Science.gov

Sample records for rift system final

  1. North Sea rift system

    NASA Astrophysics Data System (ADS)

    Ziegler, P. A.

    1992-07-01

    The Mesozoic North Sea rift forms an integral part of the Arctic-North Atlantic rift system. Rifting activity in the North Sea commenced during the earliest Triassic. During the mid-Jurassic the central North Sea underwent a temporary doming stage. Crustal extension peaked during the Late Jurassic-earliest Cretaceous, abated subsequently and terminated altogether during the Paleocene. The saucer-shaped Cenozoic post-rift basin straddles the axis of the Viking and Central grabens. This speaks for the applicability of a depth dependent pure shear model rather than a simple shear model. Geophysical data indicate an important discrepancy between upper and lower crustal attenuation across the North Sea rift, suggesting that during rifting processes the Mono-discontinuity was seriously destabilized. This requires a basic modification of currently favoured crustal stretching models.

  2. 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.

  3. The East African rift system

    NASA Astrophysics Data System (ADS)

    Chorowicz, Jean

    2005-10-01

    This overview paper considers the East African rift system (EARS) as an intra-continental ridge system, comprising an axial rift. It describes the structural organization in three branches, the overall morphology, lithospheric cross-sections, the morphotectonics, the main tectonic features—with emphasis on the tension fractures—and volcanism in its relationships with the tectonics. The most characteristic features in the EARS are narrow elongate zones of thinned continental lithosphere related to asthenospheric intrusions in the upper mantle. This hidden part of the rift structure is expressed on the surface by thermal uplift of the rift shoulders. The graben valleys and basins are organized over a major failure in the lithospheric mantle, and in the crust comprise a major border fault, linked in depth to a low angle detachment fault, inducing asymmetric roll-over pattern, eventually accompanied by smaller normal faulting and tilted blocks. Considering the kinematics, divergent movements caused the continent to split along lines of preexisting lithospheric weaknesses marked by ancient tectonic patterns that focus the extensional strain. The hypothesis favored here is SE-ward relative divergent drifting of a not yet well individualized Somalian plate, a model in agreement with the existence of NW-striking transform and transfer zones. The East African rift system comprises a unique succession of graben basins linked and segmented by intracontinental transform, transfer and accommodation zones. In an attempt to make a point on the rift system evolution through time and space, it is clear that the role of plume impacts is determinant. The main phenomenon is formation of domes related to plume effect, weakening the lithosphere and, long after, failure inducing focused upper mantle thinning, asthenospheric intrusion and related thermal uplift of shoulders. The plume that had formed first at around 30 Ma was not in the Afar but likely in Lake Tana region (Ethiopia), its almost 1000 km diameter panache weakening the lithosphere and preparing the later first rifting episode along a preexisting weak zone, a Pan-African suture zone bordering the future Afar region. From the Afar, the rift propagated afterward from north to south on the whole, with steps of local lithospheric failure nucleations along preexisting weak zones. These predisposed lines are mainly suture zones, in which partial activation of low angle detachment faults reworked former thrust faults verging in opposite directions, belonging to double verging ancient belts. This is responsible for eventual reversal in rift asymmetry from one basin to the next. Supposing the plume migrated southward, or other plumes emplaced, the rift could propagate following former weaknesses, even outside areas influenced by plumes. This view of rift formation reconciles the classical models: active plume effect triggered the first ruptures; passive propagations of failure along lithospheric scale weak zones were responsible for the onset of the main rift segments. Various other aspects are shortly considered, such as tectonics and sedimentation, and relationships of the 'cradle of Mankind' with human evolution. By its size, structure and occurrence of oceanic lithosphere in the Afar, the EARS can be taken as a model of the prelude of oceanic opening inside a continent.

  4. 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.

  5. 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.

  6. The diverging volcanic rift system

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  10. The Offshore East African Rift System

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  11. The Albertine Rift, East Africa: Initial rifting, long-term landscape evolution and final surface uplift

    NASA Astrophysics Data System (ADS)

    Bauer, Friederike U.; Glasmacher, Ulrich A.; Ring, Uwe; Grobe, René W.; Starz, Matthias; Mambo, Vikandy S.

    2013-04-01

    The Albertine Rift and associated Rwenzori Mountains form a striking feature at the north-western portion of the East African Rift System. The Rwenzori Mtns are built up by a dissected Precambrian metamorphic basement block that has been uplifted to heights of more than 5 km. The fundamental subject addressed by this study is the temporal and spatial evolution of the Rwenzori Mtns and adjacent Albertine Rift (western Uganda and Eastern Congo) at different time scales. In order to unlock how and at what time the extreme surface uplift occurred, low-temperature thermochronology methods were applied and combined with thermokinematic modelling. By means of apatite fission-track, apatite and zircon (U-Th-Sm)/He dating, combined with 2D (HeFTy) and 3D (Pecube) thermokinematic modelling different phases of landscape evolution could be determined for the Albertine area, where movements of surface uplift can be traced from Palaeozoic to Neogene times. Since the Palaeozoic several cooling events affected the Albertine area and Rwenzori Mtns, as revealed from samples along the rift shoulders and across the mountain range. Results from low-temperature thermochronology and thermokinematic modelling demonstrate that the Rwenzoris were not exhumed as a coherent block but are composed of distinct decoupled blocks with diverging exhumation histories and block movements along inherited faults. Thus, the evolution of the Rwenzoris was not solely triggered by Neogene rifting; moreover, a Mesozoic topographic Albertine high is conceivable. Since the Miocene renewed rock and surface uplift of distinct blocks with forced movements at the western flank of the Rwenzoris occurred. Rock uplift, thereby, outweighed erosion, resulting in the recent high topography of the Rwenzoris and their asymmetric character. Detrital thermochronology data confirm a Neogene surface uplift and indicate transition of erosional forces in Plio-/Pleistocene times. Thermokinematic modelling, applied to samples from different parts of the working area allows better constraining the cooling history of the Rwenzori Mtns and surrounding Albertine Rift and will be discussed in the frame of this presentation.

  12. The offshore East African Rift System: Structural framework at the toe of a juvenile rift

    NASA Astrophysics Data System (ADS)

    Franke, Dieter; Jokat, Wilfried; Ladage, Stefan; Stollhofen, Harald; Klimke, Jennifer; Lutz, Ruediger; Mahanjane, Estevão. Stefane; Ehrhardt, Axel; Schreckenberger, Bernd

    2015-10-01

    The Cenozoic East African Rift System (EARS) extends from the Red Sea to Mozambique. Here we use seismic reflection and bathymetric data to investigate the tectonic evolution of the offshore branch of the EARS. The data indicate multiple and time transgressive neotectonic deformations along ~800 km of the continental margin of northern Mozambique. We observe a transition from a mature rift basin in the north to a juvenile fault zone in the south. The respective timing of deformation is derived from detailed seismic stratigraphy. In the north, a ~30 km wide and more than 150 km long, N-S striking symmetric graben initiated as half-graben in the late Miocene. Extension accelerated in the Pliocene, causing a continuous conjugate border fault and symmetric rift graben. Coevally, the rift started to propagate southward, which resulted in a present-day ~30 km wide half-graben, approximately 200 km farther south. Since the Pleistocene, the rift has continued to propagate another ~300 km, where the incipient rift is reflected by subrecent small-scale normal faulting. Estimates of the overall brittle extension of the matured rift range between 5 and 12 km, with an along-strike southward decrease of the extension rate. The offshore portion of the EARS evolves magma poor, similar to the onshore western branch. The structural evolution of the offshore EARS is suggested to be related to and controlled by differing inherited lithospheric fabrics. Preexisting fabrics may not only guide and focus extension but also control rift architecture.

  13. 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.

  14. Model of the midcontinent rift system in northeastern Kansas

    SciTech Connect

    Woelk, T.S.; Hinze, W.J. )

    1991-03-01

    Recent drilling of the midcontinent rift system in northeastern Kansas reveals a transposed Keweenawan stratigraphy of mafic volcanic rocks overlying thick clastic sedimentary rocks. A reprocessed version of COCORP Kansas Line 1 indicates that the drillhole penetrated a series of west-dipping reflectors associated with a reverse fault bounding the east side of the rift basin. Reanalysis of the original COCORP line also reveals a west-bounding reverse fault and evidence of crustal thickening. This information is integrated with gravity and magnetic data to define a model of the rift in northeastern Kansas. The model, consisting of an asymmetric basin bounded by reverse faults with thickened crust beaneath the rift, is similar to models proposed for northern segments of the rift system, and argues for homogeneity in the structural style and tectonic evolution along the length of the rift.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    SciTech Connect

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

    1983-08-01

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

  17. 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.

  18. Gravity study of the Central African Rift system: A model of continental disruption 1. The Ngaoundere and Abu Gabra Rifts

    NASA Astrophysics Data System (ADS)

    Browne, S. E.; Fairhead, J. D.

    1983-05-01

    A regional compilation of published and unpublished gravity data for Central Africa is presented and reveals the presence of a major rift system, called here, the Central African Rift System. It is proposed that the junction area between the Ngaoundere and Abu Gabra rift arms in Western Sudan forms an incipient intraplate, triple-junction with the as yet unfractured, but domally uplifted and volcanically active, Darfur swell. It is only the Darfur swell that shows any similarities to the uplift and rift history of East Africa. The other two rifts arms are considered to be structurally similar to the early stages of passive margin development and thus reflect more closely the initial processes of continental fragmentation than the structures associated with rifting in East Africa.

  19. 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.

  20. 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.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  3. 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.

  4. Geophysical studies of the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

    Behrendt, J. C.; Lemasurier, W. E.; Cooper, A. K.; Tessensohn, F.; TréHu, A.; Damaske, D.

    1991-12-01

    The West Antarctic rift system extends over a 3000 × 750 km, largely ice covered area from the Ross Sea to the base of the Antarctic Peninsula, comparable in area to the Basin and Range and the East African rift system. A spectacular rift shoulder scarp along which peaks reach 4-5 km maximum elevation marks one flank and extends from northern Victoria Land-Queen Maud Mountains to the Ellsworth-Whitmore-Horlick Mountains. The rift shoulder has maximum present physiographic relief of 5 km in the Ross Embayment and 7 km in the Ellsworth Mountains-Byrd Subglacial Basin area. The Transantarctic Mountains part of the rift shoulder (and probably the entire shoulder) has been interpreted as rising since about 60 Ma, at episodic rates of ˜1 km/m.y., most recently since mid-Pliocene time, rather than continuously at the mean rate of 100 m/m.y. The rift system is characterized by bimodal alkaline volcanic rocks ranging from at least Oligocene to the present. These are exposed asymmetrically along the rift flanks and at the south end of the Antarctic Peninsula. The trend of the Jurassic tholeiites (Ferrar dolerites, Kirkpatric basalts) marking the Jurassic Transantarctic rift is coincident with exposures of the late Cenozoic volcanic rocks along the section of the Transantarctic Mountains from northern Victoria Land to the Horlick Mountains. The Cenozoic rift shoulder diverges here from the Jurassic tholeiite trend, and the tholeiites are exposed continuously (including the Dufek intrusion) along the lower- elevation (1-2 km) section of Transantarctic Mountains to the Weddell Sea. Widely spaced aeromagnetic profiles in West Antarctica indicate the absence of Cenozoic volcanic rocks in the ice covered part of the Whitmore-Ellsworth-Mountain block and suggest their widespread occurrence beneath the western part of the ice sheet overlying the Byrd Subglacial Basin. A German Federal Institute for Geosciences and Natural Resources (BGR)-U.S. Geological Survey (USGS) aeromagnetic survey over the Ross Sea continental shelf indicates rift fabric and suggests numerous submarine volcanoes along discrete NNW trending zones. A Bouguer anomaly range of approximately 200 (+50 to -150) mGal having 4-7 mGal/km gradients where measured in places marks the rift shoulder from northern Victoria Land possibly to the Ellsworth Mountains (where data are too sparse to determine maximum amplitude and gradient). The steepest gravity gradients across the rift shoulder require high density (mafic or ultramafic?) rock within the crust as well as at least 12 km of thinner crust beneath the West Antarctic rift system in contrast to East Antarctica. Sparse land seismic data reported along the rift shoulder, where velocities are greater than 7 km/s, and marine data indicating velocities above 7 km/s beneath the Ross Sea continental shelf support this interpretation. The maximum Bouguer gravity range in the Pensacola Mountains area of the Transantarctic Mountains is only about 130 mGal with a maximum 2 mGal/km gradient, which can be explained solely by 8 km of crustal thickening. Large offset seismic profiles over the Ross Sea shelf collected by the German Antarctic North Victoria Land Expedition V (GANOVEX V) combined with earlier USGS and other results indicate 17-21 km thickness for the crust beneath the Ross Sea shelf which we interpret as evidence of extended rifted continental crust. A regional positive Bouguer anomaly (0 to +50 mGal), the width of the rift, extends from the Ross Sea continental shelf throughout the Ross Embayment and Byrd Subglacial Basin area of the West Antarctic rift system and indicates that the Moho is approximately 20 km deep tied to the seismic results (probably coincident with the top of the asthenosphere) rather than the 30 km reported in earlier interpretations. The interpretation of horst and graben structures in the Ross Sea, made from marine seismic reflection data, probably can be extended throughout the rift (i.e., the Ross Ice shelf and the Byrd Subglacial Basin areas). The near absence of earthquakes in the West Antarctic r

  5. 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.

  6. 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.

  7. Unraveling the Interaction Between Mantle Processes and the Tectono-Sedimentary Evolution During Final Rifting Based on the Study of Remnants of the Alpine Tethys Rifted Margins Exposed in the Alps

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    The tectonic, sedimentary and isostatic evolution of distal rifted margins are poorly constrained and the available data from present-day magma-poor rifted margins, such as the Iberia-Newfoundland or the Southern Atlantic margins suggest that its evolution is complex and very different from that of proximal margins. In contrast to present-day rifted margins, where rift structures are covered by sediments and are at abyssal depth, remnants of ancient margins preserved in collisional orogens bear, if not overprinted by later deformation, important information on the stratigraphic, tectonic and mantle evolution during rifting. This is particularly true for the Adriatic and parts of the European margins exposed in the Alps in Central Europe. From these margins remnants of the first oceanic crust, the subcontinental mantle, from lower crustal rocks, detachment systems, remnants of the distal and proximal margins and the stratigraphic record of rifting, including pre-, syn- and post-rift sediments are preserved. A paleogeographic reconstruction of all these structures including the associated stratigraphy and the underlying basement represents a unique opportunity to study the relations between shallow crustal and mantle processes during rifting. Previous studies suggested that the margins in the Alps resulted from a complex poly-phase evolution that initiated with distributed stretching (220 to 190 Ma), continued with localized thinning (around 180 Ma) and terminated with exhumation of mantle rocks and first MOR-type magmatism (at 160 Ma). Thus, rifting leading to breakup and opening of the Alpine Tethys was shown to be the result of strain localization and to include a transition from decoupled to coupled deformation in which detachment faulting played an important role. How crustal thinning is linked in detail with strain localization, uplift of distal domains and melt infiltration in the rising mantle during crustal thinning is, however, not yet understood. We will present preliminary results from the study of the most distal Adriatic (Canavese/Err/Bernina domains) the conjugate European margin (Briançonnais domain), and the Sesia/Lanzo and the Ivrea/Balmuccia zones, representing deep crustal and mantle portions. These units bear the information of how mantle, lower crustal and upper crustal domains evolved during final rifting in Middle Jurassic time (180 to 160 Ma) and how their evolution is recorded in the stratigraphic record of the Alpine Tethys margins.

  8. The West Antarctic Rift System - some outstanding issues

    NASA Astrophysics Data System (ADS)

    Davey, F. J.

    2010-12-01

    The West Antarctic Rift System (WARS) is the product of several phases of deformation since the Jurassic with an early history related to that of New Zealand and Tasmania. Several outstanding issues exist in reconstructing the evolution of the West Antarctic Rift System. An early (mid-Cretaceous) intracontinental extensional episode led to the broad crustal thinning of WARS. Recent models propose a 50 km thick crust prior to the onset of extension, but the broad evidence for this is equivocal, as it must have also affected Tasmania and southern New Zealand as well as Antarctica prior to break-up of this part of Gondwana. Several more recent extensional episodes, largely W-E extension, have been proposed, in the early, mid and late Cenozoic, that give rise to a series of N-S trending extensional sedimentary basins. How well are these episodes defined, spatially distributed and how do they relate to a further hypothesis that NW-SE dextral strike slip faulting has had a dominant influence on this extension and basin formation? WARS sedimentary basins are moderately well defined under the Ross Sea, although their age of origin is often not well constrained, but their extension under the Ross Ice Shelf is also controversial. Gravity data have been used to infer their existence but the limited seismic data available do not confirm these models. A direct relationship between the Transantarctic Mountains (TAM), a major mountain range forming the major rift margin of the WARS, and the extensional structures is also equivocal as a major sedimentary basin in the adjacent rift floor only occurs along part of the rift margin.

  9. Ouachita trough: Part of a Cambrian failed rift system

    NASA Astrophysics Data System (ADS)

    Lowe, Donald R.

    1985-11-01

    Pre-flysch (Cambrian-Mississippian) strata of the Ouachita Mountains of Arkansas and Oklahoma include two main sandstone lithofacies: (1) a craton-derived lithofacies made up largely of mature medium- to coarse-grained quartzose and carbonate detritus and, in some units, sediment eroded from exposed basement rocks and (2) an orogen-derived facies made up mainly of fine-grained quartzose sedimentary and metasedimentary debris and possibly, in lower units, a volcaniclastic component. Paleocurrent and distribution patterns indicate that detritus of facies I in the Benton uplift was derived from north and detritus of facies II throughout the Ouachitas was derived from south and east of the depositional basin. Overall sedimentological results suggest that the Ouachita trough was a relatively narrow, two-sided basin throughout most and probably all of its existence and never formed the southern margin of the North American craton. Regional comparisons suggest that it was one of several basins, including the Southern Oklahoma aulacogen, Reelfoot Rift, Illinois Basin, and Rome trough, that formed as a Cambrian failed rift system 150 to 250 m.y. after initial rifting along the Appalachian margin of the North American craton.

  10. 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.

  11. Calving of large tabular icebergs from ice shelf rift systems

    NASA Astrophysics Data System (ADS)

    Joughin, Ian; MacAyeal, Douglas R.

    2005-01-01

    We used Interferometric Synthetic Aperture Radar to study the detachment process that allowed two large icebergs to calve from the Ross Ice Shelf, Antarctica. Time series of rift geometries indicate that rift widths increased steadily, whereas rift lengths increased episodically through several discrete rift-tip propagation events. We also conducted modeling experiments constrained by the observed rift geometry. Both the observations and model suggest that rift opening, and, thus, tabular-iceberg calving, are largely driven by ``glaciological'' stresses-stress introduced by the effect of gravity on the ice shelf-rather than by stress introduced by the ocean and atmosphere, e.g., tides and storms. This style of rift propagation is expected to determine the steady, background calving rate of ice shelves and, thus, differs significantly from styles that led to the recent disintegration of ice shelves in response to climate warming, e.g., the Larsen B Ice Shelf on the Antarctic Peninsula.

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

    NASA Astrophysics Data System (ADS)

    Leppard, Christopher W.; Gawthorpe, Rob L.

    2006-09-01

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

  13. 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.

  14. Dual continental rift systems generated by plume-lithosphere interaction

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    Although many continental rifts and passive margins are magmatic, some are not. This observation prompted endmember views of the mechanisms driving continental rifting, where magma-rich or active rifts would be caused by deep mantle plumes, whereas magma-poor or passive rifts would result from the stretching of the lithosphere under far-field plate forces. The Central East African Rift provides a unique setting to investigate the mechanisms of continental rifting because it juxtaposes a magma-rich (eastern) branch and magma-poor (western) branch on either side of the 250-km-thick Tanzanian craton. Here we investigate this contrasted behavior using a high-resolution rheologically consistent three-dimensional thermo-mechanical numerical model. The model reproduces the rise of a mantle plume beneath a craton experiencing tensional far-field stress. In our numerical experiments the plume is deflected by the cratonic keel and preferentially channelled along one of its sides. This leads to the coeval development of magma-rich and magma-poor rifts along opposite craton sides, fed by melt from a single mantle source. Our numerical experiments show strong similarities to the observed evolution of the Central East African Rift, reconcile the passive and active rift models, and demonstrate the possibility of developing both magmatic and amagmatic rifts in identical geotectonic environments.

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

    NASA Astrophysics Data System (ADS)

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

    1994-09-01

    On the basis of a test experiment in 1985 (KRISP 85) an integrated seismic-refraction/teleseismic survey (KRISP 90) was undertaken to study the deep structure beneath the Kenya rift down to depths of 100-150 km. This paper summarizes the highlights of KRISP 90 as reported in this volume and discusses their broad implications as well as the structure of the Kenya rift in the general framework of other continental rifts. Major scientific goals of this phase of KRISP were to reveal the detailed crustal and upper mantle structure under the Kenya rift, to study the relationship between mantle updoming and the development of sedimentary basins and other shallow structures within the rift, to understand the role of the Kenya rift within the Afro-Arabian rift system and within a global perspective and to elucidate fundamental questions such as the mode and mechanism of continental rifting. The KRISP results clearly demonstrate that the Kenya rift is associated with sharply defined lithospheric thinning and very low upper mantle velocities down to depths of over 150 km. In the south-central portion of the rift, the lithospheric mantle has been thinned much more than the crust. To the north, high-velocity layers detected in the upper mantle appear to require the presence of anistropy in the form of the alignment of olivine crystals. Major axial variations in structure were also discovered, which correlate very well with variations in the amount of extension, the physiographic width of the rift valley, the regional topography and the regional gravity anomalies. Similar relationships are particularly well documented in the Rio Grande rift. To the extent that truly comparable data sets are available, the Kenya rift shares many features with other rift zones. For example, crustal structure under the Kenya, Rio Grande and Baikal rifts and the Rhine Graben is generally symmetrically centered on the rift valleys. However, the Kenya rift is distinctive, but not unique, in terms of the amount of volcanism. This volcanic activity would suggest large-scale modification of the crust by magmatism. Although there is evidence of underplating in the form of a relatively high-velocity lower crustal layer, there are no major seismic velocity anomalies in the middle and upper crust which would suggest pervasive magmatism. This apparent lack of major modification is an enigma which requires further study.

  16. 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.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  19. The stratigraphic architecture of hyper-extended rift systems: A field perspective from Aps, Pyrenees and Baja-California

    NASA Astrophysics Data System (ADS)

    Masini, Emmanuel; Manatschal, Gianreto; Tugend, Julie; Mohn, Geoffroy; Robin, Cécile; Geoffroy, Laurent; Unternehr, Patrick

    2013-04-01

    The discovery of hyper-extended domains in deep water rifted margins challenged the classical view of the evolution of rift systems leading to continental breakup. In these hyper-extended domains, rift basins occur over less than 10km thick extended continental crust or exhumed subcontinental mantle. Neither their imaged stratigraphic architecture and drilled facies nor the subsidence history can be explained by classical McKenzie-type rift models. Studies performed on off- and on-shore examples demonstrate the importance of tectonic exhumation by detachment faulting. However, despite their apparent widespread occurrence in present-day rifted margins, the overall tectono-sedimentary evolution of these systems remains poorly understood. In this study we review and compare key multi-scale observations from 3 different hyper-extended rift systems. 1) The first example, in the Western Pyrenees, corresponds to a complete sediment-rich Cretaceous hyper-extended rift system that can be investigated. 2) The second example in the Swiss Alps, gives the access to supra-detachment sedimentary evolution in a sediment-starved context. 3) The last example exposed in Baja California Sur, shows supra-detachment sedimentary evolution in sediment-rich and shallow water environment. Based on these studies in three different settings, we conclude that the basins forming in the lower and upper plate position respective to detachment fault polarity develop as two different types of basins. Lower plate basins develop over top-basement detachment systems and discontinuous pieces of pre-rift strata (extensional allochthons). In this setting, the sequential development of low-angle detachment systems implies the creation of new real estate crust (new seafloor surfaces) and a complex syn-rift stratigraphic architecture. Through this domain, the deposition of syn- and post-tectonic sediments above exhumation surfaces are diachronous along stretching direction illustrating relative migration of exhumation processes. Syn-tectonic deposits correspond to the erosion of exhumed material and mass-wasting processes along active detachment fault scarps. Once active exhumation migrates, inactive parts of detachment merge to form a lower plate sag basin under thermal subsidence. In contrast, the upper plate basin records a single isochronous sag phase over weakly extended pre-rift strata. This observation suggests that upper plate sag formation is controlled by depth-dependent crustal extension. As illustrated by the different study cases, the sag phase sedimentary record of upper and lower plate settings strongly depends on their respective connection with sediment sourcing systems. Finally, we used the Rifter software developed within the Margin Modelling Phase 3 (MM3) consortium to generate equilibrated lithospheric sections based on our observations. Through these kinematic numerical experiments, we aim to quantify the tectonic, thermal and isostatic evolution of hyper-extended rift systems.

  20. 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.

  1. 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.

  2. Simple shear detachment fault system and marginal grabens in the southernmost Red Sea rift

    NASA Astrophysics Data System (ADS)

    Tesfaye, Samson; Ghebreab, Woldai

    2013-11-01

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

  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. East Antarctic Rift Systems - key to understanding of Gondwana break-up

    NASA Astrophysics Data System (ADS)

    Golynsky, D. A.; Golynsky, A. V.

    2012-04-01

    The results of analysis of radio-echo sounding surveys, the RADARSAT satellite data, magnetic and gravity information give evidence that East Antarctica contains 13 riftogenic systems and/or large linear tectonic structures. Among known and suggested rifts of East Antarctica the Lambert rift has a pivotal position and it manifests oneself as symmetry axis. Six additional systems are revealed on both sides of it and any one of them possesses special features in geologic and geomorphologic aspects. In most cases they inherited the anisotropy of long-lived cratonic blocks. Riftogenic and/or large linear tectonic structures along the East Antarctica coastal regions are distributed with a steady regularity with average distance between them about 650 km. For six (7) structures from 13 (Lambert, Jutulstraumen-Pencksökket, Vestfjella, Mellor-Slessor (Bailey), Wilkes Basin, Gaussberg (?) and Rennick) there is a distinct spatial coupling with trough complexes of the Beacon Supergroup and their subsequent reactivation in Late Jurassic - Permian time when the East Gondwana started break-up. Rift system of the Lambert-Amery Glaciers and Prydz Bay is related to Mesozoic extension events and it inherited structures of Paleozoic grabens. The total length of the rift system exceeds 4000 km of the same scale as largest the World rift belts. The length of the western branch of the Lambert rift that includes the Mellor rift and graben-like structures of the Bailey and Slessor glaciers exceeds 2300 km. Results of radio-echo sounding investigation of the subglacial Aurora Basin allow to suggest that this large basin of sub-meridian extension is underlain by an extensive (> 1000 km) riftogenic structure that is running towards the Transantarctic Mountains where it forms a triple junction with the eastern branch of the Lambert rift and structures of the Wilkes Basin. It is hereby proposed that Aurora-Scott rift is formed by complex system of sub-parallel depressions divided by fragmentary horsts. The spatial correlation of the Aurora-Scott rift system, Permian basins of the Western Australia margin and coal-bearing basins in Rajmahal Hills allows suggesting that this East Antarctic structure was also formed during Permian time and about the existence of triple junction rift systems (Aurora-Scott, Perth, Rajmahal) in the pre-breakup Gondwana.

  5. 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.

  6. 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

  7. 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.

  8. 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. The new fault map of the main Ethiopian rift, based on aerial photo compilations, generally agrees well with the maps produced from ERTS-1 imagery. Characteristically, the ERTS-1 imagery shows some of the major faults to be more extensive than realized from ground studies, though due to the angle of sun illumination some east-facing fault scarps are not easily discernible on the imagery. The Corbetti caldera, shows up surprisingly poor on the imagery, and is shown to be an adjunct to an older, larger caldera now occupied by Lakes Awassa and Shallo. The lithological boundaries mapped by De Paola in the rift are difficult to discern on the ERTS-1 imagery. On the Somalian plateau, east of the rift, a denuded caldera has been identified as the source of much of the lavas of the Batu Mountains. Further south, ERTS-1 imagery amplifies the structural and lithological mapping of the Precambrian rocks of the Shakisso-Arero area, and of the Kenya-Ethiopia border region. For the first time with some certainty, it is now possible to say that on the evidence of the ERTS-1 imagery, the Western Rift does not continue northeast beyond the Sudan-Uganda border, and is thus not to be sought in western Ethiopia.

  9. Extending Thickened Continental Crust: Implications for the Transantarctic Mountains and West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

    Bialas, R. W.; Buck, W. R.; Studinger, M.; Fitzgerald, P. G.

    2005-12-01

    The Transantarctic Mountains (TAM) are often described as the largest rift related mountains in the world. They define the western edge of the West Antarctic rift system (WARS) and are usually assumed to have uplifted in the Eocene during a phase of rapid denudation associated with Eocene rifting in the WARS. Previous models have difficulty reconciling large uplift of the TAM with distributed extension of the WARS. We propose a model where the TAM represents an edge of a plateau comprising parts of East and West Antarctica and New Zealand that retains significant elevation, even as the plateau is lowered and extended during the Cretaceous WARS rifting event. Regional scale two-dimensional numerical models are presented showing a layer of thickened continental crust and adjacent crust of normal thickness underlain by a mantle layer extended by pulling at the edges. The temperature-dependent viscous rheology is based on power-law creep flow law for diabase. Temperature profiles are calculated using conductive heat transport and radiogenic heat production that decreases exponentially with depth. Temperature profiles are altered by varying the bottom mantle heat flow and thermal conductivities within acceptable ranges. Different styles of extension including core complex, wide rifting, and narrow rifting are observed for different temperature structures. In the models, a remnant edge, analogue to the ancestral TAM, are observed.

  10. 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.

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

    USGS Publications Warehouse

    Behrendt, John C.

    1999-01-01

    The active West Antarctic Rift System, which extends from the continental shelf of the Ross Sea, beneath the Ross Ice Shelf and the West Antarctic Ice Sheet, is comparable in size to the Basin and Range in North America, or the East African rift systems. Geophysical surveys (primarily marine seismic and aeromagnetic combined with radar ice sounding) have extended the information provided by sparse geologic exposures and a few drill holes over the ice and sea covered area. Rift basins developed in the early Cretaceous accompanied by the major extension of the region. Tectonic activity has continued episodically in the Cenozoic to the present, including major uplift of the Transantarctic Mountains. The West Antarctic ice sheet, and the late Cenozoic volcanic activity in the West Antarctic Rift System, through which it flows, have been coeval since at least Miocene time. The rift is characterized by sparse exposures of late Cenozoic alkaline volcanic rocks extending from northern Victoria Land throughout Marie Byrd Land. The aeromagnetic interpretations indicate the presence of > 5 x 105 km2 (> 106 km3) of probable late Cenozoic volcanic rocks (and associated subvolcanic intrusions) in the West Antarctic rift. This great volume with such limited exposures is explained by glacial removal of the associated late Cenozoic volcanic edifices (probably hyaloclastite debris) concomitantly with their subglacial eruption. Large offset seismic investigations in the Ross Sea and on the Ross Ice Shelf indicate a ~ 17-24-km-thick, extended continental crust. Gravity data suggest that this extended crust of similar thickness probably underlies the Ross Ice Shelf and Byrd Subglacial Basin. Various authors have estimated maximum late Cretaceous-present crustal extension in the West Antarctic rift area from 255-350 km based on balancing crustal thickness. Plate reconstruction allowed < 50 km of Tertiary extension. However, paleomagnetic measurements suggested about 1000 km of post-middle Cretaceous translation between East Antarctica and Pacific West Antarctica. Because a great amount of crustal extension in late Cenozoic time is unlikely, alternate mechanisms have been proposed for the late Cenozoic volcanism. Its vast volume and the ocean island basalt chemistry of the exposed late Cenozoic alkaline volcanic rocks were interpreted as evidence for a mantle plume head. An alternative or supplemental explanation to the mantle plume hypothesis is significantly greater lower lithosphere (mantle) stretching resulting in greater decompression melting than the limited Cenozoic crustal extension allows. Because of very slow rates of late Cenozoic extension in the West Antarctic Rift System, the amount of advected heat is small compared with the conductive heat. Therefore, phase transition probably would not explain the large subsidence with low extension observed in the West Antarctic Rift System. (C) 1999 Elsevier Science B.V.

  12. Geodyamic Models of the Tectonomagmatic Evolution of the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

    Anoka, J. L.; Harry, D. L.

    2007-12-01

    Finite element geodynamic models reproduce the general aspects of the style and timing of extension in the West Antarctic Rift System (WARS). In particular, the models simulate a prolonged period of diffuse extension throughout the WARS during the Cretaceous and early Cenozoic followed by later focused extension in the Victoria Land Basin during the middle Paleogene. Two families of models are identified that are consistent with the Paleogene onset of magmatism in the West Antarctic Rift System under both normal and warm (70-120º hotter than global average) mantle potential temperatures. The two families of models produce distinctly different melt distribution patterns across the WARS. In models invoking normal mantle temperatures the greatest thickness of melt is confined to the Victoria Land Basin region. In models invoking warmer mantle temperatures, the greatest thickness of melt is widely distributed in the region currently underlaying the West Antarctic Ice Sheet. The models indicate that 1) the onset of Cenozoic magmatism in the Victoria Land Basin can be explained as rift induced without requiring the impingement of a plume or a change in plate motion, 2) if rifting is associated with a plume then the magmatic rocks under the West Antarctic Ice Sheet should be late Cretaceous to early Cenozoic in age, and 3) if the magmatic rocks under the West Antarctic Ice Sheet are older or younger than the main stage of rifting (ca. 105 Ma to 35 Ma), a syn-extensional plume could not have been present.

  13. The hydrothermal system associated with the Kilauea East Rift Zone, Hawaii

    SciTech Connect

    Thomas, D.M.; Conrad, M.E.

    1997-12-31

    During the last twenty years drilling and fluid production on the Kilauea East Rift Zone (KERZ) has shown that an active hydrothermal system is associated with much of the rift. Well logging and fluid geochemistry indicate that reservoir temperatures exceed 360 C but are highly variable. Although neither well testing nor pressure decline data have clearly demonstrated the lateral limits of the reservoir, divergent fluid compositions over short distances suggest that the larger hydrothermal system is strongly compartmentalized across the rift zone. The chemical compositions of production fluids indicate that recharge is derived from ocean water and meteoric recharge and isotopic data suggest that the latter may be derived from subsurface inflow from the flanks of Mauna Loa.

  14. 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.

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

    SciTech Connect

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

    1995-11-01

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

  16. Where is the West Antarctic Rift System in the Amundsen Sea and Bellingshausen Sea sectors?

    NASA Astrophysics Data System (ADS)

    Gohl, Karsten; Kalberg, Thomas; Eagles, Graeme; Dziadek, Ricarda; Kaul, Norbert; Spiegel, Cornelia; Lindow, Julia

    2015-04-01

    The West Antarctic Rift System (WARS) is one of the largest continental rifts globally, but its lateral extent, distribution of local rifts, timing of rifting phases, and mantle processes are still largely enigmatic. It has been presumed that the rift and its crustal extensional processes have widely controlled the history and development of West Antarctic glaciation with an ice sheet of which most is presently based at sub-marine level and which is, therefore, likely to be highly sensitive to ocean warming. While the western domain of the WARS in the Ross Sea has been studied in some detail, only recently have various geophysical and geochemical/thermochronological analyses revealed indications for its eastern extent in the Amundsen Sea and Bellingshausen Sea sectors of the South Pacific realm. The current model, based on these studies and additional data, suggests that the WARS activity included tectonic translateral, transtensional and extensional processes from the Amundsen Sea Embayment to the Bellingshausen Sea region of the southern Antarctic Peninsula. We present the range of existing hypotheses regarding the extent of the eastern WARS as well as published and yet unpublished data that support a conceptual WARS model for the eastern West Antarctica with implications for glacial onset and developments.

  17. 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.

  18. The tectono-sedimentary evolution of a hyper-extended rift basin: the example of the Arzacq-Mauléon rift system (Western Pyrenees, SW France)

    NASA Astrophysics Data System (ADS)

    Masini, Emmanuel; Manatschal, Gianreto; Tugend, Julie; Mohn, Geoffroy; Flament, Jean-Marie

    2014-09-01

    In this paper, we present a sedimentary and structural analysis that together with maps, sections and new Ar/Ar data enable to describe the tectono-sedimentary evolution of the Mauléon hyper-extended rift basin exposed in the W-Pyrenees. Hyper-extension processes that ultimately resulted in exhuming mantle rocks are the result of the subsequent development of two diachronous detachment systems related to two evolutional stages of rifting. An initial Late Aptian Early Albian crustal thinning phase is first recorded by the development of a crustal necking zone controlled by the north-vergent Southern Mauléon Detachment system. During a subsequent exhumation phase, active faulting migrates to the north with the emplacement of the Northern Mauléon detachment system that exhumed north section thinned continental crust and mantle rocks. This diachronous crustal thinning and exhumation processes are also recorded by the diachronous deposition of syn-tectonic sedimentary tracts above the two supra-detachment sub-basins. Syn-tectonic sedimentary tracts record the progressive exhumation of footwall rocks along detachment systems. Tectonic migration from the southern to the northern Mauléon Detachment system is recorded by the coeval deposition of "sag" deposits above the necking zone basin and of syn-tectonic tracts above exhumed rocks north section. Located on a hanging-wall situation related to the Mauléon hyper-extension structures, the Arzacq Basin also records a major crustal thinning phase as shown by its subsidence evolution so as by deep seismic images. The absence of major top-basement structures and its overall sag morphology suggest that crustal thinning processes occurred by decoupled extension of lower crustal levels contrasting with the Southern Mauléon Detachment system. Reconciling observations from the Mauléon and Arzacq Basins, we finally propose in this paper that they were the result of one and the same asymmetric crustal thinning and exhumation processes, where extension is accommodated into the upper crust in the Mauléon Basin (lower plate basin) and relayed in ductile lower crust below the Arzacq Basin (upper plate basin).

  19. 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.

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

    SciTech Connect

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

    1994-04-01

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

  1. 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.

  2. 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.

  3. 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 fields, to carry out a regional survey for engineering work.

  4. Tectonic development of the SW Arabian Plate margin within the central Arabian flank of the Red Sea rift system

    NASA Astrophysics Data System (ADS)

    Szymanski, E.; Stockli, D. F.; Johnson, P. R.; Kattan, F. H.; Cosca, M. A.

    2009-12-01

    The Red Sea rift system is a prime example of continental rifting and has contributed significantly to our understanding of the geologic processes that manage the rupture of continental lithosphere. Using a combined geo- and thermochronometric approach, we explore the modes and mechanisms of rift margin development by studying Red Sea rift-related geologic products along the central Saudi Arabian flank of the rift system, north of Jeddah. We use apatite and zircon (U-Th)/He thermochronometry and whole-rock 40Ar/39Ar dating of basalt to define the spatiotemporal relationship between rift flank extensional structures and rift-related harrat volcanism. This technical approach permits the reconstruction of the tectonic margin from early rift architecture, to strain distribution during progressive rifting, and through subsequent whole-scale modifications of the rift flank due to thermal and isostatic factors. Constraints on the dynamics of rift flank deformation are achieved through the collection of geologic samples along long-baseline thermochronometric transects that traverse the entire Arabian shield from the coastal escarpment to the inland Paleozoic sedimentary cover sequences. Long-baseline transects resolve the timing of rift flank uplift and reveal the pattern of lithospheric modification during the rupturing of continental lithosphere. Locally, short-baseline elevation transects map the footwall exhumation of major normal faults that delineate both the modern rift margin and inland extensional basins such as the NW-trending Hamd-Jizil basin, a prominent syn-extensional basin comprised of two distinct half-grabens (Jizil and Hamd) located NW of Medina. Diffuse lithospheric extension during the Oligo-Miocene affected a widespread area well inboard from the modern rift margin; samples from footwall blocks that bound the inland Jizil and Hamd half-grabens yield apatite (U-Th)/He cooling ages of 14.7 ± 0.9 Ma and 24.5 ± 1.5 Ma, respectively. The mid-Miocene age is doubly-significant since it reveals not only a Red Sea rift signal 140 km inboard from the modern border fault complex but also underscores the importance of fault reactivation during progressive rifting since the Jizil half-graben is structurally delineated by faults formed within the Neoproterozoic Najd shear zone fabric. Oligo-Miocene apatite (U-Th)/He ages from Jabal Radwa, a pluton exhumed within the border fault complex, show that rift flank exhumation and extensional faulting occurred within the central portion of the Arabian rift flank penecontemporaneous to faulting in the Hamd-Jizil half-graben system. Within the rift flank fault systems, an absence of footwall exhumation ages younger than ~13 Ma confirms that major extensional faulting migrated basin-ward in the middle Miocene during a time of rift reorganization and the establishment of the Dead Sea-Gulf of Aqaba transform. However, minor deepening of the inland Hamd-Jizil basin continued through the late Miocene as relatively young, basin-internal faults cut 17 Ma - 10 Ma basalt flows from harrat Khaybar that had blanketed the region.

  5. 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. Lake Tara lies within a previously recognized asymmetric graben situated on the Ethiopian plateau and about 250 km west of the plateau-Afar margin. ERTS-1 imagery confirms the stronger deformation of the western side of the Tara graben, with intense faulting and some associated monoclinal mapping extending between latitudes 12 deg and 14 deg N, and lying close to meridian 37 deg E. The zone of deformation is gently arcuate in plan, trending NNE in the south NNW in the north. In the north, the Quaternary faulting dies out in the alluvial plains of the Takazze Valley; in the south the faulting appears to die out in coincidence with a large erosional escapement trending S30W from Lake Tara to precisely latitude 11 deg N. This escapement aligns with the massive NE-SW escapement of western Simien, northeast of Lake Tara, and may represent erosional recession from major faulting and tilting much older than that of the superimposed, obliquely trending Tara graben. A 30 km diameter circular feature has been identified from the ERTS-1 imagery of the Tara graben, centered on 13 deg 05 min N, 37 deg 20 min E. ERTS-1 imagery further shows that the Tara graben and its associated young volcanics have no direct connection with the Red Sea or Ethiopian rift valley.

