eu anomaly and a positive Ce anomaly in some of the silicic volcanic rocks. We observe strong depletions in Sr and higher concentrations of Zr, Hf, Th, Nb and Ta. We hypothesize that the silicic rocks may be residues from a plume-derived enriched magma source, following partial melting with fractional crystallization of plagioclase at shallow magma chambers. The absence of Nb-Ta anomaly shows no crustal assimilation by magmas. Sr isotopes, in conjunction with Nd and Pb isotopes and a strong Ce anomaly could reflect interaction of the parent magma with a deep saline aquifer or brine. Nd isotopic ratios (?Nd = 1.9 to 4.6) show similarity of the silicic tuffs and basalts in their isotopic compositions except for some ~6 Ma lavas showing MORB-like values (?Nd = 5 to 8.7) that suggest involvement of the asthenosphere with the plume source. Except for one basaltic tuff, the whole rock oxygen isotopic ratios of the Gona basalts range from +5.8‰ to +7.9‰, higher than the ? values for typical MORB, +5.7. The oxygen isotopes in whole rocks from the rhyolite tuffs vary from 14.6‰ to 20.9‰ while their Sr isotope ratios <0.706, indicative of post-depositional low T alteration of these silicic rocks by a fluid derived from seawater or some crustal fluid not enriched in radiogenic Sr. The bimodality of the volcanic rocks may be genetically related by fractional crystallization or by partial melting of a hydrothermally altered mafic crust from earlier magma generation in the rift, without continental crustal assimilation. The geochemical data, along with geophysical and geodetic studies, assist our understanding of the tectonics of continental break up and plume magmatism in the Afar depression and the East African Rift system.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  16. The northwest-trending Euphrates graben sys-tem is an aborted intracontinental rift of Late

    E-print Network

    rift that also holds signifi- cant petroleum reserves, but a comprehensive anal- ysis of its history, from a possible Proterozoic suture 1173 ©Copyright 1998. The American Association of Petroleum Petroleum Company, Ministry of Petroleum and Mineral Resources, Damascus, Syria. Seismic and well data

  17. Control of rift obliquity on the evolution and segmentation of the main Ethiopian rift

    NASA Astrophysics Data System (ADS)

    Corti, Giacomo

    2008-04-01

    The main Ethiopian rift is an active rift in the break-up stage, and it marks the incipient boundary between the Nubia and Somalia plates. Rifting started with the activation of large boundary faults and diffuse volcanism, followed by focused magmatism and faulting in the rift floor, along step-like segments oblique to the rift axis that now act as a protoridge for future seafloor spreading. This concentration of volcano-tectonic activity has been thought to be either magma assisted or controlled by a change in rift kinematics, with a late oblique rifting phase that would have caused the development of the step-like fault segments that focused magma upwelling. Geodetic, seismic and stress-field data confirm current oblique rifting kinematics, but plate kinematics models do not predict a change in Nubia-Somalia motion in the past 11 million years. Here, I use lithospheric-scale analogue models of oblique rifting to analyse the development of the main Ethiopian rift. I find that neither magma weakening nor a change in plate kinematics are required to simulate a two-phase evolution with successive activation of differently oriented fault systems. I conclude that rift evolution and segmentation are controlled by rift obliquity, independent of magmatic processes.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    SciTech Connect

    Bartok, P. )

    1993-02-01

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

  20. Parga Chasma: Coronae and Rifting on Venus

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  1. Continental Rifts: Evolution, Structure and Tectonics

    NASA Astrophysics Data System (ADS)

    Bally, A. W.

    Twenty one “friends of continental rifts” wrote Continental Rifts: Evolution, Structureand Tectonics. They define the object of their passion as elongate tectonic depressions along which the entire lithosphere has been modified by extension. Strictly speaking, passive margins and highly extended terranes such as the Basin and Range are not included in this definition, but the authors consider them to be related to continental rifts. The authors hail from academia and set as their main goal “an improved understanding of the fundamental lithospheric processes of rifting, with primary focus on deep structures and processes associated with rifting.” Consequently, many well-known extensional systems, for example, the North Sea grabens, the Suez Basin, onshore and offshore eastern China, and large areas of southeast Asia, are barely considered. Rift aficionados from the petroleum industry will find very little to interest them in this book.

  2. The provenance and chemical variation of sandstones associated with the Mid-continent Rift System, U.S.A.

    USGS Publications Warehouse

    Cullers, R.L.; Berendsen, P.

    1998-01-01

    Sandstones along the northern portion of the Precambrian Mid-continent Rift System (MRS) have been petrographically and chemically analyzed for major elements and a variety of trace elements, including the REE. After the initial extrusion of the abundant basalts along the MRS, dominantly volcaniclastic sandstones of the Oronto Group were deposited. These volcaniclastic sandstones are covered by quartzose and subarkosic sandstones of the Bayfield Group. Thus the sandstones of the Oronto Group were derived from previously extruded basalts, whereas, the sandstones of the Bayfield Group were derived from Precambrian granitic gneisses located on the rift flanks. The chemical variation of these sandstones closely reflects the changing detrital modes with time. The elemental composition of the sandstones confirms the source lithologies suggested by the mineralogy and clasts. The Oronto Group sandstones contain lower ratios of elements concentrated in silicic source rocks (La or Th) relative to elements concentrated in basic source rocks (Co, Cr, or Sc) than the Bayfield Group. Also, the average size of the negative Eu anomaly of the sandstones of the Oronto Group is significantly less (Eu/Eu* mean ?? standard deviation = 0.79 ?? 0.13) than that of the Bayfield Group (mean + standard deviation = 0.57 ?? 0.09), also suggesting a more basic source for the former than the latter. Mixing models of elemental ratios give added insight as to the evolution of the rift. These models suggest that the volcanistic sandstones of the lower portion of the Oronto Group are derived from about 80 to 90 percent basalt and 10 to 20 percent granitoids. The rest of the Oronto Group and the lower to middle portion of the Bayfield Group could have formed by mixing of about 30 to 60 percent basalt and 40 to 70 percent granitoids. The upper portion of the Bayfield Group is likely derived from 80 to 100 percent granitoids and zero to 20 percent basalt.

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

    USGS Publications Warehouse

    Behrendt, John C.; Cooper, A.

    1991-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

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

    USGS Publications Warehouse

    Siddoway, C.S.

    2007-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  7. The subsurface structure and stratigraphic architecture of rift-related units in the Lishu Depression of the Songliao Basin, China

    NASA Astrophysics Data System (ADS)

    Wang, Hongyu; Fan, Tailiang; Wu, Yue

    2015-03-01

    This contribution reports the basin configuration feature, stratigraphy and sedimentary architecture of the Lishu Depression in the Songliao Basin, China. The activity rate, distribution and style of local faulting demonstrate the timing and extent of regional rifting. Distinct episodes of compressional tectonic activity caused uplift and exposure of strata evident as the traditional syn- and post-rift stages of basin evolution. These episodes led to the sequential denudation of the Upper Jurassic Huoshiling Formation, Lower Cretaceous Yingcheng and Denglouku Formations, and corresponding regional unconformities. Acting in tandem with regional compression, activity along the major boundary faults influenced the evolving basin configuration, as well as seismic sequences and sedimentary patterns. Seismic, well log and drill core data described here show subdivision sections of the Lishu Depression strata according to discrete phases of the traditional syn-rift stage of deposition. We refer to these sub-stages as the initial rifting, the intensive rifting and the recession phases. The basin configuration shifted from a graben/half-graben configuration during the initial rifting phase, to a dustpan-shaped half-graben pattern during the subsequent phase of intensive rifting, and finally into a gentle sedimentary basin during the final recession phase. The early seismic sequence divides into a lowstand systems tract (LST), transgressive systems tract (TST) and highstand systems tract (HST). Evidence of the LST within the seismic sequence becomes less apparent with the intensive rifting phase, while the HST occupied an increasing proportion of the section. The shallow water depositional fill formed during the final recession phase consists only of TST and HST components. Depositional environment then shifts from alluvial fan and shallow lacustrine systems to fan delta, braided delta - lake, and finally to a braided fluvial setting. The vertical stacking pattern shifts from retrogradational, to progradational, to aggradational. Identification of sub-structural units and interpretation of their genetic relationships helps clarify basin evolution, and thus serves larger-scale continental basin analysis.

  8. Relations between deformation and sediment-hosted copper mineralization: Evidence from the White Pine part of the Midcontinent rift system

    SciTech Connect

    Mauk, J.L.; Kelly, W.C.; Pluijm, B.A. van der ); Seasor, R.W. )

    1992-05-01

    Detailed studies over the past decade have significantly extended and revised our knowledge of the geologic history of the well-known White Pine mining district of northern Michigan, and indicate that the location of faults exerted a strong control on copper mineralization in this part of the Midcontinent rift system. At White Pine there is evidence for three episodes of faulting: (1) synsedimentary faulting, (2) subsequent high-angle, dominantly normal faulting, and (3) thrusting. Two stages of copper mineralization are present at White Pine and in the nearby Presque Isle syncline. The first, main-stage mineralization, formed a classic sediment-hosted stratiform copper deposit during early diagenesis. Synsedimentary faults may have provided important conduits for cupriferous brines flowing from underlying red beds of the Copper Harbor Conglomerate into the reduced silts and shales of the Nonesuch Formation, where main-stage copper sulfides and native copper were precipitated. The second stage of copper mineralization was synchronous with thrusting and introduced additional copper to the White Pine ore body and the Presque Isle syncline. Thrust faults and cogenetic tear faults provided conduits for second-stage mineralizing fluids. Collectively, these observations indicate strong control by regional deformation on fluid migration and mineralization in the rocks of the Midcontinent rift, similar to proposed relations between deformation and mineralization in other tectonic settings.

  9. Calibration Systems Final Report

    SciTech Connect

    Myers, Tanya L.; Broocks, Bryan T.; Phillips, Mark C.

    2006-02-01

    The Calibration Systems project at Pacific Northwest National Laboratory (PNNL) is aimed towards developing and demonstrating compact Quantum Cascade (QC) laser-based calibration systems for infrared imaging systems. These on-board systems will improve the calibration technology for passive sensors, which enable stand-off detection for the proliferation or use of weapons of mass destruction, by replacing on-board blackbodies with QC laser-based systems. This alternative technology can minimize the impact on instrument size and weight while improving the quality of instruments for a variety of missions. The potential of replacing flight blackbodies is made feasible by the high output, stability, and repeatability of the QC laser spectral radiance.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  11. Rift processes and crustal structure of the Amundsen Sea Embayment, West Antarctica, from 3D potential field modelling

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The westward-tilted Kivu rift in East Africa is bounded by the ~100 km-long, seismically active West Kivu border fault, and dammed at its northern end by flows from the Virunga Volcanic Province. Earlier work delineated faults along the basin margins, but little was known of active faults beneath Lake Kivu, and the lithospheric structure was unexplored. The aims of this study are to determine the kinematics of normal faults and their relation to pre-existing basement structures; to examine the locations of earthquakes with respect to faults in order to delineate zones of active faulting; to evaluate models for the modification of lithosphere by extension and mantle plume processes using seismic shear wave splitting measurements; and to evaluate the role of volcanic loading within the Virunga volcanic province on the evolution of the Kivu basin. We determine rift fault and volcanic fissure locations and orientations using merged high-resolution CHIRP bathymetric and Space Radar Topography Mission data. The majority of faults in the northern sector strike NNE, whereas NE faults are equally important in the southern basin, marking the Kivu-Rusizi accommodation zone. Seismic data was acquired from an 8-station array deployed between March 2012 and April 2013. Although the majority of earthquakes beneath the rift (excluding the active volcanoes) occur at depths of 8-20 km, unusually shallow earthquakes (2-4 km) are located along submerged faults within the East Kivu basin and suggest high pore pressures within the upper crust. Using simple elastic plate flexure model calculations we estimate the maximum deflection of the plate to be ~7 km, using an effective elastic thickness of ~7.5 km. We propose that the rapid subsidence of the ~400 m deep northern Kivu basin occurred in response to volcanic construction. We evaluate models for the modification of lithosphere using shear wave splitting measurements. Splitting results with backazimuths ranging from 88? - 98? and 240? - 286? showed fast polarization directions in close agreement with the apparent plate motion (330?), while results ranging from 32? - 48? have fast polarization directions consistent with the magmatic fabric of the Eastern Kivu Province (NE), suggesting that fluid flow associated with mantle plume processes have modified the lithosphere.

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

    NASA Astrophysics Data System (ADS)

    Tedrow, Christine Atkins

    The primary goal in this study was to explore remote sensing, ecological niche modeling, and Geographic Information Systems (GIS) as aids in predicting candidate Rift Valley fever (RVF) competent vector abundance and distribution in Virginia, and as means of estimating where risk of establishment in mosquitoes and risk of transmission to human populations would be greatest in Virginia. A second goal in this study was to determine whether the remotely-sensed Normalized Difference Vegetation Index (NDVI) can be used as a proxy variable of local conditions for the development of mosquitoes to predict mosquito species distribution and abundance in Virginia. As part of this study, a mosquito surveillance database was compiled to archive the historical patterns of mosquito species abundance in Virginia. In addition, linkages between mosquito density and local environmental and climatic patterns were spatially and temporally examined. The present study affirms the potential role of remote sensing imagery for species distribution prediction, and it demonstrates that ecological niche modeling is a valuable predictive tool to analyze the distributions of populations. The MaxEnt ecological niche modeling program was used to model predicted ranges for potential RVF competent vectors in Virginia. The MaxEnt model was shown to be robust, and the candidate RVF competent vector predicted distribution map is presented. The Normalized Difference Vegetation Index (NDVI) was found to be the most useful environmental-climatic variable to predict mosquito species distribution and abundance in Virginia. However, these results indicate that a more robust prediction is obtained by including other environmental-climatic factors correlated to mosquito densities (e.g., temperature, precipitation, elevation) with NDVI. The present study demonstrates that remote sensing and GIS can be used with ecological niche and risk modeling methods to estimate risk of virus establishment in mosquitoes and transmission to humans. Maps delineating the geographic areas in Virginia with highest risk for RVF establishment in mosquito populations and RVF disease transmission to human populations were generated in a GIS using human, domestic animal, and white-tailed deer population estimates and the MaxEnt potential RVF competent vector species distribution prediction. The candidate RVF competent vector predicted distribution and RVF risk maps presented in this study can help vector control agencies and public health officials focus Rift Valley fever surveillance efforts in geographic areas with large co-located populations of potential RVF competent vectors and human, domestic animal, and wildlife hosts. Keywords. Rift Valley fever, risk assessment, Ecological Niche Modeling, MaxEnt, Geographic Information System, remote sensing, Pearson's Product-Moment Correlation Coefficient, vectors, mosquito distribution, mosquito density, mosquito surveillance, United States, Virginia, domestic animals, white-tailed deer, ArcGIS

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

    USGS Publications Warehouse

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

    2009-01-01

    To characterize mercury (Hg) isotopes and isotopic fractionation in hydrothermal systems we analyzed fluid and precipitate samples from hot springs in the Yellowstone Plateau volcanic field and vent chimney samples from the Guaymas Basin sea-floor rift. These samples provide an initial indication of the variability in Hg isotopic composition among marine and continental hydrothermal systems that are controlled predominantly by mantle-derived magmas. Fluid samples from Ojo Caliente hot spring in Yellowstone range in ?202Hg from - 1.02‰ to 0.58‰ (± 0.11‰, 2SD) and solid precipitate samples from Guaymas Basin range in ?202Hg from - 0.37‰ to - 0.01‰ (± 0.14‰, 2SD). Fluid samples from Ojo Caliente display mass-dependent fractionation (MDF) of Hg from the vent (?202Hg = 0.10‰ ± 0.11‰, 2SD) to the end of the outflow channel (&delta202Hg = 0.58‰ ± 0.11‰, 2SD) in conjunction with a decrease in Hg concentration from 46.6pg/g to 20.0pg/g. Although a small amount of Hg is lost from the fluids due to co-precipitation with siliceous sinter, we infer that the majority of the observed MDF and Hg loss from waters in Ojo Caliente is due to volatilization of Hg0(aq) to Hg0(g) and the preferential loss of Hg with a lower ?202Hg value to the atmosphere. A small amount of mass-independent fractionation (MIF) was observed in all samples from Ojo Caliente (?199Hg = 0.13‰ ±1 0.06‰, 2SD) but no significant MIF was measured in the sea-floor rift samples from Guaymas Basin. This study demonstrates that several different hydrothermal processes fractionate Hg isotopes and that Hg isotopes may be used to better understand these processes.

  16. A new geodynamical thermal model of rift evolution, with application to the Dnieper Donets Basin, Ukraine

    NASA Astrophysics Data System (ADS)

    Starostenko, V. I.; Danilenko, V. A.; Vengrovitch, D. B.; Kutas, R. I.; Stovba, S. M.; Stephenson, R. A.; Kharitonov, O. M.

    1999-11-01

    A model of the lithosphere, incorporating both dynamic and thermal processes, has been developed by solving a coupled system of differential equations governing stress and temperature in a 2-D block-structured geophysical medium. Designed to study the roles of tectonic and geothermal factors in continental rift formation and evolution, the model incorporates syn-sedimentary and/or erosional faulting of an upper crustal layer and allows the thermal regime of the lithosphere to be calculated through time. The method has been applied to the formation and evolution of the northwest Dnieper-Donets Basin (DDB) along one regional profile controlled by seismic and other geophysical and subsurface data. The results are compared with those published earlier for the same profile using different methods of modelling the rift and early post-rift development of the region. The final basement geometry at the end of the rifting stage predicted by the new model satisfactorily corresponds with geological data and is qualitatively similar to that predicted by the previously published models. However, the new results imply an important role for an active mechanism during rifting that generates greater mantle thinning than crustal thinning and elevated temperatures in the upper mantle beneath the rift.

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

    SciTech Connect

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

    1993-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Ojakangas, Richard W.; Dickas, Albert B.

    2002-03-01

    The Midcontinent Rift System (MRS) of central North America is a 1.1-Ga, 2500-km long structural feature that has been interpreted as a triple-junction rift developed over a mantle plume. As much as 20 km of subaerial lava flows, mainly flood basalts, are overlain by as much as 10 km of sedimentary rocks that are mostly continental fluvial red beds. This rock sequence, known as the Keweenawan Supergroup, has been penetrated by a few deep boreholes in the search for petroleum. In this paper, two deep boreholes in the Upper Peninsula of Michigan are described in detail for the first time. Both the Amoco Production #1-29R test, herein referred to as the St. Amour well, and the nearby Hickey Creek well drilled by Cleveland Cliffs Mining Services, were 100% cored. The former is 7238 ft (2410 m) deep and the latter is 5345 ft (1780 m) deep. The entirety of the stratigraphic succession of the Hickey Creek core correlates very well with the upper portion of the St. Amour core, as determined by core description and point-counting of 43 thin sections selected out of 100 studied thin sections. Two Lower Paleozoic units and two Keweenawan red bed units—the Jacobsville Sandstone and the underlying Freda Sandstone—are described. The Jacobsville is largely a feldspatholithic sandstone and the Freda is largely a lithofeldspathic sandstone. Below the Freda, the remaining footage of the St. Amour core consists of a thick quartzose sandstone unit that overlies a heterogenous unit of intercalated red bed units of conglomerate, sandstone, siltstone, and shale; black shale; individual basalt flows; and a basal ignimbritic rhyolite. This lower portion of the St. Amour core presents an enigma, as it correlates very poorly with other key boreholes located to the west and southwest. While a black shale sequence is similar to the petroleum-bearing Nonesuch Formation farther west, there is no conglomerate unit to correlate with the Copper Harbor Conglomerate. Other key boreholes are distributed over a 1300-km distance along the better known southwest arm of the triple-junction MRS, and can be correlated rather well with the units that are exposed in the Lake Superior region. However, a definitive explanation of the anomalous, deeper St. Amour stratigraphy is elusive and any explanation is tenuous. A possible explanation for this anomalous stratigraphy may be the geographic proximity of the St. Amour borehole to the Keweenawan Hot Spot (mantle plume), the suggested thermal force behind the development of the MRS. Similarly, a drastic change in structural architecture may be explained by this geographic relationship. Thus, within the locale of this rifting center, complexities of expansion tectonics may well be responsible for igneous and sedimentary sequences that differ considerably from those found farther west along the rift arm.

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

    SciTech Connect

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

    1991-04-01

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

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

    USGS Publications Warehouse

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

    1986-01-01

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

  1. Elliptical caldera formation throughout the Kenyan Rift

    NASA Astrophysics Data System (ADS)

    Robertson, Elspeth; Biggs, Juliet; Cashman, Katharine; Floyd, Michael; Vye-Brown, Charlotte

    2014-05-01

    Many of the world's calderas are elliptical in shape, and their orientation is often used as a proxy for the local stress regime. However, in some rift settings, pre-existing structural trends have been shown to control caldera orientation. We test these competing hypotheses in the Kenyan Rift, which consists of two distinct rift segments, with different tectonic and magmatic characteristics. Of the fourteen Quaternary volcanoes lying along the central rift axis, seven have undergone caldera collapse and six are highly elliptical. We present a remote-sensing study that investigates the structural and tectonic control on caldera ellipticity and orientation within the Kenyan Rift. Satellite-based mapping using ArcGIS on imagery derived from ASTER and GDEM data to identify the orientations of the main East African Rift border faults, intra-rift faults and the geometry of Kenyan calderas to determine the extensional setting, horizontal compressive stress orientations and the pre-existing rift fabric direction. Other data sources included the GPS-derived plate-kinematic model of East Africa and information from the literature. We find that deformation in the Kenyan Rift is characterised by orthogonal extension in the north and oblique opening in the south, suggesting that both tectonic stresses and magmatic pressures drive intra-rift fault formation. The long axis elongation of calderas are orientated NW-SE in the north, aligned with pre-existing structures and perpendicular to recent rift-faults. In contrast, the long axes are aligned NE-SW in the southern group of volcanoes, at an angle which is highly oblique to the recent rift faults, but aligned with pre-existing structures. Thus we conclude that in oblique continental rifts, pre-existing structures play a dominant role in the rise of magma through the crust. Understanding the geometry of caldera systems gives us important information as to the structural controls on magmatic and tectonic behaviour in extensional settings and the mechanisms by which continental rifts evolve from fault-controlled basins into mid-ocean ridges.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

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

    NASA Astrophysics Data System (ADS)

    Rychert, Catherine A.; Harmon, Nicholas

    2015-04-01

    Heating, melting, and stretching destroy continents at volcanic rifts. Mantle plumes are often invoked to thermally weaken the continental lithosphere and accommodate rifting through the influx of magma. However the relative effects of mechanical stretching vs. melt infiltration and weakening are not well quantified during the evolution of rifting. S-to-p (Sp) imaging beneath the Afar Rift provides additional constraints. We use two methodologies to investigate structure and locate robust features: 1) binning by conversion point and then simultaneous deconvolution in the frequency domain, and 2) extended multitaper followed by migration and stacking. We image a lithosphere-asthenosphere boundary at ~75 km beneath the flank of the Afar Rift vs. its complete absence beneath the rift. Instead, a strong velocity increase with depth at ~75 km depth is imaged. Beneath the rift axis waveform modeling suggests the lack of a mantle lithosphere with a velocity increase at ~75 km depth. Geodynamic models that include high melt retention and suppress thermal convection easily match the required velocity-depth profile, the velocity increase arising from a drop in melt percentage at the onset of decompression melting. Whereas, models with conservative melt retention that include thermal buoyancy effects cannot reproduce the strong velocity increase. The shallow depth of the onset of melting is consistent with a mantle potential temperature = 1350 - 1400°C, i.e., typical for adiabatic decompression melting. Trace element signatures and geochemical modeling have been used to argue for a thick lithosphere beneath the rift and slightly higher mantle potential temperatures ~1450°C, although overall, given modeling assumptions, the results are not in disagreement. Therefore, although a plume initially destroyed the mantle lithosphere, its influence directly beneath Afar today is not strong. Volcanism continues via adiabatic decompression melting assisted by strong melt buoyancy effects. This contrasts with a similar feature at much deeper depth, ~150 km, beneath Hawaii, Iceland, and Galapagos. Improved high resolution imaging of rifting, ridges, and hotspots in a variety of stages and tectonic settings will increase constraints on the forces sustaining volcanism and the factors that dictate the style of breakup beneath rifts.

  6. Cenozoic rift tectonics of the Japan Sea

    SciTech Connect

    Kimura, K.

    1988-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  8. New magnitude scales M L and spectrum-based M w for the area around Shanxi Rift System, North China

    NASA Astrophysics Data System (ADS)

    Li, Bin; Havskov, Jens; Ottemöller, Lars; Sørensen, Mathilde Bøttger

    2015-01-01

    A new locally calibrated M L scale was derived for the area around the Shanxi rift system, North China, from 83 events recorded on 56 stations of the Shanxi Seismic Network (SSN) resulting in 2,633 observations during the period of 2008-2012. It is expressed as M L = log( A) + 0.80log( R) + 0.00187 R - 1.4, where A is the maximum amplitude of vertical component in nanometer (nm) measured on a simulated Wood-Anderson seismogram at a hypocentral distance R. The new M L scale is valid for distances up to 600 km and is an improvement comparing to the currently used SSN scale, with a reduction in variance of 39 % in magnitude residuals. The moment magnitude M w was also calculated for the whole data set based on spectral analysis. To validate the Q-function used for spectral M w, we carried out moment tensor inversion for 17 moderate size events and selected the regional attenuation model which gave spectral M w on average closest to moment tensor M w. The most appropriate Q-function was found to be Q( f) = 299.4 f 0.563. The determination of the M w magnitudes makes it possible to derive a relationship between the M L and M w scales of this region, which is expressed as M w = 0.85 M L + 0.58, similar to relationships found elsewhere for similar tectonic environments.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Park, Munjae; Jung, Haemyeong; Kil, Youngwoo

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Gawthorpe, Robert; Ford, Mary

    2015-04-01

    Existing models for the tectono-sedimentary evolution of rift basins are strongly linked the growth and linkage of normal fault segments and localization of fault activity. Early stages of faulting (rift initiation phase) are characterized by distributed, short, low displacement fault segments, subdued fault-related topography and small depocentres within which sedimentation keeps pace with subsidence. Following linkage and displacement localization (rift climax phase), deformation if focused onto major, crustal-scale fault zones with kilometre-scale displacement. These major faults generate pronounced tilted fault-block topography, with subsidence rates that outpace sedimentation causing a pronounced change to deep-water deposition. Such models have been successful in helping to understand the gross structural and sedimentary evolution of rift basins, but recent work has suggested that pre-existing structures, normal fault interaction with pre-rift salt and antecedent drainage systems significantly alter this initiation-to-climax perspective of rift basin development. The E-W-striking, Pliocene-Pleistocene Corinth rift, central Greece, is an excellent natural laboratory for studying the tectono-sedimentary evolution of rift basins due to its young age, excellent onshore exposure of syn-rift structure and stratigraphy and extensive offshore seismic data. The rift cuts across the NW-SE-striking Hellenide mountain belt and has migrated northward and westward during its evolution. The Hellenide mountain belt significantly influences topography and drainage in the west of the rift. High topography and large antecedent drainage systems, focused along palaeovalleys, provided high sediment flux to NE-flowing alluvial systems that overfilled early-rift depocentres. Further east, away from the main antecedent drainage networks, contemporaneous deposits comprise deep-lacustrine turbidite channel and lobe complexes and basinal marls. Thus the stratigraphic expression within the Pliocene rift fill is similar to rift initiation in high sediment flux locations in the west and rift climax in low sediment flux locations in the east. Major shifts in the locus of fault activity within the Corinth Rift further complicate tectono-stratigraphy analysis of its basin fill. Pliocene depocentres are largely located onshore, south of the present-day Gulf of Corinth and involved activity that was distributed among north- and south-dipping faults. A northward shift in the southern rift margin in the early Pleistocene, established the present-day Gulf of Corinth as the site of several main depocentres and caused abandonment, uplift and reworking of a large portion of the Pliocene rift. Changes in the locus of fault activity during the Pleistocene record a change from activity on north- and south-dipping faults to mainly north-dipping faults. Such shifts in fault activity have a profound effect on the basin fill, with new footwall areas subject to subaerial exposure and incision while contemporaneous hangingwall depocentres undergo rapid subsidence and drowning. Such local complexity is not surprising, but factors such as major antecedent sediment transport pathways and marked temporal and spatial shifts in fault activity make application of conventional tectono-sedimentary subdivsions of pre-, syn-, and post-rift difficult to apply at the basin-scale.

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

    NASA Astrophysics Data System (ADS)

    Huismans, Ritske S.

    2015-04-01

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

  13. Style of rifting and the stages of Pangea breakup

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  14. A simple continental rift classification

    NASA Astrophysics Data System (ADS)

    Merle, Olivier

    2011-12-01

    A continental rift is conventionally described as a thinning process of the lithosphere ultimately leading to the rupture of the continent and the formation of a mid-oceanic ridge. Rifting is the initial and fundamental process by which the separation of two continents into two tectonic plates takes place. Previous classifications, particularly the one into "active" and "passive" rifting, are briefly presented, together with their limitations. The new classification presented here links continental rifts to the major plate tectonics structures which are at the origin of their formation. Thus, four types of rift can be defined: the subduction-related rift, the plume-related rift, the mountain-related rift and the transform-related rift. A number of examples representative of these four types of rift are then presented. This classification is shown to lie at the heart of our understanding of the major plate tectonic processes at work on Earth.

  15. Cool-water carbonates in active rift systems: An Oligocene example from the West Coast region of New Zealand

    NASA Astrophysics Data System (ADS)

    Riordan, N. K.; Reid, C. M.; Bassett, K. N.

    2013-12-01

    Detailed sedimentology of a mixed carbonate-clastic succession along the west coast of New Zealand contains a record of an Oligo-Miocene cool-water carbonate factory operating within a tectonically active, scarp-bounded, extensional basin. Cool-water carbonates have not been previously documented in extensional systems, and our findings suggest this to be a function of lack of identification in the rock record rather than environmental incompatibility. The Little Wanganui formation accumulated within the northern reaches of the West Coast Rift System, exposed today in coastal outcrops in the West Coast region of New Zealand. Through a combination of field and petrographic analyses, the Little Wanganui succession is broken broadly into two parts, a lower section dominated by clastic boulder facies, clastic turbidites, and hemipelagic wackestones, and an upper section with an increasingly carbonate-rich composition. We interpret the clastic boulder facies as scarp-derived sediments deposited into a deep-water carbonate setting, reflecting active faulting on a basin-bounding fault scarp. The persistent, albeit diminishing contributions of clastic boulder facies upward is evidence of continued synsedimentary scarp growth. The upper section reflects cessation of faulting and burial of the scarp. The transition from clastic to carbonate-rich turbidites is interpreted to be a function of relative sea level fluctuations and diminished hinterland accompanied by expanding neritic and scarp-derived carbonate factories. Therefore, cool-water carbonate factories can persist in extensional settings (proximal to active faulting) as long as fault movement is episodic and other sources of clastic sediments (e.g. platform, hinterland) are not significant. The resulting lithologies will likely be mixed in composition with the relative abundance of clastic and carbonate components a function of fault activity,proximity of the shoreline and productivity of the carbonate factory.

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

    USGS Publications Warehouse

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

    2005-01-01

    We present an updated global earthquake catalogue for stable continental regions (SCRs; i.e. intraplate earthquakes) that is available on the Internet. Our database contains information on location, magnitude, seismic moment and focal mechanisms for over 1300 M (moment magnitude) ??? 4.5 historic and instrumentally recorded crustal events. Using this updated earthquake database in combination with a recently published global catalogue of rifts, we assess the correlation of intraplate seismicity with ancient rifts on a global scale. Each tectonic event is put into one of five categories based on location: (i) interior rifts/taphrogens, (ii) rifted continental margins, (iii) non-rifted crust, (iv) possible interior rifts and (v) possible rifted margins. We find that approximately 27 per cent of all events are classified as interior rifts (i), 25 per cent are rifted continental margins (ii), 36 per cent are within non-rifted crust (iii) and 12 per cent (iv and v) remain uncertain. Thus, over half (52 per cent) of all events are associated with rifted crust, although within the continental interiors (i.e. away from continental margins), non-rifted crust has experienced more earthquakes than interior rifts. No major change in distribution is found if only large (M ??? 6.0) earthquakes are considered. The largest events (M ??? 7.0) however, have occurred predominantly within rifts (50 per cent) and continental margins (43 per cent). Intraplate seismicity is not distributed evenly. Instead several zones of concentrated seismicity seem to exist. This is especially true for interior rifts/taphrogens, where a total of only 12 regions are responsible for 74 per cent of all events and as much as 98 per cent of all seismic moment released in that category. Of the four rifts/taphrogens that have experienced the largest earthquakes, seismicity within the Kutch rift, India, and the East China rift system, may be controlled by diffuse plate boundary deformation more than by the presence of the ancient rifts themselves. The St. Lawrence depression, Canada, besides being an ancient rift, is also the site of a major collisional suture. Thus only at the Reelfoot rift (New Madrid seismic zone, NMSZ, USA), is the presence of features associated with rifting itself the sole candidate for causing seismicity. Our results suggest that on a global scale, the correlation of seismicity within SCRs and ancient rifts has been overestimated in the past. Because the majority of models used to explain intraplate seismicity have focused on seismicity within rifts, we conclude that a shift in attention more towards non-rifted as well as rifted crust is in order. ?? 2005 RAS.

  17. How many rifts are there in West Africa?

    NASA Astrophysics Data System (ADS)

    Freeth, S. J.

    1984-02-01

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

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

    E-print Network

    depositional patterns by creating sites of uplift and erosion, by controlling pathways of sediment transport, and by defining the accommodation space for sediment deposition and preservation. The relationships among basin activities, have identified and mapped many of the world's subsurface rift basins (e.g., t

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rift Valley fever (RVF) is a mosquito-borne viral disease with pronounced health and economic impacts to domestic animals and humans in much of sub-Saharan Africa. Epizootics and epidemics of RVF are closely linked to the occurrence of the warm phase of the El Niño/Southern Oscillation (ENSO) phenom...

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    Sublatitudinal Baikal-Mondy (Tunka) left-lateral strike-slip fault accommodates North Mongolia submeridional rift basins opening (Darkhad and Khubsugul). It is the connecting link between the central and south-western parts of the Baikal rift system. We investigated the present-day activity of faulting on southern border of Mondy basin, which is due to their position at the junction of east-west trending active faults of the Baikal-Mondy fault system with submeridional structures of Khubsugul basin. The investigated area is characterized by high seismic activity. The epicenter of one of the strongest Mondy earthquake 1950 (Mw = 7.0) is located within the Mondy basin. Reconstruction of Late Cenozoic tectonic stress field shows a predominance of strike-slip deformation regime with NW-SE direction of the minimum compression axis and NE-SW direction of the maximum compression axis, which correlates with the present-day stress field derived from the data on earthquake focal mechanisms. On the top of the southern shoulder of Mondy basin a series of extended NE trending surface ruptures that cut the crust of weathering and bedrock across the local watershed were discovered. The rupture length reaches 180 m, width ruptures bedrock reaches 0.6 m. In the bedrock tectonic microfractures of NW and NE directions are dominated, but the NW trending surface ruptures are not observed. In the area of contemporary ruptures the geodetic measurements were carried out in the period 2009-2013. The results of processing the measurement data on the local testing ground showed that most divergent baselines undergoes extension with maximum values reaching 30 mm/year. The block experienced elongation in all directions, but the morphology of ruptures suggests that the main direction of stretching is NW-SE. The intensity of cracks opening decreases markedly with time. According to eyewitnesses known that active crack opening at about 100 mm/year started 4 years before Kultuk earthquake (27.08.2008, Mw = 6.3), the epicenter of which was located near the southern tip of the Baikal basin. The existence of centimeter level deformations is confirmed using of differential SAR interferometry method. A pair of images taken with an interval of 2 years highlighted the linear zone of active deformation in the centimeter level. The length of the structure is about 4 kilometers. The offset along the Line-of-Sight (LOS) direction is from 18 to 42 mm, which corresponds to the vertical displacement of 22 to 50 mm, or a horizontal displacement of 32 to 74 mm (Lebedeva et al., 2013). Along with the described ruptures we discovered normal faults with an amplitude greater than 2 m, which can be traced along the submeridional local watershed. The length of the normal faults reaches 800 m. The morphology and position of these faults can be attributed to their sackung structures. We conclude that the detected current surface ruptures have complex origins and develop under the influence of endogenous (tectonic) and exogenous forces. They founded along NE trending ancient tectonic structures within wide strike-slip zone and main direction of opening corresponds to the direction of extension of paleo- and present-day stress field. According to the dynamics of ruptures opening, the main phase of their formation is connected with stage of Kultuk earthquake preparation. As for geodetic data the block is stretched in all directions, it can be assumed that, by analogy with closely spaced sacking

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The Main Ethiopian Rift (MER) and Afar uniquely capture the final stages of transition from continental rifting in the broader East African Rift System to incipient seafloor spreading above a mantle hotspot. Studies of the region increasingly point to magmatism as a controlling factor on continental extension. However, the character and depth extent of these melt products remain contentious. Radial anisotropy derived from surface waves provides a unique diagnostic constraint on the presence of oriented melt pockets versus broader oriented anisotropic fabrics. This study investigates the thermal and radially anisotropic structure beneath the broader MER and Afar to resolve the magmatic character of the region and ultimately to understand the role of magmatism in present day rift development. We utilize 104 stations from 4 collocated arrays in the MER/Afar region to constrain radial anisotropy within the upper mantle via the inversion of Love- and Rayleigh-wave observations between 25 and 100 s period. We employ a multi-channel cross-correlation algorithm to obtain inter-station phase and amplitude information. The multi-channel phase observations are inverted for dynamic phase velocity across the array, which are then corrected for focusing and multipathing using the amplitude observations via Helmholtz tomography. We jointly invert Love- and Rayleigh-wave structural phase velocity measurements employing crustal constraints from co-located active source experiments to obtain estimates of Vsv and Vsh between 50 - 170 km depth. Preliminary results readily reveal the distinct shear velocity structure beneath the MER and Afar. Within the MER, shear velocity structure suggests pronounced low velocities accompanied by strong anisotropy between 80 - 140 km depth beneath the western Ethiopian plateau and rift valley. Within Afar, shear velocity structure is more varied with the slowest velocities found at shallow depths (less than 70 km depth), accompanied by weak anisotropy. The pronounced changes in the depth extent of slow velocities and strength of anisotropy interpreted to be associated with asthenosphere may reflect variations in the distribution and magnitude of temperature anomalies/melt between continental rifting in the MER and incipient, hot-spot influenced seafloor spreading in Afar.

  4. Organic Geochemical and tectonic evolution of the Midcontinent Rift system. Final report

    SciTech Connect

    Hayes, J.M.; Pratt, L.M.; Knoll, A.H.

    1992-12-31

    The older assemblages stand in contrast with the ca. 1000 Ma old Hunting Formation, Arctic Canada, which contains what may be the oldest evidence for modem algae - red algal fossils that compare closely with members of the extant family Bangiophyceae (Butterfield et al., 1990). Taken together the Nonesuch, Shaler, Hunting and other assemblages support the hypothesis of a major episode of eukaryotic diversification ca. 1000 Ma ago. Prior to this time, eukaryotic primary producers must have been physiologically primitive (and now extinct) algae whose abundance in ecosystems is poorly constrained by analogies with the present oceans. Cyanobacteria were major primary producers in a wide range of marine environments. After 1000 Ma, diversifying red green and chromophyte algae contributed significantly to primary production in all save microbial mat communities in restricted environments. It bears mention that such mat communities remained significant potential sources of buried organic matter until the end of the Proterozoic, necessitating exploration strategies that differ from those commonly employed for younger rocks (Knoll, in press). As in Phanerozoic basins, petroleum exploration in Proterozoic rocks requires tools for stratigraphic correlation. In Neoproterozoic (<1000 Ma) rocks, biostratigraphy is possible, and it is aided significantly by C and Sr isotopic chemostratigraphy. New data from the Shaler Group contribute to the construction of C and Sr isotopic curves for Neoproterozoic time, making possible much improved chronostratigraphy for this time interval. (Asmerom et al., 1991; Hayes et al., ms. in preparation).

  5. The Rwenzori Mountains of western Uganda - Aspects on the evolution of their remarkable morphology within the Albertine Rift

    NASA Astrophysics Data System (ADS)

    Bauer, F. U.; Karl, M.; Glasmacher, U. A.; Nagudi, B.; Schumann, A.; Mroszewski, L.

    2012-09-01

    The Rwenzori Mountains form a narrow mountain range within the western branch of the East African Rift System. They rise to heights of more than 5000 m a.s.l. and are composed of Precambrian metamorphic rocks. Lacking a volcanic origin the Rwenzoris are regarded as an extreme example of rift flank uplift and a key area to study rift-related uplift processes within an extensional setting. To determine these processes and underlying rift dynamics, the presented study provides constraints on the temporal and spatial exhumation history of the Rwenzori Mts. Recent and former geomorphology is investigated, addressing geomorphologic proxies as well as the cooling history. Associated erosion rates are derived from thermochronological data, allowing constraining relief changes over time. It could be demonstrated, that inherited tectonic structures play a major role in routing erosion processes. The cooling history of the Rwenzori Mts derived from low-temperature thermochronology reaches back to Jurassic times. Final exhumation was recorded for Neogene times, with differentiated erosion and uplift movements during the last 10 Ma and a fast final uplift of the Rwenzoris in the near past, where erosion could not compensate for (Bauer et al., 2010a). This paper integrates geomorphologic and thermochronological constraints, in order to provide a basis for understanding the development of the evolution of the Albertine Rift area, with focus placed on the Mesozoic and Cenozoic history of the central Rwenzori Mts.

  6. Continental rifting: a planetary perspective

    SciTech Connect

    Muehlberger, W.R.

