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Sample records for rift system final

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  2. 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.

  3. Cenozoic rifting in the West Antarctic Rift System

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  4. 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. 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.

  6. 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.

  7. 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

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

    SciTech Connect

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

    1984-04-01

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

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

    SciTech Connect

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

    1984-04-01

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

  10. 3D Dynamics of Oblique Rift Systems: Fault Evolution from Rift to Break-up

    NASA Astrophysics Data System (ADS)

    Brune, S.

    2014-12-01

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

  11. 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.

  12. The Mesoproterozoic Midcontinent Rift System, Lake Superior Region, USA

    NASA Astrophysics Data System (ADS)

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

    2001-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

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

    SciTech Connect

    Cunningham, A.C.; Armentrout, J.M.; Prebish, M. )

    1996-01-01

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

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

    SciTech Connect

    Cunningham, A.C.; Armentrout, J.M.; Prebish, M.

    1996-12-31

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

  2. 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.

  3. 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.

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

    NASA Technical Reports Server (NTRS)

    Mohr, P. A. (Principal Investigator)

    1973-01-01

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

  5. 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.

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

    NASA Technical Reports Server (NTRS)

    Mohr, P. A. (Principal Investigator)

    1972-01-01

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

  7. Benue trough and the mid-African rift system

    SciTech Connect

    Thomas, D.

    1996-01-29

    Large areas of the Anambra and Gongola basins have distinct petroleum exploration problems: a geologically persistent high geothermal gradient that promoted Cretaceous source rock maturation into the gas phase very early on; intrusive lead-zinc mineralization veins attributed to the Senonian igneous and folding event; and meteoric water-flushing along the periphery of the basins. From preliminary analysis, these basins have to be considered high risk for the discovery of commercial oil accumulations. On the other hand, the petroleum potential of the Bornu basins seems favorable. This Nigerian northernmost rift basin continues into the Kanem basin of western Chad, which has proven oil accumulations in Coniacian deltaic sands. Cretaceous paleofacies is considered to be relatively continuous throughout both basins. Paleo-geothermal history is also considered to be similar, although some igneous activity is recorded in the Bornu basin (Senonian?). There is a very real possibility of kerogen-rich non-marine basal Albo-Aptian basin fill lacustrine source rocks, as found in the Doba basin, could be present in the deepest sections of the Nigerian rift basins. Due to the depths involved, no well is expected to penetrate the incipient graben-fill stage sequences; however, possible oil migration from these tectono-stratigraphic units would certainly enhance the petroleum potential of cooler sections of the rift system. As opposed to interpreted thermogenic gas which seems to be prevalent in the Anambra basin.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

    Rilling, Sarah E.

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

  13. 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 Maulon 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.

  14. 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 β = 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.

  15. 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.

  16. Volcanic water flows could have flooded Ganymede's planetary rift system

    SciTech Connect

    Allison, M.L.; Clifford, S.M.

    1985-01-01

    Global expansion on Ganymede of only 1 or 2% created a planetary rift system which was resurfaced over a significant period of the planet's history creating bright, grooved terrain. The most reasonable model entails flooding of grabens by water or slush magmas which rose to the surface along normal faults in the rift system. Various models exist for the origin of the water magmas including isostatic rise of freezing ice I or diapirs of unstable ice III. A model considering the heat balance at the surface of an ice-covered water flow is constructed with the simplifying assumption that both laminar flow and a solid ice cover are achieved relatively soon after eruption. The ice cover will thicken until the underlying flowing water is entirely frozen. Energy into the system comes from solar radiation and the latent heat of freezing. Energy lost will be by evaporative and radiative cooling at the ice surface and by conduction into the substratum. Solving the heat balance allows a prediction for the volume of magma that can flood the surface. For example a flow 5 m thick will take tens of days to freeze, so that discharge rates equal to that of average terrestrial basalt flows could flood relatively large areas of the surface before freezing. Volcanic flooding is therefore a physically viable mechanism for the origin of bright terrain. During freezing the water/ice volume increases, lifting and fracturing the ice cover. These fractures may localize continued tectonic forces producing large displacements and creating the present grooved terrain.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. Plate kinematics of the Afro-Arabian Rift System with emphasis on the Afar Depression, Ethiopia

    NASA Astrophysics Data System (ADS)

    Bottenberg, Helen Carrie

    This work utilizes the Four-Dimensional Plates (4DPlates) software, and Differential Interferometric Synthetic Aperture Radar (DInSAR) to examine plate-scale, regional-scale and local-scale kinematics of the Afro-Arabian Rift System with emphasis on the Afar Depression in Ethiopia. First, the 4DPlates is used to restore the Red Sea, the Gulf of Aden, the Afar Depression and the Main Ethiopian Rift to development of a new model that adopts two poles of rotation for Arabia. Second, the 4DPlates is used to model regional-scale and local-scale kinematics within the Afar Depression. Most plate reconstruction models of the Afro-Arabian Rift System relies on considering the Afar Depression as a typical rift-rift-rift triple junction where the Arabian, Somali and Nubian (African) plates are separating by the Red Sea, the Gulf of Aden and the Main Ethiopian Rift suggesting the presence of "sharp and rigid" plate boundaries. However, at the regional-scale the Afar kinematics are more complex due to stepping of the Red Sea propagator and the Gulf of Aden propagator onto Afar as well as the presence of the Danakil, Ali Sabieh and East Central Block "micro-plates". This study incorporates the motion of these micro-plates into the regional-scale model and defined the plate boundary between the Arabian and the African plates within Afar as likely a diffused zone of extensional strain within the East Central Block. Third, DInSAR technology is used to create ascending and descending differential interferograms from the Envisat Advanced Synthetic Aperture Radar (ASAR) C-Band data for the East Central Block to image active crustal deformation related to extensional tectonics and volcanism. Results of the DInSAR study indicate no strong strain localization but rather a diffused pattern of deformation across the entire East Central Block.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Twenty-five years of geodetic measurements along the Tadjoura-Asal rift system, Djibouti, East Africa

    NASA Astrophysics Data System (ADS)

    Vigny, Christophe; de Chabalier, Jean-Bernard; Ruegg, Jean-Claude; Huchon, Philippe; Feigl, Kurt L.; Cattin, Rodolphe; Asfaw, Laike; Kanbari, Khaled

    2007-06-01

    Since most of Tadjoura-Asal rift system sits on dry land in the Afar depression near the triple junction between the Arabia, Somalia, and Nubia plates, it is an ideal natural laboratory for studying rifting processes. We analyze these processes in light of a time series of geodetic measurements from 1978 through 2003. The surveys used triangulation (1973), trilateration (1973, 1979, and 1981-1986), leveling (1973, 1979, 1984-1985, and 2000), and the Global Positioning System (GPS, in 1991, 1993, 1995, 1997, 1999, 2001, and 2003). A network of about 30 GPS sites covers the Republic of Djibouti. Additional points were also measured in Yemen and Ethiopia. Stations lying in the Danakil block have almost the same velocity as Arabian plate, indicating that opening near the southern tip of the Red Sea is almost totally accommodated in the Afar depression. Inside Djibouti, the Asal-Ghoubbet rift system accommodates 16 ± 1 mm/yr of opening perpendicular to the rift axis and exhibits a pronounced asymmetry with essentially null deformation on its southwestern side and significant deformation on its northeastern side. This rate, slightly higher than the large-scale Arabia-Somalia motion (13 ± 1 mm/yr), suggests transient variations associated with relaxation processes following the Asal-Ghoubbet seismovolcanic sequence of 1978. Inside the rift, the deformation pattern exhibits a clear two-dimensional pattern. Along the rift axis, the rate decreases to the northwest, suggesting propagation in the same direction. Perpendicular to the rift axis, the focus of the opening is clearly shifted to the northeast, relative to the topographic rift axis, in the "Petit Rift," a rift-in-rift structure, containing most of the active faults and the seismicity. Vertical motions, measured by differential leveling, show the same asymmetric pattern with a bulge of the northeastern shoulder. Although the inner floor of the rift is subsiding with respect to the shoulders, all sites within the rift system show uplift at rates varying from 0 to 10 mm/yr with respect to a far-field reference outside the rift.

  18. 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.

  19. 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.

  20. 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.