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

    Abstract<p label="1">Past plate motion between East and West Antarctica along the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> had important regional and global implications. Although extensively studied, the kinematics of the <span class="hlt">rift</span> during Eocene-Oligocene time still remains elusive. Based on a recent detailed aeromagnetic survey from the Adare and Northern Basins, located in the northwestern Ross Sea, we present the first well-constrained kinematic model with four rotations for Anomalies 12o, 13o, 16y, and 18o (26.5-40.13 Ma). These rotation poles form a cluster suggesting a stable sense of motion during that period of time. The poles are located close to the central part of the <span class="hlt">rift</span> implying that the local motion varied from extension in the western Ross Sea sector (Adare Basin, Northern Basin, and Victoria Land Basin) to dextral transcurrent motion in the Ross Ice Shelf and to oblique convergence in the eastern end of the <span class="hlt">rift</span> zone. The results confirm previous estimates of 95 km of extension in the Victoria Land Basin.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JAfES.111..288S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JAfES.111..288S"><span id="translatedtitle">Sedimentary budgets of the Tanzania coastal basin and implications for uplift history of the East African <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Said, Aymen; Moder, Christoph; Clark, Stuart; Abdelmalak, Mohamed Mansour</p> <p>2015-11-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span>. 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 <span class="hlt">Rift</span> <span class="hlt">System</span> and earlier <span class="hlt">rift</span> shoulders and plume uplifts. Indeed, rapid cooling in the <span class="hlt">rift</span> <span class="hlt">system</span> 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 <span class="hlt">rift</span> flanks and thus seems more likely due to climatic and eustatic variations. We show that the <span class="hlt">rift</span> shoulders of the East African <span class="hlt">rift</span> <span class="hlt">system</span> have inherited their present relief from at least three epeirogenic uplift pulses of middle Jurassic, Campanian-Palaeocene, and Miocene ages.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.7623T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.7623T"><span id="translatedtitle">Mapping hyper-extended <span class="hlt">rift</span> <span class="hlt">systems</span> offshore and onshore: insights from the Bay of Biscay- Western Pyrenees</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tugend, Julie; Manatschal, Gianreto; Kusznir, Nicolas J.; Masini, Emmanuel; Thinon, Isabelle</p> <p>2013-04-01</p> <p>Research conducted at present-day passive continental margins shows more varied crustal architectures than previously assumed. New seismic data together with drill-holes have revealed the occurrence of extremely thinned continental crust in the distal part of the margin as well as exhumed serpentinised sub-continental mantle oceanwards. In addition the understanding of the formation of hyper-extended <span class="hlt">rift</span> <span class="hlt">systems</span> has also greatly benefited from the study of onshore analogs preserved in mountain belts. The Bay of Biscay and Western Pyrenees correspond to a Lower Cretaceous <span class="hlt">rift</span> <span class="hlt">system</span> leading to the development of hyper-extended domains and ultimately oceanic crust in the Bay of Biscay. This domain represents one of the best natural laboratories to study the formation processes and evolution of hyper-extended domains. During late Cretaceous compression, these <span class="hlt">rifted</span> domains were inverted resulting in the present-day Pyrenean mountain belt. In this contribution, we present a new paleogeographic map of the Bay of Biscay-Pyrenean <span class="hlt">rift</span> <span class="hlt">system</span>. We integrate results from previous works and new work using different mapping methods to distinguish distinctive crustal domains related to hyper-extended <span class="hlt">systems</span> both offshore and onshore. We combine seismic interpretations with gravity anomaly inversion and residual depth anomaly analysis to distinguish the different crustal domains across the offshore margin. Onshore, we use an innovative approach based on observations from present-day <span class="hlt">rifted</span> margin architecture associated with classical field work to map the former hyper-extended domains. Another outcome of this work is the creation of a crustal thickness map using gravity inversion linking offshore and onshore domains from the Bay of Biscay to that of the Western-Pyrenees. This multidisciplinary approach enables us to investigate the spatial and temporal evolution of the Bay of Biscay <span class="hlt">rift</span> <span class="hlt">system</span> with the aim of better understanding the formation of hyper-extended domains. Results from both the interpretation of Bay of Biscay <span class="hlt">rift</span> <span class="hlt">system</span> and of the crustal thickness map suggest that (1) the spatial evolution of the hyper-extended <span class="hlt">rift</span> <span class="hlt">system</span> is more complex than previously assumed and (2) the <span class="hlt">rift</span> <span class="hlt">system</span> is strongly segmented at different scales by inherited transfer faults and shear zones bounding different <span class="hlt">rift</span> basins (e.g. the Pamplona fault, onshore) or delimiting major changes of architecture (e.g. the South Armorican Shear Zone, offshore). Through this work, we aim to illustrate and investigate the processes related to the formation the Bay of Biscay-Western Pyrenees <span class="hlt">rift</span> <span class="hlt">system</span>. Moreover, the mapping methods used in this study may be applied to better understand other hyper-extended <span class="hlt">rift</span> <span class="hlt">systems</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5198544','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5198544"><span id="translatedtitle">Sedimentary fill of 1100 Ma mid-continent <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ojakangas, R.W.</p> <p>1986-05-01</p> <p>In the Lake Superior region, four sequences of sedimentary rocks reflect the tectonic-sedimentary framework before, during, and after the magmatic event that resulted in 10,000 m of dominantly basaltic volcanic rocks and large layered gabbroic intrusions. The oldest sequence includes four geographically separated, thin (100 m) pre-volcanic, white to pink, quartzose sandstone units that were deposited in braided alluvial plain-lacustrine environments within the shallow basin that was the initial manifestation of <span class="hlt">rifting</span>. The second sedimentary sequence consists of immature sediment, largely derived from the volcanic sequence and deposited in alluvial fan, fluvial, and lacustrine environments during intervals between extrusive episodes. These red silty to conglomeratic units range from a few centimeters to hundreds of meters in thickness. The Oronto Group and the younger Bayfield Group and their equivalents are post-volcanic, dominantly red-bed sequences of siltstone, sandstone, and conglomerate, deposited in alluvial fan, fluvial, and lacustrine environments within the elongate basin. The Oronto Group (600 m) includes the Copper Harbor Conglomerate, the Nonesuch Shale (gray, carbonaceous, pyritiferous, and cupriferous argillaceous siltstone) and the Freda Sandstone. The Bayfield Group (2100 m) includes the Orienta Sandstone, the Devils Island Sandstone (100 m of orthoquartzite), and the Chequamegon Sandstone. Whereas volcanic detritus is dominant in most of the Oronto Group and the equivalent Solor Church Formation, extrabasinal granitic detritus dominants in the Bayfield Group and its equivalents (Fond de Lac Formation, Hinckley Sandstone, and Jacobsville Sandstone). Paleocurrent data indicate a general basinward transport of sediment during deposition of the four sequences, 1100 Ma(.) to 950 Ma(.).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70021879','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70021879"><span id="translatedtitle">Tectonic and sediment supply control of deep <span class="hlt">rift</span> lake turbidite <span class="hlt">systems</span>: Lake Baikal, Russia</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Nelson, C.H.; Karabanov, E.B.; Colman, Steven M.; Escutia, C.</p> <p>1999-01-01</p> <p>Tectonically influenced half-graben morphology controls the amount and type of sediment supply and consequent type of late Quaternary turbidite <span class="hlt">systems</span> developed in the active <span class="hlt">rift</span> basins of Lake Baikal, Russia. Steep border fault slopes (footwall) on the northwest sides of half-graben basins provide a limited supply of coarser grained clastic material to multiple small fan deltas. These multiple sediment sources in turn laterally feed small (65 km) axially fed elongate mud-rich fans sourced by regional exterior drainage of the Selenga River that supplies large quantities of silt. Basin plain turbidites in the center of the linear basins and axial channels that are controlled by <span class="hlt">rift</span>-parallel faults are fed from, and interfinger with, aprons and fans. The predictability of the turbidite <span class="hlt">systems</span> in Lake Baikal provides the best example yet studied of how tectonics and sediment supply interact to control the development of a wide variety of coeval turbidite <span class="hlt">systems</span> on a single basin floor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.5869C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.5869C"><span id="translatedtitle">Diachronous Growth of Normal Fault <span class="hlt">Systems</span> in Multiphase <span class="hlt">Rift</span> Basins: Structural Evolution of the East Shetland Basin, Northern North Sea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Claringbould, Johan S.; Bell, Rebecca E.; A-L. Jackson, Christopher; Gawthorpe, Robert L.; Odinsen, Tore</p> <p>2015-04-01</p> <p>Our ability to determine the structural evolution and interaction of fault <span class="hlt">systems</span> (kinematically linked group of faults that are in the km to 10s of km scale) within a <span class="hlt">rift</span> basin is typically limited by the spatial extent and temporal resolution of the available data and methods used. Physical and numerical models provide predictions on how fault <span class="hlt">systems</span> nucleate, grow and interact, but these models need to be tested with natural examples. Although field studies and individual 3D seismic surveys can provide a detailed structural evolution of individual fault <span class="hlt">systems</span>, they are often spatially limited and cannot be used examine the interaction of fault <span class="hlt">systems</span> throughout the entire basin. In contrast, regional subsurface studies, commonly conducted on widely spaced 2D seismic surveys, are able to capture the general structural evolution of a <span class="hlt">rift</span> basin, but lack the spatial and temporal detail. Moreover, these studies typically describe the structural evolution of <span class="hlt">rifts</span> as comprising multiple discrete tectonic stages (i.e. pre-, syn- and post-<span class="hlt">rift</span>). This simplified approach does not, however, consider that the timing of activity can be strongly diachronous along and between faults that form part of a kinematically linked <span class="hlt">system</span> within a <span class="hlt">rift</span> basin. This study focuses on the East Shetland Basin (ESB), a multiphase <span class="hlt">rift</span> basin located on the western margin of the North Viking Graben, northern North Sea. Most previous studies suggest the basin evolved in response to two discrete phases of extension in the Permian-Triassic and Middle-Late Jurassic, with the overall geometry of the latter <span class="hlt">rift</span> to be the result of selective reactivation of faults associated with the former <span class="hlt">rift</span>. Gradually eastwards thickening intra-<span class="hlt">rift</span> strata (deposited between two <span class="hlt">rift</span> phases) that form wedges between and within fault blocks have led to two strongly contrasting tectonic interpretations: (i) Early-Middle Jurassic differential thermal subsidence after Permian-Triassic <span class="hlt">rifting</span>; or (ii) Triassic syn-<span class="hlt">rift</span> 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-<span class="hlt">rift</span> deposits are observed along large (>20 km long), NE-SW-striking faults. Elsewhere in the basin, post-<span class="hlt">rift</span> deposits gradually thicken eastward, suggesting differential Triassic post-<span class="hlt">rift</span> 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 <span class="hlt">system</span> 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 <span class="hlt">rifts</span>, highlight the power of 3D mega-merge seismic reflection data, and demonstrate that the conventional <span class="hlt">rift</span> package nomenclature of pre-, syn-, and post-<span class="hlt">rift</span> is difficult to apply at the basin-scale.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015DokES.464.1069K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015DokES.464.1069K"><span id="translatedtitle">Energy structure of seismicity at the southwestern flank of the Baikal <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Klyuchevskii, A. V.; Dem'yanovich, V. M.; Klyuchevskaya, A. A.</p> <p>2015-10-01</p> <p>The energy structure of seismicity at the southwestern flank of the Baikal <span class="hlt">rift</span> <span class="hlt">system</span> (BRS) is analyzed on the data of the annual and total numbers of earthquakes. It is characterized by three parameters of the earthquake occurrence plot: the maximum energy class K max, the slope ?, and the level A 10. The parameters change most significantly after strong earthquakes and the series of aftershocks. With time and the increase in number of earthquakes used, they attain the limiting values that characterize the long-term distribution of shocks by the scale of energy classes. In spite of the unusual modern geodynamics of the Baikal <span class="hlt">rift</span> <span class="hlt">system</span>, the energy structure of seismicity of the southwestern flank corresponds to the model of the stationary seismic process.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.2307D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.2307D"><span id="translatedtitle">Sismotectonics in the western branch of the East African <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Delvaux, Damien; Kervyn, François; Mulumba, Jean-Luc; Kipata, Louis; Sebagenzi, Stanislas; Mavonga, Georges; Macheyeki, Athanas; Temu, Elly Bryan</p> <p>2013-04-01</p> <p>The western branch of the East African <span class="hlt">rift</span> <span class="hlt">system</span> is known of its particular seismic activity with larger magnitude (up to Ms 7.3) and more frequent destructive earthquakes than in the eastern branch. As a contribution to the IGCP 601 project Seismotectonic Map of Africa, we compiled the known active faults, thermal springs and historical seismicity in Central Africa. Using the rich archives of the Royal Museum for Central Africa, publications and own field observations, we present a compilation of available data relative to the current seismotectonic activity along the western branch of the East African <span class="hlt">rift</span> <span class="hlt">system</span>, in DRC, Rwanda, Burundi and Tanzania. Neotectonic activity related to the western <span class="hlt">rift</span> branch is in general well expressed and relatively well studied in the eastern flank of this <span class="hlt">rift</span> branch, in Uganda, Rwanda, Burundi and Tanzania. In contrast, the western flank of this <span class="hlt">rift</span> branch, largely exposed in the DRC, has attracted less attention. However, data collected during the colonial times show significant sismotectonic activity in East DRC, not only in the western flank of the western <span class="hlt">rift</span> branch, but extending far westwards up to the margin of the Congo basin. In particular, our predecessors paid a special attention to the mapping and description of thermal springs, noticing that they are often controlled by active faults. In addition, the operators of the relatively dense network of meteorological stations installed in the DRC, Rwanda and Burundi also recorded were with variable level of completeness and detail the earthquakes that they could felt. This provides a rich database that is used to complete the existing knowledge on historical seismicity. An important effort has still to be paid to identify and map potentially active fault due to poor field accessibility, tropical climate weathering and vegetation coverage. The main problem in the compilation of active fault data is that very few of them have been investigated by paleoseismic trenching. Therefore, this compilation will highlight the pattern of neotectonic faults (those active since the onset of the last and currently active tectonic stage) rather than those of active faults (with proven activity during the last 10 Ka). The first- and second-order stress field of this region is relatively well known thanks to the stress inversion of earthquake focal mechanisms, but the more detailed stress field related to the interaction of fault segments has still to be defined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70021976','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70021976"><span id="translatedtitle">Transect across the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> in the Ross Sea, Antarctica</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Trey, H.; Cooper, A. K.; Pellis, G.; Della, Vedova B.; Cochrane, G.; Brancolini, Giuliano; Makris, J.</p> <p>1999-01-01</p> <p>In 1994, the ACRUP (Antarctic Crustal Profile) project recorded a 670-km-long geophysical transect across the southern Ross Sea to study the velocity and density structure of the crust and uppermost mantle of the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>. Ray-trace modeling of P- and S-waves recorded on 47 ocean bottom seismograph (OBS) records, with strong seismic arrivals from airgun shots to distances of up to 120 km, show that crustal velocities and geometries vary significantly along the transect. The three major sedimentary basins (early-<span class="hlt">rift</span> grabens), the Victoria Land Basin, the Central Trough and the Eastern Basin are underlain by highly extended crust and shallow mantle (minimum depth of about 16 km). Beneath the adjacent basement highs, Coulman High and Central High, Moho deepens, and lies at a depth of 21 and 24 km, respectively. Crustal layers have P-wave velocities that range from 5.8 to 7.0 km/s and S-wave velocities from 3.6 to 4.2 km/s. A distinct reflection (PiP) is observed on numerous OBS from an intra-crustal boundary between the upper and lower crust at a depth of about 10 to 12 km. Local zones of high velocities and inferred high densities are observed and modeled in the crust under the axes of the three major sedimentary basins. These zones, which are also marked by positive gravity anomalies, may be places where mafic dikes and sills pervade the crust. We postulate that there has been differential crustal extension across the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, with greatest extension beneath the early-<span class="hlt">rift</span> grabens. The large amount of crustal stretching below the major <span class="hlt">rift</span> basins may reflect the existence of deep crustal suture zones which initiated in an early stage of the <span class="hlt">rifting</span>, defined areas of crustal weakness and thereby enhanced stress focussing followed by intense crustal thinning in these areas. The ACRUP data are consistent with the prior concept that most extension and basin down-faulting occurred in the Ross Sea during late Mesozoic time, with relatively small extension, concentrated in the western half of the Ross Sea, during Cenozoic time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007E%26PSL.255..133H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007E%26PSL.255..133H"><span id="translatedtitle">The transition from diffuse to focused extension: Modeled evolution of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huerta, Audrey D.; Harry, Dennis L.</p> <p>2007-03-01</p> <p>Two distinct stages of extension are recognized in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">system</span> (WARS). During the first stage, beginning in the Late Cretaceous, extension was broadly distributed throughout much of West Antarctica. A second stage of extension in the late Paleogene was focused primarily in the Victoria Land Basin, near the boundary with the East Antarctic craton. The transition to focused extension was roughly coeval with volcanic activity and strike-slip faulting in the adjacent Transantarctic Mountains. This spatial and temporal correspondence suggests that the transition in extensional style could be the result of a change in plate motions or impingement of a plume. Here we use finite element models to study the processes and conditions responsible for the two-stage evolution of <span class="hlt">rifting</span> in the WARS. Model results indicate that the transition from a prolonged period of broadly distributed extension to a later period of focused <span class="hlt">rifting</span> did not require a change in the regional stress regime (changes in plate motion), or deep mantle thermal state (impingement of a plume). Instead, we attribute the transition from diffuse to focused extension to an early stage dominated by the initially weak accreted lithosphere of West Antarctica, and a later stage that concentrated around a secondary weakness located at the boundary between the juvenile West Antarctica lithosphere and Precambrian East Antarctic craton. The modeled transition in extension from the initially weak West Antarctica region to the secondary weakness at the West Antarctic-East Antarctic boundary is precipitated by strengthening of the West Antarctica lithosphere during syn-extensional thinning and cooling. The modeled syn-extensional strengthening of the WARS lithosphere promotes a wide-<span class="hlt">rift</span> mode of extension between 105 and ˜ 65 Ma. By ˜ 65 Ma most of the extending WARS region becomes stronger than the area immediately adjacent to the East Antarctic craton and extension becomes concentrated near the East Antarctic/West Antarctic boundary, forming the Victoria Land Basin region. Mantle necking in this region leads to syn-extensional weakening that promotes a narrow-<span class="hlt">rift</span> mode of extension that becomes progressively more focused with time, resulting in formation of the Terror <span class="hlt">Rift</span> in the western Victoria Land Basin. The geodynamic models demonstrate that the transition from diffuse to focused extension occurs only under a limited set of initial and boundary conditions, and is particularly sensitive to the pre-<span class="hlt">rift</span> thermal state of the crust and upper mantle. Models that predict diffuse extension in West Antarctica followed by localization of <span class="hlt">rifting</span> near the boundary between East and West Antarctica require upper mantle temperatures of 730 ± 50 °C and sufficient concentration of heat producing elements in the crust to account for ˜ 50% of the upper mantle temperature. Models with upper mantle temperatures < ca. 680 °C and/or less crustal heat production initially undergo diffuse extension in West Antarctica, and quickly develop a lithospheric neck at the model edge furthest from East Antarctica. Models with upper mantle temperatures > ca. 780 °C do not develop focused <span class="hlt">rifts</span>, and predict indefinite diffuse extension in West Antarctica.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T43C2693M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T43C2693M"><span id="translatedtitle">Nature of the Mantle Sources and Bearing on Tectonic Evolution in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mukasa, S. B.; Rilling-Hall, S.; Marcano, M. C.; Wilson, T. J.; Lawver, L. A.; LeMasurier, W. E.</p> <p>2012-12-01</p> <p>We collected samples from subaerial lava flows and dredged some Neogene basanitic lavas from seven volcanic edifices in the Ross Sea, Antarctica - a part of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (WARS) and one of the world's largest alkaline magmatic provinces - for a study aimed at two principal objectives: (1) Geochemical interrogation of the most primitive magmatic rocks to try and understand the nature of the seismically abnormal mantle domain recently identified beneath the shoulder of the Transantarctic Mountains (TAM), the Ross Sea Embayment and Marie Byrd Land; and (2) Using 40Ar/39Ar geochronology to establish a temporal link between magmatism and tectonism, particularly in the Terror <span class="hlt">Rift</span>. We have attempted to answer the questions of whether magmatism is due to a hot mantle or wet mantle, and whether <span class="hlt">rifting</span> in the area triggered magmatic activity or vice versa. Results show that the area does not have an age-progressive hotspot track, and the magmatism post-dates the main phase of extension along the Terror <span class="hlt">Rift</span> within the WARS, which supports a decompression-melting model without the benefit of a significant thermal anomaly. In fact, preliminary volatile measurements on olivine-hosted melt inclusions have yielded water concentrations in excess of 2 wt%, indicating that flux melting was an important complementary process to decompression melting. The major oxide compositions of lavas in the WARS are best matched to experimental melts of carbonated peridotite, though garnet pyroxenite can also be a minor source. The Pb and Nd isotopic <span class="hlt">systems</span> are decoupled from each other, suggesting removal of fluid-mobile elements from the mantle source possibly during the long history of subduction along the Paleo-Pacific margin of Gondwana. Extremely unradiogenic 187Os/188Os ranging to as low as 0.1081 ± 0.0001 hints at the involvement of lithospheric components in generation of magmas in the WARS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1987Tectp.143..217G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1987Tectp.143..217G"><span id="translatedtitle">On the geotectonic nature of the Fen-Wei <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guoda, Chen</p> <p>1987-11-01</p> <p>The Fen-Wei <span class="hlt">rift</span> <span class="hlt">system</span>, 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 <span class="hlt">rift</span> <span class="hlt">system</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span> 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 <span class="hlt">rift</span> 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).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T43A4705S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T43A4705S"><span id="translatedtitle">Regional 3D Numerical Modeling of the Lithosphere-Mantle <span class="hlt">System</span>: Implications for Continental <span class="hlt">Rift</span>-Parallel Surface Velocities</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stamps, S.; Bangerth, W.; Hager, B. H.</p> <p>2014-12-01</p> <p>The East African <span class="hlt">Rift</span> <span class="hlt">System</span> (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-<span class="hlt">rift</span> motions that contradict this simple model. Here, we test the role of mantle flow at the <span class="hlt">rift</span>-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-<span class="hlt">rift</span> in the Western Branch can drive upper mantle flow that is consistent with geodetic observations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1614484S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1614484S"><span id="translatedtitle">Mode of <span class="hlt">rifting</span> in magmatic-rich setting: Tectono-magmatic evolution of the Central Afar <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stab, Martin; Bellahsen, Nicolas; Pik, Raphaël; Leroy, Sylvie; Ayalew, Dereje</p> <p>2014-05-01</p> <p>Observation of deep structures related to break-up processes at volcanic passive margins (VPM) is often a troublesome exercise: thick pre- to syn-breakup seaward-dipping reflectors (SDR) usually mask the continent-ocean boundary and hide the syn-<span class="hlt">rift</span> tectonic structures that accommodate crustal stretching and thinning. Some of the current challenges are about clarifying 1) if tectonic stretching fits the observed thinning and 2) what is the effect of continuous magma supply and re-thickening of the crust during extension from a rheological point of view? The Afar region in Ethiopia is an ideal natural laboratory to address those questions, as it is a highly magmatic <span class="hlt">rift</span> that is probably close enough to breakup to present some characteristics of VPM. Moreover, the structures related to <span class="hlt">rifting</span> since Oligocene are out-cropping, onshore and well preserved. In this contribution, we present new structural field data and lavas (U-Th/He) datings along a cross-section from the Ethiopian Plateau, through the marginal graben down to the Manda-Hararo active <span class="hlt">rift</span> axis. We mapped continent-ward normal fault array affecting highly tilted trapp series unconformably overlain by tilted Miocene (25-7 Ma) acid series. The main extensional and necking/thinning event took place during the end of this Miocene magmatic episode. It is itself overlain by flat lying Pliocene series, including the Stratoid. Balanced cross-sections of those areas allow us to constrain a surface stretching factor of about 2.1-2.9. Those findings have the following implications: - High beta factor constrained from field observations is at odd with thinning factor of ~1.3 predicted by seismic and gravimetric studies. We propose that the continental crust in Central Afar has been re-thickened by the emplacement of underplated magma and SDR. - The deformation in Central Afar appears to be largely distributed through space and time. It has been accommodated in a 200-300 km wide strip being a diffuse incipient plate boundary until the formation of present-day magmatic segments. - The difference in tectono-magmatic style between Central Afar (distributed extension and thick crust) and Northern Afar, i.e. Erta Ale segment (narrow graben, thin crust) may be explained by the difference of magma volume (extruded & underplated) brought to the crust during extension. Magma supply in Central Afar allows the crust to be stretched without subsequent thinning despite high degree of extension. - Presence or absence of thinned crust does not necessarily announce break-up. It may occur in both Central and Northern Afar, depending upon a sudden change in magmatic regime. The striking difference between the two tectono-magmatic styles of Central and Northern Afar are probably due to a combination of: 1) magma supply that affects both crustal thickness and rheology, 2) the amount of extension that may be higher in Central Afar, 3) the distance to the magmatic province, and 4) the presence of an early syn-<span class="hlt">rift</span> transfer/transform between the two segments that might have controlled the distribution of magmatic activity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015IJEaS.tmp...40K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015IJEaS.tmp...40K"><span id="translatedtitle">The Rwenzori Mountains, a Palaeoproterozoic crustal shear belt crossing the Albertine <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koehn, D.; Link, K.; Sachau, T.; Passchier, C. W.; Aanyu, K.; Spikings, A.; Harbinson, R.</p> <p>2015-04-01</p> <p>This contribution discusses the development of the Palaeoproterozoic Buganda-Toro belt in the Rwenzori Mountains and its influence on the western part of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> in Uganda. The Buganda-Toro belt is composed of several thick-skinned nappes consisting of Archaean Gneisses and Palaeoproterozoic cover units that are thrusted northwards. The high Rwenzori Mountains are located in the frontal unit of this belt with retrograde greenschist facies gneisses towards the north, which are unconformably overlain by metasediments and amphibolites. Towards the south, the metasediments are overthrust by the next migmatitic gneiss unit that belongs to a crustal-scale nappe. The southwards dipping metasedimentary and volcanic sequence in the high Rwenzori Mountains shows an inverse metamorphic grade with greenschist facies conditions in the north and amphibolite facies conditions in the south. Early D1 deformation structures are overgrown by cordierite, which in turn grows into D2 deformation, representing the major northwards directed thrusting event. We argue that the inverse metamorphic gradient develops because higher grade rocks are exhumed in the footwall of a crustal-scale nappe, whereas the exhumation decreases towards the north away from the nappe leading to a decrease in metamorphic grade. The D2 deformation event is followed by a D3 E-W compression, a D4 with the development of steep shear zones with a NNE-SSW and SSE-NNW trend including the large Nyamwamba shear followed by a local D5 retrograde event and D6 brittle reverse faulting. The Palaeoproterozoic Buganda-Toro belt is relatively stiff and crosses the NNE-SSW running <span class="hlt">rift</span> <span class="hlt">system</span> exactly at the node where the highest peaks of the Rwenzori Mountains are situated and where the Lake George <span class="hlt">rift</span> terminates towards the north. Orientation of brittle and ductile fabrics show some similarities indicating that the cross-cutting Buganda-Toro belt influenced <span class="hlt">rift</span> propagation and brittle fault development within the Rwenzori Mountains and that this stiff belt may form part of the reason why the Rwenzori Mountains are relatively high within the <span class="hlt">rift</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li class="active"><span>4</span></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_4 --> <div id="page_5" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li class="active"><span>5</span></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="81"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T13A2512A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T13A2512A"><span id="translatedtitle">Melt generation in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>: the volatile legacy of Gondwana subduction?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aviado, K.; Rilling-Hall, S.; Mukasa, S. B.; Bryce, J. G.; Cabato, J.</p> <p>2013-12-01</p> <p>The West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (WARS) represents one of the largest extensional alkali volcanic provinces on Earth, yet the mechanisms responsible for driving <span class="hlt">rift</span>-related magmatism remain controversial. The failure of both passive and active models of decompression melting to explain adequately the observed volume of volcanism has prompted debate about the relative roles of thermal plume-related melting and ancient subduction-related flux melting. The latter is supported by roughly 500 Ma of subduction along the paleo-Pacific margin of Gondwana, although both processes are capable of producing the broad seismic anomaly imaged beneath most of the Southern Ocean. Olivine-hosted melt inclusions from basanitic lavas provide a means to evaluate the volatile budget of the mantle responsible for active <span class="hlt">rifting</span> beneath the WARS. We present H2O, CO2, F, S and Cl concentrations determined by SIMS and major oxide compositions by EMPA for olivine-hosted melt inclusions from lavas erupted in Northern Victoria Land (NVL) and Marie Byrd Land (MBL). The melt inclusions are largely basanitic in composition (4.05 - 17.09 wt % MgO, 37.86 - 45.89 wt % SiO2, and 1.20 - 5.30 wt % Na2O), and exhibit water contents ranging from 0.5 up to 3 wt % that are positively correlated with Cl and F. Coupling between Cl and H2O indicates metasomatic enrichment by subduction-related fluids produced during dehydration reactions; coupling between H2O and F, which is more highly retained in subducting slabs, may be related to partial melting of slab remnants [1]. Application of source lithology filters [2] to whole rock major oxide data shows that primitive lavas (MgO wt % >7) from the Terror <span class="hlt">Rift</span>, considered the locus of on-going tectonomagmatic activity, have transitioned from a pyroxenite source to a volatilized peridotite source over the past ~4 Ma. Integrating the volatile data with the modeled characteristics of source lithologies suggests that partial melting of lithosphere modified by subduction processes is the source of pyroxenite and volatiles in the mantle beneath the present-day <span class="hlt">rift</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.3832H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.3832H"><span id="translatedtitle">Seismic anisotropy of the lithosphere/asthenosphere <span class="hlt">system</span> beneath the Rwenzori region of the East-African <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Homuth, Benjamin; Löbl, Ulrike; Batte, Arthur; Link, Klemens; Kasereka, Celestine; Rümpker, Georg</p> <p>2014-05-01</p> <p>We present results from a temporary seismic network of 32 broad-band stations located around the Rwenzori region of the Albertine <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span>-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 <span class="hlt">rift</span> is located within the mantle. We use finite-frequency waveform modeling to test different models of anisotropy within the lithosphere/asthenosphere <span class="hlt">system</span> of the <span class="hlt">rift</span>. The results show that the <span class="hlt">rift</span>-parallel fast polarizations are consistent with HTI anisotropy caused by <span class="hlt">rift</span>-parallel magmatic intrusions or lenses located within the lithospheric mantle - as it would be expected during the early stages of continental <span class="hlt">rifting</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JAfES.101..232M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JAfES.101..232M"><span id="translatedtitle">History of the development of the East African <span class="hlt">Rift</span> <span class="hlt">System</span>: A series of interpreted maps through time</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Macgregor, Duncan</p> <p>2015-01-01</p> <p>This review paper presents a series of time reconstruction maps of the 'East African <span class="hlt">Rift</span> <span class="hlt">System</span>' ('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 <span class="hlt">rifting</span> commenced in the petroliferous South Lokichar Basin of northern Kenya in the Late Eocene to Oligocene, though there seem to be few further deep <span class="hlt">rifts</span> of this age other than those immediately adjoining it. At various times during the Mid-Late Miocene, a series of small <span class="hlt">rifts</span> and depressions formed between Ethiopia and Malawi, heralding the main regional <span class="hlt">rift</span> subsidence phase and further <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1991Tectp.191...55C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1991Tectp.191...55C"><span id="translatedtitle">Post-Pan-African tectonic evolution of South Malawi in relation to the Karroo and recent East African <span class="hlt">rift</span> <span class="hlt">systems</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Castaing, C.</p> <p>1991-05-01</p> <p>Structural studies conducted in the Lengwe and Mwabvi Karroo basins and in the basement in South Malawi, using regional maps and published data extended to cover Southeast Africa, serve to propose a series of geodynamic reconstructions which reveal the persistence of an extensional tectonic regime, the minimum stress ?3 of which has varied through time. The period of Karroo <span class="hlt">rifting</span> and the tholeiitic and alkaline magmatism which terminated it, were controlled by NW-SE extension, which resulted in the creation of roughly NE-SW troughs articulated by the Tanganyika-Malawi and Zambesi pre-transform <span class="hlt">systems</span>. These were NW-SE sinistral-slip <span class="hlt">systems</span> with directions of movement dipping slightly to the Southeast, which enabled the Mwanza fault to play an important role in the evolution of the Karroo basins of the Shire Valley. The Cretaceous was a transition period between the Karroo <span class="hlt">rifting</span> and the formation of the Recent East African <span class="hlt">Rift</span> <span class="hlt">System</span>. Extension was NE-SW, with some evidence for a local compressional episode in the Lengwe basin. Beginning in the Cenozoic, the extension once more became NW-SE and controlled the evolution in transtension of the Recent East African <span class="hlt">Rift</span> <span class="hlt">System</span>. This history highlights the major role of transverse faults <span class="hlt">systems</span> dominated by strike-slip motion in the evolution and perpetuation of the continental <span class="hlt">rift</span> <span class="hlt">systems</span>. These faults are of a greater geological persistence than the normal faults bounding the grabens, especially when they are located on major basement anisotropies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T11C4571C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T11C4571C"><span id="translatedtitle">Tectonoestratigraphic and Thermal Models of the Tiburon and Wagner Basins, northern Gulf of California <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Contreras, J.; Ramirez Zerpa, N. A.; Negrete-Aranda, R.</p> <p>2014-12-01</p> <p>The northern Gulf of California <span class="hlt">Rift</span> <span class="hlt">System</span> consist sofa series faults that accommodate both normal and strike-slip motion. The faults formed a series of half-greens filled with more than 7 km of siliciclastic suc­cessions. Here, we present tectonostratigraphic and heat flow models for the Tiburón basin, in the southern part of the <span class="hlt">system</span>, and the Wag­ner basin in the north. The models are constrained by two-dimensional seis­mic lines and by two deep boreholes drilled by PEMEX­-PEP. Analysis of the seismic lines and models' results show that: (i) subsidence of the basins is controlled by high-angle normal faults and by flow of the lower crust, (ii) basins share a common history, and (iii) there are significant differences in the way brittle strain was partitioned in the basins, a feature frequently observed in <span class="hlt">rift</span> basins. On one hand, the bounding faults of the Tiburón basin have a nested geometry and became active following a west-to-east sequence of activation. The Tiburon half-graben was formed by two pulses of fault activity. One took place during the protogulf extensional phase in the Miocene and the other during the opening of Gulf of California in the Pleistocene. On the other hand, the Wagner basin is the result of two fault generations. During the late-to middle Miocene, the west-dipping Cerro Prieto and San Felipe faults formed a domino array. Then, during the Pleistocene the Consag and Wagner faults dissected the hanging-wall of the Cerro Prieto fault forming the modern Wagner basin. Thermal modeling of the deep borehole temperatures suggests that the heat flow in these basins in the order of 110 mW/m2 which is in agreement with superficial heat flow measurements in the northern Gulf of California <span class="hlt">Rift</span> <span class="hlt">System</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T21A2519Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T21A2519Z"><span id="translatedtitle">Active fault <span class="hlt">systems</span> of the Kivu <span class="hlt">rift</span> and Virunga volcanic province, and implications for geohazards</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zal, H. J.; Ebinger, C. J.; Wood, D. J.; Scholz, C. A.; d'Oreye, N.; Carn, S. A.; Rutagarama, U.</p> <p>2013-12-01</p> <p>H Zal, C Ebinger, D. Wood, C. Scholz, N. d'Oreye, S. Carn, U. Rutagarama The weakly magmatic Western <span class="hlt">rift</span> <span class="hlt">system</span>, East Africa, is marked by fault-bounded basins filled by freshwater lakes that record tectonic and climatic signals. One of the smallest of the African Great Lakes, Lake Kivu, represents a unique geohazard owing to the warm, saline bottom waters that are saturated in methane, as well as two of the most active volcanoes in Africa that effectively dam the northern end of the lake. Yet, the dynamics of the basin <span class="hlt">system</span> and the role of magmatism were only loosely constrained prior to new field and laboratory studies in Rwanda. In this work, we curated, merged, and analyzed historical and digital data sets, including spectral analyses of merged Shuttle Radar Topography Mission topography and high resolution CHIRP bathymetry calibrated by previously mapped fault locations along the margins and beneath the lake. We quantitatively compare these fault maps with the time-space distribution of earthquakes located using data from a temporary array along the northern sector of Lake Kivu, as well as space-based geodetic data. During 2012, seismicity rates were highest beneath Nyiragongo volcano, where a range of low frequency (1-3 s peak frequency) to tectonic earthquakes were located. Swarms of low-frequency earthquakes correspond to periods of elevated gas emissions, as detected by Ozone Monitoring Instrument (OMI). Earthquake swarms also occur beneath Karisimbi and Nyamuragira volcanoes. A migrating swarm of earthquakes in May 2012 suggests a sill intrusion at the DR Congo-Rwanda border. We delineate two fault sets: SW-NE, and sub-N-S. Excluding the volcano-tectonic earthquakes, most of the earthquakes are located along subsurface projections of steep border faults, and intrabasinal faults calibrated by seismic reflection data. Small magnitude earthquakes also occur beneath the uplifted <span class="hlt">rift</span> flanks. Time-space variations in seismicity patterns provide a baseline for hazard assessment, and guide future studies in the Kivu <span class="hlt">rift</span>, and document the role of magmatism in <span class="hlt">rifting</span> processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.6082H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.6082H"><span id="translatedtitle">Seismic hazard assessment of the Kivu <span class="hlt">rift</span> segment based on a new sismo-tectonic zonation model (Western Branch of the East African <span class="hlt">Rift</span> <span class="hlt">system</span>)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Havenith, Hans-Balder; Delvaux, Damien</p> <p>2015-04-01</p> <p>In the frame of the Belgian GeoRisCA multi-risk assessment project focused on the Kivu and Northern Tanganyika Region, a seismic hazard map has been produced for this area. It is based on a on a recently re-compiled catalogue using various local and global earthquake catalogues. The use of macroseismic epicenters determined from felt earthquakes allowed to extend the time-range back to the beginning of the 20th century, thus spanning about 100 years. The magnitudes have been homogenized to Mw and the coherence of the catalogue has been checked and validated. The seismo-tectonic zonation includes 10 seismic source areas that have been defined on the basis of the regional geological structure, neotectonic fault <span class="hlt">systems</span>, basin architecture and distribution of earthquake epicenters. The seismic catalogue was filtered by removing obvious aftershocks and Gutenberg-Richter Laws were determined for each zone. On the basis of this seismo-tectonic information and existing attenuation laws that had been established by Twesigomwe (1997) and Mavonga et al. (2007) for this area, seismic hazard has been computed with the Crisis 2012 (Ordaz et al., 2012) software. The outputs of this assessment clearly show higher PGA values (for 475 years return period) along the <span class="hlt">Rift</span> than the previous estimates by Twesigomwe (1997) and Mavonga (2007) while the same attenuation laws had been used. The main reason for these higher PGA values is likely to be related to the more detailed zonation of the <span class="hlt">Rift</span> structure marked by a strong gradient of the seismicity from outside the <span class="hlt">rift</span> zone to the inside. Mavonga, T. (2007). An estimate of the attenuation relationship for the strong ground motion in the Kivu Province, Western <span class="hlt">Rift</span> Valley of Africa. Physics of the Earth and Planetary Interiors 62, 13-21. Ordaz M, Martinelli F, Aguilar A, Arboleda J, Meletti C, D'Amico V. (2012). CRISIS 2012, Program for computing seismic hazard. Instituto de Ingeniería, Universidad Nacional Autónoma de México. Twesigomwe, E. (1997). Probabilistic seismic hazard assessment of Uganda, Ph.D. Thesis, Dept. of Physics, Makare University, Uganda.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5872335','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5872335"><span id="translatedtitle">Age relationships for magmatic units of Mid-Continent <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Van Schmus, W.R.</p> <p>1989-03-01</p> <p>K-Ar ages ranging from about 600 to 1000 Ma have recently been reported for gabbro and basalt recovered from the Texaco 1 Poersch well in Kansas. This has prompted suggestions that <span class="hlt">rift</span> magmatism there may be distinctly younger than that in the Lake Superior region, and that development of the <span class="hlt">rift</span> may have lasted several hundred million years. Review of ages from Keweenawan volcanic and plutonic rocks in the Lake Superior region shows that the best results are obtained from U-Pb analyses of zircon and baddeleyite; recent published results range from 1087 to 1108 Ma, with uncertainties on individual ages of /plus minus/ 4 m.y. This finding is consistent with earlier reported U-Pb zircon results. Virtually all other techniques are susceptible to geologic error and generally yield ages of significant less than 1100 Ma. The reliability decreases approximately in the sequence Rb-Sr (whole rock), K-Ar (biotite), Ar/sup 39/-Ar/sup 40/ (whole rock), K-Ar (whole rock), with fresh, coarse-grained plutonic rocks yielding older ages than altered, fine-grained volcanic rocks. K-Ar data on altered, fine-grained mafic rocks, therefore, are very poor indicators of original crystallization ages. Since the rocks from the Texaco 1 Poersch well are fine grained and slightly to moderately altered, their true ages are probably substantially older than 800-900 Ma. Interpretations based on the K-Ar ages from this well are ill advised; tectonic interpretation of the Mid-Continent <span class="hlt">rift</span> <span class="hlt">system</span> must wait for more accurate results. Several possibilities exist for obtaining more reliable ages from samples of the Poersch well and other, older wells in the region. These studies are in progress, and any available results will be presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1614255D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1614255D"><span id="translatedtitle">Ambient Noise Tomography of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> in Mozambique</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Domingues, Ana; Custódio, Susana; Chamussa, José; Silveira, Graça; Chang, Sung-Joon; Lebedev, Sergei; Ferreira, Ana; Fonseca, João</p> <p>2014-05-01</p> <p>Project MOZART - MOZAmbique <span class="hlt">Rift</span> 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 <span class="hlt">Rift</span> <span class="hlt">System</span> (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 <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5011365','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5011365"><span id="translatedtitle">The influence of the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> on known and potential mineral resources in Nebraska</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Carlson, M.P. . Nebraska Geological Survey)</p> <p>1993-03-01</p> <p>Twenty wells have encountered Keweenawan-age volcanics and 18 have drilled Keweenawan-age sediments in southeastern Nebraska. The central horst of the Nebraska Segment of the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> subcrops at the Precambrian surface and is composed of volcanics except for small areas of sediment-filled grabens. The flanking basins contain younger Keweenawan-age sediments estimated to range up to four kilometers in thickness although maximum penetration by drilling has been only about 500 meters. Indications of potential resources have been noted in both the volcanics and the sediments associated with the <span class="hlt">rift</span>. Zinc and copper have been found in trace amounts in a core from the Keweenawan volcanics. A core of the older graben-filling-sediments consists of siltstone and sandstone with occasional gravel-boulder conglomerates, all tightly cemented. Calcite-lined fractures contain traces of pyrite, but no detailed mineralogical analysis has been done. A single analysis of a dark mudstone interval showed a bitumen content of 3 ppm. The sedimentary section in this core is believed to be the environmental equivalent of the Copper Harbor-Nonesuch section in the Lake Superior region. The sands and silts in the flanking basins are known from only rotary drill cuttings and although permeability and porosity appear high no testing has been done. The combination of a reservoir rock and Nonesuch-like source rocks suggest potential for petroleum exploration. Reactivation of <span class="hlt">rift</span> structures during the Phanerozoic has provided mineral potential in younger rocks. Traps were created for mineral-laden fluids and petroleum. Uplift and erosion has allowed access to older bedrock for quarries and mines.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMDI33A4294H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMDI33A4294H"><span id="translatedtitle">Seismic Anisotropy of the Lithosphere/Asthenosphere <span class="hlt">System</span> Beneath the Rwenzori Region of the East-African <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Homuth, B.; Löbl, U.; Batte, A.; Link, K.; Kasereka, C.; Rumpker, G.</p> <p>2014-12-01</p> <p>We present results from a temporary seismic network of 32 broad-band stations located around the Rwenzori region of the Albertine <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span>-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 <span class="hlt">rift</span> is located within the mantle. We use finite-frequency waveform modeling to test different models of anisotropy within the lithosphere/asthenosphere <span class="hlt">system</span> of the <span class="hlt">rift</span>. The results show that the <span class="hlt">rift</span>-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 <span class="hlt">rifting</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014IJEaS.tmp...96S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014IJEaS.tmp...96S"><span id="translatedtitle">The East African <span class="hlt">Rift</span> <span class="hlt">System</span> and the impact of orographic changes on regional climate and the resulting aridification</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sommerfeld, Anja; Prömmel, Kerstin; Cubasch, Ulrich</p> <p>2014-11-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) induced by tectonic forcing during the last 20 million years. To investigate the impact of the orography and especially of the <span class="hlt">rifts</span>, 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 <span class="hlt">rifts</span> 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 <span class="hlt">rifts</span> are elevated, resulting in a smoothed orography structure with less altitude difference between the shoulders and <span class="hlt">rifts</span>. 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 <span class="hlt">rift</span> 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 <span class="hlt">rifts</span> only in the northern model domain.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012SedG..281...21F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012SedG..281...21F"><span id="translatedtitle">Footwall progradation in syn-<span class="hlt">rift</span> carbonate platform-slope <span class="hlt">systems</span> (Early Jurassic, Northern Apennines, Italy)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fabbi, Simone; Santantonio, Massimo</p> <p>2012-12-01</p> <p>The so-called Umbria-Marche Domain of Northern Apennines represents a vast depositional <span class="hlt">system</span>, 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 <span class="hlt">rifting</span> 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 <span class="hlt">rifting</span> had ceased, so that the Pliensbachian to Early Cretaceous hangingwall deposits represent a post-<span class="hlt">rift</span> 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-<span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70015574','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70015574"><span id="translatedtitle">Mineralization potential along the trend of the Keweenawan- age Central North American <span class="hlt">Rift</span> <span class="hlt">System</span> in Iowa, Nebraska, and Kansas</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Berendsen, P.</p> <p>1989-01-01</p> <p>The tectonic and sedimentary environment of the Central North American <span class="hlt">Rift</span> <span class="hlt">System</span> (CNARS) provides an excellent setting for major mineral deposits. Major north-northeast-trending high-angle normal or reverse faults and northwest-trending transcurrent fault <span class="hlt">systems</span> may exercise control over ore forming processes. Gabbro and basalt are the dominant igneous rock types. Carbonatite and kimberlite occur in Nebraska and Kansas. Concentrations of Cu, Ni, Co, Ti, Au, Ag and PG minerals are known to occur in this setting. Arkosic sandstone, siltstone, shale, and minor carbonate units occur on top of the <span class="hlt">rift</span> basalts and in flanking basins where they may reach thicknesses of 10 km (6 miles). The potential for stratiform or unconformity-related metalliferous deposits should be considered. The <span class="hlt">rift</span> as a whole remains largely unexplored.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/22026612','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/22026612"><span id="translatedtitle">Ancient origin and recent divergence of a haplochromine cichlid lineage from isolated water bodies in the East African <span class="hlt">Rift</span> <span class="hlt">system</span>.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hermann, C M; Sefc, K M; Koblmüller, S</p> <p>2011-11-01</p> <p>Phylogenetic analysis identified haplochromine cichlids from isolated water bodies in the eastern branch of the East African <span class="hlt">Rift</span> <span class="hlt">system</span> as an ancient lineage separated from their western sister group in the course of the South Kenyan-North Tanzanian <span class="hlt">rift</span> <span class="hlt">system</span> formation. Within this lineage, the close phylogenetic relatedness among taxa indicates a recent common ancestry and historical connections between now separated water bodies. In connection with a total lack of local genetic diversity attributable to population bottlenecks, the data suggest cycles of extinction and colonization in the unstable habitat provided by the small lakes and rivers in this geologically highly active area. PMID:22026612</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993Tecto..12..441B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993Tecto..12..441B"><span id="translatedtitle">Prebreakup geology of the Gulf of Mexico-Caribbean: Its relation to Triassic and Jurassic <span class="hlt">rift</span> <span class="hlt">systems</span> of the region</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bartok, Peter</p> <p>1993-01-01</p> <p>A review of the prebreakup geology of west central Pangea, comprising northern South America, the Gulf of Mexico, and West Africa, combined with a study of the Mesozoic <span class="hlt">rift</span> trends of the region confirms a relation between the <span class="hlt">rift</span> <span class="hlt">systems</span> and the underlying older grain of deformation. The prebreakup 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 west central Pangea. Along the northern South American margin and Yucatan a paleo northeast trending Pan-African aged fold belt is documented. A second <span class="hlt">system</span> is observed along West Africa extending from the High Atlas to the Mauritanides and Rockelides. Similar aged orogenies in the Appalachians are compared. 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 <span class="hlt">system</span> is northeast-southwest and essentially parallels the Guayana craton and West African and eastern North American cratons. Mesozoic rifling closely followed either the Precambrian trends or the late Paleozoic orogenic belt. The Triassic component focused along the western portions of the Gulf of Mexico continuing into eastern Mexico and western South America. The Jurassic <span class="hlt">rift</span> trend followed along the separation between Yucatan and northern South America. At Lake Maracaibo the Jurassic <span class="hlt">rift</span> <span class="hlt">system</span> eventually overlaps the Triassic <span class="hlt">rifts</span>. The Jurassic <span class="hlt">rift</span> resulted in the "Hispanic Corridor" that permitted Tethyan and Pacific marine faunas to mix at a time when the Gulf of Mexico underwent continental sedimentation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5993676','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5993676"><span id="translatedtitle">Stratigraphy of Mid-Continent <span class="hlt">rift</span> <span class="hlt">system</span> in Kansas as revealed by recent exploration wells</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Newell, K.D.; Berendsen, P.; Watney, W.L.; Doveton, J.H.; Steeples, D.</p> <p>1989-03-01</p> <p>The Texaco 1 Poersch well in Kansas (11,300 ft TD) was the first significant exploration test of the Mid-Continent <span class="hlt">Rift</span> <span class="hlt">System</span> (MRS). An upper succession of <span class="hlt">rift</span>-related rocks (2846-7429 ft) contains approximately 90% mafic igneous rocks with minor pegmatites and 10% oxidized siltstone and arkose. Arkose and subarkose with minor siltstone and shale make up 90% of a lower succession (7429 ft to TD). The remaining lower succession is composed of mafic igneous rocks. Mafic rocks are typically alkali basalts. Individual flows (detected by presence of amygdules, interflow sediments, compositional differences, and oxidized zones) range in thickness from 20 to 250 ft. Sedimentary rocks in the lower succession are divided into three sequences, each 1000-2000 ft thick. The sequences overlie relatively thin mafic flows or intrusives. Each sequence is generally composed of fining-upward units (50-150 ft thick) attributed to episodic movement and erosion of fault blocks in alluvial fan-dominated sedimentary environments. Shales and siltstones are too oxidized to be viable petroleum source rocks, but gray shale with approximately 0.5% total organic carbon was found in the MRS by the 1-4 Finn well, 21 mi to the northeast. Geologic examination of several shallower Precambrian tests holes near 1 Poersch shows considerable variability in sedimentary and tectonic settings along the MRS. Correlation between wells in Kansas and exposed areas of the MRS is still problematic. Additional wells will be necessary to better understand its hydrocarbon potential.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70138180','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70138180"><span id="translatedtitle">Variations in the reflectivity of the moho transition zone beneath the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> of North America: results from true amplitude analysis of GLIMPCE data</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hutchinson, Deborah R.; Lee, Myung W.; Behrendt, John C.; Cannon, William F.; Green, Adrian</p> <p>1992-01-01</p> <p>True amplitude processing of The Great Lakes International Multidisciplinary Program on Crustal Evolution seismic reflection data from the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> of North America shows large differences in the reflectivity of the Moho transition zone beneath the axial <span class="hlt">rift</span>, beneath the <span class="hlt">rift</span> flanks, and outside of the <span class="hlt">rift</span>. The Moho reflection from the axial <span class="hlt">rift</span> has a discontinuous, diffractive character marginally stronger (several decibels) than an otherwise transparent lower crust and upper mantle. Beneath the axial <span class="hlt">rift</span>, Moho is interpreted to be a synrift igneous feature. Beneath the <span class="hlt">rift</span> flanks, the reflectivity of the Moho transition is generally well developed with two identifiable boundaries, although in places it is weakly reflective to nonreflective, similar to Moho outside the <span class="hlt">rift</span>. The two boundaries are interpreted as the base of essentially intact, although stretched, prerift Archean crust (upper boundary) and new synrift Moho 1-2 s (6-7 km) deeper (lower boundary). Beneath the <span class="hlt">rift</span> flanks, the layered reflection Moho transition results from the preexisting crustal composition and fabric modified by synrift igneous processes and extensional tectonic/metamorphic processes. The geologic evidence for extensive basaltic magmatism in the <span class="hlt">rift</span> is the basis for interpreting the Moho signature as a Keweenawan structure that has been preserved for 1.1 b.y. Extension and magmatism appear to enhance reflectivity in the lower crust and Moho transition zone only where stretching factors are moderate (<span class="hlt">rift</span> flanks) and not where they are extreme (axial <span class="hlt">rift</span>). This leads to the prediction that the reflectivity across analogous volcanic passive continental margins should be greatest beneath the moderately stretched continental shelves and should decrease towards the ocean-continent boundary.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T31C4635D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T31C4635D"><span id="translatedtitle">Syn-<span class="hlt">Rift</span> <span class="hlt">Systems</span> of East Godavari Sub Basin: Its Evolution and Hydrocarbon Prospectivity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dash, J., Jr.; Zaman, B.</p> <p>2014-12-01</p> <p>Krishna Godavari (K.G.) basin is a passive margin basin developed along the Eastern coast of India. This basin has a polyhistoric evolution with multiple <span class="hlt">rift</span> <span class="hlt">systems</span>. <span class="hlt">Rift</span> basin exploration has provided the oil and gas industry with almost one third of discovered global hydrocarbon resources. Understanding synrift sequences, their evolution, depositional styles and hydrocarbon prospectivity has become important with recent discovery of the wells, G-4-6,YS-AF and KG-8 in the K.G. offshore basin. The East Godavari subbasin is a hydrocarbon producing basin from synrift and pre-<span class="hlt">rift</span> sediments, and hence this was selected as the study area for this research. The study has been carried out by utilizing data of around 58 wells (w1-w58) drilled in the study area 25 of which are hydrocarbon bearing with organic thickness varying from 200 m to 600 m. Age data generated by palaentology and palynology studies have been utilized for calibration of key well logs to differentiate between formations within prerift and synrift sediments. The electrologs of wells like resistivity, gamma ray, neutron, density and sonic logs have been utilized for correlation of different formations in all the drilled wells. The individual thicknesses of sand, shale and coal in the formations have been calculated and tabulated. For Golapalli formation, the isopach and isolith maps were generated which revealed that there were four depocentres with input from the north direction. Schematic geological cross sections were prepared using the well data and seismic data to understand the facies variation across the basin. The sedimentological and petrophysical analysis reports and electro log suites were referred to decipher the environment of deposition, the reservoir characteristics, and play types. The geochemical reports [w4 (Tmax)= 455-468 °C; w1 (Tmax) = 467-514 °C; w4(VRO)= 0.65-0.85; w1(VRO)= 0.83-1.13] revealed the source facies, its maturation and migration timings i.e. the petroleum <span class="hlt">systems</span>. It was concluded these fluvial channel <span class="hlt">systems</span> constitute the main hydrocarbon play for the Mandapeta and Gollapalli formations and these channel <span class="hlt">systems</span> if found at a structurally advantageous positions should prove to be good hydrocarbon targets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.6710L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.6710L"><span id="translatedtitle">The Okavango Dike Swarm (ODS) of Northern Botswana: Was it associated with a failed <span class="hlt">Rift</span> <span class="hlt">System</span>?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>LePera, Alan; Atekwana, Estella; Abdelsalam, Mohamed</p> <p>2014-05-01</p> <p>Dikes and dike swarms often play a significant role in the initiation and extension of <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">Rift</span> Zone (ORZ), a zone of incipient <span class="hlt">rifting</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span> 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.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li class="active"><span>5</span></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_5 --> <div id="page_6" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="101"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985aot..conf.....B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985aot..conf.....B"><span id="translatedtitle"><span class="hlt">Rift</span> basins - Origin, history, and distribution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Burke, K. C.</p> <p>1985-05-01</p> <p><span class="hlt">Rifts</span> are elongate depressions overlying places where the lithosphere has ruptured in extension. Where filled with sediment they may contain exploitable quantities of oil and gas. Because rits form in a variety of tectonic settings, it is helpful to define the particular tectonic environment in which a specific <span class="hlt">rift</span> or set of <span class="hlt">rifts</span> has developed. A useful approach has been to relate that environment to the Wilson Cycle of the opening and the closing of oceans. This appreciation of tectonic setting can help in better understanding of the depositional, structural and thermal history of individual <span class="hlt">rift</span> <span class="hlt">systems</span>. The global distribution of <span class="hlt">rifts</span> can also be related to tectonic environment. For example, <span class="hlt">rifts</span> associated with continental rupture at a temporary still-stand of a continent over the mantle convective <span class="hlt">system</span> (<span class="hlt">rifts</span> like those active in East Africa today) can be distinguished from those associated with continental collision (<span class="hlt">rifts</span> like the Cenozoic <span class="hlt">rifts</span> of China).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JVGR..303..112M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JVGR..303..112M"><span id="translatedtitle"><span class="hlt">Rift</span> zones and magma plumbing <span class="hlt">system</span> of Piton de la Fournaise volcano: How do they differ from Hawaii and Etna?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Michon, Laurent; Ferrazzini, Valérie; Di Muro, Andrea; Villeneuve, Nicolas; Famin, Vincent</p> <p>2015-09-01</p> <p>On ocean basaltic volcanoes, magma transfer to the surface proceeds by subvertical ascent from the mantle lithosphere through the oceanic crust and the volcanic edifice, possibly followed by lateral propagation along <span class="hlt">rift</span> zones. We use a 19-year-long database of volcano-tectonic seismic events together with detailed mapping of the cinder cones and eruptive fissures to determine the geometry and the dynamics of the magma paths intersecting the edifice of Piton de la Fournaise volcano. We show that the overall plumbing <span class="hlt">system</span>, from about 30 km depth to the surface, is composed of two structural levels that feed distinct types of <span class="hlt">rift</span> zones. The deep plumbing <span class="hlt">system</span> is rooted between Piton des Neiges and Piton de la Fournaise volcanoes and has a N30-40 orientation. Above 20 km below sea level (bsl), the main axis switches to a N120 orientation, which permits magma transfer from the lithospheric mantle to the base of the oceanic crust, below the summit of Piton de la Fournaise. The related NW-SE <span class="hlt">rift</span> zone is 15 km wide, linear, spotted by small to large pyroclastic cones and related lava flows and emits slightly alkaline magmas resulting from high-pressure fractionation of clinopyroxene ± olivine. This <span class="hlt">rift</span> zone has low magma production rate of ~ 0.5-3.6 × 10- 3 m3s- 1 and an eruption periodicity of around 200 years over the last 30 ka. Seismic data suggest that the long-lasting activity of this <span class="hlt">rift</span> zone result from regional NNE-SSW extension, which reactivates inherited lithospheric faults by the effect of underplating and/or thermal erosion of the mantle lithosphere. The shallow plumbing <span class="hlt">system</span> (< 11 km bsl) connects the base of the crust with the Central Cone. It is separated from the deep plumbing <span class="hlt">system</span> by a relatively large aseismic zone between 8 and 11 km bsl, which may represent a deep storage level of magma. The shallow plumbing <span class="hlt">system</span> feeds frequent, short-lived summit and flank (NE and SE flanks) eruptions along summit and outer <span class="hlt">rift</span> zones, respectively. Summit <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> zones, sill intrusions, and subsequent magma injections along the outer <span class="hlt">rift</span> 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 <span class="hlt">system</span> whereas the dynamics of their summit <span class="hlt">system</span> is governed by shallow stress variations (above 5-10 km bsl) due to edifice deformation and magma transfers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T21B2542Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T21B2542Y"><span id="translatedtitle">Crustal and mantle structure and anisotropy beneath the incipient segments of the East African <span class="hlt">Rift</span> <span class="hlt">System</span>: Preliminary results from the ongoing SAFARI</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yu, Y.; Reed, C. A.; Gao, S. S.; Liu, K. H.; Massinque, B.; Mdala, H. S.; moidaki, M.; Mutamina, D. M.; Atekwana, E. A.; Ingate, S. F.; Reusch, A.; Barstow, N.</p> <p>2013-12-01</p> <p>Despite the vast wealth of research conducted toward understanding processes associated with continental <span class="hlt">rifting</span>, the extent of our knowledge is derived primarily from studies focused on mature <span class="hlt">rift</span> <span class="hlt">systems</span>, such as the well-developed portions of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) north of Lake Malawi. To explore the dynamics of early <span class="hlt">rift</span> evolution, the SAFARI (Seismic Arrays for African <span class="hlt">Rift</span> Initiation) team deployed 50 PASSCAL broadband seismic stations across the Malawi, Luangwa, and Okavango <span class="hlt">rifts</span> of the EARS during the summer of 2012. The cumulative length of the profiles is about 2500 km and the planned recording duration is 2 years. Here we present the preliminary results of systematic analyses of data obtained from the first year of acquisition for all 50 stations. A total of 446 high-quality shear-wave splitting measurements using PKS, SKKS, and SKS phases from 84 teleseismic events were used to constrain fast polarization directions and splitting times throughout the region. The Malawi and Okavango <span class="hlt">rifts</span> are characterized by mostly NE trending fast directions with a mean splitting time of about 1 s. The fast directions on the west side of the Luangwa <span class="hlt">Rift</span> Zone are parallel to the <span class="hlt">rift</span> valley, and those on the east side are more N-S oriented. Stacking of approximately 1900 radial receiver functions reveals significant spatial variations of both crustal thickness and the ratio of crustal P and S wave velocities, as well as the thickness of the mantle transition zone. Stations situated within the Malawi <span class="hlt">rift</span> demonstrate a southward increase in observed crustal thickness, which is consistent with the hypothesis that the Malawi <span class="hlt">rift</span> originated at the northern end of the <span class="hlt">rift</span> <span class="hlt">system</span> and propagated southward. Both the Okavango and Luangwa <span class="hlt">rifts</span> are associated with thinned crust and increased Vp/Vs, although additional data is required at some stations to enhance the reliability of the observations. Teleseismic P-wave travel-time residuals show a delay of about 1 s at stations in the Okavango <span class="hlt">rift</span> relative to the Limpopo belt. The study region is characterized by a relatively average mantle transition zone thickness of 250 km except for stations located within and to the immediate NW of the Okavango <span class="hlt">rift</span>, where it is probably abnormally thin. Additional seismological techniques will be applied to the data set, and the preliminary results from the above initial analyses will be confirmed or modified by data from the SAFARI stations in the second year.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=STS032-94-040&hterms=green+tea&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dgreen%2Btea','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=STS032-94-040&hterms=green+tea&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dgreen%2Btea"><span id="translatedtitle">East African <span class="hlt">Rift</span> Valley, Kenya</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1990-01-01</p> <p>This rare, cloud free view of the East African <span class="hlt">Rift</span> Valley, Kenya (1.5N, 35.5E) shows a clear view of the Turkwell River Valley, an offshoot of the African REift <span class="hlt">System</span>. The East African <span class="hlt">Rift</span> 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 <span class="hlt">rift</span> margin and tea plantations occupy the cooler higher ground.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T43A4674Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T43A4674Y"><span id="translatedtitle">Exploring Crustal Structure and Mantle Seismic Anisotropy Associated with the Incipient Southern and Southwestern Branches of the East African <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p>2014-12-01</p> <p>In spite of numerous geoscientific studies, the mechanisms responsible for the initiation and development of continental <span class="hlt">rifts</span> are still poorly understood. The key information required to constrain various geodynamic models on <span class="hlt">rift</span> initiation can be derived from the crust/mantle structure and anisotropy beneath incipient <span class="hlt">rifts</span> such as the Southern and Southwestern branches of the East African <span class="hlt">Rift</span> <span class="hlt">System</span>. As part of a National Science Foundation funded interdisciplinary project, 50 PASSCAL broadband seismic stations were deployed across the Malawi, Luangwa, and Okavango <span class="hlt">rift</span> zones from the summer of 2012 to the summer of 2014. Preliminary results from these 50 SAFARI (Seismic Arrays for African <span class="hlt">Rift</span> 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 <span class="hlt">rift</span> valley. Meanwhile, fast orientations beneath the eastern Luangwa <span class="hlt">rift</span> flank rotate from NNW to NNE along the western border of the Malawi <span class="hlt">rift</span>. Stations located alongside the western Malawi <span class="hlt">rift</span> 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 <span class="hlt">rift</span> basins. Receiver function results reveal that, relative to the adjacent Pan-African mobile belts, the Luangwa <span class="hlt">rift</span> zone has a thin (30 to 35 km) crust. The crustal thickness within the Okavango <span class="hlt">rift</span> basin is highly variable. Preliminary findings indicate a northeastward thinning along the southeast Okavango border fault <span class="hlt">system</span> 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 <span class="hlt">rift</span> zones are relatively high, probably suggesting ancient or ongoing magmatic emplacement. The Pan-African mobile belts enveloping the <span class="hlt">rift</span> zones are mostly characterized by more felsic and thicker crust.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70014173','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70014173"><span id="translatedtitle">The Goodman swell: a lithospheric flexure caused by crustal loading along the Midcontinent <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Peterman, Z.E.; Sims, P.K.</p> <p>1988-01-01</p> <p>Rb-Sr biotite ages of Archean and Early to Middle Proterozoic crystalline rocks in northern Wisconsin and adjacent Upper Peninsula of Michigan describe a regionally systematic pattern related to differential uplift. An "age low' occurs in northern Wisconsin where values range from 1070-1172 Ma for rocks with crystallization ages of 1760 to 1865 Ma. These values overlap with the main episode of mafic igneous activity (1090 to 1120 Ma) along the Midcontinent <span class="hlt">rift</span> <span class="hlt">system</span> (MRS). We interpret these low biotite ages as registering closure due to cooling below the 300??C isotherm as a consequence of uplift and rapid erosion of an area that we are informally naming the Goodman swell. We interpret the swell to be a forebulge imposed on an elastic crust by loading of mafic igneous rocks along and within the axis of the MRS. -from Authors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.2683S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.2683S"><span id="translatedtitle">On abrupt transpression to transtension transition in the South Baikal <span class="hlt">rift</span> <span class="hlt">system</span> (Tunka - South Baikal segment)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sankov, Vladimir; Parfeevets, Anna; Lukhnev, Andrey; Miroshnitchenko, Andrey; Ashurkov, Sergey; Sankov, Alexey; Usynin, Leonid; Eskin, Alexander; Bryzhak, Evgeny</p> <p>2013-04-01</p> <p>This work addresses to relation of transpression and extension stress-strain conditions in intracontinental <span class="hlt">rift</span> <span class="hlt">system</span>. 