    1985-01-01

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

  7. Open System evolution of peralkaline trachyte and phonolite from the Suswa volcano, Kenya rift

    NASA Astrophysics Data System (ADS)

    White, John Charles; Espejel-García, Vanessa V.; Anthony, Elizabeth Y.; Omenda, Peter

    2012-11-01

    Suswa is the southernmost volcanic center in the Central Kenya Peralkaline Province (CKPP) and represents the only salic center to have erupted significant volumes of peralkaline silica-undersaturated lavas and tuffs (trachyte, nepheline trachyte and phonolite). The eruptive products of Suswa can be clearly divided into two series, which correspond closely to the volcano's eruptive history. The earlier series (C1) includes lavas and tuffs that built the initial shield volcano (pre-caldera, unit S1) and erupted during the first caldera collapse (syn-caldera, units S2-S5); these rocks are dominated by peralkaline, silica-saturated to mildly under-saturated trachyte. The later series (C2) includes lavas and tuffs that erupted within the caldera structure following the initial collapse (post-caldera, units S6-S7) and during the creation of a second smaller, nested caldera and central "island block" (ring trench group, RTG, unit S8); these rocks are dominated by peralkaline phonolite. In this study, we combine mineralogical evidence with the results of major-element, trace-element, and thermodynamic modelling to propose a complex model for the origin of the Suswa volcano. From these results we conclude that C1 is the result of protracted fractional crystallization of a fairly "dry" alkali basalt (< 1 wt.% H2O) under relatively high pressure (400 MPa) and low oxygen fugacity (FMQ to FMQ-1). Although C1 appears to be primarily the result of closed system processes, a variety of open system processes are responsible for C2. We propose that crystallization of C1 trachyte resulted in the formation of a syenitic residue, which was assimilated (Ma/Mc = 0.1) during a later stage of recharge and differentiation of alkali basalt to produce post-caldera ne-trachyte. Post-caldera (S6-7) phonolites were in turn the result of fractional crystallization of this ne-trachyte. RTG phonolites, however, are the result of feldspar resorption prompted perhaps by magma recharge as evidenced by reverse zoning in alkali feldspar and linear compatible trace element patterns.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  9. Rift initiation with volatiles and magma

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  10. Intracontinental Rifts As Glorious Failures

    NASA Astrophysics Data System (ADS)

    Burke, K.

    2012-12-01

    Rifts: "Elongate depressions overlying places where the lithosphere has ruptured in extension" develop in many environments because rocks are weak in extension (Sengor 2nd edn. Springer Encycl. Solid Earth Geophys.). I focus on intra-continental rifts in which the Wilson Cycle failed to develop but in which that failure has led to glory because rocks and structures in those rifts throw exceptional light on how Earth's complex continental evolution can operate: The best studied record of human evolution is in the East African Rift; The Ventersdorp rifts (2.7 Ga) have yielded superb crustal-scale rift seismic reflection records; "Upside-down drainage" (Sleep 1997) has guided supra-plume-head partial melt into older continental rifts leading Deccan basalt of ~66Ma to erupt into a Late Paleozoic (~ 300Ma) rift and the CAMP basalts of ~201 Ma into Ladinian, ~230 Ma, rifts. Nepheline syenites and carbonatites, which are abundant in rifts that overlie sutures in the underlying mantle lithosphere, form by decompression melting of deformed nepheline syenites and carbonatites ornamenting those sutures (Burke et al.2003). Folding, faulting and igneous episodes involving decompression melting in old rifts can relate to collision at a remote plate margin (Guiraud and Bosworth 1997, Dewey and Burke 1974) or to passage of the rift over a plume generation zone (PGZ Burke et al.2008) on the Core Mantle Boundary (e.g.Lake Ellen MI kimberlites at ~206 Ma).

  11. The midcontinent rift system

    E-print Network

    Van Schmus, W. R.; Hinze, W. J.

    1985-01-01

    : mostly Keweenawan detritus (Oronto Group and equivalent) anorthosite - Early volcanic flows, - _ sills, dikes_ _ .... - - - - - Prevoleanie sediments ca. 1100 1100 to 1200 OZ Pre... arguments for the existence of two main igenous sequences in the Duluth Complex. The earlier phase involved extensive and efficient melt and crystal segregation to produce rock types with very contrasting mineralogies, such as peridotite, anorthosite...

  12. Petrogenesis of the Ni-Cu-PGE sulfide-bearing Tamarack Intrusive Complex, Midcontinent Rift System, Minnesota

    NASA Astrophysics Data System (ADS)

    Taranovic, Valentina; Ripley, Edward M.; Li, Chusi; Rossell, Dean

    2015-01-01

    The Tamarack Intrusive Complex (TIC, 1105.6 ± 1.2 Ma) in NE Minnesota, was emplaced during the early stages of the development of the Midcontinent Rift System (MRS, "Early Stage": 1110-1106 Ma). Country rocks of the TIC are those of the Paleoproterozoic Thomson Formation, part of the Animikie Group including sulfide-bearing metasedimentary black shale. The magmatic system is composed of at least two principal mafic-ultramafic intrusive sequences: the sulfide-barren Bowl Intrusion in the south and the "dike" area intrusions in the north which host Ni-Cu-Platinum Group Elements (PGE) mineralization with up to 2.33% Ni, 1.24% Cu, 0.34 g/t Pt, 0.23 g/t Pd and 0.18 g/t Au. Two distinct intrusive units in the "dike" area are the CGO (coarse-grained olivine-bearing) Intrusion, a sub-vertical dike-like body, and the overlying sub-horizontal FGO (fine-grained olivine-bearing) Intrusion. Both intrusions comprise peridotite, feldspathic peridotite, feldspathic pyroxenite, melatroctolite and melagabbro. Massive sulfides are volumetrically minor and mainly occur as lenses emplaced into the country rocks associated with both intrusions. Semi-massive (net-textured) sulfides are distributed at the core of the CGO Intrusion, surrounded by a halo of the disseminated sulfides. Disseminated sulfides also occur in lenses along the base of the FGO Intrusion. Olivine compositions in the CGO Intrusion are between Fo89 and Fo82 and in the FGO Intrusion from Fo84 to Fo82. TIC intrusions have more primitive olivine compositions than that of olivine in the sheet-like intrusions in the Duluth Complex (below Fo70), as well as olivine from the smaller, conduit-related, Eagle and East Eagle Intrusions in Northern Michigan (Fo86 to Fo75). The FeO/MgO ratios of the CGO and FGO Intrusion parental magmas, inferred from olivine compositions, are similar to those of picritic basalts erupted during the early stages of the MRS formation. Trace element ratios differ slightly from other intrusions in the MRS, and are indicative of significant crustal contamination. Differences in textures, whole-rock and mineral compositions, and sulfide distribution are consistent with the emplacement of at least two distinct sulfide saturated magmatic pulses. Ni-enrichment in the TIC indicates that sulfide saturation was attained prior to the sequestration of major proportions of Ni by olivine, possibly at a deeper chamber in the magmatic system. The addition of crustal S from the Thomson Formation sulfidic country rocks is thought to have been the principal process which drove the early attainment of sulfide saturation in the magmas. The CGO Intrusion carried the greater abundance of sulfide liquid, but both the CGO and FGO intrusive sequences represent the accumulation of dense silicate minerals and sulfide liquid in a conduit system. The genetic processes that were operative in the formation of Ni-Cu-PGE mineralization in the Tamarack Intrusive Complex appear to be typical of conduit-style magmatic sulfide deposits associated with large continental basaltic provinces.

  13. Fluoride and Geothermal Activities In Continental Rift Zones, Ethiopia

    NASA Astrophysics Data System (ADS)

    Weldesenbet, S. F.

    2012-12-01

    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 (< 500mg/l) Ca-Mg-HCO3 dominated 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 98?g/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 (<30mg/l) thermal 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 strongly correlated with the concentrations in groundwaters in the local vicinity. The readily leachable hot spring deposits and local lacustrine sediments, which were leached easily as high as three fold of other sediments leachability, are considered as the reservoir for the potential fluoride contamination of the rift groundwater. Leaching of fluoride in the sub-surface system is simulated with sediment-packed column leached by flowing water and applying temporary interruption of flow during the experiment. The result indicated that a sharp increase of fluoride concentration (up to 58mg/kg) observed in leachates before one pore-volume of water eluted from the column. The concentration of leached fluoride consequently declined with the increased flowing pore-volume of water and finally the lowest concentrations of leached fluoride occurred in the end of the experiment. Flow interruption during column leaching experiment causes a noticeable fluoride concentration perturbation due to the heterogeneity of the sediment.

  14. High Fluoride and Geothermal Activities In Continental Rift Zones, Ethiopia

    NASA Astrophysics Data System (ADS)

    Weldesenbet, S. F.; Wohnlich, S.

    2012-12-01

    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 (< 500mg/l) Ca-Mg-HCO3 dominated 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 98?g/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 (<30mg/l) thermal 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 strongly correlated with the concentrations in groundwaters in the local vicinity. The readily leachable hot spring deposits and local lacustrine sediments, which were leached easily as high as three fold of other sediments leachability, are considered as the reservoir for the potential fluoride contamination of the rift groundwater. Leaching of fluoride in the sub-surface system is simulated with sediment-packed column leached by flowing water and applying temporary interruption of flow during the experiment. The result indicated that a sharp increase of fluoride concentration (up to 58mg/kg) observed in leachates before one pore-volume of water eluted from the column. The concentration of leached fluoride consequently declined with the increased flowing pore-volume of water and finally the lowest concentrations of leached fluoride occurred in the end of the experiment. Flow interruption during column leaching experiment causes a noticeable fluoride concentration perturbation due to the heterogeneity of the sediment.

  15. Seismic anisotropy beneath the incipient Okavango rift: Implications for rifting initiation

    NASA Astrophysics Data System (ADS)

    Yu, Youqiang; Gao, Stephen S.; Moidaki, Moikwathai; Reed, Cory A.; Liu, Kelly H.

    2015-11-01

    This study represents the first shear-wave splitting investigation of the Okavango rift zone (ORZ), an incipient continental rift belonging to the East African rift system in northern Botswana. Analysis of broadband seismic data recorded along a 750 km long profile of 22 stations traversing the ORZ and adjacent Congo and Kalahari cratons and several Precambrian orogenic zones reveals dominantly NE-SW fast orientations, which are parallel to both the absolute plate motion direction (based on the NNR-NUVEL-1A model) and the trend of most tectonic boundaries, including that of the ORZ. Spatial coherence analysis of the splitting parameters and correspondence between the observed fast orientations and the trend of tectonic features indicate that the main source of observed anisotropy is most likely in the upper asthenosphere, probably due to simple shear associated with the relative movement of the lithosphere against the asthenosphere. The presence of consistently rift-parallel fast orientations and normal splitting times in the ORZ and most parts of southern Africa implies that neither an upper mantle plume nor small-scale convection is the dominant source for rift initiation and development. The first shear-wave splitting measurements in the vicinity of the ORZ favor a model in which continental rifting develops in response to intra-plate relative movement of continental blocks along zones of weakness produced by ancient tectonic events.

  16. Continental rifting - Progress and outlook

    SciTech Connect

    Baker, B.H.; Morgan, P.

    1981-07-21

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

  17. Rift Valley Fever Review

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  18. Geochemistry of hypabyssal rocks of the Midcontinent Rift system in Minnesota, and implications for a Keweenawan magmatic ``family tree``

    SciTech Connect

    Jerde, E.A.

    1998-11-01

    The hypabyssal rocks associated with the Keweenawan (1.1 Ga) Midcontinent Rift along the Minnesota shore of Lake Superior are a distinct suite within the rock associations of this region. These rocks are found predominantly as ophitic diabase dikes and sills of various sizes, ranging from a few meters to several hundred meters across. Chilled margins were sampled and analyzed by neutron activation analysis and microprobe fused-bead techniques for bulk chemistry. Mineral compositions were obtained by electron microprobe. Variations in composition were found that are consistent with fractionation. Major-element modeling of fractionation indicates that the majority of the hypabyssal rocks formed at moderate pressures ({approximately}6 kbar), although a number show evidence of fractionation at near-surface levels, and some deeper ({approximately}10 kbar). Resorption features seen in plagioclase phenocrysts are evidence for magmatic evolution at varying levels in the crust. It is possible to relate the varied hypabyssal rocks to a single primary parent through polybaric fractionation. This parent is a high-Al primitive olivine tholeiite--a magma composition common among the volcanic rocks associated with the Midcontinent Rift. Trace-element modeling with this same parent composition yields results consistent with the formation of some hypabyssal rocks as products of a periodically tapped and replenished, constantly fractionating magma chamber, which can decouple the behavior of major and trace elements.

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

    NASA Astrophysics Data System (ADS)

    Brune, Sascha

    2015-04-01

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

  20. Evaluation of geothermal potential of Rio Grande rift and Basin and Range province, New Mexico. Final technical report, January 1, 1977-May 31, 1978

    SciTech Connect

    Callender, J.F.

    1985-04-01

    A study was made of the geological, geochemical and geophysical characteristics of potential geothermal areas in the Rio Grande rift and Basin and Range province of New Mexico. Both regional and site-specific information is presented. Data was collected by: (1) reconnaissance and detailed geologic mapping, emphasizing Neogene stratigraphy and structure; (2) petrologic studies of Neogene igneous rocks; (3) radiometric age-dating; (4) geochemical surveying, including regional and site-specific water chemistry, stable isotopic analyses of thermal waters, whole-rock and mineral isotopic studies, and whole-rock chemical analyses; and (5) detailed geophysical surveys, using electrical, gravity and magnetic techniques, with electrical resistivity playing a major role. Regional geochemical water studies were conducted for the whole state. Integrated site-specific studies included the Animas Valley, Las Cruces area (Radium Springs and Las Alturas Estates), Truth or Consequences region, the Albuquerque basin, the San Ysidro area, and the Abiquiu-Ojo Caliente region. The Animas Valley and Las Cruces areas have the most significant geothermal potential of the areas studied. The Truth or Consequences and Albuquerque areas need further study. The San Ysidro and Abiquiu-Ojo Caliente regions have less significant geothermal potential. 78 figs., 16 tabs.

  1. Experimental lithium system. Final report

    SciTech Connect

    Kolowith, R.; Berg, J.D.; Miller, W.C.

    1985-04-01

    A full-scale mockup of the Fusion Materials Irradiation Test (FMIT) Facility lithium system was built at the Hanford Engineering Development Laboratory (HEDL). This isothermal mockup, called the Experimental Lithium System (ELS), was prototypic of FMIT, excluding the accelerator and dump heat exchanger. This 3.8 m/sup 3/ lithium test loop achieved over 16,000 hours of safe and reliable operation. An extensive test program demonstrated satisfactory performance of the system components, including the HEDL-supplied electromagnetic lithium pump, the lithium jet target, the purification and characterization hardware, as well as the auxiliary argon and vacuum systems. Experience with the test loop provided important information on system operation, performance, and reliability. This report presents a complete overview of the entire Experimental Lithium System test program and also includes a summary of such areas as instrumentation, coolant chemistry, vapor/aerosol transport, and corrosion.

  2. Depositional and tectonic framework of the rift basins of Lake Baikal from multichannel seismic data

    USGS Publications Warehouse

    Hutchinson, D.R.; Golmshtok, A.J.; Zonenshain, L.P.; Moore, T.C.; Scholz, C.A.; Klitgord, Kim D.

    1992-01-01

    Recent multichannel seismic reflection data from Lake Baikal, located in a large, active, continental rift in central Asia, image three major stratigraphic units totalling 3.5 to 7.5 km thick in four subbasins. A major change in rift deposition and faulting between the oldest and middle-rift units probably corresponds to the change from slow to fast rifting. A brief comparison of the basins of Lake Baikal with those of the East African rift system highlights differences in structural style that can be explained by differences in age and evolution of the surrounding basement rocks. -from Authors

  3. Laboratory test system. Final report

    SciTech Connect

    Asher, G.L.

    1980-03-01

    This project was initiated to develop a laboratory test capability for evaluating new and existing digital product designs. In recent years, Bendix Kansas City has become more active in syppling early development hardware to the design laboratories for evaluation. Because of the more complex electronic designs being used in new components, more highly automated test systems are needed to evaluate development hardware. To meet this requirement, a universal test system was developed to provide both basic test capabilities and flexibility to adapt easily to specific product applications. This laboratory evaluation system will reduce the need to develop complex dedicated test systems for each new product design, while still providing the benefits of an automated system. A special purpose interface chassis was designed and fabricated to permit a standardized interface between the test system and the product application. Connector assignments by system functions provide convenience and function isolation. Standard cables were used to reduce the need for special purpose hardware. Electrical testing of a developmental electronics assembly demonstrated the adaptability of this system for a typical product application. Both the interface hardware and the software were developed for this application.

  4. Final focus systems for linear colliders

    SciTech Connect

    Erickson, R.A.

    1987-11-01

    The final focus system of a linear collider must perform two primary functions, it must focus the two opposing beams so that their transverse dimensions at the interaction point are small enough to yield acceptable luminosity, and it must steer the beams together to maintain collisions. In addition, the final focus system must transport the outgoing beams to a location where they can be recycled or safely dumped. Elementary optical considerations for linear collider final focus systems are discussed, followed by chromatic aberrations. The design of the final focus system of the SLAC Linear Collider (SLC) is described. Tuning and diagnostics and steering to collision are discussed. Most of the examples illustrating the concepts covered are drawn from the SLC, but the principles and conclusions are said to be generally applicable to other linear collider designs as well. 26 refs., 17 figs. (LEW)

  5. Gas isotopic signatures (He, C, and Ar) in the Lake Kivu region (western branch of the East African rift system): Geodynamic and volcanological implications

    NASA Astrophysics Data System (ADS)

    Tedesco, D.; Tassi, F.; Vaselli, O.; Poreda, R. J.; Darrah, T.; Cuoco, E.; Yalire, M. M.

    2010-01-01

    On 17 January 2002, the city of Goma was partly destroyed by two of the several lava flows erupted from a roughly N-S oriented fracture system opened along the southern flank of Mount Nyiragongo (Democratic Republic of Congo), in the western branch of the East African rift system. A humanitarian and scientific response was promptly organized by international, governmental, and nongovernmental agencies coordinated by the United Nations and the European Union. Among the different scientific projects undertaken to study the mechanisms triggering this and possible future eruptions, we focused on the isotopic (He, C, and Ar) analysis of the magmatic-hydrothermal and cold gas discharges related to the Nyiragongo volcanic system, the Kivu and Virunga region. The studied area includes the Nyiragongo volcano, its surroundings, and peripheral areas inside and outside the rift. They have been subdivided into seven regions characterized by distinct 3He/4He (expressed as R/Rair) ratios and/or ?13C-CO2 values. The Nyiragongo summit crater fumaroles, whose R/Rair and ?13C-CO2 values are up to 8.73 and from -3.5‰ to -4.0‰ VPDB, respectively, show a clear mantle, mid-ocean ridge basalt (MORB)-like contribution. Similar mantle-like He isotopic values (6.5-8.3 R/Rair) are also found in CO2-rich gas emanations (mazukus) along the northern shoreline of Lake Kivu main basin, whereas the 13?C-CO2 values range from -5.3‰ to -6.8‰ VPDB. The mantle influence progressively decreases in (1) dissolved gases of Lake Kivu (2.6-5.5 R/Rair) and (2) the distal gas discharges within and outside the two sides of the rift (from 0.1 to 1.7 R/Rair). Similarly, ?13C-CO2 ratios of the peripheral gas emissions are lighter (from -5.9‰ to -11.6‰ VPDB) than those of the crater fumaroles. Therefore, the spatial distribution of He and C signatures in the Lake Kivu region is mainly produced by mixing of mantle-related (e.g., Nyiragongo crater fumaroles and/or mazukus gases) and crustal-related (e.g., gas discharges in the Archean craton) fluids. The CO2/3He ratio (up to 10 × 1010) is 1 order of magnitude higher than those found in MORB, and it is due to the increasing solubility of CO2 in the foiditic magma feeding the Nyiragongo volcano. However, the exceptionally high 40Ar*/4He ratio (up to 8.7) of the Nyiragongo crater fumaroles may be related to the difference between He and Ar solubility in the magmatic source. The results of the present investigation suggest that in this area the uprising of mantle-originated f luids seems strongly controlled by regional tectonics in relation to the geodynamic assessment of the rift. These fluids are mainly localized in a relatively small zone between Lake Kivu and Nyiragongo volcano, with important implications in terms of volcanic activity.

  6. Final Barrier: Small System Compliance

    EPA Science Inventory

    This presentation will discuss the use of point-of-use (POU) technology for small drinking water systems. Information will be provided on the USEPA regulations that allow the use of POU for compliance and the technologies that are listed as SSCT for radium and arsenic. Listing o...

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

    E-print Network

    ten Brink, Uri S.; Taylor, Michael Halford

    2002-07-16

    The Cenozoic rift system of Baikal, located in the interior of the largest continental mass on Earth, is thought to represent a potential analog of the early stage of breakup of supercontinents. We present a detailed P wave velocity structure...

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

    NASA Astrophysics Data System (ADS)

    Loule, Jean-Pierre; Pospisil, Lubomil

    2013-01-01

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

  9. Deformation and seismicity associated with continental rift zones propagating toward continental margins

    NASA Astrophysics Data System (ADS)

    Lyakhovsky, V.; Segev, A.; Schattner, U.; Weinberger, R.

    2012-01-01

    We study the propagation of a continental rift and its interaction with a continental margin utilizing a 3-D lithospheric model with a seismogenic crust governed by a damage rheology. A long-standing problem in rift-mechanics, known as thetectonic force paradox, is that the magnitude of the tectonic forces required for rifting are not large enough in the absence of basaltic magmatism. Our modeling results demonstrate that under moderate rift-driving tectonic forces the rift propagation is feasible even in the absence of magmatism. This is due to gradual weakening and "long-term memory" of fractured rocks that lead to a significantly lower yielding stress than that of the surrounding intact rocks. We show that the style, rate and the associated seismicity pattern of the rift zone formation in the continental lithosphere depend not only on the applied tectonic forces, but also on the rate of healing. Accounting for the memory effect provides a feasible solution for thetectonic force paradox. Our modeling results also demonstrate how the lithosphere structure affects the geometry of the propagating rift system toward a continental margin. Thinning of the crystalline crust leads to a decrease in the propagation rate and possibly to rift termination across the margin. In such a case, a new fault system is created perpendicular to the direction of the rift propagation. These results reveal that the local lithosphere structure is one of the key factors controlling the geometry of the evolving rift system and seismicity pattern.

  10. Rifts in Spreading Wax Layers

    E-print Network

    Rolf Ragnarsson; J. Lewis Ford; Christian D. Santangelo; Eberhard Bodenschatz

    1995-10-19

    We report experimental results on the rift formation between two freezing wax plates. The plates were pulled apart with constant velocity, while floating on the melt, in a way akin to the tectonic plates of the earth's crust. At slow spreading rates, a rift, initially perpendicular to the spreading direction, was found to be stable, while above a critical spreading rate a "spiky" rift with fracture zones almost parallel to the spreading direction developed. At yet higher spreading rates a second transition from the spiky rift to a zig-zag pattern occurred. In this regime the rift can be characterized by a single angle which was found to be dependent on the spreading rate. We show that the oblique spreading angles agree with a simple geometrical model. The coarsening of the zig-zag pattern over time and the three-dimensional structure of the solidified crust are also discussed.

  11. Low lower crustal velocity across Ethiopia: Is the Main Ethiopian Rift a narrow rift in a hot craton?

    USGS Publications Warehouse

    Keranen, K.M.; Klemperer, S.L.; Julia, J.; Lawrence, J. F.; Nyblade, A.A.

    2009-01-01

    [1] The Main Ethiopian Rift (MER) is a classic narrow rift that developed in hot, weak lithosphere, not in the initially cold, thick, and strong lithosphere that would be predicted by common models of rift mode formation. Our new 1-D seismic velocity profiles from Rayleigh wave/receiver function joint inversion across the MER and the Ethiopian Plateau indicate that hot lower crust and upper mantle are present throughout the broad region affected by Oligocene flood basalt volcanism, including both the present rift and the adjacent Ethiopian Plateau hundreds of kilometers from the rift valley. The region of hot lithosphere closely corresponds to the region of flood basalt volcanism, and we interpret that the volcanism and thermal perturbation were jointly caused by impingement of the Afar plume head. Across the affected region, Vs is 3.6-3.8 km/s in the lowermost crust and ???4.3 km/s in the uppermost mantle, both ??0.3 km/s lower than in the eastern and western branches of the East African Rift System to the south. We interpret the low Vs in the lower crust and upper mantle as indicative of hot lithosphere with partial melt. Our results lead to a hybrid rift mode, in which the brittle upper crust has developed as a narrow rift along the Neoproterozoic suture between East and West Gondwana, while at depth lithospheric deformation is distributed over the broad region (??400 km wide) thermally perturbed by the broad thermal upwelling associated with the Afar plume head. Development of both the East African Rift System to the south (in cold, strong lithosphere) and the MER to the north (in hot, weak lithosphere) as narrow rifts, despite their vastly different initial thermal states and depth-integrated lithospheric strength, indicates that common models of rift mode formation that focus only on temperature, thickness, and vertical strength profiles do not apply to these classic continental rifts. Instead, inherited structure and associated lithospheric weaknesses are the primary control on the mode of extension. ?? 2009 by the American Geophysical Union.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  13. Hydrothermal flow systems in the Midcontinent Rift: Oxygen and hydrogen isotopic studies of the North Shore Volcanic Group and related hypabyssal sills, Minnesota

    SciTech Connect

    Park, Y.R.; Ripley, E.M.

    1999-06-01

    Rift-related lavas of the North Shore Volcanic Group (NSVG) are intruded by plutonic rocks of the Duluth Complex along the unconformity between the NSVG and the underlying Proterozoic metasedimentary rocks (Animikie Group) and Archean volcano-sedimentary and plutonic rocks. Heat associated with the emplacement of the mafic intrusions generated fluid flow in the overlying plateau lavas. {delta}{sup 18}O values for whole rocks from the NSVG and hypabyssal sills range from 5.5 to 17.7{per_thousand} and 5.3 to 11.5{per_thousand}, respectively, and most values are higher than those considered normal for basaltic rocks (5.4 to 6.0{per_thousand}). In general, there is a positive correlation between whole rock {delta}{sup 18}O and water content, which suggests that elevated {delta}{sup 18}O values are related primarily to secondary mineral growth and isotopic exchange during hydrothermal alteration and metamorphism. {delta}{sup 18}O{sub H{sub 2}O} values computed from amygdule-filling minerals such as smectite, chlorite, and epidote found in low- to high-temperature metamorphic zones range from {approximately}{minus}1 to 6{per_thousand} with an average value of {approximately}3{per_thousand}. Smectite in the lower-grade zones gives computed {delta}D{sub H{sub 2}O} values between {minus}26 and {minus}83{per_thousand}, whereas epidote in the higher-grade zones gives {delta}D{sub H{sub 2}O} values of {minus}15 to 6{per_thousand}. Fluid isotopic compositions computed from epidote and smectite values are suggestive of the involvement of at least two fluids during the early stages of amygdule filling. Fluid {delta}D and {delta}{sup 18}O values determined from epidote at the higher metamorphic grades indicate that seawater dominated the deeper portions of the system where greenschist facies assemblages and elevated {delta}{sup 18}O values were produced in flow interiors, as well as margins. Smectite isotopic compositions suggest that meteoric water was predominant in the shallower portions of the system. The increase in {delta}{sup 18}O values of massive flow interiors with depth is interpreted as a result of rock interaction with a fluid of constant oxygen isotopic composition with increasing temperature. The stable isotopic data are supportive of previous suggestions that seawater was involved in the hydrothermal system associated with the Midcontinent Rift. Although the origin of the seawater remains problematic, it appears that marine incursions may have occurred during the late stages of Portage Lake volcanism, and periodically thereafter.

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

    USGS Publications Warehouse

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

    2002-01-01

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

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

    USGS Publications Warehouse

    Burton, William C.; Southworth, Scott

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  17. Age constraints for the present fault configuration in the Imperial Valley, California: Evidence for northwestward propagation of the Gulf of California rift system

    NASA Technical Reports Server (NTRS)

    Larsen, Shawn; Reilinger, Robert

    1990-01-01

    Releveling and other geophysical data for the Imperial Valley of southern California suggest the northern section of the Imperial-Brawley fault system, which includes the Mesquite Basin and Brawley Seismic Zone, is much younger than the 4 to 5 million year age of the valley itself. A minimum age of 3000 years is calculated for the northern segment of the Imperial fault from correlations between surface topography and geodetically observed seismic/interseismic vertical movements. Calculations of a maximum age of 80,000 years is based upon displacements in the crystalline basement along the Imperial fault, inferred from seismic refraction surveys. This young age supports recent interpretations of heat flow measurements, which also suggest that the current patterns of seismicity and faults in the Imperial Valley are not long lived. The current fault geometry and basement morphology suggest northwestward growth of the Imperial fault and migration of the Brawley Seismic Zone. It is suggested that this migration is a manifestation of the propagation of the Gulf of California rift system into the North American continent.

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

    NASA Astrophysics Data System (ADS)

    Paton, Douglas; Mortimer, Estelle; Hodgson, Neil

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Earth's mantle possesses distinct and variable volatile characteristics as sampled by magmatic activity in different tectonic environments. In general, trace element depleted mid-ocean ridge basalts, with low Sr and Pb isotope values (but high ?Nd and ?Hf), release mantle-derived noble gases characterised by 3He/4He ~8 ± 1RA, (21Ne/22Ne)ex ~0.06 and 40Ar/36Ar ? 10,000 with CO2 and N2 having ?13C~-5‰ and ?15N ~-5‰, respectively. In contrast, enriched intraplate lavas possess higher 3He/4He (up to 50RA), lower (21Ne/22Ne)ex ~0.035 and 40Ar/36Ar ? 10,000 with generally higher but variable ?13C and ?15N. These isotopic attributes of mantle-derived volatiles can be exploited to map the extent, and mixing characteristics, of enriched (plume) mantle with depleted asthenospheric mantle ± the effects of over-riding lithosphere and/or crust. The East African Rift System (EARS) is superimposed upon two massive plateaux - the Ethiopia and Kenya domes - regarded as geophysical manifestations of a superplume source, a huge thermochemical anomaly originated at the core-mantle boundary and providing dynamic support for the plateaux. We present new volatile isotopic and relative abundance data (on the same samples) for geothermal fluids (He-CO2-N2), lavas (He-Ne-Ar) and xenoliths (He-Ne-Ar-CO2-N2) which provide an unprecedented overview of the distribution of mantle volatiles of the Ethiopia Dome, from the Red Sea via the Afar region and Main Ethiopian Rift (MER) to the Turkana Depression. Notably, peaks in geothermal fluid 3He/4He (16RA) and ?15N (+6.5‰) are coincident within the MER but the maximum ?13C (-0.78‰) lies ~100 km to the south. Highs in 3He/4He (14RA), ?13C (~-1‰) and ?15N (+3.4‰) for mafic crystals occur in the Afar region ~ 500km to the north. We assess the significance of the off-set in these volatile isotope signals, for sampling volatile heterogeneity in the plume source and/or the relative sensitivity of different volatiles to admixture of plume- with asthenospheric and lithospheric mantle. These results are contrasted with volatile data from the Kenya Dome where the plume signal is muted and the lithospheric mantle exerts a stronger control on geothermal/lava volatile characteristics.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    The isotope geochemistry of pedogenic carbonate and fossil herbivore enamel is a powerful tool to reconstruct paleoenvironmental conditions in particular when climate change plays a key role in the evolution of ecosystems. Here, we present the first Plio-Pleistocene long-term carbon (?13C), oxygen (?18O) and clumped isotope (?47) records from pedogenic carbonate and herbivore teeth in the Malawi Rift. These data represent an important southern hemisphere record in the East African Rift System (EARS), a key region for reconstructing vegetation patterns in today's Zambezian Savanna and correlation with data on the evolution and migration of early hominids across the Inter-Tropical Convergence Zone. As our study site is situated between the well-known hominid-bearing sites of eastern and southern Africa in the Somali-Masai Endemic Zone and Highveld Grassland it fills an important geographical gap for early hominid research. 5.0 to 0.6 Ma fluviatile and lacustrine deposits of the Chiwondo Beds (NE shore of Lake Malawi) comprise abundant pedogenic carbonate and remains of a diverse fauna dominated by large terrestrial mammals. These sediments are also home to two hominid fossil remains, a mandible of Homo rudolfensis and a maxillary fragment of Paranthropus boisei, both dated around 2.4 Ma. The Chiwondo Beds therefore document early co-existence of these two species. We evaluate ?13C data from fossil enamel of different suid, bovid, and equid species and contrast these with ?13C and ?18O values of pedogenic carbonate. We complement the latter with clumped isotope soil temperature data. Results of almost 800 pedogenic carbonate samples from over 20 sections consistently average ?13C = -8.5 ‰ over the past 5 Ma with no significant short-term ?13C excursions or long-term trends. The data from molar tooth enamel of nine individual suids of the genera Metridiochoerus, Notochoerus and Nyanzachoerus support these findings with average ?13C = -10.0 ‰. The absence of long-term trends towards more positive ?13C values contrasts the increasing role of C4-grasslands in the southern EARS which is well documented for sites in Ethiopia, Kenya and Tanzania. Our data hence point to regional differences in climate and vegetation dynamics during the Plio-Pleistocene in the EARS and documents persistence of paleoenvironmental conditions in the southern branch of the EARS at times of early hominid evolution.

  1. The Eagle and East Eagle sulfide ore-bearing mafic-ultramafic intrusions in the Midcontinent Rift System, upper Michigan: Geochronology and petrologic evolution

    NASA Astrophysics Data System (ADS)

    Ding, Xin; Li, Chusi; Ripley, Edward M.; Rossell, Dean; Kamo, Sandra

    2010-03-01

    The Eagle and East Eagle intrusions are small, subvertical dike-like mafic-ultramafic bodies that cut Proterozoic sedimentary strata in the Baraga Basin in northern Michigan. The Eagle intrusion hosts a newly discovered magmatic Ni-Cu-PGE deposit. The nearby East Eagle intrusion also contains sulfide mineralization, but the extent of this mineralization has yet to be determined by further drilling. Both intrusions contain olivine-bearing rocks such as feldspathic peridotite, melatroctolite, and olivine melagabbro. Sulfide accumulations range from disseminated at both Eagle and East Eagle to semimassive and massive at Eagle. U-Pb baddeleyite dating gives a crystallization age of 1107.2 ± 5.7 Ma for the Eagle intrusion, coeval with eruption of picritic basalts at the base of the volcanic succession in the Midcontinent Rift System (MRS). The Fo contents of olivine cores in the Eagle and East Eagle intrusions vary between 75 and 85 mol %, higher than those of olivine in larger layered intrusions in the MRS such as the Duluth Complex. The FeO/MgO ratios and Al2O3 contents of the parental magmas for the Eagle and East Eagle intrusions inferred from olivine and spinel compositions are similar to those of picritic basalts in the base of the MRS volcanic succession. These petrochemical data suggest that the Eagle and East Eagle intrusions are the intrusive equivalents of high-MgO basalts that erupted in the early stages of continental magmatism associated with the development of the rift. Variations in mineral compositions and incompatible trace element ratios suggest that at least three major pulses of magmas were involved in the formation of low-sulfide rocks in the Eagle intrusion. Lower Fo contents of olivine associated with semimassive sulfides as compared to that of olivine in low-sulfide rocks suggest that the magma associated with the semimassive sulfide was more fractionated than the parental magmas of the low-sulfide rocks in the Eagle intrusion. Accumulation of suspended olivine crystals and sulfide droplets from ascending magmas as they passed through wide parts of the conduits at Eagle and East Eagle played a critical role in the genesis of olivine-rich rocks and sulfide ores in the intrusions. The Eagle Ni-Cu-PGE deposit typifies the conduit-style of magmatic sulfide deposition that is associated with continental basaltic magmatism.

  2. Relationship of coronae, regional plains and rift zones on Venus

    NASA Astrophysics Data System (ADS)

    Krassilnikov, A. S.; Kostama, V.-P.; Aittola, M.; Guseva, E. N.; Cherkashina, O. S.

    2012-08-01

    Coronae and rifts are the most prominent volcano-tectonic features on the surface of Venus. Coronae are large radial-concentric structures with diameters of 100 to over 1000 km. They have varied topographical shapes, radial and concentric fracturing and compressional tectonic structures are common for their annuli. Massive volcanism is also connected with some of the structures. Coronae are interpreted to be the result of updoming and fracturing on the surface due to interaction of mantle diapirs with the lithosphere and its subsequent gravitational relaxation. According to Stofan et al. (2001), two types of coronae are observed: type 1 - coronae that have annuli of concentric ridges and/or fractures (407 structures), and type 2 that have similar characteristics to type 1 but lack a complete annulus of ridges and fractures (107 structures). We analyzed 20% of this coronae population (we chose each fifth structure from the Stofan et al. (2001) catalog; 82 coronae of type 1 and 22 coronae of type 2, in total 104 coronae) for the (1) spatial distribution of rift structures and time relationship of rift zones activity with time of regional volcanic plains emplacement, and (2) tectonics, volcanism, age relative to regional plains and relationship with rifts. Two different age groups of rifts on Venus were mapped at the scale 1:50 000 000: old rifts that predate and young rifts that postdate regional plains. Most of young rifts inherit strikes of old rifts and old rifts are reworked by them. This may be evidence of rift-produced uplift zones that were probably mostly stable during both types of rifts formation. Evolution of distribution of rift systems with time (decreasing of distribution and localization of rift zones) imply thickening of the lithosphere with time. Coronae-producing mantle diapirism and uplift of mantle material in rift zones are not well correlated at least in time in most cases, because majority of coronae (77%) of both types has no genetic association with rifts. Majority of coronae (72%) were mostly active before regional plains formation, and only 3% appear to have begun to form after the plains emplacement, which may be also due to thickening of the lithosphere. According to the relationship with regional plains type 2 coronae are in general older than type 1 coronae. Three types of corona-related volcanic activity were observed: shield volcanoes and their clusters, as well as extensive lobate lava flows and smooth volcanic plains. Shield volcanoes during coronae evolution were mostly active before regional plains emplacement. Most active phase of volcanism of corona may not coincide with the time of the major tectonic activity of corona, as majority of coronae (77%) were most active before regional plains formation, but almost half of all coronae have traces of post regional plains volcanism. Detailed mapping and stratigraphic analysis of seven regions with 34 examples of coronae showed a similarity in the sequence of regional geologic units.

  3. DCE Bio Detection System Final Report

    SciTech Connect

    Lind, Michael A.; Batishko, Charles R.; Morgen, Gerald P.; Owsley, Stanley L.; Dunham, Glen C.; Warner, Marvin G.; Willett, Jesse A.

    2007-12-01

    The DCE (DNA Capture Element) Bio-Detection System (Biohound) was conceived, designed, built and tested by PNNL under a MIPR for the US Air Force under the technical direction of Dr. Johnathan Kiel and his team at Brooks City Base in San Antonio Texas. The project was directed toward building a measurement device to take advantage of a unique aptamer based assay developed by the Air Force for detecting biological agents. The assay uses narrow band quantum dots fluorophores, high efficiency fluorescence quenchers, magnetic micro-beads beads and selected aptamers to perform high specificity, high sensitivity detection of targeted biological materials in minutes. This final report summarizes and documents the final configuration of the system delivered to the Air Force in December 2008

  4. The continent-ocean transition of the rifted South China continental margin

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    The continent to ocean transition (COT) architecture of rifted margins represents a key aspect in the study of the variability of different rifting systems and thus, to understand lithospheric extension and final break-up processes. We used 2250 km of reprocessed multichannel seismic data along 4 regional lines and magnetic data acquired across the NW South China continental margin to investigate a previously poorly defined COT. The along-strike structure of the NW subbasin of the South China Sea presents different amounts of extension allowing the study of conjugate pairs of continental margins and their COT in a relative small region. The time-migrated seismic sections allow us to interpreted clear continental and oceanic domains from differences in internal reflectivity, faulting style, fault-block geometry, the seismic character of the top of the basement, the geometry of sediment deposits, and Moho reflections. The continental domain is characterized by arrays of normal faults and associated tilted blocks overlaid by syn-rift sedimentary units. The Moho is imaged as sub-horizontal reflections that define a fairly continuous boundary typically at 8-10 s TWT. Estimation of the thickness of the continental crust using 6 km/s average velocity indicates a ~22 km-thick continental crust under the uppermost slope thinning abruptly to ~9-6 km under the lower slope. The oceanic crust has a comparatively highly reflective top of basement, little-faulting, not discernible syn-tectonic strata, and fairly constant thickness (4-8 km) over tens of km distance defined by usually clear Moho reflections. The COT can be very well defined based on MSC images and occurs across a ~5-10 km narrow zone. Rifting in the NW subbasin resulted in asymmetric conjugate margins. Arrays of tilted fault blocks covered by abundant syn-rift sediment are displayed across the northwestern South China continental margin, whereas the conjugate Macclesfield Bank margin shows abrupt thinning and little faulting. Seismic profiles also show a clear change in the tectonic structure of the margin from NE to SW. On the two NE-most lines, the abrupt crustal thinning occurs over a 20-40 km wide area resulting in final breakup. To the SW, the area of stretched continental crust extends over a comparatively broader ~100-110 km segment of tilted fault-blocks. We interpret that the 3D structural variability and the narrow COT is related to the lateral NE to SW propagation of a spreading center. The early spreading center propagation in the NE suddenly stopped continental stretching during ongoing rifting, causing an abrupt break-up and a narrow COT. Later arrival of spreading center to the SW resulted in a comparatively broader segment of highly stretched continental crust. We suggest that the final structure of the northwest South China continental margin have been governed by the 3D interaction between rifting and oceanic spreading center propagation to a degree larger than by the local lithospheric structure during rifting.

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

    SciTech Connect

    Bishop, M.G. )

    1991-03-01

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

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

    NASA Astrophysics Data System (ADS)

    Sachau, Till; Koehn, Daniel

    2010-10-01

    In this contribution, we present a new model of passive rifting and related rift-flank uplift. The numerical model is based on a lattice spring network coupled with a viscous particle model so that we can simulate visco-elasto-plastic behaviour with dynamic fault development. In our model, we show that rift-flank uplift can be achieved best when extension in the crust is localized and the lower crust is strong so that major rift faults transect the whole crust. Uplift of rift flanks follows a smooth function whereas down-throw in the rift basin takes place in steps. The geometry of the developing faults has also an influence on the uplift; in this case, displacement along major rift faults produces higher flanks than distributed displacement on many faults. Our model also shows that the relative elastic thickness of the crust has only a minor influence on the uplift since fault depth and elastic thickness are not independent. In addition, we show with a second set of simulations and analytically that a strain misfit between the upper and lower boundaries of a stretched crust, which is created by the horizontal extension, leads to an active uplift driven by elastic forces. We compare the numerical simulations, the analytical solution and real surface data from the Albertine rift in the East African Rift System and show that our new model can reproduce realistic features. Our two-layer beam model with strain misfit can also explain why a thick crust in the simulations can have an even higher rift flank than a thin crust even though the thin crust topography has a higher curvature. We discuss the implications of our simulations for real rift systems and for the current theory of rift-flank uplift.