  1. 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/2008AGUFM.S31A1879K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.S31A1879K"><span id="translatedtitle">Surface-wave Tomography of East African <span class="hlt">Rift</span> <span class="hlt">System</span> using Ambient Seismic Noise</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kim, S.; Kang, T.; Baag, C.; Nyblade, A. A.</p> <p>2008-12-01</p> <p>The surface-wave tomography technique for the ambient seismic noise is applied to the east African <span class="hlt">rift</span> <span class="hlt">system</span> to investigate shallow crustal structures of the region. Even if the technique has been widely used in many regions to investigate crustal structure in the world, there have been difficulties in application of the technique to the east African region because of unstable data conditions of PASSCAL experiments. A meticulous check of record by record enables us of applying the technique to understand the tectonic environment of the region. The long-period data of one month showing good quality in cross-correlation results are used in this study. They are from the 1994-95 Tanzania Passive-Source Seismic Experiment for the Tanzania craton and its surrounding <span class="hlt">rift</span> zone, and from the 2000-02 Ethiopia/Kenya Broadband Seismic Experiment and the adjacent permanent stations of the African Array for the Ethiopia <span class="hlt">rift</span>. The Rayleigh- and Love-wave group-speed maps were inverted using LSQR algorithm for several period bands (5 - 50 s). The preliminary group-speed distribution maps yield results roughly consistent with regional geology. The tomographic images of the Tanzania region show a strong high velocity anomaly at the location corresponding to the Tanzania craton and low velocity anomalies at the surrounding <span class="hlt">rift</span> regions. For the Ethiopia regions, the features of low velocity anomalies roughly agree with the Tertiary volcanic regions. Combining the Tanzania and Ethiopia broadband arrays, the outline of the east African <span class="hlt">rift</span> <span class="hlt">system</span> can be identified as the low velocity anomalies in the surface-wave tomographic results. The structural variation with depth and the feature of the regional shear-wave anisotropy of crust will be explored by converting group- speed dispersion curves into shear-wave velocity structure.</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://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/2009Tectp.468...28A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009Tectp.468...28A"><span id="translatedtitle">Crustal rheology and depth distribution of earthquakes: Insights from the central and southern 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>Albaric, Julie; Déverchère, Jacques; Petit, Carole; Perrot, Julie; Le Gall, Bernard</p> <p>2009-04-01</p> <p>The seismicity depth distribution in the central and southern East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) is investigated using available catalogs from local, regional and global networks. We select well-determined events and make a re-assessment of these catalogs, including a relocation of 40 events and, where necessary, a declustering. About 560 events are <span class="hlt">finally</span> used for determining foci depth distribution within 6 areas of the EARS. Assuming that short-term deformation expressed by seismicity reflects the long-term mechanical properties of the lithosphere, we build yield strength envelopes from seismicity depth distribution. Using brittle and ductile laws, we predict the strength percentage spaced every 5 km (or sometimes 2 km) in the crust, for a given composition and a specific geotherm, and constrain it with the relative abundance of seismicity. Results of this modeling indicate significant local and regional variations of the thermo-mechanical properties of the lithosphere which are broadly consistent with previous studies based on independent modelings. In order to explain relatively deep earthquakes, a highly resistant, mafic lower crust is generally required. We also find evidence for changes in the strength magnitude and in the depth of the brittle-ductile transitions which are clearly correlated to tectonic provinces, characterized by contrasted thermal gradients and basement types. A clear N-S increase and deepening of the peak strength level is evidenced along the eastern branch of the EARS, following a consistent southward migration of <span class="hlt">rifting</span> since ~ 8 Ma. We also detect the presence of a decoupling layer in the Kenya <span class="hlt">rift</span>, which suggests persisting influences of the deep crustal structures (Archaean and Proterozoic) on the behavior of the extending crust. More generally, our results suggest that seismicity peaks and cut-off depths may provide good proxies for bracketing the brittle-ductile transitions within the continental crust.</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://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/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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFM.T11A1232P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFM.T11A1232P"><span id="translatedtitle">Neogene-Quaternary Volcanic Alignments in the Transantarctic Mountains and West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> of Southern Victoria Land, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Paulsen, T. S.; Wilson, T. J.</p> <p>2004-12-01</p> <p>Neogene-Quaternary volcanism in southern Victoria Land, Antarctica, produced the Erebus Volcanic Province, a suite of alkaline volcanic rocks that extend from the Transantarctic Mountains <span class="hlt">rift</span>-flank uplift to offshore localities within the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>. We are mapping volcanic vent patterns in the province to detect alignments indicative of stress/strain patterns during <span class="hlt">rift</span> evolution. In the southern sector of the Erebus Volcanic Province in the Royal Society Range Block of the Transantarctic Mountains, mapping shows that elliptical scoria cones, fissures, dikes, and linear vent arrays define volcanic alignments that have a dominant NNE trend, with subsidiary WNW trends. Age data for the alignments suggest that this pattern persisted from 14.6 to 0.25 Ma. We are currently completing mapping along an east-west transect crossing the <span class="hlt">rift</span> margin, and results obtained so far within the <span class="hlt">rift</span> region indicate a similar pattern of alignments. On the northern flank of Mount Morning, a large volcano just to the east of the Royal Society Range, elliptical scoria cones and linear vent arrays define volcanic alignments that have a dominant NE trend, with a subsidiary NNW trend. Available age data suggest that many of these cone alignments may be of Quaternary age. At Brown Peninsula, further east from the <span class="hlt">rift</span> flank, cone alignments trend NNE and available ages range from 2 to 3 Ma. To the east of Brown Peninsula, cone alignments trend NW at Black Island, but are of uncertain age; age data on Black Island range from 11 to 3.4 Ma. At White Island, the farthest east into the <span class="hlt">rift</span>, cone alignments trend NNE and available age data suggest volcanism as young as 0.2 Ma. Although some differences in cone alignment trends are apparent between the <span class="hlt">rift</span> flank and the <span class="hlt">rift</span> <span class="hlt">system</span> across our transect, both regions appear to be dominated by NE trending alignments, which implies a WNW to NW minimum horizontal stress (Shmin) direction. This is oblique to the ENE Shmin Cape Roberts in situ contemporary stress direction determined from borehole breakouts and induced core fractures, and to a single volcanic stress alignment of Neogene age within the <span class="hlt">rift</span> flank in that sector. In both regions the Shmin direction is perpendicular to the interpreted trend of the structural boundary of the <span class="hlt">rift</span>. The stress directions inferred from volcanic alignments are thus consistent with spatial changes in the Neogene-to-contemporary stress field.</p> </li> <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/1987Geo....15..430W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1987Geo....15..430W"><span id="translatedtitle">Chow Bahir <span class="hlt">rift</span>: A “failed” <span class="hlt">rift</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>W-Gabriel, Giday; Aronson, James L.</p> <p>1987-05-01</p> <p>The Chow Bahir <span class="hlt">rift</span> <span class="hlt">system</span> is a major graben in a 300-km-broad <span class="hlt">rift</span> zone recognized in southern Ethiopia between the Kenyan and Ethiopian domes where the East African <span class="hlt">rift</span> is not well defined. An extinct (failed) <span class="hlt">rift</span> discovered along the Omo Canyon to the north and on strike with the Chow Bahir <span class="hlt">rift</span> ceased activity about 4 m.y. ago. Chow Bahir is in a younger stage of abandonment as the main Ethiopian <span class="hlt">rift</span> propagates south into this region.</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/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> </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://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/2009AGUFM.T31B1815F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.T31B1815F"><span id="translatedtitle"><span class="hlt">Rift</span>-Related Volcanism in Afar</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ferguson, D. J.; Barnie, T. D.; Pyle, D. M.; Oppenheimer, C.; Yirgu, G.; Hamling, I. J.</p> <p>2009-12-01</p> <p>Opportunities to observe active magma-mediated <span class="hlt">rifting</span> episodes are rare, and consequently the volcanic characteristics of dynamic <span class="hlt">rift</span> <span class="hlt">systems</span> are not well known. The currently ongoing phase of magmatic <span class="hlt">rifting</span> along a section of the Red Sea <span class="hlt">system</span> in Afar, Ethiopia, presents an exceptional opportunity to provide constraints on the volcanic component of crustal growth and to examine the relations between intrusive and extrusive magmatism. Here we characterise two recent (August 2007 and June 2009) basaltic fissure eruptions from the Manda-Hararo <span class="hlt">rift</span>, Afar, and evaluate the role and significance of volcanism in the <span class="hlt">rifting</span> process. Both eruptions were short period events (36-72 hours) with erupted bulk lava volumes of 4.4 - 18 × 10^6 m3 erupted from a fissure <span class="hlt">system</span> 4 - 6.5 km in length. Supplementing field observations with data from a range of satellite borne instrumentation (i.e., MODIS, OMI, ASTER, ALI) was critical to both the identification and subsequent analysis of these eruptions. Combing data on these eruptions with geophysical models of the intrusive activity in Afar we assess the partitioning of magma between intrusion and volcanism for the Afar <span class="hlt">rifting</span> phase thus far. By comparing this to data from the 1975-1984 Krafla <span class="hlt">rifting</span> cycle we examine the likely evolution of intrusive - extrusive magma relations as the Afar activity progresses. The current activity in Afar (since Sept. 2005) has an intrusive to extrusive magma volume ratio of ~180:1. This is similar to the equivalent stage of the Krafla cycle, which had a <span class="hlt">final</span> volume ratio of 3:1. Comparing the temporal trends of intrusive and extrusive magmatism and the physical features of volcanism (fissure length, duration, volume) between Krafla and Afar we expect that, should the Afar activity continue, the volcanic output will increase significantly and will be accommodated by eruptions of increasingly large size, rather then by more frequent but small magnitude events.</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; Prmmel, 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://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://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://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/543374','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/543374"><span id="translatedtitle">Estimating the age of formation of lakes: An example from Lake Tanganyika, East African <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>Cohen, A.; Soreghan, M.J.; Scholz, C.A.</p> <p>1993-06-01</p> <p>Age estimates for ancient lakes are important for determining their histories and their rates of biotic and tectonic evolution. In the absence of dated core material from the lake`s sedimentary basement, several techniques have been used to generate such age estimates. The most common of these, herein called the reflection seismic-radiocarbon method (RSRM), combines estimates of short-term sediment-accumulation rates derived from radiocarbon-dated cores and depth-to-basement estimates derived from reflection-seismic data at or near the same locality to estimate an age to basement. Age estimates form the RSRM suggest that the structural basins of central Lake Tanganyika began to form between 9 and 12 Ma. Estimates for the northern and southern basins are younger (7 to 8 Ma and 2 to 4 Ma, respectively). The diachroneity of estimates for different segments of the lake is equivocal, and may be due to erosional loss of record in the northern and southern structural basins or to progressive opening of the <span class="hlt">rift</span>. The RSRM age estimates for Lake Tanganyika are considerably younger than most prior estimates and clarify the extensional history of the western branch of the East African <span class="hlt">Rift</span> <span class="hlt">system</span>. 31 refs., 3 figs., 1 tab.</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://www.ncbi.nlm.nih.gov/pubmed/17778134','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/17778134"><span id="translatedtitle">The 1990 to 1991 Sudan earthquake sequence and the extent of 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>Girdler, R W; McConnell, D A</p> <p>1994-04-01</p> <p>One of the largest earthquakes ever recorded in Africa (surface wave magnitude M(s) = 7.2) occurred about 50 kilometers east of the Upper River Nile on 20 May 1990. Four days later, two more large earthquakes (M(s) = 6.4 and 7.0) occurred about 50 kilometers to the northwest in the Nile Valley. In the following months, a further 60 events were recorded by seismic stations worldwide. The earthquakes are associated with two fault <span class="hlt">systems</span>: one east of the Nile with azimuth southeast and one along the Nile Valley with azimuth north-northeast. The activity alternated between the two fault <span class="hlt">systems</span> and indicates that the northern extremity of the western branch of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> extends at least 350 kilometers north of Lake Albert. PMID:17778134</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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T41G..08R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T41G..08R"><span id="translatedtitle">Development of Magma Reservoirs during the <span class="hlt">Final</span> Stages of <span class="hlt">Rifting</span> - the Role of the Continental Lithosphere in Magma Genesis in the 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>Rooney, T. O.; Yirgu, G.; Dosso, L.</p> <p>2012-12-01</p> <p>The Afar depression, which lies at the intersection of the East African <span class="hlt">Rift</span> <span class="hlt">system</span>, the Red Sea and Gulf of Aden, is a key target in understanding the transition from continental <span class="hlt">rifting</span> to oceanic spreading. Critical to this transition is thinning of the lithospheric mantle and the commencement of dominantly asthenospheric decompression melting. Lithospheric stretching and elevated mantle potential temperatures have facilitated melt production and these magmatic products may be used to probe conditions of melt generation beneath the Afar depression. Quaternary basalts in the region exhibit an array of trace element characteristics that extend from enriched to somewhat depleted. The more trace element enriched samples share similar characteristics to basalts from the Main Ethiopian <span class="hlt">Rift</span>, interpreted to represent a mixture of asthenospheric and lithospheric reservoirs. However, a subset of basalts from the Afar depression exhibits a distinctive depletion in the most incompatible trace elements, Ti, K, and P. These Afar depression depleted basalts (ADDB) have no correlative within the Ethiopian <span class="hlt">Rift</span> and are distinguished from regional MORB suites by radiogenic Pb and Sr values. The ADDB suite have Pb isotopes that overlap with the least radiogenic end of the Main Ethiopian <span class="hlt">rift</span> array, but display more radiogenic Nd isotopes. The ɛHf- ɛNd values of the ADDB suite fall in a tight cluster substantially above the mantle array. The isotopic characteristics of the ADDB suite cannot be explained by melting of existing inferred asthenospheric or lithospheric reservoirs. Alternatively, we suggest the ADDB suite is the result of melting at shallow levels in the lithospheric mantle. Advanced lithospheric thinning within the Afar depression has exposed this shallow reservoir to melt generation. In less extended regions, such as in the Ethiopian <span class="hlt">rift</span>, thicker lithospheric mantle prevents melt generation within this shallow lithospheric mantle reservoir, consistent with the restricted occurrence of the ADDB suite to the Afar depression. Thus, in addition to asthenospheric decompression melting, the lithospheric mantle is contributing to melt production within the Afar depression. When combined with enriched trace element and isotopic values for other basalts in the Afar depression, our data indicate a wide array of potential melt sources in the region that includes the Afar plume, continental lithosphere and ambient asthenosphere. These data have significant implications for existing interpretations that link low-velocity seismic anomalies to melt derived from oceanic-ridge style decompression melting of the ambient asthenosphere beneath the Afar depression. Instead, the continued presence and melting of the continental lithosphere dictates that the Afar depression remains a transitional structure between a continental <span class="hlt">rift</span> and an oceanic spreading center.</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/2005IJEaS..94..594Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005IJEaS..94..594Z"><span id="translatedtitle">Evolution of the lithosphere in the area of the Rhine <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>Ziegler, P. A.; Dèzes, P.</p> <p>2005-09-01</p> <p>The Rhine <span class="hlt">Rift</span> <span class="hlt">System</span> (RRS) forms part of the European Cenozoic <span class="hlt">Rift</span> <span class="hlt">System</span> (ECRIS) and transects the Variscan Orogen, Permo-Carboniferous troughs and Late Permian to Mesozoic thermal sag basins. Crustal and lithospheric thicknesses range in the RRS area between 24 36 km and 50 120 km, respectively. We discuss processes controlling the transformation of the orogenically destabilised Variscan lithosphere into an end-Mesozoic stabilised cratonic lithosphere, as well as its renewed destabilisation during the Cenozoic development of ECRIS. By end-Westphalian times, the major sutures of the Variscan Orogen were associated with 45 60 km deep crustal roots. During the Stephanian-Early Permian, regional exhumation of the Variscides was controlled by their wrench deformation, detachment of subducted lithospheric slabs, asthenospheric upwelling and thermal thinning of the mantle-lithosphere. By late Early Permian times, when asthenospheric temperatures returned to ambient levels, lithospheric thicknesses ranged between 40 km and 80 km, whilst the thickness of the crust was reduced to 28 35 km in response to its regional erosional and local tectonic unroofing and the interaction of mantle-derived melts with its basal parts. Re-equilibration of the lithosphere-asthenosphere <span class="hlt">system</span> governed the subsidence of Late Permian-Mesozoic thermal sag basins that covered much of the RRS area. By end-Cretaceous times, lithospheric thicknesses had increased to 100 120 km. Paleocene mantle plumes caused renewed thermal weakening of the lithosphere. Starting in the late Eocene, ECRIS evolved in the Pyrenean and Alpine foreland by passive <span class="hlt">rifting</span> under a collision-related north-directed compressional stress field. Following end-Oligocene consolidation of the Pyrenees, west- and northwest-directed stresses originating in the Alps controlled further development of ECRIS. The RRS remained active until the Present, whilst the southern branch of ECRIS aborted in the early Miocene. Extensional strain across ECRIS amounts to some 7 km. Plume-related thermal thinning of the lithosphere underlies uplift of the Rhenish Massif and Massif Central. Lithospheric folding controlled uplift of the Vosges-Black Forest Arch.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19850053973&hterms=Cenozoic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3DCenozoic','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19850053973&hterms=Cenozoic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3DCenozoic"><span id="translatedtitle"><span class="hlt">Rift</span> basins - Origin, history, and distribution</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burke, K. C.</p> <p>1985-01-01</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://www.osti.gov/scitech/servlets/purl/1254465','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1254465"><span id="translatedtitle">Hawaii <span class="hlt">Rifts</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Nicole Lautze</p> <p>2015-01-01</p> <p><span class="hlt">Rifts</span> mapped through reviewing the location of dikes and vents on the USGS 2007 Geologic Map of the State of Hawaii, as well as our assessment of topography, and, to a small extent, gravity data. Data is in shapefile format.</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> </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://ntrs.nasa.gov/search.jsp?R=19910031351&hterms=fever&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dfever','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19910031351&hterms=fever&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dfever"><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://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://ntrs.nasa.gov/search.jsp?R=19890042926&hterms=asthenosphere&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dasthenosphere','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19890042926&hterms=asthenosphere&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dasthenosphere"><span id="translatedtitle"><span class="hlt">Rift</span> propagation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Parmentier, E. M.; Schubert, G.</p> <p>1989-01-01</p> <p>A model for <span class="hlt">rift</span> propagation which treats the <span class="hlt">rift</span> as a crack in an elastic plate which is filled from beneath by upwelling viscous asthenosphere as it lengthens and opens. Growth of the crack is driven by either remotely applied forces or the pressure of buoyant asthenosphere in the crack and is resisted by viscous stresses associated with filling the crack. The model predicts a time for a <span class="hlt">rift</span> to form which depends primarily on the driving stress and asthenosphere viscosity. For a driving stress on the order of 10 MPa, as expected from the topography of <span class="hlt">rifted</span> swells, the development of <span class="hlt">rifts</span> over times of a few Myr requires an asthenosphere viscosity of 10 to the 16th Pa s (10 to the 17th poise). This viscosity, which is several orders of magnitude less than values determined by postglacial rebound and at least one order of magnitude less than that inferred for spreading center propagation, may reflect a high temperature or large amount of partial melting in the mantle beneath a <span class="hlt">rifted</span> swell.</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/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 (σ3) appears to be consistent and stable, the orientations, especially the plunges, of the maximum and intermediate stresses (σ1 and σ2) 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=east+african+rift&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Deast%2Bafrican%2Brift','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19950015372&hterms=east+african+rift&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Deast%2Bafrican%2Brift"><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://www.osti.gov/scitech/biblio/6326946','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6326946"><span id="translatedtitle">Hydrocarbon potential of intracratonic <span class="hlt">rift</span> basins</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Baker, D.G.; Derksen, S.J.</p> <p>1984-09-01</p> <p>Significant world oil reserves have been added in recent years from <span class="hlt">rift</span> <span class="hlt">system</span>. Examples of petroliferous <span class="hlt">rift</span> basins may be found on nearly every major continent. As our understanding of the mechanisms of sedimentation and structure in <span class="hlt">rift</span> basins grows, more <span class="hlt">rift</span> <span class="hlt">systems</span> will be found. With a few notable exceptions, <span class="hlt">rifts</span> that have been explored in the past are those that formed along continental margins. These contain marine sediments, and the conditions of source rock, sediment type, depositional environment, and structural style are well-known exploration concepts. Intracratonic <span class="hlt">rift</span> <span class="hlt">systems</span> containing continental sediments, and also because of the problems perceived to accompany continental sedimentation. A good modern analog is the East African <span class="hlt">rift</span> <span class="hlt">system</span>. Several companies have made significant oil discoveries in different components of the Central African <span class="hlt">rift</span> <span class="hlt">system</span>. Average daily production for 1982 from the basins associated with the Benue trough was 107.928 BOPD. In the Abu Gabra <span class="hlt">rift</span> component, where Marathon is currently exploring, Chevron has drilled approximately 60 wells. Nineteen of these were discoveries and tested an average rate per well of 3,500 BOPD. The Abu Gabra <span class="hlt">rift</span> may contain up to 10 billion bbl of oil. Research indicates that this type of <span class="hlt">rift</span> <span class="hlt">system</span> is present in other areas of the world. Ongoing worldwide exploration has shown that intracratonic <span class="hlt">rift</span> basins have the potential to make a significant contribution to world oil reserves.</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. δ18O and δD 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 δ 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/2015EGUGA..17.3695L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3695L"><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; Sørensen, Mathilde; Atakan, Kuvvet; Havskov, Jens</p> <p>2015-04-01</p> <p>The Shanxi <span class="hlt">rift</span> <span class="hlt">system</span> is one of the most outstanding intra-plate transtensional fault zones in the North China block. Earthquake focal mechanisms of the <span class="hlt">rift</span> <span class="hlt">system</span> are investigated for the time period 1965 - Apr. 2014. A total of 143 focal mechanisms of ML ≥ 3.0 earthquakes were compiled. Among them, 105 solutions are newly determined by combining the P-wave first motions and full waveform inversion, and 38 solutions are from available published data. Stress tensor inversion was then performed based on the new database. The results show that most solutions exhibit normal or strike-slip faulting, and the regional stress field is transtensional and dominated by NNW-SSE extension. This correlates well with results from GPS data, geological field observations and leveling measurements across the faults. Heterogeneity exists in the regional stress field, as indicated by individual stress tensor inversions conducted for five subzones. While the minimum stress axis (σ3) appears to be consistent and stable, the orientations, especially the plunges, of the maximum and intermediate stresses (σ1 and σ2) vary significantly among the different subzones. Based on our results and combining multidisciplinary observations from geological surveys, GPS and cross-fault monitoring, a kinematic model is proposed, in which the Shanxi <span class="hlt">rift</span> <span class="hlt">system</span> is situated between two opposite rotating blocks, exhibiting a transtensional stress regime. This model illustrates the present-day stress field and its correlation with the regional tectonics, as well as the current crustal deformation of the Shanxi <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 of North China.</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/7013067','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/7013067"><span id="translatedtitle">Anatomy of a <span class="hlt">rift</span> <span class="hlt">system</span>: Triassic-Jurassic basins of eastern North America</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Schlische, R.W. ); Olsen, P.E. )</p> <p>1991-03-01</p> <p>Basins containing the early Mesozoic Newark Supergroup formed during the incipient <span class="hlt">rifting</span> of Pangaea. The basins are characterized by the following: (1) The border fault <span class="hlt">systems</span> (BFS) represent reactivated older faults. (2) A regionally persistent northwest-southeast to west-northeast-east-southeast extension direction reactivated northeast- to north-striking structures as predominantly normal dip-slip faults. (3) The half-grabens are lozenge-shaped basins in which subsidence-fault slip was greatest at or near the center of the BFS and decreased to zero toward either end. (4) Transverse folds in the hanging walls immediately adjacent to the BFS formed as a result of higher-frequency variations in subsidence. (5) Subsidence also decreased in a direction perpendicular to the BFS. (6) Intrabasinal faults are overwhelmingly synthetic and predominantly post-depositional. (7) Younger strata progressively onlap prerift rocks of the hanging wall block; this indicates that the basins grew both in width and length as they filled. (8) In all basins initial sedimentation was fluvial, reflecting an oversupply of sediment with respect to basin capacity. (9) Sediments were derived largely from the hanging wall block, which sloped toward the basin, and from streams that entered the basin axially; a direct footwall source was minor, owing to footwall uplift. (10) In strike-slip-dominated basins, subsidence was considerably less than in dip-slip basins, and mosaics of strike- and dip-slip faults are common.