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 <span class="hlt">system</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span>. 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 <span class="hlt">rift</span> <span class="hlt">system</span> 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).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19910031351&hterms=infectious+disease+research&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dinfectious%2Bdisease%2Bresearch','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19910031351&hterms=infectious+disease+research&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dinfectious%2Bdisease%2Bresearch"><span id="translatedtitle">Modelling <span class="hlt">Rift</span> Valley fever (RVF) disease vector habitats using active and passive remote sensing <span class="hlt">systems</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ambrosia, Vincent G.; Linthicum, K. G.; Bailey, C. L.; Sebesta, P.</p> <p>1989-01-01</p> <p>The NASA Ames Ecosystem Science and Technology Branch and the U.S. Army Medical Research Institute of Infectious Diseases are conducting research to detect <span class="hlt">Rift</span> Valley fever (RVF) vector habitats in eastern Africa using active and passive remote-sensing. The normalized difference vegetation index (NDVI) calculated from Landsat TM and SPOT data is used to characterize the vegetation common to the Aedes mosquito. Relationships have been found between the highest NDVI and the 'dambo' habitat areas near Riuru, Kenya on both wet and dry data. High NDVI values, when combined with the vegetation classifications, are clearly related to the areas of vector habitats. SAR data have been proposed for use during the rainy season when optical <span class="hlt">systems</span> are of minimal use and the short frequency and duration of the optimum RVF mosquito habitat conditions necessitate rapid evaluation of the vegetation/moisture conditions; only then can disease potential be stemmed and eradication efforts initiated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JSAES..56....1B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JSAES..56....1B"><span id="translatedtitle">Lower Pliensbachian caldera volcanism in high-obliquity <span class="hlt">rift</span> <span class="hlt">systems</span> in the western North Patagonian Massif, Argentina</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Benedini, Leonardo; Gregori, Daniel; Strazzere, Leonardo; Falco, Juan I.; Dristas, Jorge A.</p> <p>2014-12-01</p> <p>In the Cerro Carro Quebrado and Cerro Catri Cura area, located at the border between the Neuquén Basin and the North Patagonian Massif, the Garamilla Formation is composed of four volcanic stages: 1) andesitic lava-flows related to the beginning of the volcanic <span class="hlt">system</span>; 2) basal massive lithic breccias that represent the caldera collapse; 3) voluminous, coarse-crystal rich massive lava-like ignimbrites related to multiple, steady eruptions that represent the principal infill of the <span class="hlt">system</span>; and, <span class="hlt">finally</span> 4) domes, dykes, lava flows, and lava domes of rhyolitic composition indicative of a post-collapse stage. The analysis of the regional and local structures, as well as, the architectures of the volcanic facies, indicates the existence of a highly oblique <span class="hlt">rift</span>, with its principal extensional strain in an NNE-SSW direction (˜N10°). The analyzed rocks are mainly high-potassium dacites and rhyolites with trace and RE elements contents of an intraplate signature. The age of these rocks (189 ± 0.76 Ma) agree well with other volcanic sequences of the western North Patagonian Massif, as well as, the Neuquén Basin, indicating that Pliensbachian magmatism was widespread in both regions. The age is also coincident with phase 1 of volcanism of the eastern North Patagonia Massif (188-178 Ma) represented by ignimbrites, domes, and pyroclastic rocks of the Marifil Complex, related to intraplate magmatism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.T41A0379S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.T41A0379S"><span id="translatedtitle">Observations From Fieldwork and (U-Th)/He Thermochronologic Study of the Central Arabian Flank of the Red Sea <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Szymanski, E.; Stockli, D. F.; Johnson, P. R.; Kattan, F. H.; Al Shammari, A.</p> <p>2007-12-01</p> <p>Improvement in our modeling of continental lithosphere rupturing and <span class="hlt">rifting</span> dynamics requires an absolute understanding of the temporal and spatial strain distribution throughout an entire <span class="hlt">rift</span> <span class="hlt">system</span>. This statement holds especially true for our understanding of Red Sea <span class="hlt">rift</span> <span class="hlt">system</span> dynamics. However, critical geologic data used to determine the tectonic evolution of the Red Sea <span class="hlt">rift</span> <span class="hlt">system</span> come mainly from the Gulf of Suez and the Egyptian and Yemeni margins of the Red Sea while the <span class="hlt">rift</span> 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 <span class="hlt">rift</span>-related Tertiary basaltic volcanism along the central Saudi Arabian <span class="hlt">rift</span> 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 <span class="hlt">rift</span>. Constraints on the dynamics of <span class="hlt">rift</span> 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 <span class="hlt">rift</span> flank uplift and exhumation while short-baseline transects address issues well inboard from the modern <span class="hlt">rift</span> margin such as structural control on pre- and syn-<span class="hlt">rift</span> 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 <span class="hlt">System</span>. 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 <span class="hlt">rift</span> flank that includes active footwall exhumation approximately 130 km inland from the <span class="hlt">rift</span> margin during the Middle Miocene.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoJI.201..505L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoJI.201..505L"><span id="translatedtitle">Stress pattern of the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>, North China, inferred from the inversion of new focal mechanisms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Bin; Atakan, Kuvvet; Sørensen, Mathilde Bøttger; Havskov, Jens</p> <p>2015-05-01</p> <p>Earthquake focal mechanisms of the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>, North China, are investigated for the time period 1965-April 2014. A total of 143 focal mechanisms of ML ? 3.0 earthquakes were compiled. Among them, 105 solutions are newly determined in this study by combining the P-wave first motions and full waveform inversion, and 38 solutions are from available published data. Stress tensor inversion was then performed based on the new database. The results show that most solutions in the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span> exhibit normal or strike-slip faulting, and the regional stress field is transtensional and dominated by NNW-SSE extension. This correlates well with results from GPS data, geological field observations and levelling measurements across the faults. Heterogeneity exists in the regional stress field, as indicated by individual stress tensor inversions conducted for five subzones. While the minimum stress axis (?3) appears to be consistent and stable, the orientations, especially the plunges, of the maximum and intermediate stresses (?1 and ?2) vary significantly along the strike of the different subzones. Based on our results and combining multidisciplinary observations from geological surveys, GPS and cross-fault monitoring, a kinematic model is proposed for the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>, in which the <span class="hlt">rift</span> is situated between two opposite rotating crustal blocks, exhibiting a transtensional stress regimes. This model illustrates the present-day stress field and its correlation to the regional tectonics, as well as the current crustal deformation of the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>. Results obtained in this study, may help to understand the geodynamics, neotectonic activity, active seismicity and potential seismic hazard in this region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.4456S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.4456S"><span id="translatedtitle">Structure of backarc inner <span class="hlt">rifts</span> as a weakest zone of arc-backarc <span class="hlt">system</span>: a case study of the Sea of Japan</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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</p> <p>2015-04-01</p> <p>A backarc inner <span class="hlt">rift</span> 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 <span class="hlt">rift</span> along the Izu-Bonin arc. Similar inner <span class="hlt">rift</span> 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 <span class="hlt">rifting</span>. The amount of shortening shows its maximum along the backarc inner <span class="hlt">rifts</span>, forming a fold-and-thrust of thick post-<span class="hlt">rift</span> sediments over all the structure of backarc. The <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> basin accords well to the mafic intrusive rocks. Syn-<span class="hlt">rift</span> volcanism was bimodal, comprising a reflective unit of mafic rocks around the <span class="hlt">rift</span> axis and a non-reflective unit of felsic rocks near the margins of the basins. Once <span class="hlt">rifting</span> ended, thermal subsidence, and subsequently, mechanical subsidence related to the onset of the compressional regime, allowed deposition of up to 5 km of post-<span class="hlt">rift</span>, deep marine to fluvial sedimentation. Continued compression produced fault-related folds in the post-<span class="hlt">rift</span> sediments, characterized by thin-skin style of deformation. The syn-<span class="hlt">rift</span> mafic intrusion in the crust forms convex shape and the boundary between pre-<span class="hlt">rift</span> crust and mafic intrusive shows outward dipping surface. Due to the post <span class="hlt">rift</span> compression, the boundary of rock units reactivated as reverse faults, commonly forming a large-scale wedge thrust and produced subsidence of <span class="hlt">rift</span> basin under compressional stress regime. Large amount of convergence of overriding plate is accommodated along the inner <span class="hlt">rift</span>, suggesting that it is a weakest zone in whole arc-backarc <span class="hlt">system</span>. The convergence between young (15 Ma) Shikoku basin and SW Japan arc produced intense shortening along the inner failed <span class="hlt">rift</span> 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 <span class="hlt">rift</span> is very sensitive for the stress produce by the subduction interface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19950015372&hterms=mantle+hotspot&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dmantle%2Bhotspot','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19950015372&hterms=mantle+hotspot&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dmantle%2Bhotspot"><span id="translatedtitle">Spatial variation of primordial 3-He in crustal fluids along the East-African <span class="hlt">Rift</span> <span class="hlt">system</span> (the Ethiopian and the Kenya <span class="hlt">Rift</span> section)</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Griesshaber, E.; Weise, S.; Darling, G.</p> <p>1994-01-01</p> <p>(3)He/(4)He compositions are presented for groundwater samples from the Ethiopian segment of the East-Afrikan <span class="hlt">Rift</span> and from its northern extension, the adjacent Afar region (Djibuti). Helium isotope data are compared to those obtained previously from the Gregory <span class="hlt">Rift</span>, south of Ethiopia. The distribution pattern of mantle-derived volatiles along the entire East-African-<span class="hlt">Rift</span> (-from south Kenya to Djibuti-) is discussed and their sources are identified. Helium isotope ratios (R) for samples from the Ethiopian part of the <span class="hlt">Rift</span> range from 6.3 to 16.0 times the atmospheric ratio (Ra=1.4 x 10(exp -6) and thus show together with a MOR component a considerable hotspot helium component. These mantle helium concentrations are comparable to those observed in groundwaters and volcanic rocks from the Afar plume region in Djibuti. Here R/Ra values range from 9 to 13 times the atmospheric composition, with mantle-derived helium concentrations being higher than at spreading ocean ridges. R/Ra values from Ethiopia and Djibuti are entirely different from those observed in groundwaters at the southerly extending Gregory <span class="hlt">Rift</span> in Kenya, where R/Ra values scatter between 0.5 and 6. At the northernmost part of the Gregory <span class="hlt">Rift</span>, close to Ethiopia mantle helium contents are slightly higher, with R/Ra-values varying between 6.5 and 8.0.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983Tectp..94..205B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983Tectp..94..205B"><span id="translatedtitle">Gravity study of the Central African <span class="hlt">Rift</span> <span class="hlt">system</span>: a model of continental disruption 2. The Darfur domal uplift and associated Cainozoic volcanism</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bermingham, P. M.; Fairhead, J. D.; Stuart, G. W.</p> <p>1983-05-01</p> <p>Gravity studies of the Darfur uplift, Western Sudan, show it to be associated with a circular negative Bouguer anomaly, 50 mGal in amplitude and 700 km across. A three-dimensional model interpretation of the Darfur anomaly, using constraints deduced from geophysical studies of similar but more evolved Kenya and Ethiopia domes, suggests either a low-density laccolithic body at mid-lithospheric depth (~ 60 km) or a thinned lithosphere with emplacement at high level of low-density asthenospheric material. The regional setting of the Darfur uplift is described in terms of it being an integral part of the Central African <span class="hlt">Rift</span> <span class="hlt">System</span> which is shown to be broadly equivalent to the early to middle Miocene stage in the development of the Afro-Arabian <span class="hlt">Rift</span> <span class="hlt">System</span>. Comparisons between these <span class="hlt">rift</span> <span class="hlt">systems</span> suggest that extensional tectonics and passive <span class="hlt">rifting</span>, resulting in the subsiding sedimentary <span class="hlt">rift</span> basins associated with the Ngaoundere, Abu Gabra, Red Sea and Gulf of Aden <span class="hlt">rifts</span>, are more typical of the early stage development of passive continental margins than the active domal uplift and development of <span class="hlt">rifted</span> features associated with the Darfur, Kenya and Ethiopia domes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110023310','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110023310"><span id="translatedtitle">DoD-GEIS <span class="hlt">Rift</span> Valley Fever Monitoring and Prediction <span class="hlt">System</span> as a Tool for Defense and US Diplomacy</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Anyamba, Assaf; Tucker, Compton J.; Linthicum, Kenneth J.; Witt, Clara J.; Gaydos, Joel C.; Russell, Kevin L.</p> <p>2011-01-01</p> <p>Over the last 10 years the Armed Forces Health Surveillance Center's Global Emerging Infections Surveillance and Response <span class="hlt">System</span> (GEIS) partnering with NASA'S Goddard Space Flight Center and USDA's USDA-Center for Medical, Agricultural & Veterinary Entomology established and have operated the <span class="hlt">Rift</span> Valley fever Monitoring and Prediction <span class="hlt">System</span> to monitor, predict and assess the risk of <span class="hlt">Rift</span> Valley fever outbreaks and other vector-borne diseases over Africa and the Middle East. This <span class="hlt">system</span> is built on legacy DoD basic research conducted by Walter Reed Army Institute of Research overseas laboratory (US Army Medical Research Unit-Kenya) and the operational satellite environmental monitoring by NASA GSFC. Over the last 10 years of operation the <span class="hlt">system</span> has predicted outbreaks of <span class="hlt">Rift</span> Valley fever in the Horn of Africa, Sudan, South Africa and Mauritania. The ability to predict an outbreak several months before it occurs provides early warning to protect deployed forces, enhance public health in concerned countries and is a valuable tool use.d by the State Department in US Diplomacy. At the international level the <span class="hlt">system</span> has been used by the Food and Agricultural Organization (FAD) and the World Health Organization (WHO) to support their monitoring, surveillance and response programs in the livestock sector and human health. This project is a successful testament of leveraging resources of different federal agencies to achieve objectives of force health protection, health and diplomacy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1611128D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1611128D"><span id="translatedtitle">Groundwater dynamics in the complex aquifer <span class="hlt">system</span> of Gidabo River Basin, southern Main Ethiopian <span class="hlt">Rift</span>: Evidences from hydrochemistry and isotope hydrology</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Degu, Abraham; Birk, Steffen; Dietzel, Martin; Winkler, Gerfried; Moggessie, Aberra</p> <p>2014-05-01</p> <p>Located in the tectonically active Main Ethiopian <span class="hlt">Rift</span> <span class="hlt">system</span>, the Gidabo River Basin in Ethiopia has a complex hydrogeological setting. The strong physiographic variation from highland to <span class="hlt">rift</span> floor, variability in volcanic structures and disruption of lithologies by cross-cutting faults contribute for their complex nature of hydrogeology in the area. Until now, the groundwater dynamics and the impact of the tectonic setting on groundwater flow in this region are not well understood, though the local population heavily depends on groundwater as the major water supply. A combined approach based on hydrochemical and isotopic data was applied to investigate the regional flow dynamics of the groundwater and the impact of tectonic setting. Groundwater evolves from slightly mineralized Ca-Mg-HCO3 on the highland to highly mineralized Na-HCO3 dominating type in the deep <span class="hlt">rift</span> floor aquifers. ?18O and ?D composition of groundwater show a general progressive enrichment from the highland to the <span class="hlt">rift</span> floor, except in thermal and deep <span class="hlt">rift</span> floor aquifers. Relatively the thermal and deep <span class="hlt">rift</span> floor aquifers are depleted and show similar signature to the groundwaters of highland, indicating groundwater inflow from the highland. Correspondingly, rising HCO3 and increasingly enriched signatures of ? 13C points to hydrochemical evolution of DIC and diffuse influx of mantle CO2 into the groundwater <span class="hlt">system</span>. Thermal springs gushing out along some of the fault zones, specifically in the vicinity of Dilla town, display clear influence of mantle CO2 and are an indication of the role of the faults acting as a conduit for deep circulating thermal water to the surface. By considering the known geological structures of the <span class="hlt">rift</span>, hydrochemical and isotopic data we propose a conceptual groundwater flow model by characterizing flow paths to the main <span class="hlt">rift</span> axis. The connection between groundwater flow and the impact of faults make this model applicable to other active <span class="hlt">rift</span> <span class="hlt">systems</span> with similar tectonic settings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.V33C2649A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V33C2649A"><span id="translatedtitle">Open <span class="hlt">system</span> evolution of trachyte and phonolite magmas from the East Africa <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Anthony, E. Y.; Espejel, V.</p> <p>2011-12-01</p> <p>The Quaternary Suswa volcanic <span class="hlt">system</span> consists of a large shield volcano that developed two nested summit calderas and erupted metaluminous to peralkaline trachyte and phonolite lavas and tuffs. Suswa is adjacent to the Greater Olkaria Volcanic Center, Longonot, Eburru, and Menengai volcanic <span class="hlt">systems</span>, which erupted trachyte, comendite, and pantellerite. These volcanoes comprise the Central Kenya Peralkaline Province and are the site of active geothermal energy production and exploration. Mafic to intermediate lavas (Elementieta, Ndabibi, and Lolonito-Akira-Tandamara volcanic fields) lie in the <span class="hlt">rift</span> floor between the shield volcanoes and occur as components of mixed magmas within the complexes. Suswa includes two suites of trachyte-phonolite lavas and tuffs. The first suite (C1) consists of lavas that built the original shield volcano and lavas and tuffs related to the formation of the first caldera; the second suite (C2) consists of lavas and tuffs erupted during and after the formation of the second caldera. Trachyte-carbonate immiscibility has been recorded in C1 ash flow units. The lavas and tuffs of the C2 suite are generally less peralkaline and more silica undersaturated than those of the C1 suite and did not share a common parental magma. Geochemical modeling precludes fractional crystallization as the sole process for Suswa magmas. Instead, assimilation of syenitic material (probably the crystal mush left over from C1 fractional crystallization), resorption, and mixing between the mafic to intermediate lavas satellite to the shield volcanoes have contributed to the composition and eruptive style of these volcanoes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.T43C2044A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.T43C2044A"><span id="translatedtitle">Transition From a Magmatic to a Tectonic <span class="hlt">Rift</span> <span class="hlt">System</span> : Seismotectonics of the Eyasi- Manyara Region, Northern Tanzania, East Africa</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Albaric, J.; Perrot, J.; Deschamps, A.; Deverchere, J.; Wambura, R. F.; Tiberi, C.; Petit, C.; Le Gall, B.; Sue, C.</p> <p>2008-12-01</p> <p>How a <span class="hlt">rift</span> <span class="hlt">system</span> propagates and breaks throughout a cold and thick continental crust remains poorly known. Only few places allow to address the question. In the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS), the eastern magma- rich branch abruptly splits into two amagmatic arms (the Eyasi and Manyara faulted <span class="hlt">systems</span>), south of a E-W volcanic chain (the Ngorongoro-Kilimanjaro transverse volcanic belt), as crossing the Archaean Tanzanian craton margin. We present the first detailed seismotectonic picture of the Eyasi-Manyara <span class="hlt">rifts</span> where a network of ~25 seismometers was settled from June to November 2007 (SEISMO-TANZ'07 seismological experiment). From the seismicity recorded by the network, we identify active faults and discuss the stress field framework obtained from the inversion of focal mechanisms. We use the determined depth of earthquakes (1) to discuss the crustal structure of the transition zone from a magma-rich to a magma-starved section of the EARS and (2) to further emphasize the rheological control on depth distributions in the EARS (Albaric et al., Tectonophysics, 2008). The stress and strain directions deduced from our work are also used to question recently published kinematics and conceptual models of the EARS (Calais et al., Geol. Soc. London, 2006 ; Le Gall et al., Tectonophysics, 2008).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/6939199','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6939199"><span id="translatedtitle">Structural style of the Turkana <span class="hlt">Rift</span>, Kenya</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dunkelman, T.J.; Karson, J.A.; Rosendahl, B.R.</p> <p>1988-03-01</p> <p>Multifold seismic reflection and geologic mapping in part of the eastern branch of the East African <span class="hlt">Rift</span> <span class="hlt">system</span> of northern Kenya reveal a major <span class="hlt">rift</span> structure containing at least 3 km of Neogene sediment fill beneath Lake Turkana. This includes a series of half-graben basins, with centrally located quaternary volcanic centers, which are linked end-to-end by structural accommodation zones. Whereas the geometry of <span class="hlt">rifting</span> is similar to that of the nonvolcanic western branch of the East African <span class="hlt">Rift</span> <span class="hlt">system</span>, the Turkana half-grabens are much smaller and may reflect extension of a thinner lithosphere or development of more closely spaced fracture patterns during <span class="hlt">rift</span> evolution, or both.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..1414231S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..1414231S"><span id="translatedtitle">Complex Stress Histories in the East African <span class="hlt">Rift</span> <span class="hlt">System</span>, paleostress <span class="hlt">systems</span> or complex new-stresses due to locallized uplift and block rotation?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sachau, T.; Koehn, D.; Aanyu, K.</p> <p>2012-04-01</p> <p>The Albertine <span class="hlt">Rift</span> <span class="hlt">System</span> in the East African <span class="hlt">Rift</span> shows outstanding morphological features including the Rwenzori mountains, a 5000 m high basement block within the <span class="hlt">rift</span>. Research in this area has shown that the Rwenzori mountains were uplfited during extension. We used stress inversion studies based on fault slip data and numerical models to understand the stress in this region. We see that the stress field in the centre of the Rwenzori block is significantly different from the stress field of the <span class="hlt">rift</span> flanks and the southern part of the Rwenzoris. In the central part of the mountain we find extension parallel to the main <span class="hlt">rift</span> opening direction (NW-SE), two strike slip regimes and a NNW directed thrusting regime. In the south of the Rwenzoris we find only two orthogonal extension regimes indicating that sigma 3 and sigma 2 may have switched during the extension and activation of faults. North of the mountain extension seems to dominate with a minor strike slip component. In the NE of the mountain, where the Rwenzoris are still connected to the Tanzania craton, we find complex inclined strike slip and normal stress fields. The stress pattern suggests that the Rwenzori block and its connecting bridge contain unusual stresses probably related to block rotation and uplift. As an alternative explanation for the complex interference of strike slip. extension and even thursting one can consider the capturing of old pre-<span class="hlt">rift</span> stress fields by the faults. However, this does not explain why the stress field varies dramatically between the <span class="hlt">rift</span> flanks and the central mountains. In order to understand these complex stress geometries we use a three-dimensional elasto-plastic model where we implement the <span class="hlt">rift</span> geometry and stretch it. The resulting three-dimensional stress patterns do indeed show a transition from extension to strike slip and even thrusting within the central block. We therefore argue that the stress inversion technique may give you actual recent stress-fields and that these stresses may result from the unusual uplift of the mountain and its possible rotation within the <span class="hlt">rift</span> setting.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_6 --> <div id="page_7" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="121"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.6029E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.6029E"><span id="translatedtitle">Characterization of basement highs in hyper-extended <span class="hlt">rift</span> <span class="hlt">systems</span>: examples from the Err nappe, SE Switzerland.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Epin, Marie-Eva; Manatschal, Gianreto; Haupert, Isabelle; Decarlis, Alessandro</p> <p>2015-04-01</p> <p>Despite of the fact that many studies investigated magma-poor <span class="hlt">rifted</span> margins, there are still open questions that are related to the nature of basement highs and the timing and processes related to their formation. While these questions are difficult to answer at present-day margins due to the lack of drill hole data, field analogues provide important insights and enable to find some answers to these questions. This is particularly true for the Err nappe in southeastern Switzerland, which is one of the world's few exposed and preserved <span class="hlt">rift</span>-related hyper-extended domains. This nappe preserves a <span class="hlt">rift</span> related extensional detachment <span class="hlt">system</span> that is exposed over more than 200km2, characterized by distinctive black gouges and green cataclasites and preserving the relation to its hanging wall and footwall rocks and the pre-, syn-, and post-tectonic sediments. The aim of our study was to investigate the 3D architecture of the detachment <span class="hlt">system</span> based on detailed mapping of this structure north and south of the Julier valley between Bivio and San Moritz in Central Grisons, SE Switzerland. Our results show the lateral variation of the morphology of the major detachment fault and its relation to extensional allochthons and the pre-, syn- and post-tectonic sediments. The main observation is that the architecture of the detachment <span class="hlt">system</span> changes over very short distance across the Julier valley. While in the north the detachment is overlain by an allochthonous block (e.g. the Bardella block), to the south this block disappears and the detachment fault is exhumed at the seafloor. The mapping of the syn-tectonic sediments show that they are thick in the north and get thinner to the south where they are locally absent and the post-<span class="hlt">rift</span> sediments directly overlie the detachment <span class="hlt">system</span>. Furthermore the syn-tectonic sediments are locally characterized by basement clasts. These relationships suggest a rapid change from a domain where the detachment is overlain by allochthons and thick syn-tectonic sediments to a domain where the detachment is exposed. The lack of syn-<span class="hlt">rift</span> 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 <span class="hlt">system</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002Geomo..45..147B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002Geomo..45..147B"><span id="translatedtitle">Fluvial <span class="hlt">systems</span> response to <span class="hlt">rift</span> margin tectonics: Makhtesh Ramon area, southern Israel</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ben-David, Ram; Eyal, Yehuda; Zilberman, Ezra; Bowman, Dan</p> <p>2002-06-01</p> <p>The geomorphic evolution of Makhtesh Ramon, a feather-shaped erosional valley, and the Nahal Neqarot drainage <span class="hlt">system</span> to the south occurred largely in response to tectonic activity along the Dead Sea <span class="hlt">Rift</span> and its western shoulder. Remnants of Miocene clastic sediments (Hazeva Formation) deposited on an erosional peneplain that formed over this area during the Oligocene epoch provide a datum plane for reconstructing subsequent fluvial evolution. These clastic remnants are presently located on the shoulders of Makhtesh Ramon at various elevations. The peneplain truncating the Makhtesh Ramon block has been tilted 0.7% northeastward since the Pliocene epoch (post-Hazeva Formation), whereas that of the Neqarot syncline, south of the Ramon, has been tilted 1.2%. The elliptical exposure of friable Lower Cretaceous sandstone, exposed in the core of the truncated Ramon structure, governed the development of a new ENE directed (riftward) drainage <span class="hlt">system</span> through capture of streams that previously drained toward the Mediterranean Sea to the northwest. Incised fluvial gaps in the southern rim of Makhtesh Ramon and alluvial fan relicts within Makhtesh Ramon attest to original drainage into the Makhtesh from the south. Remnants of the Plio-Pleistocene Arava Conglomerate on the eastern end of the Neqarot syncline contain clasts from rocks exposed within Makhtesh Ramon, also indicating that streams flowed into the Makhtesh from the southern Neqarot block through the western gaps, then turning eastward and exiting the Makhtesh via the next (Sha'ar-Ramon) gap to the east. Further down-faulting of the Neqarot block during Mid-Late Pleistocene time led to westward retreat of the Neqarot valley and capture of the last stream flowing northward into the Ramon, leaving the modern Makhtesh Ramon isolated from the southern drainage <span class="hlt">system</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70027062','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70027062"><span id="translatedtitle">A hydrogeologic model of stratiform copper mineralization in the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span>, Northern Michigan, USA</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Swenson, J.B.; Person, M.; Raffensperger, J.P.; Cannon, W.F.; Woodruff, L.G.; Berndt, M.E.</p> <p>2004-01-01</p> <p>This paper presents a suite of two-dimensional mathematical models of basin-scale groundwater flow and heat transfer for the middle Proterozoic Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span>. The models were used to assess the hydrodynamic driving mechanisms responsible for main-stage stratiform copper mineralization of the basal Nonesuch Formation during the post-volcanic/pre-compressional phase of basin evolution. Results suggest that compaction of the basal aquifer (Copper Harbor Formation), in response to mechanical loading during deposition of the overlying Freda Sandstone, generated a pulse of marginward-directed, compaction-driven discharge of cupriferous brines from within the basal aquifer. The timing of this pulse is consistent with the radiometric dates for the timing of mineralization. Thinning of the basal aquifer near White Pine, Michigan, enhanced stratiform copper mineralization. Focused upward leakage of copper-laden brines into the lowermost facies of the pyrite-rich Nonesuch Formation resulted in copper sulfide mineralization in response to a change in oxidation state. Economic-grade mineralization within the White Pine ore district is a consequence of intense focusing of compaction-driven discharge, and corresponding amplification of leakage into the basal Nonesuch Formation, where the basal aquifer thins dramatically atop the Porcupine Mountains volcanic structure. Equilibrium geochemical modeling and mass-balance calculations support this conclusion. We also assessed whether topography and density-driven flow <span class="hlt">systems</span> could have caused ore genesis at White Pine. Topography-driven flow associated with the Ottawan orogeny was discounted because it post-dates main-stage ore genesis and because recent seismic interpretations of basin inversion indicates that basin geometry would not be conductive to ore genesis. Density-driven flow <span class="hlt">systems</span> did not produce focused discharge in the vicinity of the White Pine ore district.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/6322627','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6322627"><span id="translatedtitle">Analogy between natural gas found in lakes of <span class="hlt">rift</span> valley <span class="hlt">system</span> of east Africa and its allied gas in Japan</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Fukuta, O.</p> <p>1984-09-01</p> <p>The Afar triangle in northeastern Ethiopia is where the Red Sea <span class="hlt">rift</span>, the Carlsberg Ridge of the Indian Ocean, and the <span class="hlt">Rift</span> Valley <span class="hlt">system</span> 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 <span class="hlt">Rift</span> Valley of east Africa for a long time. In 1980, Gold and Soter stated that Lake Kivu, which occupies part of the East African <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeoJI.193.1353D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeoJI.193.1353D"><span id="translatedtitle">Seismic and aseismic deformation along the East African <span class="hlt">Rift</span> <span class="hlt">System</span> from a reanalysis of the GPS velocity field of Africa</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Déprez, Aline; Doubre, Cécile; Masson, Frédéric; Ulrich, Patrice</p> <p>2013-06-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span> (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 <span class="hlt">rift</span>, of the proportion of geodetic moment seismically accommodated suggests a significant control of the thermal structure associated with different states of <span class="hlt">rifting</span> evolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/19198772','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/19198772"><span id="translatedtitle">Tectonics of the baikal <span class="hlt">rift</span> deduced from volcanism and sedimentation: a review oriented to the Baikal and Hovsgol lake <span class="hlt">systems</span>.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ivanov, Alexei V; Demonterova, Elena I</p> <p>2009-01-01</p> <p>As known from inland sedimentary records, boreholes, and geophysical data, the initiation of the Baikal <span class="hlt">rift</span> basins began as early as the Eocene. Dating of volcanic rocks on the <span class="hlt">rift</span> shoulders indicates that volcanism started later, in the Early Miocene or probably in the Late Oligocene. Prominent tectonic uplift took place at about 20 Ma, but information (from both sediments and volcanics) on the initial stage of the <span class="hlt">rifting</span> is scarce and incomplete. A comprehensive record of sedimentation derived from two stacked boreholes drilled at the submerged Akademichesky ridge indicates that the deep freshwater Lake Baikal existed for at least 8.4 Ma, while the exact formation of the lake in its roughly present-day shape and volume is unknown. Four important events of tectonic/environmental changes at about approximately 7, approximately 5, approximately 2.5, and approximately 0.1 Ma are seen in that record. The first event probably corresponds to a stage of <span class="hlt">rift</span> propagation from the historical center towards the wings of the <span class="hlt">rift</span> <span class="hlt">system</span>. <span class="hlt">Rifting</span> in the Hovsgol area was initiated at about this time. The event of ~5 Ma is a likely candidate for the boundary between slow and fast stages of <span class="hlt">rifting</span>. It is reflected in a drastic change of sedimentation rate due to isolation of the Akademichesky ridge from the central and northern Lake Baikal basins. The youngest event of 0.1 Ma is reflected by the (87)0Sr/ (86)Sr ratio increase in Lake Baikal waters and probably related to an increasing rate of mountain growth (and hence erosion) resulting from glacial rebounding. The latter is responsible for the reorganization of the outflow pattern with the termination of the paleo-Manzurka outlet and the formation of the Angara outlet. The event of approximately 2.5 Ma is reflected in the decrease of the (87)Sr/(86)Sr and Na/Al ratios in Lake Baikal waters. We suggest that it is associated with a decrease of the dust load due to a reorganization of the atmospheric circulations in Mainland Asia. All these tectonic and climatic events could (and actually did) influence the biota of Lake Baikal. The Hovsgol <span class="hlt">rift</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1710322S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1710322S"><span id="translatedtitle">Segmented lateral dyke growth in a <span class="hlt">rifting</span> event at Bárðarbunga volcanic <span class="hlt">system</span>, Iceland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S.; Ófeigsson, Benedikt; Rafn Heimisson, Elías; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Guðmundsson, Gunnar B.; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T.; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert; Ágústsdóttir, Thorbjörg; Björnsson, Helgi; Bean, Christopher J.</p> <p>2015-04-01</p> <p>Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of km long. Previous models of <span class="hlt">rifting</span> events indicate either a lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens, or magma flowing vertically into dykes from an underlying source, with the role of topography on the evolution of lateral dykes not clear. We show how a recent segmented dyke intrusion in the Bárðarbunga volcanic <span class="hlt">system</span>, grew laterally for over 45 km at a variable rate, with an influence of topography on the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning <span class="hlt">System</span> (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bárðarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with a magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of M>5 earthquakes. The dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Natur.517..191S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Natur.517..191S"><span id="translatedtitle">Segmented lateral dyke growth in a <span class="hlt">rifting</span> event at Bárðarbunga volcanic <span class="hlt">system</span>, Iceland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S.; Ófeigsson, Benedikt G.; Heimisson, Elías Rafn; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Gudmundsson, Gunnar B.; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T.; Högnadóttir, Thórdís; Fridriksdóttir, Hildur María; Hensch, Martin; Einarsson, Páll; Magnússon, Eyjólfur; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert S.; Ágústsdóttir, Thorbjörg; Greenfield, Tim; Green, Robert G.; Hjartardóttir, Ásta Rut; Pedersen, Rikke; Bennett, Richard A.; Geirsson, Halldór; La Femina, Peter C.; Björnsson, Helgi; Pálsson, Finnur; Sturkell, Erik; Bean, Christopher J.; Möllhoff, Martin; Braiden, Aoife K.; Eibl, Eva P. S.</p> <p>2015-01-01</p> <p>Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long. Previous models of <span class="hlt">rifting</span> events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens, or magma flowing vertically into dykes from an underlying source, with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Bárðarbunga volcanic <span class="hlt">system</span> grew laterally for more than 45 kilometres at a variable rate, with topography influencing the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred primarily over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning <span class="hlt">System</span> (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bárðarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of magnitude M > 5 earthquakes. Dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70016278','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70016278"><span id="translatedtitle">GLIMPCE Seismic reflection evidence of deep-crustal and upper-mantle intrusions and magmatic underplating associated with the Midcontinent <span class="hlt">Rift</span> <span class="hlt">system</span> of North America</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Behrendt, John C.; Hutchinson, D.R.; Lee, M.; Thornber, C.R.; Trehu, A.; Cannon, W.; Green, A.</p> <p>1990-01-01</p> <p>Deep-crustal and Moho reflections, recorded on vertical incidence and wide angle ocean bottom Seismometer (OBS) data in the 1986 GLIMPCE (Great Lakes International Multidisciplinary Program on Crustal Evolution) experiment, provide evidence for magmatic underplating and intrusions within the lower crust and upper mantle contemporaneous with crustal extension in the Midcontinent <span class="hlt">Rift</span> <span class="hlt">system</span> at 1100 Ma. The <span class="hlt">rift</span> fill consists of 20-30 km (7-10 s) of basalt flows, secondary syn-<span class="hlt">rift</span> volcaniclastic and post-basalt sedimentary rock. Moho reflections recorded in Lake Superior over the Midcontinent <span class="hlt">Rift</span> <span class="hlt">system</span> have times from 14-18 s (about 46 km to as great as 58 km) in contrast to times of about 11-13 s (about 36-42 km crustal thickness) beneath the surrounding Great Lakes. The Seismically complex deep-crust to mantle transition zone (30-60 km) in north-central Lake Superior, which is 100 km wider than the <span class="hlt">rift</span> half-graben, reflects the complicated products of tectonic and magmatic interaction of lower-crustal and mantle components during evolution or shutdown of the aborted Midcontinent <span class="hlt">Rift</span>. In effect, mantle was changed into crust by lowering Seismic velocity (through intrusion of lower density magmatic rocks) and increasing Moho (about 8.1 km s-1 depth. ?? 1990.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.T31D..06W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.T31D..06W"><span id="translatedtitle">The Magma Plumbing <span class="hlt">System</span> of Dabbahu and Gabho volcanoes (Afar <span class="hlt">rift</span>, Ethiopia) from InSAR, GPS and Seismicity data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p>2008-12-01</p> <p>In September 2005, a 60-km-long dike, up to 8 meters thick, was intruded into the Dabbahu <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> segment since 2005 (nine by July 2008). Despite the remarkably similar behavior to the Krafla <span class="hlt">system</span> in Iceland, which underwent a <span class="hlt">rifting</span> episode from 1975 to 1984, these observations require a more complex magma plumbing <span class="hlt">system</span>. In contrast to the single inferred shallow chamber beneath Krafla, multiple magmatic sources are required in the Dabbahu <span class="hlt">rift</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T11F..03D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T11F..03D"><span id="translatedtitle">Ambient Noise Tomography of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> in Mozambique</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Domingues, A.; Chamussa, J.; Silveira, G. M.; Custodio, S.; Lebedev, S.; Chang, S.; Ferreira, A. M.; Fonseca, J. F.</p> <p>2013-12-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span> (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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19850056208&hterms=Cenozoic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DCenozoic','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19850056208&hterms=Cenozoic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DCenozoic"><span id="translatedtitle">Cenozoic <span class="hlt">rift</span> formation in the northern Caribbean</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mann, P.; Burke, K.</p> <p>1984-01-01</p> <p><span class="hlt">Rifts</span> form in many different tectonic environments where the lithosphere is put into extension. An outline is provided of the distribution, orientation, and relative ages of 16 Cenozoic <span class="hlt">rifts</span> along the northern edge of the Caribbean plate and it is suggested that these structures formed successively by localized extension as the Caribbean plate moved eastward past a continental promontory of North America. Evidence leading to this conclusion includes (1) recognition that the <span class="hlt">rifts</span> become progressively younger westward; (2) a two-phase subsidence history in a <span class="hlt">rift</span> exposed by upthrusting in Jamaica; (3) the absence of <span class="hlt">rifts</span> east of Jamaica; and (4) the observation that removal of 1400 km of strike-slip displacement on the Cayman Trough fault <span class="hlt">system</span> places the Paleogene <span class="hlt">rifts</span> of Jamaica in an active area of extension south of Yucatan where the <span class="hlt">rifts</span> of Honduras and Guatemala are forming today.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoJI.203.1642L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoJI.203.1642L"><span id="translatedtitle">Coulomb stress evolution in the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>, North China, since 1303 associated with coseismic, post-seismic and interseismic deformation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Bin; Sørensen, Mathilde Bøttger; Atakan, Kuvvet</p> <p>2015-12-01</p> <p>The Shanxi <span class="hlt">rift</span> <span class="hlt">system</span> is one of the most active intraplate tectonic zones in the North China Block, resulting in devastating seismicity. Since 1303, the <span class="hlt">rift</span> has experienced fifteen Ms ? 6.5 earthquakes. Aiming at a better understanding of Coulomb stress evolution and its relationship with the seismicity in the <span class="hlt">rift</span> <span class="hlt">system</span>, we investigated the Coulomb stress changes due to coseismic slip and post-seismic relaxation processes following strong earthquakes as well as the interseismic tectonic loading since the 1303 Hongdong Ms = 8.0 earthquake. Our calculation applies a specified regional medium model, takes the gravity effect into account and uses the fault geometry of the next event as the receiver fault in a given calculation. Our results show that nine out of 12 Ms ? 6.5 earthquakes since the 1303 Hongdong earthquake and more than 82 per cent of small-medium instrumental events after the 1989 Datong-Yanggao Ms = 6.1 earthquake fall into the total stress increased areas. Our results also reveal the different roles of the coseismic, post-seismic and interseismic Coulomb stress changes in the earthquake triggering process in the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>. In a short period after a strong event, the stress field changes are dominated by coseismic Coulomb stress due to sudden slip of the ruptured fault, while in the long term, the stress field is mainly dominated by the accumulation of interseismic tectonic loading. Post-seismic stress changes play an important role by further modifying the distribution of stress and therefore cannot be ignored. Based on the current stress status in the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>, the Linfen basin, southern and northern Taiyuan basin, Xinding basin and the north part of the <span class="hlt">rift</span> <span class="hlt">system</span> are identified as the most likely locations of large events in the future. The results of this study can provide important clues for the further understanding of seismic hazard in the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span> and thus help guiding earthquake risk mitigation efforts in the future.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/878274','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/878274"><span id="translatedtitle">Calibration <span class="hlt">Systems</span> <span class="hlt">Final</span> Report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Myers, Tanya L.; Broocks, Bryan T.; Phillips, Mark C.</p> <p>2006-02-01</p> <p>The Calibration <span class="hlt">Systems</span> project at Pacific Northwest National Laboratory (PNNL) is aimed towards developing and demonstrating compact Quantum Cascade (QC) laser-based calibration <span class="hlt">systems</span> for infrared imaging <span class="hlt">systems</span>. These on-board <span class="hlt">systems</span> 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 <span class="hlt">systems</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..1411434B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..1411434B"><span id="translatedtitle">Initial <span class="hlt">rifting</span> and long-term landscape evolution of the Albertine <span class="hlt">Rift</span> in East Africa</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bauer, F. U.; Glasmacher, U. A.; Ring, U.; Starz, M.; Grobe, R. W.; Mambo, V. S.</p> <p>2012-04-01</p> <p>In East Africa, the feedback between tectonic uplift, erosional denudation and associated possible climate changes is being studied by a multidisciplinary research group, '<span class="hlt">Rift</span>Link'. The group's focus is the Albertine <span class="hlt">Rift</span> of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS), and therein rising Rwenzori Mountains that stretch along the border of the D.R. Congo (DRC) and Uganda. Major questions relate to temporal and spatial evolution of the Rwenzori Mountains and surrounding Albertine <span class="hlt">Rift</span>: is the surface uplift of the Rwenzoris (>5 km) directly linked to <span class="hlt">rift</span> movements in Neogene times, or was there a topographic high long before [1]. To understand the morphological evolution of an area or landscape, knowledge about phases of (dis-)equilibrium between rock exhumation and rock uplift governed by climatic and tectonic processes is essential. Low-temperature thermochronology, like fission-track and (U-Th-Sm)/He dating on apatite and zircon (AFT, AHe, ZHe) are well established tools to trace rock displacements through the upper crust. And, therefore, provide fundamental information helping to decipher the long-term landscape evolution of an area. Thermokinematic modelling, applied to samples from different parts of the working area allow to better constrain the cooling history and landscape evolution of the Rwenzori Mts as well as surrounding Albertine <span class="hlt">Rift</span> which will be discussed in the frame of this presentation. Samples taken along and across the Albertine <span class="hlt">Rift</span>, cover the area around the Rwenzori Mts and the mountain range itself. From thermochronological analyses (AFT, AHe & ZHe) and subsequent thermal modelling a protracted cooling history since Palaeozoic times can be revealed. This allows tracing back the thermal evolution of this area, long before initiation of the EARS, with the latter showing only minor effects on the cooling of the samples. Striking is the distinct cooling pattern within the Rwenzori Mts, where different blocks can be distinguished revealing differentiated cooling histories. Samples from the southern to south-central part reveal Carboniferous to Permian AFT ages, whereas samples further to the north show Jurassic to Carboniferous AFT cooling ages. Youngest AHe cooling ages of ~25 (0.5) Ma, obtained from this area point to a near surface position of these rocks since Miocene/Oligocene times and very recent (Plio-/Pleistocene) <span class="hlt">final</span> surface uplift, where erosion could not compensate for. Thermokinematic modelling, applied to samples from different parts of the working area allow to better constrain the cooling history of the Rwenzori Mts and surrounding Albertine <span class="hlt">Rift</span> and will be discussed in the frame of this presentation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/6064904','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6064904"><span id="translatedtitle">Pre-breakup geology of the Gulf of Mexico-Caribbean: Its relation to Triassic and Jurassic <span class="hlt">rift</span> <span class="hlt">systems</span> of the region</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bartok, P. )</p> <p>1993-02-01</p> <p>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 <span class="hlt">rift</span> trends of the region confirms a relation between the <span class="hlt">rift</span> <span class="hlt">systems</span> 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 <span class="hlt">system</span> 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 <span class="hlt">system</span> is northeast-southwest and essentially parallels the Gyayana Shield, West African, and eastern North American cratons. Mesozoic <span class="hlt">rifting</span> 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 <span class="hlt">rift</span> trend followed along the separation between Yucatan and northern South America. At Lake Maracaibo the Jurassic <span class="hlt">rift</span> <span class="hlt">system</span> eventually overlaps the Triassic <span class="hlt">rifts</span>. The Jurassic <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JAfES..59..168A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JAfES..59..168A"><span id="translatedtitle">Influence of pre-existing fabrics on fault kinematics and <span class="hlt">rift</span> geometry of interacting segments: Analogue models based on the Albertine <span class="hlt">Rift</span> (Uganda), Western Branch-East African <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aanyu, K.; Koehn, D.</p> <p>2011-02-01</p> <p>This study aims at showing how far pre-existing crustal weaknesses left behind by Proterozoic mobile belts, that pass around cratonic Archean shields (Tanzania Craton to the southeast and Congo Craton to the northwest), control the geometry of the Albertine <span class="hlt">Rift</span>. Focus is laid on the development of the Lake Albert and Lake Edward/George sub-segments and between them the greatly uplifted Rwenzori Mountains, a horst block located within the <span class="hlt">rift</span> and whose highest peak rises to >5000 m above mean sea level. In particular we study how the southward propagating Lake Albert sub-segment to the north interacts with the northward propagating Lake Edward/George sub-segment south of it, and how this interaction produces the structures and geometry observed in this section of the western branch of the East African <span class="hlt">Rift</span>, especially within and around the Rwenzori horst. We simulate behaviour of the upper crust by conducting sandbox analogue experiments in which pre-cut rubber strips of varying overstep/overlap connected to a basal sheet and oriented oblique and/or orthogonal to the extension vector, are placed below the sand-pack. The points of connection present velocity discontinuities to localise deformation, while the rubber strips represent ductile domain affected by older mobile belts. From fault geometry of developing <span class="hlt">rift</span> segments in plan view and section cuts, we study kinematics resulting from a given set of boundary conditions, and results are compared with the natural scenario. Three different basal model-configurations are used to simulate two parallel <span class="hlt">rifts</span> that propagate towards each other and interact. Wider overstep (model SbR3) produces an oblique transfer zone with deep grabens (max. 7.0 km) in the adjoining segments. Smaller overlap (model SbR4) ends in offset <span class="hlt">rift</span> segments without oblique transfer faults to join the two, and produces moderately deep grabens (max. 4.6 km). When overlap doubles the overstep (model SbR5), <span class="hlt">rifts</span> propagate sub-orthogonal to the extension direction and form shallow valleys (max. 2.9 km). Relative ratios of overlap/overstep between <span class="hlt">rift</span> segments dictate the kind of transition zone that develops and whether or not a block (like the Rwenzoris) is captured and rotates; hence determining the end-member geometry. Rotation direction is controlled by pre-existing fabrics. Fault orientation, fault kinematics, and block rotation (once in play) reinforce each other; and depending on the local kinematics, different parts of a captured block may rotate with variable velocities but in the same general direction. Mechanical strength anisotropy of pre-structured crust only initially centres fault nucleation and propagation parallel to the grain of weakness of the basement, but at later stages of a protracted period of crustal extension, such boundaries are locally defied.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S13B4454Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S13B4454Z"><span id="translatedtitle">Crustal Structure of and near the North American Mid-continent <span class="hlt">Rift</span> <span class="hlt">System</span> from Receiver Function Studies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, H.; van der Lee, S.; Wolin, E.; Bollmann, T. A.; Revenaugh, J.; Aleqabi, G. I.; Wiens, D. A.; Frederiksen, A. W.; Darbyshire, F. A.</p> <p>2014-12-01</p> <p>The more than 1000-km-long main branch of the mid-continent <span class="hlt">rift</span> <span class="hlt">system</span> (MRS) near Lake Superior and the Minnesota-Wisconsin border nearly took North America apart, but ceased <span class="hlt">rifting</span> soon after it began. Thermal and magmatic events and subsidence- related sedimentary processes significantly changed the structure of the upper crust across and along the MRS. To map the depth extent and lateral changes in deep lithospheric structure related to the MRS, we estimated and studied receiver functions (RFs) from 82 SPREE (Superior Province <span class="hlt">Rifting</span> EarthScope Experiment) broadband seismic stations and seven EarthScope Transportable Array stations. We inverted the RFs for depths of seismic-velocity discontinuities and shear-velocity structure of the crust. The RFs for each station are derived from the deconvolution of the radial component with the vertical component in the time domain (Ammon et al., 1991). Using a relatively high corner frequency in the deconvolution passband helps us resolve multiple layers within the crust. The most prominent feature of the RFs is the P-to-S wave converted at the Moho (Fig. 1), which reflects the contrast in rock properties between the lower crust and upper mantle. This Moho-generated P-to-S converted wave is very clear in RFs for stations outside of the MRS. Inside the MRS, the RFs are more ambiguous and suggestive of a basal crustal layer with shear velocities in between typical lower crust and upper mantle values. There is more variation among the RFs for stations within the MRS than among stations outside of the MRS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JAfES..57..345K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JAfES..57..345K"><span id="translatedtitle">Active fault segments as potential earthquake sources: Inferences from integrated geophysical mapping of the Magadi fault <span class="hlt">system</span>, southern Kenya <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kuria, Z. N.; Woldai, T.; van der Meer, F. D.; Barongo, J. O.</p> <p>2010-06-01</p> <p>Southern Kenya <span class="hlt">Rift</span> has been known as a region of high geodynamic activity expressed by recent volcanism, geothermal activity and high rate of seismicity. The active faults that host these activities have not been investigated to determine their subsurface geometry, faulting intensity and constituents (fluids, sediments) for proper characterization of tectonic <span class="hlt">rift</span> extension. Two different models of extension direction (E-W to ESE-WNW and NW-SE) have been proposed. However, they were based on limited field data and lacked subsurface investigations. In this research, we delineated active fault zones from ASTER image draped on ASTER DEM, together with relocated earthquakes. Subsequently, we combined field geologic mapping, electrical resistivity, ground magnetic traverses and aeromagnetic data to investigate the subsurface character of the active faults. Our results from structural studies identified four fault sets of different age and deformational styles, namely: normal N-S; dextral NW-SE; strike slip ENE-WSW; and sinistral NE-SW. The previous studies did not recognize the existence of the sinistral oblique slip NE-SW trending faults which were created under an E-W extension to counterbalance the NW-SE faults. The E-W extension has also been confirmed from focal mechanism solutions of the swarm earthquakes, which are located where all the four fault sets intersect. Our findings therefore, bridge the existing gap in opinion on neo-tectonic extension of the <span class="hlt">rift</span> suggested by the earlier authors. Our results from resistivity survey show that the southern faults are in filled with fluid (0.05 and 0.2 Ωm), whereas fault zones to the north contain high resistivity (55-75 Ωm) material. The ground magnetic survey results have revealed faulting activity within active fault zones that do not contain fluids. In addition, the 2D inversion of the four aero-magnetic profiles (209 km long) revealed: major vertical to sub vertical faults (dipping 75-85° east or west); an uplifted, heavily fractured and deformed basin to the north (highly disturbed magnetic signatures) characteristic of on going active <span class="hlt">rifting</span>; and a refined architecture of the asymmetry graben to the south with an intrarift horst, whose western graben is 4 km deep and eastern graben is much deeper (9 km), with a zone of significant break in magnetic signatures at that depth, interpreted as source of the hot springs south of Lake Magadi (a location confirmed near surface by ground magnetic and resistivity data sets). The magnetic sources to the north are shallow at 15 km depth compared to 22 km to the south. The loss of magnetism to the north is probably due to increased heat as a result of magmatic intrusion supporting active <span class="hlt">rifting</span> model. Conclusively, the integrated approach employed in this research confirms that fault <span class="hlt">system</span> delineated to the north is actively deforming under E-W normal extension and is a potential earthquake source probably related to magmatic intrusion, while the presence of fluids within the south fault zone reduce intensity of faulting activity and explains lack of earthquakes in a continental <span class="hlt">rift</span> setting.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050176001','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050176001"><span id="translatedtitle">Parga Chasma: Coronae and <span class="hlt">Rifting</span> on Venus</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smrekar, S. E.; Stofan, E. R.; Buck, W. R.; Martin, P.</p> <p>2005-01-01</p> <p>The majority of coronae (quasicircular volcano-tectonic features) are found along <span class="hlt">rifts</span> or fracture belts, and the majority of <span class="hlt">rifts</span> have coronae [e.g. 1,2]. However, the relationship between coronae and <span class="hlt">rifts</span> remains unclear [3-6]. There is evidence that coronae can form before, after, or synchronously with <span class="hlt">rifts</span> [3,4]. The extensional fractures in the <span class="hlt">rift</span> zones have been proposed to be a result of broad scale upwelling and traction on the lower lithosphere [7]. However, not all <span class="hlt">rift</span> <span class="hlt">systems</span> have a significant positive geoid anomaly, as would be expected for an upwelling site [8]. This could be explained if the <span class="hlt">rifts</span> lacking anomalies are no longer active. Coronae are generally accepted to be sites of local upwelling [e.g. 1], but the observed <span class="hlt">rifting</span> is frequently not radial to the coronae and extends well beyond the coronae into the surrounding plains. Thus the question remains as to whether the <span class="hlt">rifts</span> represent regional extension, perhaps driven by mantle tractions, or if the coronae themselves create local thinning and extension of the lithosphere. In the first case, a regional extension model should be consistent with the observed characteristics of the <span class="hlt">rifts</span>. In the latter case, a model of lithospheric loading and fracturing would be more appropriate. A good analogy may be the propagation of oceanic intraplate volcanoes [9].</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_7 --> <div id="page_8" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="141"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/ofr20071047KP09','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/ofr20071047KP09"><span id="translatedtitle">Tectonics of the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>: new light on the history and dynamics of distributed intracontinental extension</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Siddoway, C.S.</p> <p>2007-01-01</p> <p>The West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> (WARS) is the product of multiple stages of intracontinental deformation from Jurassic to Present. The Cretaceous <span class="hlt">rifting</span> phase accomplished >100 percent extension across the Ross Sea and central West Antarctica, and is widely perceived as a product of pure shear extension orthogonal to the Transantarctic Mountains that led to breakup and opening of the Southern Ocean between West Antarctica and New Zealand. New structural, petrological, and geochronological data from Marie Byrd Land reveal aspects of the kinematics, thermal history, and chronology of the Cretaceous intracontinental extension phase that cannot be readily explained by a single progressive event. Elevated temperatures in "Lachlan-type" crust caused extensive crustal melting and mid-crustal flow within a dextral transcurrent strain environment, leading to rapid extension and locally to exhumation and rapid cooling of a migmatite dome and detachment footwall structures. Peak metamorphism and onset of crustal flow that brought about WARS extension between 105 Ma and 90 Ma is kinematically, temporally, and spatially linked to the active convergent margin <span class="hlt">system</span> of East Gondwana. West Antarctica-New Zealand breakup is distinguished as a separate event at 83-70 Ma, from the standpoint of kinematics and thermal evolution</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70016810','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70016810"><span id="translatedtitle">Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> and a speculation on possible climate forcing</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Behrendt, John C.; Cooper, A.</p> <p>1991-01-01</p> <p>The Cenozoic West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, characterized by Cenozoic bimodal alkalic volcanic rocks, extends over a largely ice-covered area, from the Ross Sea nearly to the Bellingshausen Sea. Various lines of evidence lead to the following interpretation: the transantarctic Mountains part of the <span class="hlt">rift</span> shoulder (and probably the entire shoulder) has been rising since about 60 Ma, at episodic rates of ~1 km/m.y., most recently since mid-Pliocene Time, rather than continuously at the mean rate of 100 m/m.y. Uplift rates vary along the scarp, which is cut by transverse faults. It is speculated that this uplift may have climatically forced the advance of the Antarctic ice sheet since the most recent warm period. A possible synergistic relation is suggested between episodic tectonism, mountain uplift, and volcanism in the Cenozoic West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> and waxing and waning of the Antarctic ice sheet beginning about earliest Oligocene time. -from Authors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19850066340&hterms=Continental+Drift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3D%2528Continental%2BDrift%2529','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19850066340&hterms=Continental+Drift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3D%2528Continental%2BDrift%2529"><span id="translatedtitle">Is the Ventersdorp <span class="hlt">rift</span> <span class="hlt">system</span> of southern Africa related to a continental collision between the Kaapvaal and Zimbabwe Cratons at 2.64 Ga AGO?</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burke, K.; Kidd, W. S. F.; Kusky, T.</p> <p>1985-01-01</p> <p>Rocks of the Ventersdorp Supergroup were deposited in a <span class="hlt">system</span> of northeast trending grabens on the Kaapvaal Craton approximately 2.64 Ga ago contemporary with a continental collision between the Kaapvaal and Zimbabwe Cratons. It is suggested that it was this collision that initiated the Ventersdorp <span class="hlt">rifting</span>. Individual grabens strike at high angles toward the continental collision zone now exposed in the Limpopo Province where late orogenic left-lateral strike-slip faulting and anatectic granites are recognized. The Ventersdorp <span class="hlt">rift</span> province is related to extension in the Kaapvaal Craton associated with the collision, and some analogy is seen with such <span class="hlt">rifts</span> as the Shansi and Baikal <span class="hlt">Systems</span> associated with the current India-Asia continental collision.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/7202218','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/7202218"><span id="translatedtitle">Relations between deformation and sediment-hosted copper mineralization: Evidence from the White Pine part of the Midcontinent <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mauk, J.L.; Kelly, W.C.; Pluijm, B.A. van der ); Seasor, R.W. )</p> <p>1992-05-01</p> <p>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 <span class="hlt">rift</span> <span class="hlt">system</span>. 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 <span class="hlt">rift</span>, similar to proposed relations between deformation and mineralization in other tectonic settings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/6455371','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6455371"><span id="translatedtitle">Fluorapatite fenites and Au-deposits, Abitibi belt: petrological constraints on <span class="hlt">rift</span>-environments of Archean gold <span class="hlt">systems</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>King, R.; Kerrich, R.</p> <p>1985-01-01</p> <p>Sporatic enrichments of fluorapatite occur in trondhjemitic intrusions, near Timmins. The sheeted trondhjemites have intruded a deformed ultramafic-Fe tholeiite complex, disposed in the hagingwall of the Destor-Porcupine fault zone. These lithologies have collectively been modified by variable intensities of muscovite-carbonate alteration with attendant vein-related Au deposition. Fluorapatite occurs in veinlets and as subhedral to euhedral crystals coevial with carbonate alteration. Most trondhjemites have REE distributions characteristic of trondjemitic rocks in general where La=150 and La/Yb=30: however a few possess unusual flat depleted patterns, such that La=10 and La/Yb=1. Fluorapatite-bearing examples have P205 up to 8 wt%, TiO2=0.60, Zr=700ppm, Y=75, Th=7, Th/U=3. La=1500 ppm and La/Yb=100, signifying extreme enrichment of certain LIL-elements, in a process interpreted to be allied to fenitization. The fenites, in conjunction with LIL-enriched potassic basalts and lamprophyres are arrayed along major structural linements which also host many of the Abitibi deposits. This petrological association is indicative of <span class="hlt">rift</span> environments, raising the possibility that major structures initiated as transcrustal listric normal faults accommodating <span class="hlt">rifting</span>, and acted as sites for extrusion of komatiites. Subsequently, during reverse translation, the fracture <span class="hlt">systems</span> formed conduits for trondhjemitic magmas from the base of the crust, for auriferous fluids, and LIL-enriched magamas generated in the upper mantle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015DokES.465.1191S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015DokES.465.1191S"><span id="translatedtitle">Modern fault formation in the Earth's crust of the Baikal <span class="hlt">rift</span> <span class="hlt">system</span> according to the data on the mechanisms of earthquake sources</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>San'kov, V. A.; Dobrynina, A. A.</p> <p>2015-11-01</p> <p>The spatial characteristics of seismotectonic deformations and the most likely fracture planes in the earthquake sources of the Baikal <span class="hlt">rift</span> <span class="hlt">system</span> (BRS) are determined using the method of cataclastic analysis of fractures [1]. It is shown that extension conditions with a strike of modern fractures parallel to the <span class="hlt">rift</span>-controlling faults are dominant in the central zone and in most of the NE flank of the BRS. The flat average dip of fractures in the earthquake sources of the main fault zones for some <span class="hlt">rift</span> depressions allow a suggestion about the flattening of faults in the middle crust. The antithetic faults are steeper. The BRS flanks are characterized by dominant shear deformations and more diverse morphogenetic faults in the earthquake sources (strike-slip faults, reversed faults, and normal faults). The modern faults at the BRS flanks weakly inherit the neotectonic structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T53B4676Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T53B4676Z"><span id="translatedtitle">Kinematics and Dynamics of the Kivu <span class="hlt">Rift</span> <span class="hlt">System</span> from Seismic Anisotropy, Seismicity, and Structural Analyses</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zal, H. J.; Wood, D. A.; Ebinger, C. J.; Scholz, C. A.; d'Oreye, N.; Carn, S. A.; Rutagarama, U.</p> <p>2014-12-01</p> <p>The westward-tilted Kivu <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> (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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.T22B..04M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.T22B..04M"><span id="translatedtitle">From hyper-extended <span class="hlt">rifts</span> to orogens: the example of the Mauléon <span class="hlt">rift</span> basin in the Western Pyrenees (SW France)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Masini, E.; Manatschal, G.; Tugend, J.</p> <p>2011-12-01</p> <p>An integral part of plate tectonic theory is that the fate of <span class="hlt">rifted</span> margins is to be accreted into mountain belts. Thus, <span class="hlt">rift</span>-related inheritance is an essential parameter controlling the evolution and architecture of collisional orogens. Although this link is well accepted, <span class="hlt">rift</span> 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 <span class="hlt">rift</span> structures. In this orogen the Late Cretaceous and Tertiary convergence overprints a Late Jurassic to Lower Cretaceous complex intracontinental <span class="hlt">rift</span> <span class="hlt">system</span> related to the opening of the North Atlantic. During the <span class="hlt">rifting</span>, 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 <span class="hlt">rifting</span> 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 <span class="hlt">rift</span> architecture of the Mauléon basin. Two major diachronous detachment <span class="hlt">systems</span> 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 <span class="hlt">final</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span>. In our presentation, we discuss the compressional reactivation of the <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> structures may control style and timing of orogenic processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013SedG..290...47S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013SedG..290...47S"><span id="translatedtitle">Sedimentological and paleoenvironmental constraints of the Statherian and Stenian Espinhaço <span class="hlt">rift</span> <span class="hlt">system</span>, Brazil</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Santos, M. N.; Chemale, F.; Dussin, I. A.; Martins, M.; Assis, T. A. R.; Jelinek, A. R.; Guadagnin, F.; Armstrong, R.</p> <p>2013-05-01</p> <p>The Espinhaço Basin in eastern Brazil contains depositional sequences developed in the São Francisco paleoplate and its margins. Detailed mapping was conducted and combined with U-Pb detrital zircon dating to determine the sedimentological-stratigraphic framework, provenance and minimum and maximum ages of the syn-<span class="hlt">rift</span>-deposits. The two cycles have minimum ages of 1192 and 923 Ma and maximum ages of 1785 and 1685 Ma. The first depositional cycle, represented by the Bandeirinha and São João da Chapada formations, is marked by contributions of Neoarchean and Paleoproterozoic detrital zircons. The second cycle, the diamond-bearing Sopa-Brumadinho Formation, also contains Mesoproterozoic zircons formed between 1300 and 1190 Ma, which suggests an additional external source of Grenvillian age, that was not previously recorded in the São Francisco Craton. The investigation of such Mesoproterozoic intraplate sedimentary records, provides clues to understanding the history of the Rodinia active margins and, therefore, the kinematic reconstruction of its paleoplates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.6338D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.6338D"><span id="translatedtitle">Neotectonic faults and stress field in the East African <span class="hlt">Rift</span> <span class="hlt">System</span> around the Tanzanian Craton - A contribution to the seismotectonic map of Africa</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Delvaux, Damien; Macheyeki, Athanas Simon; Fernandes, Rui-Manuel; Ayele, Atalay; Meghraoui, Mustapha</p> <p>2015-04-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">Rift</span> 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 <span class="hlt">rift</span> segments, as in the Rukwa <span class="hlt">rift</span>, Mbeya southern junction between the eastern and western <span class="hlt">rift</span> branches, and in the Manyara-Natron area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010PhDT........19T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010PhDT........19T"><span id="translatedtitle">Using remote sensing, ecological niche modeling, and Geographic Information <span class="hlt">Systems</span> for <span class="hlt">Rift</span> Valley fever risk assessment in the United States</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tedrow, Christine Atkins</p> <p></p> <p>The primary goal in this study was to explore remote sensing, ecological niche modeling, and Geographic Information <span class="hlt">Systems</span> (GIS) as aids in predicting candidate <span class="hlt">Rift</span> Valley fever (RVF) competent vector abundance and distribution in Virginia, and as means of estimating where risk of establishment in mosquitoes and risk of transmission to human populations would be greatest in Virginia. A second goal in this study was to determine whether the remotely-sensed Normalized Difference Vegetation Index (NDVI) can be used as a proxy variable of local conditions for the development of mosquitoes to predict mosquito species distribution and abundance in Virginia. As part of this study, a mosquito surveillance database was compiled to archive the historical patterns of mosquito species abundance in Virginia. In addition, linkages between mosquito density and local environmental and climatic patterns were spatially and temporally examined. The present study affirms the potential role of remote sensing imagery for species distribution prediction, and it demonstrates that ecological niche modeling is a valuable predictive tool to analyze the distributions of populations. The MaxEnt ecological niche modeling program was used to model predicted ranges for potential RVF competent vectors in Virginia. The MaxEnt model was shown to be robust, and the candidate RVF competent vector predicted distribution map is presented. The Normalized Difference Vegetation Index (NDVI) was found to be the most useful environmental-climatic variable to predict mosquito species distribution and abundance in Virginia. However, these results indicate that a more robust prediction is obtained by including other environmental-climatic factors correlated to mosquito densities (e.g., temperature, precipitation, elevation) with NDVI. The present study demonstrates that remote sensing and GIS can be used with ecological niche and risk modeling methods to estimate risk of virus establishment in mosquitoes and 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 <span class="hlt">Rift</span> 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. <span class="hlt">Rift</span> Valley fever, risk assessment, Ecological Niche Modeling, MaxEnt, Geographic Information <span class="hlt">System</span>, remote sensing, Pearson's Product-Moment Correlation Coefficient, vectors, mosquito distribution, mosquito density, mosquito surveillance, United States, Virginia, domestic animals, white-tailed deer, ArcGIS</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JAESc..99...13W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JAESc..99...13W"><span id="translatedtitle">The subsurface structure and stratigraphic architecture of <span class="hlt">rift</span>-related units in the Lishu Depression of the Songliao Basin, China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Hongyu; Fan, Tailiang; Wu, Yue</p> <p>2015-03-01</p> <p>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 <span class="hlt">rifting</span>. Distinct episodes of compressional tectonic activity caused uplift and exposure of strata evident as the traditional syn- and post-<span class="hlt">rift</span> 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-<span class="hlt">rift</span> stage of deposition. We refer to these sub-stages as the initial <span class="hlt">rifting</span>, the intensive <span class="hlt">rifting</span> and the recession phases. The basin configuration shifted from a graben/half-graben configuration during the initial <span class="hlt">rifting</span> phase, to a dustpan-shaped half-graben pattern during the subsequent phase of intensive <span class="hlt">rifting</span>, and <span class="hlt">finally</span> into a gentle sedimentary basin during the <span class="hlt">final</span> recession phase. The early seismic sequence divides into a lowstand <span class="hlt">systems</span> tract (LST), transgressive <span class="hlt">systems</span> tract (TST) and highstand <span class="hlt">systems</span> tract (HST). Evidence of the LST within the seismic sequence becomes less apparent with the intensive <span class="hlt">rifting</span> phase, while the HST occupied an increasing proportion of the section. The shallow water depositional fill formed during the <span class="hlt">final</span> recession phase consists only of TST and HST components. Depositional environment then shifts from alluvial fan and shallow lacustrine <span class="hlt">systems</span> to fan delta, braided delta - lake, and <span class="hlt">finally</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70032593','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70032593"><span id="translatedtitle">Mercury isotopic composition of hydrothermal <span class="hlt">systems</span> in the Yellowstone Plateau volcanic field and Guaymas Basin sea-floor <span class="hlt">rift</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Sherman, L.S.; Blum, J.D.; Nordstrom, D.K.; McCleskey, R.B.; Barkay, T.; Vetriani, C.