  7. Rift Stability and Localization in Devana Chasma, Venus

    NASA Astrophysics Data System (ADS)

    Martone, A. A.; Montési, L. G. J.

    2015-05-01

    The rift zone of Devana Chasma greatly resembles Earth's rift zones, especially the East African Rift, despite the lack of global plate tectonics. The stability of rifts on Venus will be characterized, and will include lithosphere weakening processes.

  8. Using of Remote Sensing Techniques for Monitoring the Earthquakes Activities Along the Northern Part of the Syrian Rift System (LEFT-LATERAL),SYRIA

    NASA Astrophysics Data System (ADS)

    Dalati, Moutaz

    Earthquake mitigation can be achieved with a better knowledge of a region's infra-and substructures. High resolution Remote Sensing data can play a significant role to implement Geological mapping and it is essential to learn about the tectonic setting of a region. It is an effective method to identify active faults from different sources of Remote Sensing and compare the capability of some satellite sensors in active faults survey. In this paper, it was discussed a few digital image processing approaches to be used for enhancement and feature extraction related to faults. Those methods include band ratio, filtering and texture statistics . The experimental results show that multi-spectral images have great potentials in large scale active faults investigation. It has also got satisfied results when deal with invisible faults. Active Faults have distinct features in satellite images. Usually, there are obvious straight lines, circular structures and other distinct patterns along the faults locations. Remotely Sensed imagery Landsat ETM and SPOT XS /PAN are often used in active faults mapping. Moderate and high resolution satellite images are the best choice, because in low resolution images, the faults features may not be visible in most cases. The area under study is located Northwest of Syria that is part of one of the very active deformation belt on the Earth today. This area and the western part of Syria are located along the great rift system (Left-Lateral or African- Syrian Rift System). Those areas are tectonically active and caused a lot of seismically events. The AL-Ghab graben complex is situated within this wide area of Cenozoic deformation. The system formed, initially, as a result of the break up of the Arabian plate from the African plate. This action indicates that these sites are active and in a continual movement. In addition to that, the statistic analysis of Thematic Mapper data and the features from a digital elevation model ( DEM )produced from SAR interferometer show the existence of spectral structures at the same sites. The Arabian plate is moving in a NNW direction, whereas the African plate is moving to the North. The left-lateral motion along the Dead Sea Fault accommodates the difference in movement rate between both plates. The analysis of TM Space Imagery and digital image processing of spectral data show that the lineaments along AL-Ghab graben maybe considered as linear conjunctions accompanied with complex fracturing system. This complex is affected by distance stresses accompanied with intensive forces. The digital image processing of Radar imagery showing the presence of active and fresh faulting zones along the AL-Ghab graben. TM and SAR-DTM data, also showed a gradual color tone and interruptions of linear-ellipse shapes which reflecting the presence of discontinuity contours along the fault zone extension .This features refer to abundance of surface morphological features indicate to Fresh Faults. Recent faulting is expressed as freshly exposed soil within the colluvial apron visible by its light tone color. These indicators had been proved by field checks. Furthermore, the statistic digital analysis of the spectral data show that there are distribution of spectral plumes. These plumes are decreasing in intensity and color contrast from the center of the site to the direction of its edges.

  9. Contribution of the FUTUREVOLC project to the study of segmented lateral dyke growth in the 2014 rifting event at Bárðarbunga volcanic system, Iceland

    NASA Astrophysics Data System (ADS)

    Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S.; Ófeigsson, Benedikt; Rafn Heimisson, Elías; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Guðmundsson, Gunnar B.; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T.; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert S.; Ágústsdóttir, Thorbjörg; Björnsson, Helgi; Bean, Christopher J.

    2015-04-01

    The FUTUREVOLC project (a 26-partner project funded by FP7 Environment Programme of the European Commission, addressing topic "Long-term monitoring experiment in geologically active regions of Europe prone to natural hazards: the Supersite concept) set aims to (i) establish an innovative volcano monitoring system and strategy, (ii) develop new methods for near real-time integration of multi-parametric datasets, (iii) apply a seamless transdisciplinary approach to further scientific understanding of magmatic processes, and (iv) to improve delivery, quality and timeliness of transdisciplinary information from monitoring scientists to civil protection. The project duration is 1 October 2012 - 31 March 2016. Unrest and volcanic activity since August 2014 at one of the focus areas of the project in Iceland, at the Bárðarbunga volcanic system, near the middle of the project duration, has offered unique opportunities for this project. On 16 August 2014 an intense seismic swarm started in Bárðarbunga, the beginning of a major volcano-tectonic rifting event forming over 45 km long dyke extending from the caldera to Holuhraun lava field outside the northern margin of Vatnajökull. A large basaltic, effusive fissure eruption began in Holuhraun on 31 August which had by January formed a lava field with a volume in excess of one cubic kilometre. We document how the FUTUREVOLC project has contributed to the study and response to the subsurface dyke formation, through increased seismic and geodetic coverage and joint interpreation of the data. The dyke intrusion in the Bárðarbunga volcanic system, grew laterally for over 45 km at a variable rate, with an influence of topography on the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning System (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bárðarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with a magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of M>5 earthquakes. Joint interpretation of seismic and geodetic data was reported daily to the civil protection of Iceland and used for effective response and mitigation of the associated hazards. The response to, and studies of, the Bárðarbunga rifting event and eruptions have thus contributed to the achievements of all the objectives of the FUTUREVOLC project.

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

    NASA Astrophysics Data System (ADS)

    Giese, JöRg; Seward, Diane; Schreurs, Guido

    2012-04-01

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

  11. Facilities management system (FMS). Final report

    SciTech Connect

    1992-04-01

    The remainder of this report provides a detailed, final status of Andersen Consulting`s participation in the FMS systems implementation project and offers suggestions for continued FMS improvements. The report presents the following topics of discussion: (1) Summary and Status of Work (2) Recommendations for Continued Success (3) Contract Deliverables and Client Satisfaction The Summary and Status of Work section presents a detailed, final status of the FMS project at the termination of Andersen`s full-time participation. This section discusses the status of each FMS sub-system and of the Andersen major project deliverables. The Recommendations section offers suggestions for continued FMS success. The topics discussed include recommendations for each of the following areas: (1) End User and Business Operations (2) AISD; Development and Computer Operations (3) Software (4) Technical Platform (5) Control Procedures The Contract Deliverables and Client Satisfaction section discusses feedback received from Johnson Controls management and FMS system users. The report also addresses Andersen`s observations from the feedback.

  12. Facilities management system (FMS). Final report

    SciTech Connect

    1992-04-01

    This report provides a detailed, final status of Andersen Consulting`s participation in the Facilities Management System (FMS) implementation project under contract with Los Alamos National Laboratory (LANL) and offers suggestions for continued FMS improvements. The report presents the following topics of discussion: (1) summary and status of work (2) recommendations for continued success (3) contract deliverables and client satisfaction. The Summary and Status of Work section presents a detailed, final status of the FMS project at the termination of Andersen`s full-time participation. This section discusses the status of each FMS sub-system and of the Andersen major project deliverables. The Recommendations section offers suggestions for continued FMS success. The topics discussed include recommendations for each of the following areas: (1) End User and Business Operations; (2) AISD; Development and Computer Operations; (3) Software; (4) Technical Platform; and (5) Control Procedures The Contract Deliverables and Client Satisfaction section discusses feedback received from Johnson Controls management and FMS system users. The report also addresses Andersen`s observations from the feedback.

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

    USGS Publications Warehouse

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

    1995-01-01

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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  16. An automated GIS/remotely sensed early warning system to detect elevated populations of vectors of Rift Valley fever, a mosquito-borne emerging virus threat

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Mosquito transmitted infectious diseases, like eastern equine encephalitis (EEE), Rift Valley fever (RVF), and West Nile virus (WNV), pose an international threat to animal and human health. An introduction of RVF into the U.S. would severely impact wild ungulate populations and the beef and dairy ...

  17. A GIS EARLY WARNING SYSTEM TO DETECT ELEVATED POPULATIONS OF VECTORS OF RIFT VALLEY FEVER AND THE CONTRIBUTIONS FROM FLORIDA'S MOSQUITO CONTROL COMMUNITY

    Technology Transfer Automated Retrieval System (TEKTRAN)

    New and emerging mosquito-borne viruses such as Rift Valley fever (RVF) virus pose a global threat to animal and human health. An introduction of RVF into the U.S. could severely impact livestock industries and wild ungulates, and cause significantly more human illness than West Nile virus (WNV). ...

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

    SciTech Connect

    James C Witcher

    2002-07-30

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  20. Unique device identification system. Final rule.

    PubMed

    2013-09-24

    The Food and Drug Administration (FDA) is issuing a final rule to establish a system to adequately identify devices through distribution and use. This rule requires the label of medical devices to include a unique device identifier (UDI), except where the rule provides for an exception or alternative placement. The labeler must submit product information concerning devices to FDA's Global Unique Device Identification Database (GUDID), unless subject to an exception or alternative. The system established by this rule requires the label and device package of each medical device to include a UDI and requires that each UDI be provided in a plain-text version and in a form that uses automatic identification and data capture (AIDC) technology. The UDI will be required to be directly marked on the device itself if the device is intended to be used more than once and intended to be reprocessed before each use. PMID:24066364

  1. The MOZART Project - MOZAmbique Rift Tomography

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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 previously unexplored region concerning the seismicity and ambient noise (see also Domingues et al, this conference), receiver function analysis, surface wave dispersion and SEM forward modelling. These preliminary results will pave the way for a tomographic model of the lithosphere, to be developed in the next stage of the project.

  2. Final Report - Regulatory Considerations for Adaptive Systems

    NASA Technical Reports Server (NTRS)

    Wilkinson, Chris; Lynch, Jonathan; Bharadwaj, Raj

    2013-01-01

    This report documents the findings of a preliminary research study into new approaches to the software design assurance of adaptive systems. We suggest a methodology to overcome the software validation and verification difficulties posed by the underlying assumption of non-adaptive software in the requirementsbased- testing verification methods in RTCA/DO-178B and C. An analysis of the relevant RTCA/DO-178B and C objectives is presented showing the reasons for the difficulties that arise in showing satisfaction of the objectives and suggested additional means by which they could be satisfied. We suggest that the software design assurance problem for adaptive systems is principally one of developing correct and complete high level requirements and system level constraints that define the necessary system functional and safety properties to assure the safe use of adaptive systems. We show how analytical techniques such as model based design, mathematical modeling and formal or formal-like methods can be used to both validate the high level functional and safety requirements, establish necessary constraints and provide the verification evidence for the satisfaction of requirements and constraints that supplements conventional testing. Finally the report identifies the follow-on research topics needed to implement this methodology.

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

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

    Topographic maps based on Pioneer Venus altimetry suggest that Beta Regio, an elevated feature centered at 27 deg N, 282 deg E, is analogous to domes associated with continental rift systems on earth. This interpretation is consistent with the commonly quoted analogy between the East African rift system and the topography of the region from Beta Regio southward to Phoebe Regio. If Beta Regio is a dome, major structural uplift of the crust of Venus is implied, suggesting a more dynamic upper mantle than would be the case if Beta Regio were simply a large volcanic construct.

  4. GIS Early-Warning System for Vectors of Rift Valley Fever: Anomaly Analysis of Climate-Population Associations

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A critical component of predicting the risk of transmission of mosquito-borne viruses is knowing the status of vector populations. Mosquito control agencies have good systems for measuring mosquito populations at county or district levels, but these data are not synthesized to regional or national ...

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

    PubMed

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

    2011-11-17

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

  6. Causality, operators and finality in systems theory

    NASA Astrophysics Data System (ADS)

    Vallée, Robert

    1998-07-01

    Causal operators acting, by definition, on the past and present functions of time are first presented. Then are described dynamic systems involving a causal operator in their evolution equation, both in the cases of a continuous and a discrete time. A first example of causal dynamic system is given by the modelling of a subject observing an object (Von Förster 1976). The operator involved acts in fact only on the present. In case of convergence it gives rise to an "eigen-behavior" representing the stabilized state of what concerns the modes of action of the subject and of what concerns the object. Then is presented the concept of "epistemo-praxiology" (Vallée, 1974, 1995) involving an "observation operator" (Vallée, 1951), then decision and effect operators. All these operators are causal (acting upon past and present). They explain the subjective limitations of the observing and deciding subject in front of an object (pragmatic indiscursibility and pragmatic inverse transfer of decisional structures). They show also the coevolution of the subject and the object as a fixed point of a composite operator having observation, decision and effection traits. The notions of "incursivity" and "hyperincursivity" (Dubois and Resconi, 1992; Dubois, 1995) involve operators acting on the past, present and future of functions of time and considerations linked to Aristotle's final causes. They give tools for solving problems of stability of certain systems.

  7. Hypogene and supergene alteration of the zeolite-bearing pyroclastic deposits at Tell Rimah, Jordan, and rift-related processes along the Dead-Sea-Transform Fault System during the Quaternary

    NASA Astrophysics Data System (ADS)

    Dill, H. G.; Techmer, A.; Botz, R.; Dohrmann, R.; Kaufhold, S.

    2012-09-01

    The boundary between the Arabian and African plates, is marked in the Middle East by one of the most prominent deep-seated lineamentary structures, called the Dead-Sea-Transform Fault System (DSTFS). Structural and mineralogical processes related to the DSTFS were correlated with equivalent processes leading to the alteration of pyroclastic deposits of alkali-olivine basaltic to nepheline basaltic composition which formed during a time span of less than 0.5 Ma. The large deposit of Tell Rimah, Jordan, is operated for the exploitation of zeolites, tuffs, and as pozzolana raw material. Four discrete stages of mineralizations have been distinguished from each other within these volcanic-hosted mineral deposits. (1) Hypogene syneruptive alteration of pyroclastic rocks produced siliceous gels ("allophane"), smectite, analcime, and phillipsite in vesicles when the groundwater level was low in the rift basin of the DSTFS. The lake-level lowstand caused the fluid system in the pyroclastic cone to become self-sufficient and it has been considered as a closed hydrothermal system. (2) Periods of tectonic and magmatic quiescence grinded the detrital sedimentation in the rift basin to a halt, while triggering a supergene alteration in the eruptive cones on the adjacent Arabian Plate. (3) Epigenetic alteration affected the pyroclastic rocks in the distal part of the DSTFS as a result of a rising water level. The water gradually filled the pore space of the permeable pyroclastic deposits almost to completeness and caused meniscus and blocky cements of calcite, phillipsite and chabazite to develop. In the rift basin, contemporaneously with the alteration of the pyroclastic rocks, freshwater limestones formed on calcareous bedrocks. Ba and Mn minerals in these freshwater limestones were supplied by subaquatic brines. Subsequently, a drastic lowering of the lake water level in the DSTFS converted the system of subaquatic freshwater limestones into subaerial tufa and travertine. As long as the basal parts of the pyroclastic units at Tell Rimah were in the reaches of the saline groundwaters, calcite and faujasite developed in the pyroclastic host rocks. (4) Another lake level lowstand within the rift basin caused the pyroclastic host rocks to get emerged and forced zeolite-carbonate mineralization in the tuffs to a complete stillstand. Hypogene and supergene alteration in these phreatomagmatic-strombolian pyroclastic cones of the Pleistocene x were correlated with lake high- and lowstands in the adjacent rift basin along the DSTFS. The results obtained by current tectono-morphological studies of the rift-related alteration of pyroclastic rocks along the DSTFS may also be applied to basin-and-swell-topographies elsewhere in the world. The current studies involved microscopy supplemented by SEM-EDX, X-ray diffraction analysis, mid (MIR) and far (FIR) infrared spectroscopy. Major and trace elements were analyzed by X-ray fluorescence spectrometry (XRF). C- and O isotope analyses were conducted on carbonate minerals, which were also targeted on by radiocarbon dating.

  8. Final design development of silicone southwall glazing system. Final report

    SciTech Connect

    Vanwert, B.; Currin, C.; Mingenbach, W.

    1983-11-01

    This cooperative solar project was undertaken to design, fabricate and test a southwall glazing system based on a flexible silicone glazing. In addition, preliminary cost, performance and market development guidelines were established. A specific silicone glazing was selected and was shown to have a solar transmission of 88%, tensile strength of greater than 50 Newtons/cm, estimated durability greater than 20 years, and to meet an industry standard flame test. A unique and simple film tensioning device was developed by the Architects Taos under contract to maintain the flexible glazing in a taunt condition over its long life without wind flutter and resulting potential damage. The selected silicone glazing was evaluated by using two southwall glazing systems: on passive test chambers and on a concrete block wall of a Dow Corning warehouse building. The evaluation was conducted at Dow Corning Midland, Michigan facilities (43.4/sup 0/N latitude) from April 1981 to March 1982. The data obtained showed that the silicone southwall glazing system using a selective adsorber on a vented concrete block wall provided over 750 MJ/m/sup 2/ of thermal energy during a winter heating system. One experiment demonstrated the performance and ease of installation of the tensioning device developed by this project. Preliminary cost estimates indicate the southwall glazing system with a selective adsorber could be installed for about $55/m/sup 2/ ($5/ft/sup 2/); with a flat black (non-selective adsorber) the installed cost is estimated to be about $40//m/sup 2/ ($4/ft/sup 2/). Prorated over a minimum ten year life, with a capital recovery factor of 0.20, this system would be cost competitive for fuel displacement with $8.00/GJ ($8.44/M Btu) heating energy when vertical wall insolation exceeds 2.5 GJ/m/sup 2/ (0.22 x 10/sup 6/ Btu/ft/sup 2/) for a heating season.

  9. Multi-Point Combustion System: Final Report

    NASA Technical Reports Server (NTRS)

    Goeke, Jerry; Pack, Spencer; Zink, Gregory; Ryon, Jason

    2014-01-01

    A low-NOx emission combustor concept has been developed for NASA's Environmentally Responsible Aircraft (ERA) program to meet N+2 emissions goals for a 70,000 lb thrust engine application. These goals include 75 percent reduction of LTO NOx from CAEP6 standards without increasing CO, UHC, or smoke from that of current state of the art. An additional key factor in this work is to improve lean combustion stability over that of previous work performed on similar technology in the early 2000s. The purpose of this paper is to present the final report for the NASA contract. This work included the design, analysis, and test of a multi-point combustion system. All design work was based on the results of Computational Fluid Dynamics modeling with the end results tested on a medium pressure combustion rig at the UC and a medium pressure combustion rig at GRC. The theories behind the designs, results of analysis, and experimental test data will be discussed in this report. The combustion system consists of five radially staged rows of injectors, where ten small scale injectors are used in place of a single traditional nozzle. Major accomplishments of the current work include the design of a Multipoint Lean Direct Injection (MLDI) array and associated air blast and pilot fuel injectors, which is expected to meet or exceed the goal of a 75 percent reduction in LTO NOx from CAEP6 standards. This design incorporates a reduced number of injectors over previous multipoint designs, simplified and lightweight components, and a very compact combustor section. Additional outcomes of the program are validation that the design of these combustion systems can be aided by the use of Computational Fluid Dynamics to predict and reduce emissions. Furthermore, the staging of fuel through the individually controlled radially staged injector rows successfully demonstrated improved low power operability as well as improvements in emissions over previous multipoint designs. Additional comparison between Jet- A fuel and a hydrotreated biofuel is made to determine viability of the technology for use with alternative fuels. Finally, the operability of the array and associated nozzles proved to be very stable without requiring additional active or passive control systems. A number of publications have been publish

  10. Thermal maturation and organic richness of potential petroleum source rocks in Proterozoic Rice Formation, North American Mid-Continent rift system, northeastern Kansas

    SciTech Connect

    Newell, K.D. ); Burruss, R.C.; Palacas, J.G. )

    1993-11-01

    A recent well in northeastern Kansas penetrated 296 ft (90.2 m) of dark gray siltstone in the Precambrian Mid-Continent rift (Proterozoic Rice Formation). Correlations indicate this unit may be as thick as 600 ft (183 m) and is possibly time-equivalent to the Nonesuch Shale (Middle Proterozoic) in the Lake Superior region. The upper half of this unit qualifies as a lean source rock (averaging 0.66 wt.% TOC), and organic matter in it is in the transition stage between oil and wet gas generation. The presence of the gray siltstone in this well and similar lithologies in other wells is encouraging because it indicates the source rock deposition may be common along the Mid-Continent rift, and that parts of the rift may remain thermally within the oil and gas window. Microscopic examination of calcite veins penetrating the dark gray siltstone reveals numerous oil-filled and subordinate aqueous fluid inclusions. Homogenization temperatures indicate these rocks have been subjected to temperature of at least 110-115[degrees]C (230-239[degrees]F). Burial during the Phanerozoic is inadequate to account for the homogenization temperatures and thermal maturity of the Precambrian rocks. With the present geothermal gradient, at least 8250 ft (2.5 km) of burial is necessary, but lesser burial may be likely with probably higher geothermal gradients during rifting. Fluorescence colors and gas chromatograms indicate compositions of oils in the fluid inclusions vary. However, oils in the fluid inclusions are markedly dissimilar to the nearest oils produced from Paleozoic rocks.

  11. Constraints on rift thermal processes from heat flow and uplift

    NASA Technical Reports Server (NTRS)

    Morgan, P.

    1983-01-01

    The implications of heat flow data available from five major Cenozoic continental rift systems for the processes of continental rifting are discussed, and simple thermal models of lithospheric thinning which predict uplift are used to further constrain the thermal processes in the lithosphere during rifting. Compilations of the heat flow data are summarized and the salient results of these compilations are briefly discussed. The uplift predictions of the slow and rapid thinning models, in which thinning is assumed to occur at a respectively slower and faster rate than heat can be conducted into the lithosphere, are presented. Comparison of uplift rates with model results indicates that the lithosphere is in a state between the two models. While uplift is predicted to continue after thinning has ceased due to thermal relaxation of the lithosphere, the rapid thinning model is always predicted to apply to surface heat flow, and an anomaly in this flow is not predicted to develop until after thinning has stopped.

  12. Melting during late-stage rifting in Afar is hot and deep.

    PubMed

    Ferguson, D J; Maclennan, J; Bastow, I D; Pyle, D M; Jones, S M; Keir, D; Blundy, J D; Plank, T; Yirgu, G

    2013-07-01

    Investigations of a variety of continental rifts and margins worldwide have revealed that a considerable volume of melt can intrude into the crust during continental breakup, modifying its composition and thermal structure. However, it is unclear whether the cause of voluminous melt production at volcanic rifts is primarily increased mantle temperature or plate thinning. Also disputed is the extent to which plate stretching or thinning is uniform or varies with depth with the entire continental lithospheric mantle potentially being removed before plate rupture. Here we show that the extensive magmatism during rifting along the southern Red Sea rift in Afar, a unique region of sub-aerial transition from continental to oceanic rifting, is driven by deep melting of hotter-than-normal asthenosphere. Petrogenetic modelling shows that melts are predominantly generated at depths greater than 80?kilometres, implying the existence of a thick upper thermo-mechanical boundary layer in a rift system approaching the point of plate rupture. Numerical modelling of rift development shows that when breakup occurs at the slow extension rates observed in Afar, the survival of a thick plate is an inevitable consequence of conductive cooling of the lithosphere, even when the underlying asthenosphere is hot. Sustained magmatic activity during rifting in Afar thus requires persistently high mantle temperatures, which would allow melting at high pressure beneath the thick plate. If extensive plate thinning does occur during breakup it must do so abruptly at a late stage, immediately before the formation of the new ocean basin. PMID:23823795

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

    NASA Astrophysics Data System (ADS)

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

    2004-07-01

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

  14. Minerals as mantle fingerprints: Sr-Nd-Pb-Hf in clinopyroxene and He in olivine distinguish an unusual ancient mantle lithosphere beneath the East African Rift System

    NASA Astrophysics Data System (ADS)

    Nelson, W. R.; Shirey, S. B.; Graham, D. W.

    2011-12-01

    The East African Rift System is a complex region that holds keys to understanding the fundamental geodynamics of continental break-up. In this region, the volcanic record preserves over 30 Myrs of geochemical variability associated with the interplay between shallow and deep asthenospheric sources, continental lithospheric mantle, and continental crust. One fundamental question that is still subject to debate concerns the relationship between the lithospheric mantle and the voluminous flood basalt province that erupted at ~30 Ma in Ethiopia and Yemen. Whole-rock Re-Os isotopic data demonstrate the high-Ti (HT2) flood basalts (187Os/188Ost = 0.1247-0.1329) and peridotite xenoliths (187Os/188Ost = 0.1235-0.1377) from NW Ethiopia have similar isotopic compositions. However, Sr-Nd-Pb-Hf isotopic signatures from peridotite clinopyroxene grains are different from those of the flood basalts. The peridotite clinopyroxene separates bear isotopic affinities to anciently depleted mantle (87Sr/86Sr = 0.7019-0.7029; ?Nd = 12.6-18.5; ?Hf = 13.8-27.6) - more depleted than the MORB source - rather than to the OIB-like 30 Ma flood basalts (87Sr/86Sr ~ 0.704; ?Nd = 4.7-6.7; ?Hf = 12.1-13.5). Peridotite clinopyroxenes display two groups of 206Pb/204Pb compositions: the higher 206Pb/204Pb group (18.7-19.3) is compositionally similar to the flood basalts (206Pb/204Pb = 18.97-19.02) whereas the lower 206Pb/204Pb group (17.1-17.9) overlaps with depleted mantle. This suggests that the Pb isotope systematics in some of the peridotites have been metasomatically perturbed. Helium isotopes were analyzed by crushing olivine separated from the peridotites and the flood basalts. Olivine in the peridotites has low He concentrations (0.78-4.7 ncc/g) and low 3He/4He (4.6-6.6 RA), demonstrating that they cannot be the petrogenetic precursor to the high 3He/4He (>12 RA) flood basalts. Notably, these peridotites have 3He/4He signatures consistent with a lithospheric mantle source. Therefore, although the flood basalts and lithospheric mantle bear some isotopic similarities, the basalts were not derived from this portion of the lithospheric mantle, nor are the peridotites crystalline cumulates derived from asthenosphere -derived magmas. The isotopic variations in these peridotites demonstrate that the Afro-Arabian lithosphere contains anciently depleted mantle, created during or prior to the late Proterozoic Pan-African orogeny.

  15. Earthquake clusters in Corinth Rift

    NASA Astrophysics Data System (ADS)

    Mesimeri, Maria; Papadimitriou, Eleftheria; Karakostas, Vasilios; Tsaklidis, George

    2013-04-01

    Clusters commonly occur as main shock-aftershock (MS-AS) sequences but also as earthquake swarms, which are empirically defined as an increase in seismicity rate above the background rate without a clear triggering main shock earthquake. Earthquake swarms occur in a variety of different environments and might have a diversity of origins, characterized by a high b-value in their magnitude distribution. The Corinth Rift, which was selected as our target area, appears to be the most recent extensional structure, with a likely rate of fault slip of about 1cm/yr and opening of 7mm/yr. High seismic activity accommodates the active deformation with frequent strong (M?6.0) events and several seismic excitations without a main shock with clearly discriminative magnitude. Identification of earthquake clusters that occurred in this area in last years and investigation of their spatio-temporal distribution is attempted, with the application of known declustering algorithms, aiming to associate their occurrence with certain patterns in seismicity behavior. The earthquake catalog of the National Hellenic Seismological Network is used, and a certain number of clusters were extracted from the dataset, with the MS-AS sequences being distinguished from earthquake swarms. Spatio-temporal properties of each subset were analyzed in detail, after determining the respective completeness magnitude. This work was supported in part by the THALES Program of the Ministry of Education of Greece and the European Union in the framework of the project entitled "Integrated understanding of Seismicity, using innovative Methodologies of Fracture mechanics along with Earthquake and non-extensive statistical physics - Application to the geodynamic system of the Hellenic Arc, SEISMO FEAR HELLARC".

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  17. Recent geodynamics and evolution of the Moma rift, Northeast Asia.

    NASA Astrophysics Data System (ADS)

    Imaev, V. S.; Imaeva, L. P.; Kozmin, B. M.; Fujita, K. S.; Mackey, K. G.

    2009-04-01

    The Cenozoic Moma rift system is a major tectonic feature in northeast Russia. It is composed of a series of basins (Selennyakh, Kyrin,Lower Moma,Upper Moma,etc.) filled with up to one km thick and bounded by the Chersky Range (up to 3100 m high) on the southwest and the Moma Range (up to 2400 m high) on the northeast. Northeast of the Moma Range is the Indigirka-Zyryanka foreland basin, composed of thick, up to 2.5 km, Eocene, Oligocene, and Miocene coal-bearing sequences, while on the southwestern side of the Chersky Range there are a number of piedmont basins (Tuostakh, Upper Adycha, Derbeke, etc.) containing up to several hundred meters of Miocene and Oligocene coal-bearing deposits. Despite considerable study over the past half-century, there is considerable debate over the origin, present-day tectonics, and evolution of the Moma rift system. The Cenozoic deposits of the basins generally become younger from northwest to southeast with the exception of the Seimchan-Buyunda basin. In the northeast, fan-shaped coal-bearing basins (e.g., Nenneli, Olzhoi, Selennyakh, Uyandina, Tommot, and others) are filled with Miocene to Pliocene deposits, while basins in the southeast (e.g., Taskan) are filled with Neogene sediments. The Seimchan-Buyunda basin, however, has sediments of Oligocene age. The Moma rift system is reflected a major step in the gravity field, presumably separating denser rocks of the Kolyma-Omolon superterrain from somewhat less dense rocks of the Verkhoyansk fold belt (margin of the North Asian Craton). Analysis of travel-times of Pn and Pg waves from local earthquakes indicates an area of thinned crust (30-35 km) southwest of the Moma rift system, extending as a "tongue" from the Lena River delta and the Laptev Sea to the upper part of the Kolyma River, as compared to 40-45 km in the surrounding areas. This region of thinned crust also coincides with a region of high heat flow values measured in boreholes of the Chersky Range (up to 88 mW/m2). Hot springs with temperatures up to +20°C are found within the Moma and Selnnyakh basins proper.The crustal inhomogeneity is also reflected in the upper mantle as indicated by a 40° rotation of the Rayleigh wave polarization angle from teleseisms recorded at Tiksi that cross the Moma rift system as opposed to those that do not. Cenozoic volcanism, chemically similar to basalts and rhyolites from rift zones elsewhere is found in the Moma rift proper. Balagan-Tas is a basaltic cinder cone which has been dated at 286,000 years based on Ar-Ar dating, while Uraga-Khaya is an undated, presumed Quaternary, rhyolitic dome. All these factors indicate that the Moma rift system originated as a continental rift, probably as an extension of the Arctic (Gakkel) Mid-Ocean Ridge. At the present, however, compressional conditions prevail within the Moma rift zone. Seismicity is generally absent from the rift basins proper or their margins; most seismicity is concentrated to the southwest of the Moma rift basins along major strike-slip fault systems. Focal mechanisms of the largest earthquakes in the Chersky Range also all show transpression. Field mapping indicates that the majority of the faults mapped in the field are strike-slip, thrust and reverse faults (86%) with only a small number of normal faults (14%) and that the Cenozoic deposits within the Moma rift are intensely folded. Re-leveling surveys conducted along the Indigirka River, which cuts across the Moma rift system, reveal a moderate rate of presnt-day vertical uplift (up to +4 mm/yr). Thus, the Moma rift system is no longer acting as a rift, but is undergoing transpression. This conclusion is also supported by recent plate motion calculations based on GPS and VLBI data, as well as slip-vectors of earthquakes, which indicates that the Euler pole between North America and Eurasia is located around 68-70°N, near the coast of the Laptev Sea. This places the Moma rift system in a zone of convergence between North America and Eurasia; this geometry also supports the extrusion of the Okhotsk Sea plate. Poles of ro

  18. Late Mesozoic and Cenozoic rifting and its dynamic setting in Eastern China and adjacent areas

    NASA Astrophysics Data System (ADS)

    Ren, Jianye; Tamaki, Kensaku; Li, Sitian; Junxia, Zhang

    2002-02-01

    During the Late Mesozoic and Cenozoic, extension was widespread in Eastern China and adjacent areas. The first rifting stage spanned in the Late Jurassic-Early Cretaceous times and covered an area of more than 2 million km 2 of NE Asia from the Lake Baikal to the Sikhot-Alin in EW direction and from the Mongol-Okhotsk fold belt to North China in NS direction. This rifting was characterized by intracontinental rifts, volcanic eruptions and transform extension along large-scale strike-slip faults. Based on the magmatic activity, filling sequence of basins, tectonic framework and subsidence analysis of basins, the evolution of this area can be divided into three main developmental phases. The first phase, calc-alkaline volcanics erupted intensely along NNE-trending faults, forming Daxing'anling volcanic belt, NE China. The second phase, Basin and Range type fault basin system bearing coal and oil developed in NE Asia. During the third phase, which was marked by the change from synrifting to thermal subsidence, very thick postrift deposits developed in the Songliao basin (the largest oil basin in NE China). Following uplift and denudation, caused by compressional tectonism in the near end of Cretaceous, a Paleogene rifting stage produced widespread continental rift systems and continental margin basins in Eastern China. These rifted basins were usually filled with several kilometers of alluvial and lacustrine deposits and contain a large amount of fossil fuel resources. Integrated research in most of these rifting basins has shown that the basins are characterized by rapid subsidence, relative high paleo-geothermal history and thinned crust. It is now accepted that the formation of most of these basins was related to a lithospheric extensional regime or dextral transtensional regime. During Neogene time, early Tertiary basins in Eastern China entered a postrifting phase, forming regional downwarping. Basin fills formed in a thermal subsidence period onlapped the fault basin margins and were deposited in a broad downwarped lacustrine depression. At the same time, within plate rifting of the Lake Baikal and Shanxi graben climaxed and spreading of the Japan Sea and South China Sea occurred. Quaternary rifting was marked by basalt eruption and accelerated subsidence in the area of Tertiary rifting. The Okinawa Trough is an active rift involving back-arc extension. Continental rifting and marginal sea opening were clearly developed in various kind of tectonic settings. Three rifting styles, intracontinental rifting within fold belt, intracontinental rifting within craton and continental marginal rifting and spreading, are distinguished on the basis of nature of the basin basement, tectonic location of rifting and relations to large strike-slip faults. Changes of convergence rates of India-Eurasia and Pacific-Eurasia may have caused NW-SE-trending extensional stress field dominating the rifting. Asthenospheric upwelling may have well assisted the rifting process. In this paper, a combination model of interactions between plates and deep process of lithosphere has been proposed to explain the rifting process in East China and adjacent areas. The research on the Late Mesozoic and Cenozoic extensional tectonics of East China and adjacent areas is important because of its utility as an indicator of the dynamic setting and deformational mechanisms involved in stretching Lithosphere. The research also benefits the exploration and development of mineral and energy resources in this area.

  19. Syn-rift evolution of the Pripyat Trough: constraints from structural and stratigraphic modelling

    NASA Astrophysics Data System (ADS)

    Kusznir, N. J.; Kovkhuto, A.; Stephenson, R. A.

    1996-12-01

    The Pripyat Trough is a Late Devonian rift basin. It forms part of the larger Pripyat-Dniepr-Donets rift system which has a length in excess of 800 km and separates the Ukrainian Shield from the Voronezh Massif. The Pripyat Trough contains a well resolved stratigraphic sub-division within the syn-rift basin fill sequence which allows the duration and rate of rifting to be determined using 2-D forward and reverse structural and stratigraphic modelling. The analysis shows that rifting was extremely rapid. Sequential decompaction and flattening of 2-D cross-sections has been applied to six syn-rift time horizons between top Upper Devonian (364 Ma) and top Middle Devonian (377 Ma) and used to quantify the syn-rift development of basin cross-sectional area in time. The evolution of basin cross-sectional area shows that some initial rifting had occurred prior to the Middle Frasnian (369 Ma); however, most rifting occurred in the Famennian (367-364 Ma). Forward syn-rift modelling using the flexural cantilever model of rift basin formation has also been applied to quantify the magnitude of extension within the Pripyat Trough in time. Forward syn-rift models are constrained by the intra syn-rift flattened and decompacted cross-sections and the observed evolution of the cross-sectional area. Most rapid rift basin formation is shown to have occurred in the Famennian with over 66% of basin cross-sectional area forming in less than 5 Myr, and with approximately 80% or more of total extension occurring in less than 3 Myr. This period of most rapid extension during the Famennian coincides with the most active period of volcanicity. Total Devonian extension across the Pripyat Trough is estimated to be of the order of 11-14 km with a maximum ? stretching factor of approximately 1.12. Extensional strain rates are estimated to be of the order of 0.8 × 10 -15 s -1.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    In the early stages of continental rifting, East African Rift (EAR) basins are conventionally depicted as asymmetric basins bounded on one side by a ~100 km-long border fault. As rifting progresses, strain concentrates into the rift center, producing intra-rift faults. The timing and nature of the transition from border fault to intra-rift-dominated strain accommodation is unclear. Our study focuses on this transitional phase of continental rifting by exploring the spatial and temporal evolution of faulting in the Natron (border fault initiation at ~3 Ma) and Magadi (~7 Ma) basins of northern Tanzania and southern Kenya, respectively. We compare the morphologies and activity histories of faults in each basin using field observations and remote sensing in order to address the relative contributions of border faults and intra-rift faults to crustal strain accommodation as rifting progresses. The ~500 m-high border fault along the western margin of the Natron basin is steep compared to many border faults in the eastern branch of the EAR, indicating limited scarp degradation by mass wasting. Locally, the escarpment shows open fissures and young scarps 10s of meters high and a few kilometers long, implying ongoing border fault activity in this young rift. However, intra-rift faults within ~1 Ma lavas are greatly eroded and fresh scarps are typically absent, implying long recurrence intervals between slip events. Rift-normal topographic profiles across the Natron basin show the lowest elevations in the lake-filled basin adjacent to the border fault, where a number of hydrothermal springs along the border fault system expel water into the lake. In contrast to Natron, a ~1600 m high, densely vegetated, border fault escarpment along the western edge of the Magadi basin is highly degraded; we were unable to identify evidence of recent rupturing. Rift-normal elevation profiles indicate the focus of strain has migrated away from the border fault into the rift center, where faults pervasively dissect 1.2-0.8 Ma trachyte lavas. Unlike Natron, intra-rift faults in the Magadi basin exhibit primarily steep, little-degraded fault scarps, implying greater activity than Natron intra-rift faults. Numerous fault-associated springs feed water into perennial Lake Magadi, which has no surface drainage input, yet survives despite a high evaporation rate that has created economically viable evaporite deposits. Calcite vein-filled joints are common along fault zones around Lake Magadi, as well as several cm veins around columnar joints that imply isotropic expansion of the fracture network under high pressures of CO2-rich fluids. Our work indicates that the locus of strain in this portion of the EAR transfers from the border fault to the center of the rift basin some time between 3 and 7 million years after rift initiation. This transition likely reflects the evolving respective roles of crustal flexure and magma budget in focusing strain, as well as the hydrothermal fluid budget along evolving fault zones.

  1. Continental rift zones without Moho uplift

    NASA Astrophysics Data System (ADS)

    Thybo, H.; Lyngsie, S.; Nielsen, C.

    2008-05-01

    Rifting is a fundamental plate tectonic process that creates elongated depressions in the Earth's surface, which become filled with sedimentary and volcanic material, as it is presently observed at the Baikal, East African, Rhine Graben and Rio Grande Rift Zones. All rifting models predict Moho uplift due to crustal thinning, and reduced seismic velocity in the uppermost mantle due to decompression or heating from the Earth's interior. However, recently acquired data from the presently active Baikal Rift zone in Siberia and the failed Dniepr-Donets rift zone in Ukraine are examples where there is no Moho topography that can related to the rifting process. Further, data from the Kenya Rift Zone shows sign of less Moho uplift than expected from the actual extension. At all these rift zones, we observe a localized zone in the lower crust which has exceptionally high seismic velocity and is highly reflective. We suggest that rift related crustal thinning took place, but the expected Moho up-warp was compensated by magmatic intrusion in the lower crust at the high-velocity zone. This finding has significant implications for modelling of the evolution of sedimentary basins around rift structures.

  2. The development of extension and magmatism in the Red Sea rift of Afar

    NASA Astrophysics Data System (ADS)

    Keir, Derek; Bastow, Ian D.; Pagli, Carolina; Chambers, Emma L.

    2013-11-01

    Despite the importance of continental breakup in plate tectonics, precisely how extensional processes such as brittle faulting, ductile plate stretching, and magma intrusion evolve in space and time during the development of new ocean basins remains poorly understood. The rifting of Arabia from Africa in the Afar depression is an ideal natural laboratory to address this problem since the region exposes subaerially the tectonically active transition from continental rifting to incipient seafloor spreading. We review recent constraints on along-axis variations in rift morphology, crustal and mantle structure, the distribution and style of ongoing faulting, subsurface magmatism and surface volcanism in the Red Sea rift of Afar to understand processes ultimately responsible for the formation of magmatic rifted continental margins. Our synthesis shows that there is a fundamental change in rift morphology from central Afar northward into the Danakil depression, spatially coincident with marked thinning of the crust, an increase in the volume of young basalt flows, and subsidence of the land towards and below sea-level. The variations can be attributed to a northward increase in proportion of extension by ductile plate stretching at the expense of magma intrusion. This is likely in response to a longer history of localised heating and weakening in a narrower rift. Thus, although magma intrusion accommodates strain for a protracted period during rift development, the final stages of breakup are dominated by a phase of plate stretching with a shift from intrusive to extrusive magmatism. This late-stage pulse of decompression melting due to plate thinning may be responsible for the formation of seaward dipping reflector sequences of basalts and sediments, which are ubiquitous at magmatic rifted margins worldwide.