</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://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/10184867','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/10184867"><span id="translatedtitle">Anatomy of the Midcontinent <span class="hlt">Rift</span> beneath Lake Superior</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Thompson, M.D.; McGinnis, L.D.; Ervin, C.P.; Mudrey, M.G.</p> <p>1994-09-01</p> <p>The structure and geometry of the 1.1-b.y.-old Midcontinent <span class="hlt">Rift</span> <span class="hlt">system</span> under Lake Superior is interpreted from 20 seismic reflection profiles recorded during the early and mid-1980s. The seismic data reveal that <span class="hlt">rift</span> basins under Lake Superior are variable in depth and are partially filled with Keweenawan age sediments to depths of 7 km or more and volcanic flows to depths of 36 km. These <span class="hlt">rift</span> basins form a continuous and sinuous feature that widens in the Allouez Basin and Marquette Basin in the western and central lake and narrows between White Ridge and the Porcupine Mountains. The <span class="hlt">rift</span> basin bends southeast around the Keweenaw Peninsula, widens to about 100 km as it extends into the eastern half of Lake Superior, and exists the lake with its axis in the vicinity of Au Sable Point in Pictured Rocks National Lake Shore, about 50 km northeast of Munising, Michigan. The axis of the <span class="hlt">rift</span> may exit the western end of the lake near Chequamegon Bay in Wisconsin. However, lack of data in that area limits interpretation at this time. Prior to late-stage reverse-faulting, a continuous basin of more uniform thickness was present beneath the lake. Crustal extension during <span class="hlt">rifting</span> of approximately 50 km was followed by plate convergence and crustal shortening of approximately 30 km, with the major component of thrust from the southeast. Crustal shortening occurred after development of <span class="hlt">rift</span> grabens and their filling with lava flows, but before deposition of the <span class="hlt">final</span> sag basin sediments. Integration of information obtained from outcrops with data reported here indicates that the Lake Superior section of the <span class="hlt">rift</span> is associated with as many as three major boundary faults.</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> </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://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>Dprez, Aline; Doubre, Ccile; Masson, Frdric; 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://adsabs.harvard.edu/abs/1987Tectp.143..119O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1987Tectp.143..119O"><span id="translatedtitle">Rio Grande <span class="hlt">rift</span>: An overview</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Olsen, Kenneth H.; Scott Baldridge, W.; Callender, Jonathan F.</p> <p>1987-11-01</p> <p>The Rio Grande <span class="hlt">rift</span> of the southwestern United States is one of the world's principal continental <span class="hlt">rift</span> <span class="hlt">systems</span>. It extends as a series of asymmetrical grabens from central Colorado, through New Mexico, to Presidio, Texas, and Chihuahua, Mexico—a distance of more than 1000 km. Although the Rio Grande <span class="hlt">rift</span> is closely related in timing and structural style to the contiguous Basin and Range extensional province, the two can be distinguished by a variety of geological and geophysical signatures. <span class="hlt">Rifts</span> (both oceanic and continental) can be defined as elongate depressions overlying places where the entire lithosphere has ruptured in extension. The lithosphere of the Rio Grande <span class="hlt">rift</span> conforms to this definition, in that: (1) the crust is moderately thinned—Moho depths range from about 45 km under the flanks to about 33 km beneath the <span class="hlt">rift</span> axis. (2) anomalously low P n velocities (7.6-7.8 km s -1) beneath the <span class="hlt">rift</span> and a long wavelength gravity low suggest that the asthenosphere is in contact with the base of the crust. The P-velocity is abnormally low (6.4-6.5 km s -1) in the lower half of the crust beneath the <span class="hlt">rift</span>, suggesting high crustal temperatures. However, associated seismic and volcanologic data indicate the sub-<span class="hlt">rift</span> lower crust is not dominated by a massive composite mafic intrusion such as is sometimes inferred for the East African <span class="hlt">rifts</span>. Seismic and magnetotelluric data suggest the presence of a thin (< 1 km) sill-like contemporary midcrustal magma body which may perhaps extend intermittently along much of the length of the <span class="hlt">rift</span>. Seismic and structural studies indicate a dominant horizontal fabric in the upper and middle crust. The brittle-ductile transition is at depths -15 km except for the major volcanic fields, where it rises to 2-3 km. Structural development of the <span class="hlt">rift</span> occurred mainly during two time intervals: the early phase beginning at -30 Ma. and lasting 10-12 m.y., and the late phase extending from -10 to 3 Ma. The early phase involved extensive low-angle normal faulting throughout the <span class="hlt">rift</span> region which was subsequently offset by high-angle normal faulting during the later deformational event. Volcanism of the Rio Grande <span class="hlt">rift</span> is minor compared to some other continental <span class="hlt">rifts</span>. Most of the volcanism is basaltic and occurred less than about 5 m.y. ago. Compositions range from alkalic to tholeiitic, with no unique spatial or temporal pattern. Magmas were probably derived from a variety of depths, indicating an unintegrated heat source with only local melting. Basaltic andesites and related calc-alkaline rocks erupted in the southern <span class="hlt">rift</span> between about 30 and 18 m.y. ago were not uniquely related to the <span class="hlt">rifting</span> process. Rather, the thermal pulse which generated these magmas was part of the previous, subduction-related event. Our interpretation of existing data concerning the evolution of the Rio Grande <span class="hlt">rift</span> does not fit either simple active or passive "end-member" models. In particular, there is no compelling evidence for a major thermal event in the mantle uniquely associated with <span class="hlt">rifting</span>. Yet heat—inherited from the immediately-preceding deformational regime—was certainly a critical factor in, and was probably a necessary condition for, <span class="hlt">rifting</span>.</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 Brarbunga 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; Hreinsdttir, Sigrn; Vogfjrd, Kristn S.; feigsson, Benedikt; Rafn Heimisson, Elas; Dumont, Stphanie; Parks, Michelle; Spaans, Karsten; Gumundsson, Gunnar B.; Drouin, Vincent; rnadttir, Thra; Jnsdttir, Kristn; Gudmundsson, Magns T.; Samsonov, Sergey; Brandsdttir, Brynds; White, Robert; gstsdttir, Thorbjrg; Bjrnsson, 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 Brarbunga 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 Brarbunga 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 Brarbunga 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 Brarbunga 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; Hreinsdttir, Sigrn; Vogfjrd, Kristn S.; feigsson, Benedikt G.; Heimisson, Elas Rafn; Dumont, Stphanie; Parks, Michelle; Spaans, Karsten; Gudmundsson, Gunnar B.; Drouin, Vincent; rnadttir, Thra; Jnsdttir, Kristn; Gudmundsson, Magns T.; Hgnadttir, Thrds; Fridriksdttir, Hildur Mara; Hensch, Martin; Einarsson, Pll; Magnsson, Eyjlfur; Samsonov, Sergey; Brandsdttir, Brynds; White, Robert S.; gstsdttir, Thorbjrg; Greenfield, Tim; Green, Robert G.; Hjartardttir, sta Rut; Pedersen, Rikke; Bennett, Richard A.; Geirsson, Halldr; La Femina, Peter C.; Bjrnsson, Helgi; Plsson, Finnur; Sturkell, Erik; Bean, Christopher J.; Mllhoff, 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 Brarbunga 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 Brarbunga 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 Brarbunga 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://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/2013AGUFM.T11F..02G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T11F..02G"><span id="translatedtitle">Evolution of bimodal volcanism in Gona, Ethiopia: geochemical associations and geodynamic implications for 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>Ghosh, N.; Basu, A. R.; Gregory, R. T.; Richards, I.; Quade, J.; Ebinger, C. J.</p> <p>2013-12-01</p> <p>The East African <span class="hlt">rift</span> <span class="hlt">system</span> in Ethiopia formed in the Earth's youngest flood basalt province, and provides a natural laboratory to study the geochemistry of bimodal volcanism and its implications for plume-derived magmatism, mantle-lithosphere interactions and evolution of continental <span class="hlt">rifts</span> from plate extension to rupture. Our geochemical studies of the ~6 Ma to recent eruptive products from Gona within the Afar <span class="hlt">Rift</span> Zone are understood in context of crustal and upper mantle seismic imaging studies that provide constraints on spatial variations. Geochemical (major element, trace element and isotope) analyses of basalts and rhyolitic tuff from Gona indicate a common magma source for these bimodal volcanics. Light rare earth elements (LREEs) are enriched with a strong negative Eu anomaly and a positive Ce anomaly in some of the silicic volcanic rocks. We observe strong depletions in Sr and higher concentrations of Zr, Hf, Th, Nb and Ta. We hypothesize that the silicic rocks may be residues from a plume-derived enriched magma source, following partial melting with fractional crystallization of plagioclase at shallow magma chambers. The absence of Nb-Ta anomaly shows no crustal assimilation by magmas. Sr isotopes, in conjunction with Nd and Pb isotopes and a strong Ce anomaly could reflect interaction of the parent magma with a deep saline aquifer or brine. Nd isotopic ratios (ɛNd = 1.9 to 4.6) show similarity of the silicic tuffs and basalts in their isotopic compositions except for some ~6 Ma lavas showing MORB-like values (ɛNd = 5 to 8.7) that suggest involvement of the asthenosphere with the plume source. Except for one basaltic tuff, the whole rock oxygen isotopic ratios of the Gona basalts range from +5.8‰ to +7.9‰, higher than the δ values for typical MORB, +5.7. The oxygen isotopes in whole rocks from the rhyolite tuffs vary from 14.6‰ to 20.9‰ while their Sr isotope ratios <0.706, indicative of post-depositional low T alteration of these silicic rocks by a fluid derived from seawater or some crustal fluid not enriched in radiogenic Sr. The bimodality of the volcanic rocks may be genetically related by fractional crystallization or by partial melting of a hydrothermally altered mafic crust from earlier magma generation in the <span class="hlt">rift</span>, without continental crustal assimilation. The geochemical data, along with geophysical and geodetic studies, assist our understanding of the tectonics of continental break up and plume magmatism in the Afar depression and the East African <span class="hlt">Rift</span> <span class="hlt">system</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990Tectp.173..595B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990Tectp.173..595B"><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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Behrendt, J. C.; Hutchinson, D. R.; Lee, M.; Thornber, C. R.; Tréhu, A.; Cannon, W.; Green, A.</p> <p>1990-02-01</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.</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/2014AGUFM.T53B4674B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T53B4674B"><span id="translatedtitle"><span class="hlt">Rift</span> Fault Geometry and Distribution in Layered Basaltic Rocks: A Comparison Between the Koa'e (Hawai'i) and Krafla (Iceland) Fault <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>Bubeck, A.; Walker, R. J.; MacLeod, C. J.; Imber, J.</p> <p>2014-12-01</p> <p>Fault <span class="hlt">systems</span> within incipient <span class="hlt">rifts</span> that cut basaltic rocks comprise an array of fine-scale structures, including networks of fractures and small displacement (<15 m) faults that accommodate regional extension. These zones of damaged rock have mechanical and physical properties distinct from the surrounding intact host rock. As the <span class="hlt">rift</span> <span class="hlt">system</span> evolves this early-formed damage can be reactivated, and influence the distribution and growth of new fractures. Constraining the role of this inter-fault deformation in <span class="hlt">rift</span> zone development is therefore important to characterizing the regional distribution of extensional strains, and the evolving physical and fluid flow properties of the host rock. Here we use high resolution field and remote mapping of the Koa'e insipient <span class="hlt">rift</span> fault <span class="hlt">system</span> on the south flank of Kilauea Volcano on Hawaii's Big Island, and the Krafla <span class="hlt">rift</span> <span class="hlt">system</span>, Iceland, to investigate the evolution of segmented <span class="hlt">rift</span> fault <span class="hlt">systems</span> in layered basalts, formed at low confining pressures. Extension in the Koa'e <span class="hlt">system</span> is accommodated dominantly by interaction of zones of opening-mode fractures and areas of surface flexure rather than surface-breaching normal faults, which is attributed to gravitational collapse of Kilauea. Extension in the Krafla <span class="hlt">system</span> is localised on segmented, large displacement (>20 m) normal faults, the development of which may have been controlled by dyke emplacement. Preliminary comparison between the Koa'e and Krafla <span class="hlt">systems</span> suggests that strain rate and/or the effective stress path plays a primary role in controlling the geometry, characteristics, and distribution of major faults, and the scale and distribution of secondary (oblique) brittle structures within <span class="hlt">rift</span> zones.</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://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/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://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://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> <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://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://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://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> </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://adsabs.harvard.edu/abs/1985JAfES...3..381S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985JAfES...3..381S"><span id="translatedtitle">Buried troughs, grabens and <span class="hlt">rifts</span> in Sudan</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Salama, R. B.</p> <p></p> <p>The deep lineaments and shear patterns of Sudan follow two main directions :NNW (Red Sea trend) and ENE (Gulf of Aden trend). Precambrian mobile belts trend NE and NW. Palaezoic(?) sediments occupy NE-SW aligned grabens. Mesozoic continental sediments with NW paleotrends were deposited in two major depressions also aligned NW. Cainozoic uplift and volcanism was associated with domal uplifts along NE and SE axes. Fracturing and faulting in NW and NE directions resulted in the formation of NW-SE fault bounded grabens ranging in depth from 1 to 11 km. Extending from the western boundaries of Sudan to the eastern borders with Ethiopia, the Sudanese Cainozoic <span class="hlt">rift</span> systemforms the largest <span class="hlt">rift</span> <span class="hlt">system</span> in Africa and includes: (a) Bahr E1 Arab <span class="hlt">Rift</span>, (b) White Nile <span class="hlt">Rift</span>, (c) Blue Nile <span class="hlt">Rift</span>, (d) River Atbara <span class="hlt">Rift</span> and (e) Wadi El Kuu <span class="hlt">Rift</span>. The grabens and trouhs within the <span class="hlt">rift</span> <span class="hlt">system</span> form the main groundwater basins of Sudan. The discovery of oil in three of these <span class="hlt">rifts</span> will encourage the exploration for oil in the others and a search for similar structures in the northern areas of Sudan.</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/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 Espinhao <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 Espinhao Basin in eastern Brazil contains depositional sequences developed in the So 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 So Joo 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 So 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://adsabs.harvard.edu/abs/2007AGUFM.C41C..03L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.C41C..03L"><span id="translatedtitle">Neogene Tectonic Events in the Marie Byrd Land Sector of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>: Their Potential Impact on Ice Sheet Evolution and Stability.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Le Masurier, W. E.</p> <p>2007-12-01</p> <p>The West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> is buried beneath 1-4 km of ice over much of its extent, obscuring vast areas that could provide clues about the potential for active volcanism beneath the ice sheet, and whether significant tectonic movement has taken place in Cenozoic time. This study explores the consequences of viewing the ice as basin fill, and of approximating the mass equivalent of ice as unconsolidated sediment. It then compares the results with active <span class="hlt">rift</span> <span class="hlt">systems</span> elsewhere in the world. The results suggest (1) that the interior <span class="hlt">rift</span> trough is relatively cool, and the potential there for destabilizing subglacial eruptions is low, (2) that extension and over- deepening of interior basins, like the Bentley Subglacial Trench, have taken place beneath the ice sheet in Neogene time, and (3) that dome uplift and the growth of large volcanoes along the Marie Byrd Land coast, together with the subsidence of interior basins, have greatly increased the topographic relief of the <span class="hlt">rift</span> <span class="hlt">system</span> in Neogene time. Recent studies suggest that West Antarctic glaciation first appeared during the Oligocene. The implication of this study is that the Oligocene ice sheet originated on a low relief landscape near sea level, adjacent to a much shallower inland sea, and has since evolved in an environment of progressive basin deepening, dome uplift, and volcanism, unlike that of any other ice sheet in the recent past.</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://adsabs.harvard.edu/abs/2009E%26PSL.279...86S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009E%26PSL.279...86S"><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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sherman, L. S.; Blum, J. D.; Nordstrom, D. K.; McCleskey, R. B.; Barkay, T.; Vetriani, C.</p> <p>2009-03-01</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 δ 202Hg from - 1.02‰ to 0.58‰ (± 0.11‰, 2SD) and solid precipitate samples from Guaymas Basin range in δ 202Hg from - 0.37‰ to - 0.01‰ (± 0.14‰, 2SD). Fluid samples from Ojo Caliente display mass-dependent fractionation (MDF) of Hg from the vent (δ 202Hg = 0.10‰ ± 0.11‰, 2SD) to the end of the outflow channel (δ 202Hg = 0.58‰ ± 0.11‰, 2SD) in conjunction with a decrease in Hg concentration from 46.6 pg/g to 20.0 pg/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 Hg 0(aq) to Hg 0(g) and the preferential loss of Hg with a lower δ 202Hg value to the atmosphere. A small amount of mass-independent fractionation (MIF) was observed in all samples from Ojo Caliente (Δ 199Hg = 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://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/2012AGUFM.T43G..02O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T43G..02O"><span id="translatedtitle">Quantitative challenges to our understanding of the tectonostratigraphic evolution of <span class="hlt">rift</span> basin <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>Olsen, P. E.; Kent, D. V.</p> <p>2012-12-01</p> <p>Pervasive orbitally-paced lake level cycles combined with magnetic polarity stratigraphy in central Pangean early Mesozoic <span class="hlt">rift</span> basins provide a thus far unique and very large-scale quantitative basis for observing patterns of basin fill and comparisons with other basins. The 32 Myr accumulation rate history of the Newark basin is segmented into intervals lasting millions of years with virtually no change in the long-term accumulation rate (at the 400-kyr-scale), and the transitions between segments are abrupt and apparently basin-wide. This is startling, because the basin geometry was, and is, a half graben - triangular in cross section and dish-shaped in along-strike section. The long periods of time with virtually no change is challenging given a simple model of basin growth (1), suggesting some kind of compensation in sediment input for the increasing surface of the area of the basin through time. Perhaps even more challenging are observations based on magnetic polarity stratigraphy and the cyclicity, that basins distributed over a huge area of central Pangea (~700,000 km2) show parallel and correlative quantitative changes in accumulation rate with those of the Newark basin. The synchronous changes in the accumulation rate in these basins suggests a very large-scale linkage, the only plausible mechanism for which would seem to be at the plate-tectonic scale, perhaps involving extension rates. Together, we can speculate that some kind of balance between extension rates, basin accommodation space and perhaps regional drainage basin size might have been in operation The most dramatic accumulation rate change in the basins' histories occurred close to, and perhaps causally related to, the Triassic-Jurassic boundary and end-Triassic extinction. The Newark basin, for example exhibits a 4-to-5-fold increase in accumulation rate during the emplacement of the brief (<1 Myr) and aerially massive Central Atlantic Magmatic Province (CAMP) beginning at 201.5 Ma, the only igneous event known during this long <span class="hlt">rifting</span> episode. Parallel and correlative accumulation rate changes are seen in several of the other northern basins within central Pangea. Surprisingly, the rate of accommodation growth apparently increased dramatically during this time, because not only did the accumulation rate dramatically increase, the lakes apparently deepened during the same time as a huge volume of CAMP igneous material entered the basins. At the same time, the more southern basins in the southeastern US, apparently ceased to subside (2). Our ability to measure time in these <span class="hlt">rift</span> basins using the orbitally-paced cycles, coupled with the ability to correlate between the basins using magnetic polarity stratigraphy, challenges us to form new mechanistic explanations and quantitative models to test against this rich library of observations. References: 1) Schlische RW & Olsen PE, 1990, Jour. Geol. 98:135. 2) Schlische et al., 2003, in Hames WE et al. (eds), Geophys. Monogr. 136:61.</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/2015JSG....71..136B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JSG....71..136B"><span id="translatedtitle">Complex <span class="hlt">rift</span> geometries resulting from inheritance of pre-existing structures: Insights and regional implications from the Barmer Basin <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>Bladon, Andrew J.; Clarke, Stuart M.; Burley, Stuart D.</p> <p>2015-02-01</p> <p>Structural studies of the Barmer Basin in Rajasthan, northwest India, demonstrate the important effect that pre-existing faults can have on the geometries of evolving fault <span class="hlt">systems</span> at both the outcrop and basin-scale. Outcrop exposures on opposing <span class="hlt">rift</span> margins reveal two distinct, non-coaxial extensional events. On the eastern <span class="hlt">rift</span> margin northwest-southeast extension was accommodated on southwest- and west-striking faults that form a complex, zig-zag fault network. On the western <span class="hlt">rift</span> margin northeast-southwest extension was accommodated on northwest-striking faults that form classical extensional geometries. Combining these outcrop studies with subsurface interpretations demonstrates that northwest-southeast extension preceded northeast-southwest extension. Structures active during the early, previously unrecognised extensional event were variably incorporated into the evolving fault <span class="hlt">systems</span> during the second. In the study area, an inherited <span class="hlt">rift</span>-oblique fault transferred extension from the <span class="hlt">rift</span> margin to a mid-<span class="hlt">rift</span> fault, rather than linking <span class="hlt">rift</span> margin fault <span class="hlt">systems</span> directly. The resultant <span class="hlt">rift</span> margin accommodation structure has important implications for early sediment routing and depocentre evolution, as well as wider reaching implications for the evolution of the <span class="hlt">rift</span> basin and West Indian <span class="hlt">Rift</span> <span class="hlt">System</span>. The discovery of early <span class="hlt">rifting</span> in the Barmer Basin supports that extension along the West Indian <span class="hlt">Rift</span> <span class="hlt">System</span> was long-lived, multi-event, and likely resulted from far-field plate reorganisations.</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/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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730006633','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730006633"><span id="translatedtitle">Mapping of the major structures of the African <span class="hlt">rift</span> <span class="hlt">system</span> using ERTS-1</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. (Principal Investigator)</p> <p>1973-01-01</p> <p>The author has identified the following significant results. The structural margin of western Afar with the Ethiopian plateau is marked by a rather wide zone of crustal deformation. ERTS-1 imagery has now permitted a more precise mapping of the structures of this marginal zone, and in particular of the discontinuous marginal graben. The tectonic style of the graben is different in the north from the south, and in the latter region the graben is discordant with the regional tectonic trend. The structural margin of the southern Afar with the Somalian plateau is formed, in the western sector, by a remarkable series of fault-zone splays. Afar-plateau boundary fault-zones successively curve northeast and then NNE to become Afar floor fault-zones, with a distance of about 25 km separating successive turnoffs. The transition from Ethiopian <span class="hlt">rift</span> to Gulf of Aden tread faulting along this margin is fascinatingly complex. A simplistic crustal thinning model is not adequate to explain all observed structural features of the Afar margins.</p> </li> <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> </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://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/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/1996EOSTr..77..255B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996EOSTr..77..255B"><span id="translatedtitle">Continental <span class="hlt">Rifts</span>: Evolution, Structure and Tectonics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bally, A. W.</p> <p></p> <p>Twenty one “friends of continental rifts” wrote Continental <span class="hlt">Rifts</span>: Evolution, Structureand Tectonics. They define the object of their passion as elongate tectonic depressions along which the entire lithosphere has been modified by extension. Strictly speaking, passive margins and highly extended terranes such as the Basin and Range are not included in this definition, but the authors consider them to be related to continental <span class="hlt">rifts</span>. The authors hail from academia and set as their main goal “an improved understanding of the fundamental lithospheric processes of <span class="hlt">rifting</span>, with primary focus on deep structures and processes associated with <span class="hlt">rifting</span>.” Consequently, many well-known extensional <span class="hlt">systems</span>, for example, the North Sea grabens, the Suez Basin, onshore and offshore eastern China, and large areas of southeast Asia, are barely considered. <span class="hlt">Rift</span> aficionados from the petroleum industry will find very little to interest them in this book.</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.V23A2562B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V23A2562B"><span id="translatedtitle">Mesozoic fault reactivation along the St. Lawrence <span class="hlt">Rift</span> <span class="hlt">System</span> as constrained by (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>Bouvier, L.; Pinti, D. L.; Tremblay, A.; Minarik, W. G.; Roden-Tice, M. K.; Pik, R.