</p> <p>2009-01-01</p> <p>To characterize mercury (Hg) isotopes and isotopic fractionation in hydrothermal <span class="hlt">systems</span> we analyzed fluid and precipitate samples from hot springs in the Yellowstone Plateau volcanic field and vent chimney samples from the Guaymas Basin sea-floor <span class="hlt">rift</span>. These samples provide an initial indication of the variability in Hg isotopic composition among marine and continental hydrothermal <span class="hlt">systems</span> that are controlled predominantly by mantle-derived magmas. Fluid samples from Ojo Caliente hot spring in Yellowstone range in δ202Hg from - 1.02‰ to 0.58‰ (± 0.11‰, 2SD) and solid precipitate samples from Guaymas Basin range in δ202Hg from - 0.37‰ to - 0.01‰ (± 0.14‰, 2SD). Fluid samples from Ojo Caliente display mass-dependent fractionation (MDF) of Hg from the vent (δ202Hg = 0.10‰ ± 0.11‰, 2SD) to the end of the outflow channel (&delta202Hg = 0.58‰ ± 0.11‰, 2SD) in conjunction with a decrease in Hg concentration from 46.6pg/g to 20.0pg/g. Although a small amount of Hg is lost from the fluids due to co-precipitation with siliceous sinter, we infer that the majority of the observed MDF and Hg loss from waters in Ojo Caliente is due to volatilization of Hg0(aq) to Hg0(g) and the preferential loss of Hg with a lower δ202Hg value to the atmosphere. A small amount of mass-independent fractionation (MIF) was observed in all samples from Ojo Caliente (Δ199Hg = 0.13‰ ±1 0.06‰, 2SD) but no significant MIF was measured in the sea-floor <span class="hlt">rift</span> samples from Guaymas Basin. This study demonstrates that several different hydrothermal processes fractionate Hg isotopes and that Hg isotopes may be used to better understand these processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tecto..34.2367T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tecto..34.2367T"><span id="translatedtitle">Cenozoic extension in the Kenya <span class="hlt">Rift</span> from low-temperature thermochronology: Links to diachronous spatiotemporal evolution of <span class="hlt">rifting</span> in East Africa</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Torres Acosta, Verónica; Bande, Alejandro; Sobel, Edward R.; Parra, Mauricio; Schildgen, Taylor F.; Stuart, Finlay; Strecker, Manfred R.</p> <p>2015-12-01</p> <p>The cooling history of <span class="hlt">rift</span> shoulders and the subsidence history of <span class="hlt">rift</span> basins are cornerstones for reconstructing the morphotectonic evolution of extensional geodynamic provinces, assessing their role in paleoenvironmental changes and evaluating the resource potential of their basin fills. Our apatite fission track and zircon (U-Th)/He data from the Samburu Hills and the Elgeyo Escarpment in the northern and central sectors of the Kenya <span class="hlt">Rift</span> indicate a broadly consistent thermal evolution of both regions. Results of thermal modeling support a three-phased thermal history since the early Paleocene. The first phase (~65-50 Ma) was characterized by rapid cooling of the <span class="hlt">rift</span> shoulders and may be coeval with faulting and sedimentation in the Anza <span class="hlt">Rift</span> basin, now located in the subsurface of the Turkana depression and areas to the east in northern Kenya. In the second phase, very slow cooling or slight reheating occurred between ~45 and 15 Ma as a result of either stable surface conditions, very slow exhumation, or subsidence. The third phase comprised renewed rapid cooling starting at ~15 Ma. This <span class="hlt">final</span> cooling represents the most recent stage of <span class="hlt">rifting</span>, which followed widespread flood-phonolite emplacement and has shaped the present-day landscape through <span class="hlt">rift</span> shoulder uplift, faulting, basin filling, protracted volcanism, and erosion. When compared with thermochronologic and geologic data from other sectors of the East African <span class="hlt">Rift</span> <span class="hlt">System</span>, extension appears to be diachronous, spatially disparate, and partly overlapping, likely driven by interactions between mantle-driven processes and crustal heterogeneities, rather than the previously suggested north-south migrating influence of a mantle plume.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JGRB..119.8267H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRB..119.8267H"><span id="translatedtitle">Seismicity and subsidence following the 2011 Nabro eruption, Eritrea: Insights into the plumbing <span class="hlt">system</span> of an off-<span class="hlt">rift</span> volcano</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hamlyn, Joanna E.; Keir, Derek; Wright, Tim J.; Neuberg, Jürgen W.; Goitom, Berhe; Hammond, James O. S.; Pagli, Carolina; Oppenheimer, Clive; Kendall, J.-Michael; Grandin, Raphaël.</p> <p>2014-11-01</p> <p>Nabro volcano, situated to the east of the Afar <span class="hlt">Rift</span> Zone, erupted on 12 June 2011. Eruptions at such off-<span class="hlt">rift</span> volcanoes are infrequent, and consequently, the plumbing <span class="hlt">systems</span> are poorly understood. We present posteruption Synthetic Aperture Radar (SAR) images from the TerraSAR-X satellite and posteruption continuous seismic activity from a local seismic array. Interferometric analysis of SAR data, reveals a circular, 12 km wide, signal subsiding at ˜200 mm/yr. We inverted for the best fit Mogi source finding a 4 ± 1 × 107 m3/yr volume decrease at 7 ± 1 km depth. Between 31 August and 7 October 2011, we located 658 and relocated 456 earthquakes with local magnitudes between -0.4 and 4.5. Seismicity beneath the SE edge of Nabro at 11 km depth is likely associated with high strain rates from deep magma flow into the modeled reservoir. This suggests that magma is supplied through a narrow conduit and then stored at ˜7 km depth. We interpret seismicity at 4-6 km depth as brittle fracturing above the inferred magma reservoir. Focal mechanisms delineate a thrust fault striking NE-SW and dipping 45° to the SE across the caldera floor. We propose that the crustal response is to slip on this fault which crosscuts the caldera rather than to deform on ring faults. The NE-SW fault plane is not associated with measurable surface deformation, indicating that it does not contribute much to the caldera deformation. We show that subsidence of the caldera is controlled by magma chamber processes rather than fault slip.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5130219','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5130219"><span id="translatedtitle">Paleoseismologic studies of the Pajarito fault <span class="hlt">system</span>, western margin of the Rio Grande <span class="hlt">rift</span> near Los Alamos, NM</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kelson, K.I. ); Hemphill-Haley, M.A.; Wong, I.G. ); Gardner, J.N.; Reneau, S.L. )</p> <p>1993-04-01</p> <p>As in much of the Basin and Range province, low levels of historical seismicity in the Rio Grande <span class="hlt">rift</span> (RGR) are inconsistent with abundant geologic evidence for large-magnitude, late Pleistocene and Holocene earthquakes. Recent trenching and surficial mapping along the 40-km-long, north-trending Pajarito fault <span class="hlt">system</span> (PFS) near Los Alamos provide evidence for multiple surface-rupture events during the late Pleistocene and Holocene. Near Los Alamos, the Pajarito fault (PAF) exhibits an east-facing scarp up to 120 m high that has had at least four surface-rupture events in the past few hundred thousand years. Four trenches across the base of the highest, easternmost fault scarp show that the most-recent rupture occurred prior to about 9 ka, and possible prior to deposition of the 100- to 150-ka El Cajete Pumice. The long-term (post-1.1 Ma) slip rate on the PAF is about 0.1 mm/yr. The down-to-the-west Rendija Canyon (RCF) and Guaje Mountain (GMF) faults both have had at least two surface ruptures since the middle Pleistocene, including most-recent events at about 7.4 ka along the RCF and about 4 to 6 ka along the GMF. Slickensides and other indirect evidence suggest right-oblique normal slip on the RCF and GMF. Long-term (post-1.1 Ma) slip rates on these two faults are approximately an order of magnitude less than that on the PAF. Based on the observed spatial and temporal variations in activity, the subparallel PAF, RCF, and GMF apparently act as independent seismic sources, although they are located only about 1 to 3 km apart. Nevertheless, the average recurrence interval for faults within the PFS is probably comparable to intervals of 10[sup 4] yr estimated along the eastern <span class="hlt">rift</span> margin near Taos.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17..977P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17..977P"><span id="translatedtitle">Basement Structure Controls on the Evolution and Geometry of <span class="hlt">Rift</span> <span class="hlt">Systems</span> - Insights from Offshore S. Norway using 3D Seismic Data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Phillips, Thomas; Jackson, Christopher; Bell, Rebecca; Duffy, Oliver; Fossen, Haakon</p> <p>2015-04-01</p> <p><span class="hlt">Rift</span> basins form within lithosphere containing a range of heterogeneities, such as thin-skinned thrust belts and larger scale structures such as thick-skinned shear zones or crustal sutures. How the presence and reactivation of these structures during later <span class="hlt">rift</span> events affect the geometry and evolution of <span class="hlt">rifts</span> remains poorly understood as they are not typically well imaged on seismic data. The main reasons for this are that crystalline basement is often buried beneath thick sedimentary successions and contains small impedance contrasts. Furthermore, larger, crustal-scale, lineaments and sutures may not be imaged at all on seismic data due to their large scale and depth. In this study, we use borehole-constrained 2D and 3D seismic reflection data located around the Egersund and Farsund Basins, offshore south Norway. In both areas, crystalline basement is exceptionally well-imaged on typical 2D and 3D reflection data due to large impedance contrasts within a highly heterogeneous, shallow basement. This allows us to map a series of intrabasement reflections and overlying <span class="hlt">rift</span> <span class="hlt">systems</span>. Within the Egersund area, two main types of intrabasement structure are identified and mapped: i) thin (100 m), shallowly dipping (0-10°W) reflections showing a ramp-flat geometry; and ii) thick (1-1.5 km), low angle (c. 30°W) structures comprising of packages of reflections. These structures correlate along-strike northwards to Caledonian orogeny related structures mapped onshore Norway. The thin structures are interpreted as thin-skinned Caledonian thrusts, whereas the thicker structures represent thick-skinned Devonian shear zones formed through orogenic collapse of the Caledonides. Through seismic-stratigraphic analysis of the cover, we document multiple stages of extensional reactivation along these structures during Devonian, Permian-Triassic and Late Jurassic-Early Cretaceous extension followed by reverse reactivation during Late Cretaceous compression. The Farsund Basin is situated above a deep crustal-scale lineament, the Tornquist zone. We also document multiple stages of reactivation and inversion within this basin, linked with motion along the underlying lineament. Reactivation of the Tornquist zone at depth leads to the formation of a deep, narrow basin at shallower levels. However, during reactivation, <span class="hlt">rift</span> propagation may be inhibited by basement heterogeneities, such as pre-existing basement ridges. We find that the type of reactivated structure can exert a strong control on the geometry and evolution of the overlying <span class="hlt">rift</span>. Low-angle, thin-skinned Caledonian thrusts have negligible effect on <span class="hlt">rift</span> evolution as these are not readily reactivated. However, reactivation of thick-skinned structures does affect <span class="hlt">rift</span> morphology. Direct reactivation of low angle Devonian shear zones forms a series of low angle <span class="hlt">rift</span>-bounding faults, creating a wide, shallow basin. Conversely, reactivation of deep seated crustal lineaments causes the localisation of strain fields, creating deep, narrow basins. In both cases, the presence of these thick skinned structures acts as a template for the location of later <span class="hlt">rifts</span>; their subsequent reactivation can then control the <span class="hlt">rift</span> geometry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013Tectp.594..118F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013Tectp.594..118F"><span id="translatedtitle">The role that plate tectonics, inferred stress changes and stratigraphic unconformities have on the evolution of the West and Central African <span class="hlt">Rift</span> <span class="hlt">System</span> and the Atlantic continental margins</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fairhead, J. D.; Green, C. M.; Masterton, S. M.; Guiraud, R.</p> <p>2013-05-01</p> <p>The Muglad <span class="hlt">rift</span> basin of Sudan, is a good example of polyphase <span class="hlt">rifting</span>, with at least three major phases of basin development. Each phase has resulted in the generation of source rock, reservoir and seal geology with structural traps often closely linked to basement highs. In this paper we investigate on a regional scale the tectonic processes that have contributed to <span class="hlt">rift</span> basin development. On a regional scale, the evolution of the Africa-wide Mesozoic <span class="hlt">rift</span> <span class="hlt">system</span> is intimately linked to relative movements of African sub-plates and to global plate tectonic processes and plate interactions. Changes in plate interactions are observed in the oceanic crust as azimuth changes of fracture zone geometries and by inference have caused significant modifications to both the orientation and magnitude of the motions of the African sub-plates. Such plate motion processes have controlled the polyphase development of the West and Central African <span class="hlt">Rift</span> <span class="hlt">System</span>. On the basinal scale, changes of sub-plate motions have resulted in changes in the stress field which have had a clear impact on the deformation and fault geometries of <span class="hlt">rift</span> basins and on the resulting stratigraphy. The construction of the first unified stratigraphic chart for the West and Central African <span class="hlt">Rift</span> <span class="hlt">System</span> shows a close correlation in the timing of the major unconformities with the timing of changes in relative plate motion as observed in the changes of the azimuthal geometry of the oceanic fracture zones in the Central Atlantic. Since similarly timed unconformities exist along the continental margins of Africa and South America, we propose that the causative mechanism is change in relative plate motion which leads to an increase or decrease in the tension on the plate and thus controls the strength or effective elastic thickness, Te, of the crust/plate beneath the margins. This results in a focused change in isostatic response of the margin during short-period changes in relative plate motion; i.e. more tension will mean that loads are not compensated locally resulting in local uplift of the margin.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002SedG..147...13O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002SedG..147...13O"><span id="translatedtitle">The 1.1-Ga Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span>, central North America: sedimentology of two deep boreholes, Lake Superior region</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ojakangas, Richard W.; Dickas, Albert B.</p> <p>2002-03-01</p> <p>The Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> (MRS) of central North America is a 1.1-Ga, 2500-km long structural feature that has been interpreted as a triple-junction <span class="hlt">rift</span> developed over a mantle plume. As much as 20 km of subaerial lava flows, mainly flood basalts, are overlain by as much as 10 km of sedimentary rocks that are mostly continental fluvial red beds. This rock sequence, known as the Keweenawan Supergroup, has been penetrated by a few deep boreholes in the search for petroleum. In this paper, two deep boreholes in the Upper Peninsula of Michigan are described in detail for the first time. Both the Amoco Production #1-29R test, herein referred to as the St. Amour well, and the nearby Hickey Creek well drilled by Cleveland Cliffs Mining Services, were 100% cored. The former is 7238 ft (2410 m) deep and the latter is 5345 ft (1780 m) deep. The entirety of the stratigraphic succession of the Hickey Creek core correlates very well with the upper portion of the St. Amour core, as determined by core description and point-counting of 43 thin sections selected out of 100 studied thin sections. Two Lower Paleozoic units and two Keweenawan red bed units—the Jacobsville Sandstone and the underlying Freda Sandstone—are described. The Jacobsville is largely a feldspatholithic sandstone and the Freda is largely a lithofeldspathic sandstone. Below the Freda, the remaining footage of the St. Amour core consists of a thick quartzose sandstone unit that overlies a heterogenous unit of intercalated red bed units of conglomerate, sandstone, siltstone, and shale; black shale; individual basalt flows; and a basal ignimbritic rhyolite. This lower portion of the St. Amour core presents an enigma, as it correlates very poorly with other key boreholes located to the west and southwest. While a black shale sequence is similar to the petroleum-bearing Nonesuch Formation farther west, there is no conglomerate unit to correlate with the Copper Harbor Conglomerate. Other key boreholes are 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 <span class="hlt">rifting</span> center, complexities of expansion tectonics may well be responsible for igneous and sedimentary sequences that differ considerably from those found farther west along the <span class="hlt">rift</span> arm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70015106','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70015106"><span id="translatedtitle">Mechanical response of the south flank of kilauea volcano, hawaii, to intrusive events along the <span class="hlt">rift</span> <span class="hlt">systems</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Dvorak, J.J.; Okamura, A.T.; English, T.T.; Koyanagi, R.Y.; Nakata, J.S.; Sako, M.K.; Tanigawa, W.T.; Yamashita, K.M.</p> <p>1986-01-01</p> <p>Increased earthquake activity and compression of the south flank of Kilauea volcano, Hawaii, have been recognized by previous investigators to accompany <span class="hlt">rift</span> intrusions. We further detail the temporal and spatial changes in earthquake rates and ground strain along the south flank induced by six major <span class="hlt">rift</span> intrusions which occurred between December 1971 and January 1981. The seismic response of the south flank to individual <span class="hlt">rift</span> intrusions is immediate; the increased rate of earthquake activity lasts from 1 to 4 weeks. Horizontal strain measurements indicate that compression of the south flank usually accompanies <span class="hlt">rift</span> intrusions and eruptions. Emplacement of an intrusion at a depth greater than about 4 km, such as the June 1982 southwest <span class="hlt">rift</span> intrusion, however, results in a slight extension of the subaerial portion of the south flank. Horizontal strain measurements along the south flank are used to locate the January 1983 east-<span class="hlt">rift</span> intrusion, which resulted in eruptive activity. The intrusion is modeled as a vertical rectangular sheet with constant displacement perpendicular to the plane of the sheet. This model suggests that the intrusive body that compressed the south flank in January 1983 extended from the surface to about 2.4 km depth, and was aligned along a strike of N66??E. The intrusion is approximately 11 km in length, extended beyond the January 1983 eruptive fissures, which are 8 km in length and is contained within the 14-km-long region of shallow <span class="hlt">rift</span> earthquakes. ?? 1986.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_8 --> <div id="page_9" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="161"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MarGR..36..263K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MarGR..36..263K"><span id="translatedtitle"><span class="hlt">Rift</span> processes and crustal structure of the Amundsen Sea Embayment, West Antarctica, from 3D potential field modelling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kalberg, Thomas; Gohl, Karsten; Eagles, Graeme; Spiegel, Cornelia</p> <p>2015-12-01</p> <p>The Amundsen Sea Embayment of West Antarctica is of particular interest as it provides critical geological boundary conditions in better understanding the dynamic behavior of the West Antarctic Ice Sheet, which is undergoing rapid ice loss in the Amundsen Sea sector. One of the highly debated hypothesis is whether this region has been affected by the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>, which is one of the largest in the world and the dominating tectonic feature in West Antarctica. Previous geophysical studies suggested an eastward continuation of this <span class="hlt">rift</span> <span class="hlt">system</span> into the Amundsen Sea Embayment. This geophysical study of the Amundsen Sea Embayment presents a compilation of data collected during two RV Polarstern expeditions in the Amundsen Sea Embayment of West Antarctica in 2006 and 2010. Bathymetry and satellite-derived gravity data of the Amundsen Sea Embayment complete the dataset. Our 3-D gravity and magnetic models of the lithospheric architecture and development of this Pacific margin improve previous interpretations from 2-D models of the region. The crust-mantle boundary beneath the continental rise and shelf is between 14 and 29 km deep. The imaged basement structure can be related to <span class="hlt">rift</span> basins within the Amundsen Sea Embayment, some of which can be interpreted as products of the Cretaceous <span class="hlt">rift</span> and break-up phase and some as products of later propagation of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> into the region. An estimate of the flexural rigidity of the lithosphere reveals a thin elastic thickness in the eastern embayment which increases towards the west. The results are comparable to estimates in other <span class="hlt">rift</span> <span class="hlt">systems</span> such as the Basin and Range province or the East African <span class="hlt">Rift</span>. Based on these results, we infer an arm of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> is superposed on a distributed Cretaceous <span class="hlt">rift</span> province in the Amundsen Sea Embayment. <span class="hlt">Finally</span>, the embayment was affected by magmatism from discrete sources along the Pacific margin of West Antarctica in the Cenozoic.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5657215','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5657215"><span id="translatedtitle">Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> and a speculation on possible climate forcing</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Behrendt, J.C. ); Cooper, A. )</p> <p>1991-04-01</p> <p>The Cenzoic West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, characterized by Cenozoic bimodal alkalic volcanic rocks, extends over a largely ice-covered area, from the Ross Sea nearly to the Bellingshausen Sea. It is bounded on one side by a spectacular 4-to 5-km-high <span class="hlt">rift</span>-shoulder scarp (maximum bedrock relief 5 to 7 km) from northern Victoria Land-Queen Maud Mountains to the Ellsworth-Whitmore-Horlick Mountains. Jurassic tholeiites crop out with the late Cenozoic volcanic rocks along the section of the Transantarctic Mountains from northern Victoria Land to the Horlick Mountains. The Cenozoic <span class="hlt">rift</span> shoulder diverges here from the Jurassic tholeiite trend, and the tholeiites are exposed discontinuously along the lower elevation (1-2 km) section of the Transantarctic Mountains to the Weddell Sea. Various lines of evidence, no one of which is independently conclusive, lead the authors (as others have also suggested) to interpret the following. The Transantarctic Mountains part of the <span class="hlt">rift</span> shoulder (and probably the entire shoulder) has been rising since about 60 Ma, at episodic rates of {approximately}1 km/m.y., most recently since mid-Pliocene time, rather than continuously at the mean rate of 100m/m.y. Uplift rates vary along the scarp, which is cut by transverse faults. The authors speculate that this uplift may have climatically forced the advance of the Antarctic ice sheet since the most recent warm period. They suggest a possible synergistic relation between episodic tectonism, mountain uplift, and volcanism in the Cenozoic West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> and waxing and waning of the Antarctic ice sheet beginning about earliest Oligocene time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1714870N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1714870N"><span id="translatedtitle">Rapid spatio-temporal variations in <span class="hlt">rift</span> zone deformation, Corinth <span class="hlt">rift</span>, Greece</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nixon, Casey; McNeill, Lisa; Bull, Jonathan; Henstock, Timothy; Bell, Rebecca; Gawthorpe, Robert; Christodoulou, Dimitris; Kranis, Haris; Ferentinos, George; Papatheodorou, George; Taylor, Brian; Ford, Mary; Sakellariou, Dimitris; Leeder, Mike; Collier, Richard; Goodliffe, Andrew; Sachpazi, Maria</p> <p>2015-04-01</p> <p>The Gulf of Corinth is a young and highly active <span class="hlt">rift</span> (<5 Ma) in its initial stages of development. An abundance of marine geophysical data and onshore exposures makes it an ideal case study for investigating early <span class="hlt">rift</span> and fault development. Using a high resolution chronstratigraphic and <span class="hlt">rift</span> fault model we investigate along strike variations in the basin development within the <span class="hlt">rift</span> over the past 1-2 Myr and establishing a history of fault activity on major basin controlling faults, at temporal resolutions of ca. 100 kyr or less. We focus on variations in depocentre development and the distribution of displacement and faulting along and across the <span class="hlt">rift</span> axis; focussing on the partitioning of deformation between N-dipping and S-dipping faults. The <span class="hlt">rift</span> basin geometry has a complex history and varies spatially along strike of the <span class="hlt">rift</span>. We highlight a major change in <span class="hlt">rift</span> structure ca. 600 ka, changing from a complex <span class="hlt">rift</span> zone to a uniform asymmetric graben. Syn-<span class="hlt">rift</span> isochore maps identify two stages that accommodate this change: 1. a switch in <span class="hlt">rift</span> polarity from a dominant N-thickening depocentre to a dominant S-thickening depocentre between ca. 620-420 ka (a rapid change in <span class="hlt">rift</span> structure and strain distribution). This change is accommodated by transfer of activity between major faults but also by formation of numerous non-basement cutting small faults. 2. Progressive localization of deformation onto major N-dipping faults on the <span class="hlt">rift</span>'s southern margin. This is characterised by depocentre growth and linkage and increased activity on major N-dipping faults since ~340 ka, with faults becoming kinematically and geometrically linked with almost equal slip rates along strike by ca. 130 ka. Ultimately our results show that the early evolution of a <span class="hlt">rift</span> fault network can be complex but that a dominant fault set eventually forms even in the earliest stages of <span class="hlt">rifting</span>. Furthermore a switch in <span class="hlt">rift</span> polarity is a progressive process with deformation becoming distributed before localizing onto a <span class="hlt">final</span> dominant fault set, but this process can occur rapidly on a timescale of 100's kyr.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4003290','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4003290"><span id="translatedtitle">Evidence of <span class="hlt">rift</span> valley fever seroprevalence in the Sahrawi semi-nomadic pastoralist <span class="hlt">system</span>, Western Sahara</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p></p> <p>2014-01-01</p> <p>Background The increasing global importance of <span class="hlt">Rift</span> Valley fever (RVF) is clearly demonstrated by its geographical expansion. The presence of a wide range of host and vector species, and the epidemiological characteristics of RVF, have led to concerns that epidemics will continue to occur in previously unaffected regions of Africa. The proximity of the Sahrawi territories of Western Sahara to endemic countries, such as Mauritania, Senegal, and Mali with periodic isolation of virus and serological evidence of RVF, and the intensive livestock trade in the region results in a serious risk of RVF spread in the Sahrawi territories, and potentially from there to the Maghreb and beyond. A sero-epidemiological survey was conducted in the Saharawi territories between March and April 2008 to investigate the possible presence of the RVF virus (RVFV) and associated risk factors. A two-stage cluster sampling design was used, incorporating 23 sampling sites. Results A total of 982 serum samples was collected from 461 sheep, 463 goats and 58 camels. Eleven samples (0.97%) tested positive for IgG against the RVFV. There were clusters of high seroprevalence located mostly in the Tifariti (7.69%) and Mehaires (7.14%) regions, with the Tifariti event having been found in one single flock (4/26 positive animals). Goats and older animals were at a significantly increased risk being seropositive (p?=?0.007 and p?=?0.007, respectively). Conclusion The results suggest potential RVF activity in the study area, where intense livestock movement and trade with neighbouring countries might be considered as a primary determinant in the spread of the disease. The importance of a continuous field investigation is reinforced, in light of the risk of RVF expansion to historically unaffected regions of Africa. PMID:24758592</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T13C4665S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T13C4665S"><span id="translatedtitle">Earthquake Rupture Forecast of M>= 6 for the Corinth <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scotti, O.; Boiselet, A.; Lyon-Caen, H.; Albini, P.; Bernard, P.; Briole, P.; Ford, M.; Lambotte, S.; Matrullo, E.; Rovida, A.; Satriano, C.</p> <p>2014-12-01</p> <p>Fourteen years of multidisciplinary observations and data collection in the Western Corinth <span class="hlt">Rift</span> (WCR) near-fault observatory have been recently synthesized (Boiselet, Ph.D. 2014) for the purpose of providing earthquake rupture forecasts (ERF) of M>=6 in WCR. The main contribution of this work consisted in paving the road towards the development of a "community-based" fault model reflecting the level of knowledge gathered thus far by the WCR working group. The most relevant available data used for this exercise are: - onshore/offshore fault traces, based on geological and high-resolution seismics, revealing a complex network of E-W striking, ~10 km long fault segments; microseismicity recorded by a dense network ( > 60000 events; 1.5<Mw<4.5), delineating steep and low-angle (blind) active fault geometries between 4 and ~10 km depth; GPS velocity vectors, indicating that most of the N-S extension rate (16 mm/y) is limited to the width of the WCR; recent historical seismicity investigations, that have led to important reassessments of magnitudes and locations of M>=5 19th century events and a few paleoseismological investigations, allowing to consider time-dependent ERF. B-value estimates are found to be catalogue-dependent (WCR, homogenized NOA+Thessaloniki, SHARE), which may call for a potential break in scaling relationship. Furthermore, observed discrepancies between seismicity rates assumed for the modeled faults and those expected from GPS deformation rates call for the presence of aseismic deformation. Uncertainty in the ERF resulting from the lack of precise knowledge concerning both, fault geometries and seismic slip rates, is quantified through a logic tree exploration. Median and precentile predictions are then compared to ERF assuming a uniform seismicity rate in the WCR region. The issues raised by this work will be discussed in the light of seismic hazard assessment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.1274D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.1274D"><span id="translatedtitle">1D model of seismic wave attenuation in the crust and upper mantle in the north-eastern flanc of the Baikal <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dobrynina, Anna; Sankov, Vladimir; Chechelnitsky, Vladimir</p> <p>2014-05-01</p> <p>The deep profiles of quality factor were obtained using coda-waves of local strong and moderate earthquakes (epicentral distances up to 50 km) occurred within north-eastern flanc of the Baikal <span class="hlt">rift</span> <span class="hlt">system</span> during 2002-2009. We used two methods: 1 - the coda envelope method [Experimental.., 1981; Kopnichev, 1991] and 2 - the sliding window method (lapse time window 10-15 sec with a step of 5 sec). Depth of coda-wave penetration was determined according to Pulli's formulae [1984], the velocity of coda-wave is 3.55 km/s (equal to shear wave velocity). For analysis we used the Q values at frequency 1 Hz since for this frequency the attenuation field heterogeneity is most evident [Aptikaeva and Kopnichev, 1991]. In result Q-profiles for eleven local areas were obtained. The Q-values vary from 50 to 170 for different profiles and depths. Herewith quality factor changes nonuniformly - the alternation of layers with high and low Q-values is observed. This phenomenon can be explained by existing velocity discontinuity. In particular for all profiles this alternation is confined to the depth about 100 km. Analysis VP-anomalies obtained in result of 2D teleseismic tomography along Baikal <span class="hlt">rift</span> <span class="hlt">system</span> [Mordvinova, 2009] shows the existence discontinuity on depth about 100 km under most of Baikal <span class="hlt">rift</span> <span class="hlt">system</span> structures. Analysis of 1D profiles of shear wave velocities in the crust and upper mantle after inversion of receiver functions [Anan'in et al., 2009] also shows presence of these discontinuity dividing high and low velocity layers. The comparison of Q-values and shear wave velocities [Anan'in et al., 2009] shown that in high velocity layers quality factor is higher too and vice versa. Multilayer quality factor model for the lithosphere in north-eastern flanc of the Baikal <span class="hlt">rift</span> <span class="hlt">system</span> with the alternation of layers with high and low attenuation determined by us together with analogous data obtained by Yu.F. Kopnichev [1992] for south-western flanc of the <span class="hlt">rift</span> <span class="hlt">system</span> can be one of inferential evidences of passive <span class="hlt">rifting</span> mechanism in studied area. The reported study was supported by RFBR (research project N12-05-31038-mol_a) and by grant of President of Russian Federation (research project N MK-1171.2014.5).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.2542G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.2542G"><span id="translatedtitle">Application of P- and S-receiver functions to investigate crustal and upper mantle structures beneath the Albertine branch of the East African <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gummert, Michael; Lindenfeld, Michael; Wölbern, Ingo; Rümpker, Georg; Kasereka, Celestin; Batte, Arthur</p> <p>2014-05-01</p> <p>The Rwenzori region at the border between Uganda and the Democratic Republic of Congo is part of the western (Albertine) branch of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS). The region is characterized by a horst structure, the Rwenzori Mountains, reaching elevations of more than 5 km and covering an area of about 120 km by 50 km. The unusual location of the mountain range, between two segments of the Albertine <span class="hlt">rift</span>, suggests complex structures of the crust and the upper mantle below. In our study, we employ P- and S-receiver functions in order to investigate the corresponding discontinuities of the lithosphere-asthenosphere <span class="hlt">system</span>. The analyses are based on recordings from a dense network of 33 seismic broadband stations operating in the region for a period of nearly two years, from September 2009 until August 2011. The crustal thickness is analysed by using P-receiver functions and the grid search method of Zhu & Kanamori (2000) which involves the stacking of amplitudes of direct converted (Ps) and multiple phases (PpPs and PpSs) originating from the Moho. The method of S-receiver functions is more effective in analysing deeper discontinuities of the upper mantle, such as the lithosphere-asthenosphere boundary (LAB). The latter method also has the advantage that the interfering influence of multiple phases from shallower discontinuities is avoided. To simplify the analysis of the S-receiver functions, we use an automatic procedure to determine incidence angles used in the rotation from the ZNE <span class="hlt">system</span> to the ray-centered LQT <span class="hlt">system</span>. We apply this approach to confirm and significantly extend results from the study of Wölbern et al. (2012), which provided evidence for an intra-lithospheric discontinuity at depths between 54 km and 104 km and the LAB between 135 km and 210 km. Our results provide evidence for significant variations of crustal thickness beneath the region. The Moho depth varies between 20 km beneath the <span class="hlt">rift</span> valley and 39 km beneath the adjacent <span class="hlt">rift</span> shoulders. We also consider influences of sediment layers and of a low-velocity intra-crustal zone on the thickness estimates. The comparison of the Moho topography with the hypocentral depth distribution of local earthquakes indicates that the seismicity extends from the surface down to the base of the crust. From our investigation, there is no evidence for a crustal root beneath the Rwenzori mountain range. This observation provides support for <span class="hlt">rift</span>-induced delamination, as recently proposed by Wallner and Schmeling (2010), to explain the unusual uplift of the Rwenzori Mountains between two <span class="hlt">rift</span> segments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.H51C1222M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.H51C1222M"><span id="translatedtitle">Exploring for geothermal resource in a dormant volcanic <span class="hlt">system</span>: The Haleakala Southwest <span class="hlt">Rift</span> Zone, Maui, Hawai'i</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martini, B. A.; Lewicki, J. L.; Kennedy, B. M.; Lide, C.; Oppliger, G.; Drakos, P. S.</p> <p>2011-12-01</p> <p>Suites of new geophysical and geochemical surveys provide compelling evidence for geothermal resource at the Haleakala Southwest <span class="hlt">Rift</span> Zone (HSWRZ) on Maui Island, Hawai'i. Ground-based gravity (~400 stations) coupled with heli-borne magnetics (~1500 line kilometers) define both deep and shallow fractures/faults while also delineating potentially widespread subsurface hydrothermal alteration on the lower flanks (below approximately 1800 feet a.s.l.). Multi-level, upward continuation calculations and 2-D gravity and magnetic modeling provide information on source depths, but lack of lithologic information leaves ambiguity in the estimates. Lithology and physical property data from future drilling will improve these interpretations. Additionally, several well-defined gravity lows (possibly vent zones) lie coincident with magnetic highs suggesting the presence of dike intrusions at depth; a potentially young source of heat for a modern geothermal <span class="hlt">system</span>. Soil CO2 fluxes were measured along transects across geophysically-defined faults and fractures as well as young cinder cones along the HSWRZ; a weak anomalous flux signal was observed at one young cinder cone location. Dissolved inorganic carbon concentrations and ?13C compositions and 3He/4He values measured in several shallow groundwater samples indicate addition of magmatic CO2 and He to the groundwater <span class="hlt">system</span>. The general lack of observed magmatic surface CO2 signals on the HSWRZ is therefore likely due to a combination of groundwater 'scrubbing' of CO2 and relatively high biogenic surface CO2 fluxes that mask magmatic CO2. Similar surveys at the Puna geothermal field on the Kilauea Lower East <span class="hlt">Rift</span> Zone (KLERZ) also showed a lack of surface CO2 flux signals attributed to a magmatic source, while aqueous geochemistry indicated contribution of magmatic CO2 and He to shallow groundwaters at both Maui and Puna. As magma has been intercepted in geothermal drilling at the Puna field, the lack of measured surface CO2 flux associated with upflow of magmatic fluids here is likely due to the aforementioned 'scrubbing' from extensive groundwater flow, as well as high background biogenic CO2 flux. Deep, temperature gradient core holes have been sited based on these geophysical and geochemical datasets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1713633R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1713633R"><span id="translatedtitle">Receiver function imaging of the lithosphere-asthenosphere boundary and melt beneath the Afar <span class="hlt">Rift</span> in comparison to other <span class="hlt">systems</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rychert, Catherine A.; Harmon, Nicholas</p> <p>2015-04-01</p> <p>Heating, melting, and stretching destroy continents at volcanic <span class="hlt">rifts</span>. Mantle plumes are often invoked to thermally weaken the continental lithosphere and accommodate <span class="hlt">rifting</span> through the influx of magma. However the relative effects of mechanical stretching vs. melt infiltration and weakening are not well quantified during the evolution of <span class="hlt">rifting</span>. S-to-p (Sp) imaging beneath the Afar <span class="hlt">Rift</span> provides additional constraints. We use two methodologies to investigate structure and locate robust features: 1) binning by conversion point and then simultaneous deconvolution in the frequency domain, and 2) extended multitaper followed by migration and stacking. We image a lithosphere-asthenosphere boundary at ~75 km beneath the flank of the Afar <span class="hlt">Rift</span> vs. its complete absence beneath the <span class="hlt">rift</span>. Instead, a strong velocity increase with depth at ~75 km depth is imaged. Beneath the <span class="hlt">rift</span> axis waveform modeling suggests the lack of a mantle lithosphere with a velocity increase at ~75 km depth. Geodynamic models that include high melt retention and suppress thermal convection easily match the required velocity-depth profile, the velocity increase arising from a drop in melt percentage at the onset of decompression melting. Whereas, models with conservative melt retention that include thermal buoyancy effects cannot reproduce the strong velocity increase. The shallow depth of the onset of melting is consistent with a mantle potential temperature = 1350 - 1400°C, i.e., typical for adiabatic decompression melting. Trace element signatures and geochemical modeling have been used to argue for a thick lithosphere beneath the <span class="hlt">rift</span> and slightly higher mantle potential temperatures ~1450°C, although overall, given modeling assumptions, the results are not in disagreement. Therefore, although a plume initially destroyed the mantle lithosphere, its influence directly beneath Afar today is not strong. Volcanism continues via adiabatic decompression melting assisted by strong melt buoyancy effects. This contrasts with a similar feature at much deeper depth, ~150 km, beneath Hawaii, Iceland, and Galapagos. Improved high resolution imaging of <span class="hlt">rifting</span>, 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 <span class="hlt">rifts</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T43F2745S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T43F2745S"><span id="translatedtitle">Minimal Role of Basal Shear Tractions in Driving Nubia-Somalia Divergence Across the East African <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stamps, D. S.; Calais, E.; Iaffaldano, G.; Flesch, L. M.</p> <p>2012-12-01</p> <p>The Nubian and Somalian plates actively diverge along the topographically high, ~5000 km long East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS). As no major subduction zones bound Africa, one can assume that the forces driving the Nubia-Somalia plate <span class="hlt">system</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5237275','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5237275"><span id="translatedtitle">Off-axis volcanism in the Gregory <span class="hlt">rift</span>, east Africa: implications for models of continental <span class="hlt">rifting</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bosworth, W.</p> <p>1987-05-01</p> <p>The largest volcanic centers of the Gregory <span class="hlt">rift</span> occur in two belts located 100 to 150 km east and west of the axis of the <span class="hlt">rift</span> valley. These off-axis volcanic belts include the highest peaks on the continent of Africa and are interpreted to lie above the intersection of low-angle detachment <span class="hlt">systems</span> with the base of a regionally thinned lithosphere. These detachment <span class="hlt">systems</span> are manifested at the surface as a series of breakaway zones and regional bounding faults that produce subbasins with half-graben form. The asymmetry of subbasins alternates along the <span class="hlt">rift</span> axis, indicating that the polarity of the underlying active detachment <span class="hlt">systems</span> also reverses. The detachments are separated laterally by regional oblique-slip accommodation zones typified by wrench-style tectonism. Off-axis from the <span class="hlt">rift</span>, the detachments are inferred to merge along strike as they cut to the base of the lithosphere. This results in irregular but persistent paired zones of volcanism and lithospheric thinning off-axis from the <span class="hlt">rift</span> proper. The development of major volcanic cones such as Mount Kilimanjaro may be controlled by the interaction of leaky accommodation zones with the regions of structurally thinned lithosphere. The central Kenya hot spot has produced the anomalous quantities of volcanic material that fills the Gregory <span class="hlt">rift</span> and probably enhances the off-axis volcanism but does not directly control its location. The model proposed here for tectonic controls of volcanism in the Gregory <span class="hlt">rift</span> may be applicable to Phanerozoic continental <span class="hlt">rifts</span> in general.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JSeis..19..141L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JSeis..19..141L"><span id="translatedtitle">New magnitude scales M L and spectrum-based M w for the area around Shanxi <span class="hlt">Rift</span> <span class="hlt">System</span>, North China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Bin; Havskov, Jens; Ottemöller, Lars; Sørensen, Mathilde Bøttger</p> <p>2015-01-01</p> <p>A new locally calibrated M L scale was derived for the area around the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/ofr20071047SRP108','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/ofr20071047SRP108"><span id="translatedtitle">Structure of the central Terror <span class="hlt">Rift</span>, western Ross Sea, Antarctica</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hall, Jerome; Wilson, Terry; Henrys, Stuart</p> <p>2007-01-01</p> <p>The Terror <span class="hlt">Rift</span> is a zone of post-middle Miocene faulting and volcanism along the western margin of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>. A new seismic data set from NSF geophysical cruise NBP04-01, integrated with the previous dataset to provide higher spatial resolution, has been interpreted in this study in order to improve understanding of the architecture and history of the Terror <span class="hlt">Rift</span>. The Terror <span class="hlt">Rift</span> contains two components, a structurally-controlled rollover anticlinal arch intruded by younger volcanic bodies and an associated synclinal basin. Offsets and trend changes in fault patterns have been identified, coincident with shifts in the location of depocenters that define <span class="hlt">rift</span> sub-basins, indicating that the Terror <span class="hlt">Rift</span> is segmented by transverse structures. Multiple phases of faulting all post-date 17 Ma, including faults cutting the seafloor surface, indicating Neogene <span class="hlt">rifting</span> and possible modern activity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..1411351B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..1411351B"><span id="translatedtitle">Constraining the thermal and erosional evolution of the Rwenzori Mtns, Albertine <span class="hlt">Rift</span>, by detrital thermochronology</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bauer, F. U.; Roller, S.; Grobe, R. W.; Glasmacher, U. A.; Hinderer, M.; Ring, U.; Mambo, V. S.</p> <p>2012-04-01</p> <p>In East Africa, the feedback between tectonic uplift, erosional denudation and associated possible climate changes is being studied by a multidisciplinary research group, '<span class="hlt">Rift</span>Link'. The group's focus is the Albertine <span class="hlt">Rift</span> of the East African <span class="hlt">Rift</span> <span class="hlt">System</span>, 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 <span class="hlt">final</span> rock uplift in Plio- to Pleistocene times, thereby, was very fast that the erosion could not keep pace [1]. In order to narrow the <span class="hlt">final</span> exhumation stage detrital thermochronology has proven to be very useful. Therefore, sedimentary successions of the Albertine <span class="hlt">Rift</span> 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 <span class="hlt">Rift</span> and will discuss its implications for the landscape evolution of this area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Tecto..33.1178S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Tecto..33.1178S"><span id="translatedtitle">Structure and kinematics of the Taupo <span class="hlt">Rift</span>, New Zealand</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Seebeck, Hannu; Nicol, Andrew; Villamor, Pilar; Ristau, John; Pettinga, Jarg</p> <p>2014-06-01</p> <p>The structure and kinematics of the continental intra-arc Taupo <span class="hlt">Rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rifting</span> in the North Island. In detail, orthogonal <span class="hlt">rifting</span> (? = 85-90°) transitions northward to oblique <span class="hlt">rifting</span> (? = 69-71°) across a paleovertical-axis rotation boundary where <span class="hlt">rift</span> 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 <span class="hlt">rift</span> by strike-slip faults in the North Island Fault <span class="hlt">System</span> (NIFS). Toward the north where the <span class="hlt">rift</span> and NIFS intersect, ~4 mm/yr strike slip is transferred into the <span class="hlt">rift</span> with net oblique extension accommodating a component of margin-parallel motion. The trend and kinematics of the Taupo <span class="hlt">Rift</span> are comparable to late Miocene-Pliocene intra-arc <span class="hlt">rifting</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5840034','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5840034"><span id="translatedtitle">Cenozoic <span class="hlt">rift</span> tectonics of the Japan Sea</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kimura, K.</p> <p>1988-08-01</p> <p>The Japan Sea is one of the back-arc basins in trench-arc <span class="hlt">systems</span> bordering the western Pacific. Recent paleomagnetic works suggest the Japan Sea opened during early to middle Miocene. Radiometric and microfossil ages of the Cenozoic onland sequences in the Japanese Islands elucidate the <span class="hlt">rift</span> tectonics of the Japan Sea. The <span class="hlt">rifting</span> history is summarized as follows: nonmarine volcanic formations of prerift stage before 50 Ma, <span class="hlt">rift</span>-onset unconformity at 40 Ma, nonmarine volcanic formations of synrift stage 20-33 Ma, breakup unconformity 19 Ma showing the opening of the Japan Sea, marine volcanic and sedimentary formations of synrift stage 14.5-18 Ma, beginning of regional subsidence 14.5 Ma corresponding to the end of the Japan Sea opening, marine sedimentary formations of postdrift stage after 14.5 Ma. <span class="hlt">Rifting</span> is not limited to the synrift stage but is continued to the syndrift stage. <span class="hlt">Rifting</span> led to a horst-and-graben structure. Thus, the Cenozoic onland sequences in the Japanese Islands are suited for a study of <span class="hlt">rift</span> tectonics because the sequences were subaerially exposed by the late Miocene-Holocene island-arc tectonics. <span class="hlt">Rift</span> tectonics cannot be studied as easily in most Atlantic-type passive margins.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T33B4659B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T33B4659B"><span id="translatedtitle">The Role of <span class="hlt">Rift</span> Obliquity During Pangea Fragmentation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brune, S.; Butterworth, N. P.; Williams, S.; Müller, D.</p> <p>2014-12-01</p> <p>Does supercontinent break-up follow specific laws? What parameters control the success and the failure of <span class="hlt">rift</span> <span class="hlt">systems</span>? Recent analytical and geodynamic modeling suggests that oblique <span class="hlt">rifting</span> is energetically preferred over orthogonal <span class="hlt">rifting</span>. This implies that during <span class="hlt">rift</span> competition, highly oblique branches proceed to break-up while less oblique ones become inactive. These models predict that the relative motion of Earth's continents during supercontinent break-up is affected by the orientation and shape of individual <span class="hlt">rift</span> <span class="hlt">systems</span>. Here, we test this hypothesis based on latest plate tectonic reconstructions. Using PyGPlates, a recently developed Python library that allows script-based access to the plate reconstruction software GPlates, we quantify <span class="hlt">rift</span> obliquity, extension velocity and their temporal evolution for continent-scale <span class="hlt">rift</span> <span class="hlt">systems</span> of the past 200 Myr. Indeed we find that many <span class="hlt">rift</span> <span class="hlt">systems</span> contributing to Pangea fragmentation involved strong <span class="hlt">rift</span> obliquity. East and West Gondwana for instance split along the East African coast with a mean obliquity of 55° (measured as the angle between local <span class="hlt">rift</span> trend normal and extension direction). While formation of the central and southern South Atlantic segment involved a low obliquity of 10°, the Equatorial Atlantic opened under a high angle of 60°. <span class="hlt">Rifting</span> between Australia and Antarctica involved two stages with 25° prior to 100 Ma followed by 50° obliquity and distinct increase of extension velocity. Analyzing the entire passive margin <span class="hlt">system</span> that formed during Pangea breakup, we find a mean obliquity of 40°, with a standard deviation of 20°. Hence 50% of these margins formed with an angle of 40° or more. Considering that many conceptual models of <span class="hlt">rifting</span> and passive margin formation assume 2D deformation, our study quantifies the degree to which such 2D models are globally applicable, and highlights the importance of 3D models where oblique <span class="hlt">rifting</span> is the dominant mode of deformation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10158587','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10158587"><span id="translatedtitle">Organic Geochemical and tectonic evolution of the Midcontinent <span class="hlt">Rift</span> <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hayes, J.M.; Pratt, L.M.; Knoll, A.H.</p> <p>1992-12-31</p> <p>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).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25517098','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25517098"><span id="translatedtitle">Segmented lateral dyke growth in a <span class="hlt">rifting</span> event at Bárðarbunga volcanic <span class="hlt">system</span>, Iceland.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S; Ófeigsson, Benedikt G; Heimisson, Elías Rafn; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Gudmundsson, Gunnar B; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T; Högnadóttir, Thórdís; Fridriksdóttir, Hildur María; Hensch, Martin; Einarsson, Páll; Magnússon, Eyjólfur; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert S; Ágústsdóttir, Thorbjörg; Greenfield, Tim; Green, Robert G; Hjartardóttir, Ásta Rut; Pedersen, Rikke; Bennett, Richard A; Geirsson, Halldór; La Femina, Peter C; Björnsson, Helgi; Pálsson, Finnur; Sturkell, Erik; Bean, Christopher J; Möllhoff, Martin; Braiden, Aoife K; Eibl, Eva P S</p> <p>2015-01-01</p> <p>Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long. Previous models of <span class="hlt">rifting</span> events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens, or magma flowing vertically into dykes from an underlying source, with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Bárðarbunga volcanic <span class="hlt">system</span> grew laterally for more than 45 kilometres at a variable rate, with topography influencing the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred primarily over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning <span class="hlt">System</span> (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bárðarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of magnitude M > 5 earthquakes. Dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries. PMID:25517098</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007epsc.conf..955G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007epsc.conf..955G"><span id="translatedtitle">Continental <span class="hlt">rifting</span> on Earth and Mars - A comparison</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Grott, M.; Hauber, E.; Kronberg, P.</p> <p>2007-08-01</p> <p>The formation of continental <span class="hlt">rift</span> <span class="hlt">systems</span> on Earth is connected to prerift uplift generated by upwelling mantle plumes and extensional stresses which originate from remote plate boundary forces. Continental <span class="hlt">rifting</span> and continental breakup on Earth are therefore intimately connected to Earth's plate tectonic environment. Recently, Martian candidate analogues to terrestrial continental <span class="hlt">rifts</span> have been investigated in detail and it has been shown that the Tempe Fossae, Acheron Fossae and Thaumasia Highland <span class="hlt">Rifts</span> bear many structural similarities to continental <span class="hlt">rifts</span> on Earth. However, the question of the <span class="hlt">rift</span> formation process has so far not been addressed and an active mechanism involving mantle plumes and local doming has usually been assumed. <span class="hlt">Rifts</span> are also sometimes thought to be at least indirect evidence for plate tectonics, although the connection of Martian <span class="hlt">rifts</span> to plate tectonic forces has so far not been discussed. We have investigated whether forces connected to plate movement are necessary to initiate <span class="hlt">rifting</span> and show that lithosphere scale faulting at the Thaumasia Highland <span class="hlt">Rift</span> is feasible even in the absence of mantle plumes or tensional plate-boundary forces. Rather, stresses originating from horizontal differences of the gravitational potential energy will be shown to be almost sufficient to induce <span class="hlt">rifting</span>, supporting the hypothesis of a passive <span class="hlt">rifting</span> mechanism in the Thaumasia Highlands. The emplacement of magma bodies in the upper crust could then sufficiently weaken the lithosphere to initiate lithosphere scale faulting and thus induce <span class="hlt">rifting</span>. This hypothesis is in good agreement with the observation of <span class="hlt">rift</span>-related volcanism as well as the fact that faults seem to initiate at volcanoes and propagate away from them before interconnecting. We conclude that <span class="hlt">rifting</span> on Mars is feasible even if key factors connected to continental <span class="hlt">rifting</span> on Earth, i.e. plate boundary forces and convection induced drag on the lower lithosphere, are absent. The absence of forces connected to plate tectonics is also consistent with the observed moderate extension of only a few kilometers. These values are typical for young terrestrial <span class="hlt">rifts</span> (e.g., the Kenya-<span class="hlt">rift</span>) and failed arms and suggest that large scale plate movement and subduction did not play a role in Martian <span class="hlt">rifting</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=204432','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=204432"><span id="translatedtitle">A <span class="hlt">Rift</span> Valley fever risk surveillance <span class="hlt">system</span> for Africa using remotely sensed data: Potential for use on other continents</span></a></p> <p><a target="_blank" href="http://www.ars.usda.gov/services/TekTran.htm">Technology Transfer Automated Retrieval System (TEKTRAN)</a></p> <p></p> <p></p> <p><span class="hlt">Rift</span> Valley fever (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...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/21080318','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/21080318"><span id="translatedtitle">TerraSAR-X high-resolution radar remote sensing: an operational warning <span class="hlt">system</span> for <span class="hlt">Rift</span> Valley fever risk.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Vignolles, Cécile; Tourre, Yves M; Mora, Oscar; Imanache, Laurent; Lafaye, Murielle</p> <p>2010-11-01</p> <p>In the vicinity of the Barkedji village (in the Ferlo region of Senegal), the abundance and aggressiveness of the vector mosquitoes for <span class="hlt">Rift</span> Valley fever (RVF) are strongly linked to rainfall events and associated ponds dynamics. Initially, these results were obtained from spectral analysis of high-resolution (~10 m) Spot-5 images, but, as a part of the French AdaptFVR project, identification of the free water dynamics within ponds was made with the new high-resolution (down to 3-meter pixels), Synthetic Aperture Radar satellite (TerraSAR-X) produced by Infoterra GmbH, Friedrichshafen/Potsdam, Germany. During summer 2008, within a 30 x 50 km radar image, it was found that identified free water fell well within the footprints of ponds localized by optical data (i.e. Spot-5 images), which increased the confidence in this new and complementary remote sensing technique. Moreover, by using near real-time rainfall data from the Tropical Rainfall Measuring Mission (TRMM), NASA/JAXA joint mission, the filling-up and flushing-out rates of the ponds can be accurately determined. The latter allows for a precise, spatio-temporal mapping of the zones potentially occupied by mosquitoes capable of revealing the variability of pond surfaces. The risk for RVF infection of gathered bovines and small ruminants (~1 park/km(2)) can thus be assessed. This new operational approach (which is independent of weather conditions) is an important development in the mapping of risk components (i.e. hazards plus vulnerability) related to RVF transmission during the summer monsoon, thus contributing to a RVF early warning <span class="hlt">system</span>. PMID:21080318</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFMGP11A0732K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFMGP11A0732K"><span id="translatedtitle">Paleomagnetism and paleointensity of Mid-Continental <span class="hlt">Rift</span> <span class="hlt">System</span> basalts at Silver Mountain and Sturgeon River Falls (Upper Michigan)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kulakov, E.; Piispa, E. J.; Laird, M. S.; Smirnov, A. V.; Diehl, J. F.</p> <p>2009-12-01</p> <p>Paleomagnetic and paleointensity data from Precambrian rocks are of great importance for understanding the early geodynamo and tectonic evolution of the Earth. We will present results from a rock magnetic and paleomagnetic investigation of basaltic lava flow sequences at Silver Mountain and Sturgeon River Falls in Upper Michigan. While the Silver Mountain and Sturgeon River Falls lava flows have not been radiometrically dated, these rocks have been assigned to the Siemens Creek Volcanics, the lowermost member of ~1.1 Ga Powder Mill Group (PMG). The PMG represents one of the oldest volcanic units associated with the Mid-Continental <span class="hlt">Rift</span> <span class="hlt">System</span> (MCRS). We sampled 13 lava flows from the Silver Mountain and two lava flows from the Sturgeon River Falls exposures (a minimum of 15 cores per flow were taken). Paleomagnetic directions were determined from detailed thermal and/or alternating field demagnetization preceded by an initial low-temperature (liquid nitrogen) demagnetization. Most specimens revealed a single- or a two-component remanent magnetization. At both locations, the characteristic remanent magnetization (ChRM) has a reversed direction with very steep inclination similar to that found in other rocks representing the early stages of MCRS. Our magnetic hysteresis measurements, unblocking temperature spectra, and scanning electron microscopy analyses suggest low-Ti, pseudosingle-domain titanomagnetite as the principal magnetic carrier in these rocks. For paleointensity determinations, we applied the multispecimen parallel differential pTRM method. These data add to the Precambrian paleointensity database which otherwise remains limited because of alteration and other factors hampering the applicability of conventional Thellier double-heating method.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5639174','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5639174"><span id="translatedtitle">Extension of the southeastern terminus of the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> southward from Michigan to the Ohio-Kentucky border</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dickas, A.B. . Dept. of Geology)</p> <p>1992-01-01</p> <p>The Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> (MRS), a 2,700 km long, horseshoe shaped, intra-continental, thermo-tectonic structure of Middle Proterozoic age, extends from central Kansas to at least southern Ohio by way of the Lake Superior basin. Its western arm, geophysically identified as the Midcontinent Gravity High, has recently been clarified structurally and lithologically as a result of extensive seismic reflection surveying and the drilling of four state record-depth hydrocarbon exploration boreholes. The 1989 discovery, in southwestern Ohio, of the Middle Run Formation, a pre-Upper Cambrian red-bed clastic sequence, together with reflection seismology identification of extension structure in western Ohio, provides for the first time compelling evidence that the eastern arm of the MRS extends at least as far south as the Ohio-Kentucky border. Representative cuts of the Middle Run (type-section) core compare petrographically with QFL analyses of the Middle Proterozoic Oronto Group, the initial synrift sedimentary sequence exposed within the classic MRS Keweenawan outcrop belt of the south shore of Lake Superior in Wisconsin and Michigan. In addition, interpretation of a short reflection profile conducted over the Middle Run basin displays half-graben structure and seismic stratigraphy similar to that mapped in recent years by MRS seismic studies both onshore and offshore Lake Superior, and by onshore Lake Superior isopach mapping of MRS units. On the basis of similarities in petrography, seismic stratigraphy, structure, and proximity to regional gravity anomalies, the Middle Run Formation and its half-graben basin is proposed as evidence for the extension of the MRS from southeastern Michigan to southwestern Ohio. Minor adjustments in the MRS axis in southwest Ohio will be possible upon separation of the regional MRS from the Grenville Front Tectonic Zone gravity and magnetic field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17..171C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17..171C"><span id="translatedtitle">Multiple mantle upwellings beneath the Northern East-African <span class="hlt">Rift</span> <span class="hlt">System</span> from relative P- and S-wave traveltime tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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</p> <p>2015-04-01</p> <p>Mantle plumes have been invoked as the likely cause of East African <span class="hlt">Rift</span> 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 <span class="hlt">rift</span>. 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 <span class="hlt">rift</span>. 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 <span class="hlt">Rift</span>, a region with off-<span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=PIA11082&hterms=Rifting+fissure&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DRifting%2Bfissure','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=PIA11082&hterms=Rifting+fissure&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DRifting%2Bfissure"><span id="translatedtitle">East African <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2008-01-01</p> <p><p/> Places where the earth's crust has formed deep fissures and the plates have begun to move apart develop <span class="hlt">rift</span> structures in which elongate blocks have subsided relative to the blocks on either side. The East African <span class="hlt">Rift</span> is a world-famous example of such <span class="hlt">rifting</span>. It is characterized by 1) topographic deep valleys in the <span class="hlt">rift</span> zone, 2) sheer escarpments along the faulted walls of the <span class="hlt">rift</span> zone, 3) a chain of lakes within the <span class="hlt">rift</span>, most of the lakes highly saline due to evaporation in the hot temperatures characteristic of climates near the equator, 4) voluminous amounts of volcanic rocks that have flowed from faults along the sides of the <span class="hlt">rift</span>, and 5) volcanic cones where magma flow was most intense. This example in Kenya displays most of these features near Lake Begoria. <p/> The image was acquired December 18, 2002, covers an area of 40.5 x 32 km, and is located at 0.1 degrees north latitude, 36.1 degrees east longitude. <p/> The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/6747539','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6747539"><span id="translatedtitle">Volcanism at <span class="hlt">rifts</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>White, R.S.; McKenzie, D.P.</p> <p>1989-07-01</p> <p>The earth's outer shell <span class="hlt">rifts</span> continuously, stretching and splitting both on the ocean's floor and on continents. Every 30 million years or so the <span class="hlt">rifting</span> becomes cataclysmic, releasing continent-size floods of magma. This paper explains that the same mechanism is at work in both cases, the difference being in the slightly hotter temperature of the parent mantle for spectacular volcanic outbursts. Two kinds of evidence are described: quantitative descriptions of rock melting and a wide range of observations made on the <span class="hlt">rifted</span> edges of continents and in the oceans that have opened between them.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.8118P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.8118P"><span id="translatedtitle">Petrofabrics of olivine in a <span class="hlt">rift</span> axis and <span class="hlt">rift</span> shoulder and their implications for seismic anisotropy beneath the Rio Grande <span class="hlt">rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Park, Munjae; Jung, Haemyeong; Kil, Youngwoo</p> <p>2015-04-01</p> <p>Mantle-derived xenoliths associated with continental <span class="hlt">rifting</span> 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 <span class="hlt">rift</span> shoulder and Elephant Butte (EB) at a <span class="hlt">rift</span> axis in the Rio Grande <span class="hlt">rift</span> (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 <span class="hlt">system</span> of (100)[001] at the <span class="hlt">rift</span> shoulder, whereas EB peridotites exhibited A-type LPO indicating a dominant slip <span class="hlt">system</span> of (010)[100] at the <span class="hlt">rift</span> 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 <span class="hlt">rift</span> shoulder (AD), whereas mantle depletion by decompression partial melting caused deformation of rocks under dry conditions (with olivine A-type LPO) at the <span class="hlt">rift</span> axis (EB). These observations provide evidence for localized hydration and physicochemical heterogeneity of the upper mantle in the Rio Grande <span class="hlt">rift</span> (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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.8501G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.8501G"><span id="translatedtitle">Tectono-Sedimentary Analysis of <span class="hlt">Rift</span> Basins: Insights from the Corinth <span class="hlt">Rift</span>, Greece</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gawthorpe, Robert; Ford, Mary</p> <p>2015-04-01</p> <p>Existing models for the tectono-sedimentary evolution of <span class="hlt">rift</span> basins are strongly linked the growth and linkage of normal fault segments and localization of fault activity. Early stages of faulting (<span class="hlt">rift</span> initiation phase) are characterized by distributed, short, low displacement fault segments, subdued fault-related topography and small depocentres within which sedimentation keeps pace with subsidence. Following linkage and displacement localization (<span class="hlt">rift</span> climax phase), deformation if focused onto major, crustal-scale fault zones with kilometre-scale displacement. These major faults generate pronounced tilted fault-block topography, with subsidence rates that outpace sedimentation causing a pronounced change to deep-water deposition. Such models have been successful in helping to understand the gross structural and sedimentary evolution of <span class="hlt">rift</span> basins, but recent work has suggested that pre-existing structures, normal fault interaction with pre-<span class="hlt">rift</span> salt and antecedent drainage <span class="hlt">systems</span> significantly alter this initiation-to-climax perspective of <span class="hlt">rift</span> basin development. The E-W-striking, Pliocene-Pleistocene Corinth <span class="hlt">rift</span>, central Greece, is an excellent natural laboratory for studying the tectono-sedimentary evolution of <span class="hlt">rift</span> basins due to its young age, excellent onshore exposure of syn-<span class="hlt">rift</span> structure and stratigraphy and extensive offshore seismic data. The <span class="hlt">rift</span> cuts across the NW-SE-striking Hellenide mountain belt and has migrated northward and westward during its evolution. The Hellenide mountain belt significantly influences topography and drainage in the west of the <span class="hlt">rift</span>. High topography and large antecedent drainage <span class="hlt">systems</span>, focused along palaeovalleys, provided high sediment flux to NE-flowing alluvial <span class="hlt">systems</span> that overfilled early-<span class="hlt">rift</span> depocentres. Further east, away from the main antecedent drainage networks, contemporaneous deposits comprise deep-lacustrine turbidite channel and lobe complexes and basinal marls. Thus the stratigraphic expression within the Pliocene <span class="hlt">rift</span> fill is similar to <span class="hlt">rift</span> initiation in high sediment flux locations in the west and <span class="hlt">rift</span> climax in low sediment flux locations in the east. Major shifts in the locus of fault activity within the Corinth <span class="hlt">Rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span>. 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-<span class="hlt">rift</span> difficult to apply at the basin-scale.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985Natur.316..625B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985Natur.316..625B"><span id="translatedtitle">Geometry of propagating continental <span class="hlt">rifts</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bosworth, W.</p> <p>1985-08-01</p> <p>The general three-dimensional character of young and aborted continental <span class="hlt">rifts</span>, which can be used to derive a structural model for the propagation of <span class="hlt">rifts</span> in continental lithosphere, is described. The <span class="hlt">rifts</span> become asymmetric as a consequence of the role played by low-angle normal faults in the overall <span class="hlt">rift</span> geometry. Geometries which may be responsible for the detachments that are thought to underlie <span class="hlt">rifts</span> are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tecto..34.1009F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tecto..34.1009F"><span id="translatedtitle">Style of <span class="hlt">rifting</span> and the stages of Pangea breakup</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Frizon de Lamotte, Dominique; Fourdan, Brendan; Leleu, Sophie; Leparmentier, François; Clarens, Philippe</p> <p>2015-05-01</p> <p>Pangea results from the progressive amalgamation of continental blocks achieved at 320 Ma. Assuming that the ancient concept of "active" versus "passive" <span class="hlt">rifting</span> remains pertinent as end-members of more complex processes, we show that the progressive Pangea breakup occurred through a succession of <span class="hlt">rifting</span> episodes characterized by different tectonic evolutions. A first episode of passive continental <span class="hlt">rifting</span> 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 <span class="hlt">rifting</span> associated to the Siberian and Emeishan large igneous provinces (LIPs) failed. The true disintegration of Pangea resulted from (1) a Triassic passive <span class="hlt">rifting</span> 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 <span class="hlt">rifting</span> 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 <span class="hlt">rifting</span> 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 <span class="hlt">rifts</span> and their breakdown or with the type of resulting margins (as magma poor or magma dominated) are not straightforward. <span class="hlt">Finally</span>, 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 <span class="hlt">rifting</span> triggers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70029536','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70029536"><span id="translatedtitle">An updated global earthquake catalogue for stable continental regions: Reassessing the correlation with ancient <span class="hlt">rifts</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Schulte, S.M.; Mooney, W.D.</p> <p>2005-01-01</p> <p>We present an updated global earthquake catalogue for stable continental regions (SCRs; i.e. intraplate earthquakes) that is available on the Internet. Our database contains information on location, magnitude, seismic moment and focal mechanisms for over 1300 M (moment magnitude) ??? 