  3. The accuracy of the Oculus Rift virtual reality head-mounted display during cervical spine mobility measurement.

    PubMed

    Xu, Xu; Chen, Karen B; Lin, Jia-Hua; Radwin, Robert G

    2015-02-26

    An inertial sensor-embedded virtual reality (VR) head-mounted display, the Oculus Rift (the Rift), monitors head movement so the content displayed can be updated accordingly. While the Rift may have potential use in cervical spine biomechanics studies, its accuracy in terms of cervical spine mobility measurement has not yet been validated. In the current study, a VR environment was designed to guide participants to perform prescribed neck movements. The cervical spine kinematics was measured by both the Rift and a reference motion tracking system. Comparison of the kinematics data between the Rift and the tracking system indicated that the Rift can provide good estimates on full range of motion (from one side to the other side) during the performed task. Because of inertial sensor drifting, the unilateral range of motion (from one side to neutral posture) derived from the Rift is more erroneous. The root-mean-square errors over a 1-min task were within 10° for each rotation axis. The error analysis further indicated that the inertial sensor drifted approximately 6° at the beginning of a trial during the initialization. This needs to be addressed when using the Rift in order to more accurately measure cervical spine kinematics. It is suggested that the front cover of the Rift should be aligned against a vertical plane during its initialization. PMID:25636855

  4. Surface processes in an active rift setting: a source to sink approach from the Sperchios delta, central Greece

    NASA Astrophysics Data System (ADS)

    Pechlivanidou, Sofia; Cowie, Patience; Gawthorpe, Rob

    2015-04-01

    This study presents an integrated source to sink approach to understand the controls on the distribution of sediments source areas, sediment routing and downstream fining in the Sperchios rift system, central Greece. The Sperchios Rift forms an active half-graben basin, which is controlled by major NW-SE trending faults. Detailed sedimentological analysis (grain size, macro/micro faunal, geochemical and mineral magnetic analysis) in conjunction with 14C age constraints reveal the stratigraphic evolution of the Sperchios delta, located at the eastern part of the rift, including the presence of a Holocene transgressive - regressive wedge overlying Late Pleistocene alluvial deposits. The process-based stratigraphic model SedFlux2D is used to simulate the delta evolution and model scenarios are compared with the measured data. A series of sensitivity tests are used to explore uncertainties associated with variations in sediment supply, tectonic subsidence rate, and Holocene relative sea level. We discuss the effects of the major controls, in particular the rate of relative sea-level rise and tectonic subsidence rate, on accommodation creation and thus delta architecture in this active rift setting during the Holocene. The transition from transgression to regression is found to be mainly controlled by the slowing rate of relative sea level rise that occurred approximately 5500 kyrs ago. Finally, we compare the sediment volumes and grain size variations preserved in the Sperchios delta to onshore erosion rates inferred from data collected on bedrock erodibility, measurements of downstream fining, as well as stream-power/transport capacity for both transverse and axial drainage networks. This comparison, when combined with information on relative uplift/subsidence patterns due to active extensional tectonics, allows us to develop a semi-quantitative, process-based source-to-sink model for this area.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  6. Feedbacks between deformation and reactive melt transport in the mantle lithosphere during rifting

    NASA Astrophysics Data System (ADS)

    Tommasi, A.; Baptiste, V.; Vauchez, A. R.; Fort, A.

    2014-12-01

    The East-African rift associates lithospheric thinning with extensive volcanism. Melts, even at low fractions, reduce the mantle viscosity. They also carry and exchange heat, mainly via reactions (latent heat), modifying the temperature and the rheology, which in turn controls their transport through the lithospheric mantle. Analysis of microstructures and crystal preferred orientations of mantle xenoliths from different localities along the East-African rift system highlights strong feedbacks between deformation, melt transport, and thermal evolution in the lithospheric mantle. Microstructures change markedly from south (young) to north (mature rift). In Tanzania, mylonitic to porphyroclastic peridotites predominate in on-axis localities, while off-axis ones are coarse-granular to porphyroclastic, pointing to heterogeneous deformation and variable annealing due to local interaction with fluids or to different time lags between deformation and extraction. Mylonites point to strain localization but there is no evidence for dominant grain boundary sliding: ubiquituous intracrystalline deformation in olivine and orthopyroxene and strong CPO record dislocation creep with dominant [100] glide in olivine. Synkinematic replacement of opx by olivine in both mylonitic and porphyroclastic peridotites suggests that deformation continued in the presence of melt under near-solidus conditions. This heating was transient: exsolutions in opx record cooling before extraction. Mega peridotites, which sample the southern border of the Ethiopian plateau, are coarse-porphyroclastic and show widespread metasomatism by basalts or by evolved volatile-rich low melt fractions. The former predated or was coeval to deformation, since olivine and pyroxene CPO are coherent. Exsolutions in opx imply that the high primary equilibration temperatures, which are consistent with the coarse-grained microstructures, are linked to transient heating. Finally, the fine-grained polygonal microstructures, with evenly distributed interstitial pyroxenes aligned in the foliation, and weak but uncorrelated olivine and pyroxenes CPO in xenoliths from the Gulf of Aden margin record post kinematic reactive melt percolation and refertilisation of the lithospheric mantle controlled by the preexisting fabric.

  7. Rift reactivation and migration during multiphase extension

    NASA Astrophysics Data System (ADS)

    Naliboff, John; Buiter, Susanne J. H.

    2015-07-01

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

  8. The tectonic evolution of the southeastern Terceira Rift/São Miguel region (Azores)

    NASA Astrophysics Data System (ADS)

    Weiß, B. J.; Hübscher, C.; Lüdmann, T.

    2015-07-01

    The eastern Azores Archipelago with São Miguel being the dominant subaerial structure is located at the intersection of an oceanic rift (Terceira Rift) with a major transform fault (Gloria Fault) representing the westernmost part of the Nubian-Eurasian plate boundary. The evolution of islands, bathymetric highs and basin margins involves strong volcanism, but the controlling geodynamic and tectonic processes are currently under debate. In order to study this evolution, multibeam bathymetry and marine seismic reflection data were collected to image faults and stratigraphy. The basins of the southeastern Terceira Rift are rift valleys whose southwestern and northeastern margins are defined by few major normal faults and several minor normal faults, respectively. Since São Miguel in between the rift valleys shows an unusual W-E orientation, it is supposed to be located on a leaky transform. South of the island and separated by a N120° trending graben system, the Monacco Bank represents a N160° oriented flat topped volcanic ridge dominated by tilted fault blocks. Up to six seismic units are interpreted for each basin. Although volcanic ridges hamper a direct linking of depositional strata between the rift and adjacent basins, the individual seismic stratigraphic units have distinct characteristics. Using these units to provide a consistent relative chrono-stratigraphic scheme for the entire study area, we suggest that the evolution of the southeastern Terceira Rift occurred in two stages. Considering age constrains from previous studies, we conclude that N140° structures developed orthogonal to the SW-NE direction of plate-tectonic extension before ~ 10 Ma. The N160° trending volcanic ridges and faults developed later as the plate tectonic spreading direction changed to WSW-ENE. Hence, the evolution of the southeastern Terceira Rift domain is predominantly controlled by plate kinematics and lithospheric stress forming a kind of a re-organized rift system.

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

    USGS Publications Warehouse

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

    2014-01-01

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

  10. The protracted development of focused magmatic intrusion during continental rifting

    NASA Astrophysics Data System (ADS)

    Rooney, Tyrone O.; Bastow, Ian D.; Keir, Derek; Mazzarini, Francesco; Movsesian, Emily; Grosfils, Eric B.; Zimbelman, James R.; Ramsey, Michael S.; Ayalew, Dereje; Yirgu, Gezahegn

    2014-06-01

    The transition from mechanical thinning toward focused magmatic intrusion during continental rifting is poorly constrained; the tectonically active Main Ethiopian Rift (MER) provides an ideal study locale to address this issue. The presence of linear magmatic-tectonic belts in the relatively immature central MER may indicate that the transition from mechanical to magmatic rifting is more spatially distributed and temporally protracted than has previously been assumed. Here we examine lava geochemistry and vent distribution of a Pliocene-Quaternary linear magmatic chain along the western margin of the central MER—the Akaki Magmatic Zone. Our results show limited variability in parental magma that evolve in a complex polybaric fractionation system that has not changed significantly over the past 3 Ma. Our results suggest the following: (1) channeling of plume material and the localization of shear- or topography-induced porosity modulates melt intrusion into the continental lithosphere. (2) Pre-existing lithospheric structures may act as catalysts for intrusion of magmas into the lithospheric mantle. (3) The midcrustal to upper crustal strain regime dictates the surface orientation of volcanic vents. Therefore, although linear magmatic belts like those in the central MER may young progressively toward the rift axis and superficially resemble oceanic style magmatism, they actually represent prebreakup magmatism on continental crust. The oldest linear magmatic belts observed seismically and magnetically at the edge of the ocean basins thus may not, as is often assumed, actually mark the onset of seafloor spreading.

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

    SciTech Connect

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

    1995-06-01

    Reflection seismic data, well data, geochemical data, and surface geology suggest that a Cretaceous rift basin exists beneath the thrusted allochthonous sedimentary sequence of the Masirah graben, Oman. The Masirah graben is located east of the Huqf uplift, parallel to the southern coast of Oman. The eastern side of the northeast-trending Huqf anticlinorium is bounded by an extensional fault system that is downthrown to the southeast, forming the western edge of the Masirah graben. This graben is limited to the east by a large wedge of sea floor sediments and oceanic crust, that is stacked as imbricate thrusts. These sediments/ophiolites were obducted onto the southern margin of the Arabian plate during the collision of the Indian/Afghan plates at the end of the Cretaceous. Most of the Masirah graben is covered by an allochthonous sedimentary sequence, which is complexly folded and deformed above a detachment. This complexly deformed sequence contrasts sharply with what is believed to be a rift sequence below the ophiolites. The sedimentary sequence in the Masirah graben was stable until further rifting of the Arabian Sea/Gulf of Aden in the late Tertiary, resulting in reactivation of earlier rift-associated faults. Wells drilled in the Masirah graben in the south penetrated reservoir quality rocks in the Lower Cretaceous Natih and Shuaiba carbonates. Analyses of oil extracted from Infracambrian sedimentary rocks penetrated by these wells suggest an origin from a Mesozoic source rock.

  12. Soil classifications systems review. Final report

    SciTech Connect

    1997-11-01

    Systems used to classify soils are discussed and compared. Major types of classification systems that are reviewed include natural systems, technical systems, the FAO/UNESCO world soil map, soil survey map units, and numerical taxonomy. Natural Classification systems discussed in detail are the United States system, Soil Taxonomy, and the Russian and Canadian systems. Included in the section on technical classification systems are reviews on the AASHO and Unified (ASTM) classification systems. The review of soil classification systems was conducted to establish improved availability of accurate ground thermal conductivity and other heat transfer related properties information. These data are intended to help in the design of closed-loop ground heat exchange systems.

  13. Rift architecture and evolution: The Sirt Basin, Libya: The influence of basement fabrics and oblique tectonics

    NASA Astrophysics Data System (ADS)

    Abdunaser, K. M.; McCaffrey, K. J. W.

    2014-12-01

    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 zones and adjoining highs. Late Eocene rocks exposed in the western part of the basin exhibit a complex network of branching segmented normal and strike-slip faults, generally with a NNW-SSE structural orientations. Many surface structural features have been interpreted from satellite images which confirm sinistral strike-slip kinematics. Relay ramp structures, numerous elongate asymmetric synclines associated with shallow west limbs and steeper dipping east limbs are developed in the hangingwalls adjacent to west downthrowing normal faults. These structural patterns reflect Cretaceous/Tertiary extensional tectonics with additional control by underlying pre-existing Pan-African basement fabrics and ENE-WSW trending Hercynian structures. We relate the Sirt Basin rift development as exemplified in our study area to the break-up of Gondwana represented by the structural evolution of the West-Central African rift system, and the South and Central Atlantic, the Tethys and the Indian Oceans.

  14. Comparing Carbonate-Depositing Hydrothermal Systems Along the Mid-Atlantic Ridge at Lost City Hydrothermal Field and Along the Rio Grande rift in the Southwestern US: Geochemistry, Geomicrobiology and Mineralogy

    NASA Astrophysics Data System (ADS)

    Cron, B. R.; Crossey, L.; Hall, J.; Takacs-Vesbach, C.; Dahm, K.; Northup, D.; Karlstrom, K.

    2008-12-01

    Both continental and marine rift settings are characterized by hydrothermal vents (smokers) that include important components of mantle-derived "endogenic" fluids. These fluids ascend along extensional faults and provide unique biologic settings. We hypothesize that deep crustal processes support near-surface metabolic strategies by delivering chemically reduced constituents to partially oxidized surface environments. Lost City hydrothermal field, a marine vent system located 15 km west of the Mid-Atlantic ridge, exhibits a range of temperatures (40 to 75°C), pH (9-9.8), and mineral compositions (carbonate rather than sulfide-dominated) that were originally thought to be non-existent in marine vent systems. Travertine depositing CO2 springs within the Rio Grande rift, NM exhibit striking similarities in many respects to vents in Lost City. Previous research has already determined the importance of methanogenic and sulfur metabolizing microorganisms in carbonate structures at Lost City. Phylogenetic analysis of 16S rRNA genes from a terrestrial CO2 spring was performed. In addition, cells from bacteria and fungi were also cultured with oligotrophic media. Both archaeal phylotypes from the terrestrial spring grouped within Marine Group I of the Crenarchaeota, a clade dominated by sequences from hydrothermal marine vents, including some from Lost City. We will report comparative analyses of sequences from Lost City and both cultured and environmental clone libraries from the terrestrial spring using UniFrac. Geochemical modeling of data (water and gas chemistry from both locations) is used to rank the energy available for dozens of metabolic reactions. SEM and microprobe data are presented to compare mineral compositions. Our results will be discussed in respect to the tectonic setting, microbial community distributions, and the geochemical composition and textural properties of the carbonates that are precipitated in each of these systems.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    The geological record at rifts and margins worldwide often reveals considerable along-strike variations in volumes of extruded and intruded igneous rocks. These variations may be the result of asthenospheric heterogeneity, variations in rate, and timing of extension; alternatively, preexisting plate architecture and/or the evolving kinematics of extension during breakup may exert first-order control on magmatism. The Main Ethiopian Rift (MER) in East Africa provides an excellent opportunity to address this dichotomy: it exposes, along strike, several sectors of asynchronous rift development from continental rifting in the south to incipient oceanic spreading in the north. Here we perform studies of volcanic cone density and rift obliquity along strike in the MER. By synthesizing these new data in light of existing geophysical, geochemical, and petrological constraints on magma generation and emplacement, we are able to discriminate between tectonic and mantle geodynamic controls on the geological record of a newly forming magmatic rifted margin. The timing of rift sector development, the three-dimensional focusing of melt, and the ponding of plume material where the rift dramatically narrows each influence igneous intrusion and volcanism along the MER. However, rifting obliquity plays an important role in localizing intrusion into the crust beneath en echelon volcanic segments. Along-strike variations in volumes and types of igneous rocks found at rifted margins thus likely carry information about the development of strain during rifting, as well as the physical state of the convecting mantle at the time of breakup.

  17. The 2003-2004 seismic swarm in the western Corinth rift: Evidence for a multiscale pore pressure diffusion process along a permeable fault system

    NASA Astrophysics Data System (ADS)

    Duverger, Clara; Godano, Maxime; Bernard, Pascal; Lyon-Caen, Hélène; Lambotte, Sophie

    2015-09-01

    Microseismic multiplets occurring in the western Corinth rift, Greece, during a large swarm are analyzed to retrieve their spatiotemporal characteristics. These multiplets activated small subfaults at depth (˜7 km), up to 1 km long, at the root of two parallel active normal faults. The swarm migrates westward nearly horizontally over 10 km at an average velocity of 50 m/d with a diffusivity of 0.5 m2 s-1. It successively activates the Aigion fault, a relay zone in its hanging wall, and the Fassouleika fault. Within each multiplet, hypocenters also migrate with diffusivities ranging from 0.001 to 0.4 m2 s-1. The largest internal diffusivities appear at the core of the layer defined by the clusters. These results are interpreted as a hydroshear process caused by pore pressure migration within permeable corridors resulting from the intersection of the major faults with a brittle geological layer inherited from the Hellenic nappe stack.

  18. Final Paper DAT Cognitive Art Therapy System

    ERIC Educational Resources Information Center

    Jacobson, Eric

    2009-01-01

    Del Giacco Art Therapy is a cognitive art therapy process that focuses on stimulating the mental sensory systems and working to stabilize the nervous system and create new neural connections in the brain. This system was created by Maureen Del Giacco, Phd. after recovering from her own traumatic brain injury and is based on extensive research of…

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

    NASA Astrophysics Data System (ADS)

    Cohen, A. S.

    2014-12-01

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

  20. Rio Grande rift: problems and perspectives

    SciTech Connect

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

    1984-01-01

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

  1. Stable isotope variation in tooth enamel from Neogene hippopotamids: monitor of meso and global climate and rift dynamics on the Albertine Rift, Uganda

    NASA Astrophysics Data System (ADS)

    Brachert, Thomas Christian; Brügmann, Gerhard B.; Mertz, Dieter F.; Kullmer, Ottmar; Schrenk, Friedemann; Jacob, Dorrit E.; Ssemmanda, Immaculate; Taubald, Heinrich

    2010-10-01

    The Neogene was a period of long-term global cooling and increasing climatic variability. Variations in African-Asian monsoon intensity over the last 7 Ma have been deduced from patterns of eolian dust export into the Indian Ocean and Mediterranean Sea as well as from lake level records in the East African Rift System (EARS). However, lake systems not only depend on rainfall patterns, but also on the size and physiography of river catchment areas. This study is based on stable isotope proxy data (18O/16O, 13C/12C) from tooth enamel of hippopotamids (Mammalia) and aims in unravelling long-term climate and watershed dynamics that control the evolution of palaeolake systems in the western branch of the EARS (Lake Albert, Uganda) during the Late Neogene (7.5 Ma to recent). Having no dietary preferences with respect to wooded (C3) versus grassland (C4) vegetation, these territorial, water-dependant mammals are particularly useful for palaeoclimate analyses. As inhabitants of lakes and rivers, hippopotamid tooth enamel isotope data document mesoclimates of topographic depressions, such as the rift valleys and, therefore, changes in relative valley depth instead of exclusively global climate changes. Consequently, we ascribe a synchronous maximum in 18O/16O and 13C/12C composition of hippopotamid enamel centred around 1.5-2.5 Ma to maximum aridity and/or maximum hydrological isolation of the rift floor from rift-external river catchment areas in response to the combined effects of rift shoulder uplift and subsidence of the rift valley floor. Structural rearrangements by ~2.5 Ma within the northern segment of the Albertine Rift are well constrained by reversals in river flow, cannibalisation of catchments, biogeographic turnover and uplift of the Rwenzori horst. However, a growing rain shadow is not obvious in 18O/16O signatures of the hippopotamid teeth of the Albertine Rift. According to our interpretation, this is the result of the overriding effect of evaporation on 18O/16O responding to aridification of the basin floor by a valley air circulation system through relative deepening of the valley. On the other hand, a synchronous arid pulse is not so clearly recorded in palaeosol data and mammalian fauna of the eastern branch of the EARS. This discrepancy indicates that rift mesoclimates may represent an underestimated aspect in previous palaeoclimate reconstructions from rift valley data and represent a clear limitation to attempts at global climate reconstructions. The results of this study also suggest that using 18O/16O data as a proxy to rain shadow evolution must take into account relative basin subsidence to properly document mountain range uplift.

  2. Manzanita Hybrid Power system Project Final Report

    SciTech Connect

    Trisha Frank

    2005-03-31

    The Manzanita Indian Reservation is located in southeastern San Diego County, California. The Tribe has long recognized that the Reservation has an abundant wind resource that could be commercially utilized to its benefit, and in 1995 the Tribe established the Manzanita Renewable Energy Office. Through the U.S. Department of Energy's Tribal Energy Program the Band received funds to install a hybrid renewable power system to provide electricity to one of the tribal community buildings, the Manzanita Activities Center (MAC building). The project began September 30, 1999 and was completed March 31, 2005. The system was designed and the equipment supplied by Northern Power Systems, Inc, an engineering company with expertise in renewable hybrid system design and development. Personnel of the National Renewable Energy Laboratory provided technical assistance in system design, and continued to provide technical assistance in system monitoring. The grid-connected renewable hybrid wind/photovoltaic system provides a demonstration of a solar/wind energy hybrid power-generating project on Manzanita Tribal land. During the system design phase, the National Renewable Energy Lab estimated that the wind turbine is expected to produce 10,000-kilowatt hours per year and the solar array 2,000-kilowatt hours per year. The hybrid system was designed to provide approximately 80 percent of the electricity used annually in the MAC building. The project proposed to demonstrate that this kind of a system design would provide highly reliable renewable power for community uses.

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

    NASA Astrophysics Data System (ADS)

    Buiter, Susanne; Tetreault, Joya; Torsvik, Trond

    2015-04-01

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

  4. Solar heating system final design package

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The system is composed of a warm air collector, a logic control unit and a universal switching and transport unit. The collector was originally conceived and designed as an integrated roof/wall system and therefore provides a dual function in the structure. The collector serves both as a solar energy conversion system and as a structural weather resistant skin. The control unit provides totally automatic control over the operation of the system. It receives input data from sensor probes in collectors, storage and living space. The logic was designed so as to make maximum use of solar energy and minimize use of conventional energy. The transport and switching unit is a high-efficiency air-handling system equipped with gear motor valves that respond to outputs from the control system. The fan unit was designed for maximum durability and efficiency in operation, and has permanently lubricated ball bearings and excellent air-handling efficiency.

  5. Statistical mechanics of polymer systems. Final

    SciTech Connect

    Kovac, J.

    1993-06-01

    Work on computer simulation of polymer dynamics and the statistical mechanics of quenched systems carried out over seven years with the support of this grant is reviewed. The computer simulation work has focused on elucidation the roles of the excluded volume and the nearest-neighbor attractive interactions in the dynamics of polymers. To study quenched systems we have applied the formalism suggested long ago by Mazo to two model systems and found qualitative agreement with the properties of real glasses.

  6. Concentrating solar collector system. Final report

    SciTech Connect

    Mingo, R.D.

    1981-08-30

    A brief report on a solar heat-collecting system for home use is presented. The primary objective of the project was to test the feasibility of using low-cost materials to construct an efficient collector. The system includes a single, large, homemade roof-mounted collector, two heat storage tanks, a moderately complex control unit, and circulating pumps. During operation the heating system provided approximately 60% of the domestic hot water needs for a family of five. (BCS)

  7. General Training System; GENTRAS. Final Report.

    ERIC Educational Resources Information Center

    International Business Machines Corp., Gaithersburg, MD. Federal Systems Div.

    GENTRAS (General Training System) is a computer-based training model for the Marine Corps which makes use of a systems approach. The model defines the skill levels applicable for career growth and classifies and defines the training needed for this growth. It also provides a training cost subsystem which will provide a more efficient means of…

  8. Proximity sensor system development. CRADA final report

    SciTech Connect

    Haley, D.C.; Pigoski, T.M.

    1998-01-01

    Lockheed Martin Energy Research Corporation (LMERC) and Merritt Systems, Inc. (MSI) entered into a Cooperative Research and Development Agreement (CRADA) for the development and demonstration of a compact, modular proximity sensing system suitable for application to a wide class of manipulator systems operated in support of environmental restoration and waste management activities. In teleoperated modes, proximity sensing provides the manipulator operator continuous information regarding the proximity of the manipulator to objects in the workspace. In teleoperated and robotic modes, proximity sensing provides added safety through the implementation of active whole arm collision avoidance capabilities. Oak Ridge National Laboratory (ORNL), managed by LMERC for the United States Department of Energy (DOE), has developed an application specific integrated circuit (ASIC) design for the electronics required to support a modular whole arm proximity sensing system based on the use of capacitive sensors developed at Sandia National Laboratories. The use of ASIC technology greatly reduces the size of the electronics required to support the selected sensor types allowing deployment of many small sensor nodes over a large area of the manipulator surface to provide maximum sensor coverage. The ASIC design also provides a communication interface to support sensor commands from and sensor data transmission to a distributed processing system which allows modular implementation and operation of the sensor system. MSI is a commercial small business specializing in proximity sensing systems based upon infrared and acoustic sensors.

  9. Power system control valuation methodology. Final report

    SciTech Connect

    Richardson, L.M.; Brander, J.A.; Larsen, E.V.

    1995-12-01

    The information and methodologies presented in this report are intended to assist electric utility planning engineers identify and valuate potential power system control device applications, both thyristor-based and conventional, to achieve greater utilization of their power transmission systems. The report presents a methodology for the economic valuation of control devices in power transmission systems. The methodology is applicable to the newer thyristor-based control technologies as well as conventional control approaches. The report also presents generalized power system scenarios, each representing a specific system operation or performance limitation, that lend themselves to potential FACTs applications, along with identification of the most applicable control devices. Descriptions of recent FACTs application studies, as detailed in EPRI reports or the technical literature, are presented in synopsis form and cross-referenced to the generalized system scenarios. References for these studies are included to direct the reader to more detailed descriptions of the specific application studies. A master control device matrix serves as a road map to guide the system planning engineer through the control device valuation process.

  10. How does the continental crust thin during rifting in magma-poor rifted margins: evidence from the Bernina/Campo/Grosina units in the Central Alps (SE-Switzerland and N-Italy)

    NASA Astrophysics Data System (ADS)

    Mohn, G.; Manatschal, G.; Masini, E.; Beltrando, M.; Muntener, O.; Kusznir, N. J.

    2010-12-01

    A long-standing problem in Earth Sciences is to understand how continents break apart to form new oceanic basins. Many of the questions that currently frame ongoing debates about continental break-up are related to the mechanics of extreme lithospheric extension. Studies conducted in several present-day magma-poor rifted margins revealed that the transition from continental crust that underwent minor thinning in proximal margins to hyper extended crust (?10 km) in distal margins occurs within a well-defined necking zone. The low resolution of the available offshore data and the lack of drilling make it difficult to study the structures and processes associated with crustal thinning in present-day rifted margins. A more direct access to the stratigraphic record and crustal architecture of deep-water rifted margins is exposed in the Alps in Western Europe. We focused our study on the Austroalpine Bernina-Campo-Grosina units, which preserve relics of the former necking zone of the Alpine Tethys rifted margin. Within this necking zone, different high-strain shear zones responsible for lithospheric thinning can be defined including: 1) a system of conjugate low-angle shear zones/detachment faults active in the brittle upper crust (Grosina detachment) and lower crust (Pogallo type shear zone); 2) mid-crustal decollements decoupling the deformation in the upper and lower crust (e.g. Eita shear zone); and 3) an extraction shear zone, whose activity resulted in the total excision of the middle crust (e.g. Margna shear zone). These high-strain zones are interpreted to accommodate crustal thinning from 30 to 10 km during Piensbachian to Toarcian time (190-180Ma). Thinning resulted in exhumation of mid-crustal rocks in the necking zone, while in the distal margin upper and lower crust are juxtaposed and overprinted by late detachment faults that cut across the thinned crust and exhume mantle rocks to the seafloor. These structures can explain the first-order crustal architecture observed at many present-day rifted margins.The results of this study will permit to better constraints the extreme thinning of the crust leading finally to the continental break up. These results have major implications for the thermal evolution and consequently for the rheology and isostasy of the extending lithosphere.

  11. Water-storage-tube systems. Final report

    SciTech Connect

    Hemker, P.

    1981-12-24

    Passive solar collection/storage/distribution systems were surveyed, designed, fabricated, and mechanically and thermally tested. The types studied were clear and opaque fiberglass tubes, metal tubes with plastic liners, and thermosyphoning tubes. (MHR)

  12. Analysis of Hybrid Hydrogen Systems: Final Report

    SciTech Connect

    Dean, J.; Braun, R.; Munoz, D.; Penev, M.; Kinchin, C.

    2010-01-01

    Report on biomass pathways for hydrogen production and how they can be hybridized to support renewable electricity generation. Two hybrid systems were studied in detail for process feasibility and economic performance. The best-performing system was estimated to produce hydrogen at costs ($1.67/kg) within Department of Energy targets ($2.10/kg) for central biomass-derived hydrogen production while also providing value-added energy services to the electric grid.

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

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Korostelev, Félicie; Weemstra, Cornelis; Leroy, Sylvie; Boschi, Lapo; Keir, Derek; Ren, Yong; Molinari, Irene; Ahmed, Abdulhakim; Stuart, Graham W.; Rolandone, Frédérique; Khanbari, Khaled; Hammond, James O. S.; Kendall, J. M.; Doubre, Cécile; Ganad, Ismail Al; Goitom, Berhe; Ayele, Atalay

    2015-04-01

    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 velocity maps of the crust and uppermost mantle of the conjugate margins of the southern Red Sea (Afar and Yemen) using ambient noise tomography to constrain crustal modification during breakup. Our images show that the low seismic velocities characterize not only the upper crust beneath the axial volcanic systems but also both upper and lower crust beneath the rift flanks where ongoing volcanism and hydrothermal activity occur at the surface. Magmatic modification of the crust beneath rift flanks likely occurs for a protracted period of time during the breakup process and may persist through to early seafloor spreading.

  15. Final Report Advanced Quasioptical Launcher System

    SciTech Connect

    Jeffrey Neilson

    2010-04-30

    This program developed an analytical design tool for designing antenna and mirror systems to convert whispering gallery RF modes to Gaussian or HE11 modes. Whispering gallery modes are generated by gyrotrons used for electron cyclotron heating of fusion plasmas in tokamaks. These modes cannot be easily transmitted and must be converted to free space or waveguide modes compatible with transmission line systems.This program improved the capability of SURF3D/LOT, which was initially developed in a previous SBIR program. This suite of codes revolutionized quasi-optical launcher design, and this code, or equivalent codes, are now used worldwide. This program added functionality to SURF3D/LOT to allow creating of more compact launcher and mirror systems and provide direct coupling to corrugated waveguide within the vacuum envelope of the gyrotron. Analysis was also extended to include full-wave analysis of mirror transmission line systems. The code includes a graphical user interface and is available for advanced design of launcher systems.

  16. National Geoscience Data Repository System. Final report

    SciTech Connect

    Schiffries, C.M.; Milling, M.E.

    1994-03-01

    The American Geological Institute (AGI) has completed the first phase of a study to assess the feasibility of establishing a National Geoscience Data Repository System to capture and preserve valuable geoscientific data. The study was initiated in response to the fact that billions of dollars worth of domestic geological and geophysical data are in jeopardy of being irrevocably lost or destroyed as a consequence of the ongoing downsizing of the US energy and minerals industry. This report focuses on two major issues. First, it documents the types and quantity of data available for contribution to a National Geoscience Data Repository System. Second, it documents the data needs and priorities of potential users of the system. A National Geoscience Data Repository System would serve as an important and valuable source of information for the entire geoscience community for a variety of applications, including environmental protection, water resource management, global change studies, and basic and applied research. The repository system would also contain critical data that would enable domestic energy and minerals companies to expand their exploration and production programs in the United States for improved recovery of domestic oil, gas, and mineral resources.

  17. [Develop mine communications system]. Final technical report

    SciTech Connect

    Meiksin, Z.H.

    1998-09-15

    The objective of this project was to develop, design, and build a system prototype to demonstrate the practicality of two-way, wireless through-the-earth communications between the interior of a mine and the surface. The system was to communicate data for process and environment monitoring and control, and provide real-time voice communication for emergency situations and for daily operations use. Transmitters and receivers were designed, built, and tested in actual mines. A wireless in-mine communications system was also developed. The feasibility of the concept and the marketability of the product were successfully demonstrated. Additional work must be done to make the product suitable for, and marketable to, the coal mining industry.

  18. The final fate of planetary systems

    NASA Astrophysics Data System (ADS)

    Gaensicke, Boris

    2015-12-01

    The discovery of the first extra-solar planet around a main-sequence star in 1995 has changed the way we think about the Universe: our solar system is not unique. Twenty years later, we know that planetary systems are ubiquitous, orbit stars spanning a wide range in mass, and form in an astonishing variety of architectures. Yet, one fascinating aspect of planetary systems has received relatively little attention so far: their ultimate fate.Most planet hosts will eventually evolve into white dwarfs, Earth-sized stellar embers, and the outer parts of their planetary systems (in the solar system, Mars and beyond) can survive largely intact for billions of years. While scattered and tidally disrupted planetesimals are directly detected at a small number of white dwarfs in the form infrared excess, the most powerful probe for detecting evolved planetary systems is metal pollution of the otherwise pristine H/He atmospheres.I will present the results of a multi-cycle HST survey that has obtained COS observations of 136 white dwarfs. These ultraviolet spectra are exquisitely sensitive to the presence of metals contaminating the white atmosphere. Our sophisticated model atmosphere analysis demonstrates that at least 27% of all targets are currently accreting planetary debris, and an additional 29% have very likely done so in the past. These numbers suggest that planet formation around A-stars (the dominant progenitors of today's white dwarf population) is similarly efficient as around FGK stars.In addition to post-main sequence planetary system demographics, spectroscopy of the debris-polluted white dwarf atmospheres provides a direct window into the bulk composition of exo-planetesimals, analogous to the way we use of meteorites to determine solar-system abundances. Our ultraviolet spectroscopy is particularly sensitive to the detection of Si, a dominant rock-forming species, and we identify up to ten additional volatile and refractory elements in the most strongly contaminated white dwarfs. The derived bulk abundances unambiguously demonstrate the predominantly rocky nature of the accreted material, with two exceptions where we detect volatile-rich debris. The relative abundance ratios suggest a wide range of parent bodies, including both primitive asteroids and fragments from differentiated planetesimals. The growing number of detailed debris abundances can provide important observational constraints on planet formation models.

  19. Spill response system configuration study. Final report

    SciTech Connect

    Desimone, R.V.; Agosta, J.M.

    1996-05-01

    This report describes the development of a prototype decision support system for oil spill response configuration planning that will help U.S. Coast Guard planners to determine the appropriate response equipment and personnel for major spills. The report discusses the application of advanced artificial intelligence planning techniques, as well as other software tools for spill trajectory modeling, plan evaluation and map display. The implementation of the prototype system is discussed in the context of two specific major spill scenarios in the San Francisco Bay.

  20. Heavy ion fusion final focus system

    SciTech Connect

    Krafft, G.

    1980-10-01

    A system for transporting and focusing a 10 GeV U/sup +4/ beam in the high current regime is outlined. First descriptions of the beam model and the beam parameters used in the design are given. The goals and requirements are then briefly discussed, and an explanation of the design approach follows. A description of the system itself is next, followed by some discussion of its tolerances, both to momentum and current deviations. A brief summary of simulation results is then included. This note concludes with a short description of possible modifications and an evaluation of the design.

  1. Immersive Visualization for Materials Science Data Analysis using the Oculus Rift

    SciTech Connect

    Drouhard, Margaret MEG G; Steed, Chad A; Hahn, Steven E; Proffen, Thomas E; Daniel, Jamison R; Matheson, Michael A

    2015-01-01

    In this paper, we propose strategies and objectives for immersive data visualization with applications in materials science using the Oculus Rift virtual reality headset. We provide background on currently available analysis tools for neutron scattering data and other large-scale materials science projects. In the context of the current challenges facing scientists, we discuss immersive virtual reality visualization as a potentially powerful solution. We introduce a prototype immersive visual- ization system, developed in conjunction with materials scientists at the Spallation Neutron Source, which we have used to explore large crystal structures and neutron scattering data. Finally, we offer our perspective on the greatest challenges that must be addressed to build effective and intuitive virtual reality analysis tools that will be useful for scientists in a wide range of fields.

  2. Visual Response System Demonstration Project. Final Report.

    ERIC Educational Resources Information Center

    Heward, William L.

    The report details development and implementation of a project to use the visual response system (VRS) to aid the mainstreaming of mildly handicapped students. The VRS uses overhead projectors, individual earphones, and other hardware at each student's desk so that students can respond to teacher presentations. The advantages are listed for the…

  3. Hydrogen energy systems studies. Final technical report

    SciTech Connect

    Ogden, J.M.; Kreutz, T.; Kartha, S.; Iwan, L.

    1996-08-13

    The results of previous studies suggest that the use of hydrogen from natural gas might be an important first step toward a hydrogen economy based on renewables. Because of infrastructure considerations (the difficulty and cost of storing, transmitting and distributing hydrogen), hydrogen produced from natural gas at the end-user`s site could be a key feature in the early development of hydrogen energy systems. In the first chapter of this report, the authors assess the technical and economic prospects for small scale technologies for producing hydrogen from natural gas (steam reformers, autothermal reformers and partial oxidation systems), addressing the following questions: (1) What are the performance, cost and emissions of small scale steam reformer technology now on the market? How does this compare to partial oxidation and autothermal systems? (2) How do the performance and cost of reformer technologies depend on scale? What critical technologies limit cost and performance of small scale hydrogen production systems? What are the prospects for potential cost reductions and performance improvements as these technologies advance? (3) How would reductions in the reformer capital cost impact the delivered cost of hydrogen transportation fuel? In the second chapter of this report the authors estimate the potential demand for hydrogen transportation fuel in Southern California.

  4. Pre-rift basement structure and syn-rift faulting at the eastern onshore Gulf of Corinth Rift

    NASA Astrophysics Data System (ADS)

    Kranis, Haralambos; Skourtsos, Emmanuel; Gawthorpe, Robert; Leeder, Mike; Stamatakis, Michael

    2015-04-01

    %B We present results of recent field-based research with a view to providing information about and constraints on the initiation and evolution of the Gulf of Corinth (GoC) Rift. The onshore geology and structure of the GoC rift has been studied intensively and extensively; however most research efforts have focused on the western and partly the central parts. The last few years, efforts are being made to extend the scope of research in less-studied areas, such as the eastern southern onshore part of the GoC rift, trying to address two major issues in rift initiation and evolution, namely syn-rift faulting and pre-rift basement structure. While fault spacing and length appears to be well-constrained for the western and central parts of the GoC Rift, further east -and especially in the uplifted onshore southern part- this is thought to increase dramatically, as there are practically no mapped faults. We argue, however, that this may be a false image, owing to (i) the difficulty in identifying fault structures within a thick, fairly monotonous syn-rift sequence; (ii) the lesser attention this part has drawn; and (ii) the fact that the published summary geological and tectonic maps of the GoC area are based on the dated geological maps that cover the eastern and northern onshore shoulders of the Rift. Moreover, new field data provide new information on pre-rift structure: while only the topmost thrust sheet of the Hellenide nappe stack (Pindos Unit) was thought to crop out at the eastern southern onshore part, we mapped the underlying, non-metamorphic carbonate Unit (Tripolis Unit), which crops out within the footwall of a key intra-basin block (Xylokastro block). A minor outcrop further east, may also belong to this Unit, providing basement control, in connection with recently published offshore fault data. The mapping of these outcrops, combined with a revised stratigraphical framework for the early syn-rift deposits, allows the identification and mapping of faults within this less studied area. Regarding the pre-rift basement structure, not only the known, or inferred, pre-rift heterogeneities along rift axis, but also ongoing lithospheric processes affect the evolution of the GoC Rift. The suggestion that the exposure of the deeper metamorphic Units at the southern border of the rift is related to an earlier (?Miocene) age, thus constituting an inherited structure, is at odds with results from geothermochronological data from the southern Peloponnesus and Kythira, which suggest that these Units lay at a depth of at least 4 km in the Middle ((?)Late) Miocene. This means that the metamorphic outcrops at the southern border of the GoC Rift are the product of a later (possibly Quaternary) process of uplift, probably resulting from localized N-S culmination, whose locus is in the central Peloponnesus. Moreover, current (and Upper Quaternary) uplift rates along the southern shoulder of the GoC may also be related to and/or reflect the uplift of the nappe pile including the lower, metamorphic basement Units.

  5. Investigation of rifting processes in the Rio Grande Rift using data from unusually large earthquake swarms

    SciTech Connect

    Sanford, A.; Balch, R.; House, L.; Hartse, H.

    1995-12-01

    San Acacia Swarm in the Rio Grande Rift. Because the Rio Grande rift is one of the best seismically instrumented rift zones in the world, studying its seismicity provides an exceptional opportunity to explore the active tectonic processes within continental rifts. We have been studying earthquake swarms recorded near Socorro in an effort to link seismicity directly to the rifting process. For FY94, our research has focused on the San Acacia swarm, which occurred 25 km north of Socorro, New Mexico, along the accommodation zone between the Albuquerque-Belen and Socorro basins of the central Rio Grande rift. The swarm commenced on 25 February 1983, had a magnitude 4.2 main shock on 2 March and ended on 17 March, 1983.

  6. Solar heating system installed at Troy, Ohio. Final report

    SciTech Connect

    1980-09-01

    This document is the Final Report of the Solar Energy System located at Troy-Miami County Public Library, Troy, Ohio. The completed system is composed of tree basic subsystems: the collector system consisting of 3264 square feet of Owens Illinois evacuated glass tube collectors; the storage system which includes a 5000-gallon insulated steel tank; and the distribution and control system which includes piping, pumping and control logic for the efficient and safe operation of the entire system. This solar heating system was installed in an existing facility and is, therefore, a retrofit system. This report includes extracts from the site files, specifications, drawings, installation, operation and maintenance instructions.