</p> <p>2011-12-01</p> <p>The Saint Lawrence <span class="hlt">Rift</span> <span class="hlt">System</span> (SLRS) is a half-graben, extending for 1000 km along St. Lawrence River valley. Late Proterozoic-Early Paleozoic faults of the graben form the contact with the metamorphic Grenvillian basement to the northwest and extend under the Paleozoic sedimentary sequences of the St. Lawrence Lowlands to the southeast. The SLRS is the second most seismically active area in Canada, but the causes of this activity remain unclear. Reactivation of the SLRS is believed to have occurred along Late Proterozoic to Early Paleozoic normal faults related to the opening of the Iapetus Ocean. The absence of strata younger than the Ordovician makes difficult to determine when the faults reactivated after the Ordovician. Field relations between the normal faults bordering the SLRS and those produced by the Charlevoix impact crater suggest a reactivation of the <span class="hlt">rift</span> younger than the Devonian, the estimated age of the impact. Apatite (U-Th)/He thermochronology is an adequate tool to recognize thermal events related to fault movements. A thermochronology study was then started along three transects across the SLRS, from Québec up to Charlevoix. Apatites were extracted and separated from five granitic to charnockitic gneisses and an amphibolite of Grenvillian age. The samples were exposed on hanging wall and footwall of the Montmorency and Saint-Laurent faults at three different locations along the SLRS. For precision and accuracy, each of the six samples was analyzed for radiogenic 4He and U-Th contents at least twice. Apatite grains were isolated by heavy liquids and magnetic separation. For each sample, ten apatite grains were selected under optical microscope and inserted into Pt capsules. Particular care was taken to isolate apatite free of mineral and fluid inclusions. Indeed, SEM investigations showed that some inclusions are U-rich monazite, which is a supplementary source of 4He to be avoided. The 4He content was determined by using a static noble gas mass spectrometer in CRPG-Nancy and duplicates using a quadrupole mass spectrometer at GEOTOP-UQAM. 4He was measured against internal He gas standards and Durango apatite, with the reference U-Th/He age of 31.13 ± 1.01 Ma. U and Th contents were determined at CRPG-Nancy and duplicated at McGill University by ICP-MS. Preliminary results of U-Th/He on St.-Laurent fault yield an age of 137±12 Ma for the hanging wall, at Sault-au-Cochon and 118±10 Ma for a sample from the footwall, at Cap-aux-oies. Previous Apatite Fission Track (AFT) performed for the two locations gave expected older ages at 149±16 Ma and 196±19 Ma for the hanging wall and the footwall, respectively. These preliminary U-Th/He results are consistent with AFT ages of the area (i.e. as expected, U-Th/He ages are younger than AFT ages) but do not yet provide new constraints for the structural evolution of the St. Lawrence <span class="hlt">rift</span> <span class="hlt">system</span>. We are determining further U-Th/He ages and these ages will constrain an exhumation model of the region.</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/2010AGUFM.S33B2105S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.S33B2105S"><span id="translatedtitle">A Strong Stress Shadow Effect of the 2004 M=9.2 Sumatra-Andaman Earthquake on the Andaman Sea Transform-<span class="hlt">Rift</span> <span class="hlt">System</span> 250 km Away</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sevilgen, V.; Stein, R. S.</p> <p>2010-12-01</p> <p>The 26 December 2004 earthquake ruptured a 1,300-km section of the Sunda megathrust. A transform-<span class="hlt">rift</span> back-arc <span class="hlt">system</span> accommodates most of the trench-parallel component of the highly oblique subduction. We used the NEIC earthquake catalog at its M≥4.7 completeness level since 1999, and at M≥4.8 since 1975, to examine the seismicity rate along the transform-<span class="hlt">rift</span> <span class="hlt">system</span>. We also combined teleseismic double-difference earthquake relocations from Pesicek et al (JGR, 2010) with Global CMT mechanisms, to more accurately associate focal mechanisms with their fault <span class="hlt">systems</span>. We find a strong drop in seismicity rate along the Andaman Sea transform <span class="hlt">system</span> east of the northern end of the 2004 rupture zone. This occurs immediately following the Sumatra-Andaman mainshock and persists to this day. The rate drop is associated with strike-slip mechanisms only; along the portions of the <span class="hlt">rift</span> <span class="hlt">system</span> with normal-faulting mechanisms, the seismicity rate increased. We calculate that the Sagaing-West Andaman transform in this region was subjected to a static Coulomb stress drop of 0.25 bar (for an assumed fault friction of 0.4), whereas the <span class="hlt">rift</span> segments sustained stress increases greater than 1 bar. Both of these calculations are in accord with the observations. Because of the large distance between the megathrust source and the back-arc receiver faults, the imparted stresses are insensitive to the unknown details of the megathrust slip and geometry; because the 2004 slip is so large, the imparted stresses are nevertheless substantial 200-300 km east of the trench, where the seismicity rate changes are observed. Thus, the seismicity shutdown associated with the 2004 earthquake stress shadow furnishes an important test of the static Coulomb stress triggering hypothesis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19930069932&hterms=east+african+rift&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Deast%2Bafrican%2Brift','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19930069932&hterms=east+african+rift&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Deast%2Bafrican%2Brift"><span id="translatedtitle">Implications of new gravity data for Baikal <span class="hlt">Rift</span> zone structure</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ruppel, C.; Kogan, M. G.; Mcnutt, M. K.</p> <p>1993-01-01</p> <p>Newly available, 2D Bouguer gravity anomaly data from the Baikal <span class="hlt">Rift</span> zone, Siberia, indicate that this discrete, intracontinental <span class="hlt">rift</span> <span class="hlt">system</span> is regionally compensated by an elastic plate about 50 km thick. However, spectral and spatial domain analyses and isostatic anomaly calculations show that simple elastic plate theory does not offer an adequate explanation for compensation in the <span class="hlt">rift</span> zone, probably because of significant lateral variations in plate strength and the presence of subsurface loads. Our results and other geophysical observations support the interpretation that the Baikal <span class="hlt">Rift</span> zone is colder than either the East African or Rio Grande <span class="hlt">rift</span>.</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://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://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://adsabs.harvard.edu/abs/2015PhDT........48Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhDT........48Y"><span id="translatedtitle">Seismological investigation of the Okavango <span class="hlt">Rift</span>, Botswana</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</p> <p></p> <p>The mechanisms of <span class="hlt">rifting</span> have been intensively investigated using geological and geophysical techniques beneath mature <span class="hlt">rift</span> zones. However, current understanding on the earliest stages of <span class="hlt">rifting</span> is seriously limited. Here we employ recently archived data from 17 broadband seismic stations traversing northern Botswana to conduct the first shear wave splitting and mantle transition zone (MTZ) studies within the Okavango <span class="hlt">Rift</span> Zone (ORZ). The ORZ is an incipient continental <span class="hlt">rift</span> situated at the terminal of the southwestern branch of the East African <span class="hlt">Rift</span> <span class="hlt">System</span>. The resulting normal MTZ thickness and consistently <span class="hlt">rift</span>-parallel fast polarizations imply an absence of significant thermal anomalies in the upper mantle, ruling out the role of mantle plumes in the initiation of the ORZ. The observed anisotropy beneath the ORZ and adjacent areas is mainly attributed to the relative movement between the lithosphere and asthenosphere with regional contributions from fabrics in the lithosphere and flow deflection by the bottom of the lithosphere. Our observations imply that the initiation and development of the ORZ can be initiated following a passive mode from the consequences of relative movements between the South African block and the rest of the African plate along a zone of lithospheric weakness between the Congo and Kalahari cratons. In addition, an approach was developed to effectively remove the near surface reverberations in the resulting receiver functions, decipher the P-to-S converted phases associated with the Moho discontinuity, and thus resolve sub-sediment crustal structure beneath stations sitting on a low-velocity sedimentary layer.</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://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=314037','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=314037"><span id="translatedtitle"><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 virus (RVFV) is a mosquito-transmitted virus or arbovirus that is endemic in sub-Saharan Africa. In the last decade, <span class="hlt">Rift</span> Valley fever (RVF) outbreaks have resulted in loss of human and animal life, as well as had significant economic impact. The disease in livestock is primarily a...</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.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://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://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://adsabs.harvard.edu/abs/2014EGUGA..1613669S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1613669S"><span id="translatedtitle">Contemporary surface ruptures in the zone of the Baikal-Mondy fault (Baikal <span class="hlt">rift</span> <span class="hlt">system</span>): dynamics of formation and origin</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; Sankov, Aleksei; Lebedeva, Marina; Ashurkov, Sergey; Parfeevets, Anna</p> <p>2014-05-01</p> <p>Sublatitudinal Baikal-Mondy (Tunka) left-lateral strike-slip fault accommodates North Mongolia submeridional <span class="hlt">rift</span> basins opening (Darkhad and Khubsugul). It is the connecting link between the central and south-western parts of the Baikal <span class="hlt">rift</span> <span class="hlt">system</span>. We investigated the present-day activity of faulting on southern border of Mondy basin, which is due to their position at the junction of east-west trending active faults of the Baikal-Mondy fault <span class="hlt">system</span> with submeridional structures of Khubsugul basin. The investigated area is characterized by high seismic activity. The epicenter of one of the strongest Mondy earthquake 1950 (Mw = 7.0) is located within the Mondy basin. Reconstruction of Late Cenozoic tectonic stress field shows a predominance of strike-slip deformation regime with NW-SE direction of the minimum compression axis and NE-SW direction of the maximum compression axis, which correlates with the present-day stress field derived from the data on earthquake focal mechanisms. On the top of the southern shoulder of Mondy basin a series of extended NE trending surface ruptures that cut the crust of weathering and bedrock across the local watershed were discovered. The rupture length reaches 180 m, width ruptures bedrock reaches 0.6 m. In the bedrock tectonic microfractures of NW and NE directions are dominated, but the NW trending surface ruptures are not observed. In the area of contemporary ruptures the geodetic measurements were carried out in the period 2009-2013. The results of processing the measurement data on the local testing ground showed that most divergent baselines undergoes extension with maximum values reaching 30 mm/year. The block experienced elongation in all directions, but the morphology of ruptures suggests that the main direction of stretching is NW-SE. The intensity of cracks opening decreases markedly with time. According to eyewitnesses known that active crack opening at about 100 mm/year started 4 years before Kultuk earthquake (27.08.2008, Mw = 6.3), the epicenter of which was located near the southern tip of the Baikal basin. The existence of centimeter level deformations is confirmed using of differential SAR interferometry method. A pair of images taken with an interval of 2 years highlighted the linear zone of active deformation in the centimeter level. The length of the structure is about 4 kilometers. The offset along the Line-of-Sight (LOS) direction is from 18 to 42 mm, which corresponds to the vertical displacement of 22 to 50 mm, or a horizontal displacement of 32 to 74 mm (Lebedeva et al., 2013). Along with the described ruptures we discovered normal faults with an amplitude greater than 2 m, which can be traced along the submeridional local watershed. The length of the normal faults reaches 800 m. The morphology and position of these faults can be attributed to their sackung structures. We conclude that the detected current surface ruptures have complex origins and develop under the influence of endogenous (tectonic) and exogenous forces. They founded along NE trending ancient tectonic structures within wide strike-slip zone and main direction of opening corresponds to the direction of extension of paleo- and present-day stress field. According to the dynamics of ruptures opening, the main phase of their formation is connected with stage of Kultuk earthquake preparation. As for geodetic data the block is stretched in all directions, it can be assumed that, by analogy with closely spaced sacking</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.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://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://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://ntrs.nasa.gov/search.jsp?R=PIA11082&hterms=east+african+rift&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Deast%2Bafrican%2Brift','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=PIA11082&hterms=east+african+rift&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Deast%2Bafrican%2Brift"><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://adsabs.harvard.edu/abs/2008Tecto..27.3013K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008Tecto..27.3013K"><span id="translatedtitle">Fault growth and propagation during incipient continental <span class="hlt">rifting</span>: Insights from a combined aeromagnetic and Shuttle Radar Topography Mission digital elevation model investigation of the Okavango <span class="hlt">Rift</span> Zone, northwest Botswana</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kinabo, B. D.; Hogan, J. P.; Atekwana, E. A.; Abdelsalam, M. G.; Modisi, M. P.</p> <p>2008-06-01</p> <p>Digital Elevation Models (DEM) extracted from the Shuttle Radar Topography Mission (SRTM) data and high-resolution aeromagnetic data are used to characterize the growth and propagation of faults associated with the early stages of continental extension in the Okavango <span class="hlt">Rift</span> Zone (ORZ), northwest Botswana. Significant differences in the height of fault scarps and the throws across the faults in the basement indicate extended fault histories accompanied by sediment accumulation within the <span class="hlt">rift</span> graben. Faults in the center of the <span class="hlt">rift</span> either lack topographic expressions or are interpreted to have become inactive, or have large throws and small scarp heights indicating waning activity. Faults on the outer margins of the <span class="hlt">rift</span> exhibit either (1) large throws or significant scarp heights and are considered older and active or (2) throws and scarp heights that are in closer agreement and are considered young and active. Fault linkages between major fault <span class="hlt">systems</span> through a process of "fault piracy" have combined to establish an immature border fault for the ORZ. Thus, in addition to growing in length (by along-axis linkage of segments), the <span class="hlt">rift</span> is also growing in width (by transferring motion to younger faults along the outer margins while abandoning older faults in the middle). <span class="hlt">Finally</span>, utilization of preexisting zones of weakness allowed the development of very long faults (>100 km) at a very early stage of continental <span class="hlt">rifting</span>, explaining the apparent paradox between the fault length versus throw for this young <span class="hlt">rift</span>. This study clearly demonstrates that the integration of the SRTM DEM and aeromagnetic data provides a 3-D view of the faults and fault <span class="hlt">systems</span>, providing new insight into fault growth and propagation during the nascent stages of continental <span class="hlt">rifting</span>.</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/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/1992Tectp.209..115B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992Tectp.209..115B"><span id="translatedtitle">Mesozoic and early Tertiary <span class="hlt">rift</span> tectonics 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>Bosworth, William</p> <p>1992-08-01</p> <p>A complex history of crustal extension occurred in east and central Africa during the Mesozoic and early Tertiary. Beginning in the Late Jurassic, this resulted in a large <span class="hlt">system</span> of <span class="hlt">rifts</span>, the Central African <span class="hlt">rift</span> <span class="hlt">system</span>, that spanned from central Sudan to southern Kenya. Late Jurassic <span class="hlt">rifting</span> is best documented in the White and Blue Nile <span class="hlt">rifts</span> of the Sudan, and records east-west extension in half-graben that were connected by large-scale shear zones and pull-apart basins. Early Cretaceous <span class="hlt">rifting</span> re-activated Jurassic basins and spread to the large South Sudan <span class="hlt">rifts</span> and Anza <span class="hlt">rift</span> in Kenya. By the Late Cretaceous, the extension direction shifted to the NE-SW, and the presently observed large-scale <span class="hlt">rift</span> geometry was established. In the early Tertiary, some Mesozoic basins were again reactivated, while other regions underwent wrench faulting and basin inversion. The large number of basins preserved in the Central African <span class="hlt">rift</span> <span class="hlt">system</span> can be used to construct an evolutionary model of continental <span class="hlt">rift</span> tectonics. Early phases of extension at low strains produced alternating half-graben/accommodation zone geometries similar to those observed in most young and active continental <span class="hlt">rifts</span>. At higher strains, some border faults were abandoned so that through-going, simpler active fault <span class="hlt">systems</span> could evolve. This is interpreted as representing a switch from complex, oppositely dipping detachment structures, with strike dimensions of 50-150 km, to regional detachment structures that continue for hundreds of kilometers parallel to the <span class="hlt">rift</span>. This change in the type of detachment was accompanied by a shift in the position of the subsidence away from the breakaway to a position focused further within the regional upper plate. Non-rotational, high angle, normal faulting dominates in the development of these late basin geometries. Deciphering similar <span class="hlt">rift</span> basin histories from passive continental margins may, in many cases, exceed the limits of available reflection seismic data. East-west striking shear zones, including the Umm Hani and South Sudan shears, served as basin-terminating structures in the Late Jurassic <span class="hlt">rift</span> <span class="hlt">system</span>. These shear zones were later reactivated during the Cretaceous and early Tertiary, controlling the positions of some accommodation zones and "jogs" (apparent offsets) in <span class="hlt">rift</span> trends. The South Sudan shear may have continued to play a role in Neogene extensional tectonics, as it connects "jogs" in both the Abu Gabra/Anza <span class="hlt">rift</span> (Jurassic? to Early Tertiary) and Turkana/Chew Bahir <span class="hlt">rift</span> (Neogene to Recent).</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://www.cdc.gov/vhf/rvf/','NIH-MEDLINEPLUS'); return false;" href="http://www.cdc.gov/vhf/rvf/"><span id="translatedtitle"><span class="hlt">Rift</span> Valley Fever (RVF)</span></a></p> <p><a target="_blank" href="http://medlineplus.gov/">MedlinePlus</a></p> <p></p> <p></p> <p>... Outbreak resources, VHF information for specific groups, virus ecology, references... RVF Distribution Map <span class="hlt">Rift</span> Valley Fever Transmission ... Outbreaks Outbreak Summaries RVF Distribution Map Resources Virus Ecology File Formats Help: How do I view different ...</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://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=59030475&CFTOKEN=17653289','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=59030475&CFTOKEN=17653289"><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://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/2006AGUFM.T53A1586P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.T53A1586P"><span id="translatedtitle">How is continental break-up recorded in 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>Peron-Pinvidic, G.; Manatschal, G.; Minshull, T.; Sawyer, D.</p> <p>2006-12-01</p> <p>In classical models of continental break-up, <span class="hlt">rifting</span> is immediately followed by seafloor spreading, which implies that break-up can be identified as a specific spatial and temporal boundary. However, this simple concept is not supported by observations at <span class="hlt">rifted</span> margins. The classical indicators for determining break-up (break-up unconformity, magnetic anomalies, distribution of high-angle faults and sedimentary wedges) may no longer be relied upon to identify unambiguously the location and age of break-up. We studied the spatial and temporal evolution of the deep Iberia-Newfoundland margins, which are the type examples of magma-poor <span class="hlt">rifted</span> margins. Our study was based on borehole data and on a mapping of the sedimentary and basement architecture in 3D on seismic reflection profiles. Our results allow us to describe the tectono-sedimentary and morpho-tectonic evolution of <span class="hlt">final</span> <span class="hlt">rifting</span> and show that continental break-up is complex. In the Iberia-Newfoundland <span class="hlt">rift</span> <span class="hlt">system</span>, the tectono-sedimentary evolution of <span class="hlt">final</span> <span class="hlt">rifting</span> can be reconstructed back to 145Ma, when the crust was already thinned to less than 10km. Two major deformation phases have been identified: a first, Tithonian to Barremian in age (145-128Ma) and a second, dated as latest Aptian (112Ma). The Tithonian-Barremian phase is characterized by a migration of the tectonic activity oceanwards and a change of the deformation mechanisms from south to north, from zones of mantle exhumed via downward concave faults to classical half-grabens formed by the normal tilting of thinned continental blocks along upward concave faults. This phase terminates with the formation of the first unequivocal magnetic anomaly (M3 128Ma) and the accretion of more than 170km of crust, at rates of about 1cm/yr, that is neither oceanic nor continental, commonly referred to as Zone of Exhumed Continental Mantle (ZECM). The late-Aptian phase is associated with a major tectono-magmatic event and is responsible for the observed basement topography in the ZECM. Although short-lived, this event is widely distributed over previously accreted crust. Our results show that the Iberia-Newfoundland <span class="hlt">rift</span> <span class="hlt">system</span> is polyphase and is characterized by the interaction of different modes of extension. These modes overlap one another in time and space. In contrast to what we expected, distributed deformation was still wide-spread after formation of the first magnetic anomalies. Therefore, break-up can not be defined as a sharp boundary or as an isochron in the deep margin. The concept of continental break-up marking the beginning of the oceanic accretion is not applicable to magma-poor <span class="hlt">rifted</span> margins such as Iberia-Newfoundland. The transition from <span class="hlt">rifting</span> to seafloor spreading in deep margins is transitional. This observation has strong implications for frequently used concepts such as the break-up unconformity and the partition of the sedimentary cover into pre-, syn- and post-<span class="hlt">rift</span> intervals. Given the length and the polyphase nature of the <span class="hlt">rifting</span>, several pre-, syn- and post-<span class="hlt">rift</span> intervals have to be defined to respect the original definitions; and no single break-up unconformity can be generated given the transitional nature from <span class="hlt">rift</span> to drift. Moreover, traditionally computed accretion rates have to take into account the superposition of different tectonic mechanisms, interacting with each other and re-utilizing old structures within the deep margin, and the potential redistribution of deformation even after generation of first magnetic anomalies.</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/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> </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/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/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/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://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> <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://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://www.osti.gov/scitech/servlets/purl/10178790','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10178790"><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>Helm, R.; Irwin, J.</p> <p>1992-08-01</p> <p><span class="hlt">Final</span> focus <span class="hlt">systems</span> for linear colliders present many exacting challenges in beam optics, component design, and beam quality. Efforts to resolve these problems as they relate to a new generation of linear colliders are under way at several laboratories around the world. We will outline criteria for <span class="hlt">final</span> focus <span class="hlt">systems</span> and discuss the current state of understanding and resolution of the outstanding problems. We will discuss tolerances on alignment, field quality and stability for optical elements, and the implications for beam parameters such as emittance, energy spread, bunch length, and stability in position and energy. Beam-based correction procedures, which in principle can alleviate many of the tolerances, will be described. Preliminary results from the <span class="hlt">Final</span> Focus Test Beam (FFTB) under construction at SLAC will be given. <span class="hlt">Finally</span>, we mention conclusions from operating experience at the Stanford Linear Collider (SLC).</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://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://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/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/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/2004E%26PSL.224..213W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004E%26PSL.224..213W"><span id="translatedtitle">Evolution of the northern Main Ethiopian <span class="hlt">rift</span>: birth of a triple junction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wolfenden, Ellen; Ebinger, Cynthia; Yirgu, Gezahegn; Deino, Alan; Ayalew, Dereje</p> <p>2004-07-01</p> <p>Models for the formation of the archetypal <span class="hlt">rift-rift-rift</span> triple junction in the Afar depression have assumed the synchronous development of the Red Sea-Aden-East African <span class="hlt">rift</span> <span class="hlt">systems</span> soon after flood basaltic magmatism at 31 Ma, but the timing of intial <span class="hlt">rifting</span> in the northern sector of the East African <span class="hlt">rift</span> <span class="hlt">system</span> had been poorly constrained. The aims of our field, geochronology, and remote sensing studies were to determine the timing and kinematics of <span class="hlt">rifting</span> in the 3rd arm, the Main Ethiopian <span class="hlt">rift</span> (MER), near its intersection with the southern Red Sea <span class="hlt">rift</span>. New structural data and 10 new SCLF 40Ar/ 39Ar dates show that extension in the northern Main Ethiopian <span class="hlt">rift</span> commenced after 11 Ma, more than 17 My after initial <span class="hlt">rifting</span> in the southern Red Sea and Gulf of Aden. The triple junction, therefore, could have developed only during the past 11 My, or 20 My after the flood basaltic magmatism. Thus, the flood basaltic magmatism and separation of Arabia from Africa are widely separated in time from the opening of the Main Ethiopian <span class="hlt">rift</span>, which marks the incipient Nubia-Somalia plate boundary; triple junction formation is not a primary feature of breakup above the Afar mantle plume. The East African <span class="hlt">rift</span> <span class="hlt">system</span> appears to have propagated northward from the Mesozoic Anza <span class="hlt">rift</span> <span class="hlt">system</span> into the Afar depression to cut across Oligo-Miocene <span class="hlt">rift</span> structures of the Red Sea and Gulf of Aden, in response to global plate reorganisations. Structural patterns reveal a change from 130°E-directed extension to 105°E-directed extension sometime in the interval 6.6 to 3 Ma, consistent with predictions from global plate kinematic studies. The along-axis propagation of <span class="hlt">rifting</span> in each of the three arms of the triple junction has led to a NE-migration of the triple junction since 11 Ma.</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 98μg/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.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 98μg/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://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> </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://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=volcanism&id=EJ394260','ERIC'); return false;" href="http://eric.ed.gov/?q=volcanism&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://ntrs.nasa.gov/search.jsp?R=19810063492&hterms=asthenosphere&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dasthenosphere','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19810063492&hterms=asthenosphere&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dasthenosphere"><span id="translatedtitle">Continental <span class="hlt">rifting</span> - Progress and outlook</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Baker, B. H.; Morgan, P.</p> <p>1981-01-01</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://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/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://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://www.ncbi.nlm.nih.gov/pubmed/24589097','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/24589097"><span id="translatedtitle">A geographical information <span class="hlt">system</span>-based multicriteria evaluation to map areas at risk for <span class="hlt">Rift</span> Valley fever vector-borne transmission in Italy.