4.5 historic and instrumentally recorded crustal events. Using this updated earthquake database in combination with a recently published global catalogue of <span class="hlt">rifts</span>, we assess the correlation of intraplate seismicity with ancient <span class="hlt">rifts</span> on a global scale. Each tectonic event is put into one of five categories based on location: (i) interior <span class="hlt">rifts</span>/taphrogens, (ii) <span class="hlt">rifted</span> continental margins, (iii) non-<span class="hlt">rifted</span> crust, (iv) possible interior <span class="hlt">rifts</span> and (v) possible <span class="hlt">rifted</span> margins. We find that approximately 27 per cent of all events are classified as interior <span class="hlt">rifts</span> (i), 25 per cent are <span class="hlt">rifted</span> continental margins (ii), 36 per cent are within non-<span class="hlt">rifted</span> crust (iii) and 12 per cent (iv and v) remain uncertain. Thus, over half (52 per cent) of all events are associated with <span class="hlt">rifted</span> crust, although within the continental interiors (i.e. away from continental margins), non-<span class="hlt">rifted</span> crust has experienced more earthquakes than interior <span class="hlt">rifts</span>. No major change in distribution is found if only large (M ??? 6.0) earthquakes are considered. The largest events (M ??? 7.0) however, have occurred predominantly within <span class="hlt">rifts</span> (50 per cent) and continental margins (43 per cent). Intraplate seismicity is not distributed evenly. Instead several zones of concentrated seismicity seem to exist. This is especially true for interior <span class="hlt">rifts</span>/taphrogens, where a total of only 12 regions are responsible for 74 per cent of all events and as much as 98 per cent of all seismic moment released in that category. Of the four <span class="hlt">rifts</span>/taphrogens that have experienced the largest earthquakes, seismicity within the Kutch <span class="hlt">rift</span>, India, and the East China <span class="hlt">rift</span> <span class="hlt">system</span>, may be controlled by diffuse plate boundary deformation more than by the presence of the ancient <span class="hlt">rifts</span> themselves. The St. Lawrence depression, Canada, besides being an ancient <span class="hlt">rift</span>, is also the site of a major collisional suture. Thus only at the Reelfoot <span class="hlt">rift</span> (New Madrid seismic zone, NMSZ, USA), is the presence of features associated with <span class="hlt">rifting</span> itself the sole candidate for causing seismicity. Our results suggest that on a global scale, the correlation of seismicity within SCRs and ancient <span class="hlt">rifts</span> has been overestimated in the past. Because the majority of models used to explain intraplate seismicity have focused on seismicity within <span class="hlt">rifts</span>, we conclude that a shift in attention more towards non-<span class="hlt">rifted</span> as well as <span class="hlt">rifted</span> crust is in order. ?? 2005 RAS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/888778','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/888778"><span id="translatedtitle">NONLINEAR DYNAMICAL <span class="hlt">SYSTEMS</span> - <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Philip Holmes</p> <p>2005-12-31</p> <p>This document is the <span class="hlt">final</span> report on the work completed on DE-FG02-95ER25238 since the start of the second renewal period: Jan 1, 2001. It supplements the annual reports submitted in 2001 and 2002. In the renewal proposal I envisaged work in three main areas: Analytical and topological tools for studying flows and maps Low dimensional models of fluid flow Models of animal locomotion and I describe the progess made on each project.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012Litho.152...84W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012Litho.152...84W"><span id="translatedtitle">Open <span class="hlt">System</span> evolution of peralkaline trachyte and phonolite from the Suswa volcano, Kenya <span class="hlt">rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>White, John Charles; Espejel-García, Vanessa V.; Anthony, Elizabeth Y.; Omenda, Peter</p> <p>2012-11-01</p> <p>Suswa is the southernmost volcanic center in the Central Kenya Peralkaline Province (CKPP) and represents the only salic center to have erupted significant volumes of peralkaline silica-undersaturated lavas and tuffs (trachyte, nepheline trachyte and phonolite). The eruptive products of Suswa can be clearly divided into two series, which correspond closely to the volcano's eruptive history. The earlier series (C1) includes lavas and tuffs that built the initial shield volcano (pre-caldera, unit S1) and erupted during the first caldera collapse (syn-caldera, units S2-S5); these rocks are dominated by peralkaline, silica-saturated to mildly under-saturated trachyte. The later series (C2) includes lavas and tuffs that erupted within the caldera structure following the initial collapse (post-caldera, units S6-S7) and during the creation of a second smaller, nested caldera and central "island block" (ring trench group, RTG, unit S8); these rocks are dominated by peralkaline phonolite. In this study, we combine mineralogical evidence with the results of major-element, trace-element, and thermodynamic modelling to propose a complex model for the origin of the Suswa volcano. From these results we conclude that C1 is the result of protracted fractional crystallization of a fairly "dry" alkali basalt (< 1 wt.% H2O) under relatively high pressure (400 MPa) and low oxygen fugacity (FMQ to FMQ-1). Although C1 appears to be primarily the result of closed <span class="hlt">system</span> processes, a variety of open <span class="hlt">system</span> processes are responsible for C2. We propose that crystallization of C1 trachyte resulted in the formation of a syenitic residue, which was assimilated (Ma/Mc = 0.1) during a later stage of recharge and differentiation of alkali basalt to produce post-caldera ne-trachyte. Post-caldera (S6-7) phonolites were in turn the result of fractional crystallization of this ne-trachyte. RTG phonolites, however, are the result of feldspar resorption prompted perhaps by magma recharge as evidenced by reverse zoning in alkali feldspar and linear compatible trace element patterns.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011Tecto..30.1002D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011Tecto..30.1002D"><span id="translatedtitle">Young <span class="hlt">rift</span> kinematics in the Tadjoura <span class="hlt">rift</span>, western Gulf of Aden, Republic of Djibouti</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Daoud, Mohamed A.; Le Gall, Bernard; Maury, René C.; Rolet, JoëL.; Huchon, Philippe; Guillou, Hervé</p> <p>2011-02-01</p> <p>The Tadjoura <span class="hlt">rift</span> forms the westernmost edge of the westerly propagating Sheba ridge, between Arabia and Somalia, as it enters into the Afar depression. From structural and remote sensing data sets, the Tadjoura <span class="hlt">rift</span> is interpreted as an asymmetrical south facing half-graben, about 40 km wide, dominated by a large boundary fault zone to the north. It is partially filled up by the 1-3 Myr old Gulf Basalts which onlapped the older Somali Basalts along its shallower southern flexural margin. The major and trace element analysis of 78 young onshore lavas allows us to distinguish and map four distinct basaltic types, namely the Gulf, Somali, Goumarre, and Hayyabley Basalts. These results, together with radiometric age data, lead us to propose a revised volcano-stratigraphic sketch of the two exposed Tadjoura <span class="hlt">rift</span> margins and to discriminate and date several distinct fault networks of this oblique <span class="hlt">rift</span>. Morphological and statistical analyses of onshore extensional fault populations show marked changes in structural styles along-strike, in a direction parallel to the <span class="hlt">rift</span> axis. These major fault disturbances are assigned to the arrest of axial fault tip propagation against preexisting discontinuities in the NS-oriented Arta transverse zone. According to our model, the sinistral jump of <span class="hlt">rifting</span> into the Asal-Ghoubbet <span class="hlt">rift</span> segment results from structural inheritance, in contrast with the en échelon or transform mechanism of propagation that prevailed along the entire length of the Gulf of Aden extensional <span class="hlt">system</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T43A4678A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T43A4678A"><span id="translatedtitle">Radial Anisotropy beneath the Main Ethiopian <span class="hlt">Rift</span> and Afar Depression</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Accardo, N. J.; Gaherty, J. B.; Jin, G.; Shillington, D. J.</p> <p>2014-12-01</p> <p>The Main Ethiopian <span class="hlt">Rift</span> (MER) and Afar uniquely capture the <span class="hlt">final</span> stages of transition from continental <span class="hlt">rifting</span> in the broader East African <span class="hlt">Rift</span> <span class="hlt">System</span> to incipient seafloor spreading above a mantle hotspot. Studies of the region increasingly point to magmatism as a controlling factor on continental extension. However, the character and depth extent of these melt products remain contentious. Radial anisotropy derived from surface waves provides a unique diagnostic constraint on the presence of oriented melt pockets versus broader oriented anisotropic fabrics. This study investigates the thermal and radially anisotropic structure beneath the broader MER and Afar to resolve the magmatic character of the region and ultimately to understand the role of magmatism in present day <span class="hlt">rift</span> development. We utilize 104 stations from 4 collocated arrays in the MER/Afar region to constrain radial anisotropy within the upper mantle via the inversion of Love- and Rayleigh-wave observations between 25 and 100 s period. We employ a multi-channel cross-correlation algorithm to obtain inter-station phase and amplitude information. The multi-channel phase observations are inverted for dynamic phase velocity across the array, which are then corrected for focusing and multipathing using the amplitude observations via Helmholtz tomography. We jointly invert Love- and Rayleigh-wave structural phase velocity measurements employing crustal constraints from co-located active source experiments to obtain estimates of Vsv and Vsh between 50 - 170 km depth. Preliminary results readily reveal the distinct shear velocity structure beneath the MER and Afar. Within the MER, shear velocity structure suggests pronounced low velocities accompanied by strong anisotropy between 80 - 140 km depth beneath the western Ethiopian plateau and <span class="hlt">rift</span> valley. Within Afar, shear velocity structure is more varied with the slowest velocities found at shallow depths (less than 70 km depth), accompanied by weak 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 <span class="hlt">rifting</span> in the MER and incipient, hot-spot influenced seafloor spreading in Afar.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.V44A..02B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.V44A..02B"><span id="translatedtitle">Examples of Models Fit to Magnetic Anomalies Observed Over Subaerial, Submarine, and Subglacial Volcanoes in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Behrendt, J. C.; Finn, C. A.; Blankenship, D. D.</p> <p>2006-12-01</p> <p>Aeromagnetic and marine magnetic surveys over the volcanically active West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, constrained by seismic reflection profiles over the Ross Sea continual shelf, and radar ice sounding surveys over the West Antarctic Ice Sheet (WAIS) allowed calculation of models fit to very high-amplitude anomalies. We present several examples: exposed 2700-m high, subaerial erupted volcano Mt Melbourne; the 750-m high source of anomaly D (Hamilton submarine volcano) in the Ross sea; and the 600-m high edifice of Mt. CASERTZ beneath the WAIS. The character of these anomalies and their sources varies greatly, and is inferred to be the result of subaerial, submarine and subglacial emplacement respectively. Mt. Melbourne erupted through the WAIS at a time when it was grounded over the Ross Sea continental shelf. Highly magnetic volcanic flows inferred to have high remanent (normal) magnetization in the present field direction produce the 600-nT positive anomaly. The flows protected the edifice above the ice from erosion. Negligible amounts of probably subglacially erupted, apparently non-magnetic hyaloclastite exist in association with Mt. Melbourne. Mt. CASERTZ is nonmagnetic and the edifice is interpreted as consisting of a transient mound of unconsolidated hyaloclastite injected into the WAIS. However Mt. CASERTZ, about 8-km diameter, overlies a 200-m high, 40-km wide highly magnetic residual edifice modeled as the top of the source (an active subglacial volcano) of a 400-nT high positive anomaly. Any former edifices comprising hyaloclastite, pillow breccia or other volcanic debris injected into the moving WAIS apparently have been removed. About 400 other high- amplitude anomalies associated with low relief (80 percent less than 200 m) edifices at the base of the ice (the tops of the sources of these steep gradient anomalies) beneath the WAIS defined by radar ice sounding have been interpreted as having former hyaloclastite edifices, which were removed by the moving ice. The source of the -1300-nT negative anomaly D projecting 600 m above the Ross Sea continental shelf is enigmatic. We interpret models as either the result of reversed magnetization (less than 780 Ka) at a time of deglaciation of the continental shelf, or a hydrothermally altered central core surrounded by highly magnetic flows erupted beneath the Ross sea since deglaciation in Holocene time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5580485','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5580485"><span id="translatedtitle">Experimental lithium <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kolowith, R.; Berg, J.D.; Miller, W.C.</p> <p>1985-04-01</p> <p>A full-scale mockup of the Fusion Materials Irradiation Test (FMIT) Facility lithium <span class="hlt">system</span> was built at the Hanford Engineering Development Laboratory (HEDL). This isothermal mockup, called the Experimental Lithium <span class="hlt">System</span> (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 <span class="hlt">system</span> 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 <span class="hlt">systems</span>. Experience with the test loop provided important information on <span class="hlt">system</span> operation, performance, and reliability. This report presents a complete overview of the entire Experimental Lithium <span class="hlt">System</span> test program and also includes a summary of such areas as instrumentation, coolant chemistry, vapor/aerosol transport, and corrosion.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5426478','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5426478"><span id="translatedtitle">Laboratory test <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Asher, G.L.</p> <p>1980-03-01</p> <p>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 <span class="hlt">systems</span> are needed to evaluate development hardware. To meet this requirement, a universal test <span class="hlt">system</span> was developed to provide both basic test capabilities and flexibility to adapt easily to specific product applications. This laboratory evaluation <span class="hlt">system</span> will reduce the need to develop complex dedicated test <span class="hlt">systems</span> for each new product design, while still providing the benefits of an automated <span class="hlt">system</span>. A special purpose interface chassis was designed and fabricated to permit a standardized interface between the test <span class="hlt">system</span> and the product application. Connector assignments by <span class="hlt">system</span> 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 <span class="hlt">system</span> for a typical product application. Both the interface hardware and the software were developed for this application.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T33D2293G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T33D2293G"><span id="translatedtitle">New Geophysical Results About the Relationship Between the Reelfoot <span class="hlt">Rift</span> and the <span class="hlt">Rifted</span> Margin of Laurentia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guo, L.; Keller, G. R.</p> <p>2010-12-01</p> <p>The Reelfoot <span class="hlt">rift</span> beneath the northern Mississippi embayment is an intracratonic graben <span class="hlt">system</span>, which formed Early Cambrian time as a result of continental breakup, and has been subsequently reactivated by compressional or tensional stresses related to plate tectonic interactions. It strikes northeastward into the continent, and is approximately perpendicular to the <span class="hlt">rifted</span> margin of the Laurentia that is shaped by the southeast-striking Alabama-Oklahoma transform fault. The northern section of the <span class="hlt">rift</span> near the town of New Madrid, Missouri, was the site of three great 1811-1812 earthquakes, and it remains the most seismically active area east of the Rocky Mountains. However, the southern end of the <span class="hlt">rift</span> is obscure, and the relationship between the Reelfoot <span class="hlt">rift</span> and the <span class="hlt">rifted</span> margin of Laurentia remains disputed. We analyzed the gravity and magnetic database for the region using new data enhancement techniques to shed some light on this relationship. We analyzed a large area to assess the regional geological structure. Complete Bouguer gravity data and and total magnetic intensity (TMI) data were assembled and gridded on a regular grid with spacing of 2km, the TMI data were then reduced to the magnetic pole. Then the data were processed with standard techniques to attenuate the high-frequency noise, and we analyzed the regional and residual anomalies. Specially, we calculated the tilt-angle derivatives of the data. We then calculated the directional horizontal derivatives of the tilt-angle derivatives both along and perpendicular to the strike of the <span class="hlt">rift</span>. The maps of these derivatives clearly delineate the boundaries of the edges of the Reelfoot <span class="hlt">rift</span>, the leading edge of the Ouachita thrust belt and the margin of Laurentia. The results of the preliminary processing indicate that the southern end of the <span class="hlt">rift</span> is near the leading edge of the Ouachita thrust belt, which produces a more curvilinear shape for the Laurentian margin than the very linear Alabama-Oklahoma transform fault suggesting its structure is more complex than usually depicted.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GGG....16.4344A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GGG....16.4344A"><span id="translatedtitle">Submarine and subaerial lavas in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>: Temporal record of shifting magma source components from the lithosphere and asthenosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aviado, Kimberly B.; Rilling-Hall, Sarah; Bryce, Julia G.; Mukasa, Samuel B.</p> <p>2015-12-01</p> <p>The petrogenesis of Cenozoic alkaline magmas in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (WARS) remains controversial, with competing models highlighting the roles of decompression melting due to passive <span class="hlt">rifting</span>, active plume upwelling in the asthenosphere, and flux melting of a lithospheric mantle metasomatized by subduction. In this study, seamounts sampled in the Terror <span class="hlt">Rift</span> region of the Ross Sea provide the first geochemical information from submarine lavas in the Ross Embayment in order to evaluate melting models. Together with subaerial samples from Franklin Island, Beaufort Island, and Mt. Melbourne in Northern Victoria Land (NVL), these Ross Sea lavas exhibit ocean island basalt (OIB)-like trace element signatures and isotopic affinities for the C or FOZO mantle endmember. Major-oxide compositions are consistent with the presence of multiple recycled lithologies in the mantle source region(s), including pyroxenite and volatile-rich lithologies such as amphibole-bearing, metasomatized peridotite. We interpret these observations as evidence that ongoing tectonomagmatic activity in the WARS is facilitated by melting of subduction-modified mantle generated during 550-100 Ma subduction along the paleo-Pacific margin of Gondwana. Following ingrowth of radiogenic daughter isotopes in high-µ (U/Pb) domains, Cenozoic extension triggered decompression melting of easily fusible, hydrated metasomes. This multistage magma generation model attempts to reconcile geochemical observations with increasing geophysical evidence that the broad seismic low-velocity anomaly imaged beneath West Antarctica and most of the Southern Ocean may be in part a compositional structure inherited from previous active margin tectonics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/6197591','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6197591"><span id="translatedtitle">Continental <span class="hlt">rifting</span>: a planetary perspective</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Muehlberger, W.R.</p> <p>1985-01-01</p> <p>The only inner planet that has abundant evidence of regional extension, and the consequent generation of <span class="hlt">rifts</span> in the earth. The absence of plate motion on the other inner planets limits their <span class="hlt">rifts</span> to localized bulges or subsidence areas. The <span class="hlt">rifting</span> of oceanic lithosphere is seldom preserved in the geological record. Thus, such <span class="hlt">rifting</span> must be inferred via plate tectonic interpretation: if there is <span class="hlt">rifting</span>, then there must be subduction whose results are commonly well preserved. Modern continental <span class="hlt">rifts</span> 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. <span class="hlt">Rift</span> basin fillings typically show rapid lateral and vertical facies and thickness changes, bimodal volcanism, and distinctive <span class="hlt">rift</span>-drift sequences. Proterozoic <span class="hlt">rifts</span> 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 <span class="hlt">rifts</span> 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 <span class="hlt">rift</span> event. The oldest proposed <span class="hlt">rift</span> 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 <span class="hlt">rifting</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Litho.212...16T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Litho.212...16T"><span id="translatedtitle">Petrogenesis of the Ni-Cu-PGE sulfide-bearing Tamarack Intrusive Complex, Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span>, Minnesota</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Taranovic, Valentina; Ripley, Edward M.; Li, Chusi; Rossell, Dean</p> <p>2015-01-01</p> <p>The Tamarack Intrusive Complex (TIC, 1105.6 ± 1.2 Ma) in NE Minnesota, was emplaced during the early stages of the development of the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> (MRS, "Early Stage": 1110-1106 Ma). Country rocks of the TIC are those of the Paleoproterozoic Thomson Formation, part of the Animikie Group including sulfide-bearing metasedimentary black shale. The magmatic <span class="hlt">system</span> is composed of at least two principal mafic-ultramafic intrusive sequences: the sulfide-barren Bowl Intrusion in the south and the "dike" area intrusions in the north which host Ni-Cu-Platinum Group Elements (PGE) mineralization with up to 2.33% Ni, 1.24% Cu, 0.34 g/t Pt, 0.23 g/t Pd and 0.18 g/t Au. Two distinct intrusive units in the "dike" area are the CGO (coarse-grained olivine-bearing) Intrusion, a sub-vertical dike-like body, and the overlying sub-horizontal FGO (fine-grained olivine-bearing) Intrusion. Both intrusions comprise peridotite, feldspathic peridotite, feldspathic pyroxenite, melatroctolite and melagabbro. Massive sulfides are volumetrically minor and mainly occur as lenses emplaced into the country rocks associated with both intrusions. Semi-massive (net-textured) sulfides are distributed at the core of the CGO Intrusion, surrounded by a halo of the disseminated sulfides. Disseminated sulfides also occur in lenses along the base of the FGO Intrusion. Olivine compositions in the CGO Intrusion are between Fo89 and Fo82 and in the FGO Intrusion from Fo84 to Fo82. TIC intrusions have more primitive olivine compositions than that of olivine in the sheet-like intrusions in the Duluth Complex (below Fo70), as well as olivine from the smaller, conduit-related, Eagle and East Eagle Intrusions in Northern Michigan (Fo86 to Fo75). The FeO/MgO ratios of the CGO and FGO Intrusion parental magmas, inferred from olivine compositions, are similar to those of picritic basalts erupted during the early stages of the MRS formation. Trace element ratios differ slightly from other intrusions in the 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 <span class="hlt">system</span>. 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 <span class="hlt">system</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=visual+AND+resources+AND+management+AND+system&pg=4&id=ED333141','ERIC'); return false;" href="http://eric.ed.gov/?q=visual+AND+resources+AND+management+AND+system&pg=4&id=ED333141"><span id="translatedtitle">Special Delivery <span class="hlt">Systems</span>. <span class="hlt">Final</span> Report.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Molek, Carol</p> <p></p> <p>The Special Delivery <span class="hlt">Systems</span> project developed a curriculum for students with learning disabilities (LD) in an adult basic education program. The curriculum was designed to assist and motivate the students in the educational process. Fourteen students with LD were recruited and screened. The curriculum addressed varied learning styles combined…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=241528&keyword=radium&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=64313435&CFTOKEN=95635793','EPA-EIMS'); return false;" href="http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=241528&keyword=radium&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=64313435&CFTOKEN=95635793"><span id="translatedtitle"><span class="hlt">Final</span> Barrier: Small <span class="hlt">System</span> Compliance</span></a></p> <p><a target="_blank" href="http://oaspub.epa.gov/eims/query.page">EPA Science Inventory</a></p> <p></p> <p></p> <p>This presentation will discuss the use of point-of-use (POU) technology for small drinking water <span class="hlt">systems</span>. 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...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/7101426','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/7101426"><span id="translatedtitle">Multiuser test <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cogan, D.L.</p> <p>1980-09-01</p> <p>A multiterminal, real-time laboratory test <span class="hlt">system</span> was developed to perform automated electrical testing on electronic components while permitting independent software production to be accomplished from other terminals at the same time. This versatility provides test capability for prototype hardware and evaluation of new product designs for several concurrent development efforts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=Stress+AND+Visual+AND+Attention&pg=2&id=ED333141','ERIC'); return false;" href="http://eric.ed.gov/?q=Stress+AND+Visual+AND+Attention&pg=2&id=ED333141"><span id="translatedtitle">Special Delivery <span class="hlt">Systems</span>. <span class="hlt">Final</span> Report.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Molek, Carol</p> <p></p> <p>The Special Delivery <span class="hlt">Systems</span> project developed a curriculum for students with learning disabilities (LD) in an adult basic education program. The curriculum was designed to assist and motivate the students in the educational process. Fourteen students with LD were recruited and screened. The curriculum addressed varied learning styles combined…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T43G..07M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T43G..07M"><span id="translatedtitle"><span class="hlt">Rift</span> inheritance in orogenes: a case study from the Western Pyrenees</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Masini, E.; Manatschal, G.; Tugend, J.; Kusznir, N. J.; Flament, J.</p> <p>2012-12-01</p> <p>In plate tectonics, there is a general assumption that <span class="hlt">rifted</span> margins represent most of the former material accreted into collisional orogenic prisms. In this regard, the former architecture, structures and composition of <span class="hlt">rifted</span> margins, i.e. the pre-orogenic inheritances, play undoubtedly a major role during tectonic inversion. Studies have shown that <span class="hlt">rifted</span> margins are more complex than a succession of tilted blocks. Indeed, the discovery of hyper-extended domains, where low-angle detachments replace high-angle normal faults and mantle material is exhumed to the seafloor implies a revision of the margin's template used in orogenic models. Because of overprint, the role of <span class="hlt">rift</span> inheritance in orogenes remains often underestimated. The Pyrenees, located along the Iberian-European plate boundary, can be considered as one of the best places to study the reactivation of hyper-extended <span class="hlt">rifts</span>. In this orogen, the Late Cretaceous and Tertiary convergence overprints a Latest Jurassic to Lower Cretaceous intracontinental <span class="hlt">rift</span> linked with the opening of the North Atlantic. There, Albian hyper-extended <span class="hlt">rift</span> basins developed where deep crustal and mantle rocks were exhumed along low-angle detachments to the seafloor. In this work we discuss the example of the Mauléon-Arzacq domain, which escaped from the most pervasive deformation because of its specific location between the western termination of the chain and the Bay of Biscay oceanic domain. Combining field study with subsurface geophysical and drillhole data, we show that the overall <span class="hlt">rift</span> domain is asymmetric. The northern European upper plate is on the hangingwall of low-angle detachment <span class="hlt">systems</span> affecting the southern Iberian Lower plate. The upper plate records depth-dependent crustal thinning and the development of a syn-<span class="hlt">rift</span> sag basin. In contrast, the lower plate resulted from the hyper-extension of Iberian continental crust accommodated at the surface by two diachronous top-basement detachment <span class="hlt">systems</span>. The first detachment <span class="hlt">system</span> separates the stable Iberian continental crust to the south from the hyper-extended domain to the north defining a crustal neck. The second detachment <span class="hlt">system</span>, further to the north, exhumed mid-crustal and mantle material to the seafloor front of the upper plate. Both <span class="hlt">systems</span> are overlain by supra-detachment basins. By comparison of cross-basin dip sections, the west to east gradation from weakly to strongly reactivated sections, reactivation modalities through the <span class="hlt">rifted</span> domain can be described. We show that most of the convergence is accommodated by the inversion of the two <span class="hlt">rift</span> structures of the lower plate in two stages: 1) An early under-thrusting of the northern hyper-extended domain beneath Europe along the northern detachment <span class="hlt">system</span>. Sediments were wedged, folded and thrust both north- and southward (thin-skin); 2) the northern structure locks and implies the southward migration of shortening. The southern crustal neck is reactivated leading to frontal nappe-stacking forming the Pyrenean high chain (thick-skin). Using the Rifter® kinematic modeller, we show that this evolution can be computed through isostatically equilibrated crustal sections. These results suggest that the Pyrenees can serve as an example of how a complex <span class="hlt">rift</span> architecture strongly controls the style and the timing of orogeny to <span class="hlt">finally</span> impacts the architecture of collisional orogenes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Geote..48..390D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Geote..48..390D"><span id="translatedtitle">Upper Devonian depositional <span class="hlt">system</span> of Bel'kov Island (New Siberian Islands): An intracontinental <span class="hlt">rift</span> or a continental margin?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Danukalova, M. K.; Kuzmichev, A. B.; Aristov, V. A.</p> <p>2014-09-01</p> <p>The archipelago of New Siberian Islands situated on the northeastern continental shelf of Eurasia is considered a part of an exotic terrane that collided with Siberia in the Early Cretaceous. Bel'kov Island is located close to the inferred western boundary of this terrane and thus should demonstrate attributes of its localization at the margin of the Paleozoic oceanic basin. The Upper Devonian section on Bel'kov Island is a continuous sequence of deepwater terrigenous rocks, which indicates a tendency toward deepening of the basin previously revealed on adjacent Kotel'ny Island. The lowermost Upper Devonian unit on Bel'kov Island is represented by thin Domanik-like strata resting on the Middle Devonian carbonate platform. The main body of the Upper Devonian sequence, more than 4 km in total thickness, is made up of gravity-flow sediments including turbidites, clay and block diamictites, and olistostromes in the upper part of the section, which accumulated at the slope of the basin or its rise. At many levels, these sediments have been redeposited by along-slope currents. The uppermost unit of organogenic limestone is evidence for compensation of the trough. According to conodont assemblages, the deepwater terrigenous rocks were deposited from the early Frasnian to the early Tournaisian. This time is known for extensive <span class="hlt">rifting</span> in the eastern Siberian Platform. The data obtained allowed us to reconstruct a NNW-trending Late Devonian <span class="hlt">rift</span> basin on the Laptev Sea shelf similar to other <span class="hlt">rifts</span> at the eastern margin of the Siberian Platform.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/10171740','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/10171740"><span id="translatedtitle">Digital imaging <span class="hlt">systems</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mozzano, S.G.; Watterson, C.E.</p> <p>1992-08-01</p> <p>The Advanced Vision Information <span class="hlt">System</span> (AVIS) was a long-term development project for the engineering technical thrust for intelligent vision <span class="hlt">systems</span>. The goal of the project was to develop an image processing capability in the laboratory through which advanced automated image analysis techniques could be achieved. From the many instruments in the Materials Evaluation laboratory which provide video output data, three were selected for initial development activities. The instruments selected were the infrared camera, the metallograph, and electron optics. To the application development activities for these instruments were added the development of the laboratory network for transferring image data, the development of a standardized image processing workstation, and a nondestructive measurement capability. Since the project had such a broad scope, each of six activities was established as a subproject.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5732012','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5732012"><span id="translatedtitle"><span class="hlt">Final</span> focus <span class="hlt">systems</span> for linear colliders</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Erickson, R.A.</p> <p>1987-11-01</p> <p>The <span class="hlt">final</span> focus <span class="hlt">system</span> 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 <span class="hlt">final</span> focus <span class="hlt">system</span> must transport the outgoing beams to a location where they can be recycled or safely dumped. Elementary optical considerations for linear collider <span class="hlt">final</span> focus <span class="hlt">systems</span> are discussed, followed by chromatic aberrations. The design of the <span class="hlt">final</span> focus <span class="hlt">system</span> 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)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3698E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3698E"><span id="translatedtitle"><span class="hlt">Rift</span> initiation with volatiles and magma</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ebinger, Cynthia; Muirhead, James; Roecker, Steve; Tiberi, Christel; Muzuka, Alfred; Ferdinand, Rrichard; Mulibo, Gabrile; Kianji, Gladys</p> <p>2015-04-01</p> <p><span class="hlt">Rift</span> initiation in cratonic lithosphere remains an outstanding problem in continental tectonics, but strain and magmatism patterns in youthful sectors of the East African <span class="hlt">rift</span> provide new insights. Few teleseisms occur in the Eastern <span class="hlt">rift</span> arm of the East African <span class="hlt">rift</span> <span class="hlt">system</span>, 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> length, including sectors on and off craton, and those with and without central <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994Tectp.236...93B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994Tectp.236...93B"><span id="translatedtitle">Structural and stratigraphic evolution of the Anza <span class="hlt">rift</span>, Kenya</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bosworth, William; Morley, Chris K.</p> <p>1994-09-01</p> <p>The Anza <span class="hlt">rift</span> is a large, multi-phase continental <span class="hlt">rift</span> basin that links the Lamu embayment of southern Kenya with the South Sudan <span class="hlt">rifts</span>. Extension and deposition of syn-<span class="hlt">rift</span> sediments are known to have commenced by the Neocomian. Aptian-Albian strata have, thus far, not been encountered during limited drilling campaigns and, in at least one well, are replaced by a significant unconformity. Widespread <span class="hlt">rifting</span> occurred during the Cenomanian to Maastrichtian, and continued into the Early Tertiary. Marine waters appear to have reached the central Anza <span class="hlt">rift</span> in the Cenomanian, and a second marine incursion may have occurred during the Campanian. As no wells have yet reached basement in the basinal deeps, the possibility exists that the Anza <span class="hlt">rift</span> may have initiated in the Late Jurassic, in conjunction with extension to the south in the Lamu embayment and to the north in the Blue Nile <span class="hlt">rift</span> of Sudan. Structural and stratigraphic evolution in the Anza <span class="hlt">rift</span> followed a pattern that has now been inferred in several <span class="hlt">rift</span> settings. Early phases of extension were accommodated by moderately dipping faults that produced large stratal rotations. Sedimentary environments were dominantly fluvial, with associated small lakes and dune fields. Volcanic activity is documented for the early Neocomian, but its extent is unknown. This initial style of deformation and sedimentation may have continued through several of the earliest pulses of <span class="hlt">rifting</span>. By the Late Cretaceous, a new <span class="hlt">system</span> of steeply dipping faults was established, that produced a deep basin without significant rotation of strata in the north, and only minor rotation in the south. This basin geometry favored the establishment of large, deep lakes, which occasionally were connected to the sea. The older basins were partly cannibalized during the sedimentary in-filling of these successor basins. Early Senonian volcanism was encountered in one well, and reflection seismic evidence suggests that one or more thick, regionally extensive igneous sills were intruded, probably during the Early Tertiary. The change in <span class="hlt">rift</span> style from early, strongly rotational, shallow basins to late, non-rotational, deep basins has been observed in the southern Gulf of Suez/northern Red Sea, the Southwestern Turkana/northern Kenyan <span class="hlt">rift</span>, and at Anza. It therefore takes place in <span class="hlt">rifts</span> in variable tectonic settings, with a wide range of volcanic activity and, presumably, with different driving mechanisms. The shift in deposition in each case is away from early <span class="hlt">rift</span>-bounding faults toward the half-graben flexural margins, further in-board to the upper structural plate. This suggests at least some component of regional simple shear in the deformation history of the <span class="hlt">rifted</span> lithosphere, either via broad shear zones or at discrete detachment surfaces.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1715136M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1715136M"><span id="translatedtitle">Volcanic field elongation, vent distribution and tectonic evolution of continental <span class="hlt">rift</span>: The Main Ethiopian <span class="hlt">Rift</span> example</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mazzarini, Francesco; Le Corvec, Nicolas; Isola, Ilaria; Favalli, Massimiliano</p> <p>2015-04-01</p> <p>Magmatism and faulting operate in continental <span class="hlt">rifts</span> and interact at a variety of scales, however their relationship is complex. The African <span class="hlt">rift</span>, being the best example for both active continental <span class="hlt">rifting</span> and magmatism, provides the ideal location to study the interplay between the two mechanisms. The Main Ethiopian <span class="hlt">Rift</span> (MER), which connects the Afar depression in the north with the Turkana depression and Kenya <span class="hlt">Rift</span> to the south, consists of two distinct <span class="hlt">systems</span> of normal faults and its floor is scattered with volcanic fields formed by tens to several hundreds monogenetic, generally basaltic, small volcanoes and composite volcanoes and small calderas. The distribution of vents defines the overall shape of the volcanic field. Previous work has shown that the distribution of volcanic vents and the shape of a field are linked to its tectonic environment and its magmatic <span class="hlt">system</span>. In order to distinguish the impact of each mechanism, we analyzed four volcanic fields located at the boundary between the central and northern MER, three of them (Debre Zeyit, Wonji and Kone) grew in the <span class="hlt">rift</span> valley and one (Akaki) on the western <span class="hlt">rift</span> shoulder. The elongation and shape of the fields were analyzed based on their vent distribution using the Principal Component Analysis (PCA), the Vent-to-Vent Distance (VVD), and the two dimensional symmetric Gaussian kernel density estimate methods. We extracted from these methods several parameters characterizing the spatial distribution of points (e.g., eccentricity (e), eigenvector index (evi), angular dispersion (Da)). These parameters allow to define at least three types of shape for volcanic fields: strong elongate (line and ellipse), bimodal/medium elongate (ellipse) and dispersed (circle) shapes. Applied to the natural example, these methods well differentiate each volcanic field. For example, the elongation of the field increases from shoulder to <span class="hlt">rift</span> axis inversely to the angular dispersion. In addition, the results show that none of 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 <span class="hlt">rift</span> axis (Wonji and Kone) are parallel to the NNE trend of the youngest fault <span class="hlt">system</span>. This parallelism decreases as we move to the <span class="hlt">rift</span> 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 <span class="hlt">rift</span>) 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T51H..01B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T51H..01B"><span id="translatedtitle">Intracontinental <span class="hlt">Rifts</span> As Glorious Failures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Burke, K.</p> <p>2012-12-01</p> <p><span class="hlt">Rifts</span>: "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 <span class="hlt">rifts</span> in which the Wilson Cycle failed to develop but in which that failure has led to glory because rocks and structures in those <span class="hlt">rifts</span> throw exceptional light on how Earth's complex continental evolution can operate: The best studied record of human evolution is in the East African <span class="hlt">Rift</span>; The Ventersdorp <span class="hlt">rifts</span> (2.7 Ga) have yielded superb crustal-scale <span class="hlt">rift</span> seismic reflection records; "Upside-down drainage" (Sleep 1997) has guided supra-plume-head partial melt into older continental <span class="hlt">rifts</span> leading Deccan basalt of ~66Ma to erupt into a Late Paleozoic (~ 300Ma) <span class="hlt">rift</span> and the CAMP basalts of ~201 Ma into Ladinian, ~230 Ma, <span class="hlt">rifts</span>. Nepheline syenites and carbonatites, which are abundant in <span class="hlt">rifts</span> 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 <span class="hlt">rifts</span> can relate to collision at a remote plate margin (Guiraud and Bosworth 1997, Dewey and Burke 1974) or to passage of the <span class="hlt">rift</span> over a plume generation zone (PGZ Burke et al.2008) on the Core Mantle Boundary (e.g.Lake Ellen MI kimberlites at ~206 Ma).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992Tectp.215...69F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992Tectp.215...69F"><span id="translatedtitle">From <span class="hlt">rifting</span> to passive margin: the examples of the Red Sea, Central Atlantic and Alpine Tethys</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Favre, P.; Stampfli, G. M.</p> <p>1992-12-01</p> <p>Evolution of the Red Sea/Gulf of Suez and the Central Atlantic <span class="hlt">rift</span> <span class="hlt">systems</span> shows that an initial, transtensive <span class="hlt">rifting</span> phase, affecting a broad area around the future zone of crustal separation, was followed by a pre-oceanic <span class="hlt">rifting</span> phase during which extensional strain was concentrated on the axial <span class="hlt">rift</span> zone. This caused lateral graben <span class="hlt">systems</span> to become inactive and they evolved into <span class="hlt">rift</span>-rim basins. The transtensive phase of diffuse crustal extension is recognized in many intra-continental <span class="hlt">rifts</span>. If controlling stress <span class="hlt">systems</span> relax, these <span class="hlt">rifts</span> abort and develop into palaeorifts. If controlling stress <span class="hlt">systems</span> persist, transtensive <span class="hlt">rift</span> <span class="hlt">systems</span> can enter the pre-oceanic <span class="hlt">rifting</span> stage, during which the <span class="hlt">rift</span> zone narrows and becomes asymmetric as a consequence of simple-shear deformation at shallow crustal levels and pure shear deformation at lower crustal and mantle-lithospheric levels. Preceding crustal separation, extensional denudation of the lithospheric mantle is possible. Progressive lithospheric attenuation entails updoming of the asthenosphere and thermal doming of the <span class="hlt">rift</span> shoulders. Their uplift provides a major clastic source for the <span class="hlt">rift</span> basins and the lateral <span class="hlt">rift</span>-rim basins. Their stratigraphic record provides a sensitive tool for dating the <span class="hlt">rift</span> shoulder uplift. Asymmetric <span class="hlt">rifting</span> leads to the formation of asymmetric continental margins, corresponding in a simple-shear model to an upper plate and a conjugate lower plate margin, as seen in the Central Atlantic passive margins of the United States and Morocco. This <span class="hlt">rifting</span> model can be successfully applied to the analysis of the Alpine Tethys palaeo-margins (such as Rif and the Western Alps).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/316236','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/316236"><span id="translatedtitle">Geochemistry of hypabyssal rocks of the Midcontinent <span class="hlt">Rift</span> <span class="hlt">system</span> in Minnesota, and implications for a Keweenawan magmatic ``family tree``</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Jerde, E.A.</p> <p>1998-11-01</p> <p>The hypabyssal rocks associated with the Keweenawan (1.1 Ga) Midcontinent <span class="hlt">Rift</span> along the Minnesota shore of Lake Superior are a distinct suite within the rock associations of this region. These rocks are found predominantly as ophitic diabase dikes and sills of various sizes, ranging from a few meters to several hundred meters across. Chilled margins were sampled and analyzed by neutron activation analysis and microprobe fused-bead techniques for bulk chemistry. Mineral compositions were obtained by electron microprobe. Variations in composition were found that are consistent with fractionation. Major-element modeling of fractionation indicates that the majority of the hypabyssal rocks formed at moderate pressures ({approximately}6 kbar), although a number show evidence of fractionation at near-surface levels, and some deeper ({approximately}10 kbar). Resorption features seen in plagioclase phenocrysts are evidence for magmatic evolution at varying levels in the crust. It is possible to relate the varied hypabyssal rocks to a single primary parent through polybaric fractionation. This parent is a high-Al primitive olivine tholeiite--a magma composition common among the volcanic rocks associated with the Midcontinent <span class="hlt">Rift</span>. Trace-element modeling with this same parent composition yields results consistent with the formation of some hypabyssal rocks as products of a periodically tapped and replenished, constantly fractionating magma chamber, which can decouple the behavior of major and trace elements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUSM.T42A..04M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUSM.T42A..04M"><span id="translatedtitle">Observations From the Alpine Tethys and the Iberia/Newfoundland Margins Pertinent to the Interpretation of Magma-Poor <span class="hlt">Rifted</span> Margins</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Manatschal, G.; Lavier, L. L.</p> <p>2005-05-01</p> <p>Although the Iberia/Newfoundland and Alpine Tethys margins are of different age and ultimately had a different fate, they share remarkable similarities. These similarities permit us to compare direct observation and unlimited sampling of the ancient Alpine margins with the drill-hole and geophysical data from the present-day Iberia/Newfoundland margins. This exercise results in new concepts for the near surface response of lithospheric rupturing at magma-poor <span class="hlt">rifted</span> margins. <span class="hlt">Rifting</span> at these two pairs of margins can be described by three modes of extension: a stretching mode, a thinning mode and an exhumation mode. Each mode is characterized by a particular isostatic response to extension, its basin architecture and fault geometry, and the bulk rheological evolution of the extending lithosphere. Initial <span class="hlt">rifting</span> was controlled by the stretching mode. Deformation in the upper crust and upper mantle was decoupled along mylonitic shear zones in the middle crust, <span class="hlt">rift</span>-shoulder uplift was moderate to weak, and basins were distributed across the whole subsiding margin. During an advanced stage of <span class="hlt">rifting</span>, extension became localized in the future distal margin and was controlled by the thinning mode. Extension in the upper crust and upper mantle were coupled along major mylonitic shear zones, <span class="hlt">rift</span>-shoulder uplift was very pronounced and resulted in sub-aerial exposure of parts of the future distal margin. During this stage, the crust in the future distal margin was thinned by more than 15 km although no evidence for upper crustal extension is found in the stratigraphic record. <span class="hlt">Final</span> <span class="hlt">rifting</span> was localized in the previously thinned crust and was controlled by the exhumation mode. During this stage, downwards-concave faults exhumed lower crustal and mantle rocks to the seafloor leading to a tens of kilometres wide Zone of Exhumed Continental Mantle (ZECM). Despite of the high extension, these faults did not produce a major fault bounded topography. This <span class="hlt">final</span> stage of <span class="hlt">rifting</span> was assisted by serpentinization and magmatism, but in contrast to the following seafloor spreading, the continental lithosphere was not yet broken apart and the asymmetry of the extending <span class="hlt">system</span> affected the whole distal margin. The <span class="hlt">rift</span>-evolution observed along the Iberia/Newfoundland and Alpine Tethys margins shows a change in the mode of extension from initially distributed and decoupled (extension mode), to localized, coupled and asymmetric (thinning and exhumation mode), to <span class="hlt">final</span> localization in a Mid Ocean Ridge. The change in the mode of deformation can be interpreted to reflect an evolution of the bulk rheology of the extending lithosphere. Initial <span class="hlt">rifting</span> appears to be controlled by inherited heterogeneities and recrystallization processes in mylonitic shear zones (stretching and thinning mode) whereas later <span class="hlt">rifting</span> and continental rupturing may be controlled by hydration (serpentinization), magmatic and thermal weakening (exhumation mode). Since both serpentinization and magmatism developed during a late stage of <span class="hlt">rifting</span> within an already thinned crust, they may control the break-up of the continental lithosphere but not the localization of <span class="hlt">rifting</span> within the area of the future break-up. The localization of <span class="hlt">rifting</span> within the area of <span class="hlt">final</span> break-up has therefore to be explained by inherited heterogeneities or another weakening process within the extending lithosphere. At other margins, these modes may interact in a different way depending on the pre-<span class="hlt">rift</span> conditions and the evolution of the rheology during <span class="hlt">rifting</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.T13A1850C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.T13A1850C"><span id="translatedtitle">Post <span class="hlt">Rift</span> Thermal Evolution of Extended Lithosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cardoso, R. R.; Hamza, V. M.</p> <p>2009-12-01</p> <p>An improved thermal model of the lithosphere extension is proposed and its influence in the petroleum <span class="hlt">system</span> in sedimentary basins examined. The new model assumes existence of time dependent variation in the lithosphere thickness during the post-<span class="hlt">rift</span> period, which was not take account in the formulation of the Mackenzie model (1978). In the present work we assume that the asymptotic growth of the lithosphere thickness, during the post-<span class="hlt">rift</span> period, may be represented by an asymptotic relation of the type: L(t)=(L/?)+(L-L/?)erf(?*t) where L(t) is lithospheric thickness at post-<span class="hlt">rift</span> time t, ? the stretching factor as defined in the McKenzie model, erf the error function and ? a suitable scaling constant. According to the above equation the syn-<span class="hlt">rift</span> value of L is (L/?). For large times the thickness of the lithosphere approaches asymptotically the pre-<span class="hlt">rift</span> value of L. The value of ? can be determined by calculating the time necessary for the stretched lithosphere (L/?) to return to original thickness. The results of numerical simulations indicate that the heat flux derived from the new model is substantially lower than the values predicted by the McKenzie model (see Figure 1). The new model has been calibrated using available information on evolution of thermal maturity indices for the Santos Basin, situated in the offshore area of southeast Brazil. Heat flow variations during the post stretch period, for the case in which the stretching factor is 2.5.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.8575B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.8575B"><span id="translatedtitle">Structural inheritance, segmentation, and <span class="hlt">rift</span> localization in the Gulf of Aden oblique <span class="hlt">rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bellahsen, Nicolas; Leroy, Sylvie; Autin, Julia; d'Acremont, Elia; Razin, Philippe; Husson, Laurent; Pik, Raphael; Watremez, Louise; Baurion, Celine; Beslier, Marie-Odile; Khanbari, Khaled; Ahmed, Abdulhakim</p> <p>2013-04-01</p> <p>The structural evolution of the Gulf of Aden passive margins was controlled by its oblique divergence kinematics, inherited structures, and the Afar hot spot. The <span class="hlt">rifting</span> between Arabia and Somalia started at 35 Ma just before the hot spot paroxysm (at 30Ma) and lasted until 18Ma, when oceanic spreading started. Fieldwork suggests that <span class="hlt">rift</span> parallel normal faults initiated in the (future) distal margins, after a first stage of distributed <span class="hlt">rifting</span>, and witness the <span class="hlt">rift</span> localization, as confirmed by 4-layer analogue models. These faults arise either from crust or lithosphere scale buoyancy forces that are strongly controlled by the mantle temperature under the influence of the Afar hot spot. This implies a transition from a distributed mode to a localized one, sharper, both in space and time, in the West (close to the hot spot) than in the East (far away from the hot spot). In this framework, first order transform F.Z. are here (re-) defined by the fact that they deform continental crust. In the Gulf of Aden, as well as in other continental margins, it appears that these F.Z. are often, if not always, located at continental transfer or "transform" fault zones. Our detailed field-study of an offshore transfer fault zone in the southeastern Gulf of Aden (Socotra Island) shows that these structures are long-lived since early <span class="hlt">rifting</span> until post <span class="hlt">rift</span> times. During the early <span class="hlt">rifting</span>, they are inherited structures reactivated as oblique normal faults before accommodating strike-slip motion. During the Ocean-Continent Transition (OCT) formation ("post syn-<span class="hlt">rift</span>" times), a significant uplift occurred in the transfer fault zone footwall as shown by stratigraphic and LT thermochronology data. Second order transform F.Z. are defined as deforming only the OCT, thus initiated at the moment of its formation. In the western Gulf of Aden, the hot spot provoked a <span class="hlt">rift</span> localization strongly oblique to the divergence and, as a consequence, several second order transform F.Z. formed (as well as third order ones that initiated after the onset of oceanic spreading). In the East, the second and third order segmentation is less pronounced as both the OCT and ridge segments are sub-perpendicular to the divergence. During post-<span class="hlt">rift</span> times, plate reorganization led to oceanic propagator development and second/third transform F.Z. migration along with deformation and vertical movements and normal displacement along the first order transform F.Z. <span class="hlt">Finally</span>, during Quaternary times, the evolving boundary conditions of the Arabian plate probably also induced vertical movements along the margins.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5788199','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5788199"><span id="translatedtitle">Evaluation of geothermal potential of Rio Grande <span class="hlt">rift</span> and Basin and Range province, New Mexico. <span class="hlt">Final</span> technical report, January 1, 1977-May 31, 1978</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Callender, J.F.</p> <p>1985-04-01</p> <p>A study was made of the geological, geochemical and geophysical characteristics of potential geothermal areas in the Rio Grande <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.V13A2831W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.V13A2831W"><span id="translatedtitle">Fluoride and Geothermal Activities In Continental <span class="hlt">Rift</span> Zones, Ethiopia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Weldesenbet, S. F.</p> <p>2012-12-01</p> <p>The Central Main Ethiopian <span class="hlt">Rift</span> basin is a continental <span class="hlt">rift</span> <span class="hlt">system</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> ward groundwater flow paths. These waters <span class="hlt">finally</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> groundwater. Leaching of fluoride in the sub-surface <span class="hlt">system</span> 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 <span class="hlt">finally</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.H21E1215W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.H21E1215W"><span id="translatedtitle">High Fluoride and Geothermal Activities In Continental <span class="hlt">Rift</span> Zones, Ethiopia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Weldesenbet, S. F.; Wohnlich, S.</p> <p>2012-12-01</p> <p>The Central Main Ethiopian <span class="hlt">Rift</span> basin is a continental <span class="hlt">rift</span> <span class="hlt">system</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> ward groundwater flow paths. These waters <span class="hlt">finally</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> groundwater. Leaching of fluoride in the sub-surface <span class="hlt">system</span> 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 <span class="hlt">finally</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.430....1Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.430....1Y"><span id="translatedtitle">Seismic anisotropy beneath the incipient Okavango <span class="hlt">rift</span>: Implications for <span class="hlt">rifting</span> initiation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yu, Youqiang; Gao, Stephen S.; Moidaki, Moikwathai; Reed, Cory A.; Liu, Kelly H.</p> <p>2015-11-01</p> <p>This study represents the first shear-wave splitting investigation of the Okavango <span class="hlt">rift</span> zone (ORZ), an incipient continental <span class="hlt">rift</span> belonging to the East African <span class="hlt">rift</span> <span class="hlt">system</span> in northern Botswana. Analysis of broadband seismic data recorded along a 750 km long profile of 22 stations traversing the ORZ and adjacent Congo and Kalahari cratons and several Precambrian orogenic zones reveals dominantly NE-SW fast orientations, which are parallel to both the absolute plate motion direction (based on the NNR-NUVEL-1A model) and the trend of most tectonic boundaries, including that of the ORZ. Spatial coherence analysis of the splitting parameters and correspondence between the observed fast orientations and the trend of tectonic features indicate that the main source of observed anisotropy is most likely in the upper asthenosphere, probably due to simple shear associated with the relative movement of the lithosphere against the asthenosphere. The presence of consistently <span class="hlt">rift</span>-parallel fast orientations and normal splitting times in the ORZ and most parts of southern Africa implies that neither an upper mantle plume nor small-scale convection is the dominant source for <span class="hlt">rift</span> initiation and development. The first shear-wave splitting measurements in the vicinity of the ORZ favor a model in which continental <span class="hlt">rifting</span> develops in response to intra-plate relative movement of continental blocks along zones of weakness produced by ancient tectonic events.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=276057','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=276057"><span id="translatedtitle"><span class="hlt">Rift</span> Valley Fever Review</span></a></p> <p><a target="_blank" href="http://www.ars.usda.gov/services/TekTran.htm">Technology Transfer Automated Retrieval System (TEKTRAN)</a></p> <p></p> <p></p> <p><span class="hlt">Rift</span> Valley fever (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...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=plate+AND+tectonics+AND+islands&id=EJ394260','ERIC'); return false;" href="http://eric.ed.gov/?q=plate+AND+tectonics+AND+islands&id=EJ394260"><span id="translatedtitle">Volcanism at <span class="hlt">Rifts</span>.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>White, Robert S.; McKenzie, Dan P.</p> <p>1989-01-01</p> <p>Investigates the nature of catastrophic volcanism and the <span class="hlt">rifting</span> process. Describes two kinds of evidence: quantitative descriptions of rock melting and a wide range of observations. Discusses examples of continent growth in the North Atlantic, India and the Seychelles islands, and the South Atlantic. (YP)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5454347','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5454347"><span id="translatedtitle">Continental <span class="hlt">rifting</span> - Progress and outlook</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Baker, B.H.; Morgan, P.</p> <p>1981-07-21</p> <p>It is noted that in spite of the flood of new data on continental <span class="hlt">rifts</span> in the last 15 years, there is little consensus about the basic mechanisms and causes of <span class="hlt">rifting</span>. The remarkable similarities in <span class="hlt">rift</span> cross sections (shown in a figure), are considered to suggest that the anomalous lithospheric structure of <span class="hlt">rifts</span> is more dependent on lithosphere properties than the mode of <span class="hlt">rifting</span>. It is thought that there is a spectrum of <span class="hlt">rifting</span> processes for which two fundamental mechanisms can be postulated: an active mechanism, whereby thermal energy is transmitted into the lithosphere from the underlying asthenosphere, and a passive mechanism by which mechanical energy is transmitted laterally through the lithosphere as a consequence of plate interactions at a distance. In order to permit the concept of the two fundamentally different mechanisms to be tested, a tentative classification is proposed that divides <span class="hlt">rifts</span> into two basic categories: active <span class="hlt">rifting</span> and passive <span class="hlt">rifting</span>. Here, the magnitude of active <span class="hlt">rifting</span> will depend on the rate at which lithosphere moves over the thermal source, with <span class="hlt">rifts</span> being restricted to stationary or slow-moving plates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.4444B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.4444B"><span id="translatedtitle">Fault Orientations at Obliquely <span class="hlt">Rifted</span> Margins: Where? When? Why?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brune, Sascha</p> <p>2015-04-01</p> <p>Present-day knowledge of <span class="hlt">rifted</span> margin formation is largely based on 2D seismic lines, 2D conceptual models, and corroborated by 2D numerical experiments. However, the 2D assumption that the extension direction is perpendicular to the <span class="hlt">rift</span> trend is often invalid. In fact, worldwide more than 75% of all <span class="hlt">rifted</span> margin segments have been formed under significant obliquity exceeding 20° (angle measured between extension direction and <span class="hlt">rift</span> trend normal): During formation of the Atlantic Ocean, oblique <span class="hlt">rifting</span> dominated at the sheared margins of South Africa and Patagonia, the Equatorial Atlantic margins, separation of Greenland and North America, and it played a major role in the protracted <span class="hlt">rift</span> history of the North East Atlantic. Outside the Atlantic Ocean, oblique <span class="hlt">rifting</span> occurred during the split between East and West Gondwana, the separation of India and Australia, India and Madagascar, Australia and Antarctica, as well as Arabia and Africa. It is presently observed in the Gulf of California, the Aegean and in the East African <span class="hlt">Rift</span>. Despite its significance, the degree to which oblique lithospheric extension affects first-order <span class="hlt">rift</span> and passive margin properties like surface stress pattern, fault azimuths, and basin geometry, is still not entirely clear. This contribution provides insight in crustal stress patterns and fault orientations by applying a 3D numerical <span class="hlt">rift</span> model to oblique extensional settings. The presented forward experiments cover the whole spectrum of oblique extension (i.e. <span class="hlt">rift</span>-orthogonal extension, low obliquity, high obliquity, strike-slip deformation) from initial deformation to breakup. They are conducted using an elasto-visco-plastic finite element model and involve crustal and mantle layers accounting for self-consistent necking of the lithosphere. Results are thoroughly compared to previous analogue experiments, which yields many similarities but also distinct differences for late <span class="hlt">rift</span> stages and for high obliquity. Even though the model 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 <span class="hlt">rift</span> <span class="hlt">systems</span>. 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 <span class="hlt">rift</span> <span class="hlt">system</span>. Moreover, the model depicts strain partitioning between <span class="hlt">rift</span>-parallel and <span class="hlt">rift</span>-perpendicular far-field velocity components that are accommodated by strike-slip faults in the <span class="hlt">rift</span> centre and normal faults at the <span class="hlt">rift</span> sides, respectively. Oblique extensional <span class="hlt">systems</span> worldwide differ in many aspects and clearly one suit of models cannot explain all <span class="hlt">rifted</span> 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 <span class="hlt">rifted</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.2376L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.2376L"><span id="translatedtitle">New insights into continental <span class="hlt">rifting</span> from a damage rheology modeling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lyakhovsky, Vladimir; Segev, Amit; Weinberger, Ram; Schattner, Uri</p> <p>2010-05-01</p> <p>Previous studies have discussed how tectonic processes could produce relative tension to initiate and propagate <span class="hlt">rift</span> zones and estimated the magnitude of the <span class="hlt">rift</span>-driving forces. Both analytic and semi-analytic models as well as numerical simulations assume that the tectonic force required to initiate <span class="hlt">rifting</span> is available. However, Buck (2004, 2006) estimated the minimum tectonic force to allow passive <span class="hlt">rifting</span> and concluded that the available forces are probably not large enough for <span class="hlt">rifting</span> of thick and strong lithosphere in the absence of basaltic magmatism (the "Tectonic Force" Paradox). The integral of the yielding stress needed for <span class="hlt">rifting</span> over the thickness of the normal or thicker continental lithosphere are well above the available tectonic forces and tectonic <span class="hlt">rifting</span> cannot happen (Buck, 2006). This conclusion is based on the assumption that the tectonic stress has to overcome simultaneously the yielding stress over the whole lithosphere thickness and ignore gradual weakening of the brittle rocks under long-term loading. In this study we demonstrate that the <span class="hlt">rifting</span> process under moderate tectonic stretching is feasible due to gradual weakening and "long-term memory" of the heavily fractured brittle rocks, which makes it significantly weaker than the surrounding intact rock. This process provides a possible solution for the tectonic force paradox. We address these questions utilizing 3-D lithosphere-scale numerical simulations of the plate motion and faulting process base on the damage mechanics. The 3-D modeled volume consists of three main lithospheric layers: an upper layer of weak sediments, middle layer of crystalline crust and lower layer of the lithosphere mantle. Results of the modeling demonstrate gradual formation of the <span class="hlt">rift</span> zone in the continental lithosphere with the flat layered structure. Successive formation of the <span class="hlt">rift</span> <span class="hlt">system</span> and associated seismicity pattern strongly depend not only on the applied tectonic force, but also on the healing parameters of the crustal rocks. Results of the modeling also demonstrate how the lithosphere structure and especially depth to the Moho interface affects the geometry of the propagating <span class="hlt">rift</span> <span class="hlt">system</span>. With the same boundary conditions and physical properties of rocks as in the case of the flat continental structure, a <span class="hlt">rift</span> terminates above the passive continental margin and a new fault <span class="hlt">system</span> is created normal to the direction of the <span class="hlt">rift</span> propagation. These results demonstrate that the local lithosphere structure is one of the major key factors controlling the geometry of the evolving <span class="hlt">rift</span> <span class="hlt">system</span>, faulting and seismicity pattern. Results of simulations suggest that under wide range of conditions a <span class="hlt">rift</span> propagating through a continental lithosphere might cease before it reaches the margin where transition to oceanic lithosphere occurs. Close to the margin different tectonic styles might take over the propagation. This behavior has been suggested for the NW continuation of the active Red Sea-Suez <span class="hlt">rift</span> <span class="hlt">system</span> and initiation of the Dead Sea Transform (Steckler and ten Brink, 1986). With the onset of the Red Sea opening (about Oligocene) the sub-parallel Azraq-Sirhan <span class="hlt">rift</span> was also activated and propagated in a NW direction from the Arabian continent toward the Levant basin oceanic crust. By applying our 3-D lithosphere-scale numerical simulations on the Azraq-Sirhan <span class="hlt">rift</span> <span class="hlt">system</span>, we conclude that thinning of the crystalline crust and strengthening of the Arabian lithosphere led to a decrease or even termination of the rate of <span class="hlt">rift</span> propagation next to the continental margin.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1039656','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1039656"><span id="translatedtitle"><span class="hlt">Final</span> Report Computational Analysis of Dynamical <span class="hlt">Systems</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Guckenheimer, John</p> <p>2012-05-08</p> <p>This is the <span class="hlt">final</span> report for DOE Grant DE-FG02-93ER25164, initiated in 1993. This grant supported research of John Guckenheimer on computational analysis of dynamical <span class="hlt">systems</span>. During that period, seventeen individuals received PhD degrees under the supervision of Guckenheimer and over fifty publications related to the grant were produced. This document contains copies of these publications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010Tectp.489..210J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010Tectp.489..210J"><span id="translatedtitle">3D architecture of a complex transcurrent <span class="hlt">rift</span> <span class="hlt">system</span>: The example of the Bay of Biscay-Western Pyrenees</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jammes, Suzon; Tiberi, Christel; Manatschal, Gianreto</p> <p>2010-06-01</p> <p>The Parentis and Arzacq-Mauléon basins located in front of the V-shaped oceanic propagator in the Bay of Biscay present evidence for extreme crustal thinning. In this paper we investigate the 3D structure of these <span class="hlt">rift</span> basins, based on field observations and the interpretation of seismic data. We compare these results with those obtained from two different and independent inversion methods: first a 3D gravity inversion and second the standard Euler deconvolution. For the Mauléon Basin our results show that the positive gravimetric anomaly identified above its southern margin is the consequence of two shallower high density bodies that are separated by the Pamplona fault and a deeper high density body. The high density bodies can be explained by the presence of mid-crustal and mantle rocks that were exhumed or uplifted at shallower depth during Early Cretaceous <span class="hlt">rifting</span> before they were reworked and integrated to the Pyrenean chain during compression phase. Also, during this reactivation phase, some slices of the exhumed mid-crustal and mantle rocks were sheared off and were integrated in the present-day thrust belt in the Mauléon basin. For the Parentis Basin we can demonstrate, based on seismic data and gravimetric inversion methods, a decrease in extension from west to east, which is compatible with the V-shape geometry of the overall basin. Along strike, a change in the fault geometry from downward concave top-basement detachment faults to upward concave high-angle faults can be observed eastwards, i.e. towards the termination of the basin. A key structure, controlling the evolution of the Parentis Basin, is the east-west trending Ibis fault. We interpret this fault to have initially formed as a strike slip fault before it was reactivated during later crustal thinning. At present, it forms the limit between an upper plate sag basin to the north and a lower plate sag basin, floored at least locally by a top-basement detachment faults to the south. The strong asymmetry of the basin is supported by the shape of the basin and the results of standard Euler deconvolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013Tectp.583...88L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013Tectp.583...88L"><span id="translatedtitle">Geophysical evidence of Cretaceous volcanics in Logone Birni Basin (Northern Cameroon), Central Africa, and consequences for the West and Central African <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Loule, Jean-Pierre; Pospisil, Lubomil</p> <p>2013-01-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span> (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 <span class="hlt">rifting</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70017177','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70017177"><span id="translatedtitle">Depositional and tectonic framework of the <span class="hlt">rift</span> basins of Lake Baikal from multichannel seismic data</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hutchinson, D.R.; Golmshtok, A.J.; Zonenshain, L.P.; Moore, T.C.; Scholz, C.A.; Klitgord, Kim D.</p> <p>1992-01-01</p> <p>Recent multichannel seismic reflection data from Lake Baikal, located in a large, active, continental <span class="hlt">rift</span> in central Asia, image three major stratigraphic units totalling 3.5 to 7.5 km thick in four subbasins. A major change in <span class="hlt">rift</span> deposition and faulting between the oldest and middle-<span class="hlt">rift</span> units probably corresponds to the change from slow to fast <span class="hlt">rifting</span>. A brief comparison of the basins of Lake Baikal with those of the East African <span class="hlt">rift</span> <span class="hlt">system</span> highlights differences in structural style that can be explained by differences in age and evolution of the surrounding basement rocks. -from Authors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/17814347','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/17814347"><span id="translatedtitle">Venus: volcanism and <span class="hlt">rift</span> formation in Beta regio.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Campbell, D B; Head, J W; Harmon, J K; Hine, A A</p> <p>1984-10-12</p> <p>A new high-resolution radar image of Beta Regio, a Venus highland area, confirms the presence of a major tectonic <span class="hlt">rift</span> <span class="hlt">system</span> and associated volcanic activity. The lack of identifiable impact craters, together with the apparent superposition of the Theia Mons volcanic structure on the <span class="hlt">rift</span> <span class="hlt">system</span>, suggest that at least some of the volcanic activity occurred in relatively recent geologic time. The presence of topographically similar highland areas elsewhere on Venus (Aphrodite Terra, Dali Chasma, and Diana Chasma) suggests that <span class="hlt">rifting</span> and volcanism are significant processes on Venus. PMID:17814347</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19850029005&hterms=Aphrodite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DAphrodite','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19850029005&hterms=Aphrodite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DAphrodite"><span id="translatedtitle">Venus - Volcanism and <span class="hlt">rift</span> formation in Beta Regio</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Campbell, D. B.; Harmon, J. K.; Hine, A. A.; Head, J. W.</p> <p>1984-01-01</p> <p>A new high-resolution radar image of Beta Regio, a Venus highland area, confirms the presence of a major tectonic <span class="hlt">rift</span> <span class="hlt">system</span> and associated volcanic activity. The lack of identifiable impact craters, together with the apparent superposition of the Theia Mons volcanic structure on the <span class="hlt">rift</span> <span class="hlt">system</span>, suggest that at least some of the volcanic activity occurred in relatively recent geologic time. The presence of topographically similar highland areas elsewhere on Venus (Aphrodite Terra, Dali Chasma, and Diana Chasma) suggests that <span class="hlt">rifting</span> and volcanism are significant processes on Venus.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984Sci...226..167C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984Sci...226..167C"><span id="translatedtitle">Venus - Volcanism and <span class="hlt">rift</span> formation in Beta Regio</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Campbell, D. B.; Head, J. W.; Harmon, J. K.; Hine, A. A.</p> <p>1984-10-01</p> <p>A new high-resolution radar image of Beta Regio, a Venus highland area, confirms the presence of a major tectonic <span class="hlt">rift</span> <span class="hlt">system</span> and associated volcanic activity. The lack of identifiable impact craters, together with the apparent superposition of the Theia Mons volcanic structure on the <span class="hlt">rift</span> <span class="hlt">system</span>, suggest that at least some of the volcanic activity occurred in relatively recent geologic time. The presence of topographically similar highland areas elsewhere on Venus (Aphrodite Terra, Dali Chasma, and Diana Chasma) suggests that <span class="hlt">rifting</span> and volcanism are significant processes on Venus.