  7. FY07 Final Report for Calibration Systems

    SciTech Connect

    Myers, Tanya L.; Broocks, Bryan T.; Cannon, Bret D.; Ho, Nicolas

    2007-12-01

    Remote infrared (IR) sensing provides a valuable method for detection and identification of materials associated with nuclear proliferation. Current challenges for remote sensors include minimizing the size, mass, and power requirements for cheaper, smaller, and more deployable instruments without affecting the measurement performance. One area that is often overlooked is sensor calibration design that is optimized to minimize the cost, size, weight, and power of the payload. Yet, an on-board calibration system is essential to account for changes in the detector response once the instrument has been removed from the laboratory. The Calibration Systems project at Pacific Northwest National Laboratory (PNNL) is aimed towards developing and demonstrating compact quantum cascade (QC) laser-based calibration systems for infrared sensor systems in order to provide both a spectral and radiometric calibration while minimizing the impact on the instrument payload. In FY05, PNNL demonstrated a multi-level radiance scheme that provides six radiance levels for an enhanced linearity check compared to the currently accepted two-point scheme. PNNL began testing the repeatability of this scheme using a cryogenically cooled, single-mode quantum cascade laser (QCL). A cyclic variation in the power was observed that was attributed to the thermal cycling of the laser's dewar. In FY06, PNNL continued testing this scheme and installed an auxiliary liquid nitrogen reservoir to limit the thermal cycling effects. Although better repeatability was achieved over a longer time period, power fluctuations were still observed due to the thermal cycling. Due to the limitations with the cryogenic system, PNNL began testing Fabry-Perot QCLs that operate continuous-wave (cw) or quasi-cw at room temperature (RT) in FY06. PNNL demonstrated a multi-level scheme that provides five radiance levels in 105 seconds with excellent repeatability. We have continued testing this repeatability in FY07. A burn-in effect appears in which the power increases over a certain time period. Repeatability better than 1%, however, is demonstrated for most of the radiance levels after this initial burn-in. In FY06, PNNL also began investigating a fiber-coupled RT QCL for a compact IR calibration source. PNNL demonstrated a uniform beam profile by measuring a time-averaged response and modulating the fiber optic with a motor to minimize the effects of speckle. In FY07, PNNL examined the power stability of fiber-coupled QCLs. Feedback appears to degrade the stability so that anti-reflective coatings for fibers may be essential. In FY07, PNNL continued to investigate the stability of room temperature QCLs as well as the measurement technique to provide a quantitative estimate for the measurement uncertainty. We designed and built a custom environmental enclosure to reduce the measurement uncertainty. After an initial burn-in, we have achieved uncertainties better than 0.1% for data collected over almost 100 hours of operation. We also built a bench-top system to demonstrate how the QC laser can be used to calibrate a microbolometer array and illustrated the importance of a multi-point calibration.

  8. Stirred Heat Exchanger (SHE) systems. Final report

    SciTech Connect

    Not Available

    1981-12-18

    A general objective of this project was to design, evaluate, and commercialize internally- and externally-stirred heat exchangers systems, particularly in applications involving energy recovery from dirty and condensing combustion products. The manufacturing and test facility was totally destroyed by fire within approximately 8 weeks of the initial contract period, along with all SHE prototypes, instrumentation, and special equipment. An externally-stirred heat exchanger was developed which incorporates certain practical features and satisfies the objectives of the project. A detailed description of this SHE is presented and its technical features in different product applications are reviewed. (MHR)

  9. Final Report of Strongly Interacting Fermion Systems

    SciTech Connect

    Wilkins, J. W.

    2001-06-25

    There has been significant progress in three broad areas: (A) Optical properties, (B) Large-scale computations, and (C) Many-body systems. In this summary the emphasis is primarily on those papers that point to the research plans. At the same time, some important analytic work is not neglected, some of it even appearing in the description of large-scale Computations. Indeed one of the aims of such computations is to give new insights which lead to development of models capable of simple analytic or nearly analytic analysis.

  10. FY2008 Calibration Systems Final Report

    SciTech Connect

    Cannon, Bret D.; Myers, Tanya L.; Broocks, Bryan T.

    2009-01-01

    The Calibrations project has been exploring alternative technologies for calibration of passive sensors in the infrared (IR) spectral region. In particular, we have investigated using quantum cascade lasers (QCLs) because these devices offer several advantages over conventional blackbodies such as reductions in size and weight while providing a spectral source in the IR with high output power. These devices can provide a rapid, multi-level radiance scheme to fit any nonlinear behavior as well as a spectral calibration that includes the fore-optics, which is currently not available for on-board calibration systems.

  11. Geophysical tomography imaging system. Final CRADA report

    SciTech Connect

    Norton, S.J.; Won, I.J.

    1998-05-20

    The Cooperative Research and Development Agreement (CRADA) between Lockheed Martin Energy Systems, Inc., and Geophex, Ltd., was established to investigate high-resolution, shallow acoustic imaging of the subsurface. The primary objectives of the CRADA were accomplished, including the evaluation of a new tomographic imaging algorithm and the testing and comparison of two different acoustic sources, the hammer/plate source and an electromagnetic vibratory source. The imaging system was composed essentially of a linear array of geophones, a digital seismograph, and imaging software installed on a personal computer. Imaging was most successful using the hammer source, which was found to be less susceptible to ground roll (surface wave) interference. It is conjectured that the vibratory source will perform better for deeper targets for which ground roll is less troublesome. Potential applications of shallow acoustic imaging are numerous, including the detection and characterization of buried solid waste, unexploded ordnance, and clandestine man-made underground structures associated with treaty verification (e.g., tunnels, underground storage facilities, hidden bunkers).

  12. Physics of Correlated Systems, Final Project Report

    SciTech Connect

    Greene, Chris H.

    2014-06-25

    The funding of this DOE project has enabled the P.I. and his collaborators to tackle a number of problems involving nonperturbatively coupled atomic systems, including their interactions with each other and/or with an external electromagnetic field of the type provided by either a continuous-wave or a femtosecond short-pulse laser. The progress includes a new, deeper understanding of an old and famous theory of autoionization lineshapes, developed initially by Ugo Fano in 1935 and later extended in a highly cited 1961 article; the new result specifically is that in a collaboration with the Heidelberg group we have been able to demonstrate an unexpectedly simple behavior in the time domain that is relevant for modern short-pulse lasers. This study also demonstrates a way to modify and even control the lineshapes of unstable atomic and molecular energy levels.

  13. Continental rift development in Precambrian and Phanerozoic Europe: EUROPROBE and the Dnieper-Donets Rift and Polish Trough basins

    NASA Astrophysics Data System (ADS)

    Stephenson, R. A.

    1993-07-01

    Upper crustal structure and lower crustal and mantle character of the European continental lithosphere differ significantly from west to east. The processes of rifting of Phanerozoic western Europe's hotter, thinner crust compared with the more stable, thicker (45 vs 30 km) Proterozoic crust of the East European Craton is being investigated by EUROPROBE case studies of western and eastern European sedimentary basins. The Dnieper—Donets basin transects the southwestern part of the East European platform in a NW—SE direction, lying between the Ukrainian Shield and the Voronezh Massif. Rifting took place from early Frasnian until perhaps the late Visean and was accompanied by major volcanic activity. The distribution of both was affected by pre-existing basement fault systems. The syn- and post-rift sedimentary succession may be as thick as 20 km in the Donets Trough. Basin evolution and the present crustal geometry have been much affected by "inversion" during the Permian in association with Uralian orogenesis. Tectonic events of Bathonian—Oxfordian (˜ 168-154 Ma) and Turonian—Santonian (˜ 91-84 Ma) age are also recorded in the basin stratigraphy. The Polish Trough lies along the boundary between the Phanerozoic and Proterozoic European crustal domains, coincident with the Trans-European Suture Zone. The presence of this rheological boundary may be paramount in structurally controlling the position of the Trough. Tectonic subsidence analysis indicates an initial (late) Rotliegendes—Early Triassic syn-rift phase of development. Subsequently, episodes of increased tectonic subsidence rate occurred during the Oxfordian—Tithonian (? 157-146 Ma) and beginning in the Cenomanian (? 95-90 Ma). The Oxfordian—Tithonian episode is likely the signature of a second extensional event (correlated with intensification of rifting within the Arctic—North Atlantic rift system) while the Cenomanian and later is a precursor to mild compressional, intraplate orogenic movements. Present-day crustal structure reflects the "docking" of Phanerozoic crust against the Proterozoic during Palaeozoic orogenies, Permo—Carboniferous wrenching and transtensional modifications leading to formation of the Polish Trough, as well as modifications during the Late Cretaceous—Early Tertiary inversion process.

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

    SciTech Connect

    Genik, G.J. )

    1993-08-01

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

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

    USGS Publications Warehouse

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

    1991-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  17. New perspectives on the evolution of narrow, modest extension continental rifts: Embryonic core complexes and localized, rapid Quaternary extension in the Rio Grande rift, central New Mexico

    NASA Astrophysics Data System (ADS)

    Ricketts, J.; Karlstrom, K. E.; Kelley, S.

    2013-12-01

    Updated models for continental rift zones need to address the role and development of low-angle normal fault networks, episodicity of extension, and interaction of 'active and passive' driving mechanisms. In the Rio Grande rift, USA, low-angle normal faults are found throughout the entire length of the rift, but make up a small percentage of the total fault population. The low-angle Jeter and Knife Edge faults, for example, crop out along the SW and NE margins of the Albuquerque basin, respectively. Apatite fission track (AFT) age-elevation data and apatite (U-Th)/He (AHe) ages from these rift flank uplifts record cooling between ~21 - 16 Ma in the NE rift flank and ~20 - 10 Ma in the SW, which coincides with times of rapid extension and voluminous syntectonic sedimentation. The timing of exhumation is also similar to rift flanks farther north in active margins based on AFT data alone. In addition, synthetic faults in the hanging wall of each low-angle fault become progressively steeper and younger basinward, and footwall blocks are the highest elevation along the rift flanks. These observations are consistent with a model where initially high-angle faults are shallowed in regions of maximum extension. As they rotate, new intrabasinal faults emerge which also can be rotated if extension continues. These relationships are similarly described in mature core complexes, and if these processes continued in the Rio Grande rift, it could eventually result in mid-crustal ductily deformed rocks in the footwall placed against surficial deposits in the hanging wall across faults that have been isostatically rotated to shallow dips. Although existing data are consistent with highest strain rates during a pulse of extension along the entire length of the rift 20-10 Ma., GPS-constrained measurements suggest that the rift is still actively-extending at 1.23-1.39 nstr/yr (Berglund et al., 2012). Additional evidence for Quaternary extension comes from travertine deposits that are cut by multiple tensile vein sets along the western margin of the Albuquerque basin in the Lucero uplift. At this location, U-series ages on travertine deposits are used to calculate strain rates at this location. These strain rates (15-105 nstr/yr) are higher than both the modern strain rates as well as the average long-term strain rates (3-14 nstr/yr) obtained from restored cross-sections across different basins in the rift. To explain these observations, we propose a model involving high fluid pressures, which promote the formation of tensile veins that are oriented with respect to the modern day stress field in the rift. These regions of anomalously-high strain need not be widespread, and are only active on timescales of the hydraulic system, but they are nevertheless an underappreciated mechanism of progressive extension in the rift. Berglund, H.T., Sheehan, A.F., Murray, M.H., Roy, M., Lowry, A.R., Nerem, R.S., and Blume, F., 2012, Distributed deformation across the Rio Grande Rift, Great Plains, and Colorado Plateau: Geology, v. 40, p. 23-26.

  18. Formation of the Shanxi Rift in North China: The control of preexisting lithospheric weakness

    NASA Astrophysics Data System (ADS)

    Lin, F.; Liu, M.; Ye, J.

    2012-12-01

    The Shanxi Rift is an active seismic zone in North China, developed mainly since Pliocene (~5 Ma). Its formation has been associated with the Indo-Asian collision; other hypothesized causes include a regional extensional stress field associated with subduction of the western pacific plate and mantle upwelling under the North China Plain. However, these mechanisms do not explain why the rift system did not form along the western boundary of the North China Plain, where lithospheric thickness changes sharply from more than 150 km under the Ordos block and the Taihangshan Mountains to the west, to less than 70 km under the North China Plain. We have used a viscoplastic finite element model to explore the conditions for localized rifting in North China. Our results show that, for all the hypothesized causes, the preferred site of rifting would be along the boundary zone of changing lithospheric thickness. The only way to initiate the Shanxi rift in its current location, which is between the Ordos block and the Taihangshan Mountains with thick lithosphere, is to have preexisting lithospheric weakening there. This lithospheric weakness was likely formed during the collision between the Easter North China block and the Western North China block during the Paleoproterozoic (~1.8 Ga). Hence the ancient tectonic event still controls the young continental rifting.

  19. Accumulation of fossil fuels and metallic minerals in active and ancient rift lakes

    USGS Publications Warehouse

    Robbins, E.I.

    1983-01-01

    A study of active and ancient rift systems around the world suggests that accumulations of fossil fuels and metallic minerals are related to the interactions of processes that form rift valleys with those that take place in and around rift lakes. The deposition of the precursors of petroleum, gas, oil shale, coal, phosphate, barite, Cu-Pb-Zn sulfides, and uranium begins with erosion of uplifted areas, and the consequent input of abundant nutrients and solute loads into swamps and tectonic lakes. Hot springs and volcanism add other nutrients and solutes. The resulting high biological productivity creates oxidized/reduced interfaces, and anoxic and H2S-rich bottom waters which preserves metal-bearing organic tissues and horizons. In the depositional phases, the fine-grained lake deposits are in contact with coarse-grained beach, delta, river, talus, and alluvial fan deposits. Earthquake-induced turbidites also are common coarse-grained deposits of rift lakes. Postdepositional processes in rifts include high heat flow and a resulting concentration of the organic and metallic components that were dispersed throughout the lakebeds. Postdepositional faulting brings organic- and metal-rich sourcebeds in contact with coarse-grained host and reservoir rocks. A suite of potentially economic deposits is therefore a characteristic of rift valleys. ?? 1983.

  20. Buried waste containment system materials. Final Report

    SciTech Connect

    Weidner, J.R.; Shaw, P.G.

    1997-10-01

    This report describes the results of a test program to validate the application of a latex-modified cement formulation for use with the Buried Waste Containment System (BWCS) process during a proof of principle (POP) demonstration. The test program included three objectives. One objective was to validate the barrier material mix formulation to be used with the BWCS equipment. A basic mix formula for initial trials was supplied by the cement and latex vendors. The suitability of the material for BWCS application was verified by laboratory testing at the Idaho National Engineering and Environmental Laboratory (INEEL). A second objective was to determine if the POP BWCS material emplacement process adversely affected the barrier material properties. This objective was met by measuring and comparing properties of material prepared in the INEEL Materials Testing Laboratory (MTL) with identical properties of material produced by the BWCS field tests. These measurements included hydraulic conductivity to determine if the material met the US Environmental Protection Agency (EPA) requirements for barriers used for hazardous waste sites, petrographic analysis to allow an assessment of barrier material separation and segregation during emplacement, and a set of mechanical property tests typical of concrete characterization. The third objective was to measure the hydraulic properties of barrier material containing a stop-start joint to determine if such a feature would meet the EPA requirements for hazardous waste site barriers.

  1. From conjugate volcanic rifted margins to micro-continent formation: Double breakup development of the Norwegian-Greenland Sea

    NASA Astrophysics Data System (ADS)

    Gernigon, Laurent; Blischke, Anett; Nasuti, Aziz; Olesen, Odleiv; Sand, Morten; Sveinn Arnarson, Thorarinn

    2014-05-01

    We re-evaluate the structure and spreading evolution of the Norwegian-Greenland Sea and surrounding volcanic (rifted) margins based on new high-resolution aeromagnetic surveys. The new dataset combined with long-offset seismic and gravity data allow us to have a better understanding of the structure and evolution of the conjugate margin systems in the Norwegian-Greenland Sea from the rifting to the drifting stage. We particularly focus on the new JAS-12 aeromagnetic survey acquired between the Aegir Ridge and the Jan Mayen micro-continent, which was initially part of the Møre-Vøring-Greenland rift system. Combined with the previous NB-07 and JAS-05 surveys, our final compilation fully covers the continent-ocean transition and the whole oceanic spreading system from the Møre margin to the conjugate Jan Mayen micro-continent with high quality, high-resolution and reliable magnetic data. The new dataset allowed a new, consistent and precise interpretation of the magnetic polarity chrons and oceanic fractures, providing the basis for more accurate rotation poles estimation, and better basin and crustal reconstructions between Norway, Greenland and the Jan Mayen micro-continent. This dataset allowed us to clarify the pre- and post-breakup configurations of the rift system and discuss the mechanisms involved during the onset of the two phases of breakup leading to the micro-continent formation. Our observations and models suggest that the pre-breakup rift system evolved through a significant Late Jurassic-Cretaceous thinning phase. This episode led to a significant thinning of the continental crust and an exhumation of pre-existing lower crust. However, we have not been able to identify and/or validate any clear domains of exhumed and denudated serpentinised mantle. The first Eocene breakup is mostly characterised by severe magmatism (sill, SDRS). Lithospheric/asthenospheric processes leading to rift localisation do not necessarily represent a continuum of lithospheric deformation with the precedent thinning system. Diking and disconnected lithospheric plumbing are proposed to explain the Eocene breakup. After the first phase of continental breakup, two major phases of spreading influenced the Norwegian-Greenland Sea. Phase I (from C24 to C21r, ~54 to 49 Ma) marks the earliest phase of spreading, probably initiated in the central and outer part of the Møre Basin. During this period, the formation of overlapping systems and pseudo-fault development, indirectly influenced by the proto-margin segmentation, suggests the presence of additional micro-plates in the Norwegian-Greenland Sea. We also observed a significant change in the oceanic spreading system in the late Early Eocene. Based on observations from the surrounding areas, this supports a major and distinct tectonic and magmatic event in the Norwegian-Greenland Sea at around C21r (49-47.9 Ma), the beginning of a second phase. During Phase II, from C21r-C12 or possibly younger (48-<32 Ma) of the Norway Basin development, spreading rates decreased, spreading direction changed leading to the formation of unexpected N-S oriented oceanic fracture zones. Phase II probably coincides with the climax of extension and possibly local spreading that is suspected in the southern part of the Jan Mayen micro-continent forming a complex area of oceanic, transitional and continental fragments before its complete dislocation from East Greenland in Latest Oligocene.

  2. Seismic velocity structure of the rifted margin of the eastern Grand Banks of Newfoundland, Canada

    E-print Network

    Shillington, Donna J.

    seaward, the continental crust tapers rapidly beneath the continental slope to $6 km thickness to the southeast from 6 to 2 km, which we interpret as highly extended continental crust. Contrary to other seismic´collement in the final stages of continental rifting. The outer edge of highly extended continental crust borders a 25-km

  3. SPREE: A Successful Seismic Array by a Failed Rift System; Analysis of Seismic Noise in the Seismically Quiet Mid-continent

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The Superior Province Rifting Earthscope Experiment (SPREE) completed its field recording phase last fall with over 96% data return. While 60% of the stations returned data 100% of the time, only 9 performed below 90% and one station had questionable timing. One station was vandalized, another stolen. One station continued recording after its solar panels were pierced by a bullet, while another two stations survived a wildfire and a blow-down, respectively. The blow-down was an extreme wind event that felled hundreds of thousands of trees around the station. SPREE stations recorded many hundreds of earthquakes. Two regional earthquakes and over 400 teleseismic earthquakes had magnitudes over 5.5 and three, smaller local earthquakes had magnitudes over 2.5. We have calculated power spectral estimates between 0.1-1000 s period for the ~2.5-year lifespan of all 82 SPREE stations. Vertical channels performed quite well across the entire frequency range, falling well below the high noise model of Peterson (1993) and usually within 10-15 dB of nearby Transportable Array stations. SPREE stations' horizontal components suffer from long-period (> 30 s) noise. This noise is quietest at night and becomes up to 30 dB noisier during the day in the summer months. We explore possible causes of this variation, including thermal and atmospheric pressure effects. One possibility is that stations are insulated by snow during the winter, reducing temperature variations within the vault. Spring snowmelt creates instability at many of the SPREE stations, evidenced by frequent recenterings and enhanced long-period noise. For all channels, power in the microseismic band (4-16 s) is strongest in the winter, corresponding to storm season in the Northern Hemisphere, and approximately 20 dB weaker during the summer. The power spectrum and temporal variation of microseismic energy is consistent across the entire SPREE array.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Over the last four years sedimentologic and thermochronologic studies in the western and eastern branches of the Cenozoic East African Rift System (EARS) have supported the notion of a broadly contemporaneous onset of normal faulting and rift-basin formation in both segments. These studies support previous interpretations based on geophysical investigations from which an onset of rifting during the Paleogene had been postulated. In light of these studies we explore the evolution of the Lake Victoria basin, a shallow, unfaulted sedimentary basin centered between both branches of the EARS and located in the interior of the East African Plateau (EAP). We quantify the fluvial catchment evolution of the Lake Victoria basin and assess the topographic response of African crust to the onset of rifting in both branches. Furthermore, we evaluate and localize the nature of strain and flexural rift-flank uplift in both branches. We use a 3D numerical forward model that includes nonlinear temperature- and stress-dependent elasto-visco-plastic rheology. The model is able to reproduce the flexural response of variably thick lithosphere to rift-related deformation processes such as lithospheric thinning and asthenospheric upwelling. The model domain covers the entire EAP and integrates extensional processes in a heterogeneous, yet cold and thick cratonic block (Archean Tanzania craton), which is surrounded by mechanically weaker Proterozoic mobile belts, which are characterized by thinner lithosphere ("thin spots"). The lower limits of the craton (170 km) and the mobile belts (120 km) are simulated by different depths of the 1300 °C lithosphere-asthenosphere boundary. We assume a constant extension rate of 4 mm/a throughout the entire simulation of 30 Ma and neglect the effect of dynamic topography and magmatism. Even though the model setup is very simple and the resolution is not high enough to calculate realistic rift-flank uplift, it intriguingly reveals important topographic trends. The model shows that elevation differences of 120 to 180 m between the plateau interior and bordering rift shoulders are pronounced enough to form a closed basin after 6.5 Ma of extension. By that time the catchment area is already comparable to the present-day Lake Victoria catchment. Moreover, the final modeled topography, including 1000 m of dynamic and 500 m of pre-plume topography, yields a base basin elevation of 1110 m, which is also in good agreement with the present-day elevation of Lake Victoria. The combined effects of the formation of an extensive lacustrine depositional environment in the interior of the EAP after 6.5 Ma and rift-shoulder uplift may have forced far-reaching environmental impacts. These may have included the onset of the Lake Victoria microclimate, the influence of the basin and surrounding orographic barriers on precipitation patterns in East Africa, and the establishment of a unique flora and fauna.

  5. Effects of Oblique Extension and Inherited Structure Geometry on Transfer Zone Development in Continental Rifts: A 4D Analogue Modeling Approach

    NASA Astrophysics Data System (ADS)

    Zwaan, Frank; Schreurs, Guido

    2015-04-01

    INTRODUCTION Inherited structures in the crust form weak zones along which deformation will focus during rifting. Along-strike connection of rift segments may occur along transfer zones, as observed in East Africa. Previous studies have focused on numerical and analog modeling of transfer zones (e.g. Acocella et al., 1999, Allken et al., 2012). We elaborate upon those by investigating the effects of 1) oblique extension and 2) the geometry of linked and non-linked inherited structures on the development of transfer zones. A further improvement is the use of X-ray Computer Tomography (CT) for detailed internal analysis. METHODS The experimental set-up (see Schreurs & Colleta, 1998) contains two sidewalls with a base of compressed foam and plexiglass bars stacked in between. Decompressing this base results in distributed deformation of the overlying model materials. Deforming the model laterally with a mobile base plate produces the strike-slip components for oblique extension. Divergence velocities are in the order of 5 mm/h, translating to ca. 5 mm/Ma in nature, and 1 cm represents 10 km. A 2 cm thick layer of viscous silicone represents the ductile lower crust and a 2 cm quartz sand layer the brittle upper crust. Inherited structures are created with thin lines of silicon laid down on top of the basal silicone layer. Several models were run in a CT-scanner to reveal the 3D evolution of internal structures with time, hence 4D. RESULTS Localization of deformation along the pre-defined structures works well. The models show that the structural style changes with extension obliquity, from wide rift structures to narrower rifts with internal oblique-slip and finally strike-slip structures. Furthermore, rift offset is an important parameter influencing the occurrence of linkage: increasing rift offset decreases linkage as previously observed by Allken et al. (2012). However, increasing divergence obliquity promotes transfer zone formation, as does the presence of rift-connecting inherited zones, whose strike is at an angle of >15° with respect to the divergence direction. CT-analysis indicates that faulting initiated shortly after the start of the experiments, while structures become only clearly visible at the surface only after 1:30h (4% extension). Rift boundary fault angles tend to decrease from an initial 70° to ca. 55° after 4:00h (10% extension). Further CT-analysis will reveal the 3D evolution of the transform zones in more detail. REFERENCES Acocella, V., Faccenna, C., Funiciello, R., Rossetti, F., 1999. Sand-box modelling of basement-controlled transfer zones in extensional domains. Terra Nova, Vol. 11, No. 4, pp 149-156 Allken, V., Huismans, R. S., Thieulot, C., 2012. Factors controlling the mode of rift interaction in brittle-ductile coupled systems: A 3D numerical study, Geochem. Geophys. Geosyst. Vol. 13, Q05010 Schreurs, G., Colletta, B. (1998) Analogue modelling of faulting in zones of continental transpression and transtension. In: Holdsworth, R. E., Strachan R. A., Dewey, J. F., (eds.) 1998. Continental Transpressional and Transtensional Tectonics. Geological Society, London, Special Publications. No. 135, pp 59-79

  6. Next-Generation Linear Collider Final Focus System Stability Tolerances

    SciTech Connect

    Roy, G.; Irwin, J.; /SLAC

    2007-04-25

    The design of final focus systems for the next generation of linear colliders has evolved largely from the experience gained with the design and operation of the Stanford Linear Collider (SLC) and with the design of the Final Focus Test Beam (FFTB). We will compare the tolerances for two typical designs for a next-generation linear collider final focus system. The chromaticity generated by strong focusing systems, like the final quadrupole doublet before the interaction point of a linear collider, can be canceled by the introduction of sextupoles in a dispersive region. These sextupoles must be inserted in pairs separated by a -I transformation (Chromatic Correction Section) in order to cancel the strong geometric aberrations generated by sextupoles. Designs proposed for both the JLC or NLC final focus systems have two separate chromatic correction sections, one for each transverse plane separated by a ''{beta}-exchanger'' to manipulate the {beta}-function between the two CCS. The introduction of sextupoles and bending magnets gives rise to higher order aberrations (long sextupole and chrome-geometries) and radiation induced aberrations (chromaticity unbalance and ''Oide effect'') and one must optimize the lattice accordingly.

  7. Formation of curved seafloor fabric by changes in rift propagation velocity and spreading rate - Application to the 95.5 deg W Galapagos propagator

    NASA Technical Reports Server (NTRS)

    Acton, Gary; Stein, Seth; Engeln, Joseph F.

    1988-01-01

    Possible rigid plate models and shear models for the formation of curved seafloor lineaments by rift propagation are investigated and are applied to the Galapagos propagation rift system at 95 deg W. It is shown that the geometry noted at the Galapagos can result from either rift propagation acceleration or a spreading rate decrease during the last few hundred thousand years. It is postulated that the reverse curvature could result from either deceleration of rift propagation or an increase in spreading rate. The data interpreted as requiring a shear zone are found to be equally consistent with two distinct models based on rigid plate tectonics.

  8. Final system instrumentation design package for Decade 80 solar house

    NASA Technical Reports Server (NTRS)

    1978-01-01

    The final configuration of the Decade 80 solar house to monitor and collect system performance data is presented. A review demonstrated by actual operation that the system and the data acquisition subsystem operated satisfactorily and installation of instrumentation was in accordance with the design. This design package is made up of (1) site and system description, (2) operating and control modes, and (3) instrumentation program (including sensor schematic).

  9. The 1974 Ethiopian rift geodimeter survey

    NASA Technical Reports Server (NTRS)

    Mohr, P.

    1977-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Weissel, Jeffrey K.

    1999-01-01

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

  11. A large-scale detachment fault system in deep water area of South China Sea under the background of continental passive rifted margin: A case study of Heshan Sag

    NASA Astrophysics Data System (ADS)

    Lin, Zi; Ren, Jianye; Han, Xiaoying; Chen, Lin

    2015-04-01

    Heshan sag locates in the deep-water area of continental passive rifted margin of northern South China Sea, where preserved strong thinning crust of the ocean-continent transition zone. This area owns particular and unique tectonic settings with the geological characteristics of lithospheric ductile deformation and high temperature gradient, which highly differs from the continental shelf area. In this research, we try to determine the detachment faults within Heshan sag and build its tectonic-stratigraphic framework and geological evolution history as well. The research achievements are as followed: (1) According to the interpretation of 2D seismic profiles covering the whole study area, we basically recognized that Heshan sag was a detachment basin which is floored by a large-scale seaward detachment fault with a very low angle of 10 degrees to 20 degrees and overlain by tilted and hyper extended hanging wall block. And the heave of detachment fault has been extended to approximately 20 km. (2) Based on the latest geophysical and geological data, in the northern part of South China Sea, the strike of Moho surface is from NE to SW. The overall Moho depth is between 10 and 29 km from north to south, from shelf to continental slope and abyssal plain, mirroring the topography of the sediment basement, which means the crustal thickness decreases from land to ocean. Our study area exactly exists in the zone that the crust is hyper-extended and has the characters of continental crust and transitional crust. (3) Continental passive rifted margin closely relates to the ocean-continent transition zone (OCT). Guided by the basin dynamic analysis and lithosphere extension and breakup theory, combined with overseas and domestic research status on OCT and the latest information of adjacent areas, we tried to elucidate the geological nature of OCT and construct continental lithosphere configuration in different tectonic units on the northern continental margin in South China Sea. Also we compared Heshan sag with the northern shelf basins and proposed that it belongs to the distal margin unit where developed extensional detachment system with the crust thinning sharply and the crustal thickness even decreases to zero in the OCT unit. Based on the research work above, we further discuss the relationship between the development of large-scale detachment fault and the spreading of the South China Sea in Cenozoic, hope this study can improve our understanding on the geodynamic construct model of the ocean-continent transition zone better in northern South China Sea, and guide the economic exploration in deep water/ultra-deep water area.

  12. Nonlinear Schrödinger systems in 2d with nondecaying final data

    NASA Astrophysics Data System (ADS)

    Hayashi, Nakao; Li, Chunhua; Naumkin, Pavel I.

    2016-01-01

    We consider nonlinear Schrödinger systems with quadratic nonlinearities in two space dimensions. We prove the existence of modified wave operators and uniform time decay of solutions when the Fourier transform of the final data does not necessarily decay at spatial infinity and is small in uniform norm.

  13. Study of a final focus system for high intensity beams

    SciTech Connect

    Henestroza, Enrique; Eylon, Shmuel; Roy, Prabir K.; Yu, Simon S.; Bieniosek, Frank M.; Shuman, Derek B.; Waldron, William L.

    2004-06-01

    The NTX experiment at the Heavy Ion Fusion Virtual National Laboratory is exploring the performance of neutralized final focus systems for high perveance heavy ion beams. The final focus scenario in an HIF driver consists of several large aperture quadrupole magnets followed by a drift section in which the beam space charge is neutralized by a plasma. This beam is required to hit a millimeter-sized target spot at the end of the drift section. The objective of the NTX experiments and associated theory and simulations is to study the various physical mechanisms that determine the final spot size (radius r{sub s}) at a given distance (f) from the end of the last quadrupole. In a fusion driver, f is the standoff distance required to keep the chamber wall and superconducting magnets properly protected. The NTX final quadrupole focusing system produces a converging beam at the entrance to the neutralized drift section where it focuses to a small spot. The final spot is determined by the conditions of the beam entering the quadrupole section, the beam dynamics in the magnetic lattice, and the plasma neutralization dynamics in the drift section. The main issues are the control of emittance growth due to high order fields from magnetic multipoles and image fields. In this paper, we will describe the theoretical and experimental aspects of the beam dynamics in the quadrupole lattice, and how these physical effects influence the final beam size. In particular, we present theoretical and experimental results on the dependence of final spot size on geometric aberrations and perveance.

  14. Crustal Deformation Field Around Rift Zone In Southeastern Afar Derived From Jers-1/in-sar

    NASA Astrophysics Data System (ADS)

    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 is also seen along the Manda-Inakir rift, and we can see the V shape of subsidence area in the east end of the Manda-Inakir rift, which is transition zone from the Manda-Inakir rift to the Mak'Arrassou strike slip zone. It may be caused that the stress along the tectonic line from the Manda-Inakir rift to the Mak'Arrasou strike slip zone is gradually change from the extension to the strike slip.

  15. Patagonian broken foreland and related synorogenic rifting: The origin of the Chubut Group Basin

    NASA Astrophysics Data System (ADS)

    Gianni, G.; Navarrete, C.; Orts, D.; Tobal, J.; Folguera, A.; Giménez, M.

    2015-05-01

    The Central Patagonia is characterized by prominent continental deposits that belong to the Cretaceous Chubut Group Basin, whose tectonic setting remains controversial. It has been interpreted as a foreland basin, an extensional basin and even as a sag stage of a rift event. Related deposits outcrop as part of the Patagonian broken foreland, east of the Patagonian Andes. Particulary, the San Bernardo fold and thrust belt, between 42° and 48°S, as the main sector of the broken foreland, constitutes a NNW-trending intraplate belt located 450 km away from the trench. Coincidentally, at these latitudes, 1200 km east of the trench, intraplate deformation has caused tectonic inversion of Mesozoic basins presently located at the Atlantic offshore area. Additionally, at the San Jorge Gulf area this orogenic system interferes with a conspicuous E-W extensional system, transversally disposed to the Andean strike, mainly active between the late Early Cretaceous and late Paleocene. We carried out an integrated analysis from structural, 2-D and 3-D seismic data at the San Bernardo FTB and the adjacent Río Mayo Basin, studying sections of the Chubut Group Basin to unravel the different evolutionary stages. Thus, surface and subsurface evidence of syn-compressional deposition indicate the development of a broken foreland basin related to the formation of the San Bernardo FTB, suggesting an initial growth during the late Early Cretaceous and probably up to the late Paleocene. Our results imply that the Cretaceous compression acted in concert with transversal foreland extension. Hence, we propose a syncontractional rift reactivation of a potential lithospheric anisotropy, triggered by regional contraction. Finally, the origin of compression during this time is discussed in relation to multiple processes that go from high convergence between plates and trenchward motion of South America, collision of mid-ocean ridges, to potential dip changes in the subducted slab, as suggested by arc expansion.

  16. The Final Focus Test Beam laser referene system

    SciTech Connect

    Bressler, V.E.; Ruland, R.E.

    1993-05-01

    The original design for the SLAC linac included an alignment reference system with 270 diffraction gratings situated along the 3000 meter linac. These gratings have provided SLAC with a global reference line repeatable to within 200 micro meters. For the Final Focus Test Beam, this laser system has been extended and 13 new diffraction gratings have been installed. Improvements targets and the availability of new instruments allows us to evaluate the performance of the laser reference system at the 510 micro meter level. An explanation of the system and the results of our evaluation are presented.

  17. Stresses and seismicity at the present stage of evolution of the Baikal rift zone lithosphere

    NASA Astrophysics Data System (ADS)

    Klyuchevskii, A. V.

    2007-12-01

    The paper presents results of studying stresses and seismicity of the lithosphere in the Baikal rift zone at the present (instrumental) stage of its evolution. These results are well consistent with the theory of self-organization of complex dynamic systems and can be used for the classification of certain features and properties of the Baikal rift seismogenic system studied. Application of the theory of nonlinear dynamic systems to the analysis of stresses and seismicity allowed us to develop a concept of a complex spatiotemporal structure of the stress state of the lithosphere and seismicity in the region. In terms of this concept, the distribution of strong earthquakes in time is explained in terms of bifurcations (catastrophes) of stresses in the rift zone. Extrapolation of the results indicates that a stress catastrophe in lithosphere of the rift zone can take place in the next few years years, which increases the probability of occurrence of strong ( M ? 7) earthquakes in the Baikal region. A model with bifurcation of triple equilibrium most consistent with the phase image of regional stresses is proposed as a scenario of the stress state evolution in the lithosphere of the Baikal rift zone.

  18. Modern and ancient mineralization in the Salton Trough Rift

    SciTech Connect

    McKibben, M.A. . Dept. Earth Sciences)

    1992-01-01

    The Salton Trough of SW North America is an active continental rift, the landward extension of the divergent tectonics of the Gulf of California. Shallow magmatic heat sources, thick porous sediments, tectonic activity and saline lakes interact to yield a variety of Pleistocene to modern hydrothermal systems. The oldest mineralization, the fish Creek evaporite, is a CASO[sub 4] deposit formed by a pre-rift Tertiary marine incursion. 4--5 million years ago the prograding Colorado River delta bisected the Trough, influencing the character of Pliocene and younger hydrothermal activity. The northern part of the Trough became a closed basin filled intermittently by large freshwater lakes. Along the W margin of the rift lies the Modoc hot spring gold deposit. This deposit occurs at the intersection of a range-front growth fault with fossil lake levels, suggesting paleohydrologic control by ancient lakes. Active geothermal systems within the Trough include low-T systems such as Heber and East Mesa, localized along high-angle faults where shallow groundwaters are conductively heated above basement highs. These blind systems have no surface expression and only moderate geophysical anomalies. High-T (> 250 C) active systems occur in sediment filled pull-apart basins developed over spreading center fragments (e.g., Salton Sea, Brawley, Cerro Prieto). These systems exhibit high heat flow, strong gravity and magnetic anomalies, and often have surface manifestations such as Quaternary volcanoes and thermal features. Many contain hot metalliferous brines that have evolved in the saline lake environment of the northern Trough.

  19. Permo-Triassic anatexis, continental rifting and the disassembly of western Pangaea

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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.

  20. Tectonic and eustatic controls on carbonate platforms of the Jurassic High Atlas rift of Morocco

    SciTech Connect

    Crevello, P. )

    1990-05-01

    Stratigraphic studies of Lower and Middle Jurassic carbonates along the southern margin of the High Atlas rift document five major stages of platform development a response to rift tectonics and eustasy. The five stages are as follows. (1) Early Sinemurian marine transgression over Triassic-Liassic continental red beds and basalts lead to the development of regionally extensive, cyclic carbonate platforms. (2) Middle to late Sinemurian marked the initiation of Liassic rifting, with synrift platforms restricted to the rift margin and to localized horsts within the rift axis. Synrift platforms developed diverse depositional systems, with a marked change to rimmed margins flanked by steep slopes and deep (400-500 m) marine basins. Two orders of cyclicity shallowing-upward cycles and bundles of cycles dominated the platform tops. (3) Late Pliensbachian subaerial exposure, resulting in termination of Liassic platform development, was recorded by regressive seaward shifts in facies belts, microkarstification, and deposition of continental red beds across the platforms. (4) Early to middle Toarcian transgression, yielding landward shifts in facies belts on platform tops, was signified by deposition of noncyclic, skeletal carbonate sequences. (5) Middle Toarcian platform drowning was followed by deposition of Toarcian-Aalenian amonite-bearing marine shales (100 m thick) blanketing (downlapping, width source from the south) the southern platform, whereas only a condensed sequence (2-3 m thick) of glauconitic, ammonite-skeletal carbonate strata covered the submerged, isolated, axial rift platform of Jebel Bou Dahar. Prolonged sediment starvation on Bou Dahar combined with depositional onlap of its slope by basin-filling shales (Toarcian to Bajocian) and distal carbonate turbidites (Aalenian), also sourced from the southern margin of the rift, produccd a drowning onlap unconformity.

  1. Extension velocity partitioning, rheological crust-mantle and intra-crustal decoupling and tectonically inherited structures: consequences for continental rifting dynamics.

    NASA Astrophysics Data System (ADS)

    Wang, Kun; Mezri, Leila; Burov, Evgueni; Le Pourhiet, Laetitia

    2015-04-01

    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 rheological layers may tend to stick together resulting in step-like strengthening of the lithosphere and deceleration of subsidence. Hence, the entire rift system may exhibit polyphase subsidence behavior, which may be entirely conditioned by its internal structure and not by external factors. In addition, velocity partitioning may also have strong impact on rift evolution. For example, symmetric partitioning of half-velocities on both rift sides does not result in the same evolution as in the case when the same total extension rate is applied at one side only. In particular, asymmetric velocity partitioning results in the development of asymmetric rift evolution without any need in rheological softening. This differences in rift evolution stem from different thermal advection rates that both influence partitioning of thermally dependent rheological strength, phase transitions and buoyancy. The experiments confirm the importance of the above mentioned factors, which have strong implications for continental rifting processes and formation of passive margins.

  2. Triggered seismicity induced by stresses from the Bárðarbunga 2014 rifting event

    NASA Astrophysics Data System (ADS)

    Green, Robert; Greenfield, Tim; White, Robert

    2015-04-01

    From 16th August 2014 a rifting event at Bárðarbunga volcano in Iceland produced large surface deformation associated with rifting and the propagation of a 45 km long dyke northward away from the central volcano. Continuous GPS data from numerous sites recorded tens of centimetres displacements (Sigmundsson et al., Nature 2014) during the emplacement of this dyke, with a maximum widening between two stations of 1.3m. This continuous GPS data along with campaign GPS, InSAR and seismicity have been used to model the geometry and volume of the intruded dyke (Sigmundsson et al., 2014). The subsequent effect on the stress field caused by this intrusive volume was felt by the many volcanic centres in the surrounding area. Tungafellsjökull, Kistufell, Kverkfjöll and Askja all saw elevated levels of seismic activity during and following the intrusion of the dyke. The rapid final northward advance on 27th August also simultaneously caused a magnitude 4.2 earthquake in the geothermal field on the south-east side of Askja caldera, where recorded earthquakes have never previously exceeded a magnitude of two. Locations of earthquakes focussed at the leading edge of the dyke map out its northward propagation in short rapid bursts, and enable a temporal stressing history to be reconstructed. This can be correlated well with seismicity rates at the nearby Askja, Kistufell and Kverkfjöll volcanoes. We present both detailed seismic analysis and stress modelling which demonstrate triggering of increased seismicity and shut off in stress shadows, allowing us to test quantitative models of stress induced seismicity. Our local seismic array covers the numerous volcanic systems beneath the Vatnajökull glacier and surrounding areas in the Icelandic interior, and has been operating for many years leading up to this rifting event, providing excellent constraint on relative seismicity rate changes. We use automatic location routines to produce an extensive earthquake catalogue over time. Further results from our manual refinement techniques (probabilistic locations and relative relocations) and fault plane solution inversion reveal the faulting mechanisms of both the background and triggered activity. We use these faults in our stress modelling to place excellent constraints on the stress evolution at these nearby volcanoes.

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

    PubMed

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

    2007-07-26

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

  4. Deep magma body beneath the summit and rift zones of Kilauea Volcano, Hawaii

    USGS Publications Warehouse

    Delaney, P.T.; Fiske, R.S.; Miklius, Asta; Okamura, A.T.; Sako, M.K.