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tran, A; Ippoliti, C; Balenghien, T; Conte, A; Gely, M; Calistri, P; Goffredo, M; Baldet, T; Chevalier, V</p> <p>2013-11-01</p> <p><span class="hlt">Rift</span> Valley fever (RVF) is a severe mosquito-borne disease that is caused by a Phlebovirus (Bunyaviridae) and affects domestic ruminants and humans. Recently, its distribution widened, threatening Europe. The probability of the introduction and large-scale spread of <span class="hlt">Rift</span> Valley fever virus (RVFV) in Europe is low, but localized RVF outbreaks may occur in areas where populations of ruminants and potential vectors are present. In this study, we assumed the introduction of the virus into Italy and focused on the risk of vector-borne transmission of RVFV to three main European potential hosts (cattle, sheep and goats). Five main potential mosquito vectors belonging to the Culex and Aedes genera that are present in Italy were identified in a literature review. We first modelled the geographical distribution of these five species based on expert knowledge and using land cover as a proxy of mosquito presence. The mosquito distribution maps were compared with field mosquito collections from Italy to validate the model. Next, the risk of RVFV transmission was modelled using a multicriteria evaluation (MCE) approach, integrating expert knowledge and the results of a literature review on host sensitivity and vector competence, feeding behaviour and abundance. A sensitivity analysis was performed to assess the robustness of the results with respect to expert choices. The resulting maps include (i) five maps of the vector distribution, (ii) a map of suitable areas for vector-borne transmission of RVFV and (iii) a map of the risk of RVFV vector-borne transmission to sensitive hosts given a viral introduction. Good agreement was found between the modelled presence probability and the observed presence or absence of each vector species. The resulting RVF risk map highlighted strong spatial heterogeneity and could be used to target surveillance. In conclusion, the geographical information <span class="hlt">system</span> (GIS)-based MCE served as a valuable framework and a flexible tool for mapping the areas at risk of a pathogen that is currently absent from a region. PMID:24589097</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19850029005&hterms=venus+volcanism&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dvenus%2Bvolcanism','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19850029005&hterms=venus+volcanism&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dvenus%2Bvolcanism"><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://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=19790043898&hterms=east+african+rift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Deast%2Bafrican%2Brift','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19790043898&hterms=east+african+rift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Deast%2Bafrican%2Brift"><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://hdl.handle.net/2060/19780016081','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19780016081"><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. V.</p> <p>1978-01-01</p> <p>The resistant parts of the canyon walls of the Martian <span class="hlt">rift</span> complex Valled Marineris were used to infer an earlier, less eroded reconstruction of the major roughs. The individual canyons were then 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>. The overall pattern 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 scarps are straighter for longer than on earth. This is probably due to the difference in tectonic histories of the two planets: the complex history of the earth and the resulting complicated basement structures influence the development of new <span class="hlt">rifts</span>. 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://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://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://adsabs.harvard.edu/abs/2004AGUSM.V43B..05W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUSM.V43B..05W"><span id="translatedtitle">Magmatic Processes Beneath the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS): Insights From Melt Inclusions in Lavas of Turkana, Kenya</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Waters, C. L.; Bryce, J. G.; Furman, T.</p> <p>2004-05-01</p> <p>The EARS is an ideal site to study the magmatic processes relevant to continental basaltic volcanism. Within the EARS, the Turkana Depression exhibits maximum extension and crustal thinning [1, 2]. Whole rock elemental and isotopic analyses of Turkana lavas demonstrate heterogeneity that is unlikely due to crustal assimilation during magma transport or storage and is instead attributed to mixing between mantle sources (plume and lithosphere) [3]. In other sites of continental basaltic volcanism, compositional studies of olivine-hosted melt inclusions (MIs) lend perspective on magma chamber processing and source diversity (e.g., [4,5]). MIs hosted in primitive olivine (ol) phenocrysts often sample numerous, discrete melts that existed prior to melt aggregation and homogenization within the continental lithosphere. Thus, ol-hosted MIs from Turkana may also provide insight into magmatic processes beneath continental <span class="hlt">rifts</span>. Furthermore, Turkana lavas afford an unusual opportunity to study MIs that are likely unaffected by crustal assimilation and provide direct evidence of mantle heterogeneity. We present major element compositional data on ol-hosted MIs from a suite of lavas from the Turkana Depression. To test for geographical control on source heterogeneity beneath the Turkana <span class="hlt">Rift</span>, analyses in progress encompass basaltic lavas that have been sampled from South and Central Islands and the Barrier. Olivine-hosted MIs in a South Island transitional basalt (MgO= 14.10 wt%, K2O/TiO2= 0.37, K2O/P2O5= 2.08; data from [3]) are dominantly alkaline in composition. Incompatible element ratios between MIs in separate, primitive ol grains (Fo= 83.8-86.7) display significant variability (K2O/TiO2= 0.32-0.63, K2O/P2O5= 1.02-4.36). Also, primitive ol grains (e.g., Fo= 86.2) host multiple MIs that consistently display similar incompatible element variability (e.g., K2O/TiO2= 0.33-0.59, K2O/P2O5=1.27-2.04). These data suggest that melt homogenization occurs at relatively shallow levels even for primitive continental lavas erupted through thin (<20 km) continental crust. Ongoing major and trace element analyses of MIs from Turkana lavas may provide more information and constraints on source variability and melt aggregation processes within the EARS. [1] Morley, C.K., Tectonophysics 236, 81-91, 1994. [2] Simiyu and Keller, Tectonophysics 278, 291-313, 1997. [3] Furman, et al., Journal of Petrology 2004, in press. [4] Kent et al., Earth and Planetary Science Letters 202, 577-594, 2002. [5] Kamenetsky and Clochiatti, Earth and Planetary Science Letters 142, 53-572, 1996.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.G43B1006K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.G43B1006K"><span id="translatedtitle">GPS Surveys to Detect <span class="hlt">Rift</span>-Related Active Faulting in the Transantarctic Mountains, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Konfal, S. A.; Wilson, T. J.; Willis, M. J.</p> <p>2006-12-01</p> <p>The Transantarctic Mountains Deformation (TAMDEF) network is a relatively dense GPS array deployed on bedrock throughout the Victoria Land region of Antarctica. The network covers nearly a quarter million square kilometers, extending approximately 675 km N-S and 350 km E-W. It spans the uplifted Transantarctic Mountains <span class="hlt">rift</span>-flank block, the bounding border fault zone, and the offshore Terror <span class="hlt">Rift</span>, where there is evidence of neotectonic activity. Embedded within this network are three local arrays of GPS sites established around known or suspected Quaternary faults to test for modern displacements. Two of these fault arrays, located in Hidden Valley and on Doorly Ridge, surround mapped faults within the Transantarctic Mountains Front, the border fault zone separating the uplifted Transantarctic Mountains <span class="hlt">rift</span> flank from the offshore <span class="hlt">rift</span> basin. The first of these arrays consists of five monuments surrounding a NE-SW trending fault showing left-lateral strike separation and cutting a hanging valley moraine, indicating Quaternary age faulting. The second fault array is located on Doorly ridge, and consists of two monuments placed on either side of a series of NE-SW trending faults showing normal sense displacements of Jurassic and older crystalline rocks. <span class="hlt">Finally</span>, six monuments surrounding a NE-SW trending fault with normal displacement of bedrock units in Beacon Valley, located in the interior of the Transantarctic Mountain range, comprise the third fault array. These local fault arrays were first surveyed during the 1996-1997 austral summer field season, and all arrays have been surveyed a minimum of three times, including the most recent survey of all networks during the 2005-2006 field season. Analysis of GPS velocities indicates how strain is being accommodated within the interior of the mountain range, helping to resolve questions regarding the degree of modern tectonic activity in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>.</p> </li> <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> </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/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://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://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/2002JGRB..107.2332Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002JGRB..107.2332Y"><span id="translatedtitle">Response of groundwater <span class="hlt">systems</span> in the Dead Sea <span class="hlt">Rift</span> Valley to the Nuweiba earthquake: Changes in head, water chemistry, and near-surface effects</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yechieli, Yoseph; Bein, Amos</p> <p>2002-12-01</p> <p>The Nuweiba earthquake (Mw = 7.1) of November 1995 had significant effects on groundwater heads, spring discharge, and chemistry in the Dead Sea <span class="hlt">Rift</span> Valley. Groundwater heads increased by 6 cm near the Dead Sea (local shallow alluvial aquifer) and by 50 cm near the sea of Galilee (regional deep confined aquifer), some 330 and 460 km north of the epicenter, respectively. In the arid central Arava valley, some 210 km north of the epicenter, the discharge of small springs increased significantly. The increase in spring discharge, as recorded in Moa spring, was accompanied by a marked change in its chemistry. However, while the change in discharge followed the earthquake, the chemistry change was found some 16 days before the earthquake. The effect of the earthquake in Moa was enhanced and prolonged because of a breach in the confinement <span class="hlt">system</span> of the shallow artesian aquifer and the formation of new flow paths along faults, cracks, and dikes. Due to the extreme aridity of the region, the sequence above the aquifer is loaded with soluble salts. Dissolution of these salts by the ascending groundwater accounts for the observed increase in salinity and changes in the spring chemistry with time. Initially, the ascending water flushed the newly formed flow paths, gradually leaching the available soluble salts. Later, as discharge shrank, upward flow was maintained within the already flushed <span class="hlt">system</span>, and the water chemistry returned to the original aquifer composition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19910056245&hterms=seismic+refraction&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dseismic%2Brefraction','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19910056245&hterms=seismic+refraction&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dseismic%2Brefraction"><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>1991-01-01</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://www.osti.gov/scitech/biblio/5849075','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5849075"><span id="translatedtitle">Multiloop integral <span class="hlt">system</span> test (MIST): <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Gloudemans, J.R. . Nuclear Power Div.)</p> <p>1991-04-01</p> <p>The Multiloop Integral <span class="hlt">System</span> Test (MIST) is part of a multiphase program started in 1983 to address small-break loss-of-coolant accidents (SBLOCAs) specific to Babcock and Wilcox designed plants. MIST is sponsored by the US Nuclear Regulatory Commission, the Babcock Wilcox Owners Group, the Electric Power Research Institute, and Babcock and Wilcox. The unique features of the Babcock and Wilcox design, specifically the hot leg U-bends and steam generators, prevented the use of existing integral <span class="hlt">system</span> data or existing integral facilities to address the thermal-hydraulic SBLOCA questions. MIST was specifically designed and constructed for this program, and an existing facility -- the Once Through Integral <span class="hlt">System</span> (OTIS) -- was also used. Data from MIST and OTIS are used to benchmark the adequacy of <span class="hlt">system</span> codes, such as RELAP5 and TRAC, for predicting abnormal plant transients. The MIST program is reported in 11 volumes. Volumes 2 through 8 pertain to groups of Phase 3 tests by type; Volume 9 presents inter-group comparisons; Volume 10 provides comparisons between the RELAP5/MOD2 calculations and MIST observations, and Volume 11 (with addendum) presents the later Phase 4 tests. This is Volume 1 of the MIST <span class="hlt">final</span> report, a summary of the entire MIST program. Major topics include, Test Advisory Group (TAG) issues, facility scaling and design, test matrix, observations, comparison of RELAP5 calculations to MIST observations, and MIST versus the TAG issues. MIST generated consistent integral-<span class="hlt">system</span> data covering a wide range of transient interactions. MIST provided insight into integral <span class="hlt">system</span> behavior and assisted the code effort. The MIST observations addressed each of the TAG issues. 11 refs., 29 figs., 9 tabs.</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://ntrs.nasa.gov/search.jsp?R=19940007574&hterms=population+estimation&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dpopulation%2Bestimation','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19940007574&hterms=population+estimation&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dpopulation%2Bestimation"><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/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://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 ɛNd and ɛHf), 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 δ13C~-5‰ and δ15N ~-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 δ13C and δ15N. 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 δ15N (+6.5‰) are coincident within the MER but the maximum δ13C (-0.78‰) lies ~100 km to the south. Highs in 3He/4He (14RA), δ13C (~-1‰) and δ15N (+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://adsabs.harvard.edu/abs/2007AGUFM.C51A0071S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.C51A0071S"><span id="translatedtitle">Moho topography of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> from inversion of aerogravity data: ramifications for geothermal heat flux and ice streaming</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Studinger, M.</p> <p>2007-12-01</p> <p>The West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, a region of thinned continental crust, dominates the lithospheric structure of the Ross Embayment in West Antarctica. Parts of the <span class="hlt">rift</span> are host to the West Antarctic Ice Sheet, a marine-based ice sheet prone to instability. It has long been hypothesized that the lithospheric structure beneath the West Antarctic Ice Sheet is a major influence on the formation, nature and dynamics of the ice sheet. The structure of the crust- mantle boundary is a fundamental geophysical parameter for understanding lithospheric processes and for geodynamic interpretation. I use aerogravity data to derive a map of the crust/mantle boundary beneath the West Antarctic Ice Sheet and to reveal the impact of relative changes in thickness of the crust and lithosphere on surface heat flow and ice streaming. Before inverting the observed Bouguer gravity field for Moho topography the gravity effect of the crust/mantle boundary has to be isolated from shallower sources. The observed radial power spectrum is matched with the model spectra of a number of equivalent source layers. First, the short wavelengths of the observed spectrum are matched with a shallow source equivalent layer model spectrum. The model spectrum is then removed from the observed power spectrum and the remaining residual spectrum is used to match the next deeper equivalent source layer. The Moho topography derived from filtered gravity coincides well with two independent seismically determined Moho estimates. In general, the geologic contributions to continental surface heat flow can be separated into mantle heat flow and radiogenic heat flow from heat producing elements within the crust. Assuming an exponentially decreasing distribution of radioactive elements, the continental surface heat flow can be expressed as a function of crustal and lithospheric thicknesses. Within the survey area there is a region of thinner crust that corresponds to elevated heat flow of several tens of mW/m2 compared to the background level. This region coincides with the confluence and onset of several ice stream tributaries, namely Kamb Ice Stream. The region with elevated heat flow appears to pin point the location of ice stream onsets and tributaries.</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/2014AGUFM.V42A..05S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V42A..05S"><span id="translatedtitle">Kīlauea's Upper East <span class="hlt">Rift</span> Zone: A <span class="hlt">Rift</span> Zone in Name Only</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Swanson, D. A.; Fiske, R. S.</p> <p>2014-12-01</p> <p>Kīlauea's upper east <span class="hlt">rift</span> zone (UERZ) extends ~3 km southeastward from the summit caldera to the Koáe fault <span class="hlt">system</span>, where it starts to bend into the main part of the ENE-trending <span class="hlt">rift</span> zone. The UERZ lacks a distinct positive gravity anomaly (though coverage is poor) and any evidence of deformation associated with magma intrusion. All ground ruptures—and the Puhimau thermal area—trend ENE, crossing the UERZ at a high angle. Lua Manu, Puhimau, and Kóokóolau craters are the only surface evidence of the UERZ. Yet the UERZ is seismically active, and all magma entering the rest of the <span class="hlt">rift</span> zone must pass through it. Rather than a <span class="hlt">rift</span> zone in the traditional sense, with abundant dikes and ground ruptures along its trend, the UERZ cuts across the ENE structural grain and serves only as a connector to the rest of the <span class="hlt">rift</span> zone, not a locus of dike formation along its length. The UERZ probably developed as a consequence of gradual SSE migration of the active part of the main east <span class="hlt">rift</span> zone at the trailing edge of the south flank. During migration, a connection to the summit reservoir complex must be maintained; otherwise, the middle and lower east <span class="hlt">rift</span> zone would starve and magma from Kīlauea's summit reservoir complex would have to go elsewhere. Over time, the UERZ lengthened and rotated clockwise to maintain the connection. Near the caldera, the UERZ may be widening westward as the summit reservoir complex migrates southward from the center of the caldera to its present position. A layered stress regime results in the upper 2-3 km mimicking the pervasive ENE structural grain of most of Kīlauea, whereas the underlying magmatic part of the UERZ responds to stresses related to SE magma transport. Magma intruding upward from the connector forms a dike that follows the ENE structural grain, as during the 1974 eruption. The active east <span class="hlt">rift</span> zone has been migrating since ~100 ka, estimated by applying a 700-y extension rate across the Koa'e fault <span class="hlt">system</span> to the ~6.5 km of migration, and presumably the UERZ connector has been developing during this time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=STS006-40-723&hterms=east+african+rift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Deast%2Bafrican%2Brift','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=STS006-40-723&hterms=east+african+rift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Deast%2Bafrican%2Brift"><span id="translatedtitle">TDRS satellite over African <span class="hlt">Rift</span> Valley, Kenya, Africa</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1983-01-01</p> <p>This post deploy view of a TDRS satellite shows a segment of the African <span class="hlt">Rift</span> Valley near Lake Baringo, Kenya, Africa (3.0S, 36.0E). The African <span class="hlt">Rift</span> Valley <span class="hlt">system</span> is a geologic fault having its origins in southern Turkey, through the near east forming the bed of the Jordan River, Gulf of Aqaba, the Red Sea and down through east Africa. The line of lakes and valleys of east Africa are the result of the faulting activity.</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.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> </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.ncbi.nlm.nih.gov/pubmed/23326620','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/23326620"><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=pubmed">PubMed</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 CO(2)-baited CDC trap without a light bulb doubled to tripled trap captures compared to control traps baited with CO(2) 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://adsabs.harvard.edu/abs/2009AGUFM.T31C1853A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.T31C1853A"><span id="translatedtitle">The importance of <span class="hlt">rift</span> history for volcanic margin formation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Armitage, J. J.; Collier, J.; Minshull, T. A.</p> <p>2009-12-01</p> <p>In the North Atlantic there is a clear association between continental breakup and onshore flood basalts. For the past two decades, largely based on the North Atlantic, it has become widely accepted that mantle temperature is the primary factor that controls melt generation during breakup. Subsequently the majority of numerical models that seek to explain variations in volcanic activity at <span class="hlt">rifted</span> margins have focused on the role of mantle temperature at the time of breakup. However, in the Northwest Indian Ocean where, despite an unequivocal link between an onshore flood basalt province, continental breakup and a hotspot track leading to an active ocean island volcano, the associated continental margins show little magmatism. Here we reconcile these observations by applying a numerical model that includes the effects of previous <span class="hlt">rifting</span> episodes. Our geodynamic model of <span class="hlt">rift</span> evolution predicts melt volumes, major and rare earth chemistry. Furthermore, we are able to predict the igneous crustal thickness and lower crustal seismic velocity that can be easily compared against geophysical observations. The melting characteristics of <span class="hlt">rifted</span> margins are highly dependant on the inherited lithosphere structure. The key issue is the sequence of geological events, rather than simply the presence of anomalously hot mantle during <span class="hlt">rifting</span>. In the North Atlantic a series of extensional basins formed off the coast of the UK and Norway prior to <span class="hlt">final</span> breakup. These thinned the thermally defined lithosphere and focused the upwelling of hot mantle, which led to enhanced melt generation. In the Northwest Indian Ocean, the extension of the failed Gop <span class="hlt">Rift</span> exhausted the mantle thermal anomaly that is associated with the onshore flood basalts of the Deccan prior to <span class="hlt">final</span> breakup. This had the effect of reducing melt generation within the Seychelles-Laxmi Ridge margin. It is therefore crucial that prior <span class="hlt">rift</span> history is considered in order to fully understand the timing and volume of magmatism observed during continental breakup.</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://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/2010EGUGA..1211538G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1211538G"><span id="translatedtitle"><span class="hlt">Rifts</span> in the tectonic structure of East Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Golynsky, Dmitry; Golynsky, Alexander</p> <p>2010-05-01</p> <p>It was established that riftogenic and/or large linear tectonic structures in East Antarctica are distributed with a steady regularity with average distance between them about 650 km. All these structures (13) represent objects of undoubted scientific and practical interest and might be considered as immediate objects for conducting integrated geological and geophysical investigations. Analysis and generalization of the RADARSAT satellite <span class="hlt">system</span> imagery and radio-echosounding survey data collected in the eastern part of Princess Elizabeth Land allow us to distinguish spatial boundaries of previously unknown continental <span class="hlt">rift</span> <span class="hlt">system</span> that was proposed to name Gaussberg (Golynsky & Golynsky, 2007). The <span class="hlt">rift</span> is about 500 km long, and taking into consideration its western continuation in the form of short (fragmented) faults, may exceed 700 km. The elevation difference between depressions and horsts reaches 3 km. The <span class="hlt">rift</span> structure consists of two sub-parallel depressions separated by segmented horst-like rises (escarpments). Deep depressions within the <span class="hlt">rift</span> reach more than 800 m bsl near the West Ice Shelf and within the central graben occupied by the Phillipi Glacier. The width of the Gaussberg <span class="hlt">Rift</span> <span class="hlt">system</span> varies from 60 km in the south-western area to 150 km near the West Ice Shelf. The Gaussberg <span class="hlt">rift</span> is considered as a part of the Lambert <span class="hlt">rift</span> <span class="hlt">system</span>, which has a complicated structure clearly recognized over both the continent and also its margin. The Gaussberg <span class="hlt">rift</span> probably exploited a weak zone between the Proterozoic mobile belt and the Archaean Vestfold-Rauer cratonic block. Supposedly it initiated at the turn of Jurassic and Permian epoch or a little bit earlier as in case of the Lambert <span class="hlt">rift</span> where the Permian graben formation with coal-bearing deposits predetermined the subsequent development of submeridional <span class="hlt">rift</span> zone. The Gaussberg and also the Scott <span class="hlt">rift</span> developed in the Queen Marie Land, may be considered as continuations of the Mahanadi Valley <span class="hlt">rift</span> and coal-bearing basins in the Rajmahal Hills of East India, respectively, in the Antarctic continent. These structures can also be considered as major drainage feeders of terrigenous sediments onto the Davis Sea continental margin. Preliminary analysis of the RADARSAT imagery shows that the Denman Glacier occupies a linear fault <span class="hlt">system</span> (> 400 km), whereas southward continuation of the Scott Glacier area represents a continuous <span class="hlt">system</span> of horsts that bound a wide central depression.The Scott Glacier together with graben-like structures hidden by ice and with the graben of Lake Vostok may represent an extensive <span class="hlt">rift</span> <span class="hlt">system</span> developed as a result of large-scale pre-breakup extension of Gondwana. We speculate that the Gaussberg <span class="hlt">rift</span> may be considered as a hypothetical accommodation zone of the Carboniferous-Permian intracontinental <span class="hlt">rift</span> along 4000 km of the west Australian and east Indian margins, which filled with thick Permian-Triassic sediment including alluvial coals.</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://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/2008cosp...37..636D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008cosp...37..636D"><span id="translatedtitle">Using of Remote Sensing Techniques for Monitoring the Earthquakes Activities Along the Northern Part of the Syrian <span class="hlt">Rift</span> <span class="hlt">System</span> (LEFT-LATERAL),SYRIA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dalati, Moutaz</p> <p></p> <p>Earthquake mitigation can be achieved with a better knowledge of a region's infra-and substructures. High resolution Remote Sensing data can play a significant role to implement Geological mapping and it is essential to learn about the tectonic setting of a region. It is an effective method to identify active faults from different sources of Remote Sensing and compare the capability of some satellite sensors in active faults survey. In this paper, it was discussed a few digital image processing approaches to be used for enhancement and feature extraction related to faults. Those methods include band ratio, filtering and texture statistics . The experimental results show that multi-spectral images have great potentials in large scale active faults investigation. It has also got satisfied results when deal with invisible faults. Active Faults have distinct features in satellite images. Usually, there are obvious straight lines, circular structures and other distinct patterns along the faults locations. Remotely Sensed imagery Landsat ETM and SPOT XS /PAN are often used in active faults mapping. Moderate and high resolution satellite images are the best choice, because in low resolution images, the faults features may not be visible in most cases. The area under study is located Northwest of Syria that is part of one of the very active deformation belt on the Earth today. This area and the western part of Syria are located along the great <span class="hlt">rift</span> <span class="hlt">system</span> (Left-Lateral or African- Syrian <span class="hlt">Rift</span> <span class="hlt">System</span>). Those areas are tectonically active and caused a lot of seismically events. The AL-Ghab graben complex is situated within this wide area of Cenozoic deformation. The <span class="hlt">system</span> formed, initially, as a result of the break up of the Arabian plate from the African plate. This action indicates that these sites are active and in a continual movement. In addition to that, the statistic analysis of Thematic Mapper data and the features from a digital elevation model ( DEM )produced from SAR interferometer show the existence of spectral structures at the same sites. The Arabian plate is moving in a NNW direction, whereas the African plate is moving to the North. The left-lateral motion along the Dead Sea Fault accommodates the difference in movement rate between both plates. The analysis of TM Space Imagery and digital image processing of spectral data show that the lineaments along AL-Ghab graben maybe considered as linear conjunctions accompanied with complex fracturing <span class="hlt">system</span>. This complex is affected by distance stresses accompanied with intensive forces. The digital image processing of Radar imagery showing the presence of active and fresh faulting zones along the AL-Ghab graben. TM and SAR-DTM data, also showed a gradual color tone and interruptions of linear-ellipse shapes which reflecting the presence of discontinuity contours along the fault zone extension .This features refer to abundance of surface morphological features indicate to Fresh Faults. Recent faulting is expressed as freshly exposed soil within the colluvial apron visible by its light tone color. These indicators had been proved by field checks. Furthermore, the statistic digital analysis of the spectral data show that there are distribution of spectral plumes. These plumes are decreasing in intensity and color contrast from the center of the site to the direction of its edges.