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19790043898&hterms=scrap&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dscrap','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19790043898&hterms=scrap&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dscrap"><span id="translatedtitle">Martian canyons and African <span class="hlt">rifts</span> - Structural comparisons and implications</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Frey, H.</p> <p>1979-01-01</p> <p>The resistant parts of the canyon walls of the Martian <span class="hlt">rift</span> complex Valles Marineris have been used to infer an earlier, less eroded reconstruction of the major troughs. The individual canyons are compared with individual <span class="hlt">rifts</span> of East Africa. When measured in units of planetary radius, Martian canyons show a distribution of lengths nearly identical to those in Africa, both for individual <span class="hlt">rifts</span> and for compound <span class="hlt">rift</span> <span class="hlt">systems</span>. A common mechanism which scales with planetary radius is suggested. Martian canyons are significantly wider than African <span class="hlt">rifts</span>. This is consistent with the longstanding idea that <span class="hlt">rift</span> width is related to crustal thickness: most evidence favors a crust on Mars at least 50% thicker than that of Africa. The overall patterns of the <span class="hlt">rift</span> <span class="hlt">systems</span> of Africa and Mars are quite different in that the African <span class="hlt">systems</span> are composed of numerous small faults with highly variable trend. On Mars the trends are less variable; individual scraps are straighter for longer than on earth. The basement and lithosphere of Mars are inferred to be simple, reflecting a relatively inactive tectonic history prior to the formation of the canyonlands.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/7141016','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/7141016"><span id="translatedtitle">The Midcontinent <span class="hlt">Rift</span> and Grenville connection</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cambray, F.W.; Fujita, K. . Dept. of Geological Sciences)</p> <p>1994-04-01</p> <p>The Mid-Proterozoic, Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> (MRS) is delineated by an inverted U shaped gravity and magnetic anomaly. It terminates in southeast Michigan but a less continuous series of anomalies and sediments, the Eastcontinent <span class="hlt">Rift</span> occur on a north-south line through Ohio and Kentucky. The geometry allows for a north-south opening, the Lake Superior section being orthogonal to opening, the western arm transtensional and the north-south trending eastern arm a transform boundary offset by pull-apart basins. The opening and closing of the <span class="hlt">rift</span> overlaps in time with the Grenville Orogeny. Grenville age rocks can also be found in the Llano uplift of Texas. The authors propose a model to explain the temporal and geographic association of the opening and closing of the MRS with the Grenville Orogeny that involves irregular suturing between two continental masses. Initiation of Grenville suturing, associated with south dipping subduction, in the northeast and in the Llano area of Texas would leave portion of unclosed ocean in between. Tensional stresses in the continental crust adjacent to the oceanic remnant could lead to its fragmentation and the formation of the MRS. The remaining oceanic lithosphere would eventually subduct, limiting the opening of the MRS. Continued convergence of the plates would induce compressional stresses thus accounting for the deformation of the MRS. An analogy is made with more recent opening of the Red Sea, Gulf of Aden <span class="hlt">Rift</span> <span class="hlt">System</span> in association with irregular collision along the Zagros-Bitlis Sutures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tecto..34.2399L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tecto..34.2399L"><span id="translatedtitle">Hierarchical segmentation of the Malawi <span class="hlt">Rift</span>: The influence of inherited lithospheric heterogeneity and kinematics in the evolution of continental <span class="hlt">rifts</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Laó-Dávila, Daniel A.; Al-Salmi, Haifa S.; Abdelsalam, Mohamed G.; Atekwana, Estella A.</p> <p>2015-12-01</p> <p>We used detailed analysis of Shuttle Radar Topography Mission-digital elevation model and observations from aeromagnetic data to examine the influence of inherited lithospheric heterogeneity and kinematics in the segmentation of largely amagmatic continental <span class="hlt">rifts</span>. We focused on the Cenozoic Malawi <span class="hlt">Rift</span>, which represents the southern extension of the Western Branch of the East African <span class="hlt">Rift</span> <span class="hlt">System</span>. This north trending <span class="hlt">rift</span> traverses Precambrian and Paleozoic-Mesozoic structures of different orientations. We found that the <span class="hlt">rift</span> can be hierarchically divided into first-order and second-order segments. In the first-order segmentation, we divided the <span class="hlt">rift</span> into Northern, Central, and Southern sections. In its Northern Section, the <span class="hlt">rift</span> follows Paleoproterozoic and Neoproterozoic terrains with structural grain that favored the localization of extension within well-developed border faults. The Central Section occurs within Mesoproterozoic-Neoproterozoic terrain with regional structures oblique to the <span class="hlt">rift</span> extent. We propose that the lack of inherited lithospheric heterogeneity favoring extension localization resulted in the development of the <span class="hlt">rift</span> in this section as a shallow graben with undeveloped border faults. In the Southern Section, Mesoproterozoic-Neoproterozoic rocks were reactivated and developed the border faults. In the second-order segmentation, only observed in the Northern Section, we divided the section into five segments that approximate four half-grabens/asymmetrical grabens with alternating polarities. The change of polarity coincides with flip-over full-grabens occurring within overlap zones associated with ~150 km long alternating border faults segments. The inherited lithospheric heterogeneity played the major role in facilitating the segmentation of the Malawi <span class="hlt">Rift</span> during its opening resulting from extension.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.T23F..06D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.T23F..06D"><span id="translatedtitle">Amagmatic Accretionary Segments, Ultraslow Spreading and Non-Volcanic <span class="hlt">Rifted</span> Margins (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dick, H. J.; Snow, J. E.</p> <p>2009-12-01</p> <p>The evolution of non-volcanic <span class="hlt">rifted</span> margins is key to understanding continental breakup and the early evolution of some of the world’s most productive hydrocarbon basins. However, the early stages of such <span class="hlt">rifting</span> are constrained by limited observations on ancient heavily sedimented margins such as Newfoundland and Iberia. Ultraslow spreading ridges, however, provide a modern analogue for early continental <span class="hlt">rifting</span>. Ultraslow spreading ridges (<20 mm/yr) comprise ~30% of the global ridge <span class="hlt">system</span> (e.g. Gakkel, Southwest Indian, Terceira, and Knipovitch Ridges). They have unique tectonics with widely spaced volcanic segments and amagmatic accretionary ridge segments. The volcanic segments, though far from hot spots, include some of the largest axial volcanoes on the global ridge <span class="hlt">system</span>, and have, unusual magma chemistry, often showing local isotopic and incompatible element enrichment unrelated to mantle hot spots. The transition from slow to ultraslow tectonics and spreading is not uniquely defined by spreading rate, and may also be moderated by magma supply and mantle temperature. Amagmatic accretionary segments are the 4th class of plate boundary structure, and, we believe, the defining tectonic feature of early continental breakup. They form at effective spreading rates <12 mm/yr, assume any orientation to spreading, and replace transform faults and magmatic segments. At amagmatic segments the earth splits apart with the mantle emplaced directly to the seafloor, and great slabs of peridotite are uplifted to form the <span class="hlt">rift</span> mountains. A thick conductive lid suppresses mantle melting, and magmatic segments form only at widely spaced intervals, with only scattered volcanics in between. Amagmatic segments link with the magmatic segments forming curvilinear plate boundaries, rather than the step-like morphology found at faster spreading ridges. These are all key features of non-volcanic <span class="hlt">rifted</span> margins; explaining, for example, the presence of mantle peridotites emplaced simultaneously on both the Newfoundland and Iberian Margins in the Jurassic and Cretaceous. Miocene Lena Trough is a new mid-ocean <span class="hlt">rift</span> plate boundary and the <span class="hlt">final</span> event in the separation of the North American and Eurasian continents. Mapping and sampling of Lena Trough confirms that it is both oblique and amagmatic, showing that initiation of seafloor spreading at a non-volcanic <span class="hlt">rifted</span> continental margin follows the same pattern as ultraslow spreading ridges.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1023141','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1023141"><span id="translatedtitle">DCE Bio Detection <span class="hlt">System</span> <span class="hlt">Final</span> Report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Lind, Michael A.; Batishko, Charles R.; Morgen, Gerald P.; Owsley, Stanley L.; Dunham, Glen C.; Warner, Marvin G.; Willett, Jesse A.</p> <p>2007-12-01</p> <p>The DCE (DNA Capture Element) Bio-Detection <span class="hlt">System</span> (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 <span class="hlt">final</span> report summarizes and documents the <span class="hlt">final</span> configuration of the <span class="hlt">system</span> delivered to the Air Force in December 2008</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Tecto..33..485P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Tecto..33..485P"><span id="translatedtitle">Evolution, distribution, and characteristics of <span class="hlt">rifting</span> in southern Ethiopia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Philippon, Melody; Corti, Giacomo; Sani, Federico; Bonini, Marco; Balestrieri, Maria-Laura; Molin, Paola; Willingshofer, Ernst; Sokoutis, Dimitrios; Cloetingh, Sierd</p> <p>2014-04-01</p> <p>Southern Ethiopia is a key region to understand the evolution of the East African <span class="hlt">rift</span> <span class="hlt">system</span>, since it is the area of interaction between the main Ethiopian <span class="hlt">rift</span> (MER) and the Kenyan <span class="hlt">rift</span>. However, geological data constraining <span class="hlt">rift</span> evolution in this remote area are still relatively sparse. In this study the timing, distribution, and style of <span class="hlt">rifting</span> in southern Ethiopia are constrained by new structural, geochronological, and geomorphological data. The border faults in the area are roughly parallel to preexisting basement fabrics and are progressively more oblique with respect to the regional Nubia-Somalia motion proceeding southward. Kinematic indicators along these faults are mainly dip slip, pointing to a progressive rotation of the computed direction of extension toward the south. Radiocarbon data indicate post 30 ka faulting at both western and eastern margins of the MER with limited axial deformation. Similarly, geomorphological data suggest recent fault activity along the western margins of the basins composing the Gofa Province and in the Chew Bahir basin. This supports that interaction between the MER and the Kenyan <span class="hlt">rift</span> in southern Ethiopia occurs in a 200 km wide zone of ongoing deformation. Fault-related exhumation at ~10-12 Ma in the Gofa Province, as constrained by new apatite fission track data, occurred later than the ~20 Ma basement exhumation of the Chew Bahir basin, thus pointing to a northward propagation of the Kenyan <span class="hlt">rift</span>-related extension in the area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/687704','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/687704"><span id="translatedtitle">Hydrothermal flow <span class="hlt">systems</span> in the Midcontinent <span class="hlt">Rift</span>: Oxygen and hydrogen isotopic studies of the North Shore Volcanic Group and related hypabyssal sills, Minnesota</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Park, Y.R.; Ripley, E.M.</p> <p>1999-06-01</p> <p><span class="hlt">Rift</span>-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 <span class="hlt">system</span> 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 <span class="hlt">system</span>. 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 <span class="hlt">system</span> associated with the Midcontinent <span class="hlt">Rift</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T43F2740M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T43F2740M"><span id="translatedtitle">The influence of oceanic fracture zones on the segmentation of continental margins and the evolution of intra-continental <span class="hlt">rift</span> <span class="hlt">systems</span>: Case studies from the Atlantic</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Masterton, S.; Fairhead, J. D.; Green, C. M.</p> <p>2012-12-01</p> <p>It has been a long held view that oceanic fracture zones play an important role in the segmentation of continental margins and therefore provide a major structural control on their evolution and the development of associated petroleum <span class="hlt">systems</span>. The geometry of fracture zones reflects the spreading history of the seafloor: subtle changes in plate motion causes stress-field reorientation, which in turn results in changes in the orientation of the fracture zone. These changes can introduce strike-perpendicular compression or extension across transform faults; the latter may lead to increased ridge segmentation and the initiation of new spreading centres. We present two examples of secondary fracture zone initiation and disappearance within the Atlantic Ocean between 1) the Atlantis and Kane major fracture zones in the Central Atlantic and 2) the Ascension and Rio de Janeiro fracture zones in the South Atlantic. We investigate the discontinuous nature of these fracture zones by exploring their relationship with major plate re-organisation events and seafloor spreading geometry. Using a series of stage reconstruction poles that represent the motion of both North and South America relative to Africa since the initiation of Atlantic seafloor spreading, we have performed a quantitative analysis of spreading directions along major Atlantic fracture zones. Our results demonstrate a notable correlation between the timing of major plate reorganisation events and the initiation and disappearance of secondary fracture zones. Such events are clearly recorded in the Atlantic margin stratigraphic record as major unconformities. We are therefore able to interpret fracture zone abundance in terms of palaeo-spreading geometry and the opening history of the Atlantic Ocean. This allows us to make important inferences about the influence of fracture zones on the segmentation and structural control of continental margins. Specifically, in our South Atlantic case study, where secondary fracture zones do not extend up to the offshore Angolan and conjugate Brazilian margins, we conclude that small offset transform faulting did not influence the evolution of the continental margin as has been previously suggested. On a regional scale, the evolution of the Africa-wide Mesozoic <span class="hlt">rift</span> <span class="hlt">system</span> is intimately linked to global plate tectonics and to changes in plate interactions. On a basinal scale, changes in the orientation of the dominant stress field resulting from plate reorganisation have had a clear impact on the deformation history and fault geometries of <span class="hlt">rift</span> basins. We demonstrate this relationship by correlating the timing of changes in South Atlantic fracture zone geometries and African margin unconformities with major unconformities that are observed in a unified stratigraphy chart for the West and Central African <span class="hlt">Rift</span> <span class="hlt">System</span>. We propose a controlling mechanism in which changes in plate stress control the effective elastic strength of a plate, resulting in a focused change in isostatic response over continental margins.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.7780W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.7780W"><span id="translatedtitle">Surface analogue outcrops of deep fractured basement reservoirs in extensional geological settings. Examples within active <span class="hlt">rift</span> <span class="hlt">system</span> (Uganda) and proximal passive margin (Morocco).</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Walter, Bastien; Géraud, Yves; Diraison, Marc</p> <p>2014-05-01</p> <p>The important role of extensive brittle faults and related structures in the development of reservoirs has already been demonstrated, notably in initially low-porosity rocks such as basement rocks. Large varieties of deep-seated resources (e.g. water, hydrocarbons, geothermal energy) are recognized in fractured basement reservoirs. Brittle faults and fracture networks can develop sufficient volumes to allow storage and transfer of large amounts of fluids. Development of hydraulic model with dual-porosity implies the structural and petrophysical characterization of the basement. Drain porosity is located within the larger fault zones, which are the main fluid transfer channels. The storage porosity corresponds both to the matrix porosity and to the volume produced by the different fractures networks (e.g. tectonic, primary), which affect the whole reservoir rocks. Multi-scale genetic and geometric relationships between these deformation features support different orders of structural domains in a reservoir, from several tens of kilometers to few tens of meters. In subsurface, 3D seismic data in basement can be sufficient to characterize the largest first order of structural domains and bounding fault zones (thickness, main orientation, internal architecture, …). However, lower order structural blocks and fracture networks are harder to define. The only available data are 1D borehole electric imaging and are used to characterize the lowest order. Analog outcrop studies of basement rocks fill up this resolution gap and help the understanding of brittle deformation, definition of reservoir geometries and acquirement of reservoir properties. These geological outcrop studies give information about structural blocks of second and third order, getting close to the field scale. This allows to understand relationships between brittle structures geometry and factors controlling their development, such as the structural inheritance or the lithology (e.g. schistosity, primary structures). Two field cases, located in Morocco and Uganda, allow us to investigate basement complexes at different stages of an extension process and give us analog geological data of similar fractured basement reservoirs. Border faults and associated fracture networks of an active <span class="hlt">rifting</span> <span class="hlt">system</span> propagated in Proterozoic basement rocks are analyzed in the Albertine <span class="hlt">rift</span> <span class="hlt">system</span> in Uganda. Brittle structures developed along a proximal passive margin of the Atlantic domain are analyzed in Proterozoic basements rocks in Western Anti-Atlas in Morocco.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900012177','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900012177"><span id="translatedtitle">Age constraints for the present fault configuration in the Imperial Valley, California: Evidence for northwestward propagation of the Gulf of California <span class="hlt">rift</span> <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Larsen, Shawn; Reilinger, Robert</p> <p>1990-01-01</p> <p>Releveling and other geophysical data for the Imperial Valley of southern California suggest the northern section of the Imperial-Brawley fault <span class="hlt">system</span>, which includes the Mesquite Basin and Brawley Seismic Zone, is much younger than the 4 to 5 million year age of the valley itself. A minimum age of 3000 years is calculated for the northern segment of the Imperial fault from correlations between surface topography and geodetically observed seismic/interseismic vertical movements. Calculations of a maximum age of 80,000 years is based upon displacements in the crystalline basement along the Imperial fault, inferred from seismic refraction surveys. This young age supports recent interpretations of heat flow measurements, which also suggest that the current patterns of seismicity and faults in the Imperial Valley are not long lived. The current fault geometry and basement morphology suggest northwestward growth of the Imperial fault and migration of the Brawley Seismic Zone. It is suggested that this migration is a manifestation of the propagation of the Gulf of California <span class="hlt">rift</span> <span class="hlt">system</span> into the North American continent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012GGG....13.1012L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012GGG....13.1012L"><span id="translatedtitle">Deformation and seismicity associated with continental <span class="hlt">rift</span> zones propagating toward continental margins</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lyakhovsky, V.; Segev, A.; Schattner, U.; Weinberger, R.</p> <p>2012-01-01</p> <p>We study the propagation of a continental <span class="hlt">rift</span> and its interaction with a continental margin utilizing a 3-D lithospheric model with a seismogenic crust governed by a damage rheology. A long-standing problem in <span class="hlt">rift</span>-mechanics, known as thetectonic force paradox, is that the magnitude of the tectonic forces required for <span class="hlt">rifting</span> are not large enough in the absence of basaltic magmatism. Our modeling results demonstrate that under moderate <span class="hlt">rift</span>-driving tectonic forces the <span class="hlt">rift</span> propagation is feasible even in the absence of magmatism. This is due to gradual weakening and "long-term memory" of fractured rocks that lead to a significantly lower yielding stress than that of the surrounding intact rocks. We show that the style, rate and the associated seismicity pattern of the <span class="hlt">rift</span> zone formation in the continental lithosphere depend not only on the applied tectonic forces, but also on the rate of healing. Accounting for the memory effect provides a feasible solution for thetectonic force paradox. Our modeling results also demonstrate how the lithosphere structure affects the geometry of the propagating <span class="hlt">rift</span> <span class="hlt">system</span> toward a continental margin. Thinning of the crystalline crust leads to a decrease in the propagation rate and possibly to <span class="hlt">rift</span> termination across the margin. In such a case, a new fault <span class="hlt">system</span> is created perpendicular to the direction of the <span class="hlt">rift</span> propagation. These results reveal that the local lithosphere structure is one of the key factors controlling the geometry of the evolving <span class="hlt">rift</span> <span class="hlt">system</span> and seismicity pattern.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19940007574&hterms=Aphrodite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DAphrodite','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19940007574&hterms=Aphrodite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DAphrodite"><span id="translatedtitle">Estimation of age of Dali-Ganis <span class="hlt">rifting</span> and associated volcanic activity, Venus</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Basilevsky, A. T.</p> <p>1993-01-01</p> <p>This paper deals with the estimation of age for the Dali and Ganis Chasma <span class="hlt">rift</span> zones and their associated volcanism based on photogeologic analysis of stratigraphic relations of <span class="hlt">rift</span>-associated features with impact craters which have associated features indicative of their age. The features are radar-dark and parabolic, and they are believed to be mantles of debris derived from fallout of the craters' ejecta. They are thought to be among the youngest features on the Venusian surface, so their 'parent' craters must also be very young, evidently among the youngest 10 percent of Venus' crater population. Dali Chasma and Ganis Chasma are a part of a <span class="hlt">system</span> of <span class="hlt">rift</span> zones contained within eastern Aphrodite and Atla Regio which is a significant component of Venus tectonics. The <span class="hlt">rifts</span> of this <span class="hlt">system</span> are fracture belts which dissect typical Venusian plains with rare islands of tessera terrain. The <span class="hlt">rift</span> zone <span class="hlt">system</span> consists of several segments following each other (Diane, Dali, Ganis) and forming the major <span class="hlt">rift</span> zone line, about 10,000 km long, which has junctions with several other <span class="hlt">rift</span> zones, including Parga Chasma <span class="hlt">Rift</span>. The junctions are usually locations of <span class="hlt">rift</span>-associated volcanism in the form of volcanic edifices (Maat and Ozza Montes) or plain-forming flows flooding some areas within the <span class="hlt">rift</span> zones and the adjacent plains.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993LPI....24...67B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993LPI....24...67B"><span id="translatedtitle">Estimation of age of Dali-Ganis <span class="hlt">rifting</span> and associated volcanic activity, Venus</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Basilevsky, A. T.</p> <p>1993-03-01</p> <p>This paper deals with the estimation of age for the Dali and Ganis Chasma <span class="hlt">rift</span> zones and their associated volcanism based on photogeologic analysis of stratigraphic relations of <span class="hlt">rift</span>-associated features with impact craters which have associated features indicative of their age. The features are radar-dark and parabolic, and they are believed to be mantles of debris derived from fallout of the craters' ejecta. They are thought to be among the youngest features on the Venusian surface, so their 'parent' craters must also be very young, evidently among the youngest 10 percent of Venus' crater population. Dali Chasma and Ganis Chasma are a part of a <span class="hlt">system</span> of <span class="hlt">rift</span> zones contained within eastern Aphrodite and Atla Regio which is a significant component of Venus tectonics. The <span class="hlt">rifts</span> of this <span class="hlt">system</span> are fracture belts which dissect typical Venusian plains with rare islands of tessera terrain. The <span class="hlt">rift</span> zone <span class="hlt">system</span> consists of several segments following each other (Diane, Dali, Ganis) and forming the major <span class="hlt">rift</span> zone line, about 10,000 km long, which has junctions with several other <span class="hlt">rift</span> zones, including Parga Chasma <span class="hlt">Rift</span>. The junctions are usually locations of <span class="hlt">rift</span>-associated volcanism in the form of volcanic edifices (Maat and Ozza Montes) or plain-forming flows flooding some areas within the <span class="hlt">rift</span> zones and the adjacent plains.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/376401','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/376401"><span id="translatedtitle">Facilities management <span class="hlt">system</span> (FMS). <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p></p> <p>1992-04-01</p> <p>This report provides a detailed, <span class="hlt">final</span> status of Andersen Consulting`s participation in the Facilities Management <span class="hlt">System</span> (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, <span class="hlt">final</span> status of the FMS project at the termination of Andersen`s full-time participation. This section discusses the status of each FMS sub-<span class="hlt">system</span> 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 <span class="hlt">system</span> users. The report also addresses Andersen`s observations from the feedback.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/376373','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/376373"><span id="translatedtitle">Facilities management <span class="hlt">system</span> (FMS). <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p></p> <p>1992-04-01</p> <p>The remainder of this report provides a detailed, <span class="hlt">final</span> status of Andersen Consulting`s participation in the FMS <span class="hlt">systems</span> 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, <span class="hlt">final</span> status of the FMS project at the termination of Andersen`s full-time participation. This section discusses the status of each FMS sub-<span class="hlt">system</span> 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 <span class="hlt">system</span> users. The report also addresses Andersen`s observations from the feedback.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1712043P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1712043P"><span id="translatedtitle">What role does crustal heterogeneity play on continental break-up; the interplay of a foldbelt, <span class="hlt">rift</span> <span class="hlt">system</span> and ocean basin in the South Atlantic</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Paton, Douglas; Mortimer, Estelle; Hodgson, Neil</p> <p>2015-04-01</p> <p>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 <span class="hlt">rifting</span> continued into the Ventana Foldbelt of Argentina but to date its location in the offshore part of South Africa remains enigmatic. Secondly, the conjugate <span class="hlt">rift</span> 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 <span class="hlt">rifting</span> 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 <span class="hlt">rifting</span>, but the Colorado <span class="hlt">rift</span> 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 <span class="hlt">rift</span> evolution and strain localisation during the subsequent <span class="hlt">rift</span> phase prior to seafloor spreading.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMDI24A..04H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMDI24A..04H"><span id="translatedtitle">Mapping Mantle Mixing and the Extent of Superplume Influence Using He-Ne-Ar-CO2-N2 Isotopes: The Case of the East Africa <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hilton, D. R.; Halldorsson, S. A.; Scarsi, P.; Castillo, P.; Abebe, T.; Kulongoski, J. T.</p> <p>2014-12-01</p> <p>Earth's mantle possesses distinct and variable volatile characteristics as sampled by magmatic activity in different tectonic environments. In general, trace element depleted mid-ocean ridge basalts, with low Sr and Pb isotope values (but high ?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 <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) is superimposed upon two massive plateaux - the Ethiopia and Kenya domes - regarded as geophysical manifestations of a superplume source, a huge thermochemical anomaly originated at the core-mantle boundary and providing dynamic support for the plateaux. We present new volatile isotopic and relative abundance data (on the same samples) for geothermal fluids (He-CO2-N2), lavas (He-Ne-Ar) and xenoliths (He-Ne-Ar-CO2-N2) which provide an unprecedented overview of the distribution of mantle volatiles of the Ethiopia Dome, from the Red Sea via the Afar region and Main Ethiopian <span class="hlt">Rift</span> (MER) to the Turkana Depression. Notably, peaks in geothermal fluid 3He/4He (16RA) and ?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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1612168L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1612168L"><span id="translatedtitle">Stable isotope-based Plio-Pleistocene ecosystem reconstruction of some of the earliest hominid fossil sites in the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (Chiwondo Beds, N Malawi)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lüdecke, Tina; Thiemeyer, Heinrich; Schrenk, Friedemann; Mulch, Andreas</p> <p>2014-05-01</p> <p>The isotope geochemistry of pedogenic carbonate and fossil herbivore enamel is a powerful tool to reconstruct paleoenvironmental conditions in particular when climate change plays a key role in the evolution of ecosystems. Here, we present the first Plio-Pleistocene long-term carbon (δ13C), oxygen (δ18O) and clumped isotope (Δ47) records from pedogenic carbonate and herbivore teeth in the Malawi <span class="hlt">Rift</span>. These data represent an important southern hemisphere record in the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS), a key region for reconstructing vegetation patterns in today's Zambezian Savanna and correlation with data on the evolution and migration of early hominids across the Inter-Tropical Convergence Zone. As our study site is situated between the well-known hominid-bearing sites of eastern and southern Africa in the Somali-Masai Endemic Zone and Highveld Grassland it fills an important geographical gap for early hominid research. 5.0 to 0.6 Ma fluviatile and lacustrine deposits of the Chiwondo Beds (NE shore of Lake Malawi) comprise abundant pedogenic carbonate and remains of a diverse fauna dominated by large terrestrial mammals. These sediments are also home to two hominid fossil remains, a mandible of Homo rudolfensis and a maxillary fragment of Paranthropus boisei, both dated around 2.4 Ma. The Chiwondo Beds therefore document early co-existence of these two species. We evaluate δ13C data from fossil enamel of different suid, bovid, and equid species and contrast these with δ13C and δ18O values of pedogenic carbonate. We complement the latter with clumped isotope soil temperature data. Results of almost 800 pedogenic carbonate samples from over 20 sections consistently average δ13C = -8.5 ‰ over the past 5 Ma with no significant short-term δ13C excursions or long-term trends. The data from molar tooth enamel of nine individual suids of the genera Metridiochoerus, Notochoerus and Nyanzachoerus support these findings with average δ13C = -10.0 ‰. The absence of long-term trends towards more positive δ13C 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010GGG....11.3003D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010GGG....11.3003D"><span id="translatedtitle">The Eagle and East Eagle sulfide ore-bearing mafic-ultramafic intrusions in the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span>, upper Michigan: Geochronology and petrologic evolution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ding, Xin; Li, Chusi; Ripley, Edward M.; Rossell, Dean; Kamo, Sandra</p> <p>2010-03-01</p> <p>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 <span class="hlt">Rift</span> <span class="hlt">System</span> (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 <span class="hlt">rift</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70034427','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70034427"><span id="translatedtitle">Low lower crustal velocity across Ethiopia: Is the Main Ethiopian <span class="hlt">Rift</span> a narrow <span class="hlt">rift</span> in a hot craton?</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Keranen, K.M.; Klemperer, S.L.; Julia, J.; Lawrence, J. F.; Nyblade, A.A.</p> <p>2009-01-01</p> <p>[1] The Main Ethiopian <span class="hlt">Rift</span> (MER) is a classic narrow <span class="hlt">rift</span> that developed in hot, weak lithosphere, not in the initially cold, thick, and strong lithosphere that would be predicted by common models of <span class="hlt">rift</span> mode formation. Our new 1-D seismic velocity profiles from Rayleigh wave/receiver function joint inversion across the MER and the Ethiopian Plateau indicate that hot lower crust and upper mantle are present throughout the broad region affected by Oligocene flood basalt volcanism, including both the present <span class="hlt">rift</span> and the adjacent Ethiopian Plateau hundreds of kilometers from the <span class="hlt">rift</span> valley. The region of hot lithosphere closely corresponds to the region of flood basalt volcanism, and we interpret that the volcanism and thermal perturbation were jointly caused by impingement of the Afar plume head. Across the affected region, Vs is 3.6-3.8 km/s in the lowermost crust and ???4.3 km/s in the uppermost mantle, both ??0.3 km/s lower than in the eastern and western branches of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> to the south. We interpret the low Vs in the lower crust and upper mantle as indicative of hot lithosphere with partial melt. Our results lead to a hybrid <span class="hlt">rift</span> mode, in which the brittle upper crust has developed as a narrow <span class="hlt">rift</span> along the Neoproterozoic suture between East and West Gondwana, while at depth lithospheric deformation is distributed over the broad region (??400 km wide) thermally perturbed by the broad thermal upwelling associated with the Afar plume head. Development of both the East African <span class="hlt">Rift</span> <span class="hlt">System</span> to the south (in cold, strong lithosphere) and the MER to the north (in hot, weak lithosphere) as narrow <span class="hlt">rifts</span>, despite their vastly different initial thermal states and depth-integrated lithospheric strength, indicates that common models of <span class="hlt">rift</span> mode formation that focus only on temperature, thickness, and vertical strength profiles do not apply to these classic continental <span class="hlt">rifts</span>. Instead, inherited structure and associated lithospheric weaknesses are the primary control on the mode of extension. ?? 2009 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V13E2076E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V13E2076E"><span id="translatedtitle">Geochemistry of 24 Ma Basalts from Northeast Egypt: Implications for Small-Scale Convection Beneath the East African <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Endress, C. A.; Furman, T.; Ali Abu El-Rus, M.</p> <p>2009-12-01</p> <p>Basalts ~24 Ma in the Cairo-Suez and Fayyum districts of NE Egypt represent the youngest and northernmost lavas potentially associated with the initiation of <span class="hlt">rifting</span> of the Red Sea. The age of these basalts corresponds to a time period of significant regional magmatism that occurred subsequent to emplacement of 30 Ma flood basalts attributed to the Afar Plume in Ethiopia and Yemen. Beginning ~28 Ma, widespread magmatism occurred across supra-equatorial Africa in Hoggar (Algeria), Tibesti (Chad), Darfur (Sudan), Turkana (Kenya) and Samalat, Bahariya, Quesir and the Sinai Peninsula (Egypt) (e.g. Allegre et al., 1981; Meneisy, 1990; Baldridge et al., 1991; Wilson and Guiraud, 1992; Furman et al., 2006; Lucassen et al., 2008). Available geochemical and isotopic data indicate that Hoggar and Darfur basalts are similar to Turkana lavas, although no direct link between the N African lavas and the Kenya Plume has been made. New geochemical data on the NE Egyptian basalts provide insight into the thermochemical, isotopic, and mineralogical characteristics of the mantle beneath the region in which they were emplaced. The basalts are subalkaline with OIB-like incompatible trace element abundances and homogeneous major element, trace element and isotopic geochemistry. They display relatively flat ITE patterns, with notable positive Pb and negative P anomalies. Isotopic (143Nd/144Nd = 0.51274-0.51285, 87Sr/86Sr = 0.7049-0.7050) and trace element signatures (Ce/Pb = 16-22, Ba/Nb = 9-14, and La/Nb = 0.9-1.0) are consistent with melting of a sub-lithospheric source that has been slightly contaminated by continental crust during ascent and emplacement. The Pb isotopic ratios (206Pb/204Pb = 18.53-18.62, 207Pb/204Pb = 15.59-15.64, and 208Pb/204Pb = 38.80-39.00) in the Egyptian basalts are close to the range of those found in the 30 Ma Ethiopian flood basalts, which are distinct from the more highly radiogenic, high-? type signature seen in basalts from Turkana, Darfur, and Hoggar. However, measured 207Pb/204Pb and 87Sr/86Sr values are higher than those observed in the Ethiopian flood basalts (Pik et al., 1999) and suites from the Red Sea and Gulf of Aden (Schilling et al., 1992; Volker and McCulloch, 1993; Volker et al., 1997), consistent with trace element evidence of crustal contamination. We aim to develop a broad framework for understanding tectono-magmatic activity throughout northern Africa since the Miocene. The NE Egyptian basalts show evidence of both lithospheric and sublithospheric contributions and represent a time period that is critical to ongoing debate surrounding the relationship between shallow magmatism, crustal extension, and deep mantle processes exemplified by the features within and beneath the African Plate. A plausible model for the widespread volcanism during the early Miocene is that each local magmatic event was related to small scale convection rising above a plume or plumes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3542179','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3542179"><span id="translatedtitle">Common Host-Derived Chemicals Increase Catches of Disease-Transmitting Mosquitoes and Can Improve Early Warning <span class="hlt">Systems</span> for <span class="hlt">Rift</span> Valley Fever Virus</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Tchouassi, David P.; Sang, Rosemary; Sole, Catherine L.; Bastos, Armanda D. S.; Teal, Peter E. A.; Borgemeister, Christian; Torto, Baldwyn</p> <p>2013-01-01</p> <p><span class="hlt">Rift</span> Valley fever (RVF), a mosquito-borne zoonosis, is a major public health and veterinary problem in sub-Saharan Africa. Surveillance to monitor mosquito populations during the inter-epidemic period (IEP) and viral activity in these vectors is critical to informing public health decisions for early warning and control of the disease. Using a combination of field bioassays, electrophysiological and chemical analyses we demonstrated that skin-derived aldehydes (heptanal, octanal, nonanal, decanal) common to RVF virus (RVFV) hosts including sheep, cow, donkey, goat and human serve as potent attractants for RVFV mosquito vectors. Furthermore, a blend formulated from the four aldehydes and combined with CO2-baited CDC trap without a light bulb doubled to tripled trap captures compared to control traps baited with CO2 alone. Our results reveal that (a) because of the commonality of the host chemical signature required for attraction, the host-vector interaction appears to favor the mosquito vector allowing it to find and opportunistically feed on a wide range of mammalian hosts of the disease, and (b) the sensitivity, specificity and superiority of this trapping <span class="hlt">system</span> offers the potential for its wider use in surveillance programs for RVFV mosquito vectors especially during the IEP. PMID:23326620</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70024528','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70024528"><span id="translatedtitle">Crustal structure of central Lake Baikal: Insights into intracontinental <span class="hlt">rifting</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>ten Brink, U.S.; Taylor, M.H.</p> <p>2002-01-01</p> <p>The Cenozoic <span class="hlt">rift</span> <span class="hlt">system</span> of Baikal, located in the interior of the largest continental mass on Earth, is thought to represent a potential analog of the early stage of breakup of supercontinents. We present a detailed P wave velocity structure of the crust and sediments beneath the Central Basin, the deepest basin in the Baikal <span class="hlt">rift</span> <span class="hlt">system</span>. The structure is characterized by a Moho depth of 39-42.5 km; an 8-km-thick, laterally continuous high-velocity (7.05-7.4 km/s) lower crust, normal upper mantle velocity (8 km/s), a sedimentary section reaching maximum depths of 9 km, and a gradual increase of sediment velocity with depth. We interpret the high-velocity lower crust to be part of the Siberian Platform that was not thinned or altered significantly during <span class="hlt">rifting</span>. In comparison to published results from the Siberian Platform, Moho under the basin is elevated by <3 km. On the basis of these results we propose that the basin was formed by upper crustal extension, possibly reactivating structures in an ancient fold-and-thrust belt. The extent and location of upper mantle extension are not revealed by our data, and it may be offset from the <span class="hlt">rift</span>. We believe that the Baikal <span class="hlt">rift</span> structure is similar in many respects to the Mesozoic Atlantic <span class="hlt">rift</span> <span class="hlt">system</span>, the precursor to the formation of the North Atlantic Ocean. We also propose that the Central Baikal <span class="hlt">rift</span> evolved by episodic fault propagation and basin enlargement, rather than by two-stage <span class="hlt">rift</span> evolution as is commonly assumed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/24066364','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/24066364"><span id="translatedtitle">Unique device identification <span class="hlt">system</span>. <span class="hlt">Final</span> rule.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p></p> <p>2013-09-24</p> <p>The Food and Drug Administration (FDA) is issuing a <span class="hlt">final</span> rule to establish a <span class="hlt">system</span> 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 <span class="hlt">system</span> 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</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/6919502','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6919502"><span id="translatedtitle">Jade data transcription <span class="hlt">system</span> <span class="hlt">final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Eaton, R.; Iskra, M.; McLean, J. . Advanced Technology Div.)</p> <p>1990-07-25</p> <p>The OWL sensor, which is used in conjunction with the Jade program, generates a tremendous volume of data during normal field operations. Historically, the dissemination of this data to analysts has been slowed by difficulties in transcribing to a widely readable media and format. TRW, under contract from Lawrence Livermore National Laboratory, was tasked by Defense Advanced Research Projects Agency (DARPA) with finding an improved method of transcribing the Jade experimental data. During the period of performance on this contract TRW helped to guide the development and operation of an improved transcription <span class="hlt">system</span>. This <span class="hlt">final</span> report summarizes the work performed, and provides a written record of information which may be helpful to future users of the newly developed data transcription <span class="hlt">system</span>. 4 figs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.4428B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.4428B"><span id="translatedtitle">Next-generation Geotectonic Data Analysis: Using pyGPlates to quantify <span class="hlt">Rift</span> Obliquity during Supercontinent Dispersal</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Butterworth, Nathaniel; Brune, Sascha; Williams, Simon; Müller, Dietmar</p> <p>2015-04-01</p> <p>Fragmentation of a supercontinent by <span class="hlt">rifting</span> is an integral part of plate tectonics, yet the dynamics that govern the success or failure of individual <span class="hlt">rift</span> <span class="hlt">systems</span> are still unclear. Recently, analytical and thermo-mechanical modelling has suggested that obliquely activated <span class="hlt">rifts</span> are mechanically favoured over orthogonal <span class="hlt">rift</span> <span class="hlt">systems</span>. Hence, where two <span class="hlt">rift</span> zones compete, the more oblique <span class="hlt">rift</span> proceeds to break-up while the less oblique one stalls and becomes an aulacogen. This implies that the orientation and shape of individual <span class="hlt">rift</span> <span class="hlt">systems</span> affects the relative motion of Earth's continents during supercontinent break-up. We test this hypothesis using the latest global plate tectonic reconstructions for the past 200 million years. The analysis is performed using pyGPlates, a recently developed Python library that allows script-based access to the plate reconstruction software GPlates. We quantify <span class="hlt">rift</span> obliquity, extension velocity and their temporal evolution for all small-scale <span class="hlt">rift</span> segments that constituted a major <span class="hlt">rift</span> <span class="hlt">system</span> during the last 200 million years. Boundaries between continental and oceanic crust (COBs) mark the end of <span class="hlt">rifting</span> and the beginning of sea floor spreading, which is why we use a global set of updated COBs in order to pinpoint continental break-up and as a proxy for the local trend of former <span class="hlt">rift</span> <span class="hlt">systems</span>. Analysing the entire length of all <span class="hlt">rift</span> <span class="hlt">systems</span> during the last 200 My, we find a mean obliquity of ~40° (measured as the angle between extension direction and local <span class="hlt">rift</span> trend normal), with a standard deviation of 25°. More than 75% of all <span class="hlt">rift</span> segments exceeded an obliquity of 20° highlighting the fact that oblique <span class="hlt">rifting</span> is the rule, not the exception. More specifically, East and West Gondwana split along the East African coast with a mean obliquity of 45°. While <span class="hlt">rifting</span> of the central and southern South Atlantic segment involved a low obliquity of 10°, the Equatorial Atlantic opened under a high angle of 60°. The separation of 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 <span class="hlt">rift</span> evolution (e.g. South Atlantic, India-Antarctica, Australia-Antarctica, Gulf of California), suggesting an underlying geodynamic correlation. Considering that most conceptual models of <span class="hlt">rift</span> evolution assume 2D deformation, we here quantify the degree to which 2D <span class="hlt">rift</span> models are globally applicable, and highlight the importance of 3D models where oblique <span class="hlt">rifting</span> is the dominant mode of deformation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140000469','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140000469"><span id="translatedtitle"><span class="hlt">Final</span> Report - Regulatory Considerations for Adaptive <span class="hlt">Systems</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wilkinson, Chris; Lynch, Jonathan; Bharadwaj, Raj</p> <p>2013-01-01</p> <p>This report documents the findings of a preliminary research study into new approaches to the software design assurance of adaptive <span class="hlt">systems</span>. 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 <span class="hlt">systems</span> is principally one of developing correct and complete high level requirements and <span class="hlt">system</span> level constraints that define the necessary <span class="hlt">system</span> functional and safety properties to assure the safe use of adaptive <span class="hlt">systems</span>. 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. <span class="hlt">Finally</span> the report identifies the follow-on research topics needed to implement this methodology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/26601442','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/26601442"><span id="translatedtitle"><span class="hlt">Rift</span> Valley fever.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Paweska, J T</p> <p>2015-08-01</p> <p><span class="hlt">Rift</span> Valley fever (RVF) is a mosquito-borne zoonotic viral disease affecting domestic and wild ruminants, camels and humans. The causative agent of RVF, the RVF virus (RVFV), has the capacity to cause large and severe outbreaks in animal and human populations and to cross significant natural geographic barriers. <span class="hlt">Rift</span> Valley fever is usually inapparent in non-pregnant adult animals, but pregnant animals and newborns can be severely affected; outbreaks are characterised by a sudden onset of abortions and high neonatal mortality. The majority of human infections are subclinical or associated with moderate to severe, non-fatal, febrile illness, but some patients may develop a haemorrhagic syndrome and/or ocular and neurological lesions. In both animals and humans, the primary site of RVFV replication and tissue pathology is the liver. Outbreaks of RVF are associated with persistent high rainfalls leading to massive flooding and the emergence of large numbers of competent mosquito vectors that transmit the virus to a wide range of susceptible vertebrate species. Outbreaks of RVF have devastating economic effects on countries for which animal trade constitutes the main source of national revenue. The propensity of the virus to spread into new territories and re-emerge in traditionally endemic regions, where it causes large outbreaks in human and animal populations, presents a formidable challenge for public and veterinary health authorities. The presence of competent mosquito vectors in RVF-free countries, the wide range of mammals susceptible to the virus, altering land use, the global changes in climate, and increased animal trade and travel are some of the factors which might contribute to international spread of RVF. PMID:26601442</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70044480','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70044480"><span id="translatedtitle">A model for Iapetan <span class="hlt">rifting</span> of Laurentia based on Neoproterozoic dikes and related rocks</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Burton, William C.; Southworth, Scott</p> <p>2010-01-01</p> <p>Geologic evidence of the Neoproterozoic <span class="hlt">rifting</span> of Laurentia during breakup of Rodinia is recorded in basement massifs of the cratonic margin by dike swarms, volcanic and plutonic rocks, and <span class="hlt">rift</span>-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 <span class="hlt">rifting</span>. The most salient features include: (1) a <span class="hlt">rift</span>-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 <span class="hlt">rift</span>-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 <span class="hlt">rifting</span> mechanisms to explain these features include <span class="hlt">rift</span>-transform and plume–triple-junction <span class="hlt">systems</span>. The <span class="hlt">rift</span>-transform <span class="hlt">system</span> best explains features 1, 2, and 3, listed here, and we propose that it represents the dominant <span class="hlt">rifting</span> 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 <span class="hlt">system</span> evolved into the <span class="hlt">rift</span>-transform <span class="hlt">system</span>. 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 <span class="hlt">rift</span>-transform <span class="hlt">system</span>. An eastern branch of this <span class="hlt">system</span> 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 <span class="hlt">rift</span>-related magmatism of Newfoundland.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014SolED...6.2885D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014SolED...6.2885D"><span id="translatedtitle">Fault evolution in the Potiguar <span class="hlt">rift</span> termination, Equatorial margin of Brazil</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>de Castro, D. L.; Bezerra, F. H. R.</p> <p>2014-10-01</p> <p>The transform shearing between South American and 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 <span class="hlt">rift</span>, which is an aborted NE-trending <span class="hlt">rift</span> arm developed during the breakup of Pangea. The Potiguar <span class="hlt">rift</span> is a Neocomian structure located in the intersection of the Equatorial and western South Atlantic and is composed of a series of NE-trending horsts and grabens. This study reveals new grabens in the Potiguar <span class="hlt">rift</span> and indicates that stretching in the southern <span class="hlt">rift</span> termination created a WNW-trending, 10 km wide and ~40 km long right-lateral strike-slip fault zone. This zone encompasses at least eight depocenters, which are bounded by a left-stepping, en-echelon <span class="hlt">system</span> of NW- to EW-striking normal faults. These depocenters form grabens up to 1200 m deep with a rhomb-shaped geometry, which are filled with <span class="hlt">rift</span> sedimentary units and capped by post-<span class="hlt">rift</span> sedimentary sequences. The evolution of the <span class="hlt">rift</span> termination is consistent with the right-lateral shearing of the Equatorial margin in the Cretaceous and occurs not only at the <span class="hlt">rift</span> termination, but also as isolated structures away from the main <span class="hlt">rift</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5349259','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5349259"><span id="translatedtitle"><span class="hlt">Final</span> design development of silicone southwall glazing <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Vanwert, B.; Currin, C.; Mingenbach, W.</p> <p>1983-11-01</p> <p>This cooperative solar project was undertaken to design, fabricate and test a southwall glazing <span class="hlt">system</span> 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 <span class="hlt">systems</span>: 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 <span class="hlt">system</span> using a selective adsorber on a vented concrete block wall provided over 750 MJ/m/sup 2/ of thermal energy during a winter heating <span class="hlt">system</span>. One experiment demonstrated the performance and ease of installation of the tensioning device developed by this project. Preliminary cost estimates indicate the southwall glazing <span class="hlt">system</span> 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 <span class="hlt">system</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T23F..01R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T23F..01R"><span id="translatedtitle">Geochemical evidence of mantle reservoir evolution during progressive <span class="hlt">rifting</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rooney, T. O.; Mohr, P.; Dosso, L.; Hall, C. M.</p> <p>2010-12-01</p> <p>The Afar region in East Africa, which represents the triple junction of three well-exposed Cenozoic <span class="hlt">rift</span> <span class="hlt">systems</span>, is a pivotal domain in the study of <span class="hlt">rift</span> evolution. The western margin of Afar, defined by a wide transitional region from plateau to <span class="hlt">rift</span> floor, developed in response to the <span class="hlt">rifting</span> of the Red Sea commencing shortly after the eruption of the ~31-29 Ma Ethiopian-Yemen flood basalts. The Oligocene lava sequence which covers this <span class="hlt">rift</span> margin was fed from intensive diking. The dikes and the block-faulting and monoclinal warping that followed provide an opportunity to probe the geochemical reservoirs preserved in the magmatic record and the development of the <span class="hlt">rifting</span> processes. Argon geochronology reveals that dikes along the western Afar margin span the entire history of <span class="hlt">rift</span> evolution from the initial Oligocene flood basalt event to the development of focused zones of intrusion in <span class="hlt">rift</span> marginal basins. Major and trace element, and isotopic results (Sr-Nd-Pb-Hf) from these dikes demonstrate temporal geochemical heterogeneity defined by variable contributions from the Afar plume, depleted mantle and African lithosphere, consistent with studies of Quaternary basalts from the Ethiopian <span class="hlt">Rift</span>. On a broader scale our results show that as the western Afar margin matures, the initially significant contribution from the Afar plume wanes in favor of shallow asthenospheric and lithospheric reservoirs. The early dikes, which are coincident with the initial weakening of the lithosphere in a magma-assisted <span class="hlt">rifting</span> model, geochemically resemble the widespread plume-derived flood basalts and shields that constitute the Ethiopian Plateau. Subsequent diking is characterized by a lesser role for the Afar plume and greater contributions from the African lithosphere and depleted mantle. During the terminal stage of dike emplacement, where focused magmatic intrusion accommodated extension, a more significant fraction is derived from the depleted mantle and less of a lithospheric signature is evident. For the terminal stages of the evolution of the western Afar <span class="hlt">rift</span> margin, our observations confirm a model where magma-generation processes become dominated by shallow decompression melting of the ambient asthenosphere during the continent-to-ocean transition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1711846S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1711846S"><span id="translatedtitle">Contribution of the FUTUREVOLC project to the study of segmented lateral dyke growth in the 2014 <span class="hlt">rifting</span> event at Bárðarbunga volcanic <span class="hlt">system</span>, Iceland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S.; Ófeigsson, Benedikt; Rafn Heimisson, Elías; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Guðmundsson, Gunnar B.; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T.; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert S.; Ágústsdóttir, Thorbjörg; Björnsson, Helgi; Bean, Christopher J.</p> <p>2015-04-01</p> <p>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 <span class="hlt">system</span> and strategy, (ii) develop new methods for near real-time integration of multi-parametric datasets, (iii) apply a seamless transdisciplinary approach to further scientific understanding of magmatic processes, and (iv) to improve delivery, quality and timeliness of transdisciplinary information from monitoring scientists to civil protection. 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 <span class="hlt">system</span>, 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 <span class="hlt">rifting</span> 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 <span class="hlt">system</span>, grew laterally for over 45 km at a variable rate, with an influence of topography on the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning <span class="hlt">System</span> (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bárðarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with a magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of M>5 earthquakes. 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 <span class="hlt">rifting</span> event and eruptions have thus contributed to the achievements of all the objectives of the FUTUREVOLC project.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012P%26SS...68...56K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012P%26SS...68...56K"><span id="translatedtitle">Relationship of coronae, regional plains and <span class="hlt">rift</span> zones on Venus</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Krassilnikov, A. S.; Kostama, V.-P.; Aittola, M.; Guseva, E. N.; Cherkashina, O. S.</p> <p>2012-08-01</p> <p>Coronae and <span class="hlt">rifts</span> 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 <span class="hlt">rift</span> structures and time relationship of <span class="hlt">rift</span> zones activity with time of regional volcanic plains emplacement, and (2) tectonics, volcanism, age relative to regional plains and relationship with <span class="hlt">rifts</span>. Two different age groups of <span class="hlt">rifts</span> on Venus were mapped at the scale 1:50 000 000: old <span class="hlt">rifts</span> that predate and young <span class="hlt">rifts</span> that postdate regional plains. Most of young <span class="hlt">rifts</span> inherit strikes of old <span class="hlt">rifts</span> and old <span class="hlt">rifts</span> are reworked by them. This may be evidence of <span class="hlt">rift</span>-produced uplift zones that were probably mostly stable during both types of <span class="hlt">rifts</span> formation. Evolution of distribution of <span class="hlt">rift</span> <span class="hlt">systems</span> with time (decreasing of distribution and localization of <span class="hlt">rift</span> zones) imply thickening of the lithosphere with time. Coronae-producing mantle diapirism and uplift of mantle material in <span class="hlt">rift</span> 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 <span class="hlt">rifts</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140006387','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140006387"><span id="translatedtitle">Multi-Point Combustion <span class="hlt">System</span>: <span class="hlt">Final</span> Report</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Goeke, Jerry; Pack, Spencer; Zink, Gregory; Ryon, Jason</p> <p>2014-01-01</p> <p>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 <span class="hlt">final</span> report for the NASA contract. This work included the design, analysis, and test of a multi-point combustion <span class="hlt">system</span>. 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 <span class="hlt">system</span> 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 <span class="hlt">systems</span> 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. <span class="hlt">Finally</span>, the operability of the array and associated nozzles proved to be very stable without requiring additional active or passive control <span class="hlt">systems</span>. A number of publications have been publish</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5862861','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5862861"><span id="translatedtitle">Sedimentary deposits in response to <span class="hlt">rift</span> geometry in Malawi, Africa</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bishop, M.G. )</p> <p>1991-03-01</p> <p>Sedimentary deposits of the Malawi continental <span class="hlt">rift</span> basin are a direct result of topography and tectonics unique to <span class="hlt">rift</span> structure. Recent models describe <span class="hlt">rifts</span> 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 <span class="hlt">rift</span> becomes a local baselevel and depocenter as regional drainage is shed away by the <span class="hlt">rift</span> 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 <span class="hlt">systems</span>, 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 <span class="hlt">rift</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1614917C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1614917C"><span id="translatedtitle">The continent-ocean transition of the <span class="hlt">rifted</span> South China continental margin</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cameselle, Alejandra L.; Ranero, César R.; Franke, Dieter; Barckhausen, Udo</p> <p>2014-05-01</p> <p>The continent to ocean transition (COT) architecture of <span class="hlt">rifted</span> margins represents a key aspect in the study of the variability of different <span class="hlt">rifting</span> <span class="hlt">systems</span> and thus, to understand lithospheric extension and <span class="hlt">final</span> 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-<span class="hlt">rift</span> 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. <span class="hlt">Rifting</span> in the NW subbasin resulted in asymmetric conjugate margins. Arrays of tilted fault blocks covered by abundant syn-<span class="hlt">rift</span> 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 <span class="hlt">final</span> 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 <span class="hlt">rifting</span>, 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 <span class="hlt">final</span> structure of the northwest South China continental margin have been governed by the 3D interaction between <span class="hlt">rifting</span> and oceanic spreading center propagation to a degree larger than by the local lithospheric structure during <span class="hlt">rifting</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=198831','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=198831"><span id="translatedtitle"><span class="hlt">RIFT</span> VALLEY FEVER: PREPARING FOR POTENTIAL NEW MOSQUITO-BORNE DISEASES IN THE U.S. WITH A VECTOR SURVEILLANCE <span class="hlt">SYSTEM</span></span></a></p> <p><a target="_blank" href="http://www.ars.usda.gov/services/TekTran.htm">Technology Transfer Automated Retrieval System (TEKTRAN)</a></p> <p></p> <p></p> <p>In this symposium we have discussed four diseases that are emerging threats in the U.S., and it may be concluded that in our best defense knowing the vector is as important as knowing the disease. <span class="hlt">Rift</span> Valley fever, Dengue, and JEE are but a few of the many emerging diseases that we can prepare for...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=203219','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=203219"><span id="translatedtitle">An automated GIS/remotely sensed early warning <span class="hlt">system</span> to detect elevated populations of vectors of <span class="hlt">Rift</span> Valley fever, a mosquito-borne emerging virus threat</span></a></p> <p><a target="_blank" href="http://www.ars.usda.gov/services/TekTran.htm">Technology Transfer Automated Retrieval System (TEKTRAN)</a></p> <p></p> <p></p> <p>Mosquito transmitted infectious diseases, like eastern equine encephalitis (EEE), <span class="hlt">Rift</span> 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 ...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=209882','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=209882"><span id="translatedtitle">A <span class="hlt">Rift</span> Valley Fever Risk Surveillance <span class="hlt">System</span> in Africa Using Remotely Sensed Data in a GIS: Potential for Use on Other Continents</span></a></p> <p><a target="_blank" href="http://www.ars.usda.gov/services/TekTran.htm">Technology Transfer Automated Retrieval System (TEKTRAN)</a></p> <p></p> <p></p> <p><span class="hlt">Rift</span> Valley fever (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...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=289622','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=289622"><span id="translatedtitle">Common host-derived chemicals increase catches of disease-transmitting mosquitoes and can improve early warning <span class="hlt">systems</span> for <span class="hlt">rift</span> valley fever virus</span></a></p> <p><a target="_blank" href="http://www.ars.usda.gov/services/TekTran.htm">Technology Transfer Automated Retrieval System (TEKTRAN)</a></p> <p></p> <p></p> <p><span class="hlt">Rift</span> Valley fever (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...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFMPP43B1255E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFMPP43B1255E"><span id="translatedtitle">Sedimentary DNA from East African <span class="hlt">Rift</span> Lakes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Epp, L. S.; Trauth, M. H.; Tiedemann, R.</p> <p>2007-12-01</p> <p>Ancient DNA research, especially that of environmental samples, has to date focused mainly on samples obtained from colder regions. We are characterizing present-day and historical planktonic communities in Kenyan <span class="hlt">Rift</span> Lakes with the use of molecular genetic methods, focussing on rotifer and diatom assemblages. Within the eastern branch of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> there are a series of shallow lakes in close proximity, yet with strikingly different hydrological and geological features. Between 15 and 5 kyrs ago the <span class="hlt">rift</span> comprised several large lakes that were fresh and several 100's of meters deep. Tectonically separated, these lakes underwent a tremendously different development in the course of a trend towards a drier climate since 6,000 years ago. Today the lakes range in alkalinity from pH 11 (Lake Elmenteita) to pH 8 (Lake Naivasha) and in depth from less than a meter to 15 meters. Within this setting we are analyzing recent samples as well as samples obtained from sediment cores. Apart from presenting molecular tools to assess the presence and dominance of taxa meaningful for ecological reconstruction, we are also attempting to trace the population structure and history of single species in the course of severe environmental change.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.9156M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.9156M"><span id="translatedtitle">Structural and stratigraphic evolution of the Iberia and Newfoundland hyper-extended <span class="hlt">rifted</span> margins: A quantitative modeling approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mohn, Geoffroy; Karner, Garry; Manatschal, Gianreto; Johnson, Christopher</p> <p>2014-05-01</p> <p><span class="hlt">Rifted</span> margins develop through polyphased extensional events leading eventually to break-up. Of particular interests are the stratigraphic and subsidence evolutions of these polyphased <span class="hlt">rift</span> events. In this contribution, we investigate the spatial and temporal evolution of the Iberia-Newfoundland <span class="hlt">rift</span> <span class="hlt">system</span> from the Permian, post-orogenic development of European crust to early Cretaceous break-up on the continental lithosphere between Iberia and Newfoundland. Based on seismic reflection and refraction and ODP drill data combined with a kinematic and flexural model for the deformation of the lithosphere, we explore the general tectono-stratigraphic evolution of Iberia-Newfoundland <span class="hlt">rift</span> <span class="hlt">system</span> and its relationship to repeated lithospheric thinning events. Our results emphasize the kinematic and isostatic interactions engendered by the distinct distribution, amplitude and depth-partitioning of extensional events that allowed the formation of the Iberia-Newfoundland <span class="hlt">rift</span> <span class="hlt">system</span>. The initial stratigraphic record is controlled by Permian, post-orogenic topographic erosion, lithospheric thinning, and its subsequent thermal re-equilibration that lead to a regional subsidence characterized by non-marine to marine sedimentation. During late Triassic and early Jurassic time, extensional deformation was characterized by broadly-distributed depth uniform thinning related to minor thinning of the crust. From the Late Jurassic onward, extensional deformation was progressively localized and associated with depth-dependent thinning that <span class="hlt">finally</span> lead to the formation of hyper-extended domains pre-dating the Late Aptian/Early Albian break-up of the Iberia-Newfoundland continental lithosphere. In particular, extension was diachronous, propagating in severity from south to north - while the southern Iberian margin was undergoing significant thinning in the Tithonian-early Berriasian, the northern margin (i.e., Galicia Bank) had yet to start <span class="hlt">rifting</span>. Break-up is likewise diachronous. These hyper-extended domains were characterized by regional subsidence with little attendant normal faulting. To match the distribution and the magnitude of the subsidence, we required significant depth-dependent middle/lower crustal and mantle thinning achieved via major decoupling horizons within the ductile middle crust. We believe that these results may provide crucial insights into the subsidence history of hyper-extended <span class="hlt">rifted</span> margins as well as on the mechanisms of continental lithosphere extension and thinning.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GGG....16.2949C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GGG....16.2949C"><span id="translatedtitle">Multiple mantle upwellings in the transition zone beneath the northern East-African <span class="hlt">Rift</span> <span class="hlt">system</span> from relative P-wave travel-time tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p>2015-09-01</p> <p>Mantle plumes and consequent plate extension have been invoked as the likely cause of East African <span class="hlt">Rift</span> 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 <span class="hlt">rift</span>. We present a new P-wave travel-time tomography model below the northern East-African, Red Sea, and Gulf of Aden <span class="hlt">rifts</span> 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 <span class="hlt">Rift</span>, a region with off-<span class="hlt">rift</span> 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.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007JGRB..112.5406D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007JGRB..112.5406D"><span id="translatedtitle">Crustal structure and magmato-tectonic processes in an active <span class="hlt">rift</span> (Asal-Ghoubbet, Afar, East Africa): 2. Insights from the 23-year recording of seismicity since the last <span class="hlt">rifting</span> event</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Doubre, C.; Manighetti, I.; Dorbath, L.; Dorbath, C.; Bertil, D.; Delmond, J. C.</p> <p>2007-05-01</p> <p>The Asal-Ghoubbet (AG) <span class="hlt">Rift</span> has sustained a major volcano-tectonic <span class="hlt">rifting</span> episode in 1978 and has been subsequently monitored with continuous geodetic and seismological surveys. It is therefore an ideal place to study the transient magmato-tectonic processes that operate after a <span class="hlt">rifting</span> episode. We examine the space-time evolution of ˜2500 Md ? 2.8 earthquakes recorded in the <span class="hlt">rift</span> from 1979 to 2001. We focus on the relationships between this seismic activity and both the three-dimensional structure of the <span class="hlt">rift</span> and its postrifting behavior depicted from geodesy. The results highlight the major role of the central magmatic <span class="hlt">system</span> (Fieale-Shark Bay) on the structure, seismic activity, and overall behavior of the <span class="hlt">rift</span>. From 1978 to 1986, the <span class="hlt">rift</span> opens at a fast rate, yet mainly aseismically; the opening is magmatically driven and accommodated. Since 1986, when the opening rate abruptly decreased, the seismicity is concentrated in the central part of the <span class="hlt">rift</span> and reveals pulses of activity of the central volcanic <span class="hlt">system</span>. These pulses result from that magmatic zone undergoing alternating stretching and inflating episodes. Thus, while the plate-driven induced stresses have been rebuilding in the <span class="hlt">rift</span> since 1987, the <span class="hlt">rift</span> opening is still essentially accommodated in the axial magmatic zone. The AG <span class="hlt">Rift</span> has thus sustained a postrifting unsteady opening over more than 23 years following its stretching episode. That transient opening has essentially occurred aseismically, and most tectonic faults remain relaxed and locked.