    1990-01-01

    A magnitude 7.2 earthquake in 1975 caused the south flank of Kilauea Volcano, Hawaii, to move seaward in response to slippage along a deep fault. Since then, a large part of the volcano's edifice has been adjusting to this perturbation. The summit of Kilauea extended at a rate of 0.26 meter per year until 1983, the south flank uplifted more than 0.5 meter, and the axes of both the volcano's rift zones extended and subsided; the summit continues to subside. These ground-surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones. Kilauea's magmatic system is, therefore, probably deeper and more extensive than previously thought; the summit and both rift zones may be underlain by a thick, near vertical dike-like magma system at a depth of 3 to 9 kilometers.

  5. Petrological constraints on the crustal structure under rift zones

    NASA Astrophysics Data System (ADS)

    Maclennan, J.; Gaetani, G. A.; Hartley, M. E.; Neave, D.; Winpenny, B.

    2012-12-01

    When magmatism occurs in extensional settings, the transfer and release of heat by magma transport and storage may control the thermal structure of the crust and uppermost mantle underlying the rift zone. The composition and mineralogy of the material added to the solid crust during magmatism is also dictated by the conditions of crystallisation. The temperature, pressure and composition of this material controls the physical response of the crust on timescales relevant both for geophysical imaging of the deep structure of rift zones and for the dynamical development of the structure of zones of extension. Examination of the petrology of the products of rift zone magmatism can be used to provide constraints on the depth distribution of crystallisation and the composition of the solid material accreted to the crust and should be a key consideration in geophysical and dynamical investigations of rift zones. A number of complementary petrological techniques have been used to determine crystallisation depths under the rift zones of Iceland. These techniques include: 1) a parametrisation of clinopyroxene-liquid equilibrium; 2) a parametrisation of the composition of liquid in joint equilibrium with the phases olivine, plagioclase and clinopyroxene; 3) assessment of the order of appearance of phases on the liquidus; 4) the relationship between melt CO2 content and pressure. However, the application of each technique is dependent upon a number of assumptions about the achievement of equilibrium between phases and also the interpolation of parametrisations between experimental conditions. Most rift zone eruptions carry large crystals that have formed in the magma storage zone and these crystals are often referred to as phenocrysts, a term that implies equilibrium between the crystals and the melts that carry them to the surface for eruption. However, careful examination of the trace element composition of Icelandic clinopyroxene phenocrysts shows that they are rarely in equilibrium with their carrier liquids. In order to avoid significant systematic errors in estimates of crystallisation depths it is therefore necessary to use both the major and trace element composition of the clinopyroxenes to establish the range of potential equilibrium liquids at the depth of crystallisation and to identify if such liquids correspond to the composition of lavas from the same magmatic system. Existing parametrisations of experimental equilibrium between clinopyroxene and basaltic liquid are prone to large errors at crustal pressures. In order to address this problem, a series of experiments was conducted using a primitive Icelandic basalt composition as a starting material. These experiments indicate that the parametrisations can robustly be used to establish the importance of crystallisation close to the Moho under Iceland, at depths of over 20 km. It is likely that crystallisation also occurs in the middle and lower crust, generating cumulate gabbro material. However, systematic errors in available parameterisations of clinopyroxene-liquid equilibrium hinder barometry over this pressure range. In order to better establish crystallisation conditions for rift zone magmas, further experimental constraints for crustal pressures are required, along with development of more systematic studies of the volatile contents of melt inclusions.

  6. Latest stages of deformation leading to breakup of the Australian-Antarctic rifted margins: new constraints from deep seismic observations and potential data.

    NASA Astrophysics Data System (ADS)

    Gillard, Morgane; Autin, Julia; Manatschal, Gianreto; Sauter, Daniel; Munschy, Marc; Schaming, Marc

    2014-05-01

    The discovery of large domains of hyper-extended continental crust and exhumed mantle along many present-day magma-poor rifted margins questions the existing models proposed to explain lithospheric breakup and onset of seafloor spreading. In particular, the amount of magma and its relation to tectonic structures is yet little understood. Trying to find answers to these questions asks to work in the most distal parts of rifted margins where the latest stage of rifting occurred and the first steady state oceanic crust was emplaced. In this aim, the Australian-Antarctic conjugated margins provide an excellent study area. Indeed, the central sector of the Great Australian Bight/Wilkes Land developed in a magma-poor probably ultra-slow setting and displays a complex and not yet well understood Ocean-Continent Transition (OCT). This distal area is well imaged by numerous high quality seismic lines covering the whole OCT and the steady-state oceanic crust. Our seismic observations allow the recognition of different tectono-sedimentary units and magmatic additions. The relation between the sedimentary units, magmatic additions and the tectonic structures enable to define a complex interaction between these processes indicating a clear polyphase evolution of rifting and migration of the deformation towards the area of future breakup. The migration of deformation is well imaged by the fact that each tectono-sedimentary unit "downlaps" oceanwards onto "new" basement, which enables to define basement units that become younger oceanwards. This observation suggests that final rifting is associated with the creation of new "basement" under conditions that are not yet those of a steady state oceanic crust. We propose that two major detachment systems are responsible for mantle exhumation forming this new basement. In particular, they can explain the different deformation phases observed in the tectono-sedimentary sequences and related magmatic additions. It appears that the sedimentary structures linked to these two detachment systems can be followed along the margins over several hundreds of kilometres, indicating that they represent a large scale asymmetric extension. The identification on potential field maps of different domains corresponding to the different basement units allows us to propose an oceanward and gradual variation in the basement composition. It is likely that the amount of magma gradually increases until the emplacement of the first steady state oceanic crust and that magma underplating may have occurred along most of the distal margin. One main question resulting from our model is related to the interpretation of the magnetic anomalies in such an asymmetric context. Answering to this question can help to solve the paleogeographic reconstructions and to better define the age of the lithospheric breakup in these margins.

  7. Simulated coal gas MCFC power plant system verification. Final report

    SciTech Connect

    1998-07-30

    The objective of the main project is to identify the current developmental status of MCFC systems and address those technical issues that need to be resolved to move the technology from its current status to the demonstration stage in the shortest possible time. The specific objectives are separated into five major tasks as follows: Stack research; Power plant development; Test facilities development; Manufacturing facilities development; and Commercialization. This Final Report discusses the M-C power Corporation effort which is part of a general program for the development of commercial MCFC systems. This final report covers the entire subject of the Unocal 250-cell stack. Certain project activities have been funded by organizations other than DOE and are included in this report to provide a comprehensive overview of the work accomplished.

  8. Thermomechanical models of the Rio Grande rift

    SciTech Connect

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

    1980-01-01

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

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

    SciTech Connect

    Witthuhn, K.M.; Teyssier, C. . Dept. of Geology and Geophysics)

    1992-01-01

    The Midcontinent Rift is a 1.1 billion year old crustal structure which has been defined primarily on the basis of geophysical studies. It displays evidence of both rifting and subsequent closure. Many studies have examined the rift from a petrologic view but few have examined it in any detail from a structural geological viewpoint. This paper examines the structural aspects of the rift, elucidates the direction of closing, and constrains the timing of the system by utilizing paleostress stratigraphy. Establishment of the relative age and sense of movement on faults was accomplished by analyzing slickensides and crystallization on the fault plane. Detailed work on the Keweenaw Peninsula of Michigan suggests a southerly direction for the closing of the rift system, while similar work on Isle Royale suggests an east-southeasterly closing direction. Faults in both areas with opposite sense of movement (dextral vs. sinistral, normal vs. reverse) have similar attitudes indicating a reversal of maximum and minimum stress directions. Stress tensors from both limbs of the Lake Superior syncline were isolated using identical methods, suggesting the geometry or lithology of the system interfered with the manifestation of the far-field stresses. The results suggest then the direction of opening and closing of the rift was constrained by the geometry of the major and minor fault systems and anisotropies in the lava flows.

  10. Joint Technical Architecture for Robotic Systems (JTARS)-Final Report

    NASA Technical Reports Server (NTRS)

    Bradley, Arthur T.; Holloway, Sidney E., III

    2006-01-01

    This document represents the final report for the Joint Technical Architecture for Robotic Systems (JTARS) project, funded by the Office of Exploration as part of the Intramural Call for Proposals of 2005. The project was prematurely terminated, without review, as part of an agency-wide realignment towards the development of a Crew Exploration Vehicle (CEV) and meeting the near-term goals of lunar exploration.

  11. Oligo-Miocene rift of Sardinia and the early history of the Western Mediterranean Basin

    NASA Astrophysics Data System (ADS)

    Cherchi, A.

    1982-08-01

    The geodynamic evolution of the Western Mediterranean Basin, in spite of many studies, is still uncertain. There is some consensus for interpreting this basin as a kind of small oceanic marginal basin. Its opening has generally been related to a subduction process which was active during the Oligocene-Miocene somewhere east of Sardinia-Corsica1-7. As the margins of the basin are deeply buried below Miocene-to-present sediments, direct lithological and stratigraphical data which could explain the events responsible for its formation are rare8-10 or missing altogether. To obtain such data, detailed field studies have been undertaken in Sardinia (Fig. 1), and the first results are presented here. This approach is justified by the fact that in that island, Oligocene and Miocene sediments were deposited in a rift (fossa tettonica sarda of Verdabasso11), which is the easternmost arm of the complex rift system that affected the European plate during Oligocene and Miocene times. One of these arms evolved towards a small oceanic basin-the Western Mediterranean or Algero-Provençal Basin-while others such as the Gulf of Valencia and the Sardinia rift aborted and remained at the rift stage. Its exceptional exposures make it possible to examine the Sardinia rift to clarify the sequence of events which created it, and to establish a sedimentological model which we believe is directly applicable to the Western Mediterranean Basin.

  12. The final analysis Little Leo: A system and service overview

    NASA Astrophysics Data System (ADS)

    Fatig, Michael

    1997-01-01

    There is an emerging commercial space industry consisting of constellations of low earth orbiting satellites to that will provide global telecommunications services. Within the set of proposed low earth orbiting satellite systems, there exists two distinct classes. One class provides high bandwidth digital voice and data services, and the other provides narrowband store and forward digital data services. The digital data service systems are called Little LEOs or Infosats. These systems will provide a variety of personal, business, environmental, and industrial digital data services on a global scale. Infosat systems provide a niche telecommunications infrastructure that benefit industries and governments of the world whether developing or industrialized; geographically homogeneous or diverse; or low, middle, or high income. The flexible nature of the service allows it to be applied in many ways to meet changing needs. This paper provides an overview of the Final Analysis Infosat system.

  13. Overview of the Final Focus Test Beam alignment system

    SciTech Connect

    Bressler, V.E.; Ruland, R.E.; Plouffe, D.

    1993-05-01

    The Final Focus Test Beam was conceived as a technological stepping stone on the way to the next linear collider. Nowhere is this more evident than with the alignment subsystems. Alignment tolerances for components prior to beam turn are almost an order of magnitude smaller than for previous projects at SLAC. Position monitoring systems which operate independent of the beam are employed to monitor motions of the components locally and globally with unprecedented precision. An overview of the FFTB alignment system is presented herein.

  14. A Dynamic Alignment System for the Final Focus Test Beam

    SciTech Connect

    Ruland, R.E.; Bressler, V.E.; Fischer, G.; Plouffe, D.; /SLAC

    2005-08-16

    The Final Focus Test Beam (FFTB) was conceived as a technological stepping stone on the way to the next linear collider. Nowhere is this more evident than with the alignment subsystems. Alignment tolerances for components prior to beam turn are almost an order of magnitude smaller than for previous projects at SLAC. Position monitoring systems which operate independent of the beam are employed to monitor motions of the components locally and globally with unprecedented precision. An overview of the FFTB alignment system is presented herein.

  15. Solar hot water system installed at Mobile, Alabama. Final report

    SciTech Connect

    1980-10-01

    This final report describes the solar energy hot water system installed at LaQuinta Motor Inn Inc., at Mobile, Alabama. The building is a 122 unit motel. The system consists of six rows of ten collectors and three rows of eleven collectors (1990 square feet) mounted on the roof. Griswald flow control valves were installed to regulate the flow to each row. Two Heliotrope electronic thermometers with a combined capability of measuring the temperatures of 22 different locations were installed for monitoring purposes. Engineering drawings, component specifications, and operator instructions are included.

  16. The use of subsurface thermal data, isotopic tracers and earthquake hypocenter locations to unravel deep regional flow systems within the crystalline basement beneath the Rio Grande rift, New Mexico. (Invited)

    NASA Astrophysics Data System (ADS)

    Person, M. A.; Woolsey, E.; Pepin, J.; Crossey, L. J.; Karlstrom, K. E.; Phillips, F. M.; Kelley, S.; Timmons, S.

    2013-12-01

    The Rio Grande rift in New Mexico hosts a number of low-temperature geothermal systems as well as the 19 km deep Socorro Magma Body. The presence of a mantle helium anomaly measured at San Acacia spring (3He/4He = 0.295 RA) and in an adjacent shallow well (50m < ; 0.8 RA) overlying the Socorro Magma Body at the southern terminus of the Albuquerque Basin suggests that deeply sourced fluids mix with the sedimentary basin groundwater flow system. Temperatures recorded at the base of the San Acacia well is elevated (29 oC). Published estimates of uplift rates and heat flow suggest that the magma body was emplaced about 1-3 ka and reflects a long-lived (several Ma) magmatic system. Further south near the southern terminus of the Engle Basin, much warmer temperatures (42 oC) occur at shallow depths within the spa district in the town of Truth or Consequences at shallow depths also suggesting deep-fluid circulation. 14C constrained apparent groundwater residence times in the spa district range between 6-10 ka. We have developed two 6-19 km deep crustal-scale, cross-sectional models that simulate subsurface fluid flow, heat and isotope (3He/4He) transport as well as groundwater residence times along the Rio Grande rift. The North-South oriented model of the Albuquerque Basin incorporates a high-permeability conduit 100 m wide having hydrologic properties differing from surrounding crystalline basement units. We use these models to constrain the crustal permeability structure and fluid circulation patterns beneath the Albuquerque and Engle Basins. Model results are compared to measurements of groundwater temperatures, residence times (14C), and 3He/4He data. We also use the distribution of earthquake hypocenters to constrain likely fault-crystalline basement hydraulic interactions in the seismogenic crust above the Socorro Magma Body. For the case of the southern Albuquerque Basin, conduit permeability associated with the Indian Hill conduit/fault zone must range between about 1.0E-13 to 1.0E-15 m2 in order for simulated 3He/4He, solute concentrations, and temperatures to match observed conditions. Basement permeability outside of the fault damage zone must range between 1.0E-17 to 1.0E-18 m2. However, a much longer transport time is required (between about 20-30 ka) in order to match observed conditions suggesting multiple magmatic intrusion events. For the case of the Engle Basin near Truth or Consequences, bulk crustal permeability between a depth of 2-6 km below the sedimentary succession must approach 1.0E-12 m2 in order to reproduce hot spring temperatures and groundwater residence times. We compare these model derived permeability estimates to published permeability-depth relationships for crustal rocks (Manning and Ingebritsen, 1999; Ingebritsen and Manning, 2010).

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

    NASA Astrophysics Data System (ADS)

    Selim, S. S.

    2015-10-01

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

  18. Statistical mechanics and scaling of fault populations with increasing strain in the Corinth Rift

    NASA Astrophysics Data System (ADS)

    Michas, Georgios; Vallianatos, Filippos; Sammonds, Peter

    2015-12-01

    Scaling properties of fracture/fault systems are studied in order to characterize the mechanical properties of rocks and to provide insight into the mechanisms that govern fault growth. A comprehensive image of the fault network in the Corinth Rift, Greece, obtained through numerous field studies and marine geophysical surveys, allows for the first time such a study over the entire area of the Rift. We compile a detailed fault map of the area and analyze the scaling properties of fault trace-lengths by using a statistical mechanics model, derived in the framework of generalized statistical mechanics and associated maximum entropy principle. By using this framework, a range of asymptotic power-law to exponential-like distributions are derived that can well describe the observed scaling patterns of fault trace-lengths in the Rift. Systematic variations and in particular a transition from asymptotic power-law to exponential-like scaling are observed to be a function of increasing strain in distinct strain regimes in the Rift, providing quantitative evidence for such crustal processes in a single tectonic setting. These results indicate the organization of the fault system as a function of brittle strain in the Earth's crust and suggest there are different mechanisms for fault growth in the distinct parts of the Rift. In addition, other factors such as fault interactions and the thickness of the brittle layer affect how the fault system evolves in time. The results suggest that regional strain, fault interactions and the boundary condition of the brittle layer may control fault growth and the fault network evolution in the Corinth Rift.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  20. Crustal Rheology and Rifted Margin Architecture: Comparing Iberia-Newfoundland, Central South Atlantic, and South China Sea

    NASA Astrophysics Data System (ADS)

    Brune, Sascha

    2015-04-01

    Crustal rheology controls the style of rifting and ultimately the architecture of rifted margins: Hot, weak, or thick continental crust is dominated by ductile deformation and extends symmetrically into a wide rift system. Extension in cold, strong, or thin crust is accommodated by brittle faults and ductile shear zones that facilitate narrow rifts with asymmetric fault geometries. This recipe provides the standard framework to understand 2D rift geometry, however, a variety of processes exert significant control on subsequent rift evolution and ultimately on the architecture of rifted margins: inherited structures, melting and volcanism, 3D effects, extension rate, and weakening mechanisms. Numerical forward modelling studies have the opportunity to evaluate the influence of these processes on rift evolution in order to understand the complex interaction between rheology and tectonic history of specific margins. Here I compare the formation of three different magma-poor margin pairs, Iberia-Newfoundland, the Central South Atlantic Rift Segment, and the South China Sea margins within a numerical forward modelling framework. I apply a 2D version of the finite element code SLIM3D, which includes nonlinear temperature- and stress-dependent elasto-visco-plastic rheology and is able to reproduces a wide range of rift-related deformation processes such as flexure, lower crustal flow, and faulting. The Iberia-Newfoundland rifted margins are marked by moderate crustal asymmetry, with ~70 km of hyper-extended crust (less than 10 km thick) on the Iberian side and a very narrow margin on the Newfoundland counterpart. Similar to the Iberia-Newfoundland conjugates, the Central South Atlantic margins are predominantly asymmetric, however involve a much stronger degree of asymmetry with more than 200 km of hyper-extended crust offshore Angola, but only few tens of km at the Brazilian side. Kinematic and numerical modelling suggests that the asymmetry is caused by lateral migration of the rift centre, which generates sequential fault activity within the brittle crust. Rift migration results from two processes: (i) Strain hardening takes place in the rift centre due to cooling of upwelling mantle material. (ii) The formation of a low viscosity crustal pocket adjacent to the rift centre is caused by heat transfer from the mantle and viscous strain softening of the lower crust. These mechanisms generate a lateral strength contrast that promotes rift migration in a steady-state manner forming a wide sliver of hyper-extended crust on one margins side, while the conjugate margin becomes narrow. In contrast to these Atlantic examples where wide margins are formed diachronously, the South China Sea evolved in wide rift mode. Here, several hundred kilometres of highly attenuated continental crust are deformed simultaneously during ~40 My of extension. Numerical modelling suggests that the presence of weak, ductile crust enabled the formation of two wide and symmetric margins. Independent indicators for a weak crust come from super-deep basins on the northern margin. These basins appear to be created after the end of active extension and with a significant deficit in brittle faulting, which suggests that subsidence was controlled by sediment loading and accommodated by lower crustal flow, a style of basin formation that is only possible in the presence of low crustal viscosity.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  3. Motion in the north Iceland volcanic rift zone accommodated by bookshelf faulting

    E-print Network

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

    2013-12-01

    beneath Askja volcano on the north Ice- land rift. Bull. Volcanol. 72, 55–62 (2009). [23] Key, J., White, R. S., Soosalu, H. & Jakobsdóttir, S. S. Mul- tiple melt injection along a spreading segment at Askja, Ice- land. Geophysical Research Letters 38, 1... , permanent ice caps in blue-white, rivers and lakes in blue, tectonic fractures[5],[6],[15] in black lines and active fissure swarms of the volcanic rift systems overlain in beige12. WNW oriented fractures5,6,15 are red lines. Black triangles are seismic...

  4. Rift Valley fever: A neglected zoonotic disease?

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  5. The 1973 Ethiopian-Rift geodimeter survey

    NASA Technical Reports Server (NTRS)

    Mohr, P. A.

    1974-01-01

    Remeasurement of the Adama, Lake Langana, and Arba Minch (Lake Margherita) geodimeter networks in 1973 has enabled Mohr's interpretation concerning possible surface ground deformation in the Ethiopian rift to be considerably developed. Extension appears to have occurred across the Mojjo-Adama horst at a rate of about 1 cm yr/1. The opposing rims of the Adama graben have not moved significantly relative to one another (between 1969 and 1973), but stations on the sliced graben floor show possible movement with a large rift-trend component. In the Wolenchiti quadrilateral, significant movement of station RABBIT is confirmed, but the radical change of vector (that of 1970-1971 to that of 1971-1973) casts doubt on a tectonic cause and seems to indicate that stations on steep hillslopes are liable to be unstable. South of the quadrilateral and east of the Adama graben, alternating rift-trend zones of extension and shortening appear to coexist. In the Lake Langana network, significant movements of the order of 0.5 cm yr/1 are directed perpendicular to the rift floor faulting.

  6. RIFT VALLEY FEVER POTENTIAL, ARABIAN PENINSULA

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  7. Molecular Rift: Virtual Reality for Drug Designers.

    PubMed

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

    2015-11-23

    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. PMID:26558887

  8. Variable-Speed Wind System Design : Final Report.

    SciTech Connect

    Lauw, Hinan K.; Weigand, Claus H.; Marckx, Dallas A.; Electronic Power Conditioning, Inc.

    1993-10-01

    Almost from the onset of the development of wind energy conversion systems (WECS), it was known that variable-speed operation of the turbine would maximize energy capture. This study was commissioned to assess the cost, efficiency gain, reduction of the cost of energy (COE), and other operating implications of converting the existing hardware of a modern fixed-speed wind energy conversion system to variable-speed operation. The purpose of this study was to develop a preliminary design for the hardware required to allow variable-speed operation using a doubly-fed generator with an existing fixed-speed wind turbine design. The turbine selected for this study is the AWT-26 designed and built by Advanced Wind Turbines Inc. of Redmond, Washington. The lowest projected COE using this variable-speed generation system is projected to be $0.0499/kWh, compared to the lowest possible COE with fixed-speed generation which is projected to be $0.0546/kWh. This translates into a 8.6% reduction of the COE using this variable-speed generation option. The preliminary system design has advanced to where the printed circuit boards can be physically laid out based on the schematics and the system software can be written based on the control flow-charts. The core of hardware and software has been proven to be successful in earlier versions of VSG systems. The body of this report presents the results of the VSWG system development. Operation under normal and fault conditions is described in detail, the system performance for variable-speed operation is estimated and compared to the original fixed-speed system performance, and specifications for all system components (generator, power electronic converter, and system controller) are given. Costs for all components are estimated, and incremental system cost is compared to incremental energy production. Finally, operational features of the VSWG which are not available in the existing FSWG system are outlined.

  9. Evolution of magma-poor continental margins from rifting to seafloor spreading.

    PubMed

    Whitmarsh, R B; Manatschal, G; Minshull, T A

    2001-09-13

    The rifting of continents involves faulting (tectonism) and magmatism, which reflect the strain-rate and temperature dependent processes of solid-state deformation and decompression melting within the Earth. Most models of this rifting have treated tectonism and magmatism separately, and few numerical simulations have attempted to include continental break-up and melting, let alone describe how continental rifting evolves into seafloor spreading. Models of this evolution conventionally juxtapose continental and oceanic crust. Here we present observations that support the existence of a zone of exhumed continental mantle, several tens of kilometres wide, between oceanic and continental crust on continental margins where magma-poor rifting has taken place. We present geophysical and geological observations from the west Iberia margin, and geological mapping of margins of the former Tethys ocean now exposed in the Alps. We use these complementary findings to propose a conceptual model that focuses on the final stage of continental extension and break-up, and the creation of a zone of exhumed continental mantle that evolves oceanward into seafloor spreading. We conclude that the evolving stress and thermal fields are constrained by a rising and narrowing ridge of asthenospheric mantle, and that magmatism and rates of extension systematically increase oceanward. PMID:11557977

  10. Development of sensitized pick coal interface detector system. Final report

    SciTech Connect

    Burchill, R.F.

    1982-01-01

    One approach for detection of the coal interface is measurement of pick cutting loads and shock through the use of pick strain gage load cells and accelerometers. The cutting drum of a long wall mining machine contains a number of cutting picks. In order to measure pick loads and shocks, one pick was instrumented and telemetry used to transmit the signals from the drum to an instrument-type tape recorder. A data system using FM telemetry was designed to transfer cutting bit load and shock information from the drum of a longwall shearer coal mining machine to a chassis mounted data recorder. The design of components in the test data system were finalized, the required instruments were assembled, the instrument system was evaluated in an above-ground simulation test, and an underground test series to obtain tape recorded sensor data was conducted.

  11. Depositional character of a dry-climate alluvial fan system from Palaeoproterozoic rift setting using facies architecture and palaeohydraulics: Example from the Par Formation, Gwalior Group, central India

    NASA Astrophysics Data System (ADS)

    Chakraborty, Partha Pratim; Paul, Pritam

    2014-09-01

    The ?20 m thick coarse-grained clastic succession in the basal part of Palaeoproterozoic Par Formation, Gwalior Group has been investigated using process-based sedimentology and deductive palaeohydraulics. Bounded between granitic basement at its base and shallow marine succession at the top, the studied stratigraphic interval represents products of an alluvial fan and its strike-wise co-existent braided river system that possibly acted as a tributary for the fan. Detailed facies, facies association analysis allowed identification of two anatomical parts for the fan system viz. proximal and mid fan. While thin proximal fan is represented by products of rock avalanche and hyperconcentrated flows with widely varying rheology, the mid fan is represented by products of sheet floods and flows within streamlets. The interpretation found support from palaeoslope estimation carried out on the fluvial part of the mid fan that plot dominantly within the alluvial fan field demarcated by Blair and McPherson (1994). Dry climatic condition suggested from dominance of stream flow over mass flow deposition within the Par alluvial fan. Strike-wise, the fan is discontinuous and juxtaposed with a braid plain system. In contrast to the fluvial part of fan system, the palaeoslope data from the braid plain system dominantly plot within the ‘natural depositional gap' defined by Blair and McPherson. A raised palaeoslope for the river systems, as suggested from Proterozoic braid plain deposits around the Globe, is found valid for the Par braid plain system as well. From preponderance of granular and sandy sediments within the alluvial fan and braid plain systems and a pervasive north-westward palaeocurrent pattern within the fluvial systems the present study infers a gently sloping bevelled source area in the south-southeast of the basin with occurrence of steep cliffs only locally.

  12. Advanced power conditioning for maglev systems. Final report

    SciTech Connect

    Nerem, A.; Bowles, E.E.; Chapelle, S.; Callanan, R.J.

    1992-08-01

    The final report contains parametric scaling data and computer models of power conditioning equipment applicable to the design of an advanced maglev system. The power conditioning topologies were selected based on data from a literature search, on characteristics of present power semiconductor technology devices, and on actual performance characterization of designs using a circuit analysis program. The analyses show that GTOs are the best switches for traction drives, input power conditioning equipment, and the braking chopper. At lower power levels, as required for auxiliary power and superconducting coil power conditioning, the IGBT appeared to be the best switch.

  13. LBT primary mirrors: the final design of the supporting system

    NASA Astrophysics Data System (ADS)

    Parodi, Giancarlo; Cerra, G. C.; Hill, John M.; Davison, Warren B.; Salinari, Piero

    1997-03-01

    The main final results in terms of stresses and optical performances are reported for the large binocular telescope (LBT) primary mirrors. The two borosilicate LBT primary mirrors f/1.14 have 8.4 diameter and are produced at the Steward Observatory Mirror Lab (SOML). They are honeycomb shaped in order to achieve light weight, short thermal constant and high stiffness. The back plate is flat and the upper is paraboloid shaped. Each elementary cell has, in the lower plate, one circular hole permitting the ventilation of cell itself. The material used is the borosilicate Ohara E6. Different supporting systems have been analyzed from the mirror casting to the operative conditions, i.e.: supporting system during the cooling of the casting phase; supporting system for the handling after the casting phase and before the optical surface grinding and polishing; supporting system for the handling after the optical surface polishing and for maintenance; passive support system in non-operative condition; supporting system in operative condition. The stress checks carried out show that the values of the maximum principal tensile stresses are below 0.7 MPa for long times and/or stresses affecting large volumes, and are below 1.05 MPa for short times and small volumes. Optical performances in operative condition respect the specification.

  14. Present-day Kinematics of the East African Rift

    NASA Astrophysics Data System (ADS)

    Stamps, D. S.; Calais, E.; Saria, E.; Mbede, E.; Ebinger, C.; Delvaux, D.; Kervyn, F.; Combrinck, L.; Hartnady, C.; Nocquet, J.; Fernandes, R.

    2007-12-01

    The East African Rift (EAR), a ~5000 km-long series of seismically active structures that mark the divergent boundary between the Somalia and Nubia plates, is often cited as a modern archetype for rifting and continental breakup. Paradoxically, its current kinematics is the least well-known of all major plate boundaries, owing to its tremendous extent, difficult access, and lack of geodetic data. The existence of two "new" tectonic plates within the EAR (Victoria and Rovuma) between the main Nubian and Somalian plates has recently been proposed through combined analysis of earthquake slip vector and (sparse) space-geodetic data (Calais et al., 2006). A third, dominantly oceanic Lwandle plate was recently postulated by a re-analysis of the post 3.2 Ma spreading rates and transform-fault azimuths along the Southwest Indian Ridge (SWIR; Horner-Johnson et al., 2007). Here we use an updated geodetic solution -- a combination of all continuous GPS stations on the Nubia, Somalia, and Antarctic plates, campaign GPS measurements in Africa, and a global DORIS solution -- together with earthquake slip vectors in the EAR and transform azimuth and spreading rates along the SWIR. We show that the space geodetic data and the 3.2 Ma average oceanic data along the SWIR are consistent with each other at the 95% confidence level. The data support a kinematic model with (1) a present-day Nubia-Somalia Euler pole located to the SE of the southern tip of Africa, (2) the existence of three distinct microplates embedded in the EAR: Victoria, Rovuma, and Lwandle. Additional geodetic data in the EAR are now needed to confirm and further refine this model. References Calais, E., C. Hartnady, C. Ebinger, and J.M. Nocquet, Kinematics of the East African Rift from GPS and earthquake slip vector data, In: Yirgu, G., Ebinger, C.J. & Maguire, P.K.H. (eds) Structure and Evolution of the Rift Systems within the Afar volcanic province, Northeast Africa, Geological Society Special Publications, 259, p.9-22, 2006. Horner-Johnson, B., R.G. Gordon, D.F. Argus, Plate kinematic evidence for the existence of a distinct plate between the Nubian and Somalian plates along the Southwest Indian Ridge, Journal of Geophysical Research, 112, 2007

  15. Tracing mantle-reacted fluids in magma-poor rifted margins: The example of Alpine Tethyan rifted margins

    NASA Astrophysics Data System (ADS)

    Pinto, Victor Hugo G.; Manatschal, Gianreto; Karpoff, Anne Marie; Viana, Adriano

    2015-09-01

    The thinning of the crust and the exhumation of subcontinental mantle in magma-poor rifted margins is accompanied by a series of extensional detachment faults. We show that exhumation along these detachments is intimately related to migration of fluids leading to changes in mineralogy and chemistry of the mantle, crustal, and sedimentary rocks. Using field observation and analytical methods, we investigate the role of fluids in the fossil distal margins of the Alpine Tethys. Using Cr-Ni-V, Fe, and Mn as tracers, we show that fluids used detachment faults as pathways and interacted with the overlying crust and sediments. These observations allow us to discuss when, where, and how this interaction happened during the formation of the rifted margin. The results show that: (i) serpentinization of mantle rocks during their exhumation results in the depletion of elements and migration of mantle-reacted fluids that are channeled along active detachment system; (ii) in earlier-stages, these fluids affected the overlying syntectonic sediments by direct migration from the underlying detachments;(iii) in later-stages, these fluids arrived at the seafloor, were introduced into, or "polluted" the seawater and were absorbed by post tectonic sediments. We conclude that a significant amount of serpentinization occurred underneath the hyperextended continental crust, and that the mantle-reacted fluids might have modified the chemical composition of the sediments and seawater. We propose that the chemical signature of serpentinization related to mantle exhumation is recorded in the sediments and may serve as a proxy to date serpentinization and mantle exhumation at present-day magma-poor rifted margins.

  16. What the volcanism of the East African Rift tells us on its evolution and dynamics: a reappraisal

    NASA Astrophysics Data System (ADS)

    Michon, Laurent

    2015-04-01

    The East African Rift (EAR) is one of the most studied tectonic structures on Earth. Classically, it is described as extending from Afar in the North to the Malawi rift in the South, along the eastern and western branches, respectively. A widely accepted consensus also exists on two main points: 1- the rift initiated first with plume emplacement below the northern part of the eastern branch and 2- extension and volcanism subsequently migrated southward along the western branch (e.g., Ebinger, 1989). However, an increasing amount of new geochronological data on the volcanic activity in the southern part of the East African Rift tends to weaken these interpretations and imposes a reassessment of the rift dynamics. The volcanic activity being one of the main characteristics of this rift, I use it here to determine the lateral extension of the rift system and to assess the rift activity through times. First, the volcanism unambiguously indicates that the rift is not limited to the African continent but can be traced in the Mozambique Channel and in Madagascar where it is closely related to active tectonics (graben and transfer faults) initiated since at least the Miocene. Moreover, the synthesis of more than 800 published geochronological data of volcanic products distributed over the overal East African Rift allows the distinction of two parts. The first part, the Northern EAR, corresponds to the sole eastern branch, which is characterized by volcanic plateaus resulting from huge magma flux during three main periods (32-28, 18-12, 6-0 Ma). Provinces of the second part, the Southern EAR (the western branch, the Mozambique Channel and Madagascar), share rift-related scattered volcanic centres characterized by coeval periods of activity since the Oligocene (28-24, 20-16 and 12-0 Ma). This synthesis highlights the lack of southward migration of the volcanism during the evolution of the East African Rift and instead reveals the almost synchronous development of the volcanism all along the rift system. Moreover, it suggests the existence of two parts that experienced different evolutions since around 30 Ma. The volcanism of the Northern EAR shows characteristics, which agrees with a mantle plume origin. On the contrary, the development of stationary volcanic centres in the Southern EAR despite the northward motion of the African plate disagrees with such an interpretation and instead suggests a tectonically-assisted origin of the volcanism along main Precambrian lithospheric structures. The occurrence of several pulses of volcanism in each part of the East African Rift, coeval with periods of crustal uplift, could stem from successive main tectonic phases favoured by mantle bursts fed by the African superswell. Reference: Ebinger, C.J., 1989, Tectonic development of the western branch of the East African rift system: Geological Society of America Bulletin, v. 101, p. 885-903.

  17. Gas Geochemistry of Volcanic and Geothermal Areas in the Kenya Rift: Implications for the Role of Fluids in Continental Rifting

    NASA Astrophysics Data System (ADS)

    Lee, H.; Fischer, T. P.; Ranka, L. S.; Onguso, B.; Kanda, I.; Opiyo-Akech, N.; Sharp, Z. D.; Hilton, D. R.; Kattenhorn, S. A.; Muirhead, J.

    2013-12-01

    The East African Rift (EAR) is an active continental rift and ideal to investigate the processes of rift initiation and the breaking apart of continental lithosphere. Mantle and crust-derived fluids may play a pivotal role in both magmatism and faulting in the EAR. For instance, large quantities of mantle-derived volatiles are emitted at Oldoinyo Lengai volcano [1, 2]. Throughout the EAR, CO2-dominated volatile fluxes are prevalent [3, 4] and often associated with faults (i.e. Rungwe area, Tanzania, [5, 6]). The purpose of this study is to examine the relationship between volcanism, faulting and the volatile compositions, focusing on the central and southern Kenyan and northern Tanzanian section of the EAR. We report our analysis results for samples obtained during a 2013 field season in Kenya. Gases were sampled at fumaroles and geothermal plants in caldera volcanoes (T=83.1-120.2°C) and springs (T=40-79.6°C and pH 8.5-10) located near volcanoes, intra-rift faults, and a transverse fault (the Kordjya fault, a key fluid source in the Magadi rift) by 4N-NaOH solution-filled and empty Giggenbach bottles. Headspace gases were analyzed by a Gas Chromatograph and a Quadrupole Mass Spectrometer at the University of New Mexico. Both N2/Ar and N2/He ratios of all gases (35.38-205.31 and 142.92-564,272, respectively) range between air saturated water (ASW, 40 and ?150,000) and MORB (100-200 and 40-50). In addition, an N2-Ar-He ternary diagram supports that the gases are produced by two component (mantle and air) mixing. Gases in the empty bottles from volcanoes and springs have N2 (90.88-895.99 mmom/mol), CO2 (2.47-681.21 mmom/mol), CH4 (0-214.78 mmom/mol), O2 (4.47-131.12 mmom/mol), H2 (0-35.78 mmom/mol), Ar (0.15-10.65 mmom/mol), He (0-2.21 mmom/mol), and CO (0-0.08 mmom/mol). Although some of the samples show an atmospheric component, CO2 is a major component in most samples, indicating both volcanoes and springs are emitting CO2. Gases from volcanoes are enriched in CH4 and H2, denoting their sources are reduced (oxygen-poor) magma chambers or hydrothermal systems. 40Ar/36Ar ratios (average of all samples=299.15) are similar to our air standard value (299.65×4.05), however, some volcanoes (~308.75) and springs (~321.96) have slightly higher ratios. The springs with elevated 40Ar imply that both the intra-rift (Lake Bogoria) and transverse (Lake Magadi) faults are possibly pathways to carry volatiles from deep sources to the surface. In future work, we will carry out wet chemistry and ion chromatography analyses of the NaOH solutions, measure 3He/4He ratios and complete C, N, and S isotope analyses to further constrain fluid sources and migration processes. [1] Fischer et al., 2009, Nature 459. [2] de Moor et al., 2013, EPSL 361. [3] Sawyer et al., 2008, G-cubed 9. [4] Tassi et al., 2009, G-cubed 10. [5] Barry et al., 2013, Chem Geol 339. [6] de Moor et al., 2013, Chem Geol 339.

  18. Tectono-magmatic evolution at distal magma-poor rifted margins: insights of the lithospheric breakup at the Australia-Antarctica margins.

    NASA Astrophysics Data System (ADS)

    Gillard, Morgane; Autin, Julia; Manatschal, Gianreto

    2015-04-01

    The discovery of large domains of hyper-extended continental crust and exhumed mantle along many present-day magma-poor rifted margins questions the processes that play during the lithospheric breakup and the onset of seafloor spreading. In particular, the amount of magma and its relation to tectonic structures is yet little understood. Trying to find answers to these questions asks to work at the most distal parts of rifted margins where the transition from rifting to steady state seafloor spreading occurred. The Australian-Antarctic conjugated margins provide an excellent study area. Indeed, the central sector of the Great Australian Bight/Wilkes Land developed in a magma-poor probably ultra-slow setting and displays a complex and not yet well understood Ocean-Continent Transition (OCT). This distal area is well imaged by numerous high quality seismic lines covering the whole OCT and the steady-state oceanic crust. The deformation recorded in the sedimentary units along these margins highlights a migration of the deformation toward the ocean and a clear polyphase evolution. In particular, the observation that each tectono-sedimentary unit downlaps oceanwards onto the basement suggests that final rifting is associated with the creation of new depositional ground under conditions that are not yet those of a steady state oceanic crust. These observations lead to a model of evolution for these distal margins implying the development of multiple detachment systems organizing out-of-sequence, each new detachment fault developing into the previously exhumed basement. This spatial and temporal organization of fault systems leads to a final symmetry of exhumed domains at both conjugated margins. Magma appears to gradually increase during the margin development and is particularly present in the more distal domain where we can observe clear magma/fault interactions. We propose that the evolution of such rifted margins is linked to cycles of delocalisation/re-localisation of the deformation which could be mainly influenced by magma and by the decoupling between the upper brittle deformation and the asthenospheric uplift. In this context, the lithospheric breakup appears to be triggered by progressive syn-extensional thermal and magmatic weakening. However, the observation of continentward dipping reflectors interpreted as flip-flop detachment systems suggests that the localisation of the spreading centre and the onset of the steady state oceanic spreading will not be necessarily associated with a clear magmatic oceanic crust. In case of a low magmatic budget we can rather observe the onset of steady state amagmatic oceanic spreading, similar to what is expected at ultra-slow spreading ridges. This model of evolution (Gillard, 2014, PhD thesis) could well explain the fact that most magma-poor margins display symmetric exhumed domains on conjugate margins. However it raises the question of the nature of magnetic anomalies in ocean-continent transitions and their value for the interpretation of the kinematic evolution of conjugate rifted margins.

  19. Chapter 34: Geology and petroleum potential of the rifted margins of the Canada Basin

    USGS Publications Warehouse

    Houseknecht, D.W.; Bird, K.J.

    2011-01-01

    Three sides of the Canada Basin are bordered by high-standing, conjugate rift shoulders of the Chukchi Borderland, Alaska and Canada. The Alaska and Canada margins are mantled with thick, growth-faulted sediment prisms, and the Chukchi Borderland contains only a thin veneer of sediment. The rift-margin strata of Alaska and Canada reflect the tectonics and sediment dispersal systems of adjacent continental regions whereas the Chukchi Borderland was tectonically isolated from these sediment dispersal systems. Along the eastern Alaska-southern Canada margin, termed herein the 'Canning-Mackenzie deformed margin', the rifted margin is deformed by ongoing Brooks Range tectonism. Additional contractional structures occur in a gravity fold belt that may be present along the entire Alaska and Canada margins of the Canada Basin. Source-rock data inboard of the rift shoulders and regional palaeogeographic reconstructions suggest three potential source-rock intervals: Lower Cretaceous (Hauterivian-Albian), Upper Cretaceous (mostly Turonian) and Lower Palaeogene. Burial history modelling indicates favourable timing for generation from all three intervals beneath the Alaska and Canada passive margins, and an active petroleum system has been documented in the Canning-Mackenzie deformed margin. Assessment of undiscovered petroleum resources indicates the greatest potential in the Canning-Mackenzie deformed margin and significant potential in the Canada and Alaska passive margins. ?? 2011 The Geological Society of London.