</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/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://adsabs.harvard.edu/abs/2009EGUGA..11.3548I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..11.3548I"><span id="translatedtitle">Recent geodynamics and evolution of the Moma <span class="hlt">rift</span>, Northeast Asia.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Imaev, V. S.; Imaeva, L. P.; Kozmin, B. M.; Fujita, K. S.; Mackey, K. G.</p> <p>2009-04-01</p> <p>The Cenozoic Moma <span class="hlt">rift</span> <span class="hlt">system</span> is a major tectonic feature in northeast Russia. It is composed of a series of basins (Selennyakh, Kyrin,Lower Moma,Upper Moma,etc.) filled with up to one km thick and bounded by the Chersky Range (up to 3100 m high) on the southwest and the Moma Range (up to 2400 m high) on the northeast. Northeast of the Moma Range is the Indigirka-Zyryanka foreland basin, composed of thick, up to 2.5 km, Eocene, Oligocene, and Miocene coal-bearing sequences, while on the southwestern side of the Chersky Range there are a number of piedmont basins (Tuostakh, Upper Adycha, Derbeke, etc.) containing up to several hundred meters of Miocene and Oligocene coal-bearing deposits. Despite considerable study over the past half-century, there is considerable debate over the origin, present-day tectonics, and evolution of the Moma <span class="hlt">rift</span> <span class="hlt">system</span>. The Cenozoic deposits of the basins generally become younger from northwest to southeast with the exception of the Seimchan-Buyunda basin. In the northeast, fan-shaped coal-bearing basins (e.g., Nenneli, Olzhoi, Selennyakh, Uyandina, Tommot, and others) are filled with Miocene to Pliocene deposits, while basins in the southeast (e.g., Taskan) are filled with Neogene sediments. The Seimchan-Buyunda basin, however, has sediments of Oligocene age. The Moma <span class="hlt">rift</span> <span class="hlt">system</span> is reflected a major step in the gravity field, presumably separating denser rocks of the Kolyma-Omolon superterrain from somewhat less dense rocks of the Verkhoyansk fold belt (margin of the North Asian Craton). Analysis of travel-times of Pn and Pg waves from local earthquakes indicates an area of thinned crust (30-35 km) southwest of the Moma <span class="hlt">rift</span> <span class="hlt">system</span>, extending as a "tongue" from the Lena River delta and the Laptev Sea to the upper part of the Kolyma River, as compared to 40-45 km in the surrounding areas. This region of thinned crust also coincides with a region of high heat flow values measured in boreholes of the Chersky Range (up to 88 mW/m2). Hot springs with temperatures up to +20°C are found within the Moma and Selnnyakh basins proper.The crustal inhomogeneity is also reflected in the upper mantle as indicated by a 40° rotation of the Rayleigh wave polarization angle from teleseisms recorded at Tiksi that cross the Moma <span class="hlt">rift</span> <span class="hlt">system</span> as opposed to those that do not. Cenozoic volcanism, chemically similar to basalts and rhyolites from <span class="hlt">rift</span> zones elsewhere is found in the Moma <span class="hlt">rift</span> proper. Balagan-Tas is a basaltic cinder cone which has been dated at 286,000 years based on Ar-Ar dating, while Uraga-Khaya is an undated, presumed Quaternary, rhyolitic dome. All these factors indicate that the Moma <span class="hlt">rift</span> <span class="hlt">system</span> originated as a continental <span class="hlt">rift</span>, probably as an extension of the Arctic (Gakkel) Mid-Ocean Ridge. At the present, however, compressional conditions prevail within the Moma <span class="hlt">rift</span> zone. Seismicity is generally absent from the <span class="hlt">rift</span> basins proper or their margins; most seismicity is concentrated to the southwest of the Moma <span class="hlt">rift</span> basins along major strike-slip fault <span class="hlt">systems</span>. Focal mechanisms of the largest earthquakes in the Chersky Range also all show transpression. Field mapping indicates that the majority of the faults mapped in the field are strike-slip, thrust and reverse faults (86%) with only a small number of normal faults (14%) and that the Cenozoic deposits within the Moma <span class="hlt">rift</span> are intensely folded. Re-leveling surveys conducted along the Indigirka River, which cuts across the Moma <span class="hlt">rift</span> <span class="hlt">system</span>, reveal a moderate rate of presnt-day vertical uplift (up to +4 mm/yr). Thus, the Moma <span class="hlt">rift</span> <span class="hlt">system</span> is no longer acting as a <span class="hlt">rift</span>, but is undergoing transpression. This conclusion is also supported by recent plate motion calculations based on GPS and VLBI data, as well as slip-vectors of earthquakes, which indicates that the Euler pole between North America and Eurasia is located around 68-70°N, near the coast of the Laptev Sea. This places the Moma <span class="hlt">rift</span> <span class="hlt">system</span> in a zone of convergence between North America and Eurasia; this geometry also supports the extrusion of the Okhotsk Sea plate. Poles of rotation calculated earlier using magnetic lineation and fracture zone data from the North Atlantic yielded poles further south, about 62°N. This, combined with other evidence for extension in northeast Russia in the Oligocene and the sedimentary record of the basins, supports the origin of the Moma <span class="hlt">rift</span> <span class="hlt">system</span> as an extension of the Arctic Mid-Ocean Ridge in the Oligocene and continuing through about Pliocene time, although the complete lack of any evidence of volcanism in the <span class="hlt">rifts</span> in this time period is mystifying. Sometime in the Quaternary, the pole of rotation shifted north, placing the Moma <span class="hlt">rift</span> <span class="hlt">system</span> into compression. The young age for Balagan-Tas would suggest that the change occurred in the not too distant past. Thus, the Moma <span class="hlt">rift</span> <span class="hlt">system</span> probably originated as an extension of the Arctic (Gakkel) Mid-Ocean Ridge into the continent in the Early Cenozoic. hi the Quaternary, movement of the Euler pole between North America and Eurasia resulted in the region being placed under compression with the development (or reactivation) of major strike-slip fault <span class="hlt">systems</span> and the compression of the former <span class="hlt">rift</span> basins.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA.....5473B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA.....5473B"><span id="translatedtitle">Oblique continental <span class="hlt">rifting</span> revealed by 3D retro-deformation : example of the Upper Rhine Graben</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bertrand, G.; Horstmann, M.; Herrmann, O.; Behrmann, J.</p> <p>2003-04-01</p> <p>Our work has been done within the EU funded ENTEC network, which goal is to study the environmental impact of tectonics in the Upper Rhine Graben (URG). The URG is a NNE-trending crustal-scale small-displacement segment of the European Cenozoic <span class="hlt">rift</span> <span class="hlt">system</span>. Subsidence and syn-<span class="hlt">rift</span> sedimentation started in the late Eocene and reached their maximum during Oligocene and lower Miocene. We present two 3D tectonic models that cover the SE and SW borders of the URG (Freiburg area, SW Germany, and Colmar area, NE France, respectively). As the URG is an asymmetric structure, it was crucial to model both sides. Our goal was to infer the movement history of the fault <span class="hlt">system</span>, to identify areas of strain concentrations that could help locating possible active movements. Our models include several pre-Tertiary geological horizons, that were retrodeformed as passive objects along the faults. Assuming that "pre-<span class="hlt">rift</span>" sediments were horizontal, our objective was to obtain this geometry by retrodeforming the models. The best quality of restoration was obtained for displacement directions of N80E to N90E on the main border faults, and N50E to N60E on inner faults. Best results also were obtained with sequences of retrodeformation from the graben center toward its borders. It suggests that faulting migrated toward the graben interior. Our study also shows considerable along-strike variations of cumulated slip on both sides of the graben, with amplitudes up to 2.5 km. This caused warping of the basement with a 30--35 km wavelength. Moreover, analyses of displacement reveal that offset of the base Tertiary is locally smaller than of older horizons, suggesting that segments of the W border fault were active prior to deposition of early Tertiary sediments. <span class="hlt">Finally</span>, the seismicity in the Freiburg model reveals close coincidence between depth projection of faults and hypocenters of recent earthquakes. This suggests on-going activity of part, at least, of the fault <span class="hlt">system</span>. Our two models are highly consistent with each other, but beyond that, their results provide crucial insights on the tectonic history of the URG: it resulted from sinistrally oblique <span class="hlt">rifting</span>; early extension concentrated on the main border faults, along a nearly E-W direction; deformation then propagated into the evolving graben interior while the extension direction rotated counter-clockwise of 20^o to 40^o. We also suggest that systematic along-strike variations of cumulated fault displacements might be characteristic of oblique <span class="hlt">rifting</span>. <span class="hlt">Finally</span>, parts of the fault <span class="hlt">system</span> have probably been active prior to late Oligocene while others still are today.</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=198240','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=198240"><span id="translatedtitle">A GIS EARLY WARNING <span class="hlt">SYSTEM</span> TO DETECT ELEVATED POPULATIONS OF VECTORS OF <span class="hlt">RIFT</span> VALLEY FEVER AND THE CONTRIBUTIONS FROM FLORIDA'S MOSQUITO CONTROL COMMUNITY</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>New and emerging mosquito-borne viruses such as <span class="hlt">Rift</span> Valley fever (RVF) virus pose a global threat to animal and human health. An introduction of RVF into the U.S. could severely impact livestock industries and wild ungulates, and cause significantly more human illness than West Nile virus (WNV). ...</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> </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/2016MinDe.tmp...12T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MinDe.tmp...12T"><span id="translatedtitle">Chalcophile element (Ni, Cu, PGE, and Au) variations in the Tamarack magmatic sulfide deposit in the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span>: implications for dynamic ore-forming processes</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>2016-03-01</p> <p>The Tamarack magmatic sulfide deposit is hosted by the Tamarack Intrusive Complex (1105.6 ± 1.2 Ma) in the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span>. The most important sulfide mineralization in the Complex occurs in the northern part, which consists of two separate intrusive units: an early funnel-shaped layered peridotite body containing relatively fine-grained olivine (referred to as the FGO Intrusion) at the top, and a late gabbro-troctolite-peridotite dike-like body containing relatively coarse-grained olivine (referred to as the CGO Intrusion) at the bottom. Disseminated, net-textured, and massive sulfides occur in the base of the FGO Intrusion as well as in the upper part of the CGO Intrusion. The widest part of the CGO Intrusion also hosts a large semi-massive (net-textured) sulfide ore body locally surrounded by disseminated sulfide mineralization. Small massive sulfide veins occur in the footwall of the FGO Intrusion and in the wall rocks of the CGO dike. The sulfide mineralization is predominantly composed of pyrrhotite, pentlandite, and chalcopyrite, plus minor magnetite. Pyrrhotite containing the highest Ni and Co contents occurs in the FGO disseminated sulfides and in the CGO semi-massive sulfide ores, respectively. The most important platinum-group minerals associated with the base metal sulfides are sperrylite (PtAs2), sudburyite (PdSb), and michenerite (PdBiTe). Nickel shows a strong positive correlation with S in all types of sulfide mineralization, and Cu shows a strong positive correlation with S in the disseminated sulfide mineralization. At a given S content, the concentrations of Pt, Pd, and Au in the CGO disseminated sulfides are significantly higher than those in the FGO disseminated sulfides. The semi-massive sulfide ores are characterized by significantly higher IPGE (Ir, Os, Ru, and Rh) concentrations than most of the massive sulfide ores. With few exceptions, all of the various textural types of sulfide mineralization collectively show a good positive correlation between Pt and Pd, and between individual IPGE. At a given Pt or Pd content, however, the semi-massive sulfide ores have higher IPGE contents than the disseminated sulfide samples. Modeling results show that the variations in PGE tenors (metals in recalculated 100 % sulfide) in the Tamarack magmatic sulfide deposit are mainly controlled by variable R factors (magma/sulfide-liquid mass ratios) during sulfide-liquid segregation and subsequent monosulfide solid solution (MSS) fractionation during cooling. The initial contents of Ir, Pt, and Pd in the parental magma, estimated from the metal tenors of the disseminated sulfides, are 0.2, 2, and 1.8 ppb, respectively, which are ˜1/5 of the values for the PGE-undepleted primitive basalts of the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span>. The variations of PGE tenors in the semi-massive and massive sulfide ores can be explained by MSS fractional crystallization from sulfide liquids. Extreme variations in the PGE contents of the massive sulfides may also in part reflect metal mobility during post-crystallization hydrothermal processes. The higher PGE tenors for the disseminated sulfides in the CGO dike relative to those in the FGO Intrusion are consistent with formation in a dynamic conduit where the early sulfide liquids left in the conduit by the FGO magma were subsequently upgraded by the subsequent surge of the CGO magma. The relatively low PGE tenors for the semi-massive and massive sulfides can be explained by lack of such an upgrading process for the sulfide due to their distal locations in a migrating conduit.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/21080319','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/21080319"><span id="translatedtitle">Planning for <span class="hlt">Rift</span> Valley fever virus: use of geographical information <span class="hlt">systems</span> to estimate the human health threat of white-tailed deer (Odocoileus virginianus)-related transmission.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kakani, Sravan; LaBeaud, A Desirée; King, Charles H</p> <p>2010-11-01</p> <p><span class="hlt">Rift</span> Valley fever (RVF) virus is a mosquito-borne phlebovirus of the Bunyaviridae family that causes frequent outbreaks of severe animal and human disease in sub-Saharan Africa, Egypt and the Arabian Peninsula. Based on its many known competent vectors, its potential for transmission via aerosolization, and its progressive spread from East Africa to neighbouring regions, RVF is considered a high-priority, emerging health threat for humans, livestock and wildlife in all parts of the world. Introduction of West Nile virus to North America has shown the potential for "exotic" viral pathogens to become embedded in local ecological <span class="hlt">systems</span>. While RVF is known to infect and amplify within domestic livestock, such as taurine cattle, sheep and goats, if RVF virus is accidentally or intentionally introduced into North America, an important unknown factor will be the role of local wildlife in the maintenance or propagation of virus transmission. We examined the potential impact of RVF transmission via white-tailed deer (Odocoileus virginianus) in a typical north-eastern United States urban-suburban landscape, where livestock are rare but where these potentially susceptible, ungulate wildlife are highly abundant. Model results, based on overlap of mosquito, human and projected deer densities, indicate that a significant proportion (497/1186 km(2), i.e. 42%) of the urban and peri-urban landscape could be affected by RVF transmission during the late summer months. Deer population losses, either by intervention for herd reduction or by RVF-related mortality, would substantially reduce these likely transmission zones to 53.1 km(2), i.e. by 89%. PMID:21080319</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Litho.220...81Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Litho.220...81Z"><span id="translatedtitle">Cathodoluminescence guided zircon Hf isotope depth profiling: Mobilization of the Lu-Hf <span class="hlt">system</span> during (U)HP rock exhumation in the Woodlark <span class="hlt">Rift</span>, Papua New Guinea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zirakparvar, N. A.</p> <p>2015-04-01</p> <p>Cathodoluminescence image guided Hf isotope depth profiling by laser ablation of zircons from two quartzofeldspathic host gneisses constrains the Lu-Hf <span class="hlt">system</span>'s behavior during rapid exhumation of (U)HP rocks in the Woodlark <span class="hlt">Rift</span>, Papua New Guinea. Investigation of the depth profiling technique in individual and composite zircon standards demonstrates that it is possible to resolve ~ 8 μm thick domains in which εHf(present) differs by as little as 4 units. In a metasedimentary gneiss, 2.89 ± 0.29 Ma zircon overgrowths on Cretaceous aged inherited cores have radiogenic εHf(present) indicating growth in a medium that was originally in equilibrium with garnet undergoing recrystallization (the 'garnet effect' of Zheng et al., 2005). In a separate gneiss sample that originated as an exhumation related anatectic melt, 3.66 ± 0.13 Ma zircons lacking inheritance contain sub-domains that differ from each other by > 15 εHf(present). Some of these sub-domains are radiogenic and can be explained by the 'garnet effect', whereas others also contain highly elevated Lu and Yb in addition to their radiogenic Hf compositions, thus necessitating a medium derived from the complete breakdown of garnet. Zircons in this sample also contain non-radiogenic sub-domains that grew in the presence of Hf mobilized from the surrounding rocks of the subducted and metamorphosed remnants of the Australian continental margin. The results confirm that rapid exhumation of (U)HP rocks can result in the following: 1) transmission of radiogenic Hf (and sometimes Lu and the other HREE) from garnet bearing mafic lithologies into the quartzofeldspathic gneisses, and 2) mobilization and transport of unradiogenic Hf present within the quartzofeldspathic remnants of subducted continental crust.</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> <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/2014JGRF..119..731H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRF..119..731H"><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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Heeszel, David S.; Fricker, Helen A.; Bassis, Jeremy N.; O'Neel, Shad; Walter, Fabian</p> <p>2014-04-01</p> <p>Iceberg calving is a dominant mass loss mechanism for Antarctic ice shelves, second only to basal melting. An important 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 apply a suite of passive seismological techniques including icequake locations, back projection, and moment tensor inversion. We confirm previous results that show ice shelf <span class="hlt">rifting</span> is characterized by periods of relative quiescence punctuated by swarms of intense seismicity of 1 to 3 h. Even during periods of quiescence, we find significant 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 the propagating ice shelf <span class="hlt">rifts</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/21295425','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/21295425"><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>Pépin, M</p> <p>2011-06-01</p> <p><span class="hlt">Rift</span> Valley Fever (RVF) is a zoonotic arbovirosis. Among animals, it mainly affects ruminants, causing abortions in gravid females and mortality among young animals. In humans, RVF virus infection is usually asymptomatic or characterized by a moderate fever. However, in 1 to 3% of cases, more severe forms of the disease (hepatitis, encephalitis, retinitis, hemorrhagic fever) can lead to the death of infected individuals or to major sequels. The RVF virus (Bunyaviridae, genus Phlebovirus) was identified for the first time in the 1930s in Kenya. It then spread over almost all African countries, sometimes causing major epizootics/epidemics. In 2000, the virus was carried out of Africa, in the Middle East Arabian Peninsula. In 2007-2008, Eastern-African countries, including Madagascar, reported significant episodes of RVF virus, this was also the case for the Comoros archipelago and the French island of Mayotte. This ability to spread associated with many vectors, including in Europe, and high viral loads in infected animals led the health authorities worldwide to warn about the potential emergence of RVF virus in areas with a temperate climate. The awareness has increased in recent years with climate changes, which may possibly modify the vector distribution and competence, and prompted many RVF virus-free countries to better prepare for a potential implantation of RVF. PMID:21295425</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://hdl.handle.net/2060/20160005862','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160005862"><span id="translatedtitle">Diverse Eruptions at Approximately 2,200 Years B.P. on the Great <span class="hlt">Rift</span>, Idaho: Inferences for Magma Dynamics Along Volcanic <span class="hlt">Rift</span> Zones</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hughes, S. S.; Nawotniak, S. E. Kobs; Borg, C.; Mallonee, H. C.; Purcell, S.; Neish, C.; Garry, W. B.; Haberle, C. W.; Lim, D. S. S.; Heldmann, J. L.</p> <p>2016-01-01</p> <p>Compositionally and morphologically diverse lava flows erupted on the Great <span class="hlt">Rift</span> of Idaho approximately 2.2 ka (kilo-annum, 1000 years ago) during a volcanic "flare-up" of activity following an approximately 2 ky (kiloyear, 1000 years) hiatus in eruptions. Volcanism at Craters of the Moon (COTM), Wapi and Kings Bowl lava fields around this time included primitive and evolved compositions, separated over 75 kilometers along the approximately 85 kilometers-long <span class="hlt">rift</span>, with striking variability in lava flow emplacement mechanisms and surface morphologies. Although the temporal associations may be coincidental, the <span class="hlt">system</span> provides a planetary analog to better understand magma dynamics along <span class="hlt">rift</span> <span class="hlt">systems</span>, including that associated with lunar floor-fractured craters. This study aims to help bridge the knowledge gap between ancient <span class="hlt">rift</span> volcanism evident on the Moon and other terrestrial planets, and active <span class="hlt">rift</span> volcanism, e.g., at Hawai'i and Iceland.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015LPICo1839.5026M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015LPICo1839.5026M"><span id="translatedtitle"><span class="hlt">Rift</span> Stability and Localization in Devana Chasma, Venus</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martone, A. A.; Montési, L. G. J.</p> <p>2015-05-01</p> <p>The <span class="hlt">rift</span> zone of Devana Chasma greatly resembles Earth's <span class="hlt">rift</span> zones, especially the East African <span class="hlt">Rift</span>, despite the lack of global plate tectonics. The stability of <span class="hlt">rifts</span> on Venus will be characterized, and will include lithosphere weakening processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=214205','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=214205"><span id="translatedtitle">GIS Early-Warning <span class="hlt">System</span> for Vectors of <span class="hlt">Rift</span> Valley Fever: Anomaly Analysis of Climate-Population Associations</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>A critical component of predicting the risk of transmission of mosquito-borne viruses is knowing the status of vector populations. Mosquito control agencies have good <span class="hlt">systems</span> for measuring mosquito populations at county or district levels, but these data are not synthesized to regional or national ...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000JGR...105.5997K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000JGR...105.5997K"><span id="translatedtitle">The chemically zoned 1949 eruption on La Palma (Canary Islands): Petrologic evolution and magma supply dynamics of a <span class="hlt">rift</span> zone eruption</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Klügel, Andreas; Hoernle, Kaj A.; Schmincke, Hans-Ulrich; White, James D. L.</p> <p>2000-03-01</p> <p>The 1949 <span class="hlt">rift</span> zone eruption along the Cumbre Vieja ridge on La Palma involved three eruptive centers, 3 km spaced apart, and was chemically and mineralogically zoned. Duraznero crater erupted tephrite for 14 days and shut down upon the opening of Llano del Banco, a fissure that issued first tephrite and, after 3 days, basanite. Hoyo Negro crater opened 4 days later and erupted basanite, tephrite, and phonotephrite, while Llano del Banco continued to issue basanite. The eruption ended with Duraznero erupting basanite with abundant crustal and mantle xenoliths. The tephrites and basanites from Duraznero and Llano del Banco show narrow compositional ranges and define a bimodal suite. Each batch ascended and evolved separately without significant intermixing, as did the Hoyo Negro basanite, which formed at lower degrees of melting. The magmas fractionated clinopyroxene +olivine±kaersutite±Ti-magnetite at 600-800 MPa and possibly 800-1100 MPa. Abundant reversely zoned phenocrysts reflect mixing with evolved melts at mantle depths. Probably as early as 1936, Hoyo Negro basanite entered the deep <span class="hlt">rift</span> <span class="hlt">system</span> at 200-350 MPa. Some shallower pockets of this basanite evolved to phonotephrite through differentiation and assimilation of wall rock. A few months prior to eruption, a mixing event in the mantle may have triggered the <span class="hlt">final</span> ascent of the magmas. Most of the erupted tephrite and basanite ascended from mantle depths within hours to days without prolonged storage in crustal reservoirs. The Cumbre Vieja <span class="hlt">rift</span> zone differs from the <span class="hlt">rift</span> zones of Kilauea volcano (Hawaii) in lacking a summit caldera or a summit reservoir feeding the <span class="hlt">rift</span> <span class="hlt">system</span> and in being smaller and less active with most of the <span class="hlt">rift</span> magma solidifying between eruptions.</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, JRg; 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 >60C 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 90-100C. 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://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://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://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/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> </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://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://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://files.eric.ed.gov/fulltext/ED247898.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED247898.pdf"><span id="translatedtitle">Selection of Microcomputer <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>Barkley, John; And Others</p> <p></p> <p>Intended to provide assistance to non-technical end-users in evaluating the applicability of microcomputer-based <span class="hlt">systems</span> to their needs and in choosing appropriate <span class="hlt">systems</span>, this document recommends first identifying requirements and then identifying and evaluating alternative sources for application software, <span class="hlt">system</span> software and hardware, and…</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/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://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://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://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://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/ED293892.