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008SedG..210..132R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008SedG..210..132R"><span id="translatedtitle">Depositional model and stratigraphic architecture of <span class="hlt">rift</span> climax Gilbert-type fan deltas (Gulf of Corinth, Greece)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rohais, Sébastien; Eschard, Rémi; Guillocheau, François</p> <p>2008-10-01</p> <p>Facies, depositional model and stratigraphic architecture of Pleistocene giant Gilbert-type fan deltas are presented, based on outcrop data from the Derveni-Akrata region along the southern coast of the Gulf of Corinth, Greece. The common tripartite consisting of topset, foreset and bottomset [Gilbert, G.K., 1885. The topographic features of lake shores: Washington, D.C., United States Geol. Survey, 5th Annual Report, 69-123.] has been identified, as well as the most distal environment consisting of turbidites, and is organised in a repetitive pattern of four main <span class="hlt">systems</span> tracts showing a clear facies and volumetric partitioning. The first <span class="hlt">systems</span> tract (ST1) is characterised by the lack of topset beds and the development of a by-pass surface instead, thick foresets and bottomset beds, and thick well-developed turbiditic <span class="hlt">systems</span>. This <span class="hlt">systems</span> tract (ST1) is organised in an overall progradational pattern. The second <span class="hlt">systems</span> tract (ST2) is characterised by a thin topset and almost no foreset equivalent. This <span class="hlt">systems</span> tract is not always well-preserved and is organised in an overall retrograding trend with a landward shift in the position of the offlap break. The offshore is characterised by massive sandy turbidites. The third <span class="hlt">systems</span> tract (ST3) is characterised by small-scale deltas prograding above the staked topsets of the giant Gilbert-type fan delta. Those small Gilbert-type fan deltas are generally organised in a pure progradation evolving to an aggradational-progradational pattern. In the distal setting of those small Gilbert-type fan deltas, almost no deposits are preserved on the remaining topography of the previous Gilbert-type fan delta. The fourth <span class="hlt">systems</span> tract (ST4) is characterised by continuous vertically aggrading topsets that laterally pass into aggrading and prograding foresets. Bottomsets and distal turbiditic <span class="hlt">systems</span> are starved. This fourth <span class="hlt">systems</span> tract (ST4) is organised in an overall aggrading trend. These giant Gilbert-type fan deltas correspond to the Middle Group of the Corinth <span class="hlt">Rift</span> infill and their stratigraphic development was strongly influenced by evolving <span class="hlt">rift</span> structure. They record the migration of the depocenter from the <span class="hlt">rift</span> shoulder to the <span class="hlt">rift</span> axis in four main sequences from ca. 1.5 to 0.7 Ma, related to the migration of fault activity. It is worth noting that the maximum paleobathymetry was recorded during the <span class="hlt">final</span> stage of the progradation of the Middle Group, suggesting that the <span class="hlt">rift</span> climax was diachronous at the scale of the entire basin. The rapid (< 1 Ma) structural and sedimentological evolution, the migration of fault activity as well as the youth of the Corinth <span class="hlt">Rift</span>, are probably exceptional factors allowing the characterisation of such diachronism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1987Tectp.133..257W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1987Tectp.133..257W"><span id="translatedtitle">The Fenwei <span class="hlt">rift</span> and its recent periodic activity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Jing-Ming</p> <p>1987-02-01</p> <p>The Fenwei <span class="hlt">rift</span> on the southern sector of the Jin—Shaan <span class="hlt">rift</span> <span class="hlt">system</span> of China is marked by a crescent-shaped valley 600 km in length and 30-90 km in width depressed up to 10 km and filled with about 7000 m of Cenozoic deposits, bounded on both northern and southern sides by majestic mountain ranges. The geometry of the <span class="hlt">rift</span> valley is characterized by six branch depressions and five intervening swells extending east-northeastward in a dextral en-echelon pattern and bounded on both sides by abrupt topographic slopes reflecting the underlying faults. These are typically a <span class="hlt">system</span> of growth faults having downthrows ranging from 800 m to 10 km and dipping toward the centre of the valley forming an asymmetric graben structure. The geometry, kinematics and evolution of these faults have had controlling influences on the neotectonic movement of the <span class="hlt">rift</span> and its recent periodic activity as the present overall form of the <span class="hlt">rift</span> valley. Estimates of the amount of extension across the <span class="hlt">rift</span> for various recent geological periods were obtained from calculations made on the fault separation of corresponding stratigraphie horizons. The total amount of extension in response to tensile stresses, acting in a direction varying from 25° NW on the west to 70° NW on the northeast is estimated to be 9065 m, since the beginning of the <span class="hlt">rift</span> formation in the Eocene whereas the rate of extension in the Recent is 4.5 mm/yr and in modern times it is 8-24 mm/yr. The amount of left-lateral displacement across the <span class="hlt">rift</span> during various stages of its development was also calculated from the observed effects of strike-slip movement on the drainage <span class="hlt">system</span>. The left-lateral offset since the mid-Pleistocene is approximately 7170 m and the offset rate in modern times is 6 mm/yr. These estimates suggest that the Fenwei <span class="hlt">rift</span> has been a place of intense neotectonic activity. Details of more recent activity of the <span class="hlt">rift</span> were investigated in terms of the various <span class="hlt">rift</span>-related phenomena such as seismic events, ground fissuring, epeirogenic movement, shifting of streams or lakes and climatic changes which have occurred in the historic period. Seven highly periodic cycles of seismicity are recognized from available historic records of the earthquakes that have occurred in the <span class="hlt">rift</span> region during the last 4000 yrs. Each cycle appears to begin with a period of intense seismicity consisting of a series of violent shocks chiefly of M6-8 and lasting approximately 200 yrs, and then passes on to a prolonged period of quiescence of about 600 yrs during which only minor seismic events occur. The 22 events of ground-fissuring recorded in the historic annals are also concentrated in several distinctive periods of intense activity which coincide with seven corresponding periods of active seismicity, suggesting that seismic events and ground fissures resulted from the same cause, both being indications of periodic tectonic activity of the <span class="hlt">rift</span>. Moreover, periodic and coincident with periods of tectonic activity are the occurrences of the natural phenomena related to <span class="hlt">rifting</span> such as the appearance and disappearance of lakes, the shifting of streams and changes of river water from clear to turbid.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1986E%26PSL..77..176M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1986E%26PSL..77..176M"><span id="translatedtitle">The geometry of propagating <span class="hlt">rifts</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McKenzie, Dan</p> <p>1986-03-01</p> <p>The kinematics of two different processes are investigated, both of which have been described as <span class="hlt">rift</span> propagation. Courtillot uses this term to describe the change from distributed to localised extension which occurs during the early development of an ocean basin. The term localisation is instead used here to describe this process, to distinguish it from Hey's type of propagation. Localisation generally leads to rotation of the direction of magnetisation. To Hey propagation means the extension of a <span class="hlt">rift</span> into the undeformed plate beyond a transform fault. Detail surveys of the Galapagos <span class="hlt">rift</span> have shown that the propagating and failing <span class="hlt">rifts</span> are not connected by a single transform fault, but by a zone which is undergoing shear. The principal deformation is simple shear, and the kinematics of this deformation are investigated in some detail. The strike of most of the lineations observed in the area can be produced by such deformation. The mode of extension on the propagating <span class="hlt">rift</span> appears to be localised for some periods but to be distributed for others. Neither simple kinematic arguments nor stretching of the lithosphere with conservation of crust can account for the observed variations in water depth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012Tecto..31.2009G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012Tecto..31.2009G"><span id="translatedtitle">Low-temperature evolution of the Morondava <span class="hlt">rift</span> basin shoulder in western Madagascar: An apatite fission track study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Giese, JöRg; Seward, Diane; Schreurs, Guido</p> <p>2012-04-01</p> <p>The evolution of the <span class="hlt">rift</span> shoulder and the sedimentary sequence of the Morondava basin in western Madagascar was mainly influenced by a Permo-Triassic continental failed <span class="hlt">rift</span> (Karroo <span class="hlt">rift</span>), 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">final</span> 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 <span class="hlt">systems</span> in the Indian Ocean.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70134359','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70134359"><span id="translatedtitle"><span class="hlt">Rift</span> flank segmentation, basin initiation and propagation: a neotectonic example from Lake Baikal</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Agar, S.M.; Klitgord, Kim D.</p> <p>1995-01-01</p> <p>New surficial data (field, Landsat TM and topography) define morpho-tectonic domains and <span class="hlt">rift</span> flank segmentation in the Ol'khon region of the Central Baikal <span class="hlt">rift</span>. Deformation, drainage and depositional patterns indicate a change in the locus of active extension that may relate to a recent (<l Ma) change in the kinematics of the Siberian plate boundary. The westwards migration of the border fault location has broadened the <span class="hlt">rift</span> 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-<span class="hlt">rift</span> deposits. Morphology, sediment thicknesses and fault scarp amplitude indicate that a segmented <span class="hlt">rift</span> flank graben has propagated southwards along the <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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-<span class="hlt">rift</span> depositional <span class="hlt">systems</span> of the Ol'khon region provide a valuable analogue for the early evolution of continental margins and the structural controls on syn-<span class="hlt">rift</span> hydrocarbon sources and reservoirs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/799225','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/799225"><span id="translatedtitle">Field Studies of Geothermal Reservoirs Rio Grande <span class="hlt">Rift</span>, New Mexico</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>James C Witcher</p> <p>2002-07-30</p> <p>The Rio Grande <span class="hlt">rift</span> provides an excellent field laboratory to study the nature of geothermal <span class="hlt">systems</span> in an extensional environment. Much of the geologic complexity that is found in the Basin and Range is absent because the <span class="hlt">rift</span> 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 <span class="hlt">rift</span> has many parallels with the Basin and Range to the west. The geology of the southern Rio Grande <span class="hlt">rift</span> is among the best characterized of any <span class="hlt">rift</span> <span class="hlt">system</span> 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 <span class="hlt">systems</span> at Rincon and San Diego Mountain.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010IJEaS..99.1633K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010IJEaS..99.1633K"><span id="translatedtitle">Active transsection faults in <span class="hlt">rift</span> transfer zones: evidence for complex stress fields and implications for crustal fragmentation processes in the western branch of the East African <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koehn, D.; Lindenfeld, M.; Rümpker, G.; Aanyu, K.; Haines, S.; Passchier, C. W.; Sachau, T.</p> <p>2010-10-01</p> <p>New structural and seismologic evidence from the Rwenzori Mountains, Uganda, indicate that continental <span class="hlt">rifts</span> can capture and rotate fragments of the lithosphere while <span class="hlt">rift</span> segments interact, in a manner analogous to the interaction of small-scale fractures. The Rwenzori Mountains are a basement block within the western branch of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> that is located at the intersection of two <span class="hlt">rift</span> segments and is apparently rotating clockwise. Structural data and new seismological data from earthquake epicentres indicate a large-scale, 20-km-long transsection fault is currently detaching the Rwenzori micro-plate on its northern margin from the larger Victoria plate (Tanzania craton), whereas it is already fully detached in the south. We propose that this fault develops due to the rotation of the Rwenzori block. In a numerical model we show how <span class="hlt">rift</span> segment interaction, block rotation and the development of transsection faults (faults that cut through the Rwenzori Mountains) evolve through time. The model suggests that uplift of the Rwenzori block can only take place after the <span class="hlt">rift</span> has opened significantly, and rotation leads to the development of transsection faults that connect two <span class="hlt">rift</span> segments, so that the block is captured within the <span class="hlt">rifts</span>. Our numerical model suggests that the majority of the uplift has taken place within the last 8 Ma.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T51H..06F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T51H..06F"><span id="translatedtitle">The MOZART Project - MOZAmbique <span class="hlt">Rift</span> Tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fonseca, J. F.; Chamussa, J. R.; Domingues, A.; Helffrich, G. R.; Fishwick, S.; Ferreira, A. M.; Custodio, S.; Brisbourne, A. M.; Grobbelaar, M.</p> <p>2012-12-01</p> <p>Project MOZART (MOZAmbique <span class="hlt">Rift</span> Tomography) is an ongoing joint effort of Portuguese, Mozambican and British research groups to investigate the geological structure and current tectonic activity of the southernmost tip of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) through the deployment of a network of 30 broad band seismic stations in Central and Southern Mozambique. In contrast with other stretches of the EARS to the North and with the Kapvaal craton to the West and South, the lithosphere of Mozambique was not previously studied with a dense seismographic deployment on account of past political instability, and many questions remain unanswered with respect to the location and characteristics of the EARS to the south of Tanzania. In recent years, space geodesy revealed the existence of three microplates in and off Mozambique - Victoria, Rovuma, Lwandle - whose borders provide a connection of the EARS to the South West Indian Ridge as required by plate tectonics. However, the picture is still coarse concerning the location of the <span class="hlt">rift</span> structures. The 2006 M7 Machaze earthquake in Central Mozambique highlighted the current tectonic activity of the region and added a further clue to the location of the continental <span class="hlt">rift</span>, prompting the MOZART deployment. Besides helping unravel the current tectonics, the project is expected to shed light on the poorly known Mesoproterozoic structure described by Arthur Holmes in 1951 as the Mozambique Belt, and on the mechanisms of transition from stable craton to <span class="hlt">rifted</span> continental crust, through the development of a tomographic model for the lithosphere. The MOZART network is distributed South of the Zambezi river at average inter-station spaces of the order of 100 km and includes four stations across the border in South Africa. Data exchange was agreed with AfricaArray. The deployment proceeded in two phases in March 2011, and November and December 2011. Decommissioning is foreseen for August 2013. We report preliminary results for this 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994Tecto..13..623F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994Tecto..13..623F"><span id="translatedtitle">Tertiary arc <span class="hlt">rifting</span> in northern Luzon, Philippines</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Florendo, Federico F.</p> <p>1994-06-01</p> <p>The North Luzon terrane (NLT), comprising the section of Luzon north of the Philippine Fault, is one of the largest arc terranes in the Philippine Archipelago. Numerous features suggest that the NLT is a late Oligocene to early Miocene analogue for the processes in the modern intra-arc <span class="hlt">rift</span> zone at the northern end of the Mariana Trough. First, the NLT has bifurcating magmatic arcs sharing similar magmatic histories. These include the Northern Sierra Madre (NSM) and Cordillera Central (CC) magmatic arcs, which are separated by the Cagayan basin but which are linked in the Caraballo Range to the south. The rock record indicates that the NSM, CC, and Caraballo Ranges were active arcs in late Eocene to late Oligocene time. Second, seismic reflection and well data indicate that the Cagayan basin formed by extensional faulting in late Oligocene to early Miocene time. Third, alkalic arc magmatism, recognized to be a precursor of intra-arc <span class="hlt">rifting</span> in modern settings, occurred at the juncture of the NSM and CC arcs in late Oligocene to early Miocene time. Fourth, oceanic crust, represented by the Itogon ophiolite, formed at the southwestern end of the Cagayan basin in late Oligocene to early Miocene time. Major and trace element chemistry show that the Itogon sheeted dikes have tholeiitic arc and backarc basin basalt affinities. The rock record and geophysical offshore data suggest that the NLT was developing in an island arc <span class="hlt">system</span> above the subducting West Philippine plate in late Eocene time. <span class="hlt">Rifting</span> occurred in the island arc from late Oligocene to early Miocene time but did not mature into backarc spreading, most likely because of the collision of the Benham Rise, a basaltic rise in the West Philippine basin, with the NLT. The arc <span class="hlt">rifting</span> in the NLT may be another manifestation of the extensional tectonism that affected most of Southeast Asia in late Oligocene to early Miocene time, during which the South China and Southeast Sulu basins formed. Subsequent to arc <span class="hlt">rifting</span>, the history of the NLT has been linked to the subduction of the South China plate along the Manila Trench. The structural history of the Cagayan basin and magmatic history of the southern CC suggest that the subduction in the Manila Trench at the latitude of the NLT began about 15 Ma.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5465920','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5465920"><span id="translatedtitle">Thermal maturation and organic richness of potential petroleum source rocks in Proterozoic Rice Formation, North American Mid-Continent <span class="hlt">rift</span> <span class="hlt">system</span>, northeastern Kansas</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Newell, K.D. ); Burruss, R.C.; Palacas, J.G. )</p> <p>1993-11-01</p> <p>A recent well in northeastern Kansas penetrated 296 ft (90.2 m) of dark gray siltstone in the Precambrian Mid-Continent <span class="hlt">rift</span> (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 <span class="hlt">rift</span>, and that parts of the <span class="hlt">rift</span> 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 <span class="hlt">rifting</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70020868','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70020868"><span id="translatedtitle">Comparative sequence stratigraphy of low-latitude versus high-latitude lacustrine <span class="hlt">rift</span> basins: Seismic data examples from the East African and Baikal <span class="hlt">rifts</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Scholz, C.A.; Moore, T.C., Jr.; Hutchinson, D.R.; Golmshtok, A. Ja; Klitgord, Kim D.; Kurotchkin, A.G.</p> <p>1998-01-01</p> <p>Lakes Baikal, Malawi and Tanganyika are the world's three largest <span class="hlt">rift</span> valley lakes and are the classic modem examples of lacustrine <span class="hlt">rift</span> basins. All the <span class="hlt">rift</span> lakes are segmented into half-graben basins, and seismic reflection datasets reveal how this segmentation controls the filling of the <span class="hlt">rift</span> basins through time. In the early stages of <span class="hlt">rifting</span>, basins are fed primarily by flexural margin and axial margin drainage <span class="hlt">systems</span>. At the climax of syn-<span class="hlt">rift</span> sedimentation, however, when the basins are deeply subsided, almost all the margins are walled off by <span class="hlt">rift</span> shoulder uplifts, and sediment flux into the basins is concentrated at accommodation zone and axial margin river deltas. Flexural margin unconformities are commonplace in the tropical lakes but less so in high-latitude Lake Baikal. Lake levels are extremely dynamic in the tropical lakes and in low-latitude <span class="hlt">systems</span> in general because of the predominance of evaporation in the hydrologic cycle in those <span class="hlt">systems</span>. Evaporation is minimized in relation to inflow in the high-latitude Lake Baikal and in most high-latitude <span class="hlt">systems</span>, and consequently, major sequence boundaries tend to be tectonically controlled in that type of <span class="hlt">system</span>. The acoustic stratigraphies of the tropical lakes are dominated by high-frequency and high-amplitude lake level shifts, whereas in high-latitude Lake Baikal, stratigraphic cycles are dominated by tectonism and sediment-supply variations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JVGR..239...49D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JVGR..239...49D"><span id="translatedtitle">Hypogene and supergene alteration of the zeolite-bearing pyroclastic deposits at Tell Rimah, Jordan, and <span class="hlt">rift</span>-related processes along the Dead-Sea-Transform Fault <span class="hlt">System</span> during the Quaternary</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dill, H. G.; Techmer, A.; Botz, R.; Dohrmann, R.; Kaufhold, S.</p> <p>2012-09-01</p> <p>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 <span class="hlt">System</span> (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 <span class="hlt">rift</span> basin of the DSTFS. The lake-level lowstand caused the fluid <span class="hlt">system</span> in the pyroclastic cone to become self-sufficient and it has been considered as a closed hydrothermal <span class="hlt">system</span>. (2) Periods of tectonic and magmatic quiescence grinded the detrital sedimentation in the <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">system</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> basin along the DSTFS. The results obtained by current tectono-morphological studies of the <span class="hlt">rift</span>-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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/114028','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/114028"><span id="translatedtitle">LANL environmental restoration site ranking <span class="hlt">system</span>: <span class="hlt">System</span> description. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Merkhofer, L.; Kann, A.; Voth, M.</p> <p>1992-10-13</p> <p>The basic structure of the LANL Environmental Restoration (ER) Site Ranking <span class="hlt">System</span> and its use are described in this document. A related document, Instructions for Generating Inputs for the LANL ER Site Ranking <span class="hlt">System</span>, contains detailed descriptions of the methods by which necessary inputs for the <span class="hlt">system</span> will be generated. LANL has long recognized the need to provide a consistent basis for comparing the risks and other adverse consequences associated with the various waste problems at the Lab. The LANL ER Site Ranking <span class="hlt">System</span> is being developed to help address this need. The specific purpose of the <span class="hlt">system</span> is to help improve, defend, and explain prioritization decisions at the Potential Release Site (PRS) and Operable Unit (OU) level. The precise relationship of the Site Ranking <span class="hlt">System</span> to the planning and overall budget processes is yet to be determined, as the <span class="hlt">system</span> is still evolving. Generally speaking, the Site Ranking <span class="hlt">System</span> will be used as a decision aid. That is, the <span class="hlt">system</span> will be used to aid in the planning and budgetary decision-making process. It will never be used alone to make decisions. Like all models, the <span class="hlt">system</span> can provide only a partial and approximate accounting of the factors important to budget and planning decisions. Decision makers at LANL will have to consider factors outside of the formal <span class="hlt">system</span> when making <span class="hlt">final</span> choices. Some of these other factors are regulatory requirements, DOE policy, and public concern. The main value of the site ranking <span class="hlt">system</span>, therefore, is not the precise numbers it generates, but rather the general insights it provides.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007QSRv...26.1771H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007QSRv...26.1771H"><span id="translatedtitle">Anatomy of a river drainage reversal in the Neogene Kivu Nile <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Holzförster, F.; Schmidt, U.</p> <p>2007-07-01</p> <p>The Neogene geological history of East Africa is characterised by the doming and extension in the course of development of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> with its eastern and western branches. In the centre of the Western <span class="hlt">Rift</span> Rise Rwanda is situated on Proterozoic basement rocks exposed in the strongly uplifted eastern <span class="hlt">rift</span> shoulder of the Kivu-Nile <span class="hlt">Rift</span> segment, where clastic sedimentation is largely restricted to the <span class="hlt">rift</span> axis itself. A small, volcanically and tectonically controlled depository in northwestern Rwanda preserved the only Neogene sediments known from the extremely uplifted <span class="hlt">rift</span> shoulder. Those (?)Pliocene to Pleistocene/Holocene fluvio-lacustrine muds and sands of the Palaeo-Nyabarongo River record the influence of Virunga volcanism on the major drainage reversal that affected East Africa in the Plio-/Pleistocene, when the originally <span class="hlt">rift</span>-parallel upper Nile drainage <span class="hlt">system</span> became diverted to the East in order to enter the Nile <span class="hlt">system</span> via Lake Victoria. Sedimentary facies development, heavy mineral distributions and palaeobiological controls, including hominid artefacts, signal a short time interval of <300-350 ka to complete this major event for the sediment supply <span class="hlt">system</span> of the Kivu-Nile <span class="hlt">Rift</span> segment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.V11H..04N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V11H..04N"><span id="translatedtitle">Minerals as mantle fingerprints: Sr-Nd-Pb-Hf in clinopyroxene and He in olivine distinguish an unusual ancient mantle lithosphere beneath the East African <span class="hlt">Rift</span> <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nelson, W. R.; Shirey, S. B.; Graham, D. W.</p> <p>2011-12-01</p> <p>The East African <span class="hlt">Rift</span> <span class="hlt">System</span> 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; ɛNd = 12.6-18.5; ɛHf = 13.8-27.6) - more depleted than the MORB source - rather than to the OIB-like 30 Ma flood basalts (87Sr/86Sr ~ 0.704; ɛNd = 4.7-6.7; ɛHf = 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70074654','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70074654"><span id="translatedtitle">Seismicity within a propagating ice shelf <span class="hlt">rift</span>: the relationship between icequake locations and ice shelf structure</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Heeszel, David S.; Fricker, Helen A.; Bassis, Jeremy N.; O'Neel, Shad; Walter, Fabian</p> <p>2014-01-01</p> <p>Iceberg calving is a dominant mass loss mechanism for Antarctic ice shelves, second only to basal melting. An important known process involved in calving is the initiation and propagation of through-penetrating fractures called <span class="hlt">rifts</span>; however, the mechanisms controlling <span class="hlt">rift</span> propagation remain poorly understood. To investigate the mechanics of ice-shelf <span class="hlt">rifting</span>, we analyzed seismicity associated with a propagating <span class="hlt">rift</span> tip on the Amery Ice Shelf, using data collected during the Austral summers of 2004-2007. We investigated seismicity associated with fracture propagation using a suite of passive seismological techniques including icequake locations, back projection, and moment tensor inversion. We confirm previous results that show that seismicity is characterized by periods of relative quiescence punctuated by swarms of intense seismicity of one to three hours. However, even during periods of quiescence, we find significant seismic deformation around the <span class="hlt">rift</span> tip. Moment tensors, calculated for a subset of the largest icequakes (MW?>?-2.0) located near the <span class="hlt">rift</span> tip, show steeply dipping fault planes, horizontal or shallowly plunging stress orientations, and often have a significant volumetric component. They also reveal that much of the observed seismicity is limited to the upper 50?m of the ice shelf. This suggests a complex <span class="hlt">system</span> of deformation that involves the propagating <span class="hlt">rift</span>, the region behind the <span class="hlt">rift</span> tip, and a <span class="hlt">system</span> of <span class="hlt">rift</span>-transverse crevasses. Small-scale variations in the mechanical structure of the ice shelf, especially <span class="hlt">rift</span>-transverse crevasses and accreted marine ice, play an important role in modulating the rate and location of seismicity associated with propagating ice shelf <span class="hlt">rifts</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19810056997&hterms=Continental+Drift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3D%2528Continental%2BDrift%2529','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19810056997&hterms=Continental+Drift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3D%2528Continental%2BDrift%2529"><span id="translatedtitle">Continental <span class="hlt">rifting</span> and the origin of Beta Regio, Venus</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mcgill, G. E.; Steenstrup, S. J.; Barton, C.; Ford, P. G.</p> <p>1981-01-01</p> <p>Topographic maps based on Pioneer Venus altimetry suggest that Beta Regio, an elevated feature centered at 27 deg N, 282 deg E, is analogous to domes associated with continental <span class="hlt">rift</span> <span class="hlt">systems</span> on earth. This interpretation is consistent with the commonly quoted analogy between the East African <span class="hlt">rift</span> <span class="hlt">system</span> and the topography of the region from Beta Regio southward to Phoebe Regio. If Beta Regio is a dome, major structural uplift of the crust of Venus is implied, suggesting a more dynamic upper mantle than would be the case if Beta Regio were simply a large volcanic construct.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/ED092141.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED092141.pdf"><span id="translatedtitle">Regional Information <span class="hlt">System</span>: Feasibility Report. <span class="hlt">Final</span> Report.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Lower Pioneer Valley Regional Planning Commission, West Springfield, MA.</p> <p></p> <p>A study was made of the feasibility of establishing a computerized regional information <span class="hlt">system</span>. Existing <span class="hlt">systems</span> were reviewed, and the location of the <span class="hlt">system</span> was discussed. The <span class="hlt">system</span>'s structure was described. A cost benefit analysis looked into capital costs and operating costs. A cooperative <span class="hlt">system</span> was found to be feasible, based on…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/22094700','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/22094700"><span id="translatedtitle">East Antarctic <span class="hlt">rifting</span> triggers uplift of the Gamburtsev Mountains.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ferraccioli, Fausto; Finn, Carol A; Jordan, Tom A; Bell, Robin E; Anderson, Lester M; Damaske, Detlef</p> <p>2011-11-17</p> <p>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 <span class="hlt">rift</span> <span class="hlt">system</span> 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) <span class="hlt">rifting</span>. Much like East Africa, the interior of East Antarctica is a mosaic of Precambrian provinces affected by <span class="hlt">rifting</span> processes. Our models show that the combination of <span class="hlt">rift</span>-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 <span class="hlt">rifting</span> and preserved orogenic roots can produce broad regions of high topography in continental interiors without significantly modifying the underlying Precambrian lithosphere. PMID:22094700</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/6887650','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6887650"><span id="translatedtitle">Episodic <span class="hlt">rifting</span> and subsidence in the South China sea</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ru, K.; Pigott, J.D.</p> <p>1986-09-01</p> <p>The South China Sea experienced at least three stages of <span class="hlt">rifting</span> and two intervening stages of sea-floor spreading since the Early Cretaceous. Its evolution can be described by an episodic model of tectonism, one of thermal cooling and subsidence, pulsed by temporally and spatially confined heating events. Analysis of regional geologic and geophysical data suggests episodes of <span class="hlt">rifting</span> and associated thermal activities initiated during the Late Cretaceous, the late Eocene, and the late early Miocene. The <span class="hlt">rift</span> <span class="hlt">system</span> corresponding to the first episode trends northeast-southwest, whereas those of the second and third trend east-west. These two trends coincide with the orientations of the major tectonic lineations within the basin. Age estimates from heat-flow and bathymetric data suggest the oceanic crust in the Southwest subbasin is considerably older (55 Ma) than that in the Northwest (35-36 Ma) or East (32 Ma) subbasins. In terms of hydrocarbon potential, the episodes of <span class="hlt">rifting</span> and drifting would be conducive to the development of overprinted structures and the deposition of several discrete transgressive packages of source rocks and reservoirs, separated by widespread unconformities. The thermal maturity of sedimentary organic matter affected by episodic <span class="hlt">rifting</span> and subsidence may be greater than expected on a purely passive margin of equivalent age that had not experienced repeated heating. 21 figures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/353209','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/353209"><span id="translatedtitle">Soil classifications <span class="hlt">systems</span> review. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p></p> <p>1997-11-01</p> <p><span class="hlt">Systems</span> used to classify soils are discussed and compared. Major types of classification <span class="hlt">systems</span> that are reviewed include natural <span class="hlt">systems</span>, technical <span class="hlt">systems</span>, the FAO/UNESCO world soil map, soil survey map units, and numerical taxonomy. Natural Classification <span class="hlt">systems</span> discussed in detail are the United States <span class="hlt">system</span>, Soil Taxonomy, and the Russian and Canadian <span class="hlt">systems</span>. Included in the section on technical classification <span class="hlt">systems</span> are reviews on the AASHO and Unified (ASTM) classification <span class="hlt">systems</span>. The review of soil classification <span class="hlt">systems</span> 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 <span class="hlt">systems</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/754794','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/754794"><span id="translatedtitle">Liquid waste treatment <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Baker, M.N.; Houston, H.M.</p> <p>1999-06-01</p> <p>Pretreatment of high-level liquid radioactive waste (HLW) at the West Valley Demonstration Project (WVDP) involved three distinct processing operations: decontamination of liquid HLW in the Supernatant Treatment <span class="hlt">System</span> (STS); volume reduction of decontaminated liquid in the Liquid Waste Treatment <span class="hlt">System</span> (LWTS); and encapsulation of resulting concentrates into an approved cement waste form in the Cement Solidification <span class="hlt">System</span> (CSS). Together, these <span class="hlt">systems</span> and operations made up the Integrated Radwaste Treatment <span class="hlt">System</span> (IRTS).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.5441M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.5441M"><span id="translatedtitle">Earthquake clusters in Corinth <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mesimeri, Maria; Papadimitriou, Eleftheria; Karakostas, Vasilios; Tsaklidis, George</p> <p>2013-04-01</p> <p>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 <span class="hlt">Rift</span>, 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 <span class="hlt">system</span> of the Hellenic Arc, SEISMO FEAR HELLARC".</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70017946','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70017946"><span id="translatedtitle">Thermal budget of the lower east <span class="hlt">rift</span> zone, Kilauea Volcano</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Delaney, Paul T.; Duffield, Wendell A.; Sass, John H.; Kauahikaua, James P.</p> <p>1993-01-01</p> <p>The lower east <span class="hlt">rift</span> zone of Kilauea has been the site of repeated fissure eruptions fed by dikes that traverse the depths of interest to geothermal explorations. We find that a hot-rock-and-magma <span class="hlt">system</span> of low permeability extending along the <span class="hlt">rift</span> zone at depths below about 4 km and replenished with magma at a rate that is small in comparison to the modern eruption rate Kilauea can supply heat to an overlying hydrothermal aquifer sufficient to maintain temperatures of about 250??C if the characteristic permeability to 4-km depth is about 10-15m2.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/ED506081.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED506081.pdf"><span id="translatedtitle"><span class="hlt">Final</span> Paper DAT Cognitive Art Therapy <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Jacobson, Eric</p> <p>2009-01-01</p> <p>Del Giacco Art Therapy is a cognitive art therapy process that focuses on stimulating the mental sensory <span class="hlt">systems</span> and working to stabilize the nervous <span class="hlt">system</span> and create new neural connections in the brain. This <span class="hlt">system</span> was created by Maureen Del Giacco, Phd. after recovering from her own traumatic brain injury and is based on extensive research of…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.5381C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.5381C"><span id="translatedtitle">Stress and slip partitioning during oblique <span class="hlt">rifting</span>: comparison between data from the Main Ethiopian <span class="hlt">Rift</span> and laboratory experiments</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Corti, G.; Philippon, M.; Sani, F.; Keir, D.</p> <p>2012-04-01</p> <p>Oblique <span class="hlt">rifting</span> in the central and northern Main Ethiopian <span class="hlt">Rift</span> (MER) has resulted in a complex structural pattern characterized by two differently oriented fault <span class="hlt">systems</span>: a set of NE-SW-trending boundary faults and a <span class="hlt">system</span> of roughly NNE-SSW-oriented fault swarms affecting the <span class="hlt">rift</span> floor (Wonji faults). Boundary faults formed oblique to the regional extension vector, likely as a result of the oblique reactivation of a pre-existing deep-seated rheological anisotropy, whereas internal Wonji faults developed sub-orthogonal to the stretching direction. Previous works have successfully reconciled this <span class="hlt">rift</span> architecture and fault distribution with the long-term plate kinematics; however, at a more local scale, fault-slip and earthquake data reveal significant variations in the orientation the minimum principal stress and related fault-slip direction across the <span class="hlt">rift</span> valley. Whereas fault measurements indicate a roughly N95°E extension on the axial Wonji faults, a N105°E to N110°E directed minimum principal stress is observed along boundary faults. Both fault-slip data and analysis of seismicity indicate a roughly pure dip-slip motion on the boundary faults, despite their orientation (oblique to the regional extension vector) should result in an oblique displacement. To shed light on the process driving the variability of data derived from fault-slip (and seismicity) analysis we present crustal-scale analogue models of oblique <span class="hlt">rifting</span>, deformed in a large-capacity centrifuge by using materials and boundary conditions described in several previous modeling works. As in these previous works, the experiments show the diachronous activation of two fault <span class="hlt">systems</span>, boundary and internal, whose pattern strikingly resemble that observed in previous lithospheric-scale modeling, as well as that described in the MER. Internal faults arrange in two different, en-echelon segments connected by a transfer zone where strike-slip displacement dominates. Whereas internal faults develop roughly orthogonal to the extension direction, boundary faults form oblique to the imposed stretching vector: as a group, the faults follow the <span class="hlt">rift</span> trend, controlled by a pre-existing weak anisotropy, but individually they form oblique to both the <span class="hlt">rift</span> margin and the extension vector. Detailed analysis of fault displacements suggest that whereas the average displacement on single internal faults is consistent with the imposed direction of extension, slip on boundary faults does not parallel this direction; the average motion on these faults is orthogonal to the faults, resulting in a roughly pure dip-slip motion. This gives rise to a marked difference in fault-slip direction between internal faults (where slip orientation follow the regional extension) and boundary faults (where displacement is oblique to the "regional" extension). A similar scenario is observed for the reconstructed direction of the minimum principal stress that follows the regional stress field within the <span class="hlt">rift</span> and is re-oriented at <span class="hlt">rift</span> margins. Minor counterclockwise block rotations accommodate the different slip along the different fault <span class="hlt">systems</span>. The model-to-nature striking is striking in terms of fault orientation, stress and slip orientation and its across-axis variations. The analogue models thus allows explaining the across-axis variability observed in natural fault-slip and earthquake data. Modeling results support that boundary faults form in response to a local stress re-orientation imposed by a deep seated anisotropy: their displacement trajectories deviate from those imposed by the regional extension, resulting in a pure dip-slip motion in an overall oblique <span class="hlt">rifting</span> kinematics, as observed in other sectors of the East African <span class="hlt">Rift</span>. Conversely, internal faults -which form later and affect a weaker, more uniform lithosphere- respond directly to the regional extension direction resulting in a fault slip sub-parallel to the Nubia-Somalia motion. Minor counterclockwise block rotations are required to accommodate the difference in slip along the different fault <span class="hlt">systems</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..1413687G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..1413687G"><span id="translatedtitle">Expected fluid residence times, thermal breakthrough, and tracer test design for characterizing a hydrothermal <span class="hlt">system</span> in the Upper Rhine <span class="hlt">Rift</span> Valley</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ghergut, I.; Meixner, J.; Rettenmaier, D.; Maier, F.; Nottebohm, M.; Ptak, T.; Sauter, M.</p> <p>2012-04-01</p> <p>Relying on the structural-hydrogeological model proposed by J. Meixner (2009) for a particular hydrothermal <span class="hlt">system</span> in South-West Germany (on the East side of the Upper Rhine <span class="hlt">Rift</span>, this reservoir being used to demonstrate electricity production by means of a well doublet), we set up a distributed-parameter model (using Feflow) enabling to numerically simulate fluid ages, temperature evolutions and tracer test signals for a number of contrasting assumptions w. r. to (a) the nature of boundary conditions and hydrogeological characteristics of remotely situated, large-scale natural faults, (b) the degree of permeability contrast between different <span class="hlt">system</span> compartments, (c) the hydrogeological characteristics of a naturally-occurring fault, located between injection and production wells. It appears that a spike dimensioning allowing for tracer signals to become detectable during the first three years after tracer injection in all of the contrasting a/b/c scenarios is not feasible in practice. In some of the a/b/c cases considered, the <span class="hlt">system</span> will act like a very large reservoir, with fluid residence times in the order of decades, and extreme dilution of injected tracers. Even using preparative-scale cleaning of samples, brine separation, sample enrichment by solid phase extraction, evaporative concentrating etc. followed by state-of-the-art chromatography techniques to separate between tracer and natural background, it will not be possible to lower tracer detection limits below a certain threshold, which is mainly dictated by the amount of certain naturally-occurring aromatics in the reservoir fluids. On practical reasons, the spike dimensioning will be limited to some hundred kilogram of one or two organic tracers. This implies that part of the above-mentioned, contrasting a/b/c scenarios will remain indistinguishable during the first three years after tracer injection. However, for this reservoir structure, there is not a bijective correspondence between early-vs.-late appearance of tracer and small-vs.-large reservoir. Therefore, we further examine the questions: How much information will be lost, and what degree of uncertainty will affect temperature predictions, as a consequence of the chosen practical ceiling on injected tracer quantities? Can single-well, dual-tracer push-pull tests (to be conducted at the geothermal re-injection and/or at the geothermal production well) contribute to reducing the ambiguity of inter-well early-signal inversion? Acknowledgement: This work pertains to a research project jointly funded by Energie Baden-Württemberg (EnBW) and by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU, project key: 0325111B), with operational support from local Energy and Water Supply Plants (EWB), from the Karlsruhe Institute of Technology (KIT, Hydrogeology Group), and from the European Institute for Energy Research (EIfER, Dr. Zorn).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/841361','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/841361"><span id="translatedtitle">Manzanita Hybrid Power <span class="hlt">system</span> Project <span class="hlt">Final</span> Report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Trisha Frank</p> <p>2005-03-31</p> <p>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 <span class="hlt">system</span> 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 <span class="hlt">system</span> was designed and the equipment supplied by Northern Power <span class="hlt">Systems</span>, Inc, an engineering company with expertise in renewable hybrid <span class="hlt">system</span> design and development. Personnel of the National Renewable Energy Laboratory provided technical assistance in <span class="hlt">system</span> design, and continued to provide technical assistance in <span class="hlt">system</span> monitoring. The grid-connected renewable hybrid wind/photovoltaic <span class="hlt">system</span> provides a demonstration of a solar/wind energy hybrid power-generating project on Manzanita Tribal land. During the <span class="hlt">system</span> 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 <span class="hlt">system</span> 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 <span class="hlt">system</span> design would provide highly reliable renewable power for community uses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/23823795','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/23823795"><span id="translatedtitle">Melting during late-stage <span class="hlt">rifting</span> in Afar is hot and deep.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ferguson, D J; Maclennan, J; Bastow, I D; Pyle, D M; Jones, S M; Keir, D; Blundy, J D; Plank, T; Yirgu, G</p> <p>2013-07-01</p> <p>Investigations of a variety of continental <span class="hlt">rifts</span> 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 <span class="hlt">rifts</span> 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 <span class="hlt">rifting</span> along the southern Red Sea <span class="hlt">rift</span> in Afar, a unique region of sub-aerial transition from continental to oceanic <span class="hlt">rifting</span>, 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 <span class="hlt">rift</span> <span class="hlt">system</span> approaching the point of plate rupture. Numerical modelling of <span class="hlt">rift</span> 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 <span class="hlt">rifting</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004EOSTr..85..273W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004EOSTr..85..273W"><span id="translatedtitle">Geoscience Methods Lead to Paleo-anthropological Discoveries in Afar <span class="hlt">Rift</span>, Ethiopia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>WoldeGabriel, Giday; Renne, Paul R.; Hart, William K.; Ambrose, Stanley; Asfaw, Berhane; White, Tim D.</p> <p>2004-07-01</p> <p>With few exceptions, most of the hominid evolutionary record in Africa is closely associated with the East African <span class="hlt">Rift</span> <span class="hlt">System</span>. 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 <span class="hlt">Rifts</span>. The <span class="hlt">rift</span> floor is wider-200 km-than other parts of the East African <span class="hlt">Rift</span> (Figure 1). Moreover, its Quaternary axial <span class="hlt">rift</span> 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 <span class="hlt">rift</span> floor and the adjacent <span class="hlt">rift</span> margins were intense and episodic during the late Neogene <span class="hlt">rift</span> evolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790017332','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790017332"><span id="translatedtitle">Solar heating <span class="hlt">system</span> <span class="hlt">final</span> design package</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1979-01-01</p> <p>The <span class="hlt">system</span> 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 <span class="hlt">system</span> and therefore provides a dual function in the structure. The collector serves both as a solar energy conversion <span class="hlt">system</span> and as a structural weather resistant skin. The control unit provides totally automatic control over the operation of the <span class="hlt">system</span>. 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 <span class="hlt">system</span> equipped with gear motor valves that respond to outputs from the control <span class="hlt">system</span>. The fan unit was designed for maximum durability and efficiency in operation, and has permanently lubricated ball bearings and excellent air-handling efficiency.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5788524','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5788524"><span id="translatedtitle">Concentrating solar collector <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mingo, R.D.</p> <p>1981-08-30</p> <p>A brief report on a solar heat-collecting <span class="hlt">system</span> 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 <span class="hlt">system</span> includes a single, large, homemade roof-mounted collector, two heat storage tanks, a moderately complex control unit, and circulating pumps. During operation the heating <span class="hlt">system</span> provided approximately 60% of the domestic hot water needs for a family of five. (BCS)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA....13902L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA....13902L"><span id="translatedtitle">Morphostructural evidence for Recent/active extension in Central Tanzania beyond the southern termination of the Kenya <span class="hlt">Rift</span>.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Le Gall, B.; Rolet, J.; Gernigon, L.; Ebinger, C.; Gloaguen, R.</p> <p>2003-04-01</p> <p>The southern tip zone of the Kenya <span class="hlt">Rift</span> on the eastern branch of the East African <span class="hlt">System</span> is usually thought to occur in the so-called North Tanzanian Divergence. In this region, the narrow (50 km-wide) axial graben of southern Kenya splays southwards, via a major EW-trending volcanic lineament, into a 200 km-wide broad <span class="hlt">rifted</span> zone with three separate arms of normal faulting and tilted fault blocks (Eyasi, Manyara and Pangani arms from W to E). Remote sensing analysis from Central Tanzania demonstrates that <span class="hlt">rift</span> morphology exists over an area lying 400 km beyond the southern termination of the Kenya <span class="hlt">Rift</span>. The most prominent <span class="hlt">rift</span> structures are observed in the Kilombero region and consist of a 100 km-wide range of uplifted basement blocks fringed to the west by an E-facing half-graben inferred to reach depths of 6-8 km from aeromagnetic dataset. Physiographic features (fault scarps), and river drainage anomalies suggest that the present-day <span class="hlt">rift</span> pattern in the Kilombero extensional province principally results from Recent/Neogene deformation. That assumption is also supported by the seismogenic character of a number of faults. The Kilombero half-graben is superimposed upon an earlier <span class="hlt">rift</span> <span class="hlt">system</span>, Karoo in age, which is totally overprinted and is only evidenced from its sedimentary infill. On the other hand, the nature and thickness of the inferred Neogene synrift section is still unknown. The Kilombero <span class="hlt">rifted</span> zone is assumed to connect northwards into the central <span class="hlt">rift</span> arm (Manyara) of the South Kenya <span class="hlt">Rift</span> via a seismically active transverse fault zone that follows ductile fabrics within the Mozambican crystalline basement. The proposed <span class="hlt">rift</span> model implies that incipient <span class="hlt">rifting</span> propagates hroughout the cold and strong crust/lithosphere of Central Tanzania along Proterozoic (N140=B0E) basement weakness zones and earlier Karoo (NS)<span class="hlt">rift</span> structures. A second belt of Recent-active linked fault/basins also extends further East from the Pangani <span class="hlt">rift</span> arm to the offshore Zanzibar-Kerimbas graben <span class="hlt">system</span>. The structural connection of the Kilombero <span class="hlt">rifted</span> zone with the Lake Malawi <span class="hlt">rift</span> further south is also envisaged and should imply the link of the eastern and western branchs of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> south of the Tanzanian craton.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=end+AND+life+AND+indicator&pg=5&id=ED229551','ERIC'); return false;" href="http://eric.ed.gov/?q=end+AND+life+AND+indicator&pg=5&id=ED229551"><span id="translatedtitle">Employability Skills <span class="hlt">System</span> Program. A <span class="hlt">Final</span> Report.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Bowers, Robert F.</p> <p></p> <p>The Employability Skills <span class="hlt">System</span> Program (ESSP) is an adult education program designed to combine academic skills with job-seeking and employability skills. The program efforts include coordinating services and creating linkages between existing delivery services within the Detroit Public School <span class="hlt">System</span> and private business and industry. In…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/ED272155.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED272155.pdf"><span id="translatedtitle">Instructional Support Software <span class="hlt">System</span>. <span class="hlt">Final</span> Report.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>McDonnell Douglas Astronautics Co. - East, St. Louis, MO.</p> <p></p> <p>This report describes the development of the Instructional Support <span class="hlt">System</span> (ISS), a large-scale, computer-based training <span class="hlt">system</span> that supports both computer-assisted instruction and computer-managed instruction. Written in the Ada programming language, the ISS software package is designed to be machine independent. It is also grouped into functional…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/663257','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/663257"><span id="translatedtitle">Proximity sensor <span class="hlt">system</span> development. CRADA <span class="hlt">final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Haley, D.C.; Pigoski, T.M.</p> <p>1998-01-01</p> <p>Lockheed Martin Energy Research Corporation (LMERC) and Merritt <span class="hlt">Systems</span>, Inc. (MSI) entered into a Cooperative Research and Development Agreement (CRADA) for the development and demonstration of a compact, modular proximity sensing <span class="hlt">system</span> suitable for application to a wide class of manipulator <span class="hlt">systems</span> 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 <span class="hlt">system</span> 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 <span class="hlt">system</span> which allows modular implementation and operation of the sensor <span class="hlt">system</span>. MSI is a commercial small business specializing in proximity sensing <span class="hlt">systems</span> based upon infrared and acoustic sensors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SolE....6..185D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SolE....6..185D"><span id="translatedtitle">Fault evolution in the Potiguar <span class="hlt">rift</span> termination, equatorial margin of Brazil</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>de Castro, D. L.; Bezerra, F. H. R.</p> <p>2015-02-01</p> <p>The transform shearing between South American and 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 <span class="hlt">systems</span> and to analyze the evolution of the eastern equatorial margin of Brazil. Our study area is the southern onshore termination of the Potiguar <span class="hlt">rift</span>, which is an aborted NE-trending <span class="hlt">rift</span> arm developed during the breakup of Pangea. The basin is located along the NNE margin of South America that faces the main transform zone that separates the North and the South Atlantic. The Potiguar <span class="hlt">rift</span> is a Neocomian structure located at the intersection of the equatorial and western South Atlantic and is composed of a series of NE-trending horsts and grabens. This study reveals new grabens in the Potiguar <span class="hlt">rift</span> and indicates that stretching in the southern <span class="hlt">rift</span> termination created a WNW-trending, 10 km wide, and ~ 40 km long right-lateral strike-slip fault zone. This zone encompasses at least eight depocenters, which are bounded by a left-stepping, en echelon <span class="hlt">system</span> of NW-SE- to NS-striking normal faults. These depocenters form grabens up to 1200 m deep with a rhomb-shaped geometry, which are filled with <span class="hlt">rift</span> sedimentary units and capped by postrift sedimentary sequences. The evolution of the <span class="hlt">rift</span> termination is consistent with the right-lateral shearing of the equatorial margin in the Cretaceous and occurs not only at the <span class="hlt">rift</span> termination but also as isolated structures away from the main <span class="hlt">rift</span>. This study indicates that the strike-slip shearing between two plates propagated to the interior of one of these plates, where faults with similar orientation, kinematics, geometry, and timing of the major transform are observed. These faults also influence <span class="hlt">rift</span> geometry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6763519','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6763519"><span id="translatedtitle">Water-storage-tube <span class="hlt">systems</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hemker, P.</p> <p>1981-12-24</p> <p>Passive solar collection/storage/distribution <span class="hlt">systems</span> 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)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatGe...9..145L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatGe...9..145L"><span id="translatedtitle">Massive and prolonged deep carbon emissions associated with continental <span class="hlt">rifting</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Hyunwoo; Muirhead, James D.; Fischer, Tobias P.; Ebinger, Cynthia J.; Kattenhorn, Simon A.; Sharp, Zachary D.; Kianji, Gladys</p> <p>2016-02-01</p> <p>Carbon from Earth’s interior is thought to be released to the atmosphere mostly via degassing of CO2 from active volcanoes. CO2 can also escape along faults away from active volcanic centres, but such tectonic degassing is poorly constrained. Here we use measurements of diffuse soil CO2, combined with carbon isotopic analyses to quantify the flux of CO2 through fault <span class="hlt">systems</span> away from active volcanoes in the East African <span class="hlt">Rift</span> <span class="hlt">system</span>. We find that about 4 Mt yr-1 of mantle-derived CO2 is released in the Magadi-Natron Basin, at the border between Kenya and Tanzania. Seismicity at depths of 15-30 km implies that extensional faults in this region may penetrate the lower crust. We therefore suggest that CO2 is transferred from upper-mantle or lower-crustal magma bodies along these deep faults. Extrapolation of our measurements to the entire Eastern <span class="hlt">rift</span> of the <span class="hlt">rift</span> <span class="hlt">system</span> implies a CO2 flux on the order of tens of megatonnes per year, comparable to emissions from the entire mid-ocean ridge <span class="hlt">system</span> of 53-97 Mt yr-1. We conclude that widespread continental <span class="hlt">rifting</span> and super-continent breakup could produce massive, long-term CO2 emissions and contribute to prolonged greenhouse conditions like those of the Cretaceous.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/972164','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/972164"><span id="translatedtitle">Analysis of Hybrid Hydrogen <span class="hlt">Systems</span>: <span class="hlt">Final</span> Report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dean, J.; Braun, R.; Munoz, D.; Penev, M.; Kinchin, C.</p> <p>2010-01-01</p> <p>Report on biomass pathways for hydrogen production and how they can be hybridized to support renewable electricity generation. Two hybrid <span class="hlt">systems</span> were studied in detail for process feasibility and economic performance. The best-performing <span class="hlt">system</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002Tectp.344..175R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002Tectp.344..175R"><span id="translatedtitle">Late Mesozoic and Cenozoic <span class="hlt">rifting</span> and its dynamic setting in Eastern China and adjacent areas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ren, Jianye; Tamaki, Kensaku; Li, Sitian; Junxia, Zhang</p> <p>2002-02-01</p> <p>During the Late Mesozoic and Cenozoic, extension was widespread in Eastern China and adjacent areas. The first <span class="hlt">rifting</span> 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 <span class="hlt">rifting</span> was characterized by intracontinental <span class="hlt">rifts</span>, 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 <span class="hlt">system</span> 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 <span class="hlt">rifting</span> stage produced widespread continental <span class="hlt">rift</span> <span class="hlt">systems</span> and continental margin basins in Eastern China. These <span class="hlt">rifted</span> 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 <span class="hlt">rifting</span> 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 <span class="hlt">rifting</span> of the Lake Baikal and Shanxi graben climaxed and spreading of the Japan Sea and South China Sea occurred. Quaternary <span class="hlt">rifting</span> was marked by basalt eruption and accelerated subsidence in the area of Tertiary <span class="hlt">rifting</span>. The Okinawa Trough is an active <span class="hlt">rift</span> involving back-arc extension. Continental <span class="hlt">rifting</span> and marginal sea opening were clearly developed in various kind of tectonic settings. Three <span class="hlt">rifting</span> styles, intracontinental <span class="hlt">rifting</span> within fold belt, intracontinental <span class="hlt">rifting</span> within craton and continental marginal <span class="hlt">rifting</span> and spreading, are distinguished on the basis of nature of the basin basement, tectonic location of <span class="hlt">rifting</span> 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 <span class="hlt">rifting</span>. Asthenospheric upwelling may have well assisted the <span class="hlt">rifting</span> process. In this paper, a combination model of interactions between plates and deep process of lithosphere has been proposed to explain the <span class="hlt">rifting</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/354842','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/354842"><span id="translatedtitle">Power <span class="hlt">system</span> disturbance prediction. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Nwankph, C.</p> <p>1998-12-01</p> <p>The application of distribution <span class="hlt">system</span> capacitor banks has been accepted as a necessary step in the design of distribution feeders. However, transient overvoltages are always a concern when capacitor switching is involved. In this report the authors address the problem of transients` characterization, distribution <span class="hlt">system</span> modeling, transient voltage prediction, and capacitor position identification. After detecting a transient, its frequency and damping factors are estimated using Prony`s method. To determine whether the transient would be damaging, Kalman filter prediction is employed to calculate the voltage N time steps ahead into the future. The transient frequency, damping factors, and instantaneous voltage are inputs to the prediction scheme. The output of the predictor (voltage N time steps ahead) is to be sent to the voltage regulating equipment allowing it to respond fast to distribution <span class="hlt">system</span> disturbances. The simulation indicated that Prony`s method is a suitable tool for identifying the transient frequency and damping factor for capacitor switching transients. Moreover, the authors have established and tested a novel Kalman filter model, that incorporates knowledge of the form of the signal to be predicted. The capacitor position is calculated from the transient frequency estimate. Approximations of the transient frequency which are computationally more efficient than the calculation from full analytical expression are obtained with perturbation methods. The authors propose an analytical solution for capacitor position determination. Although the solution is for a third-order <span class="hlt">system</span>, it can be extended to higher-order <span class="hlt">systems</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10141858','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10141858"><span id="translatedtitle">National Geoscience Data Repository <span class="hlt">System</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Schiffries, C.M.; Milling, M.E.</p> <p>1994-03-01</p> <p>The American Geological Institute (AGI) has completed the first phase of a study to assess the feasibility of establishing a National Geoscience Data Repository <span class="hlt">System</span> 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 <span class="hlt">System</span>. Second, it documents the data needs and priorities of potential users of the <span class="hlt">system</span>. A National Geoscience Data Repository <span class="hlt">System</span> 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 <span class="hlt">system</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1011381','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1011381"><span id="translatedtitle"><span class="hlt">Final</span> Report Advanced Quasioptical Launcher <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Jeffrey Neilson</p> <p>2010-04-30</p> <p>This program developed an analytical design tool for designing antenna and mirror <span class="hlt">systems</span> 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 <span class="hlt">systems</span>.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 <span class="hlt">systems</span> 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 <span class="hlt">systems</span>. The code includes a graphical user interface and is available for advanced design of launcher <span class="hlt">systems</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/6907904','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6907904"><span id="translatedtitle">California Smart Traveler <span class="hlt">System</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Behnke, R.W.</p> <p>1992-02-01</p> <p>The report describes how audiotex and videotex information <span class="hlt">systems</span> can be used to develop new modes of public transportation (e.g., parataxis or single-trip carpools) and how these new modes can be integrated with conventional transit, paratransit and ridesharing modes to reduce traffic congestion, gasoline consumption, air pollution and mobility problems at a low cost to taxpayers. This report also describes how these telephone-based information services can be used to develop low-cost, user-friendly Advanced Traveler Information <span class="hlt">Systems</span> (ATIS) that will tell drivers and riders the 'best' ways to get between any two points in an area via either private vehicle or public transportation. The proposed California Smart Traveler (CST) <span class="hlt">System</span> will enable travelers to obtain more timely and accurate information on which to base their local or regional travel decisions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5719436','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5719436"><span id="translatedtitle">New passive solar cooking <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Schlussler, L.</p> <p>1981-11-01</p> <p>The development of a solar cooking <span class="hlt">system</span> which uses a phase change process to passively transfer heat from a collector to a cooker is presented. In the design of this cooking <span class="hlt">system</span> steam is produced in the collector and then is used as the heat transfer fluid in the cooker. The most efficient use of the <span class="hlt">system</span> is to heat food directly by condensing the steam onto the food, whereas a heat exchanger is necessary to heat an oven or a frying pan. A pressure cooker was successfully built and tested using the steam from the collector. Brief discussions on the collector design and performance, and heat storage phase change materials are provided. (BCS)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/670070','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/670070"><span id="translatedtitle">[Develop mine communications <span class="hlt">system</span>]. <span class="hlt">Final</span> technical report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Meiksin, Z.H.</p> <p>1998-09-15</p> <p>The objective of this project was to develop, design, and build a <span class="hlt">system</span> prototype to demonstrate the practicality of two-way, wireless through-the-earth communications between the interior of a mine and the surface. The <span class="hlt">system</span> 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 <span class="hlt">system</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/918761','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/918761"><span id="translatedtitle">Autonomous microexplosives subsurface tracing <span class="hlt">system</span> <span class="hlt">final</span> report.</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Engler, Bruce Phillip; Nogan, John; Melof, Brian Matthew; Uhl, James Eugene; Dulleck, George R., Jr.; Ingram, Brian V.; Grubelich, Mark Charles; Rivas, Raul R.; Cooper, Paul W.; Warpinski, Norman Raymond; Kravitz, Stanley H.</p> <p>2004-04-01</p> <p>The objective of the autonomous micro-explosive subsurface tracing <span class="hlt">system</span> is to image the location and geometry of hydraulically induced fractures in subsurface petroleum reservoirs. This <span class="hlt">system</span> is based on the insertion of a swarm of autonomous micro-explosive packages during the fracturing process, with subsequent triggering of the energetic material to create an array of micro-seismic sources that can be detected and analyzed using existing seismic receiver arrays and analysis software. The project included investigations of energetic mixtures, triggering <span class="hlt">systems</span>, package size and shape, and seismic output. Given the current absence of any technology capable of such high resolution mapping of subsurface structures, this technology has the potential for major impact on petroleum industry, which spends approximately $1 billion dollar per year on hydraulic fracturing operations in the United States alone.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/207362','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/207362"><span id="translatedtitle">Sequencing Information Management <span class="hlt">System</span> (SIMS). <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Fields, C.</p> <p>1996-02-15</p> <p>A feasibility study to develop a requirements analysis and functional specification for a data management <span class="hlt">system</span> for large-scale DNA sequencing laboratories resulted in a functional specification for a Sequencing Information Management <span class="hlt">System</span> (SIMS). This document reports the results of this feasibility study, and includes a functional specification for a SIMS relational schema. The SIMS is an integrated information management <span class="hlt">system</span> that supports data acquisition, management, analysis, and distribution for DNA sequencing laboratories. The SIMS provides ad hoc query access to information on the sequencing process and its results, and partially automates the transfer of data between laboratory instruments, analysis programs, technical personnel, and managers. The SIMS user interfaces are designed for use by laboratory technicians, laboratory managers, and scientists. The SIMS is designed to run in a heterogeneous, multiplatform environment in a client/server mode. The SIMS communicates with external computational and data resources via the internet.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015ESS.....350205G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015ESS.....350205G"><span id="translatedtitle">The <span class="hlt">final</span> fate of planetary <span class="hlt">systems</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gaensicke, Boris</p> <p>2015-12-01</p> <p>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 <span class="hlt">system</span> is not unique. Twenty years later, we know that planetary <span class="hlt">systems</span> are ubiquitous, orbit stars spanning a wide range in mass, and form in an astonishing variety of architectures. Yet, one fascinating aspect of planetary <span class="hlt">systems</span> 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 <span class="hlt">systems</span> (in the solar <span class="hlt">system</span>, 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 <span class="hlt">systems</span> 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 <span class="hlt">system</span> 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-<span class="hlt">system</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/518722','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/518722"><span id="translatedtitle">Spill response <span class="hlt">system</span> configuration study. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Desimone, R.V.; Agosta, J.M.</p> <p>1996-05-01</p> <p>This report describes the development of a prototype decision support <span class="hlt">system</span> 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 <span class="hlt">system</span> is discussed in the context of two specific major spill scenarios in the San Francisco Bay.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5907572','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5907572"><span id="translatedtitle">Lightning protection of distribution <span class="hlt">systems</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Uman, M.A.</p> <p>1985-02-01</p> <p>Analyses are presented of experimental data obtained in the Tampa Bay area during 1978 and 1979 concerning the physical and phenomenological properties of lightning and the interaction of that lightning with the local distribution power <span class="hlt">systems</span>. Specific results are given regarding: (1) the physical and phenomenology properties of lightning in the Tampa Bay area and its relation to lightning elsewhere; (2) measurement and theory concerning lightning-induced voltages on distribution lines; (3) distribution <span class="hlt">system</span> operation in the presence of lightning and analytical modeling and prediction of that operation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T21B2543M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T21B2543M"><span id="translatedtitle">The evolving contribution of border faults and intra-<span class="hlt">rift</span> faults in early-stage East African <span class="hlt">rifts</span>: insights from the Natron (Tanzania) and Magadi (Kenya) basins</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muirhead, J.; Kattenhorn, S. A.; Dindi, E.; Gama, R.</p> <p>2013-12-01</p> <p>In the early stages of continental <span class="hlt">rifting</span>, East African <span class="hlt">Rift</span> (EAR) basins are conventionally depicted as asymmetric basins bounded on one side by a ~100 km-long border fault. As <span class="hlt">rifting</span> progresses, strain concentrates into the <span class="hlt">rift</span> center, producing intra-<span class="hlt">rift</span> faults. The timing and nature of the transition from border fault to intra-<span class="hlt">rift</span>-dominated strain accommodation is unclear. Our study focuses on this transitional phase of continental <span class="hlt">rifting</span> 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-<span class="hlt">rift</span> faults to crustal strain accommodation as <span class="hlt">rifting</span> 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 <span class="hlt">rift</span>. However, intra-<span class="hlt">rift</span> faults within ~1 Ma lavas are greatly eroded and fresh scarps are typically absent, implying long recurrence intervals between slip events. <span class="hlt">Rift</span>-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 <span class="hlt">system</span> 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. <span class="hlt">Rift</span>-normal elevation profiles indicate the focus of strain has migrated away from the border fault into the <span class="hlt">rift</span> center, where faults pervasively dissect 1.2-0.8 Ma trachyte lavas. Unlike Natron, intra-<span class="hlt">rift</span> faults in the Magadi basin exhibit primarily steep, little-degraded fault scarps, implying greater activity than Natron intra-<span class="hlt">rift</span> 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 <span class="hlt">rift</span> basin some time between 3 and 7 million years after <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=%22information+output%22&pg=5&id=ED160888','ERIC'); return false;" href="http://eric.ed.gov/?q=%22information+output%22&pg=5&id=ED160888"><span id="translatedtitle">Alabama Vocational Management Information <span class="hlt">System</span>. <span class="hlt">Final</span> Report.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Patterson, Douglas; And Others</p> <p></p> <p>A project was developed to design and implement a management information <span class="hlt">system</span> (MIS) to provide decision makers with accurate, usable, and timely data and information concerning input, output, and impact of vocational education. The objectives were to (1) design an MIS embracing student accounting, fiscal accounting, manpower analysis, and…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/ED083144.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED083144.pdf"><span id="translatedtitle">Incentive <span class="hlt">Systems</span> for Education Personnel. <span class="hlt">Final</span> Report.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Guttenberg, Richard</p> <p></p> <p>Herein are discussed the question of what is an incentive; the use of incentives in industry; the current patterns of reward and punishment in the schools; policy implications of the patterns of reward and punishment currently found in the schools; from an historical view, the incentive <span class="hlt">systems</span> that the schools have tried out in the past,…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=Accounting+AND+information+AND+system+AND+planning&pg=3&id=ED160888','ERIC'); return false;" href="http://eric.ed.gov/?q=Accounting+AND+information+AND+system+AND+planning&pg=3&id=ED160888"><span id="translatedtitle">Alabama Vocational Management Information <span class="hlt">System</span>. <span class="hlt">Final</span> Report.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Patterson, Douglas; And Others</p> <p></p> <p>A project was developed to design and implement a management information <span class="hlt">system</span> (MIS) to provide decision makers with accurate, usable, and timely data and information concerning input, output, and impact of vocational education. The objectives were to (1) design an MIS embracing student accounting, fiscal accounting, manpower analysis, and…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/290910','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/290910"><span id="translatedtitle">Hydrogen energy <span class="hlt">systems</span> studies. <span class="hlt">Final</span> technical report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ogden, J.M.; Kreutz, T.; Kartha, S.; Iwan, L.</p> <p>1996-08-13</p> <p>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 <span class="hlt">systems</span>. 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 <span class="hlt">systems</span>), 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 <span class="hlt">systems</span>? (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 <span class="hlt">systems</span>? 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.3624V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.3624V"><span id="translatedtitle">Uplift history of <span class="hlt">rifted</span> margins</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>van Wijk, Jolante; Meyer, Romain; Coblentz, David</p> <p>2013-04-01</p> <p><span class="hlt">Rifted</span> continent margins form after stretching and thinning of continental lithosphere. This process is predicted to result in subsidence and sediment deposition. A compilation of <span class="hlt">rifted</span> margins of the world shows that margins undergo a phase of uplift starting just prior to rupture. This uplift ranges from ~500 m to ~2000 m, and is found on all margins, both magmatic and magma-starved. After breakup subsidence resumes, but may be interrupted by later periods of (relative) uplift. The uplift changes the lateral distribution of potential energy of the lithosphere, increasing deviatoric tension and facilitating breakup. We investigated processes that could be responsible for the observed uplift around the time of continent rupture. Dynamic uplift by mantle flow only contributes several hundred meters to the uplift. Phase transitions in the shallow mantle may theoretically result in up to 1 km of uplift. Isostatic calculations suggest that removal of mantle lithosphere is a necessary and effective mechanism for the observed uplift. The combination of mantle phase transitions and a very thin mantle lid produces an excess potential energy state and a positive geoid anomaly, and leads to tensional forces favorable for rupture. We propose a new model for continental rupture which includes removal of mantle lithosphere (by detachment or instabilities). Observations of depth-dependent thinning on <span class="hlt">rifted</span> margins and geochemical data support the model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T13G..01N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T13G..01N"><span id="translatedtitle">Tag team tectonics: mantle upwelling and lithospheric heterogeneity ally to <span class="hlt">rift</span> continents (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nelson, W. R.; Furman, T.