  20. Lateral variation in structural style along an evaporite-influenced rift fault system in the Halten Terrace, Norway: Influence of basement structure and evaporite facies

    NASA Astrophysics Data System (ADS)

    Wilson, Paul; Elliott, Gavin M.; Gawthorpe, Rob L.; Jackson, Christopher A.-L.; Michelsen, Lisa; Sharp, Ian R.

    2015-10-01

    The Halten Terrace is underlain by a Triassic evaporitic package, resulting in vertically decoupled normal fault systems following subsequent extension. Four structural domains are identified along the eastern margin of the Halten Terrace, characterised by: i) thick-skinned normal faults affecting both sub-salt and supra-salt cover, ii) basement-restricted normal faults associated with fault-propagation folds, iii) thick-skinned, distributed normal faults, and iv) thick-skinned, localised normal faults. A fault domain boundary associated with an NE-SW striking basement fault corresponds to an abrupt change in style in the north of the Halten Terrace. Summed throw and estimated strain measurements show that throw and strain accommodated by the fault system increase southward, corresponding to a transition from distributed to localised faulting. The evaporite package is variable in thickness, but those variations do not correspond spatially to variations in structural style. Wells that penetrate the evaporite package, and volume attribute analysis of 3D seismic data, suggest variable evaporite facies. A change in seismic attributes from high-amplitude, low variance to low-amplitude, high variance corresponds to a change from decoupled to thick-skinned faulting. The sub-evaporite fault template, amount of strain accommodated across the fault system, and facies variations in the evaporite package are key influences on structural style.

  1. Diabase dikes of the Midcontinent Rift in Minnesota: a record of Keweenawan magmatism and tectonic development

    SciTech Connect

    Green, J.C.; Chandler, V.C.

    1985-01-01

    Swarms of both reversed-polarity (R, older) and normal-polarity (N, younger) basaltic dikes help to define the evolution of the Minnesota portion of the Midcontinent Rift of North America. Each swarm, representing fissure-feeders for a package of overlying plateau lavas now eroded away, shows the direction of least principal stress at that time and place in the complex evolution of this abortive but nearly-successful rift. Paleomagnetic pole determinations for Carlton county (CC) and Grand Portage (GP) R dikes are coincident along the Logan Loop of the Proterozoic track, showing essential contemporaneity, though their trends are different (N.30/sup 0/E vs. N. 70-90/sup 0/E.) and they are 250 km apart. These poles match that of the R lavas of the North Shore Volcanic Group (NSVG) and imply a younger age than the R Logan sills and dikes. The geochemistry of the dikes (71 analyses) also correlates well with NSVG flows, ranging from olivine tholeiites to transitional basalts and basaltic andesites and is similar to tholeiites of Columbia River, Parana, and Tertiary No. Atlantic provinces. Though each swarm shows a range of compositions, some are dominantly more evolved, whereas others contain more primitive dikes with higher Al, Mg/Fe, Cr and Ni and lower Fe, Ti, P and LIL's. An early major episode of rifting during the R polarity interval was followed by at least one major N episode in Minnesota before the final one along the present Lake Superior syncline axis. Rifting directions and mantle sources were different for each episode as shown by cross-trending dike sets, indicating complex rift development.

  2. Miocene initiation and acceleration of extension in the South Lunggar rift, western Tibet: Evolution of an active detachment system from structural mapping and (U-Th)/He thermochronology

    E-print Network

    Styron, Richard H.; Taylor, Michael Halford; Sundell, Kurt E.; Stockli, Daniel F.; Oalmann, Jeffrey A. G.; Mö ller, Andreas; McCallister, Andrew T.; Liu, Deliang

    2013-07-20

    ° 80° 85° 85° 90° 90° 95° 95° 100° 100° 105° 105° 25° 25° 30° 30° 35° 35° 40° 40° Tarim basin India Lhasa Block H i m a l a y a IYS China Figure 2 Qiangtang block R a n g e Nepal BNS Tibetan plateau Figure 1. Active tectonic map of the Himalayan... episodically throughout the Oligocene and early Miocene, expressed as activity on the north- dipping South Tibetan Detachment system [Burg and Chen, 1984; Burchfiel and Royden, 1985] and the development of the South Kailas Basin between the Gangdese arc...

  3. Load leveling on industrial refrigeration systems. Final report

    SciTech Connect

    Bierenbaum, H.S.; Kraus, A.D.

    1982-01-01

    This project addressed the problem of developing, validating, and demonstrating an optimized methodology for maximizing the benefits of load levelling, energy conservation through efficiency improvements, and reject heat recovery on large, energy intensive industrial compressor systems. A typical industrial food processing plant, a brewery, with a 2000 horsepower compressor/refrigeration system was used as a model facility and as a site for demonstration and validation of strategies developed. The approach used in this work was to construct a computer model of the facility and its energy systems and validate the model against actual data. The next step was to simulate the various conservation and load management options using the validated model. Finally, the savings available for implementing the most promising options were verified by trials in the brewery. Results showed that an optimized methodology for implementing load leveling and energy conservation consisted of first adjusting (or tuning) refrigeration systems controller variables - gain and reset - to minimize unnecessary compressor starts. Second, the primary refrigeration system operating parameters, compressor suction pressure, and discharge pressure are carefully controlled (modulated) to satisfy product quality constraints (as well as in-process material cooling rates and temperature levels) and simultaneously improve energy efficiency and peak demand. Third, energy cost savings for recovery of heat from the reject side of the refrigeration system are estimated using the newly determined compressor operating conditions as a basis for evaluating the energy cost savings associated with reject heat recovery. Fourth, a decision is made to implement the reject heat recovery system based on a cost/benefits analysis.

  4. Using Lake Superior Parks to Present the Midcontinent Rift

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  5. Correlation of geophysical datasets in rifted margin studies

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  6. The North Polar Spur and Aquila Rift

    NASA Astrophysics Data System (ADS)

    Sofue, Yoshiaki

    2015-03-01

    Soft X-ray intensity at 0.89 keV along the North Polar Spur (NPS) is shown to follow the extinction law due to the interstellar gas in the Aquila Rift by analysing the ROSAT archival data, which proves that the NPS is located behind the rift. The Aquila-Serpens molecular clouds, where the X-ray optical depth exceeds unity, are shown to have a mean LSR velocity of v = 7.33 ± 1.94 km s-1, corresponding to a kinematic distance of r = 0.642 ± 0.174 kpc. Assuming a shell structure, a lower limit of the distance to NPS is derived to be 1.01 ± 0.25 kpc, with the shell centre being located farther than 1.1 kpc. Based on the distance estimation, we argue that the NPS is a Galactic halo object.

  7. Practical reliability and uncertainty quantification in complex systems : final report.

    SciTech Connect

    Grace, Matthew D.; Ringland, James T.; Marzouk, Youssef M.; Boggs, Paul T.; Zurn, Rena M.; Diegert, Kathleen V.; Pebay, Philippe Pierre; Red-Horse, John Robert

    2009-09-01

    The purpose of this project was to investigate the use of Bayesian methods for the estimation of the reliability of complex systems. The goals were to find methods for dealing with continuous data, rather than simple pass/fail data; to avoid assumptions of specific probability distributions, especially Gaussian, or normal, distributions; to compute not only an estimate of the reliability of the system, but also a measure of the confidence in that estimate; to develop procedures to address time-dependent or aging aspects in such systems, and to use these models and results to derive optimal testing strategies. The system is assumed to be a system of systems, i.e., a system with discrete components that are themselves systems. Furthermore, the system is 'engineered' in the sense that each node is designed to do something and that we have a mathematical description of that process. In the time-dependent case, the assumption is that we have a general, nonlinear, time-dependent function describing the process. The major results of the project are described in this report. In summary, we developed a sophisticated mathematical framework based on modern probability theory and Bayesian analysis. This framework encompasses all aspects of epistemic uncertainty and easily incorporates steady-state and time-dependent systems. Based on Markov chain, Monte Carlo methods, we devised a computational strategy for general probability density estimation in the steady-state case. This enabled us to compute a distribution of the reliability from which many questions, including confidence, could be addressed. We then extended this to the time domain and implemented procedures to estimate the reliability over time, including the use of the method to predict the reliability at a future time. Finally, we used certain aspects of Bayesian decision analysis to create a novel method for determining an optimal testing strategy, e.g., we can estimate the 'best' location to take the next test to minimize the risk of making a wrong decision about the fitness of a system. We conclude this report by proposing additional fruitful areas of research.

  8. Seismotectonics of Reelfoot rift basement structures

    SciTech Connect

    Dart, R.L.; Swolfs, H.S. )

    1993-03-01

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

  9. Early Paleozoic sedimentation in Reelfoot rift

    SciTech Connect

    Houseknecht, D.W.; Weaverling, P.H.

    1983-09-01

    Analysis of subsurface data from deep tests drilled in the northern Mississippi embayment and southern Mid-Continent suggests that earliest Paleozoic sedimentation was dominated by the tectonic evolution of the Reelfoot rift. Throughout most of the Mid-Continent, the Upper Cambrian Lamotte (Mt. Simon) sandstone rests nonconformably on Precambrian basement and is overlain by the Bonneterre (Eau Claire) Formation. However, in the area of the Reelfoot rift, both the Lamotte and Bonneterre grade into thick, basinal shales that locally display evidence of episodic deposition of coarse clastics, perhaps on submarine fans. Moreover, two major sedimentary units are present beneath the Lamotte-Bonneterre basinal facies within the Reelfoot rift. Immediately underlying the Lamotte-Bonneterre shale is a carbonate stratum (probably dolomite) that thickens to more than 1,000 ft (300 m) along the axis of the basin in eastern Arkansas. Underlying this carbonate is a detrital unit that grades from arkosic sandstone near the northern terminus of the basin to a basinal shale southward. This basinal shale is at least several hundred feet thick near the axis of the basin. These two strata occupy the stratigraphic position of the Conasauga (Middle Cambrian) and Rome (Lower Cambrian) Formations of the southern Appalachians. The axial and transverse distribution of these strata suggests that the Reelfoot evolved as paired grabens or half grabens during the Early and Middle Cambrian. Subsequently, the Reelfoot remained the axis for more widespread subsidence and sedimentation throughout much of the Paleozoic.

  10. Volcano Deformation in the Main Ethiopian Rift

    NASA Astrophysics Data System (ADS)

    Biggs, J.; Bastow, I.; Keir, D.; Hutchison, W.

    2012-04-01

    Magmatism strongly influences continental rift development yet the mechanism, distribution and timescales on which melt is emplaced and erupted through the shallow crust are not well characterized. The Main Ethiopian Rift (MER) has experienced significant volcanism and the mantle beneath is characterized by high temperatures and partial melt. Despite its magma-rich geological record, only one eruption has been historically recorded and no dedicated monitoring networks exist. Consequently, the present-day magmatic processes in the region remain poorly documented, and the associated hazard neglected. We use satellite-based InSAR observations to demonstrate that significant deformation has occurring at 4 volcanic edifices in the MER (Alutu, Corbetti, Bora and Haledebi) from 1993-2010. This raises the number of volcanoes known to be deforming in East Africa beyond 12, comparable to many subduction arcs despite the smaller number of recorded eruptions. The largest displacements are at Alutu volcano, the site of a geothermal plant, which showed two pulses of rapid inflation (10-15 cm) in 2004 and 2008 separated by gradual subsidence. Our observations indicate a shallow (<10 km), frequently replenished zone of magma storage associated with volcanic edifices and add to the growing body of observations that indicate shallow magmatic processes operating on a decadal timescale are ubiquitous throughout the East African Rift. In the absence of detailed historical records of volcanic activity, satellite-based observations of monitoring parameters, such as deformation, could play an important role in assessing volcanic hazard.

  11. Urban Integrated Industrial Cogeneration Systems Analysis. Phase II final report

    SciTech Connect

    Not Available

    1984-01-01

    Through the Urban Integrated Industrial Cogeneration Systems Analysis (UIICSA), the City of Chicago embarked upon an ambitious effort to identify the measure the overall industrial cogeneration market in the city and to evaluate in detail the most promising market opportunities. This report discusses the background of the work completed during Phase II of the UIICSA and presents the results of economic feasibility studies conducted for three potential cogeneration sites in Chicago. Phase II focused on the feasibility of cogeneration at the three most promising sites: the Stockyards and Calumet industrial areas, and the Ford City commercial/industrial complex. Each feasibility case study considered the energy load requirements of the existing facilities at the site and the potential for attracting and serving new growth in the area. Alternative fuels and technologies, and ownership and financing options were also incorporated into the case studies. Finally, site specific considerations such as development incentives, zoning and building code restrictions and environmental requirements were investigated.

  12. Geodynamic Evolution of the Southern Flank of the Corinth Rift

    NASA Astrophysics Data System (ADS)

    Jousselin, D.; Bourlange, S.; Ford, M.; Le Carlier, C.; Rohais, S.

    2005-12-01

    The Gulf of Corinth is the most seismically active area of Europe extending in a N-S direction at a rate of 12mm/yr. Many studies have focused on currently active normal faults, which bound the southern flank of the Corinth rift. However, many prominent faults, that are considered no longer active, outcrop over a broader area along with their syn-rift sedimentary sequence. The normal fault network and related synrift succession have been mapped and studied at a scale of 1:25,000. The geometry of the fault network in 3D has been reconstructed in the gOcad 3D geomodelling package. Based on these detailed field data we propose a geodynamic model for the evolution of the region in three steps over the last two million years. From 2 to 1 Ma, extension affected a broad area at least twenty kilometers wide. Alluvial conglomerates and sandstones, deposited in grabens and half grabens, were derived from erosion of the pre-existing (Hellenic) high relief to the south in the Peloponnese massif. Around 1Ma, a regional uplift led to the migration of the depocenter to the north. New faults are activated closer to the coast, in places generating forced folds that tilted synrift fluvial formations northward over a 2-3 kilometers wide area. Considerable accommodation space was generated by these faults and, with an increased sediment supply from the south, a series of giant marine Gilbert deltas developed in their hangingwalls. Finally, from 0.5 Ma to present, the activation of a series of major new faults further to the north (near the current coastline) coincided with regional uplift of the south coastal belt, and initiated the formation of a second generation of Gilbert delta, currently building out into the gulf. The faults can be divided into three families. The main one (74 data) is oriented N110, dipping 45 to 60° to the north. It includes 5 major faults spaced 3 to 5 km from south to north, with a throw larger than 1000m. A secondary set (41 data) strikes N60, dipping to the NW, it includes only one fault with a throw larger than 500m; the other secondary set (43 data) is antithetic to the two first ones as it strikes N60 to N110, dipping to the south, the largest fault it includes has a throw of about 400m. Most faults are planar and the importance of listric faults seems minor in the rift history.

  13. Statistical analysis of Port Systems requirements. Final analysis report

    SciTech Connect

    Green, J.R.; Thomas, R.W.L.; Youngmann, K.C.

    1984-02-01

    This is a report of a study conducted under the Port Systems Project for the Naval Facilities Engineering Command. An objective of the Port Systems Project is to investigate methods of predicting the utility requirements of the port facilities that must be met to support future fleets. This report starts with a brief overview of the first phase of the methodology development and continues with the technical approach and the principles of statistical theory applied. Examples are used to relate these principles to the analysis to electric power requirements as an aid in understanding the analytical process inherent in the Methodology. An overview of the analytical procedures that constitute the basis of the Port Systems Requirements Prediction Methodology is presented. Computer programs used to calculate statistics are appended. Finally the results achieved are presented. The unique feature of this approach to port utility prediction is that it identifies and accommodates the contribution made by correlating the time usage of electric power consumption data among different ship classes. This results in non-zero correlation coefficients, which have an affect on the quality of the prediction. It is shown that as the number of ships using electrical power increases, the accuracy of the prediction is reduced.

  14. Development of the Barents Sea rift and its influence on sedimentation and hydrocarbon formation

    NASA Astrophysics Data System (ADS)

    Balanyuk, Inna; Dmitrievsky, Anatoly; Shapovalov, Sergey; Chaikina, Olga

    2010-05-01

    A special attention is given to the geodynamic active zone of the Barents Sea rift. Its development was accompanied by vigorous tectonic activity, propagation of deep faults, deep fractured zones that played an important role in fluid dynamic and thermobaric regime of the whole region. Geodynamic development of the Barents Sea rift not only played a substantial role in formation of as unique oil and gas fields as Shtokman, Prirazlomnoe and others, but created prerequisites for possible gas outbursts into near-surface sediments that could result, in some cases, in hydrocarbon formation. All the Barents Sea deposits are situated in the epicenter of the rift and, most important, over the zone of listric faults intersection, which set up a knot system over the mantle diapir. It is confirmed by prospecting seismology. Intrusion of hot mantle matter with further cooling down of abnormal lense might be a possible cause of appearance and evolution of ultradeep depressions. A high "seismic stratification" of the lower crust (nearly reaching the basement surface) at time scale about 8 sec. is typical for the deepest part of the depression. Supposing the "seismic stratified" lower crust correspond to "basalt" layer, this area is nearly upper crust ("granitic-gneiss") free. This fact confurmes conception on development of "granite free gaps" in the depression basement. Thick blocks of "seismically transparent" upper crust corresponding to the "granitic-gneiss" layer are marked out within Kolsk-Kanin monocline. An abrupt thickness decrease and appearance of "stratified" areas takes place at the southern edge of the depression. A filling of the over-rift sag with sediments, revival of the faults and their effect on the filtration processes and gas hydrates formation took place in the South Barents Sea depression. Repeating activation of the fault blocks in the basement, especially during late Jurassic - early Cretaceous period contributed to formation of the structures related to the greatest deposits of this depression. An extended field acoustic data collected in the Barents Sea led to understanding of general fundamental problems for all Arctic Seas and, first of all, the problem of Quaternary glaciations. An analysis of Eurasian-Arctic continental margin shows correspondence between the rift systems of the shelf with those of the ocean. This relation can be observed by an example of the central Arctic region. All the rift systems underlying the sediment basin are expressed in the sea bed relief as spacious and extensive graben valleys burnished by lobes. The rift structures and the sediment cover are connected by the systems of transversal (or oblique) faults. A study of the regional geologic structure of basins affords believing in the very complicated inner riftogenic structure of the base and the lower part of the sediment cover, which is represented by a combination of grabens and horsts bound by the same tectonic border in the form of high amplitude fault zones, and have a very high density of fault-fractured tectonics. In the same time, a branching of the rift structures related to rounding of large solid blocks of the crust, represented by Archaean or Baikal base prominences, takes place. Their frequent structural connection with the continental paleo-rift structures is ascertained, but the shelf rift system are not their straight prolongation and separated by base thresholds concealed under the sediment cover or by bulkheads expressed even in the modern relief. The information on geodynamic development of the region, thermal convection and modern sedimentation enable assessment of the real potentiality for underwater works in the region, potential gas hydrates resources, and will help to assign a strategy of prospecting work, to range the known fields, to carry out a regional survey for engineering work.

  15. Acoustic Resonance Spectroscopy (ARS) Munition Classification System enhancements. Final report

    SciTech Connect

    Vela, O.A.; Huggard, J.C.

    1997-09-18

    Acoustic Resonance Spectroscopy (ARS) is a non-destructive evaluation technology developed at the Los Alamos National Laboratory (LANL). This technology has resulted in three generations of instrumentation, funded by the Defense Special Weapons Agency (DSWA), specifically designed for field identification of chemical weapon (CW) munitions. Each generation of ARS instrumentation was developed with a specific user in mind. The ARS1OO was built for use by the U.N. Inspection Teams going into Iraq immediately after the Persian Gulf War. The ARS200 was built for use in the US-Russia Bilateral Chemical Weapons Treaty (the primary users for this system are the US Onsite Inspection Agency (OSIA) and their Russian counterparts). The ARS300 was built with the requirements of the Organization for the Prohibition of Chemical Weapons (OPCW) in mind. Each successive system is an improved version of the previous system based on learning the weaknesses of each and, coincidentally, on the fact that more time was available to do a requirements analysis and the necessary engineering development. The ARS300 is at a level of development that warrants transferring the technology to a commercial vendor. Since LANL will supply the computer software to the selected vendor, it is possible for LANL to continue to improve the decision algorithms, add features where necessary, and adjust the user interface before the final transfer occurs. This paper describes the current system, ARS system enhancements, and software enhancements. Appendices contain the Operations Manual (software Version 3.01), and two earlier reports on enhancements.

  16. Erosion controls on the metamorphic core complex dynamics and its relationship with syn- rift basin evolution

    NASA Astrophysics Data System (ADS)

    Wang, Kun; Burov, Evgueni; Gumiaux, Charles; Chen, Yan; Zhao, Liang

    2015-04-01

    The wide rifting evolves towards asymmetric extensional thinning of the entire crust and development of different characteristic features such as basins, half-grabens and metamorphic core complexes (MCC). In this context, formation of supra-detachment basins is also a common feature, along with the exhumation of metamorphic rocks and considerable displacements along the hanging wall. Initiation, geometry and mechanisms of metamorphic core complexes have been already largely debated on the basis field observations, analog and numerical models. For example, it has been well demonstrated that strain softening favors asymmetric deformation and accounts for different styles of brittle and ductile strain localization. However, the temporal and spatial relations between the dome formation and basin evolution are still poorly understood. In particular, most of the existing numerical models predict a topographical depression above the metamorphic dome, whereas in nature dome formation often corresponds to a topographical uplift. To explain these phenomena, we have integrated surface erosion, sedimentary processes and strain softening into a state-of-the-art 2-D numerical thermo-mechanical model of MCC development. In the numerical experiments, we first reproduce formation of a univergent MCC by implementing strain softening and testing a large spectrum of lithospheric structures. In the next series of experiments we apply erosion/sedimentation and test model sensitivity to different erosion parameters. The results show two distinctive stages of MCC dynamics and syn-rift basin development. One single broad basin forms above the dome and is divided onto an inactive basin located at the distal detachment and an active supradetachment basin that deepens with further extension, characterized by crustal necking and dome amplificationduring the MCC formation. It is noteworthy that without strain softening, erosion at of the rift flanks mayresult in complete burial of the dome below the sedimentary cover. The experiments also demonstrate strong dependence of the system evolution on the initial thermo-rheological structure. The geometry and topography of the rift system is largely controlled by syn-extensional erosion that also strongly affects vertical and lateral movements during the rifting phase. The predicted rift dynamics can be compared to the case of the wide rift system of the eastern part of North China Craton.

  17. Variable styles of rifting expressed in crustal structure across three rift segments of the Gulf of California

    NASA Astrophysics Data System (ADS)

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

    2007-05-01

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

  18. FY 93 Thermal Loading Systems Study Final Report

    SciTech Connect

    S.F. Saterlie

    1994-08-29

    The objective of the Mined Geologic Disposal System (MGDS) Thermal Loading Systems Study being conducted by the is to identify a thermal strategy that will meet the performance requirements for waste isolation and will be safe and licensable. Specifically, both postclosure and preclosure performance standards must be met by the thermal loading strategy ultimately selected. In addition cost and schedule constraints must be considered. The Systems Engineering approach requires structured, detailed analyses that will ultimately provide the technical basis for the development, integration, and evaluation of the overall system, not just a subelement of that system. It is also necessary that the systems study construct options from within the range that are allowed within the current legislative and programmatic framework. For example the total amount of fuel that can legally be emplaced is no more than 70,000 metric tons of uranium (MTU) which is composed of 63,000 MTU spent fuel and 7,000 MTU of defense high level waste. It is the intent of this study to begin the structured development of the basis for a thermal loading decision. However, it is recognized that to be able to make a final decision on thermal loading will require underground data on the effects of heating as well as a suite of ''validated'' models. It will be some time before these data and models are available to the program. Developing a final, thermal loading decision will, therefore, be an iterative process. In the interim, the objective of the thermal loading systems study has been to utilize the information available to assess the impact of thermal loading. Where technical justification exists, recommendations to narrow the range of thermal loading options can be made. Additionally, recommendations as to the type of testing and accuracy of the testing needed to establish the requisite information will be made. A constraint on the ability of the study to select an option stems from the lack of primary hard data, uncertainties in derived data, unsubstantiated models, and the inability to fully consider simultaneously coupled processes. As such, the study must rely on idealized models and available data to compare the thermal loading options. This report presents the findings of the FY 1993 MGDS Thermal Loading Systems Study. The objectives of the study were to: (1) if justified, place bounds on the thermal loading which would establish the loading that is ''too hot''; (2) ''grade'' or evaluate the performance as a function of thermal loading of the potential repository to contain high level spent nuclear fuel against performance criteria; (3) evaluate the performance of the various options with respect to cost, safety, and operability; and (4) recommend the additional types of tests and/or analyses to be conducted to provide the necessary information for a thermal loading selection.

  19. Commercial thermal distribution systems, Final report for CIEE/CEC

    SciTech Connect

    Xu, Tengfang; Bechu, Olivier; Carrie, Remi; Dickerhoff, Darryl; Fisk, William; Franconi, Ellen; Kristiansen, Oyvind; Levinson, Ronnen; McWilliams, Jennifer; Wang, Duo; Modera, Mark; Webster, Tom; Ring, Erik; Zhang, Qiang; Huizenga, Charlie; Bauman, Fred; Arens, Ed

    1999-12-01

    According to the California Energy Commission (CEC 1998a), California commercial buildings account for 35% of statewide electricity consumption, and 16% of statewide gas consumption. Space conditioning accounts for roughly 16,000 GWh of electricity and 800 million therms of natural gas annually, and the vast majority of this space conditioning energy passes through thermal distribution systems in these buildings. In addition, 8600 GWh per year is consumed by fans and pumps in commercial buildings, most of which is used to move the thermal energy through these systems. Research work at Lawrence Berkeley National Laboratory (LBNL) has been ongoing over the past five years to investigate the energy efficiency of these thermal distribution systems, and to explore possibilities for improving that energy efficiency. Based upon that work, annual savings estimates of 1 kWh/ft{sup 2} for light commercial buildings, and 1-2 kWh/ft{sup 2} in large commercial buildings have been developed for the particular aspects of thermal distribution system performance being addressed by this project. Those savings estimates, combined with a distribution of the building stock based upon an extensive stock characterization study (Modera et al. 1999a), and technical penetration estimates, translate into statewide saving potentials of 2000 GWh/year and 75 million thermal/year, as well as an electricity peak reduction potential of 0.7 GW. The overall goal of this research program is to provide new technology and application knowledge that will allow the design, construction, and energy services industries to reduce the energy waste associated with thermal distribution systems in California commercial buildings. The specific goals of the LBNL efforts over the past year were: (1) to advance the state of knowledge about system performance and energy losses in commercial-building thermal distribution systems; (2) to evaluate the potential of reducing thermal losses through duct sealing, duct insulation, and improved equipment sizing; and (3) to develop and evaluate innovative techniques applicable to large buildings for sealing ducts and encapsulating internal duct insulation. In the UCB fan project, the goals were: (1) to develop a protocol for testing, analyzing and diagnosing problems in large commercial building built-up air handling systems, and (2) to develop low-cost measurement techniques to improve short term monitoring practices. To meet our stated goals and objectives, this project: (1) continued to investigate and characterize the performance of thermal distribution systems in commercial buildings; (2) performed energy analyses and evaluation for duct-performance improvements for both small and large commercial buildings; (3) developed aerosol injection technologies for both duct sealing and liner encapsulation in commercial buildings; and (4) designed energy-related diagnostic protocols based on short term measurement and used a benchmarking database to compare subject systems with other measured systems for certain performance metrics. This year's efforts consisted of the following distinct tasks: performing characterization measurements for five light commercial building systems and five large-commercial-building systems; analyzing the potential for including duct performance in California's Energy Efficiency Standards for Residential and Non-Residential Buildings (Title 24), including performing energy and equipment sizing analyses of air distribution systems using DOE 2.1E for non-residential buildings; conducting laboratory experiments, field experiments, and modeling of new aerosol injection technologies concepts for sealing and coating, including field testing aerosol-based sealing in two large commercial buildings; improving low-cost fan monitoring techniques measurements, and disseminating fan tools by working with energy practitioners directly where possible and publishing the results of this research and the tools developed on a web-site. The final report consists of five sections listed below. Each section includes its related

  20. Magmatism on rift flanks: insights from Ambient-Noise Phase-velocity in Afar region

    NASA Astrophysics Data System (ADS)

    Korostelev, Félicie; Weemstra, Cornelis; Leroy, Sylvie; Boschi, Lapo; Ren, Yong; Ahmed, Abdulhakim; Keir, Derek; Stuart, Graham W.; Rolandone, Frédérique; Khanbari, Khaled; Hammond, James O. S.; Kendall, J. Michael; Doubre, Cécile; Ganad, Ismail Al

    2015-04-01

    During the breakup of continent in the presence of magma, strain is commonly assumed to initially occur by border faulting, and progressively migrate in space and time towards axial magma intrusion. Magmatic processes near the rift flanks are commonly ignored. We present phase-velocity maps of the crust and uppermost mantle of the conjugate margins of the southern Red Sea (Afar and Yemen) using ambient noise tomography to constrain crustal modification during breakup. Our images show that the low seismic velocities characterize not only upper crust beneath the axial volcanic systems, but also both upper and lower crust beneath rift flanks where ongoing volcanism and hydrothermal activity occurs at the surface. The results show that magmatic modification of the crust beneath rift flanks likely occurs for a protracted period of time during the breakup process, and may persist through to early seafloor spreading. Since ongoing flank magmatism during breakup impacts the thermal evolution of the lithosphere, it has implications for the subsidence history of the rift.

  1. Non-cylindricity of mountain belts: a case for rheological and rift inheritance

    NASA Astrophysics Data System (ADS)

    Jammes, Suzon; Huismans, Ritske S.; Muñoz, Josep Anton

    2013-04-01

    Many mountain belts exhibit significant along strike variation in structural style with changes in the width of the orogen, the thickness of thick-skinned thrust sheets, the geometry and kinematics of the crustal-scale thrust system, and the degree of partitioning between pro- and retro-wedge deformation. While the main factors controlling structural style are understood to first order the cause of these lateral variations remains to be resolved. Here we focus on the Pyrenean example that is characterized by significant lateral variation in structural style with an antiformal stack in the eastern section and thick-skinned deformation in its western part. The Mesozoic rifting event preceding Pyrenean mountain building was similarly characterized by significant lateral variation in structure, with wide distributed extension in the eastern segment and very narrow rifting in its western part leading to mantle exhumation. We integrate the available geological and geophysical data with forward numerical models of both the rifting event and lithosphere scale inversion leading to mountain building. We show that a lateral variation in crustal strength related to inherited Variscan crustal composition explains both the variation in structural style during Mesozoic rifting as well as those observed during Pyrenean mountain building.

  2. From rift-inherited hyper-extension to orogenesis: De-coding the axial zone of orogenic belts

    NASA Astrophysics Data System (ADS)

    Beltrando, Marco; Manatschal, Gianreto; Mohn, Geoffroy

    2015-04-01

    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-metamorphic evolution of ophiolites, continental basement and meta-sediments. The partial preservation of rift-related relationships despite subduction to (U)HP conditions indicates that the association of serpentinites and continental basement, which in the Western Alps has often been ascribed to chaotic counter-flow in a subduction channel, may also be an inherited feature from the rifting history. Within this context, the high-pressure Alpine tectono-metamorphic units were probably detached from the downgoing lithosphere along a hydration front that is typically observed in present-day distal margins. The relationship between the architecture of the Jurassic rifted margins and the distribution/extent of Alpine metamorphism indicates that the axial zone of the Western Alps, which records multi-stage deformation and high-pressure metamorphism, originated entirely from the European and Adriatic hyper-extended rifted margins. Relative plate motion during Cretaceous-Tertiary inversion was largely accommodated at the transition between hyper-extended domains, floored by extremely thinned crust or hydrated subcontinental mantle, and proximal domains consisting of thicker continental crust. As a result, distal hyper-extended margins were preferentially subducted, whereas the proximal domains underwent relatively minor deformation and metamorphism. The final stage of continent-continent collision was achieved following subduction of the distal European margin, when the European necking zone reached the subduction zone.

  3. Crustal structure and magmato-tectonic processes in an active rift (Asal-Ghoubbet, Afar, East Africa): 1. Insights from a 5-month seismological experiment

    NASA Astrophysics Data System (ADS)

    Doubre, C.; Manighetti, I.; Dorbath, C.; Dorbath, L.; Jacques, E.; Delmond, J. C.

    2007-05-01

    We seek to characterize how magmatic and tectonic activities combine and interact during the continental rifting process. We address this question in two companion papers. In both, we analyze the seismicity that occurs in an active magmato-tectonic rift, Asal-Ghoubbet (East Africa), to identify the features and/or processes responsible for its activity. Here, we report results from a 5-month experiment that we conducted in the rift. Eleven seismometers were deployed to complement the eight-station permanent network. This allowed recording ˜400 earthquakes in the rift; 200 events could be well located (precision <40 m) and used in a tomographic inversion. Focal mechanisms were also determined for 71 events. The results show that current activity in the rift is mainly magmatically induced or accommodated. A ˜2-km-wide pipe of hot rock is evidenced below the central Fieale-Shark Bay volcanic complex, likely above a deeper (>5-6 km) magma reservoir. Most events concentrate at the roof of the pipe (at 3-4 km) and result from up and down slip ruptures on both the volcanic (ring) and tectonic faults that enclose the pipe at depth. The up and down motions are likely driven by pressure changes in the magma reservoir. Hence, although a few rift faults were associated with seismicity, most remained seismically silent during the experiment. In the companion paper, we analyze the seismic activity in the rift over the 23 years that followed its last rifting episode. This confirms the importance of the Fieale-Shark Bay plumbing system in the overall rift behavior.

  4. Melt generation and supply at a magmatic rift zone in Afar

    NASA Astrophysics Data System (ADS)

    Ferguson, D. J.; Pyle, D. M.; Maclennan, J.; Blundy, J. D.; Yirgu, G.; Bastow, I. D.; Plank, T.

    2012-12-01

    The thermochemical state of the mantle and the extension rate of the lithopshere play a fundamental role in governing melt volumes during continental rifting. Afar in northern Ethiopia has a prolonged history of extension and magmatism and is an ideal location to investigate mechanisms of melt production during the latter stages of continental break-up. However, current melting conditions here remain poorly constrained. In this study we use geochemical analysis of mafic lavas to develop a petrogenetic model for melt production beneath an active rift zone/segment in west-central Afar. Trace element and isotopic data show that melts are derived from a fertile mantle source, and all the lavas are enriched in incompatible trace elements compared to typical MORB compositions. We investigate primary melting using forward and inverse models of rare earth element (REE) concentrations in partial melts produced from a polybaric melting column. Best-fitting models of melt production with depth constrain melting to occur between depths of ~100-70 km, consistent with melting of upwelling mantle with a potential temperature of 1450 °C. The relatively deep termination of melting given by our results implies that asthenospheric ascent and melting beneath Afar are restricted by an upper thermo-mechanical boundary layer. This suggests that despite its long history of extension a significant thickness of the pre-rift African lithospheric plate still exists in this region. Major element thermobarometry shows that melts erupted at the rift axis preserve compositions consistent with melt-mantle equilibrium at the top of the melting column at ~70km depth, while off-axis lavas show evidence for major element re-equilibration at shallower depths (~60-40 km) within the upper mantle, in agreement with recent geophysical evidence for melt distribution beneath the rift zone. Overall, our results support rifting models where large extents of melt intrusion conserve plate thickness and may compensate for tectonic thinning. Melting beneath Afar still largely resembles a continental rather than oceanic rift system.

  5. Volcanic rifting at Martian grabens Daniel Me`ge,1

    E-print Network

    Mege, Daniel

    with terrestrial rifts. The DEMs were obtained from Mars Observer Laser Altimeter, Viking Orbiter stereo images February 2003; published 22 May 2003. [1] A large fraction of surface extension on Mars occurred. A Martian rift evolution model is proposed on the basis of new geomorphological and structural

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

    E-print Network

    ten Brink, Uri S.

    Crustal structure of central Lake Baikal: Insights into intracontinental rifting Uri S. ten Brink Related to Geographic Region: Asia; KEYWORDS: Lake Baikal, continental rifts, Newark basin, crustal of Baikal, located in the interior of the largest continental mass on Earth, is thought to represent

  7. Midplate seismicity exterior to former rift-basins

    USGS Publications Warehouse

    Dewey, J.W.

    1988-01-01

    Midplate seismicity associated with some former rift-zones is distributed diffusely near, but exterior to, the rift basins. This "basin-exterior' seismicity cannot be attributed to reactivation of major basin-border faults on which uppercrustal extension was concentrated at the time of rifting, because the border faults dip beneath the basins. The seismicity may nonetheless represent reactivation of minor faults that were active at the time of rifting but that were located outside of the principal zones of upper-crustal extension; the occurrence of basin-exterior seismicity in some present-day rift-zones supports the existence of such minor basin-exterior faults. Other hypotheses for seismicity exterior to former rift-basins are that the seismicity reflects lobes of high stress due to lithospheric-bending that is centered on the axis of the rift, that the seismicity is localized on the exteriors of rift-basins by basin-interiors that are less deformable in the current epoch than the basin exteriors, and that seismicity is localized on the basin-exteriors by the concentration of tectonic stress in the highly elastic basin-exterior upper-crust. -from Author

  8. Inland thinning of West Antarctic Ice Sheet steered along subglacial rifts.

    PubMed

    Bingham, Robert G; Ferraccioli, Fausto; King, Edward C; Larter, Robert D; Pritchard, Hamish D; Smith, Andrew M; Vaughan, David G

    2012-07-26

    Current ice loss from the West Antarctic Ice Sheet (WAIS) accounts for about ten per cent of observed global sea-level rise. Losses are dominated by dynamic thinning, in which forcings by oceanic or atmospheric perturbations to the ice margin lead to an accelerated thinning of ice along the coastline. Although central to improving projections of future ice-sheet contributions to global sea-level rise, the incorporation of dynamic thinning into models has been restricted by lack of knowledge of basal topography and subglacial geology so that the rate and ultimate extent of potential WAIS retreat remains difficult to quantify. Here we report the discovery of a subglacial basin under Ferrigno Ice Stream up to 1.5?kilometres deep that connects the ice-sheet interior to the Bellingshausen Sea margin, and whose existence profoundly affects ice loss. We use a suite of ice-penetrating radar, magnetic and gravity measurements to propose a rift origin for the basin in association with the wider development of the West Antarctic rift system. The Ferrigno rift, overdeepened by glacial erosion, is a conduit which fed a major palaeo-ice stream on the adjacent continental shelf during glacial maxima. The palaeo-ice stream, in turn, eroded the 'Belgica' trough, which today routes warm open-ocean water back to the ice front to reinforce dynamic thinning. We show that dynamic thinning from both the Bellingshausen and Amundsen Sea region is being steered back to the ice-sheet interior along rift basins. We conclude that rift basins that cut across the WAIS margin can rapidly transmit coastally perturbed change inland, thereby promoting ice-sheet instability. PMID:22837002

  9. Numerical modeling of seismicity and geodynamics of the Kachchh rift zone, Gujarat, India

    NASA Astrophysics Data System (ADS)

    Vorobieva, Inessa; Mandal, Prantik; Gorshkov, Alexander

    2014-11-01

    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.

  10. Astronaut Michael Collins Undergoes Communications Systems Final Check

    NASA Technical Reports Server (NTRS)

    1969-01-01

    Dunned in his space suit, Command Module (CM) pilot Michael Collins does a final check of his communications system before the boarding of the Apollo 11 mission. Launched via a Saturn V launch vehicle, the first manned lunar mission launched from the Kennedy Space Center, Florida on July 16, 1969 and safely returned to Earth on July 24, 1969. The Saturn V vehicle was developed by the Marshall Space Flight Center (MSFC) under the direction of Dr. Wernher von Braun. The 3-man crew aboard the flight consisted of astronauts Collins; Neil A. Armstrong, Mission Commander; and Edwin E. Aldrin, Jr., Lunar Module (LM) Pilot. Armstrong was the first human to ever stand on the lunar surface, followed by Edwin (Buzz) Aldrin. Meanwhile, astronaut Collins piloted the CM in a parking orbit around the Moon. During a 2½ hour surface exploration, the crew collected 47 pounds of lunar surface material which was returned to Earth for analysis. With the success of Apollo 11, the national objective to land men on the Moon and return them safely to Earth had been accomplished.

  11. Astronaut Neil A. Armstrong Undergoes Communications Systems Final Check

    NASA Technical Reports Server (NTRS)

    1969-01-01

    Dunned in his space suit, mission commander Neil A. Armstrong does a final check of his communications system before before the boarding of the Apollo 11 mission. Launched via a Saturn V launch vehicle, the first manned lunar mission launched from the Kennedy Space Center, Florida on July 16, 1969 and safely returned to Earth on July 24, 1969. The Saturn V vehicle was developed by the Marshall Space Flight Center (MSFC) under the direction of Dr. Wernher von Braun. The 3-man crew aboard the flight consisted of astronauts Armstrong; Michael Collins, Command Module (CM) pilot; and Edwin E. Aldrin, Jr., Lunar Module (LM) Pilot. Armstrong was the first human to ever stand on the lunar surface, followed by Edwin (Buzz) Aldrin. Meanwhile, astronaut Collins piloted the CM in a parking orbit around the Moon. During a 2½ hour surface exploration, the crew collected 47 pounds of lunar surface material which was returned to Earth for analysis. With the success of Apollo 11, the national objective to land men on the Moon and return them safely to Earth had been accomplished.

  12. Optical Diagnostic System for Solar Sails: Phase 1 Final Report

    NASA Technical Reports Server (NTRS)

    Pappa, Richard S.; Blandino, Joseph R.; Caldwell, Douglas W.; Carroll, Joseph A.; Jenkins, Christopher H. M.; Pollock, Thomas C.

    2004-01-01

    NASA's In-Space Propulsion program recently selected AEC-ABLE Engineering and L'Garde, Inc. to develop scale-model solar sail hardware and demonstrate its functionality on the ground. Both are square sail designs with lightweight diagonal booms (<100 g/m) and ultra-thin membranes (<10 g/sq m). To support this technology, the authors are developing an integrated diagnostics instrumentation package for monitoring solar sail structures such as these in a near-term flight experiment. We refer to this activity as the "Optical Diagnostic System (ODS) for Solar Sails" project. The approach uses lightweight optics and photogrammetric techniques to measure solar sail membrane and boom shape and dynamics, thermography to map temperature, and non-optical sensors including MEMS accelerometers and load cells. The diagnostics package must measure key structural characteristics including deployment dynamics, sail support tension, boom and sail deflection, boom and sail natural frequencies, sail temperature, and sail integrity. This report summarizes work in the initial 6-month Phase I period (conceptual design phase) and complements the final presentation given in Huntsville, AL on January 14, 2004.