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED293892.pdf"><span id="translatedtitle">Multilevel Evaluation <span class="hlt">Systems</span> Project. <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>Herman, Joan L.</p> <p></p> <p>Several studies were conducted in 1987 by the Multilevel Evaluation <span class="hlt">Systems</span> Project, which focuses on developing a model for a multi-purpose, multi-user evaluation <span class="hlt">system</span> to facilitate educational decision making and evaluation. The project model emphasizes on-going integrated assessment of individuals, classes, and programs using a variety of…</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://adsabs.harvard.edu/abs/2004AGUFM.T41E1260D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFM.T41E1260D"><span id="translatedtitle">Seismological Constraints on the Magmato-tectonic Behavior of the Asal-Ghoubbet <span class="hlt">Rift</span> (Afar Depression, Republic of Djibouti) Since the Last 1978-<span class="hlt">Rifting</span> Episode</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.; Bertil, D.; Dorbath, C.; Dorbath, L.; Jacques, E.</p> <p>2004-12-01</p> <p>The Asal-Ghoubbet <span class="hlt">rift</span> was the locus of a seismic and volcanic crisis in 1978 followed by 8 years of rapid opening (60 mm/yr) before returning to its long-term opening rate of 16 mm/yr. We analyze the space-time evolution of the seismicity that occurred in the <span class="hlt">rift</span> between 1979 and 2001. The data recorded by the Djibouti Observatory provide only hypocentral locations before 1995 and P and S-wave arrival times since 1996. Additional data acquired during a five months experiment in 2000-2001 allowed us to determine a 3D-velocity model of the <span class="hlt">rift</span>, used to precisely relocate post 1996 events. The 2545 small-magnitude earthquakes (Md ≤ 3.2) recorded in the <span class="hlt">rift</span> since the 1978 crisis provide a negligible contribution to the total extension across the <span class="hlt">rift</span>, which occurs essentially aseismically. The temporal evolution of the seismicity reveals two distinct phases consistent with those observed in the geodetic data. The post-crisis period (1979-1986) is characterized by large-magnitude earthquakes exclusively located below the northern <span class="hlt">rift</span> shoulder. These events are associated with the contraction of the side of the <span class="hlt">rift</span> resulting from the fast opening of the central dyke <span class="hlt">system</span>. The subsequent period (1987-2001) corresponding to normal opening rate across the <span class="hlt">rift</span> is characterized by a micro-seismicity essentially located below the major <span class="hlt">rift</span> caldera (Fieale). Most recorded events during this period concentrate within the <span class="hlt">rift</span> inner floor at the top of an aseismic, low velocity zone located below the Fiale caldera, which we interpret as hot material above the magma chamber. Outside from post-crisis periods, the seismicity tends to cluster in time in response to stress changes in the brittle layer induced by episodic magmatic movements.</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://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.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> <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://www.osti.gov/scitech/biblio/10147596','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/10147596"><span id="translatedtitle">Visualizing power <span class="hlt">system</span> data. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Christie, R.D.; Mahadev, P.M.</p> <p>1994-04-01</p> <p>Practical use of computational tools requires that people be able to understand the results the tools produce. This is a particular problem for real world power <span class="hlt">systems</span> because of their massive amount of data, and because existing representational methods do not provide quick and efficient communication of the qualitative information contained in that data. Instead they require users to create internal, mental representations of the data and then analyze them to extract desired information. Physical realization of these internal representations -- a visualization of the data -- should provide a breakthrough in ease of comprehension. Scientific visualization is the general name for this field. Power <span class="hlt">systems</span> pose some unique problems that require extensions of existing visualization techniques. The resulting pictures should prove useful for power <span class="hlt">system</span> operators and engineers, and also for lay persons with an interest in power <span class="hlt">systems</span>, such as accountants, regulators, legislators and the general public. Energy Management <span class="hlt">System</span> (EMS) full graphics user interfaces, and the high resolution graphics capabilities commonly available on PCs and workstations, now provide the hardware to make visualization possible on a routine basis, but adequate representations for data have not yet been developed. This project identifies general characteristics of good representations, and develops graphical representations for power <span class="hlt">system</span> operating state and power <span class="hlt">system</span> static security to illustrate the application of these characteristics to power <span class="hlt">system</span> problems. Representations are developed in X Windows using X Toolkit primitives and run on a wide variety of Unix workstations. However, implementation issues have not been considered in this work. The emphasis is on developing new and effective presentation methods. The effectiveness of presentation methods is difficult to measure. A method for objectively measuring this effectiveness is described.</p> </li> <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://www.osti.gov/scitech/servlets/purl/6364857','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6364857"><span id="translatedtitle"><span class="hlt">Final</span> report on the FMIT Control <span class="hlt">System</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Johnson, J.A.</p> <p>1985-01-01</p> <p>The computer control <span class="hlt">system</span> for the Fusion Materials Irradiation Test Facility (FMIT) prototype accelerator was designed using distributed intelligence driven by a distributed database. The <span class="hlt">system</span> consists of two minicomputers in the central control room and four microcomputers residing in CAMAC crates located near appropriate subsystems of the accelerator. The <span class="hlt">system</span> uses single vendor hardware as much as practical in an attempt to minimize the maintenance problems. Local control consoles are an integral part of each node computer to provide subsystem check-out. The main console is located in the central control room and permits one-point operation of the complete control <span class="hlt">system</span>. Automatic surveillance is provided for each data channel by the node computer with out-of-bounds alarms sent to the main console. Report by exception is used for data logging. This control <span class="hlt">system</span> has been operational for two years. The computers are too heavily loaded and the operator response is slower than desired. A <span class="hlt">system</span> upgrade to a faster local-area network has been undertaken and is scheduled to be operational by conference time.</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> </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/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/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/6767717','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6767717"><span id="translatedtitle">Postaccident liquid sampling <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>Davidson, G.R.; Lahti, G.P.</p> <p>1984-05-01</p> <p>The postaccident and routine analysis of reactor coolant water for gamma fission product activity, boron concentration, pH, and chloride ion concentration was studied. Objectives were (1) to evaluate NRC postaccident monitoring guidelines, (2) to characterize postaccident conditions, (3) to evaluate post-accident monitoring methods and equipment, and (4) to investigate improvements. These issues were explored by (1) comparing postaccident information needs in comparison with regulatory requirements, (2) calculating postaccident radioactivity concentrations, (3) assembling data on commercial postaccident monitoring <span class="hlt">systems</span>, and (4) performing laboratory tests. Postaccident gamma spectrometry was investigated. Effects of ambient airborne radioactivity, high count rates, and count rate reduction techniques were studied. A prototype automated on-line analysis <span class="hlt">system</span> incorporating chemical separation and sample holdup for decay was developed. Performance specifications and techniques of commercial on-line <span class="hlt">systems</span> are assessed, and relative merits of on-line and grab sample <span class="hlt">systems</span> are discussed. Several methods of chemical analysis were evaluated. For boron, these were titration of the mannitol-borate complex, potentiometry with Na/sup +/ and H/sup +/ ion-selective electrodes, and a method not yet commercially used for reactor coolant, spectrophotometry with the reagent azomethine; for pH, potentiometry with the glass electrode; and for chloride ion, ion chromatography and potentiometry with the chloride ion-selective electrode. While most of the methods satisfied NRC guidelines, the performance of some was marginal.</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://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://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://ntrs.nasa.gov/search.jsp?R=19830060639&hterms=Cenozoic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DCenozoic','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19830060639&hterms=Cenozoic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DCenozoic"><span id="translatedtitle">Constraints on <span class="hlt">rift</span> thermal processes from heat flow and uplift</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Morgan, P.</p> <p>1983-01-01</p> <p>The implications of heat flow data available from five major Cenozoic continental <span class="hlt">rift</span> <span class="hlt">systems</span> for the processes of continental <span class="hlt">rifting</span> are discussed, and simple thermal models of lithospheric thinning which predict uplift are used to further constrain the thermal processes in the lithosphere during <span class="hlt">rifting</span>. Compilations of the heat flow data are summarized and the salient results of these compilations are briefly discussed. The uplift predictions of the slow and rapid thinning models, in which thinning is assumed to occur at a respectively slower and faster rate than heat can be conducted into the lithosphere, are presented. Comparison of uplift rates with model results indicates that the lithosphere is in a state between the two models. While uplift is predicted to continue after thinning has ceased due to thermal relaxation of the lithosphere, the rapid thinning model is always predicted to apply to surface heat flow, and an anomaly in this flow is not predicted to develop until after thinning has stopped.</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/355084','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/355084"><span id="translatedtitle">AC drive <span class="hlt">system</span> efficiency evaluation. <span class="hlt">Final</span> report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Langley, R.</p> <p>1998-12-01</p> <p>Industrial and commercial facilities are continually searching for ways to reduce costs while increasing revenues. One way of accomplishing this objective is to reduce energy consumption costs. Industrial and commercial facilities, in their heavy reliance on electric motors, are by far the largest consumers of electric power. In fact, electric motors consume more than fifty percent of all generated electric energy. The use of energy efficient motors and electronic adjustable-speed drives (ASDs) can provide industries with a means for reducing energy costs. Taking advantage of available contracts with incentives for energy conservation, industries can justify the costs for retrofitting old inefficient production lines with state-of-the-art, efficient, process equipment. The use of ASDs for improving process control and increasing process efficiency has been well documented. To this point, however, there are no published research reports or technical papers presenting energy efficiency data for ASDs and ASD/motor <span class="hlt">systems</span> at load conditions other than rated load conditions. The IEC-1800 standard does call for manufacturers to report the ASD or the ASD/motor <span class="hlt">system</span> efficiency at rated load and base speed conditions. This report presents energy efficiency test data for two 150-hp ASD/motor combinations. Each test was conducted at multiple load torque and speed setpoints, which includes interpretations and discussions of the test results. The report presents test standards, test procedures, and test data that show how the energy efficiencies of ASD/motor <span class="hlt">system</span> components relate. 51 figs., 13 tabs.</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/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://www.osti.gov/scitech/servlets/purl/665884','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/665884"><span id="translatedtitle">Geophysical tomography imaging <span class="hlt">system</span>. <span class="hlt">Final</span> CRADA report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Norton, S.J.; Won, I.J.</p> <p>1998-05-20</p> <p>The Cooperative Research and Development Agreement (CRADA) between Lockheed Martin Energy <span class="hlt">Systems</span>, Inc., and Geophex, Ltd., was established to investigate high-resolution, shallow acoustic imaging of the subsurface. The primary objectives of the CRADA were accomplished, including the evaluation of a new tomographic imaging algorithm and the testing and comparison of two different acoustic sources, the hammer/plate source and an electromagnetic vibratory source. The imaging <span class="hlt">system</span> was composed essentially of a linear array of geophones, a digital seismograph, and imaging software installed on a personal computer. Imaging was most successful using the hammer source, which was found to be less susceptible to ground roll (surface wave) interference. It is conjectured that the vibratory source will perform better for deeper targets for which ground roll is less troublesome. Potential applications of shallow acoustic imaging are numerous, including the detection and characterization of buried solid waste, unexploded ordnance, and clandestine man-made underground structures associated with treaty verification (e.g., tunnels, underground storage facilities, hidden bunkers).</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..500A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004EOSTr..85..500A"><span id="translatedtitle">The life cycle of continental <span class="hlt">rifting</span> as a focus for U.S.-African scientific collaboration</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Abdelsalam, Mohamed G.; Atekwana, Estella A.; Keller, G. Randy; Klemperer, Simon L.</p> <p>2004-11-01</p> <p>The East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) provides the unique opportunity found nowhere else on Earth, to investigate extensional processes from incipient <span class="hlt">rifting</span> in the Okavango Delta, Botswana, to continental breakup and creation of proto-oceanic basins 3000 km to the north in the Afar Depression in Ethiopia, Eritrea, and Djibouti.The study of continental <span class="hlt">rifts</span> is of great interest because they represent the initial stages of continental breakup and passive margin development, they are sites for large-scale sediment accumulation, and their geomorphology may have controlled human evolution in the past and localizes geologic hazards in the present. But there is little research that provides insights into the linkage between broad geodynamic processes and the life cycle of continental <span class="hlt">rifts</span>: We do not know why some <span class="hlt">rifts</span> evolve into mid-ocean ridges whereas others abort their evolution to become aulacogens. Numerous studies of the EARS and other continental <span class="hlt">rifts</span> have significantly increased our understanding of <span class="hlt">rifting</span> processes, but we particularly lack studies of the embryonic stages of <span class="hlt">rift</span> creation and the last stages of extension when continental breakup occurs.</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> </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/2008JAfES..51..163M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008JAfES..51..163M"><span id="translatedtitle">Fault kinematics and tectonic stress in the seismically active Manyara Dodoma <span class="hlt">Rift</span> segment in Central Tanzania Implications for 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>Macheyeki, Athanas S.; Delvaux, Damien; De Batist, Marc; Mruma, Abdulkarim</p> <p>2008-07-01</p> <p>The Eastern Branch of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> is well known in Ethiopia (Main Ethiopian <span class="hlt">Rift</span>) and Kenya (Kenya or Gregory <span class="hlt">Rift</span>) and is usually considered to fade away southwards in the North Tanzanian Divergence, where it splits into the Eyasi, Manyara and Pangani segments. Further towards the south, <span class="hlt">rift</span> structures are more weakly expressed and this area has not attracted much attention since the mapping and exploratory works of the 1950s. In November 4, 2002, an earthquake of magnitude Mb = 5.5 struck Dodoma, the capital city of Tanzania. Analysis of modern digital relief, seismological and geological data reveals that ongoing tectonic deformation is presently affecting a broad N-S trending belt, extending southward from the North Tanzanian Divergence to the region of Dodoma, forming the proposed "Manyara-Dodoma <span class="hlt">Rift</span> segment". North of Arusha-Ngorongoro line, the <span class="hlt">rift</span> is confined to a narrow belt (Natron graben in Tanzania) and south of it, it broadens into a wide deformation zone which includes both the Eyasi and Manyara grabens. The two-stage <span class="hlt">rifting</span> model proposed for Kenya and North Tanzania also applies to the Manyara-Dodoma <span class="hlt">Rift</span> segment. In a first stage, large, well-expressed topographic and volcanogenic structures were initiated in the Natron, Eyasi and Manyara grabens during the Late Miocene to Pliocene. From the Middle Pleistocene onwards, deformations related to the second <span class="hlt">rifting</span> stage propagated southwards to the Dodoma region. These young structures have still limited morphological expressions compared to the structures formed during the first stage. However, they appear to be tectonically active as shown by the high concentration of moderate earthquakes into earthquake swarms, the distribution of He-bearing thermal springs, the morphological freshness of the fault scarps, and the presence of open surface fractures. Fault kinematic and paleostress analysis of geological fault data in basement rocks along the active fault lines show that recent faults often reactivate older fault <span class="hlt">systems</span> that were formed under E-W to NW-SE horizontal compression, compatible with late Pan-African tectonics. The present-day stress inverted from earthquake focal mechanisms shows that the Manyara-Dodoma <span class="hlt">Rift</span> segment is presently subjected to an extensional stress field with a N080°E direction of horizontal principal extension. Under this stress field, the <span class="hlt">rift</span> develops by: (1) reactivation of the pre-existing tectonic planes of weakness, and (2) progressive development of a new fault <span class="hlt">system</span> in a more N-S trend by the linkage of existing <span class="hlt">rift</span> faults. This process started about 1.2 Ma ago and is still ongoing.</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://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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SoSyR..50..184G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SoSyR..50..184G"><span id="translatedtitle">Classification of the <span class="hlt">rift</span> zones of venus: <span class="hlt">Rift</span> valleys and graben belts</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guseva, E. N.</p> <p>2016-05-01</p> <p>The spatial distribution of <span class="hlt">rift</span> zones of Venus, their topographic configuration, morphometric parameters, and the type of volcanism associating with <span class="hlt">rifts</span> were analyzed. This allowed the main characteristic features of <span class="hlt">rifts</span> to be revealed and two different types of <span class="hlt">rift</span>-forming structures, serving for classification of <span class="hlt">rift</span> zones as <span class="hlt">rift</span> valleys and graben belts, to be isolated. These structural types (facies) of <span class="hlt">rift</span> zones are differently expressed in the relief: <span class="hlt">rift</span> valleys are individual deep (several kilometers) W-shaped canyons, while graben belts are clusters of multiple V-shaped and rather shallow (hundreds of meters) depressions. Graben belts are longer and wider, as compared to <span class="hlt">rift</span> valleys. <span class="hlt">Rift</span> valleys are spatially associated with dome-shaped volcanic rises and large volcanos (concentrated volcanic sources), while graben belts do not exhibit such associations. Volcanic activity in the graben belts are presented by spacious lava fields with no apparent sources of volcanism. Graben belts and <span class="hlt">rift</span> valleys were formed during the Atlian Period of geologic history of Venus, and they characterized the tectonic style of the planet at the late stages of its geologic evolution. Formation of this or that structural facies of the <span class="hlt">rift</span> zones of Venus were probably governed by the thickness of the lithosphere, its rheological properties, and the development degree of the mantle diapirs associating with <span class="hlt">rift</span> zones.</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://adsabs.harvard.edu/abs/1996Tectp.268..221K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996Tectp.268..221K"><span id="translatedtitle">Syn-<span class="hlt">rift</span> evolution of the Pripyat Trough: constraints from structural and stratigraphic modelling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kusznir, N. J.; Kovkhuto, A.; Stephenson, R. A.</p> <p>1996-12-01</p> <p>The Pripyat Trough is a Late Devonian <span class="hlt">rift</span> basin. It forms part of the larger Pripyat-Dniepr-Donets <span class="hlt">rift</span> <span class="hlt">system</span> which has a length in excess of 800 km and separates the Ukrainian Shield from the Voronezh Massif. The Pripyat Trough contains a well resolved stratigraphic sub-division within the syn-<span class="hlt">rift</span> basin fill sequence which allows the duration and rate of <span class="hlt">rifting</span> to be determined using 2-D forward and reverse structural and stratigraphic modelling. The analysis shows that <span class="hlt">rifting</span> was extremely rapid. Sequential decompaction and flattening of 2-D cross-sections has been applied to six syn-<span class="hlt">rift</span> time horizons between top Upper Devonian (364 Ma) and top Middle Devonian (377 Ma) and used to quantify the syn-<span class="hlt">rift</span> development of basin cross-sectional area in time. The evolution of basin cross-sectional area shows that some initial <span class="hlt">rifting</span> had occurred prior to the Middle Frasnian (369 Ma); however, most <span class="hlt">rifting</span> occurred in the Famennian (367-364 Ma). Forward syn-<span class="hlt">rift</span> modelling using the flexural cantilever model of <span class="hlt">rift</span> basin formation has also been applied to quantify the magnitude of extension within the Pripyat Trough in time. Forward syn-<span class="hlt">rift</span> models are constrained by the intra syn-<span class="hlt">rift</span> flattened and decompacted cross-sections and the observed evolution of the cross-sectional area. Most rapid <span class="hlt">rift</span> basin formation is shown to have occurred in the Famennian with over 66% of basin cross-sectional area forming in less than 5 Myr, and with approximately 80% or more of total extension occurring in less than 3 Myr. This period of most rapid extension during the Famennian coincides with the most active period of volcanicity. Total Devonian extension across the Pripyat Trough is estimated to be of the order of 11-14 km with a maximum β stretching factor of approximately 1.12. Extensional strain rates are estimated to be of the order of 0.8 × 10 -15 s -1.</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://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://adsabs.harvard.edu/abs/1991Tectp.197..203G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1991Tectp.197..203G"><span id="translatedtitle">Crustal structure and tectonic evolution of the anza <span class="hlt">rift</span>, northern Kenya</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Greene, L. C.; Richards, D. R.; Johnson, R. A.</p> <p>1991-10-01</p> <p>The Anza trough is a Mesozoic <span class="hlt">rift</span> located in northern Kenya that appears to be the failed third arm of a paleo-triple junction which allowed the separation of Madagascar from Africa during the Jurassic. The <span class="hlt">rift</span> is oriented NW-SE and its tectonic evolution is related to that of the Mesozoic southern Sudan <span class="hlt">rift</span> <span class="hlt">system</span>. We analyzed seismic and gravity data from the southwestern side of the Anza <span class="hlt">rift</span> including the Chalbi Desert to gain a better understanding of <span class="hlt">rift</span> structure. Gravity data delineate the main <span class="hlt">rift</span> basins as well as a small sub-basin on the southwest side of the main <span class="hlt">rift</span>. Normal faulting evident on the NW end of a 42-km-long, NW-SE oriented Vibroseis® profile, marks the western boundary of the sub-basin. This sub-basin is offset from the trend of the main Anza trough; the western boundary may be a complex fault zone accommodating a change in direction of the main <span class="hlt">rift</span> trend. Gravity values increase to the NW in the faulted area, suggesting shallowing of basement. A strong NW-dipping reflection from 0.5 s to almost 3 s is interpreted as a pre- to mid-Cretaceous unconformity. The configuration of the unconformity and the normal faulting strongly resembles the half-graben geometry imaged in the East African <span class="hlt">Rift</span>. Numerous discontinuous reflections can be seen deeper in the section between 6 and 9 s, but a distinct reflection Moho cannot be interpreted with certainty. In addition to seismic and gravity data, regional geologic and well data lead us to conclude that there are probably Jurassic marine sediments in the bottom of the Anza <span class="hlt">rift</span>.</p> </li> <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://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> <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/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://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.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/1997Tectp.278..329Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997Tectp.278..329Z"><span id="translatedtitle">Styles of continental <span class="hlt">rifting</span>: crust-mantle detachment and mantle plumes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zeyen, Hermann; Volker, Frank; Wehrle, Veronika; Fuchs, Karl; Sobolev, Stephan V.; Altherr, Rainer</p> <p>1997-09-01</p> <p>Observations made in different continental <span class="hlt">rift</span> <span class="hlt">systems</span> (European, Red Sea-Gulf of Aden, and East African <span class="hlt">Rift</span> <span class="hlt">Systems</span>) were investigated in terms of the influence of different parameters on the style of <span class="hlt">rifting</span>. Apart from the lithospheric thermal regime at the time of <span class="hlt">rift</span> initiation, the process of <span class="hlt">rifting</span> seems to be mainly controlled by the far-field stress regime and the presence or absence of a mantle plume. In a hot lithosphere the low viscosity of the lower crust enables the upper crust to be detached from the mantle and be deformed independently under far-field stresses. Therefore, in western Europe the main <span class="hlt">rifts</span> could open obliquely to the direction of mantle movement in crustal levels without appreciable extension in the lithospheric mantle. In contrast, the colder lithosphere of Arabia did not allow detachment of crust and mantle. Therefore, despite being in a similar tectonic situation as in western Europe, i.e. <span class="hlt">rifting</span> in front of an orogen, the whole lithosphere deformed congruently. <span class="hlt">Rift</span> opening occurred parallel to mantle movement, i.e. parallel to the direction of extensional stress in the lithospheric mantle induced by the pull of the subducting slab at the orogenic front. The forces needed to extend the whole relatively cool Arabian lithosphere could, however, not be produced by slab pull alone. Additional forces and weakening of the lithosphere were produced by the Afar mantle plume. Mantle plumes are generally not able to break very thick cratonic lithosphere but they deflect sidewards when hitting this kind of lithosphere. Warmer (but still relatively cool) lithosphere like in the surroundings of the East African Tanzania craton or in Arabia can, by the buoyancy of a plume, be bent strongly enough to break. As a consequence, long linear <span class="hlt">rift</span> structures develop with generally high shoulders. The presence of a plume explains thus the position of the East African and Red Sea-Gulf of Aden <span class="hlt">rifts</span>. Under far-field compression, <span class="hlt">rifts</span> will open only a small amount, whereas under far-field extension continental break-up may occur. A plume hitting a hot lithosphere may penetrate it without producing long linear <span class="hlt">rifts</span>. Instead, crustal deformation will be distributed in parallel basins over a wide area with only minor amounts of <span class="hlt">rift</span> shoulder uplift as has happened in northern Kenya and the French Massif Central.