</p> <p>2013-12-01</p> <p>The configuration of continents we know today is the result of several billion years of active Wilson Cycle tectonics. The <span class="hlt">rifting</span> of continents and subsequent development of ocean basins is an integral part of long-term planetary-scale recycling processes. The products of this process can be seen globally, and the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) provides a unique view of extensional processes that actively divide a continent. Taken together with the adjoining Red Sea and Gulf of Aden, the EARS has experienced over 40 Ma of volcanism and ~30 Ma of extension. While early (pre-<span class="hlt">rift</span>) volcanism in the region is attributed to mantle plume activity, much of the subsequent volcanism occurs synchronously with continental <span class="hlt">rifting</span>. Numerous studies indicate that extension and magmatism are correlated: extension leads to decompression melting while magmatism accommodates further extension (e.g. Stein et al., 1997; Buck 2004; Corti 2012). Evaluation of the entire EARS reveals significant geochemical patterns - both spatial and temporal - in the volcanic products. Compositional variations are tied directly to the melt source(s), which changes over time. These variations can be characterized broadly by region: the Ethiopian plateau and Turkana Depression, the Kenya <span class="hlt">Rift</span>, and the Western <span class="hlt">Rift</span>. In the Ethiopian plateau, early flood basalt volcanism is dominated by mantle plume contributions with variable input from lherzolitic mantle lithosphere. Subsequent alkaline shield volcanism flanking the juvenile Main Ethiopian <span class="hlt">Rift</span> records the same plume component as well as contributions from a hydrous peridotitic lithosphere. The hydrous lithosphere does not contribute indefinitely. Instead, young (< 2 Ma) volcanism taps a combination of the mantle plume and anhydrous depleted lithospheric mantle. In contrast, volcanism in the Kenya <span class="hlt">Rift</span> and the Western <span class="hlt">Rift</span> are derived dominantly from metasomatized lithospheric mantle rather than mantle plume material. These <span class="hlt">rifts</span> lie in the mobile belts flanking the Archean Tanzanian craton, suggesting the lithosphere in these regions has a complex geodynamic history that provides an avenue of weakness for <span class="hlt">rift</span> development around the craton. In the Tanzanian portion of the Kenya <span class="hlt">Rift</span>, highly sodic mafic and carbonatitic lavas dominate both the <span class="hlt">rift</span> valleys and <span class="hlt">rift</span> shoulders. Mantle xenoliths from this region show petrographic and isotopic evidence for ancient and recent metasomatic events. In the Western <span class="hlt">Rift</span>, highly potassic mafic lavas dominate the volcanic landscape in the <span class="hlt">rift</span> valley and <span class="hlt">rift</span> margins. The lithospheric mantle underlying this region is highly metasomatized, as evidenced by the presence of clinopyroxenite, websterite and glimmerite xenoliths and the absence of peridotite. The highly fusible metasomatized mantle beneath both the Kenya and Western <span class="hlt">rifts</span> enables lithospheric melting with comparatively minor P-T perturbation. Regardless of which process begot the other, lithospheric thinning promotes melting while volcanism promotes lithospheric weakness and enables <span class="hlt">rift</span> propagation. When viewed holistically, both mantle plume activity and lithospheric heterogeneities have played a vital role in the initiation and subsequent evolution of the <span class="hlt">rifting</span> throughout eastern Africa.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013Tectp.607...98K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013Tectp.607...98K"><span id="translatedtitle">The development of extension and magmatism in the Red Sea <span class="hlt">rift</span> of Afar</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Keir, Derek; Bastow, Ian D.; Pagli, Carolina; Chambers, Emma L.</p> <p>2013-11-01</p> <p>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 <span class="hlt">rifting</span> 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 <span class="hlt">rifting</span> to incipient seafloor spreading. We review recent constraints on along-axis variations in <span class="hlt">rift</span> morphology, crustal and mantle structure, the distribution and style of ongoing faulting, subsurface magmatism and surface volcanism in the Red Sea <span class="hlt">rift</span> of Afar to understand processes ultimately responsible for the formation of magmatic <span class="hlt">rifted</span> continental margins. Our synthesis shows that there is a fundamental change in <span class="hlt">rift</span> 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 <span class="hlt">rift</span>. Thus, although magma intrusion accommodates strain for a protracted period during <span class="hlt">rift</span> development, the <span class="hlt">final</span> 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 <span class="hlt">rifted</span> margins worldwide.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1035012','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1035012"><span id="translatedtitle">FY07 <span class="hlt">Final</span> Report for Calibration <span class="hlt">Systems</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Myers, Tanya L.; Broocks, Bryan T.; Cannon, Bret D.; Ho, Nicolas</p> <p>2007-12-01</p> <p>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 <span class="hlt">system</span> is essential to account for changes in the detector response once the instrument has been removed from the laboratory. The Calibration <span class="hlt">Systems</span> project at Pacific Northwest National Laboratory (PNNL) is aimed towards developing and demonstrating compact quantum cascade (QC) laser-based calibration <span class="hlt">systems</span> for infrared sensor <span class="hlt">systems</span> 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 <span class="hlt">system</span>, 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 <span class="hlt">system</span> to demonstrate how the QC laser can be used to calibrate a microbolometer array and illustrated the importance of a multi-point calibration.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5478187','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5478187"><span id="translatedtitle">Stirred Heat Exchanger (SHE) <span class="hlt">systems</span>. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Not Available</p> <p>1981-12-18</p> <p>A general objective of this project was to design, evaluate, and commercialize internally- and externally-stirred heat exchangers <span class="hlt">systems</span>, 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)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/993365','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/993365"><span id="translatedtitle">FY2008 Calibration <span class="hlt">Systems</span> <span class="hlt">Final</span> Report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cannon, Bret D.; Myers, Tanya L.; Broocks, Bryan T.</p> <p>2009-01-01</p> <p>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 <span class="hlt">systems</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/836268','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/836268"><span id="translatedtitle"><span class="hlt">Final</span> Report of Strongly Interacting Fermion <span class="hlt">Systems</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Wilkins, J. W.</p> <p>2001-06-25</p> <p>There has been significant progress in three broad areas: (A) Optical properties, (B) Large-scale computations, and (C) Many-body <span class="hlt">systems</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.421...58N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.421...58N"><span id="translatedtitle"><span class="hlt">Rift</span> reactivation and migration during multiphase extension</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Naliboff, John; Buiter, Susanne J. H.</p> <p>2015-07-01</p> <p>Passive margins may undergo multiple phases of extension with distinct structural, petrological and sedimentary processes before achieving breakup. Observations of <span class="hlt">rift</span> axis migration through time may reflect cooling, hardening and subsequent abandonment of the <span class="hlt">rift</span> axis during either long-term periods of slow extension or periods of tectonic quiescence. Here, we use 2D thermo-mechanical numerical models to examine <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> and surrounding regions, rather than the total integrated strength, largely controls <span class="hlt">rift</span> reactivation versus migration. The tectonic quiescence (cooling) duration required to induce <span class="hlt">rift</span> 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 <span class="hlt">rifts</span> after extensive (>20 Myr) cooling periods in some cases develop asymmetric margins with deformation patterns stepping toward the future <span class="hlt">rift</span>, such as characterizing most of the Atlantic conjugate margins.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1134810','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1134810"><span id="translatedtitle">Physics of Correlated <span class="hlt">Systems</span>, <span class="hlt">Final</span> Project Report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Greene, Chris H.</p> <p>2014-06-25</p> <p>The funding of this DOE project has enabled the P.I. and his collaborators to tackle a number of problems involving nonperturbatively coupled atomic <span class="hlt">systems</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25636855','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25636855"><span id="translatedtitle">The accuracy of the Oculus <span class="hlt">Rift</span> virtual reality head-mounted display during cervical spine mobility measurement.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Xu, Xu; Chen, Karen B; Lin, Jia-Hua; Radwin, Robert G</p> <p>2015-02-26</p> <p>An inertial sensor-embedded virtual reality (VR) head-mounted display, the Oculus <span class="hlt">Rift</span> (the <span class="hlt">Rift</span>), monitors head movement so the content displayed can be updated accordingly. While the <span class="hlt">Rift</span> 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 <span class="hlt">Rift</span> and a reference motion tracking <span class="hlt">system</span>. Comparison of the kinematics data between the <span class="hlt">Rift</span> and the tracking <span class="hlt">system</span> indicated that the <span class="hlt">Rift</span> 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 <span class="hlt">Rift</span> 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 <span class="hlt">Rift</span> in order to more accurately measure cervical spine kinematics. It is suggested that the front cover of the <span class="hlt">Rift</span> should be aligned against a vertical plane during its initialization. PMID:25636855</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoRL..42.7374D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoRL..42.7374D"><span id="translatedtitle">The 2003-2004 seismic swarm in the western Corinth <span class="hlt">rift</span>: Evidence for a multiscale pore pressure diffusion process along a permeable fault <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Duverger, Clara; Godano, Maxime; Bernard, Pascal; Lyon-Caen, Hélène; Lambotte, Sophie</p> <p>2015-09-01</p> <p>Microseismic multiplets occurring in the western Corinth <span class="hlt">rift</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMPP31G..01C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMPP31G..01C"><span id="translatedtitle">A Review of New and Anticipated High-Resolution Paleoclimate Records from the East African <span class="hlt">Rift</span> <span class="hlt">System</span> and Their Implications for Hominin Evolution and Demography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cohen, A. S.</p> <p>2014-12-01</p> <p>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 <span class="hlt">rifts</span> are now available spanning nearly the entire latitudinal range of the East Africa <span class="hlt">Rift</span>. 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/578546','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/578546"><span id="translatedtitle">Buried waste containment <span class="hlt">system</span> materials. <span class="hlt">Final</span> Report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Weidner, J.R.; Shaw, P.G.</p> <p>1997-10-01</p> <p>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 <span class="hlt">System</span> (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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.B51D0407C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.B51D0407C"><span id="translatedtitle">Comparing Carbonate-Depositing Hydrothermal <span class="hlt">Systems</span> Along the Mid-Atlantic Ridge at Lost City Hydrothermal Field and Along the Rio Grande <span class="hlt">rift</span> in the Southwestern US: Geochemistry, Geomicrobiology and Mineralogy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cron, B. R.; Crossey, L.; Hall, J.; Takacs-Vesbach, C.; Dahm, K.; Northup, D.; Karlstrom, K.</p> <p>2008-12-01</p> <p>Both continental and marine <span class="hlt">rift</span> 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 <span class="hlt">system</span> 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 <span class="hlt">systems</span>. Travertine depositing CO2 springs within the Rio Grande <span class="hlt">rift</span>, 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 <span class="hlt">systems</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999Geo....27..791S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999Geo....27..791S"><span id="translatedtitle">Basin-scale migration of continental-<span class="hlt">rift</span> brines: Paleohydrologic modeling of the Dead Sea basin</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stanislavsky, Eyal; Gvirtzman, Haim</p> <p>1999-09-01</p> <p>It was suggested that brine of the Dead Sea <span class="hlt">rift</span> has originated from a residual product of intensively evaporated seawater that invaded the <span class="hlt">rift</span>, precipitated halite, and later interacted through dolomitization with the host rock during subsurface migration. Detection of this brine in many deep wells located at distances as far as 100 km away from the <span class="hlt">rift</span> was attributed to long-distance migration of the brine. The physical feasibility of such migration, which probably spanned the past 3 6 m.y., is quantitatively tested and verified in this study by using paleohydrologic modeling. The structural formation of the <span class="hlt">rift</span> is described by a chronological sequence of geologic cross sections serving as the basis for hydrodynamic calculations, which assess the effects of the structure on fluid migration, salinity redistribution, and heat transport across the sedimentary basin. Results indicate that two basin-scale ground-water <span class="hlt">systems</span>, one atop the other but with opposite flow directions, coexisted in the Dead Sea <span class="hlt">rift</span> valley. The first is a topography-driven flow of meteoric water from the surrounding highlands toward the <span class="hlt">rift</span> through relatively shallow aquifers (? 1 km). The second is a density-driven migration of the Dead Sea brine through deep aquifers (4 5 km) in the opposite direction. The configuration of these flow <span class="hlt">systems</span> has changed during the structural evolution of the Dead Sea <span class="hlt">rift</span>, illustrating the interrelationships among basin formation, paleohydrology, and paleogeochemistry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1712251P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1712251P"><span id="translatedtitle">Surface processes in an active <span class="hlt">rift</span> setting: a source to sink approach from the Sperchios delta, central Greece</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pechlivanidou, Sofia; Cowie, Patience; Gawthorpe, Rob</p> <p>2015-04-01</p> <p>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 <span class="hlt">rift</span> <span class="hlt">system</span>, central Greece. The Sperchios <span class="hlt">Rift</span> 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 <span class="hlt">rift</span>, 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 <span class="hlt">rift</span> 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. <span class="hlt">Finally</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.5444H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.5444H"><span id="translatedtitle"><span class="hlt">Rift</span> flank uplift and thermal evolution of an intracratonic <span class="hlt">rift</span> basin (eastern Canada) determined by combined apatite and zircon (U-Th)/He thermochronology</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hardie, Rebecca; Schneider, David; Metcalf, James; Flowers, Rebecca</p> <p>2015-04-01</p> <p>As a significant portion of the world's oil reserves are retrieved from <span class="hlt">rift</span> <span class="hlt">systems</span>, a better understanding of the timing of thermal evolution and burial history of these <span class="hlt">systems</span> will increase the potential for the discovery of hydrocarbon-bearing <span class="hlt">rifts</span>. The Ottawa Embayment of the St. Lawrence Platform of eastern Canada is a reactivated intracratonic <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span>, from Mont-Tremblant, Québec (~900 m) to the central axis of the Paleozoic <span class="hlt">rift</span> in the Southern Ontario Lowlands (~300 m). Targets included Neoproterozoic metamorphic rocks of the Grenville Province along the <span class="hlt">rift</span> flank and basinal Cambro-Ordovician Potsdam Group. Samples from the <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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-<span class="hlt">rift</span> 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 <span class="hlt">system</span> and improve our understanding of the <span class="hlt">rift</span> related history of the region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T33D..08T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T33D..08T"><span id="translatedtitle">Feedbacks between deformation and reactive melt transport in the mantle lithosphere during <span class="hlt">rifting</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tommasi, A.; Baptiste, V.; Vauchez, A. R.; Fort, A.</p> <p>2014-12-01</p> <p>The East-African <span class="hlt">rift</span> 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 <span class="hlt">rift</span> <span class="hlt">system</span> highlights strong feedbacks between deformation, melt transport, and thermal evolution in the lithospheric mantle. Microstructures change markedly from south (young) to north (mature <span class="hlt">rift</span>). 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. <span class="hlt">Finally</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JSG....77..191B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JSG....77..191B"><span id="translatedtitle">Fault deformation mechanisms and fault rocks in micritic limestones: Examples from Corinth <span class="hlt">rift</span> normal faults</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bussolotto, M.; Benedicto, A.; Moen-Maurel, L.; Invernizzi, C.</p> <p>2015-08-01</p> <p>A multidisciplinary study investigates the influence of different parameters on fault rock architecture development along normal faults affecting non-porous carbonates of the Corinth <span class="hlt">rift</span> southern margin. Here, some fault <span class="hlt">systems</span> cut the same carbonate unit (Pindus), and the gradual and fast uplift since the initiation of the <span class="hlt">rift</span> led to the exhumation of deep parts of the older faults. This exceptional context allows superficial active fault zones and old exhumed fault zones to be compared. Our approach includes field studies, micro-structural (optical microscope and cathodoluminescence), geochemical analyses (δ13C, δ18O, trace elements) and fluid inclusions microthermometry of calcite sin-kinematic cements. Our main results, in a depth-window ranging from 0 m to about 2500 m, are: i) all cements precipitated from meteoric fluids in a close or open circulation <span class="hlt">system</span> depending on depth; ii) depth (in terms of P/T condition) determines the development of some structures and their sealing; iii) lithology (marly levels) influences the type of structures and its cohesive/non-cohesive nature; iv) early distributed rather than <span class="hlt">final</span> total displacement along the main fault plane is the responsible for the fault zone architecture; v) petrophysical properties of each fault zone depend on the variable combination of these factors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6832285','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6832285"><span id="translatedtitle">Solar heating <span class="hlt">system</span> installed at Troy, Ohio. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p></p> <p>1980-09-01</p> <p>This document is the <span class="hlt">Final</span> Report of the Solar Energy <span class="hlt">System</span> located at Troy-Miami County Public Library, Troy, Ohio. The completed <span class="hlt">system</span> is composed of tree basic subsystems: the collector <span class="hlt">system</span> consisting of 3264 square feet of Owens Illinois evacuated glass tube collectors; the storage <span class="hlt">system</span> which includes a 5000-gallon insulated steel tank; and the distribution and control <span class="hlt">system</span> which includes piping, pumping and control logic for the efficient and safe operation of the entire <span class="hlt">system</span>. This solar heating <span class="hlt">system</span> was installed in an existing facility and is, therefore, a retrofit <span class="hlt">system</span>. This report includes extracts from the site files, specifications, drawings, installation, operation and maintenance instructions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/86606','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/86606"><span id="translatedtitle">Masirah Graben, Oman: A hidden Cretaceous <span class="hlt">rift</span> basin</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Beauchamp, W.H.; Ries, A.C.; Coward, M.P.</p> <p>1995-06-01</p> <p>Reflection seismic data, well data, geochemical data, and surface geology suggest that a Cretaceous <span class="hlt">rift</span> 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 <span class="hlt">system</span> 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 <span class="hlt">rift</span> sequence below the ophiolites. The sedimentary sequence in the Masirah graben was stable until further <span class="hlt">rifting</span> of the Arabian Sea/Gulf of Aden in the late Tertiary, resulting in reactivation of earlier <span class="hlt">rift</span>-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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.usgs.gov/of/2010/1083/p/pdf/ofr2010-1083p.pdf','USGSPUBS'); return false;" href="http://pubs.usgs.gov/of/2010/1083/p/pdf/ofr2010-1083p.pdf"><span id="translatedtitle">Seismicity of the Earth 1900-2013 East African <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hayes, Gavin P.; Jones, Eric S.; Stadler, Timothy J.; Barnhart, William D.; McNamara, Daniel E.; Benz, Harley M.; Furlong, Kevin P.; Villaseñor, Antonio</p> <p>2014-01-01</p> <p><span class="hlt">Rifting</span> in East Africa is not all coeval; volcanism and faulting have been an ongoing phenomenon on the continent since the Eocene (~45 Ma). The <span class="hlt">rifting</span> 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 <span class="hlt">rift</span> separating Africa and Arabia. Since the initiation of <span class="hlt">rifting</span> in northeastern Africa, the <span class="hlt">system</span> 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.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Tecto..33..875R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Tecto..33..875R"><span id="translatedtitle">The protracted development of focused magmatic intrusion during continental <span class="hlt">rifting</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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</p> <p>2014-06-01</p> <p>The transition from mechanical thinning toward focused magmatic intrusion during continental <span class="hlt">rifting</span> is poorly constrained; the tectonically active Main Ethiopian <span class="hlt">Rift</span> (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 <span class="hlt">rifting</span> 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 <span class="hlt">system</span> 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 <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tectp.654...75W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tectp.654...75W"><span id="translatedtitle">The tectonic evolution of the southeastern Terceira <span class="hlt">Rift</span>/São Miguel region (Azores)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Weiß, B. J.; Hübscher, C.; Lüdmann, T.</p> <p>2015-07-01</p> <p>The eastern Azores Archipelago with São Miguel being the dominant subaerial structure is located at the intersection of an oceanic <span class="hlt">rift</span> (Terceira <span class="hlt">Rift</span>) 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 <span class="hlt">Rift</span> are <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">system</span>, 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 <span class="hlt">rift</span> 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 <span class="hlt">Rift</span> 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 <span class="hlt">Rift</span> domain is predominantly controlled by plate kinematics and lithospheric stress forming a kind of a re-organized <span class="hlt">rift</span> <span class="hlt">system</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S53F..04R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S53F..04R"><span id="translatedtitle">Unloading-Driven Off-<span class="hlt">Rift</span> Distribution of Volcanism in <span class="hlt">Rift</span> Zones</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rivalta, E.; Maccaferri, F.; Keir, D.; Acocella, V.</p> <p>2014-12-01</p> <p>Prolonged extension of the continents results in deep elongated <span class="hlt">rift</span> valleys at the surface and a <span class="hlt">rift</span>-centered magma ponding zones at the crust-mantle boundary. The ascending magma sometimes erupts to the surface producing volcanism both in the <span class="hlt">rift</span> valley, or counterintuitively, at off-<span class="hlt">rift</span> volcanic fields offset by tens of kilometers from the source of magma at depth. The driving forces behind the off-<span class="hlt">rift</span> surface distribution of magmatism remain enigmatic. Here we demonstrate, with numerical boundary element models of dyke propagation, that the gravitational unloading induced by crustal thinning and <span class="hlt">rift</span> border faulting can steer dykes away from the deep magma ponding zone towards the <span class="hlt">rift</span> sides, eventually causing eruptions at tens of kilometers outside the <span class="hlt">rift</span> border. Furthermore, our models predict the formation of stacked magmatic sills in the lower crust above the magma ponding zone, and the along-<span class="hlt">rift</span> propagation of shallow dykes in <span class="hlt">rifting</span> events. Gravitational unloading, which facilitates decompression melting of the asthenosphere, is fundamental in controlling the transfer of magma from depth to the surface. Our predictions are consistent with the location and shape of intrusions, as well as the distribution of volcanism from <span class="hlt">rift</span> zones around the Earth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tecto..34..464K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tecto..34..464K"><span id="translatedtitle">The origin of along-<span class="hlt">rift</span> variations in faulting and magmatism in the Ethiopian <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Keir, Derek; Bastow, Ian D.; Corti, Giacomo; Mazzarini, Francesco; Rooney, Tyrone O.</p> <p>2015-03-01</p> <p>The geological record at <span class="hlt">rifts</span> 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 <span class="hlt">Rift</span> (MER) in East Africa provides an excellent opportunity to address this dichotomy: it exposes, along strike, several sectors of asynchronous <span class="hlt">rift</span> development from continental <span class="hlt">rifting</span> in the south to incipient oceanic spreading in the north. Here we perform studies of volcanic cone density and <span class="hlt">rift</span> 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 <span class="hlt">rifted</span> margin. The timing of <span class="hlt">rift</span> sector development, the three-dimensional focusing of melt, and the ponding of plume material where the <span class="hlt">rift</span> dramatically narrows each influence igneous intrusion and volcanism along the MER. However, <span class="hlt">rifting</span> 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 <span class="hlt">rifted</span> margins thus likely carry information about the development of strain during <span class="hlt">rifting</span>, as well as the physical state of the convecting mantle at the time of breakup.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/26595942','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/26595942"><span id="translatedtitle">Dental Devices; Reclassification of Electrical Salivary Stimulator <span class="hlt">System</span>. <span class="hlt">Final</span> order.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p></p> <p>2015-11-20</p> <p>The Food and Drug Administration (FDA) is issuing a <span class="hlt">final</span> order to reclassify the salivary stimulator <span class="hlt">system</span>, a postamendments Class III device, into class II (special controls) and to rename the device the "electrical salivary stimulator <span class="hlt">system</span>." The Agency is classifying the device into class II (special controls) in order to provide a reasonable assurance of safety and effectiveness of the device. PMID:26595942</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JAfES.100..203A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JAfES.100..203A"><span id="translatedtitle"><span class="hlt">Rift</span> architecture and evolution: The Sirt Basin, Libya: The influence of basement fabrics and oblique tectonics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Abdunaser, K. M.; McCaffrey, K. J. W.</p> <p>2014-12-01</p> <p>The Cretaceous-Tertiary northwest-trending Sirt Basin <span class="hlt">system</span>, Libya, is a <span class="hlt">rift</span>/sag basin formed on Pan-African to Paleozoic-aged basement of North Africa. In this study, we investigate the <span class="hlt">rift</span>-basin architecture and tectonic framework of the western Sirt Basin. Using remote sensed data, supported by borehole data from about 300 deep wells and surface geologic maps, we constructed geological cross sections and surface geology maps. Indication of the relative timing of structures and movement along faults has been determined where possible. Direction statistics for all the interpreted linear features acquired in the study area were calculated and given as a total distribution and then the totals are broken down by the major basin elements of the area. Hundreds of lineaments were recognized. Their lengths, range between a hundred meters up to hundreds of kilometers and the longest of the dominant trends are between N35W-N55W and between N55E-N65E which coincides with Sirt Basin structures. The produced rose diagrams reveal that the majority of the surface linear features in the region have four preferred orientations: N40-50W in the Zallah Trough, N45-55W in the Dur al Abd Trough, N35-55W in the Az Zahrah-Al Hufrah Platform, and in contrast in the Waddan Uplift a N55-65E trend. We recognize six lithostratigraphic sequences (phases) in the area's stratigraphic framework. A Pre-graben (Pre-<span class="hlt">rift</span>) initiation stage involved the Pre-Cretaceous sediments formed before the main Sirt Basin subsidence. Then followed a Cretaceous to Eocene graben-fill stage that can divided into four structurally-active and structurally-inactive periods, and <span class="hlt">finally</span> a terminal continental siliciclastics-rich package representing the post-<span class="hlt">rift</span> stage of the development in post-Eocene time. In general five major fault <span class="hlt">systems</span> dissect and divide the study area into geomorphological elevated blocks and depressions. Most of the oil fields present in the study area are associated with structural hinge 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 <span class="hlt">rift</span> development as exemplified in our study area to the break-up of Gondwana represented by the structural evolution of the West-Central African <span class="hlt">rift</span> <span class="hlt">system</span>, and the South and Central Atlantic, the Tethys and the Indian Oceans.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.S11B2231I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.S11B2231I"><span id="translatedtitle">Evidence of Ancient <span class="hlt">Rifts</span> Beneath Texas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Irie, K.; Velasco, A. A.</p> <p>2011-12-01</p> <p>Continental <span class="hlt">rifts</span> are defined as geological features where Earth's lithosphere is pulled away by surface expansion of the Earth. Their physiographic features include linear <span class="hlt">rift</span> valleys associated with active volcanism. Many <span class="hlt">rifts</span> fail to split a continent and ancient <span class="hlt">rifts</span> that failed to split can be found by using seismic waves to image these ancient structures. Using seismic data collected by EarthScope USArray stations in Texas, we calculate teleseismic receiver functions and utilized surface wave dispersion curves to simultaneously invert for the velocity structure beneath each seismic station. With the calculated receiver functions, we generate maps to show preliminary 3-D crust/upper mantle boundary structure, the velocity ratio of P and S waves, and the S-wave velocity structure. We expect to characterize the ancient <span class="hlt">rift</span> zones that exist in Texas and compare these results with the Rio Grande <span class="hlt">Rift</span> in New Mexico. The goal for this comparison is to determine whether Rio Grande <span class="hlt">rift</span> is still active or doomed to be another failed <span class="hlt">rift</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3840870','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3840870"><span id="translatedtitle"><span class="hlt">Rift</span> Valley Fever in Namibia, 2010</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Monaco, Federica; Pinoni, Chiara; Khaiseb, Siegfried; Calistri, Paolo; Molini, Umberto; Bishi, Alec; Conte, Annamaria; Scacchia, Massimo; Lelli, Rossella</p> <p>2013-01-01</p> <p>During May–July 2010 in Namibia, outbreaks of <span class="hlt">Rift</span> Valley fever were reported to the National Veterinary Service. Analysis of animal specimens confirmed virus circulation on 7 farms. Molecular characterization showed that all outbreaks were caused by a strain of <span class="hlt">Rift</span> Valley fever virus closely related to virus strains responsible for outbreaks in South Africa during 2009–2010. PMID:24274469</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999JVGR...94...21W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999JVGR...94...21W"><span id="translatedtitle">Volcanic <span class="hlt">rift</span> zones and their intrusion swarms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Walker, George P. L.</p> <p>1999-12-01</p> <p>Most volcanoes have <span class="hlt">rift</span> zones, underlain by swarms of dykes or other minor intrusions. This paper reviews the subject and presents some new data and ideas. It plots <span class="hlt">rift</span> zone width against length for different volcano types, and finds that the zones on strato- and central volcanoes are on the whole narrower and shorter than on other types. Among the longest and narrowest zones are those on Hawaiian shield volcanoes; there are several reasons for the focussing. Hawaiian <span class="hlt">rift</span> zones however become diffuse when volcanic activity declines. Monogenetic volcano fields include some that have clearly identifiable <span class="hlt">rift</span> zones, and others that have vent-fields lacking fissures or dykes. Here the vent-field justifiably can be taken to proxy for a <span class="hlt">rift</span> zone. The zones visited in several volcanic areas, (including the Azores and Samoa), are localised by deep crustal structures or tectonic activity, and often involve strike-slip faults. This paper then suggests how insertion of dykes could cause structural changes such as bending or initiation of a <span class="hlt">rift</span> zone, and how departures from the "normal" balance between magma flux and extensional strain rate could determine whether <span class="hlt">rift</span> zones are vertical or horizontal. This leads to a possible mechanism for the circumferential (annular) <span class="hlt">rift</span> zones of some Galapagos volcanoes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T53A4666G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T53A4666G"><span id="translatedtitle"><span class="hlt">Rifting</span> and Post-<span class="hlt">Rift</span> Reactivation of The Eastern Sardinian Margin (Western Tyrrhenian Back-Arc Basin) Evidenced by the Messinian Salinity Crisis Markers and Salt Tectonics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gaullier, V.; Chanier, F.; Vendeville, B.; Lymer, G.; Lofi, J.; Sage, F.; Maillard, A.; Thinon, I.</p> <p>2014-12-01</p> <p>The Eastern Sardinian margin formed during the opening of the Tyrrhenian Sea, a back-arc basin created by continental <span class="hlt">rifting</span> and oceanic spreading related to the eastward migrating Apennine subduction <span class="hlt">system</span> 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 <span class="hlt">rifting</span> 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 <span class="hlt">rifting</span> and post-<span class="hlt">rift</span> 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 <span class="hlt">rifted</span> basin already existed by the Messinian times, revealing a major pre-MSC <span class="hlt">rifting</span> episode across the entire domain. Because salt tectonics can create fan-shaped geometries in sediments, syn-<span class="hlt">rift</span> deposits have to be carefully re-examined in order to decipher the effects of crustal tectonics (<span class="hlt">rifting</span>) and salt tectonics. Our data surprisingly showed that there are no clues for Messinian syn-<span class="hlt">rift</span> sediments along the East-Sardinia Basin and Cornaglia Terrace, hence no evidence for <span class="hlt">rifting</span> after Late Tortonian times. Nevertheless, widespread deformation occurred during the Pliocene and is attributed to post-<span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70034615','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70034615"><span id="translatedtitle">East Antarctic <span class="hlt">rifting</span> triggers uplift of the Gamburtsev Mountains</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Ferraccioli, F.; Finn, Carol A.; Jordan, Tom A.; Bell, Robin E.; Anderson, Lester M.; Damaske, Detlef</p> <p>2011-01-01</p> <p>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 <span class="hlt">rift</span> <span class="hlt">system</span> 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) <span class="hlt">rifting</span>. Much like East Africa, the interior of East Antarctica is a mosaic of Precambrian provinces affected by <span class="hlt">rifting</span> processes. Our models show that the combination of <span class="hlt">rift</span>-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 <span class="hlt">rifting</span> and preserved orogenic roots can produce broad regions of high topography in continental interiors without significantly modifying the underlying Precambrian lithosphere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19950045496&hterms=tectonics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dtectonics','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19950045496&hterms=tectonics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dtectonics"><span id="translatedtitle">Tectonic controls on <span class="hlt">rift</span> basin morphology: Evolution of the northern Malawi (Nyasa) <span class="hlt">rift</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ebinger, C. J.; Deino, A. L.; Tesha, A. L.; Becker, T.; Ring, U.</p> <p>1993-01-01</p> <p>Radiometric (K-Ar and Ar-40/Ar-39) age determinations of volcanic and volcaniclastic rocks, combined with structural, gravity, and seismic reflection data, are used to constrain the age of sedimentary strata contained within the seismically and volcanically active northern Malawi (Nyasa) <span class="hlt">rift</span> and to characterize changes in basin and flank morphologies with time. Faulting and volcanism within the Tukuyu-Karonga basin began at approximately 8.6 Ma, when sediments were deposited in abroad, initially asymmetric lake basin bounded on its northeastern side by a border fault <span class="hlt">system</span> with minor topographic relief. Extensions, primarily by a slip along the border fault, and subsequent regional isostatic compensation led to the development of a 5-km-deep basin bounded by broad uplifted flanks. Along the low-relief basin margin opposite border fault, younger stratigraphic sequences commonly onlap older wedge-shaped sequences, although their internal geometry is often progradational. Intrabasinal faulting, flankuplift, and basaltic and felsic volcanism from centers at the northern end of the basin became more important at about 2.5 Ma when cross-<span class="hlt">rift</span> transfer faults developed to link the Tukuyu-Karonga basin to the Rukwa basin. Local uplift and volcanic construction at the northern end of the basin led to a southeastward shift in the basin's depocenter. Sequence boundaries are commonly erosional along this low-relief (hanging wall) margin and conformable in the deep lake basin. The geometry of stratigraphic sequences and the distribution of the erosion indicate that horizontal and vertical crustal movements both across and along the length of the <span class="hlt">rift</span> basin led to changes in levels of the lake, irrespective of paleoclimatic fluctuations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.6499B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.6499B"><span id="translatedtitle">Geodynamic models of the Wilson Cycle: From <span class="hlt">rifts</span> to mountains to <span class="hlt">rifts</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Buiter, Susanne; Tetreault, Joya; Torsvik, Trond</p> <p>2015-04-01</p> <p>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 <span class="hlt">systems</span>. 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 <span class="hlt">rifted</span> 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 <span class="hlt">rift</span> area. The resulting <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009QSRv...28.2804B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009QSRv...28.2804B"><span id="translatedtitle">Tectonic and climatic control on evolution of <span class="hlt">rift</span> lakes in the Central Kenya <span class="hlt">Rift</span>, East Africa</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bergner, A. G. N.; Strecker, M. R.; Trauth, M. H.; Deino, A.; Gasse, F.; Blisniuk, P.; Dühnforth, M.</p> <p>2009-12-01</p> <p>The long-term histories of the neighboring Nakuru-Elmenteita and Naivasha lake basins in the Central Kenya <span class="hlt">Rift</span> illustrate the relative importance of tectonic versus climatic effects on <span class="hlt">rift</span>-lake evolution and the formation of disparate sedimentary environments. Although modern climate conditions in the Central Kenya <span class="hlt">Rift</span> are very similar for these basins, hydrology and hydrochemistry of present-day lakes Nakuru, Elmenteita and Naivasha contrast dramatically due to tectonically controlled differences in basin geometries, catchment size, and fluvial processes. In this study, we use eighteen 14C and 40Ar/ 39Ar dated fluvio-lacustrine sedimentary sections to unravel the spatiotemporal evolution of the lake basins in response to tectonic and climatic influences. We reconstruct paleoclimatic and ecological trends recorded in these basins based on fossil diatom assemblages and geologic field mapping. Our study shows a tendency towards increasing alkalinity and shrinkage of water bodies in both lake basins during the last million years. Ongoing volcano-tectonic segmentation of the lake basins, as well as reorganization of upstream drainage networks have led to contrasting hydrologic regimes with adjacent alkaline and freshwater conditions. During extreme wet periods in the past, such as during the early Holocene climate optimum, lake levels were high and all basins evolved toward freshwater <span class="hlt">systems</span>. During drier periods some of these lakes revert back to alkaline conditions, while others maintain freshwater characteristics. Our results have important implications for the use and interpretation of lake sediment as climate archives in tectonically active regions and emphasize the need to deconvolve lacustrine records with respect to tectonics versus climatic forcing mechanisms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010IJEaS..99.1663B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010IJEaS..99.1663B"><span id="translatedtitle">Stable isotope variation in tooth enamel from Neogene hippopotamids: monitor of meso and global climate and <span class="hlt">rift</span> dynamics on the Albertine <span class="hlt">Rift</span>, Uganda</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brachert, Thomas Christian; Brügmann, Gerhard B.; Mertz, Dieter F.; Kullmer, Ottmar; Schrenk, Friedemann; Jacob, Dorrit E.; Ssemmanda, Immaculate; Taubald, Heinrich</p> <p>2010-10-01</p> <p>The Neogene was a period of long-term global cooling and increasing climatic variability. Variations in 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 <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS). However, lake <span class="hlt">systems</span> not only depend on rainfall patterns, but also on the size and physiography of river catchment areas. This study is based on stable isotope proxy data (18O/16O, 13C/12C) from tooth enamel of hippopotamids (Mammalia) and aims in unravelling long-term climate and watershed dynamics that control the evolution of palaeolake <span class="hlt">systems</span> in the western branch of the EARS (Lake Albert, Uganda) during the Late Neogene (7.5 Ma to recent). Having no dietary preferences with respect to wooded (C3) versus grassland (C4) vegetation, these territorial, water-dependant mammals are particularly useful for palaeoclimate analyses. As inhabitants of lakes and rivers, hippopotamid tooth enamel isotope data document mesoclimates of topographic depressions, such as the <span class="hlt">rift</span> valleys and, therefore, changes in relative valley depth instead of exclusively global climate changes. Consequently, we ascribe a synchronous maximum in 18O/16O and 13C/12C composition of hippopotamid enamel centred around 1.5-2.5 Ma to maximum aridity and/or maximum hydrological isolation of the <span class="hlt">rift</span> floor from <span class="hlt">rift</span>-external river catchment areas in response to the combined effects of <span class="hlt">rift</span> shoulder uplift and subsidence of the <span class="hlt">rift</span> valley floor. Structural rearrangements by ~2.5 Ma within the northern segment of the Albertine <span class="hlt">Rift</span> are well constrained by reversals in river flow, cannibalisation of catchments, biogeographic turnover and uplift of the Rwenzori horst. However, a growing rain shadow is not obvious in 18O/16O signatures of the hippopotamid teeth of the Albertine <span class="hlt">Rift</span>. According to our interpretation, this is the result of the overriding effect of evaporation on 18O/16O responding to aridification of the basin floor by a valley air circulation <span class="hlt">system</span> 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 <span class="hlt">rift</span> mesoclimates may represent an underestimated aspect in previous palaeoclimate reconstructions from <span class="hlt">rift</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790011284','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790011284"><span id="translatedtitle"><span class="hlt">Final</span> <span class="hlt">system</span> instrumentation design package for Decade 80 solar house</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1978-01-01</p> <p>The <span class="hlt">final</span> configuration of the Decade 80 solar house to monitor and collect <span class="hlt">system</span> performance data is presented. A review demonstrated by actual operation that the <span class="hlt">system</span> 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 <span class="hlt">system</span> description, (2) operating and control modes, and (3) instrumentation program (including sensor schematic).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.T51D..02R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.T51D..02R"><span id="translatedtitle">Middle Jurassic - Early Cretaceous <span class="hlt">rifting</span> on the Chortis Block in Honduras: Implications for proto-Caribbean opening (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rogers, R. D.; Emmet, P. A.</p> <p>2009-12-01</p> <p>Regional mapping integrated with facies analysis, age constraints and airborne geophysical data reveal WNW and NE trends of Middle Jurassic to Early Cretaceous basins which intersect in southeast Honduras that we interpret as the result of <span class="hlt">rifting</span> associated with the breakup of the Americas and opening of the proto-Caribbean seaway. The WNW-trending <span class="hlt">rift</span> is 250 km long by 90 km wide and defined by a basal 200 to 800 m thick sequence of Middle to Late Jurassic fluvial channel and overbank deposits overlain by transgressive clastic shelf strata. At least three sub-basins are apparent. Flanking the WNW trending <span class="hlt">rift</span> basins are fault bounded exposures of the pre-Jurassic continental basement of the Chortis block which is the source of the conglomeratic channel facies that delineate the axes of the <span class="hlt">rifts</span>. Cretaceous terrigenous strata mantle the exposed basement-cored <span class="hlt">rift</span> flanks. Lower Cretaceous clastic strata and shallow marine limestone strata are dominant along this trend indicating that post-<span class="hlt">rift</span> related subsidence continued through the Early Cretaceous. The <span class="hlt">rifts</span> coincide with a regional high in the total magnetic intensity data. We interpret these trends to reflect NNE-WSW extension active from the Middle Jurassic through Early Cretaceous. These <span class="hlt">rifts</span> were inverted during Late Cretaceous shortening oriented normal to the <span class="hlt">rift</span> axes. To the east and at a 120 degree angle to the WNW trending <span class="hlt">rift</span> is the 300 km long NE trending Guayape fault <span class="hlt">system</span> that forms the western shoulder of the Late Jurassic Agua Fria <span class="hlt">rift</span> basin filled by > 2 km thickness of clastic marine shelf and slope strata. This NE trending basin coincides with the eastern extent of the surface exposure of continental basement rocks and a northeast-trending fabric of the Jurassic (?) metasedimentary basement rocks. We have previously interpreted the eastern basin to be the Jurassic <span class="hlt">rifted</span> margin of the Chortis block with the Guayape originating as a normal fault <span class="hlt">system</span>. These two <span class="hlt">rifts</span> basin intersect at near 120 degree angle in southeastern Honduras. We suggest that the intersection of these two trends represents part of a R-R-R triple junction during the breakup of the Americas. The WNW trending <span class="hlt">rift</span> produced the WNW trending fabric of the central Chortis block and failed in the Early Cretaceous while the NE trending <span class="hlt">rift</span> continued opening to form the south-facing passive margin of the northern proto-Caribbean basin.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19770028469&hterms=Trachyte&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DTrachyte','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19770028469&hterms=Trachyte&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DTrachyte"><span id="translatedtitle">The Sagatu Ridge dike swarm, Ethiopian <span class="hlt">rift</span> margin. [tectonic evolution</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mohr, P. A.; Potter, E. C.</p> <p>1976-01-01</p> <p>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 <span class="hlt">rift</span>-valley margin. Intrusion of the dikes and buildup of the flood-lava pile, largely hawaiitic but with trachyte preponderant in the <span class="hlt">final</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">rift</span> structures of unknown type appear to have limited the development of the ridge to the north and south.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Tectp.632...21M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Tectp.632...21M"><span id="translatedtitle">Left-lateral transtension along the Ethiopian <span class="hlt">Rift</span> and constrains on the mantle-reference plate motions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muluneh, Ameha A.; Cuffaro, Marco; Doglioni, Carlo</p> <p>2014-09-01</p> <p>We present the kinematics of the Ethiopian <span class="hlt">Rift</span>, in the northern part of East African <span class="hlt">Rift</span> <span class="hlt">System</span>, derived from compilation of geodetic velocities, focal mechanism inversions, structural data analysis and geological profiles. In the central Ethiopian <span class="hlt">Rift</span>, the GPS velocity field shows a systematic magnitude increase in ENE direction, and the incremental extensional strain axes recorded by earthquake focal mechanisms and fault slip inversion show ? N100°E orientation. This deviation between direction of GPS velocity vectors and orientation of incremental extensional strain is developed due to left lateral transtensional deformation along the NE-SW trending segment of the <span class="hlt">rift</span>. This interpretation is consistent with the en-échelon pattern of tensional and transtensional faults, plus the distribution of the volcanic centers, and the asymmetry of the <span class="hlt">rift</span> itself. We analyzed the kinematics of the Ethiopian <span class="hlt">Rift</span> also relative to the mantle comparing the results in the deep and shallow hotspot reference frames. While the oblique orientation of the <span class="hlt">rift</span> was controlled by the pre-existing lithospheric fabric, the two reference frames predict different kinematics of Africa and Somalia plates along the <span class="hlt">rift</span> itself, both in magnitude and direction, and with respect to the mantle. However, the observed kinematics and tectonics along the <span class="hlt">rift</span> are more consistent with a faster WSW-ward motion of Africa than Somalia observed in the shallow hotspot framework. The faster WSW motion of Africa with respect to Somalia plate is inferred to be due to the lower viscosity in the top asthenosphere (LVZ-low-velocity zone) beneath Africa. These findings have significant implication for the evolution of continental <span class="hlt">rifting</span> in transtensional settings and provide evidence for the kinematics of the Ethiopian <span class="hlt">Rift</span> in the context of the Africa-Somalia plate interaction in the mantle reference frame.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.2575K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.2575K"><span id="translatedtitle">Pre-<span class="hlt">rift</span> basement structure and syn-<span class="hlt">rift</span> faulting at the eastern onshore Gulf of Corinth <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kranis, Haralambos; Skourtsos, Emmanuel; Gawthorpe, Robert; Leeder, Mike; Stamatakis, Michael</p> <p>2015-04-01</p> <p>%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) <span class="hlt">Rift</span>. The onshore geology and structure of the GoC <span class="hlt">rift</span> 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 <span class="hlt">rift</span>, trying to address two major issues in <span class="hlt">rift</span> initiation and evolution, namely syn-<span class="hlt">rift</span> faulting and pre-<span class="hlt">rift</span> basement structure. While fault spacing and length appears to be well-constrained for the western and central parts of the GoC <span class="hlt">Rift</span>, 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-<span class="hlt">rift</span> 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 <span class="hlt">Rift</span>. Moreover, new field data provide new information on pre-<span class="hlt">rift</span> 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-<span class="hlt">rift</span> deposits, allows the identification and mapping of faults within this less studied area. Regarding the pre-<span class="hlt">rift</span> basement structure, not only the known, or inferred, pre-<span class="hlt">rift</span> heterogeneities along <span class="hlt">rift</span> axis, but also ongoing lithospheric processes affect the evolution of the GoC <span class="hlt">Rift</span>. The suggestion that the exposure of the deeper metamorphic Units at the southern border of the <span class="hlt">rift</span> 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 <span class="hlt">Rift</span> 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.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.4609K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.4609K"><span id="translatedtitle">Along-margin variations of magmatism at volcanic passive margins: Numerical models of continental extension with <span class="hlt">rift</span> propagation barriers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koopmann, Hannes; Brune, Sascha; Franke, Dieter; Breuer, Sonja</p> <p>2015-04-01</p> <p>Seaward-dipping reflectors (SDRs) constitute a first-order feature of volcanic <span class="hlt">rifted</span> margins and are imaged in seismic reflection profiles of the North and South Atlantic. Recent studies describe distinct along-strike variations in the distribution of SDRs, where abundance of volcanic material could be spatially linked to transfer fault <span class="hlt">systems</span>. These segmented the propagating <span class="hlt">rift</span> that later developed into the ocean, and are interpreted as <span class="hlt">rift</span> propagation barriers. Here we present 3d numerical forward models of a segmented <span class="hlt">rift</span> <span class="hlt">system</span> suggesting a causal link between segment boundaries and magmatic volume variations. Our results explain along-strike variations in magmatism by significant <span class="hlt">rift</span>-parallel mantle flow across segment boundaries. This <span class="hlt">rift</span>-parallel flow is caused by a lateral pressure gradient between sequentially opening segments. The along-strike flow of hot material near the segment boundary leads to elevated temperature and thus decompression melting if compared to the segment interior. This takes place without enhancing crustal thinning near the transfer zones and generates peaks in overall pre-break-up melt volumes. We conclude that delayed <span class="hlt">rift</span> propagation at inherited structures can play an important part in enhancing and localizing volcanic activity by controlling the mantle flow beneath the <span class="hlt">rift</span> axis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JDE...260.1472H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JDE...260.1472H"><span id="translatedtitle">Nonlinear Schrödinger <span class="hlt">systems</span> in 2d with nondecaying <span class="hlt">final</span> data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hayashi, Nakao; Li, Chunhua; Naumkin, Pavel I.</p> <p>2016-01-01</p> <p>We consider nonlinear Schrödinger <span class="hlt">systems</span> 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 <span class="hlt">final</span> data does not necessarily decay at spatial infinity and is small in uniform norm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/ED244581.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED244581.pdf"><span id="translatedtitle">Instructional <span class="hlt">Systems</span> Development Model for Interactive Videodisc. <span class="hlt">Final</span> Report.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Campbell, J. Olin; And Others</p> <p></p> <p>This third and <span class="hlt">final</span> report on a 3-year project, which developed authoring and production procedures for interactive videodisc based on the Interservice Procedures for Instructional <span class="hlt">Systems</span> Development (IPISD), reviews the current state of the art, provides an overview of the project, and describes two videodiscs made for the project and the…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/ED087154.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED087154.pdf"><span id="translatedtitle">Aural Study <span class="hlt">Systems</span> for the Visually Handicapped. <span class="hlt">Final</span> Report.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Nolan, Carson Y.; Morris, June E.</p> <p></p> <p>Presented is the <span class="hlt">final</span> report on development of an aural study <span class="hlt">system</span> which involved approximately 1000 visually handicapped elementary, secondary, and college students. Given is background information such as the relative effectiveness of reading and listening during study, and factors that affect listening comprehension such as learner…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5843286','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5843286"><span id="translatedtitle">Chromaticity corrections in the SLC <span class="hlt">final</span> focus <span class="hlt">system</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Toge, N.; Brown, K.; Burke, D.; Jacobsen, R.; Krejcik, P.; Ziemann, V.</p> <p>1991-05-01</p> <p>To best minimize the beam spot sizes at the interaction region in a linear collider, it is important to reduce chromatic aberrations at the focal point among other optical errors. In this paper we describe the chromaticity correction techniques that have been developed and applied to the SLC <span class="hlt">final</span> focus <span class="hlt">system</span>. The resultant improvements and procedural issues are discussed. 8 refs., 4 figs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T33C2283M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T33C2283M"><span id="translatedtitle">How does the continental crust thin during <span class="hlt">rifting</span> in magma-poor <span class="hlt">rifted</span> margins: evidence from the Bernina/Campo/Grosina units in the Central Alps (SE-Switzerland and N-Italy)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mohn, G.; Manatschal, G.; Masini, E.; Beltrando, M.; Muntener, O.; Kusznir, N. J.</p> <p>2010-12-01</p> <p>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 <span class="hlt">rifted</span> 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 <span class="hlt">rifted</span> margins. A more direct access to the stratigraphic record and crustal architecture of deep-water <span class="hlt">rifted</span> 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 <span class="hlt">rifted</span> margin. Within this necking zone, different high-strain shear zones responsible for lithospheric thinning can be defined including: 1) a <span class="hlt">system</span> 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 <span class="hlt">rifted</span> margins.The results of this study will permit to better constraints the extreme thinning of the crust leading <span class="hlt">finally</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/842264','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/842264"><span id="translatedtitle">Study of a <span class="hlt">final</span> focus <span class="hlt">system</span> for high intensity beams</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Henestroza, Enrique; Eylon, Shmuel; Roy, Prabir K.; Yu, Simon S.; Bieniosek, Frank M.; Shuman, Derek B.; Waldron, William L.</p> <p>2004-06-01</p> <p>The NTX experiment at the Heavy Ion Fusion Virtual National Laboratory is exploring the performance of neutralized <span class="hlt">final</span> focus <span class="hlt">systems</span> for high perveance heavy ion beams. The <span class="hlt">final</span> 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 <span class="hlt">final</span> 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 <span class="hlt">final</span> quadrupole focusing <span class="hlt">system</span> produces a converging beam at the entrance to the neutralized drift section where it focuses to a small spot. The <span class="hlt">final</span> 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 <span class="hlt">final</span> beam size. In particular, we present theoretical and experimental results on the dependence of <span class="hlt">final</span> spot size on geometric aberrations and perveance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoRL..42.2179K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoRL..42.2179K"><span id="translatedtitle">Magmatism on <span class="hlt">rift</span> flanks: Insights from ambient noise phase velocity in Afar region</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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</p> <p>2015-04-01</p> <p>During the breakup of continents in magmatic settings, the extension of the <span class="hlt">rift</span> 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 <span class="hlt">rift</span> 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 <span class="hlt">systems</span> but also both upper and lower crust beneath the <span class="hlt">rift</span> flanks where ongoing volcanism and hydrothermal activity occur at the surface. Magmatic modification of the crust beneath <span class="hlt">rift</span> flanks likely occurs for a protracted period of time during the breakup process and may persist through to early seafloor spreading.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S13B4453W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S13B4453W"><span id="translatedtitle">SPREE: A Successful Seismic Array by a Failed <span class="hlt">Rift</span> <span class="hlt">System</span>; Analysis of Seismic Noise in the Seismically Quiet Mid-continent</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wolin, E.; van der Lee, S.; Bollmann, T. A.; Revenaugh, J.; Aleqabi, G. I.; Darbyshire, F. A.; Frederiksen, A. W.; Wiens, D.; Shore, P.</p> <p>2014-12-01</p> <p>The Superior Province <span class="hlt">Rifting</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6281389','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6281389"><span id="translatedtitle">A conceptual design of <span class="hlt">Final</span> Focus <span class="hlt">Systems</span> for linear colliders</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Brown, K.L.</p> <p>1987-06-01</p> <p>Linear colliders are a relatively recent development in the evolution of particle accelerators. This report discusses some of the approaches that have been considered for the design of <span class="hlt">Final</span> Focus <span class="hlt">Systems</span> to demagnify the beam exiting from a linac to the small size suitable for collisions at the interaction point. The <span class="hlt">system</span> receiving the most attention is the one adopted for the SLAC Linear Collider. However, the theory and optical techniques discussed should be applicable to the design efforts for future machines.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/148695','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/148695"><span id="translatedtitle">Investigation of <span class="hlt">rifting</span> processes in the Rio Grande <span class="hlt">Rift</span> using data from unusually large earthquake swarms</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Sanford, A.; Balch, R.; House, L.; Hartse, H.</p> <p>1995-12-01</p> <p>San Acacia Swarm in the Rio Grande <span class="hlt">Rift</span>. Because the Rio Grande <span class="hlt">rift</span> is one of the best seismically instrumented <span class="hlt">rift</span> zones in the world, studying its seismicity provides an exceptional opportunity to explore the active tectonic processes within continental <span class="hlt">rifts</span>. We have been studying earthquake swarms recorded near Socorro in an effort to link seismicity directly to the <span class="hlt">rifting</span> 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 <span class="hlt">rift</span>. The swarm commenced on 25 February 1983, had a magnitude 4.2 main shock on 2 March and ended on 17 March, 1983.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997JSG....19..755M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997JSG....19..755M"><span id="translatedtitle">Controls on the development and evolution of transfer zones: the influence of basement structure and sedimentary thickness in the Suez <span class="hlt">rift</span> and Red Sea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Moustafa, Adel R.</p> <p>1997-06-01</p> <p>Detailed field mapping of the northern part of the Gebel Um Hammad-Gebel Duwi area on the western margin of the Red Sea indicates oppositely dipping <span class="hlt">rift</span> blocks separated by a 60-km long, WNW-ESE-oriented, reactivated pre-<span class="hlt">rift</span> fault of Late Precambrian age parallel to the Najd fault <span class="hlt">system</span> of the Arabian-Nubian Shield. This fault forms the Sudmain transfer zone between the oppositely tilted half-grabens in the northwestern Red Sea region and is associated by a SE-plunging syncline. This pre-<span class="hlt">rift</span> fault was reactivated by dextral transtension during the Late Oligocene <span class="hlt">rift</span> opening. Compared to the transfer zones of the Suez <span class="hlt">rift</span>, the Sudmain transfer zone is narrower. The Gebel Sufr El Dara transfer zone (between the southern and central half-grabens of the Suez <span class="hlt">rift</span>) is 20 km wide and is also controlled by pre-<span class="hlt">rift</span> faults oriented ENE-WSW. The latter were reactivated by left-lateral slip during the <span class="hlt">rift</span> opening. On the other hand, the Gharandal transfer zone (northern part of the Suez <span class="hlt">rift</span>) is 40-60 km wide and is not affected by the pre-<span class="hlt">rift</span> faults in the Precambrian basement, perhaps owing to the large thickness of pre-<span class="hlt">rift</span> sedimentary rocks in this area. The location of the Gharandal transfer zone was controlled by a NE-SW-oriented 'Syrian arc' fold. This study suggests that the northward increase in the width of transfer zones as well as the northward decrease in the length of half-grabens in the Suez-northern Red Sea <span class="hlt">rift</span> <span class="hlt">system</span> are related to the corresponding increase in the thickness of pre-<span class="hlt">rift</span> Phanerozoic sedimentary section from about 400 m in the south to about 1800 m in the north.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.8467S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.8467S"><span id="translatedtitle">Three-Dimensional (3D) Structure of the Malawi <span class="hlt">Rift</span> from Remote Sensing and Geophysics Data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Salmi, Haifa S. Al; Abdelsalam, Mohamed G.</p> <p>2014-05-01</p> <p>The Malawi <span class="hlt">rift</span> is a Cenozoic aged <span class="hlt">rift</span> representing the southernmost segment of the Western Branch of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS). This <span class="hlt">rift</span> extends over 900 km from the Rungwe volcanic province (Tanzania) in the north to the Urema graben (Mozambique) to the south, with an average width of 50km. It traverses a complex array of Proterozoic orogenic belts of different ages and Permo-Triassic (Karoo) and cretaceous graben <span class="hlt">systems</span>. The <span class="hlt">rift</span>'s depth is between 3 to 5km partitioned between the topographic escarpment and the sediments fill. The basin's subsidence reflects accumulation of sediments and <span class="hlt">rift</span> flank uplift. Regardless of its importance in understanding <span class="hlt">rift</span> tectonics, especially in Africa, the three-dimensional (3D) geometry of the <span class="hlt">rift</span> is not fully understood. This research presents results from detailed analysis of Digital Elevation Model (DEM) extracted from the Shuttle Radar Topography Mission (SRTM) data to map surface morphological expressions of the entire basin. These results are compared with available seismic data to provide along-strike and at depth variation of the geometry of the border fault <span class="hlt">systems</span>, nature of <span class="hlt">rift</span> segmentation and alternation of the polarity of half-grabens, and the partitioning of displacement between exposed and sub-surface border faults. Our results show the following: (1) Surface expression of border faults show that, unlike the typical half-graben en-echelon <span class="hlt">rift</span> model, where half-graben segments with opposite polarity are linked together through accommodation zones indicative of soft linkage, the Malawi <span class="hlt">rift</span> shows along-strike segmentation by changing geometry from half-graben to full graben geometry. A half-graben with specific polarity passes through a full-graben geometry before giving place to a half-graben with the opposite polarity. The length of half-gaben and graben segments becomes shorter as the <span class="hlt">rift</span> progresses from north to south, and this is accompanied by a decrease in displacement within border faults. This geometry is indicative of the propagation of border faults through hard linkage. (2) The continuation of border faults at the subsurface show patterns consistent with those observed at the surface. At the sub-surface, the general trend of <span class="hlt">rift</span> segmentation, formation of full grabens at the end of each segment, and the decreases in the length of the segments from north to south is consistent with observations at the surface. This suggests the homogeneity of strain accommodation throughout the depth of border faults. (3) Zones of segmentation of the Malawi <span class="hlt">rift</span> coincide with regions where the pre-existing structures (both the Proterozoic basement and the Karoo grabens) are at high angle to the trend of the <span class="hlt">rift</span> whereas well-developed border faults of the basin coincides with N-trending pre-existing structures sub-parallel to the <span class="hlt">rift</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1225431','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1225431"><span id="translatedtitle">Immersive Visualization for Materials Science Data Analysis using the Oculus <span class="hlt">Rift</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Drouhard, Margaret MEG G; Steed, Chad A; Hahn, Steven E; Proffen, Thomas E; Daniel, Jamison R; Matheson, Michael A</p> <p>2015-01-01</p> <p>In this paper, we propose strategies and objectives for immersive data visualization with applications in materials science using the Oculus <span class="hlt">Rift</span> 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 <span class="hlt">system</span>, developed in conjunction with materials scientists at the Spallation Neutron Source, which we have used to explore large crystal structures and neutron scattering data. <span class="hlt">Finally</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhDT.......147H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhDT.......147H"><span id="translatedtitle">Geophysical investigations of the Espanola basin, Rio Grande <span class="hlt">rift</span>, northern New Mexico</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Harper, Christopher</p> <p></p> <p>Seismic and gravity data collected by the Summer of Applied Geophysical Experience (SAGE), along with energy-industry seismic data, well data, and geologic maps, go into the construction of geologic cross sections transecting the Rio Grande <span class="hlt">rift</span> in the area of the Espanola basin. These cross sections reveal several key structures within the basin including the eastern bounding fault of the Los Alamos graben, and the Agua Fria fault <span class="hlt">system</span> near the eastern boundary of the basin. Additionally, I find no evidence in the data presented here supporting the linking of the Embudo and Santa Clara faults. <span class="hlt">Finally</span>, by flattening the geologic cross sections on several unconformity surfaces, a temporal structural progression of the study area is developed. Using the resulting paleo cross sections, I show that the trend of the Laramide Sangre de Cristo uplift likely varied markedly from the modern uplift.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GGG....14.2575S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GGG....14.2575S"><span id="translatedtitle">Quantification and restoration of extensional deformation along the Western Iberia and Newfoundland <span class="hlt">rifted</span> margins</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sutra, Emilie; Manatschal, Gianreto; Mohn, Geoffroy; Unternehr, Patrick</p> <p>2013-08-01</p> <p>Many recent papers describe the structure of the Iberia and Newfoundland <span class="hlt">rifted</span> margins; however, none of them propose kinematic restorations of the complete <span class="hlt">rift</span> <span class="hlt">system</span> to quantify the amount of extension necessary to exhume mantle and initiate seafloor spreading. In our study, we use two pairs of cross sections considered as conjugate lines: one across the Galicia Bank-Flemish Cap and the other across the Southern Iberia Abyssal Plain-Flemish Pass. Both transects have been imaged by reflection- and refraction-seismic methods and have been drilled during Ocean Drilling Program Legs 103, 149, 173, and 210. Drilling penetrated parts of the <span class="hlt">rift</span> stratigraphy and the underlying basement. The cross sections can therefore be considered as the best-documented conjugate transects across present-day hyperextended, magma-poor <span class="hlt">rifted</span> margins. The aim of this paper is threefold: (1) provide a detailed description of the crustal architecture of the two conjugate sections, (2) define the extensional structures and their ages, and (3) quantify the amount of strain and strain rate accommodated along these lines. This paper proposes a quantitative description of extension along the Iberia-Newfoundland <span class="hlt">rift</span> <span class="hlt">system</span> and discusses the limitations and problems in quantifying extensional deformation along hyperextended <span class="hlt">rifted</span> margins.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA.....2716D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA.....2716D"><span id="translatedtitle"><span class="hlt">Rift</span> to drift transition in Siberian Arctic and its impact on continental margin architecture</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Drachev, S. S.</p> <p>2003-04-01</p> <p>The East Siberian Arctic Continental Margin (ESAM) represents a rare case of <span class="hlt">rifting</span> to spreading transition. Present-day geodynamics of this plate tectonic interplay is characterized by a very slow plate divergence in the Laptev Sea as this regions is located just landward of the slowest spreading center worldwide (the Gakkel Ridge), close to the pole of North American/Eurasian plate rotation. However the existing geological and geophysical data, mainly seismic reflection and potential field data, allow conclusion that this situation has been far different in the past. Just after its formation at the end of Late Cretaceous through a series of plate convergence and folding episodes the crust of the ESAM has been strongly modified by an intense <span class="hlt">rifting</span>. The earliest <span class="hlt">rift</span> episode took place eastward of the present Laptev Sea, in the East Siberian Sea and probably Chukchi seas, where presently abandoned <span class="hlt">rifts</span> are stretched landward along the principal weakened zones in the ESAM basement. This <span class="hlt">rifting</span> might have been related to a spreading episode in the Amerasia Basin and perhaps was triggered by a mantle plume ca. 120 mln. yr. ago (De Long and Franz Joseph Land basalts). Outer parts of the ERAM might have also been <span class="hlt">rifted</span> away to create marginal blocks, as the Arlis and Chukchi plateau. Second <span class="hlt">rift</span> event was clearly related to the opening of the Eurasia Basin, preceding it and remaining active through the Cenozoic. The <span class="hlt">rift</span> to drift transition has been taking place in a huge, “dry” and still active Laptev <span class="hlt">Rift</span> <span class="hlt">System</span>, which is a landward projection of the Gakkel Ridge spreading axis. This extension had a major effect on the western ERAM causing strong normal faulting and crustal thinning, up to 70% in some places. However, total crustal extension in the Laptev <span class="hlt">Rift</span> <span class="hlt">System</span> is considerably smaller than a value of total opening of the Eurasia Basin, so the spreading is not completely accommodated by the <span class="hlt">rifting</span>. It may be speculated that a major portion of this extension, especially at its initial stage, has been transferred along the Khatanga-Lomonosov Fracture (Charlie Fault by A. Grantz) far to the east. These transcurrent movements shifted the Lomonosov Ridge eastward along the Laptev Sea margin. Further to the east the Early Tertiary extensional features of the Chukchi Borderland and Maastrichtian-Paleocene alkaline volcanism of the Chukchi Peninsula may be attributed