  13. Active volcanism on Venus in the Ganiki Chasma rift zone

    NASA Astrophysics Data System (ADS)

    Shalygin, E. V.; Markiewicz, W. J.; Basilevsky, A. T.; Titov, D. V.; Ignatiev, N. I.; Head, J. W.

    2015-06-01

    Venus is known to have been volcanically resurfaced in the last third of solar system history and to have undergone a significant decrease in volcanic activity a few hundred million years ago. However, fundamental questions remain: Is Venus still volcanically active today, and if so, where and in what geological and geodynamic environment? Here we show evidence from the Venus Express Venus Monitoring Camera for transient bright spots that are consistent with the extrusion of lava flows that locally cause significantly elevated surface temperatures. The very strong spatial correlation of the transient bright spots with the extremely young Ganiki Chasma, their similarity to locations of rift-associated volcanism on Earth, provide strong evidence for their volcanic origin and suggests that Venus is currently geodynamically active.

  14. Rift Valley Fever Outbreaks in Mauritania and Related Environmental Conditions

    PubMed Central

    Caminade, Cyril; Ndione, Jacques A.; Diallo, Mawlouth; MacLeod, Dave A.; Faye, Ousmane; Ba, Yamar; Dia, Ibrahima; Morse, Andrew P.

    2014-01-01

    Four large outbreaks of Rift Valley Fever (RVF) occurred in Mauritania in 1998, 2003, 2010 and 2012 which caused lots of animal and several human deaths. We investigated rainfall and vegetation conditions that might have impacted on RVF transmission over the affected regions. Our results corroborate that RVF transmission generally occurs during the months of September and October in Mauritania, similarly to Senegal. The four outbreaks were preceded by a rainless period lasting at least a week followed by heavy precipitation that took place during the second half of the rainy season. First human infections were generally reported three to five weeks later. By bridging the gap between meteorological forecasting centers and veterinary services, an early warning system might be developed in Senegal and Mauritania to warn decision makers and health services about the upcoming RVF risk. PMID:24413703

  15. Integration of geophysical and geochemical data for the study of the North-Est Rift dynamics on Mount Etna volcano

    NASA Astrophysics Data System (ADS)

    Tripaldi, Simona; Balasco, Marianna; Lapenna, Vincenzo; Loddo, Mariano; Moretti, Pierpaolo; Neri, Marco; Piscitelli, Sabatino; Romano, Gerardo; Schiavone, Domenico; Siniscalchi, Agata

    2010-05-01

    Mount Etna volcano is located at the front of the Apennine-Maghrebian Chain, along the Malta Escarpment, and lies on the Pliocene-Pleistocene foredeep deposits. The apparatus is characterized by a central conduit divided, at surface, into four summit craters, with a maximum elevation of 3329 m above sea level. In the upper part (>1500 m), three main "rift zones" can be identified: the NE Rift, the S Rift and the W Rift. These structures are probably shallow, do not tap deep magma and are usually directly fed by the central conduit, rather than from an underlying shallow magma chamber. The volcano is characterized by the displacement of its eastern to southern flanks, involving an on-shore area of >700 km2. This is confined to the north by the Pernicana fault system (PFS). The PFS, located on the NE sector of Mt. Etna, is >18 km long, from the NE Rift to the coastline. The western PFS is seismogenetic, while the eastern PFS undergoes creep movements. In its westernmost section, the PFS is divided into two main segments, the more northerly of these starting from the Monte Nero area of the NE Rift and the more southerly from Piano Provenzana. The PFS is kinematically connected, with a feedback mechanism, to eruptions occurring on the NE Rift. In spite of this relationship, the PFS has shown continuous activity between 1947 and 2002, a period when no eruptions occurred on the NE Rift, with major surface fracturing and seismic activity in 1984-1988. Geophysical-geochemical investigation were conducted in the area where PFS is connected with the NE Rift, including the areas characterized by a consistent slip, as well as those structures through which the motion occurs. The aim of this work is to provide a multidisciplinary frame to characterize this dynamic and structural natural system. Magnetotelluric, geoelectric, self-potential and and soil gas emissions measurements give a comprehensive view on the geometry and depth of the lithological units together with fluid circulation insights. Here, the sedimentary basement, detected by the resistivity models, interfaces media with different physical characteristics where fluids flow play a crucial role interacting onto the Pernicana fault activity.

  16. Expanded studies of linear collider final focus systems at the Final Focus Test Beam

    SciTech Connect

    Tenenbaum, P.G.

    1995-12-01

    In order to meet their luminosity goals, linear colliders operating in the center-of-mass energy range from 3,50 to 1,500 GeV will need to deliver beams which are as small as a few Manometers tall, with x:y aspect ratios as large as 100. The Final Focus Test Beam (FFTB) is a prototype for the final focus demanded by these colliders: its purpose is to provide demagnification equivalent to those in the future linear collider, which corresponds to a focused spot size in the FFTB of 1.7 microns (horizontal) by 60 manometers (vertical). In order to achieve the desired spot sizes, the FFTB beam optics must be tuned to eliminate aberrations and other errors, and to ensure that the optics conform to the desired final conditions and the measured initial conditions of the beam. Using a combination of incoming-beam diagnostics. beam-based local diagnostics, and global tuning algorithms, the FFTB beam size has been reduced to a stable final size of 1.7 microns by 70 manometers. In addition, the chromatic properties of the FFTB have been studied using two techniques and found to be acceptable. Descriptions of the hardware and techniques used in these studies are presented, along with results and suggestions for future research.

  17. Quantifying the temporal and spatial response of channel steepness to changes in rift basin architecture

    NASA Astrophysics Data System (ADS)

    Robinson, S. M.; Whipple, K. X.; Arrowsmith, R.; Heimsath, A. M.; Foster, M.; Cohen, A. S.

    2013-12-01

    Quantifying the temporal evolution of active continental rifts contributes to our understanding of fault system evolution and seismic hazards. Rift basins also preserve robust paleoenvironmental records that may help untangle feedbacks between climate and tectonics. Here we quantify the spatial and temporal history of rift flank uplift by exploiting landscape memory along footwall escarpments in the Malawi segment of the East Africa Rift. Our work helps answer a suite of questions that are widely applicable to continental rift settings; (1) Is rift-flank uplift well described by theoretical elliptical displacement patterns? (2) Do orographic climate patterns induced by rift topography affect rift-flank uplift? (3) Is footwall exhumation influenced by the evolution of depocenters and rift lakes? In Malawi, 100 km long border faults of alternating polarity bound half-graben sedimentary basins containing up to 4km of basin fill and water depths up to 700m. Orographically driven precipitation produces climatic gradients along footwall escarpments resulting in mean annual precipitation that varies spatially from 800 to 2500mm. Temporal oscillations in climate have also resulted in lake lowstands 500m below the modern Lake Malawi. We examine bedrock river profiles crossing the Livingstone and Usisya Border Faults in northern Malawi using the channel steepness index (Ksn). River profiles reveal consistent patterns of Ksn throughout the study area. Typical profiles contain a lower reach with Ksn values between 150-300 and an upper reach with values between 50-150. Some channels display an uppermost reach with values less than 100 that are interpreted to represent the pre to early-rift relief of the region. This progressive downstream steepening is consistent with acceleration of slip along the main border faults or reduction in climatically modulated erosional efficiency. Spatial patterns of Ksn and knickpoint elevations are not consistent with theoretical along fault displacement models or expected patterns from the observed climatic gradients. Instead, knickpoint elevations decrease from ~1000m to ~400m above watershed outlets from north to south. This pattern suggests that an acceleration of slip initiated in the northern part of the basin. Alternatively, this pattern is also consistent with increased hangingwall subsidence (instead of footwall uplift) relative to baselevel due to loading from depocenters. Unlike the Livingstone Fault, there is little along strike variation in hangingwall loading adjacent to the bordering Usisya Fault to the south. Ksn values of rivers crossing the Usisya border fault range from 100-250 in the middle section of the fault and decrease to <100 at the tips showing some consistency with elliptical displacement models. Our data indicating a discrete acceleration of footwall uplift are highly suggestive of a connection between basin architecture and the temporal and spatial distribution of this uplift. Erosion rate measurements beneath the knickpoint are needed to constrain the timing of this acceleration and establish a link to the basins well-documented depositional history.

  18. The mode of rifting of the Tyrrhenian Sea

    NASA Astrophysics Data System (ADS)

    Milia, Alfonsa; Torrente, Maurizio M.

    2014-05-01

    The back-arc evolution of the Tyrrhenian Sea has mainly been attributed to the roll-back towards the south-east of the subducting Ionian plate that could have provided the bulk of the space required for this extension. The Tyrrhenian Sea is a triangular basin characterized by two large bathyal basins (Vavilov and Marsili basins) that are covered by some hundred meters of sediments, and a number of peri- Tyrrhenian basins filled by thousands of meters of clastic and/or volcaniclastic sediments. The stratigraphic record of these basins offers an opportunity to study the timing and kinematics of the basin-forming faults that are relevant for the creation of a model on the opening of the Tyrrhenian Sea. Basin analysis was performed using interpretation of seismic reflection profiles and well logs. The interpretation of these data was made using seismic and sequence stratigraphy and structural geology in a GIS-dedicated environment. The sequence stratigraphy interpretation of the deepest wells were performed using discontinuities and trends in wireline log pattern. Systems tracts and transgressive-regressive cycles were identified in well log succession and seismic profiles. The sequence stratigraphy approach allows the identification of 4th-order depositional sequences (100 ka). The geologic evolution, in terms of age of basin formation, style of deformation, timing of activity of the fault bounding basins, tectonic subsidence, post-rift infill and volcanic activity, was analyzed for several peri-Tyrrhenian basins. The study reconstructed the three-dimensional architecture of the peri-Tyrrhenian basins and illustrated the link between the bathyal basin and the Tyrrhenian margin. We document that during the evolution of the Tyrrhenian region several basins opened contemporaneously with different direction of extension and a progressive change in rifting direction occurred along the Campania Margin. The mode of rifting of the Tyrrhenian Sea was characterized by different styles of the extensional basins and detachment faulting. Taking into account the published geological data, we propose a kinematic evolution of the Tyrrhenian basin over the last 12 Ma.

  19. A NEW (or old) RIFT IN EASTERN CALIFORNIA

    NASA Astrophysics Data System (ADS)

    Calzia, J.

    2009-12-01

    The Eastern California Shear Zone (ECSZ) includes a broad network of right-lateral faults in the Mojave Desert and southern Basin-Ranges of California. Seven large earthquakes, including the 1992 M7.4 Landers and 1999 M7.1 Hector Mine earthquakes, have occurred within this zone in the last 60 years. This severe seismic activity is complicated by two puzzling facts: 1) the hypocenter of the Landers and Hector Mine earthquakes occur at shallow crustal depths (10±4 km); and 2) the aftershock patterns associated with these earthquakes cross cut the structural grain of the ECSZ at an acute angle. GPS data indicate that crustal rocks within the Mojave Desert segment of the ECSZ are moving as much as 14 mm/year to the northwest relative to Station FUNE in Death Valley; crustal rocks within the Basin-Ranges segment are moving 12.5 mm/year northwestward. Dokka and Travis (1990) concluded that the ECZS accommodates 20-25 percent of relative plate motion along the North American-Pacific plate margin inboard of the San Andreas Fault Zone. Nur and others (1993) reported that the large earthquakes may occur along a new fault system that cuts across the older faults; they named this young fault the Landers-Mojave earthquake line. Neither model, however, considers Quaternary volcanic centers in eastern CA and NV just east of and locally within the ECSZ. Rocks within these volcanic centers, including (from north to south) Lathrop Wells, Cima, Pisgah, Amboy, and Obsidian Butte, are younger than but chemically and isotopically similar to Neogene volcanic rocks that bound the rift province of the northern Gulf of California. The seismic and GPS data, combined with petrologic data from nearby volcanic centers, suggests that the ECZS is the active margin of an incipient transtensional rift as the Gulf of California propagates northward. Given the volume of volcanic rocks and prehistoric seismic history in California, it is not certain if this rift is growing or dying; only time will tell.

  20. Lithospheric Decoupling and Rotations: Hints from Ethiopian Rift

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Plates move relative to the mantle because some torques are acting on them. The shear in the low-velocity zone (LVZ) at the base of the lithosphere is the expression of these torques. The decoupling is allowed by the low viscosity in the LVZ, which is likely few orders of magnitudes lower than previously estimated. The viscosity value in the LVZ controls the degree of coupling/decoupling between the lithosphere and the underlying mantle. Lateral variations in viscosity within the LVZ may explain the velocity gradient among tectonic plates as the one determining the Ethiopian Rift (ER) separating Africa from Somalia. While it remains not fully understood the mechanisms of the torques acting on the lithosphere (thermally driven mantle convection or the combination of mantle convection with astronomical forces such as the Earth's rotation and tidal drag), the stresses are transmitted across the different mechanical layers (e.g., the brittle upper crust, down to the viscous-plastic ductile lower crust and upper mantle). Differential basal shear traction at the base of the lithosphere beneath the two sides of the East African Rift System (EARS) is assumed to drive and sustain rifting. In our analysis, the differential torques acting on the lithospheric/crustal blocks drive kinematics and block rotations. Since, ER involves the whole lithosphere, we do not expect large amount of rotation. Rotation can be the result of the whole plate motion on the sphere moving along the tectonic equator, or the second order sub-rotation of a single plate. Further rotation may occur along oblique plate boundaries (e.g., left lateral transtensional setting at the ER). Small amount of vertical axis rotation of blocks in northern ER could be related to the presence of local, shallower decollement layers. Shallow brittle-ductile transition (BDT) zone and differential tilting of crustal blocks in the northern ER could hint a possibility of detachment surface between the flow in the lower crust relative to the brittle crust above. Our study suggests that kinematics of crustal blocks in the ER is controlled by Africa and Somalia plates interaction at different scale and layers.

  1. Characterizing and identifying structural domains at rifted continental margins: application to the Bay of Biscay margins and its Western Pyrenean fossil remnants

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Over the past decade, the occurrence of hyperextended domains at rifted continental margins consisting of extremely thinned crust and/or exhumed mantle has been increasingly recognized both at present-day rifted margins and in fossils analogues preserved in collisional orogens. However, at present, most studies aiming to characterize rifted continental margin structure and the extreme thinning of the continental crust were either focused offshore relying on indirect geophysical methods, or onshore in deformed remnants offering direct access to geological observations. Marine and onshore examples provide complementary datasets, but their different scale and resolution of observations prevent direct correlations to be done. We use the Bay of Biscay and Western Pyrenees as a natural laboratory to develop and apply an innovative approach to characterize and identify distinctive rifted margin domains in offshore and onshore settings. The Bay of Biscay and Western Pyrenees offer the unique possibility to have access to seismically imaged, drilled and exposed parts of one and the same hyperextended rift margin system. Offshore, we use a gravity inversion technique and flexural backstripping combined with seismic interpretation to provide quantitative estimates of accommodation space, crustal thickness and lithosphere thinning. Onshore, we focus on key outcrops preserving remnants of the former rift domain to describe the nature of sediment and basement rocks and of their interface. This qualitative and quantitative characterisation provides the essential diagnostic elements for the identification of five distinct domains at magma-poor rifted margins and their fossil analogues. We name these 5 domains proximal, necking, hyperthinned, exhumed mantle and oceanic. This new approach can be used to reconcile offshore and onshore observations and aid interpretation especially when only local observations are available. Onshore remnants can be placed in an offshore rifted margin context, enabling the prediction of first order crustal architecture. For the interpretation of offshore seismic reflection sections, geological insights on rift structures and basement nature can be suggested based on onshore analogies. This combined onshore-offshore multidisciplinary approach enables us to identify and distinguish the distinct structural domains of rifted margins, resulting in a new paleogeographic map of the Bay of Biscay and Pyrenean rift. The approach underlying this mapping has general application to unravelling the spatial and temporal complexity of rifted margin structural domains.

  2. Plate-Based Fuel Processing System Final Report

    SciTech Connect

    Carlos Faz; Helen Liu; Jacques Nicole; David Yee

    2005-12-22

    On-board reforming of liquid fuels into hydrogen is an enabling technology that could accelerate consumer usage of fuel cell powered vehicles. The technology would leverage the convenience of the existing gasoline fueling infrastructure while taking advantage of the fuel cell efficiency and low emissions. Commercial acceptance of on-board reforming faces several obstacles that include: (1) startup time, (2) transient response, and (3) system complexity (size, weight and cost). These obstacles are being addressed in a variety of projects through development, integration and optimization of existing fuel processing system designs. In this project, CESI investigated steam reforming (SR), water-gas-shift (WGS) and preferential oxidation (PrOx) catalysts while developing plate reactor designs and hardware where the catalytic function is integrated into a primary surface heat exchanger. The plate reactor approach has several advantages. The separation of the reforming and combustion streams permits the reforming reaction to be conducted at a higher pressure than the combustion reaction, thereby avoiding costly gas compression for combustion. The separation of the two streams also prevents the dilution of the reformate stream by the combustion air. The advantages of the plate reactor are not limited to steam reforming applications. In a WGS or PrOx reaction, the non-catalytic side of the plate would act as a heat exchanger to remove the heat generated by the exothermic WGS or PrOx reactions. This would maintain the catalyst under nearly isothermal conditions whereby the catalyst would operate at its optimal temperature. Furthermore, the plate design approach results in a low pressure drop, rapid transient capable and attrition-resistant reactor. These qualities are valued in any application, be it on-board or stationary fuel processing, since they reduce parasitic losses, increase over-all system efficiency and help perpetuate catalyst durability. In this program, CESI took the initial steam reforming plate-reactor concept and advanced it towards an integrated fuel processing system. A substantial amount of modeling was performed to guide the catalyst development and prototype hardware design and fabrication efforts. The plate-reactor mechanical design was studied in detail to establish design guidelines which would help the plate reactor survive the stresses of repeated thermal cycles (from start-ups and shut-downs). Integrated system performance modeling was performed to predict system efficiencies and determine the parameters with the most significant impact on efficiency. In conjunction with the modeling effort, a significant effort was directed towards catalyst development. CESI developed a highly active, sulfur tolerant, coke resistant, precious metal based reforming catalyst. CESI also developed its own non-precious metal based water-gas shift catalyst and demonstrated the catalysts durability over several thousands of hours of testing. CESI also developed a unique preferential oxidation catalyst capable of reducing 1% CO to < 10 ppm CO over a 35 C operating window through a single pass plate-based reactor. Finally, CESI combined the modeling results and steam reforming catalyst development efforts into prototype hardware. The first generation 3kW(e) prototype was fabricated from existing heat-exchanger plates to expedite the fabrication process. This prototype demonstrated steady state operation ranging from 5 to 100% load conditions. The prototype also demonstrated a 20:1 turndown ratio, 10:1 load transient operation and rapid start-up capability.

  3. Volcanic rocks and subglacial volcanism beneath the West Antarctic Ice Sheet in the West Antarctic Rift System, (WAIS) from aeromagnetic and radar ice sounding - Thiel Subglacial Volcano as possible source of the ash layer in the WAISCORE

    NASA Astrophysics Data System (ADS)

    Behrendt, J. C.

    2012-12-01

    Radar ice sounding and aeromagnetic surveys reported over the West Antarctic Ice Sheet (WAIS) have been interpreted as evidence of subglacial volcanic eruptions over a very extensive area (>500,000 km2 ) of the volcanically active West Antarctic rift system interpreted as caused by subglacial volcanic rocks. Several active volcanoes have shown evidence of eruption through the WAIS and several other active volcanoes are present beneath the WAIS reported from radar and aeromagnetic data. Five-kilometer spaced coincident aeromagnetic and radar ice sounding surveys since 1990 provide three dimensional characterization of the magnetic field and bed topography beneath the ice sheet. These 5-50-km-width, semicircular magnetic anomalies range from 100->1000 nT as observed ~1 km over the 2-3 km thick ice have been interpreted as evidence of subglacial eruptions. Comparison of a carefully selected subset of ~400 of the >1000 high-amplitude anomalies in the CWA survey having topographic expression at the glacier bed, showed >80% had less than 200-m relief. About 18 high-amplitude subglacial magnetic sources also have high topography and bed relief (>600 m) interpreted as subaerially erupted volcanic peaks when the WAIS was absent, whose competent lava flows protected their edifices from erosion. All of these would have high elevation above sea-level, were the ice removed and glacial rebound to have occurred. Nine of these subaerially erupted volcanoes are concentrated in the WAIS divide area. Behrendt et al., 1998 interpreted a circular ring of positive magnetic anomalies overlying the WAIS divide as caused by a volcanic caldera. The area is characterized by high elevation bed topography. The negative regional magnetic anomaly surrounding the caldera anomalies was interpreted as the result of a shallow Curie isotherm. High heat flow inferred from temperature logging in the WAISCORE (G. Clow 2012, personal communication; Conway, 2011) and a prominent volcanic ash layer in the core (Dunbar, 2011) are consistent with the magnetic data. A prominent subaerially-erupted subglacial volcano, here named Mt Thiel, about 100 km distant to the NE, at approximately 78o 25' S, 111o 20' W, may be the source of the ash layer. This peak is characterized by a ~400-nT positive magnetic anomaly which Behrendt el, 2004, modeled as having apparent susceptibility contrasts of .034 and .15 SI. From its appearance (and the moat surrounding it), Mt. Thiel has subsided somewhat since initial eruption as is the case for Mt. Erebus and the Hawaiian Island chain. I suggest that Mt Thiel, about 100 km distance from the WAISCORE, may be the source of the ash layer. The present rapid changes in the WAIS resulting from global warming, could be accelerated by subglacial volcanism

  4. The Salton Seismic Imaging Project: Tomographic characterization of a sediment-filled rift valley and adjacent ranges, southern California

    NASA Astrophysics Data System (ADS)

    Davenport, K.; Hole, J. A.; Stock, J. M.; Fuis, G. S.; Carrick, E.; Tikoff, B.

    2011-12-01

    The Salton Trough in Southern California represents the northernmost rift of the Gulf of California extensional system. Relative motion between the Pacific and North American plates is accommodated by continental rifting in step-over zones between the San Andreas, Imperial, and Cerro Prieto transform faults. Rapid sedimentation from the Colorado River has isolated the trough from the southern portion of the Gulf of California, progressively filling the subsiding rift basin. Based on data from previous seismic surveys, the pre-existing continent has ruptured completely, and a new ~22 km thick crust has been created entirely by sedimentation overlying rift-related magmatism. The MARGINS, EarthScope, and USGS-funded Salton Seismic Imaging Project (SSIP) was designed to investigate the nature of this new crust, the ongoing process of continental rifting, and associated earthquake hazards. SSIP, acquired in March 2011, comprises 7 lines of onshore seismic refraction / wide-angle reflection data, 2 lines of refraction / reflection data in the Salton Sea, and a line of broadband stations. This presentation focuses on the refraction / wide-angle reflection line across the Imperial Valley, extending ~220 km across California from Otay Mesa, near Tijuana, to the Colorado River. The data from this line includes seventeen 100-160 kg explosive shots and receivers at 100 m spacing across the Imperial Valley to constrain the structure of the Salton Trough rift basin, including the Imperial Fault. Eight larger shots (600-920 kg) at 20-35 km spacing and receivers at 200-500 m spacing extend the line across the Peninsular Ranges and the Chocolate Mountains. These data will contrast the structure of the rift to that of the surrounding crust and provide constraints on whole-crust and uppermost mantle structure. Preliminary work has included tomographic inversion of first-arrival travel times across the Valley, emphasizing a minimum-structure approach to create a velocity model of the upper crust. Ongoing modeling provides constraints on the basin margins, showing a steeply dipping western edge of the rift valley approximately coincident to the shoreline of the ancient Lake Cahuilla. Low velocity sediments and low velocity crystalline crust within the Imperial Valley are consistent with previous studies and contrast with faster crystalline rocks near the surface outside the rift. Ongoing analysis will provide a more detailed image of upper crustal structure, as well as preliminary modeling of the entire crust.

  5. The transition from craton to rift in south eastern Africa: Preliminary surface wave tomography from the MOZambique Rift Tomography (MOZART) project

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    We present preliminary results from the MOZART (Mozambique Rift Tomography) experiment in the context of the transition from the old and cold lithosphere associated with the Kalahari Craton, to the continental lithosphere associated with the southern tip of the East African Rift System (EARS) in Mozambique. The initial stage of surface wave data recorded on the network of 30 broadband seismic stations deployed in 2011 are incorporated into an earlier continental scale tomographic model of Africa (Fishwick, 2010). These data provide a significant increase in potential resolution of upper mantle velocities, in a region where there has previously been little knowledge of the detailed lithospheric structure. Furthermore they allow a better comparison with the velocities observed beneath the Kaapvaal Craton where data from the dense network of seismometers deployed in the earlier Southern Africa Seismic Experiment (SASE) have already been included in the regional tomography. From the new tomographic models we investigate the lateral gradients in seismic velocity at upper mantle depths of 75-250km in order to place better constraints on the thermal and/or chemical transitions from the craton to the rift. In order to test the reliability of these estimates of the velocity gradient we compare different parameterisations and regularisations, but also investigate to what degree the addition of new data to the tomographic model alters the estimated velocities. The regional tomographic model produced will provide a useful new reference model for more detailed inter-station and array tomography when project MOZART is completed in mid-2013.

  6. Climatic influence on rift structure: Axial rift evolution in Guaymas Basin during the past 250,000 years

    NASA Astrophysics Data System (ADS)

    Kluesner, J. W.; Lonsdale, P.; Kirtland, S. E.

    2009-12-01

    Newly collected, high-resolution seismic profiles in the Southern Trough of Guaymas Basin display temporal changes in axial graben structure; ages of these structures correlate to glacial-interglacial cycles over the past quarter millennium. During glacial periods the southern spreading trough in Guaymas Basin is overwhelmed with turbidites, whereas during interglacials, extension out-paces sedimentation and the trough deepens. Glacial low-stand shedding--caused by lower sea level, shelf exposure, and enhanced precipitation--results in the erosion of shelf sediments and transportation of these to the deeper basins in the Gulf. Major offshore canyon systems directly southwest of the Southern Trough capture eroded sediments from the exposed continental shelf and funnel these sediments into the axial graben as turbidites. In contrast, the higher sea level and reduced precipitation characteristic of interglacials limits the introduction of terrestrial sediments into the axial trough; sedimentation during these periods predominately consists of redistributed pelagic sediments swept into the trough by tidal and bottom currents. These sediments, dominated by diatomaceous ooze, appear as acoustically transparent layers in seismic profiles, whereas turbidites composed of fluvial and reworked shelf material appear as high-amplitude reflector packages. Systematic changes between the two sediment types are apparent on seismic profiles within the Southern Trough of Guaymas Basin as well as Carmen Basin. In addition, the regional extent of the youngest acoustically transparent layer imaged with multichannel seismic profiling approximately matches modern distribution and deposition patterns of sediments dominated by diatomaceous ooze, further supporting our interpretation that the acoustically transparent layers represent sediment packages composed mainly of pelagic material. Plotting paleo-temperature and sea-level curves along the MCS profile crossing the Southern Trough shows a striking correlation between climatic cycles, sedimentation rate, acoustic character of sediment packages, and changes in rift structure. Off-axis intrusion of young sills masks past trough floor structures resulting in only the paleo-rift flanks being imaged on seismic profiles. Assuming a constant spreading rate of 45 km/My and the relationship between different sediment packages and changes in climate, sediments imaged on off-axis flanks in the Southern Trough of Guaymas Basin record the evolution of the axial graben and flanks during the past 250,000 years. The relationship between climatic change and rift structure observed in the Southern Trough, Guaymas Basin may provide insight into how sedimentation and axial structure of a young intercontinental ocean basin have been modulated by climate change.

  7. Final design review summary report for the TN-WHC cask and transportation system

    SciTech Connect

    Kee, A.T.

    1997-01-17

    This document represents comments generated from a review of Transnuclear`s Final Design Package distributed on December 10, 1996 and a review of the Final Design Analysis Report meeting held on December 17 & 18, 1996. The Final design describes desicn features and presents final analyses @j performed to fabricate and operate the system while meeting the Cask/Transportation Functions and Requirements, WHC-SD-SNF-FRD-011, Rev. 0 and specification WHC-S-0396, Rev. 1.

  8. Evidence for hot Mississippi Valley-type brines in the Reelfoot Rift complex, south-central United States, in Late Pennsylvanian-Early Permian

    USGS Publications Warehouse

    Leach, D.L.; Apodaca, L.E.; Repetski, J.E.; Powell, J.W.; Rowan, E.L.

    1997-01-01

    Petrographic and fluid inclusion studies of sparry dolomite cement from Upper Cambrian to Lower Ordovician rocks and conodont thermal-alteration indices provide evidence that hot mississippi valley-type brines were once present in the Reelfoot Rift complex. The cathodoluminescent microstratigraphy of sparry dolomite cement in the Reelfoot Rift resembles that of sparry dolomite cement associated with widespread mississippi valley-type deposition in the Ozark region. If correlative cathodoluminescent zones in the sparry dolomite from the Ozark and Reelfoot Rift regions indicate broadly contemporaneous dolomite deposition, then the results show that the Ozark MVT-type hydrothermal system extended into the Reelfoot region and onto the western flank of the Nashville Dome. Independent evidence supports migration of MVT-type brines into the Ozark region from the Reelfoot Rift complex in late Paleozoic time.

  9. Rifting and lower crustal reflectivity: A case study of the intracratonic Dniepr-Donets rift zone, Ukraine

    NASA Astrophysics Data System (ADS)

    Lyngsie, Stig B.; Thybo, Hans; Lang, Rasmus

    2007-12-01

    Intracratonic rifting, caused by late Devonian extensional stresses in the East European Craton, created the largest rift zone in Europe, the Pripyat-Dniepr-Donets rift (southeast Ukraine). The rift basin is approximately 2000 km long, up to 170 km wide, and 22 km deep. Wide-angle refraction and reflection seismic data from the Donbas Basin deep seismic Refraction and Reflection Experiments (DOBRE'99) project together with gravity and magnetic data are analyzed for the structure and evolution of the Donbas Fold Belt, which is the uplifted and deformed part of the Dniepr-Donets Basin. The seismic data are used for identification of large-scale crustal structures and modeling of the seismic velocities of the crust and uppermost mantle. A ray-trace-based velocity and density model is derived by joint inversion of gravity and traveltime data. The inversion result reveals a zone of high density and velocity beneath the basin at middle to lower crustal levels, slightly offset to the NE of the rift axis. Full waveform synthetic seismograms, matching the observed data, show high-amplitude and low-frequency arrivals from this high-density body as well as from the Moho. We interpret the high-amplitude, low-frequency signals as reflections from layered magmatic rocks, which intruded into the ductile lower crust during the main rift phase and subsequently were sorted by fractional crystallization. The intrusive material thickened the lower crust by approximately 50%. This may explain the enigmatic flat Moho topography across the rift zone which has been significantly stretched (? = 1.3). The rifting initiated in the late Devonian (Frasnien) as a consequence of back-arc extension in relation to subduction of the Paleo-Tethys Ocean. The subducting oceanic slab may have enriched the mantle with volatiles and created convection, leading to strong partial melting, upwelling, and continued rifting in the Famennien. We interpret the asymmetrical rift geometry as a combination of pure and simple shear tectonic processes.

  10. Papers presented to the Conference on the Processes of Planetary Rifting

    NASA Technical Reports Server (NTRS)

    1981-01-01

    The basic problems of processes of planetary rifting are addressed from the following viewpoints: (1) speculation as to the origin and development of rifts; (2) rifts on other planets; (3) tectonics; (4) geology; (5) chemistry of the lithosphere; (6) physics of the lithosphere; and (7) resources associated with rifting. The state of ignorance on the subject and its remedy is debated.

  11. Conjugate volcanic rifted margins, spreading and micro-continent: Lessons from the Norwegian-Greenland Sea

    NASA Astrophysics Data System (ADS)

    Gernigon, L.; Blischke, A.; Nasuti, A.; Sand, M.

    2014-12-01

    We have acquired and processed new aeromagnetic data that covers the entire Norway Basin oceanic spreading system located between the Møre volcanic rifted margin and its (intermediate) conjugate system, the Jan Mayen microcontinent (JMMC). The new compilation allows us to revisit its entire structure and spreading evolution from the Early Eocene breakup to the Late Oligocene abortion of the Aegir Ridge. We here discuss the dynamics of conjugate volcanic (rifted) margin formation and reconstruct the subsequent spreading evolution of the Norway Basin until its abortion. We have estimated a new set of Euler poles of rotation for the Norway Basin derived from more than 88,000 km of new magnetic profiles. The new compilation confirms that a fan-shaped spreading evolution of the Norway Basin was particularly active before the cessation of seafloor spreading and abortion of the Aegir Ridge. The Norway Basin shows a more complex system of micro-plates and asymmetric segments locally affected by episodic ridge jumps. The new observations have implications for the syn- and post-breakup stratigraphic and rifted-margin tectonic development of the JMMC and its conjugate margins. In particular, an important Mid-Eocene geodynamic event at around magnetic chron C21r is recognized in the Norway Basin. This event coincides with the onset of diking and rifting between the proto-JMMC and the East Greenland margin, leading to a second phase of breakup in the Norwegian-Greenland Sea ~26 My later in the Oligocene. Restored in its pre-breakup configuration, the new surveys also allow us to discuss further the tectonic and crustal evolution of the conjugate volcanic rifted margins and associated transform and oblique segments. The applicability of magma-poor concepts, off Norway, for example, remains questionable for us. The significant amount of breakup magmatism, the huge amount of pre-breakup sag sedimentation and the presence of thinned and preserved continental crust without the systematic occurrence of underlying and/or exhumed serpentinised terranes. The mid-Norwegian volcanic rifted margins appear quite different from the Iberian type, magma-poor margin, even if the processes leading to the early (and aborted) thinning events seems to be similar to some extent.

  12. Thermochronologic constraints on Jurassic rift flank denudation in the Thiel Mountains, Antarctica

    USGS Publications Warehouse

    Fitzgerald, P.G.; Baldwin, S.L.

    2007-01-01

    The Thiel Mountains are part of the Transantarctic Mountains (TAM) and occupy a strategic position close to the East-West Antarctic boundary. They occur in a region of relatively subdued topography distal from high topography and high relief of most of the TAM adjacent to the West Antarctic rift system. Low-temperature thermochronology on samples collected from the Reed Ridge granite on the north flank of the Thiel Mountains constrain the thermal and hence tectonic history. Apatite fission track data plus thermal models indicate cooling from ca. 165-150 Ma. In conjunction with 40Ar/39Ar K-feldspar data, the results indicate cooling was due to relatively slow erosional denudation, and not thermal relaxation following Jurassic tholeiitic magmatism. Denudation was most likely associated with the formation of the Jurassic rift system across Antarctica that marked the initial breakup of Gondwana. This is the oldest episode of denudation associated with formation of the present day TAM

  13. A Blowing Snow Model for Ice Shelf Rifts

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

    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.

  14. Composition of the crust beneath the Kenya rift

    USGS Publications Warehouse

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

    1994-01-01

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

  15. Stability of rift axis magma reservoirs: Spatial and temporal evolution of magma supply in the Dabbahu rift segment (Afar, Ethiopia) over the past 30 kyr

    NASA Astrophysics Data System (ADS)

    Medynski, S.; Pik, R.; Burnard, P.; Vye-Brown, C.; France, L.; Schimmelpfennig, I.; Whaler, K.; Johnson, N.; Benedetti, L.; Ayelew, D.; Yirgu, G.

    2015-01-01

    Unravelling the volcanic history of the Dabbahu/Manda Hararo rift segment in the Afar depression (Ethiopia) using a combination of cosmogenic (36Cl and 3He) surface exposure dating of basaltic lava-flows, field observations, geological mapping and geochemistry, we show in this paper that magmatic activity in this rift segment alternates between two distinct magma chambers. Recent activity in the Dabbahu rift (notably the 2005-2010 dyking crises) has been fed by a seismically well-identified magma reservoir within the rift axis, and we show here that this magma body has been active over the last 30 kyr. However, in addition to this axial magma reservoir, we highlight in this paper the importance of a second, distinct magma reservoir, located 15 km west of the current axis, which has been the principal focus of magma accumulation from 15 ka to the subrecent. Magma supply to the axial reservoir substantially decreased between 20 ka and the present day, while the flank reservoir appears to have been regularly supplied with magma since 15 ka ago, resulting in less variably differentiated lavas. The trace element characteristics of magmas from both reservoirs were generated by variable degrees of partial melting of a single homogeneous mantle source, but their respective magmas evolved separately in distinct crustal plumbing systems. Magmatism in the Dabbahu/Manda Hararo rift segment is not focussed within the current axial depression but instead is spread out over at least 15 km on the western flank. This is consistent with magneto-telluric observations which show that two magma bodies are present below the segment, with the main accumulation of magma currently located below the western flank, precisely where the most voluminous recent (<15 ka) flank volcanism is observed at the surface. Applying these observations to slow spreading mid-ocean ridges indicates that magma bodies likely have a lifetime of a least 20 ka, and that the continuity of magmatic activity is maintained by a system of separate relaying reservoirs, which could in return control the location of spreading. This long term (>105 yr) alternation between distinct crustal reservoirs located broadly at the same location relative to the segment appears to be a key feature for organizing and maintaining active spreading centres over stable soft points in the mantle.

  16. The tectono-stratigraphic evolution of basement highs in hyper extended deep-water rifted margins : the example of the Briançonnais domain in the Alps and comparisons with modern analogues

    NASA Astrophysics Data System (ADS)

    Haupert, Isabelle; Manatschal, Gianreto; Unternehr, Patrick; Decarlis, Alessandro

    2013-04-01

    The discovery of hydrocarbon systems in hyper-extended deep-water rifted margins, in conjunction with technical developments, expanded the hydrocarbon exploration into domains that are yet little investigated. The increasing number of high-quality reflection and refraction seismic surveys and drill hole data show that deep-water rifted margins are very different from proximal rifted margins. The new data show evidence for a polyphase rift evolution resulting in complex rift architectures with variable amounts of magmatic addition and local mantle exhumation that cannot be predicted by classical rift models. Thus, understanding the thermal structure, subsidence history, depositional environment and sedimentary architecture is a prerequisite to apply the "play elements" in these yet little investigated domains, which is essential to evaluate the survivability of syn- to post-rift petroleum systems. Although a big progress was made in the understanding of deep water rifted margins in the last 5 years, there are still many fundamental questions that remain open and ask for further research on this topic. One open scientific question is related to the tectono-sedimentary evolution and subsidence history of basement highs in deep water rifted margins. Péron-Pinvidic and Manatschal (2010) showed that different types of basement highs can be distinguished in rifted margins. These highs include micro-continents, continental ribbons, H-blocks and extensional allochthons. Mapping these highs and properly define their stratigraphic and tectonic evolution provide important insights into the tectonic evolution of rifted margins. However, these blocks are often at deep-water and sealed by thick post-rift sediments. Therefore access to direct observations requires expensive drillings. An alternative way to study these blocks is to use field analogues. One of which is the Briançonnais domain in the Alps. To achieve our goal we propose to review the existing structural, stratigraphic and age data from the whole Briançonnais domain (from Liguria/Italy, across the French Alps to Grisons in Switzerland). We propose to construct key tectonic sections across the Briançonnais domain. These data will form the basis to discuss the rift-related tectono-stratigraphic and subsidence evolution and to constrain the along and across strike stratigraphic architecture of the Briançonnais. These observations will be compared with that of seismically imaged basement highs in deep-water rifted margins (e.g. outer high in Campos or Santos). In our presentation we will show results of our preliminary works on the Briançonnais domain in the French Alps and a comparisons with seismically imaged basement highs imaged offshore Newfoundland.

  17. The formation of the northwestern Dniepr-Donets Basin: 2-D forward and reverse syn-rift and post-rift modelling

    NASA Astrophysics Data System (ADS)

    Kusznir, N. J.; Stovba, S. M.; Stephenson, R. A.; Poplavskii, K. N.

    1996-12-01

    Forward and reverse modelling of structure and stratigraphy have been used to investigate the syn-rift (Devonian) and early post-rift (Carboniferous) evolution of the northwestern Dniepr-Donets Basin. Modelling shows that basin formation is consistent with Frasnian-Famennian rifting followed by post-rift subsidence starting in the early Tournaisian. Forward syn-rift modelling, using the flexural cantilever model of rift basin formation, satisfactorily models the observed syn-rift stratigraphic thicknesses and structure within the basin using total syn-rift extension of approximately 15 km in the region studied with a maximum ? stretching factor of 1.3. Forward structural and stratigraphic modelling suggests that the Devonian rifting, which formed the northwestern Dniepr-Donets Basin, was accompanied by regional uplift of the order of 300 m. Both forward and reverse (flexural backstripping) modelling of post-rift stratigraphy through the Carboniferous suggest that post-rift thermal subsidence, which commenced in the Tournaisian following Devonian rifting, was augmented by additional regional subsidence of the order of 300 m in middle Carboniferous times. It is suggested that this transient regional uplift event, which accompanied rifting and decayed in middle Carboniferous times, was generated by a mantle plume.

  18. Motivation Introduction Linear maps as stream circuits Final semantics In conclusion Linear systems, coalgebraically

    E-print Network

    Rutten, Jan

    Motivation Introduction Linear maps as stream circuits Final semantics In conclusion Linear systems, coalgebraically Jan Rutten CWI & Vrije Universiteit Amsterdam CALCO 2007 #12;Motivation Introduction Linear maps as stream circuits Final semantics In conclusion Motivation Why linear systems, coalgebraically? · Very

  19. Faults kinematics, paleo- and present-day stress-strain state in the Central Baikal rift

    NASA Astrophysics Data System (ADS)

    Sankov, Vladimir; Lukhnev, Andrey; Miroshnitchenko, Andrey; Ashurkov, Sergey; Byzov, Leonid; Sankov, Alexey; Dembelov, Mihkail

    2013-04-01

    The central part of the Baikal rift system