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1991Tectp.197..245G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1991Tectp.197..245G"><span id="translatedtitle">A preliminary description of the Gan-Hang failed <span class="hlt">rift</span>, southeastern china</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Goodell, P. C.; Gilder, S.; Fang, X.</p> <p>1991-10-01</p> <p>The Gan-Hang failed <span class="hlt">rift</span>, as defined by present-day topography, extends at least 450 km in length and 50 km in width. It is a northeast-southwest trending series of features spanning from Hangzhou Bay in Zhejiang province into Jiangxi province through Fuzhou City. Southwest of Fuzhou, the <span class="hlt">rift</span> splits into two portions: one continuing along the southwestern trend, and the other diverging westward. The total extent of the <span class="hlt">rift</span> cannot be defined at this time. The <span class="hlt">rift</span> is superimposed upon a major suture zone of Caledonian or early Mesozoic age. The suture represents the fusing of the South China (Huanan) and Yangtze cratons. Perhaps in Late Triassic, but for sure by Late-Middle Jurassic time, the <span class="hlt">rifting</span> was initiated and followed this older suture, in part. This time corresponds roughly to the middle stage of the Yanshanian orogeny and to the subduction of the postulated Pacific- Kula ridge southeast of the continental margin. The total thickness of the sediments and volcanics filling the <span class="hlt">rift</span> valley reaches more than 10,000 m. Peak intensity of extension was between Late-Middle Jurassic and Middle to Late Cretaceous. Sedimentation within the <span class="hlt">rift</span> was not continuous and is marked with periodic unconformities. Sediments within the <span class="hlt">rift</span> include red beds, sandstones, siltstones, mudstones, conglomerates, breccias, tuffs, and ignimbrites. Vertebrate fossils and dinosaur eggs are also found. Contemporaneous volcanics within and flanking the <span class="hlt">rift</span> include basalts, rhyolites, granites, gabbros, dacites, and andesites. Silicic volcanics are mostly attributed to caldera <span class="hlt">systems</span>. Early basalts are tholeiitic and later change to alkaline-olivine basalt. Bimodal volcanism is recognized. Peak intensity of volcanism ranges between 135 and 75 Ma. In Early Cenozoic time, the area was a topographic low. Paleocene- Eocene sediments and evaporites are the last rocks to be deposited in the <span class="hlt">rift</span>. Today the <span class="hlt">rift</span> is delineated by major, high-angle faults (the Pingxiang-Guangfeng deep fault belt), red beds, and volcanically derived U deposits. Scismic study of P-wave velocities has produced an earth model which shows substantial crustal thinning under the Gan-Hang <span class="hlt">rift</span>. The region has been included in the southeastern China Mesozoic fault-depression <span class="hlt">system</span>, and has not generally been recognized as a distinct "failed <span class="hlt">rift</span>".</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 75C), 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://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/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> </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/2014APS..APRM15004J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014APS..APRM15004J"><span id="translatedtitle">The <span class="hlt">Final</span> Spin of a Binary Black-Hole <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>Jani, Karan; Shoemaker, Deirdre</p> <p>2014-03-01</p> <p>The coalescence of a binary black-hole (BBH) results in a space-time described by the Lorentz boosted Kerr metric. The <span class="hlt">final</span> BH thus purely lies in a 7-dimensional parameter space consisting of the mass, spin and recoil velocity . The initial BBH <span class="hlt">system</span> however, even in the regime of being a quasi-circular orbit, is described by 14 parameters, namely the two masses, their spins and their momenta. As a one-one map between the initial and <span class="hlt">final</span> parameter space cannot exist, several attempts have been made in the past to provide an analytical formula that maps a set of initial binary BH parameters to a given value of <span class="hlt">final</span> mass and <span class="hlt">final</span> spin. In this study, we test the validity of the most used analytical spin formula listed in Barausse & Rezzolla (2009) using the extensive, 484 simulations of generic BBH configurations, catalog from the Georgia Tech Numerical Relativity group.</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://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/2015EGUGA..17.6390D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.6390D"><span id="translatedtitle">Initiation and development of the Kivu <span class="hlt">rift</span> segment in Central Africa by reactivating un-favorably oriented structural weaknesses</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; Smets, Benoît</p> <p>2015-04-01</p> <p>The Kivu <span class="hlt">rift</span> region forms the central segment of the western branch of the East African <span class="hlt">rift</span> <span class="hlt">system</span>, between the northern termination of the Tanganyika <span class="hlt">rift</span> and the southern extension of the Edward-George <span class="hlt">rift</span>. Its structure and geological evolution has been revised in the light of a compilation of existing data on earthquake epicenters, focal depth, focal mechanisms, thermal springs and neotectonic faults. It has long been shown that the link between the Kivu <span class="hlt">rift</span> basin and the Northern termination of the Tanganyika <span class="hlt">rift</span> basin forms an accommodation zone in which the Rusizi tectonic depression occupies a central place (Ebinger, 1989). In addition, our compilation suggests that the NNE-trending Kivu <span class="hlt">rift</span> basin and the N-S northern half of the Tanganyika <span class="hlt">rift</span> basin initiated as separated, partly overlapping and differently oriented basins. The orientation and development of the Kivu <span class="hlt">rift</span> basin was controlled by an inferred Mid-Proterozoic crustal shear zone and a Pan-African reverse fault front. It was not optimally oriented with the general (first-order) stress field characterized by roughly E-W extension. In a later stage, the more optimally N-S oriented North Tanganyika basin progressed towards the North and connected to Kivu <span class="hlt">rift</span> in its middle in a region now occupied by the town of Bukavu. This accommodation zone is marked by Quaternary volcanism, warm thermal springs, frequent and relatively shallow seismicity. The southwestern part of the Kivu <span class="hlt">rift</span> became progressively abandoned but it is still seismically active and hosts a number of warm thermal springs. This particular architecture influences the present-day stress field. This work is a contribution to the Belgian GeoRisCA project. Ebinger, C.J. 1989. Geometric and kinematic development of border faults and accommodation zones, Kivu-Rusizi <span class="hlt">Rift</span>, Africa. Tectonics, 8, 117-133</p> </li> <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://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> <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://adsabs.harvard.edu/abs/2008AGUFM.V41D2112F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V41D2112F"><span id="translatedtitle">Volcano-Tectonic Interactions in the Dabbahu-Manda Harraro <span class="hlt">Rift</span> Segment, Afar</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ferguson, D. J.; Pyle, D.</p> <p>2008-12-01</p> <p>The Dabbahu-Manda Harraro (DMH) <span class="hlt">rift</span> segment lies at the southern extensions of the Red Sea <span class="hlt">Rift</span> propagator into central Afar, Ethiopia. The ~ 60 x 15km magmatic segment is composed of highly attenuated magmatically modified crust and is almost entirely floored by fissural basaltic lava flows, cut by numerous faults. In addition to the large volume of basalt lavas the segment also contains significant erupted volumes of silicic lavas that form discrete volcanic centres, occurring both along and adjacent to the main <span class="hlt">rift</span> axis. Here we examine the structural and stratigraphic context of the silicic centres in the DMH segment and the interaction between central volcanoes and extensional tectonics. Local modification of the regional stress field around the silicic centres alters fault orientations and may affect offsets, rates of extension and the direction of <span class="hlt">rift</span> propagation. Using field observations and analysis of remote sensing imagery we relate the patterns seen in the DMH segment to published analogue models (van Wyk de Vries and Merle, Geology, 1996) of volcano-<span class="hlt">rift</span> interaction. In the case of an edifice located on the spreading axis faults bend towards the volcano, altering the mean strike direction of the <span class="hlt">rift</span> axis. For a volcano sited adjacent to the <span class="hlt">rift</span> (~ 16km from the axis) strain appears to be "captured" from the main <span class="hlt">rift</span> and faults propagate away from the segment towards the volcano. We extend this analysis to recent theories of <span class="hlt">rift</span> propagation (Lahitte et al, EPSL, 2003) and the potential feedback <span class="hlt">system</span> created by the interaction between magmatic <span class="hlt">systems</span> and fracture propagation; whereby increased crustal permeability promotes a higher melt flux causing erupted composition to become more mafic and thus further promoting magmatically induced extension and fracturing of the crust. Planned geochemical and geochronological studies will be used to test these ideas by providing quantitative constraints on the relationships between volcanism and fault propagation.</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/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://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://files.eric.ed.gov/fulltext/ED457608.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED457608.pdf"><span id="translatedtitle">New York Partnership for Statewide <span class="hlt">Systems</span> Change, 2000. <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>Price, Melissa</p> <p></p> <p>This <span class="hlt">final</span> report describes activities and accomplishments of the New York Partnership for Statewide <span class="hlt">Systems</span> Change 2000, a 5-year project to increase and improve inclusive educational services to New York State students with severe disabilities at the secondary level and students with serious emotional disturbance at the elementary and middle…</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://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://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=315824','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=315824"><span id="translatedtitle">Detection and Response for <span class="hlt">Rift</span> Valley fever</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 is a viral disease that impacts domestic livestock and humans in Africa and the Middle East, and poses a threat to military operations in these areas. We describe a <span class="hlt">Rift</span> Valley fever Risk Monitoring website, and its ability to predict risk of disease temporally and spatially. We al...</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://www.ncbi.nlm.nih.gov/pubmed/24447334','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/24447334"><span id="translatedtitle"><span class="hlt">Rift</span> Valley fever outbreak, southern Mauritania, 2012.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Sow, Abdourahmane; Faye, Ousmane; Ba, Yamar; Ba, Hampathé; Diallo, Diawo; Faye, Oumar; Loucoubar, Cheikh; Boushab, Mohamed; Barry, Yahya; Diallo, Mawlouth; Sall, Amadou Alpha</p> <p>2014-02-01</p> <p>After a period of heavy rainfall, an outbreak of <span class="hlt">Rift</span> Valley fever occurred in southern Mauritania during September-November 2012. A total of 41 human cases were confirmed, including 13 deaths, and 12 <span class="hlt">Rift</span> Valley fever virus strains were isolated. Moudjeria and Temchecket Departments were the most affected areas. PMID:24447334</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> </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/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/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/1989NIMPA.276..427O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1989NIMPA.276..427O"><span id="translatedtitle">A <span class="hlt">final</span> focus <span class="hlt">system</span> for flat-beam linear colliders</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Oide, Katsunobu</p> <p>1989-04-01</p> <p>A <span class="hlt">final</span> focus <span class="hlt">system</span> is designed for a flat-beam linear collider with the parameters suggested by R.B. Palmer. A method of chromaticity correction which uses one family of sextupoles is realized so as to correct both horizontal and vertical chromaticities simultaneously. A computer code has been written to find the solution, and a result with a momentum acceptance twice that of Palmer's requirement is obtained. It is shown that the designed optics is almost at the limit of focusing which is given by the synchrotron radiation in the <span class="hlt">final</span> quadrupole.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009Tecto..28.6010P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009Tecto..28.6010P"><span id="translatedtitle">Height of faceted spurs, a proxy for determining long-term throw rates on normal faults: Evidence from the North Baikal <span class="hlt">Rift</span> <span class="hlt">System</span>, Siberia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petit, Carole; Meyer, Bertrand; Gunnell, Yanni; Jolivet, Marc; San'kov, Vladimir; Strak, Vincent; Gonga-Saholiariliva, Nahossio</p> <p>2009-12-01</p> <p>We present new results on the long-term throw rates of active normal faults in the North Baikal <span class="hlt">Rift</span> (NBR), eastern Siberia, based on a statistical analysis of triangular faceted scarps. Fault-bounded ridges in the NBR display typical morphologies with several contiguous facets separated by fault-perpendicular catchments. Over a range of 20 fault segments analyzed, triangular facet heights vary from ˜200 to >900 m. As fault scarps have been developing under similar long-term climatic conditions, we infer that the scatter in mean facet height arises from long-term differences in fault throw rate. We compare the morphology of NBR facets with results obtained in a previously published numerical model of facet growth. Using facet height as an input, model results provide estimates of the long-term fault throw rate. NBR throw rates vary between 0.2 and 1.2 mm yr-1. The throw rates are then compared with the cumulated throw, which has been constrained by geophysical and stratigraphic data in the basins. This provides an estimate of the age of fault and basin initiation. We show that the modern stage of basin development started circa 3 Myr ago, except for the North Baikal basin (˜8 Ma). Our results also suggest that a proportion of the observed throw is inherited from an earlier tectonic stage.</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/2060/19890005728','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890005728"><span id="translatedtitle">Simulated <span class="hlt">final</span> approach path captures using the microwave landing <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>Feather, J. B.</p> <p>1988-01-01</p> <p>Computer simulation results are presented for intercepting <span class="hlt">final</span> approach paths using various Microwave Landing <span class="hlt">System</span> (MLS) path capture concepts. This study, conducted under the Advanced Transport Operating <span class="hlt">System</span> (ATOPS) program, simulated these captures using the MD-80 aircraft as the study model. Several different capture concepts were investigated. <span class="hlt">Systems</span> that could be retrofitted into existing aircraft with minimum hardware and software changes were considered. An enhanced ILS look-alike capture provided improved tracking performance over conventional ILS without using a full-up path computer. The other concepts used waypoint databases and path computers to provide smart captures. These captures included lateral path intercepts as well as vertical path control. Winds, turbulence, and MLS noise were included in the simulation. In all cases, acceptable tracking errors were obtained during transition to the <span class="hlt">final</span> approach path.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T14A..02O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T14A..02O"><span id="translatedtitle">The Effect of Continental <span class="hlt">Rifting</span> on Lithospheric Fabric: Evidence From the Mid-Continent <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>Ola, O. B.; Frederiksen, A. W.</p> <p>2013-12-01</p> <p>The Mid-Continent <span class="hlt">Rift</span> (MCR) is a major feature of the North American continent: a 1.1 Ga <span class="hlt">rift</span> that failed to develop into an ocean basin. Though the crustal expression of the <span class="hlt">rift</span> is preserved, it is impossible to determine from crustal evidence the nature of the lithospheric contribution to the <span class="hlt">rifting</span> process. The installation of teleseismic instrumentation through the Superior Province <span class="hlt">Rifting</span> Earthscope Experiment (SPREE) is allowing investigation of the lithosphere beneath the MCR, which will help in addressing questions about the initiation, propagation, and failure of the <span class="hlt">rift</span> structure. We focus on observing the strength and orientation of lithospheric fabric through measurements of the splitting of teleseismic SK(K)S waves at instruments in and near the <span class="hlt">rift</span> axis, using the method of Silver and Chan (1991) to find the set of parameters that optimally restores linear particle motion. Our results show that the fast direction varies only subtly across the study area, with the exception of localized outliers. The fast direction is close to the direction of absolute plate motion, but shows greater scatter within the MCR itself. Split times show strong variations (from near-zero to 1.5 s), with lower values within the <span class="hlt">rift</span>; the Nipigon Embayment stands out as a particularly low-anisotropy region. These measurements suggest that the <span class="hlt">rifting</span> process thinned the lithosphere or reset its fabric, indicating significant lithospheric participation in the <span class="hlt">rifting</span> process.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1987Tectp.143..193B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1987Tectp.143..193B"><span id="translatedtitle"><span class="hlt">Rift</span> propagation along the southern Dead Sea <span class="hlt">rift</span> (Gulf of Elat)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ben-Avraham, Zvi</p> <p>1987-11-01</p> <p>The Gulf of Elat is located at the southern part of the Dead Sea <span class="hlt">rift</span> and at the northern part of the Red Sea. Geophysical data suggest that it can be divided into three distinct segments, northern, central and southern, on the basis of shallow and deep structures. The shallow structure of the Gulf of Elat, as well as of other parts of the Dead Sea <span class="hlt">rift</span> is dominated by the presence of grabens which are usually interpreted as pull-apart basins formed by the horizontal motion on faults along the Dead Sea <span class="hlt">rift</span>. This <span class="hlt">rift</span> is considered to be a plate boundary of the transform type. Various geophysical data including heat flow, gravity, magnetics and seismic refraction indicate systematic changes along the length of the Gulf of Elat. The <span class="hlt">rifting</span> activity is probably more advanced in the southern portion of the gulf. This advanced <span class="hlt">rifting</span> activity propagate from south northward. Within the southern portion of the Gulf of Elat, the transition from the structure of the Red Sea to that of the Dead Sea <span class="hlt">rift</span> actually takes place. Of the entire length of the Dead Sea <span class="hlt">rift</span> only in the southern part and possibly also in the central part of the Gulf of Elat is actual mantle upwelling now taking place. This upwelling is also associated with a widening of the <span class="hlt">rift</span> zone at depth. The two processes, the transform motion and the propagation of <span class="hlt">rifting</span> activity, probably proceed independently.</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://files.eric.ed.gov/fulltext/ED042050.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED042050.pdf"><span id="translatedtitle">Occupational Training Information <span class="hlt">System</span>. <span class="hlt">Final</span> Report Complete with <span class="hlt">System</span> Documentation.</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>Braden, Paul V.; And Others</p> <p></p> <p>The overall purpose of the Occupational Training Information <span class="hlt">System</span> (OTIS) is to provide improved data for evaluating recommended changes in Oklahoma's State Plan for Vocational Education. In addition to matching manpower supply and demand to show net demand, the project includes components and cost analysis, a followup, underdeveloped human…</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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/663481','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/663481"><span id="translatedtitle">Simulated coal gas MCFC power plant <span class="hlt">system</span> verification. <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>1998-07-30</p> <p>The objective of the main project is to identify the current developmental status of MCFC <span class="hlt">systems</span> and address those technical issues that need to be resolved to move the technology from its current status to the demonstration stage in the shortest possible time. The specific objectives are separated into five major tasks as follows: Stack research; Power plant development; Test facilities development; Manufacturing facilities development; and Commercialization. This <span class="hlt">Final</span> Report discusses the M-C power Corporation effort which is part of a general program for the development of commercial MCFC <span class="hlt">systems</span>. This <span class="hlt">final</span> report covers the entire subject of the Unocal 250-cell stack. Certain project activities have been funded by organizations other than DOE and are included in this report to provide a comprehensive overview of the work accomplished.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20060010177','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20060010177"><span id="translatedtitle">Joint Technical Architecture for Robotic <span class="hlt">Systems</span> (JTARS)-<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>Bradley, Arthur T.; Holloway, Sidney E., III</p> <p>2006-01-01</p> <p>This document represents the <span class="hlt">final</span> report for the Joint Technical Architecture for Robotic <span class="hlt">Systems</span> (JTARS) project, funded by the Office of Exploration as part of the Intramural Call for Proposals of 2005. The project was prematurely terminated, without review, as part of an agency-wide realignment towards the development of a Crew Exploration Vehicle (CEV) and meeting the near-term goals of lunar exploration.</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://adsabs.harvard.edu/abs/2010EGUGA..12.3463P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.3463P"><span id="translatedtitle">Height of faceted spurs, a proxy for determining long-term throw rates on normal faults: Evidence from the North Baikal <span class="hlt">Rift</span> <span class="hlt">System</span>, Siberia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petit, Carole; Meyer, Bertrand; Gunnell, Yanni; Jolivet, Marc; San'kov, Vladimir; Strak, Vincent; Gonga-Saholiariliva, Nahossio</p> <p>2010-05-01</p> <p>We present new results on the long-term throw rates of active normal faults in the North Baikal <span class="hlt">Rift</span> (NBR), eastern Siberia, based on a statistical analysis of triangular faceted scarps. Faceted spurs or triangular facets are morphologic features frequently observed along normal fault scarps, and result from the progressive denudation and incision of the footwall during fault activity. Fault-bounded ridges in the NBR display such typical morphologies with several contiguous facets separated by fault-perpendicular catchments. Over a range of 20 fault segments analyzed, triangular facet heights vary from ~200 to >900 m. As fault scarps have been developing under similar long-term climatic conditions, we infer that the scatter in mean facet height arises from long-term differences in fault throw rate. We compare the morphology of NBR facets with results obtained in a previously published numerical model of facet growth, which predicts that the mean height of triangular facets is proportional to the fault throw rate. Using facet height as an input, model results provide estimates of the long-term fault throw rates in the NBR. These vary between 0.2 and 1.2 mm/yr. The throw rates are then compared with the cumulated throw, which has been constrained by geophysical and stratigraphic data in the basins. This provides an estimate of the age of fault and basin initiation. We show that the modern stage of basin development started circa 3 Myr ago, except for the North Baikal basin (~ 8 Ma). Our results also suggest that a proportion of the observed throw is inherited from an earlier tectonic stage.</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://ntrs.nasa.gov/search.jsp?R=19920068131&hterms=energy+storage+FLYWHEEL&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Denergy%2Bstorage%2BFLYWHEEL','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19920068131&hterms=energy+storage+FLYWHEEL&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Denergy%2Bstorage%2BFLYWHEEL"><span id="translatedtitle"><span class="hlt">Final</span> prototype of magnetically suspended flywheel energy storage <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>Anand, D. K.; Kirk, J. A.; Zmood, R. B.; Pang, D.; Lashley, C.</p> <p>1991-01-01</p> <p>A prototype of a 500 Wh magnetically suspended flywheel energy storage <span class="hlt">system</span> was designed, built, and tested. The authors present the work done and include the following: (1) a <span class="hlt">final</span> design of the magnetic bearing, control <span class="hlt">system</span>, and motor/generator, (2) construction of a prototype <span class="hlt">system</span> consisting of the magnetic bearing stack, flywheel, motor, container, and display module, and (3) experimental results for the magnetic bearings, motor, and the entire <span class="hlt">system</span>. The successful completion of the prototype <span class="hlt">system</span> has achieved: (1) manufacture of tight tolerance bearings, (2) stability and spin above the first critical frequency, (3) use of inside sensors to eliminate runout problems, and (4) integration of the motor and magnetic bearings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997AIPC..387..969F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997AIPC..387..969F"><span id="translatedtitle">The <span class="hlt">final</span> analysis Little Leo: A <span class="hlt">system</span> and service overview</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fatig, Michael</p> <p>1997-01-01</p> <p>There is an emerging commercial space industry consisting of constellations of low earth orbiting satellites to that will provide global telecommunications services. Within the set of proposed low earth orbiting satellite <span class="hlt">systems</span>, there exists two distinct classes. One class provides high bandwidth digital voice and data services, and the other provides narrowband store and forward digital data services. The digital data service <span class="hlt">systems</span> are called Little LEOs or Infosats. These <span class="hlt">systems</span> will provide a variety of personal, business, environmental, and industrial digital data services on a global scale. Infosat <span class="hlt">systems</span> provide a niche telecommunications infrastructure that benefit industries and governments of the world whether developing or industrialized; geographically homogeneous or diverse; or low, middle, or high income. The flexible nature of the service allows it to be applied in many ways to meet changing needs. This paper provides an overview of the <span class="hlt">Final</span> Analysis Infosat <span class="hlt">system</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/627600','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/627600"><span id="translatedtitle">The <span class="hlt">final</span> analysis Little Leo: A <span class="hlt">system</span> and service overview</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Fatig, M.</p> <p>1997-01-01</p> <p>There is an emerging commercial space industry consisting of constellations of low earth orbiting satellites to that will provide global telecommunications services. Within the set of proposed low earth orbiting satellite <span class="hlt">systems</span>, there exists two distinct classes. One class provides high bandwidth digital voice and data services, and the other provides narrowband store and forward digital data services. The digital data service <span class="hlt">systems</span> are called Little LEOs or Infosats. These <span class="hlt">systems</span> will provide a variety of personal, business, environmental, and industrial digital data services on a global scale. Infosat <span class="hlt">systems</span> provide a niche telecommunications infrastructure that benefit industries and governments of the world whether developing or industrialized; geographically homogeneous or diverse; or low, middle, or high income. The flexible nature of the service allows it to be applied in many ways to meet changing needs. This paper provides an overview of the <span class="hlt">Final</span> Analysis Infosat <span class="hlt">system</span>. {copyright} {ital 1997 American Institute of Physics.}</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> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'